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Sample records for nanocrystalline cacu3ti4o12 powders

  1. Microwave synthesis and sintering characteristics of CaCu 3 Ti 4 O 12

    CaCu3Ti4O12 (CCTO) was synthesized and sintered by microwave processing at 2.45 GHz, 1.1 kW. The optimum calcination temperature using microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were sintered to 94% density at 1000°C/60 min.

  2. Chemical solution deposition of CaCu3Ti4O12 thin film

    Administrator

    CaCu3Ti4O12; thin film; chemical solution deposition; dielectric properties. 1. Introduction. The CaCu3Ti4O12. (CCTO) compound has recently attracted considerable ... and Kelvin probe force microscopy (Chung et al 2004). Intrinsic .... SEM images of CCTO thin films as a function of sintering temperature. silicon based ...

  3. Synthesis of Nanoparticles of the Giant Dielectric Material, CaCu3Ti4O12 from a Precursor Route

    Thomas, P.; Dwarakanath, K.; Varma, K. B. R.; Kutty, T. R. N.

    2013-01-01

    A complex oxalate precursor, CaCu3(TiO)4(C2O4)8.9H2O, was synthesized and the precipitate that obtained was confirmed to be monophasic by the wet chemical analyses, X-ray diffraction, FTIR absorption and TG, DTA analyses. The thermal decomposition of this oxalate precursor led to the formation of phase-pure calcium copper titanate, CaCu3Ti4O12, at 680oC. The bright field TEM micrographs revealed that the size of the as synthesized crystallites to be in the 30 to 80 nm range. The powders so ob...

  4. Nanoparticles of the giant dielectric material, CaCu3Ti4O12 from a precursor route

    Thomas, P.; Dwarakanath, K.; Varma, K. B. R.; Kutty, T. R. N.

    2013-01-01

    A method of preparing the nanoparticles of CaCu3Ti4O12 (CCTO) with the crystallite size varying from 30 to 200 nm is optimized at a temperature as low as 680 1C from the exothermic thermal decomposition of an oxalate precursor, CaCu3(TiO)4(C2O4)8 ? 9H2O. The phase singularity of the complex oxalate precursor is confirmed by the wet chemical analyses, X-ray diffraction, FT-IR and TGA,DTA analyses. The UV Vis reflectance and ESR spectra of CCTO powders indicate that the Cu(II) coordination chan...

  5. Chemical solution deposition of CaCu 3 Ti 4 O 12 thin film

    CaCu3Ti4O12 (CCTO) thin film was successfully deposited on boron doped silica substrate by chemical solution deposition and rapid thermal processing. The phase and microstructure of the deposited films were studied as a function of sintering temperature, employing X-ray diffractometry and scanning electron ...

  6. Experimental and numerical investigation of a ceramic dielectric resonator (DRA): CaCu3Ti4O12 (CCTO)

    Almeida, A.F.L.; Silva, R.R.; Rocha, H.H.B.; Fechine, P.B.A.; Cavalcanti, F.S.A.; Valente, M.A.; Freire, F.N.A.; Sohn, R.S.T.M.

    2008-01-01

    In this study, the CaCu 3 Ti 4 O 12 (CCTO) ceramic phase was synthesized by microwave heating in a much shorter time compared to the conventional heating methods. The results indicate that microwave processing is a promising method for preparing CCTO ceramics. CCTO was prepared using a domestic microwave oven operated at 2.45 GHz with 800 W. After a few minutes of microwave irradiation the formation of CCTO was confirmed by X-ray powder diffraction. The CCTO ceramic was studied in the medium-frequency (MF) range (100 Hz-1 MHz) and in the microwave range of frequencies. The experimental and theoretical characteristics of the dielectric resonator antenna are investigated

  7. Electron paramagnetic resonance investigation of polycrystalline CaCu3Ti4O12

    Mozzati, Maria Cristina; Azzoni, Carlo Bruno; Capsoni, Doretta; Bini, Marcella; Massarotti, Vincenzo

    2003-01-01

    Electron paramagnetic resonance (EPR) measurements on pure polycrystalline CaCu 3 Ti 4 O 12 have been performed and are discussed within a crystal-field approach. A symmetric signal centred at g = 2.15 is observed for T>25 K, with no evidence of hyperfine structure. At this temperature an antiferromagnetic transition is observed as confirmed by static magnetization data. Cu defective and 2% doped (V, Cr, Mn, La) samples were also prepared and considered, mainly to understand the nature of the observed paramagnetic centre. Substitutions in the octahedral sites, causing variations of the configuration in CuO 4 -TiO 6 -CuO 4 complexes, change the magnetic and EPR features. To justify the EPR response a strong copper-hole delocalization is suggested

  8. Synthesis and characterization of CCTO (CaCu3Ti4O12)

    Fernandes, T.S.M.; Silva, M.A.S. da; Simao, S.H.C.; Silva, C.C.; Sombra, A.S.B.; Sales, J.C.

    2011-01-01

    The objective of this work is to study the ceramic material CCTO (CaCu 3 Ti 4 O 12 ) by X-Ray Diffraction. The CCTO is a material with a giant dielectric constant at room temperature and good temperature stability over a wide temperature and frequency ranges. The preparation method has a great influence on the structure and dielectric properties of this material. The CCTO was prepared by solid state method in a planetary high energy ball milling (Fritsch Pulverisette 5). Stoichiometric quantities of CaCO 3 (Aldrich 99%), TiO 2 (Merck 99%) and CuO (Analar 98%) were dry milled during 30h with a rotational speed of 370 rpm and then calcined at 1050 deg C for 12h. After, the CCTO was studied by X-ray diffraction (XRD). The refinement showed that the CCTO was formed with 100% mass, the graph of Williamson-Hall showed a homogeneous sample, with a contraction in the crystal lattice and a reasonably small particle size. (author)

  9. PENGUKURAN NILAI DIELEKTRIK MATERIAL CALCIUM COPPER TITANAT ( CaCu3Ti4O12 MENGGUNAKAN SPEKTROSKOPI IMPEDANSI TERKOMPUTERISASI

    Widodo Budi Kurniawan

    2017-05-01

    ABSTRACT   The measurement of the complex dielectric constant and the magnitude of the capacitor impedances of the ceramic materials Calcium Copper Titanate CaCu3Ti4O12 (CCTO with purity of 99% has been done by using the method of computerized impedance spectroscopy in the frequency range 5 kHz - 120 kHz. The highest dielectric constant of the material was found to be 745 at 5 kHz in the sample sintered 7000C and the highest impedance of capacitor occured in CCTO sample non sintered that is 150434Ω. The results showed that complex dielectric constant and impedance of the capacitor of the material under study was frequency dependent.   Keywords : impedance spectroscopy, CaCu3Ti4O12,complex dielectric constant and impedance of capacitor

  10. Room temperature magnetic and dielectric properties of cobalt doped CaCu3Ti4O12 ceramics

    Mu, Chunhong; Song, Yuanqiang; Wang, Haibin; Wang, Xiaoning

    2015-05-01

    CaCu3Ti4-xCoxO12 (x = 0, 0.2, 0.4) ceramics were prepared by a conventional solid state reaction, and the effects of cobalt doping on the room temperature magnetic and dielectric properties were investigated. Both X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the presence of Cu and Co rich phase at grain boundaries of Co-doped ceramics. Scanning electron microscopy micrographs of Co-doped samples showed a striking change from regular polyhedral particle type in pure CaCu3Ti4O12 (CCTO) to sheet-like grains with certain growth orientation. Undoped CaCu3Ti4O12 is well known for its colossal dielectric constant in a broad temperature and frequency range. The dielectric constant value was slightly changed by 5 at. % and 10 at. % Co doping, whereas the second relaxation process was clearly separated in low frequency region at room temperature. A multirelaxation mechanism was proposed to be the origin of the colossal dielectric constant. In addition, the permeability spectra measurements indicated Co-doped CCTO with good magnetic properties, showing the initial permeability (μ') as high as 5.5 and low magnetic loss (μ″ < 0.2) below 3 MHz. And the interesting ferromagnetic superexchange coupling in Co-doped CaCu3Ti4O12 was discussed.

  11. Comportamiento dieléctrico de cerámicos de CaCu3Ti4O12

    Castro, M. S.

    2011-08-01

    Full Text Available In this work, CaCu3Ti4O12 (CCTO ceramics were prepared by solid state reaction at 900°C for 12 h and sintered at 1100°C during 3 h. The main phase detected through X-ray diffraction (XRD was CCTO. Also, by means of Raman spectroscopy, it was observed a secondary phase rich in CuO. A dielectric constant higher than 13.000ε0 was obtained by Impedance spectroscopy measurements in the range between 25 to 106Hz. The value could be explained by the effect of dipolar and space charge polarization processes.En este trabajo se prepararon cerámicos basados en CaCu3Ti4O12 (CCTO por reacción en estado sólido a 900°C y posterior sinterizado a 1100°C. Mediante difracción de rayos X (DRX se comprobó la presencia de CCTO. A través de espectroscopía Raman se observó la presencia de una fase secundaria rica en CuO. Las mediciones de espectroscopía de impedancia demostraron que este material presenta una constante dieléctrica mayor a 13.000ε0 en el intervalo comprendido entre 25 y 106 Hz. Este valor es atribuido a la presencia de mecanismos de polarización de carga espacial y dipolar.

  12. Giant dielectric response in (Sr, Sb) codoped CaCu3Ti4O12 ceramics: A novel approach

    Pradhan, M. K.; Rao, T. Lakshmana; Karna, Lipsarani; Dash, S.

    2018-04-01

    The CaCu3Ti4O12 (CCTO) remains as the best material for practical applications due to its high dielectric constant. To improve further the dielectric properties of CCTO to several orders in magnitude, a novel approach is adopted by codoping of Sr, Sb ions. The ceramic samples were fabricated by the conventional solid state route. The structure, morphology and detail dielectric properties were investigated systematically. All the samples crystalizes in a cubic symmetry with Im-3 space group. Sr substituted in Ca site can effectively suppress the grain growth, achieving a fine grained ceramic structure; however the grain size decreased slightly as Sb concentration increased further; whereas the dielectric permittivity of the ceramics increased drastically. The giant dielectric response was considered to be closely related with a reduction in the potential barrier height at grain boundaries (GBs) supported by the reduction in the activation energy for the conduction process.

  13. Role of strained nano-regions in the formation of subgrains in CaCu3Ti4O12

    Fang, Tsang-Tse; Wang, Yong-Huei; Kuo, Jui-Chao

    2011-07-01

    Single-phase CaCu3Ti4O12 (CCTO) was synthesized by solid-state reaction. Electron backscatter diffraction, scanning electron microscopy, and atomic force microscopy were adopted to characterize the grain orientation, microstructure, and surface morphology of the CCTO samples with or without thermal etching. Bump strained nano-regions induced by the local compositional disorder at a nano-scale have been discovered, being the origin of the formation of subgrains in CCTO. The proposed mechanism for the formation of subgrains involves the formation of etched pits and subboundaries pertaining to the strained nano-regions rather than dislocation displacement. The dielectric response inside the grains of CCTO relevant to the strained nano-regions is also discussed.

  14. CaCu3Ti4O12: A Bifunctional Perovskite Electrocatalyst for Oxygen Evolution and Reduction Reaction in Alkaline Medium

    Kushwaha, H.S.; Halder, Aditi; Thomas, P.; Vaish, Rahul

    2017-01-01

    Highlights: •A cost effective double perovskite CaCu 3 Ti 4 O 12 have been synthesized using oxalate precursor method. •CCTO electrocatalyst exhibit enhanced bifunctional electrocatalytic activities. •CCTO electrocatalyst have lower overpotential and higher mass activity as compared to noble metal oxide and well-known perovskite catalysts. •Electrochemical impedance spectroscopy investigations of oxygen reactions on perovskite surfaces. -- Abstract: Perovskite oxides are prominent materials as the bifunctional electrocatalysts for both oxygen reduction/evolution reactions (ORR/OER) for the electrochemical energy conversion and storage using regenerative fuel cells and rechargeable metal-air batteries. In this work, a quadruple perovskite CaCu 3 Ti 4 O 12 has been synthesized oxalate precursor route. X-ray diffraction pattern shows phase purity of the synthesized electrocatalyst. The synthesized CCTO electrocatalyst have crystallite size of 26 nm. Electrochemical investigations reveal that CCTO exhibit efficient catalytic activity. More interestingly, an extremely high OER activity is observed for CCTO electrocatalysts which is found superior than similar class of perovskites. Additionally, CCTO shows efficient ORR activity with an onset potential of 0.83 V which is better than that of Pt/C catalyst (≈0.94 V). These results demonstrate the significant potential of CCTO perovskite as a bifunctional electrode material for alkaline fuel cells and metal-air batteries.

  15. Role of doping and CuO segregation in improving the giant permittivity of CaCu3Ti4O12

    Capsoni, D.; Bini, M.; Massarotti, V.; Chiodelli, G.; Mozzatic, M.C.; Azzoni, C.B.

    2004-01-01

    The dopant role on the electric and dielectric properties of the perovskite-type CaCu 3 Ti 4 O 12 (CCTO) compound is evidenced. Impedance spectroscopy measurements show that the relevant permittivity value attributed to sintered CCTO is due to grain boundary (g.b.) effects. The g.b. permittivity value of the pure CCTO can be increased of 1-2 orders of magnitude by cation substitution on Ti site and/or segregation of CuO phase, while the bulk permittivity keeps values 90εr180. Bulk and g.b. conductivity contributions are discussed: electrons are responsible for the charge transport and a mean bulk activation energy of 0.07eV is obtained at room temperature for all the examined samples. The g.b. activation energy ranges between 0.54 and 0.76eV. Defect models related to the transport properties are proposed, supported by electron paramagnetic resonance measurements

  16. Dielectric behavior of CaCu3Ti4O12: Poly Vinyl Chloride ceramic polymer composites at different temperature and frequencies

    Ajay Pratap Singh

    2016-12-01

    Full Text Available In this study, the efforts have been made to obtain relatively high dielectric constant polymer-ceramic composite by incorporating the giant dielectric constant material, calcium copper titanate (CCTO in a PVC polymer matrix. We have prepared composites of CaCu3Ti4O12 (CCTO ceramic and Poly Vinyl Chloride (PVC polymer in various ratios (by volume in addition to pure CCTO. For this, CCTO was prepared by the conventional oxide route (solid-state reaction method. The structural, the microstructural and the dielectric properties of the composites were studied using X-ray diffraction, Scanning Electron Microscope, and impedance analyzer respectively. The study of dielectric constant and dielectric loss of the pure CCTO and the composites reveal that there is good range of dielectric constants and dielectric losses for the studied composites. The pure sample of CCTO exhibits giant dielectric constant at low frequency within the studied temperature range. As frequency increases, dielectric constant drastically decreases and approaching a constant value at 1 MHz. Above the intermediate temperature, the dielectric constant and dielectric loss for pure CCTO is more frequency dependent than its composites.

  17. Phase formation and dielectric properties of the perovskite-like structure CaCu3Ti4O-12

    Porfirio, T.C.; Muccillo, E.N.S.

    2012-01-01

    The perovskite-like structure compound titanate and calcium copper has attracted great scientific interest due to its giant electric permittivity, which enables its application in electronic devices such as supercapacitors and access memories volatile. In this paper, a study of phase formation, densification and dielectric properties of ceramics prepared from powders obtained by solid state reaction were made. Calcinations were performed at 900 and 950°C and sintering between 1060 and 1100°C for times from 5 to 18 hours. The characterization techniques used were X-ray diffraction, density measurement, and the electrical permittivity by impedance spectroscopy. Hydrostatic density results showed that was possible to obtain high densification (over 92% of theoretical density), with cubic phase (perovskite-like structure) and electrical permittivity around 10 4 at room temperature. (author)

  18. Microstructure and electric characteristics of AETiO3 (AE=Mg, Ca, Sr doped CaCu3Ti4O12 thin films prepared by the sol–gel method

    Dong Xu

    2015-10-01

    Full Text Available This paper focuses on the effects of alkline-earth metal titante AETiO3 (AE=Mg, Ca, Sr doping on the microstructure and electric characteristics of CaCu3Ti4O12 thin films prepared by the sol–gel method. The results showed that the grain size of CCTO thin films could be increased by MgTiO3 doping. The movement of the grain boundaries was impeded by the second phases of CaTiO3 and SrTiO3 concentrating at grain boundaries in CaTiO3 and SrTiO3 doped CCTO thin films. Rapid ascent of dielectric constant could be observed in 0.1Mg TiO3 doped CCTO thin films, which was almost as three times high as pure CCTO thin film and the descent of the dielectric loss at low frequency could also be observed. In addition, the nonlinear coefficient (α, threshold voltage (VT and leakage current (IL of AETiO3 doped CCTO thin films (AE=Mg, Ca, Sr showed different variation with the increasing content of the MgTiO3, CaTiO3 and SrTiO3.

  19. Effect of processing routes on microstructure, electrical and dielectric behavior of Mg-doped CaCu3Ti4O12 electro-ceramic

    Singh, Laxman; Rai, U. S.; Mandal, K. D.; Rai, Alok Kumar

    2013-09-01

    In the present communication, data on magnesium-doped calcium copper titanate CaCu2.90Mg0.10Ti4O12 (CCMTO) electro-ceramic, synthesized by the semi-wet route (SWR), ball-milled route (BMR) and solid-state route (SSR), is characterized by TG-DTA, XRD, SEM, EDX and TEM techniques. XRD confirmed the formation of single phase in CCMTO ceramic. The CuO phase present at grain boundaries in SWR ceramic was shown by the SEM micrograph, which was verified by EDX. The TEM image of SWR ceramic shows nanocrystalline particles in the range 80±20 nm. The value of the dielectric constant of SWR ( ɛ r ˜20091) ceramic is higher than those of BMR and SSR ( ɛ r ˜1247) ceramics at 1 kHz at 450 K. A dielectric relaxation has been observed in the frequency range 100 Hz-100 kHz. The high-temperature dielectric dispersion shows one large low-frequency response and two Debye-type relaxations. The impedance and modulus studies show the highest grain-boundary resistance for BMR ceramic.

  20. Application of CaCu3Ti4O12 based quadruple perovskites as a promising candidate for optoelectronic devices

    Pal, Kamalesh; Jana, Rajkumar; Dey, Arka; Ray, Partha P.; Seikh, Md Motin; Gayen, Arup

    2018-05-01

    We report the synthesis of nanosized (40-50 nm) CaCu3-xMnxTi4-xMnxO12 (x = 0, 0.5 and 1) quadruple perovskite (QP) semiconductor via a modified combustion method for use as Schottky barrier diode (SBD) at the Al/QP junction. The fabricated SBD is analysed on the basis of thermionic emission theory to observe its quality and some important diode parameters. For insight analysis of charge transport mechanism through metal-semiconductor junction, theory of space charge limited currents is applied and discussed in the light of parameters like carrier concentration, mobility-lifetime product and diffusion length. The Mn-doped exhibit better device performance compared to parent material.

  1. Influence of interface point defect on the dielectric properties of Y doped CaCu3Ti4O12 ceramics

    Jianming Deng

    2016-03-01

    Full Text Available CaCu3Ti4−xYxO12 (0≤x≤0.12 ceramics were fabricated with conventional solid-state reaction method. Phase structure and microstructure of prepared ceramics were characterized by X-ray diffraction (XRD and scanning electron microscopy (SEM, respectively. The impedance and modulus tests both suggested the existence of two different relaxation behavior, which were attributed to bulk and grain boundary response. In addition, the conductivity and dielectric permittivity showed a step-like behavior under 405K. Meanwhile, frequency independence of dc conduction became dominant when above 405K. In CCTO ceramic, rare earth element Y3+ ions as an acceptor were used to substitute Ti sites, decreasing the concentration of oxygen vacancy around grain-electrode and grain boundary. The reason to the reduction of dielectric behavior in low frequencies range was associated with the Y doping in CCTO ceramic.

  2. Grain growth studies on nanocrystalline Ni powder

    Rane, G.K.; Welzel, U.; Mittemeijer, E.J.

    2012-01-01

    The microstructure of nanocrystalline Ni powder produced by ball-milling and its thermal stability were investigated by applying different methods of X-ray diffraction line-profile analysis: single-line analysis, whole powder-pattern modelling and the (modified) Warren–Averbach method were employed. The kinetics of grain growth were investigated by both ex-situ and in-situ X-ray diffraction measurements. With increasing milling time, the grain-size reduction is accompanied by a considerable narrowing of the size distribution and an increase in the microstrain. Upon annealing, initial, rapid grain growth occurs, accompanied by the (almost complete) annihilation of microstrain. For longer annealing times, the grain-growth kinetics depend on the initial microstructure: a smaller microstrain with a broad grain-size distribution leads to linear grain growth, followed by parabolic grain growth, whereas a larger microstrain with a narrow grain-size distribution leads to incessant linear grain growth. These effects have been shown to be incompatible with grain-boundary curvature driven growth. The observed kinetics are ascribed to the role of excess free volume at the grain boundaries of nanocrystalline material and the prevalence of an “abnormal grain-growth” mechanism.

  3. Characterisation of Suspension Precipitated Nanocrystalline Hydroxyapatite Powders

    Mallik, P K; Swain, P.K.; Patnaik, S.C

    2016-01-01

    Hydroxyapatite (HA) is a well-known biomaterial for coating on femoral implants, filling of dental cavity and scaffold for tissue replacement. Hydroxyapatite possess limited load bearing capacity due to their brittleness. In this paper, the synthesis of nanocrystalline hydroxyapatite powders was prepared by dissolving calcium oxide in phosphoric acid, followed by addition of ammonia liquor in a beaker. The prepared solution was stirred by using magnetic stirrer operated at temperature of 80°C for an hour. This leads to the formation of hydroxyapatite precipitate. The precipitate was dried in oven for overnight at 100°C. The dried agglomerated precipitate was calcined at 800°C in conventional furnace for an hour. The influence of calcium oxide concentration and pH on the resulting precipitates was studied using BET, XRD and SEM. As result, a well-defined sub-rounded morphology of powders size of ∼41 nm was obtained with a salt concentration of 0.02 M. Finally, it can be concluded that small changes in the reaction conditions led to large changes in final size, shape and degree of aggregation of the hydroxyapatite particles. (paper)

  4. Production of nanocrystalline metal powders via combustion reaction synthesis

    Frye, John G.; Weil, Kenneth Scott; Lavender, Curt A.; Kim, Jin Yong

    2017-10-31

    Nanocrystalline metal powders comprising tungsten, molybdenum, rhenium and/or niobium can be synthesized using a combustion reaction. Methods for synthesizing the nanocrystalline metal powders are characterized by forming a combustion synthesis solution by dissolving in water an oxidizer, a fuel, and a base-soluble, ammonium precursor of tungsten, molybdenum, rhenium, or niobium in amounts that yield a stoichiometric burn when combusted. The combustion synthesis solution is then heated to a temperature sufficient to substantially remove water and to initiate a self-sustaining combustion reaction. The resulting powder can be subsequently reduced to metal form by heating in a reducing gas environment.

  5. Incipient ferroelectric to a possible ferroelectric transition in Te4+ doped calcium copper titanate (CaCu3Ti4O12 ceramics at low temperature as evidenced by Raman and dielectric spectroscopy

    Nabadyuti Barman

    2017-03-01

    Full Text Available Partial replacement of Ti4+ by Te4+ ions in calcium copper titanate lattice improved its dielectric behaviour mostly due to cubic-to-tetragonal structural transformation and associated distortion in TiO6 octahedra. The relative permittivity values (23–30 x 103 of Te4+ doped ceramics is more than thrice that of un-doped ceramics (8 x 103 at 1 kHz. A decreasing trend in relative permittivity with increasing temperature (50–300 K is observed for all the samples. Barrett’s formula, as a signature of incipient ferroelectricity, is invoked to rationalize the relative permittivity variation as a function of temperature. A systematic investigation supported by temperature dependent Raman studies reveal a possible ferroelectric transition in Te4+ doped ceramic samples below 120 K. The possible ferroelectric transition is attributed to the interactions between quasi-local vibrations associated with the micro-clusters comprising TiO6 and TeO6 structural units and indirect dipole-dipole interactions of off-center B–cations (Ti4+ and Te4+ in double perovskite lattice.

  6. Fe-based nanocrystalline powder cores with ultra-low core loss

    Wang, Xiangyue, E-mail: wangxiangyue1986@163.com [China Iron and Steel Research Institute Group, Beijing 100081 (China); Center of Advanced Technology and Materials Co., Ltd., Beijing 100081 (China); Lu, Zhichao; Lu, Caowei; Li, Deren [China Iron and Steel Research Institute Group, Beijing 100081 (China); Center of Advanced Technology and Materials Co., Ltd., Beijing 100081 (China)

    2013-12-15

    Melt-spun amorphous Fe{sub 73.5}Cu{sub 1}Nb{sub 3}Si{sub 15.5}B{sub 7} alloy strip was crushed to make flake-shaped fine powders. The passivated powders by phosphoric acid were mixed with organic and inorganic binder, followed by cold compaction to form toroid-shaped bonded powder-metallurgical magnets. The powder cores were heat-treated to crystallize the amorphous structure and to control the nano-grain structure. Well-coated phosphate-oxide insulation layer on the powder surface decreased the the core loss with the insulation of each powder. FeCuNbSiB nanocrystalline alloy powder core prepared from the powder having phosphate-oxide layer exhibits a stable permeability up to high frequency range over 2 MHz. Especially, the core loss could be reduced remarkably. At the other hand, the softened inorganic binder in the annealing process could effectively improve the intensity of powder cores. - Highlights: • Fe-based nanocrystalline powder cores were prepared with low core loss. • Well-coated phosphate-oxide insulation layer on the powder surface decreased the core loss. • Fe-based nanocrystalline powder cores exhibited a stable permeability up to high frequency range over 2 MHz. • The softened inorganic binder in the annealing process could effectively improve the intensity of powder cores.

  7. Thermoluminescent properties of ZnS:Mn nanocrystalline powders

    Ortiz-Hernández, Arturo Agustín; Méndez García, Víctor Hugo; Pérez Arrieta, María Leticia; Ortega Sígala, José Juan

    2015-01-01

    Thermoluminescent ZnS nanocrystals doped with Mn 2+ ions were synthesized by chemical co-precipitation method. From X-ray diffraction studies it was observed that the synthesized nanoparticles have cubic zinc blende structure with average sizes of about 40–50 nm. Morphology was analyzed by TEM. Photoluminescence studies showed two transitions, one of them close to 396 nm and other close to 598 nm, which is enhanced with increasing dopant concentration, this behavior was also observed in the cathodoluminescence spectrum. The thermoluminescence gamma dose-response has linear behavior over dose range 5–100 mGy, the glow curve structure shows two glow peaks at 436 K and at 518 K that were taken into account to calculate the kinetic parameters using the Computerized Glow Curve Deconvolution procedure. - Highlights: • Nanocrystals in powder of ZnS:Mn were synthesized using the co-precipitation method. • The integrated TL spectra has a linear behavior on the dose range 5–100 mGy of γ-radiation. • The kinetic parameters were obtained by the CGCD procedure. • Results support the possible use of nanocrystalline ZnS:Mn as a new γ-dose nanoTLD

  8. Structural characterization of nanocrystalline cadmium sulphide powder prepared by solvent evaporation technique

    Pandya, Samir; Tandel, Digisha; Chodavadiya, Nisarg

    2018-05-01

    CdS is one of the most important compounds in the II-VI group of semiconductor. There are numerous applications of CdS in the form of nanoparticles and nanocrystalline. Semiconductors nanoparticles (also known as quantum dots), belong to state of matter in the transition region between molecules and solids, have attracted a great deal of attention because of their unique electrical and optical properties, compared to bulk materials. In the field of optoelectronic, nanocrystalline form utilizes mostly in the field of catalysis and fluid technology. Considering these observations, presented work had been carried out, i.e. based on the nanocrystalline material preparation. In the present work CdS nano-crystalline powder was synthesized by a simple and cost effective chemical technique to grow cadmium sulphide (CdS) nanoparticles at 200 °C with different concentrations of cadmium. The synthesis parameters were optimized. The synthesized powder was structurally characterized by X-ray diffraction and particle size analyzer. In the XRD analysis, Micro-structural parameters such as lattice strain, dislocation density and crystallite size were analysed. The broadened diffraction peaks indicated nanocrystalline particles of the film material. In addition to that the size of the prepared particles was analyzed by particle size analyzer. The results show the average size of CdS particles ranging from 80 to 100 nm. The overall conclusion of the work can be very useful in the synthesis of nanocrystalline CdS powder.

  9. Synthesis and sintering of nanocrystalline hydroxyapatite powders by citric acid sol-gel combustion method

    Han Yingchao; Li Shipu; Wang Xinyu; Chen Xiaoming

    2004-01-01

    The citric acid sol-gel combustion method has been used for the synthesis of nanocrystalline hydroxyapatite (HAP) powder from calcium nitrate, diammonium hydrogen phosphate and citric acid. The phase composition of HAP powder was characterized by X-ray powder diffraction analysis (XRD). The morphology of HAP powder was observed by transmission electron microscope (TEM). The HAP powder has been sintered into microporous ceramic in air at 1200 deg. C with 3 h soaking time. The microstructure and phase composition of the resulting HAP ceramic were characterized by scanning electron microscope (SEM) and XRD, respectively. The physical characterization of open porosity and flexural strength have also been carried out

  10. Production of nanocrystalline cermet thermal spray powders for wear resistant coatings by high-energy milling

    Eigen, N.; Klassen, T.; Aust, E.; Bormann, R.; Gaertner, F.

    2003-01-01

    TiC-Ni based nanocrystalline cermet powders for thermal spraying were produced by high-energy milling. Milling experiments were performed in an attrition mill and a vibration mill in kilogram scale, and powder morphologies and microstructures were characterized using scanning electron microscopy, X-ray diffraction, and laser scattering for particle size analysis. Milling time and powder input were optimized with respect to the desired microstructure and particle sizes, and the results using both types of mill were compared. Powders with homogeneously dispersed hard phase particles below 300 nm could be produced in both mills. Additional processes for the refinement of powder morphology and particle size distribution are discussed

  11. Preparation of high-quality ultrathin transmission electron microscopy specimens of a nanocrystalline metallic powder.

    Riedl, Thomas; Gemming, Thomas; Mickel, Christine; Eymann, Konrad; Kirchner, Alexander; Kieback, Bernd

    2012-06-01

    This article explores the achievable transmission electron microscopy specimen thickness and quality by using three different preparation methods in the case of a high-strength nanocrystalline Cu-Nb powder alloy. Low specimen thickness is essential for spatially resolved analyses of the grains in nanocrystalline materials. We have found that single-sided as well as double-sided low-angle Ar ion milling of the Cu-Nb powders embedded into epoxy resin produced wedge-shaped particles of very low thickness (coating on the sections consisting of epoxy deployed as the embedding material and considerable nanoscale thickness variations. Copyright © 2011 Wiley Periodicals, Inc.

  12. Powder-based synthesis of nanocrystalline material components for structural application. Final report

    Ilyuschenko, A.F.; Ivashko, V.S.; Okovity, V.A. [Powder Metallurgy Research Inst., Minsk (Belarus)] [and others

    1998-12-01

    Hydroxiapate spray coatings and substrates for implant production as well as multilayered metal ceramic coatings from nanocrystalline materials are a subject of the investigation. The work aims at the improvement of quality of said objects. This study has investigated the processes of hydroxiapatite powder production. Sizes, shapes and relief of initial HA powder surface are analyzed using SEM and TEM. Modes of HA plasma spraying on a substrate from titanium and associated compositions of traditional and nanocrystalline structure are optimized. The quality of the sprayed samples are studied using X-ray phase analysis and metallographic analysis. The results of investigations of bioceramic coating spraying on titanium are theoretically generalized, taking into account obtained experimental data. The results of investigations of ion-beam technology are presented for spraying multilayered coatings consisting of alternating metal-ceramic layers of nanocrystalline structure.

  13. Novel Fe-based nanocrystalline powder cores with excellent magnetic properties produced using gas-atomized powder

    Chang, Liang; Xie, Lei; Liu, Min; Li, Qiang; Dong, Yaqiang; Chang, Chuntao; Wang, Xin-Min; Inoue, Akihisa

    2018-04-01

    FeSiBPNbCu nanocrystalline powder cores (NPCs) with excellent magnetic properties were fabricated by cold-compaction of the gas-atomized amorphous powder. Upon annealing at the optimum temperature, the NPCs showed excellent magnetic properties, including high initial permeability of 88, high frequency stability up to 1 MHz with a constant value of 85, low core loss of 265 mW/cm3 at 100 kHz for Bm = 0.05 T, and superior DC-bias permeability of 60% at a bias field of 100 Oe. The excellent magnetic properties of the present NPCs could be attributed to the ultrafine α-Fe(Si) phase precipitated in the amorphous matrix and the use of gas-atomized powder coated with a uniform insulation layer.

  14. Characterization of nanocrystalline zirconia powders by electron optical techniques

    Bursill, L.A.

    1989-01-01

    Electron optical techniques are described for the characterization of the size distribution of agglomerates, aggregates and primary micro- and nanocrystallites of as-processed zirconia powders. These techniques allow for direct identification of individual crystallites as tetragonal or monoclinic, by optical transform of high-resolution electron micrographs. The latter also permit surface morphology to be examined with atomic resolution. Applications to a range of pure and doped zirconia powders, of recent commercial interest, are presented, which enable the results of concurrent studies by sedimentation, surface specific area measurements, porosity and sinterability to be correctly interpreted. 18 figs

  15. Nanocrystalline AL2 O2 powders produced by laser induced gas phase reactions

    Borsella, E.; Botti, S.; Martelli, S.; Zappa, G.; Giorgi, R.; Turt, S.

    1993-01-01

    Nanocrystalline Al 2 O 3 powders were successfully synthesized by a CO 2 laser-driven gas-phase reaction involving trimethylaluminium (Al(CH 3 ) 3 ) and nitrous-oxide (N 2 O). Ethylene (C 2 H 4 ) was added as gas sensitizer. The as-synthesized powder particles showed a considerable carbon contamination and an amorphous-like structure. After thermal treatment at 1200-1400 degrees C, the powder was transformed to hexagonal a-Al 2 O 3 with very low carbon contamination as confirmed by X-ray diffraction, X-ray photo-electron spectroscopy and chemical analysis. The calcinated powders resulted to be spherical single crystal nanoparticles with a mean size of 15-20 nm, as determined by X-ray diffraction, electron microscopy and B.E.T. specific surface measurements. The laser synthesized Al 2 O 3 particles are well suited dispersoids for intermetallic alloy technology

  16. Broadband magnetic losses of nanocrystalline ribbons and powder cores

    Beatrice, Cinzia, E-mail: c.beatrice@inrim.it [Istituto Nazionale di Ricerca Metrologica, Nanoscience and Materials Division, Torino (Italy); Dobák, Samuel [Institute of Physics, Faculty of Science, P.J. Šafárik University, Košice (Slovakia); Ferrara, Enzo; Fiorillo, Fausto [Istituto Nazionale di Ricerca Metrologica, Nanoscience and Materials Division, Torino (Italy); Ragusa, Carlo [Politecnico di Torino, Energy Department, Torino (Italy); Füzer, Ján; Kollár, Peter [Institute of Physics, Faculty of Science, P.J. Šafárik University, Košice (Slovakia)

    2016-12-15

    Finemet type alloys have been investigated from DC to 1 GHz at different induction levels upon different treatments: as amorphous precursors, as ribbons nanocrystallized with and without an applied saturating field, as consolidated powders. The lowest energy losses at all frequencies and maximum Snoek's product are exhibited by the transversally field-annealed ribbons. This is understood in terms of rotation-dominated magnetization process in the low-anisotropy material. Intergrain eddy currents are responsible for the fast increase of the losses with frequency and for early permeability relaxation of the powder cores. Evidence for resonant phenomena at high frequencies and for the ensuing inadequate role of the static magnetic constitutive equation of the material in solving the magnetization dynamics via the Maxwell's diffusion equation of the electromagnetic field is provided. It is demonstrated that, by taking the Landau–Lifshitz–Gilbert equation as a constitutive relation, the excellent frequency response of the transverse anisotropy ribbons can be described by analytical method.

  17. Superior sinterability of nano-crystalline gadolinium doped ceria powders synthesized by co-precipitation method

    Hari Prasad, D.; Kim, H.-R.; Park, J.-S.; Son, J.-W.; Kim, B.-K.; Lee, H.-W.; Lee, J.-H.

    2010-01-01

    Reduced sintering temperature of doped ceria can greatly simplify the fabrication process of solid oxide fuel cells (SOFCs) by utilizing the co-firing of all cell components with a single step. In the present study, nano-crystalline gadolinium doped ceria (GDC) powders of high sinterability at lower sintering temperature has been synthesized by co-precipitation at room temperature. The successful synthesis of nano-crystalline GDC was confirmed by XRD, TEM and Raman spectroscopy analysis. Dilatometry studies showed that GDC prepared by this method can be fully densified (97% relative density) at a sintering temperature of 950 o C which is fairly lower than ever before. It has also been found that the sintered samples have a higher ionic conductivity of 1.64 x 10 -2 S cm -1 at 600 o C which is suitable for the intermediate temperature SOFC application.

  18. Synthesis of nanocrystalline magnesium nitride (Mg3N2) powder using thermal plasma

    Kim, Dong-Wook; Kim, Tae-Hee; Park, Hyun-Woo; Park, Dong-Wha

    2011-01-01

    Nanocrystalline magnesium nitride (Mg 3 N 2 ) powder was synthesized from bulk magnesium by thermal plasma at atmospheric pressure. Magnesium vapor was generated through heating the bulk magnesium by DC plasma jet and reacted with ammonia gas. Injecting position and flow rates of ammonia gas were controlled to investigate an ideal condition for Mg 3 N 2 synthesis. The synthesized Mg 3 N 2 was cooled and collected on the chamber wall. Characteristics of the synthesized powders for each experimental condition were analyzed by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and thermogravity analysis (TGA). In absence of NH 3 , magnesium metal powder was formed. The synthesis with NH 3 injection in low temperature region resulted in a formation of crystalline magnesium nitride with trigonal morphology, whereas the mixture of magnesium metal and amorphous Mg 3 N 2 was formed when NH 3 was injected in high temperature region. Also, vaporization process of magnesium was discussed.

  19. Bulk synthesis of nanocrystalline urania powders by citrate gel-combustion method

    Sanjay Kumar, D.; Ananthasivan, K.; Venkata Krishnan, R.; Amirthapandian, S.; Dasgupta, Arup

    2016-01-01

    Bulk quantities (60 g) of nanocrystalline (nc) free flowing urania powders with crystallite size ranging from 38 to 252 nm have been synthesized for the first time by the citrate gel combustion method. A systematic study of the influence of the fuel (citric acid) to oxidant (nitrate) ratio (R) on the characteristics of the urania powders has been carried out for the first time. Mixture with an "R" value of 0.25 exhibited a vigorous auto-ignition reaction. This reaction was investigated with Differential Scanning Calorimetry (DSC) and in-situ thermogravimetry coupled with differential thermal analysis and mass spectrometry (TG-DTA-MS). The bulk density, specific surface area, X-ray crystallite size, residual carbon and size distribution of particles of this powder were unique. Microscopic and microstructural investigation of selected samples revealed the presence of nanocrystals with irregular exfoliated morphology; their Electron Energy Loss Spectra testified the covalency of the U-O bond.

  20. Structure and magnetic properties of nanocrystalline Fe75Si25 powders prepared by mechanical alloying

    Kalita, M.P.C.; Perumal, A.; Srinivasan, A.

    2008-01-01

    Nanocrystalline Fe 75 Si 25 powders were prepared by mechanical alloying in a planetary ball mill. The evolution of the microstructure and magnetic properties during the milling process were studied by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer measurements. The evolution of non-equilibrium solid solution Fe (Si) during milling was accompanied by refinement of crystallite size down to 10 nm and the introduction of high density of dislocations of the order of 10 17 m -2 . During the milling process, Fe sites get substituted by Si. This structural change and the resulting disorder are reflected in the lattice parameters and average magnetic moment of the powders milled for various time periods. A progressive increase of coercivity was also observed with increasing milling time. The increase of coercivity could be attributed to the introduction of dislocations and reduction of powder particle size as a function of milling time

  1. Laser fabrication nanocrystalline coatings using simultaneous powders/wire feed

    Li, Jianing; Zhai, Tongguang; Zhang, Yuanbin; Shan, Feihu; Liu, Peng; Ren, Guocheng

    2016-07-01

    Laser melting deposition (LMD) fabrication is used to investigate feasibilty of simultaneously feeding TC17 wire and the Stellite 20-Si3N4-TiC-Sb mixed powders in order to increase the utilization ratio of materials and also quality of LMD composite coatings on the TA1 substrate. SEM images indicated that such LMD coating with metallurgical joint to substrate was formed free of the obvious defects. Lots of the ultrafine nanocrystals (UNs) were produced, which distributed uniformly in some coating matrix location, retarding growth of the ceramics in a certain extent; UNs were intertwined with amorphous, leading the yarn-shape materials to be produced. Compared with substrate, an improvement of wear resistance was achieved for such LMD coating.

  2. A new dental powder from nanocrystalline melt-spun Ag-Sn-Cu alloy ribbons

    Do-Minh, N.; Le-Thi, C.; Nguyen-Anh, S.

    2003-01-01

    A new non-gamma-two dental powder has been developed from nanocrystalline melt-spun Ag-Sn-Cu alloy ribbons. The amalgam made from this powder exhibits excellent properties for dental filling. The nanocrystalline microstructure was found for the first time in as-spun and heat treated Ag(27-28)Sn(9-32) Cu alloy ribbons, using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. As-spun ribbons exhibited a multi-phase microstructure with preferred existence of β (Ag 4 Sn) phase formed during rapid solidification (RS) due to supersaturating of copper (Cu) atoms and homogenous nanostructure with subgrain size of about (40-50) nm, which seems to be developed during RS process and can be caused by eutectic reaction of the Ag 3 Sn/Ag 4 Sn-Cu 3 Sn system. In heat treated ribbons the clustering of Cu atoms was always favored and stable in an ageing temperature and time interval determined by Cu content. The heat treatment led to essential changes of subgrain morphology, resulted in the appearance of large-angle boundaries with fine Cu 3 Sn precipitates and forming typical recrystallization twins. Such a microstructure variation in melt-spun ribbons could eventually yield enhanced technological, clinical and physical properties of the dental products, controlled by the ADA Specification N deg 1 and reported before. Thus, using the rapid solidification technique a new non-gamma-two dental material of high quality, nanocrystalline ribbon powder, can be produced. Copyright (2003) AD-TECH - International Foundation for the Advancement of Technology Ltd

  3. Doped titanium dioxide nanocrystalline powders with high photocatalytic activity

    Castro, A.L.; Nunes, M.R.; Carvalho, M.D.; Ferreira, L.P.; Jumas, J.-C.; Costa, F.M.; Florencio, M.H.

    2009-01-01

    Doped titanium dioxide nanopowders (M:TiO 2 ; M=Fe, Co, Nb, Sb) with anatase structure were successfully synthesized through an hydrothermal route preceded by a precipitation doping step. Structural and morphological characterizations were performed by powder XRD and TEM. Thermodynamic stability studies allowed to conclude that the anatase structure is highly stable for all doped TiO 2 prepared compounds. The photocatalytic efficiency of the synthesized nanopowders was tested and the results showed an appreciable enhancement in the photoactivity of the Sb:TiO 2 and Nb:TiO 2 , whereas no photocatalytic activity was detected for the Fe:TiO 2 and Co:TiO 2 nanopowders. These results were correlated to the doping ions oxidation states, determined by Moessbauer spectroscopy and magnetization data. - Graphical abstract: Doped titanium dioxide nanopowders (M:TiO 2 ; M=Fe, Co, Nb, Sb) with highly stable anatase structure were successfully synthesized through an hydrothermal route. The photocatalytic efficiencies of the synthesized nanopowders were tested and the results show an appreciable enhancement in the photoactivity of the Sb:TiO 2 and Nb:TiO 2 .

  4. Formation and mechanism of nanocrystalline AZ91 powders during HDDR processing

    Liu, Yafen; Fan, Jianfeng, E-mail: fanjianfeng@tyut.edu.cn; Zhang, Hua; Zhang, Qiang; Gao, Jing; Dong, Hongbiao, E-mail: hd38@leicester.ac.uk; Xu, Bingshe

    2017-03-15

    Grain sizes of AZ91 alloy powders were markedly refined to about 15 nm from 100 to 160 μm by an optimized hydrogenation-disproportionation-desorption-recombination (HDDR) process. The effect of temperature, hydrogen pressure and processing time on phase and microstructure evolution of AZ91 alloy powders during HDDR process was investigated systematically by X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy, respectively. The optimal HDDR process for preparing nanocrystalline Mg alloy powders is hydriding at temperature of 350 °C under 4 MPa hydrogen pressure for 12 h and dehydriding at 350 °C for 3 h in vacuum. A modified unreacted core model was introduced to describe the mechanism of grain refinement of during HDDR process. - Highlights: • Grain size of the AZ91 alloy powders was significantly refined from 100 μm to 15 nm. • The optimal HDDR technology for nano Mg alloy powders is obtained. • A modified unreacted core model of grain refinement mechanism was proposed.

  5. Mechanochemical preparation of nanocrystalline TiO2 powders and their behavior at high temperatures

    Gajovic, A.; Furic, K.; Tomasic, N.; Popovic, S.; Skoko, Z.; Music, S.

    2005-01-01

    Nanocrystalline TiO 2 powders were prepared by high-energy ball-milling using zirconia vial and balls. The changes of microstructure caused by material processing were studied using Raman spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The milling of the starting TiO 2 powder (anatase + rutile in traces) induced phase transitions to high-pressure polymorph, TiO 2 II, and rutile. We found that the phase transition to TiO 2 II was initiated at the surface of the small particles, while transition to rutile started in their center. Changes in crystallite size during milling process were obtained by the Scherrer method, while the particle size changes were monitored by TEM. The kinetics of phase changes, a decrease in crystallite/particle size, as well as zirconia contamination depended on the powder-to-ball weight ratio. The starting powder and some selected ball-milled samples were investigated in situ by Raman spectroscopy and XRD at high temperatures (up to 1300 deg. C) to examine their behavior during the sintering process. A difference in the results obtained by these two techniques was explained in frame of basic physical properties characterizing both methods. The morphology of the final sinters was monitored by scanning electron microscopy (SEM)

  6. Bulk synthesis of nanocrystalline urania powders by citrate gel-combustion method

    Sanjay Kumar, D.; Ananthasivan, K.; Venkata Krishnan, R.; Amirthapandian, S.; Dasgupta, Arup

    2016-01-01

    Bulk quantities (60 g) of nanocrystalline (nc) free flowing urania powders with crystallite size ranging from 38 to 252 nm have been synthesized for the first time by the citrate gel combustion method. A systematic study of the influence of the fuel (citric acid) to oxidant (nitrate) ratio (R) on the characteristics of the urania powders has been carried out for the first time. Mixture with an “R” value of 0.25 exhibited a vigorous auto-ignition reaction. This reaction was investigated with Differential Scanning Calorimetry (DSC) and in-situ thermogravimetry coupled with differential thermal analysis and mass spectrometry (TG-DTA-MS). The bulk density, specific surface area, X-ray crystallite size, residual carbon and size distribution of particles of this powder were unique. Microscopic and microstructural investigation of selected samples revealed the presence of nanocrystals with irregular exfoliated morphology; their Electron Energy Loss Spectra testified the covalency of the U–O bond. - Highlights: • Bulk quantities of nanocrystalline urania were prepared for the first time using citrate gel combustion method. • Volume combustion was observed in mixtures with fuel to nitrate ratio (R) 0.25. • The value of R was found to significantly influence the characteristics of the final product. • Typical exfoliated microstructure and nanopores were observed. • Established correlation between particle size distribution and bulk density, X-ray crystallite size and lattice strain. • Relationship between fuel to nitrate (R) mole ratio and physical characteristics of powders were also established.

  7. Combustion synthesis of nanocrystalline ceria (CeO2) powders by a dry route

    Hwang, C.-C.; Huang, T.-H.; Tsai, J.-S.; Lin, C.-S.; Peng, C.-H.

    2006-01-01

    In this study, ceria (CeO 2 ) powders were synthesized with 50 g per batch via a combustion technique using two kinds of starting materials-urea [(NH 2 ) 2 CO] (as a fuel) and ceric ammonium nitrate [Ce(NH 4 ) 2 (NO 3 ) 6 ] (acting as both the source of cerium ion and an oxidizer). The starting materials were mixed thoroughly without adding water, and then ignited in the air at room temperature. It underwent a self-combustion process with a large amount of smoke, a voluminous loose product. The as-synthesized powders were characterized by X-ray diffraction (XRD) analysis, transmission electron microscope (TEM), scanning electron microscope (SEM), CHN elemental analyzer, surface area measurements, and sinterability. Experimental results revealed that the nanocrystalline CeO 2 powders with low impurity content ( 2 /g and ∼25 nm, respectively, through the stoichiometric fuel/oxidizer ratio reaction. The powder, when cold pressed and sintered in the air at 1250 deg. C for 1 h, was measured to attain the sintered density ∼92% of theoretical density having submicron grain size. In addition, the thermal decomposition and combustion process of the reactant mixture were investigated using thermogravimetry (TG), differential scanning calorimetry (DSC), and mass spectrometry (MS) techniques simultaneously. Based on the results of thermal analysis, a possible mechanism concerning the combustion reaction is proposed

  8. Doped nanocrystalline ZnO powders for non-linear resistor applications by spray pyrolysis method.

    Hembram, Kaliyan; Vijay, R; Rao, Y S; Rao, T N

    2009-07-01

    Homogeneous and doped nanocrystalline ZnO powders (30-200 nm) were synthesized by spray pyrolysis technique. The spray pyrolysed powders were calcined in the temperature range of 500-750 degrees C. Formation of insulating pyrochlore phase started from 700 degrees C during the calcination itself. The calcined powders were compacted and sintered at different temperatures ranging from 900-1200 degrees C for 0.5-4 h. The densification behavior was found to be dependent on calcination temperature of the nanopowder. The resulting discs were found to have density (5.34-5.62 g/cc) in the range of 96-99% of theoretical density. The breakdown voltage value obtained for the nanopowder based non-linear resistor is 10.3 kV/cm with low leakage current density of 0.7 microA/cm2 and coefficient of nonlinearity as high as 193. The activation energy for grain growth of the doped ZnO nanopowder powders is 449.4 +/- 15 kJ/mol.

  9. Synthesis of nano-crystalline NiFe2O4 powders in subcritical and supercritical ethanol

    Ćosović, A.; Žák, Tomáš; Glisić, S.; Sokić, M.; Lazarević, S.; Ćosović, V.; Orlović, A.

    2016-01-01

    Roč. 113, JUL (2016), s. 96-105 ISSN 0896-8446 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : supercritical * subcritical * nano-crystalline powders * nickel ferrite * metal oxide * magnetic properties Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.991, year: 2016

  10. Synthesis, Structure, and Luminescent Properties of Europium-Doped Hydroxyapatite Nanocrystalline Powders

    Ciobanu, C.S.; Iconaru, S.L.; Predoi, D.; Massuyeau, F.; Constantin, L.V.; Costescu, A.

    2012-01-01

    The luminescent europium-doped hydroxyapatite (Eu:HAp, Ca 10-x Eu x (PO 4 ) 6 (OH) 2 ) with 0>x>0.2 nanocrystalline powders was synthesized by coprecipitation. The structural, morphological, and textural properties were well characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The vibrational studies were performed by Fourier transform infrared, Raman, and photoluminescence spectroscopies. The X-ray diffraction analysis revealed that hydroxyapatite is the unique crystalline constituent of all the samples, indicating that Eu has been successfully inserted into the HAp lattice. Eu doping inhibits HAp crystallization, leading to a decrease of the average crystallite size from around 20 nm in the undoped sample to around 7 nm in the sample with the highest Eu concentration. Furthermore, the samples show the characteristic 5 D 0 → 7 F 0 transition observed at 578 nm related to Eu 3+ ions distributed on Ca 2+ sites of the apatitic structure

  11. Low temperature synthesis of nanocrystalline lanthanum monoaluminate powders by chemical coprecipitation

    Kuo, C.-L. [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Wang, C.-L. [Department of Materials Science and Engineering, I-Shou University, 1 Section 1, Hsueh-Cheng Road, Ta-Hsu Hsiang, Kaohsiung 840, Taiwan (China); Chen, T.-Y. [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Chen, G.-J. [Department of Materials Science and Engineering, I-Shou University, 1 Section 1, Hsueh-Cheng Road, Ta-Hsu Hsiang, Kaohsiung 840, Taiwan (China); Hung, I-M. [Department of Chemical Engineering and Materials Science, Yuan Ze University, 135 Yuan-Tung Road, Chungli, Taoyuan 320, Taiwan (China); Shih, C.-J. [Faculty of Fragrance and Cosmetics, Kaohsiung Medical University, 100 Shi-Chuan 1st Road, Kaohsiung 807, Taiwan (China)]. E-mail: CJShih@kmu.edu.tw; Fung, K.-Z. [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China)

    2007-08-16

    Nanocrystalline lanthanum monoaluminate (LaAlO{sub 3}) powders were prepared by chemical coprecipitation using 25 vol.% of NH{sub 4}OH, 0.05 M La(NO{sub 3}){sub 3}.6H{sub 2}O and 0.05 M Al(NO{sub 3}){sub 3}.9H{sub 2}O aqueous solutions as the starting materials. Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analyses (TGA/DTA), X-ray diffraction (XRD), Raman spectrometry, specific surface area (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) were utilized to characterize the LaAlO{sub 3} powders prepared by chemical coprecipitation. The crystallization temperature of the LaAlO{sub 3} precursor gels precipitated at pH 9 is estimated as 810 deg. C by TG/DTA. The XRD pattern of the LaAlO{sub 3} precursor gels precipitated at pH 8-12 and calcined at 700 deg. C for 6 h shows a broad arciform continuum exist between 24{sup o} and 32{sup o} and sharp peaks of LaAlO{sub 3} except the precursor gels precipitated at pH 9. For the LaAlO{sub 3} precursor gels precipitated at pH 9 and calcined at 700 deg. C for 6 h, the formation of the perovskite LaAlO{sub 3} phase occurs and the presence of crystalline impurities is not found. The crystallite size of LaAlO{sub 3} slightly increases from 37.8 to 41.5 nm with calcination temperature increasing from 700 to 900 deg. C for 6 h. The LaAlO{sub 3} powders prepared by chemical coprecipitation have a considerably large specific surface of 30 m{sup 2}/g. The relative density greater than 97% is obtained when these nanocrystalline LaAlO{sub 3} powders are sintered at 1550 deg. C for 2 h.

  12. Preparation and characterisation of nanocrystalline IrxSn1-xO2 electrocatalytic powders

    Marshall, A.; Borresen, B.; Hagen, G.; Tsypkin, M.; Tunold, R.

    2005-01-01

    Nanocrystalline oxide powders of the type Ir x Sn 1-x O 2 (0.2-bar x-bar 1) have been produced and characterised. These oxides have been developed primarily as oxygen evolution electrocatalysts for proton exchange membrane (PEM) water electrolysers. Two methods were used to produce the oxide materials: the modified polyol method and the Adams fusion method. X-ray diffraction analysis suggests that an iridium-tin oxide solid solution with a rutile structure can be produced using the modified polyol method, with a linear relationship between the lattice parameters and composition. The crystal size of the solid solution phase is below 15-bar nm for all compositions. The Adams fusion method results in at least two separate oxide phases, namely a tin rich oxide and an iridium rich oxide. X-ray photoelectron spectroscopy (XPS) analysis revealed no significant difference between the bulk and surface compositions, and that the iridium was present in at least two valent states. The electrical resistivity of the powders was compared, and an exponential increase in resistivity with tin addition was found. Overall the resistivity measurements suggest that the limit for tin addition is around 50-60-bar mol% due to the high ohmic losses expected at higher tin contents in a PEM water electrolyser

  13. In-Flight Formation of Nano-Crystalline Titanium Dioxide Powder in a Plasma Jet and Its Characterization

    Ananthapadmanabhan, P. V.; Thiyagarajan, T. K.; Sreekumar, K. P.; Vijay, M.; Selvarajan, V.; Yu, Jiaguo; Liu, Shengwei

    2010-01-01

    Nanocrystalline titanium dioxide powder was synthesized by in-flight oxidation of titanium dihydride (TiH 2 ) powder in a thermal plasma jet. TiH 2 powder was injected into the thermal plasma jet and allowed to react with oxygen injected downstream the jet. Characterization of the powder by various analytical tools indicated that the powder consisted of nano-sized titanium dioxide particles consisting predominantly of the anatase phase. It is suggested that the thermo-chemistry of the oxidation process contributes significantly to the formation of nano-sized titania. The large energy released during the oxidation process dissociates the TiO 2 particles into TiO (g) and titanium vapour, which recombine downstream with oxygen and form nano particles of TiO 2 .

  14. Formation of nanocrystalline and amorphous phase of Al-Pb-Si-Sn-Cu powder during mechanical alloying

    Ran Guang; Zhou Jingen; Xi Shengqi; Li Pengliang

    2006-01-01

    Al-15%Pb-4%Si-1%Sn-1.5%Cu alloys (mass fraction, %) were prepared by mechanical alloying (MA). Phase transformation and microstructure characteristics of the alloy powders were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the nanocrystalline supersaturated solid solutions and amorphous phase in the powders are obtained during MA. The effect of ball milling is more evident to lead than to aluminum. During MA, the mixture powders are firstly fined, alloyed, nanocrystallized and then the nanocrystalline partly transforms to amorphous phase. A thermodynamic model is developed based on semi-experimental theory of Miedema to calculate the driving force for phase evolution. The thermodynamic analysis shows that there is no chemical driving force to form a crystalline solid solution from the elemental components. But for the amorphous phase, the Gibbs free energy is higher than 0 for the alloy with lead content in the ranges of 0-86.8 at.% and 98.4-100 at.% and lower than 0 in range of 86.8-98.4 at.%. For the Al-2.25 at.%Pb (Al-15%Pb, mass fraction, %), the driving force for formation of amorphization and nanocrystalline supersaturated solid solutions are provided not by the negative heat of mixing but by mechanical work

  15. Nanocrystalline TiAl powders synthesized by high-energy ball milling: effects of milling parameters on yield and contamination

    Bhattacharya, Prajina; Bellon, Pascal; Averback, Robert S.; Hales, Stephen J.

    2004-01-01

    High-energy ball milling was employed to produce nanocrystalline Ti-Al powders. As sticking of the powders can be sufficiently severe to result in a near zero yield, emphasis was placed on varying milling conditions so as to increase the yield, while avoiding contamination of the powders. The effects of milling parameters such as milling tools, initial state of the powders and addition of process control agents (PCA's) were investigated. Cyclohexane, stearic acid and titanium hydride were used as PCA's. Milling was conducted either in a Cr-steel vial with C-steel balls, or in a tungsten carbide (WC) vial with WC balls, using either elemental or pre-alloyed powders. Powder samples were characterized using X-ray diffraction, scanning and transmission electron microscopy. In the absence of PCA's mechanical alloying in a WC vial and attrition milling in a Cr-steel vial were shown to lead to satisfactory yields, about 65-80%, without inducing any significant contamination of the powders. The results suggest that sticking of the powders on to the milling tools is correlated with the phase evolution occurring in these powders during milling

  16. Synthesis, Structure, and Luminescent Properties of Europium-Doped Hydroxyapatite Nanocrystalline Powders

    Carmen Steluta Ciobanu

    2012-01-01

    Full Text Available The luminescent europium-doped hydroxyapatite (Eu:HAp, Ca10−xEux(PO46(OH2 with 0≤x≤0.2 nanocrystalline powders was synthesized by coprecipitation. The structural, morphological, and textural properties were well characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The vibrational studies were performed by Fourier transform infrared, Raman, and photoluminescence spectroscopies. The X-ray diffraction analysis revealed that hydroxyapatite is the unique crystalline constituent of all the samples, indicating that Eu has been successfully inserted into the HAp lattice. Eu doping inhibits HAp crystallization, leading to a decrease of the average crystallite size from around 20 nm in the undoped sample to around 7 nm in the sample with the highest Eu concentration. Furthermore, the samples show the characteristic 5D0→7F0 transition observed at 578 nm related to Eu3+ ions distributed on Ca2+ sites of the apatitic structure.

  17. Green synthesis of nanocrystalline α-Al2O3 powders by both wet-chemical and mechanochemical methods

    Gao, Huiying; Li, Zhiyong; Zhao, Peng

    2018-03-01

    Nanosized α-Al2O3 powders were prepared with AlCl3ṡ6H2O and NH4HCO3 as raw materials by both wet-chemical and mechanochemical methods, through the synthesis of the ammonium aluminum carbonate hydroxide (AACH) precursor followed by calcination. The environmentally benign starch was used as an effective dispersant during the preparation of nanocrystalline α-Al2O3 powders. X-ray diffraction (XRD), thermogravimetric differential thermal analysis (TG-DTA), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to characterize the precursor AACH and products. The results show that nanosized spherical α-Al2O3 powders without hard agglomeration and with particle size in the range of 20-40 nm can be obtained by the two methods. Comparing the two “green” processes, the mechanochemical method has better prospects for commercial production.

  18. CoFe2O4 nanocrystalline powders prepared by citrate-gel methods: Synthesis, structure and magnetic properties

    Cannas, C.; Falqui, A.; Musinu, A.; Peddis, D.; Piccaluga, G.

    2006-01-01

    Nanocrystalline CoFe 2 O 4 powders were prepared by decomposition of metal ion citrate precursors. Four samples were synthesized from precursor solutions having different pH values in the range 2 physisorption and Transmission Electron Microscopy. Magnetic properties were explored by a SQUID magnetometer. Three out of the four samples, coming from solutions of pH 2, 4 and 7, were produced by an autocombustion reaction and are very similar as regards average size of the nanoparticles (about 20 nm), their morphology and the magnetic properties, while the fourth sample was produced by a slower thermal decomposition and is composed of smaller nanoparticles (about 10 nm)

  19. AC magnetic properties of the soft magnetic composites based on Supermalloy nanocrystalline powder prepared by mechanical alloying

    Neamtu, B.V., E-mail: bogdan.neamtu@stm.utcluj.ro [Materials Science and Engineering Department, Technical University of Cluj-Napoca, 400614 Cluj-Napoca (Romania); Institut Neel, CNRS/Universite J. Fourier, BP166, 38042 Grenoble, Cedex 9 (France); Geoffroy, O. [Institut Neel, CNRS/Universite J. Fourier, BP166, 38042 Grenoble, Cedex 9 (France); Grenoble Electrical Engineering, University J. Fourier, BP 46, F-38402 Saint-Martin d' Heres Cedex (France); Chicinas, I. [Materials Science and Engineering Department, Technical University of Cluj-Napoca, 400614 Cluj-Napoca (Romania); Isnard, O. [Institut Neel, CNRS/Universite J. Fourier, BP166, 38042 Grenoble, Cedex 9 (France)

    2012-05-25

    Highlights: Black-Right-Pointing-Pointer Nanocrystalline soft magnetic composites were obtained. Black-Right-Pointing-Pointer The cutting frequency of the produced nanocrystalline SMC exceeds 100 kHz. Black-Right-Pointing-Pointer A long annealing at low temperature leads to an improvement of the permeability (12%). - Abstract: The preparation and characterization of the nanocrystalline soft magnetic composite core based on Supermalloy powder obtained via mechanical alloying route are presented. The AC magnetic properties of the compacts were determined in frequency range from 100 Hz to 100 kHz for flux densities of 0.05 and 0.1 T. Composite materials were obtained by covering the Supermalloy particles with a polymer binder, then compacted into toroidal shape and finally polymerized. It is found that an increase of the compacting pressure from 600 MPa to 800 MPa leads to an increase of the compacts permeability by more than 8%. Also, reducing the polymer content from 2 wt.% to 0.5 wt.% leads to an increase of the magnetic losses (at 100 kHz and 0.1 T) by 380%. The removal of the stresses induced during compaction has been accomplished by a heat treatment at 170 Degree-Sign C for 120 h. This leads to a significant increase (12%) of the relative initial permeability of the compacts.

  20. Nano ZrO{sub 2} particles in nanocrystalline Fe–14Cr–1.5Zr alloy powders

    Xu, W.Z.; Li, L.L.; Saber, M.; Koch, C.C.; Zhu, Y.T., E-mail: ytzhu@ncsu.edu; Scattergood, R.O.

    2014-09-15

    Here we report on the formation of nano ZrO{sub 2} particles in Fe–14Cr–1.5Zr alloy powders synthesized by mechanical alloying. The nano ZrO{sub 2} particles were found uniformly dispersed in the ferritic matrix powders with an average size of about 3.7 nm, which rendered the alloy powders so stable that it retained nanocrystalline structure after annealing at 900 °C for 1 h. The ZrO{sub 2} nanoparticles have a tetragonal crystal structure and the following orientation relationship with the matrix: (0 0 2){sub ZrO2}//(0 0 2){sub Matrix} and [0 1 0]{sub ZrO2}//[1 2 0]{sub Matrix}. The size and dispersion of the ZrO{sub 2} particles are comparable to those of Y–Ti–O enriched oxides reported in irradiation-resistant ODS alloys. This suggests a potential application of the new alloy powders for nuclear energy applications.

  1. The effect of process control agent on the structure and magnetic properties of nanocrystalline mechanically alloyed Fe–45% Ni powders

    Gheisari, Kh., E-mail: khgheisari@scu.ac.ir [Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University, Ahvaz (Iran, Islamic Republic of); Javadpour, S. [Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of)

    2013-10-15

    In this study, nanocrystalline Fe-45 wt% Ni alloy powders were prepared by mechanical alloying via high-energy ball milling. The effect of adding stearic acid as a process control agent (PCA) on the particle size, structure and magnetic properties of Fe-45 wt% Ni alloy powders have been studied by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer measurements. The results show that the addition of 1 wt% PCA causes fine uniform spherical powder particles of the fcc γ-(Fe, Ni) phase to be formed after 48 h milling time. It is also found that crystallite size, lattice strain and content of γ-(Fe, Ni) phase are three of the most important variables that are significantly affected by PCA content and can influence the magnetic properties. - Highlights: • Different amount of stearic acid as a PCA was used during milling. • Particle size and crystallite size decrease with increasing PCA content. • The addition of 1 wt% PCA leads to a good combination of structure and magnetic properties.

