WorldWideScience

Sample records for carbide stabilizing elements

  1. Stabilization of boron carbide via silicon doping.

    Science.gov (United States)

    Proctor, J E; Bhakhri, V; Hao, R; Prior, T J; Scheler, T; Gregoryanz, E; Chhowalla, M; Giulani, F

    2015-01-14

    Boron carbide is one of the lightest and hardest ceramics, but its applications are limited by its poor stability against a partial phase separation into separate boron and carbon. Phase separation is observed under high non-hydrostatic stress (both static and dynamic), resulting in amorphization. The phase separation is thought to occur in just one of the many naturally occurring polytypes in the material, and this raises the possibility of doping the boron carbide to eliminate this polytype. In this work, we have synthesized boron carbide doped with silicon. We have conducted a series of characterizations (transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and x-ray diffraction) on pure and silicon-doped boron carbide following static compression to 50 GPa non-hydrostatic pressure. We find that the level of amorphization under static non-hydrostatic pressure is drastically reduced by the silicon doping.

  2. Stability of MC Carbide Particles Size in Creep Resisting Steels

    Directory of Open Access Journals (Sweden)

    Vodopivec, F.

    2006-01-01

    Full Text Available Theoretical analysis of the dependence microstructure creep rate. Discussion on the effects of carbide particles size and their distribution on the base of accelerated creep tests on a steel X20CrMoV121 tempered at 800 °C. Analysis of the stability of carbide particles size in terms of free energy of formation of the compound. Explanation of the different effect of VC and NbC particles on accelerated creep rate.

  3. Influence of electronegativity on the electronic structures and stabilities of microclusters of carbides MC_n (M : transition, rare-earth or normal element, n < 10)

    Science.gov (United States)

    Leleyter, M.

    1991-10-01

    MC_n, clusters (n rare-earth metals, on the positions of the dσ and degenerate dδ levels due to the M atom, which are governed by Pauling's electronegativity (EN) of atom M. For transition or lanthanide metals, the alternations are “even" if EN le 1.7 (deficient d electron-elements: columns IIIA to VIIA; empty dσ and δ levels) or “odd" in the reverse case (rich d electron elements: column VIIIA bonding dσ and δ levels). For normal elements, the limit of EN seems to be the EN of C (2.5) and the alternations are “even" if EN le 2.5 or “odd" in the other case. Thus it is possible to infer a likely electronic configuration of the MC_n clusters and 2 tables give the compared electronic structures of these clusters for normal or transition elements. Such a kind of structure is only able to explain the parity effect origin of the MC_n clusters and even enable to foreknow for transition or rare-earth metal carbides which are not studied yet if the alternations will be “even" (EN le 1.7) or “odd". Les agrégats MC_n obtenus à partir de carbures par diverses méthodes expérimentales (SIMS, SSMS, vaporisation laser, effusion de Knudsen à haute température, etc.) présentent des alternances dans leurs intensités d'émission I(MC^+_n) avec maximums pour n impair si M = H, F, CI ou Fe, Ni, Rh, Ir, Pt ou au contraire pour n pair si M = B, Si, Ba, Ge ou Sc, Ti, V, Cr, Y, Zr, La, Ce, W, Th, U ou même n'existent que pour n pair (Nd, Dy, Ho, Er). D'autre part, seuls sont connus CO, C_3O, CN et C_3N pour l'oxygène et l'azote. Ces phénomènes sont interprétés tout d'abord à l'aide de la règle bien connue de correspondance qui relie de fortes (resp. faibles) intensités ou fréquences d'émissions d'ions MC^+_n à de fortes (resp. faibles) stabilités des amas correspondants. En second lieu, ces résultats s'expliquent dans le cadre du modèle de Pitzer et Clementi (hybridation sp en théorie de Hückel) corroboré par des calculs CNDO: on suppose que les

  4. Palladium in cubic silicon carbide: Stability and kinetics

    Science.gov (United States)

    Roma, Guido

    2009-12-01

    Several technological applications of silicon carbide are concerned with the introduction of palladium impurities. Be it intentional or not, this may lead to the formation of silicides. Not only this process is not well understood, but the basic properties of palladium impurities in silicon carbide, such as solubility or diffusion mechanisms, are far from being known. Here the stability and kinetics of isolated Pd impurities in cubic silicon carbide are studied by first principles calculations in the framework of density functional theory. The preferential insertion sites, as well as the main migration mechanisms, are analyzed and presented here, together with the results for solution and migration energies. The early stages of nucleation are discussed based on the properties of isolated impurities and the smallest clusters.

  5. Note: Silicon Carbide Telescope Dimensional Stability for Space-based Gravitational Wave Detectors

    Science.gov (United States)

    Sanjuah, J.; Korytov, D.; Mueller, G.; Spannagel, R.; Braxmaier, C.; Preston, A.; Livas, J.

    2012-01-01

    Space-based gravitational wave detectors are conceived to detect gravitational waves in the low frequency range by measuring the distance between proof masses in spacecraft separated by millions of kilometers. One of the key elements is the telescope which has to have a dimensional stability better than 1 pm Hz(exp -1/2) at 3 mHz. In addition, the telescope structure must be light, strong, and stiff. For this reason a potential telescope structure consisting of a silicon carbide quadpod has been designed, constructed, and tested. We present dimensional stability results meeting the requirements at room temperature. Results at -60 C are also shown although the requirements are not met due to temperature fluctuations in the setup.

  6. High temperature stability of Cr-carbides in an experimental Co-Re-based alloy

    Energy Technology Data Exchange (ETDEWEB)

    Mukherji, Debashis; Klauke, Michael; Roesler, Joachim [Technische Universitaet Braunschweig (Germany). Institut fuer Werkstoffe; Strunz, Pavel [Nuclear Physics Institute and Research Center Rez (Czech Republic); Zizak, Ivo [Berliner Elektronenspeicherring-Gesellschaft fuer Synchrotronstrahlung, Berlin (Germany); Schumacher, Gerhard; Wiedenmann, Albrecht [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany)

    2010-03-15

    The stability of the microstructure at high temperatures was studied in an experimental Co-Re-based alloy. The experimental alloy is mainly strengthened by Cr-carbides, particularly by those in the form of thin lamellar plates. Electron microscopic investigation on samples exposed for up to 1000 h to temperatures of 1000 and 1200 C showed that Cr{sub 23}C{sub 6} type carbides present in the alloy in different morphologies are unstable at these temperatures. It was also observed that the alloy hardness dropped after exposing the samples to elevated temperatures and much of this loss occurred within the first 100 h. In-situ diffraction measurements with synchrotron radiation showed that carbide dissolution started as early as 3 h of holding at 1000 C. Moreover, in-situ small angle neutron scattering results indicated that the carbides at the grain boundaries and the blocky carbides dissolve first and then the thin lamellar carbides. Further, the enrichment of Cr in the Co-matrix phase, which took place due to the dissolution of Cr-carbides, stabilized a Cr-Re-rich {sigma} phase. Although the dissolution of lamellar carbides results in a significant loss of strength, the formation of {sigma} phase with extremely high hardness partly compensated the for loss. The {sigma} phase is stable even at 1200 C. (orig.)

  7. Synthesis, thermal stability, and photocatalytic activity of nanocrystalline titanium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Youjian; Zhang, Hong [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325027 (China); Ma, DeKun [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325027 (China); Nanomaterials and Chemistry Key Laboratory, Advanced Materials Research Center of Wenzhou, Wenzhou University, Wenzhou, Zhejiang 325027 (China); Ma, Jianhua, E-mail: mjh820@ustc.edu [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325027 (China); Nanomaterials and Chemistry Key Laboratory, Advanced Materials Research Center of Wenzhou, Wenzhou University, Wenzhou, Zhejiang 325027 (China); Ye, Hongnan; Qian, Gaojin; Ye, Yi [Oujiang College, Wenzhou University, Wenzhou, Zhejiang 325027 (China)

    2011-11-15

    Highlights: {yields} The synthesized temperature is lower than some conventional methods. {yields} These raw materials are safe; all manipulations are rather safe and convenient. {yields} The product exhibits photocatalytic activity in degradation of Rhodamine-B. -- Abstract: Titanium carbide (TiC) was prepared via one simple route by the reaction of metallic magnesium powders with titanium dioxide (TiO{sub 2}) and potassium acetate (CH{sub 3}COOK) in an autoclave at 600 {sup o}C and 8 h. Phase structure and morphology were characterized by X-ray powder diffraction (XRD) and Scanning electron microscopy (SEM). The results indicated that the product was cubic TiC, which consisted of particles with an average size of about 100 nm in diameter. The product was also studied by the thermogravimetric analysis (TGA) and its photocatalysis. It had good thermal stability and oxidation resistance below 350 {sup o}C in air. In addition, we discovered that the cubic TiC powders exhibited photocatalytic activity in degradation of Rhodamine-B (RhB) under 500 W mercury lamp light irradiation.

  8. Controlling the microstructure of binary carbide films with elemental substitutions

    Science.gov (United States)

    Feller, K.; Haider, M.; Hodges, A.; Spreng, R.; Posbergh, E.; Woodward, H.; Lofland, S. E.; Hettinger, J. D.; Heon, M.; Gogotsi, Y.

    2011-03-01

    We report on experiments to control the microstructure of textured binary carbide thin films deposited by reactive magnetron sputter deposition. Controlling the microstructure in these materials is important as the microstructure of these films provides a template for the resulting carbide-derived carbon (CDC) film and impacts their performance. Specifically, a combinatorial approach is used to add chromium to TiC films creating a compositional gradient as a function of position. We present a measurement of surface roughness as a function of material composition. The resulting materials, (Ti 1-x Cr x) C films, are significantly smoother than their pure TiC counterparts and the resulting CDC's have correlated defects which will improve the performance of the CDC in supercapacitor applications. This work was supported by Rowan University and NSF under contract DMR-0503711.

  9. Synthesis of Binary Transition Metal Nitrides, Carbides and Borides from the Elements in the Laser-Heated Diamond Anvil Cell and Their Structure-Property Relations

    Directory of Open Access Journals (Sweden)

    Lkhamsuren Bayarjargal

    2011-09-01

    Full Text Available Transition metal nitrides, carbides and borides have a high potential for industrial applications as they not only have a high melting point but are generally harder and less compressible than the pure metals. Here we summarize recent advances in the synthesis of binary transition metal nitrides, carbides and borides focusing on the reaction of the elements at extreme conditions generated within the laser-heated diamond anvil cell. The current knowledge of their structures and high-pressure properties like high-(p; T stability, compressibility and hardness is described as obtained from experiments.

  10. Sensitivity analysis of a PWR fuel element using zircaloy and silicon carbide claddings

    Energy Technology Data Exchange (ETDEWEB)

    Faria, Rochkhudson B. de; Cardoso, Fabiano; Salome, Jean A.D.; Pereira, Claubia; Fortini, Angela, E-mail: rochkhudson@ufmg.br, E-mail: claubia@nuclear.ufmg.br [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil). Escola de Engenharia. Departamento de Engenharia Nuclear

    2015-07-01

    The alloy composed of zirconium has been used effectively for over 50 years in claddings of nuclear fuel, especially for PWR type reactors. However, to increase fuel enrichment with the aim of raising the burning and maintaining the safety of nuclear plants is of great relevance the study of new materials that can replace safely and efficiently zircaloy cladding. Among several proposed material, silicon carbide (SiC) has a potential to replace zircaloy as fuel cladding material due to its high-temperature tolerance, chemical stability and low neutron affinity. In this paper, the goal is to expand the study with silicon carbide cladding, checking its behavior when submitted to an environment with boron, burnable poison rods, and temperature variations. Sensitivity calculation and the impact in multiplication factor to both claddings, zircaloy and silicon carbide, were performed during the burnup. The neutronic analysis was made using the SCALE 6.0 (Standardized Computer Analysis for Licensing Evaluation) code. (author)

  11. Effects of carbon on the stability and chemical performance of transition metal carbides: A density functional study

    Science.gov (United States)

    Liu, Ping; Rodriguez, José A.

    2004-03-01

    Density functional theory was employed to study the stabilities and chemical activities of transition metal carbides. Here we take the well-known Mo carbides and Ti carbides as an example. Different kinds of structures including the bulk surfaces [Mo2C(001), MoC(001), and TiC(001)] and metcars [Mo8C12 and Ti8C12] are taken into consideration. Systematic studies show that by raising the C coordination number of the metal atoms in the carbides, in general the stability of the carbides increases (metcars are an exception since they include both high-coordinated and low-coordinated metal atoms.); at the same time, the chemical activities of the carbides decrease due to a downshift of the metal d-band center (ligand effect). Considering the better catalysts those that combine high stability and moderate chemical activity, our results suggest that the catalytic potential of Mo carbide systems should decrease in the following sequence: Mo8C12>Mo2C(001) or MoC(001)>pure Mo(110). In spite of having the largest C/Mo ratio, the metcar appears as the most attractive system. Our studies also indicate that the "magic" behavior of metcars is not unique for Mo carbides. Similar behavior is also observed for Ti carbides. This implies that nanoparticles like metcar species could exhibit better performances than the corresponding bulk metal carbides as catalysts.

  12. Molybdenum carbide stabilized on graphene with high electrocatalytic activity for hydrogen evolution reaction.

    Science.gov (United States)

    Pan, Lin Feng; Li, Yu Hang; Yang, Shuang; Liu, Peng Fei; Yu, Ming Quan; Yang, Hua Gui

    2014-11-01

    In this work, we developed a general two-step method to prepare molybdenum carbide (Mo2C) nanoparticles stabilized by a carbon layer on reduced graphene oxide (RGO) sheets. The Mo2C-RGO hybrid showed excellent performance, which is attributed to the intimate interactions between Mo2C and graphene as well as the outer protection of the carbon layer.

  13. High current density stability of ohmic contacts to silicon carbide

    Science.gov (United States)

    Downey, Brian P.

    The materials properties of SiC, such as wide bandgap, high breakdown electric field, and good thermal conductivity, make it an appealing option for high temperature and high power applications. The replacement of Si devices with SiC components could lead to a reduction in device size, weight, complexity, and cooling requirements along with an increase in device efficiency. One area of concern under high temperature or high current operation is the stability of the ohmic contacts. Ohmic contact degradation can cause an increase in parasitic resistance, which can diminish device performance. While contact studies have primarily focused on the high temperature stability of ohmic contacts to SiC, different failure mechanisms may arise under high current density stressing due to the influence of electromigration. In addition, preferential degradation may occur at the anode or cathode due to the directionality of current flow, known as a polarity effect. The failure mechanisms of ohmic contacts to p-type SiC under high current density stressing are explored. Complementary materials characterization techniques were used to analyze contact degradation, particularly the use of cross-sections prepared by focused ion beam for imaging using field emission scanning electron microscopy and elemental analysis using Auger electron spectroscopy. Initially the degradation of commonly studied Ni and Al-based contacts was investigated under continuous DC current. The contact metallization included a bond pad consisting of a TiW diffusion barrier and thick Au overlayer. The Ni contacts were found to degrade due to the growth of voids within the ohmic contact layer, which were initially produced during the high temperature Ni/SiC ohmic contact anneal. The Al-based contacts degraded due to the movement of Al from the ohmic contact layer to the surface of the Au bond pad, and the movement of Au into the ohmic contact layer from the bond pad. The inequality of Al and Au fluxes generated

  14. Effect of the additions of carbide-forming elements on the microstructure and mechanical properties of steel shot

    Science.gov (United States)

    Shchennikova, T. L.; Zalazinskii, G. G.; Leont'ev, L. I.; Rybalko, O. F.

    2009-02-01

    The effect of the additions of carbide-forming elements (vanadium, titanium, chromium, molybdenum) on the microstructure and mechanical properties of the steel shot produced by the atomization of an iron-carbon melt (0.8% C) by water at a low pressure (0.2 MPa) is studied. The introduction of alloying elements is shown to affect the sizes of the structural constituents that form during the solidification of shot particles and, hence, the mechanical properties (hardness, wear resistance) of the shot. The additions can decrease the grain size in the shot by a factor of 2.5-3. The formation of the MC ( M is a carbide-forming element), VC, TiC, or M 2C (e.g., Mo2C) carbide increases the hardness of the shot material. Chromium and molybdenum form solid solutions with iron and complex (Fe, M)3C carbides.

  15. Influence of Nanosized Silicon Carbide on Dimensional Stability of Al/SiC Nanocomposite

    Directory of Open Access Journals (Sweden)

    S. M. Zebarjad

    2008-01-01

    Full Text Available This study concentrated on the role of particle size of silicon carbide (SiC on dimensional stability of aluminum. Three kinds of Al/SiC composite reinforced with different SiC particle sizes (25 μm, 5 μm, and 70 nm were produced using a high-energy ball mill. The standard samples were fabricated using powder metallurgy method. The samples were heated from room temperature up to 500∘C in a dilatometer at different heating rates, that is, 10, 30, 40, and 60∘C/min. The results showed that for all materials, there was an increase in length change as temperature increased and the temperature sensitivity of aluminum decreased in the presence of both micro- and nanosized silicon carbide. At the same condition, dimensional stability of Al/SiC nanocomposite was better than conventional Al/SiC composites.

  16. Escape of carbon element in surface ablation of cobalt cemented tungsten carbide with pulsed UV laser

    Science.gov (United States)

    Li, Tiejun; Lou, Qihong; Dong, Jingxing; Wei, Yunrong; Liu, Jingru

    2001-03-01

    Surface ablation of cobalt cemented tungsten carbide hardmetal has been carried out in this work using a 308 nm, 30 ns XeCl excimer laser. The surface phase transformation on different pulse number of laser shots has been investigated by means of XRD and microphotography as well as AES at laser fluence of 2.5 J/cm 2. The experimental results showed that the phase structure of irradiated area has partly transformed from original WC to β-WC 1- x, then to α-W 2C and CW 3, and finally to W crystal. It is suggested that the formation of non-stoichiometric tungsten carbide should result from the escaping of carbon element due to accumulated heating of surface by pulsed laser irradiation.

  17. Elements of magnetohydrodynamic stability theory

    Energy Technology Data Exchange (ETDEWEB)

    Spies, G O

    1976-11-01

    The nonlinear equations of ideal magnetohydrodynamics are discussed along with the following topics: (1) static equilibrium, (2) strict linear theory, (3) stability of a system with one degree of freedom, (4) spectrum and variational principles in magnetohydrodynamics, (5) elementary proof of the modified energy principle, (6) sufficient stability criteria, (7) local stability, and (8) normal modes. (MOW)

  18. Experimental Study of Stabilized Soil Utilizing Circulating Fluidized Bed Combustion Desulfurization Ash with Carbide Slag and Desulfurization Gypsum

    OpenAIRE

    2015-01-01

    This paper discusses the feasibility of preparing soil stabilizer which is circulating fluidized bed combustion ash-based, supplemented with carbide slag and desulfurization gypsum, composed entirely of complete industrial wastes. The results show that CFBC ash has better pozzolanic activity than fly ash. When stabilizer total content is 10% and the ratio of CFBC ash : carbide slag : desulfurization gypsum is 7.2 : 1.8 : 1, compressive strength of stabilized soil can reach the maximum of 2.12...

  19. Electronic metal-support interaction enhanced oxygen reduction activity and stability of boron carbide supported platinum

    Science.gov (United States)

    Jackson, Colleen; Smith, Graham T.; Inwood, David W.; Leach, Andrew S.; Whalley, Penny S.; Callisti, Mauro; Polcar, Tomas; Russell, Andrea E.; Levecque, Pieter; Kramer, Denis

    2017-06-01

    Catalysing the reduction of oxygen in acidic media is a standing challenge. Although activity of platinum, the most active metal, can be substantially improved by alloying, alloy stability remains a concern. Here we report that platinum nanoparticles supported on graphite-rich boron carbide show a 50-100% increase in activity in acidic media and improved cycle stability compared to commercial carbon supported platinum nanoparticles. Transmission electron microscopy and x-ray absorption fine structure analysis confirm similar platinum nanoparticle shapes, sizes, lattice parameters, and cluster packing on both supports, while x-ray photoelectron and absorption spectroscopy demonstrate a change in electronic structure. This shows that purely electronic metal-support interactions can significantly improve oxygen reduction activity without inducing shape, alloying or strain effects and without compromising stability. Optimizing the electronic interaction between the catalyst and support is, therefore, a promising approach for advanced electrocatalysts where optimizing the catalytic nanoparticles themselves is constrained by other concerns.

  20. Sulfur-Tolerant Molybdenum Carbide Catalysts Enabling Low-Temperature Stabilization of Fast Pyrolysis Bio-Oil

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhenglong; Choi, Jae Soon; Wang, Huamin; Lepore, Andrew W.; Connatser, Raynella M.; Lewis, Sam; Meyer, Harry; Santosa, Daniel M.; Zacher, Alan H.

    2017-08-18

    Low-temperature hydrogenation of carbonyl fractions can greatly improve the thermal stability of fast pyrolysis bio-oil which is crucial to achieve long-term operation of high-temperature upgrading reactors. The current state of the art, precious metals such as ruthenium, although highly effective in carbonyl hydrogenation, rapidly loses performance due to sulfur sensitivity. The present work showed that molybdenum carbides were active and sulfur-tolerant in low-temperature conversion carbonyl compounds. Furthermore, due to surface bifunctionality (presence of both metallic and acid sites), carbides catalyzed both C-O bond hydrogenation and C-C coupling reactions retaining most of carbon atoms in liquid products as more stable and higher molecular weight oligomeric compounds while consuming less hydrogen than ruthenium. The carbides proved to be resistant to other deactivation mechanisms including hydrothermal aging, oxidation, coking and leaching. These properties enabled carbides to achieve and maintain good catalytic performance in both aqueous-phase furfural conversion and real bio-oil stabilization with sulfur present. This finding strongly suggests that molybdenum carbides can provide a catalyst solution necessary for the development of commercially viable bio-oil stabilization technology.

  1. Design and finite element analysis of lightmass silicon carbide primary mirror

    Institute of Scientific and Technical Information of China (English)

    HAN Yuan-yuan; ZHANG Yu-min; HAN Jie-cai; ZHANG Jian-han; YAO Wang; ZHOU Yu-feng

    2006-01-01

    Primary mirror is one of the key components in the space remote sensing system. To minimize the mass of the mirror without compromising its stiffness and decrease the deformation of the mirror surface at the different temperatures are the mainly two objects in the development of the primary mirror. Silicon carbide (SiC),the most promising optical material,was used as the material of the primary mirror with triangle lightmass structure in a Cassegrain system. By using finite element method,the properties of the SiC mirror were compared with that of the traditional Be mirror and fused silica mirror. The results of static,dynamic and thermo-mechanical analysis indicate that the deformation of the mirror surface caused by temperature field is much bigger than that caused by gravity field. The SiC mirror has the best overall properties,and the SiC material is much suitable for the primary mirror.

  2. Role of alloying elements and carbides in the chlorine-induced corrosion of steels and alloys

    Directory of Open Access Journals (Sweden)

    Hans Jürgen Grabke

    2004-03-01

    Full Text Available The high temperature corrosion of steels and Ni-base alloys in oxidizing and chloridizing environments is of practical interest in relation to problems in waste incineration plants and power plants using Cl containing fuels. The behaviour of the most important alloying elements Fe, Cr, Ni, Mo, Mn, Si, Al upon corrosion in an oxidizing and chloridizing atmosphere was elucidated: the reactions and kinetics can be largely understood on the base of thermodynamic data, i.e. free energy of chloride formation, vapor pressure of the chlorides and oxygen pressure pO2 needed for the conversion chlorides -> oxides. The mechanism is described by 'active oxidation', comprising inward penetration of chlorine into the scale, formation of chlorides at the oxide/metal interface, evaporation of the chlorides and conversion of the evaporating chlorides into oxides, which occurs in more or less distance from the surface (depending on pO2. This process leads to loose, fragile, multilayered oxides which are unprotective (therefore: active oxidation. Fe and Cr are rapidly transferred into such scale, Ni and Mo are relatively resistant. In many cases, the grain boundaries of the materials are strongly attacked, this is due to a susceptibility of chromium carbides to chloridation. In contrast the carbides Mo2C, TiC and NbC are less attacked than the matrix. Alloys on the basis Fe-Cr-Si proved to be rather resistant, and the alloying elements Ni and Mo clearly retard the attack in an oxidizing and chloridizing environment.

  3. Deterioration of yttria-stabilized zirconia by boron carbide alone or mixed with metallic or oxidized Fe, Cr, Zr mixtures

    Energy Technology Data Exchange (ETDEWEB)

    De Bremaecker, A., E-mail: adbremae@sckcen.be [Belgian Nuclear Research Center (SCK-CEN), NMS, Mol (Belgium); Ayrault, L., E-mail: laurent.ayrault@cea.fr [Institut de Radio-Protection et Sûreté Nucléaire/DPAM/SEMIC, Bât 702, CEN de Cadarache BP3, F-13115 Saint-Paul-lez-Durance (France); Clément, B. [Institut de Radio-Protection et Sûreté Nucléaire/DPAM/SEMIC, Bât 702, CEN de Cadarache BP3, F-13115 Saint-Paul-lez-Durance (France)

    2014-08-01

    In the frame of severe accident conditions (PHEBUS FPT3 test), different experiments were carried out on the interactions of 20% yttria-stabilized zirconia (YSZ) and 20% ceria-stab zirconia with boron carbide or its oxidation products (B{sub 2}O{sub 3}): either tests under steam between 1230° and 1700 °C with B{sub 4}C alone or B{sub 4}C mixed with metals, either tests under Ar with boron oxide present in a mixture of iron and chromium oxides. In all cases an interaction was observed with formation of intergranular yttrium borate. At 1700 °C boron oxide is able to “pump out” the Y stabiliser from the YSZ grains but also some trace elements (Ca and Al) and to form a eutectic containing YBO{sub 3} and yttrium calcium oxy-borate (YCOB). At the same time a substantial swelling (“bloating”) of the zirconia happens, qualitatively similar to the foaming of irradiated fuel in contact with a Zr-melt. In all samples the lowering of the Y (or Ce)-content in the YSZ grains is so sharp that in the interaction layers zirconia is no longer stabilized. This is important when YSZ is envisaged as simulant of UO{sub 2} or as inert matrix for Am-transmutation.

  4. Deterioration of yttria-stabilized zirconia by boron carbide alone or mixed with metallic or oxidized Fe, Cr, Zr mixtures

    Science.gov (United States)

    De Bremaecker, A.; Ayrault, L.; Clément, B.

    2014-08-01

    In the frame of severe accident conditions (PHEBUS FPT3 test), different experiments were carried out on the interactions of 20% yttria-stabilized zirconia (YSZ) and 20% ceria-stab zirconia with boron carbide or its oxidation products (B2O3): either tests under steam between 1230° and 1700 °C with B4C alone or B4C mixed with metals, either tests under Ar with boron oxide present in a mixture of iron and chromium oxides. In all cases an interaction was observed with formation of intergranular yttrium borate. At 1700 °C boron oxide is able to “pump out” the Y stabiliser from the YSZ grains but also some trace elements (Ca and Al) and to form a eutectic containing YBO3 and yttrium calcium oxy-borate (YCOB). At the same time a substantial swelling (“bloating”) of the zirconia happens, qualitatively similar to the foaming of irradiated fuel in contact with a Zr-melt. In all samples the lowering of the Y (or Ce)-content in the YSZ grains is so sharp that in the interaction layers zirconia is no longer stabilized. This is important when YSZ is envisaged as simulant of UO2 or as inert matrix for Am-transmutation.

  5. Hydrogen evolution activity and electrochemical stability of selected transition metal carbides in concentrated phosphoric acid

    DEFF Research Database (Denmark)

    Tomás García, Antonio Luis; Jensen, Jens Oluf; Bjerrum, Niels J.

    2014-01-01

    Alternative catalysts based on carbides of Group 5 (niobium and tantalum) and 6 (chromium, molybdenum and tungsten) metals were prepared as films on the metallic substrates. The electrochemical activities of these carbide electrodes towards the hydrogen evolution reaction (HER) in concentrated......, attributable to the different electronic structures. Tungsten carbide among the studied electrode samples exhibited the highest HER activity. Upon anodic potential scans in the presence of oxygen, chromium, tantalum and tungsten carbides displayed passivation due to the formation of stable surface layers...

  6. Experimental Study of Stabilized Soil Utilizing Circulating Fluidized Bed Combustion Desulfurization Ash with Carbide Slag and Desulfurization Gypsum

    Directory of Open Access Journals (Sweden)

    Dezhi Shao

    2015-01-01

    Full Text Available This paper discusses the feasibility of preparing soil stabilizer which is circulating fluidized bed combustion ash-based, supplemented with carbide slag and desulfurization gypsum, composed entirely of complete industrial wastes. The results show that CFBC ash has better pozzolanic activity than fly ash. When stabilizer total content is 10% and the ratio of CFBC ash : carbide slag : desulfurization gypsum is 7.2 : 1.8 : 1, compressive strength of stabilized soil can reach the maximum of 2.12 MPa at the age of 28 d of curing. Stabilizer can meet the strength requirements of cement-soil mixing pile composite foundation and cement-soil mixing pile waterproof curtain.

  7. Stability and `volatility ` of element 104 oxychloride

    Energy Technology Data Exchange (ETDEWEB)

    Eichler, B.; Gaeggeler, H.W. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1997-09-01

    The formation enthalpies {Delta}H{sup *} of solid and gaseous oxychlorides of element 104 from free atoms were estimated by extrapolation. Stability and volatility of these compounds are compared to those of the homologous and neighbouring elements in the periodic system. It can be supposed that in a gas adsorption chromatographic process with oxygen containing chlorinating carrier gas the transport with the carrier gas flow occurs in the chemical state 104Cl{sub 4}. Only in the absorbed state the compound 104OCl{sub 2} is formed. (author) 1 fig., 3 refs.

  8. In Vitro Biocompatibility of Si Alloyed Multi-Principal Element Carbide Coatings

    Science.gov (United States)

    Vladescu, Alina; Titorencu, Irina; Dekhtyar, Yuri; Jinga, Victor; Pruna, Vasile; Balaceanu, Mihai; Dinu, Mihaela; Pana, Iulian; Vendina, Viktorija

    2016-01-01

    In the current study, we have examined the possibility to improve the biocompatibility of the (TiZrNbTaHf)C through replacement of either Ti or Ta by Si. The coatings were deposited on Si and 316L stainless steel substrates by magnetron sputtering in an Ar+CH4 mixed atmosphere and were examined for elemental composition, chemical bonds, surface topography, surface electrical charge and biocompatible characteristics. The net surface charge was evaluated at nano and macroscopic scale by measuring the electrical potential and work function, respectively. The biocompatible tests comprised determination of cell viability and cell attachment to the coated surface. The deposited coatings had C/(metal+Si) ratios close to unity, while a mixture of metallic carbide, free-carbon and oxidized species formed on the film surface. The coatings’ surfaces were smooth and no influence of surface roughness on electrical charge or biocompatibility was found. The biocompatible characteristics correlated well with the electrical potential/work function, suggesting a significant role of surface charge in improving biocompatibility, particularly cell attachment to coating's surface. Replacement of either Ti or Ta by Si in the (TiZrNbTaHf)C coating led to an enhanced surface electrical charge, as well as to superior biocompatible properties, with best results for the (TiZrNbSiHf)C coating. PMID:27571361

  9. In Vitro Biocompatibility of Si Alloyed Multi-Principal Element Carbide Coatings.

    Science.gov (United States)

    Vladescu, Alina; Titorencu, Irina; Dekhtyar, Yuri; Jinga, Victor; Pruna, Vasile; Balaceanu, Mihai; Dinu, Mihaela; Pana, Iulian; Vendina, Viktorija; Braic, Mariana

    2016-01-01

    In the current study, we have examined the possibility to improve the biocompatibility of the (TiZrNbTaHf)C through replacement of either Ti or Ta by Si. The coatings were deposited on Si and 316L stainless steel substrates by magnetron sputtering in an Ar+CH4 mixed atmosphere and were examined for elemental composition, chemical bonds, surface topography, surface electrical charge and biocompatible characteristics. The net surface charge was evaluated at nano and macroscopic scale by measuring the electrical potential and work function, respectively. The biocompatible tests comprised determination of cell viability and cell attachment to the coated surface. The deposited coatings had C/(metal+Si) ratios close to unity, while a mixture of metallic carbide, free-carbon and oxidized species formed on the film surface. The coatings' surfaces were smooth and no influence of surface roughness on electrical charge or biocompatibility was found. The biocompatible characteristics correlated well with the electrical potential/work function, suggesting a significant role of surface charge in improving biocompatibility, particularly cell attachment to coating's surface. Replacement of either Ti or Ta by Si in the (TiZrNbTaHf)C coating led to an enhanced surface electrical charge, as well as to superior biocompatible properties, with best results for the (TiZrNbSiHf)C coating.

  10. Stabilization and strengthening effects of functional groups in two-dimensional titanium carbide

    Science.gov (United States)

    Fu, Z. H.; Zhang, Q. F.; Legut, D.; Si, C.; Germann, T. C.; Lookman, T.; Du, S. Y.; Francisco, J. S.; Zhang, R. F.

    2016-09-01

    Two-dimensional (2D) materials have attracted considerable interest due to their remarkable properties and potential applications for nanoelectronics, electrodes, energy storage devices, among others. However, many well-studied 2D materials lack appreciable conductivity and tunable mechanical strength, limiting their applications in flexible devices. Newly developed MXenes open up the opportunity to design novel flexible conductive electronic materials. Here, using density functional theory (DFT), we investigate systematically the effects of several functional groups on the stabilization, mechanical properties, and electronic structures of a representative MXene. It is found that oxygen possesses the largest adsorption energy as compared to other functional groups, indicating its good thermodynamic stabilization. In comparison with bare and other functionalized titanium carbides, the oxygen functionalized one exhibits the most superior ideal strength; however, the premature softening of the long-wave phonon modes might limit the intrinsic strength for T i3C2O2 . Furthermore, the introduction of functional groups can induce a strong anisotropy under tensile loading. By analyzing the deformation paths and the electronic instability under various loadings, we demonstrate that the unique strengthening by oxygen functional groups is attributed to a significant charge transfer from inner bonds to outer surface ones after functionalization. Our results shed a novel view into exploring a variety of MXenes for their potential applications in flexible electronic and energy storage devices.

  11. Finite Element Simulations of Micro Turning of Ti-6Al-4V using PCD and Coated Carbide tools

    Science.gov (United States)

    Jagadesh, Thangavel; Samuel, G. L.

    2016-07-01

    The demand for manufacturing axi-symmetric Ti-6Al-4V implants is increasing in biomedical applications and it involves micro turning process. To understand the micro turning process, in this work, a 3D finite element model has been developed for predicting the tool chip interface temperature, cutting, thrust and axial forces. Strain gradient effect has been included in the Johnson-Cook material model to represent the flow stress of the work material. To verify the simulation results, experiments have been conducted at four different feed rates and at three different cutting speeds. Since titanium alloy has low Young's modulus, spring back effect is predominant for higher edge radius coated carbide tool which leads to the increase in the forces. Whereas, polycrystalline diamond (PCD) tool has smaller edge radius that leads to lesser forces and decrease in tool chip interface temperature due to high thermal conductivity. Tool chip interface temperature increases by increasing the cutting speed, however the increase is less for PCD tool as compared to the coated carbide tool. When uncut chip thickness decreases, there is an increase in specific cutting energy due to material strengthening effects. Surface roughness is higher for coated carbide tool due to ploughing effect when compared with PCD tool. The average prediction error of finite element model for cutting and thrust forces are 11.45 and 14.87 % respectively.

  12. Finite Element Simulations of Micro Turning of Ti-6Al-4V using PCD and Coated Carbide tools

    Science.gov (United States)

    Jagadesh, Thangavel; Samuel, G. L.

    2017-02-01

    The demand for manufacturing axi-symmetric Ti-6Al-4V implants is increasing in biomedical applications and it involves micro turning process. To understand the micro turning process, in this work, a 3D finite element model has been developed for predicting the tool chip interface temperature, cutting, thrust and axial forces. Strain gradient effect has been included in the Johnson-Cook material model to represent the flow stress of the work material. To verify the simulation results, experiments have been conducted at four different feed rates and at three different cutting speeds. Since titanium alloy has low Young's modulus, spring back effect is predominant for higher edge radius coated carbide tool which leads to the increase in the forces. Whereas, polycrystalline diamond (PCD) tool has smaller edge radius that leads to lesser forces and decrease in tool chip interface temperature due to high thermal conductivity. Tool chip interface temperature increases by increasing the cutting speed, however the increase is less for PCD tool as compared to the coated carbide tool. When uncut chip thickness decreases, there is an increase in specific cutting energy due to material strengthening effects. Surface roughness is higher for coated carbide tool due to ploughing effect when compared with PCD tool. The average prediction error of finite element model for cutting and thrust forces are 11.45 and 14.87 % respectively.

  13. Finite element analysis of thermal residual stresses at cemented carbide rock drill buttons with cobalt-gradient structure

    Institute of Scientific and Technical Information of China (English)

    HUANG Zi-qian; HE Yue-hui; CAI Hai-tao; XIAO Yi-feng; HUANG Bai-yun

    2008-01-01

    The aim of this study is to apply the concept of functionally graded materials (FGMs) to cemented carbides and to develop high-performance rock drill buttons.Cobalt-gradient structure was introduced to the surface zone of the buttons by carburizing process.Finite element method and XRD measurement were used to decide the distribution of thermal residual stress.Constitutive parameters were determined by constraint factor.Numerical results show that residual stresses of gradient buttons mainly concentrate in cobalt-gradient zone.There is compressive stress in the surface zone and tensile stress in the cobalt-rich zone.The maximum value of surface compressive stress is 180 MPa for WC-6Co cemented carbides.And the numerical results agree with the results of XRD measurement.

  14. Stability of Chromium Carbide/Chromium Oxide Based Porous Ceramics in Supercritical Water

    Science.gov (United States)

    Dong, Ziqiang

    This research was aimed at developing porous ceramics as well as ceramic-metal composites that can be potentially used in Gen-IV supercritical water reactors (SCWR). The research mainly includes two parts: 1) fabricating and engineering the porous ceramics and porous ceramic-metal composite; 2) Evaluating the stability of the porous ceramics in SCW environments. Reactive sintering in carbonaceous environments was used to fabricate porous Cr3C2/Cr2O3-based ceramic. A new process consisting of freeze casting and reactive sintering has also been successfully developed to fabricate highly porous Cr3C 2 ceramics with multiple interconnected pores. Various amounts of cobalt powders were mixed with ceramic oxides in order to modify the porous structure and property of the porous carbide obtained by reactive sintering. The hardness of the M(Cr,Co)7C3-Co composite has been evaluated and rationalized based on the solid solution of cobalt in the ceramic phase, the composite effect of soft Co metal and the porous structure of the ceramic materials. Efforts have also been made in fabricating and evaluating interpenetrating Cr3C2-Cu composites formed by infiltrating liquid copper into porous Cr3C2. The corrosion evaluation mainly focused on assessing the stability of porous Cr3C2 and Cr2O3 under various SCW conditions. The corrosion tests showed that the porous Cr3C 2 is stable in SCW at temperatures below 425°C. However, cracking and disintegrating of the porous Cr3C2 occurred when the SCW temperature increased above 425°C. Mechanisms of the corrosion attack were also investigated. The porous Cr2O3 obtained by oxidizing the porous Cr3C2 was exposed to various SCW environments. It was found that the stability of Cr 2O 3 was dependent on its morphology and the SCW testing conditions. Increasing SCW temperature increased the dissociation rate of the Cr2O 3. Adding proper amount of Y2O3 can increase the stability of the porous Cr2O3 in SCW. It was also concluded that decreasing

  15. Stability and activity of molybdenum carbide catalysts for the oxidative reforming of methane

    Science.gov (United States)

    Lamont, David Charles

    Molybdenum carbide catalysts have been studied for oxidative reforming, in particular, the effect on reforming activity of the method by which they were synthesized, their stability under conditions of varying mass transfer, and the measurement of their inherent reaction kinetics. These catalysts show promise as possible alternatives to both conventional supported nickel catalysts, as well as to the rare and expensive noble metal catalysts. Samples of Mo 2C were synthesized in house and compared to a commercial sample of Mo2C for the CO2 (dry) reforming of methane. It was found that high surface areas, previously thought to be important for activity, were not a property of the Mo2C, but instead were attributable to large amounts of excess carbon. This carbon had a detrimental effect on catalyst stability under dry reforming conditions, because it enhanced deposition of refractory carbon via methane cracking. The commercial sample of Mo 2C, while of low surface area and containing no excess carbon, behaved more stably over time. In another investigation, Mo2C was studied for its stability under varying mass transfer conditions, because of evidence showing that the Mo2C can undergo redox chemistry at reforming conditions. Under dry reforming conditions, it was found that some feed mixtures are net oxidizing, but that oxidation in the presence of such feed mixtures could be prevented by operating under mass transfer limited conditions, which resulted in sufficiently high partial pressures of CO and H2 in the catalyst boundary layer. Similar stability was achieved by co-feeding CO to the catalyst bed, which allowed for stable operation under conditions that were not mass transfer limited. Using this approach, measurements of the intrinsic reaction kinetics of Mo2C for dry reforming were successfully achieved. These results pointed to a strong dependence of dry reforming rate on both CH4 and CO2 partial pressures, as well as evidence for a reaction mechanism unique from

  16. Trace elements study of high purity nanocrystalline silicon carbide (3C-SiC) using k0-INAA method

    Science.gov (United States)

    Huseynov, Elchin; Jazbec, Anze

    2017-07-01

    Silicon carbide (3C-SiC) nanoparticles have been irradiated by neutron flux (2×1013 n·cm-2·s-1) at TRIGA Mark II type research reactor. After neutron irradiation, the radioisotopes of trace elements in the nanocrystalline 3C-SiC were studied as time functions. The identification of isotopes which significantly increased the activity of the samples as a result of neutron radiation was carried out. Nanocrystalline 3C-SiC are synthesized by standard laser technique and the purity of samples was determined by the k0-based Instrumental Neutron Activation Analysis (k0-INAA) method. Trace elements concentration in the 3C-SiC nanoparticles were determined by the radionuclides of appropriate elements. The trace element isotopes concentration have been calculated in percentage according to k0-INAA method.

  17. ELASTO-PLASTIC DEFORMATION OF COMPOSITE POWDERS WITH LAYERED CARBON AND CARBIDE-FORMING ELEMENT COATING

    Directory of Open Access Journals (Sweden)

    V. Kovalevsky

    2012-01-01

    Full Text Available Coating structure formation under magnetron spraying of titanium and carbon cathodes and combined cathodes, namely cobalt (EP 131 – nickel, tungsten – carbon have been investigated under conditions of carbide separate synthesis within the temperature range of 650–1200 °C. Usage of cobalt and nickel particles as matrix material leads to their rapid thermal expansion under heating during sintering process in the dilatometer. Subsequent plastic deformation of sintered samples provides obtaining a composite powder material that is a composite with framing structure of cobalt, titanium and tungsten carbides in the coatings.

  18. Stability and electrokinetic potential of silicon carbide suspensions in aqueous organic media

    Science.gov (United States)

    Yeremenko, B. V.; Lyubchenko, I. N.; Skobets, I. Y.

    1984-01-01

    The method of electroosmosis was used to study the dependence of the electrokinetic potential of silicon carbide suspensions in mixtures of water -n. alcohol. The reasons for the dependence of the electrokinetic potential on the composition of the intermicellar liquid are discussed.

  19. Aluminum nitride-silicon carbide whisker composites: Processing, properties, and microstructural stability

    Energy Technology Data Exchange (ETDEWEB)

    Cross, M.T.

    1990-01-01

    Aluminum nitride -- silicon carbide whisker composites with up to 20 vol % whiskers were fabricated by pressureless sintering (1750{degree}--1800{degree}C) and by hot-pressing (1700{degree}--1800{degree}C). Silicon carbide whiskers were found to degrade depending on the type of protective powder bed used during sintering. Whiskers were found to degraded in high oxygen containing samples by reaction with sintering additives. Whisker degradation was also due to the formation of silicon carbide -- aluminum nitride solid solution. No whisker degradation was observed in hot-pressed samples. For these samples Young's modulus and fracture toughness were measured. A 33% increase in the fracture toughness was measured by the indentation technique for a 20 vol % whisker composite. Operative toughening mechanisms were investigated using scanning electron microscopy. Crack deflection and whisker bridging were the dominant mechanisms. It was also shown that load transfer from matrix to whiskers can be a contributing factor to toughening. 88 refs., 34 figs., 11 tabs.

  20. In situ thermal imaging and three-dimensional finite element modeling of tungsten carbide-cobalt during laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Xiong Yuhong [Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616 (United States); Hofmeister, William H. [Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, TN 37388 (United States); Cheng Zhao [Earth Mechanics Inc., Oakland, CA 94621 (United States); Smugeresky, John E. [Sandia National Laboratories, Livermore, CA 94551 (United States); Lavernia, Enrique J. [Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616 (United States); Schoenung, Julie M., E-mail: jmschoenung@ucdavis.edu [Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616 (United States)

    2009-10-15

    Laser deposition is being used for the fabrication of net shapes from a broad range of materials, including tungsten carbide-cobalt (WC-Co) cermets (composites composed of a metallic phase and a hard refractory phase). During deposition, an unusual thermal condition is created for cermets, resulting in rather complex microstructures. To provide a fundamental insight into the evolution of such microstructures, we studied the thermal behavior of WC-Co cermets during laser deposition involving complementary results from in situ high-speed thermal imaging and three-dimensional finite element modeling. The former allowed for the characterization of temperature gradients and cooling rates in the vicinity of the molten pool, whereas the latter allowed for simulation of the entire sample. By combining the two methods, a more robust analysis of the thermal behavior was achieved. The model and the imaging results correlate well with each other and with the alternating sublayers observed in the microstructure.

  1. Automatic generation of 2D micromechanical finite element model of silicon–carbide/aluminum metal matrix composites: Effects of the boundary conditions

    DEFF Research Database (Denmark)

    Qing, Hai

    2013-01-01

    Two-dimensional finite element (FE) simulations of the deformation and damage evolution of Silicon–Carbide (SiC) particle reinforced aluminum alloy composite including interphase are carried out for different microstructures and particle volume fractions of the composites. A program is developed...

  2. Arginine residues as stabilizing elements in proteins

    NARCIS (Netherlands)

    MRABET, NT; VANDENBROECK, A; VANDENBRANDE, JL; STANSSENS, P; LAROCHE, Y; LAMBEIR, AM; MATTHIJSSENS, G; JENKINS, J; CHIADMI, M; VANTILBEURGH, H; REY, F; JANIN, J; QUAX, WJ; LASTERS, [No Value; DEMAEYER, M; WODAK, SJ

    1992-01-01

    Site-specific substitutions of arginine for lysine in the thermostable D-xylose isomerase (XI) from Actinoplanes missouriensis are shown to impart significant heat stability enhancement in the presence of sugar substrates most probably by interfering with nonenzymatic glycation. The same substitutio

  3. Stability of pattern placed revetment elements

    NARCIS (Netherlands)

    Dorst, K.; Provoost, Y.; Verhagen, H.J.

    2012-01-01

    A revetment of pattern placed elements, or a so called pitching, is used worldwide to protect shorelines and embankments. Also in The Netherlands more than 500 km of river, lake and sea dikes is protected by pitchings. Until the 60’s the design and construction of pitchings was based on experience.

  4. Investigation of silver and iodine transport through silicon carbide layers prepared for nuclear fuel element cladding

    Science.gov (United States)

    Friedland, E.; van der Berg, N. G.; Malherbe, J. B.; Hancke, J. J.; Barry, J.; Wendler, E.; Wesch, W.

    2011-03-01

    Transport of silver and iodine through polycrystalline SiC layers produced by PBMR (Pty) Ltd. for cladding of TRISO fuel kernels was investigated using Rutherford backscattering analysis and electron microscopy. Fluences of 2 × 10 16 Ag + cm -2 and 1 × 10 16 I + cm -2 were implanted at room temperature, 350 °C and 600 °C with an energy of 360 keV, producing an atomic density of approximately 1.5% at the projected ranges of about 100 nm. The broadening of the implantation profiles and the loss of diffusors through the front surface during vacuum annealing at temperatures up to 1400 °C was determined. The results for room temperature implantations point to completely different transport mechanisms for silver and iodine in highly disordered silicon carbide. However, similar results are obtained for high temperature implantations, although iodine transport is much stronger influenced by lattice defects than is the case for silver. For both diffusors transport in well annealed samples can be described by Fickian grain boundary diffusion with no abnormal loss through the surface as would be expected from the presence of nano-pores and/or micro-cracks. At 1100 °C diffusion coefficients for silver and iodine are below our detection limit of 10 -21 m 2 s -1, while they increase into the 10 -20 m 2 s -1 range at 1300 °C.

  5. Stability of Titanium Nitride and Titanium Carbide When Exposed to Hydrogen Atoms from 298 to 1950 K

    Science.gov (United States)

    Philipp, Warren H.

    1961-01-01

    Titanium nitride and titanium carbide deposited on tungsten wires were exposed to hydrogen atoms (10(exp -4) atm pressure) produced by the action of microwave radiation on molecular hydrogen. The results of these experiments in the temperature range 298 to 1950 K indicate that no appreciable reaction takes place between atomic hydrogen and TiN or TiC. The formation of reaction products (NH3, CH4, C2H2) should be favored at lower temperatures. However, because of the high catalytic activity of Ti for H atom recombination, the rate of such reactions with H atoms is controlled by the rate of evaporation of Ti from the surface, this rate being low at temperatures below 1200 K. In order to interpret the stability of TiN and TiC in H atoms more fully, the stability of TiN and TiC in vacuum and H2 gas was also studied. The thermodynamic computations conform in order of magnitude to the experimentally found rates of decomposition of TiN and TiC in vacuum and are also consistent with the fact that no appreciable reaction is found with these compounds in molecular H2 at a pressure of 10(exp -3) atmosphere in the temperature range 2980 to 2060 K. When TiN or TiC was heated in atomic H or molecular H2, no reaction products other than those obtained from the simple decomposition of the nitride and carbide were observed. The gaseous products were analyzed in a mass spectrometer.

  6. Square lattice honeycomb tri-carbide fuels for 50 to 250 KN variable thrust NTP design

    Science.gov (United States)

    Anghaie, Samim; Knight, Travis; Gouw, Reza; Furman, Eric

    2001-02-01

    Ultrahigh temperature solid solution of tri-carbide fuels are used to design an ultracompact nuclear thermal rocket generating 950 seconds of specific impulse with scalable thrust level in range of 50 to 250 kilo Newtons. Solid solutions of tri-carbide nuclear fuels such as uranium-zirconium-niobium carbide. UZrNbC, are processed to contain certain mixing ratio between uranium carbide and two stabilizing carbides. Zirconium or niobium in the tri-carbide could be replaced by tantalum or hafnium to provide higher chemical stability in hot hydrogen environment or to provide different nuclear design characteristics. Recent studies have demonstrated the chemical compatibility of tri-carbide fuels with hydrogen propellant for a few to tens of hours of operation at temperatures ranging from 2800 K to 3300 K, respectively. Fuel elements are fabricated from thin tri-carbide wafers that are grooved and locked into a square-lattice honeycomb (SLHC) shape. The hockey puck shaped SLHC fuel elements are stacked up in a grooved graphite tube to form a SLHC fuel assembly. A total of 18 fuel assemblies are arranged circumferentially to form two concentric rings of fuel assemblies with zirconium hydride filling the space between assemblies. For 50 to 250 kilo Newtons thrust operations, the reactor diameter and length including reflectors are 57 cm and 60 cm, respectively. Results of the nuclear design and thermal fluid analyses of the SLHC nuclear thermal propulsion system are presented. .

  7. Plasma Spraying and Characterization of Tungsten Carbide-Cobalt Coatings by the Water-Stabilized System WSP

    Directory of Open Access Journals (Sweden)

    Pavel Ctibor

    2009-01-01

    Full Text Available Tungsten carbide-cobalt powders (WC-17wt% Co were plasma sprayed by a water-stabilized system WSP. Experiments with variable feeding distances and spray distances were carried out. Thinner coatings were deposited on carbon steel substrates and thicker coatings on stainless steel substrates to compare different cooling conditions. Basic characterization of coatings was done by XRD, SEM, and light microscopy plus image analysis. Microhardness was measured on polished cross-sections. The main focus of investigation was resistance against wear in dry as well as wet conditions. The appropriate tests were performed with set-ups based on ASTM G65 and G75, respectively. The influence of spray parameters onto coating wear performance was observed. The results of mechanical tests were discussed in connection with changes of phase composition and with the quality of the coating's microstructure. The results show that for obtaining the best possible WC-17Co coating with WSP process, from the viewpoint of wear resistance, the desired parameters combination is long feeding distance combined with short spray distance.

  8. Effect of alloying elements on the composition of carbide phases and mechanical properties of the matrix of high-carbon chromium-vanadium steel

    Science.gov (United States)

    Titov, V. I.; Tarasenko, L. V.; Utkina, A. N.

    2017-01-01

    Based on the results of phase physicochemical analysis of high-carbon chromium-vanadium steel, the predominant type of carbide that provides high wear resistance has been established, and its amount and amount of carbon in martensite have been determined. Data on the composition and the amount of carbide phase and on the chemical composition of the martensite of high-carbon steel have been obtained, which allows determination of the alloying-element concentration limits. The mechanical testing of heats of a chosen chemical composition has been carried out after quenching and low-temperature tempering. The tests have demonstrated benefits of new steel in wear resistance and bending strength with the fatigue strength being retained, compared to steels subjected to cementation. The mechanism of secondary strengthening of the steel upon high-temperature tempering has been revealed. High-temperature tempering can be applied to articles that are required to possess both high wear resistance and heat resistance.

  9. Review of Combustion Stability Characteristics of Swirl Coaxial Element Injectors

    Science.gov (United States)

    Hulka, J. R.; Casiano, M. J.

    2013-01-01

    Liquid propellant rocket engine injectors using coaxial elements where the center liquid is swirled have become more common in the United States over the past several decades, although primarily for technology or advanced development programs. Currently, only one flight engine operates with this element type in the United States (the RL10 engine), while the element type is very common in Russian (and ex-Soviet) liquid propellant rocket engines. In the United States, the understanding of combustion stability characteristics of swirl coaxial element injectors is still very limited, despite the influx of experimental and theoretical information from Russia. The empirical and theoretical understanding is much less advanced than for the other prevalent liquid propellant rocket injector element types, the shear coaxial and like-on-like paired doublet. This paper compiles, compares and explores the combustion stability characteristics of swirl coaxial element injectors tested in the United States, dating back to J-2 and RL-10 development, and extending to very recent programs at the NASA MSFC using liquid oxygen and liquid methane and kerosene propellants. Included in this study are several other relatively recent design and test programs, including the Space Transportation Main Engine (STME), COBRA, J-2X, and the Common Extensible Cryogenic Engine (CECE). A presentation of the basic data characteristics is included, followed by an evaluation by several analysis techniques, including those included in Rocket Combustor Interactive Design and Analysis Computer Program (ROCCID), and methodologies described by Hewitt and Bazarov.

  10. First-principles calculations of structural stability and mechanical properties of tungsten carbide under high pressure

    Science.gov (United States)

    Li, Xinting; Zhang, Xinyu; Qin, Jiaqian; Zhang, Suhong; Ning, Jinliang; Jing, Ran; Ma, Mingzhen; Liu, Riping

    2014-11-01

    The structural stability and mechanical properties of WC in WC-, MoC- and NaCl-type structures under high pressure are investigated systematically by first-principles calculations. The calculated equilibrium lattice constants at zero pressure agree well with available experimental and theoretical results. The formation enthalpy indicates that the most stable WC is in WC-type, then MoC-type finally NaCl-type. By the elastic stability criteria, it is predicted that the three structures are all mechanically stable. The elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν of the three structures are studied in the pressure range from 0 to 100 GPa. Furthermore, by analyzing the B/G ratio, the brittle/ductile behavior under high pressure is assessed. Moreover, the elastic anisotropy of the three structures up to 100 GPa is also discussed in detail.

  11. Finite element exterior calculus: from Hodge theory to numerical stability

    CERN Document Server

    Arnold, Douglas N; Winther, Ragnar

    2009-01-01

    This article reports on the confluence of two streams of research, one emanating from the fields of numerical analysis and scientific computation, the other from topology and geometry. In it we consider the numerical discretization of partial differential equations that are related to differential complexes so that de Rham cohomology and Hodge theory are key tools for the continuous problem. After a brief introduction to finite element methods, the discretization methods we consider, we develop an abstract Hilbert space framework for analyzing stability and convergence. In this framework, the differential complex is represented by a complex of Hilbert spaces and stability is obtained by transferring Hodge theoretic structures from the continuous level to the discrete. We show stable discretization discretization is achieved if the finite element spaces satisfy two hypotheses: they form a subcomplex and there exists a bounded cochain projection from the full complex to the subcomplex. Next, we consider the mos...

  12. First-principles study of the stability and diffusion properties of hydrogen in zirconium carbide

    Science.gov (United States)

    Yang, Xiao-Yong; Lu, Yong; Zhang, Ping

    2016-10-01

    The stability and diffusion properties of interstitial hydrogen atom in bulk ZrC have been investigated by first-principles calculations. In energy, hydrogen atoms prefer to occupy the carbon substitutional site (C-SS) with a negative formation energy, consistent with the experimental observations. In the C-SS, the hydrogen atom obtains 0.702 electrons from its 1 NN Zr atoms, tending to achieve the most stable 1s2 electronic state. Two hydrogen atoms in the same tetrahedral interstitial site are able to form a pairing cluster along the direction with the Hsbnd H pair equilibrium distance of 1.30 Å, nearly twice the length of H2 bond, suggesting a relatively weak interaction between the Hsbnd H pair. The diffusion energy barriers of hydrogen in pure and vacancy pre-existing ZrC matrix are calculated. It is found that the presence of native vacancies will capture the hydrogen atoms due to the large energy barrier to jump out the vacancy. Furthermore, the temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium in ZrC are predicted using the transition state theory.

  13. Tungsten-zirconium carbide-rhenium alloys with extraordinary thermal stability

    Energy Technology Data Exchange (ETDEWEB)

    Yang, X.D. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Xie, Z.M.; Miao, S. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Liu, R.; Jiang, W.B. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Zhang, T., E-mail: zhangtao@issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Wang, X.P., E-mail: xpwang@issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Fang, Q.F. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); University of Science and Technology of China, Hefei 230026 (China); Liu, C.S., E-mail: csliu@issp.ac.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Luo, G.N. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Liu, X. [Southwest Institute of Plasma Physics, Chengdu (China)

    2016-05-15

    The low recrystallization temperature (1200 °C) of pure W is a serious limitation for application as facing plasma materials in fusion reactor. In this paper, W-0.5wt.%ZrC-1wt.%Re (WZR) alloy with recrystallization temperature up to 1800 °C was prepared by mechanical milling and spark plasma sintering. The grain size of WZR alloy is about 2.6 μm, smaller than that of pure W (4.4 μm), which keeps unchanged until the annealing temperature increases to 1800 °C. Tensile tests indicate that the WZR alloys exhibit excellent comprehensive properties: the ductile to brittle transition temperature of WZR is in the range from 400 °C to 500 °C, about 200 °C lower than that of pure W prepared by the same process; the total elongation (TE) of WZR at 600 °C is above 30%, which is about 2 times that of pure W (at 700 °C). Meanwhile its tensile strength keeps ∼450 MPa before and after 1800 °C annealing as well as its TE increases after annealing. WZR alloy exhibits higher hardness (489HV) than that of pure W (453HV) at room temperature. Microstructure analysis indicates that the strengthening of nano-sized ZrC particles dispersion and Re solid solution improve tensile properties and thermal stability of WZR alloy.

  14. PYROLYTIC CARBIDE DEVELOPMENT PROGRAM

    Science.gov (United States)

    and injector design changes were made to improve the quality of the carbide produced. Niobium carbide and tantalum carbide coated nozzles are described...Additional data for pyrolytic niobium carbide and hafnium carbide is also presented. (Author)

  15. The influence of annealing in the ferrite-plus-austenite phase field on the stability of vanadium carbide precipitates

    Science.gov (United States)

    Locci, I. E.; Michal, G. M.

    1989-01-01

    The effect of rapid excursions into the ferrite-plus-austenite two-phase field on V4C3 precipitates formed by tempering in the ferrite phases was investigated. Heat treatments were first performed to produce a starting microstructure of fine vanadium carbide particles precipitated in a ferrite matrix, and the microstructure was then subjected to various short-time heat treatment cycles that transformed part of the matrix to austenite. TEM was used to determine the effects of the matrix change on the size, morphology, and distribution of the vanadium carbide particles.

  16. Biocompatibility of beta-stabilizing elements of titanium alloys.

    Science.gov (United States)

    Eisenbarth, E; Velten, D; Müller, M; Thull, R; Breme, J

    2004-11-01

    In comparison to the presently used alpha + beta titanium alloys for biomedical applications, beta-titanium alloys have many advantageous mechanical properties, such as an improved wear resistance, a high elasticity and an excellent cold and hot formability. This will promote their future increased application as materials for orthopaedic joint replacements. Not all elements with beta-stabilizing properties in titanium alloys are suitable for biomaterial applications-corrosion and wear processes cause a release of these alloying elements to the surrounding tissue. In this investigation, the biocompability of alloying elements for beta- and near beta-titanium alloys was tested in order to estimate their suitability for biomaterial components. Titanium (grade 2) and the implant steel X2CrNiMo18153 (AISI 316 L) were tested as reference materials. The investigation included the corrosion properties of the elements, proliferation, mitochondrial activity, cell morphology and the size of MC3T3-E1 cells and GM7373 cells after 7 days incubation in direct contact with polished slices of the metals. The statistical significance was considered by Weir-test and Lord-test (alpha = 0.05). The biocompatibility range of the investigated metals is (decreasing biocompatibility): niobium-tantalum, titanium, zirconium-aluminium-316 L-molybdenum.

  17. Extended X-Ray Absorption Fine Structure Investigation of Carbon Stabilized Expanded Austenite and Carbides in Stainless Steel AISI 316

    DEFF Research Database (Denmark)

    Oddershede, Jette; Christiansen, Thomas; Ståhl, Kenny;

    2011-01-01

    Low temperature carburized AISI 316 stainless steel - carbon expanded austenite - was investigated with EXAFS and synchrotron diffraction together with synthesized carbides of the type M3C2, M7C3 and M23C6. It was found that the chemical environment of carbon expanded austenite is not associated ...

  18. Epitaxial Stabilization between Intermetallic and Carbide Domains in the Structures of Mn16SiC4 and Mn17Si2C4.

    Science.gov (United States)

    Fredrickson, Rie T; Guo, Yiming; Fredrickson, Daniel C

    2016-01-13

    The concept of frustration between competing geometrical or bonding motifs is frequently evoked in explaining complex phenomena in the structures and properties of materials. This idea is of particular importance for metallic systems, where frustration forms the basis for the design of metallic glasses, a source of diverse magnetic phenomena, and a rationale for the existence of intermetallics with giant unit cells containing thousands of atoms. Unlike soft materials, however, where conflicts can be synthetically encoded in the molecular structure, staging frustration in the metallic state is challenging due to the ease of macroscopic segregation of incompatible components. In this Article, we illustrate one approach for inducing the intergrowth of incompatible bonding motifs with the synthesis and characterization of two new intermetallic carbides: Mn16SiC4 (mC42) and Mn17Si2C4 (mP46). Similar to the phases Mn5SiC and Mn8Si2C in the Mn-Si-C system, these compounds appear as intergrowths of Mn3C and tetrahedrally close-packed (TCP) regions reminiscent of Mn-rich Mn-Si phases. The nearly complete spatial segregation of Mn-Si (intermetallic) and Mn-C (carbide) interactions in these structures can be understood from the differing geometrical requirements of C and Si. Rather than macroscopically separating into distinct phases, though, the two bonding types are tightly interwoven, with most Mn atoms being on the interfaces. DFT chemical pressure analysis reveals a driving force stabilizing these interfaces: the major local pressures acting between the Mn atoms in the Mn-Si and Mn-C systems are of opposite signs. Joining the intermetallic and carbide domains together then provides substantial relief to these local pressures, an effect we term epitaxial stabilization.

  19. Nanostructured Metal Carbides for Aprotic Li-O2 Batteries: New Insights into Interfacial Reactions and Cathode Stability.

