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Sample records for bimetallic ni-fe catalysts

  1. CO methanation over supported bimetallic Ni-Fe catalysts: From computational studies towards catalyst optimization

    DEFF Research Database (Denmark)

    Kustov, Arkadii; Frey, Anne Mette; Larsen, Kasper Emil;

    2007-01-01

    DFT calculations combined with a computational screening method have previously shown that bimetallic Ni-Fe alloys should be more active than the traditional Ni-based catalyst for CO methanation. That was confirmed experimentally for a number of bimetallic Ni-Fe catalysts supported on MgAl2O4. He...

  2. Bimetallic Catalysts.

    Science.gov (United States)

    Sinfelt, John H.

    1985-01-01

    Chemical reaction rates can be controlled by varying composition of miniscule clusters of metal atoms. These bimetallic catalysts have had major impact on petroleum refining, where work has involved heterogeneous catalysis (reacting molecules in a phase separate from catalyst.) Experimentation involving hydrocarbon reactions, catalytic…

  3. Degradation of tetrachloromethane and tetrachloroethene by Ni/Fe bimetallic nanoparticles

    Science.gov (United States)

    Huang, Y. Y.; Liu, F.; Li, H. D.

    2009-09-01

    The study investigated the potential of nanoscale Ni/Fe bimetallic particles reduction for carbon tetrachloride (CT) and tetrachloroethene (PCE). BET specific surface areas of the laboratory synthesized Ni/Fe (2% wt.) particle, with diameter on the order of 20-60nm, was approximately 52.61m2/g. Batch studies demonstrated that rapid transformations of PCE and CT were achieved with nanoscale Ni/Fe particles. The degradation process appeared to be pseudo-first-order. Values of the surface area normalized rate coefficients (KSA) of PCE and CT for the reaction with nano Ni/Fe were 2.068mL/(m2·h), 10.08mL/(m2·h), respectively. This indicated that the degradation rate of CT was about 5 times larger than that of PCE under comparable environmental condition. Significant amounts of DCM were detected for the reaction with CT unlike the PCE transformation where ethane was the only end-product, amount to 103% of the initial PCE carbon. Both DCM (~15%) and methane (~27%) were the major end products for CT reaction. Based on the rapid rate of degradation and no or less chlorinated byproducts, the nanoscale particles technology offered great opportunities for both fundamental research and technological application for remediation of contaminated ground water.

  4. Degradation of tetrachloromethane and tetrachloroethene by Ni/Fe bimetallic nanoparticles

    International Nuclear Information System (INIS)

    The study investigated the potential of nanoscale Ni/Fe bimetallic particles reduction for carbon tetrachloride (CT) and tetrachloroethene (PCE). BET specific surface areas of the laboratory synthesized Ni/Fe (2% wt.) particle, with diameter on the order of 20-60nm, was approximately 52.61m2/g. Batch studies demonstrated that rapid transformations of PCE and CT were achieved with nanoscale Ni/Fe particles. The degradation process appeared to be pseudo-first-order. Values of the surface area normalized rate coefficients (KSA) of PCE and CT for the reaction with nano Ni/Fe were 2.068mL/(m2·h), 10.08mL/(m2·h), respectively. This indicated that the degradation rate of CT was about 5 times larger than that of PCE under comparable environmental condition. Significant amounts of DCM were detected for the reaction with CT unlike the PCE transformation where ethane was the only end-product, amount to 103% of the initial PCE carbon. Both DCM (∼15%) and methane (∼27%) were the major end products for CT reaction. Based on the rapid rate of degradation and no or less chlorinated byproducts, the nanoscale particles technology offered great opportunities for both fundamental research and technological application for remediation of contaminated ground water.

  5. Remediation of polybrominated diphenyl ethers in soil using Ni/Fe bimetallic nanoparticles: Influencing factors, kinetics and mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Yingying [School of Chemistry and Environment, South China Normal University, Guangzhou 51006 (China); Guangdong Technology Research Center for Ecological Management and Remediation of Urban Water System, Guangzhou 51006 (China); Fang, Zhanqiang, E-mail: zhqfang@scnu.edu.cn [School of Chemistry and Environment, South China Normal University, Guangzhou 51006 (China); Guangdong Technology Research Center for Ecological Management and Remediation of Urban Water System, Guangzhou 51006 (China); Cheng, Wen [School of Chemistry and Environment, South China Normal University, Guangzhou 51006 (China); Guangdong Technology Research Center for Ecological Management and Remediation of Urban Water System, Guangzhou 51006 (China); Tsang, Pokeung Eric [Department of Science and Environmental Studies, The Hong Kong Institute of Education, Hong Kong 00852 (China); Zhao, Dongye [Environmental Engineering Program, Department of Civil Engineering, Auburn University, Auburn, AL 36849 (United States)

    2014-07-01

    Polybrominated diphenyl ethers (PBDEs) are commonly used as additive flame retardants in all kinds of electronic products. PBDEs are now ubiquitous in the environment, with soil as a major sink, especially in e-waste recycling sites. This study investigated the degradation of decabromodiphenyl ether (BDE209) in a spiked soil using Ni/Fe bimetallic nanoparticles. The results indicated that Ni/Fe bimetallic nanoparticles are able to degrade BDE209 in soil at ambient temperature and the removal efficiency can reach 72% when an initial pH of 5.6 and at a Ni/Fe dosage of 0.03 g/g. A declining trend in degradation was noticed with decreasing Ni loading and increasing of initial BDE209 concentration. The degradation products of BDE209 were analyzed by GC-MS, which showed that the degradation of BDE209 was a process of stepwise debromination from nBr to (n − 1)Br. And a possible debromination pathway was proposed. At last, the degradation process was analyzed as two-step mechanism, mass transfer and reaction. This current study shows the potential ability of Ni/Fe nanoparticles to be used for removal of PBDEs in contaminated soil. - Highlights: • Ni/Fe bimetallic nanoparticles could effectively degradate BDE209 in soil. • The effects of various factors on remediation of BDE209 in soil using Ni/Fe were considered. • The degradation of BDE209 was a process of stepwise debromination from nBr to (n − 1)Br. • A possible debromination pathway and mechanism about removal of BDE209 in soil were proposed.

  6. Alloyed Ni-Fe nanoparticles as catalysts for NH3 decomposition

    DEFF Research Database (Denmark)

    Simonsen, Søren Bredmose; Chakraborty, Debasish; Chorkendorff, Ib;

    2012-01-01

    A rational design approach was used to develop an alloyed Ni-Fe/Al2O3 catalyst for decomposition of ammonia. The dependence of the catalytic activity is tested as a function of the Ni-to-Fe ratio, the type of Ni-Fe alloy phase, the metal loading and the type of oxide support. In the tests with hi...... smallest particles in terms of catalytic activity per active site. Compared with SiO2, ZrO2 and TiO2, the support materials Al2O3 or Mg-Al-spinel give the highest performance in the high temperature range....

  7. Cu2O Photocathode for Low Bias Photoelectrochemical Water Splitting Enabled by NiFe-Layered Double Hydroxide Co-Catalyst

    Science.gov (United States)

    Qi, Huan; Wolfe, Jonathan; Fichou, Denis; Chen, Zhong

    2016-08-01

    Layered double hydroxides (LDHs) are bimetallic hydroxides that currently attract considerable attention as co-catalysts in photoelectrochemical (PEC) systems in view of water splitting under solar light. A wide spectrum of LDHs can be easily prepared on demand by tuning their chemical composition and structural morphology. We describe here the electrochemical growth of NiFe-LDH overlayers on Cu2O electrodes and study their PEC behavior. By using the modified Cu2O/NiFe-LDH electrodes we observe a remarkable seven-fold increase of the photocurrent intensity under an applied voltage as low as ‑0.2 V vs Ag/AgCl. The origin of such a pronounced effect is the improved electron transfer towards the electrolyte brought by the NiFe-LDH overlayer due to an appropriate energy level alignment. Long-term photostability tests reveal that Cu2O/NiFe-LDH photocathodes show no photocurrent loss after 40 hours of operation under light at ‑0.2 V vs Ag/AgCl low bias condition. These improved performances make Cu2O/NiFe-LDH a suitable photocathode material for low voltage H2 production. Indeed, after 8 hours of H2 production under ‑0.2 V vs Ag/AgCl the PEC cell delivers a 78% faradaic efficiency. This unprecedented use of Cu2O/NiFe-LDH as an efficient photocathode opens new perspectives in view of low biasd or self-biased PEC water splitting under sunlight illumination.

  8. In situ studies of surface of NiFe2O4 catalyst during complete oxidation of methane

    Science.gov (United States)

    Zhang, Shiran; Shan, Junjun; Nie, Longhui; Nguyen, Luan; Wu, Zili; Tao, Franklin (Feng)

    2016-06-01

    NiFe2O4 with an inverse spinel structure exhibits high activity for a complete oxidation of methane at 400 °C-425 °C and a higher temperature. The surface of the catalyst and its adsorbates were well characterized with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ infrared spectroscopy (IR). In situ studies of the surface of NiFe2O4 using AP-XPS suggest the formation of methoxy-like and formate-like intermediates at a temperature lower than 200 °C, supported by the observed vibrational signatures in in situ IR studies. Evolutions of C1s photoemission features and the nominal atomic ratios of C/(Ni + Fe) of the catalyst surface suggest that the formate-like intermediate is transformed to product molecules CO2 and H2O in the temperature range of 250-300 °C. In situ studies suggest the formation of a spectator, - Olatticesbnd CH2sbnd Olattice -. It strongly bonds to surface through Csbnd O bonds and cannot be activated even at 400 °C.

  9. Ternary NiFeMn layered double hydroxides as highly-efficient oxygen evolution catalysts.

    Science.gov (United States)

    Lu, Zhiyi; Qian, Li; Tian, Yang; Li, Yaping; Sun, Xiaoming; Duan, Xue

    2016-01-18

    Layered double hydroxides (LDHs) are a family of layer materials that receive heightened attention. Herein a ternary NiFeMn-LDH is investigated with superior oxygen evolution activity, which is attributed to the Mn(4+) doping in the intralayer, which modifies the electronic structure and improves the conductivity of the electrocatalyst. PMID:26579843

  10. Neutral bimetallic transition metal phenoxyiminato catalysts and related polymerization methods

    Science.gov (United States)

    Marks, Tobin J.; Rodriguez, Brandon A.; Delferro, Massimiliano

    2012-08-07

    A catalyst composition comprising a neutral bimetallic diphenoxydiiminate complex of group 10 metals or Ni, Pd or Pt is disclosed. The compositions can be used for the preparation of homo- and co-polymers of olefinic monomer compounds.

  11. Platinum-Bismuth Bimetallic Catalysts: Synthesis, Characterization and Applications

    OpenAIRE

    Saucedo, Jose A, Jr; Xiao, Yang; Varma, Arvind

    2015-01-01

    Bimetallic catalysts have been explored and shown to exhibit unique characteristics which are not present in monometallic catalysts. Platinum is well known as an effective catalyst for oxidation and reduction reactions, and it can be made more effective when bismuth is introduced as a promotor. Thus, the effectiveness of the Pt-Bi catalyst was demonstrated in prior work. What is not clear, however, is the mechanism behind the catalyst function; why addition of bismuth to platinum decreases de...

  12. [NiFe] hydrogenase structural and functional models: new bio-inspired catalysts for hydrogen evolution

    International Nuclear Information System (INIS)

    Hydrogenase enzymes reversibly catalyze the oxidation and production of hydrogen in a range close to the thermodynamic potential. The [NiFe] hydrogenase active site contains an iron-cyano-carbonyl moiety linked to a nickel atom which is in an all sulphur environment. Both the active site originality and the potential development of an hydrogen economy make the synthesis of functional and structural models worthy. To take up this challenge, we have synthesised mononuclear ruthenium models and more importantly, nickel-ruthenium complexes, mimicking some structural features of the [NiFe] hydrogenase active site. Ruthenium is indeed isoelectronic to iron and some of its complexes are well-known to bear hydrides. The compounds described in this study have been well characterised and their activity in proton reduction has been successfully tested. Most of them are able to catalyze this reaction though their electrocatalytic potentials remain much more negative compared to which of platinum. The studied parameters point out the importance of the complexes electron richness, especially of the nickel environment. Furthermore, the proton reduction activity is stable for several hours at good rates. The ruthenium environment seems important for this stability. Altogether, these compounds represent the very first catalytically active [NiFe] hydrogenase models. Important additional results of this study are the synergetic behaviour of the two metals in protons reduction and the evidence of a protonation step as the limiting step of the catalytic cycle. We have also shown that a basic site close to ruthenium improves the electrocatalytic potential of the complexes. (author)

  13. Improvements in NOx reduction by carbon using bimetallic catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Illan-Gomez, M.J.; Brandan, S.; Salinas-Martinez de Lecea, C.; Linares-Solano, A. [Universidad de Alicante, Alicante (Spain). Departamento de Quimica Inorganica

    2001-11-30

    A catalysis of the C-NOx reaction has been studied to optimize the composition of the catalysts in order to decrease the carbon consumption by oxygen. Both the metal content and the composition of the catalysts have been investigated. The activity of bimetallic (KNi, NiCo and NiCu) catalysts for NOx reduction by carbon has been studied using both isothermal reactions at 300{sup o}C and temperature programmed reaction up to 500{sup o}C. It has been found that the experimental variables (i.e. amount of catalysts and nature of the bimetallic catalysts) determine the selectivity against carbon combustion by oxygen. Thus, it has been observed that the amount of catalyst greatly affects the C-O{sub 2} reaction but only lightly the C-NOx reaction and, consequently, modifies the selectivity of the catalyst for NOx reduction. Among the bimetallic catalysts tested, NiCu catalyst presents the best performance, at a temperature as low as 250{sup o}C, a high de-NOx activity and a high NOx selectivity due to a low carbon burn-off, with the additional advantage of the absence of N{sub 2}O and CO in the reaction products. Thus, the results obtained in this study show, in comparison with our previous results, that better selectivities are achieved. 20 refs., 3 figs., 2 tabs.

  14. Modelling the active site of NiFe hydrogenases: new catalysts for the electro-production of H2 and mechanistic studies

    International Nuclear Information System (INIS)

    NiFe hydrogenases are unique metalloenzymes that catalyze H+/H2 interconversion with remarkable efficiency close to the thermodynamic potential. Their active site consists of a hetero-bimetallic complex containing a nickel ion in a sulphur-rich environment connected by two thiolate bridges to an organometallic cyano-carbonyl iron moiety. In order to improve the understanding of the enzymatic mechanism and to obtain new base-metal electrocatalysts for H2 production, we synthesized a series of bio-inspired low molecular weight model complexes with the butterfly structure Ni(μ-S2)M (M= Ru, Mn and Fe). All these compounds displayed a catalytic activity of hydrogen production. Modulating the electronic and steric properties of the ruthenium center allowed optimizing the catalytic performances of these compounds in terms of stability, catalytic rate and overpotential. Mechanistic studies of the catalytic cycle of the Ni-Ru complexes have also been carried out. They allowed us to suggest a bio-relevant bridging hydride as the catalytic intermediate. Finally, we synthesized one of the first Ni-Fe complexes that is both a structural and a functional model of NiFe hydrogenase. (author)

  15. High pressure CO hydrogenation over bimetallic Pt-Co catalysts

    DEFF Research Database (Denmark)

    Christensen, Jakob Munkholt; Medford, Andrew James; Studt, Felix;

    2014-01-01

    The potential of bimetallic Pt-Co catalysts for production of higher alcohols in high pressure CO hydrogenation has been assessed. Two catalysts (Pt3Co/SiO2 and PtCo/SiO2) were tested, and the existing literature on CO hydrogenation over Pt-Co catalysts was reviewed. It is found that the catalysts...... produce mainly methanol in the Pt-rich composition range andmainly hydrocarbons (and to a modest extent higher alcohols) in the Co-rich composition range. The transition between the two types of behavior occurs in a narrow composition range around a molar Pt:Co ratio of 1:1....

  16. Theoretical predictions of platinum-rhodium bimetallic catalysts

    International Nuclear Information System (INIS)

    After a general introduction to supported bimetallic catalysts and automobile catalytic converters (supports, base metal promoters, noble metals, deterioration of 3-way catalysts, current/future technology), a paper is presented for surface segregation in bimetallic catalysts: The catalytic properties are influenced by the structure of the cluster surface. Two methods are described to treat this problem, from the demanding corrected effective medium (CEM) theory (a non-self-consistent density functional based method) and the simple method of surface modified pair potentials. Predictions are compared with experiment for the heat of formation in RhxPt1-x alloys and for surface segregation in Rh0.9Pt0.1(111). Results on shape, site composition, surface micromixing are shown for 201 atom clusters (dispersion of 0.6) and RhxPt1-x(111). The CEM calculated cohesive energy of Rh is slightly smaller than for Pt, but the surface energy of Rh is larger: the driving force for surface segregation is the relative surface energies, not the relative cohesive energies. One can predict surface energy differences by accounting for the variation of the bond energy with coordination. Recommendations for the development of improved automobile exhaust catalysts are given. The Monte Carlo bimetallic simulation program is described

  17. Bimetallic catalysts for upgrading of biomass to fuels and chemicals.

    Science.gov (United States)

    Alonso, David Martin; Wettstein, Stephanie G; Dumesic, James A

    2012-12-21

    Research interest in biomass conversion to fuels and chemicals has increased significantly in the last decade as the necessity for a renewable source of carbon has become more evident. Accordingly, many different reactions and processes to convert biomass into high-value products and fuels have been proposed in the literature. Special attention has been given to the conversion of lignocellulosic biomass, which does not compete with food sources and is widely available as a low cost feedstock. In this review, we start with a brief introduction on lignocellulose and the different chemical structures of its components: cellulose, hemicellulose, and lignin. These three components allow for the production of different chemicals after fractionation. After a brief overview of the main reactions involved in biomass conversion, we focus on those where bimetallic catalysts are playing an important role. Although the reactions are similar for cellulose and hemicellulose, which contain C(6) and C(5) sugars, respectively, different products are obtained, and therefore, they have been reviewed separately. The third major fraction of lignocellulose that we address is lignin, which has significant challenges to overcome, as its structure makes catalytic processing more challenging. Bimetallic catalysts offer the possibility of enabling lignocellulosic processing to become a larger part of the biofuels and renewable chemical industry. This review summarizes recent results published in the literature for biomass upgrading reactions using bimetallic catalysts. PMID:22872312

  18. Bimetallic Catalysts Containing Gold and Palladium for Environmentally Important Reactions

    Directory of Open Access Journals (Sweden)

    Ahmad Alshammari

    2016-07-01

    Full Text Available Supported bimetallic nanoparticles (SBN are extensively used as efficient redox catalysts. This kind of catalysis particularly using SBN has attracted immense research interest compared to their parent metals due to their unique physico-chemical properties. The primary objective of this contribution is to provide comprehensive overview about SBN and their application as promising catalysts. The present review contains four sections in total. Section 1 starts with a general introduction, recent progress, and brief summary of the application of SBN as promising catalysts for different applications. Section 2 reviews the preparation and characterization methods of SBN for a wide range of catalytic reactions. Section 3 concentrates on our own results related to the application of SBN in heterogeneous catalysis. In this section, the oxidation of cyclohexane to adipic acid (an eco-friendly and novel approach will be discussed. In addition, the application of bimetallic Pd catalysts for vapor phase toluene acetoxylation in a fixed bed reactor will also be highlighted. Acetoxylation of toluene to benzyl acetate is another green route to synthesize benzyl acetate in one step. Finally, Section 4 describes the summary of the main points and also presents an outlook on the application of SBN as promising catalysts for the production of valuable products.

  19. Direct comparison of the performance of a bio-inspired synthetic nickel catalyst and a [NiFe]-hydrogenase, both covalently attached to electrodes.

    Science.gov (United States)

    Rodriguez-Maciá, Patricia; Dutta, Arnab; Lubitz, Wolfgang; Shaw, Wendy J; Rüdiger, Olaf

    2015-10-12

    The active site of hydrogenases has been a source of inspiration for the development of molecular catalysts. However, direct comparisons between molecular catalysts and enzymes have not been possible because different techniques are used to evaluate both types of catalysts, minimizing our ability to determine how far we have come in mimicking the enzymatic performance. The catalytic properties of the [Ni(P(Cy) 2 N(Gly) 2 )2 ](2+) complex with the [NiFe]-hydrogenase from Desulfovibrio vulgaris immobilized on a functionalized electrode were compared under identical conditions. At pH 7, the enzyme shows higher activity and lower overpotential with better stability, while at low pH, the molecular catalyst outperforms the enzyme in all respects. This is the first direct comparison of enzymes and molecular complexes, enabling a unique understanding of the benefits and detriments of both systems, and advancing our understanding of the utilization of these bio-inspired complexes in fuel cells. PMID:26140506

  20. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction

    Energy Technology Data Exchange (ETDEWEB)

    Chunshan, Song; Kirby, S.; Schmidt, E. [Pennsylvania State Univ., University Park, PA (United States)] [and others

    1995-12-31

    The objective of this project is to explore bimetallic dispersed catalysts for more efficient coal liquefaction. Coal liquefaction involves cleavage of methylene, dimethylene and ether bridges connecting various aromatic units and the reactions of various oxygen functional groups. This paper describes recent results on (1) hydrodeoxygenation of O-containing polycyclic model compounds using novel organometallic catalyst precursors; and (2) activity and selectivity of dispersed Fe catalysts from organometallic and inorganic precursors for hydrocracking of 4-(1-naphthylmethyl) bibenzyl. The results showed that some iron containing catalysts have higher activity in the sulfur-free form, contrary to conventional wisdom. Adding sulfur to Fe precursors with Cp-ligands decreased the activity of the resulting catalyst. This is in distinct contrast to the cases with iron pentacarbonyl and superfine Fe{sub 2}O{sub 3}, where S addition increased their catalytic activity substantially. A positive correlation between sulfur addition and increased activity can be seen, but a reversed trend between Fe cluster size and hydrocracking conversion could be observed, for carbonyl-type Fe precursors. It is apparent that the activity and selectivity of Fe catalysts for NMBB conversion depends strongly on both the type of ligand environment, the oxidation state and the number of intermetal bonds in the molecular precursor.

  1. Fundamental investigations of supported monometallic and bimetallic catalysts by proton magnetic resonance spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Xi.

    1990-09-21

    Proton magnetic resonance spectroscopy, or nuclear magnetic resonance (NMR) of hydrogen, has been applied to investigate silica-supported Group VIII monometallic and Group VIII-Group IB bimetallic catalysts and alumina- and silica-supported platinum-rhenium bimetallic catalysts. Two adsorbed states of hydrogen, i.e., irreversible and reversible hydrogen, on the surfaces of monometallic Ru, Pt, and Cu particles and bimetallic Ru-Group Ib, Pt-Group Ib, and Pt-Re particles were observed directly via proton NMR. The same amounts of the irreversible hydrogen adsorbed on pure Ru catalysts were measured by both proton NMR and the volumetric technique. The electronic environments on surfaces of monometallic catalysts are sensitive to changes in metal dispersion, state of adsorbed hydrogen, and residual chlorine. Surface compositions for the Ru--Cu and Pt--Cu bimetallic catalysts were determined by NMR of adsorbed hydrogen. 297 refs., 96 figs., 19 tabs.

  2. Direct Comparison of the Performance of a Bio-inspired Synthetic Nickel Catalyst and a [NiFe]-Hydrogenase, Both Covalently Attached to Electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Macia, Patricia; Dutta, Arnab; Lubitz, Wolfgang; Shaw, Wendy J.; Rudiger, Olaf

    2015-10-12

    The active site of hydrogenases has been a source of inspiration for the development of molecular catalysts. However, direct comparisons between molecular catalysts and enzymes have not been possible because different techniques are used to evaluate both types of catalysts, minimizing our ability to determine how far we’ve come in mimicking the impressive enzymatic performance. Here we directly compare the catalytic properties of the [Ni(PCy2NGly2)2]2+ complex with the [NiFe]-hydrogenase from Desulfobivrio vulgaris Miyazaki F (DvMF) immobilized to a functionalized electrode under identical conditions. At pH=7, the enzyme has higher performance in both activity and overpotential, and is more stable, while at low pH, the molecular catalyst outperforms the enzyme in all respects. The Ni complex also has increased tolerance to CO. This is the first direct comparison of enzymes and molecular complexes, enabling a unique understanding of the benefits and detriments of both systems, and advancing our understanding of the utilization of these bioinspired complexes in fuel cells. AD and WJS acknowledge the Office of Science Early Career Research Program through the US Department of Energy (US DOE), Office of Science, Office of Basic Energy Sciences (BES), and Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the US DOE.

  3. Enantioselective Epoxide Polymerization Using a Bimetallic Cobalt Catalyst

    KAUST Repository

    Thomas, Renee M.

    2010-11-24

    A highly active enantiopure bimetallic cobalt complex was explored for the enantioselective polymerization of a variety of monosubstituted epoxides. The polymerizations were optimized for high rates and stereoselectivity, with s-factors (kfast/kslow) for most epoxides exceeding 50 and some exceeding 300, well above the threshold for preparative utility of enantiopure epoxides and isotactic polyethers. Values for mm triads of the resulting polymers are typically greater than 95%, with some even surpassing 98%. In addition, the use of a racemic catalyst allowed the preparation of isotactic polyethers in quantitative yields. The thermal properties of these isotactic polyethers are presented, with many polymers exhibiting high T m values. This is the first report of the rapid synthesis of a broad range of highly isotactic polyethers via the enantioselective polymerization of racemic epoxides. © 2010 American Chemical Society.

  4. Direct decomposition of methane over SBA-15 supported Ni, Co and Fe based bimetallic catalysts

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Synthesis and characterization of Ni, Co and Fe based bimetallic catalysts supported over SBA-15. • Thermocatalytic decomposition of methane over the SBA-15 supported bimetallic catalysts. • Enhanced catalytic efficiency of the bimetallic catalysts for the production of COx free hydrogen and nanocarbon. • Production of value added open tip hollow multi-walled carbon nanotubes. • Crystalline characterization of carbon nanotubes by XRD, Raman and thermogravimetric analysis. - Abstract: Thermocatalytic decomposition of methane is an alternative route for the production of COx-free hydrogen and carbon nanomaterials. In this work, a set of novel Ni, Co and Fe based bimetallic catalysts supported over mesoporous SBA-15 was synthesized by a facile wet impregnation route, characterized for their structural, textural and reduction properties and were successfully used for the methane decomposition. The fine dispersion of metal oxide particles on the surface of SBA-15, without affecting its mesoporous texture was clearly shown in the low angle X-ray diffraction patterns and the transmission electron microscopy (TEM) images. The nitrogen sorption analysis showed the reduced specific surface area and pore volume of SBA-15, after metal loading due to the partial filling of hexagonal mesopores by metal species. The results of methane decomposition experiments indicated that all of the bimetallic catalysts were highly active and stable for the reaction at 700 °C even after 300 min of time on stream (TOS). However, a maximum hydrogen yield of ∼56% was observed for the NiCo/SBA-15 catalyst within 30 min of TOS. A high catalytic stability was shown by the CoFe/SBA-15 catalyst with 51% of hydrogen yield during the course of reaction. The catalytic stability of the bimetallic catalysts was attributed to the formation of bimetallic alloys. Moreover, the deposited carbons were found to be in the form of a new set of hollow multi

  5. Direct decomposition of methane over SBA-15 supported Ni, Co and Fe based bimetallic catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Pudukudy, Manoj, E-mail: manojpudukudy@gmail.com [Fuel Cell Institute, Universiti Kebangsaan Malaysia, UKM, Bangi 43600, Selangor (Malaysia); Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, UKM, Bangi 43600, Selangor (Malaysia); Yaakob, Zahira, E-mail: zahirayaakob65@gmail.com [Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, UKM, Bangi 43600, Selangor (Malaysia); Akmal, Zubair Shamsul [Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, UKM, Bangi 43600, Selangor (Malaysia)

    2015-03-01

    Graphical abstract: - Highlights: • Synthesis and characterization of Ni, Co and Fe based bimetallic catalysts supported over SBA-15. • Thermocatalytic decomposition of methane over the SBA-15 supported bimetallic catalysts. • Enhanced catalytic efficiency of the bimetallic catalysts for the production of CO{sub x} free hydrogen and nanocarbon. • Production of value added open tip hollow multi-walled carbon nanotubes. • Crystalline characterization of carbon nanotubes by XRD, Raman and thermogravimetric analysis. - Abstract: Thermocatalytic decomposition of methane is an alternative route for the production of CO{sub x}-free hydrogen and carbon nanomaterials. In this work, a set of novel Ni, Co and Fe based bimetallic catalysts supported over mesoporous SBA-15 was synthesized by a facile wet impregnation route, characterized for their structural, textural and reduction properties and were successfully used for the methane decomposition. The fine dispersion of metal oxide particles on the surface of SBA-15, without affecting its mesoporous texture was clearly shown in the low angle X-ray diffraction patterns and the transmission electron microscopy (TEM) images. The nitrogen sorption analysis showed the reduced specific surface area and pore volume of SBA-15, after metal loading due to the partial filling of hexagonal mesopores by metal species. The results of methane decomposition experiments indicated that all of the bimetallic catalysts were highly active and stable for the reaction at 700 °C even after 300 min of time on stream (TOS). However, a maximum hydrogen yield of ∼56% was observed for the NiCo/SBA-15 catalyst within 30 min of TOS. A high catalytic stability was shown by the CoFe/SBA-15 catalyst with 51% of hydrogen yield during the course of reaction. The catalytic stability of the bimetallic catalysts was attributed to the formation of bimetallic alloys. Moreover, the deposited carbons were found to be in the form of a new set of hollow

  6. Non-Precious Bimetallic Catalysts for Selective Dehydrogenation of an Organic Chemical Hydride System

    KAUST Repository

    Shaikh Ali, Anaam

    2015-07-06

    Methylcyclohexane (MCH)-Toluene (TOL) chemical hydride cycles as a hydrogen carrier system is successful with the selective dehydrogenation reaction of MCH to TOL, which has been achieved only using precious Pt-based catalysts. Herein, we report improved selectivity using non-precious metal nickel-based bimetallic catalysts, where the second metal occupies the unselective step sites.

  7. Methods to synthesize NiPt bimetallic nanoparticles by a reversed-phase microemulsion, deposition of NiPt bimetallic nanoparticles on a support, and application of the supported catalyst for CO.sub.2 reforming of methane

    KAUST Repository

    Biausque, Gregory

    2015-04-28

    Methods to synthesize NiPt bimetallic nanoparticles by a reversed-phase microemulsion, deposition of NiPt bimetallic nanoparticles on a support, and application of the supported catalyst for CO.sub.2 reforming of methane

  8. Synergistic Effects in Bimetallic Palladium-Copper Catalysts Improve Selectivity in Oxygenate Coupling Reactions.

    Science.gov (United States)

    Goulas, Konstantinos A; Sreekumar, Sanil; Song, Yuying; Kharidehal, Purnima; Gunbas, Gorkem; Dietrich, Paul J; Johnson, Gregory R; Wang, Y C; Grippo, Adam M; Grabow, Lars C; Gokhale, Amit A; Toste, F Dean

    2016-06-01

    Condensation reactions such as Guerbet and aldol are important since they allow for C-C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO. PMID:27195582

  9. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Chunshan Song; Schobert, H.H.; Parfitt, D.P. [and others

    1997-11-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that dispersed catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on exploring novel bimetallic dispersed catalysts for coal liquefaction and the effectiveness of temperature-programmed liquefaction using dispersed catalysts. The primary objective of this research was to explore novel bimetallic dispersed catalysts from organometallic molecular precursors, that could be used in low concentrations but exhibit relatively high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. We have synthesized and tested various catalyst precursors in liquefaction of subbituminous and bituminous coals and in model compound studies to examine how do the composition and structure of the catalytic precursors affect their effectiveness for coal liquefaction under different reaction conditions, and how do these factors affect their catalytic functions for hydrogenation of polyaromatic hydrocarbons, for cleavage of C-C bonds in polycyclic systems such as 4-(1-naphthylmethyl)bibenzyl, for hydrogenolysis of C-O bond such as that in dinaphthylether, for hydrodeoxygenation of phenolic compounds and other oxygen-containing compounds such as xanthene, and for hydrodesulfurization of polycyclic sulfur compounds such as dibenzothiophene. The novel bimetallic and monometallic precursors synthesized and tested in this project include various Mo- and Fe-based compounds.

  10. Levulinic acid hydrogenolysis on Al2O3-based Ni-Cu bimetallic catalysts

    Institute of Scientific and Technical Information of China (English)

    Iker Obregón; Eriz Corro; Urko Izquierdo; Jesus Requies; Pedro L. Arias

    2014-01-01

    Inexpensive γ-alumina-based nickel-copper bimetallic catalysts were studied for the hydrogenolysis of levulinic acid, a key platform molecule for biomass conversion to biofuels and other valued chemicals, into γ-valerolactone as a first step towards the production of 2-methyltetrahydrofurane. The activities of both monometallic and bimetallic catalysts were tested. Their textural and chemical characteristics were determined by nitrogen physisorption, elemental analysis, temperature-pro-grammed ammonia desorption, and temperature-programmed reduction. The monometallic nickel catalyst showed high activity but the highest by-product production and significant amounts of carbon deposited on the catalyst surface. The copper monometallic catalyst showed the lowest activity but the lowest carbon deposition. The incorporation of the two metals generated a bimetal-lic catalyst that displayed a similar activity to that of the Ni monometallic catalyst and significantly low by-product and carbon contents, indicating the occurrence of important synergetic effects. The influence of the preparation method was also examined by studying impregnated- and sol-gel-derived bimetallic catalysts. A strong dependency on the preparation procedure and calcina-tion temperature was observed. The highest activity per metal atom was achieved using the sol-gel-derived catalyst that was calcined at 450 °C. High reaction rates were achieved;the total levulinic acid conversion was obtained in less than 2 h of reaction time, yielding up to 96%γ-valerolactone, at operating temperature and pressure of 250 °C and 6.5 MPa hydrogen, respec-tively.

  11. Synergy between metals in bimetallic zeolite supported catalyst for NO-promoted N2O decomposition

    NARCIS (Netherlands)

    Pieterse, J.A.Z.; Mul, G.; Melian-Cabrera, I.; van den Brink, R.W.

    2005-01-01

    The detrimental effect of NO on N2O decomposition over zeolite supported noble metal catalysts can be (partly) eliminated by combining noble metal with iron or cobalt. In the presence of NO, the total conversion of N2O over these bimetallic-zeolites exceeds the sum of conversions over the monometall

  12. Comparison of Bimetallic and Trimetallic Catalyst in Reductive Dechlorination; Influence of Copper Addition

    Czech Academy of Sciences Publication Activity Database

    Kaštánek, František; Kaštánek, Petr; Maléterová, Ywetta; Kallistová, A.; Šolcová, Olga

    2015-01-01

    Roč. 2, č. 7 (2015), s. 1954-1958. E-ISSN 3159-0040 R&D Projects: GA TA ČR TA04020700 Institutional support: RVO:67985858 ; RVO:67985831 Keywords : PCB * reductive dechlorination * bimetallic and trimetallic catalysts Subject RIV: CI - Industrial Chemistry, Chemical Engineering http://www.jmest.org/wp-content/uploads/JMESTN42350950.pdf

  13. Controlled surface segregation leads to efficient coke-resistant nickel/platinum bimetallic catalysts for the dry reforming of methane

    KAUST Repository

    Li, Lidong

    2015-02-03

    Surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. The evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core-shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. These catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure. The reform of reforming: A series of alumina-supported Ni/Pt bimetallic nanoparticles (NPs) with controlled surface composition and structure are prepared. Remarkable surface segregation for these bimetallic NPs is observed upon thermal treatment. These bimetallic NPs are active catalysts for CO2 reforming of CH4, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.

  14. Controlled Surface Segregation Leads to Efficient Coke-Resistant Nickel/Platinum Bimetallic Catalysts for the Dry Reforming of Methane

    Energy Technology Data Exchange (ETDEWEB)

    Li, Lidong [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); Zhou, Lu [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); Ould-Chikh, Samy [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); Anjum, Dalaver H. [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); Kanoun, Mohammed B. [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); Scaranto, Jessica [SABIC Corporate Research and Innovation Center, Thuwal (Saudi Arabia); Hedhili, Mohamed N. [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); Khalid, Syed [Brookhaven National Lab. (BNL), Upton, NY (United States); Laveille, Paco V. [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); D' Souza, Lawrence [SABIC Corporate Research and Innovation Center, Thuwal (Saudi Arabia); Clo, Alain [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia); Basset, Jean-Marie [King Abdullah Univ. of Science and Technology, Thuwal (Saudi Arabia)

    2015-02-03

    The surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. Moreover, the evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. The catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.

  15. Nanosegregated bimetallic oxide anode catalyst for proton exchange membrane electrolyzer

    Energy Technology Data Exchange (ETDEWEB)

    Danilovic, Nemanja; Kang, Yijin; Markovic, Nenad; Stamenkovic, Vojislav; Myers, Deborah J.; Subbaraman, Ram

    2016-08-23

    A surface segregated bimetallic composition of the formula Ru.sub.1-xIr.sub.x wherein 0.1.ltoreq.x.ltoreq.0.75, wherein a surface of the material has an Ir concentration that is greater than an Ir concentration of the material as a whole is provided. The surface segregated material may be produced by a method including heating a bimetallic composition of the formula Ru.sub.1-xIr.sub.x, wherein 0.1.ltoreq.x.ltoreq.0.75, at a first temperature in a reducing environment, and heating the composition at a second temperature in an oxidizing environment. The surface segregated material may be utilized in electrochemical devices.

  16. SULFUR-RESISTANT BIMETALLIC NOBLE METAL CATALYSTS FOR AROMATIC HYDROGENATION OF DIESEL FUEL

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Y zeolite supporting noble metal catalysts, as the important industrial catalysts for aromatics hydrogenation, have received increasing attention in recent years. Pd-M/Y bimetallic catalysts, where M is non-noble metal element, were prepared to investigate the effects of the addition of a second metal. Pd-M/Y catalysts were evaluated under the following conditions: H2 pressure 4.2 MPa, MHSV 4.0 h-1, sulfur content in feed 3000 μg/g. The microreactor results indicated that the second metal remarkably affects the hydrogenation activity of Pd/Y catalysts. Among them, Cr and W improve the sulfur resistance of Pd/Y, but La, Mn, Mo and Ag make the sulfur resistance worse and the second metals have no evident influence on product selectivity and acidic properties of the catalysts.

  17. Selective hydrogenation of citral over Au-based bimetallic catalysts in supercritical carbon dioxide

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Selective hydrogenation of citral was investigated over Au-based bimetallic catalysts in the environmentally benign supercritical carbon dioxide (scCO2) medium.The catalytic performances were different in citral hydrogenation when Pd or Ru was mixed (physically and chemically) with Au.Compared with the corresponding monometallic catalyst,the total conversion and the selectivity to citronellal (CAL) were significantly enhanced over TiO2 supported Pd and Au bimetallic catalysts (physically and chemically mixed);however,the conversion and selectivity did not change when Ru was physically mixed with Au catalyst compared to the monometallic Ru/TiO2,and the chemically mixed Ru-Au/TiO2 catalyst did not show any activity.The effect of CO2 pressure on the conversion of citral and product selectivity was significantly different over the Au/TiO2,Pd-Au/TiO2,and Pd/TiO2 catalysts.It was assumed to be ascribed to the difference in the interactions between Au,Pd nanoparticles and CO2 under different CO2 pressures.

  18. Bimetallic Palladium Catalysts for Methane Combustion in Gas Turbines

    OpenAIRE

    Persson, Katarina

    2006-01-01

    Catalytic combustion is a promising combustion technology for gas turbines, which results in ultra low emission levels of nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons (UHC). Due to the low temperature achieved in catalytic combustion almost no thermal NOx is formed. This thesis is concentrated on the first stage in a catalytic combustion chamber, i.e. the ignition catalyst. The catalyst used for this application is often a supported palladium based catalyst due to its...

  19. Exceptional methanol electro-oxidation activity by bimetallic concave and dendritic Pt-Cu nanocrystals catalysts

    Science.gov (United States)

    Wang, Ying-Xia; Zhou, Hui-Jing; Sun, Ping-Chuan; Chen, Tie-Hong

    2014-01-01

    PtCux (x = 1, 2 and 3) bimetallic nanocrystals with concave surface and dendritic morphology were prepared and used as electrocatalysts in methanol oxidation reaction (MOR) for polymer electrolyte membrane fuel cells. The bimetallic nanocrystals were synthesized via one-pot co-reduction of H2PtCl6 and Cu(acac)2 by oleylamine and polyvinyl pyrrolidone (PVP) in an autoclave at 180 °C. The concave dendritic bimetallic nanostructure consisted of a core rich in Cu and nanodendrites rich in Pt, which was formed via galvanic replacement of Cu by Pt. It was found that PVP played an important role in initiating, facilitating, and directing the replacement reaction. The electrochemical properties of the PtCux were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The concave dendritic PtCu2/C nanocrystals exhibited exceptionally high activity and strong poisoning resistance in MOR. At 0.75 V (vs. reversible hydrogen electrode, RHE) the mass activity and specific activity of PtCu2/C were 3.3 and 4.1 times higher than those of the commercial Pt/C catalysts, respectively. The enhanced catalytic activity could be attributed to the unique concave dendritic morphology of the bimetallic nanocrystals.

  20. Enantioselective polymerization of epoxides using biaryl-linked bimetallic cobalt catalysts: A mechanistic study

    KAUST Repository

    Ahmed, Syud M.

    2013-12-18

    The enantioselective polymerization of propylene oxide (PO) using biaryl-linked bimetallic salen Co catalysts was investigated experimentally and theoretically. Five key aspects of this catalytic system were examined: (1) the structural features of the catalyst, (2) the regio- and stereoselectivity of the chain-growth step, (3) the probable oxidation and electronic state of Co during the polymerization, (4) the role of the cocatalyst, and (5) the mechanism of monomer enchainment. Several important insights were revealed. First, density functional theory (DFT) calculations provided detailed structural information regarding the regio- and stereoselective chain-growth step. Specifically, the absolute stereochemistry of the binaphthol linker determines the enantiomer preference in the polymerization, and the interaction between the salen ligand and the growing polymer chain is a fundamental aspect of enantioselectivity. Second, a new bimetallic catalyst with a conformationally flexible biphenol linker was synthesized and found to enantioselectively polymerize PO, though with lower enantioselectivity than the binaphthol linked catalysts. Third, DFT calculations revealed that the active form of the catalyst has two active exo anionic ligands (chloride or carboxylate) and an endo polymer alkoxide which can ring-open an adjacent cobalt-coordinated epoxide. Fourth, calculations showed that initiation is favored by an endo chloride ligand, while propagation is favored by the presence of two exo carboxylate ligands. © 2013 American Chemical Society.

  1. Effects of bimetallic catalysts on synthesis of nitrogen-doped carbon nanotubes as nanoscale energetic materials

    Institute of Scientific and Technical Information of China (English)

    Hao Liu; Yong Zhang; Ruying Li; Xueliang Sun; Hakima Abou-Rachid

    2011-01-01

    Well aligned nitrogen-doped carbon nanotubes (CNx-NTs),as energetic materials,are synthesized on a silicon substrate by aerosol-assisted chemical vapor deposition.Tungsten (W) and molybdenum (Mo) metals are respectively introduced to combine with iron (Fe) to act as a bimetallic co-catalyst layer.Correlations between the composition and shape of the co-catalyst and morphology,size,growth rate and nitrogen doping amount of the synthesized CNx-NTs are investigated by secondary and backscattered electron imaging in a field emission scanning electron microscope (FESEM) and X-ray photoelectron spectrometer (XPS).Compared to pure iron catalyst.W-Fe co-catalyst can result in lower growth rate,larger diameter and wider size distribution of the CNx-NTs; while incorporation of molybdenum into the iron catalyst layer can reduce the diameter and size distribution of the nanotubes.Compared to the sole iron catalyst,Fe-W catalyst impedes nitrogen doping while Fe-Mo catalyst promotes the incorporation of nitrogen into the nanotubes.The present work indicates that CNx-NTs with modulated size,growth rate and nitrogen doping concentration are expected to be synthesized by tuning the size and composition of co-catalysts,which may find great potential in producing CNx-NTs with controlled structure and properties.

  2. Understanding and controlling nanoporosity formation for improving the stability of bimetallic fuel cell catalysts.

    Science.gov (United States)

    Gan, Lin; Heggen, Marc; O'Malley, Rachel; Theobald, Brian; Strasser, Peter

    2013-03-13

    Nanoporosity is a frequently reported phenomenon in bimetallic particle ensembles used as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. It is generally considered a favorable characteristic, because it increases the catalytically active surface area. However, the effect of nanoporosity on the intrinsic activity and stability of a nanoparticle electrocatalyst has remained unclear. Here, we present a facile atmosphere-controlled acid leaching technique to control the formation of nanoporosity in Pt-Ni bimetallic nanoparticles. By statistical analysis of particle size, composition, nanoporosity, and atomic-scale core-shell fine structures before and after electrochemical stability test, we uncover that nanoporosity formation in particles larger than ca. 10 nm is intrinsically tied to a drastic dissolution of Ni and, as a result of this, a rapid drop in intrinsic catalytic activity during ORR testing, translating into severe catalyst performance degradation. In contrast, O2-free acid leaching enabled the suppression of nanoporosity resulting in more solid core-shell particle architectures with thin Pt-enriched shells; surprisingly, such particles maintained high intrinsic activity and improved catalytic durability under otherwise identical ORR tests. On the basis of these findings, we suggest that catalytic stability could further improve by controlling the particle size below ca. 10 nm to avoid nanoporosity. Our findings provide an explanation for the degradation of bimetallic particle ensembles and show an easy to implement pathway toward more durable fuel cell cathode catalysts. PMID:23360425

  3. Reverse Micelle Synthesis and Characterization of Supported Pt/Ni Bimetallic Catalysts on gamma-Al2O3

    Energy Technology Data Exchange (ETDEWEB)

    B Cheney; J Lauterbach; J Chen

    2011-12-31

    Reverse micelle synthesis was used to improve the nanoparticle size uniformity of bimetallic Pt/Ni nanoparticles supported on {gamma}-Al{sub 2}O{sub 3}. Two impregnation methods were investigated to optimize the use of the micelle method: (1) step-impregnation, where Ni nanoparticles were chemically reduced in microemulsion and then supported, followed by Pt deposition using incipient wetness impregnation, and (2) co-impregnation, where Ni and Pt were chemically reduced simultaneously in microemulsion and then supported. Transmission electron microscopy (TEM) was used to characterize the particle size distribution. Atomic absorption spectroscopy (AAS) was used to perform elemental analysis of bimetallic catalysts. Extended X-ray absorption fine structure (EXAFS) measurements were utilized to confirm the formation of the Pt-Ni bimetallic bond in the step-impregnated catalyst. CO pulse chemisorption and Fourier transform infrared spectroscopy (FTIR) studies of 1,3-butadiene hydrogenation in a batch reactor were performed to determine the catalytic activity. Step-impregnated Pt/Ni catalyst demonstrated enhanced hydrogenation activity over the parent monometallic Pt and Ni catalysts due to bimetallic bond formation. The catalyst synthesized using co-impregnation showed no enhanced activity, behaving similarly to monometallic Ni. Overall, our results indicate that reverse micelle synthesis combined with incipient wetness impregnation produced small, uniform nanoparticles with bimetallic bonds that enhanced hydrogenation activity.

  4. Strategies for designing supported gold-palladium bimetallic catalysts for the direct synthesis of hydrogen peroxide.

    Science.gov (United States)

    Edwards, Jennifer K; Freakley, Simon J; Carley, Albert F; Kiely, Christopher J; Hutchings, Graham J

    2014-03-18

    Hydrogen peroxide is a widely used chemical but is not very efficient to make in smaller than industrial scale. It is an important commodity chemical used for bleaching, disinfection, and chemical manufacture. At present, manufacturers use an indirect process in which anthraquinones are sequentially hydrogenated and oxidized in a manner that hydrogen and oxygen are never mixed. However, this process is only economic at a very large scale producing a concentrated product. For many years, the identification of a direct process has been a research goal because it could operate at the point of need, producing hydrogen peroxide at the required concentration for its applications. Research on this topic has been ongoing for about 100 years. Until the last 10 years, catalyst design was solely directed at using supported palladium nanoparticles. These catalysts require the use of bromide and acid to arrest peroxide decomposition, since palladium is a very active catalyst for hydrogen peroxide hydrogenation. Recently, chemists have shown that supported gold nanoparticles are active when gold is alloyed with palladium because this leads to a significant synergistic enhancement in activity and importantly selectivity. Crucially, bimetallic gold-based catalysts do not require the addition of bromide and acids, but with carbon dioxide as a diluent its solubility in the reaction media acts as an in situ acid promoter, which represents a greener approach for peroxide synthesis. The gold catalysts can operate under intrinsically safe conditions using dilute hydrogen and oxygen, yet these catalysts are so active that they can generate peroxide at commercially significant rates. The major problem associated with the direct synthesis of hydrogen peroxide concerns the selectivity of hydrogen usage, since in the indirect process this factor has been finely tuned over decades of operation. In this Account, we discuss how the gold-palladium bimetallic catalysts have active sites for the

  5. Using supported Au nanoparticles as starting material for preparing uniform Au/Pd bimetallic catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Villa, Alberto [Universita di Milano, Italy; Prati, Laura [Universita di Milano, Italy; Su, Dangshen [Fritz Haber Institute of the Max Planck Society, Berlin, Germany; Wang, Di [Fritz Haber Institute of the Max Planck Society, Berlin, Germany; Veith, Gabriel M [ORNL

    2010-01-01

    One of the best methods for producing bulk homogeneous (composition) supported bimetallic AuPd clusters involves the immobilization of a protected Au seed followed by the addition of Pd. This paper investigates the importance of this gold seed in controlling the resulting bimetallic AuPd clusters structures, sizes and catalytic activities by investigating three different gold seeds. Uniform Au-Pd alloy were obtained when a steric/electrostatic protecting group, poly(vinyl alcohol) (PVA), was used to form the gold clusters on activated carbon (AC). In contrast Au/AC precursors prepared using Au nanoparticles with only electrostatic stabilization (tetrakis(hydroxypropyl)phosphonium chloride (THPC)), or no stabilization (magnetron sputtering) produced inhomogeneous alloys and segregation of the gold and palladium. The uniform alloyed catalyst (Pd{at}Au{sub PVA}/AC) is the most active and selective catalyst, while the inhomogenous catalysts are less active and selective. Further study of the PVA protected Au clusters revealed that the amount of PVA used is also critical for the preparation of uniform alloyed catalyst, their stability, and their catalytic activity.

  6. Ethanol oxidation on carbon supported platinum-rhodium bimetallic catalysts

    International Nuclear Information System (INIS)

    Platinum is the most investigated catalyst for the electrochemical oxidation of small organic molecules. This metal presents high overpotentials for the oxidation of organic compounds and the poisoning of active sites by strongly adsorbed intermediates, mainly CO, which decrease the efficiency of a direct alcohol fuel cell (DAFC). Ethanol is an ideal fuel for these DAFC systems due to its high energy density, but one of the problems with the electro-oxidation of this fuel is the low yield for the total oxidation to CO2. The purpose of the work reported here was to study the influence of the composition of Pt-Rh/C catalysts on the CO2 yields. In addition, using the differential electrochemical mass spectrometry (DEMS) technique, it is shown that Pt-Rh/C catalysts enhance the total ethanol oxidation with respect to pure Pt/C by driving the reaction via the CO2 route. The faradaic current efficiency for the oxidation of ethanol to CO2 increased from 0.08 on pure Pt/C to 0.5 on the Pt47Rh53/C catalyst at 0.7 V vs. RHE. It was concluded that electronic effects play a key role in the mechanism of ethanol oxidation on Pt-Rh/C electrodes

  7. Final technical report. Bimetallic complexes as methanol oxidation catalysts

    Energy Technology Data Exchange (ETDEWEB)

    McElwee-White, Lisa

    2002-01-21

    Our work on the electrocatalyzed oxidation of methanol was initially motivated by the interest in methanol as an anodic reactant in fuel cells. The literature on electrochemical oxidation of alcohols can be roughly grouped into two sets: fuel cell studies and inorganic chemistry studies. Work on fuel cells primarily focuses on surface-catalyzed oxidation at bulk metal anodes, usually Pt or Pt/Ru alloys. In the surface science/electrochemistry approach to these studies, single molecule catalysts are generally not considered. In contrast, the inorganic community investigates the electrooxidation of alcohols in homogeneous systems. Ruthenium complexes have been the most common catalysts in these studies. The alcohol substrates are typically either secondary alcohols (e.g., isopropanol) such that the reaction stops after 2 e{sup -} oxidation to the aldehyde and 4 e{sup -} oxidation to the carboxylic acid can be observed. Methanol, which can also undergo 6 e{sup -} oxidation to CO{sub 2}, rarely appears in the homogeneous catalysis studies. Surface studies have shown that two types of metal centers with different functions result in more effective catalysts than a single metal; however, application of this concept to homogeneous systems has not been demonstrated. The major thrust of the work is to apply this insight from the surface studies to homogeneous catalysis. Even though homogeneous systems would not be appropriate models for active sites on Pt/Ru anodes, it is possible that heterobimetallic catalysts could also utilize two metal centers for different roles. Starting from that perspective, this work involves the preparation and investigation of heterobinuclear catalysts for the electrochemical oxidation of methanol.

  8. Synthesis and Characterization of Cluster-Derived Supported Bimetallic Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Adams, Richard D; Amiridis, Michael D

    2008-10-10

    New procedures have been developed for synthesizing di- and tri-metallic cluster complexes. The chemical properties of the new complexes have been investigated, particularly toward the activation of molecular hydrogen. These complexes were then converted into bi- and tri-metallic nanoparticles on silica and alumina supports. These nanoparticles were characterized by electron microscopy and were then tested for their ability to produce catalytic hydrogenation of unsaturated hydrocarbons and for the preferential oxidation of CO in the presence of hydrogen. The bi- and tri-metallic nanoparticles exhibited far superior activity and selectivity as hydrogenation catalysts when compared to the individual metallic components. It was found that the addition of tin greatly improved the selectivity of the catalysts for the hydrogenation of polyolefins. The addition of iron improves the catalysts for the selective oxidation of CO by platinum in the presence of hydrogen. The observations should lead to the development of lower cost routes to molecules that can be used to produce polymers and plastics for use by the general public and for procedures to purify hydrogen for use as an alternative energy in the hydrogen economy of the future.

  9. Synergetic effects leading to coke-resistant NiCo bimetallic catalysts for dry reforming of methane

    KAUST Repository

    Li, Lidong

    2015-01-08

    A new dry reforming of methane catalyst comprised of NiCo bimetallic nanoparticles and a Mgx(Al)O support that exhibits high coke resistance and long-term on-stream stability is reported. The structural characterization by XRD, TEM, temperature-programmed reduction, and BET analysis demonstrates that the excellent performance of this catalyst is ascribed to the synergy of various parameters, including metal-nanoparticle size, metal-support interaction, catalyst structure, ensemble size, and alloy effects.

  10. High-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles for phenol hydrogenation

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Chao [The Key Laboratory of Fuel Cell Technology of Guangdong Province and The Key Laboratory for New Energy of Guangdong Universities, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou (China); Yang, Xu [Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou (China); Yang, Hui; Huang, Peiyan; Song, Huiyu [The Key Laboratory of Fuel Cell Technology of Guangdong Province and The Key Laboratory for New Energy of Guangdong Universities, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou (China); Liao, Shijun, E-mail: chsjliao@scut.edu.cn [The Key Laboratory of Fuel Cell Technology of Guangdong Province and The Key Laboratory for New Energy of Guangdong Universities, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou (China)

    2014-10-01

    Graphical abstract: The addition of Ru could significantly improve the performance of the mesoporous silica nanoparticles supported PdRu/MSN catalyst, which showed over 5 times higher mass activity than the mono-Pd/MSN towards the liquid-phase hydrogenation of phenol. The improved dispersion and the electronic interaction contributed to the enhanced catalytic activity for the catalyst towards phenol hydrogenation. - Highlights: • PdRu bimetal catalyst supported on mesoporous silica nanoparticles was prepared. • The average sizeof PdRu alloy is smaller than that of mono-Pd. • The addition of Ru to Pd modulates the electronic properties between Pd and Ru. • PdRu/MSN catalyst shows superior activity on phenol hydrogenation than Pd/MSN. • PdRu/MSN catalyst shows good selectivity for cyclohexanol to some extent. - Abstract: A high-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles (MSN), PdRu/MSN, was prepared by a facile impregnation–hydrogen reduction method. It was found that PdRu/MSN showed 5 times higher activity than that of Pd/MSN towards the liquid-phase hydrogenation of phenol. The catalysts were characterized comprehensively by multiple techniques, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature program reduction (TPR). It was revealed that adding Ru could effectively improve the Pd dispersion and promote the electronic interaction between the Pd and Ru, both of which contribute to enhancing the catalytic activity.

  11. Nanocrystalline MgO supported nickel-based bimetallic catalysts for carbon dioxide reforming of methane

    Energy Technology Data Exchange (ETDEWEB)

    Meshkani, Fereshteh [Catalyst and Advanced Materials Research Laboratory, Chemical Engineering Department, Faculty of Engineering, University of Kashan, Kashan (Iran); Rezaei, Mehran [Catalyst and Advanced Materials Research Laboratory, Chemical Engineering Department, Faculty of Engineering, University of Kashan, Kashan (Iran); Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan (Iran)

    2010-10-15

    Nanocrystalline magnesium oxide with high surface area and plate-like shape was employed as catalyst support for preparation of nickel-based bimetallic catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N{sub 2} adsorption (BET), Temperature programmed oxidation and desorption (TPO-TPD), Thermal gravimetric and differential thermal gravimetric (TGA-DTG), H{sub 2} chemisorption and Transmission and electron microscopies (TEM and SEM) analyses. CO{sub 2}-TPD data showed the high CO{sub 2} adsorption capacity of catalysts which improves the resistance of catalysts against the carbon formation. The H{sub 2} chemisorption results also indicated that the addition of Pt to nickel catalyst improved the nickel dispersion. The obtained results revealed that the prepared catalysts showed a high activity and stability during the reaction with a low amount of deposited carbon. Addition of Pt to nickel catalyst improved both the activity and resistivity against carbon formation. (author)

  12. High-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles for phenol hydrogenation

    International Nuclear Information System (INIS)

    Graphical abstract: The addition of Ru could significantly improve the performance of the mesoporous silica nanoparticles supported PdRu/MSN catalyst, which showed over 5 times higher mass activity than the mono-Pd/MSN towards the liquid-phase hydrogenation of phenol. The improved dispersion and the electronic interaction contributed to the enhanced catalytic activity for the catalyst towards phenol hydrogenation. - Highlights: • PdRu bimetal catalyst supported on mesoporous silica nanoparticles was prepared. • The average sizeof PdRu alloy is smaller than that of mono-Pd. • The addition of Ru to Pd modulates the electronic properties between Pd and Ru. • PdRu/MSN catalyst shows superior activity on phenol hydrogenation than Pd/MSN. • PdRu/MSN catalyst shows good selectivity for cyclohexanol to some extent. - Abstract: A high-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles (MSN), PdRu/MSN, was prepared by a facile impregnation–hydrogen reduction method. It was found that PdRu/MSN showed 5 times higher activity than that of Pd/MSN towards the liquid-phase hydrogenation of phenol. The catalysts were characterized comprehensively by multiple techniques, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature program reduction (TPR). It was revealed that adding Ru could effectively improve the Pd dispersion and promote the electronic interaction between the Pd and Ru, both of which contribute to enhancing the catalytic activity

  13. Exploration of Cocatalyst Effects on a Bimetallic Cobalt Catalyst System: Enhanced Activity and Enantioselectivity in Epoxide Polymerization

    KAUST Repository

    Widger, Peter C. B.

    2011-07-26

    Organic ionic compounds were synthesized and investigated as cocatalysts with a bimetallic cobalt complex for enantioselective epoxide polymerization. The identities of both the cation and the anion were systematically varied, and the subsequent reactivity was studied. The nature of the ionic cocatalyst dramatically impacted the rate and enantioselectivity of the catalyst system. The ionic cocatalyst [P(N=P(N(CH2)4)3) 4 +][tBuCO2 -] in combination with a bimetallic cobalt complex produced a catalyst system that exhibited the greatest activity and selectivity for a variety of monosubstituted epoxides. © 2011 American Chemical Society.

  14. A superlattice of alternately stacked Ni-Fe hydroxide nanosheets and graphene for efficient splitting of water.

    Science.gov (United States)

    Ma, Wei; Ma, Renzhi; Wang, Chengxiang; Liang, Jianbo; Liu, Xiaohe; Zhou, Kechao; Sasaki, Takayoshi

    2015-02-24

    Cost-effective electrocatalysts based on nonprecious metals for efficient water splitting are crucial for various technological applications represented by fuel cell. Here, 3d transition metal layered double hydroxides (LDHs) with varied contents of Ni and Fe were successfully synthesized through a homogeneous precipitation. The exfoliated Ni-Fe LDH nanosheets were heteroassembled with graphene oxide (GO) as well as reduced graphene oxide (rGO) into superlattice-like hybrids, in which two kinds of oppositely charged nanosheets are stacked face-to-face in alternating sequence. Heterostructured composites of Ni2/3Fe1/3 LDH nanosheets and GO (Ni2/3Fe1/3-GO) exhibited an excellent oxygen evolution reaction (OER) efficiency with a small overpotential of about 0.23 V and Tafel slope of 42 mV/decade. The activity was further improved via the combination of Ni2/3Fe1/3 LDH nanosheets with more conductive rGO (Ni2/3Fe1/3-rGO) to achieve an overpotential as low as 0.21 V and Tafel plot of 40 mV/decade. The catalytic activity was enhanced with an increased Fe content in the bimetallic Ni-Fe system. Moreover, the composite catalysts were found to be effective for hydrogen evolution reaction. An electrolyzer cell powered by a single AA battery of 1.5 V was demonstrated by using the bifunctional catalysts. PMID:25605063

  15. CATALYSIS SCIENCE INITIATIVE: From First Principles Design to Realization of Bimetallic Catalysts for Enhanced Selectivity

    Energy Technology Data Exchange (ETDEWEB)

    MAVRIKAKIS, MANOS

    2007-05-03

    In this project, we have integrated state-of-the-art Density Functional Theory (DFT) models of heterogeneous catalytic processes with high-throughput screening of bimetallic catalytic candidates for important industrial problems. We have studied a new class of alloys characterized by a surface composition different from the bulk composition, and investigated their stability and activity for the water-gas shift reaction and the oxygen reduction reaction. The former reaction is an essential part of hydrogen production; the latter is the rate-limiting step in low temperature H2 fuel cells. We have identified alloys that have remarkable stability and activity, while having a much lower material cost for both of these reactions. Using this knowledge of bimetallic interactions, we have also made progress in the industrially relevant areas of carbohydrate reforming and conversion of biomass to liquid alkanes. One aspect of this work is the conversion of glycerol (a byproduct of biodiesel production) to synthesis gas. We have developed a bifunctional supported Pt catalyst that can cleave the carbon-carbon bond while also performing the water-gas shift reaction, which allows us to better control the H2:CO ratio. Knowledge gained from the theoretical metal-metal interactions was used to develop bimetallic catalysts that perform this reaction at low temperature, allowing for an efficient coupling of this endothermic reaction with other reactions, such as Fischer-Tropsch or methanol synthesis. In our work on liquid alkane production from biomass, we have studied deactivation and selectivity in these areas as a function of metal-support interactions and reaction conditions, with an emphasis on the bifunctionality of the catalysts studied. We have identified a stable, active catalyst for this process, where the selectivity and yield can be controlled by the reaction conditions. While complete rational design of catalysts is still elusive, this work demonstrates the power of

  16. Low-temperature aqueous-phase reforming of ethanol on bimetallic PdZn catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Xiong, Haifeng; DelaRiva, Andrew; Wang, Yong; Dayte, Abhaya

    2015-01-01

    Bimetallic PdZn catalysts supported on carbon black (CB) and carbon nanotubes (CNTs) were found to be selective for CO-free H-2 production from ethanol at low temperature (250 degrees C). On Pd, the H-2 yield was low (similar to 0.3 mol H-2/mol ethanol reacted) and the CH4/CO2 ratio was high (similar to 1.7). Addition of Zn to Pd formed the intermetallic PdZn beta phase (atomic ratio of Zn to Pd is 1) with increased H-2 yield (similar to 1.9 mol H-2/mol ethanol reacted) and CH4/CO2 ratio of <1. The higher H-2 yield and low CH4 formation was related to the improved dehydrogenation activity of the L1(0) PdZn beta phase. The TOF increased with particle size and the CNTs provided the most active and selective catalysts, which may be ascribed to pore-confinement effects. Furthermore, no significant changes in either the supports or the PdZn beta particles was found after aqueous-phase reforming (APR) indicating that the metal nanoparticles and the carbon support are hydrothermally stable in the aqueous phase at elevated temperatures and pressures (>200 degrees C, 65 bar). No CO was detected for all the catalysts performed in aqueous-phase reaction, indicating that both monometallic Pd and bimetallic PdZn catalysts have high water-gas shift activity during APR. However, the yield of H-2 is considerably lower than the theoretical value of 6 H-2 per mole ethanol which is due to the presence of oxygenated products and methane on the PdZn catalysts.

  17. thesis of high-purity carbon nanotubes over alumina and silica supported bimetallic catalysts

    Directory of Open Access Journals (Sweden)

    Sanja Ratković

    2009-10-01

    Full Text Available Carbon nanotubes (CNTs were synthesized by a catalytic chemical vapor deposition method (CCVD of ethylene over alumina and silica supported bimetallic catalysts based on Fe, Co and Ni. The catalysts were prepared by a precipitation method, calcined at 600 °C and in situ reduced in hydrogen flow at 700 °C. The CNTs growth was carried out by a flow the mixture of C2H4 and nitrogen over the catalyst powder in a horizontal oven. The structure and morphology of as-synthesized CNTs were characterized using SEM. The as-synthesized nanotubes were purified by acid and basic treatments in order to remove impurities such as amorphous carbon, graphite nanoparticles and metal catalysts. XRD and DTA/TG analyses showed that the amounts of by-products in the purified CNTs samples were reduced significantly. According to the observed results, ethylene is an active carbon source for growing high-density CNTs with high yield but more on alumina-supported catalysts than on their silica- supported counterparts. The last might be explained by SMSI formed in the case of alumina-supported catalysts, resulting in higher active phase dispersion.

  18. Surface-Bound Ligands Modulate Chemoselectivity and Activity of a Bimetallic Nanoparticle Catalyst

    KAUST Repository

    Vu, Khanh B.

    2015-04-03

    "Naked" metal nanoparticles (NPs) are thermodynamically and kinetically unstable in solution. Ligands, surfactants, or polymers, which adsorb at a particle\\'s surface, can be used to stabilize NPs; however, such a mode of stabilization is undesirable for catalytic applications because the adsorbates block the surface active sites. The catalytic activity and the stability of NPs are usually inversely correlated. Here, we describe an example of a bimetallic (PtFe) NP catalyst stabilized by carboxylate surface ligands that bind preferentially to one of the metals (Fe). NPs stabilized by fluorous ligands were found to be remarkably competent in catalyzing the hydrogenation of cinnamaldehyde; NPs stabilized by hydrocarbon ligands were significantly less active. The chain length of the fluorous ligands played a key role in determining the chemoselectivity of the FePt NP catalysts. (Chemical Presented). © 2015 American Chemical Society.

  19. Performance enhancement of bimetallic Co-Ru/CNTs nano catalysts using microemulsion technique

    Institute of Scientific and Technical Information of China (English)

    Ahmad; Tavasoli; Somayeh; Taghavi

    2013-01-01

    Bimetallic cobalt-ruthenium nano catalysts supported on carbon nanotubes(CNTs)are prepared using microemultion technique with water-to-surfactant ratios of 0.5—1.5.The nano catalysts were extensively characterized by different methods and their activity and selectivity in Fischer-Tropsch synthesis(FTS)have been assessed in a fixed-bed microreactor.The physicochemical properties and performance of the nanocatalysts were compared with the catalyst prepared by impregnation method.Very narrow particle size distribution has been produced by the microemulsion technique at relatively high loadings of active metals(15 wt%Co and 1 wt%Ru).According to TEM images,small Co particles(2—7 nm)were mostly confined inside the CNTs.Comparing with the catalyst prepared by impregnation,the use of microemulsion technique with water to surfactant ratio of 0.5 decreased the average cobalt oxide particle size to 4.8 nm,the dispersion was almost doubled and the reduction increased by 28%.Activity and selectivity were found to be dependent on the catalyst preparation method and water-to-surfactant ratio(as well as cobalt particle sizes).CO conversion increased from 59.1%to 75.1%and the FTS rate increased from 0.291 to0.372 gHC/(gcath).C5+liquid hydrocarbons selectivity decreased from 92.4%to 87.6%.

  20. Pt-Pd bimetallic nanoparticles on MWCNTs: catalyst for hydrogen peroxide electrosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Felix-Navarro, R. M., E-mail: moi6salazar@hotmail.com; Beltran-Gastelum, M.; Salazar-Gastelum, M. I.; Silva-Carrillo, C.; Reynoso-Soto, E. A.; Perez-Sicairos, S.; Lin, S. W. [Centro de Graduados e Investigacion, Instituto Tecnologico de Tijuana (Mexico); Paraguay-Delgado, F. [Centro de Investigacion en Materiales Avanzados (Mexico); Alonso-Nunez, G. [Centro de Nanociencias y Nanotecnologia (Mexico)

    2013-08-15

    Bimetallic nanoparticles of Pt-Pd were deposited by the microemulsion method on a multiwall carbon nanotube (MWCNTs) to obtain a Pt-Pd/MWCNTs for electrocatalytic reduction of O{sub 2} to H{sub 2}O{sub 2}. The activity and selectivity of the catalyst was determined qualitatively by the rotating disk electrode method in acidic medium. The catalyst was spray-coated onto a reticulated vitreous carbon substrate and quantitatively was tested in bulk electrolysis for 20 min under potentiostatic conditions (0.5 V vs Ag/AgCl) in a 0.5 M H{sub 2}SO{sub 4} electrolyte using dissolved O{sub 2}. The bulk electrolysis experiments show that the Pt-Pd/MWCNTs catalyst is more efficient for H{sub 2}O{sub 2} electrogeneration than a MWCNTs catalyst. Nitrobenzene degradation by electrogenerated H{sub 2}O{sub 2} alone and Electro-Fenton process were also tested. Our results show that both processes decompose nitrobenzene, but the Electro-Fenton process does it more efficiently. The prepared nanoparticulated catalyst shows a great potential in environmental applications.

  1. Highly selective bimetallic Pt-Cu/Mg(Al)O catalysts for the aqueous-phase reforming of glycerol

    NARCIS (Netherlands)

    Boga, D.A.; Oord, R.; Beale, A.M.; Chung, Y.M.; Bruijnincx, P.C.A.; Weckhuysen, B.M.

    2013-01-01

    Monometallic Pt and bimetallic Pt-Cu catalysts supported on Mg(Al)O mixed oxides, obtained by calcination of the corresponding layered double hydroxides (LDHs), were prepared and tested in the aqueous-phase reforming (APR) of glycerol. The effect of the Mg/Al ratio and calcination temperature of the

  2. Enhancement of bimetallic Fe-Mn/CNTs nano catalyst activity and product selectivity using microemulsion technique

    Institute of Scientific and Technical Information of China (English)

    Zahra; Zolfaghari; Ahmad; Tavasoli; Saber; Tabyar; Ali; Nakhaei; Pour

    2014-01-01

    Bimetallic Fe-Mn nano catalysts supported on carbon nanotubes(CNTs) were prepared using microemulsion technique with water-to-surfactant ratios of 0.4-1.6. The nano catalysts were extensively characterized by different methods and their activity and selectivity in Fischer-Tropsch synthesis(FTS) have been assessed in a fixed-bed microreactor. The physicochemical properties and performance of the nanocatalysts were compared with the catalyst prepared by impregnation method. Very narrow particle size distribution has been produced by the microemulsion technique at relatively high loading of active metal. TEM images showed that small metal nano particles in the range of 3–7 nm were not only confined inside the CNTs but also located on the outer surface of the CNTs. Using microemulsion technique with water to surfactant ratio of0.4 decreased the average iron particle sizes to 5.1 nm. The reduction percentage and dispersion percentage were almost doubled. Activity and selectivity were found to be dependent on the catalyst preparation method and average iron particle size. CO conversion and FTS rate increased from 49.1% to 71.0% and 0.144 to 0.289 gHC/(gcat h), respectively. While the WGS rate decreased from 0.097 to 0.056 gCO2/(gcat h). C5+liquid hydrocarbons selectivity decreased slightly and olefins selectivity almost doubled.

  3. Selective Liquid-Phase Semihydrogenation of Functionalized Acetylenes and Propargylic Alcohols with Silica-Supported Bimetallic Palladium—Copper Catalysts

    NARCIS (Netherlands)

    Koten, G. van; Spee, M.P.R.; Meijer, M.D.; Slagt, M.Q.; Geus, John W.

    2001-01-01

    Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed wit

  4. Bimetallic Catalysts and Platinum Surfaces Studied by X-ray Absorption Spectroscopy and Scanning Tunnelling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roenning, Magnus

    2000-07-01

    Bimetallic catalyst systems used in Fischer-Tropsch synthesis (Co-Re/Al{sub 2}O{sub 3}) and in the naphtha reforming process (Pt-Re/Al{sub 2}O{sub 3}) have been studied in situ using X-ray absorption spectroscopy (EXAFS). Additionally, the adsorption of ethene on platinum single crystal surfaces has been investigated using scanning tunnelling microscopy. In situ EXAFS at the cobalt K absorption edge have been carried out at 450{sup o}C on the hydrogen reduction of a rhenium-promoted Co{sub 3}O{sub 4}/Al{sub 2}O{sub 3} catalyst. Reductions carried out using 100% hydrogen and 5% hydrogen in helium gave different results. Whereas the reduction using dilute hydrogen leads to bulk-like metallic cobalt particles (hcp or fcc), reaction with pure hydrogen yields a more dispersed system with smaller cobalt metal particles (< 40 A). The results are rationalised in terms of different degrees of reoxidation of cobalt by the higher and lower concentrations of water generated during the reduction of cobalt oxide by 100% and 5% hydrogen, respectively. Additionally, in both reduction protocols a small fraction (3 -4 wt%) of the cobalt content is randomly dispersed over the tetrahedral vacancies of the alumina support. This dispersion occurs during reduction and not calcination. The cobalt in these sites cannot be reduced at 450 {sup o}C. The local environments about the rhenium atoms in Co-Re/{gamma}-A1{sub 2}O{sub 3} catalyst after different reduction periods have been studied by X-ray absorption spectroscopy. A bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium L{sub III} EXAFS analysis shows that bimetallic particles are formed after reduction at 450{sup o}C with the average particle size being 10-15 A. Rhenium is shown to be reduced at a later stage than cobalt. The fraction of cobalt atoms entering the support obstructs the access to the support for the

  5. Bimetallic Catalysts and Platinum Surfaces Studied by X-ray Absorption Spectroscopy and Scanning Tunnelling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roenning, Magnus

    2000-07-01

    Bimetallic catalyst systems used in Fischer-Tropsch synthesis (Co-Re/Al{sub 2}O{sub 3}) and in the naphtha reforming process (Pt-Re/Al{sub 2}O{sub 3}) have been studied in situ using X-ray absorption spectroscopy (EXAFS). Additionally, the adsorption of ethene on platinum single crystal surfaces has been investigated using scanning tunnelling microscopy. In situ EXAFS at the cobalt K absorption edge have been carried out at 450{sup o}C on the hydrogen reduction of a rhenium-promoted Co{sub 3}O{sub 4}/Al{sub 2}O{sub 3} catalyst. Reductions carried out using 100% hydrogen and 5% hydrogen in helium gave different results. Whereas the reduction using dilute hydrogen leads to bulk-like metallic cobalt particles (hcp or fcc), reaction with pure hydrogen yields a more dispersed system with smaller cobalt metal particles (< 40 A). The results are rationalised in terms of different degrees of reoxidation of cobalt by the higher and lower concentrations of water generated during the reduction of cobalt oxide by 100% and 5% hydrogen, respectively. Additionally, in both reduction protocols a small fraction (3 -4 wt%) of the cobalt content is randomly dispersed over the tetrahedral vacancies of the alumina support. This dispersion occurs during reduction and not calcination. The cobalt in these sites cannot be reduced at 450 {sup o}C. The local environments about the rhenium atoms in Co-Re/{gamma}-A1{sub 2}O{sub 3} catalyst after different reduction periods have been studied by X-ray absorption spectroscopy. A bimetallic catalyst containing 4.6 wt% cobalt and 2 wt% rhenium has been compared with a corresponding monometallic sample with 2 wt% rhenium on the same support. The rhenium L{sub III} EXAFS analysis shows that bimetallic particles are formed after reduction at 450{sup o}C with the average particle size being 10-15 A. Rhenium is shown to be reduced at a later stage than cobalt. The fraction of cobalt atoms entering the support obstructs the access to the support for the

  6. Ag-Cu Bimetallic Nanoparticles Prepared by Microemulsion Method as Catalyst for Epoxidation of Styrene

    Directory of Open Access Journals (Sweden)

    Hong-Kui Wang

    2012-01-01

    Full Text Available Ag/Cu bimetallic nanocatalysts supported on reticulate-like γ-alumina were prepared by a microemulsion method using N2H4·H2O as the reducing agent. The catalysts were activated by calcination followed with hydrogen reduction at 873K, and the properties were confirmed using various characterization techniques. Compared with metal oxides particles, Ag-Cu particles exhibited smaller sizes (<5 nm after calcination in H2 at 873K. XPS results indicated that the binding energies changed with the Ag/Cu ratios, suggesting that increasing the copper content gave both metals a greater tendency to lose electrons. Furthermore, Ag-Cu bimetallic nanoparticles supported on γ-alumina showed better catalytic activity on the epoxidation of styrene as compared with the corresponding monometallic silver or copper. The styrene oxide selectivity could reach 76.6% at Ag/Cu molar ratio of 3/1, while the maximum conversion (up to 94.6% appeared at Ag/Cu molar ratio of 1/1 because of the maximum interaction between silver and copper.