  2. The effect of process control agent on the structure and magnetic properties of nanocrystalline mechanically alloyed Fe–45% Ni powders

    Gheisari, Kh.; Javadpour, S.

    2013-01-01

    In this study, nanocrystalline Fe-45 wt% Ni alloy powders were prepared by mechanical alloying via high-energy ball milling. The effect of adding stearic acid as a process control agent (PCA) on the particle size, structure and magnetic properties of Fe-45 wt% Ni alloy powders have been studied by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer measurements. The results show that the addition of 1 wt% PCA causes fine uniform spherical powder particles of the fcc γ-(Fe, Ni) phase to be formed after 48 h milling time. It is also found that crystallite size, lattice strain and content of γ-(Fe, Ni) phase are three of the most important variables that are significantly affected by PCA content and can influence the magnetic properties. - Highlights: • Different amount of stearic acid as a PCA was used during milling. • Particle size and crystallite size decrease with increasing PCA content. • The addition of 1 wt% PCA leads to a good combination of structure and magnetic properties

  3. Effect of compacting pressure, powder degassing and thermobaric treatment on densification and properties of nanocrystalline titanium nitride

    Andrei V. Kapylou

    2009-09-01

    Full Text Available The effects of compacting pressure, powder degassing and high pressure sintering temperature and time on the densification and properties of nanocrystalline titanium nitride have been investigated. For this reason, TiN powder with a mean particle size of 55 nm was pressed in the range of compacting pressure from 0.2 to 1.0 GPa and sintered under static pressure of 3.5 GPa in the temperature range of 900–1600°C for 45–120 s. Some of green bodies were degassed in vacuum before sintering. It was shown that samples compacted in the pressure range of 0.2–0.6 GPa have the highest density after the thermobaric treatment. The maximum density (about 97.3 %TD was obtained with degassed samples. Microhardness and microstructure investigations have shown that recrystallization of the TiN nanopowder begins at the sintering temperatures of 1100–1200°C and sintering time less than one minute. The maximum microhardness obtained was 23.2±1.0 GPa and themaximum Young modulus was 370 GPa.

  4. Preparation of Cu2ZnSnS4 nano-crystalline powder by mechano-chemical method

    Alirezazadeh, Farzaneh; Sheibani, Saeed; Rashchi, Fereshteh

    2018-01-01

    Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is one of the most promising ceramic materials as an absorber layer in solar cells due to its suitable band gap, high absorption coefficient and non-toxic and environmental friendly constituent elements. In this work, nano-crystalline CZTS powder was synthesized by mechanical milling. Elemental powders of Cu, Zn, Sn and were mixed in atomic ratio of 2:1:1:4 according to the stoichiometry of Cu2ZnSnS4 and then milled in a planetary high energy ball mill under argon atmosphere. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffusion reflectance spectroscopy (DRS). XRD results confirm the formation of single-phase CZTS with kesterite structure after 20 h of milling. Also, the mean crystallite size was about 35 nm. SEM results show that after 20 h of milling, the product has a relatively uniform particle size distribution. Optical properties of the product indicate that the band gap of prepared CZTS is 1.6 eV which is near to the optimum value for photovoltaic solar cells showing as a light absorber material in solar energy applications.

  5. Structural, microstructural and Mössbauer studies of nanocrystalline Fe100-x Alx powders elaborated by mechanical alloying

    Akkouche K.

    2012-06-01

    Full Text Available Nanocrystalline Fe100-xAlx powders (x= 25, 30, 34 and 40 at % were prepared by the mechanical alloying process using a vario-planetary high-energy ball mill for a milling time of 35 h. The formation and physical properties of the alloys were investigated as a function of Al content by means of X-ray diffraction, scanning electron microscopy (SEM, energy dispersive X-ray and Mössbauer spectroscopy. For all Fe100-xAlx samples, the complete formation of bcc phase was observed after 35 h of milling. As Al content increases, the lattice parameter increases, whereas the grain size decreases from 106 to 12 nm. The powder particle morphology for different compositions was observed by SEM. The Mössbauer spectra were adjusted with a singlet line and a sextet containing two components. The singlet was attributed to the formation of paramagnetic A2 disordered structure rich with Al. About the sextet, the first component indicated the formation of Fe clusters/ Fe-rich phases; however, the second component is characteristic of disordered ferromagnetic phase.

  6. Analysis of a nanocrystalline polymer dispersion of ebselen using solid-state NMR, Raman microscopy, and powder X-ray diffraction.

    Vogt, Frederick G; Williams, Glenn R

    2012-07-01

    Nanocrystalline drug-polymer dispersions are of significant interest in pharmaceutical delivery. The purpose of this work is to demonstrate the applicability of methods based on two-dimensional (2D) and multinuclear solid-state NMR (SSNMR) to a novel nanocrystalline pharmaceutical dispersion of ebselen with polyvinylpyrrolidone-vinyl acetate (PVP-VA), after initial characterization with other techniques. A nanocrystalline dispersion of ebselen with PVP-VA was prepared and characterized by powder X-ray diffraction (PXRD), confocal Raman microscopy and mapping, and differential scanning calorimetry (DSC), and then subjected to detailed 1D and 2D SSNMR analysis involving ¹H, ¹³C, and ⁷⁷Se isotopes and ¹H spin diffusion. PXRD was used to show that dispersion contains nanocrystalline ebselen in the 35-60 nm size range. Confocal Raman microscopy and spectral mapping were able to detect regions where short-range interactions may occur between ebselen and PVP-VA. Spin diffusion effects were analyzed using 2D SSNMR experiments and are able to directly detect interactions between ebselen and the surrounding PVP-VA. The methods used here, particularly the 2D SSNMR methods based on spin diffusion, provided detailed structural information about a nanocrystalline polymer dispersion of ebselen, and should be useful in other studies of these types of materials.

  7. Synthesis and Characterization of Nanocrystalline Al-20 at. % Cu Powders Produced by Mechanical Alloying

    Molka Ben Makhlouf

    2016-06-01

    Full Text Available Mechanical alloying is a powder processing technique used to process materials farther from equilibrium state. This technique is mainly used to process difficult-to-alloy materials in which the solid solubility is limited and to process materials where nonequilibrium phases cannot be produced at room temperature through conventional processing techniques. This work deals with the microstructural properties of the Al-20 at. % Cu alloy prepared by high-energy ball milling of elemental aluminum and copper powders. The ball milling of powders was carried out in a planetary mill in order to obtain a nanostructured Al-20 at. % Cu alloy. The obtained powders were characterized using scanning electron microscopy (SEM, differential scanning calorimetry (DSC and X-ray diffraction (XRD. The structural modifications at different stages of the ball milling are investigated with X-ray diffraction. Several microstructure parameters such as the crystallite sizes, microstrains and lattice parameters are determined.

  8. Complex permeability and core loss of soft magnetic Fe-based nanocrystalline powder cores

    Füzerová, Jana, E-mail: jana.fuzerova@tuke.sk [Faculty of Mechanical Engineering, Technical University, Letná 1, 042 00 Košice (Slovakia); Füzer, Ján; Kollár, Peter [Institute of Physics, P.J. Šafárik University, Park Angelinum 9, 040 23 Košice (Slovakia); Bureš, Radovan; Fáberová, Mária [Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 043 53 Košice (Slovakia)

    2013-11-15

    Rapidly quenched ribbons of Fe{sub 73}Cu{sub 1}Nb{sub 3}Si{sub 16}B{sub 7} were ball milled and cryomilled to get powder and warm consolidated to get bulk compacts. The data presented here are relative to different experimental procedures, one corresponding to milling at room temperature (sample R1) and the other corresponding to cryomilling at temperature of liquid nitrogen (sample L1). It was found that the properties of the initial powder influenced the density, the electrical resistivity and electromagnetic properties of the resulting bulk alloys. Permeability and core loss are structure sensitive and depend on factors such as powder size and shape, porosity, purity, and internal stress. Permeability spectra of sample R1 decreases with increasing the frequency and its values are larger than that for sample L1 at low frequencies. On the other hand the permeability of sample L1 remains steady up to 1 kHz and at certain frequency is larger than that for sample R1. Also there are different frequency dependences of the imaginary parts of permeability and loss factor, respectively. The cryomilling of the amorphous ribbon positively influences on the AC magnetic properties at higher frequencies (above 100 Hz) of resulting bulk sample. - Highlights: • We prepared two different amorphous powder vitroperm samples. • We have examined changes in the properties of the bulk samples prepared by compaction. • It was found that properties of the initial powder influence the density, the electrical resistivity and electromagnetic properties of the resulting bulk alloys.

  9. Determination of Crystallite Size Distribution Histogram in Nanocrystalline Anatase Powders by XRD

    Matěj, Z.; Matějová, Lenka; Novotný, F.; Drahokoupil, Jan; Kužel, R.

    2011-01-01

    Roč. 1, - (2011), s. 87-92 [European Powder Diffraction Conference EPDIC 12 /12./. Darmstadt, 27.08.2010-30.08.2010] R&D Projects: GA AV ČR KAN400720701 Institutional research plan: CEZ:AV0Z40720504; CEZ:AV0Z10100520 Keywords : titanium dioxide * crystallite size * crystallite size distribution Subject RIV: CA - Inorganic Chemistry http://www.oldenbourg-link.com/ toc /zkpr/current

  10. Mechanochemical synthesis evaluation of nanocrystalline bone-derived bioceramic powder using for bone tissue engineering

    Amirsalar Khandan

    2014-01-01

    Full Text Available Introduction: Bone tissue engineering proposes a suitable way to regenerate lost bones. Different materials have been considered for use in bone tissue engineering. Hydroxyapatite (HA is a significant success of bioceramics as a bone tissue repairing biomaterial. Among different bioceramic materials, recent interest has been risen on fluorinated hydroxyapatites, (FHA, Ca 10 (PO 4 6 F x (OH 2−x . Fluorine ions can promote apatite formation and improve the stability of HA in the biological environments. Therefore, they have been developed for bone tissue engineering. The aim of this study was to synthesize and characterize the FHA nanopowder via mechanochemical (MC methods. Materials and Methods: Natural hydroxyapatite (NHA 95.7 wt.% and calcium fluoride (CaF 2 powder 4.3 wt.% were used for synthesis of FHA. MC reaction was performed in the planetary milling balls using a porcelain cup and alumina balls. Ratio of balls to reactant materials was 15:1 at 400 rpm rotation speed. The structures of the powdered particles formed at different milling times were evaluated by X-ray diffraction (XRD, scanning electron microscopy (SEM and transmission electron microscopy (TEM. Results: Fabrication of FHA from natural sources like bovine bone achieved after 8 h ball milling with pure nanopowder. Conclusion: F− ion enhances the crystallization and mechanical properties of HA in formation of bone. The produced FHA was in nano-scale, and its crystal size was about 80-90 nm with sphere distribution in shape and size. FHA powder is a suitable biomaterial for bone tissue engineering.

  11. Determination of Size Distributions in Nanocrystalline Powders by TEM, XRD and SAXS

    Jensen, Henrik; Pedersen, Jørgen Houe; Jørgensen, Jens Erik

    2006-01-01

    Crystallite size distributions and particle size distributions were determined by TEM, XRD, and SAXS for three commercially available TiO2 samples and one homemade. The theoretical Guinier Model was fitted to the experimental data and compared to analytical expressions. Modeling of the XRD spectra...... the size distribution obtained from the XRD experiments; however, a good agreement was obtained between the two techniques. Electron microscopy, SEM and TEM, confirmed the primary particle sizes, the size distributions, and the shapes obtained by XRD and SAXS. The SSEC78 powder and the commercially...

  12. Direct synthesis of nanocrystalline oxide powders by wet-chemical techniques

    Vladimir V. Srdić

    2010-09-01

    Full Text Available In a recent period there is a great need for increasing the knowledge of tailoring the innovative procedures for the synthesis of electroceramic nanopowders and materials with improved quality for specific application. In order to produce electroceramics with desirable microstructure and properties, synthesis of stoichiometric, ultra-fine and agglomerate free powders with narrow size distributions is one of the most important steps. Within this scope, in the present paper we summarize our recent results on direct synthesis of some important perovskites and ferrites nanopowders by wet-chemical techniques.

  13. Fabrication of an Fe80.5Si7.5B6Nb5Cu Amorphous-Nanocrystalline Powder Core with Outstanding Soft Magnetic Properties

    Zhang, Zongyang; Liu, Xiansong; Feng, Shuangjiu; Rehman, Khalid Mehmood Ur

    2018-03-01

    In this study, the melt spinning method was used to develop Fe80.5Si7.5B6Nb5Cu amorphous ribbons in the first step. Then, the Fe80.5Si7.5B6Nb5Cu amorphous-nanocrystalline core with a compact microstructure was obtained by multiple processes. The main properties of the magnetic powder core, such as micromorphology, thermal behavior, permeability, power loss and quality factor, have been analyzed. The obtained results show that an Fe80.5Si7.5B6Nb5Cu amorphous-nanocrystalline duplex core has high permeability (54.8-57), is relatively stable at different frequencies and magnetic fields, and the maximum power loss is only 313 W/kg; furthermore, it has a good quality factor.

  14. Room temperature ferromagnetism in nano-crystalline Co:ThO2 powders

    Bhide, M.K.; Kadam, R.M.; Godbole, S.V.; Tyagi, A.K.; Salunke, H.G.

    2012-01-01

    The major interest in dilute magnetic semiconductors (DMS's) had been directed towards the synthesis of room temperature ferromagnetic (RTF) materials for their potential applications in spintronic devices. Room temperature (RT) ferromagnetism was initially reported in Co doped TiO 2 , ZnO 2 and SnO 2 thin films and in the recent past in transition metal doped wide band gap materials. In the present paper we report the synthesis of Co doped ThO 2 nano powders by urea combustion method. The XRD characterization of 300℃ annealed samples confirmed formation of ThO 2 in the cubic phase and the average crystallite size obtained using Scherrer's formula was around 6 nm

  15. Design, Modeling and Optimization of a Piezoelectric Pressure Sensor based on a Thin-Film PZT Membrane Containing Nanocrystalline Powders

    Vahid MOHAMMADI

    2009-11-01

    Full Text Available In this paper fabrication of a 0-3 ceramic/ceramic composite lead zirconate titanate, Pb(Zr0.52Ti0.48O3 thin film has been presented and then a pressure sensor based on multilayer thin-film PZT diaphragm contain of Lead Zirconate Titanate nanocrystalline powders was designed, modeled and optimized. Dynamics characteristics of this multilayer diaphragm have been investigated by ANSYS® FE software. By this simulation the effective parameters of the multilayer PZT diaphragm for improving the performance of a pressure sensor in different ranges of pressure are optimized. The optimized thickness ratio of PZT layer to SiO2 was given in the paper to obtain the maximum deflection of the multilayer thin-film PZT diaphragm. A 0-3 ceramic/ceramic composite lead zirconate titanate, Pb(Zr0.52Ti0.48O3 film has been developed to fabricate the pressure sensor by a hybrid sol gel process. PZT nanopowders fabricated via conventional sol gel method and uniformly dispersed in PZT precursor solution by an attrition mill. XRD analysis shows that perovskite structure would be formed due to the presence of a significant amount of ceramic nanopowders. This texture has a good effect on piezoelectric properties of perovskite structure. The film forms a strongly bonded network and less shrinkage occurs, so the films do not crack during process. Also the aspect ratio through this process would be increased. SEM micrographs indicated that PZT films were uniform, crack free and have a composite microstructure and a piezoelectric coefficient d31 of -40 pC.N-1 and d33 ranged from 50pm.N-1 to 60pm.N-1.

  16. Magnetic properties of nanocrystalline CoFe{sub 2}O{sub 4} powders prepared at room temperature: variation with crystallite size

    Rajendran, M.; Pullar, R.C.; Bhattacharya, A.K. E-mail: ashokbhattacharya@warwick.ac.uk; Das, D.; Chintalapudi, S.N.; Majumdar, C.K

    2001-06-01

    The magnetic properties of nanocrystalline CoFe{sub 2}O{sub 4} powders prepared by a redox process at room temperature have been studied by vibrating sample magnetometer (VSM). The average crystallite size of the powders varied from 6 to 20 nm by changing the synthesis conditions and the corresponding saturation magnetisation (M{sub s}) value ranged from 9 to 38 emu g{sup -1}. On heating, the crystallite size increased with corresponding increase in M{sub s} values. At 1073 K all samples achieved M{sub s} values close to 73 emu g{sup -1}. On increasing the crystallite size, the coercivity (H{sub c}) increased passed through a maximum and dropped. Cobalt ferrite powder with an average crystallite size of 6 nm prepared at room temperature achieved desirable values of M{sub s}=60 emu g{sup -1} and H{sub c}=1.42 kOe after thermal annealing at 973 K. The Moessbauer spectra were recorded for CoFe{sub 2}O{sub 4} having a range of crystallite sizes at room temperature and at low temperatures down to 40 K. The magnetic and Moessbauer results are provided for nanocrystalline CoFe{sub 2}O{sub 4} as a function of crystallite size and measurement temperature.

  17. Europium concentration effect on characteristics and luminescent properties of hydroxyapatite nanocrystalline powders

    Nikolaev, Anton; Kolesnikov, Ilya; Frank-Kamenetskaya, Olga; Kuz'mina, Maria

    2017-12-01

    Series of Eu-apatites were synthesized by precipitation from aqueous solutions with the Eu/Ca atomic ratio from 0.5% to 5% at T = 90 °C. Resulting precipitates were studied using different experimental techniques including X-ray powder diffraction, infrared and raman spectroscopy, scanning elecrton microscopy, EDX and photoluminescent spectroscopy. Eu-doped Ca-deficit nanosized non-stoichiometric hydroxyapatite with high water content has been obtained throughout the experiment. Europium content in the synthesized apatites reaches 0.24 apfu (Eu/Ca = 2.5%). Relations between Eu content is the solution and precipitate have been established. It was shown that Eu-monacite starts to precipitate as secondary phase at Eu/Ca ratio in starting solution 1% or higher. Maximum luminescence is observed in apatite with ∼2% Eu/Ca ratio (which equals to ∼0.2 apfu and corresponds to 3% Eu/Ca ratio in the starting solution). As an important and brand-new result, apatite with 2% Eu/Ca ratio can be considered as the most appropriate material for the producing biolabels for luminescent research in medicine and biology.

  18. Nanocrystalline spinel ferrite (MFe2O4, M = Ni, Co, Mn, Mg, Zn) powders prepared by a simple aloe vera plant-extracted solution hydrothermal route

    Phumying, Santi; Labuayai, Sarawuth; Swatsitang, Ekaphan; Amornkitbamrung, Vittaya; Maensiri, Santi

    2013-01-01

    Graphical abstract: This figure shows the specific magnetization curves of the as-prepared MFe 2 O 4 (M = Ni, Co, Mn, Mg, Zn) powders obtained from room temperature VSM measurement. These curves are typical for a soft magnetic material and indicate hysteresis ferromagnetism in the field ranges of ±500 Oe, ±1000 Oe, and ±2000 Oe for the CoFe 2 O 4 , MgFe 2 O 4 and MnFe 2 O 4 respectively, whereas the samples of NiFe 2 O 4 and ZnFe 2 O 4 show a superparamagnetic behavior. Highlights: ► Nanocrystalline MFe 2 O 4 powders were synthesized by a novel hydrothermal method. ► Metal acetylacetonates and aloe vera plant-extracted solution are used. ► This biosynthetic route is very simple and provides high-yield oxide nanomaterials. ► XRD and TEM results indicate that the prepared samples have only spinel structure. ► The maximum M s of 68.9 emu/g at 10 kOe were observed for the samples of MnFe 2 O 4 . - Abstract: Nanocrystalline spinel ferrite MFe 2 O 4 (M = Ni, Co, Mn, Mg, Zn) powders were synthesized by a novel hydrothermal method using Fe(acac) 3 , M(acac) 3 (M = Ni, Co, Mn, Mg, Zn) and aloe vera plant extracted solution. The X-ray diffraction and selected-area electron diffraction results indicate that the synthesized nanocrystalline have only spinel structure without the presence of other phase impurities. The crystal structure and morphology of the spinel ferrite powders, as revealed by TEM, show that the NiFe 2 O 4 and CoFe 2 O 4 samples contain nanoparticles, whereas the MnFe 2 O 4 and MgFe 2 O 4 samples consist of many nanoplatelets and nanoparticles. Interestingly, the ZnFe 2 O 4 sample contains plate-like structure of networked nanocrystalline particles. Room temperature magnetization results show a ferromagnetic behavior of the CoFe 2 O 4 , MnFe 2 O 4 and MgFe 2 O 4 samples, whereas the samples of NiFe 2 O 4 and ZnFe 2 O 4 exhibit a superparamagnetic behavior

  19. Preparation and Properties of Anisotropic Nano-crystalline NdFeB Powders Made by Hydrogen Decrepitation of Die Upsetting Magnets

    Yi, P P; Lee, D; Yan, A R, E-mail: ypp@nimte.ac.cn [Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201 (China)

    2011-01-01

    Anisotropic nanocrystalline NdFeB powders were prepared by hydrogen decrepitation (HD) of die upsetting magnets. The effects of varying temperatures of HD on the microstructure and magnetic properties of the anisotropic NdFeB particles were studied. It shows that the powders which obtained by HD process at higher temperature were larger than that at lower temperature, and the HD powders show a well anisotropy at 723 K, the remanence (B{sub r}) was more than 12.46 kG, the maximum energy product ((BH){sub max}) was 19.06 MGOe, and the coercivity (H{sub cj}) was 7.2 kOe. The microstructure of the anisotropic powders revealed that with a reasonable HD temperature, the platelet grains were not destroyed. They were nearly 150-300 nm long and 30-50 nm wide. The results indicate that HD process was an effective way to prepare the anisotropic NdFeB powders.

  20. Sintered powder cores of high Bs and low coreloss Fe84.3Si4B8P3Cu0.7 nano-crystalline alloy

    Yan Zhang

    2013-06-01

    Full Text Available Nano-crystalline Fe-rich Fe84.3Si4B8P3Cu0.7 alloy ribbon with saturation magnetic flux density (Bs close to Si-steel exhibits much lower core loss (Wt than Si-Steels. Low glass forming ability of this alloy limits fabrication of magnetic cores only to stack/wound types. Here, we report on fabrication, structural, thermal and magnetic properties of bulk Fe84.3Si4B8P3Cu0.7 cores. Partially crystallized ribbons (obtained after salt-bath annealing treatment were crushed into powdered form (by ball milling, and were compacted to high-density (∼88% bulk cores by spark plasma sintering (SPS. Nano-crystalline structure (consisting of α-Fe grain in remaining amorphous matrix similar to wound ribbon cores is preserved in the compacted cores. At 50 Hz, cores sintered at Ts = 680 K show Wt 1 kHz. A trade-off between porosity and electrical resistivity is necessary to get low Wt at higher f. In the f range of ∼1 to 100 kHz, we have shown that the cores mixed with SiO2 exhibit much lower Wt than Fe-powder cores, non-oriented Si-steel sheets and commercially available sintered cores. We believe our core material is very promising to make power electronics/electrical devices much more energy-efficient.

  1. Microstructural evolution during the synthesis of bulk components from nanocrystalline ceramic powder, part II: microstructure and properties

    Ajaal, T. T.; Metak, A. M.

    2004-01-01

    Part I of this review, published in 5 /4th of Al-Nawah magazine, was devoted to the synthetic techniques used in the production processes of a bulk components of nanocrystalline materials. In this part, the microstructural evolution and its effect on the materials properties will be detailed. Minimizing grain growth and maximizing densification during the sintering stage of the ultrafine particles as well as the homogeneous densification in pressureless sintering, grain growth and rapid rate pressureless sintering will be discussed. Ceramics are well known for their high strength at elevated temperatures, as well as the extreme brittleness that prevents their application in many critical components. However, researchers have found that brittleness can be overcome by reducing particle sizes to nanometer levels. These fine grain structures are believed to provide improved ductility the individual grains can slide over one another without causing cracks. In addition, nanophase ceramics are more easily formed than their conventional counterparts, and easier to machine without cracking or breaking. Shrinkage during sintering is also greatly reduced in nanophase ceramics, and they can be sintered at lower temperatures than conventional ceramics. As a result, nanophase ceramics have the potential to deliver an ideal combination of ductility and high-temperature strength, allowing increased efficiency in applications ranging from automobile engines to jet aircraft. This part of the review covers the microstructural evolution during the synthetic process of nanocrystalline ceramic materials and its effects on the materials properties.(author)

  2. Production of nano-crystalline zirconia powders and fabrication of high strength ultra-fine-grained ceramics

    Rajendran, S.

    1993-01-01

    Hydrous zirconia containing 2 and 2.5 mol% Y 2 O 3 was prepared by a hydroxide co-precipitation method and portions were dispersed in ethanol before drying(P2), milled in ethanol after drying (P3) or after calcination at 550 deg C (P4) or milled in iso-propanal after calcination at 1000 deg C (P5). The crystallisation behaviour and sintering characteristics of the materials were investigated. The calcined as dried powder (P1) has strongly bonded hard aggregates and the material reached a density of only about 80% of theoretical after sintering at 1500 deg C. Powder characteristics and the sinterability of the alcohol treated materials depended on the conditions of processing and heat treatment. The sinter-activity of the powders decreased from P2 to P5. Powder P3 was composed of relatively weakly bonded crystallites and could be sintered at 1400 deg C, while the powders P4 and P5 contained hard agglomerates and required a sintering temperature of 1450 and 1550 deg C respectively to achieve similar density. Powder (P2) had zirconium alkoxide species on the particle surface which decomposed at about 300 deg C. The calcined powder had very weak agglomerates composed of fine, uniform zirconia crystals and/or aggregates and sintered to high density at 1150 deg C. The final ceramic had a very uniform microstructure with an average grain size of about 150nm and exhibited fracture strength as high as 1700 MPa. A detailed account of the formation of aggregates of strongly bonded crystallites during calcination of hydrous zirconia, influence of alcohol in producing soft agglomerates and the sintering characteristics of the powders is reported. 46 refs., 2 tabs., 15 figs

  3. Synthesis of Nanocrystalline RuO2(60%)-SnO2(40%)Powders by Amorphous Citrate Route

    2007-01-01

    Nanometer RuO2-SnO2was synthesized by the citrate-gel method using RuCl3, SnCl4 as cation sources, citric acid as complexing agent and anhydrous ethanol as solvent. The structures of the derived powders were characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, transmission electron microscope, and Brunauer-Emmett-Teller surface area measurement. The pure, fine and amorphous powders was obtained at 160℃. The materials calcined at above 400 ℃ were composed of rutile-type oxide phases having particle sizes of fairly narrow distribution and good thermal resistant properties. By adding SnO2 to RUO2, the Ru metallic phase can be effectively controlled under a traditional temperature of preparation for dimensional stable anode.

  4. New synthesis parameters of GGG:Nd nanocrystalline powder prepared by sol–gel method: Structural and spectroscopic investigation

    Alshikh Mohamad, Yassin, E-mail: yassinm@mail.ru; Atassi, Yomen; Moussa, Zafer

    2015-09-15

    GGG:Nd nanopowder is synthesized by the sol–gel method using formic acid and acetic acid as chelating agents and ethylene glycol as a cross linking agent. TGA–DSC, XRD, photoluminescence spectroscopy and fluorescence life time analysis (τ) are used to characterize the powder. XRD is used to optimize the synthesis parameters. According to XRD, complete phase of GGG nanopowder is formed at 800 °C for 1 min. Fluorescence life time analyses reveal that the optimum crystallization temperature is 1000 °C. - Highlights: • GGG:Nd nanopowder was prepared using formic acid by the sol gel method. • Optimization of sol gel parameters was done. • GGG phase formation was complete at 800 °C for 1 min • According to τ measurements, optimal temperature treatment is at 1000 °C. • Nanopowder prepared with formic acid was better than that formed with acetic acid.

  5. Synthesis of nanocrystalline NiO/ZnO heterostructured composite powders by sol-gel auto combustion method and their characterizations

    Tangcharoen, Thanit; Klysubun, Wantana; Kongmark, Chanapa

    2018-03-01

    Nanocrystalline NiO/ZnO heterostructured composite powders were prepared by the sol-gel auto combustion method, based on nickel and zinc nitrate precursors and using diethanolamine (DEA) as novel fuel. The composition of different NiO and ZnO ratios, ranging from 100/0, 95/5, 90/10, 80/20, 60/40, 50/50, 40/60, 20/80, 10/90, 5/95 to 0/100, were studied. The structural, chemical bonding, morphological, optical, and fluorescence properties including the local atomic structure of each calcined sample were systematically investigated by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-DRS), photoluminescence (PL) spectroscopy, and synchrotron X-ray absorption spectroscopy (XAS), respectively. For the ZnO concentration below 20%, both XRD and Raman spectroscopy results revealed only the NiO phase. This conformed to the observation of Zn K-edge and Ni K-edge X-ray absorption near edge structure (XANES). The Zn ions found in the samples of low ZnO concentration exhibited six-fold coordination with oxygen atoms rather than the four-fold coordination found in the wurtzite (WZ) structure of ZnO. In contrast, the Ni ions which are found in the samples of low NiO concentration (≤10%) are coordinated both tetrahedrally and octahedrally by four or six oxygen atoms, respectively, rather than the six-fold coordination which is usually observed for Ni ions in the rock salt (RS) form of NiO. All analytical results obtained from experimental XANES spectra were verified by the theoretical calculation of absorption spectra using the FEFF9.7 code. The UV-DRS results showed that there was an increase in the reflectance efficiency for both infrared and visible light conditions as the content of ZnO increases; meanwhile, the values for the energy gap (Eg) of all composite samples were higher than that of pure NiO and ZnO. In addition, the PL spectra revealed major blue emission bands observed at 490

  6. Consolidation of mechanically alloyed nanocrystalline Cu-Nb-ZrO{sub 2} powder by spark plasma sintering

    Eymann, K., E-mail: Konrad.Eymann@tu-dresden.de [Institute of Materials Science, Technische Universitaet Dresden, 01062 Dresden (Germany); Riedl, T.; Bram, A.; Ruhnow, M.; Boucher, R.; Kirchner, A.; Kieback, B. [Institute of Materials Science, Technische Universitaet Dresden, 01062 Dresden (Germany)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer Solid solution of Cu-Nb was achieved by mechanically alloying Cu, Nb and ZrO{sub 2}. Black-Right-Pointing-Pointer In as-milled state the Cu-Nb-ZrO{sub 2} powders show an average Cu grain size of 16 nm. Black-Right-Pointing-Pointer Mechanical and electrical properties are studied in dependence of thermal exposure. Black-Right-Pointing-Pointer Compaction at 1000 Degree-Sign C/1 min using SPS increases Cu grain size to 43 nm. Black-Right-Pointing-Pointer Bulk samples reach a maximum IACS of 16% and 98% relative density. - Abstract: This work presents the synthesis of ultra fine grained high-strength Cu-Nb-ZrO{sub 2} bulk samples via mechanical alloying and spark plasma sintering. Technologically relevant properties such as density, micro-hardness, and electrical conductivity were studied in terms of the compaction parameters, in particular the sintering temperature and holding time. An optimum process parameter combination has been found T = 950 Degree-Sign C, t = 1 min, and 65 MPa, which yield a micro-hardness of 325 HV, 97.5% relative density, and electrical conductivity of 10% IACS. The dependence of these properties on the compaction parameters is explained by analyzing the microstructure, i.e. grain size, presence and distribution of phases, and porosity, with X-ray diffraction, optical and electron microscopy as well as with an Archimedes densitometer.

  7. Nanocrystalline spinel ferrite (MFe{sub 2}O{sub 4}, M = Ni, Co, Mn, Mg, Zn) powders prepared by a simple aloe vera plant-extracted solution hydrothermal route

    Phumying, Santi; Labuayai, Sarawuth; Swatsitang, Ekaphan; Amornkitbamrung, Vittaya [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Integrated Nanotechnology Research Center (INRC), Khon Kaen University, Khon Kaen 40002 (Thailand); Maensiri, Santi, E-mail: santimaensiri@gmail.com [School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand)

    2013-06-01

    Graphical abstract: This figure shows the specific magnetization curves of the as-prepared MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders obtained from room temperature VSM measurement. These curves are typical for a soft magnetic material and indicate hysteresis ferromagnetism in the field ranges of ±500 Oe, ±1000 Oe, and ±2000 Oe for the CoFe{sub 2}O{sub 4}, MgFe{sub 2}O{sub 4} and MnFe{sub 2}O{sub 4} respectively, whereas the samples of NiFe{sub 2}O{sub 4} and ZnFe{sub 2}O{sub 4} show a superparamagnetic behavior. Highlights: ► Nanocrystalline MFe{sub 2}O{sub 4} powders were synthesized by a novel hydrothermal method. ► Metal acetylacetonates and aloe vera plant-extracted solution are used. ► This biosynthetic route is very simple and provides high-yield oxide nanomaterials. ► XRD and TEM results indicate that the prepared samples have only spinel structure. ► The maximum M{sub s} of 68.9 emu/g at 10 kOe were observed for the samples of MnFe{sub 2}O{sub 4}. - Abstract: Nanocrystalline spinel ferrite MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders were synthesized by a novel hydrothermal method using Fe(acac){sub 3}, M(acac){sub 3} (M = Ni, Co, Mn, Mg, Zn) and aloe vera plant extracted solution. The X-ray diffraction and selected-area electron diffraction results indicate that the synthesized nanocrystalline have only spinel structure without the presence of other phase impurities. The crystal structure and morphology of the spinel ferrite powders, as revealed by TEM, show that the NiFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} samples contain nanoparticles, whereas the MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples consist of many nanoplatelets and nanoparticles. Interestingly, the ZnFe{sub 2}O{sub 4} sample contains plate-like structure of networked nanocrystalline particles. Room temperature magnetization results show a ferromagnetic behavior of the CoFe{sub 2}O{sub 4}, MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples, whereas the

  8. Structure and thermal stability of nanocrystalline materials

    In addition, study of the thermal stability of nanocrystalline materials against significant grain growth is both scientific and technological interest. A sharp increase in grain size (to micron levels) during consolidation of nanocrystalline powders to obtain fully dense materials may consequently result in the loss of some unique ...

  9. An assessment of the homogeneity of nano-crystalline Fe–Cu powders as studied by means of APT

    Wille, Catharina

    2009-04-01

    In this contribution the homogeneity of mechanically alloyed Fe-Cu powders for two different compositions (Fe-10 and Fe-2.5 at%Cu) has been systematically characterised by atom probe tomography. Since Fe-Cu exhibits the Invar effect, it is among the most attractive systems for technical application. Furthermore, this system is immiscible and characterised by a large positive heat of mixing. In combination with the widespread application and accessibility, this predestines Fe-Cu as a binary model alloy to elaborate the enforced nonequilibrium enhanced solubility for immiscible systems. Depending on the parameters composition and milling time, results on the extension of the solubility limit and on the homogeneity of the alloy are presented, discussed and compared to earlier works. Only for the alloy with lower Cu content and for the prolonged milling time of 50 h, chemical homogeneity of the sample as measured by the atom probe was fully reached on the nano-scale. For all other parameter combinations homogeneity could not be achieved, even for long milling times and for those samples that appear to be homogeneous via X-ray analysis. Moreover, impurities were determined, mostly stemming from the fabrication procedure. The arrangement and homogeneity of the most common impurity, oxygen, was evaluated from atom probe data for different samples. Thus, the local concentration, segregation effects and the distribution of impurities could be quantified on the nano-scale, depending on the different nominal compositions and processing parameters. Additionally, structural information could be gained employing transmission electron microscopy and diffraction measurements. (C) 2008 Elsevier B.V. All rights reserved.

  10. An assessment of the homogeneity of nano-crystalline Fe-Cu powders as studied by means of APT

    Wille, Catharina, E-mail: cwille@ump.gwdg.de [Georg-August-University Goettingen, Institute for Materials Physics, Goettingen 37077 (Germany); Al-Kassab, Talaat [Georg-August-University Goettingen, Institute for Materials Physics, Goettingen 37077 (Germany); Choi, Pyuck-Pa [Korea Institute of Science and Technology, Nano-Materials Research Center, Seoul (Korea, Republic of); Kwon, Young-Soon [Research Center for Machine Parts and Materials Processing, University of Ulsan, Ulsan (Korea, Republic of); Kirchheim, Reiner [Georg-August-University Goettingen, Institute for Materials Physics, Goettingen 37077 (Germany)

    2009-04-15

    In this contribution the homogeneity of mechanically alloyed Fe-Cu powders for two different compositions (Fe-10 and Fe-2.5 at%Cu) has been systematically characterised by atom probe tomography. Since Fe-Cu exhibits the Invar effect, it is among the most attractive systems for technical application. Furthermore, this system is immiscible and characterised by a large positive heat of mixing. In combination with the widespread application and accessibility, this predestines Fe-Cu as a binary model alloy to elaborate the enforced nonequilibrium enhanced solubility for immiscible systems. Depending on the parameters composition and milling time, results on the extension of the solubility limit and on the homogeneity of the alloy are presented, discussed and compared to earlier works. Only for the alloy with lower Cu content and for the prolonged milling time of 50 h, chemical homogeneity of the sample as measured by the atom probe was fully reached on the nano-scale. For all other parameter combinations homogeneity could not be achieved, even for long milling times and for those samples that appear to be homogeneous via X-ray analysis. Moreover, impurities were determined, mostly stemming from the fabrication procedure. The arrangement and homogeneity of the most common impurity, oxygen, was evaluated from atom probe data for different samples. Thus, the local concentration, segregation effects and the distribution of impurities could be quantified on the nano-scale, depending on the different nominal compositions and processing parameters. Additionally, structural information could be gained employing transmission electron microscopy and diffraction measurements.

  11. Hot deformed anisotropic nanocrystalline NdFeB based magnets prepared from spark plasma sintered melt spun powders

    Hou, Y.H.; Huang, Y.L. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China); School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Liu, Z.W., E-mail: zwliu@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Zeng, D.C. [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Ma, S.C.; Zhong, Z.C. [School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063 (China)

    2013-09-01

    Highlights: • Microstructure evolution and its influence on the magnetic properties were investigated. • The increase of stray field and weakening of domain-wall pinning effects were the main reasons of the decrease of the coercivity with increasing the compression ratio. • The influences of non-uniform plastic deformation on the microstructure and magnetic properties were investigated. • Magnetic properties and temperature coefficient of coercivity are indeed very promising without heavy rare earth elements. -- Abstract: Anisotropic magnets were prepared by spark plasma sintering (SPS) followed by hot deformation (HD) using melt-spun powders as the starting material. Good magnetic properties with the remanence J{sub r} > 1.32 T and maximum of energy product (BH){sub max} > 303 kJ/m{sup 3} have been obtained. The microstructure evolution during HD and its influence on the magnetic properties were investigated. The fine grain zone and coarse grain zone formed in the SPS showed different deformation behaviors. The microstructure also had an important effect on the temperature coefficients of coercivity. A strong domain-wall pinning model was valid to interpret the coercivity mechanism of the HDed magnets. The increase of stray field and weakening of domain-wall pinning effects were the main reasons of the decrease of the coercivity with increasing the compression ratio. The influences of non-uniform plastic deformation on the microstructure and magnetic properties were investigated. The polarization characteristics of HDed magnets were demonstrated. It was found out that the HDed magnets had better corrosion resistance than the counterpart sintered magnet.

  12. An assessment of the homogeneity of nano-crystalline Fe-Cu powders as studied by means of APT

    Wille, Catharina; Al-Kassab, Talaat; Choi, Pyuck-Pa; Kwon, Young-Soon; Kirchheim, Reiner

    2009-01-01

    In this contribution the homogeneity of mechanically alloyed Fe-Cu powders for two different compositions (Fe-10 and Fe-2.5 at%Cu) has been systematically characterised by atom probe tomography. Since Fe-Cu exhibits the Invar effect, it is among the most attractive systems for technical application. Furthermore, this system is immiscible and characterised by a large positive heat of mixing. In combination with the widespread application and accessibility, this predestines Fe-Cu as a binary model alloy to elaborate the enforced nonequilibrium enhanced solubility for immiscible systems. Depending on the parameters composition and milling time, results on the extension of the solubility limit and on the homogeneity of the alloy are presented, discussed and compared to earlier works. Only for the alloy with lower Cu content and for the prolonged milling time of 50 h, chemical homogeneity of the sample as measured by the atom probe was fully reached on the nano-scale. For all other parameter combinations homogeneity could not be achieved, even for long milling times and for those samples that appear to be homogeneous via X-ray analysis. Moreover, impurities were determined, mostly stemming from the fabrication procedure. The arrangement and homogeneity of the most common impurity, oxygen, was evaluated from atom probe data for different samples. Thus, the local concentration, segregation effects and the distribution of impurities could be quantified on the nano-scale, depending on the different nominal compositions and processing parameters. Additionally, structural information could be gained employing transmission electron microscopy and diffraction measurements.

  13. Application of Powder Diffraction Methods to the Analysis of Short- and Long-Range Atomic Order in Nanocrystalline Diamond and SiC: The Concept of the Apparent Lattice Parameter (alp)

    Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.

    2003-01-01

    Two methods of the analysis of powder diffraction patterns of diamond and SiC nanocrystals are presented: (a) examination of changes of the lattice parameters with diffraction vector Q ('apparent lattice parameter', alp) which refers to Bragg scattering, and (b), examination of changes of inter-atomic distances based on the analysis of the atomic Pair Distribution Function, PDF. Application of these methods was studied based on the theoretical diffraction patterns computed for models of nanocrystals having (i) a perfect crystal lattice, and (ii), a core-shell structure, i.e. constituting a two-phase system. The models are defined by the lattice parameter of the grain core, thickness of the surface shell, and the magnitude and distribution of the strain field in the shell. X-ray and neutron experimental diffraction data of nanocrystalline SiC and diamond powders of the grain diameter from 4 nm up to micrometers were used. The effects of the internal pressure and strain at the grain surface on the structure are discussed based on the experimentally determined dependence of the alp values on the Q-vector, and changes of the interatomic distances with the grain size determined experimentally by the atomic Pair Distribution Function (PDF) analysis. The experimental results lend a strong support to the concept of a two-phase, core and the surface shell structure of nanocrystalline diamond and SiC.

  14. Synthesis and characterization of nanocrystalline zinc ferrite

    Jiang, J.S.; Yang, X.L.; Gao, L.

    1999-01-01

    Nanocrystalline zinc ferrite powders with a partially inverted spinel structure were synthesized by high-energy ball milling in a closed container at ambient temperature from a mixture of alpha-Fe2O3 and ZnO crystalline powders in equimolar ratio. From low-temperature and in-field Mossbauer...

  15. Nanocrystalline solids

    Gleiter, H.

    1991-01-01

    Nanocrystalline solids are polycrystals, the crystal size of which is a few (typically 1 to 10) nanometres so that 50% or more of the solid consists of incoherent interfaces between crystals of different orientations. Solids consisting primarily of internal interfaces represent a separate class of atomic structures because the atomic arrangement formed in the core of an interface is known to be an arrangement of minimum energy in the potential field of the two adjacent crystal lattices with different crystallographic orientations on either side of the boundary core. These boundary conditions result in atomic structures in the interfacial cores which cannot be formed elsewhere (e.g. in glasses or perfect crystals). Nanocrystalline solids are of interest for the following four reasons: (1) Nanocrystalline solids exhibit an atomic structure which differs from that of the two known solid states: the crystalline (with long-range order) and the glassy (with short-range order). (2) The properties of nanocrystalline solids differ (in some cases by several orders of magnitude) from those of glasses and/or crystals with the same chemical composition, which suggests that they may be utilized technologically in the future. (3) Nanocrystalline solids seem to permit the alloying of conventionally immiscible components. (4) If small (1 to 10 nm diameter) solid droplets with a glassy structure are consolidated (instead of small crystals), a new type of glass, called nanoglass, is obtained. Such glasses seem to differ structurally from conventional glasses. (orig.)

  16. Solid state consolidation nanocrystalline copper-tungsten using cold spray

    Hall, Aaron Christopher [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sarobol, Pylin [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Argibay, Nicolas [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Clark, Blythe [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Diantonio, Christopher [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    It is well known that nanostructured metals can exhibit significantly improved properties compared to metals with conventional grain size. Unfortunately, nanocrystalline metals typically are not thermodynamically stable and exhibit rapid grain growth at moderate temperatures. This severely limits their processing and use, making them impractical for most engineering applications. Recent work has shown that a number of thermodynamically stable nanocrystalline metal alloys exist. These alloys have been prepared as powders using severe plastic deformation (e.g. ball milling) processes. Consolidation of these powders without compromise of their nanocrystalline microstructure is a critical step to enabling their use as engineering materials. We demonstrate solid-state consolidation of ball milled copper-tantalum nanocrystalline metal powder using cold spray. Unfortunately, the nanocrystalline copper-tantalum powder that was consolidated did not contain the thermodynamically stable copper-tantalum nanostructure. Nevertheless, this does this demonstrates a pathway to preparation of bulk thermodynamically stable nanocrystalline copper-tantalum. Furthermore, it demonstrates a pathway to additive manufacturing (3D printing) of nanocrystalline copper-tantalum. Additive manufacturing of thermodynamically stable nanocrystalline metals is attractive because it enables maximum flexibility and efficiency in the use of these unique materials.

  17. Influence of Ba/Fe mole ratios on magnetic properties, crystallite size and shifting of X-ray diffraction peaks of nanocrystalline BaFe12O19 powder, prepared by sol gel auto combu

    Suastiyanti, Dwita; Sudarmaji, Arif; Soegijono, Bambang

    2012-06-01

    Barium hexaferrite BaFe12O19 (BFO) is of great importance as permanent magnets, particularly for magnetic recording as well as in microwave devices. Nano-crystalline BFO powders were prepared by sol gel auto combustion method in citric acid - metal nitrates system. Hence the mole ratios of Ba/Fe were variated at 1:12; 1:11.5 and 1:11. Ratio of cation to fuel was fixed at 1:1. An appropriate amount of amonia solution was added dropwise to this solution with constant stirring until the PH reached 7 in all cases. Heating at 850oC for 10 hours for each sample to get final formation of BFO nanocrystalline. The data from XRD showing the lattice parameters a,c and the unit-cell volume V, confirm that BFO with ratio 1:12 has same crystall parameters with ratio 1:11. Ratio of Ba/Fe 1:12 and 1:11 have diffraction pattern similarly at almost each 2 θ for each samples. Ratio of Ba/Fe 1: 11.5 has the finest crystallite size 22 nm. Almost diffraction pattern peaks of Ba/Fe 1:11.5 move to the left from of Ba/Fe 1:12 then return to diffraction pattern of Ba/Fe 1:12 for Ba/Fe 1:11. SEM observations show the particle size less than 100 nm and the same shape for each sample. Ratio of Ba/Fe 1: 12 gives the highest intrinsic coercive Hc = 427.3 kA/m. The highest remanent magnetization is at ratio 1:11 with Mr = 0.170 T. BFO with mole ratio 1:11.5 has the finest grain 22 nm, good magnetic properties and the highest value of best FoM 89%.

  18. Bimodal microstructure and deformation of cryomilled bulk nanocrystalline Al-7.5Mg alloy

    Lee, Z.; Witkin, D.B.; Radmilovic, V.; Lavernia, E.J.; Nutt, S.R.

    2005-01-01

    The microstructure, mechanical properties and deformation response of bimodal structured nanocrystalline Al-7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al-7.5Mg powders, and then cryomilled nanocrystalline powders blended with 15 and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk nanocrystalline alloys. Bimodal bulk nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions, show balanced mechanical properties of enhanced yield and ultimate strength and reasonable ductility and toughness compared to comparable conventional alloys and nanocrystalline metals. The investigation of tensile and hardness test suggests unusual deformation mechanisms and interactions between ductile coarse-grain bands and nanocrystalline regions

  19. Development of Bulk Nanocrystalline Cemented Tungsten Carbide for Industrial Applicaitons

    Z. Zak Fang, H. Y. Sohn

    2009-03-10

    This report contains detailed information of the research program entitled "Development of Bulk Nanocrystalline Cemented Tungsten Carbide Materials for Industrial Applications". The report include the processes that were developed for producing nanosized WC/Co composite powders, and an ultrahigh pressure rapid hot consolidation process for sintering of nanosized powders. The mechanical properties of consolidated materials using the nanosized powders are also reported.

  20. Identification of Optimum Magnetic Behavior of NanoCrystalline CmFeAl Type Heusler Alloy Powders Using Response Surface Methodology

    Srivastava, Y.; Srivastava, S.; Boriwal, L.

    2016-09-01

    Mechanical alloying is a novelistic solid state process that has received considerable attention due to many advantages over other conventional processes. In the present work, Co2FeAl healer alloy powder, prepared successfully from premix basic powders of Cobalt (Co), Iron (Fe) and Aluminum (Al) in stoichiometric of 60Co-26Fe-14Al (weight %) by novelistic mechano-chemical route. Magnetic properties of mechanically alloyed powders were characterized by vibrating sample magnetometer (VSM). 2 factor 5 level design matrix was applied to experiment process. Experimental results were used for response surface methodology. Interaction between the input process parameters and the response has been established with the help of regression analysis. Further analysis of variance technique was applied to check the adequacy of developed model and significance of process parameters. Test case study was performed with those parameters, which was not selected for main experimentation but range was same. Response surface methodology, the process parameters must be optimized to obtain improved magnetic properties. Further optimum process parameters were identified using numerical and graphical optimization techniques.

  1. High Pressure X-Ray Diffraction Studies on Nanocrystalline Materials

    Palosz, B.; Stelmakh, S.; Grzanka, E.; Gierlotka, S.; Pielaszek, R.; Bismayer, U.; Werner, S.; Palosz, W.

    2003-01-01

    Application of in situ high pressure powder diffraction technique for examination of specific structural properties of nanocrystals based on the experimental data of SiC nanocrystalline powders of 2 to 30 nrn diameter in diameter is presented. Limitations and capabilities of the experimental techniques themselves and methods of diffraction data elaboration applied to nanocrystals with very small dimensions (nanoparticles of different grain size.

  2. Nanocrystalline ceramic materials

    Siegel, Richard W.; Nieman, G. William; Weertman, Julia R.

    1994-01-01

    A method for preparing a treated nanocrystalline metallic material. The method of preparation includes providing a starting nanocrystalline metallic material with a grain size less than about 35 nm, compacting the starting nanocrystalline metallic material in an inert atmosphere and annealing the compacted metallic material at a temperature less than about one-half the melting point of the metallic material.

  3. Hot pressing of nanocrystalline tantalum using high frequency induction heating and pulse plasma sintering

    Jakubowicz, J.; Adamek, G.; Sopata, M.; Koper, J. K.; Siwak, P.

    2017-12-01

    The paper presents the results of nanocrystalline powder tantalum consolidation using hot pressing. The authors used two different heating techniques during hot pressing: high-frequency induction heating (HFIH) and pulse plasma sintering (PPS). A comparison of the structure, microstructure, mechanical properties and corrosion resistance of the bulk nanocrystalline tantalum obtained in both techniques was performed. The nanocrystalline powder was made to start from the microcrystalline one using the high-energy ball milling process. The nanocrystalline powder was hot-pressed at 1000 °C, whereas, for comparison, the microcrystalline powder was hot pressed up to 1500 °C for proper consolidation. The authors found that during hot pressing, the powder partially reacts with the graphite die covered by boron nitride, which facilitated punches and powder displacement in the die during densification. Tantalum carbide and boride in the nanocrystalline material was found, which can improve the mechanical properties. The hardness of the HFIH and PPS nanocrystalline tantalum was as high as 625 and 615 HV, respectively. The microstructure was more uniform in the PPS nanomaterial. The corrosion resistance in both cases deteriorated, in comparison to the microcrystalline material, while the PPS material corrosion resistance was slightly better than that of the HFIH one.

  4. Nanocrystalline and ultrafine grain copper obtained by mechanical attrition

    Rodolfo Rodríguez Baracaldo

    2010-01-01

    Full Text Available This article presents a method for the sample preparation and characterisation of bulk copper having grain size lower than 1 μm (ultra-fine grain and lower than 100 nm grain size (nanocrystalline. Copper is initially manufactured by a milling/alloying me- chanical method thereby obtaining a powder having a nanocrystalline structure which is then consolidated through a process of warm compaction at high pressure. Microstructural characterisation of bulk copper samples showed the evolution of grain size during all stages involved in obtaining it. The results led to determining the necessary conditions for achieving a wide range of grain sizes. Mechanical characterisation indicated an increase in microhardness to values of around 3.40 GPa for unconsolida- ted nanocrystalline powder. Compressivee strength was increased by reducing the grain size, thereby obtaining an elastic limit of 650 MPa for consolidated copper having a ~ 62 nm grain size.

  5. Bulletin of Materials Science | Indian Academy of Sciences

    Home; Journals; Bulletin of Materials Science. K B R Varma. Articles written in Bulletin of Materials Science. Volume 30 Issue 6 December 2007 pp 567-570 Ceramics and Glasses. Microwave synthesis and sintering characteristics of CaCu3Ti4O12 · P Thomas L N Sathapathy K Dwarakanath K B R Varma · More Details ...

  6. Effects of fillers on the properties of liquid silicone rubbers (LSRs)

    Yu, Liyun; Vudayagiri, Sindhu; Zakaria, Shamsul Bin

    low viscosities, which is favorable for loading of inorganic fillers [5]. In this study, commercially available fillers, such as fumed silica (SiO2), titanium dioxide (TiO2), barium titanate (BaTiO3), copper calcium titanate (CaCu3Ti4O12, CCTO), multi-walled carbon nanotubes (MWCNTs) were added...

  7. Bioactive nanocrystalline wollastonite synthesized by sol–gel ...

    The sol–gel combustion method was employed to synthesize the nanocrystalline wollastonite by taking the raw eggshell powder as a calcium source and TEOS as a source of silicate. Glycine was .... 94·37% CaCO3, hence in order to prepare 1 M Ca2+ ion solu- ... requires an acid or base catalyst hence the pH of the solu-.

  8. Bioactive nanocrystalline wollastonite synthesized by sol–gel ...

    The sol–gel combustion method was employed to synthesize the nanocrystalline wollastonite by taking the raw eggshell powder as a calcium source and TEOS as a source of silicate. Glycine was used as a reductant or fuel and nitrate ions present in metal nitrate acts as an oxidizer. The phase purity of the wollastonite was ...

  9. Thermally Stable Nanocrystalline Steel

    Hulme-Smith, Christopher Neil; Ooi, Shgh Woei; Bhadeshia, Harshad K. D. H.

    2017-10-01

    Two novel nanocrystalline steels were designed to withstand elevated temperatures without catastrophic microstructural changes. In the most successful alloy, a large quantity of nickel was added to stabilize austenite and allow a reduction in the carbon content. A 50 kg cast of the novel alloy was produced and used to verify the formation of nanocrystalline bainite. Synchrotron X-ray diffractometry using in situ heating showed that austenite was able to survive more than 1 hour at 773 K (500 °C) and subsequent cooling to ambient temperature. This is the first reported nanocrystalline steel with high-temperature capability.

  10. Structure and properties of nanocrystalline soft magnetic composite materials with silicon polymer matrix

    Dobrzanski, L.A.; Nowosielski, R.; Konieczny, J.; PrzybyI, A.; WysIocki, J.

    2005-01-01

    The paper concerns investigation of nanocrystalline composites technology preparation. The composites in the form of rings with rectangular transverse section, and with polymer matrix and nanocrystalline metallic powders fulfillment were made, for obtaining good ferromagnetic properties. The nanocrystalline ferromagnetic powders were manufactured by high-energy ball milling of metallic glasses strips in an as-quenched state. Generally for investigation, Co matrix alloys with the silicon polymer were used. Magnetic properties in the form of hysteresis loop by rings method were measured. Generally composite cores showed lower soft ferromagnetic properties than winded cores of nanocrystalline strips, but composite cores showed interesting mechanical properties. Furthermore, the structure of strips and powders on properties of composites were investigated

  11. Preparation of porous ceramics from nanocrystalline zirconia and its microstructure

    Nikitin, D.S.; Zhukov, V.A.; Kul'kov, S.N.; Perkov, V.V.; Buyakova, S.P.

    2004-01-01

    The behaviour of ZrO 2 (Y) nanocrystalline powder under pressing, the effect of forming pressure, the temperature and the time of sintering on the structure of the sintered porous ceramics are under study. It is shown that on pressing the fracturing of powder particles and their agglomerates takes place even at low pressures (≅50 MPa). The change of densification mechanisms is revealed - from quasi-liquid displacement of powder particles at the beginning of mechanical action to fracture of coarse structural elements. It is established that a strong skeleton responsible for needed porosity is formed even at the initial stage of sintering [ru

  12. Microstructure characterization and cation distribution of nanocrystalline cobalt ferrite

    Abbas, Y.M., E-mail: ymabbas@live.com [Suez Canal University, Faculty of Science, Physics Department, Ismailia (Egypt); Mansour, S.A.; Ibrahim, M.H. [Suez Canal University, Faculty of Science, Physics Department, Ismailia (Egypt); Ali, Shehab E., E-mail: shehab_physics@yahoo.com [Suez Canal University, Faculty of Science, Physics Department, Ismailia (Egypt)

    2011-11-15

    Nanocrystalline cobalt ferrite has been synthesized using two different methods: ceramic and co-precipitation techniques. The nanocrystalline ferrite phase has been formed after 3 h of sintering at 1000 deg. C. The structural and microstructural evolutions of the nanophase have been studied using X-ray powder diffraction and the Rietveld method. The refinement result showed that the type of the cationic distribution over the tetrahedral and octahedral sites in the nanocrystalline lattice is partially an inverse spinel. The transmission electronic microscope analysis confirmed the X-ray results. The magnetic properties of the samples were characterized using a vibrating sample magnetometer. - Highlights: > The refinement result showed that the cationic distribution over the sites in the lattice is partially an inverse spinel. > The transmission electronic microscope analysis confirmed the X-ray results. > The magnetic properties of the samples were characterized using a vibrating sample magnetometer.

  13. Microstructure characterization and cation distribution of nanocrystalline cobalt ferrite

    Abbas, Y.M.; Mansour, S.A.; Ibrahim, M.H.; Ali, Shehab E.

    2011-01-01

    Nanocrystalline cobalt ferrite has been synthesized using two different methods: ceramic and co-precipitation techniques. The nanocrystalline ferrite phase has been formed after 3 h of sintering at 1000 deg. C. The structural and microstructural evolutions of the nanophase have been studied using X-ray powder diffraction and the Rietveld method. The refinement result showed that the type of the cationic distribution over the tetrahedral and octahedral sites in the nanocrystalline lattice is partially an inverse spinel. The transmission electronic microscope analysis confirmed the X-ray results. The magnetic properties of the samples were characterized using a vibrating sample magnetometer. - Highlights: → The refinement result showed that the cationic distribution over the sites in the lattice is partially an inverse spinel. → The transmission electronic microscope analysis confirmed the X-ray results. → The magnetic properties of the samples were characterized using a vibrating sample magnetometer.

  14. Strain rate sensitivity studies on bulk nanocrystalline aluminium by nanoindentation

    Varam, Sreedevi; Rajulapati, Koteswararao V., E-mail: kvrse@uohyd.ernet.in; Bhanu Sankara Rao, K.

    2014-02-05

    Nanocrystalline aluminium powder synthesized using high energy ball milling process was characterized by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The studies indicated the powder having an average grain size of ∼42 nm. The consolidation of the powder was carried out by high-pressure compaction using a uni-axial press at room temperature by applying a pressure of 1.5 GPa. The cold compacted bulk sample having a density of ∼98% was subjected to nanoindentation which showed an average hardness and elastic modulus values of 1.67 ± 0.09 GPa and 83 ± 8 GPa respectively at a peak force of 8000 μN and a strain rate of 10{sup −2} s{sup −1}. Achieving good strength along with good ductility is challenging in nanocrystalline metals. When enough sample sizes are not available to measure ductility and other mechanical properties as per ASTM standards, as is the case with nanocrystalline materials, nanoindentation is a very promising technique to evaluate strain rate sensitivity. Strain rate sensitivity is a good measure of ductility and in the present work it is measured by performing indentation at various loads with varying loading rates. Strain rate sensitivity values of 0.024–0.054 are obtained for nanocrystalline Al which are high over conventional coarse grained Al. In addition, Scanning Probe Microscopy (SPM) image of the indent shows that there is some plastically flown region around the indent suggesting that this nanocrystalline aluminium is ductile.

  15. Characterization of nano-crystalline ZrO{sub 2} synthesized via reactive plasma processing

    Jayakumar, S., E-mail: sjayakumar.physics@gmail.com [Research and Development Centre, Bharathiar University, Coimbatore 641 014 (India); Ananthapadmanabhan, P.V. [Laser and Plasma Technology Division, BARC, Trombay, Mumbai 400 085 (India); Perumal, K. [Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore 641 020 India (India); Thiyagarajan, T.K. [Laser and Plasma Technology Division, BARC, Trombay, Mumbai 400 085 (India); Mishra, S.C. [Department of Metallurgical and Materials Engg, National Institute of Technology, Rourkela 769 008 (India); Su, L.T.; Tok, A.I.Y.; Guo, J. [School of Materials Science and Engg, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639 798 (Singapore)

    2011-07-25

    Highlights: > Direct conversion of micron-sized zirconium hydride powder to nanocrystalline ZrO{sub 2} powder. > The experimental approach uses reactive plasma processing technique. > The product has been characterized by various analytical tools to support the findings. - Abstract: Nano-crystalline ZrO{sub 2} powder has been synthesized via reactive plasma processing. The synthesized ZrO{sub 2} powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and FTIR spectroscopy. The synthesized powder consists of a mixture of tetragonal and monoclinic phases of zirconia. Average crystallite size calculated from the XRD pattern shows that particles with crystallite size 20 nm or less than 20 nm are in tetragonal phase, whereas particles greater than 20 nm are in the monoclinic phase. TEM results show that particles have spherical morphology with maximum percentage of particles distributed in a narrow size from about 15 nm to 30 nm.

  16. Synthesis of nanocrystalline hydroxyapatite by using precipitation method

    Mobasherpour, I.; Heshajin, M. Soulati; Kazemzadeh, A.; Zakeri, M.

    2007-01-01

    In this investigation, hydroxyapatite powder has been synthesized from the calcium nitrate hydrated and di-ammonium hydrogen phosphate solution by precipitation method and heat treatment of hydroxyapatite powders. In order to study the structural evolution, the Fourier transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD) and simultaneous thermal analysis (STA) were used. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to estimate the particle size of the powder and observe the morphology and agglomeration state of the powder. Results show that hydroxyapatite nanocrystalline can successfully be produced by precipitation technique from raw materials. Hydroxyapatite grain gradually increased in size when temperature increased from 100 to 1200 o C, and the hydroxyapatite hexagonal-dipyramidal phase was not transformed to the other calcium phosphates phases up to 1200 o C

  17. Nanocrystalline hydroxyapatite doped with magnesium and zinc: Synthesis and characterization

    Kalita, Samar J. [Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816-2450 (United States)]. E-mail: samar@mail.ucf.edu; Bhatt, Himesh A. [Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816-2450 (United States)

    2007-05-16

    During recent years, there have been efforts in developing nanocrystalline bioceramics, to enhance their mechanical and biological properties for use in tissue engineering applications. In this research, we made an attempt to synthesize nanocrystalline bioactive hydroxyapatite (Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}, HAp) ceramic powder in the lower-end of nano-range (2-10 nm), using a simple low-temperature sol-gel technique and studied its densification behavior. We further studied the effects of metal ion dopants during synthesis on powder morphology, and the properties of the sintered structures. Calcium nitrate and triethyl phosphite were used as precursors for calcium and phosphorous, respectively, for sol-gel synthesis. Calculated quantities of magnesium oxide and zinc oxide were incorporated as dopants into amorphous dried powder, prior to calcination at 250-550 {sup o}C. The synthesized powders were analyzed for their phases using X-ray diffraction technique and characterized for powder morphology and particle size using transmission electron microscopy (TEM). TEM analysis showed that the average particle size of the synthesized powders were in the range of 2-10 nm. The synthesized nano-powders were uniaxially compacted and then sintered at 1250 {sup o}C and 1300 {sup o}C for 6 h, separately, in air. A maximum average sintered density of 3.29 g/cm{sup 3} was achieved in structures sintered at 1300 {sup o}C, developed from nano-powder doped with magnesium. Vickers hardness testing was performed to determine the hardness of the sintered structures. Uniaxial compression tests were performed to evaluate the mechanical properties. Bioactivity and biodegradation behavior of the sintered structures were assessed in simulated body fluid (SBF) and maintained in a dynamic state.

  18. Formation of nanocrystalline TiC from titanium and different carbon sources by mechanical alloying

    Jia Haoling [Key Lab of Liquid Structure and Heredity of Materials, Jingshi Road 73, Jinan 250061, Shandong (China); Zhang Zhonghua [Key Lab of Liquid Structure and Heredity of Materials, Jingshi Road 73, Jinan 250061, Shandong (China)], E-mail: zh_zhang@sdu.edu.cn; Qi Zhen [Key Lab of Liquid Structure and Heredity of Materials, Jingshi Road 73, Jinan 250061, Shandong (China); Liu Guodong [School of Materials Science and Engineering, Shandong University, Jingshi Road 73, Jinan 250061 (China); Bian Xiufang [Key Lab of Liquid Structure and Heredity of Materials, Jingshi Road 73, Jinan 250061, Shandong (China)

    2009-03-20

    In this paper, the formation of nanocrystalline TiC from titanium powders and different carbon resources by mechanical alloying (MA) has been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The experimental results show that nanocrystalline TiC can be synthesized from Ti powders and different carbon resources (activated carbon, carbon fibres or carbon nanotubes) by MA at room temperature. Titanium and different carbon resources have a significant effect on the Ti-C reaction and the formation of TiC during MA. Moreover, the formation of nanocrystalline TiC is governed by a gradual diffusion reaction mechanism during MA, regardless of different carbon resources.