    Science.gov (United States)

    Kundu, Dipan; Black, Robert; Adams, Brian; Harrison, Katharine; Zavadil, Kevin; Nazar, Linda F

    2015-06-18

    The development of nonaqueous Li-oxygen batteries, which relies on the reversible reaction of Li + O2 to give lithium peroxide (Li2O2), is challenged by several factors, not the least being the high charging voltage that results when carbon is typically employed as the cathode host. We report here on the remarkably low 3.2 V potential for Li2O2 oxidation on a passivated nanostructured metallic carbide (Mo2C), carbon-free cathode host. Online mass spectrometry coupled with X-ray photoelectron spectroscopy unequivocally demonstrates that lithium peroxide is simultaneously oxidized together with the Li(x)MoO3-passivated conductive interface formed on the carbide, owing to their close redox potentials. The process rejuvenates the surface on each cycle upon electrochemical charge by releasing Li(x)MoO3 into the electrolyte, explaining the low charging potential.

  20. Stability Estimates for ℎ- Spectral Element Methods for Elliptic Problems

    Indian Academy of Sciences (India)

    Pravir Dutt; Satyendra Tomar; B V Rathish Kumar

    2002-11-01

    In a series of papers of which this is the first we study how to solve elliptic problems on polygonal domains using spectral methods on parallel computers. To overcome the singularities that arise in a neighborhood of the corners we use a geometrical mesh. With this mesh we seek a solution which minimizes a weighted squared norm of the residuals in the partial differential equation and a fractional Sobolev norm of the residuals in the boundary conditions and enforce continuity by adding a term which measures the jump in the function and its derivatives at inter-element boundaries, in an appropriate fractional Sobolev norm, to the functional being minimized. Since the second derivatives of the actual solution are not square integrable in a neighborhood of the corners we have to multiply the residuals in the partial differential equation by an appropriate power of $r_k$, where $r_k$ measures the distance between the point and the vertex $A_k$ in a sectoral neighborhood of each of these vertices. In each of these sectoral neighborhoods we use a local coordinate system $(_k, _k)$ where $_k = ln r_k$ and $(r_k, _k)$ are polar coordinates with origin at $A_k$, as first proposed by Kondratiev. We then derive differentiability estimates with respect to these new variables and a stability estimate for the functional we minimize. In [6] we will show that we can use the stability estimate to obtain parallel preconditioners and error estimates for the solution of the minimization problem which are nearly optimal as the condition number of the preconditioned system is polylogarithmic in , the number of processors and the number of degrees of freedom in each variable on each element. Moreover if the data is analytic then the error is exponentially small in .

  1. Stability against $\\alpha$ decay of some recently observed superheavy elements

    CERN Document Server

    Chowdhury, Partha Roy; Bhattacharyya, Abhijit

    2011-01-01

    The probability of $\\alpha$ particle emission for some recently observed superheavy nuclei (SHN) are investigated. The $\\alpha$-decay half lives of SHN are calculated in a quantum tunneling model with density dependent M3Y (DDM3Y) effective nuclear interaction using theoretical and measured $Q_\\alpha$ values. We determine the density distribution of $\\alpha$ and daughter nuclei from the relativistic mean field theory (RMF) using FSUGold force, NL3 and TM1 parameter sets. The double folded nuclear potential is numerically calculated in a more microscopic manner using these density distributions. The estimated values of $\\alpha$-decay half-lives are in good agreement with the recent data. We compare our results with recently detected $\\alpha$-decay chains from new element with atomic number Z=117 reported by JINR, Dubna. Finally, we determine the half-lives of superheavy elements with Z=108-120 and neutron number N=152-190 to explore the long-standing predictions on the existence of an "island of stability" due...

  2. Recent developments and on-line tests of uranium carbide targets for production of nuclides far from stability

    CERN Document Server

    Panteleev, V.N; Barzakh, A.E; Fedorov, D.V; Ionan, A.M; Ivanov, V.S; Mezilev, K.A; Molkanov, P.L; Moroz, F.V; Orlov, S.Yu; Volkov, Yu.M; Alyakrinskiy, O; Lanchais, A; Lau, C; Lhersonneau, G; Rizzi, V; Stroe, L; Tecchio, L.B; Dubois, M; Eleon, C; Gaubert, G; Jardin, P; Saint Laurent, M.G; Villari, A.C.C; Essabaa, S; O. Bajeat; Mhamed, C; Leroy, R; 10.1140/epjst/e2007-00328-y

    2007-01-01

    The capacity of uranium carbide target materials of different structure and density for production of neutron-rich and heavy neutron-deficient nuclides have been investigated. The yields of Cs and Fr produced by a 1 GeV proton beam of the PNPI synchrocyclotron and release properties of different targets have been measured. The comparison of the yields and release efficiencies of Cs and Fr produced from a high density UC target material and from low density UCx prepared by the ISOLDE method at IRIS in the collaboration with PARRNe group from Orsay are presented. The yields from ISOLDE original target are presented for comparison as well.

  3. Effects of Carbon, Nitrogen and Stabilizing Elements(Ti, Nb) On the Intergranular Corrosion of Type 409 Stainless Steel

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Mee Cha [Pohang College, Pohang (Korea, Republic of); Kim, Dai Ryong [Kyungpook National University, Daegu (Korea, Republic of)

    1996-03-15

    The effects of carbon, nitrogen and titanium(niobium) on the intergranular corrosion(IGC) behavior of type 409 stainless steel were investigated. The alloys were heat treated at three different annealing temperature for times varying between 6 minutes and 5 hours and then tested for intergranular corrosion susceptibility in acidified copper-copper sulfate solution. For the nonstabilized alloys, susceptibility to IGC increased due to precipitate chromium carbides and nitrides at grain boundaries by annealing at 550 .deg. C and 1050 .deg. C. Sensitization was due to the precipitation behavior produced during isothermal annealing in the 550 .deg. C and during slow cooling from 1050 .deg. C of specimen. In the effect of addition elements on the IGC, alloys containing 0.024%C plus 0.018%N were shown the most severe IGC with eventual grain dropping when they were annealed at 550 .deg. C. Influence of carbon on IGC was dominant for short heating time at 1050 .deg. C and that of nitrogen was dominant for long heating time. The stabilized alloys have good resistance to IGC because the amount of titanium and niobium was sufficient to stabilize carbon and nitrogen in this chemical etch solution.

  4. Structure, bonding and stability of semi-carbides M{sub 2}C and sub-carbides M{sub 4}C (M=V, Cr, Nb, Mo, Ta, W): A first principles investigation

    Energy Technology Data Exchange (ETDEWEB)

    Abderrahim, F.Z., E-mail: sara_ais@yahoo.fr [Unite de Recherche Materiaux et Energie Renouvelables, URMER, Universite de Tlemcen (Algeria); Faraoun, H.I. [Unite de Recherche Materiaux et Energie Renouvelables, URMER, Universite de Tlemcen (Algeria); Ouahrani, T. [Laboratoire de Physique Theorique, Universite de Tlemcen B.P. 230, 13000 Tlemcen (Algeria); Ecole Preparatoire en Sciences et Techniques, B.P. 230, 13000 Tlemcen (Algeria)

    2012-09-15

    Density functional theory within the generalized gradient approximation (GGA) is used to investigate the electronic structure and formation energies of semi-carbides M{sub 2}C and sub-carbides M{sub 4}C (where M=V, Cr, Nb, Mo, Ta and W). Our results show that M{sub 2}C carbides are more stable than M{sub 4}C. Total and partial densities of states were obtained and analyzed systematically for these phases. Moreover, the bonding nature of M{sub 2}C polymorphs is studied from the point of view of the Quantum Theory of Atoms in Molecules (QTAIM). It is found that inter-atomic interactions in these carbides are of mixed type including ionic, covalent and metallic components.

  5. Hydroxide catalysis bonding of silicon carbide

    NARCIS (Netherlands)

    Veggel, A.A. van; Ende, D.A. van den; Bogenstahl, J.; Rowan, S.; Cunningham, W.; Gubbels, G.H.M.; Nijmeijer, H.

    2008-01-01

    For bonding silicon carbide optics, which require extreme stability, hydroxide catalysis bonding is considered [Rowan, S., Hough, J. and Elliffe, E., Silicon carbide bonding. UK Patent 040 7953.9, 2004. Please contact Mr. D. Whiteford for further information: D.Whiteford@admin.gla.ac.uk]. This techn

  6. Silicon carbide reinforced silicon carbide composite

    Science.gov (United States)

    Lau, Sai-Kwing (Inventor); Calandra, Salvatore J. (Inventor); Ohnsorg, Roger W. (Inventor)

    2001-01-01

    This invention relates to a process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.

  7. Carbon-rich icosahedral boron carbides beyond B4C and their thermodynamic stabilities at high temperature and pressure from first principles

    Science.gov (United States)

    Ektarawong, A.; Simak, S. I.; Alling, B.

    2016-08-01

    We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from B4C to B2C , using first-principles calculations. Apart from B4C , generally addressed in the literature, B2.5C , represented by B10C2p (C-C), where Cp and (C-C) denote a carbon atom occupying the polar site of the icosahedral cluster and a diatomic carbon chain, respectively, is predicted to be thermodynamically stable under high pressures with respect to B4C as well as pure boron and carbon phases. The thermodynamic stability of B2.5C is determined by the Gibbs free energy G as a function of pressure p and temperature T , in which the contributions from the lattice vibrations and the configurational disorder are obtained within the quasiharmonic and the mean-field approximations, respectively. The stability range of B2.5C is then illustrated through the p -T phase diagrams. Depending on the temperatures, the stability range of B2.5C is predicted to be within the range between 40 and 67 GPa. At T ≳ 500 K, the icosahedral Cp atoms in B2.5C configurationally disorder at the polar sites. By investigating the properties of B2.5C , e.g., elastic constants and phonon and electronic density of states, we demonstrate that B2.5C is both mechanically and dynamically stable at zero pressure, and is an electrical semiconductor. Furthermore, based on the sketched phase diagrams, a possible route for experimental synthesis of B2.5C as well as a fingerprint for its characterization from the simulations of x-ray powder diffraction pattern are suggested.

  8. Determination of the stability limit of a thermoacoustic engine by means of finite elements

    NARCIS (Netherlands)

    de Jong, Anne; Wijnant, Ysbrand H.; de Boer, Andries

    2013-01-01

    A finite element model is presented to obtain the stability limit of, as an example, 2D standing wave thermoacoustic engine. The stability limit is the required heating to obtain self-sustained (thermo)acoustic oscillations. The method used to obtain the stability limit is not restricted to the exam

  9. Chemical Modification Methods of Nanoparticles of Silicon Carbide Surface

    OpenAIRE

    Anton S. Yegorov; Vitaly S. Ivanov; Alexey V. Antipov; Alyona I. Wozniak; Kseniia V. Tcarkova.

    2015-01-01

    silicon carbide exhibits exceptional properties: high durability, high thermal conductivity, good heat resistance, low thermal expansion factor and chemical inactivity. Reinforcement with silicon carbide nanoparticles increases polymer’s tensile strength and thermal stability.Chemical methods of modification of the silicon carbide surface by means of variety of reagents from ordinary molecules to macromolecular polymers are reviewed in the review.The structure of silicon carbide surface layer...

  10. Finite Element Formulation for Stability and Free Vibration Analysis of Timoshenko Beam

    Directory of Open Access Journals (Sweden)

    Abbas Moallemi-Oreh

    2013-01-01

    Full Text Available A two-node element is suggested for analyzing the stability and free vibration of Timoshenko beam. Cubic displacement polynomial and quadratic rotational fields are selected for this element. Moreover, it is assumed that shear strain of the element has the constant value. Interpolation functions for displacement field and beam rotation are exactly calculated by employing total beam energy and its stationing to shear strain. By exploiting these interpolation functions, beam elements' stiffness matrix is also examined. Furthermore, geometric stiffness matrix and mass matrix of the proposed element are calculated by writing governing equation on stability and beam free vibration. At last, accuracy and efficiency of proposed element are evaluated through numerical tests. These tests show high accuracy of the element in analyzing beam stability and finding its critical load and free vibration analysis.

  11. Synthesis and characterization of transition metal carbides and their catalytic applications

    Science.gov (United States)

    Wan, Cheng

    Transition metal (both monometallic and bimetallic) carbides have been synthesized by an amine-metal oxide composite (AMOC) method. The composite reduces the diffusion distances among each element and allows the formation of carbides to take place as low as 610°C, which is significantly lower than traditional carbide synthesis methods (above 1500°C). Additionally, amines act not only as carbon sources and reducing agents, but also morphological templates which helps to make uniform transition metal carbide (TMC) nanocrystals with various shapes. Beyond morphology control, AMOC method can also help to synthesize multiple phases of monometallic carbides, which includes four phases of molybdenum carbides (alpha-MoC1-x, beta-Mo2C, eta-MoC, and gamma-MoC), two phases of tungsten carbides (W2C and WC), and three phases of chromium carbides (Cr3C2-x, Cr7C3, and Cr3C2). Molybdenum carbide has been proposed as a possible alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Previous studies were limited to only one phase, which is beta-Mo2C with an Fe 2N structure. Here, four molybdenum carbide materials including gamma-MoC with a WC type structure which was stabilized for the first time as a phase pure nanomaterial. Moreover, a wide range of magnetic iron-doped molybdenum carbide (Mo2-xFexC) nanomaterials were also synthesized, which exhibits a better HER activity to non-doped beta-Mo2C. A group of (CrxFe1-x)7C3 (0.2< x<1) solid solutions have also been synthesized for the first time as nanomaterials via AMOC method, which demonstrate excellent catalytic activities for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Other carbides/nitrides made from AMOCs include WN1-x, Fe3C, Fe3-xN, Fe3Mo3C, N 2Mo3C, Ni3Mo3C, Ni6Mo 6C, and Mo0.5W0.5C.

  12. Synthesis and thermal stability of two-dimensional carbide MXene Ti{sub 3}C{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhengyang; Wang, Libo; Sun, Dandan; Zhang, Yude; Liu, Baozhong; Hu, Qianku; Zhou, Aiguo, E-mail: zhouag@hpu.edu.cn

    2015-01-15

    Graphical abstract: - Highlights: • Ti{sub 3}C{sub 2} from PLS-Ti{sub 3}AlC{sub 2} was highly oriented compared to that from HP-Ti{sub 3}AlC{sub 2}. • Small balls of possible AlF{sub 3} attached on the edge of MXene sheets were observed. • MXene is thermally stable in Ar atmosphere up to 800 °C. • A structure of nano-anatase on 2D Ti{sub 3}C{sub 2} was formed by 200 °C oxidization. - Abstract: We investigated the synthesis of quasi-two-dimensional carbide (Ti{sub 3}C{sub 2}), with the name of MXene, by immersing Ti{sub 3}AlC{sub 2} in 40% or 49% hydrofluoric acid (HF) at 0 °C, 15 °C or 60 °C. The influences of time, temperature, and source of Ti{sub 3}AlC{sub 2} on the synthesis were researched. It was found that Ti{sub 3}C{sub 2} synthesized from pressureless synthesized Ti{sub 3}AlC{sub 2} was highly oriented compared to that from hot-pressed Ti{sub 3}AlC{sub 2}. As-synthesized Ti{sub 3}C{sub 2} could be further exfoliated by intercalation with urea, dimethylsulfoxide or ammonia. From the results of thermogravimetry and differential scanning calorimetry, Ti{sub 3}C{sub 2} MXene with F/OH termination was found to be stable in argon atmosphere at temperature up to 800 °C. In oxygen atmosphere, at 200 °C, parts of MXene layers were oxidized to obtain an interesting structure: anatase nano-crystals were evenly distributed on 2D Ti{sub 3}C{sub 2} layers. At 1000 °C, MXene layers were completely oxidized and anatase phase fully transformed to rutile in oxygen atmosphere.

  13. Dispersing stability of nano boron carbide in water-based fluid%纳米碳化硼在水基础液中的分散稳定性

    Institute of Scientific and Technical Information of China (English)

    宋铮铮; 吴张永; 莫子勇; 王娴; 王娟

    2015-01-01

    以纳米碳化硼粉体为纳米材料,聚乙二醇、羧甲基纤维素钠为分散剂,蒙脱石为抗沉降稳定剂,RO反渗透膜处理水为分散介质,采用两步法制备了水基纳米碳化硼溶液。研究了不同分散条件对纳米碳化硼在水基础液中的分散情况,并采用沉降稳定性分析、流变特性分析来评价其分散效果。实验结果表明,分散剂种类、分散剂质量分数、纳米碳化硼的粒径、纳米碳化硼的质量分数都会对溶液分散稳定性产生一定的影响。研究得出,用质量分数为0.4%的聚乙二醇(PEG600)作为分散剂、用粒径为60nm的纳米碳化硼且质量分数为0.8%~0.9%时,能够使得纳米碳化硼在水基础液中达到最佳稳定分散的效果。%Water-based nano boron solution was prepared with nano boron carbide powder as nanomaterial,polyethylene glycol,sodium carboxymethyl cellulose as dispersing agent, montmorillonite as antisedimentation stabilizer,RO reverse osmosis membrane-treated water as dispersion medium by using the two-step method. To study the different dispersion conditions of nano boron carbide dispersion in water-based fluid,sedimentation stability and rheological characteristics analysis were used to evaluate its dispersion effect. The experimental results showed that dispersant type,mass fraction of dispersant,particle size of nano boron carbide,mass fraction of nano boron carbide could affect stability of solution dispersion. Polyethylene glycol 600 as a dispersant,mass fraction of 0.4%,60nm particle size of nano-boron carbide and mass fraction of 0.8%-0.9%,could achieve stable dispersion of nano boron carbide in water-based fluid.

  14. CONVERGENCE OF SIMPLIFIED AND STABILIZED MIXED ELEMENT FORMATS BASED ON BUBBLE FUNCTION FOR THE STOKES PROBLEM

    Institute of Scientific and Technical Information of China (English)

    罗振东; 朱江

    2002-01-01

    Two simplified and stabilized mixed element formats for the Stokes problem are derived by bubble function, and their convergence,i.e,error analysis, are proved.These formats can save more freedom degrees than other usual formats.

  15. Numerical Investigations on Several Stabilized Finite Element Methods for the Stokes Eigenvalue Problem

    Directory of Open Access Journals (Sweden)

    Pengzhan Huang

    2011-01-01

    Full Text Available Several stabilized finite element methods for the Stokes eigenvalue problem based on the lowest equal-order finite element pair are numerically investigated. They are penalty, regular, multiscale enrichment, and local Gauss integration method. Comparisons between them are carried out, which show that the local Gauss integration method has good stability, efficiency, and accuracy properties, and it is a favorite method among these methods for the Stokes eigenvalue problem.

  16. Full gradient stabilized cut finite element methods for surface partial differential equations

    Science.gov (United States)

    Burman, Erik; Hansbo, Peter; Larson, Mats G.; Massing, André; Zahedi, Sara

    2016-10-01

    We propose and analyze a new stabilized cut finite element method for the Laplace-Beltrami operator on a closed surface. The new stabilization term provides control of the full $\\mathbb{R}^3$ gradient on the active mesh consisting of the elements that intersect the surface. Compared to face stabilization, based on controlling the jumps in the normal gradient across faces between elements in the active mesh, the full gradient stabilization is easier to implement and does not significantly increase the number of nonzero elements in the mass and stiffness matrices. The full gradient stabilization term may be combined with a variational formulation of the Laplace-Beltrami operator based on tangential or full gradients and we present a simple and unified analysis that covers both cases. The full gradient stabilization term gives rise to a consistency error which, however, is of optimal order for piecewise linear elements, and we obtain optimal order a priori error estimates in the energy and $L^2$ norms as well as an optimal bound of the condition number. Finally, we present detailed numerical examples where we in particular study the sensitivity of the condition number and error on the stabilization parameter.

  17. Numerical research orthotropic geometrically nonlinear shell stability using the mixed finite element method

    Science.gov (United States)

    Stupishin, L.; Nikitin, K.; Kolesnikov, A.

    2017-05-01

    A methodology for shell stability research and determining buckling load, based on the mixed finite element method are proposed. Axisymmetric geometrically nonlinear shallow shells made of orthotropic material are considered. The results of numerical research of stability by changing the shape of shells, ratio of elastic modulus of the material and parameters of the support contour are presented.

  18. Stability of a laser cavity with non-parabolic phase transformation elements

    CSIR Research Space (South Africa)

    Litvin, IA

    2013-05-01

    Full Text Available In this paper we present a general approach to determine the stability of a laser cavity which can include non-conventional phase transformation elements. We consider two pertinent examples of the detailed investigation of the stability of a laser...

  19. Tribological and thermal stability study of nanoporous amorphous boron carbide films prepared by pulsed plasma chemical vapor deposition

    Science.gov (United States)

    Liza, Shahira; Ohtake, Naoto; Akasaka, Hiroki; Munoz-Guijosa, Juan M.

    2015-06-01

    In this work, the thermal stability and the oxidation and tribological behavior of nanoporous a-BC:H films are studied and compared with those in conventional diamond-like carbon (DLC) films. a-BC:H films were deposited by pulsed plasma chemical vapor deposition using B(CH3)3 gas as the boron source. A DLC interlayer was used to prevent the a-BC:H film delamination produced by oxidation. Thermal stability of a-BC:H films, with no delamination signs after annealing at 500 °C for 1 h, is better than that of the DLC films, which completely disappeared under the same conditions. Tribological test results indicate that the a-BC:H films, even with lower nanoindentation hardness than the DLC films, show an excellent boundary oil lubricated behavior, with lower friction coefficient and reduce the wear rate of counter materials than those on the DLC film. The good materials properties such as low modulus of elasticity and the formation of micropores from the original nanopores during boundary regimes explain this better performance. Results show that porous a-BC:H films may be an alternative for segmented DLC films in applications where severe tribological conditions and complex shapes exist, so surface patterning is unfeasible.

  20. A conservative stabilized finite element method for the magneto-hydrodynamic equations

    Science.gov (United States)

    Ben Salah, Nizar; Soulaimani, Azzeddine; Habashi, Wagdi G.; Fortin, Michel

    1999-03-01

    This work presents a finite element solution of the 3D magneto-hydrodynamics equations. The formulation takes explicitly into account the local conservation of the magnetic field, giving rise to a conservative formulation and introducing a new scalar variable. A stabilization technique is used in order to allow equal linear interpolation on tetrahedral elements of all the variables. Numerical tests are performed in order to assess the stability and the accuracy of the resulting methods. The convergence rates are calculated for different stabilization parameters. Well-known MHD benchmark tests are calculated. Results show good agreement with analytical solutions. Copyright

  1. Solidification/Stabilization of Elemental Mercury Waste by Amalgamation

    Energy Technology Data Exchange (ETDEWEB)

    Yim, S. P.; Ahn, B. G.; Lee, H. J.; Shon, J. S.; Chung, H.; Kim, K. J.; Lee, C. K.

    2003-02-24

    Experiments on solidification of elemental mercury waste were conducted by amalgamation with several metal powders such as copper, zinc, tin, brass and bronze. Unlike the previous studies which showed a dispersible nature after solidification, the waste forms were found to possess quite large compressive strengths in both copper and bronze amalgam forms. The durability was also confirmed by showing very minor changes of strength after 90 days of water immersion. Leachability from the amalgam forms is also shown to be low: measured mercury concentration in the leachate by the Toxicity Characteristic Leaching Procedure (TCLP) was well below the Environmental Protection Agency (EPA) limit. Long term leaching behavior by Accelerated Leach Test (ALT) has shown that the leaching process was dominated by diffusion and the effective diffusion coefficient was quite low (around 10-19 cm2/sec). The mercury vapor concentration from the amalgam forms were reduced to a 20% level of that for elemental mercury and to one-hundredth after 3 months.

  2. Stabilization of numerical interchange in spectral-element magnetohydrodynamics

    Science.gov (United States)

    Sovinec, C. R.

    2016-08-01

    Auxiliary numerical projections of the divergence of flow velocity and vorticity parallel to magnetic field are developed and tested for the purpose of suppressing unphysical interchange instability in magnetohydrodynamic simulations. The numerical instability arises with equal-order C0 finite- and spectral-element expansions of the flow velocity, magnetic field, and pressure and is sensitive to behavior at the limit of resolution. The auxiliary projections are motivated by physical field-line bending, and coercive responses to the projections are added to the flow-velocity equation. Their incomplete expansions are limited to the highest-order orthogonal polynomial in at least one coordinate of the spectral elements. Cylindrical eigenmode computations show that the projections induce convergence from the stable side with first-order ideal-MHD equations during h-refinement and p-refinement. Hyperbolic and parabolic projections and responses are compared, together with different methods for avoiding magnetic divergence error. The projections are also shown to be effective in linear and nonlinear time-dependent computations with the NIMROD code Sovinec et al. [17], provided that the projections introduce numerical dissipation.

  3. Stability of silicon and titanium carbide suspensions in electrolyte, poly(ethylene oxide), and PEO-surfactant solutions.

    Science.gov (United States)

    Barany, Sandor; Eremenko, Boris V; Malysheva, Mariya L

    2004-07-01

    It has been shown that the coagulation values of counterions for SiC and TiC suspensions with particle radius from 0.5 to 5 microm obey a z(2.5-3.5) law and there is an insufficient change in the critical concentration of 1-1 electrolytes (CCE) when the surface potential of particles increases more than two times. Also, the CCE values hardly depend on the position of counterions in the lyotropic sequence. This is explained by aggregation of SiC and TiC particles at a secondary minimum, which is proved by calculations of the potential curves of interparticle interactions using the DLVO theory. The adsorption of poly(ethylene oxide) on the surfaces studied does not cause--in contradiction to dispersions with smaller particles--an unlimited growth in the stability of suspensions. This is due to the aggregation of large particles with adsorbed PEO, as in polymer-free dispersions, under barrierless conditions in which the coordinates of the secondary minimum are determined by superposition of molecular attractive forces and steric repulsive forces of adsorbed polymeric chains, without a contribution from the electric repulsion term. PEO-anionic surfactant complexes possess higher stabilizing capacity compared to the individual components of the mixture. Our results show that the adsorbed polymer layers may hinder the aggregation both in the primary and in the secondary minimum for not very large particles only, the critical size of which depends on the dispersed phase nature and the molecular mass of the polymer.

  4. Titanium Carbide-Graphite Composites

    Science.gov (United States)

    1991-11-08

    titanium carbide , titanium carbide with free graphite, titanium carbide /vanadium carbide alloy with free graphite, and titanium carbide with...from melts. The test pins were drawn across hot pressed titanium carbide wear plates with 5 newtons of normal force. The lowest friction coefficient at...22 C was 0.12 obtained with pure titanium carbide . The lowest friction coefficient at 900 C was 0.19 obtained with titanium carbide with boron and

  5. Dynamic stability of deformable elements of one class of aeroelastic constructions

    Science.gov (United States)

    Velmisov, Petr A.; Ankilov, Andrey V.; Semenova, Elizaveta P.

    2016-12-01

    At designing of the constructions and the devices interacting with the flow of gas or liquid, it is necessary to solve the problems associated with the investigation of the stability required for their functioning and operational reliability. The definition of stability of an elastic body corresponds to the Lyapunov's concept of stability of dynamical system. A mathematical model of the device relating to the vibration technique, which is intended for intensification of technological processes, for example, the process of mixing, is considered. The action of these devices is based on the oscillations of elastic elements at the flowing around gas or liquid flow. The dynamic stability of the elastic element, located inside of the flow channel with the subsonic flow of gas or liquid (in an ideal model of a compressible environment) is investigated. The model is described by coupled system of partial differential equations for the unknown functions - the potential of the gas velocity and deformation of the elastic element. On the basis of the construction of functional, the sufficient conditions of the dynamical stability, imposing restrictions on the free-stream velocity of the gas, the flexural stiffness of the elastic element, and other parameters of the mechanical system are obtained. The examples of construction of the stability regions for particular parameters of the mechanical system are presented.

  6. Tribochemical interactions of boron carbides against steel

    Energy Technology Data Exchange (ETDEWEB)

    Gogotsi, Yu.G. (Univ. Karlsruhe, Inst. fuer Keramik im Maschinenbau (Germany)); Koval' chenko, A.M.; Kossko, I.A. (Inst. for Problems of Materials Science, Ukrainian Academy of Sciences, Kiev (Ukraine))

    1992-04-15

    Auger electron spectroscopy and electron microscopy were used to investigate the surface chemistry and tribological properties of boron carbide sliding against steel. It was revealed that the interacting process was accompanied by the diffusion of the ceramic elements into steel and by the oxidation of the steel and ceramic surfaces due to the oxygen presence in the atmosphere. It was established that the oxidation process in air or during friction tests leads to a graphitized layer on the boron carbide surface under the B{sub 2}O{sub 3} film. It was demonstrated that the oxidation caused a decrease in the friction coefficient of boron carbide sliding against steel. (orig.).

  7. Cerium carbide embedded in nitrogen-doped carbon as a highly active electrocatalyst for oxygen reduction reaction

    Science.gov (United States)

    Wang, Wei; Xue, Shouyuan; Li, Jinmei; Wang, Fengxia; Kang, Yumao; Lei, Ziqiang

    2017-08-01

    In this study, cerium carbide embedded in nitrogen-doped carbon (CeCx-NC) has been prepared by a facile pyrolysis of melamine formaldehyde resin containing rare-earth element. The as-prepared CeCx-NC catalyst shows high electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline electrolyte, with the half wave potential being almost equal to commercial Pt/C, nearly four electron transfer number, good toxicity tolerance durability and cycle stability. This rare-earth metal carbide opens a novel avenue for advanced electrocatalyst.

  8. Interval finite element method and its application on anti-slide stability analysis

    Institute of Scientific and Technical Information of China (English)

    SHAO Guo-jian; SU Jing-bo

    2007-01-01

    The problem of interval correlation results in interval extension is discussed by the relationship of interval-valued functions and real-valued functions. The methods of reducing interval extension are given. Based on the ideas of the paper, the formulas of sub-interval perturbed finite element method based on the elements are given. The sub-interval amount is discussed and the approximate computation formula is given. At the same time, the computational precision is discussed and some measures of improving computational efficiency are given. Finally, based on sub-interval perturbed finite element method and anti-slide stability analysis method, the formula for computing the bounds of stability factor is given. It provides a basis for estimating and evaluating reasonably anti-slide stability of structures.

  9. Quantitative evaluation of carbides in nickel-base superalloy MAR-M247

    Science.gov (United States)

    Szczotok, A.

    2011-05-01

    It has been established that carbides in superalloys serve three functions. Fine carbides precipitated in the matrix give strengthening results. Carbides also can tie up certain elements that would otherwise promote phase instability during service. Grain boundary carbides prevent or retard grain-boundary sliding and strengthen the grain boundary, which depends significantly on carbide shape, size and distribution. Various types of carbides are possible, depending on superalloy composition and processing. In the paper optical and scanning electron microscopy investigations of carbides occurring in specimens of the polycrystalline nickel-base superalloy MAR-M247 were carried out. Conditions of carbides revealing and microstructure images acquisition have been described. Taking into consideration distribution and morphology of the carbides in matrix a method of quantitative description of Chinese script-like and blocky primary carbides on the basis of image analysis was proposed.

  10. Experimental study of the thermal stability of austempered ductile irons

    Science.gov (United States)

    Pérez, M. J.; Cisneros, M. M.; Valdés, E.; Mancha, H.; Calderón, H. A.; Campos, R. E.

    2002-10-01

    A nonisothermal annealing was applied to austempered Ni-Cu-Mo alloyed and unalloyed ductile irons to determine the thermal stability of the ausferritic structure. Differential thermal analysis (DTA) results were used to build the corresponding stability diagrams. The transformation starting temperature of the high carbon austenite was found to be strongly dependent on the austempering temperature, the heating rate, and the chemical composition of the iron. The Ni-Cu-Mo alloying elements and high austempering temperature increased the stability. The transformation of the austenite to ferrite and cementite is achieved via the precipitation of transition carbides identified as silico-carbides of triclinic structure.

  11. Carbides in Nodular Cast Iron with Cr and Mo

    Directory of Open Access Journals (Sweden)

    S. Pietrowski

    2007-07-01

    Full Text Available In these paper results of elements microsegregation in carbidic nodular cast iron have been presented. A cooling rate in the centre of the cross-section and on the surface of casting and change of moulding sand temperature during casting crystallization and its self-cooling have been investigated. TDA curves have been registered. The linear distribution of elements concentration in an eutectic grain, primary and secondary carbides have been made. It was found, that there are two kinds of carbides: Cr and Mo enriched. A probable composition of primary and secondary carbides have been presented.

  12. Numerical Study on Several Stabilized Finite Element Methods for the Steady Incompressible Flow Problem with Damping

    Directory of Open Access Journals (Sweden)

    Jilian Wu

    2013-01-01

    Full Text Available We discuss several stabilized finite element methods, which are penalty, regular, multiscale enrichment, and local Gauss integration method, for the steady incompressible flow problem with damping based on the lowest equal-order finite element space pair. Then we give the numerical comparisons between them in three numerical examples which show that the local Gauss integration method has good stability, efficiency, and accuracy properties and it is better than the others for the steady incompressible flow problem with damping on the whole. However, to our surprise, the regular method spends less CPU-time and has better accuracy properties by using Crout solver.

  13. Solute element distribution and carbide formation in Ni-base superalloys fabricated by rheocasting. Kaiten kakuhan gyokoshita Ni ki chogokin ni okeru yoshitsu genso no bunpu to tankabutsu seisei

    Energy Technology Data Exchange (ETDEWEB)

    Okazaki, Y.; Ichikawa, K. (Mechanical Engineering Laboratory, Tsukuba (Japan)); Matsuo, M. (Nippon Steel Corp., Tokyo (Japan))

    1991-07-20

    An attention has begun being given on a method for manufacturing highly ductile metallic materials by means of mechanically stirring the materials in solid-liquid coexisting region and uniformly micronizing the structure. This study discussed effects of the rotation stirring on the microstructures, distribution of solute elements, carbide formation, phosphorous segregation and solid-liquid distribution coefficients in the Ni-base superalloy TMP-3. The results obtained may be summarized as: In the agitated structural material stirred at 70 rev/s in the solid-liquid coexisting region, the dendrite structure was broken up and equiaxed grain structure with the primary solid particle size of 65{plus minus}15{mu}m was formed; the element distribution of Ni, Cr, Co, Al, Ti, Mo, Nb, and W showed no noticeable difference by positions in the structure; the size of{gamma}{prime} phase precipitated on crystal boundaries decreases when cast by rheocasting than when cast stationarily; and the carbides of Nb, Ti and Mo precipitate uniformly along grain boundaries, different from that they precipitate in a plate form in stationary casting. 19 refs., 13 figs., 3 tabs.

  14. Experimental evaluation of the stability and mechanical behavior of contacts in silicon carbide for the design of the basic angle monitoring system of GAIA

    NARCIS (Netherlands)

    Veggel, A.A. van; Berkhout, W.J.; Schalkx, M.K.; Wielders, A.A.; Rosielle, P.C.J.N.; Nijmeijer, H.

    2005-01-01

    The satellite GAIA will be launched in ca. 2010 to make a 3-D map of our Galaxy. The payload module of the satellite will carry two astrometric telescopes amongst other instrumentation. The optical bench and astrometric telescopes will be constructed for a large part in Silicon Carbide (SiC). A trus

  15. NONCONFORMING STABILIZED FINITE ELEMENT METHODS BASED ON RIESZ-REPRESENTING OPERATORS

    Institute of Scientific and Technical Information of China (English)

    DuanHuoyuan

    1999-01-01

    Following the framework of the finite element methods based on Riesz-representingoperators developed by Duan Huoyuan in 1997,through discrete Rieszonsome virtual(non-) conforming finite-dimensional subspaces,a stabilization formulation is presented for the Stokes problem by employing nonconforming elements. This formulation is uni-tormly coercive and not subject to the Babus Ka-Brezzi condition,and the resulted linearalgebraic system is positive definite with the spectral condition number O(h-2).Quasi-optimal error bounds are obtained,which is consistent with the interpolation properties of the finite elements used.

  16. Nonconforming stabilized combined finite element method for Reissner-Mindlin plate

    Institute of Scientific and Technical Information of China (English)

    Min-fu FENG; Yan YANG; Tian-xiao ZHOU

    2009-01-01

    Based on combination of two variational principles, a nonconforming sta-bilized finite element method is presented for the Reissner-Mindlin plates. The method is convergent when the finite element space is energy-compatible. Error estimates are derived. In particular, three finite element spaces are applied in the computation. Nu-merical results show that the method is insensitive to the mesh distortion and has better performence than the MITC4 and DKQ methods. With properly chosen parameters, high accuracy can be obtained at coarse meshes.

  17. INTERNET BRANDING AS AN ELEMENT OF MARKET STABILITY OF A MODERN UNIVERSITY

    Directory of Open Access Journals (Sweden)

    Nataliya V. Tikhomirova

    2013-01-01

    Full Text Available First of all the necessity of the development of electronic information model for the formation of virtual image of the university is connected with the dynamic tendencies of the development of modern society. Branding as an element of market stability of the university brings superiority over the competitors and thus increases its competitiveness.

  18. Stability estimates for h-p spectral element methods for general elliptic problems on curvilinear domains

    NARCIS (Netherlands)

    Dutt, Pravir; Tomar, Satyendra

    2003-01-01

    In this paper we show that the h-p spectral element method developed in [3,8,9] applies to elliptic problems in curvilinear polygons with mixed Neumann and Dirichlet boundary conditions provided that the Babuska-Brezzi inf-sup conditions are satisfied. We establish basic stability estimates for a no

  19. Finite element analysis of dynamic stability of skeletal structures under periodic loading

    Institute of Scientific and Technical Information of China (English)

    THANA Hemantha Kumar; AMEEN Mohammed

    2007-01-01

    This paper addresses the dynamic stability problem of columns and frames subjected to axially applied periodic loads. Such a structure can become unstable under certain combinations of amplitudes and frequencies of the imposed load acting on its columns/beams. These are usually shown in the form of plots which describe regions of instability. The finite element method (FEM) is used in this work to analyse dynamic stability problems of columns. Two-noded beam elements are used for this purpose.The periodic loading is decomposed into various harmonics using Fourier series expansion. Computer codes in C++ using object oriented concepts are developed to determine the stability regions of columns subjected to periodic loading. A number of numerical examples are presented to illustrate the working of the program. The direct integration of the equations of motions of the discretised system is carried out using Newmark's method to verify the results.

  20. Stability Estimates for ℎ- Spectral Element Methods for General Elliptic Problems on Curvilinear Domains

    Indian Academy of Sciences (India)

    Pravir Dutt; Satyendra Tomar

    2003-11-01

    In this paper we show that the ℎ- spectral element method developed in [3,8,9] applies to elliptic problems in curvilinear polygons with mixed Neumann and Dirichlet boundary conditions provided that the Babuska–Brezzi inf-sup conditions are satisfied. We establish basic stability estimates for a non-conforming ℎ- spectral element method which allows for simultaneous mesh refinement and variable polynomial degree. The spectral element functions are non-conforming if the boundary conditions are Dirichlet. For problems with mixed boundary conditions they are continuous only at the vertices of the elements. We obtain a stability estimate when the spectral element functions vanish at the vertices of the elements, which is needed for parallelizing the numerical scheme. Finally, we indicate how the mesh refinement strategy and choice of polynomial degree depends on the regularity of the coefficients of the differential operator, smoothness of the sides of the polygon and the regularity of the data to obtain the maximum accuracy achievable.

  1. Chemical Modification Methods of Nanoparticles of Silicon Carbide Surface

    Directory of Open Access Journals (Sweden)

    Anton S. Yegorov

    2015-09-01

    Full Text Available silicon carbide exhibits exceptional properties: high durability, high thermal conductivity, good heat resistance, low thermal expansion factor and chemical inactivity. Reinforcement with silicon carbide nanoparticles increases polymer’s tensile strength and thermal stability.Chemical methods of modification of the silicon carbide surface by means of variety of reagents from ordinary molecules to macromolecular polymers are reviewed in the review.The structure of silicon carbide surface layer and the nature of modificator bonding with the surface of SiC particles are reviewed. General examples of surface modification methodologies and composite materials with the addition of modified SiC are given.

  2. Novel fabrication of silicon carbide based ceramics for nuclear applications

    Science.gov (United States)

    Singh, Abhishek Kumar

    Advances in nuclear reactor technology and the use of gas-cooled fast reactors require the development of new materials that can operate at the higher temperatures expected in these systems. These materials include refractory alloys based on Nb, Zr, Ta, Mo, W, and Re; ceramics and composites such as SiC--SiCf; carbon--carbon composites; and advanced coatings. Besides the ability to handle higher expected temperatures, effective heat transfer between reactor components is necessary for improved efficiency. Improving thermal conductivity of the fuel can lower the center-line temperature and, thereby, enhance power production capabilities and reduce the risk of premature fuel pellet failure. Crystalline silicon carbide has superior characteristics as a structural material from the viewpoint of its thermal and mechanical properties, thermal shock resistance, chemical stability, and low radioactivation. Therefore, there have been many efforts to develop SiC based composites in various forms for use in advanced energy systems. In recent years, with the development of high yield preceramic precursors, the polymer infiltration and pyrolysis (PIP) method has aroused interest for the fabrication of ceramic based materials, for various applications ranging from disc brakes to nuclear reactor fuels. The pyrolysis of preceramic polymers allow new types of ceramic materials to be processed at relatively low temperatures. The raw materials are element-organic polymers whose composition and architecture can be tailored and varied. The primary focus of this study is to use a pyrolysis based process to fabricate a host of novel silicon carbide-metal carbide or oxide composites, and to synthesize new materials based on mixed-metal silicocarbides that cannot be processed using conventional techniques. Allylhydridopolycarbosilane (AHPCS), which is an organometal polymer, was used as the precursor for silicon carbide. Inert gas pyrolysis of AHPCS produces near-stoichiometric amorphous

  3. Large eddy simulation for wind field analysis based on stabilized finite element method

    Institute of Scientific and Technical Information of China (English)

    Cheng HUANG; Yan BAO; Dai ZHOU; Jin-quan XU

    2011-01-01

    In this paper, a stabilized finite element technique, actualized by streamline upwind Petrov-Galerkin (SUPG) stabilized method and three-step finite element method (FEM), for large eddy simulation (LES) is developed to predict the wind flow with high Reynolds numbers. Weak form of LES motion equation is combined with the SUPG stabilized term for the spatial finite element discretization. An explicit three-step scheme is implemented for the temporal discretization. For the numerical example of 2D wind flow over a square rib at Re=4.2×105, the Smagorinsky's subgrid-scale (SSGS) model, the DSGS model, and the DSGS model with Cabot near-wall model are applied, and their results are analyzed and compared with experimental results. Furthermore, numerical examples of 3D wind flow around a surface-mounted cube with different Reynolds numbers are performed using DSGS model with Cabot near-wall model based on the present stabilized method to study the wind field and compared with experimental and numerical results. Finally, vortex structures for wind flow around a surface-mounted cube are studied by present numerical method. Stable and satisfactory results are obtained, which are consistent with most of the measurements even under coarse mesh.

  4. Stability and reinforcement analysis of rock slope based on elasto-plastic finite element method

    Institute of Scientific and Technical Information of China (English)

    刘耀儒; 武哲书; 常强; 李波; 杨强

    2015-01-01

    The rigid body limit equilibrium method (RBLEM) and finite element method (FEM) are two widely used approaches for rock slope’s stability analysis currently. RBLEM introduced plethoric assumptions; while traditional FEM relied on artificial factors when determining factor of safety (FOS) and sliding surfaces. Based on the definition of structure instability that an elasto-plastic structure is not stable if it is unable to satisfy simultaneously equilibrium condition, kinematical admissibility and constitutive equations under given external loads, deformation reinforcement theory (DRT) is developed. With this theory, plastic complementary energy (PCE) can be used to evaluate the overall stability of rock slope, and the unbalanced force beyond the yield surface could be the identification of local failure. Compared with traditional slope stability analysis approaches, the PCE norm curve to strength reduced factor is introduced and the unbalanced force is applied to the determination of key sliding surfaces and required reinforcement. Typical and important issues in rock slope stability are tested in TFINE(a three-dimensional nonlinear finite element program), which is further applied to several representatives of high rock slope’s stability evaluation and reinforcement engineering practice in southwest of China.

  5. Stability Analysis of Anchored Soil Slope Based on Finite Element Limit Equilibrium Method

    Directory of Open Access Journals (Sweden)

    Rui Zhang

    2016-01-01

    Full Text Available Under the condition of the plane strain, finite element limit equilibrium method is used to study some key problems of stability analysis for anchored slope. The definition of safe factor in slices method is generalized into FEM. The “true” stress field in the whole structure can be obtained by elastic-plastic finite element analysis. Then, the optimal search for the most dangerous sliding surface with Hooke-Jeeves optimized searching method is introduced. Three cases of stability analysis of natural slope, anchored slope with seepage, and excavation anchored slope are conducted. The differences in safety factor quantity, shape and location of slip surface, anchoring effect among slices method, finite element strength reduction method (SRM, and finite element limit equilibrium method are comparatively analyzed. The results show that the safety factor given by the FEM is greater and the unfavorable slip surface is deeper than that by the slice method. The finite element limit equilibrium method has high calculation accuracy, and to some extent the slice method underestimates the effect of anchor, and the effect of anchor is overrated in the SRM.

  6. SILICON CARBIDE FOR SEMICONDUCTORS

    Science.gov (United States)

    This state-of-the-art survey on silicon carbide for semiconductors includes a bibliography of the most important references published as of the end...of 1964. The various methods used for growing silicon carbide single crystals are reviewed, as well as their properties and devices fabricated from...them. The fact that the state of-the-art of silicon carbide semiconductors is not further advanced may be attributed to the difficulties of growing

  7. Silicon Carbide Shapes.

    Science.gov (United States)

    Free-standing silicon carbide shapes are produced by passing a properly diluted stream of a reactant gas, for example methyltrichlorosilane, into a...reaction chamber housing a thin walled, hollow graphite body heated to 1300-1500C. After the graphite body is sufficiently coated with silicon carbide , the...graphite body is fired, converting the graphite to gaseous CO2 and CO and leaving a silicon carbide shaped article remaining.

  8. Acoustic Transfer Functions Derived from Finite Element Modeling for Thermoacoustic Stability Predictions of Gas Turbine Engines

    OpenAIRE

    Black, Paul Randall

    2007-01-01

    Acoustic Transfer Functions Derived from Finite Element Modeling for Thermoacoustic Stability Predictions of Gas Turbine Engines Design and prediction of thermoacoustic instabilities is a major challenge in aerospace propulsion and the operation of power generating gas turbine engines. This is a complex problem in which multiple physical systems couple together. Traditionally, thermoacoustic models can be reduced to dominant physics which depend only on flame dynamics and acoustics. Th...

  9. Variational multiscale stabilization of finite and spectral elements for dry and moist atmospheric problems

    OpenAIRE

    Marras, Simone

    2012-01-01

    Premi extraordinari doctorat curs 2012-2013, àmbit d’Enginyeria Civil In this thesis the finite and spectral element methods (FEM and SEM, respectively) applied to problems in atmospheric simulations are explored through the common thread of Variational Multiscale Stabilization (VMS). This effort is justified by three main reasons. (i) the recognized need for new solvers that can efficiently execute on massively parallel architectures ¿a spreading framework in most fields of co...

  10. Computational analysis of noise reduction devices in axial fans with stabilized finite element formulations

    Science.gov (United States)

    Corsini, A.; Rispoli, F.; Sheard, A. G.; Tezduyar, T. E.

    2012-12-01

    The paper illustrates how a computational fluid mechanic technique, based on stabilized finite element formulations, can be used in analysis of noise reduction devices in axial fans. Among the noise control alternatives, the study focuses on the use of end-plates fitted at the blade tips to control the leakage flow and the related aeroacoustic sources. The end-plate shape is configured to govern the momentum transfer to the swirling flow at the blade tip. This flow control mechanism has been found to have a positive link to the fan aeroacoustics. The complex physics of the swirling flow at the tip, developing under the influence of the end-plate, is governed by the rolling up of the jet-like leakage flow. The RANS modelling used in the computations is based on the streamline-upwind/Petrov-Galerkin and pressure-stabilizing/Petrov-Galerkin methods, supplemented with the DRDJ stabilization. Judicious determination of the stabilization parameters involved is also a part of our computational technique and is described for each component of the stabilized formulation. We describe the flow physics underlying the design of the noise control device and illustrate the aerodynamic performance. Then we investigate the numerical performance of the formulation by analysing the inner workings of the stabilization operators and of their interaction with the turbulence model.

  11. The structure and function of the rous sarcoma virus RNA stability element.

    Science.gov (United States)

    Withers, Johanna B; Beemon, Karen L

    2011-11-01

    For simple retroviruses, such as the Rous sarcoma virus (RSV), post-transcriptional control elements regulate viral RNA splicing, export, stability, and packaging into virions. These RNA sequences interact with cellular host proteins to regulate and facilitate productive viral infections. One such element, known as the RSV stability element (RSE), is required for maintaining stability of the full-length unspliced RNA. This viral RNA serves as the mRNA for the Gag and Pol proteins and also as the genome packaged in progeny virions. When the RSE is deleted from the viral RNA, the unspliced RNA becomes unstable and is degraded in a Upf1-dependent manner. Current evidence suggests that the RSE inhibits recognition of the viral gag termination codon by the nonsense-mediated mRNA decay (NMD) pathway. We believe that the RSE acts as an insulator to NMD, thereby preventing at least one of the required functional steps that target an mRNA for degradation. Here, we discuss the history of the RSE and the current model of how the RSE is interacting with cellular NMD factors.

  12. Local Projection-Based Stabilized Mixed Finite Element Methods for Kirchhoff Plate Bending Problems

    Directory of Open Access Journals (Sweden)

    Xuehai Huang

    2013-01-01

    Full Text Available Based on stress-deflection variational formulation, we propose a family of local projection-based stabilized mixed finite element methods for Kirchhoff plate bending problems. According to the error equations, we obtain the error estimates of the approximation to stress tensor in energy norm. And by duality argument, error estimates of the approximation to deflection in H1-norm are achieved. Then we design an a posteriori error estimator which is closely related to the equilibrium equation, constitutive equation, and nonconformity of the finite element spaces. With the help of Zienkiewicz-Guzmán-Neilan element spaces, we prove the reliability of the a posteriori error estimator. And the efficiency of the a posteriori error estimator is proved by standard bubble function argument.

  13. SILICON CARBIDE DATA SHEETS

    Science.gov (United States)

    These data sheets present a compilation of a wide range of electrical, optical and energy values for alpha and beta- silicon carbide in bulk and film...spectrum. Energy data include energy bands, energy gap and energy levels for variously-doped silicon carbide , as well as effective mass tables, work

  14. Role of loops connecting secondary structure elements in the stabilization of proteins isolated from thermophilic organisms.

    Science.gov (United States)

    Balasco, Nicole; Esposito, Luciana; De Simone, Alfonso; Vitagliano, Luigi

    2013-07-01

    It has been recently discovered that the connection of secondary structure elements (ββ-unit, βα- and αβ-units) in proteins follows quite stringent principles regarding the chirality and the orientation of the structural units (Koga et al., Nature 2012;491:222-227). By exploiting these rules, a number of protein scaffolds endowed with a remarkable thermal stability have been designed (Koga et al., Nature 2012;491:222-227). By using structural databases of proteins isolated from either mesophilic or thermophilic organisms, we here investigate the influence of supersecondary associations on the thermal stability of natural proteins. Our results suggest that β-hairpins of proteins from thermophilic organisms are very frequently characterized by shortenings of the loops. Interestingly, this shortening leads to states that display a very strong preference for the most common connectivity of the strands observed in native protein hairpins. The abundance of selective states in these proteins suggests that they may achieve a high stability by adopting a strategy aimed to reduce the possible conformations of the unfolded ensemble. In this scenario, our data indicate that the shortening is effective if it increases the adherence to these rules. We also show that this mechanism may operate in the stabilization of well-known protein folds (thioredoxin and RNase A). These findings suggest that future investigations aimed at defining mechanism of protein stabilization should also consider these effects.

  15. Carbide Type Influence on Tribological Properties of Hard Faced Steel Layer - Part I - Theoretical Considerations

    Directory of Open Access Journals (Sweden)

    V. Lazic

    2010-06-01

    Full Text Available This paper gives a theoretical review of influence of the most important alloying elements on steel, and review of the most important carbide-forming elements and states the conditions which elements should fulfill in order to be considered as carbide-forming. It primarily involves alloying elements which in the iron-carbon system can form simple, complex or special carbides, i.e. phases of interstitial and substitutive type. It also gives a review of carbide types that are formed during either production or reparatory hard facing of steel parts with different types of filler materials.

  16. Stability of the micromachined membrane deformable mirror as a freeform optical element

    Science.gov (United States)

    Vdovin, Gleb; Soloviev, Oleg; Patlan, Seva

    2014-09-01

    Micromachined membrane deformable mirror (MMDM) can serve as an ad hoc" free-form optical element. To test the repeatability and stability of the standard MMDM, we have conducted the test of surface figure during multiple thermal cycling, test of figure drift at elevated temperatures, and a long-term 16-day stability test of actively formed mirror figure. The average rms error did not exceed λ =25 at λ = 633 nm, after repeated cycling from -14 to +70 C, with return to the room temperature. The existing design provides ~10° stability in the temperature range of ~10°. Optimization of the design, eliminating astigmatism, would allow one to extend the temperature range to about 30. The long-term mirror figure instability at a constant temperature reaches λ/20 rms in 16 days. The P-V error with respect to the nearest sphere changes from λ/20 in the first day, to about λ/10 in the 16-th day. The tests show that MMDM is stable enough to make a reasonable alternative to free-form optics in applications that require various optical shapes to be formed with a single element.

  17. [Finite element analysis of the initial stability of subtalar arthrodesis with double-screw fixation].

    Science.gov (United States)

    Cui, Zhuang; Yu, Bin; Li, Xue; Xu, Changpeng; Song, Jinqi; Ouyang, Hanbin; Diao, Xicai; Chen, Liguang

    2012-11-01

    To assess the optimal configuration of double-screw fixation for subtalar arthrodesis using finite element analysis. Three-dimensional finite element double-screw models of subtalar arthrodesis were reconstructed using Mimics 13.0, Geomagic 10.0 and solid works software based on the 3-D images of the volunteer's right foot. The external and internal rotation torques of 4 N·m were applied, and the micromotion at the bone-to-bone interface were measured to evaluate the initial stability of subtalar arthrodesis. A neck screw plus an anterolateral dome screw was the most stable model. The peak micromotion at the fusion site of this fixation configuration were 41.67mnplus;0.49 and 42.64mnplus;0.75 µm in response to the respectively. A neck screw plus a posteromedial dome screw was the least stable model, with peak micromotion at the bone-to-bone interface of 61.76mnplus;1.00 and 62.32mnplus;0.90 µm, respectively. A neck screw plus an anterolateral dome screw is the best fixation configuration while a neck screw plus a posteromedial screw provides the least stability of subtalar arthrodesis. Three-dimensional finite element models allow effective preoperative planning of the screw number and placement.

  18. Thermal Transport in Refractory Carbides.

    Science.gov (United States)

    Thermal energy transport mechanisms in titanium carbide and zirconium carbide have been studied. Several compositions of vanadium carbide alloyed...with titanium carbide were used. The electronic component of the thermal conductivity exceeded the values computed using the classical value for L in

  19. An implicit stabilized finite element method for the compressible Navier-Stokes equations using finite calculus

    Science.gov (United States)

    Kouhi, Mohammad; Oñate, Eugenio

    2015-07-01

    A new implicit stabilized formulation for the numerical solution of the compressible Navier-Stokes equations is presented. The method is based on the finite calculus (FIC) scheme using the Galerkin finite element method (FEM) on triangular grids. Via the FIC formulation, two stabilization terms, called streamline term and transverse term, are added to the original conservation equations in the space-time domain. The non-linear system of equations resulting from the spatial discretization is solved implicitly using a damped Newton method benefiting from the exact Jacobian matrix. The matrix system is solved at each iteration with a preconditioned GMRES method. The efficiency of the proposed stabilization technique is checked out in the solution of 2D inviscid and laminar viscous flow problems where appropriate solutions are obtained especially near the boundary layer and shock waves. The work presented here can be considered as a follow up of a previous work of the authors Kouhi, Oñate (Int J Numer Methods Fluids 74:872-897, 2014). In that paper, the stabilized Galerkin FEM based on the FIC formulation was derived for the Euler equations together with an explicit scheme. In the present paper, the extension of this work to the Navier-Stokes equations using an implicit scheme is presented.

  20. Stability and Convergence of an Effective Finite Element Method for Multiterm Fractional Partial Differential Equations

    Directory of Open Access Journals (Sweden)

    Jingjun Zhao

    2013-01-01

    Full Text Available A finite element method (FEM for multiterm fractional partial differential equations (MT-FPDEs is studied for obtaining a numerical solution effectively. The weak formulation for MT-FPDEs and the existence and uniqueness of the weak solutions are obtained by the well-known Lax-Milgram theorem. The Diethelm fractional backward difference method (DFBDM, based on quadrature for the time discretization, and FEM for the spatial discretization have been applied to MT-FPDEs. The stability and convergence for numerical methods are discussed. The numerical examples are given to match well with the main conclusions.

  1. Metallicity of boron carbides at high pressure

    Science.gov (United States)

    Dekura, Haruhiko; Shirai, Koun; Yanase, Akira

    2010-03-01

    Electronic structure of semiconducting boron carbide at high pressure has been theoretically investigated, because of interests in the positive pressure dependence of resistivity, in the gap closure, and in the phase transition. The most simplest form B12(CCC) is assumed. Under assumptions of hydrostatic pressure and neglecting finite-temperature effects, boron carbide is quite stable at high pressure. The crystal of boron carbide is stable at least until a pressure higher than previous experiments showed. The gap closure occurs only after p=600 GPa on the assumption of the original crystal symmetry. In the low pressure regime, the pressure dependence of the energy gap almost diminishes, which is an exceptional case for semiconductors, which could be one of reasons for the positive pressure dependence of resistivity. A monotonous increase in the apex angle of rhombohedron suggests that the covalent bond continues to increase. The C chain inserted in the main diagonal of rhombohedral structure is the chief reason of this stability.

  2. Process for making silicon carbide reinforced silicon carbide composite

    Science.gov (United States)

    Lau, Sai-Kwing (Inventor); Calandra, Salavatore J. (Inventor); Ohnsorg, Roger W. (Inventor)

    1998-01-01

    A process comprising the steps of: a) providing a fiber preform comprising a non-oxide ceramic fiber with at least one coating, the coating comprising a coating element selected from the group consisting of carbon, nitrogen, aluminum and titanium, and the fiber having a degradation temperature of between 1400.degree. C. and 1450.degree. C., b) impregnating the preform with a slurry comprising silicon carbide particles and between 0.1 wt % and 3 wt % added carbon c) providing a cover mix comprising: i) an alloy comprising a metallic infiltrant and the coating element, and ii) a resin, d) placing the cover mix on at least a portion of the surface of the porous silicon carbide body, e) heating the cover mix to a temperature between 1410.degree. C. and 1450.degree. C. to melt the alloy, and f) infiltrating the fiber preform with the melted alloy for a time period of between 15 minutes and 240 minutes, to produce a ceramic fiber reinforced ceramic composite.

  3. Mirror Surface Grinding of Steel Bonded Carbides

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The steel bonded carbide, a composite material, is very difficult to be machined to a fine finish mirror surface. In this paper, an electrolytic in-process dressing (ELID) grinding with metallic bond super-hard abrasive wheel was developed for grinding steel bonded carbide GT35. Factors affecting ELID grinding performance were analyzed by an atomic force microscope (AFM). Based on the analysis of AFM topography of the fine ground mirror surface of the steel bonded carbide, a schematic diagram of the mechanism of micro-removal of the ground surface was described. The AFM topography also shows that the hard brittle carbide particles, on the surface of steel bonded carbide, were machined out by ductile cutting. Since the grinding cracks in the ground surface are due to temperature gradient, temperature distribution in the grinding area was analyzed by finite element method (FEM). Experimental results indicate that a good mirror surface with Ra<0.02pm can be obtained by the developed ELID grinding system.

  4. Generation of Accelerated Stability Experiment Profile of Inertial Platform Based on Finite Element

    Institute of Scientific and Technical Information of China (English)

    CHEN Yunxia; HUANG Xiaokai; KANG Rui

    2012-01-01

    The residual stress generated in the manufacturing process of inertial platform causes the drift of inertial platform parameters in long-term storage condition.However,the existing temperature cycling experiment could not meet the increased repeatability technical requirements of inertial platform parameters.In order to solve this problem,in this paper,firstly the Unigraphics (UG) software and the interface compatibility of ANSYS software are used to establish the inertial platform finite element model.Secondly,the residual stress is loaded into finite element model by ANSYS function editor in the form of surface loads to analyze the efficiency.And then,the generation based on ANSYS simulation inertial platform to accelerate the stability of experiment profile is achieved by the application of the analysis method of orthogonal experimental design and ANSYS thermal-structural coupling.The optimum accelerated stability experiment profile is determined finally,which realizes the rapid,effective release of inertial platform residual stress.The research methodology and conclusion of this paper have great theoretical and practical significance to the production technology of inertial platform.

  5. A stabilized finite element formulation for liquid shells and its application to lipid bilayers

    Science.gov (United States)

    Sauer, Roger A.; Duong, Thang X.; Mandadapu, Kranthi K.; Steigmann, David J.

    2017-02-01

    This paper presents a new finite element (FE) formulation for liquid shells that is based on an explicit, 3D surface discretization using C1-continuous finite elements constructed from NURBS interpolation. Both displacement-based and mixed displacement/pressure FE formulations are proposed. The latter is needed for area-incompressible material behavior, where penalty-type regularizations can lead to misleading results. In order to obtain quasi-static solutions for liquid shells devoid of shear stiffness, several numerical stabilization schemes are proposed based on adding stiffness, adding viscosity or using projection. Several numerical examples are considered in order to illustrate the accuracy and the capabilities of the proposed formulation, and to compare the different stabilization schemes. The presented formulation is capable of simulating non-trivial surface shapes associated with tube formation and protein-induced budding of lipid bilayers. In the latter case, the presented formulation yields non-axisymmetric solutions, which have not been observed in previous simulations. It is shown that those non-axisymmetric shapes are preferred over axisymmetric ones.

  6. Probabilistic analysis of embankment slope stability in frozen ground regions based on random finite element method

    Institute of Scientific and Technical Information of China (English)

    Xi Chen; JianKun Liu; Nan Xie; HuiJing Sun

    2015-01-01

    Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer (i.e., mass equation) and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety (FOS), which is definitely useful for embankment design in frozen ground regions.

  7. 2D-3D hybrid stabilized finite element method for tsunami runup simulations

    Science.gov (United States)

    Takase, S.; Moriguchi, S.; Terada, K.; Kato, J.; Kyoya, T.; Kashiyama, K.; Kotani, T.

    2016-09-01

    This paper presents a two-dimensional (2D)-three-dimensional (3D) hybrid stabilized finite element method that enables us to predict a propagation process of tsunami generated in a hypocentral region, which ranges from offshore propagation to runup to urban areas, with high accuracy and relatively low computational costs. To be more specific, the 2D shallow water equation is employed to simulate the propagation of offshore waves, while the 3D Navier-Stokes equation is employed for the runup in urban areas. The stabilized finite element method is utilized for numerical simulations for both of the 2D and 3D domains that are independently discretized with unstructured meshes. The multi-point constraint and transmission methods are applied to satisfy the continuity of flow velocities and pressures at the interface between the resulting 2D and 3D meshes, since neither their spatial dimensions nor node arrangements are consistent. Numerical examples are presented to demonstrate the performance of the proposed hybrid method to simulate tsunami behavior, including offshore propagation and runup to urban areas, with substantially lower computation costs in comparison with full 3D computations.