  7. Catalytic reductive dechlorination of p-chlorophenol in water using Ni/Fe nanoscale particles

    Institute of Scientific and Technical Information of China (English)

    ZHANG Wei-hua; QUAN Xie; ZHANG Zhuo-yong

    2007-01-01

    Nanoscale bimetallic Ni/Fe particles were synthesized from the reaction of sodium borohydride (NaBH4)with reduction of Ni2+and Fe2+ in aqueous solution.The obtained Ni/Fe particles were characterized by TEM(transmission electron microscope),XRD(X-ray diffractometer),and N2-BET The dechlorination activity of the Ni/Fe was investigated using P-chlorophenol (p-CP)as a pmbe agent.Results demonstrated that the nanoscale Ni/Fe could effectively dechlorinate P-CP at relatively low metal to solution ratio of 0.4 g/L (Ni 5 wt%).The target with initial concentration of P-CP O.625 mmol/L was dechlorinted completely in 60 min under ambient temperature and pressure.Factors affecting dechlorination efficiency,including reaction temperature,pH,Ni loading percentage over Fe,and metal to solution ratio.were investigated.The possible mechanism of dechlorination of P-CP was proposed and discussed.The pseudo-first-order reaction took place on the surface of the Ni/Fe bimetallic particles,and the activation energy of the dechlorination reaction was determined to be 21.2 kJ/mol at the temperature rang of 287-313 K.

  8. Desorption of Furfural from Bimetallic Pt-Fe Oxides/Alumina Catalysts

    Directory of Open Access Journals (Sweden)

    Gloria Lourdes Dimas-Rivera

    2014-01-01

    Full Text Available In this work, the desorption of furfural, which is a competitive intermediate during the production of biofuel and valuable aromatic compounds, was studied using pure alumina, as well as alumina impregnated with iron and platinum oxides both individually and in combination, using thermogravimetric analysis (TGA. The bimetallic sample exhibited the lowest desorption percentage for furfural. High-resolution transmission electron microscopy (HRTEM imaging revealed the intimate connection between the iron and platinum oxide species on the alumina support. The mechanism of furfural desorption from the Pt-Fe/Al2O3 0.5%-0.5% sample was determined using physisorbed furfural instead of chemisorbed furfural; this mechanism involved the oxidation of the C=O group on furfural by the catalyst. The oxide nanoparticles on γ-Al2O3 support helped to stabilize the furfural molecule on the surface.

  9. Design of Pd-Based Bimetallic Catalysts for ORR: A DFT Calculation Study

    Directory of Open Access Journals (Sweden)

    Lihui Ou

    2015-01-01

    Full Text Available Developing Pd-lean catalysts for oxygen reduction reaction (ORR is the key for large-scale application of proton exchange membrane fuel cells (PEMFCs. In the present paper, we have proposed a multiple-descriptor strategy for designing efficient and durable ORR Pd-based alloy catalysts. We demonstrated that an ideal Pd-based bimetallic alloy catalyst for ORR should possess simultaneously negative alloy formation energy, negative surface segregation energy of Pd, and a lower oxygen binding ability than pure Pt. By performing detailed DFT calculations on the thermodynamics, surface chemistry and electronic properties of Pd-M alloys, Pd-V, Pd-Fe, Pd-Zn, Pd-Nb, and Pd-Ta, are identified theoretically to have stable Pd segregated surface and improved ORR activity. Factors affecting these properties are analyzed. The alloy formation energy of Pd with transition metals M can be mainly determined by their electron interaction. This may be the origin of the negative alloy formation energy for Pd-M alloys. The surface segregation energy of Pd is primarily determined by the surface energy and the atomic radius of M. The metals M which have smaller atomic radius and higher surface energy would tend to favor the surface segregation of Pd in corresponding Pd-M alloys.

  10. Preparation and characterization of bi-metallic nanoparticle catalyst having better anti-coking properties using reverse micelle technique

    Science.gov (United States)

    Zacharia, Thomas

    Energy needs are rising on an exponential basis. The mammoth energy sources like coal, natural gas and petroleum are the cause of pollution. The large outcry for an alternate energy source which is environmentally friendly and energy efficient is heard during the past few years. This is where “Clean-Fuel” like hydrogen gained its ground. Hydrogen is mainly produced by steam methane reforming (SMR). An alternate sustainable process which can reduce the cost as well as eliminate the waste products is Tri-reforming. In both these reforming processes nickel is used as catalyst. However as the process goes on the catalyst gets deactivated due to coking on the catalytic surface. This goal of this thesis work was to develop a bi-metallic catalyst which has better anti-coking properties compared to the conventional nickel catalyst. Tin was used to dope nickel. It was found that Ni3Sn complex around a core of Ni is coking resistant compared to pure nickel catalyst. Reverse micelle synthesis of catalyst preparation was used to control the size and shape of catalytic particles. These studies will benefit researches on hydrogen production and catalyst manufactures who work on different bi-metallic combinations.

  11. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, July--September 1993

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, E.; Song, C.; Schobert, H.H.

    1994-01-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that dispersed catalysts can be superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. The primary objective of this research is to explore novel bimetallic dispersed catalysts from heterometallic molecular precursors, that can be used in low concentrations but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. This quarterly report describes the preparation of two precursors. The first is a heterometallic complex consisting of two transition metals, Mo and Ni, and sulfur in a single molecule synthesized. The second is a thiocubane type cluster consisting of iron and sulfur.

  12. A mini review on NiFe-based materials as highly active oxygen evolution reaction electrocatalysts

    OpenAIRE

    Gong, Ming; Dai, Hongjie

    2014-01-01

    Oxygen evolution reaction (OER) electrolysis, as an important reaction involved in water splitting and rechargeable metal-air battery, has attracted increasing attention for clean energy generation and efficient energy storage. Nickel/iron (NiFe)-based compounds have been known as active OER catalysts since the last century, and renewed interest has been witnessed in recent years on developing advanced NiFe-based materials for better activity and stability. In this review, we present the earl...

  13. Electrochemical insights into the mechanism of NiFe membrane-bound hydrogenases.

    Science.gov (United States)

    Flanagan, Lindsey A; Parkin, Alison

    2016-02-15

    Hydrogenases are enzymes of great biotechnological relevance because they catalyse the interconversion of H2, water (protons) and electricity using non-precious metal catalytic active sites. Electrochemical studies into the reactivity of NiFe membrane-bound hydrogenases (MBH) have provided a particularly detailed insight into the reactivity and mechanism of this group of enzymes. Significantly, the control centre for enabling O2 tolerance has been revealed as the electron-transfer relay of FeS clusters, rather than the NiFe bimetallic active site. The present review paper will discuss how electrochemistry results have complemented those obtained from structural and spectroscopic studies, to present a complete picture of our current understanding of NiFe MBH. PMID:26862221

  14. Facile Synthesis of Porous Dendritic Bimetallic Platinum-Nickel Nanocrystals as Efficient Catalysts for the Oxygen Reduction Reaction.

    Science.gov (United States)

    Eid, Kamel; Wang, Hongjing; Malgras, Victor; Alothman, Zeid Abdullah; Yamauchi, Yusuke; Wang, Liang

    2016-05-01

    Certain bimetallic nanocrystals (NCs) possess promising catalytic properties for electrochemical energy conversion. Herein, we report a facile method for the one-step synthesis of porous dendritic PtNi NCs in aqueous solution at room temperature that contrasts with the traditional multistep thermal decomposition approach. The dendritic PtNi NCs assembled by interconnected arms are efficient catalysts for the oxygen reduction reaction. This direct and efficient method is favorable for the up-scaled synthesis of active catalysts used in electrochemical applications. PMID:26879517

  15. Designing supported palladium-on-gold bimetallic nano-catalysts for controlled hydrogenation of acetylene in large excess of ethylene

    Science.gov (United States)

    Malla, Pavani

    Ethylene is used as a starting point for many chemical intermediates in the petrochemical industry. It is predominantly produced through steam cracking of higher hydrocarbons (ethane, propane, butane, naphtha, and gas oil). During the cracking process, a small amount of acetylene is produced as a side product. However, acetylene must be removed since it acts as a poison for ethylene polymerization catalysts at even ppm concentrations (>5 ppm). Thus, the selective hydrogenation of acetylene to ethylene is an important process for the purification of ethylene. Conventional, low weight loading Pd catalysts are used for this selective reaction in high concentration ethylene streams. Gold was initially considered to be catalytically inactive for a long time. This changed when gold was seen in the context of the nanometric scale, which has indeed shown it to have excellent catalytic activity as a homogeneous or a heterogeneous catalyst. Gold is proved to have high selectivity to ethylene but poor at conversion. Bimetallic Au and Pd catalysts have exhibited superior activity as compared to Pd particles in semi-hydrogenation. Hydrogenation of acetylene was tested using this bimetallic combination. The Pd-on-Au bimetallic catalyst structure provides a new synthesis approach in improving the catalytic properties of monometallic Pd materials. TiO 2 as a support material and 0.05%Pd loading on 1%Au on titania support and used different treatment methods like washing plasma and reduction between the two metal loadings and was observed under 2:1 ratio. In my study there were two set of catalysts which were prepared by a modified incipient wetness impregnation technique. Out of all the reaction condition the catalyst which was reduced after impregnating gold and then impregnating palladium which was further treated in non-thermal hydrogen plasma and then pretreated in hydrogen till 250°C for 1 hour produced the best activity of 76% yield at 225°C. Stability tests were conducted

  16. Combination of supported bimetallic rhodium–molybdenum catalyst and cerium oxide for hydrogenation of amide

    International Nuclear Information System (INIS)

    Hydrogenation of cyclohexanecarboxamide to aminomethylcyclohexane was conducted with silica-supported bimetallic catalysts composed of noble metal and group 6–7 elements. The combination of rhodium and molybdenum with molar ratio of 1:1 showed the highest activity. The effect of addition of various metal oxides was investigated on the catalysis of Rh–MoOx/SiO2, and the addition of CeO2 much increased the activity and selectivity. Higher hydrogen pressure and higher reaction temperature in the tested range of 2–8 MPa and 393–433 K, respectively, were favorable in view of both activity and selectivity. The highest yield of aminomethylcyclohexane obtained over Rh–MoOx/SiO2 + CeO2 was 63%. The effect of CeO2 addition was highest when CeO2 was not calcined, and CeO2 calcined at >773 K showed a smaller effect. The use of CeO2 as a support rather decreased the activity in comparison with Rh–MoOx/SiO2. The weakly-basic nature of CeO2 additive can affect the surface structure of Rh–MoOx/SiO2, i.e. reducing the ratio of Mo–OH/Mo–O− sites. (focus issue paper)

  17. Combination of supported bimetallic rhodium-molybdenum catalyst and cerium oxide for hydrogenation of amide

    Science.gov (United States)

    Nakagawa, Yoshinao; Tamura, Riku; Tamura, Masazumi; Tomishige, Keiichi

    2015-02-01

    Hydrogenation of cyclohexanecarboxamide to aminomethylcyclohexane was conducted with silica-supported bimetallic catalysts composed of noble metal and group 6-7 elements. The combination of rhodium and molybdenum with molar ratio of 1:1 showed the highest activity. The effect of addition of various metal oxides was investigated on the catalysis of Rh-MoOx/SiO2, and the addition of CeO2 much increased the activity and selectivity. Higher hydrogen pressure and higher reaction temperature in the tested range of 2-8 MPa and 393-433 K, respectively, were favorable in view of both activity and selectivity. The highest yield of aminomethylcyclohexane obtained over Rh-MoOx/SiO2 + CeO2 was 63%. The effect of CeO2 addition was highest when CeO2 was not calcined, and CeO2 calcined at >773 K showed a smaller effect. The use of CeO2 as a support rather decreased the activity in comparison with Rh-MoOx/SiO2. The weakly-basic nature of CeO2 additive can affect the surface structure of Rh-MoOx/SiO2, i.e. reducing the ratio of Mo-OH/Mo-O- sites.

  18. One-pot synthesis of NiFe layered double hydroxide/reduced graphene oxide composite as an efficient electrocatalyst for electrochemical and photoelectrochemical water oxidation

    Science.gov (United States)

    Youn, Duck Hyun; Park, Yoon Bin; Kim, Jae Young; Magesh, Ganesan; Jang, Youn Jeong; Lee, Jae Sung

    2015-10-01

    As an efficient non-precious metal catalyst for oxygen evolution reaction (OER) in electrochemical and photoelectrochemical water splitting, NiFe layered double hydroxide (LDH)/reduced graphene oxide (NiFe/RGO) composite is synthesized by a simple solvothermal method in one-pot. NiFe LDHs are uniformly deposited on RGO layers of high electrical conductivity and large surface area. In electrochemical water splitting, NiFe/RGO shows superior OER performance compared to bare NiFe and reference IrO2 with a lower benchmark η10 value (required overpotential to drive 10 mA cm-2) of 0.245 V. Furthermore, NiFe/RGO substantially increases the performance of a hematite photoanode in photoelectrochemical water oxidation, demonstrating its potential as an OER co-catalyst for photoelectrodes.

  19. [NiFe] hydrogenase structural and functional models: new bio-inspired catalysts for hydrogen evolution; Modeles structuraux et fonctionnels du site actif des hydrogenases [NiFe]: de nouveaux catalyseurs bio-inspires pour la production d'hydrogene

    Energy Technology Data Exchange (ETDEWEB)

    Oudart, Y

    2006-09-15

    Hydrogenase enzymes reversibly catalyze the oxidation and production of hydrogen in a range close to the thermodynamic potential. The [NiFe] hydrogenase active site contains an iron-cyano-carbonyl moiety linked to a nickel atom which is in an all sulphur environment. Both the active site originality and the potential development of an hydrogen economy make the synthesis of functional and structural models worthy. To take up this challenge, we have synthesised mononuclear ruthenium models and more importantly, nickel-ruthenium complexes, mimicking some structural features of the [NiFe] hydrogenase active site. Ruthenium is indeed isoelectronic to iron and some of its complexes are well-known to bear hydrides. The compounds described in this study have been well characterised and their activity in proton reduction has been successfully tested. Most of them are able to catalyze this reaction though their electrocatalytic potentials remain much more negative compared to which of platinum. The studied parameters point out the importance of the complexes electron richness, especially of the nickel environment. Furthermore, the proton reduction activity is stable for several hours at good rates. The ruthenium environment seems important for this stability. Altogether, these compounds represent the very first catalytically active [NiFe] hydrogenase models. Important additional results of this study are the synergetic behaviour of the two metals in protons reduction and the evidence of a protonation step as the limiting step of the catalytic cycle. We have also shown that a basic site close to ruthenium improves the electrocatalytic potential of the complexes. (author)

  20. Catalytic thermal decomposition of methane to COx-free hydrogen and carbon nanotubes over MgO supported bimetallic group VIII catalysts

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Bimetallic of group VIII/MgO catalysts were tested for methane decomposition reaction. • Fe–Co/MgO catalyst showed superior activity and stability toward H2 production. • Both Ni–Fe and Ni–Co catalysts exhibited lower catalytic activities. • The formation of MgxNi(1−x)O leads to the inhibition of catalytic activity. • High quality MWCNTs were obtained over all binary catalysts. - Abstract: Bimetallic Ni–Fe, Ni–Co and Fe–Co supported on MgO catalysts with a total metals content of 50 wt.% were evaluated for decomposition of methane to CO/CO2 free hydrogen and carbon nanomaterials. The catalytic runs were carried out at 700 °C under atmospheric pressure using fixed bed horizontal flow reactor. The materials were characterized by XRD, TEM, Raman spectroscopy, surface analysis and TGA–DTG. The data showed that the bimetallic 25% Fe–25%Co/MgO catalyst exhibited remarkable higher activity and stability up to ∼10 h time-on-stream with respect to H2 production. However, the catalytic activity and durability was greatly declined after incorporating 25%Ni to either 25%Fe or 25%Co/MgO catalysts at all time on stream. The main reason for the catalytic inhibition of Ni containing catalysts is consuming NiO during the formation of rock-salt MgxNi(1−x)O solid solution. However, the almost complete segregation of Fe2O3 and Co3O4 oxides played an important role for the high activity of the Fe–Co based catalyst. TEM images illustrate that the accumulated carbon over all catalysts are multi-walled carbon nanotubes in nature. The TG data showed that a higher yield of MWCNTs was achieved over bimetallic Fe–Co catalyst compared to the Ni–Fe or Ni–Co containing catalysts

  1. Model bimetallic Pd-Ni automotive exhaust catalysts. Influence of thermal aging and hydrocarbon self-poisoning

    Energy Technology Data Exchange (ETDEWEB)

    Hungria, A.B.; Martinez-Arias, A. [Instituto de Catalisis y Petroleoquimica, CSIC, C/Marie Curie 2, Campus Cantoblanco, 28049 Madrid (Spain); Calvino, J.J. [Dpto. de Ciencia de los Materiales e Ingenieria Metalurgica y Quimica Inorganica, Facultad de Ciencias, Universidad de Cadiz, 11510 Puerto Real, Cadiz (Spain); Anderson, J.A. [Surface Chemistry and Catalysis Group, Department of Chemistry, University of Aberdeen, AB24 3UE Scotland (United Kingdom)

    2006-02-22

    Bimetallic Pd-Ni catalysts supported on Al{sub 2}O{sub 3} and (Ce,Zr)O{sub x}/Al{sub 2}O{sub 3} were examined with respect to their catalytic performance for the elimination of CO, NO and C{sub 3}H{sub 6} under stoichiometric conditions. The effects of a thermal aging treatment at 1273K, reactant competition in the presence of the hydrocarbon and the influence of the presence of nickel in the catalyst have been analysed by XRD, HREM, catalytic activity measurements and in situ DRIFTS spectroscopy. Self-poisoning effects, induced by the presence of the hydrocarbon in the reactant mixture, were identified as the main factor affecting the light-off activity. While a Ni-induced preferential interaction between Pd and the Ce-Zr mixed oxide component appears, in general terms, to be beneficial for the catalytic performance of the fresh (Ce,Zr)O{sub x}/Al{sub 2}O{sub 3}-supported bimetallic catalyst, it is shown to be detrimental for the aged system as a consequence of a facilitated degradation of the (Ce,Zr)O{sub x} component and encapsulation of the active palladium particles. (author)

  2. Low-temperature 1 3-butadiene Hydrogenation over Supported Pt/3d/gamma-Al2O3 Bimetallic Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    W Lonergan; X Xing; R Zheng; S Qi; B Huang; J Chen

    2011-12-31

    Low-temperature 1,3-butadiene hydrogenation is used as a probe reaction to investigate the hydrogenation activity over several {gamma}-Al{sub 2}O{sub 3} supported Pt/3d (3d = Co, Ni, Cu) bimetallic catalysts. Batch and flow reactor studies are employed to quantify the kinetic activity and steady-state conversion, respectively, of each catalyst. Transmission electron microscopy (TEM) is utilized to characterize particle sizes and extended X-ray absorption fine structure (EXAFS) measurements are performed to verify the Pt-3d bimetallic bond formation. Pulse carbon monoxide chemisorption measurements are also performed to characterize the number of active sites. Additionally, density functional theory (DFT) calculations are included to determine the binding energies of 1,3-butadiene and atomic hydrogen on the corresponding model surfaces. The binding energies of the adsorbates are found to correlate with the hydrogenation activity, allowing for use of such correlation to potentially predict hydrogenation catalysts with enhanced activity based on the binding energies of the adsorbates of interest.

  3. Hydrotreatment of wood-based pyrolysis oil using zirconia-supported mono- and bimetallic (Pt, Pd, Rh) catalysts

    OpenAIRE

    Ardiyanti, A. R.; GUTIERREZ, A.; Honkela, M. L.; Krause, A.O.I.; Heeres, H. J.

    2011-01-01

    Fast pyrolysis oil (PO), the liquid product of fast pyrolysis of lignocellulosic biomass, requires upgrading to extent its application range and for instance to allow for co-feeding in an existing oil-refinery. Catalytic hydrotreatment reactions (350 degrees C, 20 MPa total pressure, and 4h reaction time) with mono- and bimetallic metal catalysts based on Rh, Pt, Pd on a zirconia support were performed in a batch set-up. Pd/ZrO(2) showed the highest activity, followed by Rh/ZrO(2). Upgraded o...

  4. Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale

    Science.gov (United States)

    Shan, Shiyao; Petkov, Valeri; Prasai, Binay; Wu, Jinfang; Joseph, Pharrah; Skeete, Zakiya; Kim, Eunjoo; Mott, Derrick; Malis, Oana; Luo, Jin; Zhong, Chuan-Jian

    2015-11-01

    The ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites is essential for understanding the correlation between the atomic structure and catalytic properties, enabling the preparation of efficient nanoalloy catalysts by design. Herein we describe a study of CO oxidation over PdCu nanoalloy catalysts focusing on gaining insights into the correlation between the atomic structures and catalytic activity of nanoalloys. PdCu nanoalloys of different bimetallic compositions are synthesized as a model system and are activated by a controlled thermochemical treatment for assessing their catalytic activity. The results show that the catalytic synergy of Pd and Cu species evolves with both the bimetallic nanoalloy composition and temperature of the thermochemical treatment reaching a maximum at a Pd : Cu ratio close to 50 : 50. The nanoalloys are characterized structurally by ex situ and in situ synchrotron X-ray diffraction, including atomic pair distribution function analysis. The structural data show that, depending on the bimetallic composition and treatment temperature, PdCu nanoalloys adopt two different structure types. One features a chemically ordered, body centered cubic (B2) type alloy consisting of two interpenetrating simple cubic lattices, each occupied with Pd or Cu species alone, and the other structure type features a chemically disordered, face-centered cubic (fcc) type of alloy wherein Pd and Cu species are intermixed at random. The catalytic activity for CO oxidation is strongly influenced by the structural features. In particular, it is revealed that the prevalence of chemical disorder in nanoalloys with a Pd : Cu ratio close to 50 : 50 makes them superior catalysts for CO oxidation in comparison with the same nanoalloys of other bimetallic compositions. However, the catalytic synergy can be diminished if the Pd50Cu50 nanoalloys undergo phase

  5. Synergy between Two Metal Catalysts: A Highly Active Silica Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane

    KAUST Repository

    Samantaray, Manoja K

    2016-06-01

    A well-defined, silica supported, bimetallic precatalyst [≡Si-O-W(Me)5 ≡Si-O-Zr(Np)3](4) has been synthesized for the first time via successively grafting two organometallic complexes [W(CH3)6 (1) followed by ZrNp4 (2)] on a single silica support. Surprisingly, multiple quantum NMR characterization demonstrates that W and Zr species are in close proximity to each other. Hydrogenation of this bimetallic catalyst at room temperature showed the easy formation of Zirconium hydride, probably facilitated by tungsten hydride which was formed at this temperature. This bimetallic W/Zr hydride precatalyst proved to be more efficient (TON: 1436) than the monometallic W hydride (TON: 650) in metathesis of n-decane at 150 0C. This synergy between Zr and W suggests that the slow step of alkane metathesis is the C-H bond activation which occurs on Zr. The produced olefin resulting from a ß–H elimination undergoes easy metathesis on W.

  6. Enhanced performance of the catalytic conversion of allyl alcohol to 3-hydroxypropionic acid using bimetallic gold catalysts.

    Science.gov (United States)

    Falletta, Ermelinda; Della Pina, Cristina; Rossi, Michele; He, Qian; Kiely, Christopher J; Hutchings, Graham J

    2011-01-01

    One of the strategic building blocks in organic synthesis is 3-hydroxypropionic acid, which is particularly important for the manufacture of high performance polymers. However, to date, despite many attempts using both biological and chemical routes, no large scale effective process for manufacturing 3-hydroxypropionic acid has been developed. One potentially useful starting point is from allyl alcohol, as this can be obtained in principle from the dehydration of glycerol, thereby presenting a bio-renewable green pathway to this important building block. The catalytic transformation of allyl alcohol to 3-hydroxypropionic acid presents interesting challenges in catalyst design, particularly with respect to the control of selectivity among the products that can be expected, as acrylic acid, acrolein and glyceric acid can also be formed. In this paper, we present a novel eco-sustainable catalytic pathway leading to 3-hydroxypropionic acid, which highlights the outstanding potential of gold-based and bimetallic catalysts in the aerobic oxidation of allyl alcohol. PMID:22455056

  7. Enhanced Hydrodeoxygenation of m -Cresol over Bimetallic Pt–Mo Catalysts through an Oxophilic Metal-Induced Tautomerization Pathway

    Energy Technology Data Exchange (ETDEWEB)

    Robinson, Allison; Ferguson, Glen Allen; Gallagher, James R.; Cheah, Singfoong; Beckham, Gregg T.; Schaidle, Joshua A.; Hensley, Jesse E.; Medlin, J. Will

    2016-07-01

    Supported bimetallic catalysts consisting of a noble metal (e.g., Pt) and an oxophilic metal (e.g., Mo) have received considerable attention for the hydrodeoxygenation of oxygenated aromatic compounds produced from biomass fast pyrolysis. Here, we report that PtMo can catalyze m-cresol deoxygenation via a pathway involving an initial tautomerization step. In contrast, the dominant mechanism on monometallic Pt/Al2O3 was found to be sequential Pt-catalyzed ring hydrogenation followed by dehydration on the support. Bimetallic Pt10Mo1 and Pt1Mo1 catalysts were found to produce the completely hydrogenated and deoxygenated product, methylcyclohexane (MCH), with much higher yields than monometallic Pt catalysts with comparable metal loadings and surface areas. Over an inert carbon support, MCH formation was found to be slow over monometallic Pt catalysts, while deoxygenation was significant for PtMo catalysts even in the absence of an acidic support material. Experimental studies of m-cresol deoxygenation together with density functional theory calculations indicated that Mo sites on the PtMo bimetallic surface dramatically lower the barrier for m-cresol tautomerization and subsequent deoxygenation. The accessibility of this pathway arises from the increased interaction between the oxygen of m-cresol and the Mo sites in the Pt surface. This interaction significantly alters the configuration of the precursor and transition states for tautomerization. A suite of catalyst characterization techniques including X-ray absorption spectroscopy (XAS) and temperature-programmed reduction (TPR) indicate that Mo was present in a reduced state on the bimetallic surface under conditions relevant for reaction. Overall, these results suggest that the use of bifunctional metal catalysts can result in new reaction pathways that are unfavorable on monometallic noble metal catalysts.

  8. Controllable synthesis of carbon nanotubes by changing the Mo content in bimetallic Fe-Mo/MgO catalyst

    International Nuclear Information System (INIS)

    Research highlights: → Increasing the Mo content in the Fe-Mo/MgO catalysts resulted in an increase in wall number, diameter and growth yield of carbon nanotubes. → The Fe interacts with MgO to form complex (MgO)x(FeO)1-x (0 4 and relative large metal Mo particles can be generated after reduction. → The avalanche-like reduction of MgMoO4 makes the catalyst particles to be small thus enhances the utilize efficiency of Fe nanoparticles. - Abstract: A series of Fe-Mo/MgO catalysts with different Mo content were prepared by combustion method and used as catalysts for carbon nanotube (CNT) growth. Transmission electron microscopy studies of the nanotubes show that the number of the CNT walls and the CNT diameters increase with the increasing of Mo content in the bimetallic catalyst. The growth yield determined by thermogravimetric analysis also follows the trend: the higher the Mo content, the higher the yield of the CNTs. However, the increase of Mo content leads to the lower degree of graphitization of CNTs. A comparative study on the morphology and catalytic functions of Fe/MgO, Mo/MgO and Fe-Mo/MgO catalysts was carried out by scanning electron microscopy and X-ray diffraction. It is found that the Fe interacts with MgO to form complexes and is then dispersed into the MgO support uniformly, resulting in very small Fe nanoparticles after reduction. The Mo interacts with MgO to form stoichiometry compound MgMoO4 and relative large metal Mo particles can be generated after reduction. High yield CNTs with small diameter can be generated from Fe-Mo/MgO because the avalanche-like reduction of MgMoO4 makes the catalyst particles to be small thus enhances the utilize efficiency of Fe nanoparticles.

  9. Aqueous Phase Glycerol Reforming by PtMo Bimetallic Nano-Particle Catalyst: Product Selectivity and Structural Characterization

    Energy Technology Data Exchange (ETDEWEB)

    Stach E. A.; Dietrich, P.J.; Lobo-Lapidus, R.J.; Wu, T.; Sumer, A.; Akatay, M.C.; Fingland, B.R.; Guo, N.; Dumesic, J.A.; Marshall, C.L.; Jellinek, J.; Delgass, W.N.; Ribeiro, F.H.; Miller, J.T.

    2012-03-01

    A carbon supported PtMo aqueous phase reforming catalyst for producing hydrogen from glycerol was characterized by analysis of the reaction products and pathway, TEM, XPS and XAS spectroscopy. Operando X-ray absorption spectroscopy (XAS) indicates the catalyst consists of bimetallic nano-particles with a Pt rich core and a Mo rich surface. XAS of adsorbed CO indicates that approximately 25% of the surface atoms are Pt. X-ray photoelectron spectroscopy indicates that there is unreduced and partially reduced Mo oxide (MoO{sub 3} and MoO{sub 2}), and Pt-rich PtMo bimetallic nano-particles. The average size measured by transmission electron microscopy of the fresh PtMo nano-particles is about 2 nm, which increases in size to 5 nm after 30 days of glycerol reforming at 31 bar and 503 K. The catalyst structure differs from the most energetically stable structure predicted by density functional theory (DFT) calculations for metallic Pt and Mo atoms. However, DFT indicates that for nano-particles composed of metallic Pt and Mo oxide, the Mo oxide is at the particle surface. Subsequent reduction would lead to the experimentally observed structure. The aqueous phase reforming reaction products and intermediates are consistent with both C-C and C-OH bond cleavage to generate H{sub 2}/CO{sub 2} or the side product CH{sub 4}. While the H{sub 2} selectivity at low conversion is about 75%, cleavage of C-OH bonds leads to liquid products with saturated carbon atoms. At high conversions (to gas), these will produced additional CH{sub 4} reducing the H{sub 2} yield and selectivity.

  10. Greatly improved electrochemical performance of lithium-oxygen batteries with a bimetallic platinum-copper alloy catalyst

    Science.gov (United States)

    Lee, Minwook; Hwang, Yubin; Yun, Kyung-Han; Chung, Yong-Chae

    2015-08-01

    Research on the cathode catalysts of lithium-oxygen (Li-O2) batteries is one of the most important branches to commercialize these batteries to overcome the sluggish kinetics during both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this study, a high performance catalyst based on a bimetallic Pt-Cu alloy is investigated for Li-O2 batteries using first-principles calculation. The theoretical prediction shows that the Pt-Cu alloy is much more effective than the pure Pt according to the electrochemical performance. In particular, the effectiveness of the catalytic property is maximized in the case of the PtCu (111) surface which greatly reduces the large overpotentials of the original Li-O2 batteries during the OER/ORR. It is identified for the first time that the charge overpotentials are affected mainly by the inherent surface charge character of the alloy catalyst. It is observed that the more negatively charged PtCu (111) surface can act as a weakly positively charged surface for the adsorption of Li-O intermediates and thus result in weak ionic bonding of the intermediates on the surface. As a result, the dominant factor improving the catalytic performance is clearly demonstrated, providing insight into the design of an efficient catalyst for Li-O2 battery technologies.

  11. Efficiently cubic platinum-cobalt bimetallic nano-catalysts for use in low-cost dye-sensitized solar cells

    International Nuclear Information System (INIS)

    Graphical abstract: Low-platinum (Pt) alloy can be expected to substitute for the conventional Pt catalyst due to its modified Pt electronic structure with highly electrocatalytic activity and Pt-skin nano-structure with high durability. Pt3Co bimetallic nano-catalysts show high catalytic activity for the reduction of triiodide to iodide and low charge transfer resistance at the electrolyte/counter electrode interface as well as those of pure cubic Pt nano-catalysts. DSSC based on Pt3Co CE achieves an enhanced efficiency of 8.16% compared to that of thermal decomposition Pt CE (7.26%). - Highlights: • Cubic Co, Pt, PtCo, and Pt3Co nano-catalysts were synthesized in the oleylamine. • Pt-metal alloy with modified Pt electronic structure shows highly electrocatalytic activity. • Pt-metal alloy with Pt-skin nano-structure shows high durability. • The efficiency of DSSC with Pt3Co bimetallic counter electrode reaches 8.16%. - Abstract: Low-platinum (Pt) alloy can be expected to substitute for the conventional Pt catalyst due to its modified Pt electronic structure with highly electrocatalytic activity and Pt-skin nano-structure with high durability. Here we synthesize the pure cobalt (Co), pure Pt, PtCo, and Pt3Co nano-catalysts in the oleylamine and use their as the counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). Cyclic voltammetry and electrochemical impedance spectroscopy measurements indicate that the cubic Pt3Co CE has a high catalytic activity for the reduction of triiodide to iodide and a low charge transfer resistance at the electrolyte/CE interface, which are close to those of the pure cubic Pt CE but superior than those of the thermal decomposition platinum (TDPt) CE due to its modified Pt electronic structure and its catalytic surfaces are composed of Pt-rich and Pt-skin nano-structure. DSSC based on Pt3Co CE achieves a photovoltaic conversion efficiency of 8.16% under full sunlight illumination (100 mW cm−2, AM1.5 G), which

  12. Stability of bimetallic Pd-Zn catalysts for the steam reforming of methanol

    OpenAIRE

    Conant, T.; Karim, A.; Lebarbier, V.; Wang, Y.; F. Girgsdies; Schlögl, R.; Datye, A.

    2008-01-01

    ZnO-supported palladium-based catalysts have been shown in recent years to be both active and selective towards the steam reforming of methanol, although they are still considered to be less active than traditional copper-based catalysts. The activity of PdZn catalysts can be significantly improved by supporting them on alumina. Here we show that the Pd/ZnO/Al2O3 catalysts have better long-term stability when compared with commercial Cu/ZnO/Al2O3 catalysts, and that they are also stable under...

  13. Electrochemical oxidation of sodium borohydride on carbon supported Pt-Zn nanoparticle bimetallic catalyst and its implications to direct borohydride-hydrogen peroxide fuel cell

    International Nuclear Information System (INIS)

    Highlights: • The Pt-Zn/C catalyst as anode catalyst for DBHFC were facilely synthesized. • The average particle size of Pt-Zn bimetallic nanoparticles is approximately 2.5 nm. • The Zn-doping can apparently improve the catalytic activity for BH4− electrochemical oxidation. • The maximum power density of DBHFC employing Pt-Zn/C as anode catalyst is as high as 79.9 mW cm−2 at 79.5 mA cm−2 and 25 °C. - Abstract: Carbon supported Pt-Zn bimetallic nanoparticle electrocatalysts (Pt-Zn/C) are facilely prepared by a modified NaBH4 reduction method in aqueous solution at room temperature and investigated as alternative anode catalysts for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared nanospherical electrocatalysts are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), chronoamperometry (CA) and fuel cell test. Based on results of TEM and XRD, the Pt-Zn nanoparticles show average particle size of approximately 2.5 nm on the carbon surface. The fundamental electrochemical results show that the Pt-Zn/C catalysts exhibit much higher catalytic activity and stability for the direct oxidation of BH4− than Pt/C catalyst since Pt atoms are partly substituted by Zn atoms in Pt-Zn catalyst. Among various Pt-Zn catalysts with different compositions, the Pt67Zn33/C catalyst presents the highest catalytic activity for BH4− electrooxidation. The DBHFC using Pt67Zn33/C as anode catalyst and Pt/C as cathode catalyst obtains the maximum power density as high as 79.9 mW cm−2 at 79.5 mA cm−2 and 25 °C

  14. Sn surface-enriched Pt-Sn bimetallic nanoparticles as a selective and stable catalyst for propane dehydrogenation

    KAUST Repository

    Zhu, Haibo

    2014-12-01

    A new one pot, surfactant-free, synthetic route based on the surface organometallic chemistry (SOMC) concept has been developed for the synthesis of Sn surface-enriched Pt-Sn nanoparticles. Bu3SnH selectively reacts with [Pt]-H formed in situ at the surface of Pt nanoparticles, Pt NPs, obtained by reduction of K2PtCl4 by LiB(C2H5)3H. Chemical analysis, 1H MAS and 13C CP/MAS solid-state NMR as well as two-dimensional double-quantum (DQ) and triple-quantum (TQ) experiments show that organo-tin moieties Sn(n-C4H9) are chemically linked to the surface of Pt NPs to produce, in fine, after removal of most of the n-butyl fragment, bimetallic Pt-Sn nanoparticles. The Sn(n-CH2CH2CH2CH3) groups remaining at the surface are believed to stabilize the as-synthesized Pt-Sn NPs, enabling the bimetallic NPs to be well dispersed in THF. Additionally, the Pt-Sn nanoparticles can be supported on MgAl2O4 during the synthesis of the nanoparticles. Some of the Pt-Sn/MgAl2O4 catalyst thus prepared exhibits high activity in PROX of CO and an extremely high selectivity and stability in propane dehydrogenation to propylene. The enhanced activity in propane dehydrogenation is associated with the high concentration of inactive Sn at the surface of Pt nanoparticles which ”isolates” the active Pt atoms. This conclusion is confirmed by XRD, NMR, TEM, and XPS analysis.

  15. Ni-Based Catalysts for Low Temperature Methane Steam Reforming: Recent Results on Ni-Au and Comparison with Other Bi-Metallic Systems

    Directory of Open Access Journals (Sweden)

    Anna M. Venezia

    2013-06-01

    Full Text Available Steam reforming of light hydrocarbons provides a promising method for hydrogen production. Ni-based catalysts are so far the best and the most commonly used catalysts for steam reforming because of their acceptably high activity and significantly lower cost in comparison with alternative precious metal-based catalysts. However, nickel catalysts are susceptible to deactivation from the deposition of carbon, even when operating at steam-to-carbon ratios predicted to be thermodynamically outside of the carbon-forming regime. Reactivity and deactivation by carbon formation can be tuned by modifying Ni surfaces with a second metal, such as Au through alloy formation. In the present review, we summarize the very recent progress in the design, synthesis, and characterization of supported bimetallic Ni-based catalysts for steam reforming. The progress in the modification of Ni with noble metals (such as Au and Ag is discussed in terms of preparation, characterization and pretreatment methods. Moreover, the comparison with the effects of other metals (such as Sn, Cu, Co, Mo, Fe, Gd and B is addressed. The differences of catalytic activity, thermal stability and carbon species between bimetallic and monometallic Ni-based catalysts are also briefly shown.

  16. Correlating ethylene glycol reforming activity with in-situ EXAFS detection of Ni segregation in supported NiPt bimetallic catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Trupy, Sarah A.; Karim, Ayman M.; Bagia, Christtina; Deng, Weihua; Huang, Yulin; Vlachos, Dionisios G.; Chen, Jingguang

    2012-10-31

    The structural changes in supported NiPt/C and NiPt/γ-Al2O3 catalysts were investigated using in-situ extended X-ray absorption fine structure (EXAFS) under aqueous phase reforming (APR) of ethylene glycol conditions. Reverse Monte Carlo is introduced to analyze the EXAFS data. Parallel reactor studies of APR of ethylene glycol showed that NiPt catalysts were initially more active than monometallic Pt catalysts. The enhanced activity was correlated to changes in the catalyst structure. Under APR conditions, Ni segregated to the surface of the catalysts, resembling Ni-terminated bimetallic surfaces that were predicted to be more active than Pt from theoretical and experimental studies on model surfaces.

  17. Domain Structures and Anisotropy in Exchange-coupled [Co/Pd]-NiFe and [Co/Ni]-NiFe Multilayers

    Science.gov (United States)

    Tryputen, Larysa; Chung, Sunjae; Mohseni, Majid; Nguyen, T. N. Anh; Åkerman, Johan; Guo, Feng; McMichael, Robert D.; Ross, Caroline A.

    2014-03-01

    Exchange-coupled multilayers [Co/Pd]5-/NiFe and [Co/Ni]4-NiFe with strong perpendicular magnetic anisotropy have been proposed to use in spin-torque switching and oscillators devices with tilted fixed and free layer to improve their functional performance. We present an experimental study of the magnetization behavior of [Co/Pd]5-/NiFe and [Co/Ni]4-NiFe multilayers measured using magnetometry, magnetic force microscopy (MFM) and ferromagnetic resonance (FMR) as a function of the thickness of the top NiFe layer. We varied the thickness of the NiFe layer in [Co/Pd]5-NiFe (t), t = 0 - 80 nm and [Co/Ni]4-NiFe (t), t = 0.5 - 2.5 nm in order to study the interplay between perpendicular magnetization of the Co/Pd or Co/Ni multilayers and in-plane magnetization of the NiFe. Our magnetometry and FMR data suggest that the [Co/Ni]4/NiFe multilayer behaves like a homogeneous ferromagnetic film with anisotropy that reorients towards in-plane as the NiFe thickness increases, whereas the [Co/Pd]5/NiFe multilayer reveals more complex behavior in which the [Co/Pd] layer retains out-of-plane anisotropy while the magnetization of NiFe layer tilts in-plane with increasing thickness. MFM showed that domains with ~0.1 +/-m size were visible in [Co/Pd]-/NiFe with NiFe thickness of 20-80 nm. Multilayers were patterned into sub-100 nm dots using ion beam etching and their magnetization behavior are compared with unpatterned films.

  18. Bimetallic catalysts for CO.sub.2 hydrogenation and H.sub.2 generation from formic acid and/or salts thereof

    Energy Technology Data Exchange (ETDEWEB)

    Hull, Jonathan F.; Himeda, Yuichiro; Fujita, Etsuko; Muckeman, James T.

    2015-08-04

    The invention relates to a ligand that may be used to create a catalyst including a coordination complex is formed by the addition of two metals; Cp, Cp* or an unsubstituted or substituted .pi.-arene; and two coordinating solvent species or solvent molecules. The bimetallic catalyst may be used in the hydrogenation of CO.sub.2 to form formic acid and/or salts thereof, and in the dehydrogenation of formic acid and/or salts thereof to form H.sub.2 and CO.sub.2.

  19. Purification of Carbon Nanotubes Synthesized by Catalytic Decomposition of Methane using Bimetallic Fe-Co Catalysts Supported on MgO

    Energy Technology Data Exchange (ETDEWEB)

    Guan, Beh Hoe; Ramli, Irmawati [Advanced Materials and Nanotechnology Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia 43400 UPM Serdang, Selangor (Malaysia); Yahya, Noorhana [Fundamental and Applied Science Department Universiti Teknologi Petronas, Bandar Seri Iskandar, 31750 Tronoh, Perak (Malaysia); Pah, Lim Kean, E-mail: irmawati@science.upm.edu.my [Physics department, Faculty of Science, Universiti Putra Malaysia 43400 UPM Serdang, Selangor (Malaysia)

    2011-02-15

    This work reports the synthesis of carbon nanotubes by catalytic decomposition of methane using bimetallic Fe-Co catalysts supported on MgO. Transmission electron microscopy (TEM) results show the as-prepared carbon nanotubes are multi-walled carbon nanotubes (MWCNTs) with diameter in the range of 15nm to 45nm. Purification of as-prepared MWCNTs was carried out by acid and heat treatment method. EDX results show the Fe, Co and MgO catalysts were successfully removed by refluxing the as-prepared MWCNTs in 3M H{sub 2}SO{sub 4}.

  20. Molecular Level Control Through Dual Site Participation Using Bimetallic Catalysts - Final Report

    Energy Technology Data Exchange (ETDEWEB)

    d' Itri, Julie, L.; Kovalchuk, Vladimir, I.

    2010-02-08

    The overall goal of this research program was to explore the hypothesis that it is possible to design a bimetallic surface such that each metal catalyzes different elementary reaction steps in an overall reaction pathway. A corollary to this hypothesis is that the different ensemble size requirements for an elementary reaction step can be used to force an elementary reaction step to occur on only one of the metals. The research program involved a combination of materials synthesis, chemical kinetics experiments, spectroscopic studies and computational investigations. The major outcome of this research program was the development and dissemination of the Dual Site Model, for which chlorocarbon reactions in the presence of hydrogen were used as model systems.

  1. Cu-Sn Bimetallic Catalyst for Selective Aqueous Electroreduction of CO2 to CO

    KAUST Repository

    Sarfraz, Saad

    2016-03-23

    We report a selective and stable electrocatalyst utilizing non-noble metals consisting of Cu and Sn for the efficient and selective reduction of CO2 to CO over a wide potential range. The bimetallic electrode was prepared through the electrodeposition of Sn species on the surface of oxide-derived copper (OD-Cu). The Cu surface, when decorated with an optimal amount of Sn, resulted in a Faradaic efficiency (FE) for CO greater than 90% and a current density of −1.0 mA cm−2 at −0.6 V vs. RHE, compared to the CO FE of 63% and −2.1 mA cm−2 for OD-Cu. Excess Sn on the surface caused H2 evolution with a decreased current density. X-ray diffraction (XRD) suggests the formation of Cu-Sn alloy. Auger electron spectroscopy of the sample surface exhibits zero-valent Cu and Sn after the electrodeposition step. Density functional theory (DFT) calculations show that replacing a single Cu atom with a Sn atom leaves the d-band orbitals mostly unperturbed, signifying no dramatic shifts in the bulk electronic structure. However, the Sn atom discomposes the multi-fold sites on pure Cu, disfavoring the adsorption of H and leaving the adsorption of CO relatively unperturbed. Our catalytic results along with DFT calculations indicate that the presence of Sn on reduced OD-Cu diminishes the hydrogenation capability—i.e., the selectivity towards H2 and HCOOH—while hardly affecting the CO productivity. While the pristine monometallic surfaces (both Cu and Sn) fail to selectively reduce CO2, the Cu-Sn bimetallic electrocatalyst generates a surface that inhibits adsorbed H*, resulting in improved CO FE. This study presents a strategy to provide a low-cost non-noble metals that can be utilized as a highly selective electrocatalyst for the efficient aqueous reduction of CO2.

  2. Catalytic performance of dealuminated H-Y zeolite supported bimetallic nano catalysts in Hydroizomerization of n-hexane and n-heptane

    International Nuclear Information System (INIS)

    A series of dealuminated Y-zeolites impregnated by 0.5 wt % Pt catalysts promoted by different amounts of Ni, Pd or Cr (0.3 and 0.6 wt %) were prepared and characterized as hydrocracking catalysts. The physicochemical and structural characterization of the solid catalysts were investigated and reported through N2 physisorption, XRD, TGA-DSC, FT-IR and TEM techniques. Solid catalysts surface acidities were investigated through FT-IR spectroscopy aided by pyridine adsorption. The solid catalytic activities were evaluated through hydro conversion of n-hexane and n-heptane employing micro-catalytic pulse technique directly connected to a gas chromatograph analyzer. The thermal stability of the solids was also investigated up to 800 degree C. Crystallinity studies using the XRD technique of all modified samples proved analogous to the parent Y-zeolite, exhibiting nearly an amorphous and microcrystalline character of the second metal oxides. Disclosure of bimetallic catalysts crystalline characterization, through XRD, was not viable. The nitrogen adsorption-desorption isotherms for all samples concluded type I adsorption isotherms, without any hysteresis loop, indicating that the entire pore system is composed of micropores. TEM micrographs of the solid catalysts demonstrate well-dispersed Pt, Ni and Cr nanoparticles having sizes of 2-4 nm and 7-8 nm, respectively. The catalytic activity results indicate that the bimetallic (0.5 Pt-0.3 Cr)/D18 H-Y catalyst is the most active towards n-hexane and n-heptane isomerization while (0.5 Pt-0.6 Ni)/D18 H-Y catalyst can be designed as most suitable as a cracking catalyst

  3. CuAu–ZnO–graphene nanocomposite: A novel graphene-based bimetallic alloy-semiconductor catalyst with its enhanced photocatalytic degradation performance

    International Nuclear Information System (INIS)

    Graphical abstract: In this work, we have successfully synthesized a novel graphene-based bimetallic alloy-semiconductor catalyst: CuAu–ZnO–Gr nanocomposite, and which behaved an enhanced photocatalytic activity. - Highlights: • A bimetallic alloy-based catalyst: CuAu–ZnO–Gr is synthesized. • CuAu–ZnO–Gr behaves an enhanced photocatalytic activity. • The detailed explanation of photocatalytic mechanism of CuAu–ZnO–Gr. - Abstract: The bimetallic alloy CuAu nanoparticles (NPs) can produce more photogenerated electrons when compared with single metal Au NPs. Moreover, graphene (Gr) sheets can help the charge separation and slow down the recombination of the electron hole pairs of ZnO. Hence, a novel graphene-based bimetallic alloy-semiconductor catalyst: CuAu–ZnO–Gr nanocomposite is synthesized. Due to the synergistic effect among CuAu NPs, ZnO nanopyramids, and Gr sheets, CuAu–ZnO–Gr behaves an enhanced photocatalytic activity for the photocatalytic degradation of synthetic colorants methyl orange (MO), methylene blue (MB), indigotin (IN), sunset yellow (SY), and tartrazine (TT) under the simulated sunlight irradiation. Furthermore, the apparent rate constants (kapp) of MO, MB, IN, SY, and TT degradation are estimated respectively. In addition, the as-prepared CuAu–ZnO–Gr nanocomposite is characterized by X-ray diffraction, UV–vis spectrum, transmission electron microscopy, energy dispersive X-ray analysis (EDX), and EDX mapping. As a result of the facile synthesis route and the enhanced photocatalytic activity, this new material CuAu–ZnO–Gr can be a promising photocatalyst for the degradation of dyes

  4. CuAu–ZnO–graphene nanocomposite: A novel graphene-based bimetallic alloy-semiconductor catalyst with its enhanced photocatalytic degradation performance

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Hong [College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000 (China); Ye, Xiaoliang [College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000 (China); College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Duan, Kaiyue; Xue, Muyin; Du, Yongling; Ye, Weichun [College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000 (China); Wang, Chunming, E-mail: wangcm@lzu.edu.cn [College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000 (China)

    2015-07-05

    Graphical abstract: In this work, we have successfully synthesized a novel graphene-based bimetallic alloy-semiconductor catalyst: CuAu–ZnO–Gr nanocomposite, and which behaved an enhanced photocatalytic activity. - Highlights: • A bimetallic alloy-based catalyst: CuAu–ZnO–Gr is synthesized. • CuAu–ZnO–Gr behaves an enhanced photocatalytic activity. • The detailed explanation of photocatalytic mechanism of CuAu–ZnO–Gr. - Abstract: The bimetallic alloy CuAu nanoparticles (NPs) can produce more photogenerated electrons when compared with single metal Au NPs. Moreover, graphene (Gr) sheets can help the charge separation and slow down the recombination of the electron hole pairs of ZnO. Hence, a novel graphene-based bimetallic alloy-semiconductor catalyst: CuAu–ZnO–Gr nanocomposite is synthesized. Due to the synergistic effect among CuAu NPs, ZnO nanopyramids, and Gr sheets, CuAu–ZnO–Gr behaves an enhanced photocatalytic activity for the photocatalytic degradation of synthetic colorants methyl orange (MO), methylene blue (MB), indigotin (IN), sunset yellow (SY), and tartrazine (TT) under the simulated sunlight irradiation. Furthermore, the apparent rate constants (k{sub app}) of MO, MB, IN, SY, and TT degradation are estimated respectively. In addition, the as-prepared CuAu–ZnO–Gr nanocomposite is characterized by X-ray diffraction, UV–vis spectrum, transmission electron microscopy, energy dispersive X-ray analysis (EDX), and EDX mapping. As a result of the facile synthesis route and the enhanced photocatalytic activity, this new material CuAu–ZnO–Gr can be a promising photocatalyst for the degradation of dyes.

  5. Driving the Oxygen Evolution Reaction by Nonlinear Cooperativity in Bimetallic Coordination Catalysts.

    Science.gov (United States)

    Wurster, Benjamin; Grumelli, Doris; Hötger, Diana; Gutzler, Rico; Kern, Klaus

    2016-03-23

    Developing efficient catalysts for electrolysis, in particular for the oxygen evolution in the anodic half cell reaction, is an important challenge in energy conversion technologies. By taking inspiration from the catalytic properties of single-atom catalysts and metallo-proteins, we exploit the potential of metal-organic networks as electrocatalysts in the oxygen evolution reaction (OER). A dramatic enhancement of the catalytic activity toward the production of oxygen by nearly 2 orders of magnitude is demonstrated for novel heterobimetallic organic catalysts compared to metallo-porphyrins. Using a supramolecular approach we deliberately place single iron and cobalt atoms in either of two different coordination environments and observe a highly nonlinear increase in the catalytic activity depending on the coordination spheres of Fe and Co. Catalysis sets in at about 300 mV overpotential with high turnover frequencies that outperform other metal-organic catalysts like the prototypical hangman porphyrins. PMID:26937997

  6. An anodic alumina supported Ni-Pt bimetallic plate-type catalysts for multi-reforming of methane, kerosene and ethanol

    KAUST Repository

    Zhou, Lu

    2014-05-01

    An anodic alumina supported Ni-Pt bimetallic plate-type catalyst was prepared by a two-step impregnation method. The trace amount 0.08 wt% of Pt doping efficiently suppressed the nickel particle sintering and improved the nickel oxides reducibility. The prepared Ni-Pt catalyst showed excellent performance during steam reforming of methane, kerosene and ethanol under both 3000 h stationary and 500-time daily start-up and shut-down operation modes. Self-activation ability of this catalyst was evidenced, which was considered to be resulted from the hydrogen spillover effect over Ni-Pt alloy. In addition, an integrated combustion-reforming reactor was proposed in this study. However, the sintering of the alumina support is still a critical issue for the industrialization of Ni-Pt catalyst. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

  7. Magnetic properties of NiFe{sub 2}O{sub 4}/carbon nanofibers from Venezuelan petcoke

    Energy Technology Data Exchange (ETDEWEB)

    Briceño, Sarah, E-mail: sbriceno@ivic.gob.ve [Laboratorio de Física de la Materia Condensada, Centro de Física, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 20632, Caracas 1020-A (Venezuela, Bolivarian Republic of); Silva, Pedro; Molina, Wilmer; Brämer-Escamilla, Werner; Alcalá, Olgi [Laboratorio de Física de la Materia Condensada, Centro de Física, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 20632, Caracas 1020-A (Venezuela, Bolivarian Republic of); Cañizales, Edgard [Área de Análisis Químico Inorgánico, PDVSA, INTEVEP, Los Teques 1070-A (Venezuela, Bolivarian Republic of)

    2015-05-01

    NiFe{sub 2}O{sub 4}/carbon nanofibers (NiFe{sub 2}O{sub 4}/CNFs) have been successfully synthesized by hydrotermal method using Venezuelan petroleum coke (petcoke) as carbon source and NiFe{sub 2}O{sub 4} as catalyst. The morphology, structural and magnetic properties of nanocomposite products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), vibrating sample magnetometry (VSM) and electron paramagnetic resonance (EPR). XRD analysis revealed a cubic spinel structure and ferrite phase with high crystallinity. HR-TEM reveals the presence of CNFs with diameters of 4±2 nm. At room temperature, NiFe{sub 2}O{sub 4}/CNFs show superparamagnetic behavior with a maximum magnetization of 15.35 emu/g. Our findings indicate that Venezuelan petroleum coke is suitable industrial carbon source for the growth of magnetic CNFs. - Highlights: • NiFe{sub 2}O{sub 4}/CNFs have been synthesized by hydrothermal method using petroleum coke. • Nickel ferrite nanoparticles were used as the catalyst. • HR-TEM reveals the presence of CNFs with diameters of 4±2 nm. • The size of the nanoparticles defines the diameter of the CNFs.

  8. Carbon-Supported bimetallic Pd-Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Junming; Karim, Ayman M.; Zhang, He; Kovarik, Libor; Li, Xiaohong S.; Hensley, Alyssa; McEwen, Jean-Sabin; Wang, Yong

    2013-10-01

    Abstract Carbon supported metal catalysts (Cu/C, Fe/C, Pd/C, Pt/C, PdFe/C and Ru/C) have been prepared, characterized and tested for vapor-phase hydrodeoxygenation (HDO) of guaiacol (GUA) at atmospheric pressure. Phenol was the major intermediate on all catalysts. Over the noble metal catalysts saturation of the aromatic ring was the major pathway observed at low temperature (250 °C), forming predominantly cyclohexanone and cyclohexanol. Substantial ring opening reaction was observed on Pt/C and Ru/C at higher reaction temperatures (e.g., 350 °C). Base metal catalysts, especially Fe/C, were found to exhibit high HDO activity without ring-saturation or ring-opening with the main products being benzene, phenol along with small amounts of cresol, toluene and trimethylbenzene (TMB). A substantial enhancement in HDO activity was observed on the PdFe/C catalysts. Compared with Fe/C, the yield to oxygen-free aromatic products (i.e., benzene/toluene/TMB) on PdFe/C increased by a factor of four at 350 °C, and by approximately a factor of two (83.2% versus 43.3%) at 450 °C. The enhanced activity of PdFe/C is attributed to the formation of PdFe alloy as evidenced by STEM, EDS and TPR.

  9. Operando Analysis of NiFe and Fe Oxyhydroxide Electrocatalysts for Water Oxidation: Detection of Fe⁴⁺ by Mössbauer Spectroscopy.

    Science.gov (United States)

    Chen, Jamie Y C; Dang, Lianna; Liang, Hanfeng; Bi, Wenli; Gerken, James B; Jin, Song; Alp, E Ercan; Stahl, Shannon S

    2015-12-01

    Nickel-iron oxides/hydroxides are among the most active electrocatalysts for the oxygen evolution reaction. In an effort to gain insight into the role of Fe in these catalysts, we have performed operando Mössbauer spectroscopic studies of a 3:1 Ni:Fe layered hydroxide and a hydrous Fe oxide electrocatalyst. The catalysts were prepared by a hydrothermal precipitation method that enabled catalyst growth directly on carbon paper electrodes. Fe(4+) species were detected in the NiFe hydroxide catalyst during steady-state water oxidation, accounting for up to 21% of the total Fe. In contrast, no Fe(4+) was detected in the Fe oxide catalyst. The observed Fe(4+) species are not kinetically competent to serve as the active site in water oxidation; however, their presence has important implications for the role of Fe in NiFe oxide electrocatalysts. PMID:26601790

  10. Template-grown NiFe/Cu/NiFe nanowires for spin transfer devices

    DEFF Research Database (Denmark)

    Piraux, L.; Renard, K.; Guillemet, R.;

    2007-01-01

    method allows the electrical connection of one single nanowire in a large assembly of wires embedded in anodic porous alumina supported on Si substrate with diameters and periodicities to be controllable to a large extent. Both magnetic excitations and switching phenomena driven by a spin......-polarized current were clearly demonstrated in our electrodeposited NiFe/Cu/ NiFe trilayer nanowires. This novel approach promises to be of strong interest for subsequent fabrication of phase-locked arrays of spin transfer nano-oscillators with increased output power for microwave applications. © 2007 American...

  11. Selectivity, activity and metal-support interactions of Group VIII bimetallic catalysts. Progress report, 15 August 1983-15 August 1984

    International Nuclear Information System (INIS)

    Progress on supported bimetallic catalysts and the development of techniques for the characterization of supported catalysts is reported. Three bimetallic systems were studied: Rh-Pt, Ru-Cu and Rh-Ag. Goal has been the determination of the effect of the support on the kind and degree of metal-metal interaction. Small particles of Rh-Pt are found to be enriched in Rh on all supports, the degree of enrichment increasing in the order SiO22O32. The kind of SiO2 used to support Ru-Cu is found to have a large influence on the change in the H/Ru ratio when Ru and Ru-Cu/SiO2 catalysts are compared although the effect on ethane hydrogenolysis is comparable. For pure Rh supported on TiO2 and reduced at high temperature, EXAFS analysis suggests direct Rh-Ti bonding following a high temperature reduction. EXAFS also indicates that there is a stronger interaction between Ag and TiO2 than Ag and SiO2 and clearly demonstrates that there is greater metal-metal interaction for Rh-Ag supported on TiO2 than for Rh-Ag supported on SiO2. A fourth system, NiMoP/Al2O3, is not a bimetallic but was chosen as an interesting and convenient catalyst on which to initiate magic angle spinning NMR research. 27Al NMR proves that formation of the surface compound Al2(MoO4)3 on Mo/Al2O3 is induced by calcination but on NiMoP/Al2O3 this compound formation is inhibited and AlPO4 is formed instead

  12. How to Determine the Core-Shell Nature in Bimetallic Catalyst Particles?

    Directory of Open Access Journals (Sweden)

    Emma Westsson

    2014-11-01

    Full Text Available Nanometer-sized materials have significantly different chemical and physical properties compared to bulk material. However, these properties do not only depend on the elemental composition but also on the structure, shape, size and arrangement. Hence, it is not only of great importance to develop synthesis routes that enable control over the final structure but also characterization strategies that verify the exact nature of the nanoparticles obtained. Here, we consider the verification of contemporary synthesis strategies for the preparation of bimetallic core-shell particles in particular in relation to potential particle structures, such as partial absence of core, alloying and raspberry-like surface. It is discussed what properties must be investigated in order to fully confirm a covering, pin-hole free shell and which characterization techniques can provide such information. Not uncommonly, characterization strategies of core-shell particles rely heavily on visual imaging like transmission electron microscopy. The strengths and weaknesses of various techniques based on scattering, diffraction, transmission and absorption for investigating core-shell particles are discussed and, in particular, cases where structural ambiguities still remain will be highlighted. Our main conclusion is that for particles with extremely thin or mono-layered shells—i.e., structures outside the limitation of most imaging techniques—other strategies, not involving spectroscopy or imaging, are to be employed. We will provide a specific example of Fe-Pt core-shell particles prepared in bicontinuous microemulsion and point out the difficulties that arise in the characterization process of such particles.

  13. Temperature dependence of electrocatalytic and photocatalytic oxygen evolution reaction rates using NiFe oxide

    KAUST Repository

    Nurlaela, Ela

    2016-01-25

    The present work compares oxygen evolution reaction (OER) in electrocatalysis and photocatalysis in aqueous solutions using nanostructured NiFeOx as catalysts. The impacts of pH and reaction temperature on the electrocatalytic and photocatalytic OER kinetics were investigated. For electrocatalysis, a NiFeOx catalyst was hydrothermally decorated on Ni foam. In 1 M KOH solution, the NiFeOx electrocatalyst achieved 10 mA cm-2 at an overpotential of 260 mV. The same catalyst was decorated on the surface of Ta3N5 photocatalyst powder. The reaction was conducted in the presence of 0.1 M Na2S2O8 as a strong electron scavenger, thus likely leading to the OER being kinetically relevant. When compared with the bare Ta3N5, NiFeOx/Ta3N5 demonstrated a 5-fold improvement in photocatalytic activity in the OER under visible light irradiation, achieving a quantum efficiency of 24 % at 480 nm. Under the conditions investigated, a strong correlation between the electrocatalytic and photocatalytic performances was identified: an improvement in electrocatalysis corresponded with an improvement in photocatalysis without altering the identity of the materials. The rate change at different pH was likely associated with electrocatalytic kinetics that accordingly influenced the photocatalytic rates. The sensitivity of the reaction rates with respective to the reaction temperature resulted in an apparent activation energy of 25 kJ mol-1 in electrocatalysis, whereas that in photocatalysis was 16 kJ mol-1. The origin of the difference in these activation energy values is likely attributed to the possible effects of temperature on the individual thermodynamic and kinetic parameters of the reaction process. The work described herein demonstrates a method of “transferring the knowledge of electrocatalysis to photocatalysis” as a strong tool to rationally and quantitatively understand the complex reaction schemes involved in photocatalytic reactions.

  14. Synthesis of nanostructured lean-NOx catalysts by direct laser deposition of monometallic Pt-, Rh- and bimetallic PtRh-nanoparticles on SiO2 support

    International Nuclear Information System (INIS)

    Monometallic Pt and Rh and bimetallic PtRh catalysts with a highly dispersed noble metal weight loading of ca. 1 wt% were produced via the direct deposition of nanoparticles on different SiO2 supports by means of pulsed ultra-violet (248 nm) excimer laser ablation of Pt, Rh bulk metal and PtRh alloy targets. Backscattered electron microscopy (BSE), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) were employed to characterize the deposited nanoparticles, which were found to exhibit narrow size distribution centred around 2.5 nm. The catalytic activities for lean NOx reduction of the monometallic and bimetallic catalyst samples were investigated in a flow reactor setup in the temperature range 100-400 deg. C using a test gas mixture representative of oxygen rich diesel engine exhaust gas. For comparison a Rh/SiO2 reference catalyst prepared by a conventional impregnation method was also tested. Further experiments were performed in which PtRh nanoparticles were deposited on a Rh/SiO2 reference catalyst sample to study the possibility for controlled modification of its activity. The catalytic activity measurements revealed that among the samples solely prepared by laser deposition the PtRh-SiO2 nanoparticle catalyst showed the highest activity for NOx reduction at low temperatures 100-300 deg. C. In addition, it could be demonstrated that the initially low NOx reduction activity and the N2 selectivity of the Rh/SiO2 reference catalyst sample for temperatures below 250 deg. C can be enhanced by post laser deposition of PtRh nanoparticles

  15. Synthesis and Electrochemical Evaluation of Carbon Supported Pt-Co Bimetallic Catalysts Prepared by Electroless Deposition and Modified Charge Enhanced Dry Impregnation

    Directory of Open Access Journals (Sweden)

    John Meynard M. Tengco

    2016-06-01

    Full Text Available Carbon-supported bimetallic Pt-Co cathode catalysts have been previously identified as higher activity alternatives to conventional Pt/C catalysts for fuel cells. In this work, a series of Pt-Co/C catalysts were synthesized using electroless deposition (ED of Pt on a Co/C catalyst prepared by modified charge enhanced dry impregnation. X-ray diffraction (XRD and scanning transmission electron microscopy (STEM characterization of the base catalyst showed highly dispersed particles. A basic ED bath containing PtCl62− as the Pt precursor, dimethylamine borane as reducing agent, and ethylenediamine as stabilizing agent successfully targeted deposition of Pt on Co particles. Simultaneous action of galvanic displacement and ED resulted in Pt-Co alloy formation observed in XRD and energy dispersive X-ray spectroscopy (XEDS mapping. In addition, fast deposition kinetics resulted in hollow shell Pt-Co alloy particles while particles with Pt-rich shell and Co-rich cores formed with controlled Pt deposition. Electrochemical evaluation of the Pt-Co/C catalysts showed lower active surface but much higher mass and surface activities for oxygen reduction reaction compared to a commercial Pt/C fuel cell catalyst.

  16. Low-Temperature 1,3-Butadiene Hydrogenation over Supported Pt/3d/gamma-Al2O3 Bimetallic Catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Lonergan, William W; Xing, X; Zheng, Renyang; Qi, Suitao; Huang, B; Chen, Jingguang

    2011-02-02

    Low-temperature 1,3-butadiene hydrogenation is used as a probe reaction to investigate the hydrogenation activity over several γ-Al{sub 2}O{sub 3} supported Pt/3d (3d = Co, Ni, Cu) bimetallic catalysts. Batch and flow reactor studies are employed to quantify the kinetic activity and steady-state conversion, respectively, of each catalyst. Transmission electron microscopy (TEM) is utilized to characterize particle sizes and extended X-ray absorption fine structure (EXAFS) measurements are performed to verify the Pt–3d bimetallic bond formation. Pulse carbon monoxide chemisorption measurements are also performed to characterize the number of active sites. Additionally, density functional theory (DFT) calculations are included to determine the binding energies of 1,3-butadiene and atomic hydrogen on the corresponding model surfaces. The binding energies of the adsorbates are found to correlate with the hydrogenation activity, allowing for use of such correlation to potentially predict hydrogenation catalysts with enhanced activity based on the binding energies of the adsorbates of interest.

  17. Preparation of highly dispersed Ru-Sn bimetallic supported catalysts from the single source precursors Cp(PPh32Ru-SnX3 (X = Cl or Br

    Directory of Open Access Journals (Sweden)

    Ana Cláudia Bernardes Silva

    2003-06-01

    Full Text Available In this work highly dispersed Ru-Sn bimetallic catalysts have been prepared from organobimetallic Cp(PPh32Ru-SnX3 (X = Cl or Br complexes. These single source precursors can be easily impregnated in high surface area supports, such as activated carbon and sol-gel SiO2, and upon controlled thermal treatment the ligands are released as volatile products resulting in the formation of the bimetallic system Ru-Sn. Catalytic reactions, such as hydrodechlorination of CCl4 and chlorobenzene and TPR (Temperature Programmed Reduction experiments carried out with these RuSn catalysts suggested a strong interaction between Ruthenium and Tin. Mössbauer measurements showed that these materials when exposed to air are immediately oxidized to form Sn (IV. It was shown that upon controlled reduction conditions with H2 it is possible to reduce selectively Sn to different oxidation states and different phases. The Sn oxidation state showed significant effect on the catalytic hydrogenation of 1,5-cyclooctadiene. The use of these single source precursors with a controlled decomposition/reduction procedure allows the preparation of unique catalysts with an intimate interaction between the components ruthenium and tin and the possibility of varying the Sn oxidation state around the Ru metal.

  18. From First Principles Design to Realization of Bimetallic Catalysts for Enhanced Selectivity

    Energy Technology Data Exchange (ETDEWEB)

    Lobo, Raul F.; Crooks, Richard M.; Mavrikakis, Manos

    2014-04-08

    “Catalysis by design” has been a dream for decades. To specify the composition and structure of matter to effect a desired catalytic transformation with desired and predicted rate and selectivity remains a monumental challenge, especially in heterogeneous catalysis. Our research thrusts have been chosen not only for their practical and scientific relevance, e.g. for more efficient and sustainable chemicals and fuels production, but also because they provide a foundation for developing and exploring broadly applicable principles and strategies for catalyst design.

  19. A Ni-Fe Layered Double Hydroxide-Carbon Nanotube Complex for Water Oxidation

    CERN Document Server

    Gong, Ming; Wang, Hailiang; Liang, Yongye; Wu, Justin Zachary; Zhou, Jigang; Wang, Jian; Regier, Tom; Wei, Fei; Dai, Hongjie

    2013-01-01

    Highly active, durable and cost-effective electrocatalysts for water oxidation to evolve oxygen gas hold a key to a range of renewable energy solutions including water splitting and rechargeable metal-air batteries. Here, we report the synthesis of ultrathin nickel iron layered double hydroxide nanoplates on mildly oxidized multi-walled carbon nanotubes. Incorporation of Fe into the nickel hydroxide induced the formation of NiFe-layered double hydroxide. The nanoplates were covalently attached to a network of nanotubes, affording excellent electrical wiring to the nanoplates. The ultra-thin Ni-Fe layered double hydroxide nanoplates/carbon nanotube complex was found to exhibit unusually high electro-catalytic activity and stability for oxygen evolution and outperformed commercial precious metal Ir catalysts.

  20. Effects of the ratio of Fe to Co over Fe-Co/SiO2 bimetallic catalysts on their catalytic performance for Fischer-Tropsch synthesis

    Institute of Scientific and Technical Information of China (English)

    Xiangdong Ma; Qiwen Sun; Weiyong Ying; Dingye Fang

    2009-01-01

    The Fe-Co/SiO2 bimetallic catalysts with different ratios of Fe to Co were prepared by aqueous incipient wetness impregnation. The catalysts of 10%Fe:0%Co/SiO2, 10%Fe:6%Co/SiO2, 10%Fe:2%Co/SiO2, 10%Fe: 10%Co/SiO2, 6%Fe: 10%Co/SiO2, 2%Fe: 10%Co/SiO2 and 0%Fe: 10%Co/SiO2 by mass were tested in a fixed reactor by the Fischer-Tropsch synthesis. Activity and hydrocarbon distribution were found to be determined by the ratio of iron to cobalt of the catalysts. Higher iron content inhibited the activity, whereas higher cobalt content enhanced the activity of the Fe-Co/SiO2 catalysts. On the other hand, for the catalysts of 10%Fe:6%Co/SiO2, 10%Fe: 10%Co/SiO2, 6%Fe: 10%Co/SiO2, and 2%Fe: 10%Co/SiO2, the total C2-C4 fraction increased (from 10.65% to 26.78%) and C5+ fraction decreased (from 75.75% to 57.63%) at 523 K. Temperature programmed reduction revealed that the addition of cobalt enhanced the reducibility of the Fe-Co/SiO2 catalyst. Metal oxides were present in those catalysts as shown by XRD. The Fe-Co alloy phase was found in the 2%Fe: 10%Co/SiO2, 6%Fe: 10%Co/SiO2, 10%Fe:10%Co/SiO2, 10%Fe:6%Co/SiO2 catalysts and their crystals were perfect.

  1. A structure investigation of Pt-Co bimetallic catalysts fabricated by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Lucariello, Marialaura; Penazzi, Nerino [Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino, C.so Duca Abruzzi n. 24, I-10129 Torino (Italy); Arca, Elisabetta; Mulas, Gabriele [Dipartimento di Chimica, Universita di Sassari, Via Vienna n. 2, I-07100 Sassari (Italy); Enzo, Stefano [Dipartimento di Chimica, Universita di Sassari, Via Vienna n. 2, I-07100 Sassari (Italy)], E-mail: enzo@uniss.it

    2009-03-15

    Three Pt-Co mixtures of composition Pt{sub 25}Co{sub 75}, Pt{sub 50}Co{sub 50} and Pt{sub 75}Co{sub 25} respectively, were synthesized using the high-energy ball milling technique of the elemental powders with a view to prepare catalysts for fuel cells. The kinetics of phase evolution, their structure and average microstructure properties were quantitatively investigated by X-ray powder diffraction with the Rietveld method. The results show that the ball milling technique is able to produce Pt-Co solid solutions soon after few minutes of mechanical treatment. Of the two polymorphs of cobalt the fcc allotrope appears to be involved preferentially in the early stage of alloying reaction with fcc platinum. For the three compositions, a sigmoidal equation based on an interdiffusion-controlled mechanism satisfactorily accounts for the evolution of the solid solution as a function of mechanical treatment time. A characteristic reaction time of 3-6 h is observed for the solid state transformation reaction with the milling conditions adopted in our reactor. In the case of the Pt{sub 25}Co{sub 75} composition, a competitive-consecutive reaction is observed. Lattice parameters of the solid solutions after extended times of milling and related atomic volumes turn out to be slightly above the values ideally predicted on the basis of the Vegard's law. For the Pt{sub 75}Co{sub 25} composition the average crystallite size is reduced down to ca. 150 A after 12 h when the lattice microstrain is also at a maximum, but further mechanical treatment increases the average crystal size value and to decrease the strain. Similar results are found for equiatomic and Co-rich compositions. Annealing of the alloyed equiatomic powders promotes a cubic-to-tetragonal transformation which is already operative at 600 deg. C. In fact, after this treatment two tetragonal phases are observed. Further thermal treatment and annealing at 700 deg. C induces peak sharpening of the diffraction patterns

  2. Toward CH4 dissociation and C diffusion during Ni/Fe-catalyzed carbon nanofiber growth: A density functional theory study

    Science.gov (United States)

    Fan, Chen; Zhou, Xing-Gui; Chen, De; Cheng, Hong-Ye; Zhu, Yi-An

    2011-04-01

    First-principles calculations have been performed to investigate CH4 dissociation and C diffusion during the Ni/Fe-catalyzed growth of carbon nanofibers (CNFs). Two bulk models with different Ni to Fe molar ratios (1:1 and 2:1) are constructed, and x-ray diffraction (XRD) simulations are conducted to evaluate their reliability. With the comparison between the calculated and experimental XRD patterns, these models are found to be well suited to reproduce the crystalline structures of Ni/Fe bulk alloys. The calculations indicate the binding of the C1 derivatives to the Ni/Fe closest-packed surfaces is strengthened compared to that on Ni(111), arising from the upshift of the weighted d-band centers of catalyst surfaces. Then, the transition states for the four successive dehydrogenation steps in CH4 dissociation are located using the dimer method. It is found that the energy barriers for the first three steps are rather close on the alloyed Ni/Fe and Ni surfaces, while the activation energy for CH dissociation is substantially lowered with the introduction of Fe. The dissolution of the generated C from the surface into the bulk of the Ni/Fe alloys is thermodynamically favorable, and the diffusion of C through catalyst particles is hindered by the Fe component. With the combination of density functional theory calculations and kinetic analysis, the C concentration in catalyst particles is predicted to increase with the Fe content. Meanwhile, other experimental conditions, such as the composition of carbon-containing gases, feedstock partial pressure, and reaction temperature, are also found to play a key role in determining the C concentration in bulk metal, and hence the microstructures of generated CNFs.