  19. Reinforced plastics and aerogels by nanocrystalline cellulose

    Leung, Alfred C. W.; Lam, Edmond; Chong, Jonathan; Hrapovic, Sabahudin; Luong, John H. T., E-mail: john.luong@cnrc-nrc.gc.ca [National Research Council Canada (Canada)

    2013-05-15

    Nanocrystalline cellulose (NCC), a rigid rod-like nanoscale material, can be produced from cellulosic biomass in powder, liquid, or gel forms by acid and chemical hydrolysis. Owing to its unique and exceptional physicochemical properties, the incorporation of a small amount of NCC into plastic enhances the mechanical strength of the latter by several orders of magnitudes. Carbohydrate-based NCC poses no serious environmental concerns, providing further impetus for the development and applications of this green and renewable biomaterial to fabricate lightweight and biodegradable composites and aerogels. Surface functionalization of NCC remains the main focus of NCC research to tailor its properties for dispersion in hydrophilic or hydrophobic media. It is of uttermost importance to develop tools and protocols for imaging of NCC in a complex matrix and quantify its reinforcement effect.

  20. Study of the sintering behavior of fine, ultrafine and nanocrystalline WC-CO mixtures obtained by high energy milling

    Salvador, M. D.; Bonache, V.; Amigo, V.; Busquets, D.

    2008-01-01

    In this work the sintering behaviour of fine, ultrafine and nanocrystalline WC-12Co mixtures obtained by high energy milling, as well commercial nano powders, have been studied, in order to evaluate the effect of the particle size and the powder processing, in the densification, microstructural development and mechanical properties of the final product. The consolidation of the mixtures has been made by uniaxial pressing and sintering in vacuum, and by hot isostatic pressing. The sintered materials have been evaluated by measures of density, hardness and indentation fracture toughness, and micro structurally characterized by optical microscopy and scanning and transmission electronic microscopy (SEM and TEM). The results show the improvements in resistant behaviour of the materials obtained from nanocrystalline powders, in spite of the grain growth experienced during the sintering. The best results were obtained for the milling nanocrystalline material, which presents values of hardness higher than 180 HV. (Author) 46 refs

  1. Synthesis of nanocrystalline fluorinated hydroxyapatite

    Fluorinated hydroxyapatite; nanocrystalline; microwave synthesis; dissolution. ... HA by the presence of other ions such as carbonate, magnesium, fluoride, etc. ... Fourier transform infrared spectroscopy (FT–IR) and laser Raman spectroscopy.

  2. Structure and soft magnetic properties of the bulk samples prepared by compaction of the mixtures of Co-based and Fe-based powders

    Fuezer, J.; Bednarcik, J.; Kollar, P.; Roth, S.

    2007-01-01

    Ball milling of CoFeZrB ribbons and subsequent compaction of the resulting powders were used to prepare bulk amorphous samples. Further, two sets of powder samples were prepared by cryomilling of FeCuNbMoSiB alloy in amorphous and nanocrystalline state. Amorphous and nanocrystalline FeCuNbMoSiB powders were blended with CoFeZrB powder at different concentrations. Such powder mixtures were consolidated and several bulk nanocomposites have been synthesized. An addition of nanocrystalline or amorphous FeCuNbMoSiB powder to amorphous CoFeZrB powder caused a decrease of the magnetostriction of the resultant bulk samples, while the coercivity shows an opposite behavior. Our results show that the powder consolidation by hot pressing is an alternative method for the preparation of bulk metallic glasses, which are difficult to prepare by casting methods

  3. The structure of denisovite, a fibrous nanocrystalline polytypic disordered `very complex' silicate, studied by a synergistic multi-disciplinary approach employing methods of electron crystallography and X-ray powder diffraction

    Ira V. Rozhdestvenskaya

    2017-05-01

    Full Text Available Denisovite is a rare mineral occurring as aggregates of fibres typically 200–500 nm diameter. It was confirmed as a new mineral in 1984, but important facts about its chemical formula, lattice parameters, symmetry and structure have remained incompletely known since then. Recently obtained results from studies using microprobe analysis, X-ray powder diffraction (XRPD, electron crystallography, modelling and Rietveld refinement will be reported. The electron crystallography methods include transmission electron microscopy (TEM, selected-area electron diffraction (SAED, high-angle annular dark-field imaging (HAADF, high-resolution transmission electron microscopy (HRTEM, precession electron diffraction (PED and electron diffraction tomography (EDT. A structural model of denisovite was developed from HAADF images and later completed on the basis of quasi-kinematic EDT data by ab initio structure solution using direct methods and least-squares refinement. The model was confirmed by Rietveld refinement. The lattice parameters are a = 31.024 (1, b = 19.554 (1 and c = 7.1441 (5 Å, β = 95.99 (3°, V = 4310.1 (5 Å3 and space group P12/a1. The structure consists of three topologically distinct dreier silicate chains, viz. two xonotlite-like dreier double chains, [Si6O17]10−, and a tubular loop-branched dreier triple chain, [Si12O30]12−. The silicate chains occur between three walls of edge-sharing (Ca,Na octahedra. The chains of silicate tetrahedra and the octahedra walls extend parallel to the z axis and form a layer parallel to (100. Water molecules and K+ cations are located at the centre of the tubular silicate chain. The latter also occupy positions close to the centres of eight-membered rings in the silicate chains. The silicate chains are geometrically constrained by neighbouring octahedra walls and present an ambiguity with respect to their z position along these walls, with displacements between neighbouring layers being

  4. Uniting Electron Crystallography and Powder Diffraction

    Shankland, Kenneth; Meshi, Louisa; Avilov, Anatoly; David, William

    2012-01-01

    The polycrystalline and nanocrystalline states play an increasingly important role in exploiting the properties of materials, encompassing applications as diverse as pharmaceuticals, catalysts, solar cells and energy storage. A knowledge of the three-dimensional atomic and molecular structure of materials is essential for understanding and controlling their properties, yet traditional single-crystal X-ray diffraction methods lose their power when only polycrystalline and nanocrystalline samples are available. It is here that powder diffraction and single-crystal electron diffraction techniques take over, substantially extending the range of applicability of the crystallographic principles of structure determination.  This volume, a collection of teaching contributions presented at the Crystallographic Course in Erice in 2011, clearly describes the fundamentals and the state-of-the-art of powder diffraction and electron diffraction methods in materials characterisation, encompassing a diverse range of discipl...

  5. Effect of degassing temperature on the microstructure of a nanocrystalline Al-Mg alloy

    Ahn, Byungmin; Newbery, A. Piers; Lavernia, Enrique J.; Nutt, Steven R.

    2007-01-01

    The microstructural evolution of a nanocrystalline Al-Mg alloy was investigated to determine the effects of degassing temperature. Al 5083 powder was ball-milled in liquid nitrogen to obtain a nanocrystalline structure, then vacuum degassed to remove contaminants. The degassed powder was consolidated by cold isostatic pressing and then forged to produce bulk, low-porosity material. The material microstructure was analyzed at different stages using optical microscopy, transmission electron microscopy, and density measurements. The impurity concentration of the final product was also measured. The forged material exhibited a bimodal grain size distribution, consisting of both ultra fine and coarse grains. The bimodal distribution was attributed to the presence of residual coarse grains in the as-milled powder. Higher degassing temperatures resulted in higher density values and lower hydrogen content in the consolidated materials, although these materials also exhibited more extensive grain growth

  6. Rapid rate sintering of nanocrystalline ZrO2-3 mol% Y2O3

    Chen, D.J.; Mayo, M.J.

    1996-01-01

    Conventional ramp-and-hold sintering with a wide range of heating rates was conducted on submicrometer and nanocrystalline ZrO 2 -3 mol% Y 2 O 3 powder compacts. Although rapid heating rates have been reported to produce high density/fine grain size products for many submicrometer and smaller starting powders, the application of this technique to ZrO 2 -3 mol% Y 2 O 3 produced mixed results. In the case of submicrometer ZrO 2 -3 mol% Y 2 O 3 , neither densification nor grain growth was affected by the heating rate used. In the case of nanocrystalline ZrO 2 -3 mol% Y 2 O 3 , fast heating rates severely retarded densification and had a minimal effect on grain growth. The large adverse effect of fast heating rates on the densification of the nanocrystalline powder was traced to a thermal gradient/differential densification effect. Microstructural evidence suggests that the rate of densification greatly exceeded the rate of heat transfer in this material; consequently, the sample interior was not able to densify before being geometrically constrained by a fully dense shell which formed at the sample exterior. This finding implies that rapid rate sintering will meet severe practical constraints in the manufacture of bulk nanocrystalline ZrO 2 -3 mol% Y 2 O 3 specimens

  7. Preparation, characterization and luminescence of nanocrystalline Y2O3:Ho

    Biljan, Tomislav; Gajovic, Andreja; Meic, Zlatko; Mestrovic, Ernest

    2007-01-01

    Nanocrystalline Y 2 O 3 :Ho was synthesized by solution combustion method with ethylene glycol as fuel. Material was characterized using powder X-ray diffraction and transmission electron microscopy (TEM). X-ray diffraction and TEM showed that the material is nanostructured. Luminescence properties were studied using Raman spectrometers with excitation in near infrared (NIR) and visible regions. The visible and NIR luminescence spectra of nanocrystalline Y 2 O 3 :Ho show some important differences from those of bulk material. The convenience of using Raman instruments for studying luminescence of lanthanide ions is demonstrated

  8. Developments in nanocrystalline magnetic alloys for industry; Alliages magnetiques nanocristallins industriels. Etat de l'art et evolution

    Waeckerle, T.; Cremer, P. [Imphy Ugine Precision, 92 - Paris la Defense (France); Gautard, D. [Mecagis, 45 - Amilly (France)

    2003-10-01

    The French industrial production of nanocrystalline precursor ribbon (Imphy Ugine Precision - IUP) and nanocrystalline wound cores (Mecagis) is now mature, promoting then one of the first worldwide provider in this market. Recent progress in ribbon elaboration will provide large increase of industrial efficiency, leading the cost of a nanocrystalline solution to be closed to the cost of a ferrite solution. The precise study and control of magnetoelastic energy allowed the production scattering to be reduced, the alloy to be weakly dependant on external stresses (production, packaging, thermal dilatation), further promoting the performances. Whatever the alloy is very brittle in the nanocrystalline state, some improvements are using or are going around this intrinsic behaviour, and are now developed: powder core for low dissipative filtering, cut core for storage and strong power transformation, wound cores from ribbon nano-crystallized with high stresses during annealing, for the storage and current metering. (authors)

  9. XRD and HREM studies of nanocrystalline Cu and Pd

    Nieman, G.W.; Weertmen, J.R.; Siegel, R.W.

    1991-01-01

    Consolidated powders of nanocrystalline Cu and Pd have been studied by x-ray diffraction (XRD) and high resolution electron microscopy (HREM) as part of an investigation of the mechanical behavior of nanocrystalline pure metals. XRD line broadening measurements were made to estimate rain size, qualitative grain size distribution and average long range strains in a number of samples. Mean grain sized range from 4-60 nm and have qualitatively narrow grain size distributions. Long range lattice strains are of the order of 0.2-3% in consolidated samples. These strains apparently persist and even increase in Cu samples after annealing at 0.35 Tm (498K) for 2h, accompanied by an apparent increase in grain size of ≥2x. Grain size, grain size distribution width and internal strains vary somewhat among samples produced under apparently identical processing conditions. HREM studies show that twins, stacking faults and low-index facets are abundant in as-consolidated nanocrystalline Cu samples. In this paper methodology, results and analysis of XRD and HREM experiments are presented

  10. Transformation of Goethite to Hematite Nanocrystallines by High Energy Ball Milling

    O. M. Lemine

    2014-01-01

    Full Text Available α-Fe2O3 nanocrystallines were prepared by direct transformation via high energy ball milling treatment for α-FeOOH powder. X-ray diffraction, Rietveld analysis, TEM, and vibrating sample magnetometer (VSM are used to characterize the samples obtained after several milling times. Phase identification using Rietveld analysis showed that the goethite is transformed to hematite nanocrystalline after 40 hours of milling. HRTEM confirm that the obtained phase is mostly a single-crystal structure. This result suggested that the mechanochemical reaction is an efficient way to prepare some iron oxides nanocrystallines from raw materials which are abundant in the nature. The mechanism of the formation of hematite is discussed in text.

  11. Microstructure characterization of nanocrystalline TiC synthesized by mechanical alloying

    Ghosh, B.; Pradhan, S.K.

    2010-01-01

    Nanocrystalline TiC is produced by mechanical milling the stoichiometric mixture of α-Ti and graphite powders at room temperature under argon atmosphere within 35 min of milling through a self-propagating combustion reaction. Microstructure characterization of the unmilled and ball-milled samples was done by both X-ray diffraction and electron microscopy. It reveals the fact that initially graphite layers were oriented along and in the course of milling, thin graphite layers were distributed evenly among the grain boundaries of α-Ti particles. Both α-Ti and TiC lattices contain stacking faults of different kinds. The grain size distribution obtained from the Rietveld's method and electron microscopy studies ensure that nanocrystalline TiC particles with almost uniform size (∼13 nm) can be prepared by mechanical alloying technique. The result obtained from X-ray analysis corroborates well with the microstructure characterization of nanocrystalline TiC by electron microscopy.

  12. Nanocrystalline Al-based alloys - lightweight materials with attractive mechanical properties

    Latuch, J; Cieslak, G; Dimitrov, H; Krasnowski, M; Kulik, T

    2009-01-01

    In this study, several ways of bulk nanocrystalline Al-based alloys' production by high-pressure compaction of powders were explored. The effect of chemical composition and compaction parameters on the structure, quality and mechanical properties of the bulk samples was studied. Bulk nanocrystalline Al-Mm-Ni-(Fe,Co) alloys were prepared by ball-milling of amorphous ribbons followed by consolidation. The maximum microhardness (540 HV0.1) was achieved for the samples compacted at 275 deg. C under 7.7 GPa (which resulted in an amorphous bulk) and nanocrystallised at 235 deg. C for 20 min. Another group of the produced materials were bulk nanocrystalline Al-Si-(Ni,Fe)-Mm alloys obtained by ball-milling of nanocrystalline ribbons and consolidation. The hardness of these samples achieved the value five times higher (350HV) than that of commercial 4xxx series Al alloys. Nanocrystalline Al-based alloys were also prepared by mechanical alloying followed by hot-pressing. In this group of materials, there were Al-Fe alloys containing 50-85 at.% of Al and ternary or quaternary Al-Fe-(Ti, Si, Ni, Mg, B) alloys. Microhardness of these alloys was in the range of 613 - 1235 HV0.2, depending on the composition.

  13. Barium strontium titanate powders prepared by spray pyrolysis

    Brankovic, G.; Brankovic, Z.; Goes, M.S.; Paiva-Santos, C.O.; Cilense, M.; Varela, J.A.; Longo, E.

    2005-01-01

    Ultasonic spray pyrolysis (SP) has been investigated for the production of the barium strontium titanate (BST) powders from the polymeric precursors. The processing parameters, such as flux of aerosol and temperature profile inside the furnace, were optimized to obtain single phase BST. The powders were characterized by the methods of X-ray diffraction analysis, SEM, EDS and TEM. The obtained powders were submicronic, consisting of spherical, polycrystalline particles, with internal nanocrystalline structure. Crystallite size of 10 nm, calculated using Rietveld refinement, is in a good agreement with results of HRTEM

  14. Nanocrystalline diamond films for biomedical applications

    Pennisi, Cristian Pablo; Alcaide, Maria

    2014-01-01

    Nanocrystalline diamond films, which comprise the so called nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD), represent a class of biomaterials possessing outstanding mechanical, tribological, and electrical properties, which include high surface smoothness, high corrosion...... performance of nanocrystalline diamond films is reviewed from an application-specific perspective, covering topics such as enhancement of cellular adhesion, anti-fouling coatings, non-thrombogenic surfaces, micropatterning of cells and proteins, and immobilization of biomolecules for bioassays. In order...

  15. Strength and structure of nanocrystalline titanium

    Noskova, N.I.; Pereturina, I.A.; Elkina, O.A.; Stolyarov, V.V.

    2004-01-01

    Investigation results on strength and plasticity of nanocrystalline titanium VT-1 are presented. Specific features of plastic deformation on tension of this material specimens in an electron microscope column are studied in situ. It is shown that nanocrystalline titanium strength and plasticity at room temperature are dependent on the structure and nanograin size. It is revealed that deformation processes in nanocrystalline titanium are characterized by activation of deformation rotational modes and microtwinning [ru

  16. (YSZ) powders

    Unknown

    109–114. © Indian Academy of Sciences. 109 ... Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400 085, India .... pensions of 900°C calcined YSZ powders. .... The sintered density data of the compacts (sintered at.

  17. Synthesis of yttria powders by electrospray pyrolysis

    Rulison, A.J.; Flagan, R.C.

    1994-01-01

    Electrospray atomization of high-concentration (∼400 g/L) chemical precursor solutions was applied to the synthesis of yttria powders. Conditions were found which led to high-quality powders, composed of dense, spheroidal, submicrometer, and nanocrystalline oxide particles. The precursor solutions were hydrated yttrium nitrates dissolved in n-propyl alcohol at concentrations ranging from 44.1 to 455 g/L. Electrospray atomization produced submicrometer precursor droplets which were dispersed in air and carried through an electric furnace for thermal decomposition at 500 C for several seconds residence time. X-ray powder diffraction patterns indicated the expected cubic phase. Transmission electron micrographs showed that the particle structure varied with solution composition, ranging from hollow, inflated spheres for 6-hydrated nitrates to dense spheroids for 5-hydrated nitrates. The use of 6-hydrated nitrates in the solutions appeared to form particle surfaces which were impermeable to alcohol vapor evolved during thermal decomposition, leading to hollow, inflated spheres

  18. Grain growth in ultrafine titanium powders during sintering

    Panigrahi, B.B.; Godkhindi, M.M.

    2006-01-01

    Grain growth behaviour of fine (∼3 μm) and attrition milled nanocrystalline (∼32 nm) titanium powers during sintering have been studied. The activation energies of grain growth (Q g ) in fine titanium were found to be 192.9 and 142.4 kJ/mol at lower and higher temperature ranges, respectively. The nanocrystalline titanium showed very low values of Q g (54.6 kJ/mol) at lower temperatures and it increased to 273.2 kJ/mol at higher temperatures. The constant (n) in nano Ti system was found to have unusually very high values of 6.5-8.2. The grain boundary rotation along with the diffusional processes could be the grain growth mechanism in nanocrystalline and in fine titanium powders

  19. Nanocrystalline diamond coatings for machining

    Frank, M.; Breidt, D.; Cremer, R. [CemeCon AG, Wuerselen (Germany)

    2007-07-01

    This history of CVD diamond synthesis goes back to the fifties of the last century. However, the scientific and economical potential was only gradually recognized. In the eighties, intensive worldwide research on CVD diamond synthesis and applications was launched. Industrial products, especially diamond-coated cutting tools, were introduced to the market in the middle of the nineties. This article shows the latest developments in this area, which comprises nanocrystalline diamond coating structures. (orig.)

  20. Mechanochemical synthesis of nanocrystalline Fe and Fe–B magnetic alloys

    Mohammadi, Majid; Ghasemi, Ali; Tavoosi, Majid

    2016-01-01

    Mechanochemical synthesis and magnetic characterization of nanocrystalline Fe and Fe–B magnetic alloys was the goal of this study. In this regard, different Fe_2O_3–B_2O_3 powder mixtures with sufficient amount of CaH_2 were milled in a planetary ball mill in order to produce nanocrystalline Fe, Fe_9_5B_5 and Fe_8_5B_1_5 alloys. The produced samples were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results showed that, nanocrystalline Fe, Fe_9_5B_5 and Fe_8_5B_1_5 alloys can be successfully synthesized by the reduction reaction of Fe_2O_3 and B_2O_3 with CaH_2 during mechanical alloying. The structure of produced Fe_9_5B_5 and Fe_8_5B_1_5 alloys was a combination of Fe and Fe_2B phases with average crystallite sizes of about 15 and 10 nm, respectively. The produced nanocrystalline alloys exhibited soft magnetic properties with the coercivity and saturation of magnetization in the range of 170–240 Oe and 9–28 emu/g, respectively. Increasing the boron content has a destructive effect on soft magnetic properties of Fe–B alloys. - Highlights: • We study the mechanochemical synthesis of nanocrystalline boron, Fe and Fe–B alloys. • We study the reduction reaction of B_2O_3–CaH_2 during milling. • We study the reduction reaction of Fe_2O_3–CaH_2 during milling. • We study the reduction reaction of Fe_2O_3–B_2O_3–CaH_2 during milling. • We study the effect of B on magnetic properties of nanocrystalline Fe–B alloys.

  1. Powder diffraction

    Hart, M.

    1995-12-31

    the importance of x-ray powder diffraction as an analytical tool for phase identification of materials was first pointed out by Debye and Scherrer in Germany and, quite independently, by Hull in the US. Three distinct periods of evolution lead to ubiquitous application in many fields of science and technology. In the first period, until the mid-1940`s, applications were and developed covering broad categories of materials including inorganic materials, minerals, ceramics, metals, alloys, organic materials and polymers. During this formative period, the concept of quantitative phase analysis was demonstrated. In the second period there followed the blossoming of technology and commercial instruments became widely used. The history is well summarized by Parrish and by Langford and Loueer. By 1980 there were probably 10,000 powder diffractometers in routine use, making it the most widely used of all x-ray crystallographic instruments. In the third, present, period data bases became firmly established and sophisticated pattern fitting and recognition software made many aspects of powder diffraction analysis routine. High resolution, tunable powder diffractometers were developed at sources of synchrotron radiation. The tunability of the spectrum made it possible to exploit all the subtleties of x-ray spectroscopy in diffraction experiments.

  2. Powder diffraction

    Hart, M.

    1995-01-01

    The importance of x-ray powder diffraction as an analytical tool for phase identification of materials was first pointed out by Debye and Scherrer in Germany and, quite independently, by Hull in the US. Three distinct periods of evolution lead to ubiquitous application in many fields of science and technology. In the first period, until the mid-1940's, applications were and developed covering broad categories of materials including inorganic materials, minerals, ceramics, metals, alloys, organic materials and polymers. During this formative period, the concept of quantitative phase analysis was demonstrated. In the second period there followed the blossoming of technology and commercial instruments became widely used. The history is well summarized by Parrish and by Langford and Loueer. By 1980 there were probably 10,000 powder diffractometers in routine use, making it the most widely used of all x-ray crystallographic instruments. In the third, present, period data bases became firmly established and sophisticated pattern fitting and recognition software made many aspects of powder diffraction analysis routine. High resolution, tunable powder diffractometers were developed at sources of synchrotron radiation. The tunability of the spectrum made it possible to exploit all the subtleties of x-ray spectroscopy in diffraction experiments

  3. Powder diffractometry

    Doucet, J.

    1983-01-01

    The new possibilities openned by the synchrotron radiation in the powder diffractometry techniques are presented. This technique is described in a general manner and some aspects which can be developed with the use of the synchrotron radiation are analyzed. (L.C.) [pt

  4. Nanocrystalline functional materials and nanocomposites synthesis through aerosol routes

    Milošević Olivera B.

    2003-01-01

    Full Text Available This paper represents the results of the design of functional nanocrystalline powders and nanocomposites using chemical reactions in aerosols. The process involves ultrasonic aerosol formation (mist generators with the resonant frequencies of 800 kHz, 1.7 and 2.5 MHz from precursor salt solutions and control over the aerosol decomposition in a high-temperature tubular flow reactor. During decomposition, the aerosol droplets undergo evaporation/drying, precipitation and thermolysis in a single-step process. Consequently, spherical, solid, agglomerate-free submicronic particles are obtained. The particle morphology, revealed as a composite structure consisting of primary crystallites smaller than 20 nm was analysed by several methods (XRD, DSC/DTA, SEM, TEM and discussed in terms of precursor chemistry and process parameters. Following the initial attempts, a more detailed aspect of nanocrystalline particle synthesis was demonstrated for the case of nanocomposites based on ZnO-MeO (MeO=Bi Cr+, suitable for electronic applications, as well as an yttrium-aluminum base complex system, suitable for phosphorus applications. The results imply that parts of the material structure responsible for different functional behaviour appear through in situ aerosol synthesis by processes of intraparticle agglomeration, reaction and sintering in the last synthesis stage.

  5. Mechanically alloyed PrFeB nanocrystalline magnets

    Kaszuwara, W.; Leonowicz, M.

    1998-01-01

    Mechanically alloyed PrFeB nanocrystalline magnets were prepared by extensive ball milling of Pr, Fe and Fe 80 B 20 powders, followed by diffusion annealing. After milling, the material consisted of nanocrystalline α-Fe crystallites embedded in amorphous Pr-rich matrix. Thermomagnetic and calorimetric investigations of the transformations which occurred during annealing showed that the amorphous phase crystallised at 240 C, leading to the formation of crystalline Pr having lattice constants 10% greater than those shown in the ASTM data. This fact indicated that mechanical alloying and low temperature annealing led to the formation of a solid solution of either Fe or B in Pr, which does not exist in the equilibrium state. The Pr 2 Fe 14 B phase was subsequently formed within a temperature range of 420-620 C. The magnetic properties of magnets depend on the phase structure and grain size. Milling time appears to be a decisive processing parameter for the tailoring of the magnetic properties. Depending on the phase structure, the coercivities varied from 100 to 1200 kA/m and, respectively, the remanences from 0.98 T to 0.6 T. The highest maximum energy product was 80 kJ/m 3 . (orig.)

  6. Dynamic recovery in nanocrystalline Ni

    Sun, Z.; Van Petegem, S.; Cervellino, A.; Durst, K.; Blum, W.; Van Swygenhoven, H.

    2015-01-01

    The constant flow stress reached during uniaxial deformation of electrodeposited nanocrystalline Ni reflects a quasi-stationary balance between dislocation slip and grain boundary (GB) accommodation mechanisms. Stress reduction tests allow to suppress dislocation slip and bring recovery mechanisms into the foreground. When combined with in situ X-ray diffraction it can be shown that grain boundary recovery mechanisms play an important role in producing plastic strain while hardening the microstructure. This result has a significant consequence for the parameters of thermally activated glide of dislocations, such as athermal stress and activation volume, which are traditionally derived from stress/strain rate change tests

  7. The electrochemical characteristics of Mg2Ni nanocrystalline hydrogen storage alloy

    Zhang Ling; Zhou Xiaosong; Peng Shuming

    2008-06-01

    The nanocrystalline Mg 2 Ni materials were prepared by mechanical alloying. The cyclic voltametry results indicated that the potential of oxidation peak was shift as the scan rate increased and the absorption property of Mg 2 Ni prepared by mechanical alloying was increased even at ambient temperature. The absorption and desorption of hydrogen in Mg 2 Ni alloy were remarkably accelerated with the rising temperature. Small angel X-ray scattering results indicated that the Mg 2 Ni powder have 1-5 nm and 5-10 nm particle size distribution, which increased the acting sites of hydrogen absorption/desorption reaction and decreased the diffusion path of hydrogen desorption. It was induced to the enhanced performance of Mg 2 Ni nanocrystalline powder. The cycle life investigated results indicated that the activation property of Mg 2 Ni nanocrystal-line hydrogen storage alloy electrode was excellent, the capacitance maintenance ration was 66% after 200 cycles. The coating of epoxy resin on one side of the electrode had no effect on the activation property and the capacitance maintenance ration was better than the uncoating one. But the anode peak current value and the cathodic peak current value were decreased remarkably which indicated that the hydrogen absorption/desorption rate and the charge/discharge degree had decreased. (authors)

  8. Nanocrystalline CdSnO3 Based Room Temperature Methanol Sensor

    Shanabhau BAGUL

    2017-04-01

    Full Text Available Synthesis of nanocrystalline CdSnO3 powder by ultrasonic atomizer assisted wet chemical method is reported in this paper. Synthesized CdSnO3 powder was characterized by X-Ray Diffraction (XRD, Field Emission Scanning Electron Microscopy (FESEM and Transmission Electron Microscopy (TEM to examine phase and microstructure. FESEM and TEM analysis reveals that the CdSnO3 powder prepared here is porous monodisperse nanocrystalline in nature, with average particle size of approximately 17 nm or smaller. The material is also characterized by UV-Visible and Photoluminescence (PL spectroscopy. Thick films of synthesized CdSnO3 powder fired at 850 0C are made by using screen printing method. The films surface is modified by using dipping method. CuCl2 (0.005 M dipped (for 2 min thick film shows high response (R= 477 to 100 ppm methanol at room temperature (35 0C. The sensor shows good selectivity and fast response recovery time to methanol. The excellent methanol sensing performance, particularly high response values is observed to be mainly due to porous CdSnO3 surface.

  9. Aqueous slip casting of MgAl2O4 spinel powder

    The reaction proceeds by counter diffusion of the cations through the product layer, .... tain powders, such as Ube E10 silicon nitride Starck, B10 silicon carbide .... 779 kg/mm2 for a nanocrystalline dense MAS consolidated by aqueous slip ...

  10. Study of the sintering behavior of fine, ultrafine and nanocrystalline WC-CO mixtures obtained by high energy milling; Estudio del comportamiento durante la sinterizacion de mezclas WC-Co finas, ultrafinas y nanocristalinas obtenidas por molienda de alta energia

    Salvador, M. D.; Bonache, V.; Amigo, V.; Busquets, D.

    2008-07-01

    In this work the sintering behaviour of fine, ultrafine and nanocrystalline WC-12Co mixtures obtained by high energy milling, as well commercial nano powders, have been studied, in order to evaluate the effect of the particle size and the powder processing, in the densification, microstructural development and mechanical properties of the final product. The consolidation of the mixtures has been made by uniaxial pressing and sintering in vacuum, and by hot isostatic pressing. The sintered materials have been evaluated by measures of density, hardness and indentation fracture toughness, and micro structurally characterized by optical microscopy and scanning and transmission electronic microscopy (SEM and TEM). The results show the improvements in resistant behaviour of the materials obtained from nanocrystalline powders, in spite of the grain growth experienced during the sintering. The best results were obtained for the milling nanocrystalline material, which presents values of hardness higher than 180 HV. (Author) 46 refs.

  11. Microstructure and physical properties of laser Zn modified amorphous-nanocrystalline coating on a titanium alloy

    Li, Jia-Ning; Gong, Shui-Li; Shi, Yi-Ning; Suo, Hong-Bo; Wang, Xi-Chang; Deng, Yun-Hua; Shan, Fei-Hu; Li, Jian-Quan

    2014-02-01

    A Zn modified amorphous-nanocrystalline coating was fabricated on a Ti-6Al-4V alloy by laser cladding of the Co-Ti-B4C-Zn-Y2O3 mixed powders. Such coating was researched by means of a scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM), etc. Experimental results indicated that the Co5Zn21 and TiB2 nanocrystalline phases were produced through in situ metallurgical reactions, which blocked the motion of dislocation, and TiB2 grew along (010), (111) and (024). The Co5Zn21 nanocrystals were produced attached to the ceramics, which mainly consisted of the Co nanoparticles embedded in a heterogeneous zinc, and had varied crystalline orientations.

  12. Development of amorphous and nanocrystalline Al65Cu35-xZrx alloys by mechanical alloying

    Manna, I.; Chattopadhyay, P.P.; Banhart, F.; Fecht, H.J.

    2004-01-01

    Mechanical alloying of Al 65 Cu 35-x Zr x (x=5, 15 and 25 at.% Zr) elemental powder blends by planetary ball milling up to 50 h yields amorphous and/or nanocrystalline products. Microstructure of the milled product at different stages of milling has been characterized by X-ray diffraction, (XRD) high-resolution transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Among the different alloys synthesized by mechanical alloying, Al 65 Cu 20 Zr 15 yields a predominantly amorphous product, while the other two alloys develop a composite microstructure comprising nanocrystalline and amorphous solid solutions in Al 65 Cu 10 Zr 25 and nano-intermetallic phase/compound in Al 65 Cu 30 Zr 5 , respectively. The genesis of solid-state amorphization in Al 65 Cu 20 Zr 15 and Al 65 Cu 10 Zr 25 is investigated

  13. Coercivities of hot-deformed magnets processed from amorphous and nanocrystalline precursors

    Tang, Xin; Sepehri-Amin, H.; Ohkubo, T.; Hioki, K.; Hattori, A.; Hono, K.

    2017-01-01

    Hot-deformed magnets have been processed from amorphous and nanocrystalline precursors and their hard magnetic properties and microstructures have been investigated in order to explore the optimum process route. The hot-deformed magnets processed from an amorphous precursor exhibited the coercivity of 1.40 T that is higher than that processed from nanocrystalline powder, ∼1.28 T. The average grain size was larger in the magnets processed from amorphous precursor. Detailed microstructure analyses by aberration corrected scanning transmission electron microscopy revealed that the Nd + Pr concentrations in the intergranular phases were higher in the hot-deformed magnet processed from the amorphous precursor, which is considered to lead to the enhanced coercivity due to a stronger pinning force against magnetic domain wall motion.

  14. Evaluation of biological activities of nanocrystalline zirconia synthesis via combustion method

    Thakare, V.G.; Omanwar, S.K.; Bhatkar, V.B.; Wadegaokar, P.A.

    2016-01-01

    The objective of the following study was synthesis of nanocrystalline zirconia by modified solution combustion synthesis method and evaluation of its structural and biological properties. The sample was characterized by powder X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and evaluated for cytotoxicity study using 3T3 mouse fibroblast cells, the antibacterial property are investigated by spread plate method against E. coli bacterial pathogen and studied for degradation using phosphate buffered saline (PBS) solution. The XRD pattern shows that the monoclinic phase of nanocrystalline zirconia was obtained. The FESEM images showed that the prepared sample consists of particles in the range of 45 nm and homogenous particle size distribution. The sample of zirconia has excellent tissue biocompatibility and does not show any toxicity towards normal 3T3 mouse fibroblast cells. It also inhibited the bacterial growth. The sample shows stability at physiological condition and does not show degradation. (author)

  15. Bilirubin adsorption on nanocrystalline titania films

    Yang Zhengpeng; Si Shihui; Fung Yingsing

    2007-01-01

    Bilirubin produced from hemoglobin metabolism and normally conjugated with albumin is a kind of lipophilic endotoxin, and can cause various diseases when its concentration is high. Bilirubin adsorption on the nanocrystalline TiO 2 films was investigated using quartz crystal microbalance, UV-vis and IR techniques, and factors affecting its adsorption such as pH, bilirubin concentration, solution ionic strength, temperature and thickness of TiO 2 films were discussed. The amount of adsorption and parameters for the adsorption kinetics were estimated from the frequency measurements of quartz crystal microbalance. A fresh surface of the nanocrystalline TiO 2 films could be photochemically regenerated because holes and hydroxyl radicals were generated by irradiating the nanocrystalline TiO 2 films with UV light, which could oxidize and decompose organic materials, and the nanocrystalline TiO 2 films can be easily regenerated when it is used as adsorbent for the removal of bilirubin

  16. Powder technology

    Agueda, Horacio

    1989-01-01

    Powder technology is experiencing nowadays a great development and has broad application in different fields: nuclear energy, medicine, new energy sources, industrial and home artifacts, etc. Ceramic materials are of daily use as tableware and also in the building industry (bricks, tiles, etc.). However, in machine construction its utilization is not so common. The same happens with metals: powder metallurgy is employed less than traditional metal forming techniques. Both cases deal with powder technology and the forming techniques as far as the final consolidation through sintering processes are very similar. There are many different methods and techniques in the forming stage: cold-pressing, slip casting, injection molding, extrusion molding, isostatic pressing, hot-pressing (which involves also the final consolidation step), etc. This variety allows to obtain almost any desired form no matter how complex it could be. Some applications are very specific as in the case of UO 2 pellets (used as nuclear fuels) but with the same technique and other materials, it is possible to manufacture a great number of different products. This work shows the characteristics and behaviour of two magnetic ceramic materials (ferrites) fabricated in the laboratory of the Applied Research Division of the Bariloche Atomic Center for different purposes. Other materials and products made with the same method are also mentioned. Likewise, densities and shrinkage obtained by different methods of forming (cold-pressing, injection molding, slip casting and extrusion molding) using high-purity alumina (99.5% Al 2 O 3 ). Finally, different applications of such methods are given. (Author) [es

  17. Synthesis and luminescence properties of nanocrystalline LiF:Mg,Cu,P phosphor

    Sahare, P.D., E-mail: pdsahare@physics.du.ac.i [Department of Physics and Astrophysics, University of Delhi, Delhi 110 007 (India); Bakare, J.S. [SSGM College of Engineering, Amravati University, Shegaon 444 203, Maharashtra (India); Dhole, S.D. [Department of Physics, University of Pune, Ganeshkhind, Pune 411 007 (India); Ingale, N.B. [Department of Physics, Professor Ram Meghe Institute of Technology and Research, Badnera-Amravati 444 605, Maharashtra (India); Rupasov, A.A. [P. N. Lebedev Physical Institute, Russian Academy of Sciences, Leninsky pr-t 53, Moscow (Russian Federation)

    2010-02-15

    Nanocrystalline LiF:Mg,Cu,P phosphor material of different shapes and sizes (microcrystalline cubic shape, nanorod shape and nanocrystalline cubical shaped) have been prepared by the chemical co-precipitation method. Thermoluminescence (TL) and other dosimetric characteristics of the phosphor are studied and presented here. The formation of the materials was confirmed by the X-ray diffraction (XRD). Its shapes and sizes were also observed using scanning electron microscope (SEM). The TL glow curve of the microcrystalline powder shows a prominent single peak at 408 K along with another peak of lesser intensity at around 638 K. On the contrary, the nanocrystalline rod shaped particles show a peak of low intensity at 401 K and a prominent peak around 700 K while the nanocrystalline particles in cubical shapes again show two peaks, one at around 407 K and the other at around 617 K, of which the lower temperature (407 K) peak is more prominent. The glow curve structure changes at very high doses (100 kRad) and some new peaks appear at around 525 and 637 K also the first peak appearing at around 401 K becomes prominent. The observed changes in TL due to the change in the shape and sizes of the nanophosphor have been reported. The PL has also been studied and various excitation and emission peaks observed due to the presence of various impurities are explained. The observed results have been explained in the light of asymmetrical crystal field effects due to asymmetrical shapes of the nanocrystalline phosphor. The comparison of these properties with the microcrystalline material prepared by the same co-precipitation method is also done.

  18. Combustion synthesis and photoluminescence in novel red emitting yttrium gadolinium pyrosilicate nanocrystalline phosphor

    Hedaoo, V.P., E-mail: vraikwar@rediffmail.com [Department of Physics, R. J. College, Ghatkopar, Mumbai, MS 400086 (India); Bhatkar, V.B. [Department of Physics, Shri Shivaji Science College, Amravati, MS 444602 (India); Omanwar, S.K. [Department of Physics, SGB Amravati University, Amravati, MS 444602 (India)

    2016-07-05

    Yttrium Gadolinium Pyrosilicate Y{sub 2-x}Gd{sub x}Si{sub 2}O{sub 7}:Eu{sup 3+} (x = 0.05, 0.10, 0.15) phosphor powder was prepared by facile and time efficient modified combustion method for the first time. The phosphor was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence excitation (PLE) and emission (PL) spectroscopy and color chromaticity coordinates. XRD revealed the monoclinic crystal structure with space group P1¯. The crystallite size was calculated by Williamson-Hall (W–H) analysis. Nanoplates-like morphology was observed in FESEM analysis with size in the range 50–80 nm. TEM images confirmed the particle size and shape. Upon excitation by 254 nm UV light, the phosphor showed the characteristic red emission peaks at 589 nm and 613 nm corresponding to {sup 5}D{sub 0} → {sup 7}F{sub 1} and {sup 5}D{sub 0} → {sup 7}F{sub 2} transitions respectively. It was observed that the nanocrystalline phosphor Y{sub 2-x}Gd{sub x}Si{sub 2}O{sub 7}:Eu{sup 3+}can be tuned to emit orange to red color by adjusting the ratio Y/Gd. This phosphor thus can be a potential candidate as orange to red color emitting tunable nanocrystalline phosphor for optical devices. - Highlights: • A novel Yttrium Gadolinium Pyrosilicate doped with Eu{sup 3+} is reported. • Facile and time efficient modified combustion method is used. • The nanocrystalline structure was shown by X-ray diffraction, W–H analysis. • FESEM and TEM images confirmed the nanocrystalline structure. • The reported phosphor can be tuned from orange to red by varying Y/Gd ratio.

  19. Flame spray synthesis under a non-oxidizing atmosphere: Preparation of metallic bismuth nanoparticles and nanocrystalline bulk bismuth metal

    Grass, Robert N.; Stark, Wendelin J. [Institute for Chemical and Bioengineering, ETH Zuerich (Switzerland)], E-mail: wendelin.stark@chem.ethz.ch

    2006-10-15

    Metallic bismuth nanoparticles of over 98% purity were prepared by a modified flame spray synthesis method in an inert atmosphere by oxygen-deficient combustion of a bismuth-carboxylate based precursor. The samples were characterized by X-ray diffraction, thermal analysis and scanning electron microscopy confirming the formation of pure, crystalline metallic bismuth nanoparticles. Compression of the as-prepared powder resulted in highly dense, nanocrystalline pills with strong electrical conductivity and bright metallic gloss.

  20. SINTERING EFFECTS ON THE DENSIFICATION OF NANOCRYSTALLINE HYDROXYAPATITE

    M. Amiriyan

    2011-06-01

    Full Text Available The effects of sintering profiles on the densification behaviour of synthesized nanocrystalline hydroxyapatite (HA powder were investigated in terms of phase stability and mechanical properties. A wet chemical precipitation method was successfully employed to synthesize a high purity and single phase HA powder. Green HA compacts were prepared and subjected to sintering in air atmosphere over a temperature range of 700° C to 1300° C. In this study two different holding times were compared, i.e. 1 minute versus the standard 120 minutes. The results revealed that the 1 minute holding time sintering profile was indeed effective in producing a HA body with high density of 98% theoretical when sintered at 1200° C. High mechanical properties such as fracture toughness of 1.41 MPa.m1/2 and hardness of 9.5 GPa were also measured for HA samples sintered under this profile. Additionally, XRD analysis indicated that decomposition of the HA phase during sintering at high temperatures was suppressed.

  1. Synthesis and electrical conductivity of nanocrystalline tetragonal FeS

    Zeng Shu-Lin; Wang Hui-Xian; Dong Cheng

    2014-01-01

    A convenient method for synthesis of tetragonal FeS using iron powder as iron source, is reported. Nanocrystalline tetragonal FeS samples were successfully synthesized by reacting metallic iron powder with sodium sulfide in acetate buffer solution. The obtained sample is single-phase tetragonal FeS with lattice parameters a = 0.3767 nm and c = 0.5037 nm, as revealed by X-ray diffraction. The sample consists of flat nanosheets with lateral dimensions from 20 nm up to 200 nm and average thickness of about 20 nm. We found that tetragonal FeS is a fairly good conductor from the electrical resistivity measurement on a pellet of the nanosheets. The temperature dependence of conductivity of the pellet was well fitted using an empirical equation wherein the effect of different grain boundaries was taken into consideration. This study provides a convenient, economic way to synthesize tetragonal FeS in a large scale and reports the first electrical conductivity data for tetragonal FeS down to liquid helium temperature. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  2. Biomimetic nanocrystalline apatite coatings synthesized by Matrix Assisted Pulsed Laser Evaporation for medical applications

    Visan, A. [National Institute for Lasers, Plasma, and Radiation Physics, 409 Atomistilor Street, RO-77125, MG-36, Magurele-Ilfov (Romania); Grossin, D. [CIRIMAT – Carnot Institute, University of Toulouse, ENSIACET, 4 Allée Emile Monso, 31030 Toulouse Cedex 4 (France); Stefan, N.; Duta, L.; Miroiu, F.M. [National Institute for Lasers, Plasma, and Radiation Physics, 409 Atomistilor Street, RO-77125, MG-36, Magurele-Ilfov (Romania); Stan, G.E. [National Institute of Materials Physics, RO-077125, Magurele-Ilfov (Romania); Sopronyi, M.; Luculescu, C. [National Institute for Lasers, Plasma, and Radiation Physics, 409 Atomistilor Street, RO-77125, MG-36, Magurele-Ilfov (Romania); Freche, M.; Marsan, O.; Charvilat, C. [CIRIMAT – Carnot Institute, University of Toulouse, ENSIACET, 4 Allée Emile Monso, 31030 Toulouse Cedex 4 (France); Ciuca, S. [Politehnica University of Bucharest, Faculty of Materials Science and Engineering, Bucharest (Romania); Mihailescu, I.N., E-mail: ion.mihailescu@inflpr.ro [National Institute for Lasers, Plasma, and Radiation Physics, 409 Atomistilor Street, RO-77125, MG-36, Magurele-Ilfov (Romania)

    2014-02-15

    Highlights: • We report the deposition by MAPLE of biomimetic apatite coatings on Ti substrates. • This is the first report of MAPLE deposition of hydrated biomimetic apatite films. • Biomimetic apatite powder was synthesized by double decomposition process. • Non-apatitic environments, of high surface reactivity, are preserved post-deposition. • We got the MAPLE complete transfer as thin film of a hydrated, delicate material. -- Abstract: We report the deposition by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique of biomimetic nanocrystalline apatite coatings on titanium substrates, with potential application in tissue engineering. The targets were prepared from metastable, nanometric, poorly crystalline apatite powders, analogous to mineral bone, synthesized through a biomimetic approach by double decomposition process. For the deposition of thin films, a KrF* excimer laser source was used (λ = 248 nm, τ{sub FWHM} ≤ 25 ns). The analyses revealed the existence, in synthesized powders, of labile non-apatitic mineral ions, associated with the formation of a hydrated layer at the surface of the nanocrystals. The thin film analyses showed that the structural and chemical nature of the nanocrystalline apatite was prevalently preserved. The perpetuation of the non-apatitic environments was also observed. The study indicated that MAPLE is a suitable technique for the congruent transfer of a delicate material, such as the biomimetic hydrated nanohydroxyapatite.

  3. Biomimetic nanocrystalline apatite coatings synthesized by Matrix Assisted Pulsed Laser Evaporation for medical applications

    Visan, A.; Grossin, D.; Stefan, N.; Duta, L.; Miroiu, F.M.; Stan, G.E.; Sopronyi, M.; Luculescu, C.; Freche, M.; Marsan, O.; Charvilat, C.; Ciuca, S.; Mihailescu, I.N.

    2014-01-01

    Highlights: • We report the deposition by MAPLE of biomimetic apatite coatings on Ti substrates. • This is the first report of MAPLE deposition of hydrated biomimetic apatite films. • Biomimetic apatite powder was synthesized by double decomposition process. • Non-apatitic environments, of high surface reactivity, are preserved post-deposition. • We got the MAPLE complete transfer as thin film of a hydrated, delicate material. -- Abstract: We report the deposition by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique of biomimetic nanocrystalline apatite coatings on titanium substrates, with potential application in tissue engineering. The targets were prepared from metastable, nanometric, poorly crystalline apatite powders, analogous to mineral bone, synthesized through a biomimetic approach by double decomposition process. For the deposition of thin films, a KrF* excimer laser source was used (λ = 248 nm, τ FWHM ≤ 25 ns). The analyses revealed the existence, in synthesized powders, of labile non-apatitic mineral ions, associated with the formation of a hydrated layer at the surface of the nanocrystals. The thin film analyses showed that the structural and chemical nature of the nanocrystalline apatite was prevalently preserved. The perpetuation of the non-apatitic environments was also observed. The study indicated that MAPLE is a suitable technique for the congruent transfer of a delicate material, such as the biomimetic hydrated nanohydroxyapatite

  4. Zeolite Encapsulated Nanocrystalline CuO: A Redox Catalyst for the Oxidation of Secondary Alcohols

    Sakthivel Vijaikumar

    2008-01-01

    Full Text Available Zeolite encapsulated nanocrystalline CuO is synthesized and characterized by powder XRD and HRTEM analyses which clearly show that the particles are less than 15 nm and the nanoparticles are highly dispersed. This nano CuO encapsulated CuY zeolite is used as catalyst in the oxidation of aromatic secondary alcohols. CuY zeolite acts as an efficient support for nano CuO, by stabilizing it and preventing its aggregation. Plausible mechanisms for the formation of the various products are also given.

  5. Structural elucidation of nanocrystalline biomaterials

    Maltsev, S.

    2008-10-23

    Bone diseases, such as osteoporosis and osteoarthritis, are the second most prevalent health problem worldwide. In Germany approximately 5 millions people are affected by arthritis. Investigating biomineralization processes and bone molecular structure is of key importance for developing new drugs for preventing and healing bone diseases. Nuclear magnetic resonance (NMR) was the primary technique used due to its advantages in characterising poorly ordered and disordered materials. Compared to all the diffraction techniques that widely applied in structural investigations, the usefulness of NMR is independent of long range molecular order. This makes NMR an outstanding technique for studies of complex/amorphous materials. Conventional NMR experiments (single pulse, spin-echo, cross polarization (CP), etc.) as well as their modifications and high-end techniques (2D HETCOR, REDOR, etc.) were used in this work. Combining the contributions from different techniques enhances the information content of the investigations and can increase the precision of the overall conclusions. Also XRD, TEM and FTIR were applied to different extent in order to get a general idea of nanocrystalline hydroxyapatite crystallite structure. Results: - A new approach named 'Solid-state NMR spectroscopy using the lost I spin magnetization in polarization transfer experiments' has been developed for measuring the transferred I spin magnetization from abundant nuclei, which is normally lost when detecting the S spin magnetization. - A detailed investigation of nanocrystalline hydroxyapatite core was made to prove that proton environment of the phosphates units and phosphorus environment of hydroxyl units are the same as in highly crystalline hydroxyapatite sample. - Using XRD it was found that the surface of the hydroxyapatite nanocrystals is not completely disordered, as it was suggested before, but resembles the hydroxyapatite structure with HPO{sub 4}{sup 2-} (and some CO{sub 3}{sup

  6. Structural elucidation of nanocrystalline biomaterials

    Maltsev, S

    2008-10-23

    Bone diseases, such as osteoporosis and osteoarthritis, are the second most prevalent health problem worldwide. In Germany approximately 5 millions people are affected by arthritis. Investigating biomineralization processes and bone molecular structure is of key importance for developing new drugs for preventing and healing bone diseases. Nuclear magnetic resonance (NMR) was the primary technique used due to its advantages in characterising poorly ordered and disordered materials. Compared to all the diffraction techniques that widely applied in structural investigations, the usefulness of NMR is independent of long range molecular order. This makes NMR an outstanding technique for studies of complex/amorphous materials. Conventional NMR experiments (single pulse, spin-echo, cross polarization (CP), etc.) as well as their modifications and high-end techniques (2D HETCOR, REDOR, etc.) were used in this work. Combining the contributions from different techniques enhances the information content of the investigations and can increase the precision of the overall conclusions. Also XRD, TEM and FTIR were applied to different extent in order to get a general idea of nanocrystalline hydroxyapatite crystallite structure. Results: - A new approach named 'Solid-state NMR spectroscopy using the lost I spin magnetization in polarization transfer experiments' has been developed for measuring the transferred I spin magnetization from abundant nuclei, which is normally lost when detecting the S spin magnetization. - A detailed investigation of nanocrystalline hydroxyapatite core was made to prove that proton environment of the phosphates units and phosphorus environment of hydroxyl units are the same as in highly crystalline hydroxyapatite sample. - Using XRD it was found that the surface of the hydroxyapatite nanocrystals is not completely disordered, as it was suggested before, but resembles the hydroxyapatite structure with HPO{sub 4}{sup 2-} (and some CO{sub 3}{sup 2

  7. Nanocrystalline Fe-Pt alloys. Phase transformations, structure and magnetism

    Lyubina, J.V.

    2006-12-21

    This work has been devoted to the study of phase transformations involving chemical ordering and magnetic properties evolution in bulk Fe-Pt alloys composed of nanometersized grains. Nanocrystalline Fe{sub 100-x}Pt{sub x} (x=40-60) alloys have been prepared by mechanical ball milling of elemental Fe and Pt powders at liquid nitrogen temperature. The as-milled Fe-Pt alloys consist of {proportional_to} 100 {mu}m sized particles constituted by randomly oriented grains having an average size in the range of 10-40 nm. Depending on the milling time, three major microstructure types have been obtained: samples with a multilayer-type structure of Fe and Pt with a thickness of 20-300 nm and a very thin (several nanometers) A1 layer at their interfaces (2 h milled), an intermediate structure, consisting of finer lamellae of Fe and Pt (below approximately 100 nm) with the A1 layer thickness reaching several tens of nanometers (4 h milled) and alloys containing a homogeneous A1 phase (7 h milled). Subsequent heat treatment at elevated temperatures is required for the formation of the L1{sub 0} FePt phase. The ordering develops via so-called combined solid state reactions. It is accompanied by grain growth and thermally assisted removal of defects introduced by milling and proceeds rapidly at moderate temperatures by nucleation and growth of the ordered phases with a high degree of the long-range order. In a two-particle interaction model elaborated in the present work, the existence of hysteresis in recoil loops has been shown to arise from insufficient coupling between the low- and the high-anisotropy particles. The model reveals the main features of magnetisation reversal processes observed experimentally in exchange-coupled systems. Neutron diffraction has been used for the investigation of the magnetic structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. (orig.)

  8. Formation of ZnO Nanocrystalline via Facile Non-Hydrolytic Route

    Ooi, M. D. Johan; Aziz, A. Abdul; Abdullah, M. J.

    2011-01-01

    Zinc oxide (ZnO) nanocrystalline were synthesized via oxidizing Zn powder in non-aqueous solvent with addition of Diethanolamine (DEA) as a stabilizing agent. The influence of DEA on the structural, optical properties and the formation of ZnO nanocrystalline were studied. The synthesized ZnO were polycrystalline in structures where sample without the addition of DEA shows high intensity peak of (002) phase compared with sample in the presence of DEA which preferred to grow in (101) direction. SEM micrograph displays the morphology of ZnO nanocrystalline for both of the samples which shows micron size and non-uniform particles for sample without DEA whereas for sample with DEA exhibit smaller size (∼110 nm) and nearly spherical in shape despite of some agglomeration occurs at the interparticle separation. The photoluminescence (PL) spectra shows UV emission peak for both of the samples where sample with the absence of DEA possess lower intensity of UV emission peak compared to samples with DEA which demonstrate stronger intensity despite of having very weak visible secondary emission peak at 530 nm.

  9. Nanocrystalline permanent magnets with enhanced properties

    Leonowicz, M.

    2002-01-01

    Parameters of permanent magnets result from the combination of intrinsic properties such as saturation magnetization, magnetic exchange, and magnetocrystalline energy, as well as microstructural parameters such as phase structure, grain size, and orientation. Reduction of grain size into nanocrystalline regime (∼ 50 nm) leads to the enhanced remanence which derives from ferromagnetic exchange coupling between highly refined grains. In this study the fundamental phenomena, quantities, and structure parameters, which define nanophase permanent magnets are presented and discussed. The theoretical considerations are confronted with experimental data for nanocrystalline Sm-Fe-N type permanent magnets. (author)

  10. Direct Coating of Nanocrystalline Diamond on Steel

    Tsugawa, Kazuo; Kawaki, Shyunsuke; Ishihara, Masatou; Hasegawa, Masataka

    2012-09-01

    Nanocrystalline diamond films have been successfully deposited on stainless steel substrates without any substrate pretreatments to promote diamond nucleation, including the formation of interlayers. A low-temperature growth technique, 400 °C or lower, in microwave plasma chemical vapor deposition using a surface-wave plasma has cleared up problems in diamond growth on ferrous materials, such as the surface graphitization, long incubation time, substrate softening, and poor adhesion. The deposited nanocrystalline diamond films on stainless steel exhibit good adhesion and tribological properties, such as a high wear resistance, a low friction coefficient, and a low aggression strength, at room temperature in air without lubrication.

  11. Mechanochemical synthesis of nanocrystalline Fe and Fe–B magnetic alloys

    Mohammadi, Majid; Ghasemi, Ali, E-mail: ali13912001@yahoo.com; Tavoosi, Majid

    2016-12-01

    Mechanochemical synthesis and magnetic characterization of nanocrystalline Fe and Fe–B magnetic alloys was the goal of this study. In this regard, different Fe{sub 2}O{sub 3}–B{sub 2}O{sub 3} powder mixtures with sufficient amount of CaH{sub 2} were milled in a planetary ball mill in order to produce nanocrystalline Fe, Fe{sub 95}B{sub 5} and Fe{sub 85}B{sub 15} alloys. The produced samples were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results showed that, nanocrystalline Fe, Fe{sub 95}B{sub 5} and Fe{sub 85}B{sub 15} alloys can be successfully synthesized by the reduction reaction of Fe{sub 2}O{sub 3} and B{sub 2}O{sub 3} with CaH{sub 2} during mechanical alloying. The structure of produced Fe{sub 95}B{sub 5} and Fe{sub 85}B{sub 15} alloys was a combination of Fe and Fe{sub 2}B phases with average crystallite sizes of about 15 and 10 nm, respectively. The produced nanocrystalline alloys exhibited soft magnetic properties with the coercivity and saturation of magnetization in the range of 170–240 Oe and 9–28 emu/g, respectively. Increasing the boron content has a destructive effect on soft magnetic properties of Fe–B alloys. - Highlights: • We study the mechanochemical synthesis of nanocrystalline boron, Fe and Fe–B alloys. • We study the reduction reaction of B{sub 2}O{sub 3}–CaH{sub 2} during milling. • We study the reduction reaction of Fe{sub 2}O{sub 3}–CaH{sub 2} during milling. • We study the reduction reaction of Fe{sub 2}O{sub 3}–B{sub 2}O{sub 3}–CaH{sub 2} during milling. • We study the effect of B on magnetic properties of nanocrystalline Fe–B alloys.

  12. Foundations of powder metallurgy

    Libenson, G.A.

    1987-01-01

    Consideration is being given to physicochemical foundations and technology of metal powders, moulding and sintering of bars, made of them or their mixtures with nonmetal powders. Data on he design of basic equipment used in the processes of powder metallurgy and its servicing are presented. General requirements of safety engineering when fabricating metal powders and products of them are mentioned

  13. Nanocrystalline (U0.5Ce0.5)O2±x solid solutions through citrate gel-combustion

    Maji, D.; Ananthasivan, K.; Venkata Krishnan, R.; Balakrishnan, S.; Amirthapandian, S.; Joseph, Kitheri; Dasgupta, Arup

    2018-04-01

    Nanocrystalline powders of (U0.5Ce0.5)O2±x solid solutions were synthesized in bulk (100-200 g) through the citrate gel combustion. The fuel (citric acid) to oxidant (nitrate) mole ratio (R) was varied from 0.1 to 1.0. Two independent lots of the products obtained through the gel-combustion were calcined at 973 K in air and in a mixture of argon containing 8% H2 respectively. All these powders were characterized for their bulk density, X-ray crystallite size, specific surface area, size distribution of the particles, porosity as well as residual carbon. The morphology and microstructures of these powders were studied by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. Nanocrystalline single phase fluorite solid solutions having a typical crystallite size of about (7-15 nm) were obtained. These powders were highly porous comprising cuboidal flaky agglomerates. The combustion mixture with an 'R' value of 0.25 was found to undergo volume combustion and was found to yield a product that was distinctly different. The systematic investigation on synthesis and characterization of nanocrystalline UCeO2 is reported for the first time.

  14. Structural transformation of nanocrystalline titania by sol-gel and the growth kinetics of crystallites

    Hu Linhua; Dai Songyuan; Wang Kongjia

    2002-05-01

    Structural transformation of nanocrystalline titania prepared by sol-gel with hydrolysis precursor titanium isopropoxide was investigated. At the same time, the growth kinetics of titania powders was also studied here. It was found that the grain size of the powders increased slowly with autoclave heating temperature up to 230 degree C, when hydrolysis pH was 0.9, but grew rapidly when heating temperature was higher that 230 degree C. The activation energies for growth of anatase crystallites in two temperature regions were calculated to be 18.5 kJ/mol and 59.7 kJ/mol respectively. The X-ray diffraction results show that the transformation from anatase phase to rutile phase starts at 230 degree C and structural transformation finished when temperature raises to 270 degree C, which is a temperature much more lower than that of the transformation by conventional literature reports

  15. Preparation of nanocrystalline ZnS by a new chemical bath deposition route

    Sartale, S.D. [Department of Heterogeneous Material Systems (SE2), Hahn-Meitner-Institut, Glienicker Strasse 100, D-14109, Berlin (Germany); Sankapal, B.R. [Department of Heterogeneous Material Systems (SE2), Hahn-Meitner-Institut, Glienicker Strasse 100, D-14109, Berlin (Germany); Lux-Steiner, M. [Department of Heterogeneous Material Systems (SE2), Hahn-Meitner-Institut, Glienicker Strasse 100, D-14109, Berlin (Germany); Ennaoui, A. [Department of Heterogeneous Material Systems (SE2), Hahn-Meitner-Institut, Glienicker Strasse 100, D-14109, Berlin (Germany)]. E-mail: ennaoui@hmi.de

    2005-06-01

    We report a new chemical bath deposition route for the preparation of dense, compact and uniform nanocrystalline ZnS thin films, where thiourea acts as a complexing agent as well as a source of sulfide ions. The structural and morphological characterizations suggest that the film and the residual powder in the bath are formed by the aggregation of clusters of ZnS, namely cluster-by-cluster growth mechanism. X-ray diffraction (XRD) and HRTEM analyses indicate that the film and powder formed in the bath have cubic zinkblende structure. The films have high transmittance of about 75% in the visible region. Post-deposition annealing in Ar slightly improves the crystallinity and decreases the optical bandgap with increasing the annealing temperature.

  16. Preparation of nanocrystalline ZnS by a new chemical bath deposition route

    Sartale, S.D.; Sankapal, B.R.; Lux-Steiner, M.; Ennaoui, A.

    2005-01-01

    We report a new chemical bath deposition route for the preparation of dense, compact and uniform nanocrystalline ZnS thin films, where thiourea acts as a complexing agent as well as a source of sulfide ions. The structural and morphological characterizations suggest that the film and the residual powder in the bath are formed by the aggregation of clusters of ZnS, namely cluster-by-cluster growth mechanism. X-ray diffraction (XRD) and HRTEM analyses indicate that the film and powder formed in the bath have cubic zinkblende structure. The films have high transmittance of about 75% in the visible region. Post-deposition annealing in Ar slightly improves the crystallinity and decreases the optical bandgap with increasing the annealing temperature

  17. Nanocrystalline hydroxyapatite doped with selenium oxyanions: a new material for potential biomedical applications.

    Kolmas, Joanna; Oledzka, Ewa; Sobczak, Marcin; Nałęcz-Jawecki, Grzegorz

    2014-06-01

    Selenium-substituted hydroxyapatites containing selenate SeO4(2-) or selenite SeO3(2-) ions were synthesized using a wet precipitation method. The selenium content was determined by atomic absorbance spectrometry. The raw, unsintered powders were also characterized using powder X-ray diffraction, middle-range FT-IR spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopic microanalysis. The synthesized apatites were found to be pure and nanocrystalline with a crystal size similar to that in bone mineral. The incorporation of selenium oxyanions into the crystal lattice was confirmed. The toxicity of hydroxyapatites containing selenite or selenate ions was evaluated with a protozoan assay and bacterial luminescence test. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. Surface effects on the magnetic behavior of nanocrystalline nickel ferrites and nickel ferrite-polymer nanocomposites

    Nathani, H.; Misra, R.D.K.

    2004-01-01

    The magnetization studies on nanocrystalline nickel ferrite as powder particles, and as diluted dispersion (10 wt.%) in polymer matrix (polymer nanocomposites) are presented. The two polymer-based nanocomposites were prepared via ball-milling and in situ polymerization, respectively. The magnetization measurements provide strong evidence of surface effects to magnetization, which explains the non-saturation of magnetization at high fields. The differences in the magnetization behavior of nickel ferrite as powder particles and in the ball-milled nanocomposite and the nanocomposite prepared via in situ polymerization are attributed to the different extent of interparticle interactions between the particles and the preparation route. The magnetization versus applied field behavior of the three ferrite systems show a similar jump in the initial part of the magnetization curve in all the cases which implies the existence of a core-shell like morphology of the particles over a large temperature range and its dominance over the interparticle interaction effects between the particles

  19. Studies on the sensing behaviour of nanocrystalline CuGa(2)O(4) towards hydrogen, liquefied petroleum gas and ammonia.

    Biswas, Soumya Kanti; Sarkar, Arpita; Pathak, Amita; Pramanik, Panchanan

    2010-06-15

    In the present article, the gas sensing behaviour of nanocrystalline CuGa(2)O(4) towards H(2), liquefied petroleum gas (LPG) and NH(3) has been reported for the first time. Nanocrystalline powders of CuGa(2)O(4) having average particle sizes in the range of 30-60nm have been prepared through thermal decomposition of an aqueous precursor solution comprising copper nitrate, gallium nitrate and triethanol amine (TEA), followed by calcination at 750 degrees C for 2h. The synthesized nanocrystalline CuGa(2)O(4) powders have been characterised through X-ray diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FESEM) study, energy dispersive X-ray (EDX) analysis and BET (Brunauer-Emmett-Teller) surface area measurement. The synthesized CuGa(2)O(4) having spinel structure with specific surface area of 40m(2)/g exhibits maximum sensitivity towards H(2), LPG, and NH(3) at 350 degrees C.

  20. Fundamentals of powder metallurgy

    Khan, I.H.; Qureshi, K.A.; Minhas, J.I.

    1988-01-01

    This book is being presented to introduce the fundamentals of technology of powder metallurgy. An attempt has been made to present an overall view of powder metallurgy technology in the first chapter, whereas chapter 2 to 8 deal with the production of metal powders. The basic commercial methods of powder production are briefly described with illustrations. Chapter 9 to 12 describes briefly metal powder characteristics and principles of testing, mixing, blending, conditioning, compaction and sintering. (orig./A.B.)

  1. Chemical vapor deposition of nanocrystalline diamond films

    Vyrovets, I.I.; Gritsyna, V.I.; Dudnik, S.F.; Opalev, O.A.; Reshetnyak, O.M.; Strel'nitskij, V.E.

    2008-01-01

    The brief review of the literature is devoted to synthesis of nanocrystalline diamond films. It is shown that the CVD method is an effective way for deposition of such nanostructures. The basic technological methods that allow limit the size of growing diamond crystallites in the film are studied.

