Science.gov

Sample records for carbides

  1. Silicon carbide

    SciTech Connect

    Ault, N.N.; Crowe, J.T. )

    1991-05-01

    This paper reports that, since silicon carbide (SiC) does not occur in nature, it must be synthesized by a high-temperature chemical reaction. The first commercial production began at the end of the 19th century when Acheson developed a process of reacting sand and coke in a resistance furnace. This process is still the basic SiC manufacturing process used today. High-quality silica sand (99.5% SiO{sub 2}), low-sulfur petroleum coke, and electricity (23.8 MJ/kg) are the major ingredients in the production of SiC. The reaction takes place in a trough-like furnace with a removable refractory side (or some similar configuration) and with permanent refractory ends holding carbon electrodes. When the furnace is started, the carbon electrodes are joined by the graphite core laid the length of the furnace near the center of the mixture which fills the furnace.

  2. SILICON CARBIDE FOR SEMICONDUCTORS

    DTIC Science & Technology

    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

  3. Silicon Carbide Shapes.

    DTIC Science & Technology

    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.

  4. Silicon carbide ceramic production

    NASA Technical Reports Server (NTRS)

    Suzuki, K.; Shinohara, N.

    1984-01-01

    A method to produce sintered silicon carbide ceramics in which powdery carbonaceous components with a dispersant are mixed with silicon carbide powder, shaped as required with or without drying, and fired in nonoxidation atmosphere is described. Carbon black is used as the carbonaceous component.

  5. Silicon Carbide Photoconductive Switches

    DTIC Science & Technology

    1994-09-01

    The optoelectronic properties of p-type 6-H silicon carbide (6H-SiC) have been investigated in an experiment that used lateral and vertical...and the bandgap was determined to be approximately 3.1 eV. 6H-SiC, Photoconductive, Photovoltaic, Absorption coefficient, Switch, Silicon carbide

  6. SILICON CARBIDE DATA SHEETS

    DTIC Science & Technology

    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

  7. Microwave sintering of boron carbide

    DOEpatents

    Blake, R.D.; Katz, J.D.; Petrovic, J.J.; Sheinberg, H.

    1988-06-10

    A method for forming boron carbide into a particular shape and densifying the green boron carbide shape. Boron carbide in powder form is pressed into a green shape and then sintered, using a microwave oven, to obtain a dense boron carbide body. Densities of greater than 95% of theoretical density have been obtained. 1 tab.

  8. Silicon carbide thyristor

    NASA Technical Reports Server (NTRS)

    Edmond, John A. (Inventor); Palmour, John W. (Inventor)

    1996-01-01

    The SiC thyristor has a substrate, an anode, a drift region, a gate, and a cathode. The substrate, the anode, the drift region, the gate, and the cathode are each preferably formed of silicon carbide. The substrate is formed of silicon carbide having one conductivity type and the anode or the cathode, depending on the embodiment, is formed adjacent the substrate and has the same conductivity type as the substrate. A drift region of silicon carbide is formed adjacent the anode or cathode and has an opposite conductivity type as the anode or cathode. A gate is formed adjacent the drift region or the cathode, also depending on the embodiment, and has an opposite conductivity type as the drift region or the cathode. An anode or cathode, again depending on the embodiment, is formed adjacent the gate or drift region and has an opposite conductivity type than the gate.

  9. Silicon carbide reinforced silicon carbide composite

    NASA Technical Reports Server (NTRS)

    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.

  10. Improved toughness of silicon carbide

    NASA Technical Reports Server (NTRS)

    Palm, J. A.

    1975-01-01

    Several techniques were employed to apply or otherwise form porous layers of various materials on the surface of hot-pressed silicon carbide ceramic. From mechanical properties measurements and studies, it was concluded that although porous layers could be applied to the silicon carbide ceramic, sufficient damage was done to the silicon carbide surface by the processing required so as to drastically reduce its mechanical strength. It was further concluded that there was little promise of success in forming an effective energy absorbing layer on the surface of already densified silicon carbide ceramic that would have the mechanical strength of the untreated or unsurfaced material. Using a process for the pressureless sintering of silicon carbide powders it was discovered that porous layers of silicon carbide could be formed on a dense, strong silicon carbide substrate in a single consolidation process.

  11. Silicon Carbide Metallization

    NASA Astrophysics Data System (ADS)

    Lescoat, F.; Tanguy, F.; Durand, P.

    2016-05-01

    A study has been done to assess the feasibility of metallization of Silicon Carbide (SiC) in order to simplify design and mounting of one or more ground reference rail needed to provide an electrical reference for electronics mounted on an SiC structure.

  12. Composition Comprising Silicon Carbide

    NASA Technical Reports Server (NTRS)

    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.

  13. Characterization of Silicon Carbide.

    DTIC Science & Technology

    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. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, C.E.; Morrow, M.S.

    1993-10-12

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  15. Process for microwave sintering boron carbide

    DOEpatents

    Holcombe, Cressie E.; Morrow, Marvin S.

    1993-01-01

    A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

  16. Silicon carbide sewing thread

    NASA Technical Reports Server (NTRS)

    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.

  17. PREPARATION AND PURIFICATION OF SILICON CARBIDE.

    DTIC Science & Technology

    the materials were divided into two parts. Part I covers problems of silicon carbide preparation and the growing of silicon carbide single crystals...and thin films for semiconductor devices. Part II treats problems of purity, including the purification and chemical analysis of silicon carbide and of starting materials for silicon carbide preparation.

  18. Methods of producing continuous boron carbide fibers

    SciTech Connect

    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.

  19. Hydrogen-silicon carbide interactions

    NASA Technical Reports Server (NTRS)

    Eckel, Andrew J.; Jacobson, Nathan S.; Misra, Ajay K.; Humphrey, Donald L.

    1989-01-01

    A study of the thermochemistry and kinetics of hydrogen environmental attack of silicon carbide was conducted for temperatures in the range from 1100 C to 1400 C. Thermodynamic maps based on the parameters of pressure and oxygen/moisture content were constructed. With increasing moisture levels, four distinct regions of attack were identified. Each region is defined by the thermodynamically stable solid phases. The theoretically stable solid phases of Region 1 are silicon carbide and silicon. Experimental evidence is provided to support this thermodynamic prediction. Silicon carbide is the single stable solid phase in Region 2. Active attack of the silicon carbide in this region occurs by the formation of gases of SiO, CO, CH4, SiH4, and SiH. Analysis of the kinetics of reaction for Region 2 at 1300 C show the attack of the silicon carbide to be controlled by gas phase diffusion of H2O to the sample. Silicon carbide and silica are the stable phases common to Regions 3 and 4. These two regions are characterized by the passive oxidation of silicon carbide and formation of a protective silica layer.

  20. Silicon Carbide Electronic Devices

    NASA Technical Reports Server (NTRS)

    Neudeck, P. G.

    2001-01-01

    The status of emerging silicon carbide (SiC) widebandgap semiconductor electronics technology is briefly surveyed. SiC-based electronic devices and circuits are being developed for use in high-temperature, high-power, and/or high-radiation conditions under which conventional semiconductors cannot function. Projected performance benefits of SiC electronics are briefly illustrated for several applications. However, most of these operational benefits of SiC have yet to be realized in actual systems, primarily owing to the fact that the growth techniques of SiC crystals are relatively immature and device fabrication technologies are not yet sufficiently developed to the degree required for widespread, reliable commercial use. Key crystal growth and device fabrication issues that limit the performance and capability of high-temperature and/or high-power SiC electronics are identified. The electrical and material quality differences between emerging SiC and mature silicon electronics technology are highlighted.

  1. Processing of boron carbide

    NASA Astrophysics Data System (ADS)

    Cho, Namtae

    The processing of boron carbide powder including sintering optimization, green body optimization and sintering behavior of nano-sized boron carbide was investigated for the development of complex shaped body armor. Pressureless sintered B4C relative densities as high as 96.7% were obtained by optimizing the soak temperature, and holding at that temperature for the minimum time required to reach terminal density. Although the relative densities of pressureless sintered specimens were lower than that of commercially produced hot-pressed B4C, their (Vickers) hardness values were comparable. For 4.45 cm dia. 1.35 cm height disk-shaped specimens, pressureless sintered to at least 93.0% relative density, post-hot isostatic pressing resulted in vast increases in relative densities (e.g. 100.0%) and hardness values significantly greater than that of commercially produced hot-pressed B 4C. The densification behavior of 20-40nm graphite-coated B4C nano-particles was studied using dilatometry, x-ray diffraction and electron microscopy. The higher than expected sintering onset from a nano-scale powder (˜1500°C) was caused by remnant B2O3 not removed by methanol washing, keeping particles separated until volatilization, and the carbon coatings, which imposed particle to particle contact of a substance more refractory than B4C. Solid state sintering (1500-1850°C) was followed by an arrest in contraction attributed to formation of eutectic liquid droplets of size more than 10X the original nano-particles. These droplets, induced to form well below known B4C-graphite eutectic temperatures by the high surface energy of nanoparticles, are interpreted to have quickly solidified to form a vast number of voids in particle packing, which in turn, impeded continued solid state sintering. Starting at 2200°C, a permanent liquid phase formed which facilitated a rapid measured contraction by liquid phase sintering and/or compact slumping.

  2. Wettability of boron carbide

    SciTech Connect

    Torvund, T.; Akselsen, O.M.; Ulvensoeen, J.H.; Grong, O.

    1994-12-31

    The wettability of boron carbide has been examined by means of the sessile drop method, using the following candidate alloys: (96wt%AG-4wt%Ti), (Ag-26.5wt%Cu-3wt%Ti), (Sn-10wt%Ag-4wt%Ti), Sn(99.95wt%) and Al(99.99wt%). The results show that B{sub 4}C is completely wetted by the Ag-based alloys. Sn-10wt%Ag-4wt%Ti alloy and pure Al partly wet the B{sub 4}C surface, while pure Sn does not wet B{sub 4}C at all. For all the alloys used, except pure Sn, a reaction layer was observed at the interface between the ceramic part and the metal drop. Although the spreading kinetics of the Al-drop was much slower compared with the Ti-containing alloys, the reaction rate was considerably higher in the former case. This suggests that aluminium is an attractive candidate material for brazing of B{sub 4}C. Formation of the low melting B{sub 2}O{sub 3} at the B{sub 4}C surface may cause oxidation of the filler metal during joining, which, in turn, leads to a low bond strength.

  3. Silicon Carbide Growth

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Andrew Trunek has focused on supporting the Sic team through the growth of Sic crystals, making observations and conducting research that meets the collective needs and requirements of the team while fulfilling program commitments. Cancellation of the Ultra Efficient Engine Technology (UEET) program has had a significant negative impact on resources and research goals. This report highlights advancements and achievements made with this cooperative agreement over the past year. NASA Glenn Research Center (GRC) continues to make advances in silicon carbide (SiC) research during the past year. Step free surfaces were used as substrates for the deposition of GaN epilayers that yielded very low dislocation densities. Defect free 3C- SiC was successfully nucleated on step free mesas and test diodes were fabricated. Web growth techniques were used to increase the usable surface area of dislocation free SiC by approximately equal to 40%. The greatest advancement has been attained on stepped surfaces of SiC. A metrology standard was developed using high temperature etching techniques titled "Nanometer Step Height Standard". This development culminated in being recognized for a 2004 R&D100 award and the process to produce the steps received a NASA Space Act award.

  4. Porous silicon carbide (SIC) semiconductor device

    NASA Technical Reports Server (NTRS)

    Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

    1996-01-01

    Porous silicon carbide is fabricated according to techniques which result in a significant portion of nanocrystallites within the material in a sub 10 nanometer regime. There is described techniques for passivating porous silicon carbide which result in the fabrication of optoelectronic devices which exhibit brighter blue luminescence and exhibit improved qualities. Based on certain of the techniques described porous silicon carbide is used as a sacrificial layer for the patterning of silicon carbide. Porous silicon carbide is then removed from the bulk substrate by oxidation and other methods. The techniques described employ a two-step process which is used to pattern bulk silicon carbide where selected areas of the wafer are then made porous and then the porous layer is subsequently removed. The process to form porous silicon carbide exhibits dopant selectivity and a two-step etching procedure is implemented for silicon carbide multilayers.

  5. Laser melting of uranium carbides

    NASA Astrophysics Data System (ADS)

    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.

  6. 500 C SILICON CARBIDE RECTIFIER PROGRAM.

    DTIC Science & Technology

    Efforts were continued on the development of 500 degree C silicon carbide rectifiers. The growth rate of silicon carbide crystals prepared by the...as obtained from a simple model. All values agree within a factor of five. The use of molten borax as an etchant for silicon carbide was studies...is possible. Details are given on the life and storage tests which were successfully passed by two silicon carbide rectifiers. An open tube-flowing

  7. Silicon Carbide Semiconductor Device Fabrication and Characterization

    DTIC Science & Technology

    1990-02-08

    SPACE ADMINISTRATION For Grant NAG 3-782 S- 1 entitled SILICON CARBIDE SEMICONDUCTOR DEVICE FABRICATION AND CHARACTERIZATION For the Period 10 February...NUMBERS Silicon Carbide ..Semiconductor Device Fabrication and PR# 335820 Characterization __________________________________________________ APP# 505-62-01...also been demonstrated. _________ 14. SUBJECT TERMS 15. NuMBER OF PACiES -~- Silicon carbide , Ysemiconductor devices, ion implantation aseeI4i

  8. Method of Fabricating Silicon Carbide Articles.

    DTIC Science & Technology

    The patent relates to a method for fabricating silicon carbide articles which comprises hot pressing a homogeneous mixture of carbonaceous particles...and silicon carbide powder. The presence of the carbon limits grain growth so that a silicon carbide product having greatly improved physical

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Anisotropic Tribological Properties of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    The anisotropic friction, deformation and fracture behavior of single crystal silicon carbide surfaces were investigated in two categories. The categories were called adhesive and abrasive wear processes, respectively. In the adhesive wear process, the adhesion, friction and wear of silicon carbide were markedly dependent on crystallographic orientation. The force to reestablish the shearing fracture of adhesive bond at the interface between silicon carbide and metal was the lowest in the preferred orientation of silicon carbide slip system. The fracturing of silicon carbide occurred near the adhesive bond to metal and it was due to primary cleavages of both prismatic (10(-1)0) and basal (0001) planes.

  12. Silicon carbide semiconductor technology for high temperature and radiation environments

    NASA Technical Reports Server (NTRS)

    Matus, Lawrence G.

    1993-01-01

    Viewgraphs on silicon carbide semiconductor technology and its potential for enabling electronic devices to function in high temperature and high radiation environments are presented. Topics covered include silicon carbide; sublimation growth of 6H-SiC boules; SiC chemical vapor deposition reaction system; 6H silicon carbide p-n junction diode; silicon carbide MOSFET; and silicon carbide JFET radiation response.

  13. Diamond-silicon carbide composite

    DOEpatents

    Qian, Jiang; Zhao, Yusheng

    2006-06-13

    Fully dense, diamond-silicon carbide composites are prepared from ball-milled microcrystalline diamond/amorphous silicon powder mixture. The ball-milled powder is sintered (P=5–8 GPa, T=1400K–2300K) to form composites having high fracture toughness. A composite made at 5 GPa/1673K had a measured fracture toughness of 12 MPa.dot.m1/2. By contrast, liquid infiltration of silicon into diamond powder at 5 GPa/1673K produces a composite with higher hardness but lower fracture toughness. X-ray diffraction patterns and Raman spectra indicate that amorphous silicon is partially transformed into nanocrystalline silicon at 5 GPa/873K, and nanocrystalline silicon carbide forms at higher temperatures.

  14. Microwave processing of silicon carbide

    SciTech Connect

    Akerman, M.A.; Baity, F.W. Jr.; Caughman, J.B.; Forrester, S.C.; Kass, M.D.; Morrow, M.S.; Holcombe, C.E. Jr.; Moyer, M.W.; Dews, T.W.

    1994-12-31

    Reaction-bonded silicon carbide ({alpha}-SiC) armor tiles were annealed at 2100{degree}C using microwave radiation at 2.45 GHz. Ultrasonic velocity measurements showed that the longitudinal and shear velocities, acoustic impedances, and acoustic moduli of the post-annealed tiles were statistically higher than for the unannealed tiles. However, the exposed surfaces of the annealed tiles experienced slight degradation, which was attributed to the high annealing temperatures.

  15. Conduction mechanism in boron carbide

    NASA Technical Reports Server (NTRS)

    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.

  16. Abrasive slurry composition for machining boron carbide

    DOEpatents

    Duran, E.L.

    1984-11-29

    An abrasive slurry particularly suited for use in drilling or machining boron carbide consists essentially of a suspension of boron carbide and/or silicon carbide grit in a carrier solution consisting essentially of a dilute solution of alkylaryl polyether alcohol in octyl alcohol. The alkylaryl polyether alcohol functions as a wetting agent which improves the capacity of the octyl alcohol for carrying the grit in suspension, yet without substantially increasing the viscosity of the carrier solution.

  17. Abrasive slurry composition for machining boron carbide

    DOEpatents

    Duran, Edward L.

    1985-01-01

    An abrasive slurry particularly suited for use in drilling or machining boron carbide consists essentially of a suspension of boron carbide and/or silicon carbide grit in a carrier solution consisting essentially of a dilute solution of alkylaryl polyether alcohol in octyl alcohol. The alkylaryl polyether alcohol functions as a wetting agent which improves the capacity of the octyl alcohol for carrying the grit in suspension, yet without substantially increasing the viscosity of the carrier solution.

  18. METHOD OF JOINING CARBIDES TO BASE METALS

    DOEpatents

    Krikorian, N.H.; Farr, J.D.; Witteman, W.G.

    1962-02-13

    A method is described for joining a refractory metal carbide such as UC or ZrC to a refractory metal base such as Ta or Nb. The method comprises carburizing the surface of the metal base and then sintering the base and carbide at temperatures of about 2000 deg C in a non-oxidizing atmosphere, the base and carbide being held in contact during the sintering step. To reduce the sintering temperature and time, a sintering aid such as iron, nickel, or cobait is added to the carbide, not to exceed 5 wt%. (AEC)

  19. Silicon carbide fibers and articles including same

    DOEpatents

    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.