  8. Research results on productivity stabilization by ultrasonic camera (plant with membrane ceramic elements during vine processing

    Directory of Open Access Journals (Sweden)

    V. T. Antufyev

    2016-01-01

    Full Text Available The article describes solutions to the problems of declining productivity of ceramic membrane elements for wine processing on the final manufacturing phase. A relative stabilization of filtration velocity, venting efficiency and wine lightening were experimentally confirmed during contacts with oscillation waves of ultrasonic transmitter on the ceramic filter. Which significantly reduced the cost of various preservatives to increase periods storage. To study the processes of wine processing by the proposed method it was made an experimental installation on the basis of pilot machine MRp-1/2 for bottling of quiet liquids and an ultrasonic device "Volna– M" UZTA-1/22-OM with a firmly, waveguide which transmits sound, fixed filter frame on the ultrasound emitter. To stabilize the performance of ultrasonic units with ceramic membrane elements without quality deterioration of wines it was empirically determined rational parameters of power of ultrasound input and pressure in the system. The given derived dependencies and graphs allow to define the time of relatively stable operating filter regime. It was revealed a significant cost reduction on filtration, as it allows escape from the contamination of the product by various preservatives, and increasing of storage duration in a sealed container during aseptic filling without a thermal sterilization. Ultrasonic emitter contact by superposition wave vibrations on the ceramic filter increases not only the efficiency of gas removal, but also improves the organoleptic characteristics, stabilizes the filters, improves their productivity. Gas removal creates unfavorable conditions for development of the yeast, which in turn increases the shelf life of semisweet wine.

  9. Rapid cost-effective silicon carbide optical component manufacturing technique

    Science.gov (United States)

    Casstevens, John M.; Plummer, Ronald; Jarocki, Jim

    1999-10-01

    Silicon carbide may well be the best known material for the manufacture of high performance optical components. A combination of extremely high specific stiffness (r/E), high thermal conductivity and outstanding dimensional stability make silicon carbide superior overall to beryllium and low- expansion glass ceramics. A major impediment to wide use of silicon carbide in optical systems has been the costs of preliminary pressing, casting, shaping and final finishing of silicon carbide. Diamond grinding of silicon carbide is a slow and expensive process even on machines specially designed for the task. The process described here begins by machining the component from a special type of graphite. This graphite is easily machined with multi-axis CNC machine tools to any level of complexity and lightweighting required. The graphite is then converted completely to silicon carbide with very small and very predictable dimensional change. After conversion to silicon carbide the optical surface is coated with very fine grain silicon carbide which is easily polished to extreme smoothness using conventional optical polishing techniques. The fabrication process and a 6 inch diameter development mirror is described.

  10. The capsule's contribution to total hip construct stability--a finite element analysis.

    Science.gov (United States)

    Elkins, Jacob M; Stroud, Nicholas J; Rudert, M James; Tochigi, Yuki; Pedersen, Douglas R; Ellis, Benjamin J; Callaghan, John J; Weiss, Jeffrey A; Brown, Thomas D

    2011-11-01

    Instability is a significant concern in total hip arthroplasty (THA), particularly when there is structural compromise of the capsule due to pre-existing pathology or due to necessities of surgical approach. An experimentally grounded fiber-direction-based finite element model of the hip capsule was developed, and was integrated with an established three-dimensional model of impingement/dislocation. Model validity was established by close similarity to results from a cadaveric experiment in a servohydraulic hip simulator. Parametric computational runs explored effects of graded levels of capsule thickness, of regional detachment from the capsule's femoral or acetabular insertions, of surgical incisions of capsule substance, and of capsule defect repairs. Depending strongly upon the specific site, localized capsule defects caused varying degrees of construct stability compromise, with several specific situations involving over 60% decrement in dislocation resistance. Construct stability was returned substantially toward intact-capsule levels following well-conceived repairs, although the suture sites involved were often at substantial risk of failure. These parametric model results underscore the importance of retaining or robustly repairing capsular structures in THA, in order to maximize overall construct stability. 

  11. Dc microgrid stabilization through fuzzy control of interleaved, heterogeneous storage elements

    Science.gov (United States)

    Smith, Robert David

    As microgrid power systems gain prevalence and renewable energy comprises greater and greater portions of distributed generation, energy storage becomes important to offset the higher variance of renewable energy sources and maximize their usefulness. One of the emerging techniques is to utilize a combination of lead-acid batteries and ultracapacitors to provide both short and long-term stabilization to microgrid systems. The different energy and power characteristics of batteries and ultracapacitors imply that they ought to be utilized in different ways. Traditional linear controls can use these energy storage systems to stabilize a power grid, but cannot effect more complex interactions. This research explores a fuzzy logic approach to microgrid stabilization. The ability of a fuzzy logic controller to regulate a dc bus in the presence of source and load fluctuations, in a manner comparable to traditional linear control systems, is explored and demonstrated. Furthermore, the expanded capabilities (such as storage balancing, self-protection, and battery optimization) of a fuzzy logic system over a traditional linear control system are shown. System simulation results are presented and validated through hardware-based experiments. These experiments confirm the capabilities of the fuzzy logic control system to regulate bus voltage, balance storage elements, optimize battery usage, and effect self-protection.

  12. Structure-performance relations of molybdenum- and tungsten carbide catalysts for deoxygenation

    NARCIS (Netherlands)

    Stellwagen, D.R.; Bitter, J.H.

    2015-01-01

    This work demonstrates for the first time that carbide particle size is a critical factor for the activity and stability of carbon supported tungsten- and molybdenum carbide catalysts in (hydro-)deoxygenation reactions. The stability of the catalyst was shown to increase for larger particles due to

  13. Physics-based Stabilization of Spectral Elements for the 3D Euler Equations of Moist Atmospheric Convection

    Science.gov (United States)

    2014-06-01

    3D Euler Equations of Moist Atmospheric Convection 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER...STABILIZATION OF SPECTRAL ELEMENTS FOR THE 3D EULER EQUATIONS OF MOIST ATMOSPHERIC CONVECTION SIMONE MARRAS, ANDREAS MÜLLER, FRANCIS X. GIRALDO Dept. Appl...spectral elements, we introduce a dissipative scheme based on the solution of the compressible Euler equations that are regularized through the addi

  14. Combustion Stability Analyses of Coaxial Element Injectors with Liquid Oxygen/Liquid Methane Propellants

    Science.gov (United States)

    Hulka, J. R.

    2010-01-01

    Liquid rocket engines using oxygen and methane propellants are being considered by the National Aeronautics and Space Administration (NASA) for in-space vehicles. This propellant combination has not been previously used in a flight-qualified engine system, so limited test data and analysis results are available at this stage of early development. NASA has funded several hardware-oriented activities with oxygen and methane propellants over the past several years with the Propulsion and Cryogenic Advanced Development (PCAD) project, under the Exploration Technology Development Program. As part of this effort, the NASA Marshall Space Flight Center has conducted combustion stability analyses of several of the configurations. This paper presents test data and analyses of combustion stability from the recent PCAD-funded test programs at the NASA MSFC. These test programs used swirl coaxial element injectors with liquid oxygen and liquid methane propellants. Oxygen was injected conventionally in the center of the coaxial element, and swirl was provided by tangential entry slots. Injectors with 28-element and 40-element patterns were tested with several configurations of combustion chambers, including ablative and calorimeter spool sections, and several configurations of fuel injection design. Low frequency combustion instability (chug) occurred with both injectors, and high-frequency combustion instability occurred at the first tangential (1T) transverse mode with the 40-element injector. In most tests, a transition between high-amplitude chug with gaseous methane flow and low-amplitude chug with liquid methane flow was readily observed. Chug analyses of both conditions were conducted using techniques from Wenzel and Szuch and from the Rocket Combustor Interactive Design and Analysis (ROCCID) code. The 1T mode instability occurred in several tests and was apparent by high-frequency pressure measurements as well as dramatic increases in calorimeter-measured heat flux

  15. Time-stepping stability of continuous and discontinuous finite-element methods for 3-D wave propagation

    Science.gov (United States)

    Mulder, W. A.; Zhebel, E.; Minisini, S.

    2014-02-01

    We analyse the time-stepping stability for the 3-D acoustic wave equation, discretized on tetrahedral meshes. Two types of methods are considered: mass-lumped continuous finite elements and the symmetric interior-penalty discontinuous Galerkin method. Combining the spatial discretization with the leap-frog time-stepping scheme, which is second-order accurate and conditionally stable, leads to a fully explicit scheme. We provide estimates of its stability limit for simple cases, namely, the reference element with Neumann boundary conditions, its distorted version of arbitrary shape, the unit cube that can be partitioned into six tetrahedra with periodic boundary conditions and its distortions. The Courant-Friedrichs-Lewy stability limit contains an element diameter for which we considered different options. The one based on the sum of the eigenvalues of the spatial operator for the first-degree mass-lumped element gives the best results. It resembles the diameter of the inscribed sphere but is slightly easier to compute. The stability estimates show that the mass-lumped continuous and the discontinuous Galerkin finite elements of degree 2 have comparable stability conditions, whereas the mass-lumped elements of degree one and three allow for larger time steps.

  16. The Effects of Various Amendments on Trace Element Stabilization in Acidic, Neutral, and Alkali Soil with Similar Pollution Index

    Science.gov (United States)

    Kim, Min-Suk; Min, Hyun-Gi; Lee, Sang-Hwan; Kim, Jeong-Gyu

    2016-01-01

    Many studies have examined the application of soil amendments, including pH change-induced immobilizers, adsorbents, and organic materials, for soil remediation. This study evaluated the effects of various amendments on trace element stabilization and phytotoxicity, depending on the initial soil pH in acid, neutral, and alkali conditions. As in all types of soils, Fe and Ca were well stabilized on adsorption sites. There was an effect from pH control or adsorption mechanisms on the stabilization of cationic trace elements from inorganic amendments in acidic and neutral soil. Furthermore, acid mine drainage sludge has shown great potential for stabilizing most trace elements. In a phytotoxicity test, the ratio of the bioavailable fraction to the pseudo-total fraction significantly affected the uptake of trace elements by bok choy. While inorganic amendments efficiently decreased the bioavailability of trace elements, significant effects from organic amendments were not noticeable due to the short-term cultivation period. Therefore, the application of organic amendments for stabilizing trace elements in agricultural soil requires further study. PMID:27835687

  17. The Effects of Various Amendments on Trace Element Stabilization in Acidic, Neutral, and Alkali Soil with Similar Pollution Index.

    Science.gov (United States)

    Kim, Min-Suk; Min, Hyun-Gi; Lee, Sang-Hwan; Kim, Jeong-Gyu

    2016-01-01

    Many studies have examined the application of soil amendments, including pH change-induced immobilizers, adsorbents, and organic materials, for soil remediation. This study evaluated the effects of various amendments on trace element stabilization and phytotoxicity, depending on the initial soil pH in acid, neutral, and alkali conditions. As in all types of soils, Fe and Ca were well stabilized on adsorption sites. There was an effect from pH control or adsorption mechanisms on the stabilization of cationic trace elements from inorganic amendments in acidic and neutral soil. Furthermore, acid mine drainage sludge has shown great potential for stabilizing most trace elements. In a phytotoxicity test, the ratio of the bioavailable fraction to the pseudo-total fraction significantly affected the uptake of trace elements by bok choy. While inorganic amendments efficiently decreased the bioavailability of trace elements, significant effects from organic amendments were not noticeable due to the short-term cultivation period. Therefore, the application of organic amendments for stabilizing trace elements in agricultural soil requires further study.

  18. Electric Heating Property from Butyl Rubber-Loaded Boron Carbide Composites

    Institute of Scientific and Technical Information of China (English)

    MENG Dechuan; WANG Ninghui; LI Guofeng

    2014-01-01

    We researched the electric heating property from butyl rubber-loaded boron carbide composite. The effects of boron carbide content on bulk resistivity, voltage-current characteristic, thermal conductivity and thermal stability of boron carbide/butyl rubber (IIR) polymer composite were introduced. The analysis results indicated that the bulk resistivity decreased greatly with increasing boron carbide content, and when boron carbide content reached to 60%, the bulk resistivity achieved the minimum. Accordingly, electric heating behavior of the composite is strongly dependent on boron carbide content as well as applied voltage. The content of boron carbide was found to be effective in achieving high thermal conductivity in composite systems. The thermal conductivity of the composite material with added boron carbide was improved nearly 20 times than that of the pure IIR. The thermal stability test showed that, compared with pure IIR, the thermal stable time of composites was markedly extended, which indicated that the boron carbide can significantly improve the thermal stability of boron carbide/IIR composite.

  19. Microstructure and corrosion behavior of binary titanium alloys with beta-stabilizing elements.

    Science.gov (United States)

    Takada, Y; Nakajima, H; Okuno, O; Okabe, T

    2001-03-01

    Binary titanium alloys with the beta-stabilizing elements of Co, Cr, Cu, Fe, Mn and Pd (up to 30%) and Ag (up to 45%) were examined through metallographic observation and X-ray diffractometry to determine whether beta phases that are advantageous for dental use could be retained. Corrosion behavior was also investigated electrochemically and discussed thermodynamically. Some cast alloys with Co, Cr, Fe, Mn, and Pd retained the beta phase, whereas those with Ag and Cu had no beta phase. In some alloys, an intermetallic compound formed, based on information from the phase diagram. The corrosion resistance deteriorated in the TiAg alloys because Ti2Ag and/or TiAg intermetallic compounds preferentially dissolved in 0.9% NaCl solution. On the other hand, the remaining titanium alloys became easily passive and revealed good corrosion resistance similar to pure titanium since their matrices seemed to thermodynamically form titanium oxides as did pure titanium.

  20. A novel approach to the island of stability of super-heavy elements search

    Directory of Open Access Journals (Sweden)

    Wieloch A.

    2016-01-01

    Full Text Available It is expected that the cross section for super-heavy nuclei production of Z > 118 is dropping into the region of tens of femto barns. This creates a serious limitation for the complete fusion technique that is used so far. Moreover, the available combinations of the neutron to proton ratio of stable projectiles and targets are quite limited and it can be difficult to reach the island of stability of super heavy elements using complete fusion reactions with stable projectiles. In this context, a new experimental investigation of mechanisms other than complete fusion of heavy nuclei and a novel experimental technique are invented for our search of super- and hyper-nuclei. This contribution is focused on that technique.

  1. On the existence and stability conditions for mixed-hybrid finite element solutions based on Reissner's variational principle

    Science.gov (United States)

    Karlovitz, L. A.; Atluri, S. N.; Xue, W.-M.

    1985-01-01

    The extensions of Reissner's two-field (stress and displacement) principle to the cases wherein the displacement field is discontinuous and/or the stress field results in unreciprocated tractions, at a finite number of surfaces ('interelement boundaries') in a domain (as, for instance, when the domain is discretized into finite elements), is considered. The conditions for the existence, uniqueness, and stability of mixed-hybrid finite element solutions based on such discontinuous fields, are summarized. The reduction of these global conditions to local ('element') level, and the attendant conditions on the ranks of element matrices, are discussed. Two examples of stable, invariant, least-order elements - a four-node square planar element and an eight-node cubic element - are discussed in detail.

  2. Comparative study of thermal stability of magnetostrictive biosensor between two kinds of biorecognition elements

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Xue-mei [School of Materials Science and Engineering, Changzhou University, Changzhou 213164 (China); Guntupalli, R.; Lakshmanan, R.S.; Chin, Bryan A. [Materials Research and Education Center, Auburn University, AL 36849 (United States); Hu, Jing, E-mail: jinghoo@126.com [School of Materials Science and Engineering, Changzhou University, Changzhou 213164 (China); Materials Research and Education Center, Auburn University, AL 36849 (United States)

    2014-08-01

    Magnetostrictive biosensors specific to Salmonella typhimurium were prepared by immobilizing antibody or phage as biorecognition elements onto the magnetostrictive sensor platform. The sensors were stored at temperatures of 25 °C (room temperature), 45 °C and 65 °C, respectively, and the ability to bind S. typhimurium was detected by testing the resonant frequency shift using a HP network analyzer after exposure to 1 mL of 1 × 10{sup 9} cfu/mL of S. typhimurium at a predetermined schedule. The binding of S. typhimurium to biosensors was confirmed by Scanning Electron Microscopy (SEM). The results showed that there existed an initial sudden drop in the average density of S. typhimurium bound to the biosensor surface versus duration at different temperatures for the two kinds of recognition elements, and the binding ability to S. typhimurium of phage-immobilized biosensors was much better than that of antibody-immobilized biosensors, with longevity longer than 30 days at all tested temperatures, though decreasing gradually over the testing period. While the longevity of antibody-immobilized biosensors was only about 30, 8 and 5 days at room temperature (25 °C), 45 °C and 65 °C, respectively. Meanwhile, the activation energy of the two kinds of biosensors was investigated, and it was found that phage immobilized sensors showed much higher activation energy than antibody immobilized sensors, which resulted in less dependency on temperature and thus having much better thermal stability than antibody immobilized sensors. - Highlights: • Phage immobilized biosensors has much better thermal stability. • The longevity of phage immobilized biosensors was longer than 30 days even at 65 °C. • The activation energy of phage immobilized biosensors is much higher.

  3. Light element ceramics

    OpenAIRE

    Rao, KJ; Varma, KBR; Raju, AR

    1988-01-01

    An overview of a few structually important light element ceramics is presented. Included in the overview are silicon nitide, sialon, aluminium nitride, boron carbide and silicon carbide. Methods of preparation, characterization and industrial applications of these ceramics are summarized. Mechanical properties, industrial production techniques and principal uses of these ceramics are emphasized.

  4. Formation mechanism of spheroidal carbide in ultra-low carbon ductile cast iron

    Directory of Open Access Journals (Sweden)

    Bin-guo Fu

    2016-09-01

    Full Text Available The formation mechanism of the spheroidal carbide in the ultra-low carbon ductile cast iron fabricated by the metal mold casting technique was systematically investigated. The results demonstrated that the spheroidal carbide belonged to eutectic carbide and crystallized in the isolated eutectic liquid phase area. The formation process of the spheroidal carbide was related to the contact and the intersection between the primary dendrite and the secondary dendrite of austenite. The oxides of magnesium, rare earths and other elements can act as heterogeneous nucleation sites for the spheroidal carbide. It was also found that the amount of the spheroidal carbide would increase with an increase in carbon content. The cooling rate has an important influence on the spheroidal carbide under the same chemical composition condition.

  5. Utilization of air pollution control residues for the stabilization/solidification of trace element contaminated soil.

    Science.gov (United States)

    Travar, I; Kihl, A; Kumpiene, J

    2015-12-01

    The aim of this study was to evaluate the stabilization/solidification (S/S) of trace element-contaminated soil using air pollution control residues (APCRs) prior to disposal in landfill sites. Two soil samples (with low and moderate concentrations of organic matter) were stabilized using three APCRs that originated from the incineration of municipal solid waste, bio-fuels and a mixture of coal and crushed olive kernels. Two APCR/soil mixtures were tested: 30% APCR/70% soil and 50% APCR/50% soil. A batch leaching test was used to study immobilization of As and co-occurring metals Cr, Cu, Pb and Zn. Solidification was evaluated by measuring the unconfined compression strength (UCS). Leaching of As was reduced by 39-93% in APCR/soil mixtures and decreased with increased amounts of added APCR. Immobilization of As positively correlated with the amount of Ca in the APCR and negatively with the amount of soil organic matter. According to geochemical modelling, the precipitation of calcium arsenate (Ca3(AsO4)2/4H2O) and incorporation of As in ettringite (Ca6Al2(SO4)3(OH)12 · 26H2O) in soil/APCR mixtures might explain the reduced leaching of As. A negative effect of the treatment was an increased leaching of Cu, Cr and dissolved organic carbon. Solidification of APCR/soil was considerably weakened by soil organic matter.

  6. Titanium Carbide: Nanotechnology, Properties, Application

    OpenAIRE

    Galevsky, G. V.; Rudneva, V. V.; Garbuzova, A. K.; Valuev, Denis Viktorovich

    2015-01-01

    The paper develops scientific and technological bases for fabrication of titanium carbide which is a nanocomponent of composite materials. The authors determine optimum technology specifications and the main titanium carbide properties: fineness of titaniferous raw materials, carbide-forming agent quantity, set temperature of plasma flow, tempering temperature, titanium carbide yield, productivity, specific surface, size and shape of particles. The paper includes equations to describe how the...

  7. Studies on Interfacial Phenomena in Titanium Carbide/Liquid Steel Systems for Development of Functionally Graded Material

    Science.gov (United States)

    Kiviö, Miia; Holappa, Lauri; Louhenkilpi, Seppo; Nakamoto, Masashi; Tanaka, Toshihiro

    2016-08-01

    In modern materials' applications, versatile, often contradictory requirements are set for properties like high strength, hardness, and toughness. However, e.g., in steel castings, typically only certain surfaces should be hard and wear resistant, whereas the other "bulk" might have only standard properties. Then the critical parts of the surface should be "locally reinforced" to get functionally graded material. Expensive alloying elements are saved, and manufacturing stages are minimized. Titanium carbide is an extremely hard material widely applied in carbide tools. It could be used to reinforce steel castings. When TiC particles are added to liquid steel, wettability, stability, and dissolution are key phenomena that should be understood to better design and control manufacturing processes. In this work, the interfacial phenomena and reactions between TiC and iron/steel melts were examined by wetting experiments with special emphasis on the influence of Cr, Ni, and Mo. No significant effect on wettability was observed by Ni or Mo. High Cr melts showed somewhat higher contact angles. Partial penetration of liquid metal took place in the substrate along the grain boundaries. Ni seemed to promote penetration. During longer experiments, re-precipitation of carbides occurred on the liquid droplet influencing the apparent wetting angle. Cr and Mo promoted carbide formation.

  8. A locally conservative stabilized continuous Galerkin finite element method for two-phase flow in poroelastic subsurfaces

    Science.gov (United States)

    Deng, Q.; Ginting, V.; McCaskill, B.; Torsu, P.

    2017-10-01

    We study the application of a stabilized continuous Galerkin finite element method (CGFEM) in the simulation of multiphase flow in poroelastic subsurfaces. The system involves a nonlinear coupling between the fluid pressure, subsurface's deformation, and the fluid phase saturation, and as such, we represent this coupling through an iterative procedure. Spatial discretization of the poroelastic system employs the standard linear finite element in combination with a numerical diffusion term to maintain stability of the algebraic system. Furthermore, direct calculation of the normal velocities from pressure and deformation does not entail a locally conservative field. To alleviate this drawback, we propose an element based post-processing technique through which local conservation can be established. The performance of the method is validated through several examples illustrating the convergence of the method, the effectivity of the stabilization term, and the ability to achieve locally conservative normal velocities. Finally, the efficacy of the method is demonstrated through simulations of realistic multiphase flow in poroelastic subsurfaces.

  9. Diamond-silicon carbide composite and method

    Science.gov (United States)

    Zhao, Yusheng

    2011-06-14

    Uniformly dense, diamond-silicon carbide composites having high hardness, high fracture toughness, and high thermal stability are prepared by consolidating a powder mixture of diamond and amorphous silicon. A composite made at 5 GPa/1673K had a measured fracture toughness of 12 MPam.sup.1/2. By contrast, liquid infiltration of silicon into diamond powder at 5 GPa/1673K produces a composite with higher hardness but lower fracture toughness.

  10. Improving the stability of peptidic radiotracers by the introduction of artificial scaffolds: which structure element is most useful?

    Science.gov (United States)

    Bacher, Lisa; Fischer, Gabriel; Litau, Shanna; Schirrmacher, Ralf; Wängler, Björn; Baller, Marko; Wängler, Carmen

    2015-08-01

    Peptidic radiotracers are highly potent substances for the specific in vivo imaging of various biological targets with Single Photon Emission Computed Tomography and Positron Emission Tomography. However, some radiolabeled peptides such as bombesin analogs were shown to exhibit only a limited stability, hampering a successful target visualization. One option to positively influence the stability of radiolabeled peptides is the introduction of certain artificial molecular scaffolds. In order to comparatively assess the influence of different structure elements on the stability of radiolabeled peptides and to identify those structure elements being most useful for peptide radiotracer stabilization, several monomeric and dimeric bombesin derivatives were synthesized, exhibiting differing molecular designs and the chelator NODAGA for (68) Ga-labeling. The radiolabeled peptides were evaluated regarding their in vitro stability in human serum to determine the influence of the introduced molecular scaffolds on the peptides' serum stabilities. The results of the evaluations showed that the introduction of scaffold structures and the overall molecular design have a substantial impact on the stabilities of the resulting peptidic radiotracers. But besides some general trends found using certain scaffold structures, the obtained results point to the necessity to empirically assess their influence on stability for each susceptible peptidic radiotracer individually.

  11. Titanium Carbide: Nanotechnology, Properties, Application

    Science.gov (United States)

    Galevsky, G. V.; Rudneva, V. V.; Garbuzova, A. K.; Valuev, D. V.

    2015-09-01

    The paper develops scientific and technological bases for fabrication of titanium carbide which is a nanocomponent of composite materials. The authors determine optimum technology specifications and the main titanium carbide properties: fineness of titaniferous raw materials, carbide-forming agent quantity, set temperature of plasma flow, tempering temperature, titanium carbide yield, productivity, specific surface, size and shape of particles. The paper includes equations to describe how the major specifications of the fabrication technique influence the content of titanium carbide and free carbon in the end product.

  12. Investigation of the Corrosion Behaviors of HVOF-Sprayed Carbide Cernet Coatings in Molten Al-Zn-Si Alloy Bath

    Institute of Scientific and Technical Information of China (English)

    JIANG Zhen-hua; TAN Xing-hai; ZHANG Yue-gang; SUN Jia-shu

    2004-01-01

    In continuous hot-dip galvanization process the corrosion and chemical stability of the sink roll in the galvanizing bath are important problem which effects on the quality and productivity. In order to protect the sink roll the carbide cermet and/or ceramic coatings were deposited on the surface of the sink roll. The WC-, Cr3 C2-cermet coatings were deposited by high velocity oxygen fuel (HVOF) spray, respectively. The coating samples were immersed in molten Zn-alloy containing 50 wt % aluminum at 833 K for 24 hr and 144 hr, respectively. The inter-diffusion and inter-reaction of Zn, Al and elements in coating and corrosion behaviors of these coatings were investigated by XRD, SEM and EPMA etc. The corrosion mechanisms of the carbide cermet coatings and ceramic coatings in molten High Al-Zn-alloy were approached.

  13. Characterization of Silicon Carbide.

    Science.gov (United States)

    The various electrical and structural measurement techniques for silicon carbide are described. The electrical measurements include conductivity, resistivity, carrier concentration, mobility, doping energy levels, and lifetime. The structural measurements include polytype determination and crystalline perfection. Both bulk and epitaxial films are included.

  14. Composition Comprising Silicon Carbide

    Science.gov (United States)

    Mehregany, Mehran (Inventor); Zorman, Christian A. (Inventor); Fu, Xiao-An (Inventor); Dunning, Jeremy L. (Inventor)

    2012-01-01

    A method of depositing a ceramic film, particularly a silicon carbide film, on a substrate is disclosed in which the residual stress, residual stress gradient, and resistivity are controlled. Also disclosed are substrates having a deposited film with these controlled properties and devices, particularly MEMS and NEMS devices, having substrates with films having these properties.

  15. Electrical, Chemical, And Microstructural Analysis of the Thermal Stability of Nickel-based Ohmic Contacts to Silicon Carbide for High-Temperature Electronics

    Science.gov (United States)

    Virshup, Ariel R.

    With increasing attention on curbing the emission of pollutants into the atmosphere, chemical sensors that can be used to monitor and control these unwanted emissions are in great demand. Examples include monitoring of hydrocarbons from automobile engines and monitoring of flue gases such as CO emitted from power plants. One of the critical limitations in high-temperature SiC gas sensors, however, is the degradation of the metal-SiC contacts over time. In this dissertation, we investigated the high-temperature stability of Pt/TaSix/Ni/SiC ohmic contacts, which have been implemented in SiC-based gas sensors developed for applications in diesel engines and power plants. The high-temperature stability of a Pt/TaSi2/Ni/SiC ohmic contact metallization scheme was characterized using a combination of current-voltage measurements, Auger electron spectroscopy, secondary ion mass spectrometry, and transmission electron microscope imaging and associated analytical techniques. Increasing the thicknesses of the Pt and TaSi2 layers promoted electrical stability of the contacts, which remained ohmic at 600°C in air for over 300 h; the specific contact resistance showed only a gradual increase from an initial value of 5.2 x 10-5 O-cm 2. We observed a continuous silicon-oxide layer in the thinner contact structures, which failed after 36 h of heating. It was found that the interface between TaSix and NiySi was weakened by the accumulation of free carbon (produced by the reaction of Ni and SiC), which in turn facilitated oxygen diffusion from the contact edges. Additional oxygen diffusion occurred along grain boundaries in the Pt overlayer. Meanwhile, thicker contacts, with less interfacial free carbon and enhanced electrical stability contained a much lower oxygen concentration that was distributed across the contact layers, precluding the formation of an electrically insulating contact structure.

  16. Unified analysis for stabilized methods of low-order mixed finite elements for stationary Navier-Stokes equations

    Institute of Scientific and Technical Information of China (English)

    陈刚; 冯民富; 何银年

    2013-01-01

    A unified analysis is presented for the stabilized methods including the pres-sure projection method and the pressure gradient local projection method of conforming and nonconforming low-order mixed finite elements for the stationary Navier-Stokes equa-tions. The existence and uniqueness of the solution and the optimal error estimates are proved.

  17. A NEW STABILIZED FINITE ELEMENT METHOD FOR SOLVING THE STOKES AND NAVIER-STOKES EQUATIONS PART II. THE NONLINEAR CASE

    Institute of Scientific and Technical Information of China (English)

    DUAN Huoyuan; LIANG Guoping

    2001-01-01

    Following Part I., we study the stabilized finite element method for the incom pressible Navier-Stokes equations. It is shown that this new methodology is stable and has an optimal error estimates for all mesh Peclet number, allowing any combination of velocity and pressure interpolation.

  18. Silicon carbide high performance optics: a cost-effective, flexible fabrication process

    Science.gov (United States)

    Casstevens, John M.; Rashed, Abuagela; Plummer, Ronald; Bray, Don; Gates, Rob L.; Lara-Curzio, Edgar; Ferber, Matt K.; Kirkland, Tim

    2001-12-01

    Silicon carbide may well be the best known material for the manufacture of high performance optical components. This material offers many advantages over glasses and metals that have historically been used in high performance optical systems. A combination of extremely high specific stiffness (E/r), high thermal conductivity and outstanding dimensional stability make silicon carbide superior overall to beryllium and low-expansion glass ceramics. A major impediment to wide use of silicon carbide in optical systems has been the cost associated with preliminary shaping and final finishing of silicon carbide. Because silicon carbide is an extremely hard and strong material, precision machining can only be done with expensive diamond tooling on very stiff high quality machine tools. Near-net-shape slip casting of silicon carbide can greatly reduce the cost of silicon carbide mirror substrates but this process still requires significant diamond grinding of the cast components. The process described here begins by machining the component from all special type of graphite. This graphite can rapidly be machined with conventional multi-axis CNC machine tools to achieve any level of complexity and lightweighting required. The graphite is then directly converted completely to silicon carbide with very small and very predictable dimensional change. After conversion to silicon carbide the optical surface is coated with very fine grain CVD silicon carbide which is easily polished to extreme smoothness. Details of the fabrication process are described and photos and performance specifications of an eight-inch elliptical demonstration mirror are provided.

  19. Recent trends in silicon carbide device research

    Directory of Open Access Journals (Sweden)

    Munish Vashishath

    2008-08-01

    Full Text Available Silicon carbide (SiC has revolutionised semiconductor power device performance. It is a wide band gap semiconductor with an energy gap wider than 2eV and possesses extremely high power, high voltage switching characteristics and high thermal, chemical and mechanical stability. The SiC wafers are available in 6H, 4H, 2H and 3C polytypes. Because of its wide band gap, the leakage current of SiC is many orders of magnitude lower than that of silicon. Also, forward resistance of SiC power devices is approximately 200 times lower than that of conventional silicon devices. The breakdown voltage of SiC is 8-10 times higher than that of silicon. In this paper, silicon carbide Schottky barrier diodes, power MOSFETs, UMOSFET, lateral power MOSFET, SIT (static induction transistor, and nonvolatile memories are discussed along with their characteristics and applications.

  20. Investigation on the Performance of Supported Molybdenum Carbide for the Partial Oxidation of Methane

    Institute of Scientific and Technical Information of China (English)

    Quanli Zhu; Jian Yang; Jiaxin Wang; Shengfu Ji; Hanqing Wang

    2003-01-01

    The performance of supported and unsupported molybdenum carbide for the partial oxida-tion of methane (POM) to syngas was investigated. An evaluation of the catalysts indicates that bulkmolybdenum carbide has a higher methane conversion during the initial stage but a lower selectivity toCO and H2/CO ratio in the products. The rapid deactivation of the catalyst is also a significant problem.However, the supported molybdenum carbide catalyst shows a much higher methane conversion, increasedselectivity and significantly improved catalytic stability. The characterization by XRD and BET specificarea measurements depict an improved dispersion of molybdenum carbide when using alumina as a carrier.The bulk or the supported molybdenum carbide exists in the β-Mo2C phase, while it is transformed intomolybdenum dioxide postcatalysis which is an important cause of molybdenum carbide deactivation.

  1. Microstructural studies of carbides in MAR-M247 nickel-based superalloy

    Science.gov (United States)

    Szczotok, A.; Rodak, K.

    2012-05-01

    Carbides play an important role in the strengthening of microstructures of nickel-based superalloys. Grain boundary carbides prevent or retard grain-boundary sliding and make the grain boundary stronger. Carbides can also tie up certain elements that would otherwise promote phase instability during service. Various types of carbides are possible in the microstructure of nickel-based superalloys, depending on the superalloy composition and processing. In this paper, scanning electron and scanning transmission electron microscopy studies of carbides occurring in the microstructure of polycrystalline MAR-M247 nickel-based superalloy were carried out. In the present work, MC and M23C6 carbides in the MAR-M247 microstructure were examined.

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

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Jingguan [University of Delaware

    2014-03-04

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

  3. STABILIZED FINITE ELEMENT METHODS FOR THE BRINKMAN EQUATION ON FITTED AND FICITITIOUS DOMAINS

    OpenAIRE

    Sogn, Jarle

    2014-01-01

    The parameter dependent Brinkman equation can be used to model viscous and porous flow. The equation covers a family of problems, ranging from the Stokes problem to the Darcy problem. We apply the stabilization methods; the pressure stabilized petrov--galerkin (PSPG) method and the continuous interior penalty (CIP) method, on the Brinkman equation with weakly imposed boundary conditions by the Nitsche method. An a priori error estimate is proved for the CIP stabilization with the Nitsche meth...

  4. Chemical Analysis Methods for Silicon Carbide

    Institute of Scientific and Technical Information of China (English)

    Shen Keyin

    2006-01-01

    @@ 1 General and Scope This Standard specifies the determination method of silicon dioxide, free silicon, free carbon, total carbon, silicon carbide, ferric sesquioxide in silicon carbide abrasive material.

  5. Carbide Dissolution during Intercritical Austenitization in Bearing Steel

    Institute of Scientific and Technical Information of China (English)

    LI Hui; MI Zhenli; ZHANG Xiaolei; TANG Di; WANG Yide

    2014-01-01

    In order to investigate the carbide dissolution mechanism of high carbon-chromium bearing steel during the intercritical austenitization, the database of TCFE7 of Thermo-calc and MOBFE of DICTRA software were used to calculate the elements diffusion kinetic and the evolution law of volume fraction of carbide. DIL805A dilatometer was used to simulate the intercritical heat treatment. The microstructure was observed by scanning electron microscopy(SEM), and the micro-hardness was tested. The experimental results indicate that the dissolution of carbide is composed of two stages:initial austenite growth governed by carbon diffusion which sharply moves up the micro-hardness of quenched martensite, and subsequent growth controlled by diffusion of Cr elements in M3C. The volume fraction of M3C decreases with the increasing holding time, and the metallographic analysis shows a great agreement with values calculated by software.

  6. The Study of Stability of Compression-Loaded Multispan Composite Panel Upon Failure of Elements Binding it to Panel Supports

    Science.gov (United States)

    Zamula, G. N.; Ierusalimsky, K. M.; Fomin, V. P.; Grishin, V. I.; Kalmykova, G. S.

    1999-01-01

    The present document is a final technical report carried out within co-operation between United States'NASA Langley RC and Russia's Goskomoboronprom in aeronautics, and continues similar programs, accomplished in 1996, 1997, and 1998, respectively). The report provides results of "The study of stability of compression-loaded multispan composite panels upon failure of elements binding it to panel supports"; these comply with requirements established at TsAGI on 24 March 1998 and at NASA on 15 September 1998.

  7. Investigation of biomechanical behavior of lumbar vertebral segments with dynamic stabilization device using finite element approach

    Science.gov (United States)

    Deoghare, Ashish B.; Kashyap, Siddharth; Padole, Pramod M.

    2013-03-01

    Degenerative disc disease is a major source of lower back pain and significantly alters the biomechanics of the lumbar spine. Dynamic stabilization device is a remedial technique which uses flexible materials to stabilize the affected lumbar region while preserving the natural anatomy of the spine. The main objective of this research work is to investigate the stiffness variation of dynamic stabilization device under various loading conditions under compression, axial rotation and flexion. Three dimensional model of the two segment lumbar spine is developed using computed tomography (CT) scan images. The lumbar structure developed is analyzed in ANSYS workbench. Two types of dynamic stabilization are considered: one with stabilizing device as pedicle instrumentation and second with stabilization device inserted around the inter-vertebral disc. Analysis suggests that proper positioning of the dynamic stabilization device is of paramount significance prior to the surgery. Inserting the device in the posterior region indicates the adverse effects as it shows increase in the deformation of the inter-vertebral disc. Analysis executed by positioning stabilizing device around the inter-vertebral disc yields better result for various stiffness values under compression and other loadings. [Figure not available: see fulltext.

  8. Silicon carbide sewing thread

    Science.gov (United States)

    Sawko, Paul M. (Inventor)

    1995-01-01

    Composite flexible multilayer insulation systems (MLI) were evaluated for thermal performance and compared with currently used fibrous silica (baseline) insulation system. The systems described are multilayer insulations consisting of alternating layers of metal foil and scrim ceramic cloth or vacuum metallized polymeric films quilted together using ceramic thread. A silicon carbide thread for use in the quilting and the method of making it are also described. These systems provide lightweight thermal insulation for a variety of uses, particularly on the surface of aerospace vehicles subject to very high temperatures during flight.

  9. A New Approach for Refining Carbide Dimensions in M42 Super Hard High-speed Steel

    Institute of Scientific and Technical Information of China (English)

    Xue-feng ZHOU; Wang-long ZHU; Hong-bing JIANG; Feng FANG; Yi-you TU; Jian-qing JIANG

    2016-01-01

    Obtaining small carbides is crucial but difficult for high-speed steels.A new approach for refining carbide dimensions in M42 super hard high-speed steel by increasing cooling rate and spheroidizing treatment was proposed. The morphologies and properties of eutectic carbides formed at different cooling rates were investigated by means of scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),X-ray diffraction (XRD),transmis-sion electron microscopy (TEM),electron back-scattered diffraction (EBSD)and differential scanning calorimeter (DSC).The results show that eutectic carbides change from a lamellar shape into a curved-rod shape as cooling rate increases.Despite different morphologies,the two carbides are both of M2 C type with a hexagonal close-packed structure and display a single crystal orientation in one eutectic colony.The morphology of M2 C mainly depends on the growing process of eutectic carbides,which is strongly influenced by cooling rate.Compared with lamellar car-bides,M2 C carbides with curved-rod shapes are less stable,and decompose into M6 C and MC at lower temperatures. They are more inclined to spheroidize during heating,which ultimately and distinguishably refines the carbide dimen-sions.As small carbides are much easier to dissolve into matrices during austenization,the process described herein improves the supersaturation of alloying elements in martensite,which leads to an increment of hardness in M42 steel.

  10. The Effect of Cocoa Beans Heavy and Trace Elements on Safety and Stability of Confectionery Products

    Directory of Open Access Journals (Sweden)

    Vītola Vineta

    2016-06-01

    Full Text Available The aim of the study was to evaluate cocoa beans quality produced in Cameroon, Ecuador, Nigeria and Ghana from safety position determining heavy and trace metals concentration and evaluating the oxidative stability of confectionery products prototypes (trials with analysing cocoa beans. For evaluation of oxidative stability of confectionery products, the main ingredients - butter and cocoa beans kernels were tested making trials as milk chocolate prototype.

  11. ENTIRELY AQUEOUS SOLUTION-GEL ROUTE FOR THE PREPARATION OF ZIRCONIUM CARBIDE, HAFNIUM CARBIDE AND THEIR TERNARY CARBIDE POWDERS

    Directory of Open Access Journals (Sweden)

    Zhang Changrui

    2016-07-01

    Full Text Available An entirely aqueous solution-gel route has been developed for the synthesis of zirconium carbide, hafnium carbide and their ternary carbide powders. Zirconium oxychloride (ZrOCl₂.8H₂O, malic acid (MA and ethylene glycol (EG were dissolved in water to form the aqueous zirconium carbide precursor. Afterwards, this aqueous precursor was gelled and transformed into zirconium carbide at a relatively low temperature (1200 °C for achieving an intimate mixing of the intermediate products. Hafnium and the ternary carbide powders were also synthesized via the same aqueous route. All the zirconium, hafnium and ternary carbide powders exhibited a particle size of ∼100 nm.

  12. Mammalian chromosomes contain cis-acting elements that control replication timing, mitotic condensation, and stability of entire chromosomes.

    Science.gov (United States)

    Thayer, Mathew J

    2012-09-01

    Recent studies indicate that mammalian chromosomes contain discrete cis-acting loci that control replication timing, mitotic condensation, and stability of entire chromosomes. Disruption of the large non-coding RNA gene ASAR6 results in late replication, an under-condensed appearance during mitosis, and structural instability of human chromosome 6. Similarly, disruption of the mouse Xist gene in adult somatic cells results in a late replication and instability phenotype on the X chromosome. ASAR6 shares many characteristics with Xist, including random mono-allelic expression and asynchronous replication timing. Additional "chromosome engineering" studies indicate that certain chromosome rearrangements affecting many different chromosomes display this abnormal replication and instability phenotype. These observations suggest that all mammalian chromosomes contain "inactivation/stability centers" that control proper replication, condensation, and stability of individual chromosomes. Therefore, mammalian chromosomes contain four types of cis-acting elements, origins, telomeres, centromeres, and "inactivation/stability centers", all functioning to ensure proper replication, condensation, segregation, and stability of individual chromosomes.

  13. Effects of Rare Earth and Alkaline Earth on Spheroidizing of Eutectic Carbides in Low Tungsten White Cast Iron

    Institute of Scientific and Technical Information of China (English)

    Fu Hanguang; Zou Dening

    2004-01-01

    Tungsten Alloy White Cast Iron(TAWCI) has great brittleness and narrow application scope. The influences of Rare earth element(Ce) and alkaline earth elements ( K, Na) on the microstructures and performances of TAWCI were researched, and the idea estimating spheroidizing effect of carbides using Circular Degree (C. D) were put forward. The result shows that eutectics carbide tums into sphericity from network after modification, and carbide is refined and uniformly distributed and the C. D of eutectic carbide increases. The mechanism of carbide spheroidizing was analyzed. The impact toughness and wear resistance of TAWCI obviously improve with the rise of C. D of carbides.The service life of modified TAWCI roll is 35 % higher than that of high chromium cast iron roll, and its production cost is reduced by 25 %.

  14. Methods of producing continuous boron carbide fibers

    Energy Technology Data Exchange (ETDEWEB)

    Garnier, John E.; Griffith, George W.

    2015-12-01

    Methods of producing continuous boron carbide fibers. The method comprises reacting a continuous carbon fiber material and a boron oxide gas within a temperature range of from approximately 1400.degree. C. to approximately 2200.degree. C. Continuous boron carbide fibers, continuous fibers comprising boron carbide, and articles including at least a boron carbide coating are also disclosed.

  15. Computational study of elements of stability of a four-helix bundle protein biosurfactant

    Science.gov (United States)

    Schaller, Andrea; Connors, Natalie K.; Dwyer, Mirjana Dimitrijev; Oelmeier, Stefan A.; Hubbuch, Jürgen; Middelberg, Anton P. J.

    2015-01-01

    Biosurfactants are surface-active molecules produced principally by microorganisms. They are a sustainable alternative to chemically-synthesized surfactants, having the advantages of being non-toxic, highly functional, eco-friendly and biodegradable. However they are currently only used in a few industrial products due to costs associated with production and purification, which exceed those for commodity chemical surfactants. DAMP4, a member of a four-helix bundle biosurfactant protein family, can be produced in soluble form and at high yield in Escherichia coli, and can be recovered using a facile thermal phase-separation approach. As such, it encompasses an interesting synergy of biomolecular and chemical engineering with prospects for low-cost production even for industrial sectors. DAMP4 is highly functional, and due to its extraordinary thermal stability it can be purified in a simple two-step process, in which the combination of high temperature and salt leads to denaturation of all contaminants, whereas DAMP4 stays stable in solution and can be recovered by filtration. This study aimed to characterize and understand the fundamental drivers of DAMP4 stability to guide further process and surfactant design studies. The complementary use of experiments and molecular dynamics simulation revealed a broad pH and temperature tolerance for DAMP4, with a melting point of 122.4 °C, suggesting the hydrophobic core as the major contributor to thermal stability. Simulation of systematically created in silico variants of DAMP4 showed an influence of number and location of hydrophilic mutations in the hydrophobic core on stability, demonstrating a tolerance of up to three mutations before a strong loss in stability occurred. The results suggest a consideration of a balance of stability, functionality and kinetics for new designs according to their application, aiming for maximal functionality but at adequate stability to allow for cost-efficient production using thermal

  16. Stability of the high-order finite elements for acoustic or elastic wave propagation with high-order time stepping

    KAUST Repository

    De Basabe, Jonás D.

    2010-04-01

    We investigate the stability of some high-order finite element methods, namely the spectral element method and the interior-penalty discontinuous Galerkin method (IP-DGM), for acoustic or elastic wave propagation that have become increasingly popular in the recent past. We consider the Lax-Wendroff method (LWM) for time stepping and show that it allows for a larger time step than the classical leap-frog finite difference method, with higher-order accuracy. In particular the fourth-order LWM allows for a time step 73 per cent larger than that of the leap-frog method; the computational cost is approximately double per time step, but the larger time step partially compensates for this additional cost. Necessary, but not sufficient, stability conditions are given for the mentioned methods for orders up to 10 in space and time. The stability conditions for IP-DGM are approximately 20 and 60 per cent more restrictive than those for SEM in the acoustic and elastic cases, respectively. © 2010 The Authors Journal compilation © 2010 RAS.

  17. Assessment of Slope Stability and Interference of Structures Considering Seismity in Complex Engineering-Geological Conditions Using the Method of Finite Elements

    Science.gov (United States)

    Menabdishvili, Papuna; Eremadze, Nelly

    2008-07-01

    There is elaborated the calculation model of slope deformation mode stability and the methodic of calculation considering the interference of structures to be built on it using the method of finite elements. There is examined the task of slope stability using the soil physically nonlinear finite element considering the seismicity 8. The deformation mode and field of coefficients of stability are obtained and slope supposed sliding curve is determined. The elaborated calculation methodic allows to determine the slope deformation mode, stability and select the optimum version of structure foundation at any slant and composition of slope layers.

  18. Growth kinetics of cubic carbide free layers in graded cemented carbides

    Science.gov (United States)

    Shi, Liu-Yong; Liu, Yi-Min; Huang, Ji-Hua; Zhang, Shou-Quan; Zhao, Xing-Ke

    2012-01-01

    In order to reveal the formation mechanism of cubic carbide free layers (CCFL), graded cemented carbides with CCFL in the surface zone were fabricated by a one-step sintering procedure in vacuum, and the analysis on microstructure and element distribution were performed by scanning electron microscopy (SEM) and electron probe micro-analyzer (EPMA), respectively. A new physical model and kinetic equation were established based on experimental results. Being different from previous models, this model suggests that nitrogen diffusion outward is only considered as an induction factor, and the diffusion of titanium through liquid phase plays a dominative role. The driving force of diffusion is expressed as the differential value between nitrogen partial pressure and nitrogen equilibrium pressure essentially. Simulation results by the kinetic equation are in good agreement with experimental values, and the effect of process parameters on the growth kinetics of CCFL can also be explained reasonably by the current model.

  19. Fivefold twinned boron carbide nanowires.

    Science.gov (United States)

    Fu, Xin; Jiang, Jun; Liu, Chao; Yuan, Jun

    2009-09-01

    Chemical composition and crystal structure of fivefold twinned boron carbide nanowires have been determined by electron energy-loss spectroscopy and electron diffraction. The fivefold cyclic twinning relationship is confirmed by systematic axial rotation electron diffraction. Detailed chemical analysis reveals a carbon-rich boron carbide phase. Such boron carbide nanowires are potentially interesting because of their intrinsic hardness and high temperature thermoelectric property. Together with other boron-rich compounds, they may form a set of multiply twinned nanowire systems where the misfit strain could be continuously tuned to influence their mechanical properties.

  20. Technology of Iron Carbide Synthesis

    Institute of Scientific and Technical Information of China (English)

    M.Bahgat

    2006-01-01

    Iron carbides are very promising metallurgical products and can be used for steelmaking process, where it plays as an alternative raw material with significant economic advantages. Also it has many other applications,e.g. catalysts, magnets, sensors. The present review investigates the different properties and uses of the iron carbides. The commercial production and the different varieties for the iron carbides synthesis (gaseous carburization, mechanochemical synthesis, laser pyrolysis, plasma pyrolysis, chemical vapor deposition and ion implantation) were reviewed. Also the effect of different factors on the carburization process like gas composition, raw material, temperature, reaction time, catalyst presence and sulfur addition was indicated.

  1. Temporal stability of otolith elemental fingerprints discriminates among lagoon nursery habitats

    Science.gov (United States)

    Tournois, Jennifer; Ferraton, Franck; Velez, Laure; McKenzie, David J.; Aliaume, Catherine; Mercier, Lény; Darnaude, Audrey M.

    2013-10-01

    The chemical composition of fish otoliths reflects that of the water masses that they inhabit. Otolith elemental compositions can, therefore, be used as natural tags to discriminate among habitats. However, for retrospective habitat identification to be valid and reliable for any adult, irrespective of its age, significant differences in environmental conditions, and therefore otolith signatures, must be temporally stable within each habitat, otherwise connectivity studies have to be carried out by matching year-classes to the corresponding annual fingerprints. This study investigated how various different combinations of chemical elements in otoliths could distinguish, over three separate years, between four coastal lagoon habitats used annually as nurseries by gilthead sea bream (Sparus aurata L.) in the Gulf of Lions (NW Mediterranean). A series of nine elements were measured in otoliths of 301 S. aurata juveniles collected in the four lagoons in 2008, 2010 and 2011. Percentages of correct re-assignment of juveniles to their lagoon of origin were calculated with the Random Forest classification method, considering every possible combination of elements. This revealed both spatial and temporal variations in accuracy of habitat identification, with correct re-assignment to each lagoon ranging from 44 to 99% depending on the year and the lagoon. There were also annual differences in the combination of elements that provided the best discrimination among the lagoons. Despite this, when the data from the three years were pooled, a combination of eight elements (B, Ba, Cu, Li, Mg, Rb, Sr and Y) provided greater than 70% correct re-assignment to each single lagoon, with a multi-annual global accuracy of 79%. When considering the years separately, discrimination accuracy with these elemental fingerprints was above 90% for 2008 and 2010. It decreased to 61% in 2011, when unusually heavy rainfall occurred, which presumably reduced chemical differences among several of the

  2. Stabilization effects of third element on CaCu5 type derivatives of rare-earth transition-metal intermetallics

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Part of the results of the key project "Search for novel rare-earth functional materials" supported by the National Natural Science Foundation of China is reviewed. In combination with reports in literature, the effects of the third element M on the formation and stability of La2(Co, M)17, R(Fe, M)12 and R3(Fe, M)29 intermetallic compounds are discussed by considering mixing enthalpy of M with rare-earth, Fe and Co, and atomic radius, electronegativity and electronic configurations, etc. It is concluded that the mixing en thalpy and atomic radius dominate the preferential sites and the minimum amount of M required to stabilize a structure, which ultimately affect the magnetic properties of a compound prominently. This review should provide some heuristic hints for exploiting novel rare-earth transition metal functional materials and for improving their performance.

  3. Rous Sarcoma Virus RNA Stability Element Inhibits Deadenylation of mRNAs with Long 3′UTRs

    Science.gov (United States)

    Balagopal, Vidya; Beemon, Karen L.

    2017-01-01

    All retroviruses use their full-length primary transcript as the major mRNA for Group-specific antigen (Gag) capsid proteins. This results in a long 3′ untranslated region (UTR) downstream of the termination codon. In the case of Rous sarcoma virus (RSV), there is a 7 kb 3′UTR downstream of the gag terminator, containing the pol, env, and src genes. mRNAs containing long 3′UTRs, like those with premature termination codons, are frequently recognized by the cellular nonsense-mediated mRNA decay (NMD) machinery and targeted for degradation. To prevent this, RSV has evolved an RNA stability element (RSE) in the RNA immediately downstream of the gag termination codon. This 400-nt RNA sequence stabilizes premature termination codons (PTCs) in gag. It also stabilizes globin mRNAs with long 3′UTRs, when placed downstream of the termination codon. It is not clear how the RSE stabilizes the mRNA and prevents decay. We show here that the presence of RSE inhibits deadenylation severely. In addition, the RSE also impairs decapping (DCP2) and 5′-3′ exonucleolytic (XRN1) function in knockdown experiments in human cells. PMID:28763028

  4. The viscous curtain: General formulation and finite-element solution for the stability of flowing viscous sheets

    Science.gov (United States)

    Perdigou, C.; Audoly, B.

    2016-11-01

    The stability of thin viscous sheets has been studied so far in the special case where the base flow possesses a direction of invariance: the linear stability is then governed by an ordinary differential equation. We propose a mathematical formulation and a numerical method of solution that are applicable to the linear stability analysis of viscous sheets possessing no particular symmetry. The linear stability problem is formulated as a non-Hermitian eigenvalue problem in a 2D domain and is solved numerically using the finite-element method. Specifically, we consider the case of a viscous sheet in an open flow, which falls in a bath of fluid; the sheet is mildly stretched by gravity and the flow can become unstable by 'curtain' modes. The growth rates of these modes are calculated as a function of the fluid parameters and of the geometry, and a phase diagram is obtained. A transition is reported between a buckling mode (static bifurcation) and an oscillatory mode (Hopf bifurcation). The effect of surface tension is discussed.

  5. Microstructural Study of Titanium Carbide Coating on Cemented Carbide

    DEFF Research Database (Denmark)

    Vuorinen, S.; Horsewell, Andy

    1982-01-01

    Titanium carbide coating layers on cemented carbide substrates have been investigated by transmission electron microscopy. Microstructural variations within the typically 5µm thick chemical vapour deposited TiC coatings were found to vary with deposit thickness such that a layer structure could...... be delineated. Close to the interface further microstructural inhomogeneities were obsered, there being a clear dependence of TiC deposition mechanism on the chemical and crystallographic nature of the upper layers of the multiphase substrate....

  6. Discontinuous Galerkin finite element method for the nonlinear hyperbolic problems with entropy-based artificial viscosity stabilization

    Science.gov (United States)

    Zingan, Valentin Nikolaevich

    This work develops a discontinuous Galerkin finite element discretization of non- linear hyperbolic conservation equations with efficient and robust high order stabilization built on an entropy-based artificial viscosity approximation. The solutions of equations are represented by elementwise polynomials of an arbitrary degree p > 0 which are continuous within each element but discontinuous on the boundaries. The discretization of equations in time is done by means of high order explicit Runge-Kutta methods identified with respective Butcher tableaux. To stabilize a numerical solution in the vicinity of shock waves and simultaneously preserve the smooth parts from smearing, we add some reasonable amount of artificial viscosity in accordance with the physical principle of entropy production in the interior of shock waves. The viscosity coefficient is proportional to the local size of the residual of an entropy equation and is bounded from above by the first-order artificial viscosity defined by a local wave speed. Since the residual of an entropy equation is supposed to be vanishingly small in smooth regions (of the order of the Local Truncation Error) and arbitrarily large in shocks, the entropy viscosity is almost zero everywhere except the shocks, where it reaches the first-order upper bound. One- and two-dimensional benchmark test cases are presented for nonlinear hyperbolic scalar conservation laws and the system of compressible Euler equations. These tests demonstrate the satisfactory stability properties of the method and optimal convergence rates as well. All numerical solutions to the test problems agree well with the reference solutions found in the literature. We conclude that the new method developed in the present work is a valuable alternative to currently existing techniques of viscous stabilization.

  7. Optimum Design of Lightweight Silicon Carbide Mirror Assembly

    Institute of Scientific and Technical Information of China (English)

    HAN Yuanyuan; ZHANG Yumin; HAN Jiecai; ZHANG Jianhan; YAO Wang; ZHOU Yufeng

    2008-01-01

    According to the design requirement and on the basis of the principle that the thermal expansion coefficient of the support structure should match with that of the mirror, a lightweight silicon carbide primary mirror assembly was designed. Finite element analysis combined with the parameter-optimized method was used during the design. Lightweight cell and rigid rib structure were used for the mirror assembly. The static, dynamic and thermal properties of the primary mirror assembly were analyzed. It is shown that after optimization, the lightweight ratio of the silicon carbide mirror is 52.5%, and the rigidity of the silicon carbide structure is high enough to support the required mirror. When temperature changes, the deformation of the mirror surface is in proportion to the temperature difference.

  8. Atomic structure of amorphous shear bands in boron carbide.

    Science.gov (United States)

    Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

    2013-01-01

    Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

  9. Wear resistant steels and casting alloys containing niobium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Theisen, W.; Siebert, S.; Huth, S. [Lehrstuhl Werkstofftechnik, Ruhr-Univ. Bochum (Germany)

    2007-12-15

    Niobium, like titanium and vanadium, forms superhard MC carbides that remain relatively pure in technical alloys on account of their low solubility for other metallic alloying elements. However, because they have a greater hardness than the precipitated chromium carbides commonly used in wear-resistant alloys, they are suitable as alternative hard phases. This contribution deals with new wear-resistant steels and casting alloys containing niobium carbide. These include a secondary hardening hardfacing alloy, a composite casting alloy for wear applications at elevated temperatures, a white cast iron as well as two variants of a corrosion-resistant cold-work tool steel produced by melt metallurgy and by powder metallurgy. A heat-resistant casting alloy is also discussed. Based on equilibrium calculations the microstructures developing during production of the alloys are analysed, and the results are discussed with respect to important properties such as abrasive wear and corrosion resistance. (orig.)

  10. Enhancing biogas production from vinasse in sugarcane biorefineries: Effects of urea and trace elements supplementation on process performance and stability.

    Science.gov (United States)

    Janke, Leandro; Leite, Athaydes F; Batista, Karla; Silva, Witan; Nikolausz, Marcell; Nelles, Michael; Stinner, Walter

    2016-10-01

    In this study, the effects of nitrogen, phosphate and trace elements supplementation were investigated in a semi-continuously operated upflow anaerobic sludge blanket system to enhance process stability and biogas production from sugarcane vinasse. Phosphate in form of KH2PO4 induced volatile fatty acids accumulation possibly due to potassium inhibition of the methanogenesis. Although nitrogen in form of urea increased the reactor's alkalinity, the process was overloaded with an organic loading rate of 6.1gCODL(-1)d(-1) and a hydraulic retention time of 3.6days. However, by supplementing urea and trace elements a stable operation even at an organic loading rate of 9.6gCODL(-1)d(-1) and a hydraulic retention time of 2.5days was possible, resulting in 79% higher methane production rate with a stable specific methane production of 239mLgCOD(-1).

  11. On the stability analysis of hyperelastic boundary value problems using three- and two-field mixed finite element formulations

    Science.gov (United States)

    Schröder, Jörg; Viebahn, Nils; Wriggers, Peter; Auricchio, Ferdinando; Steeger, Karl

    2017-05-01

    In this work we investigate different mixed finite element formulations for the detection of critical loads for the possible occurrence of bifurcation and limit points. In detail, three- and two-field formulations for incompressible and quasi-incompressible materials are analyzed. In order to apply various penalty functions for the volume dilatation in displacement/pressure mixed elements we propose a new consistent scheme capturing the non linearities of the penalty constraints. It is shown that for all mixed formulations, which can be reduced to a generalized displacement scheme, a straight forward stability analysis is possible. However, problems based on the classical saddle-point structure require a different analyses based on the change of the signature of the underlying matrix system. The basis of these investigations is the work from Auricchio et al. (Comput Methods Appl Mech Eng 194:1075-1092, 2005, Comput Mech 52:1153-1167, 2013).

  12. Finite element analysis of the stability of combined plate internal fixation in posterior wall fractures of acetabulum.

    Science.gov (United States)

    Liu, Xi-Ming; Pan, Chang-Wu; Wang, Guo-Dong; Cai, Xian-Hua; Chen, Lei; Meng, Cheng-Fei; Huang, Jin-Cheng

    2015-01-01

    This study aims to explore the mechanical stability of combined plate internal fixation in posterior wall fractures of the acetabulum. The fracture and internal fixation models were established in this study and they were divided into four kinds of internal fixation models, finite element analysis was performed. The four groups were 2 mini-plates and 1 reconstruction plate fixation (A), Reconstruction plate internal fixation group (B), 2 screws internal fixation group (C) and mini-plates internal fixation group (D). The displacement of each node was measured and evaluated. There was no distortion in the geometric shape of the finite element model. The results of stress showed that it was less in the anterior pelvic ring and distributed uniform in labrum acetabulare; the stress was bigger in the upper and middle of sacroiliac joint and sciatic notch in sitting position. Combined plate internal fixation for posterior wall fractures of acetabular were stable and reliable, it is better than the other three methods.

  13. Ballistic Evaluation of rolled Homogeneous Steel Armor with Tungsten Carbide and Titanium Carbide Facing.

    Science.gov (United States)

    1960-12-01

    LABORATORIES BALLISTIC EVALUATION OF ROLLED HMtOGE14EOUS STEEL ASWKR f VITH TUNGSTEN CARBIDE AND TITANIUM CARBIDE FACING (U) TECHNICAL REPORT NO. WAL...carbide steel and titanium carbide steel composite armor when attacked by cal. .40 H19B WC cores, cal. .0 AP W2 projectiles, ZOIN fragment simulating...determine the effectiveness of tungsten car- bide (WC) and titanium carbide (TIC) facing on steel armor for the defeat of steel and tungsten carbide

  14. Variational Multiscale Stabilization of High-Order Spectral Elements for the Convection-Diffusion Equation

    Science.gov (United States)

    2012-06-19

    by Canuto and coworkers in [17, 18, 19, 52], and later by Hughes and coworkers in [21] using non-uniform rational B-splines ( NURBS ). In this paper we...finite elements, NURBS , exact geometry and mesh refinement, Comput. Methods Appl. Mech. Engrg. 194 (2005) 4135–4195. [22] S. Godunov, A difference method

  15. Microstructure and mechanical properties of WC-Ni-Al based cemented carbides developed for engineering applications

    Energy Technology Data Exchange (ETDEWEB)

    Correa, Edmilson O.; Santos, Julio N. [Universidade Federal de Itajuba, Minas Gerais (Brazil). Inst. de Engenharia Mecanica; Klein, Aloisio N. [Universidade Federal de Santa Catarina, Florianopolis (Brazil). Dept. de Engenharia de Materiais

    2011-11-15

    In this paper the influence of the Ni binder metal and Al as an additional alloying element on the microstructure and mechanical properties of WC-based cemented carbides processed by conventional powder metallurgy was studied. Microstructural examinations of the cemented carbides with 3 and 5 wt.% of Al in the binder metal indicated the presence of a very low and evenly distributed porosity as well as the presence of islands of metal binder in the microstructure. With the cemented carbide with 7 wt.% of Al in the metal binder, the presence of brittle needle-like regions was observed. The WC particles inside these regions were rounded and had a larger mean free path. Vickers hardness and flexural strength tests indicated that the cemented carbide WC-Ni - Al with addition of 5 wt.% of Al in the binder metal presented bulk hardness similar to the conventional WC-Co cemented carbides as well as superior flexure strength and fracture toughness. (orig.)

  16. Exploring the stability of super heavy elements: First Measurement of the Fission Barrier of 254No

    Directory of Open Access Journals (Sweden)

    Henning G.