  2. Multiphase Nanocrystalline Ceramic Concept for Nuclear Fuel

    Mecartnery, Martha [Univ. of California, Irvine, CA (United States); Graeve, Olivia [Univ. of California, San Diego, CA (United States); Patel, Maulik [Univ. of Liverpool (United Kingdom)

    2017-05-25

    The goal of this research is to help develop new fuels for higher efficiency, longer lifetimes (higher burn-up) and increased accident tolerance in future nuclear reactors. Multiphase nanocrystalline ceramics will be used in the design of simulated advanced inert matrix nuclear fuel to provide for enhanced plasticity, better radiation tolerance, and improved thermal conductivity

  3. Multiphase Nanocrystalline Ceramic Concept for Nuclear Fuel

    Mecartnery, Martha; Graeve, Olivia; Patel, Maulik

    2017-01-01

    The goal of this research is to help develop new fuels for higher efficiency, longer lifetimes (higher burn-up) and increased accident tolerance in future nuclear reactors. Multiphase nanocrystalline ceramics will be used in the design of simulated advanced inert matrix nuclear fuel to provide for enhanced plasticity, better radiation tolerance, and improved thermal conductivity

  4. Characterization of nanocrystalline silicon germanium film and ...

    The nanocrystalline silicon-germanium films (Si/Ge) and Si/Ge nanotubes have low band gaps and high carrier mobility, thus offering appealing potential for absorbing gas molecules. Interaction between hydrogen molecules and bare as well as functionalized Si/Ge nanofilm and nanotube was investigated using Monte ...

  5. Biocompatible nanocrystalline natural bonelike carbonated hydroxyapatite synthesized by mechanical alloying in a record minimum time

    Lala, S. [Materials Science Division, Department of Physics, The University of Burdwan, Golapbag, Burdwan-713104, West Bengal (India); Brahmachari, S.; Das, P.K. [Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700 032 (India); Das, D. [UGC-DAE Consortium for Scientific Research, Kolkata-700098 (India); Kar, T. [Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032 (India); Pradhan, S.K., E-mail: skp_bu@yahoo.com [Materials Science Division, Department of Physics, The University of Burdwan, Golapbag, Burdwan-713104, West Bengal (India)

    2014-09-01

    Single phase nanocrystalline biocompatible A-type carbonated hydroxyapatite (A-cHAp) powder has been synthesized by mechanical alloying the stoichiometric mixture of CaCO{sub 3} and CaHPO{sub 4}.2H{sub 2}O powders in open air at room temperature within 2 h of milling. The A-type carbonation in HAp is confirmed by FTIR analysis. Structural and microstructure parameters of as-milled powders are obtained from both Rietveld's powder structure refinement analysis and transmission electron microscopy. Size and lattice strain of nanocrystalline HAp particles are found to be anisotropic in nature. Mechanical alloying causes amorphization of a part of crystalline A-cHAp which is analogous to native bone mineral. Some primary bond lengths of as-milled samples are critically measured. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay test reveals high percentage of cell viability and hence confirms the biocompatibility of the sample. The overall results indicate that the processed A-cHAp has a chemical composition very close to that of biological apatite. - Graphical abstract: Biocompatible A-Type Carbonated Hydroxyapatite (A-cHAp) has been synthesized by mechanical alloying in polycrystalline form within 2 h of milling. The shape and position of CO channel have been shown. - Highlights: • A-cHAp phase is completed within 2 h of milling. • FTIR analysis confirms A-type carbonation in HAp. • Amorphization of a part of crystalline A-cHAp. • Particle size and strain are anaisotropic in nature. • High cell viability under MTT assay.

  6. Nanocrystalline cellulose as an eco-friendly reinforcing additive to polyurethane coating for augmented anticorrosive behavior.

    Abd El-Fattah, M; Hasan, Abdulraheim M A; Keshawy, Mohamed; El Saeed, Ashraf M; Aboelenien, Ossama M

    2018-03-01

    Nanocrystalline cellulose (NCC) and micro-powdered cellulose (MPC) were extracted from rice straw by mechanical and alkali treatment methods, then characterized via infrared spectroscopy and dynamic light scattering. A series of polyurethane nanocrystalline cellulose composite (PNCCC) and polyurethane micro-powdered cellulose composite (PMPCC) coatings were prepared with various loading levels of NCC and MPC from 0.5 to 2.0 wt.%, and the coatings were applied onto the pretreated mild steel substrate at room temperature. The results showed that the NCC and MPC influenced positively the studied properties of the polyurethane coating; furthermore the most pronounced anticorrosive properties were obtained at 1 wt.% NCC and MPC, as confirmed by open circuit potential (OCP) study, electrochemical impedance spectroscopy (EIS) study and salt spray test. However, the optimum enhancement of mechanical properties was found at 1.5 wt.% loading level, after which further loading of NCC and MPC led to the reduction in the mechanical properties. Copyright © 2018 Elsevier Ltd. All rights reserved.

  7. Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

    Sherly, K. B.; Rakesh, K. [Mahatma Gandhi University Regional Research Center in Chemistry, Department of Chemistry, Mar Athanasius College, Kothamangalam-686666, Kerala (India)

    2014-01-28

    Nanoscaled materials are of great interest due to their unique enhanced optical, electrical and magnetic properties. Sulfate-promoted zirconia has been shown to exhibit super acidic behavior and high activity for acid catalyzed reactions. Nanocrystalline zirconia was prepared in the presence of polysaccharide template by interaction between ZrOCl{sub 2}⋅8H{sub 2}O and chitosan template. The interaction was carried out in aqueous phase, followed by the removal of templates by calcination at optimum temperature and sulfation. The structural and textural features were characterized by powder XRD, TG, SEM and TEM. XRD patterns showed the peaks of the diffractogram were in agreement with the theoretical data of zirconia with the catalytically active tetragonal phase and average crystalline size of the particles was found to be 9 nm, which was confirmed by TEM. TPD using ammonia as probe, FTIR and BET surface area analysis were used for analyzing surface features like acidity and porosity. The BET surface area analysis showed the sample had moderately high surface area. FTIR was used to find the type species attached to the surface of zirconia. UV-DRS found the band gap of the zirconia was found to be 2.8 eV. The benzylation of o-xylene was carried out batchwise in atmospheric pressure and 433K temperature using sulfated zirconia as catalyst.

  8. Characterization of nanocrystalline anatase titania: an in situ HTXRD study

    Jagtap, Neelam; Bhagwat, Mahesh; Awati, Preeti; Ramaswamy, Veda

    2005-01-01

    Nanocrystalline titania was synthesized by the hydrolysis of titanium iso-propoxide using ultrasonication. The powder XRD patterns of the sample were recorded in static air and vacuum using a Philips X-pert Pro diffractometer equipped with a high-temperature attachment (HTK16) from room temperature (298 K) to 1173 K and were analyzed by the Rietveld refinement technique. The anatase to rutile phase transformation was observed at 1173 K for the data collected in static air. Only 3% of anatase titania transformed to rutile when the experiments were carried out at 1173 K in vacuum. The phase transformation from anatase to rutile is accompanied by a continuous increase in the crystallite size of the anatase phase from 9 nm at room temperature to 28 nm at 873 K and then to 50 nm at 1173 K in air while the process of crystallite growth was suppressed in vacuum. A linear increase in the unit cell parameters 'a' and 'c', and thus, an overall linear increase in the unit cell volume was observed as a function of temperature in static air as well as vacuum. The lattice and volume thermal expansion coefficients (TEC), α a , α c and α V at 873 K are 8.57 x 10 -6 , 8.71 x 10 -6 and 25.91 x 10 -6 K -1 in air and 18.01 x 10 -6 , 14.95 x 10 -6 and 51.13 x 10 -6 K -1 in vacuum, respectively

  9. F-centre luminescence in nanocrystalline CeO2

    Aškrabić, S; Dohčević-Mitrović, Z D; Araújo, V D; Ionita, G; De Lima, M M Jr; Cantarero, A

    2013-01-01

    Nanocrystalline CeO 2 powders were synthesized by two cost-effective methods: the self-propagating room temperature (SPRT) method and the precipitation method. Differently prepared samples exhibited different temperature-dependent photoluminescence (PL) in the ultraviolet and visible regions. The PL signals originated from different kinds of oxygen-deficient defect centres with or without trapped electrons (F 0 , F + or F ++ centres). The temperature-dependent PL spectra were measured using different excitation lines, below (457, 488 and 514 nm) or comparable (325 nm) to the ceria optical band gap energy, in order to investigate the positions of intragap localized defect states. Evidence for the presence of F + centres was supported by the signals observed in electron paramagnetic resonance (EPR) measurements. Based on PL and EPR measurements it was shown that F + centres dominate in the CeO 2 sample synthesized by the SPRT method, whereas F 0 centres are the major defects in the CeO 2 sample synthesized by the precipitation method. The luminescence from F ++ states, as shallow trap states, was registered in both samples. Energy level positions of these defect states in the ceria band gap were proposed. (paper)

  10. F-centre luminescence in nanocrystalline CeO2

    Aškrabić, S.; Dohčević-Mitrović, Z. D.; Araújo, V. D.; Ionita, G.; de Lima, M. M., Jr.; Cantarero, A.

    2013-12-01

    Nanocrystalline CeO2 powders were synthesized by two cost-effective methods: the self-propagating room temperature (SPRT) method and the precipitation method. Differently prepared samples exhibited different temperature-dependent photoluminescence (PL) in the ultraviolet and visible regions. The PL signals originated from different kinds of oxygen-deficient defect centres with or without trapped electrons (F0, F+ or F++ centres). The temperature-dependent PL spectra were measured using different excitation lines, below (457, 488 and 514 nm) or comparable (325 nm) to the ceria optical band gap energy, in order to investigate the positions of intragap localized defect states. Evidence for the presence of F+ centres was supported by the signals observed in electron paramagnetic resonance (EPR) measurements. Based on PL and EPR measurements it was shown that F+ centres dominate in the CeO2 sample synthesized by the SPRT method, whereas F0 centres are the major defects in the CeO2 sample synthesized by the precipitation method. The luminescence from F++ states, as shallow trap states, was registered in both samples. Energy level positions of these defect states in the ceria band gap were proposed.

  11. The modified nanocrystalline cellulose for hydrophobic drug delivery

    Qing, Weixia [Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004 (China); Medical College, Henan University, Kaifeng 475004 (China); Wang, Yong [Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004 (China); Wang, Youyou [Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004 (China); Key Lab of Natural Medicine and Immun-engineering of Henan Province, Henan University, Kaifeng 475004 (China); Zhao, Dongbao [Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004 (China); Liu, Xiuhua, E-mail: ll514527@163.com [Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004 (China); Key Lab of Natural Medicine and Immun-engineering of Henan Province, Henan University, Kaifeng 475004 (China); Zhu, Jinhua [Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004 (China)

    2016-03-15

    Graphical abstract: - Highlights: • Torispherical NCC was synthesized through the improvements on the hydrolysis method. • NCC was firstly modified with CTMAB as a drug carrier. • Luteolin and luteoloside loading CTMAB-coated NCC were studied. - Abstract: In this work, torispherical nanocrystalline cellulose (NCC) was synthesized, and firstly modified with a cationic surfactant cetyltrimethylammonium bromide (CTMAB). It was proved that the kinetics of NCC adsorbing CTMAB followed the pseudo-second-order kinetics equation, and the adsorption isotherm model followed Freundlich which was multi molecular layer adsorption model. The morphology and structure of NCC and CTMAB-coated NCC were characterized by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Stabilities of NCC and CTMAB-coated NCC were assayed by zeta potential. The results showed that NCC in CTMAB solution was well-dispersed and stable. Moreover, the drug loading and release performance of CTMAB-coated NCC were studied using luteolin (LUT) and luteoloside (LUS) as model drugs.

  12. Electrical and optical properties of highly oriented nanocrystalline vanadium pentoxide

    Bahgat, A.A.; Ibrahim, F.A.; El-Desoky, M.M.

    2005-01-01

    Highly oriented nanocrystalline hydrated vanadium pentoxide, V 2 O 5 .nH 2 O, were grown epitaxially on a glass substrate along the c-axis to form a film of 200 nm thick. The films were prepared by dissolving V 2 O 5 powder in hydrogen peroxide, H 2 O 2 , solution. X-ray diffraction, transmission electron micrograph and electron diffraction were used to identify the structure of the obtained nanocrystals. Homogenous nanocrystals of 7.0 ± 1.0 nm in size were obtained and were closed packed and are distributed evenly. Electrical conductivity and thermoelectric power were measured in the temperature range 300-480 K for the as prepared films parallel to the substrate surface; i.e. normal to the c-axis. The obtained results showed an n-type semiconducting behavior within the whole temperature range. It is also clear to see that a reversible abnormality at about 340 K is realized during the cooling electrical conductivity measurements. On the other hand, optical transmission and reflection were used to evaluate different optical parameters such as; optical band gap, nature of donor levels and different absorption bands parameters. Both the electrical and optical data are correlated and accordingly the conduction mechanism is verified. Electronic parameters such as effective mass, carriers' type and concentration and drift mobility were evaluated

  13. Nanocomposites Based on Polyethylene and Nanocrystalline Silicon Films

    Olkhov Anatoliy Aleksandrovich

    2014-12-01

    Full Text Available High-strength polyethylene films containing 0.5-1.0 wt. % of nanocrystalline silicon (nc-Si were synthesized. Samples of nc-Si with an average core diameter of 7-10 nm were produced by plasmochemical method and by laser-induced decomposition of monosilane. Spectral studies revealed almost complete (up to ~95 % absorption of UV radiation in 200- 400 nm spectral region by 85 micron thick film if the nc-Si content approaches to 1.0 wt. %. The density function of particle size in the starting powders and polymer films containing immobilized silicon nanocrystallites were obtained using the modeling a complete profile of X-ray diffraction patterns, assuming spherical grains and the lognormal distribution. The results of X-ray analysis shown that the crystallite size distribution function remains almost unchanged and the crystallinity of the original polymer increases to about 10 % with the implantation of the initial nc-Si samples in the polymer matrix.

  14. The modified nanocrystalline cellulose for hydrophobic drug delivery

    Qing, Weixia; Wang, Yong; Wang, Youyou; Zhao, Dongbao; Liu, Xiuhua; Zhu, Jinhua

    2016-01-01

    Graphical abstract: - Highlights: • Torispherical NCC was synthesized through the improvements on the hydrolysis method. • NCC was firstly modified with CTMAB as a drug carrier. • Luteolin and luteoloside loading CTMAB-coated NCC were studied. - Abstract: In this work, torispherical nanocrystalline cellulose (NCC) was synthesized, and firstly modified with a cationic surfactant cetyltrimethylammonium bromide (CTMAB). It was proved that the kinetics of NCC adsorbing CTMAB followed the pseudo-second-order kinetics equation, and the adsorption isotherm model followed Freundlich which was multi molecular layer adsorption model. The morphology and structure of NCC and CTMAB-coated NCC were characterized by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Stabilities of NCC and CTMAB-coated NCC were assayed by zeta potential. The results showed that NCC in CTMAB solution was well-dispersed and stable. Moreover, the drug loading and release performance of CTMAB-coated NCC were studied using luteolin (LUT) and luteoloside (LUS) as model drugs.

  15. Aluminum powder metallurgy processing

    Flumerfelt, J.F.

    1999-02-12

    The objective of this dissertation is to explore the hypothesis that there is a strong linkage between gas atomization processing conditions, as-atomized aluminum powder characteristics, and the consolidation methodology required to make components from aluminum powder. The hypothesis was tested with pure aluminum powders produced by commercial air atomization, commercial inert gas atomization, and gas atomization reaction synthesis (GARS). A comparison of the GARS aluminum powders with the commercial aluminum powders showed the former to exhibit superior powder characteristics. The powders were compared in terms of size and shape, bulk chemistry, surface oxide chemistry and structure, and oxide film thickness. Minimum explosive concentration measurements assessed the dependence of explosibility hazard on surface area, oxide film thickness, and gas atomization processing conditions. The GARS aluminum powders were exposed to different relative humidity levels, demonstrating the effect of atmospheric conditions on post-atomization processing conditions. The GARS aluminum powders were exposed to different relative humidity levels, demonstrating the effect of atmospheric conditions on post-atomization oxidation of aluminum powder. An Al-Ti-Y GARS alloy exposed in ambient air at different temperatures revealed the effect of reactive alloy elements on post-atomization powder oxidation. The pure aluminum powders were consolidated by two different routes, a conventional consolidation process for fabricating aerospace components with aluminum powder and a proposed alternative. The consolidation procedures were compared by evaluating the consolidated microstructures and the corresponding mechanical properties. A low temperature solid state sintering experiment demonstrated that tap densified GARS aluminum powders can form sintering necks between contacting powder particles, unlike the total resistance to sintering of commercial air atomization aluminum powder.

  16. Room temperature mechanosynthesis and microstructure characterization of nanocrystalline Si{sub 0.9}Al{sub 0.1}C

    Bandyopadhyay, S. [Department of Physics, The University of Burdwan, Golapbag, Burdwan, 713104, West Bengal (India); Dutta, H. [Department of Physics, Vivekananda College, Burdwan, 713103, West Bengal (India); Kar, T. [Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, 700032, West Bengal (India); Pradhan, S.K., E-mail: skp_bu@yahoo.com [Department of Physics, The University of Burdwan, Golapbag, Burdwan, 713104, West Bengal (India)

    2016-02-01

    This article reports the synthesis and microstructure characterization of nanocrystalline Si{sub 0.9}Al{sub 0.1}C powder obtained by mechanical milling the mixture of Si, Al and graphite powders at room temperature under inert atmosphere. XRD patterns of ball-milled powders clearly reveal the nucleation of Si{sub 0.9}Al{sub 0.1}C phase after 5 h of milling and the stoichiometric cubic Si{sub 0.9}Al{sub 0.1}C is formed after 10 h of milling with crystallite size of ∼3 nm. Microstructure of ball-milled powders in terms of different lattice imperfections is characterized by employing both Rietveld's method of structure refinement using XRD data and high resolution transmission electron microscope (HRTEM). HRTEM micrographs of 10 h milled powder substantiate the formation of nanocrystalline Si{sub 0.9}Al{sub 0.1}C compound without any contamination and confirm the findings of Rietveld analysis using XRD data. - Highlights: • Cubic Si{sub 0.9}Al{sub 0.1}C is formed after 5 h of milling of Si, Al and graphite powders. • Nanocrystalline Si{sub 0.9}Al{sub 0.1}C with particle size ∼3 nm is obtained after 10 h milling. • Average particle size of Si{sub 0.9}Al{sub 0.1}C from XRD analysis and HRTEM is very close.

  17. Radiation influence on properties of nanocrystalline alloy

    Holkova, D.; Sitek, J.; Novak, P.; Dekan, J.

    2016-01-01

    Our work is focused on the studied of structural changes amorphous and nanocrystalline alloys after irradiation with electrons. For the analysis of these alloy we use two spectroscopic methods: Moessbauer spectroscopy and XRD. Measurements of nanocrystalline (Fe 3 Ni 1 ) 81 Nb 7 B 12 samples before and after electrons irradiation by means of Moessbauer spectroscopy and XRD showed that the electrons causes changes in magnetic structure which is reflected changes of direction of net magnetic moment. Structural changes occurs in the frame of error indicated by both spectroscopic methods. We can confirm that this kind alloys a resistive again electrons irradiation up to doses of 4 MGy. We observed in this frame only beginning of the radiation damage. (authors)

  18. Ultrafast Terahertz Conductivity of Photoexcited Nanocrystalline Silicon

    Cooke, David; MacDonald, A. Nicole; Hryciw, Aaron

    2007-01-01

    The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described by a class...... in the silicon nanocrystal films is dominated by trapping at the Si/SiO2 interface states, occurring on a 1–100 ps time scale depending on particle size and hydrogen passivation......The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described...

  19. Solubility of Carbon in Nanocrystalline -Iron

    Alexander Kirchner; Bernd Kieback

    2012-01-01

    A thermodynamic model for nanocrystalline interstitial alloys is presented. The equilibrium solid solubility of carbon in -iron is calculated for given grain size. Inside the strained nanograins local variation of the carbon content is predicted. Due to the nonlinear relation between strain and solubility, the averaged solubility in the grain interior increases with decreasing grain size. The majority of the global solubility enhancement is due to grain boundary enrichment however. Therefor...

  20. Characterization of amorphous and nanocrystalline carbon films

    Chu, Paul K.; Li Liuhe

    2006-01-01

    Amorphous and nanocrystalline carbon films possess special chemical and physical properties such as high chemical inertness, diamond-like properties, and favorable tribological proprieties. The materials usually consist of graphite and diamond microstructures and thus possess properties that lie between the two. Amorphous and nanocrystalline carbon films can exist in different kinds of matrices and are usually doped with a large amount of hydrogen. Thus, carbon films can be classified as polymer-like, diamond-like, or graphite-like based on the main binding framework. In order to characterize the structure, either direct bonding characterization methods or the indirect bonding characterization methods are employed. Examples of techniques utilized to identify the chemical bonds and microstructure of amorphous and nanocrystalline carbon films include optical characterization methods such as Raman spectroscopy, Ultra-violet (UV) Raman spectroscopy, and infrared spectroscopy, electron spectroscopic and microscopic methods such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, transmission electron microscopy, and electron energy loss spectroscopy, surface morphology characterization techniques such as scanning probe microscopy (SPM) as well as other characterization methods such as X-ray reflectivity and nuclear magnetic resonance. In this review, the structures of various types of amorphous carbon films and common characterization techniques are described

  1. Spherical rhenium metal powder

    Leonhardt, T.; Moore, N.; Hamister, M.

    2001-01-01

    The development of a high-density, spherical rhenium powder (SReP) possessing excellent flow characteristics has enabled the use of advanced processing techniques for the manufacture of rhenium components. The techniques that were investigated were vacuum plasma spraying (VPS), direct-hot isostatic pressing (D-HIP), and various other traditional powder metallurgy processing methods of forming rhenium powder into near-net shaped components. The principal disadvantages of standard rhenium metal powder (RMP) for advanced consolidation applications include: poor flow characteristics; high oxygen content; and low and varying packing densities. SReP will lower costs, reduce processing times, and improve yields when manufacturing powder metallurgy rhenium components. The results of the powder characterization of spherical rhenium powder and the consolidation of the SReP are further discussed. (author)

  2. Synthesis and characterization of nanosized ceria powders by microwave-hydrothermal method

    Bonamartini Corradi, A.; Bondioli, F.; Ferrari, A.M.; Manfredini, T.

    2006-01-01

    Nanocrystalline ceria powders (CeO 2 ) have been prepared by adding NaOH to a cerium ammonium nitrate aqueous solution under microwave-hydrothermal conditions. In particular the effect of the synthesis conditions (time, pressure and concentration of both the precursor and the precipitant agent solutions) on the physical properties of the crystals have been evaluated. Microwave-hydrothermal treatment of 5 min at 13.4 atm allows to obtain almost crystallized powders (amorphous phase 4%) as underlined by Rietveld-reference intensity ratio (RIR) results

  3. The synthesis and characterization of mixed Y2O3-doped ZrO2 and ¿-Fe2O3 nanosized powders

    Raming, T.P.; Winnubst, Aloysius J.A.; Verweij, H.

    2002-01-01

    Several wet chemical precipitation methods used to synthesise nanocrystalline composite powders containing zirconium oxide, yttrium oxide and iron(III) oxide are described. The crystallisation and phase composition of the precipitates were studied as a function of temperature. A co-precipitation

  4. Photocatalytic behaviors and structural characterization of nanocrystalline Fe-doped TiO2 synthesized by mechanical alloying

    Kim, Dong Hyun; Hong, Hyun Seon; Kim, Sun Jae; Song, Jae Sung; Lee, Kyung Sub

    2004-01-01

    Nanocrystalline Fe-doped TiO 2 powders were synthesized by mechanical alloying (MA) with varying Fe contents from 0 up to 4.8 wt.% to shift the absorption threshold into the visible light region. The photocatalytic feasibility of the Fe-doped TiO 2 powder was evaluated by quantifying the visible light absorption capacity using ultraviolet and visible (UV-Vis) spectroscopy and photoluminescence spectroscopy. Effects of Fe additions on the crystal structures and the morphologies of the Fe-doped powders were also investigated as a function of the doping content using transmission electron microscopy-electron diffraction pattern (TEM-EDP), X-ray diffraction (XRD) and energy dispersive X-ray (EDAX) and X-ray photoelectron spectroscopy (XPS). The UV-Vis study showed that the UV absorption for the Fe-doped powder moved to a longer wavelength (red shift) and the photoefficiency was enhanced. Based on the analysis of the photoluminescence spectra, the red shift was believed to be induced by localizing the dopant level near the valence band of TiO 2 . The UV-Vis absorption depended on the Fe concentration. TEM-EDP and XRD investigations showed that the Fe-doped powder had a rutile phase in which the added Fe atoms were dissolved. The rutile phase was composed of spherical particles and chestnut bur shaped particles, resulting in a larger surface area than the spherical P-25 powder

  5. Nanocrystalline NdFeB magnet prepared by mechanically activated disproportionation and desorption-recombination in-situ sintering

    Xiaoya, Liu; Yuping, Li; Lianxi, Hu

    2013-01-01

    The process of mechanically activated disproportionation and desorption-recombination in-situ sintering was proposed to synthesize highly densified nanocrystalline NdFeB magnet, and its validity was demonstrated by experimental investigation with the use of a Nd 16 Fe 76 B 8 (atomic ratio) alloy. Firstly, the as-cast alloy was disproportionated by mechanical milling in hydrogen, with the starting micron-sized Nd 2 Fe 14 B phase decomposed into an intimate mixture of nano-structured NdH 2.7 , Fe 2 B and α-Fe phases. The as-disproportionated alloy powders were compacted by cold pressing and then subjected to desorption-recombination in-situ sintering. The microstructure of both the as-disproportionated and the subsequently sintered samples was characterized by X-ray diffraction and electron transmission microscopy, respectively. The magnetic properties of the sintered samples were measured by using vibrating sample magnetometer. The results showed that, by vacuum sintering, not only was the powder compact consolidated, but also the as-disproportionated microstucture transformed into nanocrystalline Nd 2 Fe 14 B phase via the well-known desorption-recombination reaction, thus giving rise to nanocrystalline NdFeB magnet. In the present study, the optimal sintering parameters were found to be 780 °C×30 min. In this case, the coercivity, the remanence, and maximum energy product of the magnet sample achieved 0.8 T, 635.3 kA/m, and 106.3 kJ/m 3 , respectively. - Highlights: ► Nano-structured disproportionated NdFeB alloy powders by mechanical milling in hydrogen. ► Highly densified green magnet compact by cold pressing of as-disproportionated NdFeB alloy powders. ► Nanocrystalline NdFeB magnets by desorption-recombination in-situ sintering under vacuum. ► Magnetic properties significantly improved by relative density enhancement and nanocrystallization of Nd 2 Fe 14 B phase. ► The effects of sintering parameters on magnetic properties and the underlying

  6. Nanocrystalline NdFeB magnet prepared by mechanically activated disproportionation and desorption-recombination in-situ sintering

    Xiaoya, Liu; Yuping, Li [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Lianxi, Hu, E-mail: hulx@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2013-03-15

    The process of mechanically activated disproportionation and desorption-recombination in-situ sintering was proposed to synthesize highly densified nanocrystalline NdFeB magnet, and its validity was demonstrated by experimental investigation with the use of a Nd{sub 16}Fe{sub 76}B{sub 8} (atomic ratio) alloy. Firstly, the as-cast alloy was disproportionated by mechanical milling in hydrogen, with the starting micron-sized Nd{sub 2}Fe{sub 14}B phase decomposed into an intimate mixture of nano-structured NdH{sub 2.7}, Fe{sub 2}B and {alpha}-Fe phases. The as-disproportionated alloy powders were compacted by cold pressing and then subjected to desorption-recombination in-situ sintering. The microstructure of both the as-disproportionated and the subsequently sintered samples was characterized by X-ray diffraction and electron transmission microscopy, respectively. The magnetic properties of the sintered samples were measured by using vibrating sample magnetometer. The results showed that, by vacuum sintering, not only was the powder compact consolidated, but also the as-disproportionated microstucture transformed into nanocrystalline Nd{sub 2}Fe{sub 14}B phase via the well-known desorption-recombination reaction, thus giving rise to nanocrystalline NdFeB magnet. In the present study, the optimal sintering parameters were found to be 780 Degree-Sign C Multiplication-Sign 30 min. In this case, the coercivity, the remanence, and maximum energy product of the magnet sample achieved 0.8 T, 635.3 kA/m, and 106.3 kJ/m{sup 3}, respectively. - Highlights: Black-Right-Pointing-Pointer Nano-structured disproportionated NdFeB alloy powders by mechanical milling in hydrogen. Black-Right-Pointing-Pointer Highly densified green magnet compact by cold pressing of as-disproportionated NdFeB alloy powders. Black-Right-Pointing-Pointer Nanocrystalline NdFeB magnets by desorption-recombination in-situ sintering under vacuum. Black-Right-Pointing-Pointer Magnetic properties significantly

  7. Photoacoustic study of nanocrystalline silicon produced by mechanical grinding

    Poffo, C.M. [Departamento de Engenharia Mecanica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Lima, J.C. de, E-mail: fsc1jcd@fisica.ufsc.b [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Trindade, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Souza, S.M.; Triches, D.M. [Departamento de Engenharia Mecanica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Grandi, T.A. [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Trindade, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Biasi, R.S. de [Secao de Engenharia Mecanica e de Materiais, Instituto Militar de Engenharia, 22290-270 Rio de Janeiro, RJ (Brazil)

    2011-04-01

    Mechanical grinding (MG) was used to produce nanocrystalline silicon and its thermal and transport properties were investigated by photoacoustic absorption spectroscopy (PAS). The experimental results suggest that in as-milled nanocrystalline silicon for 10 h the heat transfer through the crystalline and interfacial components is similar, and after annealed at 470 {sup o}C the heat transfer is controlled by crystalline component.

  8. Photoacoustic study of nanocrystalline silicon produced by mechanical grinding

    Poffo, C.M.; Lima, J.C. de; Souza, S.M.; Triches, D.M.; Grandi, T.A.; Biasi, R.S. de

    2011-01-01

    Mechanical grinding (MG) was used to produce nanocrystalline silicon and its thermal and transport properties were investigated by photoacoustic absorption spectroscopy (PAS). The experimental results suggest that in as-milled nanocrystalline silicon for 10 h the heat transfer through the crystalline and interfacial components is similar, and after annealed at 470 o C the heat transfer is controlled by crystalline component.

  9. Nano crystalline high energy milled 5083 Al powder deposited using cold spray

    Rokni, M.R., E-mail: mohammadreza.rokni@mines.sdsmt.edu [Department of Materials and Metallurgical Engineering, Advanced Materials Processing Center, South Dakota School of Mines and Technology (SDSM and T), SD (United States); Widener, C.A. [Department of Materials and Metallurgical Engineering, Advanced Materials Processing Center, South Dakota School of Mines and Technology (SDSM and T), SD (United States); Nardi, A.T. [United Technologies Research Center, East Hartford, CT (United States); Champagne, V.K. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD (United States)

    2014-06-01

    Electron microscopy and nanoindentation are used to investigate the relationship between microstructure and nanohardness of a non-cryomilled, nanocrystalline 5083 Al alloy powder before and after being deposited by cold spray. Microstructural investigations observed the presence of nano grains in the powder microstructure, ranging from 20 to 80 nm and with a typical grain size of 40–50 nm. It was also revealed that the nanocrystalline structure of the powder is retained after cold spraying. As a result, almost no change in nanohardness was indicated between the powder and the particles interior in the cold sprayed layer. However, hardness was substantially higher in some regions in the cold sprayed layer, which was attributed to the particle–particle interfaces or other areas with very small nano grain size. The presence of some un-joined particle remnant lines was also found in the deposition and explained through Critical Velocity Ratio (CVR) of powder particles. Although cold spray is a high deformation process, there is little evidence of dislocations within the nanograins of the cold sprayed layer. The latter observation is rationalized through intragranular dislocation slip and recovery mechanisms.

  10. Studies on the synthesis of nanocrystalline Y{sub 2}O{sub 3} and ThO{sub 2} through volume combustion and their sintering

    Sanjay Kumar, D. [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Ananthasivan, K., E-mail: asivan@igcar.gov.in [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Venkata Krishnan, R. [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Amirthapandian, S. [Material Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Dasgupta, Arup [Microscopy and Thermo-Physical Property Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India)

    2016-10-15

    Volume combustion was observed in the auto-ignition of the citrate gels containing the nitrates of yttrium/thorium for the first time in mixture with a fuel (citric acid) to oxidant (Y{sup 3+} or Th{sup 4+} nitrate) ratio close to that demanded by the stoichiometry. These nanocrystalline powders were characterized for their bulk density, specific surface area, particle size distribution, carbon residue and X-ray crystallite size and were sintered by both the conventional and the two-step method. The maximum relative sintered density of Y{sub 2}O{sub 3} was 98.9% TD. The sintered density of thoria (97.8% TD) is the highest among the values reported so far, for nanocrystalline ThO{sub 2}. Characterization of the pellets and powders by using scanning electron microscopy and transmission electron microscopy reaffirmed nanocrystallinity and that the sintered pellets comprised faceted sintered grains. The two-step sintering was found to restrict “runaway” sintering. - Highlights: • Scaled-up synthesis of nanocrystalline Y{sub 2}O{sub 3} and ThO{sub 2} using citrate gel-combustion method. • VCR was observed at a fuel to nitrate ratio (R) of 0.125 and 0.17 in mixtures containing Th(NO{sub 3}){sub 4} and Y(NO{sub 3}){sub 3} respectively. • The calcined powders were compacted and sintered by using a novel two-step sintering method. • Sintered densities as high as 97.8% T.D. (ThO{sub 2}, T{sub H} = 0.48) and 98.9% T.D. (Y{sub 2}O{sub 3}, T{sub H} = 0.61) were obtained.

  11. SAF line powder operations

    Frederickson, J.R.; Horgos, R.M.

    1983-10-01

    An automated nuclear fuel fabrication line is being designed for installation in the Fuels and Materials Examination Facility (FMEF) near Richland, Washington. The fabrication line will consist of seven major process systems: Receiving and Powder Preparation; Powder Conditioning; Pressing and Boat Loading; Debinding, Sintering, and Property Adjustment; Boat Transport; Pellet Inspection and Finishing; and Pin Operations. Fuel powder processing through pellet pressing will be discussed in this paper

  12. Two layer powder pressing

    Schreiner, H.

    1979-01-01

    First, significance and advantages of sintered materials consisting of two layers are pointed out. By means of the two layer powder pressing technique metal powders are formed resulting in compacts with high accuracy of shape and mass. Attributes of basic powders, different filling methods and pressing techniques are discussed. The described technique is supposed to find further applications in the field of two layer compacts in the near future

  13. Operation whey powder

    Brunner, E.

    1987-01-01

    The odyssey of the contaminated whey powder finally has come to an end, and the 5000 tonnes of whey now are designated for decontamination by means of an ion exchange technique. The article throws light upon the political and economic reasons that sent the whey powder off on a chaotic journey. It is worth mentioning in this context that the natural radioactivity of inorganic fertilizers is much higher than that of the whey powder in question. (HP) [de

  14. Ceria powders by homogeneous precipitation technique

    Ramanathan, S.; Roy, S.K.

    2003-01-01

    Formation of precursors for ceria by two homogeneous precipitation reactions - (cerium chloride + urea at 95 degC - called reaction A and cerium chloride + hexamethylenetetramine at 85 degC - called reaction B) - has been studied. The variation of size of the colloidal particles formed and the zeta potential of the suspensions with progress of reactions exhibited similar trends for both the precipitation processes. Particle size increased from 100 to 300 nm with increasing temperature and extent of reaction. The zeta potential was found to decrease with increasing extent of precipitation in the pH range of 5 to 7. Filtration and drying led to agglomeration of the fine particles in case of the precursor from reaction B. The as-formed precursors were crystalline - a basic carbonate in case of reaction A and hydrous oxide in case of reaction B. It was found that nano-crystalline ceria powders (average crystallite size -10 nm) formed above 400 degC from both these precursors. The agglomerate size (D50) of the precursors and ceria powders formed after calcination at 600 degC varied from 0.7 to 3 μm. Increasing calcination temperature up to 800 degC, increased the crystallite size (50 nm). The zeta potential variation with pH and concentration of an anionic dispersant (Calgon) for the ceria powders formed was studied to determine the ideal conditions for suspension stability. It was found to be maximum (i.e., the suspensions stable) in the pH range of 3 to 4 or Calgon concentration of 0.01 to 0.1 weight percent. (author)

  15. Structural, electrical and dielectric properties of nanocrystalline Mg-Zn ferrites

    Anis-ur-Rehman, M.; Malik, M.A.; Nasir, S.; Mubeen, M.; Khan, K.; Maqsood, A.

    2011-01-01

    The nanocrystalline Mg-Zn ferrites having general formula Mg/sub 1-x/Zn/sub x/Fe/sub 2/O/sub 4/ (x=0, 0.1, 0.2, 0.3, 0.4, 0. 5) were prepared by WOWS sol-gel route. All prepared samples were sintered at 700 deg. C for 2 h. X-ray powder diffraction (XRD) technique was used to investigate structural properties of the samples. The crystal structure was found to be spinel. The crystallite size, lattice parameters and porosity of samples were calculated by XRD data analysis as function of zinc concentration. The crystallite size for each sample was calculated using the Scherrer formula considering the most intense (3 1 1) peak and the range obtained was 34-68 nm. The dielectric constant, dielectric loss tangent and AC electrical conductivity of nanocrystalline Mg-Zn ferrites are investigated as a function of frequency. The dielectric constant, dielectric loss tangent increased with increase of Zn concentration. All the electrical properties are explained in accordance with Maxwell Wagner model and K/sub oops/ phenomenological theory. (author)

  16. Properties and in vivo investigation of nanocrystalline hydroxyapatite obtained by mechanical alloying

    Silva, C.C.; Pinheiro, A.G.; Oliveira, R.S. de; Goes, J.C.; Aranha, N.; Oliveira, L.R. de; Sombra, A.S.B

    2004-06-01

    Mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) using three different procedures. The milled HA was studied by X-ray diffraction, Infrared, Raman scattering spectroscopy and Scanning Electron Microscopy (SEM). We obtained HA with different degrees of crystallinity and time of milling. The grain size analysis through SEM and XRD shows particles with dimensions of 36.9, 14.3 and 35.5 nm (for (R1), (R2) and (R3), respectively) forming bigger units with dimensions given by 117.2, 110.8 and 154.4 nm (for (R1), (R2) and (R3), respectively). The Energy-Dispersive Spectroscopy (EDS) analysis showed that an atomic ratio of Ca/P=1.67, 1.83 and 1.50 for reactions (R1), (R2) and (R3), respectively. These results suggest that the R1 nanocrystalline ceramic is closer to the expected value for the ratio Ca/P for hydroxyapatite, which is 5/3 congruent with 1.67. The bioactivity analysis shows that all the samples implanted into the rabbits can be considered biocompatible, since they had been considered not toxic, had not caused inflammation and reject on the part of the organisms of the animals, during the period of implantation. The samples implanted in rabbits had presented new osseous tissue formation with the presence of osteoblasts cells.

  17. Properties and in vivo investigation of nanocrystalline hydroxyapatite obtained by mechanical alloying

    Silva, C.C.; Pinheiro, A.G.; Oliveira, R.S. de; Goes, J.C.; Aranha, N.; Oliveira, L.R. de; Sombra, A.S.B.

    2004-01-01

    Mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) using three different procedures. The milled HA was studied by X-ray diffraction, Infrared, Raman scattering spectroscopy and Scanning Electron Microscopy (SEM). We obtained HA with different degrees of crystallinity and time of milling. The grain size analysis through SEM and XRD shows particles with dimensions of 36.9, 14.3 and 35.5 nm (for (R1), (R2) and (R3), respectively) forming bigger units with dimensions given by 117.2, 110.8 and 154.4 nm (for (R1), (R2) and (R3), respectively). The Energy-Dispersive Spectroscopy (EDS) analysis showed that an atomic ratio of Ca/P=1.67, 1.83 and 1.50 for reactions (R1), (R2) and (R3), respectively. These results suggest that the R1 nanocrystalline ceramic is closer to the expected value for the ratio Ca/P for hydroxyapatite, which is 5/3 congruent with 1.67. The bioactivity analysis shows that all the samples implanted into the rabbits can be considered biocompatible, since they had been considered not toxic, had not caused inflammation and reject on the part of the organisms of the animals, during the period of implantation. The samples implanted in rabbits had presented new osseous tissue formation with the presence of osteoblasts cells

  18. Pharmaceutical powder compaction technology

    Çelik, Metin

    2011-01-01

    ... through the compaction formulation process and application. Compaction of powder constituents both active ingredient and excipients is examined to ensure consistent and reproducible disintegration and dispersion profiles...

  19. Magnetic behavior of nanocrystalline nickel ferrite

    Nathani, H.; Gubbala, S.; Misra, R.D.K.

    2005-01-01

    In the previous papers [R.D.K. Misra, A. Kale, R.S. Srivatsava, O. Senkov, Mater. Sci. Technol. 19 (2003) 826; R.D.K. Misra, A. Kale, B. Hooi, J.Th. DeHosson, Mater. Sci. Technol. 19 (2003) 1617; A. Kale, S. Gubbala, R.D.K. Misra, J. Magn. Magn. Mater. 277 (2004) 350; S. Gubbala, H. Nathani, K. Koizol, R.D.K. Misra, Phys. B 348 (2004) 317; R.D.K. Misra, S. Gubbala, A. Kale, W.F. Egelhoff, Mater. Sci. Eng. B. 111 (2004) 164], we reported the synthesis, structural characterization and magnetic behavior of nanocrystalline ferrites of inverse and mixed spinel structure made by reverse micelle technique that enabled a narrow particle size distribution to be obtained. In the present paper, the reverse micelle approach has been extended to synthesize nanocrystalline ferrites with varying surface roughness of 8-18 A (the surface roughness was measured by atomic force microscopy) and the magnetic behavior studied by SQUID magnetometer. Two different kinds of measurement were performed: (a) zero-field cooling (ZFC) and field cooling (FC) magnetization versus temperature measurements and (b) magnetization as a function of applied field. The analysis of magnetic measurement suggests significant influence of surface roughness of particles on the magnetic behavior. While the superparamagnetic behavior is retained by the nanocrystalline ferrites of different surface roughness at 300 K, the hysteresis loop at 2 K becomes non-squared and the coercivity increases with increase in surface roughness. This behavior is discussed in terms of broken bonds and degree of surface spin disorder

  20. Structural and magnetic properties of nanocrystalline stannic substituted cobalt ferrite

    Abbas, Y.M., E-mail: ymabbas@live.com [Physics Department, Faculty of Science, Suez Canal University, Ismailia (Egypt); Mansour, S.A. [Physics Department, Faculty of Science, Suez Canal University, Ismailia (Egypt); Physics Department, Faculty of Science, King AbdulAziz University, Rabegh (Saudi Arabia); Ibrahim, M.H. [Physics Department, Faculty of Science, Suez Canal University, Ismailia (Egypt); Physics Department, Faculty of Science, King AbdulAziz University (Saudi Arabia); Ali, Shehab. E., E-mail: shehab_ali@science.suez.edu.eg [Physics Department, Faculty of Science, Suez Canal University, Ismailia (Egypt)

    2012-09-15

    The structural and magnetic properties of the spinel ferrite system Co{sub 1+x}Fe{sub 2-2x}Sn{sub x}O{sub 4} (x=0.0-1.0) have been studied. Samples in the series were prepared by the ceramic technique. The structural and microstructural evolutions of the nanophase have been studied using X-ray powder diffraction and the Rietveld method. The refinement result showed that the type of the cationic distribution over the tetrahedral and octahedral sites in the nanocrystalline lattice is partially an inverse spinel. Far infrared absorption spectra show two significant absorption bands, around 600 cm{sup -1} and 425 cm{sup -1}, which are respectively attributed to tetrahedral (A) and octahedral [B] vibrations of the spinel. Scanning Electron Microscopy (SEM) was used to study surface morphology. SEM images reveal particles in the nanosize range. The transmission electronic microscope (TEM) reveals that the grains are spherical in shape. TEM analysis confirmed the X-ray results. The magnetic properties of the prepared samples were characterized by using a vibrating sample magnetometer. - Highlights: Black-Right-Pointing-Pointer The spinel ferrite system has been formed at 1000 Degree-Sign C by using ceramic techniques. Black-Right-Pointing-Pointer Structural and microstructural evolutions have been studied using XRD and the Rietveld method. Black-Right-Pointing-Pointer The refinement result showed cationic distribution in the lattice is partially an inverse spinel. Black-Right-Pointing-Pointer The transmission electronic microscope analysis confirmed the X-ray results. Black-Right-Pointing-Pointer Magnetic properties of the samples were characterized by using a vibrating sample magnetometer.

  1. Structural and magnetic properties of nanocrystalline stannic substituted cobalt ferrite

    Abbas, Y.M.; Mansour, S.A.; Ibrahim, M.H.; Ali, Shehab. E.

    2012-01-01

    The structural and magnetic properties of the spinel ferrite system Co 1+x Fe 2−2x Sn x O 4 (x=0.0–1.0) have been studied. Samples in the series were prepared by the ceramic technique. The structural and microstructural evolutions of the nanophase have been studied using X-ray powder diffraction and the Rietveld method. The refinement result showed that the type of the cationic distribution over the tetrahedral and octahedral sites in the nanocrystalline lattice is partially an inverse spinel. Far infrared absorption spectra show two significant absorption bands, around 600 cm −1 and 425 cm −1 , which are respectively attributed to tetrahedral (A) and octahedral [B] vibrations of the spinel. Scanning Electron Microscopy (SEM) was used to study surface morphology. SEM images reveal particles in the nanosize range. The transmission electronic microscope (TEM) reveals that the grains are spherical in shape. TEM analysis confirmed the X-ray results. The magnetic properties of the prepared samples were characterized by using a vibrating sample magnetometer. - Highlights: ► The spinel ferrite system has been formed at 1000 °C by using ceramic techniques. ► Structural and microstructural evolutions have been studied using XRD and the Rietveld method. ► The refinement result showed cationic distribution in the lattice is partially an inverse spinel. ► The transmission electronic microscope analysis confirmed the X-ray results. ► Magnetic properties of the samples were characterized by using a vibrating sample magnetometer.

  2. Transparent nanocrystalline diamond coatings and devices

    Sumant, Anirudha V.; Khan, Adam

    2017-08-22

    A method for coating a substrate comprises producing a plasma ball using a microwave plasma source in the presence of a mixture of gases. The plasma ball has a diameter. The plasma ball is disposed at a first distance from the substrate and the substrate is maintained at a first temperature. The plasma ball is maintained at the first distance from the substrate, and a diamond coating is deposited on the substrate. The diamond coating has a thickness. Furthermore, the diamond coating has an optical transparency of greater than about 80%. The diamond coating can include nanocrystalline diamond. The microwave plasma source can have a frequency of about 915 MHz.

  3. Simulations of intergranular fracture in nanocrystalline molybdenum

    Frederiksen, Søren Lund; Jacobsen, Karsten Wedel; Schiøtz, Jakob

    2004-01-01

    Using molecular dynamics simulations we investigate the plastic deformation of nanocrystalline molybdenum with a grain size of 12 nm at high strain rates. The simulations are performed with an interatomic potential which is obtained through matching of atomic forces to a database generated...... with density-functional calculations. The simulations show the plastic deformation to involve both grain boundary processes and dislocation migration which in some cases lead to twin boundary formation. A large component of the strain is accommodated through the formation of cracks in the grain boundaries...

  4. Effect of silver addition on the properties of combustion synthesized nanocrystalline LiCoO2

    Ghosh, Paromita; Mahanty, S.; Basu, R.N.

    2008-01-01

    Nanocrystalline (∼50 nm) LiCoO 2 powders containing 0-10 mol% of Ag have been prepared by combustion synthesis using citrate-nitrate combustion route. Thermal analyses show a sharp decomposition of the gel at ∼177 deg. C for pristine LiCoO 2 . With addition of silver, the decomposition becomes sluggish and it completes only above 430 deg. C. X-ray powder diffraction analyses show an increase in lattice parameter, c, with increasing Ag content suggesting the occupation of Ag within LiCoO 2 interlayer spacings. Transmission electron microscopy indicates diffusion of Ag into LiCoO 2 grains. It has been observed that adding 1.0 mol% silver increases the room temperature electrical conductivity by more than two orders of magnitude (1.5 x 10 -3 S cm -1 ). Galvanostatic charge-discharge profiles of coin cells fabricated with the synthesized powders show a two-fold enhancement in the discharge capacity for 1.0 mol% Ag-added LiCoO 2 cathode (140 mAh g -1 ) compared to that for pristine LiCoO 2 (70 mAh g -1 )

  5. Biaxially textured articles formed by powder metallurgy

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2003-08-05

    A biaxially textured alloy article having a magnetism less than pure Ni includes a rolled and annealed compacted and sintered powder-metallurgy preform article, the preform article having been formed from a powder mixture selected from the group of ternary mixtures consisting of: Ni powder, Cu powder, and Al powder, Ni powder, Cr powder, and Al powder; Ni powder, W powder and Al powder; Ni powder, V powder, and Al powder; Ni powder, Mo powder, and Al powder; the article having a fine and homogeneous grain structure; and having a dominant cube oriented {100} orientation texture; and further having a Curie temperature less than that of pure Ni.

  6. Ag diffusion and interface segregation in nanocrystalline γ-FeNi alloy with a two-scale microstructure

    Divinski, S.V.; Hisker, F.; Kang, Y.-S.; Lee, J.-S.; Herzig, Chr.

    2004-01-01

    Solute diffusion of Ag in nanocrystalline γ-Fe - 40wt%Ni alloy was studied by means of the radiotracer technique in an extended temperature interval (489-1200 K). The powder metallurgical method was applied to produce nanomaterial which consisted of micrometer-large clusters (agglomerates) of nanometer sized grains. Two types of internal interfaces contributed as short-circuit paths for diffusion: the nanocrystalline grain boundaries (GB) and the inter-agglomerate interfaces (subscript a). Combining the recent results on Ag GB diffusion in coarse-grained γ-Fe - 40wt%Ni alloy and the present diffusion data in the nanocrystalline alloy the Ag segregation was determined as function of temperature. Ag segregates strongly at GBs in the γ-Fe - 40wt%Ni alloy with a segregation enthalpy of H s =-47 kJ/mol. Knowing the segregation factor, the experimental data on Ag diffusion along both nanocrystalline and inter-agglomerate interfaces in the nanomaterial were systematically analyzed in dependence on the different kinetic regimes. The sensitive radiotracer experiments and the subsequent diffusion profile analysis resulted in a consistent set of diffusion data in the whole investigated temperature range with Arrhenius behavior for both the Ag nano-GB diffusion (D 0 gb =4.7x10 -4 m 2 /s, H gb =173 kJ/mol) as well as for the much faster inter-agglomerate interface diffusion (D 0 a =8.1x10 -5 m 2 /s, H a =91 kJ/mol)

  7. Synthesis of free standing nanocrystalline Cu by ball milling at cryogenic temperature

    Barai, K. [Department of Metallurgy and Materials Engineering, Bengal Engineering College, Shibpur, Howrah 711103 (India); Tiwary, C.S. [Department of Materials Engineering, Indian Institute of Science, Bangalore 560012 (India); Chattopadhyay, P.P. [Department of Metallurgy and Materials Engineering, Bengal Engineering College, Shibpur, Howrah 711103 (India); Chattopadhyay, K., E-mail: kamanio@materials.iisc.ernet.in [Department of Materials Engineering, Indian Institute of Science, Bangalore 560012 (India)

    2012-12-15

    This paper reports for the first time synthesis of free standing nano-crystalline copper crystals of a {approx}30-40 nm by ball milling of copper powder at 150 K under Argon atmosphere in a specially designed cryomill. The detailed characterization of these particles using multiple techniques that includes transmission electron microscopy confirms our conclusion. Careful analysis of the chemistry of these particles indicates that these particles are essentially contamination free. Through the analysis of existing models of grain size refinements during ball milling and low temperature deformation, we argue that the suppression of thermal processes and low temperature leads to formation of free nanoparticles as the process of fracture dominates over possible cold welding at low temperatures.

  8. Crystallite growth in nanocrystalline tungsten; rate determining mechanism and the role of contaminations

    Hegedűs, Zoltán; Meka, Sai Ramudu; Mittemeijer, Eric J.

    2016-01-01

    The thermal stability of nanocrystalline tungsten was investigated by tracing the evolution of the microstructure as a function of (isothermal) annealing time at different temperatures (800−875 °C). To this end especially in situ X-ray diffraction and transmission electron microscopy methods were applied to ball milled tungsten powder. Initially the dislocation density and the crystallite/domain size decreased and increased rapidly, respectively. Upon prolonged annealing the crystallite growth rate decelerated and even became nil: a saturation crystallite size, increasing with increasing annealing temperature, was attained. Application of all available isothermal growth models to the experimental data resulted in very low values for the activation energy (60−120 kJ/mol) indicating that recovery of the deformed microstructure is the dominantly occurring process, leading to pronounced crystallite/domain growth. The effect on the growth kinetics of different levels of contaminations, which exert a drag force on the moving boundaries, was also investigated.

  9. Chemical synthesis of nanocrystalline magnesium aluminate spinel via nitrate-citrate combustion route

    Saberi, Ali; Golestani-Fard, Farhad; Sarpoolaky, Hosein; Willert-Porada, Monika; Gerdes, Thorsten; Simon, Reinhard

    2008-01-01

    Nanocrystalline magnesium aluminate spinel (MgAl 2 O 4 ) was synthesized using metal nitrates, citric acid and ammonium solutions. The precursor and the calcined powders at different temperatures were characterized by X-ray diffraction (XRD), simultaneous thermal analysis (STA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The combustion mechanism was also studied by a quadrupole mass spectrometer (QMS) which coupled to STA. The generated heat through the combustion of the mixture of ammonium nitrate and citrate based complexes decreased the synthesis temperature of MgAl 2 O 4 spinel. The synthesized MgAl 2 O 4 spinel at 900 deg. C has faced shape with crystallite size in the range of 18-24 nm

  10. Synthesis and characterization of nanocrystalline Ni-YSZ cermet anode for SOFC

    Priyatham, T.; Bauri, Ranjit

    2010-01-01

    Ni-YSZ cermet anode has been synthesized in one step using a simple and cost effective combustion synthesis process. The processed powder of NiO-YSZ is found to be nanocrystalline with crystallite sizes of 29 and 22 nm for NiO and YSZ respectively by X-ray diffraction and transmission electron microscopy analysis. X-ray diffraction analysis also shows that the precursor salts are converted to highly crystalline phases of NiO and YSZ (8 mol% Y 2 O 3 ) without any intermediate calcination step and no undesirable phases are present. Comparison with the X-ray diffraction pattern of a commercial YSZ sample shows that the process is also effective in maintaining a close compositional control. The microstructure of the sintered and reduced sample shows a well defined network of pores which is necessary for the effective functioning of the anode. The electrical conductivity as a function of temperature shows metallic behavior.

  11. Crystallographic and magnetic properties of nanocrystalline perovskite structure SmFeO3 orthoferrite

    Kumar, Ashwini; Shen, Jingdong; Zhao, Huihui; Zhengjian, Qi; Li, Qi

    2018-05-01

    In this article, we present the structural and magnetic studies of pristine SmFeO3 nanocrystalline ceramic samples as sintered at temperature 850 °C and 1000 °C. X-ray powder diffraction data confirm the existence of single-phase nature with orthorhombic (Pbnm) structure of the samples. The SEM image reveals spherical particles with a size range of 60-130 nm for SFO-850 and SFO-1000 samples. X-ray absorption spectroscopy studies on Fe L3,2 and O K-edges of SmFeO3 sample revealed the homo-valence state of Fe in these materials. From magnetization studies it has been observed the materials exhibit ferromagnetic and antiferromagnetic (canted spin structure) sub-lattices, which results strong magnetic anisotropy in the system.

  12. Characterization of Ni ferrites powders prepared by plasma arc discharge process

    Safari, A. [Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University, Ahvaz (Iran, Islamic Republic of); Gheisari, Kh., E-mail: khgheisari@scu.ac.ir [Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University, Ahvaz (Iran, Islamic Republic of); Farbod, M. [Physics Department, Shahid Chamran University, Ahvaz (Iran, Islamic Republic of)

    2017-01-01

    The aim of this work was to synthesize a single-phase spinel structure from a mixture of zinc, iron and nickel powders by plasma arc discharge method. A mixture of zinc, iron and nickel powders with the appropriate molar ratio was prepared and formed into a cylindrical shape. The synthesis process was performed in air, oxygen and argon atmospheres with the applied arc current of 400 A and pressure of 1 atm. After establishing an arc between the electrodes, the produced powders were collected and their structure and magnetic properties were examined by XRD and VSM, respectively. ZnO as an impurity was appeared in the as-produced powders owing to the high reactivity of zinc atoms, preventing the formation of Ni–Zn ferrite. A pure spinel structure with the highest saturation magnetization (43.8 emu/g) was observed as zinc powders removed completely from the initial mixture. Morphological evaluations using field emission scanning electron microscopy showed that the mean size of fabricated nanoparticles was in the range 100–200 nm and was dependent on the production conditions. - Highlights: • Nanocrystalline Ni ferrite powders are prepared by plasma arc discharge process. • The mean particle size of the as-synthesized ceramic powders is about 100 nm. • The highest saturation magnetization is observed as zinc powders removed completely from the initial mixture.

  13. A Highly Selective Room Temperature NH3 Gas Sensor based on Nanocrystalline a-Fe2O3

    Priyanka A. PATIL

    2017-05-01

    Full Text Available Nanocrystalline a-Fe2O3 powder was synthesized by simple, inexpensive sol-gel method. The obtained powder was calcined at 700 0C in air atmosphere for 2 hours. The structural and morphological properties of calcined powder were studied by X-ray diffraction (XRD and Field Emission Scanning Electron Microscopy (FESEM respectively. Thermal properties of dried gel were studied by Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC. The XRD pattern of the powder confirmed the a-Fe2O3 (hematite phase of iron oxide with average crystalline size of 30.87 nm calculated from Scherrer equation. The FESEM images showed uniform wormlike morphology of a-Fe2O3 powder. TGA result indicated that a-Fe2O3 is thermodynamically stable. Room temperature NH3 sensing characteristics of a-Fe2O3 were studied for various concentration levels (250-2500 ppm of NH3 at various humid conditions. The sensor based on a-Fe2O3 exhibited good selectivity and excellent sensitivity (S=92 towards 1000 ppm of NH3 with quick response of 4 sec and fast recovery of 9 sec. Room temperature sensing mechanism is also discussed.

  14. Sintered aluminium powders

    Stepanova, M.G.; Matveev, B.I.

    1974-01-01

    The mechanical and physical properties of aluminium powder alloys and the various methods employed to produce them are considered. Data are given on the hardening of the alloys SAP and SPAK-4, as well as the powder-alloy system Al-Cr-Zr. (L.M.)

  15. Microhardness studies of nanocrystalline lead molybdate

    Anandakumar, V.M.; Abdul Khadar, M.

    2009-01-01

    Nanocrystalline lead molybdate (PbMoO 4 ) of four different grain sizes were synthesized through chemical precipitation technique and the grain sizes and crystal structure are determined using the broadening of X-ray diffraction patterns and transmission electron microscopy. The microhardness of nanocrystalline lead molybdate (PbMoO 4 ) with different grain sizes were measured using a Vicker's microhardness tester for various applied loads ranging from 0.049 to 1.96 N. The microhardness values showed significant indentation size effect at low indentation loads. The proportional specimen resistance model put forward by Li and Bradt and energy balance model put forward by Gong and Li were used to analyze the behaviour of measured microhardness values under different indentation loads. The microhardness data obtained for samples of different grain sizes showed grain size dependent strengthening obeying normal Hall-Petch relation. The dependence of compacting pressure and annealing temperature on microhardness of the nanostructured sample with grain size of ∼18 nm were also studied. The samples showed significant increase in microhardness values as the compacting pressure and annealing time were increased. The variation of microhardness of the material with pressure of pelletization and annealing time are discussed in the light of change of pore size distribution of the samples.

  16. Investigation of the structure of nanocrystalline refractory oxides by X-ray diffraction, electron microscopy, and atomic force microscopy

    Ulyanova, T. M.; Titova, L. V.; Medichenko, S. V.; Zonov, Yu. G.; Konstantinova, T. E.; Glazunova, V. A.; Doroshkevich, A. S.; Kuznetsova, T. A.

    2006-01-01

    The structures of nanocrystalline fibrous powders of refractory oxides have been investigated by different methods: determination of coherent-scattering regions, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic-force microscopy (AFM). The sizes of nanograins of different crystalline phases of refractory metal oxides have been determined during the formation of these nanograins and the dynamics of their growth during heat treatment in the temperature range 600-1600 deg. C has been studied. The data on the structure of nanocrystalline refractory oxide powders, obtained by different methods, are in good agreement. According to the data on coherent-scattering regions, the sizes of the ZrO 2 (Y 2 O 3 ) and Al 2 O 3 grains formed are in the range 4-6 nm, and the particle sizes determined according to the TEM and AFM data are in the ranges 5-7 and 2-10 nm, respectively. SEM analysis made it possible to investigate the dynamics of nanoparticle growth at temperatures above 1000 deg. C and establish the limiting temperatures of their consolidation in fibers

  17. Gas response properties of citrate gel synthesized nanocrystalline MgFe2O4: Effect of sintering temperature

    Patil, J.Y.; Mulla, I.S.; Suryavanshi, S.S.

    2013-01-01

    Graphical abstract: Display Omitted Highlights: ► Synthesis of nanocrystalline MgFe 2 O 4 by economical citrate gel combustion method. ► Structural, morphological, and gas response properties of MgFe 2 O 4 . ► Enhancement in selectivity of MgFe 2 O 4 towards LPG with sintering temperature. ► Use of MgFe 2 O 4 to detect different gases at different operating temperatures. -- Abstract: Spinel type MgFe 2 O 4 material was synthesized by citrate gel combustion method. The effect of sintering temperature on structural, morphological, and gas response properties was studied. The powder X-ray diffraction pattern and transmission electron microscope study confirms nanocrystalline spinel structure of the synthesized powder. The material was tested for response properties to various reducing gases like liquid petroleum gas (LPG), acetone, ethanol, and ammonia. The results demonstrated n-type semiconducting behavior of MgFe 2 O 4 material. It was revealed that MgFe 2 O 4 sintered at 973 K was most sensitive to LPG at 648 K and to acetone at 498 K. However MgFe 2 O 4 sintered at 1173 K exhibited higher response and selectivity to LPG with marginal increase in the operating temperature. Furthermore, the sensor exhibited a fast response and a good recovery. It was observed that the particles size, porosity, and surface activity of the sensor material is affected by the sintering temperature.

  18. Nanocrystalline (Fe{sub 60}Al{sub 40}){sub 80}Cu{sub 20} alloy prepared by mechanical alloying

    Krifa, M.; Mhadhbi, M. [Laboratoire de Chimie Inorganique, 99/UR/12-22, FSS – Université de Sfax, B.P. 1171, Sfax 3018 (Tunisia); Escoda, L.; Güell, J.M. [Dept. de Fisica, Universitat de Girona, Campus Montilivi, 17071 Girona (Spain); Suñol, J.J., E-mail: joanjosep.sunyol@udg.edu [Dept. de Fisica, Universitat de Girona, Campus Montilivi, 17071 Girona (Spain); Llorca-Isern, N.; Artieda-Guzmán, C. [Dept. CMEM, Universitat de Barcelona, Martí Franques 1, 08028 Barcelona (Spain); Khitouni, M. [Laboratoire de Chimie Inorganique, 99/UR/12-22, FSS – Université de Sfax, B.P. 1171, Sfax 3018 (Tunisia)

    2013-03-25

    Highlights: ► Nanocrystalline Fe(Al, Cu) powdered alloy (10 nm) has been synthesized by MA. ► Decreasing the crystallite size increases coercivity and squareness ratio. ► As low crystallites size stronger hard ferromagnetic material results. -- Abstract: A nanostructured disordered Fe(Al, Cu) solid solution was obtained from prealloyed FeAl and elemental Cu powders using a high-energy ball mill. The transformations occurring in the material during milling were studied with the use of X-ray diffraction. The transformation of the phase depends upon the milling time. With the increase of milling time all Cu atoms became dissolved in the bcc Fe and the final product of the MA process was the nanocrystalline Fe(Al, Cu) solid solution with a mean crystallite size of 10 nm. Scanning electron microscopy (SEM) was employed to examine the morphology of the samples as a function of milling times. Magnetic properties were also investigated and were related to the microstructural changes. The system showed hard magnetic behavior.

  19. Measurement of loose powder density

    Akhtar, S.; Ali, A.; Haider, A.; Farooque, M.

    2011-01-01

    Powder metallurgy is a conventional technique for making engineering articles from powders. Main objective is to produce final products with the highest possible uniform density, which depends on the initial loose powder characteristics. Producing, handling, characterizing and compacting materials in loose powder form are part of the manufacturing processes. Density of loose metallic or ceramic powder is an important parameter for die design. Loose powder density is required for calculating the exact mass of powder to fill the die cavity for producing intended green density of the powder compact. To fulfill this requirement of powder metallurgical processing, a loose powder density meter as per ASTM standards is designed and fabricated for measurement of density. The density of free flowing metallic powders can be determined using Hall flow meter funnel and density cup of 25 cm/sup 3/ volume. Density of metal powders like cobalt, manganese, spherical bronze and pure iron is measured and results are obtained with 99.9% accuracy. (author)

  20. Synthesis of nanocrystalline fluorinated hydroxyapatite by ...

    The biological hydroxyapatite in the human bone and tooth is of nanosize and ... The crystal size and morphology of the nanopowders were examined by X-ray powder diffraction .... tal growth along the c axis of HA crystalline structure. The.

  1. Single step synthesis of GdAlO3 powder

    Sinha, Amit; Nair, S.R.; Sinha, P.K.