  20. Methods for producing silicon carbide fibers

    DOEpatents

    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.

  1. Titanium Carbide Bipolar Plate for Electrochemical Devices

    SciTech Connect

    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.

  2. 500 C SILICON CARBIDE RECTIFIER PROGRAM

    DTIC Science & Technology

    Silicon carbide crystals of the hexagonal type were grown in a Kroll-type furnace by the sublimation technique. Both homogeneous and grown junction...feasibility of vapor-phase chemical reaction methods was investigated for the controlled growth of silicon carbide platelets and sheets. The growth of

  3. Titanium carbide bipolar plate for electrochemical devices

    DOEpatents

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

    2000-07-04

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

  4. Silicon nitride/silicon carbide composite powders

    DOEpatents

    Dunmead, Stephen D.; Weimer, Alan W.; Carroll, Daniel F.; Eisman, Glenn A.; Cochran, Gene A.; Susnitzky, David W.; Beaman, Donald R.; Nilsen, Kevin J.

    1996-06-11

    Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.

  5. Process for making silicon carbide reinforced silicon carbide composite

    NASA Technical Reports Server (NTRS)

    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.

  6. Preparation of silicon carbide fibers

    DOEpatents

    Wei, G.C.

    1983-10-12

    Silicon carbide fibers suitable for use in the fabrication of dense, high-strength, high-toughness SiC composites or as thermal insulating materials in oxidizing environments are fabricated by a new, simplified method wherein a mixture of short-length rayon fibers and colloidal silica is homogenized in a water slurry. Water is removed from the mixture by drying in air at 120/sup 0/C and the fibers are carbonized by (pyrolysis) heating the mixture to 800 to 1000/sup 0/C in argon. The mixture is subsequently reacted at 1550 to 1900/sup 0/C in argon to yield pure ..beta..-SiC fibers.

  7. Manufacture of silicon carbide using solar energy

    DOEpatents

    Glatzmaier, Gregory C.

    1992-01-01

    A method is described for producing silicon carbide particles using solar energy. The method is efficient and avoids the need for use of electrical energy to heat the reactants. Finely divided silica and carbon are admixed and placed in a solar-heated reaction chamber for a time sufficient to cause a reaction between the ingredients to form silicon carbide of very small particle size. No grinding of silicon carbide is required to obtain small particles. The method may be carried out as a batch process or as a continuous process.

  8. LIQUID PHASE SINTERING OF METALLIC CARBIDES

    DOEpatents

    Hammond, J.; Sease, J.D.

    1964-01-21

    An improved method is given for fabricating uranium carbide composites, The method comprises forming a homogeneous mixture of powdered uranium carbide, a uranium intermetallic compound which wets and forms a eutectic with said carbide and has a non-uranium component which has a relatively high vapor pressure at a temperature in the range 1200 to 1500 deg C, and an organic binder, pressing said mixture to a composite of desired green strength, and then vacuum sintering said composite at the eutectic forming temperature for a period sufficient to remove at least a portion of the non-uranium containing component of said eutectic. (AEC)

  9. Thermal Expansion of Hafnium Carbide

    NASA Technical Reports Server (NTRS)

    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.

  10. Structural diversity in lithium carbides

    NASA Astrophysics Data System (ADS)

    Lin, Yangzheng; Strobel, Timothy A.; Cohen, R. E.

    2015-12-01

    The lithium-carbon binary system possesses a broad range of chemical compounds, which exhibit fascinating chemical bonding characteristics, which give rise to diverse and technologically important properties. While lithium carbides with various compositions have been studied or suggested previously, the crystal structures of these compounds are far from well understood. In this work, we present the first comprehensive survey of all ground state (GS) structures of lithium carbides over a broad range of thermodynamic conditions, using ab initio density functional theory (DFT) crystal structure searching methods. Thorough searches were performed for 29 stoichiometries ranging from Li12C to LiC12 at 0 and 40 GPa. Based on formation enthalpies from optimized van der Waals density functional calculations, three thermodynamically stable phases (Li4C3 , Li2C2 , and LiC12) were identified at 0 GPa, and seven thermodynamically stable phases (Li8C , Li6C , Li4C , Li8C3 , Li2C , Li3C4 , and Li2C3 ) were predicted at 40 GPa. A rich diversity of carbon bonding, including monomers, dimers, trimers, nanoribbons, sheets, and frameworks, was found within these structures, and the dimensionality of carbon connectivity existing within each phase increases with increasing carbon concentration. We find that the well-known composition LiC6 is actually a metastable one. We also find a unique coexistence of carbon monomers and dimers within the predicted thermodynamically stable phase Li8C3 , and different widths of carbon nanoribbons coexist in a metastable phase of Li2C2 (Imm2). Interesting mixed sp2-sp3 carbon frameworks are predicted in metastable phases with composition LiC6.

  11. Electroextraction of boron from boron carbide scrap

    SciTech Connect

    Jain, Ashish; Anthonysamy, S.; Ghosh, C.; Ravindran, T.R.; Divakar, R.; Mohandas, E.

    2013-10-15

    Studies were carried out to extract elemental boron from boron carbide scrap. The physicochemical nature of boron obtained through this process was examined by characterizing its chemical purity, specific surface area, size distribution of particles and X-ray crystallite size. The microstructural characteristics of the extracted boron powder were analyzed by using scanning electron microscopy and transmission electron microscopy. Raman spectroscopic examination of boron powder was also carried out to determine its crystalline form. Oxygen and carbon were found to be the major impurities in boron. Boron powder of purity ∼ 92 wt. % could be produced by the electroextraction process developed in this study. Optimized method could be used for the recovery of enriched boron ({sup 10}B > 20 at. %) from boron carbide scrap generated during the production of boron carbide. - Highlights: • Recovery of {sup 10}B from nuclear grade boron carbide scrap • Development of process flow sheet • Physicochemical characterization of electroextracted boron • Microscopic examination of electroextracted boron.

  12. Method for preparing boron-carbide articles

    DOEpatents

    Benton, S.T.; Masters, D.R.

    1975-10-21

    The invention is directed to the preparation of boron carbide articles of various configurations. A stoichiometric mixture of particulate boron and carbon is confined in a suitable mold, heated to a temperature in the range of about 1250 to 1500$sup 0$C for effecting a solid state diffusion reaction between the boron and carbon for forming the boron carbide (B$sub 4$C), and thereafter the resulting boron-carbide particles are hot-pressed at a temperature in the range of about 1800 to 2200$sup 0$C and a pressure in the range of about 1000 to 4000 psi for densifying and sintering the boron carbide into the desired article.

  13. Calcium carbide poisoning via food in childhood.

    PubMed

    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.

  14. Selective etching of silicon carbide films

    DOEpatents

    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.

  15. Fabrication of thorium bearing carbide fuels

    DOEpatents

    Gutierrez, R.L.; Herbst, R.J.; Johnson, K.W.R.

    Thorium-uranium carbide and thorium-plutonium carbide fuel pellets have been fabricated by the carbothermic reduction process. Temperatures of 1750/sup 0/C and 2000/sup 0/C were used during the reduction cycle. Sintering temperatures of 1800/sup 0/C and 2000/sup 0/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 reproductibility of chemical and phase composition.

  16. Combustion synthesis of novel boron carbide

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Handbook of refractory carbides and nitrides: Properties, characteristics, processing and applications

    SciTech Connect

    Pierson, H.O.

    1997-12-31

    This reference work provides a complete review of the structure properties, processing and applications of refractory carbides and nitrides. The contents include: the refractory carbides; interstitial carbides, structure and composites; titanium, zirconium, and hafnium carbides; vanadium, niobium and tantalum carbides; chromium, molybdenum, and tungsten carbides; covalent carbides--structure and composition; characteristics and properties of silicon carbide and boron carbide; the refractory nitrides; interstitial nitrides--structure and composition; interstitial nitrides--properties and general characteristics; covalent nitrides--composition and structure; covalent nitrides--properties and general characteristics; processing of refractory carbides and nitrides and applications of refractory carbides and nitrides.

  19. Selective surface reactions of single crystal metal carbides: alkene production from short chain alcohols on titanium carbide and vanadium carbide

    NASA Astrophysics Data System (ADS)

    Guenard, Rebecca L.; Fernández-Torres, Luis C.; Kim, Byung-Il; Perry, Scott S.; Frantz, Peter; Didziulis, Stephen V.

    2002-08-01

    The adsorption and reaction of ethanol and 2-propanol on the (1 0 0) surface of single crystal vanadium carbide (VC) and titanium carbide (TiC) have been studied using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy. A mixture of molecular and dissociative adsorption is observed at cryogenic temperatures on both of the carbide surfaces. Dissociative adsorption of the short chain alcohols leads to the formation of an alkoxy intermediate at 153 K on both VC(1 0 0) and TiC(1 0 0). With increasing temperature, the alkoxy intermediate selectively reacts with the carbide surfaces to produce an alkene. A comparison of TPD intensities indicates that dissociative adsorption occurs to a greater extent on TiC; however, the reaction yield for dehydration of the alkoxy surface species is ˜20% greater on VC(1 0 0) as compared to TiC(1 0 0). Specific isotopic labeling studies of the ethanol reaction identify γ-hydride elimination as a key step in alkene formation on VC(1 0 0). This pattern of reactivity on metal carbide surfaces significantly differs from the decomposition reactions, producing carbon monoxide and hydrogen, or the β-hydride elimination reactions, producing an aldehyde and hydrogen, that are observed on most transition metal surfaces.

  20. Method of fabricating porous silicon carbide (SiC)

    NASA Technical Reports Server (NTRS)

    Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

    1995-01-01

    Porous silicon carbide is fabricated according to techniques which result in a significant portion of nanocrystallites within the material in a sub 10 nanometer regime. There is described techniques for passivating porous silicon carbide which result in the fabrication of optoelectronic devices which exhibit brighter blue luminescence and exhibit improved qualities. Based on certain of the techniques described porous silicon carbide is used as a sacrificial layer for the patterning of silicon carbide. Porous silicon carbide is then removed from the bulk substrate by oxidation and other methods. The techniques described employ a two-step process which is used to pattern bulk silicon carbide where selected areas of the wafer are then made porous and then the porous layer is subsequently removed. The process to form porous silicon carbide exhibits dopant selectivity and a two-step etching procedure is implemented for silicon carbide multilayers.

  1. As-cast carbides in high-speed steels

    NASA Astrophysics Data System (ADS)

    Ding, Peidao; Shi, Gongqi; Zhou, Shouze

    1993-06-01

    The spatial distribution and structure of as-cast carbides and the effects of W, Mo, and V content on the morphology and amount of as-cast carbides in high-speed steels were studied systematically. It was shown that increasing the Mo and decreasing the W content led to a decrease in the amount of total eutectic carbide and an increase in the MC and M2C carbides. The eutectic morphology changed from skeletal to platelike when the content of Mo increased. The presence of V favored not only the formation of MC carbide but also the formation of M2C carbide and reduced the formation of M2C carbide. Increasing V led to an increase in the size of the eutectic carbides.

  2. 64. INTERIOR VIEW OF THE CARBIDE COOLING SHED. VIEW IS ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    64. INTERIOR VIEW OF THE CARBIDE COOLING SHED. VIEW IS SHOWING CALCIUM CARBIDE IN COOLING CARS ON THE FLOOR. DECEMBER 26, 1918. - United States Nitrate Plant No. 2, Reservation Road, Muscle Shoals, Muscle Shoals, Colbert County, AL

  3. Deposition method for producing silicon carbide high-temperature semiconductors

    DOEpatents

    Hsu, George C.; Rohatgi, Naresh K.

    1987-01-01

    An improved deposition method for producing silicon carbide high-temperature semiconductor material comprising placing a semiconductor substrate composed of silicon carbide in a fluidized bed silicon carbide deposition reactor, fluidizing the bed particles by hydrogen gas in a mildly bubbling mode through a gas distributor and heating the substrate at temperatures around 1200.degree.-1500.degree. C. thereby depositing a layer of silicon carbide on the semiconductor substrate.

  4. The diffusion bonding of silicon carbide and boron carbide using refractory metals

    SciTech Connect

    Cockeram, B.V.

    1999-10-01

    Joining is an enabling technology for the application of structural ceramics at high temperatures. Metal foil diffusion bonding is a simple process for joining silicon carbide or boron carbide by solid-state, diffusive conversion of the metal foil into carbide and silicide compounds that produce bonding. Metal diffusion bonding trials were performed using thin foils (5 {micro}m to 100 {micro}m) of refractory metals (niobium, titanium, tungsten, and molybdenum) with plates of silicon carbide (both {alpha}-SiC and {beta}-SiC) or boron carbide that were lapped flat prior to bonding. The influence of bonding temperature, bonding pressure, and foil thickness on bond quality was determined from metallographic inspection of the bonds. The microstructure and phases in the joint region of the diffusion bonds were evaluated using SEM, microprobe, and AES analysis. The use of molybdenum foil appeared to result in the highest quality bond of the metal foils evaluated for the diffusion bonding of silicon carbide and boron carbide. Bonding pressure appeared to have little influence on bond quality. The use of a thinner metal foil improved the bond quality. The microstructure of the bond region produced with either the {alpha}-SiC and {beta}-SiC polytypes were similar.

  5. Carrier lifetimes in silicon carbide

    NASA Astrophysics Data System (ADS)

    Nigam, Saurav

    Carrier lifetimes are one of the most crucial parameters that govern the performance of high voltage/high power devices. The lack of understanding of the factors that determine the carrier lifetimes in silicon carbide is currently a major impediment in the development of high voltage/high power technology based on this material. The objective of this dissertation was to identify and subsequently, characterize various recombination channels present in silicon carbide. Of special importance was identification of lifetime limiting defects in the high quality epitaxial layers grown by state-of-the-art chemical vapor deposition technique for high voltage application. The effect of growth conditions (C/Si ratio, growth temperature, seed polarity, epilayer thickness, and background doping) on the concentrations of various defects were investigated with the aim of manipulating carrier lifetimes by controlling different growth parameters. Based on the qualitative correlations between various point defects and carrier lifetimes in more than thirty epitaxial layers, three defects (Z-defect, EH6/7 center, and P1 center) were identified as potential lifetime limiting defects. The P1 center was shown to act as efficient recombination channel whenever present in concentrations greater than 1013 cm-3. Such concentrations were observed in layers grown on the C-face and at low C/Si ratio (less than 1.5). The measurement of recombination rates of electrons and holes via the Z-defect and the EH6/7 center (as a function of temperature) were performed by analyzing the carrier dynamics in specially designed p-n diodes. At 300 K, the capture cross section of the two states of the Z-defect were sigman1˜6x10-15 cm2 (electron capture at the donor state), sigmap1˜2x1014 cm2 (hole capture at the donor state), sigman2˜1x10 16 cm2 (electron capture at the acceptor state), and sigma p2˜1e-13 cm2 (hole capture at the acceptor state). The electron capture cross section for the EH6/7 centers was

  6. Silicon Carbide Solar Cells Investigated

    NASA Technical Reports Server (NTRS)

    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.

  7. Organosilane Polymers. IV. Polycarbosilane Precursors for Silicon Carbide.

    DTIC Science & Technology

    1981-01-01

    The current objectives of this project are: (1) optimized preparations of tractable polycarbosilane precursors for silicon carbide ; (2) conversion of...such polycarbosilanes to silicon carbide including shaped articles thereof, such as fibers; and (3) development of fundamental understanding of the...vinylic or chloromethyl (ClCH2-) silanes. These polymers are directly convertible to silicon carbide compositions by atmospheric pressure pyrolysis

  8. Varying potential silicon carbide gas sensor

    NASA Technical Reports Server (NTRS)

    Shields, Virgil B. (Inventor); Ryan, Margaret A. (Inventor); Williams, Roger M. (Inventor)

    1997-01-01

    A hydrocarbon gas detection device operates by dissociating or electro-chemically oxidizing hydrocarbons adsorbed to a silicon carbide detection layer. Dissociation or oxidation are driven by a varying potential applied to the detection layer. Different hydrocarbon species undergo reaction at different applied potentials so that the device is able to discriminate among various hydrocarbon species. The device can operate at temperatures between 100.degree. C. and at least 650.degree. C., allowing hydrocarbon detection in hot exhaust gases. The dissociation reaction is detected either as a change in a capacitor or, preferably, as a change of current flow through an FET which incorporates the silicon carbide detection layers. The silicon carbide detection layer can be augmented with a pad of catalytic material which provides a signal without an applied potential. Comparisons between the catalytically produced signal and the varying potential produced signal may further help identify the hydrocarbon present.

  9. Silicon carbide, an emerging high temperature semiconductor

    NASA Technical Reports Server (NTRS)

    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.

  10. Carbides composite surface layers produced by (PTA)

    SciTech Connect

    Tajoure, Meloud; Tajouri, Ali E-mail: dr.mokhtarphd@yahoo.com; Abuzriba, Mokhtar E-mail: dr.mokhtarphd@yahoo.com; Akreem, Mosbah

    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.

  11. Fabrication of thorium bearing carbide fuels

    DOEpatents

    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.

  12. Mechanical Properties of Crystalline Silicon Carbide Nanowires.

    PubMed

    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.

  13. METHOD FOR COATING GRAPHITE WITH METALLIC CARBIDES

    DOEpatents

    Steinberg, M.A.

    1960-03-22

    A method for producing refractory coatings of metallic carbides on graphite was developed. In particular, the graphite piece to be coated is immersed in a molten solution of 4 to 5% by weight of zirconium, titanium, or niobium dissolved in tin. The solution is heated in an argon atmosphere to above 1400 deg C, whereby the refractory metal reacts with the surface of the graphite to form a layer of metalic carbide. The molten solution is cooled to 300 to 400 deg C, and the graphite piece is removed. Excess tin is wiped from the graphite, which is then heated in vacuum to above 2300 deg C. The tin vaporizes from the graphite surface, leaving the surface coated with a tenacious layer of refractory metallic carbide.

  14. Titanium carbide nanocrystals in circumstellar environments.

    PubMed

    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.