    2014-03-01

    Full Text Available The gamma-ray multiplicity and total energy emitted by the heavy nucleus 254No have been measured at 2 different beam energies. From these measurements, the initial distributions of spin I and excitation energy E∗ of 254No were constructed. The distributions display a saturation in excitation energy, which allows a direct determination of the fission barrier. 254No is the heaviest shell-stabilized nucleus with a measured fission barrier.

  17. Structural Evolution of Molybdenum Carbides in Hot Aqueous Environments and Impact on Low-Temperature Hydroprocessing of Acetic Acid

    Directory of Open Access Journals (Sweden)

    Jae-Soon Choi

    2015-03-01

    Full Text Available We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils.

  18. An Oseen Two-Level Stabilized Mixed Finite-Element Method for the 2D/3D Stationary Navier-Stokes Equations

    Directory of Open Access Journals (Sweden)

    Aiwen Wang

    2012-01-01

    Full Text Available We investigate an Oseen two-level stabilized finite-element method based on the local pressure projection for the 2D/3D steady Navier-Stokes equations by the lowest order conforming finite-element pairs (i.e., Q1−P0 and P1−P0. Firstly, in contrast to other stabilized methods, they are parameter free, no calculation of higher-order derivatives and edge-based data structures, implemented at the element level with minimal cost. In addition, the Oseen two-level stabilized method involves solving one small nonlinear Navier-Stokes problem on the coarse mesh with mesh size H, a large general Stokes equation on the fine mesh with mesh size h=O(H2. The Oseen two-level stabilized finite-element method provides an approximate solution (uh,ph with the convergence rate of the same order as the usual stabilized finite-element solutions, which involves solving a large Navier-Stokes problem on a fine mesh with mesh size h. Therefore, the method presented in this paper can save a large amount of computational time. Finally, numerical tests confirm the theoretical results. Conclusion can be drawn that the Oseen two-level stabilized finite-element method is simple and efficient for solving the 2D/3D steady Navier-Stokes equations.

  19. Analysis of powdered tungsten carbide hard-metal precursors and cemented compact tungsten carbides using laser-induced breakdown spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Novotny, K. [Laboratory of Atomic Spectrochemistry, Department of Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, 611 37 Brno (Czech Republic)], E-mail: codl@sci.muni.cz; Stankova, A. [Laboratory of Atomic Spectrochemistry, Department of Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, 611 37 Brno (Czech Republic); Haekkaenen, H.; Korppi-Tommola, J. [Department of Chemistry, University of Jyvaeskylae, P.O. BOX 35, FIN-40014 (Finland); Otruba, V.; Kanicky, V. [Laboratory of Atomic Spectrochemistry, Department of Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, 611 37 Brno (Czech Republic)

    2007-12-15

    Laser-induced breakdown spectroscopy (LIBS) has been applied to the direct analysis of powdered tungsten carbide hard-metal precursors and cemented tungsten carbides. The aim of this work was to examine the possibility of quantitative determination of the niobium, titanium, tantalum and cobalt. The investigated samples were in the form of pellets, pressed with and without binder (powdered silver) and in the form of cemented tungsten carbides. The pellets were prepared by pressing the powdered material in a hydraulic press. Cemented tungsten carbides were embedded in resin for easier manipulation. Several lasers and detection systems were utilized. The Nd:YAG laser working at a basic wavelength of 1064 nm and fourth-harmonic frequency of 266 nm with a gated photomultiplier or ICCD detector HORIBA JY was used for the determination of niobium which was chosen as a model element. Different types of surrounding gases (air, He, Ar) were investigated for analysis. The ICCD detector DICAM PRO with Mechelle 7500 spectrometer with ArF laser (193 nm) and KrF laser (248 nm) were employed for the determination of niobium, titanium, tantalum and cobalt in samples under air atmosphere. Good calibration curves were obtained for Nb, Ti, and Ta (coefficients of determination r{sup 2} > 0.96). Acceptable calibration curves were acquired for the determination of cobalt (coefficient of determination r{sup 2} = 0.7994) but only for the cemented samples. In the case of powdered carbide precursors, the calibration for cobalt was found to be problematic.

  20. Analysis of powdered tungsten carbide hard-metal precursors and cemented compact tungsten carbides using laser-induced breakdown spectroscopy

    Science.gov (United States)

    Novotný, K.; Staňková, A.; Häkkänen, H.; Korppi-Tommola, J.; Otruba, V.; Kanický, V.

    2007-12-01

    Laser-induced breakdown spectroscopy (LIBS) has been applied to the direct analysis of powdered tungsten carbide hard-metal precursors and cemented tungsten carbides. The aim of this work was to examine the possibility of quantitative determination of the niobium, titanium, tantalum and cobalt. The investigated samples were in the form of pellets, pressed with and without binder (powdered silver) and in the form of cemented tungsten carbides. The pellets were prepared by pressing the powdered material in a hydraulic press. Cemented tungsten carbides were embedded in resin for easier manipulation. Several lasers and detection systems were utilized. The Nd:YAG laser working at a basic wavelength of 1064 nm and fourth-harmonic frequency of 266 nm with a gated photomultiplier or ICCD detector HORIBA JY was used for the determination of niobium which was chosen as a model element. Different types of surrounding gases (air, He, Ar) were investigated for analysis. The ICCD detector DICAM PRO with Mechelle 7500 spectrometer with ArF laser (193 nm) and KrF laser (248 nm) were employed for the determination of niobium, titanium, tantalum and cobalt in samples under air atmosphere. Good calibration curves were obtained for Nb, Ti, and Ta (coefficients of determination r2 > 0.96). Acceptable calibration curves were acquired for the determination of cobalt (coefficient of determination r2 = 0.7994) but only for the cemented samples. In the case of powdered carbide precursors, the calibration for cobalt was found to be problematic.

  1. Sputter deposition of transition-metal carbide films — A critical review from a chemical perspective

    Energy Technology Data Exchange (ETDEWEB)

    Jansson, Ulf, E-mail: ulf.jansson@kemi.uu.se [Department of Chemistry, Ångström, Uppsala Universitet (Sweden); Lewin, Erik [Laboratory for Nanoscale Materials Science, Empa (Switzerland); Department of Chemistry, Ångström, Uppsala Universitet (Sweden)

    2013-06-01

    Thin films based on transition-metal carbides exhibit many interesting physical and chemical properties making them attractive for a variety of applications. The most widely used method to produce metal carbide films with specific properties at reduced deposition temperatures is sputter deposition. A large number of papers in this field have been published during the last decades, showing that large variations in structure and properties can be obtained. This review will summarise the literature on sputter-deposited carbide films based on chemical aspects of the various elements in the films. By considering the chemical affinities (primarily towards carbon) and structural preferences of different elements, it is possible to understand trends in structure of binary transition-metal carbides and the ternary materials based on these carbides. These trends in chemical affinity and structure will also directly affect the growth process during sputter deposition. A fundamental chemical perspective of the transition-metal carbides and their alloying elements is essential to obtain control of the material structure (from the atomic level), and thereby its properties and performance. This review covers a wide range of materials: binary transition-metal carbides and their nanocomposites with amorphous carbon; the effect of alloying carbide-based materials with a third element (mainly elements from groups 3 through 14); as well as the amorphous binary and ternary materials from these elements deposited under specific conditions or at certain compositional ranges. Furthermore, the review will also emphasise important aspects regarding materials characterisation which may affect the interpretation of data such as beam-induced crystallisation and sputter-damage during surface analysis.

  2. Temporal stability of otolith elemental fingerprints discriminates among lagoon nursery habitats

    OpenAIRE

    Tournois, J.; Ferraton, Franck; Velez, Laure; D.J. McKenzie; Aliaume, C.; L. Mercier; Darnaude, A. M.

    2013-01-01

    The chemical composition of fish otoliths reflects that of the water masses that they inhabit. Otolith elemental compositions can, therefore, be used as natural tags to discriminate among habitats. However, for retrospective habitat identification to be valid and reliable for any adult, irrespective of its age, significant differences in environmental conditions, and therefore otolith signatures, must be temporally stable within each habitat, otherwise connectivity studies have to be carried ...

  3. Stability analysis of flexible wind turbine blades using finite element method

    Science.gov (United States)

    Kamoulakos, A.

    1982-01-01

    Static vibration and flutter analysis of a straight elastic axis blade was performed based on a finite element method solution. The total potential energy functional was formulated according to linear beam theory. The inertia and aerodynamic loads were formulated according to the blade absolute acceleration and absolute velocity vectors. In vibration analysis, the direction of motion of the blade during the first out-of-lane and first in-plane modes was examined; numerical results involve NASA/DOE Mod-0, McCauley propeller, north wind turbine and flat plate behavior. In flutter analysis, comparison cases were examined involving several references. Vibration analysis of a nonstraight elastic axis blade based on a finite element method solution was performed in a similar manner with the straight elastic axis blade, since it was recognized that a curved blade can be approximated by an assembly of a sufficient number of straight blade elements at different inclinations with respect to common system of axes. Numerical results involve comparison between the behavior of a straight and a curved cantilever beam during the lowest two in-plane and out-of-plane modes.

  4. Structural Stability and Dynamics of FGM Plates Using an Improved 8-ANS Finite Element

    Directory of Open Access Journals (Sweden)

    Weon-Tae Park

    2016-01-01

    Full Text Available I investigate the vibration and buckling analysis of functionally graded material (FGM structures, using a modified 8-node shell element. The properties of FGM vary continuously through the thickness direction according to the volume fraction of constituents defined by sigmoid function. The modified 8-ANS shell element has been employed to study the effect of power law index on dynamic analysis of FGM plates with various boundary conditions and buckling analysis under combined loads, and interaction curves of FGM plates are carried out. To overcome shear and membrane locking problems, the assumed natural strain method is employed. In order to validate and compare the finite element numerical solutions, the reference results of plates based on Navier’s method, the series solutions of sigmoid FGM (S-FGM plates are compared. Results of the present study show good agreement with the reference results. The solutions of vibration and buckling analysis are numerically illustrated in a number of tables and figures to show the influence of power law index, side-to-thickness ratio, aspect ratio, types of loads, and boundary conditions in FGM structures. This work is relevant to the simulation of wing surfaces, aircrafts, and box structures under various boundary conditions and loadings.

  5. 碳化硼的研究进展%Progress of Research on Boron Carbide

    Institute of Scientific and Technical Information of China (English)

    刘珅楠; 孙帆; 谭章娜; 袁青; 周凯静; 马剑华

    2015-01-01

    碳化硼是高性能陶瓷材料中的一种重要原料,包含诸多的优良性能,除了高硬度、低密度等性能外,它还具备高化学稳定性和中子吸收截面及热电性能等特性,在国防军事设备、功能陶瓷、热电元件等诸多领域具有十分广泛的应用。本文重点介绍了碳化硼的相关性质、研究进展和应用现状。详细地介绍了碳化硼的制备方法,如电弧炉碳热还原法、自蔓延高温法、化学气相沉积法、溶胶-凝胶法等方法,并分析了它们的优缺点。%Boron carbide is a kind of important raw materials of high performanceceramic material, including many excellent performance. In addition to highhardness and low density properties, it also has high chemical stability andneutron absorption cross section and thermoelectric properties, which are widely used in national defense and military equipment, functional ceramics and thermoelectric element fields. The current research progress and application of relevant properties, boron carbide were introduced. The preparation methods of boron carbide, such as carbon arc furnace reduction method, self-propagating high temperature method, chemical vapor deposition, sol-gel method, were mainly introduced, and their advantages and disadvantages were analyzed.

  6. First-principles study on the lattice stability of elemental Co, Rh, and Ir in the ⅧB group

    Institute of Scientific and Technical Information of China (English)

    TAO Huijin; YIN Jian; YIN Zhimin; ZHANG Chuangfu; LI Jie; HUANG Boyun

    2009-01-01

    Lattice constants, total energies, and densities of state of transition metals Co, Rh, and Ir in the VIIIB group with different crystalline structures were calculated via generalized gradient approximation (GGA) of the total energy plane wave pseudopotentiai method in first-principles. The lattice stabilities of Rh and Ir are △Gbcc-hcp △Gfcc-hcp 0, agreeing well with those of the projector augmented wave method in first-principles and the CALPHAD method in spite of elemental Co. Analyses of the electronic smlctures to lattice stability show that crystalline Rh and Ir with fcc structures have the obvious characteristic of a stable phase, agreeing with the results of total energy calculations. Analyses of atomic populations show that the transition rate of electrons from the s state to the p or d state for hop, fcc, and bcc crystals of Co and Rh increases with the elemental period number to form a stronger cohesion, a higher cohesive energy, or a more stable lattice between atoms in heavier metals.

  7. RESEARCH OF ULTRASONIC SENSING AND MIXING ELEMENTS FOR CONTROL OF MAGNETORHEOLOGICAL FLUIDS STABILITY

    Directory of Open Access Journals (Sweden)

    E. Dragašius

    2011-01-01

    Full Text Available  Using of magnetorheological fluids (MRF can reduce energy costs and weight and increase the devices speed and lifetime. In order to fully use all the qualities of MRF properties one must from time to time mix them and measure their properties. These systems are still being designed and tested in the laboratories. There are many structures with rheological fluid, but in many devices fluids are sealed and mechanical mixing and direct measurement of fluid properties are not possible. Effective stability control system for the rheological fluids, which supports homogeneity of the fluid, is described

  8. Steric hindrance and the enhanced stability of light rare-earth elements in hydrothermal fluids

    Science.gov (United States)

    Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I.-Ming

    2009-01-01

    A series of X-ray absorption spectroscopy (XAS) experiments were made to determine the structure and stability of aqueous REE (La, Nd, Gd, and Yb) chloride complexes to 500 ??C and 520 MPa. The REE3+ ions exhibit inner-sphere chloroaqua complexation with a steady increase of chloride coordination with increasing temperature in the 150 to 500 ??C range. Furthermore, the degree of chloride coordination of REE3+ inner-sphere chloroaqua complexes decreases significantly from light to heavy REE. These results indicate that steric hindrance drives the reduction of chloride coordination of REE3+ inner-sphere chloroaqua complexes from light to heavy REE. This results in greater stability and preferential transport of light REE3+ over heavy REE3+ ions in saline hydrothermal fluids. Accordingly, the preferential mobility of light REE directly influences the relative abundance of REE in rocks and minerals and thus needs to be considered in geochemical modeling of petrogenetic and ore-forming processes affected by chloride-bearing hydrothermal fluids.

  9. Stability of CII is a key element in the cold stress response of bacteriophage lambda infection.

    Science.gov (United States)

    Obuchowski, M; Shotland, Y; Koby, S; Giladi, H; Gabig, M; Wegrzyn, G; Oppenheim, A B

    1997-10-01

    Bacteria are known to adapt to environmental changes such as temperature fluctuations. It was found that temperature affects the lysis-lysogeny decision of lambda such that at body temperature (37 degrees C) the phage can select between the lytic and lysogenic pathways, while at ambient temperature (20 degrees C) the lytic pathway is blocked. This temperature-dependent discriminatory developmental pathway is governed mainly by the phage CII activity as a transcriptional activator. Mutations in cII or point mutations at the pRE promoter lead to an over-1,000-fold increase in mature-phage production at low temperature while mutations in cI cause a smaller increase in phage production. Interference with CII activity can restore lytic growth at low temperature. We found that at low temperature the stability of CII in vivo is greatly increased. It was also found that phage DNA replication is blocked at 20 degrees C but can be restored by supplying O and P in trans. It is proposed that CII hampers transcription of the rightward pR promoter, thus reducing the levels of the lambda O and P proteins, which are necessary for phage DNA replication. Our results implicate CII itself or host proteins affecting CII stability as a "molecular thermometer".

  10. Silicon Carbide Solar Cells Investigated

    Science.gov (United States)

    Bailey, Sheila G.; Raffaelle, Ryne P.

    2001-01-01

    The semiconductor silicon carbide (SiC) has long been known for its outstanding resistance to harsh environments (e.g., thermal stability, radiation resistance, and dielectric strength). However, the ability to produce device-quality material is severely limited by the inherent crystalline defects associated with this material and their associated electronic effects. Much progress has been made recently in the understanding and control of these defects and in the improved processing of this material. Because of this work, it may be possible to produce SiC-based solar cells for environments with high temperatures, light intensities, and radiation, such as those experienced by solar probes. Electronics and sensors based on SiC can operate in hostile environments where conventional silicon-based electronics (limited to 350 C) cannot function. Development of this material will enable large performance enhancements and size reductions for a wide variety of systems--such as high-frequency devices, high-power devices, microwave switching devices, and high-temperature electronics. These applications would supply more energy-efficient public electric power distribution and electric vehicles, more powerful microwave electronics for radar and communications, and better sensors and controls for cleaner-burning, more fuel-efficient jet aircraft and automobile engines. The 6H-SiC polytype is a promising wide-bandgap (Eg = 3.0 eV) semiconductor for photovoltaic applications in harsh solar environments that involve high-temperature and high-radiation conditions. The advantages of this material for this application lie in its extremely large breakdown field strength, high thermal conductivity, good electron saturation drift velocity, and stable electrical performance at temperatures as high as 600 C. This behavior makes it an attractive photovoltaic solar cell material for devices that can operate within three solar radii of the Sun.

  11. Stiffness Characteristics of Joshi’s External Stabilization System under Axial Compression: a Finite Element Method Based Study

    Directory of Open Access Journals (Sweden)

    Rajeev Kumar

    2014-07-01

    Full Text Available A finite element model of fractured tibia with Joshi’s External Stabilizing System (JESS mounted on it was developed using 3D beam elements in the ANSYS software. The model was loaded in axial compression and the average axial stiffness of the model was calculated. The analytical value of axial stiffness was compared with reported experimental value to validate the finite element model. The validated model was used to carry out parametric studies on the model to determine the axial properties of JESS. It was observed that axial stiffness of JESS increased by 58% when k-wire diameter was varied from 2 mm to 4 mm while keeping other geometric configurations of the device constant; however, the axial stiffness of the device does not show any significant improvement when the diameter of medio-lateral pins in diaphyseal hold were increased. The findings should help in understanding the axial properties of JESS so that it can be used judiciously in clinical applications.

  12. Effects of chemisorption of electron acceptor elements on the stability of platinum clusters

    Science.gov (United States)

    Halachev, T. D.; Ruckenstein, E.

    1981-07-01

    The extended Hückel method (EHM) is used here to investigate how the bond strengths of Pt(100) and Pt(111) clusters, containing 9 and 10 atoms, respectively, are affected by the chemisorbed H, O, Cl, or S atoms. Three adsorption sites are considered on each cluster. For most adsorption sites Cl and S weaken all the PtPt bonds, while H and O strengthen the bonds between some Pt atoms and weaken the bonds between some other Pt atoms. The enhanced mobility of the Pt atoms, that occurs upon adsorption of the above elements, is proposed as the mechanism behind the first step in corrosive chemisorption and in the redispersion of supported Pt catalysts. The strong destabilizing effect of S and Cl is attributed to the empty d orbitais of these elements. An attempt is made to explain the poisoning by Sulfur on the basis of long range structural and electronic changes that occur in the Pt clusters upon chemisorption of S.

  13. Studies of silicon carbide and silicon carbide nitride thin films

    Science.gov (United States)

    Alizadeh, Zhila

    Silicon carbide semiconductor technology is continuing to advance rapidly. The excellent physical and electronic properties of silicon carbide recently take itself to be the main focused power device material for high temperature, high power, and high frequency electronic devices because of its large band gap, high thermal conductivity, and high electron saturation drift velocity. SiC is more stable than Si because of its high melting point and mechanical strength. Also the understanding of the structure and properties of semiconducting thin film alloys is one of the fundamental steps toward their successful application in technologies requiring materials with tunable energy gaps, such as solar cells, flat panel displays, optical memories and anti-reflecting coatings. Silicon carbide and silicon nitrides are promising materials for novel semiconductor applications because of their band gaps. In addition, they are "hard" materials in the sense of having high elastic constants and large cohesive energies and are generally resistant to harsh environment, including radiation. In this research, thin films of silicon carbide and silicon carbide nitride were deposited in a r.f magnetron sputtering system using a SiC target. A detailed analysis of the surface chemistry of the deposited films was performed using x-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy whereas structure and morphology was studied atomic force microscopy (AFM), and nonoindentation.

  14. Palladium interaction with silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Gentile, M., E-mail: Marialuisa.Gentile@manchester.ac.uk [Centre for Nuclear Energy Technology (C-NET), School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL (United Kingdom); Xiao, P. [Materials Science Centre, School of Materials, The University of Manchester, Manchester M13 9PL (United Kingdom); Abram, T. [Centre for Nuclear Energy Technology (C-NET), School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL (United Kingdom)

    2015-07-15

    In this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermoscans were carried out on pellets of palladium, α-SiC and β-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide reaction. Thermoscans of α-SiC pellets containing 5 at.%Pd show that during differential calorimetry scans three exothermic peaks occurred at 773 K, 1144 K and 1615 K, while thermoscans of β-SiC pellets containing 3 at.%Pd and 5 at.%Pd do not show peaks. For the pellet α-SiC–5 at.%Pd XRD spectra reveal that the first peak is associated with the formation of Pd{sub 3}Si and SiO{sub 2} phases, while the second peak and the third peak are correlated with the formation of Pd{sub 2}Si phase and the active oxidation of silicon carbide respectively. Thermogravimetry scans show weight gain and weight loss peaks due to the SiO{sub 2} phase formation and the active oxidation. Additionally XPS fittings reveal the development of SiC{sub x}O{sub y} phase during the first exothermic peak up to the temperature of 873 K. The experimental data reveals that alpha silicon carbide is attacked by palladium at lower temperatures than beta silicon carbide and the reaction mechanism between silicon carbide and palladium is strongly affected by silicon carbide oxidation.

  15. Palladium interaction with silicon carbide

    Science.gov (United States)

    Gentile, M.; Xiao, P.; Abram, T.

    2015-07-01

    In this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermoscans were carried out on pellets of palladium, α-SiC and β-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide reaction. Thermoscans of α-SiC pellets containing 5 at.%Pd show that during differential calorimetry scans three exothermic peaks occurred at 773 K, 1144 K and 1615 K, while thermoscans of β-SiC pellets containing 3 at.%Pd and 5 at.%Pd do not show peaks. For the pellet α-SiC-5 at.%Pd XRD spectra reveal that the first peak is associated with the formation of Pd3Si and SiO2 phases, while the second peak and the third peak are correlated with the formation of Pd2Si phase and the active oxidation of silicon carbide respectively. Thermogravimetry scans show weight gain and weight loss peaks due to the SiO2 phase formation and the active oxidation. Additionally XPS fittings reveal the development of SiCxOy phase during the first exothermic peak up to the temperature of 873 K. The experimental data reveals that alpha silicon carbide is attacked by palladium at lower temperatures than beta silicon carbide and the reaction mechanism between silicon carbide and palladium is strongly affected by silicon carbide oxidation.

  16. Production of copper-niobium carbide nanocomposite powders via mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Marques, M.T. [INETI-DMTP, Estrada do Paco do Lumiar, 22, 1649-038 Lisbon (Portugal)]. E-mail: tmarques@ineti.pt; Livramento, V. [INETI-DMTP, Estrada do Paco do Lumiar, 22, 1649-038 Lisbon (Portugal); Correia, J.B. [INETI-DMTP, Estrada do Paco do Lumiar, 22, 1649-038 Lisbon (Portugal); Almeida, A. [IST-Dep. Eng. de Materiais, Av. Rovisco Pais, 1049-001 Lisbon (Portugal); Vilar, R. [IST-Dep. Eng. de Materiais, Av. Rovisco Pais, 1049-001 Lisbon (Portugal)

    2005-06-15

    Nanocrystalline niobium carbide was synthesed in situ in a copper matrix during high-energy milling of elemental powders. Three powder batches were produced with nominal compositions of 5, 10 and 20 vol.% NbC. Characterisation by X-ray diffraction and scanning electron microscopy indicates that early during the milling process a carbide dispersion is formed within a nanostructured copper matrix. After annealing at 873 K, the carbide structure and particle size are maintained, reflecting the ability of the microstructure to resist to coarsening. The hardness levels attained are more than twice those of nanostructured copper.

  17. Tungsten carbide promoted Pd and Pd-Co electrocatalysts for formic acid electrooxidation

    Science.gov (United States)

    Yin, Min; Li, Qingfeng; Jensen, Jens Oluf; Huang, Yunjie; Cleemann, Lars N.; Bjerrum, Niels J.; Xing, Wei

    2012-12-01

    Tungsten carbide (WC) promoted palladium (Pd) and palladium-cobalt (Pd-Co) nanocatalysts are prepared and characterized for formic acid electrooxidation. The WC as the dopant to carbon supports is found to enhance the CO tolerance and promote the activity of the Pd-based catalysts for formic acid oxidation. Alloying of Pd with Co further improves the electrocatalytic activity and stability of the WC supported catalysts, attributable to a synergistic effect of the carbide support and PdCo alloy nanoparticles.

  18. Application of Reaction-Bonded Silicon Carbide in Manufacturing of Spacecraft Combustion Chamber

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Silicon carbide (SiC) ceramics is a good structural ceramics material, which have a lot of excellent properties such as superior high-temperature strength up to a temperature of 1 350 ℃, chemical stability, good resistance to thermal shock and high abrasion resistance. The silicon carbide ceramics material has so far been used widely for manufacturing various components such as heat exchangers, rolls, rockets combustion chamber. Sintering of ceramics structural parts have many technological method, the reac...

  19. Laser melting of uranium carbides

    Science.gov (United States)

    Utton, C. A.; De Bruycker, F.; Boboridis, K.; Jardin, R.; Noel, H.; Guéneau, C.; Manara, D.

    2009-03-01

    In the context of the material research aimed at supporting the development of nuclear plants of the fourth Generation, renewed interest has recently arisen in carbide fuels. A profound understanding of the behaviour of nuclear materials in extreme conditions is of prime importance for the analysis of the operation limits of nuclear fuels, and prediction of possible nuclear reactor accidents. In this context, the main goal of the present paper is to demonstrate the feasibility of laser induced melting experiments on stoichiometric uranium carbides; UC, UC1.5 and UC2. Measurements were performed, at temperatures around 3000 K, under a few bars of inert gas in order to minimise vaporisation and oxidation effects, which may occur at these temperatures. Moreover, a recently developed investigation method has been employed, based on in situ analysis of the sample surface reflectivity evolution during melting. Current results, 2781 K for the melting point of UC, 2665 K for the solidus and 2681 K for the liquidus of U2C3, 2754 K for the solidus and 2770 K for the liquidus of UC2, are in fair agreement with early publications where the melting behaviour of uranium carbides was investigated by traditional furnace melting methods. Further information has been obtained in the current research about the non-congruent (solidus-liquidus) melting of certain carbides, which suggest that a solidus-liquidus scheme is followed by higher ratio carbides, possibly even for UC2.

  20. Sol–gel processing of carbidic glasses

    Indian Academy of Sciences (India)

    L M Manocha; E Yasuda; Y Tanabe; S Manocha; D Vashistha

    2000-02-01

    Carbon incorporation into the silicate network results in the formation of rigid carbidic glasses with improved physical, mechanical and thermal properties. This generated great interest in the development of these heteroatom structured materials through different processing routes. In the present studies, sol–gel processing has been used to prepare silicon based glasses, especially oxycarbides through organic–inorganic hybrid gels by hydrolysis–condensation reactions in silicon alkoxides, 1,4-butanediol and furfuryl alcohol with an aim to introduce Si–C linkages in the precursors at sol level. The incorporation of these linkages has been studied using IR and NMR spectroscopy. These bonds, so introduced, are maintained throughout the processing, especially during pyrolysis to high temperatures. In FFA–TEOS system, copolymerization with optimized mol ratio of the two results in resinous mass. This precursor on pyrolysis to 1000°C results in Si–O–C type amorphous solid black mass. XRD studies on the materials heated to 1400°C exhibit presence of crystalline Si–C and cristobalites in amorphous Si–O–C mass. In organic–inorganic gel system, the pyrolysed mass exhibits phase stability up to much higher temperatures. The carbidic materials so produced have been found to exhibit good resistance against oxidation at 1000°C.

  1. The p53 target Wig-1 regulates p53 mRNA stability through an AU-rich element

    DEFF Research Database (Denmark)

    Vilborg, Anna; Glahder, Jacob-Andreas Harald; Wilhelm, Margareta T

    2009-01-01

    The p53 target gene Wig-1 encodes a double-stranded-RNA-binding zinc finger protein. We show here that Wig-1 binds to p53 mRNA and stabilizes it through an AU-rich element (ARE) in the 3' UTR of the p53 mRNA. This effect is mirrored by enhanced p53 protein levels in both unstressed cells and cells...... exposed to p53-activating stress agents. Thus, the p53 target Wig-1 is a previously undescribed ARE-regulating protein that acts as a positive feedback regulator of p53, with implications both for the steady-state levels of p53 and for the p53 stress response. Our data reveal a previously undescribed link...

  2. Stability analysis of non-axisymmetric three-dimensional finite element rotor models with partial and full mass lumping

    Indian Academy of Sciences (India)

    Smitadhi Ganguly; A Nandi; S Neogy

    2014-06-01

    Unlike structural dynamics, the three-dimensional finite-element model of non-axisymmetric rotors on orthotropic bearings generates a large gyroscopic system with parametric stiffness. The present work explores the use of mass-lumping in stability analysis of such systems. Using a variant of Hill’s method, the problem reduces to a generalized Eigen value problem of order $nm \\times nm$, with as the order of the system in state vector representation and as the number of terms in the assumed solution. The matrices in both the sides of the Eigen value problem are expressed in terms of Kronecker products where the mass-matrix appears twice as a sub-matrix in both the sides of the equation. A particular one or both of them can be made diagonal. Both options produce sufficiently accurate results with considerable savings, even with a coarse mesh.

  3. Existence and stability, and discrete BB and rank conditions, for general mixed-hybrid finite elements in elasticity

    Science.gov (United States)

    Xue, W.-M.; Atluri, S. N.

    1985-01-01

    In this paper, all possible forms of mixed-hybrid finite element methods that are based on multi-field variational principles are examined as to the conditions for existence, stability, and uniqueness of their solutions. The reasons as to why certain 'simplified hybrid-mixed methods' in general, and the so-called 'simplified hybrid-displacement method' in particular (based on the so-called simplified variational principles), become unstable, are discussed. A comprehensive discussion of the 'discrete' BB-conditions, and the rank conditions, of the matrices arising in mixed-hybrid methods, is given. Some recent studies aimed at the assurance of such rank conditions, and the related problem of the avoidance of spurious kinematic modes, are presented.

  4. Fully Discrete Finite Element Approximation for the Stabilized Gauge-Uzawa Method to Solve the Boussinesq Equations

    Directory of Open Access Journals (Sweden)

    Jae-Hong Pyo

    2013-01-01

    Full Text Available The stabilized Gauge-Uzawa method (SGUM, which is a 2nd-order projection type algorithm used to solve Navier-Stokes equations, has been newly constructed in the work of Pyo, 2013. In this paper, we apply the SGUM to the evolution Boussinesq equations, which model the thermal driven motion of incompressible fluids. We prove that SGUM is unconditionally stable, and we perform error estimations on the fully discrete finite element space via variational approach for the velocity, pressure, and temperature, the three physical unknowns. We conclude with numerical tests to check accuracy and physically relevant numerical simulations, the Bénard convection problem and the thermal driven cavity flow.

  5. Effect of rock mass structure and block size on the slope stability--Physical modeling and discrete element simulation

    Institute of Scientific and Technical Information of China (English)

    LI; Shihai; LIAN; Zhenzhong; J.; G.; Wang

    2005-01-01

    This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.

  6. Stabilized Discretization in Spline Element Method for Solution of Two-Dimensional Navier-Stokes Problems

    Directory of Open Access Journals (Sweden)

    Neng Wan

    2014-01-01

    Full Text Available In terms of the poor geometric adaptability of spline element method, a geometric precision spline method, which uses the rational Bezier patches to indicate the solution domain, is proposed for two-dimensional viscous uncompressed Navier-Stokes equation. Besides fewer pending unknowns, higher accuracy, and computation efficiency, it possesses such advantages as accurate representation of isogeometric analysis for object boundary and the unity of geometry and analysis modeling. Meanwhile, the selection of B-spline basis functions and the grid definition is studied and a stable discretization format satisfying inf-sup conditions is proposed. The degree of spline functions approaching the velocity field is one order higher than that approaching pressure field, and these functions are defined on one-time refined grid. The Dirichlet boundary conditions are imposed through the Nitsche variational principle in weak form due to the lack of interpolation properties of the B-splines functions. Finally, the validity of the proposed method is verified with some examples.

  7. Analysis of the effects of weak floor strata on longwall face stability using finite element modeling

    Institute of Scientific and Technical Information of China (English)

    MA Jin-rong; Debasis Deb; Y. P. Chugh

    2001-01-01

    Higher production, better safety standard, and potential for automation are some of the benefits of longwall mining. Today, longwall face advances at a faster rate exposing many diversified rock layers in a short period of time. It is now a serious challenge to cope with ground control problems such as roof falls, face and floor failure, and excessive shield loading as fast as possible to minimize production and monetary losses. In Illinois Coal Mines, the existence of week floor strata blow the coal seam may pose additional problems related to floor heaving,shield base punching, and associated roof and face falls. In this study, the effects of week floor on longwall grouJd control are analyzed using two-dimensional finite element models. A two-leg 635.6 ton (700-short-ton) yielding capacity shield is included in the models to evaluate the effects of different thicknees and material properties of the weak floor. The study indicates that the thickness and material properties of weak floor have significant effects on shield loading, the distribution and intensity of front abutment stress, failure zones in the surrounding strata, roof-to-floor convergence, and floor punching by the shield base.

  8. Silicon Carbide Telescope Investigations for the LISA Mission

    Science.gov (United States)

    Sanjuan, J.; Spannagel, R.; Braxmaier, C.; Korytov, D.; Mueller, G.; Preston, A.; Livas, J.

    2013-01-01

    Space-based gravitational wave (GW) detectors are conceived to detect GWs in the low frequency range (mili-Hertz) by measuring the distance between free-falling proof masses in spacecraft (SC) separated by 5 Gm. The reference in the last decade has been the joint ESA-NASA mission LISA. One of the key elements of LISA is the telescope since it simultaneously gathers the light coming from the far SC (approximately or equal to 100 pW) and expands, collimates and sends the outgoing beam (2 W) to the far SC. Demanding requirements have been imposed on the telescope structure: the dimensional stability of the telescope must be approximately or equal to 1pm Hz(exp-1/2) at 3 mHz and the distance between the primary and the secondary mirrors must change by less than 2.5 micrometer over the mission lifetime to prevent defocussing. In addition the telescope structure must be light, strong and stiff. For this reason a potential on-axis telescope structure for LISA consisting of a silicon carbide (SiC) quadpod structure has been designed, constructed and tested. The coefficient of thermal expansion (CTE) in the LISA expected temperature range has been measured with a 1% accuracy which allows us to predict the shrinkage/expansion of the telescope due to temperature changes, and pico-meter dimensional stability has been measured at room temperature and at the expected operating temperature for the LISA telescope (around -6[deg]C). This work is supported by NASA Grants NNX10AJ38G and NX11AO26G,

  9. Discontinuum-Equivalent Continuum Analysis of the Stability of Tunnels in a Deep Coal Mine Using the Distinct Element Method

    Science.gov (United States)

    Shreedharan, Srisharan; Kulatilake, Pinnaduwa H. S. W.

    2016-05-01

    An imperative task for successful underground mining is to ensure the stability of underground structures. This is more so for deep excavations which may be under significantly high stresses. In this manuscript, we present stability studies on two tunnels, a horseshoe-shaped and an inverted arch-shaped tunnel, in a deep coal mine in China, performed using the 3DEC distinct element code. The rock mass mechanical property values for the tunnel shapes have been estimated through a back-analysis procedure using available field deformation data. The back-analysis has been carried out through a pseudo-time dependent support installation routine which incorporates the effect of time through a stress-relaxation mechanism. The back-analysis indicates that the rock mass cohesion, tensile strength, uniaxial compressive strength, and elastic modulus values are about 35-45 % of the corresponding intact rock property values. Additionally, the importance of incorporating stress relaxation before support installation has been illustrated through the increased support factor of safety and reduced grout failures. The calibrated models have been analyzed for different supported and unsupported cases to estimate the significance and adequacy of the current supports being used in the mine and to suggest a possible optimization. The effects of supports have been demonstrated using deformations and yield zones around the tunnels, and average factors of safety and grout failures of the supports. The use of longer supports and floor bolting has provided greater stability for the rock masses around the tunnels. Finally, a comparison between the two differently shaped tunnels establishes that the inverted arch tunnel may be more efficient in reducing roof sag and floor heave for the existing geo-mining conditions.

  10. High pressure stability of the monosilicides of cobalt and the platinum group elements

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez, J.A., E-mail: jeanalexis.hernandez@ens-lyon.fr [Laboratoire de géologie de Lyon, CNRS UMR 5276, École Normale Supérieure de Lyon, Université Claude Bernard Lyon 1, 46 Allée d’Italie, 69364 Lyon Cedex 07 (France); Vočadlo, L.; Wood, I.G. [Department of Earth Sciences, University College London, WC1E 6BT (United Kingdom)

    2015-03-25

    Highlights: • We model the high-pressure phases of cobalt- and platinum-group-monosilicides. • CoSi, RuSi, OsSi transform with pressure from the ε-FeSi to the CsCl structure. • RhSi and IrSi transform with pressure from the MnP structure to the ε-FeSi structure. • PdSi and PtSi transform with pressure from the MnP structure to the CuTi structure. - Abstract: The high pressure stability of CoSi, RuSi, RhSi, PdSi, OsSi, IrSi and PtSi was investigated by static first-principles calculations up to 300 GPa at 0 K. As found experimentally, at atmospheric pressure, CoSi, RuSi and OsSi were found to adopt the cubic ε-FeSi structure (P2{sub 1}3) whereas RhSi, PdSi, IrSi and PtSi were found to adopt the orthorhombic MnP (Pnma) structure. At high pressure, CoSi, RuSi and OsSi show a phase transition to the CsCl structure (Pm3{sup ¯}m) structure at 270 GPa, 7 GPa and 6 GPa respectively. RhSi and IrSi were found to transform to an ε-FeSi structure at 10 GPa and 25 GPa. For PdSi and PtSi, a transformation from the MnP structure to the tetragonal CuTi structure (P4/nmm) occurs at 13 GPa and 20 GPa. The pressure dependence of the electronic density of states reveals that RuSi and OsSi are semiconductors in the ε-FeSi structure and become metallic in the CsCl structure. RhSi and IrSi are metals in the MnP structure and become semimetals in their high pressure ε-FeSi form. CoSi in the ε-FeSi configuration is a semimetal. PdSi and PtSi remain metallic throughout up to 300 GPa.

  11. Thermal conductivity of boron carbides

    Science.gov (United States)

    Wood, C.; Emin, D.; Gray, P. E.

    1985-01-01

    Knowledge of the thermal conductivity of boron carbide is necessary to evaluate its potential for high-temperature thermoelectric energy conversion applications. Measurements have been conducted of the thermal diffusivity of hot-pressed boron carbide BxC samples as a function of composition (x in the range from 4 to 9), temperature (300-1700 K), and temperature cycling. These data, in concert with density and specific-heat data, yield the thermal conductivities of these materials. The results are discussed in terms of a structural model that has been previously advanced to explain the electronic transport data. Some novel mechanisms for thermal conduction are briefly discussed.

  12. Influence of nanometric silicon carbide on phenolic resin composites properties

    Indian Academy of Sciences (India)

    GEORGE PELIN; CRISTINA-ELISABETA PELIN; ADRIANA STEFAN; ION DINC\\u{A}; ANTON FICAI; ECATERINA ANDRONESCU; ROXANA TRUSC\\u{A}

    2016-06-01

    This paper presents a preliminary study on obtaining and characterization of phenolic resin-based composites modified with nanometric silicon carbide. The nanocomposites were prepared by incorporating nanometric silicon carbide (nSiC) into phenolic resin at 0.5, 1 and 2 wt% contents using ultrasonication to ensure uniform dispersion of the nanopowder, followed by heat curing of the phenolic-based materials at controlled temperature profile up to 120$^{\\circ}$C. The obtained nanocomposites were characterized by FTIR spectroscopy and scanning electron microscopy analysis and evaluated in terms of mechanical, tribological and thermal stability under load. The results highlight the positive effect of the nanometric silicon carbide addition in phenolic resin on mechanical, thermo-mechanical and tribological performance, improving their strength, stiffness and abrasive properties. The best results were obtained for 1 wt% nSiC, proving that this value is the optimum nanometric silicon carbide content. The results indicate that these materials could be effectively used to obtain ablative or carbon–carbon composites in future studies.

  13. Stabilization

    Directory of Open Access Journals (Sweden)

    Muhammad H. Al-Malack

    2016-07-01

    Full Text Available Fuel oil flyash (FFA produced in power and water desalination plants firing crude oils in the Kingdom of Saudi Arabia is being disposed in landfills, which increases the burden on the environment, therefore, FFA utilization must be encouraged. In the current research, the effect of adding FFA on the engineering properties of two indigenous soils, namely sand and marl, was investigated. FFA was added at concentrations of 5%, 10% and 15% to both soils with and without the addition of Portland cement. Mixtures of the stabilized soils were thoroughly evaluated using compaction, California Bearing Ratio (CBR, unconfined compressive strength (USC and durability tests. Results of these tests indicated that stabilized sand mixtures could not attain the ACI strength requirements. However, marl was found to satisfy the ACI strength requirement when only 5% of FFA was added together with 5% of cement. When the FFA was increased to 10% and 15%, the mixture’s strength was found to decrease to values below the ACI requirements. Results of the Toxicity Characteristics Leaching Procedure (TCLP, which was performed on samples that passed the ACI requirements, indicated that FFA must be cautiously used in soil stabilization.

  14. Reinforcement of tungsten carbide grains by nanoprecipitates in cemented carbides.

    Science.gov (United States)

    Liu, Xingwei; Song, Xiaoyan; Wang, Haibin; Hou, Chao; Liu, Xuemei; Wang, Xilong

    2016-10-14

    In contrast to the conventional method that obtains a high fracture strength of tungsten carbide-cobalt (WC-Co) cemented carbides by reducing WC grain size to near-nano or nanoscale, a new approach has been developed to achieve ultrahigh fracture strength by strengthening the WC grains through precipitate reinforcement. The cemented carbides were prepared by liquid-state sintering the in situ synthesized WC-Co composite powders with a little excess carbon and pre-milled Cr3C2 particles having different size scales. It was found that the nanoscale dispersed particles precipitate in the WC grains, which mainly have a coherent or semi-coherent interface with the matrix. The pinning effect of the nanoparticles on the motion of dislocations within the WC grains was observed. The mechanisms for the precipitation of nanoparticles in the WC grains were discussed, based on which a new method to enhance the resistance against the transgranular fracture of cemented carbides was proposed.

  15. Reinforcement of tungsten carbide grains by nanoprecipitates in cemented carbides

    Science.gov (United States)

    Liu, Xingwei; Song, Xiaoyan; Wang, Haibin; Hou, Chao; Liu, Xuemei; Wang, Xilong

    2016-10-01

    In contrast to the conventional method that obtains a high fracture strength of tungsten carbide-cobalt (WC-Co) cemented carbides by reducing WC grain size to near-nano or nanoscale, a new approach has been developed to achieve ultrahigh fracture strength by strengthening the WC grains through precipitate reinforcement. The cemented carbides were prepared by liquid-state sintering the in situ synthesized WC-Co composite powders with a little excess carbon and pre-milled Cr3C2 particles having different size scales. It was found that the nanoscale dispersed particles precipitate in the WC grains, which mainly have a coherent or semi-coherent interface with the matrix. The pinning effect of the nanoparticles on the motion of dislocations within the WC grains was observed. The mechanisms for the precipitation of nanoparticles in the WC grains were discussed, based on which a new method to enhance the resistance against the transgranular fracture of cemented carbides was proposed.

  16. Influence of oversized elements (Hf, Zr, Ti and Nb) on the thermal stability of vacancies in type 316L stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Yabuuchi, A., E-mail: yabuuchi.atsushi@21c.osakafu-u.ac.jp [Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan); Maekawa, M.; Kawasuso, A. [Advanced Science Research Center, Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan)

    2012-11-15

    To reveal the influence of oversized elements on the thermal stability of vacancies in type 316L stainless steels, vacancy recovery processes were investigated by means of positron annihilation spectroscopy. Although vacancies in additive-free 316L stainless steels were mobile at 300 Degree-Sign C, which is a typical nuclear reactor operating temperature, vacancies in oversized elements doped 316L were stable up to 300-350 Degree-Sign C. This result indicates that oversized elements stabilize vacancies in stainless steels. Stability of vacancies inhibits the radiation-induced grain boundary segregation and may also lead to suppression of high-temperature water stress corrosion cracking that is observed in nuclear materials.

  17. Predicted boron-carbide compounds: a first-principles study.

    Science.gov (United States)

    Wang, De Yu; Yan, Qian; Wang, Bing; Wang, Yuan Xu; Yang, Jueming; Yang, Gui

    2014-06-14

    By using developed particle swarm optimization algorithm on crystal structural prediction, we have explored the possible crystal structures of B-C system. Their structures, stability, elastic properties, electronic structure, and chemical bonding have been investigated by first-principles calculations with density functional theory. The results show that all the predicted structures are mechanically and dynamically stable. An analysis of calculated enthalpy with pressure indicates that increasing of boron content will increase the stability of boron carbides under low pressure. Moreover, the boron carbides with rich carbon content become more stable under high pressure. The negative formation energy of predicted B5C indicates its high stability. The density of states of B5C show that it is p-type semiconducting. The calculated theoretical Vickers hardnesses of B-C exceed 40 GPa except B4C, BC, and BC4, indicating they are potential superhard materials. An analysis of Debye temperature and electronic localization function provides further understanding chemical and physical properties of boron carbide.

  18. ℎ- Spectral element methods for three dimensional elliptic problems on non-smooth domains, Part-II: Proof of stability theorem

    Indian Academy of Sciences (India)

    P Dutt; Akhlaq Husain; A S Vasudeva Murthy; C S Upadhyay

    2015-08-01

    This is the second of a series of papers devoted to the study of ℎ- spectral element methods for three dimensional elliptic problems on non-smooth domains. The present paper addresses the proof of the main stability theorem.We assume that the differential operator is a strongly elliptic operator which satisfies Lax–Milgram conditions. The spectral element functions are non-conforming. The stability estimate theorem of this paper will be used to design a numerical scheme which give exponentially accurate solutions to three dimensional elliptic problems on non-smooth domains and can be easily implemented on parallel computers.

  19. Stability Study of Rare Earth Elements in Electroless Nickel Solution%无电解镀镍液稳定性研究

    Institute of Scientific and Technical Information of China (English)

    邵国强

    2014-01-01

    Some research developments about rare earth elements on the stability of electroless nickel solution was reviewed. Influence factor and action mechanism of rare earth elements were also introduced.%综述了稀土在提高无电解镀镍液稳定性中的研究进展,并分析了稀土促进镀液稳定性的影响因素和作用机理。

  20. Synthesis of vanadium carbide nanoparticles by thermal decomposition of the precursor

    Science.gov (United States)

    Mahajan, Mani; Singh, K.; Pandey, O. P.

    2013-06-01

    Vanadium carbide is a typical class of material used for different industrial applications due to its high melting point, high hardness and toughness. For its improved properties, the particle size has to be reduced to nanosize. In this work, a different synthesis approach adopted to synthesize nano vanadium carbide at high pressure and low temperature is reported. Here vanadium carbide is synthesized via thermal decomposition of the precursor in a specially designed stainless steel autoclave. The process parameters which affect the size and shape of the nanoparticles have been discussed. The size, shape and stability of synthesized particles are analysed by XRD, SEM and TEM. The study shows that carbides can be easily synthesized at low temperatures.

  1. Comparison of the biomechanical effect of pedicle-based dynamic stabilization: a study using finite element analysis.

    Science.gov (United States)

    Jahng, Tae-Ahn; Kim, Young Eun; Moon, Kyung Yun

    2013-01-01

    Recently, nonfusion pedicle-based dynamic stabilization systems (PBDSs) have been developed and used in the management of degenerative lumbar spinal diseases. Still effects on spinal kinematics and clinical effects are controversial. Little biomechanical information exists for providing biomechanical characteristics of pedicle-based dynamic stabilization according to the PBDS design before clinical implementation. To investigate the effects of implanting PBDSs into the spinal functional unit and elucidate the differences in biomechanical characteristics according to different materials and design. The biomechanical effects of implantation of PBDS were investigated using the nonlinear three-dimensional finite element model of L4-L5. An already validated three-dimensional, intact osteoligamentous L4-L5 finite element model was modified to incorporate the insertion of pedicle screws. The implanted models were constructed after modifying the intact model to simulate postoperative changes using four different fixation systems. Four models instrumented with PBDS (Dynesys, NFlex, and polyetheretherketone [PEEK]) and rigid fixation systems (conventional titanium rod) were developed for comparison. The instrumented models were compared with those of the intact and rigid fixation model. Range of motion (ROM) in three motion planes, center of rotation (COR), force on the facet joint, and von Mises stress distribution on the vertebral body and implants with flexion-extension were compared among the models. Simulated results demonstrated that implanted segments with PBDSs have limited ROM when compared with the intact spine. Flexion motion was the most limited, and axial rotation was the least limited, after device implantation. Among the PBDS selected in this analysis, the NFlex system had the closest instantaneous COR compared with the intact model and a higher ROM compared with other PBDS. Contact force on the facet joint in extension increased with an increase of moment in

  2. Modeling of high pressure arc-discharge with a fully-implicit Navier-Stokes stabilized finite element flow solver

    Science.gov (United States)

    Sahai, A.; Mansour, N. N.; Lopez, B.; Panesi, M.

    2017-05-01

    This work addresses the modeling of high pressure electric discharge in an arc-heated wind tunnel. The combined numerical solution of Poisson’s equation, radiative transfer equations, and the set of Favre-averaged thermochemical nonequilibrium Navier-Stokes equations allows for the determination of the electric, radiation, and flow fields, accounting for their mutual interaction. Semi-classical statistical thermodynamics is used to determine the plasma thermodynamic properties, while transport properties are obtained from kinetic principles with the Chapman-Enskog method. A multi-temperature formulation is used to account for thermal non-equilibrium. Finally, the turbulence closure of the flow equations is obtained by means of the Spalart-Allmaras model, which requires the solution of an additional scalar transport equation. A Streamline upwind Petrov-Galerkin stabilized finite element formulation is employed to solve the Navier-Stokes equation. The electric field equation is solved using the standard Galerkin formulation. A stable formulation for the radiative transfer equations is obtained using the least-squares finite element method. The developed simulation framework has been applied to investigate turbulent plasma flows in the 20 MW Aerodynamic Heating Facility at NASA Ames Research Center. The current model is able to predict the process of energy addition and re-distribution due to Joule heating and thermal radiation, resulting in a hot central core surrounded by colder flow. The use of an unsteady three-dimensional treatment also allows the asymmetry due to a dynamic electric arc attachment point in the cathode chamber to be captured accurately. The current work paves the way for detailed estimation of operating characteristics for arc-heated wind tunnels which are critical in testing thermal protection systems.

  3. Kinetics and Mechanisms of Creep in Sintered Alpha Silicon Carbide and Niobium Carbide.

    Science.gov (United States)

    1985-09-18

    CARBIDE AND NIOBIUM CARBIDE Supported by 30 F (DMR-812-0804) and ARO (MIPR’s 43-48, 127-83, 141-84) U August, 1985 NCSU .LET tow A CL School of Engineering...SILICON CARBIDE AND NIOBIUM CARBIDE Supported by NSF (DMR-812-0804) and ARO (MIPR’s 43-48, 127-83, 141-84) August, 1985 L. U. 1’ ’’ b b MASTER COPY - FOR...and Mechanisms of Creep in Sintered May 1, 1982-June 15, 1985 Alpha Silicon Carbide and Niobium Carbide 6. PERFORMING ORG. REPORT NUMBER 7. AUTHOR(*) 11

  4. Reaction-Based SiC Materials for Joining Silicon Carbide Composites for Fusion Energy

    Energy Technology Data Exchange (ETDEWEB)

    Lewinsohn, Charles A.; Jones, Russell H.; Singh, M.; Serizawa, H.; Katoh, Y.; Kohyama, A.

    2000-09-01

    The fabrication of large or complex silicon carbide-fiber-reinforced silicon carbide (SiC/SiC) components for fusion energy systems requires a method to assemble smaller components that are limited in size by manufacturing constraints. Previous analysis indicates that silicon carbide should be considered as candidate joint materials. Two methods to obtain SiC joints rely on a reaction between silicon and carbon to produce silicon carbide. This report summarizes preliminary mechanical properties of joints formed by these two methods. The methods appear to provide similar mechanical properties. Both the test methods and materials are preliminary in design and require further optimization. In an effort to determine how the mechanical test data is influenced by the test methodology and specimen size, plans for detailed finite element modeling (FEM) are presented.

  5. Lattice parameters and stability of the spinel compounds in relation to the ionic radii and electronegativities of constituting chemical elements.

    Science.gov (United States)

    Brik, Mikhail G; Suchocki, Andrzej; Kamińska, Agata

    2014-05-19

    A thorough consideration of the relation between the lattice parameters of 185 binary and ternary spinel compounds, on one side, and ionic radii and electronegativities of the constituting ions, on the other side, allowed for establishing a simple empirical model and finding its linear equation, which links together the above-mentioned quantities. The derived equation gives good agreement between the experimental and modeled values of the lattice parameters in the considered group of spinels, with an average relative error of about 1% only. The proposed model was improved further by separate consideration of several groups of spinels, depending on the nature of the anion (oxygen, sulfur, selenium/tellurium, nitrogen). The developed approach can be efficiently used for prediction of lattice constants for new isostructural materials. In particular, the lattice constants of new hypothetic spinels ZnRE2O4, CdRE2S4, CdRE2Se4 (RE = rare earth elements) are predicted in the present Article. In addition, the upper and lower limits for the variation of the ionic radii, electronegativities, and their certain combinations were established, which can be considered as stability criteria for the spinel compounds. The findings of the present Article offer a systematic overview of the structural properties of spinels and can serve as helpful guides for synthesis of new spinel compounds.

  6. Effect of cooling rate on MC carbide in directionally solidified nickel-based superalloy under high thermal gradient

    Directory of Open Access Journals (Sweden)

    Zhang Weiguo

    2012-02-01

    Full Text Available A series of directional solidification experiments have been performed to study the effect of cooling rate on the precipitation behavior of MC carbide in nickel-based superalloy under the temperature gradient of 500 K·s-1. Results reveal that the morphology of MC carbide changes from coarse block to fine strip, then to Chinese-script, and their sizes reduce gradually with the increasing of cooling rate from 2.53 K·s-1 to 36.4 K·s-1. At low cooling rates, most of these carbides are found to be located at the grain boundary and interdendritic regions, while the coupled growth of some carbides and γ matrix in the center of γ grains is occurred at high cooling rate. The main elements forming MC carbide are Ta, W, and Hf.

  7. An Exploration of Neutron Detection in Semiconducting Boron Carbide

    Science.gov (United States)

    Hong, Nina

    The 3He supply problem in the U.S. has necessitated the search for alternatives for neutron detection. The neutron detection efficiency is a function of density, atomic composition, neutron absorption cross section, and thickness of the neutron capture material. The isotope 10B is one of only a handful of isotopes with a high neutron absorption cross section---3840 barns for thermal neutrons. So a boron carbide semiconductor represents a viable alternative to 3He. This dissertation provides an evaluation of the performance of semiconducting boron carbide neutron detectors grown by plasma enhance chemical vapor deposition (PECVD) in order to determine the advantages and drawbacks of these devices for neutron detection. Improved handling of the PECVD system has resulted in an extremely stable plasma, enabling deposition of thick films of semiconducting boron carbide. A variety of material and semiconducting characterization tools have been used to investigate the structure and electronic properties of boron carbide thin films, including X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, infrared/Raman spectroscopy, current-voltage measurements and capacitance-voltage measurements. Elemental concentrations in the boron carbide films have been obtained from Rutherford backscattering and elastic recoil detection analysis. Solid state neutron detection devices have been fabricated in the form of heterostructured p-n diodes, p-type boron carbide/n-type Si. Operating conditions, including applied bias voltage, and time constants, have been optimized for maximum detection efficiency and correlated to the semiconducting properties investigated in separate electronic measurements. Accurate measurements of the neutron detection efficiency and the response of the detector to a wide range of neutron wavelengths have been performed at a well calibrated, tightly collimated, "white" cold neutron beam source using time-of-flight neutron detection technique

  8. Barrier properties of nano silicon carbide designed chitosan nanocomposites.

    Science.gov (United States)

    Pradhan, Gopal C; Dash, Satyabrata; Swain, Sarat K

    2015-12-10

    Nano silicon carbide (SiC) designed chitosan nanocomposites were prepared by solution technique. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used for studying structural interaction of nano silicon carbide (SiC) with chitosan. The morphology of chitosan/SiC nanocomposites was investigated by field emission scanning electron microscope (FESEM), and high resolution transmission electron microscope (HRTEM). The thermal stability of chitosan was substantially increased due to incorporation of stable silicon carbide nanopowder. The oxygen permeability of chitosan/SiC nanocomposites was reduced by three folds as compared to the virgin chitosan. The chemical resistance properties of chitosan were enhanced due to the incorporation of nano SiC. The biodegradability was investigated using sludge water. The tensile strength of chitosan/SiC nanocomposites was increased with increasing percentage of SiC. The substantial reduction in oxygen barrier properties in combination with increased thermal stability, tensile strength and chemical resistance properties; the synthesized nanocomposite may be suitable for packaging applications.

  9. Silicon Carbide Mounts for Fabry-Perot Interferometers

    Science.gov (United States)

    Lindemann, Scott

    2011-01-01

    Etalon mounts for tunable Fabry- Perot interferometers can now be fabricated from reaction-bonded silicon carbide structural components. These mounts are rigid, lightweight, and thermally stable. The fabrication of these mounts involves the exploitation of post-casting capabilities that (1) enable creation of monolithic structures having reduced (in comparison with prior such structures) degrees of material inhomogeneity and (2) reduce the need for fastening hardware and accommodations. Such silicon carbide mounts could be used to make lightweight Fabry-Perot interferometers or could be modified for use as general lightweight optical mounts. Heretofore, tunable Fabry-Perot interferometer structures, including mounting hardware, have been made from the low-thermal-expansion material Invar (a nickel/iron alloy) in order to obtain the thermal stability required for spectroscopic applications for which such interferometers are typically designed. However, the high mass density of Invar structures is disadvantageous in applications in which there are requirements to minimize mass. Silicon carbide etalon mounts have been incorporated into a tunable Fabry-Perot interferometer of a prior design that originally called for Invar structural components. The strength, thermal stability, and survivability of the interferometer as thus modified are similar to those of the interferometer as originally designed, but the mass of the modified interferometer is significantly less than the mass of the original version.

  10. A new criterion for predicting rolling-element fatigue lives of through-hardened steels.

    Science.gov (United States)

    Chevalier, J. L.; Zaretsky, E. V.; Parker, R. J.

    1972-01-01

    A carbide factor was derived based upon a statistical analysis which related rolling-element fatigue life to the total number of residual carbide particles per unit area, median residual carbide size, and percent residual carbide area. An equation was empirically determined which predicts material hardness as a function of temperature. The limiting temperatures of all of the materials studied were dependent on initial room temperature hardness and tempering temperature. An equation was derived combining the effects of material hardness, carbide factor, and bearing temperature to predict rolling-element bearing life.

  11. Stability

    Directory of Open Access Journals (Sweden)

    Nada S. Abdelwahab

    2017-05-01

    Full Text Available The present work concerns with the development of stability indicating the RP-HPLC method for simultaneous determination of guaifenesin (GUF and pseudoephedrine hydrochloride (PSH in the presence of guaifenesin related substance (Guaiacol. GUC, and in the presence of syrup excepients with minimum sample pre-treatment. In the developed RP-HPLC method efficient chromatographic separation was achieved for GUF, PSH, GUC and syrup excepients using ODS column as a stationary phase and methanol: water (50:50, v/v, pH = 4 with orthophosphoric acid as a mobile phase with a flow rate of 1 mL min−1 and UV detection at 210 nm. The chromatographic run time was approximately 10 min. Calibration curves were drawn relating the integrated area under peak to the corresponding concentrations of PSH, GUF and GUC in the range of 1–8, 1–20, 0.4–8 μg mL−1, respectively. The developed method has been validated and met the requirements delineated by ICH guidelines with respect to linearity, accuracy, precision, specificity and robustness. The validated method was successfully applied for determination of the studied drugs in triaminic chest congestion® syrup; moreover its results were statistically compared with those obtained by the official method and no significant difference was found between them.

  12. Thermo-Mechanical Characterization of Silicon Carbide-Silicon Carbide Composites at Elevated Temperatures Using a Unique Combustion Facility

    Science.gov (United States)

    2009-09-10

    F THERMO-MECHANICAL CHARACTERIZATION OF SILICON CARBIDE - SILICON CARBIDE COMPOSITES AT ELEVATED...MECHANICAL CTERIZATION OF SILICON CARBIDE -SILIC BIDE COMPOSITES AT LEVATED TEMPER S USING A UNIQUE COMBUSTION FACILITY DISSERTATI N Ted T. Kim...THERMO-MECHANICAL CHARACTERIZATION OF SILICON CARBIDE - SILICON CARBIDE COMPOSITES AT ELEVATED TEMPERATURES USING A UNIQUE COMBUSTION FACILITY

  13. [Calcium carbide of different crystal formation synthesized by calcium carbide residue].

    Science.gov (United States)

    Lu, Zhong-yuan; Kang, Ming; Jiang, Cai-rong; Tu, Ming-jing

    2006-04-01

    To recycle calcium carbide residue effectively, calcium carbide of different crystal form, including global aragonite, calcite and acicular calcium carbide was synthesized. Both the influence of pretreatment in the purity of calcium carbide, and the influence of temperatures of carbonization reaction, release velocity of carbon dioxide in the apparition of calcium carbide of different crystal form were studied with DTA-TG and SEM. The result shows that calcium carbide residue can take place chemistry reaction with ammonia chlorinate straight. Under the condition that pH was above 7, the purity of calcium carbide was above 97%, and the whiteness was above 98. Once provided the different temperatures of carbonization reaction and the proper release velocity of carbon dioxide, global aragonite, calcite and acicular calcium carbide were obtained.

  14. Room temperature quantum emission from cubic silicon carbide nanoparticles.

    Science.gov (United States)

    Castelletto, Stefania; Johnson, Brett C; Zachreson, Cameron; Beke, David; Balogh, István; Ohshima, Takeshi; Aharonovich, Igor; Gali, Adam

    2014-08-26

    The photoluminescence (PL) arising from silicon carbide nanoparticles has so far been associated with the quantum confinement effect or to radiative transitions between electronically active surface states. In this work we show that cubic phase silicon carbide nanoparticles with diameters in the range 45-500 nm can host other point defects responsible for photoinduced intrabandgap PL. We demonstrate that these nanoparticles exhibit single photon emission at room temperature with record saturation count rates of 7 × 10(6) counts/s. The realization of nonclassical emission from SiC nanoparticles extends their potential use from fluorescence biomarker beads to optically active quantum elements for next generation quantum sensing and nanophotonics. The single photon emission is related to single isolated SiC defects that give rise to states within the bandgap.

  15. Laser-induced phase separation of silicon carbide

    Science.gov (United States)

    Choi, Insung; Jeong, Hu Young; Shin, Hyeyoung; Kang, Gyeongwon; Byun, Myunghwan; Kim, Hyungjun; Chitu, Adrian M.; Im, James S.; Ruoff, Rodney S.; Choi, Sung-Yool; Lee, Keon Jae

    2016-11-01

    Understanding the phase separation mechanism of solid-state binary compounds induced by laser-material interaction is a challenge because of the complexity of the compound materials and short processing times. Here we present xenon chloride excimer laser-induced melt-mediated phase separation and surface reconstruction of single-crystal silicon carbide and study this process by high-resolution transmission electron microscopy and a time-resolved reflectance method. A single-pulse laser irradiation triggers melting of the silicon carbide surface, resulting in a phase separation into a disordered carbon layer with partially graphitic domains (~2.5 nm) and polycrystalline silicon (~5 nm). Additional pulse irradiations cause sublimation of only the separated silicon element and subsequent transformation of the disordered carbon layer into multilayer graphene. The results demonstrate viability of synthesizing ultra-thin nanomaterials by the decomposition of a binary system.