  3. One-pot fabrication of NiFe2O4 nanoparticles on α-Ni(OH)2 nanosheet for enhanced water oxidation

    Science.gov (United States)

    Chen, Hong; Yan, Junqing; Wu, Huan; Zhang, Yunxia; Liu, Shengzhong (Frank)

    2016-08-01

    Water splitting has been intensively investigated as a promising solution to resolve the future environmental and energy crises. The oxygen evolution reaction (OER) of the photo- and electric field-induced water splitting limits the development of other reactions, including hydrogen evolution reaction (HER). Fe, Ni and NiFe (hydro) oxide-based catalysts are generally acknowledged among the best candidates of OER catalysts for water splitting. Herein, we developed a one-pot simple hydrothermal process to assemble NiFe2O4 nanoparticles onto the α-Ni(OH)2 nanosheets. The first formed NiFe2O4 under high temperature and pressure environment induces and assists the α-Ni(OH)2 formation without any further additives, because the distance between the neighboring Ni atoms in the cubic NiFe2O4 is similar to that in the α-Ni(OH)2 {003} facets. We have synthesized a series of NiFe2O4/α-Ni(OH)2 compounds and find that the overpotential decreases with the increase of Ni(OH)2 content while the OER kinetics stays unchanged, suggesting that Ni(OH)2 plays a major role in overpotential while NiFe2O4 mainly affects the OER kinetics. The obtained NiFe2O4/α-Ni(OH)2 compounds is also found to be a promising co-catalyst for the photocatalytic water oxidation. In fact, it is even more active than the noble PtOx with acceptable stability for the oxygen generation.

  4. Substrate dependent ultrafast dynamics in thin NiFe films

    Science.gov (United States)

    Bosco, C. A. C.; Azevedo, A.; Acioli, L. H.

    2003-09-01

    We have studied the ultrafast electronic response of thin NiFe films by femtosecond transient reflectivity measurements. The experiments were performed on films with varying thicknesses, substrates, and pump fluences. It has been observed that for high excitation densities the electron cooling time depends strongly on the nature of the underlying substrate and we attribute our results to transport of hot carriers out of the excited region. In particular, we have observed that for NiFe over NiO, carrier transport should be less important than for NiFe over Si.

  5. Synthesis of coal-derived single-walled carbon nanotube from coal by varying the ratio of Zr/Ni as bimetallic catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Rajesh, E-mail: rajeshbhu1@gmail.com [Banaras Hindu University, Nanoscience and Nanotechnology Unit, Department of Physics (India); Singh, Rajesh Kumar, E-mail: rksbhu@gmail.com [Indian Institute of Technology (Banaras Hindu University), Department of Applied Physics (India); Ghosh, A. K.; Sen, Raja; Srivastava, S. K. [Central Institute of Mining and Fuel Research (India); Tiwari, R. S.; Srivastava, O. N. [Banaras Hindu University, Nanoscience and Nanotechnology Unit, Department of Physics (India)

    2013-01-15

    In this paper coal, source has been used in place of graphite for synthesis of single-walled carbon nanotubes (SWCNTs) with new Zr/Ni bimetallic catalyst. Using coal as starting material to produce the high-value-added SWCNTs is an economically competent route. SWCNTs have been synthesized by the electric arc discharge method using the so-called heterogeneous annealed coal anode filled with Zr and Ni catalyst. SWCNTs have been synthesized using annealed coal rod. The SWCNTs bundles synthesized generally have diameters of 4-10 nm. Most of those produced with Zr/Ni as the catalyst has a diameter ranging from 2.0 to 1.0 nm. The as-synthesized SWCNTs have been characterized employing XRD, HRTEM, EDX, Raman spectroscopy, and FTIR. It has been found that the change of the ratio of Zr and Ni concentration (wt%) in the catalyst affects the yield of SWCNTs. However, the purity of SWCNTs is very sensitive to the concentration of Zr. An optimal range of Zr/Ni compositions for synthesis of SWCNTs with relatively high purity and yield is obtained at specific concentration of 3:1.

  6. Carbon nanotubes supported Cu-Ni bimetallic catalysts and their properties for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide

    International Nuclear Information System (INIS)

    Multi-walled carbon nanotubes (MWCNTs) supported Cu-Ni bimetallic catalysts for the direct synthesis of dimethyl carbonate (DMC) from CH3OH and CO2 were synthesized and investigated. The supporting materials and the synthesized catalysts were fully characterized using FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) techniques. The catalytic activities were investigated by performing micro-reactions. The experimental results showed that the metal phase and Cu-Ni alloy phase in the catalyst were partially formed during the calcination and activation step. Active metal particles were dispersed homogeneously on the surface of the MWCNTs. Cu-Ni/MWCNTs catalysts were efficient for the direct synthesis of DMC. The highest conversion of CH3OH was higher than 4.3% and the selectivity of DMC was higher than 85.0% under the optimal catalytic conditions of 120 deg. C and around 1.2 MPa. The high catalytic activity of Cu-Ni/MWCNTs in DMC synthesis can be attributed to the synergetic effects of metal Cu, Ni and Cu-Ni alloy in the activation of CH3OH and CO2, the unique structure of MWCNTs and the interaction between the metal particles and the supports.

  7. Role of Pt(0) in bimetallic (Pt,Fe)-FER catalysts in the N2O decomposition

    Czech Academy of Sciences Publication Activity Database

    Tabor, Edyta; Jíša, Kamil; Nováková, Jana; Bastl, Zdeněk; Vondrová, Alena; Závěta, K.; Sobalík, Zdeněk

    2013-01-01

    Roč. 165, JAN 2013 (2013), s. 40-47. ISSN 1387-1811 R&D Projects: GA ČR GA203/09/1627 Institutional support: RVO:61388955 Keywords : bimetallic Pt,Fe- FER * Pt- FER * Pt(0) clusters Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.209, year: 2013

  8. Magnetic behaviour investigation on symmetric spin valves of Co/Cu/NiFe and NiFe/Cu/Co

    Institute of Scientific and Technical Information of China (English)

    李铁; 沈鸿烈

    2002-01-01

    In this paper, we have obtained and investigated the magnetic behaviours of the ferromagnetic layer in thesymmetric spin valves of Co/Cu/NiFe and NiFe/Cu/Co by measuring with a vibrating sample magnetometer andanalysing in terms of the multi-domain Ising models. It has been found that some magnetic layer can have quitedifferent magnetic behaviours in different structures of spin valves, depending on the properties of the under-layer. Inour investigation, we have found that the magnetic behaviour of a Co layer depends mainly on the magnetization of theunder-layer, whereas this is not the case for the NiFe layer.

  9. Preparation of highly dispersed Ru-Sn bimetallic supported catalysts from the single source precursors Cp(PPh3)2Ru-SnX3 (X = Cl or Br)

    OpenAIRE

    Ana Cláudia Bernardes Silva; Ana Paula Guimarães de Sousa; José Domingos Ardisson; Helmuth Guido Luna Siebald; Edmilson Moura; Eduardo Nicolau dos Santos; Nelcy Della Santina Mohallem; Rochel Montero Lago

    2003-01-01

    In this work highly dispersed Ru-Sn bimetallic catalysts have been prepared from organobimetallic Cp(PPh3)2Ru-SnX3 (X = Cl or Br) complexes. These single source precursors can be easily impregnated in high surface area supports, such as activated carbon and sol-gel SiO2, and upon controlled thermal treatment the ligands are released as volatile products resulting in the formation of the bimetallic system Ru-Sn. Catalytic reactions, such as hydrodechlorination of CCl4 and chlorobenzene and TPR...

  10. Comparative Study of Thermal Stability of NiFe and NiFeTa Thin Films Grown by Cosputtering Technique

    Science.gov (United States)

    Phuoc, Nguyen N.; Ong, C. K.

    2016-08-01

    A comparative study of the thermal behavior of dynamic permeability spectra for compositionally graded NiFeTa and uniform-composition NiFe thin films has been carried out. We found that the resonance frequency of the compositionally graded NiFeTa film increased with increasing temperature, while it decreased for the case of the uniform-composition NiFe thin film. This finding unambiguously suggests that the compositional gradient of the film is the only reason for the increase of the magnetic anisotropy with temperature due to its stress-induced origin, while the cosputtering technique does not play any role in this peculiar behavior. The temperature dependence of the frequency linewidth is also presented and discussed.

  11. Design of heterogeneous catalysts

    DEFF Research Database (Denmark)

    Frey, Anne Mette

    was inspired by a computational screening, suggesting that alloys such as Ni-Fe, Co-Ni, and Co-Fe should show superior activity to the industrially used nickel catalyst. Especially the Ni-Fe system was considered to be interesting, since such alloy catalysts should be both more active and cheaper than...... turned out to work well, and the best catalyst prepared had a C5+ yield almost a factor of two higher than a standard air calcined Co catalyst. In the NH3-SCR reaction it is desirable to develop an active and stable catalyst for NOx removal in automotive applications, since the traditionally used...

  12. Heterogenized Bimetallic Pd-Pt-Fe3O4 Nanoflakes as Extremely Robust, Magnetically Recyclable Catalysts for Chemoselective Nitroarene Reduction.

    Science.gov (United States)

    Byun, Sangmoon; Song, Yeami; Kim, B Moon

    2016-06-15

    A very simple synthesis of bimetallic Pd-Pt-Fe3O4 nanoflake-shaped alloy nanoparticles (NPs) for cascade catalytic reactions such as dehydrogenation of ammonia-borane (AB) followed by the reduction of nitro compounds (R-NO2) to anilines or alkylamines (R-NH2) in methanol at ambient temperature is described. The Pd-Pt-Fe3O4 NPs were easily prepared via a solution phase hydrothermal method involving the simple one-pot coreduction of potassium tetrachloroplatinate (II) and palladium chloride (II) in polyvinylpyrrolidone with subsequent deposition on commercially available Fe3O4 NPs. The bimetallic Pd-Pt alloy NPs decorated on Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. Various nitroarene derivatives were reduced to anilines with very specific chemoselectivity in the presence of other reducible functional groups. The bimetallic Pd-Pt-Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. The nitro reduction proceeded in 5 min with nearly quantitative conversions and yields. Furthermore, the magnetically recyclable nanocatalysts were readily separated using an external magnet and reused up to 250 times without any loss of catalytic activity. A larger scale (10 mmol) reaction was also successfully performed with >99% yield. This efficient, recyclable Pd-Pt-Fe3O4 NPs system can therefore be repetitively utilized for the reduction of various nitro-containing compounds. PMID:27191706

  13. Oxygen Evolution Reaction Dynamics, Faradaic Charge Efficiency, and the Active Metal Redox States of Ni-Fe Oxide Water Splitting Electrocatalysts.

    Science.gov (United States)

    Görlin, Mikaela; Chernev, Petko; Ferreira de Araújo, Jorge; Reier, Tobias; Dresp, Sören; Paul, Benjamin; Krähnert, Ralph; Dau, Holger; Strasser, Peter

    2016-05-01

    Mixed Ni-Fe oxides are attractive anode catalysts for efficient water splitting in solar fuels reactors. Because of conflicting past reports, the catalytically active metal redox state of the catalyst has remained under debate. Here, we report an in operando quantitative deconvolution of the charge injected into the nanostructured Ni-Fe oxyhydroxide OER catalysts or into reaction product molecules. To achieve this, we explore the oxygen evolution reaction dynamics and the individual faradaic charge efficiencies using operando differential electrochemical mass spectrometry (DEMS). We further use X-ray absorption spectroscopy (XAS) under OER conditions at the Ni and Fe K-edges of the electrocatalysts to evaluate oxidation states and local atomic structure motifs. DEMS and XAS data consistently reveal that up to 75% of the Ni centers increase their oxidation state from +2 to +3, while up to 25% arrive in the +4 state for the NiOOH catalyst under OER catalysis. The Fe centers consistently remain in the +3 state, regardless of potential and composition. For mixed Ni100-xFex catalysts, where x exceeds 9 atomic %, the faradaic efficiency of O2 sharply increases from ∼30% to 90%, suggesting that Ni atoms largely remain in the oxidation state +2 under catalytic conditions. To reconcile the apparent low level of oxidized Ni in mixed Ni-Fe catalysts, we hypothesize that a kinetic competition between the (i) metal oxidation process and the (ii) metal reduction step during O2 release may account for an insignificant accumulation of detectable high-valent metal states if the reaction rate of process (ii) outweighs that of (i). We conclude that a discussion of the superior catalytic OER activity of Ni-FeOOH electrocatalysts in terms of surface catalysis and redox-inactive metal sites likely represents an oversimplification that fails to capture essential aspects of the synergisms at highly active Ni-Fe sites. PMID:27031737

  14. Wear mechanism of electrodeposited amorphous Ni-Fe-P alloys

    Institute of Scientific and Technical Information of China (English)

    高诚辉; 赵源

    2004-01-01

    The wear mechanism of amorphous Ni-Fe-P coating was discussed. The wear resistance of the amor phous Ni-Fe-P coatings was tested on a Timken wear apparatus, and the wear track of the amorphous Ni-Fe-P coat ings as-deposited and heated at various temperatures was observed by SEM. The results show that the wear resistthe coating will change with the heating temperature increasing from pitting+plowing at 200 ℃ to pitting at 400 ℃,and to plowing at 600 ℃. The pits on the worn surface of the amorphous Ni-Fe-P coating result from the tribo-fatigue fracture. The cracks of spalling initiate at pits and propagate at certain angle with the sliding direction on sur face, and then extend into sub-surface along the poor P layers or the interface between layers. Finally under repeated action of the stress in the rubbing process the cracks meet and the debris forms. The generation of the pits and spal-ling is related with the internal stress, brittleness and layer structure of the amorphous Ni-Fe-P coating.

  15. Surface structure and reaction property of CuCl2-PdCl2 bimetallic catalyst in methanol oxycarbonylation: A DFT approach

    International Nuclear Information System (INIS)

    Surface structure of CuCl2-PdCl2 bimetallic catalyst (Wacker-type catalyst) was built employing density functional theory (DFT) calculations, and the reaction mechanism of methanol oxycarbonylation over the CuCl2-PdCl2 surfaces was also investigated. On the CuCl2-PdCl2 surface, the active site for methanol oxidation was confirmed as Cu-Cl-Cu (Pd). Comparing with pure CuCl2 surface, the introduction of Pd atom causes the electron repopulation on the surface and lowers the energy barrier for methanol oxidation, but the number of the active site decreases with the increasing of Pd doping volume. Agreed with previous experimental results, the Pd site is most favorable for the CO insertion, indicated by the lowest activation barrier for the formation of COOCH3 on Pd atom. The lowest energy barrier for the formation of DMC appears when COOCH3 species adsorbed on Pd atom and methoxyl adsorbed on Cu atoms, which is 0.42 eV. Finally, the reconstruction of the unsaturated surface is a spontaneous and exothermic process. Comparing with other surfaces, the rate-limiting step, methanol oxidation, on CuCl2-PdCl2 surface with Pd/Cu = 1:17 has the lowest energy barrier, which is agreed with the experimental observation that PdCl2-CuCl2 catalyst with Pd/Cu = 1:20 has the favorable activity. The adsorbed methoxyl will further lower the activation barrier of methanol oxidation, which is agreed with experimental observation that the Wacker-type catalysts have an induction period in the methanol oxidative carbonylation system.

  16. Spreading of Ni - Fe - W melts over polycrystalline tungsten

    Energy Technology Data Exchange (ETDEWEB)

    Yupko, V.L.; Minakova, R.V.; Kolchin, O.P.; Vodop' yanova, L.S.; Monastyreva, N.I.; Vojtenko, V.L. (AN Ukrainskoj SSR, Kiev. Inst. Problem Materialovedeniya)

    1983-09-01

    The method of filming was employed to study the spread over dense and porous polycrystalline tungsten of Ni-Fe-W melts. When tungsten amount grows and the W-(Ni-Fe-W) system approaches the thermodynamic equilibrium state the melts spread deteriorates; in case of porous tungsten it is worse than in case of dense one. The observed porosity effect on the spread testifies to intensification of the liquid motion turbulence. Difference in the spread over polycrystalline tungsten between melts with a constant tungsten content (24%) and with the Ni:Fe ratio varying over wide ranges is within the limits of the experimental error, which is due to similar physicochemical properties of nickel and iron.

  17. Solvothermal synthesis of octahedral NiFe2O4 nanocrystals and catalytic properties for the reduction of some aromatic nitrocompounds

    International Nuclear Information System (INIS)

    In this paper, we report the successful synthesis of octahedral NiFe2O4 nanocrystals with room-temperature ferrimagnetism via a mixed solvothermal process at 170 °C for 15 h, using Fe(NO3)3 and NiCl2 as starting reactants. The phase and morphology of the as-prepared product is characterized by means of powder X-ray diffraction, energy dispersive spectrometry, selected area electron diffraction (SAED), (high resolution) transmission electron microscopy, and scanning electron microscopy. Experiments showed that the as-prepared octahedral NiFe2O4 nanocrystals owned strong catalytic activity for the reduction of some aromatic nitro-compounds such as 4-nitrophenol, 2-nitroaniline, 4-nitroaniline, and 2,4-dinitrophenol. Under the presence of 9 mg NiFe2O4 nanocrystals, the rate constants of the reductive reactions were in turn 3.16 × 10−2 min−1 for 4-nitrophenol, 4.28 × 10−2 min−1 for 2-nitroaniline, 6.79 × 10−2 min−1 for 4-nitroaniline, and 3.26 × 10−2 min−1 for 2,4-dinitrophenol. Moreover, the present catalyst could be conveniently recycled due to its magnetism. After ten cycles, its catalytic efficiency did not obviously decrease. - Highlights: • Octahedral NiFe2O4 nanocrystals were successfully prepared by an emulsion-solvothermal route. • NiFe2O4 nanocrystals with the room-temperature magnetism could be used as a recyclable catalyst. • NiFe2O4 nanocrystals showed strong catalytic activity for the reduction of 4-NP in NaBH4 solution

  18. Solvothermal synthesis of octahedral NiFe{sub 2}O{sub 4} nanocrystals and catalytic properties for the reduction of some aromatic nitrocompounds

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Hangsong [College of Chemistry and Materials Science, Key Laboratory of Functional Molecular Solids of Ministry of Education, Anhui Laboratory of Molecule-Based Materials, Anhui Key Laboratory of Functional Molecular Solids, Anhui Normal University, 1 Beijing Eastern Road, Wuhu 241000 (China); Ni, Yonghong, E-mail: niyh@mail.ahnu.edu.cn [College of Chemistry and Materials Science, Key Laboratory of Functional Molecular Solids of Ministry of Education, Anhui Laboratory of Molecule-Based Materials, Anhui Key Laboratory of Functional Molecular Solids, Anhui Normal University, 1 Beijing Eastern Road, Wuhu 241000 (China); Xiang, Nannan [College of Chemistry and Materials Science, Key Laboratory of Functional Molecular Solids of Ministry of Education, Anhui Laboratory of Molecule-Based Materials, Anhui Key Laboratory of Functional Molecular Solids, Anhui Normal University, 1 Beijing Eastern Road, Wuhu 241000 (China); Ma, Xiang [Center of Modern Analyses, Nanjing University, Nanjing 210093 (China); Wan, Fengying [Library of Anhui Normal University, 1 Beijing Eastern Road, Wuhu 241000 (China)

    2015-05-05

    In this paper, we report the successful synthesis of octahedral NiFe{sub 2}O{sub 4} nanocrystals with room-temperature ferrimagnetism via a mixed solvothermal process at 170 °C for 15 h, using Fe(NO{sub 3}){sub 3} and NiCl{sub 2} as starting reactants. The phase and morphology of the as-prepared product is characterized by means of powder X-ray diffraction, energy dispersive spectrometry, selected area electron diffraction (SAED), (high resolution) transmission electron microscopy, and scanning electron microscopy. Experiments showed that the as-prepared octahedral NiFe{sub 2}O{sub 4} nanocrystals owned strong catalytic activity for the reduction of some aromatic nitro-compounds such as 4-nitrophenol, 2-nitroaniline, 4-nitroaniline, and 2,4-dinitrophenol. Under the presence of 9 mg NiFe{sub 2}O{sub 4} nanocrystals, the rate constants of the reductive reactions were in turn 3.16 × 10{sup −2} min{sup −1} for 4-nitrophenol, 4.28 × 10{sup −2} min{sup −1} for 2-nitroaniline, 6.79 × 10{sup −2} min{sup −1} for 4-nitroaniline, and 3.26 × 10{sup −2} min{sup −1} for 2,4-dinitrophenol. Moreover, the present catalyst could be conveniently recycled due to its magnetism. After ten cycles, its catalytic efficiency did not obviously decrease. - Highlights: • Octahedral NiFe{sub 2}O{sub 4} nanocrystals were successfully prepared by an emulsion-solvothermal route. • NiFe{sub 2}O{sub 4} nanocrystals with the room-temperature magnetism could be used as a recyclable catalyst. • NiFe{sub 2}O{sub 4} nanocrystals showed strong catalytic activity for the reduction of 4-NP in NaBH{sub 4} solution.

  19. A Novelγ-Alumina Supported Fe-Mo Bimetallic Catalyst for Reverse Water Gas Shift Reaction

    Institute of Scientific and Technical Information of China (English)

    Abolfazl Gharibi Kharaji; Ahmad Shariati; Mohammad Ali Takassi

    2013-01-01

    In reverse water gas shift (RWGS) reaction CO2 is converted to CO which in turn can be used to pro-duce beneficial chemicals such as methanol. In the present study, Mo/Al2O3, Fe/Al2O3 and Fe-Mo/Al2O3 catalysts were synthesised using impregnation method. The structures of catalysts were studied using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, inductively coupled plasma atomic emission spectrometer (ICP-AES), temperature programmed reduction (H2-TPR), CO chemisorption, energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) techniques. Kinetic properties of all catalysts were investigated in a batch re-actor for RWGS reaction. The results indicated that Mo existence in structure of Fe-Mo/Al2O3 catalyst enhances its activity as compared to Fe/Al2O3. This enhancement is probably due to better Fe dispersion and smaller particle size of Fe species. Stability test of Fe-Mo/Al2O3 catalyst was carried out in a fixed bed reactor and a high CO yield for 60 h of time on stream was demonstrated. Fe2(MoO4)3 phase was found in the structures of fresh and used catalysts. TPR results also indicate that Fe2(MoO4)3 phase has low reducibility, therefore the Fe2(MoO4)3 phase significantly inhibits the reduction of the remaining Fe oxides in the catalyst, resulted in high stability of Fe-Mo/Al2O3 catalyst. Overall, this study introduces Fe-Mo/Al2O3 as a novel catalyst with high CO yield, almost no by-products and fairly stable for RWGS reaction.

  20. Hydride bridge in [NiFe]-hydrogenase observed by nuclear resonance vibrational spectroscopy

    Science.gov (United States)

    Ogata, Hideaki; Krämer, Tobias; Wang, Hongxin; Schilter, David; Pelmenschikov, Vladimir; van Gastel, Maurice; Neese, Frank; Rauchfuss, Thomas B.; Gee, Leland B.; Scott, Aubrey D.; Yoda, Yoshitaka; Tanaka, Yoshihito; Lubitz, Wolfgang; Cramer, Stephen P.

    2015-08-01

    The metabolism of many anaerobes relies on [NiFe]-hydrogenases, whose characterization when bound to substrates has proven non-trivial. Presented here is direct evidence for a hydride bridge in the active site of the 57Fe-labelled fully reduced Ni-R form of Desulfovibrio vulgaris Miyazaki F [NiFe]-hydrogenase. A unique `wagging' mode involving H- motion perpendicular to the Ni(μ-H)57Fe plane was studied using 57Fe-specific nuclear resonance vibrational spectroscopy and density functional theory (DFT) calculations. On Ni(μ-D)57Fe deuteride substitution, this wagging causes a characteristic perturbation of Fe-CO/CN bands. Spectra have been interpreted by comparison with Ni(μ-H/D)57Fe enzyme mimics [(dppe)Ni(μ-pdt)(μ-H/D)57Fe(CO)3]+ and DFT calculations, which collectively indicate a low-spin Ni(II)(μ-H)Fe(II) core for Ni-R, with H- binding Ni more tightly than Fe. The present methodology is also relevant to characterizing Fe-H moieties in other important natural and synthetic catalysts.

  1. Fabrication of PdCo Bimetallic Nanoparticles Anchored on Three-Dimensional Ordered N-Doped Porous Carbon as an Efficient Catalyst for Oxygen Reduction Reaction.

    Science.gov (United States)

    Xue, Hairong; Tang, Jing; Gong, Hao; Guo, Hu; Fan, Xiaoli; Wang, Tao; He, Jianping; Yamauchi, Yusuke

    2016-08-17

    PdCo bimetallic nanoparticles (NPs) anchored on three-dimensional (3D) ordered N-doped porous carbon (PdCo/NPC) were fabricated by an in situ synthesis. Within this composite, N-doped porous carbon (NPC) with an ordered mesoporous structure possesses a high surface area (659.6 m(2) g(-1)), which can facilitate electrolyte infiltration. NPC also acts as a perfect 3D conductive network, guaranteeing fast electron transport. In addition, homogeneously distributed PdCo alloy NPs (∼15 nm) combined with the doping of the N element can significantly improve the electrocatalytic activity for the oxygen reduction reaction (ORR). Due to the structural and material superiority, although the weight percentage of PdCo NPs (∼8 wt%) is much smaller than that of commercial Pt/C (20 wt%), the PdCo/NPC catalyst exhibits similar excellent electrocatalytic activity; however, its superior durability and methanol-tolerance ability of the ORR are as great as those of commercial Pt/C in alkaline media. PMID:27441490

  2. Uninterrupted galvanic reaction for scalable and rapid synthesis of metallic and bimetallic sponges/dendrites as efficient catalysts for 4-nitrophenol reduction.

    Science.gov (United States)

    Barman, Barun Kumar; Nanda, Karuna Kar

    2015-03-01

    Here, we demonstrate an uninterrupted galvanic replacement reaction (GRR) for the synthesis of metallic (Ag, Cu and Sn) and bimetallic (Cu-M, M=Ag, Au, Pt and Pd) sponges/dendrites by sacrificing the low reduction potential metals (Mg in our case) in acidic medium. The acidic medium prevents the oxide formation on Mg surface and facilitates the uninterrupted reaction. The morphology of dendritic/spongy structures is controlled by the volume of acid used for this reaction. The growth mechanism of the spongy/dendritic microstructures is explained by diffusion-limited aggregate model (DLA), which is also largely affected by the volume of acid. The significance of this method is that the yield can be easily predicted, which is a major challenge for the commercialization of the products. Furthermore, the synthesis is complete in 1-2 minutes at room temperature. We show that the sponges/dendrites efficiently act as catalysts to reduce 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4-a widely studied conversion process. PMID:25628256

  3. Influence on the transport behaviors of spin-polarized electrons exerted by MgO/NiFe and NiFe/MgO heterointerfaces

    International Nuclear Information System (INIS)

    This work reports on the influence of different MgO/NiFe and NiFe/MgO heterointerfaces on the transport behaviors of spin-polarized electrons. It is found that the NiFe films with MgO underneath exhibit better transport properties than those coated by an MgO layer. The MgO/NiFe interface can significantly enhance the specular reflection of spin-polarized electrons and favor the electronic transport. In contrast, a greater lattice mismatch between NiFe and MgO will emerge because of the epitaxial relationship at the NiFe(111)/MgO(111) interface, with the resultant formation of oxygen-deficient MgOx phase at the NiFe/MgO interface. Significantly diffusive scattering of conduction electrons from such vacancy defects can substantially degrade the electron transport properties. - Highlights: • Multilayers were grown on thermally oxidized Si wafers by magnetron sputtering. • The influence of two heterointerfaces on NiFe films properties was investigated. • The NiFe film with MgO underneath shows better properties than that with MgO coating. • The interface status plays a crucial role in determining the transport properties. • Our study advances understanding of electron transport at metal/oxide interfaces

  4. Influence on the transport behaviors of spin-polarized electrons exerted by MgO/NiFe and NiFe/MgO heterointerfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Chong-Jun [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Wu, Zheng-Long [Analytical and Testing Center, Beijing Normal University, Beijing 100875 (China); Zhao, Zhi-Duo [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Ding, Lei [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Lu, Xiang-An; Li, Xu-Jing; Zhang, Jing-Yan [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Guang-Hua, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)

    2014-11-15

    This work reports on the influence of different MgO/NiFe and NiFe/MgO heterointerfaces on the transport behaviors of spin-polarized electrons. It is found that the NiFe films with MgO underneath exhibit better transport properties than those coated by an MgO layer. The MgO/NiFe interface can significantly enhance the specular reflection of spin-polarized electrons and favor the electronic transport. In contrast, a greater lattice mismatch between NiFe and MgO will emerge because of the epitaxial relationship at the NiFe(111)/MgO(111) interface, with the resultant formation of oxygen-deficient MgO{sub x} phase at the NiFe/MgO interface. Significantly diffusive scattering of conduction electrons from such vacancy defects can substantially degrade the electron transport properties. - Highlights: • Multilayers were grown on thermally oxidized Si wafers by magnetron sputtering. • The influence of two heterointerfaces on NiFe films properties was investigated. • The NiFe film with MgO underneath shows better properties than that with MgO coating. • The interface status plays a crucial role in determining the transport properties. • Our study advances understanding of electron transport at metal/oxide interfaces.

  5. Sulfided heterogeneous, bimetallic RuMo catalysts derived from mixtures of Ru{sub 3}(CO){sub 12} (or RuCl{sub 3}) and a molybdenum heteropolyanion. The reactions of ethanol with tetrahydroquinoline

    Energy Technology Data Exchange (ETDEWEB)

    Koo, Sang-Man; Ryan, D.; Laine, R.M.

    1992-09-01

    Efforts have been made to develop Ru/Mo bimetallic catalyst systems for hydrodenitrogenation (HDN) of tetrahydroquinoline (THQ)- In the course of these studies, it was discovered that in ethanol, under H{sub 2} and in the presence Of CS2, Precatalyst solutions containing Ru [as Ru{sub 3} (CO){sub 12} or RuCl{sub 3}] and Mo [as the H{sub 3}PMO{sub 12}0{sub 40} heteropolyanion (HPA)] decompose to form bimetallic, sulfided particles. Particle diameters run from 0.1 to 5 {mu}m depending on the rate of stirring. Catalyst particles with sizes ranging from 0.1--1 {mu}m can be prepared reproducibly. BET measured surface areas for these size particles ranged from 2 to 20 m2/g. These sulfided particles were found to catalyze, at temperatures of 200--250{degrees}C and hydrogen pressures of 200--1000 psig H{sub 2}, the N-ethylation of THQ to form NEt-THQ; rather than the formation of propylcyclohexane or propylbenzene, reaction products expected for HDN of THQ. Monometallic heterogeneous catalysts prepared from the individual precatalyst complexes, under identical conditions, show minimal activity for N-ethylation by comparison with the bimetallic catalyst. In the absence of H{sub 2}, the reaction proceeds such that THQ is converted to Q, N-EtTHQ, N-C{sub 6}H{sub 9}-THQ, and N-C{sub 6}H{sub 13}-THQ. The latter products appear to arise via acetaldehyde, formed as an intermediate by dehydrogenation of ethanol. Acetaldehyde either condenses with THQ to form N-Et-THQ, or self condenses (aldol condensation) prior to reaction with THQ thereby giving higher homolog alkylation products.

  6. Sulfided heterogeneous, bimetallic RuMo catalysts derived from mixtures of Ru sub 3 (CO) sub 12 (or RuCl sub 3 ) and a molybdenum heteropolyanion. The reactions of ethanol with tetrahydroquinoline

    Energy Technology Data Exchange (ETDEWEB)

    Koo, Sang-Man; Ryan, D.; Laine, R.M.

    1992-01-01

    Efforts have been made to develop Ru/Mo bimetallic catalyst systems for hydrodenitrogenation (HDN) of tetrahydroquinoline (THQ)- In the course of these studies, it was discovered that in ethanol, under H{sub 2} and in the presence Of CS2, Precatalyst solutions containing Ru (as Ru{sub 3} (CO){sub 12} or RuCl{sub 3}) and Mo (as the H{sub 3}PMO{sub 12}0{sub 40} heteropolyanion (HPA)) decompose to form bimetallic, sulfided particles. Particle diameters run from 0.1 to 5 {mu}m depending on the rate of stirring. Catalyst particles with sizes ranging from 0.1--1 {mu}m can be prepared reproducibly. BET measured surface areas for these size particles ranged from 2 to 20 m2/g. These sulfided particles were found to catalyze, at temperatures of 200--250{degrees}C and hydrogen pressures of 200--1000 psig H{sub 2}, the N-ethylation of THQ to form NEt-THQ; rather than the formation of propylcyclohexane or propylbenzene, reaction products expected for HDN of THQ. Monometallic heterogeneous catalysts prepared from the individual precatalyst complexes, under identical conditions, show minimal activity for N-ethylation by comparison with the bimetallic catalyst. In the absence of H{sub 2}, the reaction proceeds such that THQ is converted to Q, N-EtTHQ, N-C{sub 6}H{sub 9}-THQ, and N-C{sub 6}H{sub 13}-THQ. The latter products appear to arise via acetaldehyde, formed as an intermediate by dehydrogenation of ethanol. Acetaldehyde either condenses with THQ to form N-Et-THQ, or self condenses (aldol condensation) prior to reaction with THQ thereby giving higher homolog alkylation products.

  7. Chirality specific and spatially uniform synthesis of single-walled carbon nanotubes from a sputtered Co-W bimetallic catalyst

    Science.gov (United States)

    An, Hua; Kumamoto, Akihito; Takezaki, Hiroki; Ohyama, Shinnosuke; Qian, Yang; Inoue, Taiki; Ikuhara, Yuichi; Chiashi, Shohei; Xiang, Rong; Maruyama, Shigeo

    2016-07-01

    Synthesis of single-walled carbon nanotubes (SWNTs) with well-defined atomic arrangements has been widely recognized in the past few decades as the biggest challenge in the SWNT community, and has become a bottleneck for the application of SWNTs in nano-electronics. Here, we report a selective synthesis of (12, 6) SWNTs with an enrichment of 50%-70% by chemical vapor deposition (CVD) using sputtered Co-W as a catalyst. This is achieved under much milder reduction and growth conditions than those in the previous report using transition-metal molecule clusters as catalyst precursors (Nature, 2014, 510, 522). Meanwhile, in-plane transmission electron microscopy unambiguously identified an intermediate structure of Co6W6C, which is strongly associated with selective growth. However, most of the W atoms disappear after a 5 min CVD growth, which implies that anchoring W may be important in this puzzling Co-W system.Synthesis of single-walled carbon nanotubes (SWNTs) with well-defined atomic arrangements has been widely recognized in the past few decades as the biggest challenge in the SWNT community, and has become a bottleneck for the application of SWNTs in nano-electronics. Here, we report a selective synthesis of (12, 6) SWNTs with an enrichment of 50%-70% by chemical vapor deposition (CVD) using sputtered Co-W as a catalyst. This is achieved under much milder reduction and growth conditions than those in the previous report using transition-metal molecule clusters as catalyst precursors (Nature, 2014, 510, 522). Meanwhile, in-plane transmission electron microscopy unambiguously identified an intermediate structure of Co6W6C, which is strongly associated with selective growth. However, most of the W atoms disappear after a 5 min CVD growth, which implies that anchoring W may be important in this puzzling Co-W system. Electronic supplementary information (ESI) available: Raman spectroscopy (G-band) of SWNTs grown from Co and Co-W catalyst; Kataura plot for chirality

  8. [NiFe] dithiolene diphosphine complex for hydrogen gas activation: a Theoretic Insight

    CERN Document Server

    GuYan, Jing

    2015-01-01

    A diphosphino-nickel-iron dithiolene complex, [Ni(bdt)(dppf)] (bdt = 1,2-benzenedithiolate, dppf = 1,1-bis(diphenylphosphino)ferrocene), has been recently found to be reasonably active on proton reduction to dihydrogen (J. Am. Chem. Soc. 2015, 137, 1109). Interestingly, this exceptional complex was found to be also reactive towards dihydrogen activation as indicated by the electrochemical investigation. However, a pure nickel dithiolene diphosphine theoretical mode, excluding the contributions from iron moiety, was applied to attribute the experimental catalytic observation. We have re-visited the theoretical approach in details for this [NiFe] catalyst and compared it with the non-active nickel dithiolene diphosphine complexes. We found that both nickel and iron moieties in this newly developed complex were imperative for the observed catalytic per-formance, particularly towards the activation of dihydrogen.

  9. Magneto-thermoelectric effects in NiFe thin films

    Energy Technology Data Exchange (ETDEWEB)

    Schmid, Maximilian

    2015-11-01

    In this thesis magneto-thermoelectric effects are investigated in a systematic way to separate the transverse spin Seebeck effect from other parasitic effects like the anomalous Nernst effect. In contrast to the first studies found in the literature, in NiFe thin films a contribution of the transverse spin Seebeck effect can be excluded. This surprising outcome was crosschecked in a variety of different sample layouts and collaborations with other universities to ensure the validity of these results. In general, this thesis solves a long time discussion about the existence of the transverse spin Seebeck effect in NiFe films and supports the importance of control measurements for the scientific community. Even if such ''negative'' results may not be the award winning ones, new discoveries should be treated with constructive criticism and be checked carefully by the scientific community.

  10. Chirality specific and spatially uniform synthesis of single-walled carbon nanotubes from a sputtered Co-W bimetallic catalyst.

    Science.gov (United States)

    An, Hua; Kumamoto, Akihito; Takezaki, Hiroki; Ohyama, Shinnosuke; Qian, Yang; Inoue, Taiki; Ikuhara, Yuichi; Chiashi, Shohei; Xiang, Rong; Maruyama, Shigeo

    2016-08-14

    Synthesis of single-walled carbon nanotubes (SWNTs) with well-defined atomic arrangements has been widely recognized in the past few decades as the biggest challenge in the SWNT community, and has become a bottleneck for the application of SWNTs in nano-electronics. Here, we report a selective synthesis of (12, 6) SWNTs with an enrichment of 50%-70% by chemical vapor deposition (CVD) using sputtered Co-W as a catalyst. This is achieved under much milder reduction and growth conditions than those in the previous report using transition-metal molecule clusters as catalyst precursors (Nature, 2014, 510, 522). Meanwhile, in-plane transmission electron microscopy unambiguously identified an intermediate structure of Co6W6C, which is strongly associated with selective growth. However, most of the W atoms disappear after a 5 min CVD growth, which implies that anchoring W may be important in this puzzling Co-W system. PMID:27412697

  11. Development of a PtSn bimetallic catalyst for direct fuel cells using bio-butanol fuel

    OpenAIRE

    Puthiyapura, V.K.; Brett, D. J. L.; Russell, A E; Lin, W.F.; Hardacre, C.

    2015-01-01

    Pt and PtSn catalysts were studied for n-butanol electro-oxidation at various temperatures. PtSn showed a higher activity towards butanol electro-oxidation compared to Pt in acidic media. The onset potential for n-butanol oxidation on PtSn is similar to 520 mV lower than that found on Pt, and significantly lower activation energy was found for PtSn compared with that for Pt.

  12. Development of a PtSn bimetallic catalyst for direct fuel cells using bio-butanol fuel.

    Science.gov (United States)

    Puthiyapura, V K; Brett, D J L; Russell, A E; Lin, W F; Hardacre, C

    2015-09-01

    Pt and PtSn catalysts were studied for n-butanol electro-oxidation at various temperatures. PtSn showed a higher activity towards butanol electro-oxidation compared to Pt in acidic media. The onset potential for n-butanol oxidation on PtSn is ∼520 mV lower than that found on Pt, and significantly lower activation energy was found for PtSn compared with that for Pt. PMID:26214283

  13. Science Letters: Structure relationship of nitrochlorobenzene catalytic degradation process in water over palladium-iron bimetallic catalyst

    Institute of Scientific and Technical Information of China (English)

    NIU Shao-feng; ZHOU Hong-yi; AO Xu-ping; XU Xin-hua; LOU Zhang-hua

    2006-01-01

    Two isomers of nitrochlorobenzene (o-, and p-NCB) were treated by a Pd/Fe catalyst in aqueous solutions through catalytic amination and dechlorination. Nitrochlorobenzenes are rapidly converted to form chloroanilines (CAN) first through an amination process, and then rapidly dechlorinated to become aniline (AN) and Cl-, without the involvement of any other intermediate reaction products. The amination and dechlorination reaction are believed to take place predominantly on the surface site of the Pd/Fe catalysts. The dechlorination rate of the reductive degradation of the two isomers of nitrochlorobenzene (o-, and p-NCB) in the presence of Pd/Fe as a catalyst was measured experimentally. In all cases, the reaction rate constants were found to increase with the decrease in the Gibbs free energy (correlation with the activation energy) of NCBs formation; the activation energy of each dechlorination reaction was measured to be 95.83 and 77.05 kJ/mol, respectively for o- and p-NCB. The results demonstrated that p-NCBs were reduced more easily than o-NCBs.

  14. TOPICAL REVIEW: Nanostructured catalysts in fuel cells

    Science.gov (United States)

    Zhong, Chuan-Jian; Luo, Jin; Fang, Bin; Wanjala, Bridgid N.; Njoki, Peter N.; Loukrakpam, Rameshwori; Yin, Jun

    2010-02-01

    support materials. The fact that some of the trimetallic nanoparticle catalysts (e.g. PtVFe or PtNiFe) exhibit electrocatalytic activities in fuel cell reactions which are four-five times higher than in pure Pt catalysts constitutes the basis for further exploration of a variety of multimetallic combinations. The fundamental insights into the control of nanoscale alloy, composition, and core-shell structures have important implications in identifying nanostructured fuel cell catalysts with an optimized balance of catalytic activity and stability.

  15. Catalyst for Ammonia Oxidation

    DEFF Research Database (Denmark)

    2015-01-01

    The present invention relates to a bimetallic catalyst for ammonia oxidation, a method for producing a bimetallic catalyst for ammonia oxidation and a method for tuning the catalytic activity of a transition metal. By depositing an overlayer of less catalytic active metal onto a more catalytic...

  16. Interface-assisted magnetoresistance behavior for ultrathin NiFe films

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Shao-Long; Chen, Xi; Yang, Kang [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Han, Gang [Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083 (China); Teng, Jiao; Li, Xu-Jing; Yang, Guang; Liu, Qian-Qian; Liu, Yi-Wei [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Ding, Lei [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Yu, Guang-Hua, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-11-01

    Interface-assisted magnetoresistance (MR) behavior has been studied in Ta/MgO/NiFe/MgO/Ta multilayers by inserting a Mg metal layer between the NiFe layer and the top MgO layer. It is shown that MR ratio is about 31% larger than that in the films without Mg insertion. X-ray photoelectron spectroscopy and high resolution transmission electron microscope analyses show that the enhanced MR is primarily ascribed to effective control of chemical states at the NiFe/MgO interface and crystallization of the top MgO layer. - Highlights: • We studied magnetic and electric transport properties of ultrathin NiFe films. • Interface chemical states have strong influence on MR in NiFe films. • Crystallization of the top MgO layer has influence on MR in NiFe films.

  17. Synergism between polyurethane and polydopamine in the synthesis of Ni-Fe alloy monoliths.

    Science.gov (United States)

    Naresh Kumar, Thangavel; Sivabalan, Santhana; Chandrasekaran, Naveen; Phani, Kanala Lakshminarasimha

    2015-02-01

    Herein, we report the first synthesis of a light-weight macroporous 3-D alloy monolith of Ni-Fe/C using synergism between polydopamine (pDA) and polyurethane (pU); in situ formed polyurethane (pU) enables efficient mixing of pDA (carbon source) and Ni-FeOx resulting in Ni-Fe alloy monoliths at a temperature as low as ∼600 °C. The monolithic Ni-Fe/C exhibits enhanced oxygen evolution activity. PMID:25531680

  18. Clarifying roughness and atomic diffusion contributions to the interface broadening in exchange-biased NiFe/FeMn/NiFe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Nascimento, V.P., E-mail: valberpn@yahoo.com.br [Departamento de Física, Universidade Federal do Espírito Santo, 29075-910 Vitória (Brazil); Merino, I.L.C.; Passamani, E.C. [Departamento de Física, Universidade Federal do Espírito Santo, 29075-910 Vitória (Brazil); Alayo, W. [Departamento de Física, Universidade de Pelotas, 96010-610 Pelotas (Brazil); Tafur, M. [Instituto de Ciências Exatas, Universidade Federal de Itajubá, 37500-903 Itajubá (Brazil); Pelegrini, F. [Instituto de Física, Universidade Federal de Goiás, 74001-970 Goiânia (Brazil); Magalhães-Paniago, R. [Universidade Federal de Minas Gerais, Belo Horizonte (Brazil); Alvarenga, A.D. [Instituto Nacional de Metrologia, 25250-020 Xerém (Brazil); Saitovitch, E.B. [Coordenação de Física Experimental e Baixas Energias, Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro (Brazil)

    2013-09-02

    NiFe(30 nm)/FeMn(13 nm)/NiFe(10 nm) heterostructures prepared by magnetron sputtering at different argon working pressures (0.27, 0.67 and 1.33 Pa) were systematically investigated by using specular and off-specular diffuse X-ray scattering experiments, combined with ferromagnetic resonance technique, in order to distinguish the contribution from roughness and atomic diffusion to the total structural disorder at NiFe/FeMn interfaces. It was shown that an increase in the working gas pressure from 0.27 to 1.33 Pa causes an enhancement of the atomic diffusion at the NiFe/FeMn interfaces, an effect more pronounced at the top FeMn/NiFe interface. In particular, this atomic diffusion provokes a formation of non-uniform magnetic dead-layers at the NiFe/FeMn interfaces (NiFeMn regions with paramagnetic or weak antiferromagnetic properties); that are responsible for the substantial reduction of the exchange bias field in the NiFe/FeMn system. Thus, this work generically helps to understand the discrepancies found in the literature regarding the influence of the interface broadening on the exchange bias properties (e.g., exchange bias field) of the NiFe/FeMn system. - Highlights: • Roughness and atomic diffusion contributions to the interface broadening • Clarification of the exchange bias field dependence on the interface disorder • Ferromagnetic, paramagnetic and antiferromagnetic phases at the magnetic interface • Magnetic dead layers formed by increasing the argon work pressure • Atomic diffusion in heterostructures prepared at higher argon pressure.

  19. Magnetic properties of closely packed NiFe nanodots

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Norbert; McCord, Jeffrey; Moench, Ingolf; Schaefer, Rudolf; Schmidt, Oliver G.; Schultz, Ludwig [Leibniz Institut fuer Festkoerper- und Werkstoffforschung IFW Dresden, Postfach 270116 (Germany); Mattheis, Roland [Institut fuer Photonische Technologien IPHT Jena, Postfach 100239 (Germany)

    2010-07-01

    Permalloy nanodots have been fabricated by means of nanosphere lithography, where a monolayer of nanospheres self assembles to a hexagonal array on top of the ferromagnetic film. To etch closely packed structures of NiFe dots with a small tilt at the dot's edge more robust Silica nanospheres in comparison to Polystyrene nanospheres are used. Therefore it is possible to decrease the dipolar interaction and favor vortex nucleation, which is necessary to achieve highly dense magnetic vortex structures. Magneto-optic hysteresis measurements and micromagnetic simulations of hexagonal dot arrays with tilted edges confirm that vortex nucleation takes place, which is mainly attributed to the shape of the dots.

  20. Magnetoresistance of electrodeposited NiFeCu alloys

    Energy Technology Data Exchange (ETDEWEB)

    Esmaili, S., E-mail: esmaili@shirazu.ac.ir [Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of); Bahrololoom, M.E. [Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of); Peter, L. [Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, Budapest (Hungary)

    2012-01-01

    NiFeCu alloy films were electrodeposited from baths containing nickel sulfate and/or nickel sulfamate. All samples were pulse plated in the potentiostatic mode. The room temperature magnetoresistances of the films were measured showing anisotropic magnetoresistances up to 1.5%. The anisotropic magnetoresistances increased with the addition of sulfamic acid to the sulfate bath. Samples deposited from the bath with high sulfamate concentration showed a giant magnetoresistance behavior. To characterize the films, scanning electron microscopy and X-ray diffraction were used.

  1. Corrosion properties of electroplated CoNiFe films

    Energy Technology Data Exchange (ETDEWEB)

    Saito, M.; Yamada, K.; Ohashi, K.; Yasue, Y.; Sogawa, Y.; Osaka, T.

    1999-08-01

    Electroplated CoNiFe films with a saturation flux density as high as 2.1 T are potentially useful in high-density magnetic recording heads. The authors found that films electroplated at a high current density (15 mA/cm{sup 2}) from a bath without saccharin have a sufficient anodic pitting-corrosion potential ({minus}65 mV). The authors also found that the pitting-corrosion potential of films electroplated under a low current density (5 mA/cm{sup 2}) from saccharin-free baths have anodic pitting-corrosion potentials of less than {minus}300 mV. However, the corrosion resistance improved after annealing at temperatures above 100 C. The crystal-grain boundaries in the as-plated film that electroplated under a low current density from saccharin-free baths are not clear (i.e., that the phase is amorphous). But the crystal grain boundaries in the annealed film are clear. Films electroplated from baths containing saccharin also have anodic pitting-corrosion potentials of less than {minus}300 mV. Their corrosion resistance did not improve when they were annealed at 250 C. The deterioration of the corrosion resistance is attributed to the defects that increase the face-centered cubic (111) lattice constant. One of the most important characteristics of a highly corrosion-resistant CoNiFe film is fine crystal structure with very few defects.

  2. Phase equilibria in the Ni-Fe-Ga alloy system

    International Nuclear Information System (INIS)

    The phase equilibria, A2/B2 and B2/L21 (or D03) order-disorder transitions and martensitic transformation on the Ni-Fe side of the Ni-Fe-Ga system were examined by electron probe microanalysis (EPMA) and differential scanning calorimetric (DSC) measurement. The equilibrium compositions of interrelations mainly among the α (A2), β (B2), β' (L21 or D03), γ (A1) and γ' (L12) phases were determined using diffusion triples which were fabricated by two-step diffusion coupling. It was confirmed that a bcc single-phase region composed of α, β and β' at 850-1000 deg. C exists in a wide composition range and that the critical temperature of the B2/L21 order-disorder transformation in the Fe3Ga-Ni3Ga pseudo-binary section gradually increases with increasing Ni content. The existing composition region of the martensite phase at room temperature was also determined by the diffusion triple method

  3. One-step preparation of optically transparent Ni-Fe oxide film electrocatalyst for oxygen evolution reaction

    International Nuclear Information System (INIS)

    Graphical abstract: The optically transparent Ni-Fe oxide films are deposited on FTO substrates by one-step reactive magnetron co-sputtering. The optimal electrocatalytic activity for oxygen evolution reaction is achieved at an atomic ratio of Fe/Ni = 3:7, which is a very promising cocatalyst for photoelectrochemical water splitting owing to its optical transparency and high electrochemical activity. Display Omitted -- Abstract: Optically transparent cocatalyst film materials is very desirable for improved photoelectrochemical (PEC) oxygen evolution reaction (OER) over light harvesting photoelectrodes which require the exciting light to irradiate through the cocatalyst side, i.e., front-side illumination. In view of the reaction overpotential at electrode/electrolyte interface, the OER electrocatalysts have been extensively used as cocatalysts for PEC water oxidation on photoanode. In this work, the feasibility of a one-step fabrication of the transparent thin film catalyst for efficient electrochemical OER is investigated. The Ni-Fe bimetal oxide films, ∼ 200 nm in thickness, are used for study. Using a reactive magnetron co-sputtering technique, transparent (> 50% in wavelength range 500-2000 nm) Ni-Fe oxide films with high electrocatalytic activities were successfully prepared at room temperature. Upon optimization, the as-prepared bimetal oxide film with atomic ratio of Fe/Ni = 3:7 demonstrates the lowest overpotential for the OER in aqueous KOH solution, as low as 329 mV at current density of 2 mA cm−2, which is 135 and 108 mV lower than that of as-sputtered FeOx and NiOx thin films, respectively. It appears that this fabrication strategy is very promising to deposit optically transparent cocatalyst films on photoabsorbers for efficient PEC water splitting

  4. NiFe{sub 2}O{sub 4}/graphene nanocomposites with tunable magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Heidari, Elham Kamali [School of Metallurgy and Materials Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay (Hong Kong); Ataie, Abolghasem, E-mail: aataie@ut.ac.ir [School of Metallurgy and Materials Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Sohi, Mahmoud Heydarzadeh [School of Metallurgy and Materials Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Kim, Jang-Kyo [Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay (Hong Kong)

    2015-04-01

    Novel NiFe{sub 2}O{sub 4}/graphene nanocomposites were synthesized via facile, one-pot solvothermal route, and the effects of processing conditions and composition on their magnetic properties have been studied. The nanocomposites consisted of monolayer graphene sheets decorated with uniformly dispersed NiFe{sub 2}O{sub 4} nanoparticles of 6 nm in diameter. Increases in solvothermal temperature and time gave rise to improved crystallinity of NiFe{sub 2}O{sub 4} nanoparticles and thus enhanced magnetic properties, while a high NiFe{sub 2}O{sub 4} content resulted in a similar ameliorating effect on saturation magnetization, demonstrating tailored functional properties. A magnetic interaction between NiFe{sub 2}O{sub 4}/graphene was observed. - Highlights: • NiFe{sub 2}O{sub 4}/graphene nanocomposites were synthesized via solvothermal route. • 6 nm NiFe{sub 2}O{sub 4} nanoparticles uniformly dispersed on monolayer graphene sheets. • Magnetic properties were tailored by changing the processing parameters. • A magnetic interaction between NiFe{sub 2}O{sub 4}/grahene was observed.

  5. NiFe2O4/graphene nanocomposites with tunable magnetic properties

    Science.gov (United States)

    Heidari, Elham Kamali; Ataie, Abolghasem; Sohi, Mahmoud Heydarzadeh; Kim, Jang-Kyo

    2015-04-01

    Novel NiFe2O4/graphene nanocomposites were synthesized via facile, one-pot solvothermal route, and the effects of processing conditions and composition on their magnetic properties have been studied. The nanocomposites consisted of monolayer graphene sheets decorated with uniformly dispersed NiFe2O4 nanoparticles of 6 nm in diameter. Increases in solvothermal temperature and time gave rise to improved crystallinity of NiFe2O4 nanoparticles and thus enhanced magnetic properties, while a high NiFe2O4 content resulted in a similar ameliorating effect on saturation magnetization, demonstrating tailored functional properties. A magnetic interaction between NiFe2O4/grahene was observed.

  6. Magnetic structure and anisotropy of [Co/Pd ] 5/NiFe multilayers

    Science.gov (United States)

    Tryputen, Larysa; Guo, Feng; Liu, Frank; Nguyen, T. N. Anh; Mohseni, Majid S.; Chung, Sunjae; Fang, Yeyu; Ã kerman, Johan; McMichael, R. D.; Ross, Caroline A.

    2015-01-01

    The magnetization behavior, magnetic anisotropy, and domain configurations of Co/Pd multilayers with perpendicular magnetic anisotropy capped with permalloy is investigated using magnetometry, magnetic force microscopy, and ferromagnetic resonance. The thickness of the Ni80Fe20 layer in [Co/Pd ] 5/NiFe (t ) was varied from t =0 to 80 nm in order to study the interplay between the anisotropy and magnetization directions of Co/Pd and NiFe. By varying the thickness of the NiFe layer, the net anisotropy changes sign, but domains with plane-normal magnetization are present even for the thickest NiFe. Ferromagnetic resonance measurements show a decrease in damping with increasing NiFe thickness. The results demonstrate how the magnetic behavior of mixed-anisotropy thin films can be controlled.

  7. CuO role in {gamma}-Fe{sub 2}O{sub 3}-supported Pt-Cu bimetallic nanoparticles synthesized by radiation-induced reduction as catalysts for preferential CO oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Moriya, Toshiharu, E-mail: t-moriya@mit.eng.osaka-u.ac.jp; Kugai, Junichiro; Seino, Satoshi; Ohkubo, Yuji; Nakagawa, Takashi [Osaka University, Graduate School of Engineering (Japan); Nitani, Hiroaki [High Energy Accelerator Research Organization (KEK), Institute of Materials Structure Science (Japan); Yamamoto, Takao A. [Osaka University, Graduate School of Engineering (Japan)

    2013-02-15

    Modification of supported Pt catalyst by transition metal is effective for improving catalytic performance in fuel processing and electrochemical processes. In order to identify the role of CuO in Pt-Cu bimetallic nanoparticle catalyst in CO preferential oxidation in H{sub 2}-rich gas, three {gamma}-Fe{sub 2}O{sub 3}-supported Pt-Cu catalyst samples consisting of Pt-Cu alloy with different CuO content were synthesized by a radiolytic process. By managing the concentrations of the copper source and oxygen dissolved in the precursor solution, the CuO content was successfully varied by an order of magnitude without changing the structure and composition of the Pt-Cu alloy. In the catalytic tests, CuO-promoted CO oxidation significantly at around 100 Degree-Sign C. The catalyst with the highest CuO content showed the highest CO and O{sub 2} conversions. It was considered that the CuO phase promotes oxygen supply to CO chemisorbed on the Pt-Cu alloy surface. The alloy-CuO contact was suggested to be critical for the promoting effect.

  8. CuO role in γ-Fe2O3-supported Pt–Cu bimetallic nanoparticles synthesized by radiation-induced reduction as catalysts for preferential CO oxidation

    International Nuclear Information System (INIS)

    Modification of supported Pt catalyst by transition metal is effective for improving catalytic performance in fuel processing and electrochemical processes. In order to identify the role of CuO in Pt–Cu bimetallic nanoparticle catalyst in CO preferential oxidation in H2-rich gas, three γ-Fe2O3-supported Pt–Cu catalyst samples consisting of Pt–Cu alloy with different CuO content were synthesized by a radiolytic process. By managing the concentrations of the copper source and oxygen dissolved in the precursor solution, the CuO content was successfully varied by an order of magnitude without changing the structure and composition of the Pt–Cu alloy. In the catalytic tests, CuO-promoted CO oxidation significantly at around 100 °C. The catalyst with the highest CuO content showed the highest CO and O2 conversions. It was considered that the CuO phase promotes oxygen supply to CO chemisorbed on the Pt–Cu alloy surface. The alloy-CuO contact was suggested to be critical for the promoting effect.

  9. The difference a Se makes? Oxygen-tolerant hydrogen production by the NiFeSe -hydrogenase from Desulfomicrobium baculatum

    International Nuclear Information System (INIS)

    Protein film voltammetry studies of the [NiFeSe]-hydrogenase from Desulfomicrobium baculatum show it to be a highly efficient H2 cycling catalyst. In the presence of 100% H2, the ratio of H2 production to H2 oxidation activity is higher than for any conventional [NiFe]-hydrogenases (lacking a seleno-cysteine ligand) that have been investigated to date. Although traces of O2 (≤≤ 1%) rapidly and completely remove H2 oxidation activity, the enzyme sustains partial activity for H2 production even in the presence of 1% O2 in the atmosphere. That H2 production should be partly allowed, whereas H2 oxidation is not, is explained because the inactive product of O2 attack is reductively reactivated very rapidly, but this requires a potential that is almost as negative as the thermodynamic potential for the 2H+/H2 Couple. The study provides further encouragement and clues regarding the feasibility of microbial/enzymatic H2 production free from restrictions of anaerobicity. (authors)

  10. Interplay between out-of-plane anisotropic L11-type CoPt and in-plane anisotropic NiFe layers in CoPt/NiFe exchange springs

    International Nuclear Information System (INIS)

    Films of L11-type CoPt/NiFe exchange springs were grown with different NiFe (Permalloy) layer thickness (tNiFe = 0–10 nm). X-ray diffraction analysis reveals that the characteristic peak position of NiFe(111) is not affected by the CoPt-layer—confirming the absence of any inter-diffusion between the CoPt and NiFe layers. Magnetic studies indicate that the magnetization orientation of NiFe layer can be tuned through varying tNiFe and the perpendicular magnetic anisotropy of L11-type CoPt/NiFe films cannot sustain for tNiFe larger than 3.0 nm due to the existence of exchange interaction at the interface of L11-CoPt and NiFe layers. Magnetic force microscopy analysis on the as-grown samples shows the changes in morphology from maze-like domains with good contrast to hazy domains when tNiFe ≥ 3.0 nm. The three-dimensional micro-magnetic simulation results demonstrate that the magnetization orientation in NiFe layer is not uniform, which continuously increases from the interface to the top of NiFe layer. Furthermore, the tilt angle of the topmost NiFe layers can be changed over a very wide range from a small number to about 75° by varying tNiFe from 1 to 10 nm. It is worth noting that there is an abrupt change in the magnetization direction at the interface, for all the tNiFe investigated. The results of present study demonstrate that the tunable tilted exchange springs can be realized with L11-type CoPt/NiFe bilayers for future applications in three-axis magnetic sensors or advanced spintronic devices demanding inclined magnetic anisotropy.

  11. Size-controlled synthesis of NiFe2O4 nanospheres via a PEG assisted hydrothermal route and their catalytic properties in oxidation of alcohols by periodic acid

    Science.gov (United States)

    Paul, Bappi; Purkayastha, Debraj Dhar; Dhar, Siddhartha Sankar

    2016-05-01

    A novel and facile approach for synthesis of spinel nickel ferrites (NiFe2O4) nanoparticles (NPs) employing homogeneous chemical precipitation followed by hydrothermal heating is reported. The synthesis involves use of tributylamine (TBA) as a hydroxylating agent in synthesis of nickel ferrites. Polyethylene glycol (PEG) 4000 was used as surfactant. As-synthesized NiFe2O4 NPs were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption isotherm (BET) and vibrating sample magnetometry (VSM). The XRD pattern revealed formation of cubic face-centered NiFe2O4 and TEM image showed spherical particles of sizes 2-10 nm. These NiFe2O4 NPs were used as magnetically recoverable catalyst in oxidation of cyclic alcohols to their corresponding aldehydes by periodic acid. This eco-friendly procedure affords products in very high yield and selectivity. The reusability of the catalyst is proved to be noteworthy as the material exhibits no significant changes in its catalytic activity even after five cycles of reuse.

  12. NiFe epitaxial films with hcp and fcc structures prepared on bcc-Cr underlayers

    Energy Technology Data Exchange (ETDEWEB)

    Higuchi, Jumpei, E-mail: higuchi@futamoto.elect.chuo-u.ac.jp [Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan); Ohtake, Mitsuru; Sato, Yoichi [Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan); Kirino, Fumiyoshi [Graduate School of Fine Arts, Tokyo National University of Fine Arts and Music, 12-8 Ueno-koen, Taito-ku, Tokyo 110-8714 (Japan); Futamoto, Masaaki [Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan)

    2011-09-30

    NiFe epitaxial films are prepared on Cr(211){sub bcc} and Cr(100){sub bcc} underlayers grown hetero-epitaxially on MgO single-crystal substrates by ultra-high vacuum rf magnetron sputtering. The film growth behavior and the crystallographic properties are studied by reflection high energy electron diffraction and pole figure X-ray diffraction. Metastable hcp-NiFe(11-bar 00) and hcp-NiFe(112-bar 0) crystals respectively nucleate on Cr(211){sub bcc} and Cr(100){sub bcc} underlayers, where the hcp-NiFe crystals are stabilized through hetero-epitaxial growth. The hcp-NiFe(11-bar 00) crystal is a single-crystal with the c-axis parallel to the substrate surface, whereas the hcp-NiFe(112-bar 0) crystal is a bi-crystal with the respective c-axes lying in plane and perpendicular each other. With increasing the film thickness, the hcp structure in the NiFe films starts to transform into more stable fcc structure by atomic displacement parallel to the hcp(0001) close packed plane. The resulting films consist of hcp and fcc crystals.

  13. NiFe epitaxial films with hcp and fcc structures prepared on bcc-Cr underlayers

    International Nuclear Information System (INIS)

    NiFe epitaxial films are prepared on Cr(211)bcc and Cr(100)bcc underlayers grown hetero-epitaxially on MgO single-crystal substrates by ultra-high vacuum rf magnetron sputtering. The film growth behavior and the crystallographic properties are studied by reflection high energy electron diffraction and pole figure X-ray diffraction. Metastable hcp-NiFe(11-bar 00) and hcp-NiFe(112-bar 0) crystals respectively nucleate on Cr(211)bcc and Cr(100)bcc underlayers, where the hcp-NiFe crystals are stabilized through hetero-epitaxial growth. The hcp-NiFe(11-bar 00) crystal is a single-crystal with the c-axis parallel to the substrate surface, whereas the hcp-NiFe(112-bar 0) crystal is a bi-crystal with the respective c-axes lying in plane and perpendicular each other. With increasing the film thickness, the hcp structure in the NiFe films starts to transform into more stable fcc structure by atomic displacement parallel to the hcp(0001) close packed plane. The resulting films consist of hcp and fcc crystals.

  14. Effect of sintering atmosphere on composition and properties of NiFe2O4 ceramic

    Institute of Scientific and Technical Information of China (English)

    田忠良; 张腾; 刘恺; 赖延清; 李劼

    2015-01-01

    NiFe2O4 ceramics were prepared in different sintering atmospheres. The phase compositions, microstructures and mechanical properties were studied. The results show that the stoichiometric compound NiFe2O4 cannot be obtained in vacuum or atmospheres with oxygen contents of 2×10−5, 2×10−4 and 2×10−3, respectively. All the samples sintered in above-mentioned atmospheres contain phases of NiFe2O4 and NiO. With increasing oxygen content, NiFe2O4 content in the ceramic increases, while NiO content appears a contrary trend. In vacuum, NiFe2O4 ceramic has average grain size of 3.94μm, and bending strength of 85.12 MPa. The changes of the phase composition and mechanical properties of NiFe2O4 based cermets are mainly caused by the alteration of their properties of NiFe2O4 ceramic.

  15. Effects of ultrasonic field in pulse electrodeposition of NiFe film on Cu substrate

    International Nuclear Information System (INIS)

    NiFe film was pulse electrodeposited on conductive Cu substrate under galvanostatic mode in the presence of an ultrasonic field. The NiFe film electrodeposited was subjected to structural and surface analyses by X-ray diffraction, energy dispersive X-ray spectroscopy, surface profiling and scanning electron microscopy, respectively. The results show that the ultrasonic field has significantly improved the surface roughness, reduced the spherical grain size in the range from 490-575 nm to 90-150 nm, and increased the Ni content from 76.08% to 79.74% in the NiFe film electrodeposited.

  16. Effects of different Pt intercalation locations on the transport properties of spin-polarized electrons in NiFe films

    International Nuclear Information System (INIS)

    Platinum (Pt), which exhibits strong spin–orbit coupling interactions, was inserted into different interface locations in Ta/NiFe/Ta films. The different Pt intercalation locations significantly affected the magnetoresistance (MR) and microstructure of the NiFe films. When Pt was 1.6 nm thick, the difference in the MRs of the NiFe films reached the maximum, and the MR (2.65%) of the Ta/Pt/NiFe/Ta film was higher than that (2.36%) of the Ta/NiFe/Pt/Ta film. Therefore, Pt intercalation in different interfaces significantly affects the subsequently deposited NiFe layer (for the Ta/Pt/NiFe/Ta films) and Ta layer (for the Ta/NiFe/Pt/Ta films) and thus results in a large difference in MRs. - Highlights: • Pt was intercalated into different interfaces of a simple Ta/NiFe/Ta structure, forming new Ta/Pt/NiFe/Ta and Ta/NiFe/Pt/Ta structures. • Different Pt intercalation locations significantly affected the transport properties of spin-polarized electrons. • Pt intercalation introduced to the different interfaces could significantly affect the microstructure of subsequently deposited layers, leading to a large difference in magnetoresistance

  17. Effects of different Pt intercalation locations on the transport properties of spin-polarized electrons in NiFe films

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Lei, E-mail: lding@hainu.edu.cn [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Dai, Chao [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Yu, Guanghua; Zhao, Chongjun; Teng, Jiao [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Xiang, Daoping [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China)

    2014-03-15

    Platinum (Pt), which exhibits strong spin–orbit coupling interactions, was inserted into different interface locations in Ta/NiFe/Ta films. The different Pt intercalation locations significantly affected the magnetoresistance (MR) and microstructure of the NiFe films. When Pt was 1.6 nm thick, the difference in the MRs of the NiFe films reached the maximum, and the MR (2.65%) of the Ta/Pt/NiFe/Ta film was higher than that (2.36%) of the Ta/NiFe/Pt/Ta film. Therefore, Pt intercalation in different interfaces significantly affects the subsequently deposited NiFe layer (for the Ta/Pt/NiFe/Ta films) and Ta layer (for the Ta/NiFe/Pt/Ta films) and thus results in a large difference in MRs. - Highlights: • Pt was intercalated into different interfaces of a simple Ta/NiFe/Ta structure, forming new Ta/Pt/NiFe/Ta and Ta/NiFe/Pt/Ta structures. • Different Pt intercalation locations significantly affected the transport properties of spin-polarized electrons. • Pt intercalation introduced to the different interfaces could significantly affect the microstructure of subsequently deposited layers, leading to a large difference in magnetoresistance.

  18. Ni-Based Catalysts for Low Temperature Methane Steam Reforming: Recent Results on Ni-Au and Comparison with Other Bi-Metallic Systems

    OpenAIRE

    Anna M. Venezia; Fabrizio Puleo; Valeria La Parola; Giuseppe Pantaleo; Hongjing Wu; Leonarda F. Liotta

    2013-01-01

    Steam reforming of light hydrocarbons provides a promising method for hydrogen production. Ni-based catalysts are so far the best and the most commonly used catalysts for steam reforming because of their acceptably high activity and significantly lower cost in comparison with alternative precious metal-based catalysts. However, nickel catalysts are susceptible to deactivation from the deposition of carbon, even when operating at steam-to-carbon ratios predicted to be thermodynamically outside...

  19. Formation mechanism of amorphous Ni-Fe-P alloys by electrodeposition

    Institute of Scientific and Technical Information of China (English)

    GAO Cheng-hui

    2005-01-01

    The formation mechanism of the amorphous Ni-Fe-P coating was studied by analysis of the forming thermodynamics, dynamics, and crystallography of the amorphous alloy. The results show that, in the initial stage of deposition a thin "crystal epitaxial growth" layer first forms, and then transforms to amorphous gradually. The cross section in Ni-Fe-P coatings by electrolytic etching exhibits a banded structure of alternate dark and light bands. It is proposed that the banded structure is caused by a change in the P content with thickness,which is due to alternated depletion and enrichment of [OH-] in the diffusion layer resulting from the generation and evolution of hydrogen gas. The amorphous Ni-Fe-P coating will be formed in proper composition, high nucleation rate and strongly hindered growth of the crystal nucleus. Amorphous Ni-Fe-P alloys form as islands, and grow up by layer.

  20. Electrodeposition behavior of nanocrystalline CoNiFe soft magnetic thin film

    Institute of Scientific and Technical Information of China (English)

    LI Jing-feng; ZHANG Zhao; YIN Jun-ying; YU Geng-hua; CAI Chao; ZHANG Jian-qing

    2006-01-01

    The electroplating behavior of nanocrystalline CoNiFe soft magnetic thin film with high saturation magnetic flux density (Bs>2.1 T) and low coercivity (Hc) was investigated using cyclic voltammetry and chronoamperometry methods in conjunction with the scanning electron microscopy (SEM/EDX). The results show that, under the experimental conditions, the co-deposition of CoNiFe film behaves anomalously due to the atomic radii of iron series elements following the order of rFe>rCo > rNi. In the case of lower electroplating current density, the co-deposition of CoNiFe film follows a 3-D progressive nucleation/growth mechanism,while in the case of higher electroplating current density, which follows a 3-D instantaneous nucleation/growth mechanism.Meanwhile, the change of nucleation mechanism of CoNiFe film with electroplating current density was interpreted theoretically in the light of quantum chemistry.

  1. Impact Factors on Removal of Perchloroethylene with Nano-Ni/Fe Methodology

    Institute of Scientific and Technical Information of China (English)

    LIU Fei; HUANG Yuanying; CUI Weihua

    2006-01-01

    Chlorinated hydrocarbons are widely detected in groundwater, but conventional removal methodologies are not time-and-cost effective. With the development of iron reducing technology in recent years, research on nano-iron and nano-bimetal has become a hot spot. The paper presents the results of impact factors on perchloroethylene (PCE) removal by nano-Ni/Fe method. The data show that the reaction rate of unexposed nano-Ni/Fe is 4 times higher than exposed one; and temperature is one of the important controlling factors. Reaction rate constant KsA increases by 2-3 times with every 10℃ increment of temperature. Within a specific range, higher Ni/Fe ratio favors dechlorination process. When the Ni/Fe is 8%, the dechlorination process reaches the highest rate. Dissoved oxygen in the solution does not favor the degradation of chlorinated hydrocarbons.

  2. Nanocrystal and surface alloy properties of bimetallic Gold-Platinum nanoparticles

    Directory of Open Access Journals (Sweden)

    Mott Derrick

    2006-01-01

    Full Text Available AbstractWe report on the correlation between the nanocrystal and surface alloy properties with the bimetallic composition of gold-platinum(AuPt nanoparticles. The fundamental understanding of whether the AuPt nanocrystal core is alloyed or phase-segregated and how the surface binding properties are correlated with the nanoscale bimetallic properties is important not only for the exploitation of catalytic activity of the nanoscale bimetallic catalysts, but also to the general exploration of the surface or interfacial reactivities of bimetallic or multimetallic nanoparticles. The AuPt nanoparticles are shown to exhibit not only single-phase alloy character in the nanocrystal, but also bimetallic alloy property on the surface. The nanocrystal and surface alloy properties are directly correlated with the bimetallic composition. The FTIR probing of CO adsorption on the bimetallic nanoparticles supported on silica reveals that the surface binding sites are dependent on the bimetallic composition. The analysis of this dependence further led to the conclusion that the relative Au-atop and Pt-atop sites for the linear CO adsorption on the nanoparticle surface are not only correlated with the bimetallic composition, but also with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals, which is the first demonstration of the nanoscale core-surface property correlation for the bimetallic nanoparticles over a wide range of bimetallic composition.

  3. Mechanism and Microstructure of Electroless Ni-Fe-P Plating on CNTs

    Institute of Scientific and Technical Information of China (English)

    XUE Ru-jun; WU Yu-cheng

    2007-01-01

    Electroless Ni-Fe-P alloy plating on the surface of CNTs was carried out with a bath using citrate salt and lactic acid as complex agents. We proposed a chemical reaction mechanism. The morphology, structure and chemical composition of the Ni-Fe-P/CNTs were studied with the aid of a scanning electronic microscope (SEM), X-ray diffraction (XRD) and an energy-dispersive X-ray spectral analysis (EDS). The results show that through a correct pretreatment and electroless plating, Ni-Fe-P/CNTs composite particles can be obtained. The optimum electroless plating parameters of 35-42 ℃ and pH of 8.5-9.7 were achieved. The as-plated Ni-Fe-P alloy is amorphous. After a heat treat-ment at 500 ℃ for 90 min in H2, the coating is transformed into crystalloid Ni3P, Fe2NiP and (Fe,Ni)3P. The Ni-Fe-P al-loy coating on the surface of CNTs is smooth and unique. The amount of Ni on the surface (mass fraction) of the Ni-Fe-P/CNTs composite particles is 29.13%, that of Fe 3.19% and that of P 2.28%.

  4. Original design of an oxygen-tolerant [NiFe] hydrogenase: Major effect of a valine-to-cysteine mutation near the active site

    OpenAIRE

    De Lacey, Antonio L.

    2011-01-01

    Hydrogenases are efficient biological catalysts of H2 oxidation and production. Most of them are inhibited by O2 and a prerequisite for their use in biotechnological applications under air is to improve their oxygen-tolerance. We have previously shown that exchanging the residue at position 74 in the large subunit of the oxygen sensitive [NiFe] hydrogenase from Desulfovibrio fructosovorans could impact the reaction of the enzyme with O2 (S. Dementin et al, J. Am. Chem. Soc. 131 10156-10164 20...

  5. [Co/Pd]4–Co–Pd–NiFe spring magnets with highly tunable and uniform magnetization tilt angles

    International Nuclear Information System (INIS)

    By varying the Pd thickness (tPd) from 0 to 8 nm in [Co/Pd]4/Co/Pd(tPd)/NiFe exchange springs, we demonstrate (i) continuous tailoring of the exchange coupling between a [Co/Pd]4/Co layer with perpendicular anisotropy, and a NiFe layer with an in-plane easy axis, (ii) tuning of the NiFe out-of-plane magnetization angle from 20○ to 80○, and (iii) an up to two-fold increase in the NiFe damping. The partial decoupling also results in a highly uniform NiFe magnetization. These properties make [Co/Pd]4/Co/Pd(tPd)/NiFe spring magnets ideal candidates for use as tilted polarizers, by combining stable and well-defined spin directions of its carriers with a high degree of angular freedom. - Highlights: ► Continuous tailoring of the exchange coupling between a [Co/Pd]4/Co layer and a NiFe layer. ►Tuning of the NiFe out-of-plane magnetization angle from 20° to 80°. ►A highly uniform NiFe magnetization. ►An up to two-fold increase in the NiFe damping.