    2011-01-01

    Research highlights: → First report on direct formation of GdAlO 3 powder using a novel combustion process. → Study of combustion characteristics of Gd(NO 3 ) 3 and Al(NO 3 ) 3 towards three fuels. → Preparation of highly sinterable GdAlO 3 powders through fuel-mixture approach. → Significant reduction in energy consumption for production of GdAlO 3 sintered body. - Abstract: A novel method for preparation of nano-crystalline gadolinium aluminate (GdAlO 3 ) powder, based on combustion synthesis, is reported. It was observed that aluminium nitrate and gadolinium nitrate exhibit different combustion characteristics with respect to urea, glycine and β-alanine. While urea was proven to be a suitable fuel for direct formation of crystalline α-Al 2 O 3 from its nitrate, glycine and β-alanine are suitable fuels for gadolinium nitrate for preparation of its oxide after combustion reaction. Based on the observed chemical characteristics of gadolinium and aluminium nitrates with respect to above mentioned fuels for the combustion reaction, the fuel mixture composition could be predicted that could lead to phase pure perovskite GdAlO 3 directly after the combustion reaction without any subsequent calcination step. The use of single fuel, on the other hand, leads to formation of amorphous precursor powders that call for subsequent calcination for the formation of crystalline GdAlO 3 . The powders produced directly after combustion reactions using fuel mixtures were found to be highly sinterable. The sintering of the powders at 1550 o C for 4 h resulted in GdAlO 3 with sintered density of more than 95%. T.D.

  2. Electrochemical passivation behaviour of nanocrystalline Fe80Si20 ...

    Abstract. Passivation behaviour of nanocrystalline coating (Fe80Si20) obtained by in situ mechanical alloying route .... is controlled by the iron oxide film in case of alloys with ..... the surface is covered, thus, producing effective protection of.

  3. Optimization of nanocrystalline γ-alumina coating for direct spray ...

    Modifications of the partial gas percentage influences the optical properties and composition ... O2 flow in the Ar ambient and substrate temperature on struc- ture and properties of ..... nism to explain mechanical behaviour of nanocrystalline.

  4. Tailoring and patterning the grain size of nanocrystalline alloys

    Detor, Andrew J.; Schuh, Christopher A.

    2007-01-01

    Nanocrystalline alloys that exhibit grain boundary segregation can access thermodynamically stable or metastable states with the average grain size dictated by the alloying addition. Here we consider nanocrystalline Ni-W alloys and demonstrate that the W content controls the grain size over a very broad range: ∼2-140 nm as compared with ∼2-20 nm in previous work on strongly segregating systems. This trend is attributed to a relatively weak tendency for W segregation to the grain boundaries. Based upon this observation, we introduce a new synthesis technique allowing for precise composition control during the electrodeposition of Ni-W alloys, which, in turn, leads to precise control of the nanocrystalline grain size. This technique offers new possibilities for understanding the structure-property relationships of nanocrystalline solids, such as the breakdown of Hall-Petch strength scaling, and also opens the door to a new class of customizable materials incorporating patterned nanostructures

  5. Amorphous and nanocrystalline materials preparation, properties, and applications

    Inoue, A

    2001-01-01

    Amorphous and nanocrystalline materials are a class of their own. Their properties are quite different to those of the corresponding crystalline materials. This book gives systematic insight into their physical properties, structure, behaviour, and design for special advanced applications.

  6. Protein-modified nanocrystalline diamond thin films for biosensor applications.

    Härtl, Andreas; Schmich, Evelyn; Garrido, Jose A; Hernando, Jorge; Catharino, Silvia C R; Walter, Stefan; Feulner, Peter; Kromka, Alexander; Steinmüller, Doris; Stutzmann, Martin

    2004-10-01

    Diamond exhibits several special properties, for example good biocompatibility and a large electrochemical potential window, that make it particularly suitable for biofunctionalization and biosensing. Here we show that proteins can be attached covalently to nanocrystalline diamond thin films. Moreover, we show that, although the biomolecules are immobilized at the surface, they are still fully functional and active. Hydrogen-terminated nanocrystalline diamond films were modified by using a photochemical process to generate a surface layer of amino groups, to which proteins were covalently attached. We used green fluorescent protein to reveal the successful coupling directly. After functionalization of nanocrystalline diamond electrodes with the enzyme catalase, a direct electron transfer between the enzyme's redox centre and the diamond electrode was detected. Moreover, the modified electrode was found to be sensitive to hydrogen peroxide. Because of its dual role as a substrate for biofunctionalization and as an electrode, nanocrystalline diamond is a very promising candidate for future biosensor applications.

  7. Effect of nanocrystalline surface of substrate on microstructure and ...

    surface layers or bulk nanocrystalline metals and alloys more effectively. ... severe plastic deformation on surface layers of bulk met- als at high strains and strain rates. .... scanning electron microscopy (SEM) (Zeiss, model: Sigma. VP), energy ...

  8. Nanocrystalline Ni-Co Alloy Synthesis by High Speed Electrodeposition

    Idris, Jamaliah; Christian, Chukwuekezie; Gaius, Eyu

    2013-01-01

    Electrodeposition of nanocrystals is economically and technologically viable production path for the synthesis of pure metals and alloys both in coatings and bulk form. The study presents nanocrystalline Ni-Co alloy synthesis by high speed electrodeposition. Nanocrystalline Ni-Co alloys coatings were prepared by direct current (DC) and deposited directly on steel and aluminum substrates without any pretreatment, using high speed electrodeposition method. The influence of the electrolysis par...

  9. Electrochemistry of Inorganic Nanocrystalline Electrode Materials for Lithium Batteries

    C. W. Kwon

    2003-01-01

    much different from that of traditional crystalline ones because of their significant ‘surface effects’. In connection with that, the nanocrystalline cathode materials are reported to have an enhanced electrochemical activity when the first significative electrochemical step is insertion of Li ions (discharge process. The “electrochemical grafting” concept will be given as a plausible explanation. As illustrative examples, electrochemical behaviors of nanocrystalline manganese oxydes are presented.

  10. Reversal of exchange bias in nanocrystalline antiferromagnetic-ferromagnetic bilayers

    Prados, C; Pina, E; Hernando, A; Montone, A

    2002-01-01

    The sign of the exchange bias in field cooled nanocrystalline antiferromagnetic-ferromagnetic bilayers (Co-O and Ni-O/permalloy) is reversed at temperatures approaching the antiferromagnetic (AFM) blocking temperature. A similar phenomenon is observed after magnetic training processes at similar temperatures. These effects can be explained assuming that the boundaries of nanocrystalline grains in AFM layers exhibit lower transition temperatures than grain cores

  11. Size dependence of elastic mechanical properties of nanocrystalline aluminum

    Xu, Wenwu; Dávila, Lilian P., E-mail: ldavila@ucmerced.edu

    2017-04-24

    The effect of grain size on the elastic mechanical properties of nanocrystalline pure metal Al is quantified by molecular dynamics simulation method. In this work, the largest nanocrystalline Al sample has a mean grain size of 29.6 nm and contains over 100 millions atoms in the modeling system. The simulation results show that the elastic properties including elastic modulus and ultimate tensile strength of nanocrystalline Al are relatively insensitive to the variation of mean grain size above 13 nm yet they become distinctly grain size dependent below 13 nm. Moreover, at a grain size <13 nm, the elastic modulus decreases monotonically with decreasing grain size while the ultimate tensile strength of nanocrystalline Al initially decreases with the decrease of the grain size down to 9 nm and then increases with further reduction of grain size. The increase of ultimate tensile strength below 9 nm is believed to be a result of an extended elasticity in the ultrafine grain size nanocrystalline Al. This study can facilitate the prediction of varied mechanical properties for similar nanocrystalline materials and even guide testing and fabrication schemes of such materials.

  12. POWDER COAT APPLICATIONS

    The report discusses an investigation of critical factors that affect the use of powder coatings on the environment, cost, quality, and production. The investigation involved a small business representative working with the National Defense Center for Environmental Excellence (ND...

  13. OIL SOLUTIONS POWDER

    Technical product bulletin: aka OIL SOLUTIONS POWDER, SPILL GREEN LS, this miscellaneous oil spill control agent used in cleanups initially behaves like a synthetic sorbent, then as a solidifier as the molecular microencapsulating process occurs.

  14. Nanocrystalline Steels’ Resistance to Hydrogen Embrittlement

    Skołek E.

    2015-04-01

    Full Text Available The aim of this study is to determine the susceptibility to hydrogen embrittlement in X37CrMoV5-1 steel with two different microstructures: a nanocrystalline carbide-free bainite and tempered martensite. The nanobainitic structure was obtained by austempering at the bainitic transformation zone. It was found, that after hydrogen charging, both kinds of microstructure exhibit increased yield strength and strong decrease in ductility. It has been however shown that the resistance to hydrogen embrittlement of X37CrMoV5-1 steel with nanobainitic structure is higher as compared to the tempered martensite. After hydrogen charging the ductility of austempered steel is slightly higher than in case of quenched and tempered (Q&T steel. This effect was interpreted as a result of phase composition formed after different heat treatments.

  15. Limitation of biocompatibility of hydrated nanocrystalline hydroxyapatite

    Minaychev, V. V.; Teleshev, A. T.; Gorshenev, V. N.; Yakovleva, M. A.; Fomichev, V. A.; Pankratov, A. S.; Menshikh, K. A.; Fadeev, R. S.; Fadeeva, I. S.; Senotov, A. S.; Kobyakova, M. I.; Yurasova, Yu B.; Akatov, V. S.

    2018-04-01

    Nanostructured hydroxyapatite (HA) in the form of hydrated paste is considered to be a promising material for a minor-invasive surgical curing of bone tissue injure. However questions about adhesion of cells on this material and its biocompatibility still remain. In this study biocompatibility of paste-formed nanosized HA (nano-HA) by in vitro methods is investigated. Nano-HA (particles sized about 20 nm) was synthesized under conditions of mechano-acoustic activation of an aqueous reaction mixture of ammonium hydrophosphate and calcium nitrate. It was ascertained that nanocrystalline paste was not cytotoxic although limitation of adhesion, spreading and growth of the cells on its surface was revealed. The results obtained point on the need of modification of hydrated nano-HA in the aims of increasing its biocompatibility and osteoplastic potential.

  16. Stability of nanocrystalline electrochemically deposited layers

    Pantleon, Karen; Somers, Marcel A. J.

    2009-01-01

    have different microstructure and properties compared to bulk materials and the thermodynamic non-equilibrium state of as-deposited layers frequently results in changes of the microstructure as a function of time and/or temperature. The evolving microstructure affects the functionality and reliability......The technological demand for manufacturing components with complex geometries of micrometer or sub-micrometer dimensions and ambitions for ongoing miniaturization have attracted particular attention to electrochemical deposition methods. Thin layers of electrochemically deposited metals and alloys...... of electrodeposited components, which can be beneficial, as for the electrical conductivity of copper interconnect lines, or detrimental, as for reduced strength of nickel in MEMS applications. The present work reports on in-situ studies of the microstructure stability of as-deposited nanocrystalline Cu-, Ag- and Ni...

  17. Application Potential of Nanocrystalline Ribbons Still Pending

    Butvin, Pavol; Butvinová, Beata; Švec, Peter; Sitek, Jozef

    2010-09-01

    Nanocrystalline soft-magnetic ribbons promised a wide-spread practical use when introduced at the beginning of nineties. After 20 years of extensive research there are still unclear material problems which are thought to be the principal reason why these materials show but marginal use. Poorly controllable magnetic anisotropy due to spontaneous intrinsic macroscopic stress that comes from an inevitable heterogeneity of the ribbon materials is pointed to in this work. Certain stress-based mechanisms are shown to induce the unintended anisotropy in the already familiar Finemets as well as in the newer Hitperms. Hysteresis loops, domain structure and power loss is used to reveal the anisotropy consequences and particular connected but still unanswered questions are pinpointed.

  18. Nanocrystalline diamond coatings for mechanical seals applications.

    Santos, J A; Neto, V F; Ruch, D; Grácio, J

    2012-08-01

    A mechanical seal is a type of seal used in rotating equipment, such as pumps and compressors. It consists of a mechanism that assists the connection of the rotating shaft to the housings of the equipments, preventing leakage or avoiding contamination. A common cause of failure of these devices is end face wear out, thus the use of a hard, smooth and wear resistant coating such as nanocrystalline diamond would be of great importance to improve their working performance and increase their lifetime. In this paper, different diamond coatings were deposited by the HFCVD process, using different deposition conditions. Additionally, the as-grown films were characterized for, quality, morphology and microstructure using scanning electron microscopy (SEM) and Raman spectroscopy. The topography and the roughness of the films were characterized by atomic force microscopy (AFM).

  19. Arsenic removal by magnetic nanocrystalline barium hexaferrite

    Patel, Hasmukh A.; Byun, Jeehye; Yavuz, Cafer T.

    2012-01-01

    Nanoscale magnetite (Fe 3 O 4 ) ( 12 O 19 , BHF) is a well-known permanent magnet (i.e., fridge magnets) and attractive due to its low cost in making large quantities. BHF offers a viable alternative to magnetite nanocrystals for arsenic removal since it features surfaces similar to iron oxides but with much enhanced magnetism. Herein, we employ BHF nanocrystalline materials for the first time in arsenic removal from wastewater. Our results show better (75 %) arsenic removal than magnetite of the similar sizes. The BHF nanoparticles, 6.06 ± 0.52 nm synthesized by thermolysis method at 320 °C do not show hexagonal phase, however, subsequent annealing at 750 °C produced pure hexagonal BHF in >200 nm assemblies. By using BHF, we demonstrate that nanoparticle removal is more efficient and fixed bed type cartridge applications are more possible.

  20. Magnetically responsive enzyme powders

    Pospiskova, Kristyna, E-mail: kristyna.pospiskova@upol.cz [Regional Centre of Advanced Technologies and Materials, Palacky University, Slechtitelu 11, 783 71 Olomouc (Czech Republic); Safarik, Ivo, E-mail: ivosaf@yahoo.com [Regional Centre of Advanced Technologies and Materials, Palacky University, Slechtitelu 11, 783 71 Olomouc (Czech Republic); Department of Nanobiotechnology, Institute of Nanobiology and Structural Biology of GCRC, Na Sadkach 7, 370 05 Ceske Budejovice (Czech Republic)

    2015-04-15

    Powdered enzymes were transformed into their insoluble magnetic derivatives retaining their catalytic activity. Enzyme powders (e.g., trypsin and lipase) were suspended in various liquid media not allowing their solubilization (e.g., saturated ammonium sulfate and highly concentrated polyethylene glycol solutions, ethanol, methanol, 2-propanol) and subsequently cross-linked with glutaraldehyde. Magnetic modification was successfully performed at low temperature in a freezer (−20 °C) using magnetic iron oxides nano- and microparticles prepared by microwave-assisted synthesis from ferrous sulfate. Magnetized cross-linked enzyme powders were stable at least for two months in water suspension without leakage of fixed magnetic particles. Operational stability of magnetically responsive enzymes during eight repeated reaction cycles was generally without loss of enzyme activity. Separation of magnetically modified cross-linked powdered enzymes from reaction mixtures was significantly simplified due to their magnetic properties. - Highlights: • Cross-linked enzyme powders were prepared in various liquid media. • Insoluble enzymes were magnetized using iron oxides particles. • Magnetic iron oxides particles were prepared by microwave-assisted synthesis. • Magnetic modification was performed under low (freezing) temperature. • Cross-linked powdered trypsin and lipase can be used repeatedly for reaction.

  1. Functionalization of nanocrystalline diamond films with phthalocyanines

    Petkov, Christo [Institute of Nanostructure Technologies and Analytics (INA), Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel (Germany); Reintanz, Philipp M. [Institute of Chemistry, Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel (Germany); Kulisch, Wilhelm [Institute of Nanostructure Technologies and Analytics (INA), Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel (Germany); Degenhardt, Anna Katharina [Institute of Chemistry, Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel (Germany); Weidner, Tobias [Max Planck Institute for Polymer Research, Mainz (Germany); Baio, Joe E. [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis, OR (United States); Merz, Rolf; Kopnarski, Michael [Institut für Oberflächen- und Schichtanalytik (IFOS), Kaiserslautern (Germany); Siemeling, Ulrich [Institute of Chemistry, Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel (Germany); Reithmaier, Johann Peter [Institute of Nanostructure Technologies and Analytics (INA), Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel (Germany); Popov, Cyril, E-mail: popov@ina.uni-kassel.de [Institute of Nanostructure Technologies and Analytics (INA), Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), University of Kassel (Germany)

    2016-08-30

    Highlights: • Grafting of phthalocyanines on nanocrystalline diamond films with different terminations. • Pc with different central atoms and side chains synthesized and characterized. • Attachment of Pc on H- and O-terminated NCD studied by XPS and NEXAFS spectroscopy. • Orientation order of phthalocyanine molecules on NCD surface. - Abstract: Phthalocyanine (Pc) derivatives containing different central metal atoms (Mn, Cu, Ti) and different peripheral chains were synthesized and comprehensively characterized. Their interaction with nanocrystalline diamond (NCD) films, as-grown by hot-filament chemical vapor deposition or after their modification with oxygen plasma to exchange the hydrogen termination with oxygen-containing groups, was studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The elemental composition as determined by XPS showed that the Pc were grafted on both as-grown and O-terminated NCD. Mn, Cu and Ti were detected together with N stemming from the Pc ring and S in case of the Ti-Pc from the peripheral ligands. The results for the elemental surface composition and the detailed study of the N 1s, S 2p and O 1s core spectra revealed that Ti-Pc grafted better on as-grown NCD but Cu-Pc and Mn-Pc on O-terminated films. Samples of Mn-Pc on as-grown and O-terminated NCD were further investigated by NEXAFS spectroscopy. The results showed ordering of the grafted molecules, laying flat on the H-terminated NCD surface while only the macrocycles were oriented parallel to the O-terminated surface with the peripheral chains perpendicular to it.

  2. Characteristics of Inconel Powders for Powder-Bed Additive Manufacturing

    Quy Bau Nguyen

    2017-10-01

    Full Text Available In this study, the flow characteristics and behaviors of virgin and recycled Inconel powder for powder-bed additive manufacturing (AM were studied using different powder characterization techniques. The results revealed that the particle size distribution (PSD for the selective laser melting (SLM process is typically in the range from 15 μm to 63 μm. The flow rate of virgin Inconel powder is around 28 s·(50 g−1. In addition, the packing density was found to be 60%. The rheological test results indicate that the virgin powder has reasonably good flowability compared with the recycled powder. The inter-relation between the powder characteristics is discussed herein. A propeller was successfully printed using the powder. The results suggest that Inconel powder is suitable for AM and can be a good reference for researchers who attempt to produce AM powders.

  3. Biaxially textured articles formed by powder metallurgy

    Goyal, Amit; Williams, Robert K.; Kroeger, Donald M.

    2003-07-29

    A biaxially textured alloy article having a magnetism less than pure Ni includes a rolled and annealed compacted and sintered powder-metallurgy preform article, the preform article having been formed from a powder mixture selected from the group of mixtures consisting of: at least 60 at % Ni powder and at least one of Cr powder, W powder, V powder, Mo powder, Cu powder, Al powder, Ce powder, YSZ powder, Y powder, Mg powder, and RE powder; the article having a fine and homogeneous grain structure; and having a dominant cube oriented {100} orientation texture; and further having a Curie temperature less than that of pure Ni.

  4. A phenomenological variational multiscale constitutive model for intergranular failure in nanocrystalline materials

    Siddiq, A.; El Sayed, Tamer S.

    2013-01-01

    We present a variational multiscale constitutive model that accounts for intergranular failure in nanocrystalline fcc metals due to void growth and coalescence in the grain boundary region. Following previous work by the authors, a nanocrystalline

  5. Surface chemical reactions during electron beam irradiation of nanocrystalline CaS:Ce3+ phosphor

    Kumar, Vinay; Pitale, Shreyas S.; Nagpure, I. M.; Coetsee, E.; Ntwaeaborwa, O. M.; Terblans, J. J.; Swart, H. C.; Mishra, Varun

    2010-01-01

    The effects of accelerating voltage (0.5-5 keV) on the green cathodoluminescence (CL) of CaS:Ce 3+ nanocrystalline powder phosphors is reported. An increase in the CL intensity was observed from the powders when the accelerating voltage was varied from 0.5 to 5 keV, which is a relevant property for a phosphor to be used in field emission displays (FEDs). The CL degradation induced by prolonged electron beam irradiation was analyzed using CL spectroscopy, x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The AES data showed the decrease in the S peak intensity and an increase in the O peak intensity during electron bombardment. The CL intensity was found to decrease to 30% of its original intensity after about 50 C/cm 2 . XPS was used to study the chemical composition of the CaS:Ce 3+ nanophosphor before and after degradation. The XPS data confirms that a nonluminescent CaSO 4 layer has formed on the surface during the degradation process, which may partially be responsible for the CL degradation. The electron stimulated surface chemical reaction mechanism was used to explain the effects of S desorption and the formation of the nonluminescent CaSO 4 layer on the surface.

  6. Nanocrystalline hydroxyapatite doped with selenium oxyanions: A new material for potential biomedical applications

    Kolmas, Joanna; Oledzka, Ewa; Sobczak, Marcin; Nałęcz-Jawecki, Grzegorz

    2014-01-01

    Selenium-substituted hydroxyapatites containing selenate SeO 4 2− or selenite SeO 3 2− ions were synthesized using a wet precipitation method. The selenium content was determined by atomic absorbance spectrometry. The raw, unsintered powders were also characterized using powder X-ray diffraction, middle-range FT-IR spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopic microanalysis. The synthesized apatites were found to be pure and nanocrystalline with a crystal size similar to that in bone mineral. The incorporation of selenium oxyanions into the crystal lattice was confirmed. The toxicity of hydroxyapatites containing selenite or selenate ions was evaluated with a protozoan assay and bacterial luminescence test. - Highlights: • We synthesized and analyzed hydroxyapatites doped with selenium oxyanions. • We used various analytical methods, i.e. XRD, TEM, AAS and FT-IR. • We confirmed incorporation of SeO 3 2− and SeO 4 2− into the crystal lattice. • The toxicity of the materials was studied

  7. Nanocrystalline hydroxyapatite doped with selenium oxyanions: A new material for potential biomedical applications

    Kolmas, Joanna, E-mail: joanna.kolmas@wum.edu.pl [Medical University of Warsaw, Faculty of Pharmacy, Department of Inorganic and Analytical Chemistry, ul. Banacha 1, 02-097 Warsaw (Poland); Oledzka, Ewa; Sobczak, Marcin [Medical University of Warsaw, Faculty of Pharmacy, Department of Inorganic and Analytical Chemistry, ul. Banacha 1, 02-097 Warsaw (Poland); Nałęcz-Jawecki, Grzegorz [Medical University of Warsaw, Faculty of Pharmacy, Department of Environmental Health Sciences, ul. Banacha 1, 02-097 Warsaw (Poland)

    2014-06-01

    Selenium-substituted hydroxyapatites containing selenate SeO{sub 4}{sup 2−} or selenite SeO{sub 3}{sup 2−} ions were synthesized using a wet precipitation method. The selenium content was determined by atomic absorbance spectrometry. The raw, unsintered powders were also characterized using powder X-ray diffraction, middle-range FT-IR spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopic microanalysis. The synthesized apatites were found to be pure and nanocrystalline with a crystal size similar to that in bone mineral. The incorporation of selenium oxyanions into the crystal lattice was confirmed. The toxicity of hydroxyapatites containing selenite or selenate ions was evaluated with a protozoan assay and bacterial luminescence test. - Highlights: • We synthesized and analyzed hydroxyapatites doped with selenium oxyanions. • We used various analytical methods, i.e. XRD, TEM, AAS and FT-IR. • We confirmed incorporation of SeO{sub 3}{sup 2−} and SeO{sub 4}{sup 2−} into the crystal lattice. • The toxicity of the materials was studied.

  8. Phase transformation and grain growth behavior of a nanocrystalline 18/8 stainless steel

    Kotan, Hasan, E-mail: hasankotan@gmail.com [Konya Necmettin Erbakan University, Department of Metallurgical & Materials Engineering, Konya 42090 (Turkey); Darling, Kris A. [US Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-F, Aberdeen Proving Ground, MD 21005-5069 (United States)

    2017-02-16

    Fe-18Cr-8Ni and Fe-18Cr-8Ni-1Y (at%) stainless steel powders were nanostructured by mechanical alloying from elemental powders and subjected to 90 min annealing treatments at various temperatures. The microstructural evolutions as a function of alloy compositions and temperatures were investigated by in-situ and ex-situ x-ray diffraction experiments, transmission electron microscopy and focused ion beam microscopy. The dependence of hardness on the microstructure was utilized to study the mechanical changes. It was found that the resulting microstructures by mechanical alloying were bcc solid solution, the so-called α’-martensite structure. The high temperature in-situ x-ray diffraction experiments showed that the martensite-to-austenite reverse phase transformation was completed above 800 and 900 °C for Fe-18Cr-8Ni and Fe-18Cr-8Ni-1Y steels, respectively. A partial or complete retransformation to martensite was observed upon cooling to room temperature. Annealing of nanocrystalline Fe-18Cr-8Ni steel yielded grain growth reaching to micron sizes at 1100 °C while addition of 1 at% yttrium stabilized the microstructure around 160 nm grain size and 6 GPa hardness after 90 min annealing at 1200 °C.

  9. ZnO-based nanocrystalline powders with applications in hybrid photovoltaic cells

    Damonte, L.C. [Dto. De Fisica, UNLP, IFLP-CCT-CONICET, C.C.67 (1900) La Plata (Argentina); Dto. De Fisica Aplicada, Universidad Politecnica de Valencia, Cami de Vera s/n (46071) Valencia (Spain); Donderis, V. [Dto. De Ingenieria Electrica, Universidad Politecnica de Valencia, Cami de Vera s/n (46071) Valencia (Spain); Ferrari, S.; Meyer, M. [Dto. De Fisica, UNLP, IFLP-CCT-CONICET, C.C.67 (1900) La Plata (Argentina); Orozco, J. [Dto. de Ingenieria Mecanica y Materiales, Universidad Politecnica de Valencia, Cami de Vera s/n (46071) Valencia (Spain); Hernandez-Fenollosa, M.A. [Dto. De Fisica Aplicada, Universidad Politecnica de Valencia, Cami de Vera s/n (46071) Valencia (Spain)

    2010-06-15

    In recent years there has been a growing interest in the development of hybrid photovoltaic cells consisting of new materials, such as devices based on the combination of a wide gap semiconductor and an organic dye (dye-sensitized solar cells, DSSC). In this paper we obtain nano-zinc oxide particles whose optical and electrical properties have been modified by the presence of small amounts of Al or In acting as dopants. The aim of this study is to improve the compatibility of each of the compounds present in the photovoltaic solar cell. The knowledge gained will provide input to guide the processes in the manufacture of hybrid solar cells. (author)

  10. Synthesis of nanocrystalline SnO2 powder at 100°C

    Unknown

    sensors, heat mirrors, transparent electrodes for solar cells, opto-electronic devices and ... to condensation–evaporation mechanism operating during sintering. ... free of anions and transferred to flask fitted with a water condenser. The gel was ...

  11. Magnetic and structural properties of spark plasma sintered nanocrystalline NdFeB-powders

    Wuest, H., E-mail: holger.wuest@de.bosch.com [Robert Bosch GmbH, Postfach 10 60 50, 70049 Stuttgart (Germany); Bommer, L., E-mail: lars.bommer@de.bosch.com [Robert Bosch GmbH, Postfach 10 60 50, 70049 Stuttgart (Germany); Weissgaerber, T., E-mail: thomas.weissgaerber@ifam-dd.fraunhofer.de [Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM), Branch Lab Dresden, Winterbergstraße 28, 01277 Dresden (Germany); Kieback, B., E-mail: bernd.kieback@ifam-dd.fraunhofer.de [Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM), Branch Lab Dresden, Winterbergstraße 28, 01277 Dresden (Germany); Technische Universität Dresden, Institute for Materials Science, Helmholtzstraße 7, 01069 Dresden (Germany)

    2015-10-15

    Near-stoichiometric NdFeB melt-spun ribbons have been subjected to spark plasma sintering varying the process temperature T{sub SPS} and pressure p{sub SPS} between 600 and 800 °C and 50–300 MPa, respectively. Produced bulk magnets were analyzed regarding microstructure and magnetic properties. For all samples the intrinsic coercivity H{sub c,J} gradually decreases with increasing sintering temperature and pressure, while residual induction B{sub r} increases simultaneously with sample density. Densities close to the theoretical limit were achieved for p{sub SPS}≥90 MPa and T{sub SPS}≥650 °C. With increasing T{sub SPS} precipitations of Nd-rich and Fe-rich phases have been observed as a result of a decomposition of the hard magnetic Nd{sub 2}Fe{sub 14}B phase. Under optimum sintering conditions of p{sub SPS}=300 MPa and T{sub SPS}=650 °C high-density bulk magnets with H{sub c,J}=652 kA/m, B{sub r}=0.86 T and (BH){sub max}=106 kJ/m{sup 3} have been produced. - Highlights: • Consolidation close to the theoretical density for p{sub SPS}≥90 MPa and T{sub SPS}≥650 °C. • Highest (BH){sub max} of 106 kJ/m{sup 3} for p{sub SPS}=300 MPa and T{sub SPS}=650 °C with 98% theo. • H{sub c,J} gradually decreases with increasing T{sub SPS}, while B{sub r} increases simultaneously with. • With increasing T{sub SPS}, Nd- and Fe-rich precipitations are observed. • Reduction in t{sub SPS} is economic but does not increase (BH){sub max} significantly.

  12. Gum Tragacanth-Mediated Synthesis of Nanocrystalline ZnO Powder for Use in Varistors

    Liu, Ting-Ting; Wang, Mao-Hua; Su, Hang; Chen, Xi; Chen, Chao; Zhang, Ruo-Chen

    2015-10-01

    Zinc oxide nanopowders were synthesized by a sol-gel method with gum tragacanth and zinc nitrate as raw materials. Gum tragacanth was used as stabilizer to control the mobility of zinc cations and the growth of the nanopowders. Thermo-gravimetric analysis, x-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, and scanning electron microscopy were used to characterize the as-prepared samples. Zinc oxide (ZnO) nanoparticles calcined at different temperatures had a hexagonal wurtzite structure with average particle size ranging from 32.29 nm to 42.83 nm. The crystallinity of ZnO nanoparticles was improved by increasing the calcination temperature. The density of ZnO varistor ceramics sintered at 1150°C for 2 h in air was 5.46 g/cm3, which was 97.5% of the theoretical density, their breakdown voltage was 4572 V/cm, and their nonlinear coefficient was ~16.8. This method can be used as an excellent alternative method for synthesis of ZnO nanoparticles with a plant extract as a raw material. Our experimental results show our method had the advantage of improving the electrical performance of ZnO varistors.

  13. Room-temperature ferromagnetism in cerium dioxide powders

    Rakhmatullin, R. M., E-mail: rrakhmat@kpfu.ru; Pavlov, V. V.; Semashko, V. V.; Korableva, S. L. [Kazan Federal University, Institute of Physics (Russian Federation)

    2015-08-15

    Room-temperature ferromagnetism is detected in a CeO{sub 2} powder with a grain size of about 35 nm and a low (<0.1 at %) manganese and iron content. The ferromagnetism in a CeO{sub 2} sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently.

  14. Ultrafine hydrogen storage powders

    Anderson, Iver E.; Ellis, Timothy W.; Pecharsky, Vitalij K.; Ting, Jason; Terpstra, Robert; Bowman, Robert C.; Witham, Charles K.; Fultz, Brent T.; Bugga, Ratnakumar V.

    2000-06-13

    A method of making hydrogen storage powder resistant to fracture in service involves forming a melt having the appropriate composition for the hydrogen storage material, such, for example, LaNi.sub.5 and other AB.sub.5 type materials and AB.sub.5+x materials, where x is from about -2.5 to about +2.5, including x=0, and the melt is gas atomized under conditions of melt temperature and atomizing gas pressure to form generally spherical powder particles. The hydrogen storage powder exhibits improved chemcial homogeneity as a result of rapid solidfication from the melt and small particle size that is more resistant to microcracking during hydrogen absorption/desorption cycling. A hydrogen storage component, such as an electrode for a battery or electrochemical fuel cell, made from the gas atomized hydrogen storage material is resistant to hydrogen degradation upon hydrogen absorption/desorption that occurs for example, during charging/discharging of a battery. Such hydrogen storage components can be made by consolidating and optionally sintering the gas atomized hydrogen storage powder or alternately by shaping the gas atomized powder and a suitable binder to a desired configuration in a mold or die.

  15. Nanocrystalline SnO2 by liquid pyrolysis

    Morante, J. R.

    2000-08-01

    Full Text Available Liquid pyrolysis is presented as a new production method of SnO2 nanocrystalline powders suitable for gas sensor devices. The method is based on a pyrolytic reaction of high tensioned stressed drops of an organic solution of SnCl4•5(H2O. The main advantages of the method are its capability to produce SnO2 nanopowders with high stability, its accurate control over the grain size and other structural characteristics, its high level of repeatability and its low industrialization implementation cost. The characterization of samples of SnO2 nanoparticles obtained by liquid pyrolysis in the range between 200ºC and 900ºC processing temperature is carried out by X-ray diffraction, transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. Results are analyzed and discussed so as to validate the advantages of the liquid pyrolysis method.La pirólisis líquida se presenta como un nuevo método para producir SnO2 nanocristalino en polvo ideal para sensores de gas. El método se basa en una reacción pirolítica de gotas altamente tensionadas procedentes de una solución orgánica de SnCl4•5(H2O. Las principales ventajas del método son la capacidad para producir nanopartículas de SnO2 con una gran estabilidad, el preciso control sobre el tamaño de grano y sobre otras características estructurales, el alto nivel de repetibilidad y el bajo coste en su implementación industrial.La caracterización de las muestras de las nanopartículas de SnO2 obtenidas por pirólisis líquida en un rango de temperatura de procesado que va de 200ºC a 900ºC se ha realizado mediante difracción de rayos X, microscopía electrónica de transmisión, espectroscopía Raman y espectroscopía fotoelectrónica de rayos X. Los resultados se han analizado y discutido. Éstos validan las ventajas del método de la pirólisis líquida.

  16. Weighing fluidized powder

    Adomitis, J.T.; Larson, R.I.

    1980-01-01

    Fluidized powder is discharged from a fluidizing vessel into a container. Accurate metering is achieved by opening and closing the valve to discharge the powder in a series of short-duration periods until a predetermined weight is measured by a load cell. The duration of the discharge period may be increased in inverse proportion to the amount of powder in the vessel. Preferably the container is weighed between the discharge periods to prevent fluctuations resulting from dynamic effects. The gas discharged into the container causes the pressures in the vessel and container to equalize thereby decreasing the rate of discharge and increasing the accuracy of metering as the weight reaches the predetermined value. (author)

  17. Baking Powder Wars

    Civitello, Linda

    2017-01-01

    How did a mid-nineteenth century American invention, baking powder, replace yeast as a leavening agent and create a culinary revolution as profound as the use of yeast thousands of years ago?The approach was two-pronged and gendered: business archives, U.S. government records and lawsuits revealed how baking powder was created, marketed, and regulated. Women’s diaries and cookbooks—personal, corporate, community, ethnic—from the eighteenth century to internet blogs showed the use women made o...

  18. Review: Plasma-enhanced chemical vapor deposition of nanocrystalline diamond

    Katsuyuki Okada

    2007-01-01

    Full Text Available Nanocrystalline diamond films have attracted considerable attention because they have a low coefficient of friction and a low electron emission threshold voltage. In this paper, the author reviews the plasma-enhanced chemical vapor deposition (PE-CVD of nanocrystalline diamond and mainly focuses on the growth of nanocrystalline diamond by low-pressure PE-CVD. Nanocrystalline diamond particles of 200–700 nm diameter have been prepared in a 13.56 MHz low-pressure inductively coupled CH4/CO/H2 plasma. The bonding state of carbon atoms was investigated by ultraviolet-excited Raman spectroscopy. Electron energy loss spectroscopy identified sp2-bonded carbons around the 20–50 nm subgrains of nanocrystalline diamond particles. Plasma diagnostics using a Langmuir probe and the comparison with plasma simulation are also reviewed. The electron energy distribution functions are discussed by considering different inelastic interaction channels between electrons and heavy particles in a molecular CH4/H2 plasma.

  19. Thermodynamic and experimental study on phase stability in nanocrystalline alloys

    Xu Wenwu; Song Xiaoyan; Lu Nianduan; Huang Chuan

    2010-01-01

    Nanocrystalline alloys exhibit apparently different phase transformation characteristics in comparison to the conventional polycrystalline alloys. The special phase stability and phase transformation behavior, as well as the essential mechanisms of the nanocrystalline alloys, were described quantitatively in a nanothermodynamic point of view. By introducing the relationship between the excess volume at the grain boundary and the nanograin size, the Gibbs free energy was determined distinctly as a function of temperature and the nanograin size. Accordingly, the grain-size-dependence of the phase stability and phase transformation characteristics of the nanocrystalline alloy were calculated systematically, and the correlations between the phase constitution, the phase transformation temperature and the critical nanograin size were predicted. A series of experiments was performed to investigate the phase transformations at room temperature and high temperatures using the nanocrystalline Sm 2 Co 17 alloy as an example. The phase constitution and phase transformation sequence found in nanocrystalline Sm 2 Co 17 alloys with various grain-size levels agree well with the calculations by the nanothermodynamic model.

  20. Strain-induced grain growth of cryomilled nanocrystalline Al in trimodal composites during forging

    Yao, B.; Simkin, B.; Majumdar, B.; Smith, C.; Bergh, M. van den; Cho, K.; Sohn, Y.H.

    2012-01-01

    Highlights: ► Grain growth of cryomilled nanocrystalline aluminum during hot forging. ► Use of hollow cone dark field imaging technique in TEM for grain size measurement. ► Grain growth model of strain, strain rate and temperature for forging optimization. - Abstract: Grain growth of nanocrystalline aluminum ( nc Al) in trimodal Al metal-matrix-composites (MMCs) during hot forging was investigated. The nc Al phase formed through cryomilling of inert gas-atomized powders in liquid nitrogen has an average grain size down to 21 nm, exhibits excellent thermal stability. However, substantial grain growth of nc Al up to 63 nm was observed when the Al MMCs were thermo-mechanically processed even at relatively low temperatures. Grain growth of the cryomilled nc Al phase in trimodal Al MMCs after hot forging was documented with respect to temperature ranging from 175 °C to 287 °C, true strain ranging from 0.4 to 1.35 and strain rate ranging from 0.1 to 0.5 s −1 . Hollow cone dark field imaging technique was employed to provide statistically confident measurements of nc Al grain size that ranged from 21 to 63 nm. An increase in forging temperature and an increase in true strain were correlated with an increase in grain size of nc Al. Results were correlated to devise a phenomenological grain growth model for forging that takes strain, strain rate and temperature into consideration. Activation energy for the grain growth during thermo-mechanical hot-forging was determined to be 35 kJ/mol, approximately a quarter of activation energy for bulk diffusion of Al and a half of activation energy for static recrystallization.

  1. Peroxidase-like activity of nanocrystalline cobalt selenide and its application for uric acid detection

    Zhuang QQ

    2017-04-01

    Full Text Available Quan-Quan Zhuang,1 Zhi-Hang Lin,1 Yan-Cheng Jiang,1 Hao-Hua Deng,2 Shao-Bin He,1,3 Li-Ting Su,4 Xiao-Qiong Shi,2 Wei Chen2 1Department of Pharmacy, Affiliated Quanzhou First Hospital of Fujian Medical University, Quanzhou, 2Department of Pharmaceutical Analysis, School of Pharmacy, Fujian Medical University, Fuzhou, 3Department of Pharmacy, Quanzhou Infectious Disease Hospital, 4Department of Pharmaceutical Analysis, Quanzhou Medical College, Quanzhou, People’s Republic of China Abstract: Dendrite-like cobalt selenide nanostructures were synthesized from cobalt and selenium powder precursors by a solvothermal method in anhydrous ethylenediamine. The as-prepared nanocrystalline cobalt selenide was found to possess peroxidase-like activity that could catalyze the reaction of peroxidase substrates in the presence of H2O2. A spectrophotometric method for uric acid (UA determination was developed based on the nanocrystalline cobalt selenide-catalyzed coupling reaction between N-ethyl-N-(3-sulfopropyl-3-methylaniline sodium salt and 4-aminoantipyrine (4-AAP in the presence of H2O2. Under optimum conditions, the absorbance was proportional to the concentration of UA over the range of 2.0–40 µM with a detection limit of 0.5 µM. The applicability of the proposed method has been validated by determination of UA in human serum samples with satisfactory results. Keywords: enzyme mimics, cobalt selenide, peroxidase-like activity, uric acid, human serum

  2. Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys

    Kalay, Yunus Eren

    2008-01-01

    deviation indicates an adiabatic type solidification path where heat of fusion is reabsorbed. It is interesting that this particle size range is also consistent with the appearance of a microcellular growth. While no glass formation is observed within this system, the smallest size powders appear to consist of a mixture of nanocrystalline Si and Al. Al-Sm alloys have been investigated within a composition range of 34 to 42 wt% Sm. Gas atomized powders of Al-Sm are investigated to explore the morphological and structural hierarchy that correlates with different degrees of departure from full equilibrium conditions. The resultant powders show a variety of structural selection with respect to amount of undercooling, with an amorphous structure appearing at the highest cooling rates. Because of the chaotic nature of gas atomization, Cu-block melt-spinning is used to produce a homogeneous amorphous structure. The as-quenched structure within Al-34 to 42 wt% Sm consists of nanocrystalline fcc-Al (on the order of 5 nm) embedded in an amorphous matrix. The nucleation density of fcc-Al after initial crystallization is on the order of 10 22 -10 23 m -3 , which is 10 5 -10 6 orders of magnitude higher than what classical nucleation theory predicts. Detailed analysis of liquid and as-quenched structures using high energy synchrotron X-ray diffraction, high energy transmission electron microscopy, and atom probe tomography techniques revealed an Al-Sm network similar in appearance to a medium range order (MRO) structure. A model whereby these MRO clusters promote the observed high nucleation density of fcc-Al nanocrystals is proposed. The devitrification path was identified using high temperature, in-situ, high energy synchrotron X-ray diffraction techniques and the crystallization kinetics were described using an analytical Johnson-Mehl-Avrami (JMA) approach.

  3. Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys

    Kalay, Yunus Eren [Iowa State Univ., Ames, IA (United States)

    2009-01-01

    each other. This deviation indicates an adiabatic type solidification path where heat of fusion is reabsorbed. It is interesting that this particle size range is also consistent with the appearance of a microcellular growth. While no glass formation is observed within this system, the smallest size powders appear to consist of a mixture of nanocrystalline Si and Al. Al-Sm alloys have been investigated within a composition range of 34 to 42 wt% Sm. Gas atomized powders of Al-Sm are investigated to explore the morphological and structural hierarchy that correlates with different degrees of departure from full equilibrium conditions. The resultant powders show a variety of structural selection with respect to amount of undercooling, with an amorphous structure appearing at the highest cooling rates. Because of the chaotic nature of gas atomization, Cu-block melt-spinning is used to produce a homogeneous amorphous structure. The as-quenched structure within Al-34 to 42 wt% Sm consists of nanocrystalline fcc-Al (on the order of 5 nm) embedded in an amorphous matrix. The nucleation density of fcc-Al after initial crystallization is on the order of 1022-1023m-3, which is 105-106 orders of magnitude higher than what classical nucleation theory predicts. Detailed analysis of liquid and as-quenched structures using high energy synchrotron X-ray diffraction, high energy transmission electron microscopy, and atom probe tomography techniques revealed an Al-Sm network similar in appearance to a medium range order (MRO) structure. A model whereby these MRO clusters promote the observed high nucleation density of fcc-Al nanocrystals is proposed. The devitrification path was identified using high temperature, in-situ, high energy synchrotron X-ray diffraction techniques and the crystallization kinetics were described using an analytical Johnson-Mehl-Avrami (JMA) approach.

  4. Crystalline-to-amorphous phase transformation in mechanically alloyed Fe50W50 powders

    Sherif El-Eskandarany, M.S.; Sumiyama, K.; Suzuki, K.

    1997-01-01

    A mechanical alloying process via a ball milling technique has been applied for preparing amorphous Fe 50 W 50 alloy powders. The results have shown that during the first and second stages of milling (0 to 360 ks) W atoms emigrate to Fe lattices to form nanocrystalline b.c.c. Fe-W solid solution, with a grain size of about 7 nm in diameter. After 720 ks of the milling time, this solid solution was transformed to an amorphous Fe-W alloy coexisting with the residual fraction of the unprocessed W powders. During the last stage of milling (720 to 1,440 ks) all of this residual W powder reacts with the amorphous phase to form a homogeneous Fe 50 W 50 amorphous alloy. The crystallization temperature and the enthalpy change of crystallization of amorphous Fe 50 W 50 powders milled for 1,440 ks were measured to be 860 K and -9kJ/mol, respectively. The amorphous Fe 50 W 50 powder produced is almost paramagnetic at room temperature. The powder comprises homogeneous and smooth spheres with an average size of about 0.5 microm in diameter

  5. Characterization of ceramic powder compacts

    Yanai, K.; Ishimoto, S.; Kubo, T.; Ito, K.; Ishikawa, T.; Hayashi, H.

    1995-01-01

    UO 2 and Al 2 O 3 powder packing structures in cylindrical powder compacts are observed by scanning electron microscopy using polished cross sections of compacts fixed by low viscosity epoxy resin. Hard aggregates which are not destroyed during powder compaction are observed in some of the UO 2 powder compacts. A technique to measure local density in powder compacts is developed based on counting characteristic X-ray intensity by energy dispersive X-ray analysis (EDX). The local density of the corner portion of the powder compact fabricated by double-acting dry press is higher than that of the inner portion. ((orig.))

  6. Thermally Stimulated Currents in Nanocrystalline Titania

    Mara Bruzzi

    2018-01-01

    Full Text Available A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO2. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5–630 K, in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 1014–1018 cm−3, associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies.

  7. Arsenic removal by magnetic nanocrystalline barium hexaferrite

    Patel, Hasmukh A.; Byun, Jeehye; Yavuz, Cafer T., E-mail: yavuz@kaist.ac.kr [Graduate School of EEWS, Korea Advanced Institute of Science and Technology (KAIST) (Korea, Republic of)

    2012-07-15

    Nanoscale magnetite (Fe{sub 3}O{sub 4}) (<15 nm) is known to remove arsenic efficiently but is very difficult to separate or require high magnetic fields to separate out from the waste water after treatment. Anisotropic hexagonal ferrite (BaFe{sub 12}O{sub 19}, BHF) is a well-known permanent magnet (i.e., fridge magnets) and attractive due to its low cost in making large quantities. BHF offers a viable alternative to magnetite nanocrystals for arsenic removal since it features surfaces similar to iron oxides but with much enhanced magnetism. Herein, we employ BHF nanocrystalline materials for the first time in arsenic removal from wastewater. Our results show better (75 %) arsenic removal than magnetite of the similar sizes. The BHF nanoparticles, 6.06 {+-} 0.52 nm synthesized by thermolysis method at 320 Degree-Sign C do not show hexagonal phase, however, subsequent annealing at 750 Degree-Sign C produced pure hexagonal BHF in >200 nm assemblies. By using BHF, we demonstrate that nanoparticle removal is more efficient and fixed bed type cartridge applications are more possible.

  8. Magnetically responsive enzyme powders

    Pospišková, K.; Šafařík, Ivo

    2015-01-01

    Roč. 380, APR 2015 (2015), s. 197-200 ISSN 0304-8853 R&D Projects: GA MŠk(CZ) LD13021 Institutional support: RVO:67179843 Keywords : enzyme powders * cross-linking * magnetic modification * magnetic separation * magnetic iron oxides particles * microwave-assisted synthesis Subject RIV: CE - Biochemistry Impact factor: 2.357, year: 2015

  9. Powder neutron diffractometers

    Adib, M.

    2002-01-01

    Basic properties and applications of powder neutron Diffractometers are described for optimum use of the continuous neutron beams. These instruments are equipped with position sensitive detectors, neutron guide tubes, and both high intensity and high resolution modes of operation are possible .The principles of both direct and Fourier reverse time-of-flight neutron Diffractometers are also given

  10. Low Temperature Powder Coating

    2011-02-09

    of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) • Legacy primers contain hexavalent chrome • Conventional powder coatings...coatings both in laboratory and field service evaluations • LTCPC allows environmental cost reductions through VOC/HAP elimination and hexavalent ... chrome reduction. • The LTCPC process greatly shortens the coating operation (LTCPC cures much more rapidly then conventional wet coatings) resulting in

  11. Laser cladding with powder

    Schneider, M.F.; Schneider, Marcel Fredrik

    1998-01-01

    This thesis is directed to laser cladding with powder and a CO2 laser as heat source. The laser beam intensity profile turned out to be an important pa6 Summary rameter in laser cladding. A numerical model was developed that allows the prediction of the surface temperature distribution that is

  12. Monoclinic β-Li{sub 2}TiO{sub 3} nanocrystalline particles employing novel urea assisted solid state route: Synthesis, characterization and sintering behavior

    Tripathi, Biranchi M., E-mail: biranchi.barc@gmail.com [Powder Metallurgy Division, Bhabha Atomic Research Centre, Vashi Complex, Navi Mumbai 400705 (India); Mohanty, Trupti; Prakash, Deep [Powder Metallurgy Division, Bhabha Atomic Research Centre, Vashi Complex, Navi Mumbai 400705 (India); Tyagi, A.K. [Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Sinha, P.K. [Powder Metallurgy Division, Bhabha Atomic Research Centre, Vashi Complex, Navi Mumbai 400705 (India)

    2017-07-15

    Pure phase monoclinic nano-crystalline Li{sub 2}TiO{sub 3} powder was synthesized by a novel urea assisted solid state synthesis method using readily available and economical precursors. A single phase and well crystalline Li{sub 2}TiO{sub 3} powder has been obtained at slightly lower temperature (600–700 °C) and shorter duration (2 h) as compared to the conventional solid state method. The proposed method has significant advantages in comparison to other viable methods mainly in terms of phase purity, powder properties and sinterability. Analysis of chemical composition using inductively coupled plasma atomic emission spectroscopy (ICP-AES) shows no loss of lithium from Li{sub 2}TiO{sub 3} in the proposed method. The emergence of monoclinic Li{sub 2}TiO{sub 3} phase was confirmed by X-ray diffraction (XRD) pattern of as-synthesized powder. The crystallite size of Li{sub 2}TiO{sub 3} powder was calculated to be in the range of 15–80 nm, which varied as a function of urea composition and temperature. The morphology of as-prepared Li{sub 2}TiO{sub 3} powders was examined by scanning electron microscope (SEM). The effect of urea composition on phase and morphology was investigated so as to delineate the role of urea. Upon sintering at < 1000 °C temperature, the Li{sub 2}TiO{sub 3} powder compact attained about 98% of the theoretical density with fine grained (grain size: 2–3 μm) microstructure. It indicates excellent sinter-ability of Li{sub 2}TiO{sub 3} powder synthesized by the proposed method. The fine grained structure is desirable for better tritium breeding performance of Li{sub 2}TiO{sub 3}. Electrochemical impedance spectroscopy at variable temperature showed good electrical properties of Li{sub 2}TiO{sub 3}. The proposed method is simple, anticipated to be cost effective and convenient to realise for large scale production of phase pure nanocrystalline and having significantly enhanced sinter-ability Li{sub 2}TiO{sub 3} powder.

  13. Creep behavior of a nanocrystalline Fe-B-Si alloy

    Xiao, M.; Kong, Q.P.

    1997-01-01

    The research of nanocrystalline materials has attracted much attention in the world. In recent years, there have been several studies on their creep behavior. Among these, the authors have studied the tensile creep of a nanocrystalline Ni-P alloy (28 nm) at temperatures around 0.5 Tm (Tm is the melting point). The samples were prepared by the method of crystallization of amorphous ribbon. Based on the data of stress exponent and activation energy, they suggested that the creep was controlled by boundary diffusion; while the creep of the same alloy with a larger grain size (257 nm) was controlled by a different mechanism. In the present paper, the authors extend the research to the creep of a nanocrystalline Fe-B-Si alloy. The samples are also prepared by crystallization of amorphous ribbon. The samples such prepared have an advantage that the interfaces are naturally formed without artificial compaction and porosity

  14. Ferromagnetism appears in nitrogen implanted nanocrystalline diamond films

    Remes, Zdenek [Institute of Physics ASCR v.v.i., Cukrovarnicka 10, 162 00 Prague 6 (Czech Republic); Sun, Shih-Jye, E-mail: sjs@nuk.edu.tw [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Varga, Marian [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Chou, Hsiung [Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Hsu, Hua-Shu [Department of Applied Physics, National Pingtung University of Education, Pingtung 900, Taiwan (China); Kromka, Alexander [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Horak, Pavel [Nuclear Physics Institute, 250 68 Rez (Czech Republic)

    2015-11-15

    The nanocrystalline diamond films turn to be ferromagnetic after implanting various nitrogen doses on them. Through this research, we confirm that the room-temperature ferromagnetism of the implanted samples is derived from the measurements of magnetic circular dichroism (MCD) and superconducting quantum interference device (SQUID). Samples with larger crystalline grains as well as higher implanted doses present more robust ferromagnetic signals at room temperature. Raman spectra indicate that the small grain-sized samples are much more disordered than the large grain-sized ones. We propose that a slightly large saturated ferromagnetism could be observed at low temperature, because the increased localization effects have a significant impact on more disordered structure. - Highlights: • Nitrogen implanted nanocrystalline diamond films exhibit ferromagnetism at room temperature. • Nitrogen implants made a Raman deviation from the typical nanocrystalline diamond films. • The ferromagnetism induced from the structure distortion is dominant at low temperature.

  15. Correlation of thermodynamics and grain growth kinetics in nanocrystalline metals

    Song Xiaoyan; Zhang Jiuxing; Li Lingmei; Yang Keyong; Liu Guoquan

    2006-01-01

    We investigated the correlation of thermodynamics and grain growth kinetics of nanocrystalline metals both theoretically and experimentally. A model was developed to describe the thermodynamic properties of nanograin boundaries, which could give reliable predictions in the destabilization characteristics of nanograin structures and the slowing down of grain growth kinetics at a constant temperature. Both the temperature-varying and isothermal nanograin growth behaviors in pure nanocrystalline Co were studied to verify the thermodynamic predictions. The experimental results showing that discontinuous nanograin growth takes place at a certain temperature and grain growth rate decreases monotonically with time confirm our thermodynamics-based description of nanograin growth characteristics. Therefore, we propose a thermodynamic viewpoint to explain the deviation of grain growth kinetics in nanocrystalline metals from those of polycrystalline materials

  16. Nanocrystalline Aluminum Truss Cores for Lightweight Sandwich Structures

    Schaedler, Tobias A.; Chan, Lisa J.; Clough, Eric C.; Stilke, Morgan A.; Hundley, Jacob M.; Masur, Lawrence J.

    2017-12-01

    Substitution of conventional honeycomb composite sandwich structures with lighter alternatives has the potential to reduce the mass of future vehicles. Here we demonstrate nanocrystalline aluminum-manganese truss cores that achieve 2-4 times higher strength than aluminum alloy 5056 honeycombs of the same density. The scalable fabrication approach starts with additive manufacturing of polymer templates, followed by electrodeposition of nanocrystalline Al-Mn alloy, removal of the polymer, and facesheet integration. This facilitates curved and net-shaped sandwich structures, as well as co-curing of the facesheets, which eliminates the need for extra adhesive. The nanocrystalline Al-Mn alloy thin-film material exhibits high strength and ductility and can be converted into a three-dimensional hollow truss structure with this approach. Ultra-lightweight sandwich structures are of interest for a range of applications in aerospace, such as fairings, wings, and flaps, as well as for the automotive and sports industries.

  17. Synthesis and characterization of nanocrystalline nuclear ceramics

    Ananthasivan, K.; Anthonysamy, S.; Chandramouli, V.; Vasudeva Rao, P.R.

    2006-01-01

    This paper highlights the utility of the gel-combustion synthesis in making solid solutions containing the oxides of U, Th, and Ce. The synthesis of a series of solid solutions of ceria with thoria and urania using the gel-combustion technique with citric acid as the fuel is presented as a typical case. The x-ray crystallite size, specific surface area, and residual carbon of the precursors and final products are discussed. The sinterability of these powders is analysed using their sintered densities. Solid solutions of thoria-ceria with a density higher than 85% TD (theoretical density) and those of urania ceria with a density as high as 96% TD were obtained. The microstructure of the thoria-ceria powders were analysed using high resolution electron microscopy. (author)

  18. Structure and performance of anisotropic nanocrystalline Nd-Fe-B magnets fabricated by high-velocity compaction followed by deformation

    Zhao, L. Z.; Deng, X. X.; Yu, H. Y.; Guan, H. J.; Li, X. Q.; Xiao, Z. Y.; Liu, Z. W.; Greneche, J. M.

    2017-12-01

    High-velocity compaction (HVC) has been proposed as an effective approach for the fabrication of nanocrystalline Nd-Fe-B magnets. In this work, the effect of powder size on the density of HVCed magnets has been studied and the anisotropic nanocrystalline Nd-Fe-B magnets were prepared by HVC followed by hot deformation (HD). It is found that a proper particle size range is beneficial to high density. The investigations on the microstructure, magnetic domain structure, and hyperfine structure, indicate that the deformed grain structure and the magnetic domain structure with uniform paramagnetic grain boundary phase give good magnetic properties of HVC + HDed magnets. These magnets also have good mechanical and anti-corrosion properties. The results indicate that HVC is not only a near-net-shape, room temperature and binder-free process but is also able to maintain uniform nanostructure and to achieve good magnetic properties in both isotropic and anisotropic magnets. As a result, HVC can be employed as an ideal alternative process for bonding or hot pressing for the conventional MQI, MQII and MQIII magnets.

  19. Hexagonal close packed to face centered cubic polymorphic transformation in nanocrystalline titanium-zirconium system by mechanical alloying

    Bera, S.; Manna, I.

    2006-01-01

    The present study reports a reversible hexagonal close packed (hcp) to face centered cubic (fcc) polymorphic phase transformation in four different nanocrystalline titanium-zirconium binary alloys in the course of mechanical alloying in a planetary ball mill. This transformation is monitored at appropriate stages by X-ray diffraction and high-resolution transmission electron microscopy. Lattice parameter of the nanocrystalline fcc phase is a function of the alloy composition. For a given alloy, the lattice parameter and hence volume per atom increase with increase in milling time under comparable conditions. On the other hand, crystallite size, measured from X-ray peak broadening, significantly decreases with the progress of milling. It is suggested that structural instability due to plastic strain, increasing lattice expansion, and negative (from core to boundary) hydrostatic pressure is responsible for this hcp → fcc polymorphic transformation. The said transformation seems reversible as isothermal annealing at 1000 deg. C for 1 h or melting the powder mass leads to partial or complete transformation of the milled product from single phase fcc to hcp

  20. Composites of amorphous and nanocrystalline Zr–Cu–Al–Nb bulk materials synthesized by spark plasma sintering

    Drescher, P., E-mail: philipp.drescher@uni-rostock.de [Fluidic Technology and Microfluidics, Faculty of Mechanical Engineering and Marine Technology, University of Rostock, 18059 Rostock (Germany); Witte, K. [Physics of New Materials, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Yang, B. [Polymer Physics, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Steuer, R.; Kessler, O. [Chair of Materials Science, Faculty of Mechanical Engineering and Marine Technology, University of Rostock, 18059 Rostock (Germany); Burkel, E. [Physics of New Materials, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Schick, C. [Polymer Physics, Institute of Physics, University of Rostock, 18051 Rostock (Germany); Seitz, H. [Fluidic Technology and Microfluidics, Faculty of Mechanical Engineering and Marine Technology, University of Rostock, 18059 Rostock (Germany)

    2016-05-15

    The fabrication of Zr{sub 70}Cu{sub 24}Al{sub 4}Nb{sub 2} bulk metallic glass composite samples by spark plasma sintering (SPS) process has been successfully realized. The unique characteristics of bulk metallic glasses could lead to the possibility of future applications as new structural and functional materials. The densification of an amorphous Zr{sub 70}Cu{sub 24}Al{sub 4}Nb{sub 2} powder was realized in a systematic study changing the sintering temperature in the SPS process leading to stable composites characteristic of amorphous and nanocrystalline structures. X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) analysis, transmission electron microscopy (TEM) as well as hardness tests were applied to determine the structural and mechanical properties of the sintered materials. A stable amorphous bulk metallic glass based on Zr{sub 70}Cu{sub 24}Al{sub 4}Nb{sub 2} with a low fraction of crystallites could be fabricated applying a nominal sintering temperature of 400 °C. Higher sintering temperatures lead to composites with high fractions of nanocrystalline material with porosities below 0.5%.

  1. Texture-dependent twin formation in nanocrystalline thin Pd films

    Wang, B.; Idrissi, H.; Shi, H.; Colla, M.S.; Michotte, S.; Raskin, J.P.; Pardoen, T.; Schryvers, D.

    2012-01-01

    Nanocrystalline Pd films were produced by electron-beam evaporation and sputter deposition. The electron-beam-evaporated films reveal randomly oriented nanograins with a relatively high density of growth twins, unexpected in view of the high stacking fault energy of Pd. In contrast, sputter-deposited films show a clear 〈1 1 1〉 crystallographic textured nanostructure without twins. These results provide insightful information to guide the generation of microstructures with enhanced strength/ductility balance in high stacking fault energy nanocrystalline metallic thin films.

  2. Engineering of giant magnetoimpedance effect of amorphous and nanocrystalline microwires

    V. Zhukova

    2016-12-01

    Full Text Available We present our studies of the factors affecting soft magnetic properties and giant magnetoimpedance effect in thin amorphous and nanocrystalline microwires. We showed that the magnetoelastic anisotropy is one of the most important parameters that determine magnetic softness and GMI effect of glass-coated microwires  and annealing can be very effective for manipulation the magnetic properties of amorphous ferromagnetic glass-coated microwires. Considerable magnetic softening and increasing of the GMI effect is observed in Fe-rich nanocrystalline FINEMET-type glass-coated microwires after the nanocrystallization.

  3. Inter- and intra-agglomerate fracture in nanocrystalline nickel.

    Shan, Zhiwei; Knapp, J A; Follstaedt, D M; Stach, E A; Wiezorek, J M K; Mao, S X

    2008-03-14

    In situ tensile straining transmission electron microscopy tests have been carried out on nanocrystalline Ni. Grain agglomerates (GAs) were found to form very frequently and rapidly ahead of an advancing crack with sizes much larger than the initial average grain size. High-resolution electron microscopy indicated that the GAs most probably consist of nanograins separated by low-angle grain boundaries. Furthermore, both inter- and intra-GA fractures were observed. The observations suggest that these newly formed GAs may play an important role in the formation of the dimpled fracture surfaces of nanocrystalline materials.

  4. High-pressure structural behaviour of nanocrystalline Ge

    Wang, H; Liu, J F; He, Y; Wang, Y; Chen, W; Jiang, J Z; Olsen, J Staun; Gerward, L

    2007-01-01

    The equation of state and the pressure of the I-II transition have been studied for nanocrystalline Ge using synchrotron x-ray diffraction. The bulk modulus and the transition pressure increase with decreasing particle size for both Ge-I and Ge-II, but the percentage volume collapse at the transition remains constant. Simplified models for the high-pressure structural behaviour are presented, based on the assumption that a large fraction of the atoms reside in grain boundary regions of the nanocrystalline material. The interface structure plays a significant role in affecting the transition pressure and the bulk modulus

  5. Method to blend separator powders

    Guidotti, Ronald A.; Andazola, Arthur H.; Reinhardt, Frederick W.

    2007-12-04

    A method for making a blended powder mixture, whereby two or more powders are mixed in a container with a liquid selected from nitrogen or short-chain alcohols, where at least one of the powders has an angle of repose greater than approximately 50 degrees. The method is useful in preparing blended powders of Li halides and MgO for use in the preparation of thermal battery separators.

  6. Plasma technology for powder particles

    Kranz, E. (Technische Hochschule, Ilmenau (German Democratic Republic))

    1983-03-01

    A survey is given of principles and applications of plasma spraying and of powder transformation and generation in plasma considering spheroidization, grain size transformation, powder particle formation, powder reduction, and melting within the power range of 10/sup 3/ to 10/sup 7/ W. The products are applied in many industrial fields such as nuclear engineering, hard metal production, metallurgy, catalysis, and semiconductor techniques.

  7. Isotropic and anisotropic nanocrystalline NdFeB bulk magnets prepared by binder-free high-velocity compaction technique

    Deng, Xiangxing [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Liu, Zhongwu, E-mail: zwliu@scut.edu.cn [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Hongya [School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640 (China); Xiao, Zhiyu [School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640 (China); Zhang, Guoqing [Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095 (China)

    2015-09-15

    NdFeB powders were consolidated into nanocrystalline bulk magnets by a near-net-shape process of high-velocity compaction (HVC) at room temperature with no binder employed. The nanostructure can be maintained after compaction. The compacted magnets with relatively high density can inherit the coercivity of the starting powders. The mechanical strength of the HVCed magnet after heat treatment is comparable to that of the conventional bonded NdFeB magnets. The anisotropic magnet has also been prepared by hot deformation using HVCed magnet as the precursor. The remanence value along the pressing direction increased from 0.64 to 0.95 T and maximum energy product (BH){sub max} increased from 65 to 120 kJ/m{sup 3} after hot deformation. The processing–structure–properties relationships for both isotropic and anisotropic magnets are discussed. - Highlights: • HVC is a feasible binder-free approach for preparing NdFeB magnets. • The compacted magnets can inherit the coercivity of the starting powders. • The magnets post heat treatment have compression strength higher than bonded magnets. • The approach of HVC is a potential pre-process for anisotropic NdFeB bulk magnets.