  15. Joining of porous silicon carbide bodies

    DOEpatents

    Bates, Carl H.; Couhig, John T.; Pelletier, Paul J.

    1990-05-01

    A method of joining two porous bodies of silicon carbide is disclosed. It entails utilizing an aqueous slip of a similar silicon carbide as was used to form the porous bodies, including the sintering aids, and a binder to initially join the porous bodies together. Then the composite structure is subjected to cold isostatic pressing to form a joint having good handling strength. Then the composite structure is subjected to pressureless sintering to form the final strong bond. Optionally, after the sintering the structure is subjected to hot isostatic pressing to further improve the joint and densify the structure. The result is a composite structure in which the joint is almost indistinguishable from the silicon carbide pieces which it joins.

  16. Ablation of carbide materials with femtosecond pulses

    NASA Astrophysics Data System (ADS)

    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.

  17. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, R.A.; Virkar, A.V.; Hurford, A.C.

    1989-05-09

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1,600 C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase. 4 figs.

  18. Liquid phase sintering of silicon carbide

    DOEpatents

    Cutler, Raymond A.; Virkar, Anil V.; Hurford, Andrew C.

    1989-01-01

    Liquid phase sintering is used to densify silicon carbide based ceramics using a compound comprising a rare earth oxide and aluminum oxide to form liquids at temperatures in excess of 1600.degree. C. The resulting sintered ceramic body has a density greater than 95% of its theoretical density and hardness in excess of 23 GPa. Boron and carbon are not needed to promote densification and silicon carbide powder with an average particle size of greater than one micron can be densified via the liquid phase process. The sintered ceramic bodies made by the present invention are fine grained and have secondary phases resulting from the liquid phase.

  19. Thermal conductivity behavior of boron carbides

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    Knowledge of the thermal conductivity of boron carbides is necessary to evaluate its potential for high temperature thermoelectric energy conversion applications. The thermal diffusivity of hot pressed boron carbide B/sub 1-x/C/sub x/ samples as a function of composition, temperature and temperature cycling was measured. These data in concert with density and specific heat data yield the thermal conductivities of these materials. The results in terms of a structural model to explain the electrical transport data and novel mechanisms for thermal conduction are discussed.

  20. Silicon Carbide Thyristors for Power Applications

    DTIC Science & Technology

    1995-07-01

    Silicon carbide has the potential to make high-performance power devices. Its high thermal conductivity, wide bandgap, high breakdown field and high saturated electron drift velocity imply a clear superiority over Si and GaAs. This work reports the fabrication and testing of three-terminal 6H-SiC thyristors. The silicon carbide thyristors show higher current density and higher temperature operation than is possible with silicon devices. Switching measurements at room temperature and at elevated temperatures are reported. SiC thyristors have

  1. On the sintering of silicon carbide

    NASA Technical Reports Server (NTRS)

    Gugel, E.

    1986-01-01

    This document deals with the sintering of silicon carbide using pressureless sintering. This technique makes it possible to sinter a primarily covalent material to usable densities up to over 98% thD without having to use a high amount of sinter additives as is the case with other non-oxide ceramic materials. The process takes place rapidly, and it is also possible to produce relatively thick-walled structural parts without major problems. This sheds more light on the true characteristics of silicon carbide in one structural part, since there is no second or nearly no second phase. Heat pressing has improved stability.

  2. Reactive deposition of tungsten and titanium carbides by induction plasma

    NASA Astrophysics Data System (ADS)

    Jiang, X. L.; Gitzhofer, F.; Boulos, M. I.; Tiwari, R.

    1995-05-01

    A study is reported on the use of induction plasma technology for the preparation of dense free-standing deposits of tungsten carbide and titanium carbide from metallic powders and methane. Phase analysis by X-ray diffraction indicates that primary carburization of the particles takes place in-flight giving rise to the formation of W2C and TiC(1 - x). Secondary carburization occurs in the deposits resulting in the formation of tungsten and titanium carbides. Microstructures revealed by optical and scanning electron microscopy show uniform small grains of the carbides. The reactive plasma spray-formed tungsten carbide shows transgranular fracture, while pure tungsten deposits show intergranular fracture.

  3. Micromachining of Silicon Carbide using femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Farsari, M.; Filippidis, G.; Zoppel, S.; Reider, G. A.; Fotakis, C.

    2007-04-01

    We have demonstrated micromachining of bulk 3C silicon carbide (3C- SiC) wafers by employing 1028nm wavelength femtosecond laser pulses of energy less than 10 nJ directly from a femtosecond laser oscillator, thus eliminating the need for an amplified system and increasing the micromachining speed by more than four orders of magnitude.

  4. Bioactivation of biomorphous silicon carbide bone implants.

    PubMed

    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.

  5. High-temperature carbidization of carboniferous rocks

    NASA Astrophysics Data System (ADS)

    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.

  6. Prealloyed catalyst for growing silicon carbide whiskers

    DOEpatents

    Shalek, Peter D.; Katz, Joel D.; Hurley, George F.

    1988-01-01

    A prealloyed metal catalyst is used to grow silicon carbide whiskers, especially in the .beta. form. Pretreating the metal particles to increase the weight percentages of carbon or silicon or both carbon and silicon allows whisker growth to begin immediately upon reaching growth temperature.

  7. Boron Carbides As Thermo-electric Materials

    NASA Technical Reports Server (NTRS)

    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.

  8. Silicon carbide diode for increased light output

    NASA Technical Reports Server (NTRS)

    Griffiths, L. B.; Mlavsky, A. I.

    1969-01-01

    Transition metals improve the overall light output and the output in particular regions of the electroluminescent of a silicon carbide semiconductor device. These metals /impurities/ introduce levels that can be pumped electrically and affect the efficiency of the recombination process involved in emission of radiation.

  9. Nonstoichiometry and growth of some Fe carbides

    NASA Astrophysics Data System (ADS)

    Walker, D.; Dasgupta, R.; Li, J.; Buono, A.

    2013-09-01

    Iron carbides containing from 31 to 17 atomic % carbon, with cohenite XRD structure and optical properties, were grown in experiments in Fe-Ni-S-C, Fe-Ni-C, and in Fe-C at 1, 6, and 7 GPa. X-ray cell volumes increase with C content. Compositions listed above vary considerably outside the nominal (Fe,Ni)3C stoichiometry of cohenite/cementite. Cohenites coexisting with Fe-C liquid are carbon poor. The Eckstrom-Adcock carbide, nominally Fe7C3, was found to show compositions from 29 to 36 atomic % C at 7 GPa in Fe-C. Both these materials are better regarded as solutions than as stoichiometric compounds, and their properties such as volume have compositional dependencies, as do the iron oxides, sulfides, silicides, and hydrides. The fraction of C dissolved in cohenite-saturated alloy is found to become smaller between 1 and 7 GPa. If this trend continues at higher pressures, the deep mantle should be easier to saturate with carbide than the shallow mantle, whether or not carbide is metastable as at ambient pressure. At temperatures below the cohenite-graphite peritectic, cohenite may grow as a compositionally zoned layer between Fe and graphite. The Eckstrom-Adcock carbide joins the assemblage at 7 GPa. Phases appear between Fe and C in an order consistent with metasomatic interface growth between chemically incompatible feed stocks. Diffusion across the carbide layer is not the growth rate limiting step. Carbon transport along the grain boundaries of solid Fe source stock at 1 GPa, to form C-saturated Fe alloy, is observed to be orders of magnitude faster than the cohenite layer growth. Growth stagnates too rapidly to be consistent with diffusion control. Furthermore, lateral variations in carbide layer thickness, convoluted inert marker horizons, and variable compositional profiles within the layers suggest that there are local transport complexities not covered by one-dimensional diffusive metasomatic growth. In contrast to many transport phenomena which slow with

  10. Boron carbide nanowires: Synthesis and characterization

    NASA Astrophysics Data System (ADS)

    Guan, Zhe

    Bulk boron carbide has been widely used in ballistic armored vest and the property characterization has been heavily focused on mechanical properties. Even though boron carbides have also been projected as a promising class of high temperature thermoelectric materials for energy harvesting, the research has been limited in this field. Since the thermal conductivity of bulk boron carbide is still relatively high, there is a great opportunity to take advantage of the nano effect to further reduce it for better thermoelectric performance. This dissertation work aims to explore whether improved thermoelectric performance can be found in boron carbide nanowires compared with their bulk counterparts. This dissertation work consists of four main parts. (1) Synthesis of boron carbide nanowires. Boron carbide nanowires were synthesized by co-pyrolysis of diborane and methane at low temperatures (with 879 °C as the lowest) in a home-built low pressure chemical vapor deposition (LPCVD) system. The CVD-based method is energy efficient and cost effective. The as-synthesized nanowires were characterized by electron microscopy extensively. The transmission electron microscopy (TEM) results show the nanowires are single crystalline with planar defects. Depending on the geometrical relationship between the preferred growth direction of the nanowire and the orientation of the defects, the as-synthesized nanowires could be further divided into two categories: transverse fault (TF) nanowires grow normal to the defect plane, while axial fault (AF) ones grow within the defect plane. (2) Understanding the growth mechanism of as-synthesized boron carbide nanowires. The growth mechanism can be generally considered as the famous vapor-liquid-solid (VLS) mechanism. TF and AF nanowires were found to be guided by Ni-B catalysts of two phases. A TF nanowire is lead by a hexagonal phase catalyst, which was proved to be in a liquid state during reaction. While an AF nanowires is catalyzed by a

  11. Processing development of 4 tantalum carbide-hafnium carbide and related carbides and borides for extreme environments

    NASA Astrophysics Data System (ADS)

    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

  12. Synthesis and characterization of monometallic niobium carbides and bimetallic niobium carbides using hafnium, titanium, and tantalum

    NASA Astrophysics Data System (ADS)

    Watts, Cassandra Jean

    As fossil fuels are rapidly depleting there is an enormous push for the development of new forms of energy based on renewable resources. Proton Exchange Membrane (PEM) fuel cells are one possible solution, but are constrained by the necessity of the platinum catalyst to initiate the oxygen reduction reaction (ORR). Transition metal carbides, like tungsten and molybdenum carbide, have shown catalytic properties that resemble platinum. This project seeks to synthesize through a low temperature solid state method with a LiCl:KCl:KF salt flux monometallic niobium carbides (NbC, Nb4C3, and Nb2C) and the bimetallic niobium carbides HfNbC, TiNbC, and TaNbC. The synthesized materials are characterized using XRD, SEM, and EDS. The results showed that a pure single phase of NbC and Nb4C 3, and a semi alloyed phase of TiNbC2 are obtainable. The remaining systems yielded phase separated carbide systems and are dominated by irreproducibility or oxidization.

  13. METHOD FOR PRODUCING CEMENTED CARBIDE ARTICLES

    DOEpatents

    Onstott, E.I.; Cremer, G.D.

    1959-07-14

    A method is described for making molded materials of intricate shape where the materials consist of mixtures of one or more hard metal carbides or oxides and matrix metals or binder metals thereof. In one embodiment of the invention 90% of finely comminuted tungsten carbide powder together with finely comminuted cobalt bonding agent is incorporated at 60 deg C into a slurry with methyl alcohol containing 1.5% paraffin, 3% camphor, 3.5% naphthalene, and 1.8% toluene. The compact is formed by the steps of placing the slurry in a mold at least one surface of which is porous to the fluid organic system, compacting the slurry, removing a portion of the mold from contact with the formed object and heating the formed object to remove the remaining organic matter and to sinter the compact.

  14. Method for fabricating boron carbide articles

    DOEpatents

    Ardary, Zane L.; Reynolds, Carl D.

    1980-01-01

    The present invention is directed to the fabrication of boron carbide articles having length-to-diameter or width ratios greater than 2 to 1. The process of the present invention is practiced by the steps comprising hot pressing boron carbide powder into article segments or portions in which the segments have a length-to-diameter or width ratio less than 1.5, aligning a plurality of the initially hot-pressed segments in a hot-pressing die with the end surfaces of the segments placed in intimate contact with one another, and then hot pressing the aligned segments into an article of the desired configuration. The resulting article exhibits essentially uniform density throughout the structure with the bonds between the segments being equivalent in hardness, strength, and density to the remainder of the article.

  15. Shock compression properties of silicon carbide

    SciTech Connect

    Grady, D.E.; Kipp, M.E.

    1993-07-01

    An investigation of the shock compression and release properties of silicon carbide ceramic has been performed. A series of planar impact experiments has been completed in which stationary target discs of ceramic were struck by plates of either similar ceramic or other appropriate material at velocities up to 2.2 km/s with a propellant gun facility. The particle velocity history at the interface between the back of the target ceramic and a lithium-fluoride window material was measured with laser velocity interferometry (VISAR). Impact stresses achieved in these experiments range between about 10 and 50 GPa. Numerical solutions and analytic methods were used to determine the dynamic compression and release stress-strain behavior of the ceramic. Further analysis of the data was performed to determine dynamic strength and compressibility properties of silicon carbide.

  16. Ultrasonic ranking of toughness of tungsten carbide

    NASA Technical Reports Server (NTRS)

    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.

  17. Synthesis of Fe carbides species by reactive milling

    NASA Astrophysics Data System (ADS)

    Lodya, J. A. L.; Gericke, H.; Ngubane, J.; Dlamini, T. H.

    2009-04-01

    The formation of iron carbides by reactive milling of α-Fe and C powders is reported. The products formed were analyzed by Mössbauer spectroscopy and X-ray diffraction. It was found that iron carbide phases start forming after an incubation period of about 3 h depending on the ball-to-powder weight ratio (BPR). Carbide amounts increased with increasing milling time while α-Fe content decreased. Energy transfer increased with increasing BPR and high BPR resulted in an increase in the reaction rate. Although it was not possible to selectively synthesise a specific Fe x C phase, samples containing predominantly one type of carbide phase, either Hägg carbide or cementite, were successfully prepared. The formation of the different iron carbide phases is discussed within the context of the Fe-C phase diagram for non-equilibrium processes.

  18. Nonlinear optical imaging of defects in cubic silicon carbide epilayers.

    PubMed

    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.

  19. Carbide coated fibers in graphite-aluminum composites

    NASA Technical Reports Server (NTRS)

    Imprescia, R. J.; Levinson, L. S.; Reiswig, R. D.; Wallace, T. C.; Williams, J. M.

    1975-01-01

    The study of protective-coupling layers of refractory metal carbides on the graphite fibers prior to their incorporation into composites is presented. Such layers should be directly wettable by liquid aluminum and should act as diffusion barriers to prevent the formation of aluminum carbide. Chemical vapor deposition was used to uniformly deposit thin, smooth, continuous coats of ZrC on the carbon fibers of tows derived from both rayon and polyacrylonitrile. A wet chemical coating of the fibers, followed by high-temperature treatment, was used, and showed promise as an alternative coating method. Experiments were performed to demonstrate the ability of aluminum alloys to wet carbide surfaces. Titanium carbide, zirconium carbide and carbide-coated graphite surfaces were successfully wetted. Results indicate that initial attempts to wet surfaces of ZrC-coated carbon fibers appear successful.

  20. Friction and deformation behavior of single-crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Friction and deformation studies were conducted with single-crystal silicon carbide in sliding contact with diamond. When the radius of curvature of the spherical diamond rider was large (0.3), deformation of silicon carbide was primarily elastic. Under these conditions the friction coefficient was low and did not show a dependence on the silicon carbide orientation. Further, there was no detectable cracking of the silicon carbide surfaces. When smaller radii of curvature of the spherical diamond riders (0.15 and 0.02 mm) or a conical diamond rider was used, plastic grooving occured and the silicon carbide exhibited anisotropic friction and deformation behavior. Under these conditions the friction coefficient depended on load. Anisotropic friction and deformation of the basal plane of silicon carbide was controlled by the slip system. 10101120and cleavage of1010.

  1. Silicon Carbide Technologies for Lightweighted Aerospace Mirrors

    DTIC Science & Technology

    2008-09-01

    Silicon Carbide Technologies for Lightweighted Aerospace Mirrors Lawrence E. Matson (1) Ming Y. Chen (1) Brett deBlonk (2) Iwona A...glass and beryllium to produce lightweighted aerospace mirror systems has reached its limits due to the long lead times, high processing costs...for making mirror structural substrates, figuring and finishing technologies being investigated to reduce cost time and cost, and non-destructive

  2. Carbide and boride laser modification of steels

    NASA Astrophysics Data System (ADS)

    Major, Boguslaw; Ebner, Reinhold

    1997-10-01

    Microstructure modification by laser remelting or laser alloying was studied on carbon Ck45 and high speed steels. Laser remelting of Ck45 by overlapping laser tracks led to a great refinement of martensitic structure, especially in the heat affected zone of subsequent laser track. High speed steel (HSS) M2 after laser remelting showed, beside the tetragonal martensite, the diffraction lines of cubic carbides of the M6C and M12C types. Laser alloying of M2 HSS using vanadium carbide (VC) additions caused increasing of eutectic in the interdendritic space, which was accompanied with reduction of the M6C and rising of the MC. M2 HSS laser alloyed with molybdenum carbide (Mo2C) showed formation of the M6C for the hipereutectic compositions while at the highest concentrations of molybdenum, primary dendrites of the M2C and stabilized ferrite were stated. High additions of borides: CrB or VB2; developed formation of the primary borides of blocky type containing a high amount of W, Cr or W, V, respectively. Laser alloying of Ck45 by means of: CrB, VB2 and B4C showed: in the case of CrB an eutectic (alpha) '/M3(C,B)/M2B as well as primary precipitates of the M2B phase for hipereutectic compositions; by adding VB2, the M3B2 and M2B phases were identified experimentally for hipereutectic concentrations; for alloying using B4C, the cellular dendritic structure together with primary borides of the (tau) -M23(C,B)6 phase were stated for hipereutectic compositions. The phase diagrams of M2 HSS + (VC or Mo2C) as well as Ck45 + B4C systems were calculated to predict changes of the constitutions due to laser alloying. Comparison of the solidification structures established experimentally with the calculated phase diagrams revealed a good correlation for the carbides, especially.

  3. Electron-Spin Resonance in Boron Carbide

    NASA Technical Reports Server (NTRS)

    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.

