Chemical stabilization of graphite surfaces

Energy Technology Data Exchange (ETDEWEB)

Bistrika, Alexander A.; Lerner, Michael M.

2018-04-03

Embodiments of a device, or a component of a device, including a stabilized graphite surface, methods of stabilizing graphite surfaces, and uses for the devices or components are disclosed. The device or component includes a surface comprising graphite, and a plurality of haloaryl ions and/or haloalkyl ions bound to at least a portion of the graphite. The ions may be perhaloaryl ions and/or perhaloalkyl ions. In certain embodiments, the ions are perfluorobenzenesulfonate anions. Embodiments of the device or component including stabilized graphite surfaces may maintain a steady-state oxidation or reduction surface current density after being exposed to continuous oxidation conditions for a period of at least 1-100 hours. The device or component is prepared by exposing a graphite-containing surface to an acidic aqueous solution of the ions under oxidizing conditions. The device or component can be exposed in situ to the solution.

Effect of Graphite Doped TiO_2 Nanoparticles on Smoke Degradation

International Nuclear Information System (INIS)

Roshasnorlyza Hazan; Mohamad Shahrizal Md Zain; Natrah Syafiqah Rosli

2016-01-01

Secondhand smoke affects in the same way as regular smoker. The best solution is to purify the air efficiently and effectively. In this study, we were successfully doped TiO_2 nanoparticle with graphite to accelerate the degradation of cigarette smoke. The graphite doped and undoped TiO_2 nanoparticles were prepared from synthetic rutile using alkaline fusion method and their photo catalytic activity were investigated under visible light irradiation. The photo catalytic activity of the TiO_2 nanoparticles was analyzed in terms of their particle size analysis, crystallization and optical band gap. TiO_2 nanoparticle act as photo catalyzer by utilization of light energy to excite electron-hole pairs in smoke degradation processes. With the aided from graphite in TiO_2 nanoparticles, the smoke degradation was accelerate up to 44.4 %. In this case, graphite helps to reduce optical band gap of TiO_2 nanoparticle, thus increasing excitation of electron from valence band to conduction band. (author)

Improvement of thermal shock resistance of isotropic graphite by Ti-doping

International Nuclear Information System (INIS)

Lopez-Galilea, I.; Ordas, N.; Garcia-Rosales, C.; Lindig, S.

2009-01-01

Ti-doped isotropic graphite is a promising candidate material for the strike point area of the ITER divertor due to its reduced chemical erosion by hydrogen bombardment and its high thermal shock resistance, mainly due the catalytic effect of TiC on the graphitization leading to an increase of thermal conductivity and to higher mechanical strength. Several manufacturing parameters such as oxidative stabilization treatment, carbonization cycle, graphitization temperature and dwell time during graphitization have been investigated in order to establish a relationship between these parameters and the final properties.

Improvement of thermal shock resistance of isotropic graphite by Ti-doping

Energy Technology Data Exchange (ETDEWEB)

Lopez-Galilea, I. [Inmaculada Lopez-Galilea, CEIT and Tecnun (University of Navarra), Po de Manuel Lardizabal, 15 E-20018 San Sebastian (Spain)], E-mail: ilopez@ceit.es; Ordas, N.; Garcia-Rosales, C. [Inmaculada Lopez-Galilea, CEIT and Tecnun (University of Navarra), Po de Manuel Lardizabal, 15 E-20018 San Sebastian (Spain); Lindig, S. [Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany)

2009-04-30

Ti-doped isotropic graphite is a promising candidate material for the strike point area of the ITER divertor due to its reduced chemical erosion by hydrogen bombardment and its high thermal shock resistance, mainly due the catalytic effect of TiC on the graphitization leading to an increase of thermal conductivity and to higher mechanical strength. Several manufacturing parameters such as oxidative stabilization treatment, carbonization cycle, graphitization temperature and dwell time during graphitization have been investigated in order to establish a relationship between these parameters and the final properties.

Nitrogen-doped graphene by ball-milling graphite with melamine for energy conversion and storage

International Nuclear Information System (INIS)

Xue, Yuhua; Chen, Hao; Qu, Jia; Dai, Liming

2015-01-01

N-doped graphene was prepared by ball milling of graphite with melamine. It was found that ball-milling reduced the size of graphite particles from 30 to 1 μm and facilitated the exfoliation of the resultant small particles into few-layer N-doped graphene nanosheets under ultrasonication. The as-prepared N-doped graphene nanoplatelets (NGnPs) exhibited a nitrogen content as high as 11.4 at.%, making them attractive as efficient electrode materials in supercapacitors for energy storage and as highly-active metal-free catalysts for oxygen reduction in fuel cells for energy conversion. (paper)

Preparation of nitrogen-doped graphitic carboncages as electrocatalyst for oxygen reduction reaction

International Nuclear Information System (INIS)

Yan, Jing; Meng, Hui; Yu, Wendan; Yuan, Xiaoli; Lin, Worong; Ouyang, Wenpeng; Yuan, Dingsheng

2014-01-01

Nitrogen-doped carbon nanomaterials have been attracted increasing research interests in lithium-O 2 and Zinc-O 2 batteries, ultracapacitors and fuel cells. Herein, nitrogen-doped graphitic carboncages (N-GCs) have been prepared by mesoporous Fe 2 O 3 as a catalyst and lysine as a nitrogen doped carbon source. Due to the catalysis of Fe 2 O 3 , the N-GCs have a high graphitization degree at a low temperature, which is detected by X-ray diffraction and Raman spectrometer. Simultaneously, the heteroatom nitrogen is in-situ doped into carbon network. Therefore, the excellent electrocatalysis performance for oxygen reduction reaction is expected. The electrochemical measurement indicates that The N-GCs for oxygen reduction reaction in O 2 -saturated 0.1 mol L −1 KOH show a four-electron transfer process and exhibit excellent electrocatalytic activity (E ORR = -0.05 V vs. Ag/AgCl) and good stability (i/i 0 = 90% at -0.35 V after 4000 s with a rotation rate of 1600 rpm)

Effects of graphite doping on critical current density and microstructure of MgB2 bulks by an improved Mg-diffusion method

International Nuclear Information System (INIS)

Pan, X.F.; Zhao, Y.; Feng, Y.; Yang, Y.; Cheng, C.H.

2008-01-01

abstract: A series of graphite-doped MgB 2 bulks with high density have been successfully prepared by an improved Mg-diffusion method in ambient pressure. The effects of graphite doping on lattice parameters, T c , J c and microstructure of MgB 2 have been investigated. The results show that compared to the nano-C-doped or CNTs-doped MgB 2 , C is not easy to substitute B in graphite-doped MgB 2 . However, at the same C content, the graphite-doped MgB 2 has a higher J c . At 10 K and self-field, the J c for MgB 1.985 C 0.015 reaches 0.58 MA/cm 2 . For the MgB 1.945 C 0.055 , at 5 K, 7 T and 10 K, 6 T the J c achieves 10,000 A/cm 2 which is two orders of magnitude higher than that for the undoped sample. In addition to improving electron scattering and intergranular connectivity, the unreacted graphite in the graphite-doped MgB 2 is proposed to be responsible to the excellent J c properties of MgB 2 in high fields, due to depressed grain growth and enhanced grain boundary flux pinning

Structural features of the adsorption layer of pentacene on the graphite surface and the PMMA/graphite hybrid surface

Science.gov (United States)

Fadeeva, A. I.; Gorbunov, V. A.; Litunenko, T. A.

2017-08-01

Using the molecular dynamics and the Monte Carlo methods, we have studied the structural features and growth mechanism of the pentacene film on graphite and polymethylmethacrylate /graphite surfaces. Monolayer capacity and molecular area, optimal angles between the pentacene molecules and graphite and PMMA/graphite surfaces as well as the characteristic angles between the neighboring pentacene molecules in the adsorption layer were estimated. It is shown that the orientation of the pentacene molecules in the film is determined by a number of factors, including the surface concentration of the molecules, relief of the surface, presence or absence of the polymer layer and its thickness. The pentacene molecules adsorbed on the graphite surface keep a horizontal position relative to the long axis at any surface coverage/thickness of the film. In the presence of the PMMA layer on the graphite, the increase of the number of pentacene molecules as well as the thickness of the PMMA layer induce the change of molecular orientation from predominantly horizontal to vertical one. The reason for such behavior is supposed to be the roughness of the PMMA surface.

Sulfur-doped graphene via thermal exfoliation of graphite oxide in H2S, SO2, or CS2 gas.

Science.gov (United States)

Poh, Hwee Ling; Šimek, Petr; Sofer, Zdeněk; Pumera, Martin

2013-06-25

Doping of graphene with heteroatoms is an effective way to tailor its properties. Here we describe a simple and scalable method of doping graphene lattice with sulfur atoms during the thermal exfoliation process of graphite oxides. The graphite oxides were first prepared by Staudenmaier, Hofmann, and Hummers methods followed by treatments in hydrogen sulfide, sulfur dioxide, or carbon disulfide. The doped materials were characterized by scanning electron microscopy, high-resolution X-ray photoelectron spectroscopy, combustible elemental analysis, and Raman spectroscopy. The ζ-potential and conductivity of sulfur-doped graphenes were also investigated in this paper. It was found that the level of doping is more dramatically influenced by the type of graphite oxide used rather than the type of sulfur-containing gas used during exfoliation. Resulting sulfur-doped graphenes act as metal-free electrocatalysts for an oxygen reduction reaction.

Effects of graphite doping on critical current density and microstructure of MgB{sub 2} bulks by an improved Mg-diffusion method

Energy Technology Data Exchange (ETDEWEB)

Pan, X.F. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhao, Y. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); School of Materials Science and Engineering, University of New South Wales, Sydney 2052, NSW (Australia)], E-mail: yshao@home.swjtu.edu.cn; Feng, Y. [Northwest Institute for Nonferrous Metal Research, P.O. Box 51, Xi' an, Shaanxi 710016 (China); Western Superconductivity Technology Company, Xi' an (China); Yang, Y. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Cheng, C.H. [Key Laboratory of Magnetic Levitation and Maglev Trains (Ministry of Education of China), Superconductivity R and D Center (SRDC), Mail Stop 165, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); School of Materials Science and Engineering, University of New South Wales, Sydney 2052, NSW (Australia)

2008-09-15

abstract: A series of graphite-doped MgB{sub 2} bulks with high density have been successfully prepared by an improved Mg-diffusion method in ambient pressure. The effects of graphite doping on lattice parameters, T{sub c}, J{sub c} and microstructure of MgB{sub 2} have been investigated. The results show that compared to the nano-C-doped or CNTs-doped MgB{sub 2}, C is not easy to substitute B in graphite-doped MgB{sub 2}. However, at the same C content, the graphite-doped MgB{sub 2} has a higher J{sub c}. At 10 K and self-field, the J{sub c} for MgB{sub 1.985}C{sub 0.015} reaches 0.58 MA/cm{sup 2}. For the MgB{sub 1.945}C{sub 0.055}, at 5 K, 7 T and 10 K, 6 T the J{sub c} achieves 10,000 A/cm{sup 2} which is two orders of magnitude higher than that for the undoped sample. In addition to improving electron scattering and intergranular connectivity, the unreacted graphite in the graphite-doped MgB{sub 2} is proposed to be responsible to the excellent J{sub c} properties of MgB{sub 2} in high fields, due to depressed grain growth and enhanced grain boundary flux pinning.

Hydrogen storage material and process using graphite additive with metal-doped complex hydrides

Science.gov (United States)

Zidan, Ragaiy [Aiken, SC; Ritter, James A [Lexington, SC; Ebner, Armin D [Lexington, SC; Wang, Jun [Columbia, SC; Holland, Charles E [Cayce, SC

2008-06-10

A hydrogen storage material having improved hydrogen absorbtion and desorption kinetics is provided by adding graphite to a complex hydride such as a metal-doped alanate, i.e., NaAlH.sub.4. The incorporation of graphite into the complex hydride significantly enhances the rate of hydrogen absorbtion and desorption and lowers the desorption temperature needed to release stored hydrogen.

N-doped graphene/graphite composite as a conductive agent-free anode material for lithium ion batteries with greatly enhanced electrochemical performance

International Nuclear Information System (INIS)

Guanghui, Wu; Ruiyi, Li; Zaijun, Li; Junkang, Liu; Zhiguo, Gu; Guangli, Wang

2015-01-01

Graphical abstract: The study reported a novel N-doped graphene/graphite anode material for lithium ion batteries. The composite exhibits a largely enhanced electrochemical performance. The study also provides an attractive approach for the fabrication of various graphite-based materials for high power batteries. Display Omitted -- Highlights: • The paper developed a new N-doped graphene/graphite composite for lithium ion battery • The composite contains a three-dimensional graphene framework with rich of open pores • The hybrid offers a higher electrical conductivity when compared with pristine graphite • The hybrid electrode provides a greatly enhanced electrochemical performance • The study provides a prominent approach for fabrication of graphite-based materials -- ABSTRACT: Present graphite anode cannot meet the increasing requirement of electronic devices and electric vehicles due to its low specific capacity, poor cycle stability and low rate capability. The study reported a promising N-doped graphene/graphite composite as a conductive agent-free anode material for lithium ion batteries. Herein, graphite oxide and urea were dispersed in ultrapure water and partly reduced by ascorbic acid. Followed by mixing with graphite and hydrothermal treatment to produce graphene oxide/graphite hydrogel. The hydrogel was dried and finally annealed in Ar/H 2 to obtain N-doped graphene/graphite composite. The result shows that all of graphite particles was dispersed in three-dimensional graphene framework with a rich of open pores. The open pore accelerates the electrolyte transport. The graphene framework works as a conductive agent and graphite particle connector and improves the electron transfer. Electrical conductivity of the composite reaches 5912 S m −1 , which is much better than that of the pristine graphite (4018 S m −1 ). The graphene framework also acts as an expansion absorber in the anodes of lithium ion battery to relieve the large strains

One-step synthesis of shell/core structural boron and nitrogen co-doped graphitic carbon/nanodiamond as efficient electrocatalyst for the oxygen reduction reaction in alkaline media

International Nuclear Information System (INIS)

Liu, Xiaoxu; Wang, Yanhui; Dong, Liang; Chen, Xi; Xin, Guoxiang; Zhang, Yan; Zang, Jianbing

2016-01-01

Shell/core structural boron and nitrogen co-doped graphitic carbon/nanodiamond (BN-C/ND) non-noble metal catalyst has been synthesized by a simple one-step heat-treatment of the mixture with nanodiamond, melamine, boric acid and FeCl 3 . In the process of the surface graphitization of nanodiamond with catalysis by FeCl 3 , B and N atoms from the decomposition of boric acid and melamine were directly introduced into the graphite lattice to form B, N co-doped graphitic carbon shell, while the core still retained the diamond structure. Electrochemical measurements of the BN-C/ND catalyst show much higher electrocatalytic activities towards oxygen reduction reaction (ORR) in alkaline medium than its analogues doped with B or N alone (B-C/ND or N-C/ND). The high catalytic activity of BN-C/ND is attributed to the synergetic effect caused by co-doping of C/ND with B and N. Meanwhile, the BN-C/ND exhibits an excellent electrochemical stability due to the special shell/core structure. There is almost no alteration occurred in the cyclic voltammetry measurements for BN-C/ND before and after 5000 cycles. All experimental results prove that the BN-C/ND may be exploited as a potentially efficient and inexpensive non-noble metal cathode catalyst for ORR to substitute Pt-based catalysts in fuel cells.

Superhydrophilic graphite surfaces and water-dispersible graphite colloids by electrochemical exfoliation

Energy Technology Data Exchange (ETDEWEB)

Li, Yueh-Feng [Department of Chemical and Materials Engineering, National Central University, Jhongli, 320 Taiwan (China); Chen, Shih-Ming; Lai, Wei-Hao [Materials and Chemical Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu, 31040 Taiwan (China); Sheng, Yu-Jane [Department of Chemical Engineering, National Taiwan University, Taipei, 106 Taiwan (China); Tsao, Heng-Kwong [Department of Chemical and Materials Engineering, Department of Physics, National Central University, Jhongli, 320 Taiwan (China)

2013-08-14

Superhydrophilic graphite surfaces and water-dispersible graphite colloids are obtained by electrochemical exfoliation with hydrophobic graphite electrodes. Such counterintuitive characteristics are caused by partial oxidation and investigated by examining both graphite electrodes and exfoliated particles after electrolysis. The extent of surface oxidation can be explored through contact angle measurement, scanning electron microscope, electrical sheet resistance, x-ray photoelectron spectroscopy, zeta-potential analyzer, thermogravimetric analysis, UV-visible, and Raman spectroscopy. The degree of wettability of the graphite anode can be altered by the electrolytic current and time. The water contact angle declines generally with increasing the electrolytic current or time. After a sufficient time, the graphite anode becomes superhydrophilic and its hydrophobicity can be recovered by peeling with adhesive tape. This consequence reveals that the anodic graphite is oxidized by oxygen bubbles but the oxidation just occurs at the outer layers of the graphite sheet. Moreover, the characteristics of oxidation revealed by UV peak shift, peak ratio between D and G bands, and negative zeta-potential indicate the presence of graphite oxide on the outer shell of the exfoliated colloids. However, thermogravimetric analysis for the extent of decomposition of oxygen functional groups verifies that the amount of oxygen groups is significantly less than that of graphite oxide prepared via Hummer method. The structure of this partially oxidized graphite may consist of a graphite core covered with an oxidized shell. The properties of the exfoliated colloids are also influenced by pH of the electrolytic solution. As pH is increased, the extent of oxidation descends and the thickness of oxidized shell decreases. Those results reveal that the degree of oxidation of exfoliated nanoparticles can be manipulated simply by controlling pH.

Effects of Oxidation on Oxidation-Resistant Graphite

Energy Technology Data Exchange (ETDEWEB)

Windes, William [Idaho National Lab. (INL), Idaho Falls, ID (United States); Smith, Rebecca [Idaho National Lab. (INL), Idaho Falls, ID (United States); Carroll, Mark [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2015-05-01

The Advanced Reactor Technology (ART) Graphite Research and Development Program is investigating doped nuclear graphite grades that exhibit oxidation resistance through the formation of protective oxides on the surface of the graphite material. In the unlikely event of an oxygen ingress accident, graphite components within the VHTR core region are anticipated to oxidize so long as the oxygen continues to enter the hot core region and the core temperatures remain above 400°C. For the most serious air-ingress accident which persists over several hours or days the continued oxidation can result in significant structural damage to the core. Reducing the oxidation rate of the graphite core material during any air-ingress accident would mitigate the structural effects and keep the core intact. Previous air oxidation testing of nuclear-grade graphite doped with varying levels of boron-carbide (B4C) at a nominal 739°C was conducted for a limited number of doped specimens demonstrating a dramatic reduction in oxidation rate for the boronated graphite grade. This report summarizes the conclusions from this small scoping study by determining the effects of oxidation on the mechanical strength resulting from oxidation of boronated and unboronated graphite to a 10% mass loss level. While the B4C additive did reduce mechanical strength loss during oxidation, adding B4C dopants to a level of 3.5% or more reduced the as-fabricated compressive strength nearly 50%. This effectively minimized any benefits realized from the protective film formed on the boronated grades. Future work to infuse different graphite grades with silicon- and boron-doped material as a post-machining conditioning step for nuclear components is discussed as a potential solution for these challenges in this report.

Interaction of boron with graphite: A van der Waals density functional study

International Nuclear Information System (INIS)

Liu, Juan; Wang, Chen; Liang, Tongxiang; Lai, Wensheng

2016-01-01

Highlights: • A van der Waals density-functional approach is applied to study the interaction of boron with graphite. • VdW-DF functionals give fair agreement of crystal parameters with experiments. • The π electron approaches boron while adsorbing on graphite surface. • The hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. • PBE cannot describe the interstitial boron in graphite because of the ignoring binding of graphite sheets. - Abstract: Boron doping has been widely investigated to improve oxidation resistance of graphite. In this work the interaction of boron with graphite is investigated by a van der Waals density-functional approach (vdW-DF). The traditional density-functional theory (DFT) is well accounted for the binding in boron-substituted graphite. However, to investigate the boron atom on graphite surface and the interstitial impurities require use of a description of graphite interlayer binding. Traditional DFT cannot describe the vdW physics, for instance, GGA calculations show no relevant binding between graphite sheets. LDA shows some binding, but they fail to provide an accurate account of vdW forces. In this paper, we compare the calculation results of graphite lattice constant and cohesive energy by several functionals, it shows that vdW-DF such as two optimized functionals optB88-vdW and optB86b-vdW give much improved results than traditional DFT. The vdW-DF approach is then applied to study the interaction of boron with graphite. Boron adsorption, substitution, and intercalation are discussed in terms of structural parameters and electronic structures. When adsorbing on graphite surface, boron behaves as π electron acceptor. The π electron approaches boron atom because of more electropositive of boron than carbon. For substitution situation, the hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. The B-doped graphite system with the hole has less

Interaction of boron with graphite: A van der Waals density functional study

Energy Technology Data Exchange (ETDEWEB)

Liu, Juan; Wang, Chen [Beijing Key Lab of Fine Ceramics, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Liang, Tongxiang, E-mail: txliang@tsinghua.edu.cn [State Key Lab of New Ceramic and Fine Processing, Tsinghua University, Beijing 100084 (China); Lai, Wensheng [Advanced Material Laboratory, School of Materials Science & Engineering, Tsinghua University, Beijing, 100084 (China)

2016-08-30

Highlights: • A van der Waals density-functional approach is applied to study the interaction of boron with graphite. • VdW-DF functionals give fair agreement of crystal parameters with experiments. • The π electron approaches boron while adsorbing on graphite surface. • The hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. • PBE cannot describe the interstitial boron in graphite because of the ignoring binding of graphite sheets. - Abstract: Boron doping has been widely investigated to improve oxidation resistance of graphite. In this work the interaction of boron with graphite is investigated by a van der Waals density-functional approach (vdW-DF). The traditional density-functional theory (DFT) is well accounted for the binding in boron-substituted graphite. However, to investigate the boron atom on graphite surface and the interstitial impurities require use of a description of graphite interlayer binding. Traditional DFT cannot describe the vdW physics, for instance, GGA calculations show no relevant binding between graphite sheets. LDA shows some binding, but they fail to provide an accurate account of vdW forces. In this paper, we compare the calculation results of graphite lattice constant and cohesive energy by several functionals, it shows that vdW-DF such as two optimized functionals optB88-vdW and optB86b-vdW give much improved results than traditional DFT. The vdW-DF approach is then applied to study the interaction of boron with graphite. Boron adsorption, substitution, and intercalation are discussed in terms of structural parameters and electronic structures. When adsorbing on graphite surface, boron behaves as π electron acceptor. The π electron approaches boron atom because of more electropositive of boron than carbon. For substitution situation, the hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. The B-doped graphite system with the hole has less

On the defect structure due to low energy ion bombardment of graphite

Science.gov (United States)

Marton, D.; Bu, H.; Boyd, K. J.; Todorov, S. S.; Al-Bayati, A. H.; Rabalais, J. W.

1995-03-01

Graphite surfaces cleaved perpendicular to the c axis have been irradiated with low doses of Ar + ions at 50 eV kinetic energy and perpendicular incidence. Scanning tunneling micrographs (STM) of these irradiated surfaces exhibited dome-like features as well as point defects. These dome-like features retain undisturbed graphite periodicity. This finding is attributed to the stopping of ions between the first and second graphite sheets. The possibility of doping semiconductors at extremely shallow depths is raised.

Electronic structure of incident carbon ions on a graphite surface

International Nuclear Information System (INIS)

Kiuchi, Masato; Takeuchi, Takae; Yamamoto, Masao.

1997-01-01

The electronic structure of an incident carbon ion on a graphite surface is discussed on the basis of ab initio molecular orbital calculations. A carbon cation forms a covalent bond with the graphite, and a carbon nonion is attracted to the graphite surface through van der Waals interaction. A carbon anion has no stable state on a graphite surface. The charge effects of incident ions become clear upon detailed examination of the electronic structure. (author)

Contact Angle Hysteresis on Graphene Surfaces and Hysteresis-free Behavior on Oil-infused Graphite Surfaces

Energy Technology Data Exchange (ETDEWEB)

Wu, Cyuan-Jhang; Li, Yueh-Feng [Department of Chemical and Materials Engineering, National Central University, Jhongli 320, Taiwan (China); Woon, Wei-Yen [Department of Physics, National Central University, Jhongli 320, Taiwan (China); Sheng, Yu-Jane, E-mail: yjsheng@ntu.edu.tw [Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan (China); Tsao, Heng-Kwong, E-mail: hktsao@cc.ncu.edu.tw [Department of Chemical and Materials Engineering, National Central University, Jhongli 320, Taiwan (China); Department of Physics, National Central University, Jhongli 320, Taiwan (China)

2016-11-01

Highlights: • Contact angle hysteresis(CAH) on four graphitic surfacesisinvestigated. • The hysteresis loopof water drops on the polished graphite sheetshowsparticularly small receding contact angle. • The significant CAH observed on CVD graphene and highly oriented pyrolytic graphite is attributed mainly to adhesion hysteresis. • An oil-infused surface of a graphite sheet is produced by imbibition of hexadecane into its porous structure. • The hysteresis-free property for water drops on such a surface is examined and quantitatively explained. - Abstract: Contact angle hysteresis (CAH) on graphitic surfaces, including chemical vapor deposition (CVD) graphene, reduced electrophoretic deposition (EPD) graphene, highly oriented pyrolytic graphite (HOPG), and polished graphite sheet, has been investigated. The hysteresis loops of water drops on the first three samples are similar but the receding contact angle is particularly small for the polished graphite sheet.The significant CAH observed on CVD graphene and HOPG associated with atom-scale roughness has to be attributed mainly to adhesion hysteresis (surface relaxation), instead of roughness or defects.The difference of the wetting behavior among those four graphitic samples has been further demonstrated by hexadecane drops. On the surface of HOPG or CVD graphene,the contact line expands continuously with time, indicating total wetting for which the contact angle does not exist and contact line pinning disappears. In contrast, on the surface of reduced EPD graphene, spontaneous spreading is halted by spikes on it and partial wetting with small contact angle (θ≈4°) is obtained. On the surface of polished graphite sheet, the superlipophilicity and porous structure are demonstrated by imbibition and capillary rise of hexadecane. Consequently, an oil-infused graphite surface can be fabricated and the ultralow CAH of water (∆θ≈2°) is achieved.

Nitrogen-doped graphene: effect of graphite oxide precursors and nitrogen content on the electrochemical sensing properties.

Science.gov (United States)

Megawati, Monica; Chua, Chun Kiang; Sofer, Zdenek; Klímová, Kateřina; Pumera, Martin

2017-06-21

Graphene, produced via chemical methods, has been widely applied for electrochemical sensing due to its structural and electrochemical properties as well as its ease of production in large quantity. While nitrogen-doped graphenes are widely studied materials, the literature showing an effect of graphene oxide preparation methods on nitrogen quantity and chemical states as well as on defects and, in turn, on electrochemical sensing is non-existent. In this study, the properties of nitrogen-doped graphene materials, prepared via hydrothermal synthesis using graphite oxide produced by various classical methods using permanganate or chlorate oxidants Staudenmaier, Hummers, Hofmann and Brodie oxidation methods, were studied; the resulting nitrogen-doped graphene oxides were labeled as ST-GO, HU-GO, HO-GO and BR-GO, respectively. The electrochemical oxidation of biomolecules, such as ascorbic acid, uric acid, dopamine, nicotinamide adenine nucleotide and DNA free bases, was carried out using cyclic voltammetry and differential pulse voltammetry techniques. The nitrogen content in doped graphene oxides increased in the order ST-GO graphene followed this trend, as shown in the cyclic voltammograms. This is a very important finding that provides insight into the electrocatalytic effect of N-doped graphene. The nitrogen-doped graphene materials exhibited improved sensitivity over bare glassy carbon for ascorbic acid, uric acid and dopamine detection. These studies will enhance our understanding of the effects of graphite oxide precursors on the electrochemical sensing properties of nitrogen-doped graphene materials.

STS Observations of Landau Levels at Graphite Surfaces

OpenAIRE

Matsui, T.; Kambara, H.; Niimi, Y.; Tagami, K.; Tsukada, M.; Fukuyama, Hiroshi

2004-01-01

Scanning tunneling spectroscopy measurements were made on surfaces of two different kinds of graphite samples, Kish graphite and highly oriented pyrolytic graphite (HOPG), at very low temperatures and in high magnetic fields. We observed a series of peaks in the tunnel spectra, which grow with increasing field, both at positive and negative bias voltages. These are associated with Landau quantization of the quasi two-dimensional electrons and holes in graphite in magnetic fields perpendicular...

Surface analysis of graphite fiber reinforced polyimide composites

Science.gov (United States)

Messick, D. L.; Progar, D. J.; Wightman, J. P.

1983-01-01

Several techniques have been used to establish the effect of different surface pretreatments on graphite-polyimide composites. Composites were prepared from Celion 6000 graphite fibers and the polyimide LARC-160. Pretreatments included mechanical abrasion, chemical etching and light irradiation. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used in the analysis. Contact angle of five different liquids of varying surface tensions were measured on the composites. SEM results showed polymer-rich peaks and polymer-poor valleys conforming to the pattern of the release cloth used durng fabrication. Mechanically treated and light irradiated samples showed varying degrees of polymer peak removal, with some degradation down to the graphite fibers. Minimal changes in surface topography were observed on concentrations of surface fluorine even after pretreatment. The light irradiation pretreatment was most effective at reducing surface fluorine concentrations whereas chemical pretreatment was the least effective. Critical surface tensions correlated directly with the surface fluorine to carbon ratios as calculated from XPS.

Fabrication and electrical resistivity of Mo-doped VO2 thin films coated on graphite conductive plates by a sol-gel method

Energy Technology Data Exchange (ETDEWEB)

Choi, W.; Jung, H.M.; Um, S. [Hanyang Univ., Seoul (Korea, Republic of). School of Mechanical Engineering

2008-07-01

Vanadium oxides (VO2) can be used in optical devices, thermochromic smart windows and sensors. This paper reported on a study in which vanadium pentoxide (V2O5) powder was prepared and mixed with Molybdenum Oxides (MoO3) to form Mo-doped and -undoped VO2 thin films by a sol-gel method on graphite conductive substrates. The micro-structure and chemical compositions of the Mo-doped and -undoped VO2 thin films was investigated using X-Ray diffraction and scanning electron microscopy. Changes in electrical resistivity were measured as a function of the stoichiometric compositions between vanadium and molybdenum. In this study. Mo-doped and -undoped VO2 thin films showed the typical metal to insulator transition (MIT), where temperature range could be adjusted by modifying the dopant atomic ratio. The through-plane substrate structure of the Mo-doped layer influences the electrical resistivity of the graphite substrate. As the amount of the molybdenum increases, the electrical resistivity of the graphite conductive substrate decreases in the lower temperature range below the freezing point of water. The experimental results showed that if carefully controlled, thermal dissipation of VO2 thin films can be used as a self-heating source to melt frozen water with the electrical current flowing through the graphite substrate. 3 refs., 3 figs.

Surface area-burnoff correlation for the steam--graphite reaction

International Nuclear Information System (INIS)

Stark, W.A. Jr.; Malinauskas, A.P.

1977-01-01

The oxidation of core graphite by steam of air represents a problem area of significant concern in safety analyses for the high temperature gas cooled reactor (HTGR). Core and core-support graphite integrity and strength deteriorate with oxidation of the graphite, and oxidation furthermore could affect the rate of fission product release under upset conditions. Consequently, modeling of core response during steam or air ingress conditions requires an expression for the rate of graphite interaction with those impurities. The steam--graphite reaction in particular is a complex interaction of mass transport within the graphite with chemi-sorption and reaction on accessible surfaces; experimental results from graphite to graphite are highly variable, and the description of the reaction is not yet completely consistent. A simple etch pit model relating surface area to burnoff has been proposed and shown to provide reasonable correlation with experimental data obtained from steam oxidation studies of nuclear grade H-327 graphite. Unaccounted differences between theory and experiment arise at burnoffs exceeding 3 to 5 percent. The model, while not complete nor comprehensive, is consistent with experimental observations of graphite oxidation by O 2 (air), CO 2 , or H 2 O, and could have some utility in safety analysis

Nitrogen-doped graphitic hierarchically porous carbon nanofibers obtained via bimetallic-coordination organic framework modification and their application in supercapacitors.

Science.gov (United States)

Yao, Yuechao; Liu, Peng; Li, Xiaoyan; Zeng, Shaozhong; Lan, Tongbin; Huang, Haitao; Zeng, Xierong; Zou, Jizhao

2018-05-17

Herein, N-doped graphitic hierarchically porous carbon nanofibers (NGHPCF) were prepared by electrospinning the composite of bimetallic-coordination metal-organic frameworks and polyacrylonitrile, followed by a pyrolysis and acid wash process. Control over the N content, specific surface area, and degree of graphitization of NGHPCF materials has been realized by adjusting the Co/Zn metal coordination content as well as the pyrolysis temperature. The obtained NGHPCF with a high specific surface area (623 m2 g-1) and nitrogen content (13.83 wt%) exhibit a high capacitance of 326 F g-1 at 0.5 A g-1. In addition, the capacitance of 170 F g-1 is still maintained at a high current density (40 A g-1); this indicates a high capacitance retention capability. Furthermore, a superb energy density (9.61 W h kg-1) is obtained with a high power density (62.4 W kg-1) using an organic electrolyte. These results fully illustrate that the prepared NGHPCF binder-free electrodes are promising candidates for high-performance supercapacitors.

N-doping effectively enhances the adsorption capacity of biochar for heavy metal ions from aqueous solution.

Science.gov (United States)

Yu, Wenchao; Lian, Fei; Cui, Guannan; Liu, Zhongqi

2018-02-01

N-doping was successfully employed to improve the adsorption capacity of biochar (BC) for Cu 2+ and Cd 2+ by direct annealing of crop straws in NH 3 . The surface N content of BC increased more than 20 times by N-doping; meanwhile the content of oxidized-N was gradually diminished but graphitic-N was formed and increased with increasing annealing temperature and duration time. After N-doping, a high graphitic-N percentage (46.4%) and S BET (418.7 m 2 /g) can be achieved for BC. As a result, the N-doped BC exhibited an excellent adsorption capacity for Cu 2+ (1.63 mmol g -1 ) and Cd 2+ (1.76 mmol g -1 ), which was up to 4.0 times higher than that of the original BC. Furthermore, the adsorption performance of the N-doped BC remained stable even at acidic conditions. A positive correlation can be found between adsorption capacity with the graphitic N content on BC surface. The surface chemistry of N-doped BC before and after the heavy metal ions adsorption was carefully examined by XPS and FTIR techniques, which indicated that the adsorption mechanisms mainly included cation-π bonding and complexation with graphitic-N and hydroxyl groups of carbon surfaces. Copyright © 2017 Elsevier Ltd. All rights reserved.

Ionic liquids at the surface of graphite: Wettability and structure

Science.gov (United States)

Bordes, Emilie; Douce, Laurent; Quitevis, Edward L.; Pádua, Agílio A. H.; Costa Gomes, Margarida

2018-05-01

The aim of this work is to provide a better understanding of the interface between graphite and different molecular and ionic liquids. Experimental measurements of the liquid surface tension and of the graphite-liquid contact angle for sixteen ionic liquids and three molecular liquids are reported. These experimental values allowed the calculation of the solid/liquid interfacial energy that varies, for the ionic liquids studied, between 14.5 mN m-1 for 1-ethyl-3-methylimidazolium dicyanamide and 37.8 mN m-1 for 3-dodecyl-1-(naphthalen-1-yl)-1H-imidazol-3-ium tetrafluoroborate. Imidazolium-based ionic liquids with large alkyl side-chains or functionalized with benzyl groups seem to interact more favourably with freshly peeled graphite surfaces. Even if the interfacial energy seems a good descriptor to assess the affinity of a liquid for a carbon-based solid material, we conclude that both the surface tension of the liquid and the contact angle between the liquid and the solid can be significant. Molecular dynamics simulations were used to investigate the ordering of the ions near the graphite surface. We conclude that the presence of large alkyl side-chains in the cations increases the ordering of ions at the graphite surface. Benzyl functional groups in the cations lead to a large affinity towards the graphite surface.

Laser surface graphitization to control friction of diamond-like carbon coatings

Science.gov (United States)

Komlenok, Maxim S.; Kononenko, Vitaly V.; Zavedeev, Evgeny V.; Frolov, Vadim D.; Arutyunyan, Natalia R.; Chouprik, Anastasia A.; Baturin, Andrey S.; Scheibe, Hans-Joachim; Shupegin, Mikhail L.; Pimenov, Sergei M.

2015-11-01

To study the role of laser surface graphitization in the friction behavior of laser-patterned diamond-like carbon (DLC) films, we apply the scanning probe microscopy (SPM) in the lateral force mode (LFM) which allows to obtain simultaneously the lateral force and topography images and to determine local friction levels in laser-irradiated and original surface areas. Based on this approach in the paper, we report on (1) laser surface microstructuring of hydrogenated a-C:H and hydrogen-free ta-C films in the regime of surface graphitization using UV laser pulses of 20-ns duration and (2) correlation between the structure and friction properties of the laser-patterned DLC surface on micro/nanoscale using SPM/LFM technique. The SPM/LFM data obtained for the surface relief gratings of graphitized microstructures have evidenced lower friction forces in the laser-graphitized regions. For the hydrogenated DLC films, the reversible frictional behavior of the laser-graphitized micropatterns is found to take place during LFM imaging at different temperatures (20 and 120 °C) in ambient air. It is revealed that the lateral force distribution in the laser-graphitized areas is shifted to higher friction levels (relative to that of the unirradiated surface) at temperature 120 °C and returned back to the lower friction during the sample cooling to 20 °C, thus confirming an influence of adsorbed water layers on the nanofriction properties of laser-graphitized micropatterns on the film surface.

Formation of Ag nanowires on graphite stepped surfaces. A DFT study

Science.gov (United States)

Ambrusi, Rubén E.; García, Silvana G.; Pronsato, María E.

2015-01-01

We investigate the feasibility of obtaining silver nanowires on graphite stepped surfaces theoretically, using density functional theory calculations. Three layer slabs are used to model graphite surfaces with and without defects. Adsorption energies for Ag atoms on graphite surfaces were calculated showing the preference of Ag adatoms to locate on the steps, forming linear structures like nanowires. An analysis of the charge densities and projected densities of states for different structures is also performed.

Ultrathin nitrogen-doped graphitized carbon shell encapsulating CoRu bimetallic nanoparticles for enhanced electrocatalytic hydrogen evolution

Science.gov (United States)

Xu, You; Li, Yinghao; Yin, Shuli; Yu, Hongjie; Xue, Hairong; Li, Xiaonian; Wang, Hongjing; Wang, Liang

2018-06-01

Design of highly active and cost-effective electrocatalysts is very important for the generation of hydrogen by electrochemical water-splitting. Herein, we report the fabrication of ultrathin nitrogen-doped graphitized carbon shell encapsulating CoRu bimetallic nanoparticles (CoRu@NCs) and demonstrate their promising feasibility for efficiently catalyzing the hydrogen evolution reaction (HER) over a wide pH range. The resultant CoRu@NC nanohybrids possess an alloy–carbon core–shell structure with encapsulated low-ruthenium-content CoRu bimetallic alloy nanoparticles (10–30 nm) as the core and ultrathin nitrogen-doped graphitized carbon layers (2–6 layers) as the shell. Remarkably, the optimized catalyst (CoRu@NC-2 sample) with a Ru content as low as 2.04 wt% shows superior catalytic activity and excellent durability for HER in acidic, neutral, and alkaline conditions. This work offers a new method for the design and synthesis of non-platium-based electrocatalysts for HER in all-pH.

Reactivity of lithium exposed graphite surface

International Nuclear Information System (INIS)

Harilal, S.S.; Allain, J.P.; Hassanein, A.; Hendricks, M.R.; Nieto-Perez, M.

2009-01-01

Lithium as a plasma-facing component has many attractive features in fusion devices. We investigated chemical properties of the lithiated graphite surfaces during deposition using X-ray photoelectron spectroscopy and low-energy ion scattering spectroscopy. In this study we try to address some of the known issues during lithium deposition, viz., the chemical state of lithium on graphite substrate, oxide layer formation mechanisms, Li passivation effects over time, and chemical change during exposure of the sample to ambient air. X-ray photoelectron studies indicate changes in the chemical composition with various thickness of lithium on graphite during deposition. An oxide layer formation is noticed during lithium deposition even though all the experiments were performed in ultrahigh vacuum. The metal oxide is immediately transformed into carbonate when the deposited sample is exposed to air.

Phonon scattering in graphite

International Nuclear Information System (INIS)

Wagner, P.

1976-04-01

Effects on graphite thermal conductivities due to controlled alterations of the graphite structure by impurity addition, porosity, and neutron irradiation are shown to be consistent with the phonon-scattering formulation 1/l = Σ/sub i equals 1/sup/n/ 1/l/sub i/. Observed temperature effects on these doped and irradiated graphites are also explained by this mechanism

Enhanced oxidation resistance of carbon fiber reinforced lithium aluminosilicate composites by boron doping

International Nuclear Information System (INIS)

Xia, Long; Jin, Feng; Zhang, Tao; Hu, Xueting; Wu, Songsong; Wen, Guangwu

2015-01-01

Highlights: • C f /LAS composites exhibit enhanced oxidation resistance by boron doping. • Boron doping is beneficial to the improvement of graphitization degree of carbon fibers. • Graphitization of carbon fibers together with the decrease of viscosity of LAS matrix is responsible to the enhancement of oxidation resistance of C f /LAS composites. - Abstract: Carbon fiber reinforced lithium aluminosilicate matrix composites (C f /LAS) modified with boron doping were fabricated and oxidized for 1 h in static air. Weight loss, residual strength and microstructure were analyzed. The results indicate that boron doping has a remarkable effect on improving the oxidation resistance for C f /LAS. The synergism of low viscosity of LAS matrix at high temperature and formation of graphite crystals on the surface of carbon fibers, is responsible for excellent oxidation resistance of the boron doped C f /LAS.

Doped graphene supercapacitors

Science.gov (United States)

Ashok Kumar, Nanjundan; Baek, Jong-Beom

2015-12-01

Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed.

Doped graphene supercapacitors

International Nuclear Information System (INIS)

Kumar, Nanjundan Ashok; Baek, Jong-Beom

2015-01-01

Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed. (topical review)

Effect of reacting surface density on the overall graphite oxidation rate

International Nuclear Information System (INIS)

Oh, Chang; Kim, Eung; Lim, Jong; Schultz, Richard; Petti, David

2009-01-01

Graphite oxidation in an air-ingress accident is presently a very important issue for the reactor safety of the very high temperature gas cooled-reactor (VHTR), the concept of the next generation nuclear plant (NGNP) because of its potential problems such as mechanical degradation of the supporting graphite in the lower plenum of the VHTR might lead to core collapse if the countermeasure is taken carefully. The oxidation process of graphite has known to be affected by various factors, including temperature, pressure, oxygen concentration, types of graphite, graphite shape and size, flow distribution, etc. However, our recent study reveals that the internal pore characteristics play very important roles in the overall graphite oxidation rate. One of the main issues regarding graphite oxidation is the potential core collapse problem that may occur following the degradation of graphite mechanical strength. In analyzing this phenomenon, it is very important to understand the relationship between the degree of oxidization and strength degradation. In addition, the change of oxidation rate by graphite oxidation degree characterization by burn-off (ratio of the oxidized graphite density to the original density) should be quantified because graphite strength degradation is followed by graphite density decrease, which highly affects oxidation rates and patterns. Because the density change is proportional to the internal pore surface area, they should be quantified in advance. In order to understand the above issues, the following experiments were performed: (1) Experiment on the fracture of the oxidized graphite and validation of the previous correlations, (2) Experiment on the change of oxidation rate using graphite density and data collection, (3) Measure the BET surface area of the graphite. The experiments were performed using H451 (Great Lakes Carbon Corporation) and IG-110 (Toyo Tanso Co., Ltd) graphite. The reason for the use of those graphite materials is because

Roughness analysis of graphite surfaces of casting elements

Directory of Open Access Journals (Sweden)

M. Wieczorowski

2010-01-01

Full Text Available In the paper profilometric measurements of graphite casting elements were described. Basic topics necessary to assess roughness of their surfaces and influence of asperities on various properties related to manufacturing and use were discussed. Stylus profilometer technique of surface irregularities measurements including its limits resulting from pickup geometry and its contact with measured object were ana-lyzed. Working principle of tactile profilometer and phenomena taking place during movement of a probe on a measured surface were shown. One of the important aspects is a flight phenomenon, which means movement of a pickup without contact with a surface during inspection resulting from too high scanning speed. results of comparison research for graphite elements of new and used mould and pin composing a set were presented. Using some surface roughness, waviness and primary profile parameters (arithmetical mean of roughness profile heights Ra, biggest roughness profile height Rz, maximum primary profile height Pt as well as maximum waviness profile height Wt a possibility of using surface asperities parameters as a measure of wear of chill graphite elements was proved. The most often applied parameter is Ra, but with a help of parameters from W and P family it was shown, that big changes occur not only for roughness but also for other components of surface irregularities.

Delamination in surface plies of graphite/epoxy caused by the edge trimming process

Science.gov (United States)

Colligan, K.; Ramulu, M.

Delamination in surface plies of graphite/epoxy laminates caused by edge trimming using polycrystalline diamond (PCD) and carbide cutters is investigated. The effect of several machining variables on formation of delaminations in the surface plies of a graphite fiber reinforced composite material is presented. Machining tests were performed to assess the impact of cutter geometry, feedrate, rotation direction, and graphite fiber orientation. Three typical delamination modes were observed and documented. Feedrate was found to have a significant effect on surface ply delamination in graphite/epoxy composite materials.

Effect of various dopant elements on primary graphite growth

International Nuclear Information System (INIS)

Valle, N; Theuwissen, K; Lacaze, J; Sertucha, J

2012-01-01

Five spheroidal graphite cast irons were investigated, a usual ferritic grade and four pearlitic alloys containing Cu and doped with Sb, Sn and Ti. These alloys were remelted in a graphite crucible, leading to volatilization of the magnesium added for spheroidization and to carbon saturation of the liquid. The alloys were then cooled down and maintained at a temperature above the eutectic temperature. During this step, primary graphite could develop showing various features depending on the doping elements added. The largest effects were that of Ti which greatly reduces graphite nucleation and growth, and that of Sb which leads to rounded agglomerates instead of lamellar graphite. The samples have been investigated with secondary ion mass spectrometry to enlighten distribution of elements in primary graphite. SIMS analysis showed almost even distribution of elements, including Mg and Al (from the inoculant) in the ferritic grade, while uneven distribution was evident in all doped alloys. Investigations are going on to clarify if the uneven distribution is associated with structural defects in the graphite precipitates.

Surface coating of graphite pebbles for Korean HCCR TBM

Energy Technology Data Exchange (ETDEWEB)

Lee, Youngmin [National Fusion Research Institute, Daejeon (Korea, Republic of); Yun, Young-Hoon, E-mail: yunh2@dsu.ac.kr [Dongshin University, Naju (Korea, Republic of); Park, Yi-Hyun; Ahn, Mu-Young; Cho, Seungyon [National Fusion Research Institute, Daejeon (Korea, Republic of)

2014-10-15

Highlights: • A CVR-SiC coating was successfully formed on graphite pebbles for neutron reflector. • Dense and fine-grained surface morphologies of the SiC coatings were observed. • Oxidation resistance of the CVR-SiC-coated graphite pebbles was improved. - Abstract: The new concept of the recently modified Helium-Cooled Ceramic Reflector (HCCR) Test Blanket Module (TBM) is to adopt a graphite reflector in the form of a pebble bed. A protective SiC coating is applied to the graphite pebbles to prohibit their reaction with steam or air as well as dust generation during TBM operation. In this research, the chemical vapor reaction (CVR) method was applied to fabricate SiC-coated graphite pebbles in a silica source. Relatively dense CVR-SiC coating was successfully formed on the graphite pebbles through the reduction of the graphite phase with SiO gas that was simply created from the silica source at 1850 °C (2 h). The microstructural features, XRD patterns, pore-size distribution and oxidation behavior of the SiC-coated graphite pebbles were investigated. To develop the practical process, which will be applied for mass production hereafter, a novel alternative method was applied to form the layer of SiC coating on the graphite pebbles over the silica source.

Surface coating of graphite pebbles for Korean HCCR TBM

International Nuclear Information System (INIS)

Lee, Youngmin; Yun, Young-Hoon; Park, Yi-Hyun; Ahn, Mu-Young; Cho, Seungyon

2014-01-01

Highlights: • A CVR-SiC coating was successfully formed on graphite pebbles for neutron reflector. • Dense and fine-grained surface morphologies of the SiC coatings were observed. • Oxidation resistance of the CVR-SiC-coated graphite pebbles was improved. - Abstract: The new concept of the recently modified Helium-Cooled Ceramic Reflector (HCCR) Test Blanket Module (TBM) is to adopt a graphite reflector in the form of a pebble bed. A protective SiC coating is applied to the graphite pebbles to prohibit their reaction with steam or air as well as dust generation during TBM operation. In this research, the chemical vapor reaction (CVR) method was applied to fabricate SiC-coated graphite pebbles in a silica source. Relatively dense CVR-SiC coating was successfully formed on the graphite pebbles through the reduction of the graphite phase with SiO gas that was simply created from the silica source at 1850 °C (2 h). The microstructural features, XRD patterns, pore-size distribution and oxidation behavior of the SiC-coated graphite pebbles were investigated. To develop the practical process, which will be applied for mass production hereafter, a novel alternative method was applied to form the layer of SiC coating on the graphite pebbles over the silica source

Heavily Graphitic-Nitrogen Self-doped High-porosity Carbon for the Electrocatalysis of Oxygen Reduction Reaction

Science.gov (United States)

Feng, Tong; Liao, Wenli; Li, Zhongbin; Sun, Lingtao; Shi, Dongping; Guo, Chaozhong; Huang, Yu; Wang, Yi; Cheng, Jing; Li, Yanrong; Diao, Qizhi

2017-11-01

Large-scale production of active and stable porous carbon catalysts for oxygen reduction reaction (ORR) from protein-rich biomass became a hot topic in fuel cell technology. Here, we report a facile strategy for synthesis of nitrogen-doped porous nanocarbons by means of a simple two-step pyrolysis process combined with the activation of zinc chloride and acid-treatment process, in which kidney bean via low-temperature carbonization was preferentially adopted as the only carbon-nitrogen sources. The results show that this carbon material exhibits excellent ORR electrocatalytic activity, and higher durability and methanol-tolerant property compared to the state-of-the-art Pt/C catalyst for the ORR, which can be mainly attributed to high graphitic-nitrogen content, high specific surface area, and porous characteristics. Our results can encourage the synthesis of high-performance carbon-based ORR electrocatalysts derived from widely-existed natural biomass.

Surface-reconstructed graphite nanofibers as a support for cathode catalysts of fuel cells.

Science.gov (United States)

Gan, Lin; Du, Hongda; Li, Baohua; Kang, Feiyu

2011-04-07

Graphite nanofibers (GNFs), on which surface graphite edges were reconstructed into nano-loops, were explored as a cathode catalyst support for fuel cells. The high degree of graphitization, as well as the surface-reconstructed nano-loops that possess topological defects for uniform metal deposition, resulted in an improved performance of the GNF-supported Pt catalyst.

Elastic representation surfaces of unidirectional graphite/epoxy composites

International Nuclear Information System (INIS)

Kriz, R.D.; Ledbetter, H.M.

1985-01-01

Unidirectional graphite/epoxy composites exhibit high elastic anisotropy and unusual geometrical features in their elastic-property polar diagrams. From the five-component transverse-isotropic elastic-stiffness tensor we compute and display representation surfaces for Young's modulus, torsional modulus, linear compressibility, and Poisson's ratios. Based on Christoffel-equation solutions, we describe some unusual elastic-wave-surface topological features. Musgrave considered in detail the differences between phase-velocity and group-velocity surfaces arising from high elastic anisotropy. For these composites, we find effects similar to, but more dramatic than, Musgrave's. Some new, unexpected results for graphite/epoxy include: a shear-wave velocity that exceeds a longitudinal velocity in the plane transverse to the fiber; a wave that changes polarization character from longitudinal to transverse as the propagation direction sweeps from the fiber axis to the perpendicular axis

Work function modifications of graphite surface via oxygen plasma treatment

Science.gov (United States)

Duch, J.; Kubisiak, P.; Adolfsson, K. H.; Hakkarainen, M.; Golda-Cepa, M.; Kotarba, A.

2017-10-01

The surface modification of graphite by oxygen plasma was investigated experimentally (X-ray diffraction, nanoparticle tracking analysis, laser desorption ionization mass spectrometry, thermogravimetry, water contact angle) and by molecular modelling (Density Functional Theory). Generation of surface functional groups (mainly sbnd OHsurf) leads to substantial changes in electrodonor properties and wettability gauged by work function and water contact angle, respectively. The invoked modifications were analyzed in terms of Helmholtz model taking into account the theoretically determined surface dipole moment of graphite-OHsurf system (μ = 2.71 D) and experimentally measured work function increase (from 0.75 to 1.02 eV) to determine the sbnd OH surface coverage (from 0.70 to 1.03 × 1014 groups cm-2). Since the plasma treatment was confined to the surface, the high thermal stability of the graphite material was preserved as revealed by the thermogravimetric analysis. The obtained results provide a suitable quantitative background for tuning the key operating parameters of carbon electrodes: electronic properties, interaction with water and thermal stability.

Brazing graphite to graphite

International Nuclear Information System (INIS)

Peterson, G.R.

1976-01-01

Graphite is joined to graphite by employing both fine molybdenum powder as the brazing material and an annealing step that together produce a virtually metal-free joint exhibiting properties similar to those found in the parent graphite. Molybdenum powder is placed between the faying surfaces of two graphite parts and melted to form molybdenum carbide. The joint area is thereafter subjected to an annealing operation which diffuses the carbide away from the joint and into the graphite parts. Graphite dissolved by the dispersed molybdenum carbide precipitates into the joint area, replacing the molybdenum carbide to provide a joint of graphite

Free-standing nano-scale graphite saturable absorber for passively mode-locked erbium doped fiber ring laser

International Nuclear Information System (INIS)

Lin, Y-H; Lin, G-R

2012-01-01

The free-standing graphite nano-particle located between two FC/APC fiber connectors is employed as the saturable absorber to passively mode-lock the ring-type Erbium-doped fiber laser (EDFL). The host-solvent-free graphite nano-particles with sizes of 300 – 500 nm induce a comparable modulation depth of 54%. The interlayer-spacing and lattice fluctuations of polished graphite nano-particles are observed from the weak 2D band of Raman spectrum and the azimuth angle shift of –0.32 ° of {002}-orientation dependent X-ray diffraction peak. The graphite nano-particles mode-locked EDFL generates a 1.67-ps pulsewidth at linearly dispersion-compensated regime with a repetition rate of 9.1 MHz. The time-bandwidth product of 0.325 obtained under a total intra-cavity group-delay-dispersion of –0.017 ps 2 is nearly transform-limited. The extremely high stability of the nano-scale graphite saturable absorber during mode-locking is observed at an intra-cavity optical energy density of 7.54 mJ/cm 2 . This can be attributed to its relatively high damage threshold (one order of magnitude higher than the graphene) on handling the optical energy density inside the EDFL cavity. The graphite nano-particle with reduced size and sufficient coverage ratio can compete with other fast saturable absorbers such as carbon nanotube or graphene to passively mode-lock fiber lasers with decreased insertion loss and lasing threshold

Chemical erosion of carbon doped with different fine-grain carbides

International Nuclear Information System (INIS)

Balden, M.; Garcia-Rosales, C.; Behrisch, R.; Roth, J.; Paz, P.; Etxeberria, J.

2001-01-01

Several carbide-doped (SiC, TiC, V 8 C 7 , WC, ZrC) graphites have been produced. The erosion of these materials at low-energy (eV) hydrogen ion bombardment has been investigated using the weight-loss method, mass spectroscopy, ion beam analysis, and scanning electron microscopy (SEM). The erosion yields of the WC- and V 8 C 7 -doped graphites are reduced by a factor of 2 for 30 eV D at 300 K compared to pure graphite. This observed reduction is partly attributed to surface enrichment of carbide due to preferential C erosion. The other part is assigned to changes in the chemical erosion process (Y surf ) as well as at elevated temperatures in the thermal activated process (Y therm ). The reduction of both erosion processes is determined for all dopants to be more than 25% of the erosion yield of the undoped graphite

Field emission from the surface of highly ordered pyrolytic graphite

Energy Technology Data Exchange (ETDEWEB)

Knápek, Alexandr, E-mail: knapek@isibrno.cz [Institute of Scientific Instruments of the ASCR, v.v.i., Královopolská 147, Brno (Czech Republic); Sobola, Dinara; Tománek, Pavel [Department of Physics, FEEC, Brno University of Technology, Technická 8, Brno (Czech Republic); Pokorná, Zuzana; Urbánek, Michal [Institute of Scientific Instruments of the ASCR, v.v.i., Královopolská 147, Brno (Czech Republic)

2017-02-15

Highlights: • HOPG shreds were created and analyzed in the UHV conditions. • Current-voltage measurements have been done to confirm electron tunneling, based on the Fowler-Nordheim theory. • Surface was characterized by other surface evaluation methods, in particular by: SNOM, SEM and AFM. - Abstract: This paper deals with the electrical characterization of highly ordered pyrolytic graphite (HOPG) surface based on field emission of electrons. The effect of field emission occurs only at disrupted surface, i.e. surface containing ripped and warped shreds of the uppermost layers of graphite. These deformations provide the necessary field gradients which are required for measuring tunneling current caused by field electron emission. Results of the field emission measurements are correlated with other surface characterization methods such as scanning near-field optical microscopy (SNOM) or atomic force microscopy.