  8. Isotropic and anisotropic nanocrystalline NdFeB bulk magnets prepared by binder-free high-velocity compaction technique

    Deng, Xiangxing; Liu, Zhongwu; Yu, Hongya; Xiao, Zhiyu; Zhang, Guoqing

    2015-01-01

    NdFeB powders were consolidated into nanocrystalline bulk magnets by a near-net-shape process of high-velocity compaction (HVC) at room temperature with no binder employed. The nanostructure can be maintained after compaction. The compacted magnets with relatively high density can inherit the coercivity of the starting powders. The mechanical strength of the HVCed magnet after heat treatment is comparable to that of the conventional bonded NdFeB magnets. The anisotropic magnet has also been prepared by hot deformation using HVCed magnet as the precursor. The remanence value along the pressing direction increased from 0.64 to 0.95 T and maximum energy product (BH) max increased from 65 to 120 kJ/m 3 after hot deformation. The processing–structure–properties relationships for both isotropic and anisotropic magnets are discussed. - Highlights: • HVC is a feasible binder-free approach for preparing NdFeB magnets. • The compacted magnets can inherit the coercivity of the starting powders. • The magnets post heat treatment have compression strength higher than bonded magnets. • The approach of HVC is a potential pre-process for anisotropic NdFeB bulk magnets

  9. Synthesis of Uranium nitride powders using metal uranium powders

    Yang, Jae Ho; Kim, Dong Joo; Oh, Jang Soo; Rhee, Young Woo; Kim, Jong Hun; Kim, Keon Sik

    2012-01-01

    Uranium nitride (UN) is a potential fuel material for advanced nuclear reactors because of their high fuel density, high thermal conductivity, high melting temperature, and considerable breeding capability in LWRs. Uranium nitride powders can be fabricated by a carbothermic reduction of the oxide powders, or the nitriding of metal uranium. The carbothermic reduction has an advantage in the production of fine powders. However it has many drawbacks such as an inevitable engagement of impurities, process burden, and difficulties in reusing of expensive N 15 gas. Manufacturing concerns issued in the carbothermic reduction process can be solved by changing the starting materials from oxide powder to metals. However, in nitriding process of metal, it is difficult to obtain fine nitride powders because metal uranium is usually fabricated in the form of bulk ingots. In this study, a simple reaction method was tested to fabricate uranium nitride powders directly from uranium metal powders. We fabricated uranium metal spherical powder and flake using a centrifugal atomization method. The nitride powders were obtained by thermal treating those metal particles under nitrogen containing gas. We investigated the phase and morphology evolutions of powders during the nitriding process. A phase analysis of nitride powders was also a part of the present work

  10. Composition and properties of nanocrystalline Zn S thin films prepared by a new chemical bath deposition route

    Sahraei, R.; Goudarzi, A.; Ahmadpoor, H.; Motedayen Aval, Gh.

    2006-01-01

    Zinc sulfide nanocrystalline thin films were prepared by a new chemical bath deposition route on soda lime glass and quartz substrates using a weak acidic bath, in which disodium salt of ethylenediaminetetraacetic acid (EDTA) acts as a complexing agent and thioacetamide acts as a source of sulfide ions. The thickness of the films varied from a few nm to 500 nm. The chemical composition of films was studied by energy-dispersive X-ray analyzer and Fourier transform infrared spectroscopy. The films are very close to Zinc sulfide stoichiometry and we did not observed any organic compounds in the impurity form in them. X-ray diffraction indicates that the film and powder formed in the same reaction bath have cubic zinc blende structure. The films have high transmittance of about 75% in the visible region. The optical band-gap energy (E g ) was determined to be 3.75 eV from the absorption spectrophotometry measurements.

  11. Synthesis of nanocrystalline Zn0.5Mn0.5Fe2O4 via in situ polymerization technique

    Liu Xianming; Fu Shaoyun

    2007-01-01

    Nanocrystalline Zn 0.5 Mn 0.5 Fe 2 O 4 was synthesized through the pyrolysis of polyacrylate salt precursors prepared via in situ polymerization of the metal salts and acrylic acid. The pyrolysis behavior of the polymeric precursors was studied by use of thermal analysis. The as-obtained product was characterized by powder X-ray diffraction (XRD), transmission electron microscope (TEM), electron diffraction (ED) pattern, scanning electron microscopy (SEM) and electron dispersive X-ray (EDX) analysis. The results revealed that the particle size is in the range of 15-25 nm for Zn-Mn ferrites with good crystallinity. Magnetic properties of the sample at 300 K were measured using a vibrating sample magnetometer, which showed that the sample exhibited characteristics of superparamagnetism

  12. The effect of anion on the magnetic properties of nanocrystalline NiO synthesized by homogeneous precipitation

    Ranga Rao Pulimi, V.; Jeevanandam, P.

    2009-01-01

    The effect of using different anions (nitrate, chloride, sulfate, and acetate) during the precursor synthesis, by homogeneous precipitation, on the magnetic properties of the final product (nanocrystalline NiO), has been studied. The precursors and the oxide were characterized by various analytical techniques including powder X-ray diffraction, FT-IR spectroscopy, thermal gravimetry (TGA), and magnetic measurements. The synthesized NiO samples possess crystallite size in the range, ∼2-6 nm, depending on the anion of the nickel salt. The nickel oxide nanoparticles exhibit superparamagnetic behavior. Acetate and sulfate anions lead to NiO with higher saturation magnetization (∼1.2-1.8 emu/g), while chloride and nitrate anions lead to NiO nanoparticles with lower saturation magnetization (∼0.1-0.4 emu/g) values. The observed magnetic behavior has been attributed to the size effect.

  13. The effect of anion on the magnetic properties of nanocrystalline NiO synthesized by homogeneous precipitation

    Ranga Rao Pulimi, V. [Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Jeevanandam, P. [Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667 (India)], E-mail: jeevafcy@iitr.ernet.in

    2009-09-15

    The effect of using different anions (nitrate, chloride, sulfate, and acetate) during the precursor synthesis, by homogeneous precipitation, on the magnetic properties of the final product (nanocrystalline NiO), has been studied. The precursors and the oxide were characterized by various analytical techniques including powder X-ray diffraction, FT-IR spectroscopy, thermal gravimetry (TGA), and magnetic measurements. The synthesized NiO samples possess crystallite size in the range, {approx}2-6 nm, depending on the anion of the nickel salt. The nickel oxide nanoparticles exhibit superparamagnetic behavior. Acetate and sulfate anions lead to NiO with higher saturation magnetization ({approx}1.2-1.8 emu/g), while chloride and nitrate anions lead to NiO nanoparticles with lower saturation magnetization ({approx}0.1-0.4 emu/g) values. The observed magnetic behavior has been attributed to the size effect.

  14. Copper removal using electrosterically stabilized nanocrystalline cellulose.

    Sheikhi, Amir; Safari, Salman; Yang, Han; van de Ven, Theo G M

    2015-06-03

    Removal of heavy metal ions such as copper using an efficient and low-cost method with low ecological footprint is a critical process in wastewater treatment, which can be achieved in a liquid phase using nanoadsorbents such as inorganic nanoparticles. Recently, attention has turned toward developing sustainable and environmentally friendly nanoadsorbents to remove heavy metal ions from aqueous media. Electrosterically stabilized nanocrystalline cellulose (ENCC), which can be prepared from wood fibers through periodate/chlorite oxidation, has been shown to have a high charge content and colloidal stability. Here, we show that ENCC scavenges copper ions by different mechanisms depending on the ion concentration. When the Cu(II) concentration is low (C0≲200 ppm), agglomerates of starlike ENCC particles appear, which are broken into individual starlike entities by shear and Brownian motion, as evidenced by photometric dispersion analysis, dynamic light scattering, and transmission electron microscopy. On the other hand, at higher copper concentrations, the aggregate morphology changes from starlike to raftlike, which is probably due to the collapse of protruding dicarboxylic cellulose (DCC) chains and ENCC charge neutralization by copper adsorption. Such raftlike structures result from head-to-head and lateral aggregation of neutralized ENCCs as confirmed by transmission electron microscopy. As opposed to starlike aggregates, the raftlike structures grow gradually and are prone to sedimentation at copper concentrations C0≳500 ppm, which eliminates a costly separation step in wastewater treatment processes. Moreover, a copper removal capacity of ∼185 mg g(-1) was achieved thanks to the highly charged DCC polyanions protruding from ENCC. These properties along with the biorenewability make ENCC a promising candidate for wastewater treatment, in which fast, facile, and low-cost removal of heavy metal ions is desired most.

  15. Tribological properties of nanocrystalline diamond films

    Erdemir, A.; Fenske, G.R.; Krauss, A.R.; Gruen, D.M.; McCauley, T.; Csencsits, R.T. [Argonne National Lab., IL (United States). Energy Technology Div.

    1999-11-01

    In this paper, we present the friction and wear properties of nanocrystalline diamond (NCD) films grown in Ar-fullerene (C{sub 60}) and Ar-CH{sub 4} microwave plasmas. Specifically, we will address the fundamental tribological issues posed by these films during sliding against Si{sub 3}N{sub 4} counterfaces in ambient air and inert gases. Grain sizes of the films grown by the new method are very small (10-30 nm) and are much smoother (20-40 nm, root mean square) than those of films grown by the conventional H{sub 2}-CH{sub 4} microwave-assisted chemical vapor deposition process. Transmission electron microscopy (TEM) revealed that the grain boundaries of these films are very sharp and free of nondiamond phases. The microcrystalline diamond films grown by most conventional methods consist of large grains and a rough surface finish, which can cause severe abrasion during sliding against other materials. The friction coefficients of films grown by the new method (i.e. in Ar-C{sub 60} and Ar-CH{sub 4} plasmas) are comparable with those of natural diamond, and wear damage on counterface materials is minimal. Fundamental tribological studies indicate that these films may undergo phase transformation during long-duration, high-speed and/or high-load sliding tests and that the transformation products trapped at the sliding interfaces can intermittently dominate friction and wear performance. Using results from a combination of TEM, electron diffraction, Raman spectroscopy, and electron energy loss spectroscopy, we describe the structural chemistry of the debris particles trapped at the sliding interfaces and elucidate their possible effects on friction and wear of NCD films in dry N{sub 2}. Finally, we suggest a few potential applications in which NCD films can improve performance and service lives. (orig.)

  16. Dispersing powders in liquids

    Nelson, RD

    1988-01-01

    This book provides powder technologists with laboratory procedures for selecting dispersing agents and preparing stable dispersions that can then be used in particle size characterization instruments. Its broader goal is to introduce industrial chemists and engineers to the phenomena, terminology, physical principles, and chemical considerations involved in preparing and handling dispersions on a commercial scale. The book introduces novices to: - industrial problems due to improper degree of dispersion; - the nomenclature used in describing particles; - the basic physica

  17. Container for nuclear fuel powders

    Etheredge, B.F.; Larson, R.I.

    1982-01-01

    A critically safe container is disclosed for the storage and rapid discharge of enriched nuclear fuel material in powder form is disclosed. The container has a hollow, slab-shaped container body that has one critically safe dimension. A powder inlet is provided on one side wall of the body adjacent to a corner thereof and a powder discharge port is provided at another corner of the body approximately diagonal the powder inlet. Gas plenum for moving the powder during discharge are located along the side walls of the container adjacent the discharge port

  18. Preparation of superconductor precursor powders

    Bhattacharya, Raghunath

    1998-01-01

    A process for the preparation of a precursor metallic powder composition for use in the subsequent formation of a superconductor. The process comprises the steps of providing an electrodeposition bath comprising an electrolyte medium and a cathode substrate electrode, and providing to the bath one or more soluble salts of one or more respective metals which are capable of exhibiting superconductor properties upon subsequent appropriate treatment. The bath is continually energized to cause the metallic and/or reduced particles formed at the electrode to drop as a powder from the electrode into the bath, and this powder, which is a precursor powder for superconductor production, is recovered from the bath for subsequent treatment. The process permits direct inclusion of all metals in the preparation of the precursor powder, and yields an amorphous product mixed on an atomic scale to thereby impart inherent high reactivity. Superconductors which can be formed from the precursor powder include pellet and powder-in-tube products.

  19. Fast response time alcohol gas sensor using nanocrystalline F

    Home; Journals; Bulletin of Materials Science; Volume 36; Issue 4. Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method. Sarbani Basu Yeong-Her Wang C Ghanshyam Pawan Kapur. Volume 36 Issue 4 August 2013 pp 521-533 ...

  20. High-pressure structural behavior of nanocrystalline Ge

    Wang, H.; Liu, J. F.; Yan, H.

    2007-01-01

    The equation of state and the pressure of the I-II transition have been studied for nanocrystalline Ge using synchrotron x-ray diffraction. The bulk modulus and the transition pressure increase with decreasing particle size for both Ge-I and Ge-II, but the percentage volume collapse at the transi...

  1. Induced anisotropy effect in nanocrystalline cores for GFCBs

    Waeckerle, T. E-mail: thierry.waeckerle@imphy.usinor.com; Verin, Ph.; Cremer, P.; Gautard, D

    2000-06-02

    Nanocrystalline materials are very efficient for GFCB cores with flat hysteresis loop, especially if permeability may be raised in keeping low the remanent induction. This can be achieved with peculiar field annealing . A thermodynamic model is proposed to explain the experimental evidence.

  2. New route to the fabrication of nanocrystalline diamond films

    Varshney, Deepak; Morell, Gerardo; Palomino, Javier; Resto, Oscar; Gil, Jennifer; Weiner, Brad R.

    2014-01-01

    Nanocrystalline diamond (NCD) thin films offer applications in various fields, but the existing synthetic approaches are cumbersome and destructive. A major breakthrough has been achieved by our group in the direction of a non-destructive, scalable, and economic process of NCD thin-film fabrication. Here, we report a cheap precursor for the growth of nanocrystalline diamond in the form of paraffin wax. We show that NCD thin films can be fabricated on a copper support by using simple, commonplace paraffin wax under reaction conditions of Hot Filament Chemical Vapor Deposition (HFCVD). Surprisingly, even the presence of any catalyst or seeding that has been conventionally used in the state-of-the-art is not required. The structure of the obtained films was analyzed by scanning electron microscopy and transmission electron microscopy. Raman spectroscopy and electron energy-loss spectroscopy recorded at the carbon K-edge region confirm the presence of nanocrystalline diamond. The process is a significant step towards cost-effective and non-cumbersome fabrication of nanocrystalline diamond thin films for commercial production

  3. Quartz crystal microbalance gas sensor with nanocrystalline diamond sensitive layer

    Varga, Marián; Laposa, A.; Kulha, Pavel; Kroutil, J.; Husák, M.; Kromka, Alexander

    2015-01-01

    Roč. 252, č. 11 (2015), s. 2591-2597 ISSN 0370-1972 R&D Projects: GA ČR(CZ) GBP108/12/G108 Institutional support: RVO:68378271 Keywords : gas sensor * nanocrystalline diamond * quartz resonator * thickness shear mode Subject RIV: JB - Sensor s, Measurment, Regulation Impact factor: 1.522, year: 2015

  4. Transparent nanocrystalline ZnO films prepared by spin coating

    Berber, M. [SusTech GmbH and Co. KG, Petersenstr. 20, 64287 Darmstadt, Hessen (Germany)]. E-mail: mete.berber@sustech.de; Bulto, V. [SusTech GmbH and Co. KG, Petersenstr. 20, 64287 Darmstadt, Hessen (Germany); Kliss, R. [SusTech GmbH and Co. KG, Petersenstr. 20, 64287 Darmstadt, Hessen (Germany); Hahn, H. [SusTech GmbH and Co. KG, Petersenstr. 20, 64287 Darmstadt, Hessen (Germany); Forschungszentrum Karlsruhe, Institute for Nanotechnology, Postfach 3640, 76021 Karlsruhe (Germany); Joint Research Laboratory Nanomaterials, TU Darmstadt, Institute of Materials Science, Petersenstr. 23, 64287 Darmstadt (Germany)

    2005-09-15

    Dispersions of zinc oxide nanoparticles synthesized by the electrochemical deposition under oxidizing conditions process with organic surfactants, were spin coated on glass substrates. After sintering, the microstructure, surface morphology, and electro-optical properties of the transparent nanocrystalline zinc oxide films have been investigated for different coating thicknesses and organic solvents.

  5. Transparent nanocrystalline ZnO films prepared by spin coating

    Berber, M.; Bulto, V.; Kliss, R.; Hahn, H.

    2005-01-01

    Dispersions of zinc oxide nanoparticles synthesized by the electrochemical deposition under oxidizing conditions process with organic surfactants, were spin coated on glass substrates. After sintering, the microstructure, surface morphology, and electro-optical properties of the transparent nanocrystalline zinc oxide films have been investigated for different coating thicknesses and organic solvents

  6. Nanocrystalline spinel ferrites by solid state reaction route

    Wintec

    Nanocrystalline spinel ferrites by solid state reaction route. T K KUNDU* and S MISHRA. Department of Physics, Visva-Bharati, Santiniketan 731 235, India. Abstract. Nanostructured NiFe2O4, MnFe2O4 and (NiZn)Fe2O4 were synthesized by aliovalent ion doping using conventional solid-state reaction route. With the ...

  7. Electrodeposited nanocrystalline bronze alloys as replacement for Ni

    Hovestad, A.; Tacken, R.A.; Mannetje, H.H.'t

    2008-01-01

    Nanocrystalline white-bronze, CuSn, electroplating was investigated as alternative to Ni plating as undercoat for noble metals in jewellery applications. A strongly acidic plating bath was developed with an organic additive to suppress hydrogen evolution and obtain bright coatings. Polarization

  8. Adhesion of osteoblasts on chemically patterned nanocrystalline diamonds

    Kalbáčová, M.; Michalíková, Lenka; Barešová, V.; Kromka, Alexander; Rezek, Bohuslav; Kmoch, S.

    2008-01-01

    Roč. 245, č. 10 (2008), s. 2124-2127 ISSN 0370-1972 R&D Projects: GA AV ČR KAN400100701 Institutional research plan: CEZ:AV0Z10100521 Keywords : cell growth * nanocrystalline diamond * surface termination Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.166, year: 2008

  9. Oxygen reduction on nanocrystalline ruthenia-local structure effects

    Abbott, Daniel F.; Mukerjee, Sanjeev; Petrykin, Valery

    2015-01-01

    Nanocrystalline ruthenium dioxide and doped ruthenia of the composition Ru1-xMxO2 (M = Co, Ni, Zn) with 0 ≤ x ≤ 0.2 were prepared by the spray-freezing freeze-drying technique. The oxygen reduction activity and selectivity of the prepared materials were evaluated in alkaline media using the RRDE ...

  10. Osteoblastic cells trigger gate currents on nanocrystalline diamond transistor

    Ižák, Tibor; Krátká, Marie; Kromka, Alexander; Rezek, Bohuslav

    2015-01-01

    Roč. 129, May (2015), 95-99 ISSN 0927-7765 R&D Projects: GA ČR GAP108/12/0996 Grant - others:AVČR(CZ) M100101209 Institutional support: RVO:68378271 Keywords : field-effect transistors * nanocrystalline diamond * osteoblastic cells * leakage currents Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.902, year: 2015

  11. Luminescence of nanocrystalline ZnSe:Mn2+

    Suyver, J.F.; Wuister, S.F.; Kelly, J.J.; Meijerink, A.

    2000-01-01

    The luminescence properties of nanocrystalline ZnSe:Mn^(2+) prepared via an inorganic chemical synthesis are described. Photoluminescence spectra show distinct ZnSe and Mn^(2+) related emissions, both of which are excited via the ZnSe host lattice. The Mn^(2+) emission wavelength and the

  12. Preparation of 50Ni-45Ti-5Zr powders by high-energy ball milling and hot pressing

    Marinzeck de Alcantara Abdala, Julia, E-mail: juabdala@yahoo.com.b [Instituto de Pesquisa e Desenvolvimento, Universidade do Vale do Paraiba, Av. Shishima Hifumi, 2911, 12244-000 Sao Jose dos Campos (Brazil); Bacci Fernandes, Bruno, E-mail: brunobacci@yahoo.com.b [Divisao de Engenharia Mecanica, Instituto Tecnologico de Aeronautica, Praca Marechal-do-Ar Eduardo Gomes, 50, 12228-904 Sao Jose dos Campos (Brazil); Santos, Dalcy Roberto dos, E-mail: dalcy@iae.cta.b [Instituto de Aeronautica e Espaco, Centro Tecnologico Aeroespacial, Praca Marechal-do-Ar Eduardo Gomes, 50, 12228-904 Sao Jose dos Campos (Brazil); Rodrigues Henriques, Vinicius Andre, E-mail: vinicius@iae.cta.b [Instituto de Aeronautica e Espaco, Centro Tecnologico Aeroespacial, Praca Marechal-do-Ar Eduardo Gomes, 50, 12228-904 Sao Jose dos Campos (Brazil); Moura Neto, Carlos de, E-mail: mneto@ita.b [Divisao de Engenharia Mecanica, Instituto Tecnologico de Aeronautica, Praca Marechal-do-Ar Eduardo Gomes, 50, 12228-904 Sao Jose dos Campos (Brazil); Saraiva Ramos, Alfeu, E-mail: alfeu@univap.b [Instituto de Pesquisa e Desenvolvimento, Universidade do Vale do Paraiba, Av. Shishima Hifumi, 2911, 12244-000 Sao Jose dos Campos (Brazil)

    2010-04-16

    This study reports on the preparation of the 50Ni-45Ti-5Zr (at.%) alloy by high-energy ball milling and hot pressing. The elemental powder mixture was processed in silicon nitride and hardened steel vials, and samples were collected after different milling times. To recover the previous powders in addition wet milling isopropyl alcohol (for 20 min) was adopted. The mechanically alloyed powders were hot-pressed under vacuum at 900 {sup o}C for 1 h using pressure levels close to 200 MPa. The milled powders were characterized by means of scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometry techniques. It was noted that the ductile starting powders were continuously cold-welded during ball milling. This fact was more pronounced during the processing of 50Ni-45Ti-5Zr powders in hardened steel vial. After milling for 5 h, the results suggested that amorphous and nanocrystalline structures were achieved. The complete consolidation was found after hot pressing of mechanically alloyed 50Ni-45Ti-5Zr powders, and a large amount of the B2-NiTi phase was formed mainly after processing in stainless steel balls and vial.

  13. Large zinc cation occupancy of octahedral sites in mechanically activated zinc ferrite powders

    Oliver, S. A.; Harris, V. G.; Hamdeh, H. H.; Ho, J. C.

    2000-01-01

    The cation site occupancy of a mechanically activated nanocrystalline zinc ferrite powder was determined as (Zn 0.55 2+ Fe 0.18 3+ ) tet [Zr 0.45 2+ Fe 1.82 3+ ] oct O 4 through analysis of extended x-ray absorption fine structure measurements, showing a large redistribution of cations between sites compared to normal zinc ferrite samples. The overpopulation of cations in the octahedral sites was attributed to the ascendance in importance of the ionic radii over the crystal energy and bonding coordination in determining which interstitial sites are occupied in this structurally disordered powder. Slight changes are observed in the local atomic environment about the zinc cations, but not the iron cations, with respect to the spinel structure. The presence of Fe 3+ on both sites is consistent with the measured room temperature magnetic properties. (c) 2000 American Institute of Physics

  14. The formation mechanism of mechanically alloyed Fe-20 at% Al powder

    Hadef, F., E-mail: hadef77@yahoo.fr [Laboratoire de Recherche sur la Physico-Chimie des Surfaces et Interfaces, LRPCSI, Universite 20 Aout 1955, BP 26, Route d' El-Hadaiek, Skikda 21000 (Algeria); Otmani, A. [Laboratoire de Recherche sur la Physico-Chimie des Surfaces et Interfaces, LRPCSI, Universite 20 Aout 1955, BP 26, Route d' El-Hadaiek, Skikda 21000 (Algeria); Djekoun, A. [Laboratoire de Magnetisme et Spectroscopie des Solides, LM2S, Universite Badji Mokhtar, BP 12 Annaba 23000 (Algeria); Greneche, J.M. [LUNAM, Universite du Maine, Institut des Molecules et Materiaux du Mans, UMR CNRS 6283, 72085 Le Mans (France)

    2013-01-15

    The formation mechanism of the mechanically alloyed Fe-20 at% Al, from elemental Fe and Al powders, has been investigated. The experimental results indicate the formation of a nanocrystalline bcc {alpha}-Fe(Al) solid solution with a lattice parameter close to a{sub {alpha}-Fe(Al)}=0.2890 nm, where each Fe atom is surrounded by (6Fe+2Al) in the first coordination sphere. The reaction mechanism of MA process seems to be controlled by a diffusion phenomenon. Aluminum particles undergo an important refinement to the nanometer scale and then they stick on Fe particles of large sizes. A large number of clear Al/Fe interface areas were generated. The short diffusion path and the presence of high concentration of defects accelerated the solid state reaction. - Highlights: Black-Right-Pointing-Pointer A nanocrystalline bcc {alpha}-Fe(Al) solid solution is formed from elemental Fe and Al powders. Black-Right-Pointing-Pointer The reaction mechanism of MA process seems to be controlled by a diffusion phenomenon. Black-Right-Pointing-Pointer Each Fe atom is surrounded by (6Fe+2Al) in the first coordination sphere.

  15. Diffraction. Powder, amorphous, liquid

    Sosnowska, I.M.

    1999-01-01

    Neutron powder diffraction is a unique tool to observe all possible diffraction effects appearing in crystal. High-resolution neutron diffractometers have to be used in this study. Analysis of the magnetic structure of polycrystalline materials requires the use of high-resolution neutron diffraction in the range of large interplanar distances. As distinguished from the double axis diffractometers (DAS), which show high resolution only at small interplanar distances, TOF (time-of-flight) diffractometry offers the best resolution at large interplanar distances. (K.A.)

  16. LARC powder prepreg system

    Baucom, Robert M.; Marchello, Joseph M.

    1990-01-01

    Thermoplastic prepregs of LARC-TPI have been produced in a fluidized bed unit on spread continuous fiber tows. The powders are melted on the fibers by radiant heating to adhere the polymer to the fiber. This process produces tow prepreg uniformly without imposing severe stress on the fibers or requiring long high temperature residence times for the polymer. Unit design theory and operating correlations have been developed to provide the basis for scale up to commercial operation. Special features of the operation are the pneumatic tow spreader, fluidized bed and resin feed systems.

  17. Low-temperature synthesis of nanocrystalline ZrC coatings on flake graphite by molten salts

    Ding, Jun, E-mail: dingjun@wust.edu.cn; Guo, Ding; Deng, Chengji; Zhu, Hongxi; Yu, Chao

    2017-06-15

    Highlights: • Uniform ZrC coatings are prepared on flake graphite at 900 °C. • ZrC coatings are composed of nanosized (30–50 nm) particles. • The template growth mechanism is believed to be dominant in the molten salt synthesis process. - Abstract: A novel molten salt synthetic route has been developed to prepare nanocrystalline zirconium carbide (ZrC) coatings on flake graphite at 900 °C, using Zr powder and flake graphite as the source materials in a static argon atmosphere, along with molten salts as the media. The effects of different molten salt media, the sintered temperature, and the heat preservation time on the phase and microstructure of the synthetic materials were investigated. The ZrC coatings formed on the flake graphite were uniform and composed of nanosized particles (30–50 nm). With an increase in the reaction temperature, the ZrC nanosized particles were more denser, and the heat preservation time and thickness of the ZrC coating also increased accordingly. Electron microscopy was used to observe the ZrC coatings on the flake graphite, indicating that a “template mechanism” played an important role during the molten salt synthesis.

  18. Preparation, deformation, and failure of functional Al-Sn and Al-Sn-Pb nanocrystalline alloys

    Noskova, N. I.; Vil'Danova, N. F.; Filippov, Yu. I.; Churbaev, R. V.; Pereturina, I. A.; Korshunov, L. G.; Korznikov, A. V.

    2006-12-01

    Changes in the structure, hardness, mechanical properties, and friction coefficient of Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb (wt %) alloys subjected to severe plastic deformation by equal-channel angular pressing (with a force of 40 tonne) and by shear at a pressure of 5 GPa have been studied. The transition into the nanocrystalline state was shown to occur at different degrees of plastic deformation. The hardness exhibits nonmonotonic variations, namely, first it increases and subsequently decreases. The friction coefficient of the Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys quenched from the melt was found to be 0.33; the friction coefficients of these alloys in the submicrocrystalline state (after equal-channel angular pressing) equal 0.24, 0.32, and 0.35, respectively. The effect of disintegration into nano-sized powders was found to occur in the Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys after severe plastic deformation to ɛ = 6.4 and subsequent short-time holding.

  19. Method of mechanochemical synthesis for the production of nanocrystalline Nb-Al alloys

    Portnoj, V.K.; Tret'yakov, K.V.; Logacheva, A.I.; Logunov, A.V.; Razumovskij, I.M.

    2004-01-01

    Using X-ray diffraction and DS analyses the process of solid phase synthesis on cooperative comminution of components (Nb, Al, Cr) in a planetary ball mill is investigated. Powder nanocrystalline Nb 3 Al base alloys of various compositions with simultaneous introduction of chromium are synthesized. High power milling results in block size of ∼ 20 nm. It is shown that final chromium dissolution and partial decomposition of Nb(Al) supersaturated solid solutions proceed after heating up to 1100 deg C only. With the help of doping with niobium by the method of mechanical alloying, a two-phase alloy Nb 3 Al + Nb 2 Al having been produced by arc melting, is corrected by composition and transferred to the two-phase region of Nb 3 Al + Nb(Al). It is revealed that the process of niobium aluminide phase formation during mechanochemical synthesis and the process of mechanical activation of Nb-Al system intermetallics enriched with niobium always proceed through formation of supersaturated solid solutions. The mechanism of the process is probably associated with stacking faults formation due to deformation [ru

  20. Low-Temperature Reverse Microemulsion Synthesis, Characterization, and Photocatalytic Performance of Nanocrystalline Titanium Dioxide

    Zhang Liu

    2012-01-01

    Full Text Available Nanocrystalline titanium dioxide (TiO2 was synthesized in microemulsions by using cetyltrimethylammonium bromide (CTAB as surfactant. In order to investigate the crystal transformation and photoactivity at low temperature, the as-prepared precipitates were aged at 65°C or calcined at various temperatures. Analyses using powder X-ray diffraction (XRD and Fourier transform infrared microscopy (FT-IR showed that precursors without aging or calcination were noncrystal and adsorbed by surfactant. After aging for 6 h, the amorphous TiO2 began to change into anatase. The obtained catalysts, which were synthesized in microemulsions with weight ratios of n-hexanol/CTAB/water as 6 : 3 : 1 and calcined at 500°C, presented the highest photocatalytic degradation rate on methyl orange (MO, while the catalysts, which were aged at 65°C for 90 h, also exhibited an outstanding photocatalytic performance and a little higher than that of the commercial titania photocatalyst Degussa P25.

  1. Synthesis and Characterization of Nanocrystalline Aluminophosphate AlPO4-5 Molecular Sieve

    Asir Alnaama

    2018-03-01

    Full Text Available Nanocrystalline aluminophosphate AlPO4-5 molecular sieves were synthesized by hydrothermal method (HTS. Synthesis parameters like time and temperature of crystallization were investigated. Type of template (R and ratio of R/P2O5 were studied also. Characterization of the synthesized AlPO4-5 were done by powder X-ray diffraction (XRD, scanning electron microscopy (SEM/EDX, Fourier transform infrared (FTIR, differential scanning calorimetry-thermogravimetry analysis (DSC-TGA, and N2 adsorption-desorption BET analysis. XRD patterns results showed excellent crystallinity for two types of templates, di-n-propylamine (DPA and tetrapropyl ammonium hydroxide (TPAOH for alumminophosphate five (AFI structure. Nano-level for particle size of 66 nm was revealed by AFM test. Good thermal stability was obtained in DSC-TGA results. Best time and temperature of crystallization of 24h and 190 O C were got. Optimum R/P2O5 for two kind of template was established.

  2. Nanocrystalline CsPbBr3 thin films: a grain boundary opto-electronic study

    Conte, G.; Somma, F.; Nikl, M.

    2005-01-01

    CsPbBr3 thin films with nanocrystalline morphology were studied by using optoelectronic techniques to infer the grain boundary region in respect of the crystallite's interior performance. Co-evaporation of puri-fied powders or crushed Bridgman single crystals were used to deposit materials and compare recombina-tion mechanism and dielectric relaxation processes within them. Nanosecond photoconduction decay was observed on both materials as well as activated hopping transport. An asymmetric Debye-like peak was evaluated from impedance spectroscopy with a FWHM value, which remains constant for 1.25 +/- 0.02 deca-des, addressing the presence of a tight conductivity relaxation times distribution. The evaluated activation energy, equal to 0.72 +/- 0.05 eV, similar to that estimated by DC measurements, is well smaller then that expected for an intrinsic material with exciton absorption at 2.36 eV. A simple model based on Voigt's elements was used to model the electronic characteristics of these nanostructured materials, to discuss observed results and define the role played by grain boundaries.

  3. Effect of sputtered titanium interlayers on the properties of nanocrystalline diamond films

    Li, Cuiping, E-mail: licp226@126.com, E-mail: limingji@163.com; Li, Mingji, E-mail: licp226@126.com, E-mail: limingji@163.com; Wu, Xiaoguo; Yang, Baohe [Tianjin Key Laboratory of Film Electronic and Communicate Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300384 (China); Dai, Wei; Xu, Sheng [Tianjin Key Laboratory of Film Electronic and Communicate Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300384 (China); College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072 (China); Li, Hongji [Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China)

    2016-04-07

    Ti interlayers with different thicknesses were sputtered on Si substrates and then ultrasonically seeded in a diamond powder suspension. Nanocrystalline diamond (NCD) films were deposited using a dc arc plasma jet chemical vapor deposition system on the seeded Ti/Si substrates. Atomic force microscopy and scanning electron microscopy tests showed that the roughness of the prepared Ti interlayer increased with increasing thickness. The effects of Ti interlayers with various thicknesses on the properties of NCD films were investigated. The results show nucleation, growth, and microstructure of the NCD films are strongly influenced by the Ti interlayers. The addition of a Ti interlayer between the Si substrate and the NCD films can significantly enhance the nucleation rate and reduce the surface roughness of the NCD. The NCD film on a 120 nm Ti interlayer possesses the fastest nucleation rate and the smoothest surface. Raman spectra of the NCD films show trans-polyacetylene relevant peaks reduce with increasing Ti interlayer thickness, which can owe to the improvement of crystalline at grain boundaries. Furthermore, nanoindentation measurement results show that the NCD film on a 120 nm Ti interlayer displays a higher hardness and elastic modulus. High resolution transmission electron microscopy images of a cross-section show that C atoms diffuse into the Ti layer and Si substrate and form TiC and SiC hard phases, which can explain the enhancement of mechanical properties of NCD.

  4. NATO Advanced Research Workshop on Properties and Applications of Nanocrystalline Alloys from Amorphous Precursors

    Idzikowski, Bogdan; Miglierini, Marcel

    2005-01-01

    Metallic (magnetic and non-magnetic) nanocrystalline materials have been known for over ten years but only recent developments in the research into those complex alloys and their metastable amorphous precursors have created a need to summarize the most important accomplishments in the field. This book is a collection of articles on various aspects of metallic nanocrystalline materials, and an attempt to address this above need. The main focus of the papers is put on the new issues that emerge in the studies of nanocrystalline materials, and, in particular, on (i) new compositions of the alloys, (ii) properties of conventional nanocrystalline materials, (iii) modeling and simulations, (iv) preparation methods, (v) experimental techniques of measurements, and (vi) different modern applications. Interesting phenomena of the physics of nanocrystalline materials are a consequence of the effects induced by the nanocrystalline structure. They include interface physics, the influence of the grain boundaries, the aver...

  5. Synthesis behavior of nanocrystalline Al-Al2O3 composite during low time mechanical milling process

    Alizadeh, Mostafa; Aliabadi, Morteza Mirzaei

    2011-01-01

    Research highlights: → In the low time milling the effect of Al 2 O 3 amount is investigated → Al 2 O 3 particles are distributed uniformly in the Al matrix → In the low time milling it is possible to produce nanostructured composite powder → Median size and bulk density measurements demonstrate reaching the steady state. - Abstract: In this work, four different volume fractions of Al 2 O 3 (10, 20, 30 and 40 vol.%) were mixed with the fine Al powder and the powder blends were milled for 5 h. Scanning electron microscopy analysis, particle size analysis and bulk density measurements were used to investigate the morphological changes and achieving the steady state conditions. The results showed that increasing the Al 2 O 3 content can provide the steady state particle size in 5 h milling process. It was found that increasing the volume fraction of Al 2 O 3 leads to increasing the uniformity of Al 2 O 3 . Standard deviations of microhardness measurements confirmed this result. The XRD pattern and XRF investigations depicted that increasing the Al 2 O 3 content causes an increase in the crystal defects, micro-strain and Fe contamination during 5 h milling process of nanocrystalline composite powders while the grain size is decreased. To investigate the effect of milling time, Al-30 vol.% Al 2 O 3 (which achieved steady state during 5 h milling process) was milled for 1-4 h. The results depicted that the milling time lower than 5 h, do not achieve to steady state conditions.

  6. Sol-gel synthesis, structure and photoluminescence properties of nanocrystalline Lu{sub 2}MoO{sub 6}:Eu

    Li, Huaiyong; Yang, Hyun Kyoung [Department of Physics, Pukyong National University, 599-1 Nam-Gu, Daeyeon 3 Dong, Busan 608-737 (Korea, Republic of); Jeong, Jung Hyun, E-mail: jhjeong@pknu.ac.kr [Department of Physics, Pukyong National University, 599-1 Nam-Gu, Daeyeon 3 Dong, Busan 608-737 (Korea, Republic of); Jang, Kiwan; Lee, Ho Sueb [Department of Physics, Changwon National University, Changwon 641-773 (Korea, Republic of); Yi, Soung Soo [Department of Electronic Material Engineering, Silla University, Busan 617-736 (Korea, Republic of)

    2011-09-15

    Highlights: {yields} Monoclinic-structural Lu{sub 2}MoO{sub 6} has strong absorption of near-UV light. {yields} The absorbed energy can be transferred from MoO{sub 5} groups to doped Eu{sup 3+} and luminescence. {yields} The absorption edge and the peak of the MoO{sub 5} excitation band shift in reverse ways. {yields} The decline of the crystallinity and the introduced defect respond for the variation. -- Abstract: In this paper, we reported the obtention of Eu{sup 3+} ion doped Lu{sub 2}MoO{sub 6} powders synthesized by a sol-gel method, and followed by annealing at different temperatures. The structure and photoluminescence properties of these powders were investigated. The X-ray diffraction pattern suggests that Lu{sub 2}MoO{sub 6} powder has a monoclinic structure. It was observed that the UV-visible and photoluminescence spectra of Lu{sub 2}MoO{sub 6}:Eu nanocrystallines varied systematically with the calcination temperature. The near-UV absorption edge shifts to long wavelength direction with the decreasing of the calcination temperature, while the peak of MoO{sub 5} excitation band shifts in an opposite way. The decline of the crystallinity and the introduced lattice defect were considered to respond for these variations. Additionally, due to the efficient red light emission under near-UV light excitation, the powder can be a candidate as red phosphor for white-light-emitting diodes.

  7. Theoretical study on recoilless fractions of simple cubic monatomic nanocrystalline particles

    Huang Jianping; Wang Luya

    2002-01-01

    Recoilless fractions of simple cubic monatomic nanocrystalline particles are calculated by using displacement-displacement Green's function. The numerical results show that the recoilless fractions on the surface of monatomic nanocrystalline particles are smaller than those in the inner, and they decrease when the particle size increase, the recoilless fractions of whole monatomic nanocrystalline particles increase when the particle size increase. These effects are more evident when the temperature is higher

  8. Vibrational thermodynamics of Fe90Zr7B3 nanocrystalline alloy from nuclear inelastic scattering

    Stankov, S.; Miglierini, M.; Chumakov, A. I.

    2010-01-01

    Recently we determined the iron-partial density of vibrational states (DOS) of nanocrystalline Fe(90)Zr(7)B(3) (Nanoperm), synthesized by crystallization of an amorphous precursor, for various stages of nanocrystallization separating the DOS of the nanograins from that of the interfaces [S. Stank......, vibrational entropy, and lattice specific heat as the material transforms from amorphous, through nanocrystalline, to fully crystallized state. The reported results shed new light on the previously observed anomalies in the vibrational thermodynamics of nanocrystalline materials....

  9. Paramagnetic centers in nanocrystalline TiC/C system

    Guskos, N.; Bodziony, T.; Maryniak, M.; Typek, J.; Biedunkiewicz, A.

    2008-01-01

    Electron paramagnetic resonance is applied to study the defect centers in nanocrystalline titanium carbide dispersed in carbon matrix (TiC x /C) synthesized by the non-hydrolytic sol-gel process. The presence of Ti 3+ paramagnetic centers is identified below 120 K along with a minor contribution from localized defect spins coupled with the conduction electron system in the carbon matrix. The temperature dependence of the resonance intensity of the latter signal indicates weak antiferromagnetic interactions. The presence of paramagnetic centers connected with trivalent titanium is suggested to be the result of chemical disorder, which can be further related to the observed anomalous behavior of conductivity, hardness, and corrosion resistance of nanocrystalline TiC x /C

  10. Electrophoretic Nanocrystalline Graphene Film Electrode for Lithium Ion Battery

    Kaprans, Kaspars; Bajars, Gunars; Kucinskis, Gints; Dorondo, Anna; Mateuss, Janis; Gabrusenoks, Jevgenijs; Kleperis, Janis; Lusis, Andrejs

    2015-01-01

    Graphene sheets were fabricated by electrophoretic deposition method from water suspension of graphene oxide followed by thermal reduction. The formation of nanocrystalline graphene sheets has been confirmed by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The electrochemical performance of graphene sheets as anode material for lithium ion batteries was evaluated by cycling voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy. Fabricated graphene sheets exhibited high discharge capacity of about 1120 mAh·g −1 and demonstrated good reversibility of lithium intercalation and deintercalation in graphene sheet film with capacity retention over 85 % after 50 cycles. Results show that nanocrystalline graphene sheets prepared by EPD demonstrated a high potential for application as anode material in lithium ion batteries

  11. Ferroelectric Polarization in Nanocrystalline Hydroxyapatite Thin Films on Silicon

    Lang, S. B.; Tofail, S. A. M.; Kholkin, A. L.; Wojtaś, M.; Gregor, M.; Gandhi, A. A.; Wang, Y.; Bauer, S.; Krause, M.; Plecenik, A.

    2013-01-01

    Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics. PMID:23884324

  12. Nanocrystalline electrodeposited Ni-Mo-C cathodes for hydrogen production

    Hashimoto, K.; Sasaki, T.; Meguro, S.; Asami, K.

    2004-01-01

    Tailoring active nickel alloy cathodes for hydrogen evolution in a hot concentrated hydroxide solution was attempted by electrodeposition. The carbon addition to Ni-Mo alloys decreased the nanocrystalline grain size and remarkably enhanced the activity for hydrogen evolution, changing the mechanism of hydrogen evolution. The Tafel slope of hydrogen evolution was about 35 mV per decade. This suggested that the rate-determining step is desorption of adsorbed hydrogen atoms by recombination. As was distinct from the binary Ni-Mo alloys, after open circuit immersion, the overpotential, that is, the activity of nanocrystalline Ni-Mo-C alloys for hydrogen evolution was not changed, indicating the sufficient durability in the practical electrolysis

  13. Nanocrystalline Ni-Co Alloy Synthesis by High Speed Electrodeposition

    Jamaliah Idris

    2013-01-01

    Full Text Available Electrodeposition of nanocrystals is economically and technologically viable production path for the synthesis of pure metals and alloys both in coatings and bulk form. The study presents nanocrystalline Ni-Co alloy synthesis by high speed electrodeposition. Nanocrystalline Ni-Co alloys coatings were prepared by direct current (DC and deposited directly on steel and aluminum substrates without any pretreatment, using high speed electrodeposition method. The influence of the electrolysis parameters, such as cathodic current density and temperature at constant pH, on electrodeposition and microstructure of Ni-Co alloys were examined. A homogeneous surface morphology was obtained at all current densities of the plated samples, and it was evident that the current density and temperature affect the coating thickness of Ni-Co alloy coatings.

  14. Grain boundary and triple junction diffusion in nanocrystalline copper

    Wegner, M., E-mail: m.wegner@uni-muenster.de; Leuthold, J.; Peterlechner, M.; Divinski, S. V., E-mail: divin@uni-muenster.de [Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Straße 10, D-48149, Münster (Germany); Song, X., E-mail: xysong@bjut.edu.cn [College of Materials Science and Engineering, Beijing University of Technology, 100124 Beijing (China); Wilde, G. [Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Straße 10, D-48149, Münster (Germany); Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, 200444 Shanghai (China)

    2014-09-07

    Grain boundary and triple junction diffusion in nanocrystalline Cu samples with grain sizes, 〈d〉, of ∼35 and ∼44 nm produced by spark plasma sintering were investigated by the radiotracer method using the {sup 63}Ni isotope. The measured diffusivities, D{sub eff}, are comparable with those determined previously for Ni grain boundary diffusion in well-annealed, high purity, coarse grained, polycrystalline copper, substantiating the absence of a grain size effect on the kinetic properties of grain boundaries in a nanocrystalline material at grain sizes d ≥ 35 nm. Simultaneously, the analysis predicts that if triple junction diffusion of Ni in Cu is enhanced with respect to the corresponding grain boundary diffusion rate, it is still less than 500⋅D{sub gb} within the temperature interval from 420 K to 470 K.

  15. Effect of power on the growth of nanocrystalline silicon films

    Kumar, Sushil; Dixit, P N; Rauthan, C M S; Parashar, A; Gope, Jhuma

    2008-01-01

    Nanocrystalline silicon thin films were grown using a gaseous mixture of silane, hydrogen and argon in a plasma-enhanced chemical vapor deposition system. These films were deposited away from the conventional low power regime normally used for the deposition of device quality hydrogenated amorphous silicon films. It was observed that, with the increase of applied power, there is a change in nanocrystalline phases which were embedded in the amorphous matrix of silicon. Atomic force microscopy micrographs show that these films contain nanocrystallite of 20-100 nm size. Laser Raman and photoluminescence peaks have been observed at 514 cm -1 and 2.18 eV, respectively, and particle sizes were estimated using the same as 8.24 nm and 3.26 nm, respectively. It has also been observed that nanocrystallites in these films enhanced the optical bandgap and electrical conductivity

  16. Effect of power on the growth of nanocrystalline silicon films

    Kumar, Sushil; Dixit, P N; Rauthan, C M S; Parashar, A; Gope, Jhuma [Plasma Processed Materials Group, National Physical Laboratory, Dr K S Krishnan Road, New Delhi 110 012 (India)], E-mail: skumar@mail.nplindia.ernet.in

    2008-08-20

    Nanocrystalline silicon thin films were grown using a gaseous mixture of silane, hydrogen and argon in a plasma-enhanced chemical vapor deposition system. These films were deposited away from the conventional low power regime normally used for the deposition of device quality hydrogenated amorphous silicon films. It was observed that, with the increase of applied power, there is a change in nanocrystalline phases which were embedded in the amorphous matrix of silicon. Atomic force microscopy micrographs show that these films contain nanocrystallite of 20-100 nm size. Laser Raman and photoluminescence peaks have been observed at 514 cm{sup -1} and 2.18 eV, respectively, and particle sizes were estimated using the same as 8.24 nm and 3.26 nm, respectively. It has also been observed that nanocrystallites in these films enhanced the optical bandgap and electrical conductivity.

  17. Research Update: Phonon engineering of nanocrystalline silicon thermoelectrics

    Junichiro Shiomi

    2016-10-01

    Full Text Available Nanocrystalline silicon thermoelectrics can be a solution to improve the cost-effectiveness of thermoelectric technology from both material and integration viewpoints. While their figure-of-merit is still developing, recent advances in theoretical/numerical calculations, property measurements, and structural synthesis/fabrication have opened up possibilities to develop the materials based on fundamental physics of phonon transport. Here, this is demonstrated by reviewing a series of works on nanocrystalline silicon materials using calculations of multiscale phonon transport, measurements of interfacial heat conduction, and synthesis from nanoparticles. Integration of these approaches allows us to engineer phonon transport to improve the thermoelectric performance by introducing local silicon-oxide structures.

  18. Size dependence of the optical spectrum in nanocrystalline silver

    Taneja, Praveen; Ayyub, Pushan; Chandra, Ramesh

    2002-01-01

    We report a detailed study of the optical reflectance in sputter-deposited, nanocrystalline silver thin films in order to understand the marked changes in color that occur with decreasing particle size. In particular, samples with an average particle size in the 20 to 35 nm range are golden yellow, while those with a size smaller than 15 nm are black. We simulate the size dependence of the observed reflection spectra by incorporating Mie's theory of scattering and absorption of light in small particles, into the bulk dielectric constant formalism given by Ehrenreich and Philipp [Phys. Rev. 128, 1622 (1962)]. This provides a general method for understanding the reflected color of a dense collection of nanoparticles, such as in a nanocrystalline thin film. A deviation from Mie's theory is observed due to strong interparticle interactions

  19. The effect of structural changes during sintering on the electric and magnetic traits of the Ni96.7Mo3.3 alloy nanostructured powder

    Ribić-Zelenović L.

    2009-01-01

    Full Text Available Ni96.7Mo3.3 powder was electrochemically obtained. An X-ray diffraction analysis determined that the powder consisted of a 20% amorphous and 80% crystalline phase. The crystalline phase consisted of a nanocrystalline solid nickel and molybdenum solution with a face-centred cubic (FCC lattice with a high density of chaotically distributed dislocations and high microstrain value. The scanning electronic microscopy (SEM showed that two particle structures were formed: larger cauliflower-like particles and smaller dendriteshaped ones. The thermal stability of the alloy was examined by differential scanning calorimetry (DSC and by measuring the temperature dependence of the electrical resistivity and magnetic permeability. Structural powder relaxation was carried out in the temperature range of 450 K to 560 K causing considerable changes in the electrical resistivity and magnetic permeability. Upon structural relaxation, the magnetic permeability of the cooled alloy was about 80% higher than the magnetic permeability of the fresh powder. The crystallisation of the amorphous portion of the powder and crystalline grain increase occurred in the 630 K to 900 K temperature interval. Upon crystallisation of the amorphous phase and crystalline grain increase, the powder had about 50% lower magnetic permeability than the fresh powder and 3.6 times lower permeability than the powder where only structural relaxation took place.

  20. THz generation from a nanocrystalline silicon-based photoconductive device

    Daghestani, N S; Persheyev, S; Cataluna, M A; Rose, M J; Ross, G

    2011-01-01

    Terahertz generation has been achieved from a photoconductive switch based on hydrogenated nanocrystalline silicon (nc-Si:H), gated by a femtosecond laser. The nc-Si:H samples were produced by a hot wire chemical vapour deposition process, a process with low production costs owing to its higher growth rate and manufacturing simplicity. Although promising ultrafast carrier dynamics of nc-Si have been previously demonstrated, this is the first report on THz generation from a nc-Si:H material

  1. Electrochemical passivation behaviour of nanocrystalline Fe 80 Si ...

    Passivation behaviour of nanocrystalline coating (Fe80Si20) obtained by in situ mechanical alloying route is studied and compared with that of the commercial pure iron and cast Fe80Si20 in sodium borate buffer solution at two different pH values (7.7 and 8.4). The coating reveals single passivation at a pH of 7.7 and ...

  2. A study of the structure and crystallisation of nanocrystalline zirconia

    Tucker, M.

    1999-12-01

    Nanocrystalline zirconia, prepared via, calcination of the hydroxide, has been studied using a variety of experimental techniques. Two chemical routes, a precipitation and a sol-gel route, were used to prepare the hydroxide. Neutron and X-ray diffraction, EXAFS, NMR and SANS have been used to study the structure and crystallisation, during in-situ and ambient condition measurements. The structural information from the diffraction data has been complimented by the other techniques to provide information on the short, medium and longer range structure of nanocrystalline zirconia. Pure and yttrium doped samples were studied, this enabled the affects of doping and preparation routes to be investigated. The amorphous hydroxide was found to have a, monoclinic-like structure for all samples, independent of preparation route or yttrium content. The crystallisation temperature was lowest for the pure precipitation sample and was increased by the addition of yttrium or by preparation via, the sol-gel route. For the precipitation samples, in addition to the crystallisation temperature being raised, doping with yttrium also had an effect on the size of the crystallites obtained at high temperatures. Due to the different incorporation method of the yttrium into the sol-gel samples the effect on crystallite size and crystallisation temperature, as seen for the precipitation samples, were not evident for the sol-gel samples. The neutron and NMR data clearly show hydrogen remains in the samples well after crystallisation has become evident. The structural picture of nanocrystalline zirconia consisting of small crystallites surrounded by material containing, or terminated by, hydroxyl groups, is supported by all the results and methods used in this thesis. The in-situ and ambient conditions data is combined into a coherent growth picture of the nanocrystalline material from the hydroxide until at high enough temperatures the bulk or polycrystalline material is formed. (author)

  3. Critical currents and fields of disordered nanocrystalline superconductors

    Yavary, H.; Shahzamanian, M.A.; Rabbani, H.

    2007-01-01

    Full text: There is an enormous effort directed at increasing the upper critical field of the superconducting materials because this upper critical field provides a fundamental limit to the maximum field a magnet system can produce. High-energy particle accelerators and medical resonance imaging body scanners are limited by the for NbTi (10 T). Gigahertz class nuclear-magnetic-resonance and high field laboratory magnets are limited by for Nb 3 Sn (23 T) [1]. However, the values of critical current density are too low for industrial use, possibly because of degraded or nonsuperconducting phases, such as MoS 2 or Mo 2 S 3 , at the grain boundaries or because the pinning site density is not high enough. It has long been known that decreasing the grain size of low-temperature superconducting (LTS) materials, such as Nb 3 Sn, increases the density of flux pinning sites and hence. Nanocrystalline materials are characterized by ultrafine grains and a high density of grain boundaries [2]. Hence nanocrystalline materials can exhibit unusual physical, chemical, and mechanical properties with respect to conventional polycrystalline materials. The purpose of this paper is to investigate the structure of currents and fields in disordered nanocrystalline superconducting materials by the use of quasiclassical many body techniques. The Keldish Greens functions are used to calculate the current density of the system. Since the disorder and microstructure of these nanocrystalline materials are on a sufficiently short length scale as to increase both the density of pinning site and the upper critical field. (authors)

  4. Investigation of microstructure thermal evolution in nanocrystalline Cu

    Zhou Kai; Li Hui; Pang Jinbiao; Wang Zhu

    2011-01-01

    The microstructure of nanocrystalline Cu prepared by compacting nanoparticles (50-60 nm in diameter) under high pressures has been studied by means of positron lifetime spectroscopy and X-ray diffraction. These nanoparticles were produced by two different methods. We found that there are order regions interior to the grains and disorder regions at the grain boundaries with a wide distribution of interatomic distances. The mean grain sizes of the nanocrystalline Cu samples decrease after being annealed at 900 o C and increase during aging at 180 o C, which are observed by X-ray diffraction, revealing that the atoms exchange between the two regions. The positron lifetime results clearly indicate that the vacancy clusters formed in the annealing process are unstable and decomposed at the aging time below 6 hours. In addition, the partially oxidized surfaces of the nanoparticles hinder grain growth when the samples age at 180 o C, and the vacancy clusters inside the disorder regions, which are related to Cu 2 O, need longer aging time to decompose. The disorder regions remain after the heat treatment in this work, in spite of the grain growth, which will be good for the samples keeping the properties of nanocrystalline material. -- Research highlights: → We use a digital positron lifetime spectrometer correlated with XRD to study the microstructure evolution of nanocrystalline Cu during thermal treatment. → An atomic scale microstructure of grain boundary is characterized. Further, the surface oxidation of the nanoparticles is considered. → The disorder regions remain after the heat treatment in this work, in spite of grain growth.

  5. Stress-induced magnetic anisotropy in nanocrystalline alloys

    Varga, L.K.; Gercsi, Zs.; Kovacs, Gy.; Kakay, A.; Mazaleyrat, F.

    2003-01-01

    Stress-annealing experiments were extended to both nanocrystalline alloy families, Finemet and Nanoperm (Hitperm), and, for comparison, to amorphous Fe 62 Nb 8 B 30 alloy. For both Finemet and bulk amorphous, stress-annealing results in a strong induced transversal anisotropy (flattening of hysteresis loop) but yields longitudinal induced anisotropy (square hysteresis loop) in Nanoperm and Hitperm. These results are interpreted in terms of back-stress theory

  6. Possible origin of superior corrosion resistance for electrodeposited nanocrystalline Ni

    Roy, I.; Yang, H.W.; Dinh, L.; Lund, I.; Earthman, J.C.; Mohamed, F.A.

    2008-01-01

    We present here for the first time observations that grain boundaries in electrodeposited (ED) nanocrystalline (nc) Ni are predominantly of Σ3 character. The results presented are based on orientation imaging microscopy (OIM) performed to produce electron backscatter diffraction (EBSD) maps. This large volume fraction of coherent low sigma coincidence site lattice (CSL) boundaries appears to be consistent with the superior corrosion resistance of ED nc-Ni in comparison with its coarse-grained counterpart

  7. Thermoelectric nanocrystalline YbCoSb laser prepared layers

    Jelínek, Miroslav; Zeipl, Radek; Kocourek, Tomáš; Remsa, Jan; Navrátil, Jiří

    2016-01-01

    Roč. 122, č. 3 (2016), s. 1-5, č. článku 155. ISSN 0947-8396 R&D Projects: GA ČR(CZ) GA13-33056S Institutional support: RVO:68378271 ; RVO:61389013 Keywords : nanocrystalline YbCoSb * thermoelectric layers * pulsed laser deposition Subject RIV: BM - Solid Matter Physics ; Magnetism; CA - Inorganic Chemistry (UMCH-V) Impact factor: 1.455, year: 2016

  8. Microwave PECVD of nanocrystalline diamond with rf induced bias nucleation

    Frgala, Z.; Jašek, O.; Karásková, M.; Zajíčková, L.; Buršíková, V.; Franta, D.; Matějková, Jiřina; Rek, Antonín; Klapetek, P.; Buršík, Jiří

    2006-01-01

    Roč. 56, Suppl. B (2006), s. 1218-1223 ISSN 0011-4626 R&D Projects: GA ČR(CZ) GA202/05/0607 Institutional research plan: CEZ:AV0Z20650511; CEZ:AV0Z20410507 Keywords : nanocrystalline diamond * plasma enhanced chemical vapor deposition * self-bias Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 0.568, year: 2006

  9. Nanocrystalline SiC film thermistors for cryogenic applications

    Mitin, V. F.; Kholevchuk, V. V.; Semenov, A. V.; Kozlovskii, A. A.; Boltovets, N. S.; Krivutsa, V. A.; Slepova, A. S.; Novitskii, S. V.

    2018-02-01

    We developed a heat-sensitive material based on nanocrystalline SiC films obtained by direct deposition of carbon and silicon ions onto sapphire substrates. These SiC films can be used for resistance thermometers operating in the 2 K-300 K temperature range. Having high heat sensitivity, they are relatively low sensitive to the magnetic field. The designs of the sensors are presented together with a discussion of their thermometric characteristics and sensitivity to magnetic fields.

  10. Quantum transport in boron-doped nanocrystalline diamond

    Mareš, Jiří J.; Hubík, Pavel; Krištofik, Jozef; Kindl, Dobroslav; Nesládek, Miloš

    2008-01-01

    Roč. 14, č. 7-8 (2008), s. 161-172 ISSN 0948-1907 R&D Projects: GA ČR GA202/07/0525; GA AV ČR IAA1010404; GA ČR(CZ) GA202/06/0040 Institutional research plan: CEZ:AV0Z10100521 Keywords : nanocrystalline diamond film * ballistic transport * superconductivity * Josephson’s effects Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.483, year: 2008

  11. Ferromagnetism appears in nitrogen implanted nanocrystalline diamond films

    Remeš, Zdeněk; Sun, S. J.; Varga, M.; Chou, H.; Hsu, H.S.; Kromka, A.; Horák, Pavel

    2015-01-01

    Roč. 394, Nov (2015), s. 477-480 ISSN 0304-8853 R&D Projects: GA ČR(CZ) GBP108/12/G108; GA MŠk(CZ) LD14011 EU Projects: European Commission(XE) COST Action MP1202 HINT Institutional support: RVO:68378271 ; RVO:61389005 Keywords : diamond * nonmetallic ferromagnetic materials * fine-particle systems * nanocrystalline materials Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.357, year: 2015

  12. Electrodeposition and characterization of nanocrystalline CoNiFe films

    Chen, Y.; Wang, Q.P. [Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027 (China); Cai, C. [School of Chemistry and chemical engineering, Ningxia University, Yinchuan 750021 (China); Yuan, Y.N. [Department of Materials and Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027 (China); Cao, F.H. [Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027 (China); Zhang, Z., E-mail: eaglezzy@zjuem.zju.edu.cn [Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027 (China); Zhang, J.Q. [Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027 (China); State Key Laboratory for Corrosion and Protection of Metals, Shenyang 110016 (China)

    2012-02-29

    Nanocrystalline Co{sub 45}Ni{sub 10}Fe{sub 24} films have been fabricated using cyclic voltammetry technique from the solutions containing sulfate, then characterized by scanning electron microscopy, X-ray diffraction and vibrating sample magnetometer. Meanwhile, Electrochemical Impedance Spectroscopy technique has been employed to probe into the nucleation/growth behavior of Co{sub 45}Ni{sub 10}Fe{sub 24} films. The results show that, the obtained Co{sub 45}Ni{sub 10}Fe{sub 24} film possesses low coercivity of 973.3 A/m and high saturation magnetic flux density of 1.59 Multiplication-Sign 10{sup 5} A/m. Under the experimental conditions, the nucleation/growth process of Co{sub 45}Ni{sub 10}Fe{sub 24} films is mainly under activation control. With the increase of the applied cathodic potential bias, the charge transfer resistance for CoNiFe deposition decreases exponentially. - Highlights: Black-Right-Pointing-Pointer Nanocrystalline Co{sub 45}Ni{sub 10}Fe{sub 24} film is obtained using cyclic voltammetry technique. Black-Right-Pointing-Pointer Nanocrystalline Co{sub 45}Ni{sub 10}Fe{sub 24} possesses low coercivity of 973.3 A/m. Black-Right-Pointing-Pointer Nanocrystalline Co{sub 45}Ni{sub 10}Fe{sub 24} possesses high saturation magnetic flux density. Black-Right-Pointing-Pointer The nucleation/growth process of CoNiFe films is mainly under activation control. Black-Right-Pointing-Pointer The charge transfer resistance for CoNiFe deposition decreases exponentially.

  13. Nanocrystalline Iron-Cobalt Alloys for High Saturation Indutance

    2016-02-24

    film deposited just like the pick-up of a turn-table music player. The contact pads provide the electrical contacts to the starting and end point of...anisotropy using the geometry of the thin toroid. We have shown experimentally that the thin film toroid calculations may be applicable to up to millimeter...thin film as well as bulk devices. 15. SUBJECT TERMS Micromagnetic Calculations, Nanocrystalline cobalt-iron, Thin Film Toroids 16. SECURITY

  14. Nuclear fuel powder transfer device

    Komono, Akira

    1998-01-01

    A pair of parallel rails are laid between a receiving portion to a molding portion of a nuclear fuel powder transfer device. The rails are disposed to the upper portion of a plurality of parallel support columns at the same height. A powder container is disposed while being tilted in the inside of the vessel main body of a transfer device, and rotational shafts equipped with wheels are secured to right and left external walls. A nuclear powder to be mixed, together with additives, is supplied to the powder container of the transfer device. The transfer device engaged with the rails on the receiving side is transferred toward the molding portion. The wheels are rotated along the rails, and the rotational shafts, the vessel main body and the powder container are rotated. The nuclear powder in the tilted powder container disposed is rotated right and left and up and down by the rotation, and the powder is mixed satisfactory when it reaches the molding portion. (I.N.)

  15. Superconductors by powder metallurgy techniques

    Pickus, M.R.; Wang, J.L.F.

    1976-05-01

    Fabrication methods for Nb 3 Sn type compounds are described. Information is included on the Bell Telephone process, the General Electric tape process, superconductor stability, the bronze process, powder metallurgy multifilamentary tapes and wires, and current assessment of powder metallurgy superconducting wire

  16. Cellulose-precursor synthesis of nanocrystalline Co0.5Cu0.5Fe2O4 spinel ferrites

    Ounnunkad, Kontad; Phanichphant, Sukon

    2012-01-01

    Highlights: ► Synthesis of spinel copper cobalt nanoferrite particles from a cellulose precursor for the first time. Control of nanosize and properties of nanoferrites can take place by varying the calcining temperature. The simple, low cost, easy cellulose process is a choice of nanoparticle processing technology. -- Abstract: Nanocrystalline Cu 0.5 Co 0.5 Fe 2 O 4 powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.

  17. Sinteractive thoria powders derived through gel-combustion and oxalate deagglomeration - a comparison

    Ananthasivan, K.; Balakrishnan, S.; Anthonysamy, S.; Ganesan, V.; Vasudeva Rao, P.R.

    2011-01-01

    Thorium dioxide finds extensive application in the nuclear industry. Pellets of thoria are used in PHWRs for flux flattening and in FBRs as a blanket material. The development of advanced methods for the synthesis and sintering of thoria is relevant to these applications. This paper attempts to compare the properties of sinteractive nanocrystalline thoria (pure and doped with Ca 2+ and Mg 2+ ) synthesized in our laboratory through two different techniques, viz. gel-combustion and oxalate de-agglomeration. In all the investigations cited above the precursors obtained by using both the procedures were calcined in air at 1073 K. The thoria powders thus obtained were characterised for their specific surface area (SSA), X-ray crystallite size (XCS), bulk density, particle size distribution and residual carbon content. These powders were pelletised and sintered at 1473, 1673, and 1873 K. The sinterability of these powders was compared by measuring the density of the sintered pellets. A matrix density as high as 96.8 % TD (gel combustion) or 98.6 % TD (de-agglomeration) could be obtained at 1873 K, with the powders doped with 0.5 mole % calcia. (author)

  18. Phase evolution in Al-Ni-(Ti, Nb, Zr) powder blends by mechanical alloying

    Samanta, A. [Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur (India); Manna, I. [Metallurgical and Materials Engineering Department, I.I.T., Kharagpur 721302 (India); Chattopadhyay, P.P. [Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur (India)], E-mail: c.partha@mailcity.com

    2007-08-25

    Mechanical alloying of Al-rich Al-Ni-ETM (ETM = Ti, Nb, Zr) elemental powder blends by planetary ball milling yielded amorphous and/or nanocrystalline products after ball milling for suitable duration. Powder samples collected at different stages of ball milling have been examined by X-ray diffraction, differential scanning caloremetry and high-resolution transmission electron microscopy to examine the solid-state phase evolution. Powder blends having nominal composition of Al{sub 80}Ni{sub 10}Ti{sub 10} and Al{sub 80}Ni{sub 10}Nb{sub 10} yielded predominantly amorphous products, while the other alloys formed composite microstructures comprising nanaocrystalline and amorphous solid solutions. The amorphous Al{sub 80}Ni{sub 10}Ti{sub 10} alloy was mixed with different amounts of Al powder, and subjected to warm rolling after consolidation within the Al-cans with or without intermediate annealing for 10 min at 500 K to obtain sheet of 2.5 mm thickness. Notable improvement in mechanical properties has been achieved for the composite sheets in comparison to the pure Al.