  4. Diamond-silicon carbide composite and method

    DOEpatents

    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.

  5. Low blow Charpy impact of silicon carbides

    NASA Technical Reports Server (NTRS)

    Abe, H.; Chandan, H. C.; Bradt, R. C.

    1978-01-01

    The room-temperature impact resistance of several commercial silicon carbides was examined using an instrumented pendulum-type machine and Charpy-type specimens. Energy balance compliance methods and fracture toughness approaches, both applicable to other ceramics, were used for analysis. The results illustrate the importance of separating the machine and the specimen energy contributions and confirm the equivalence of KIc and KId. The material's impact energy was simply the specimen's stored elastic strain energy at fracture.

  6. Microalloying Boron Carbide with Silicon to Achieve Dramatically Improved Ductility

    DTIC Science & Technology

    2014-11-18

    Microalloying Boron Carbide with Silicon to Achieve Dramatically Improved Ductility Qi An and William A. Goddard, III* Materials and Process... Boron carbide (B4C) is a hard material whose value for extended engineering applications such as body armor; is limited by its brittleness under...Plasmonics, Optical Materials, and Hard Matter Superhard materials, such as diamond, cubic boron nitride,and boron carbide (B4C), exhibit many

  7. Mechanical Testing of Silicon Carbide on MISSE-7

    DTIC Science & Technology

    2012-07-15

    JS) ii Abstract Silicon carbide ( SiC ) mechanical test specimens were included on the second Optical and Reflector Materials Experiment (ORMatE II...2. Vendor 2 EFS Weibull Results (normalized to Extra Disks Weibull parameters) 12 1. Introduction Silicon carbide ( SiC ) mechanical test...AEROSPACE REPORT NO ATR-2012(8921)-5 Mechanical Testing of Silicon Carbide on MISSE-7 Jul> 15. 2012 David B. Witkin Space Materials Laboratory

  8. Controlled Thin-Film Growth Of Silicon Carbide Polytypes

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony; Larkin, David J.

    1995-01-01

    Improved deposition process to grows thin layers of silicon carbide having chosen crystalline structures. Process incorporated into sequences of deposition and etching steps used to fabricate silicon-carbide-based semiconductor devices. Important advance because silicon carbide emerging as superior semiconductor for devices operating under conditions of high power, high temperature, and/or high frequency. Furthermore, various crystalline structures of SiC have different electronic properties, each suited to specific application.

  9. Single Molecule Source Reagents for CVD of Beta Silicon Carbide

    DTIC Science & Technology

    1991-06-30

    Beta silicon carbide is an excellent candidate semiconductor material for demanding applications in high power and high temperature electronic...devices due to its high breakdown voltage, relatively large band gap, high thermal conductivity and high melting point. Use of silicon carbide thin films is...equipment has been used in the CVD systems, but small disparities remain between successive deposited films. The production of practical beta silicon carbide devices

  10. Fundamental Studies and Device Development in Beta Silicon Carbide

    DTIC Science & Technology

    1990-02-28

    The dependence of growth rate of alpha-SiC on alpha- Silicon Carbide substrates and surface morphology on temperature, source gas/carrier gas flow...Hydrogen- Silicon Carbide films during deposition have also been studied. Device research has involved studies of suitable ohmic and rectifying...semiconductor field effect transistor and Impact Avalanche transit-time diodes. Alpha silicon carbide , Semi-conductors, Growth rate, Aluminum dopant, Nitrogen dopant, Ohmic contacts, Schottky contacts, MESFET, MOSFET, IMPATT.

  11. Research on Silicon, Carbon, and Silicon Carbide Heterostructures

    DTIC Science & Technology

    1990-09-14

    0Innr Jc9&9b 1. TITLE (Include Security Classification) Research on Silicon, Carbon, and Silicon Carbide Heterostructures Z. PERSONAL AUTHOR(S) W. D...and identify by block number) FIELD I GROUP SUB-GROUP PLASMAS. DEPOSITION. THIN FILMS. SILICON CARBIDE . DIAMOND. SURFACES. DESORPTION. CHARACTERIZATION...AND SILICON CARBIDE HETEROSTRUCTURES W. D. Partlow (P.I.), W. J. Choyke, J. T. Yates, Jr., C. C. Cheng, H. Gutleben, L. E. Kline, R. R. Mitchell, J

  12. Optical waveguide formed by cubic silicon carbide on sapphire substrates

    NASA Technical Reports Server (NTRS)

    Tang, Xiao; Wongchotigul, Kobchat; Spencer, Michael G.

    1991-01-01

    Optical confinement in beta silicon carbide (beta-SiC) thin films on sapphire substrate is demonstrated. Measurements are performed on waveguides formed by the mechanical transfer of thin beta-SiC films to sapphire. Recent results of epitaxial films of SiC on sapphire substrates attest to the technological viability of optoelectronic devices made from silicon carbide. Far-field mode patterns are shown. It is believed that this is the first step in validating a silicon carbide optoelectronic technology.

  13. Boron-carbide-aluminum and boron-carbide-reactive metal cermets

    DOEpatents

    Halverson, Danny C.; Pyzik, Aleksander J.; Aksay, Ilhan A.

    1986-01-01

    Hard, tough, lightweight boron-carbide-reactive metal composites, particularly boron-carbide-aluminum composites, are produced. These composites have compositions with a plurality of phases. A method is provided, including the steps of wetting and reacting the starting materials, by which the microstructures in the resulting composites can be controllably selected. Starting compositions, reaction temperatures, reaction times, and reaction atmospheres are parameters for controlling the process and resulting compositions. The ceramic phases are homogeneously distributed in the metal phases and adhesive forces at ceramic-metal interfaces are maximized. An initial consolidation step is used to achieve fully dense composites. Microstructures of boron-carbide-aluminum cermets have been produced with modulus of rupture exceeding 110 ksi and fracture toughness exceeding 12 ksi.sqroot.in. These composites and methods can be used to form a variety of structural elements.

  14. Silicon carbide sintered body manufactured from silicon carbide powder containing boron, silicon and carbonaceous additive

    NASA Technical Reports Server (NTRS)

    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.

  15. Chemical state of fission products in irradiated uranium carbide fuel

    NASA Astrophysics Data System (ADS)

    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.

  16. HEAT-RESISTANT MATERIAL WITH SILICON CARBIDE AS A BASE,

    DTIC Science & Technology

    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

  17. Ion-Beam Milling of Silicon Carbide Epitaxial Layers.

    DTIC Science & Technology

    1982-08-04

    Ion milling of photolithographically processed silicon carbide heteroepitaxially grown layers on Si is feasible using an aluminum mask which is produced by standard photolithographic procedures and techniques. (Author)

  18. Tribological properties of sintered polycrystalline and single crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

    1982-01-01

    Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

  19. Preparation and electrocatalytic activity of tungsten carbide and titania nanocomposite

    SciTech Connect

    Hu, Sujuan; Shi, Binbin; Yao, Guoxing; Li, Guohua; Ma, Chunan

    2011-10-15

    Graphical abstract: The electrocatalytic activity of tungsten carbide and titania nanocomposite is related to the structure, crystal phase and chemical components of the nanocomposite, and is also affected by the property of electrolyte. A synergistic effect exists between tungsten carbide and titania of the composite. Highlights: {yields} Electrocatalytic activity of tungsten carbide and titania nanocomposite with core-shell structure. {yields} Activity is related to the structure, crystal phase and chemical component of the nanocomposite. {yields} The property of electrolyte affects the electrocatalytic activity. {yields} A synergistic effect exists between tungsten carbide and titania of the composite. -- Abstract: Tungsten carbide and titania nanocomposite was prepared by combining a reduced-carbonized approach with a mechanochemical approach. The samples were characterized by X-ray diffraction, transmission electron microscope under scanning mode and X-ray energy dispersion spectrum. The results show that the crystal phases of the samples are composed of anatase, rutile, nonstoichiometry titanium oxide, monotungsten carbide, bitungsten carbide and nonstoichiometry tungsten carbide, and they can be controlled by adjusting the parameters of the reduced-carbonized approach; tungsten carbide particles decorate on the surface of titania support, the diameter of tungsten carbide particle is smaller than 20 nm and that of titania is around 100 nm; the chemical components of the samples are Ti, O, W and C. The electrocatalytic activity of the samples was measured by a cyclic voltammetry with three electrodes. The results indicate that the electrocatalytic activities of the samples are related to their crystal phases and the property of electrolyte in aqueous solution. A synergistic effect between titania and tungsten carbide is reported for the first time.

  20. Direct Electrochemical Preparation of Cobalt, Tungsten, and Tungsten Carbide from Cemented Carbide Scrap

    NASA Astrophysics Data System (ADS)

    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.

  1. Surface and Bulk Carbide Transformations in High-Speed Steel

    NASA Astrophysics Data System (ADS)

    Godec, M.; Večko Pirtovšek, T.; Šetina Batič, B.; McGuiness, P.; Burja, J.; Podgornik, B.

    2015-11-01

    We have studied the transformation of carbides in AISI M42 high-speed steels in the temperature window used for forging. The annealing was found to result in the partial transformation of the large, metastable M2C carbides into small, more stable grains of M6C, with an associated change in the crystal orientation. In addition, MC carbides form during the transformation of M2C to M6C. From the high-speed-steel production point of view, it is beneficial to have large, metastable carbides in the cast structure, which later during annealing, before the forging, transform into a structure of polycrystalline carbides. Such carbides can be easily decomposed into several small carbides, which are then randomly distributed in the microstructure. The results also show an interesting difference in the carbide-transformation reactions on the surface versus the bulk of the alloy, which has implications for in-situ studies of bulk phenomena that are based on surface observations.

  2. Surface and Bulk Carbide Transformations in High-Speed Steel.

    PubMed

    Godec, M; Večko Pirtovšek, T; Šetina Batič, B; McGuiness, P; Burja, J; Podgornik, B

    2015-11-05

    We have studied the transformation of carbides in AISI M42 high-speed steels in the temperature window used for forging. The annealing was found to result in the partial transformation of the large, metastable M2C carbides into small, more stable grains of M6C, with an associated change in the crystal orientation. In addition, MC carbides form during the transformation of M2C to M6C. From the high-speed-steel production point of view, it is beneficial to have large, metastable carbides in the cast structure, which later during annealing, before the forging, transform into a structure of polycrystalline carbides. Such carbides can be easily decomposed into several small carbides, which are then randomly distributed in the microstructure. The results also show an interesting difference in the carbide-transformation reactions on the surface versus the bulk of the alloy, which has implications for in-situ studies of bulk phenomena that are based on surface observations.

  3. Aluminum/Silicon Carbide Matrix Material for Targeting System

    DTIC Science & Technology

    2006-07-21

    most common MMC is cast aluminum reinforced with various amounts of silicon carbide . LMMFC is currently machining very high precision components for...targeting systems from cast aluminum/ silicon carbide (AISiC) matrix material (with a very high SiC content) and are experiencing difficulty achieving the

  4. Process Development for Silicon Carbide Based Structural Ceramics

    DTIC Science & Technology

    1983-01-01

    The objective of this program is to develop a process for making shaped silicon carbide based ceramic materials with reduced microstructural flaw...identical conditions. The fracture toughness, KIC, measured by Vickers indentation testing was approximately the same as hot pressed Silicon carbide (NC203

  5. Aluminum / Silicon Carbide Matrix Material Machining for Targeting Systems

    DTIC Science & Technology

    2006-07-21

    most common (MMC) is cast aluminum reinforced with various amounts of silicon carbide . (LMMFC) is currently machining very high precision components for...targeting systems made from cast aluminum/ silicon carbide (AISiC) matrix material (with a very high SiC content) and is experiencing difficulty

  6. Process Development for Silicon Carbide Based Structural Ceramics.

    DTIC Science & Technology

    1982-02-01

    The objective of this program is to develop a process for making shaped silicon carbide based ceramic materials with reduced microstructural flaw...micrometers and a Weibull characteristic four point bend strength of 660 mPa, which significantly exceeds other reaction bonded silicon carbide materials

  7. METHOD OF COATING GRAPHITE WITH STABLE METAL CARBIDES AND NITRIDES

    DOEpatents

    Gurinsky, D.H.

    1959-10-27

    A method is presented for forming protective stable nitride and carbide compounds on the surface of graphite. This is accomplished by contacting the graphite surface with a fused heavy liquid metal such as bismuth or leadbismuth containing zirconium, titanium, and hafnium dissolved or finely dispersed therein to form a carbide and nitride of at least one of the dissolved metals on the graphite surface.

  8. Method of coating graphite tubes with refractory metal carbides

    DOEpatents

    Wohlberg, C.

    1973-12-11

    A method of coating graphite tubes with a refractory metal carbide is described. An alkali halide is reacted with a metallic oxide, the metallic portion being selected from the IVth or Vth group of the Periodic Table, the resulting salt reacting in turn with the carbon to give the desired refractory metal carbide coating. (Official Gazette)

  9. Method of forming impermeable carbide coats on graphite

    DOEpatents

    Wohlberg, C.

    1973-12-11

    A method of forming an impermeable refractory metal carbide coating on graphite is described in which a metal containing oxidant and a carbide former are applied to the surface of the graphite, heated to a temperature of between 1200 and 1500 deg C in an inert gas, under a vacuum and continuing to heat to about 2300 deg C. (Official Gazette)

  10. Molybdenum disilicide composites reinforced with zirconia and silicon carbide

    SciTech Connect

    Petrovic, J.J.

    1992-12-31

    This patent pertains to compositions consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia. Fabrication, fracture toughness, and bend strength are covered.

  11. Surface and Bulk Carbide Transformations in High-Speed Steel

    PubMed Central

    Godec, M.; Večko Pirtovšek, T.; Šetina Batič, B.; McGuiness, P.; Burja, J.; Podgornik, B.

    2015-01-01

    We have studied the transformation of carbides in AISI M42 high-speed steels in the temperature window used for forging. The annealing was found to result in the partial transformation of the large, metastable M2C carbides into small, more stable grains of M6C, with an associated change in the crystal orientation. In addition, MC carbides form during the transformation of M2C to M6C. From the high-speed-steel production point of view, it is beneficial to have large, metastable carbides in the cast structure, which later during annealing, before the forging, transform into a structure of polycrystalline carbides. Such carbides can be easily decomposed into several small carbides, which are then randomly distributed in the microstructure. The results also show an interesting difference in the carbide-transformation reactions on the surface versus the bulk of the alloy, which has implications for in-situ studies of bulk phenomena that are based on surface observations. PMID:26537780

  12. Method for producing silicon nitride/silicon carbide composite

    DOEpatents

    Dunmead, Stephen D.; Weimer, Alan W.; Carroll, Daniel F.; Eisman, Glenn A.; Cochran, Gene A.; Susnitzky, David W.; Beaman, Donald R.; Nilsen, Kevin J.

    1996-07-23

    Silicon carbide/silicon nitride composites are prepared by carbothermal reduction of crystalline silica powder, carbon powder and optionally crsytalline silicon nitride powder. The crystalline silicon carbide portion of the composite has a mean number diameter less than about 700 nanometers and contains nitrogen.

  13. Carbide Transformations in Tempering of Complexly Alloyed White Cast Iron

    NASA Astrophysics Data System (ADS)

    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.

  14. Molybdenum disilicide composites reinforced with zirconia and silicon carbide

    DOEpatents

    Petrovic, John J.

    1995-01-01

    Compositions consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia.

  15. Molybdenum disilicide composites reinforced with zirconia and silicon carbide

    DOEpatents

    Petrovic, J.J.

    1995-01-17

    Compositions are disclosed consisting essentially of molybdenum disilicide, silicon carbide, and a zirconium oxide component. The silicon carbide used in the compositions is in whisker or powder form. The zirconium oxide component is pure zirconia or partially stabilized zirconia or fully stabilized zirconia.

  16. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, T. J.; Winterbottom, W. L.

    1986-01-01

    Work performed to develop silicon carbide materials of high strength and to form components of complex shape and high reliability is described. A beta-SiC powder and binder system was adapted to the injection molding process and procedures and process parameters developed capable of providing a sintered silicon carbide material with improved properties. The initial effort has been to characterize the baseline precursor materials (beta silicon carbide powder and boron and carbon sintering aids), develop mixing and injection molding procedures for fabricating test bars, and characterize the properties of the sintered materials. Parallel studies of various mixing, dewaxing, and sintering procedures have been carried out in order to distinguish process routes for improving material properties. A total of 276 MOR bars of the baseline material have been molded, and 122 bars have been fully processed to a sinter density of approximately 95 percent. The material has a mean MOR room temperature strength of 43.31 ksi (299 MPa), a Weibull characteristic strength of 45.8 ksi (315 MPa), and a Weibull modulus of 8.0. Mean values of the MOR strengths at 1000, 1200, and 14000 C are 41.4, 43.2, and 47.2 ksi, respectively. Strength controlling flaws in this material were found to consist of regions of high porosity and were attributed to agglomerates originating in the initial mixing procedures. The mean stress rupture lift at 1400 C of five samples tested at 172 MPa (25 ksi) stress was 62 hours and at 207 MPa (30 ksi) stress was 14 hours. New fluid mixing techniques have been developed which significantly reduce flaw size and improve the strength of the material. Initial MOR tests indicate the strength of the fluid-mixed material exceeds the baseline property by more than 33 percent.

  17. METHOD FOR COATING GRAPHITE WITH NIOBIUM CARBIDE

    DOEpatents

    Kane, J.S.; Carpenter, J.H.; Krikorian, O.H.