  6. Interplay between out-of-plane anisotropic L1{sub 1}-type CoPt and in-plane anisotropic NiFe layers in CoPt/NiFe exchange springs

    Energy Technology Data Exchange (ETDEWEB)

    Saravanan, P. [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Defence Metallurgical Research Laboratory, Hyderabad 500058 (India); Hsu, Jen-Hwa, E-mail: jhhsu@phys.ntu.edu.tw; Tsai, C. L. [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Tsai, C. Y.; Lin, Y. H. [Graduate Institute of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan (China); Kuo, C. Y.; Wu, J.-C. [Department of Physics, National Chang Hua University of Education, Chang Hua 50000, Taiwan (China); Lee, C.-M. [Graduate School of Materials Science, National Yunlin University of Science and Technology, Douliou 64002, Taiwan (China)

    2014-06-28

    Films of L1{sub 1}-type CoPt/NiFe exchange springs were grown with different NiFe (Permalloy) layer thickness (t{sub NiFe} = 0–10 nm). X-ray diffraction analysis reveals that the characteristic peak position of NiFe(111) is not affected by the CoPt-layer—confirming the absence of any inter-diffusion between the CoPt and NiFe layers. Magnetic studies indicate that the magnetization orientation of NiFe layer can be tuned through varying t{sub NiFe} and the perpendicular magnetic anisotropy of L1{sub 1}-type CoPt/NiFe films cannot sustain for t{sub NiFe} larger than 3.0 nm due to the existence of exchange interaction at the interface of L1{sub 1}-CoPt and NiFe layers. Magnetic force microscopy analysis on the as-grown samples shows the changes in morphology from maze-like domains with good contrast to hazy domains when t{sub NiFe} ≥ 3.0 nm. The three-dimensional micro-magnetic simulation results demonstrate that the magnetization orientation in NiFe layer is not uniform, which continuously increases from the interface to the top of NiFe layer. Furthermore, the tilt angle of the topmost NiFe layers can be changed over a very wide range from a small number to about 75° by varying t{sub NiFe} from 1 to 10 nm. It is worth noting that there is an abrupt change in the magnetization direction at the interface, for all the t{sub NiFe} investigated. The results of present study demonstrate that the tunable tilted exchange springs can be realized with L1{sub 1}-type CoPt/NiFe bilayers for future applications in three-axis magnetic sensors or advanced spintronic devices demanding inclined magnetic anisotropy.

  7. Production of biohydrogen by recombinant expression of [NiFe]-hydrogenase 1 in Escherichia coli

    Directory of Open Access Journals (Sweden)

    Kim Jaoon YH

    2010-07-01

    Full Text Available Abstract Background Hydrogenases catalyze reversible reaction between hydrogen (H2 and proton. Inactivation of hydrogenase by exposure to oxygen is a critical limitation in biohydrogen production since strict anaerobic conditions are required. While [FeFe]-hydrogenases are irreversibly inactivated by oxygen, it was known that [NiFe]-hydrogenases are generally more tolerant to oxygen. The physiological function of [NiFe]-hydrogenase 1 is still ambiguous. We herein investigated the H2 production potential of [NiFe]-hydrogenase 1 of Escherichia coli in vivo and in vitro. The hyaA and hyaB genes corresponding to the small and large subunits of [NiFe]-hydrogenase 1 core enzyme, respectively, were expressed in BL21, an E. coli strain without H2 producing ability. Results Recombinant BL21 expressing [NiFe]-hydrogenase 1 actively produced H2 (12.5 mL H2/(h·L in 400 mL glucose minimal medium under micro-aerobic condition, whereas the wild type BL21 did not produce H2 even when formate was added as substrate for formate hydrogenlyase (FHL pathway. The majority of recombinant protein was produced as an insoluble form, with translocation of a small fraction to the membrane. However, the membrane fraction displayed high activity (~65% of total cell fraction, based on unit protein mass. Supplement of nickel and iron to media showed these metals contribute essentially to the function of [NiFe]-hydrogenase 1 as components of catalytic site. In addition, purified E. coli [NiFe]-hydrogenase 1 using his6-tag displayed oxygen-tolerant activity of ~12 nmol H2/(min·mg protein under a normal aeration environment, compared to [FeFe]-hydrogenase, which remains inactive under this condition. Conclusions This is the first report on physiological function of E. coli [NiFe]-hydrogenase 1 for H2 production. We found that [NiFe]-hydrogenase 1 has H2 production ability even under the existence of oxygen. This oxygen-tolerant property is a significant advantage because it is

  8. Magnetic oxides EuO and NiFe2O4 for spintronics

    International Nuclear Information System (INIS)

    Magnetic oxides provide the rare combination of electrical insulation and ferromagnetism and - prepared as thin films - are well-suited as tunnel barriers in efficient spinfilters. We optimize thin films of EuO and NiFe2O4 in crystal structure, magnetic and electronic properties. EuO thin films were prepared using an oxide MBE system. EuO single-crystalline thin films can be grown epitaxially on MgO and lattice-matched YSZ substrates, where on the latter a sustained layer-by-layer growth was achieved. A meticulous regulation of the oxygen supply renders EuO thin films possible (tEuO≥20 nm) with bulk-like magnetization msat=7μB and TC=69 K. The chemical states of EuO on silicon were studied in detail by HAXPES which clearly confirmed the high stoichiometric quality of EuO. The room temperature ferromagnetic spinel NiFe2O4 (NFO) was prepared by pulsed laser deposition (PLD). The chemical oxidation states and site occupancy (octahedral vs. tetrahedral) of the metal cations (Ni, Fe), investigated by Core-level XPS experiments, determine the magnetic behavior of NFO. In our NiFe2O4 samples exhibit msat=1.2μB. Magnetic oxides EuO and NiFe2O4 with high-quality magnetic, structural and chemical properties were prepared to be exerted as tunnel barriers in spinfilters.

  9. Microstructure of the Al-La-Ni-Fe system

    Energy Technology Data Exchange (ETDEWEB)

    Vasil’ev, A. L., E-mail: a.vasiliev56@gmail.com [National Research Centre “Kurchatov Institute” (Russian Federation); Ivanova, A. G. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Bakhteeva, N. D. [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation); Kolobylina, N. N. [National Research Centre “Kurchatov Institute” (Russian Federation); Orekhov, A. S. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Presnyakov, M. Yu. [National Research Centre “Kurchatov Institute” (Russian Federation); Todorova, E. V. [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation)

    2015-01-15

    The microstructure of alloys based on the Al-La-Ni-Fe system, which are characterized by a unique ability to form metal glasses and nanoscale composites in a wide range of compositions, has been investigated. Al{sub 85}Ni{sub 7}Fe{sub 4}La{sub 4} and Al{sub 85}Ni{sub 9}Fe{sub 2}La{sub 4} alloys have been analyzed by electron microscopy (including high-resolution scanning transmission electron microscopy), energy-dispersive X-ray microanalysis, electron diffraction (ED), and X-ray diffraction (XRD). It is found that, along with fcc Al and Al{sub 4}La (Al{sub 11}La{sub 3}) particles, these alloys contain a ternary phase Al{sub 3}Ni{sub 1−x}Fe{sub x} (sp. gr. Pnma) isostructural to the Al{sub 3}Ni phase and a quaternary phase Al{sub 8}Fe{sub 2−x}Ni{sub x}La isostructural to the Al{sub 8}Fe{sub 2}Eu phase (sp. gr. Pbam). The unit-cell parameters of the Al{sub 3}Ni{sub 1−x}Fe{sub x} and Al{sub 8}Fe{sub 2−x}Ni{sub x}La compounds, determined by ED and refined by XRD, are a = 0.664(1) nm, b = 0.734(1) nm, and c = 0.490(1) nm for Al{sub 3}Ni{sub 1−x}Fe{sub x} and a = 1.258(3) nm, b = 1.448(3) nm, and c = 0.405(8) nm for Al{sub 8}Fe{sub 2−x}Ni{sub x}La. In both cases Ni and Fe atoms are statistically arranged, and no ordering is found. Al{sub 8}Fe{sub 2−x}Ni{sub x}La particles contain inclusions in the form of Al{sub 3}Fe δ layers.

  10. Enhancement of exchange bias with crystal orientation in NiFe/CoO and CoO/NiFe bilayers grown on MgO(100) and MgO(111)

    International Nuclear Information System (INIS)

    We present the comparative study of the structural and magnetic properties of the NiFe/CoO and CoO/NiFe bilayers grown on both MgO(111) and MgO(100) substrates by using the ion beam sputtering technique. We observed that crystallographic orientation and crystal quality strongly affected the exchange bias properties of the bilayers. The NiFe layers showed fourfold magnetocrystalline anisotropy when we used MgO(100) substrate and uniaxial anisotropy when we used MgO(111) substrate. When the CoO layer is grown on MgO(111) and MgO(100) substrates as a first layer, instead of the NiFe, the increase of the crystalline quality and stoichiometric CoO phase has been achieved so that the exchange bias field increases by five and three times for NiFe/CoO/MgO(111) and NiFe/CoO/MgO(100) systems, respectively. The blocking temperature significantly increases for NiFe/CoO on MgO(111) and (100) substrates, indicating the increase of the stoichiometric stable Co1O1 phase in the exchange-biased system. The magnitude of the exchange bias field is 800 Oe at 10 K for NiFe/CoO/MgO(111) and more than two times as compared to that of NiFe/CoO/MgO(100). This high exchange bias value observed for NiFe/CoO/MgO(111) was explained with the uncompensated spins in CoO(111) surface. We also carried out training effect measurements to observe the durability of the exchange bias for technological applications. - Highlights: • This paper analyses magnetization dynamic of exchange biased of NiFe/CoO thin films. • Exchange bias is enhanced by crystal orientation and quallity. • High exchange bias value observed due to the uncompensated spins in CoO(111) surface

  11. Effect of the kind of fuel in the synthesis of the catalyzer NiFe{sub 2}O{sub 4} to displacement reaction of water gas (WGRS); Efeito do tipo de combustivel na sintese do catalisador NiFe{sub 2}O{sub 4} para reacao de deslocamento do gas agua (WGRS)

    Energy Technology Data Exchange (ETDEWEB)

    Santos, P.T.A.; Barros, B.S.; Costa, A.C.F.M.; Gama, L. [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Dept. de Engenharia de Materiais], e-mail: anacristina@dema.ufcg.edu.br; Jesus, A.A.; Andrade, H.M.C. [Universidade Federal da Bahia (UFBA), Salvador, BA (Brazil). Inst. de Quimica

    2006-07-01

    This work has as objective synthesizes and to characterize the NiFe{sub 2}O{sub 4} catalyst by combustion reaction using different fuels: urea and glycine seeking your application in the water gas shift reaction (WGSR), promoting the purification of the methane for the elimination of the carbon monoxide. The powders were prepared in agreement with the chemistry of the propellants using as recipient a vitreous silica crucible; the maximum temperature and the medium time of flame were verified. The powders were characterized by X-ray diffraction (DRX), Scanning electronic microscopy and catalytic tests. The results show that the catalysts presented inverse spinel structure as majority phase for the two types of fuels. However, it was observed that using the urea, there was the presence of a second phase of NiO and when the glycine was used, there was the presence of lines of Ni. The catalyst NiFe{sub 2}O{sub 4} using urea as fuel, presented better catalytic acting. (author)

  12. Effects of Rapid Recurrent Thermal Annealing on Giant Magnetoresistance NiFe/Ag Multilayers

    Institute of Scientific and Technical Information of China (English)

    文岐业; 张怀武; 蒋向东; 唐晓莉; 张万里

    2003-01-01

    NiFe/Ag multilayers were prepared by dc sputtering onto glass-ceramic substrates directly at room temperature.The samples were thermally processed by rapid recurrent thermal anneal (RRTA). We studied the effects of RRTA on giant magnetoresistance (GMR) NiFe/Ag multilayer by controlling the anneal temperature as well as the rapid anneal cycle. The samples after three RRTA cycles have a similar annealing temperature dependence of GMR responses to the ordinary annealed samples. With the increasing anneal cycle, the GMR response improved at first and then reached an unexpected high value of 9% before descent rapidly. Microstructure study shows that this effect is ascribed to the transformation of continuous NiFe layer into discontinuous one, and then into a granular like film in a step-by-step way.

  13. Electroless Plating of Ni-Fe-P Alloy and Corrosion Resistance of the Deposit

    Institute of Scientific and Technical Information of China (English)

    Senlin WANG

    2005-01-01

    Electroless Ni-Fe-P alloys in an alkaline bath were plated. Theeffects of deposition parameters on the plating rate and the coating composition were examined. The weight loss test and the anodic polarization measurement of the deposits in 3.5 wt pct NaCl solution (pH7.0) showed that the deposits with the mole ratio of NiSO4/FeSO4 being 0.07:0.03, pH8.0 and 7.5 possess better corrosion resistance than that of the other deposits and the Ni-Fe-P deposits did not form passive films in this environment. In 5.0 wt pct NaOH solution, the Ni-Fe-P deposits have better corrosion resistance and formed passive films.

  14. Strong magnetization damping induced by Ag nanostructures in Ag/NiFe/Ag trilayers

    Science.gov (United States)

    Ley Domínguez, D.; da Silva, G. L.; Rodríguez-Suárez, R. L.; Rezende, S. M.; Azevedo, A.

    2013-07-01

    Ferromagnetic resonance has been used to investigate the magnetization relaxation in trilayers of Ag(t)/NiFe(10 nm)/Ag(t), sputter deposited on Si(001) where the thickness of the Ag layer varied from 0 nm to 24 nm. In the first stages of formation, the Ag layers form islands that work as mold to imprint defects or inhomogeneities on the NiFe film surface. The magnetic inhomogeneities and defects imprinted on the surface of the NiFe film act as extrinsic sources of magnetization relaxation in addition to the intrinsic Gilbert damping mechanism. Weak inhomogeneities are associated to the two-magnon scattering source and the strong inhomogeneities are associated to the fluctuations of the local magnetization. By adding the three different sources of magnetization damping, we were able to explain the azimuthal dependence of the ferromagnetic resonance linewidth.

  15. Soft magnetic CoNiFe films electrodeposited under centrifugal forces

    International Nuclear Information System (INIS)

    Physical and magnetic properties of soft magnetic CoNiFe films electrodeposited under centrifugal forces were investigated. It was demonstrated that employing an external centrifugal force during the deposition process provides stronger magnetic properties of the soft magnet electrodeposited. Based on the approach proposed, preparation of soft magnetic CoNiFe film with Bs higher than 2.1 T and Hc lower than 1.1 Ωe is possible. For a conventional CoNiFe film with Bs of 1.96 T (electrodeposited under Earth's gravity), the saturation induction can be increased to 2.14 T by applying a 290g centrifugal force during the electrodeposition process, while the Hc approximately remained the same. It is thought that this enhancement provided by an applied centrifugal force is due to the increase of bcc/fcc ratio, where this increase is not associated with a significant crystallite growth in this case

  16. Tensile Properties and Deformation Characteristics of a Ni-Fe-Base Superalloy for Steam Boiler Applications

    Science.gov (United States)

    Zhong, Zhihong; Gu, Yuefeng; Yuan, Yong; Shi, Zhan

    2014-01-01

    Ni-Fe-base superalloys due to their good manufacturability and low cost are the proper candidates for boiler materials in advanced power plants. The major concerns with Ni-Fe-base superalloys are the insufficient mechanical properties at elevated temperatures. In this paper, tensile properties, deformation, and fracture characteristics of a Ni-Fe-base superalloy primarily strengthened by γ' precipitates have been investigated from room temperature to 1073 K (800 °C). The results showed a gradual decrease in the strength up to about 973 K (700 °C) followed by a rapid drop above this temperature and a ductility minimum at around 973 K (700 °C). The fracture surfaces were studied using scanning electron microscopy and the deformation mechanisms were determined by the observation of deformed microstructures using transmission electron microscopy. An attempt has been made to correlate the tensile properties and fracture characteristics at different temperatures with the observed deformation mechanisms.

  17. A study on electrodeposited NiFe1− alloy films

    Indian Academy of Sciences (India)

    M Bedir; Ö F Bakkaloğlu; İ H Karahan; M Öztaş

    2006-06-01

    NiFe1− (0.22 ≤ ≤ 0.62) alloy films were grown by electrodeposition technique. A shift in diffraction peaks of NiFe and Ni3Fe was detected with increasing Ni content. The highest positive magnetoresistance ratio was detected as 5% in Ni0.51Fe0.49. Positive and negative anisotropic magnetoresistance were observed in longitudinal and transverse geometries respectively. The highest anisotropic magnetoresistance ratio of 9.8% was also detected in Ni0.51Fe0.49. The angular variation of magnetoresistance was studied. Magnetisation loop curves show that NiFe alloy films have a linear decreasing anisotropy constant with increasing Ni deposit content and show a decreasing behavior of coercivity which indicates soft magnetic property with increasing Ni deposit content.

  18. Bimetallic Wiregauze Supported Pt-Ru Nanocatalysts for Hydrogen Mitigation.

    Science.gov (United States)

    Sanap, Kiran K; Varma, S; Waghmode, S B; Sharma, P; Manoj, N; Vatsa, R K; Bharadwaj, S R

    2015-05-01

    Passive autocatalytic recombiner (PAR) is one of the most suitable devices for mitigation of hydrogen, generated in nuclear power plant under accidental conditions. For this purpose we report development of stainless steel wire gauze supported Pt-Ru nanoparticles as catalysts. Simultaneous electroless deposition has been employed for the synthesis of the catalysts. Pt-Ru based bimetallic catalysts were characterized for their rate of coating kinetics, noble metal loading, phase purity by XRD and surface morphology by SEM, TEM and elemental analysis by SIMS. Developed catalysts were found to be active for efficient recombination of hydrogen and oxygen in air as well as in presence of various prospective poisons like CO2, CH4, CO and relative humidity. Pt-Ru based bimetallic catalyst with 0.9% loading was found to be active for CO poisoning up to 400 ppm of CO. PMID:26504972

  19. High-temperature Mossbauer spectroscopy of mechanically milled NiFe2O4

    DEFF Research Database (Denmark)

    Helgason, O.; Jiang, Jianzhong

    2002-01-01

    Oxide spinels, in particular those containing iron, often exhibit technically important electrical- and magnetic-properties. We report here on X-ray powder diffraction and Mossbauer studies of nanostructured NiFe2O4 particles prepared by high-energy ball milling from bulk NiFe2O4, which is an...... inverse spinel. The Mossbauer spectra were recorded in situ at different temperatures in the range of 300-850 K. The Mossbauer spectra of the milled samples show a broad distribution of magnetic hyperfine fields together with a paramagnetic state at room temperature. Initially, at 700 K the spectrum is...

  20. Hydride bridge in [NiFe]-hydrogenase observed by nuclear resonance vibrational spectroscopy

    OpenAIRE

    Ogata, Hideaki; Krämer, Tobias; Wang, Hongxin; Schilter, David; Pelmenschikov, Vladimir; van Gastel, Maurice; Neese, Frank; Rauchfuss, Thomas B.; Gee, Leland B.; Scott, Aubrey D.; Yoda, Yoshitaka; Tanaka, Yoshihito; Lubitz, Wolfgang; Cramer, Stephen P.

    2015-01-01

    The metabolism of many anaerobes relies on [NiFe]-hydrogenases, whose characterization when bound to substrates has proven non-trivial. Presented here is direct evidence for a hydride bridge in the active site of the 57Fe-labeled fully reduced Ni-R form of Desulfovibrio vulgaris Miyazaki F (DvMF) [NiFe]-hydrogenase. A unique ‘wagging’ mode involving H− motion perpendicular to the Ni(μ-H)57Fe plane was studied using 57Fe-specific nuclear resonance vibrational spectroscopy (NRVS) and density fu...

  1. Catalytic Combustion of Voc in Air Stream Over Bimetallic Chromium-Copper Supported On Sicl4-Modified H-Zsm-5 Catalyst

    Directory of Open Access Journals (Sweden)

    A.Z. Abdullah

    2010-09-01

    Full Text Available The performance of chromium (Cr and copper (Cu on silicon tetrachloride modified H-ZSM-5 (SiCl4-Z catalyst in VOC combustion is reported. H-ZSM-5, modified with SiCl4 at 500?C for 3 h was impregnated with 1.0 wt. % of Cr and 0.5 wt. % of Cu. Performance studies were carried out at GHSV of 3,800 to 32,000 h-1 with 2,000 to 35,000 ppm of VOC. Changes in the activity of Cr-Cu/ SiCl4-Z were ascribed to extra framework deposits, surface acidity and pore characteristics. Cr-Cu/SiCl4-Z catalyst was more stable to coking, humidity and HCl than Cr-Cu/Z. In the combustion of chlorinated VOC, the chlorination of metal species deactivated the catalyst by rendering lower redox ability.

  2. High-sensitivity planar Hall sensor based on simple gaint magneto resistance NiFe/Cu/NiFe structure for biochip application

    International Nuclear Information System (INIS)

    The planar Hall effect (PHE) sensor based on a simple giant magneto resistance (GMR) trilayer structure NiFe/Cu/NiFe has been designed and fabricated successfully using conventional clean room fabrication methods. The PHE sensor is integrated by 24 sensor patterns with dimensions of 50 × 50 μm. Influence of individual layer thickness to sensitivity of sensor has been investigated. Sensitivity and planar Hall voltage increases with the decrease of Cu-layer thickness. The results are discussed in terms of the reinforcement of the antiferromagnetic interaction between NiFe layers and shunting current through the layer Cu. The optimum configuration has been found in the structure with the Cu-layer of 1 nm. In this case a single planar Hall effect sensor exhibits a high sensitivity of about 8 μV Oe−1 and a maximal of the signal change as large as ▵V ∼ 55 μV. These values are comparable to those of the typical PHE sensor based on complex GMR spin-valve structure. With a high sensitivity and simple structure, this sensor is very promising for practical detection of magnetic beads and identifying multiple biological agents in the environment. (paper)

  3. Preparation, characterization, and antibacterial activity of NiFe2O4/PAMA/Ag-TiO2 nanocomposite

    Science.gov (United States)

    Allafchian, Alireza; Jalali, Seyed Amir Hossein; Bahramian, Hamid; Ahmadvand, Hossein

    2016-04-01

    We have described a facile fabrication of silver deposited on the TiO2, Poly Acrylonitrile Co Maleic Anhydride (PAMA) polymer and nickel ferrite composite (NiFe2O4/PAMA/Ag-TiO2) through a three-step procedure. A pre-synthesized NiFe2O4 was first coated with PAMA polymer and then Ag-TiO2 was deposited on the surface of PAMA polymer shell. After the characterization of this three-component composite by various techniques, such as FTIR, XRD, FESEM, BET, TEM and VSM, it was impregnated in standard antibiotic discs. The antibacterial activity of NiFe2O4/PAMA/Ag-TiO2 nanocomposite was investigated against some gram positive and gram negative bacteria by employing disc diffusion assay and then compared with that of naked NiFe2O4, NiFe2O4/Ag, AgNPs and NiFe2O4/PAMA. The results demonstrated that the AgNPs, when embedded in TiO2 and combined with NiFe2O4/PAMA, became an excellent antibacterial agent. The NiFe2O4/PAMA/Ag-TiO2 nanocomposite could be readily separated from water solution after the disinfection process by applying an external magnetic field.

  4. Structure-Property Relationship in Metal Carbides and Bimetallic Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Jingguan [University of Delaware

    2014-03-04

    The primary objective of our DOE/BES sponsored research is to use carbide and bimetallic catalysts as model systems to demonstrate the feasibility of tuning the catalytic activity, selectivity and stability. Our efforts involve three parallel approaches, with the aim at studying single crystal model surfaces and bridging the “materials gap” and “pressure gap” between fundamental surface science studies and real world catalysis. The utilization of the three parallel approaches has led to the discovery of many intriguing catalytic properties of carbide and bimetallic surfaces and catalysts. During the past funding period we have utilized these combined research approaches to explore the possibility of predicting and verifying bimetallic and carbide combinations with enhanced catalytic activity, selectivity and stability.

  5. Thermal annealing and magnetic anisotropy of NiFe thin films on n{sup +}-Si for spintronic device applications

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Q.H. [School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Department of Physics, Semiconductor Photonics Research Center, Xiamen University, Xiamen 361005, People’s Republic of China (China); Gansu Key Laboratory of Sensor and Sensor Technology, Institute of Sensor Technology, Gansu Academy of Science, Lanzhou 730000 (China); Huang, R. [Department of Physics, Semiconductor Photonics Research Center, Xiamen University, Xiamen 361005, People’s Republic of China (China); Wang, L.S. [Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005 (China); Wu, Z.G., E-mail: zgwu@lzu.edu.cn [School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Li, C., E-mail: lich@xmu.edu.cn [Department of Physics, Semiconductor Photonics Research Center, Xiamen University, Xiamen 361005, People’s Republic of China (China); Luo, Q. [Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005 (China); Zuo, S.Y. [School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China); Li, J. [Department of Physics, Semiconductor Photonics Research Center, Xiamen University, Xiamen 361005, People’s Republic of China (China); Peng, D.L. [Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005 (China); Han, G.L. [Gansu Key Laboratory of Sensor and Sensor Technology, Institute of Sensor Technology, Gansu Academy of Science, Lanzhou 730000 (China); Yan, P.X. [School of Physical Science and Technology, Lanzhou University, Lanzhou 730000 (China)

    2015-11-15

    To ensure that the magnetic metal electrodes can meet the requirements of the spin injection, NiFe films prepared both on HfO{sub 2} dielectric layer and n{sup +}-Si directly by sputtering deposition, and treated by conventional furnace annealing and/or high vacuum magnetic field annealing were investigated. It was found that thermal annealing at 250 °C improved the crystalline quality and reduced surface roughness of the NiFe films, thus enhancing its saturation magnetization intensity. The 100 nm thick NiFe films had too large coercive force and saturation magnetization intensity in vertical direction to meet the requirements of Hanle curve detection. While, 30 nm thick NiFe films showed paramagnetic hysteresis loops in vertical direction, and the magnetization intensity of the sample after annealing at 250 °C for 30 min was less than 2% to the parallel when the external magnetic field was given between ±10 Oe. This was preferred to Hanle curve detection. The thin HfO{sub 2} dielectric layer between metal and Si partially suppressed the diffusion of Ni in NiFe into Si substrate and formation of NiSi, greatly enhancing the saturation magnetization intensity of the Al/NiFe/HfO{sub 2}/Si sample by thermal annealing. Those results suggest that Al/NiFe/HfO{sub 2}/Si structure, from the point view of magnetic electrodes, would be suitable for spin injection and detection applications. - Highlights: • The saturation magnetization intensity of NiFe thin-film was enhanced by thermal annealing. • A paramagnetic hysteresis loop of NiFe thin-film was observed in vertical direction. • The thin HfO{sub 2} dielectric layer between NiFe and Si partially suppressed the diffusion of Ni into Si.

  6. Thermal annealing and magnetic anisotropy of NiFe thin films on n+-Si for spintronic device applications

    International Nuclear Information System (INIS)

    To ensure that the magnetic metal electrodes can meet the requirements of the spin injection, NiFe films prepared both on HfO2 dielectric layer and n+-Si directly by sputtering deposition, and treated by conventional furnace annealing and/or high vacuum magnetic field annealing were investigated. It was found that thermal annealing at 250 °C improved the crystalline quality and reduced surface roughness of the NiFe films, thus enhancing its saturation magnetization intensity. The 100 nm thick NiFe films had too large coercive force and saturation magnetization intensity in vertical direction to meet the requirements of Hanle curve detection. While, 30 nm thick NiFe films showed paramagnetic hysteresis loops in vertical direction, and the magnetization intensity of the sample after annealing at 250 °C for 30 min was less than 2% to the parallel when the external magnetic field was given between ±10 Oe. This was preferred to Hanle curve detection. The thin HfO2 dielectric layer between metal and Si partially suppressed the diffusion of Ni in NiFe into Si substrate and formation of NiSi, greatly enhancing the saturation magnetization intensity of the Al/NiFe/HfO2/Si sample by thermal annealing. Those results suggest that Al/NiFe/HfO2/Si structure, from the point view of magnetic electrodes, would be suitable for spin injection and detection applications. - Highlights: • The saturation magnetization intensity of NiFe thin-film was enhanced by thermal annealing. • A paramagnetic hysteresis loop of NiFe thin-film was observed in vertical direction. • The thin HfO2 dielectric layer between NiFe and Si partially suppressed the diffusion of Ni into Si

  7. Nanotube wall thickness dependent magnetization reversal properties of NiFe nanotubes

    Science.gov (United States)

    Sharif, R.; Shamaila, S.; Shaheen, F.; Naseem, S.; Chen, J. Y.; Khaleeq-ur-Rahman, M.; Hussain, K.; Han, X. F.

    2013-01-01

    Nanotube wall thickness dependent magnetization properties of NiFe nanotube arrays electrodeposited in polycarbonate membranes are investigated. A systematic variation of nanotube wall thickness (tw) has been investigated. The magnetization reversal properties are strongly influenced by the variation of tw keeping length and external radius constant.

  8. Facile synthesis of inverse spinel NiFe2O4 nanocrystals and their superparamagnetic properties

    Directory of Open Access Journals (Sweden)

    Jie Tan

    2012-01-01

    Full Text Available Spinel NiFe2O4 nanocrystals have been obtained by means of a novel composite-hydroxide-salt-mediated approach, which is based on a reaction between metallic salt and metallic oxide in the solution of composite-hydroxide-salt eutectic at ~225 ºC and normal atmosphere without any organic dispersant or capping agent. The obtained products are characterized by an X-ray diffraction (XRD, a transmission electron microscopy (TEM and an alternating gradient magnetometer (AGM. The formation process of NiFe2O4 nanosheet is proposed to begin with a ‘‘dissolution-recrystallization’’ which is followed by an ‘‘Ostwald ripening’’ mechanism. The NiFe2O4 nano-octahedrons can be obtained through adjusting the reaction water content in the hydroxide melts at constant temperature. At 300 K, magnetic hysteresis loops at an applied field of 15 kOe show zero coercivity, indicating the superparamagnetic behavior of the as-prepared NiFe2O4 nanocrystals.

  9. Structural and microwave properties of silica-coated NiFeMo flakes/polymer composites

    International Nuclear Information System (INIS)

    The microwave properties of sheets containing silica-coated NiFeMo flakes are investigated and discussed according to the sheet structure, the silica layer uniformity and thickness. Commercial NiFeMo flakes are coated using the Stoeber method and embedded in polymer using the doctor blade process. The silica layer thickness is estimated by transmission electron microscopy (TEM) and the coating quality is probed by scanning electron microscopy (SEM). The in-plane orientation of magnetic moments within the sheet is evidenced by 57Fe Mössbauer spectrometry. As a result, the permittivity of composites is strongly reduced when the NiFeMo flakes are completely coated, whereas the permeability level is weakly and progressively altered when the silica thickness increases. We show that the frequency range for microwave absorption can be tuned according to the silica thickness and the flake loading. Reflection losses of −13 dB are obtained in the 1–2 GHz range for a normal incident electromagnetic wave interacting with 3 mm sheets backed by a perfect conductor and loaded with silica (90 nm width)-coated NiFeMo flakes. (paper)

  10. Magnetic NiFe/Au barcode nanowires with self-powered motion

    Science.gov (United States)

    Jeon, In Tak; Yoon, Seung Jae; Kim, Bong Gun; Lee, Ji Sung; An, Boo Hyun; Ju, Jae-Seon; Wu, Jun Hua; Kim, Young Keun

    2012-04-01

    NiFe/Au barcode nanowires were synthesized by pulsed electrodeposition using anodic aluminum oxide nanotemplate, comprising magnetic, catalytic, and optical segments, respectively. The self-powered motion of the BNWs due to the catalytic reaction was observed in aqueous H2O2. The approach demonstrates how sophistication in barcode nanoarchitecture can be used to synthesize a wide range of hybrid materials.

  11. Influence of magnetostriction of NiFe electroplated film on the noise of fluxgate

    Czech Academy of Sciences Publication Activity Database

    Butta, M.; Janosek, M.; Ripka, P.; Kraus, Luděk; El Kammouni, R.

    2014-01-01

    Roč. 50, č. 11 (2014), s. 4006504. ISSN 0018-9464 R&D Projects: GA ČR GAP102/12/2177 Institutional support: RVO:68378271 Keywords : fluxgate * electroplating * magnetic sensors * magnetostriction * NiFe * noise * ring core Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2014

  12. Facile synthesis of inverse spinel NiFe2O4 nanocrystals and their superparamagnetic properties

    Directory of Open Access Journals (Sweden)

    Jie Tan

    2013-02-01

    Full Text Available Spinel NiFe2O4 nanocrystals have been obtained by means of a novel composite-hydroxide-salt-mediated approach, which is based on a reaction between metallic salt and metallic oxide in the solution of composite-hydroxide-salt eutectic at ~225 ºC and normal atmosphere without any organic dispersant or capping agent. The obtained products are characterized by an X-ray diffraction (XRD, a transmission electron microscopy (TEM and an alternating gradient magnetometer (AGM. The formation process of NiFe2O4 nanosheet is proposed to begin with a ‘‘dissolution-recrystallization’’ which is followed by an ‘‘Ostwald ripening’’ mechanism. The NiFe2O4 nano-octahedrons can be obtained through adjusting the reaction water content in the hydroxide melts at constant temperature. At 300 K, magnetic hysteresis loops at an applied field of 15 kOe show zero coercivity, indicating the superparamagnetic behavior of the as-prepared NiFe2O4 nanocrystals.

  13. Point Contact Andreev Reflection Measurement of the Spin Polarization of Ferromagnetic Alloy NiFeSb

    Institute of Scientific and Technical Information of China (English)

    李壮志; 陶宏杰; 闻海虎; 张铭; 柳祝红; 崔玉亭; 吴光恒

    2002-01-01

    We have studied the temperature-dependent and barrier-strength-dependent Andreev reflection tunnelling spectroscopy with point contacts consisting of the newly synthesized half-metallic alloy NiFeSb and a Nb tip. By fitting the data to the generalized Blonder-Tinkham-Klapwijk theory, a spin polarization P = 0.52 has been obtained.

  14. Promotion of the electrocatalytic activity of a bimetallic platinum-ruthenium catalyst by repetitive redox treatments for direct methanol fuel cell

    Science.gov (United States)

    Huang, Sheng-Yang; Yeh, Chuin-Tih

    Pt-Ru/C catalyst (12 wt%) was prepared by the incipient wetness impregnation method followed by a redox heat-treatment. Transmission electron microscopy (TEM) results revealed uniformly distributed metallic crystallites of Pt-Ru alloy nanoparticles (d PtRu = 2.1 ± 1.0 nm). The effect of redox treatments of the impregnated catalysts on methanol oxidation reaction (MOR) was examined by cyclic voltammetry (CV). The MOR activity of the PtRu/C was significantly improved after each oxidation step of the redox treatment cycles. The enhanced catalytic activity was found to be quite stable in chronoamperometry (CA) measurements. CV, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results strongly suggested that the improved catalytic activity was due to the formation of a stable c-RuO x (x = 2-3) domain during the oxidation treatments. A bifunctional based mechanism was proposed for the MOR on the oxidized PtRu/C catalysts. Formation of Ru-OH species on the surface of c-RuO x domains was suggested as stale sites for the oxidation of carbon monoxide adsorbed on the Pt catalytic sites.

  15. Dye-Sensitized Cu2 XSnS4 (X=Zn, Ni, Fe, Co, and Mn) Nanofibers for Efficient Photocatalytic Hydrogen Evolution.

    Science.gov (United States)

    Gonce, Mehmet Kerem; Aslan, Emre; Ozel, Faruk; Hatay Patir, Imren

    2016-03-21

    The photocatalytic hydrogen evolution activities of low-cost and noble-metal-free Cu2 XSnS4 (X=Zn, Ni, Fe, Co, and Mn) nanofiber catalysts have been investigated using triethanolamine as an electron donor and eosin Y as a photosensitizer under visible-light irradiation. The rates of hydrogen evolution by Cu2 XSnS4 (X=Zn, Ni, Fe, Co, and Mn) nanofibers have been compared with each other and with that of the noble metal Pt. The hydrogen evolution rates for the nanofibers change in the order Cu2 NiSnS4 >Cu2 FeSnS4 >Cu2 CoSnS4 >Cu2 ZnSnS4 >Cu2 MnSnS4 (2028, 1870, 1926, 1420, and 389 μmol g(-1)  h(-1) , respectively). The differences between the hydrogen evolution rates of the nanofibers could be attributed to their energy levels. Moreover, Cu2 NiSnS4 , Cu2 FeSnS4 , and Cu2 CoSnS4 nanofibers show higher and more stable photocatalytic hydrogen production rates than that of the noble metal Pt under long-term irradiation with visible light. PMID:26880355

  16. Role of the antiferromagnetic pinning layer on spin wave properties in IrMn/NiFe based spin-valves

    Energy Technology Data Exchange (ETDEWEB)

    Gubbiotti, G., E-mail: gubbiotti@fisica.unipg.it; Tacchi, S. [Istituto Officina dei Materiali del CNR (IOM-CNR), Unità di Perugia, I-06123 Perugia (Italy); Del Bianco, L. [Department of Physics and Astronomy, University of Bologna, I-40127 Bologna (Italy); Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Bonfiglioli, E.; Giovannini, L.; Spizzo, F.; Zivieri, R. [Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Tamisari, M. [Department of Physics and Earth Sciences and CNISM, University of Ferrara, I-44122 Ferrara (Italy); Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia (Italy)

    2015-05-07

    Brillouin light scattering (BLS) was exploited to study the spin wave properties of spin-valve (SV) type samples basically consisting of two 5 nm-thick NiFe layers (separated by a Cu spacer of 5 nm), differently biased through the interface exchange coupling with an antiferromagnetic IrMn layer. Three samples were investigated: a reference SV sample, without IrMn (reference); one sample with an IrMn underlayer (10 nm thick) coupled to the bottom NiFe film; one sample with IrMn underlayer and overlayer of different thickness (10 nm and 6 nm), coupled to the bottom and top NiFe film, respectively. The exchange coupling with the IrMn, causing the insurgence of the exchange bias effect, allowed the relative orientation of the NiFe magnetization vectors to be controlled by an external magnetic field, as assessed through hysteresis loop measurements by magneto-optic magnetometry. Thus, BLS spectra were acquired by sweeping the magnetic field so as to encompass both the parallel and antiparallel alignment of the NiFe layers. The BLS results, well reproduced by the presented theoretical model, clearly revealed the combined effects on the spin dynamic properties of the dipolar interaction between the two NiFe films and of the interface IrMn/NiFe exchange coupling.

  17. Synthesis of Supported NiPt Bimetallic Nanoparticles, Methods for Controlling the Surface Coverage of Ni Nanoparticles With Pt, Methods Of Making NiPt Multilayer Core-Shell Structures and Application of the Supported Catalysts for CO2 Reforming

    KAUST Repository

    Li, Lidong

    2015-06-25

    Embodiments of the present disclosure provide for supported Ni/Pt bimetallic nanoparticles, compositions including supported NiPt nanoparticles, methods of making supported NiPt nanoparticles, methods of using supported NiPt nanoparticles, and the like.

  18. Relation between anaerobic inactivation and oxygen tolerance in a large series of NiFe hydrogenase mutants.

    Science.gov (United States)

    Abou Hamdan, Abbas; Liebgott, Pierre-Pol; Fourmond, Vincent; Gutiérrez-Sanz, Oscar; De Lacey, Antonio L; Infossi, Pascale; Rousset, Marc; Dementin, Sébastien; Léger, Christophe

    2012-12-01

    Nickel-containing hydrogenases, the biological catalysts of oxidation and production, reversibly inactivate under anaerobic, oxidizing conditions. We aim at understanding the mechanism of (in)activation and what determines its kinetics, because there is a correlation between fast reductive reactivation and oxygen tolerance, a property of some hydrogenases that is very desirable from the point of view of biotechnology. Direct electrochemistry is potentially very useful for learning about the redox-dependent conversions between active and inactive forms of hydrogenase, but the voltammetric signals are complex and often misread. Here we describe simple analytical models that we used to characterize and compare 16 mutants, obtained by substituting the position-74 valine of the -sensitive NiFe hydrogenase from Desulfovibrio fructosovorans. We observed that this substitution can accelerate reactivation up to 1,000-fold, depending on the polarity of the position 74 amino acid side chain. In terms of kinetics of anaerobic (in)activation and oxygen tolerance, the valine-to-histidine mutation has the most spectacular effect: The V74H mutant compares favorably with the -tolerant hydrogenase from Aquifex aeolicus, which we use here as a benchmark. PMID:23169623

  19. Biosensors Incorporating Bimetallic Nanoparticles

    Directory of Open Access Journals (Sweden)

    John Rick

    2015-12-01

    Full Text Available This article presents a review of electrochemical bio-sensing for target analytes based on the use of electrocatalytic bimetallic nanoparticles (NPs, which can improve both the sensitivity and selectivity of biosensors. The review moves quickly from an introduction to the field of bio-sensing, to the importance of biosensors in today’s society, the nature of the electrochemical methods employed and the attendant problems encountered. The role of electrocatalysts is introduced with reference to the three generations of biosensors. The contributions made by previous workers using bimetallic constructs, grouped by target analyte, are then examined in detail; following which, the synthesis and characterization of the catalytic particles is examined prior to a summary of the current state of endeavor. Finally, some perspectives for the future of bimetallic NPs in biosensors are given.

  20. Isobaric Thermal Expansion and Isothermal Compression of Powdered NiFe Based Alloys Studied by In-Situ EDXRD

    OpenAIRE

    Olekšáková, D.; J. Füzer; Kollár, P.; Bednarčík, J.; Lathe, C.

    2014-01-01

    The aim of the present work was to study the isothermal compression and isobaric thermal expansion behaviour of ball-milled NiFe (81 wt.% of Ni) and NiFeMo (79 wt.% of Ni, 16 wt.% of Fe) alloy and follow its phase evolution when exposed to high pressure and temperature. In-situ pressure-temperature energy dispersive X-ray (EDXRD) diffraction experiments were performed at the MAX80 instrument (beamline F2.1). The compressibility of NiFe alloy at 400 °C was evaluated for pressure values of up t...

  1. Catalytic Combustion of Voc in Air Stream Over Bimetallic Chromium-Copper Supported On Sicl4-Modified H-Zsm-5 Catalyst

    OpenAIRE

    Abdullah, A.Z.; M.Z. Abu Bakar; Bhatia, S

    2010-01-01

    The performance of chromium (Cr) and copper (Cu) on silicon tetrachloride modified H-ZSM-5 (SiCl4-Z) catalyst in VOC combustion is reported. H-ZSM-5, modified with SiCl4 at 500?C for 3 h was impregnated with 1.0 wt. % of Cr and 0.5 wt. % of Cu. Performance studies were carried out at GHSV of 3,800 to 32,000 h-1 with 2,000 to 35,000 ppm of VOC. Changes in the activity of Cr-Cu/ SiCl4-Z were ascribed to extra framework deposits, surface acidity and pore characteristics. Cr-Cu/SiCl4-Z cat...

  2. Signature effects of spin clustering and distribution of spin couplings on magnetization behaviour in Ni-Fe-Mo and Ni-Fe-W alloys

    International Nuclear Information System (INIS)

    Spontaneous magnetization as a function of temperature is investigated for a number of disordered Ni-Fe-Mo and Ni-Fe-W alloys using superconducting quantum interference device magnetometry, with a focus on the low-T behaviour as well as the critical exponents associated with the magnetic phase transition. While the low-T magnetization is found to be well described by Bloch's T3/2 law, extraordinary enhancements of the spin-wave parameter B and the reduced coefficient B3/2 = BTC3/2 are observed with increasing Fe dilution as compared to conventional 3d ferromagnets, whereas the critical amplitudes are found to decrease systematically. Recent locally self-consistent calculations of finite-temperature spin dynamics in a generic diluted magnet provide an understanding in terms of two distinct energy scales associated with weakly coupled bulk spins in the ferromagnetic matrix and strongly coupled cluster spins. In view of the similar behaviour observed in diluted magnetic semiconductors and other ferromagnetic alloys, it is proposed that these distinctive features corresponding to the three important temperature regimes provide macroscopic indicators of signature effects of spin clustering on the magnetization behaviour in disordered ferromagnets.

  3. Synthesis and Characterization of NiFe2O4 Magnetic Nanoparticles by Combustion Method

    Institute of Scientific and Technical Information of China (English)

    M. Kooti; A. Naghdi Sedeh

    2013-01-01

    Magnetic nanoparticles of nickel ferrite (NiFe2O4) have been successfully synthesized by microwave-assisted combustion method using stable ferric and nickel salts as precursors and glycine as fuel.The as-synthesized samples were characterized by Fourier transform infrared spectroscopy (FT-IR),X-ray diffraction (XRD),transmission electron microscopy (TEM),vibrating sample magnetometer (VSM) and field emission scanning electron microscopy (FESEM).The effect of different dose of glycine on the structural parameters and magnetic properties of the prepared NiFe2O4 nanoparticles was also investigated.This study revealed that it was possible to produce larger size of nanoparticles with lower saturation magnetization by using higher dose of fuel.

  4. Room temperature spin valve effect in NiFe/WS2/Co junctions

    Science.gov (United States)

    Iqbal, Muhammad Zahir; Iqbal, Muhammad Waqas; Siddique, Salma; Khan, Muhammad Farooq; Ramay, Shahid Mahmood

    2016-02-01

    The two-dimensional (2D) layered electronic materials of transition metal dichalcogenides (TMDCs) have been recently proposed as an emerging canddiate for spintronic applications. Here, we report the exfoliated single layer WS2-intelayer based spin valve effect in NiFe/WS2/Co junction from room temperature to 4.2 K. The ratio of relative magnetoresistance in spin valve effect increases from 0.18% at room temperature to 0.47% at 4.2 K. We observed that the junction resistance decreases monotonically as temperature is lowered. These results revealed that semiconducting WS2 thin film works as a metallic conducting interlayer between NiFe and Co electrodes.

  5. Dependence of magnetization process in a Ni-Fe nanowire on the width of the nanowire

    Energy Technology Data Exchange (ETDEWEB)

    Endo, Y; Matsumura, Y; Nakatani, R; Yamamoto, M [Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)], E-mail: endo@mat.eng.osaka-u.ac.jp

    2008-03-15

    We investigated the dependence of the magnetization process in 30-nm-thick Ni-Fe nanowires on the width of the nanowire using the magnetic field sweeping (MFS) - magnetic force microscopy (MFM), which measures phase changes (stray field changes) using a MFM tip as a detector. The phase changes are dependent on the width of the nanowire; hysteresis loops of the phase and plateau areas of the phase are observed at local points for the widths between 100 - 600 nm, while local points, each, display the hysteresis loops of the phase and the valleys of the phase for the width of 800 nm. These results demonstrate that the dominant factor in the magnetization process of 30-nm-thick Ni-Fe nanowires changes from 'domain wall motion and domain wall pinning' to 'domain wall motion with increasing the width of the nanowires'.

  6. Effect of Magnetic Carrier NiFe2O4 Nanoparticles on Physicochemical and Catalytic Properties of Magnetically Separable Photocatalyst TiO2/NiFe2O4

    Institute of Scientific and Technical Information of China (English)

    XU Shi-hong; TAN Dong-dong; BI De-fu; SHI Peng-hui; LU Wei; SHANGGUAN Wen-feng; MA Chun-yan

    2013-01-01

    A series of magnetically separable photocatalyst TiO2/NiFe2O4(TN) with different mass ratios of NiFe2O4 to TiO2 was prepared by sol-gel method.The X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),ultraviolet-visible spectroscopy(UV-Vis),Brunauer-Emmett-Teller(BET) surface analysis and photoluminescence spectroscopy(PL) were used to characterize the photocatalyst TN.The XRD patterns of TN indicate that adulterating a smidgen of NiFe2O4 into TiO2(about 0.1%,mass ratio) can promote the phase transformation of TiO2,however,when the doped amount of NiFe2O4 surpasses 1%,the introduction of NiFe2O4 can inhibit the growth of TiO2 crystal grain and reduce the size of TiO2 crystal grain.The XPS results of TN indicate that some Fe3+ replace Ti4+ of the TiO2 lattice forming Fe—O—Ti bonds.The PL analysis of TN shows that the NiFe2O4 nanoparticles in photocatalyst TN play the role of the effective recombination centre of the photogenerated electrons and holes,leading to the decrease in photocatalytic activity.

  7. Manipulating NiFe/AlO{sub x} interfacial chemistry for the spin-polarized electrons transport

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Chong-Jun [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Sun, Li [Department of Mechanical Engineering and Texas Center for Superconductivity (TcSUH), University of Houston, Houston, Texas 77204 (United States); Ding, Lei [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Li, Jian-Wei; Zhang, Jing-Yan; Cao, Yi [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Guang-Hua, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)

    2013-10-15

    Through vacuum annealing, interfacial chemical composition of sputter-deposited AlO{sub x}/NiFe/AlO{sub x} can be controlled for electron transport manipulation. Chemical status change at the NiFe/AlO{sub x} interface was quantified by X-ray photoelectron spectroscopy and correlated to the structure and electron transport properties of the heterostructure. It is found that elemental Al existed in the insulting AlO{sub x} after annealing at intermediate temperature can improve the AlO{sub x}/NiFe interface and thus favor the electronic transport. Annealing at higher temperature will result in native AlO{sub x} formation and degrade transport properties due to the NiFe/AlO{sub x} interfaces deterioration caused by significant difference in thermal expansion coefficients of the two materials.

  8. Magnetic Properties of Ni-Fe Nanowire Arrays: Effect of Template Material and Deposition Conditions

    OpenAIRE

    Aravamudhan, Shyam; Singleton, John; Goddard, Paul A.; Bhansali, Shekhar

    2008-01-01

    The objective of this work is to study the magnetic properties of arrays of Ni-Fe nanowires electrodeposited in different template materials such as porous silicon, polycarbonate and alumina. Magnetic properties were studied as a function of template material, applied magnetic field (parallel and perpendicular) during deposition, wire length, as well as magnetic field orientation during measurement. The results show that application of magnetic field during deposition strongly influences the ...

  9. Modified Precipitation Route for Preparation of Nanocrystalline NiFe204

    Czech Academy of Sciences Publication Activity Database

    Ćosović, V.; Ćosović, A.; Živković, D.; Žák, Tomáš; David, Bohumil; Talijan, N.

    Belgrade : Serbian Ceramic Society, 2013 - (Mitić, V.; Obradović, N.; Mančić, L.). s. 30-30 ISBN 978-86-915627-1-7. [Advanced Ceramics And Application. 30.09.2013-01.10.2013, Belgrade] Institutional support: RVO:68081723 Keywords : nanocrystalline NiFe2O4 * precipitation method * structural analysis * magnetic properties Subject RIV: BM - Solid Matter Physics ; Magnetism

  10. NiFe2O4/activated carbon nanocomposite as magnetic material from petcoke

    International Nuclear Information System (INIS)

    Nickel ferrite (NiFe2O4) was supported on activated carbon (AC) from petroleum coke (petcoke). Potassium hydroxide (KOH) was employed with petcoke to produce activated carbon. NiFe2O4 were synthesized using PEG-Oleic acid assisted hydrothermal method. The structural and magnetic properties were determined using thermogravimetric and differential thermal analysis (TGA–DTA), X-ray diffraction (XRD), Fourier Transform Infrared (IR-FT), surface area (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). XRD analysis revealed the cubic spinel structure and ferrite phase with high crystallinity. IR-FT studies showed that chemical modification promoted the formation of surface oxygen functionalities. Morphological investigation by SEM showed conglomerates of spherical nanoparticles with an average particle size of 72 nm and TEM showed the formation of NiFe2O4/carbon nanofibers. Chemical modification and activation temperature of 800 °C prior to activation dramatically increased the BET surface area of the resulting activated carbon to 842.4 m2/g while the sulfur content was reduced from 6 to 1%. Magnetic properties of nanoparticles show strong dependence on the particle size. - Highlights: • TEM showed the formation of NiFe2O4/carbon nanofibers. • Nanoparticles were supported on the activated carbon from petcoke. • Activation dramatically increased the BET surface area to 842 m2/g. • Magnetic properties show strong dependence on the particle size. • Sulphur content was reduced from 6 to 1% with the petcoke activation

  11. Phase and magnetic studies of the high-energy alloyed Ni-Fe

    Czech Academy of Sciences Publication Activity Database

    Jirásková, Yvonna; Buršík, Jiří; Turek, Ilja; Hapla, Miroslav; Titov, A.; Životský, O.

    2014-01-01

    Roč. 594, May (2014), s. 133-140. ISSN 0925-8388 R&D Projects: GA ČR(CZ) GAP108/11/1350 Grant ostatní: VŠB(CZ) CZ.1.07/2.3.00/20.0074 Institutional support: RVO:68081723 Keywords : Ni-Fe * mechanical alloying * magnetic properties * microstructure * particle interactions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.999, year: 2014

  12. Magnetic Response of NiFe2O4 nanoparticles in polymer matrix

    OpenAIRE

    Poddar, A.; R. N. Bhowmik; De, Amitabha; Sen, Pintu

    2008-01-01

    We report the magnetic properties of magnetic nano-composite, consisting of different quantity of NiFe2O4 nanoparticles in polymer matrix. The nanoparticles exhibited a typical magnetization blocking, which is sensitive on the variation of magnetic field, mode of zero field cooled/field cooled experiments and particle quantity in the matrix. The samples with lower particle quantity showed an upturn of magnetization down to 5 K, whereas the blocking of magnetization dominates at lower temperat...

  13. Heterologous Expression and Maturation of an NADP-Dependent [NiFe]-Hydrogenase: A Key Enzyme in Biofuel Production

    OpenAIRE

    Sun, Junsong; Hopkins, Robert C.; Jenney, Francis E.; McTernan, Patrick M.; Adams, Michael W. W.

    2010-01-01

    Hydrogen gas is a major biofuel and is metabolized by a wide range of microorganisms. Microbial hydrogen production is catalyzed by hydrogenase, an extremely complex, air-sensitive enzyme that utilizes a binuclear nickel-iron [NiFe] catalytic site. Production and engineering of recombinant [NiFe]-hydrogenases in a genetically-tractable organism, as with metalloprotein complexes in general, has met with limited success due to the elaborate maturation process that is required, primarily in the ...

  14. Magnetic properties of Ni-Fe nanowire arrays: effect of template material and deposition conditions

    International Nuclear Information System (INIS)

    The objective of this work is to study the magnetic properties of arrays of Ni-Fe nanowires electrodeposited in different template materials such as porous silicon, polycarbonate and alumina. Magnetic properties were studied as a function of template material, applied magnetic field (parallel and perpendicular) during deposition, wire length, as well as magnetic field orientation during measurement. The results show that the application of magnetic field during deposition strongly influences the c-axis preferred orientation growth of the Ni-Fe nanowires. The samples with magnetic field perpendicular to the template plane during deposition exhibit strong perpendicular anisotropy with greatly enhanced coercivity and squareness ratio, particularly in the Ni-Fe nanowires deposited in polycarbonate templates. In the case of polycarbonate template, as magnetic field during deposition increases, both coercivity and squareness ratio also increase. The wire length dependence was also measured for polycarbonate templates. As wire length increases, coercivity and squareness ratio decrease, saturation field increases. Such magnetic behaviour (dependence on template material, magnetic field, wire length) can be qualitatively explained by preferential growth phenomena, dipolar interactions among nanowires and perpendicular shape anisotropy in individual nanowires.

  15. Magnetic properties of Ni-Fe nanowire arrays: effect of template material and deposition conditions

    Science.gov (United States)

    Aravamudhan, S.; Singleton, J.; Goddard, P. A.; Bhansali, S.

    2009-06-01

    The objective of this work is to study the magnetic properties of arrays of Ni-Fe nanowires electrodeposited in different template materials such as porous silicon, polycarbonate and alumina. Magnetic properties were studied as a function of template material, applied magnetic field (parallel and perpendicular) during deposition, wire length, as well as magnetic field orientation during measurement. The results show that the application of magnetic field during deposition strongly influences the c-axis preferred orientation growth of the Ni-Fe nanowires. The samples with magnetic field perpendicular to the template plane during deposition exhibit strong perpendicular anisotropy with greatly enhanced coercivity and squareness ratio, particularly in the Ni-Fe nanowires deposited in polycarbonate templates. In the case of polycarbonate template, as magnetic field during deposition increases, both coercivity and squareness ratio also increase. The wire length dependence was also measured for polycarbonate templates. As wire length increases, coercivity and squareness ratio decrease, saturation field increases. Such magnetic behaviour (dependence on template material, magnetic field, wire length) can be qualitatively explained by preferential growth phenomena, dipolar interactions among nanowires and perpendicular shape anisotropy in individual nanowires.

  16. Spectroscopy studies of NiFe2O4 nanosized powders obtained using coconut water

    International Nuclear Information System (INIS)

    High-quality NiFe2O4 nanosized powders were prepared by a new route using a natural proteic solution of coconut water and metal ions. The transition from the superparamagnetic to the ferrimagnetic state was observed with the increase of the heat-treatment temperature from 400 deg. C to 800 deg. C. In this work, Electron Paramagnetic Resonance (EPR), a.c. magnetic susceptibility (χa.c.) measurements, infrared (FT-IR) and Raman spectroscopy have been employed to obtain additional information about the structural evolution of the NiFe2O4 nanoparticles, with the increase of the heat-treatment temperature. The obtained results show that the heat-treatment temperature makes remarkable changes in the structure of the samples. The NiFe2O4 nanocrystallite samples, treated at 1200 deg. C, exhibit a large a.c. magnetic susceptibility which was related with the formation of a mixed spinel phase. This is in agreement with the Moessbauer spectroscopy results. The increase of the volume of the nickel ferrite leads to an increase of the magnetic susceptibility. The magnetic properties of these nanoparticles are clearly size dependent.

  17. Magnetic properties of Ni-Fe nanowire arrays: effect of template material and deposition conditions

    Energy Technology Data Exchange (ETDEWEB)

    Singleton, John [Los Alamos National Laboratory; Aravamudhan, Shyan [U OF SOUTH FL; Goddard, Paul A [U OF OXFORD; Bhansali, Shekhar [U OF SOUTH FL

    2008-01-01

    The objective of this work is to study the magnetic properties of arrays of Ni-Fe nanowires electrodeposited in different template materials such as porous silicon, polycarbonate and alumina. Magnetic properties were studied as a function of template material, applied magnetic field (parallel and perpendicular) during deposition, wire length, as well as magnetic field orientation during measurement. The results show that application of magnetic field during deposition strongly influences the c-axis preferred orientation growth of Ni-Fe nanowires. The samples with magnetic field perpendicular to template plane during deposition exhibits strong perpendicular anisotropy with greatly enhanced coercivity and squareness ratio, particularly in Ni-Fe nanowires deposited in polycarbonate templates. In case of polycarbonate template, as magnetic field during deposition increases, both coercivity and squareness ratio also increase. The wire length dependence was also measured for polycarbonate templates. As wire length increases, coercivity and squarness ratio decrease, but saturation field increases. Such magnetic behavior (dependence on template material, magnetic field, wire length) can be qualitatively explained by preferential growth phenomena, dipolar interactions among nanowires, and perpendicular shape anisotropy in individual nanowires.

  18. Elemental redistribution in a nanocrystalline Ni-Fe alloy induced by high-pressure torsion

    International Nuclear Information System (INIS)

    Highlights: · Elemental distribution of a nc Ni-Fe alloy before and after high-pressure torsion. · The supersaturated Ni-Fe solid solution was stable under HPT. · C and S atoms further segregated to the remaining GBs during grain growth. · GB diffusion and the motion of defects facilitate the elemental redistribution. - Abstract: An electrochemically deposited nanocrystalline supersaturated face-centred-cubic Ni-21 at.% Fe alloy with an initial average grain size of ∼21 nm was processed using high-pressure torsion (HPT) that resulted in grain growth via grain rotation and coalescence to an average grain size of ∼53 nm. Atom probe tomography investigations revealed that the supersaturated Ni-Fe solid solution was stable under HPT and that C and S atoms, which are the major impurities in the material and segregated to the grain boundaries (GBs) of the as-deposited material, migrated from disappearing GBs to the remaining GBs during HPT. We propose that the elemental redistribution was facilitated by GB diffusion and the motion of a large volume of HPT-induced defects at the GB regions during the grain growth process. This elemental redistribution process is different from other HPT-induced elemental redistribution processes reported in the literature.

  19. Large enhancement of magnetoresistance in NiFe film with MgO layers sandwiched after annealing

    International Nuclear Information System (INIS)

    Highlights: • Ta/MgO/Ni81Fe19/MgO/Ta and Ta/Ni81Fe19/Ta were prepared by magnetron sputtering. • The electronic transport properties were studied. • The microstructure of NiFe film (100 nm) with MgO sandwiched was measured by HRTEM. • The average grain size and the crystallinity were determined from X-ray diffraction studies. • Δρ and ρ for samples as function of the NiFe thickness were analyzed. - Abstract: A large enhancement of magnetoresistance (MR) up to 6.0% has been observed in NiFe sandwiched by MgO layers, which is 50% larger than the highest MR (4%) in bulk materials. The great improvement of MR derives from the slight increase in corresponding resistivity change Δρ and the great decrease in resistivity ρ. The enhancement of Δρ is attributed to the strengthened spin-dependent scattering of the interfacial conductive electrons but the contribution will be slight with the increase in NiFe thickness. The main contribution is from the significant decrease in ρ, originating from confinement effect on electrons from well-formed oxide/metal interfaces after annealing. Surprisingly, this effect still exists when the NiFe thickness reaches 100 nm. Meanwhile, the oxide (MgO) layers inserted prevents the atomic interdiffusion of Ta and NiFe at the interfaces, which decreases the thickness of magnetic dead layer

  20. Amperometric hydrogen peroxide and glucose biosensor based on NiFe2/ordered mesoporous carbon nanocomposites.

    Science.gov (United States)

    Xiang, Dong; Yin, Longwei; Ma, Jingyun; Guo, Enyan; Li, Qun; Li, Zhaoqiang; Liu, Kegao

    2015-01-21

    Nanocomposites of NiFex embedded in ordered mesoporous carbon (OMC) (x = 0, 1, 2) were prepared by a wet impregnation and hydrogen reduction process and were used to construct electrochemical biosensors for the amperometric detection of hydrogen peroxide (H2O2) or glucose. The NiFe2/OMC nanocomposites were demonstrated to have a large surface area, suitable mesoporous channels, many edge-plane-like defective sites, and a good distribution of alloyed nanoparticles. The NiFe2/OMC and Nafion modified glass carbon electrode (GCE) exhibited excellent electrocatalytic activities toward the reduction of H2O2 as well. By utilizing it as a bioplatform, GOx (glucose oxidase) cross-linked with Nafion was immobilized on the surface of the electrode for the construction of an amperometric glucose biosensor. Our results indicated that the amperometric hydrogen peroxide biosensor (NiFe2/OMC + Nafion + GCE) showed good analytical performances in term of a high sensitivity of 4.29 μA mM(-1) cm(-2), wide linearity from 6.2 to 42,710 μM and a low detection limit of 0.24 μM at a signal-to-noise ratio of 3 (S/N = 3). This biosensor exhibited excellent selectivity, high stability and negligible interference for the detection of H2O2. In addition, the immobilized enzyme on NiFe2/OMC + Nafion + GCE, retaining its bioactivity, exhibited a reversible two-proton and two-electron transfer reaction, a fast heterogeneous electron transfer rate and an effective Michaelis-Menten constant (K) (3.18 mM). The GOx + NiFe2/OMC + Nafion + GCE could be used to detect glucose based on the oxidation of glucose catalyzed by GOx and exhibited a wide detection range of 48.6-12,500 μM with a high sensitivity of 6.9 μA mM(-1) cm(-2) and a low detection limit of 2.7 μM (S/N = 3). The enzymic biosensor maintained a high selectivity and stability features, and shows great promise for application in the detection of glucose. PMID:25429370

  1. Electronic structure and half-metallicity of new quaternary Heusler alloys NiFeTiZ (Z=Si, P, Ge, and As)

    Science.gov (United States)

    Karimian, N.; Ahmadian, F.

    2015-12-01

    The electronic structure and magnetic properties of NiFeTiZ (Z=Si, P, Ge, and As) quaternary Heusler compounds were investigated using the full-potential linearized augmented plane wave (FPLAPW) method in framework of the density functional theory (DFT). The results showed that NiFeTiZ (Z=Si, P, Ge, and As) compounds were stable in YI structure and the NiFeTiP and NiFeTiSi compounds were true half-metallic (HM) ferromagnets. The NiFeTiGe had a nearly HM characteristic, while NiFeTiAs was a conventional ferromagnet. The majority and half-metallic band gaps were respectively 0.44 and 0.3 eV for NiFeTiP and 0.18 and 0.08 eV for NiFeTiSi. The origin and mechanism of the formation of majority band gap in NiFeTiP were also verified. The total magnetic moments of NiFeTiP and NiFeTiSi compounds were respectively obtained 1μB and 2μB per formula unit, which were in agreement with Slater-Pauling rule (Mtot=28-Ztot). Half-metalliciy exists in relatively wide ranges of 5.43-5.80 Å and 5.60-5.87 Å for NiFeTiP and NiFeTiSi compounds, respectively, which makes them promising candidates in spintronics.

  2. The chemical properties of bimetallic surfaces: Importance of ensemble and electronic effects in the adsorption of sulfur and SO 2

    Science.gov (United States)

    Rodriguez, José A.

    The understanding of the interaction of sulfur with bimetallic surfaces is a critical issue for preventing the deactivation of hydrocarbon reforming catalysts and for the design of better hydrodesulfurization catalysts. The alloying or combination of two metals can lead to materials with special chemical properties due to an interplay of “ensemble” and “electronic” effects. In recent years, several new interesting phenomena have been discovered when studying the interaction of sulfur with bimetallic surfaces using the modern techniques of surface science. Very small amounts of sulfur are able to induce dramatic changes in the morphology of bimetallic surfaces that combine noble metals (Cu, Ag, Au) and transition metals. This phenomenon can lead to big modifications in the activity and selectivity of bimetallic catalysts used for hydrocarbon reforming. In many cases, bimetallic bonding produces a significant redistribution of charge around the bonded metals. The electronic perturbations associated with the formation of a heteronuclear metal-metal bond can affect the reactivity of the bonded metals toward sulfur. This can be a very important issue to consider when trying to minimize the negative effects of sulfur poisoning (Sn/Pt versus Ag/Pt and Cu/Pt catalysts) or when trying to improve the performance of desulfurization catalysts (Co/Mo and Ni/Mo systems). Clearly much more work is necessary in this area, but new concepts are emerging that can be useful for designing more efficient bimetallic catalysts.

  3. Microstructures of NiFe/nonmagnetic metal spacer/FeMn films and their influences on exchange coupling

    Institute of Scientific and Technical Information of China (English)

    LI; Minghua(李明华); YU; Guanghua(于广华); ZHU; Fengwu(朱逢吾); HE; Ke(何珂); LAI; Wuyan(赖武彦)

    2003-01-01

    Ta/NiFe/nonmagnetic metal spacer/FeMn films were prepared by magnetron sputtering. The dependences of the exchange coupling field (Hex) between an antiferromagnetic FeMn layer and a ferromagnetic NiFe layer on the thickness of nonmagnetic metal spacer layers were systematically studied. The results show that the Hex dramatically decreases with the increase in the thicknesses of Bi and Ag spacer layers. However, it gradually decreases with the increase in the thickness of a Cu spacer layer. For a Cu space layer, its crystalline structure is the same as that of NiFe and the lattice parameters of them are close to each other. The Cu layer and FeMn layer will epitaxially grow on the NiFe layer in succession, so the (111) texture of the FeMn layer will not be damaged. As a result, the Hex gradually decreases with the deposition thickness of a Cu layer. For an Ag space layer, its crystalline structure is the same as that of NiFe, but its lattice parameter is very different from that of NiFe. Thus, neither an Ag nor an FeMn layer will epitaxially grow on the NiFe layer and the (111) texture of the FeMn layer will be damaged. The Hex rapidly decreases with the increase in the deposition thickness of an Ag layer. For a Bi spacer layer, not only its crystalline structure but also its lattice parameter is greatly different from that of NiFe. For the same reason, the Bi and FeMn layer cannot epitaxially grow on the NiFe layer. The texture of the FeMn layer will also be damaged. Therefore, the Hex rapidly decreases with the increase in the deposition thickness of a Bi layer as well. However, the research result of X-ray photoelectron spectroscopy indicates that a very small amount of surfactant Bi atoms will migrate to the FeMn layer surface when they are deposited on the NiFe/FeMn interface. Thus, the Hex will hardly decrease.

  4. Magnetic hybride layers. Magnetic properties of locally exchange-coupled NiFe/IrMn layers; Magnetische Hybridschichten. Magnetische Eigenschaften lokal austauschgekoppelter NiFe/IrMn-Schichten

    Energy Technology Data Exchange (ETDEWEB)

    Hamann, Christine

    2010-10-06

    By the lateral modification of the magnetic properties of exchange-coupled NiFe/IrMn layers soft-magnetic layers were produced, which show both new static and dynamic properties. As lateral structuration methods hereby the localoxidation as well as ion implantation were applied. By means of thes procedures it has been succeeded to mould specific magnetic domain configurations with strp structure into the layers. In dependence of the structure orientation as well as strip period the remagnetization behavior as well as the magnetic-resonance frequency and damping of the layers could directly be modified. The new dynamical properties are hereby discussed in the framework of the coupling via dynamical charges and the direct affection of the effective field of the artificially inserted domain state. The presented results prove by this the large potential of the lateral magneto-structuration for the tuning of specifical static as well as dynamic properties of magnetically thin layers.

  5. Novel multifunctional NiFe2O4/ZnO hybrids for dye removal by adsorption, photocatalysis and magnetic separation

    Science.gov (United States)

    Zhu, Hua-Yue; Jiang, Ru; Fu, Yong-Qian; Li, Rong-Rong; Yao, Jun; Jiang, Sheng-Tao

    2016-04-01

    Novel multifunctional NiFe2O4/ZnO hybrids were prepared by a hydrothermal method and their physicochemical properties were characterized by XRD, SEM, TEM, TGA, VSM, BET and UV-vis DRS. The adsorption and photocatalytic performance of NiFe2O4/ZnO hybrids were systematically investigated using congo red as a model contaminant. With the introduction of NiFe2O4, NiFe2O4/ZnO hybrids can absorb the whole light from 300 nm to 700 nm. The adsorption capacity (221.73 mg g-1) of NiFe2O4/ZnO hybrids is higher than those of NiFe2O4, ZnO and mechanically mixed NiFe2O4/ZnO hybrids. The removal of congo red solution (20 mg L-1) by NiFe2O4/ZnO hybrids was about 94.55% under simulated solar light irradiation for 10 min. rad OH and h+ play important roles in the decolorization of congo red solution by NiFe2O4/ZnO hybrids under simulated solar light irradiation. The decolorization efficiency of congo red solution is 97.23% for the fifth time by NiFe2O4/ZnO hybrids under simulate solar light irradiation, indicating the high photostability and durability. NO3- and Cl- anions which are ubiquitous components in dye-containing wastewater have negligible influence on the effectiveness of NiFe2O4/ZnO hybrids. Moreover, the magnetic NiFe2O4/ZnO hybrids can be easily separated from the reacted solution by an external magnet.

  6. Surface morphology, optical, and electrochromic properties of nanostructured nickel ferrite (NiFe2O4) prepared by sol-gel method: effects of Ni/Fe molar ratios

    Science.gov (United States)

    Bazhan, Z.; Ghodsi, F. E.; Mazloom, J.

    2016-05-01

    Nanostructured nickel ferrite (NF) was prepared by the sol-gel method and calcined at 500 °C for 2 h. The effect of Ni/Fe molar ratios (0, 10, 30, 50 %) on structural, morphological, compositional, optical, and magnetic properties of samples was investigated using analytical tools. XRD patterns indicated the presence of hematite phase in the pure and 10 % NF samples. The samples of 30 and 50 % Ni/Fe molar ratios showed the formation of nickel ferrite structure. Using AFM images, power spectrum density analysis were performed for Ni/Fe with different molar ratio. Also the effect of thickness on morphology of 30 % sample was studied. The fractal dimension increases by increasing the Ni/Fe molar ratio. Optical parameters were evaluated by theoretical approach, and compositional dependence of these parameters was discussed comprehensively. Band gap narrowing was observed in nickel ferrite thin films by increasing the nickel contents from 10 to 50 %. Magnetic analysis revealed that increasing nickel content improved the saturation magnetization. Electrochemical measurements indicated that NF thin films have higher total charge density rather than Fe2O3 thin films and the ion storage capacitance of NF thin films increased by increasing the Ni/Fe content.

  7. Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO2/NiFe trilayers near simultaneous ferromagnetic resonance

    Science.gov (United States)

    Soh, Wee Tee; Peng, Bin; Ong, C. K.

    2015-08-01

    The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO2 spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.

  8. Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO{sub 2}/NiFe trilayers near simultaneous ferromagnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Soh, Wee Tee, E-mail: a0046479@u.nus.edu; Ong, C. K. [Center for Superconducting and Magnetic Materials, Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551 (Singapore); Peng, Bin [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China)

    2015-08-15

    The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO{sub 2} spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.

  9. Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO2/NiFe trilayers near simultaneous ferromagnetic resonance

    International Nuclear Information System (INIS)

    The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO2 spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer

  10. Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO2/NiFe trilayers near simultaneous ferromagnetic resonance

    Directory of Open Access Journals (Sweden)

    Wee Tee Soh

    2015-08-01

    Full Text Available The spin rectification effect (SRE, a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO2 spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.

  11. Synthesis and characterization of NiFe{sub 2}O{sub 4} nanoparticles and nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Sivakumar, P., E-mail: p_siva1978@yahoo.co.in [T.S. Srinivasan Centre for Polytechnic College and Advanced Training (CPAT-TVS), Vanagaram, Chennai 600 095, Tamilnadu (India); Ramesh, R. [Center for Materials Science and Nano Devices, Department of Physics, SRM University, Kattankulathur, Kancheepuram 603 203, Tamilnadu (India); Ramanand, A. [Department of Physics, Loyola College, Nungambakkam, Chennai 600 034, Tamilnadu (India); Ponnusamy, S.; Muthamizhchelvan, C. [Center for Materials Science and Nano Devices, Department of Physics, SRM University, Kattankulathur, Kancheepuram 603 203, Tamilnadu (India)

    2013-06-25

    Highlights: ► NiFe{sub 2}O{sub 4} nanorods synthesized by co-precipitation method at high concentration of PEO. ► PEO play an important role in the formation, size and shape control of the nanorods. ► Nanorods with representative diameter of 60–65 nm and length of 142–147 nm. ► The shape anisotropy enhances the coercive field and decreases the magnetization. ► Synthesized nanostructures exhibit ferromagnetic behavior at room temperature. -- Abstract: Highly ordered single crystalline nickel ferrite (NiFe{sub 2}O{sub 4}) nanorods have been successfully synthesized by a polymer assisted co-precipitation method using polyethylene oxide (PEO) as a capping and a polymer structure directing reagent. In this synthesis, the addition of high concentration of PEO seems to play an important role in the formation, size and shape control of the nanorods. Powder X-ray diffraction (XRD) and selected area electron diffraction (SAED) exhibit that the obtained nanorods can be indexed to single crystalline inverse spinel with Fd3m space group. The synthesized NiFe{sub 2}O{sub 4} products were characterized in terms of their structural and magnetic properties. The morphological investigations using high resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM) reveal that the grown products are rod-like structure with the diameters in the range of 60–65 nm and length of 142–147 nm. The coercivity of prepared nanorods with high concentration of PEO reached as high as 904.46 Oe at room temperature (300 K), superior to that of nanoparticles obtained with low concentration of PEO. Hence, it can be used for high frequency electronics and gas sensing applications. On the basis of these experimental results, possible influence mechanisms in the growth processes are discussed.

  12. Phonon densities of states of face-centered-cubic Ni-Fe alloys

    Energy Technology Data Exchange (ETDEWEB)

    Lucas, Matthew [United States Air Force Research Laboratory, Wright-Patterson Air Force Base; Mauger, L [California Institute of Technology, W. M. Keck Laboratory, Pasadena; Munoz, Jorge A. [California Institute of Technology, Pasadena; Halevy, I [California Institute of Technology, Pasadena; Horwath, J [United States Air Force Research Laboratory, Wright-Patterson Air Force Base; Semiatin, S L [United States Air Force Research Laboratory, Wright-Patterson Air Force Base; Leontsev, S. O. [University of Kentucky, Lexington; Stone, Matthew B [ORNL; Abernathy, Douglas L [ORNL; Xiao, Yuming [Carnegie Institution of Washington; Chow, P [HPCAT Geophysical Lab, Argonne, IL; Fultz, B. [California Institute of Technology, Pasadena

    2013-01-01

    Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to determine the phonon densities of states of face-centered-cubic Ni-Fe alloys. Increasing Fe concentration results in an average softening of the phonon modes. Chemical ordering of the Ni0.72Fe0.28 alloy results in a reduction of the partial vibrational entropy of the Fe atoms but does not significantly change the partial vibrational entropy of the Ni atoms. Changes in the phonon densities of states with composition and chemical ordering are discussed and analyzed with a cluster expansion method.