  16. CALCIUM CARBIDE: AN EFFICIENT ALTERNATIVE TO THE USE OF ALUMINUM

    Directory of Open Access Journals (Sweden)

    Amilton Carlos Pinheiro Cardoso Filho

    2013-03-01

    Full Text Available The steel demand for fine applications have increased considerably in the last years, and the criteria for its production are even stricter, mainly in relation to the residual elements content and cleanness required. In relation to the steel cleanness, the main problem faced is the control of the amount and morphology of alumina inclusions, generated in the steel deoxidation with aluminum. Besides harming the products quality, the presence of non metallic inclusions can originate nozzle clogging, and consequently interruptions in the process flux. Aiming to improve the steel cleanness and to minimize nozzle clogging, this study is developed to evaluate the partial substitution of aluminum by calcium carbide in the steel deoxidation. Along the operational procedures, the calcium carbide was applied to 397 heats, through what the improvement in steel cleanness is confirmed, with consequent reduction in the nozzle clogging occurrence.

  17. Conduction mechanism in boron carbide

    Science.gov (United States)

    Wood, C.; Emin, D.

    1984-01-01

    Electrical conductivity, Seebeck-coefficient, and Hall-effect measurements have been made on single-phase boron carbides, B(1-x)C(x), in the compositional range from 0.1 to 0.2 X, and between room temperature and 1273 K. The results indicate that the predominant conduction mechanism is small-polaron hopping between carbon atoms at geometrically inequivalent sites.

  18. Thermal properties of wood-derived silicon carbide and copper-silicon carbide composites

    Science.gov (United States)

    Pappecena, Kristen E.

    Wood-derived ceramics and composites have been of interest in recent years due to their unique microstructures, which lead to tailorable properties. The porosity and pore size distribution of each wood type is different, which yields variations in properties in the resultant materials. The thermal properties of silicon carbide ceramics and copper-silicon carbide composites derived from wood were studied as a function of their pore structures. Wood was pyrolyzed at temperatures ranging from 300-2400°C to yield porous carbon. The progression toward long-range order was studied as a function of pyrolyzation temperature. Biomorphic silicon carbide (bioSiC) is a porous ceramic material resulting from silicon melt infiltration of these porous carbon materials. BioSiC has potential applicability in many high temperature environments, particularly those in which rapid temperature changes occur. To understand the behavior of bioSiC at elevated temperatures, the thermal and thermo-mechanical properties were studied. The thermal conductivity of bioSiC from five precursors was determined using flash diffusivity at temperatures up to 1100°C. Thermal conductivity results varied with porosity, temperature and orientation, and decreased from 42-13 W/mK for porosities of 43-69%, respectively, at room temperature. The results were compared with to object-oriented finite-element analysis (OOF). OOF was also used to model and understand the heat-flow paths through the complex bioSiC microstructures. The thermal shock resistance of bioSiC was also studied, and no bioSiC sample was found to fail catastrophically after up to five thermal shock cycles from 1400°C to room temperature oil. Copper-silicon carbide composites have potential uses in thermal management applications due to the high thermal conductivity of each phase. Cu-bioSiC composites were created by electrodeposition of copper into bioSiC pores. The detrimental Cu-SiC reaction was avoided by using this room temperature

  19. Structures and stabilities of group 17 fluorides EF3 (E = I, At, and element 117) with spin-orbit coupling.

    Science.gov (United States)

    Yang, Dong-Dong; Wang, Fan

    2012-12-05

    In this work, a recently developed CCSD(T) approach with spin-orbit coupling (SOC) as well as density functional theory (DFT) using various exchange-correlation (XC) functionals are employed to investigate structures and stabilities of group 17 fluorides EF(3) (E = I, At, and element 117). These molecules are predicted to have bent T-shaped C(2v) structures according to the second-order Jahn-Teller (SOJT) effects or the valance shell electron pair repulsion (VSEPR) theory. For IF(3) and (117)F(3), our results are consistent with previous SOC-DFT calculations. However, different XC functionals provide different results for AtF(3) and our SOC-CCSD(T) calculations show that both the C(2v) and D(3h) structures are minima on the potential energy surface and the C(2v) structure is the global minimum for AtF(3). The performance of XC functionals on structures and stabilities of IF(3) and AtF(3) is found to depend on the fraction of the Hartree-Fock exchange (HFX) included in the XC functionals and the M06-2X functional with 54% of HFX providing results that agree best with CCSD(T) results. In addition, although both the C(2v) and D(3h) structures are minima for AtF(3), the energy barrier between them is only 8 kJ mol(-1) for the C(2v) structure and 0.05 kJ mol(-1) for the D(3h) structure. This indicates that the D(3h) structure could not possibly be observed experimentally and AtF(3) can convert easily between the three C(2v) structures. The SOJT term is shown to be reduced by electron correlation for IF(3) and AtF(3). On the other hand, although SOC decreases the energy difference between the C(2v) and D(3h) structures and reduces the deviation of the C(2v) structure from the D(3h) structure, it decreases the frequency of the bond bending mode, which may indicate that SOC actually increases the SOJT term. This could be related to mixing of spin-singlet E' states to low-energy spin-triplet states due to SOC.

  20. Elastic and electronic properties of antiperovskite-type Pd- and Pt-based ternary carbides from first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Bannikov, V.V.; Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru

    2013-11-15

    Highlights: • 23 Pd- and Pt-based antiperovskite-type ternary carbides are probed from first principles. • Structural, elastic, electronic properties and inter-atomic bonding are evaluated. • A rich variety of mechanical and electronic properties was predicted. -- Abstract: By means of first-principles calculations, the structural, elastic, and electronic properties of a broad series of proposed Pd- and Pt-based antiperovskite-type ternary carbides AC(Pd,Pt){sub 3}, where A are Zn, Ca, Al, Ga, In, Ge, Hg, Sn, Cd, Pb, Ag, Sc, Ti, Y, Nb, Mo, and Ta, have been studied, and their stability, elastic constants, bulk, shear, and Young’s moduli, compressibility, Pugh’s indicator, Poisson’s ratio, indexes of elastic anisotropy, as well as electronic properties have been evaluated. We found that these materials should demonstrate a rich variety of mechanical and electronic properties depending on the type of A sublattices, which can include (unlike the majority of known 3d-metal-based antiperovskites) both sp elements and d atoms. We believe that the presented results will be useful for future synthesis of these phases, as well as for expanding our knowledge of this interesting group of antiperovskite-type materials.

  1. Advanced microstructure of boron carbide.

    Science.gov (United States)

    Werheit, Helmut; Shalamberidze, Sulkhan

    2012-09-26

    The rhombohedral elementary cell of the complex boron carbide structure is composed of B(12) or B(11)C icosahedra and CBC, CBB or B□B (□, vacancy) linear arrangements, whose shares vary depending on the actual chemical compound. The evaluation of the IR phonon spectra of isotopically pure boron carbide yields the quantitative concentrations of these components within the homogeneity range. The structure formula of B(4.3)C at the carbon-rich limit of the homogeneity range is (B(11)C) (CBC)(0.91) (B□B)(0.09) (□, vacancy); and the actual structure formula of B(13)C(2) is (B(12))(0.5)(B(11)C)(0.5)(CBC)(0.65)(CBB)(0.16) (B□B)(0.19), and deviates fundamentally from (B(12))CBC, predicted by theory to be the energetically most favourable structure of boron carbide. In reality, it is the most distorted structure in the homogeneity range. The spectra of (nat)B(x)C make it evident that boron isotopes are not randomly distributed in the structure. However, doping with 2% silicon brings about a random distribution.

  2. Investigation of Infiltrated and Sintered Titanium Carbide

    Science.gov (United States)

    1952-04-01

    taneive investigations in this field during the ’time preceding this contract, and concentrated their effort® On titanium carbide as the’ refractospy...component • The Basic work of this investigation consisted of? X, KpälfiCÄVtloh and refinement of cOmätrcial grades of titanium carbide hj...facilitate a comparison between the different methods» an investigation was then carried out with composite bodies* consisting of titanium carbide asd

  3. Shock-wave strength properties of boron carbide and silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Grady, D.E.

    1994-02-01

    Time-resolved velocity interferometry measurements have been made on boron carbide and silicon carbide ceramics to assess dynamic equation-of-state and strength properties of these materials. Hugoniot pecursor characteristics, and post-yield shock and release wave properties, indicated markedly different dynamic strength and flow behavior for the two carbides.

  4. Oxidation induced ionization and reactions of metal carbide clusters (Nb, Zr, V, Ta)

    Science.gov (United States)

    Deng, H. T.; Kerns, K. P.; Bell, R. C.; Castleman, A. W.

    1997-11-01

    Following our recent report of the oxidation induced formation of Ti8C12+ (H.T. Deng, K.P. Kerns, and A.W. Castleman, Jr., J. Chem. Phys. 104 (1996) 4862), the oxidation induced ionization of niobium and zirconium carbide clusters are studied using a triple quadrupole mass spectrometer coupled with a laser induced plasma reaction source. It was found that reactions of both of these neutral carbide clusters with dioxygen leads to formation of carbide ions. The ion product distributions show that zirconium carbide clusters mainly take the form of Met--Car cations, but niobium carbide clusters favor a cubic-like crystalline pattern. Furthermore, reactions of mass-selected NbxCy+ with dioxygen result in a sequential loss of C2 units from NbxCy+, and leads to formation of Nbx+ and NbxC+ depending on y being an even or odd number. However, NbxCy+ shows comparably low reactivity towards nitrous oxide through a single oxygen abstraction mechanism. In comparison with the reaction products of VxCy+ with dioxygen, the complementary information obtained in the present study suggests that the C2 unit is a basic building block for formation of small early transition metal carbide clusters. The oxidation induced ionization mechanisms are also discussed in relation with the stability, ionization potentials, and structures of the clusters.

  5. Processing of mixed uranium/refractory metal carbide fuels for high temperature space nuclear reactors

    Science.gov (United States)

    Knight, Travis; Anghaie, Samim

    2000-01-01

    Single phase, solid-solution mixed uranium/refractory metal carbides have been proposed as an advanced nuclear fuel for high performance, next generation space power and propulsion systems. These mixed carbides such as the pseudo-ternary, (U, Zr, Nb)C, hold significant promise because of their high melting points (typically greater than 3200 K), thermochemical stability in a hot hydrogen environment, and high thermal conductivity. However, insufficient test data exist under nuclear thermal propulsion conditions of temperature and hot hydrogen environment to fully evaluate their performance. Various compositions of (U, Zr, Nb)C were processed with 5% and 10% metal mole fraction of uranium. Stoichiometric samples were processed from the constituent carbide powders while hypostoichiometric samples with carbon-to-metal (C/M) ratios of 0.95 were processed from uranium hydride, graphite, and constituent refractory carbide powders. Processing techniques of cold pressing, sintering, and hot pressing were investigated to optimize the processing parameters necessary to produce dense (low porosity), homogeneous, single phase, solid-solution mixed carbide nuclear fuels for testing. This investigation was undertaken to evaluate and characterize the performance of these mixed uranium/refractory metal carbides for space power and propulsion applications. .

  6. Silicon carbide fibers and articles including same

    Energy Technology Data Exchange (ETDEWEB)

    Garnier, John E; Griffith, George W

    2015-01-27

    Methods of producing silicon carbide fibers. The method comprises reacting a continuous carbon fiber material and a silicon-containing gas in a reaction chamber at a temperature ranging from approximately 1500.degree. C. to approximately 2000.degree. C. A partial pressure of oxygen in the reaction chamber is maintained at less than approximately 1.01.times.10.sup.2 Pascal to produce continuous alpha silicon carbide fibers. Continuous alpha silicon carbide fibers and articles formed from the continuous alpha silicon carbide fibers are also disclosed.

  7. Methods for producing silicon carbide fibers

    Energy Technology Data Exchange (ETDEWEB)

    Garnier, John E.; Griffith, George W.

    2016-03-01

    Methods of producing silicon carbide fibers. The method comprises reacting a continuous carbon fiber material and a silicon-containing gas in a reaction chamber at a temperature ranging from approximately 1500.degree. C. to approximately 2000.degree. C. A partial pressure of oxygen in the reaction chamber is maintained at less than approximately 1.01.times.10.sup.2 Pascal to produce continuous alpha silicon carbide fibers. Continuous alpha silicon carbide fibers and articles formed from the continuous alpha silicon carbide fibers are also disclosed.

  8. Stabilization of Mass Absorption Cross Section of Elemental Carbon for Filter-Based Absorption Photometer by Heated Inlet

    Science.gov (United States)

    Kondo, Y.; Sahu, L.; Takegawa, N.; Miyazaki, Y.; Han, S.; Moteki, N.; Hu, M.; Kim Oanh, N.; Kim, Y.

    2008-12-01

    Accurate measurements of elemental carbon (EC) or black carbon on a long-term basis are important for the studies of impacts of EC on climate and human health. In principle, mass concentrations of EC (MEC) can be estimated by the measurement of light absorption coefficient by EC. Filter-based methods, which quantify the absorption coefficient (kabs) from the change in transmission through a filter loaded with particles, have been widely used to measure MEC because of the ease of the operation. However, in practice, reliable determination of MEC has been very difficult because of the large variability in the mass absorption cross sections (Cabs), which is a conversion factor from kabs to MEC. Coating of EC by volatile compounds and co-existence of light-scattering particles greatly contributes to the variability of Cabs. In order to overcome this difficulty, volatile aerosol components were removed before collection of EC particles on filters by heating an inlet section to 400°C. The heated inlet vaporized almost completely sulfate, nitrate, ammonium, and organics without any detectable loss of EC. Simultaneous measurements of kabs by two types photometers (Particle Soot Absorption Photometer (PSAP) and Continuous Soot Monitoring System (COSMOS)) together with MEC by the EC-OC analyzer were made to determine Cabs at 6 different locations in Asia (Japan, Korea, China, and Thailand) in different seasons. The Cabs was stable to be 10.5±0.7 m2 g-1 at the wavelength of 565 nm for EC strongly impacted by emissions from vehicles and biomass burning. The stability of the Cabs for different EC sources and under the different physical and chemical conditions provides a firm basis for its use in estimating MEC in fine mode with an accuracy of about 10%.

  9. Use of neutralized industrial residue to stabilize trace elements (Cu, Cd, Zn, As, Mo, and Cr) in marine dredged sediment from South-East of France.

    Science.gov (United States)

    Taneez, Mehwish; Marmier, Nicolas; Hurel, Charlotte

    2016-05-01

    Management of marine dredged sediments polluted with trace elements is prime issue in the French Mediterranean coast. The polluted sediments possess ecological threats to surrounding environment on land disposal. Therefore, stabilization of contaminants in multi-contaminated marine dredged sediment is a promising technique. Present study aimed to assess the effect of gypsum neutralized bauxaline(®) (bauxite residue) to decrease the availability of pollutants and inherent toxicity of marine dredged sediment. Bauxaline(®), (alumia industry waste) contains high content of iron oxide but its high alkalinity makes it not suitable for the stabilization of all trace elements from multi-contaminated dredged sediments. In this study, neutralized bauxaline(®) was prepared by mixing bauxaline(®) with 5% of plaster. Experiments were carried out for 3 months to study the effect of 5% and 20% amendment rate on the availability of Cu, Cd, Zn, As, Mo, and Cr. Trace elements concentration, pH, EC and dissolved organic carbon were measured in all leachates. Toxicity of leachates was assessed against marine rotifers Brachionus plicatilis. The Results showed that both treatments have immobilization capacity against different pollutants. Significant stabilization of contaminants (Cu, Cd, Zn) was achieved with 20% application rate whereas As, Mo, and Cr were slightly stabilized. Toxicity results revealed that leachates collected from treated sediment were less toxic than the control sediment. These results suggest that application of neutralized bauxaline(®) to dredged sediment is an effective approach to manage large quantities of dredged sediments as well as bauxite residue itself.

  10. Transient and stability analysis of large scale rotor-bearing system with strong nonlinear elements by the mode summation-transfer matrix method

    Science.gov (United States)

    Gu, Zhiping

    This paper extends Riccati transfer matrix method to the transient and stability analysis of large scale rotor-bearing systems with strong nonlinear elements, and proposes a mode summation-transfer matrix method, in which the field transfer matrix of a distributed mass uniform shaft segment is obtained with the aid of the idea of mode summation and Newmark beta formulation, and the Riccati transfer matrix method is adopted to stablize the boundary value problem of the nonlinear systems. In this investigation, the real nonlinearity of the strong nonlinear elements is considered, not linearized, and the advantages of the Riccati transfer matrix are retained. So, this method is especially applicable to analyze the transient response and stability of large-scale rotor-bear systems with strong nonlinear elements. One example, a single-spool rotating system with strong nonlinear elements, is given. The obtained results show that this method is superior to that of Gu and Chen (1990) in accuracy, stability, and economy.

  11. Solid oxide membrane-assisted controllable electrolytic fabrication of metal carbides in molten salt.

    Science.gov (United States)

    Zou, Xingli; Zheng, Kai; Lu, Xionggang; Xu, Qian; Zhou, Zhongfu

    2016-08-15

    Silicon carbide (SiC), titanium carbide (TiC), zirconium carbide (ZrC), and tantalum carbide (TaC) have been electrochemically produced directly from their corresponding stoichiometric metal oxides/carbon (MOx/C) precursors by electrodeoxidation in molten calcium chloride (CaCl2). An assembled yttria stabilized zirconia solid oxide membrane (SOM)-based anode was employed to control the electrodeoxidation process. The SOM-assisted controllable electrochemical process was carried out in molten CaCl2 at 1000 °C with a potential of 3.5 to 4.0 V. The reaction mechanism of the electrochemical production process and the characteristics of these produced metal carbides (MCs) were systematically investigated. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses clearly identify that SiC, TiC, ZrC, and TaC carbides can be facilely fabricated. SiC carbide can be controlled to form a homogeneous nanowire structure, while the morphologies of TiC, ZrC, and TaC carbides exhibit porous nodular structures with micro/nanoscale particles. The complex chemical/electrochemical reaction processes including the compounding, electrodeoxidation, dissolution-electrodeposition, and in situ carbonization processes in molten CaCl2 are also discussed. The present results preliminarily demonstrate that the molten salt-based SOM-assisted electrodeoxidation process has the potential to be used for the facile and controllable electrodeoxidation of MOx/C precursors to micro/nanostructured MCs, which can potentially be used for various applications.

  12. Synthesis of boron carbide nanoflakes via a bamboo-based carbon thermal reduction method

    Energy Technology Data Exchange (ETDEWEB)

    Du, Jun [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China); Li, Qianqian [Institute of Applied Mechanics, Zhejiang University, Hangzhou 310027 (China); Xia, Yang; Cheng, Xuejuan; Gan, Yongping; Huang, Hui [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China); Zhang, Wenkui, E-mail: msechem@zjut.edu.cn [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China); Tao, Xinyong, E-mail: tao@zjut.edu.cn [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310014 (China)

    2013-12-25

    Graphical abstract: B{sub 4}C nanoflakes were synthesized via a facile and cost-effective bamboo-based carbon thermal reduction method. Highlights: •Boron carbide nanoflakes were successfully synthesized via a bamboo-based carbon thermal reduction method. •A fluoride-assisted VLS nucleation and VS growth mechanism were proposed. •We studied the resistivity of boron carbide nanoflakes via in situ TEM techniques for the first time. -- Abstract: Boron carbide nanoflakes have been successfully synthesized by a facile and cost-effective bamboo-based carbon thermal reduction method. The majority of the boron carbide products exhibited a flake-like morphology with lateral dimensions of 0.5–50 μm in width and more than 50 μm in length, while the thickness was less than 150 nm. The structural, morphological, and elemental analyses demonstrated that these nanoflakes grew via the fluoride-assisted vapor–liquid–solid combined with vapor–solid growth mechanism. The corresponding growth model was proposed. In addition, the electrical property of individual boron carbide nanoflake was investigated by an in situ two point method inside a transmission electron microscope. The resistivity of boron carbide nanoflakes was measured to be 0.14 MΩ cm.

  13. Tribology of carbide derived carbon films synthesized on tungsten carbide

    Science.gov (United States)

    Tlustochowicz, Marcin

    Tribologically advantageous films of carbide derived carbon (CDC) have been successfully synthesized on binderless tungsten carbide manufactured using the plasma pressure compaction (P2CRTM) technology. In order to produce the CDC films, tungsten carbide samples were reacted with chlorine containing gas mixtures at temperatures ranging from 800°C to 1000°C in a sealed tube furnace. Some of the treated samples were later dechlorinated by an 800°C hydrogenation treatment. Detailed mechanical and structural characterizations of the CDC films and sliding contact surfaces were done using a series of analytical techniques and their results were correlated with the friction and wear behavior of the CDC films in various tribosystems, including CDC-steel, CDC-WC, CDC-Si3N4 and CDC-CDC. Optimum synthesis and treatment conditions were determined for use in two specific environments: moderately humid air and dry nitrogen. It was found that CDC films first synthesized at 1000°C and then hydrogen post-treated at 800°C performed best in air with friction coefficient values as low as 0.11. However, for dry nitrogen applications, no dechlorination was necessary and both hydrogenated and as-synthesized CDC films exhibited friction coefficients of approximately 0.03. A model of tribological behavior of CDC has been proposed that takes into consideration the tribo-oxidation of counterface material, the capillary forces from adsorbed water vapor, the carbon-based tribofilm formation, and the lubrication effect of both chlorine and hydrogen.

  14. Development and Processing of Nickel Aluminide-Carbide Alloys

    Science.gov (United States)

    Newport, Timothy Scott

    1996-01-01

    With the upper temperature limit of the Ni-based superalloys attained, a new class of materials is required. Intermetallics appear as likely candidates because of their attractive physical properties. With a relatively low density, high thermal conductivity, excellent oxidation resistance, high melting point, and simple crystal structure, nickel aluminide (NiAl) appears to be a potential candidate. However, NiAl is limited in structural applications due to its low room temperature fracture toughness and poor elevated temperature strength. One approach to improving these properties has been through the application of eutectic composites. Researchers have shown that containerless directional solidification of NiAl-based eutectic alloys can provide improvement in both the creep strength and fracture toughness. Although these systems have shown improvements in the mechanical properties, the presence of refractory metals increases the density significantly in some alloys. Lower density systems, such as the carbides, nitrides, and borides, may provide NiAl-based eutectic structure. With little or no information available on these systems, experimental investigation is required. The objective of this research was to locate and develop NiAl-carbide eutectic alloys. Exploratory arc-melts were performed in NiAl-refractory metal-C systems. Refractory metal systems investigated included Co, Cr, Fe, Hf, Mo, Nb, Ta, Ti, W, and Zr. Systems containing carbides with excellent stability (i.e.,HfC, NbC, TaC, TiC, and ZrC) produced large blocky cubic carbides in an NiAl matrix. The carbides appeared to have formed in the liquid state and were randomly distributed throughout the polycrystalline NiAl. The Co, Cr, Fe, Mo, and W systems contained NiAl dendrites with a two-phase interdendritic microconstituent present. Of these systems, the NiAl-Mo-C system had the most promising microstructure for in-situ composites. Three processing techniques were used to evaluate the NiAl-Mo-C system

  15. Stabilization of Oncostatin-M mRNA by Binding of Nucleolin to a GC-Rich Element in Its 3'UTR.

    Science.gov (United States)

    Saha, Sucharita; Chakraborty, Alina; Bandyopadhyay, Sumita Sengupta

    2016-04-01

    Oncostatin-M (OSM) is a patho-physiologically important pleiotropic, multifunctional cytokine. OSM mRNA sequence analysis revealed that its 3'UTR contains three highly conserved GC-rich cis-elements (GCREs) whose role in mRNA stability is unidentified. In the present study, the functional role of the proximal GC-rich region of osm 3'-UTR (GCRE-1) in post-transcriptional regulation of osm expression in U937 cells was assessed by transfecting construct containing GCRE-1 at 3'-end of a fairly stable reporter gene followed by analysis of the expression of the reporter. GCRE-1 showed mRNA destabilizing activity; however, upon PMA treatment the reporter message containing GCRE-1 was stabilized. This stabilization is owing to a time-dependent progressive binding of trans-factors (at least five proteins) to GCRE-1 post-PMA treatment. Nucleolin was identified as one of the proteins in the RNP complex of GCRE-1 with PMA-treated U937 cytosolic extracts by oligo-dT affinity chromatography of poly-adenylated GCRE-1. Immuno-blot revealed time-dependent enhancement of nucleolin in the cytoplasm which in turn directly binds GCRE-1. RNA co-immunoprecipitation confirmed the GCRE-1-nucleolin interaction in vivo. To elucidate the functional role of nucleolin in stabilization of osm mRNA, nucleolin was overexpressed in U937 cells and found to stabilize the intrinsic osm mRNA, where co-transfection with the reporter containing GCRE-1 confirms the role of GCRE-1 in stabilization of the reporter mRNA. Thus, in conclusion, the results asserted that PMA treatment in U937 cells leads to cytoplasmic translocation of nucleolin that directly binds GCRE-1, one of the major GC-rich instability elements, thereby stabilizing the osm mRNA.

  16. Disorder and defects are not intrinsic to boron carbide

    Science.gov (United States)

    Mondal, Swastik; Bykova, Elena; Dey, Somnath; Ali, Sk Imran; Dubrovinskaia, Natalia; Dubrovinsky, Leonid; Parakhonskiy, Gleb; van Smaalen, Sander

    2016-01-01

    A unique combination of useful properties in boron-carbide, such as extreme hardness, excellent fracture toughness, a low density, a high melting point, thermoelectricity, semi-conducting behavior, catalytic activity and a remarkably good chemical stability, makes it an ideal material for a wide range of technological applications. Explaining these properties in terms of chemical bonding has remained a major challenge in boron chemistry. Here we report the synthesis of fully ordered, stoichiometric boron-carbide B13C2 by high-pressure–high-temperature techniques. Our experimental electron-density study using high-resolution single-crystal synchrotron X-ray diffraction data conclusively demonstrates that disorder and defects are not intrinsic to boron carbide, contrary to what was hitherto supposed. A detailed analysis of the electron density distribution reveals charge transfer between structural units in B13C2 and a new type of electron-deficient bond with formally unpaired electrons on the C–B–C group in B13C2. Unprecedented bonding features contribute to the fundamental chemistry and materials science of boron compounds that is of great interest for understanding structure-property relationships and development of novel functional materials.

  17. Disorder and defects are not intrinsic to boron carbide.

    Science.gov (United States)

    Mondal, Swastik; Bykova, Elena; Dey, Somnath; Ali, Sk Imran; Dubrovinskaia, Natalia; Dubrovinsky, Leonid; Parakhonskiy, Gleb; van Smaalen, Sander

    2016-01-18

    A unique combination of useful properties in boron-carbide, such as extreme hardness, excellent fracture toughness, a low density, a high melting point, thermoelectricity, semi-conducting behavior, catalytic activity and a remarkably good chemical stability, makes it an ideal material for a wide range of technological applications. Explaining these properties in terms of chemical bonding has remained a major challenge in boron chemistry. Here we report the synthesis of fully ordered, stoichiometric boron-carbide B13C2 by high-pressure-high-temperature techniques. Our experimental electron-density study using high-resolution single-crystal synchrotron X-ray diffraction data conclusively demonstrates that disorder and defects are not intrinsic to boron carbide, contrary to what was hitherto supposed. A detailed analysis of the electron density distribution reveals charge transfer between structural units in B13C2 and a new type of electron-deficient bond with formally unpaired electrons on the C-B-C group in B13C2. Unprecedented bonding features contribute to the fundamental chemistry and materials science of boron compounds that is of great interest for understanding structure-property relationships and development of novel functional materials.

  18. Amorphous silicon carbide passivating layers for crystalline-silicon-based heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Boccard, Mathieu; Holman, Zachary C. [School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287-5706 (United States)

    2015-08-14

    Amorphous silicon enables the fabrication of very high-efficiency crystalline-silicon-based solar cells due to its combination of excellent passivation of the crystalline silicon surface and permeability to electrical charges. Yet, amongst other limitations, the passivation it provides degrades upon high-temperature processes, limiting possible post-deposition fabrication possibilities (e.g., forcing the use of low-temperature silver pastes). We investigate the potential use of intrinsic amorphous silicon carbide passivating layers to sidestep this issue. The passivation obtained using device-relevant stacks of intrinsic amorphous silicon carbide with various carbon contents and doped amorphous silicon are evaluated, and their stability upon annealing assessed, amorphous silicon carbide being shown to surpass amorphous silicon for temperatures above 300 °C. We demonstrate open-circuit voltage values over 700 mV for complete cells, and an improved temperature stability for the open-circuit voltage. Transport of electrons and holes across the hetero-interface is studied with complete cells having amorphous silicon carbide either on the hole-extracting side or on the electron-extracting side, and a better transport of holes than of electrons is shown. Also, due to slightly improved transparency, complete solar cells using an amorphous silicon carbide passivation layer on the hole-collecting side are demonstrated to show slightly better performances even prior to annealing than obtained with a standard amorphous silicon layer.

  19. Titanium Carbide Bipolar Plate for Electrochemical Devices

    Energy Technology Data Exchange (ETDEWEB)

    LaConti, Anthony B.; Griffith, Arthur E.; Cropley, Cecelia C.; Kosek, John A.

    1998-05-08

    Titanium carbide comprises a corrosion resistant, electrically conductive, non-porous bipolar plate for use in an electrochemical device. The process involves blending titanium carbide powder with a suitable binder material, and molding the mixture, at an elevated temperature and pressure.

  20. Boron carbide whiskers produced by vapor deposition

    Science.gov (United States)

    1965-01-01

    Boron carbide whiskers have an excellent combination of properties for use as a reinforcement material. They are produced by vaporizing boron carbide powder and condensing the vapors on a substrate. Certain catalysts promote the growth rate and size of the whiskers.

  1. Ligand sphere conversions in terminal carbide complexes

    DEFF Research Database (Denmark)

    Morsing, Thorbjørn Juul; Reinholdt, Anders; Sauer, Stephan P. A.

    2016-01-01

    Metathesis is introduced as a preparative route to terminal carbide complexes. The chloride ligands of the terminal carbide complex [RuC(Cl)2(PCy3)2] (RuC) can be exchanged, paving the way for a systematic variation of the ligand sphere. A series of substituted complexes, including the first exam...

  2. Origin of Predominance of Cementite among Iron Carbides in Steel at Elevated Temperature

    NARCIS (Netherlands)

    Fang, C.M.; Sluiter, M.H.F.; Van Huis, M.A.; Ande, C.K.; Zandbergen, H.W.

    2010-01-01

    A long-standing challenge in physics is to understand why cementite is the predominant carbide in steel. Here we show that the prevalent formation of cementite can be explained only by considering its stability at elevated temperature. A systematic highly accurate quantum mechanical study was conduc

  3. Thermal Analysis of Tantalum Carbide-Hafnium Carbide Solid Solutions from Room Temperature to 1400 °C

    Directory of Open Access Journals (Sweden)

    Cheng Zhang

    2017-07-01

    Full Text Available The thermogravimetric analysis on TaC, HfC, and their solid solutions has been carried out in air up to 1400 °C. Three solid solution compositions have been chosen: 80TaC-20 vol % HfC (T80H20, 50TaC-50 vol % HfC (T50H50, and 20TaC-80 vol % HfC (T20H80, in addition to pure TaC and HfC. Solid solutions exhibit better oxidation resistance than the pure carbides. The onset of oxidation is delayed in solid solutions from 750 °C for pure TaC, to 940 °C for the T50H50 sample. Moreover, T50H50 samples display the highest resistance to oxidation with the retention of the initial carbides. The oxide scale formed on the T50H50 sample displays mechanical integrity to prevent the oxidation of the underlying carbide solid solution. The improved oxidation resistance of the solid solution is attributed to the reaction between Ta2O5 and HfC, which stabilizes the volume changes induced by the formation of Ta2O5 and diminishes the generation of gaseous products. Also, the formation of solid solutions disturbs the atomic arrangement inside the lattice, which delays the reaction between Ta and O. Both of these mechanisms lead to the improved oxidation resistances of TaC-HfC solid solutions.

  4. AU-RICH ELEMENTS IN THE 3′-UTR REGULATE THE STABILITY OF THE 141 AMINO ACID ISOFORM OF PARATHYROID HORMONE-RELATED PROTEIN mRNA

    Science.gov (United States)

    Luchin, Alexander I.; Nadella, Murali V.P.; Thudi, Nanda K.; Dirksen, Wessel P.; Gulati, Parul; Fernandez, Soledad A.; Rosol, Thomas J.

    2012-01-01

    We demonstrated previously that parathyroid hormone-related protein (PTHrP) 1-141 mRNA is the least stable of three isoforms and is the only isoform that is stabilized by TGF-β. In order to understand how PTHrP mRNA is stabilized by TGF-β, we first sought to elucidate the mechanism(s) that are responsible for the instability of PTHrP isoform 1-141 mRNA. The 3′-UTR of isoform 1-141 contains four AU-rich elements (AREs), which are known to mediate mRNA degradation. We utilized a luciferase reporter system to test whether these four AREs are responsible for the short half-life of PTHrP 1-141 mRNA. Our results demonstrated that ARE elements in the 3′-UTR of PTHrP 1-141 mRNA play a significant role in regulation of the stability of the mRNA. It is known that AREs mediate their effects on mRNA stability through a number of ARE-binding proteins that recruit the exosome, a complex of exonucleases that degrades the mRNA. We identified tristetraproline (TTP) as an RNA-binding protein that may be involved in ARE-mediated degradation of PTHrP 1-141 mRNA. PMID:22960231

  5. AU-rich elements in the 3'-UTR regulate the stability of the 141 amino acid isoform of parathyroid hormone-related protein mRNA.

    Science.gov (United States)

    Luchin, Alexander I; Nadella, Murali V P; Thudi, Nanda K; Dirksen, Wessel P; Gulati, Parul; Fernandez, Soledad A; Rosol, Thomas J

    2012-11-25

    We demonstrated previously that parathyroid hormone-related protein (PTHrP) 1-141 mRNA is the least stable of three isoforms and is the only isoform that is stabilized by TGF-β. In order to understand how PTHrP mRNA is stabilized by TGF-β, we first sought to elucidate the mechanism(s) that are responsible for the instability of PTHrP isoform 1-141 mRNA. The 3'-UTR of isoform 1-141 contains four AU-rich elements (AREs), which are known to mediate mRNA degradation. We utilized a luciferase reporter system to test whether these four AREs are responsible for the short half-life of PTHrP 1-141 mRNA. Our results demonstrated that ARE elements in the 3'-UTR of PTHrP 1-141 mRNA play a significant role in regulation of the stability of the mRNA. It is known that AREs mediate their effects on mRNA stability through a number of ARE-binding proteins that recruit the exosome, a complex of exonucleases that degrades the mRNA. We identified tristetraproline (TTP) as an RNA-binding protein that may be involved in ARE-mediated degradation of PTHrP 1-141 mRNA. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  6. PROPERTIES OF DEFECTS AND IMPLANTS IN Mg+ IMPLANTED SILICON CARBIDE

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Weilin; Zhu, Zihua; Varga, Tamas; Bowden, Mark E.; Manandhar, Sandeep; Roosendaal, Timothy J.; Hu, Shenyang Y.; Henager, Charles H.; Kurtz, Richard J.; Wang, Yongqiang

    2013-09-25

    As a candidate material for fusion reactor designs, silicon carbide (SiC) under high-energy neutron irradiation undergoes atomic displacement damage and transmutation reactions that create magnesium as one of the major metallic products. The presence of Mg and lattice disorder in SiC is expected to affect structural stability and degrade thermo-mechanical properties that could limit SiC lifetime for service. We have initiated a combined experimental and computational study that uses Mg+ ion implantation and multiscale modeling to investigate the structural and chemical effects in Mg implanted SiC and explore possible property degradation mechanisms.

  7. A Stability Analysis of Cylindrical Panels Using a Finite Element Formulation. Ph.D. Thesis - Va. Polytechnic Inst. and State Univ.

    Science.gov (United States)

    Snyder, R. E.

    1971-01-01

    A cylindrical finite element suitable for the linear stability analysis of cylindrical shells is developed. Energy principles and variational methods lead to a problem formulation which lends itself to physical interpretations of the governing matrices of the finite element. By properly grouping the terms which result from taking the second variation of the potential energy of the element, it is possible to identify three distinct types of matrices. The first matrix is the conventional stiffness matrix; the second is an initial stress stiffness matrix; and the third is an initial displacement stiffness matrix. With the assumption of linearity, the buckling problem is stated in terms of the classical linear real eigenvalue equation. This problem formulation was programmed on the CDC 6600 series computer. The computer program is used to analyze the buckling of a variety of structures. Columns, arches, flat plates and curved panels with and without cutouts are considered.

  8. ON THE STABILITY ANALYSIS OF PLATES AND SHELLS USING A QUADRILATERAL,16-DEGREES OF FREEDOM PLAT SHELL ELEMENT DKQ16

    Institute of Scientific and Technical Information of China (English)

    郑长良; 李丽华; 钟万勰

    2004-01-01

    The linear buckling problems of plates and shells were analysed using a recently developped quadrilateral, 16-degrees of freedom flat shell element (called DKQ16). The geometrical stiffness matrix was established. Comparison of the numerical results for several typical problems shows that the DKQ16 element has a very good precision for the linear buckling problems of plates and shells.

  9. Predicting Two-Dimensional Silicon Carbide Monolayers.

    Science.gov (United States)

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.

  10. Hollow Spheres of Iron Carbide Nanoparticles Encased in Graphitic Layers as Oxygen Reduction Catalysts

    DEFF Research Database (Denmark)

    Hu, Yang; Jensen, Jens Oluf; Zhang, Wei;

    2014-01-01

    of uniform iron carbide (Fe3C) nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles without depriving them of their catalytic activity towards the oxygen reduction reaction (ORR......). As a result the catalyst is highly active and stable in both acid and alkaline electrolytes. The synthetic approach, the carbide‐based catalyst, the structure of the catalysts, and the proposed mechanism open new avenues for the development of ORR catalysts....

  11. Molybdenum isotopic composition of single silicon carbides from supernovae.

    Energy Technology Data Exchange (ETDEWEB)

    Amari, S.; Clayton, R. N.; Davis, A. M.; Lewis, R. S.; Pellin, M. J.

    1999-02-03

    Presolar silicon carbide grains form in a variety of types of stars, including asymptotic giant branch red giant stars and supernovae. The dominant mechanisms of heavy element nucleosynthesis, the s-process and r-process, are thought to occur in AGB stars and supernovae, respectively. We have previously reported that mainstream SiC grains have strong enrichments in the s-process isotopes of Sr, Zr and Mo. We report here the first measurements of Mo isotopes in X-type SiC grains, which have previously been identified as having formed from supernova ejecta.

  12. Precipitating Mechanism of Carbide in Cold-Welding Surfacing Metals

    Institute of Scientific and Technical Information of China (English)

    Yuanbin ZHANG; Dengyi REN

    2004-01-01

    Carbides in a series of cold-welding weld metals were studied by means of SEM, TEM and EPMA, and the forming mechanism of carbide was proposed according to their distribution and morphology. Due to their different carbide-forming tendency, Nb and Ti could combine with C to form particulate carbide in liquid weld metal and depleted the carbon content in matrix, while V induced the carbide precipitated along grain boundary. But too much Nb or Ti alone resulted in coarse carbide and poor strengthened matrix. When suitable amount of Nb, Ti and V coexisted in weld metal, both uniformly distributed particulate carbide and well strengthened matrix could be achieved. It was proposed that the carbide nucleated on the oxide which dispersed in liquid weld metal, and then grew into multi-layer complex carbide particles by epitaxial growth. At different sites, carbide particles may present as different morphologies.

  13. Nanostructured carbide catalysts for the hydrogen economy

    Energy Technology Data Exchange (ETDEWEB)

    Ram Seshadri, Susannah Scott, Juergen Eckert

    2008-07-21

    The above quote, taken from the executive summary of the Report from the US DOE Basic Energy Sciences Workshop held August 6–8, 2007,[1] places in context the research carried out at the University of California, Santa Barbara, which is reported in this document. The enormous impact of heterogeneous catalysis is exemplified by the Haber process for the synthesis of ammonia, which consumes a few % of the world’s energy supply and natural gas, and feeds as many as a third of the world’s population. While there have been numerous advances in understanding the process,[2] culminating in the awarding of the Nobel Prize to Gerhard Ertl in 2007, it is interesting to note that the catalysts themselves have changed very little since they were discovered heuristically in the the early part of the 20th century. The thesis of this report is that modern materials chemistry, with all the empirical knowledge of solid state chemistry, combined with cutting edge structural tools, can help develop and better heterogeneous catalysis. The first part of this report describes research in the area of early transition metal carbides (notably of Mo and W), potentially useful catalysts for water gas shift (WGS) and related reactions of use to the hydrogen economy. Although these carbides have been known to be catalytically useful since the 1970s,[3] further use of these relatively inexpensive materials have been plagued by issues of low surface areas and ill-defined, and often unreactive surfaces, in conjunction with deactivation. We have employed for the first time, a combination of constant-wavelength and time-of-flight neutron scattering, including a total scattering analysis of the latter data, to better understand what happens in these materials, in a manner that for the first time, reveals surface graphitic carbon in these materials in a quantitative manner. Problems of preparation, surface stability, and irreversible reactivity have become manifest in this class of materials

  14. Hydrothermal synthesis of xonotlite from carbide slag

    Institute of Scientific and Technical Information of China (English)

    Jianxin Cao; Fei Liu; Qian Lin; Yu Zhang

    2008-01-01

    Carbide slag was used as the calcareous materials for the first time to prepare xonotlite via dynamic hydrothermal synthesis.The effects of influential factors including different calcination temperatures,pretreatment methods of the carbide slag and process param-eters of hydrothermal synthesis on the microstructure and morphology of xonotlite were explored using XRD and SEM techniques.The results indicate that the carbide slag after proper calcination could be used to prepare pure xonotlite;and different calcination tern-peratures have little effect on the crystallinity of synthesized xonotlitc,but have great impact on the morphology of secondary particles.The different pretreatment methods of the carbide slag pose great impact on the crystallinity and morphology of secondary particles of xonotlite.Xonotlite was also synthesized from pure CaO under the salne experimental conditions as that prepared from calcined carbide slag for comparison.Little amount of impurities in carbide slag has no effect on the mechanism of hydrothermal synthesizing xonotlite from carbide slag.

  15. Processing of solid solution, mixed uranium/refractory metal carbides for advanced space nuclear power and propulsion systems

    Science.gov (United States)

    Knight, Travis Warren

    Nuclear thermal propulsion (NTP) and space nuclear power are two enabling technologies for the manned exploration of space and the development of research outposts in space and on other planets such as Mars. Advanced carbide nuclear fuels have been proposed for application in space nuclear power and propulsion systems. This study examined the processing technologies and optimal parameters necessary to fabricate samples of single phase, solid solution, mixed uranium/refractory metal carbides. In particular, the pseudo-ternary carbide, UC-ZrC-NbC, system was examined with uranium metal mole fractions of 5% and 10% and corresponding uranium densities of 0.8 to 1.8 gU/cc. Efforts were directed to those methods that could produce simple geometry fuel elements or wafers such as those used to fabricate a Square Lattice Honeycomb (SLHC) fuel element and reactor core. Methods of cold uniaxial pressing, sintering by induction heating, and hot pressing by self-resistance heating were investigated. Solid solution, high density (low porosity) samples greater than 95% TD were processed by cold pressing at 150 MPa and sintering above 2600 K for times longer than 90 min. Some impurity oxide phases were noted in some samples attributed to residual gases in the furnace during processing. Also, some samples noted secondary phases of carbon and UC2 due to some hyperstoichiometric powder mixtures having carbon-to-metal ratios greater than one. In all, 33 mixed carbide samples were processed and analyzed with half bearing uranium as ternary carbides of UC-ZrC-NbC. Scanning electron microscopy, x-ray diffraction, and density measurements were used to characterize samples. Samples were processed from powders of the refractory mono-carbides and UC/UC 2 or from powders of uranium hydride (UH3), graphite, and refractory metal carbides to produce hypostoichiometric mixed carbides. Samples processed from the constituent carbide powders and sintered at temperatures above the melting point of UC

  16. Evidence for a silicon oxycarbide phase in the Nicalon silicon carbide fibre

    Energy Technology Data Exchange (ETDEWEB)

    Porte, L.; Sartre, A.

    1989-01-01

    The Nicalon silicon carbide fibre has been studied by X-ray photoelectron spectroscopy. Elements entering the fiber are carbon, silicon and oxygen. In addition to previously reported chemical entities (silicon carbide, silica and graphitic carbon) evidence is found of the presence of a new supplementary phase which is attributed to an intermediate silicon oxycarbide phase. As this phase is found to participate in very appreciable proportions to the composition of the fiber, some influence on the properties of this fiber can be anticipated. 17 references.

  17. Characterization of Transition Metal Carbide Layers Synthesized by Thermo-reactive Diffusion Processes

    DEFF Research Database (Denmark)

    Laursen, Mads Brink; Fernandes, Frederico Augusto Pires; Christiansen, Thomas Lundin

    2015-01-01

    Hard wear resistant surface layers of transition metal carbides can be produced by thermo-reactive diffusion processes where interstitial elements from a steel substrate together with external sources of transition metals (Ti, V, Cr etc.) form hard carbide and/or nitride layers at the steel surface...... electron microscopy, X-ray diffraction and Vickers hardness testing. The study shows that porosityfree, homogenous and very hard surface layers can be produced by thermo-reactive diffusion processes. The carbon availability of the substrate influences thickness of obtained layers, as Vanadis 6 tool steel...

  18. Method 200.12 - Determination of Trace Elements in Marine Waters by StabilizedTemperature Graphite Furnace Atomic Absorption

    Science.gov (United States)

    This method provides procedures for the determination of total recoverable elements by graphite furnace atomic absorption (GFAA) in marine waters, including estuarine, ocean and brines with salinities of up to 35 ppt.

  19. Carbide Coatings for Nickel Alloys, Graphite and Carbon/Carbon Composites to be used in Fluoride Salt Valves

    Energy Technology Data Exchange (ETDEWEB)

    Nagle, Denis [Johns Hopkins Univ., Baltimore, MD (United States); Zhang, Dajie [Johns Hopkins Univ., Baltimore, MD (United States)

    2015-10-22

    The focus of this research was concerned with developing materials technology that supports the evolution of Generation IV Advanced High Temperature Reactor (AHTR) concepts. Specifically, we investigate refractory carbide coatings for 1) nickel alloys, and 2) commercial carbon-carbon composites (CCCs). Numerous compelling reasons have driven us to focus on carbon and carbide materials. First, unlike metals, the strength and modulus of CCCs increase with rising temperature. Secondly, graphite and carbon composites have been proven effective for resisting highly corrosive fluoride melts such as molten cryolite [Na₃AlF₆] at ~1000°C in aluminum reduction cells. Thirdly, graphite and carbide materials exhibit extraordinary radiation damage tolerance and stability up to 2000°C. Finally, carbides are thermodynamically more stable in liquid fluoride salt than the corresponding metals (i.e. Cr and Zr) found in nickel based alloys.

  20. Penalty-Finite Element Analysis of the Eddy Current Loss in a Fully-Stabilized Multifilamentary Superconducting Wire

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The paper is mainly concerned with the penalty incurred in finiteelement analysis of the eddy-current loss problem in a fully established multi-filamentary superconducting wire. A finite element model with 4-node quadrilateral isoparametric elements is formulated for the present problem. Unlike the conventional vector potential scheme in use for electromagnetic field problem, the present work features a direct computational approach to eddy current loss. Simplicity and remarkable enhancement in computational accuracy can be obtained with the proposed method.

  1. Formation of nanoscale titanium carbides in ferrite: an atomic study

    Science.gov (United States)

    Lv, Yanan; Hodgson, Peter; Kong, Lingxue; Gao, Weimin

    2016-03-01

    The formation and evolution of nanoscale titanium carbide in ferrite during the early isothermal annealing process were investigated via molecular dynamics simulation. The atomic interactions of titanium and carbon atoms during the initial formation process explained the atoms aggregation and carbides formation. It was found that the aggregation and dissociation of titanium carbide occurred simultaneously, and the composition of carbide clusters varied in a wide range. A mechanism for the formation of titanium carbide clusters in ferrite was disclosed.

  2. Application of three-dimensional discrete element face-to-face contact model with fissure water pressure to stability analysis of landslide in Panluo iron mine

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Lei; WEI; Zuoan; LIU; Xiaoyu; LI; Shihai

    2005-01-01

    Three-dimensional discrete element face-to-face contact model with fissure water pressure is established in this paper and the model is used to simulate three-stage process of landslide under fissure water pressure in the opencast mine, according to the actual state of landslide in Panluo iron mine where landslide happened in 1990 and was fathered in 1999. The calculation results show that fissure water pressure on the sliding surface is the main reason causing landslide and the local soft interlayer weakens the stability of slope. If the discrete element method adopts the same assumption as the limit equilibrium method, the results of two methods are in good agreement; while if the assumption is not adopted in the discrete element method, the critical φ numerically calculated is less than the one calculated by use of the limit equilibrium method for the sameC. Thus, from an engineering point of view, the result from the discrete element model simulation is safer and has more widely application since the discrete element model takes into account the effect of rock mass structures.

  3. Synthesis of thermal and chemical resistant oxygen barrier starch with reinforcement of nano silicon carbide.

    Science.gov (United States)

    Dash, Satyabrata; Swain, Sarat K

    2013-09-12

    Starch/silicon carbide (starch/SiC) bionanocomposites were synthesized by solution method using different wt% of silicon carbide with starch matrix. The interaction between starch and silicon carbide was studied by Fourier transform infrared (FTIR) spectroscopy. The structure of the bionanocomposites was investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). Thermal property of starch/SiC bionanocomposites was measured and a significant enhancement of thermal resistance was noticed. The oxygen barrier property of the composites was studied and a substantial reduction in permeability was observed as compared to the virgin starch. The reduction of oxygen permeability with enhancement of thermal stability of prepared bionanocomposites may enable the materials suitable for thermal resistant packaging and adhesive applications.

  4. Reactivity of carbides in synthesis of MgB 2 bulks

    Science.gov (United States)

    Yamamoto, Akiyasu; Shimoyama, Jun-ichi; Ueda, Shinya; Horii, Shigeru; Kishio, Kohji

    2006-10-01

    The reactivity of various carbides (B4C, Al4C3, SiC, TiC, ZrC, NbC, Mo2C, HfC and WC) with magnesium and boron in synthesis of MgB2 was systematically studied. Decreases in the a-axis length and transition temperature were observed in all the carbide doped MgB2 bulks, reflecting a certain amount of carbon substituted for boron site in MgB2. The reactivity of each carbide estimated by the carbon content in MgB2 was found to be different depending on the chemical stability. Our results suggest that carbon content in MgB2 lattice can be controlled to its optimal doping level by adjusting synthesis conditions and selection of doping reagents.

  5. Effect of β-stabilizer elements on stacking faults energies and ductility of α-titanium using first-principles calculations

    Science.gov (United States)

    Salloom, R.; Banerjee, R.; Srinivasan, S. G.

    2016-11-01

    The effect of W, Mo, V, Ta, and Nb, five common β-stabilizing substitutional elements, on α-Ti stacking fault energy has been studied using first principle calculations. The generalized stacking fault energy (GSFE) curves have been determined for different concentrations of β-stabilizers at the fault plane using supercells with up to 360 atoms. Both basal and prismatic slip systems with the stable (γSF) and unstable (γUSF) stacking faults and twinning fault energies were determined. All the alloying elements reduce the stacking fault energy for Ti for both basal and prismatic slip. At higher concentration of 25 at. % of V, Ta, and Nb at the slip plane, the basal slip becomes more favorable than the prismatic slip in Ti. Ti-Mo and Ti-W systems also show a significant shift in the GSFE curve towards a higher shear deformation strain along due to the change in bond character between Ti and those two elements. Using Rice criterion, which employs γS/γUSF ratio to estimate ductility, we show that all the alloying elements likely improve the ductility of α-Ti with Ti-25 at. % Nb exhibiting the most ductile behavior. However, according to the Tadmor and Bernstein model, all the alloying elements considered here do not improve the partial dislocation emission or the twinning propensity in spite of decreasing the stacking fault energies for α-Ti and. Hence, a better empirical model that incorporates changes in the character of directional bonding upon alloying is needed to estimate how alloying influences ductility in hcp metals.

  6. Characterization of Nanometric-Sized Carbides Formed During Tempering of Carbide-Steel Cermets

    OpenAIRE

    Matus K.; Pawlyta M.; Matula G.; Gołombek K.

    2016-01-01

    The aim of this article of this paper is to present issues related to characterization of nanometric-sized carbides, nitrides and/or carbonitrides formed during tempering of carbide-steel cermets. Closer examination of those materials is important because of hardness growth of carbide-steel cermet after tempering. The results obtained during research show that the upswing of hardness is significantly higher than for high-speed steels. Another interesting fact is the displacement of secondary ...

  7. Synthesis of Mo and W carbide and nitride nanoparticles via a simple "urea glass" route.

    Science.gov (United States)

    Giordano, Cristina; Erpen, Christian; Yao, Weitang; Antonietti, Markus

    2008-12-01

    A simple, inexpensive, and versatile route for the synthesis of metal nitrides and carbides (such as Mo2N, Mo2C, W2N and WC) nanoparticles was set up. For the first time, metal carbides were obtained using urea as carbon-source. MoCl5 and WCl4 are in a first step contacted with alcohols and an appropriate amount of urea to form a polymer-like, glassy phase, which acts as the starting product for further conversions. Just by heating this phase it was possible to prepare either molybdenum and tungsten nitrides or carbides simply by changing the metal precursor/urea molar ratio. In this procedure, urea plays a double role as a nitrogen/carbon source and stabilizing agent (necessary for the nanoparticle dispersion). Molybdenum and tungsten nitride and carbides synthesized are almost pure and highly crystalline. Sizes estimated by WAXS range around 20 and 4 nm in diameter for Mo and W nitrides or carbides, respectively. The specific surface area was found between 10 and 80 m2/g, depending on the metal and the initial ratio of metal precursor to urea.

  8. Direct determination of impurities in high purity silicon carbide by inductively coupled plasma optical emission spectrometry using slurry nebulization technique.

    Science.gov (United States)

    Wang, Zheng; Qiu, Deren; Ni, Zheming; Tao, Guangyi; Yang, Pengyuan

    2006-09-08

    A novel method for the determination of Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni and Ti in high purity silicon carbide (SiC) using slurry introduction axial viewed inductively coupled plasma optical emission spectrometry (ICP-OES) was described. The various sizes of SiC slurry were dispersed by adding dispersant polyethylene imine (PEI). The stability of slurry was characterized by zeta potential measurement, SEM observation and signal stability testing. The optimal concentration of PEI was found to be 0.5 wt% for the SiC slurry. Analytical results of sub-mum size SiC by the slurry introduction were in good accordance with those by the alkaline fusion method which verified that determination could be calibrated by aqueous standards. For mum size SiC, results of most elements have a negative deviation and should be calibrated by the Certified Reference Material slurry. Owing to a rather low contamination in the sample preparation and stability of the slurry, the limits of detection (LODs), which are in the range of 40-2000 ng g(-1), superior to those of the conventional nebulization technique by ICP-OES or ICP-MS.

  9. Chromium and copper influence on the nodular cast iron with carbides microstructure

    Directory of Open Access Journals (Sweden)

    G. Gumienny

    2010-10-01

    Full Text Available In this paper chromium to 1,00% and copper to 1,50% influence at constant molybdenum content of about 1,50% on the nodular cast ironwith carbides microstructure has been presented. It was found, that as a result of synergic addition of above-mentioned elements there isthe possibility obtaining an ausferrite in nodular cast iron with carbides castings. Conditions have been given, when in nodular cast iron with carbides at cooling at first in the form, then air-cooling austenite transformation to upper bainite, its mixture with lower bainite, martensite or ausferrite takes place. Transformations proceed during cooling and the crystallization of cast iron have been determined and the casting hardness has been presented.

  10. Investigation of the Electrolyte Effects on Formation of Vanadium Carbide via Plasma Electrolytic Saturation Method (pes)

    Science.gov (United States)

    Ghorbanian, Babak; Khoie, Seyed Mohammad Mousavi; Rasouli, Mahmood; Doodran, Ramona Javadi

    2016-02-01

    One of the most important hardening methods of tool steel is the use of carbide coatings. During this process, vanadium atoms diffuse the specimen’s surface at high temperature and reacts with the available carbon in steel and create vanadium carbide with high hardness. During the plasma electrolytic saturation (PES) process, the vanadium element diffuses with the help of plasma and increases up to around 950∘ as a result of the temperature, providing conditions for the creation of vanadium carbide. The best combination of electrolyte is 4g vanadium oxide and 50mL hydrochloric acid and different concern of sodium hydroxide. The results indicate that the formed coating is about 30μm. As the conductivity increases, the condition for diffusion is provided; however, with increase in the temperature, the diffusion decreases. The coating formation is observed in the current at 9-11 A and hardness of this coating is about 1400vickers.

  11. Thermal Expansion of Hafnium Carbide

    Science.gov (United States)

    Grisaffe, Salvatore J.

    1960-01-01

    Since hafnium carbide (HfC) has a melting point of 7029 deg. F, it may have many high-temperature applications. A literature search uncovered very little information about the properties of HfC, and so a program was initiated at the Lewis Research Center to determine some of the physical properties of this material. This note presents the results of the thermal expansion investigation. The thermal-expansion measurements were made with a Gaertner dilatation interferometer calibrated to an accuracy of +/- 1 deg. F. This device indicates expansion by the movement of fringes produced by the cancellation and reinforcement of fixed wave-length light rays which are reflected from the surfaces of two parallel quartz glass disks. The test specimens which separate these disks are three small cones, each approximately 0.20 in. high.

  12. Carbothermal synthesis of silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Janney, M.A.; Wei, G.C.; Kennedy, C.R.; Harris, L.A.

    1985-05-01

    Silicon carbide powders were synthesized from various silica and carbon sources by a carbothermal reduction process at temperatures between 1500 and 1600/sup 0/C. The silica sources were fumed silica, methyltrimethoxysilane, and microcrystalline quartz. The carbon sources were petroleum pitch, phenolic resin, sucrose, and carbon black. Submicron SiC powders were synthesized. Their morphologies included equiaxed loosely-bound agglomerates, equiaxed hard-shell agglomerates, and whiskers. Morphology changed with the furnace atmosphere (argon, nitrogen, or nitrogen-4% hydrogen). The best sintering was observed in SiC derived from the fumed-silica-pitch and fumed-silica-sucrose precursors. The poorest sintering was observed in SiC derived from microcrystalline quartz and carbon black. 11 refs., 16 figs., 10 tabs.

  13. Structural and electrical characterization of ohmic contacts to graphitized silicon carbide.

    Science.gov (United States)

    Maneshian, Mohammad H; Lin, Ming-Te; Diercks, David; Shepherd, Nigel D

    2009-12-09

    Titanium was deposited onto silicon carbide (6H-SiC) using the 248 nm line of an excimer laser in a vacuum of 10(-6) Torr, and ohmic contacts were formed by annealing the structure at approximately 1000 degrees C. Further anneals between 1350 and 1430 degrees C did not degrade the formed contacts, and Raman analysis confirmed that sublimation of silicon from the near surface layers of the silicon carbide between the contact pads resulted in graphene formation after 5 min, 1428 degrees C anneals. The graphene formation was accompanied by a significant enhancement of ohmic behavior, and, it was found to be sensitive to the temperature ramp-up rate and annealing time. High-resolution transmission electron microscopy showed that the interface between the metal and silicon carbide remained sharp and free of macroscopic defects even after 30 min, 1430 degrees C anneals. The interface was determined to be carbon rich by elemental analysis, which indicates metal carbide formation. The potential of this approach for achieving ohmic contacts and graphene formation on silicon carbide substrates is discussed. A mechanism for the sequential formation of ohmic contacts then graphene is proposed.

  14. Strength Reduction Method for Stability Analysis of Local Discontinuous Rock Mass with Iterative Method of Partitioned Finite Element and Interface Boundary Element

    Directory of Open Access Journals (Sweden)

    Tongchun Li

    2015-01-01

    element is proposed to solve the safety factor of local discontinuous rock mass. Slope system is divided into several continuous bodies and local discontinuous interface boundaries. Each block is treated as a partition of the system and contacted by discontinuous joints. The displacements of blocks are chosen as basic variables and the rigid displacements in the centroid of blocks are chosen as motion variables. The contact forces on interface boundaries and the rigid displacements to the centroid of each body are chosen as mixed variables and solved iteratively using the interface boundary equations. Flexibility matrix is formed through PFE according to the contact states of nodal pairs and spring flexibility is used to reflect the influence of weak structural plane so that nonlinear iteration is only limited to the possible contact region. With cohesion and friction coefficient reduced gradually, the states of all nodal pairs at the open or slip state for the first time are regarded as failure criterion, which can decrease the effect of subjectivity in determining safety factor. Examples are used to verify the validity of the proposed method.

  15. Study on the preparation and stability of uranium carbide samples for the determination of oxygen, hydrogen and nitrogen by fusion under high vacuum; Estudio sobre la preparacion y estabilidad de las muestras de carburo de uranio para la determinacion de oxigeno, hidrogeno y nitrogeno por fusion en alto vacio

    Energy Technology Data Exchange (ETDEWEB)

    Perez Garcia, M.

    1966-07-01

    In view of the high reactivity of uranium carbide, the method employed for the preparation of the sample for the analysis of its gas content: oxygen, hydrogen and nitrogen, has a decisive influence on the analytical results. The variation in the O{sub 2}, H{sub 2} and N{sub 2} content of the uranium carbide has been studied in this paper with the methods utilized for the sample preparation (grinding and cutting). (Author) 9 refs.

  16. Parametric Trends in the Combustion Stability Characteristics of a Single-Element Gas-Gas Rocket Engine

    Science.gov (United States)

    2013-12-01

    toroidal recirculation zone which promotes flame stabilization.16 For rocket applications swirl injectors are less sensitive to manufacturing defects and...were there are geometric changes. The mesh contains 5 of 22 American Institute of Aeronautics and Astronautics Figure 2: Geometric details of the

  17. Numerical modelling of suffusion by discrete element method: a new internal stability criterion based on mechanical behaviour of eroded soil

    Science.gov (United States)

    Abdoulaye Hama, Nadjibou; Ouahbi, Tariq; Taibi, Said; Souli, Hanène; Fleureau, Jean-Marie; Pantet, Anne

    2017-06-01

    Non-cohesive soils subjected to a flow may have a behavior in which fine particles migrate through the interstices of the solid skeleton formed by the large particles. This phenomenon is termed internal instability, internal erosion or suffusion, and can occur both in natural soil deposits and also in geotechnical structures such as dams, dikes or barrages. Internal instability of a granular material is its inability to prevent the loss of its fine particles under flow effect. It is geometrically possible if the fine particles can migrate through the pores of the coarse soil matrix and results in a change in its mechanical properties. In this work, we uses the three-dimensional Particle Flow Code (PFC3D/DEM) to study the stability/instability of granular materials and their mechanical behavior. Kenney and Lau criterion sets a safe boundary for engineering design. However, it tends to identify stable soils as unstable ones. The effects of instability and erosion, simulated by clipping fine particles from the grading distribution, on the mechanical behaviour of glass ball samples were analysed. The mechanical properties of eroded samples, in which erosion is simulated and gives a new approach for internal stability. A proposal for a new internal stability criterion is established, it is deduced from the analysis of relations between the mechanical behaviour and internal stability, including material contractance.

  18. Calcium carbide poisoning via food in childhood.

    Science.gov (United States)

    Per, Hüseyin; Kurtoğlu, Selim; Yağmur, Fatih; Gümüş, Hakan; Kumandaş, Sefer; Poyrazoğlu, M Hakan

    2007-02-01

    The fast ripening of fruits means they may contain various harmful properties. A commonly used agent in the ripening process is calcium carbide, a material most commonly used for welding purposes. Calcium carbide treatment of food is extremely hazardous because it contains traces of arsenic and phosphorous. Once dissolved in water, the carbide produces acetylene gas. Acetylene gas may affect the neurological system by inducing prolonged hypoxia. The findings are headache, dizziness, mood disturbances, sleepiness, mental confusion, memory loss, cerebral edema and seizures. We report the case of a previously healthy 5 year-old girl with no chronic disease history who was transferred to our Emergency Department with an 8-h history of coma and delirium. A careful history from her father revealed that the patient ate unripe dates treated with calcium carbide.