    1962-01-16

    A method is given for coating graphite with a hard, tenacious layer of niobium carbide up to 30 mils or more thick. The method makes use of the discovery that niobium metal, if degassed and heated rapidly below the carburization temperature in contact with graphite, spreads, wets, and penetrates the graphite without carburization. The method includes the obvious steps of physically contacting niobium powders or other physical forms of niobium with graphite, degassing the assembly below the niobium melting point, e.g., 1400 deg C, heating to about 2200 to 2400 deg C within about 15 minutes while outgassing at a high volume throughput, and thereafter carburizing the niobium. (AEC)

  18. Current Status of Cemented Carbide Technology

    DTIC Science & Technology

    1958-06-01

    1100-1300 201 Q-2370 T i o2 - lampb I ack 1700-1900 309o-3q5o Zro2 - lampblack 1800-2000 3270-3630 v2o3 or v2o5 - lampblack II 00-1200 201Q-2190...is added to the powder as a solute in a solvent such as benzene or carbon-tetrachlor ide, and intensive aixing produces surface films around the...King. F. E., THIN , DUCTILE CARBIDE COATING POSSIBLE WITH NEW METHOD. Matorials and Mtthods. 40_. 112-4 (1952). Kingston. W. E.. od

  19. Titanium carbide coatings for aerospace ball bearings

    NASA Technical Reports Server (NTRS)

    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.

  20. Structural and mechanical properties of thorium carbide

    SciTech Connect

    Aynyas, Mahendra; Pataiya, Jagdeesh; Arya, B. S.; Singh, A.; Sanyal, S. P.

    2015-06-24

    We have investigated the cohesive energies, equilibrium lattice constants, pressure-volume relationship, phase transition pressure and elastic constant for thorium carbide using an interionic potential theory with modified ionic charge, which includes Coulomb screening effect due to d-electrons. This compound undergoes structural phase transition from NaCl (B{sub 1}) to CsCl (B{sub 2}) structure at high pressure 40 GPa. We have also calculated bulk, Young, and shear moduli, Poisson ratio and anisotropic ratio in NaCl (B{sub 1}) structure and compared them with other experimental and theoretical results which show a good agreement.

  1. Electrocatalysis using transition metal carbide and oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    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

  2. High temperature intermetallic binders for HVOF carbides

    SciTech Connect

    Shaw, K.G.; Gruninger, M.F.; Jarosinski, W.J.

    1994-12-31

    Gas turbines technology has a long history of employing the desirable high temperature physical attributes of ceramic-metallic (cermet) materials. The most commonly used coatings incorporate combinations of WC-Co and Cr{sub 3}C{sub 2}-NiCr, which have also been successfully utilized in other non-turbine coating applications. Increased turbine operating temperatures and other high temperature service conditions have made apparent the attractive notion of increasing the temperature capability and corrosion resistance of these coatings. In this study the intermetallic binder NiAl has been used to replace the cobalt and NiCr constituents of conventional WC and Cr{sub 3}C{sub 2} cermet powders. The composite carbide thermal spray powders were fabricated for use in the HVOF coating process. The structure of HVOF deposited NiAl-carbide coatings are compared directly to the more familiar WC-Co and Cr{sub 3}C{sub 2}-NiCr coatings using X-ray diffraction, back-scattered electron imaging (BEI) and electron dispersive spectroscopy (EDS). Hardness variations with temperature are reported and compared between the NiAl and Co/NiCr binders.

  3. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1987-01-01

    This is the second annual technical report entitled, Improved Silicon Carbide for Advanced Heat Engines, and includes work performed during the period February 16, 1986 to February 15, 1987. The program is conducted for NASA under contract NAS3-24384. The objective is the development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines. The fabrication methods used are to be adaptable for mass production of such parts on an economically sound basis. Injection molding is the forming method selected. This objective is to be accomplished in a two-phase program: (1) to achieve a 20 percent improvement in strength and a 100 percent increase in Weibull modulus of the baseline material; and (2) to produce a complex shaped part, a gas turbine rotor, for example, with the improved mechanical properties attained in the first phase. Eight tasks are included in the first phase covering the characterization of the properties of a baseline material, the improvement of those properties and the fabrication of complex shaped parts. Activities during the first contract year concentrated on two of these areas: fabrication and characterization of the baseline material (Task 1) and improvement of material and processes (Task 7). Activities during the second contract year included an MOR bar matrix study to improve mechanical properties (Task 2), materials and process improvements (Task 7), and a Ford-funded task to mold a turbocharger rotor with an improved material (Task 8).

  4. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1988-01-01

    This is the third annual technical report for the program entitled, Improved Silicon Carbide for Advanced Heat Engines, for the period February 16, 1987 to February 15, 1988. The objective of the original program was the development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines. Injection molding is the forming method selected for the program because it is capable of forming complex parts adaptable for mass production on an economically sound basis. The goals of the revised program are to reach a Weibull characteristic strength of 550 MPa (80 ksi) and a Weibull modulus of 16 for bars tested in 4-point loading. Two tasks are discussed: Task 1 which involves materials and process improvements, and Task 2 which is a MOR bar matrix to improve strength and reliability. Many statistically designed experiments were completed under task 1 which improved the composition of the batches, the mixing of the powders, the sinter and anneal cycles. The best results were obtained by an attritor mixing process which yielded strengths in excess of 550 MPa (80 ksi) and an individual Weibull modulus of 16.8 for a 9-sample group. Strengths measured at 1200 and 1400 C were equal to the room temperature strength. Annealing of machined test bars significantly improved the strength. Molding yields were measured and flaw distributions were observed to follow a Poisson process. The second iteration of the Task 2 matrix experiment is described.

  5. Microwave behavior of silicon carbide/high alumina cement composites

    NASA Astrophysics Data System (ADS)

    Leiser, Kristie Sue

    2001-09-01

    Microwave susceptors have been fabricated from composites of silicon carbide/high alumina cement. These composites are very useful for microwave processing other materials. By using these composites for microwave hybrid heating, both ordinary and unique materials have the potential to be fabricated. The use of the susceptors can help to produce a more even temperature distribution across a material being microwave heated. This composite of silicon carbide particles embedded in high alumina cement only needed to be better characterized to enhance its applicability to more systems. This goal was accomplished in this study. During the course of the study, the factors affecting the heating rate of the composites were identified. These factors included silicon carbide particle size, weight percent silicon carbide in the composite, silicon carbide phase, processing atmosphere, and the maximum temperature experienced by the composite. A systematic study was designed to examine the importance of factors such as these and their effects upon the heating rate of high alumina cement/silicon carbide composites. Statistical design was employed to determine the significance of the factors of interest. The effects of these factors on the heating rate of the composites were determined. As the amount of silicon carbide in the composite increased, the heating rate tended to increase. The effects observed were explained by a combination of dielectric mixing equations, a heat transfer model and percolation theory. The silicon carbide particle size also affected the heating rate of the composites. Mathematical modeling showed that the particle size effect was a geometric effect that was dependent upon imperfect thermal contact between the silicon carbide particle and the cement matrix. The silicon carbide particle size also affected the percolation threshold of the composites. The heating rate of the composites increased when calcium carbonate present in the cement was pyrolyzed to form

  6. Development of Nanoporous Carbide-Derived Carbon Electrodes for High-Performance Lithium-Ion Batteries

    DTIC Science & Technology

    2011-09-01

    exceptionally high surface area [11]. SiC Silicon Carbide Nb2C Niobium Carbide TiC Titanium Carbide NbC Niobium Carbide Mo2C Molybdenum Carbide SrC2...its electrochemical performance. Studies were conducted on three titanium carbide (TiC)-based CDC powders, synthesized at 600, 1000, and 1200 °C...were conducted on three titanium carbide (TiC)-based CDC powders, synthesized at 600, 1,000, and 1,200 °C. Custom-made CDC anodes were fabricated

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Salt flux synthesis of single and bimetallic carbide nanowires

    NASA Astrophysics Data System (ADS)

    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.

  9. Computational Studies of Physical Properties of Boron Carbide

    SciTech Connect

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Method of preparing silicon carbide particles dispersed in an electrolytic bath for composite electroplating of metals

    DOEpatents

    Peng, Yu-Min; Wang, Jih-Wen; Liue, Chun-Ying; Yeh, Shinn-Horng

    1994-01-01

    A method for preparing silicon carbide particles dispersed in an electrolytic bath for composite electroplating of metals includes the steps of washing the silicon carbide particles with an organic solvent; washing the silicon carbide particles with an inorganic acid; grinding the silicon carbide particles; and heating the silicon carbide particles in a nickel-containing solution at a boiling temperature for a predetermined period of time.

  12. Field Emission of Thermally Grown Carbon Nanostructures on Silicon Carbide

    DTIC Science & Technology

    2012-03-22

    process, current CNT field emission issues, and patterning of silicon carbide ( SiC ). 2.2. CNT Background 2.2.1. CNT Structure CNT’s basic...density is obtain when S=3h [46] 2.5. Patterning of SiC 2.5.1. Silicon Carbide Properties As a result of its structure and material, SiC has...Its chemical inertness, however, limits the available techniques needed to pattern a SiC wafer. 2.5.2. Silicon Carbide Etching Because SiC

  13. Hugoniot equation of state and dynamic strength of boron carbide

    SciTech Connect

    Grady, Dennis E.

    2015-04-28

    Boron carbide ceramics have been particularly problematic in attempts to develop adequate constitutive model descriptions for purposes of analysis of dynamic response in the shock and impact environment. Dynamic strength properties of boron carbide ceramic differ uniquely from comparable ceramics. Furthermore, boron carbide is suspected, but not definitely shown, to undergoing polymorphic phase transformation under shock compression. In the present paper, shock-wave compression measurements conducted over the past 40 years are assessed for the purpose of achieving improved understanding of the dynamic equation of state and strength of boron carbide. In particular, attention is focused on the often ignored Los Alamos National Laboratory (LANL) Hugoniot measurements performed on porous sintered boron carbide ceramic. The LANL data are shown to exhibit two compression anomalies on the shock Hugoniot within the range of 20–60 GPa that may relate to crystallographic structure transitions. More recent molecular dynamics simulations on the compressibility of the boron carbide crystal lattice reveal compression transitions that bear similarities to the LANL Hugoniot results. The same Hugoniot data are complemented with dynamic isentropic compression data for boron carbide extracted from Hugoniot measurements on boron carbide and copper granular mixtures. Other Hugoniot measurements, however, performed on near-full-density boron carbide ceramic differ markedly from the LANL Hugoniot data. These later data exhibit markedly less compressibility and tend not to show comparable anomalies in compressibility. Alternative Hugoniot anomalies, however, are exhibited by the near-full-density data. Experimental uncertainty, Hugoniot strength, and phase transformation physics are all possible explanations for the observed discrepancies. It is reasoned that experimental uncertainty and Hugoniot strength are not likely explanations for the observed differences. The notable

  14. Separation of Nuclear Fuel Surrogates from Silicon Carbide Inert Matrix

    SciTech Connect

    Dr. Ronald Baney

    2008-12-15

    The objective of this project has been to identify a process for separating transuranic species from silicon carbide (SiC). Silicon carbide has become one of the prime candidates for the matrix in inert matrix fuels, (IMF) being designed to reduce plutonium inventories and the long half-lives actinides through transmutation since complete reaction is not practical it become necessary to separate the non-transmuted materials from the silicon carbide matrix for ultimate reprocessing. This work reports a method for that required process.l

  15. Hugoniot equation of state and dynamic strength of boron carbide

    NASA Astrophysics Data System (ADS)

    Grady, Dennis E.

    2015-04-01

    Boron carbide ceramics have been particularly problematic in attempts to develop adequate constitutive model descriptions for purposes of analysis of dynamic response in the shock and impact environment. Dynamic strength properties of boron carbide ceramic differ uniquely from comparable ceramics. Furthermore, boron carbide is suspected, but not definitely shown, to undergoing polymorphic phase transformation under shock compression. In the present paper, shock-wave compression measurements conducted over the past 40 years are assessed for the purpose of achieving improved understanding of the dynamic equation of state and strength of boron carbide. In particular, attention is focused on the often ignored Los Alamos National Laboratory (LANL) Hugoniot measurements performed on porous sintered boron carbide ceramic. The LANL data are shown to exhibit two compression anomalies on the shock Hugoniot within the range of 20-60 GPa that may relate to crystallographic structure transitions. More recent molecular dynamics simulations on the compressibility of the boron carbide crystal lattice reveal compression transitions that bear similarities to the LANL Hugoniot results. The same Hugoniot data are complemented with dynamic isentropic compression data for boron carbide extracted from Hugoniot measurements on boron carbide and copper granular mixtures. Other Hugoniot measurements, however, performed on near-full-density boron carbide ceramic differ markedly from the LANL Hugoniot data. These later data exhibit markedly less compressibility and tend not to show comparable anomalies in compressibility. Alternative Hugoniot anomalies, however, are exhibited by the near-full-density data. Experimental uncertainty, Hugoniot strength, and phase transformation physics are all possible explanations for the observed discrepancies. It is reasoned that experimental uncertainty and Hugoniot strength are not likely explanations for the observed differences. The notable mechanistic

  16. Process Development for Silicon Carbide Based Structural Ceramics

    DTIC Science & Technology

    1980-12-31

    silicon carbide base structural ceramics with reduced microstructural flaw size by in situ reaction of silicon with fine, ultra-uniform pored carbon skeletons that are produced from liquid polymer solutions without particulate additions. Thus far, very uniform carbon skeletons in two pore sizes (2.5 and 0.27 microns) have been produced and siliconized. Very uniform samples of approx 1 cm cross section have been produced in a silicon carbide material of approx 5 microns average size. Limited regions of material with carbide size less than 1 micron have

  17. Colloidal characterization of ultrafine silicon carbide and silicon nitride powders

    NASA Technical Reports Server (NTRS)

    Whitman, Pamela K.; Feke, Donald L.

    1986-01-01

    The effects of various powder treatment strategies on the colloid chemistry of aqueous dispersions of silicon carbide and silicon nitride are examined using a surface titration methodology. Pretreatments are used to differentiate between the true surface chemistry of the powders and artifacts resulting from exposure history. Silicon nitride powders require more extensive pretreatment to reveal consistent surface chemistry than do silicon carbide powders. As measured by titration, the degree of proton adsorption from the suspending fluid by pretreated silicon nitride and silicon carbide powders can both be made similar to that of silica.

  18. Plasma metallurgical production of nanocrystalline borides and carbides

    NASA Astrophysics Data System (ADS)

    Galevsky, G. V.; Rudneva, V. V.; Cherepanov, A. N.; Galevsky, S. G.; Efimova, K. A.

    2016-09-01

    he experience in production and study of properties of nanocrystalline borides and chromium carbides, titanium, silicon was summarized. The design and features of the vertical three-jet once-through reactor with power 150 kW, used in the plasma metallurgical production, was described. The technological, thermotechnical and resource characteristics of the reactor were identified. The parameters of borides and carbides synthesis, their main characteristics in the nanodispersed state and equipment-technological scheme of production were provided. Evaluation of engineering-and-economical performance of the laboratory and industrial levels of borides and carbides production and the state corresponding to the segment of the world market was carried out.

  19. Creep behavior of uranium carbide-based alloys

    NASA Technical Reports Server (NTRS)

    Seltzer, M. S.; Wright, T. R.; Moak, D. P.

    1975-01-01

    The present work gives the results of experiments on the influence of zirconium carbide and tungsten on the creep properties of uranium carbide. The creep behavior of high-density UC samples follows the classical time-dependence pattern of (1) an instantaneous deformation, (2) a primary creep region, and (3) a period of steady-state creep. Creep rates for unalloyed UC-1.01 and UC-1.05 are several orders of magnitude greater than those measured for carbide alloys containing a Zr-C and/or W dispersoid. The difference in creep strength between alloyed and unalloyed materials varies with temperature and applied stress.

  20. Microwave hybrid synthesis of silicon carbide nanopowders

    SciTech Connect

    Ebadzadeh, Touradj Marzban-Rad, Ehsan

    2009-01-15

    Nanosized silicon carbide powders were synthesised from a mixture of silica gel and carbon through both the conventional and microwave heating methods. Reaction kinetics of SiC formation were found to exhibit notable differences for the samples heated in microwave field and furnace. In the conventional method SiC nanopowders can be synthesised after 105 min heating at 1500 deg. C in a coke-bed using an electrical tube furnace. Electron microscopy studies of these powders showed the existence of equiaxed SiC nanopowders with an average particle size of 8.2 nm. In the microwave heating process, SiC powders formed after 60 min; the powder consisted of a mixture of SiC nanopowders (with two average particle sizes of 13.6 and 58.2 nm) and particles in the shape of long strands (with an average diameter of 330 nm)

  1. Amorphization of Silicon Carbide by Carbon Displacement

    SciTech Connect

    Devanathan, Ram; Gao, Fei; Weber, William J.

    2004-05-10

    We have used molecular dynamics simulations to examine the possibility of amorphizing silicon carbide (SiC) by exclusively displacing C atoms. At a defect generation corresponding to 0.2 displacements per atom, the enthalpy surpasses the level of melt-quenched SiC, the density decreases by about 15%, and the radial distribution function shows a lack of long-range order. Prior to amorphization, the surviving defects are mainly C Frenkel pairs (67%), but Si Frenkel pairs (18%) and anti-site defects (15%) are also present. The results indicate that SiC can be amorphized by C sublattice displacements. Chemical short-range disorder, arising mainly from interstitial production, plays a significant role in the amorphization.

  2. Neutron irradiation induced amorphization of silicon carbide

    SciTech Connect

    Snead, L.L.; Hay, J.C.

    1998-09-01

    This paper provides the first known observation of silicon carbide fully amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60 C to a total fast neutron fluence of 2.6 {times} 10{sup 25} n/m{sup 2}. Amorphization was seen in both materials, as evidenced by TEM, electron diffraction, and x-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density ({minus}10.8%), elastic modulus as measured using a nanoindentation technique ({minus}45%), hardness as measured by nanoindentation ({minus}45%), and standard Vickers hardness ({minus}24%). Similar property changes are observed for the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than 130 C.

  3. Laser Induced Fluorescence Spectroscopy of Boron Carbide

    NASA Astrophysics Data System (ADS)

    Cheung, A. S.-C.; Ng, Y. W.; Pang, H. F.

    2011-06-01

    Laser induced fluorescence spectrum of boron carbide (BC) between 490 and 560 nm has been recorded and analyzed. Gas-phase BC molecule was produced by the reaction of B2H6 and CH4 in the presence of magnesium atom from laser ablation process. The (0, 0), (1, 0), and (2, 0) bands of the B4 Σ- - X4 Σ- transition were recorded and rotationally analyzed. Spectra of both isotopes: 10BC and 11BC were observed. Equilibrium molecular constants for the B4 Σ- and the X4 Σ- states for both isotopes were determined. A comparison of the determined gas-phase molecular constants with those obtained using matrix isolation spectroscopy and the theoretical calculations will be presented. Financial support from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 701008P) is gratefully acknowledged.