  13. Effect of pre-deformation on hysteresis in TiNiFe shape memory alloys

    International Nuclear Information System (INIS)

    The mechanical properties, shape memory effect and martensitic transformation temperatures in the TiNiFe alloys were measured. A ductility of more than 20% and shape recovery strain of 5.8% were obtained in these alloys. The shape memory effect increased with the increase of deformation, and reached a maximum value appearing at 8% total strain. The pre-deformation raised significantly the reverse transformation temperatures and the hysteresis was enlarged by more than 40 C when the total strain exceeded 6%. (orig.)

  14. Effect of biquadratic coupling on current induced magnetization switching in Co/Cu/Ni-Fe nanopillar

    Science.gov (United States)

    Aravinthan, D.; Sabareesan, P.; Daniel, M.

    2016-05-01

    The effect of biquadratic coupling on spin current induced magnetization switching in a Co/Cu/Ni-Fe nanopillar device is investigated by solving the free layer magnetization switching dynamics governed by the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. The LLGS equation is numerically solved by using Runge-Kutta fourth order procedure for an applied current density of 5 × 1012 Am-2. Presence of biquadratic coupling in the ferromagnetic layers reduces the magnetization switching time of the nanopillar device from 61 ps to 49 ps.

  15. Substitutional impurities and their effect on fracture peculiarities in W-Ni-Fe-alloy

    Energy Technology Data Exchange (ETDEWEB)

    Minakova, R.V.; Bazhenova, L.G.; Verkhovodov, P.A.; Kolchin, O.P.; Nedelyaeva, L.P.; Tolstunov, A.V. (AN Ukrainskoj SSR, Kiev. Inst. Problem Materialovedeniya)

    1983-11-01

    The paper deals with distribution of admixture elements, shape, size, content, chemical composition, distribution of nonmetal inclusions and their effect on peculiarities of W-Ni-Fe-alloy deformation and fractures. It is established that non-metal inclusions play the part of additional ''notches'' decreasing the size of the slow crack growth area in a refractory component. Segregation of the impurities and the film on the boundaries of nickel base solid solution promote intercrystalline fracture of the alloy.

  16. Nanocrystalline NiFe2O4 synthesized by modified precipitation method

    Czech Academy of Sciences Publication Activity Database

    Ćosović, A.; Ćosović, V.; Balanović, Lj.; Živković, D.; Žák, Tomáš; Talijan, N.

    Belgrade: Association of Metallurgical Engineers of Serbia , 2013 - (Romhanji, E.; Jovanović, M.; Radović, N.), s. 92-98 ISBN 978-86-87183-24-7. [Metallurgical & Materials Engineering Congress of South-East Europe /1./. Belgrade (RS), 23.05.2013-25.05.2013] R&D Projects: GA ČR(CZ) GAP108/11/1350; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : nanocrastalline NiFe2O4 * precipitation method * structural analysis * phase composition * magnetic properties Subject RIV: BM - Solid Matter Physics ; Magnetism

  17. Preparation and properties of 4. 25Cu-0.75Ni/NiFe2O4 cermet

    Institute of Scientific and Technical Information of China (English)

    LI Jie; ZHANG Gang; LAI Yan-qing; TIAN Zhong-liang; QIN Qing-wei

    2005-01-01

    4.25Cu-0.75Ni/NiFe2 O4 cermets were prepared by doping NiFe2 O4 ceramic matrix with the mixed powders of Cu and Ni or Cu-Ni alloy powder as the electrical conducting metallic elements. The effects of technological parameters, such as the adding modes of metallic elements, the ball milling time, the sintering time and the sintering temperature, on the relative density and resistivity of the cermets were studied. The results show that the resistivity of 4.25Cu-0.75Ni/NiFe2 O4 cermets decreases with increasing temperature, and has a turning point at 590 ℃, which is similar to that of NiFe2 O4 ceramic. The sintering temperature and adding modes of metallic elements have a great influence on the properties of 4. 25Cu-0. 75Ni/NiFe2O4 cermets. When the sintering temperature increases from 1 200 ℃ to 1 300 ℃, the relative density increases from 89.86% to 95.33 %0, and the resistivity at 960 ℃ decreases and Ni, the cermets of finely and uniformly dispersed metallic phase, high density and electric conductivity are obples sintered at 1 200 ℃ for 2 h, which are both better than those of the cermets prepared under the same technique conditions but with the metallic elements added as 85Cu-15Ni alloy powders.

  18. The influence of an MgO nanolayer on the planar Hall effect in NiFe films

    International Nuclear Information System (INIS)

    The Planar Hall Effect (PHE) in NiFe films was studied using MgO as the buffer and capping layer to reduce the shunt effect. The thermal annealing was found to be effective in increasing the sensitivity. The sensitivity of the magnetic field reached as high as 865 V/AT in a MgO (3 nm)/NiFe (5 nm)/MgO(3 nm)/Ta(3 nm) structure after annealing at 500 °C for 2 h, which is close to the sensitivity of semiconductor Hall Effect (HE) sensors. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used to study the sample. The results show that the top crystallization of MgO and NiFe (111) texture were improved by proper annealing. The smooth and clear bottom MgO/NiFe and top NiFe/MgO interface is evident from our data. In addition, the shunt current of Ta was decreased. These combined factors facilitate the improvement of the sensitivity of the magnetic field

  19. Effects of annealing temperature on the magnetoresistance in Ta/NiFe/Ta films by ZnO intercalations

    International Nuclear Information System (INIS)

    Zinc oxide (ZnO) exhibiting many superior physical properties was inserted into the Ta/NiFe/Ta films as nano-oxide intercalations. Different annealing temperatures and ZnO thickness significantly affected the magnetoresistance (MR) in NiFe films. The 4-nm thick ZnO film annealed at 200 °C had a MR of 2.41%, which was more than 70% higher than that of the 1-nm thick ZnO annealed film (MR=1.40%). However, the further increase in annealing temperature to 300 °C rapidly deteriorated the MR performance of the films. Diffusion and interface reactions occur between the crystal ZnO and the adjacent NiFe layer. Lower-temperature annealing improved the interface, increasing the specular reflection of spin-polarized electrons to some extent. However, higher-temperature annealing induced severe diffusion and interface reactions, which led to a sharp decline in MR performance. - Highlights: • Combining NiFe with ZnO, thereby producing NiFe/ZnO interfaces. • Investigating the effects of annealing temperatures on the magnetoresistance. • Explaining the corresponding relationship between MR and microstructure

  20. Effects of interfacial Fe electronic structures on magnetic and electronic transport properties in oxide/NiFe/oxide heterostructures

    International Nuclear Information System (INIS)

    Highlights: • The magnetic and transport properties of oxide/NiFe/oxide films were studied. • The oxide (SiO2, MgO and HfO2) has different elemental electronegativity. • Redox reaction at different NiFe/oxide interface is dependent on the oxide layer. • Different interfacial electronic structures shown by XPS influence the properties. - Abstract: We report that the magnetic and electronic transport properties in oxide/NiFe(2 nm)/oxide film (oxide = SiO2, MgO or HfO2) are strongly influenced by the electronic structure of NiFe/oxide interface. Magnetic measurements show that there exist magnetic dead layers in the SiO2 sandwiched film and MgO sandwiched film, whereas there is no magnetic dead layer in the HfO2 sandwiched film. Furthermore, in the ultrathin SiO2 sandwiched film no magnetoresistance (MR) is detected, while in the ultrathin MgO sandwiched film and HfO2 sandwiched film the MR ratios reach 0.35% and 0.88%, respectively. The investigation by X-ray photoelectron spectroscopy reveals that the distinct interfacial redox reactions, which are dependent on the oxide layers, lead to the variation of magnetic and transport properties in different oxide/NiFe/oxide heterostructures

  1. Effects of interfacial Fe electronic structures on magnetic and electronic transport properties in oxide/NiFe/oxide heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Qianqian; Chen, Xi; Zhang, Jing-Yan [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Yang, Meiyin [SKLSM, Institute of Semiconductors, CAS, P.O. Box 912, Beijing 100083 (China); Li, Xu-Jing; Jiang, Shao-Long; Liu, Yi-Wei; Cao, Yi [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Wu, Zheng-Long [Analytical and Testing Center, Beijing Normal University, Beijing 100875 (China); Feng, Chun [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Ding, Lei [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Yu, Guang-Hua, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-09-15

    Highlights: • The magnetic and transport properties of oxide/NiFe/oxide films were studied. • The oxide (SiO{sub 2}, MgO and HfO{sub 2}) has different elemental electronegativity. • Redox reaction at different NiFe/oxide interface is dependent on the oxide layer. • Different interfacial electronic structures shown by XPS influence the properties. - Abstract: We report that the magnetic and electronic transport properties in oxide/NiFe(2 nm)/oxide film (oxide = SiO{sub 2}, MgO or HfO{sub 2}) are strongly influenced by the electronic structure of NiFe/oxide interface. Magnetic measurements show that there exist magnetic dead layers in the SiO{sub 2} sandwiched film and MgO sandwiched film, whereas there is no magnetic dead layer in the HfO{sub 2} sandwiched film. Furthermore, in the ultrathin SiO{sub 2} sandwiched film no magnetoresistance (MR) is detected, while in the ultrathin MgO sandwiched film and HfO{sub 2} sandwiched film the MR ratios reach 0.35% and 0.88%, respectively. The investigation by X-ray photoelectron spectroscopy reveals that the distinct interfacial redox reactions, which are dependent on the oxide layers, lead to the variation of magnetic and transport properties in different oxide/NiFe/oxide heterostructures.

  2. Effects of annealing temperature on the magnetoresistance in Ta/NiFe/Ta films by ZnO intercalations

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Lei, E-mail: Lding@hainu.edu.cn [Key Laboratory of Advanced Materials of Tropical Island Resources, Ministry of Education, Hainan University, Haikou 570228 (China); Yu, Guang-hua; Zhang, Min; Zhao, Chong-jun; Teng, Jiao [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Xiang, Dao-ping [Key Laboratory of Advanced Materials of Tropical Island Resources, Ministry of Education, Hainan University, Haikou 570228 (China)

    2015-09-01

    Zinc oxide (ZnO) exhibiting many superior physical properties was inserted into the Ta/NiFe/Ta films as nano-oxide intercalations. Different annealing temperatures and ZnO thickness significantly affected the magnetoresistance (MR) in NiFe films. The 4-nm thick ZnO film annealed at 200 °C had a MR of 2.41%, which was more than 70% higher than that of the 1-nm thick ZnO annealed film (MR=1.40%). However, the further increase in annealing temperature to 300 °C rapidly deteriorated the MR performance of the films. Diffusion and interface reactions occur between the crystal ZnO and the adjacent NiFe layer. Lower-temperature annealing improved the interface, increasing the specular reflection of spin-polarized electrons to some extent. However, higher-temperature annealing induced severe diffusion and interface reactions, which led to a sharp decline in MR performance. - Highlights: • Combining NiFe with ZnO, thereby producing NiFe/ZnO interfaces. • Investigating the effects of annealing temperatures on the magnetoresistance. • Explaining the corresponding relationship between MR and microstructure.

  3. The influence of an MgO nanolayer on the planar Hall effect in NiFe films

    Energy Technology Data Exchange (ETDEWEB)

    Li, Minghua, E-mail: mhli@ustb.edu.cn [Department of Material Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Zhao, Zhiduo; Ma, Lin; Lu, Xiangan; Teng, Jiao; Yu, Guanghua [Department of Material Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Guoqiang; Amiri, Pedram Khalili; Wang, Kang L. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Zhou, Wenping [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Department of Physics, Inner Mongolia University, Hohhot 010021 (China)

    2015-03-28

    The Planar Hall Effect (PHE) in NiFe films was studied using MgO as the buffer and capping layer to reduce the shunt effect. The thermal annealing was found to be effective in increasing the sensitivity. The sensitivity of the magnetic field reached as high as 865 V/AT in a MgO (3 nm)/NiFe (5 nm)/MgO(3 nm)/Ta(3 nm) structure after annealing at 500 °C for 2 h, which is close to the sensitivity of semiconductor Hall Effect (HE) sensors. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used to study the sample. The results show that the top crystallization of MgO and NiFe (111) texture were improved by proper annealing. The smooth and clear bottom MgO/NiFe and top NiFe/MgO interface is evident from our data. In addition, the shunt current of Ta was decreased. These combined factors facilitate the improvement of the sensitivity of the magnetic field.

  4. Synthesis of supported bimetallic nanoparticles with controlled size and composition distributions for active site elucidation

    Energy Technology Data Exchange (ETDEWEB)

    Hakim, Sikander H.; Sener, Canan; Alba Rubio, Ana C.; Gostanian, Thomas M.; O' neill, Brandon J; Ribeiro, Fabio H.; Miller, Jeffrey T.; Dumesic, James A

    2015-08-01

    Elucidation of active sites in supported bimetallic catalysts is complicated by the high level of dispersity in the nanoparticle size and composition that is inherent in conventional methods of catalyst preparation. We present a synthesis strategy that leads to highly dispersed, bimetallic nanoparticles with uniform particle size and composition by means of controlled surface reactions. We demonstrate the synthesis of three systems, RhMo, PtMo, and RhRe, consisting of a highly reducible metal with an oxophilic promoter. These catalysts are characterized by FTIR, CO chemisorption, STEM/EDS, TPR, and XAS analysis. The catalytic properties of these bimetallic nanoparticles were probed for the selective CO hydrogenolysis of (hydroxymethyl)tetrahydropyran to produce 1,6 hexanediol. Based on the characterization results and reactivity trends, the active sites in the hydrogenolysis reaction are identified to be small ensembles of the more noble metal (Rh, Pt) adjacent to highly reduced moieties of the more oxophilic metal (Mo, Re).

  5. Self-assembled NiFe2O4/carbon nanotubes sponge for enhanced glucose biosensing application

    Science.gov (United States)

    Li, Yingchun; Zhao, Minggang; Chen, Jing; Fan, Sisi; Liang, Jingjing; Ding, Longjiang; Chen, Shougang

    2016-01-01

    In this work, self-assembled NiFe2O4/carbon nanotubes (CNTs) sponge was prepared by ice-templating method. The device synergized the advantageous features of both the 3D porous nanostructure and the catalytic properties of CNTs with GOx and NiFe2O4 nanoparticles. The porous network construction of the NiFe2O4/CNTs sheets offered enlarged specific surface for GOx immobilization and opened channels for facilitating the electrons transport and reactants diffusion. With the help of the abnormal-valence elements Ni and Fe, double catalysis has happened and the enhanced glucose biosensing performance has been achieved. The fabricated glucose biosensor exhibited two large linear ranges (0-3.0 and 3.2-12.4 mM) and distinct sensitivities (84.1 and 24.6 μA mM-1 cm-2).

  6. Formation of magnetic microstructure of the nanosized NiFe2O4 synthesized via solid-state reaction

    Directory of Open Access Journals (Sweden)

    Žák T.

    2012-01-01

    Full Text Available Magnetic NiFe2O4 structure formation was studied through structural, compositional and magnetic characterization of obtained reaction products of a simple, high yielding and low-cost solid-state reaction. Initial annealing of the starting oxides mixture at 700ºC did not allow us to observe formation of the desired magnetic phase. In contrast, subsequent thermomagnetic measurements up to 800ºC indicated the considerable increase of the magnetic moment, which can be reasonably assigned to the changes in phase composition and formation of magnetic NiFe2O4 structure during the heating cycle of measurements. Nanosized NiFe2O4 phase formation has been confirmed by the following XRD and MS phase analyses and its nanocrystalline structure by XRD and SEM/TEM techniques. The obtained hysteresis loop taken after TM measurements suggest the increased volume of magnetically active material and thus additionally support the previous findings.

  7. A study on the electrodeposition of NiFe alloy thin films using chronocoulometry and electrochemical quartz crystal microgravimetry

    CERN Document Server

    Myung, N S

    2001-01-01

    Ni, Fe and NiFe alloy thin films were electrodeposited at a polycrystalline Au surface using a range of electrolytes and potentials. Coulometry and EQCM were used for real-time monitoring of electroplating efficiency of the Ni and Fe. The plating efficiency of NiFe alloy thin films was computed with the aid of ICP spectrometry. In general, plating efficiency increased to a steady value with deposition time. Plating efficiency of Fe was lower than that of Ni at -0.85 and -1.0 V but the efficiency approached to the similar plateau value to that of Ni at more negative potentials. The films with higher content of Fe showed different stripping behavior from the ones with higher content of Ni. Finally, compositional data and real-time plating efficiency are presented for films electrodeposited using a range of electrolytes and potentials.

  8. Thickness effects on magnetic properties and ferromagnetic resonance of Co-Ni-Fe soft magnetic thin films

    International Nuclear Information System (INIS)

    In order to apply Co-Ni-Fe thin films for high-frequency magnetic devices, the thickness effects on the magnetic properties of these films have been studied. Coercivity and electrical resistivity of these films increase from 1.5 to 8.9 Oe, and 25 to 88 μΩ cm, respectively, with the decrease of film thickness. The effective permeability of these films is 1300, which is maintained above 700 MHz at 0.1 μm thickness and below. Also, Hk increases from 22 to 65 Oe with the decrease of film thickness, which plays an important role in enhancing the high-frequency characteristics in Co-Ni-Fe thin films with the increase of electrical resistivity. From the XRD, TEM, and FMR investigations of Co-Ni-Fe films, it is certain that the magnetic phases change from amorphous to crystalline phase with the increase of the film thickness

  9. Control of spin-polarized electron magnetoresistance in Ta/NiFe/Ta films by intercalation of Au

    International Nuclear Information System (INIS)

    Intercalation layers of Au were formed in Ta/NiFe/Ta films to control the interface properties of the films. It was found that small amounts of Au may enhance the magnetoresistance (MR) value up to 2.63%. The intercalation at different interfaces had different effects. Intercalation of Au at the top (bottom) interface with respect to the substrate exhibits weak (strong) diffusion of Au into NiFe. At weak diffusion, a homogeneous Au layer is formed which explains the large MR effect. At strong diffusion, since Au possesses a relatively strong spin-orbit interaction, the enhanced MR effect was explained by the spin-orbit scattering of polarized electrons in the NiFe layer.

  10. Novel synthesis of Ni-ferrite (NiFe2O4) electrode material for supercapacitor applications

    International Nuclear Information System (INIS)

    Novel nanocrystalline NiFe2O4 has been synthesized through combustion route using citric acid as a fuel. Phase of the synthesized material was analyzed using powder X-ray diffraction. The XRD study revealed the formation of spinel phase cubic NiFe2O4 with high crystallinity. The average crystallite size of NiFe2O4 nanomaterial was calculated from scherrer equation. The electrochemical properties were realized by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. The electrode material shows a maximum specific capacitance of 454 F/g with pseudocapacitive behavior. High capacitance retention of electrode material over 1000 continuous charging-discharging cycles suggests its excellent electrochemical stability. The results revealed that the nickel ferrite electrode is a potential candidate for energy storage applications in supercapacitor

  11. Novel synthesis of Ni-ferrite (NiFe2O4) electrode material for supercapacitor applications

    Science.gov (United States)

    Venkatachalam, V.; Jayavel, R.

    2015-06-01

    Novel nanocrystalline NiFe2O4 has been synthesized through combustion route using citric acid as a fuel. Phase of the synthesized material was analyzed using powder X-ray diffraction. The XRD study revealed the formation of spinel phase cubic NiFe2O4 with high crystallinity. The average crystallite size of NiFe2O4 nanomaterial was calculated from scherrer equation. The electrochemical properties were realized by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. The electrode material shows a maximum specific capacitance of 454 F/g with pseudocapacitive behavior. High capacitance retention of electrode material over 1000 continuous charging-discharging cycles suggests its excellent electrochemical stability. The results revealed that the nickel ferrite electrode is a potential candidate for energy storage applications in supercapacitor.

  12. Modified combustion synthesis of Nano-NiFe2O4: Optimization using Taguchi experimental design

    International Nuclear Information System (INIS)

    Abstarct: Nano-NiFe2O4 powders were prepared by modified combustion of DTPA as a new fuel. Three factors such as fuel to oxidizer ratio (F/O), added fuel type and added to the main fuel ratio were evaluated under Taguchi L8 experimental design and analysis. Urea and EDTA were selected as added fuels and sterile gauze was used as a template for the first time. The crystal sizes were optimized as the responses of the experiments. Optimum condition for production of smaller crystals was determined as using EDTA as added fuel and added/main fuels molar ratio of 0.75. The structural and morphological properties of the products were characterized using, field emission scanning electron microscopy (FESEM), Energy Dispersive Spectroscopy mapping, transmission electron microscopy (TEM), X-ray diffraction (XRD). FESEM and TEM micrographs showed agglomerated spherical and cubic nanoparticles with an average particle size of 60 nm. XRD analysis revealed the cubic spinel structure and ferrite phase with high crystallinity in the range of 13–23 nm. - Highlights: • Highly pure Nano-NiFe2O4 were prepared by modified combustion of Diethylene triamine pentaacetic acid as a new fuel. • Sterile gauze was used as template for the first time. • Nickel ferrite powders with average particle size of 60 nm have been successfully synthesized

  13. Supersolar Ni/Fe production in the Type IIP SN 2012ec

    CERN Document Server

    Jerkstrand, Anders; Sollerman, Jesper; Inserra, Cosimo; Fraser, Morgan; Spyromilio, Jason; Fransson, Claes; Chen, Ting-Wan; Barbarino, Cristina; Dall'Ora, Massimo; Botticella, Maria Teresa; Della Valle, Massimo; Gal-Yam, Avishay; Valenti, Stefano; Maguire, Kate; Mazzali, Paolo; Tomasella, Lina

    2014-01-01

    SN 2012ec is a Type IIP supernova (SN) with a progenitor detection and comprehensive photospheric-phase observational coverage. Here, we present Very Large Telescope and PESSTO observations of this SN in the nebular phase. We model the nebular [O I] 6300, 6364 lines and find their strength to suggest a progenitor main-sequence mass of 13-15 Msun. SN 2012ec is unique among hydrogen-rich SNe in showing a distinct and unblended line of stable nickel [Ni II] 7378. This line is produced by 58Ni, a nuclear burning ash whose abundance is a sensitive tracer of explosive burning conditions. Using spectral synthesis modelling, we use the relative strengths of [Ni II] 7378 and [Fe II] 7155 (the progenitor of which is 56Ni) to derive a Ni/Fe production ratio of 0.19pm0.07, which is a factor 3.5pm1.2 times the solar value. High production of stable nickel is confirmed by a strong [Ni II] 1.939 micron line. This is the third reported case of a core-collapse supernova producing a Ni/Fe ratio far above the solar value, which...

  14. Visualization of vortex core polarity in NiFe nanodots by tilted Fresnel images

    International Nuclear Information System (INIS)

    We illustrate an approach which allows determining the out-of-plane component of the vortex core (polarity) in NiFe nanodots using Fresnel imaging in Lorentz electron microscopy. Using tilted Fresnel images, contribution of the polarity is introduced into the Fresnel image. However, this contribution is relatively small and a difference image from two symmetrically tilted Fresnel images must be used to eliminate the strong contribution from the in-plane curling magnetization and non-magnetic contrast. The sense of the polarity appears as a bipolar white-black contrast in the difference image on the tilt axis. A vortex core with a diameter of 16.5±2.5 nm is experimentally measured. Image tilting, displacement and geometrical distortion may disturb the difference image, and hence subtraction of the difference image must be aligned by cross-correlation. The method is also justified by a study of the observed contrast characteristic due to misalignment. The method is confirmed to be superior to similar approach with direct interpretation of information and more information subtracted. -- Highlights: → The sense of polarity appears as a bipolar white-black contrast in the difference image. → It allows determining a core diameter of 16.5±2.5 nm as commonly seen in NiFe nanodots. → Difference image in misaligned case shows characteristic behavior of bipolar contrast. → Method is direct interpretation, resolution-free effect and more quantitative quantification.

  15. Wetting of mono- and polycrystalline tungsten with Ni-Fe-W alloys

    Energy Technology Data Exchange (ETDEWEB)

    Yupko, V.L.; Monastyreva, N.I.; Verkhovodov, P.A.; Minakova, R.V.; Lotsko, D.V.; Nedolyaeva, L.P.; Vojtenko, V.L. (AN Ukrainskoj SSR, Kiev. Inst. Problem Materialovedeniya)

    1984-09-01

    Wetting mono- and polycrystalline tungsten on (111) and (110) faces with Ni-Fe-W alloys is studied in vacuum of 5-10 MPa and hydrogen atmosphere (P/sub H2/) approximately 19 rPa) in the 1760-1920 K range of temperatures during combined and separate heating of substrate and liquid phase. Surface tension and alloy density are measured within 1720-1890 K in helium atmosphere under pressure of 4 MPa. It is shown that difference in wetting of mono- and polycrystalline tungsten on (110) and (111) faces during separate heating in vacuum (1760 K) is in the limits of the experiment error: finite values of Ni-Fe-W alloy contact angles are equal to 1-3 deg independent of composition. Rates of coating of different types of tungsten with alloys of the composition given are also similar and fall with an increase of its content in a liquid phase. It is found that q=1-3 deg during polycrystalline tungsten wetting in the hydrogen atmosphere (1760 K) as well as in vacuum, however coating rates of all alloys are higher. Experiments on joint heating at temperatures 1760, 1820, 1870, 1920 K also confirm identity of wetting of monocrystalline tungsten of (111) and (110) faces and polycrystalline tungsten at all temperatures on all types of substrates q=1-3 deg.

  16. Moessbauer studies of superexchange interactions in NiFe sub 2 O sub 4

    CERN Document Server

    Kim, S J; Kim, C S; Lee, S W

    2000-01-01

    NiFe sub 2 O sub 4 has been studied using Moessbauer spectroscopy and X-ray diffraction. The crystal was found to have a inverse cubic spinel structure with the lattice constant a sub 0 =8.326+-0.003 A. Moessbauer spectra of NiFe sub 2 O sub 4 was obtained at various absorber temperatures from 13 K to the Neel temperature. The Moessbauer spectra consisted of two sets of six lines corresponding to Fe sup + sup 3 at the tetrahedral (A) and the octahedral (B) sites. The temperature dependence of the magnetic hyperfine fields at sup 5 sup 7 Fe nuclei at the tetrahedral (A) and the octahedral (B) sites was analyzed by the Neel theory of ferrimagnetism. The intersublattice A-O-B and intrasublattice A-O-A superexchange interactions were found to be antiferromagnetic with strengths of J sub A sub - sub B =-25.0 k sub B and J sub A sub - sub A =-4.0 K sub B , respectively, while the intrasublattice B-O-B superexchange interaction is ferromagnetic with a strength J sub B sub - sub B =4.2 k sub B.

  17. Isotopic fractionation associated with [NiFe]- and [FeFe]-hydrogenases

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Hui; Gandhi, Hasand; Cornish, Adam J.; Moran, James J.; Kreuzer, Helen W.; Ostrom, Nathaniel; Hegg, Eric L.

    2016-01-30

    Hydrogenases catalyze the reversible formation of H2 from electrons and protons with high efficiency. Understanding the relationships between H2 production, H2 uptake, and H2-H2O exchange can provide insight into the metabolism of microbial communities in which H2 is an essential component in energy cycling. In this manuscript, we used stable H isotopes (1H and 2H) to probe the isotope effects associated with three [FeFe]-hydrogenases and three [NiFe]-hydrogenases. All six hydrogenases displayed fractionation factors for H2 formation that were significantly less than 1, producing H2 that was severely depleted in 2H relative to the substrate, water. Consistent with differences in their active site structure, the fractionation factors for each class appear to cluster, with the three [NiFe]-hydrogenases (α = 0.27-0.40) generally having smaller values than the three [FeFe]-hydrogenases (α = 0.41-0.55). We also obtained isotopic fractionation factors associated with H2 uptake and H2-H2O exchange under conditions similar to those utilized for H2 production, providing us with a more complete picture of the three reactions catalyzed by hydrogenases. The fractionation factors determined in our studies can be used as signatures for different hydrogenases to probe their activity under different growth conditions and to ascertain which hydrogenases are most responsible for H2 production and/or uptake in complex microbial communities.

  18. Effect of Al addition on properties of TiNiFe shape memory alloys

    Institute of Scientific and Technical Information of China (English)

    XIAO Li; LIU Fu-shun; XU Hui-bin

    2006-01-01

    A little amount of aluminum substituting for Ni was added to Ti50Ni48Fe2 and Ti50Ni47.5Fe2.5 alloys to improve the mechanical properties, especially the yield stress of the TiNiFe alloys. The martensitic transformation temperature and mechanical properties of Ti50Ni48-xFe2Alx and Ti50Ni47.5-xFe2.5Alx (x=0, 0.5, 1) alloys were examined, and it was revealed that 0.5% and 1%(mole fraction) aluminum addition lead to about 10℃ and 60-80 ℃ martensitic transformation temperature (MS) decrease, respectively. 1%(mole fraction) aluminum addition enhances remarkably the yield stresses of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 to 560 and 580 MPa, respectively. The systemic microstructure analysis indicates that the second phase Ti2Ni at the grain boundaries plays an important role in improving the mechanical properties of TiNiFe shape memory alloys.

  19. Synthesis and characterization of NiFe2O4 electrocatalyst for the hydrogen evolution reaction in alkaline water electrolysis using different polymer binders

    Science.gov (United States)

    Chanda, Debabrata; Hnát, Jaromír; Paidar, Martin; Schauer, Jan; Bouzek, Karel

    2015-07-01

    NiFe2O4 electrocatalyst for the hydrogen evolution reaction (HER) has been synthesized using the co-precipitation method of the respective metal ions from water solution. After calcination of the precipitate, the resulting electrocatalyst was characterized by a broad range of techniques to obtain information on its crystallographic structure, specific surface area, morphology and chemical composition. The electrocatalytic activity towards HER in alkaline water electrolysis was investigated by means of linear sweep voltammetry. The catalyst showed promising electrocatalytic properties. Subsequently three types of binders were used to prepare a cathode catalytic layer based on a catalyst synthesized on top of a nickel foam support, namely an anion-selective quaternized poly(phenylene oxide) (qPPO) ionomer, an electroneutral polymer polytetrafluoroethylene and cation-selective Nafion®. The resulting membrane-electrode assemblies (MEAs), based on an anion-selective membrane, were tested in an alkaline water electrolyzer. In a single-cell test the MEA with a qPPO ionomer exhibited higher HER activity compared to the remaining binders tested. The current density obtained using a MEA containing qPPO binder attained a value of 125 mA cm-2 at a cell voltage of 1.85 V. The stability of the MEA containing qPPO binder was examined by continuous operation for 143 h, followed by 55 h intermittent electrolysis.

  20. Analysis of the influence of fuel on NiFe2O4 nanocrystalline obtained by solution combustion synthesis

    International Nuclear Information System (INIS)

    This paper investigates the effect of different fuels used on a structural properties stoichiometric composition of NiFe2O4 obtained from the combustion synthesis. Precursor solutions were prepared from iron nitrate nonahydrate and nickel nitrate hexahydrate, and complexing agents as maleic anhydride, oxalic acid and sucrose. The samples were characterized by X-ray diffraction to evaluate the presents phases, and crystallite size from single-line method, specific surface area (BET) and scanning electron microscopy (SEM) for morphological analysis of powders. The results indicate that NiFe2O4 can be obtained after heat treatment at 800 deg C with particle size of approximately 60nm. (author)

  1. Facile synthesis of Cu-Pd bimetallic multipods for application in cyclohexane oxidation

    Science.gov (United States)

    Zhang, Zhuo-Qun; Huang, Jianliu; Zhang, Lan; Sun, Mei; Wang, You-Cheng; Lin, Yue; Zeng, Jie

    2014-10-01

    The synergy between Cu and Pd makes Cu-Pd bimetallic nanocrystals interesting materials for investigation. The scarcity of shapes of Cu-Pd bimetallic nanocrystals motivated us to explore highly branched structures, which may promote a wide range of applications. In this communication, we report a facile synthesis of Cu-Pd bimetallic multipods (19.2 ± 1.2 nm), on branches of which some high-index facets were exposed. Modification of reaction parameters concerning capping agents and reductant led to the formation of other shapes, including sphere-like nanocrystals (SNCs). When loaded onto TiO2, the as-prepared Cu-Pd bimetallic multipods exhibited excellent catalytic activity for the oxidation of cyclohexane by hydrogen peroxide and higher selectivity towards cyclohexanone than monometallic catalysts and SNCs/TiO2.

  2. Facile synthesis of Cu-Pd bimetallic multipods for application in cyclohexane oxidation

    International Nuclear Information System (INIS)

    The synergy between Cu and Pd makes Cu-Pd bimetallic nanocrystals interesting materials for investigation. The scarcity of shapes of Cu-Pd bimetallic nanocrystals motivated us to explore highly branched structures, which may promote a wide range of applications. In this communication, we report a facile synthesis of Cu-Pd bimetallic multipods (19.2 ± 1.2 nm), on branches of which some high-index facets were exposed. Modification of reaction parameters concerning capping agents and reductant led to the formation of other shapes, including sphere-like nanocrystals (SNCs). When loaded onto TiO2, the as-prepared Cu-Pd bimetallic multipods exhibited excellent catalytic activity for the oxidation of cyclohexane by hydrogen peroxide and higher selectivity towards cyclohexanone than monometallic catalysts and SNCs/TiO2. (paper)

  3. Light-induced reactivation of O2-tolerant membrane-bound [Ni-Fe] hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus under turnover conditions.

    OpenAIRE

    Ciaccafava, Alexandre; Hamon, Cyrille; Infossi, Pascale; Marchi, Valérie; Giudici-Orticoni, Marie-Thérèse; Lojou, Elisabeth

    2013-01-01

    We report the effect of UV-Vis light on the membrane-bound [Ni-Fe] hydrogenase from Aquifex aeolicus under turnover conditions. Using electrochemistry, we show a potential dependent light sensitivity and propose that a light-induced structural change of the [Ni-Fe] active site is related to an enhanced reactivation of the hydrogenase under illumination at high potentials.

  4. Sonochemically synthesized mono and bimetallic Au-Ag reduced graphene oxide based nanocomposites with enhanced catalytic activity.

    Science.gov (United States)

    Neppolian, Bernaurdshaw; Wang, Chang; Ashokkumar, Muthupandian

    2014-11-01

    Graphene oxide (GO) supported Ag and Au mono-metallic and Au-Ag bimetallic catalysts were synthesized using a sonochemical method. Bimetallic catalysts containing different weight ratios of Au and Ag were loaded onto GO utilizing a low frequency horn-type ultrasonicator. High frequency ultrasonication was used to efficiently reduce Ag(I) and Au(III) ions in the presence of polyethylene glycol and 2-propanol. Transmission electron microscopy (TEM-EDX) and X-ray photoelectron spectroscopy were used to analyze the morphology, size, shape and chemical oxidation states of the prepared metallic catalysts on GO. The catalytic efficiency of the prepared catalysts were compared using 4-nitrophenol (4-NP) reduction reaction and the subsequent formation of 4-aminophenol (4-AP) that was also monitored using UV-vis spectrophotometry. The results revealed that Au-Ag-GO bimetallic catalysts showed high activity for the conversion of 4-NP to 4-AP than their monometallic counterparts. Amongst different weight ratios (1:1, 1:2 and 2:1) between Au and Ag, the 1:2 (Au:Ag) catalyst exhibited very good catalytic performance for the conversion of 4-NP to 4-AP. A total reduction of 4-NP took place within a short period of time if Au-GO was reduced first followed by Ag reduction, whereas a lower reduction rate was observed if Ag-GO was reduced first. The same trend was observed for all the ratios of bimetallic catalysts prepared by this method. The initial unfavorable reduction potential of Ag(I) is likely to be responsible for the above order. It was found that applying dual frequency ultrasonication was a highly effective way of preparing bimetallic catalysts requiring relatively low levels of added chemicals and producing bimetallic catalysts with GO with improved catalytic efficiency. PMID:24582660

  5. 铈对化学镀Ni-Fe-Co-P镀液及镀层性能的影响%Effects of Cerium on Electroless Ni-Fe-Co-P Bath and Properties of the Coating

    Institute of Scientific and Technical Information of China (English)

    贾瑛; 冯程; 张颖

    2012-01-01

    Based on the established bath of electroless Ni-Fe-Co-P plating, cerium nitrate was added to the bath, and a Ni-Fe-Co-P-Ce alloy coating was prepared on polyester fibers. The effects of the mass concentration of cerium nitrate on the deposition rate, surface morphology,composition,corrosion resistance of the coating were discussed,obtaining an optimal mass concentration as 0. 4 g/L.%在确定化学镀Ni-Fe-Co-P镀液配方的基础上,往镀液中加入硝酸铈,在涤沦织物上制备Ni-Fe-Co-P-Ce合金镀层.讨论了硝酸铈的质量浓度对镀层的沉积速率、表面形貌、成分及耐蚀性能等的影响,得出其最佳的质量浓度为0.4 g/L.

  6. Hierarchical SrTiO3/NiFe2O4 composite nanostructures with excellent light response and magnetic performance synthesized toward enhanced photocatalytic activity

    Science.gov (United States)

    Jing, Panpan; Du, Jinlu; Wang, Jianbo; Lan, Wei; Pan, Lining; Li, Jianan; Wei, Jinwu; Cao, Derang; Zhang, Xinlei; Zhao, Chenbo; Liu, Qingfang

    2015-08-01

    Being capable of gathering advanced optical, electrical and magnetic properties originating from different components, multifunctional composite nanomaterials have been of concern increasingly. Herein, we have successfully demonstrated the preparation of SrTiO3/NiFe2O4 porous nanotubes (PNTs) and SrTiO3/NiFe2O4 particle-in-tubes (PITs) via a single-spinneret electrospinning and a side-by-side-spinneret electrospinning, respectively. The products were characterized by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV-visible diffuse reflectance spectra and a vibrating sample magnetometer in detail. The results indicate that SrTiO3/NiFe2O4 PNTs are the heterojunction nanotubes by connecting perovskite SrTiO3 and spinel NiFe2O4 nanoparticles, but SrTiO3/NiFe2O4 PITs are the self-assembled core/shell structures by embedding SrTiO3 nanoparticles into NiFe2O4 nanotubes. Compared with pure SrTiO3 nanofibers, the two SrTiO3/NiFe2O4 composites exhibit a powerful light response and excellent room temperature ferromagnetism. The magnetic separations directly reveal that such amazing recycling efficiencies of about 95% for SrTiO3/NiFe2O4 PNTs and about 99.5% for SrTiO3/NiFe2O4 PITs are obtained. Furthermore, both the magnetic composites perform considerable photocatalytic activity in the degradation of rhodamine B. We propose that Kirkendall-diffusion and phase-separation are probably responsible for the formation of SrTiO3/NiFe2O4 PITs, and this work could provide a feasible way to assemble the core/shell structures of different materials.

  7. Hierarchical SrTiO3/NiFe2O4 composite nanostructures with excellent light response and magnetic performance synthesized toward enhanced photocatalytic activity.

    Science.gov (United States)

    Jing, Panpan; Du, JinLu; Wang, Jianbo; Lan, Wei; Pan, Lining; Li, Jianan; Wei, Jinwu; Cao, Derang; Zhang, Xinlei; Zhao, Chenbo; Liu, Qingfang

    2015-09-21

    Being capable of gathering advanced optical, electrical and magnetic properties originating from different components, multifunctional composite nanomaterials have been of concern increasingly. Herein, we have successfully demonstrated the preparation of SrTiO3/NiFe2O4 porous nanotubes (PNTs) and SrTiO3/NiFe2O4 particle-in-tubes (PITs) via a single-spinneret electrospinning and a side-by-side-spinneret electrospinning, respectively. The products were characterized by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV-visible diffuse reflectance spectra and a vibrating sample magnetometer in detail. The results indicate that SrTiO3/NiFe2O4 PNTs are the heterojunction nanotubes by connecting perovskite SrTiO3 and spinel NiFe2O4 nanoparticles, but SrTiO3/NiFe2O4 PITs are the self-assembled core/shell structures by embedding SrTiO3 nanoparticles into NiFe2O4 nanotubes. Compared with pure SrTiO3 nanofibers, the two SrTiO3/NiFe2O4 composites exhibit a powerful light response and excellent room temperature ferromagnetism. The magnetic separations directly reveal that such amazing recycling efficiencies of about 95% for SrTiO3/NiFe2O4 PNTs and about 99.5% for SrTiO3/NiFe2O4 PITs are obtained. Furthermore, both the magnetic composites perform considerable photocatalytic activity in the degradation of rhodamine B. We propose that Kirkendall-diffusion and phase-separation are probably responsible for the formation of SrTiO3/NiFe2O4 PITs, and this work could provide a feasible way to assemble the core/shell structures of different materials. PMID:26285104

  8. Formation of Magnetic Microstructure of the Nanosized NiFe2O4 Synthesized Via Solid-State Reaction

    Czech Academy of Sciences Publication Activity Database

    Žák, Tomáš; Ćosović, V.; Ćosović, A.; David, Bohumil; Talijan, N.; Živoković, D.

    2012-01-01

    Roč. 44, č. 1 (2012), s. 103-112. ISSN 0350-820X R&D Projects: GA ČR(CZ) GAP108/11/1350 Institutional support: RVO:68081723 Keywords : NiFe2O4 nanoparticles * Solid-state reaction * Phase composition * Magnetic properties Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.278, year: 2012

  9. Synthesis of porous NiFe2O4 microparticles and its catalytic properties for methane combustion

    International Nuclear Information System (INIS)

    Highlights: → Microporous NiFe2O4 spinel particles with uniform size of 1-2 μm was prepared by oxalic acid co-precipitation method. → The NiFe2O4 exhibits a good catalytic activity for methane combustion with the methane light-off temperature below 350 deg. C. → The excellent catalytic activity may be attributed to the surface oxygen vacancies arising from the peculiar inverse spinel structure with Oh site occupied by Fe2+ and Ni2+. - Abstract: In this paper, we report the obtention of agglomerate porous NiFe2O4 microparticles type-spinel with uniform size of 1-2 μm by the oxalic acid co-precipitation method. The structure, morphology and surface of microparticles as-synthesized were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), respectively. Fixed bed reactor test confirmed that the NiFe2O4 microparticles exhibit a good catalytic activity for methane combustion with the methane light-off temperature below 350 deg. C. XPS spectrum revealed that the excellent catalytic activity may be attributed to the surface oxygen vacancies arising from the peculiar inverse spinel structure with octahedral (Oh) site occupied by Fe2+ and Ni2+ cations.

  10. NiFe2O4 Spinel Protection Coating for High-Temperature Solid Oxide Fuel Cell Interconnect Application

    Science.gov (United States)

    Irankhah, Reza; Raissi, Babak; Maghsoudipour, Amir; Irankhah, Abdullah; Ghashghai, Sasan

    2016-04-01

    In the present study, Ni-Fe spinel powder was synthesized via a solid state reaction. In the next step, the electrophoretic deposition (EPD) method was used to apply the NiFe2O4 spinel, as an oxidation-resistant layer, on a commercially available stainless steel (SUS 430) in a potential range of 100 to 300 V. Microscopic studies of the deposited layers showed that crack-free NiFe2O4 films were obtained at 100 V. The coated and uncoated samples were then pre-sintered in air and 5% H2 bal Ar atmospheres at 900 °C for 3 h followed by cyclic oxidation at 800 °C for 500 h. The investigation of the oxidation resistance of the samples using Energy Dispersive Spectroscopy (EDS) revealed that the NiFe2O4 coating acted as an effective barrier against chromium migration into the coating. The oxidation resistance of 5% H2 bal Ar pre-sintered sample was enhanced with an oxidation rate constant ( K P) of 8.9 × 10-15 g2 cm-4 s-1.

  11. Microscopic domain structures in unidirectional and isotropic exchange-coupled NiO/NiFe bilayers

    International Nuclear Information System (INIS)

    The dependence on nickel oxide thickness in unidirectional and isotropic exchange-coupled NiO/NiFe bilayer films was investigated by magnetic force microscopy to better understand exchange biasing at microscopic length scales. As the NiO thickness increased, the domain structure of unidirectional biased films formed smaller and more complex in-plane domains. By contrast, for the isotropically coupled films, large domains generally formed with increasing NiO thickness including a new cross type domain with out-of-plane magnetization orientation. The density of the cross domain is proportional to exchange biasing field, and the fact that the domain mainly originated from the strongest exchange coupled region was confirmed by imaging in an applied external field during a magnetization cycle

  12. A ferromagnetic resonance study of NiFe alloy thin films

    Energy Technology Data Exchange (ETDEWEB)

    Diaz de Sihues, M. [Departamento de Fisica, Facultad de Ciencias, Universidad del Zulia, Apartado. Postal 526, Maracaibo 4001, Zulia (Venezuela); Durante-Rincon, C.A. [Departamento de Fisica, Facultad de Ciencias, Universidad del Zulia, Apartado. Postal 526, Maracaibo 4001, Zulia (Venezuela); Fermin, J.R. [Departamento de Fisica, Facultad de Ciencias, Universidad del Zulia, Apartado. Postal 526, Maracaibo 4001, Zulia (Venezuela)]. E-mail: jfermin@luz.edu.ve

    2007-09-15

    NiFe alloy films with thicknesses in the range from 60 to 150 A were sputtered onto Si (0 0 1) wafers by DC magnetron sputtering, and then characterized by in-plane ferromagnetic resonance technique (FMR) at x-band. The FMR field (H {sub R}) and linewidth ({delta}H) were studied as a function of the in-plane angle, {phi} {sub H}, film thickness, t, and temperature, T. The main effects of temperature on the magnetic properties of these films is to increase the in-plane uniaxial anisotropy and to induce a surface anisotropy that pushes the magnetization out-of-plane. These anisotropies were found to vary with thickness and temperature. The main processes that determine the line broadening are the intrinsic conduction mechanism and the in-plane uniaxial dispersions.

  13. Structural and magnetic properties of Ni/Fe nanostructures on Ir(111)

    Science.gov (United States)

    Iaia, Davide; Kubetzka, André; von Bergmann, Kirsten; Wiesendanger, Roland

    2016-04-01

    The structural and magnetic properties of one atomic layer thin nanostructures of Ni deposited on fcc Fe monolayer stripes on Ir(111) have been studied by (spin-resolved) scanning tunneling microscopy measurements. Ni grows dominantly in fcc stacking on Ir(111), whereas it forms a dense reconstruction pattern on Fe/Ir(111), with bridge site dislocation lines separating triangularly shaped fcc and hcp regions. In the interior of the Ni nanostructures, fcc and hcp areas are of comparable size, but the fcc stacking dominates at the edges. The magnetic nanoskyrmion lattice of Fe/Ir(111) undergoes a transition to ferromagnetism where covered with a single layer of Ni. The Ni/Fe bilayer islands show an out-of-plane easy axis and can be switched by external magnetic fields of only 1.0 T-1.5 T.

  14. Some features of Ni-Fe-Ga shape memory alloys under compression

    International Nuclear Information System (INIS)

    Three Ni-Fe-Ga ferromagnetic polycrystalline alloys having a martensitic transformation close to room temperature have been produced. Some results on their stress-strain behaviour under compression will be presented in this work. At temperatures below Af (finish of the reverse martensitic transformation), multiple steps in the stress-strain curves indicate the possibility of stress-induced martensite to martensite transformations. In this temperature domain, the critical stress to induce the variant reorientation and intermartensitic transformations is nearly temperature independent. In addition, the alloys show almost perfect strain recovery on unloading, that is the so-called rubber-like effect. As the temperature is increased (T>=Af) the multiple step stress-strain curves evolve to a single-step transformation corresponding to stress-induced martensite from the parent phase

  15. Fractographic features of W-Ni-Fe (90:7:3) alloy fractures. Review

    Energy Technology Data Exchange (ETDEWEB)

    Minakova, R.V.; Vojtenko, V.L.; Verkhovodov, P.A.; Nedelyaeva, L.P.; Kalinyuk, N.N. (AN Ukrainskoj SSR, Kiev. Inst. Problem Materialovedeniya)

    1985-02-01

    Fractographic peculiarities of W-Ni-Fe (90:7:3) alloy fractures are considered as well as their correlation with mechanical properties depending on thermal treatment conditions after liquid phase sintering and conditions of mechanical tests. It is shown that intergranular and transcrystallite failure of structural components occurs on the stages of crack formation and propagation. Tungsten-base refractory component may transcrystallitically fail forming fan and herring-bone patterns. Nickel-base ..gamma..-solid solution may fail transcrystallitically and on grain-colonies boundaries. The main failure varieties are established on boundaries of basic structural components. Their formation is associated with variation of adhesion strength of the boundary and geometry of ..gamma..-solid solution (grain body and near-boundary volumes) depending on conditions of thermal treatment after liquid phase sintering. It is shown that the greatest plasticity and strength at room temperature is peculiar for the alloy where transcrystallitic failure is predominant for both components.

  16. Interfacial Reactions Between In-Sn Solder and Ni-Fe Platings

    Science.gov (United States)

    Daghfal, John P.; Shang, P. J.; Liu, Z. Q.; Shang, J. K.

    2009-12-01

    Interfacial interactions in a Ni- xFe-Sn-In eutectic solder ( x = 30 at.%, 55 at.%) have been examined. Transmission and scanning electron microscopy (TEM/SEM) were utilized to investigate the structure, composition, and morphology of the intermetallic compounds (IMCs). Upon reflow, Ni3Sn4 and FeSn2 phases appeared at the interface along with Cu6Sn5 in the solder. Annealing experiments revealed the formation of a bilayer IMC that was Fe-rich adjacent to the Ni-Fe metallization and Ni-rich on the solder side. Kinetic studies established the apparent activation energies for both systems to be 51.8 kJ/mol and 85.1 kJ/mol, for 30 at.% and 55 at.% Fe contents, respectively. In the Fe-rich system, globular Ni3Sn4 crystals were formed upon reflow, but were changed into a cubic/faceted structure after annealing.

  17. Magnetic response of NiFe2O4 nanoparticles in polymer matrix

    International Nuclear Information System (INIS)

    We report the magnetic properties of magnetic nano-composite, consisting of different quantity of NiFe2O4 nanoparticles in polymer matrix. The nanoparticles exhibited a typical magnetization blocking, which is sensitive on the variation of magnetic field, mode of zero-field-cooled/field-cooled experiments and particle quantity in the matrix. The samples with lower particle quantity showed an upturn of magnetization down to 5 K, whereas the blocking of magnetization dominates at lower temperatures as the particle quantity increases in the polymer. We examine such magnetic behaviour in terms of the competitive magnetic ordering between core and surface spins of nanoparticles, taking into account the effect of inter-particle (dipole-dipole) interactions on nanoparticle magnetic dynamics.

  18. Magnetic response of NiFe{sub 2}O{sub 4} nanoparticles in polymer matrix

    Energy Technology Data Exchange (ETDEWEB)

    Poddar, A. [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Bhowmik, R.N. [Department of Physics, Pondicherry University, R. V. Nagar, Kalapet, Pondicherry 605014 (India)], E-mail: rnbhowmik.phy@pondiuni.edu.in; De, Amitabha [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Sen, Pintu [Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata 700064 (India)

    2009-07-15

    We report the magnetic properties of magnetic nano-composite, consisting of different quantity of NiFe{sub 2}O{sub 4} nanoparticles in polymer matrix. The nanoparticles exhibited a typical magnetization blocking, which is sensitive on the variation of magnetic field, mode of zero-field-cooled/field-cooled experiments and particle quantity in the matrix. The samples with lower particle quantity showed an upturn of magnetization down to 5 K, whereas the blocking of magnetization dominates at lower temperatures as the particle quantity increases in the polymer. We examine such magnetic behaviour in terms of the competitive magnetic ordering between core and surface spins of nanoparticles, taking into account the effect of inter-particle (dipole-dipole) interactions on nanoparticle magnetic dynamics.

  19. Synthesis and magnetic properties of multilayer Ni/Cu and NiFe/Cu nanowires

    Indian Academy of Sciences (India)

    R S Liu; S C Chang; I Baginskiy; S F Hu; C Y Huang

    2006-07-01

    Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm. The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer (VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices.

  20. Synthesis and characteristics of W-Ni-Fe nano-composite powders prepared by mechanical alloying

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The mixture of 90W-7Ni-3Fe(mass fraction, %) powders was milled in a planetary ball mill. Its structurechanged during milling, the surface characteristics and thermal stability of the milled powders were studied with X-raydiffraction(XRD), Brunaure-Emmett-Teller (BET) nitrogen adsorption technique and differential thermal analysis(DTA). The results show that high-energy ball milling leads to the formation of composite powders with amorphousbinder phase and supersaturated W(Ni, Fe) nano-crystalline grains in which great lattice distortion exists. The crystallization temperature of the amorphous binder phase during heating decreases with milling time. The specific surface area andthe pore size of the powder mixtures decreases with milling time due to agglomeration and welding hetween particles

  1. Chemically driven growth of tungsten grains during liquid phase sintering of W-Ni-Fe alloys

    International Nuclear Information System (INIS)

    In the alloys where the solid grains immersed in liquid matrix grow by Ostwald ripening process, the growth rate can be suddenly altered by changing the matrix composition. In this study, W-Ni-(Fe) specimens have been sintered and annealed at the temperatures around 15000C until the grains have coarsened, and then annealed further after adding Fe or Ni. After adding Fe or Ni and further annealing treatments, strong etching has revealed that a new solid phase in equilibrium with the changed matrix composition has been deposited preferentially on the larger grains. The smaller grains, which would be dissolving continuously, have maintained the old composition. This composition difference between the new solid phase on the larger grains and the old solid phase on the smaller ones can provide a driving force for grain coarsening in addition to that arising from the size difference. When Fe is added to sintered W-Ni, the grain coarsening rate during further annealing momentarily increases. The calculation shows that the molar free energy of the new solid phase should be lower than that of the old solid phase. Therefore, the solution reprecipitation process is ascelerated by this chemical free energy difference. If, on the other hand, Ni is added to sintered W-Ni-Fe, the coarsening rate decreases during further annealing. The calculation shows indeed that in this case the new solid phase should have higher molar free energy than the old. It is therefore demonstrated that if the matrix composition is altered during Ostwald ripening, the grain coarsening can be accelerated or retarded because of the chemical composition difference between the old grains and the newly precipitated solid phase on the larger grains. (author)

  2. Influence of Ti addition and sintering method on microstructure and mechanical behavior of a medium-entropy Al0.6CoNiFe alloy

    International Nuclear Information System (INIS)

    The influence of Ti addition and sintering method on the microstructure and mechanical behavior of a medium-entropy alloy, Al0.6CoNiFe alloy, was studied in detail. Alloying behavior, microstructure, phase evolution and mechanical properties of Al0.6CoNiFe and Ti0.4Al0.6CoNiFe alloys were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), as well as by mechanical testing. During the mechanical alloying (MA) process, a supersaturated solid solution consisting of both BCC and FCC phases was formed in the Al0.6CoNiFe alloy. With Ti addition, the Ti0.4Al0.6CoNiFe alloy exhibited a supersaturated solid solution with a single FCC phase. Following hot pressing (HP), the HP sintered (HP’ed) Al0.6CoNiFe bulk alloy was composed of a major BCC phase and a minor FCC phase. The HP’ed Ti0.4Al0.6CoNiFe alloy exhibited a FCC phase, two BCC phases and a trace unidentified phase. Nanoscale twins were present in the HP’ed Ti0.4Al0.6CoNiFe alloy, where deformation twins were observed in the FCC phase. Our results suggest that the addition of Ti facilitated the formation of nanoscale twins. The compressive strength and Vickers hardness of HP’ed Ti0.4Al0.6CoNiFe alloy were slightly lower than the corresponding values of the HP’ed Al0.6CoNiFe alloy. In contrast with HP’ed Al0.6CoNiFe alloy, spark plasma sintered (SPS’ed) Al0.6CoNiFe alloy exhibited a major FCC phase and a minor BCC phase. Moreover, the SPS’ed Al0.6CoNiFe alloy exhibited a lower compressive strength and Vickers hardness, but singificantly higher plasticity, as compared to those of the HP’ed counterpart material

  3. Kinetics and Mechanism of Carbon Tetrachloride Rapid Reduction by Nanoscale Ni-Fe Particles Using Scanning Electron Microscope%利用扫描电镜技术研究纳米Ni-Fe 颗粒对四氯化碳快速脱氯的机理

    Institute of Scientific and Technical Information of China (English)

    黄园英; 王倩; 韩子金; 刘菲

    2015-01-01

    for treatment of CT is the low yield of chlorinated by-product.Due to the presence of catalyst (Ni)on the surface,dechlorination rate was significantly increased and production of chlorinated byproducts was notably reduced.Catalytic metal Ni from the nanoscale Ni-Fe particles would not dissolve into water so that it would not form a secondary contamination of water body.The laboratory-synthesized nanoscale particles are quite stable under ambient conditions.For nano-scale Ni-Fe particles system, the end-product CH4 were reduced by 13% compared with nanoscale Pd-Fe particles.Although tnano-scale Pd-Fe particles are effective in dechlorination of chlorinated organic compounds,nano-scale Ni-Fe particles are more economically viable which made it possible for the large scale remediation of water and soil contaminated by chlorinated organic compounds.

  4. Effect of MnO2 on properties of NiFe2O4 spinel based inert anode

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    In order to improve the properties of NiFe2O4 spinel based inert anode, some additive MnO2 were added to raw materials. NiFe2O4 spinel with MnO2 was made by solid-phase reaction at 1200℃for 6 h. XRD were carried out and the effects of MnO2 on density, conductivity and corrosion resistance were measured. XRD shows when MnO2 was added no new phases exist and MnO2 and NiFe2O4 formed solid solution; Mn4+ replaced parts of Fe3+ and the sample still had the structure of NiFe2O4 spinel. The crystal lattice of NiFe2 O4 spinel became aberrated when MnO2 was added, which can promote sintering, and improve density. Because Mn4+ replaces parts of Fe3+ and produces conduction electron, which can improve conductivity.The corrosion resistance of the samples was enhanced. When MnO2 is 1.0%, the sample's corrosion rate is 1/5 of that of the sample without MnO2. The reason is that Al2 O3 in the melt reacts with Mn4+ in the sample to produce MnAl2O4. MnAl2 O4 forms a dense protecting coat, which can prevent melt from eroding further.Because the key problem with inert anodes is anode corrosion, so we consider the optimal amount of MnO2 is 1.0%.

  5. Methanol Oxidation on Model Elemental and Bimetallic Transition Metal Surfaces

    DEFF Research Database (Denmark)

    Tritsaris, G. A.; Rossmeisl, J.

    2012-01-01

    Direct methanol fuel cells are a key enabling technology for clean energy conversion. Using density functional theory calculations, we study the methanol oxidation reaction on model electrodes. We discuss trends in reactivity for a set of monometallic and bimetallic transition metal surfaces, fla...... active sites on the surface and to screen for novel bimetallic surfaces of enhanced activity. We suggest platinum copper surfaces as promising anode catalysts for direct methanol fuel cells....... and stepped, which includes platinum-based alloys with ruthenium, tin, and copper, as well as nonprecious alloys, overlayer structures, and modified edges. A common lower bound on the overpotential is estimated (ca. 0.3 V). A model for bifunctional alloys is employed to investigate the nature of the...

  6. Preparation and millimeter wave attenuation properties of NiFe{sub 2}O{sub 4}/expanded graphite composites by low-temperature combustion synthesis

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiong-biao; Zhu, Wen-feng; Wei, Xu; Zhang, Yao-xuan; Chen, Hou-he, E-mail: chhh42792@sina.cn

    2014-07-01

    Highlights: • NiFe{sub 2}O{sub 4}/EG composites are prepared by low-temperature combustion synthesis. • NiFe{sub 2}O{sub 4}/EG composites are uniform and have a good crystallinity. • The MMW attenuation performance was studied upon MMV radar measurement device. • NiFe{sub 2}O{sub 4}/EG composites exhibit better MMW attenuation properties than EG. • We report a simple synthesis route for the preparation of MMW attenuation composites. - Abstract: In this paper, NiFe{sub 2}O{sub 4}/expanded graphite (EG) composites are successfully prepared by low-temperature combustion synthesis method. The morphology, structure and millimeter wave (MMW) attenuation properties of the NiFe{sub 2}O{sub 4}/EG composites are investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and MMV radar measurement device. The effects of fuel and stoichiometric ratio on the composites are also investigated. The results show that NiFe{sub 2}O{sub 4}/EG composites are uniform and have a good crystallinity. The composites possess better MMW attenuation properties than EG. The 3 and 8 MMW attenuation performances of NiFe{sub 2}O{sub 4}/EG composites are 8.5 dB and 14.6 dB, respectively.

  7. Preparation and millimeter wave attenuation properties of NiFe2O4/expanded graphite composites by low-temperature combustion synthesis

    International Nuclear Information System (INIS)

    Highlights: • NiFe2O4/EG composites are prepared by low-temperature combustion synthesis. • NiFe2O4/EG composites are uniform and have a good crystallinity. • The MMW attenuation performance was studied upon MMV radar measurement device. • NiFe2O4/EG composites exhibit better MMW attenuation properties than EG. • We report a simple synthesis route for the preparation of MMW attenuation composites. - Abstract: In this paper, NiFe2O4/expanded graphite (EG) composites are successfully prepared by low-temperature combustion synthesis method. The morphology, structure and millimeter wave (MMW) attenuation properties of the NiFe2O4/EG composites are investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and MMV radar measurement device. The effects of fuel and stoichiometric ratio on the composites are also investigated. The results show that NiFe2O4/EG composites are uniform and have a good crystallinity. The composites possess better MMW attenuation properties than EG. The 3 and 8 MMW attenuation performances of NiFe2O4/EG composites are 8.5 dB and 14.6 dB, respectively

  8. Dendritic Pt-Cu bimetallic nanocrystals with a high electrocatalytic activity toward methanol oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Jintao; Ma Jizhen [Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576 (Singapore); Wan Yong [Institute of Multifunctional Materials (IMM), Laboratory of New Fiber Materials and Modern Textile, Growing Base for State Key Laboratory, Qingdao University, Qingdao 266071 (China); Jiang Jianwen [Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576 (Singapore); Zhao, X.S., E-mail: george.zhao@uq.edu.au [Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576 (Singapore); Institute of Multifunctional Materials (IMM), Laboratory of New Fiber Materials and Modern Textile, Growing Base for State Key Laboratory, Qingdao University, Qingdao 266071 (China)

    2012-02-15

    Highlights: Black-Right-Pointing-Pointer Dendritic Pt-Cu bimetallic nanocrystals were synthesized by one-step aqueous-phase reduction. Black-Right-Pointing-Pointer The formation process of dendritic Pt-Cu bimetallic nanocrystals can be carried out under mild conditions. Black-Right-Pointing-Pointer The dendritic Pt-Cu bimetallic nanocrystals exhibited a higher catalytic activity toward the electro-oxidation of methanol than commercial Pt/C catalysts. Black-Right-Pointing-Pointer The new findings are of fundamental importance to the development of high-performance electrocatalysts for direct methanol fuel cell. - Abstract: Dendritic Pt-Cu bimetallic nanocrystals were synthesized by one-step aqueous-phase reduction of H{sub 2}PtCl{sub 6} and CuCl{sub 2} at a mild temperature (60 Degree-Sign C). The morphology and composition of the dendritic Pt-Cu nanocrystals were characterized by means of high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectrometer. The electrochemical properties were characterized by the cyclic voltammetry technique. It was found that the dendritic Pt-Cu bimetallic nanocrystals exhibited a higher catalytic activity toward the electro-oxidation of methanol than commercial Pt/C catalyst The enhanced catalytic activity would be contributed to the unique dendritic structure and the formation of Pt-Cu alloy nanocrystals.

  9. Magnetically Recoverable Supported Ruthenium Catalyst for Hydrogenation of Alkynes and Transfer Hydrogenation of Carbonyl Compounds

    Science.gov (United States)

    A ruthenium (Ru) catalyst supported on magnetic nanoparticles (NiFe2O4) has been successfully synthesized and used for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The cata...

  10. Roughness development in electrodeposited soft magnetic CoNiFe films in the presence of organic additives

    Directory of Open Access Journals (Sweden)

    STEVE RIEMER

    2003-05-01

    Full Text Available The effects of three additives, sodium lauryl sulfate (NaLS, saccharin (Sacc, and NaLS + Sacc, on roughness development during the electrodeposition of CoNiFe films were investigated. The characterization of these films by atomic force microscopy shows that the electrodeposits produced from NaLS containing solution result in a rough surface. The role of NaLS surfactant is to change the interfacial tension and clean non-polar species like hydrogen bubbles from the surface. In Sacc containing solution, the evolution of a smooth surface is controlled by adsorbed Sacc molecule at the interface. The kinetic roughening of these deposits was investigated by dynamic scaling analysis. It was demonstrated that the roughness of CoNiFe films, obtained in the presence of NaLS + Sacc additives, was also dependent on current density, roughness of substrate, and the temperature of plating bath.

  11. Magnetic and structural properties of NiFe 2O 4 ferrite nanopowder doped with Zn 2+

    Science.gov (United States)

    Costa, A. C. F. M.; Silva, V. J.; Cornejo, D. R.; Morelli, M. R.; Kiminami, R. H. G. A.; Gama, L.

    This work involved an investigation to ascertain how the substitution of nickel ions for zinc ions affects the structural, morphological and magnetic properties of NiFe 2O 4 ferrite samples. Ni 1-xZn xFe 2O 4 ( x=0.0, 0.3 0.5, 0.7) powders were prepared by combustion reaction and characterized structurally by X-ray diffraction. The specific surface area of the powders was determined by the nitrogen adsorption method (BET). Magnetization measurements were taken using an alternative gradient magnetometer (AGM), which revealed that the powders prepared by combustion reaction resulted in nanosized particles with a particle size of 18-27 nm. The crystallite size and lattice parameter increased as the concentration of Zn increased. Moreover, augmenting the Zn content in the NiFe 2O 4 ferrite increased the saturation magnetization and coercive field.

  12. Giant magneto-impedance and low-frequency magneto-resistance effect in NiFeB coated composite wires

    Institute of Scientific and Technical Information of China (English)

    YUAN Wangzhi; WANG Xinzheng; ZHAO Zhenjie; RUAN Jianzhong; LI Xiaodong; YANG Xielong

    2004-01-01

    Composite wires of 100 μm insulated CuBe wire plated with a layer of NiFeB were produced by electroless-deposition, and their magnetic properties were studied. The results showed that a good magneto-impedance (MI) effect can be obtained at relatively low frequency. The largest MI ratio (△Z/Z)max obtained is 250% at 500 kHz. Magneto-resistance effect was also observed at low frequency, with the (△R/R)max observed to be -8.5% at 540 Hz and 38.7% at 10 kHz. Results are discussed, and the equivalent resistance and inductance as the result of the NiFeB layer are taken into account.

  13. SIMULATION OF THE MAGNETIZATION REVERSAL PROCESS OF RECTANGLE-SHAPED NiFe FILM ELEMENTS UNDER AN ORTHOGONAL MAGNETIC FIELD

    Institute of Scientific and Technical Information of China (English)

    W.L. Zhang; R.J. Tang; W.X. Zhang; B. Peng; H.C. Jiang; H. W. Zhang

    2005-01-01

    The magnetization reversal process of nano-size rectangle-shaped NiFe film elements with different aspect ratios have been investigated under the orthogonally applied magnetic fields by micromagnetic simulation. Different magnetization reversal modes can appear depending on whether the bias field is applied or not. When there is no bias field, double "C" state is the initial reversal state. However, when there is a bias field, "S" state is the starting mode. The larger the aspect ratio is, the larger the switching field is. But, when the aspect ratio is larger than 3, the increase of the switching field ceases. These results can provide useful information to the application of the patterned NiFe film with rectangular elements.

  14. Electrodeposited Ni,Fe,Co and Cu single and multilayer nanowire arrays on anodic aluminum oxide template

    Institute of Scientific and Technical Information of China (English)

    Bobomurod HAMRAKULOV; In-Soo KIM; M.G.LEE; B.H.PARK

    2009-01-01

    The Ni, Fe, Co and Cu single and multilayer nanowire arrays to make perpendicular magnetic recording media were fabricated with nanoporous anodic aluminum oxide (AAO) templates from Watt solution and additives by the DC electrodeposition. The results show that the diameters of Ni, Fe, Co and Cu single and multilayer nanowires in AAO templates are 40-80 nm and the lengths are about 30 μm with the aspect ratio of 350-750. The magnetic properties of the prepared nanowires are different under different electrodepositing conditions. The remanences (Br) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires, and coercivity (Hc) of Ni/Cu/Fe multilayer nanowires are lower than those of others multilayer nanowires. These are compatible with the required conditions of high density magnetic media devices that should have the low coercivity to easily success magnetization and high remanence to keep magnetization after removal of magnetic field.

  15. Effect of CaO doping on mechanical properties and thermal shock resistance of 10NiO-NiFe2O4 composite ceramics

    Institute of Scientific and Technical Information of China (English)

    LAI Yan-qing; ZHANG Yong; ZHANG Gang; TIAN Zhong-liang; LI Jie

    2008-01-01

    The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance of 10NiO-NiFe2O4 composite ceramics were studied. The results show that the samples mainly consist of NiO and NiFe2O4 when content of CaO is less than4%(mass fraction), bending strength increases obviously by CaO doping. Bending strength of the samples doped with 2% CaO is above 185 Mpa, but that of the samples without CaO is only 60 Mpa. Fracture toughness is improved obviously by CaO doping, the undoped ceramics. CaO doping is bad to thermal shock resistance of 10NiO-NiFe2O4 composite ceramics.

  16. Study on sintering technique of NiFe2O4/SiCp used as matrix of inert anodes in aluminium electrolysis

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    In order to improve deficiencies of NiFe2O4 spinel used as matrix of inert anode in aluminium electrolysis, NiFe2O4/SiCp were prepared by the solid state reaction for the first time. Microstructural changes were observed by scanning electronic microscope and phase was determined with X-ray detector. Effect of sintering temperature and times on density, porosity and microstructure were researched, and the reasons that caused the difference were discussed deeply. At the same time the thermodynamical compatibility of NiFe2O4 and SiC was proved under 1200℃ by DTA.The results showed that the microstructure was more homogeneous when the sintering temperature reached 1 180℃and the density attained their maximum about 6 h sintering. The appropriate sintering technique of NiFe2 O4/SiCw composite materials was 1180℃× 6 h.

  17. Platinum-cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfural

    Science.gov (United States)

    Wang, Guang-Hui; Hilgert, Jakob; Richter, Felix Herrmann; Wang, Feng; Bongard, Hans-Josef; Spliethoff, Bernd; Weidenthaler, Claudia; Schüth, Ferdi

    2014-03-01

    The synthesis of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) is a highly attractive route to a renewable fuel. However, achieving high yields in this reaction is a substantial challenge. Here it is described how PtCo bimetallic nanoparticles with diameters of 3.6 ± 0.7 nm can solve this problem. Over PtCo catalysts the conversion of HMF was 100% within 10 min and the yield to DMF reached 98% after 2 h, which substantially exceeds the best results reported in the literature. Moreover, the synthetic method can be generalized to other bimetallic nanoparticles encapsulated in hollow carbon spheres.

  18. NiFe{sub 2}O{sub 4}/activated carbon nanocomposite as magnetic material from petcoke

    Energy Technology Data Exchange (ETDEWEB)

    Briceño, Sarah, E-mail: sbriceno@ivic.gob.ve [Laboratorio de Física de la Materia Condensada, Centro de Física, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 20632, Caracas 1020-A (Venezuela, Bolivarian Republic of); Brämer-Escamilla, W., E-mail: wbramer@ivic.gob.ve [Laboratorio de Física de la Materia Condensada, Centro de Física, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 20632, Caracas 1020-A (Venezuela, Bolivarian Republic of); Silva, P. [Laboratorio de Física de la Materia Condensada, Centro de Física, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 20632, Caracas 1020-A (Venezuela, Bolivarian Republic of); García, J.; Del Castillo, H.; Villarroel, M. [Laboratorio de Cinética y Catálisis, Departamento de Química, Facultad de Ciencias, Universidad de Los Andes ULA, Mérida 5101-A (Venezuela, Bolivarian Republic of); Rodriguez, J.P. [Laboratorio de Microscopia Electrónica. Instituto de Estudios Científicos y Tecnológicos IDECYT. Apartado 47925 - Caracas 1041-A (Venezuela, Bolivarian Republic of); Ramos, M.A.; Morales, R. [Instituto Zuliano de Investigaciones Tecnológicas INZIT. Apdo. Postal 331. La Cañada-Maracaibo (Venezuela, Bolivarian Republic of); Diaz, Y. [Centro de Química, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 20632, Caracas 1020-A (Venezuela, Bolivarian Republic of)

    2014-06-01

    Nickel ferrite (NiFe{sub 2}O{sub 4}) was supported on activated carbon (AC) from petroleum coke (petcoke). Potassium hydroxide (KOH) was employed with petcoke to produce activated carbon. NiFe{sub 2}O{sub 4} were synthesized using PEG-Oleic acid assisted hydrothermal method. The structural and magnetic properties were determined using thermogravimetric and differential thermal analysis (TGA–DTA), X-ray diffraction (XRD), Fourier Transform Infrared (IR-FT), surface area (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). XRD analysis revealed the cubic spinel structure and ferrite phase with high crystallinity. IR-FT studies showed that chemical modification promoted the formation of surface oxygen functionalities. Morphological investigation by SEM showed conglomerates of spherical nanoparticles with an average particle size of 72 nm and TEM showed the formation of NiFe{sub 2}O{sub 4}/carbon nanofibers. Chemical modification and activation temperature of 800 °C prior to activation dramatically increased the BET surface area of the resulting activated carbon to 842.4 m{sup 2}/g while the sulfur content was reduced from 6 to 1%. Magnetic properties of nanoparticles show strong dependence on the particle size. - Highlights: • TEM showed the formation of NiFe{sub 2}O{sub 4}/carbon nanofibers. • Nanoparticles were supported on the activated carbon from petcoke. • Activation dramatically increased the BET surface area to 842 m{sup 2}/g. • Magnetic properties show strong dependence on the particle size. • Sulphur content was reduced from 6 to 1% with the petcoke activation.

  19. Nano and picosecond magnetization dynamics of weakly coupled CoFe/Cr/NiFe trilayers studied by a multitechnique approach

    OpenAIRE

    Kaiser, A. M.; Schoppner, C.; Schneider, C. M.; Romer, F.M.; Hassel, C.; Wiemann, C; Cramm, S.; Nickel, F.; Grychtol, P..; Tieg, C.; Lindner, J.

    2011-01-01

    We present results on the magnetization dynamics in heterostructures of the CoFe/Cr/NiFe type. We have employed a combination of different layer-selective methods covering a broad range from quasistatic hysteresis measurements by x-ray magnetic circular dichroism (XMCD), over time-resolved photoemission electron microscopy (PEEM) at subnanosecond timescales to high-frequency ferromagnetic resonance (FMR) experiments. With increasing driving frequency, we found a different influence of the cou...

  20. Synthesis and characterization of multilayered BaTiO3/NiFe2O4 thin films

    Directory of Open Access Journals (Sweden)

    Branimir Bajac

    2013-03-01

    Full Text Available Presented research was focused on the fabrication of multiferroic thin film structures, composed of ferrielectric barium titanate perovskite phase and magnetostrictive nickel ferrite spinel phase. The applicability of different, solution based, deposition techniques (film growth from solution, dip coating and spin coating for thefabrication of multilayered BaTiO3 /NiFe2O4 thin films was investigated. It was shown that only spin coating produces films of desired nanostructure, thickness and smooth and crackfree surfaces.

  1. Anodic behaviour of oxidised Ni-Fe alloys in cryolite-alumina melts

    Energy Technology Data Exchange (ETDEWEB)

    Chapman, Vivien, E-mail: v.singleton@student.unsw.edu.a [Centre for Electrochemical and Mineral Processing, School of Chemical Engineering, University of New South Wales, Sydney 2052 (Australia); Welch, Barry J. [Welbank Consulting Ltd., PO Box 207, Whitianga 3542 (New Zealand); Skyllas-Kazacos, Maria [Centre for Electrochemical and Mineral Processing, School of Chemical Engineering, University of New South Wales, Sydney 2052 (Australia)

    2011-01-01

    Nickel-iron alloys have been identified as promising inert anode candidates for the Hall-Heroult process. In this study, binary Ni-Fe alloys of various compositions were subjected to short-term galvanostatic electrolysis in a cryolite-alumina bath at 960 {sup o}C. Prior to electrolysis, the anodes were oxidised at 800 {sup o}C for 48 h, forming a protective scale. Fe{sub 2}O{sub 3}, Ni{sub x}Fe{sub 3-x}O{sub 4} and Ni{sub x}Fe{sub 1-x}O were identified as the major scale components using a combination of X-ray diffraction (XRD) analysis and energy dispersive X-ray spectroscopy (EDX). Anodes having Ni content of 50-65 wt% performed adequately during short-term electrolysis, operating at a steady potential of 3-3.5 V vs. AlF{sub 3}/Al. Overall, it was found that the pre-formed oxide scale was effective in reducing anode wear and fluoridation. In the absence of a pre-formed scale, anodes were shown to undergo appreciable internal corrosion and/or passivation due to metal fluoride formation. Analysis of the anodes following electrolysis was performed using XRD and electron microprobe analysis (EPMA).

  2. Magnetic characteristics of a high-layer-number NiFe/FeMn multilayer

    Science.gov (United States)

    Paterson, G. W.; Gonçalves, F. J. T.; McFadzean, S.; O'Reilly, S.; Bowman, R.; Stamps, R. L.