  19. Distinct Structural Elements Govern the Folding, Stability, and Catalysis in the Outer Membrane Enzyme PagP.

    Science.gov (United States)

    Iyer, Bharat Ramasubramanian; Mahalakshmi, Radhakrishnan

    2016-09-06

    The outer membrane enzyme PagP is indispensable for lipid A palmitoylation in Gram-negative bacteria and has been implicated in resistance to host immune defenses. PagP possesses an unusual structure for an integral membrane protein, with a highly dynamic barrel domain that is tilted with respect to the membrane normal. In addition, it contains an N-terminal amphipathic helix. Recent functional and structural studies have shown that these molecular factors are critical for PagP to carry out its function in the challenging environment of the bacterial outer membrane. However, the precise contributions of the N-helix to folding and stability and residues that can influence catalytic rates remain to be addressed. Here, we identify a sequence-dependent stabilizing role for the N-terminal helix of PagP in the measured thermodynamic stability of the barrel. Using chimeric barrel sequences, we show that the Escherichia coli PagP N-terminal helix confers 2-fold greater stability to the Salmonella typhimurium barrel. Further, we find that the W78F substitution in S. typhimurium causes a nearly 20-fold increase in the specific activity in vitro for the phospholipase reaction, compared to that of E. coli PagP. Here, phenylalanine serves as a key regulator of catalysis, possibly by increasing the reaction rate. Through coevolution analysis, we detect an interaction network between seemingly unrelated segments of this membrane protein. Exchanging the structural and functional features between homologous PagP enzymes from E. coli and S. typhimurium has provided us with an understanding of the molecular factors governing PagP stability and function.

  20. On the Role of Carbides in the Formation of Hydrocarbons from Deep Carbon

    Science.gov (United States)

    Vecht, A.

    2012-12-01

    The origin of hydrocarbons found in rocks has been a matter of dispute for over a century. Scientists of the former Soviet Union favoured an inorganic origin, while in the west an organic origin was thought the most likely. Both hypotheses may be reconciled by considering the origin of carbon compounds from the core upwards or from the Earth surface downwards. Carbides are the key to understanding the development and distribution of global carbon compounds. They are precursors in the formation of hydrocarbons. It has been estimated that the Earth's core is composed of between 2-4% carbon. It is found in metallic form and is substantially denser that the surrounding mantle. Wood has proposed that the inner core is a carbide probably iron carbide(1). This conclusion is consistent with studies of meteorites, shock waves and densities Carbides can be divided into four groups:- (a) Interstitial: -Ti, V, Cr, Zr, Nb, Hf, Ta and W. (b) Covalent:- B and Si (c) Intermediate:- Ti, V, Cr, Mn, Fe, Co and Ni. (d) Salt like:- Groups I, II, and III. Groups (a) (b) and (c) should be included as candidates for carbides found in the inner core. Such carbides are stable at high temperature and will react with water and/or oxygen to form hydrocarbons and CO or CO2 respectively., carbides can be described as examples of a 'reactive minerals' as we suggested in 2007(2). Carbides which are stable at high temperatures react with water to yield hydrocarbons. This points to an abiotic origin for a range of natural hydrocarbons. A detailed review by Cataldo(3) analysed the relevant evidence for biological vs. inorganic origins. He suggests that metal carbides when hydrolysed yield organic 'matter'. Amongst the carbides suggested are (Cr, Fe, Ni, V, Mn and Co}. These carbides are correlated to the relative abundance of these elements in the solar system. We propose similar reactions based on carbides of calcium and aluminium for the formation of methane hydrate. The reactions are expected to

  1. Comparative Evaluation of the Implant Made of Yttrium-partially Stabilized Zirconia and Pure Titanium on Stress Distribution by Anisotropic Finite Element Method

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The purpose of this research is to analyze and compare stress distribution patterns around dental implant made of pure titanium and yttrium-partial stabilized zirconia (YPSZ) in anisotropic versus isotropic finite element method under vertical and oblique loads. Although the properties of implant and crown were changed,similar stress distribution and close stress level were observed in two different implant finite element models. The stress values were a little lower in the YPSZ model. In the bone, anisotropy increased the stress values by 30%-70% in the isotropic cases. The YPSZ implant could be more valuable choice for implant because of esthetic requirement. Anisotropy had subtle, yet significant effects on the stress level.

  2. Selective etching of silicon carbide films

    Science.gov (United States)

    Gao, Di; Howe, Roger T.; Maboudian, Roya

    2006-12-19

    A method of etching silicon carbide using a nonmetallic mask layer. The method includes providing a silicon carbide substrate; forming a non-metallic mask layer by applying a layer of material on the substrate; patterning the mask layer to expose underlying areas of the substrate; and etching the underlying areas of the substrate with a plasma at a first rate, while etching the mask layer at a rate lower than the first rate.

  3. Advanced Ceramics for Use as Fuel Element Materials in Nuclear Thermal Propulsion Systems

    Science.gov (United States)

    Valentine, Peter G.; Allen, Lee R.; Shapiro, Alan P.

    2012-01-01

    With the recent start (October 2011) of the joint National Aeronautics and Space Administration (NASA) and Department of Energy (DOE) Advanced Exploration Systems (AES) Nuclear Cryogenic Propulsion Stage (NCPS) Program, there is renewed interest in developing advanced ceramics for use as fuel element materials in nuclear thermal propulsion (NTP) systems. Three classes of fuel element materials are being considered under the NCPS Program: (a) graphite composites - consisting of coated graphite elements containing uranium carbide (or mixed carbide), (b) cermets (ceramic/metallic composites) - consisting of refractory metal elements containing uranium oxide, and (c) advanced carbides consisting of ceramic elements fabricated from uranium carbide and one or more refractory metal carbides [1]. The current development effort aims to advance the technology originally developed and demonstrated under Project Rover (1955-1973) for the NERVA (Nuclear Engine for Rocket Vehicle Application) [2].

  4. Conservation of a Triple-Helix-Forming RNA Stability Element in Noncoding and Genomic RNAs of Diverse Viruses

    Directory of Open Access Journals (Sweden)

    Kazimierz T. Tycowski

    2012-07-01

    Full Text Available Abundant expression of the long noncoding (lnc PAN (polyadenylated nuclear RNA by the human oncogenic gammaherpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV depends on a cis-element called the expression and nuclear retention element (ENE. The ENE upregulates PAN RNA by inhibiting its rapid nuclear decay through triple-helix formation with the poly(A tail. Using structure-based bioinformatics, we identified six ENE-like elements in evolutionarily diverse viral genomes. Five are in double-stranded DNA viruses, including mammalian herpesviruses, insect polydnaviruses, and a protist mimivirus. One is in an insect picorna-like positive-strand RNA virus, suggesting that the ENE can counteract cytoplasmic as well as nuclear RNA decay pathways. Functionality of four of the ENEs was demonstrated by increased accumulation of an intronless polyadenylated reporter transcript in human cells. Identification of these ENEs enabled the discovery of PAN RNA homologs in two additional gammaherpesviruses, RRV and EHV2. Our findings demonstrate that searching for structural elements can lead to rapid identification of lncRNAs.

  5. 16-element photodiode array for the angular microdeflection detector and for stabilization of a laser radiation direction

    Science.gov (United States)

    Wegrzecki, Maciej; Piotrowski, Tadeusz; Bar, Jan; Dobrowolski, Rafał; Klimov, Andrii; Klos, Helena; Marchewka, Michał; Nieprzecki, Marek; Panas, Andrzej; Prokaryn, Piotr; Seredyński, Bartłomiej; Sierakowski, Andrzej; Słysz, Wojciech; Szmigiel, Dariusz; Zaborowski, Michal

    2016-12-01

    In this paper, the design and technology of two types of 16-element photodiode arrays is described. The arrays were developed by the ITE and are to be used in detection of microdeflection of laser radiation at the Institute of Metrology and Biomedical Engineering in the Faculty of Mechatronics of Warsaw University of Technology. The electrical and photoelectrical parameters of the arrays are presented.

  6. Combustion synthesis of novel boron carbide

    Science.gov (United States)

    Harini, R. Saai; Manikandan, E.; Anthonysamy, S.; Chandramouli, V.; Eswaramoorthy, D.

    2013-02-01

    The solid-state boron carbide is one of the hardest materials known, ranking third behind diamond and cubic boron nitride. Boron carbide (BxCx) enriched in the 10B isotope is used as a control rod material in the nuclear industry due to its high neutron absorption cross section and other favorable physico-chemical properties. Conventional methods of preparation of boron carbide are energy intensive processes accompanied by huge loss of boron. Attempts were made at IGCAR Kalpakkam to develop energy efficient and cost effective methods to prepare boron carbide. The products of the gel combustion and microwave synthesis experiments were characterized for phase purity by XRD. The carbide formation was ascertained using finger-print spectroscopy of FTIR. Samples of pyrolized/microwave heated powder were characterized for surface morphology using SEM. The present work shows the recent advances in understanding of structural and chemical variations in boron carbide and their influence on morphology, optical and vibrational property results discussed in details.

  7. Polymer-derived silicon carbide fibers with near-stoichiometric composition and low oxygen content

    Energy Technology Data Exchange (ETDEWEB)

    Sacks, M.D.; Scheiffele, G.W.; Saleem, M.; Staab, G.A.; Morrone, A.A.; Williams, T.J. [Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering

    1995-10-01

    Fine-diameter ({approximately} 10--15 {micro}m), polymer-derived SiC fibers were characterized. The average tensile strength of the fibers was {approximately} 2.8 GPa, although some lots had average strengths exceeding 3.5 GPa. Microstructure observations showed that fibers had fine grain sizes (mostly {approximately} 0.05--0.2 {micro}m), high densities ({approximately} 3.1--3.2 g/cm{sup 3}), and small residual pore sizes ({le} 0.1 {micro}m). Elemental analysis showed that fibers had near-stoichiometric composition. Electron and X-ray diffraction analyses indicated that fibers were primarily beta silicon carbide, with a minor amount of the alpha phase. A small amount of graphitic carbon was detected in some samples using high resolution transmission electron microscopy. The residual oxygen content in the fibers was {le} 0.1 wt%. Fibers exhibited good thermomechanical stability, as heat treatment at 1,800 C for 4 h in argon resulted in only an {approximately} 8% decrease in strength.

  8. Ferromagnetism in homogeneous (Al,Co)-codoped 4H-silicon carbides

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, X.H.; Han, J.C [Center for Composite Materials, Harbin Institute of Technology, Harbin 150080 (China); Zhou, J.G. [Canadian Light Source Inc., Saskatoon, Saskatchewan, Canada S7N 0X4 (Canada); Xin, C. [Department of Physics, Harbin Institute of Technology, Harbin 150080 (China); Zhang, Z.H. [Liaoning Key Materials Laboratory for Railway, School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028 (China); Song, B., E-mail: songbo@hit.edu.cn [Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080 (China)

    2014-08-01

    In view of the recent controversies on above room-temperature (RT) ferromagnetism (FM) in transition-metal (TM) doped silicon carbides (SiC), the present paper aims to shed some light on the natural origin of long-range magnetic order by investigating the (Al, Co)-doped 4H-SiC, both experimentally and theoretically. A combination of characterizations means including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray absorption near-edge structure spectroscopy (XANES) measurement eliminated the presence of any nanoclusters or secondary phases as the source of FM. X-ray absorption near-edge structure spectroscopy analyses provided convincing evidence that no secondary phases such as Co metallic clusters were present when Co and Al are homogeneously inserted in the SiC matrix. RT FM originates from a composite mechanism based on the Ruderman–Kittel–Kasuya–Yosida, and double-exchange interactions. The dopant Al is found to stabilize the crystal structure as well as show the experimental possibility of tuning the magnetization by codoping. - Highlights: • High-quality (Al, Co)-codoped 4H-SiC are synthesized via solid state reaction. • Doping element Al and Co are proved to be the origin for the observed magnetism. • Ferromagnetism may originate from a composite mechanism. • Annoying issues including SiC polytypes and magnetic secondary phases were solved.

  9. Evidence of amorphisation of B4C boron carbide under slow, heavy ion irradiation

    Science.gov (United States)

    Gosset, D.; Miro, S.; Doriot, S.; Victor, G.; Motte, V.

    2015-12-01

    Boron carbide is widely used either as armor-plate or neutron absorber. In both cases, a good structural stability is required. However, a few studies have shown amorphisation may occur in severe conditions. Hard impacts lead to the formation of amorphous bands. Some irradiations in electronic regime with H or He ions have also shown amorphisation of the material. Most authors however consider the structure is not drastically affected by irradiations in the ballistic regime. Here, we have irradiated at room temperature dense boron carbide pellets with Au 4 MeV ions, for which most of the damage is in the ballistic regime. This study is part of a program devoted to the behavior of boron carbide under irradiation. Raman observations have been performed after the irradiations together with transmission electron microscopy (TEM). Raman observations show a strong structural damage at moderate fluences (1014/cm2, about 0.1 dpa), in agreement with previous studies. On the other hand, TEM shows the structure remains crystalline up to 1015/cm2 then partially amorphises. The amorphisation is heterogeneous, with the formation of nanometric amorphous zones with increasing density. It then appears short range and long range disorder occurs at quite different damage levels. Further experiments are in progress aiming at studying the structural stability of boron carbide and isostructural materials (α-B, B6Si,…).

  10. The influence of contact ratio and its location on the primary stability of cementless total hip arthroplasty: A finite element analysis.

    Science.gov (United States)

    Reimeringer, M; Nuño, N

    2016-05-03

    Cementless hip stems are fixed to the surrounding bone by means of press-fit. To ensure a good press-fit, current surgical technique specifies an under-reaming of the bone cavity using successively larger broaches. Nevertheless, this surgical technique is inaccurate. Several studies show that the contact ratio (percentage of stem interface in contact with bone) achieved after surgery can vary between 20% and 95%. Therefore, this study aimed to investigate the influence of the contact ratio and its location on the primary stability of a cementless total hip arthroplasty using finite element analysis. A straight tapered femoral stem implanted in a composite bone was subjected to stair climbing. Micromotion of 7600 nodes at the stem-bone interface was computed for different configurations of contact ratios between 2% and 98%) along the hip stem. Considering the 15 configurations evaluated, the average micromotion ranges between 27μm and 54μm. The percentage of the porous interface of the stem having micromotion below 40μm that allows bone ingrowth range between 25-57%. The present numerical study shows that full contact (100%) between stem and bone is not necessary to obtain a good primary stability. The stem primary stability is influenced by both the contact ratio and its location. Several configurations with contact ratio lower than 100% and involving either the proximal or the cortical contact provide better primary stability than the full contact configuration. However, with contact ratio lower than 40%, the stem should be in contact with cortical bone to ensure a good primary stability.

  11. Structural characterization of “carbide-free” bainite in a Fe–0.2C–1.5Si–2.5Mn steel

    Energy Technology Data Exchange (ETDEWEB)

    Hofer, Christina, E-mail: christina.hofer@unileoben.ac.at [Department of Physical Metallurgy and Materials Testing, Montanuniversitaet Leoben, Franz-Josef-Straße 18, 8700 Leoben (Austria); Leitner, Harald [Böhler Edelstahl GmbH & Co KG, Mariazeller Straße 25, 8605 Kapfenberg (Austria); Winkelhofer, Florian [voestalpine Stahl Linz GmbH, voestalpine-Straße 3, 4020 Linz (Austria); Clemens, Helmut; Primig, Sophie [Department of Physical Metallurgy and Materials Testing, Montanuniversitaet Leoben, Franz-Josef-Straße 18, 8700 Leoben (Austria)

    2015-04-15

    Low-alloyed, low C containing carbide-free bainitic steels are attractive candidates for applications in the automotive industry due to their well-balanced combination of high strength and ductility achieved in an economic way. In this work, their complex microstructure consisting of a mixture of bainitic ferrite, austenite with different morphologies and stabilities, martensite, M/A constituent and a few carbides has been investigated with metallographic and high-resolution techniques. After specific isothermal heat treatments in a dilatometer, a combination of LePera and Nital etching was applied to distinguish between bainite and martensite. Site-specific atom probe tips were prepared by means of scanning electron microscopy, electron backscatter diffraction and focused ion beam, revealing that “carbide-free” bainite consists of C depleted bainitic ferrite, C enriched retained austenite and occasional ε-carbides. Furthermore, it was found that the M/A constituent is highly dislocated and mainly martensitic. Its C content is increased compared to the nominal composition, but below the values obtained for retained austenite, explaining the lower transformation resistance. - Highlights: • Detailed top-down characterization of low C “carbide-free” bainitic steel • APT of all constituents in “carbide-free” bainite • Identification of ε-carbide based on its C content determined by APT • M/A constituent is mainly martensitic with austenitic areas at the boundaries • Lower C content of M/A constituent explains its lower stability.

  12. Variational Multiscale Stabilization and p-adaptivity of High-Order Spectral Elements for the Convection-Diffusion Equation (Preprint)

    Science.gov (United States)

    2011-07-26

    Cottrell, and Bazilevs in [21], where NURBS were used as high-order basis functions, un- expected convergence to monotone results were obtained...methods by Canuto and coworkers in [17, 18, 19, 52], and later by Hughes and coworkers in [21] using non-uniform rational B-splines ( NURBS ). In this...Hughes, J. A. Cottrell, Y. Bazilevs, Isogeometric analysis: CAD, finite elements, NURBS , exact geometry and mesh refinement, Comput. Methods Appl

  13. Metamagnetism of η-carbide-type transition-metal carbides and nitrides

    Science.gov (United States)

    Waki, T.; Terazawa, S.; Umemoto, Y.; Tabata, Y.; Sato, K.; Kondo, A.; Kindo, K.; Nakamura, H.

    2011-09-01

    η-carbide-type transition-metal compounds include the frustrated stella quadran-gula lattice. Due to characteristics of the lattice, we expect subtle transitions between frustrated and non-frustrated states. Here, we report metamagnetic transitions newly found in η-carbide-type compounds Fe3W3C, Fe6W6C and Co6W6C.

  14. 有限元数值模拟分析采空区地基稳定性%On goaf foundation stability with finite element numeric simulation analysis

    Institute of Scientific and Technical Information of China (English)

    张德鹏

    2015-01-01

    基于开采沉陷的理论特征及规律,应用有限元模拟方法研究了采空区地基的稳定性,根据采空区实际情况,将某煤矿采空区剖面抽象为平面应变模型,以有限元模拟软件GeoStudio为工具进行模拟计算,研究了其应力应变规律和影响采空区地基稳定性的主要因素。%Based on the theoretic features and laws for the exploitation settlement,the paper adopts the finite element simulation methods to adopt the stability of the goaf foundation,regards the profile of the goaf of some coal mine as the plain strain model,undertakes the simulation calcula-tion by taking the finite element simulation software GeoStudio as the tool,and researches its strain law and main factors affecting the goaf founda-tion stability.

  15. Promotion of the Growth of Boron-Carbide Nanowires

    Science.gov (United States)

    Kranov, Yanko; Zhang, Daqing; McIlroy, David; Norton, Grant

    2000-03-01

    Boron carbide, is a wide bandgap semiconductor (2.1eV) with a high melting temperature in excess of 2400^circC. Initial studies indicate that nanowires of boron carbide approximately 25 ~30 μm in length and less than 100 nm in diameter can be grown by the technique of plasma enhanced chemical vapor deposition by a mode of the vapor-liquid-solid mechanism [1] at relatively low temperatures ( ~1150^circC). Through the use of boron based eutectics such as FeB, NiB and PtB nanowire growth at temperatures below 1150^circC. These metal borides have successively lower melting temperatures, respectively. In this paper we will discuss a simple technique for making submicron metal boride particles, as well as a simple means of depositing them onto a surface. In addition, the effect of droplet size on nanowire diameter and the stability of the size of the metal boride droplet during growth will be discussed. These studies demonstrate that the surface can be selectively seeded thereby controlling the location of the nanowires, i.e. select area deposition. Lastly, the techniques and materials used to grow boron carbide nanowires can easily be used to grow other types of nanowires, as well as carbon nanotubes. [1]. D. N. McIlroy, Daqing Zhang, Robert M. Cohen, J. Wharton, Yongjun Geng, M. Grant Norton, G. De Stasio, B.Gilbert, L.Perfetti, J.H.Streiff, B.Broocks and J.L. McHale, Phys. Rev. B 60 (1999) 4874

  16. Analysis of effort of carbides and austenite in austenitic cast steel cooled violently

    Directory of Open Access Journals (Sweden)

    J. Tuleja

    2010-01-01

    Full Text Available This work presents the analysis the effort of phases which are present in the austenitic cast steel Fe-Ni-Cr-C, applied for elements of technological instrumentation for carburising furnaces. The reduced stresses σred in the carbides and the austenitic matrix were determined in accordance with the assumed hypotheses of effort, on the basis of the structural stresses σx, σy, σz and σ1, σ2, σ3 calculated by the finite element method for two model location cases of the carbides towards the cast steel surface. The hypotheses referred to the crack condition were applied to evaluate the elastic carbide efforts, while for the elastic-plastic austenitic matrix - the hypotheses referred to the plasticity condition were used. There were compared the reduced stresses σred determined in accordance with various hypotheses and the correctness of their applying. It was demonstrated on the basis of the executed analysis of the effort that the carbides are destroyed only when they are not entirely surrounded by the austenitic matrix.

  17. Molybdenum Carbides, Active and In Situ Regenerable Catalysts in Hydroprocessing of Fast Pyrolysis Bio-Oil

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Jae-Soon; Zacher, Alan H.; Wang, Huamin; Olarte, Mariefel V.; Armstrong, Beth L.; Meyer, Harry M.; Soykal, I. Ilgaz; Schwartz, Viviane

    2016-06-16

    We assessed molybdenum carbides as a potential catalyst for fast pyrolysis bio-oil hydroprocessing. Currently, high catalyst cost, short catalyst lifetime, and lack of effective regeneration methods are hampering the development of this otherwise attractive renewable hydrocarbon technology. A series of metal-doped bulk Mo carbides were synthesized, characterized and evaluated in sequential low-temperature stabilization and high-temperature deoxygenation of a pine-derived bio-oil. During a typical 60-h run, Mo carbides were capable of upgrading raw bio-oil to a level suitable for direct insertion into the current hydrocarbon infrastructure with residual oxygen content and total acid number of upgraded oils below 2 wt% and 0.01 mg KOH g-1, respectively. The performance was shown to be sensitive to the type of metal dopant, Ni-doped Mo carbides outperforming Co-, Cu-, or Ca-doped counterparts; a higher Ni loading led to a superior catalytic performance. No bulk oxidation or other significant structural changes were observed. Besides the structural robustness, another attractive property of Mo carbides was in situ regenerability. The effectiveness of regeneration was demonstrated by successfully carrying out four consecutive 60-h runs with a reductive decoking between two adjacent runs. These results strongly suggest that Mo carbides are promising catalytic materials which could lead to a significant cost reduction in hydroprocessing bio-oils. This paper highlights areas for future research which will be needed to further understand carbide structure-function relationships and help design practical bio-oil upgrading catalysts based on Mo carbides.

  18. Accuracy and stability of a set of free-surface time-domain boundary element models based on B-splines

    Science.gov (United States)

    Büchmann, Bjarne

    2000-05-01

    An analysis is given for the accuracy and stability of some perturbation-based time-domain boundary element models (BEMs) with B-spline basis functions, solving hydrodynamic free-surface problems, including forward speed effects. The spatial convergence rate is found as a function of the order of the B-spline basis. It is shown that for all the models examined the mixed implicit-explicit Euler time integration scheme is correct to second order. Stability diagrams are found for models based on B-splines of orders third through to sixth for two different time integration schemes. The stability analysis can be regarded as an extension of the analysis by Vada and Nakos [Vada T, Nakos DE. Time marching schemes for ship motion simulations. In Proceedings of the 8th International Workshop on Water Waves and Floating Bodies, St. John's, Newfoundland, Canada, 1993; 155-158] to include B-splines of orders higher than three (piecewise quadratic polynomials) and to include finite water depth and a current at an oblique angle to the model grid. Copyright

  19. Heat Shock Protein 90 Modulates Lipid Homeostasis by Regulating the Stability and Function of Sterol Regulatory Element-binding Protein (SREBP) and SREBP Cleavage-activating Protein.

    Science.gov (United States)

    Kuan, Yen-Chou; Hashidume, Tsutomu; Shibata, Takahiro; Uchida, Koji; Shimizu, Makoto; Inoue, Jun; Sato, Ryuichiro

    2017-02-17

    Sterol regulatory element-binding proteins (SREBPs) are the key transcription factors that modulate lipid biosynthesis. SREBPs are synthesized as endoplasmic reticulum-bound precursors that require proteolytic activation in the Golgi apparatus. The stability and maturation of precursor SREBPs depend on their binding to SREBP cleavage-activating protein (SCAP), which escorts the SCAP-SREBP complex to the Golgi apparatus. In this study, we identified heat shock protein (HSP) 90 as a novel SREBP regulator that binds to and stabilizes SCAP-SREBP. In HepG2 cells, HSP90 inhibition led to proteasome-dependent degradation of SCAP-SREBP, which resulted in the down-regulation of SREBP target genes and the reduction in intracellular triglyceride and cholesterol levels. We also demonstrated in vivo that HSP90 inhibition decreased SCAP-SREBP protein, down-regulated SREBP target genes, and reduced lipids levels in mouse livers. We propose that HSP90 plays an indispensable role in SREBP regulation by stabilizing the SCAP-SREBP complex, facilitating the activation of SREBP to maintain lipids homeostasis.

  20. Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

    Science.gov (United States)

    Chaudhari, Pradip; Singh, Arvind; Topkar, Anita; Dusane, Rajiv

    2015-04-01

    In order to utilize the well established silicon detector technology for neutron detection application, a silicon based thermal neutron detector was fabricated by integrating a thin boron carbide layer as a neutron converter with a silicon PIN detector. Hot wire chemical vapor deposition (HWCVD), which is a low cost, low temperature process for deposition of thin films with precise thickness was explored as a technique for direct deposition of a boron carbide layer over the metalized front surface of the detector chip. The presence of B-C bonding and 10B isotope in the boron carbide film were confirmed by Fourier transform infrared spectroscopy and secondary ion mass spectrometry respectively. The deposition of HWCVD boron carbide layer being a low temperature process was observed not to cause degradation of the PIN detector. The response of the detector with 0.2 μm and 0.5 μm thick boron carbide layer was examined in a nuclear reactor. The pulse height spectrum shows evidence of thermal neutron response with signature of (n, α) reaction. The results presented in this article indicate that HWCVD boron carbide deposition technique would be suitable for low cost industrial fabrication of PIN based single element or 1D/2D position sensitive thermal neutron detectors.

  1. Generation and Characteristics of IV-VI transition Metal Nitride and Carbide Nanoparticles using a Reactive Mesoporous Carbon Nitride

    KAUST Repository

    Alhajri, Nawal Saad

    2016-02-22

    Interstitial nitrides and carbides of early transition metals in groups IV–VI exhibit platinum-like electronic structures, which make them promising candidates to replace noble metals in various catalytic reactions. Herein, we present the preparation and characterization of nano-sized transition metal nitries and carbides of groups IV–VI (Ti, V, Nb, Ta, Cr, Mo, and W) using mesoporous graphitic carbon nitride (mpg-C3N4), which not only provides confined spaces for restricting primary particle size but also acts as a chemical source of nitrogen and carbon. We studied the reactivity of the metals with the template under N2 flow at 1023 K while keeping the weight ratio of metal to template constant at unity. The produced nanoparticles were characterized by powder X-ray diffraction, CHN elemental analysis, nitrogen sorption, X-ray photoelectron spectroscopy, and transmission electron microscopy. The results show that Ti, V, Nb, Ta, and Cr form nitride phases with face centered cubic structure, whereas Mo and W forme carbides with hexagonal structures. The tendency to form nitride or carbide obeys the free formation energy of the transition metal nitrides and carbides. This method offers the potential to prepare the desired size, shape and phase of transition metal nitrides and carbides that are suitable for a specific reaction, which is the chief objective of materials chemistry.

  2. Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhari, Pradip, E-mail: pradipcha@gmail.com [Semiconductor Thin Films and Plasma Processing Laboratory, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai – 400076 (India); Singh, Arvind, E-mail: arvindsingh1884@gmail.com [Electronics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085 (India); Topkar, Anita, E-mail: anita.topkar@gmail.com [Electronics Division, Bhabha Atomic Research Centre, Trombay, Mumbai – 400085 (India); Dusane, Rajiv, E-mail: rodusane@iitb.ac.in [Semiconductor Thin Films and Plasma Processing Laboratory, Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai – 400076 (India)

    2015-04-11

    In order to utilize the well established silicon detector technology for neutron detection application, a silicon based thermal neutron detector was fabricated by integrating a thin boron carbide layer as a neutron converter with a silicon PIN detector. Hot wire chemical vapor deposition (HWCVD), which is a low cost, low temperature process for deposition of thin films with precise thickness was explored as a technique for direct deposition of a boron carbide layer over the metalized front surface of the detector chip. The presence of B-C bonding and {sup 10}B isotope in the boron carbide film were confirmed by Fourier transform infrared spectroscopy and secondary ion mass spectrometry respectively. The deposition of HWCVD boron carbide layer being a low temperature process was observed not to cause degradation of the PIN detector. The response of the detector with 0.2 µm and 0.5 µm thick boron carbide layer was examined in a nuclear reactor. The pulse height spectrum shows evidence of thermal neutron response with signature of (n, α) reaction. The results presented in this article indicate that HWCVD boron carbide deposition technique would be suitable for low cost industrial fabrication of PIN based single element or 1D/2D position sensitive thermal neutron detectors.

  3. Ubiquitous Chromatin Opening Elements (UCOEs) effect on transgene position and expression stability in CHO cells following methotrexate (MTX) amplification.

    Science.gov (United States)

    Betts, Zeynep; Dickson, Alan J

    2016-03-01

    The requirement for complex therapeutic proteins has resulted in mammalian cells, especially CHO cells, being the dominant host for recombinant protein manufacturing. In creating recombinant CHO cell lines, the expression vectors integrate into various parts of the genome leading to variable levels of expression and stability of protein production. This makes mammalian cell line development a long and laborious process. Therefore, with the intention to accelerate process development of recombinant protein production in CHO systems, UCOEs are utilized to diminish instability of production by maintaining an open chromatin surrounding in combination with MTX amplification. Chromosome painting and FISH analysis were performed to provide detailed molecular evaluation on the location of amplified genes and its relationship to the productivity and stability of the amplified cell lines. In summary, cell lines generated with vectors containing UCOEs retained stable GFP expression with MTX present (but instability was observed in the absence of MTX). UCOE cell lines displayed a higher frequency of integration into >1 chromosome than non-UCOE group. Cell populations were more homogenous in terms of transgene location at the end of Long-term culture (LTC). Overall our findings suggest variation in eGFP fluorescence may be attributed to changes in transgene integration profile over LTC.

  4. Tungsten carbide nanoparticles as efficient cocatalysts for photocatalytic overall water splitting

    KAUST Repository

    Garcia Esparza, Angel T.

    2012-12-17

    Tungsten carbide exhibits platinum-like behavior, which makes it an interesting potential substitute for noble metals in catalytic applications. Tungsten carbide nanocrystals (≈5 nm) are directly synthesized through the reaction of tungsten precursors with mesoporous graphitic C3N 4 (mpg-C3N4) as the reactive template in a flow of inert gas at high temperatures. Systematic experiments that vary the precursor compositions and temperatures used in the synthesis selectively generate different compositions and structures for the final nanocarbide (W 2C or WC) products. Electrochemical measurements demonstrate that the WC phase with a high surface area exhibits both high activity and stability in hydrogen evolution over a wide pH range. The WC sample also shows excellent hydrogen oxidation activity, whereas its activity in oxygen reduction is poor. These tungsten carbides are successful cocatalysts for overall water splitting and give H2 and O2 in a stoichiometric ratio from H 2O decomposition when supported on a Na-doped SrTiO3 photocatalyst. Herein, we present tungsten carbide (on a small scale) as a promising and durable catalyst substitute for platinum and other scarce noble-metal catalysts in catalytic reaction systems used for renewable energy generation. Platinum replacement: The phase-controlled synthesis of tungsten carbide nanoparticles from the nanoconfinement of a mesoporous graphite C 3N4 (mpg-C3N4) reactive template is shown. The nanomaterials catalyze hydrogen evolution/oxidation reactions, but are inactive in the oxygen reduction reaction. Tungsten carbide is an effective cocatalyst for photocatalytic overall water splitting (see picture). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. QM/MD simulation of SWNT nucleation on transition-metal carbide nanoparticles.

    Science.gov (United States)

    Page, Alister J; Yamane, Honami; Ohta, Yasuhito; Irle, Stephan; Morokuma, Keiji

    2010-11-10

    The mechanism and kinetics of single-walled carbon nanotube (SWNT) nucleation from Fe- and Ni-carbide nanoparticle precursors have been investigated using quantum chemical molecular dynamics (QM/MD) methods. The dependence of the nucleation mechanism and its kinetics on environmental factors, including temperature and metal-carbide carbon concentration, has also been elucidated. It was observed that SWNT nucleation occurred via three distinct stages, viz. the precipitation of the carbon from the metal-carbide, the formation of a "surface/subsurface" carbide intermediate species, and finally the formation of a nascent sp(2)-hybidrized carbon structure supported by the metal catalyst. The SWNT cap nucleation mechanism itself was unaffected by carbon concentration and/or temperature. However, the kinetics of SWNT nucleation exhibited distinct dependences on these same factors. In particular, SWNT nucleation from Ni(x)C(y) nanoparticles proceeded more favorably compared to nucleation from Fe(x)C(y) nanoparticles. Although SWNT nucleation from Fe(x)C(y) and Ni(x)C(y) nanoparticle precursors occurred via an identical route, the ultimate outcomes of these processes also differed substantially. Explicitly, the Ni(x)-supported sp(2)-hybridized carbon structures tended to encapsulate the catalyst particle itself, whereas the Fe(x)-supported structures tended to form isolated SWNT cap structures on the catalyst surface. These differences in SWNT nucleation kinetics were attributed directly to the relative strengths of the metal-carbon interaction, which also dictates the precipitation of carbon from the nanoparticle bulk and the longevity of the resultant surface/subsurface carbide species. The stability of the surface/subsurface carbide was also influenced by the phase of the nanoparticle itself. The observations agree well with experimentally available data for SWNT growth on iron and nickel catalyst particles.

  6. Mercury contamination - Amalgamate (contract with NFS and ADA). Stabilize Elemental Mercury Wastes. Mixed Waste Focus Area. OST Reference Number 1675

    Energy Technology Data Exchange (ETDEWEB)

    None, None

    1999-09-01

    Through efforts led by the Mixed Waste Focus Area (MWFA) and its Mercury Working Group (HgWG), the inventory of bulk elemental mercury contaminated with radionuclides stored at various U. S. Department of Energy (DOE) sites is thought to be approximately 16 m3 (Conley et al. 1998). At least 19 different DOE sites have this type of mixed low-level waste in their storage facilities. The U. S. Environmental Protection Agency (EPA) specifies amalgamation as the treatment method for radioactively contaminated elemental mercury. Although the chemistry of amalgamation is well known, the practical engineering of a sizable amalgamation process has not been tested (Tyson 1993). To eliminate the existing DOE inventory in a reasonable timeframe, scaleable equipment is needed that can: produce waste forms that meet the EPA definition of amalgamation, produce waste forms that pass the EPA Toxicity Characteristic Leaching Procedure (TCLP) limit of 0.20 mg/L, limit mercury vapor concentrations during processing to below the Occupational Safety and Health Administration’s (OSHA) 8-hour worker exposure limit (50 mg/m3) for mercury, and perform the above economically.

  7. Mercury contamination - Amalgamate (contract with NFS and ADA). Stabilize Elemental Mercury Wastes. Mixed Waste Focus Area. OST Reference Number 1675

    Energy Technology Data Exchange (ETDEWEB)

    None, None

    1999-09-01

    Through efforts led by the Mixed Waste Focus Area (MWFA) and its Mercury Working Group (HgWG), the inventory of bulk elemental mercury contaminated with radionuclides stored at various U. S. Department of Energy (DOE) sites is thought to be approximately 16 m3 (Conley et al. 1998). At least 19 different DOE sites have this type of mixed low-level waste in their storage facilities. The U. S. Environmental Protection Agency (EPA) specifies amalgamation as the treatment method for radioactively contaminated elemental mercury. Although the chemistry of amalgamation is well known, the practical engineering of a sizable amalgamation process has not been tested (Tyson 1993). To eliminate the existing DOE inventory in a reasonable timeframe, scaleable equipment is needed that can: produce waste forms that meet the EPA definition of amalgamation, produce waste forms that pass the EPA Toxicity Characteristic Leaching Procedure (TCLP) limit of 0.20 mg/L, limit mercury vapor concentrations during processing to below the Occupational Safety and Health Administration’s (OSHA) 8-hour worker exposure limit (50 mg/m3) for mercury, and perform the above economically.

  8. Direct multielement trace analyses of silicon carbide powders by spark ablation simultaneous inductively coupled plasma optical emission spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Kiera, Arne F.; Schmidt-Lehr, Sebastian; Song, Ming [Institute for Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg (Germany); Bings, Nicolas H. [Institute for Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg (Germany)], E-mail: bings@chemie.uni-hamburg.de; Broekaert, Jose A.C. [Institute for Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg (Germany)

    2008-02-15

    A procedure for the direct analysis of silicon carbide powders (SiC) by simultaneous detection inductively coupled plasma optical emission spectrometry using a Spectro-CIROS{sup TM} spectrometer (CCD-ICP-OES) and a novel spark ablation system Spectro-SASSy (SA) as sample introduction technique is described. The sample preparation procedure for SA of non-conducting material is based on mixing the sample powders with a conducting matrix, in this case copper and briquetting pellets. Pressing time, pressure and mixing ratio are shown to be important parameters of the pelleting technique with respect to their mechanical stability for the reliability of the analysis results. A mixing ratio of 0.2 g +0.6 g for SiC and Cu, a pressure of 10 t cm{sup -2} and a pressing time of 8 min have been found optimum. It has also been shown that the spark parameters selected are crucial for uniform volatilization. Electron probe micrographs of the burning spots and the analytical signal magnitude showed that a rather hard spark at 100 Hz was optimum. The determination of trace elements in silicon carbide powders is demonstrated using a calibration based on the addition of standard solutions. For Al, Ti, V, Mn and Fe detection limits in the lower {mu}g g{sup -1} range can be achieved. Internal standardization with Y in combination with the addition of standard solutions allows relative standard deviations in the range of 4 to 24% for concentration levels of the order of 3 to 350 {mu}g g{sup -1}.

  9. Insertion of core CpG island element into human CMV promoter for enhancing recombinant protein expression stability in CHO cells.

    Science.gov (United States)

    Mariati; Yeo, Jessna H M; Koh, Esther Y C; Ho, Steven C L; Yang, Yuansheng

    2014-01-01

    The human cytomegalovirus promoter (hCMV) is susceptible to gene silencing in CHO cells, most likely due to epigenetic events, such as DNA methylation and histone modifications. The core CpG island element (IE) from the hamster adenine phosphoribosyltransferase gene has been shown to prevent DNA methylation. A set of modified hCMV promoters was developed by inserting one or two copies of IE in either forward or reverse orientations either upstream of the hCMV enhancer, between the enhancer and core promoter (CP), or downstream of the CP. The modified hCMV with one copy of IE inserted between the enhancer and core promoter in reverse orientation (MR1) was most effective at enhancing expression stability without compromising expression level when compared with the wild-type (WT) hCMV. A third of 18 EGFP expressing clones generated using MR1 retained 70% of their starting expression level after 8 weeks of culture in the absence of selection pressure, while none of 18 WT hCMV generated clones had expression above 50%. MR1 also improved antibody expression stability of methotrexate (MTX) amplified CHO cell lines. Stably transfected pools generated using MR1 maintained 62% of their original monoclonal antibody titer after 8 weeks of culture in the absence of MTX, compared to only 37% for WT hCMV pools. Low levels of CpG methylation within both WT hCMV and MR1 were observed in all the analyzed cell lines and the methylation levels did not correlate to the expression stability, suggesting IE enhances expression stability by other mechanisms other than preventing methylation. © 2014 American Institute of Chemical Engineers.

  10. High capacitance of coarse-grained carbide derived carbon electrodes

    Science.gov (United States)

    Dyatkin, Boris; Gogotsi, Oleksiy; Malinovskiy, Bohdan; Zozulya, Yuliya; Simon, Patrice; Gogotsi, Yury

    2016-02-01

    We report exceptional electrochemical properties of supercapacitor electrodes composed of large, granular carbide-derived carbon (CDC) particles. Using a titanium carbide (TiC) precursor, we synthesized 70-250 μm sized particles with high surface area and a narrow pore size distribution. Electrochemical cycling of these coarse-grained powders defied conventional wisdom that a small particle size is strictly required for supercapacitor electrodes and allowed high charge storage densities, rapid transport, and good rate handling ability. The material showcased capacitance above 100 F g-1 at sweep rates as high as 250 mV s-1 in organic electrolyte. 250-1000 micron thick dense CDC films with up to 80 mg cm-2 loading showed superior areal capacitances. The material significantly outperformed its activated carbon counterpart in organic electrolytes and ionic liquids. Furthermore, large internal/external surface ratio of coarse-grained carbons allowed the resulting electrodes to maintain high electrochemical stability up to 3.1 V in ionic liquid electrolyte. In addition to presenting novel insights into the electrosorption process, these coarse-grained carbons offer a pathway to low-cost, high-performance implementation of supercapacitors in automotive and grid-storage applications.

  11. 薄壁构件整体稳定性的有限元模拟%Finite element modelling of thin-walled members in overall stability analysis

    Institute of Scientific and Technical Information of China (English)

    张磊; 童根树

    2011-01-01

    In the overall stability analysis of thin-walled members employing the general purpose finite element (FE) softwares, the members are generally modelled using the thin-walled beam elements or the thin shell elements. The modelling details of these two FE models were presented, and a new thin shell element model, capable of prohibiting the local buckling modes in the overall buckling analysis, was proposed. The two types of FE models were then adopted into the buckling analysis of thin-walled members, including the beams and columns with doubly and singly symmetric sections, beam-columns, tapered beams. The comparisons of the results from FE analyses, analytical solutions and literature show that the proposed thin shell element model is superior to the existing models of this type; the thin-walled beam element of ANSYS is not applicable to the flexural-torsional buckling analysis of thin-walled beams and beam-columns of mono-symmetric section, and significant error may arise in buckling analysis of tapered beams using this element. The results from the presented shell element model can also be used as the benchmark results in verifying the buckling theory of thin-walled members. The outcome of this study may be helpful for modelling thin-walled members in overall stability analysis using general FE packages, not limited to ANSYS.%对薄壁构件整体稳定性分析中的薄壁梁单元和壳体单元两种有限元模型的特点进行了讨论,并提出一种新的适用于薄壁构件整体稳定分析的壳体单元模型,该模型可以有效消除各种局部屈曲模态的影响.采用通用有限元软件ANSYS,分别利用壳体单元模型和薄壁梁单元模型,分析了双轴对称截面梁、单轴对称截面梁、轴心受压构件、压弯构件和变截面梁的稳定性,通过与经典解或已有研究结果的比较对有限元模型的可靠性以及存在的问题进行了讨论.通过分析,发现ANSYS的薄壁梁单元模型不能用于分

  12. Genesis Silicon Carbide Concentrator Target 60003 Preliminary Ellipsometry Mapping Results

    Science.gov (United States)

    Calaway, M. J.; Rodriquez, M. C.; Stansbery, E. K.

    2007-01-01

    The Genesis concentrator was custom designed to focus solar wind ions primarily for terrestrial isotopic analysis of O-17/O-16 and O-18/O-16 to +/-1%, N-15/N-14 to +/-1%, and secondarily to conduct elemental and isotopic analysis of Li, Be, and B. The circular 6.2 cm diameter concentrator target holder was comprised of four quadrants of highly pure semiconductor materials that included one amorphous diamond-like carbon, one C-13 diamond, and two silicon carbide (SiC). The amorphous diamond-like carbon quadrant was fractured upon impact at Utah Test and Training Range (UTTR), but the remaining three quadrants survived fully intact and all four quadrants hold an important collection of solar wind. The quadrants were removed from the target holder at NASA Johnso n Space Center Genesis Curation Laboratory in April 2005, and have been housed in stainless steel containers under continual nitrogen purge since time of disintegration. In preparation for allocation of a silicon carbide target for oxygen isotope analyses at UCLA, the two SiC targets were photographed for preliminary inspection of macro particle contamination from the hard non-nominal landing as well as characterized by spectroscopic ellipsometry to evaluate thin film contamination. This report is focused on Genesis SiC target sample number 60003.

  13. PIXE characterization of by-products resulting from the zinc recycling of industrial cemented carbides

    Energy Technology Data Exchange (ETDEWEB)

    Freemantle, C.S. [School of Chemical & Metallurgical Engineering and DST-NRF Centre of Excellence in Strong Materials, University of the Witwatersrand, P/Bag 3, Wits 2050 (South Africa); Pilot Tools (Pty) (Ltd), P.O. Box 27420, Benrose 2011 (South Africa); Sacks, N. [School of Chemical & Metallurgical Engineering and DST-NRF Centre of Excellence in Strong Materials, University of the Witwatersrand, P/Bag 3, Wits 2050 (South Africa); Topic, M. [iThemba LABS, National Research Foundation, P.O. Box 722, Somerset West 7129 (South Africa); Pineda-Vargas, C.A. [iThemba LABS, National Research Foundation, P.O. Box 722, Somerset West 7129 (South Africa); Faculty of Health & Wellness Sciences, CPUT, Bellville (South Africa)

    2015-11-15

    By-product materials of the widely used zinc recycling process of cemented carbides have been studied. Scanning electron microscopy and micro-PIXE techniques have identified elemental concentrations, distributions and purity of by-product materials from an industrial zinc recycling plant. Cobalt surface enrichment, lamellar microstructures of varying composition, including alternating tungsten carbide (WC) grains and globular cobalt, and regions of excess zinc contamination were found in materials with incomplete zinc penetration. Liquid Co–Zn formation occurred above 72 wt.% Zn at the furnace temperature of 930 °C, and was extracted towards the surface of poorly zinc infiltrated material, primarily by the vacuum used for zinc distillation. Surface enrichment was not observed in material that was zinc infiltrated to the sample center, which was more friable and exhibited more homogeneous porosity and elemental concentrations. The result of incomplete zinc infiltration was an enriched surface zone of up to 60 wt.% Co, compared to an original sample composition of ∼10–15 wt.% Co. The impact on resulting powders could be higher or inhomogeneous cobalt content, as well as unacceptably high zinc concentrations. PIXE has proven it can be a powerful technique for solving industrial problems in the cemented carbide cutting tool industry, by identifying trace elements and their locations (such as Zn to 0.1 wt.% accuracy), as well as the distribution of major elements within WC–Co materials.

  14. PIXE characterization of by-products resulting from the zinc recycling of industrial cemented carbides

    Science.gov (United States)

    Freemantle, C. S.; Sacks, N.; Topic, M.; Pineda-Vargas, C. A.

    2015-11-01

    By-product materials of the widely used zinc recycling process of cemented carbides have been studied. Scanning electron microscopy and micro-PIXE techniques have identified elemental concentrations, distributions and purity of by-product materials from an industrial zinc recycling plant. Cobalt surface enrichment, lamellar microstructures of varying composition, including alternating tungsten carbide (WC) grains and globular cobalt, and regions of excess zinc contamination were found in materials with incomplete zinc penetration. Liquid Co-Zn formation occurred above 72 wt.% Zn at the furnace temperature of 930 °C, and was extracted towards the surface of poorly zinc infiltrated material, primarily by the vacuum used for zinc distillation. Surface enrichment was not observed in material that was zinc infiltrated to the sample center, which was more friable and exhibited more homogeneous porosity and elemental concentrations. The result of incomplete zinc infiltration was an enriched surface zone of up to 60 wt.% Co, compared to an original sample composition of ∼10-15 wt.% Co. The impact on resulting powders could be higher or inhomogeneous cobalt content, as well as unacceptably high zinc concentrations. PIXE has proven it can be a powerful technique for solving industrial problems in the cemented carbide cutting tool industry, by identifying trace elements and their locations (such as Zn to 0.1 wt.% accuracy), as well as the distribution of major elements within WC-Co materials.

  15. Theoretical investigation of nano zirconium carbide sheet: A study of NMR, NBO, EPR and Polar

    Directory of Open Access Journals (Sweden)

    Roya Rouhani

    2015-09-01

    Full Text Available In this work, we have focused on the zirconium carbide (ZrC sheet. The result exhibited that ZrC exhibits various outstanding physical and chemical properties, such as high hardness (25 Gpa, high melting point (3420°C, high corrosion and wear resistance, solid-state phase stability as well as chemical stability. Hence, ZrC has been considered a good potential material for ultra-high temperature applications. Applications range from cutting tools, grinding wheels and abrasives for mechanical as well as structural components in chemical and electronic industries. Abinitio calculation was carried out for Zirconium carbide sheet (ZrC using Gaussian 09 program for the first time (Fig 1. We choose B3LYP for calculating natural bond orbital (NBO, Nuclear magnetic resonance (NMR, Electron paramagnetic resonance (EPR and polar.

  16. Multiple phases of molybdenum carbide as electrocatalysts for the hydrogen evolution reaction.

    Science.gov (United States)

    Wan, Cheng; Regmi, Yagya N; Leonard, Brian M

    2014-06-16

    Molybdenum carbide has been proposed as a possible alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Previous studies were limited to only one phase, β-Mo2C with an Fe2N structure. Here, four phases of Mo-C were synthesized and investigated for their electrocatalytic activity and stability for HER in acidic solution. All four phases were synthesized from a unique amine-metal oxide composite material including γ-MoC with a WC type structure which was stabilized for the first time as a phase pure nanomaterial. X-ray photoelectron spectroscopy (XPS) and valence band studies were also used for the first time on γ-MoC. γ-MoC exhibits the second highest HER activity among all four phases of molybdenum carbide, and is exceedingly stable in acidic solution.

  17. Surface science and electrochemical studies of metal-modified carbides for fuel cells and hydrogen production

    Science.gov (United States)

    Kelly, Thomas Glenn

    Carbides of the early transition metals have emerged as low-cost catalysts that are active for a wide range of reactions. The surface chemistry of carbides can be altered by modifying the surface with small amounts of admetals. These metal-modified carbides can be effective replacements for Pt-based bimetallic systems, which suffer from the drawbacks of high cost and low thermal stability. In this dissertation, metal-modified carbides were studied for reactions with applications to renewable energy technologies. It is demonstrated that metal-modified carbides possess high activity for alcohol reforming and electrochemical hydrogen production. First, the surface chemistry of carbides towards alcohol decomposition is studied using density functional theory (DFT) and surface science experiments. The Vienna Ab initio Simulation Package (VASP) was used to calculate the binding energies of alcohols and decomposition intermediates on metal-modified carbides. The calculated binding energies were then correlated to reforming activity determined experimentally using temperature programmed desorption (TPD). In the case of methanol decomposition, it was found that tungsten monocarbide (WC) selectively cleaved the C-O bond to produce methane. Upon modifying the surface with a single layer of metal such as Ni, Pt, or Rh, the selectivity shifted towards scission of the C-H bonds while leaving the C-O bond intact, producing carbon monoxide (CO) and H2. High resolution energy loss spectroscopy (HREELS) was used to examine the bond breaking sequence as a function of temperature. From HREELS, it was shown that the surfaces followed an activity trend of Rh > Ni > Pt. The Au-modified WC surface possessed too low of a methanol binding energy, and molecular desorption of methanol was the most favorable pathway on this surface. Next, the ability of Rh-modified WC to break the C-C bond of C2 and C3 alcohols was demonstrated. HREELS showed that ethanol decomposed through an acetaldehyde

  18. Ionisation Potentials of Metal Carbide Clusters

    Science.gov (United States)

    Dryza, Viktoras; Addicoat, M.; Gascooke, Jason; Buntine, Mark; Metha, Gregory

    2006-03-01

    Photo-Ionisation Efficiency (PIE) experiments have been performed on gas phase niobium and tantalum carbide clusters to determine their ionisation potentials (IPs). For TanCm (n = 3-4, m = 0-4) clusters an oscillatory behaviour is observed such that clusters with an odd number of carbon atoms have higher IPs and clusters with an even number of carbons have lower IPs. Excellent agreement is found with relative IPs calculated using density functional theory for the lowest energy structures, which are consistent with the development of a 2x2x2 face-centred nanocrystal. For the niobium carbide clusters we observe the species Nb4C5 and Nb4C6. Initial calculations suggest that these clusters contain carbon-carbon bonding. Interestingly, the stoichiometry for Nb4C6 is half that of a metcar, M8C12. Preliminary data will also be shown on bimetallic-carbide clusters.

  19. Fabrication of thorium bearing carbide fuels

    Science.gov (United States)

    Gutierrez, Rueben L.; Herbst, Richard J.; Johnson, Karl W. R.

    1981-01-01

    Thorium-uranium carbide and thorium-plutonium carbide fuel pellets have been fabricated by the carbothermic reduction process. Temperatures of 1750.degree. C. and 2000.degree. C. were used during the reduction cycle. Sintering temperatures of 1800.degree. C. and 2000.degree. C. were used to prepare fuel pellet densities of 87% and >94% of theoretical, respectively. The process allows the fabrication of kilogram quantities of fuel with good reproducibility of chemicals and phase composition. Methods employing liquid techniques that form carbide microspheres or alloying-techniques which form alloys of thorium-uranium or thorium-plutonium suffer from limitation on the quantities processed of because of criticality concerns and lack of precise control of process conditions, respectively.

  20. Carbides composite surface layers produced by (PTA)

    Energy Technology Data Exchange (ETDEWEB)

    Tajoure, Meloud, E-mail: Tajoore2000@yahoo.com [MechanicalEng.,HIHM,Gharian (Libya); Tajouri, Ali, E-mail: Tajouri-am@yahoo.com, E-mail: dr.mokhtarphd@yahoo.com; Abuzriba, Mokhtar, E-mail: Tajouri-am@yahoo.com, E-mail: dr.mokhtarphd@yahoo.com [Materials and Metallurgical Eng., UOT, Tripoli (Libya); Akreem, Mosbah, E-mail: makreem@yahoo.com [Industrial Research Centre,Tripoli (Libya)

    2013-12-16

    The plasma transferred arc technique was applied to deposit a composite layer of nickel base with tungsten carbide in powder form on to surface of low alloy steel 18G2A type according to polish standard. Results showed that, plasma transferred arc hard facing process was successfully conducted by using Deloro alloy 22 plus tungsten carbide powders. Maximum hardness of 1489 HV and minimum dilution of 8.4 % were achieved by using an arc current of 60 A. However, when the current was further increased to 120 A and the dilution increases with current increase while the hardness decreases. Microstructure of the nickel base deposit with tungsten carbide features uniform distribution of reinforcement particles with regular grain shape half - dissolved in the matrix.

  1. Mechanical Properties of Crystalline Silicon Carbide Nanowires.

    Science.gov (United States)

    Zhang, Huan; Ding, Weiqiang; Aidun, Daryush K

    2015-02-01

    In this paper, the mechanical properties of crystalline silicon carbide nanowires, synthesized with a catalyst-free chemical vapor deposition method, were characterized with nanoscale tensile testing and mechanical resonance testing methods inside a scanning electron microscope. Tensile testing of individual silicon carbide nanowire was performed to determine the tensile properties of the material including the tensile strength, failure strain and Young's modulus. The silicon carbide nanowires were also excited to mechanical resonance in the scanning electron microscope vacuum chamber using mechanical excitation and electrical excitation methods, and the corresponding resonance frequencies were used to determine the Young's modulus of the material according to the simple beam theory. The Young's modulus values from tensile tests were in good agreement with the ones obtained from the mechanical resonance tests.

  2. Silicon carbide, an emerging high temperature semiconductor

    Science.gov (United States)

    Matus, Lawrence G.; Powell, J. Anthony

    1991-01-01

    In recent years, the aerospace propulsion and space power communities have expressed a growing need for electronic devices that are capable of sustained high temperature operation. Applications for high temperature electronic devices include development instrumentation within engines, engine control, and condition monitoring systems, and power conditioning and control systems for space platforms and satellites. Other earth-based applications include deep-well drilling instrumentation, nuclear reactor instrumentation and control, and automotive sensors. To meet the needs of these applications, the High Temperature Electronics Program at the Lewis Research Center is developing silicon carbide (SiC) as a high temperature semiconductor material. Research is focussed on developing the crystal growth, characterization, and device fabrication technologies necessary to produce a family of silicon carbide electronic devices and integrated sensors. The progress made in developing silicon carbide is presented, and the challenges that lie ahead are discussed.

  3. Titanium carbide nanocrystals in circumstellar environments.

    Science.gov (United States)

    von Helden, G; Tielens, A G; van Heijnsbergen, D; Duncan, M A; Hony, S; Waters, L B; Meijer, G

    2000-04-14

    Meteorites contain micrometer-sized graphite grains with embedded titanium carbide grains. Although isotopic analysis identifies asymptotic giant branch stars as the birth sites of these grains, there is no direct observational identification of these grains in astronomical sources. We report that infrared wavelength spectra of gas-phase titanium carbide nanocrystals derived in the laboratory show a prominent feature at a wavelength of 20.1 micrometers, which compares well to a similar feature in observed spectra of postasymptotic giant branch stars. It is concluded that titanium carbide forms during a short (approximately 100 years) phase of catastrophic mass loss (>0.001 solar masses per year) in dying, low-mass stars.

  4. Experimental and computational insights into the stabilization of low-valent main group elements using crown ethers and related ligands.

    Science.gov (United States)

    Macdonald, Charles L B; Bandyopadhyay, Rajoshree; Cooper, Benjamin F T; Friedl, Warren W; Rossini, Aaron J; Schurko, Robert W; Eichhorn, S Holger; Herber, Rolfe H

    2012-03-07

    A series of tin(II) triflate and chloride salts in which the cations are complexed by either cyclic or acyclic polyether ligands and which have well-characterized single-crystal X-ray structures are investigated using a variety of experimental and computational techniques. Mössbauer spectroscopy illustrates that the triflate salts tend to have valence electrons with higher s-character, and solid-state NMR spectroscopy reveals marked differences between superficially similar triflate and chloride salts. Cyclic voltammetry investigations of the triflate salts corroborate the results of the Mössbauer and NMR spectroscopy and reveal substantial steric and electronic effects for the different polyether ligands. MP2 and DFT calculations provide insight into the effects of ligands and substituents on the stability and reactivity of the low-valent metal atom. Overall, the investigations reveal the existence of more substantial binding between tin and chlorine in comparison to the triflate substituent and provide a rationale for the considerably increased reactivity of the chloride salts.

  5. Non-Newtonian Study of Blood Flow in an Abdominal Aortic Aneurysm with a Stabilized Finite Element Method

    Science.gov (United States)

    Marrero, Victor; Sahni, Onkar; Jansen, Kenneth; Tichy, John; Taylor, Charles

    2008-11-01

    In recent years the methods of computational fluid dynamics (CFD) have been applied to the human cardiovascular system to better understand the relationship between arterial blood flow and the disease process, for example in an abdominal aortic aneurysm (AAA). Obviously, the technical challenges associated with such modeling are formidable. Among the many problems to be addressed, in this paper we add yet another complication -- the known non-Newtonian nature of blood. In this preliminary study, we used a patient-based AAA model with rigid walls. The pulsatile nature of the flow and the RCR outflow boundary condition are considered. We use the Carreau-Yasuda model to describe the non-Newtonian viscosity variation. Preliminary results for 200K, 2M, and 8M elements mesh are presented for the Newtonian and non-Newtonian cases. The broad fundamental issue we wish to eventually resolve is whether or not non-Newtonian effects in blood flow are sufficiently strong in unhealthy vessels that they must be addressed in meaningful simulations. Interesting differences during the flow cycle shed light on the problem, but further research is needed.

  6. Silicon Carbide-Based Hydrogen Gas Sensors for High-Temperature Applications

    OpenAIRE

    Sangchoel Kim; Jehoon Choi; Minsoo Jung; Seongjeen Kim; Sungjae Joo

    2013-01-01

    We investigated SiC-based hydrogen gas sensors with metal-insulator-semiconductor (MIS) structure for high temperature process monitoring and leak detection applications in fields such as the automotive, chemical and petroleum industries. In this work, a thin tantalum oxide (Ta2O5) layer was exploited with the purpose of sensitivity improvement, because tantalum oxide has good stability at high temperature with high permeability for hydrogen gas. Silicon carbide (SiC) was used as a substrate ...

  7. Templated Growth of Hexagonal Nickel Carbide Nanocrystals on Vertically Aligned Carbon Nanotubes (PREPRINT)

    Science.gov (United States)

    2010-01-01

    centered cubic ( FCC ) structure . Interestingly, there have been reports in the literature related to the stabilization of a non-equilibrium hexagonal...crystallite size (~ 4 nm) and changes to the equilibrium FCC structure for larger crystallite sizes [9-10]. Nickel does not form a carbide under equilibrium...a single weak ring corresponding to the face-centered cubic ( FCC ) structure of Ni. The lattice parameter of the HCP phase was determined to be a

  8. Ablation of carbide materials with femtosecond pulses

    Science.gov (United States)

    Dumitru, Gabriel; Romano, Valerio; Weber, Heinz P.; Sentis, Marc; Marine, Wladimir

    2003-01-01

    The response of cemented tungsten carbide and of titanium carbonitride was investigated with respect to damage and ablation properties, under interaction with ultrashort laser pulses. These carbide materials present high microhardness and are of significant interest for tribological applications. The experiments were carried out in air with a commercial Ti:sapphire laser at energy densities on the target up to 6.5 J/cm 2. The irradiated target surfaces were analyzed with optical, SEM and AFM techniques and the damage and ablation threshold values were determined using the measured spot diameters and the calculated incident energy density distributions.

  9. Silicon carbide microsystems for harsh environments

    CERN Document Server

    Wijesundara, Muthu B J

    2011-01-01

    Silicon Carbide Microsystems for Harsh Environments reviews state-of-the-art Silicon Carbide (SiC) technologies that, when combined, create microsystems capable of surviving in harsh environments, technological readiness of the system components, key issues when integrating these components into systems, and other hurdles in harsh environment operation. The authors use the SiC technology platform suite the model platform for developing harsh environment microsystems and then detail the current status of the specific individual technologies (electronics, MEMS, packaging). Additionally, methods

  10. Ultrarapid microwave synthesis of superconducting refractory carbides

    Energy Technology Data Exchange (ETDEWEB)

    Vallance, Simon R. [Department of Chemical and Environmental Engineering, University of Nottingham (United Kingdom); School of Chemistry, University Nottingham (United Kingdom); Round, David M. [School of Chemistry, University Nottingham (United Kingdom); Ritter, Clemens [Institut Laue-Langevin, Grenoble (France); Cussen, Edmund J. [WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow (United Kingdom); Kingman, Sam [Department of Chemical and Environmental Engineering, University of Nottingham (United Kingdom); Gregory, Duncan H. [WestCHEM, Department of Chemistry, University of Glasgow (United Kingdom)

    2009-11-26

    Nb{sub 1-x}Ta{sub x}C Carbides can be synthesized by high power MW methods in less than 30 s. In situ and ex situ techniques probing changes in temperature and dielectric properties with time demonstrate that the reactions self-terminate as the loss tangent of the materials decreases. The resulting carbides are carbon deficient and superconducting; T{sub c} correlates linearly to unit cell volume, reaching a maximum at NbC. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  11. Fracture reduction with positive medial cortical support: a key element in stability reconstruction for the unstable pertrochanteric hip fractures.