  19. Structural evolution of Fe-50 at.% Al powders during mechanical alloying and subsequent annealing processes

    Haghighi, Sh. Ehtemam; Janghorban, K.; Izadi, S.

    2010-01-01

    Iron aluminides, despite having desirable properties like excellent corrosion resistance, present low room-temperature ductility and low strength at high temperatures. Mechanical alloying as a capable process to synthesize nanocrystalline materials is under consideration to modify these drawbacks. In this study, the microstructure of iron aluminide powders synthesized by mechanical alloying and subsequent annealing was investigated. Elemental Fe and Al powders with the same atomic percent were milled in a planetary ball mill for 15 min to 100 h. The powder milled for 80 h was annealed at temperatures of 300, 500 and 700 o C for 1 h. The alloyed powders were disordered Fe(Al) solid solutions which were transformed to FeAl intermetallic after annealing. The effect of the milling time and annealing treatment on structural parameters, such as crystallite size, lattice parameter and lattice strain was evaluated by X-ray diffraction. Typically, these values were 15 nm, 2.92 A and 3.1% for the disordered Fe(Al) solid solution milled for 80 h and were 38.5 nm, 2.896 A and 1.2% for the FeAl intermetallic annealed at 700 o C, respectively.

  20. Uncertainty propagation in a multiscale model of nanocrystalline plasticity

    Koslowski, M.; Strachan, Alejandro

    2011-01-01

    We characterize how uncertainties propagate across spatial and temporal scales in a physics-based model of nanocrystalline plasticity of fcc metals. Our model combines molecular dynamics (MD) simulations to characterize atomic-level processes that govern dislocation-based-plastic deformation with a phase field approach to dislocation dynamics (PFDD) that describes how an ensemble of dislocations evolve and interact to determine the mechanical response of the material. We apply this approach to a nanocrystalline Ni specimen of interest in micro-electromechanical (MEMS) switches. Our approach enables us to quantify how internal stresses that result from the fabrication process affect the properties of dislocations (using MD) and how these properties, in turn, affect the yield stress of the metallic membrane (using the PFMM model). Our predictions show that, for a nanocrystalline sample with small grain size (4 nm), a variation in residual stress of 20 MPa (typical in today's microfabrication techniques) would result in a variation on the critical resolved shear yield stress of approximately 15 MPa, a very small fraction of the nominal value of approximately 9 GPa. - Highlights: → Quantify how fabrication uncertainties affect yield stress in a microswitch component. → Propagate uncertainties in a multiscale model of single crystal plasticity. → Molecular dynamics quantifies how fabrication variations affect dislocations. → Dislocation dynamics relate variations in dislocation properties to yield stress.

  1. Size-dependent deformation behavior of nanocrystalline graphene sheets

    Yang, Zhi [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Huang, Yuhong [College of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, Shaanxi (China); Ma, Fei, E-mail: mafei@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Sun, Yunjin [Faculty of Food Science and Engineering, Beijing University of Agriculture, Beijing Key Laboratory of Agricultural Product Detection and Control of Spoilage Organisms and Pesticide Residue, Beijing Laboratory of Food Quality and Safety, Beijing 102206 (China); Xu, Kewei, E-mail: kwxu@mail.xjtu.edu.cn [State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi (China); Department of Physics and Opt-electronic Engineering, Xi’an University of Arts and Science, Xi’an 710065, Shaanxi (China); Chu, Paul K., E-mail: paul.chu@cityu.edu.hk [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

    2015-08-15

    Highlights: • MD simulation is conducted to study the deformation of nanocrystalline graphene. • Unexpectedly, the elastic modulus decreases with the grain size considerably. • But the fracture stress and strain are nearly insensitive to the grain size. • A composite model with grain domains and GBs as two components is suggested. - Abstract: Molecular dynamics (MD) simulation is conducted to study the deformation behavior of nanocrystalline graphene sheets. It is found that the graphene sheets have almost constant fracture stress and strain, but decreased elastic modulus with grain size. The results are different from the size-dependent strength observed in nanocrystalline metals. Structurally, the grain boundaries (GBs) become a principal component in two-dimensional materials with nano-grains and the bond length in GBs tends to be homogeneously distributed. This is almost the same for all the samples. Hence, the fracture stress and strain are almost size independent. As a low-elastic-modulus component, the GBs increase with reducing grain size and the elastic modulus decreases accordingly. A composite model is proposed to elucidate the deformation behavior.

  2. Remediation of arsenic and lead with nanocrystalline zinc sulfide.

    Piquette, Alan; Cannon, Cody; Apblett, Allen W

    2012-07-27

    Nanocrystalline (1.7 ± 0.3 nm) zinc sulfide with a specific surface area up to 360 m(2) g(-1) was prepared from the thermal decomposition of a single-source precursor, zinc ethylxanthate. Zinc ethylxanthate decomposes to cubic zinc sulfide upon exposure to temperatures greater than or equal to 125 °C. The resulting zinc sulfide was tested as a water impurity extractant. The target impurities used in this study were As(5+), As(3+), and Pb(2+). The reaction of the nanocrystalline ZnS with Pb(2+) proceeds as a replacement reaction where solid PbS is formed and Zn(2+) is released into the aqueous system. Removal of lead to a level of less than two parts per billion is achievable. The results of a detailed kinetics experiment between the ZnS and Pb(2+) are included in this study. Unlike the instance of lead, both As(5+) and As(3+) adsorb on the surface of the ZnS extractant as opposed to an ion-exchange process. An uptake capacity of > 25 mg g(-1) for the removal of As(5+) is possible. The uptake of As(3+) appears to proceed by a slower process than that of the As(5+) with a capacity of nearly 20 mg g(-1). The nanocrystalline zinc sulfide was extremely successful for the removal of arsenic and lead from simulated oil sand tailing pond water.

  3. Light extinction in metallic powder beds: Correlation with powder structure

    Rombouts, M.; Froyen, L.; Gusarov, A.V.; Bentefour, E.H.; Glorieux, C.

    2005-01-01

    A theoretical correlation between the effective extinction coefficient, the specific surface area, and the chord length distribution of powder beds is verified experimentally. The investigated powder beds consist of metallic particles of several tens of microns. The effective extinction coefficients are measured by a light-transmission technique at a wavelength of 540 nm. The powder structure is characterized by a quantitative image analysis of powder bed cross sections resulting in two-point correlation functions and chord length distributions. The specific surface area of the powders is estimated by laser-diffraction particle-size analysis and by the two-point correlation function. The theoretically predicted tendency of increasing extinction coefficient with specific surface area per unit void volume is confirmed by the experiments. However, a significant quantitative discrepancy is found for several powders. No clear correlation of the extinction coefficient with the powder material and particle size, and morphology is revealed, which is in line with the assumption of geometrical optics

  4. Hyperfine interactions and structural features of Fe–44Co–6Mo (wt.%) nanostructured powders

    Moumeni, Hayet; Nemamcha, Abderrafik; Alleg, Safia; Grenèche, Jean Marc

    2013-01-01

    Nanocrystalline Fe–44Co–6Mo (wt.%) powders have been prepared by high-energy ball milling from elemental Fe, Co and Mo pure powders in a P7 planetary ball mill. The obtained powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Mössbauer spectrometry techniques. The influence of milling process and Mo substitution for Co in equiatomic FeCo have been examined in order to study structural evolution and formation mechanism of nanostructured Fe(CoMo) solid solution. XRD results show the formation of a BCC Fe(CoMo) solid solution (a = 0.2874 nm) where unmixed nanocrystalline Mo with a BCC structure is embedded. Disordered Fe(CoMo) solid solution is characterized by a broad hyperfine magnetic field distribution with two regions centered at B 1 = 35.0 T and B 2 = 30.7 T, respectively, attributed to disordered Fe(Co) solid solution and CoMo enriched environments. Prolonged milling and Mo addition cause the decrease of average hyperfine magnetic field while the average isomer shift remains nearly constant. - Highlights: ► BCC nanostructured Fe(CoMo) solid solution is prepared by milling of Fe, Co and Mo. ► Formation mechanism: Co diffusion into Fe lattice and Mo dissolution in Fe(Co). ► Crystallite size of Fe(CoMo) solid solution reaches 11 nm after 24 h of milling. ► Mössbauer analysis reveals 3 components: high field, enriched Co and low field

  5. Hyperfine interactions and structural features of Fe–44Co–6Mo (wt.%) nanostructured powders

    Moumeni, Hayet, E-mail: hmoumeni@yahoo.fr [Laboratoire de Chimie Computationnelle et Nanostructures, Département des Sciences de la Matière, Faculté des Mathématiques et de l' Informatique et des Sciences de la Matière, Université 08 Mai 1945 - Guelma, B.P. 401, Guelma 24000 (Algeria); Nemamcha, Abderrafik [Laboratoire d' Analyses Industrielles et Génie des Matériaux, Faculté des Sciences et de la Technologie, Université 08 Mai 1945 - Guelma, B.P. 401, Guelma 24000 (Algeria); Alleg, Safia [Laboratoire de Magnétisme et de Spectroscopie des Solides, Département de Physique, Faculté des Sciences, Université de Annaba, B.P. 12, Annaba 23000 (Algeria); Grenèche, Jean Marc [Laboratoire de Physique de l' Etat Condensé, UMR CNRS 6087, Institut de Recherche en Ingénierie Moléculaire et Matériaux Fonctionnels IRIM2F, FR CNRS 2575, Université du Maine, 72085 Le Mans Cedex 9 (France)

    2013-02-15

    Nanocrystalline Fe–44Co–6Mo (wt.%) powders have been prepared by high-energy ball milling from elemental Fe, Co and Mo pure powders in a P7 planetary ball mill. The obtained powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Mössbauer spectrometry techniques. The influence of milling process and Mo substitution for Co in equiatomic FeCo have been examined in order to study structural evolution and formation mechanism of nanostructured Fe(CoMo) solid solution. XRD results show the formation of a BCC Fe(CoMo) solid solution (a = 0.2874 nm) where unmixed nanocrystalline Mo with a BCC structure is embedded. Disordered Fe(CoMo) solid solution is characterized by a broad hyperfine magnetic field distribution with two regions centered at B{sub 1} = 35.0 T and B{sub 2} = 30.7 T, respectively, attributed to disordered Fe(Co) solid solution and CoMo enriched environments. Prolonged milling and Mo addition cause the decrease of average hyperfine magnetic field while the average isomer shift remains nearly constant. - Highlights: ► BCC nanostructured Fe(CoMo) solid solution is prepared by milling of Fe, Co and Mo. ► Formation mechanism: Co diffusion into Fe lattice and Mo dissolution in Fe(Co). ► Crystallite size of Fe(CoMo) solid solution reaches 11 nm after 24 h of milling. ► Mössbauer analysis reveals 3 components: high field, enriched Co and low field.

  6. Effect of milling time on the structure, micro-hardness, and thermal behavior of amorphous/nanocrystalline TiNiCu shape memory alloys developed by mechanical alloying

    Alijani, Fatemeh; Amini, Rasool; Ghaffari, Mohammad; Alizadeh, Morteza; Okyay, Ali Kemal

    2014-01-01

    Highlights: • Potential to produce B1′ (thermal- and stress-induced) and B2 was established. • Martensitic transformation occurred without the formation of intermediate R-phase. • Formation of unwanted intermetallics during heating was hindered by milling. • During milling, microhardness was increased, then reduced, and afterward re-increased. • By milling evolution, thermal crystallization steps changed from 3 to 2. - Abstract: In the present paper, the effect of milling process on the chemical composition, structure, microhardness, and thermal behavior of Ti–41Ni–9Cu compounds developed by mechanical alloying was evaluated. The structural characteristic of the alloyed powders was evaluated by X-ray diffraction (XRD). The chemical composition homogeneity and the powder morphology and size were studied by scanning electron microscopy coupled with electron dispersive X-ray spectroscopy. Moreover, the Vickers micro-indentation hardness of the powders milled for different milling times was determined. Finally, the thermal behavior of the as-milled powders was studied by differential scanning calorimetery. According to the results, at the initial stages of milling (typically 0–12 h), the structure consisted of a Ni solid solution and amorphous phase, and by the milling evolution, nanocrystalline martensite (B19′) and austenite (B2) phases were initially formed from the initial materials and then from the amorphous phase. It was found that by the milling development, the composition uniformity is increased, the inter-layer thickness is reduced, and the powders microhardness is initially increased, then reduced, and afterward re-increased. It was also realized that the thermal behavior of the alloyed powders and the structure of heat treated samples is considerably affected by the milling time

  7. Dielectric and electrical characteristics of Sr modified Ca1Cu3Ti4O12

    Sahu, M.; Choudhary, R. N. P.; Roul, B. K.

    2018-05-01

    This paper mainly reports on the effect of Sr substitution on dielectric and electrical properties of CaCu3Ti4O12 at different temperature and frequency. Preliminary analysis of X-ray diffraction data of sintered samples confirms the reported cubic structure. Study of surface morphology shows that the surface of the samples contains well-defined and uniformly distributed grains. Some electrical parameters (permittivity, tangent loss and impedance) of the materials were measured and analyzed over a wide range of temperature (25 to 315 °C) and frequency (50 to 2x106 Hz). The ultra high dielectric constant and low energy dissipation have been observed in the said experimental conditions of phase-pure prepared compounds. It is expected that the addition of nano-size compounds or oxide will help to enhance the above properties useful for fabrication of super-capacitor.

  8. Application of laser in powder metallurgy

    Tolochko, N.K.

    1995-01-01

    Modern status of works in the field of laser application in powder metallurgy (powders preparation, sintering, coatings formation, powder materials processing) is considered. The attention is paid to the new promising direction in powder products shape-formation technology - laser layer-by-layer selective powders sintering and bulk sintering of packaged layered profiles produced by laser cutting of powder-based sheet blanks. 67 refs

  9. Black powder in gas pipelines

    Sherik, Abdelmounam [Saudi Aramco, Dhahran (Saudi Arabia)

    2009-07-01

    Despite its common occurrence in the gas industry, black powder is a problem that is not well understood across the industry, in terms of its chemical and physical properties, source, formation, prevention or management of its impacts. In order to prevent or effectively manage the impacts of black powder, it is essential to have knowledge of its chemical and physical properties, formation mechanisms and sources. The present paper is divided into three parts. The first part of this paper is a synopsis of published literature. The second part reviews the recent laboratory and field work conducted at Saudi Aramco Research and Development Center to determine the compositions, properties, sources and formation mechanisms of black powder in gas transmission systems. Microhardness, nano-indentation, X-ray Diffraction (XRD), X-ray Fluorescence (XRF) and Scanning Electron Microscopy (SEM) techniques were used to analyze a large number of black powder samples collected from the field. Our findings showed that black powder is generated inside pipelines due to internal corrosion and that the composition of black powder is dependent on the composition of transported gas. The final part presents a summary and brief discussion of various black powder management methods. (author)

  10. Accumulation and recovery of defects in ion-irradiated nanocrystalline gold

    Chimi, Y. E-mail: chimi@popsvr.tokai.jaeri.go.jp; Iwase, A.; Ishikawa, N.; Kobiyama, M.; Inami, T.; Okuda, S

    2001-09-01

    Effects of 60 MeV {sup 12}C ion irradiation on nanocrystalline gold (nano-Au) are studied. The experimental results show that the irradiation-produced defects in nano-Au are thermally unstable because of the existence of a large volume fraction of grain boundaries. This suggests a possibility of the use of nanocrystalline materials as irradiation-resistant materials.

  11. Enhanced Activity of Nanocrystalline Zeolites for Selective Catalytic Reduction of NOx

    Sarah C. Larson; Vicki H. Grassian

    2006-01-01

    Nanocrystalline zeolites with discrete crystal sizes of less than 100 nm have different properties relative to zeolites with larger crystal sizes. Nanocrystalline zeolites have improved mass transfer properties and very large internal and external surface areas that can be exploited for many different applications. The additional external surface active sites and the improved mass transfer properties of nanocrystalline zeolites offer significant advantages for selective catalytic reduction (SCR) catalysis with ammonia as a reductant in coal-fired power plants relative to current zeolite based SCR catalysts. Nanocrystalline NaY was synthesized with a crystal size of 15-20 nm and was thoroughly characterized using x-ray diffraction, electron paramagnetic resonance spectroscopy, nitrogen adsorption isotherms and Fourier Transform Infrared (FT-IR) spectroscopy. Copper ions were exchanged into nanocrystalline NaY to increase the catalytic activity. The reactions of nitrogen dioxides (NO x ) and ammonia (NH 3 ) on nanocrystalline NaY and CuY were investigated using FT-IR spectroscopy. Significant conversion of NO 2 was observed at room temperature in the presence of NH 3 as monitored by FT-IR spectroscopy. Copper-exchanged nanocrystalline NaY was more active for NO 2 reduction with NH 3 relative to nanocrystalline NaY

  12. (TECTONA GRANDIS LEAF POWDER

    Yash Mishra

    2015-01-01

    Full Text Available In this study, the adsorption potential of Teak (Tectona grandis leaf powder (TLP toremove Methylene blue (MB and Malachite Green (MG dye molecules from aqueoussolution was investigated. Batch experiments were conducted to evaluate the influenceof operational parameters such as, pH (2−9, adsorbent dosage (1−7 g/L, contact time(15−150 minutes and initial dye concentration (20−120 mg/L at stirring speed of 150rpm for the adsorption of MB and MG on TLP. Maximum removal efficiency of 98.4%and 95.1% was achieved for MB and MG dye, respectively. The experimentalequilibrium data were analysed using Langmuir, Freundlich and Temkin isothermmodels and it was found that, it fitted well to the Freundlich isotherm model. Thesurface structure and morphology of the adsorbent was characterized using scanningelectron microscopy (SEM and the presence of functional groups and its interactionwith the dye molecules were analysed using Fourier transform infrared spectroscopy(FTIR. Based on the investigation, it has been demonstrated that the teak leaf powderhas good potential for effective adsorption of methylene blue and malachite green dye.

  13. Fabrication and thermal characterization of amorphous and nanocrystalline Al{sub 9}FeNi/Al{sub 3}Ti compound

    Tavoosi, Majid, E-mail: ma.tavoosi@gmail.com

    2017-01-15

    In this study, the fabrication and structural characterization of amorphous/nanocrystalline Al{sub 9}FeNi/Al{sub 3}Ti phase has been performed. In this regards, milling and annealing processes were applied on Al{sub 80}Fe{sub 10}Ti{sub 5}Ni{sub 5} (at. %) powder mixture for different periods of time. The prepared samples were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) and differential scanning calorimetery (DSC). According to the results, supersaturated solid solution, nanocrystalline Al{sub 9}FeNi/Al{sub 3}Ti (with average crystallite size of about 7 nm) and amorphous phases indicated three different microstructures which can be formed in Al{sub 80}Fe{sub 10}Ti{sub 5}Ni{sub 5} system during milling process. The formed supersaturated solid solution and amorphous phases were unstable and transformed to Al{sub 9}FeNi/Al{sub 3}Ti intermetallic compound during annealing process. It is shown that, Al{sub 9}FeNi phase in Al{sub 9}FeNi/Al{sub 3}Ti intermetallic compound can decompose into Al{sub 3}Ni, Al{sub 13}Fe{sub 4} and liquid phases during a reversible peritectic reaction at 809 °C. - Highlights: • We study the effect of milling process on Al{sub 80}Fe{sub 10}Ti{sub 5}Ni{sub 5} alloy. • We study the effect of annealing on Al{sub 80}Fe{sub 10}Ti{sub 5}Ni{sub 5} supersaturated solid solution phase. • We study the effect of annealing on Al{sub 80}Fe{sub 10}Ti{sub 5}Ni{sub 5} amorphous phase. • We study the thermal behaviour of Al{sub 9}FeNi/Al{sub 3}Ti compound.

  14. Low pressure powder injection moulding of stainless steel powders

    Zampieron, J.V.; Soares, J.P.; Mathias, F.; Rossi, J.L. [Powder Processing Center CCP, Inst. de Pesquisas Energeticas e Nucleares, Sao Paulo, SP (Brazil); Filho, F.A. [IPEN, Inst. de Pesquisas Energeticas e Nucleares, Cidade Univ., Sao Paulo, SP (Brazil)

    2001-07-01

    Low-pressure powder injection moulding was used to obtain AISI 316L stainless steel parts. A rheological study was undertaken using gas-atomised powders and binders. The binders used were based on carnauba wax, paraffin, low density polyethylene and microcrystalline wax. The metal powders were characterised in terms of morphology, particle size distribution and specific surface area. These results were correlated to the rheological behaviour. The mixture was injected in the shape of square bar specimens to evaluate the performance of the injection process in the green state, and after sintering. The parameters such as injection pressure, viscosity and temperature were analysed for process optimisation. The binders were thermally removed in low vacuum with the assistance of alumina powders. Debinding and sintering were performed in a single step. This procedure shortened considerably the debinding and sintering time. (orig.)

  15. Effect of annealing and impurity concentration on the TL characteristics of nanocrystalline Mn-doped CaF2

    Sahare, P.D.; Singh, Manveer; Kumar, Pratik

    2015-01-01

    Nanocrystalline samples of Mn-doped CaF 2 were synthesized by chemical coprecipitation method. The impurity concentration was varied in the range of 0.5–4.0 mol%. The structure of the synthesized material was confirmed using powder XRD analysis. TEM images of the nanoparticles show their size occurring mostly in the range of 35–40 nm, with clusters of some impurity phases formed on annealing of the material at higher temperatures. Detailed studies on TL showed that the structures of glow curves depend on Mn concentrations and annealing temperatures. Optimization of the concentration and annealing temperature showed that the sample (doped with 3.0 mol% and annealed at 673 K) has almost a single dosimetric glow peak appearing at around 492 K. EPR and PL spectra were further studied to understand the reasons for changes in the glow curve structures. All detailed studies on TL, PL and EPR showed that the changes in glow curve structures are caused not only by the stress connected with the difference in ionic radii of host Ca 2+ and the guest impurity Mn 3+ /Mn 2+ , but are also governed by other reasons, like diffusion of atmospheric oxygen and formation of impurity aggregates, such as, MnO 2 , Mn 3 O 4 , etc. This is true not only for nanocrystalline CaF 2 :Mn but could also be so for the bulk CaF 2 :Mn (TLD-400) and would thus help in understanding complex glow curve structure, high fading and the loss of reusability on annealing beyond 673 K. - Highlights: • Nanocrystalline material CaF 2 :Mn is prepared by simple coprecipitation method. • The material is studied by XRD, TEM, ESR, TL and PL techniques. • High impurity concentrations give rise to clusters causing material instability. • Changes in ESR and PL and glow curve structures are studied and explained. • Better characteristics than the bulk make the nanophosphor useful for dosimetry

  16. Shock compaction of molybdenum powder

    Ahrens, T. J.; Kostka, D.; Vreeland, T., Jr.; Schwarz, R. B.; Kasiraj, P.

    1983-01-01

    Shock recovery experiments which were carried out in the 9 to 12 GPa range on 1.4 distension Mo and appear adequate to compact to full density ( 45 (SIGMA)m) powders were examined. The stress levels, however, are below those calculated to be from 100 to approx. 22 GPa which a frictional heating model predicts are required to consolidate approx. 10 to 50 (SIGMA)m particles. The model predicts that powders that have a distension of m=1.6 shock pressures of 14 to 72 GPa are required to consolidate Mo powders in the 50 to 10 (SIGMA)m range.

  17. Synthesis and characterization of nanocrystalline Cu-Al coatings

    Lau, M.L.; He, J.; Schweinfest, R.; Ruehle, M.; Levi, C.G.; Lavernia, E.J.

    2003-01-01

    Commercially pure Cu and Al powders were blended in a 90:10 ratio by weight and then mechanically milled in methanol or in liquid nitrogen. The milled powders, as well as as-blended (non-milled) powder, were deposited as coatings using high velocity oxygen fuel thermal spraying. Scanning and transmission electron microscopy techniques were used to investigate the microstructure of the powders and coatings. The results showed that milling of the powders in methanol induced the conversion of most of the Al into amorphous Al 2 O 3 , precluding the desired mechanical alloying. This experimental observation was consistent with available thermodynamic data. In contrast, cryomilling exhibited no significant oxidation and induced mechanical alloying of the powders, albeit incomplete. The non-milled powder generated a coating with a bimodal grain structure consisting of fine Cu grains and coarse Al grains. Amorphous oxide regions and coarse Al grains were observed intermixed with the finer Cu matrix in the coatings sprayed using the powders milled in methanol. Coatings based on cryomilled powders consisted primarily of equiaxed Cu grains and twinned martensite regions, with occasional inclusion of elongated amorphous Al 2 O 3 regions

  18. Effect of grain size on corrosion of nanocrystalline copper in NaOH solution

    Luo Wei; Xu Yimin; Wang Qiming; Shi Peizhen; Yan Mi

    2010-01-01

    Research highlights: → Coppers display an active-passive-transpassive behaviour with duplex passive film. → Grain size variation has little effect on the overall corrosion behaviour of Cu. → Little effect on corrosion may be due to duplex passivation in NaOH solution. → Bulk nanocrystalline Cu show bamboo-like flake corrosion structure. - Abstract: Effect of grain size on corrosion of bulk nanocrystalline copper was investigated using potentiodynamic polarization measurements in 0.1 M NaOH solution. Bulk nanocrystalline copper was prepared by inert gas condensation and in situ warm compress (IGCWC) method. The grain sizes of all bulk nanocrystalline samples were determined to be 48, 68 and 92 nm using X-ray diffraction (XRD). Results showed that bulk coppers displayed an active-passive-transpassive behaviour with duplex passive films. From polycrystalline to nanocrystalline, grain size variation showed little effect on the overall corrosion resistance of copper samples.

  19. Infrared absorption study of hydrogen incorporation in thick nanocrystalline diamond films

    Tang, C.J.; Neves, A.J.; Carmo, M.C.

    2005-01-01

    We present an infrared (IR) optical absorbance study of hydrogen incorporation in nanocrystalline diamond films. The thick nanocrystalline diamond films were synthesized by microwave plasma-assisted chemical vapor deposition and a high growth rate about 3.0 μm/h was achieved. The morphology, phase quality, and hydrogen incorporation were assessed by means of scanning electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Large amount of hydrogen bonded to nanocrystalline diamond is clearly evidenced by the huge CH stretching band in the FTIR spectrum. The mechanism of hydrogen incorporation is discussed in light of the growth mechanism of nanocrystalline diamond. This suggests the potential of nanocrystalline diamond for IR electro-optical device applications

  20. In vitro corrosion, cytotoxicity and hemocompatibility of bulk nanocrystalline pure iron

    Nie, F L; Zheng, Y F; Wei, S C; Hu, C; Yang, G

    2010-01-01

    Bulk nanocrystalline pure iron rods were fabricated by the equal channel angular pressure (ECAP) technique up to eight passes. The microstructure and grain size distribution, natural immersion and electrochemical corrosion in simulated body fluid, cellular responses and hemocompatibility were investigated in this study. The results indicate that nanocrystalline pure iron after severe plastic deformation (SPD) would sustain durable span duration and exhibit much stronger corrosion resistance than that of the microcrystalline pure iron. The interaction of different cell lines reveals that the nanocrystalline pure iron stimulates better proliferation of fibroblast cells and preferable promotion of endothelialization, while inhibits effectively the viability of vascular smooth muscle cells (VSMCs). The burst of red cells and adhesion of the platelets were also substantially suppressed on contact with the nanocrystalline pure iron in blood circulation. A clear size-dependent behavior from the grain nature deduced by the gradual refinement microstructures was given and well-behaved in vitro biocompatibility of nanocrystalline pure iron was concluded.

  1. Effects of precursors on the crystal structure and photoluminescence of CdS nanocrystalline

    Fu Zuoling; Zhou Shihong; Shi Jinsheng; Zhang Siyuan

    2005-01-01

    A series of cadmium sulfide (CdS) nanocrystalline were synthesized by precipitation from a mixture of aqueous solutions of cadmium salts and sulfur salts without adding any surface-termination agent. Their crystal structures and particle sizes were determined by X-ray diffraction (XRD). The CdS nanocrystalline precipitated from different precursors exhibited three cases: cubic phase, hexagonal phase and a hybrid of cubic and hexagonal phases. The photoluminescence (PL) of cadmium salt precursors and CdS nanocrystalline is also analyzed. Similar spectral band structure of cadmium salt precursors and CdS nanocrystalline is found. The PL of 3.4, 2.4 and 2.0 nm sized CdS nanocrystalline with the same crystal structure indicated quantum confinement effect

  2. Rhometal interface in pseudo-core shell powders like Permalloy/Rhometal type

    Chicinaş, I.; Marinca, T.F.; Popa, F.; Neamţu, B.V.

    2015-12-15

    Highlights: • Pseudo-core shell powders like Permalloy/Rhometal type obtained by microalloying. • During annealing, by interdiffusion, Rhometal phase is formed at the interface. • Both bcc and fcc structures of the Rhometal have been evidenced in interface. - Abstract: The nanocrystalline Ni{sub 3}Fe (around Permalloy composition) powders were prepared by dry mechanical alloying. The nanocrystalline Ni{sub 3}Fe and carbonyl Fe mixture powders and green compacts have been subjected to heat treatments in an argon atmosphere in order to obtain pseudo-core-shell like particles by micro-alloying in the temperature range of 400–900 °C. The large Permalloy particles are partially covered by very small Fe particles and at the interface a layer of Rhometal is formed by micro-alloying. The Permalloy particles remain in the nanocrystalline/nanostructured state after the annealing independent on the annealing temperature up to 900 °C. Structural, microstructural characterisation and local elemental chemical analysis have been performed by X-ray diffraction, scanning electron microscopy and X-ray microanalysis. The Rhometal interface was studied and evidenced by Fe and Ni concentration profile (EDX microanalysis) and X-ray diffraction. It was found that by a heat treatment up to 900 °C the interface is in the iron zone and at the heat treatment temperature of 900 °C the interface is in both Permalloy and iron zones. By XRD the bcc and fcc structures of the Rhometal have been evidenced. The interface length in iron zones is about 0.8 μm for the heat treatment at 400 °C and reaches 2.5 μm for heat treatment at 900 °C. The interface reaches 10 μm for a temperature of a heat treatment of 900 °C. The iron zones welded by Permalloy zones is evidenced the presence of the Ni atoms up to 4.7 at%. Also, in Permalloy particles are evidenced two zones with a different amount of Ni: one around Ni{sub 0.6}Fe{sub 0.4} composition close to the interface and the second in the

  3. Ultrasonic wave propagation in powders

    Al-Lashi, R. S.; Povey, M. J. W.; Watson, N. J.

    2018-05-01

    Powder clumps (cakes) has a significant effect on the flowability and stability of powders. Powder caking is mainly caused by moisture migration due to wetting and environmental (temperature and humidity) changes. The process of moisture migration caking involves creating liquid bridges between the particles during condensation which subsequently harden to form solid bridges. Therefore, an effective and reliable technique is required to quantitatively and non-invasively monitor caking kinetics and effective stiffness. This paper describes two ultrasonic instruments (ultrasonic velocity pulse and airborne ultrasound systems) that have been used to monitor the caking phenomenon. Also, it discusses the relationship between the ultrasonic velocity and attenuation measurements and tracking caking kinetics and the effective stiffness of powders.

  4. Neutron Powder Diffraction in Sweden

    Tellgren, R.

    1986-01-01

    Neutron powder diffraction in Sweden has developed around the research reactor R2 in Studsvik. The article describes this facility and presents a historical review of research results obtained. It also gives some ideas of plans for future development

  5. Powder metallurgy - some economic considerations

    Kassem, M.E.

    1982-01-01

    As a forming process powder metallurgy offers reductions in material and energy consumption. The engineering prerequisites and economics are discussed in relation to several industrial applications including automobile parts. 14 refs.

  6. Powder metallurgy of refractory metals

    Eck, R.

    1979-01-01

    This paper reports on the powder metallurgical methods for the production of high-melting materials, such as pure metals and their alloys, compound materials with a tungsten base and hard metals from liquid phase sintered carbides. (author)

  7. Dry and coating of powders

    Alonso, M.; Alguacil, F. J.

    1999-01-01

    This paper presents a review on the mixing and coating of powders by dry processes. The reviews surveys fundamental works on mixture characterization (mixing index definitions and sampling techniques), mixing mechanisms and models, segregation with especial emphasis on free-surface segregation, mixing of cohesive powders and interparticle forces, ordered mixing (dry coating) including mechanism, model and applications and mixing equipment selection. (Author) 180 refs

  8. Pressurized Anneal of Consolidated Powders

    Nemir, David Charles (Inventor); Rubio, Edward S. (Inventor); Beck, Jan Bastian (Inventor)

    2017-01-01

    Systems and methods for producing a dense, well bonded solid material from a powder may include consolidating the powder utilizing any suitable consolidation method, such as explosive shockwave consolidation. The systems and methods may also include a post-processing thermal treatment that exploits a mismatch between the coefficients of thermal expansion between the consolidated material and the container. Due to the mismatch in the coefficients, internal pressure on the consolidated material during the heat treatment may be increased.

  9. Laser shock wave consolidation of nanodiamond powders on aluminum 319

    Molian, Pal [Laboratory for Lasers, MEMS, and Nanotechnology, Department of Mechanical Engineering, Iowa State University, Ames, IA 50011-2161 (United States)], E-mail: molian@iastate.edu; Molian, Raathai; Nair, Rajeev [Laboratory for Lasers, MEMS, and Nanotechnology, Department of Mechanical Engineering, Iowa State University, Ames, IA 50011-2161 (United States)

    2009-01-01

    A novel coating approach, based on laser shock wave generation, was employed to induce compressive pressures up to 5 GPa and compact nanodiamond (ND) powders (4-8 nm) on aluminum 319 substrate. Raman scattering indicated that the coating consisted of amorphous carbon and nanocrystalline graphite with peaks at 1360 cm{sup -1} and 1600 cm{sup -1} respectively. Scanning electron microscopy revealed a wavy, non-uniform coating with an average thickness of 40 {mu}m and absence of thermal effect on the surrounding material. The phase transition from nanodiamond to other phases of carbon is responsible for the increased coating thickness. Vicker's microhardness test showed hardness in excess of 1000 kg{sub f}/mm{sup 2} (10 GPa) while nanoindentation test indicated much lower hardness in the range of 20 MPa to 2 GPa. Optical surface profilometry traces displayed slightly uneven surfaces compared to the bare aluminum with an average surface roughness (R{sub a}) in the range of 1.5-4 {mu}m depending on the shock wave pressure and type of confining medium. Ball-on-disc tribometer tests showed that the coefficient of friction and wear rate were substantially lower than the smoother, bare aluminum sample. Laser shock wave process has thus aided in the generation of a strong, wear resistant, durable carbon composite coating on aluminum 319 substrate.

  10. Investigation on the structural, magnetic and magnetocaloric properties of nanocrystalline Pr-deficient Pr1-xSrxMnO3-δ manganites

    Arun, B.; Athira, M.; Akshay, V. R.; Sudakshina, B.; Mutta, Geeta R.; Vasundhara, M.

    2018-02-01

    We have investigated the structural, magnetic and magnetocaloric properties of nanocrystalline Pr-deficient Pr1-xSrxMnO3-δ Perovskite manganites. Rietveld refinement of the X-ray powder diffraction patterns confirms that all the studied compounds have crystallized into an orthorhombic structure with Pbnm space group. Transmission electron microscopy analysis reveals nanocrystalline compounds with crystallite size less than 50 nm. The selected area electron diffraction patterns reveal the highly crystalline nature of the compounds and energy dispersive X-ray spectroscopic analysis shows that the obtained compositions are nearly identical with the nominal one. The oxygen stoichiometry is estimated by iodometric titration method and stoichiometric compositions are confirmed by X-ray Fluorescence Spectrometry analysis. A large bifurcation is observed in the ZFC/FC curves and Arrott plots not show a linear relation but have a convex curvature nature. The temperature dependence of inverse magnetic susceptibility at higher temperature confirms the existence of ferromagnetic clusters. The experimental results reveal that the reduction of crystallite size to nano metric scale in Pr-deficient manganites adversely influences structural, magnetic and magnetocaloric properties as compared to its bulk counterparts reported earlier.

  11. The radiation response of mesoporous nanocrystalline zirconia thin films

    Manzini, Ayelén M.; Alurralde, Martin A. [Comisión Nacional de Energía Atómica, Centro Atómico Constituyentes, Av. General Paz 1499, 1650 San Martin, Provincia de Buenos Aires (Argentina); Giménez, Gustavo [Instituto Nacional de Tecnología Industrial - CMNB, Av. General Paz 5445, 1650 San Martín, Provincia de Buenos Aires (Argentina); Luca, Vittorio, E-mail: vluca@cnea.gov.ar [Comisión Nacional de Energía Atómica, Centro Atómico Constituyentes, Av. General Paz 1499, 1650 San Martin, Provincia de Buenos Aires (Argentina)

    2016-12-15

    The next generation of nuclear systems will require materials capable of withstanding hostile chemical, physical and radiation environments over long time-frames. Aside from its chemical and physical stability, crystalline zirconia is one of the most radiation tolerant materials known. Here we report the first ever study of the radiation response of nanocrystalline and mesoporous zirconia and Ce{sup 3+}-stabilized nanocrystalline zirconia (Ce{sub 0.1}Zr{sub 0.9}O{sub 2}) thin films supported on silicon wafers. Zirconia films prepared using the block copolymer Brij-58 as the template had a thickness of around 60–80 nm. In the absence of a stabilizing trivalent cation they consisted of monoclinic and tetragonal zirconia nanocrystals with diameters in the range 8–10 nm. Films stabilized with Ce{sup 3+} contained only the tetragonal phase. The thin films were irradiated with iodine ions of energies of 70 MeV and 132 keV at low fluences (10{sup 13} - 10{sup 14} cm{sup −2}) corresponding to doses of 0.002 and 1.73 dpa respectively, and at 180 keV and high fluences (2 × 10{sup 16} cm{sup −2}) corresponding to 82.4 dpa. The influence of heavy ion irradiation on the nanocrystalline structure was monitored through Rietveld analysis of grazing incidence X-ray diffraction (GIXRD) patterns recorded at angles close to the critical angle to ensure minimum contribution to the diffraction pattern from the substrate. Irradiation of the mesoporous nanocrystalline zirconia thin films with 70 MeV iodine ions, for which electronic energy loss is dominant, resulted in slight changes in phase composition and virtually no change in crystallographic parameters as determined by Rietveld analysis. Iodine ion bombardment in the nuclear energy loss regime (132–180 keV) at low fluences did not provoke significant changes in phase composition or crystallographic parameters. However, at 180 keV and high fluences the monoclinic phase was totally eliminated from the GIXRD

  12. Nanocrystalline CdTe thin films by electrochemical synthesis

    Ramesh S. Kapadnis

    2013-03-01

    Full Text Available Cadmium telluride thin films were deposited onto different substrates as copper, Fluorine-doped tin oxide (FTO, Indium tin oxide (ITO, Aluminum and zinc at room temperature via electrochemical route. The morphology of the film shows the nanostructures on the deposited surface of the films and their growth in vertical direction. Different nanostructures developed on different substrates. The X-ray diffraction study reveals that the deposited films are nanocrystalline in nature. UV-Visible absorption spectrum shows the wide range of absorption in the visible region. Energy-dispersive spectroscopy confirms the formation of cadmium telluride.

  13. Nanocrystalline iron nitride films with perpendicular magnetic anisotropy

    Gupta, Ajay; Dubey, Ranu; Leitenberger, W.; Pietsch, U.

    2008-01-01

    Nanocrystalline α-iron nitride films have been prepared using reactive ion-beam sputtering. Films develop significant perpendicualr magnetic anisotropy (PMA) with increasing thickness. A comparison of x-ray diffraction patterns taken with scattering vectors in the film plane and out of the film plane provides a clear evidence for development of compressive strain in the film plane with thickness. Thermal annealing results in relaxation of the strain, which correlates very well with the relaxation of PMA. This suggests that the observed PMA is a consequence of the breaking of the symmetry of the crystal structure due to the compressive strain

  14. Inversion degree and saturation magnetization of different nanocrystalline cobalt ferrites

    Concas, G.; Spano, G.; Cannas, C.; Musinu, A.; Peddis, D.; Piccaluga, G.

    2009-01-01

    The inversion degree of a series of nanocrystalline samples of CoFe 2 O 4 ferrites has been evaluated by a combined study, which exploits the saturation magnetization at 4.2 K and 57 Fe Moessbauer spectroscopy. The samples, prepared by sol-gel autocombustion, have different thermal history and particle size. The differences observed in the saturation magnetization of these samples are explained in terms of different inversion degrees, as confirmed by the analysis of the components in the Moessbauer spectra. It is notable that the inversion degrees of the samples investigated are set among the highest values reported in the literature.

  15. Elemental separation in nanocrystalline Cu-Al alloys

    Wang, Y. B.; Liao, X. Z.; Zhao, Y. H.; Cooley, J. C.; Horita, Z.; Zhu, Y. T.

    2013-06-01

    Nanocrystallization by high-energy severe plastic deformation has been reported to increase the solubility of alloy systems and even to mix immiscible elements to form non-equilibrium solid solutions. In this letter, we report an opposite phenomenon—nanocrystallization of a Cu-Al single-phase solid solution by high-pressure torsion separated Al from the Cu matrix when the grain sizes are refined to tens of nanometers. The Al phase was found to form at the grain boundaries of nanocrystalline Cu. The level of the separation increases with decreasing grain size, which suggests that the elemental separation was caused by the grain size effect.

  16. Tailoring the wettability of nanocrystalline TiO 2 films

    Liang, Qiyu; Chen, Yan; Fan, Yuzun; Hu, Yong; Wu, Yuedong; Zhao, Ziqiang; Meng, Qingbo

    2012-01-01

    The water contact angle (WCA) of nanocrystalline TiO2 films was adjusted by fluoroalkylsilane (FAS) modification and photocatalytic lithography. FAS modification made the surface hydrophobic with the WCA up to ∼156°, while ultraviolet (UV) irradiation changed surface to hydrophilic with the WCA down to ∼0°. Both the hydrophobicity and hydrophilicity were enhanced by surface roughness. The wettability can be tailored by varying the concentration of FAS solution and soaking time, as well as the UV light intensity and irradiation time. Additionally, with the help of photomasks, hydrophobic-hydrophilic micropatterns can be fabricated and manifested via area-selective deposition of polystyrene particles.

  17. Mueller matrix spectroscopic ellipsometry study of chiral nanocrystalline cellulose films

    Mendoza-Galván, Arturo; Muñoz-Pineda, Eloy; Ribeiro, Sidney J. L.; Santos, Moliria V.; Järrendahl, Kenneth; Arwin, Hans

    2018-02-01

    Chiral nanocrystalline cellulose (NCC) free-standing films were prepared through slow evaporation of aqueous suspensions of cellulose nanocrystals in a nematic chiral liquid crystal phase. Mueller matrix (MM) spectroscopic ellipsometry is used to study the polarization and depolarization properties of the chiral films. In the reflection mode, the MM is similar to the matrices reported for the cuticle of some beetles reflecting near circular left-handed polarized light in the visible range. The polarization properties of light transmitted at normal incidence for different polarization states of incident light are discussed. By using a differential decomposition of the MM, the structural circular birefringence and dichroism of a NCC chiral film are evaluated.

  18. Stacking fault-mediated ultrastrong nanocrystalline Ti thin films

    Wu, K.; Zhang, J. Y.; Li, G.; Wang, Y. Q.; Cui, J. C.; Liu, G.; Sun, J.

    2017-11-01

    In this work, we prepared nanocrystalline (NC) Ti thin films with abundant stacking faults (SFs), which were created via partial dislocations emitted from grain boundaries and which were insensitive to grain sizes. By employing the nanoindentation test, we investigated the effects of SFs and grain sizes on the strength of NC Ti films at room temperature. The high density of SFs significantly strengthens NC Ti films, via dislocation-SF interactions associated with the reported highest Hall-Petch slope of ˜20 GPa nm1/2, to an ultrahigh strength of ˜4.4 GPa, approaching ˜50% of its ideal strength.

  19. Electron holography of Fe-based nanocrystalline magnetic materials (invited)

    Shindo, Daisuke; Park, Young-Gil; Gao, Youhui; Park, Hyun Soon

    2004-01-01

    Magnetic domain structures of nanocrystalline magnetic materials were extensively investigated by electron holography with a change in temperature or magnetic field applied. In both soft and hard magnetic materials, the distribution of lines of magnetic flux clarified in situ by electron holography was found to correspond well to their magnetic properties. An attempt to produce a strong magnetic field using a sharp needle made of a permanent magnet, whose movement is controlled by piezo drives has been presented. This article demonstrates that the attempt is promising to investigate the magnetization process of hard magnetic materials by electron holography

  20. 21 CFR 73.1647 - Copper powder.

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Copper powder. 73.1647 Section 73.1647 Food and... ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1647 Copper powder. (a) Identity. (1) The color additive copper powder is a very fine free-flowing metallic powder prepared from virgin electrolytic copper. It...

  1. Convenient hydrothermal decomposition process for preparation of nanocrystalline mineral Cu3BiS3 and Pb1-xBi2x/3S

    Hu Junqing; Deng Bin; Wang Chunrui; Tang Kaibin; Qian Yitai

    2003-01-01

    Mineral nanocrystalline Cu 3 BiS 3 and Pb 1-x Bi 2x/3 S (or Bi 0.22 Pb 0.89 S 1.22 ) have been prepared at low synthetic temperature of 100-150 deg. C by convenient hydrothermal decomposition process. X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectra, and element analysis were used to characterize and measure the samples. The as-prepared Cu 3 BiS 3 sample consisted of whisker-like particles with an average size of 50x10 nm 2 and the Pb 1-x Bi 2x/3 S sample displayed aggregative particles with size in the range of 30-50 nm. Preliminary results showed that the prepared precursors, reaction temperature and time played a role in the formation of the final products. A possible reaction mechanism was also discussed briefly

  2. Low-Temperature Preparation of Amorphous-Shell/Nanocrystalline-Core Nanostructured TiO2 Electrodes for Flexible Dye-Sensitized Solar Cells

    Dongshe Zhang

    2008-01-01

    Full Text Available An amorphous shell/nanocrystalline core nanostructured TiO2 electrode was prepared at low temperature, in which the mixture of TiO2 powder and TiCl4 aqueous solution was used as the paste for coating a film and in this film amorphous TiO2 resulted from direct hydrolysis of TiCl4 at 100∘C sintering was produced to connect the particles forming a thick crack-free uniform nanostructured TiO2 film (12 μm, and on which a photoelectrochemical solar cell-based was fabricated, generating a short-circuit photocurrent density of 13.58 mA/cm2, an open-circuit voltage of 0.647 V, and an overall 4.48% light-to-electricity conversion efficiency under 1 sun illumination.

  3. EXAFS and XRD studies of nanocrystalline cerium oxide: the effect of preparation method on the microstructure

    Savin, S.L.P.; Chadwick, A.V.; Smith, M.E.; O'Dell, L.A.

    2007-01-01

    There is considerable interest in nanocrystalline materials due to their unusual properties, such as enhanced ionic conductivity in the case of nanocrystalline ionic solids. This has potential commercial applications, particularly for oxide ion conductors. However, a detailed knowledge of the microstructure is important in fully understanding the novel properties exhibited by nanocrystalline materials. The final microstructure of a material is dependent on the preparation method used, for example, sol-gel and ball-milling methods are commonly used in the preparation of nanocrystalline oxides. Additionally, there is a problem in maintaining the materials in nanocrystalline form when they are subjected to elevated temperatures. We have been exploring strategies to restrict the growth of nanocrystalline oxides and have found that adding a small amount of an inert material, e.g. SiO 2 or Al 2 O 3 , is particularly effective. We will report XRD and EXAFS studies of nanocrystalline ceria prepared by sol-gel, sol-gel pinned and ball-milling methods and the effect of preparation method on the final microstructure. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. White light emission from Er2O3 nano-powder excited by infrared radiation

    Tabanli, Sevcan; Eryurek, Gonul; Di Bartolo, Baldassare

    2017-07-01

    Phosphors of Er2O3 nano-crystalline powders were synthesized by the thermal decomposition method. The structural properties of the nano-powders were investigated with XRD and HRTEM measurements. The cubic phase with a = 10.540 Å was the only phase observed. The average crystalline sizes and the widths of the grain size distribution curves were determined to be 27.2, 18.7 and 9.7 nm, respectively. The spectroscopic properties of the Er2O3 nano-powder were studied by measuring the luminescence, decay and rise patterns under 808 and 975 nm diode laser excitations. A peculiar effect of the pressure was observed since an optically active ion (Er) is part of the complex and not a dopant. A broad band of the white light emission combined with blue, green and red up-conversion emission bands of Er3+ ions were observed at 0.03 mbar pressure under both excitation wavelengths. Only, an intense broad band white light emission was observed from these nanocrystals at atmospheric pressure. Rising patterns show that the white light intensity reaches its maximum value more rapidly under 975 nm excitation although it decays slower than that of 808 nm excitation. The color quality parameters such as the color coordinate (CRI), correlated color temperature and the color rendering index were found to vary with both the excitation wavelength and the ambient pressure indicating that these nanocrystals could be considered good white light emitting source under the infrared excitations.

  5. Synthesis of Yttria-stabilized zirconia nanoparticles by decomposition of metal nitrates coated on carbon powder

    Jiang, S.; Stangle, G.C.; Amarakoon, V.R.; Schulze, W.A.

    1996-01-01

    Weakly agglomerated nanoparticles of yttria-stabilized zirconia (YSZ) were synthesized by a novel process which involved the decomposition of metal nitrates that had been coated on ultrafine carbon black powder, after which the carbon black was gasified. The use of ultrafine, high-surface-area carbon black powder apparently allowed the nanocrystalline oxide particles to form and remain separate from each other, after which the carbon black was gasified at a somewhat higher temperature. As a result, the degree of agglomeration was shown to be relatively low. The average crystallite size and the specific surface area of the as-synthesized YSZ nanoparticles were 5∼6 nm and 130 m 2 /g, respectively, for powder synthesized at 650 degree C. The as-synthesized YSZ nanoparticles had a light brown color and were translucent, which differs distinctly from conventional YSZ particles which are typically white and opaque. The mechanism of the synthesis process was investigated, and indicated that the gasification temperature had a direct effect on the crystallite size of the as-synthesized YSZ nanoparticles. High-density and ultrafine-grained YSZ ceramic articles were prepared by fast-firing, using a dwell temperature of 1250 degree C and a dwell time of two minutes or less. copyright 1996 Materials Research Society

  6. Mechanically Strain-Induced Modification of Selenium Powders in the Amorphization Process

    Fuse, Makoto; Shirakawa, Yoshiyuki; Shimosaka, Atsuko; Hidaka, Jusuke

    2003-01-01

    For the fabrication of particles designed in the nanoscale structure, or the nanostructural modification of particles using mechanical grinding process, selenium powders ground by a planetary ball mill at various rotational speeds have been investigated. Structural analyses, such as particle size distributions, crystallite sizes, lattice strains and nearest neighbour distances were performed using X-ray diffraction, scanning electron microscopy and dynamical light scattering.By grinding powder particles became spherical composites consisting of nanocrystalline and amorphous phase, and had a distribution with the average size of 2.7 μm. Integral intensities of diffraction peaks of annealed crystal selenium decreased with increasing grinding time, and these peaks broadened due to lattice strains and reducing crystallite size during the grinding. The ground powder at 200 rpm did not have the lattice strain and showed amorphization for the present grinding periods. It indicates that the amorphization of Se by grinding accompanies the lattice strain, and the lattice strain arises from a larger energy concerning intermolecular interaction. In this process, the impact energy is spent on thermal and structural changes according to energy accumulation in macroscopic (the particle size distribution) and microscopic (the crystallite size and the lattice strain) range

  7. Synthesis of nano-sized hydroxyapatite powders through solution combustion route under different reaction conditions

    Ghosh, Samir Kumar; Roy, Sujit Kumar; Kundu, Biswanath; Datta, Someswar; Basu, Debabrata

    2011-01-01

    Calcium hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 (HAp) was synthesized by combustion in the aqueous system containing calcium nitrate-diammonium hydrogen orthophosphate with urea and glycine as fuels. These ceramics are important materials for biomedical applications. Thermo-gravimetric and differential thermal analysis were employed to understand the nature of synthesis process during combustion. Effects of different process parameters namely, nature of fuel (urea and glycine), fuel to oxidizer ratio (0.6-4.0) and initial furnace temperature (300-700 o C) on the combustion behavior as well as physical properties of as-formed powders were investigated. A series of combustion reactions were carried out to optimize the reaction parameters for synthesis of nano-sized HAp powders. The combustion temperature (T f ) for the oxidant and fuels were calculated to be 896 deg. C and 1035 deg. C for the stoichiometric system of urea and glycine respectively. The stoichiometric glycine-calcium nitrate produced higher flame temperature (both calculated and measured) and powder with lower specific surface area (8.75 m 2 /g) compared to the stoichiometric urea-calcium nitrate system (10.50 m 2 /g). Fuel excess combustion in both glycine and urea produced powders with higher surface area. Nanocrystalline HAp powder could be synthesized in situ with a large span of fuel to oxidizer ratio (φ) in case of urea system (0.8 < φ < 4) and (0.6 < φ < 1.5) for the glycine system. Calcium hydroxyapatite particles having diameters ranging between 20 nm and 120 nm could be successfully synthesized through optimized process variable.

  8. Gas response properties of citrate gel synthesized nanocrystalline MgFe{sub 2}O{sub 4}: Effect of sintering temperature

    Patil, J.Y. [School of Physical Sciences, Solapur University Solapur-413255 (India); Mulla, I.S. [Emeritus Scientist (CSIR), Centre for Materials for Electronic Technology(C-MET) Pune-411 008 (India); Suryavanshi, S.S., E-mail: sssuryavanshi@rediffmail.com [School of Physical Sciences, Solapur University Solapur-413255 (India)

    2013-02-15

    Graphical abstract: Display Omitted Highlights: ► Synthesis of nanocrystalline MgFe{sub 2}O{sub 4} by economical citrate gel combustion method. ► Structural, morphological, and gas response properties of MgFe{sub 2}O{sub 4}. ► Enhancement in selectivity of MgFe{sub 2}O{sub 4} towards LPG with sintering temperature. ► Use of MgFe{sub 2}O{sub 4} to detect different gases at different operating temperatures. -- Abstract: Spinel type MgFe{sub 2}O{sub 4} material was synthesized by citrate gel combustion method. The effect of sintering temperature on structural, morphological, and gas response properties was studied. The powder X-ray diffraction pattern and transmission electron microscope study confirms nanocrystalline spinel structure of the synthesized powder. The material was tested for response properties to various reducing gases like liquid petroleum gas (LPG), acetone, ethanol, and ammonia. The results demonstrated n-type semiconducting behavior of MgFe{sub 2}O{sub 4} material. It was revealed that MgFe{sub 2}O{sub 4} sintered at 973 K was most sensitive to LPG at 648 K and to acetone at 498 K. However MgFe{sub 2}O{sub 4} sintered at 1173 K exhibited higher response and selectivity to LPG with marginal increase in the operating temperature. Furthermore, the sensor exhibited a fast response and a good recovery. It was observed that the particles size, porosity, and surface activity of the sensor material is affected by the sintering temperature.

  9. Preparation and properties of Cobalt-based soft magnetic material prepared by novel powder metallurgy

    Srivastava, Yogesh, E-mail: 123209001_yogesh@manit.ac.in; Srivastava, Sanjay

    2017-02-01

    The present work deals with the development of nanocrystalline 60Co–26Fe–14Al (wt%) soft magnetic materials via mechanical milling of elemental powders. The evolution of solid solution during milling proceeded with continuous decrease in atomic order and the crystallite size, and an introduction of internal strain and dislocations. The milling-induced lattice defects, crystallite size reduction, and atomic disorder exhibited a decrease in saturation magnetization, remanence magnetization, squareness ratio, and blocking temperature with increasing milling time. It has been demonstrated that, at subzero temperatures, the magnetization decreases with increasing temperature due to the development of an effective anisotropy caused by an evolution of canted spin structure owing to the introduction of lattice defects during milling. - Highlights: • Co-based HA have been fabricated by mechanical alloying. • The effect of milling time was investigated. • The saturation magnetization can be reached up to 140.79 emu/g.

  10. Shock diffraction in alumina powder

    Venz, G.; Killen, P.D.; Page, N.W.

    1996-01-01

    In order to produce complex shaped components by dynamic compaction of ceramic powders detailed knowledge of their response under shock loading conditions is required. This work attempts to provide data on release effects and shock attenuation in 1 μm and 5 μm α-alumina powders which were compacted to between 85 % and 95 % of the solid phase density by the impact of high velocity steel projectiles. As in previous work, the powder was loaded into large cylindrical dies with horizontal marker layers of a contrasting coloured powder to provide a record of powder displacement in the recovered specimens. After recovery and infiltration with a thermosetting resin the specimens were sectioned and polished to reveal the structure formed by the passage of the projectile and shock wave. Results indicate that the shock pressures generated were of the order of 0.5 to 1.4 GPa and higher, with shock velocities and sound speeds in the ranges 650 to 800 m/s and 350 to 400 m/s respectively

  11. Magnetic properties of nanocrystalline pyrrhotite prepared by high-energy milling

    Balaz, P.; Godocikova, E.; Alacova, A.

    2004-01-01

    The nanocrystalline pyrrhotite was prepared by high-energy milling of lead sulphide with elemental Fe acting as reducing element. X-ray diffractometry, Mossbauer spectroscopy and VSM magnetometry were used to determine the properties of nanocrystalline iron sulphide prepared by the corresponding...... mechanochemical reaction. Pyrrhotite Fe1-xS together with the residual Fe metal were identified by the X-ray diffractometry. The kinetic studies performed by Mossbauer spectroscopy and VSM magnetometry allowed us to follow in more details the progress of the nanocrystalline magnetic phase formation during...

  12. Syntheses of nanocrystalline BaTiO3 and their optical properties

    Yu, J.; Chu, J.; Zhang, M.

    Stoichiometric and titanium-excess nanocrystalline barium titanates were synthesized using a hydrothermal process at various hydrothermal temperatures and with further heat treatment at 500 °C and 900 °C. Owing to the different process conditions, the excess titanium exists in different states and configurations within the nanocrystalline BaTiO3 matrix; this was demonstrated by X-ray diffraction, Raman scattering, and photoluminescence. In these nanocrystalline BaTiO3, the 590, 571, 543 and 694 nm light emission bands were observed; mechanisms leading to such emissions were also discussed.

  13. Fabrication and structure of bulk nanocrystalline Al-Si-Ni-mishmetal alloys

    Latuch, Jerzy; Cieslak, Grzegorz; Kulik, Tadeusz

    2007-01-01

    Al-based alloys of structure consisting of nanosized Al crystals, embedded in an amorphous matrix, are interesting for their excellent mechanical properties, exceeding those of the commercial crystalline Al-based alloys. Recently discovered nanocrystalline Al alloys containing silicon (Si), rare earth metal (RE) and late transition metal (Ni), combine high tensile strength and good wear resistance. The aim of this work was to manufacture bulk nanocrystalline alloys from Al-Si-Ni-mishmetal (Mm) system. Bulk nanostructured Al 91-x Si x Ni 7 Mm 2 (x = 10, 11.6, 13 at.%) alloys were produced by ball milling of nanocrystalline ribbons followed by high pressure hot isostating compaction

  14. Interface effects on effective elastic moduli of nanocrystalline materials

    Wang Gangfeng; Feng Xiqiao; Yu Shouwen; Nan Cewen

    2003-01-01

    Interfaces often play a significant role in many physical properties and phenomena of nanocrystalline materials (NcMs). In the present paper, the interface effects on the effective elastic property of NcMs are investigated. First, an atomic potential method is suggested for estimating the effective elastic modulus of an interface phase. Then, the Mori-Tanaka effective field method is employed to determine the overall effective elastic moduli of a nanocrystalline material, which is regarded as a binary composite consisting of a crystal or inclusion phase with regular lattice connected by an amorphous-like interface or matrix phase. Finally, the stiffening effects of strain gradients are examined on the effective elastic property by using the strain gradient theory to analyze a representative unit cell. Our analysis shows two physical mechanisms of interfaces that influence the effective stiffness and other mechanical properties of materials. One is the softening effect due to the distorted atomic structures and the increased atomic spacings in interface regions, and another is the baffling effect due to the existence of boundary layers between the interface phase and the crystalline phase

  15. A variational multiscale constitutive model for nanocrystalline materials

    Gurses, Ercan

    2011-03-01

    This paper presents a variational multi-scale constitutive model in the finite deformation regime capable of capturing the mechanical behavior of nanocrystalline (nc) fcc metals. The nc-material is modeled as a two-phase material consisting of a grain interior phase and a grain boundary effected zone (GBAZ). A rate-independent isotropic porous plasticity model is employed to describe the GBAZ, whereas a crystal-plasticity model which accounts for the transition from partial dislocation to full dislocation mediated plasticity is employed for the grain interior. The constitutive models of both phases are formulated in a small strain framework and extended to finite deformation by use of logarithmic and exponential mappings. Assuming the rule of mixtures, the overall behavior of a given grain is obtained via volume averaging. The scale transition from a single grain to a polycrystal is achieved by Taylor-type homogenization where a log-normal grain size distribution is assumed. It is shown that the proposed model is able to capture the inverse HallPetch effect, i.e., loss of strength with grain size refinement. Finally, the predictive capability of the model is validated against experimental results on nanocrystalline copper and nickel. © 2010 Elsevier Ltd. All rights reserved.

  16. Low cost and efficient photovoltaic conversion by nanocrystalline solar cells

    Graetzel, M. [Institut de Chimie Physique, Ecole Polytechnique Federal de Lausanne (Switzerland)

    1996-09-01

    Solar cells are expected to provide environmentally friendly solutions to the world`s energy supply problem. Learning from the concepts used by green plants we have developed a molecular photovoltaic device whose overall efficiency for AM 1.5 solar light to electricity has already attained 8-11%. The system is based on the sensitization of nanocrystalline oxide films by transition metal charge transfer sensitizers. In analogy to photosynthesis, the new chemical solar cell achieves the separation of the light absorption and charge carrier transport processes. Extraordinary yields for the conversion of incident photons into electric current are obtained, exceeding 90% for transition metal complexes within the wavelength range of their absorption band. The use of molten salt electrolytes together with coordination complexes of ruthenium as sensitizers and adequate sealing technology has endowed these cells with a remarkable stability making practical applications feasible. Seven industrial cooperations are presently involved in the development to bring these cells to the market. The first cells will be applied to supply electric power for consumer electronic devices. The launching of production of several products of this type is imminent and they should be on the market within the next two years. Quite aside from their intrinsic merits as photovoltaic device, the mesoscopic oxide semiconductor films developed in our laboratory offer attractive possibilities for a number of other applications. Thus, the first example of a nanocrystalline rocking chair battery will be demonstrated and its principle briefly discussed.

  17. Mechanical properties of nanocrystalline palladium prepared by magnetron sputtering

    Castrup, Anna; Hahn, Horst [Forschungszentrum Karlsruhe (Germany); Technical University of Darmstadt (Germany); Scherer, Torsten; Ivanisenko, Yulia; Choi, In-Suk; Kraft, Oliver [Forschungszentrum Karlsruhe (Germany)

    2009-07-01

    Nanocrystalline metals and alloys with grain sizes well below 100 nm often demonstrate unique deformation behaviour and therefore attract a great interest in material science. The understanding of deformation mechanisms operating in nanocrystalline materials is important to predict their mechanical properties. In the present study Pd films of 1{mu}m thickness were prepared using UHV rf magnetron sputtering on dog bone shaped Kapton substrates and on Si/SiO2 wafers. The films were sputtered using multilayer technology with an individual layer thickness of 10 nm. This resulted in grain sizes of about 20 nm. Initial microstructure and texture were characterized using conventional XRD measurements and transmission electron microscopy (TEM) in both cross section- and plane view. The mechanical properties were investigated using tensile testing and nanoindentation at several strain rates. An increased hardness and strength as compared to coarse grained Pd was observed, as well as high strain rate sensitivity. The microstructure in the gauge section after tensile testing was again analyzed using TEM in order to reveal signatures of deformation mechanisms like dislocation motion or twinning.

  18. Visualizing decoupling in nanocrystalline alloys: A FORC-temperature analysis

    Rivas, M.; Martínez-García, J. C.; Gorria, P.

    2016-02-01

    Devitrifying ferromagnetic amorphous precursors in the adequate conditions may give rise to disordered assemblies of densely packed nanocrystals with extraordinary magnetic softness well explained by the exchange coupling among multiple crystallites. Whether the magnetic exchange interaction is produced by direct contact or mediated by the intergranular amorphous matrix has a strong influence on the behaviour of the system above room temperature. Multi-phase amorphous-nanocrystalline systems dramatically harden when approaching the amorphous Curie temperature (TC) due to the hard grains decoupling. The study of the thermally induced decoupling of nanosized crystallites embedded in an amorphous matrix has been performed in this work by the first-order reversal curves (FORCs) analysis. We selected a Fe-rich amorphous alloy with TC = 330 K, in order to follow the evolution of the FORC diagrams obtained below and above such temperature in samples with different percentages of nanocrystalline phase. The existence of up to four regions exhibiting unlike magnetic behaviours is unambiguously determined from the temperature evolution of the FORC.

  19. New atom probe approaches to studying segregation in nanocrystalline materials

    Samudrala, S.K.; Felfer, P.J.; Araullo-Peters, V.J.; Cao, Y.; Liao, X.Z.; Cairney, J.M.