    2015-11-01

    We report the static and dynamic magnetic characteristics of a high-layer-number NiFe/FeMn multilayer test structure with potential applications in broadband absorber and filter devices. To allow fine control over the absorption linewidths and to understand the mechanisms governing the resonances in a tailored structure similar to that expected to be used in real world applications, the multilayer was intentionally designed to have layer thickness and interface roughness variations. Magnetometry measurements show that the sample has complex hysteresis loops with features consistent with single ferromagnetic film reversals. Characterisation by transmission electron microscopy allows us to correlate the magnetic properties with structural features, including the film widths and interface roughnesses. Analysis of resonance frequencies from broadband ferromagnetic resonance measurements as a function of field magnitude and orientation provide values of the local exchange bias, rotatable anisotropy, and uniaxial anisotropy fields for specific layers in the stack and explain the observed mode softening. The linewidths of the multilayer are adjustable around the bias field, approaching twice that seen at larger fields, allowing control over the bandwidth of devices formed from the structure.

  3. Cubic superparamagnetic nanoparticles of NiFe2O4 via fast microwave heating

    International Nuclear Information System (INIS)

    This study demonstrated the possibility of using microwave heating as a fast and cheap method for synthesizing superparamagnetic nanoparticles. In this sense, NiFe2O4 samples were subjected to microwave heating at various temperatures to determine the lowest temperature at which the crystalline phase of the nanoparticles occurs. X-Ray powder diffraction, 57Fe Mössbauer spectroscopy, and transmission electron microscopy of the samples were performed to confirm the formed nanoparticles. It was observed a cubic structure of inverse spinel type with good crystallinity. The magnetic properties of the samples were studied using a vibrating sample magnetometer and was found to zero values to remanent magnetization and coercivity field. This behavior suggests superparamagnetic features for all samples. The crystallite size (9, 10, and 12 nm) and saturation magnetization (31–45 emu/g) were used as a function of the increase of the temperature treatment time. Blocking temperature was found by tracing remanent magnetization versus temperature

  4. Enhanced magnetization and conductive phase in NiFe2O4

    International Nuclear Information System (INIS)

    Recent advances on nanometer films observed magnetization enhanced NiFe2O4 (NFO) in insulating phase as well as in conductive state with highly spin-polarized current which together can be integrated for potential applications in spintronics. In this brief report, we demonstrate, using density-functional-based calculations, how various cation distributions and magnetic orders can lead to a quadruple enhanced magnetization in NFO and the possible tuning of their electronic properties. The ground-state phase was identified as a structure having a tetragonal symmetry space group of P4322 which is consistent with the most recent experimental conclusion. The energetically most likely phase exhibiting enhanced magnetization is an insulating inverse spinel phase while the experimentally observed conductive phase likely originates from a phase with cation inversion. - Highlights: ► Density-functional-based calculations were used to study Ni ferrite. ► The ground-state structure is shown to have P4322 tetragonal group. ► The most probable magnetization enhanced phase is an insulating inverse spinel phase. ► Only the normal spinel phases show metallic property.

  5. Microstructure Modeling of a Ni-Fe-Based Superalloy During the Rotary Forging Process

    Science.gov (United States)

    Loyda, A.; Hernández-Muñoz, G. M.; Reyes, L. A.; Zambrano-Robledo, P.

    2016-06-01

    The microstructure evolution of Ni-Fe superalloys has a great influence on the mechanical behavior during service conditions. The rotary forging process offers an alternative to conventional bulk forming processes where the parts can be rotary forged with a fraction of the force commonly needed by conventional forging techniques. In this investigation, a numerical modeling of microstructure evolution for design and optimization of the hot forging operations has been used to manufacture a heat-resistant nickel-based superalloy. An Avrami model was implemented into finite element commercial platform DEFORM 3D to evaluate the average grain size and recrystallization during the rotary forging process. The simulations were carried out considering three initial temperatures, 980, 1000, and 1050 °C, to obtain the microstructure behavior after rotary forging. The final average grain size of one case was validated by comparing with results of previous experimental work of disk forging operation. This investigation was aimed to explore the influence of the rotary forging process on microstructure evolution in order to obtain a homogenous and refined grain size in the final component.

  6. Magnetic characteristics of a high-layer-number NiFe/FeMn multilayer

    International Nuclear Information System (INIS)

    We report the static and dynamic magnetic characteristics of a high-layer-number NiFe/FeMn multilayer test structure with potential applications in broadband absorber and filter devices. To allow fine control over the absorption linewidths and to understand the mechanisms governing the resonances in a tailored structure similar to that expected to be used in real world applications, the multilayer was intentionally designed to have layer thickness and interface roughness variations. Magnetometry measurements show that the sample has complex hysteresis loops with features consistent with single ferromagnetic film reversals. Characterisation by transmission electron microscopy allows us to correlate the magnetic properties with structural features, including the film widths and interface roughnesses. Analysis of resonance frequencies from broadband ferromagnetic resonance measurements as a function of field magnitude and orientation provide values of the local exchange bias, rotatable anisotropy, and uniaxial anisotropy fields for specific layers in the stack and explain the observed mode softening. The linewidths of the multilayer are adjustable around the bias field, approaching twice that seen at larger fields, allowing control over the bandwidth of devices formed from the structure

  7. Microstructure and magnetic properties of micro NiFe alloy arrays for MEMS application

    International Nuclear Information System (INIS)

    NiFe alloy arrays with various geometry sizes and shapes were designed, fabricated and investigated. Electrodeposition was introduced as a highly effective integrated method to fabricate the alloy film. The influence of dimensional size and geometry shape of the array unit was discussed. With decreasing size, the soft magnetic properties of the samples are improved with a 78.6% decrease of coercivity and an 65.0% decrease of squareness ratio. Compared with square and rectangular arrays, circular arrays exhibit smaller coercivity, higher permeability and smaller squareness ratio. Additionally, different compositional arrays were also tested for their crystal structures. It is found that the alloy with a content of Ni80Fe20 can achieve a face-centered cubic structure and realize the best soft magnetic properties. A coercivity of 0.383 Oe, a squareness ratio of 4.21 × 10−4 and a saturation magnetization of 4.2 T have been successfully achieved in circular arrays within an area of 2000 × 2000 µm2. (paper)

  8. Combustion synthesis and characterization of Sn4+ substituted nanocrystalline NiFe2O4

    International Nuclear Information System (INIS)

    A series of Sn4+ substituted NiFe2O4 with general formula Ni1-xSn xFe2O4 (x = 0.0, 0.2, 0.4, 0.6, and 0.8) has been prepared by novel combustion synthetic method. The prepared compounds have been sintered at 1000 deg. C and evaluated for their structural and electrical properties. XRD studies reveal the synthesized compounds are nanocrystalline size with cubic structure. The Fourier transform infrared (FT-IR) spectra show the characteristic features of the synthesized ferrite compounds. The UV-vis spectra reveal the optical band gap of the synthesized compounds. The dc electrical conductivity of the compounds found to increase with increasing measuring temperature. A maximum dc electrical conductivity of 6.0 S cm-1 was obtained at a measuring temperature of 1000 deg. C in the composition of x = 0.8, for which the activation energy for conduction is found to be minimum

  9. Current induced magnetization switching in Co/Cu/Ni-Fe nanopillar with orange peel coupling

    Energy Technology Data Exchange (ETDEWEB)

    Aravinthan, D.; Daniel, M. [Centre for Nonlinear Dynamics, School of Physics, Bharathidasan University, Tiruchirappalli - 620 024 (India); Sabareesan, P. [Centre for Nonlinear Science and Engineering, School of Electrical and Electronics Engineering, SASTRA University, Thanjavur - 613 401 (India)

    2015-07-15

    The impact of orange peel coupling on spin current induced magnetization switching in a Co/Cu/Ni-Fe nanopillar device is investigated by solving the switching dynamics of magnetization of the free layer governed by the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation. The value of the critical current required to initiate the magnetization switching is calculated analytically by solving the LLGS equation and verified the same through numerical analysis. Results of numerical simulation of the LLGS equation using Runge-Kutta fourth order procedure shows that the presence of orange peel coupling between the spacer and the ferromagnetic layers reduces the switching time of the nanopillar device from 67 ps to 48 ps for an applied current density of 4 × 10{sup 12}Am{sup −2}. Also, the presence of orange peel coupling reduces the critical current required to initiate switching, and in this case, from 1.65 × 10{sup 12}Am{sup −2} to 1.39 × 10{sup 12}Am{sup −2}.

  10. Anodic behaviour of oxidised Ni-Fe alloys in cryolite-alumina melts

    International Nuclear Information System (INIS)

    Nickel-iron alloys have been identified as promising inert anode candidates for the Hall-Heroult process. In this study, binary Ni-Fe alloys of various compositions were subjected to short-term galvanostatic electrolysis in a cryolite-alumina bath at 960 oC. Prior to electrolysis, the anodes were oxidised at 800 oC for 48 h, forming a protective scale. Fe2O3, NixFe3-xO4 and NixFe1-xO were identified as the major scale components using a combination of X-ray diffraction (XRD) analysis and energy dispersive X-ray spectroscopy (EDX). Anodes having Ni content of 50-65 wt% performed adequately during short-term electrolysis, operating at a steady potential of 3-3.5 V vs. AlF3/Al. Overall, it was found that the pre-formed oxide scale was effective in reducing anode wear and fluoridation. In the absence of a pre-formed scale, anodes were shown to undergo appreciable internal corrosion and/or passivation due to metal fluoride formation. Analysis of the anodes following electrolysis was performed using XRD and electron microprobe analysis (EPMA).

  11. Irradiation-induced softening of Ni3P and (Ni, Fe, Cr)3P alloys

    International Nuclear Information System (INIS)

    Production of amorphous alloys by solid state reactions (SSR) has attracted much interest during the last few years. One of the methods to induce such a reaction is the irradiation of suitable crystalline alloys by fast particles. Examination of this kind of SSR in M3P type of brazing alloys (M: Metal) is attractive because of the following reason: In brazed joints of candidate structural materials like 316L stainless steel for applications in fusion reactors, crystalline intermetallic phases have been detected which are unstable relative to the amorphous state when irradiated at moderate temperatures with fast particles. It is expected that the transition to the amorphous state is accompanied by changes of the mechanical properties, which are of fundamental interest in this context. Until now, only a few studies on the evolution of mechanical properties during amorphization have been performed. Measurements of microhardness of the crystalline and the corresponding amorphous phase do not exist to the authors knowledge. In this communication, the authors present results on changes of microhardness, due to amorphization by fast ions. The measurements have been performed on a model alloy Ni3P and on the brazed joint of stainless steel 316L, containing M3P (M: Ni, Fe, Cr) as one of the phases. Though microhardness is not a fundamental property of materials, it is a manifestation of several related properties, such as yield stress, ductility, work-hardening, elastic modulus and residual stress states. It represents a resistance for indentation and is, therefore, appropriate for comparative purposes

  12. Light-induced reactivation of O2-tolerant membrane-bound [Ni-Fe] hydrogenase from the hyperthermophilic bacterium Aquifex aeolicus under turnover conditions.

    Science.gov (United States)

    Ciaccafava, Alexandre; Hamon, Cyrille; Infossi, Pascale; Marchi, Valérie; Giudici-Orticoni, Marie-Thérèse; Lojou, Elisabeth

    2013-10-21

    We report the effect of UV-Vis light on the membrane-bound [Ni-Fe] hydrogenase from Aquifex aeolicus under turnover conditions. Using electrochemistry, we show a potential dependent light sensitivity and propose that a light-induced structural change of the [Ni-Fe] active site is related to an enhanced reactivation of the hydrogenase under illumination at high potentials. PMID:23999766

  13. Evaluation of Kinetic and Equilibrium Parameters of NiFe2O4 Nanoparticles on Adsorption of Reactive Orange Dye from Water

    Directory of Open Access Journals (Sweden)

    Raziyeh Zandipak

    2016-02-01

    Full Text Available Background: Among different pollutants released into the environment, dyes are considered as one of the most dangerous contaminants. In recent years, magnetic nanomaterials have attracted much attention for their dye removal capacity. The aim of this study was to explore the adsorption kinetics of an anionic dye (Reactive Orange 13 (RO by NiFe2O4 nanoparticles (NiFe2O4 NPs under various conditions. Methods: NiFe2O4 nanoparticles (NiFe2O4 NPs were prepared and characterized by X-ray diffraction (XRD, transmission electronic microscopy (TEM, pHpzc and BET methods. The adsorption characteristics of the NiFe2O4 NPs adsorbent were examined using Reactive Orange 13 as an adsorbate. The influences of parameters including pH, dose of adsorbent and contact time were investigated to find the optimum adsorption conditions. Results: Decreasing solution pH and increasing contact time were favorable for improving adsorption efficiency. The kinetic and isotherm data of RO adsorption on NiFe2O4 NPs were well fitted by pseudo-second-order and Langmuir models, respectively. Conclusion: The maximal adsorption capacity of RO was 243.9 mg g-1 at 25◦C and pH 3.0 and the adsorption of RO on the NiFe2O4 NPs follows a monolayer coverage model. NiFe2O4 NPs might be an effective and potential adsorbent for removing anionic dyes from aqueous solutions.

  14. High performance NiFe layered double hydroxide for methyl orange dye and Cr(VI) adsorption.

    Science.gov (United States)

    Lu, Yi; Jiang, Bin; Fang, Liang; Ling, Faling; Gao, Jiemei; Wu, Fang; Zhang, Xihua

    2016-06-01

    The NiFe layered double hydroxides (LDHs) with different mole ratio of Ni/Fe (4:1, 3:1, 7:3 and 1:1) were prepared by a simple coprecipitation method. The adsorption performance were evaluated by the removal of methyl orange (MO) dye and hexavalent chromium(VI) heavy metal ion. It is found that Ni4Fe1-LDH can remove more than 92% of MO in 10 min at the 10 mg/L MO initial concentration, and 97% of Cr(VI) in 1 h at 4 mg/L Cr2O7(2-) initial concentration. The saturated adsorption capacity of Ni4Fe1-LDH is found to be as large as 205.76 mg/g for MO and 26.78 mg/g for Cr(VI). The adsorption behavior of this new adsorbent is fitted well with Langmuir isotherm and the pseudo-second-order kinetic model, indicative of a monolayer and chemical adsorption that synergistically originates from exchangeable anions mechanism and layer charge density. Due to the excellent removal capacity of MO and Cr(VI), the NiFe-LDHs could be a promising adsorbent for wastewater treatment. PMID:26999751

  15. Surface structure and catalytic activity of electrodeposited Ni-Fe-Co-Mo alloy electrode by partially leaching Mo and Fe

    Institute of Scientific and Technical Information of China (English)

    LUO Bei-ping; GONG Zhu-qing; REN Bi-ye; YANG Yu-fang; CHEN Meng-jun

    2006-01-01

    Ni-Fe-Mo-Co alloy electrode was prepared in a citrate solution by electrodeposition, and then Mo and Fe were partially leached out from the electrode in 30% KOH solution. The unique surface micromorphology of a hive-like structure was obtained with an average pore size of about 50 nm. The electrode has a very large real surface area and a stable structure. The effects of sodium molybdate concentration on the composition, surface morphology, and structure of electrodes were analyzed by EDS, SEM and XRD. The polarization curves of the different electrodes show that the catalytic activity of electrodes is strongly correlated with the mole fraction of alloy elements (Ni, Fe, Mo, Co), and the addition of cobalt element to Ni-Fe-Mo alloy improves the catalytic activity. The Ni35.63Fe24.67Mo23.52Co16.18 electrode has the best activity for hydrogen evolution reaction(HER), with an over-potential of 66.2 mV, in 30% KOH at 80 ℃ and 200 mA/cm2. The alloy maintains its good catalytic activity for HER during continuous or intermittent electrolysis. Its electrochemical activity and catalytic stability are much higher than the other iron-group with Mo alloy electrodes.

  16. Inverse spin Hall effect of antiferromagnetic MnIr in exchange biased NiFe/MnIr films

    International Nuclear Information System (INIS)

    Antiferromagnetic Mn3Ir, which is widely employed in exchange-biased applications, has attracted much attention recently due to its predicted and subsequently observed large spin Hall effect, therefore increasing its potential for spintronic devices in place of conventional paramagnetic 5d spin Hall metals. (Pt, Ta and W) Via the electrical detection of ferromagnetic resonance, we study a series of exchange biased NiFe/MnIr films for various MnIr thicknesses. In these systems, spin-pumped spin currents from NiFe are converted into dc voltages within MnIr via the inverse spin Hall effect (ISHE), which mixes with spin rectification voltages generated from NiFe. Through angular measurements, we separate these different voltage contributions to qualitatively detect non-zero ISHE in MnIr, which coexists with a non-zero unidirectional anisotropy. We find significant extrinsic damping contributions which prevent the accurate quantification of spin pumping-induced ISHE in MnIr films. The results show that spin currents may propagate and dissipate in MnIr films through ISHE in the presence of exchange bias. (paper)

  17. Synthesis, structural and magnetic characterization of nanocrystalline nickel ferrite-NiFe2O4 obtained by reactive milling

    International Nuclear Information System (INIS)

    Highlights: → Nanocrystalline NiFe2O4 synthesized from nickel and iron oxides by reactive milling. → Non-saturated magnetization caused by spin canted and/or superparamagnetism effects. → Disordered spinel structure reduced the magnetization of NiFe2O4 obtained by milling. - Abstract: Nanocrystalline nickel ferrite (NiFe2O4) has been synthesized from a stoichiometric mixture of oxides NiO and α-Fe2O3 in a high energy planetary mill. An annealing at 350 deg. C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 ± 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure.

  18. Controllable Catalysis with Nanoparticles: Bimetallic Alloy Systems and Surface Adsorbates

    KAUST Repository

    Chen, Tianyou

    2016-05-16

    Transition metal nanoparticles are privileged materials in catalysis due to their high specific surface areas and abundance of active catalytic sites. While many of these catalysts are quite useful, we are only beginning to understand the underlying catalytic mechanisms. Opening the “black box” of nanoparticle catalysis is essential to achieve the ultimate goal of catalysis by design. In this Perspective we highlight recent work addressing the topic of controlled catalysis with bimetallic alloy and “designer” adsorbate-stabilized metal nanoparticles.

  19. Adhesive forces at bimetallic interfaces

    International Nuclear Information System (INIS)

    Force concepts in condensed systems have progressed significantly in recent years. In the context of bimetallic interfaces we consider the Pauli-Hellman-Feynman theorem, use it to check the variational calculations of interfacial energies and estimate the force constants. (author). 13 refs, 2 figs, 2 tabs

  20. A new method to improve surface morphology of Ni-Fe-Mo-Co alloy electrode and its catalytic activity for HER

    Institute of Scientific and Technical Information of China (English)

    LUO Beiping; REN Buye; XU You; ZHENG Yajie

    2007-01-01

    A new pretreatment method has been developed to improve the catalytic activity of the Ni-Fe-Mo-Co alloy electrode for hydrogen evolution reaction (HER). The procedure involves pm-electrolyzing the Ni-Fe-Mo-Co alloy electrode in 30% KOH solution containing 10% potassium sodium tartrate at 70℃ for 2 h, until some of the Mo and Fe elements are leached out. The surface morphology of the Ni-Fe-Mo-Co alloy demonstrates a unique hive-like structure after the pretreatment, which has the pore size in a nanometer range (about 50 nm), a very large real surface area, and good stability.The results of the electrochemical studies show that compared to other similar electrode materials and the treated Ni-Fe-Mo-Co electrode by leaching method, the pre-treated Ni-Fe-Mo-Co electrode has a much lower overpotential and much higher exchange current density for HER. In addition, a long-term continuous electrolysis test with a current interruption shows that the Ni-Fe-Mo-Co alloy has excellent catalytic stability.

  1. Kinetics of Oxidation of L-Leucine by Mono-and Bimetallic Gold and Silver Nanoparticles in Hydrogen Peroxide Solution

    Institute of Scientific and Technical Information of China (English)

    P.VENKATESAN; J.SANTHANALAKSHMI

    2012-01-01

    The catalytic activity of surfactant stabilized mono- and bimetallic Au and Ag nanoparticles for the oxidation of an amino acid,L-leucine,was studied using hydrogen peroxide as the oxidant.The Au and Ag nanoparticle catalysts exhibited very good catalytic activity and the kinetics of the reaction were found to be pseudo-first order with respect to the amino acid.The effects of several factors,such as oxidant concentration,ionic strength,pH,and catalyst concentration on the reaction,were also investigated.In particular,optimal oxidant and catalyst concentrations were determined.Very high concentrations of the metal nano-catalysts or the oxidant led to a dramatic increase in reaction rate.Moreover,bimetallic Au-Ag catalysts provided higher selectivity than pure Au or Ag.

  2. Monometallic Pd and Pt and Bimetallic Pd-Pt/Al2O3-TiO2 for the HDS of DBT: Effect of the Pd and Pt Incorporation Method

    Directory of Open Access Journals (Sweden)

    Reynaldo Martínez Guerrero

    2014-01-01

    Full Text Available The effect of the preparation method of monometallic Pd and Pt and bimetallic Pd-Pt/Al2O3-TiO2 catalysts on the hydrodesulfurization (HDS of dibenzothiophene (DBT was investigated in this study. The synthesis was accomplished using three methods: (A impregnation, (B metal organic chemical vapor deposition (MOCVD, and (C impregnation-MOCVD. The bimetallic Pd-Pt catalyst prepared by the impregnation-MOCVD method was most active for the HDS of DBT compared to those prepared by the single impregnation or MOCVD method due to the synergetic effect between both noble metals. The greater selectivity toward biphenyl indicated that this bimetallic Pd-Pt catalyst preferentially removes sulfur via the direct desulfurization mechanism. However, the bimetallic Pd-Pt catalyst prepared using the single MOCVD method did not produce any cyclohexylbenzene, which is most likely associated with the hydrogenation/dehydrogenation sites.

  3. Autothermal reforming of propane over Ni-based hydrotalcite catalysts.

    Science.gov (United States)

    Park, Sun-Young; Kim, Jong-Ho; Moon, Dong-Ju; Park, Nam-Cook; Kim, Young-Chul

    2010-05-01

    Ni-based hydrotalcite catalysts were investigated for ATR of propane in a fixed-bed flow reactor. The reactions were carried out with a H2O/C/O2 stream ratio of 3/1/0.73 at temperatures ranging from 300 to 700 degrees C. The solvents used in the manufacture of Ni-based catalysts noble metal/Ni/MgAl catalysts or substituted active material were changed in order to decrease the level of catalyst deactivation. The use of a mixture of ethanol and water during the formation of the Pd-Ni/MgAl catalyst produced a higher hydrogen yield than that using water only. In addition, the use of acetone in the synthesis of Ru-Ni/MgAl catalyst produced a higher hydrogen yield than using water only. This shows that the solvents used for the noble metals affect the degree of dispersion and particle size of the nickel and prevented carbon deposition resulting in the enhanced hydrogen selectivity and catalyst activity. Active metals were substituted during the preparation of hydrotalcite catalysts. Among the catalysts prepared with various ratio (Ni:Fe) tested at high temperature, the ratio, Ni:Fe = 75:25, showed best performance. There was less sintering of Ni particles due to substitution of the active metal at the optimal ratio. PMID:20358916

  4. Electrochemical and structural characterization of carbon-supported Pt-Pd bimetallic electrocatalysts prepared by electroless deposition

    Energy Technology Data Exchange (ETDEWEB)

    Ohashi, Masato; Beard, Kevin D.; Ma Shuguo; Blom, Douglas A.; St-Pierre, Jean; Van Zee, John W. [Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208 (United States); Monnier, John R., E-mail: monnier@cec.sc.ed [Department of Chemical Engineering, University of South Carolina, Columbia, SC 29208 (United States)

    2010-10-01

    Electrochemical and structural characteristics of various Pt-Pd/C bimetallic catalysts prepared by electroless deposition (ED) methods have been investigated. Structural analysis was conducted by X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy (EDS). Monometallic Pt or Pd particles were not detected by EDS, indicating the ED methodology formed only bimetallic particles. The size of the Pt-Pd bimetallic particles was smaller than those of a commercially available Pt/C catalyst. The morphology of the Pt on Pd/C catalysts was identified and corresponded to Pd particles partially encapsulated by Pt. The electrochemical characteristics of the lowest Pd loading catalyst (7.0% Pt on 0.5% Pd/C) for the oxygen reduction reaction (ORR) have been investigated by the rotating ring disk electrode technique. The electrochemical activity was equal or lower than the commercially available Pt/C catalyst; however, the amount of hydrogen peroxide observed at the ring was reduced by the Pd, suggesting that such a catalyst has the potential to decrease ionomer degradation in applications. The Pt on Pd/C catalysts also show a higher tolerance to ripening induced by potential cycling. Therefore, catalyst suitability cannot be judged solely by its initial performance; information related to specific degradation mechanisms is also needed for a more complete assessment.

  5. Surface composition changes of redox stabilized bimetallic CoCu nanoparticles supported on silica under H-2 and O-2 atmospheres and during reaction between CO2 and H-2 : in situ X-ray spectroscopic characterization.

    OpenAIRE

    Alayoglu, S.; Beaumont, Simon K.; Melaet, G.; Lindeman, A.E.; Musselwhite, N.; Brooks, C J; Marcus, M. A.; Guo, J. G.; Liu, Z.; Kruse, N; Somorjai, G.A.

    2013-01-01

    In this paper, we report the colloidal synthesis and detailed characterization of 11 nm bimetallic CoCu nanoparticle catalysts. Presently Co and Cu is an attractive combination because of their respective properties for industrially important Fischer–Tropsch and methanol synthesis reactions of CO (and CO2) with H2. We report the preparation of catalysts by deposition of bimetallic metal nanoparticles, both within mesoporous silica (MCF-17) and on the native oxide surface of a silicon wafer. S...

  6. Synthesis and magnetic characterization of NiFe2O4 nanoparticles

    International Nuclear Information System (INIS)

    Full text: Soft ferrite nanoparticles have been in intense research due to their possible device applications with low electrical conductivity, low eddy current losses, operation at high frequencies, mechanical hardness, high Curie temperature and chemical stability. From the last few years, scientist trying to synthesize homogenized fine ferrite nanoparticles for applications such as core material for transformers, inductors, magnetic data storage, targeted drug delivery, gas sensing, radar absorbing paint and many others. Nickel ferrite (NiFe2O4) is one of the soft magnetic ferrite materials with inverse spinel structure. We have already prepared six samples of Nickel ferrite nanoparticles by coprecipitation method. These samples were annealed at different temperatures ranging from 600 to 1000oC. Structure of spinel nickel ferrite was confirmed through x-ray diffraction and TEM measurements. The particle size increases with increase in annealing temperature. Further, we will study the annealing effects on magnetic properties by SQUID measurements. The ferrite nanoparticles have a strong tendency to aggregate, which makes the study of their behavior difficult. To overcome the aggregation, one has to disperse these nanoparticles in some non-magnetic matrix. By dispersing nanoparticles in non-magnetic matrix, the size of the nanoparticles can be minimized and narrow particle size distribution can be achieved. In addition, one can control the magnetic properties by changing the weight percentage of the matrix in the nanocomposite. To avoid aggregation and for narrow particle distribution, we are also planning to synthesize the nanocomposite of nickel ferrite nanoparticles dispersed in SiO2 matrix and polyaniline matrix by sol-gel method. For structural analysis, we will use x-ray diffraction and TEM measurements. Moreover, the interaction between silicon and nickel ferrite nanoparticles will be observed by FTIR measurements. To study the effect of the matrix content

  7. Stress Corrosion Cracking of Ni-Fe-Cr Alloys Relevant to Nuclear Power Plants

    Science.gov (United States)

    Persaud, Suraj

    Stress corrosion cracking (SCC) of Ni-Fe-Cr alloys and weld metals was investigated in simulated environments representative of high temperature water used in the primary and secondary circuits of nuclear power plants. The mechanism of primary water SCC (PWSCC) was studied in Alloys 600, 690, 800 and Alloy 82 dissimilar metal welds using the internal oxidation model as a guide. Initial experiments were carried out in a 480°C hydrogenated steam environment considered to simulate high temperature reducing primary water. Ni alloys underwent classical internal oxidation intragranularly resulting in the expulsion of the solvent metal, Ni, to the surface. Selective intergranular oxidation of Cr in Alloy 600 resulted in embrittlement, while other alloys were resistant owing to their increased Cr contents. Atom probe tomography was used to determine the short-circuit diffusion path used for Ni expulsion at a sub-nanometer scale, which was concluded to be oxide-metal interfaces. Further exposures of Alloys 600 and 800 were done in 315°C simulated primary water and intergranular oxidation tendency was comparable to 480°C hydrogenated steam. Secondary side work involved SCC experiments and electrochemical measurements, which were done at 315°C in acid sulfate solutions. Alloy 800 C-rings were found to undergo acid sulfate SCC (AcSCC) to a depth of up to 300 microm in 0.55 M sulfate solution at pH 4.3. A focused-ion beam was used to extract a crack tip from a C-ring and high resolution analytical electron microscopy revealed a duplex oxide structure and the presence of sulfur. Electrochemical measurements were taken on Ni alloys to complement crack tip analysis; sulfate was concluded to be the aggressive anion in mixed sulfate and chloride systems. Results from electrochemical measurements and crack tip analysis suggested a slip dissolution-type mechanism to explain AcSCC in Ni alloys.

  8. Theoretical analysis of experimental tracer and interdiffusion data in Cu-Ni-Fe alloys

    International Nuclear Information System (INIS)

    In this paper, we present strategies to extract fundamental atomistic information from measured diffusion coefficients in a ternary alloy system. The strategies are exemplified with Cu-Ni-Fe alloys at 1271 K where recent extensive interdiffusion coefficients and tracer diffusion coefficients for all three components have become available. We develop new defining phenomenological expressions for the vacancy-wind factors in terms of the diffusion coefficients. We show that the measured tracer diffusion coefficients can be processed using the Manning and Moleko, Allnatt and Allnatt random alloy diffusion kinetics formalisms (with and without the assumption of the Gibbs-Duhem relation between the thermodynamic activities) to give jump frequencies, tracer correlation factors, vacancy-wind factors and phenomenological coefficients. It is shown for example that Cu is generally the most correlated component in its diffusion behavior and that the off-diagonal phenomenological coefficients can be as high as 64% of the smallest of the diagonal phenomenological coefficients. It is also shown that the Darken formalism (which ignores off-diagonal phenomenological coefficients) is in fact a reasonable approximation for expressing the diagonal phenomenological coefficients in terms of the tracer diffusion coefficients. It is then shown how the measured interdiffusivities can be processed with these formalisms to give tracer diffusivities, vacancy-wind factors and phenomenological coefficients. Finally, we show how a straightforward strategy starting with the Darken analysis that is then followed by the Manning or Moleko, Allnatt and Allnatt analysis can be used to gain access to the vacancy-wind factors and the off-diagonal phenomenological coefficients

  9. Characterization and Preparation of Bimetallic Nanoparticles

    Institute of Scientific and Technical Information of China (English)

    Bing; Joe; Hwang; Ching; Hsiang; Chen; Loka; Subramanyam; Sarma; Din-gao; Liu; Jyh; Fu; Lee

    2007-01-01

    1 Results Bimetallic particles in the nanometer size range are of substantial interest due to their vast applications in catalysis[1].The synthesis of bimetallic nanoparticles with definite size with a well-control over their nanostructure remains a challenging problem.Thus there exists a great demand for both synthesis and atomic level characterization of nanostructure of bimetallic nanoparticles (NPs).With the recent advent of high-intensity tunable sources of X-rays,now available at synchrotron radia...

  10. The effect of lanthanum addition on the catalytic activity of ?-alumina supported bimetallic Co–Mo carbides for dry methane reforming

    OpenAIRE

    France, Liam J; Du, Xian; Almuqati, Naif; Vladimir L. Kuznetsov; Zhao, Yongxiang; Jiang, Zheng; Xiao, Tiancun; Bagabas, Abdulaziz; Almegren, Hamid; Edwards, Peter P.

    2014-01-01

    The effect of lanthanum addition to ?-alumina supported bimetallic carbides has been studied for the reaction of dry methane reforming using four different lanthanum loading levels of 1, 5, 10 and 15 wt% of lanthanum. It has been demonstrated that the addition of lanthanum to supported bimetallic carbides at low loading levels (1 wt%) results in smaller carbide crystallite sizes compared to catalysts containing either no lanthanum or higher lanthanum loading levels (5–15 wt%). Increased lanth...

  11. 电沉积非晶态Ni-Fe-P合金屏蔽织物的制备及其表征∗%Preparation and characterization of shielding fabric coated by electrical deposition of amorphous Ni-Fe-P alloy

    Institute of Scientific and Technical Information of China (English)

    张晓艺; 安振涛; 宣兆龙; 闫军

    2015-01-01

    A flexible shielding fabric with dense uniform coating was prepared after electrical deposition of amor-phous Ni-Fe-P alloy on copper-coated polyethylene terephthalate (PET)fabric.The manufacturing process was studied using orthogonal test with 8 factors and 3 levels.Analyzed the components of the plating solution on the influence of the disposition rate and composition of coating.The morphology,composition,and structure of coating were analyzed by SEM,EDS and XRD characterizations.The EMI shielding effectiveness was also test-ed.The results indicate the processing conditions of electrical deposition amorphous Ni-Fe-P alloy coated fabric are:135 g/L NiSO4 ·6H2O,105 g/L FeSO4 ·7H2O,8 g/L NaH2PO2 ·H2O,24 g/L C6H8O6,36 g/L C6H8O7,22 g/L H3PO3,65 ℃,pH=1.5,and current density =13 A/dm2.The results fabric possesses dense,smooth,and uniform coating,which consists of amorphous Ni-Fe-P alloy with 18.67wt% P.The EMI shielding effectiveness of this coated fabric achieves 60.82-73.63 dB in a broad frequency range between 300 kHz-1 .5 GHz.%在已镀铜涤纶织物表面采用电镀技术制备了一种非晶态 Ni-Fe-P 合金屏蔽织物。选用8因素3水平的正交试验对制备工艺进行了探讨研究,分析了电镀液组成对镀层沉积速率及组分的影响,借助SEM、EDS和XRD对镀层表面形貌、成分及结构进行了分析,并测试了合金织物的电磁屏蔽效能。结果表明,制备非晶态 Ni-Fe-P 合金织物的电镀工艺为硫酸镍135 g/L,硫酸亚铁105 g/L,次亚磷酸钠8 g/L,抗坏血酸24 g/L,柠檬酸36 g/L,亚磷酸22 g/L,温度65℃,pH 值=1.5,电流密度13 A/dm2,合金织物表面镀层致密均匀,结晶细致,镀层为非晶态结构的 Ni-Fe-P合金,其中 P 的质量分数为18.67%,在300 kHz~1.5 GHz频率范围内,合金织物电磁屏蔽效能达到了60.82~73.63 dB。

  12. Preparation, characterization and enhanced adsorption performance for Cr(VI) of mesoporous NiFe{sub 2}O{sub 4} by twice pore-forming method

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Zhigang, E-mail: zjchemyue@126.com [School of Chemistry and Chemical Engineering, Anhui University of Technology, No. 59 Hudong Road, Ma' anshan 243002, Anhui Province (China); Peng, Kuankuan; Xu, Lixin [School of Chemistry and Chemical Engineering, Anhui University of Technology, No. 59 Hudong Road, Ma' anshan 243002, Anhui Province (China)

    2012-10-15

    Magnetic mesoporous NiFe{sub 2}O{sub 4} with higher surface area has been prepared by the twice pore-forming method, including the calcination of the oxalate precursor and leaching of ZnO pore-forming agent. The X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and BET surface area measurement are used to evaluate the pore structural parameters and surface chemistry of the adsorbent respectively. The pore-forming mechanism is proposed based on the experimental results. The adsorption behavior of mesoporous NiFe{sub 2}O{sub 4} for Cr(VI) is investigated in detail. The results show that kinetic data follow a pseudo-second-order model and equilibrium data are well fitted by the Langmuir model. The maximum adsorption capacity is 43.68 mg g{sup -1} at pH 2. The removal for Cr(VI) is mainly physisorption process derived from coulombic interaction. The as-prepared TPF-NiFe{sub 2}O{sub 4} is promising as sorbent for Cr(VI) removal because of its higher adsorption capacity, separation convenience and highly efficient reusability. -- Highlights: Black-Right-Pointing-Pointer The increase of BET area was realized by leaching of ZnO from mesoporous ZnO/NiFe{sub 2}O{sub 4}. Black-Right-Pointing-Pointer TPF-NiFe{sub 2}O{sub 4} demenstrates higher adsorption capacity for Cr(VI) in aqueous solution. Black-Right-Pointing-Pointer TPF-NiFe{sub 2}O{sub 4} with magnetic sensitivity is promosing for Cr(VI) removal. Black-Right-Pointing-Pointer The used TPF-NiFe{sub 2}O{sub 4} adsorbent can be recycled.

  13. Facile Fabrication of Composition-Tuned Ru-Ni Bimetallics in Ordered Mesoporous Carbon for Levulinic Acid Hydrogenation

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ying; Gao, Guang; Zhang, Xin; Li, Fuwei [ChinaU - Petroleum; (Chinese Aca. Sci.)

    2016-02-04

    Bimetallic catalysts are of great importance due to their unique catalytic properties. However, their conventional synthesis requires tedious multistep procedures and prolonged synthetic time, and the resulting bimetallics usually disperse unevenly and show poor stability. It is challenging to develop a facile and step-economic synthetic methodology for highly efficient bimetallic catalysts. In this study, we report an elegant metal complex-involved multicomponent assembly route to highly efficient Ru–Ni bimetallics in ordered mesoporous carbons (OMC). The fabrication of composition-tuned Ru–Ni bimetallics in OMC (RuxNi1–x–OMC, x = 0.5–0.9) was facilely realized via in situ construction of CTAB-directed cubic Ia3d chitosan-ruthenium–nickel–silica mesophase before pyrolysis and silica removal. The resulting RuxNi1–x–OMC materials are in-depth characterized with X-ray diffraction, N2 adsorption–desorption, transmission electron microscopy, infrared spectrum, and X-ray absorption fine structure. This facile fabrication method renders homogeneously dispersed Ru–Ni bimetallics embedded in the mesoporous carbonaceous framework and creates a highly active and stable Ru0.9Ni0.1–OMC catalyst for the hydrogenation of levulinic acid (LA) to prepare γ-valerolactone (GVL), a biomass-derived platform molecule with wide application in the preparation of renewable chemicals and liquid transportation fuels. A high TOF (>2000 h–1) was obtained, and the Ru0.9Ni0.1–OMC catalyst could be used at least 15 times without obvious loss of its catalytic performance.

  14. One step electrochemical synthesis of bimetallic PdAu supported on nafion–graphene ribbon film for ethanol electrooxidation

    Energy Technology Data Exchange (ETDEWEB)

    Shendage, Suresh S., E-mail: sureshsshendage@gmail.com; Singh, Abilash S.; Nagarkar, Jayashree M., E-mail: jm.nagarkar@ictmumbai.edu.in

    2015-10-15

    Highlights: • Electrochemical deposition of bimetallic PdAu NPs. • Highly loaded PdAu NPs are obtained. • Nafion–graphene supported PdAu NPs shows good activity for ethanol electrooxidation. - Abstract: A nafion–graphene ribbon (Nf–GR) supported bimetallic PdAu nanoparticles (PdAu/Nf–GR) catalyst was prepared by electrochemical codeposition of Pd and Au at constant potential. The prepared catalyst was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). The average particle size of PdAu nanoparticles (NPs) determined from XRD was 3.5 nm. The electrocatalytic activity of the PdAu/Nf–GR catalyst was examined by cyclic voltametry. It was observed that the as prepared catalyst showed efficient activity and good stability for ethanol electrooxidation in alkaline medium.

  15. Thermo-therapeutic applications of chitosan- and PEG-coated NiFe2O4 nanoparticles

    Science.gov (United States)

    Manjura Hoque, S.; Tariq, Mehrin; Liba, S. I.; Salehin, F.; Mahmood, Z. H.; Khan, M. N. I.; Chattopadhayay, K.; Islam, Rafiqul; Akhter, S.

    2016-07-01

    The paper reports the thermo-therapeutic applications of chitosan- and PEG-coated nickel ferrite (NiFe2O4) nanoparticles. In this study NiFe2O4 nanoparticles were synthesized by the co-precipitation method, tuning the particle size through heat treatment in the temperature range from 200–800 °C for 3 h. XRD and TEM analysis revealed that the the ultrafine nanoparticles were of size 2–58 nm. Crystallinity of the NiFe2O4 nanoparticles in the as-dried condition with the particle size ∼2–3 nm was confirmed from the presence of a lattice fringe in the HRTEM image. VSM measurements showed that a superparamagnetic/ferromagnetic transition occurs with increasing particle size, which was further confirmed by Mössbauer spectroscopy. The nickel ferrite nanoparticles with optimum particle size of 10 nm were then coated with materials commonly used for biomedical applications, i.e. chitosan and PEG, to form homogeneous suspensions. The hydrodynamic diameter and the polydispersity index (PDI) were analyzed by dynamic light scattering at the physiological temperature of 37 °C and found to be 187 nm and 0.21 for chitosan-coated nanoparticles and 285 nm and 0.32 for PEG-coated ones. The specific loss power of rf induction heating by the set-up for hyperthermia and r 2 relaxivity by the nuclear magnetic resonance were determined. The results of induction heating measurements showed that the temperature attained by the nanoparticles of size 10 nm and concentration of about 20 mg ml‑1 was >70 °C (for chitosan) and >64 °C (for PEG). It has been demonstrated that the required temperature for hyperthermia heating could be tuned by tuning the particle size, shape and magnetization and the concentration of solution. For other potential biomedical applications of the NiFe2O4 nanoparticle solution, e.g. magnetic resonance imaging, the NMR studies yielded the T 1 and T 2 relaxivities as 0.348 and 89 mM‑1 s‑1 respectively. The fact that the T 2 relaxivity is orders of

  16. Structure and properties of nanosize NiFe2O4 prepared by template and precipitation methods

    Czech Academy of Sciences Publication Activity Database

    Ćosović, A.; Ćosović, B.; Žák, Tomáš; David, Bohumil; Talijan, N.

    2013-01-01

    Roč. 49, č. 3 (2013), s. 271-277. ISSN 1450-5339 R&D Projects: GA ČR(CZ) GAP108/11/1350; GA MŠk(CZ) ED1.1.00/02.0068 Institutional research plan: CEZ:AV0Z2041904 Institutional support: RVO:68081723 Keywords : nanosized NiFe2O4 * template method * precipitation route * microstructure * phase composition * magnetic properties Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.135, year: 2013

  17. Laser-wavelength dependence of the picosecond ultrasonic response of a NiFe/NiO/Si structure

    Science.gov (United States)

    Bosco, C. A.; Azevedo, A.; Acioli, L. H.

    2002-09-01

    Ultrafast optical excitation and detection of acoustic phonons has been used to analyze ultrathin films composed of NiFe/NiO/Si which are important for applications in magnetic storage and processing. Results are presented on the wavelength dependence of the ultrasonic response of the thin NiO film and bulk Si. Significant changes are observed between detection using the fundamental and the second harmonic of the femtosecond laser as the probe beam. Beatings between low order longitudinal phonons in the NiO layer are observed and measurements of its refractive index and absorption coefficients are performed.

  18. Recrystallization and development of cube texture in Ti and Ti+Cr added Ni-Fe-Cu alloys

    Energy Technology Data Exchange (ETDEWEB)

    Manna, I. (Dept. of Metallurgical Engineering , I.I.T., Kharagpur (India)); Ray, R.K. (Dept. of Metallurgical Engineering, I.I.T., Kanpur (India)); Gupta, K.P. (Dept. of Metallurgical Engineering, I.I.T., Kanpur (India))

    1994-06-01

    The development of a sharp cube or [l brace]100[r brace]<100> texture in two Ti and Ti+Cr added Ni-Fe-Cu alloys is presented. Texture studies in deformed as well as recrystallized conditions have been carried out by both conventional pole figure and orientation distribution function analysis. Microstructural evolution in course of recrystallization texture development has been extensively studied with both optical and electron microscopes. Heavy cold deformation (97 to 98%) followed by annealing at 1050 C for 2 h has been found to optimize the conditions for the desired texture development. (orig.)

  19. Thermo-therapeutic applications of chitosan- and PEG-coated NiFe2O4 nanoparticles.

    Science.gov (United States)

    Hoque, S Manjura; Tariq, Mehrin; Liba, S I; Salehin, F; Mahmood, Z H; Khan, M N I; Chattopadhayay, K; Islam, Rafiqul; Akhter, S

    2016-07-15

    The paper reports the thermo-therapeutic applications of chitosan- and PEG-coated nickel ferrite (NiFe2O4) nanoparticles. In this study NiFe2O4 nanoparticles were synthesized by the co-precipitation method, tuning the particle size through heat treatment in the temperature range from 200-800 °C for 3 h. XRD and TEM analysis revealed that the the ultrafine nanoparticles were of size 2-58 nm. Crystallinity of the NiFe2O4 nanoparticles in the as-dried condition with the particle size ∼2-3 nm was confirmed from the presence of a lattice fringe in the HRTEM image. VSM measurements showed that a superparamagnetic/ferromagnetic transition occurs with increasing particle size, which was further confirmed by Mössbauer spectroscopy. The nickel ferrite nanoparticles with optimum particle size of 10 nm were then coated with materials commonly used for biomedical applications, i.e. chitosan and PEG, to form homogeneous suspensions. The hydrodynamic diameter and the polydispersity index (PDI) were analyzed by dynamic light scattering at the physiological temperature of 37 °C and found to be 187 nm and 0.21 for chitosan-coated nanoparticles and 285 nm and 0.32 for PEG-coated ones. The specific loss power of rf induction heating by the set-up for hyperthermia and r 2 relaxivity by the nuclear magnetic resonance were determined. The results of induction heating measurements showed that the temperature attained by the nanoparticles of size 10 nm and concentration of about 20 mg ml(-1) was >70 °C (for chitosan) and >64 °C (for PEG). It has been demonstrated that the required temperature for hyperthermia heating could be tuned by tuning the particle size, shape and magnetization and the concentration of solution. For other potential biomedical applications of the NiFe2O4 nanoparticle solution, e.g. magnetic resonance imaging, the NMR studies yielded the T 1 and T 2 relaxivities as 0.348 and 89 mM(-1) s(-1) respectively. The fact that the T 2 relaxivity is orders of magnitude

  20. Study of the microstructure and of microhardness variation of a Ni-Fe-Cr austenitic alloy by niobium

    International Nuclear Information System (INIS)

    The mechanisms of hardening and corrosion resistance increase in Ni-Fe-Cr austenitic stainless steels by Nb additions are of interest to nuclear technology Niobium additions to a 321 type stainless steel were made in order to study the microhardness, electrical resistivity and metallography. Experimental measurements results are shown. The effect of Nb additions as a micro-alloying element and the thermal and mechanical processes (cold working in particular) in the microstructure and microhardness properties of the 11% Ni - 70%Fe - 17% Cr austenitic alloys were studied. (Author)

  1. Segregation property and trial manufacturing large ingot of Ni-Fe base superalloy for A-USC steam turbine

    Energy Technology Data Exchange (ETDEWEB)

    Imano, Shinya; Sato, Jun [Hitachi Research Lab., Ltd. (Japan); Takahashi, Tatsuya; Kajikawa, Koji [Japan Steel Works (Japan). Muroran Lab.

    2008-07-01

    Research and development of A-USC steam turbine rotor materials (low-cost Ni-Fe base superalloy FENIX-700) applied up to 700 C have been conducted. The dependency of the segregation properties of FENIX-700 on chemical composition was evaluated. Based on the results, trial melting of a large ingot was carried out using ESR process. The diameter of the ingot was 850mm, which exceeds the manufacturing limit of Alloy706. We have succeeded in the trial melting of 850 mm diameter ingot of FENIX-700 by ESR process. The 850 mm diameter ingot does not have macro segregations and chemical composition variations are within the intended range. (orig.)

  2. Structural and magnetic properties of CoFe2O4/NiFe2O4 core/shell nanocomposite prepared by the hydrothermal method

    International Nuclear Information System (INIS)

    CoFe2O4/NiFe2O4 core/shell magnetic nanocomposite was synthesized by using hydrothermal method.The analysis of XRD indicated the coexistence of CoFe2O4, NiFe2O4as core/shell composite. The core/shell structure of the composite sample has been confirmed by HR-TEM images, EDX and FT-IR measurements. The size of obtained core/shell nanoparticles was 17 nm in core diameter and about 3 nm in shell thickness. The magnetization measurements showed that both the coercive field and the saturation magnetization of the resulting core/shell nanocomposite were slightly decreased compared to those of the CoFe2O4 core but the thermal stability is of the magnetization parameter was enhanced. Furthermore, superparamagnetic phase is established at temperatures higher than the room temperature. The results were discussed in terms of the surface pinning and the magnetic interaction at the interface between the core and shell. - Highlights: • CoFe2O4/NiFe2O4 core/shell could be prepared by hydrothermal method. • The structural analysis proved the formation of NiFe2O4 shell with thickness 3 nm. • The thermal stability of Ms and Hc is enhanced due to the presence of NiFe2O4 as a shell. • Super paramagnetic transition is confirmed and the effective magnetic anisotropy was calculated

  3. Effect of metallic phase content on mechanical properties of (85Cu- 15Ni)/(10NiO-NiFe2O4) cermet inert anode for aluminum electrolysis

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    (85Cu-15Ni)/(10NiO-NiFe2O4) cermets were prepared with Cu-Ni mixed powders as toughening metallic phase and 10NiO-NiFe2O4 as ceramic matrix. The phase composition, microstructure of composite and the effect of metallic phase content on bending strength, hardness, fracture toughness and thermal shock resistance were studied. X-ray diffraction analysis indicates the coexistence of (Cu-Ni), NiO and NiFe2O4 phases in the cermets. Within the content range of metallic phase from 0% to 20% (mass fraction), the maximal bending strength (176.4 MPa) and the minimal porosity (3.9%) of composite appear at the metallic phase content of 5%. The fracture toughness increases and Vickers' hardness decreases with increasing metal content. When the thermal shock temperature difference (△t) is below 200 ℃, the loss rate of residual strength for 10NiO-NiFe2O4 ceramic is only 8%, but about 40% for (85Cu-15Ni)/(10NiO-NiFe2O4) cermets. As △t is above 200 ℃, the residual strength sharply decreases for sample CN0 and falls slowly for samples CN5-CN20.

  4. NiFe/Pt薄膜中角度相关的逆自旋霍尔效应∗%Angle dep endent inverse spin Hall effect in NiFe/Pt thin film

    Institute of Scientific and Technical Information of China (English)

    韩方彬; 张文旭; 彭斌; 张万里

    2015-01-01

    In NiFe/Pt bilayer, when spin current originating from the magnetization procession of NiFe is inject into the adjacent Pt layer under ferromagnetic resonance (FMR), the direct current (DC) voltage VISHE generated by inverse spin Hall effect (ISHE) will be added to the voltage VSRE generated by spin rectification effect (SRE), therefore the measured voltage in experiment is the sum of VISHE and VSRE. It is crucial to separate these contributions, which has been often overlooked before, in order to make a reasonable comparison of the ISHE among different materials. The voltages having symmetric (Lorentz type) and anti-symmetric (dispersive type) components both vary with the static magnetic field strength. However, they have different static magnetic field angle dependences according to our theoretical analysis. In order to distinguish the contribution of ISHE from that of SRE, in this paper, we employ a method, in which the voltage across the sample is measured when the static magnetic field is applied to different directions, to analyze the voltage by varying magnetic field angle in a range from 0◦ to 360◦ in steps of 10◦, thereby separating the VISHE. The separation is carried out by fitting the angle dependent symmetric and anti-symmetric curves to different theoretical formulas of ISHE and SRE. The voltages of the two different contributions together with the phase angle of the microwave are obtained. At the same time, the FMR line width and the resonant field can be read out. The results show that the ferromagnetic resonance line width in NiFe(20 nm)/Pt(10 nm) sample is larger than that in NiFe(20 nm) sample due to the injection of spin current from NiFe to Pt in the bi-layer sample. We notice that in the curves of voltage vs. static magnetic field, the Lorentz symmetry components of the voltage from the bi-layer sample weight more than those from the single-layer sample. This is explained as a result of the existence of the ISHE in the bi-layer sample

  5. Amorphous mixed-metal hydroxide nanostructures for advanced water oxidation catalysts

    Science.gov (United States)

    Gao, Y. Q.; Liu, X. Y.; Yang, G. W.

    2016-02-01

    The design of highly efficient, durable, and earth-abundant catalysts for the oxygen evolution reaction (OER) is crucial in order to promote energy conversion and storage processes. Here, we synthesize amorphous mixed-metal (Ni-Fe) hydroxide nanostructures with a homogeneous distribution of Ni/Fe as well as a tunable Ni/Fe ratio by a simple, facile, green and low-cost electrochemical technique, and we demonstrate that the synthesized amorphous nanomaterials possess ultrahigh activity and super long-term cycle stability in the OER process. The amorphous Ni0.71Fe0.29(OH)x nanostructure affords a current density of 10 mA cm-2 at an overpotential of a mere 0.296 V and a small Tafel slope of 58 mV dec-1, while no deactivation is detected in the CV testing even up to 30 000 cycles, which suggests the promising application of these amorphous nanomaterials in electrochemical oxidation. Meanwhile, the distinct catalytic activities among these amorphous Ni-Fe hydroxide nanostructures prompts us to take notice of the composition of the alloy hydroxides/oxides when studying their catalytic properties, which opens an avenue for the rational design and controllable preparation of such amorphous nanomaterials as advanced OER electrocatalysts.The design of highly efficient, durable, and earth-abundant catalysts for the oxygen evolution reaction (OER) is crucial in order to promote energy conversion and storage processes. Here, we synthesize amorphous mixed-metal (Ni-Fe) hydroxide nanostructures with a homogeneous distribution of Ni/Fe as well as a tunable Ni/Fe ratio by a simple, facile, green and low-cost electrochemical technique, and we demonstrate that the synthesized amorphous nanomaterials possess ultrahigh activity and super long-term cycle stability in the OER process. The amorphous Ni0.71Fe0.29(OH)x nanostructure affords a current density of 10 mA cm-2 at an overpotential of a mere 0.296 V and a small Tafel slope of 58 mV dec-1, while no deactivation is detected in the CV

  6. Porous Diatomite-Immobilized Cu–Ni Bimetallic Nanocatalysts for Direct Synthesis of Dimethyl Carbonate

    Directory of Open Access Journals (Sweden)

    Yong Chen

    2012-01-01

    Full Text Available A series of diatomite-immobilized Cu–Ni bimetallic nanocatalysts was prepared under ultrasonication and evaluated for the direct synthesis of dimethyl carbonate under various conditions. Upon being fully characterized by TPR, TPD, BET, SEM, XRD, and XPS methodologies, it is found that the bimetallic composite is effectively alloyed and well immobilized inside or outside the pore of diatomite. Under the optimal conditions of 1.2 MPa and 120∘C, the prepared catalyst with loading of 15% exhibited the highest methanol conversion of 6.50% with DMC selectivity of 91.2% as well as more than 10-hour lifetime. The possible reaction mechanism was proposed and discussed in detail. To our knowledge, this is the first report to use diatomite as a catalyst support for direct DMC synthesis from methanol and CO2.

  7. Nano structural Formation of Pd-Co Bimetallic Complex on HOPG Surfaces: XPS and AFM Studies

    International Nuclear Information System (INIS)

    A new single source approach was developed to synthesize Pd-Co nanoparticles using a bimetallic compound, [Et3NH]2[CoPd2(μ-4-I-3,5-Me2pz)4Cl4](CoPd2), as a molecular precursor to obtain dispersed catalyst on highly ordered pyrolytic graphite (HOPG) surface, in view of preparing oxygen reduction catalysts for low temperature fuel cells. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were employed to characterize the nano structure formations and to determine the composition and morphology of the complex on the HOPG. Results of high resolution XPS analysis (HR-XPS) revealed the binding energies corresponding to the atomic constituents of the precursor. When the precursor solution was placed on the surface of the HOPG, the bimetallic complex assumes a tubular structure and it appears that the surface of the HOPG offers a ground for the self-organization of nano structural formations.

  8. Rhodium-technetium catalysts in dehydrogenation of cyclohexane

    International Nuclear Information System (INIS)

    Catalytic properties of Rh-Tc/support (γ-Al2O3, SiO2 or MgO) system in dehydrogenation of cyclohexane were studied. A nonadditive increase in catalytic activity of bimetallic catalysts in comparison with monometallic catalysts has been established. Diffuse reflectance spectra have shown the presence of ionic forms of the metals in bimetallic catalysts. From the comparison of catalytic and optical properties a conclusion was drawn about the nature of synergism observed, which was accounted for by the formation of RhxTcy clusters. 6 refs.; 5 figs.; 1 tab

  9. Selection of fiber reinforcement for NiFe2O4­based inert anode materials in aluminum electrolysis%铝电解NiFe2O4基惰性阳极材料纤维增强体的选择

    Institute of Scientific and Technical Information of China (English)

    华中胜; 姚广春; 龙秀丽; 王海川; 赵卓

    2013-01-01

    NiFe2O4 spinel was synthesized via solid­state sintering technology using NiO and Fe2O3 as the raw materials, and fiber/NiFe2O4 inert anode materials were prepared by adding short fiber into NiFe2O4. The high temperature stability of some fibers in NiFe2O4 matrix was investigated to select the appropriate fiber reinforcement for NiFe2O4­based inert anode materials. The results indicate that carbon fiber, glass fiber, alumina fiber and silicon carbide fiber are thermodynamically incompatible with the NiFe2O4 matrix, also the nickel­coated carbon fiber and nickel fiber cannot stably exist in the matrix at 1 200℃, while ZrO2(f) has favorable physical and chemical compatibility with the NiFe2O4 matrix at 1 400℃. The mechanical properties of the anodes samples are improved significantly by adding 3% ZrO2(f) (mass fraction). Therefore, ZrO2(f) can be used as the fiber reinforcement for NiFe2O4­based inert anode.%  以NiO和Fe2O3为原料采用固相烧结法合成NiFe2O4尖晶石,通过向其中添加短纤维制备纤维/NiFe2O4惰性阳极材料。为选择适合于NiFe2O4基惰性阳极材料的纤维增强体,对几种纤维在NiFe2O4基体中的高温稳定性进行考察。结果表明,高温下碳纤维、玻璃纤维、氧化铝纤维和碳化硅纤维与NiFe2O4基体是热力学不相容的;1200℃时镀镍碳纤维和镍纤维不能在基体中稳定存在;1400℃时ZrO2(f)与NiFe2O4基体具有良好的物理和化学相容性,添加3%ZrO2(f)(质量分数)阳极试样的力学性能得到明显改善。因此,ZrO2(f)可作为NiFe2O4基惰性阳极的纤维增强体。

  10. Screening of NiFe2O4 Nanoparticles as Oxygen Carrier in Chemical Looping Hydrogen Production

    DEFF Research Database (Denmark)

    Liu, Shuai; He, Fang; Huang, Zhen;

    2016-01-01

    ) porosity test. The performance of the prepared materials was first evaluated in a TGA reactor through a CO reduction and subsequent steam oxidation process. Then a complete redox process was conducted in a fixed-bed reactor, where the NiFe2O4 oxygen carrier was first reduced by simulated biomass pyrolysis...... gas (24% H2 + 24% CO + 12% CO2 + N2 balance), then reacted with steam to produce H2, and finally fully oxidized by air. The NiFe2O4 oxygen carrier prepared by the sol gel method showed the best capacity for hydrogen production and the highest recovery degree of lattice oxygen, in agreement with the......The objective of this paper is to systematically investigate the influences of different preparation methods on the properties of NiFe2O4 nanoparticles as oxygen carrier in chemical looping hydrogen production (CLH). The solid state (SS), coprecipitation (CP), hydrothermal (HT), and sol-gel (SG...

  11. Microstructural evolution of NiFe2O4-10NiO powder prepared by high temperature solid state reaction

    Institute of Scientific and Technical Information of China (English)

    ZHANG Lei; ZHOU Ke-chao; LI Zhi-you; YANG Wen-jie

    2006-01-01

    The NiFe2O4-10NiO powder for inert anode of aluminium electrolysis was prepared by high temperature solid state reaction. The microstructural evolution from the raw materials NiO and Fe2O3 to the NiFe2O4-10NiO powder was studied by SEM. The results show that the domain structure making up of the agglomerate particles of Fe2O3 remains after high temperature solid state reaction, and the diffusion of Ni2+ into Fe2O3 structure is the control step of the reaction process. A microstructure with compact structure and fine grain inside the particle results from the sintering of NiFe2O4-10NiO powder.

  12. Synthesis of SiO2 coated NiFe2O4 nanoparticles and the effect of SiO2 shell thickness on the magnetic properties

    Science.gov (United States)

    Coşkun, M.; Korkmaz, M.; Fırat, T.; Jaffari, G. H.; Shah, S. I.

    2010-05-01

    In this work, the results of synthesis of core-shell NiFe2O4 nanoparticles and influence of silica coating on the magnetic properties of nanoparticles are presented. Spherical NiFe2O4 nanoparticles were prepared via a normal micelles process. NiFe2O4 nanoparticles homogeneously coated with SiO2 of various shell thickness were synthesized by reverse microemulsion. The interparticle spacing was varied by changing the amount of added tetraethylorthosilicate. The microstructures and morphologies of these nanoparticles were studied by x-ray diffraction and transmission electron microscopy techniques. The magnetic parameters such as saturation magnetizations, blocking temperatures, and magnetic anisotropies have been calculated from dc magnetization and ac susceptibility measurements.

  13. Ring head recording on perpendicular media: Output spectra for CoCr and CoCr/NiFe media

    Science.gov (United States)

    Stubbs, D. P.; Whisler, J. W.; Moe, C. D.; Skorjanec, J.

    1985-04-01

    The recording density response for sputtered CoCr (thickness=0.5 μm) and CoCr/NiFe (t=0.25 μm/0.5 μm) as well as evaporated CoNi (t=0.12 μm) and Co surface-doped iron oxide particulate media has been measured by reading and writing with Mn-Zn ferrite heads (gap length=0.375 μm, track width=37 μm) in contact with the media. Measurements to 200 kfc/i (thousand flux changes per inch) show a gap null around 115 kfc/i. The data have been normalized by dividing out the head sensitivity to obtain the value of spacing plus transition width (d+a) for the various media. For the CoCr media this value varied from 0.075-0.088 μm; for CoNi, 0.100 μm, and for the particulate medium, 0.163 μm. In addition, testing with a larger gapped Mn-Zn ferrite head (g=2.43 μm) shows that the head fields are distorted by the soft magnetic underlayer in dual layer CoCr/NiFe samples when the gap length is large compared to the distance to the underlayer.

  14. EFFECT OF MnO2 ADDITIVE ON PERFORMANCES OF NiFe2O4 SPINEL BASED INERT ANODE

    Institute of Scientific and Technical Information of China (English)

    W.L. Jiao; L. Zhang; G. C. Yao

    2005-01-01

    The NiFe2O4 inert anode is synthesized by high-temperature solid-state reaction method using NiO and Fe2O3 as main raw materials and adding MnO2 powder as additive. Archimedes method using water immersion technique is used to measure the sintering performances of samples. The static thermal corrosion rates of samples are measured by weight loss. SEM is employed for the observation of material microstructure, and phase structure of the sample surface after corrosion is determined by XRD. The experimental results indicate that a suitable MnO2additive content is 2%, while the sintering performance is the best, and the static thermal corrosion rate is the lowest. Because of MnO2 dopant enriching at crystal boundary, the corrosion reaction of molten salt to crystal grain creates Mn2AlO4 phase, which is denser than NiFe2O4phase, and prevents the cryolite molten salt to penetrate into the inert anode, thus reducing the corrosion.

  15. Evidence of spin phonon coupling in magnetoelectric NiFe{sub 2}O{sub 4}/PMN-PT composite

    Energy Technology Data Exchange (ETDEWEB)

    Ahlawat, Anju; Satapathy, S., E-mail: srinu73@rrcat.gov.in, E-mail: srinusatapathy@gmail.com; Gupta, P. K. [Nano Functional Materials Laboratory, Laser Materials Development and Devices Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Sathe, V. G.; Choudhary, R. J. [UGC-DAE Consortium for Scientific Research, Indore 452017 (India)

    2013-12-16

    The coupling of phonon with spin in strain coupled magnetoelectric NiFe{sub 2}O{sub 4} (NFO)/0.65Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–0.35PbTiO{sub 3} (PMN-PT) composite was investigated by temperature-dependent Raman spectroscopy and magnetic measurements in the range 30–350 °C. Pure NFO shows usual ferromagnetic behaviour in this temperature range while NFO/PMN-PT composite show dramatic change in magnetic moment across ferroelectric transition temperature (T{sub c} ∼ 180 °C) of PMN-PT. The temperature evolution of the Raman spectra for the composite shows significant phonon anomalies in T-site (Fe-O) and O-site (Ni/Fe-O) phonon modes at ferroelectric transition temperature is attributed to spin phonon coupling in NFO/PMN-PT composite. The strain mediated magnetoelectric coupling mechanism in this composite is apparent from the observed spin phonon interaction.

  16. Structural and magnetic properties of sol–gel derived NiFe2O4 thin films on silicon substrates

    International Nuclear Information System (INIS)

    Spinel NiFe2O4 thin films are derived via chemical solution deposition on silicon substrates. The films show a granular microstructure with surface roughness of less than 3 nm. The effects of varying the pyrolysis and annealing conditions on the microstructure and resulting magnetic properties have been studied. Microstructural studies confirm the formation of randomly oriented, phase-pure spinel nickel ferrite for pyrolysis at 100 °C to 500 °C and crystallization at 650 °C to 900 °C for 10 to 30 min. It is shown that the pyrolysis temperature does not affect the microstructure and the resulting magnetic properties, while increasing annealing temperature results in increased grain size and saturation magnetization. Transmission electron microcopy shows that no intermediate or secondary phase has formed at the interface even at annealing temperature as high as 900 °C. - Highlights: • Nanocrystalline NiFe2O4 thin films are derived by a chemical solution deposition. • The pyrolysis temperature has no effect on microstructure and magnetic properties. • Increase in annealing temperature results in larger grain size. • Higher annealing temperature leads to higher saturation magnetization. • TEM confirms purity of the films even at annealing temperature as high as 900 °C

  17. One Step Quick Detection of Cancer Cell Surface Marker by Integrated NiFe-based Magnetic Biosensing Cell Cultural Chip

    Institute of Scientific and Technical Information of China (English)

    Chenchen Bao; Lei Chen; Tao Wang; Chong Lei; Furong Tian; Daxiang Cui; Yong Zhou

    2013-01-01

    RGD peptides has been used to detect cell surface integrin and direct clinical effective therapeutic drug selection. Herein we report that a quick one step detection of cell surface marker that was realized by a specially designed NiFe-based magnetic biosensing cell chip combined with functionalized magnetic nanoparti-cles. Magnetic nanoparticles with 20-30 nm in diameter were prepared by coprecipitation and modified with RGD-4C, and the resultant RGD-functionalized magnetic nanoparticles were used for targeting cancer cells cul-tured on the NiFe-based magnetic biosensing chip and distinguish the amount of cell surface receptor-integrin. Cell lines such as Calu3, Hela, A549, CaFbr, HEK293 and HUVEC exhibiting different integrin expression were chosen as test samples. Calu3, Hela, HEK293 and HUVEC cells were successfully identified. This approach has advantages in the qualitative screening test. Compared with traditional method, it is fast, sensitive, low cost, easy-operative, and needs very little human intervention. The novel method has great potential in applications such as fast clinical cell surface marker detection, and diagnosis of early cancer, and can be easily extended to other biomedical applications based on molecular recognition.

  18. Modified combustion synthesis of Nano-NiFe{sub 2}O{sub 4}: Optimization using Taguchi experimental design

    Energy Technology Data Exchange (ETDEWEB)

    Norouzbeigi, Reza, E-mail: norouzbeigi@iust.ac.ir [Cement Research Center, Iran University of Science and Technology, 16765-163, Narmak, Tehran (Iran, Islamic Republic of); School of Chemical Engineering, Iran University of Science and Technology, P.B. 16765-163, Narmak, Tehran (Iran, Islamic Republic of); Majdabadi Farahani, Shahrzad [School of Chemical Engineering, Iran University of Science and Technology, P.B. 16765-163, Narmak, Tehran (Iran, Islamic Republic of)

    2015-06-15

    Abstarct: Nano-NiFe{sub 2}O{sub 4} powders were prepared by modified combustion of DTPA as a new fuel. Three factors such as fuel to oxidizer ratio (F/O), added fuel type and added to the main fuel ratio were evaluated under Taguchi L{sub 8} experimental design and analysis. Urea and EDTA were selected as added fuels and sterile gauze was used as a template for the first time. The crystal sizes were optimized as the responses of the experiments. Optimum condition for production of smaller crystals was determined as using EDTA as added fuel and added/main fuels molar ratio of 0.75. The structural and morphological properties of the products were characterized using, field emission scanning electron microscopy (FESEM), Energy Dispersive Spectroscopy mapping, transmission electron microscopy (TEM), X-ray diffraction (XRD). FESEM and TEM micrographs showed agglomerated spherical and cubic nanoparticles with an average particle size of 60 nm. XRD analysis revealed the cubic spinel structure and ferrite phase with high crystallinity in the range of 13–23 nm. - Highlights: • Highly pure Nano-NiFe{sub 2}O{sub 4} were prepared by modified combustion of Diethylene triamine pentaacetic acid as a new fuel. • Sterile gauze was used as template for the first time. • Nickel ferrite powders with average particle size of 60 nm have been successfully synthesized.

  19. The effect of annealing on microstructure and cation distribution of NiFe{sub 2}O{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Cvejić, Ž., E-mail: zeljkac@uns.ac.rs [Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 4, 21000 Novi Sad (Serbia); Đurđić, E.; Ivković Ivandekić, G. [Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 4, 21000 Novi Sad (Serbia); Bajac, B. [Department of Materials Engineering, Faculty of Technology, University of Novi Sad, Bulevar Cara Lazara 1, 21000 Novi Sad (Serbia); Postolache, P.; Mitoseriu, L. [Faculty of Physics, University “Al. I. Cuza”, Bv. Carol I Nr 11, RO-Iasi 700506 (Romania); Srdić, V.V. [Department of Materials Engineering, Faculty of Technology, University of Novi Sad, Bulevar Cara Lazara 1, 21000 Novi Sad (Serbia); Rakić, S. [Department of Physics, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 4, 21000 Novi Sad (Serbia)

    2015-11-15

    Nickel ferrite nanopowder was synthesized using a co-precipitation method, and further annealed at three different temperatures of 500 °C, 750 °C and 900 °C. The effect of annealing process was explored on particle size, cation distribution and magnetic properties of NiFe{sub 2}O{sub 4}. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and with the use of a vibrating sample magnetometer. The X-ray diffraction patterns at different annealing temperatures demonstrated the existence of only spinel phase of NiFe{sub 2}O{sub 4}. The results of Rietveld analysis showed that the sample annealed at 750 °C possesses inverse spinel structure, while the others have partially inverted spinel structure. The SEM analysis indicated a change of particle size and morphology at higher annealing temperature. The change in Raman modes was observed with the change of particle size and cation distribution. The highest value of the saturation magnetization (38 emu g{sup −1}) was obtained at annealing temperatures of 900 °C. - Highlights: • Nickel ferrite nanopowders were synthesized by the co-precipitation method. • The particle size, cation distribution and magnetic properties were explored. • The intensity of obtained Raman spectra is closely related to the grains size. • The magnetic saturation depends on the cation distribution and on a grain size.

  20. Flexible in-plane microsupercapacitors with electrospun NiFe2O4 nanofibers for portable sensing applications.

    Science.gov (United States)

    Li, La; Lou, Zheng; Han, Wei; Shen, Guozhen

    2016-08-11

    The development of wearable electronic devices in recent decades has brought new opportunities in the exploration of micro-supercapacitors as energy storage units. In this work, we report the fabrication of flexible NiFe2O4 nanofiber based in-plane micro-supercapacitors (MSCs), which can serve as energy storage receptors to drive a portable graphene pressure sensor. The obtained NiFe2O4 nanofiber electrodes exhibited a specific capacitance of 2.23 F cm(-3) at the scan rate of 100 mV s(-1), and excellent rate capability and robust cycling stability with a capacitance retention of 93.6% after 10 000 charge/discharge cycles. Moreover, the in-plane MSCs have superior flexibility and outstanding stability even after repetition of charge/discharge cycles during the convex and concave bending states. The MSCs offered a high energy density of 0.197 mWh cm(-3) and power density up to 2.07 W cm(-3). We also coupled the MSCs with a graphene pressure sensor as a micro-integrated system to implement it's pressure response function and used MATLAB to simulate this system behavior as well. The performance of the designed systems exhibited a stable pressure response, and the simulated results coincide well with the experimental data, demonstrating its feasibility in wearable electronic devices. PMID:27466001

  1. Dielectric and magnetic properties of NiFe2O4 at 2.45 GHz and heating capacity for potential uses under microwaves

    International Nuclear Information System (INIS)

    This paper presents the dielectric and magnetic properties, measured at 2.45 GHz, of a new nickel ferrite, NiFe2O4, synthetized by plasma technology. These properties were measured by the small perturbation method in a resonant cavity, from 293 to 513 K. Using these values, the adiabatic heating of nanoparticles of NiFe2O4 under microwave irradiation was also modeled. The wave propagation equation (Maxwell's equation) coupled to the heat transfer in the solid was numerically solved. The influence of parameters such as the bed volume, its porosity, the microwave incident power or the microwave system geometry is discussed. This study demonstrates that NiFe2O4 nanoparticles can be rapidly heated up to at least 513 K under microwaves and can probably achieve higher temperatures according to the thermal insulation. The magnetic contribution to heating overcomes the dielectric one in the explored temperature range. Very efficient energy yield (>90%) can then be achieved when the magnetic field position is centered over the bed. - Highlights: • A new nickel ferrite, NiFe2O4, was synthetized by plasma technology. • Its dielectric and magnetic properties were measured at 2.45 GHz. • The adiabatic heating of nanoparticles of NiFe2O4 under microwave was modeled. • NiFe2O4 nanoparticles can be rapidly heated up to at least 513 K. • The magnetic contribution to heating overcomes the dielectric one from 293 K to 513 K

  2. Crystal structures and magnetic properties of polyethylene glycol (PEG-4000) and silica-encapsulated nickel ferrite (NiFe2O4) nanoparticles

    Science.gov (United States)

    Shofiah, Siti; Muflihatun, Suharyadi, Edi

    2016-04-01

    Crystal structures and magnetic properties of polyethylene glycol (PEG-4000) and silica encapsulated nickel ferrite (NiFe2O4) nanoparticles comparable sizes have been studied in detail. NiFe2O4 were prepared by co-precipitation methods. Crystalline size is 4.8 ± 0.2 nm became 1.6 ± 0.1 nm and 10.6 ± 0.3 nm after encapsulated PEG-4000 and silica, respectively. Transmission electron microscopy (TEM) showed that encapsulated PEG-4000 and silica decreased agglomeration, controlled shape of nanoparticles more spherical and dispersed. Coercivity of NiFe2O4 was 46.2 Oe and then increased after encapsulated PEG-4000 to 47.8 Oe can be related to the multi-domains of NiFe2O4 as influence the crystalline size was decreased. Meanwhile, after encapsulated silica, coercivity of NiFe2O4 became 93 Oe as influence the crystalline size was increased at single-domains due to its strong shape anisotropy. Magnetization value decreased from 5.7 emu/g to 5.3 emu/g and 3.6 emu/g after encapsulated PEG-4000 and silica, respectively. The remanent magnetization showed decreasing when saturation magnetization decreased, and conversely. However, it also depends on presence of α-Fe2O3 phases and their material non magnetic of encapsulating. Based on the result, The magnetic properties exhibit a strong dependence on the crystalline size as influence PEG-4000 and silica encapsulated NiFe2O4 nanoparticles.

  3. Dielectric and magnetic properties of NiFe{sub 2}O{sub 4} at 2.45 GHz and heating capacity for potential uses under microwaves

    Energy Technology Data Exchange (ETDEWEB)

    Polaert, Isabelle, E-mail: isabelle.polaert@insa-rouen.fr [LSPC (Laboratoire de Sécurité des Procédés Chimiques). Institut National des Sciences Appliquées INSA Rouen (France); Bastien, Samuel [Département de génie chimique et de génie biotechnologique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 (Canada); Legras, Benoit [LSPC (Laboratoire de Sécurité des Procédés Chimiques). Institut National des Sciences Appliquées INSA Rouen (France); Département de génie chimique et de génie biotechnologique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 (Canada); Estel, Lionel [LSPC (Laboratoire de Sécurité des Procédés Chimiques). Institut National des Sciences Appliquées INSA Rouen (France); Braidy, Nadi [Département de génie chimique et de génie biotechnologique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 (Canada)

    2015-01-15

    This paper presents the dielectric and magnetic properties, measured at 2.45 GHz, of a new nickel ferrite, NiFe{sub 2}O{sub 4}, synthetized by plasma technology. These properties were measured by the small perturbation method in a resonant cavity, from 293 to 513 K. Using these values, the adiabatic heating of nanoparticles of NiFe{sub 2}O{sub 4} under microwave irradiation was also modeled. The wave propagation equation (Maxwell's equation) coupled to the heat transfer in the solid was numerically solved. The influence of parameters such as the bed volume, its porosity, the microwave incident power or the microwave system geometry is discussed. This study demonstrates that NiFe{sub 2}O{sub 4} nanoparticles can be rapidly heated up to at least 513 K under microwaves and can probably achieve higher temperatures according to the thermal insulation. The magnetic contribution to heating overcomes the dielectric one in the explored temperature range. Very efficient energy yield (>90%) can then be achieved when the magnetic field position is centered over the bed. - Highlights: • A new nickel ferrite, NiFe{sub 2}O{sub 4}, was synthetized by plasma technology. • Its dielectric and magnetic properties were measured at 2.45 GHz. • The adiabatic heating of nanoparticles of NiFe{sub 2}O{sub 4} under microwave was modeled. • NiFe{sub 2}O{sub 4} nanoparticles can be rapidly heated up to at least 513 K. • The magnetic contribution to heating overcomes the dielectric one from 293 K to 513 K.