Field emission from the surface of highly ordered pyrolytic graphite

International Nuclear Information System (INIS)

Knápek, Alexandr; Sobola, Dinara; Tománek, Pavel; Pokorná, Zuzana; Urbánek, Michal

2017-01-01

Highlights: • HOPG shreds were created and analyzed in the UHV conditions. • Current-voltage measurements have been done to confirm electron tunneling, based on the Fowler-Nordheim theory. • Surface was characterized by other surface evaluation methods, in particular by: SNOM, SEM and AFM. - Abstract: This paper deals with the electrical characterization of highly ordered pyrolytic graphite (HOPG) surface based on field emission of electrons. The effect of field emission occurs only at disrupted surface, i.e. surface containing ripped and warped shreds of the uppermost layers of graphite. These deformations provide the necessary field gradients which are required for measuring tunneling current caused by field electron emission. Results of the field emission measurements are correlated with other surface characterization methods such as scanning near-field optical microscopy (SNOM) or atomic force microscopy.

Interaction of the Helium, Hydrogen, Air, Argon, and Nitrogen Bubbles with Graphite Surface in Water.

Science.gov (United States)

Bartali, Ruben; Otyepka, Michal; Pykal, Martin; Lazar, Petr; Micheli, Victor; Gottardi, Gloria; Laidani, Nadhira

2017-05-24

The interaction of the confined gas with solid surface immersed in water is a common theme of many important fields such as self-cleaning surface, gas storage, and sensing. For that reason, we investigated the gas-graphite interaction in the water medium. The graphite surface was prepared by mechanical exfoliation of highly oriented pyrolytic graphite (HOPG). The surface chemistry and morphology were studied by X-ray photoelectron spectroscopy, profilometry, and atomic force microscopy. The surface energy of HOPG was estimated by contact angle measurements using the Owens-Wendt method. The interaction of gases (Ar, He, H 2 , N 2 , and air) with graphite was studied by a captive bubble method, in which the gas bubble was in contact with the exfoliated graphite surface in water media. The experimental data were corroborated by molecular dynamics simulations and density functional theory calculations. The surface energy of HOPG equaled to 52.8 mJ/m 2 and more of 95% of the surface energy was attributed to dispersion interactions. The results on gas-surface interaction indicated that HOPG surface had gasphilic behavior for helium and hydrogen, while gasphobic behavior for argon and nitrogen. The results showed that the variation of the gas contact angle was related to the balance between the gas-surface and gas-gas interaction potentials. For helium and hydrogen the gas-surface interaction was particularly high compared to gas-gas interaction and this promoted the favorable interaction with graphite surface.

Surface impurity removal from DIII-D graphite tiles by boron carbide grit blasting

International Nuclear Information System (INIS)

Lee, R.L.; Hollerbach, M.A.; Holtrop, K.L.; Kellman, A.G.; Taylor, P.L.; West, W.P.

1993-11-01

During the latter half of 1992, the DIII-D tokamak at General Atomics (GA) underwent several modifications of its interior. One of the major tasks involved the removal of accumulated metallic impurities from the surface of the graphite tiles used to line the plasma facing surfaces inside of the tokamak. Approximately 1500 graphite tiles and 100 boron nitride tiles from the tokamak were cleaned to remove the metallic impurities. The cleaning process consisted of several steps: the removed graphite tiles were permanently marked, surface blasted using boron carbide (B 4 C) grit media (approximately 37 μm. diam.), ultrasonically cleaned in ethanol to remove loose dust, and outgassed at 1000 degrees C. Tests were done using, graphite samples and different grit blaster settings to determine the optimum propellant and abrasive media pressures to remove a graphite layer approximately 40-50 μm deep and yet produce a reasonably smooth finish. EDX measurements revealed that the blasting technique reduced the surface Ni, Cr, and Fe impurity levels to those of virgin graphite. In addition to the surface impurity removal, tritium monitoring was performed throughout the cleaning process. A bubbler system was set up to monitor the tritium level in the exhaust gas from the grit blaster unit. Surface wipes were also performed on over 10% of the tiles. Typical surface tritium concentrations of the tiles were reduced from about 500 dpm/100 cm 2 to less than 80 dpm/100 cm 2 following the cleaning. This tile conditioning, and the installation of additional graphite tiles to cover a high fraction of the metallic plasma facing surfaces, has substantially reduced metallic impurities in the plasma discharges which has allowed rapid recovery from a seven-month machine opening and regimes of enhanced plasma energy confinement to be more readily obtained. Safety issues concerning blaster operator exposure to carcinogenic metals and radioactive tritium will also be addressed

Non-activated high surface area expanded graphite oxide for supercapacitors

Energy Technology Data Exchange (ETDEWEB)

Vermisoglou, E.C.; Giannakopoulou, T.; Romanos, G.E.; Boukos, N.; Giannouri, M. [Institute of Nanoscience and Nanotechnology “Demokritos”, 153 43 Ag. Paraskevi, Attikis (Greece); Lei, C.; Lekakou, C. [Division of Mechanical, Medical, and Aerospace Engineering, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH (United Kingdom); Trapalis, C., E-mail: c.trapalis@inn.demokritos.gr [Institute of Nanoscience and Nanotechnology “Demokritos”, 153 43 Ag. Paraskevi, Attikis (Greece)

2015-12-15

Graphical abstract: - Highlights: • One-step exfoliation and reduction of graphite oxide via microwave irradiation. • Effect of pristine graphite (type, flake size) on the microwave expanded material. • Effect of pretreatment and oxidation cycles on the produced expanded material. • Expanded graphene materials with high BET surface areas (940 m{sup 2}/g–2490 m{sup 2}/g). • Non-activated graphene based materials suitable for supercapacitors. - Abstract: Microwave irradiation of graphite oxide constitutes a facile route toward production of reduced graphene oxide, since during this treatment both exfoliation and reduction of graphite oxide occurs. In this work, the effect of pristine graphite (type, size of flakes), pretreatment and oxidation cycles on the finally produced expanded material was examined. All the types of graphite that were tested afforded materials with high BET surface areas ranging from 940 m{sup 2}/g to 2490 m{sup 2}/g, without intervening an activation stage at elevated temperature. SEM and TEM images displayed exfoliated structures, where the flakes were significantly detached and curved. The quality of the reduced graphene oxide sheets was evidenced both by X-ray photoelectron spectroscopy and Raman spectroscopy. The electrode material capacitance was determined via electrochemical impedance spectroscopy and cyclic voltammetry. The materials with PEDOT binder had better performance (∼97 F/g) at low operation rates while those with PVDF binder performed better (∼20 F/g) at higher rates, opening up perspectives for their application in supercapacitors.

Erosion of graphite surface exposed to hot supersonic hydrogen gas

Science.gov (United States)

Sharma, O. P.

1972-01-01

A theoretical model based on laminar boundary layer flow equations was developed to predict the erosion rate of a graphite (AGCarb-101) surface exposed to a hot supersonic stream of hydrogen gas. The supersonic flow in the nozzle outside the boundary layer formed over the surface of the specimen was determined by assuming one-dimensional isentropic conditions. An overall surface reaction rate expression based on experimental studies was used to describe the interaction of hydrogen with graphite. A satisfactory agreement was found between the results of the computation, and the available experimental data. Some shortcomings of the model and further possible improvements are discussed.

Improved numerical calculation of the generation of a neutral beam by charge transfer between chlorine ions/neutrals and a graphite surface

International Nuclear Information System (INIS)

Kubota, Tomohiro; Samukawa, Seiji; Watanabe, Naoki; Ohtsuka, Shingo; Iwasaki, Takuya; Ono, Kohei; Iriye, Yasuroh

2014-01-01

The charge transfer process between chlorine particles (ions or neutrals) and a graphite surface on collision was investigated by using a highly stable numerical simulator based on time-dependent density functional theory to understand the generation mechanism of a high-efficiency neutral beam developed by Samukawa et al (2001 Japan. J. Appl. Phys. 40 L779). A straightforward calculation was achieved by adopting a large enough unit cell. The dependence of the neutralization efficiency on the incident energy of the particle was investigated, and the trend of the experimental result was reproduced. It was also found that doping the electrons and holes into graphite could change the charge transfer process and neutralization probability. This result suggests that it is possible to develop a neutral beam source that has high neutralization efficiency for both positive and negative ions. (paper)

Synthesis of partially graphitic ordered mesoporous carbons with high surface areas

Energy Technology Data Exchange (ETDEWEB)

Gao, Wenjun; Wan, Ying [Department of Chemistry, Key Laboratory of Resource Chemistry of Ministry of Education, Shanghai Normal University, Shanghai 200234 (China); Dou, Yuqian; Zhao, Dongyuan [Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433 (China)

2011-01-01

Graphitic carbons with ordered mesostructure and high surface areas (of great interest in applications such as energy storage) have been synthesized by a direct triblock-copolymer-templating method. Pluronic F127 is used as a structure-directing agent, with a low-molecular-weight phenolic resol as a carbon source, ferric oxide as a catalyst, and silica as an additive. Inorganic oxides can be completely eliminated from the carbon. Small-angle XRD and N{sub 2} sorption analysis show that the resultant carbon materials possess an ordered 2D hexagonal mesostructure, uniform bimodal mesopores (about 1.5 and 6 nm), high surface area ({proportional_to}1300 m{sup 2}/g), and large pore volumes ({proportional_to}1.50 cm{sup 3}/g) after low-temperature pyrolysis (900 C). All surface areas come from mesopores. Wide-angle XRD patterns demonstrate that the presence of the ferric oxide catalyst and the silica additive lead to a marked enhancement of graphitic ordering in the framework. Raman spectra provide evidence of the increased content of graphitic sp{sup 2} carbon structures. Transmission electron microscopy images confirm that numerous domains in the ordered mesostructures are composed of characteristic graphitic carbon nanostructures. The evolution of the graphitic structure is dependent on the temperature and the concentrations of the silica additive, and ferric oxide catalyst. Electrochemical measurements performed on this graphitic mesoporous carbon when used as an electrode material for an electrochemical double layer capacitor shows rectangular-shaped cyclic voltammetry curves over a wide range of scan rates, even up to 200 mV/s, with a large capacitance of 155 F/g in KOH electrolyte. This method can be widely applied to the synthesis of graphitized carbon nanostructures. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

In Situ Activation of Nitrogen-Doped Graphene Anchored on Graphite Foam for a High-Capacity Anode.

Science.gov (United States)

Ji, Junyi; Liu, Jilei; Lai, Linfei; Zhao, Xin; Zhen, Yongda; Lin, Jianyi; Zhu, Yanwu; Ji, Hengxing; Zhang, Li Li; Ruoff, Rodney S

2015-08-25

We report the fabrication of a three-dimensional free-standing nitrogen-doped porous graphene/graphite foam by in situ activation of nitrogen-doped graphene on highly conductive graphite foam (GF). After in situ activation, intimate "sheet contact" was observed between the graphene sheets and the GF. The sheet contact produced by in situ activation is found to be superior to the "point contact" obtained by the traditional drop-casting method and facilitates electron transfer. Due to the intimate contact as well as the use of an ultralight GF current collector, the composite electrode delivers a gravimetric capacity of 642 mAh g(-1) and a volumetric capacity of 602 mAh cm(-3) with respect to the whole electrode mass and volume (including the active materials and the GF current collector). When normalized based on the mass of the active material, the composite electrode delivers a high specific capacity of up to 1687 mAh g(-1), which is superior to that of most graphene-based electrodes. Also, after ∼90 s charging, the anode delivers a capacity of about 100 mAh g(-1) (with respect to the total mass of the electrode), indicating its potential use in high-rate lithium-ion batteries.

Surface studies on graphite furnace platforms covered with Pd, Rh and Ir as modifiers in graphite furnace atomic absorption spectrometry of tellurium

Energy Technology Data Exchange (ETDEWEB)

Pedro, Juana [Area de Química Analítica, Departamento de Química, Facultad de Ingeniería Química, Universidad Nacional del Litoral, Santiago del Estero 2829 (S3000GL.N), Santa Fe (Argentina); Stripekis, Jorge [Laboratorio de Análisis de Trazas, Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria (1428), Buenos Aires (Argentina); Departamento de Ingeniería Química, Instituto Tecnológico de Buenos Aires, Av. Eduardo Madero 399 (1106), Buenos Aires (Argentina); Bonivardi, Adrian [Area de Química Analítica, Departamento de Química, Facultad de Ingeniería Química, Universidad Nacional del Litoral, Santiago del Estero 2829 (S3000GL.N), Santa Fe (Argentina); Tudino, Mabel, E-mail: tudino@qi.fcen.uba.ar [Laboratorio de Análisis de Trazas, Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria (1428), Buenos Aires (Argentina)

2015-05-01

The main objective of this work is the study of correlations between the efficiency of the distribution of the permanent platinum group modifiers Pd, Rh and Ir over the graphite surface with the aim of improving analytical signal of tellurium. Modifier solution was deposited onto the platform and pyrolysed after drying. In the case of Pd, the physical vaporization/deposition technique was also tested. In order to analyze the differences amongst coverings (morphology, topology and distribution), the graphite surfaces were studied with scanning electron microscopy and energy dispersive X-ray microscopy. Micrographs for physical vaporization and pyrolytic deposition of Pd were also analyzed in order to explain the lack of signal obtained for tellurium with the first alternative. Similar micrographs were obtained for pyrolytic deposition of Ir and Rh and then, compared to those of Pd. Ir showed the most homogeneous distribution on the graphite surface and the tallest and sharpest transient. With the aim of improving the analytical signal of tellurium, the correlation between the surface studies and the tellurium transient signal (height, area and shape) is discussed. - Highlights: • Distribution of Rh, Pd and Ir onto graphite furnaces is evaluated by SEM and EDX • Micrographs and spectra showed that surface distribution could influence Te signal. • Ir showed the best signal together with the most homogeneous surface distribution. • Pd-PVD micrographs revealed the absence of graphite and no signal for Te.

X-ray photoelectron spectroscopy of graphitic carbon nanomaterials doped with heteroatoms

Directory of Open Access Journals (Sweden)

Toma Susi

2015-01-01

Full Text Available X-ray photoelectron spectroscopy (XPS is one of the best tools for studying the chemical modification of surfaces, and in particular the distribution and bonding of heteroatom dopants in carbon nanomaterials such as graphene and carbon nanotubes. Although these materials have superb intrinsic properties, these often need to be modified in a controlled way for specific applications. Towards this aim, the most studied dopants are neighbors to carbon in the periodic table, nitrogen and boron, with phosphorus starting to emerge as an interesting new alternative. Hundreds of studies have used XPS for analyzing the concentration and bonding of dopants in various materials. Although the majority of works has concentrated on nitrogen, important work is still ongoing to identify its precise atomic bonding configurations. In general, care should be taken in the preparation of a suitable sample, consideration of the intrinsic photoemission response of the material in question, and the appropriate spectral analysis. If this is not the case, incorrect conclusions can easily be drawn, especially in the assignment of measured binding energies into specific atomic configurations. Starting from the characteristics of pristine materials, this review provides a practical guide for interpreting X-ray photoelectron spectra of doped graphitic carbon nanomaterials, and a reference for their binding energies that are vital for compositional analysis via XPS.

Modifications of Graphite and Multiwall Carbon Nanotubes in the Presence of Urea

Science.gov (United States)

Duraia, El-Shazly M.; Fahami, Abbas; Beall, Gary W.

2018-02-01

The effect of high-energy ball milling on two carbon allotropes, graphite and multiwall carbon nanotubes (MWCNT) in the presence of urea has been studied. Samples were investigated using Raman spectroscopy, x-ray diffraction, scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS). Nitrogen-doped graphene has been successfully synthesized via a simple scalable mechanochemistry method using urea and graphite powder precursors. XPS results revealed the existence of the different nitrogen atoms configurations including pyridine, pyrrodic and graphitic N. SEM observations showed that the graphene nanosheets morphology become more wrinkles folded and crumbled as the milling time increased. The ID/IG ratio also increased as the milling time rose. The presence of both D' and G + D bands at 1621 cm-1 and 2940 cm-1, respectively, demonstrated the nitrogen incorporation in the graphene lattice Two factors contribute to the used urea: first it helps to exfoliate graphite into graphene, and second it preserves the graphitic structure from damage during the milling process as well as acting as a solid-state nitrogen source. Based on the phase analysis, the d-spacing of MWCNT samples in the presence of urea decreased due to the mechanical force in the milling process as the milling time increased. On the other hand, in the graphite case, due to its open flat surface, the graphite (002) peak shifts toward lower two theta as the milling time increase. Such findings are important and could be used for large-scale production of N-doped graphene, diminishing the use of either dangerous chemicals or sophisticated equipment.

Photocatalysis with chromium-doped TiO2: Bulk and surface doping

KAUST Repository

Ould-Chikh, Samy

2014-04-15

The photocatalytic properties of TiO2 modified by chromium are usually found to depend strongly on the preparation method. To clarify this problem, two series of chromium-doped titania with a chromium content of up to 1.56 wt % have been prepared under hydrothermal conditions: the first series (Cr:TiO2) is intended to dope the bulk of TiO2, whereas the second series (Cr/TiO2) is intended to load the surface of TiO2 with Cr. The catalytic properties have been compared in the photocatalytic oxidation of formic acid. Characterization data provides evidence that in the Cr/TiO2 catalysts chromium is located on the surface of TiO2 as amorphous CrOOH clusters. In contrast, in the Cr:TiO 2 series, chromium is mostly dissolved in the titania lattice, although a minor part is still present on the surface. Photocatalytic tests show that both series of chromium-doped titania demonstrate visible-light-driven photo-oxidation activity. Surface-doped Cr/TiO2 solids appear to be more efficient photocatalysts than the bulk-doped Cr:TiO2 counterparts. It\\'s classified! The photocatalytic properties of TiO2 modified by chromium depend strongly on the preparation method. To clarify this problem, two types of modified titania are discussed: one with CrIII doped in the bulk and one with CrOOH clusters on the TiO2 surface (see picture). Both series show visible-light-driven photo-oxidation activity. However, surface modification appears to be a more efficient strategy. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reduction Expansion Synthesis as Strategy to Control Nitrogen Doping Level and Surface Area in Graphene

Directory of Open Access Journals (Sweden)

Russell Canty

2015-10-01

Full Text Available Graphene sheets doped with nitrogen were produced by the reduction-expansion (RES method utilizing graphite oxide (GO and urea as precursor materials. The simultaneous graphene generation and nitrogen insertion reactions are based on the fact that urea decomposes upon heating to release reducing gases. The volatile byproducts perform two primary functions: (i promoting the reduction of the GO and (ii providing the nitrogen to be inserted in situ as the graphene structure is created. Samples with diverse urea/GO mass ratios were treated at 800 °C in inert atmosphere to generate graphene with diverse microstructural characteristics and levels of nitrogen doping. Scanning electron microscopy (SEM and transmission electron microscopy (TEM were used to study the microstructural features of the products. The effects of doping on the samples structure and surface area were studied by X-ray diffraction (XRD, Raman Spectroscopy, and Brunauer Emmet Teller (BET. The GO and urea decomposition-reduction process as well as nitrogen-doped graphene stability were studied by thermogravimetric analysis (TGA coupled with mass spectroscopy (MS analysis of the evolved gases. Results show that the proposed method offers a high level of control over the amount of nitrogen inserted in the graphene and may be used alternatively to control its surface area. To demonstrate the practical relevance of these findings, as-produced samples were used as electrodes in supercapacitor and battery devices and compared with conventional, thermally exfoliated graphene.

Thermal migration of deuterium implanted in graphite: Influence of free surface proximity and structure

Energy Technology Data Exchange (ETDEWEB)

Le Guillou, M. [Institut de Physique Nucléaire de Lyon, CNRS/IN2P3 UMR 5822, Université Claude Bernard Lyon 1, Université de Lyon, F-69622 Villeurbanne cedex (France); Moncoffre, N., E-mail: n.moncoffre@ipnl.in2p3.fr [Institut de Physique Nucléaire de Lyon, CNRS/IN2P3 UMR 5822, Université Claude Bernard Lyon 1, Université de Lyon, F-69622 Villeurbanne cedex (France); Toulhoat, N. [Institut de Physique Nucléaire de Lyon, CNRS/IN2P3 UMR 5822, Université Claude Bernard Lyon 1, Université de Lyon, F-69622 Villeurbanne cedex (France); CEA/DEN – Centre de Saclay, F-91191 Gif-sur-Yvette cedex (France); Pipon, Y. [Institut de Physique Nucléaire de Lyon, CNRS/IN2P3 UMR 5822, Université Claude Bernard Lyon 1, Université de Lyon, F-69622 Villeurbanne cedex (France); Institut Universitaire Technologique, Université Claude Bernard Lyon 1, Université de Lyon, F-69622 Villeurbanne cedex (France); Ammar, M.R. [CNRS, CEMHTI UPR3079, Université Orléans, CS90055, F-45071 Orléans cedex 2 (France); Rouzaud, J.N.; Deldicque, D. [Laboratoire de Géologie de l’Ecole Normale Supérieure, Paris, UMR CNRS ENS 8538, F-75231 Paris cedex 5 (France)

2016-03-15

This paper is a contribution to the study of the behavior of activation products produced in irradiated nuclear graphite, graphite being the moderator of the first French generation of CO{sub 2} cooled nuclear fission reactors. This paper is focused on the thermal release of Tritium, a major contributor to the initial activity, taking into account the role of the free surfaces (open pores and graphite surface). Two kinds of graphite were compared. On one hand, Highly Oriented Pyrolitic Graphite (HOPG), a model well graphitized graphite, and on the other hand, SLA2, a porous less graphitized nuclear graphite. Deuterium ion implantation at three different energies 70, 200 and 390 keV allows simulating the presence of Tritium at three different depths, corresponding respectively to projected ranges R{sub p} of 0.75, 1.7 and 3.2 μm. The D isotopic tracing is performed thanks to the D({sup 3}He,p){sup 4}He nuclear reaction. The graphite structure is studied by Raman microspectrometry. Thermal annealing is performed in the temperature range 200–1200 °C up to 300 h annealing time. As observed in a previous study, the results show that the D release occurs according to three kinetic regimes: a rapid permeation through open pores, a transient regime corresponding to detrapping and diffusion of D located at low energy sites correlated to the edges of crystallites and finally a saturation regime attributed to detrapping of interstitial D located at high energy sites inside the crystallites. Below 600 °C, D release is negligible whatever the implantation depth and the graphite type. The present paper clearly puts forward that above 600 °C, the D release decreases at deeper implantation depths and strongly depends on the graphite structure. In HOPG where high energy sites are more abundant, the D release is less dependent on the surface proximity compared to SLA2. In SLA2, in which the low energy sites prevail, the D release curves are clearly shifted towards lower

Trampoline motions in Xe-graphite(0 0 0 1) surface scattering

Science.gov (United States)

Watanabe, Yoshimasa; Yamaguchi, Hiroki; Hashinokuchi, Michihiro; Sawabe, Kyoichi; Maruyama, Shigeo; Matsumoto, Yoichiro; Shobatake, Kosuke

2005-09-01

We have investigated Xe scattering from the graphite(0 0 0 1) surface at hyperthermal incident energies using a molecular beam-surface scattering technique and molecular dynamics simulations. For all incident conditions, the incident Xe atom conserves the momentum parallel to the surface and loses approximately 80% of the normal incident energy. The weak interlayer potential of graphite disperses the deformation over the wide range of a graphene sheet. The dynamic corrugation induced by the collision is smooth even at hyperthermal incident energy; the graphene sheet moves like a trampoline net and the Xe atom like a trampoliner.

Electrostatic force microscopy on oriented graphite surfaces: coexistence of insulating and conducting behaviors.

Science.gov (United States)

Lu, Yonghua; Muñoz, M; Steplecaru, C S; Hao, Cheng; Bai, Ming; Garcia, N; Schindler, K; Esquinazi, P

2006-08-18

We present measurements of the electric potential fluctuations on the surface of highly oriented pyrolytic graphite using electrostatic force and atomic force microscopy. Micrometric domainlike potential distributions are observed even when the sample is grounded. Such potential distributions are unexpected given the good metallic conductivity of graphite because the surface should be an equipotential. Our results indicate the coexistence of regions with "metalliclike" and "insulatinglike" behaviors showing large potential fluctuations of the order of 0.25 V. In lower quality graphite, this effect is not observed. Experiments are performed in Ar and air atmospheres.

N- and S-doped high surface area carbon derived from soya chunks as scalable and efficient electrocatalysts for oxygen reduction

Science.gov (United States)

Rana, Moumita; Arora, Gunjan; Gautam, Ujjal K.

2015-02-01

Highly stable, cost-effective electrocatalysts facilitating oxygen reduction are crucial for the commercialization of membrane-based fuel cell and battery technologies. Herein, we demonstrate that protein-rich soya chunks with a high content of N, S and P atoms are an excellent precursor for heteroatom-doped highly graphitized carbon materials. The materials are nanoporous, with a surface area exceeding 1000 m2 g-1, and they are tunable in doping quantities. These materials exhibit highly efficient catalytic performance toward oxygen reduction reaction (ORR) with an onset potential of -0.045 V and a half-wave potential of -0.211 V (versus a saturated calomel electrode) in a basic medium, which is comparable to commercial Pt catalysts and is better than other recently developed metal-free carbon-based catalysts. These exhibit complete methanol tolerance and a performance degradation of merely ˜5% as compared to ˜14% for a commercial Pt/C catalyst after continuous use for 3000 s at the highest reduction current. We found that the fraction of graphitic N increases at a higher graphitization temperature, leading to the near complete reduction of oxygen. It is believed that due to the easy availability of the precursor and the possibility of genetic engineering to homogeneously control the heteroatom distribution, the synthetic strategy is easily scalable, with further improvement in performance.

Heat Transfer During Evaporation of Cesium From Graphite Surface in an Argon Environment

Directory of Open Access Journals (Sweden)

Bespala Evgeny

2016-01-01

Full Text Available The article focuses on discussion of problem of graphite radioactive waste formation and accumulation. It is shown that irradiated nuclear graphite being inalienable part of uranium-graphite reactor may contain fission and activation products. Much attention is given to the process of formation of radioactive cesium on the graphite element surface. It is described a process of plasma decontamination of irradiated graphite in inert argon atmosphere. Quasi-one mathematical model is offered, it describes heat transfer process in graphite-cesium-argon system. Article shows results of calculation of temperature field inside the unit cell. Authors determined the factors which influence on temperature change.

Green synthesis of nitrogen-doped graphitic carbon sheets with use of Prunus persica for supercapacitor applications

Energy Technology Data Exchange (ETDEWEB)

Atchudan, Raji, E-mail: atchudanr@yu.ac.kr [School of Chemical Engineering, Yeungnam University, Gyeongsan 38541 (Korea, Republic of); Edison, Thomas Nesakumar Jebakumar Immanuel [School of Chemical Engineering, Yeungnam University, Gyeongsan 38541 (Korea, Republic of); Perumal, Suguna [Department of Applied Chemistry, Kyungpook National University, Daegu 41566 (Korea, Republic of); Lee, Yong Rok, E-mail: yrlee@yu.ac.kr [School of Chemical Engineering, Yeungnam University, Gyeongsan 38541 (Korea, Republic of)

2017-01-30

Highlights: • N-GCSs was synthesized from the unripe Prunus persica by direct hydrothermal method. • The resulting N-GCSs-2 exhibit an excellent graphitization with 9.33% of nitrogen. • N-GCSs-2 provide high C{sub s} of 176 F g{sup −1} at current density of 0.1 A g{sup −1} in 1 M H{sub 2}SO{sub 4}. • N-GCSs-2 have high capacitance retention and 20% capacity growth after 2000 cycles. • First time, N-GCSs resulted from peach via green route for flexible supercapacitors. - Abstract: Nitrogen-doped graphitic carbon sheets (N-GCSs) were prepared from the extract of unripe Prunus persica fruit by a direct hydrothermal method. The synthesized N-GCSs were examined by high resolution transmission electron microscopy (HRTEM), nitrogen adsorption-desorption isotherms, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) spectroscopy. HRTEM showed that the synthesized carbon sheets were graphitic with lattice fringes and an inter-layer distance of 0.36 nm. Doping with the nitrogen moiety present over the synthesized GCSs was confirmed by XPS, FT-IR spectroscopy, and energy dispersive X-ray spectroscopy elemental mapping. The fruit extract associated with hydrothermal-carbonization method is economical and eco-friendly with a single step process. The resulting carbon sheets could be modified and are promising candidates for nano-electronic applications, including supercapacitors. The synthesized N-GCSs-2 provided a high specific capacitance of 176 F g{sup −1} at a current density of 0.1 A g{sup −1}. This electrode material has excellent cyclic stability, even after 2000 cycles of charge-discharge at a current density of 0.5 A g{sup −1}.

Enhanced visible light photocatalytic degradation of Rhodamine B over phosphorus doped graphitic carbon nitride

Energy Technology Data Exchange (ETDEWEB)

Chai, Bo, E-mail: willycb@163.com; Yan, Juntao; Wang, Chunlei; Ren, Zhandong; Zhu, Yuchan

2017-01-01

Highlights: • The phosphorus doped g-C{sub 3}N{sub 4} photocatalysts are synthesized by a co-pyrolysis procedure. • The crystal phase, morphology, and optical property of P doped g-C{sub 3}N{sub 4} are characterized. • The P doped g-C{sub 3}N{sub 4} photocatalysts show the improved photocatalytic activity. • The possible mechanism for enhanced photocatalytic activity is proposed. - Abstract: Phosphorus doped graphitic carbon nitride (g-C{sub 3}N{sub 4}) was easily synthesized using ammonium hexafluorophosphate (NH{sub 4}PF{sub 6}) as phosphorus source, and ammonium thiocyanate (NH{sub 4}SCN) as g-C{sub 3}N{sub 4} precursor, through a direct thermal co-polycondensation procedure. The obtained phosphorus doped g-C{sub 3}N{sub 4} was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), UV–vis diffuse reflectance absorption spectra (UV-DRS), photoelectrochemical measurement and photoluminescence spectra (PL). The photocatalytic activities of phosphorus doped g-C{sub 3}N{sub 4} samples were evaluated by degradation of Rhodamine B (RhB) solution under visible light irradiation. The results showed that the phosphorus doped g-C{sub 3}N{sub 4} had a superior photocatalytic activity than that of pristine g-C{sub 3}N{sub 4}, attributing to the phosphorus atoms substituting carbon atoms of g-C{sub 3}N{sub 4} frameworks to result in light harvesting enhancement and delocalized π-conjugated system of this copolymer, beneficial for the increase of photocatalytic performance. The photoelectrochemical measurements also verified that the charge carrier separation efficiency was promoted by phosphorus doping g-C{sub 3}N{sub 4}. Moreover, the tests of radical scavengers demonstrated that the holes (h{sup +}) and superoxide radicals (·O{sub 2}{sup −}) were the main active species for the

Promoting mechanism of N-doped single-walled carbon nanotubes for O2 dissociation and SO2 oxidation

Science.gov (United States)

Chen, Yanqiu; Yin, Shi; Chen, Yang; Cen, Wanglai; Li, Jianjun; Yin, Huaqiang

2018-03-01

Although heteroatom doping in carbon based catalysts have recently received intensive attentions, the role of the intrinsically porous structure of practical carbon materials and their potential synergy with doping atoms are still unclear. To investigate the complex effects, a range of N-doped single-walled carbon nanotubes (SWCNTs) were used to investigate their potential use for O2 dissociation and the subsequent SO2 oxidation using density functional theory. It is found that graphite N doping can synergize with the outer surface of SWCNTs to facilitate the dissociation of O2. The barrier for the dissociation on dual graphite N-doped SWCNT-(8, 8) is as low as 0.3 eV, and the subsequent SO2 oxidation is thermodynamically favorable and kinetically feasible. These results spotlight on developing promising carboncatalyst via utilization of porous gemometry and heteroatom-doping of carbon materials simultaneously.

Hybrid Doping of Few-Layer Graphene via a Combination of Intercalation and Surface Doping

KAUST Repository

Mansour, Ahmed

2017-05-23

Surface molecular doping of graphene has been shown to modify its work function and increase its conductivity. However, the associated shifts in work function and increases in carrier concentration are highly coupled and limited by the surface coverage of dopant molecules on graphene. Here we show that few-layer graphene (FLG) can be doped using a hybrid approach, effectively combining surface doping by larger (metal-)organic molecules, while smaller molecules, such as Br2 and FeCl3, intercalate into the bulk. Intercalation tunes the carrier concentration more effectively, whereas surface doping of intercalated FLG can be used to tune its work function without reducing the carrier mobility. This multi-modal doping approach yields a very high carrier density and tunable work function for FLG, demonstrating a new versatile platform for fabricating graphene-based contacts for electronic, optoelectronic and photovoltaic applications.

Hybrid Doping of Few-Layer Graphene via a Combination of Intercalation and Surface Doping

KAUST Repository

Mansour, Ahmed; Kirmani, Ahmad R.; Barlow, Stephen; Marder, Seth R.; Amassian, Aram

2017-01-01

Surface molecular doping of graphene has been shown to modify its work function and increase its conductivity. However, the associated shifts in work function and increases in carrier concentration are highly coupled and limited by the surface coverage of dopant molecules on graphene. Here we show that few-layer graphene (FLG) can be doped using a hybrid approach, effectively combining surface doping by larger (metal-)organic molecules, while smaller molecules, such as Br2 and FeCl3, intercalate into the bulk. Intercalation tunes the carrier concentration more effectively, whereas surface doping of intercalated FLG can be used to tune its work function without reducing the carrier mobility. This multi-modal doping approach yields a very high carrier density and tunable work function for FLG, demonstrating a new versatile platform for fabricating graphene-based contacts for electronic, optoelectronic and photovoltaic applications.

Study of Coating Geometries and Photoluminescence Properties of Metal Nanoparticles/Graphite Composites

Directory of Open Access Journals (Sweden)

Pasquale Barone

2014-01-01

Full Text Available In this work we present the results of a study of growth and characterization of metal nanoparticles (Ag, Au, and Co/carbon surfaces. The nanoparticles grew by laser ablation technique and their dimensions were controlled by light scattering study and AFM microscopy before their insertion on graphite surface. Nanoparticles appear randomly disposed on carbon surfaces aggregating to form big particles only in the case of silver. The different behavior of metal nanoparticles on carbon surface was explained in terms of different metal wetting of surface, in agreement with previous theoretical results of He et al. Chemical information, obtained by X-ray photoelectron spectroscopy, indicated that the doping process is a simple physisorption while the interfacial interaction between particles and carbon layers causes local defects in graphite structure and the appearance of a strong photoluminescence signal for all composites. Moreover, the visible optical absorption decreases about 10% indicating the progressive metallization of carbon surface.

SEM/XPS analysis of fractured adhesively bonded graphite fibre surface resin-rich/graphite fibre composites

Science.gov (United States)

Devilbiss, T. A.; Wightman, J. P.; Progar, D. J.

1988-01-01

Samples of graphite fiber-reinforced polyimide were fabricated allowing the resin to accumulate at the composite surface. These surface resin-rich composites were then bonded together and tested for lap shear strength both before and after thermal aging. Lap shear strength did not appear to show a significant improvement over that previously recorded for resin-poor samples and was shown to decrease with increasing aging time and temperature.

Nitrogen-Rich Polyacrylonitrile-Based Graphitic Carbons for Hydrogen Peroxide Sensing

Directory of Open Access Journals (Sweden)

Brandon Pollack

2017-10-01

Full Text Available Catalytic substrate, which is devoid of expensive noble metals and enzymes for hydrogen peroxide (H2O2, reduction reactions can be obtained via nitrogen doping of graphite. Here, we report a facile fabrication method for obtaining such nitrogen doped graphitized carbon using polyacrylonitrile (PAN mats and its use in H2O2 sensing. A high degree of graphitization was obtained with a mechanical treatment of the PAN fibers embedded with carbon nanotubes (CNT prior to the pyrolysis step. The electrochemical testing showed a limit of detection (LOD 0.609 µM and sensitivity of 2.54 µA cm−2 mM−1. The promising sensing performance of the developed carbon electrodes can be attributed to the presence of high content of pyridinic and graphitic nitrogens in the pyrolytic carbons, as confirmed by X-ray photoelectron spectroscopy. The reported results suggest that, despite their simple fabrication, the hydrogen peroxide sensors developed from pyrolytic carbon nanofibers are comparable with their sophisticated nitrogen-doped graphene counterparts.

Tailoring thermal transport properties of graphene by nitrogen doping

Energy Technology Data Exchange (ETDEWEB)

Zhang, Tingting; Li, Jianhua; Cao, Yuwei; Zhu, Liyan, E-mail: lyzhu@hytc.edu.cn; Chen, Guibin, E-mail: gbchen@hytc.edu.cn [Huaiyin Normal University, School of Physics and Electronic & Electrical Engineering (China)

2017-02-15

The influence of two different nitrogen doping configurations, graphite-like and pyridinic-like nitrogen doping (denoted as graphite-N and pyridinic-N hereafter, respectively), on the thermal conduction of graphene is carefully studied via non-equilibrium molecular dynamic (NEMD) simulations. The thermal conductivity is more strongly suppressed in the pyridinic-N-doped graphene than that in the graphite-N-doped sample, which can be well understood from the changes in bond strength between nitrogen and carbon atoms, phonon group velocities, phonon density of states, participation ratio, and phonon transmission. Our study indicates that the pyridinic-N doping is an efficient method to tune the thermal conduction in graphene, especially for the situation where low thermal conductivity is requested, e.g., thermoelectric applications and thermal shielding.

Growth of nitrogen-doped graphene on copper: Multiscale simulations

Science.gov (United States)

Gaillard, P.; Schoenhalz, A. L.; Moskovkin, P.; Lucas, S.; Henrard, L.

2016-02-01

We used multiscale simulations to model the growth of nitrogen-doped graphene on a copper substrate by chemical vapour deposition (CVD). Our simulations are based on ab-initio calculations of energy barriers for surface diffusion, which are complemented by larger scale Kinetic Monte Carlo (KMC) simulations. Our results indicate that the shape of grown doped graphene flakes depends on the temperature and deposition flux they are submitted during the process, but we found no significant effect of nitrogen doping on this shape. However, we show that nitrogen atoms have a preference for pyridine-like sites compared to graphite-like sites, as observed experimentally.

Adsorption of charged albumin subdomains on a graphite surface.

Science.gov (United States)

Raffaini, Giuseppina; Ganazzoli, Fabio

2006-03-01

We report some new molecular dynamics simulation results about the adsorption on a hydrophobic graphite surface of two albumin subdomains, each formed by three different alpha-helices, considering the correctly charged side groups at pH = 7 instead of the neutral ones as done in our previous exploratory paper (Raffaini and Ganazzoli, Langmuir 2003;19:3403-3412). We find that the presence of charges affects somewhat the initial adsorption stage on the electrostatically neutral surface, but not the final one. Thus, we recover the result that a monolayer of aminoacids is eventually formed, with a rough parallelism of distant strands to optimize both the intramolecular and the surface interactions. This feature is consistent with the adsorption on the hydrophobic surface being driven by dispersion forces only, and with the "soft" nature of albumin. Additional optimizations of the final monolayer carried out at pH = 3 and 11 do not modify appreciably this picture, suggesting that adsorption on graphite is basically independent of pH. The enhanced hydration of the final adsorption state due to the (delocalized) charges of the side groups is also discussed in comparison with similar results of the neutralized subdomains. (c) 2005 Wiley Periodicals, Inc.

Control of work function of graphene by plasma assisted nitrogen doping

International Nuclear Information System (INIS)

Akada, Keishi; Terasawa, Tomo-o; Imamura, Gaku; Obata, Seiji; Saiki, Koichiro

2014-01-01

Nitrogen doping is expected to provide several intriguing properties to graphene. Nitrogen plasma treatment to defect-free and defective highly oriented pyrolytic graphite (HOPG) samples causes doping of nitrogen atom into the graphene layer. Nitrogen atoms are initially doped at a graphitic site (inside the graphene) for the defect-free HOPG, while doping to a pyridinic or a pyrrolic site (edge of the graphene) is dominant for the defective HOPG. The work function of graphene correlates strongly with the site and amount of doped nitrogen. Nitrogen atoms doped at a graphitic site lower the work function, while nitrogen atoms at a pyridinic or a pyrrolic site increase the work function. Control of plasma treatment time and the amount of initial defect could change the work function of graphite from 4.3 eV to 5.4 eV, which would open a way to tailor the nature of graphene for various industrial applications

Voronoi-Tessellated Graphite Produced by Low-Temperature Catalytic Graphitization from Renewable Resources.

Science.gov (United States)

Zhao, Leyi; Zhao, Xiuyun; Burke, Luke T; Bennett, J Craig; Dunlap, Richard A; Obrovac, Mark N

2017-09-11

A highly crystalline graphite powder was prepared from the low temperature (800-1000 °C) graphitization of renewable hard carbon precursors using a magnesium catalyst. The resulting graphite particles are composed of Voronoi-tessellated regions comprising irregular sheets; each Voronoi-tessellated region having a small "seed" particle located near their centroid on the surface. This suggests nucleated outward growth of graphitic carbon, which has not been previously observed. Each seed particle consists of a spheroidal graphite shell on the inside of which hexagonal graphite platelets are perpendicularly affixed. This results in a unique high surface area graphite with a high degree of graphitization that is made with renewable feedstocks at temperatures far below that conventionally used for artificial graphites. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Non-activated high surface area expanded graphite oxide for supercapacitors

Science.gov (United States)

Vermisoglou, E. C.; Giannakopoulou, T.; Romanos, G. E.; Boukos, N.; Giannouri, M.; Lei, C.; Lekakou, C.; Trapalis, C.

2015-12-01

Microwave irradiation of graphite oxide constitutes a facile route toward production of reduced graphene oxide, since during this treatment both exfoliation and reduction of graphite oxide occurs. In this work, the effect of pristine graphite (type, size of flakes), pretreatment and oxidation cycles on the finally produced expanded material was examined. All the types of graphite that were tested afforded materials with high BET surface areas ranging from 940 m2/g to 2490 m2/g, without intervening an activation stage at elevated temperature. SEM and TEM images displayed exfoliated structures, where the flakes were significantly detached and curved. The quality of the reduced graphene oxide sheets was evidenced both by X-ray photoelectron spectroscopy and Raman spectroscopy. The electrode material capacitance was determined via electrochemical impedance spectroscopy and cyclic voltammetry. The materials with PEDOT binder had better performance (∼97 F/g) at low operation rates while those with PVDF binder performed better (∼20 F/g) at higher rates, opening up perspectives for their application in supercapacitors.

Synthesis of Graphite Oxide with Different Surface Oxygen Contents Assisted Microwave Radiation

Directory of Open Access Journals (Sweden)

Adriana Ibarra-Hernández

2018-02-01

Full Text Available Graphite oxide is synthesized via oxidation reaction using oxidant compounds that have lattice defects by the incorporation of unlike functional groups. Herein, we report the synthesis of the graphite oxide with diverse surface oxygen content through three (B, C, D different modified versions of the Hummers method assisted microwave radiation compared with the conventional graphite oxide sample obtained by Hummers method (A. These methods allow not only the production of graphite oxide but also reduced graphene oxide, without undergoing chemical, thermal, or mechanical reduction steps. The values obtained of C/O ratio were ~2, 3.4, and ~8.5 for methodologies C, B, and D, respectively, indicating the presence of graphite oxide and reduced graphene oxide, according to X-ray photoelectron spectroscopy. Raman spectroscopy of method D shows the fewest structural defects compared to the other methodologies. The results obtained suggest that the permanganate ion produces reducing species during graphite oxidation. The generation of these species is attributed to a reversible reaction between the permanganate ion with π electrons, ions, and radicals produced after treatment with microwave radiation.

Visible-light induced photocatalysis of AgCl@Ag/titanate nanotubes/nitrogen-doped reduced graphite oxide composites

Science.gov (United States)

Pan, Hongfei; Zhao, Xiaona; Fu, Zhanming; Tu, Wenmao; Fang, Pengfei; Zhang, Haining

2018-06-01

High recombination rate of photogenerated electron-hole pairs and relatively narrow photoresponsive range of TiO2-based photocatalysts are the remaining challenges for their practical applications. To address such challenges, photocatalysts consisting of AgCl covered Ag nanoparticles (AgCl@Ag), titanate nanotubes (TiNT), and nitrogen-doped reduced graphite oxide (rGON) are fabricated through alkaline hydrothermal process, followed by deposition and in situ surface-oxidation of silver nanoparticles. In the synthesized photocatalysts, the titanate nanotubes have average length of about 100 nm with inner diameters of about 5 nm and the size of the formed silver nanoparticles is in the range of 50-100 nm. The synthesized photocatalyst degrades almost all the model organic pollutant Rhodamine B in 35 min and remains 90% of photocatalytic efficiency after 5 degradation cycles under visible light irradiation. Since the oxidant FeCl3 applied for oxidation of surface Ag to AgCl is difficult to be completely removed due to the high adsorption capacity of TiNT and rGON, the effect of reside Fe atoms on photocatalytic activity is evaluated and the results reveal that the residue Fe atom only affect the initial photodegradation performance. Nevertheless, the results demonstrate that the formed composite catalyst is a promising candidate for antibiosis and remediation in aquatic environmental contamination.

Atomization of magnesium, strontium, barium and lead nitrates on surface of graphite atomizers

International Nuclear Information System (INIS)

Nagdaev, V.K.; Pupyshev, A.A.

1982-01-01

Modelling of the processes on graphite surface using differential-thermal analysis and graphite core with identification of decomposition products of magnesium, strontium, barium and lead nitrates by X-ray analysis has shown that carbon promotes the formation of strontium, barium and lead carbonates. The obtained temperatures of strontium and barium carbonate decomposition to oxides agree satisfactorily with calculation ones. Magnesium nitrate does not react with carbon. Formation of strontium and barium carbonates results in considerable slowing down of the process of gaseous oxide dissociation. Lead carbonate is unstable and rapidly decomposes to oxide with subsequent reduction to free metal. Formation of magnesium, strontium and barium free atoms is connected with appearance of gaseous oxides in analytical zone. Oxide and free metal lead are present on graphite surface simultaneously

Influence of the Interaction Between Graphite and Polar Surfaces of ZnO on the Formation of Schottky Contact

Science.gov (United States)

Yatskiv, R.; Grym, J.

2018-03-01

We show that the interaction between graphite and polar surfaces of ZnO affects electrical properties of graphite/ZnO Schottky junctions. A strong interaction of the Zn-face with the graphite contact causes interface imperfections and results in the formation of laterally inhomogeneous Schottky contacts. On the contrary, high quality Schottky junctions form on the O-face, where the interaction is significantly weaker. Charge transport through the O-face ZnO/graphite junctions is well described by the thermionic emission model in both forward and reverse directions. We further demonstrate that the parameters of the graphite/ZnO Schottky diodes can be significantly improved when a thin layer of ZnO2 forms at the interface between graphite and ZnO after hydrogen peroxide surface treatment.

Direct synthesis of sp-bonded carbon chains on graphite surface by femtosecond laser irradiation

International Nuclear Information System (INIS)

Hu, A.; Rybachuk, M.; Lu, Q.-B.; Duley, W. W.

2007-01-01

Microscopic phase transformation from graphite to sp-bonded carbon chains (carbyne) and nanodiamond has been induced by femtosecond laser pulses on graphite surface. UV/surface enhanced Raman scattering spectra and x-ray photoelectron spectra displayed the local synthesis of carbyne in the melt zone while nanocrystalline diamond and trans-polyacetylene chains form in the edge area of gentle ablation. These results evidence possible direct 'writing' of variable chemical bonded carbons by femtosecond laser pulses for carbon-based applications

The Impact of Alkaliphilic Biofilm Formation on the Release and Retention of Carbon Isotopes from Nuclear Reactor Graphite.

Science.gov (United States)

Rout, S P; Payne, L; Walker, S; Scott, T; Heard, P; Eccles, H; Bond, G; Shah, P; Bills, P; Jackson, B R; Boxall, S A; Laws, A P; Charles, C; Williams, S J; Humphreys, P N

2018-03-13

14 C is an important consideration within safety assessments for proposed geological disposal facilities for radioactive wastes, since it is capable of re-entering the biosphere through the generation of 14 C bearing gases. The irradiation of graphite moderators in the UK gas-cooled nuclear power stations has led to the generation of a significant volume of 14 C-containing intermediate level wastes. Some of this 14 C is present as a carbonaceous deposit on channel wall surfaces. Within this study, the potential of biofilm growth upon irradiated and 13 C doped graphite at alkaline pH was investigated. Complex biofilms were established on both active and simulant samples. High throughput sequencing showed the biofilms to be dominated by Alcaligenes sp at pH 9.5 and Dietzia sp at pH 11.0. Surface characterisation revealed that the biofilms were limited to growth upon the graphite surface with no penetration of the deeper porosity. Biofilm formation resulted in the generation of a low porosity surface layer without the removal or modification of the surface deposits or the release of the associated 14 C/ 13 C. Our results indicated that biofilm formation upon irradiated graphite is likely to occur at the pH values studied, without any additional release of the associated 14 C.

Comparison on exfoliated graphene nano-sheets and triturated graphite nano-particles for mode-locking the Erbium-doped fibre lasers

Science.gov (United States)

Yang, Chun-Yu; Lin, Yung-Hsiang; Wu, Chung-Lun; Cheng, Chih-Hsien; Tsai, Din-Ping; Lin, Gong-Ru

2018-06-01

Comparisons on exfoliated graphene nano-sheets and triturated graphite nano-particles for mode-locking the Erbium-doped fiber lasers (EDFLs) are performed. As opposed to the graphite nano-particles obtained by physically triturating the graphite foil, the tri-layer graphene nano-sheets is obtained by electrochemically exfoliating the graphite foil. To precisely control the size dispersion and the layer number of the exfoliated graphene nano-sheet, both the bias of electrochemical exfoliation and the speed of centrifugation are optimized. Under a threshold exfoliation bias of 3 volts and a centrifugation at 1000 rpm, graphene nano-sheets with an average diameter of 100  ±  40 nm can be obtained. The graphene nano-sheets with an area density of 15 #/µm2 are directly imprinted onto the end-face of a single-mode fiber made patchcord connector inside the EDFL cavity. Such electrochemically exfoliated graphene nano-sheets show comparable saturable absorption with standard single-graphene and perform the self-amplitude modulation better than physically triturated graphite nano-particles. The linear transmittance and modulation depth of the inserted graphene nano-sheets are 92.5% and 53%, respectively. Under the operation with a power gain of 21.5 dB, the EDFL can be passively mode-locked to deliver a pulsewidth of 454.5 fs with a spectral linewidth of 5.6 nm. The time-bandwidth product of 0.31 is close to the transform limit. The Kelly sideband frequency spacing of 1.34 THz is used to calculate the chirp coefficient as  ‑0.0015.

Advanced Surface and Microstructural Characterization of Natural Graphite Anodes for Lithium Ion Batteries

Energy Technology Data Exchange (ETDEWEB)

Gallego, Nidia C [ORNL; Contescu, Cristian I [ORNL; Meyer III, Harry M [ORNL; Howe, Jane Y [ORNL; Meisner, Roberta Ann [ORNL; Payzant, E Andrew [ORNL; Lance, Michael J [ORNL; Yoon, Steve [A123 Systems, Inc.; Denlinger, Matthew [A123 Systems, Inc.; Wood III, David L [ORNL

2014-01-01

Natural graphite powders were subjected to a series of thermal treatments in order to improve the anode irreversible capacity loss (ICL) and capacity retention during long-term cycling of lithium ion batteries. A baseline thermal treatment in inert Ar or N2 atmosphere was compared to cases with a proprietary additive to the furnace gas environment. This additive substantially altered the surface chemistry of the natural graphite powders and resulted in significantly improved long-term cycling performance of the lithium ion batteries over the commercial natural graphite baseline. Different heat-treatment temperatures were investigated ranging from 950-2900 C with the intent of achieving the desired long-term cycling performance with as low of a maximum temperature and thermal budget as possible. A detailed summary of the characterization data is also presented, which includes X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and temperature-programed desorption mass spectroscopy (TPD-MS). This characterization data was correlated to the observed capacity fade improvements over the course of long-term cycling at high charge-discharge rates in full lithium-ion coin cells. It is believed that the long-term performance improvements are a result of forming a more stable solid electrolyte interface (SEI) layer on the anode graphite surfaces, which is directly related to the surface chemistry modifications imparted by the proprietary gas environment during thermal treatment.

Electrochemical characteristics of Shewanella loihica on carbon nanotubes-modified graphite surfaces

International Nuclear Information System (INIS)

Zhang, Xiaoming; Epifanio, Monica; Marsili, Enrico

2013-01-01

Highlights: • We deposited CNT coatings on graphite electrode by electrophoretic deposition. • CNT coating increased extracellular electron transfer in Shewanella loihica biofilms. • Thick electroactive biofilms hinder the electroactivity of CNT coatings. -- Abstract: High specific surface and electrocatalytic activity of the electrode surface favour extracellular electron transfer from electrochemically active biofilms to polarized electrodes. We coated layer-by-layer carbon nanotubes (CNTs) on graphite electrodes through electrophoretic deposition, thus increasing the electrocatalytic activity. After determining the optimal number of CNT layers through electrochemical methods, we grew Shewanella loihica PV-4 biofilms on the CNT-coated electrodes to quantify the increase in extracellular electron transfer rate compared with unmodified electrodes. Current density on CNT-modified electrodes was 1.7 times higher than that observed on unmodified electrodes after 48 h from inoculation. Rapid microbial cells attachment on CNT-coated electrodes, as determined from scanning electronic microscopy, explained the rapid increase of the current. Also, the CNT reduced the charge transfer resistance of the graphite electrodes, as measured by Electrochemical Impedance Spectroscopy. However, the electrocatalytic activity of the CNT-coated electrode decreased as the biofilm grew thicker and covered the CNT-coating. These result confirmed that surface-modified electrodes improve the electron transfer rate in thin biofilms (<5 μm), but are not feasible for power production in microbial fuel cells, where the biofilm thickness is much higher

Surface modification by vacuum annealing for field emission from heavily phosphorus-doped homoepitaxial (1 1 1) diamond

International Nuclear Information System (INIS)

Yamada, Takatoshi; Nebel, Christoph E.; Somu, Kumaragurubaran; Shikata, Shin-ichi

2008-01-01

The relationship between field emission properties and C 1s core level shifts of heavily phosphorus-doped homoepitaxial (1 1 1) diamond is investigated as a function of annealing temperature in order to optimize surface carbon bonding configurations for device applications. A low field emission threshold voltage is observed from surfaces annealed at 800 deg. C for hydrogen-plasma treated surface, while a low field emission threshold voltage of wet-chemical oxidized surface is observed after annealing at 900 deg. C. The C 1s core level by X-ray photoelectron spectroscopy (XPS) showed a shoulder peak at 1 eV below the main peak over 800 and 900 deg. C annealing temperature for hydrogen-plasma treated and wet-chemical oxidized surfaces, respectively. When the shoulder peak intensity is less than 10% of the main peak intensity, lower threshold voltages are observed. This is due to the carbon-reconstruction which gives rise to a small positive electron affinity. By increasing annealing temperature, the shoulder peak ratios also increase, which indicates that a surface graphitization takes place. This leads to higher threshold voltages

Thermally exfoliated graphite oxide

Science.gov (United States)

Prud'Homme, Robert K. (Inventor); Aksay, Ilhan A. (Inventor); Abdala, Ahmed (Inventor)

2011-01-01

A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from about 300 sq m/g to 2600 sq m/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as determined by X-ray diffraction.

An in situ vapour phase hydrothermal surface doping approach for fabrication of high performance Co3O4 electrocatalysts with an exceptionally high S-doped active surface.

Science.gov (United States)

Tan, Zhijin; Liu, Porun; Zhang, Haimin; Wang, Yun; Al-Mamun, Mohammad; Yang, Hua Gui; Wang, Dan; Tang, Zhiyong; Zhao, Huijun

2015-04-04

A facile in situ vapour phase hydrothermal (VPH) surface doping approach has been developed for fabrication of high performance S-doped Co3O4 electrocatalysts with an unprecedentedly high surface S content (>47%). The demonstrated VPH doping approach could be useful for enrichment of surface active sites for other metal oxide electrocatalysts.