    Science.gov (United States)

    Chang, Shi-Min; Zhang, Ying-Qi; Ma, Zhuo; Li, Qing; Dargel, Jens; Eysel, Peer

    2015-06-01

    To introduce the concept of fracture reduction with positive medial cortical support and its clinical and radiological correlation in geriatric unstable pertrochanteric fractures. A retrospective analysis of 127 patients (32 men and 95 women, with mean age 78.7 years) with AO/OTA 31A2.2 and 2.3 hip fractures treated with cephalomedullary nail (PFNA-II or Gamma-3) between July 2010 and June 2013 was performed. They were classified into three groups according the grade of medial cortical support in postoperative fracture reduction (positive, neutral, and negative). The positive cortex support was defined that the medial cortex of the head-neck fragment displaced and located a little bit superomedially to the medial cortex of the shaft. If the neck cortex is located laterally to the shaft, it is negative with no cortical buttress, and if the two cortices contact smoothly, it is in neutral position. The demographic baseline, postoperative radiographic femoral neck-shaft angle and neck length, rehabilitation progress and functional recovery scores of each group were recorded and compared. There were 89 cases (70 %) in positive, 26 in neutral, and 12 in negative support. No statistical differences were found between the three groups among patient age, sex ratio, prefracture score of activity of daily living, walking ability score, ASA physical risk score, number of medical comorbidities, osteoporosis Singh index, fracture reduction quality (Garden alignments), and the position of lag screw or helical blade in femoral head (TAD). In follow-up, patients in positive medial cortical support reduction group had the least loss in neck-shaft angle and neck length, and got ground-walking much earlier than negative reduction group, with good functional outcomes and less hip-thigh pain presence. Fracture reduction with nonanatomic positive medial cortical support allows limited sliding of the head-neck fragment to contact with the femur shaft and achieve secondary stability

  12. Catastrophic degradation of the interface of epitaxial silicon carbide on silicon at high temperatures

    Science.gov (United States)

    Pradeepkumar, Aiswarya; Mishra, Neeraj; Kermany, Atieh Ranjbar; Boeckl, John J.; Hellerstedt, Jack; Fuhrer, Michael S.; Iacopi, Francesca

    2016-07-01

    Epitaxial cubic silicon carbide on silicon is of high potential technological relevance for the integration of a wide range of applications and materials with silicon technologies, such as micro electro mechanical systems, wide-bandgap electronics, and graphene. The hetero-epitaxial system engenders mechanical stresses at least up to a GPa, pressures making it extremely challenging to maintain the integrity of the silicon carbide/silicon interface. In this work, we investigate the stability of said interface and we find that high temperature annealing leads to a loss of integrity. High-resolution transmission electron microscopy analysis shows a morphologically degraded SiC/Si interface, while mechanical stress measurements indicate considerable relaxation of the interfacial stress. From an electrical point of view, the diode behaviour of the initial p-Si/n-SiC junction is catastrophically lost due to considerable inter-diffusion of atoms and charges across the interface upon annealing. Temperature dependent transport measurements confirm a severe electrical shorting of the epitaxial silicon carbide to the underlying substrate, indicating vast predominance of the silicon carriers in lateral transport above 25 K. This finding has crucial consequences on the integration of epitaxial silicon carbide on silicon and its potential applications.

  13. Synthesis and Characterization of In-situ Copper-Niobium Carbide Composite

    Science.gov (United States)

    Zuhailawati, H.; Othman, R.; Bui, D. L.; Umemoto, M.

    2008-03-01

    In this work, synthesis of copper matrix composite powder reinforced by in situ niobium carbide particle was prepared by mechanical alloying of elemental powder and subsequent heat treatment. Elemental powders of Cu-Nb-C correspond to Cu-40wt%Nb-10%wtC composition was milled for 54 hours at room temperature in a planetary ball mill. The effect of heat treatment temperature on the formation of niobium carbide was analyzed. Characterization by X-ray diffraction was done on the milled powder and heat-treated powder in order to investigate NbC formation. Results indicate that NbC began to precipitate after mechanical alloying for about 54h with heat treatment temperature of 900 °C and 1000 °C.

  14. Analysis of double stub tuner control stability in a many element phased array antenna with strong cross-coupling

    Energy Technology Data Exchange (ETDEWEB)

    Wallace, G. M.; Fitzgerald, E.; Johnson, D. K.; Kanojia, A. D.; Koert, P.; Lin, Y.; Murray, R.; Shiraiwa, S.; Terry, D. R.; Wukitch, S. J. [MIT Plasma Science and Fusion Center, Cambridge, MA 02139 (United States); Hillairet, J. [CEA-IRFM, Saint-Paul-lez-Durance (France)

    2014-02-12

    Active stub tuning with a fast ferrite tuner (FFT) allows for the system to respond dynamically to changes in the plasma impedance such as during the L-H transition or edge localized modes (ELMs), and has greatly increased the effectiveness of fusion ion cyclotron range of frequency systems. A high power waveguide double-stub tuner is under development for use with the Alcator C-Mod lower hybrid current drive (LHCD) system. Exact impedance matching with a double-stub is possible for a single radiating element under most load conditions, with the reflection coefficient reduced from Γ to Γ{sup 2} in the “forbidden region.” The relative phase shift between adjacent columns of a LHCD antenna is critical for control of the launched n{sub ∥} spectrum. Adding a double-stub tuning network will perturb the phase of the forward wave particularly if the unmatched reflection coefficient is high. This effect can be compensated by adjusting the phase of the low power microwave drive for each klystron amplifier. Cross-coupling of the reflected power between columns of the launcher must also be considered. The problem is simulated by cascading a scattering matrix for the plasma provided by a linear coupling model with the measured launcher scattering matrix and that of the FFTs. The solution is advanced in an iterative manner similar to the time-dependent behavior of the real system. System performance is presented under a range of edge density conditions from under-dense to over-dense and a range of launched n{sub ∥}.

  15. Using Discrete Element Method to Simulate Influence of Vertical Joints and Upward Groundwater on The Stability of Dip Slope: A Case Study on Formosa Freeway

    Science.gov (United States)

    Lu, An; Hsieh, Pei-Chen; Wu, Liang-Chun; Lin, Ming-Lang

    2017-04-01

    Earthquake and rainfall weakening potential sliding surface are common causes of dip slope failure. But in recent years, certain dip slopes failure, for example dip slope sliding without rain on the roadside of Formosa Freeway in northern Taiwan, are caused by uplift groundwater in vertical joints eventually weakening the potential sliding surface. The mechanism of sliding failure should be analyzed in more detail. Furthermore, prestress dissipating in anchors causing dip slope failure is also considered in this study. In this study, conceptual model is simplified from the case of Formosa Freeway in northern Taiwan and the main control factors including angle of slope, stratum, attitude of joints. In addition, drilling data, such as hydraulic conductivity, strength, friction angle and cohesion, are utilized to discuss mechanism and dominant factors of dip slope failure caused by uplift groundwater in vertical joints. UDEC(Universal Distinct Element Code) which is particularly well suited to problems involving jointed media and has been used extensively in stability analysis of jointed rock slopes is utilized in this study. The influence of external factors such as groundwater pressure on block sliding and deformation can also be simulated in UDEC. When the results from numerical simulation fit the condition of slope failure on the roadside of Formosa Freeway, the influence of prestress dissipating in anchors on slope stability is considered subsequently. Finally, simulation results by UDEC are compared with previous research results by FLAC, and discuss the difference between each other.

  16. Thermal treatment of stabilized air pollution control residues in a waste incinerator pilot plant. Part 1: Fate of elements and dioxins.

    Science.gov (United States)

    Bergfeldt, Brita; Jay, Klaus; Seifert, Helmuth; Vehlow, Jürgen; Christensen, Thomas H; Baun, Dorthe L; Mogensen, Erhardt P B

    2004-02-01

    Air pollution control (APC) residues from municipal solid waste incinerator plants that are treated by means of the Ferrox process can be more safely disposed of due to reduction of soluble salts and stabilization of heavy metals in an iron oxide matrix. Further stabilization can be obtained by thermal treatment inside a combustion chamber of a municipal solid waste incinerator. The influence of the Ferrox products on the combustion process, the quality of the residues, and the partitioning of heavy metals between the various solids and the gas have been investigated in the Karlsruhe TAM-ARA pilot plant for waste incineration. During the experiments only few parameters were influenced. An increase in the SO2 concentration in the raw gas and slightly lower temperatures in the fuel bed could be observed compared with reference tests. Higher contents of Fe and volatile heavy metals such as Zn, Cd, Pb and partly Hg in the Ferrox products lead to increased concentration of these elements in the solid residues of the co-feeding tests. Neither the burnout nor the PCDD/F formation was altered by the addition of the Ferrox products. Co-feeding of treated APC residues seems to be a feasible approach for obtaining a single solid residue from waste incineration.

  17. Stabilization of secondary structure elements by specific combinations of hydrophilic and hydrophobic amino acid residues is more important for proteins encoded by GC-poor genes.

    Science.gov (United States)

    Khrustalev, Vladislav Victorovich; Barkovsky, Eugene Victorovich

    2012-12-01

    Stabilization of secondary structure elements by specific combinations of hydrophobic and hydrophilic amino acids has been studied by the way of analysis of pentapeptide fragments from twelve partial bacterial proteomes. PDB files describing structures of proteins from species with extremely high and low genomic GC-content, as well as with average G + C were included in the study. Amino acid residues in 78,009 pentapeptides from alpha helices, beta strands and coil regions were classified into hydrophobic and hydrophilic ones. The common propensity scale for 32 possible combinations of hydrophobic and hydrophilic amino acid residues in pentapeptide has been created: specific pentapeptides for helix, sheet and coil were described. The usage of pentapeptides preferably forming alpha helices is decreasing in alpha helices of partial bacterial proteomes with the increase of the average genomic GC-content in first and second codon positions. The usage of pentapeptides preferably forming beta strands is increasing in coil regions and in helices of partial bacterial proteomes with the growth of the average genomic GC-content in first and second codon positions. Due to these circumstances the probability of coil-sheet and helix-sheet transitions should be increased in proteins encoded by GC-rich genes making them prone to form amyloid in certain conditions. Possible causes of the described fact that importance of alpha helix and coil stabilization by specific combinations of hydrophobic and hydrophilic amino acids is growing with the decrease of genomic GC-content have been discussed.

  18. A review of oxide, silicon nitride, and silicon carbide brazing

    Energy Technology Data Exchange (ETDEWEB)

    Santella, M.L.; Moorhead, A.J.

    1987-01-01

    There is growing interest in using ceramics for structural applications, many of which require the fabrication of components with complicated shapes. Normal ceramic processing methods restrict the shapes into which these materials can be produced, but ceramic joining technology can be used to overcome many of these limitations, and also offers the possibility for improving the reliability of ceramic components. One method of joining ceramics is by brazing. The metallic alloys used for bonding must wet and adhere to the ceramic surfaces without excessive reaction. Alumina, partially stabilized zirconia, and silicon nitride have high ionic character to their chemical bonds and are difficult to wet. Alloys for brazing these materials must be formulated to overcome this problem. Silicon carbide, which has some metallic characteristics, reacts excessively with many alloys, and forms joints of low mechanical strength. The brazing characteristics of these three types of ceramics, and residual stresses in ceramic-to-metal joints are briefly discussed.

  19. First-principles study of point defects in thorium carbide

    Science.gov (United States)

    Pérez Daroca, D.; Jaroszewicz, S.; Llois, A. M.; Mosca, H. O.

    2014-11-01

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

  20. First-principles study of point defects in thorium carbide

    Energy Technology Data Exchange (ETDEWEB)

    Pérez Daroca, D., E-mail: pdaroca@tandar.cnea.gov.ar [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Jaroszewicz, S. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Llois, A.M. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas, (1033) Buenos Aires (Argentina); Mosca, H.O. [Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina); Instituto de Tecnología Jorge A. Sabato, UNSAM-CNEA, Av. General Paz 1499, (1650) San Martin, Buenos Aires (Argentina)

    2014-11-15

    Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors’ knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

  1. Joining of Silicon Carbide Through the Diffusion Bonding Approach

    Science.gov (United States)

    Halbig, Michael .; Singh, Mrityunjay

    2009-01-01

    In order for ceramics to be fully utilized as components for high-temperature and structural applications, joining and integration methods are needed. Such methods will allow for the fabrication the complex shapes and also allow for insertion of the ceramic component into a system that may have different adjacent materials. Monolithic silicon carbide (SiC) is a ceramic material of focus due to its high temperature strength and stability. Titanium foils were used as an interlayer to form diffusion bonds between chemical vapor deposited (CVD) SiC ceramics with the aid of hot pressing. The influence of such variables as interlayer thickness and processing time were investigated to see which conditions contributed to bonds that were well adhered and crack free. Optical microscopy, scanning electron microscopy, and electron microprobe analysis were used to characterize the bonds and to identify the reaction formed phases.

  2. In situ electrochemical dilatometry of carbide-derived carbons

    Energy Technology Data Exchange (ETDEWEB)

    Hantel, M M [Paul Scherrer Institut, Villigen, Switzerland; Presser, Volker [ORNL; Gogotsi, Yury [ORNL

    2011-01-01

    The long life durability and extraordinary stability of supercapacitors are ascribed to the common concept that the charge storage is purely based on double-layer charging. Therefore the ideal supercapacitor electrode should be free of charge induced microscopic structural changes. However, recent in-situ investigations on different carbon materials for supercapacitor electrodes have shown that the charge and discharge is accompanied by dimensional changes of the electrode up to several percent. This work studies the influence of the pore size on the expansion behavior of carbon electrodes derived from titanium carbide-derived carbons with an average pore size between 5 and 8 Using tetraethylammonium tetrafluoroborate in acetonitrile, the swelling of the electrodes was measured by in situ dilatometry. The experiments revealed an increased expansion on the negatively charged electrode for pores below 6 , which could be described with pore swelling.

  3. High surface area silicon carbide-coated carbon aerogel

    Science.gov (United States)

    Worsley, Marcus A; Kuntz, Joshua D; Baumann, Theodore F; Satcher, Jr, Joe H

    2014-01-14

    A metal oxide-carbon composite includes a carbon aerogel with an oxide overcoat. The metal oxide-carbon composite is made by providing a carbon aerogel, immersing the carbon aerogel in a metal oxide sol under a vacuum, raising the carbon aerogel with the metal oxide sol to atmospheric pressure, curing the carbon aerogel with the metal oxide sol at room temperature, and drying the carbon aerogel with the metal oxide sol to produce the metal oxide-carbon composite. The step of providing a carbon aerogel can provide an activated carbon aerogel or provide a carbon aerogel with carbon nanotubes that make the carbon aerogel mechanically robust. Carbon aerogels can be coated with sol-gel silica and the silica can be converted to silicone carbide, improved the thermal stability of the carbon aerogel.

  4. Chemical, Electrical and Thermal Characterization of Nanoceramic Silicon Carbide

    Science.gov (United States)

    Martin, Hervie; Abunaemeh, Malek; Smith, Cydale; Muntele, Claudiu; Budak, Satilmish; Ila, Daryush

    2009-03-01

    Silicon carbide (SiC) is a lightweight high bandgap semiconductor material that can maintain dimensional and chemical stability in adverse environments and very high temperatures. These properties make it suitable for high temperature thermoelectric converters. At the Center for Irradiaton of Materials (CIM) we design, manufacture and fabricate nanoceramic SiC, and perform electrical, thermal and chemical characterization of the material using particle induced X-ray emission (PIXE), Rutherford backscattering spectroscopy (RBS), Seebeck coefficient, electrical conductivity, and thermal conductivity measurements to calculate its efficiency as a thermoelectric generator. We are looking to compare the electrical and thermal properties of SiC ceramics with some other materials used for the same purposes.

  5. Fe-15Ni-13Cr austenitic stainless steels for fission and fusion reactor applications - Part II: Effects of minor elements on precipitate phase stability during thermal aging

    Science.gov (United States)

    Lee, E. H.; Mansur, L. K.

    2000-01-01

    The precipitate phase stability in Fe-15Ni-13Cr base austenitic alloys was investigated as a function of minor alloying additions after thermally aging at 600°C and 675°C for times ranging from 24 h to one year. Seven major precipitate phases were found in aged specimens, including M 23C 6, Laves, Eta (η), TiO, NbC, MC, and M 2P. The types and amounts of precipitate phases varied with alloying element additions, aging temperature, and aging time. By analyzing the composition of each individual particle, it was possible to determine the essential constituent elements for each phase. From this information, a strategy to promote or suppress certain precipitate phases was developed. Among the seven phases, the most desirable precipitate phases were considered to be MC and M 2P, because these particles form on a fine scale with a high number density and, therefore, can serve as effective gas atom trap sites under irradiation.

  6. Contribution to assessing the stiffness reduction of structural elements in the global stability analysis of precast concrete multi-storey buildings

    Directory of Open Access Journals (Sweden)

    M. C. Marin

    Full Text Available This study deals with the reduction of the stiffness in precast concrete structural elements of multi-storey buildings to analyze global stability. Having reviewed the technical literature, this paper present indications of stiffness reduction in different codes, standards, and recommendations and compare these to the values found in the present study. The structural model analyzed in this study was constructed with finite elements using ANSYS® software. Physical Non-Linearity (PNL was considered in relation to the diagrams M x N x 1/r, and Geometric Non-Linearity (GNL was calculated following the Newton-Raphson method. Using a typical precast concrete structure with multiple floors and a semi-rigid beam-to-column connection, expressions for a stiffness reduction coefficient are presented. The main conclusions of the study are as follows: the reduction coefficients obtained from the diagram M x N x 1/r differ from standards that use a simplified consideration of PNL; the stiffness reduction coefficient for columns in the arrangements analyzed were approximately 0.5 to 0.6; and the variation of values found for stiffness reduction coefficient in concrete beams, which were subjected to the effects of creep with linear coefficients from 0 to 3, ranged from 0.45 to 0.2 for positive bending moments and 0.3 to 0.2 for negative bending moments.

  7. ℎ- Spectral element methods for three dimensional elliptic problems on non-smooth domains, Part-I: Regularity estimates and stability theorem

    Indian Academy of Sciences (India)

    P Dutt; Akhlaq Husain; A S Vasudeva Murthy; C S Upadhyay

    2015-05-01

    This is the first of a series of papers devoted to the study of ℎ- spectral element methods for solving three dimensional elliptic boundary value problems on non-smooth domains using parallel computers. In three dimensions there are three different types of singularities namely; the vertex, the edge and the vertex-edge singularities. In addition, the solution is anisotropic in the neighbourhoods of the edges and vertex-edges. To overcome the singularities which arise in the neighbourhoods of vertices, vertex-edges and edges, we use local systems of coordinates. These local coordinates are modified versions of spherical and cylindrical coordinate systems in their respective neighbourhoods. Away from these neighbourhoods standard Cartesian coordinates are used. In each of these neighbourhoods we use a geometrical mesh which becomes finer near the corners and edges. The geometrical mesh becomes a quasi-uniform mesh in the new system of coordinates. We then derive differentiability estimates in these new set of variables and state our main stability estimate theorem using a non-conforming ℎ- spectral element method whose proof is given in a separate paper.

  8. Oxygen diffusion in the Ti3X alloys with elements from the IIIA or IVA groups and stability of their DO19 crystal structure

    Science.gov (United States)

    Bilić, Ante; Gibson, Mark A.; Wilson, Nick; McGregor, Kathie

    2017-01-01

    Oxygen diffusion in Ti3X binary alloys, where X = Al, Ga, In, Si, Ge, or Sn, with the hexagonal close-packed DO19 crystal structure has been investigated in the 600-1200 K temperature range by kinetic Monte Carlo simulations, using the activation energies and exponential prefactors obtained from the literature. The results predict a vastly reduced oxygen mobility relative to that in α-Ti, in particular, along the basal directions, with the most notable reduction in the diffusivity evaluated for the alloys with heavier elements In and Sn. However, an insight from the crystal structure prediction based on the USPEX evolutionary optimization algorithm and first principles total energy calculations, suggests that the DO19 type crystal lattice is not the most stable for the elements in the carbon group. Rather, a distorted lattice with an orthorhombic crystal and spacegroup number 63 is predicted to be stable in the case of Sn, whereas larger tetragonal structures are predicted to be stable for Si and Ge. The dynamic stability of their lattices has been confirmed from the calculated vibrational normal mode spectra in the harmonic approximation.

  9. Performance and kinetic evaluation of a semi-continuously fed anaerobic digester treating food waste: effect of trace elements on the digester recovery and stability.

    Science.gov (United States)

    Wei, Quanyuan; Zhang, Wanqin; Guo, Jianbin; Wu, Shubiao; Tan, Tianwei; Wang, Fang; Dong, Renjie

    2014-12-01

    This study investigated the effects of trace elements (TEs: Fe, Co, and Ni) on the anaerobic digestion of food waste in laboratory scale semi-continuously fed anaerobic digesters. The digesters were operated for approximately 460 d at organic loading rates (OLRs) ranging from 1.0 to 5.0 g VS L(-1)d(-1) at 37°C. Results showed that methane production was severely inhibited when volatile fatty acids (VFAs) concentration was 30,000 mg L(-1) at OLR of 4.0 g VS L(-1)d(-1) without the addition of TEs. However, the inhibition was gradually decreased and the methane production increased from 0.13 up to 0.44 L g(-1)VS added when the TEs was added. Fe was proved to be the essential element in maintaining the stability of the digester. The conversion coefficient of substrate into biogas (YS/G) was 1.00 and 1.26 gVS removedL(-1) biogas with and without TEs addition, respectively. The estimated biomass yield with feeding TEs (0.06 g VSS g(-1)COD removed) was higher three times than that without TEs (0.02 gVSS g(-1)COD removed).

  10. Ultra-rapid processing of refractory carbides; 20 s synthesis of molybdenum carbide, Mo2C.

    Science.gov (United States)

    Vallance, Simon R; Kingman, Sam; Gregory, Duncan H

    2007-02-21

    The microwave synthesis of molybdenum carbide, Mo(2)C, from carbon and either molybdenum metal or the trioxide has been achieved on unprecedented timescales; Ex- and in-situ characterisation reveals key information as to how the reaction proceeds.

  11. Production of carbide-free thin ductile iron castings

    Institute of Scientific and Technical Information of China (English)

    M. Ashraf Sheikh

    2008-01-01

    The fast cooling rate of thin ductile iron castings requires special consideration to produce carbide-free castings. Extraor-dinary care was taken to select the charge to produce castings of 100-mm long round bars with 16-ram diameter. The castings show the presence of carbides in the bars. Seven melts were made with different temperatures and with different compositions to get rid of carbides. After chemical analyses, it was found that the extra purity of the charge with less than 0.008wt% sulfur in the castings was the cause of carbides. To remove the carbides fi'om the castings, sulfur should be added to the charge.

  12. Energetic stability and magnetic moment of tri-, tetra-, and octa- ferromagnetic element nitrides predicted by first-principle calculations

    Energy Technology Data Exchange (ETDEWEB)

    Imai, Yoji, E-mail: imai-y@aist.go.jp [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, Higashi 1-1, Tsukuba, Ibaraki 305-8565 (Japan); Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8573 (Japan); Sohma, Mitsugu [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, Higashi 1-1, Tsukuba, Ibaraki 305-8565 (Japan); Suemasu, Takashi [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8573 (Japan)

    2014-10-25

    Highlights: • Formation energies of tri-, tetra-, and octa-metal nitrides of Fe, Co and Ni were calculated. • It is predicted that Fe{sub 4}N is stable, Ni{sub 4}N is metastable, and Co{sub 4}N is unstable. • Octa-metal nitrides with the α″-Fe{sub 16}N{sub 2} type structure is stable only for Fe. • All the tri-metal nitrides with the Ni{sub 3}N type structure are stable. - Abstract: Formation energies and magnetic moments of tri-, tetra-, and octa- ferromagnetic element nitrides have been calculated using spin-polarized Perdew–Wang generalized gradient approximations of the density functional theory. From the energetic point of view, Fe{sub 4}N are more stable compared to Fe and N{sub 2} gas. Ni{sub 4}N may be a metastable phase since mixture of Ni{sub 3}N and Ni would be more energetically stable. Fe{sub 4}N may be also a metastable from energetic point of view but effect of configurational entropy caused by N-vacancy and of disregarded random occupation of interstitial sites by N observed in Fe{sub 3}N must be evaluated so as to make precise evaluation, which is beyond the scope of the present work. Co{sub 4}N are not stable compared to Co metal with the hcp structure and N{sub 2} gas, but more stable in case Co metal with the fcc structure is used as a reference state. Only Fe{sub 8}N with the α″-Fe{sub 16}N{sub 2} type structure would be stable among octa-metal nitrides with the assumed structure of the α″-Fe{sub 16}N{sub 2} type and the Ni{sub 32}N{sub 4} type structure. All of Fe{sub 3}N, Co{sub 3}N, and Ni{sub 3}N are stable, but Ni{sub 3}N would be non-magnetic in contrast to ferromagnetism of other tri-metal nitrides.

  13. [Study on the Interface Characteristics of Cemented Carbide after Stripping Ti Department Coatings].

    Science.gov (United States)

    Yan, Qiang; Liang, Zheng; Song, Hui-jin; Wu, Tao; Wu, Jun

    2015-04-01

    TiAlN Coatings were stripped by chemical method, which were deposited on Y WZ Alloy by arc ion plating. The surface morphology and composition of the cemented carbide after stripping TiAlN coatings by chemistry method were analyzed. It was found that TiA1N coatings on the cemented carbide substrates could be removed by being taken in 30% of hydrogen peroxide and potassium oxalate in alkaline mixed solution (V(NaOH so1ution):V(3O%H2O2):V(COOK solution) = 1:1:1) at 45 °C for 45 minutes. The surface of the cemented carbide substrate was bright, and the color was the same as that before depositing TiA1N coatings. The surface of the substrate after removing was studied by X-ray photoelectron spectrum (XPS). The results showed that binding energies of the W element and the main peak of N element on the substrate surface were much close to the criterion binding energy in the XPS data-base; and the valence of the element on the YW2 alloy changed little. The Al, Ti and N elements diffusing into the superficial zone of the sample during the coating depositing process made their contents increase and the band energy location offset after stripping the coating. TiN and A1N were formed, which benefit to increase the film-substrate cohesion during re-preparing coatings. The influence of stripping solution on the corrosion degree of cemented carbide substrate was small.

  14. Silicon carbide hollow fiber membranes: obtainment and characterization; Membranas de fibra oca de carbeto de silicio: obtencao e caracterizacao

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, S.S.L.; Ferreira, R.S.B.; Araujo, B.A.; Medeiros, K.M.; Lucena, H.L.; Araujo, E.M., E-mail: sandriely_sonaly@hotmail.com [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Departamento de Engenharia de Materiais

    2016-07-01

    Silicon carbide is a promising material for the production of membranes due to its high melting temperature, thermal shock resistance, excellent mechanical and chemical stability. So, this study aims to characterize silicon carbide membranes in order to apply them in the separation of oil-water. A solution (SiC + PES + 1-Methyl- 2-Pyrrolidone) and through the extrusion technique by immersion precipitation membranes were obtained with hollow fiber geometry was prepared. And then sintered at 1500 ° C. For the characterization analyzes were made XRD, FTIR and SEM to evaluate the morphology and composition of the membranes obtained before and after sintering. (author)

  15. Band structure, elastic and magnetic properties, and stability of antiperovskites MCNi3( M = Y - Ag) according to FLAPW-GGA calculations

    Science.gov (United States)

    Bannikov, V. V.; Shein, I. R.; Ivanovskiĭ, A. L.

    2007-09-01

    Using the full-potential linearized augmented plane wave method (FLAPW) and the WIEN2k software package, calculations of the band structure and the elastic and magnetic properties of the ternary antiperovskite carbides MCNi3, where M = Y, Zr, ..., Ag (overall, nine compounds) are performed and the features of interatomic interactions in them are considered. Stability of these antiperovskite compounds depending on the 4 d metal is discussed based on the calculated energies of formation of MCNi3 from the corresponding elements (according to the formal reaction M + C + 3Ni → MCNi3), and the conclusion is drawn that the YCNi3, ZrCNi3, and PdCNi3 antiperovskites can be synthesized. The obtained results are compared with the available data on known isostructural nickel-based carbides (antiperovskites MgCNi3, ZnCNi3).

  16. Method of preparing a porous silicon carbide

    NARCIS (Netherlands)

    Moene, R.; Tazelaar, F.W.; Makkee, M.; Moulijn, J.A.

    1994-01-01

    Abstract of NL 9300816 (A) Described is a method of preparing a porous silicon carbide suitable for use as a catalyst or as a catalyst support. Porous carbon is provided with a catalyst which is suitable for catalysing gasification of carbon with hydrogen, and with a catalyst suitable for cataly

  17. Casimir force measurements from silicon carbide surfaces

    NARCIS (Netherlands)

    Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.

    2016-01-01

    Using an atomic force microscope we performed measurements of the Casimir force between a gold-coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was mea

  18. Boron carbide morphology changing under purification

    Science.gov (United States)

    Rahmatullin, I. A.; Sivkov, A. A.

    2015-10-01

    Boron carbide synthesized by using coaxial magnetoplasma accelerator with graphite electrodes was purified by two different ways. XRD-investigations showed content changing and respectively powder purification. Moreover TEM-investigations demonstrated morphology changing of product under purification that was discussed in the work.

  19. High-temperature carbidization of carboniferous rocks

    Science.gov (United States)

    Goldin, B. A.; Grass, V. E.; Nadutkin, A. V.; Nazarova, L. Yu.

    2009-08-01

    Processes of thermal metamorphism of carboniferous rocks have been studied experimentally. The conditions of high-temperature interaction of shungite carbon with components of the contained rocks, leading to formation of carbide compounds, have been determined. The results of this investigation contribute to the works on searching for new raw material for prospective material production.

  20. Titanium carbide nanocrystals in circumstellar environments

    NARCIS (Netherlands)

    von Helden, G; Tielens, ACGM; van Heijnsbergen, D; Duncan, MA; Hony, S; Waters, LBFM; Meijer, G.

    2000-01-01

    Meteorites contain micrometer-sized graphite grains with embedded titanium carbide grains. Although isotopic analysis identifies asymptotic giant branch stars as the birth sites of these grains, there is no direct observational identification of these grains in astronomical sources. We report that i

  1. Bioactivation of biomorphous silicon carbide bone implants.

    Science.gov (United States)

    Will, Julia; Hoppe, Alexander; Müller, Frank A; Raya, Carmen T; Fernández, Julián M; Greil, Peter

    2010-12-01

    Wood-derived silicon carbide (SiC) offers a specific biomorphous microstructure similar to the cellular pore microstructure of bone. Compared with bioactive ceramics such as calcium phosphate, however, silicon carbide is considered not to induce spontaneous interface bonding to living bone. Bioactivation by chemical treatment of biomorphous silicon carbide was investigated in order to accelerate osseointegration and improve bone bonding ability. Biomorphous SiC was processed from sipo (Entrandrophragma utile) wood by heating in an inert atmosphere and infiltrating the resulting carbon replica with liquid silicon melt at 1450°C. After removing excess silicon by leaching in HF/HNO₃ the biomorphous preform consisted of β-SiC with a small amount (approximately 6wt.%) of unreacted carbon. The preform was again leached in HCl/HNO₃ and finally exposed to CaCl₂ solution. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared analyses proved that oxidation of the residual carbon at the surface induced formation of carboxyl [COO⁻] groups, which triggered adsorption of Ca(2+), as confirmed by XPS and inductively coupled plasma optical emission spectroscopy measurements. A local increase in Ca(2+) concentration stimulated in vitro precipitation of Ca₅(PO₄)₃OH (HAP) on the silicon carbide preform surface during exposure to simulated body fluid, which indicates a significantly increased bone bonding activity compared with SiC.

  2. Method of preparing a porous silicon carbide

    NARCIS (Netherlands)

    Moene, R.; Tazelaar, F.W.; Makkee, M.; Moulijn, J.A.

    1994-01-01

    Abstract of NL 9300816 (A) Described is a method of preparing a porous silicon carbide suitable for use as a catalyst or as a catalyst support. Porous carbon is provided with a catalyst which is suitable for catalysing gasification of carbon with hydrogen, and with a catalyst suitable for cataly

  3. Silicon Carbide Technologies for Lightweighted Aerospace Mirrors

    Science.gov (United States)

    2008-09-01

    silicon carbide (SiC) based materials. It is anticipated that SiC can be utilized for most applications from cryogenic to high temperatures. This talk will focus on describing the SOA for these (near term) SiC technology solutions for making mirror structural substrates, figuring and finishing technologies being investigated to reduce cost time

  4. Casimir forces from conductive silicon carbide surfaces

    NARCIS (Netherlands)

    Sedighi Ghozotkhar, Mehdi; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.

    2014-01-01

    Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of fr

  5. CLAD CARBIDE NUCLEAR FUEL, THERMIONIC POWER, MODULES.

    Science.gov (United States)

    The general objective is to evaluate a clad carbide emitter, thermionic power module which simulates nuclear reactor installation, design, and...performance. The module is an assembly of two series-connected converters with a single common cesium reservoir. The program goal is 500 hours

  6. Boron Carbides As Thermo-electric Materials

    Science.gov (United States)

    Wood, Charles

    1988-01-01

    Report reviews recent theoretical and experimental research on thermoelectric materials. Recent work with narrow-band semiconductors demonstrated possibility of relatively high thermoelectric energy-conversion efficiencies in materials withstanding high temperatures needed to attain such efficiencies. Among promising semiconductors are boron-rich borides, especially boron carbides.

  7. Titanium carbide nanocrystals in circumstellar environments

    NARCIS (Netherlands)

    von Helden, G.; Tielens, Acgm; van Heijnsbergen, D.; Duncan, M. A.; Hony, S.; Waters, Lbfm; Meijer, G.

    2000-01-01

    Meteorites contain micrometer-sized graphite grains with embedded titanium carbide grains. Although isotopic analysis identifies asymptotic giant branch stars as the birth sites of these grains, there is no direct observational identification of these grains in astronomical sources. We report that i

  8. Method of preparing a porous silicon carbide

    NARCIS (Netherlands)

    Moene, R.; Tazelaar, F.W.; Makkee, M.; Moulijn, J.A.

    1994-01-01

    Abstract of NL 9300816 (A) Described is a method of preparing a porous silicon carbide suitable for use as a catalyst or as a catalyst support. Porous carbon is provided with a catalyst which is suitable for catalysing gasification of carbon with hydrogen, and with a catalyst suitable for

  9. Laser cladding in-situ carbide particle reinforced Fe-based composite coatings with rare earth oxide addition

    Institute of Scientific and Technical Information of China (English)

    吴朝锋; 马明星; 刘文今; 钟敏霖; 张红军; 张伟明

    2009-01-01

    Particulate reinforced metal matrix composite(PR-MMC) has excellent properties such as good wear resistance,corrosion resistance and high temperature properties.Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles.Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements,was favorable for the formation of in-situ synthesized carbide particles.In this paper,rare earth oxide(RE2O3) was added into t...

  10. Carburization and heat treatment to cause carbide precipitation in gamma/gamma prime-delta eutectic alloys

    Science.gov (United States)

    Tewari, S. N.; Dreshfield, R. L.

    1977-01-01

    In an attempt to improve their longitudinal shear strength, several directionally solidified eutectic alloy compositions with minor element modifications were pact, carburized, and heat treated to provide selective carbide precipitation at the cell and grain boundaries. The directionally solidified Ni-17.8 Nb-6Cr-2.5Al-3Ta (weight percent) alloy was selected for the shear strength evaluation because it showed the shallowest delta-denuded zone at the carburized surface. The carburization-carbide precipitation treatment, however, did not appear to improve the longitudinal shear strength of the alloy.

  11. A new class of electrocatalysts for hydrogen production from water electrolysis: metal monolayers supported on low-cost transition metal carbides.

    Science.gov (United States)

    Esposito, Daniel V; Hunt, Sean T; Kimmel, Yannick C; Chen, Jingguang G

    2012-02-15

    This work explores the opportunity to substantially reduce the cost of hydrogen evolution reaction (HER) catalysts by supporting monolayer (ML) amounts of precious metals on transition metal carbide substrates. The metal component includes platinum (Pt), palladium (Pd), and gold (Au); the low-cost carbide substrate includes tungsten carbides (WC and W(2)C) and molybdenum carbide (Mo(2)C). As a platform for these studies, single-phase carbide thin films with well-characterized surfaces have been synthesized, allowing for a direct comparison of the intrinsic HER activity of bare and Pt-modified carbide surfaces. It is found that WC and W(2)C are both excellent cathode support materials for ML Pt, exhibiting HER activities that are comparable to bulk Pt while displaying stable HER activity during chronopotentiometric HER measurements. The findings of excellent stability and HER activity of the ML Pt-WC and Pt-W(2)C surfaces may be explained by the similar bulk electronic properties of tungsten carbides to Pt, as is supported by density functional theory calculations. These results are further extended to other metal overlayers (Pd and Au) and supports (Mo(2)C), which demonstrate that the metal ML-supported transition metal carbide surfaces exhibit HER activity that is consistent with the well-known volcano relationship between activity and hydrogen binding energy. This work highlights the potential of using carbide materials to reduce the costs of hydrogen production from water electrolysis by serving as stable, low-cost supports for ML amounts of precious metals.

  12. Effects of Ti element on the microstructural stability of 9Cr–WVTiN reduced activation martensitic steel under ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Fengfeng [Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education, Hubei Nuclear Solid Physics Key Laboratory and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Guo, Liping, E-mail: guolp@whu.edu.cn [Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education, Hubei Nuclear Solid Physics Key Laboratory and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Jin, Shuoxue; Li, Tiecheng; Chen, Jihong [Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education, Hubei Nuclear Solid Physics Key Laboratory and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Suo, Jinping; Yang, Feng [State Key Laboratory of Mould Technology, Institute of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Yao, Z. [Department of Mechanical and Materials Engineering, Queen’s University, Kingston K7L 3N6, ON (Canada)

    2014-12-15

    Microstructure of 9Cr–WVTiN reduced-activation martensitic steels with two different Ti concentrations irradiated with Fe{sup +}, He{sup +} and H{sup +} at 300 °C was studied with transmission electron microscopy. Small dislocation loops were observed in the irradiated steels. The mean size and number density of dislocation loops decreased with the increase of Ti concentration. The segregation of Cr and Fe in carbides was observed in both irradiated steels, and the enrichment of Cr and depletion of Fe were more severe in the low Ti-concentration 9Cr–WVTiN steel.

  13. Elemental profiling of laser cladded multilayer coatings by laser induced breakdown spectroscopy and energy dispersive X-ray spectroscopy

    Science.gov (United States)

    Lednev, V. N.; Sdvizhenskii, P. A.; Filippov, M. N.; Grishin, M. Ya.; Filichkina, V. A.; Stavertiy, A. Ya.; Tretyakov, R. S.; Bunkin, A. F.; Pershin, S. M.

    2017-09-01

    Multilayer tungsten carbide wear resistant coatings were analyzed by laser induced breakdown spectroscopy (LIBS) and energy dispersive X-ray (EDX) spectroscopy. Coaxial laser cladding technique was utilized to produce tungsten carbide coating deposited on low alloy steel substrate with additional inconel 625 interlayer. EDX and LIBS techniques were used for elemental profiling of major components (Ni, W, C, Fe, etc.) in the coating. A good correlation between EDX and LIBS data was observed while LIBS provided additional information on light element distribution (carbon). A non-uniform distribution of tungsten carbide grains along coating depth was detected by both LIBS and EDX. In contrast, horizontal elemental profiling showed a uniform tungsten carbide particles distribution. Depth elemental profiling by layer-by-layer LIBS analysis was demonstrated to be an effective method for studying tungsten carbide grains distribution in wear resistant coating without any sample preparation.

  14. Computational-Experimental Processing of Boride/Carbide Composites by Reactive Infusion of Hf Alloy Melts into B4C

    Science.gov (United States)

    2015-09-16

    elements from the Hf family (i.e., Hf, Ti and Zr ) into a capillary to understand the effects of surface tension and viscosity during processing of melts...project primarily investigated computationally the infusion of liquid elements from the Hf family (i.e., Hf, Ti and Zr ) into a capillary to understand the... effects of surface tension and viscosity during processing of melts with a packed bed of B4C to form boride-carbide precipitates. Although the

  15. Processing development of 4 tantalum carbide-hafnium carbide and related carbides and borides for extreme environments

    Science.gov (United States)

    Gaballa, Osama Gaballa Bahig

    Carbides, nitrides, and borides ceramics are of interest for many applications because of their high melting temperatures and good mechanical properties. Wear-resistant coatings are among the most important applications for these materials. Materials with high wear resistance and high melting temperatures have the potential to produce coatings that resist degradation when subjected to high temperatures and high contact stresses. Among the carbides, Al4SiC4 is a low density (3.03 g/cm3), high melting temperature (>2000°C) compound, characterized by superior oxidation resistance, and high compressive strength. These desirable properties motivated this investigation to (1) obtain high-density Al4SiC4 at lower sintering temperatures by hot pressing, and (2) to enhance its mechanical properties by adding WC and TiC to the Al4SiC4. Also among the carbides, tantalum carbide and hafnium carbide have outstanding hardness; high melting points (3880°C and 3890°C respectively); good resistance to chemical attack, thermal shock, and oxidation; and excellent electronic conductivity. Tantalum hafnium carbide (Ta4HfC 5) is a 4-to-1 ratio of TaC to HfC with an extremely high melting point of 4215 K (3942°C), which is the highest melting point of all currently known compounds. Due to the properties of these carbides, they are considered candidates for extremely high-temperature applications such as rocket nozzles and scramjet components, where the operating temperatures can exceed 3000°C. Sintering bulk components comprised of these carbides is difficult, since sintering typically occurs above 50% of the melting point. Thus, Ta4 HfC5 is difficult to sinter in conventional furnaces or hot presses; furnaces designed for very high temperatures are expensive to purchase and operate. Our research attempted to sinter Ta4HfC5 in a hot press at relatively low temperature by reducing powder particle size and optimizing the powder-handling atmosphere, milling conditions, sintering

  16. Characterization of silicon carbide and diamond detectors for neutron applications

    Science.gov (United States)

    Hodgson, M.; Lohstroh, A.; Sellin, P.; Thomas, D.

    2017-10-01

    The presence of carbon atoms in silicon carbide and diamond makes these materials ideal candidates for direct fast neutron detectors. Furthermore the low atomic number, strong covalent bonds, high displacement energies, wide bandgap and low intrinsic carrier concentrations make these semiconductor detectors potentially suitable for applications where rugged, high-temperature, low-gamma-sensitivity detectors are required, such as active interrogation, electronic personal neutron dosimetry and harsh environment detectors. A thorough direct performance comparison of the detection capabilities of semi-insulating silicon carbide (SiC–SI), single crystal diamond (D–SC), polycrystalline diamond (D–PC) and a self-biased epitaxial silicon carbide (SiC–EP) detector has been conducted and benchmarked against a commercial silicon PIN (Si–PIN) diode, in a wide range of alpha (Am-241), beta (Sr/Y-90), ionizing photon (65 keV to 1332 keV) and neutron radiation fields (including 1.2 MeV to 16.5 MeV mono-energetic neutrons, as well as neutrons from AmBe and Cf-252 sources). All detectors were shown to be able to directly detect and distinguish both the different radiation types and energies by using a simple energy threshold discrimination method. The SiC devices demonstrated the best neutron energy discrimination ratio (E\\max (n=5 MeV)/E\\max (n=1 MeV)  ≈5), whereas a superior neutron/photon cross-sensitivity ratio was observed in the D–PC detector (E\\max (AmBe)/E\\max (Co-60)  ≈16). Further work also demonstrated that the cross-sensitivity ratios can be improved through use of a simple proton-recoil conversion layer. Stability issues were also observed in the D–SC, D–PC and SiC–SI detectors while under irradiation, namely a change of energy peak position and/or count rate with time (often referred to as the polarization effect). This phenomenon within the detectors was non-debilitating over the time period tested (> 5 h) and, as such, stable

  17. Thermodynamic analysis of carbide precipitates in a niobium-zirconium-carbon alloy

    Energy Technology Data Exchange (ETDEWEB)

    Farkas, D.M.; Groza, J.R.; Mukherjee, A.K. [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science

    1996-01-01

    Precipitation-strengthened niobium alloys have shown promise as high-temperature structural materials for aerospace applications. The achievement of suitable properties and superior creep resistance at service conditions requires that the second phase particles remain relatively small, stable, and evenly dispersed in the matrix. The key to this development lies in the thermodynamic evolution of the precipitate phase. This paper focuses on the thermodynamic driving force for formation of carbides in a precipitation-strengthened refractory metal alloy of niobium; Nb-1%Zr-0.1%C commercially known as PWC-11. An examination of the free energies of formation of the different carbide phases, their evolution and stability at the high temperatures, and a comparison with experimental analysis was made.

  18. Mass production of beta-silicon carbide nanofibers by the novel method of Forcespinning

    Science.gov (United States)

    Salinas, Alfonso

    Non-oxide Ceramics such as silicon carbide have very unique properties, for example high toughness, thermal stability, wear resistant, and thermal shock resistance these properties make these ceramic fibers excellent for high temperature applications. Here we present the development of Silicon Carbide nanofibers utilizing a Polystyrene/Polycarbomethylsilane solution as the precursor materials. The ForcespinningRTM was performed under a controlled nitrogen environment to prevent fiber oxidation. Characterization was conducted using scanning electron microscopy, x-ray diffraction, and thermogravimetric analysis. The results show successful formation of high yield, long continuous bead-free nanofibers with diameters ranging from 280nm to 2 micron depending on the selected processing parameters. The sintered precursors show formation of SiC nanofibers with a beta phase crystalline structure and oxygen content below 15%.

  19. Hollow Spheres of Iron Carbide Nanoparticles Encased in Graphitic Layers as Oxygen Reduction Catalysts

    DEFF Research Database (Denmark)

    Hu, Yang; Jensen, Jens Oluf; Zhang, Wei

    2014-01-01

    Nonprecious metal catalysts for the oxygen reduction reaction are the ultimate materials and the foremost subject for low‐temperature fuel cells. A novel type of catalysts prepared by high‐pressure pyrolysis is reported. The catalyst is featured by hollow spherical morphologies consisting...... of uniform iron carbide (Fe3C) nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles without depriving them of their catalytic activity towards the oxygen reduction reaction (ORR......). As a result the catalyst is highly active and stable in both acid and alkaline electrolytes. The synthetic approach, the carbide‐based catalyst, the structure of the catalysts, and the proposed mechanism open new avenues for the development of ORR catalysts....

  20. A spatially stabilized TDG based finite element framework for modeling biofilm growth with a multi-dimensional multi-species continuum biofilm model

    Science.gov (United States)

    Feng, D.; Neuweiler, I.; Nackenhorst, U.

    2017-02-01

    We consider a model for biofilm growth in the continuum mechanics framework, where the growth of different components of biomass is governed by a time dependent advection-reaction equation. The recently developed time-discontinuous Galerkin (TDG) method combined with two different stabilization techniques, namely the Streamline Upwind Petrov Galerkin (SUPG) method and the finite increment calculus (FIC) method, are discussed as solution strategies for a multi-dimensional multi-species biofilm growth model. The biofilm interface in the model is described by a convective movement following a potential flow coupled to the reaction inside of the biofilm. Growth limiting substrates diffuse through a boundary layer on top of the biofilm interface. A rolling ball method is applied to obtain a boundary layer of constant height. We compare different measures of the numerical dissipation and dispersion of the simulation results in particular for those with non-trivial patterns. By using these measures, a comparative study of the TDG-SUPG and TDG-FIC schemes as well as sensitivity studies on the time step size, the spatial element size and temporal accuracy are presented.

  1. A spatially stabilized TDG based finite element framework for modeling biofilm growth with a multi-dimensional multi-species continuum biofilm model

    Science.gov (United States)

    Feng, D.; Neuweiler, I.; Nackenhorst, U.

    2017-06-01

    We consider a model for biofilm growth in the continuum mechanics framework, where the growth of different components of biomass is governed by a time dependent advection-reaction equation. The recently developed time-discontinuous Galerkin (TDG) method combined with two different stabilization techniques, namely the Streamline Upwind Petrov Galerkin (SUPG) method and the finite increment calculus (FIC) method, are discussed as solution strategies for a multi-dimensional multi-species biofilm growth model. The biofilm interface in the model is described by a convective movement following a potential flow coupled to the reaction inside of the biofilm. Growth limiting substrates diffuse through a boundary layer on top of the biofilm interface. A rolling ball method is applied to obtain a boundary layer of constant height. We compare different measures of the numerical dissipation and dispersion of the simulation results in particular for those with non-trivial patterns. By using these measures, a comparative study of the TDG-SUPG and TDG-FIC schemes as well as sensitivity studies on the time step size, the spatial element size and temporal accuracy are presented.

  2. Spin and orbital moments of Co-carbide nanoparticles for permanent magnet applications

    Science.gov (United States)

    Arena, D. A.; Sterbinsky, G. E.; Carroll, K. J.; Yoon, H.; Meng, S.; Huba, Z. J.; Carpenter, E. E.

    2014-03-01

    Many efforts are currently devoted to the development of rare earth free permanent magnets (REFPMs). In newly developed permanent magnet materials, examination of the atomic scale magnetic properties is critical to gaining knowledge of the mechanisms of magnetism and hence furthering the development of these materials. X-ray magnetic circular dichroism (XMCD) is a core-level technique ideally suited for such studies as it provides element-specific information on magnetic properties. We present an XMCD study of the REFPM nanoparticulate Co-carbide using a new high-field end-station at beamline U4B of the National Synchrotron Light Source. This end-station facilitates measurement of XMCD spectra from magnetically hard materials. The Co-Carbide nanoparticles (NPs) under study are synthesized via wet chemical methods, which can lead to differences between the atomic and magnetic structures of the surface and bulk of NPs. To separate the determination of the surface and bulk magnetic properties we have combined our XMCD measurements with in-situ surface treatment. Preliminary measurements of Co L-edge XMCD spectra and element specific hysteresis point to the role of the Co orbital and spin moments in the establishment of the high coercive field and (BH)max in Co-carbide NPs.

  3. Probing Field Emission from Boron Carbide Nanowires

    Institute of Scientific and Technical Information of China (English)

    TIAN Ji-Fa; GAO Hong-Jun; BAO Li-Hong; WANG Xing-Jun; HUI Chao; LIU Fei; LI Chen; SHEN Cheng-Min; WANG Zong-Li; GU Chang-Zhi

    2008-01-01

    High density boron carbide nanowires are grown by an improved carbon thermal reduction technique. Transmission electron microscopy and electron energy lose spectroscopy of the sample show that the synthesized nanowires are B4 C with good crystallization. The field emission measurement for an individual boron nanowire is performed by using a Pt tip installed in the focused ion beam system. A field emission current with enhancement factor of 106 is observed and the evolution process during emission is also carefully studied. Furthermore, a two-step field emission with stable emission current density is found from the high-density nanowire film. Our results together suggest that boron carbide nanowires are promising candidates for electron emission nanodevices.

  4. Behavior of disordered boron carbide under stress.

    Science.gov (United States)

    Fanchini, Giovanni; McCauley, James W; Chhowalla, Manish

    2006-07-21

    Gibbs free-energy calculations based on density functional theory have been used to determine the possible source of failure of boron carbide just above the Hugoniot elastic limit (HEL). A range of B4C polytypes is found to be stable at room pressure. The energetic barrier for shock amorphization of boron carbide is by far the lowest for the B12(CCC) polytype, requiring only 6 GPa approximately = P(HEL) for collapse under hydrostatic conditions. The results clearly demonstrate that the collapse of the B12(CCC) phase leads to segregation of B12 and amorphous carbon in the form of 2-3 nm bands along the (113) lattice direction, in excellent agreement with recent transmission electron microscopy results.

  5. Ultrasonic ranking of toughness of tungsten carbide

    Science.gov (United States)

    Vary, A.; Hull, D. R.

    1983-01-01

    The feasibility of using ultrasonic attenuation measurements to rank tungsten carbide alloys according to their fracture toughness was demonstrated. Six samples of cobalt-cemented tungsten carbide (WC-Co) were examined. These varied in cobalt content from approximately 2 to 16 weight percent. The toughness generally increased with increasing cobalt content. Toughness was first determined by the Palmqvist and short rod fracture toughness tests. Subsequently, ultrasonic attenuation measurements were correlated with both these mechanical test methods. It is shown that there is a strong increase in ultrasonic attenuation corresponding to increased toughness of the WC-Co alloys. A correlation between attenuation and toughness exists for a wide range of ultrasonic frequencies. However, the best correlation for the WC-Co alloys occurs when the attenuation coefficient measured in the vicinity of 100 megahertz is compared with toughness as determined by the Palmqvist technique.

  6. Nonlinear optical imaging of defects in cubic silicon carbide epilayers.

    Science.gov (United States)

    Hristu, Radu; Stanciu, Stefan G; Tranca, Denis E; Matei, Alecs; Stanciu, George A

    2014-06-11

    Silicon carbide is one of the most promising materials for power electronic devices capable of operating at extreme conditions. The widespread application of silicon carbide power devices is however limited by the presence of structural defects in silicon carbide epilayers. Our experiment demonstrates that optical second harmonic generation imaging represents a viable solution for characterizing structural defects such as stacking faults, dislocations and double positioning boundaries in cubic silicon carbide layers. X-ray diffraction and optical second harmonic rotational anisotropy were used to confirm the growth of the cubic polytype, atomic force microscopy was used to support the identification of silicon carbide defects based on their distinct shape, while second harmonic generation microscopy revealed the detailed structure of the defects. Our results show that this fast and noninvasive investigation method can identify defects which appear during the crystal growth and can be used to certify areas within the silicon carbide epilayer that have optimal quality.

  7. Laser surface infiltration of tungsten-carbide in steel and aluminum alloys

    Energy Technology Data Exchange (ETDEWEB)

    Dahotre, N.B.; Mukherjee, K. (Michigan State Univ., East Lansing (USA))

    It has been demonstrated that surface modification in metals and alloys can be achieved by laser melting in conjunction with injection of particulate alloying elements in the heated zone. In our current experiments the authors have successfully implanted tungsten-carbide particles on the surface of several grades of carbon-steels as well as on the surface of a structural aluminum alloy. In both cases a significant increase in microhardness has been detected. Hardness profile from the interaction zone to the heat affected zone (HAZ) has been determined. The microstructural features of both the implanted zone and HAZ also have been determined. Effect of laser input energy, nature of tungsten-carbide particle size, size distribution and method of powder injection on the hardness profile have been investigated. Some preliminary examination of surface wear of such implanted material is also conducted. These results are discussed in detail.

  8. Growth of silicon carbide crystals on a seed while pulling silicon crystals from a melt

    Science.gov (United States)

    Ciszek, T. F.; Schwuttke, G. H. (Inventor)

    1979-01-01

    A saturated solution of silicon and an element such as carbon having a segregation coefficient less than unity is formed by placing a solid piece of carbon in a body of molten silicon having a temperature differential decreasing toward the surface. A silicon carbide seed crystal is disposed on a holder beneath the surface of the molten silicon. As a rod or ribbon of silicon is slowly pulled from the melt, a supersaturated solution of carbon in silicon is formed in the vicinity of the seed crystal. Excess carbon is emitted from the solution in the form of silicon carbide which crystallizes on the seed crystal held in the cool region of the melt.

  9. Electron-Spin Resonance in Boron Carbide

    Science.gov (United States)

    Wood, Charles; Venturini, Eugene L.; Azevedo, Larry J.; Emin, David

    1987-01-01

    Samples exhibit Curie-law behavior in temperature range of 2 to 100 K. Technical paper presents studies of electron-spin resonance of samples of hot pressed B9 C, B15 C2, B13 C2, and B4 C. Boron carbide ceramics are refractory solids with high melting temperatures, low thermal conductives, and extreme hardnesses. They show promise as semiconductors at high temperatures and have unusually large figures of merit for use in thermoelectric generators.

  10. Stereology of carbide phase in modified hypereutectic chromium cast iron

    Directory of Open Access Journals (Sweden)

    J. Suchoń

    2010-04-01

    Full Text Available In paper are presented results of studies of carbide phase stereology modified hypereutectic wear resistance chromium cast iron which contains carbon about 3,5% and chromium about 25%. Three substances were applied to the modification: boron carbide (B4C, ferroniobium (FeNb and mixture of ferroniobium and rare-earth (RE. The measurements of geometrical features of carbides were conducted on microsection taken from castings wich were cooled with various velocities.

  11. Characterization of boron carbide with an electron microprobe

    Science.gov (United States)

    Matteudi, G.; Ruste, J.

    1983-01-01

    Within the framework of a study of heterogeneous materials (Matteudi et al., 1971: Matteudi and Verchery, 1972) thin deposits of boron carbide were characterized. Experiments using an electronic probe microanalyzer to analyze solid boron carbide or boron carbide in the form of thick deposits are described. Quantitative results on boron and carbon are very close to those obtained when applying the Monte Carlo-type correction calculations.

  12. Field Emission of Thermally Grown Carbon Nanostructures on Silicon Carbide

    Science.gov (United States)

    2012-03-22

    thermal decomposition of silicon carbide does not utilize a catalyst, therefore relatively defect free. One drawback to this method, however is that the CNT...In this thesis, silicon carbide samples are patterned to create elevated emission sites in an attempt to minimize the field emission screening effect...Patterning is accomplished by using standard photolithography methods to implement a masking nickel layer on the silicon carbide . Pillars are created

  13. Delivering carbide ligands to sulfide-rich clusters.

    Science.gov (United States)

    Reinholdt, Anders; Herbst, Konrad; Bendix, Jesper

    2016-02-01

    The propensity of the terminal ruthenium carbide Ru(C)Cl2(PCy3)2 (RuC) to form carbide bridges to electron-rich transition metals enables synthetic routes to metal clusters with coexisting carbide and sulfide ligands. Electrochemical experiments show the Ru≡C ligand to exert a relatively large electron-withdrawing effect compared with PPh3, effectively shifting redox potentials.

  14. Combustion Dynamics and Stability Modeling of a Liquid Oxygen/RP-2 Oxygen-Rich Staged Combustion Preburner and Thrust Chamber Assembly with Gas-Centered Swirl Coaxial Injector Elements

    Science.gov (United States)

    Casiano, M. J.; Kenny, R. J.; Protz, C. S.; Garcia, C. P.; Simpson, S. P.; Elmore, J. L.; Fischbach, S. R.; Giacomoni, C. B.; Hulka, J. R.

    2016-01-01

    The Combustion Stability Tool Development (CSTD) project, funded by the Air Force Space and Missile Systems Center, began in March 2015 supporting a renewed interest in the development of a liquid oxygen/hydrocarbon, oxygen-rich combustion engine. The project encompasses the design, assembly, and hot-fire testing of the NASA Marshall Space Flight Center 40-klbf Integrated Test Rig (MITR). The test rig models a staged-combustion configuration by combining an oxygen-rich preburner (ORPB), to generate hot gas, with a thrust chamber assembly (TCA) using gas-centered swirl coaxial injector elements. There are five separately designed interchangeable injectors in the TCA that each contain 19- or 27- injector elements. A companion paper in this JANNAF conference describes the design characteristics, rationale, and fabrication issues for all the injectors. The data acquired from a heavily instrumented rig encompasses several injectors, several operating points, and stability bomb tests. Another companion paper in this JANNAF conference describes this test program in detail. In this paper, dynamic data from the hot-fire testing is characterized and used to identify the responses in the ORPB and TCA. A brief review of damping metrics are discussed and applied as a measure of stability margin for damped acoustic modes. Chug and longitudinal combustion stability models and predictions are described which includes new dynamic models for compressible flow through an orifice and a modification to incorporate a third feed line for inclusion of the fuel-film coolant. Flow-acoustics finite element modeling is used to investigate the anticipated TCA acoustics, the effects of injector element length on stability margin, and the potential use of an ORPB orifice trip ring for improving longitudinal stability margin.

  15. Sintering of nano crystalline silicon carbide by doping with boron carbide

    Indian Academy of Sciences (India)

    M S Datta; A K Bandyopadhyay; B Chaudhuri

    2002-06-01

    Sinterable nano silicon carbide powders of mean particle size (37 nm) were prepared by attrition milling and chemical processing of an acheson type alpha silicon carbide having mean particle size of 0.39 m (390 nm). Pressureless sintering of these powders was achieved by addition of boron carbide of 0.5 wt% together with carbon of 1 wt% at 2050°C at vacuum (3 mbar) for 15 min. Nearly 99% sintered density was obtained. The mechanism of sintering was studied by scanning electron microscopy and transmission electron microscopy. This study shows that the mechanism is a solid-state sintering process. Polytype transformation from 6H to 4H was observed.

  16. Silicon carbide sintered body manufactured from silicon carbide powder containing boron, silicon and carbonaceous additive

    Science.gov (United States)

    Tanaka, Hidehiko

    1987-01-01

    A silicon carbide powder of a 5-micron grain size is mixed with 0.15 to 0.60 wt% mixture of a boron compound, i.e., boric acid, boron carbide (B4C), silicon boride (SiB4 or SiB6), aluminum boride, etc., and an aluminum compound, i.e., aluminum, aluminum oxide, aluminum hydroxide, aluminum carbide, etc., or aluminum boride (AlB2) alone, in such a proportion that the boron/aluminum atomic ratio in the sintered body becomes 0.05 to 0.25 wt% and 0.05 to 0.40 wt%, respectively, together with a carbonaceous additive to supply enough carbon to convert oxygen accompanying raw materials and additives into carbon monoxide.

  17. Silicon Carbide Corrugated Mirrors for Space Telescopes Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Trex Enterprises Corporation (Trex) proposes technology development to manufacture monolithic, lightweight silicon carbide corrugated mirrors (SCCM) suitable for...

  18. HEAT-RESISTANT MATERIAL WITH SILICON CARBIDE AS A BASE,

    Science.gov (United States)

    A new high-temperature material, termed SG-60, is a silicon carbide -graphite composite in which the graphite is the thermostability carrier since it...is more heat-conducting and softer (heat conductivity of graphite is 0.57 cal/g-cm-sec compared with 0.02 cal/g-cm-sec for silicon carbide ) while... silicon carbide is the carrier of high-temperature strength and hardness. The high covalent bonding strength of the atoms of silicon carbide (283 kcal

  19. Chemical state of fission products in irradiated uranium carbide fuel

    Science.gov (United States)

    Arai, Yasuo; Iwai, Takashi; Ohmichi, Toshihiko

    1987-12-01

    The chemical state of fission products in irradiated uranium carbide fuel has been estimated by equilibrium calculation using the SOLGASMIX-PV program. Solid state fission products are distributed to the fuel matrix, ternary compounds, carbides of fission products and intermetallic compounds among the condensed phases appearing in the irradiated uranium carbide fuel. The chemical forms are influenced by burnup as well as stoichiometry of the fuel. The results of the present study almost agree with the experimental ones reported for burnup simulated carbides.

  20. Precipitation Effect on Mechanical Properties and Phase Stability of High Manganese Steel

    Science.gov (United States)

    Bae, Cheoljun; Kim, Rosa; Lee, Un-Hae; Kim, Jongryoul

    2017-09-01

    High manganese (Mn) steels are attractive for automotive applications due to their excellent tensile strength and superior elongation. However, the relatively low yield strength of Mn steels compared to other advanced high-strength steels is a critical problem limiting their use in structural parts. In order to increase the yield strength, the precipitation hardening effect of Mn steels was investigated by the addition of carbide-forming elements. Changes in the austenite phase stability were also evaluated in terms of stacking fault energy (SFE). As a result, fine V(C,N) precipitates were found to increase the yield strength effectively but to lower the SFE by the consumption of matrix carbons. For achieving precipitation hardening without sacrificing austenite stability, the soluble carbon content was discussed.

  1. Characterization of silicon-silicon carbide ceramic derived from carbon-carbon silicon carbide composites

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Vijay K. [Indian Institute of Technology, Varanasi (India). Dept. of Mechanical Engineering; Krenkel, Walter [Univ. of Bayreuth (Germany). Dept. of Ceramic Materials Engineering

    2013-04-15

    The main objective of the present work is to process porous silicon - silicon carbide (Si - SiC) ceramic by the oxidation of carboncarbon silicon carbide (C/C - SiC) composites. Phase studies are performed on the oxidized porous composite to examine the changes due to the high temperature oxidation. Further, various characterization techniques are performed on Si- SiC ceramics in order to study the material's microstructure. The effects of various parameters such as fiber alignment (twill weave and short/chopped fiber) and phenolic resin type (resol and novolak) are characterized.