  4. Synthesis and characterization of the NiFe2O4/Ni3Fe nanocomposite powder and compacts obtained by mechanical milling and spark plasma sintering

    International Nuclear Information System (INIS)

    Nanocomposite powder and compacts of NiFe2O4/Ni3Fe type were synthesized using mechanical milling and spark plasma sintering (SPS) techniques. The samples have been investigated by X-ray diffraction (XRD), laser particles size analysis, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The nanocomposite powder was obtained by mechanical milling in a high planetary ball mill of nanocrystalline NiFe2O4 and nanocrystalline Ni3Fe powders. The nanocomposite powder consists from Ni3Fe particles covered at the surface with a layer of NiFe2O4 fine particles and NiFe2O4 particles. The nanocomposite particles have the median diameter d50 of 1.6 μm. The sintering in 400–600 °C temperature range preserve the nanocomposite phases but lead to a high porosity. The nanocomposite compacts consist in Ni3Fe clusters surrounded by NiFe2O4. A sintering temperature of 800 °C leads to a good density for the nanocomposite compacts and to the new phase formation. The new phase is a wustite type (Fe1−xNixO) and is formed at the metal/ceramic interface. A change in the Ni/Fe ratio, in the spinel structure, was evidenced during sintering. Sintering at a temperature of 800 °C, leads to the formation of a mixed iron–nickel ferrite with a very small amount of nickel, Ni1−xFexFe2O4.

  5. 复合电沉积制备Ni/NiFe2O4电极及其电催化析氧性能%Ni/NiFe2O4 Composite Electrode Prepared by Electro-deposition and Its Electro-catalytic Performance Towards Oxygen Evolution Reaction

    Institute of Scientific and Technical Information of China (English)

    王丽品; 王森林; 段钱花

    2013-01-01

    采用共沉淀法制备尖晶石型NiFe2O4粉体,然后将其加入瓦特镀镍液中,采用复合电沉积制备Ni/NiFe2O4复合电极.通过改变镀液的pH值、阴极电流密度jk等条件,探索最佳工艺条件.运用扫描电子显微镜(SEM)、能谱分析(EDS)和X射线衍射仪(XRD)表征粉体以及复合电极的组成和结构.结果表明,在镀液pH值为5.8~6.0、jk为40×10-3 ~60×10-3 A/cm2条件下,所得复合电极中NiFe2O4的质量分数最高可达55.15%.采用循环伏安、稳态极化以及恒电势阶跃,研究了电极在5 mol/L KOH溶液中的电催化析氧性能.与Ni电极对比,Ni/NiFe2O4复合电极的电催化析氧性能更好,比表面积是镍电极的23.02倍,表观活化能降低了62.07 kJ/mol.恒电势长时间电解析氧实验表明,Ni/NiFe2 O4复合电极在碱性介质中具有较高的析氧稳定性.%The spinel-type NiFe2 O4 powders have been synthesized by a hydroxide co-precipitation method.The Ni/NiFe2O4 composite coating was prepared through electro-deposition in Watt nickel plating by adding some NiFe2O4 powders.The optimized plating conditions for the composite electro-deposition were investigated by varying parameters,such as the plating solution pH and the cathode current density jk.The composition and structure of the Ni/NiFe2O4 composite coating were characterized by scanning electron microscopy(SEM),energy X-ray diffraction(XRD) and dispersive spectrometer(EDS).The results show that the NiFe2O4 mass content in the Ni/NiFe2 O4 composite coating is the highest (55.15%) at optimized plating conditions of a solution pH =5.8 ~6.0 and a cathodic current density jk =40 × 10-3 ~60 × 10-3 A/cm2.In 5 mol/L KOH solution,the electro-catalytic properties towards the oxygen evolution reaction (OER) of the Ni/NiFe2O4 composite electrode was studied using cyclic voltammetry,steady-state polarization,and chronoamperometry.Compared with the nickel electrode,the electro-catalytic properties towards OER of

  6. Bimetallic nanoparticles for arsenic detection.

    Science.gov (United States)

    Moghimi, Nafiseh; Mohapatra, Mamata; Leung, Kam Tong

    2015-06-01

    Effective and sensitive monitoring of heavy metal ions, particularly arsenic, in drinking water is very important to risk management of public health. Arsenic is one of the most serious natural pollutants in soil and water in more than 70 countries in the world. The need for very sensitive sensors to detect ultralow amounts of arsenic has attracted great research interest. Here, bimetallic FePt, FeAu, FePd, and AuPt nanoparticles (NPs) are electrochemically deposited on the Si(100) substrate, and their electrochemical properties are studied for As(III) detection. We show that trace amounts of As(III) in neutral pH could be determined by using anodic stripping voltammetry. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, and Pd) than pristine noble metal NPs (without Fe alloying). Limit of detection and linear range are obtained for FePt, FeAu, and FePd NPs. The best performance is found for FePt NPs with a limit of detection of 0.8 ppb and a sensitivity of 0.42 μA ppb(-1). The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), as the most detrimental interferer ion for As detection. The bimetallic NPs therefore promise to be an effective, high-performance electrochemical sensor for the detection of ultratrace quantities of arsenic. PMID:25938763

  7. Mechanical alloying of a hydrogenation catalyst used for the remediation of contaminated compounds

    Science.gov (United States)

    Quinn, Jacqueline W. (Inventor); Clausen, Christian A. (Inventor); Geiger, Cherie L. (Inventor); Aitken, Brian S. (Inventor)

    2012-01-01

    A hydrogenation catalyst including a base material coated with a catalytic metal is made using mechanical milling techniques. The hydrogenation catalysts are used as an excellent catalyst for the dehalogenation of contaminated compounds and the remediation of other industrial compounds. Preferably, the hydrogenation catalyst is a bimetallic particle including zero-valent metal particles coated with a catalytic material. The mechanical milling technique is simpler and cheaper than previously used methods for producing hydrogenation catalysts.

  8. P–C-Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine–Boranes**

    Science.gov (United States)

    Johnson, Heather C; Weller, Andrew S

    2015-01-01

    {Rh(xantphos)}-based phosphido dimers form by P–C activation of xantphos (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2BNMeH]n from H3B⋅NMeH2 and dimeric [H2BNMe2]2 from H3B⋅NMe2H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization. PMID:26140498

  9. The annealing temperature dependences of microstructures and magnetic properties in electro-chemical deposited CoNiFe thin films

    Science.gov (United States)

    Suharyadi, Edi; Riyanto, Agus; Abraha, Kamsul

    2016-04-01

    CoNiFe thin films with various compositions had been successfully fabricated using electro-chemical deposition method. The crystal structure of Co65Ni15Fe20, Co62Ni15Fe23, and Co55Ni15Fe30 thin films was fcc, bcc-fcc mix, and bcc, respectively. The difference crystal structure results the difference in magnetic properties. The saturation magnetic flux density (Bs) of Co65Ni15Fe20, Co62Ni15Fe23, and Co55Ni15Fe30 thin films was 1.89 T, 1.93 T, and 2.05 T, respectively. An optimal annealing temperature was determined for controlling the microstructure and magnetic properties of CoNiFe thin films. Depending on annealing temperature, the ratio of bcc and fcc structure varied without changing the film composition. By annealing at temperature of T ≥ 350°C, the intensity ratio of X-ray diffraction peaks for bcc(110) to fcc(111) increased. The increase of phase ratio of bcc(110) to fcc(111) caused the increase of Bs, from 1.89 T to 1.95 T. Coercivity (Hc) also increased after annealing, from 2.6 Oe to 18.6 Oe for fcc phase thin films, from 2.0 Oe to 12.0 Oe for fcc-bcc mix phase thin films, and 7.8 Oe to 8 Oe for bcc phase thin films. The changing crystal structures during annealing process indicated that the thermal treatment at high temperature cause the changing crystallinity and atomic displacement. The TEM bright-field images with corresponding selected-area electron diffraction (SAED) patterns showed that there are strongly effects of thermal annealing on the size of fcc and bcc phase crystalline grain as described by size of individual spot and discontinuous rings. The size of crystalline grains increased by thermal annealing. The evolution of bcc and fcc structures of CoNiFe during annealing is though to be responsible for the change of magnetic properties.

  10. Determination of Quantity of Silicon Contained in Amorphous Ni-Fe-Si-B by Photometric Method%钼兰光度法测定Ni-Fe-Si-B非晶中硅含量

    Institute of Scientific and Technical Information of China (English)

    朱佳

    2011-01-01

    The determination of the quantity of silicon contained in amorphous Ni-Fe-Si-B has been investigated according to applied photometric method. The sample is put into the thin acid solution , and silicic acid can be reacted with molybdic acid to generate silicon-molybdenum heteropoly acid in thin acid solution. After the saturated boric acid is mixed with extra fluoride ions, ferrous ammonium sulphate can be reduced to silicon-molybdenum blue with the help of oxalic acid, and then the colorimetric analysis can be obtained at the wavelength of 680 nm. The experiment showed that the data by means of the appied photometric method is the same as that by the gravimetric determination. The applied photometric method can be used to measure the quantity of silicon in middle content.%本文应用光度法对Ni-Fe-Si-B非晶中硅含量的测定进行了研究.试样料在微酸性溶液中,硅酸与钼酸铵生成硅钼杂多酸,饱和硼酸络合过量氟离子,再用草酸-硫酸亚铁铵还原成硅钼蓝,在680 nm波长条件下进行比色分析.实验结果表明,本方法测定结果与重量法测定结果相符吻合,能满足非晶中中硅含量的测定.

  11. Bimetallic Nanocatalysts in Mesoporous Silica for Hydrogen Production from Coal-Derived Fuels

    Energy Technology Data Exchange (ETDEWEB)

    Kuila, Debasish; Ilias, Shamsuddin

    2013-02-13

    In steam reforming reactions (SRRs) of alkanes and alcohols to produce H2, noble metals such as platinum (Pt) and palladium (Pd) are extensively used as catalyst. These metals are expensive; so, to reduce noble-metal loading, bi-metallic nanocatalysts containing non-noble metals in MCM-41 (Mobil Composition of Material No. 41, a mesoporous material) as a support material with high-surface area were synthesized using one-pot hydrothermal procedure with a surfactant such as cetyltrimethylammonium bromide (CTAB) as a template. Bi-metallic nanocatalysts of Pd-Ni and Pd-Co with varying metal loadings in MCM-41 were characterized by x-ray diffraction (XRD), N2 adsorption, and Transmission electron microscopy (TEM) techniques. The BET surface area of MCM-41 (~1000 m2/g) containing metal nanoparticles decreases with the increase in metal loading. The FTIR studies confirm strong interaction between Si-O-M (M = Pd, Ni, Co) units and successful inclusion of metal into the mesoporous silica matrix. The catalyst activities were examined in steam reforming of methanol (SRM) reactions to produce hydrogen. Reference tests using catalysts containing individual metals (Pd, Ni and Co) were also performed to investigate the effect of the bimetallic system on the catalytic behavior in the SRM reactions. The bimetallic system remarkably improves the hydrogen selectivity, methanol conversion and stability of the catalyst. The results are consistent with a synergistic behavior for the Pd-Ni-bimetallic system. The performance, durability and thermal stability of the Pd-Ni/MCM-41 and Pd-Co/MCM-41 suggest that these materials may be promising catalysts for hydrogen production from biofuels. A part of this work for synthesis and characterization of Pd-Ni-MCM-41 and its activity for SRM reactions has been published (“Development of Mesoporous Silica Encapsulated Pd-Ni Nanocatalyst for Hydrogen Production” in “Production and Purification of Ultraclean

  12. Partial oxidation of methane over bimetallic copper- and nickel-actinide oxides (Th, U)

    International Nuclear Information System (INIS)

    The study of partial oxidation of methane (POM) over bimetallic nickel- or copper-actinide oxides was undertaken. Binary intermetallic compounds of the type AnNi2 (An = Th, U) and ThCu2 were used as precursors and the products (2NiO.UO3, 2NiO.ThO2 and 2CuO.ThO2) characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and temperature-programmed reduction. The catalysts were active and selective for the conversion of methane to H2 and CO and stable for a period of time of ∼18 h on stream. The nickel catalysts were more active and selective than the copper catalyst and, under the same conditions, show a catalytic behaviour comparable to that of a platinum commercial catalyst, 5 wt% Pt/Al2O3. The catalytic activity increases when uranium replaces thorium and the selectivity of this type of materials is clearly different from that of single metal oxides and/or mechanical mixtures. The good catalytic behaviour of the bimetallic copper- and nickel-actinide oxides was attributed to an unusual interaction between copper or nickel oxide and the actinide oxide phase as showed by H2-TPR, XPS and Raman analysis of the catalysts before and after reaction.

  13. Science Letters:Dechlorination mechanism of 2,4-dichlorophenol by Ni/Fe nanoparticles in the presence of humic acid

    Institute of Scientific and Technical Information of China (English)

    Jing-jing WO; Zhen ZHANG; Xin-hua XU

    2009-01-01

    To understand the feasibility of its application to the in situ remediation of contaminated groundwater, the dechlori-nation of 2,4-dichlorophenol (2,4-DCP) by Ni/Fe nanoparticles in the presence of humic acid (HA) was investigated. We found that, as high performance liquid chromatography (HPLC) was used, the 2,4-DCP was first quickly reduced to o-chlorophenol (o-CP) andp-chlorophenol (p-CP), and then reduced to phenol as the final product. Our experimental results indicated that HA had an adverse effect on the dechlorination of 2,4-DCP by Ni/Fe nanoparticles, as the HA concentration increased, the removal rate decreased evidently. It also demonstrated that 2,4-DCP was reduced more easily to o-CP than to p-CP, and that the sequence of the tendency in dechlorination of intermediates was p-CP>o-CP. Transmission electron microscope (TEM) showed that HA could act as an adsorbate to compete reactive sites on the surface of Ni/Fe nanoparticles to decrease the dechlorination rate. Also we con-cluded that the dechlorination reaction of 2,4-DCP over Ni/Fe nanoparticles progressed through catalytic reductive dechlorination.

  14. Facile hybridization of Ni@Fe2O3 superparticles with functionalized reduced graphene oxide and its application as anode material in lithium-ion batteries.

    Science.gov (United States)

    Backert, Gregor; Oschmann, Bernd; Tahir, Muhammad Nawaz; Mueller, Franziska; Lieberwirth, Ingo; Balke, Benjamin; Tremel, Wolfgang; Passerini, Stefano; Zentel, Rudolf

    2016-09-15

    In our present work we developed a novel graphene wrapping approach of Ni@Fe2O3 superparticles, which can be extended as a concept approach for other nanomaterials as well. It uses sulfonated reduced graphene oxide, but avoids thermal treatments and use of toxic agents like hydrazine for its reduction. The modification of graphene oxide is achieved by the introduction of sulfate groups accompanied with reduction and elimination reactions, due to the treatment with oleum. The successful wrapping of nanoparticles is proven by energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The developed composite material shows strongly improved performance as anode material in lithium-ion batteries (compared to unwrapped Ni@Fe2O3) as it offers a reversible capacity of 1051mAhg(-1) after 40 cycles at C/20, compared with 460mAhg(-1) for unwrapped Ni@Fe2O3. The C rate capability is also improved by the wrapping approach, as specific capacities for wrapped particles are about twice of those offered by unwrapped particles. Additionally, the benefit for the use of the advanced superparticle morphology is demonstrated by comparing wrapped Ni@Fe2O3 particles with wrapped Fe2O3 nanorice. PMID:27295319

  15. Influence of CoFe and NiFe pinned layers on sensitivity of planar Hall biosensors based on spin-valve structures

    International Nuclear Information System (INIS)

    This paper deals with the magnetization, magnetoresistance and planar Hall effect (PHE) of NiFe(10)/Cu(1.2)/NiFe(tp)/IrMn(15) (nm) and NiFe(10)/Cu(1.2)/CoFe(tp)/IrMn(15) (nm) spin-valve structures with various thicknesses of pinned layer tp = 2, 6, 9, 12 nm and a fixed free layer NiFe of tf = 10 nm. Experimental investigations are performed for 50 × 50 μm junctions fabricated using lithography technique. The results show that the thinner the pinned layers, the higher is the PHE sensitivity obtained in both systems. In addition, in the spin-valve structures with the same pinned layer thickness, the CoFe-based system exhibits higher magnetoresistive ratio, but lower PHE sensitivity with respect to those of the FeNi-based system. The results are discussed in terms of the spin twist as well as the coherent rotation of the magnetization in the individual ferromagnetic layers. The highest PHE sensitivity S of 110 μV (kA m−1)−1 has been obtained in the FeNi-based spin-valve structure with tp = 2 nm. This result is rather promising for the spintronic biochip developments. (paper)

  16. Krypton Derivatization of an O2 -Tolerant Membrane-Bound [NiFe] Hydrogenase Reveals a Hydrophobic Tunnel Network for Gas Transport.

    Science.gov (United States)

    Kalms, Jacqueline; Schmidt, Andrea; Frielingsdorf, Stefan; van der Linden, Peter; von Stetten, David; Lenz, Oliver; Carpentier, Philippe; Scheerer, Patrick

    2016-04-25

    [NiFe] hydrogenases are metalloenzymes catalyzing the reversible heterolytic cleavage of hydrogen into protons and electrons. Gas tunnels make the deeply buried active site accessible to substrates and inhibitors. Understanding the architecture and function of the tunnels is pivotal to modulating the feature of O2 tolerance in a subgroup of these [NiFe] hydrogenases, as they are interesting for developments in renewable energy technologies. Here we describe the crystal structure of the O2 -tolerant membrane-bound [NiFe] hydrogenase of Ralstonia eutropha (ReMBH), using krypton-pressurized crystals. The positions of the krypton atoms allow a comprehensive description of the tunnel network within the enzyme. A detailed overview of tunnel sizes, lengths, and routes is presented from tunnel calculations. A comparison of the ReMBH tunnel characteristics with crystal structures of other O2 -tolerant and O2 -sensitive [NiFe] hydrogenases revealed considerable differences in tunnel size and quantity between the two groups, which might be related to the striking feature of O2 tolerance. PMID:26913499

  17. Hydrogen induced dis-proportionation studies on Zr-Co-M (M=Ni, Fe, Ti) ternary alloys

    International Nuclear Information System (INIS)

    The intermetallic compound ZrCo is considered as a suitable material for storage, supply and recovery of hydrogen isotopes in International Thermonuclear Experimental Reactor (ITER). However, upon repeated hydriding-dehydriding cycles, the hydrogen storage capacity of ZrCo decreases, which is attributed to the disproportionate reaction ZrCo + H2 ↔ ZrH2 + ZrCo2. The reduction of hydrogen storage capacity of ZrCo is not desirable for its use in tritium facilities. In our previous studies, attempts were made to improve the durability of ZrCo against dis-proportionation by including a third element. The present study is aimed to investigate the hydrogen induced dis-proportionation of Zr-Co-M (M=Ni, Fe and Ti) ternary alloys under hydrogen delivery conditions

  18. Ruthenium sulfate complexes forming during electrochemical dissolution of Ni-Fe-Ru alloys in sulfuric acid solutions

    International Nuclear Information System (INIS)

    Ruthenium sulfate complexes, prepared by anodic dissolution of Ni-Fe-Ru alloys in sulfuric acid solutions, have been studied. Ruthenium oxidation states in the complexes, their charge, dimensions, are determined, and Fe effect on the formation of different forms of complexes is clarified. Using the method of gel-chromatography, it is established, that at the anode potential >= 1w0 V ruthenium transfers into solution in the form of several neutral and anion complex forms of Ru(4): grey-violet polymeric ones (dimensions 1.6-2.3 nm), presumably containing the groupings (Rusub(n)(OH)sub(2(n-1))) or [Rusub(n)Osub(2(n-1))], where n>=3, red dimeric ones, containing (RuO)2, mixture of monomeric browngrey sulfate complexes with the grouping RuO. Fe hinders the formation of Ru complex polymeric forms

  19. Effects of Electron Beam Irradiation on the Magnetic Properties of Nickel Ferrite (NiFe2O4) Nanoparticles

    International Nuclear Information System (INIS)

    The effects of electron beam irradiation on the magnetic properties of Nickel Ferrite (NiFe2O4) nanoparticles in doses of 0, 100 and 200 kGy was analyzed. The values of saturation magnetization (MS) results at room temperature increased from 31.33, 35.12 and 39.36 emu/ g respectively. Xray diffraction (XRD) analysis of the samples showed that the crystallite size of the particles decreased from 13.16 nm to 7.52 nm with increasing doses of irradiation. The lattice parameter of the cubic structure decreases with increasing irradiation doses, due to ionisation of Fe2+ to Fe3+ producing a closed packing in the cubic crystal structure. (author)

  20. Hydrogen peroxide biosensor based on horseradish peroxidase immobilized on chitosan-wrapped NiFe2O4 nanoparticles

    International Nuclear Information System (INIS)

    A biosensor for hydrogen peroxide was constructed by immobilizing horseradish peroxidase on chitosan-wrapped NiFe2O4 nanoparticles on a glassy carbon electrode (GCE). The electron mediator carboxyferrocene was also immobilized on the surface of the GCE. UV-vis spectra, Fourier transform IR spectra, scanning electron microscopy, and electrochemical impedance spectra were acquired to characterize the biosensor. The experimental conditions were studied and optimized. The biosensor responds linearly to H2O2 in the range from 1.0 x 10-5 to 2.0 x 10-3 M and with a detection limit of 2.0 x 10-6 M (at S/N = 3). (author)

  1. Exchange biased FeNi/FeMn bilayers with coercivity and switching field enhanced by FeMn surface oxidation

    Directory of Open Access Journals (Sweden)

    A. V. Svalov

    2013-09-01

    Full Text Available FeNi/FeMn bilayers were grown in a magnetic field and subjected to heat treatments at temperatures of 50 to 350 °C in vacuum or in a gas mixture containing oxygen. In the as-deposited state, the hysteresis loop of 30 nm FeNi layer was shifted. Low temperature annealing leads to a decrease of the exchange bias field. Heat treatments at higher temperatures in gas mixture result in partial oxidation of 20 nm thick FeMn layer leading to a nonlinear dependence of coercivity and a switching field of FeNi layer on annealing temperature. The maximum of coercivity and switching field were observed after annealing at 300 °C.

  2. Impact of different polyimide-based substrates on the soft magnetic properties of NiFe thin films

    Science.gov (United States)

    Rittinger, Johannes; Taptimthong, Piriya; Jogschies, Lisa; Wurz, Marc C.; Rissing, Lutz

    2015-05-01

    We investigated the impact of polymer substrates on the magnetic properties of soft magnetic thin films. Experiments were carried out to evaluate the performance of AMR (anisotropic magnetoresistive) sensors deposited on polymeric substrates and to give indications for the design of future sensors on flexible substrates. Sputtered permalloy (NiFe 81/19) was used as a soft magnetic thin film layer. As substrate materials, liquid polyimide precursors and DuPont Kapton® HN foil were examined. Surface roughness was determined for each substrate material. The dynamic of soft magnetic behavior of the permalloy thin films was observed in a homogenous alternating magnetic field. Resulting R-Hcurves were evaluated in regard to the magnitude of the magnetoresistive effect (ΔR / R0-ratio), as well as the resulting magnetic anisotropy of the tested samples. B-H-curves were obtained by means of a vibrating sample magnetometer (VSM).

  3. Microfabrication of magnetostrictive beams based on NiFe film doped with B and Mo for integrated sensor systems

    KAUST Repository

    Alfadhel, Ahmed

    2012-03-09

    This paper reports the development of integrated micro-sensors consisting of 1 -µm-thick magnetostrictive cantilevers or bridges with 500 µm in length and conducting interrogation elements. The thin films are fabricated by sputter deposition of NiFe doped with B and Mo, and the magnetic properties are enhanced by field annealing, resulting in a coercivity of 2.4 Oe. In operation, an alternating current applied to the interrogation elements magnetizes the magnetostrictive structures. The longitudinal resonant frequency is detected as an impedance change of the interrogation elements. The magnetostrictive micro-beams provide high resonant frequencies—2.95 MHz for the cantilever and 5.46 MHz for the bridge—which can be exploited to develop sensors of high sensitivity.

  4. Control of domain wall pinning by localised focused Ga + ion irradiation on Au capped NiFe nanowires

    International Nuclear Information System (INIS)

    Understanding domain wall pinning and propagation in nanowires are important for future spintronics and nanoparticle manipulation technologies. Here, the effects of microscopic local modification of the magnetic properties, induced by focused-ion-beam intermixing, in NiFe/Au bilayer nanowires on the pinning behavior of domain walls was investigated. The effects of irradiation dose and the length of the irradiated features were investigated experimentally. The results are considered in the context of detailed quasi-static micromagnetic simulations, where the ion-induced modification was represented as a local reduction of the saturation magnetization. Simulations show that domain wall pinning behavior depends on the magnitude of the magnetization change, the length of the modified region, and the domain wall structure. Comparative analysis indicates that reduced saturation magnetisation is not solely responsible for the experimentally observed pinning behavior.

  5. Studies on the structural and magnetics properties in NiFe2O4 nanoparticles for biomedical applications

    International Nuclear Information System (INIS)

    The possibility of biomedical applications of nanoparticles NiFe2O4 motivated the study of magnetic and structural properties of these ferrites. The nanoparticles were synthesized by proteic sol-gel, starting from an aqueous solution of edible gelatin with salts of nickel and iron, drying formed a resin that was burned in 400, 600, 800 and 1000 deg C, these were characterized by diffraction X-rays and the structural parameters determined using Rietveld refinement, the size of the nanoparticles was determined by Scherrer equation. Nanoparticles of nickel ferrite were sizes 7 nm and 68 nm for samples calcined at 400 deg C and 1000 deg C, respectively. The magnetic properties were investigated by Moessbauer spectroscopy, which determined superparamagnetic nanoparticles calcined at 400 deg C, these were functionalized and coated with biocompatible polymer, objective use as a carrier for drugs. The size distribution of the smallest nanoparticles was investigated by small angle scattering. (author)

  6. Bimetallic materials for large diameter pipelines

    International Nuclear Information System (INIS)

    The results are presented of the investigation of bimetallic pipes made of Ni-Mn-Mo-V + Cb08Kh19N10G2B steel and of 19MN5 (type 22K) + SB 08Kh19N10G2B steels, manufactured in Japan for piping nuclear power stations for service under corrosion attack by coolants at high both pressure and temperature and under heavy cyclic loads. The procedures are described for manufacturing elements of piping from bimetallic seamless large-diameter pipes. A study has been made of the variation in bimetallic microstructure of the short-time mechanical properties, of the impact strength, of the critical brittleness point in initial and aged states of the cyclic strength and of the strength of the bimetallic joint

  7. Co-Ni-NiFe2O4金属陶瓷的制备及抗氧化性研究%THE PREPARATION OF Co-Ni-NiFe2O4 CERMET AND STUDY OF ANTI-OXIDATION

    Institute of Scientific and Technical Information of China (English)

    王俊茹; 李玉胶; 朱春城

    2009-01-01

    采用传统的粉末冶金技术及真空固相烧结的方法,制备出了Co-Ni-NiFe2O4金属陶瓷惰性阳极材料,通过研究确定了制备NiFe2O4粉体及真空固相烧结Co-Ni-NiFe2O4金属陶瓷的合理工艺.实验表明:Co-Ni-NiFe2O4金属陶瓷在960℃条件下的氧化动力学曲线近似符合抛物线规律,NiFe2O4含量越多,试样的抗氧化性越强;并且在高温氧化后,氧化膜在生长过程中产生明显的择优取向.

  8. Crystal structures of the carbamoylated and cyanated forms of HypE for [NiFe] hydrogenase maturation.

    Science.gov (United States)

    Tominaga, Taiga; Watanabe, Satoshi; Matsumi, Rie; Atomi, Haruyuki; Imanaka, Tadayuki; Miki, Kunio

    2013-12-17

    Hydrogenase pleiotropically acting protein (Hyp)E plays a role in biosynthesis of the cyano groups for the NiFe(CN)2CO center of [NiFe] hydrogenases by catalyzing the ATP-dependent dehydration of the carbamoylated C-terminal cysteine of HypE to thiocyanate. Although structures of HypE proteins have been determined, until now there has been no structural evidence to explain how HypE dehydrates thiocarboxamide into thiocyanate. Here, we report the crystal structures of the carbamoylated and cyanated forms of HypE from Thermococcus kodakarensis in complex with nucleotides at 1.53- and 1.64-Å resolution, respectively. Carbamoylation of the C-terminal cysteine (Cys338) of HypE by chemical modification is clearly observed in the present structures. In the presence of ATP, the thiocarboxamide of Cys338 is successfully dehydrated into the thiocyanate. In the carbamoylated state, the thiocarboxamide nitrogen atom of Cys338 is close to a conserved glutamate residue (Glu272), but the spatial position of Glu272 is less favorable for proton abstraction. On the other hand, the thiocarboxamide oxygen atom of Cys338 interacts with a conserved lysine residue (Lys134) through a water molecule. The close contact of Lys134 with an arginine residue lowers the pKa of Lys134, suggesting that Lys134 functions as a proton acceptor. These observations suggest that the dehydration of thiocarboxamide into thiocyanate is catalyzed by a two-step deprotonation process, in which Lys134 and Glu272 function as the first and second bases, respectively. PMID:24297906

  9. A Facile Molten-Salt Route for Large-Scale Synthesis of NiFe2O4 Nanoplates with Enhanced Lithium Storage Capability.

    Science.gov (United States)

    Huang, Gang; Du, Xinchuan; Zhang, Feifei; Yin, Dongming; Wang, Limin

    2015-09-28

    Binary metal oxides have been deemed as a promising class of electrode materials for high-performance lithium ion batteries owing to their higher conductivity and electrochemical activity than corresponding monometal oxides. Here, NiFe2O4 nanoplates consisting of nanosized building blocks have been successfully fabricated by a facile, large-scale NaCl and KCl molten-salt route, and the changes in the morphology of NiFe2O4 as a function of the molten-salt amount have been systemically investigated. The results indicate that the molten-salt amount mainly influences the diameter and thickness of the NiFe2O4 nanoplates as well as the morphology of the nanosized building blocks. Cyclic voltammetry (CV) and galvanostatic charge-discharge measurements have been conducted to evaluate the lithium storage properties of the NiFe2O4 nanoplates prepared with a Ni(NO3)2/Fe(NO3)3/KCl/NaCl molar ratio of 1:2:20:60. A high reversible capacity of 888 mAh g(-1) is delivered over 100 cycles at a current density of 100 mA g(-1). Even at a current density of 5000 mA g(-1) , the discharge capacity could still reach 173 mAh g(-1). Such excellent electrochemical performances of the NiFe2O4 nanoplates are contributed to the short Li(+) diffusion distance of the nanosized building blocks and the synergetic effect of the Ni(2+) and Fe(3+) ions. PMID:26251115

  10. Bimetallic nanoalloys in heterogeneous catalysis of industrially important reactions: synergistic effects and structural organization of active components

    International Nuclear Information System (INIS)

    The review is concerned with correlations between the synergistic effects and structural organization of the surface of bimetallic alloys that are used as active components of catalysts for selective hydrogenation of organic compounds and for CO oxidation in hydrogen-rich mixtures. Studies on the preparation of novel highly efficient catalysts using modern theoretical approaches, computer-assisted molecular design and original synthetic procedures are considered. It is shown that introduction of the second metal into the monometallic catalyst and subsequent formation of alloy particles with modified structure of the surface and near-surface layers leads to nonadditive enhancement of catalytic activity and/or selectivity. The bibliography includes 203 references

  11. Catalysts and process for liquid hydrocarbon fuel production

    Energy Technology Data Exchange (ETDEWEB)

    White, Mark G.; Ranaweera, Samantha A.; Henry, William P.

    2016-08-02

    The present invention provides a novel process and system in which a mixture of carbon monoxide and hydrogen synthesis gas, or syngas, is converted into hydrocarbon mixtures composed of high quality distillates, gasoline components, and lower molecular weight gaseous olefins in one reactor or step. The invention utilizes a novel supported bimetallic ion complex catalyst for conversion, and provides methods of preparing such novel catalysts and use of the novel catalysts in the process and system of the invention.

  12. Structural Characterization of Bimetallic Nanocrystal Electrocatalysts

    Energy Technology Data Exchange (ETDEWEB)

    Cullen, David A [ORNL

    2016-01-01

    Late transition metal nanocrystals find applications in heterogeneous catalysis such as plasmon-enhanced catalysis and as electrode materials for fuel cells, a zero-emission and sustainable energy technology. Their commercial viability for automotive transportation has steadily increased in recent years, almost exclusively due to the discovery of more efficient bimetallic nanocatalysts for the oxygen reduction reaction (ORR) at the cathode. Despite improvements to catalyst design, achieving high activity while maintaining durability is essential to further enhance their performance for this and other important applications in catalysis. Electronic effects arising from the generation of metal-metal interfaces, from plasmonic metals, and from lattice distortions, can vastly improve sorption properties at catalytic surfaces, while increasing durability.[1] Multimetallic lattice-strained nanoparticles are thus an interesting opportunity for fundamental research.[2,3] A colloidal synthesis approach is demonstrated to produce AuPd alloy and Pd@Au core-shell nanoicosahedra as catalysts for electro-oxidations. The nanoparticles are characterized using aberration-corrected scanning transmission electron microscopy (ac-STEM) and large solid angle energy dispersive X-ray spectroscopy (EDS) on an FEI Talos 4-detector STEM/EDS system. Figure 1 shows bright-field (BF) and high-angle annular dark-field (HAADF) ac-STEM images of the alloy and core-shell nanoicosahedra together with EDS line-scans and elemental maps. These structures are unique in that the presence of twin boundaries, alloying, and core-shell morphology could create highly strained surfaces and interfaces. The shell thickness of the core-shell structures observed in HAADF-STEM images is tuned by adjusting the ratio between metal precursors (Figure 2a-f) to produce shells ranging from a few to several monolayers. Specific activity was measured in ethanol electro-oxidation to examine the effect of shell thickness on

  13. Electrochemical synthesis of NiFe2O4 nanoparticles: Characterization and their catalytic applications

    International Nuclear Information System (INIS)

    Highlights: ► Nickel ferrite nanoparticles were synthesized by new electrochemical method. ► Stoichometric nanoparticles with 20 nm of size can be prepared with this method. ► Nickel ferrites nanoparticles were used as catalysts in the direct oxidation of glucose at pH 7. - Abstract: In this work a new route for preparation of nickel ferrites nanoparticles has been developed. The synthesis is carried out in an electrochemical cell using three electrodes, a sheet of iron was employed as cathode and two sheets of iron and nickel were used as sacrificial anodes. The obtained nanoparticles were washed several times with distilled water, separated magnetically and dried under vacuum with constant temperature for 12 h. The characterization of the nanoparticles was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Inductively coupled plasma mass spectrometry (ICP–MS). Magnetic measurements were carried out using a vibrating sample magnetometer (VSM). To evaluate the catalytical properties of these nanoparticles against the oxidation of glucose a graphite paste electrode (GPE) was made. The proportions of the nanoparticles in GPE were 5, 10, 20 and 50% in weight. The electrode shows promising properties for its use as catalyst in the glucose oxidation.

  14. Connection between the microstructure of steels Fe-23 % Ni, Fe-33 % Ni, Fe-23 % Ni-0.4 % C and Fe-Cr-Ni 18-10 in the austenitic or martensitic state and their behaviour after cathodic loading with tritium

    International Nuclear Information System (INIS)

    The microstructure of the alloys: Fe-23 % Ni, Fe-33 % Ni, Fe-23 % Ni-0.4 % C, Z2CN18-10 (304L), Z5CNT18-10 (321) which plays an important part in metal embrittlement by hydrogen, is studied by optical microscopy, scanning and transmission electron microscopy. An extensive study of carbon segregation is carried out in acicular martensite Fe-Ni-C using high resolution C 14 autoradiography because of the importance of hydrogen-carbon interaction out of the solution on hydrogen trapping in hydrogen embrittlement of iron alloys

  15. Synthesis, characterization, and growth simulations of Cu–Pt bimetallic nanoclusters

    Directory of Open Access Journals (Sweden)

    Subarna Khanal

    2014-08-01

    Full Text Available Highly monodispersed Cu–Pt bimetallic nanoclusters were synthesized by a facile synthesis approach. Analysis of transmission electron microscopy (TEM and spherical aberration (Cs-corrected scanning transmission electron microscopy (STEM images shows that the average diameter of the Cu–Pt nanoclusters is 3.0 ± 1.0 nm. The high angle annular dark field (HAADF-STEM images, intensity profiles, and energy dispersive X-ray spectroscopy (EDX line scans, allowed us to study the distribution of Cu and Pt with atomistic resolution, finding that Pt is embedded randomly in the Cu lattice. A novel simulation method is applied to study the growth mechanism, which shows the formation of alloy structures in good agreement with the experimental evidence. The findings give insight into the formation mechanism of the nanosized Cu–Pt bimetallic catalysts.

  16. Correlation between Fischer-Tropsch catalytic activity and composition of catalysts

    Directory of Open Access Journals (Sweden)

    Subbarao Duvvuri

    2011-11-01

    Full Text Available Abstract This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on alumina. The catalysts were prepared by a wet impregnation method. Samples were characterized using temperature-programmed reduction (TPR, temperature-programmed oxidation (TPO, CO-chemisorption, transmission electron microscopy (TEM, field emission scanning electron microscopy (FESEM-EDX and N2-adsorption analysis. Fischer-Tropsch synthesis (FTS was carried out in a fixed-bed microreactor at 543 K and 1 atm, with H2/CO = 2 v/v and space velocity, SV = 12L/g.h. The physicochemical properties and the FTS activity of the bimetallic catalysts were analyzed and compared with those of monometallic cobalt and iron catalysts at similar operating conditions. H2-TPR analysis of cobalt catalyst indicated three temperature regions at 506°C (low, 650°C (medium and 731°C (high. The incorporation of iron up to 30% into cobalt catalysts increased the reduction, CO chemisorption and number of cobalt active sites of the catalyst while an opposite trend was observed for the iron-riched bimetallic catalysts. The CO conversion was 6.3% and 4.6%, over the monometallic cobalt and iron catalysts, respectively. Bimetallic catalysts enhanced the CO conversion. Amongst the catalysts studied, bimetallic catalyst with the composition of 70Co30Fe showed the highest CO conversion (8.1% while exhibiting the same product selectivity as that of monometallic Co catalyst. Monometallic iron catalyst showed the lowest selectivity for C5+ hydrocarbons (1.6%.

  17. Elastic and hierarchical porous carbon nanofibrous membranes incorporated with NiFe2O4 nanocrystals for highly efficient capacitive energy storage

    Science.gov (United States)

    Ge, Jianlong; Fan, Gang; Si, Yang; He, Jianxin; Kim, Hak-Yong; Ding, Bin; Al-Deyab, Salem S.; El-Newehy, Mohamed; Yu, Jianyong

    2016-01-01

    Flexible membranes created from porous carbon nanofibers (CNFs) hold great promise in the next generation wearable energy storage devices, but challenges still remain due to the poor mechanical properties of porous carbon nanofibers. Here, we report a facile strategy to fabricate elastic and hierarchical porous CNF membranes with NiFe2O4 nanocrystals embedded via multicomponent electrospinning and nano-doping methods. Benefiting from the scattering effect of NiFe2O4 nanocrystals and graphitized carbon layers for the condensed stress, the resultant CNF membranes exhibit an enhanced elasticity with a bending radius Benefiting from the robust mechanical stability, hierarchical porous structures and good electrochemical properties, the NiFe2O4 doped CNF membranes demonstrate a high electrical capacitance of 343 F g-1, and good reversibility with a cycling efficiency of 97.4% even after 10 000 cycles. The successful synthesis of elastic porous CNF membranes also provided a versatile platform for the design and development of functional CNF based materials for various applications.Flexible membranes created from porous carbon nanofibers (CNFs) hold great promise in the next generation wearable energy storage devices, but challenges still remain due to the poor mechanical properties of porous carbon nanofibers. Here, we report a facile strategy to fabricate elastic and hierarchical porous CNF membranes with NiFe2O4 nanocrystals embedded via multicomponent electrospinning and nano-doping methods. Benefiting from the scattering effect of NiFe2O4 nanocrystals and graphitized carbon layers for the condensed stress, the resultant CNF membranes exhibit an enhanced elasticity with a bending radius Benefiting from the robust mechanical stability, hierarchical porous structures and good electrochemical properties, the NiFe2O4 doped CNF membranes demonstrate a high electrical capacitance of 343 F g-1, and good reversibility with a cycling efficiency of 97.4% even after 10 000

  18. Catalytic Activity of Mono- and Bi-Metallic Nanoparticles Synthesized via Microemulsions

    Directory of Open Access Journals (Sweden)

    Ramona Y.G. König

    2014-07-01

    Full Text Available Water-in-oil (w/o microemulsions were used as a template for the synthesis of mono- and bi-metallic nanoparticles. For that purpose, w/o-microemulsions containing H2PtCl6, H2PtCl6 + Pb(NO32 and H2PtCl6 + Bi(NO3, respectively, were mixed with a w/o-microemulsion containing the reducing agent, NaBH4. The results revealed that it is possible to synthesize Pt, PtPb and PtBi nanoparticles of ~3–8 nm in diameter at temperatures of about 30°C. The catalytic properties of the bimetallic PtBi and PtPb nanoparticles were studied and compared with monometallic platinum nanoparticles. Firstly, the electrochemical oxidation of formic acid to carbon monoxide was investigated, and it was found that the resistance of the PtBi and PtPb nanoparticles against the catalyst-poisoning carbon monoxide was significantly higher compared to the Pt nanoparticles. Secondly, investigating the reduction of 4-nitrophenol to 4-aminophenol,we found that the bimetallic NPs are most active at 23 °C, while the order of the activity changes at higher temperatures, i.e., that the Pt nanoparticles are the most active ones at 36 and 49 °C. Furthermore, we observed a strong influence of the support, which was either a polymer or Al2O3. Thirdly, for the hydrogenation of allylbenzene to propylbenzene, the monometallic Pt NPs turned out to be the most active catalysts, followed by the PtPb and PtBi NPs. Comparing the two bimetallic nanoparticles, one sees that the PtPb NPs are significantly more active than the respective PtBi NPs.

  19. Formic acid oxidation at platinum-bismuth catalysts

    Directory of Open Access Journals (Sweden)

    Popović Ksenija Đ.

    2015-01-01

    Full Text Available The field of heterogeneous catalysis, specifically catalysis on bimetallic surfaces, has seen many advances over the past few decades. Bimetallic catalysts, which often show electronic and chemical properties that are distinct from those of their parent metals, offer the opportunity to obtain new catalysts with enhanced selectivity, activity, and stability. The oxidation of formic acid is of permanent interest as a model reaction for the mechanistic understanding of the electrooxidation of small organic molecules and because of its technical relevance for fuel cell applications. Platinum is one of the most commonly used catalysts for this reaction, despite the fact that it shows a few significant disadvantages: high cost and extreme susceptibility to poisoning by CO. To solve this problem, several approaches have been used, but generally, they all consist in the modification of platinum with a second element. Especially, bismuth has received significant attention as Pt modifier. According to the results presented in this survey dealing with the effects influencing the formic acid oxidation it was found that two types of Pt-Bi bimetallic catalysts (bulk and low loading deposits on GC showed superior catalytic activity in terms of the lower onset potential and oxidation current density, as well as exceptional stability compared to Pt. The findings in this report are important for the understanding of mechanism of formic acid electrooxidation on a bulk alloy and decorated surface, for the development of advanced anode catalysts for direct formic acid fuel cells, as well as for the synthesis of novel low-loading bimetallic catalysts. The use of bimetallic compounds as the anode catalysts is an effective solution to overcoming the problems of the formic acid oxidation current stability for long term applications. In the future, the tolerance of both CO poisoning and electrochemical leaching should be considered as the key factors in the development

  20. Cyanide-bridged NiCr and alternate NiFe-NiCr magnetic ultrathin films on functionalized Si(100) surface

    International Nuclear Information System (INIS)

    Sequential growth in solution (SGS) was performed for the magnetic cyanide-bridged network obtained from the reaction of Ni(H2O)2+ and Cr(CN)63- (referred to as NiCr) on a Si(100) wafer already functionalized by a Ni(II) complex. The growth process led to isolated dots and a low coverage of the surface. We used the NiFe network as a template to improve the growth of the magnetic network. We elaborated alternate NiFe (paramagnetic)-NiCr (ferromagnetic) ultrathin films around 6 nm thick. The magnetic behaviour confirmed the alternate structure with the ferromagnetic zones isolated between the paramagnetic ones since the evolution of the blocking temperature is consistent with the evolution of the layers' thickness expected from the SGS process. (authors)

  1. Cyanide-bridged NiCr and alternate NiFe-NiCr magnetic ultrathin films on functionalized Si(100) surface.

    Science.gov (United States)

    Tricard, Simon; Costa-Coquelard, Claire; Mazerat, Sandra; Rivière, Eric; Huc, Vincent; David, Christophe; Miserque, Frédéric; Jegou, Pascale; Palacin, Serge; Mallah, Talal

    2012-04-21

    Sequential growth in solution (SGS) was performed for the magnetic cyanide-bridged network obtained from the reaction of Ni(H(2)O)(2+) and Cr(CN)(6)(3-) (referred to as NiCr) on a Si(100) wafer already functionalized by a Ni(II) complex. The growth process led to isolated dots and a low coverage of the surface. We used the NiFe network as a template to improve the growth of the magnetic network. We elaborated alternate NiFe (paramagnetic)-NiCr (ferromagnetic) ultrathin films around 6 nm thick. The magnetic behaviour confirmed the alternate structure with the ferromagnetic zones isolated between the paramagnetic ones since the evolution of the blocking temperature is consistent with the evolution of the layers' thickness expected from the SGS process. PMID:22344390

  2. Effect of metallic phase species on the corrosion resistance of M/(10NiO-NiFe2O4) cermet inert anode of aluminum electrolysis

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    NiFe2O4-based cermet inert anodes with metallic phase compositions of Cu, Ni and 85Cu15Ni were prepared by cold pressing-sintering. Their corrosion resistance was also investigated in Na3 AlF6-Al2 O3 melts. The results show that the metallic phase species in cermets have no effect on the concentration of impurities in bath during electrolysis, the total steady-state concentration of impurities is almost the same, I.e. Between 4.12 × 10-4- 4.80 × 10-4. There exists metal preferential corrosion for the cermet inert anode with metal Ni as metallic phase. For NiFe2 O4-based cermets, the cermet with metal Cu as metallic phase exhibits better corrosion resistance than the others.

  3. Simulating cyclic voltammograms of bimetallic model surfaces

    International Nuclear Information System (INIS)

    Cyclic voltammograms recorded at bimetallic surfaces reflect the superposition of current contributions from adsorption, desorption, and reaction processes at surface regions with laterally varying chemical properties. As will be demonstrated for some selected well-defined single crystalline model systems including Pt films on Ru(0001) and PtAu/Pt(111) surface alloys, voltammetric features at bimetallic surfaces can be simulated using the corresponding features for the monometallic surfaces in combination with information on the adsorption properties and abundance of the dominating sites at the bimetallic surfaces. Trends in the local adsorption properties can be predicted based on density functional theory calculations, whereas the necessary information about the local vertical and lateral metal distribution is obtained from scanning tunnelling microscopy imaging.

  4. Study of structural, morphological and electrical properties of Ce doped NiFe2O4 nanoparticles and their electronic structure investigation

    International Nuclear Information System (INIS)

    Highlights: •• Structural and electrical properties of Ce doped NiFe2O4 nanoparticles are studied. •• Samples NiFe2-xCexO4 are prepared by chemical route and shows pure spinel phase up to x = 003. •• Resistivity and dielectric measurements were done for the study of electrical properties. •• Sample with x = 0.04 shows maximum resistivity and x = 0.02 highest dielectric constant. •• Observed results are discussed by XAS on the basis of change in the electronic structure. -- Abstract: Present work reports the structural, morphological, electrical properties of the Ce doped nickel ferrite (NiFe2O4) compounds and their electronic structures studied by X-ray absorption spectroscopy. The samples of NiFe2−xCexO4 (x = 0.0–0.10) were prepared by the chemical route and sintered at 1100 °C for 3 h. X-ray diffraction patterns of these sintered pellets show that Ce doped samples exhibit pure spinel phase up to x = 0.03. With increase of Ce concentration the crystallite size of the samples change randomly, however lattice parameters do not exhibit any significant change. Temperature dependent resistivity shows semiconducting nature for all the compositions. Sample with Ce concentration x = 0.04 shows maximum resistivity. The sample with x = 0.02 shows highest dielectric constant in the frequency range of 75 kHz–1 MHz at room temperature. The observed results are discussed on the basis of change in the electronic structure of these compounds with the Ce concentration. It has been observed that valence state of Ce ion is playing dominant role in determining the electrical and dielectric properties of the synthesized system

  5. Microstructure and mechanical properties of NiFe2O4 ceramics reinforced with ZrO2 particles with different sintering temperatures

    International Nuclear Information System (INIS)

    Highlights: ► ZrO2/NiFe2O4 composite ceramics were synthesized by powder metallurgy methods. ► The microstructure was investigated at different sintering temperatures. ► The grain size increases with increasing of the sintering temperature. ► The composite ceramics sintering at 1400°C show superior mechanical properties. ► Main toughening mechanisms are densification, phase transformation toughening. - Abstract: NiFe2O4 ceramics reinforced with ZrO2 particle was fabricated by conventional high-temperature solid state reaction. Effect of the sintering temperature (1100–1500 °C) on the microstructure and mechanical properties of the ZrO2/NiFe2O4 composite ceramics was investigated in detail. The fracture surfaces of NiFe2O4 composite ceramics were observed by scanning electron microscopy (SEM). Elemental analysis of micro-structural phases was performed using energy dispersive spectroscopy (EDS), attached with SEM. Flexural strength by three-point bending techniques and fracture toughness were measured. It was indicated that when the sintering temperature was above 1400 °C, phase transformation causing crack can directly lead to the strength degradation. The grain size of ZrO2 increases with increasing of the sintering temperature. The samples sintering at 1400 °C had the highest flexural strength of 192 ± 10 MPa and fracture toughness of 3.38 ± 0.05 MPa m1/2 due to densification, phase transformation.

  6. Comparative analysis of termoscale effects, isomerization and stability of TM-nanoclusters (Pd,Ni,Fe and Si in dependence on interatomic potentials. MD-simulations

    Directory of Open Access Journals (Sweden)

    Galashev А.Е.

    2011-05-01

    Full Text Available Basing on the MD-simulated data the comparison of physicochemical properties of TM-nanoclusters (Pd,Ni,Fe, and Si-nanoparticles has been carried on in the purpose to understand the specificity of structure changes in depending on nature of interatomic bonds and initial structures (fcc, bcc, icosahedral – Ih. MDsimulation of thermic evolution including melting of TM- and Si- clusters was carried on up to 2000K.

  7. Study of structural, morphological and electrical properties of Ce doped NiFe{sub 2}O{sub 4} nanoparticles and their electronic structure investigation

    Energy Technology Data Exchange (ETDEWEB)

    Dixit, Gagan, E-mail: gagandikshit@yahoo.in [Materials Science Division, Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067 (India); Department of Physics, G.B. Pant University of Ag. and Technology, Pantnagar 263 145 (India); Singh, Jitendra Pal [Materials Science Division, Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067 (India); Chen, C.L. [Institute of Physics, Academia Sinica, Taipei 11529, Taiwan (China); Dong, C.L. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Srivastava, R.C.; Agrawal, H.M. [Department of Physics, G.B. Pant University of Ag. and Technology, Pantnagar 263 145 (India); Pong, W.F. [Department of Physics, Tamkang University, Tamsui, Taipei County, Taiwan (China); Asokan, K. [Materials Science Division, Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110 067 (India)

    2013-12-25

    Highlights: •• Structural and electrical properties of Ce doped NiFe{sub 2}O{sub 4} nanoparticles are studied. •• Samples NiFe{sub 2-x}Ce{sub x}O{sub 4} are prepared by chemical route and shows pure spinel phase up to x = 003. •• Resistivity and dielectric measurements were done for the study of electrical properties. •• Sample with x = 0.04 shows maximum resistivity and x = 0.02 highest dielectric constant. •• Observed results are discussed by XAS on the basis of change in the electronic structure. -- Abstract: Present work reports the structural, morphological, electrical properties of the Ce doped nickel ferrite (NiFe{sub 2}O{sub 4}) compounds and their electronic structures studied by X-ray absorption spectroscopy. The samples of NiFe{sub 2−x}Ce{sub x}O{sub 4} (x = 0.0–0.10) were prepared by the chemical route and sintered at 1100 °C for 3 h. X-ray diffraction patterns of these sintered pellets show that Ce doped samples exhibit pure spinel phase up to x = 0.03. With increase of Ce concentration the crystallite size of the samples change randomly, however lattice parameters do not exhibit any significant change. Temperature dependent resistivity shows semiconducting nature for all the compositions. Sample with Ce concentration x = 0.04 shows maximum resistivity. The sample with x = 0.02 shows highest dielectric constant in the frequency range of 75 kHz–1 MHz at room temperature. The observed results are discussed on the basis of change in the electronic structure of these compounds with the Ce concentration. It has been observed that valence state of Ce ion is playing dominant role in determining the electrical and dielectric properties of the synthesized system.

  8. Synthesis of highly ordered 30 nm NiFe{sub 2}O{sub 4} particles by the microwave-combustion method

    Energy Technology Data Exchange (ETDEWEB)

    Mahmoud, M.H.; Elshahawy, A.M. [Physics Department, Faculty of Science, Assiut University, Assiut 71516 (Egypt); Makhlouf, Salah A., E-mail: smakhlouf@gmail.com [Physics Department, Faculty of Science, Assiut University, Assiut 71516 (Egypt); Deanship of Scientific Research, Al Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 11463 (Saudi Arabia); Hamdeh, H.H. [Department of Physics, Wichita State University, Wichita, KS (United States)

    2014-11-15

    NiFe{sub 2}O{sub 4} of 30 nm average size was synthesized by microwave combustion and subsequent solid state reaction at 1273 K. The materials were characterized by X-ray diffraction, TEM, vibrating sample magnetometery and Mössbauer spectroscopy. The microwave combustion produced materials were comprised chemically of ferrites and a smaller amount of hematite. The NiFe{sub 2}O{sub 4} particles have the cubic spinel structure with crystallites of sizes less than 10 nm, and were found to have low magnetization, and essentially no hysteresis loop; characteristics of superparamagnetism. Upon annealing at temperatures 973 K and below, crystallite growth was accompanied by increase in both coercive field and magnetization. The coercive field was a maximum for the sample annealed at 973 K. On the other hand, crystallite growth at higher annealing temperatures yielded mainly ferrites and improvement in soft magnetic properties. Mössbauer and magnetization measurements indicate that the fine NiFe{sub 2}O{sub 4} particles produced at the annealing temperature of 1273 K are in good chemical and magnetic order, excluding the spins arrangement at the surface of the particles which show spin glass-like behavior. - Highlights: • Highly ordered 30 nm NiFe{sub 2}O{sub 4} was synthesized by a microwave combustion method and annealing. • The crystallite size (D) increases with increasing the annealing temperature. • Reduced activation energy was observed for grain growth. • H{sub c} increases and then decreases with increasing D, whereas M{sub s} has increased. • Mössbauer spectra elucidate the nature of formed phases and cation distribution.

  9. Densification behavior of nanocrystalline W-Ni-Fe composite powders prepared by sol-spray drying and hydrogen reduction process

    International Nuclear Information System (INIS)

    This paper studied the densification behavior of nanocrystalline composite powders of 93W-4.9Ni-2.1Fe (wt.%) and 93W-4.9Ni-2.1Fe-0.03Y synthesized by sol-spray drying and hydrogen reduction process. The X-ray diffraction (XRD) analysis showed that γ-(Ni, Fe) phase was formed in the final obtained powders. Powders morphology characterized by scanning electron microscope (SEM) showed that the 93W-4.9Ni-2.1Fe nanocrystalline composite powders exhibited larger agglomeration and grain size compared with the 93W-4.9Ni-2.1Fe-0.03Y nanocrystalline composite powders. Both kinds of green compacts can obtain full density if sintered at 1410 oC for 1 h. When sintering temperature was above 1410 oC, the sintering density for both compacts decreased rapidly. In addition, the sintering density, densification rate and grain coarsening rate of 93W-4.9Ni-2.1Fe compacts were higher than those of 93W-4.9Ni-2.1Fe-0.03Y. The effect of trace yttrium on the densification behavior of nanocrystalline composite powders was also discussed.

  10. Point defect evolution in Ni, NiFe and NiCr alloys from atomistic simulations and irradiation experiments

    International Nuclear Information System (INIS)

    Using molecular dynamics simulations, we elucidate irradiation-induced point defect evolution in fcc pure Ni, Ni0.5Fe0.5, and Ni0.8Cr0.2 solid solution alloys. We find that irradiation-induced interstitials form dislocation loops that are of 1/3〈1 1 1〉{1 1 1}-type, consistent with our experimental results. While the loops are formed in all the three materials, the kinetics of formation is considerably slower in NiFe and NiCr than in pure Ni, indicating that defect migration barriers and extended defect formation energies could be higher in the alloys than pure Ni. As a result, while larger size clusters are formed in pure Ni, smaller and more clusters are observed in the alloys. Vacancy diffusion occurs at relatively higher temperatures than interstitials, and their clustering leads to the formation of stacking fault tetrahedra, consistent with our experiments. The results also show that the surviving Frenkel pairs are composition dependent and are largely Ni dominated

  11. The evolution of the total magnetization of a Ni-Fe heterostructure after exposure to a femtosecond laser pulse

    Science.gov (United States)

    Yastremsky, I. A.; Kireev, V. E.

    2016-04-01

    A study of how the total magnetization of a Ni-Fe heterostructure evolves during the relaxation of non-equilibrium, inhomogeneous, magnetization distributions toward an equilibrium state. These distributions occur within the framework of a superdiffusive mechanism of ultrafast demagnetization, after exposure to a femtosecond laser pulse. We account for relativistic (local) and exchange (non-local) relaxation mechanisms. This question is all the more interesting because exchange relaxation conserves the total magnetization of the sample. For sufficiently smooth distributions (typical dimensions are about several tens of nanometers), the evolution of the total magnetization is determined by different rates of relativistic relaxation in Ni and Fe. However, for sufficiently inhomogeneous magnetization distributions (with a scale of several nanometers, which is realized in the experiment), non-local relaxation is manifested by the fact that the spin current transfers magnetization from the Fe layer to Ni. As such, the difference in the rates of relativistic relaxation in Ni and Fe is expressed to a lesser extent. It is shown that for experimentally realized parameters of magnetic distribution in magnetic heterostructures, the variation of total magnetization decreases by more than two times, due to the spin current.

  12. Protonation states of intermediates in the reaction mechanism of [NiFe] hydrogenase studied by computational methods.

    Science.gov (United States)

    Dong, Geng; Ryde, Ulf

    2016-06-01

    The [NiFe] hydrogenases catalyse the reversible conversion of H2 to protons and electrons. The active site consists of a Fe ion with one carbon monoxide, two cyanide, and two cysteine (Cys) ligands. The latter two bridge to a Ni ion, which has two additional terminal Cys ligands. It has been suggested that one of the Cys residues is protonated during the reaction mechanism. We have used combined quantum mechanical and molecular mechanics (QM/MM) geometry optimisations, large QM calculations with 817 atoms, and QM/MM free energy simulations, using the TPSS and B3LYP methods with basis sets extrapolated to the quadruple zeta level to determine which of the four Cys residues is more favourable to protonate for four putative states in the reaction mechanism, Ni-SIa, Ni-R, Ni-C, and Ni-L. The calculations show that for all states, the terminal Cys-546 residue is most easily protonated by 14-51 kJ/mol, owing to a more favourable hydrogen-bond pattern around this residue in the protein. PMID:26940957

  13. Fracture mechanics behavior of a Ni-Fe superalloy sheath for superconducting fusion magnets. Pt. 2. Magnet life analysis model

    International Nuclear Information System (INIS)

    For pt.1 see ibid., p.251-67,(1997). From previous results of fatigue crack growth and fracture toughness measurements for a Ni-Fe base superalloy, a primary candidate for the International Thermonuclear Experimental Reactor (ITER) central solenoid (CS) conduit, we derive an improved magnet life analysis model from the framework of Newman and Raju. For the superalloy conduit with an initial semielliptical surface crack in its thickness direction, the model predicts the evolution of crack aspect ratio for a wide range of initial crack geometries under pure tension and bending fatigue. The prediction of final fracture due to fatigue crack growth using the linear elastic fracture mechanics approach is shown to be underconservative. An alternative model based on Newman's elastic-plastic fracture toughness parameter is derived for the base metal with nearly semicircular cracks. The improved life analysis model taking into account the fatigue and fracture behavior is applied to the ITER CS magnet and the results are compared with those from earlier models. Accounting for the crack shape evolution leads to significantly longer life compared to assuming a constant aspect ratio. For the superalloy base metal we find that the expected fatigue life of engineering design activity design of the CS magnet is about eight times the design requirement. Even the conceptual design activity design with a free-standing CS meets the life requirement when analyzed by the improved model. (orig.)

  14. Cubic superparamagnetic nanoparticles of NiFe{sub 2}O{sub 4} via fast microwave heating

    Energy Technology Data Exchange (ETDEWEB)

    Galvão, W. S.; Freire, R. M. [Universidade Federal do Ceará–UFC, Grupo de Química de Materiais Avançados (GQMAT), Departamento de Química Analítica e Físico-Química (Brazil); Ribeiro, T. S.; Vasconcelos, I. F. [Universidade Federal do Ceará, Departamento de Engenharia Metalúrgica e de Materiais (Brazil); Costa, L. S. [State University of Campinas–UNICAMP, Department of Inorganic Chemistry, Institute of Chemistry (Brazil); Freire, V. N.; Sales, F. A. M. [Universidade Federal do Ceará, Departamento de Física, Centro de Ciências (Brazil); Denardin, J. C. [Universidad de Santiago de Chile, USACH, Departamento de Física (Chile); Fechine, P. B. A., E-mail: fechine@ufc.br [Universidade Federal do Ceará–UFC, Grupo de Química de Materiais Avançados (GQMAT), Departamento de Química Analítica e Físico-Química (Brazil)

    2014-12-15

    This study demonstrated the possibility of using microwave heating as a fast and cheap method for synthesizing superparamagnetic nanoparticles. In this sense, NiFe{sub 2}O{sub 4} samples were subjected to microwave heating at various temperatures to determine the lowest temperature at which the crystalline phase of the nanoparticles occurs. X-Ray powder diffraction, {sup 57}Fe Mössbauer spectroscopy, and transmission electron microscopy of the samples were performed to confirm the formed nanoparticles. It was observed a cubic structure of inverse spinel type with good crystallinity. The magnetic properties of the samples were studied using a vibrating sample magnetometer and was found to zero values to remanent magnetization and coercivity field. This behavior suggests superparamagnetic features for all samples. The crystallite size (9, 10, and 12 nm) and saturation magnetization (31–45 emu/g) were used as a function of the increase of the temperature treatment time. Blocking temperature was found by tracing remanent magnetization versus temperature.

  15. Room temperature giant positive junction magnetoresistance of NiFe2O4/n-Si heterojunction for spintronics application

    International Nuclear Information System (INIS)

    Electronic- and magnetic-transport properties of NiFe2O4 (NFO)–SiO2–Si heterojunction fabricated by depositing NFO thin films on silicon substrates with the intermediate native oxide (SiO2) layer have been investigated in details. The current–voltage (I–V) characteristics across the junction have been recorded in the temperature range of 10–300 K. All I–V curves show non-linear behavior throughout the temperature range. The dominating current transport mechanism is found to be temperature dependent tunneling assisted by Frenkel–Poole type emission. In this paper, we report the junction magnetoresistance (JMR) properties of this heterojunction in the temperature range of 10–300 K. With increasing temperature, the JMR of the heterojunction increases accordingly. The high positive JMR (∼54%) has been observed at room temperature (RT). The origin of high positive JMR at RT is attributed to efficient spin-polarized carrier transport across the junction

  16. Probing exotic magnetic phases and electrical transport in Cr-rich γ-NiFeCr alloys

    International Nuclear Information System (INIS)

    We have identified ferromagnetic, antiferromagnetic, and re-entrant spin-glass-like phases in Cr-rich γ-NiFeCr alloys and studied their critical magnetic behavior. Their electrical resistivity exhibits distinct minima between 10 and 24 K with ρ∞−√T due to electron–electron interaction effects. Electron–phonon and electron–magnon contributions to ρ are isolated. The magnetoresistance shows hysteresis effects, a signature of spin-glass-like phases and a sign reversal with change of magnetic states. We have also observed that the nature of magnetic states strongly depends on the concentration of Fe and Cr. In this system, even a small amount of Fe enhances ferromagnetism a lot while addition of a little bit of Cr suppresses ferromagnetism and takes the system to the antiferromagnetic regime. The correlation between the magnetic and the electrical properties are more meaningful here since both studies were done on the same set of samples which have rather high melting points. - Highlights: • Identified ferro, antiferro, and re-entrant spin-glass phases in Ni–Fe–Cr alloys. • Resistivity ρ~−√T shows minima from 10–24 K due to electron–electron interaction. • Electron–phonon and electron–magnon contributions to ρ are isolated. • Magneto-transport measurements strengthened the magnetic phases identified. • Correlation in magnetic/electrical properties more meaningful if same samples used

  17. Probing exotic magnetic phases and electrical transport in Cr-rich γ-NiFeCr alloys

    Energy Technology Data Exchange (ETDEWEB)

    Pal, Pampa [S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098 (India); Majumdar, A.K., E-mail: akm@bose.res.in [S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098 (India); Ramakrishna Mission Vivekananda University, PO Belur Math, Howrah 711202 (India); Nigam, A.K. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)

    2015-05-01

    We have identified ferromagnetic, antiferromagnetic, and re-entrant spin-glass-like phases in Cr-rich γ-NiFeCr alloys and studied their critical magnetic behavior. Their electrical resistivity exhibits distinct minima between 10 and 24 K with ρ∞−√T due to electron–electron interaction effects. Electron–phonon and electron–magnon contributions to ρ are isolated. The magnetoresistance shows hysteresis effects, a signature of spin-glass-like phases and a sign reversal with change of magnetic states. We have also observed that the nature of magnetic states strongly depends on the concentration of Fe and Cr. In this system, even a small amount of Fe enhances ferromagnetism a lot while addition of a little bit of Cr suppresses ferromagnetism and takes the system to the antiferromagnetic regime. The correlation between the magnetic and the electrical properties are more meaningful here since both studies were done on the same set of samples which have rather high melting points. - Highlights: • Identified ferro, antiferro, and re-entrant spin-glass phases in Ni–Fe–Cr alloys. • Resistivity ρ~−√T shows minima from 10–24 K due to electron–electron interaction. • Electron–phonon and electron–magnon contributions to ρ are isolated. • Magneto-transport measurements strengthened the magnetic phases identified. • Correlation in magnetic/electrical properties more meaningful if same samples used.

  18. Magneto-optical response in bimetallic metamaterials

    CERN Document Server

    Atmatzakis, Evangelos; Fedotov, Vassili; Vienne, Guillaume; Zheludev, Nikolay I

    2016-01-01

    We demonstrate resonant Faraday polarization rotation in plasmonic arrays of bimetallic nano-ring resonators consisting of Au and Ni sections. This metamaterial design allows to optimize the trade-off between the enhancement of magneto-optical effects and plasmonic dissipation. Although Ni sections correspond to as little as ~6% of the total surface of the metamaterial, the resulting magneto-optically induced polarization rotation is equal to that of a continuous film. Such bimetallic metamaterials can be used in compact magnetic sensors, active plasmonic components and integrated photonic circuits.

  19. [NiFe] hydrogenases from Desulfovibrio vulgaris Miyazaki F and Aquifex aeolicus studied by FTIR, EPR and electrochemical techniques: Redox intermediates, O2/CO sensitivity and light-induced effects

    OpenAIRE

    Pandelia, Maria-Eirini

    2010-01-01

    [NiFe]-Hydrogenasen sind Enzyme, die die reversible Oxidation von molekularem Wasserstoff katalysieren. Das Verständnis ihres Mechanismus ist notwendig für die Synthese biomimetischer katalytischer Systeme und für ein zukünftige “grüne“ Biotechnologie. In dieser Arbeit wurden [NiFe]-Hydrogenasen aus zwei unterschiedlichen Organismen untersucht, eine aus dem streng anaeroben Bakterium Desulfovibrio vulgaris Miyazaki F und eine aus dem mikro-aerophilen hyperthermophilen Bakterium Aquifex aeolic...

  20. Multiphase and Double-Layer NiFe2O4@NiO-Hollow-Nanosphere-Decorated Reduced Graphene Oxide Composite Powders Prepared by Spray Pyrolysis Applying Nanoscale Kirkendall Diffusion.

    Science.gov (United States)

    Park, Gi Dae; Cho, Jung Sang; Kang, Yun Chan

    2015-08-01

    Multicomponent metal oxide hollow-nanosphere decorated reduced graphene oxide (rGO) composite powders are prepared by spray pyrolysis with nanoscale Kirkendall diffusion. The double-layer NiFe2O4@NiO-hollow-nanosphere decorated rGO composite powders are prepared using the first target material. The NiFe-alloy-nanopowder decorated rGO powders are prepared as an intermediate product by post-treatment under the reducing atmosphere of the NiFe2O4/NiO-decorated rGO composite powders obtained by spray pyrolysis. The different diffusion rates of Ni (83 pm for Ni(2+)) and Fe (76 pm for Fe(2+), 65 pm for Fe(3+)) cations with different radii during nanoscale Kirkendall diffusion result in multiphase and double-layer NiFe2O4@NiO hollow nanospheres. The mean size of the hollow NiFe2O4@NiO nanospheres decorated uniformly within crumpled rGO is 14 nm. The first discharge capacities of the nanosphere-decorated rGO composite powders with filled NiFe2O4/NiO and hollow NiFe2O4@NiO at a current density of 1 A g(-1) are 1168 and 1319 mA h g(-1), respectively. Their discharge capacities for the 100th cycle are 597 and 951 mA h g(-1), respectively. The discharge capacity of the NiFe2O4@NiO-hollow-nanosphere-decorated rGO composite powders at the high current density of 4 A g(-1) for the 400th cycle is 789 mA h g(-1). PMID:26186601

  1. Multiscale simulations give insight into the hydrogen in and out pathways of [NiFe]-hydrogenases from Aquifex aeolicus and Desulfovibrio fructosovorans.

    Science.gov (United States)

    Oteri, Francesco; Baaden, Marc; Lojou, Elisabeth; Sacquin-Mora, Sophie

    2014-12-01

    [NiFe]-hydrogenases catalyze the cleavage of molecular hydrogen into protons and electrons and represent promising tools for H2-based technologies such as biofuel cells. However, many aspects of these enzymes remain to be understood, in particular how the catalytic center can be protected from irreversible inactivation by O2. In this work, we combined homology modeling, all-atom molecular dynamics, and coarse-grain Brownian dynamics simulations to investigate and compare the dynamic and mechanical properties of two [NiFe]-hydrogenases: the soluble O2-sensitive enzyme from Desulfovibrio fructosovorans, and the O2-tolerant membrane-bound hydrogenase from Aquifex aeolicus. We investigated the diffusion pathways of H2 from the enzyme surface to the central [NiFe] active site, and the possible proton pathways that are used to evacuate hydrogen after the oxidation reaction. Our results highlight common features of the two enzymes, such as a Val/Leu/Arg triad of key residues that controls ligand migration and substrate access in the vicinity of the active site, or the key role played by a Glu residue for proton transfer after hydrogen oxidation. We show specificities of each hydrogenase regarding the enzymes internal tunnel network or the proton transport pathways. PMID:25399809

  2. Influence of SiC nanoparticles and saccharin on the structure and properties of electrodeposited Ni-Fe/SiC nanocomposite coatings

    Energy Technology Data Exchange (ETDEWEB)

    Ataee-Esfahani, Hamed [Materials and Energy Research Center, P.O. Box 14155-4777, Tehran (Iran, Islamic Republic of)] [Department of Materials Science and Engineering, Sharif University of Technology, P.O. Box 11365-9466, Tehran (Iran, Islamic Republic of); Vaezi, M.R., E-mail: vaezi9016@yahoo.co [Materials and Energy Research Center, P.O. Box 14155-4777, Tehran (Iran, Islamic Republic of); Nikzad, Leila; Yazdani, Bahare [Materials and Energy Research Center, P.O. Box 14155-4777, Tehran (Iran, Islamic Republic of); Sadrnezhaad, S.K. [Materials and Energy Research Center, P.O. Box 14155-4777, Tehran (Iran, Islamic Republic of)] [Department of Materials Science and Engineering, Sharif University of Technology, P.O. Box 11365-9466, Tehran (Iran, Islamic Republic of)

    2009-09-18

    In this study, Ni-Fe/SiC nanocomposite coatings with smooth and crack-free surface were successfully prepared by means of the conventional electrodeposition in the presence of saccharin in electrolyte. The goal of this work was to investigate the effect of SiC nanoparticles and saccharin on the structure and properties of permalloy nanocomposite coatings. The nanocomposite coatings were characterized using optical and scanning electron microscopy, energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) technique. The significant variation in the crystallographic texture of the coatings was observed due to the addition of SiC nanoparticles and saccharin in the electrodeposition bath. Increasing the amount of saccharin in the electrolyte led to a change in the texture from a (2 0 0) fiber texture to mixed (3 1 1) and (2 0 0) textures. Our results indicated that inclusion of SiC nanoparticles suppressed the preferred growth direction of the Ni-Fe matrix, resulting in a decrease in the sharpness of the (2 0 0) fiber texture and formation of a more random texture. The presence of SiC nanoparticles in the metallic matrix also led to the production of composite films with better corrosion resistance and higher microhardness than the Ni-Fe coating.

  3. Magnetic properties of NiFe2−xRExO4 (RE=Dy, Gd) using magnetic Compton scattering

    International Nuclear Information System (INIS)

    Temperature dependent spin momentum densities of NiFe2−xRExO4 (x=0, 0.05; RE=Dy, Gd) ferrites have been measured using a magnetic Compton spectrometer available at SPring-8, Japan. The experimental profiles of NiFe2O4 (NFO) with doping of Dy and Gd show almost similar spin moment as of undoped NFO. The contribution of different constituents in the formation of total spin moment is also deduced from the analysis of Compton line shape. It is seen that 5% doping of Dy3+ or Gd3+ ions at Fe3+ sites leads to a redistribution of spin moment at Fe3+ and RE3+ sites. The magnetic Compton data when compared with the magnetization data (using a vibrating sample magnetometer) show almost a constant orbital moment (0.21±0.03 µB/f.u.) in the doped and undoped NFO. - Highlights: • Reported first ever magnetic Compton profiles (MCPs) of NiFe2−xRExO4 (RE=Dy, Gd). • MCPs are analyzed to determine site specific contributions in total spin moment. • Doping of RE3+ ions at Fe3+ sites redistributes the spin moment at Fe3+ and RE3+ sites. • The orbital moments in doped and undoped ferrites are found to be almost constant

  4. Effect of CaO doping on corrosion resistance of Cu/(NiFe2O4-10NiO) cermet inert anode for aluminum electrolysis

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The CaO-doped Cu/(NiFe2O4-10NiO) cermet inert anodes were prepared by the cold isostatic pressing-sintering process,and their corrosion resistance to Na3AlF6-K3AlF6-AI2O3 melt was studied.The results show that the relative density of 5Cu/(NiFe2O4-10NiO) cermet sintered at 1 200 ℃ increases from 82.83% to 97.63% when 2% CaO (mass fraction) is added.During the electrolysis,the relative density of cermet inert anode descends owing to the chemical dissolution of additive CaO atceramic grain boundary,which accelerates the penetration of electrolyte.Thus,the corrosion resistance to melts ofCu/(NiFe2O4-10NiO) cermet inert anode is reduced.To improve the corrosion resistance of the cermet inert anode,the content of CaO doped should be decreased and the technology of cleaning the ceramic grain boundary should be applied.