    2013-01-01

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. - Highlights: ► New data treatment methods allow delineation of grain boundaries, even without segregation. ► Proxigrams calculated from the surfaces accurately show the extent of segregation. ► Tessellation of the data volume can be used to map the Gibbsian interfacial excess

  20. Nanocrystalline zinc oxide for the decontamination of sarin

    Mahato, T.H. [Defense R and D Establishment, Jhansi Road, 474002, Gwalior, MP (India); Prasad, G.K., E-mail: gkprasad@lycos.com [Defense R and D Establishment, Jhansi Road, 474002, Gwalior, MP (India); Singh, Beer; Acharya, J.; Srivastava, A.R.; Vijayaraghavan, R. [Defense R and D Establishment, Jhansi Road, 474002, Gwalior, MP (India)

    2009-06-15

    Nanocrystalline zinc oxide materials were prepared by sol-gel method and were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetry, nitrogen adsorption and infrared spectroscopy techniques. The data confirmed the formation of zinc oxide materials of zincite phase with an average crystallite size of {approx}55 nm. Obtained material was tested as destructive adsorbent for the decontamination of sarin and the reaction was followed by GC-NPD and GC-MS techniques. The reaction products were characterized by GC-MS and the data explored the role of hydrolysis reaction in the detoxification of sarin. Sarin was hydrolyzed to form surface bound non-toxic phosphonate on the surface of nano-zinc oxide. The data also revealed the values of rate constant and half-life to be 4.12 h{sup -1} and 0.16 h in the initial stages of the reaction and 0.361 h{sup -1} and 1.9 h at the final stages of the reaction for the decontamination reaction on nanocrystalline ZnO.

  1. Nanocrystalline zinc oxide for the decontamination of sarin

    Mahato, T.H.; Prasad, G.K.; Singh, Beer; Acharya, J.; Srivastava, A.R.; Vijayaraghavan, R.

    2009-01-01

    Nanocrystalline zinc oxide materials were prepared by sol-gel method and were characterized by X-ray diffraction, scanning electron microscopy, thermogravimetry, nitrogen adsorption and infrared spectroscopy techniques. The data confirmed the formation of zinc oxide materials of zincite phase with an average crystallite size of ∼55 nm. Obtained material was tested as destructive adsorbent for the decontamination of sarin and the reaction was followed by GC-NPD and GC-MS techniques. The reaction products were characterized by GC-MS and the data explored the role of hydrolysis reaction in the detoxification of sarin. Sarin was hydrolyzed to form surface bound non-toxic phosphonate on the surface of nano-zinc oxide. The data also revealed the values of rate constant and half-life to be 4.12 h -1 and 0.16 h in the initial stages of the reaction and 0.361 h -1 and 1.9 h at the final stages of the reaction for the decontamination reaction on nanocrystalline ZnO.

  2. Nanocrystalline materials: recent advances in crystallographic characterization techniques

    Emilie Ringe

    2014-11-01

    Full Text Available Most properties of nanocrystalline materials are shape-dependent, providing their exquisite tunability in optical, mechanical, electronic and catalytic properties. An example of the former is localized surface plasmon resonance (LSPR, the coherent oscillation of conduction electrons in metals that can be excited by the electric field of light; this resonance frequency is highly dependent on both the size and shape of a nanocrystal. An example of the latter is the marked difference in catalytic activity observed for different Pd nanoparticles. Such examples highlight the importance of particle shape in nanocrystalline materials and their practical applications. However, one may ask `how are nanoshapes created?', `how does the shape relate to the atomic packing and crystallography of the material?', `how can we control and characterize the external shape and crystal structure of such small nanocrystals?'. This feature article aims to give the reader an overview of important techniques, concepts and recent advances related to these questions. Nucleation, growth and how seed crystallography influences the final synthesis product are discussed, followed by shape prediction models based on seed crystallography and thermodynamic or kinetic parameters. The crystallographic implications of epitaxy and orientation in multilayered, core-shell nanoparticles are overviewed, and, finally, the development and implications of novel, spatially resolved analysis tools are discussed.

  3. Magnetic induction heating of FeCr nanocrystalline alloys

    Gómez-Polo, C.; Larumbe, S.; Pérez-Landazábal, J.I.; Pastor, J.M.; Olivera, J.; Soto-Armañanzas, J.

    2012-01-01

    In this work the thermal effects of magnetic induction heating in (FeCr) 73.5 Si 13.5 Cu 1 B 9 Nb 3 amorphous and nanocrystalline wires were analyzed. A single piece of wire was immersed in a glass capillary filled with water and subjected to an ac magnetic field (frequency, 320 kHz). The initial temperature rise enabled the determination of the effective Specific Absorption Rate (SAR). Maximum SAR values are achieved for those samples displaying high magnetic susceptibility, where the eddy current losses dominate the induction heating behavior. Moreover, the amorphous sample with Curie temperature around room temperature displays characteristic features of self-regulated hyperthermia. - Highlights: ► Amorphous and nanocrystalline Fe based alloys with tailored Curie temperature of the amorphous phase. ► Induction heating effects under the action of a ac magnetic field. ► Self-regulated characteristics based on the control of the Curie temperature. ► Dominant role of the eddy-current losses in the self-heating phenomena.

  4. Magnetotransport in nanocrystalline SmB6 thin films

    Jie Yong

    2015-07-01

    Full Text Available SmB6 has been predicted to be a prototype of topological Kondo insulator (TKI but its direct experimental evidence as a TKI is still lacking to date. Here we report on our search for the signature of a topological surface state and investigation of the effect of disorder on transport properties in nanocrystalline SmB6 thin films through longitudinal magnetoresistance and Hall coefficient measurements. The magnetoresistance (MR at 2 K is positive and linear (LPMR at low field and become negative and quadratic at higher field. While the negative part is understood from the reduction of the hybridization gap due to Zeeman splitting, the positive dependence is similar to what is observed in other topological insulators (TI. We conclude that the LPMR is a characteristic of TI and is related to the linear dispersion near the Dirac cone. The Hall resistance shows a sign change around 50K. It peaks and becomes nonlinear around 10 K then decreases below 10 K. This indicates that carriers with opposite signs emerge below 50 K. These properties indicate that the surface states are robust and probably topological in our nanocrystalline films.

  5. New atom probe approaches to studying segregation in nanocrystalline materials

    Samudrala, S.K.; Felfer, P.J.; Araullo-Peters, V.J. [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); The Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia); Cao, Y.; Liao, X.Z. [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); Cairney, J.M., E-mail: julie.cairney@sydney.edu.au [School of Aerospace, Mechanical and Mechatronic Engineering, University of Sydney, NSW 2006 (Australia); The Australian Centre for Microscopy and Microanalysis, The University of Sydney, NSW 2006 (Australia)

    2013-09-15

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. - Highlights: ► New data treatment methods allow delineation of grain boundaries, even without segregation. ► Proxigrams calculated from the surfaces accurately show the extent of segregation. ► Tessellation of the data volume can be used to map the Gibbsian interfacial excess.

  6. New atom probe approaches to studying segregation in nanocrystalline materials.

    Samudrala, S K; Felfer, P J; Araullo-Peters, V J; Cao, Y; Liao, X Z; Cairney, J M

    2013-09-01

    Atom probe is a technique that is highly suited to the study of nanocrystalline materials. It can provide accurate atomic-scale information about the composition of grain boundaries in three dimensions. In this paper we have analysed the microstructure of a nanocrystalline super-duplex stainless steel prepared by high pressure torsion (HPT). Not all of the grain boundaries in this alloy display obvious segregation, making visualisation of the microstructure challenging. In addition, the grain boundaries present in the atom probe data acquired from this alloy have complex shapes that are curved at the scale of the dataset and the interfacial excess varies considerably over the boundaries, making the accurate characterisation of the distribution of solute challenging using existing analysis techniques. In this paper we present two new data treatment methods that allow the visualisation of boundaries with little or no segregation, the delineation of boundaries for further analysis and the quantitative analysis of Gibbsian interfacial excess at boundaries, including the capability of excess mapping. Copyright © 2013 Elsevier B.V. All rights reserved.

  7. Investigation of nanocrystalline Gd films loaded with hydrogen

    Hruška, Petr; Čí žek, Jakub; Dobroň, Patrik; Anwand, Wolfgang; Mü cklich, Arndt; Gemma, Ryota; Wagner, Stefan; Uchida, Helmut; Pundt, Astrid

    2015-01-01

    The present work reports on microstructure studies of hydrogen-loaded nanocrystalline Gd films prepared by cold cathode beam sputtering on sapphire (112¯0) substrates. The Gd films were electrochemically step-by-step charged with hydrogen and the structural development with increasing concentration of absorbed hydrogen was studied by transmission electron microscopy and in-situ   X-ray diffraction using synchrotron radiation. The relaxation of hydrogen-induced stresses was examined by acoustic emission measurements. In the low concentration range absorbed hydrogen occupies preferentially vacancy-like defects at GBs typical for nanocrystalline films. With increasing hydrogen concentration hydrogen starts to occupy interstitial sites. At the solid solution limit the grains gradually transform into the ββ-phase (GdH2). Finally at high hydrogen concentrations xH>2.0xH>2.0 H/Gd, the film structure becomes almost completely amorphous. Contrary to bulk Gd specimens, the formation of the γγ-phase (GdH3) was not observed in this work.

  8. Sintering of Cu–Al2O3 nano-composite powders produced by a thermochemical route

    MARIJA KORAC

    2007-11-01

    Full Text Available This paper presents the synthesis of nano-composite Cu–Al2O3 powder by a thermochemical method and sintering, with a comparative analysis of the mechanical and electrical properties of the obtained solid samples. Nano-crystalline Cu–Al2O3 powders were produced by a thermochemical method through the following stages: spray-drying, oxidation of the precursor powder, reduction by hydrogen and homogenization. Characterization of powders included analytical electron microscopy (AEM coupled with energy dispersive spectroscopy (EDS, differenttial thermal and thermogravimetric (DTA–TGA analysis and X-ray diffraction (XRD analysis. The size of the produced powders was 20–50 nm, with a noticeable presence of agglomerates. The composite powders were characterized by a homogenous distribution of Al2O3 in a copper matrix. The powders were cold pressed at a pressure of 500 MPa and sintered in a hydrogen atmosphere under isothermal conditions in the temperature range from 800 to 900 °C for up to 120 min. Characterization of the Cu–Al2O3 sintered system included determination of the density, relative volume change, electrical and mechanical properties, examination of the microstructure by SEM and focused ion beam (FIB analysis, as well as by EDS. The obtained nano-composite, the structure of which was, with certain changes, presserved in the final structure, provided a sintered material with a homogenеous distribution of dispersoid in a copper matrix, with exceptional effects of reinforcement and an excellent combination of mechanical and electrical properties.

  9. Magnetic characterization of nanocrystalline Fe80−xCrxCo20 (15≤x≤35) alloys during milling and subsequent annealing

    Rastabi, Reza Amini; Ghasemi, Ali; Tavoosi, Majid; Sodaee, Tahmineh

    2016-01-01

    Magnetic characterization of nanocrystalline Fe–Cr–Co alloys during milling and annealing process was the goal of this study. To formation of Fe 80−x Cr x Co 20 (15≤x≤35) solid solution, different powder mixtures of Fe, Cr and Co elements were mechanically milled in a planetary ball mill. The annealing process was done in as-milled samples at different temperature in the range of 500–640 °C for 2 h. The produced samples were characterized using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and vibrating sample magnetometer. Performed mechanical alloying in different powder mixtures lead to the formation of Fe–Cr–Co α-phase solid solution with average crystallite sizes of about 10 nm. The produced nanocrystalline alloys exhibit magnetic properties with the coercivity and saturation of magnetization in the range of 110–200 Oe and 150–220 emu/g, respectively. The coercivity of produced alloys after annealing process decreased and reached to about 40–150 Oe. The highest value of coercivity in as-milled and annealed samples was achieved in alloys with higher Cr contents. - Highlights: • Hc and Ms of produced alloys obtained in the range of 110–200 Oe and 150–220 emu/g. • The highest value of Hc in milled and annealed samples was achieved in Fe 45 Cr 35 Co 20 . • Hc of produced alloys after spinodal decomposition decreased to about 40–150 Oe. • The effect of crystalline defects and residual strain on magnetic fields pinning in milled samples is higher than spinodal decomposition in annealed samples. • The highest value of Hc in as-milled and annealed samples was achieved in Fe 45 Cr 35 Co 20 . The coercivity of produced alloys after annealing process decreased and reach to about 40–150 Oe. • The produced nanocrystalline alloys exhibit magnetic properties with the coercivity and saturation of magnetization in the range of 110–200 Oe and 150–220 emu/g, respectively.

  10. Method of solidifying powderous wastes

    Kakimoto, Akira; Miyake, Takashi; Sato, Shuichi; Inagaki, Yuzo.

    1985-01-01

    Purpose: To improve the properties of solidification products, in the case of solidifying powderous wastes with thermosetting resins. Method. A solvent for the solution of the thermosetting resin is admixed with the powderous wastes into a paste-like form prior to adding the resin to the wastes, which are then mixed with the resin solution. As the result, those solidification products having the specific gravity and the compression strength more excellent than those of the conventional ones, and much higher than the reference values can be obtained. (Kamimura, M.)

  11. The analysis of powder diffraction data

    David, W.I.F.; Harrison, W.T.A.

    1986-01-01

    The paper reviews neutron powder diffraction data analysis, with emphasis on the structural aspects of powder diffraction and the future possibilities afforded by the latest generation of very high resolution neutron and x-ray powder diffractometers. Traditional x-ray powder diffraction techniques are outlined. Structural studies by powder diffraction are discussed with respect to the Rietveld method, and a case study in the Rietveld refinement method and developments of the Rietveld method are described. Finally studies using high resolution powder diffraction at the Spallation Neutron Source, ISIS at the Rutherford Appleton Laboratory are summarized. (U.K.)

  12. Magnetic properties of nanocrystalline KNbO3

    Golovina, I. S.; Shanina, B. D.; Kolesnik, S. P.; Geifman, I. N.; Andriiko, A. A.

    2013-01-01

    Newly synthesized undoped and iron-doped nanoscale powders of KNbO 3 are investigated using magnetic resonance and static magnetization methods in order to determine how the crystal size and doping affect the structure of magnetic defects and material properties. Although the bulk crystals of KNbO 3 are nonmagnetic, the undoped KNbO 3 powder with average particle size of 80 nm exhibits magnetic properties. The ferromagnetic resonance signal and the magnetization curve registered on the powder are thoroughly analyzed. It is concluded that the appearance of the defect driven ferromagnetism in the undoped powder is due to the nano-size of the particles. This effect disappears in the iron-doped KNbO 3 powder with particle sizes above 300 nm. In case of low doping ( eff  = 4.21 is found out in the KNbO 3 :Fe powder. Such a signal has not been observed in the bulk crystals of KNbO 3 :Fe. We suppose that this signal corresponds to individual paramagnetic Fe 3+ ions having rhombic symmetry

  13. Magnetic properties of nanocrystalline KNbO{sub 3}

    Golovina, I. S., E-mail: golovina@isp.kiev.ua; Shanina, B. D.; Kolesnik, S. P. [Institute of Semiconductor Physics of NAS of Ukraine, Pr. Nauky 41, 03028 Kyiv (Ukraine); Geifman, I. N. [Quality Engineering Education, Inc., Buffalo Grove, Illinois 60089 (United States); Andriiko, A. A. [National Technical University of Ukraine “KPI”, pr. Peremogy 37, 03056 Kyiv (Ukraine)

    2013-11-07

    Newly synthesized undoped and iron-doped nanoscale powders of KNbO{sub 3} are investigated using magnetic resonance and static magnetization methods in order to determine how the crystal size and doping affect the structure of magnetic defects and material properties. Although the bulk crystals of KNbO{sub 3} are nonmagnetic, the undoped KNbO{sub 3} powder with average particle size of 80 nm exhibits magnetic properties. The ferromagnetic resonance signal and the magnetization curve registered on the powder are thoroughly analyzed. It is concluded that the appearance of the defect driven ferromagnetism in the undoped powder is due to the nano-size of the particles. This effect disappears in the iron-doped KNbO{sub 3} powder with particle sizes above 300 nm. In case of low doping (<1 mol. % Fe), a new electron paramagnetic resonance signal with g{sub eff} = 4.21 is found out in the KNbO{sub 3}:Fe powder. Such a signal has not been observed in the bulk crystals of KNbO{sub 3}:Fe. We suppose that this signal corresponds to individual paramagnetic Fe{sup 3+} ions having rhombic symmetry.

  14. A constitutive model of nanocrystalline metals based on competing grain boundary and grain interior deformation mechanisms

    Gurses, Ercan; El Sayed, Tamer S.

    2011-01-01

    In this work, a viscoplastic constitutive model for nanocrystalline metals is presented. The model is based on competing grain boundary and grain interior deformation mechanisms. In particular, inelastic deformations caused by grain boundary

  15. Preparation and mechanical properties of ultra-high-strength nanocrystalline metals

    Marek, I.; Vojtěch, D.; Michalcová, A.; Kubatík, Tomáš František

    2015-01-01

    Roč. 15, č. 4 (2015), s. 596-600 ISSN 1213-2489 Institutional support: RVO:61389021 Keywords : Mechanical properties * Nanocrystalline materials * Selective leaching * Silver * Spark plasma sintering Subject RIV: JG - Metallurgy

  16. Synthesis, characterization and photoluminescence properties of Dy3+ -doped nano-crystalline SnO2.

    Pillai, SK

    2010-04-15

    Full Text Available the crystallite size. The experimental result on photoluminescence characteristics originating from Dy3+-doping in nanocrystalline SnO2 reveals the dependence of the luminescent intensity on dopant concentration....

  17. Surface Properties of a Nanocrystalline Fe-Ni-Nb-B Alloy After Neutron Irradiation

    Pavùk, Milan; Sitek, Jozef; Sedlačková, Katarína

    2014-09-01

    The effect of neutron radiation on the surface properties of the nanocrystalline (Fe0.25Ni0.75)81Nb7B12 alloy was studied. Firstly, amorphous (Fe0.25Ni0.75)81Nb7B12 ribbon was brought by controlled annealing to the nanocrystalline state. After annealing, the samples of the nanocrystalline ribbon were irradiated in a nuclear reactor with neutron fluences of 1×1016cm-2 and 1 × 1017cm-2 . By utilizing the magnetic force microscopy (MFM), topography and a magnetic domain structure were recorded at the surface of the ribbon-shaped samples before and after irradiation with neutrons. The results indicate that in terms of surface the nanocrystalline (Fe0.25Ni0.75)81Nb7B12 alloy is radiation-resistant up to a neutron fluence of 1 × 1017cm-2 . The changes in topography observed for both irradiated samples are discussed

  18. On tension-compression asymmetry in ultrafine-grained and nanocrystalline metals

    Gurses, Ercan; El Sayed, Tamer S.

    2010-01-01

    We present a physically motivated computational study explaining the tension/compression (T/C) asymmetry phenomenon in nanocrystalline (nc) and ultrafine-grained (ufg) face centered cubic (fcc) metals utilizing a variational constitutive model where

  19. Round table discussion: Present and future applications of nanocrystalline magnetic materials

    Herzer, G.; Vazquez, M.; Knobel, M.; Zhukov, A.; Reininger, T.; Davies, H.A.; Groessinger, R.; Sanchez Ll, J.L.

    2005-01-01

    Examples of existing or potential applications of nanocrystalline magnetic materials, ranging from soft to hard magnetic alloys, are presented and discussed by experts in the respective fields of research and technology

  20. Thermal stability of grain boundaries in nanocrystalline Zn studied by positron lifetime spectroscopy

    Zhou Kai; Li Hui; Pang Jinbiao; Wang Zhu

    2012-01-01

    Nanocrystalline Zn prepared by compacting nanoparticles with mean grain size about 55 nm at 15 MPa has been studied by positron lifetime spectroscopy. For the bulk Zn sample, the vacancy defect is annealed out at about 350 °C, but for the nanocrystalline Zn sample, the vacancy cluster in grain boundaries is quite difficult to be annealed out even at very high temperature (410 °C). In the grain boundaries of nanocrystalline Zn, the small free volume defect (not larger than divacancy) is dominant according to the high relative intensity for the short positron lifetime (τ 1 ). The oxide (ZnO) inside the grain boundaries has been found having an effect to hinder the decrease of average positron lifetime (τ av ), which probably indicates that the oxide stabilizes the microstructure of the grain boundaries. This stabilization is very important for the nanocrystalline materials using as radiation resistant materials.

  1. Structure and coercivity of nanocrystalline Fe–Si–B–Nb–Cu alloys

    Unknown

    Fe–Si–B–Nb–Cu alloy; melt-spinning; crystallization; nanocrystalline ... to possess a unique combination of soft magnetic properties ... meability and high electrical resistivity (Yoshizawa et al ... ture and thermal stability of the alloy ribbons.

  2. Plasma synthesis and HPHT consolidation of BN nanoparticles, nanospheres, and nanotubes to produce nanocrystalline cubic boron nitride

    Stout, Christopher

    Plasma methods offer a variety of advantages to nanomaterials synthesis. The process is robust, allowing varying particle sizes and phases to be generated simply by modifying key parameters. The work here demonstrates a novel approach to nanopowder synthesis using inductively-coupled plasma to decompose precursor, which are then quenched to produce a variety of boron nitride (BN)-phase nanoparticles, including cubic phase, along with short-range-order nanospheres (e.g., nano-onions) and BN nanotubes. Cubic BN (c-BN) powders can be generated through direct deposition onto a chilled substrate. The extremely-high pyrolysis temperatures afforded by the equilibrium plasma offer a unique particle growth environment, accommodating long deposition times while exposing resulting powders to temperatures in excess of 5000K without any additional particle nucleation and growth. Such conditions can yield short-range ordered amorphous BN structures in the form of 20nm diameter nanospheres. Finally, when introducing a rapid-quenching counter-flow gas against the plasma jet, high aspect ratio nanotubes are synthesized, which are collected on substrate situated radially. The benefits of these morphologies are also evident in high-pressure/high-temperature consolidation experiments, where nanoparticle phases can offer a favorable conversion route to super-hard c-BN while maintaining nanocrystallinity. Experiments using these morphologies are shown to begin to yield c-BN conversion at conditions as low as 2.0 GPa and 1500°C when using micron sized c-BN seeding to create localized regions of high pressures due to Hertzian forces acting on the nanoparticles.

  3. Metallography of powder metallurgy materials

    Lawley, Alan; Murphy, Thomas F.

    2003-01-01

    The primary distinction between the microstructure of an ingot metallurgy/wrought material and one fabricated by the powder metallurgy route of pressing followed by sintering is the presence of porosity in the latter. In its various morphologies, porosity affects the mechanical, physical, chemical, electrical and thermal properties of the material. Thus, it is important to be able to characterize quantitatively the microstructure of powder metallurgy parts and components. Metallographic procedures necessary for the reliable characterization of microstructures in powder metallurgy materials are reviewed, with emphasis on the intrinsic challenges presented by the presence of porosity. To illustrate the utility of these techniques, five case studies are presented involving powder metallurgy materials. These case studies demonstrate problem solving via metallography in diverse situations: failure of a tungsten carbide-coated precipitation hardening stainless steel, failure of a steel pump gear, quantification of the degree of sinter (DOS), simulation of performance of a porous filter using automated image analysis, and analysis of failure in a sinter brazed part assembly

  4. Electro/powder separation process

    Dunn, J.P.

    1977-01-01

    A report is presented to introduce the ELECTRO/POWDER process to the P/M Industry. The process effectively uses electrostatic forces to convey, sort, meter, and blend fine powders. The major advantages of this separating process consist of the processing of primary particles, low particle energy due to particle velocity control and the pattern of particle movement over the sieve (vertical oscillation of particles above the sieve aperture). The report briefly describes the forces involved in both mechanical and sieving devices, with major emphasis on the operating principles of this process. Sieve separation of particulates is basically the result of two physical separating processes which occur simultaneously or independently; separation (dispersion) of particulates from each other and the size separation by passage through fixed apertures. In order to accomplish this goal, mechanical sieving devices utilize various motions to induce shear forces between the sieve surface and the particulates, and between the particulates themselves. It is noted that the ELECTRO/POWDER process is making steady progress in becoming an industrial tool for sieving and feeding of fine particles. Its potential extends into both the blending and admixing of powders, either by incorporating two opposing feeders, one being charged with the opposite polarity or by modifying the ELECTRO/SIEVE to incorporate more than one input and a solid electrode to replace the sieve electrode

  5. Amorphous and nanocrystalline titanium nitride and carbonitride materials obtained by solution phase ammonolysis of Ti(NMe2)4

    Jackson, Andrew W.; Shebanova, Olga; Hector, Andrew L.; McMillan, Paul F.

    2006-01-01

    Solution phase reactions between tetrakisdimethylamidotitanium (Ti(NMe 2 ) 4 ) and ammonia yield precipitates with composition TiC 0.5 N 1.1 H 2.3 . Thermogravimetric analysis (TGA) indicates that decomposition of these precursor materials proceeds in two steps to yield rocksalt-structured TiN or Ti(C,N), depending upon the gas atmosphere. Heating to above 700 deg. C in NH 3 yields nearly stoichiometric TiN. However, heating in N 2 atmosphere leads to isostructural carbonitrides, approximately TiC 0.2 N 0.8 in composition. The particle sizes of these materials range between 4-12 nm. Heating to a temperature that corresponds to the intermediate plateau in the TGA curve (450 deg. C) results in a black powder that is X-ray amorphous and is electrically conducting. The bulk chemical composition of this material is found to be TiC 0.22 N 1.01 H 0.07 , or Ti 3 (C 0.17 N 0.78 H 0.05 ) 3.96 , close to Ti 3 (C,N) 4 . Previous workers have suggested that the intermediate compound was an amorphous form of Ti 3 N 4 . TEM investigation of the material indicates the presence of nanocrystalline regions x (C,N) y crystalline phases

  6. Ammonia Gas Sensing Properties of Nanocrystalline Zn1-xCuxFe2O4 Doped with Noble Metal

    S. V. JAGTAP

    2010-11-01

    Full Text Available The sensors are required basically for monitoring of trace gases in environment. In order to detect, measure and control these gases; one should know the amount and type of gases present in the environment. Among the most toxic and hazardous gases, it is necessary to detect and monitor the ammonia gas because this is enhance in the agricultural sector by the addition of large amounts of NH3 to cultivated farmland in the form of fertilizers. Nanocrystalline spinel type Zn1-xCuxFe2O4 (x=0, 0.2, 0.4 0.6 & 0.8 has been synthesized by sol-gel citrate method. The synthesized powders were characterized by XRD and SEM. The results revealed that the particle size is in the range of 40–45 nm for Cu–Zn ferrite with good crystallinity. The gas sensing properties were studied towards reducing gases like CO, LPG, NH3 and H2S and it is observed that Cu–Zn ferrite shows high response to ammonia gas at relatively lower operating temperature. The Zn0.6Cu0.4Fe2O4 nanomaterial shows better sensitivity towards NH3 gas at an operating temperature 300 0C. Incorporation of Pd improved the sensitivity, selectivity, response time and reduced the operating temperature from 300 0C to 250 0C for NH3 sensor.

  7. A Modified Thermal Treatment Method for the Up-Scalable Synthesis of Size-Controlled Nanocrystalline Titania

    Aysar Sabah Keiteb

    2016-10-01

    Full Text Available Considering the increasing demand for titania nanoparticles with controlled quality for various applications, the present work reports the up-scalable synthesis of size-controlled titanium dioxide nanocrystals with a simple and convenient thermal treatment route. Titanium dioxide nanocrystals with tetragonal structure were synthesized directly from an aqueous solution containing titanium (IV isopropoxide as the main reactant, polyvinyl pyrrolidone (PVP as the capping agent, and deionized water as a solvent. With the elimination of the drying process in a thermal treatment method, an attempt was made to decrease the synthesis time. The mixture directly underwent calcination to form titanium dioxide (TiO2 nanocrystalline powder, which was confirmed by FT-IR, energy dispersive X-ray spectroscopy (EDX, and X-ray diffraction (XRD analysis. The control over the size and optical properties of nanocrystals was achieved via variation in calcination temperatures. The obtained average sizes from XRD spectra and transmission electron microscopy (TEM images showed exponential variation with increasing calcination temperature. The optical properties showed a decrease in the band gap energy with increasing calcination temperature due to the enlargement of the nanoparticle size. These results prove that direct calcination of reactant solution is a convenient thermal treatment route for the potential large-scale production of size-controlled Titania nanoparticles.

  8. Low-temperature fabrication of TiO2 nanocrystalline film electrodes for dye-sensitized solar cells

    Shan, G.; Lee, K.E.; Charboneau, C.; Demopoulos, G.P.; Gauvin, R. [McGill Univ., Montreal, PQ (Canada). Dept. of Materials Engineering; Savadogo, O. [Ecole Polytechnique de Montreal, PQ (Canada). Dept. de Genie Chimique

    2008-07-01

    Dye-sensitized solar cells (DSSCs) have the potential to render solar energy widely accessible. The deposition of titania nano-crystalline powders on a substrate is an important step in the manufacture of the DSSC. The deposition forms a mesoporous thin film that is followed by thermal treatment and sensitization. Usually titania films are deposited on glass by screen printing and then annealed at temperatures as high as 530 degrees C to provide a good electrical contact between the semiconductor particles and crystallization of the anatase phase. Several research and development efforts have focused on the deposition of titania film on flexible plastic substrates that will simplify the whole manufacturing process in terms of flexibility, weight, application and cost. Lower temperature processing is needed for the preparation of plastic-based titania film electrodes, but this has proven to be counterproductive when it comes to the cell's conversion efficiency. This paper presented a comprehensive evaluation of the different coating and annealing techniques at low temperature as well as important processing factors for improvement. To date, these techniques include pressing, hydrothermal process, electrodeposition, electrophoretic deposition, microwave or UV irradiation, and lift-off technique.

  9. Grain size stability and hardness in nanocrystalline Cu–Al–Zr and Cu–Al–Y alloys

    Roy, D., E-mail: droy2k6@gmail.com [Material Science and Engineering Department, North Carolina State University, Raleigh, NC 27606 (United States); Materials and Metallurgical Engineering Department, NIFFT, Ranchi 834003 (India); Mahesh, B.V. [Department of Mechanical and Aerospace Engineering, Monash University (Australia); Atwater, M.A. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-F, Aberdeen Proving Ground, MD 21005-5069 (United States); Chan, T.E.; Scattergood, R.O.; Koch, C.C. [Material Science and Engineering Department, North Carolina State University, Raleigh, NC 27606 (United States)

    2014-03-01

    Cryogenic high energy ball milling has been used to synthesize nanocrystalline Cu–14Al, Cu–12Al–2Zr and Cu–12Al–2Y alloys by mechanical alloying. The alloys were studied with the aim of comparing the effect of substituting Y and Zr in place of Al, in Cu–Al alloys, on the grain size stability at elevated temperatures. The as-milled alloys were subjected to annealing at various temperatures between 200 and 900 °C and the resulting grain morphology has been studied using X-ray diffraction and transmission electron microscopy. The addition of Y results in significantly reduced susceptibility to grain growth whereas in case of CuAl and CuAlZr alloys, the susceptibility to grain growth was much higher. The hardness is substantially increased due to Zr and Y addition in the as-milled CuAl powders. However, the hardness of Cu–12Al–2Zr gradually decreases and approaches that of Cu–14Al alloy after the annealing treatment whereas in case of Cu–12Al–2Y alloy, the relative drop in the hardness is much lower after annealing. Accordingly, the efficacy of grain size stabilization by Y addition at high homologous temperatures has been explained on the basis of a recent thermodynamic stabilization models.

  10. Grain size stability and hardness in nanocrystalline Cu–Al–Zr and Cu–Al–Y alloys

    Roy, D.; Mahesh, B.V.; Atwater, M.A.; Chan, T.E.; Scattergood, R.O.; Koch, C.C.

    2014-01-01

    Cryogenic high energy ball milling has been used to synthesize nanocrystalline Cu–14Al, Cu–12Al–2Zr and Cu–12Al–2Y alloys by mechanical alloying. The alloys were studied with the aim of comparing the effect of substituting Y and Zr in place of Al, in Cu–Al alloys, on the grain size stability at elevated temperatures. The as-milled alloys were subjected to annealing at various temperatures between 200 and 900 °C and the resulting grain morphology has been studied using X-ray diffraction and transmission electron microscopy. The addition of Y results in significantly reduced susceptibility to grain growth whereas in case of CuAl and CuAlZr alloys, the susceptibility to grain growth was much higher. The hardness is substantially increased due to Zr and Y addition in the as-milled CuAl powders. However, the hardness of Cu–12Al–2Zr gradually decreases and approaches that of Cu–14Al alloy after the annealing treatment whereas in case of Cu–12Al–2Y alloy, the relative drop in the hardness is much lower after annealing. Accordingly, the efficacy of grain size stabilization by Y addition at high homologous temperatures has been explained on the basis of a recent thermodynamic stabilization models

  11. Isotropic and anisotropic nanocrystalline NdFeB-based magnets prepared by spark plasma sintering and hot deformation

    Liu, Z.W.; Huang, Y.L.; Huang, H.Y.; Zhong, X.C.; Yu, Y.H.; Zeng, D.C.

    2011-01-01

    Isotropic and anisotropic NdFeB permanent magnets were prepared by Spark Plasma Sintering (SPS) and SPS followed hot deformation (HD), respectively, using melt spun NdFeB ribbons with various compositions as starting materials. It is found that, based on RE-rich composition, SPSed magnets sintered at low temperatures (<700 C) almost maintained the uniform fine grain structure inherited from rapid quenching. At higher temperatures, a distinct two-zone (coarse grain and fine grain zones) structure was formed in the SPSed magnets. The SPS temperature and pressure have important effects on the grain structure, which led to the variations in the magnetic properties. By employing low SPS temperature and high pressure, high-density magnets with negligible coarse grain zone and an excellent combination of magnetic properties can be obtained. For single phase NdFeB alloy, because of the deficiency of Nd-rich phases, it is relatively difficult to consolidate micro-sized melt spun powders into high density bulk magnet, but generally a larger particle size is beneficial to achieve better magnetic properties. Anisotropic magnets with a maximum energy product of approx. equal to 38 MGOe were produced by the SPS+HD process. HD did not lead to obvious grain growth and the two-zone structure still existed in the hot deformed magnets. The results indicated that nanocrystalline NdFeB magnets without significant grain growth and with excellent properties could be obtained by SPS and HD processes. (author)

  12. Microstructure and Properties of Nanocrystalline Copper Strengthened by a Low Amount of Al2O3 Nanoparticles

    Ďurišinová, Katarína; Ďurišin, Juraj; Ďurišin, Martin

    2017-03-01

    Dispersion-strengthened Cu-Al2O3 materials have been studied over recent years to find an optimum processing route to obtain a high strength, thermal-stable copper alloy designed for modern applications in electrical engineering. The study analyses the influence of 1 vol.% of alumina content on strengthening the copper matrix. Microstructure of the Cu-Al2O3 composite was studied by x-ray diffraction as well as scanning and transmission electron microscopy. The composite shows a homogeneous, thermal-stable nanostructure up to 900 °C due to dispersed alumina nanoparticles. The particles effectively strengthen crystallite/grain boundaries in processes of powder consolidation and annealing of the compact. In contrast to monolithic Cu, the Cu-1 vol.% Al2O3 exhibits more than double strength and hardness. The nanocrystalline matrix and the low amount of alumina particles result in a yield strength of 288 MPa and a ductility of 15% which is a good combination for practical utilization of the material.

  13. Nanoindentation study of WC-12Co hardmetals obtained from nanocrystalline powders: Evaluation of hardness and modulus on individual phases

    Bonache, V.; Rayon, E.; Salvador, M.D.; Busquets, D.

    2010-01-01

    With the development of finer hardmetals, the study of mechanical properties of the different constituents down the micrometric level is a question of concern for materials optimization. Nanoindentation has been developed in last years in order to cope with mechanical characterisation at the nanolevel, but difficulties on phase detection are an issue. In the present work, individual hardness and Young's modulus of the constituents of WC-12Co composite were obtained by the use of very shallow nanoindentations (30 nm depth), with the aid of in situ 3D imaging to identify these. By this method three different phases at the sub-micrometric level have been identified and characterised: namely cobalt matrix, tungsten carbide and η phase. The presence of the latter phase and its characterisation is of paramount importance in understanding the behaviour of hardmetals. Values of hardness from 8 (cobalt matrix) to 25 GPa (η phase) have been obtained. Also, for these phases Young's modulus varied from 250 to 400 GPa respectively. Furthermore, it is firstly reported these values for the WC prismatic planes {1 0 1 0} being in the range of 40-55 and 700-900 GPa respectively. These values decrease to a hardness in the range of 25-30 GPa and modulus in the range from 450 to 550 GPa for the WC basal plane {0 0 0 1}.

  14. Effect of Flake Thickness on Coercivity of Nanocrystalline SmCo5 Bulk Prepared from Anisotropic Nanoflake Powder (Postprint)

    2016-08-23

    s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org...281, 23 (1998). 5 J. Zhou, R. Skomski, and D. J. Sellmyer, J. Appl . Phys. 93, 6495 (2003). 6 M. Yue, J. H. Zuo, W. Q. Liu, W. C. Lu, D. T. Zhang, J...X. Zhang, Z. H. Guo, and W. Li, J. Appl . Phys. 109, 07A700 (2011). 7 A. M. Gabay, M. Marinescu, J. F. Liu, and G. C. Hadjipanayis, J. Magn. Magn

  15. Rapid formation of nanocrystalline HfO2 powders from amorphous hafnium hydroxide under ultrasonically assisted hydrothermal treatment

    Meskin, Pavel E.; Sharikov, Felix Yu.; Ivanov, Vladimir K.; Churagulov, Bulat R.; Tretyakov, Yury D.

    2007-01-01

    Peculiarities of hafnium hydroxide hydrothermal decomposition were studied by in situ heat flux calorimetry for the first time. It was shown that this process occurs in one exothermal stage (ΔH = -17.95 kJ mol -1 ) at 180-250 deg. C resulting in complete crystallization of amorphous phase with formation of pure monoclinic HfO 2 . It was found that the rate of m-HfO 2 formation can be significantly increased by combining hydrothermal treatment with simultaneous ultrasonic activation

  16. Synthesis of nanocrystalline TiB2 powder from TiO2, B2O3 and Mg ...

    gered by using: (i) a furnace or (ii) an electrical element touching the surface ... plicity, low energy consumption and good purity of the products. [12,13]. SHS method .... Similar to the TiO2–Mg system, by increasing the ini- tial temperature, the ...

  17. XRD Analysis of Nanocrystalline Anatase Powders Prepared by Various Chemical Routes: Correlations between Micro-structure and Crystal Structure Parameters

    Matěj, Z.; Matějová, Lenka; Kužel, R.

    2013-01-01

    Roč. 28, Suppl. 2 (2013), s. 161-183 ISSN 0885-7156 Grant - others:UK(CZ) UNCE 204023/2012; MŠk(CZ) GAP108/11/1539 Institutional support: RVO:67985858 Keywords : anatase * crystallite size * lattice parameters * XRD * vacancies * anisotropy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.586, year: 2013

  18. An assessment of the homogeneity of nano-crystalline Fe–Cu powders as studied by means of APT

    Wille, Catharina; Al-Kassab, Talaat; Choi, Pyuck-Pa; Kwon, Young-Soon; Kirchheim, Reiner

    2009-01-01

    alloy to elaborate the enforced nonequilibrium enhanced solubility for immiscible systems. Depending on the parameters composition and milling time, results on the extension of the solubility limit and on the homogeneity of the alloy are presented

  19. Biologically inspired rosette nanotubes and nanocrystalline hydroxyapatite hydrogel nanocomposites as improved bone substitutes

    Zhang Lijie; Webster, Thomas J; Rodriguez, Jose; Raez, Jose; Myles, Andrew J; Fenniri, Hicham

    2009-01-01

    Today, bone diseases such as bone fractures, osteoporosis and bone cancer represent a common and significant public health problem. The design of biomimetic bone tissue engineering materials that could restore and improve damaged bone tissues provides exciting opportunities to solve the numerous problems associated with traditional orthopedic implants. Therefore, the objective of this in vitro study was to create a biomimetic orthopedic hydrogel nanocomposite based on the self-assembly properties of helical rosette nanotubes (HRNs), the osteoconductive properties of nanocrystalline hydroxyapatite (HA), and the biocompatible properties of hydrogels (specifically, poly(2-hydroxyethyl methacrylate), pHEMA). HRNs are self-assembled nanomaterials that are formed from synthetic DNA base analogs in water to mimic the helical nanostructure of collagen in bone. In this study, different geometries of nanocrystalline HA were controlled by either hydrothermal or sintering methods. 2 and 10 wt% nanocrystalline HA particles were well dispersed into HRN hydrogels using ultrasonication. The nanocrystalline HA and nanocrystalline HA/HRN hydrogels were characterized by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Mechanical testing studies revealed that the well dispersed nanocrystalline HA in HRN hydrogels possessed improved mechanical properties compared to hydrogel controls. In addition, the results of this study provided the first evidence that the combination of either 2 or 10 wt% nanocrystalline HA and 0.01 mg ml -1 HRNs in hydrogels greatly increased osteoblast (bone-forming cell) adhesion up to 236% compared to hydrogel controls. Moreover, this study showed that HRNs stimulated HA nucleation and mineralization along their main axis in a way that is very reminiscent of the HA/collagen assembly pattern in natural bone. In summary, the presently observed excellent properties of the biomimetic nanocrystalline HA/HRN hydrogel composites

  20. Nanocrystalline sp{sup 2} and sp{sup 3} carbons: CVD synthesis and applications

    Terranova, M. L. [Università degli Studi di Roma “Tor Vergata,” via Della Ricerca Scientifica, Dipartimento di Scienze e Tecnologie Chimiche—MinimaLab (Italy); Rossi, M. [Università degli Studi di Roma “Sapienza,” via A. Scarpa, Dipartimento di Scienze di Base e Applicate per l’Ingegneria and Centro di Ricerca per le Nanotecnologie Applicate all’Ingegneria (CNIS) (Italy); Tamburri, E., E-mail: emanuela.tamburri@uniroma2.it [Università degli Studi di Roma “Tor Vergata,” via Della Ricerca Scientifica, Dipartimento di Scienze e Tecnologie Chimiche—MinimaLab (Italy)

    2016-11-15

    The design and production of innovative materials based on nanocrystalline sp{sup 2}- and sp{sup 3}-coordinated carbons is presently a focus of the scientific community. We present a review of the nanostructures obtained in our labs using a series of synthetic routes, which make use of chemical vapor deposition (CVD) techniques for the selective production of non-planar graphitic nanostructures, nanocrystalline diamonds, and hybrid two-phase nanostructures.

  1. Topological characterization of nanocrystalline cellulose reinforced Poly (lactic acid) and Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) bionanocomposites

    Bhat, A. H.; Dasan, Y. K.; Khan, Ihsan Ullah; Ahmad, Faiz; Ayoub, Muhammad

    2016-11-01

    This study was conducted to evaluate the morphological and barrier properties of nanocrystalline cellulose reinforced Poly (lactic acid) and Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) bionanocomposites. Nanocrystalline cellulose was isolated from waste oil palm empty fruit bunch fiber using Sulphuric acid hydrolysis. Chemical modifications of nanocrystalline cellulose was performed to allow good compatibilization between fiber and the polymer matrices and also to improve dispersion of fillers. Bionanocomposite materials were produced from these nanocrystalline cellulose reinforced Poly (lactic acid) and Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) using solvent casting and evaporation techniques. The properties of extracted nanocrystalline cellulose were examined using FT-IR spectroscopy, X-ray diffractometer, TEM and AFM. Besides that, the properties of bionanocomposites were examined through FESEM and oxygen permeability properties analysis. Better barrier and morphological properties were obtained for nanocrystalline cellulose reinforced bionanocomposites than for neat polymer blend.

  2. Polymer quenched prealloyed metal powder

    Hajaligol, Mohammad R.; Fleischhauer, Grier; German, Randall M.

    2001-01-01

    A powder metallurgical process of preparing a sheet from a powder having an intermetallic alloy composition such as an iron, nickel or titanium aluminide. The sheet can be manufactured into electrical resistance heating elements having improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The iron aluminide has an entirely ferritic microstructure which is free of austenite and can include, in weight %, 4 to 32% Al, and optional additions such as .ltoreq.1% Cr, .gtoreq.0.05% Zr .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Ni, .ltoreq.0.75% C, .ltoreq.0.1% B, .ltoreq.1% submicron oxide particles and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, and/or .ltoreq.3 % Cu. The process includes forming a non-densified metal sheet by consolidating a powder having an intermetallic alloy composition such as by roll compaction, tape casting or plasma spraying, forming a cold rolled sheet by cold rolling the non-densified metal sheet so as to increase the density and reduce the thickness thereof and annealing the cold rolled sheet. The powder can be a water, polymer or gas atomized powder which is subjecting to sieving and/or blending with a binder prior to the consolidation step. After the consolidation step, the sheet can be partially sintered. The cold rolling and/or annealing steps can be repeated to achieve the desired sheet thickness and properties. The annealing can be carried out in a vacuum furnace with a vacuum or inert atmosphere. During final annealing, the cold rolled sheet recrystallizes to an average grain size of about 10 to 30 .mu.m. Final stress relief annealing can be carried out in the B2 phase temperature range.

  3. Silver film on nanocrystalline TiO{sub 2} support: Photocatalytic and antimicrobial ability

    Vukoje, Ivana D., E-mail: ivanav@vinca.rs [Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11000 Belgrade (Serbia); Tomašević-Ilić, Tijana D., E-mail: tommashev@gmail.com [Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11000 Belgrade (Serbia); Zarubica, Aleksandra R., E-mail: zarubica2000@yahoo.com [Department of Chemistry, Faculty of Science and Mathematics, University of Niš, Višegradska 33, 18000 Niš (Serbia); Dimitrijević, Suzana, E-mail: suzana@tmf.bg.ac.rs [Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade (Serbia); Budimir, Milica D., E-mail: mickbudimir@gmail.com [Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11000 Belgrade (Serbia); Vranješ, Mila R., E-mail: mila@vinca.rs [Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11000 Belgrade (Serbia); Šaponjić, Zoran V., E-mail: saponjic@vinca.rs [Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11000 Belgrade (Serbia); Nedeljković, Jovan M., E-mail: jovned@vinca.rs [Vinča Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11000 Belgrade (Serbia)

    2014-12-15

    Highlights: • Simple photocatalytic rout for deposition of Ag on nanocrystalline TiO{sub 2} films. • High antibactericidal efficiency of deposited Ag on TiO{sub 2} support. • Improved photocatalytic performance of TiO{sub 2} films in the presence of deposited Ag. - Abstract: Nanocrystalline TiO{sub 2} films were prepared on glass slides by the dip coating technique using colloidal solutions consisting of 4.5 nm particles as a precursor. Photoirradiation of nanocrystalline TiO{sub 2} film modified with alanine that covalently binds to the surface of TiO{sub 2} and at the same time chelate silver ions induced formation of metallic silver film. Optical and morphological properties of thin silver films on nanocrystalline TiO{sub 2} support were studied by absorption spectroscopy and atomic force microscopy. Improvement of photocatalytic performance of nanocrystalline TiO{sub 2} films after deposition of silver was observed in degradation reaction of crystal violet. Antimicrobial ability of deposited silver films on nanocrystalline TiO{sub 2} support was tested in dark as a function of time against Escherichia coli, Staphylococcus aureus, and Candida albicans. The silver films ensured maximum cells reduction of both bacteria, while the fungi reduction reached satisfactory 98.45% after 24 h of contact.

  4. Cold compaction behavior of nano-structured Nd–Fe–B alloy powders prepared by different processes

    Liu, Xiaoya; Hu, Lianxi; Wang, Erde

    2013-01-01

    Graphical abstract: Relative density enhancement and nanocrystallization of Nd 2 Fe 14 B phase are two major effective means to improve magnetic properties. Since the matrix Nd 2 Fe 14 B phase in the starting Nd–Fe–B alloy can be disproportionated into a nano-structured mixture of NdH 2.7 , Fe 2 B, and α-Fe phases during mechanical milling in hydrogen. It is thus important to study the densification behavior of nanocrystalline powders to evaluate and predict the cold compactibility of powders. By comparison with the as milled as well as melt-spun Nd 16 Fe 76 B 8 alloy powders, we find that the as-disproportionated Nd 16 Fe 76 B 8 alloy powder exhibits the best cold compactibility. As evident from the illustration presented below, compaction parameters (representing the powder compactibility) have been determined by fitting density–pressure data with double logarithm compaction equation. Densification mechanisms involved during cold compaction process are clarified in our work by referring to microstructure observation of samples prepared by various methods. As a result, highly densified green magnet compact can be obtained by cold pressing of as-disproportionated NdFeB alloy powders. Highlights: ► Nano-structured disproportionated Nd–Fe–B alloy powders by mechanical milling in hydrogen. ► Highly densified green magnet compact by cold pressing of as-disproportionated Nd–Fe–B alloy powders. ► Density–pressure data fitted well by an empirical powder compaction model. ► As-disproportionated powder showed better compactibility than as milled and melt-spun counterparts. ► The effects of physical properties on powder compactibility and densification mechanisms are clarified. - Abstract: The compaction behavior of nano-structured Nd 16 Fe 76 B 8 (atomic ratio) alloy powders, which were prepared by three different processing routes including melt spinning, mechanical milling in argon, and mechanically activated disproportionation by milling in

  5. Cold compaction behavior of nano-structured Nd-Fe-B alloy powders prepared by different processes

    Liu, Xiaoya [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Hu, Lianxi, E-mail: hulx@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Wang, Erde [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2013-02-25

    Graphical abstract: Relative density enhancement and nanocrystallization of Nd{sub 2}Fe{sub 14}B phase are two major effective means to improve magnetic properties. Since the matrix Nd{sub 2}Fe{sub 14}B phase in the starting Nd-Fe-B alloy can be disproportionated into a nano-structured mixture of NdH{sub 2.7}, Fe{sub 2}B, and {alpha}-Fe phases during mechanical milling in hydrogen. It is thus important to study the densification behavior of nanocrystalline powders to evaluate and predict the cold compactibility of powders. By comparison with the as milled as well as melt-spun Nd{sub 16}Fe{sub 76}B{sub 8} alloy powders, we find that the as-disproportionated Nd{sub 16}Fe{sub 76}B{sub 8} alloy powder exhibits the best cold compactibility. As evident from the illustration presented below, compaction parameters (representing the powder compactibility) have been determined by fitting density-pressure data with double logarithm compaction equation. Densification mechanisms involved during cold compaction process are clarified in our work by referring to microstructure observation of samples prepared by various methods. As a result, highly densified green magnet compact can be obtained by cold pressing of as-disproportionated NdFeB alloy powders. Highlights: Black-Right-Pointing-Pointer Nano-structured disproportionated Nd-Fe-B alloy powders by mechanical milling in hydrogen. Black-Right-Pointing-Pointer Highly densified green magnet compact by cold pressing of as-disproportionated Nd-Fe-B alloy powders. Black-Right-Pointing-Pointer Density-pressure data fitted well by an empirical powder compaction model. Black-Right-Pointing-Pointer As-disproportionated powder showed better compactibility than as milled and melt-spun counterparts. Black-Right-Pointing-Pointer The effects of physical properties on powder compactibility and densification mechanisms are clarified. - Abstract: The compaction behavior of nano-structured Nd{sub 16}Fe{sub 76}B{sub 8} (atomic ratio) alloy

  6. Electrochemically assisted photocatalysis using nanocrystalline semiconductor thin films

    Vinodgopal, K [Department of Chemistry, Indiana University Northwest, Gary, Indiana (United States); Kamat, Prashant V [Notre Dame Radiation Laboratory, Notre Dame, Indiana (United States)

    1995-08-01

    The principle and usefulness of electrochemically assisted photocatalysis has been illustrated with the examples of 4-chlorophenol and Acid Orange 7 degradation in aqueous solutions. Thin nanocrystalline semiconductor films coated on a conducting glass surface when employed as a photoelectrode in an electrochemical cell are effective for degradation of organic contaminants. The degradation rate can be greatly improved even in the absence of oxygen by applying an anodic bias to the TiO{sub 2} film electrodes. A ten-fold enhancement in the degradation rate was observed when TiO{sub 2} particles were coupled with SnO{sub 2} nanocrystallites at an applied bias potential of 0.83 V versus SCE

  7. Grain boundaries and mechanical properties of nanocrystalline diamond films.

    Busmann, H.-G.; Pageler, A.; Gruen, D. M.

    1999-08-06

    Phase-pure nanocrystalline diamond thin films grown from plasmas of a hydrogen-poor carbon argon gas mixture have been analyzed regarding their hardness and elastic moduli by means of a microindentor and a scanning acoustic microscope.The films are superhard and the moduli rival single crystal diamond. In addition, Raman spectroscopy with an excitation wavelength of 1064 nm shows a peak at 1438 l/cm and no peak above 1500 l/cm, and X-ray photoelectron spectroscopy a shake-up loss at 4.2 eV. This gives strong evidence for the existence of solitary double bonds in the films. The hardness and elasticity of the films then are explained by the assumption, that the solitary double bonds interconnect the nanocrystals in the films, leading to an intergrain boundary adhesion of similar strength as the intragrain diamond cohesion. The results are in good agreement with recent simulations of high-energy grain boundaries.

  8. Nanocrystalline diamond in carbon implanted SiO{sub 2}.

    Tsoi, K.A.; Prawer, S.; Nugent, K.W.; Walker, R. J.; Weiser, P.S. [Melbourne Univ., Parkville, VIC (Australia). School of Physics

    1996-12-31

    Recently, it was reported that nanocrystalline diamond can be produced via laser annealing of a high dose C implanted fused quartz (SiO{sub 2}) substrate. The aim of this investigation is to reproduce this result on higher C{sup +} dose samples and the non-implanted silicon sample, as well as optimise the power range and annealing time for the production of these nanocrystals of diamond. In order to provide a wide range of laser powers the samples were annealed using an Ar ion Raman laser. The resulting annealed spots were analysed using scanning electron microscopy (SEM) and Raman analysis. These techniques are employed to determine the type of bonding produced after laser annealing has occurred. 4 refs., 5 figs.

  9. Spectroellipsometric and ion beam analytical investigation of nanocrystalline diamond layers

    Lohner, T., E-mail: lohner@mfa.kfki.h [Research Institute for Technical Physics and Materials Science, H-1121 Budapest, Konkoly Thege Miklos ut 29-33 (Hungary); Csikvari, P. [Department of Atomic Physics, Budapest University of Technology and Economics, H-1111 Budapest, Budafoki ut 8 (Hungary); Khanh, N.Q. [Research Institute for Technical Physics and Materials Science, H-1121 Budapest, Konkoly Thege Miklos ut 29-33 (Hungary); David, S. [Department of Electronics Technology, Budapest University of Technology and Economics, H-1111 Budapest, Goldmann Gy. ter 3 (Hungary); Horvath, Z.E.; Petrik, P. [Research Institute for Technical Physics and Materials Science, H-1121 Budapest, Konkoly Thege Miklos ut 29-33 (Hungary); Hars, G. [Department of Atomic Physics, Budapest University of Technology and Economics, H-1111 Budapest, Budafoki ut 8 (Hungary)

    2011-02-28

    Optical properties of nanocrystalline and ultrananocrystalline diamond films were studied by ex situ variable angle spectroscopic ellipsometry. The films were prepared by Microwave Plasma Enhanced Chemical Vapor Deposition method. In the experiments Ar, CH{sub 4}, and H{sub 2} gases were used as source gases. Elastic recoil detection analysis was applied to measure the hydrogen content of the deposited layers. Three-layer optical models were constructed for the evaluation of the measured ellipsometric spectra. Besides the Cauchy relation, the effective medium approximation and the Tauc-Lorentz dispersion relation were also used for the modeling of the optical properties of the diamond films. Atomic force microscopy was applied to investigate the surface roughness in function of the deposition conditions.

  10. 1H-15N correlation spectroscopy of nanocrystalline proteins

    Morcombe, Corey R.; Paulson, Eric K.; Gaponenko, Vadim; Byrd, R. Andrew; Zilm, Kurt W.

    2005-01-01

    The limits of resolution that can be obtained in 1 H- 15 N 2D NMR spectroscopy of isotopically enriched nanocrystalline proteins are explored. Combinations of frequency switched Lee-Goldburg (FSLG) decoupling, fast magic angle sample spinning (MAS), and isotopic dilution via deuteration are investigated as methods for narrowing the amide 1 H resonances. Heteronuclear decoupling of 15 N from the 1 H resonances is also studied. Using human ubiquitin as a model system, the best resolution is most easily obtained with uniformly 2 H and 15 N enriched protein where the amides have been exchanged in normal water, MAS at ∼20 kHz, and WALTZ-16 decoupling of the 15 N nuclei. The combination of these techniques results in average 1 H lines of only ∼0.26 ppm full width at half maximum. Techniques for optimizing instrument stability and 15 N decoupling are described for achieving the best possible performance in these experiments

  11. Nanocrystalline diamond in carbon implanted SiO{sub 2}.

    Tsoi, K A; Prawer, S; Nugent, K W; Walker, R J; Weiser, P S [Melbourne Univ., Parkville, VIC (Australia). School of Physics

    1997-12-31

    Recently, it was reported that nanocrystalline diamond can be produced via laser annealing of a high dose C implanted fused quartz (SiO{sub 2}) substrate. The aim of this investigation is to reproduce this result on higher C{sup +} dose samples and the non-implanted silicon sample, as well as optimise the power range and annealing time for the production of these nanocrystals of diamond. In order to provide a wide range of laser powers the samples were annealed using an Ar ion Raman laser. The resulting annealed spots were analysed using scanning electron microscopy (SEM) and Raman analysis. These techniques are employed to determine the type of bonding produced after laser annealing has occurred. 4 refs., 5 figs.

  12. Science at the interface : grain boundaries in nanocrystalline metals.

    Rodriguez, Mark Andrew; Follstaedt, David Martin; Knapp, James Arthur; Brewer, Luke N.; Holm, Elizabeth Ann; Foiles, Stephen Martin; Hattar, Khalid M.; Clark, Blythe B.; Olmsted, David L.; Medlin, Douglas L.

    2009-09-01

    Interfaces are a critical determinant of the full range of materials properties, especially at the nanoscale. Computational and experimental methods developed a comprehensive understanding of nanograin evolution based on a fundamental understanding of internal interfaces in nanocrystalline nickel. It has recently been shown that nanocrystals with a bi-modal grain-size distribution possess a unique combination of high-strength, ductility and wear-resistance. We performed a combined experimental and theoretical investigation of the structure and motion of internal interfaces in nanograined metal and the resulting grain evolution. The properties of grain boundaries are computed for an unprecedented range of boundaries. The presence of roughening transitions in grain boundaries is explored and related to dramatic changes in boundary mobility. Experimental observations show that abnormal grain growth in nanograined materials is unlike conventional scale material in both the level of defects and the formation of unfavored phases. Molecular dynamics simulations address the origins of some of these phenomena.

  13. Chemical synthesis of hexagonal indium nitride nanocrystallines at low temperature

    Wang, Liangbiao; Shen, Qianli; Zhao, Dejian; Lu, Juanjuan; Liu, Weiqiao; Zhang, Junhao; Bao, Keyan; Zhou, Quanfa

    2017-08-01

    In this study, hexagonal indium nitride nanocystallines with high crystallinity have been prepared by the reaction of InCl3·4H2O, sulfur and NaNH2 in an autoclave at 160 °C. The crystal structures and morphologies of the obtained InN sample are characterized by X-ray diffraction and scanning electron microscope. As InCl3·4H2O is substituted by In(NO3)3·4.5H2O, InN nanocrystallines could also be obtained by using the similar method. The photoluminescence spectrum shows that the InN emits a broad peak positioned at 2.3 eV.

  14. Synthesis and characterization of a nanocrystalline diamond aerogel

    Pauzauskie, Peter J.; Crowhurst, Jonathan C.; Worsley, Marcus A.; Laurence, Ted A.; Kilcoyne, A. L. David; Wang, Yinmin; Willey, Trevor M.; Visbeck, Kenneth S.; Fakra, Sirine C.; Evans, William J.; Zaug, Joseph M.; Satcher, Jr., Joe H.

    2011-07-06

    Aerogel materials have myriad scientific and technological applications due to their large intrinsic surface areas and ultralow densities. However, creating a nanodiamond aerogel matrix has remained an outstanding and intriguing challenge. Here we report the high-pressure, high-temperature synthesis of a diamond aerogel from an amorphous carbon aerogel precursor using a laser-heated diamond anvil cell. Neon is used as a chemically inert, near-hydrostatic pressure medium that prevents collapse of the aerogel under pressure by conformally filling the aerogel's void volume. Electron and X-ray spectromicroscopy confirm the aerogel morphology and composition of the nanodiamond matrix. Time-resolved photoluminescence measurements of recovered material reveal the formation of both nitrogen- and silicon- vacancy point-defects, suggesting a broad range of applications for this nanocrystalline diamond aerogel.

  15. Mesoporous nanocrystalline film architecture for capacitive storage devices

    Dunn, Bruce S.; Tolbert, Sarah H.; Wang, John; Brezesinski, Torsten; Gruner, George

    2017-05-16

    A mesoporous, nanocrystalline, metal oxide construct particularly suited for capacitive energy storage that has an architecture with short diffusion path lengths and large surface areas and a method for production are provided. Energy density is substantially increased without compromising the capacitive charge storage kinetics and electrode demonstrates long term cycling stability. Charge storage devices with electrodes using the construct can use three different charge storage mechanisms immersed in an electrolyte: (1) cations can be stored in a thin double layer at the electrode/electrolyte interface (non-faradaic mechanism); (2) cations can interact with the bulk of an electroactive material which then undergoes a redox reaction or phase change, as in conventional batteries (faradaic mechanism); or (3) cations can electrochemically adsorb onto the surface of a material through charge transfer processes (faradaic mechanism).

  16. Electrochromic properties of nanocrystalline MoO3 thin films

    Hsu, C.-S.; Chan, C.-C.; Huang, H.-T.; Peng, C.-H.; Hsu, W.-C.

    2008-01-01

    Electrochromic MoO 3 thin films were prepared by a sol-gel spin-coating technique. The spin-coated films were initially amorphous; they were calcined, producing nanocrystalline MoO 3 thin films. The effects of annealing temperatures ranging from 100 o C to 500 o C were investigated. The electrochemical and electrochromic properties of the films were measured by cyclic voltammetry and by in-situ optical transmittance techniques in 1 M LiClO 4 /propylene carbonate electrolyte. Experimental results showed that the transmittance of MoO 3 thin films heat-treated at 350 o C varied from 80% to 35% at λ = 550 nm (ΔT = ∼ 45%) and from 86% to 21% at λ ≥ 700 nm (ΔT = ∼ 65%) after coloration. Films heat-treated at 350 deg. C exhibited the best electrochromic properties in the present study

  17. In vitro behaviour of nanocrystalline silver-sputtered thin films

    Piedade, A P; Vieira, M T; Martins, A; Silva, F

    2007-01-01

    Silver thin films were deposited with different preferential orientations and special attention was paid to the bioreactivity of the surfaces. The study was essentially focused on the evaluation of the films by x-ray diffraction (XRD), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), electron probe microanalysis (EPMA) and contact angle measurements. The deposited thin films were characterized before and after immersion in S-enriched simulated human plasma in order to estimate the influence of the preferential crystallographic orientation on the in vitro behaviour. Silver thin films with and without (111) preferential crystallographic orientation were deposited by r.f. magnetron sputtering to yield nanocrystalline coatings, high compact structures, very hydrophobic surfaces and low roughness. These properties reduce the chemisorption of reactive species onto the film surface. The in vitro tests indicate that silver thin films can be used as coatings for biomaterials applications

  18. Preparation, characterization and photoluminescence of nanocrystalline calcium molybdate

    Phuruangrat, Anukorn; Thongtem, Titipun; Thongtem, Somchai

    2009-01-01

    Nanocrystalline calcium molybdate was successfully synthesized from Ca(NO 3 ) 2 and Na 2 MoO 4 in ethylene glycol using a microwave radiation method. Body-centered tetragonal structured calcium molybdate with narrow nanosized distribution was detected using XRD, SAED and TEM. A diffraction pattern was also simulated and was found to be in accordance with those obtained from the experiment and JCPDS standard. Raman and FTIR spectra show the Mo-O prominent stretching bands in the [MoO 4 ] 2- tetrahedrons at 879.59 and 743-895 cm -1 , respectively. Photoluminescence emission of CaMoO 4 was detected at 477 nm, caused by the annihilation of a self-trapped excitons from the [MoO 4 ] 2- excited complex.

  19. Torsion-induced magnetoimpedance in nanocrystalline Fe-based wires

    Santos, J.D.; Olivera, J.; Alvarez, P.; Sanchez, T.; Perez, M.J.; Sanchez, M.L.; Gorria, P.; Hernando, B.

    2007-01-01

    The magnetic field influence on the real and imaginary parts of axial-diagonal (ζ zz ) and off-diagonal (ζ φz ) components of the surface magnetoimpedance (MI) tensor has been studied in amorphous and nanocrystalline Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3 wires. Twisted and untwisted wires were annealed at a temperature near to that of primary crystallization. The MI response has been measured at 1MHz and 5mA rms drive current in all the samples. Even though the higher values for both components of the MI tensor are achieved for the untwisted annealed wire, the most interesting features are observed in the torsion annealed wire

  20. Nanocrystalline diamond film as cathode for gas discharge sensors

    Jou, Shyankay, E-mail: sjou@mail.ntust.edu.t [Graduate Institute of Materials Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Huang, Bohr-Ran [Graduate Institute of Electro-Optical Engineering and Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Wu, Meng-Chang [Department of Electronic Engineering, National Yunlin University of Science and Technology, Touliu 640, Taiwan (China)

    2010-05-31

    Nanocrystalline diamond (NCD) film was deposited on a silicon substrate utilizing microwave plasma-enhanced chemical vapor deposition in a mixed flow of methane, hydrogen and argon. The deposited film had a cauliflower-like morphology, and was composed of NCD, carbon clusters and mixed sp{sup 2}- and sp{sup 3}-bonded carbon. Electron field emission (EFE) in vacuum and electrical discharges in Ar, N{sub 2} and O{sub 2} using the NCD film as the cathode were characterized. The turn-on field for EFE and the geometric enhancement factor for the NCD film were 8.5 V/{mu}m and 668, respectively. The breakdown voltages for Ar, N{sub 2} and O{sub 2} increased with pressures from 1.33 x 10{sup 4} Pa to 1.01 x 10{sup 5} Pa, following the right side of the normal Paschen curve.