  2. Epitaxial and bulk growth of cubic silicon carbide on off-oriented 4H-silicon carbide substrates

    OpenAIRE

    Norén, Olof

    2015-01-01

    The growth of bulk cubic silicon carbide has for a long time seemed to be something for the future. However, in this thesis the initial steps towards bulk cubic silicon carbide have been taken. The achievement of producing bulk cubic silicon carbide will have a great impact in various fields of science and industry such as for example the fields of semiconductor technology within electronic- and optoelectronic devices and bio-medical applications. The process that has been used to grow the bu...

  3. Synthesis of IV-VI Transition Metal Carbide and Nitride Nanoparticles Using a Reactive Mesoporous Template for Electrochemical Hydrogen Evolution Reaction

    KAUST Repository

    Alhajri, Nawal Saad

    2016-01-01

    Interstitial carbides and nitrides of early transition metals in Groups IV-VI exhibit platinum-like behavior which makes them a promising candidate to replace noble metals in a wide variety of reactions. Most synthetic methods used to prepare these materials lead to bulk or micron size powder which limits their use in reactions in particular in catalytic applications. Attempts toward the production of transition metal carbide and nitride nanoparticles in a sustainable, simple and cheap manner have been rapidly increasing. In this thesis, a new approach was presented to prepare nano-scale transition metal carbides and nitrides of group IV-VI with a size as small as 3 nm through the reaction of transition metal precursor with mesoporous graphitic carbon nitride (mpg-C3N4) that not only provides confined spaces for nanoparticles formation but also acts as a chemical source of nitrogen and carbon. The produced nanoparticles were characterized by powder X-ray diffraction (XRD), temperature-programmed reaction with mass spectroscopy (MS), CHN elemental analyses, thermogravimetric analyses (TGA), nitrogen sorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The effects of the reaction temperature, the ratio of the transition metal precursor to the reactive template (mpg-C3N4), and the selection of the carrier gas (Ar, N2, and NH3) on the resultant crystal phases and structures were investigated. The results indicated that different tantalum phases with cubic structure, TaN, Ta2CN, and TaC, can be formed under a flow of nitrogen by changing the reaction temperatures. Two forms of tantalum nitride, namely TaN and Ta3N5, were selectively formed under N2 and NH3 flow, respectively. Significantly, the formation of TaC, Ta2CN, and TaN can be controlled by altering the weight ratio of the C3N4 template relative to the Ta precursor at 1573 K under a flow of nitrogen where high C3N4/Ta precursor ratio generally resulted in high carbide

  4. Co元素对硬质合金基底金刚石涂层膜基界面结合强度的影响∗%The Influence of Co binding phase on adhesive strength of diamond coating with cemented carbide substrate

    Institute of Scientific and Technical Information of China (English)

    简小刚; 陈军

    2015-01-01

    Diamond coating has many excellent properties as the same as those of the natural diamond, such as extreme hard-ness, high thermal conductivity, low thermal expansion coefficient, high chemical stability, and good abrasive resistance, which is considered as the best tool coating material applied to the high-silicon aluminum alloy cutting. We can use the hot filament chemical vapor deposition method (HFCVD) to deposit a 2—20 µm diamond coating on the cemented carbide tool to improve the cutting performance and increase the tool life significantly. Many experiments have proved that the existence of cobalt phase can weaken the adhesive strength of diamond coating. However, we still lack a perfect theory to explain why the Co element can reduce the adhesive strength of diamond coating is still lacking. What we can do now is only to improve the adhesive strength of diamond coating by doing testing many times in experiments. Compared with these traditional experiments, the first principles simulation based on quantum mechanics can describe the microstructure property and electron density of materials. It is successfully used to investigate the surface, interface, electron component, and so on etc. We can also use this method to study the interface problem at an atomic level. So the first principles based upon density functional theory (DFT) is used to investigate the influence of cobalt binding phase in cemented carbide substrate on adhesive strength of diamond coating. In this article, we uses Material Studios software to build WC/diamond and WC-Co/diamond interface models to evaluate the influence of cobalt phase on the adhesive strength of diamond coating with CASTEP program which can calculate the most stablest structure of film-substrate interface. We use PBE functional form to obtain the exchange potential and relevant potential, and to solve the self-consistent Kohn-Sham equations. We calculate the interfacial bonding energy, analyse the electron density of

  5. Direct Electrochemical Preparation of Cobalt, Tungsten, and Tungsten Carbide from Cemented Carbide Scrap

    Science.gov (United States)

    Xiao, Xiangjun; Xi, Xiaoli; Nie, Zuoren; Zhang, Liwen; Ma, Liwen

    2017-02-01

    A novel process of preparing cobalt, tungsten, and tungsten carbide powders from cemented carbide scrap by molten salt electrolysis has been investigated in this paper. In this experiment, WC-6Co and NaCl-KCl salt were used as sacrificial anode and electrolyte, respectively. The dissolution potential of cobalt and WC was determined by linear sweep voltammetry to be 0 and 0.6 V ( vs Ag/AgCl), respectively. Furthermore, the electrochemical behavior of cobalt and tungsten ions was investigated by a variety of electrochemical techniques. Results of cyclic voltammetry (CV) and square-wave voltammetry show that the cobalt and tungsten ions existed as Co2+ and W2+ on melts, respectively. The effect of applied voltage, electrolysis current, and electrolysis times on the composition of the product was studied. Results showed that pure cobalt powder can be obtained when the electrolysis potential is lower than 0.6 V or during low current and short times. Double-cathode and two-stage electrolysis was utilized for the preparation of cobalt, tungsten carbide, and tungsten powders. Additionally, X-ray diffraction results confirm that the product collected at cathodes 1 and 2 is pure Co and WC, respectively. Pure tungsten powder was obtained after electrolysis of the second part. Scanning electron microscope results show that the diameters of tungsten, tungsten carbide, and cobalt powder are smaller than 100, 200, and 200 nm, respectively.

  6. Direct Electrochemical Preparation of Cobalt, Tungsten, and Tungsten Carbide from Cemented Carbide Scrap

    Science.gov (United States)

    Xiao, Xiangjun; Xi, Xiaoli; Nie, Zuoren; Zhang, Liwen; Ma, Liwen

    2016-10-01

    A novel process of preparing cobalt, tungsten, and tungsten carbide powders from cemented carbide scrap by molten salt electrolysis has been investigated in this paper. In this experiment, WC-6Co and NaCl-KCl salt were used as sacrificial anode and electrolyte, respectively. The dissolution potential of cobalt and WC was determined by linear sweep voltammetry to be 0 and 0.6 V (vs Ag/AgCl), respectively. Furthermore, the electrochemical behavior of cobalt and tungsten ions was investigated by a variety of electrochemical techniques. Results of cyclic voltammetry (CV) and square-wave voltammetry show that the cobalt and tungsten ions existed as Co2+ and W2+ on melts, respectively. The effect of applied voltage, electrolysis current, and electrolysis times on the composition of the product was studied. Results showed that pure cobalt powder can be obtained when the electrolysis potential is lower than 0.6 V or during low current and short times. Double-cathode and two-stage electrolysis was utilized for the preparation of cobalt, tungsten carbide, and tungsten powders. Additionally, X-ray diffraction results confirm that the product collected at cathodes 1 and 2 is pure Co and WC, respectively. Pure tungsten powder was obtained after electrolysis of the second part. Scanning electron microscope results show that the diameters of tungsten, tungsten carbide, and cobalt powder are smaller than 100, 200, and 200 nm, respectively.

  7. Characterization of Nanometric-Sized Carbides Formed During Tempering of Carbide-Steel Cermets

    Directory of Open Access Journals (Sweden)

    Matus K.

    2016-06-01

    Full Text Available The aim of this article of this paper is to present issues related to characterization of nanometric-sized carbides, nitrides and/or carbonitrides formed during tempering of carbide-steel cermets. Closer examination of those materials is important because of hardness growth of carbide-steel cermet after tempering. The results obtained during research show that the upswing of hardness is significantly higher than for high-speed steels. Another interesting fact is the displacement of secondary hardness effect observed for this material to a higher tempering temperature range. Determined influence of the atmosphere in the sintering process on precipitations formed during tempering of carbide-steel cermets. So far examination of carbidesteel cermet produced by powder injection moulding was carried out mainly in the scanning electron microscope. A proper description of nanosized particles is both important and difficult as achievements of nanoscience and nanotechnology confirm the significant influence of nanocrystalline particles on material properties even if its mass fraction is undetectable by standard methods. The following research studies have been carried out using transmission electron microscopy, mainly selected area electron diffraction and energy dispersive spectroscopy. The obtained results and computer simulations comparison were made.

  8. Stress in tungsten carbide-diamond like carbon multilayer coatings

    NARCIS (Netherlands)

    Pujada, B.R.; Tichelaar, F.D.; Janssen, G.C.A.M.

    2007-01-01

    Tungsten carbide-diamond like carbon (WC-DLC) multilayer coatings have been prepared by sputter deposition from a tungsten-carbide target and periodic switching on and off of the reactive acetylene gas flow. The stress in the resulting WC-DLC multilayers has been studied by substrate curvature. Peri

  9. Carbide Transformations in Tempering of Complexly Alloyed White Cast Iron

    Science.gov (United States)

    Vdovin, K. N.; Gorlenko, D. A.; Zavalishchin, A. N.

    2015-07-01

    Variation of the chemical composition of all phases and structural components (metallic matrix, eutectic and secondary carbides) in complexly alloyed cast iron is studied after crystallization and different variants of tempering. It is shown that several groups of secondary carbides may be distinguished according to their morphology and chemical composition.

  10. Preparation and Electrocatalytic Activity of Tungsten Carbide Nanorod Arrays

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    High density tungsten carbide nanorod arrays have been prepared by magnetron sputtering (MS) using the aluminum lattice membrane (ALM) as template. Electrocatalytic properties of nitromethane electroreduction on the tungsten carbide nanorod arrays electrode were investigated by electrochemical method, and their electrocatalytic activity is approached to that of the Pt foil electrode.

  11. Interface Defeat of Long Rods Impacting Oblique Silicon Carbide

    Science.gov (United States)

    2011-02-01

    Test data for gold rods impacting unconfined silicon carbide targets are reported. This work focuses on the dwell phenomenon exhibited by silicon ... carbide for targets at obliquity. Experiments are presented for obliquities of 30 deg, 45 deg and 60 deg, with and without cover plates. Results are compared to normal impact.

  12. Silicon Carbide Tiles for Sidewall Lining in Aluminium Electrolysis Cells

    Institute of Scientific and Technical Information of China (English)

    RUANBo; ZHAOJunguo; 等

    1999-01-01

    The paper introduces the nitride bonded silicon carbide used for sidewall lining in aluminium eletrolysis cells ,including technical process,main properties and application results.Comparison tests on various physical properties of silicon carbide products made by LIRR and other producers worldwide have also been conducted in an independent laboratory.

  13. Titanium Carbide-Nickel Cermets: Processing and Joing

    Science.gov (United States)

    1952-03-01

    Titanium carbide -nickel cermets can be sintered to have transverse rupture strengths over 250,000 pounds per square inch. To do so, four principal...enough to allow thorough degassing. Joining titanium - carbide cermets to high-temperature alloys has been accomplished by vacuum diffusion, and gives

  14. TITANIUM CARBIDE CONTENT EFFECT ON EROSION IN CERMET ROCKET NOZZLES

    Science.gov (United States)

    class investigated consisted of an AISI Type 316 stainless steel matrix incorporating a hard phase of titanium carbide ranging in content from 20% to...55% by volume. The results of the study indicated that under the test conditions, increases in the titanium carbide constituents did increase the

  15. Development and characterization of solid solution tri-carbides

    Science.gov (United States)

    Knight, Travis; Anghaie, Samim

    2001-02-01

    Solid-solution, binary uranium/refractory metal carbide fuels have been shown to be capable of performing at high temperatures for nuclear thermal propulsion applications. More recently, tri-carbide fuels such as (U, Zr, Nb)C1+x with less than 10% metal mole fraction uranium have been studied for their application in ultra-high temperature, high performance space nuclear power systems. These tri-carbide fuels require high processing temperatures greater than 2600 K owing to their high melting points in excess of 3600 K. This paper presents the results of recent studies involving hypostoichiometric, single-phase tri-carbide fuels. Processing techniques of cold uniaxial pressing and sintering were investigated to optimize the processing parameters necessary to produce high density (low porosity), single phase, solid solution mixed carbide nuclear fuels for testing. Scanning electron microscopy and xray diffraction were used to analyze samples. Liquid phase sintering with UC1+x at temperatures near 2700 K was shown to be instrumental in achieving good densification in hyper- and near-stoichiometric mixed carbides. Hypostoichiometric carbides require even higher processing temperatures greater than 2800 K in order to achieve liquid phase sintering with a UC liquid phase and good densification of the final solid solution, tri-carbide fuel. .

  16. Zirconium carbide coating for corium experiments related to water-cooled and sodium-cooled reactors

    Science.gov (United States)

    Plevacova, K.; Journeau, C.; Piluso, P.; Zhdanov, V.; Baklanov, V.; Poirier, J.

    2011-07-01

    Since the TMI and Chernobyl accidents the risk of nuclear severe accident is intensively studied for existing and future reactors. In case of a core melt-down accident in a nuclear reactor, a complex melt, called corium, forms. To be able to perform experiments with prototypic corium materials at high temperature, a coating which resists to different corium melts related to Generation I and II Water Reactors and Generation IV sodium fast reactor was researched in our experimental platforms both in IAE NNC in Kazakhstan and in CEA in France. Zirconium carbide was selected as protective coating for graphite crucibles used in our induction furnaces: VCG-135 and VITI. The method of coating application, called reactive wetting, was developed. Zirconium carbide revealed to resist well to the (U x, Zr y)O 2-z water reactor corium. It has also the advantage not to bring new elements to this chemical system. The coating was then tested with sodium fast reactor corium melts containing steel or absorbers. Undesirable interactions were observed between the coating and these materials, leading to the carburization of the corium ingots. Concerning the resistance of the coating to oxide melts without ZrO 2, the zirconium carbide coating keeps its role of protective barrier with UO 2-Al 2O 3 below 2000 °C but does not resist to a UO 2-Eu 2O 3 mixture.

  17. Wettability and Bonding between Ni and Ti(C, N) with Multiple Carbide Additions

    Institute of Scientific and Technical Information of China (English)

    Ning LIU; Minghai CHEN; Yudong XU; Jie ZHOU; Min SHI

    2005-01-01

    The wettability and bonding in Ni/Ti(C, N) systems with multiple carbide additions were studied by sessile drop technique and vacuum brazing technique, respectively. The phase characterizations of substrates and fracture surfaces were conducted by XRD. The microstructures at metal/ceramic interfaces and fracture surfaces were observed via SEM in back scattered mode and second electron mode, respectively. Furthermore, an X-ray energy-dispersive spectrometer (EDS) attached to SEM was used to study the elements diffusion in interfacial regions. The results reveal that diffusion and dissolution mechanism controlled reactive wetting takes place in the system in high temperature wetting. Results also show that the contact angles decrease with multiple carbide additions, and the effect of multiple carbide additions is stronger than that of single additions. The contact angle reaches the lowest value in the lowest TiC content case. The enhancement of the wettability is due to alloying procedure during high temperature wetting when metallic atoms diffuse into Ni phase, which decreases the interfacial energy of Ni/Ti(C, N) systems. The bonding results show that the interfacial bonding strength is higher than that of solid solutions, that makes most of the specimens fail in ceramics matrix.

  18. Effect of Various Carbides on the Wettability in Ni/Ti( C, N) System

    Institute of Scientific and Technical Information of China (English)

    LIU Ning; CHEN Minghai; XU Yudong; ZHOU Jie; SHI Min

    2005-01-01

    The wettability in Ni / Ti ( C, N) systems with various carbides additions was investigated by the sessile drop technique. The substrates prepared by HP at 2073 K for lh before and after wetting were characterized by XRD. The microstructure at metal/ceramics interfaces was observed via SEM in a back scattered mode. Furthermore, an X-ray energy-dispersive spectrometer (EDS) attached to SEM was used to study the element diffusion in interracial regions. The results reveal that reactive wetting takes place in the system in high temperature wetting procedure, which is controlled by diffusion and dissolution mechanism. Results also show that the contact angles decrease with various carbides aditions, including WC, Mo2 C, TaC, NbC and VC, and decrease continuously with the increasing of additions. The order of the contact angles in Ni/Ti(C,N) systems with 10 wt% carbides additions is Mo2 C < TaC < WC < VC < NbC. The enhancement of the wettability is due to an alloying procedure during high temperature wetting when metallic atoms diffuse into Ni phase, which decreases the interfacial energy of Ni/Ti(C,N) systems.

  19. Electro-Explosive Doping of VT6 Titanium Alloy Surface by Boron Carbide

    Science.gov (United States)

    Kobzareva, T. Yu; Gromov, V. E.; Ivanov, Yu F.; Budovskkh, E. A.; Konovalov, S. V.

    2016-09-01

    The studies carried out in this work target detection of changes in the surface layer of titanium alloy VT6 after electro-explosive alloying (EEA) by boron carbide. EEA of VT6 titanium alloy surface is the plasma alloying formed during the electric explosion of foil with the sample powder of boron carbide. Carbon fibers with weight 140 mg were used as an explosive conductor. Sample powder of boron carbide B4C was placed in the area of explosion on the carbon fibers. It was revealed that EEA of the surface layers of titanium alloy samples VT6 leads to the modification of the layer, thickness of which changes from 10 pm to 50 pm. Heterogeneous distribution of alloying elements was found in the treatment zone by the methods of X-ray microanalysis. A significant difference in their concentration in the identified layers leads to difference in their structural and tribological behaviour. It was revealed that after electro-explosive alloying the microhardness of titanium alloy VT6 significantly increases. Electro-explosive alloying leads to the formation of a structure of submicro- and nano-scale level. It allows strength and tribological properties of the treated surface to be increased.

  20. Phase transformation during surface ablation of cobalt-cemented tungsten carbide with pulsed UV laser

    Energy Technology Data Exchange (ETDEWEB)

    Li, T. [Academia Sinica, Shanghai, SH (China). Shanghai Inst. of Optics and Fine Mechanics; Northwest Institute of Nuclear Technology, Xi' an (China); Lou, Q.; Dong, J.; Wei, Y. [Academia Sinica, Shanghai, SH (China). Shanghai Inst. of Optics and Fine Mechanics; Liu, J. [Northwest Institute of Nuclear Technology, Xi' an (China)

    2001-09-01

    Surface ablation of cobalt-cemented tungsten carbide hard metal has been carried out in this work using a 308 nm, 20 ns XeCl excimer laser. Surface microphotography and XRD, as well as an electron probe have been used to investigate the transformation of phase and microstructure as a function of the pulse-number of laser shots at a laser fluence of 2.5 J/cm{sup 2}. The experimental results show that the microstructure of cemented tungsten carbide is transformed from the original polygonal grains of size 3 {mu}m to interlaced large, long grains with an increase in the number of laser shots up to 300, and finally to gross grains of size 10 {mu}m with clear grain boundaries after 700 shots of laser irradiation. The crystalline structure of the irradiated area is partly transformed from the original WC to {beta}WC{sub 1-x}, then to {alpha}W{sub 2}C and CW{sub 3}, and finally to W crystal. It is suggested that the undulating 'hill-valley' morphology may be the result of selective removal of cobalt binder from the surface layer of the hard metal. The formation of non-stoichiometric tungsten carbide may result from the escape of elemental carbon due to accumulated heating of the surface by pulsed laser irradiation. (orig.)

  1. Phase transformation during surface ablation of cobalt-cemented tungsten carbide with pulsed UV laser

    Science.gov (United States)

    Li, T.; Lou, Q.; Dong, J.; Wei, Y.; Liu, J.

    Surface ablation of cobalt-cemented tungsten carbide hard metal has been carried out in this work using a 308 nm, 20 ns XeCl excimer laser. Surface microphotography and XRD, as well as an electron probe have been used to investigate the transformation of phase and microstructure as a function of the pulse-number of laser shots at a laser fluence of 2.5 J/cm2. The experimental results show that the microstructure of cemented tungsten carbide is transformed from the original polygonal grains of size 3 μm to interlaced large, long grains with an increase in the number of laser shots up to 300, and finally to gross grains of size 10 μm with clear grain boundaries after 700 shots of laser irradiation. The crystalline structure of the irradiated area is partly transformed from the original WC to βWC1-x, then to αW2C and CW3, and finally to W crystal. It is suggested that the undulating `hill-valley' morphology may be the result of selective removal of cobalt binder from the surface layer of the hard metal. The formation of non-stoichiometric tungsten carbide may result from the escape of elemental carbon due to accumulated heating of the surface by pulsed laser irradiation.

  2. Iron carbide as a source of carbon for graphite and diamond formation under lithospheric mantle P-T parameters

    Science.gov (United States)

    Bataleva, Yuliya V.; Palyanov, Yuri N.; Borzdov, Yuri M.; Bayukov, Oleg A.; Zdrokov, Evgeniy V.

    2017-08-01

    Experimental modeling of natural carbide-involving reactions, implicated in the graphite and diamond formation and estimation of the iron carbide stability in the presence of S-bearing fluids, sulfide melts as well as mantle silicates and oxides, was performed using a multi-anvil high-pressure split-sphere apparatus. Experiments were carried out in the carbide-sulfur (Fe3C-S), carbide-sulfur-oxide (Fe3C-S-SiO2-MgO) and carbide-sulfide (Fe3C-FeS2) systems, at pressure of 6.3 GPa, temperatures in the range of 900-1600 °C and run time of 18-40 h. During the interaction of cohenite with S-rich reduced fluid or pyrite at 900-1100 °C, extraction of carbon from carbide was realized, resulting in the formation of graphite in assemblage with pyrrhotite and cohenite. At higher temperatures complete reaction of cohenite with newly-formed sulfide melt was found to produce metal-sulfide melt with dissolved carbon (Fe64S27C9 (1200 °C)-Fe54S40C6 (1500 °C), at.%), which acted as a crystallization medium for graphite (1200-1600 °C) and diamond growth on seeds (1300-1600 °C). Reactions of cohenite and oxides with S-rich reduced fluid resulted in the formation of graphite in assemblage with highly ferrous orthopyroxene and pyrrhotite (900-1100 °C) or in hypersthene formation, as well as graphite crystallization and diamond growth on seeds in the Fe-S-C melt (1200-1600 °C). We show that the main processes of carbide interaction with S-rich fluid or sulfide melt are recrystallization of cohenite (900-1100 °C), extraction of carbon and iron in the sulfide melt, and graphite formation and diamond growth in the metal-sulfide melt with dissolved carbon. Our results evidence that iron carbide can act as carbon source in the processes of natural graphite and diamond formation under reduced mantle conditions. We experimentally demonstrate that cohenite in natural environments can be partially consumed in the reactions with mantle silicates and oxides, and is absolutely unstable in

  3. Novel Polymer Nanocomposite With Silicon Carbide Nanoparticles

    Directory of Open Access Journals (Sweden)

    Alyona I. Wozniak

    2015-09-01

    Full Text Available Polyimides are ranked among the most heat-resistant polymers and are widely used in high temperature plastics, adhesives, dielectrics, photoresistors, nonlinear optical materials, membrane materials for gasseparation, and Langmuir–Blodgett (LB films, among others. While there is a variety of high temperature stable polyimides, there is a growing demand for utilizing these materials at higher temperatures in oxidizing and aggressive environments. Therefore, we sought to use oxidation-resistant materials to enhance properties of the polyimide composition maintaining polyimide weights and processing advantages. In this paper we introduced results of utilizing inorganic nanostructured silicon carbide particles to produce an inorganic particle filled polyimide materials.

  4. Mechanical characteristics of microwave sintered silicon carbide

    Indian Academy of Sciences (India)

    S Mandal; A Seal; S K Dalui; A K Dey; S Ghatak; A K Mukhopadhyay

    2001-04-01

    The present work deals with the sintering of SiC with a low melting additive by microwave technique. The mechanical characteristics of the products were compared with that of conventionally sintered products. The failure stress of the microwave sintered products, in biaxial flexure, was superior to that of the products made by conventional sintering route in ambient condition. In firing of products by conventionally sintered process, SiC grain gets oxidized producing SiO2 (∼ 32 wt%) and deteriorates the quality of the product substantially. Partially sintered silicon carbide by such a method is a useful material for a varieties of applications ranging from kiln furniture to membrane material.

  5. Niobium carbide precipitation in microalloyed steel

    Energy Technology Data Exchange (ETDEWEB)

    Klinkenberg, C.; Hulka, K. [Niobium Products Co. GmbH, Duesseldorf (Germany); Bleck, W. [Inst. for Ferrous Metallurgy, RWTH Aachen Univ., Aachen (Germany)

    2004-11-01

    The precipitation of niobium carbo-nitrides in the austenite phase, interphase and ferrite phase of microalloyed steel was assessed by a critical literature review and a round table discussion. This work analyses the contribution of niobium carbide precipitates formed in ferrite in the precipitation hardening of commercially hot rolled strip. Thermodynamics and kinetics of niobium carbo-nitride precipitation as well as the effect of deformation and temperature on the precipitation kinetics are discussed in various examples to determine the amount of niobium in solid solution that will be available for precipitation hardening after thermomechanical rolling in the austenite phase and successive phase transformation. (orig.)

  6. Titanium carbide coatings for aerospace ball bearings

    Science.gov (United States)

    Boving, Hans J.; Haenni, Werner; Hintermann, HANS-E.

    1988-01-01

    In conventional ball bearings, steel to steel contacts between the balls and the raceways are at the origin of microwelds which lead to material transfer, surface roughening, lubricant breakdown, and finally to a loss in the bearing performances. To minimize the microwelding tendencies of the contacting partners it is necessary to modify their surface materials; the solid to solid collisions themselves are difficult to avoid. The use of titanium carbide coated steel balls can bring spectacular improvements in the performances and lifetimes of both oil-grease lubricated and oil-grease free bearings in a series of severe applications.

  7. Supported molybdenum carbide for higher alcohol synthesis from syngas

    DEFF Research Database (Denmark)

    Wu, Qiongxiao; Christensen, Jakob Munkholt; Chiarello, Gian Luca

    2013-01-01

    Molybdenum carbide supported on active carbon, carbon nanotubes, and titanium dioxide, and promoted by K2CO3, has been prepared and tested for methanol and higher alcohol synthesis from syngas. At optimal conditions, the activity and selectivity to alcohols (methanol and higher alcohols) over...... supported molybdenum carbide are significantly higher compared to the bulk carbide. The CO conversion reaches a maximum, when about 20wt% Mo2C is loaded on active carbon. The selectivity to higher alcohols increases with increasing Mo2C loading on active carbon and reaches a maximum over bulk molybdenum...... carbide, while the selectivity to methanol follows the opposite trend. The effect of Mo2C loading on the alcohol selectivity at a fixed K/Mo molar ratio of 0.14 could be related to the amount of K2CO3 actually on the active Mo2C phase and the size, structure and composition of the supported carbide...

  8. Synthesis and photoluminescence property of boron carbide nanowires

    Institute of Scientific and Technical Information of China (English)

    Bao Li-Hong; Li Chen; Tian Yuan; Tian Ji-Fa; Hui Chao; Wang Xing-Jun; Shen Cheng-Min; Gao Hong-Jun

    2008-01-01

    Large scale, high density boron carbide nanowires have been synthesized by using an improved carbothermal reduction method with B/B2O3/C powder precursors under an argon flow at 1100~C. The boron carbide nanowires are 5-10 μm in length and 80-100 nm in diameter. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) characterizations show that the boron carbide nanowire has a B4C rhombohedral structure with good crystallization. The Raman spectrum of the as-grown boron carbide nanowires is consistent with that of a B4C structure consisting of B11C icosahedra and C-B-C chains. The room temperature photoluminescence spectrum of the boron carbide nanowires exhibits a visible range of emission centred at 638 nm.

  9. Análisis de pérdida de estabilidad no lineal de elementos estructurales sometidos a compresión. // Slender structural elements non lineal stability analysis.

    Directory of Open Access Journals (Sweden)

    C. Fabré Sentile

    2007-01-01

    Full Text Available En el presente artículo se muestra el análisis de perdida de estabilidad en elementos estructurales delgados bajocompresión. Se realiza la exposición de las consideraciones del análisis lineal y no lineal de perdida de estabilidad y seejemplifica con una estructura modelada mediante elementos finitos, estableciéndose conclusiones interesantes.Palabras claves: Estructuras esbeltas, estabilidad no-lineal, Euler.______________________________________________________________________________Abstract:Presently paper deals with stability analysis in structural elements. The considerations of lineal and non lineal analysis ofstability are exposed and it is exemplified with a finite element structure model, settling down interesting conclusions.Key words: Slender structures, non-lineal stability, Euler.

  10. Electrocatalysis using transition metal carbide and oxide nanocrystals

    Science.gov (United States)

    Regmi, Yagya N.

    Carbides are one of the several families of transition metal compounds that are considered economic alternatives to catalysts based on noble metals and their compounds. Phase pure transition metal carbides of group 4-6 metals, in the first three periods, were synthesized using a common eutectic salt flux synthesis method, and their electrocatalytic activities compared under uniform electrochemical conditions. Mo2C showed highest hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) activities among the nine metal carbides investigated, but all other metal carbides also showed substantial activities. All the metal carbides showed remarkable enhancement in catalytic activities as supports, when compared to traditional graphitic carbon as platinum support. Mo2C, the most active transition metal carbide electrocatalyst, was prepared using four different synthesis routes, and the synthesis route dependent activities compared. Bifunctional Mo 2C that is HER as well as oxygen evolution reaction (OER) active, was achieved when the carbide was templated on a multiwalled carbon nanotube using carbothermic reduction method. Bimetallic carbides of Fe, Co, and Ni with Mo or W were prepared using a common carbothermic reduction method. Two different stoichiometries of bimetallic carbides were obtained for each system within a 60 °C temperature window. While the bimetallic carbides showed relatively lower electrocatalytic activities towards HER and ORR in comparison to Mo2C and WC, they revealed remarkably higher OER activities than IrO2 and RuO2, the state-of-the-art OER catalysts. Bimetallic oxides of Fe, Co, and Ni with Mo and W were also prepared using a hydrothermal synthesis method and they also revealed OER activities that are much higher than RuO2 and IrO2. Additionally, the OER activities were dependent on the degree and nature of hydration in the bimetallic oxide crystal lattice, with the completely hydrated, as synthesized, cobalt molybdate and nickel

  11. Modification of σ-Donor Properties of Terminal Carbide Ligands Investigated Through Carbide-Iodine Adduct Formation.

    Science.gov (United States)

    Reinholdt, Anders; Vosch, Tom; Bendix, Jesper

    2016-09-26

    The terminal carbide ligands in [(Cy3 P)2 X2 Ru≡C] complexes (X=halide or pseudohalide) coordinate molecular iodine, affording charge-transfer complexes rather than oxidation products. Crystallographic and vibrational spectroscopic data show the perturbations of iodine to vary with the auxiliary ligand sphere on ruthenium, demonstrating the σ-donor properties of carbide complexes to be tunable.

  12. Novel niobium carbide/carbon porous nanotube electrocatalyst supports for proton exchange membrane fuel cell cathodes

    Science.gov (United States)

    Nabil, Y.; Cavaliere, S.; Harkness, I. A.; Sharman, J. D. B.; Jones, D. J.; Rozière, J.

    2017-09-01

    Niobium carbide/carbon nanotubular porous structures have been prepared using electrospinning and used as electrocatalyst supports for proton exchange membrane fuel cells. They were functionalised with 3.1 nm Pt particles synthesised by a microwave-assisted polyol method and characterised for their electrochemical properties. The novel NbC-based electrocatalyst demonstrated electroactivity towards the oxygen reduction reaction as well as greater stability over high potential cycling than a commercial carbon-based electrocatalyst. Pt/NbC/C was integrated at the cathode of a membrane electrode assembly and characterised in a single fuel cell showing promising activity and power density.

  13. Formation of nanocrystalline niobium carbide (NbC) with a convenient route at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Ma Jianhua [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325027 (China); Nanomaterials and Chemistry Key Laboratory, Advanced Materials Research Center of Wenzhou, Wenzhou University, Wenzhou, Zhejiang 325027 (China)], E-mail: mjh820@ustc.edu; Wu Meining [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325027 (China); Du Yihong [City College, Wenzhou University, Wenzhou, Zhejiang 325035 (China); Chen Suqin; Jin Wu; Fu Li; Yang Qiongyao; Wen Aifei [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang 325027 (China)

    2009-05-05

    Nanocrystalline NbC has been prepared via a convenient route by the reaction of metallic magnesium powders with niobium pentoxide and basic magnesium carbonate in an autoclave at 550 deg. C. X-ray powder diffraction pattern indicated that the product was cubic niobium carbide, and the cell constant was a = 4.461 A. Transmission electron microscopy (TEM) image showed that it consisted of particles with an average size of about 30 nm in diameter. The product was also studied by BET and TGA. It had good thermal stability and oxidation resistance below 400 deg. C in air.

  14. Rf-plasma synthesis of nanosize silicon carbide and nitride. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Buss, R.J.

    1997-02-01

    A pulsed rf plasma technique is capable of generating ceramic particles of 10 manometer dimension. Experiments using silane/ammonia and trimethylchlorosilane/hydrogen gas mixtures show that both silicon nitride and silicon carbide powders can be synthesized with control of the average particle diameter from 7 to 200 nm. Large size dispersion and much agglomeration appear characteristic of the method, in contrast to results reported by another research group. The as produced powders have a high hydrogen content and are air and moisture sensitive. Post-plasma treatment in a controlled atmosphere at elevated temperature (800{degrees}C) eliminates the hydrogen and stabilizes the powder with respect to oxidation or hydrolysis.

  15. First-principles prediction of Si-doped Fe carbide as one of the possible constituents of Earth's inner core

    Science.gov (United States)

    Das, Tilak; Chatterjee, Swastika; Ghosh, Sujoy; Saha-Dasgupta, Tanusri

    2017-09-01

    We perform a computational study based on first-principles calculations to investigate the relative stability and elastic properties of the doped and undoped Fe carbide compounds at 200-364 GPa. We find that upon doping a few weight percent of Si impurities at the carbon sites in Fe7C3 carbide phases, the values of Poisson's ratio and density increase while VP, and VS decrease compared to their undoped counterparts. This leads to marked improvement in the agreement of seismic parameters such as P wave and S wave velocity, Poisson's ratio, and density with the Preliminary Reference Earth Model (PREM) data. The agreement with PREM data is found to be better for the orthorhombic phase of iron carbide (o-Fe7C3) compared to hexagonal phase (h-Fe7C3). Our theoretical analysis indicates that Fe carbide containing Si impurities can be a possible constituent of the Earth's inner core. Since the density of undoped Fe7C3 is low compared to that of inner core, as discussed in a recent theoretical study, our proposal of Si-doped Fe7C3 can provide an alternative solution as an important component of the Earth's inner core.

  16. Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

    Institute of Scientific and Technical Information of China (English)

    Wang Mingjia; Mu Songmei; Sun Feifei; Wang Yan

    2007-01-01

    The influence of rare earth (RE) elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry (DSC) and scanning electron microscopy energy dispersive spectrometry (SEM-EDS). The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing long-pole MC carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.

  17. Effect of Powder-Feeding Modes During Plasma Spray on the Properties of Tungsten Carbide Composite Coatings

    Science.gov (United States)

    Zhong, Yi-ming; Du, Xiao-dong; Wu, Gang

    2017-05-01

    A WC-reinforced composite coating was fabricated on the surface of 45 steel samples by plasma, cladding process with WC powder added to the molten pool synchronously or in the tail of the molten pool. The microstructure, phase composition, and element distribution in the coating were analyzed. The results show that the undissolved WC particles and crystallized carbide (WC, W2C) were distributed uniformly in the sub-eutectic matrix in both cases. Fewer of the WC particles are dissolved in the matrix when they are injected into the tail of the molten pool. There are fewer needle-like tungsten carbide formations seen in the composite coating fabricated by back-feeding process than in that formed by synchronous feeding. The former results in a finer microstructure and a higher concentration gradient of elements near the interface between the WC particles and the coating matrix.

  18. Transient liquid phase sintering of tantalum carbide ceramics by using silicon as the sintering aid and its effects on microstructure and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, Lianbing [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Liu, Limeng, E-mail: liulimeng@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Worsch, Christian; Gonzalez, Jesus; Springer, André [Otto Schott Institute of Materials Research, Friedrich-Schiller-University Jena, Lobdergraben 32, D-07743 Jena (Germany); Ye, Feng [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2015-01-15

    Tantalum carbide composites with 0.76–8.85 wt.% elemental silicon as a sintering aid were fabricated by spark plasma sintering (SPS) at 1700 °C and 30 MPa for 5 min. The transient-liquid-phase sintering behavior, the microstructures and the mechanical properties of the tantalum carbide composites were investigated. Oxide impurities present on the surfaces of the tantalum carbide particles were eliminated by reactions with the elemental silicon in a temperature range from 1271 °C to 1503 °C to benefit densification. Then the silicon melted at its melting point temperature of 1413 °C to facilitate rearrangement of the tantalum carbide particles. By the end of the densification, the elemental silicon transformed into more refractory TaSi{sub 2} and SiC in the consolidated ceramics by reactions with the tantalum carbide at temperatures lower than 1773 °C. Both TaSi{sub 2} and SiC particles improved densification by physically pinning growth of the tantalum carbide grains. Further densification was resulted from creep flow of the silicides after brittle-to-ductile transformation of the silicides at temperatures <1650 °C. Due to the good effects of using elemental silicon as the sintering aid, all the compositions reached densities >96.7% theoretical. The average grain sizes in the consolidated materials decreased with the silicon addition from about 19 μm in the 0.76 wt.% Si composition to about 9 μm in the 8.85 wt.% Si composition. A good flexural strength up to ∼709 MPa was reached in the 8.85 wt.% Si material due to full density and fine microstructure. - Highlights: • Tantalum carbide ceramics were densified by using 0.76–8.85 wt.% silicon as the sintering aids. • The transient liquid phase sintering behavior of the material system was discussed. • The elemental silicon improved densification and subsequently replaced by TaSi{sub 2} and SiC. • The tantalum carbide ceramic with 8.85 wt.% silicon addition showed a good flexural

  19. A stabilized second-order time accurate finite element formulation for incompressible viscous flow with heat transfer; Uma formulacao de elementos finitos estabilizada de segunda ordem no tempo para escoamentos viscosos com transferencia de calor

    Energy Technology Data Exchange (ETDEWEB)

    Curi, Marcos Filardy

    2011-07-01

    In view of the problem of global warming and the search for clean energy sources, a worldwide expansion on the use of nuclear energy is foreseen. Thus, the development of science and technology regarding nuclear power plants is essential, in particular in the field of reactor engineering. Fluid mechanics and heat transfer play an important role in the development of nuclear reactors. Computational Fluid Mechanics (CFD) is becoming ever more important in the optimization of cost and safety of the designs. This work presents a stabilized second-order time accurate finite element formulation for incompressible flows with heat transfer. A second order time discretization precedes a spatial discretization using finite elements. The terms that stabilize the finite element method arise naturally from the discretization process, rather than being introduced a priori in the variational formulation. The method was implemented in the program 'ns{sub n}ew{sub s}olvec2d{sub av}2{sub M}PI' written in FORTRAN90, developed in the Parallel Computing Laboratory at the Institute of Nuclear Engineering (LCP/IEN). Numerical solutions of some representative examples, including free, mixed and forced convection, demonstrate that the proposed stabilized formulation attains very good agreement with experimental and computational results available in the literature. (author)

  20. Ultrasmall Carbide Nanospheres - Formation and Electronic Properties

    Science.gov (United States)

    Reinke, Petra; Monazami, Ehsan; McClimon, John

    2015-03-01

    Metallic nanoparticles are highly coveted but are subject to rapid Ostwald ripening even at moderate temperatures limiting study of their properties. Ultrasmall transition metal carbide ``nanospheres'' are synthesized by a solid-state reaction between fullerene as carbon scaffold, and a W surface. This produces nanospheres with a narrow size distribution below 2.5 nm diameter. The nanosphere shape is defined by the scaffold and densely packed arrays can be achieved. The metal-fullerene reaction is temperature driven and progresses through an intermediate semiconducting phase until the fully metallic nanospheres are created at about 350 C. The reaction sequence is observed with STM, and STS maps yield the local density of states. The reaction presumably progresses by stepwise introduction of W-atoms in the carbon scaffold. The results of high resolution STM/STS in combination with DFT calculations are used to unravel the reaction mechanism. We will discuss the transfer of this specific reaction mechanism to other transition metal carbides. The nanospheres are an excellent testbed for the physics and chemistry of highly curved surfaces.

  1. Dynamic compaction of tungsten carbide powder.

    Energy Technology Data Exchange (ETDEWEB)

    Gluth, Jeffrey Weston; Hall, Clint Allen; Vogler, Tracy John; Grady, Dennis Edward

    2005-04-01

    The shock compaction behavior of a tungsten carbide powder was investigated using a new experimental design for gas-gun experiments. This design allows the Hugoniot properties to be measured with reasonably good accuracy despite the inherent difficulties involved with distended powders. The experiments also provide the first reshock state for the compacted powder. Experiments were conducted at impact velocities of 245, 500, and 711 m/s. A steady shock wave was observed for some of the sample thicknesses, but the remainder were attenuated due to release from the back of the impactor or the edge of the sample. The shock velocity for the powder was found to be quite low, and the propagating shock waves were seen to be very dispersive. The Hugoniot density for the 711 m/s experiment was close to ambient crystal density for tungsten carbide, indicating nearly complete compaction. When compared with quasi-static compaction results for the same material, the dynamic compaction data is seen to be significantly stiffer for the regime over which they overlap. Based on these initial results, recommendations are made for improving the experimental technique and for future work to improve our understanding of powder compaction.

  2. Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires

    Science.gov (United States)

    Yu, Zhiyang; Luo, Jian; Shi, Baiou; Zhao, Jiong; Harmer, Martin P.; Zhu, Jing

    2015-11-01

    Aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was employed to study the distribution of barium atoms on the surfaces and in the interiors of boron carbide based nanowires. Barium based dopants, which were used to control the crystal growth, adsorbed to the surfaces of the boron-rich crystals in the form of nanometer-thick surficial films (a type of surface complexion). During the crystal growth, these dopant-based surface complexions became embedded inside the single crystalline segments of fivefold boron-rich nanowires collectively, where they were converted to more ordered monolayer and bilayer modified complexions. Another form of bilayer complexion stabilized at stacking faults has also been identified. Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries. In contrast, our study revealed the previously-unrecognized possibility of incorporating dopants and impurities inside an otherwise perfect crystal without the association to any twin boundary or stacking fault. Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

  3. Amorphisation of boron carbide under slow heavy ion irradiation

    Science.gov (United States)

    Gosset, D.; Miro, S.; Doriot, S.; Moncoffre, N.

    2016-08-01

    Boron carbide B4C is widely used as a neutron absorber in nuclear plants. Most of the post-irradiation examinations have shown that the structure of the material remains crystalline, in spite of very high atomic displacement rates. Here, we have irradiated B4C samples with 4 MeV Au ions with different fluences at room temperature. Transmission electron microscopy (TEM) and Raman spectroscopy have been performed. The Raman analyses show a high structural disorder at low fluence, around 10-2 displacements per atoms (dpa). However, the TEM observations show that the material remains crystalline up to a few dpa. At high fluence, small amorphous areas a few nanometers large appear in the damaged zone but the long range order is preserved. Moreover, the size and density of the amorphous zones do not significantly grow when the damage increases. On the other hand, full amorphisation is observed in the implanted zone at a Au concentration of about 0.0005. It can be inferred from those results that short range and long range damages arise at highly different fluences, that heavy ions implantation has drastic effects on the structure stability and that in this material self-healing mechanisms are active in the damaged zone.

  4. Solution growth of silicon carbide using unary chromium solvent

    Science.gov (United States)

    Miyasaka, Ryo; Kawanishi, Sakiko; Narumi, Taka; Sasaki, Hideaki; Yoshikawa, Takeshi; Maeda, Masafumi

    2017-02-01

    Solution growth of silicon carbide (SiC) using unary chromium (Cr) solvent was studied because the system enables a high solubility difference and a low degree of supersaturation, which would lead to rapid growth with a stabilized growth interface. The liquidus composition at SiC saturation in a quasi-binary Cr-SiC system was studied at 1823-2173 K. The measured carbon (C) contents are in good agreement with the thermodynamic evaluation using the sub-regular solution model. In addition, growth experiments using a unary Cr solvent were performed by the bottom-seeded travelling solvent method. The obtained growth rates at 1803-1923 K with a temperature difference of 15-70 K were proportional to the solubility difference between the seed and source temperatures, indicating that the growth was controlled by the mass transfer of C in the solution. The maximum growth rate of 720 μm/h at 1803 K was much higher than the growth rate by Si-rich solvents, suggesting that the Cr-rich solvent is suitable for the rapid growth at a low temperature.

  5. MAGNESIUM PRECIPITATION AND DIFUSSION IN Mg+ ION IMPLANTED SILICON CARBIDE

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Weilin; Jung, Hee Joon; Kovarik, Libor; Wang, Zhaoying; Roosendaal, Timothy J.; Zhu, Zihua; Edwards, Danny J.; Hu, Shenyang Y.; Henager, Charles H.; Kurtz, Richard J.; Wang, Yongqiang

    2015-03-02

    As a candidate material for fusion reactor applications, silicon carbide (SiC) undergoes transmutation reactions under high-energy neutron irradiation with magnesium as the major metallic transmutant; the others include aluminum, beryllium and phosphorus in addition to helium and hydrogen gaseous species. Calculations by Sawan et al. predict that at a dose of ~100 dpa (displacements per atom), there is ~0.5 at.% Mg generated in SiC. The impact of these transmutants on SiC structural stability is currently unknown. This study uses ion implantation to introduce Mg into SiC. Multiaxial ion-channeling analysis of the as-produced damage state indicates a lower dechanneling yield observed along the <100> axis. The microstructure of the annealed sample was examined using high-resolution scanning transmission electron microscopy. The results show a high concentration of likely non-faulted tetrahedral voids and possible stacking fault tetrahedra near the damage peak. In addition to lattice distortion, dislocations and intrinsic and extrinsic stacking faults are also observed. Magnesium in 3C–SiC prefers to substitute for Si and it forms precipitates of cubic Mg2Si and tetragonal MgC2. The diffusion coefficient of Mg in 3C–SiC single crystal at 1573 K has been determined to be 3.8 ± 0.4E-19 m2/s.

  6. Silicon carbide as a basis for spaceflight optical systems

    Science.gov (United States)

    Curcio, Michael E.

    1994-09-01

    New advances in the areas of microelectronics and micro-mechanical devices have created a momentum in the development of lightweight, miniaturized, electro-optical space subsystems. The performance improvements achieved and new observational techniques developed as a result, have provided a basis for a new range of Small Explorer, Discovery-class and other low-cost mission concepts for space exploration. However, the ultimate objective of low-mass, inexpensive space science missions will only be achieved with a companion development in the areas of flight optical systems and sensor instrument benches. Silicon carbide (SiC) is currently emerging as an attractive technology to fill this need. As a material basis for reflective, flight telescopes and optical benches, SiC offers: the lightweight and stiffness characteristics of beryllium; glass-like inherent stability consistent with performance to levels of diffraction-limited visible resolution; superior thermal properties down to cryogenic temperatures; and an existing, commercially-based material and processing infrastructure like aluminum. This paper will describe the current status and results of on-going technology developments to utilize these material properties in the creation of lightweight, high- performing, thermally robust, flight optical assemblies. System concepts to be discussed range from an 18 cm aperture, 4-mirror, off-axis system weighing less than 2 kg to a 0.5 m, 15 kg reimager. In addition, results in the development of a thermally-stable, `GOES-like' scan mirror will be presented.

  7. Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires.

    Science.gov (United States)

    Yu, Zhiyang; Luo, Jian; Shi, Baiou; Zhao, Jiong; Harmer, Martin P; Zhu, Jing

    2015-11-26

    Aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was employed to study the distribution of barium atoms on the surfaces and in the interiors of boron carbide based nanowires. Barium based dopants, which were used to control the crystal growth, adsorbed to the surfaces of the boron-rich crystals in the form of nanometer-thick surficial films (a type of surface complexion). During the crystal growth, these dopant-based surface complexions became embedded inside the single crystalline segments of fivefold boron-rich nanowires collectively, where they were converted to more ordered monolayer and bilayer modified complexions. Another form of bilayer complexion stabilized at stacking faults has also been identified. Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries. In contrast, our study revealed the previously-unrecognized possibility of incorporating dopants and impurities inside an otherwise perfect crystal without the association to any twin boundary or stacking fault. Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

  8. Investigation of exotic stable calcium carbides using theory and experiment

    Science.gov (United States)

    Li, Yan-Ling; Wang, Sheng-Nan; Oganov, Artem R.; Gou, Huiyang; Smith, Jesse S.; Strobel, Timothy A.

    2015-05-01

    It is well known that pressure causes profound changes in the properties of atoms and chemical bonding, leading to the formation of many unusual materials. Here we systematically explore all stable calcium carbides at pressures from ambient to 100 GPa using variable-composition evolutionary structure predictions using the USPEX code. We find that Ca5C2, Ca2C, Ca3C2, CaC, Ca2C3 and CaC2 have stability fields on the phase diagram. Among these, Ca2C and Ca2C3 are successfully synthesized for the first time via high-pressure experiments with excellent structural correspondence to theoretical predictions. Of particular significance is the base-centred monoclinic phase (space group C2/m) of Ca2C, a quasi-two-dimensional metal with layers of negatively charged calcium atoms, and the primitive monoclinic phase (space group P21/c) of CaC with zigzag C4 groups. Interestingly, strong interstitial charge localization is found in the structure of R-3m-Ca5C2 with semi-metallic behaviour.

  9. Lithium and calcium carbides with polymeric carbon structures.

    Science.gov (United States)

    Benson, Daryn; Li, Yanling; Luo, Wei; Ahuja, Rajeev; Svensson, Gunnar; Häussermann, Ulrich

    2013-06-01

    We studied the binary carbide systems Li2C2 and CaC2 at high pressure using an evolutionary and ab initio random structure search methodology for crystal structure prediction. At ambient pressure Li2C2 and CaC2 represent salt-like acetylides consisting of C2(2-) dumbbell anions. The systems develop into semimetals (P3m1-Li2C2) and metals (Cmcm-Li2C2, Cmcm-CaC2, and Immm-CaC2) with polymeric anions (chains, layers, strands) at moderate pressures (below 20 GPa). Cmcm-CaC2 is energetically closely competing with the ground state structure. Polyanionic forms of carbon stabilized by electrostatic interactions with surrounding cations add a new feature to carbon chemistry. Semimetallic P3m1-Li2C2 displays an electronic structure close to that of graphene. The π* band, however, is hybridized with Li-sp states and changed into a bonding valence band. Metallic forms are predicted to be superconductors. Calculated critical temperatures may exceed 10 K for equilibrium volume structures.

  10. In Situ Synthesis of Uranium Carbide and its High Temperature Cubic Phase

    Energy Technology Data Exchange (ETDEWEB)

    Reiche, Helmut Matthias [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Vogel, Sven C. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-03-25

    New in situ data for the U-C system are presented, with the goal of improving knowledge of the phase diagram to enable production of new ceramic fuels. The none quenchable, cubic, δ-phase, which in turn is fundamental to computational methods, was identified. Rich datasets of the formation synthesis of uranium carbide yield kinetics data which allow the benchmarking of modeling, thermodynamic parameters etc. The order-disorder transition (carbon sublattice melting) was observed due to equal sensitivity of neutrons to both elements. This dynamic has not been accurately described in some recent simulation-based publications.

  11. Thermal residual stress analysis of diamond coating on graded cemented carbides

    Institute of Scientific and Technical Information of China (English)

    HUANG Zi-qian; HE Yue-hui; CAI Hai-tao; WU Cong-hai; XIAO Yi-feng; HUANG Bai-yun

    2008-01-01

    Finite element model was developed to analyze thermal residual stress distribution of diamond coating on graded and homogeneous substrates. Graded cemented carbides were formed by carburizing pretreatment to reduce the cobalt content in the surface layer and improve adhesion of diamond coating. The numerical calculation results show that the surface compressive stress of diamond coating is 950 MPa for graded substrate and 1 250 MPa for homogenous substrate, the thermal residual stress decreases by around 24% due to diamond coating. Carburizing pretreatment is good for diamond nucleation rate, and can increase the interface strength between diamond coating and substrate.

  12. Processes and applications of silicon carbide nanocomposite fibers

    Science.gov (United States)

    Shin, D. G.; Cho, K. Y.; Jin, E. J.; Riu, D. H.

    2011-10-01

    Various types of SiC such as nanowires, thin films, foam, and continuous fibers have been developed since the early 1980s, and their applications have been expanded into several new applications, such as for gas-fueled radiation heater, diesel particulate filter (DPF), ceramic fiber separators and catalyst/catalyst supports include for the military, aerospace, automobile and electronics industries. For these new applications, high specific surface area is demanded and it has been tried by reducing the diameter of SiC fiber. Furthermore, functional nanocomposites show potentials in various harsh environmental applications. In this study, silicon carbide fiber was prepared through electrospinning of the polycarbosilane (PCS) with optimum molecular weight distribution which was synthesized by new method adopting solid acid catalyst such as ZSM-5 and γ-Al2O3. Functional elements such as aluminum, titanium, tungsten and palladium easily doped in the precursor fiber and remained in the SiC fiber after pyrolysis. The uniform SiC fibers were produced at the condition of spinning voltage over 20 kV from the PCS solution as the concentration of 1.3 g/ml in DMF/Toluene (3:7) and pyrolysis at 1200°C. Pyrolyzed products were processed into several interesting applications such as thermal batteries, hydrogen sensors and gas filters.

  13. Processes and applications of silicon carbide nanocomposite fibers

    Energy Technology Data Exchange (ETDEWEB)

    Shin, D G; Cho, K Y; Riu, D H [Nanomaterials Team, Korea Institute of Ceramic Engineering and Technology, 233-5 Gasan-dong, Guemcheon-gu, Seoul 153-801 (Korea, Republic of); Jin, E J, E-mail: dhriu15@seoultech.ac.kr [Battelle-Korea Laborotary, Korea University, Anamdong, Seongbuk-gu, Seoul (Korea, Republic of)

    2011-10-29

    Various types of SiC such as nanowires, thin films, foam, and continuous fibers have been developed since the early 1980s, and their applications have been expanded into several new applications, such as for gas-fueled radiation heater, diesel particulate filter (DPF), ceramic fiber separators and catalyst/catalyst supports include for the military, aerospace, automobile and electronics industries. For these new applications, high specific surface area is demanded and it has been tried by reducing the diameter of SiC fiber. Furthermore, functional nanocomposites show potentials in various harsh environmental applications. In this study, silicon carbide fiber was prepared through electrospinning of the polycarbosilane (PCS) with optimum molecular weight distribution which was synthesized by new method adopting solid acid catalyst such as ZSM-5 and {gamma}-Al{sub 2}O{sub 3}. Functional elements such as aluminum, titanium, tungsten and palladium easily doped in the precursor fiber and remained in the SiC fiber after pyrolysis. The uniform SiC fibers were produced at the condition of spinning voltage over 20 kV from the PCS solution as the concentration of 1.3 g/ml in DMF/Toluene (3:7) and pyrolysis at 1200deg. C. Pyrolyzed products were processed into several interesting applications such as thermal batteries, hydrogen sensors and gas filters.

  14. Ultrafast laser-triggered emission from hafnium carbide tips

    Science.gov (United States)

    Kealhofer, Catherine; Foreman, Seth M.; Gerlich, Stefan; Kasevich, Mark A.

    2012-07-01

    Electron emission from hafnium carbide (HfC) field emission tips induced by a sub-10-fs, 150-MHz repetition rate Ti:sapphire laser is studied. Two-photon emission is observed at low power with a moderate electric bias field applied to the tips. As the bias field and/or laser power is increased, the average current becomes dominated by thermally enhanced field emission due to laser heating: both the low thermal conductivity of HfC and the laser's high repetition rate can lead to a temperature rise of several hundred Kelvin at the tip apex. The contribution of current from a thermal transient at times shorter than the electron-phonon coupling time is considered in the context of the two-temperature model (TTM). Under the conditions of this experiment, the integrated current from the thermal transient is shown to be negligible in comparison with the two-photon emission. A finite element model of the laser heating and thermal conduction supports these conclusions and is also used to compare the nature of thermal effects in HfC, tungsten, and gold tips.

  15. Synthesis of silicon carbide by carbothermal reduction of silica

    Energy Technology Data Exchange (ETDEWEB)

    Abel, J.L.; Ambrozio, F.; Beneduce, F. [Centro Universitario FEI, Itajuba, MG (Brazil); Instituto de Pesquisas Tecnologicas (IPT), Sao Paulo, SP (Brazil)

    2009-07-01

    Full text: The production of silicon carbide (SiC) in an industrial scale still by carbothermal reduction of silica for its synthesis. This study aims to identify, in a comparative way, among the common reducers like petroleum coke, carbon black, charcoal and graphite the carbothermal reduction of silica from peat or organic soil. It is shown that peat, also occurs in nature together with high purity silica sand deposits, where the proximity of raw materials and their quality are key elements that determine the type, purity and cost of production of SiC. Tests were running from samples produced in the electric resistance furnace with controlled atmosphere at temperatures of 1550 deg C, 1600°C and 1650°C, both the precursors and products of reaction of carbothermal reduction were characterized by applying techniques of X-ray diffraction, scanning electron microscopy (SEM) and Energy- Dispersive X-ray analysis Spectroscopy (EDS). The results showed the formation of SiC for all common reducers, as well as for peat, but it was not possible to realize clearly the difference between them, being necessary, specific tests. (author)

  16. Precipitation behavior of carbides in high-carbon martensitic stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Qin-tian; Li, Jing; Shi, Cheng-bin; Yu, Wen-tao; Shi, Chang-min [University of Science and Technology, Beijing (China). State Key Laboratory of Advanced Metallurgy; Li, Ji-hui [Yang Jiang Shi Ba Zi Group Co., Ltd, Guangdong (China)

    2017-01-15

    A fundamental study on the precipitation behavior of carbides was carried out. Thermo-calc software, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy, X-ray diffractometry and high-temperature confocal laser scanning microscopy were used to study the precipitation and transformation behaviors of carbides. Carbide precipitation was of a specific order. Primary carbides (M7C3) tended to be generated from liquid steel when the solid fraction reached 84 mol.%. Secondary carbides (M7C3) precipitated from austenite and can hardly transformed into M23C6 carbides with decreasing temperature in air. Primary carbides hardly changed once they were generated, whereas secondary carbides were sensitive to heat treatment and thermal deformation. Carbide precipitation had a certain effect on steel-matrix phase transitions. The segregation ability of carbon in liquid steel was 4.6 times greater that of chromium. A new method for controlling primary carbides is proposed.

  17. Salt flux synthesis of single and bimetallic carbide nanowires

    Science.gov (United States)

    Leonard, Brian M.; Waetzig, Gregory R.; Clouser, Dale A.; Schmuecker, Samantha M.; Harris, Daniel P.; Stacy, John M.; Duffee, Kyle D.; Wan, Cheng

    2016-07-01

    Metal carbide compounds have a broad range of interesting properties and are some of the hardest and highest melting point compounds known. However, their high melting points force very high reaction temperatures and thus limit the formation of high surface area nanomaterials. To avoid the extreme synthesis temperatures commonly associated with these materials, a new salt flux technique has been employed to reduce reaction temperatures and form these materials in the nanometer regime. Additionally, the use of multiwall carbon nanotubes as a reactant further reduces the diffusion distance and provides a template for the final carbide materials. The metal carbide compounds produced through this low temperature salt flux technique maintain the nanowire morphology of the carbon nanotubes but increase in size to ˜15-20 nm diameter due to the incorporation of metal in the carbon lattice. These nano-carbides not only have nanowire like shape but also have much higher surface areas than traditionally prepared metal carbides. Finally, bimetallic carbides with composition control can be produced with this method by simply using two metal precursors in the reaction. This method provides the ability to produce nano sized metal carbide materials with size, morphology, and composition control and will allow for these compounds to be synthesized and studied in a whole new size and temperature regime.

  18. Effects of carbides on fatigue characteristics of austempered ductile iron

    Science.gov (United States)

    Stokes, B.; Gao, N.; Reed, P. A. S.; Lee, K. K.

    2005-04-01

    Crack initiation and growth behavior of an austempered ductile iron (ADI) austenitized at 800 °C and austempered at 260 °C have been assessed under three-point bend fatigue conditions. Initiation sites have been identified as carbides remaining from the as-cast ductile iron due to insufficient austenization. The number of carbides cracking on loading to stresses greater than 275 MPa is critical in determining the failure mechanism. In general, high carbide area fractions promote coalescence-dominated fatigue crack failure, while low area fractions promote propagation-dominated fatigue crack failure. Individual carbides have been characterized using finite body tessellation (FBT) and adaptive numerical modeling (Support vector Parsimonious Analysis Of Variance (SUPANOVA)) techniques in an attempt to quantify the factors promoting carbide fracture. This indicated that large or long and thin carbides on the whole appear to be susceptible to fracture, and carbides that are locally clustered and aligned perpendicular to the tensile axis are particularly susceptible to fracture.

  19. Computational Studies of Physical Properties of Boron Carbide

    Energy Technology Data Exchange (ETDEWEB)

    Lizhi Ouyang

    2011-09-30

    The overall goal is to provide valuable insight in to the mechanisms and processes that could lead to better engineering the widely used boron carbide which could play an important role in current plight towards greener energy. Carbon distribution in boron carbide, which has been difficult to retrieve from experimental methods, is critical to our understanding of its structure-properties relation. For modeling disorders in boron carbide, we implemented a first principles method based on supercell approach within our G(P,T) package. The supercell approach was applied to boron carbide to determine its carbon distribution. Our results reveal that carbon prefers to occupy the end sites of the 3-atom chain in boron carbide and further carbon atoms will distribute mainly on the equatorial sites with a small percentage on the 3-atom chains and the apex sites. Supercell approach was also applied to study mechanical properties of boron carbide under uniaxial load. We found that uniaxial load can lead to amorphization. Other physical properties of boron carbide were calculated using the G(P,T) package.

  20. Preparation and characterization for mineral elements and total dietary fiber and testing for stability of {beta}-carotene of an ARC/CL carrot powder multipurpose candidate reference material

    Energy Technology Data Exchange (ETDEWEB)

    Kumpulainen, J.T. [Agricultural Research Centre of Finland (Finland). Lab. of Food Chemistry; Hyvaerinen, H. [Agricultural Research Centre of Finland (Finland). Lab. of Food Chemistry; Haegg, M. [Agricultural Research Centre of Finland (Finland). Lab. of Food Chemistry; Plaami, S. [Agricultural Research Centre of Finland (Finland). Lab. of Food Chemistry; Tahvonen, R. [Agricultural Research Centre of Finland (Finland). Lab. of Food Chemistry

    1995-05-01

    As part of the analytical assurance system of the FAO European Cooperative Research Network on Trace Elements programme an ARC/CL-coded carrot flakes powder (CFP) candidate reference material (RM) has been prepared from a lot of commercial carrot flakes. The candidate RM has been homogenized using a Robot Coupe blender fitted with titanium blades, carefully homogenized in large teflon/polypropylene containers, bottled in 1000 numbered polyethylene containers (20 g samples) and tested for homogeneity. Interlaboratory comparison studies for 9 essential elements, cadmium and total dietary fiber (TDF) based on the AOAC-method resulted in the characterization of the contents of those compounds in the above material. After exclusion of outliers, mean values from at least nine different laboratories based altogether on three independent analytical principles have been used to calculate the recommended concentration ranges for mineral elements. Testing of homogeneity and stability for {beta}-carotene over a period of one year has been additionally carried out. The mean water content in the material amounted to 4.97% and remained stable over a one-year period. Homogeneity of the RM was within 3.0% for almost all included mineral elements as tested for a sample size of 0.5 g. The 95% confidence limits for the mean values of the established recommended concentrations of mineral elements in the present ARC/CL Carrot Powder candidate RM fell within 5% for all the other elements and TDF except for Fe (6.3%) and B (5.7%). The stability of {beta}-carotene in the present candidate RM stored in darkness over a one-year period at room temperature was within 6.3%. (orig.)