Nitrogen-doped graphene prepared by a transfer doping approach for the oxygen reduction reaction application

Science.gov (United States)

Mo, Zaiyong; Zheng, Ruiping; Peng, Hongliang; Liang, Huagen; Liao, Shijun

2014-01-01

Well defined nitrogen-doped graphene (NG) is prepared by a transfer doping approach, in which the graphene oxide (GO) is deoxidized and nitrogen doped by the vaporized polyaniline, and the GO is prepared by a thermal expansion method from graphite oxide. The content of doped nitrogen in the doped graphene is high up to 6.25 at% by the results of elements analysis, and oxygen content is lowered to 5.17 at%. As a non-precious metal cathode electrocatalyst, the NG catalyst exhibits excellent activity toward the oxygen reduction reaction, as well as excellent tolerance toward methanol. In 0.1 M KOH solution, its onset potential, half-wave potential and limiting current density for the oxygen reduction reaction reach 0.98 V (vs. RHE), 0.87 V (vs. RHE) and 5.38 mA cm-2, respectively, which are comparable to those of commercial 20 wt% Pt/C catalyst. The well defined graphene structure of the catalyst is revealed clearly by HRTEM and Raman spectra. It is suggested that the nitrogen-doping and large surface area of the NG sheets give the main contribution to the high ORR catalytic activity.

Electrolysis of acidic sodium chloride solution with a graphite anode. I. Graphite electrode

NARCIS (Netherlands)

Janssen, L.J.J.; Hoogland, J.G.

1969-01-01

A graphite anode evolving Cl from a chloride soln. is slowly oxidized to CO and CO2. This oxidn. causes a change in the characteristics of the electrode in aging, comprising a change of the nature of the graphite surface and an increase of the surface area. It appears that a new graphite electrode

Significance of Graphitic Surfaces in Aurodicyanide Adsorption by Activated Carbon: Experimental and Computational Approach

Science.gov (United States)

Bhattacharyya, Dhiman; Depci, Tolga; Prisbrey, Keith; Miller, Jan D.

Despite tremendous developments in industrial use of activated carbon (AC) for gold adsorption, specific aurodicyanide [Au(CN)2-] adsorption sites on the carbon have intrigued researchers. The graphitic structure of AC has been well established. Previously radiochemical and now, XPS and Raman characterizations have demonstrated higher site-specific gold adsorption on graphitic edges. Morphological characterizations have revealed the presence of slit-pores (5-10 Å). Molecular-dynamics-simulation (MDS) performed on graphitic slit-pores illustrated gold-cyanide ion-pair preferentially adsorbs on edges. Ab-initio simulations predicted lower barrier for electron sharing in pores with aurodic yanide, indicating tighter bonding than graphitic surface and was well supported by Gibbs energy calculations too. Interaction energy as function of the separation distance indicated tighter bonding of gold cyanide to the graphite edges than water molecules. Selective adsorption of aurodicyanide ion-pair seems to be related to low polarity of gold complex and its accommodation at graphitic edges.

Formation of Reversible Solid Electrolyte Interface on Graphite Surface from Concentrated Electrolytes

Energy Technology Data Exchange (ETDEWEB)

Lu, Dongping; Tao, Jinhui; Yan, Pengfei; Henderson, Wesley A.; Li, Qiuyan; Shao, Yuyan; Helm, Monte L.; Borodin, Oleg; Graff, Gordon L.; Polzin, Bryant; Wang, Chong-Min; Engelhard, Mark; Zhang, Ji-Guang; De Yoreo, James J.; Liu, Jun; Xiao, Jie

2017-02-10

Interfacial phenomena have always been key determinants for the performance of energy storage technologies. The solid electrolyte interfacial (SEI) layer, pervasive on the surfaces of battery electrodes for numerous chemical couples, directly affects the ion transport, charge transfer and lifespan of the entire energy system. Almost all SEI layers, however, are unstable resulting in the continuous consumption of the electrolyte. Typically, this leads to the accumulation of degradation products on/restructuring of the electrode surface and thus increased cell impedance, which largely limits the long-term operation of the electrochemical reactions. Herein, a completely new SEI formation mechanism has been discovered, in which the electrolyte components reversibly self-assemble into a protective surface coating on a graphite electrode upon changing the potential. In contrast to the established wisdom regarding the necessity of employing the solvent ethylene carbonate (EC) to form a protective SEI layer on graphite, a wide range of EC-free electrolytes are demonstrated for the reversible intercalation/deintercalation of Li+ cations within a graphite lattice, thereby providing tremendous flexibility in electrolyte tailoring for battery couples. This novel finding is broadly applicable and provides guidance for how to control interfacial reactions through the relationship between ion aggregation and solvent decomposition at polarized interfaces.

Thermal desorption of formamide and methylamine from graphite and amorphous water ice surfaces

Science.gov (United States)

Chaabouni, H.; Diana, S.; Nguyen, T.; Dulieu, F.

2018-04-01

Context. Formamide (NH2CHO) and methylamine (CH3NH2) are known to be the most abundant amine-containing molecules in many astrophysical environments. The presence of these molecules in the gas phase may result from thermal desorption of interstellar ices. Aims: The aim of this work is to determine the values of the desorption energies of formamide and methylamine from analogues of interstellar dust grain surfaces and to understand their interaction with water ice. Methods: Temperature programmed desorption (TPD) experiments of formamide and methylamine ices were performed in the sub-monolayer and monolayer regimes on graphite (HOPG) and non-porous amorphous solid water (np-ASW) ice surfaces at temperatures 40-240 K. The desorption energy distributions of these two molecules were calculated from TPD measurements using a set of independent Polanyi-Wigner equations. Results: The maximum of the desorption of formamide from both graphite and ASW ice surfaces occurs at 176 K after the desorption of H2O molecules, whereas the desorption profile of methylamine depends strongly on the substrate. Solid methylamine starts to desorb below 100 K from the graphite surface. Its desorption from the water ice surface occurs after 120 K and stops during the water ice sublimation around 150 K. It continues to desorb from the graphite surface at temperatures higher than160 K. Conclusions: More than 95% of solid NH2CHO diffuses through the np-ASW ice surface towards the graphitic substrate and is released into the gas phase with a desorption energy distribution Edes = 7460-9380 K, which is measured with the best-fit pre-exponential factor A = 1018 s-1. However, the desorption energy distribution of methylamine from the np-ASW ice surface (Edes = 3850-8420 K) is measured with the best-fit pre-exponential factor A = 1012 s-1. A fraction of solid methylamine monolayer of roughly 0.15 diffuses through the water ice surface towards the HOPG substrate. This small amount of methylamine

Oxidation behavior of IG and NBG nuclear graphites

Energy Technology Data Exchange (ETDEWEB)

Choi, Woong-Ki; Kim, Byung-Joo [Jeonju Institute of Machinery and Carbon Composites Palbokdong-2ga, 817, Jeonju, Jeollabuk-do 561-844 (Korea, Republic of); Kim, Eung-Seon; Chi, Se-Hwan [Dept. of Nuclear Hydrogen Project, Korea Atomic Energy Research Institute, Daejeon 305-353 (Korea, Republic of); Park, Soo-Jin, E-mail: sjpark@inha.ac.k [Dept. of Chemistry, Inha Univ., 253, Nam-gu, Incheon 402-751 (Korea, Republic of)

2011-01-15

Graphical abstract: Water contact angles on nuclear graphite before and after oxidation treatments: the pictures show the contact angles obtained under deionized water on oxidation-treated and untreated nuclear graphite. The water contact angles are decreased after oxidation due to the increase in the hydrophilic. Display Omitted Research highlights: The average pore size of graphites shows an increase after the oxidation treatments. They also show that oxidation produces the surface functional groups on the graphite surfaces. The surface area of each graphite behaves in a unique manner. - Abstract: This work studies the oxidation-induced characteristics of four nuclear graphites (NBG-17, NBG-25, IG-110, and IG-430). The oxidation characteristics of the nuclear graphites were measured at 600 {sup o}C. The surface properties of the oxidation graphites were characterized by means of scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle methods. The N{sub 2}/77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were investigated by means of BET and t-plot methods. The experimental results show an increase in the average pore size of graphites; they also show that oxidation produces the surface functional groups on the graphite surfaces. The surface area of each graphite behaves in a unique manner. For example the surface area of NBG-17 increases slightly whereas the surface area of IG-110 increases significantly. This result confirms that the original surface state of each graphite is unique.

Bubble Departure from Metal-Graphite Composite Surfaces and Its Effects on Pool Boiling Heat Transfer

Science.gov (United States)

Chao, David F.; Sankovic, John M.; Motil, Brian J.; Yang, W-J.; Zhang, Nengli

2010-01-01

The formation and growth processes of a bubble in the vicinity of graphite micro-fiber tips on metal-graphite composite boiling surfaces and their effects on boiling behavior are investigated. It is discovered that a large number of micro bubbles are formed first at the micro scratches and cavities on the metal matrix in pool boiling. By virtue of the non-wetting property of graphite, once the growing micro bubbles touch the graphite tips, the micro bubbles are sucked by the tips and merged into larger micro bubbles sitting on the end of the tips. The micro bubbles grow rapidly and coalesce to form macro bubbles, each spanning several tips. The necking process of a detaching macro bubble is analyzed. It is revealed that a liquid jet is produced by sudden break-off of the bubble throat. The composite surfaces not only have higher temperatures in micro- and macrolayers but also make higher frequency of the bubble departure, which increase the average heat fluxes in both the bubble growth stage and in the bubble departure period. Based on these analyses, the enhancement mechanism of pool boiling heat transfer on composite surfaces is clearly revealed.

Outgassing tests on graphites in temperature range 100-1600 degrees C

International Nuclear Information System (INIS)

Alessandrini, C.; Apicella, M.L.; Verdini, L.

1993-01-01

Graphite is a an interesting material for plasma-facing components in fusion experiments, mainly because of its low atomic number and excellent thermal properties. Nevertheless, it contains a large amount of gaseous impurities, which can be released by plasma-surface interactions and affect the purity of the deuterium-tritium plasma. To investigate the outgassing behaviour of graphites, CFC's and doped C composites, a facility was set up to perform outgassing tests on samples, as a function of temperature in the range between 100 and 1600 degrees C. The experimental apparatus, designed to work in UHV conditions, allows outgassing measurements by a quadrupole mass spectrometer (1-200 AMU) using two different methods. The test facility, the quadrupole calibration and preliminary quantitative outgassing measurements on SEP CARB N112 samples are described

Examination of Surface Deposits on Oldbury Reactor Core Graphite to Determine the Concentration and Distribution of 14C.

Directory of Open Access Journals (Sweden)

Liam Payne

Full Text Available Pile Grade A graphite was used as a moderator and reflector material in the first generation of UK Magnox nuclear power reactors. As all of these reactors are now shut down there is a need to examine the concentration and distribution of long lived radioisotopes, such as 14C, to aid in understanding their behaviour in a geological disposal facility. A selection of irradiated graphite samples from Oldbury reactor one were examined where it was observed that Raman spectroscopy can distinguish between underlying graphite and a surface deposit found on exposed channel wall surfaces. The concentration of 14C in this deposit was examined by sequentially oxidising the graphite samples in air at low temperatures (450°C and 600°C to remove the deposit and then the underlying graphite. The gases produced were captured in a series of bubbler solutions that were analysed using liquid scintillation counting. It was observed that the surface deposit was relatively enriched with 14C, with samples originating lower in the reactor exhibiting a higher concentration of 14C. Oxidation at 600°C showed that the remaining graphite material consisted of two fractions of 14C, a surface associated fraction and a graphite lattice associated fraction. The results presented correlate well with previous studies on irradiated graphite that suggest there are up to three fractions of 14C; a readily releasable fraction (corresponding to that removed by oxidation at 450°C in this study, a slowly releasable fraction (removed early at 600°C in this study, and an unreleasable fraction (removed later at 600°C in this study.

Moiré pattern induced by the electronic coupling between 1-octanol self-assembled monolayers and graphite surface

International Nuclear Information System (INIS)

Silly, Fabien

2012-01-01

Two-dimensional self-assembly of 1-octanol molecules on a graphite surface is investigated using scanning tunneling microscopy (STM) at the solid/liquid interface. STM images reveal that this molecule self-assembles into a compact hydrogen-bonded herringbone nanoarchitecture. Molecules are preferentially arranged in a head-to-head and tail-to-tail fashion. A Moiré pattern appears in the STM images when the 1-octanol layer is covering the graphite surface. The large Moiré stripes are perpendicular to the 1-octanol lamellae. Interpretation of the STM images suggests that the Moiré periodicity is governed by the electronic properties of the graphite surface and the 1-octanol layer periodicity. (paper)

Surface Characterization and Electrochemical Oxidation of Metal Doped Uranium Dioxide

Energy Technology Data Exchange (ETDEWEB)

Lee, Jeongmook; Kim, Jandee; Youn, Young-Sang; Kim, Jong-Goo; Ha, Yeong-Keong; Kim, Jong-Yun [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

Trivalent element in UO{sub 2} matrix makes the oxygen vacancy from loss of oxygen for charge compensation. Tetravalent element alters lattice parameter of UO{sub 2} due to diameter difference between the tetravalent element and replaced U. These structural changes have significant effect on not only relevant fuel performance but also the kinetics of fuel oxidation. Park and Olander explained the stabilization of Ln (III)-doped UO{sub 2} against oxidation based on oxygen potential calculations. In this work, we have been investigated the effect of Gd{sup 3+} and Th{sup 4+} doping on the UO{sub 2} structure with Raman spectroscopy and X-ray diffraction to characterize the surface structure of nuclear fuel material. For Gd doped UO{sub 2}, its electrochemical oxidation behaviors are also investigated. The Gd and Th doped uranium dioxide solid solution pellets with various doping level were investigated by XRD, Raman spectroscopy, SEM, electrochemical experiments to investigate surface structure and electro chemical oxidation behaviors. The lattice parameter evaluated from XRD spectra indicated the formation of solid solutions. Raman spectra showed the existence of the oxygen vacancy. SEM images showed the grain structure on the surface of Gd doped uranium dioxide depending on doping level and oxygen-to-metal ratio.

Graphite intercalated polyaniline composite with superior anticorrosive and hydrophobic properties, as protective coating material on steel surfaces

Energy Technology Data Exchange (ETDEWEB)

Rathnayake, R.M.N.M. [National Institute of Fundamental Studies, Kandy (Sri Lanka); Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Mantilaka, M.M.M.G.P.G. [Sri Lanka Institute of Nanotechnology, Nanotechnology and Science Park, Mahenwatte, Pitipana, Homagama (Sri Lanka); Hara, Masanori; Huang, Hsin-Hui [Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Wijayasinghe, H.W.M.A.C., E-mail: athula@ifs.ac.lk [National Institute of Fundamental Studies, Kandy (Sri Lanka); Yoshimura, Masamichi [Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Pitawala, H.M.T.G.A. [Department of Geology, University of Peradeniya, Peradeniya (Sri Lanka)

2017-07-15

Highlights: • In this paper, it has been utilized a novel method to prepare a new composite material of PANI/NPG graphite composite, using NPG vein graphite variety. • It is found that the composite works as an anti-corrosive coating on steel surfaces. Further, the prepared composite shows good hydrophobic ability, which is very useful in preventing corrosion on metal surfaces. • The prepared PANI/NPG composite material shows a significantly high corrosion resistance compared to alkyd resin/PANI coatings or alkyd resin coatings, on steel surfaces. - Abstract: Solid polymer composite systems are widely being used for potential technological applications in secondary energy sources and electrochromic devices. In this study, we synthesized and characterized a composite material composed of polyaniline (PANI) and natural needle platy (NPG) vein graphite. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), cyclic voltammetry (CV), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), micro-Raman analysis, thermogravimetric and differential thermal analysis (TGA/DTA), transmission electron microscopy (TEM) were used to study the structural and electrochemical properties of the prepared PANI/NPG graphite composite. XPS, FTIR, and micro-Raman analysis confirmed the existence of relevant functional groups and bonding in the prepared PANI/NPG composite material. The composite shows a very low corrosion rate, approximately 29 μm per year, and high hydrophobicity on steel surfaces, which helps to prevent the corrosion due to O{sub 2} penetration towards the metal surface. It indicates that the composite can be used as a high potential surface coating material to anticorrosion. The specific capacitance of PANI/NPG composite is 833.3 F g{sup −1}, which is higher than that of PANI. This synergistic electrical performance result proves the prepared PANI/NPG graphite composite as a suitable protective coating material for steel

Curing characteristics of an epoxy resin in the presence of functional graphite oxide with amine-rich surface

Energy Technology Data Exchange (ETDEWEB)

Li, Le [The State Key Lab of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065 (China); Zeng, Zhong [Safety Environment Quality Surveillance and Inspection Research Institute of CNPC Chuanqing Drilling & Exploration Corporation, Chengdu 618300 (China); Zou, Huawei, E-mail: hwzou@163.com [The State Key Lab of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065 (China); Liang, Mei, E-mail: liangmeiww@163.com [The State Key Lab of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065 (China)

2015-08-20

Highlights: • Functional graphite oxide with amine-rich surface was prepared and characterized. • Kinetic parameters were calculated by Kissinger method and autocatalytic model. • The incorporation of GO and DGO brings in an effect of inhibition on curing. • The inhibition effect weakens for its good compatibility and catalytic effect of DGO. - Abstract: Functional graphite oxide (DGO) with amine-rich surface was successfully prepared through the amidation reaction and characterized by X-ray diffraction analyses (XRD), Fourier transform infrared spectra (FTIR) and Raman spectra. The effects of functional graphite oxide on the curing kinetics of epoxy (EP) were investigated by means of differential scanning calorimetry (DSC). The curing kinetic parameters of EP, EP/graphite oxide (GO) and EP/functional graphite oxide were obtained. There was not much difference in total heat of reaction ΔH and peak temperature T{sub p} with the incorporation of GO or DGO. However, the activation energy, E{sub a}, and the overall order of reaction m + n were enhanced. Comprehensive kinetic analyses indicated that the incorporation of GO sheets brought in an effect of inhibition on curing process. While the inhibition effect weaken when the GO is modified with amine-rich surface. The possible curing mechanism and reaction pathways were proposed to provide a reasonable explanation.

Curing characteristics of an epoxy resin in the presence of functional graphite oxide with amine-rich surface

International Nuclear Information System (INIS)

Li, Le; Zeng, Zhong; Zou, Huawei; Liang, Mei

2015-01-01

Highlights: • Functional graphite oxide with amine-rich surface was prepared and characterized. • Kinetic parameters were calculated by Kissinger method and autocatalytic model. • The incorporation of GO and DGO brings in an effect of inhibition on curing. • The inhibition effect weakens for its good compatibility and catalytic effect of DGO. - Abstract: Functional graphite oxide (DGO) with amine-rich surface was successfully prepared through the amidation reaction and characterized by X-ray diffraction analyses (XRD), Fourier transform infrared spectra (FTIR) and Raman spectra. The effects of functional graphite oxide on the curing kinetics of epoxy (EP) were investigated by means of differential scanning calorimetry (DSC). The curing kinetic parameters of EP, EP/graphite oxide (GO) and EP/functional graphite oxide were obtained. There was not much difference in total heat of reaction ΔH and peak temperature T p with the incorporation of GO or DGO. However, the activation energy, E a , and the overall order of reaction m + n were enhanced. Comprehensive kinetic analyses indicated that the incorporation of GO sheets brought in an effect of inhibition on curing process. While the inhibition effect weaken when the GO is modified with amine-rich surface. The possible curing mechanism and reaction pathways were proposed to provide a reasonable explanation

Polymer surfaces graphitization by low-energy He{sup +} ions irradiation

Energy Technology Data Exchange (ETDEWEB)

Geworski, A.; Lazareva, I.; Gieb, K.; Koval, Y.; Müller, P. [Department of Physics, Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, 91058 Erlangen (Germany)

2014-08-14

The electrical and optical properties of surfaces of polyimide and AZ5214e graphitized by low-energy (1 keV) He{sup +} irradiation at different polymer temperatures were investigated. The conductivity of the graphitized layers can be controlled with the irradiation temperature within a broad range and can reach values up to ∼1000 S/cm. We show that the electrical transport in low-conducting samples is governed by thermally activated hopping, while the samples with a high conductivity show a typical semimetallic behavior. The transition from thermally activated to semimetallic conductance governed by the irradiation temperature could also be observed in optical measurements. The semimetallic samples show an unusually high for graphitic materials carrier concentration, which results in a high extinction coefficient in the visible light range. By analyzing the temperature dependence of the conductance of the semimetallic samples, we conclude that the scattering of charge carriers is dominated by Coulomb interactions and can be described by a weak localization model. The transition from a three to two dimensional transport mechanism at low temperatures consistently explains the change in the temperature dependence of the conductance by cooling, observed in experiments.

Graphitization of boron predeposited 6H-SiC(0 0 0 1) surface

International Nuclear Information System (INIS)

Okonogi, Yuta; Aoki, Yuki; Hirayama, Hiroyuki

2012-01-01

Highlights: ► We have tried to dope the B atoms into epitaxial graphene during the graphene growing process. ► The B induced changes in the surface were characterized by low-energy electron microscopy, auger electron spectroscopy, atomic force microscopy, and scanning tunneling icroscopy. ► No obvious B atoms doping evidence into the graphene was observed. - Abstract: We examined the substitutional doping of B atoms into epitaxial graphene on the SiC(0 0 0 1) surface. B atoms were deposited on the SiC(0 0 0 1) surface in advance of the growth of graphene. The B-induced changes in the surface morphology and chemical composition were characterized at the four thermal treatment stages in the growth of graphene (at 1120, 1370, 1520, and 1770 K) by low-energy electron diffraction (LEED), auger electron spectroscopy (AES), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). The B atoms were found to hinder the formation of a spatially uniform graphene layer. However, local deformation of the graphene lattice, which should be observed if B atoms are successfully doped substitutionally, was not observed in STM.

Wettability of graphitic-carbon and silicon surfaces: MD modeling and theoretical analysis

International Nuclear Information System (INIS)

Ramos-Alvarado, Bladimir; Kumar, Satish; Peterson, G. P.

2015-01-01

The wettability of graphitic carbon and silicon surfaces was numerically and theoretically investigated. A multi-response method has been developed for the analysis of conventional molecular dynamics (MD) simulations of droplets wettability. The contact angle and indicators of the quality of the computations are tracked as a function of the data sets analyzed over time. This method of analysis allows accurate calculations of the contact angle obtained from the MD simulations. Analytical models were also developed for the calculation of the work of adhesion using the mean-field theory, accounting for the interfacial entropy changes. A calibration method is proposed to provide better predictions of the respective contact angles under different solid-liquid interaction potentials. Estimations of the binding energy between a water monomer and graphite match those previously reported. In addition, a breakdown in the relationship between the binding energy and the contact angle was observed. The macroscopic contact angles obtained from the MD simulations were found to match those predicted by the mean-field model for graphite under different wettability conditions, as well as the contact angles of Si(100) and Si(111) surfaces. Finally, an assessment of the effect of the Lennard-Jones cutoff radius was conducted to provide guidelines for future comparisons between numerical simulations and analytical models of wettability

Electropolymerization of 3-aminophenol on carbon graphite surface: Electric and morphologic properties

Energy Technology Data Exchange (ETDEWEB)

Franco, Diego L.; Afonso, Andre S.; Vieira, Sabrina N.; Ferreira, Lucas F. [Institute of Chemistry, Federal University of Uberlandia, Av. Joao Naves de Avila 2121, 38400-902 Uberlandia (Brazil); Goncalves, Rafael A. [School of Mechanical Engineering, Federal University of Uberlandia, Av. Joao Naves de Avila 2121, 38400-902 Uberlandia (Brazil); Brito-Madurro, Ana G. [Institute of Chemistry, Federal University of Uberlandia, Av. Joao Naves de Avila 2121, 38400-902 Uberlandia (Brazil); Madurro, Joao M. [Institute of Chemistry, Federal University of Uberlandia, Av. Joao Naves de Avila 2121, 38400-902 Uberlandia (Brazil)], E-mail: jmadurro@ufu.br

2008-02-15

This paper reports the formation of electropolymerized films derived from 3-aminophenol on graphite electrode by cyclic voltammetry, prepared in different pH conditions. With increase of pH values, a shift of the oxidation potential of 3-aminophenol to more cathodic potentials was observed. 3-Aminophenol electrooxidation, in acid and basic media, yielded polymeric films onto graphite surface. In ferrocyanide/ferricyanide solution, the polymer produced in acid medium showed higher electron transfer efficiency. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and FT-IR were used to investigate some properties of the graphite electrode modified with poly(3-aminophenol). Scanning electron microscopy showed that the morphology of the films is strongly dependent on the pH of the electropolymerization medium. FT-IR spectra of polymer films produced for either acid or basic media suggest that the monomer is polymerized by NH{sub 2} group.

Electropolymerization of 3-aminophenol on carbon graphite surface: Electric and morphologic properties

International Nuclear Information System (INIS)

Franco, Diego L.; Afonso, Andre S.; Vieira, Sabrina N.; Ferreira, Lucas F.; Goncalves, Rafael A.; Brito-Madurro, Ana G.; Madurro, Joao M.

2008-01-01

This paper reports the formation of electropolymerized films derived from 3-aminophenol on graphite electrode by cyclic voltammetry, prepared in different pH conditions. With increase of pH values, a shift of the oxidation potential of 3-aminophenol to more cathodic potentials was observed. 3-Aminophenol electrooxidation, in acid and basic media, yielded polymeric films onto graphite surface. In ferrocyanide/ferricyanide solution, the polymer produced in acid medium showed higher electron transfer efficiency. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and FT-IR were used to investigate some properties of the graphite electrode modified with poly(3-aminophenol). Scanning electron microscopy showed that the morphology of the films is strongly dependent on the pH of the electropolymerization medium. FT-IR spectra of polymer films produced for either acid or basic media suggest that the monomer is polymerized by NH 2 group

Formation of carbon nanotubes in the graphite surface by Ar ion sputtering

International Nuclear Information System (INIS)

Wang Zhenxia; Zhu Fuying; Wang Wenmin; Yu Guoqing; Ruan Meiling; Zhang Huiming; Zhu Jingping

1998-01-01

The authors have investigated structures and topography features of sputtered graphite surface using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and demonstrated that carbon nanotubes can be grown up by sputtered-atom deposition on a protrusion of topography feature

Graphite-graphite oxide composite electrode for vanadium redox flow battery

International Nuclear Information System (INIS)

Li Wenyue; Liu Jianguo; Yan Chuanwei

2011-01-01

Highlights: → A new composite electrode is designed for vanadium redox flow battery (VRB). → The graphite oxide (GO) is used as electrode reactions catalyst. → The excellent electrode activity is attributed to the oxygen-containing groups attached on the GO surface. → A catalytic mechanism of the GO towards the redox reactions is presumed. - Abstract: A graphite/graphite oxide (GO) composite electrode for vanadium redox battery (VRB) was prepared successfully in this paper. The materials were characterized with X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The specific surface area was measured by the Brunauer-Emmett-Teller method. The redox reactions of [VO 2 ] + /[VO] 2+ and V 3+ /V 2+ were studied with cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that the electrochemical performances of the electrode were improved greatly when 3 wt% GO was added into graphite electrode. The redox peak currents of [VO 2 ] + /[VO] 2+ and V 3+ /V 2+ couples on the composite electrode were increased nearly twice as large as that on the graphite electrode, and the charge transfer resistances of the redox pairs on the composite electrode are also reduced. The enhanced electrochemical activity could be ascribed to the presence of plentiful oxygen functional groups on the basal planes and sheet edges of the GO and large specific surface areas introduced by the GO.

Mesoscopic self-organization of a self-assembled supramolecular rectangle on highly oriented pyrolytic graphite and Au(111) surfaces.

Science.gov (United States)

Gong, Jian-Ru; Wan, Li-Jun; Yuan, Qun-Hui; Bai, Chun-Li; Jude, Hershel; Stang, Peter J

2005-01-25

A self-assembled supramolecular metallacyclic rectangle was investigated with scanning tunneling microscopy on highly oriented pyrolytic graphite and Au(111) surfaces. The rectangles spontaneously adsorb on both surfaces and self-organize into well ordered adlayers. On highly oriented pyrolytic graphite, the long edge of the rectangle stands on the surface, forming a 2D molecular network. In contrast, the face of the rectangle lays flat on the Au(111) surface, forming linear chains. The structures and intramolecular features obtained through high-resolution scanning tunneling microscopy imaging are discussed.

Nickel Oxide and Nickel Co-doped Graphitic Carbon Nitride Nanocomposites and its Octylphenol Sensing Application

KAUST Repository

Gong, Wanyun; Zou, Jing; Zhang, Sheng; Zhou, Xin; Jiang, Jizhou

2015-01-01

Nickel oxide and nickel co-doped graphitic carbon nitride (NiO-Ni-GCN) nanocomposites were successfully prepared by thermal treatment of melamine and NiCl2 6H2O. NiO-Ni-GCN nanocomposites showed superior electrochemical catalytic activity for the oxidation of octylphenol to pure GCN. A detection method of octylphenol in environmental water samples was developed based at NiO-Ni-GCN nanocomposites modified electrode under infrared light irradiation. Differential pulse voltammetry was used as the analytic technique of octylphenol, exhibiting stable and specific concentration-dependent oxidation signal in the presence of octylphenol in the range of 10nM to 1μM and 1μM to 50μM, with a detection limit of 3.3nM (3S/N). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nickel Oxide and Nickel Co-doped Graphitic Carbon Nitride Nanocomposites and its Octylphenol Sensing Application

KAUST Repository

Gong, Wanyun

2015-11-16

Nickel oxide and nickel co-doped graphitic carbon nitride (NiO-Ni-GCN) nanocomposites were successfully prepared by thermal treatment of melamine and NiCl2 6H2O. NiO-Ni-GCN nanocomposites showed superior electrochemical catalytic activity for the oxidation of octylphenol to pure GCN. A detection method of octylphenol in environmental water samples was developed based at NiO-Ni-GCN nanocomposites modified electrode under infrared light irradiation. Differential pulse voltammetry was used as the analytic technique of octylphenol, exhibiting stable and specific concentration-dependent oxidation signal in the presence of octylphenol in the range of 10nM to 1μM and 1μM to 50μM, with a detection limit of 3.3nM (3S/N). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of graphite composite anodes surfaces by atomic force microscopy and related techniques

Energy Technology Data Exchange (ETDEWEB)

Hirasawa, Karen Akemi; Nishioka, Keiko; Sato, Tomohiro; Yamaguchi, Shoji; Mori, Shoichiro [Mitsubishi Chemical Corp., Tsukuba Research Center, Ibaraki (Japan)

1997-11-01

The surface of a synthetic graphite (KS-44) and polyvinylidene difluoride binder (PVDF) anode for lithium-ion secondary batteries is imaged using atomic force microscopy (AFM) and several related scanning probe microscope (SPM) instruments including: dynamic force microscopy (DFM), friction force microscopy (FFM), laterally-modulated friction force microscopy (LM-FFM), visco-elasticity atomic force microscopy (VE-AFM), and AFM/simultaneous current measurement mode (SCM). DFM is found to be an exceptional mode for topographic imaging while FFM results in the clearest contrast distinction between PVDF binder and KS-44 graphite regions. (orig.)

N/S/B-doped graphitized carbon encased Fe species as a highly active and durable catalyst towards oxygen reduction reaction.

Science.gov (United States)

Li, Guang-Lan; Cheng, Guang-Chun; Chen, Wen-Wen; Liu, Cai-Di; Yuan, Li-Fang; Yang, Bei-Bei; Hao, Ce

2018-03-15

Exploring cost-effective, high-performance and durable non-precious metal catalysts is of great significance for the acceleration of sluggish oxygen reduction reaction (ORR). Here, we report an intriguing heteroatom-doped graphitized carbon encased Fe species composite by introducing N, S and B sequentially. The experimental approach was designed ingeniously for that the FeCl 3 ·6H 2 O could catalyze thiourea to synthesize N, S co-doped carbon materials which would further react with H 3 BO 3 and NH 3 (emerged at the heat-treatment process) to prepare N, S and B co-doped carbon materials (Fe-N/S/B-C). The Fe-N/S/B-C exhibits an impressive ORR activity for its half-wave potential of -0.1 V, which is 36 mV or 19 mV higher than that of the corresponding single or dual doped counterparts (Fe-N-C or Fe-N/S-C) and 31 mV positive than that of Pt/C catalyst, respectively. Further chronoamperometric measurement and accelerated aging test confirm the excellent electrochemical durability of Fe-N/S/B-C with the stable core-shell structure. The remarkable ORR performance and facile preparation method enable Fe-N/S/B-C as a potential candidate in electrochemical energy devices. Copyright © 2017 Elsevier Inc. All rights reserved.

Ab initio study of friction of graphene flake on graphene/graphite or SiC surface

Science.gov (United States)

Gulseren, Oguz; Tayran, Ceren; Sayin, Ceren Sibel

Recently, the rich dynamics of graphene flake on graphite or SiC surfaces are revealed from atomic force microcopy experiments. The studies toward to the understanding of microscopic origin of friction are getting a lot of attention. Despite the several studies of these systems using molecular dynamics methods, density functional theory based investigations are limited because of the huge system sizes. In this study, we investigated the frictional force on graphene flake on graphite or SiC surfaces from pseudopotential planewave calculations based on density functional theory. In both cases, graphene flake (24 C) on graphite or SiC surface, bilayer flake is introduced by freezing the top layer as well as the bottom layer of the surface slab. After fixing the load with these frozen layers, we checked the relative motion of the flake over the surface. A minimum energy is reached when the flake is moved on graphene to attain AB stacking. We also conclude that edge reconstruction because of the finite size of the flake is very critical for frictional properties of the flake; therefore the saturation of dangling bonds with hydrogen is also addressed. Not only the symmetric configurations remaining parameter space is extensively studied. Supported by TUBITAK Project No: 114F162. This work is supported by TUBITAK Project No: 114F162.

Research on Lessening of Bonding Effects Between the Metallic and Non-Metallic Surfaces Through the Graphite Films Deposited with Pulsed Electrical Discharges Process

Science.gov (United States)

Marin, L.; Topala, P.

2017-06-01

The paper presents the results of experimental research on the physics of natural graphite film formation, the establishment of chemical composition and functional properties of the graphite films, formed on metal surfaces, as a result of the action of plasma in the air environment, at a normal pressure, under the electrical discharge in impulse conditions (EDI). The researchings were performed in the frame of doctoral thesis “Research on lessening of the bonding effects between the metallic and nonmetallic surfaces through the graphite films” and aimed to identify the phenomena that occur at the interface metal/ film of graphite, and to identify also the technological applications that it may have the surface treatment for submitting the films of graphite on metallic surfaces achieved through an innovative process of electrical pulsed discharges. After the research works from the PhD theme above mentioned, a number of interesting properties of graphite pellicle have been identified ie reducing of metal surface polarity. This led to drastic decreases for the values of adhesion when bonding of metal surfaces was performed using a structural polyurethane adhesive designed by ICECHIM. Following the thermo-gravimetric analysis, performed of the graphite film obtained by process of electrical pulsed discharges, have been also discovered other interesting properties for this, ie reversible mass additions at specific values of the working temperature Chemical and scanning electron microscopy analysis have revealed that on the metallic surface subjected to electrical pulsed discharges process, outside the graphite film, it is also obtained a series of spatial formation composed of carbon atoms fullerenes type which are responsible for the phenomenon of addition of mass.

Ion beam induced surface graphitization of CVD diamond for x-ray beam position monitor applications

International Nuclear Information System (INIS)

Liu, Chian; Shu, D.; Kuzay, T.M.; Wen, L.; Melendres, C.A.; Argonne National Lab., IL

1996-01-01

The Advanced Photon Source at ANL is a third-generation synchrotron facility that generates powerful x-ray beams on its undulator beamlines. It is important to know the position and angle of the x- ray beam during experiments. Due to very high heat flux levels, several patented x-ray beam position monitors (XBPM) exploiting chemical vapor deposition (CVD) diamond have been developed. These XBPMs have a thin layer of low-atomic-mass metallic coating so that photoemission from the x rays generate a minute but measurable current for position determination. Graphitization of the CVD diamond surface creates a very thin, intrinsic and conducting layer that can stand much higher temperatures and minimal x-ray transmission losses compared to the coated metallic layers. In this paper, a laboratory sputter ion source was used to transform selected surfaces of a CVD diamond substrate into graphite. The effect of 1-5 keV argon ion bombardment on CVD diamond surfaces at various target temperatures from 200 to 500 C was studied using Auger electron spectroscopy and in-situ electrical resistivity measurements. Graphitization after the ion bombardment has been confirmed and optimum conditions for graphitization studied. Raman spectroscopy was used to identify the overall diamond structure in the bulk of CVD diamond substrate after the ion bombardments. It was found that target temperature plays an important role in stability and electrical conductivity of the irradiated CVD diamonds

A graphite nanoeraser

DEFF Research Database (Denmark)

Liu, Ze; Bøggild, Peter; Yang, Jia-rui

2011-01-01

We present here a method for cleaning intermediate-size (up to 50 nm) contamination from highly oriented pyrolytic graphite and graphene. Electron-beam-induced deposition of carbonaceous material on graphene and graphite surfaces inside a scanning electron microscope, which is difficult to remove...... by conventional techniques, can be removed by direct mechanical wiping using a graphite nanoeraser, thus drastically reducing the amount of contamination. We discuss potential applications of this cleaning procedure....

SURFACE MODIFICATION OF SEMICONDUCTOR THIN FILM OF TiO2 ON GRAPHITE SUBSTRATE BY Cu-ELECTRODEPOSITION

Directory of Open Access Journals (Sweden)

Fitria Rahmawati

2010-06-01

Full Text Available Surface modification of graphite/TiO2 has been done by mean of Cu electrodeposition. This research aims to study the effect of Cu electrodeposition on photocatalytic enhancing of TiO2. Electrodeposition has been done using CuSO4 0,4 M as the electrolyte at controlled current. The XRD pattern of modified TiO2 thin film on graphite substrate exhibited new peaks at 2θ= 43-44o and 2θ= 50-51o that have been identified as Cu with crystal cubic system, face-centered crystal lattice and crystallite size of 26-30 nm. CTABr still remains in the material as impurities. Meanwhile, based on morphological analysis, Cu particles are dissipated in the pore of thin film. Graphite/TiO2/Cu has higher photoconversion efficiency than graphite/TiO2.   Keywords: semiconductor, graphite/TiO2, Cu electrodeposition

Evaluation of cutting force and surface roughness in high-speed milling of compacted graphite iron

Directory of Open Access Journals (Sweden)

Azlan Suhaimi Mohd

2017-01-01

Full Text Available Compacted Graphite Iron, (CGI is known to have outstanding mechanical strength and weight-to-strength ratio as compared to conventional grey cast iron, (CI. The outstanding characteristics of CGI is due to its graphite particle shape, which is presented as compacted vermicular particle. The graphite is interconnected with random orientation and round edges, which results in higher mechanical strength. Whereas, graphite in the CI consists of a smooth-surfaced flakes that easily propagates cracks which results in weaker and brittle properties as compared to CGI. Owing to its improved properties, CGI is considered as the best candidate material in substituting grey cast iron that has been used in engine block applications for years. However, the smooth implementation of replacing CI with CGI has been hindered due to the poor machinability of CGI especially at high cutting speed. The tool life is decreased by 20 times when comparing CGI with CI under the same cutting condition. This study investigates the effect of using cryogenic cooling and minimum quantity lubrication (MQL during high-speed milling of CGI (grade 450. Results showed that, the combination of internal cryogenic cooling and enhanced MQL improved the tool life, cutting force and surface quality as compared to the conventional flood coolant strategy during high-speed milling of CGI.

Method of manufacturing a graphite coated fuel can

International Nuclear Information System (INIS)

Saito, Koichi; Uchida, Shunsuke.

1984-01-01

Purpose: To improve the close bondability and homogeneity of a graphite coating formed at the inner surface of a fuel can. Method: A coating containing graphite dispersed in a volatile organic solvent is used and a graphite coating is formed to the inner surface of a fuel can by way of a plunger method. After applying graphite coating, an inert gas is caused to flow at a certain flow rate to the inside of the fuel can horizontally rotaged so that gassification and evaporation of the volatile organic solvent contained in the graphite coating may be promoted. Since drying of the graphite coating coated to the inner surface of the fuel can thus be controlled, a graphite coating with satisfactory close bondability and homogeneity can be formed. (Kawakami, Y.)

N-doped graphene coupled with Co nanoparticles as an efficient electrocatalyst for oxygen reduction in alkaline media

Science.gov (United States)

Zhang, Geng; Lu, Wangting; Cao, Feifei; Xiao, Zhidong; Zheng, Xinsheng

2016-01-01

Development of low-cost and highly efficient electrocatalysts for oxygen reduction reaction (ORR) is still a great challenge for the large-scale application of fuel cells and metal-air batteries. Herein, a noble metal-free ORR electrocatalyst in the form of N-doped graphene coupled with part of Co nanoparticles encased in N-doped graphitic shells (named as SUCo-0.03-800) is prepared by facile one-step pyrolysis of the mixture of sucrose, urea and cobalt nitrate. The novel structure is confirmed by High Resolution-TEM, XRD, XPS and Raman spectroscopy. SUCo-0.03-800 presents comparable ORR catalytic activity to commercial Pt/C catalyst with a dominating four-electron pathway under alkaline conditions, and both of its mass activity and volume activity also outperform Co-free N-doped graphene and other Co/N-C hybrids with higher Co content, which may probably be ascribed to the high specific surface area, novel structure and synergistic effect between encased Co nanoparticles and N-doped graphitic shell. Additionally, SUCo-0.03-800 also shows outstanding stability and improved selectivity towards ORR, making it a promising alternative to Pt with potential application in fuel cells and metal-air batteries.

Graphite oxidation in HTGR atmosphere

International Nuclear Information System (INIS)

Growcock, F.B.; Barry, J.J.; Finfrock, C.C.; Rivera, E.; Heiser, J.H. III

1982-01-01

On-going and recently completed studies of the effect of thermal oxidation on the structural integrity of HTGR candidate graphites are described, and some results are presented and discussed. This work includes the study of graphite properties which may play decisive roles in the graphites' resistance to oxidation and fracture: pore size distribution, specific surface area and impurity distribution. Studies of strength loss mechanisms in addition to normal oxidation are described. Emphasis is placed on investigations of the gas permeability of HTGR graphites and the surface burnoff phenomenon observed during recent density profile measurements. The recently completed studies of catalytic pitting and the effects of prestress and stress on reactivity and ultimate strength are also discussed

Electronic and spectroscopic properties of early 3d metal atoms on a graphite surface

Science.gov (United States)

Rakotomahevitra, A.; Garreau, G.; Demangeat, C.; Parlebas, J. C.

1995-07-01

High-sensitivity magneto-optic Kerr effect experiments failed to detect manifestations of magnetism in epitaxial films of V on Ag(100) substrates. More recently V 3s XPS of freshly evaporated V clusters on graphite exhibited the appearance of a satellite structure which has then been interpreted by the effect of surface magnetic moments on V. It is the absence of unambiguous results on the electronic properties of early 3d supported metals that prompts us to examine the problem. Our purpose is twofold. In a first part, after a total energy calculation within a tight-binding method which yields the equilibrium position of a given adatom, we use the Hartree-Fock approximation to find out a possible magnetic solution of V (or Cr) upon graphite for a reasonable value of the exchange integral Jdd. In a second part the informations given by the density of states of the graphite surface as well as the additional states of the adsorbed atom are taken into account through a generalised impurity Anderson Hamiltonian which incorporates the various Coulomb and exchange interactions necessary to analyse the 3s XPS results.

Graphite crystals grown within electromagnetically levitated metallic droplets

International Nuclear Information System (INIS)

Amini, Shaahin; Kalaantari, Haamun; Mojgani, Sasan; Abbaschian, Reza

2012-01-01

Various graphite morphologies were observed to grow within the electromagnetically levitated nickel–carbon melts, including primary flakes and spheres, curved surface graphite and eutectic flakes, as well as engulfed and entrapped particles. As the supersaturated metallic solutions were cooled within the electromagnetic (EM) levitation coil, the primary graphite flakes and spheres formed and accumulated near the periphery of the droplet due to EM circulation. The primary graphite islands, moreover, nucleated and grew on the droplet surface which eventually formed a macroscopic curved graphite crystal covering the entire liquid. Upon further cooling, the liquid surrounding the primary graphite went under a coupled eutectic reaction while the liquid in the center formed a divorced eutectic due to EM mixing. This brought about the formation of graphite fine flakes and agglomerated particles close to the surface and in the center of the droplet, respectively. The graphite morphologies, growth mechanisms, defects, irregularities and growth instabilities were interpreted with detailed optical and scanning electron microscopies.

Separation medium containing thermally exfoliated graphite oxide

Science.gov (United States)

Prud'homme, Robert K. (Inventor); Aksay, Ilhan A. (Inventor); Herrera-Alonso, Margarita (Inventor)

2012-01-01

A separation medium, such as a chromatography filling or packing, containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m.sup.2/g to 2600 m.sup.2/g, wherein the thermally exfoliated graphite oxide has a surface that has been at least partially functionalized.

Possible room temperature superconductivity in conductors obtained by bringing alkanes into contact with a graphite surface

Directory of Open Access Journals (Sweden)

Yasushi Kawashima

2013-05-01

Full Text Available Electrical resistances of conductors obtained by bringing alkanes into contact with a graphite surface have been investigated at room temperatures. Ring current in a ring-shaped container into which n-octane-soaked thin graphite flakes were compressed did not decay for 50 days at room temperature. After two HOPG plates were immersed into n-heptane and n-octane at room temperature, changes in resistances of the two samples were measured by four terminal technique. The measurement showed that the resistances of these samples decrease to less than the smallest resistance that can be measured with a high resolution digital voltmeter (0.1μV. The observation of persistent currents in the ring-shaped container suggests that the HOPG plates immersed in n-heptane and n-octane really entered zero-resistance state at room temperature. These results suggest that room temperature superconductor may be obtained by bringing alkanes into contact with a graphite surface.

Electrochemical Control of Peptide Self-Organization on Atomically Flat Solid Surfaces: A Case Study with Graphite.

Science.gov (United States)

Seki, Takakazu; So, Christopher R; Page, Tamon R; Starkebaum, David; Hayamizu, Yuhei; Sarikaya, Mehmet

2018-02-06

The nanoscale self-organization of biomolecules, such as proteins and peptides, on solid surfaces under controlled conditions is an important issue in establishing functional bio/solid soft interfaces for bioassays, biosensors, and biofuel cells. Electrostatic interaction between proteins and surfaces is one of the most essential parameters in the adsorption and self-assembly of proteins on solid surfaces. Although the adsorption of proteins has been studied with respect to the electrochemical surface potential, the self-assembly of proteins or peptides forming well-organized nanostructures templated by lattice structure of the solid surfaces has not been studied in the relation to the surface potential. In this work, we utilize graphite-binding peptides (GrBPs) selected by the phage display method to investigate the relationship between the electrochemical potential of the highly ordered pyrolytic graphite (HOPG) and peptide self-organization forming long-range-ordered structures. Under modulated electrical bias, graphite-binding peptides form various ordered structures, such as well-ordered nanowires, dendritic structures, wavy wires, amorphous (disordered) structures, and islands. A systematic investigation of the correlation between peptide sequence and self-organizational characteristics reveals that the presence of the bias-sensitive amino acid modules in the peptide sequence has a significant effect on not only surface coverage but also on the morphological features of self-assembled structures. Our results show a new method to control peptide self-assembly by means of applied electrochemical bias as well as peptide design-rules for the construction of functional soft bio/solid interfaces that could be integrated in a wide range of practical implementations.

Low temperature vapor phase digestion of graphite

Energy Technology Data Exchange (ETDEWEB)

Pierce, Robert A.

2017-04-18

A method for digestion and gasification of graphite for removal from an underlying surface is described. The method can be utilized to remove graphite remnants of a formation process from the formed metal piece in a cleaning process. The method can be particularly beneficial in cleaning castings formed with graphite molding materials. The method can utilize vaporous nitric acid (HNO.sub.3) or vaporous HNO.sub.3 with air/oxygen to digest the graphite at conditions that can avoid damage to the underlying surface.

Collective modes in superconducting rhombohedral graphite

Energy Technology Data Exchange (ETDEWEB)

Kauppila, Ville [O.V. Lounasmaa Laboratory, Aalto University (Finland); Hyart, Timo; Heikkilae, Tero [University of Jyvaeskylae (Finland)

2015-07-01

Recently it was realized that coupling particles with a Dirac dispersion (such as electrons in graphene) can lead to a topologically protected state with flat band dispersion. Such a state could support superconductivity with unusually high critical temperatures. Perhaps the most promising way to realize such coupling in real materials is in the surface of rhombohedrally stacked graphite. We consider collective excitations (i.e. the Higgs modes) in surface superconducting rhombohedral graphite. We find two amplitude and two phase modes corresponding to the two surfaces of the graphite where the superconductivity lives. We calculate the dispersion of these modes. We also derive the Ginzburg-Landau theory for this material. We show that in superconducting rhombohedral graphite, the collective modes, unlike in conventional BCS superconductors, give a large contribution to thermodynamic properties of the material.

Special graphites; Graphites speciaux

Energy Technology Data Exchange (ETDEWEB)

Leveque, P [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1964-07-01

A large fraction of the work undertaken jointly by the Commissariat a l'Energie Atomique (CEA) and the Pechiney Company has been the improvement of the properties of nuclear pile graphite and the opening up of new fields of graphite application. New processes for the manufacture of carbons and special graphites have been developed: forged graphite, pyro-carbons, high density graphite agglomeration of graphite powders by cracking of natural gas, impervious graphites. The physical properties of these products and their reaction with various oxidising gases are described. The first irradiation results are also given. (authors) [French] Ameliorer les proprietes du graphite nucleaire pour empilements et ouvrir de nouveaux domaines d'application au graphite constituent une part importante de l'effort entrepris en commun par le Commissariat a l'Energie Atomique (CEA) et la compagnie PECHINEY. Des procedes nouveaux de fabrication de carbones et graphites speciaux ont ete mis au point: graphite forge, pyrocarbone, graphite de haute densite, agglomeration de poudres de graphite par craquage de gaz naturel, graphites impermeables. Les proprietes physiques de ces produits ainsi que leur reaction avec differents gaz oxydants sont decrites. Les premiers resultats d'irradiation sont aussi donnes. (auteurs)

Coating of hydroxyapatite doped Ag on commercially pure titanium surface

International Nuclear Information System (INIS)

Vieira, Jonas de Oliveira; Vercik, Luci Cristina de Oliveira; Rigo, Eliana Cristina da Silva

2012-01-01

This paper presents results of bioactive coating on commercially pure titanium surface (CpTi) doped with Ag ions. The coating consists of 3 steps, in step 1- surface chemical treatment of the samples with NaOH, step 2 - immersing the substrate in question in a sodium silicate solution (SS) to the nucleation and step 3 - reimmersion these substrates in synthetic solution that simulates the blood serum for precipitation and growth of apatite layer. After the coating step the AgNO 3 substrates were immersed in solutions with concentrations of 20 ppm and 100 ppm at 37 ° C for 48h. The substrates were characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). By the results verified the formation of an apatite layer with aspects of cells, on the surface of CpTi. The increase in Ag concentration causes an increase in Ag amount doped in apatite layer. With the results we concluded that it is possible to obtain an apatite layer on a metal surface as the CpTi doped with Ag ions

Facile synthesis of phosphorus doped graphitic carbon nitride polymers with enhanced visible-light photocatalytic activity

International Nuclear Information System (INIS)

Zhang, Ligang; Chen, Xiufang; Guan, Jing; Jiang, Yijun; Hou, Tonggang; Mu, Xindong

2013-01-01

Graphical abstract: - Highlights: • P-doped g-C 3 N 4 has been prepared by a one-pot green synthetic approach. • The incorporation of P resulted in favorable textural and electronic properties. • Doping with P enhanced the visible-light photocatalytic activity of g-C 3 N 4 . • A postannealing treatment further enhanced the activity of P-doped g-C 3 N 4 . • Photogenerated holes were the main species responsible for the activity. - Abstract: Phosphorus-doped carbon nitride materials were prepared by a one-pot green synthetic approach using dicyandiamide monomer and a phosphorus containing ionic liquid as precursors. The as-prepared materials were subjected to several characterizations and investigated as metal-free photocatalysts for the degradation of organic pollutants (dyes like Rhodamine B, Methyl orange) in aqueous solution under visible light. Results revealed that phosphorus-doped carbon nitride have a higher photocatalytic activity for decomposing Rhodamine B and Methyl orange in aqueous solution than undoped g-C 3 N 4 , which was attributed to the favorable textural, optical and electronic properties caused by doping with phosphorus heteroatoms into carbon nitride host. A facile postannealing treatment further improved the activity of the photocatalytic system, due to the higher surface area and smaller structural size in the postcalcined catalysts. The phosphorus-doped carbon nitride showed high visible-light photocatalytic activity, making them promising materials for a wide range of potential applications in photochemistry

Polymer Adsorption on Graphite and CVD Graphene Surfaces Studied by Surface-Specific Vibrational Spectroscopy.

Science.gov (United States)

Su, Yudan; Han, Hui-Ling; Cai, Qun; Wu, Qiong; Xie, Mingxiu; Chen, Daoyong; Geng, Baisong; Zhang, Yuanbo; Wang, Feng; Shen, Y R; Tian, Chuanshan

2015-10-14

Sum-frequency vibrational spectroscopy was employed to probe polymer contaminants on chemical vapor deposition (CVD) graphene and to study alkane and polyethylene (PE) adsorption on graphite. In comparing the spectra from the two surfaces, it was found that the contaminants on CVD graphene must be long-chain alkane or PE-like molecules. PE adsorption from solution on the honeycomb surface results in a self-assembled ordered monolayer with the C-C skeleton plane perpendicular to the surface and an adsorption free energy of ∼42 kJ/mol for PE(H(CH2CH2)nH) with n ≈ 60. Such large adsorption energy is responsible for the easy contamination of CVD graphene by impurity in the polymer during standard transfer processes. Contamination can be minimized with the use of purified polymers free of PE-like impurities.

Dynamics of graphite flake on a liquid

Science.gov (United States)

Miura, K.; Tsuda, D.; Kaneta, Y.; Harada, R.; Ishikawa, M.; Sasaki, N.

2006-11-01

One-directional motion, where graphite flakes are driven by a nanotip on an octamethylcyclotetrasiloxane (OMCTS) liquid surface, is presented. A transition from quasiperiodic to chaotic motions occurs in the dynamics of a graphite flake when its velocity is increased. The dynamics of graphite flakes pulled by the nanotip on an OMCTS liquid surface can be treated as that of a nanobody on a liquid.

Adsorption and Electronic Structure of Sr and Ag Atoms on Graphite Surfaces: a First-Principles Study

Science.gov (United States)

Luo, Xiao-Feng; Fang, Chao; Li, Xin; Lai, Wen-Sheng; Sun, Li-Feng; Liang, Tong-Xiang

2013-06-01

The adsorption behaviors of radioactive strontium and silver nuclides on the graphite surface in a high-temperature gas-cooled reactor are studied by first-principles theory using generalized gradient approximation (GGA) and local density approximation (LDA) pseudo-potentials. It turns out that Sr prefers to be absorbed at the hollow of the carbon hexagonal cell by 0.54 eV (GGA), while Ag likes to sit right above the carbon atom with an adsorption energy of almost zero (GGA) and 0.45 eV (LDA). Electronic structure analysis reveals that Sr donates its partial electrons of the 4p and 5s states to the graphite substrate, while Ag on graphite is a physical adsorption without any electron transfer.

The influence of Fe doping on the surface topography of GaN epitaxial material

International Nuclear Information System (INIS)

Cui Lei; Yin Haibo; Jiang Lijuan; Wang Quan; Feng Chun; Xiao Hongling; Wang Cuimei; Wang Xiaoliang; Gong Jiamin; Zhang Bo; Li Baiquan; Wang Zhanguo

2015-01-01

Fe doping is an effective method to obtain high resistivity GaN epitaxial material. But in some cases, Fe doping could result in serious deterioration of the GaN material surface topography, which will affect the electrical properties of two dimensional electron gas (2DEG) in HEMT device. In this paper, the influence of Fe doping on the surface topography of GaN epitaxial material is studied. The results of experiments indicate that the surface topography of Fe-doped GaN epitaxial material can be effectively improved and the resistivity could be increased after increasing the growth rate of GaN materials. The GaN material with good surface topography can be manufactured when the Fe doping concentration is 9 × 10 19 cm −3 . High resistivity GaN epitaxial material which is 1 × 10 9 Ω·cm is achieved. (paper)

Spin-density wave state in simple hexagonal graphite

Science.gov (United States)

Mosoyan, K. S.; Rozhkov, A. V.; Sboychakov, A. O.; Rakhmanov, A. L.