  5. Switching behavior of Fe-Pt/Ni-Fe exchange-spring films studied by resonant soft-x-ray magneto-optical Kerr effect

    International Nuclear Information System (INIS)

    We have studied the magnetic switching behavior of exchange-coupled Fe55Pt45/Ni80Fe20 films. On top of magnetically hard Fe55Pt45 films having coercive fields up to 10 kOe were deposited soft magnetic NiFe films of different thickness values to form exchange-spring magnet structures. Magnetometry measurements exhibit the loop shapes characteristic of the exchange coupling between hard and soft magnetic phases; a reversible switching of the soft layer at low fields and an irreversible switching of the hard layer at higher fields. To investigate the switching behavior in more detail we prepared samples with 20-Aa Co layers either deposited on top of the soft magnetic NiFe film or at the NiFe-FePt interface. Soft-x-ray magneto-optical Kerr effect measurements performed at the Co L-edge resonance allows us to use the Co layer as a local probe of the reversal process. The element-specific Kerr loops reveal that the reversible twist in the soft layer is not pinned rigidly at the interface but rather propagates significantly into the hard magnetic layer. As a consequence the reversible magnetization is not only stored in the soft layer, as often assumed. Additionally the major loops do not exhibit any well-defined switching field of the hard layer. Instead the results indicate that the irreversible switching of the hard phase evolves continuously with increasing external field in this materials system

  6. Relative contributions of surface and grain boundary scattering to the spin-polarized electrons transport in the AlN/NiFe/AlN heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Chong-Jun; Zhao, Zhi-Duo [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Wu, Zheng-Long [Analytical and Testing Center, Beijing Normal University, Beijing 100875 (China); Yang, Guang; Liu, Fen [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Ding, Lei [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Zhang, Jing-Yan [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Guang-Hua, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)

    2014-04-01

    Highlights: • Ta/AlN/Ni{sub 81}Fe{sub 19}/AlN/Ta films were prepared by magnetron sputtering. The electronic transport properties were studied. • Chemical status change at the NiFe/AlN interface was quantified by X-ray photoelectron spectroscopy. • The average grain size as well as the crystallinity was determined from X-ray diffraction studies. • The relative contributions of surface and grain boundary scattering to the electrons transport were analyzed. - Abstract: When the film thickness approaches the electron mean free path (MFP), the relative contributions of surface/grain boundary scattering to the resistivity remain indefinitive. In this work, series of NiFe films sandwiched by AlN barriers were employed to study the transport properties. Surface scattering is found to provide the strongest contribution to the resistivity increase for very thin films (d{sub NiFe} ≤ 10 nm). With the increase of the film thickness, the effect of the grain boundary scattering gradually increases while the surface scattering decreases. When the thickness of the film is over 30 nm, the former becomes predominant.

  7. Engineering of high performance supercapacitor electrode based on Fe-Ni/Fe{sub 2}O{sub 3}-NiO core/shell hybrid nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Ashutosh K., E-mail: ashuvishen@gmail.com, E-mail: aksingh@bose.res.in; Mandal, Kalyan [Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake City, Kolkata 700098 (India)

    2015-03-14

    The present work reports on fabrication and supercapacitor applications of a core/shell Fe-Ni/Fe{sub 2}O{sub 3}-NiO hybrid nanostructures (HNs) electrode. The core/shell Fe-Ni/Fe{sub 2}O{sub 3}-NiO hybrid nanostructures have been fabricated through a two step method (nanowire fabrication and their controlled oxidation). The 1D hybrid nanostructure consists of highly porous shell layer (redox active materials NiO and Fe{sub 2}O{sub 3}) and the conductive core (FeNi nanowire). Thus, the highly porous shell layer allows facile electrolyte diffusion as well as faster redox reaction kinetics; whereas the conductive FeNi nanowire core provides the proficient express way for electrons to travel to the current collector, which helps in the superior electrochemical performance. The core/shell Fe-Ni/Fe{sub 2}O{sub 3}-NiO hybrid nanostructures electrode based supercapacitor shows very good electrochemical performances in terms of high specific capacitance nearly 1415 F g{sup −1} at a current density of 2.5 A g{sup −1}, excellent cycling stability and rate capability. The high quality electrochemical performance of core/shell hybrid nanostructures electrode shows its potential as an alternative electrode for forthcoming supercapacitor devices.

  8. Effect of Yb2O3 doping on the grain boundary of NiFe2O4-10NiO-based cermets after sintering

    Science.gov (United States)

    He, Han-bing

    2015-12-01

    xYb2O3-15(20Ni-Cu)/(85 - x)(NiFe2O4-10NiO) ( x = 0, 0.25, 0.5, 0.75, 1.0, 2.0, and 10.0) cermets for aluminum electrolysis were prepared to investigate the effect of Yb2O3 doping on the grain boundary of the cermets after sintering. The results showed that each interface was very clear and that with increasing Yb2O3 content, most of the Yb was evenly distributed at the grain boundary. Moreover, according to the phase composition and microstructural analysis by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), and electron probe microanalysis (EPMA), YbFeO3 was produced along the grain boundary. The YbFeO3 was concluded to not only have formed from the interaction between the NiFe2O4 or Fe2O3 component and Yb2O3 at the grain boundary of the cermets, but also from the decomposition of NiFe2O4 into NiO and Fe2O3 and the subsequent reaction of Fe2O3 with Yb2O3. Thus, the production of YbFeO3 resulted in a cermet with high relative density, good electrical conductivity, and good corrosion resistance.

  9. Impact of interface manipulation of oxide on electrical transport properties and low-frequency noise in MgO/NiFe/MgO heterojunctions

    International Nuclear Information System (INIS)

    Low-frequency noise and magnetoresistance in sputtered-deposited Ta(5 nm)/MgO (3 nm)/NiFe(10 nm)/MgO(3 nm)/Ta(3 nm) films have been measured as a function of different annealing times at 400°C. These measurements did not change synchronously with annealing time. A significant increase in magnetoresistance is observed for short annealing times (of the order of minutes) and is correlated with a relatively small reduction in 1/f noise. In contrast, a significant reduction in 1/f noise is observed for long annealing times (of the order of hours) accompanied by a small change in magnetoresistance. After annealing for 2 hours, the 1/f noise decreases by three orders of magnitude. Transmission electron microscopy and slow positron annihilation results implicate the cause being micro-structural changes in the MgO layers and interfaces following different annealing times. The internal vacancies in the MgO layers gather into vacancy clusters to reduce the defect density after short annealing times, whereas the MgO/NiFe and the NiFe/MgO interfaces improve significantly after long annealing times with the amorphous MgO layers gradually crystallizing following the release of interfacial stress

  10. Impact of interface manipulation of oxide on electrical transport properties and low-frequency noise in MgO/NiFe/MgO heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Jian-wei [School of Materials Science and Engineering, Shanghai University, Shanghai 200072 (China); School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Zhao, Chong-jun; Feng, Chun; Yu, Guang-hua [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Zhou, Zhongfu [School of Materials Science and Engineering, Shanghai University, Shanghai 200072 (China)

    2015-08-15

    Low-frequency noise and magnetoresistance in sputtered-deposited Ta(5 nm)/MgO (3 nm)/NiFe(10 nm)/MgO(3 nm)/Ta(3 nm) films have been measured as a function of different annealing times at 400°C. These measurements did not change synchronously with annealing time. A significant increase in magnetoresistance is observed for short annealing times (of the order of minutes) and is correlated with a relatively small reduction in 1/f noise. In contrast, a significant reduction in 1/f noise is observed for long annealing times (of the order of hours) accompanied by a small change in magnetoresistance. After annealing for 2 hours, the 1/f noise decreases by three orders of magnitude. Transmission electron microscopy and slow positron annihilation results implicate the cause being micro-structural changes in the MgO layers and interfaces following different annealing times. The internal vacancies in the MgO layers gather into vacancy clusters to reduce the defect density after short annealing times, whereas the MgO/NiFe and the NiFe/MgO interfaces improve significantly after long annealing times with the amorphous MgO layers gradually crystallizing following the release of interfacial stress.

  11. Identification of an Isothiocyanate on the HypEF Complex Suggests a Route for Efficient Cyanyl-Group Channeling during [NiFe]-Hydrogenase Cofactor Generation.

    Directory of Open Access Journals (Sweden)

    Sven T Stripp

    Full Text Available [NiFe]-hydrogenases catalyze uptake and evolution of H2 in a wide range of microorganisms. The enzyme is characterized by an inorganic nickel/ iron cofactor, the latter of which carries carbon monoxide and cyanide ligands. In vivo generation of these ligands requires a number of auxiliary proteins, the so-called Hyp family. Initially, HypF binds and activates the precursor metabolite carbamoyl phosphate. HypF catalyzes removal of phosphate and transfers the carbamate group to HypE. In an ATP-dependent condensation reaction, the C-terminal cysteinyl residue of HypE is modified to what has been interpreted as thiocyanate. This group is the direct precursor of the cyanide ligands of the [NiFe]-hydrogenase active site cofactor. We present a FT-IR analysis of HypE and HypF as isolated from E. coli. We follow the HypF-catalyzed cyanation of HypE in vitro and screen for the influence of carbamoyl phosphate and ATP. To elucidate on the differences between HypE and the HypEF complex, spectro-electrochemistry was used to map the vibrational Stark effect of naturally cyanated HypE. The IR signature of HypE could ultimately be assigned to isothiocyanate (-N=C=S rather than thiocyanate (-S-C≡N. This has important implications for cyanyl-group channeling during [NiFe]-hydrogenase cofactor generation.

  12. Self-assembly formation of hollow Ni-Fe-O nanocage architectures by metal-organic frameworks with high-performance lithium storage

    Science.gov (United States)

    Guo, Hong; Li, Tingting; Chen, Weiwei; Liu, Lixiang; Qiao, Jinli; Zhang, Jiujun

    2015-09-01

    A hollow hybrid Ni-Fe-O nanomaterial (NiFe2O4) is synthesized using a precursor of metal-organic frameworks through a simple and cost-effective method. The unique hollow nanocage structures shorten the length of Li-ion diffusion. The hollow structure offers a sufficient void space, which sufficiently alleviates the mechanical stress caused by volume change. Besides, the hybrid elements allow the volume change to take place in a stepwise manner during electrochemical cycle. And thus, the hierarchical hollow NiFe2O4 nanocage electrode exhibits extraordinary electrochemical performance. The stable cyclic performance is obtained for all rates from 1 C to 10 C. Even when the current reaches 10 C, the capacity can also arrive at 652 mAhg-1. Subsequently, a specific capacity of ca. 975 mAhg-1 is recovered when the current rate reduces back to 1 C after 200 cycles. This strategy that derived from NMOFs may shed light on a new route for large-scale synthesis of hollow porous hybrid nanocages for energy storage, environmental remediation and other novel applications.

  13. Highly branched PtCu bimetallic alloy nanodendrites with superior electrocatalytic activities for oxygen reduction reactions

    Science.gov (United States)

    Fu, Shaofang; Zhu, Chengzhou; Shi, Qiurong; Xia, Haibing; Du, Dan; Lin, Yuehe

    2016-02-01

    Morphology control is a promising strategy to improve the catalytic performance of Pt-based catalysts. In this work, we reported a facile synthesis of PtCu bimetallic alloy nanodendrites using Brij 58 as a template. The highly branched structures and porous features offer relatively large surface areas, which is beneficial to the enhancement of the catalytic activity for oxygen reduction reactions in fuel cells. In addition, the elimination of carbon supports showed an important effect on the stability of the catalysts. By tuning the ratio of Pt and Cu precursors, PtCu nanodendrites were almost four times more active on the basis of an equivalent Pt mass for oxygen reduction reactions than the commercial Pt/C catalyst.Morphology control is a promising strategy to improve the catalytic performance of Pt-based catalysts. In this work, we reported a facile synthesis of PtCu bimetallic alloy nanodendrites using Brij 58 as a template. The highly branched structures and porous features offer relatively large surface areas, which is beneficial to the enhancement of the catalytic activity for oxygen reduction reactions in fuel cells. In addition, the elimination of carbon supports showed an important effect on the stability of the catalysts. By tuning the ratio of Pt and Cu precursors, PtCu nanodendrites were almost four times more active on the basis of an equivalent Pt mass for oxygen reduction reactions than the commercial Pt/C catalyst. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07682j

  14. Temperature-programmed oxidation of coked noble metal catalysts after autothermal reforming of n-hexadecane

    Energy Technology Data Exchange (ETDEWEB)

    Kauppi, E.I.; Linnekoski, J.A.; Krause, A.O.I.; Veringa Niemelae, M.K. [Aalto University, School of Science and Technology, Department of Biotechnology and Chemical Technology, Research Group Industrial Chemistry, P.O. Box 16100, FI-00076 Aalto (Finland); Kaila, R.K. [VTT Technical Research Centre of Finland, Biologinkuja 7, Espoo, P.O. Box 1001, FI-02044 VTT (Finland)

    2010-08-15

    Autothermal reforming (ATR) of n-hexadecane was carried out on zirconia-supported mono- and bimetallic noble metal (Rh, Pt) catalysts at 600, 700, and 800 C. After ATR, the reactivity of coke deposits (2.8-9.9 wt%) on the catalysts was investigated by temperature-programmed oxidation (TPO). Analysis of the results obtained from ATR and TPO experiments at various temperatures and on the different catalysts gave information on the reaction conditions where the detrimental coke can be minimized and allows estimating the nature of carbon deposits. H{sub 2} production increased with temperature on the tested Rh-containing catalysts and the ZrO{sub 2} support, but decreased as a function of temperature on the Pt catalyst. The formation of coke was least at 800 C, evidently due to the intensifying reaction of carbon and steam with increasing temperature, as well as to the better activity of the catalysts. The amount of coke formed was highest at 700 C. Comparison of the TPO profiles obtained for the monometallic Rh and Pt catalysts with the bimetallic RhPt revealed differences in the nature of carbon deposits on their surface. At 600 C, the coke formed on the monometallic Rh and Pt catalysts was located mostly on the support, whereas on the bimetallic RhPt catalyst the formation of this type of coke was suppressed. The bimetallic RhPt catalyst also exhibited better tolerance toward coking at 700 C. Therefore, although the selectivity toward hydrogen was not related to the amount of coke formed, the deactivation patterns differed on the mono- and bimetallic catalysts. (author)

  15. Binary supported nickel catalysts for the deuterium exchange reaction between hydrogen and water vapour

    International Nuclear Information System (INIS)

    Nickel catalysts supported by Fe2O3, CuO, MnO and CeO were prepared from the corresponding metal nitrates. Chemical treatment of the catalysts was carried out at room temperature, while thermal treatment was made at 350 0C. The total surface area of the catalysts was measured by nitrogen adsorption at -195 0C using the BET equation. The specific metallic surface area was measured by hydrogen chemisorption at liquid nitrogen temperature. The activity of the catalysts was tested for the isotopic exchange reaction of deuterium between hydrogen and water vapour. The results obtained showed that Ni-Fe2O3, Ni-CuO and Ni-MnO catalysts exhibit catalytic activity for the deuterium exchange between hydrogen and water vapour, while the catalyst supported by CeO has no such activity. (author)

  16. Pt-Doped NiFe₂O₄ Spinel as a Highly Efficient Catalyst for H₂ Selective Catalytic Reduction of NO at Room Temperature.

    Science.gov (United States)

    Sun, Wei; Qiao, Kai; Liu, Ji-Yuan; Cao, Li-Mei; Gong, Xue-Qing; Yang, Ji

    2016-04-11

    H2 selective catalytic reduction (H2-SCR) has been proposed as a promising technology for controlling NOx emission because hydrogen is clean and does not emit greenhouse gases. We demonstrate that Pt doped into a nickel ferrite spinel structure can afford a high catalytic activity of H2-SCR. A superior NO conversion of 96% can be achieved by employing a novel NiFe1.95Pt0.05O4 spinel-type catalyst at 60 °C. This novel catalyst is different from traditional H2-SCR catalysts, which focus on the role of metallic Pt species and neglect the effect of oxidized Pt states in the reduction of NO. The obtained Raman and XPS spectra indicate that Pt in the spinel lattice has different valence states with Pt(2+) occupying the tetrahedral sites and Pt(4+) residing in the octahedral ones. These oxidation states of Pt enhance the back-donation process, and the lack of filling electrons of the 5d band causes Pt to more readily hybridize with the 5σ orbital of the NO molecule, especially for octahedral Pt(4+), which enhances the NO chemisorption on the Pt sites. We also performed DFT calculations to confirm the enhancement of adsorption of NO onto Pt sites when doped into the Ni-Fe spinel structure. The prepared Pt/Ni-Fe catalysts indicate that increasing the dispersity of Pt on the surfaces of the individual Ni-Fe spinel-type catalysts can efficiently promote the H2-SCR activity. Our demonstration provides new insight into designing advanced catalysts for H2-SCR. PMID:26982816

  17. Monodispersed bimetallic PdAg nanoparticles with twinned structures: Formation and enhancement for the methanol oxidation

    Science.gov (United States)

    Yin, Zhen; Zhang, Yining; Chen, Kai; Li, Jing; Li, Wenjing; Tang, Pei; Zhao, Huabo; Zhu, Qingjun; Bao, Xinhe; Ma, Ding

    2014-03-01

    Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd80Ag20, Pd65Ag35 and Pd46Ag54 can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd80Ag20 nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system.

  18. Influence of silver on the glycerol electro-oxidation over AuAg/C catalysts in alkaline medium: a cyclic voltammetry and in situ FTIR spectroscopy study

    International Nuclear Information System (INIS)

    In the present work, we investigated the influence of silver on the glycerol electro-oxidation over carbon-supported AuAg catalysts by cyclic voltammetry and in situ FTIR spectroscopy. We observed that the presence of Ag in the bimetallic materials provided a more efficient catalyst in terms of the ability to electro-oxidize glycerol at relatively low potentials. On the other hand, the bimetallic catalysts were found to be less promising than the Au/C catalyst with respect to the reaction rate. Ag addition influenced the mechanism of glycerol electro-oxidation, favoring the C-C-C bond breaking, as evidenced by the selective formation of formic acid on the bimetallic catalysts. The impact of Ag on the glycerol electro-oxidation over AuAg/C may be driven by electronic modifications and Ag segregation on the catalysts surface

  19. Final Technical Report: First Principles Investigations for the Ensemble Effects of PdAu and PtAu Bimetallic Nanocatalysts

    Energy Technology Data Exchange (ETDEWEB)

    Ruqian Wu

    2012-05-18

    Bimetallic surfaces with tunable chemical properties have attracted broad attention in recent years due to their ample potential for heterogeneous catalysis applications. The local chemical properties of constituents are strongly altered from their parent metals by 'ligand effect', a term encompassing the influences of charge transfer, orbital rehybridization and lattice strain. In comparison to the aforementioned, the 'ensemble effect' associated with particular arrangements of the active constituents have received much less attention, despite their notable importance towards the determination of reactivity and selectivity of bimetallic catalysts. We performed theoretical studies for understanding the ensemble effects on bimetallic catalysis: (i) simulations for the formation of different ensembles on PdAu and PtAu nanoclusters; (ii) studies of the size, shape, and substrate dependence of their electronic properties; and (iii) simulations for model reactions such as CO oxidation, methanol, ethylene and water dehydrogenation on PdAu and PtAu nanoclusters. In close collaboration with leading experimental groups, our theoretical research elucidated the fundamentals of Au based bimetallic nanocatalysts.

  20. Bi2MoO6/Ni-Fe LDH复合材料的制备及可见光催化性能%Preparation and Visible Light Responsive Photocatalytic Activity of Bi2MoO6/Ni-Fe LDH Composites

    Institute of Scientific and Technical Information of China (English)

    曲婷; 黄强; 赵振波

    2015-01-01

    采用水热法和共沉淀法结合制备Bi2MoO6/Ni-Fe LDH复合材料,通过XRD、FT-IR、SEM、TEM、XPS和N2物理吸附等对样品的结构和形貌进行表征。以甲基橙、亚甲基蓝、罗丹明 B和苯酚为目标降解物,在可见光下进行复合材料的光催化性能测试,以降解甲基橙溶液为例研究复合材料的光催化反应机理。结果表明,复合材料的BET比表面积随着Ni-Fe LDH含量的增加而增大,光催化活性明显提高。Bi2MoO6/Ni-Fe LDH复合材料中Ni-Fe LDH的含量为4.5%时具有最好的光催化效果,可见光照射60 min,甲基橙的降解率达91%,较Bi2MoO6和Ni-Fe LDH分别提高52%和16%。Bi2MoO6/Ni-Fe LDH复合材料具有良好的稳定性,循环使用5次,甲基橙(MO)的降解率为88%。复合材料光催化降解甲基橙反应遵循一级反应动力学。%Bi2MoO6/Ni-Fe LDH composites were prepared by hydrothermal method and co-precipitation. The morphology and structure of the sample were characterized by XRD, FT-IR, SEM, TEM, XPS and N2-physisorption. Photocatalytic degradation activity and mechanism of the samples were investigated by the photocatalytic degrada-tion of methyl orange (MO), methylene blue, butyl rhodamine B and phenol under visible light irradiation. The re-sults showed that BET specific surface area of the composites increased with the LDH content increase. Photocata-lytic degradation activity of MO under visible irradiation exhibited significant enhancement. After visible light ir-radiation for 60 min, the Bi2MoO6/Ni-Fe LDH composites with LDH content of 4.5wt% showed the highest degra-dation rate of 91%, higher than that of Bi2MoO6and Ni-Fe LDH by 52% and 16%, respectively. And the composites photocatalytic degradation followed first-order reaction kinetics. The composites decolorizing rate still remained 88% after 5 times recycle, showing high catalytic stability.

  1. Multiscale simulation reveals multiple pathways for H2 and O2 transport in a [NiFe]-hydrogenase.

    Science.gov (United States)

    Wang, Po-hung; Best, Robert B; Blumberger, Jochen

    2011-03-16

    Hydrogenases are enzymes that catalyze the reversible conversion of hydrogen molecules to protons and electrons. The mechanism by which the gas molecules reach the active site is important for understanding the function of the enzyme and may play a role in the selectivity for hydrogen over inhibitor molecules. Here, we develop a general multiscale molecular simulation approach for the calculation of diffusion rates and determination of pathways by which substrate or inhibitor gases can reach the protein active site. Combining kinetic data from both equilibrium simulations and enhanced sampling, we construct a master equation describing the movement of gas molecules within the enzyme. We find that the time-dependent gas population of the active site can be fit to the same phenomenological rate law used to interpret experiments, with corresponding diffusion rates in very good agreement with experimental data. However, in contrast to the conventional picture, in which the gases follow a well-defined hydrophobic tunnel, we find that there is a diverse network of accessible pathways by which the gas molecules can reach the active site. The previously identified tunnel accounts for only about 60% of the total flux. Our results suggest that the dramatic decrease in the diffusion rate for mutations involving the residue Val74 could be in part due to the narrowing of the passage Val74-Arg476, immediately adjacent to the binding site, explaining why mutations of Leu122 had only a negligible effect in experiment. Our method is not specific to the [NiFe]-hydrogenase and should be generally applicable to the transport of small molecules in proteins. PMID:21341658

  2. Platinum-ruthenium bimetallic clusters on graphite: a comparison of vapor deposition and electroless deposition methods.

    Science.gov (United States)

    Galhenage, Randima P; Xie, Kangmin; Diao, Weijian; Tengco, John Meynard M; Seuser, Grant S; Monnier, John R; Chen, Donna A

    2015-11-14

    Bimetallic Pt-Ru clusters have been grown on highly ordered pyrolytic graphite (HOPG) surfaces by vapor deposition and by electroless deposition. These studies help to bridge the material gap between well-characterized vapor deposited clusters and electrolessly deposited clusters, which are better suited for industrial catalyst preparation. In the vapor deposition experiments, bimetallic clusters were formed by the sequential deposition of Pt on Ru or Ru on Pt. Seed clusters of the first metal were grown on HOPG surfaces that were sputtered with Ar(+) to introduce defects, which act as nucleation sites for Pt or Ru. On the unmodified HOPG surface, both Pt and Ru clusters preferentially nucleated at the step edges, whereas on the sputtered surface, clusters with relatively uniform sizes and spatial distributions were formed. Low energy ion scattering experiments showed that the surface compositions of the bimetallic clusters are Pt-rich, regardless of the order of deposition, indicating that the interdiffusion of metals within the clusters is facile at room temperature. Bimetallic clusters on sputtered HOPG were prepared by the electroless deposition of Pt on Ru seed clusters from a Pt(+2) solution using dimethylamine borane as the reducing agent at pH 11 and 40 °C. After exposure to the electroless deposition bath, Pt was selectively deposited on Ru, as demonstrated by the detection of Pt on the surface by XPS, and the increase in the average cluster height without an increase in the number of clusters, indicating that Pt atoms are incorporated into the Ru seed clusters. Electroless deposition of Ru on Pt seed clusters was also achieved, but it should be noted that this deposition method is extremely sensitive to the presence of other metal ions in solution that have a higher reduction potential than the metal ion targeted for deposition. PMID:26018140

  3. 非晶态Ni-Fe-P和Ni-P合金屏蔽织物的制备及其性能比较研究∗%Contrast studies of the process optimization and characterization of shielding fabric by amorphous Ni-Fe-P and Ni-P alloy

    Institute of Scientific and Technical Information of China (English)

    吴雪艳; 姚恺; 安振涛; 高欣宝; 张倩

    2015-01-01

    A flexible shielding fabric with dense uniform coating was prepared after electrical deposition of amor-phous Ni-Fe-P and Ni-P alloy on copper-coated polyethylene terephthalate (PET)fabric.The effects of coating composition and the deposition rate were discussed by the current density,temperature and pH value.The mor-phology,composition,and structure of coating were analyzed by SEM,EDS,and XRD characterizations.The EMI shielding effectiveness and corrosion resistance were also tested.The results fabric possesses dense, smooth,and uniform coating,when the processing conditions are 60 ℃,pH=1.5,and current density=8.7 A/dm2 .The coating fabric consists of amorphous Ni-Fe-P alloy with 16.62% P (weight percent),which has excellent of corrosion resistance.By contrast the EMI shielding effectiveness of amorphous Ni-Fe-P was better than amorphous Ni-P.The EMI shielding effectiveness of this coated fabric achieves 69.20-80.30 dB in a broad frequency range between 300 kHz-1.5 GHz.%在已化学镀铜涤纶织物上电沉积非晶态Ni-Fe-P和 Ni-P 合金,制备了镀层致密均匀的柔性金属化屏蔽织物.讨论了电流密度、温度及 pH 值对镀层组成和沉积速率的影响,借助SEM、EDS和XRD测试仪器对镀层表面形貌、成分及结构进行了分析,并测试了镀层织物电磁屏蔽效能.结果表明,当电流密度为8.7 A/dm2,温度为60℃,pH 值=1.5时,非晶态 Ni-Fe-P合金的织物镀层结晶细致,致密均匀,镀层为 P含量为16.62%的非晶态结构.通过对比分析,非晶态Ni-Fe-P合金织物的电磁屏蔽效能较好.在300 kHz~1.5 GHz频率范围内,镀层织物电磁屏蔽效能达到了69.20~80.30 dB.

  4. The study of structural properties of carbon nanotubes decorated with NiFe2O4 nanoparticles and application of nano-composite thin film as H2S gas sensor

    International Nuclear Information System (INIS)

    Nano-composite of multiwall carbon nanotube, decorated with NiFe2O4 nanoparticles (NiFe2O4–MWCNT), was synthesized using the sol–gel method. NiFe2O4–MWCNTs were characterized using different methods such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and vibrating sample magnetometer (VSM). The average size of the crystallites is 23.93 nm. The values of the saturation magnetization (MS), coercivity (HC) and retentivity (MR) of NiFe2O4–MWCNTs are obtained as 15 emu g−1, 21 Oe and 5 emu g−1, respectively. In this research, NiFe2O4–MWCNT thin films were prepared with the spin-coating method. These thin films were used as the H2S gas sensor. The results suggest the possibility of the utilization of NiFe2O4–MWCNT nano-composite, as the H2S detector. The sensor shows appropriate response towards 100 ppm of H2S at 300 °C. - Highlights: • Nano-composite the average size of the crystallites is 23.93 nm. • NiFe2O4 thin films were prepared with spin-coating method. • These thin films were used as the H2s gas sensor. • The sensor shows appropriate response towards 100 ppm of H2S at 300 °C

  5. Synchrotron radiation studies of supported metal catalysts

    International Nuclear Information System (INIS)

    Metallic clusters supported on refractory oxides have been used extensively for several decades in the production of chemicals and petroleum derived transportation fuels. Catalysts containing more than one metal component are of particular interest since the addition of a second metal provides a method of controlling the selectivity of the catalyst. That is, the second metal can alter the rates of competing reactions in a complex reaction sequence and thus alter the final product distribution of the reaction. In this work the reactions of cyclohexane in hydrogen over silica supported ruthenium and osmium catalysts were studied. Bimetallic catalysts represent an important class of materials that are of interest both scientifically and technologically. Despite the importance and long-standing use of supported metal catalysts, detailed information on the structure of the metal clusters has been difficult to obtain. The development of x-ray absorption spectroscopy with the increasing availability of synchrotron radiation, however, has provided a powerful and versatile tool for studying the structure of these complex systems. Using the Extended X-ray Absorption Fine Structure (EXAFS) technique, it is possible to obtain information on the local atomic structure of supported monometallic catalytic metals and their interaction with the support. In the discussion that follows the authors will focus on results that have been obtained on the structure of supported bimetallic cluster catalysts

  6. Investigations of the microstructural stability of wrought Ni-(Fe)-based syperalloys for steam turbine rotor application beyond 700 C; Untersuchungen der Strukturstabilitaet von Ni-(Fe)-Basislegierungen fuer Rotorwellen in Dampfturbinen mit Arbeitstemperaturen ueber 700 C

    Energy Technology Data Exchange (ETDEWEB)

    Seliga, T.

    2005-07-01

    There is a continuous trend to improve the efficiency of modern power plants with steam turbine require operating steam temperature from 700 to 720 C. For substantial parts like turbine rotors and discs this means increased requirements on the high temperature resistance, which can not longer be fulfilled by the presently used steel. As new materials for the components, which are thermo-mechanically loaded, only Ni-based superalloys are suitable for their fabrication, structure stability and thermo-mechanical characteristics. With view on creep and creep crack growth resistance as suitable candidates in the context a DFG research project wrought Ni-based superalloy Waspaloy and Ni-Fe-based alloy Inconel 706 were selected, which exhibited different hardening mechanisms. Waspaloy is a {gamma}'-hardened material with small portion of carbides on the grain boundaries. Inconel 706 is a particle hardened alloy with a very complex microstructure, it consists of {gamma}', {gamma}{sup ''}-particle, {eta}-phase und carbides. Concerning to their castability, forgeability, creep and creep crack growth and microstructural stability these candidate materials have been investigated and modelled. The knowledge about their long time stability of the microstructure, castability, forgeability and mechanical properties leads to the two new modification (Waspaloy{yields}DT750 and Inconel 706{yields}DT706). The modification of the Waspaloy to DT 750 served better castability (elimination of the Freckle formation). An improvement of the long-term stability of the microstructure was not necessary, by a changed heat treatment was reached a homogeneous, monomodale {gamma}'-particle distribution. The modification of Inconel 706 to DT 706 served to stabilize the {gamma}'-phase and to reduce of the {gamma}{sup ''} phase without suppressing the cellular {eta}-phase colonies on the grain boundaries. This work presents the test results for the structural

  7. The effects of heat treatment on the synthesis of nickel ferrite (NiFe2O4) nanoparticles using the microwave assisted combustion method

    International Nuclear Information System (INIS)

    NiFe2O4 nanoparticles were synthesized using the microwave assisted combustion method based on metal nitrate salts and urea. To remain of organic matters and to stabilize the particles, samples were thermally treated at various temperatures from 300–800 °C. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The heat treated samples show the reflection planes of (111), (220), (222), (311), (400), (422), (511), and (440) which perfectly confirm to a cubic spinel phase of NiFe2O4 and no secondary phases were detected in the XRD patterns of the samples. The crystallite sizes calculated using the Debye–Scherrer formula were found to increase with the heat treatment temperature, from about 4 nm at 300 °C–85 nm at 800 °C. EDX results verify that the compositional mass rations were relevant, as expected from the synthesis. The micrographs of SEM and TEM showed that all of the samples have nano-crystalline behavior and particles indication cubic shape. Magnetization measurements were obtained at room temperature by using a VSM, which demonstrated that the all of the samples synthesized with heat treatment exhibited ferromagnetic behaviors. - Highlights: • The only microwave effect is not enough in synthesis of NiFe2O4 nanoparticles. • Nanoparticles were treated thermally for stabilization at various temperatures. • Crystallinity of the nanoparticles has become a more regular with heat treatment. • Average particle size of the nanoparticles increased with increasing temperature. • Magnetic properties of the nanoparticles improved with increasing temperature

  8. One-Pot Synthesis of (NiFe2O4)x-(SrFe12O19)1-x Nanocomposites and Their Microwave Absorption Properties.

    Science.gov (United States)

    Hazra, Subhenjit; Ghosh, Barun Kumar; Patra, Manoj Kumar; Jani, Raj Kumar; Vadera, Sampat Raj; Ghosh, Narendra Nath

    2015-09-01

    In this paper, we report a simple but novel aqueous solution based 'one-pot' method for preparation of (NiFe2O4)x-(SrFe12O19)1-x nanocomposites consist of hard ferrite-soft ferrite phases. A physical mixing method has also been employed to prepare nanocomposites having same compositions. The effects of synthetic methodologies on the microstructures of the nanocomposites as well as their magnetic and microwave absorption properties have been evaluated. Crystal structures and microstructures of these composites have been investigated by using X-ray diffraction, transmission electron microscope and scanning electron microscope. In the nanocomposites, prepared by both methods, presence of nanocrystalline NiFe2O4 and SrFe12O19 phases was detected. However, nanocomposites, prepared by one-pot method, possessed better homogeneous distribution of hard and soft ferrite phases than the nanocomposites, prepared by physical mixing method. Nanocomposites, prepared by one-pot method, demonstrated significant spring exchange coupling interaction between hard and soft ferrite phases and exhibited magnetically single phase behaviour. The spring exchange coupling interaction enhanced the magnetic properties (high saturation magnetization and coercivity) and microwave absorption properties of the nanocomposites, prepared by one-pot method, in comparison with the nanocomposites prepared by physical mixing method as well as pure NiFe2O4 and SrFe12O19 nanoparticles. Minimum reflection loss of the composite was ~ -17 dB (i.e., 98% absorption) at 8.2 GHz for an absorber thickness of 3.2 mm. PMID:26716212

  9. The effects of heat treatment on the synthesis of nickel ferrite (NiFe{sub 2}O{sub 4}) nanoparticles using the microwave assisted combustion method

    Energy Technology Data Exchange (ETDEWEB)

    Karcıoğlu Karakaş, Zeynep, E-mail: kzeynep@atauni.edu.tr [Atatürk University, Faculty of Engineering, Department of Environmental Engineering, Erzurum (Turkey); Boncukcuoğlu, Recep [Atatürk University, Faculty of Engineering, Department of Environmental Engineering, Erzurum (Turkey); Karakaş, İbrahim Hakkı [Bayburt University, Faculty of Engineering, Department of Chemical Engineering, Bayburt (Turkey); Ertuğrul, Mehmet [Atatürk University, Faculty of Engineering, Department of Electric - Electronic Engineering, Erzurum (Turkey)

    2015-01-15

    NiFe{sub 2}O{sub 4} nanoparticles were synthesized using the microwave assisted combustion method based on metal nitrate salts and urea. To remain of organic matters and to stabilize the particles, samples were thermally treated at various temperatures from 300–800 °C. The prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The heat treated samples show the reflection planes of (111), (220), (222), (311), (400), (422), (511), and (440) which perfectly confirm to a cubic spinel phase of NiFe{sub 2}O{sub 4} and no secondary phases were detected in the XRD patterns of the samples. The crystallite sizes calculated using the Debye–Scherrer formula were found to increase with the heat treatment temperature, from about 4 nm at 300 °C–85 nm at 800 °C. EDX results verify that the compositional mass rations were relevant, as expected from the synthesis. The micrographs of SEM and TEM showed that all of the samples have nano-crystalline behavior and particles indication cubic shape. Magnetization measurements were obtained at room temperature by using a VSM, which demonstrated that the all of the samples synthesized with heat treatment exhibited ferromagnetic behaviors. - Highlights: • The only microwave effect is not enough in synthesis of NiFe{sub 2}O{sub 4} nanoparticles. • Nanoparticles were treated thermally for stabilization at various temperatures. • Crystallinity of the nanoparticles has become a more regular with heat treatment. • Average particle size of the nanoparticles increased with increasing temperature. • Magnetic properties of the nanoparticles improved with increasing temperature.

  10. Analysis of the influence of fuel on NiFe{sub 2}O{sub 4} nanocrystalline obtained by solution combustion synthesis; Influencia do tipo de combustivel sobre NiFe{sub 2}O{sub 4} nanocristalina obtida a partir da sintese por combustao em solucao

    Energy Technology Data Exchange (ETDEWEB)

    Dalt, S. Da; Bergmann, C.P., E-mail: silvana.da.dalt@ufrgs.b [Universidade Federal do Rio Grande do Sul (LACER/UFRGS), Porto Alegre, RS (Brazil). Escola de Engenharia. Lab. de Materiais Ceramicos

    2009-07-01

    This paper investigates the effect of different fuels used on a structural properties stoichiometric composition of NiFe{sub 2}O{sub 4} obtained from the combustion synthesis. Precursor solutions were prepared from iron nitrate nonahydrate and nickel nitrate hexahydrate, and complexing agents as maleic anhydride, oxalic acid and sucrose. The samples were characterized by X-ray diffraction to evaluate the presents phases, and crystallite size from single-line method, specific surface area (BET) and scanning electron microscopy (SEM) for morphological analysis of powders. The results indicate that NiFe{sub 2}O{sub 4} can be obtained after heat treatment at 800 deg C with particle size of approximately 60nm. (author)

  11. Tetranuclear Zn/4f coordination clusters as highly efficient catalysts for Friedel-Crafts alkylation.

    Science.gov (United States)

    Griffiths, Kieran; Kumar, Prashant; Akien, Geoffrey R; Chilton, Nicholas F; Abdul-Sada, Alaa; Tizzard, Graham J; Coles, Simon J; Kostakis, George E

    2016-06-14

    A series of custom-designed, high yield, isoskeletal tetranuclear Zn/4f coordination clusters showing high efficiency as catalysts with low catalytic loadings in Friedel-Crafts alkylation are described for the first time. The possibility of altering the 4f centers in these catalysts without altering the core topology allows us to further confirm their stability via EPR and NMR, as well to gain insights into the plausible reaction mechanism, showcasing the usefulness of these bimetallic systems as catalysts. PMID:27248829

  12. Stainless Steel to Titanium Bimetallic Transitions

    Energy Technology Data Exchange (ETDEWEB)

    Kaluzny, J. A. [Fermilab; Grimm, C. [Fermilab; Passarelli, D. [Fermilab

    2015-01-01

    In order to use stainless steel piping in an LCLS-II (Linac Coherent Light Source Upgrade) cryomodule, stainless steel to titanium bimetallic transitions are needed to connect the stainless steel piping to the titanium cavity helium vessel. Explosion bonded stainless steel to titanium transition pieces and bimetallic transition material samples have been tested. A sample transition tube was subjected to tests and x-ray examinations between tests. Samples of the bonded joint material were impact and tensile tested at room temperature as well as liquid helium temperature. The joint has been used successfully in horizontal tests of LCLS-II cavity helium vessels and is planned to be used in LCLS-II cryomodules. Results of material sample and transition tube tests will be presented.

  13. Impact of interface manipulation of oxide on electrical transport properties and low-frequency noise in MgO/NiFe/MgO heterojunctions

    OpenAIRE

    Jian-wei Li; Chong-jun Zhao; Chun Feng; Zhongfu Zhou; Guang-hua Yu

    2015-01-01

    Low-frequency noise and magnetoresistance in sputtered-deposited Ta(5 nm)/MgO (3 nm)/NiFe(10 nm)/MgO(3 nm)/Ta(3 nm) films have been measured as a function of different annealing times at 400°C. These measurements did not change synchronously with annealing time. A significant increase in magnetoresistance is observed for short annealing times (of the order of minutes) and is correlated with a relatively small reduction in 1/f noise. In contrast, a significant reduction in 1/f noise is observe...

  14. Spin tunneling magnetoresistance in NiFe/Al{sub 2}O{sub 3}/Co junctions with reduced dimensions formed using photolithography

    Energy Technology Data Exchange (ETDEWEB)

    Kumagai, S. [Tohoku Univ., Sendai (Japan). Dept. of Applied Physics; Yaoi, T. [Sony Corp., Yokohama (Japan). Research Center; Miyazaki, T. [Tohoku Univ., Sendai (Japan). Dept. of Applied Physics

    1997-02-01

    The spin tunneling magnetoresistive effect has been investigated for NiFe/Al{sub 2}O{sub 3}/Co junctions with a small junction area down to 3.5 x 3.5 {mu}m{sup 2} fabricated using photolithography. About 75 of the prepared junctions exhibit the spin tunneling magnetoresistive effect, the maximum value being around 1 at room temperature. Negative interlayer exchange coupling (J<0) is found in these junctions. The strength of the coupling tends to increase with decreasing junction area. (orig.).

  15. SYNTHESIS OF POLYMER-STABILIZED PLATINUM/RUTHENIUM BIMETALLIC COLLOIDS AND THEIR CATALYTIC PROPERTIES FOR SELECTIVE HYDROGENATION OF CROTONALDEHYDE

    Institute of Scientific and Technical Information of China (English)

    Wei-xia Tu; Han-fan Liu

    2005-01-01

    Polymer-stabilized platinum/ruthenium bimetallic colloids (Pt/Ru) were synthesized by polyol reduction with microwave irradiation and characterized by TEM and XPS. The colloidal nanoparticles have small and narrow size distributions. Catalytic performance of the Pt/Ru colloidal catalysts was investigated on the selective hydrogenation of crontonaldehyde (CRAL). A suitable amount of the added metal ions and base can improve the selectivity of CRAL to crotylalcohol (CROL) remarkably. The catalytic activity and the selectivity are dependent on the compositions of bimetallic colloids. Thereinto, PVP-stabilized 9Pt/1Ru colloid with a molar ratio of metals Pt:Ru = 9:1 shows the highest catalytic selectivity 77.3% to CROL at 333 K under 4.0 MPa of hydrogen.

  16. Removal of trichloroethylene DNAPL trapped in porous media using nanoscale zerovalent iron and bimetallic nanoparticles: Direct observation and quantification

    International Nuclear Information System (INIS)

    Highlights: ► TCE DNAPL removal inside pores using NZVI or bimetals in a 2-D system was visualized. ► Presence of nitrate and humic substances decrease the TCE DNAPL removal efficiency. ► Presence of ethanol increases the TCE DNAPL removal efficiency. ► Metal catalysts enhance the TCE DNAPL removal using NZVI in a short term reaction. ► Metal catalysts do not increase the DNAPL removal efficiency for a long term reaction. - Abstract: Direct trichloroethylene (TCE) dense non-aqueous phase liquid (DNAPL) removal inside pore areas using nanoscale zerovalent iron (NZVI) and bimetallic nanoparticles were first investigated in a water-saturated porous glass micromodel. Effects of nitrate, aqueous ethanol co-solvent, humic substance, and elapsed time on TCE DNAPL removal using NZVI were studied by direct visualization. The removal efficiency was then quantified by directly measuring the remaining TCE DNAPL blobs area using an image analyzer. As ethanol content of co-solvent increased, TCE DNAPL removal by NZVI was also increased implying sequential TCE DNAPL removal mechanisms: as dissolved TCE was degraded by NZVI, TCE dissolution from TCE blobs would be then facilitated and the TCE blob areas would be eventually reduced. The presence of nitrate and humic substance hindered the NZVI reactivity for the TCE DNAPL removal. In contrast, the TCE DNAPL removal efficiency was enhanced using bimetallic nanoparticles in a short-term reaction by generating atomic hydrogen for catalytic hydro-dechlorination. However, all TCE DNAPL removal efficiencies reached the same level after long-term reaction using both NZVI and bimetallic nanoparticles. Direct TCE DNAPL observation clearly implied that TCE blobs existed for long time even though all TCE blobs were fully exposed to NZVI and bimetallic nanoparticles.

  17. Converse magnetoelectric coupling in NiFe/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3} nanocomposite thin films grown on Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Ming [School of Materials Science and Engineering and State Key Lab of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084 (China); Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Siping 136000 (China); Hu, Jiamian; Wang, Jianjun; Li, Zheng; Shu, Li; Nan, C. W. [School of Materials Science and Engineering and State Key Lab of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084 (China)

    2013-11-04

    Multiferroic NiFe (∼30 nm)/Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–PbTiO{sub 3}(PMN–PT, ∼220 nm) bilayered thin films were grown on common Pt/Ti/SiO{sub 2}/Si substrates by a combination of off-axis magnetron sputtering and sol-gel spin-coating technique. By using AC-mode magneto-optical Kerr effect technique, the change in the Kerr signal (magnetization) of the NiFe upon applying a low-frequency AC voltage to the PMN–PT film was in situ acquired at zero magnetic field. The obtained Kerr signal versus voltage loop essentially tracks the electromechanical strain curve of the PMN–PT thin film, clearly demonstrating a strain-mediated converse magnetoelectric coupling, i.e., voltage-modulated magnetization, in the NiFe/PMN–PT nanocomposite thin films.

  18. 非晶态Ni-Fe-P合金屏蔽织物的工艺优化及耐蚀性研究%Study of the process optimization and corrosion resistant of shielding fabric by amorphous Ni-Fe-P alloy

    Institute of Scientific and Technical Information of China (English)

    张晓艺; 安振涛; 吴雪艳; 王维

    2015-01-01

    通过在已化学镀铜涤纶织物上电沉积非晶态 Ni-Fe-P 合金,制备出一种镀层致密均匀的柔性金属化屏蔽织物.研究和分析了电流密度、温度和 pH值对合金织物方阻值、增重率及屏蔽效能的影响,从而制定出最佳工艺.通过对比腐蚀前后非晶态 Ni-Fe-P合金和非晶态 Ni-P 合金镀层表面形貌、成分和电磁屏蔽效能可以得出,在电流密度为8.7 A/dm2,温度为60℃,pH 值=1.5的工艺条件下所制备的非晶态 Ni-Fe-P 合金织物结晶更加细化、光亮,致密性和均质性都得以明显提高,并具有良好的耐腐蚀性能,且在300 kHz~1.5 GHz 频率范围内的电磁屏蔽效能达到了69.20~80.30 dB.%A flexible shielding fabric with dense uniform coating was prepared after electrical deposition of amor-phous Ni-Fe-P alloy on copper-coated polyethylene terephthalate (PET)fabric.The effects of alloy fabric ohms per square,weight gain rate and shielding effectiveness were discussed by the current density,temperature and pH value.The morphology and composition of coating of amorphous Ni-Fe-P alloy and amorphous Ni-P alloy were analyzed by SEM and EDS.The EMI shielding effectiveness and corrosion resistance were also tested.The results fabric possesses dense,smooth,and uniform coating,when the processing conditions are 60 ℃,pH=1.5,and current density =8.7 A/dm2 .The alloy fabric has excellent of corrosion resistance.The EMI shielding effectiveness of this alloy fabric achieves 69.20-80.30 dB in a broad frequency range between 300 kHz-1.5 GHz.

  19. Large enhancement of Blocking temperature by control of interfacial structures in Pt/NiFe/IrMn/MgO/Pt multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xi; Wang, Shouguo, E-mail: sgwang@ustb.edu.cn; Han, Gang; Jiang, Shaolong; Yang, Kang; Liu, Qianqian; Yu, Guanghua, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Liu, Jialong [Department of Physics, Beijing University of Aeronautics and Astronautics, Beijing 100191 (China); Department of Physics, University of Science and Technology Beijing, Beijing 100083 (China); Wang, Rongming [Department of Physics, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-09-15

    The Blocking temperature (T{sub B}) of Pt/NiFe/IrMn/MgO/Pt multilayers was greatly enhanced from far below room temperature (RT) to above RT by inserting 1 nm thick Mg layer at IrMn/MgO interface. Furthermore, the exchange bias field (H{sub eb}) was increased as well by the control of interfacial structures. The evidence for a significant fraction of Mn-O bonding at IrMn/MgO interface without Mg insertion layer was provided by X-ray photoelectron spectroscopy. The bonding between Mn and O can decrease the antiferromagnetism of IrMn film, leading to lower value of T{sub B} in Pt/NiFe/IrMn/MgO/Pt multilayers. Ultrathin Mg film inserted at IrMn/MgO interface acting as an oxygen sinking layer can suppress the oxidation reactions between Mn and O and reduce the formation of Mn-O bonding greatly. The oxidation suppression results in the recovery of the antiferromagnetism of IrMn film, which can enhance T{sub B} and H{sub eb}. Furthermore, the high resolution transmission electron microscopy demonstrates that the Mg insertion layer can efficiently promote a high-quality MgO (200) texture. This study will enhance the understanding of physics in antiferromagnet-based spintronic devices.

  20. Large enhancement of Blocking temperature by control of interfacial structures in Pt/NiFe/IrMn/MgO/Pt multilayers

    Directory of Open Access Journals (Sweden)

    Xi Chen

    2015-09-01

    Full Text Available The Blocking temperature (TB of Pt/NiFe/IrMn/MgO/Pt multilayers was greatly enhanced from far below room temperature (RT to above RT by inserting 1 nm thick Mg layer at IrMn/MgO interface. Furthermore, the exchange bias field (Heb was increased as well by the control of interfacial structures. The evidence for a significant fraction of Mn-O bonding at IrMn/MgO interface without Mg insertion layer was provided by X-ray photoelectron spectroscopy. The bonding between Mn and O can decrease the antiferromagnetism of IrMn film, leading to lower value of TB in Pt/NiFe/IrMn/MgO/Pt multilayers. Ultrathin Mg film inserted at IrMn/MgO interface acting as an oxygen sinking layer can suppress the oxidation reactions between Mn and O and reduce the formation of Mn-O bonding greatly. The oxidation suppression results in the recovery of the antiferromagnetism of IrMn film, which can enhance TB and Heb. Furthermore, the high resolution transmission electron microscopy demonstrates that the Mg insertion layer can efficiently promote a high-quality MgO (200 texture. This study will enhance the understanding of physics in antiferromagnet-based spintronic devices.

  1. Influence of carboxylic acid type on microstructure and magnetic properties of polymeric complex sol-gel driven NiFe2O4

    Science.gov (United States)

    Hessien, M. M.; Mostafa, Nasser Y.; Abd-Elkader, Omar H.

    2016-01-01

    Citric, oxalic and tartaric acids were used for synthesis of NiFe2O4 using polymeric complex precursor route. The dry precursor gels were calcined at various temperatures (400-1100 °C) for 2 h. All carboxylic acids produce iron-deficient NiFe2O4 with considerable amount of α-Fe2O3 at 400 °C. Increase in the annealing temperature caused reaction of α-Fe2O3 with iron-deficient ferrite phase. The amount of initially formed α-Fe2O3 is directly correlated with stability constant and inversely correlated with the decomposition temperature of Fe(III) carboxylate precursors. In case of tartaric acid precursor, single phase of the ferrite was obtained at 450 °C. However, in case of oxalic acid and citric acid precursors, single phase ferrite was obtained at 550 °C and 700 °C, respectively. The lattice parameters were increased with increasing annealing temperature and with decreasing the amount of α-Fe2O3. Maximum saturation magnetization (55 emu/g) was achieved using tartaric acid precursor annealed at 1100 °C.

  2. Temperature dependence of magnetization and anisotropy in uniaxial NiFe2O4 nanomagnets: Deviation from the Callen-Callen power law

    International Nuclear Information System (INIS)

    The thermal variation of magnetic anisotropy (K) and saturation magnetization (MS) for uniaxial nickel ferrite (NiFe2O4) nanomagnets are investigated. Major magnetic hysteresis loops are measured for the sample at temperatures over the range 5–280 K using a vibrating sample magnetometer. The high-field regimes of the hysteresis loops are modeled using the law of approach to saturation, based on the assumption that at sufficiently high field only direct rotation of spin-moment take place, with an additional forced magnetization term that is linear with applied field. The uniaxial anisotropy constant K is calculated from the fitting of the data to the theoretical equation. As temperature increases from 5 K to 280 K, a 49% reduction of K, accompanied by an 85% diminution of MS is observed. Remarkably, K is linearly proportional to MS2.6 in the whole temperature range violating the existing theoretical model by Callen and Callen. The unusual power-law behavior for the NiFe2O4 uniaxial nanomagnets is ascribed to the non-negligible contributions from inter-sublattice pair interactions, Neel surface anisotropy, and higher order anisotropies. A complete realization of the unusual anisotropy-magnetization scaling behavior for nanoscale two-sublattice magnetic materials require a major modification of the existing theory by considering the exact mechanism of each contributions to the effective anisotropy.

  3. Effect of additive V2O5 on sintering mechanism and properties of inert anodes of NiFe2O4 spinel

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    In order to improve the properties of inert anode of NiFe2O4 spinel, some additive V2O5 was added to raw materials-powders of NiO and Fe2O3. The powders of NiO, Fe2O3 were mixed with slight amount of V2O5, then they are moulded and sintered at 1200℃ for 6h. The sintering mechanism of powders of NiO and Fe2O3 with some additive V2 O5 was researched. The effect of V2O5 on density, electrical conductivity and corrosion resistance of inert anode of NiFe2O4 spinel was studied at the same time. The results show that the sintering mechanism for powders of NiO and Fe2O3 with some additive V2O5 is liquid-phase sintering. Additive V2O5 can increase the density of the samples, especially it improves the corrosion resistance of the samples remarkably. When the amount of V2 O5 is 1.5 %, the sample's corrosion rate is 1/80 of that of sample without V2 O5. But the electrical conductivity of the samples with V2O5 is lower than that of the sample without V2O5.

  4. Large enhancement of Blocking temperature by control of interfacial structures in Pt/NiFe/IrMn/MgO/Pt multilayers

    International Nuclear Information System (INIS)

    The Blocking temperature (TB) of Pt/NiFe/IrMn/MgO/Pt multilayers was greatly enhanced from far below room temperature (RT) to above RT by inserting 1 nm thick Mg layer at IrMn/MgO interface. Furthermore, the exchange bias field (Heb) was increased as well by the control of interfacial structures. The evidence for a significant fraction of Mn-O bonding at IrMn/MgO interface without Mg insertion layer was provided by X-ray photoelectron spectroscopy. The bonding between Mn and O can decrease the antiferromagnetism of IrMn film, leading to lower value of TB in Pt/NiFe/IrMn/MgO/Pt multilayers. Ultrathin Mg film inserted at IrMn/MgO interface acting as an oxygen sinking layer can suppress the oxidation reactions between Mn and O and reduce the formation of Mn-O bonding greatly. The oxidation suppression results in the recovery of the antiferromagnetism of IrMn film, which can enhance TB and Heb. Furthermore, the high resolution transmission electron microscopy demonstrates that the Mg insertion layer can efficiently promote a high-quality MgO (200) texture. This study will enhance the understanding of physics in antiferromagnet-based spintronic devices

  5. Fabrication of glass/Ni-Fe-P ternary alloy core/shell composite hollow microspheres through a modified electroless plating process

    Science.gov (United States)

    An, Zhen-guo; Zhang, Jing-jie; Pan, Shun-long

    2008-12-01

    Glass/Ni-Fe-P ternary alloy core/shell composite hollow microspheres were fabricated by a modified electroless plating process. In the process, a coupling procedure was employed with 3-aminopropyltriethoxy silane as the coupling agent and silver nitrate was used as the activator. The effect of process parameters, such as mole ratio of (NH 4) 2Fe(SO 4) 2/NiSO 4, pH value of the plating solution and reaction temperature, on plating rate and properties of the composite microspheres were investigated. The results showed that the coupling treatment could improve the uniformity of Ni-Fe-P deposits remarkably. The plating rate was reduced rapidly with the increase of mole ratio of (NH 4) 2Fe(SO 4) 2/NiSO 4. The increase of the pH value could enhance the plating rate and the percentage of iron in the deposits. The as-obtained microspheres were magnetically soft at room temperature and their magnetic properties got better with the enhancement of the percentage of iron in the deposits.

  6. Magnetic, local ferroelectricity and magnetodielectric properties of NiFe2O4-poly (vinylidene-fluoride)-BaTiO3 composite film

    Science.gov (United States)

    Kumar, Amit; Yadav, K. L.

    2016-04-01

    We report the magnetic, dielectric, and magnetoelctric properties of NiFe2O4-poly (vinylidene-fluoride)-BaTiO3 composite film. The coercive field (±2H c ∼ 344 Oe) and remnant magnetization (M r ∼ 6.1 emu g‑1) were observed at room temperature. The dielectric permittivity at room temperature (ε‧RT ∼ 281) was found to decrease with increase in frequency. The magnetocapacitance was found to be ∼5.9% at an applied dc magnetic field of 8 kOe (frequency = 1 kHz). Magnetoelectric coupling coefficient (α E ∼ 4.1 mV cm‑1 Oe‑1) measured by dynamic method (at ac magnetic field = 30 Oe) is observed higher (two times) than those reported for some materials. In addition, we have observed the image of ferroelectric domain using piezoelectric force microscopy at room temperature. Large magnetodielectric/magnetoelectric response in this composite is possibly a result of the effective mechanical interaction between NiFe2O4 and BaTiO3 through the polymer matrix.

  7. Squeezing and stretching Pd thin films: A high-resolution STM study of Pd/Au(111) and Pd/Cu(111) bimetallics

    Science.gov (United States)

    Blecher, Mishan E.; Lewis, Emily A.; Pronschinske, Alex; Murphy, Colin J.; Mattera, Michael F. G.; Liriano, Melissa L.; Sykes, E. Charles H.

    2016-04-01

    Pd bimetallic alloys are promising catalysts, especially for heterogeneous reactions involving hydrogen, as they exhibit increased activity and reduced demand for expensive precious metals. Using scanning tunneling microscopy, we examine the structure of Pd thin films on Cu(111) and Au(111) and demonstrate compression and expansion, respectively, of the bulk Pd lattice constant in the film. The relative binding strength of H to the two surfaces, inferred via tip-induced diffusion barriers, suggests that the strain in these systems may alter adsorbate binding and corroborates well-known trends in d-band shifts calculated by the density functional theory. Modification to the topography and activity of Pd films based on the choice of substrate metal illustrates the value of bimetallic systems for designing less expensive, tunable catalysts.

  8. Synthesis and characterization of Fe-Co catalyst prepared via reverse microemulsion method

    Science.gov (United States)

    Mohd Zabidi, Noor Asmawati; Abdul Aziz, Muhammad Nur Azizi; Ali, Sardar; Taha, Mohd Faisal

    2012-09-01

    This paper reports the characterization of bimetallic catalyst systems comprising cobalt and iron on CNTs support prepared via reverse microemulsion method. The properties of the bimetallic catalyst were characterized using TEM, FESEM and N2 adsorption. Based on TEM analyses, the calculated average particle sizes ranged from 4.6 nm to 5.2 nm for the various catalyst compositions. The performance of the Co-based catalyst in a Fischer-Tropsch reaction was evaluated in a fixed-bed reactor at 220°C, 1 atm and H2/CO v/v ratio of 2:1 v/v and space velocity of 12 L/g.h. Amongst the catalysts tested, the 90Co10Fe/CNTs resulted in the highest CO conversion of 14.1% whereas the 100Co/CNTs resulted in the highest C5+ hydrocarbon selectivity.

  9. Analysis of Manufacturing Bimetallic Tubes by the Cold Drawing Process

    Directory of Open Access Journals (Sweden)

    Halaczek D.

    2016-03-01

    Full Text Available Drawing processes apply to obtain the bimetallic tubes from the different metals and alloys, combined in the solid state, which significantly affects the specificity of this process. The manufacturing of bimetallic tubes by drawing process depends on many factors which include: preparation of the surface of materials joined in the solid state, the geometric parameters of the working tool, technological parameters of the drawing process (drawing speed, type of lubricant, the use of back pull etc.. Generally, the cold drawing process of producing the bimetallic tubes refers to metals which have high ductility (copper, aluminum, etc.. The tube sinking (tube drawing without a mandrel of bimetallic tubes together with joining them at the interface of the two metal in the solid-state is applied for tubes of the diameter range between 6 to 20 mm and based on of the reducing the diameter of the tube. However, a slight increase of wall thickness ca. 0.05 ÷ 0.10 mm can appear, which is not dangerous phenomenon in case of producing the bimetallic tubes by joining in the solid-state. The aim of the research was to investigate the technology of tubes drawing process from non-ferrous metal, drawing process of bimetallic tubes and the production of bimetallic tubes in layers composition: cooper Cu-ETP - brass CuZn37 and CuZn37 brass - copper Cu-ETP in the tube sinking process. The research program included: production of bimetallic tubes with a different composition (Cu- ETP-CuZn37 and CuZn37-Cu-ETP and a different percentage of the cross-section components; analysis of changes of tube wall thickness and the layer composition of the bimetallic tube, based on measurements on the workshop microscope; analysis of the material flow in the process of the bimetallic tubes production based on the measurements results of a profilograph CP-200.

  10. Steam reforming of ethanol over bimetallic RhPt/La2O3: Long-term stability under favorable reaction conditions

    OpenAIRE

    Cobo, Martha; Pieruccini, Diana; Abello, Ricardo; Ariza, Laura; Córdoba, Luis Fernando; Conesa Ferrer, Juan Antonio

    2013-01-01

    Recently, the steam reforming of biofuels has been presented as a potential hydrogen source for fuel cells. Because this scenario represents an interesting opportunity for Colombia (South America), which produces large amounts of bioethanol, the steam reforming of ethanol was studied over a bimetallic RhPt/La2O3 catalyst under bulk mass transfer conditions. The effect of temperature and the initial concentrations of ethanol and water were evaluated at space velocities above 55,000 h−1 to dete...

  11. Insight into the Catalytic Mechanism of Bimetallic Platinum–Copper Core–Shell Nanostructures for Nonaqueous Oxygen Evolution Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Lu; Luo, Xiangyi; Kropf, A. Jeremy; Wen, Jianguo; Wang, Xiaoping; Lee, Sungsik; Myers, Deborah J.; Miller, Dean; Wu, Tianpin; Lu, Jun; Amine, Khalil

    2016-01-01

    The oxygen evolution reaction (OER) plays a critical role in multiple energy conversion and storage applications. However, its sluggish kinetics usually results in large voltage polarization and unnecessary energy loss. Therefore, designing efficient catalysts that could facilitate this process has become an emerging topic. Here, we present a unique Pt–Cu core–shell nanostructure for catalyzing the nonaqueous OER. The catalysts were systematically investigated with comprehensive spectroscopic techniques, and applied in nonaqueous Li–O2 electrochemical cells, which exhibited dramatically reduced charging overpotential (<0.2 V). The superior performance is explained by the robust Cu(I) surface sites stabilized by the Pt core in the nanostructure. The insights into the catalytic mechanism of the unique Pt–Cu core–shell nanostructure gained in this work are expected to serve as a guide for future design of other nanostructured bimetallic OER catalysts.

  12. Enhanced Dry Reforming of Methane on Ni and Ni-Pt Catalysts Synthesized by Atomic Layer Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Gould, Troy D.; Montemore, Matthew M.; Lubers, Alia M.; Ellis, Lucas D.; Weimer, Alan; Falconer, John L.; Medlin, James W.

    2015-02-25

    Atomic layer deposition (ALD) was used to deposit Ni and Pt on alumina supports to form monometallic and bimetallic catalysts with initial particle sizes of 1–2.4 nm. The ALD catalysts were more active (per mass of metal) than catalysts prepared by incipient wetness (IW) for dry reforming of methane (DRM), and they did not form carbon whiskers during reaction due to their sufficiently small size. Catalysts modified by Pt ALD had higher rates of reaction per mass of metal and inhibited coking, whereas NiPt catalysts synthesized by IW still formed carbon whiskers. Temperature-programmed reduction of Ni catalysts modified by Pt ALD indicated the presence of bimetallic interaction. Density functional theory calculations suggested that under reaction conditions, the NiPt surfaces form Ni-terminated surfaces that are associated with higher DRM rates (due to their C and O adsorption energies, as well as the CO formation and CH4 dissociation energies).

  13. A facile reflux procedure to increase active surface sites form highly active and durable supported palladium@platinum bimetallic nanodendrites

    Science.gov (United States)

    Wang, Qin; Li, Yingjun; Liu, Baocang; Xu, Guangran; Zhang, Geng; Zhao, Qi; Zhang, Jun

    2015-11-01

    A series of well-dispersed bimetallic Pd@Pt nanodendrites uniformly supported on XC-72 carbon black are fabricated by using different capping agents. These capping agents are essential for the branched morphology control. However, the surfactant adsorbed on the nanodendrites surface blocks the access of reactant molecules to the active surface sites, and the catalytic activities of these bimetallic nanodendrites are significantly restricted. Herein, a facile reflux procedure to effectively remove the capping agent molecules without significantly affecting their sizes is reported for activating supported nanocatalysts. More significantly, the structure and morphology of the nanodendrites can also be retained, enhancing the numbers of active surface sites, catalytic activity and stability toward methanol and ethanol electro-oxidation reactions. The as-obtained hot water reflux-treated Pd@Pt/C catalyst manifests superior catalytic activity and stability both in terms of surface and mass specific activities, as compared to the untreated catalysts and the commercial Pt/C and Pd/C catalysts. We anticipate that this effective and facile removal method has more general applicability to highly active nanocatalysts prepared with various surfactants, and should lead to improvements in environmental protection and energy production.

  14. Thermodynamic equilibrium in Co-Ni-Fe-Mn complexation−precipitation system%Co-Ni-Fe-Mn配合−沉淀体系的平衡热力学

    Institute of Scientific and Technical Information of China (English)

    马立文; 聂祚仁; 席晓丽; 韩新罡

    2013-01-01

      根据质量守恒和同时平衡原理,以Me(Co、Ni、Fe、Mn)为金属元素,建立Me-OH−、Me-OH−-CO32−、Me-OH−-S2−、Me-OH−-NH3和 Me-OH−-NH3-CO32−等多个配合−沉淀体系的热力学平衡模型.结果表明:Fe3+可以在Me-OH−、Me-OH−-NH3体系中通过调节pH=3预先沉淀分离,而Co、Ni、Mn仅在Me-OH−-NH3-CO32−体系中有分离效果.Me-OH−-NH3-CO32−体系热力学计算表明:Co、Ni、Mn在溶液中的行为受pH值、配合剂、沉淀剂浓度共同影响,碳酸根初始总浓度[C]增大和氨初始总浓度[N]减小有利于Co、Ni、Mn形成沉淀.当[C]=1 mol/L、[N]=2 mol/L、pH值为9~10时,大部分Ni以高级氨配离子[Ni(NH3)42+]、[Ni(NH3)52+]、[Ni(NH3)62+]的形式保留在溶液中,而Co、Mn以MnCO3、CoCO3的形式沉淀出来.Co可在Me-OH−-S2−体系中通过调节pH<6从溶液中与Mn分离.研究结果可为钴镍二次资源综合回收钴镍、制备钴镍产品提供理论指导.%Based on mass balance principle and simultaneous equilibrium principle, the metal element Me (Co, Ni, Fe, Mn), complexing agent of OH− and NH3, and precipitant of OH−, S2− and CO32− were chosen to form the complexation–precipitation systems of Me-OH−, Me-OH−-CO32−, Me-OH−-S2−, Me-OH−-NH3 and Me-OH−-NH3-CO32−. The thermodynamic equilibriums of these systems were studied. The results show that Fe3+in systems of Me-OH− and Me-OH−-NH3 can be separated by precipitation through adjusting the pH value to 3. However, Co, Ni and Mn can be separated only in Me-OH−-NH3-CO32−system. The theoretical calculations show that the behavior of Co, Ni and Mn in Me-OH−-NH3-CO32−system is affected by pH value, complexing agent concentration and precipitant concentration. The increase of the total concentration of carbonate [C] is in favor of the precipitation of Ni, Co and Mn, but the increase of the total ammonia concentration [N] has the opposite effect. When [C]=1 mol

  15. Effect of Co addition on densification and mechanical properties of 17Ni-(10NiO-NiFe2O4) cermet%Co添加对17Ni-(10NiO-NiFe2O4)金属陶瓷的致密化及力学性能的影响

    Institute of Scientific and Technical Information of China (English)

    林启权; 赵爽; 姜滔; 董文正

    2015-01-01

    为了改善17Ni-(10NiO-NiFe2O4)金属陶瓷惰性阳极中金属相的分布,在原料中添加不同含量的Co,以Co-Ni取代纯Ni作为金属相,采用真空烧结方法制备17(xCo-Ni)-(10NiO-NiFe 2 O 4)金属陶瓷,并研究Co添加量对金属陶瓷物相组成、显微组织、致密度及力学性能的影响。结果表明:烧结样品主要由Co-Ni、NiFe 2 O 4、NiO组成,部分Co与陶瓷基体反应生成CoO与Fe 2 O 3。添加适量Co可以改善金属相在陶瓷相的分布和形貌,使团聚孤立的金属相分布均匀,且部分球状金属相变为长条状金属相;同时,添加适量Co还可以促进烧结,提高试样的致密度。适量Co的添加还能降低晶粒尺寸,大幅提高金属陶瓷材料强度与韧性。当Co质量分数为金属相的20%时,金属陶瓷的综合性能最好,致密度、抗弯强度、断裂韧性及硬度分别达到96.87%、163.65 MPa、8.38 MPa/m1/2和820.81HV。%In order to improve the distribution of metal phase in the 17Ni-(10NiO-NiFe2O4)cermet, 17(xCo-Ni)-(10NiO-NiFe2O4)cermet were prepared by vacuum sintering method using Co-Ni instead of Ni as the metal phase. And the effects of Co content on the phase composition, microstructure, relative density and mechanical properties of the cermet were investigated. The results show that the cermet is composed of Co-Ni, NiFe2O4and NiO, a part of Co reacts with ceramic matrix to form CoO and Fe2O3. The proper addition of Co can significantly improve the distribution and morphology of the metal phase, the agglomerate isolated metal phases can distribute uniformly and a part of spherical metal phases can change to elongated metal phases. Moreover, the proper addition of Co can promote sintering and increase the density of sample. Co addition can refine the grain size and greatly increase the strength and the toughness of cermet. When the mass fraction of Co in metal phase is 20%, the combination properties of sample are the best. The

  16. Development of Cu and Ni catalysts supported on ZrO{sub 2} for the generation of H{sub 2} by means of the reaction of reformed methanol in atmosphere oxidizer; Desarrollo de catalizadores de Cu y Ni soportados en ZrO{sub 2} para la generacion de H{sub 2} mediante la reaccion de reformado de metanol en atmosfera oxidante

    Energy Technology Data Exchange (ETDEWEB)

    Lopez C, P.

    2012-07-01

    ZrO{sub 2} was prepared by the sol-gel method and calcined at 450 C. The prepared zirconia was impregnated with an aqueous solution of Cu(CH{sub 3}CO{sub 2}){sub 2}{center_dot}H{sub 2}O or NiNO{sub 3}{center_dot}6H{sub 2}O at an appropriate concentration to yield 3 wt % of copper or nickel, respectively, in the mono metallic catalysts. Three bimetallic samples were prepared at 80% Cu and 20% Ni respectively to obtain 3 wt % of total metallic phase. Surface area of the Cu-Ni base catalysts supported on ZrO{sub 2} oxide showed differences as a function of the metal addition. Between them, the Cu/ZrO{sub 2} catalyst had the lowest surface area than other catalysts. X-ray diffraction patterns of the bimetallic catalysts did not show diffraction peaks of the Cu, Ni or bimetallic Cu-Ni alloys. In addition, TPR profiles of the bimetallic catalysts had the lowest reduction temperature compared with the mono metallic samples. The reactivity of the catalysts in the range of 250-350 C showed that the samples prepared by successive impregnation had the highest catalytic activity than the other catalysts studied. Also the selectivity for H{sub 2} production was higher for these catalysts. This finding was associated to the presence of the bimetallic Cu-Ni nanoparticles, as was evidenced by Tem-EDX analysis. (Author)

  17. PdPt bimetallic nanoparticles enabled by shape control with halide ions and their enhanced catalytic activities.

    Science.gov (United States)

    Zhang, Jinfeng; Wan, Lei; Liu, Lei; Deng, Yida; Zhong, Cheng; Hu, Wenbin

    2016-02-11

    In this study, a new and convenient one step approach is described for synthesizing shape controlled PdPt bimetallic nanoparticles. It is found that the resultant morphologies of these PdPt nanoparticles can be well controlled by simply altering the participation of different halide ions that serve as shape controlling agents in the reaction solution. The dendritic core-shell PdPt bimetallic nanoparticles generated with Pt atoms adopt usual island growth pattern in the presence of Cl(-) ions, whereas the introduction of Br(-) ions with a relatively strong adsorption effect facilitate the formation of a layered core-shell structure due to the layered growth mode of Pt atoms on the exterior surface of the central Pd core. Moreover, the stronger adsorption function of I(-) ions and the resulting fast atomic diffusion promoted the generation of mesoporous core-shell PdPt bimetallic nanoparticles with many pore channels. In addition, the size of these synthesized PdPt nanoparticles exhibited a significant dependence on the concentration of the halide ions involved. Due to their specific structural features and synergistic effects, these PdPt catalysts exhibited shape-dependent catalytic performance and drastically enhanced electrocatalytic activities relative to that of commercial Pt black and Pt/C toward methanol oxidation. PMID:26511671

  18. Atomic structure and thermal stability of Pt-Fe bimetallic nanoparticles: from alloy to core/shell architectures.

    Science.gov (United States)

    Huang, Rao; Wen, Yu-Hua; Shao, Gui-Fang; Sun, Shi-Gang

    2016-06-22

    Bimetallic nanoparticles comprising noble metal and non-noble metal have attracted intense interest over the past few decades due to their low cost and significantly enhanced catalytic performances. In this article, we have explored the atomic structure and thermal stability of Pt-Fe alloy and core-shell nanoparticles by molecular dynamics simulations. In Fe-core/Pt-shell nanoparticles, Fe with three different structures, i.e., body-centered cubic (bcc), face-centered cubic (fcc), and amorphous phases, has been considered. Our results show that Pt-Fe alloy is the most stable configuration among the four types of bimetallic nanoparticles. It has been discovered that the amorphous Fe cannot stably exist in the core and preferentially transforms into the fcc phase. The phase transition from bcc to hexagonal close packed (hcp) has also been observed in bcc-Fe-core/Pt-shell nanoparticles. In contrast, Fe with the fcc structure is the most preferred as the core component. These findings are helpful for understanding the structure-property relationships of Pt-Fe bimetallic nanoparticles, and are also of significance to the synthesis and application of noble metal based nanoparticle catalysts. PMID:27297782

  19. BIMETALLIC LITHIUM BOROHYDRIDES TOWARD REVERSIBLE HYDROGEN STORAGE

    Energy Technology Data Exchange (ETDEWEB)

    Au, M.

    2010-10-21

    Borohydrides such as LiBH{sub 4} have been studied as candidates for hydrogen storage because of their high hydrogen contents (18.4 wt% for LiBH{sub 4}). Limited success has been made in reducing the dehydrogenation temperature by adding reactants such as metals, metal oxides and metal halides. However, full rehydrogenation has not been realized because of multi-step decomposition processes and the stable intermediate species produced. It is suggested that adding second cation in LiBH{sub 4} may reduce the binding energy of B-H. The second cation may also provide the pathway for full rehydrogenation. In this work, several bimetallic borohydrides were synthesized using wet chemistry, high pressure reactive ball milling and sintering processes. The investigation found that the thermodynamic stability was reduced, but the full rehydrogenation is still a challenge. Although our experiments show the partial reversibility of the bimetallic borohydrides, it was not sustainable during dehydriding-rehydriding cycles because of the accumulation of hydrogen inert species.

  20. Preparation of NiFe2O4/graphene nanocomposite and its application as a modifier for the fabrication of an electrochemical sensor for the simultaneous determination of tramadol and acetaminophen

    International Nuclear Information System (INIS)

    Highlights: • A new modified electrochemical sensor was constructed and used. • NiFe2O4/graphene was used as the modifier. • The sensor was used for the determination of tramadol and acetaminophen in real samples. • Modification improved the sensitivity and detection limit of the method. • The oxidation of tramadol and acetaminophen at the surface of the electrode was studied. - Abstract: An effective electrochemical sensor for the rapid and simultaneous determination of tramadol and acetaminophen based on carbon paste electrode (CPE) modified with NiFe2O4/graphene nanoparticles was developed. The structures of the synthesized NiFe2O4/graphene nanocomposite and the electrode composition were confirmed by X-ray diffraction (XRD) spectrometry, Fourier transform infrared (FT-IR) spectrometry and scanning electron microscopy (SEM). The peak currents of square wave voltammetry of tramadol and acetaminophen increased linearly with their concentration in the range of 0.01–9 μmol L−1. The detection limit for their determination was found to be 0.0036 and 0.0030 μmol L−1, respectively. The results show that the combination of graphene and NiFe2O4 nanoparticles causes a dramatic enhancement in the sensitivity of the sensor. The fabricated sensor exhibited high sensitivity and good stability, and would be valuable for the clinical assay of tramadol and acetaminophen