  4. Development of a silicon carbide sewing thread

    NASA Technical Reports Server (NTRS)

    Sawko, Paul M.; Vasudev, Anand

    1989-01-01

    A silicon carbide (SiC) sewing thread has been designed which consists of a two-ply yarn in a 122 turns-per-meter-twist construction. Two processing aids in thread construction were evaluated. Prototype blankets were sewn using an SiC thread prepared either with polytetrafluoroethylene sizing or with an overwrap of rayon/dacron service yarn. The rayon/dacron-wrapped SiC thread was stronger, as shown by higher break-strength retention and less damage to the outer-mold-line fabric. This thread enables thermal protection system articles to be sewn or joined, or have perimeter close-out of assembled parts when using SiC fabric for high-temperature applications.

  5. Plastic deformation of polycrystalline zirconium carbide

    NASA Technical Reports Server (NTRS)

    Darolia, R.; Archbold, T. F.

    1976-01-01

    The compressive yield strength of arc-melted polycrystalline zirconium carbide has been found to vary from 77 kg per sq mm at 1200 C to 19 kg per sq mm at 1800 C. Yield drops were observed with plastic strain-rates greater than 0.003/sec but not with slower strain rates. Strain-rate change experiments yielded values for the strain-rate sensitivity parameter m which range from 6.5 at 1500 C to 3.8 at 1800 C, and the product dislocation velocity stress exponent times T was found to decrease linearly with increasing temperature. The deformation rate results are consistent with the Kelly-Rowcliffe model in which the diffusion of carbon assists the motion of dislocations.

  6. Stable field emission from nanoporous silicon carbide.

    PubMed

    Kang, Myung-Gyu; Lezec, Henri J; Sharifi, Fred

    2013-02-15

    We report on a new type of stable field emitter capable of electron emission at levels comparable to thermal sources. Such an emitter potentially enables significant advances in several important technologies which currently use thermal electron sources. These include communications through microwave electronics, and more notably imaging for medicine and security where new modalities of detection may arise due to variable-geometry x-ray sources. Stable emission of 6 A cm(-2) is demonstrated in a macroscopic array, and lifetime measurements indicate these new emitters are sufficiently robust to be considered for realistic implementation. The emitter is a monolithic structure, and is made in a room-temperature process. It is fabricated from a silicon carbide wafer, which is formed into a highly porous structure resembling an aerogel, and further patterned into an array. The emission properties may be tuned both through control of the nanoscale morphology and the macroscopic shape of the emitter array.

  7. Tunable plasticity in amorphous silicon carbide films.

    PubMed

    Matsuda, Yusuke; Kim, Namjun; King, Sean W; Bielefeld, Jeff; Stebbins, Jonathan F; Dauskardt, Reinhold H

    2013-08-28

    Plasticity plays a crucial role in the mechanical behavior of engineering materials. For instance, energy dissipation during plastic deformation is vital to the sufficient fracture resistance of engineering materials. Thus, the lack of plasticity in brittle hybrid organic-inorganic glasses (hybrid glasses) often results in a low fracture resistance and has been a significant challenge for their integration and applications. Here, we demonstrate that hydrogenated amorphous silicon carbide films, a class of hybrid glasses, can exhibit a plasticity that is even tunable by controlling their molecular structure and thereby leads to an increased and adjustable fracture resistance in the films. We decouple the plasticity contribution from the fracture resistance of the films by estimating the "work-of-fracture" using a mean-field approach, which provides some insight into a potential connection between the onset of plasticity in the films and the well-known rigidity percolation threshold.

  8. Polymeric synthesis of silicon carbide with microwaves.

    PubMed

    Aguilar, Juan; Urueta, Luis; Valdez, Zarel

    2007-01-01

    The aim of this work is conducting polymeric synthesis with microwaves for producing beta-SiC. A polymeric precursor was prepared by means of hydrolysis and condensation reactions from pheniltrimethoxysilane, water, methanol, ammonium hydroxide and chloride acid. The precursor was placed into a quartz tube in vacuum; pyrolysis was carried out conventionally in a tube furnace, and by microwaves at 2.45 GHz in a multimode cavity. Conventional tests took place in a scheme where temperature was up to 1500 degrees C for 120 minutes. Microwave heating rate was not controlled and tests lasted 60 and 90 minutes, temperature was around 900 degrees C. Products of the pyrolysis were analyzed by means of x-ray diffraction; in the microwave case the diffraction patterns showed a strong background of either very fine particles or amorphous material, then infrared spectroscopy was also employed for confirming carbon bonds. In both processes beta-SiC was found as the only produced carbide.

  9. Silicon carbide - Progress in crystal growth

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony

    1987-01-01

    Recent progress in the development of two processes for producing large-area high-quality single crystals of SiC is described: (1) a modified Lely process for the growth of the alpha polytypes (e.g., 6H SiC) initially developed by Tairov and Tsvetkov (1978, 1981) and Ziegler et al. (1983), and (2) a process for the epitaxial growth of the beta polytype on single-crystal silicon or other substrates. Growth of large-area cubic SiC on Si is described together with growth of defect-free beta-SiC films on alpha-6H SiC crystals and TiC lattice. Semiconducting qualities of silicon carbide crystals grown by various techniques are discussed.

  10. Stored energy in irradiated silicon carbide

    SciTech Connect

    Snead, L.L.; Burchell, T.D.

    1997-04-01

    This report presents a short review of the phenomenon of Wigner stored energy release from irradiated graphite and discusses it in relation to neutron irradiation of silicon carbide. A single published work in the area of stored energy release in SiC is reviewed and the results are discussed. It appears from this previous work that because the combination of the comparatively high specific heat of SiC and distribution in activation energies for recombining defects, the stored energy release of SiC should only be a problem at temperatures lower than those considered for fusion devices. The conclusion of this preliminary review is that the stored energy release in SiC will not be sufficient to cause catastrophic heating in fusion reactor components, though further study would be desirable.

  11. Asymmetric twins in rhombohedral boron carbide

    SciTech Connect

    Fujita, Takeshi Guan, Pengfei; Madhav Reddy, K.; Hirata, Akihiko; Guo, Junjie; Chen, Mingwei

    2014-01-13

    Superhard materials consisting of light elements have recently received considerable attention because of their ultrahigh specific strength for a wide range of applications as structural and functional materials. However, the failure mechanisms of these materials subjected to high stresses and dynamic loading remain to be poorly known. We report asymmetric twins in a complex compound, boron carbide (B{sub 4}C), characterized by spherical-aberration-corrected transmission electron microscopy. The atomic structure of boron-rich icosahedra at rhombohedral vertices and cross-linked carbon-rich atomic chains can be clearly visualized, which reveals unusual asymmetric twins with detectable strains along the twin interfaces. This study offers atomic insights into the structure of twins in a complex material and has important implications in understanding the planar defect-related failure of superhard materials under high stresses and shock loading.

  12. Silicon Carbide Nanotube Oxidation at High Temperatures

    NASA Technical Reports Server (NTRS)

    Ahlborg, Nadia; Zhu, Dongming

    2012-01-01

    Silicon Carbide Nanotubes (SiCNTs) have high mechanical strength and also have many potential functional applications. In this study, SiCNTs were investigated for use in strengthening high temperature silicate and oxide materials for high performance ceramic nanocomposites and environmental barrier coating bond coats. The high · temperature oxidation behavior of the nanotubes was of particular interest. The SiCNTs were synthesized by a direct reactive conversion process of multiwall carbon nanotubes and silicon at high temperature. Thermogravimetric analysis (TGA) was used to study the oxidation kinetics of SiCNTs at temperatures ranging from 800degC to1300degC. The specific oxidation mechanisms were also investigated.

  13. Method of producing silicon carbide articles

    DOEpatents

    Milewski, John V.

    1985-01-01

    A method of producing articles comprising reaction-bonded silicon carbide (SiC) and graphite (and/or carbon) is given. The process converts the graphite (and/or carbon) in situ to SiC, thus providing the capability of economically obtaining articles made up wholly or partially of SiC having any size and shape in which graphite (and/or carbon) can be found or made. When the produced articles are made of an inner graphite (and/or carbon) substrate to which SiC is reaction bonded, these articles distinguish SiC-coated graphite articles found in the prior art by the feature of a strong bond having a gradual (as opposed to a sharply defined) interface which extends over a distance of mils. A method for forming SiC whisker-reinforced ceramic matrices is also given. The whisker-reinforced articles comprise SiC whiskers which substantially retain their structural integrity.

  14. Nanoporous Silicon Carbide for Nanoelectromechanical Systems Applications

    NASA Technical Reports Server (NTRS)

    Hossain, T.; Khan, F.; Adesida, I.; Bohn, P.; Rittenhouse, T.; Lienhard, Michael (Technical Monitor)

    2003-01-01

    A major goal of this project is to produce porous silicon carbide (PSiC) via an electroless process for eventual utilization in nanoscale sensing platforms. Results in the literature have shown a variety of porous morphologies in SiC produced in anodic cells. Therefore, predictability and reproducibility of porous structures are initial concerns. This work has concentrated on producing morphologies of known porosity, with particular attention paid toward producing the extremely high surface areas required for a porous flow sensor. We have conducted a parametric study of electroless etching conditions and characteristics of the resulting physical nanostructure and also investigated the relationship between morphology and materials properties. Further, we have investigated bulk etching of SiC using both photo-electrochemical etching and inductively-coupled-plasma reactive ion etching techniques.

  15. Superhard Diamond/tungsten Carbide Nanocomposites

    SciTech Connect

    Z Lin; J Zhang; B Li; L Wang; H Mao; R Hemley; Y Zhao

    2011-12-31

    We investigated the processing conditions of diamond/tungsten carbide (WC) composites using in situ synchrotron x-ray diffraction (XRD) and reactive sintering techniques at high pressure and high temperatures. The as-synthesized composites were characterized by synchrotron XRD, scanning electron microscopy, high-resolution transmission electron microscopy, and indentation hardness measurements. Through tuning of the reaction temperature and time, we produced fully reacted, well-sintered, and nanostructured diamond composites with Vickers hardness of about 55 GPa and the grain size of WC binding matrix smaller than 50 nm. A specific set of orientation relationships between WC and tungsten is identified to gain microstructural insight into the reaction mechanism between diamond and tungsten.

  16. Temperature-dependent reflectivity of silicon carbide

    NASA Technical Reports Server (NTRS)

    Ng, Daniel

    1992-01-01

    The spectral reflectivity of a commercial silicon carbide (SiC) ceramic surface was measured at wavelengths from 2.5 to 14.5 microns and at temperatures ranging from 358 to 520 K using a NASA-developed multiwavelength pyrometer. The SiC surface reflectivity was low at the short wavelengths, decreasing to almost zero at 10 microns, then increasing rapidly to a maximum at approximately 12.5 microns, and decreasing gradually thereafter. The reflectivity maximum increased in magnitude with increasing surface temperature. The wavelength and temperature dependence can be explained in terms of the classical dispersion theory of crystals and the Lorentz electron theory. Electronic transitions between the donor state and the conduction band states were responsible for the dispersion. The concentration of the donor state in SiC was determined to be approximately 4 x 10 exp 18 and its ionization energy was determined to be approximately 71 meV.

  17. Radiation damage of transition metal carbides

    SciTech Connect

    Dixon, G.

    1991-01-01

    In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC[sub 0.88] in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V[sub 8]C[sub 7] superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

  18. Carbide-reinforced metal matrix composite by direct metal deposition

    NASA Astrophysics Data System (ADS)

    Novichenko, D.; Thivillon, L.; Bertrand, Ph.; Smurov, I.

    Direct metal deposition (DMD) is an automated 3D laser cladding technology with co-axial powder injection for industrial applications. The actual objective is to demonstrate the possibility to produce metal matrix composite objects in a single-step process. Powders of Fe-based alloy (16NCD13) and titanium carbide (TiC) are premixed before cladding. Volume content of the carbide-reinforced phase is varied. Relationships between the main laser cladding parameters and the geometry of the built-up objects (single track, 2D coating) are discussed. On the base of parametric study, a laser cladding process map for the deposition of individual tracks was established. Microstructure and composition of the laser-fabricated metal matrix composite objects are examined. Two different types of structures: (a) with the presence of undissolved and (b) precipitated titanium carbides are observed. Mechanism of formation of diverse precipitated titanium carbides is studied.

  19. Silicon Carbide Threads For High-Temperature Service

    NASA Technical Reports Server (NTRS)

    Sawko, Paul M.; Vasudev, Anand

    1991-01-01

    New thread material outperforms silica. Sewing threads containing silicon carbide (SiC) yarn withstand temperatures of more than 1,100 degrees C. Intended for use in stitching thermally insulating blankets.

  20. BETA-SILICON CARBIDE AND ITS POTENTIAL FOR DEVICES

    DTIC Science & Technology

    BETA- SILICON CARBIDE AND ITS POTENTIAL FOR DEVICES. GROWTH OF BETA SIC CRYSTALS FROM SOLUTION USING MOLTEN SI AS SOLVENT. INCREASED RESISTIVITY (FROM 0.5 TO 3.8 OHM/CM) ACCOMPANIED DECREASE IN N CONTAMINATION SOURCES.

  1. Process for preparing fine grain silicon carbide powder

    DOEpatents

    Wei, G.C.

    Method of producing fine-grain silicon carbide powder comprises combining methyltrimethoxysilane with a solution of phenolic resin, acetone and water or sugar and water, gelling the resulting mixture, and then drying and heating the obtained gel.

  2. Conventional and Microwave Joining of Silicon Carbide Using Displacement Reactions

    NASA Technical Reports Server (NTRS)

    Kingsley, J.; Yiin, T.; Barmatz, M.

    1995-01-01

    Microwave heating was used to join Silicon Carbide rods using a thin TiC /Si tape interlayer . Microwaves quickly heated the rods and tape to temperatures where solid-state displacement reactions between TiC and Si occurred.

  3. Chemical vapour deposition: Transition metal carbides go 2D

    DOE PAGES

    Gogotsi, Yury

    2015-08-17

    Here, the research community has been steadily expanding the family of few-atom-thick crystals beyond graphene, discovering new materials or producing known materials in a 2D state and demonstrating their unique properties1, 2. Recently, nanometre-thin 2D transition metal carbides have also joined this family3. Writing in Nature Materials, Chuan Xu and colleagues now report a significant advance in the field, showing the synthesis of large-area, high-quality, nanometre-thin crystals of molybdenum carbide that demonstrate low-temperature 2D superconductivity4. Moreover, they also show that other ultrathin carbide crystals, such as tungsten and tantalum carbides, can be grown by chemical vapour deposition with a highmore » crystallinity and very low defect concentration.« less

  4. Chemical vapour deposition: Transition metal carbides go 2D

    SciTech Connect

    Gogotsi, Yury

    2015-08-17

    Here, the research community has been steadily expanding the family of few-atom-thick crystals beyond graphene, discovering new materials or producing known materials in a 2D state and demonstrating their unique properties1, 2. Recently, nanometre-thin 2D transition metal carbides have also joined this family3. Writing in Nature Materials, Chuan Xu and colleagues now report a significant advance in the field, showing the synthesis of large-area, high-quality, nanometre-thin crystals of molybdenum carbide that demonstrate low-temperature 2D superconductivity4. Moreover, they also show that other ultrathin carbide crystals, such as tungsten and tantalum carbides, can be grown by chemical vapour deposition with a high crystallinity and very low defect concentration.

  5. Single Molecule Source Reagents for CVD of Beta Silicon Carbide

    DTIC Science & Technology

    1991-08-31

    silicon carbide is an excellent candidate semiconductor material for demanding applications in high power and high temperature electronic devices due to its high breakdown voltage, relatively large band gap, high thermal conductivity and high melting point. Use of silicon carbide thin films is hampered, however, by the inability to reproducibly grow stoichiometric films free from excess silicon or carbon. The principal difficulty is that absolutely reproducible flows of the source gases cannot be provided with existing gas flow control equipment. The

  6. Process for preparing fine-grain metal carbide powder

    DOEpatents

    Kennedy, C.R.; Jeffers, F.P.

    Fine-grain metal carbide powder suitable for use in the fabrication of heat resistant products is prepared by coating bituminous pitch on SiO/sub 2/ or Ta/sub 2/O/sub 5/ particles, heating the coated particles to convert the bituminous pitch to coke, and then heating the particles to a higher temperature to convert the particles to a carbide by reaction of said coke therewith.

  7. Single-Event Effects in Silicon Carbide Power Devices

    NASA Technical Reports Server (NTRS)

    Lauenstein, Jean-Marie; Casey, Megan C.; LaBel, Kenneth A.; Ikpe, Stanley; Topper, Alyson D.; Wilcox, Edward P.; Kim, Hak; Phan, Anthony M.

    2015-01-01

    This report summarizes the NASA Electronic Parts and Packaging Program Silicon Carbide Power Device Subtask efforts in FY15. Benefits of SiC are described and example NASA Programs and Projects desiring this technology are given. The current status of the radiation tolerance of silicon carbide power devices is given and paths forward in the effort to develop heavy-ion single-event effect hardened devices indicated.

  8. Friction and wear behavior of single-crystal silicon carbide in contact with titanium

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Sliding friction experiments were conducted with single crystal silicon carbide in sliding contact with titanium. Results indicate that the friction coefficient is greater in vacuum than in argon and that this is due to the greater adhesion or adhesive transfer in vacuum. Thin films of silicon carbide transferred to titanium also adhered to silicon carbide both in argon at atmospheric pressure and in high vacuum. Cohesive bonds fractured on both the silicon carbide and titanium surfaces. The wear debris of silicon carbide created by fracture plowed the silicon carbide surface in a plastic manner. The friction characteristics of titanium in contact with silicon carbide were sensitive to the surface roughness of silicon carbide, and the friction coefficients were higher for a rough surface of silicon carbide than for a smooth one. The difference in friction results was due to plastic deformation (plowing of titanium).