2018-02-01

Simple hexagonal graphite, also known as AA graphite, is a metastable configuration of graphite. Using tight-binding approximation, it is easy to show that AA graphite is a metal with well-defined Fermi surface. The Fermi surface consists of two sheets, each shaped like a rugby ball. One sheet corresponds to electron states, another corresponds to hole states. The Fermi surface demonstrates good nesting: a suitable translation in the reciprocal space superposes one sheet onto another. In the presence of the electron-electron repulsion, a nested Fermi surface is unstable with respect to spin-density-wave ordering. This instability is studied using the mean-field theory at zero temperature, and the spin-density-wave order parameter is evaluated.

Adsorption behavior of bisphenol A on CTAB-modified graphite

Science.gov (United States)

Wang, Li-Cong; Ni, Xin-jiong; Cao, Yu-Hua; Cao, Guang-qun

2018-01-01

In this work, the adsorption behavior of BPA on CTAB-modified graphite was investigated thoroughly to develop a novel absorbent material. Atomic force microscopy revealed that conical admicelles formed on the surface of graphite. The surface area of graphite decreased significantly from 1.46 to 0.95 m2 g-1, which confirmed the formation of the larger size admicelle instead of the original smaller particle on the surface. CTAB concentration and incubation time affected the progress of admicelle formation on the surface of graphite. Adsolubilization is key in BPA adsorption by CTAB-modified graphite. An extraordinary cation-π electron interaction between CTAB and BPA, revealed by a red-shift in the ultraviolet spectrum, as well as a hydrophobic interaction contribute substantially to BPA adsolubilization. The equilibrium adsorption capacity of the modified graphite for BPA was 125.01 mg g-1. The adsorption kinetic curves of BPA on modified graphite were shown to follow a pseudosecond-order rate. The adsorption process was observed to be both spontaneous and exothermic complied with the Freundlich model.

A 2-D nucleation-growth model of spheroidal graphite

International Nuclear Information System (INIS)

Lacaze, Jacques; Bourdie, Jacques; Castro-Román, Manuel Jesus

2017-01-01

Analysis of recent experimental investigations, in particular by transmission electron microscopy, suggests spheroidal graphite grows by 2-D nucleation of new graphite layers at the outer surface of the nodules. These layers spread over the surface along the prismatic direction of graphite which is the energetically preferred growth direction of graphite when the apparent growth direction of the nodules is along the basal direction of graphite. 2-D nucleation-growth models first developed for precipitation of pure substances are then adapted to graphite growth from the liquid in spheroidal graphite cast irons. Lateral extension of the new graphite layers is controlled by carbon diffusion in the liquid. This allows describing quantitatively previous experimental results giving strong support to this approach.

Evaluation of microstructures and oxidation behaviors of graphite for core support structure

International Nuclear Information System (INIS)

Park, Soo Jin; Bae, Kyung Min

2010-03-01

This work studies the oxidation-induced characteristics of five nuclear graphites (NBG-17, NBG-18, NBG-25, IG-110, and IG-430). The oxidation characteristics of the nuclear graphites were measured at 600 .deg. C. The surface properties of the oxidation graphites were characterized by means of scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle methods. The N2/77K adsorption isotherm characteristics, including the specific surface area and micropore volume, were investigated by means of BET and t-plot methods. The experimental results show an increase in the average pore size of graphites; they also show that oxidation produces the surface functional groups on the graphite surfaces. The surface area of each graphite behaves in a unique manner. For example the surface area of NBG-17 increases slightly whereas the surface area of IG-110 increases significantly. This result confirms that the original surface state of each graphite is unique

Electrochemical treatment of graphite

International Nuclear Information System (INIS)

Podlovilin, V.I.; Egorov, I.M.; Zhernovoj, A.I.

1983-01-01

In the course of investigating various modes of electroche-- mical treatment (ECT) it has been found that graphite anode treatment begins under the ''glow mode''. A behaviour of some marks of graphite with the purpose of ECT technique development in different electrolytes has been tested. Electrolytes have been chosen of three types: highly alkaline (pH 13-14), neutral (pH-Z) and highly acidic (pH 1-2). For the first time parallel to mechanical electroerosion treatment ECT graphite and carbon graphite materials previously considered chemically neutral is proposed. ECT of carbon graphite materials has a number of advantages as compared with electroerrosion and mechanical ones this is treatment rate and purity (ronghness) of the surface. A sMall quantity of sludge (6-8%) under ECT is in highly alkali electrolytes

Raman spectroscopy of boron-doped single-layer graphene.

Science.gov (United States)

Kim, Yoong Ahm; Fujisawa, Kazunori; Muramatsu, Hiroyuki; Hayashi, Takuya; Endo, Morinobu; Fujimori, Toshihiko; Kaneko, Katsumi; Terrones, Mauricio; Behrends, Jan; Eckmann, Axel; Casiraghi, Cinzia; Novoselov, Kostya S; Saito, Riichiro; Dresselhaus, Mildred S

2012-07-24

The introduction of foreign atoms, such as nitrogen, into the hexagonal network of an sp(2)-hybridized carbon atom monolayer has been demonstrated and constitutes an effective tool for tailoring the intrinsic properties of graphene. Here, we report that boron atoms can be efficiently substituted for carbon in graphene. Single-layer graphene substitutionally doped with boron was prepared by the mechanical exfoliation of boron-doped graphite. X-ray photoelectron spectroscopy demonstrated that the amount of substitutional boron in graphite was ~0.22 atom %. Raman spectroscopy demonstrated that the boron atoms were spaced 4.76 nm apart in single-layer graphene. The 7-fold higher intensity of the D-band when compared to the G-band was explained by the elastically scattered photoexcited electrons by boron atoms before emitting a phonon. The frequency of the G-band in single-layer substitutionally boron-doped graphene was unchanged, which could be explained by the p-type boron doping (stiffening) counteracting the tensile strain effect of the larger carbon-boron bond length (softening). Boron-doped graphene appears to be a useful tool for engineering the physical and chemical properties of graphene.

Characterization of boron doped nanocrystalline diamonds

International Nuclear Information System (INIS)

Peterlevitz, A C; Manne, G M; Sampaio, M A; Quispe, J C R; Pasquetto, M P; Iannini, R F; Ceragioli, H J; Baranauskas, V

2008-01-01

Nanostructured diamond doped with boron was prepared using a hot-filament assisted chemical vapour deposition system fed with an ethyl alcohol, hydrogen and argon mixture. The reduction of the diamond grains to the nanoscale was produced by secondary nucleation and defects induced by argon and boron atoms via surface reactions during chemical vapour deposition. Raman measurements show that the samples are nanodiamonds embedded in a matrix of graphite and disordered carbon grains, while morphological investigations using field electron scanning microscopy show that the size of the grains ranges from 20 to 100 nm. The lowest threshold fields achieved were in the 1.6 to 2.4 V/μm range

Pyrolytic graphite gauge for measuring heat flux

Science.gov (United States)

Bunker, Robert C. (Inventor); Ewing, Mark E. (Inventor); Shipley, John L. (Inventor)

2002-01-01

A gauge for measuring heat flux, especially heat flux encountered in a high temperature environment, is provided. The gauge includes at least one thermocouple and an anisotropic pyrolytic graphite body that covers at least part of, and optionally encases the thermocouple. Heat flux is incident on the anisotropic pyrolytic graphite body by arranging the gauge so that the gauge surface on which convective and radiative fluxes are incident is perpendicular to the basal planes of the pyrolytic graphite. The conductivity of the pyrolytic graphite permits energy, transferred into the pyrolytic graphite body in the form of heat flux on the incident (or facing) surface, to be quickly distributed through the entire pyrolytic graphite body, resulting in small substantially instantaneous temperature gradients. Temperature changes to the body can thereby be measured by the thermocouple, and reduced to quantify the heat flux incident to the body.

Tungsten and carbon surface change under high dose plasma exposure

International Nuclear Information System (INIS)

Martynenko, Y.V.; Khripunov, B.I.; Petrov, V.B.

2009-01-01

Study of surface composition dynamics has been made on the LENTA linear plasma simulator. Experiments have been made on tungsten and carbon materials subjected to steady-state plasma exposure. The achieved ion doses on the surface were 10 21 ion cm -2 . WL 10 tungsten containing 1% of La2O3 oxide and titanium-doped graphite RG-T were studied. The following experimental conditions were varied in these experiments: energy of ions, surface temperature, working gas. Irradiations of tungsten WL 10 were executed in deuterium plasma at low ion energies (about 20 eV) and at 200 eV for temperatures below 340 K. Graphite RG-T was exposed at 1300 K. Elevated surface temperature (about 1050K) was also characteristic of experiments on tungsten sample under nitrogen plasma impact (simulated inter-ELMs condition). Surface microstructure modification has been observed and surface composition changes were found on the materials showing influence of high dose plasma irradiations on element redistribution in the near surface layers. (author)

Disposable screen printed graphite electrode for the direct electrochemical determination of ibuprofen in surface water

KAUST Repository

Amin, Sidra; Soomro, M. Tahir; Memon, Najma; Solangi, Amber R.; Sirajuddin; Qureshi, Tahira; Behzad, Ali Reza

2014-01-01

The potential of square wave voltammetry (SWV) for the determination of ibuprofen in aqueous solution, applying baseline correction, is reported. A screen printed graphite electrodes (SPGEs), especially pretreated for this purpose, were used to investigate the electrochemical oxidation and detection of ibuprofen. After optimization of SWV parameters, measurements were carried out at 200 Hz modulation frequency, 4 mV step potential and 40 mV pulse amplitude for the determination of ibuprofen. The surfaces of both untreated and pretreated SPGEs were characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The electro-catalytic properties of both the electrodes were correlated with the surface treatment. The pretreated screen printed graphite electrode exhibited a high sensitivity toward ibuprofen even in low concentration. The developed method was found rapid, cost-effective and reproducible for in-field ibuprofen detection.

Disposable screen printed graphite electrode for the direct electrochemical determination of ibuprofen in surface water

KAUST Repository

Amin, Sidra

2014-08-01

The potential of square wave voltammetry (SWV) for the determination of ibuprofen in aqueous solution, applying baseline correction, is reported. A screen printed graphite electrodes (SPGEs), especially pretreated for this purpose, were used to investigate the electrochemical oxidation and detection of ibuprofen. After optimization of SWV parameters, measurements were carried out at 200 Hz modulation frequency, 4 mV step potential and 40 mV pulse amplitude for the determination of ibuprofen. The surfaces of both untreated and pretreated SPGEs were characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The electro-catalytic properties of both the electrodes were correlated with the surface treatment. The pretreated screen printed graphite electrode exhibited a high sensitivity toward ibuprofen even in low concentration. The developed method was found rapid, cost-effective and reproducible for in-field ibuprofen detection.

Electrochemical treatment of graphite

Energy Technology Data Exchange (ETDEWEB)

Podlovilin, V.I.; Egorov, I.M.; Zhernovoj, A.I.

1983-01-01

In the course of investigating various modes of electrochemical treatment (ECT) it has been found that graphite anode treatment begins under the ''glow mode''. A behaviour of some marks of graphite with the purpose of ECT technique development in different electrolytes has been tested. Electrolytes have been chosen of three types: highly alkaline (pH 13-14), neutral (pH-Z) and highly acidic (pH 1-2). For the first time parallel to mechanical electroerosion treatment, ECT of graphite and carbon graphite materials previously considered chemically neutral is proposed. ECT of carbon graphite materials has a number of advantages as compared with electroerrosion and mechanical ones with respect to the treatment rate and purity (ronghness) of the surface. A small quantity of sludge (6-8%) under ECT is in highly alkali electrolytes.

Nitrogen–doped graphitized carbon shell encapsulated NiFe nanoparticles: A highly durable oxygen evolution catalyst

Energy Technology Data Exchange (ETDEWEB)

Du, Lei; Luo, Langli; Feng, Zhenxing; Engelhard, Mark; Xie, Xiaohong; Han, Binghong; Sun, Junming; Zhang, Jianghao; Yin, Geping; Wang, Chongmin; Wang, Yong; Shao, Yuyan

2017-09-01

Oxygen evolution reaction (OER) plays a crucial role in various energy conversion devices such as water electrolyzers and metal–air batteries. Precious metal catalysts such as Ir, Ru and their oxides are usually used for enhancing reaction kinetics but are limited by their scarce resource. The challenges associated with alternative non–precious metal catalysts such as transition metal oxides and (oxy)hydroxides etc. are their low electronic conductivity and durability. Herein, we report a highly active (360 mV overpotential at 10 mA cm–2GEO) and durable (no degradation after 20000 cycles) OER catalyst derived from bimetallic metal–organic frameworks (MOFs) precursors. This catalyst consists of NiFe nanoparticles encapsulated by nitrogen–doped graphitized carbon shells. The electron-donation/deviation from Fe and tuned electronic structure of metal cores by Ni are revealed to be primary contributors to the enhanced OER activity, whereas N concentration contributes negligibly. We further demonstrated that the structure and morphology of encapsulating carbon shells, which are the key factors influencing the durability, are facilely controlled by the chemical state of precursors.

Analysis of the deconvolution of the thermoluminescent curve of the zirconium oxide doped with graphite

International Nuclear Information System (INIS)

Salas C, P.; Estrada G, R.; Gonzalez M, P.R.; Mendoza A, D.

2003-01-01

In this work, we present a mathematical analysis of the behavior of the thermoluminescent curve (Tl) induced by gamma radiation in samples made of zirconium oxide doped with different amounts of graphite. In accordance with the results gamma radiation induces a Tl curve with two maximum of emission localized in the temperatures at 139 and 250 C, the area under the curve is increasing as a function of the time of exposition to the radiation. The analysis of curve deconvolution, in accordance with the theory which indicates that this behavior must be obey a Boltzmann distribution, we found that each one of them has a different growth velocity as the time of exposition increase. In the same way, we observed that after the irradiation was suspended each one of the maximum decrease with different velocity. The behaviour observed in the samples is very interesting because the zirconium oxide has attracted the interest of many research groups, this material has demonstrated to have many applications in thermoluminescent dosimetry and it can be used in the quantification of radiation. (Author)

Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

Directory of Open Access Journals (Sweden)

Wei Xun

2017-07-01

Full Text Available Based on first-principles calculations, the BaTiO3(BTO film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

Discrete impurity band from surface danging bonds in nitrogen and phosphorus doped SiC nanowires

Science.gov (United States)

Li, Yan-Jing; Li, Shu-Long; Gong, Pei; Li, Ya-Lin; Cao, Mao-Sheng; Fang, Xiao-Yong

2018-04-01

The electronic structure and optical properties of the nitrogen and phosphorus doped silicon carbide nanowires (SiCNWs) are investigated using first-principle calculations based on density functional theory. The results show doping can change the type of the band gap and improve the conductivity. However, the doped SiCNWs form a discrete impurity levels at the Fermi energy, and the dispersion degree decreases with the diameter increasing. In order to reveal the root of this phenomenon, we hydrogenated the doped SiCNWs, found that the surface dangling bonds were saturated, and the discrete impurity levels are degeneracy, which indicates that the discrete impurity band of the doped SiCNWs is derived from the dangling bonds. The surface passivation can degenerate the impurity levels. Therefore, both doping and surface passivation can better improve the photoelectric properties of the SiCNWs. The result can provide additional candidates in producing nano-optoelectronic devices.

Effects of doped copper on electrochemical performance of the raw carbon nanotubes anode

Energy Technology Data Exchange (ETDEWEB)

Yang, Zhanhong; Simard, Benoit [SIMS, National Research Council, 100 Sussex Dr., Ottawa, ON (Canada); Li, Zaifeng [ICPET, National Research Council, 1200 Montreal Road, Ottawa, ON (Canada); Wu, Haoqing [Department of Chemistry, Fudan University, Shanghai 200433 (China)

2003-07-01

The raw carbon nanotubes pre-doped with copper are used as anode materials for lithium ion batteries. Constant current discharge and charge tests using the raw carbon nanotubes pre-doped with copper as Li{sup +} storage compounds show lower specific capacities than that of the acid-oxidized carbon nanotubes. The acids play an important role; H{sub 2}SO{sub 4} and HNO{sub 3} can easily permeate through the graphene sheets, then they will make the defects or pores in the graphene sheets, and this reaction can make the expansion of the graphite. Meanwhile, Cu{sup 2+} will diffuse into the pores and onto the outer surfaces of the carbon nanotubes. Cu{sup 2+} can be easily turned into Cu at high temperature in the presence of the carbon nanomaterial. So parts of the pores and the surfaces of the carbon nanotubes will be filled with the Cu atom. Once the space positions of the nanotubes were occupied, lithium cannot intercalate into the pores and onto the outer surface of the carbon nanotubes, thus the doped carbon nanotubes will have a low specific capacity.

Protection of nuclear graphite toward fluoride molten salt by glassy carbon deposit

International Nuclear Information System (INIS)

Bernardet, V.; Gomes, S.; Delpeux, S.; Dubois, M.; Guerin, K.; Avignant, D.; Renaudin, G.; Duclaux, L.

2009-01-01

Molten salt reactor represents one of the promising future Generation IV nuclear reactors families where the fuel, a liquid molten fluoride salt, is circulating through the graphite reactor core. The interactions between nuclear graphite and fluoride molten salt and also the graphite surface protection were investigated in this paper by powder X-ray diffraction, micro-Raman spectroscopy and scanning electron microscopy coupled with X-ray microanalysis. Nuclear graphite discs were covered by two kinds of protection deposit: a glassy carbon coating and a double coating of pyrolitic carbon/glassy carbon. Different behaviours have been highlighted according to the presence and the nature of the coated protection film. Intercalation of molten salt between the graphite layers did not occur. Nevertheless the molten salt adhered more or less to the surface of the graphite disc, filled more or less the graphite surface porosity and perturbed more or less the graphite stacking order at the disc surface. The behaviour of unprotected graphite was far to be satisfactory after two days of immersion of graphite in molten salt at 500 deg. C. The best protection of the graphite disc surface, with the maximum of inertness towards molten salt, has been obtained with the double coating of pyrolitic carbon/glassy carbon

Superionic Conductivity of Sm3+, Pr3+, and Nd3+ Triple-Doped Ceria through Bulk and Surface Two-Step Doping Approach.

Science.gov (United States)

Liu, Yanyan; Fan, Liangdong; Cai, Yixiao; Zhang, Wei; Wang, Baoyuan; Zhu, Bin

2017-07-19

Sufficiently high oxygen ion conductivity of electrolyte is critical for good performance of low-temperature solid oxide fuel cells (LT-SOFCs). Notably, material conductivity, reliability, and manufacturing cost are the major barriers hindering LT-SOFC commercialization. Generally, surface properties control the physical and chemical functionalities of materials. Hereby, we report a Sm 3+ , Pr 3+ , and Nd 3+ triple-doped ceria, exhibiting the highest ionic conductivity among reported doped-ceria oxides, 0.125 S cm -1 at 600 °C. It was designed using a two-step wet-chemical coprecipitation method to realize a desired doping for Sm 3+ at the bulk and Pr 3+ /Nd 3+ at surface domains (abbreviated as PNSDC). The redox couple Pr 3+ /Pr 4+ contributes to the extraordinary ionic conductivity. Moreover, the mechanism for ionic conductivity enhancement is demonstrated. The above findings reveal that a joint bulk and surface doping methodology for ceria is a feasible approach to develop new oxide-ion conductors with high impacts on advanced LT-SOFCs.

Electronic structure of graphene nanoribbons doped with nitrogen atoms: a theoretical insight.

Science.gov (United States)

Torres, A E; Fomine, S

2015-04-28

The electronic structure of graphene nanoribbons doped with a graphitic type of nitrogen atoms has been studied using B3LYP, B2PLYP and CAS methods. In all but one case the restricted B3LYP solutions were unstable and the CAS calculations provided evidence for the multiconfigurational nature of the ground state with contributions from two dominant configurations. The relative stability of the doped nanoribbons depends mostly on the mutual position of the dopant atoms and notably less on the position of nitrogen atoms within the nanoribbon. N-graphitic doping affects cationic states much more than anionic ones due the participation of the nitrogen atoms in the stabilization of the positive charge, resulting in a drop in ionization energies (IPs) for N-graphitic doped systems. Nitrogen atoms do not participate in the negative charge stabilization of anionic species and, therefore, the doping does not affect the electron affinities (EAs). The unrestricted B3LYP method is the method of choice for the calculation of IPs and EAs. Restricted B3LYP and B2PLYP produces unreliable results for both IPs and EAs while CAS strongly underestimates the electron affinities. This is also true for the reorganization energies where restricted B3LYP produces qualitatively incorrect results. Doping changes the reorganization energy of the nanoribbons; the hole reorganization energy is generally higher than the corresponding electron reorganization energy due to the participation of nitrogen atoms in the stabilization of the positive charge.

Characterization of Ignalina NPP RBMK Reactors Graphite

International Nuclear Information System (INIS)

Hacker, P.J.; Neighbour, G.B.; Levinskas, R.; Milcius, D.

2001-01-01

The paper concentrates on the investigations of the initial physical properties of graphite used in production of graphite bricks of Ignalina NPP. These graphite bricks are used as nuclear moderator and major core structural components. Graphite bulk density is calculated by mensuration, pore volumes are measured by investigation of helium gas penetration in graphite pore network, the Young's modulus is determined using an ultrasonic time of flight method, the coefficient of thermal expansion is determined using a Netzsch dilatometer 402C, the fractured and machined graphite surfaces are studied using SEM, impurities are investigated qualitatively by EDAX, the degree of graphitization of the material is tested using X-ray diffraction. (author)

Neutron transmutation doping of polycrystalline silicon

International Nuclear Information System (INIS)

Cleland, J.W.; Westbrook, R.D.; Wood, R.F.; Young, R.T.

1976-04-01

Chemical vapor deposition (CVD) of doped silane has been used by others to deposit a polycrytalline silicon film (polysil) on metal or graphite substrates, but dopant migration to grain boundaries during deposition apparently prohibits attaining a uniform or desired dopant concentration. In contrast, we have used neutron transmutation doping to introduce a uniform phosphorus dopant concentration in commercially available undoped CVD polysil at doping concentrations greater than or equal to 2 x 10 15 cm -3 . Radiation damage annealing to 800 0 C did not indicate dopant migration. Carrier mobility increased with doping concentration and the minority carrier lifetime (MCL) appears to be comparable to that of neutron transmutation doped (NTD) single crystal Si. Application of this technique to photovoltaic solar cell fabrication is discussed

Doping profile measurement on textured silicon surface

Science.gov (United States)

Essa, Zahi; Taleb, Nadjib; Sermage, Bernard; Broussillou, Cédric; Bazer-Bachi, Barbara; Quillec, Maurice

2018-04-01

In crystalline silicon solar cells, the front surface is textured in order to lower the reflection of the incident light and increase the efficiency of the cell. This texturing whose dimensions are a few micrometers wide and high, often makes it difficult to determine the doping profile measurement. We have measured by secondary ion mass spectrometry (SIMS) and electrochemical capacitance voltage profiling the doping profile of implanted phosphorus in alkaline textured and in polished monocrystalline silicon wafers. The paper shows that SIMS gives accurate results provided the primary ion impact angle is small enough. Moreover, the comparison between these two techniques gives an estimation of the concentration of electrically inactive phosphorus atoms.

Effects of graphite surface roughness on bypass flow computations for an HTGR

Energy Technology Data Exchange (ETDEWEB)

Tung, Yu-Hsin, E-mail: touushin@gmail.com [Idaho National Laboratory, P.O. Box 1625, M.S. 3855, Idaho Falls, ID (United States); Johnson, Richard W., E-mail: Rich.Johnson@inl.gov [Idaho National Laboratory, P.O. Box 1625, M.S. 3855, Idaho Falls, ID (United States); Sato, Hiroyuki, E-mail: sato.hiroyuki09@jaea.go.jp [Idaho National Laboratory, P.O. Box 1625, M.S. 3855, Idaho Falls, ID (United States)

2012-11-15

Highlights: Black-Right-Pointing-Pointer CFD calculations are made of bypass flow between graphite blocks in HTGR. Black-Right-Pointing-Pointer Several turbulence models are employed to compare to friction and heat transfer correlations. Black-Right-Pointing-Pointer Parameters varied include bypass gap width and surface roughness. Black-Right-Pointing-Pointer Surface roughness causes increases in max fuel and coolant temperatures. Black-Right-Pointing-Pointer Surface roughness does not cause increase in outlet coolant temperature variation. - Abstract: Bypass flow in a prismatic high temperature gas reactor (HTGR) occurs between graphite blocks as they sit side by side in the core. Bypass flow is not intentionally designed to occur in the reactor, but is present because of tolerances in manufacture, imperfect installation and expansion and shrinkage of the blocks from heating and irradiation. It is desired to increase the knowledge of the effects of such flow; it has been suggested that it may be as much as 20% of the total helium coolant flow [INL Report 2007, INL/EXT-07-13289]. Computational fluid dynamic (CFD) simulations can provide estimates of the scale and impacts of bypass flow. Previous CFD calculations have examined the effects of bypass gap width, level and distribution of heat generation and effects of shrinkage. The present contribution examines the effects of graphite surface roughness on the bypass flow for different relative roughness factors for three gap widths. Such calculations should be validated using specific bypass flow measurements. While such experiments are currently underway for the specific reference prismatic HTGR design for the next generation nuclear plant (NGNP) program of the U.S. Dept. of Energy, the data are not yet available. To enhance confidence in the present calculations, wall shear stress and heat transfer results for several turbulence models and their associated wall treatments are first compared for steady flow in a

Low-energy electron observation of graphite and molybdenite crystals. Application to the study of graphite oxidation

International Nuclear Information System (INIS)

David, G.

1969-01-01

The LEED study of cleaved (0001) faces of crystals having a layered structure allowed to investigate flakes free of steps on graphite and molybdenite, to show twinning on natural graphite. By intensity measurements and computation in the case of a kinematical approximation it has been possible to determine an inner potential of 19 eV for graphite and to identify the direction of the Mo-S bond of the surface layer of molybdenite. The oxidation of graphite has been studied by observing changes, in symmetry of the diffraction patterns and by mass spectrometry of the gases evolved during the oxidation. No surface compounds have been detected and the carbon layers appeared to be peeled off one after the other. The oxidation took place at temperatures higher than 520 C under an oxygen pressure of 10 -5 torr. (author) [fr

NMR studies on graphite-methanol system

International Nuclear Information System (INIS)

El-Akkad, T.M.

1977-01-01

The nuclear magnetic relaxation times for protons of methanol on graphite have been studied. The perpendicular and the transversal magnetization as a function of temperature were measured. The results show that the presence of graphite slowed down the methanol movement compared with that in the pure alcohol, and that the methanol molecules are attached to the graphite surface via methyl groups. (author)

Effect of Ag Doping on the Electronic Structure and Optical Properties of ZnO(0001 Surface

Directory of Open Access Journals (Sweden)

Xiang Qian

2018-01-01

Full Text Available Using first-principle calculations, the geometrical structure, the electronic and optical properties of Ag-doped ZnO(0001 surface have been investigated. We found that Ag-doped ZnO(0001 surface is more easily formed on the first layer. On the other hand, the doped surface has gradually become an equipotential body, showing obvious metallic characteristics. We found that a new peak appeared in the low energy region after Ag doping, which was mainly due to the electron transition between the two orbital levels of Ag-4d and O-2p.

Preparation and Characterization of Graphite Waste/CeO2 Composites

Science.gov (United States)

Kusrini, E.; Utami, C. S.; Nasruddin; Prasetyanto, E. A.; Bawono, Aji A.

2018-03-01

In this research, the chemical modification of graphite waste with CeO2 was developed and characterized. Graphite waste was pretreated with mechanical to obtain the size 200 mesh (75 μm), and thermal methods at 110°C oven for 6 hours. Here, we demonstrate final properties of graphite before modification (GBM), activated graphite (GA) and graphite/CeO2 composite with variation of 0.5, 1 and 2 g of CeO2 (G0.5; G1; G2). The effect of CeO2 concentration was observed. The presence of cerium in modified graphite samples (G0.5; G1; G2) were analyzed using SEM-EDX. The results show that the best surface area was found in G2 is 26.82 m2/g. The presence of CeO2 onto graphite surface does not significantly increase the surface area of composites.

A Universal Strategy for Hollow Metal Oxide Nanoparticles Encapsulated into B/N Co-Doped Graphitic Nanotubes as High-Performance Lithium-Ion Battery Anodes.

Science.gov (United States)

Tabassum, Hassina; Zou, Ruqiang; Mahmood, Asif; Liang, Zibin; Wang, Qingfei; Zhang, Hao; Gao, Song; Qu, Chong; Guo, Wenhan; Guo, Shaojun

2018-02-01

Yolk-shell nanostructures have received great attention for boosting the performance of lithium-ion batteries because of their obvious advantages in solving the problems associated with large volume change, low conductivity, and short diffusion path for Li + ion transport. A universal strategy for making hollow transition metal oxide (TMO) nanoparticles (NPs) encapsulated into B, N co-doped graphitic nanotubes (TMO@BNG (TMO = CoO, Ni 2 O 3 , Mn 3 O 4 ) through combining pyrolysis with an oxidation method is reported herein. The as-made TMO@BNG exhibits the TMO-dependent lithium-ion storage ability, in which CoO@BNG nanotubes exhibit highest lithium-ion storage capacity of 1554 mA h g -1 at the current density of 96 mA g -1 , good rate ability (410 mA h g -1 at 1.75 A g -1 ), and high stability (almost 96% storage capacity retention after 480 cycles). The present work highlights the importance of introducing hollow TMO NPs with thin wall into BNG with large surface area for boosting LIBs in the terms of storage capacity, rate capability, and cycling stability. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Intermodulation distortion and surface resistance in impurity-doped YBCO and MgB{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Agassi, Y.D. [Naval Surface Warfare Center, Carderock Division, Bethesda, MD 20817 (United States); Oates, D.E., E-mail: oates@ll.mit.edu [MIT-Lincoln Laboratory, Lexington, MA 02420 (United States)

2014-11-15

Highlights: • Calculations of impurity-doping effects on surface resistance and intermodulation distortion. • The calculations are compared with previously published measurements in YBCO and MgB{sub 2}. • Excellent agreement between calculations and experiments are shown. • The effects of the symmetry of the energy gap are presented and discussed. - Abstract: Calculations of the microwave intermodulation distortion (IMD) and surface resistance of impurity-doped YBCO, MgB{sub 2} and Nb are presented. These are qualitatively distinct superconductors due to their energy-gap symmetries, d-wave (ℓ = 2), i-wave (ℓ = 6) and s-wave (ℓ = 0), respectively. The calculations are compared with previously published IMD and surface-resistance measurements of impurity-doped YBCO and Nb. The agreement between the data and fitted calculations is excellent in all cases. In the absence of IMD and surface-resistance measurements for doped MgB{sub 2}, we present representative predictions. The calculations are based on a Green’s-function approach that yields analytical expressions for the penetration depth and the nonlinear kernel in the constitutive relation. This penetration-depth expression reproduces the measured T{sup 2} low-temperature variation for doped superconductors and the surface-resistance reduction over that of the pure material. Regarding the IMD in superconductors with a nodal energy gap, the effect of doping is to enhance its magnitude and suppress its low-temperature 1/T{sup 2} divergence predicted by the nonlinear Meissner effect.

An enhanced hydrogen adsorption enthalpy for fluoride intercalated graphite compounds.

Science.gov (United States)

Cheng, Hansong; Sha, Xianwei; Chen, Liang; Cooper, Alan C; Foo, Maw-Lin; Lau, Garret C; Bailey, Wade H; Pez, Guido P

2009-12-16

We present a combined theoretical and experimental study on H(2) physisorption in partially fluorinated graphite. This material, first predicted computationally using ab initio molecular dynamics simulation and subsequently synthesized and characterized experimentally, represents a novel class of "acceptor type" graphite intercalated compounds that exhibit significantly higher isosteric heat of adsorption for H(2) at near ambient temperatures than previously demonstrated for commonly available porous carbon-based materials. The unusually strong interaction arises from the semi-ionic nature of the C-F bonds. Although a high H(2) storage capacity (>4 wt %) at room temperature is predicted not to be feasible due to the low heat of adsorption, enhanced storage properties can be envisaged by doping the graphitic host with appropriate species to promote higher levels of charge transfer from graphene to F(-) anions.

In situ synthesis of cylindrical spongy polypyrrole doped protonated graphitic carbon nitride for cholesterol sensing application.

Science.gov (United States)

Shrestha, Bishnu Kumar; Ahmad, Rafiq; Shrestha, Sita; Park, Chan Hee; Kim, Cheol Sang

2017-08-15

Herein, we demonstrate the exfoliation of bulk graphitic carbon nitrides (g-C 3 N 4 ) into ultra-thin (~3.4nm) two-dimensional (2D) nanosheets and their functionalization with proton (g-C 3 N 4 H + ). The layered semiconductor g-C 3 N 4 H + nanosheets were doped with cylindrical spongy shaped polypyrrole (CSPPy-g-C 3 N 4 H + ) using chemical polymerization method. The as-prepared nanohybrid composite was utilized to fabricate cholesterol biosensors after immobilization of cholesterol oxidase (ChOx) at physiological pH. Large specific surface area and positive charge nature of CSPPy-g-C 3 N 4 H + composite has tendency to generate strong electrostatic attraction with negatively charged ChOx, and as a result they formed stable bionanohybrid composite with high enzyme loading. A detailed electrochemical characterization of as-fabricated biosensor electrode (ChOx-CSPPy-g-C 3 N 4 H + /GCE) exhibited high-sensitivity (645.7 µAmM -1 cm -2 ) in wide-linear range of 0.02-5.0mM, low detection limit (8.0μM), fast response time (~3s), long-term stability, and good selectivity during cholesterol detection. To the best of our knowledge, this novel nanocomposite was utilized for the first time for cholesterol biosensor fabrication that resulted in high sensing performance. Hence, this approach opens a new prospective to utilize CSPPy-g-C 3 N 4 H + composite as cost-effective, biocompatible, eco-friendly, and superior electrocatalytic as well as electroconductive having great application potentials that could pave the ways to explore many other new sensors fabrication and biomedical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Graphite nanoreinforcements in polymer nanocomposites

Science.gov (United States)

Fukushima, Hiroyuki

Nanocomposites composed of polymer matrices with clay reinforcements of less than 100 nm in size, are being considered for applications such as interior and exterior accessories for automobiles, structural components for portable electronic devices, and films for food packaging. While most nanocomposite research has focused on exfoliated clay platelets, the same nanoreinforcement concept can be applied to another layered material, graphite, to produce nanoplatelets and nanocomposites. Graphite is the stiffest material found in nature (Young's Modulus = 1060 GPa), having a modulus several times that of clay, but also with excellent electrical and thermal conductivity. The key to utilizing graphite as a platelet nanoreinforcement is in the ability to exfoliate this material. Also, if the appropriate surface treatment can be found for graphite, its exfoliation and dispersion in a polymer matrix will result in a composite with not only excellent mechanical properties but electrical properties as well, opening up many new structural applications as well as non-structural ones where electromagnetic shielding and high thermal conductivity are requirements. In this research, a new process to fabricate exfoliated nano-scale graphite platelets was established (Patent pending). The size of the resulted graphite platelets was less than 1 um in diameter and 10 nm in thickness, and the surface area of the material was around 100 m2/g. The reduction of size showed positive effect on mechanical properties of composites because of the increased edge area and more functional groups attached with it. Also various surface treatment techniques were applied to the graphite nanoplatelets to improve the surface condition. As a result, acrylamide grafting treatment was found to enhance the dispersion and adhesion of graphite flakes in epoxy matrices. The resulted composites showed better mechanical properties than those with commercially available carbon fibers, vapor grown carbon fibers

Mechanism of yttrium atom formation in electrothermal atomization from metallic and metal-carbide surfaces of a heated graphite atomizer in atomic absorption spectrometry

International Nuclear Information System (INIS)

Wahab, H.S.; Chakrabarti, C.L.

1981-01-01

Mechanism of Y atom formation from pyrocoated graphite, tantalum and tungsten metal surfaces of a graphite tube atomizer has been studied and a mechanism for the formation for Y atoms is proposed for the first time. (author)

The effect of material composition of 3-dimensional graphene oxide and self-doped polyaniline nanocomposites on DNA analytical sensitivity.

Science.gov (United States)

Yang, Tao; Chen, Huaiyin; Yang, Ruirui; Wang, Xinxing; Nan, Fuxin; Jiao, Kui

2015-09-01

Until now, morphology effects of 2-dimensional or 3-dimensional graphene nanocomposites and the effect of material composition on the biosensors have been rarely reported. In this paper, the various nanocomposites based on graphene oxide and self-doped polyaniline nanofibres for studying the effect of morphology and material composition on DNA sensitivity were directly reported. The isolation and dispersion of graphene oxide were realized via intercalated self-doped polyaniline and ultrasonication, where the ultrasonication prompts the aggregates of graphite oxide to break up and self-doped polyaniline to diffuse into the stacked graphene oxide. Significant electrochemical enhancement has been observed due to the existence of self-doped polyaniline, which bridges the defects for electron transfer and, in the mean time, increases the basal spacing between graphene oxide sheets. Different morphologies can result in different ssDNA surface density, which can further influence the hybridization efficiency. Compared with 2-dimensional graphene oxide, self-doped polyaniline and other morphologies of nanocomposites, 3-dimensional graphene oxide-self-doped polyaniline nanowalls exhibited the highest surface density and hybridization efficiency. Furthermore, the fabricated biosensors presented the broad detection range with the low detection limit due to the specific surface area, a large number of electroactive species, and open accessible space supported by nanowalls. Copyright © 2015 Elsevier B.V. All rights reserved.

Calculated bond properties of K adsorbed on graphite

International Nuclear Information System (INIS)

Hjortstam, O.; Wills, J.M.; Johansson, B.; Eriksson, O.

1998-01-01

The properties of the chemical bond of K adsorbed on a graphite(0001) surface have been studied for different coverages, by means of a full-potential slab method. Specific modifications of the Hamiltonian are performed in order to make it possible to study K on graphite in the disperse phase (dilute limit). It is found that K forms a metallic state when covering a graphite surface with a (2x2) coverage. For a (3x3) coverage as well as in the disperse phase K is found to form an ionic bond with graphite. It is shown that in the disperse phase, the hybridization between the K 4s level and graphite is weak. Our findings are consistent with recent experiments. Furthermore the cohesive energies of K adsorption on graphite are found to be larger in the (2x2) coverage compared to the (3x3) coverage. copyright 1998 The American Physical Society

Hydrothermal synthesis of highly nitrogen-doped few-layer graphene via solid–gas reaction

International Nuclear Information System (INIS)

Liang, Xianqing; Zhong, Jun; Shi, Yalin; Guo, Jin; Huang, Guolong; Hong, Caihao; Zhao, Yidong

2015-01-01

Highlights: • A novel approach to synthesis of N-doped few-layer graphene has been developed. • The high doping levels of N in products are achieved. • XPS and XANES results reveal a thermal transformation of N bonding configurations. • The developed method is cost-effective and eco-friendly. - Abstract: Nitrogen-doped (N-doped) graphene sheets with high doping concentration were facilely synthesized through solid–gas reaction of graphene oxide (GO) with ammonia vapor in a self-designed hydrothermal system. The morphology, surface chemistry and electronic structure of N-doped graphene sheets were investigated by TEM, AFM, XRD, XPS, XANES and Raman characterizations. Upon hydrothermal treatment, up to 13.22 at% of nitrogen could be introduced into the crumpled few-layer graphene sheets. Both XPS and XANES analysis reveal that the reaction between oxygen functional groups in GO and ammonia vapor produces amide and amine species in hydrothermally treated GO (HTGO). Subsequent thermal annealing of the resultant HTGO introduces a gradual transformation of nitrogen bonding configurations in graphene sheets from amine N to pyridinic and graphitic N with the increase of annealing temperature. This study provides a simple but cost-effective and eco-friendly method to prepare N-doped graphene materials in large-scale for potential applications

Tailoring the surface chemical bond states of the NbN films by doping Ag: Achieving hard hydrophobic surface

Energy Technology Data Exchange (ETDEWEB)

Ren, Ping; Zhang, Kan; Du, Suxuan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun, 130012 (China); Meng, Qingnan [College of Construction Engineering, Jilin University, Changchun, 130026 (China); He, Xin [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun, 130012 (China); Wang, Shuo [Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871 (China); Wen, Mao, E-mail: wenmao225@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun, 130012 (China); Zheng, Weitao, E-mail: WTZheng@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun, 130012 (China)

2017-06-15

Highlights: • Intrinsically hydrophilic NbN films can transfer to hydrophobic Nb-Ag-N films by doping Ag atoms into NbN sublattice. • Solute Ag can promote that the hydrophobic Ag{sub 2}O groups formed on the Nb-Ag-N film surface through self-oxidation. • The present work may provide a straightforward approach for the production of robust hydrophobic ceramic surfaces. - Abstract: Robust hydrophobic surfaces based on ceramics capable of withstanding harsh conditions such as abrasion, erosion and high temperature, are required in a broad range of applications. The metal cations with coordinative saturation or low electronegativity are commonly chosen to achieve the intrinsically hydrophobic ceramic by reducing Lewis acidity, and thus the ceramic systems are limited. In this work, we present a different picture that robust hydrophobic surface with high hardness (≥20 GPa) can be fabricated through doping Ag atoms into intrinsically hydrophilic ceramic film NbN by reactive co-sputtering. The transition of wettability from hydrophilic to hydrophobic of Nb-Ag-N films induced by Ag doping results from the appearance of Ag{sub 2}O groups on the films surfaces through self-oxidation, because Ag cations (Ag{sup +}) in Ag{sub 2}O are the filled-shell (4d{sup 10}5S{sup 0}) electronic structure with coordinative saturation that have no tendency to interact with water. The results show that surface Ag{sub 2}O benefited for hydrophobicity comes from the solute Ag atoms rather than precipitate metal Ag, in which the more Ag atoms incorporated into Nb-sublattice are able to further improve the hydrophobicity, whereas the precipitation of Ag nanoclusters would worsen it. The present work opens a window for fabricating robust hydrophobic surface through tailoring surface chemical bond states by doping Ag into transition metal nitrides.

Structural and electronic properties of Mg and Mg-Nb co-doped TiO2 (101) anatase surface

International Nuclear Information System (INIS)

Sasani, Alireza; Baktash, Ardeshir; Mirabbaszadeh, Kavoos; Khoshnevisan, Bahram

2016-01-01

Highlights: • Formation energy of Mg and Mg-Nb co-doped TiO_2 anatase surface (101) is studied. • Effect of Mg defect to the TiO_2 anatase (101) surface and bond length distribution of the surface is studied and it is shown that Mg defects tend to stay far from each other. • Effect of Mg and Nb to the bond length distribution of the surface studied and it is shown that these defects tend to stay close to each other. • Effects of Mg and Mg-Nb defects on DSSCs using TiO_2 anatase hosting these defects are studied. - Abstract: In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO_2 anatase (101) surfaces are studied. By studying the formation energy of the defects and the bond length distribution of the surface, it is shown that Mg defects tend to stay as far as possible to induce least possible lattice distortion while Nb and Mg defects stay close to each other to cause less stress to the surface. By investigating band structure of the surface and changes stemmed from the defects, potential effects of Mg and Mg-Nb co-doping of TiO_2 surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase J_S_C of the surface while slightly decreasing V_O_C compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

Electronic Properties of a 1D Intrinsic/p-Doped Heterojunction in a 2D Transition Metal Dichalcogenide Semiconductor

KAUST Repository

Song, Zhibo; Schultz, Thorsten; Ding, Zijing; Lei, Bo; Han, Cheng; Amsalem, Patrick; Lin, Tingting; Chi, Dongzhi; Wong, Swee Liang; Zheng, Yu Jie; Li, Ming-yang; Li, Lain-Jong; Chen, Wei; Koch, Norbert; Huang, Yu Li; Wee, Andrew Thye Shen

2017-01-01

Two-dimensional (2D) semiconductors offer a convenient platform to study 2D physics, for example, to understand doping in an atomically thin semiconductor. Here, we demonstrate the fabrication and unravel the electronic properties of a lateral doped/intrinsic heterojunction in a single-layer (SL) tungsten diselenide (WSe2), a prototype semiconducting transition metal dichalcogenide (TMD), partially covered with a molecular acceptor layer, on a graphite substrate. With combined experiments and theoretical modeling, we reveal the fundamental acceptor-induced p-doping mechanism for SL-WSe2. At the 1D border between the doped and undoped SL-WSe2 regions, we observe band bending and explain it by Thomas-Fermi screening. Using atomically resolved scanning tunneling microscopy and spectroscopy, the screening length is determined to be in the few nanometer range, and we assess the carrier density of intrinsic SL-WSe2. These findings are of fundamental and technological importance for understanding and employing surface doping, for example, in designing lateral organic TMD heterostructures for future devices.

Electronic Properties of a 1D Intrinsic/p-Doped Heterojunction in a 2D Transition Metal Dichalcogenide Semiconductor

KAUST Repository

Song, Zhibo

2017-07-28

Two-dimensional (2D) semiconductors offer a convenient platform to study 2D physics, for example, to understand doping in an atomically thin semiconductor. Here, we demonstrate the fabrication and unravel the electronic properties of a lateral doped/intrinsic heterojunction in a single-layer (SL) tungsten diselenide (WSe2), a prototype semiconducting transition metal dichalcogenide (TMD), partially covered with a molecular acceptor layer, on a graphite substrate. With combined experiments and theoretical modeling, we reveal the fundamental acceptor-induced p-doping mechanism for SL-WSe2. At the 1D border between the doped and undoped SL-WSe2 regions, we observe band bending and explain it by Thomas-Fermi screening. Using atomically resolved scanning tunneling microscopy and spectroscopy, the screening length is determined to be in the few nanometer range, and we assess the carrier density of intrinsic SL-WSe2. These findings are of fundamental and technological importance for understanding and employing surface doping, for example, in designing lateral organic TMD heterostructures for future devices.

Kinetic electron emission from highly oriented pyrolytic graphite surfaces induced by singly charged ions

CERN Document Server

Cernusca, S; Winter, H; Aumayr, F; Loerincik, J; Sroubek, Z

2002-01-01

We present total electron yields determined by current measurements for normal impact of H sup + , H sub 2 sup + , H sub 3 sup + , C sup + , N sup + and O sup + ions (E<=10 keV) on a clean highly oriented pyrolytic graphite surface. The kinetic energy of the projectiles has been varied from near threshold up to 10 keV. By comparing the results to similar data obtained for a polycrystalline Au surface the role of different target properties for kinetic electron emission can be analysed.

Synthesis of graphene nanoplatelets from peroxosulfate graphite intercalation compounds

OpenAIRE

MELEZHYK A.V.; TKACHEV A.G.

2014-01-01

Ultrasonic exfoliation of expanded graphite compound obtained by cold expansion of graphite intercalated with peroxodisulfuric acid was shown to allow the creation of graphene nanoplatelets with thickness of about 5-10 nm. The resulting graphene material contained surface oxide groups. The expanded graphite intercalation compound was exfoliated by ultrasound much easier than thermally expanded graphite. A mechanism for the cleavage of graphite to graphene nanoplatelets is proposed. It include...

Comparative inhalation toxicity of multi-wall carbon nanotubes, graphene, graphite nanoplatelets and low surface carbon black.

Science.gov (United States)

Ma-Hock, Lan; Strauss, Volker; Treumann, Silke; Küttler, Karin; Wohlleben, Wendel; Hofmann, Thomas; Gröters, Sibylle; Wiench, Karin; van Ravenzwaay, Bennard; Landsiedel, Robert

2013-06-17

Carbon nanotubes, graphene, graphite nanoplatelets and carbon black are seemingly chemically identical carbon-based nano-materials with broad technological applications. Carbon nanotubes and carbon black possess different inhalation toxicities, whereas little is known about graphene and graphite nanoplatelets. In order to compare the inhalation toxicity of the mentioned carbon-based nanomaterials, male Wistar rats were exposed head-nose to atmospheres of the respective materials for 6 hours per day on 5 consecutive days. Target concentrations were 0.1, 0.5, or 2.5 mg/m3 for multi-wall carbon nanotubes and 0.5, 2.5, or 10 mg/m3 for graphene, graphite nanoplatelets and low-surface carbon black. Toxicity was determined after end of exposure and after three-week recovery using broncho-alveolar lavage fluid and microscopic examinations of the entire respiratory tract. No adverse effects were observed after inhalation exposure to 10 mg/m3 graphite nanoplatelets or relatively low specific surface area carbon black. Increases of lavage markers indicative for inflammatory processes started at exposure concentration of 0.5 mg/m3 for multi-wall carbon nanotubes and 10 mg/m3 for graphene. Consistent with the changes in lavage fluid, microgranulomas were observed at 2.5 mg/m3 multi-wall carbon nanotubes and 10 mg/m3 graphene. In order to evaluate volumetric loading of the lung as the key parameter driving the toxicity, deposited particle volume was calculated, taking into account different methods to determine the agglomerate density. However, the calculated volumetric load did not correlate to the toxicity, nor did the particle surface burden of the lung. The inhalation toxicity of the investigated carbon-based materials is likely to be a complex interaction of several parameters. Until the properties which govern the toxicity are identified, testing by short-term inhalation is the best option to identify hazardous properties in order to avoid unsafe applications or select

Comparative inhalation toxicity of multi-wall carbon nanotubes, graphene, graphite nanoplatelets and low surface carbon black

Science.gov (United States)

2013-01-01

Background Carbon nanotubes, graphene, graphite nanoplatelets and carbon black are seemingly chemically identical carbon-based nano-materials with broad technological applications. Carbon nanotubes and carbon black possess different inhalation toxicities, whereas little is known about graphene and graphite nanoplatelets. Methods In order to compare the inhalation toxicity of the mentioned carbon-based nanomaterials, male Wistar rats were exposed head-nose to atmospheres of the respective materials for 6 hours per day on 5 consecutive days. Target concentrations were 0.1, 0.5, or 2.5 mg/m3 for multi-wall carbon nanotubes and 0.5, 2.5, or 10 mg/m3 for graphene, graphite nanoplatelets and low-surface carbon black. Toxicity was determined after end of exposure and after three-week recovery using broncho-alveolar lavage fluid and microscopic examinations of the entire respiratory tract. Results No adverse effects were observed after inhalation exposure to 10 mg/m3 graphite nanoplatelets or relatively low specific surface area carbon black. Increases of lavage markers indicative for inflammatory processes started at exposure concentration of 0.5 mg/m3 for multi-wall carbon nanotubes and 10 mg/m3 for graphene. Consistent with the changes in lavage fluid, microgranulomas were observed at 2.5 mg/m3 multi-wall carbon nanotubes and 10 mg/m3 graphene. In order to evaluate volumetric loading of the lung as the key parameter driving the toxicity, deposited particle volume was calculated, taking into account different methods to determine the agglomerate density. However, the calculated volumetric load did not correlate to the toxicity, nor did the particle surface burden of the lung. Conclusions The inhalation toxicity of the investigated carbon-based materials is likely to be a complex interaction of several parameters. Until the properties which govern the toxicity are identified, testing by short-term inhalation is the best option to identify hazardous properties in

Nucleation of ripplocations through atomistic modeling of surface nanoindentation in graphite

Science.gov (United States)

Freiberg, D.; Barsoum, M. W.; Tucker, G. J.

2018-05-01

In this work, we study the nucleation and subsequent evolution behavior of ripplocations - a newly proposed strain accommodating defect in layered materials where one, or more, layers buckle orthogonally to the layers - using atomistic modeling of graphite. To that effect, we model the response to cylindrical indenters with radii R of 50, 100, and 250 nm, loaded edge-on into graphite layers and the strain gradient effects beneath the indenter are quantified. We show that the response is initially elastic followed by ripplocation nucleation, and growth of multiple fully reversible ripplocation boundaries below the indenter. In the elastic region, the stress is found to be a function of indentation volume; beyond the elastic regime, the interlayer strain gradient emerges as paramount in the onset of ripplocation nucleation and subsequent in-plane stress relaxation. Furthermore, ripplocation boundaries that nucleate from the alignment of ripplocations on adjacent layers are exceedingly nonlocal and propagate, wavelike, away from the indented surface. This work not only provides a critical understanding of the mechanistic underpinnings of the deformation of layered solids and formation of kink boundaries, but also provides a more complete description of the nucleation mechanics of ripplocations and their strain field dependence.

La modified TiO{sub 2} photoanode and its effect on DSSC performance: A comparative study of doping and surface treatment on deep and surface charge trapping

Energy Technology Data Exchange (ETDEWEB)

Ako, Rajour Tanyi [Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Negara Brunei Darussalam (Brunei Darussalam); Ekanayake, Piyasiri, E-mail: piyasiri.ekanayake@ubd.edu.bn [Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Negara Brunei Darussalam (Brunei Darussalam); Centre for Advanced Material and Energy Sciences (CAMES), Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Negara Brunei Darussalam (Brunei Darussalam); Tan, Ai Ling [Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Negara Brunei Darussalam (Brunei Darussalam); Young, David James [Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Negara Brunei Darussalam (Brunei Darussalam); Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Maroochydore DC, Queensland, 4558 (Australia); Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research - A*STAR, #08-03, 2 Fusionopolis Way, Innovis, 138634 (Singapore)

2016-04-01

The effect of Lanthanum ions (La{sup 3+}) on charge trapping in dye-sensitized solar cell (DSSC) photoanodes has been investigated with doped and surface-treated TiO{sub 2} nanoparticles. Doped nanoparticles consisting of 0.5 mol.% Mg and La co-doped TiO{sub 2}, 0.5 mol.% Mg doped TiO{sub 2} and pure TiO{sub 2} were synthesized by the sol gel method. Surface-treated nanoparticles of Mg doped TiO{sub 2} and pure TiO{sub 2} were prepared by ball milling in 0.05 M aqueous La{sup 3+} solution. All materials were analyzed by XRD, XPS and UV–Vis DRS. Cell performance, surface free energy state changes and electron injection efficiency of DSSCs based on these nanoparticles were evaluated using current –voltage measurements, EIS and Incident photon to current conversion efficiency. Doped materials had La and Mg ions incorporated into the TiO{sub 2} lattice, while no lattice changes were observed for the surface-treated materials. Less visible light was absorbed by treated oxides compared with doped oxide samples. The overall power conversion efficiencies (PCE) of DSSC photoanodes based on doped materials were twice those of photoanodes fabricated from treated nanoparticles. Doping establishes deep traps that reduce the recombination of electron–hole (e–h) pairs. Conversely, the presence of absorbed oxygen in treated materials enhances e–h recombination with electrolyte at surface trap sites. - Highlights: • DSSC performance is investigated using photoanodes of doped and La{sup 3+} surface treated TiO{sub 2}. • TiO{sub 2} and Mg–TiO{sub 2} treated with La{sup 3+} absorbed less visible light. • A high concentration of absorbed oxygen on surface treated oxides reduced band bending. • Increased surface free energy in the modified DSSC anodes is caused more by Mg{sup 2+} at Ti{sup 4+} than by La{sup 3+} at the surfaces. • Near surface charge traps due to La{sup 3+} treatment promotes e–h recombination.

Effect of airborne contaminants on the wettability of supported graphene and graphite.

Science.gov (United States)

Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P; Li, Lei; Liu, Haitao

2013-10-01

It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment. Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.

Effect of airborne contaminants on the wettability of supported graphene and graphite

Science.gov (United States)

Li, Zhiting; Wang, Yongjin; Kozbial, Andrew; Shenoy, Ganesh; Zhou, Feng; McGinley, Rebecca; Ireland, Patrick; Morganstein, Brittni; Kunkel, Alyssa; Surwade, Sumedh P.; Li, Lei; Liu, Haitao

2013-10-01

It is generally accepted that supported graphene is hydrophobic and that its water contact angle is similar to that of graphite. Here, we show that the water contact angles of freshly prepared supported graphene and graphite surfaces increase when they are exposed to ambient air. By using infrared spectroscopy and X-ray photoelectron spectroscopy we demonstrate that airborne hydrocarbons adsorb on graphitic surfaces, and that a concurrent decrease in the water contact angle occurs when these contaminants are partially removed by both thermal annealing and controlled ultraviolet-O3 treatment. Our findings indicate that graphitic surfaces are more hydrophilic than previously believed, and suggest that previously reported data on the wettability of graphitic surfaces may have been affected by unintentional hydrocarbon contamination from ambient air.

Redox behavior of a low-doped Pr-CeO_2(111) surface. A DFT+U study

International Nuclear Information System (INIS)

Milberg, Brian; Juan, Alfredo; Irigoyen, Beatriz

2017-01-01

Highlights: • Pr doping facilitates oxygen donation due to the easy formation of Pr"3"+/Pr"4"+ and Ce"3"+/Ce"4"+ redox couples. • Pr doping also favors the formation of superoxide (O_2"−) radicals on surface O-holes. • CO can be oxidized by superoxide radical forming a CO_2 molecule floating on the surface. • CO can also interact on the (O_2"−)/Pr"3"+ interphase and forms weakly adsorbed carbonate-type intermediates. - Abstract: In this work, we investigated the redox behavior (donation and replenishing of oxygen) of a low praseodymium (Pr)-doped CeO_2(111) surface. We considered a 3.7 at.% Pr doping and performed density functional calculations using the GGA formalism with the ‘U’ correction on Ce(4f) and Pr(4f) orbitals. Our results indicate that Pr doping promotes oxygen donation by lowering the energy necessary to form surface anionic vacancies. When the Ce_0_._9_6_3Pr_0_._0_3_7O_2(111) surface donates one oxygen, the two excess electrons locate on Pr and Ce cations and reduce them to Pr"3"+ and Ce"3"+ ones. Praseodymium doping also favors the activation of O_2 molecule on surface O-holes, leading to formation of a superoxide (O_2"−) radical as well as to reoxidation of the Ce"3"+ cation to Ce"4"+ one. Additionally, we used the CO molecular adsorption for testing the reactivity of those superoxide species. The calculations expose the ability of these radicals to oxidize CO forming a CO_2 molecule floating on the surface. However, when the superoxide is in the immediate vicinity of Pr dopant a carbonate-type species is formed. Our theoretical results may help to gain insight into redox properties and improved catalytic performance of low-doped Pr-CeO_2 solids.

Structural and electronic properties of Mg and Mg-Nb co-doped TiO2 (101) anatase surface

Energy Technology Data Exchange (ETDEWEB)

Sasani, Alireza [Department of Science, Karaj Islamic Azad University, Karaj, Alborz, P.O. Box 31485-313 (Iran, Islamic Republic of); Baktash, Ardeshir [Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167 (Iran, Islamic Republic of); Mirabbaszadeh, Kavoos, E-mail: mirabbas@aut.ac.ir [Department of Energy Engineering and Physics, Amirkabir University of Technology, Tehran, P. O. Box 15875-4413 (Iran, Islamic Republic of); Khoshnevisan, Bahram [Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167 (Iran, Islamic Republic of)

2016-10-30

Highlights: • Formation energy of Mg and Mg-Nb co-doped TiO{sub 2} anatase surface (101) is studied. • Effect of Mg defect to the TiO{sub 2} anatase (101) surface and bond length distribution of the surface is studied and it is shown that Mg defects tend to stay far from each other. • Effect of Mg and Nb to the bond length distribution of the surface studied and it is shown that these defects tend to stay close to each other. • Effects of Mg and Mg-Nb defects on DSSCs using TiO{sub 2} anatase hosting these defects are studied. - Abstract: In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO{sub 2} anatase (101) surfaces are studied. By studying the formation energy of the defects and the bond length distribution of the surface, it is shown that Mg defects tend to stay as far as possible to induce least possible lattice distortion while Nb and Mg defects stay close to each other to cause less stress to the surface. By investigating band structure of the surface and changes stemmed from the defects, potential effects of Mg and Mg-Nb co-doping of TiO{sub 2} surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase J{sub SC} of the surface while slightly decreasing V{sub OC} compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

Hydrogen pumping and release by graphite under high flux plasma bombardment

International Nuclear Information System (INIS)

Hirooka, Y.; Leung, W.K.; Conn, R.W.; Goebel, D.M.; LaBombard, B.; Nygren, R.; Wilson, K.L.

1988-01-01

Inert gas (helium or argon) plasma bombardment has been found to increase the surface gas adsorptivity of isotropic graphite (POCO-graphite), which can then getter residual gases in a high vacuum system. The inert gas plasma bombardment was carried out at a flux ≅ 1 x 10 18 ions s -1 cm -2 to a fluence of the order of 10 21 ions/cm 2 and at temperatures around 800 0 C. The gettering capability of graphite can be easily recovered by repeating inert gas plasma bombardment. The activated graphite surface exhibits a smooth, sponge-like morphology with significantly increased pore openings, which correlates with the observed increase in the surface gas adsorptivity. The activated graphite surface has been observed to pump hydrogen plasma particles as well. From calibrated H-alpha measurements, the dynamic hydrogen retention capacity is evaluated to be as large as 2 x 10 18 H/cm 2 at temperatures below 100 0 C and at a plasma bombarding energy of 300 eV. The graphite temperature was varied between 15 and 480 0 C. Due to the plasma particle pumping capability, hydrogen recycling from the activated graphite surface is significantly reduced, relative to that from a pre-saturated surface. A pre-saturated surface was also observed to reproducibly pump a hydrogen plasma to a concentration of 9.5 x 10 17 H/cm 2 . The hydrogen retention capacity of graphite is found to decrease with increasing temperature. A transient pumping mechanism associated with the sponge-like surface morphology is conjectured to explain the large hydrogen retention capacity. Hydrogen release behavior under helium and argon plasma bombardment was also investigated, and the result indicated the possibility of some in-pore retrapping effect. 43 refs., 11 figs

Cluster-surface interaction: from soft landing to implantation

DEFF Research Database (Denmark)

Popok, Vladimir; Barke, Ingo; Campbell, Eleanor E.B.

2011-01-01

applications of keV-energy cluster ion beams. This includes ultra-shallow doping of semiconductors and formation of ultrathin insulating layers. A few examples of MeV-energy cluster implantation, leading to the formation of nanosize hillocks or pillars on the surface as well as to local phase transitions (for...... instance, graphite-to-diamond) are also discussed. The review is finalized by an outlook on the future development of cluster beam research....

Investigation of fluorine adsorption on nitrogen doped MgAl_2O_4 surface by first-principles

International Nuclear Information System (INIS)

Lv, Xiaojun; Xu, Zhenming; Li, Jie; Chen, Jiangan; Liu, Qingsheng

2016-01-01

Graphical abstract: First-principles calculations indicate that MgAl_2O_4 surface is fluorine-loving, but hydrophobic. N doped MgAl_2O_4 (100) surface structure shows the highest fluorine adsorption performance and fluorine atom is more preferentially adsorbed on the Mg-Al bridge site. The fluorine adsorption intensity follow this order: N doped MgAl_2O_4 (100) > Al_2O_3 (0001) > MgAl_2O_4 (100) > MgO (100). N doped MgAl_2O_4 is a promising candidate for fluorine removal. - Highlights: • MgAl_2O_4 surface is fluorine-loving, not hydrophilic. • Fluorine preferentially adsorbs on the Mg-Al bridge site. • Adsorption intensity follow this order: N doped MgAl_2O_4 > Al_2O_3 > MgAl_2O_4 > MgO. • Excellent adsorption performance attributes to electron compensation of N atom. • Nitrogen doped MgAl_2O_4 is a promising candidate for fluorine removal. - Abstract: The nature of fluorine adsorption on pure and N doped MgAl_2O_4 surface has been investigated by first-principles calculations based on the density functional theory. Calculated results indicate that MgAl_2O_4 surface is fluorine-loving, not hydrophilic. Nitrogen doped MgAl_2O_4 (100) surface shows the highest fluorine adsorption performance and fluorine atom preferentially adsorbs on the Mg-Al bridge site. The fluorine adsorption intensity follow this order: Nitrogen doped MgAl_2O_4 (100) > Al_2O_3 (0001) > MgAl_2O_4 (100) > MgO (100). In-depth PDOS analysis suggested that 2p orbitals of F atom strongly hybridized with 3s- and 3p-orbitals of Al atom contribute to its high adsorption intensity. According to the analysis of Hirshfeld charge, the excellent fluorine adsorption performance of nitrogen doped MgAl_2O_4 attributes to the electron compensation effect of nitrogen atom and strong electrostatic interactions. All these evidences demonstrate a fact nitrogen doped MgAl_2O_4 is a promising candidate for fluorine removal.

In situ formation of graphene layers on graphite surfaces for efficient anodes of microbial fuel cells.

Science.gov (United States)

Tang, Jiahuan; Chen, Shanshan; Yuan, Yong; Cai, Xixi; Zhou, Shungui

2015-09-15

Graphene can be used to improve the performance of the anode in a microbial fuel cell (MFC) due to its good biocompatibility, high electrical conductivity and large surface area. However, the chemical production and modification of the graphene on the anode are environmentally hazardous because of the use of various harmful chemicals. This study reports a novel method based on the electrochemical exfoliation of a graphite plate (GP) for the in situ formation of graphene layers on the surface of a graphite electrode. When the resultant graphene-layer-based graphite plate electrode (GL/GP) was used as an anode in an MFC, a maximum power density of 0.67 ± 0.034 W/m(2) was achieved. This value corresponds to 1.72-, 1.56- and 1.26-times the maximum power densities of the original GP, exfoliated-graphene-modified GP (EG/GP) and chemically-reduced-graphene-modified GP (rGO/GP) anodes, respectively. Electrochemical measurements revealed that the high performance of the GL/GP anode was attributable to its macroporous structure, improved electron transfer and high electrochemical capacitance. The results demonstrated that the proposed method is a facile and environmentally friendly synthesis technique for the fabrication of high-performance graphene-based electrodes for use in microbial energy harvesting. Copyright © 2015 Elsevier B.V. All rights reserved.

Electrospun N-doped Hierarchical Porous Carbon Nanofiber with Improved Graphitization Degree for High Performance Lithium Ion Capacitor.

Science.gov (United States)

Li, Baohua; Shi, Ruiying; Han, Cuiping; Xu, Xiaofu; Qing, Xianying; Xu, Lei; Li, Hongfei; Li, Junqin; Wong, Ching-Ping

2018-05-14

Lithium ion capacitor (LIC) has been regarded as a promising device to combine the merits of lithium ion batteries and supercapacitors, which can meet the requirements for both high energy and power density. The development of advanced electrode is the key. Herein, we demonstrate the bottom-up synthesis of activated carbon nanofiber (a-PANF) with hierarchical porous structure and high graphitization degree. Electrospinning is employed to prepare interconnected fiber network with macropores and ferric acetylacetonate is introduced as both mesopore creating agent and graphitic catalyst to increase the graphitization degree. Furthermore, chemical activation enlarges the specific surface area by producing rich micropores. Half cell evaluation of the as-prepared a-PANF displays a discharge capacity of 80 mAh g-1 at 0.1 A g-1 within 2~4.5 V and no capacity fading after 1000 cycles at 2 A g-1, which is significantly higher than conventional activated carbon. Furthermore, the as-assembled LIC with a-PANF cathode and Fe3O4 anode achieves a superior energy density of 124.6 Wh kg-1 at a specific power of 93.8 W kg-1, and remains 103.7 Wh kg-1 at 4687.5 W kg-1, demonstrating the promising application of a-PANF as potential electrode candidates for efficient energy storage systems. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low-energy electron observation of graphite and molybdenite crystals. Application to the study of graphite oxidation; Observation au moyen d'electrons de faible energie de cristaux de graphite et de molybdenite. Application a l'etude de l'oxydation du graphite

Energy Technology Data Exchange (ETDEWEB)

David, G [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1969-07-01

The LEED study of cleaved (0001) faces of crystals having a layered structure allowed to investigate flakes free of steps on graphite and molybdenite, to show twinning on natural graphite. By intensity measurements and computation in the case of a kinematical approximation it has been possible to determine an inner potential of 19 eV for graphite and to identify the direction of the Mo-S bond of the surface layer of molybdenite. The oxidation of graphite has been studied by observing changes, in symmetry of the diffraction patterns and by mass spectrometry of the gases evolved during the oxidation. No surface compounds have been detected and the carbon layers appeared to be peeled off one after the other. The oxidation took place at temperatures higher than 520 C under an oxygen pressure of 10{sup -5} torr. (author) [French] L'etude par diffraction des electrons lents des faces (0001) de cristaux ayant une structure en feuillet a permis de mettre en evidence des plages sans gradins sur des clivages de graphite et de molybdenite caracterisees par la symetrie ternaire des diagrammes, de montrer l'existence de macles sur des cristaux de graphite naturel. Un calcul utilisant une approximation cinematique a ete applique aux intensites mesurees des taches de diffraction; il a ete ainsi possible de determiner un potentiel interne de 19 eV pour le graphite et de preciser la direction de la liaison Mo-S du feuillet superficiel de la molybdenite. L'oxydation du graphite a ete etudiee en mettant en relation des changements de symetrie des diagrammes de diffraction avec l'analyse des gaz provenant de la reaction carbone-oxygene. Il a ete montre qu'il n'y avait pas formation de composes de surface et que les couches de carbone etaient enlevees les unes apres les autres. L'oxydation a ete observee sous une pression d'oxygene de 10{sup -5} torr au-dessus de 520 C. (auteur)

A graphite foam reinforced by graphite particles

Energy Technology Data Exchange (ETDEWEB)

Zhu, J.J.; Wang, X.Y.; Guo, L.F.; Wang, Y.M.; Wang, Y.P.; Yu, M.F.; Lau, K.T.T. [DongHua University, Shanghai (China). College of Material Science and Engineering

2007-11-15

Graphite foam was obtained after carbonization and graphitization of a pitch foam formed by the pyrolysis of coal tar based mesophase pitch mixed with graphite particles in a high pressure and temperature chamber. The graphite foam possessed high mechanical strength and exceptional thermal conductivity after adding the graphite particles. Experimental results showed that the thermal conductivity of modified graphite foam reached 110W/m K, and its compressive strength increased from 3.7 MPa to 12.5 MPa with the addition of 5 wt% graphite particles. Through the microscopic observation, it was also found that fewer micro-cracks were formed in the cell wall of the modified foam as compared with pure graphite foam. The graphitization degree of modified foam reached 84.9% and the ligament of graphite foam exhibited high alignment after carbonization at 1200{sup o}C for 3 h and graphitization at 3000{sup o}C for 10 min.

Initial Reduction of CO2 on Pd-, Ru-, and Cu-Doped CeO2(111) Surfaces: Effects of Surface Modification on Catalytic Activity and Selectivity.

Science.gov (United States)

Guo, Chen; Wei, Shuxian; Zhou, Sainan; Zhang, Tian; Wang, Zhaojie; Ng, Siu-Pang; Lu, Xiaoqing; Wu, Chi-Man Lawrence; Guo, Wenyue

2017-08-09

Surface modification by metal doping is an effective treatment technique for improving surface properties for CO 2 reduction. Herein, the effects of doped Pd, Ru, and Cu on the adsorption, activation, and reduction selectivity of CO 2 on CeO 2 (111) were investigated by periodic density functional theory. The doped metals distorted the configuration of a perfect CeO 2 (111) by weakening the adjacent Ce-O bond strength, and Pd doping was beneficial for generating a highly active O vacancy. The analyses of adsorption energy, charge density difference, and density of states confirmed that the doped metals were conducive for enhancing CO 2 adsorption, especially for Cu/CeO 2 (111). The initial reductive dissociation CO 2 → CO* + O* on metal-doped CeO 2 (111) followed the sequence of Cu- > perfect > Pd- > Ru-doped CeO 2 (111); the reductive hydrogenation CO 2 + H → COOH* followed the sequence of Cu- > perfect > Ru- > Pd-doped CeO 2 (111), in which the most competitive route on Cu/CeO 2 (111) was exothermic by 0.52 eV with an energy barrier of 0.16 eV; the reductive hydrogenation CO 2 + H → HCOO* followed the sequence of Ru- > perfect > Pd-doped CeO 2 (111). Energy barrier decomposition analyses were performed to identify the governing factors of bond activation and scission along the initial CO 2 reduction routes. Results of this study provided deep insights into the effect of surface modification on the initial reduction mechanisms of CO 2 on metal-doped CeO 2 (111) surfaces.

Theoretical and experimental study of the vibrational excitations in ethane monolayers adsorbed on graphite (0001) surfaces

DEFF Research Database (Denmark)

Hansen, Flemming Yssing; Taub, H.

1987-01-01

The collective vibrational excitations of two different crystalline monolayer phases of ethane (C2H6) adsorbed on the graphite (0001) surface have been investigated theoretically and experimentally. The monolayer phases studied are the commensurate 7/8 ×4 structure in which the ethane molecules lie...

Electrocatalytic properties of N-doped graphite felt in electro-Fenton process and degradation mechanism of levofloxacin.

Science.gov (United States)

Liu, Xiaocheng; Yang, Danxing; Zhou, Yaoyu; Zhang, Jiachao; Luo, Lin; Meng, Sijun; Chen, Song; Tan, Mengjiao; Li, Zhicheng; Tang, Lin

2017-09-01

The degradation of antibiotic levofloxacin was investigated by dimensionally stable anode as well as modified cathode using low-cost chemical reagents of hydrazine hydrate and ethanol for electro-Fenton in an undivided cell at pH 3.0 under room temperature. Comparison of unmodified and modified cathode was performed. The apparent rate constant of levofloxacin decay was found to be 0.2883 min -1 for graphite felt-10 with the best performance at 200 mA, which is lower than graphite felt at 400 mA. The optimum modified cathode showed a significant improvement of complete mineralization of levofloxacin, reaching a 92% TOC removal at 200 mA for 480 min higher than unmodified one at twice the current. Surface physicochemical properties and morphology were investigated by scanning electron microscope, contact angle and X-ray photoelectron spectroscopy. The electrochemical characterization of hydrogen evolution reaction was adopted to clarify a possible pathway for the higher mineralization of levofloxacin, indicating a potential pilot-scale study to the pollution with the similar structure. Copyright © 2017 Elsevier Ltd. All rights reserved.

Exceptionally crystalline and conducting acid doped polyaniline films by level surface assisted solution casting approach

Energy Technology Data Exchange (ETDEWEB)

Puthirath, Anand B.; Varma, Sreekanth J.; Jayalekshmi, S., E-mail: jayalekshmi@cusat.ac.in [Division for Research in Advanced Materials, Department of Physics, Cochin University of Science and Technology, Cochin, Kerala 682022 (India); Methattel Raman, Shijeesh [Nanophotonic and Optoelectronic Devices Laboratory, Department of Physics, Cochin University of Science and Technology, Cochin, Kerala 682022 (India)

2016-04-18

Emeraldine salt form of polyaniline (PANI) was synthesized by chemical oxidative polymerisation method using ammonium persulfate as oxidant. Resultant emeraldine salt form of PANI was dedoped using ammonia solution and then re-doped with camphor sulphonic acid (CSA), naphthaline sulphonic acid (NSA), hydrochloric acid (HCl), and m-cresol. Thin films of these doped PANI samples were deposited on glass substrates using solution casting method with m-cresol as solvent. A level surface was employed to get homogeneous thin films of uniform thickness. Detailed X-ray diffraction studies have shown that the films are exceptionally crystalline. The crystalline peaks observed in the XRD spectra can be indexed to simple monoclinic structure. FTIR and Raman spectroscopy studies provide convincing explanation for the exceptional crystallinity observed in these polymer films. FESEM and AFM images give better details of surface morphology of doped PANI films. The DC electrical conductivity of the samples was measured using four point probe technique. It is seen that the samples also exhibit quite high DC electrical conductivity, about 287 S/cm for CSA doped PANI, 67 S/cm for NSA doped PANI 65 S/cm for HCl doped PANI, and just below 1 S/cm for m-cresol doped PANI. Effect of using the level surface for solution casting is studied and correlated with the observed crystallinity.

Arsenic Removal from Water by Adsorption on Iron-Contaminated Cryptocrystalline Graphite

Science.gov (United States)

Yang, Qiang; Yang, Lang; Song, Shaoxian; Xia, Ling

This work aimed to study the feasibility of using iron-contaminated graphite as an adsorbent for As(V) removal from water. The adsorbent was prepared by grinding graphite concentrate with steel ball. The study was performed through the measurements of adsorption capacity, BET surface area and XPS analysis. The experimental results showed that the iron-contaminated graphite exhibited significantly high adsorption capacity of As(V). The higher the iron contaminated on the graphite surface, the higher the adsorption capacity of As(V) on the material obtained. It was suggested that the ion-contaminated graphite was a good adsorbent for As(V) removal.

Graphite

Science.gov (United States)

Robinson, Gilpin R.; Hammarstrom, Jane M.; Olson, Donald W.; Schulz, Klaus J.; DeYoung,, John H.; Seal, Robert R.; Bradley, Dwight C.

2017-12-19

Graphite is a form of pure carbon that normally occurs as black crystal flakes and masses. It has important properties, such as chemical inertness, thermal stability, high electrical conductivity, and lubricity (slipperiness) that make it suitable for many industrial applications, including electronics, lubricants, metallurgy, and steelmaking. For some of these uses, no suitable substitutes are available. Steelmaking and refractory applications in metallurgy use the largest amount of produced graphite; however, emerging technology uses in large-scale fuel cell, battery, and lightweight high-strength composite applications could substantially increase world demand for graphite.Graphite ores are classified as “amorphous” (microcrystalline), and “crystalline” (“flake” or “lump or chip”) based on the ore’s crystallinity, grain-size, and morphology. All graphite deposits mined today formed from metamorphism of carbonaceous sedimentary rocks, and the ore type is determined by the geologic setting. Thermally metamorphosed coal is the usual source of amorphous graphite. Disseminated crystalline flake graphite is mined from carbonaceous metamorphic rocks, and lump or chip graphite is mined from veins in high-grade metamorphic regions. Because graphite is chemically inert and nontoxic, the main environmental concerns associated with graphite mining are inhalation of fine-grained dusts, including silicate and sulfide mineral particles, and hydrocarbon vapors produced during the mining and processing of ore. Synthetic graphite is manufactured from hydrocarbon sources using high-temperature heat treatment, and it is more expensive to produce than natural graphite.Production of natural graphite is dominated by China, India, and Brazil, which export graphite worldwide. China provides approximately 67 percent of worldwide output of natural graphite, and, as the dominant exporter, has the ability to set world prices. China has significant graphite reserves, and

Preparation of iron-deposited graphite surface for application as cathode material during electrochemical vat-dyeing process

International Nuclear Information System (INIS)

Anbu Kulandainathan, M.; Kiruthika, K.; Christopher, G.; Babu, K. Firoz; Muthukumaran, A.; Noel, M.

2008-01-01

Iron-deposited graphite surfaces were prepared, characterized and employed as cathode materials for electrochemical vat-dyeing process containing very low concentration of sodium dithionite. The electrodeposition, in presence of ammonium thiocyanate and gelatin or animal glue as binding additives, were found to give finer iron deposits for improved electrochemical dyeing application. The electrodeposits were characterized using scanning electron microscopy, electron-dispersive X-ray spectroscopy and X-ray diffraction methods, before and after electrochemical dyeing process. The electrochemical activity of the iron-deposited graphite electrodes always stored in water seems to depend on the surface-bound Fe 3+ /Fe 2+ redox species. Vat dyes like C.I. Vat Violet 1, C.I. Vat Green 1 and C.I. Vat Blue 4 could be efficiently dyed employing these above electrode materials. The colour intensity and washing fastness of the dyed fabrics were found to be equal with conventionally dyed fabrics. The electrodes could also be reused for the dyeing process

Direct conversion of graphite into diamond through electronic excited states

CERN Document Server

Nakayama, H

2003-01-01

An ab initio total energy calculation has been performed for electronic excited states in diamond and rhombohedral graphite by the full-potential linearized augmented plane wave method within the framework of the local density approximation (LDA). First, calculations for the core-excited state in diamond have been performed to show that the ab initio calculations based on the LDA describe the wavefunctions in the electronic excited states as well as in the ground state quite well. Fairly good coincidence with both experimental data and theoretical prediction has been obtained for the lattice relaxation of the core exciton state. The results of the core exciton state are compared with nitrogen-doped diamond. Next, the structural stability of rhombohedral graphite has been investigated to examine the possibility of the transition into the diamond structure through electronic excited states. While maintaining the rhombohedral symmetry, rhombohedral graphite can be spontaneously transformed to cubic diamond. Tota...

Towards graphite-free hot zone for directional solidification of silicon

Science.gov (United States)

Dropka, Natasha; Buchovska, Iryna; Herrmann-Geppert, Iris; Klimm, Detlef; Kiessling, Frank M.; Degenhardt, Ulrich

2018-06-01

The reduction of SiC, Si3N4 and transition metals impurities in directionally solidified Si ingots poses one of the crucial challenges in the solar cells production. Particularly strong contamination comes from the graphite parts in the hot zone. Therefore, we selected three massive ceramic materials to replace graphite, developed the novel design of the crucible support and cover and compared the crystals grown in them with ingots from the standard graphite design. The experiments were performed for phosphorus n-doped silicon of G0 size. The ingots were compared with respect to O- and C-content, metal impurities, resistivity and lifetime. The superior performance of TiC relative to other ceramics was observed, particularly due to the lower concentration of substitutional carbon in Si ingot (up to 2.6 times) and the higher minority carrier lifetime of (up to 4.4 times) with narrow red zones.

Stability of boron-doped graphene/copper interface: DFT, XPS and OSEE studies

Science.gov (United States)

Boukhvalov, D. W.; Zhidkov, I. S.; Kukharenko, A. I.; Slesarev, A. I.; Zatsepin, A. F.; Cholakh, S. O.; Kurmaev, E. Z.

2018-05-01

Two different types of boron-doped graphene/copper interfaces synthesized using two different flow rates of Ar through the bubbler containing the boron source were studied. X-ray photoelectron spectra (XPS) and optically stimulated electron emission (OSEE) measurements have demonstrated that boron-doped graphene coating provides a high corrosion resistivity of Cu-substrate with the light traces of the oxidation of carbon cover. The density functional theory calculations suggest that for the case of substitutional (graphitic) boron-defect only the oxidation near boron impurity is energetically favorable and creation of the vacancies that can induce the oxidation of copper substrate is energetically unfavorable. In the case of non-graphitic boron defects oxidation of the area, a nearby impurity is metastable that not only prevent oxidation but makes boron-doped graphene. Modeling of oxygen reduction reaction demonstrates high catalytic performance of these materials.

Tire containing thermally exfoliated graphite oxide

Science.gov (United States)

Prud'homme, Robert K. (Inventor); Aksay, Ilhan A. (Inventor)

2011-01-01

A tire, tire lining or inner tube, containing a polymer composite, made of at least one rubber and/or at least one elastomer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 sq m/g to 2600 sq m/g.

Thermal shock test of TiC and graphite

International Nuclear Information System (INIS)

Shirakawa, H.; Okamura, J.; Son, P.; Miyake, M.

1989-01-01

Thermal shock tests were performed by pulse electron beam heating on chemically vapor deposited coatings of TiC on Poco graphite, bulk TiC, and several kinds of isotropic graphite. The specimens were heated at various power densities (10-45 MW/m 2 ) for various pulse durations (1-2 s) to examine the dependence of thermal failures on heating conditions. The TiC coating on graphite suffered cracking, surface melting and evaporation by the thermal pulse. The surface melting limit, defined as F τ 1/2 , where F is the minimum power density that causes surface melting for a specified pulse duration τ, was approximately 48 MWs 1/2 /m 2 for the TiC coating. The combined-Carbon/Titanium ratio of the coating after electron beam heating decreased with increasing power density and pulse duration. The bulk TiC specimens were so brittle that they fractured at heat load conditions where the coating showed no damage. The graphite specimens showed sublimation as a principal damage mechanism by the thermal pulse, and the sublimation weight loss decreased with increasing the thermal conductivity of the specimen. It was confirmed that the TiC coating on graphite had favorable resistance to thermal shock as compared to the bulk TiC and that graphite with high thermal conductivity is promising material as a high heat flux component. (orig.)

Scaling Relations for Adsorption Energies on Doped Molybdenum Phosphide Surfaces

International Nuclear Information System (INIS)

Fields, Meredith; Tsai, Charlie; Chen, Leanne D.; Abild-Pedersen, Frank; Nørskov, Jens K.; Chan, Karen

2017-01-01

Molybdenum phosphide (MoP), a well-documented catalyst for applications ranging from hydrotreating reactions to electrochemical hydrogen evolution, has yet to be mapped from a more fundamental perspective, particularly in the context of transition-metal scaling relations. In this work, we use periodic density functional theory to extend linear scaling arguments to doped MoP surfaces and understand the behavior of the phosphorus active site. The derived linear relationships for hydrogenated C, N, and O species on a variety of doped surfaces suggest that phosphorus experiences a shift in preferred bond order depending on the degree of hydrogen substitution on the adsorbate molecule. This shift in phosphorus hybridization, dependent on the bond order of the adsorbate to the surface, can result in selective bond weakening or strengthening of chemically similar species. As a result, we discuss how this behavior deviates from transition-metal, sulfide, carbide, and nitride scaling relations, and we discuss potential applications in the context of electrochemical reduction reactions.

Quenching of surface traps in Mn doped ZnO thin films for enhanced optical transparency

International Nuclear Information System (INIS)

Ilyas, Usman; Rawat, R.S.; Roshan, G.; Tan, T.L.; Lee, P.; Springham, S.V.; Zhang, Sam; Fengji Li; Chen, R.; Sun, H.D.

2011-01-01

The structural and photoluminescence analyses were performed on un-doped and Mn doped ZnO thin films grown on Si (1 0 0) substrate by pulsed laser deposition (PLD) and annealed at different post-deposition temperatures (500-800 deg. C). X-ray diffraction (XRD), employed to study the structural properties, showed an improved crystallinity at elevated temperatures with a consistent decrease in the lattice parameter 'c'. The peak broadening in XRD spectra and the presence of Mn 2p3/2 peak at ∼640 eV in X-ray Photoelectron Spectroscopic (XPS) spectra of the doped thin films confirmed the successful incorporation of Mn in ZnO host matrix. Extended near band edge emission (NBE) spectra indicated the reduction in the concentration of the intrinsic surface traps in comparison to the doped ones resulting in improved optical transparency. Reduced deep level emission (DLE) spectra in doped thin films with declined PL ratio validated the quenching of the intrinsic surface traps thereby improving the optical transparency and the band gap, essential for optoelectronic and spintronic applications. Furthermore, the formation and uniform distribution of nano-sized grains with improved surface features of Mn-doped ZnO thin films were observed in Field Emission Scanning Electron Microscopy (FESEM) images.

Preparation, quantitative surface analysis, intercalation characteristics and industrial implications of low temperature expandable graphite

Science.gov (United States)

Peng, Tiefeng; Liu, Bin; Gao, Xuechao; Luo, Liqun; Sun, Hongjuan

2018-06-01

Expandable graphite is widely used as a new functional carbon material, especially as fire-retardant; however, its practical application is limited due to the high expansion temperature. In this work, preparation process of low temperature and highly expandable graphite was studied, using natural flake graphite as raw material and KMnO4/HClO4/NH4NO3 as oxidative intercalations. The structure, morphology, functional groups and thermal properties were characterized during expanding process by Fourier transform infrared spectroscopy (FTIR), Raman spectra, thermo-gravimetry differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscope (SEM). The analysis showed that by oxidation intercalation, some oxygen-containing groups were grafted on the edge and within the graphite layer. The intercalation reagent entered the graphite layer to increase the interlayer spacing. After expansion, the original flaky expandable graphite was completely transformed into worm-like expanded graphite. The order of graphite intercalation compounds (GICs) was proposed and determined to be 3 for the prepared expandable graphite, based on quantitative XRD peak analysis. Meanwhile, the detailed intercalation mechanisms were also proposed. The comprehensive investigation paved a benchmark for the industrial application of such sulfur-free expanded graphite.

Graphene nanoribbons exfoliated from graphite surface dislocation bands by electrostatic force

International Nuclear Information System (INIS)

Sidorov, Anton N; Ouseph, P J; Sumanasekera, Gamini; Bansal, Tanesh

2010-01-01

We have developed a novel technique to produce long and narrow graphene ribbons with smooth edges. This technique is free of any chemical treatments and involves a combination of two steps: (i) creation of surface dislocation ribbons by high velocity clusters impacting the graphite surface and (ii) electrostatic transferring of the dislocation ribbons to a desired substrate. The width of the ribbons can be controlled by varying the impact velocity of a cluster jet stream from a gas jet impactor. The electrical transport properties were investigated on the ribbons in field effect transistor (FET) configuration. The p-type behavior observed under ambient conditions was found to be reversed upon annealing at 180 deg. C in a vacuum of 10 -7 Torr. Charge transfer effects were observed when the degassed graphene was exposed to N 2 O and NH 3 .

High thermoelectric performance of graphite nanofibers.

Science.gov (United States)

Tran, Van-Truong; Saint-Martin, Jérôme; Dollfus, Philippe; Volz, Sebastian

2018-02-22

Graphite nanofibers (GNFs) have been demonstrated to be a promising material for hydrogen storage and heat management in electronic devices. Here, by means of first-principles and transport simulations, we show that GNFs can also be an excellent material for thermoelectric applications thanks to the interlayer weak van der Waals interaction that induces low thermal conductance and a step-like shape in the electronic transmission with mini-gaps, which are necessary ingredients to achieve high thermoelectric performance. This study unveils that the platelet form of GNFs in which graphite layers are perpendicular to the fiber axis can exhibit outstanding thermoelectric properties with a figure of merit ZT reaching 3.55 in a 0.5 nm diameter fiber and 1.1 in a 1.1 nm diameter one. Interestingly, by introducing 14 C isotope doping, ZT can even be enhanced up to more than 5, and more than 8 if we include the effect of finite phonon mean free path, which demonstrates the amazing thermoelectric potential of GNFs.

Density functional theory prediction for diffusion of lithium on boron-doped graphene surface

International Nuclear Information System (INIS)

Gao Shuanghong; Ren Zhaoyu; Wan Lijuan; Zheng Jiming; Guo Ping; Zhou Yixuan

2011-01-01

The density functional theory (DFT) investigation shows that graphene has changed from semimetal to semiconductor with the increasing number of doped boron atoms. Lithium and boron atoms acted as charge contributors and recipients, which attracted to each other. Further investigations show that, the potential barrier for lithium diffusion on boron-doped graphene is higher than that of intrinsic graphene. The potential barrier is up to 0.22 eV when six boron atoms doped (B 6 C 26 ), which is the lowest potential barrier in all the doped graphene. The potential barrier is dramatically affected by the surface structure of graphene.

Deuterium pumping and erosion behavior of selected graphite materials under high flux plasma bombardment in PISCES

International Nuclear Information System (INIS)

Hirooka, Y.; Conn, R.W.; Goebel, D.M.; LaBombard, B.; Lehmer, R.; Leung, W.K.; Nygren, R.E.; Ra, Y.

1988-06-01

Deuterium plasma recycling and chemical erosion behavior of selected graphite materials have been investigated using the PISCES-A facility. These materials include: Pyro-graphite; 2D-graphite weave; 4D-graphite weave; and POCO-graphite. Deuterium plasma bombardment conditions are: fluxes around 7 /times/ 10 17 ions s/sup /minus/1/cm/sup /minus/2/; exposure time in the range from 10 to 100 s; bombarding energy of 300 eV; and graphite temperatures between 20 and 120/degree/C. To reduce deuterium plasma recycling, several approaches have been investigated. Erosion due to high-fluence helium plasma conditioning significantly increases the surface porosity of POCO-graphite and 4D-graphite weave whereas little change for 2D-graphite weave and Pyro-graphite. The increased pore openings and refreshed in-pore surface sites are found to reduce the deuterium plasma recycling and chemical erosion rates at transient stages. The steady state recycling rates for these graphite materials can be also correlated to the surface porosity. Surface topographical modification by machined-grooves noticeably reduces the steady state deuterium recycling rate and the impurity emission from the surface. These surface topography effects are attributed to co-deposition of remitted deuterium, chemically sputtered hydrocarbon and physically sputtered carbon under deuterium plasma bombardment. The co-deposited film is found to have a characteristic surface morphology with dendritic microstructures. 18 ref., 4 figs., 1 tab

A synthesis method for cobalt doped carbon aerogels with high surface area and their hydrogen storage properties

Energy Technology Data Exchange (ETDEWEB)

Tian, H.Y.; Buckley, C.E. [Department of Imaging and Applied Physics, Curtin University of Technology, GPO Box U 1987, Perth 6845, WA (Australia); CSIRO National Hydrogen Materials Alliance, CSIRO Energy Centre, 10 Murray Dwyer Circuit, Steel River Estate, Mayfield West, NSW 2304 (Australia); Sheppard, D.A.; Paskevicius, M. [Department of Imaging and Applied Physics, Curtin University of Technology, GPO Box U 1987, Perth 6845, WA (Australia); Hanna, N. [CSIRO Process Science and Engineering, Waterford, WA (Australia)

2010-12-15

Carbon aerogels doped with nanoscaled Co particles were prepared by first coating activated carbon aerogels using a wet-thin layer coating process. The resulting metal-doped carbon aerogels had a higher surface area ({proportional_to}1667 m{sup 2} g{sup -1}) and larger micropore volume ({proportional_to}0.6 cm{sup 3} g{sup -1}) than metal-doped carbon aerogels synthesised using other methods suggesting their usefulness in catalytic applications. The hydrogen adsorption behaviour of cobalt doped carbon aerogel was evaluated, displaying a high {proportional_to}4.38 wt.% H{sub 2} uptake under 4.6 MPa at -196 C. The hydrogen uptake capacity with respect to unit surface area was greater than for pure carbon aerogel and resulted in {proportional_to}1.3 H{sub 2} (wt. %) per 500 m{sup 2} g{sup -1}. However, the total hydrogen uptake was slightly reduced as compared to pure carbon aerogel due to a small reduction in surface area associated with cobalt doping. The improved adsorption per unit surface area suggests that there is a stronger interaction between the hydrogen molecules and the cobalt doped carbon aerogel than for pure carbon aerogel. (author)

London forces in highly oriented pyrolytic graphite

Directory of Open Access Journals (Sweden)

L.V. Poperenko

2017-07-01

Full Text Available Surface of highly oriented pyrolytic graphite with terrace steps was studied using scanning tunneling microscopy with high spatial resolution. Spots with positive and negative charges were found in the vicinity of the steps. Values of the charges depended both on the microscope needle scan velocity and on its motion direction. The observed effect was theoretically explained with account of London forces that arise between the needle tip and the graphite surface. In this scheme, a terrace step works as a nanoscale diode for surface electric currents.

The effects of antimony doping on the surface structure of rutile TiO2(110)

International Nuclear Information System (INIS)

Bechstein, Ralf; Schuette, Jens; Kuehnle, Angelika; Kitta, Mitsunori; Onishi, Hiroshi

2009-01-01

Titanium dioxide represents a very important wide bandgap photocatalyst that is known to be sensitized to visible light by transition metal doping. Antimony doping has been demonstrated to provide photocatalytic activity when codoped with chromium at an optimum dopant ratio [Sb]/[Cr] of about 1.5. Here, the role of antimony doping on the surface structure of rutile TiO 2 (110) is studied using non-contact atomic force microscopy (NC-AFM) under ultra-high vacuum conditions. At first glance, the surface structure of antimony-doped TiO 2 (110) resembles the structure of pristine TiO 2 (110). However, in contrast to what is found in pristine TiO 2 (110), a dense layer of protruding features is observed upon antimony doping, which is tentatively ascribed to antimony-rich clusters. Moreover, homogeneously distributed holes are found on the surface, which differ in depth and shape depending on the preparation conditions. Holes with depths ranging from a few up to more than a hundred monatomic steps are observed. These holes are explained by surface segregation of antimony during annealing, as the ionic radius of Sb 3+ is considerably larger than the ionic radius of Ti 4+ . Our finding provides an indication of why an antimony concentration larger than the optimum ratio results in decreased photocatalytic activity. Moreover, controlling annealing temperature seems to constitute a promising strategy for creating nanosized holes on TiO 2 surfaces.

Toward tunable doping in graphene FETs by molecular self-assembled monolayers

Science.gov (United States)

Li, Bing; Klekachev, Alexander V.; Cantoro, Mirco; Huyghebaert, Cedric; Stesmans, André; Asselberghs, Inge; de Gendt, Stefan; de Feyter, Steven

2013-09-01

In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic dopant.In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic

Synergetic action of doping and coating on electrochemical ...

Indian Academy of Sciences (India)

was equipped with a diffracted beam graphite monochroma- tor. The diffraction data were ... (Diamond) high temperature thermal analyzer with 5–20 mg samples and a .... means that Cr, Co, Fe and Ni multi-doping did not change the intrinsic ...

Nitrogen–doped graphitized carbon shell encapsulated NiFe nanoparticles: A highly durable oxygen evolution catalyst

Energy Technology Data Exchange (ETDEWEB)

Du, Lei; Luo, Langli; Feng, Zhenxing; Engelhard, Mark; Xie, Xiaohong; Han, Binghong; Sun, Junming; Zhang, Jianghao; Yin, Geping; Wang, Chongmin; Wang, Yong; Shao, Yuyan

2017-09-01

Oxygen evolution reaction (OER) plays a crucial role in various energy conversion devices such as water electrolyzers and metal–air batteries. Precious metal catalysts such as Ir, Ru and their oxides are usually used for enhanced reaction kinetics but are limited by their scarce resource. The challenges associated with alternative non–precious metal catalysts such as transition metal oxides and (oxy)hydroxides etc. are their low electronic conductivity and poor durability. Here, we report OER catalysts of NiFe nanoparticles encapsulated by nitrogen–doped graphitized carbon shells derived from bimetallic metal–organic frameworks (MOFs) precursors. The optimal OER catalyst shows excellent activity (360 mV overpotential at 10 mA cm–2GEO) and durability (no obvious degradation after 20 000 cycles). The electron-donation from Fe and tuned electronic structure of metal cores by Ni are revealed to be primary contributors to the enhanced OER activity. We further demonstrated that the structure and morphology of encapsulating carbon shells, which are the key factors influencing the durability, are facilely controlled by chemical state of precursors. Severe metal particle growth probably caused by oxidation of carbon shells and encapsulated nanoparticles is believed to the main mechanism for activity degradation in these catalysts.

Thermogravimetric and Differential Scanning Calorimetric Behavior of Ball-Milled Nuclear Graphite

Energy Technology Data Exchange (ETDEWEB)

Kim, Eung Seon; Kim, Min Hwan; Kim, Yong Wan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Park, Yi Hyun; Cho, Seung Yon [National Fusion Research Institute, Daejeon (Korea, Republic of)

2013-10-15

An examination was made to characterize the oxidation behavior of ball-milled nuclear graphite powder through a TG-DSC analysis. With the ball milling time, the BET surface area increased with the reduction of particle size, but decreased with the chemisorptions of O{sub 2} on the activated surface. The enhancement of the oxidation after the ball milling is attributed to both increases in the specific surface area and atomic scale defects in the graphite structure. In a high temperature gas-cooled reactor, nuclear graphite has been widely used as fuel elements, moderator or reflector blocks, and core support structures owing to its excellent moderating power, mechanical properties and machinability. For the same reason, it will be used in a helium cooled ceramic reflector test blanket module for the ITER. Each submodule has a seven-layer breeding zone, including three neutron multiplier layers packed with beryllium pebbles, three lithium ceramic pebbles packed tritium breeder layers, and a reflector layer packed with 1 mm diameter graphite pebbles to reduce the volume of beryllium. The abrasion of graphite structures owing to relative motion or thermal cycle during operation may produce graphite dust. It is expected that graphite dust will be more oxidative than bulk graphite, and thus the oxidation behavior of graphite dust must be examined to analyze the safety of the reactors during an air ingress accident. In this study, the thermal stability of ball-milled graphite powder was investigated using a simultaneous thermogravimeter-differential scanning calorimeter.

Self-energy behavior away from the Fermi surface in doped Mott insulators.

Science.gov (United States)

Merino, J; Gunnarsson, O; Kotliar, G

2016-02-03

We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.

Surface study of gallium- and aluminum- doped graphenes upon adsorption of cytosine: DFT calculations

International Nuclear Information System (INIS)

Shokuhi Rad, Ali; Zareyee, Daryoush; Peyravi, Majid; Jahanshahi, Mohsen

2016-01-01

Highlights: • P1 and P4 are the most stable adsorption configurations for cytosine. • NBO analysis show n-type semiconductor property for both Al- and Ga-doped graphenes. • Important changes in the HOMO and LUMO of doped graphene upon adsorption of cytosine. • Increase in the conductivity of system when cytosine is adsorbed on doped graphenes. - Abstract: The adsorption of cytosine molecule on Al- and Ga- doped graphenes is studied using first-principles density functional theory (DFT) calculations. The energetically most stable geometries of cytosine on both Al- and Ga- doped graphenes are determined and the adsorption energies are calculated. The net charge of transfer as well as local charge of doped atoms upon adsorption of cytosine are studied by natural bond orbitals (NBO) analysis. Orbital hybridizing of complexes was searched by frontier molecular orbital theory (FMO), and density of states (DOS). Depending on the side of cytosine, there are four possible sites for its adsorption on doped graphene; denoted as P1, P2, P3, and P4, respectively. The order of binding energy in the case of Al-doped graphene is found as P1 > P4 > P3 > P2. Interestingly, the order in the case of Ga-doped graphene changes to: P4 ∼ P1 > P3 > P2. Both surfaces show superior adsorbent property, resulting chemisorption of cytosine, especially at P1 and P4 position configurations. The NBO charge analysis reveals that the charge transfers from Al- and Ga- doped graphene sheets to cytosine. The electronic properties of both surfaces undertake important changes after cytosine adsorption, which indicates notable change in its electrical conductivity.

Surface study of gallium- and aluminum- doped graphenes upon adsorption of cytosine: DFT calculations

Energy Technology Data Exchange (ETDEWEB)

Shokuhi Rad, Ali, E-mail: a.shokuhi@gmail.com [Department of Chemical Engineering, Qaemshahr Branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Zareyee, Daryoush [Department of Chemistry, Qaemshahr Branch, Islamic Azad University, Qaemshahr (Iran, Islamic Republic of); Peyravi, Majid; Jahanshahi, Mohsen [Faculty of Chemical Engineering, Babol University of Technology, Babol (Iran, Islamic Republic of)

2016-12-30

Highlights: • P1 and P4 are the most stable adsorption configurations for cytosine. • NBO analysis show n-type semiconductor property for both Al- and Ga-doped graphenes. • Important changes in the HOMO and LUMO of doped graphene upon adsorption of cytosine. • Increase in the conductivity of system when cytosine is adsorbed on doped graphenes. - Abstract: The adsorption of cytosine molecule on Al- and Ga- doped graphenes is studied using first-principles density functional theory (DFT) calculations. The energetically most stable geometries of cytosine on both Al- and Ga- doped graphenes are determined and the adsorption energies are calculated. The net charge of transfer as well as local charge of doped atoms upon adsorption of cytosine are studied by natural bond orbitals (NBO) analysis. Orbital hybridizing of complexes was searched by frontier molecular orbital theory (FMO), and density of states (DOS). Depending on the side of cytosine, there are four possible sites for its adsorption on doped graphene; denoted as P1, P2, P3, and P4, respectively. The order of binding energy in the case of Al-doped graphene is found as P1 > P4 > P3 > P2. Interestingly, the order in the case of Ga-doped graphene changes to: P4 ∼ P1 > P3 > P2. Both surfaces show superior adsorbent property, resulting chemisorption of cytosine, especially at P1 and P4 position configurations. The NBO charge analysis reveals that the charge transfers from Al- and Ga- doped graphene sheets to cytosine. The electronic properties of both surfaces undertake important changes after cytosine adsorption, which indicates notable change in its electrical conductivity.

Fundamental studies of graphene/graphite and graphene-based Schottky photovoltaic devices

Science.gov (United States)

Miao, Xiaochang

In the carbon allotropes family, graphene is one of the most versatile members and has been extensively studied since 2004. The goal of this dissertation is not only to investigate the novel fundamental science of graphene and its three-dimensional sibling, graphite, but also to explore graphene's promising potential in modern electronic and optoelectronic devices. The first two chapters provide a concise introduction to the fundamental solid state physics of graphene (as well as graphite) and the physics at the metal/semiconductor interfaces. In the third chapter, we demonstrate the formation of Schottky junctions at the interfaces of graphene (semimetal) and various inorganic semiconductors that play dominating roles in today's semiconductor technology, such as Si, SiC, GaAs and GaN. As shown from their current-voltage (I -V) and capacitance-voltage (C-V) characteristics, the interface physics can be well described within the framework of the Schottky-Mott model. The results are also well consist with that from our previous studies on graphite based Schottky diodes. In the fourth chapter, as an extension of graphene based Schottky work, we investigate the photovoltaic (PV) effect of graphene/Si junctions after chemically doped with an organic polymer (TFSA). The power conversion efficiency of the solar cell improves from 1.9% to 8.6% after TFSA doping, which is the record in all graphene based PVs. The I -V, C-V and external quantum efficiency measurements suggest 12 that such a significant enhancement in the device performance can be attributed to a doping-induced decrease in the series resistance and a simultaneous increase in the built-in potential. In the fifth chapter, we investigate for the first time the effect of uniaxial strains on magneto-transport properties of graphene. We find that low-temperature weak localization effect in monolayer graphene is gradually suppressed under increasing strains, which is due to a strain-induced decreased intervalley

Adsorption of sugars on Al- and Ga-doped boron nitride surfaces: A computational study

Energy Technology Data Exchange (ETDEWEB)

Darwish, Ahmed A. [Center for Nanotechnology, Zewail City of Science and Technology, Giza 12588 (Egypt); Department of Nuclear and Radiation Engineering, Faculty of Engineering, Alexandria University, Alexandria (Egypt); Fadlallah, Mohamed M. [Center for Fundamental Physics, Zewail City of Science and Technology, Giza 12588 (Egypt); Department of Physics, Faculty of Science, Benha University, Benha (Egypt); Badawi, Ashraf [Center for Nanotechnology, Zewail City of Science and Technology, Giza 12588 (Egypt); Maarouf, Ahmed A., E-mail: ahmed.maarouf@egnc.gov.eg [Center for Fundamental Physics, Zewail City of Science and Technology, Giza 12588 (Egypt); Egypt Nanotechnology Center & Department of Physics, Faculty of Science, Cairo University, Giza 12613 (Egypt)

2016-07-30

Highlights: • Doping boron nitride sheets with aluminum or gallium atoms significantly enhances their molecular adsorption properties. • Adsorption of glucose or glucosamine on Al- and Ga-doped boron nitride sheets changes the band gap. • Doping concentration changes the bad gap, but has a minor effect on the adsorption energy. - Abstract: Molecular adsorption on surfaces is a key element for many applications, including sensing and catalysis. Non-invasive sugar sensing has been an active area of research due to its importance to diabetes care. The adsorption of sugars on a template surface study is at the heart of matter. Here, we study doped hexagonal boron nitride sheets (h-BNNs) as adsorbing and sensing template for glucose and glucosamine. Using first principles calculations, we find that the adsorption of glucose and glucosamine on h-BNNs is significantly enhanced by the substitutional doping of the sheet with Al and Ga. Including long range van der Waals corrections gives adsorption energies of about 2 eV. In addition to the charge transfer occurring between glucose and the Al/Ga-doped BN sheets, the adsorption alters the size of the band gap, allowing for optical detection of adsorption. We also find that Al-doped boron nitride sheet is better than Ga-doped boron nitride sheet to enhance the adsorption energy of glucose and glucosamine. The results of our work can be potentially utilized when designing support templates for glucose and glucosamine.

Non-covalent doping of graphitic carbon nitride with ultrathin graphene oxide and molybdenum disulfide nanosheets: an effective binary heterojunction photocatalyst under visible light irradiation.

Science.gov (United States)

Hu, S W; Yang, L W; Tian, Y; Wei, X L; Ding, J W; Zhong, J X; Chu, Paul K

2014-10-01

A proof of concept integrating binary p-n heterojunctions into a semiconductor hybrid photocatalyst is demonstrated by non-covalent doping of graphite-like carbon nitride (g-C3N4) with ultrathin GO and MoS2 nanosheets using a facile sonochemical method. In this unique ternary hybrid, the layered MoS2 and GO nanosheets with a large surface area enhance light absorption to generate more photoelectrons. On account of the coupling between MoS2 and GO with g-C3N4, the ternary hybrid possesses binary p-n heterojunctions at the g-C3N4/MoS2 and g-C3N4/GO interfaces. The space charge layers created by the p-n heterojunctions not only enhance photogeneration, but also promote charge separation and transfer of electron-hole pairs. In addition, the ultrathin MoS2 and GO with high mobility act as electron mediators to facilitate separation of photogenerated electron-hole pairs at each p-n heterojunction. As a result, the ternary hybrid photocatalyst exhibits improved photoelectrochemical and photocatalytic activity under visible light irradiation compared to other reference materials. The results provide new insights into the large-scale production of semiconductor photocatalysts. Copyright © 2014 Elsevier Inc. All rights reserved.

Strong compensation hinders the p-type doping of ZnO: a glance over surface defect levels

Science.gov (United States)

Huang, B.

2016-07-01

We propose a surface doping model of ZnO to elucidate the p-type doping and compensations in ZnO nanomaterials. With an N-dopant, the effects of N on the ZnO surface demonstrate a relatively shallow acceptor level in the band gap. As the dimension of the ZnO materials decreases, the quantum confinement effects will increase and render the charge transfer on surface to influence the shifting of Fermi level, by evidence of transition level changes of the N-dopant. We report that this can overwhelm the intrinsic p-type conductivity and transport of the ZnO bulk system. This may provide a possible route of using surface doping to modify the electronic transport and conductivity of ZnO nanomaterials.

Graphite surface topography induced by Ta cluster impact and oxidative etching

International Nuclear Information System (INIS)

Reimann, C.T.; Olsson, L.; Erlandsson, R.; Henkel, M.; Urbassek, H.M.

1998-01-01

Freshly cleaved highly oriented pyrolytic graphite (HOPG), when baked in air at ∝630 C, forms one-monolayer(ML)-deep circular pits due to oxidation initiated at surface defect sites. We found that the areal density and depths of these pits could be modulated by deliberately introducing surface and sub-surface defects by energetic ion bombardment prior to baking. Bombardment by 555-eV/atom Ta 1 + , Ta 2 + , Ta 4 + , or Ta 9 + , always enhanced the areal density of etch pits, but only bombardment by Ta 4 + , or Ta 9 + significantly enhanced the depths of the pits. We performed molecular dynamics simulations of Ta n cluster bombardment of HOPG (n = 1, 2, 4, and 9) with the aim of characterizing the damage structures induced by the bombardment and correlating them with the experimental data. For Ta 9 + , the simulations showed a high level of damage extending from the surface down to nine MLs, in agreement with the most probable etch pit depth observed. For other cluster species, predicted etch pit depths were deeper than the observed ones. Annealing or steric requirements for initiating oxidation may account for some of the differences between simulations and experimental results. (orig.)

Sulfur impregnated in tunable porous N-doped carbon as sulfur cathode: effect of pore size distribution

International Nuclear Information System (INIS)

Wang, Sha; Zhao, Zhenxia; Xu, Hui; Deng, Yuanfu; Li, Zhong; Chen, Guohua

2015-01-01

Highlights: •Effects of pore size were investigated on electrochemistry for S cathode. •Activation energy of sulfur desorption from the PDA-C was estimated. •Strong interaction was formed between sulfur and porous N-doped carbon. •PDA-C@S showed good cycling performance of 608 mA h g −1 at 2 C over 300 cycles. •PDA-C@S showed good rate stability and high rate capacity. -- Abstract: A novel porous N-doped carbon microsphere (polymer-dopamine derived carbon, PDA-C) with high specific surface area was synthesized as sulfur host for high performance of lithium-sulfur batteries. We used KOH to adjust the pore size and surface area of the PDA-C materials, and then impregnated sulfur into the PDA-C samples by vapor-melting diffusion method. Effects of pore size of the PDA-C samples on the electrochemical performance of the PDA-C@sulfur cathodes were systematically investigated. Raman spectra indicated an enhanced trend of the degree of graphitization of the PDA-C samples with increasing calcination temperature. The surface area of the PDA-C samples increases with amount of the KOH in the pore-creating process. The graphitized porous N-doped carbon provides the high electronic conductive network. Meanwhile, the PDA-C with high surface area and uniform micropores ensures a high interaction toward sulfur as well as the high dispersion of nanoscale sulfur layer on it. The microporous PDA-C@S cathode material exhibits the excellent high rate discharge capability (636 mA h g −1 at 2.0 C) and good low/high-rate cycling stability (893 mA h g −1 (0.5 C) and 608 mA h g −1 (2.0 C) over 100 and 300 cycles). Cyclic voltammogram curves and electrochemical impedance plots show that both the impedance and polarization of the cells increase with decreasing pore size

Zinc (hydr)oxide/graphite oxide/AuNPs composites: role of surface features in H₂S reactive adsorption.

Science.gov (United States)

Giannakoudakis, Dimitrios A; Bandosz, Teresa J

2014-12-15

Zinc hydroxide/graphite oxide/AuNPs composites with various levels of complexity were synthesized using an in situ precipitation method. Then they were used as H2S adsorbents in visible light. The materials' surfaces were characterized before and after H2S adsorption by various physical and chemical methods (XRD, FTIR, thermal analysis, potentiometric titration, adsorption of nitrogen and SEM/EDX). Significant differences in surface features and synergistic effects were found depending on the materials' composition. Addition of graphite oxide and the deposition of gold nanoparticles resulted in a marked increase in the adsorption capacity in comparison with that on the zinc hydroxide and zinc hydroxide/AuNP. Addition of AuNPs to zinc hydroxide led to a crystalline ZnO/AuNP composite while the zinc hydroxide/graphite oxide/AuNP composite was amorphous. The ZnOH/GO/AuNPs composite exhibited the greatest H2S adsorption capacity due to the increased number of OH terminal groups and the conductive properties of GO that facilitated the electron transfer and consequently the formation of superoxide ions promoting oxidation of hydrogen sulfide. AuNPs present in the composite increased the conductivity, helped with electron transfer to oxygen, and prevented the fast recombination of the electrons and holes. Copyright © 2014 Elsevier Inc. All rights reserved.