  9. Tribological properties of silicon carbide in metal removal process

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    Material properties are considered as they relate to adhesion, friction, and wear of single crystal silicon carbide in contact with metals and alloys that are likely to be involved in a metal removal process such as grinding. Metal removal from adhesion between sliding surfaces in contact and metal removal as a result of the silicon carbide sliding against a metal, indenting into it, and plowing a series of grooves or furrows are discussed. Fracture and deformation characteristics of the silicon carbide surface are also covered. The adhesion, friction, and metal transfer to silicon carbide is related to the relative chemical activity of the metals. The more active the metal, the higher the adhesion and friction, and the greater the metal transfer to silicon carbide. Atomic size and content of alloying elements play a dominant role in controlling adhesion, friction, and abrasive wear properties of alloys. The friction and abrasive wear (metal removal) decrease linearly as the shear strength of the bulk metal increases. They decrease as the solute to solvent atomic radius ratio increases or decreases linearly from unity, and with an increase of solute content. The surface fracture of silicon carbide is due to cleavages of 0001, 10(-1)0, and/or 11(-2)0 planes.

  10. Understanding the Irradiation Behavior of Zirconium Carbide

    SciTech Connect

    Motta, Arthur; Sridharan, Kumar; Morgan, Dane; Szlufarska, Izabela

    2013-10-11

    Zirconium carbide (ZrC) is being considered for utilization in high-temperature gas-cooled reactor fuels in deep-burn TRISO fuel. Zirconium carbide possesses a cubic B1-type crystal structure with a high melting point, exceptional hardness, and good thermal and electrical conductivities. The use of ZrC as part of the TRISO fuel requires a thorough understanding of its irradiation response. However, the radiation effects on ZrC are still poorly understood. The majority of the existing research is focused on the radiation damage phenomena at higher temperatures (>450{degree}C) where many fundamental aspects of defect production and kinetics cannot be easily distinguished. Little is known about basic defect formation, clustering, and evolution of ZrC under irradiation, although some atomistic simulation and phenomenological studies have been performed. Such detailed information is needed to construct a model describing the microstructural evolution in fast-neutron irradiated materials that will be of great technological importance for the development of ZrC-based fuel. The goal of the proposed project is to gain fundamental understanding of the radiation-induced defect formation in zirconium carbide and irradiation response by using a combination of state-of-the-art experimental methods and atomistic modeling. This project will combine (1) in situ ion irradiation at a specialized facility at a national laboratory, (2) controlled temperature proton irradiation on bulk samples, and (3) atomistic modeling to gain a fundamental understanding of defect formation in ZrC. The proposed project will cover the irradiation temperatures from cryogenic temperature to as high as 800{degree}C, and dose ranges from 0.1 to 100 dpa. The examination of this wide range of temperatures and doses allows us to obtain an experimental data set that can be effectively used to exercise and benchmark the computer calculations of defect properties. Combining the examination of radiation

  11. Development and characterization of nickel based tungsten carbide laser cladded coatings

    NASA Astrophysics Data System (ADS)

    Rombouts, Marleen; Persoons, Rosita; Geerinckx, Eric; Kemps, Raymond; Mertens, Myrjam; Hendrix, Willy; Chen, Hong

    Laser cladded coatings consisting of various types of tungsten carbides embedded in a NiCrBSiCFe matrix are characterized. At optimal process parameters crack-free coatings with a thickness of 0.85-1 mm, excellent bonding with the substrate, carbide concentrations up to 60 wt% and a hardness in the range of 40-55 HRC are obtained. During laser cladding the carbides have partly dissolved in the matrix as indicated by the presence of dispersed carbides in the matrix and by a carbide phase growing into the matrix along the edges of the particles. The wear coefficient during sliding contact decreases logarithmically with increasing carbide concentration.

  12. Nanostructured carbide catalysts for the hydrogen economy

    SciTech Connect

    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

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

    NASA Astrophysics Data System (ADS)

    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

  14. Kinetics and Mechanisms of Primary and Steady State Creep in B- and Al- Containing Alpha Silicon Carbide

    DTIC Science & Technology

    1989-07-01

    silicon carbide , devoid of sintering aids, creeps by dislocation motion and climb. Silicon carbide containing...impurity substitution in the sintered silicon carbide . Experimental measurements of grain boundary sliding offsets on polycrystalline silicon carbide have... carbide whisker reinforcement has no beneficial effect on the creep resistance of Si3N4, whereas, in the more easily deformed mullite, silicon carbide whisker reinforcement does result in a reduced steady state

  15. Feasibility study of fluxless brazing cemented carbides to steel

    NASA Astrophysics Data System (ADS)

    Tillmann, W.; Sievers, N.

    2017-03-01

    One of the most important brazing processes is the joints between cemented carbides and steel for the tool industry such as in rotary drill hammers or saw blades. Even though this technique has already been used for several decades, defects in the joint can still occur and lead to quality loss. Mostly, the joining process is facilitated by induction heating and the use of a flux to enhance the wetting of the filler alloy on the surface of the steel and cemented carbide in an ambient atmosphere. However, although the use of flux enables successful joining, it also generates voids within the joint, which reduces the strength of the connection while the chemicals within the flux are toxic and polluting. In this feasibility study, a fluxless brazing process is used to examine the joint between cemented carbides and steel for the first time. For this, ultrasound is applied during induction heating to enable the wetting between the liquid filler metal and the surfaces of the cemented carbide and steel. The ultrasound generates cavitations within the liquid filler metal, which remove the oxides from the surface. Several filler metals such as a silver based alloy Ag449, pure Zn, and an AlSi-alloy were used to reduce the brazing temperature and to lower the thermal residual stresses within the joint. As a result, every filler metal successfully wetted both materials and led to a dense connection. The ultrasound has to be applied carefully to prevent a damage of the cemented carbide. In this regard, it was observed that single grains of the cemented carbide broke out and remained in the joint. This positive result of brazing cemented carbides to steel without a flux but using ultrasound, allows future studies to focus on the shear strength of these joints as well as the behavior of the thermally induced residual stresses.

  16. Methods for producing silicon carbide architectural preforms

    NASA Technical Reports Server (NTRS)

    DiCarlo, James A. (Inventor); Yun, Hee (Inventor)

    2010-01-01

    Methods are disclosed for producing architectural preforms and high-temperature composite structures containing high-strength ceramic fibers with reduced preforming stresses within each fiber, with an in-situ grown coating on each fiber surface, with reduced boron within the bulk of each fiber, and with improved tensile creep and rupture resistance properties for each fiber. The methods include the steps of preparing an original sample of a preform formed from a pre-selected high-strength silicon carbide ceramic fiber type, placing the original sample in a processing furnace under a pre-selected preforming stress state and thermally treating the sample in the processing furnace at a pre-selected processing temperature and hold time in a processing gas having a pre-selected composition, pressure, and flow rate. For the high-temperature composite structures, the method includes additional steps of depositing a thin interphase coating on the surface of each fiber and forming a ceramic or carbon-based matrix within the sample.

  17. Silicon Carbide Technologies for Lightweighted Aerospace Mirrors

    NASA Astrophysics Data System (ADS)

    Matson, L.; Chen, M.; Deblonk, B.; Palusinski, I.

    The use of monolithic glass and beryllium to produce lightweighted aerospace mirror systems has reached its limits due to the long lead times, high processing costs, environmental effects and launch load/weight requirements. New material solutions and manufacturing processes are required to meet DoD's directed energy weapons, reconnaissance/surveillance, and secured communications needs. Over the past several years the Air Force, MDA, and NASA has focused their efforts on the fabrication, lightweighting, and scale-up of numerous 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 and cost, and non-destructive evaluation methods being investigated to help eliminate risk. Mirror structural substrates made out of advanced engineered materials (far term solutions) such as composites, foams, and microsphere arrays for ultra lightweighting will also be briefly discussed.

  18. Resonant Optical Forces in Silicon Carbide Nanostructures

    NASA Astrophysics Data System (ADS)

    Li, Dongfang; Zia, Rashid

    2012-02-01

    Silicon carbide (SiC) materials are widely used for their exceptional electronic, mechanical, and thermal properties. For example, given its high stiffness to density ratio, SiC is an ideal material for mechanical resonators, and it has been explored for applications in nanoelectromechanical systems (NEMS). SiC also supports strong surface phonon-polariton resonances in the infrared region, which could enable its use for optomechanics. Similar to surface plasmon-polaritons supported by metal-dielectric interfaces, these surface waves at a SiC-vacuum interface can be used to guide and confine intense electromagnetic energy. Here, we investigate the resonant optical forces induced by phonon-polariton modes in different SiC nanostructures. Specifically, we calculate optical forces using the Maxwell Stress Tensor for three geometries: spherical particles, slab waveguides, and rectangular waveguides. We find that the high quality factor phonon-polariton modes in SiC can produce very large forces, more than two orders of magnitude larger than the plasmonic forces in similar metal nanostructures. These strong resonant forces, combined with its mechanical and thermal properties, make SiC a promising material for optomechanical applications.

  19. Neutron irradiation induced amorphization of silicon carbide

    NASA Astrophysics Data System (ADS)

    Snead, L. L.; Hay, J. C.

    1999-07-01

    This paper provides the properties of bulk stoichiometric silicon carbide which has been amorphized under neutron irradiation. Both high purity single crystal hcp and high purity, highly faulted (cubic) chemically vapor deposited (CVD) SiC were irradiated at approximately 60°C to a total fast neutron fluence of 2.6 × 10 25 n/m 2. Amorphization was seen in both materials as evidenced by TEM, electron diffraction and X-ray diffraction techniques. Physical properties for the amorphized single crystal material are reported including large changes in density (-10.8%), elastic modulus as measured using a nanoindentation technique (-45%), hardness as measured by nanoindentation (-45%), and standard Vickers hardness (-24%). Similar property changes are observed for the amorphized CVD SiC. Using measured thermal conductivity data for the CVD SiC sample, the critical temperature for amorphization at this neutron dose and flux, above which amorphization is not possible, is estimated to be greater than ˜125°C.

  20. Palladium Implanted Silicon Carbide for Hydrogen Sensing

    NASA Technical Reports Server (NTRS)

    Muntele, C. I.; Ila, D.; Zimmerman, R. L.; Muntele, L.; Poker, D. B.; Hensley, D. K.; Larkin, David (Technical Monitor)

    2001-01-01

    Silicon carbide is intended for use in fabrication of high-temperature, efficient hydrogen sensors. Traditionally, when a palladium coating is applied on the exposed surface of SiC, the chemical reaction between palladium and hydrogen produces a detectable change in the surface chemical potential. We have produced both a palladium coated SiC as well as a palladium, ion implanted SiC sensor. The palladium implantation was done at 500 C into the Si face of 6H, N-type SiC at various energies, and at various fluences. Then, we measured the hydrogen sensitivity response of each fabricated sensor by exposing them to hydrogen while monitoring the current flow across the p-n junction(s), with respect to time. The sensitivity of each sensor was measured at temperatures between 27 and 300 C. The response of the SiC sensors produced by Pd implantation has revealed a completely different behaviour than the SiC sensors produced by Pd deposition. In the Pd-deposited SiC sensors as well as in the ones reported in the literature, the current rises in the presence of hydrogen at room temperature as well as at elevated temperatures. In the case of Pd-implanted SiC sensors, the current decreases in the presence of hydrogen whenever the temperature is raised above 100 C. We will present the details and conclusions from the results obtained during this meeting.

  1. Large silicon carbide optics for manufacturability

    NASA Astrophysics Data System (ADS)

    Pepi, John W.; Robichaud, Joseph; Milsap, Gary

    2013-09-01

    For space-based use, projected needs are for large optics of the one-meter class that lie under 30 kg/m2 in mass areal density. Current space programs using glass optics, such as Kepler, exhibit a mass of 45 kg/m2, while JWST beryllium optics, including hardware attachment, are as low as 18 kg/m2. Silicon carbide optics can be made lighter than glass, although not as light as beryllium; however, distinct advantages in thermal conductivity and expansion coefficient are evidenced at all temperatures, allowing for greater thermal flux , minimizing gradients and maximizing performance, both earth and space looking. For manufacturability and production, it is desirable to minimize weight while maintaining reasonable cell spacing for open back lightweight design, which will reduce both cost and risk. To this end we perform a trade study to design such an optic that meets both mass and stiffness requirements while being within the regime of ease of manufacture. The design study chooses a hexagonal segment, 1.2 meters across flats (1.4 meters corner to corner), mimicking the JWST design. Polishing, mounting, test, and environmental operational errors are duly considered.

  2. Improved silicon carbide for advanced heat engines

    NASA Technical Reports Server (NTRS)

    Whalen, Thomas J.

    1989-01-01

    The development of high strength, high reliability silicon carbide parts with complex shapes suitable for use in advanced heat engines is studied. Injection molding was the forming method selected for the program because it is capable of forming complex parts adaptable for mass production on an economically sound basis. The goals were to reach a Weibull characteristic strength of 550 MPa (80 ksi) and a Weibull modulus of 16 for bars tested in four-point loading. Statistically designed experiments were performed throughout the program and a fluid mixing process employing an attritor mixer was developed. Compositional improvements in the amounts and sources of boron and carbon used and a pressureless sintering cycle were developed which provided samples of about 99 percent of theoretical density. Strengths were found to improve significantly by annealing in air. Strengths in excess of 550 MPa (80 ksi) with Weibull modulus of about 9 were obtained. Further improvements in Weibull modulus to about 16 were realized by proof testing. This is an increase of 86 percent in strength and 100 percent in Weibull modulus over the baseline data generated at the beginning of the program. Molding yields were improved and flaw distributions were observed to follow a Poisson process. Magic angle spinning nuclear magnetic resonance spectra were found to be useful in characterizing the SiC powder and the sintered samples. Turbocharger rotors were molded and examined as an indication of the moldability of the mixes which were developed in this program.

  3. Predicting Two-Dimensional Silicon Carbide Monolayers.

    PubMed

    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.

  4. Thermal equation of state of silicon carbide

    DOE PAGES

    Wang, Yuejian; Liu, Zhi T. Y.; Khare, Sanjay V.; ...

    2016-02-11

    A large volume press coupled with in-situ energy-dispersive synchrotron X-ray was used to probe the change of silicon carbide (SiC) under high pressure and temperature (P-T) up to 8.1 GPa and 1100 K. The obtained pressure–volume–temperature (P-V-T) data were fitted to a modified high-T Birch-Murnaghan equation of state, yielding values of a series of thermo-elastic parameters, such as, the ambient bulk modulus KTo = 237(2) GPa, temperature derivative of bulk modulus at constant pressure (∂K/∂T)P = -0.037(4) GPa K-1, volumetric thermal expansivity α(0, T)=a+bT with a = 5.77(1)×10-6 K-1 and b = 1.36(2)×10-8 K-2, and pressure derivative of thermal expansionmore » at constant temperature (∂α/∂P)T =6.53±0.64×10-7 K-1GPa-1. Furthermore, we found the temperature derivative of bulk modulus at constant volume, (∂KT/∂T)V, equal to -0.028(4) GPa K-1 by using a thermal pressure approach. In addition, the elastic properties of SiC were determined by density functional theory through the calculation of Helmholtz free energy. Lastly, the computed results generally agree well with the experimental values.« less

  5. High Resolution Laser Spectroscopy of Rhenium Carbide

    NASA Astrophysics Data System (ADS)

    Adam, Allan G.; Hall, Ryan M.; Linton, Colan; Tokaryk, Dennis

    2014-06-01

    The first spectroscopic study of rhenium carbide, ReC, has been performed using both low and high resolution techniques to collect rotationally resolved electronic spectra from 420 to 500nm. Laser-induced fluorescence (LIF), and dispersed fluorescence (DF) techniques were employed. ReC was formed in our laser ablation molecular jet apparatus by ablating a rhenium target rod in the presence of 1% methane in helium. The low resolution spectrum identified four bands of an electronic system belonging to ReC, three of which have been studied so far. Extensive hyperfine structure composed of six hyperfine components was observed in the high resolution spectrum, as well as a clear distinction between the 187ReC and 185ReC isotopologues. The data seems consistent with a ^4Π - ^4Σ- transition, as was predicted before experimentation. Dispersed fluorescence spectra allowed us to determine the ground state vibrational frequency (ωe"=994.4 ± 0.3 wn), and to identify a low-lying electronically excited state at Te"=1118.4 ± 0.4 wn with a vibrational frequency of ωe"=984 ± 2 wn. Personal communication, F. Grein, University of New Brunswick

  6. Analysis of boron carbides' electronic structure

    NASA Technical Reports Server (NTRS)

    Howard, Iris A.; Beckel, Charles L.

    1986-01-01

    The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

  7. Thin films in silicon carbide semiconductor devices

    NASA Astrophysics Data System (ADS)

    Ostling, Mikael; Koo, Sang-Mo; Lee, Sang-Kwon; Zetterling, Carl-Mikael; Grishin, Alexander

    2004-12-01

    Silicon carbide (SiC) semiconductor devices have been established during the last decade as very useful high power, high speed and high temperature devices because of their inherent outstanding semiconductor materials properties. Due to its large band gap, SiC possesses a very high breakdown field and low intrinsic carrier concentration, which accordingly makes high voltage and high temperature operation possible. SiC is also suitable for high frequency device applications, because of the high saturation drift velocity and low permittivity. Thin film technology for various functions in the devices has been heavily researched. Suitable thin film technologies for Ohmic and low-resistive contact formation, passivation and new functionality utilizing ferroelectric materials have been developed. In ferroelectrics, the spontaneous polarization can be switched by an externally applied electric field, and thus are attractive for non-volatile memory and sensor applications. A novel integration of Junction-MOSFETs (JMOSFETs) and Nonvolatile FETs (NVFETs) on a single 4H-SiC substrate is realized. SiC JMOSFET controls the drain current effectively from the buried junction gate thereby allowing for a constant current level at elevated temperatures. SiC NVFET has similar functions with non-volatile memory capability due to ferroelectric gate stack, which operated up to 300°C with memory function retained up to 200°C.