Synthesis of Carbon Dots with Multiple Color Emission by Controlled Graphitization and Surface Functionalization.

Science.gov (United States)

Miao, Xiang; Qu, Dan; Yang, Dongxue; Nie, Bing; Zhao, Yikang; Fan, Hongyou; Sun, Zaicheng

2018-01-01

Multiple-color-emissive carbon dots (CDots) have potential applications in various fields such as bioimaging, light-emitting devices, and photocatalysis. The majority of the current CDots to date exhibit excitation-wavelength-dependent emissions with their maximum emission limited at the blue-light region. Here, a synthesis of multiple-color-emission CDots by controlled graphitization and surface function is reported. The CDots are synthesized through controlled thermal pyrolysis of citric acid and urea. By regulating the thermal-pyrolysis temperature and ratio of reactants, the maximum emission of the resulting CDots gradually shifts from blue to red light, covering the entire light spectrum. Specifically, the emission position of the CDots can be tuned from 430 to 630 nm through controlling the extent of graphitization and the amount of surface functional groups, COOH. The relative photoluminescence quantum yields of the CDots with blue, green, and red emission reach up to 52.6%, 35.1%, and 12.9%, respectively. Furthermore, it is demonstrated that the CDots can be uniformly dispersed into epoxy resins and be fabricated as transparent CDots/epoxy composites for multiple-color- and white-light-emitting devices. This research opens a door for developing low-cost CDots as alternative phosphors for light-emitting devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Density functional theory study of hydrogenation mechanism in Fe-doped Mg(0 0 0 1) surface

International Nuclear Information System (INIS)

Wu Guangxin; Zhang Jieyu; Wu Yongquan; Li Qian; Chou Kuochih; Bao Xinhua

2009-01-01

Using density functional theory (DFT) in combination with nudged elastic band (NEB) method, the dissociative chemisorptions and diffusion processes of hydrogen on both pure and Fe-doped Mg(0 0 0 1) surfaces are studied. Firstly, the dissociation pathway of H 2 and the relative barrier were investigated. The calculated dissociation barrier (1.08 eV) of hydrogen molecule on a pure Mg(0 0 0 1) surface is in good agreement with comparable experimental and theoretical studies. For the Fe-doped Mg(0 0 0 1) surface, the activated barrier decreases to 0.101 eV due to the strong interaction between the s orbital of H and the d orbital of Fe. Then, the diffusion processes of atomic hydrogen on pure and Fe-doped Mg(0 0 0 1) are presented. The obtained diffusion barrier to the first subsurface is 0.45 eV and 0.98 eV, respectively. Finally, Chou method was used to investigate the hydrogen sorption kinetic mechanism of pure MgH 2 and Mg mixed with 5 at.% Fe atoms composites. The obtained activation energies are 0.87 ± 0.02 and 0.31 ± 0.01 eV for H 2 dissociation on the pure surface and H atom diffusion in Fe-doped Mg surfaces, respectively. It suggests that the rate-controlling step is dissociation of H 2 on the pure Mg surface while it is diffusion of H atom in the Fe-doped Mg surface. And both of fitting data are matching well with our calculation results.

Preparation of platinum-decorated porous graphite nanofibers, and their hydrogen storage behaviors.

Science.gov (United States)

Kim, Byung-Joo; Lee, Young-Seak; Park, Soo-Jin

2008-02-15

In this work, the hydrogen storage behaviors of porous graphite nanofibers (GNFs) decorated by Pt nanoparticles were investigated. The Pt nanoparticles were introduced onto the GNF surfaces using a well-known chemical reduction method. We investigated the hydrogen storage capacity of the Pt-doped GNFs for the platinum content range of 1.3-7.5 mass%. The microstructure of the Pt/porous GNFs was characterized by X-ray diffraction and transmission electron microscopy. The hydrogen storage behaviors of the Pt/GNFs were studied using a PCT apparatus at 298 K and 10 MPa. It was found that amount of hydrogen stored increased with increasing Pt content to 3.4 mass%, and then decreased. This result indicates that the hydrogen storage capacity of porous carbons is based on both their metal content and dispersion rate.

Observation of non-uniform erosion and deposition phenomena on graphite after plasma exposure

International Nuclear Information System (INIS)

Hildebrandt, D.; Grote, H.; Schneider, W.; Wienhold, P.; Seggern, J. von

1999-01-01

The modifications of fine grain isotropic graphite surfaces after plasma exposure have been investigated using surface analysis techniques with high spatial resolution in area and depth. The samples are graphite target tiles of ASDEX-upgrade and coated graphite collector samples exposed for special erosion/deposition experiments in the divertor plasma of ASDEX-upgrade or in the scrape-off plasma of TEXTOR-94. In addition, a graphite sample was exposed to a low temperature, clean deuterium plasma to study the modifications of the surface morphology during plasma exposure. The results give clear indications of non-uniform erosion and deposition processes. The change of the surface morphology during these processes is discussed. (orig.)

Synthesis of TiO2-doped SiO2 composite films and its applications

Indian Academy of Sciences (India)

Wintec

structure of the titanium oxide species in the TiO2-doped SiO2 composite films and the photocatalytic reactiv- ity in order to ... gaku D-max γA diffractometer with graphite mono- chromized ... FT–IR absorption spectra of TiO2-doped SiO2 com-.

Hydrogen pumping and release by graphite under high flux plasma bombardment

International Nuclear Information System (INIS)

Hirooka, Y.; Leung, W.K.; Conn, R.W.; Goebel, D.M.; Labombard, B.; Nygren, R.; Wilson, K.L.

1988-01-01

Inert gas (helium or argon) plasma bombardment has been found to increase the surface gas adsorptivity of isotropic graphite (POCO-graphite), which can then getter residual gases in a high vacuum system. The inert gas plasma bombardment was carried out at a flux ∼ 1 x 10 18 ions s -1 cm -2 to a fluence of the order of 10 21 ions/cm 2 and at temperatures around 800 degree C. The plasma bombarding energy was varied between 100 and 200 eV. The gettering speed of the activated graphite surface is estimated to be as large as 25 liters s -1 cm -2 at total pressures between 10 -6 and 10 -7 torr. The gettering capacity estimated is 0.025 torr-liter/cm 2 at room temperature. The gettering capability of graphite can be easily recovered by repeating inert gas plasma bombardment. The activated graphite surface exhibits a smooth, sponge-like morphology with significantly increased pore openings, which correlates with the observed increase in the surface gas adsorptivity. The activated graphite surface has been observed to pump hydrogen plasma particles as well. From calibrated H-alpha measurements, the dynamic hydrogen retention capacity is evaluated to be as large as 2 x 10 18 H/cm 2 at temperatures below 100 degree C and at a plasma bombarding energy of 300 eV

Performance enhancement of spherical natural graphite by phenol resin in lithium ion batteries

International Nuclear Information System (INIS)

Wu, Y.-S.; Wang, Y.-H.; Lee, Y.-H.

2006-01-01

The capacity of natural graphite in the lithium ion battery anode decays seriously. The phenol resin is used as a reaction material to modify the electrochemical performance of spherical graphite as the anode material in lithium ion batteries. Measuring the reversible capacity indicates change in the surface structure of spherical graphite. A dense layer of methyl groups was thus formed. Some structural imperfections are removed and the stability of the graphite structure is increased. Clearly, reducing the irreversible capacity is beneficial in controlling the uniformity of the spherical graphite surface structure

Statistical analysis of surface roughness of machined graphite by means of CNC milling

Directory of Open Access Journals (Sweden)

Orquídea Sánchez López

2016-09-01

Full Text Available The aim of this research is to analyze the influence of cutting speed, feed rate and cutting depth on the surface finish of grade GSP-70 graphite specimens for use in electrical discharge machining (EDM for material removal by means of Computer Numerical Control (CNC milling with low-speed machining (LSM. A two-level factorial design for each of the three established factors was used for the statistical analysis. The analysis of variance (ANOVA indicates that cutting speed and feed rate are the two most significant factors with regard to the roughness obtained with grade GSP-70 graphite by means of CNC milling. A second order regression analysis was also conducted to estimate the roughness average (Ra in terms of the cutting speed, feed rate and cutting depth. Finally, the comparison between predicted roughness by means of a second order regression model and the roughness obtained by machined specimens considering the combinations of low and high levels of roughness is also presented.

Improving the electrochemical properties of nanosized LiFePO4-based electrode by boron doping

International Nuclear Information System (INIS)

Trócoli, Rafael; Franger, Sylvain; Cruz, Manuel; Morales, Julián; Santos-Peña, Jesús

2014-01-01

Highlights: • Thermal treatment of boron phosphate with LiFePO 4 provides electrode materials with high performance in lithium half-cells: 160 mAh·g -1 (90% of theoretical capacity) under C/5 rate • The products are composites containing boron-modified LiFePO 4 , FePO 4 and an amorphous phase with ionic diffusion properties • The boron treatment affects textural, conductive and lithium diffusivity of the electrode material leading to higher performance • A limited boron-doping of the phospholivine structure is observed - Abstract: Electrode materials with homogeneous distribution of boron were obtained by heating mixtures of nanosized carbon-coated lithium iron phosphate and BPO 4 in 3-9% weight at 700 °C. The materials can be described as nanocomposites containing i) LiFePO 4 , possibly doped with a low amount of boron, ii) FePO 4 and iii) an amorphous layer based on Li 4 P 2 O 7 -derived material that surrounds the phosphate particles. The thermal treatment with BPO 4 also triggered changes in the carbon coating graphitic order. Galvanostatic and voltammetric studies in lithium half-cells showed smaller polarisation, higher capacity and better cycle life for the boron-doped composites. For instance, one of the solids, called B 6 -LiFePO 4 , provided close to 150 and 140 mAhg -1 (87% and 81% of theoretical capacity, respectively) under C/2.5 and C regimes after several cycles. Improved specific surface area, carbon graphitization, conductivity and lithium ion diffusivity in the boron-doped phospholivine network account for this excellent rate performance. The properties of an amorphous layer surrounding the phosphate particles also account for such higher performance

Graphite suspension in carbon dioxide

International Nuclear Information System (INIS)

Roche, R.

1965-01-01

Since 1963 the Atomic Division of SNECMA has been conducting, under a contract with the CEA, an experimental work with a two-component fluid comprised of carbon dioxide and small graphite particles. The primary purpose was the determination of basic engineering information pertaining to the stability and the flowability of the suspension. The final form of the experimental loop consists mainly of the following items: a light-phase compressor, a heavy-phase pump, an electrical-resistance type heater section, a cooling heat exchanger, a hairpin loop, a transparent test section and a separator. During the course of the testing, it was observed that the fluid could be circulated quite easily in a broad range of variation of the suspension density and velocity - density from 30 to 170 kg/m 3 and velocity from 2 to 24 m/s. The system could be restarted and circulation maintained without any difficulty, even with the heavy-phase pump alone. The graphite did not have a tendency to pack or agglomerate during operation. No graphite deposition was observed on the wall of the tubing. A long period run (250 hours) has shown the evolution of the particle dimensions. Starting with graphite of surface area around 20 m 2 /g (graphite particles about 1 μ), the powder surface area reaches an asymptotic value of 300 m 2 /g (all the particles less than 0.3 μ). Moisture effect on flow stability, flow distribution between two parallel channels, pressure drop in straight tubes, recompression ratio in diffusers were also investigated. (author) [fr

Surface modification of sol–gel synthesized TiO{sub 2} nanoparticles induced by La-doping

Energy Technology Data Exchange (ETDEWEB)

Grujić-Brojčin, M., E-mail: myramyra@ipb.ac.rs [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia); Armaković, S. [Department of Chemistry, Biochemistry and Environmental Protection, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 3, 21000 Novi Sad (Serbia); Tomić, N. [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia); Abramović, B. [Department of Chemistry, Biochemistry and Environmental Protection, Faculty of Sciences, University of Novi Sad, Trg D. Obradovića 3, 21000 Novi Sad (Serbia); Golubović, A.; Stojadinović, B. [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia); Kremenović, A. [Faculty of Mining and Geology, Laboratory for Crystallography, University of Belgrade, Đušina 7, 11000 Belgrade (Serbia); Babić, B. [Institute of Nuclear Sciences “Vinča”, University of Belgrade, 11001 Belgrade (Serbia); Dohčević-Mitrović, Z.; Šćepanović, M. [Institute of Physics, University of Belgrade, Pregrevica 118, 11080 Belgrade (Serbia)

2014-02-15

The influence of La-doping in the range of 0.5–6.0 mol% on structural and morphological properties of TiO{sub 2} nanopowders synthesized by sol–gel routine has been investigated by XRPD, AFM, EDS and BET measurements, as well as Raman spectroscopy. The XRPD and Raman measurements have revealed the anatase phase as dominant in all nanopowders, with crystallite size decreasing from ∼ 15 nm in pure TiO{sub 2} to ∼ 12 nm in La-doped samples. The BET data suggest that all samples are fully mesoporous, with mean pore diameters in the range of ∼ 6–8 nm. The specific surface area and the complexity of pore structure are greater in doped samples than in pure TiO{sub 2} sample. The spectroscopic ellipsometry has apparently shown that the band gap has been gradually increased with the increase of La content. The STM and STS techniques have been used successfully to evaluate the surface morphology and electronic properties of La-doped nanopowders. All investigated properties have been related to photocatalytic activity, tested in degradation of a metoprolol tartrate salt (0.05 mM), and induced by UV-radiation. All doped samples showed increased photocatalytic activity compared to pure TiO{sub 2}, among which the 0.65 mol% La-doped sample appeared to be the most efficient. - Highlights: • Effects of La-doping on structural, morphological and electronic properties of TiO{sub 2} nanopowders. • Surface morphology and electronic properties of La-doped nanopowders evaluated by STM/STS. • Spectroscopic ellipsometry shown gradual increase of bandgap with the increase of La content. • Photocatalytic activity of samples was tested in degradation of MET under UV light.

Measurements of print-through in graphite fiber epoxy composites

Science.gov (United States)

Jaworske, Donald A.; Jeunnette, Timothy T.; Anzic, Judith M.

1989-01-01

High-reflectance accurate-contour mirrors are needed for solar dynamic space power systems. Graphite fiber epoxy composites are attractive candidates for such applications owing to their high modulus, near-zero coefficient of thermal expansion, and low mass. However, mirrors prepared from graphite fiber epoxy composite substrates often exhibit print-through, a distortion of the surface, which causes a loss in solar specular reflectance. Efforts to develop mirror substrates without print-through distortion require a means of quantifying print-through. Methods have been developed to quantify the degree of print-through in graphite fiber epoxy composite specimens using surface profilometry.

Vapor pressure of plutonium carbide adsorbed on graphite

International Nuclear Information System (INIS)

Tallent, O.K.; Wichner, R.P.; Towns, R.L.; Godsey, T.T.

1984-09-01

An investigation was conducted to obtain data needed to make realistic estimates of plutonium contamination in the primary coolant system in High Temperature Gas-Cooled Reactors (HTGRs). The vapor pressure of plutonium over plutonium sesquicarbide (Pu 2 C 3 ) adsorbed on the surface of H-451 graphite was found to be defined by adsorption isotherms at test temperatures of 1000, 1200, and 1400 0 C. The vapor pressures at low concentrations of Pu 2 C 3 on the surface of the graphite were up to three orders of magnitude below that of pure Pu 2 C 3 at a given temperature. The heat of adsorption increases with decreasing Pu 2 C 3 surface coverage with the measured value at 0.05 μmol Pu 2 C 3 /m 2 being 107.9 kcal/mol. The Pu 2 C 3 concentration required for monolayer surface coverage on the graphite was found to be 3.27 μmol/m 2

Ion doping of surface layers in conducting electrical materials

International Nuclear Information System (INIS)

Zukowski, P.; Karwat, Cz.; Kozak, Cz. M.; Kolasik, M.; Kiszczak, K.

2009-01-01

The presented article gives basic component elements of an implanter MKPCz-99, its parameters and methods for doping surface layers of conducting electrical materials. The discussed device makes possible to dope the materials with ions of gaseous elements. At the application of cones made of solid-element sheets it is possible to perform doping with atoms that do not chemically react with the modified material. By performing voltage drop measurements with a specialized circuit between a movable testing electrode and the modified sample the dependence of transition resistance on pressure force of the testing electrode on the sample can be determined. The testing can be performed at the current passage of a determined value for surfaces modified with ions of gaseous elements or atoms of solid elements. A computer stand for switch testing makes possible to measure temperature of switch contacts and voltage drop at the contact and thereby to determine contact resistance of a switch depending on the number of switch cycles (ON-OFF). Pattern recording of current and voltage at the switch contacts and the application of an adequate computer software makes possible to determined the value of energy between fixed and moving contacts at their getting apart. In order to eliminate action of the environment onto the switch operation measurements can be performed at placing the tested switch together with the driving system in an atmosphere of noble gas like argon. (authors)

Redox behavior of a low-doped Pr-CeO{sub 2}(111) surface. A DFT+U study

Energy Technology Data Exchange (ETDEWEB)

Milberg, Brian [ITHES, UBA-CONICET, Departamento de Ingeniería Química, Pabellón de Industrias, Ciudad Universitaria, 1428 Buenos Aires (Argentina); Juan, Alfredo [Departamento de Física & IFISUR, UNS-CONICET, Avda. Alem 1253, 8000 Bahía Blanca (Argentina); Irigoyen, Beatriz, E-mail: beatriz@di.fcen.uba.ar [ITHES, UBA-CONICET, Departamento de Ingeniería Química, Pabellón de Industrias, Ciudad Universitaria, 1428 Buenos Aires (Argentina)

2017-04-15

Highlights: • Pr doping facilitates oxygen donation due to the easy formation of Pr{sup 3+}/Pr{sup 4+} and Ce{sup 3+}/Ce{sup 4+} redox couples. • Pr doping also favors the formation of superoxide (O{sub 2}{sup −}) radicals on surface O-holes. • CO can be oxidized by superoxide radical forming a CO{sub 2} molecule floating on the surface. • CO can also interact on the (O{sub 2}{sup −})/Pr{sup 3+} interphase and forms weakly adsorbed carbonate-type intermediates. - Abstract: In this work, we investigated the redox behavior (donation and replenishing of oxygen) of a low praseodymium (Pr)-doped CeO{sub 2}(111) surface. We considered a 3.7 at.% Pr doping and performed density functional calculations using the GGA formalism with the ‘U’ correction on Ce(4f) and Pr(4f) orbitals. Our results indicate that Pr doping promotes oxygen donation by lowering the energy necessary to form surface anionic vacancies. When the Ce{sub 0.963}Pr{sub 0.037}O{sub 2}(111) surface donates one oxygen, the two excess electrons locate on Pr and Ce cations and reduce them to Pr{sup 3+} and Ce{sup 3+} ones. Praseodymium doping also favors the activation of O{sub 2} molecule on surface O-holes, leading to formation of a superoxide (O{sub 2}{sup −}) radical as well as to reoxidation of the Ce{sup 3+} cation to Ce{sup 4+} one. Additionally, we used the CO molecular adsorption for testing the reactivity of those superoxide species. The calculations expose the ability of these radicals to oxidize CO forming a CO{sub 2} molecule floating on the surface. However, when the superoxide is in the immediate vicinity of Pr dopant a carbonate-type species is formed. Our theoretical results may help to gain insight into redox properties and improved catalytic performance of low-doped Pr-CeO{sub 2} solids.

Preparation of graphite derivatives by selective reduction of graphite oxide and isocyanate functionalization

Czech Academy of Sciences Publication Activity Database

Kumar, A. R. S. S.; Piana, Francesco; Mičušík, M.; Pionteck, J.; Banerjee, S.; Voit, B.

2016-01-01

Roč. 182, 1 October (2016), s. 237-245 ISSN 0254-0584 Institutional support: RVO:61389013 Keywords : graphite oxide * surface modification * conductive nanoparticles Subject RIV: CD - Macromolecular Chemistry Impact factor: 2.084, year: 2016

The effects of antimony doping on the surface structure of rutile TiO{sub 2}(110)

Energy Technology Data Exchange (ETDEWEB)

Bechstein, Ralf; Schuette, Jens; Kuehnle, Angelika [Fachbereich Physik, Universitaet Osnabrueck, Barbarastrasse 7, D-49076 Osnabrueck (Germany); Kitta, Mitsunori; Onishi, Hiroshi [Department of Chemistry, Kobe University, Rokko-dai, Nada-ku, Kobe 657-8501 (Japan)], E-mail: kuehnle@uos.de

2009-07-01

Titanium dioxide represents a very important wide bandgap photocatalyst that is known to be sensitized to visible light by transition metal doping. Antimony doping has been demonstrated to provide photocatalytic activity when codoped with chromium at an optimum dopant ratio [Sb]/[Cr] of about 1.5. Here, the role of antimony doping on the surface structure of rutile TiO{sub 2}(110) is studied using non-contact atomic force microscopy (NC-AFM) under ultra-high vacuum conditions. At first glance, the surface structure of antimony-doped TiO{sub 2}(110) resembles the structure of pristine TiO{sub 2}(110). However, in contrast to what is found in pristine TiO{sub 2}(110), a dense layer of protruding features is observed upon antimony doping, which is tentatively ascribed to antimony-rich clusters. Moreover, homogeneously distributed holes are found on the surface, which differ in depth and shape depending on the preparation conditions. Holes with depths ranging from a few up to more than a hundred monatomic steps are observed. These holes are explained by surface segregation of antimony during annealing, as the ionic radius of Sb{sup 3+} is considerably larger than the ionic radius of Ti{sup 4+}. Our finding provides an indication of why an antimony concentration larger than the optimum ratio results in decreased photocatalytic activity. Moreover, controlling annealing temperature seems to constitute a promising strategy for creating nanosized holes on TiO{sub 2} surfaces.

Brillouin spectroscopy with surface acoustic waves on intermediate valent, doped SmS

International Nuclear Information System (INIS)

Schaerer, U.; Jung, A.; Wachter, P.

1998-01-01

Brillouin scattering on surface acoustic waves is a very powerful tool to determine the elastic constants of intermediate valent crystals, since the method is non-destructive and no mechanical contact is needed. A strong evidence for intermediate valence is a negative value of Poisson's ratio, which describes the behavior of the volume under uniaxial pressure. SmS by itself makes a semiconductor-metal transition at a pressure of more than 6.5 kbar. When substituting the divalent Sm by a trivalent cation, like Y, La or Tm, SmS can become - depending on the doping concentration - intermediate valent without any applied, external pressure. In this work, we will present measurements of the velocities of the surface acoustic waves and the calculation of the elastic constants of La- and Tm-doped SmS compounds. We found a clear dependence of Poisson's ratio on the doping concentration and on the valence of the materials. Furthermore, we will discuss the mechanism leading to intermediate valence when substituting Sm. Besides the internal, chemical pressure, which is produced by the built in trivalent cations with their smaller ionic radii, we have clear evidence, that the free electrons in the 5d band, induced by the substituting atoms, also play an important role in making doped SmS intermediate valent. (orig.)

Mechanical, dielectric and surface analysis of hydroxyapatite doped anions for implantations

Science.gov (United States)

Helen, S.; Kumar, A. Ruban

2018-04-01

Calcium Phosphate has broad applications in field of medicine and in tissue engineering. In that hydroxyapatite is one of the calcium phosphate similar to bone and teeth mineral phase. The aim of this paper is to improve mechanical property of hydroxyapatite which has less mechanical strength by doping of ions. The ions increase its strength which can be used in various medical applications. Surface property of hydroxyapatite and electrical property of ion doped hydroxyapatite analyzed and shown that it can be used in implantations, coatings.

Work Function Characterization of Potassium-Intercalated, Boron Nitride Doped Graphitic Petals

Directory of Open Access Journals (Sweden)

Patrick T. McCarthy

2017-07-01

Full Text Available This paper reports on characterization techniques for electron emission from potassium-intercalated boron nitride-modified graphitic petals (GPs. Carbon-based materials offer potentially good performance in electron emission applications owing to high thermal stability and a wide range of nanostructures that increase emission current via field enhancement. Furthermore, potassium adsorption and intercalation of carbon-based nanoscale emitters decreases work functions from approximately 4.6 eV to as low as 2.0 eV. In this study, boron nitride modifications of GPs were performed. Hexagonal boron nitride is a planar structure akin to graphene and has demonstrated useful chemical and electrical properties when embedded in graphitic layers. Photoemission induced by simulated solar excitation was employed to characterize the emitter electron energy distributions, and changes in the electron emission characteristics with respect to temperature identified annealing temperature limits. After several heating cycles, a single stable emission peak with work function of 2.8 eV was present for the intercalated GP sample up to 1,000 K. Up to 600 K, the potassium-intercalated boron nitride modified sample exhibited improved retention of potassium in the form of multiple emission peaks (1.8, 2.5, and 3.3 eV resulting in a large net electron emission relative to the unmodified graphitic sample. However, upon further heating to 1,000 K, the unmodified GP sample demonstrated better stability and higher emission current than the boron nitride modified sample. Both samples deintercalated above 1,000 K.

Two-stage preparation of magnetic sorbent based on exfoliated graphite with ferrite phases for sorption of oil and liquid hydrocarbons from the water surface

Science.gov (United States)

Pavlova, Julia A.; Ivanov, Andrei V.; Maksimova, Natalia V.; Pokholok, Konstantin V.; Vasiliev, Alexander V.; Malakho, Artem P.; Avdeev, Victor V.

2018-05-01

Due to the macropore structure and the hydrophobic properties, exfoliated graphite (EG) is considered as a perspective sorbent for oil and liquid hydrocarbons from the water surface. However, there is the problem of EG collection from the water surface. One of the solutions is the modification of EG by a magnetic compound and the collection of EG with sorbed oil using the magnetic field. In this work, the method of the two-stage preparation of exfoliated graphite with ferrite phases is proposed. This method includes the impregnation of expandable graphite in the mixed solution of iron (III) chloride and cobalt (II) or nickel (II) nitrate in the first stage and the thermal exfoliation of impregnated expandable graphite with the formation of exfoliated graphite containing cobalt and nickel ferrites in the second stage. Such two-stage method makes it possible to obtain the sorbent based on EG modified by ferrimagnetic phases with high sorption capacity toward oil (up to 45-51 g/g) and high saturation magnetization (up to 42 emu/g). On the other hand, this method allows to produce the magnetic sorbent in a short period of time (up to 10 s) during which the thermal exfoliation is carried out in the air atmosphere.

Automotive body panel containing thermally exfoliated graphite oxide

Science.gov (United States)

Prud'Homme, Robert K. (Inventor); Aksay, Ilhan A. (Inventor); Adamson, Douglas (Inventor); Abdala, Ahmed (Inventor)

2011-01-01

An automotive body panel containing a polymer composite formed of at least one polymer and a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m.sup.2/g to 2600 m.sup.2/g.

Molecular dynamics simulation of chemical sputtering of hydrogen atom on layer structured graphite

International Nuclear Information System (INIS)

Ito, A.; Wang, Y.; Irle, S.; Morokuma, K.; Nakamura, H.

2008-10-01

Chemical sputtering of hydrogen atom on graphite was simulated using molecular dynamics. Especially, the layer structure of the graphite was maintained by interlayer intermolecular interaction. Three kinds of graphite surfaces, flat (0 0 0 1) surface, armchair (1 1 2-bar 0) surface and zigzag (1 0 1-bar 0) surface, are dealt with as targets of hydrogen atom bombardment. In the case of the flat surface, graphene layers were peeled off one by one and yielded molecules had chain structures. On the other hand, C 2 H 2 and H 2 are dominant yielded molecules on the armchair and zigzag surfaces, respectively. In addition, the interaction of a single hydrogen isotope on a single graphene is investigated. Adsorption, reflection and penetration rates are obtained as functions of incident energy and explain hydrogen retention on layered graphite. (author)

Highly conductive bridges between graphite spheres to improve the cycle performance of a graphite anode in lithium-ion batteries

Energy Technology Data Exchange (ETDEWEB)

Wang, Hongyu [IM and T Ltd., Advanced Research Center, Saga University, Yoga-machi 1341, Saga 840-0047 (Japan); Umeno, Tatsuo; Mizuma, Koutarou [Research Center, Mitsui Mining Co. Ltd., Hibiki-machi 1-3, Wakamatsu-ku, Kitakyushu 808-0021 (Japan); Yoshio, Masaki [Advanced Research Center, Saga University, Yoga-machi 1341, Saga 840-0047 (Japan)

2008-01-10

Spherical carbon-coated natural graphite (SCCNG) is a promising anode material for lithium-ion batteries, but the smooth surface of graphite spheres is difficult to wet with an aqueous binder solution, and lacks electrical contacts. As a result, the cycle performance of such a graphite anode material is not satisfactory. An effective method has been introduced to tightly connect adjacent SCCNG particles by a highly conductive binder, viz. acetylene black bridges. The effect of the conductive bridges on the cyclability of SCCNG electrode has been investigated. (author)

Coating of graphite flakes with MgO/carbon nanocomposite via gas state reaction

International Nuclear Information System (INIS)

Sharif, M.; Faghihi-Sani, M.A.; Golestani-Fard, F.; Saberi, A.; Soltani, Ali Khalife

2010-01-01

Coating of graphite flakes with MgO/carbon nanocomposite was carried out via gaseous state reaction between mixture of Mg metal, CO gas and graphite flakes at 1000 o C. XRD and FE-SEM analysis of coating showed that the coating was comprised of MgO nano particles and amorphous carbon distributed smoothly and covered the graphite surface evenly. Thermodynamic calculations were employed to predict the reaction sequences as well as phase stability. The effect of coating on water wettability and oxidation resistance of graphite was studied using contact angle measurement and TG analysis, respectively. It was demonstrated that the reaction between Mg and CO could result in MgO/C nanocomposite deposition. The coating improved water wettability of graphite and also enhanced the oxidation resistance of graphite flakes significantly. Also the graphite coating showed significant phenolic resin-wettabilty owing to high surface area of such hydrophilic nano composite coating. The importance of graphite coating is explained with emphasis on its potential application in graphite containing refractories.

Polyphase diffusion of fission products in graphite

International Nuclear Information System (INIS)

Dannert, V.

1989-05-01

The report attempts to give an introduction into the subject of fission product transport in nuclear graphite and results in an extended proposal of a transport-model. Beginning with a rough description of the graphite in question, an idea about the physical transport-phenomena in graphite is developed. Some of the basic experimental methods, especially techniques of porosimetry, determination of sorption-isotherms and of course several transport-experiments, are briefly described and their results are discussed. Some of the most frequent transport models are introduced and assessed with the criteria emphasized in this report. An extended model is proposed including the following main ideas: The transport of the fission-products is regarded as a two-phase-diffusion process through the open pores of the graphite. The two phases are: surface-diffusion and gas-diffusion. A time-dependent coupling of the two diffusion-phases by sorption-isotherms and a concentration-dependence of the surface diffusion coefficient, also related to the physical behaviour of the sorption-isotherms, are the basic properties of the proposed model. (orig./HP) [de

In-Situ-Activated N-Doped Mesoporous Carbon from a Protic Salt and Its Performance in Supercapacitors.

Science.gov (United States)

Mendes, Tiago C; Xiao, Changlong; Zhou, Fengling; Li, Haitao; Knowles, Gregory P; Hilder, Matthias; Somers, Anthony; Howlett, Patrick C; MacFarlane, Douglas R

2016-12-28

Protic salts have been recently recognized to be an excellent carbon source to obtain highly ordered N-doped carbon without the need of tedious and time-consuming preparation steps that are usually involved in traditional polymer-based precursors. Herein, we report a direct co-pyrolysis of an easily synthesized protic salt (benzimidazolium triflate) with calcium and sodium citrate at 850 °C to obtain N-doped mesoporous carbons from a single calcination procedure. It was found that sodium citrate plays a role in the final carbon porosity and acts as an in situ activator. This results in a large surface area as high as 1738 m 2 /g with a homogeneous pore size distribution and a moderate nitrogen doping level of 3.1%. X-ray photoelectron spectroscopy (XPS) measurements revealed that graphitic and pyridinic groups are the main nitrogen species present in the material, and their content depends on the amount of sodium citrate used during pyrolysis. Transmission electron microscopy (TEM) investigation showed that sodium citrate assists the formation of graphitic domains and many carbon nanosheets were observed. When applied as supercapacitor electrodes, a specific capacitance of 111 F/g in organic electrolyte was obtained and an excellent capacitance retention of 85.9% was observed at a current density of 10 A/g. At an operating voltage of 3.0 V, the device provided a maximum energy density of 35 W h/kg and a maximum power density of 12 kW/kg.

Doped and codoped silicon nanocrystals: The role of surfaces and interfaces

Science.gov (United States)

Marri, Ivan; Degoli, Elena; Ossicini, Stefano

2017-12-01

Si nanocrystals have been extensively studied because of their novel properties and their potential applications in electronic, optoelectronic, photovoltaic, thermoelectric and biological devices. These new properties are achieved through the combination of the quantum confinement of carriers and the strong influence of surface chemistry. As in the case of bulk Si the tuning of the electronic, optical and transport properties is related to the possibility of doping, in a controlled way, the nanocrystals. This is a big challenge since several studies have revealed that doping in Si nanocrystals differs from the one of the bulk. Theory and experiments have underlined that doping and codoping are influenced by a large number of parameters such as size, shape, passivation and chemical environment of the silicon nanocrystals. However, the connection between these parameters and dopant localization as well as the occurrence of self-purification effects are still not clear. In this review we summarize the latest progress in this fascinating research field considering free-standing and matrix-embedded Si nanocrystals both from the theoretical and experimental point of view, with special attention given to the results obtained by ab-initio calculations and to size-, surface- and interface-induced effects.

Microstructure and high-temperature tribological properties of Si-doped hydrogenated diamond-like carbon films

Science.gov (United States)

Zhang, Teng Fei; Wan, Zhi Xin; Ding, Ji Cheng; Zhang, Shihong; Wang, Qi Min; Kim, Kwang Ho

2018-03-01

Si-doped DLC films have attracted great attention for use in tribological applications. However, their high-temperature tribological properties remain less investigated, especially in harsh oxidative working conditions. In this study, Si-doped hydrogenated DLC films with various Si content were synthesized and the effects of the addition of Si on the microstructural, mechanical and high-temperature tribological properties of the films were investigated. The results indicate that Si doping leads to an obvious increase in the sp3/sp2 ratio of DLC films, likely due to the silicon atoms preferentially substitute the sp2-hybridized carbon atoms and augment the number of sp3 sites. With Si doping, the mechanical properties, including hardness and adhesion strength, were improved, while the residual stress of the DLC films was reduced. The addition of Si leads to higher thermal and mechanical stability of DLC films because the Si atoms inhibit the graphitization of the films at an elevated temperature. Better high-temperature tribological properties of the Si-DLC films under oxidative conditions were observed, which can be attributed to the enhanced thermal stability and formation of a Si-containing lubricant layer on the surfaces of the wear tracks. The nano-wear resistance of the DLC films was also improved by Si doping.

Carbon Papers and Aerogels Based on Graphene Layers and Chitosan: Direct Preparation from High Surface Area Graphite.

Science.gov (United States)

Barbera, Vincenzina; Guerra, Silvia; Brambilla, Luigi; Maggio, Mario; Serafini, Andrea; Conzatti, Lucia; Vitale, Alessandra; Galimberti, Maurizio

2017-12-11

In this work, carbon papers and aerogels based on graphene layers and chitosan were prepared. They were obtained by mixing chitosan (CS) and a high surface area nanosized graphite (HSAG) in water in the presence of acetic acid. HSAG/CS water dispersions were stable for months. High resolution transmission electron microscopy revealed the presence of few graphene layers in water suspensions. Casting or lyophilization of such suspensions led to the preparation of carbon paper and aerogel, respectively. In X-ray spectra of both aerogels and carbon paper, peaks due to regular stacks of graphene layers were not detected: graphene with unaltered sp 2 structure was obtained directly from graphite without the use of any chemical reaction. The composites were demonstrated to be electrically conductive thanks to the graphene. Chitosan thus makes it possible to obtain monolithic carbon aerogels and flexible and free-standing graphene papers directly from a nanosized graphite by avoiding oxidation to graphite oxide and successive reduction. Strong interaction between polycationic chitosan and the aromatic substrate appears to be at the origin of the stability of HSAG/CS adducts. Cation-π interaction is hypothesized, also on the basis of X-ray photoelectron spectroscopy findings. This work paves the way for the easy large-scale preparation of carbon papers through a method that has a low environmental impact and is based on a biosourced polymer, graphene, and water.

Disorder-driven metal-insulator-transition assisted by interband Coulomb repulsion in a surface transfer doped electron system

Science.gov (United States)

Francisco Sánchez-Royo, Juan

2012-12-01

The two-dimensional conducting properties of the Si(111) \\sqrt {3} \\times \\sqrt {3} surface doped by the charge surface transfer mechanism have been calculated in the frame of a semiclassical Drude-Boltzmann model considering donor scattering mechanisms. To perform these calculations, the required values of the carrier effective mass were extracted from reported angle-resolved photoemission results. The calculated doping dependence of the surface conductance reproduces experimental results reported and reveals an intricate metallization process driven by disorder and assisted by interband interactions. The system should behave as an insulator even at relatively low doping due to disorder. However, when doping increases, the system achieves to attenuate the inherent localization effects introduced by disorder and to conduct by percolation. The mechanism found by the system to conduct appears to be connected with the increasing of the carrier effective mass observed with doping, which seems to be caused by interband interactions involving the conducting band and deeper ones. This mass enhancement reduces the donor Bohr radius and, consequently, promotes the screening ability of the donor potential by the electron gas.

Laminated exfoliated graphite composite-metal compositions for fuel cell flow field plate or bipolar plate applications

Science.gov (United States)

Zhamu, Aruna; Shi, Jinjun; Guo, Jiusheng; Jang, Bor Z

2014-05-20

An electrically conductive laminate composition for fuel cell flow field plate or bipolar plate applications. The laminate composition comprises at least a thin metal sheet having two opposed exterior surfaces and a first exfoliated graphite composite sheet bonded to the first of the two exterior surfaces of the metal sheet wherein the exfoliated graphite composite sheet comprises: (a) expanded or exfoliated graphite and (b) a binder or matrix material to bond the expanded graphite for forming a cohered sheet, wherein the binder or matrix material is between 3% and 60% by weight based on the total weight of the first exfoliated graphite composite sheet. Preferably, the first exfoliated graphite composite sheet further comprises particles of non-expandable graphite or carbon in the amount of between 3% and 60% by weight based on the total weight of the non-expandable particles and the expanded graphite. Further preferably, the laminate comprises a second exfoliated graphite composite sheet bonded to the second surface of the metal sheet to form a three-layer laminate. Surface flow channels and other desired geometric features can be built onto the exterior surfaces of the laminate to form a flow field plate or bipolar plate. The resulting laminate has an exceptionally high thickness-direction conductivity and excellent resistance to gas permeation.

On residual gas analysis during high temperature baking of graphite tiles

International Nuclear Information System (INIS)

Prakash, A A; Chaudhuri, P; Khirwadkar, S; Reddy, D Chenna; Saxena, Y C; Chauhan, N; Raole, P M

2008-01-01

Steady-state Super-conducting Tokamak-1 (SST-1) is a medium size tokamak with major radius of 1.1 m and minor radius of 0.20 m. It is designed for plasma discharge duration of 1000 seconds to obtain fully steady-state plasma operation. Plasma Facing Components (PFC), consisting of divertors, passive stabilizers, baffles and poloidal limiters are also designed to be UHV compatible for steady state operation. All PFC are made up of graphite tiles mechanically attached to the copper alloy substrate. Graphite is one of the preferred first wall armour material in present day tokamaks. High thermal shock resistance and low atomic number of carbon are the most important properties of graphite for this application. High temperature vacuum baking of graphite tiles is the standard process to remove the impurities. Residual Gas Analyzer (RGA) has been used for qualitative and quantitative measurements of released gases from graphite tiles during baking. Surface Analysis of graphite tiles has also been done before and after baking. This paper describes the residual gas analysis during baking and surface analysis of graphite tiles

On residual gas analysis during high temperature baking of graphite tiles

Energy Technology Data Exchange (ETDEWEB)

Prakash, A A; Chaudhuri, P; Khirwadkar, S; Reddy, D Chenna; Saxena, Y C [Institute for Plasma Research, Bhat, Gandhinagar - 382 428 (India); Chauhan, N; Raole, P M [Facilitation Center for Industrial Plasma Technologies, IPR, Gandhinagar (India)], E-mail: arun@ipr.res.in

2008-05-01

Steady-state Super-conducting Tokamak-1 (SST-1) is a medium size tokamak with major radius of 1.1 m and minor radius of 0.20 m. It is designed for plasma discharge duration of 1000 seconds to obtain fully steady-state plasma operation. Plasma Facing Components (PFC), consisting of divertors, passive stabilizers, baffles and poloidal limiters are also designed to be UHV compatible for steady state operation. All PFC are made up of graphite tiles mechanically attached to the copper alloy substrate. Graphite is one of the preferred first wall armour material in present day tokamaks. High thermal shock resistance and low atomic number of carbon are the most important properties of graphite for this application. High temperature vacuum baking of graphite tiles is the standard process to remove the impurities. Residual Gas Analyzer (RGA) has been used for qualitative and quantitative measurements of released gases from graphite tiles during baking. Surface Analysis of graphite tiles has also been done before and after baking. This paper describes the residual gas analysis during baking and surface analysis of graphite tiles.

Mechanical activation of graphite in air: A way to advanced carbon nanomaterials

Energy Technology Data Exchange (ETDEWEB)

Baklanova, O.N., E-mail: baklanova@ihcp.ru; Drozdov, V.A.; Lavrenov, A.V.; Vasilevich, A.V.; Muromtsev, I.V.; Trenikhin, M.V.; Arbuzov, A.B.; Likholobov, V.A.; Gorbunova, O.V.

2015-10-15

A high-energy planetary mill AGO-2 was used for mechanical activation of synthetic graphite with the particle size of 25–30 μm and specific surface area S{sub BET} = 3.0 m{sup 2}/g in air for 1–60 min at a 100 g acceleration of milling bodies. The X-ray diffraction, Raman spectroscopy and electron microscopy studies showed that the 60 min mechanical activation of graphite decreases the number of graphene layers in graphite crystallites to 8–12 and induces their turbostratic disorder. The size of graphite particles decreases to 6.9 μm after 30 min of mechanical activation and increases to 12.1 μm when the time of mechanical activation is extended to 60 min. Similar changes are observed for the true density of graphite: after 60 min of mechanical activation it becomes equal to 2.48 ⋅ 10{sup 3} kg/m{sup 3}, which is by 10% higher than the true density of graphite not subjected to such treatment. The specific adsorption surface of graphite (S{sub BET}) reaches its maximum values, 427–460 m{sup 2}/g, after 7–12 min of mechanical activation. A further increase in the activation time to 30–60 min decreases S{sub BET} of graphite to 230–250 m{sup 2}/g. Due to attrition of steel milling bodies caused by mechanical activation, iron is accumulated in the samples and its content exceeds 5%. Iron is distributed uniformly in the graphite as the 30–100 and 3–5 nm particles of hematite and iron carbide. The IR spectroscopy study revealed the formation of 0.8 mEq/g of the hydroxyl, phenolic, lactone and carbonyl groups on the graphite surface in the course of mechanical activation. - Highlights: • Graphite was mechanically activated in air at a 100 g acceleration of milling bodies. • The amount of graphenes in graphite crystallites decreases to 8–12. • Graphite transforms into a nanocrystalline X-ray amorphous state. • A metal–graphite composite with the 30–100 and 3–5 nm iron particles is formed. • Oxygen-containing groups in the amount of

Evaluation of plasma disruption simulating short pulse laser irradiation experiments on boronated graphites and CFCs [carbon fibre composites

International Nuclear Information System (INIS)

Stad, R.C.L. van der; Klippel, H.T.; Kraaij, G.J.

1992-12-01

New experimental and numerical results from disruption heat flux simulations in the millisecond range with laser beams are discussed. For a number of graphites, boronated graphites and carbon fibre composites, the effective enthalpy of ablation is determined as 30 ± 3 MJ/kg, using laser pulses of about -.3 ms. The numerical results predict the experimental results rather well. No effect of boron doping on the ablation enthalpy is found. (author). 9 refs., 4 figs., 1 tab

Corrosion behavior of a positive graphite electrode in vanadium redox flow battery

International Nuclear Information System (INIS)

Liu Huijun; Xu Qian; Yan Chuanwei; Qiao Yonglian

2011-01-01

Graphical abstract: The overpotential for gas evolution on positive graphite electrode decreases due to the functional groups of COOH and C=O introduced on the surface of graphite electrode during corrosion process, which can self-catalyze the oxidation of carbon atoms therefore, accelerates corrosion process. Highlights: → Initial potential for gas evolution is higher than 1.60 V vs SCE. → Factors affecting the graphite corrosion are investigated. → Functional groups of COOH and C=O introduced during corrosion process. → The groups can self-catalyze the oxidation of carbon atoms. - Abstract: The graphite plate is easily suffered from corosion because of CO 2 evolution when it acts as the positive electrode for vanadium redox flow battery. The aim is to obtain the initial potential for gas evolution on a positive graphite electrode in 2 mol dm -3 H 2 SO 4 + 2 mol dm -3 VOSO 4 solution. The effects of polarization potential, operating temperature and polarization time on extent of graphite corrosion are investigated by potentiodynamic and potentiostatic techniques. The surface characteristics of graphite electrode before and after corrosion are examined by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The results show that the gas begins to evolve on the graphite electrode when the anodic polarization potential is higher than 1.60 V vs saturated calomel electrode at 20 deg. C. The CO 2 evolution on the graphite electrode can lead to intergranular corrosion of the graphite when the polarization potential reaches 1.75 V. In addition, the functional groups of COOH and C=O introduced on the surface of graphite electrode during corrosion can catalyze the formation of CO 2 , therefore, accelerates the corrosion rate of graphite electrode.

Special graphites

International Nuclear Information System (INIS)

Leveque, P.

1964-01-01

A large fraction of the work undertaken jointly by the Commissariat a l'Energie Atomique (CEA) and the Pechiney Company has been the improvement of the properties of nuclear pile graphite and the opening up of new fields of graphite application. New processes for the manufacture of carbons and special graphites have been developed: forged graphite, pyro-carbons, high density graphite agglomeration of graphite powders by cracking of natural gas, impervious graphites. The physical properties of these products and their reaction with various oxidising gases are described. The first irradiation results are also given. (authors) [fr

Surface analysis of model systems: From a metal-graphite interface to an intermetallic catalyst

Energy Technology Data Exchange (ETDEWEB)

Kwolek, Emma J. [Iowa State Univ., Ames, IA (United States)

2016-10-25

This thesis summarizes research completed on two different model systems. In the first system, we investigate the deposition of the elemental metal dysprosium on highly-oriented pyrolytic graphite (HOPG) and its resulting nucleation and growth. The goal of this research is to better understand the metal-carbon interactions that occur on HOPG and to apply those to an array of other carbon surfaces. This insight may prove beneficial to developing and using new materials for electronic applications, magnetic applications and catalysis.

Misorientations in spheroidal graphite: some new insights about spheroidal graphite growth in cast irons

International Nuclear Information System (INIS)

Lacaze, J; Theuwissen, K; Laffont, L; Véron, M

2016-01-01

Local diffraction patterning, orientation mapping and high resolution transmission electron microscopy imaging have been used to characterize misorientations in graphite spheroids of cast irons. Emphasis is put here on bulk graphite, away from the nucleus as well as from the outer surface of the spheroids in order to get information on their growth during solidification. The results show that spheroidal graphite consists in conical sectors made of elementary blocks piled up on each other. These blocks are elongated along the prismatic a direction of graphite with the c axes roughly parallel to the radius of the spheroids. This implies that the orientation of the blocks rotates around the spheroid centre giving low angle tilting misorientations along tangential direction within each sector. Misorientations between neighbouring sectors are of higher values and their interfaces show rippled layers which are characteristic of defects in graphene. Along a radius of the spheroid, clockwise and anticlockwise twisting between blocks is observed. These observations help challenging some of the models proposed to explain spheroidal growth in cast ions. (paper)

Electron transfer kinetics on natural crystals of MoS2 and graphite.

Science.gov (United States)

Velický, Matěj; Bissett, Mark A; Toth, Peter S; Patten, Hollie V; Worrall, Stephen D; Rodgers, Andrew N J; Hill, Ernie W; Kinloch, Ian A; Novoselov, Konstantin S; Georgiou, Thanasis; Britnell, Liam; Dryfe, Robert A W

2015-07-21

Here, we evaluate the electrochemical performance of sparsely studied natural crystals of molybdenite and graphite, which have increasingly been used for fabrication of next generation monolayer molybdenum disulphide and graphene energy storage devices. Heterogeneous electron transfer kinetics of several redox mediators, including Fe(CN)6(3-/4-), Ru(NH3)6(3+/2+) and IrCl6(2-/3-) are determined using voltammetry in a micro-droplet cell. The kinetics on both materials are studied as a function of surface defectiveness, surface ageing, applied potential and illumination. We find that the basal planes of both natural MoS2 and graphite show significant electroactivity, but a large decrease in electron transfer kinetics is observed on atmosphere-aged surfaces in comparison to in situ freshly cleaved surfaces of both materials. This is attributed to surface oxidation and adsorption of airborne contaminants at the surface exposed to an ambient environment. In contrast to semimetallic graphite, the electrode kinetics on semiconducting MoS2 are strongly dependent on the surface illumination and applied potential. Furthermore, while visibly present defects/cracks do not significantly affect the response of graphite, the kinetics on MoS2 systematically accelerate with small increase in disorder. These findings have direct implications for use of MoS2 and graphene/graphite as electrode materials in electrochemistry-related applications.

Reinforcement of cement-based matrices with graphite nanomaterials

Science.gov (United States)

Sadiq, Muhammad Maqbool

Cement-based materials offer a desirable balance of compressive strength, moisture resistance, durability, economy and energy-efficiency; their tensile strength, fracture energy and durability in aggressive environments, however, could benefit from further improvements. An option for realizing some of these improvements involves introduction of discrete fibers into concrete. When compared with today's micro-scale (steel, polypropylene, glass, etc.) fibers, graphite nanomaterials (carbon nanotube, nanofiber and graphite nanoplatelet) offer superior geometric, mechanical and physical characteristics. Graphite nanomaterials would realize their reinforcement potential as far as they are thoroughly dispersed within cement-based matrices, and effectively bond to cement hydrates. The research reported herein developed non-covalent and covalent surface modification techniques to improve the dispersion and interfacial interactions of graphite nanomaterials in cement-based matrices with a dense and well graded micro-structure. The most successful approach involved polymer wrapping of nanomaterials for increasing the density of hydrophilic groups on the nanomaterial surface without causing any damage to the their structure. The nanomaterials were characterized using various spectrometry techniques, and SEM (Scanning Electron Microscopy). The graphite nanomaterials were dispersed via selected sonication procedures in the mixing water of the cement-based matrix; conventional mixing and sample preparation techniques were then employed to prepare the cement-based nanocomposite samples, which were subjected to steam curing. Comprehensive engineering and durability characteristics of cement-based nanocomposites were determined and their chemical composition, microstructure and failure mechanisms were also assessed through various spectrometry, thermogravimetry, electron microscopy and elemental analyses. Both functionalized and non-functionalized nanomaterials as well as different

The influence of roughness on tribological properties of nuclear grade graphite

International Nuclear Information System (INIS)

Luo Xiaowei; Yu Suyuan; Sheng Xuanyu; He Shuyan

2006-01-01

The influence of surface roughness on tribological properties of graphite IG-11 was investigated on a standard SRV tester. The experimental condition was selected as: 30 N normal load, room temperature and a 10 Hz frequency with different strokes. The experiments environments included helium and air. Five types of roughness were studied in the experiments. The experiments revealed that the surface roughness greatly affected the graphite friction behavior. When the friction surface was smooth, the friction coefficient was high because of intensive adhesion accompanied by many pits at the friction surface. When the friction surface was rough, the adhesion was very poor, but the wear was excessive and generated many graphite particles at the friction surface. These particles can separate the friction surfaces, which reduced the friction action between them. For very rough specimens, the friction coefficient decreased with sliding velocity at about 0.004 m/s and then increases gradually

The role of oxygen in the uptake of deuterium in lithiated graphite

Energy Technology Data Exchange (ETDEWEB)

Taylor, C. N.; Luitjohan, K. E. [School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Dadras, J. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37998 (United States); Allain, J. P. [School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Birck Nanotechnology Center, West Lafayette, Indiana 47907 (United States); Krstic, P. S. [Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37998 (United States); Joint Institute of Computational Sciences, University of Tennessee, Knoxville, Tennessee 37998 (United States); Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Skinner, C. H. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2013-12-14

We investigate the mechanism of deuterium retention by lithiated graphite and its relationship to the oxygen concentration through surface sensitive experiments and atomistic simulations. Deposition of lithium on graphite yielded 5%–8% oxygen surface concentration and when subsequently irradiated with D ions at energies between 500 and 1000 eV/amu and fluences over 10{sup 16} cm{sup −2} the oxygen concentration rose to between 25% and 40%. These enhanced oxygen levels were reached in a few seconds compared to about 300 h when the lithiated graphite was allowed to adsorb oxygen from the ambient environment under equilibrium conditions. Irradiating graphite without lithium deposition, however, resulted in complete removal of oxygen to levels below the detection limit of XPS (e.g., <1%). These findings confirm the predictions of atomistic simulations, which had concluded that oxygen was the primary component for the enhanced hydrogen retention chemistry on the lithiated graphite surface.

Investigation of fluorine adsorption on nitrogen doped MgAl{sub 2}O{sub 4} surface by first-principles

Energy Technology Data Exchange (ETDEWEB)

Lv, Xiaojun; Xu, Zhenming [School of Metallurgy and Environment, Central South University, Changsha 410083 (China); Li, Jie, E-mail: 15216105346@163.com [School of Metallurgy and Environment, Central South University, Changsha 410083 (China); Chen, Jiangan [Faculty of Resource and Environmental Engineering, Jiangxi University of Science and Technology, Ganzhou 341000 (China); Liu, Qingsheng [Faculty of Metallurgical and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000 (China)

2016-07-15

Graphical abstract: First-principles calculations indicate that MgAl{sub 2}O{sub 4} surface is fluorine-loving, but hydrophobic. N doped MgAl{sub 2}O{sub 4} (100) surface structure shows the highest fluorine adsorption performance and fluorine atom is more preferentially adsorbed on the Mg-Al bridge site. The fluorine adsorption intensity follow this order: N doped MgAl{sub 2}O{sub 4} (100) > Al{sub 2}O{sub 3} (0001) > MgAl{sub 2}O{sub 4} (100) > MgO (100). N doped MgAl{sub 2}O{sub 4} is a promising candidate for fluorine removal. - Highlights: • MgAl{sub 2}O{sub 4} surface is fluorine-loving, not hydrophilic. • Fluorine preferentially adsorbs on the Mg-Al bridge site. • Adsorption intensity follow this order: N doped MgAl{sub 2}O{sub 4} > Al{sub 2}O{sub 3} > MgAl{sub 2}O{sub 4} > MgO. • Excellent adsorption performance attributes to electron compensation of N atom. • Nitrogen doped MgAl{sub 2}O{sub 4} is a promising candidate for fluorine removal. - Abstract: The nature of fluorine adsorption on pure and N doped MgAl{sub 2}O{sub 4} surface has been investigated by first-principles calculations based on the density functional theory. Calculated results indicate that MgAl{sub 2}O{sub 4} surface is fluorine-loving, not hydrophilic. Nitrogen doped MgAl{sub 2}O{sub 4} (100) surface shows the highest fluorine adsorption performance and fluorine atom preferentially adsorbs on the Mg-Al bridge site. The fluorine adsorption intensity follow this order: Nitrogen doped MgAl{sub 2}O{sub 4} (100) > Al{sub 2}O{sub 3} (0001) > MgAl{sub 2}O{sub 4} (100) > MgO (100). In-depth PDOS analysis suggested that 2p orbitals of F atom strongly hybridized with 3s- and 3p-orbitals of Al atom contribute to its high adsorption intensity. According to the analysis of Hirshfeld charge, the excellent fluorine adsorption performance of nitrogen doped MgAl{sub 2}O{sub 4} attributes to the electron compensation effect of nitrogen atom and strong electrostatic interactions. All these

Coating of graphite flakes with MgO/carbon nanocomposite via gas state reaction

Energy Technology Data Exchange (ETDEWEB)

Sharif, M., E-mail: Sharif_m@metaleng.iust.ac.i [Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Faghihi-Sani, M.A. [Sharif University of Technology, Tehran (Iran, Islamic Republic of); Golestani-Fard, F. [Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Saberi, A. [Tabriz University (Iran, Islamic Republic of); Soltani, Ali Khalife [Iran University of Science and Technology, Tehran (Iran, Islamic Republic of)

2010-06-18

Coating of graphite flakes with MgO/carbon nanocomposite was carried out via gaseous state reaction between mixture of Mg metal, CO gas and graphite flakes at 1000 {sup o}C. XRD and FE-SEM analysis of coating showed that the coating was comprised of MgO nano particles and amorphous carbon distributed smoothly and covered the graphite surface evenly. Thermodynamic calculations were employed to predict the reaction sequences as well as phase stability. The effect of coating on water wettability and oxidation resistance of graphite was studied using contact angle measurement and TG analysis, respectively. It was demonstrated that the reaction between Mg and CO could result in MgO/C nanocomposite deposition. The coating improved water wettability of graphite and also enhanced the oxidation resistance of graphite flakes significantly. Also the graphite coating showed significant phenolic resin-wettabilty owing to high surface area of such hydrophilic nano composite coating. The importance of graphite coating is explained with emphasis on its potential application in graphite containing refractories.

NO and NO{sub 2} adsorption on subsurface doped MgO (100) and BaO (100) surfaces. A density functional study

Energy Technology Data Exchange (ETDEWEB)

Añez, Rafael, E-mail: ranez@ivic.gob.ve [Laboratorio de Química Física y Catálisis Computacional, Centro de Química, Instituto Venezolano de Investigaciones Científicas, Apartado 21827, Caracas (Venezuela, Bolivarian Republic of); Sierraalta, Aníbal [Laboratorio de Química Física y Catálisis Computacional, Centro de Química, Instituto Venezolano de Investigaciones Científicas, Apartado 21827, Caracas (Venezuela, Bolivarian Republic of); Soto, Lenin J. Díaz [Pontifícia Universidade Católica do Rio de Janeiro, Departamento de Física, 22451-900 Rio de Janeiro, RJ (Brazil); Instituto de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, CT Bloco A sala 412, Rio de Janeiro, RJ 21949-900 (Brazil)

2017-05-15

Highlights: • Subsurface doped BaO(100) and MgO(100) surfaces. • NO and NO{sub 2} adsorption on doped BaO(100) and MgO(100) surfaces. • Surface distortion produced by the doped improves the interaction with the surface. • NO and NO{sub 2} adsorption energies displayed good correlation with the transferred charge. - Abstract: A periodic DFT approach was used to study the energetic, electronic and structural changes produced by the V, Fe and Ni sub layer doped of the MgO (100) and BaO (100) surfaces and the effect of these changes over the adsorption of NO and NO{sub 2}. Results indicate that the higher capacity of donating charge of the transition metal atoms improves the ability of the surfaces to transfer charge to the molecules. The charge transferred goes to NO and NO{sub 2} antibonding orbitals which makes them more reactive hence the interaction becomes stronger. A good lineal correlation between the charge transferred and the calculated adsorption energy was found, that is, as the charge transferred increases the adsorption energy increases. The interaction between the NO or NO{sub 2} molecule on doped surfaces not only depends of the charge transferred, surface structural changes produced by the doping with transition metal atoms increase the adsorption energy specially on the BaO (100) surface where the surface structural changes were more noticeable. Calculated stretching frequency of a NO in a η{sup 1} –N configuration indicates that this is the most stable specie found for the adsorption of NO on terraces of the MgO (100) surface around 77 K and that the sub layer Ni doped BaO (100) surface could be a promising material for the decomposition of NO{sub 2}.

Ab-initio study of Mg-doped InN(0001 surface

Directory of Open Access Journals (Sweden)

A. Belabbes

2013-01-01

Full Text Available We study the incorporation of Mg atoms into the InN(0001 surface. Energies and atomic geometries are described within density functional theory, while the electronic structure is investigated by an approximate quasiparticle method that yields a gap value of 0.7 eV for bulk InN. The formation of substitutional Mg is energetically favored in the surface layer. The surface electronic structure is less influenced by Mg-derived states. The Fermi level is pinned by In-derived surface states. With increasing depth of Mg beneath the surface the Fermi-level position moves toward the valence band top, suggesting formation of holes and, hence, p-doping of Mg in bulk-like layers.

Ion irradiated graphite exposed to fusion-relevant deuterium plasma

International Nuclear Information System (INIS)

Deslandes, Alec; Guenette, Mathew C.; Corr, Cormac S.; Karatchevtseva, Inna; Thomsen, Lars; Ionescu, Mihail; Lumpkin, Gregory R.; Riley, Daniel P.

2014-01-01

Graphite samples were irradiated with 5 MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. The ion irradiated graphite samples were then exposed to a deuterium plasma in the linear plasma device, MAGPIE, for a total ion fluence of ∼1 × 10 24 ions m −2 . Raman and near edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize modifications to the graphitic structure. Ion irradiation was observed to decrease the graphitic content and induce disorder in the graphite. Subsequent plasma exposure decreased the graphitic content further. Structural and surface chemistry changes were observed to be greatest for the sample irradiated with the greatest fluence of MeV ions. D retention was measured using elastic recoil detection analysis and showed that ion irradiation increased the amount of retained deuterium in graphite by a factor of four

Method for producing dustless graphite spheres from waste graphite fines

Science.gov (United States)

Pappano, Peter J [Oak Ridge, TN; Rogers, Michael R [Clinton, TN

2012-05-08

A method for producing graphite spheres from graphite fines by charging a quantity of spherical media into a rotatable cylindrical overcoater, charging a quantity of graphite fines into the overcoater thereby forming a first mixture of spherical media and graphite fines, rotating the overcoater at a speed such that the first mixture climbs the wall of the overcoater before rolling back down to the bottom thereby forming a second mixture of spherical media, graphite fines, and graphite spheres, removing the second mixture from the overcoater, sieving the second mixture to separate graphite spheres, charging the first mixture back into the overcoater, charging an additional quantity of graphite fines into the overcoater, adjusting processing parameters like overcoater dimensions, graphite fines charge, overcoater rotation speed, overcoater angle of rotation, and overcoater time of rotation, before repeating the steps until graphite fines are converted to graphite spheres.

Thermal grafting of fluorinated molecular monolayers on doped amorphous silicon surfaces

International Nuclear Information System (INIS)

Sabbah, H.; Zebda, A.; Ababou-Girard, S.; Solal, F.; Godet, C.; Conde, J. P.; Chu, V.

2009-01-01

Thermally induced (160-300 deg. C) gas phase grafting of linear alkene molecules (perfluorodecene) was performed on hydrogenated amorphous silicon (a-Si:H) films, either nominally undoped or doped with different boron and phosphorus concentrations. Dense and smooth a-Si:H films were grown using plasma decomposition of silane. Quantitative analysis of in situ x-ray photoelectron spectroscopy indicates the grafting of a single layer of organic molecules. The hydrophobic properties of perfluorodecene-modified surfaces were studied as a function of surface coverage. Annealing experiments in ultrahigh vacuum show the covalent binding and the thermal stability of these immobilized layers up to 370 deg. C; this temperature corresponds to the Si-C bond cleavage temperature. In contrast with hydrogenated crystalline Si(111):H, no heavy wet chemistry surface preparation is required for thermal grafting of alkene molecules on a-Si:H films. A threshold grafting temperature is observed, with a strong dependence on the doping level which produces a large contrast in the molecular coverage for grafting performed at 230 deg. C

Glassy carbon coated graphite for nuclear applications

International Nuclear Information System (INIS)

Delpeux S; Cacciaguerra T; Duclaux L

2005-01-01

Taking into account the problems caused by the treatment of nuclear wastes, the molten salts breeder reactors are expected to a great development. They use a molten fluorinated salt (mixture of LiF, BeF 2 , ThF 4 , and UF 4 ) as fuel and coolant. The reactor core, made of graphite, is used as a neutrons moderator. Despite of its compatibility with nuclear environment, it appears crucial to improve the stability and inertness of graphite against the diffusion of chemicals species leading to its corrosion. One way is to cover the graphite surface by a protective impermeable deposit made of glassy carbon obtained by the pyrolysis of phenolic resin or polyvinyl chloride precursors. The main difficulty in the synthesis of glassy carbon is to create exclusively, in the primary pyrolysis product, a micro-porosity of about twenty Angstroms which closes later at higher temperature. Therefore, the evacuation of the volatile products occurring mainly between 330 and 600 C, must progress slowly to avoid the material to crack. In this study, the optimal parameters for the synthesis of glassy carbon as well as glassy carbon deposits on nuclear-type graphite pieces are discussed. Both thermal treatment of phenolic and PVC resins have been performed. The structure and micro-texture of glassy carbon have been investigated by X-ray diffraction, scanning and transmission electron microscopies and helium pycno-metry. Glassy carbon samples (obtained at 1200 C) show densities ranging from 1.3 to 1.55 g/cm 3 and closed pores with nano-metric size (∼ 5 to 10 nm) appear clearly on the TEM micrographs. Then, a thermal treatment to 2700 C leads to the shrinkage of the entangled graphene ribbons, in good agreement with the proposed texture model for glassy carbon. Glassy carbon deposits on nuclear graphite have been developed by an impregnation method. The uniformity of the deposit depends clearly on the surface texture and the chemistry of the graphite substrate. The deposit regions where

Glassy carbon coated graphite for nuclear applications

Energy Technology Data Exchange (ETDEWEB)

Delpeux, S.; Cacciaguerra, T.; Duclaux, L. [Orleans Univ., CRMD, CNRS, 45 (France)

2005-07-01

Taking into account the problems caused by the treatment of nuclear wastes, the molten salts breeder reactors are expected to a great development. They use a molten fluorinated salt (mixture of LiF, BeF{sub 2}, ThF{sub 4}, and UF{sub 4}) as fuel and coolant. The reactor core, made of graphite, is used as a neutrons moderator. Despite of its compatibility with nuclear environment, it appears crucial to improve the stability and inertness of graphite against the diffusion of chemicals species leading to its corrosion. One way is to cover the graphite surface by a protective impermeable deposit made of glassy carbon obtained by the pyrolysis of phenolic resin [1,2] or polyvinyl chloride [3] precursors. The main difficulty in the synthesis of glassy carbon is to create exclusively, in the primary pyrolysis product, a micro-porosity of about twenty Angstroms which closes later at higher temperature. Therefore, the evacuation of the volatile products occurring mainly between 330 and 600 C, must progress slowly to avoid the material to crack. In this study, the optimal parameters for the synthesis of glassy carbon as well as glassy carbon deposits on nuclear-type graphite pieces are discussed. Both thermal treatment of phenolic and PVC resins have been performed. The structure and micro-texture of glassy carbon have been investigated by X-ray diffraction, scanning and transmission electron microscopies and helium pycno-metry. Glassy carbon samples (obtained at 1200 C) show densities ranging from 1.3 to 1.55 g/cm{sup 3} and closed pores with nano-metric size ({approx} 5 to 10 nm) appear clearly on the TEM micrographs. Then, a thermal treatment to 2700 C leads to the shrinkage of the entangled graphene ribbons (Fig 1), in good agreement with the proposed texture model for glassy carbon (Fig 2) [4]. Glassy carbon deposits on nuclear graphite have been developed by an impregnation method. The uniformity of the deposit depends clearly on the surface texture and the chemistry

Relation between film thickness and surface doping of MoS2 based field effect transistors

Science.gov (United States)

Lockhart de la Rosa, César J.; Arutchelvan, Goutham; Leonhardt, Alessandra; Huyghebaert, Cedric; Radu, Iuliana; Heyns, Marc; De Gendt, Stefan

2018-05-01

Ultra-thin MoS2 film doping through surface functionalization with physically adsorbed species is of great interest due to its ability to dope the film without reduction in the carrier mobility. However, there is a need for understanding how the thickness of the MoS2 film is related to the induced surface doping for improved electrical performance. In this work, we report on the relation of MoS2 film thickness with the doping effect induced by the n-dopant adsorbate poly(vinyl-alcohol). Field effect transistors built using MoS2 films of different thicknesses were electrically characterized, and it was observed that the ION/OFF ratio after doping in thin films is more than four orders of magnitudes greater when compared with thick films. Additionally, a semi-classical model tuned with the experimental devices was used to understand the spatial distribution of charge in the channel and explain the observed behavior. From the simulation results, it was revealed that the two-dimensional carrier density induced by the adsorbate is distributed rather uniformly along the complete channel for thin films (<5.2 nm) contrary to what happens for thicker films.

Surface Modification of Exfoliated Graphite Nano-Reinforcements, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — Nano forms of graphite and carbon, such as flakes, worms, and tubes, can significantly modify the properties of polymers when used as reinforcements. Challenges...

Structural disorder of graphite and implications for graphite thermometry

Science.gov (United States)

Kirilova, Martina; Toy, Virginia; Rooney, Jeremy S.; Giorgetti, Carolina; Gordon, Keith C.; Collettini, Cristiano; Takeshita, Toru

2018-02-01

Graphitization, or the progressive maturation of carbonaceous material, is considered an irreversible process. Thus, the degree of graphite crystallinity, or its structural order, has been calibrated as an indicator of the peak metamorphic temperatures experienced by the host rocks. However, discrepancies between temperatures indicated by graphite crystallinity versus other thermometers have been documented in deformed rocks. To examine the possibility of mechanical modifications of graphite structure and the potential impacts on graphite thermometry, we performed laboratory deformation experiments. We sheared highly crystalline graphite powder at normal stresses of 5 and 25 megapascal (MPa) and aseismic velocities of 1, 10 and 100 µm s-1. The degree of structural order both in the starting and resulting materials was analyzed by Raman microspectroscopy. Our results demonstrate structural disorder of graphite, manifested as changes in the Raman spectra. Microstructural observations show that brittle processes caused the documented mechanical modifications of the aggregate graphite crystallinity. We conclude that the calibrated graphite thermometer is ambiguous in active tectonic settings.

Asymptomatic Intracorneal Graphite Deposits following Graphite Pencil Injury

OpenAIRE

Philip, Swetha Sara; John, Deepa; John, Sheeja Susan

2012-01-01

Reports of graphite pencil lead injuries to the eye are rare. Although graphite is considered to remain inert in the eye, it has been known to cause severe inflammation and damage to ocular structures. We report a case of a 12-year-old girl with intracorneal graphite foreign bodies following a graphite pencil injury.

Study of gadolinia-doped ceria solid electrolyte surface by XPS

International Nuclear Information System (INIS)

Datta, Pradyot; Majewski, Peter; Aldinger, Fritz

2009-01-01

Gadolinia-doped ceria (CGO) is an important material to be used as electrolyte for solid oxide fuel cell for intermediate temperature operation. Ceria doped with 10 mol% gadolinia (Ce 0.9 Gd 0.1 O 1.95 ) was prepared by conventional solid state synthesis and found to be single phase by room temperature X-ray diffraction (XRD). The chemical states of the surface of the prepared sample were analyzed by X-ray photoelectron spectroscopy (XPS). Though Gd was present in its characteristic chemical state, Ce was found in both Ce 4+ and Ce 3+ states. Presence of Ce 3+ state was ascribed to the differential yield of oxygen atoms in the sputtering process

Thermal diffusion boron doping of single-crystal natural diamond

Energy Technology Data Exchange (ETDEWEB)

Seo, Jung-Hun; Mikael, Solomon; Mi, Hongyi; Venkataramanan, Giri; Ma, Zhenqiang, E-mail: mazq@engr.wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Wu, Henry; Morgan, Dane [Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Blanchard, James P. [Department of Nuclear Engineering and Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Zhou, Weidong [Department of Electrical Engineering, NanoFAB Center, University of Texas at Arlington, Arlington, Texas 76019 (United States); Gong, Shaoqin [Department of Biomedical Engineering and Wisconsin Institute for Discovery, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2016-05-28

With the best overall electronic and thermal properties, single crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors requires overcoming doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional doping in SCD without inducing graphitization transition or lattice damage can be readily realized with thermal diffusion at relatively low temperatures by using heavily doped Si nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancy exchange boron doping mechanism that occurs at the bonded interface between Si and diamond. We further demonstrate selectively doped high voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high voltage power conversion systems and for other novel diamond based electronic devices. The novel doping mechanism may find its critical use in other wide bandgap semiconductors.

Thermal diffusion boron doping of single-crystal natural diamond

International Nuclear Information System (INIS)

Seo, Jung-Hun; Mikael, Solomon; Mi, Hongyi; Venkataramanan, Giri; Ma, Zhenqiang; Wu, Henry; Morgan, Dane; Blanchard, James P.; Zhou, Weidong; Gong, Shaoqin

2016-01-01

With the best overall electronic and thermal properties, single crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors requires overcoming doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional doping in SCD without inducing graphitization transition or lattice damage can be readily realized with thermal diffusion at relatively low temperatures by using heavily doped Si nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancy exchange boron doping mechanism that occurs at the bonded interface between Si and diamond. We further demonstrate selectively doped high voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high voltage power conversion systems and for other novel diamond based electronic devices. The novel doping mechanism may find its critical use in other wide bandgap semiconductors.

A facile self-template strategy to fabricate three-dimensional nitrogen-doped hierarchical porous carbon/graphene for conductive agent-free supercapacitors with excellent electrochemical performance

International Nuclear Information System (INIS)

Yuanyuan, Yin; Ruiyi, Li; Zaijun, Li; Junkang, Liu; Zhiguo, Gu; Guangli, Wang

2014-01-01

Graphical abstract: - Highlights: • The paper reported a facile template-free strategy to fabricate three-dimensional nitrogen-doped hierarchical porous carbon/graphene (3D-NHPC/G). • Such a new concept of strategy creates 3D carbon framework, hierarchical pore distribution, moderate graphitization and appropriate nitrogen doping. • The 3D-NHPC/G offers high electric conductivity, mass transfer and specific surface area. • The 3D-NHPC/G electrode displays an largely enhanced electrochemical performance. - Abstract: Carbon materials with large surface area, high conductivity and suitable pore distribution are highly desirable for high-performance supercapacitors. The paper reported a self-template strategy for the fabrication of three-dimensional nitrogen-doped hierarchical porous carbon/graphene (3D-NHPC/G). The mixture of beer yeast cells, graphite oxide, urea, potassium hydroxide and phytic acid was dispersed in water by ultrasonication to form homogeneous slurry, which was then dried by spray drying and finally heated at 850°C in Ar/H 2 environment. The study shows that such a new strategy creates a 3D carbon framework, hierarchical pore distribution, moderate graphitization and appropriate nitrogen doping. The as-prepared 3D-NHPC/G offers excellent dispersion, specific surface area of 3108.7 m 2 g −1 and electronic conductivity of 3096 S m −1 , which is more than six-fold that of 3D-NHPC (494 S m −1 ). Owing to the greatly enchanced electron transfer and mass transport, the 3D-NHPC/G electrode displays the largely enhanced electrochemical performance. In 6 mol l −1 potassium hydroxide aqueous electrolyte, its specific capacitance is 318 F g −1 at the current density of 1 A g −1 , 277 F g −1 at the current density of 10 A g −1 , and 155 F g −1 at the current density of 100 A g −1 that can remain at least 96.5% after 10000 cycles. In 1 mol l −1 tetraethylammonium tetrafluoroborate organic electrolyte, the specific capacitance is 138

The electrochemical properties of graphite and carbon

International Nuclear Information System (INIS)

Yeager, E.; Gupta, S.; Molla, J.A.

1983-01-01

Carbon and graphite are often used as supports for electrocatalysts, but also have an electrocatalytic function in such electrode reactions as O 2 reduction in alkaline electrolytes, Cl 2 generation in brine and SOCl 2 reduction in lithium-thionyl chloride batteries. These catalytic functions involve specific chemical functional groups bound to the carbon and graphite surfaces. The factors controlling O 2 reduction with various types of carbon electrodes of both low and high surface area are reviewed. Of particular importance is the role of hydrogen peroxide. The role of the functionality of the carbon in the electrocatalysis will be discussed

Trapping of hydride forming elements within miniature electrothermal devices. Part 2. Investigation of collection of arsenic and selenium hydrides on a surface and in a cavity of a graphite rod

International Nuclear Information System (INIS)

Docekal, Bohumil

2004-01-01

The interaction of arsenic and selenium hydrides with bare and modified graphite was investigated by atomic absorption spectrometry and by radiotracer technique using 75 Se radionuclide in a laboratory made brass cylindrical chamber equipped with a vertical quartz tube torch for supporting miniature hydrogen diffusion flame atomizer. Strong interaction was observed at elevated temperatures above 800 deg. C. In contrast to the very often-reported data for conventional graphite tube atomizers, this high temperature interaction was also accompanied by a pronounced trapping of analytes at elevated temperatures close to 1100-1200 deg. C when modified graphite was used. Comparing modifiers tested (Ir, Pt and Rh), iridium appeared the only useful permanent modifier. Among various graphite-rod traps designed, the most efficient trapping of analytes was achieved in a graphite cavity. The net selenium trapping efficiencies of approximately 53% and 70% were found by radiotracer technique for the iridium-treated graphite surface and the iridium-treated graphite cavity, respectively. In contrast to the molybdenum surface, bare graphite did not exhibit any significant trapping effect. Trapping isotherms obtained at different temperatures displayed non-linear course in the range up to the upper limit of the analytical relevance of 100 ng of an analyte, indicating a limited trapping capacity of the modified graphite surface and the same trapping mechanism at low and elevated temperatures applied (300-1300 deg. C). Radiography experiments with 75 Se radiotracer showed that a major part of selenium was collected within the small cavity of the graphite rod and that selenium was also deposited after the trapping and vaporization steps in the trap chamber and on the quartz tube wall of the burner. Complementary experiments performed with the conventional transversally heated graphite tube and with bare and thermally shielded injection capillaries for hydride introduction, showed that

Surface passivation of n-type doped black silicon by atomic-layer-deposited SiO2/Al2O3 stacks

Science.gov (United States)

van de Loo, B. W. H.; Ingenito, A.; Verheijen, M. A.; Isabella, O.; Zeman, M.; Kessels, W. M. M.

2017-06-01

Black silicon (b-Si) nanotextures can significantly enhance the light absorption of crystalline silicon solar cells. Nevertheless, for a successful application of b-Si textures in industrially relevant solar cell architectures, it is imperative that charge-carrier recombination at particularly highly n-type doped black Si surfaces is further suppressed. In this work, this issue is addressed through systematically studying lowly and highly doped b-Si surfaces, which are passivated by atomic-layer-deposited Al2O3 films or SiO2/Al2O3 stacks. In lowly doped b-Si textures, a very low surface recombination prefactor of 16 fA/cm2 was found after surface passivation by Al2O3. The excellent passivation was achieved after a dedicated wet-chemical treatment prior to surface passivation, which removed structural defects which resided below the b-Si surface. On highly n-type doped b-Si, the SiO2/Al2O3 stacks result in a considerable improvement in surface passivation compared to the Al2O3 single layers. The atomic-layer-deposited SiO2/Al2O3 stacks therefore provide a low-temperature, industrially viable passivation method, enabling the application of highly n- type doped b-Si nanotextures in industrial silicon solar cells.

Passivation of phosphorus diffused silicon surfaces with Al2O3: Influence of surface doping concentration and thermal activation treatments

International Nuclear Information System (INIS)

Richter, Armin; Benick, Jan; Kimmerle, Achim; Hermle, Martin; Glunz, Stefan W.

2014-01-01

Thin layers of Al 2 O 3 are well known for the excellent passivation of p-type c-Si surfaces including highly doped p + emitters, due to a high density of fixed negative charges. Recent results indicate that Al 2 O 3 can also provide a good passivation of certain phosphorus-diffused n + c-Si surfaces. In this work, we studied the recombination at Al 2 O 3 passivated n + surfaces theoretically with device simulations and experimentally for Al 2 O 3 deposited with atomic layer deposition. The simulation results indicate that there is a certain surface doping concentration, where the recombination is maximal due to depletion or weak inversion of the charge carriers at the c-Si/Al 2 O 3 interface. This pronounced maximum was also observed experimentally for n + surfaces passivated either with Al 2 O 3 single layers or stacks of Al 2 O 3 capped by SiN x , when activated with a low temperature anneal (425 °C). In contrast, for Al 2 O 3 /SiN x stacks activated with a short high-temperature firing process (800 °C) a significant lower surface recombination was observed for most n + diffusion profiles without such a pronounced maximum. Based on experimentally determined interface properties and simulation results, we attribute this superior passivation quality after firing to a better chemical surface passivation, quantified by a lower interface defect density, in combination with a lower density of negative fixed charges. These experimental results reveal that Al 2 O 3 /SiN x stacks can provide not only excellent passivation on p + surfaces but also on n + surfaces for a wide range of surface doping concentrations when activated with short high-temperature treatments

A discussion of possible mechanisms affecting fission product transport in irradiated and unirradiated nuclear grade graphite

International Nuclear Information System (INIS)

Firth, M.J.

1977-09-01

137 Cs, 85 Sr, and sup(110m)Ag adsorption experiments were conducted on three graphite powders with differing amounts of specific basal and edge surface areas. No direct proportionality was found between the specific amounts of the isotopes adsorbed and either of the surface characteristics. There appears to be some correlation with the specific basal surface area despite the fact that each isotope behaves differently. Factors that might influence the adsorption behaviour of Cs and Ag during reactor irradiation and heat treatment of nuclear grade graphites are discussed. These include the form of Cs with the graphite surface. A model based on Cs adsorption at vacancy clusters is used to analyse adsorption experiments. A possible explanation for the behaviour of Ag through the migration of graphite impurities from the bulk of the graphite to the pore surface is also discussed. (author)

Graphite limiter and armour damage in Doublet III

International Nuclear Information System (INIS)

McKelvey, T.; Taylor, T.; Trester, P.

1983-01-01

Graphite coated with TiC has been used extensively in Doublet III for limiters and neutral beam armour. Performance of these components has been superior to that of the metal components previously used. Damage to the coated graphite has occurred and can be classified into three categories: (1) gross failure of the graphite due to thermal stresses induced by the combination of high applied energy fluxes and mechanical restraint, (2) surface failure of the graphite due to runaway electron impingement, and (3) loss of TiC coating due to arcing, sputtering, vaporization and spalling, primarily during plasma disruptions and other abnormal plasma conditions. Design improvements are being continually implemented to minimize this damage and its consequences. (author)

Graphite suspension in carbon dioxide; Suspension de graphite dans le gaz carbonique

Energy Technology Data Exchange (ETDEWEB)

Roche, R [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires; Moussez, C; Rouvillois, X; Brevet, R [Societe Nationale d' Etude et de Construction de Moteurs d' Aviation (SNECMA), 75 - Paris (France)

1965-07-01

Since 1963 the Atomic Division of SNECMA has been conducting, under a contract with the CEA, an experimental work with a two-component fluid comprised of carbon dioxide and small graphite particles. The primary purpose was the determination of basic engineering information pertaining to the stability and the flowability of the suspension. The final form of the experimental loop consists mainly of the following items: a light-phase compressor, a heavy-phase pump, an electrical-resistance type heater section, a cooling heat exchanger, a hairpin loop, a transparent test section and a separator. During the course of the testing, it was observed that the fluid could be circulated quite easily in a broad range of variation of the suspension density and velocity - density from 30 to 170 kg/m{sup 3} and velocity from 2 to 24 m/s. The system could be restarted and circulation maintained without any difficulty, even with the heavy-phase pump alone. The graphite did not have a tendency to pack or agglomerate during operation. No graphite deposition was observed on the wall of the tubing. A long period run (250 hours) has shown the evolution of the particle dimensions. Starting with graphite of surface area around 20 m{sup 2}/g (graphite particles about 1 {mu}), the powder surface area reaches an asymptotic value of 300 m{sup 2}/g (all the particles less than 0.3 {mu}). Moisture effect on flow stability, flow distribution between two parallel channels, pressure drop in straight tubes, recompression ratio in diffusers were also investigated. (author) [French] Depuis 1963 la Division Atomique de la SNECMA conduit, dans le cadre d'un contrat avec le Commissariat A l'Energie Atomique, l'etude experimentale d'une suspension de fines particules de graphite dans le gaz carbonique. L'objectif principal est d'obtenir des informations d'ordre mecanique et technologique sur la mise en oeuvre de l'ecoulement de ce fluide diphase. Le circuit experimental comprend principalement: un

Hydrophilization of graphite using plasma above/in a solution

Science.gov (United States)

Hoshino, Shuhei; Kawahara, Kazuma; Takeuchi, Nozomi

2018-01-01

A hydrophilization method for graphite is required for applications such as conductive ink. In typical chemical oxidation methods for graphite have the problems of producing many defects in graphite and a large environmental impact. In recent years, the plasma treatment has attracted attention because of the high quality of the treated samples and the low environmental impact. In this study, we proposed an above-solution plasma treatment with a high contact probability of graphite and plasma since graphite accumulates on the solution surface due to its hydrophobicity, which we compared with a so-called solution plasma treatment. Graphite was hydrophilized via reactions with OH radicals generated by the plasma. It was confirmed that hydroxyl and carboxyl groups were modified to the graphite and the dispersibility was improved. The above-solution plasma achieved more energy-efficient hydrophilization than the solution plasma and it was possible to enhance the dispersibility by increasing the plasma-solution contact area.

Structural disorder of graphite and implications for graphite thermometry

Directory of Open Access Journals (Sweden)

M. Kirilova

2018-02-01

Full Text Available Graphitization, or the progressive maturation of carbonaceous material, is considered an irreversible process. Thus, the degree of graphite crystallinity, or its structural order, has been calibrated as an indicator of the peak metamorphic temperatures experienced by the host rocks. However, discrepancies between temperatures indicated by graphite crystallinity versus other thermometers have been documented in deformed rocks. To examine the possibility of mechanical modifications of graphite structure and the potential impacts on graphite thermometry, we performed laboratory deformation experiments. We sheared highly crystalline graphite powder at normal stresses of 5 and 25  megapascal (MPa and aseismic velocities of 1, 10 and 100 µm s−1. The degree of structural order both in the starting and resulting materials was analyzed by Raman microspectroscopy. Our results demonstrate structural disorder of graphite, manifested as changes in the Raman spectra. Microstructural observations show that brittle processes caused the documented mechanical modifications of the aggregate graphite crystallinity. We conclude that the calibrated graphite thermometer is ambiguous in active tectonic settings.

Surface Charge Transfer Doping of Monolayer Phosphorene via Molecular Adsorption.

Science.gov (United States)

He, Yuanyuan; Xia, Feifei; Shao, Zhibin; Zhao, Jianwei; Jie, Jiansheng

2015-12-03

Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

Surface science. Adhesion and friction in mesoscopic graphite contacts.

Science.gov (United States)

Koren, Elad; Lörtscher, Emanuel; Rawlings, Colin; Knoll, Armin W; Duerig, Urs

2015-05-08

The weak interlayer binding in two-dimensional layered materials such as graphite gives rise to poorly understood low-friction characteristics. Accurate measurements of the adhesion forces governing the overall mechanical stability have also remained elusive. We report on the direct mechanical measurement of line tension and friction forces acting in sheared mesoscale graphite structures. We show that the friction is fundamentally stochastic in nature and is attributable to the interaction between the incommensurate interface lattices. We also measured an adhesion energy of 0.227 ± 0.005 joules per square meter, in excellent agreement with theoretical models. In addition, bistable all-mechanical memory cell structures and rotational bearings have been realized by exploiting position locking, which is provided solely by the adhesion energy. Copyright © 2015, American Association for the Advancement of Science.

Subsurface methane formation in graphite due to exposure to H+ and D+

International Nuclear Information System (INIS)

Chiu, S.; Haasz, A.A.

1994-01-01

The extent of H-D mixing in the form of mixed-isotope methane formation during simultaneous H + /D + bombardment of graphite was measured and found to be a sensitive function of H + -D + ion range separation. The result strongly supports the model that methane molecules are formed at the end of ion range in the bulk of graphite. A long steadily decreasing transient was observed in the methane emission when bombarding a virgin graphite sample with 10 keV D + at 800 K. The effect was less pronounced for low density fine grain isographites (EK98) than for high density pyrolytic graphite (HPG99) and monocrystal carbons. We propose a model which attributes this transient to the creation of new internal ''surfaces'', formed during ion irradiation along with ion-created micropaths. The increase in internal surface area effectively ''dilutes'' the inner surface hydrogen concentration in the region where incident hydrogen ions thermalize. We propose that, initially, methane molecules are formed mainly on inherent internal surfaces (pore and grain/crystallite boundary surfaces) in the region where hydrogen ions thermalize; then as damage builds up, newly produced internal ''surfaces'' also contribute to methane formation. (orig.)

Nitrogen-doped porous carbon from Camellia oleifera shells with enhanced electrochemical performance

International Nuclear Information System (INIS)

Zhai, Yunbo; Xu, Bibo; Zhu, Yun; Qing, Renpeng; Peng, Chuan; Wang, Tengfei; Li, Caiting; Zeng, Guangming

2016-01-01

Nitrogen doped porous activated carbon was prepared by annealing treatment of Camellia oleifera shell activated carbon under NH 3 . We found that nitrogen content of activated carbon up to 10.43 at.% when annealed in NH 3 at 800 °C. At 600 °C or above, the N-doped carbon further reacts with NH 3 , leads to a low surface area down to 458 m 2 /g and low graphitization degree. X-ray photoelectron spectroscope (XPS) analysis indicated that the nitrogen functional groups on the nitrogen-doped activated carbons (NACs) were mostly in the form of pyridinic nitrogen. We discovered that the oxygen groups and carbon atoms at the defect and edge sites of graphene play an important role in the reaction, leading to nitrogen atoms incorporated into the lattice of carbon. When temperatures were lower than 600 °C the nitrogen atoms displaced oxygen groups and formed nitrogen function groups, and when temperatures were higher than 600 °C and ~ 4 at.% carbon atoms and part of oxygen function groups reacted with NH 3 . When compared to pure activated carbon, the nitrogen doped activated carbon shows nearly four times the capacitance (191 vs 51 F/g). - Highlights: • The nitrogen content up to 10.43 at % during CAC pyrolysis under NH3 at 800 °C. • The oxygen groups and carbon atoms played an important role in the nitrogen doping. • NAC-600 shows a much higher specific capacitance than CAC.

Surface Patterning of Benzene Carboxylic Acids on Graphite: Influence of structure, solvent, and concentration on molecular self-assembly

Science.gov (United States)

Florio, Gina; Stiso, Kimberly; Campanelli, Joseph; Dessources, Kimberly; Folkes, Trudi

2012-02-01

Scanning tunneling microscopy (STM) was used to investigate the molecular self-assembly of four different benzene carboxylic acid derivatives at the liquid/graphite interface: pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), trimellitic acid (1,2,4-benzenetricarboxylic acid), trimesic acid (1,3,5-benzenetricarboxylic acid), and 1,3,5-benzenetriacetic acid. A range of two dimensional networks are observed that depend sensitively on the number of carboxylic acids present, the nature of the solvent, and the solution concentration. We will describe our recent efforts to determine (a) the preferential two-dimensional structure(s) for each benzene carboxylic acid at the liquid/graphite interface, (b) the thermodynamic and kinetic factors influencing self-assembly (or lack thereof), (c) the role solvent plays in the assembly, (e) the effect of in situ versus ex situ dilution on surface packing density, and (f) the temporal evolution of the self-assembled monolayer. Results of computational analysis of analog molecules and model monolayer films will also be presented to aid assignment of network structures and to provide a qualitative picture of surface adsorption and network formation.

Elaboration of aluminum oxide-based graphite containing castables

Science.gov (United States)

Zhou, Ningsheng

The aim of this work was set to develop effective and practicable new methods to incorporate natural flake graphite (FG) into the Al2O 3 based castables for iron and steel making applications. Three approaches, viz. micro-pelletized graphite (PG), crushed briquette of Al2O3-graphite (BAG) and TiO2 coated graphite (CFG), have been developed to insert flake graphite into Al2O 3 rich Al2O3-SiC based and Al2O 3-MgO based castables. These approaches were put into effect as countermeasures against the problems caused by FG in order: (1) to agglomerate the FG powders so as to decrease the specific surface area; (2) to diminish the density difference by using crushed carbon bonded compact of oxide-FG mixture; (3) to modify the surface of the flake graphite by forming hydrophilic coating; (4) to control the dispersion state of the graphite in the castable to maintain enough bonding strength; and (5) to use appropriate antioxidants to inhibit the oxidation of FG. The whole work was divided into two stages. In stage one, Al2O 3-SiC-C castables were dealt with to compare 4 modes of inserting graphite, i.e., by PG, BAG, CFG and FG. Overall properties were measured, all in correlation with graphite amount and incorporating mode. In stage two, efforts were made to reduce water demand in the Al2O3-MgO castables system. For this purpose, the matrix portion of the castable mixes was extracted and a coaxial double cylinder viscometer was adopted to investigate rheological characteristics of the matrix slurries vs. 4 kinds of deflocculants, through which the best deflocculant and its appropriate amount were found. Efforts were then made to add up to 30% MgO into the castables, using a limited amount of powders (antioxidants, Si, SiC, B4C and ZrB2, were added respectively or in combination. Overall properties of the castables, were investigated in correlation with MgO amount and graphite and antioxidant packages. Optimization work on oxidation and slag resistance was pursued. Finally

Review: BNL Tokamak graphite blanket design concepts

International Nuclear Information System (INIS)

Fillo, J.A.; Powell, J.R.

1976-01-01

The BNL minimum activity graphite blanket designs are reviewed, and three are discussed in the context of an experimental power reactor (EPR) and commercial power reactor. Basically, the three designs employ a 30 cm or thicker graphite screen. Bremsstrahlung energy is deposited on the graphite surface and re-radiated away as thermal radiation. Fast neutrons are slowed down in the graphite, depositing most of their energy, which is then radiated to a secondary blanket with coolant tubes, as in types A and B, or removed by intermittent direct gas cooling (type C). In types A and B, radiation damage to the coolant tubes in the secondary blanket is reduced by one or two orders of magnitude, while in type C, the blanket is only cooled when the reactor is shut down, so that coolant cannot quench the plasma. (Auth.)

Nitrogen-doped graphene as transparent counter electrode for efficient dye-sensitized solar cells

International Nuclear Information System (INIS)

Wang, Guiqiang; Fang, Yanyan; Lin, Yuan; Xing, Wei; Zhuo, Shuping

2012-01-01

Graphical abstract: Display Omitted Highlights: ► NG sheets are prepared through a hydrothermal reduction of graphite oxide. ► The transparent NG counter electrodes of DSCs are fabricated at room temperature. ► Transparent NG electrode exhibits excellent catalytic activity for the reduction of I 3 − . ► The DSC with NG electrode achieves a comparable efficiency to that of the Pt-based cell. ► The efficiency of rear illumination is about 85% that of front illumination. -- Abstract: Nitrogen-doped graphene sheets are prepared through a hydrothermal reduction of graphite oxide in the presence of ammonia and applied to fabricate the transparent counter electrode of dye-sensitized solar cells. The atomic percentage of nitrogen in doped graphene sample is about 2.5%, and the nitrogen bonds display pyridine and pyrrole-like configurations. Cyclic voltammetry studies demonstrate a much higher electrocatalytic activity toward I − /I 3 − redox reaction for nitrogen-doped graphene, as compared with pristine graphene. The dye-sensitized solar cell with this transparent nitrogen-doped graphene counter electrode shows conversion efficiencies of 6.12% and 5.23% corresponding to front-side and rear-side illumination, respectively. Meanwhile, the cell with a Pt counter electrode shows a conversion efficiency of 6.97% under the same experimental condition. These promising results highlight the potential application of nitrogen-doped graphene in cost-effective, transparent dye-sensitized solar cells.

Direct brazing of ceramics, graphite, and refractory metals

International Nuclear Information System (INIS)

Canonico, D.A.; Cole, N.C.; Slaughter, G.M.

1976-03-01

ORNL has been instrumental in the development of brazing filler metals for joining ceramics, graphite, and refractory metals for application at temperatures above 1000 0 C. The philosophy and techniques employed in the development of these alloys are presented. A number of compositions are discussed that have been satisfactorily used to braze ceramics, graphite, and refractory metals without a prior surface treatment. One alloy, Ti--25 percent Cr--21 percent V, has wet and flowed on aluminum oxide and graphite. Further, it has been utilized in making brazes between different combinations of the three subject materials. The excellent flowability of this alloy and alloys from the Ti--Zr--Ge system is evidenced by the presence of filler metal in the minute pores of the graphite and ceramics

Molecular Structure and Dynamics in Thin Water Films at the Silica and Graphite Surfaces

Energy Technology Data Exchange (ETDEWEB)

Argyris, Dr. Dimitrios [University of Oklahoma; Tummala, Dr. Naga Rajesh [University of Oklahoma; StrioloDr., A [Vanderbilt University; Cole, David R [ORNL

2008-01-01

The structure and dynamic properties of interfacial water at the graphite and silica solid surfaces were investigated using molecular dynamics simulations. The effect of surface properties on the characteristics of interfacial water was quantified by computing density profiles, radial distribution functions, surface density distributions, orientation order parameters, and residence and reorientation correlation functions. In brief, our results show that the surface roughness, chemical heterogeneity, and surface heterogeneous charge distribution affect the structural and dynamic properties of the interfacial water molecules, as well as their rate of exchange with bulk water. Most importantly, our results indicate the formation of two distinct water layers at the SiO2 surface covered by a large density of hydroxyl groups. Further analysis of the data suggests a highly confined first layer where the water molecules assume preferential hydrogen-down orientation and a second layer whose behavior and characteristics are highly dependent on those of the first layer through a well-organized hydrogen bond network. The results suggest that water-water interactions, in particular hydrogen bonds, may be largely responsible for macroscopic interfacial properties such as adsorption and contact angle.

Chemical vapor deposition of TiB2 on graphite

International Nuclear Information System (INIS)

Pierson, H.O.; Randich, E.; Mattox, D.M.

1978-01-01

This study is an experimental investigation of the coating of graphite with TiB 2 by chemical vapor deposition (CVD) using the hydrogen reduction of BCl 3 and TiCl 4 at 925 0 C and 1 atm. Reasonable matching of the thermal expansion of TiB 2 and graphite was necessary to eliminate cracking. A suitable graphite was POCO DFP-1. Adhesion was improved by having a slightly rough graphite surface. Heat treatment at 2000 0 C and above resulted in a certain degree of diffusion. No melting or solid phases other than TiB 2 and graphite were detected up to 2400 0 C. The coatings showed no failure when repeatedly submitted to an electron beam pulse of 2 KW/cm 2 for 0.8 sec

Characterization of graphite dust produced by pneumatic lift

Energy Technology Data Exchange (ETDEWEB)

Shen, Ke [Guangdong Provincial Key Laboratory of Thermal Management Engineering and Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong (China); Peng, Wei; Liu, Bing [Institute of Nuclear and New Energy Technology of Tsinghua University, Advanced Nuclear Energy Technology Cooperation Innovation Center, The Key Laboratory of Advanced Nuclear Engineering and Safety, Ministry of Education, Beijing 100084 (China); Kang, Feiyu [Guangdong Provincial Key Laboratory of Thermal Management Engineering and Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, Guangdong (China); Yang, Xiaoyong; Li, Weihua [Institute of Nuclear and New Energy Technology of Tsinghua University, Advanced Nuclear Energy Technology Cooperation Innovation Center, The Key Laboratory of Advanced Nuclear Engineering and Safety, Ministry of Education, Beijing 100084 (China); Yu, Suyuan, E-mail: suyuan@tsinghua.edu.cn [Center for Combustion Energy, The Key Laboratory for Thermal Science and Power Engineering, Ministry of Educations, Tsinghua University, Beijing 100084 (China)

2016-08-15

Highlights: • Generation of graphite dust by pneumatic lift. • Determination of morphology and particle size distribution of graphite dust. • The size of graphite dust in this study is compared to AVR and THTR-300 results. • Graphite dust originates from both filler and binder of the matrix graphite. - Abstract: Graphite dust is an important safety concern of high-temperature gas-cooled reactor (HTR). The graphite dust could adsorb fission products, and the radioactive dust is transported by the coolant gas and deposited on the surface of the primary loop. The simulation of coagulation, aggregation, deposition, and resuspension behavior of graphite dust requires parameters such as particle size distribution and particle shape, but currently very limited data on graphite dust is available. The only data we have are from AVR and THTR-300, however, the AVR result is likely to be prejudiced by the oil ingress. In pebble-bed HTR, graphite dust is generally produced by mechanical abrasion, in particular, by the abrasion of graphite pebbles in the lifting pipe of the fuel handling system. Here we demonstrate the generation and characterization of graphite dust that were produced by pneumatic lift. This graphite dust could substitute the real dust in HTR for characterization. The dust, exhibiting a lamellar morphology, showed a number-weighted average particle size of 2.38 μm and a volume-weighted average size of 14.62 μm. These two sizes were larger than the AVR and THTR results. The discrepancy is possibly due to the irradiation effect and prejudice caused by the oil ingress accident. It is also confirmed by the Raman spectrum that both the filler particle and binder contribute to the dust generation.

Influence of silver doping on surface defect characteristics of TiO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Tripathi, S. K., E-mail: surya@pu.ac.in [Department of Physics, Center of Advanced Study in Physics, Panjab University, Chandigarh-160 014 (India); Rani, Mamta [Department of Physics, Center of Advanced Study in Physics, Panjab University, Chandigarh-160 014 (India); Department of Physics, DAV University Jalandhar, - 144 001, Punjab (India)

2015-08-28

In the present work, we proposed a novel silver doped TiO{sub 2} polyethylene conjugated films to improve the performance of DSSCs. Oxides nanoparticles dispersed in a semiconducting polymer form the active layer of a solar cell. Localized surface plasmon resonance effects associated with spatially dispersed silver (Ag) nanoparticles can be exploited to enhance the light-harvesting efficiency, the photocurrent density and the overall light-to electrical-energy-conversion efficiency of high-area DSSCs based TiO{sub 2} photoanodes. Silver doped titanium dioxide (TiO{sub 2}:Ag) is prepared by sol-gel technique and deposited on fluorine doped indium oxide (FTO) coated glass substrates by using doctor blade technique at 550°C from aqueous solutions of titanium butoxide and silver nitrate precursors. The effect of Ag doping on electrical properties of films is studied. The Ag-TiO{sub 2} films are about 548 times more photosensitive as compare to the pure TiO{sub 2} sample. The presence of metallic Ag nanoparticles and oxygen vacancy on the surface of TiO{sub 2} nanoparticles promotes the separation of photogenerated electron-hole pairs and thus enhances the photosensitivity. Photoconduction mechanism of all prepared samples is investigated by performing transient photoconductivity measurements on TiO{sub 2} and Ag-TiO{sub 2} films keeping intensity of light constant.

Nitrogen-doped graphene network supported copper nanoparticles encapsulated with graphene shells for surface-enhanced Raman scattering

Science.gov (United States)

Zhang, Xiang; Shi, Chunsheng; Liu, Enzuo; Li, Jiajun; Zhao, Naiqin; He, Chunnian

2015-10-01

In this study, we demonstrated nitrogen-doped graphene network supported few-layered graphene shell encapsulated Cu nanoparticles (NPs) (Cu@G-NGNs) as a sensing platform, which were constructed by a simple and scalable in situ chemical vapor deposition (CVD) technique with the assistance of a self-assembled three-dimensional (3D) NaCl template. Compared with pure Cu NPs and graphene decorated Cu NPs, the graphene shells can strengthen the plasmonic coupling between graphene and Cu, thereby contributing to an obvious improvement in the local electromagnetic field that was validated by finite element numerical simulations, while the 3D nitrogen-doped graphene walls with a large surface area facilitated molecule adsorption and the doped nitrogen atoms embedded in the graphene lattice can reduce the surface energy of the system. With these merits, a good surface enhanced Raman spectroscopy (SERS) activity of the 3D Cu@G-NGN painting film on glass was demonstrated using rhodamine 6G and crystal violet as model analytes, exhibiting a satisfactory sensitivity, reproducibility and stability. As far as we know, this is the first report on the in situ synthesis of nitrogen-doped graphene/copper nanocomposites and this facile and low-cost Cu-based strategy tends to be a good supplement to Ag and Au based substrates for SERS applications.In this study, we demonstrated nitrogen-doped graphene network supported few-layered graphene shell encapsulated Cu nanoparticles (NPs) (Cu@G-NGNs) as a sensing platform, which were constructed by a simple and scalable in situ chemical vapor deposition (CVD) technique with the assistance of a self-assembled three-dimensional (3D) NaCl template. Compared with pure Cu NPs and graphene decorated Cu NPs, the graphene shells can strengthen the plasmonic coupling between graphene and Cu, thereby contributing to an obvious improvement in the local electromagnetic field that was validated by finite element numerical simulations, while the 3D nitrogen-doped

Irradiation test plan of oxidation-resistant graphite in WWR-K Research Reactor

International Nuclear Information System (INIS)

Sumita, Junya; Shibata, Taiju; Sakaba, Nariaki; Osaki, Hirotaka; Kato, Hideki; Fujitsuka, Kunihiro; Muto, Takenori; Gizatulin, Shamil; Shaimerdenov, Asset; Dyussambayev, Daulet; Chakrov, Petr

2014-01-01

Graphite materials are used for the in-core components of High Temperature Gas-cooled Reactor (HTGR) which is a graphite-moderated and helium gas-cooled reactor. In the case of air ingress accident in HTGR, SiO_2 protective layer is formed on the surface of SiC layer in TRISO CFP and oxidation of SiC does not proceed and fission products are retained inside the fuel particle. A new safety concept for the HTGR, called Naturally Safe HTGR, has been recently proposed. To enhance the safety of Naturally Safe HTGR ultimately, it is expected that oxidation-resistant graphite is used for graphite components to prevent the TRISO CFPs and fuel compacts from failure. SiC coating is one of candidate methods for oxidation-resistant graphite. JAEA and four graphite companies launched R&Ds to develop the oxidation-resistant graphite and the International Science and Technology Center (ISTC) partner project with JAEA and INP was launched to investigate the irradiation effects on the oxidation-resistant graphite. To determine grades of the oxidation-resistant graphite which will be adopted as irradiation test, a preliminary oxidation test was carried out. This paper described the results of the preliminary oxidation test, the plan of out-of-pile test, irradiation test and post-irradiation test (PIE) of the oxidation-resistant graphite. The results of the preliminary oxidation test showed that the integrity of the oxidation resistant graphite was confirmed and that all of grades used in the preliminary test can be adopted as the irradiation test. Target irradiation temperature was determined to be 1473 (K) and neutron fluence was determined to be from 0.54 × 10"2"5through 1.4 × 10"2"5 (/m"2, E>0.18MeV). Weight change, oxidation rate, activation energy, surface condition, etc. will be evaluated in out-of-pile test and weight change, irradiation effect on oxidation rate and activation energy, surface condition, etc. will be evaluated in PIE. (author)

Surface structure modification of single crystal graphite after slow, highly charged ion irradiation

Science.gov (United States)

Alzaher, I.; Akcöltekin, S.; Ban-d'Etat, B.; Manil, B.; Dey, K. R.; Been, T.; Boduch, P.; Rothard, H.; Schleberger, M.; Lebius, H.

2018-04-01

Single crystal graphite was irradiated by slow, highly charged ions. The modification of the surface structure was studied by means of Low-Energy Electron Diffraction. The observed damage cross section increases with the potential energy, i.e. the charge state of the incident ion, at a constant kinetic energy. The potential energy is more efficient for the damage production than the kinetic energy by more than a factor of twenty. Comparison with earlier results hints to a strong link between early electron creation and later target atom rearrangement. With increasing ion fluence, the initially large-scale single crystal is first transformed into μ m-sized crystals, before complete amorphisation takes place.

Friction and wear of carbon-graphite materials for high-energy brakes

Science.gov (United States)

Bill, R. C.

1978-01-01

Caliper type brake simulation experiments were conducted on seven different carbon graphite materials formulations against a steel disk material and against a carbon graphite disk material. The effects of binder level, boron carbide (B4C) additions, SiC additions, graphite fiber additions, and graphite cloth reinforcement on friction and wear behavior were investigated. Reductions in binder level, additions of B4C, and additions of SiC each resulted in increased wear. The wear rate was not affected by the addition of graphite fibers. Transition to severe wear and high friction was observed in the case of graphite-cloth-reinforced carbon sliding against a disk of similar composition. The transition was related to the disruption of a continuous graphite shear film that must form on the sliding surfaces if low wear is to occur.

Surface photovoltage in heavily doped GaN:Si,Zn

Science.gov (United States)

McNamara, J. D.; Behrends, A.; Mohajerani, M. S.; Bakin, A.; Waag, A.; Baski, A. A.; Reshchikov, M. A.

2014-02-01

In n-type GaN, an upward band bending of about 1 eV is caused by negative charge at the surface. UV light reduces the band bending by creating a surface photovoltage (SPV), which can be measured by a Kelvin probe. Previously, we reported a fast SPV signal of about 0.6 eV in undoped and moderately doped GaN. In this work, we have studied degenerate GaN co-doped with Zn and Si, with a Si concentration of about 1019 cm-3 and a Zn concentration of 6×1017 cm-3. At room temperature, a fast component of about 0.6 eV was observed. However, after preheating the sample at 600 K for one hour and subsequently cooling the sample to 300 K (all steps performed in vacuum), the fast component disappeared. Instead, a very slow (minutes) and logarithmic in time rise of the SPV was observed with UV illumination. The total change in SPV was about 0.4 eV. This slow SPV transient can be reversibly converted into the "normal" fast (subsecond) rise by letting air or dry oxygen in at room temperature. Possible explanations of the observed unusual SPV transients are discussed.

Enhancing biodegradation and energy generation via roughened surface graphite electrode in microbial desalination cell.

Science.gov (United States)

Ebrahimi, Atieh; Yousefi Kebria, Daryoush; Najafpour Darzi, Ghasem

2017-09-01

The microbial desalination cell (MDC) is known as a newly developed technology for water and wastewater treatment. In this study, desalination rate, organic matter removal and energy production in the reactors with and without desalination function were compared. Herein, a new design of plain graphite called roughened surface graphite (RSG) was used as the anode electrode in both microbial fuel cell (MFC) and MDC reactors for the first time. Among the three type of anode electrodes investigated in this study, RSG electrode produced the highest power density and salt removal rate of 10.81 W/m 3 and 77.6%, respectively. Such a power density was 2.33 times higher than the MFC reactor due to the junction potential effect. In addition, adding the desalination function to the MFC reactor enhanced columbic efficiency from 21.8 to 31.4%. These results provided a proof-of-concept that the use of MDC instead of MFC would improve wastewater treatment efficiency and power generation, with an added benefit of water desalination. Furthermore, RSG can successfully be employed in an MDC or MFC, enhancing the bio-electricity generation and salt removal.

Thermoexpanded graphite modification by titanium dioxide

International Nuclear Information System (INIS)

Semko, L.S.; Gorbik, P.P.; Chujko, O.O.; Kruchek, Ya.Yi.; Dzyubenko, L.S.; Orans'ka, O.Yi.

2006-01-01

A method of the synthesis of thermoexpanded graphite (TEG) powders coated by titanium dioxide is developed. The conversion of n-buthylorthotitanate into TiO 2 on the TEG surface is investigated. The optimal parameters of the synthesis and the structure of titanium dioxide clusters on the TEG surface are determined

Transient photoresponse of nitrogen-doped ultrananocrystalline diamond electrodes in saline solution

Energy Technology Data Exchange (ETDEWEB)

Ahnood, Arman, E-mail: arman.ahnood@unimelb.edu.au; Ganesan, Kumaravelu; Stacey, Alastair; Prawer, Steven [School of Physics, University of Melbourne, Melbourne, Victoria 3010 (Australia); Simonov, Alexandr N.; Spiccia, Leone [School of Chemistry and the ARC Centre of Excellence for Electromaterials Science, Monash University, Melbourne, Victoria 3800 (Australia); Laird, Jamie S. [CSIRO, Minerals Resources Flagship, School of Physics, University of Melbourne, Melbourne, Victoria 3010 (Australia); Maturana, Matias I. [National Vision Research Institute, Australian College of Optometry, Carlton, Victoria 3053 (Australia); NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of Melbourne, Parkville, Victoria 3010 (Australia); Ibbotson, Michael R. [National Vision Research Institute, Australian College of Optometry, Carlton, Victoria 3053 (Australia); ARC Centre of Excellence for Integrative Brain Function, Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Victoria 3010 (Australia)

2016-03-07

Beyond conventional electrically-driven neuronal stimulation methods, there is a growing interest in optically-driven approaches. In recent years, nitrogen-doped ultrananocrystalline diamond (N-UNCD) has emerged as a strong material candidate for use in electrically-driven stimulation electrodes. This work investigates the electrochemical activity of N-UNCD in response to pulsed illumination, to assess its potential for use as an optically-driven stimulation electrode. Whilst N-UNCD in the as-grown state exhibits a weak photoresponse, the oxygen plasma treated film exhibits two orders of magnitude enhancement in its sub-bandgap open circuit photovoltage response. The enhancement is attributed to the formation of a dense network of oxygen-terminated diamond nanocrystals at the N-UNCD surface. Electrically connected to the N-UNCD bulk via sub-surface graphitic grain boundaries, these diamond nanocrystals introduce a semiconducting barrier between the sub-surface graphitic semimetal and the electrolyte solution, leading to a photovoltage under irradiation with wavelengths of λ = 450 nm and shorter. Within the safe optical exposure limit of 2 mW mm{sup −2}, charge injection capacity of 0.01 mC cm{sup −2} is achieved using a 15 × 15 μm electrode, meeting the requirements for extracellular and intercellular stimulation. The nanoscale nature of processes presented here along with the diamond's biocompatibility and biostability open an avenue for the use of oxygen treated N-UNCD as optically driven stimulating electrodes.

Transient photoresponse of nitrogen-doped ultrananocrystalline diamond electrodes in saline solution

International Nuclear Information System (INIS)

Ahnood, Arman; Ganesan, Kumaravelu; Stacey, Alastair; Prawer, Steven; Simonov, Alexandr N.; Spiccia, Leone; Laird, Jamie S.; Maturana, Matias I.; Ibbotson, Michael R.

2016-01-01

Beyond conventional electrically-driven neuronal stimulation methods, there is a growing interest in optically-driven approaches. In recent years, nitrogen-doped ultrananocrystalline diamond (N-UNCD) has emerged as a strong material candidate for use in electrically-driven stimulation electrodes. This work investigates the electrochemical activity of N-UNCD in response to pulsed illumination, to assess its potential for use as an optically-driven stimulation electrode. Whilst N-UNCD in the as-grown state exhibits a weak photoresponse, the oxygen plasma treated film exhibits two orders of magnitude enhancement in its sub-bandgap open circuit photovoltage response. The enhancement is attributed to the formation of a dense network of oxygen-terminated diamond nanocrystals at the N-UNCD surface. Electrically connected to the N-UNCD bulk via sub-surface graphitic grain boundaries, these diamond nanocrystals introduce a semiconducting barrier between the sub-surface graphitic semimetal and the electrolyte solution, leading to a photovoltage under irradiation with wavelengths of λ = 450 nm and shorter. Within the safe optical exposure limit of 2 mW mm"−"2, charge injection capacity of 0.01 mC cm"−"2 is achieved using a 15 × 15 μm electrode, meeting the requirements for extracellular and intercellular stimulation. The nanoscale nature of processes presented here along with the diamond's biocompatibility and biostability open an avenue for the use of oxygen treated N-UNCD as optically driven stimulating electrodes.

Microstructure and Wear Behavior of TiC Coating Deposited on Spheroidized Graphite Cast Iron Using Laser Surfacing

Directory of Open Access Journals (Sweden)

E. R. I. Mahmoud

2014-10-01

Full Text Available Spheroidal graphite cast iron was laser cladded with TiC powder using a YAG fiber laser at powers of 700, 1000, 1500 and 2000 W. The powder was preplaced on the surface of the specimens with 0.5 mm thickness. Sound cladding and fusion zones were observed at 700, 1000 and 1500 W powers. However, at 2000 W, cracking was observed in the fusion zone. At 700 W, a build-up zone consisted of fine TiC dendrites inside a matrix composed of martensite, cementite (Fe3C, and some blocks of retained austenite was observed. In this zone, all graphite nodules were totally melted. In the fusion zone, some undissolved and partially dissolved graphite nodules appeared in a matrix containing bainite, ferrite, martensite and retained austenite. At 1500 W, the fusion zone had more iron carbides and ferrite, and the HAZ consisted of martensitic structure. At 2000 W, the build-up zone was consisted of TiC particles precipitated in a matrix of eutectic carbides, martensite plus an inter-lamellar retained austenite. The hardness of the cladded area was remarkably improved (1330 HV in case of 700 W: 5.5 times of the hardness of substrate

Influence of the surface chemistry on the nanotribological behaviour of (AFM tip/graphite) couples

International Nuclear Information System (INIS)

Jradi, Khalil; Schmitt, Marjorie; Bistac, Sophie

2012-01-01

The development of the nanotechnology has made essential the knowledge of the tribological behaviour of carbonaceous materials, and more particularly of graphite. Atomic force microscopy (AFM) is thus used to study the friction properties at this nanoscopic scale. In this work, results concerning the friction of AFM tips against graphite pins are presented, with a particular emphasis on the effect of the chemical modification of these tips on the tribological behaviour of graphite.

New insights into canted spiro carbon interstitial in graphite

Science.gov (United States)

EL-Barbary, A. A.

2017-12-01

The self-interstitial carbon is the key to radiation damage in graphite moderator nuclear reactor, so an understanding of its behavior is essential for plant safety and maximized reactor lifetime. The density functional theory is applied on four different graphite unit cells, starting from of 64 carbon atoms up to 256 carbon atoms, using AIMPRO code to obtain the energetic, athermal and mechanical properties of carbon interstitial in graphite. This study presents first principles calculations of the energy of formation that prove its high barrier to athermal diffusion (1.1 eV) and the consequent large critical shear stress (39 eV-50 eV) necessary to shear graphite planes in its presence. Also, for the first time, the gamma surface of graphite in two dimensions is calculated and found to yield the critical shear stress for perfect graphite. Finally, in contrast to the extensive literature describing the interstitial of carbon in graphite as spiro interstitial, in this work the ground state of interstitial carbon is found to be canted spiro interstitial.

Degradation of unglazed rough graphite-aluminium solar absorber surfaces in simulated acid and neutral rain

International Nuclear Information System (INIS)

Konttinen, P.; Lund, P.D.; Salo, T.

2005-01-01

Degradation mechanisms of unglazed solar absorber surfaces based on aluminium substrate were studied. Rough graphite-aluminium surfaces were total-immersion subjected to aerated and de-aerated simulated neutral and acid rain. Test conditions were based on calculated absorber stagnation temperature and global rain acidity measurements. Changes in optical properties, elemental composition and sample mass were examined by spectrometry, energy dispersive X-ray spectrometry and thermogravimetry, respectively. The absorbers exhibited almost no degradation at pH value of 3.5. At pH 5.5 alumina on the surface hydrated significantly degrading the optical properties of the surfaces severely in most cases. Therefore these absorber surfaces can not be recommended to be used in non-glazed applications if they are exposed to rain with pH exceeding ∼ 3.5-4.5. The total-immersion test needs to be developed further as the test results exhibited poor temperature and time dependency thus preventing accurate service lifetime estimates. Still, these tests were useful in determining favourable and non-favourable operating conditions for the absorber surfaces based on aluminium substrate. (author)

Patterned structures of graphene and graphitic carbon and methods for their manufacture

Energy Technology Data Exchange (ETDEWEB)

Polsky, Ronen; Xiao, Xiaoyin; Burckel, David Bruce; Wheeler, David R.; Brozik, Susan M.; Beechem, Thomas Edwin

2018-01-09

A patterned graphene or graphitic body is produced by providing a three-dimensionally patterned carbonaceous body; coating the body with a catalytic metal whereby is formed a coating having an inner surface proximal the body and an outer surface distal the body; and annealing the coated body under time and temperature conditions effective to form a graphene or graphitic layer on the outer surface of the catalytic metal coating.

Release enhancement of tritium from graphite by addition of hydrogen

International Nuclear Information System (INIS)

Saeki, Masakatsu; Masaki, N.M.

1989-01-01

The release behavior of tritium from graphite was studied in pure He and He + H 2 atmosphere. The release from powdered graphite was significantly enhanced in hydrogen environment. Apparent diffusion coefficients of tritium in graphite also became much higher in an atmosphere containing hydrogen than values obtained in pure helium atmosphere. A careful investigation of the release processes resulted in the conclusion that the most important process of tritium behaviour in graphite was diffusion, but the desorption process of tritium from the surface played a significant role. The enhancement of the desorption process was controlled by atomic hydrogen. (orig.)

Studies of mechanical properties and irradiation damage nucleation of HTGR graphites. Final report

International Nuclear Information System (INIS)

Thrower, P.A.

1981-05-01

Since the submission of the last report (COO-2712-6) work has concentrated on the examination of the effects of oxidation on the compressive strengths of graphites doped with iron, vanadium and calcium. The purpose of the investigation was to determine the relative effects of the impurities on the rates of oxidation in air, CO 2 and H 2 O and the resultant reduction in compressive strength

Preparation of nanoporous carbons from graphite nanofibres

Energy Technology Data Exchange (ETDEWEB)

Kim, Byung-Joo [Department of Green Chemistry and Environmental Biotechnology, University of Science and Technology, PO Box 107, Yuseong, Daejeon 305-600 (Korea, Republic of); Park, Soo-Jin [Department of Chemistry, Inha University, 253, Nam-gu, Incheon 402-751 (Korea, Republic of)

2006-09-14

In this study we manufactured highly porous graphite nanofibres (GNFs) by physical activation in order to develop promising energy storage materials. The activation was performed at activation temperatures in the range of 800-1050 deg. C. The pore structures of the porous GNFs were analysed using N{sub 2}/77 K adsorption isotherms. After the activation, the porous GNFs showed a decrease in diameter and scratches on their surfaces, resulting from surface oxidation and the opening of the graphitic layers, respectively. It was found that the specific surface area of the porous GNFs prepared at 1050 deg. C was more than 2000 m{sup 2} g{sup -1} without loss of their fibre shape or serious increase in electrical resistivity. This result indicates that porous GNFs prepared under optimal conditions can have a much higher specific surface area and are promising materials for energy storage technologies.

Superlubricity of Graphite Induced by Multiple Transferred Graphene Nanoflakes.

Science.gov (United States)

Li, Jinjin; Gao, Tianyang; Luo, Jianbin

2018-03-01

2D or 3D layered materials, such as graphene, graphite, and molybdenum disulfide, usually exhibit superlubricity properties when sliding occurs between the incommensurate interface lattices. This study reports the superlubricity between graphite and silica under ambient conditions, induced by the formation of multiple transferred graphene nanoflakes on the asperities of silica surfaces after the initial frictional sliding. The friction coefficient can be reduced to as low as 0.0003 with excellent robustness and is independent of the surface roughness, sliding velocities, and rotation angles. The superlubricity mechanism can be attributed to the extremely weak interaction and easy sliding between the transferred graphene nanoflakes and graphite in their incommensurate contact. This finding has important implications for developing approaches to achieve superlubricity of layered materials at the nanoscale by tribointeractions.

Controllable magnetic doping of the surface state of a topological insulator

DEFF Research Database (Denmark)

Schlenk, T.; Bianchi, M.; Koleini, Mohammad

2013-01-01

A combined experimental and theoretical study of doping individual Fe atoms into Bi2Se3 is presented. It is shown through a scanning tunneling microscopy study that single Fe atoms initially located at hollow sites on top of the surface (adatoms) can be incorporated into subsurface layers by ther...

Electrochemical Ultracapacitors Using Graphitic Nanostacks

Science.gov (United States)

Marotta, Christopher

2012-01-01

Electrochemical ultracapacitors (ECs) have been developed using graphitic nanostacks as the electrode material. The advantages of this technology will be the reduction of device size due to superior power densities and relative powers compared to traditional activated carbon electrodes. External testing showed that these materials display reduced discharge response times compared to state-of-the-art materials. Such applications are advantageous for pulsed power applications such as burst communications (satellites, cell phones), electromechanical actuators, and battery load leveling in electric vehicles. These carbon nanostructures are highly conductive and offer an ordered mesopore network. These attributes will provide more complete electrolyte wetting, and faster release of stored charge compared to activated carbon. Electrochemical capacitor (EC) electrode materials were developed using commercially available nanomaterials and modifying them to exploit their energy storage properties. These materials would be an improvement over current ECs that employ activated carbon as the electrode material. Commercially available graphite nanofibers (GNFs) are used as precursor materials for the synthesis of graphitic nanostacks (GNSs). These materials offer much greater surface area than graphite flakes. Additionally, these materials offer a superior electrical conductivity and a greater average pore size compared to activated carbon electrodes. The state of the art in EC development uses activated carbon (AC) as the electrode material. AC has a high surface area, but its small average pore size inhibits electrolyte ingress/egress. Additionally, AC has a higher resistivity, which generates parasitic heating in high-power applications. This work focuses on fabricating EC from carbon that has a very different structure by increasing the surface area of the GNF by intercalation or exfoliation of the graphitic basal planes. Additionally, various functionalities to the GNS

Process for the fabrication of aluminum metallized pyrolytic graphite sputtering targets

Science.gov (United States)

Makowiecki, Daniel M.; Ramsey, Philip B.; Juntz, Robert S.

1995-01-01

An improved method for fabricating pyrolytic graphite sputtering targets with superior heat transfer ability, longer life, and maximum energy transmission. Anisotropic pyrolytic graphite is contoured and/or segmented to match the erosion profile of the sputter target and then oriented such that the graphite's high thermal conductivity planes are in maximum contact with a thermally conductive metal backing. The graphite contact surface is metallized, using high rate physical vapor deposition (HRPVD), with an aluminum coating and the thermally conductive metal backing is joined to the metallized graphite target by one of four low-temperature bonding methods; liquid-metal casting, powder metallurgy compaction, eutectic brazing, and laser welding.

Packaging material and flexible medical tubing containing thermally exfoliated graphite oxide

Science.gov (United States)

Prud'homme, Robert K. (Inventor); Aksay, Ilhan A. (Inventor)

2011-01-01

A packaging material or flexible medical tubing containing a modified graphite oxide material, which is a thermally exfoliated graphite oxide with a surface area of from about 300 m.sup.2/g to 2600 m.sup.2/g.

Fe/N/C hollow nanospheres by Fe(iii)-dopamine complexation-assisted one-pot doping as nonprecious-metal electrocatalysts for oxygen reduction

Science.gov (United States)

Zhou, Dan; Yang, Liping; Yu, Linghui; Kong, Junhua; Yao, Xiayin; Liu, Wanshuang; Xu, Zhichuan; Lu, Xuehong

2015-01-01

In this work, a series of hollow carbon nanospheres simultaneously doped with N and Fe-containing species are prepared by Fe3+-mediated polymerization of dopamine on SiO2 nanospheres, carbonization and subsequent KOH etching of the SiO2 template. The electrochemical properties of the hollow nanospheres as nonprecious-metal electrocatalysts for oxygen reduction reaction (ORR) are characterized. The results show that the hollow nanospheres with mesoporous N-doped carbon shells of ~10 nm thickness and well-dispersed Fe3O4 nanoparticles prepared by annealing at 750 °C (Fe/N/C HNSs-750) exhibit remarkable ORR catalytic activity comparable to that of a commercial 20 wt% Pt/C catalyst, and high selectivity towards 4-electron reduction of O2 to H2O. Moreover, it displays better electrochemical durability and tolerance to methanol crossover effect in an alkaline medium than the Pt/C. The excellent catalytic performance of Fe/N/C HNSs-750 towards ORR can be ascribed to their high specific surface area, mesoporous morphology, homogeneous distribution of abundant active sites, high pyridinic nitrogen content, graphitic nitrogen and graphitic carbon, as well as the synergistic effect of nitrogen and iron species for catalyzing ORR.In this work, a series of hollow carbon nanospheres simultaneously doped with N and Fe-containing species are prepared by Fe3+-mediated polymerization of dopamine on SiO2 nanospheres, carbonization and subsequent KOH etching of the SiO2 template. The electrochemical properties of the hollow nanospheres as nonprecious-metal electrocatalysts for oxygen reduction reaction (ORR) are characterized. The results show that the hollow nanospheres with mesoporous N-doped carbon shells of ~10 nm thickness and well-dispersed Fe3O4 nanoparticles prepared by annealing at 750 °C (Fe/N/C HNSs-750) exhibit remarkable ORR catalytic activity comparable to that of a commercial 20 wt% Pt/C catalyst, and high selectivity towards 4-electron reduction of O2 to H2O

Adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO surface

KAUST Repository

Yadav, Manoj Kumar

2016-06-16

The adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO(100) surface has been studied employing density functional theory. It is found that all these transition metals (TM) on MgO(100) surface are capable of adsorbing dinitrogen (N2), however there is no dissociative adsorption of N2 on single transition metal dopant. When two TM atoms are doped on MgO(100) surface, dissociative adsorption of dinitrogen occurs in all the three cases. Whether the dissociation is spontaneous or is it associated with activation barrier depends on the orientation of N2 molecule approaching the dopant site.

Measurement of surface recombination velocity on heavily doped indium phosphide

International Nuclear Information System (INIS)

Jenkins, P.; Ghalla-Goradia, M.; Faur, M.; Bailey, S.

1990-01-01

The controversy surrounding the published low values of surface recombination velocity (SRV) in n-InP, solidified in recent years when modeling of existing n/p InP solar cells revealed that the front surface SRV had to be higher than 1 x 10 6 cm/sec in order to justify the poor blue response that is characteristic of all n/p InP solar cells. In this paper, SRV on heavily doped (>10 18 cm -3 )n-type and p-type InP is measured as a function of surface treatment. For the limited range of substrates and surface treatments studied, SRV and surface stability depend strongly on the surface treatment. SRVs of ∼10 5 cm/sec in both p-type and n-type InP are obtainable, but in n-type the low SRV surfaces were unstable, and the only stable surfaces on n-type had SRVs of >10 6 cm/sec

Experimental modelling of plasma-graphite surface interaction in ITER

Energy Technology Data Exchange (ETDEWEB)

Martynenko, Yu.V.; Guseva, M.I.; Gureev, V.M.; Danelyan, L.S.; Neumoin, V.E.; Petrov, V.B.; Khripunov, B.I.; Sokolov, Yu.A.; Stativkina, O.V.; Stolyarova, V.G. [Rossijskij Nauchnyj Tsentr ``Kurchatovskij Inst.``, Moscow (Russian Federation); Vasiliev, V.I.; Strunnikov, V.M. [TRINITI, Troizk (Russian Federation)

1998-10-01

The investigation of graphite erosion under normal operation ITER regime and disruption was performed by means of exposure of RGT graphite samples in a stationary deuterium plasma to a dose of 10{sup 22} cm{sup -2} and subsequent irradiation by power (250 MW/cm{sup 2}) pulse deuterium plasma flow imitating disruption. The stationary plasma exposure was carried out in the installation LENTA with the energy of deuterium ions being 200 eV at target temperatures of 770 C and 1150 C. The preliminary exposure in stationary plasma at temperature of physical sputtering does not essentially change the erosion due to a disruption, whereas exposure at the temperature of radiation enhanced sublimation dramatically increases the erosion due to disruption. In the latter case, the depth of erosion due to a disruption is determined by the depth of a layer with decreased strength. (orig.) 9 refs.

A first principles study of adhesion and electronic structure at Fe (110)/graphite (0001) interface

Energy Technology Data Exchange (ETDEWEB)

Liu, Yangzhen; Xing, Jiandong; Li, Yefei, E-mail: yefeili@126.com; Sun, Liang; Wang, Yong

2017-05-31

Highlights: • The surface energy of graphite (0001) and Fe (110) has been calculated and the number of layers of graphite slab and Fe slab has been estimated. • The work of adhesion of Fe (110)/graphite (0001) interface with different interfacial separation d{sub 0} (1.7–3 Å) has been systematically discussed. • The total electron density and electron density difference of Fe (110)/graphite (0001) are used to study the bonding characteristics. • The Interfacial energy and fracture toughness of Fe (110)/graphite (0001) are estimated. - Abstract: Using first–principles calculations, we discuss the bulk properties of bcc Fe and graphite and that of the surface, the work of adhesion, and the electronic structure of Fe (110)/graphite (0001) interface. In this study, the experimental results of the bulk properties of bcc Fe and graphite reveal that our adopted parameters are reliable. Moreover, the results of surface energy demonstrate that nine atomic layers of graphite (0001) and five atomic layers of Fe (110) exhibit bulk–like interiors. The lattice mismatch of Fe (110)/graphite (0001) interface is about 6%. The results also exhibit that the Fe atom residing on top of the second layer of graphite slab (HCP structure) is the preferred stacking sequence. The work of adhesion (W{sub ad}) of the optimized Fe/graphite interface of HCP structure is 1.36 J/m{sup 2}. Electronic structures indicate that the bonding characteristics are a mixture of covalent and ionic bonds in the HCP interface. Moreover, the magnetic moment of atoms at the interface was studied using the spin polarized density of states.

Analysis of a T-10 graphite limiter

International Nuclear Information System (INIS)

Hildebrandt, D.; Laux, M.; Lingertat, J.; Pech, P.; Reiner, H.D.; Strusny, H.; Wolff, H.

1981-01-01

Parts of a T-10 graphite limiter used during ohmic heated discharges have been investigated. Erosion and deposition phenomena have been studied by morphological and elemental surface analysis methods. From the results estimates of the plasma parameters near the limiter surface have been made. (orig.)

Transition between scanning tunneling microscopy images of alkane derivatives on graphite

International Nuclear Information System (INIS)

Hibino, Masahiro; Tsuchiya, Hiroshi

2015-01-01

Graphical abstract: - Highlights: • SAMs of dialkyl sulfides form at the liquid–graphite interface. • STM contrast of molecules change reversibly between zigzag and aligned bright spot patterns. • The free energy for contrast change is smaller than the thermal energy (RT). • STM contrast change is caused by electronic effects and registry of the alkyl chains. - Abstract: Self-assembled monolayers of alkylated sulfides containing two alkyl chains and a sulfur atom positioned at the center of the molecules were studied on a graphite surface using scanning tunneling microscopy (STM). STM images of the closed-packed alkyl chains that extend linearly from the sulfur atoms change reversibly between a zigzag pattern and an aligned bright spot pattern on a time scale of minutes. The observation times of the zigzag and aligned bright spot patterns indicate that the difference between the free energies of these two stable molecular configurations with respect to the graphite surface is smaller than their thermal energies in the presence of a solvent, and 10 times smaller than the theoretical free energy between parallel and perpendicular configurations of the alkyl chains on graphite under vacuum. The change in the contrast of the STM images occurred owing to the electronic effects that depend on the registry of the alkyl chains on the graphite surface, and not by the classical observation of transfer between parallel and perpendicular orientations of alkyl chains on the surface.

Controllable fabrication of Pt nanocatalyst supported on N-doped carbon containing nickel nanoparticles for ethanol oxidation.

Science.gov (United States)

Yu, Jianguo; Dai, Tangming; Cao, Yuechao; Qu, Yuning; Li, Yao; Li, Juan; Zhao, Yongnan; Gao, Haiyan

2018-08-15

In this paper, platinum nanoparticles were deposited on a carbon carrier with the partly graphitized carbon and the highly dispersive carbon-coated nickel particles. An efficient electron transfer structure can be fabricated by controlling the contents of the deposited platinum. The high resolution transmission electron microscopy images of Pt 2 /Ni@C N-doped sample prove the electron transfer channel from Pt (1 1 1) crystal planes to graphite (1 0 0) or Ni (1 1 1) crystal planes due to these linked together crystal planes. The Pt 3 /Ni@C N-doped with low Pt contents cannot form the electron transfer structure and the Pt 1 /Ni@C N-doped with high Pt contents show an obvious aggregation of Pt nanoparticles. The electrochemical tests of all the catalysts show that the Pt 2 /Ni@C N-doped sample presents the highest catalytic activity, the strongest CO tolerance and the best catalytic stability. The high performance is attributed to the efficient electronic transport structure of the Pt 2 /Ni@C N-doped sample and the synergistic effect between Pt and Ni nanoparticles. This paper provides a promising method for enhancing the conductivity of electrode material. Copyright © 2018 Elsevier Inc. All rights reserved.

Azide photochemistry for facile modification of graphitic surfaces: preparation of DNA-coated carbon nanotubes for biosensing

International Nuclear Information System (INIS)

Moghaddam, Minoo J; Yang Wenrong; Bojarski, Barbara; Gengenbach, Thomas R; Gao Mei; Zareie, Hadi; McCall, Maxine J

2012-01-01

A facile, two-step method for chemically attaching single-stranded DNA to graphitic surfaces, represented here by carbon nanotubes, is reported. In the first step, an azide-containing compound, N-5-azido-nitrobenzoyloxy succinimide (ANB-NOS), is used to form photo-adducts on the graphitic surfaces in a solid-state photochemical reaction, resulting in active ester groups being oriented for the subsequent reactions. In the second step, pre-synthesized DNA strands bearing a terminal amine group are coupled in an aqueous solution with the active esters on the photo-adducts. The versatility of the method is demonstrated by attaching pre-synthesized DNA to surfaces of carbon nanotubes in two platforms—as vertically-aligned multi-walled carbon nanotubes on a solid support and as tangled single-walled carbon nanotubes in mats. The reaction products at various stages were characterized by x-ray photoelectron spectroscopy. Two different assays were used to check that the DNA strands attached to the carbon nanotubes were able to bind their partner strands with complementary base sequences. The first assay, using partner DNA strands tethered to gold nanoparticles, enabled the sites of DNA attachment to the carbon nanotubes to be identified in TEM images. The second assay, using radioactively labelled partner DNA strands, quantified the density of functional DNA strands attached to the carbon nanotubes. The diversity of potential applications for these DNA-modified carbon-nanotube platforms is exemplified here by the successful use of a DNA-modified single-walled carbon-nanotube mat as an electrode for the specific detection of metal ions. (paper)

Comparison on graphite, graphene oxide and reduced graphene oxide: Synthesis and characterization

Science.gov (United States)

Hidayah, N. M. S.; Liu, Wei-Wen; Lai, Chin-Wei; Noriman, N. Z.; Khe, Cheng-Seong; Hashim, U.; Lee, H. Cheun

2017-10-01

Graphene oxide (GO) and reduced graphene oxide (RGO) are known to have superior properties for various applications. This work compares the properties of GO and RGO with graphite. GO was prepared by using Improved Hummer's method whereas the produced GO was subjected to chemical reduction with the use of hydrazine hydrate. Graphite, GO and RGO had different morphologies, quality, functionalized groups, UV-Vis absorption peaks and crystallinity. With the removal of oxygen-containing functional group during reduction for RGO, the quality of samples was decreased due to higher intensity of D band than G band was seen in Raman results. In addition, platelet-like surface can be observed on the surface of graphite as compared to GO and RGO where wrinkled and layered flakes, and crumpled thin sheets were observed on GO and RGO surface respectively. Fourier Transform Infra-Red (FTIR) analysis showed the presence of abundant oxygen-containing functional groups in GO as compared to RGO and graphite. The characteristic peaks at 26.62°, 9.03° and 24.10° for graphite, GO and RGO, respectively, can be detected from X-Ray diffraction (XRD). Furthermore, the reduction also caused red shift at 279nm from 238nm, as obtained from ultraviolet visible (UV-Vis) analysis. The results proved that GO was successfully oxidized from graphite whereas RGO was effectively reduced from GO.

Co3O4 nanocrystals with exposed low-surface-energy planes anchored on chemically integrated graphitic carbon nitride-modified nitrogen-doped graphene: A high-performance anode material for lithium-ion batteries

Science.gov (United States)

Zhang, Wenyao; Fu, Yongsheng; Wang, Xin

2018-05-01

A facile strategy to synthesize a composite composed of cubic Co3O4 nanocrystals anchored on chemically integrated g-C3N4-modified N-graphene (CN-NG) as an advanced anode material for high-performance lithium-ion batteries is reported. It is found that the morphology of the Co3O4 nanocrystals contains blunt-edge nanocubes with well-demarcated boundaries and numerous exposed low-index (1 1 1) crystallographic facets. These planes can be directly involved in the electrochemical reactions, providing rapid Li-ion transport channels for charging and discharging and thus enhancing the round-trip diffusion efficiency. On the other hand, the CN-NG support displays unusual textural features, such as superior structural stability, accessible active sites, and good electrical conductivity. The experimental results reveal that the chemical and electronic coupling of graphitic carbon nitride and nitrogen-doped graphene synergistically facilitate the anchoring of Co3O4 nanocrystals and prevents their migration. The resulting Co3O4/CN-NG composite exhibits a high specific reversible capacity of up to 1096 mAh g-1 with excellent cycling stability and rate capability. We believe that such a hybrid carbon support could open a new path for applications in electrocatalysis, sensors, supercapacitors, etc., in the near future.

Development, installation, and initial operation of DIII-D graphite armor tiles

International Nuclear Information System (INIS)

Anderson, P.M.; Baxi, C.B.; Reis, E.E.; Smith, J.P.; Smith, P.D.

1988-04-01

An upgrade of the DIII-D vacuum vessel protection system has been completed. The ceiling, floor, and inner wall have been armored to enable operation of CIT-relevant doublenull diverted plasmas and to enable the use of the inner wall as a limiting surface. The all- graphite tiles replace the earlier partial coverage armor configuration which consisted of a combination of Inconel tiles and graphite brazed to Inconel tiles. A new all-graphite design concept was chosen for cost and reliability reasons. The 10 minute duration between plasma discharges required the tiles to be cooled by conduction to the water-cooled vessel wall. Using two and three- dimensional analyses, the tile design was optimized to minimize thermal stresses with uniform thermal loading on the plasma-facing surface. Minimizing the stresses around the tile hold-down feature and eliminating stress concentrators were emphasized in the design. The design of the tile fastener system resulted in sufficient hold-down forces for good thermal conductance to the vessel and for securing the tile against eddy current forces. The tiles are made of graphite, and a program to select a suitable grade of graphite was undertaken. Initially, graphites were compared based on published technical data. Graphite samples were then tested for thermal shock capacity in an electron beam test facility at the Sandia National Laboratory (SNLA) in Albuquerque, New Mexico, USA. 4 refs., 6 figs

Graphitic carbon nitride nanosheets doped graphene oxide for electrochemical simultaneous determination of ascorbic acid, dopamine and uric acid

International Nuclear Information System (INIS)

Zhang, Hanqiang; Huang, Qitong; Huang, Yihong; Li, Feiming; Zhang, Wuxiang; Wei, Chan; Chen, Jianhua; Dai, Pingwang; Huang, Lizhang; Huang, Zhouyi; Kang, Lianping; Hu, Shirong; Hao, Aiyou

2014-01-01

Graphical abstract: Schematic drawing of electrochemical oxidize AA, DA and UA on graphitic carbon nitride nanosheets-graphene oxide composite modified electrode. - Highlights: • Synthesize g-C 3 N 4 , GO and CNNS-GO composite. • CNNS-GO composite was the first time for simultaneous determination of AA, DA and UA. • CNNS-GO/GCE displays fantastic selectivity and sensitivity for AA, DA and UA. • CNNS-GO/GCE was applied to detect real sample with satisfactory results. - Abstract: Graphitic carbon nitride nanosheets with a graphite-like structure have strong covalent bonds between carbon and nitride atoms, and nitrogen atoms in the carbon architecture can accelerate the electron transfer and enhance electrical properties effectually. The graphitic carbon nitride nanosheets-graphene oxide composite was synthesized. And the electrochemical performance of the composite was investigated by cyclic voltammetry and differential pulse voltammetry ulteriorly. Due to the synergistic effects of layer-by-layer structures by π-π stacking or charge-transfer interactions, graphitic carbon nitride nanosheets-graphene oxide composite can improved conductivity, electro-catalytic and selective oxidation performance. The proposed graphitic carbon nitride nanosheets-graphene oxide composite modified electrode was employed for simultaneous determination of ascorbic acid, dopamine and uric acid in their mixture solution, it exhibited distinguished sensitivity, wide linear range and low detection limit. Moreover, the modified electrode was applied to detect urine and dopamine injection sample, and then the samples were spiked with certain concentration of three substances with satisfactory recovery results

Biocompatibility of Mg Ion Doped Hydroxyapatite Films on Ti-6Al-4V Surface by Electrochemical Deposition.

Science.gov (United States)

Lee, Kang; Choe, Han-Cheol

2016-02-01

In this study, we prepared magnesium (Mg) doped nano-phase hydroxyapatite (HAp) films on the TiO2 nano-network surface using electrochemical deposition method. Ti-6Al-4V ELI surface was anodized in 5 M NaOH solution at 0.3 A for 10 min. Nano-network TiO2 surface were formed by these anodization steps which acted as templates and anchorage for growth of the Mg doped HAp during subsequent pulsed electrochemical deposition process at 85 degrees C. The phase and morphologies of HAp deposits were influenced by the Mg ion concentration.

Low cost sic coated erosion resistant graphite

International Nuclear Information System (INIS)

Zafar, M.F.; Nicholls, J.R.

2007-01-01

The development of materials with unique and improved properties using low cost processes is essential to increase performance and reduce cost of the solid rocket motors. Specifically advancements are needed for boost phase nozzle. As these motors operate at very high pressure and temperatures, the nozzle must survive high thermal stresses with minimal erosion to maintain performance. Currently three material choices are being exploited; which are refractory metals, graphite and carbon-carbon composites. Of these three materials graphite is the most attractive choice because of its low cost, light weight, and easy forming. However graphite is prone to erosion, both chemical and mechanical, which may affect the ballistic conditions and mechanical properties of the nozzle. To minimize this erosion high density graphite is usually preferred; which is again very expensive. Another technique used to minimize the erosion is Pyrolytic Graphite (PG) coating inside the nozzle. However PG coating is prone to cracking and spallation along with very cumbersome deposition process. Another possible methodology to avoid this erosion is to convert the inside surface of the rocket nozzle to Silicon Carbide (SiC), which is very erosion resistant and have much better thermal stability compared to graphite and even PG. Due to its functionally gradient nature such a layer will be very adherent and resistant to spallation. The current research is focused on synthesizing, characterizing and oxidation testing of such a converted SiC layer on commercial grade graphite. (author)

Contribution to the study of the reactivity of graphite with respect to carbon dioxide and air; Contribution a l'etude de la reactivite du graphite vis-a-vis du gaz corbonique et de l'air

Energy Technology Data Exchange (ETDEWEB)

Jacquet, M [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1959-09-15

The oxidation of nuclear-quality graphite by air and carbon dioxide has been studied at temperatures at which the reaction becomes measurable. These experiments have been carried out on graphites differing in the concentration and nature of their ash, and in their mode of preparation. The reaction velocities measured have been compared in an attempt to correlate these two factors. Ten types of graphite have thus been studied. Since the oxidation reactions are of the type gas-solid, their velocities have also been compared to the BET surface areas of the graphite studied and to the diameter distribution of the pores of this surface. The conclusion is that, even for these low impurity contents, the law relating the reaction velocity to the surface is masked by the impurities which appear to behave as preferential reaction sites. This has been shown by carrying out successive purifications on various types of graphite, which treatment results in an important decrease in the reactivity of all the samples studied. (author) [French] On a etudie l'oxydation de graphites de qualites nucleaires par l'air et par le gaz carbonique, a des temperatures telles que la reaction commence a etre mesurable. Ces essais ont porte sur des graphites differents aux points de vue de la concentration et de la nature des cendres, et differents par le mode de preparation. Les vitesses de reaction mesurees ont ete comparees afin de tenter de les relier a ces deux facteurs. Dix qualites de graphite ont ainsi ete etudiees. Les reactions d'oxydation etant des reactions gaz-solide, les vitesses ont ete egalement comparees aux surfaces specifiques B.E.T. des echantillons de graphite etudies et a la repartition par diametres des pores de cette surface. La conclusion est que, meme a ces teneurs faibles en impuretes, la loi de variation de la vitesse de reaction en fonction de la surface est masquee par les impuretes qui paraissent jouer le role de sites privilegies de reaction comme l'ont montre les

Spatially resolved nanostructural transformation in graphite under femtosecond laser irradiation

International Nuclear Information System (INIS)

Marcu, A.; Avotina, L.; Porosnicu, C.; Marin, A.; Grigorescu, C.E.A.; Ursescu, D.; Lungu, M.; Demitri, N.; Lungu, C.P.

2015-01-01

Graphical abstract: - Highlights: • Polycrystalline graphite was irradiated with a high power fs (IR) laser. • Presence of a diamond peak was detected by synchrotron XRD. • XPS and Raman showed in-depth sp 3 % increase at tens of nm below the surface. • sp 3 % is increasing with laser power density but it is independent of photon absorption rate. • Graphite crystallite size locally increase at tens of nanometers below the irradiated spots. - Abstract: A polycrystalline graphite target was irradiated using infrared (800 nm) femtosecond (120 fs) laser pulses of different energies. Increase of sp 3 bonds percentage and possible diamond crystal formation were investigated ‘in-depth’ and on the irradiated surfaces. Synchrotron X-ray diffraction pattern have shown the presence of a diamond peak in one of the irradiated zones while X-ray photoelectron spectroscopy investigations have shown an increasing tendency of the sp 3 percent in the low power irradiated areas and similarly ‘in the depth’ of the higher power irradiated zones. Multiple wavelength Micro-Raman investigations have confirmed this trend along with an ‘in-depth’ (but not on the surface) increase of the crystallite size. Based on the wavelength dependent photon absorption into graphite, the observed effects are correlated with high density photon per atom and attributed to the melting and recrystallization processes taking place tens of nanometers below the target surface.

From Graphite to Graphene via Scanning Tunneling Microscopy

Science.gov (United States)

Qi, Dejun

The primary objective of this dissertation is to study both graphene on graphite and pristine freestanding grapheme using scanning tunneling microscopy (STM) and density functional theory (DFT) simulation technique. In the experiment part, good quality tungsten metalic tips for experiment were fabricated using our newly developed tip making setup. Then a series of measurements using a technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) of our own development were performed on a highly oriented pyrolytic graphite (HOPG) surface. The electrostatic interaction between the STM tip and the sample can be tuned to produce both reversible and irreversible large-scale movement of the graphite surface. Under this influence, atomic-resolution STM images reveal that a continuous electronic transition between two distinct patterns can be systematically controlled. DFT calculations reveal that this transition can be related to vertical displacements of the top layer of graphite relative to the bulk. Evidence for horizontal shifts in the top layer of graphite is also presented. Excellent agreement is found between experimental STM images and those simulated using DFT. In addition, the EM-STM technique was also used to controllably and reversibly pull freestanding graphene membranes up to 35 nm from their equilibrium height. Atomic-scale corrugation amplitudes 20 times larger than the STM electronic corrugation for graphene on a substrate were observed. The freestanding graphene membrane responds to a local attractive force created at the STM tip as a highly conductive yet flexible grounding plane with an elastic restoring force.

Adhesive properties and adhesive joints strength of graphite/epoxy composites

Science.gov (United States)

Rudawska, Anna; Stančeková, Dana; Cubonova, Nadezda; Vitenko, Tetiana; Müller, Miroslav; Valášek, Petr

2017-05-01

The article presents the results of experimental research of the adhesive joints strength of graphite/epoxy composites and the results of the surface free energy of the composite surfaces. Two types of graphite/epoxy composites with different thickness were tested which are used to aircraft structure. The single-lap adhesive joints of epoxy composites were considered. Adhesive properties were described by surface free energy. Owens-Wendt method was used to determine surface free energy. The epoxy two-component adhesive was used to preparing the adhesive joints. Zwick/Roell 100 strength device were used to determination the shear strength of adhesive joints of epoxy composites. The strength test results showed that the highest value was obtained for adhesive joints of graphite-epoxy composite of smaller material thickness (0.48 mm). Statistical analysis of the results obtained, the study showed statistically significant differences between the values of the strength of the confidence level of 0.95. The statistical analysis of the results also showed that there are no statistical significant differences in average values of surface free energy (0.95 confidence level). It was noted that in each of the results the dispersion component of surface free energy was much greater than polar component of surface free energy.

RBS investigations of high-temperature reactions on graphite substrates

Energy Technology Data Exchange (ETDEWEB)

Eloi, C.C. [Kentucky Univ., Lexington, KY (United States). Dept. of Chemistry]|[Center for Applied Energy Research, University of Kentucky, Lexington, KY 40506 (United States); Robertson, J.D. [Kentucky Univ., Lexington, KY (United States). Dept. of Chemistry]|[Center for Applied Energy Research, University of Kentucky, Lexington, KY 40506 (United States); Majidi, V. [Kentucky Univ., Lexington, KY (United States). Dept. of Chemistry

1995-05-01

While graphite furnace atomic absorption spectrometry (GFAAS) is one of the most powerful techniques for ultratrace analysis of Pb, it is often plagued by matrix interferences. These interferences are minimized by the addition of matrix modifiers which stabilize the analyte signal through unknown mechanisms. Using RBS, the high temperature reactions of nitrate salts of Pb were studied on pyrolytically coated graphite with and without matrix modifiers. The addition of an ammonium phosphate modifier was found to stabilize Pb through the formation of a metal oxy-phosphorus compound. Moreover, the depth profiles demonstrated that the pyrolytically coated graphite was not impervious as previously thought. Pre-treatment of the surface with O{sub 2} is also known to cause a delay in the vaporization of Pb. While a surface effect had previously been postulated, the 3.04 MeV resonance {sup 16}O({alpha}, {alpha}){sup 16}O elastic scattering measurements show that it proceeds through the formation of surface bound lead-oxygen species as the number of oxygen atoms chemisorbed and the number of lead atoms, present on the surface prior to vaporization, are nearly equal. (orig.).

Friction and wear of carbon-graphite materials for high energy brakes

Science.gov (United States)

Bill, R. C.

1975-01-01

Caliper-type brakes simulation experiments were conducted on seven different carbon-graphite material formulations against a steel disk material and against a carbon-graphite disk material. The effects of binder level, boron carbide (B4C) additions, graphite fiber additions, and graphite cloth reinforcement on friction and wear behavior were investigated. Reductions in binder level and additions of B4C each resulted in increased wear. The wear rate was not affected by the addition of graphite fibers. Transition to severe wear and high friction was observed in the case of graphite-cloth-reinforced carbon sliding against a disk of similar composition. This transition was related to the disruption of a continuous graphite shear film that must form on the sliding surfaces if low wear is to occur. The exposure of the fiber structure of the cloth constituent is believed to play a role in the shear film disruption.

Enhanced surface transfer doping of diamond by V{sub 2}O{sub 5} with improved thermal stability

Energy Technology Data Exchange (ETDEWEB)

Crawford, Kevin G., E-mail: k.crawford.2@research.gla.ac.uk; Moran, David A. J. [School of Engineering, University of Glasgow, Glasgow G12 8LT (United Kingdom); Cao, Liang [High Magnetic Field Laboratory, Chinese Academy of Sciences, 350 Shushanhu Road, Hefei 230031, Anhui (China); Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, Singapore 117542 (Singapore); Qi, Dongchen, E-mail: d.qi@latrobe.edu.au [Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086 (Australia); Tallaire, Alexandre [LSPM-CNRS, Université Paris 13, Villetaneuse 93430 (France); Limiti, E.; Verona, C. [Department of Industrial Engineering, “Tor Vergata” University, Rome 00173 (Italy); Wee, Andrew T. S. [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, Singapore 117542 (Singapore)

2016-01-25

Surface transfer doping of hydrogen-terminated diamond has been achieved utilising V{sub 2}O{sub 5} as a surface electron accepting material. Contact between the oxide and diamond surface promotes the transfer of electrons from the diamond into the V{sub 2}O{sub 5} as revealed by the synchrotron-based high resolution photoemission spectroscopy. Electrical characterization by Hall measurement performed before and after V{sub 2}O{sub 5} deposition shows an increase in hole carrier concentration in the diamond from 3.0 × 10{sup 12} to 1.8 × 10{sup 13 }cm{sup −2} at room temperature. High temperature Hall measurements performed up to 300 °C in atmosphere reveal greatly enhanced thermal stability of the hole channel produced using V{sub 2}O{sub 5} in comparison with an air-induced surface conduction channel. Transfer doping of hydrogen-terminated diamond using high electron affinity oxides such as V{sub 2}O{sub 5} is a promising approach for achieving thermally stable, high performance diamond based devices in comparison with air-induced surface transfer doping.

Electrostatic Manipulation of Graphene On Graphite

Science.gov (United States)

Untiedt, Carlos; Rubio-Verdu, Carmen; Saenz-Arce, Giovanni; Martinez-Asencio, Jesús; Milan, David C.; Moaied, Mohamed; Palacios, Juan J.; Caturla, Maria Jose

2015-03-01

Here we report the use of a Scanning Tunneling Microscope (STM) under ambient and vacuum conditions to study the controlled exfoliation of the last layer of a graphite surface when an electrostatic force is applied from a STM tip. In this work we have focused on the study of two parameters: the applied voltage needed to compensate the graphite interlayer attractive force and the one needed to break atomic bonds to produce folded structures. Additionally, we have studied the influence of edge structure in the breaking geometry. Independently of the edge orientation the graphite layer is found to tear through the zig-zag direction and the lifled layer shows a zig-zag folding direction. Molecular Dinamics simulations and DFT calculations have been performed to understand our results, showing a strong correlation with the experiments. Comunidad Valenciana through Prometeo project.

Stabilization of Reactive MgO Surfaces by Ni Doping

Science.gov (United States)

Mazheika, Aliaksei; Levchenko, Sergey V.

Ni-MgO solid solutions are promising materials for catalytic reduction of CO2 and dry reforming of CH4. To explain the catalytic activity, an ab initio study of Ni-substitutional defects in MgO (NiMg) has been performed. At first, the validation of the theory level was done. We compared results of CCSD(T) embedded-cluster calculations of NiMg formation energies and adsorption energies of CO, CO2 and H2 on them to the HSE(α) hybrid DFT functional with the fraction of the exact exchange α varied between 0 and 1. HSE(0.3) was found to be the best compromise in this study. Our periodic HSE(0.3) calculations show that NiMg defects are most stable at corner sites, followed by steps, and are least stable at (001) terraces. Thus, Ni-doping stabilizes stepped MgO surfaces. The dissociative adsorption of H2 on the terrace is found to be endothermic (+ 1 . 1 eV), whereas on (110) surface with NiMg it is highly exothermic (- 1 . 6 eV). Adsorbed CO2 is also significantly stabilized (- 0 . 6 vs. - 2 . 2 eV). These findings explain recent microcalorimetry measurements of H2 and CO2 adsorption at doped Ni-MgO samples. partially supported by UniCat (Deutsche Forschungsgemeinschaft).

Density functional theory study of elemental mercury adsorption on boron doped graphene surface decorated by transition metals

Energy Technology Data Exchange (ETDEWEB)

Jungsuttiwong, Siriporn, E-mail: siriporn.j@ubu.ac.th [Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ubon Ratchathani University, Ubon Ratchathani 34190 (Thailand); Wongnongwa, Yutthana [Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Ubon Ratchathani University, Ubon Ratchathani 34190 (Thailand); Namuangruk, Supawadee [National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), Klong Luang, Pathum Thani 12120 (Thailand); Kungwan, Nawee [Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Promarak, Vinich [Department of Material Science and Engineering, School of Molecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology, Rayong 21210 (Thailand); Kunaseth, Manaschai, E-mail: manaschai@nanotec.or.th [National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), Klong Luang, Pathum Thani 12120 (Thailand)

2016-01-30

Graphical abstract: Decoration of Pd{sub 4}-A (square planar) on B-doped graphene significantly promotes Hg{sup 0} adsorption, a single site of Pd{sub 4} cluster on BDG could strongly adsorb up to six Hg atoms. - Highlights: • Transition metal atom and cluster binds strongly on B-doped graphene surface. • Decoration of transition metal on B-doped graphene significantly promotes Hg{sup 0} adsorption. • Adsorption strength of Hg{sup 0} atom on metal decorated B-doped graphene: Pd > Pt > Ru > W > Cu. • One site decorated Pd4 cluster adsorbed Hg{sup 0} strongly up to six atoms.

Pt nanoparticles embedded on reduced graphite oxide with excellent electrocatalytic properties

Energy Technology Data Exchange (ETDEWEB)

Saravanan, Gengan, E-mail: saravanan3che@gmail.com [Central University of Tamil Nadu, Department of Chemistry, Thiruvarur, 610101 (India); Mohan, Subramanian, E-mail: sanjnamohan@yahoo.com [EMFT Division, CSIR-Central Electrochemical Research Institute, Tamilnadu, Karaikudi 630 006 (India)

2016-11-15

Graphical abstract: RGO/Nano Pt: This study explore the electrocatalytic oxidation performance of reduced graphite oxide (RGO) anchored with nano Pt. This graphene composite reveal superior electrooxidation performance that is associated with the flexible RGO matrix and the uniform distribution of Pt particles, which enhances surface area, fast electron transfer, uniform particle size distribution; consequently, the RGO matrix provides more stability to Pt particles during electrooxidation process. Display Omitted - Highlights: • Greener electrochemical method applied to prepare well-dispersed Pt-rGO. • Pt-rGO large surface area excellent charge transfer better catalytic activity. • Low-cost highly efficient carbon-based electrodes for direct formic acid fuel cell. • rGO an excellent support to anchor Pt nanoparticles on its surface. • Pt-rGO distinctly enhanced current density towards formic acid electrooxidation. - Abstract: Economically viable electrochemical approach has been developed for the synthesis of Pt nanoparticles through electrodeposition technique on the surface of Reduced Graphite Oxide (RGO). Pt nanoparticles embedded Reduced Graphite Oxide on Glassy Carbon Electrode are employed (Pt-rGO/GCE) for electrooxidation of formic acid. Scanning Electron Microscopy (SEM) image and Transmission Electron Microscopy (TEM) image shows that reduced graphite oxide act as an excellent support to anchor the Pt nanoparticles. Cyclic voltammetry results confirmed that Pt-rGO/GCE enhanced current density as many folds than that of bare platinum electrode for electrooxidation of formic acid. X-ray diffraction (XRD) patterns for Pt-graphene composites illustrate that peaks at 69.15 and 23° for Pt (220) and graphene carbon (002) respectively. {sup 13}C NMR spectrum of the electrochemically reduced graphite oxide resonance contains only one peak at 133 ppm which retains graphitic sp{sup 2} carbon and does not contain any oxygenated carbon and the carbonyl

Nitrogen-doped porous carbon from Camellia oleifera shells with enhanced electrochemical performance

Energy Technology Data Exchange (ETDEWEB)

Zhai, Yunbo, E-mail: ybzhai@hnu.edu.cn [College of Environmental Science and Engineering, Hunan University, Changsha 410082 (China); Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082 (China); Xu, Bibo [College of Environmental Science and Engineering, Hunan University, Changsha 410082 (China); Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082 (China); Zhu, Yun [Office of Scientific R& D, Hunan University, Changsha 410082 (China); Qing, Renpeng; Peng, Chuan; Wang, Tengfei; Li, Caiting; Zeng, Guangming [College of Environmental Science and Engineering, Hunan University, Changsha 410082 (China); Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082 (China)

2016-04-01

Nitrogen doped porous activated carbon was prepared by annealing treatment of Camellia oleifera shell activated carbon under NH{sub 3}. We found that nitrogen content of activated carbon up to 10.43 at.% when annealed in NH{sub 3} at 800 °C. At 600 °C or above, the N-doped carbon further reacts with NH{sub 3}, leads to a low surface area down to 458 m{sup 2}/g and low graphitization degree. X-ray photoelectron spectroscope (XPS) analysis indicated that the nitrogen functional groups on the nitrogen-doped activated carbons (NACs) were mostly in the form of pyridinic nitrogen. We discovered that the oxygen groups and carbon atoms at the defect and edge sites of graphene play an important role in the reaction, leading to nitrogen atoms incorporated into the lattice of carbon. When temperatures were lower than 600 °C the nitrogen atoms displaced oxygen groups and formed nitrogen function groups, and when temperatures were higher than 600 °C and ~ 4 at.% carbon atoms and part of oxygen function groups reacted with NH{sub 3}. When compared to pure activated carbon, the nitrogen doped activated carbon shows nearly four times the capacitance (191 vs 51 F/g). - Highlights: • The nitrogen content up to 10.43 at % during CAC pyrolysis under NH3 at 800 °C. • The oxygen groups and carbon atoms played an important role in the nitrogen doping. • NAC-600 shows a much higher specific capacitance than CAC.

Modelling of pulsed electron beam induced graphite ablation: Sublimation versus melting

Science.gov (United States)

Ali, Muddassir; Henda, Redhouane

2017-12-01

Pulsed electron beam ablation (PEBA) has recently emerged as a very promising technique for the deposition of thin films with superior properties. Interaction of the pulsed electron beam with the target material is a complex process, which consists of heating, phase transition, and erosion of a small portion from the target surface. Ablation can be significantly affected by the nature of thermal phenomena taking place at the target surface, with subsequent bearing on the properties, stoichiometry and structure of deposited thin films. A two stage, one-dimensional heat conduction model is presented to describe two different thermal phenomena accounting for interaction of a graphite target with a polyenergetic electron beam. In the first instance, the thermal phenomena are comprised of heating, melting and vaporization of the target surface, while in the second instance the thermal phenomena are described in terms of heating and sublimation of the graphite surface. In this work, the electron beam delivers intense electron pulses of ∼100 ns with energies up to 16 keV and an electric current of ∼400 A to a graphite target. The temperature distribution, surface recession velocity, ablated mass per unit area, and ablation depth for the graphite target are numerically simulated by the finite element method for each case. Based on calculation findings and available experimental data, ablation appears to occur mainly in the regime of melting and vaporization from the surface.

Boron-doped Diamond Electrodes: Electrochemical, Atomic Force Microscopy and Raman Study towards Corrosion-modifications at Nanoscale

International Nuclear Information System (INIS)

Kavan, Ladislav; Vlckova Zivcova, Zuzana; Petrak, Vaclav; Frank, Otakar; Janda, Pavel; Tarabkova, Hana; Nesladek, Milos; Mortet, Vincent

2015-01-01

Highlights: • B-doped diamond is nanostructured by corrosion-driven modifications occurring at carbonaceous impurity sites (sp 2 -carbons). • The electrochemical oxidation partly transforms a hydrogen-terminated diamond surface to O-terminated one, but the electrocatalytic activity of plasmatically O-terminated diamond is not achieved. • In contrast to all usual sp 2 carbons, the Raman spectra of B-doped diamond electrodes do not change upon electrochemical charging/discharging. - Abstract: Comparative studies of boron-doped diamonds electrodes (polycrystalline, single-crystalline, H-/O-terminated, and with different sp 3 /sp 2 ratios) indicate morphological modifications of diamond which are initiated by corrosion at nanoscale. In-situ electrochemical AFM imaging evidences that the textural changes start at non-diamond carbonaceous impurity sites treated at high positive potentials (>2.2 V vs. Ag/AgCl). The primary perturbations subsequently develop into sub-micron-sized craters. Raman spectroscopy shows that the primary erosion site is graphite-like (sp 2 -carbon), which is preferentially removed by anodic oxidation. Other non-diamond impurity, viz. tetrahedral amorphous carbon (t-aC), is less sensitive to oxidative decomposition. The diamond-related Raman features, including the B-doping-assigned modes, are intact during reversible electrochemical charging/discharging, which is a salient difference from all usual sp 2 -carbons. The electrochemical oxidation partly transforms a hydrogen-terminated diamond surface to O-terminated one, but the electrocatalytic activity of plasmatically O-terminated diamond is not achieved for a model redox couple, Fe 3+/2+ . Electrochemical impedance spectra were fitted to six different equivalent circuits. The determination of acceptor concentrations is feasible even for highly-doped diamond electrodes.

Surface studies on benzophenone doped PDMS microstructures fabricated using KrF excimer laser direct write lithography

International Nuclear Information System (INIS)

Kant, Madhushree Bute; Shinde, Shashikant D.; Bodas, Dhananjay; Patil, K.R.; Sathe, V.G.; Adhi, K.P.; Gosavi, S.W.

2014-01-01

Graphical abstract: - Highlights: • Use of KrF Laser micromachining for Lab-On-Chip applications at lower fluence. • Addition of Benzophenone in PDMS enhances its self development sensitivity. • Benzophenone helps efficient energy transfer for equal density of bond scissioning. • Correlation of chemical composition with laser dose and microstructure. • Microstructures with well defined clean sidewalls. - Abstract: This paper discusses microfabrication process for benzophenone doped polydimethylsiloxane (PDMS) using laser lithography. KrF excimer laser of 248 nm with 20 ns pulse width at repetition rate of 1 Hz was used for microfabrication of undoped and benzophenone doped PDMS. The doped-PDMS shows sensitivity below 365 nm, permitting processing under ambient light. The analysis of etch depth revealed that doped PDMS shows self developable sensitivity at lower fluence of ∼250 mJ/cm 2 . The unexposed and exposed surface was studied using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Scanning electron microscopy (SEM). Spectrocopic analysis indicated increase in C-O, C=O, Si-O 3 and Si-O 4 bonding at the expense of Si-C and Si-O 2 bonds of PDMS. In case of laser exposed doped-PDMS, removal of benzophenone from probe depth of spectroscopy was observed. Whereas the surface morphology of exposed and unexposed doped-PDMS was observed to be same, indicating clean development of PDMS micropatterns. The present study indicates that addition of 3.0 wt.% benzophenone in PDMS enhance self development sensitivity of PDMS. The self developable results on doped-PDMS are quite encouraging for its potential use in point of care Lab-On-Chip applications, for fabricating micropatterns using direct write laser lithography technology

Evaluation of Accelerated Graphitic Corrosion Test of Gray Cast Iron