  8. Material testing of silicon carbide mirrors

    NASA Astrophysics Data System (ADS)

    Witkin, David B.; Palusinski, Iwona A.

    2009-08-01

    The Aerospace Corporation is developing a space qualification method for silicon carbide optical systems that covers material verification through system development. One of the initial efforts has been to establish testing protocols for material properties. Three different tests have been performed to determine mechanical properties of SiC: modulus of rupture, equibiaxial flexural strength and fracture toughness. Testing materials and methods have been in accordance with the respective ASTM standards. Material from four vendors has been tested to date, as part of the MISSE flight program and other programs. Data analysis has focused on the types of issues that are important when building actual components- statistical modeling of test results, understanding batch-to-batch or other source material variations, and relating mechanical properties to microstructures. Mechanical properties are needed as inputs to design trade studies and development and analysis of proof tests, and to confirm or understand the results of non-destructive evaluations of the source materials. Measuring these properties using standardized tests on a statistically valid number of samples is intended to increase confidence for purchasers of SiC spacecraft components that materials and structures will perform as intended at the highest level of reliability.

  9. A simple route to nanocrystalline silicon carbide

    NASA Astrophysics Data System (ADS)

    Ying, Yongcheng; Gu, Yunle; Li, Zhefeng; Gu, Hongzhou; Cheng, Luyang; Qian, Yitai

    2004-11-01

    Nanocrystalline silicon carbide has been prepared via reacting magnesium silicide (Mg 2Si) with carbon tetrachloride (CCl 4) in an autoclave at 450-600°C. X-ray diffraction patterns of the products can be indexed as the cubic cell of SiC with the lattice constant, a=4.352 Å, in good agreement with a=4.349 Å (JCPDS card No. 75-0254). The transmission electron microscopy images show that the sample mainly consists of nanoparticles with an average size from 30 to 80 nm co-existing with a small fraction of nanorods and nanowires. Typically the nanorods range from 20 to 40 nm in diameter and the nanowires have diameters of 20 nm and lengths up to 10 μm. The Raman spectrum shows a characteristic sharp peak at 790 cm -1. X-ray photoelectron spectra (XPS) gives an atomic ratio of Si to C as 1.08:1.00 from the quantification of the peak intensities. Photoluminescence spectrum reveals that the SiC sample emits ultraviolet light of 328 nm. A possible mechanism and the influence of temperature on the formation of crystalline SiC are proposed.

  10. Reactions of water and C1 molecules on carbide and metal-modified carbide surfaces.

    PubMed

    Wan, Weiming; Tackett, Brian M; Chen, Jingguang G

    2017-02-23

    The formation of carbides can significantly modify the physical and chemical properties of the parent metals. In the current review, we summarize the general trends in the reactions of water and C1 molecules over transition metal carbide (TMC) and metal-modified TMC surfaces and thin films. Although the primary focus of the current review is on the theoretical and experimental studies of reactions of C1 molecules (CO, CO2, CH3OH, etc.), the reactions of water will also be reviewed because water plays an important role in many of the C1 transformation reactions. This review is organized by discussing separately thermal reactions and electrochemical reactions, which provides insights into the application of TMCs in heterogeneous catalysis and electrocatalysis, respectively. In thermal reactions, we discuss the thermal decomposition of water and methanol, as well as the reactions of CO and CO2 over TMC surfaces. In electrochemical reactions, we summarize recent studies in the hydrogen evolution reaction, electrooxidation of methanol and CO, and electroreduction of CO2. Finally, future research opportunities and challenges associated with using TMCs as catalysts and electrocatalysts are also discussed.

  11. Occurrence of airborne silicon carbide fibers during industrial production of silicon carbide.

    PubMed

    Bye, E; Eduard, W; Gjønnes, J; Sørbrøden, E

    1985-04-01

    Airborne dust from the production of silicon carbide has been analyzed for particle morphology and composition. Fibers of alpha silicon carbide were identified by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) with selected area electron diffraction techniques (SAED). Micrographs taken at high magnification revealed several stacking periods along the fiber axis, and one or more of the polytypes 2H, 4H, or 6H could be distinguished. Preliminary investigations applying SEM showed that 80% of the fibers had diameters of less than 0.5 micron and a length greater than 5 micron. Fiber concentrations were examined by the counting of stationary and personal samples in an optical phase contrast microscope. The fiber levels in the three plants investigated were low and less than 1 fiber/cc of air (10(6) fibers/m3). Dust samples from the handling of raw material, including recycled material, contained up to 5 fibers/cc (5 X 10(6) fibers/m3).

  12. Hot forging of graphite-carbide composites. Final report

    SciTech Connect

    Jenkins, G.M.; Holland, L.R.

    1998-07-15

    This project was aimed at hot shaping of titanium carbide/graphite and vanadium carbide/graphite composite materials by heating them to above 2000 degrees celsius and pressing into an electrographite die. The sample was to be a preformed cylinder of powdered graphite mixed with powdered titanium or vanadium, lightly sintered. The preform would be heated in a hot press and the titanium or vanadium would react with some of the graphite to form titanium or vanadium carbide. The remaining (excess) graphite would form a composite with the carbide, and this could then be deformed plastically at temperatures well below the onset of plasticity in pure graphite. There were to be two major thrusts in the research: In the first, an electron beam furnace at Sandia Laboratory was to be used for rapid heating of the sample, which would then be transferred into the press. The second thrust was to be entirely at Alabama A and M University, and here they intended to use a heated, controlled atmosphere press to forge the graphite/carbide preforms at a steady temperature and measure their viscosity as a function of temperature. This report discusses the progress made on this project.

  13. Microwave versus conventional sintering of silicon carbide tiles

    SciTech Connect

    Kass, M.D.; Caughman, J.B.O.; Forrester, S.C.; Akerman, A.

    1997-05-07

    Silicon carbide is being evaluated as an armor material because of its lightweight, high-hardness, and excellent armor efficiency. However, one of the problems associated with silicon carbide is the high cost associated with achieving fully dense tiles. Full density requires either hot pressing and sintering or reaction bonding. Past efforts have shown that hot pressed tiles have a higher armor efficiency than those produced by reaction bonded sintering. An earlier stuy showed that the acoustic properties of fully-dense silicon carbide tiles were enhanced through the use of post-sintered microwave heat treatments. One of the least expensive forming techniques is to isostatically press-and-sinter. In this study, the authors have used microwave energy to densify silicon carbide green bodies. Microwave sintering has been demonstrated to be a very quick way to sinter ceramics such as alumina to exceptionally high densities. Previous work has shown that microwave post treatment of fully-dense reaction bonded silicon carbide tiles significantly improves the acoustic properties of the tiles. These properties include Poisson`s ratio, Young`s modulus, shear modulus, and bulk modulus.

  14. Phase Behavior of Pseudobinary Precious Metal-Carbide Systems

    SciTech Connect

    Gregoire, John M.; Tague, Michele E.; Smith, Eva H.; Dale, Darren; DiSalvo, Francis J.; Abruña, Héctor D.; Hennig, Richard G.; van Dover, R. Bruce

    2010-11-15

    Transition metal carbides exhibit a variety of interesting material properties, including electrochemical stability. When combined with precious metals, Ta and W carbides have shown promise as fuel cell electrode materials; yet, the phase behavior of these precious metal-carbide systems is largely unexplored. We investigated P-M-C phase behavior with P = Pt, Pd, and Ru and M = Ta and W using composition spread thin films. We attained limited control of the deposited carbide phase through variation of the sputter atmosphere and demonstrated decreased corrosion of W-C materials with increasing C content. A high-throughput X-ray diffraction and X-ray fluorescence experiment was employed for thin film characterization, which revealed solubility of Pt, Pd, and Ru in cubic WC. Density functional calculations of the lattice parameter dependence on carbon concentration enabled the determination of carbon concentration from the X-ray data as a function of transition metal stoichiometry. Our measurement of variations in the C stoichiometry and evolution of thin film texture with transition metal composition yielded surprising results. We detail how the combination of the composition spread technique, the high-throughput thin film characterization, and the density functional modeling of ternary carbide alloys provided a deep understanding of the chemical systems.

  15. Converting a carbon preform object to a silicon carbide object

    NASA Technical Reports Server (NTRS)

    Levin, Harry (Inventor)

    1990-01-01

    A process for converting in depth a carbon or graphite preform object to a silicon carbide object, silicon carbide/silicon object, silicon carbide/carbon-core object, or a silicon carbide/silicon/carbon-core object, by contacting it with silicon liquid and vapor over various lengths of contact time in a reaction chamber. In the process, a stream comprised of a silicon-containing precursor material in gaseous phase below the decomposition temperature of said gas and a coreactant, carrier or diluent gas such as hydrogen is passed through a hole within a high emissivity, thin, insulating septum into the reaction chamber above the melting point of silicon. The thin septum has one face below the decomposition temperature of the gas and an opposite face exposed to the reaction chamber. Thus, the precursor gas is decomposed directly to silicon in the reaction chamber. Any stream of decomposition gas and any unreacted precursor gas from the reaction chamber is removed. A carbon or graphite preform object placed in the reaction chamber is contacted with the silicon. The carbon or graphite preform object is recovered from the reactor chamber after it has been converted to a desired silicon carbide, silicon and carbon composition.

  16. Thermal equation of state of silicon carbide

    SciTech Connect

    Wang, Yuejian; Liu, Zhi T. Y.; Khare, Sanjay V.; Collins, Sean Andrew; Zhang, Jianzhong; Wang, Liping; Zhao, Yusheng

    2016-02-11

    A large volume press coupled with in-situ energy-dispersive synchrotron X-ray was used to probe the change of silicon carbide (SiC) under high pressure and temperature (P-T) up to 8.1 GPa and 1100 K. The obtained pressure–volume–temperature (P-V-T) data were fitted to a modified high-T Birch-Murnaghan equation of state, yielding values of a series of thermo-elastic parameters, such as, the ambient bulk modulus KTo = 237(2) GPa, temperature derivative of bulk modulus at constant pressure (∂K/∂T)P = -0.037(4) GPa K-1, volumetric thermal expansivity α(0, T)=a+bT with a = 5.77(1)×10-6 K-1 and b = 1.36(2)×10-8 K-2, and pressure derivative of thermal expansion at constant temperature (∂α/∂P)T =6.53±0.64×10-7 K-1GPa-1. Furthermore, we found the temperature derivative of bulk modulus at constant volume, (∂KT/∂T)V, equal to -0.028(4) GPa K-1 by using a thermal pressure approach. In addition, the elastic properties of SiC were determined by density functional theory through the calculation of Helmholtz free energy. Lastly, the computed results generally agree well with the experimental values.

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

    NASA Astrophysics Data System (ADS)

    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.

  18. Method for making hot-pressed fiber-reinforced carbide-graphite composite

    DOEpatents

    Riley, Robert E.; Wallace Sr., Terry C.

    1979-01-01

    A method for the chemical vapor deposition of a uniform coating of tantalum metal on fibers of a woven graphite cloth is described. Several layers of the coated cloth are hot pressed to produce a tantalum carbide-graphite composite having a uniformly dispersed, fine grained tantalum carbide in graphite with compositions in the range of 15 to 40 volume percent tantalum carbide.

  19. 40 CFR 424.50 - Applicability; description of the other calcium carbide furnaces subcategory.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... calcium carbide furnaces subcategory. 424.50 Section 424.50 Protection of Environment ENVIRONMENTAL... CATEGORY Other Calcium Carbide Furnaces Subcategory § 424.50 Applicability; description of the other calcium carbide furnaces subcategory. The provisions of this subpart are applicable to...

  20. 40 CFR 424.50 - Applicability; description of the other calcium carbide furnaces subcategory.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... calcium carbide furnaces subcategory. 424.50 Section 424.50 Protection of Environment ENVIRONMENTAL... CATEGORY Other Calcium Carbide Furnaces Subcategory § 424.50 Applicability; description of the other calcium carbide furnaces subcategory. The provisions of this subpart are applicable to...

  1. 40 CFR 424.50 - Applicability; description of the other calcium carbide furnaces subcategory.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... other calcium carbide furnaces subcategory. 424.50 Section 424.50 Protection of Environment... SOURCE CATEGORY Other Calcium Carbide Furnaces Subcategory § 424.50 Applicability; description of the other calcium carbide furnaces subcategory. The provisions of this subpart are applicable to...

  2. 40 CFR 424.50 - Applicability; description of the other calcium carbide furnaces subcategory.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... calcium carbide furnaces subcategory. 424.50 Section 424.50 Protection of Environment ENVIRONMENTAL... CATEGORY Other Calcium Carbide Furnaces Subcategory § 424.50 Applicability; description of the other calcium carbide furnaces subcategory. The provisions of this subpart are applicable to...

  3. 40 CFR 424.50 - Applicability; description of the other calcium carbide furnaces subcategory.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... calcium carbide furnaces subcategory. 424.50 Section 424.50 Protection of Environment ENVIRONMENTAL... CATEGORY Other Calcium Carbide Furnaces Subcategory § 424.50 Applicability; description of the other calcium carbide furnaces subcategory. The provisions of this subpart are applicable to...

  4. Surface Figure Measurement of Silicon Carbide Mirrors at Cryogenic Temperatures

    NASA Technical Reports Server (NTRS)

    Blake, Peter; Mink, Ronald G.; Chambers, John; Robinson, F. David; Content, David; Davila, Pamela

    2005-01-01

    The surface figure of a developmental silicon carbide mirror, cooled to 87 K and then 20 K within a cryostat, was measured with unusually high precision at the Goddard Space Flight Center (GSFC). The concave spherical mirror, with a radius of 600 mm and a clear aperture of 150 mm, was fabricated of sintered silicon carbide. The mirror was mounted to an interface plate representative of an optical bench, made of the material Cesic@, a composite of silicon, carbon, and silicon carbide. The change in optical surface figure as the mirror and interface plate cooled from room temperature to 20 K was 3.7 nm rms, with a standard uncertainty of 0.23 nm in the rms statistic. Both the cryo-change figure and the uncertainty are among the lowest such figures yet published. This report describes the facilities, experimental methods, and uncertainty analysis of the measurements.

  5. Thermal shock and erosion resistant tantalum carbide ceramic material

    NASA Technical Reports Server (NTRS)

    Honeycutt, L., III; Manning, C. R. (Inventor)

    1978-01-01

    Ceramic tantalum carbide artifacts with high thermal shock and mechanical erosion resistance are provided by incorporating tungsten-rhenium and carbon particles in a tantalum carbide matrix. The mix is sintered by hot pressing to form the ceramic article which has a high fracture strength relative to its elastic modulus and thus has an improved thermal shock and mechanical erosion resistance. The tantalum carbide is preferable less than minus 100 mesh, the carbon particles are preferable less than minus 100 mesh, and the tungsten-rhenium particles are preferable elongate, having a length to thickness ratio of at least 2/1. Tungsten-rhenium wire pieces are suitable as well as graphite particles.

  6. Processing, texture and mechanical properties of sintered silicon carbide

    NASA Technical Reports Server (NTRS)

    Landfermann, H.; Hausner, H.

    1988-01-01

    With regard to its favorable properties, in particular those shown at high temperatures, silicon carbide is of great interest for applications related to the construction of engines and turbines. Thus, silicon carbide could replace heat-resisting alloys with the objective to achieve a further increase in operational temperature. The present investigation is concerned with approaches which can provide silicon carbide material with suitable properties for the intended applications, taking into account the relations between characteristics of the raw material, material composition, sinter conditions, and results of the sintering process. The effects of density and texture formation on the mechanical properties are studied. It is found that a dense material with a fine-grained microstructure provides optimal mechanical properties, while any deviation from this ideal condition can lead to a considerable deterioration with respect to the material properties.

  7. Palladium in cubic silicon carbide: Stability and kinetics

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Chen, Jingguan

    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.

  9. Implanted bottom gate for epitaxial graphene on silicon carbide

    NASA Astrophysics Data System (ADS)

    Waldmann, D.; Jobst, J.; Fromm, F.; Speck, F.; Seyller, T.; Krieger, M.; Weber, H. B.

    2012-04-01

    We present a technique to tune the charge density of epitaxial graphene via an electrostatic gate that is buried in the silicon carbide substrate. The result is a device in which graphene remains accessible for further manipulation or investigation. Via nitrogen or phosphor implantation into a silicon carbide wafer and subsequent graphene growth, devices can routinely be fabricated using standard semiconductor technology. We have optimized samples for room temperature as well as for cryogenic temperature operation. Depending on implantation dose and temperature we operate in two gating regimes. In the first, the gating mechanism is similar to a MOSFET, the second is based on a tuned space charge region of the silicon carbide semiconductor. We present a detailed model that describes the two gating regimes and the transition in between.

  10. Characterization of individual straight and kinked boron carbide nanowires

    NASA Astrophysics Data System (ADS)

    Cui, Zhiguang

    Boron carbides represent a class of ceramic materials with p-type semiconductor natures, complex structures and a wide homogeneous range of carbon compositions. Bulk boron carbides have long been projected as promising high temperature thermoelectric materials, but with limited performance. Bringing the bulk boron carbides to low dimensions (e.g., nanowires) is believed to be an option to enhance their thermoelectric performance because of the quantum size effects. However, the fundamental studies on the microstructure-thermal property relation of boron carbide nanowires are elusive. In this dissertation work, systematic structural characterization and thermal conductivity measurement of individual straight and kinked boron carbide nanowires were carried out to establish the true structure-thermal transport relation. In addition, a preliminary Raman spectroscopy study on identifying the defects in individual boron carbide nanowires was conducted. After the synthesis of single crystalline boron carbide nanowires, straight nanowires accompanied by the kinked ones were observed. Detailed structures of straight boron carbide nanowires have been reported, but not the kinked ones. After carefully examining tens of kinked nanowires utilizing Transmission Electron Microscopy (TEM), it was found that they could be categorized into five cases depending on the stacking faults orientations in the two arms of the kink: TF-TF, AF-TF, AF-AF, TF-IF and AF-IF kinks, in which TF, AF and IF denotes transverse faults (preferred growth direction perpendicular to the stacking fault planes), axial faults (preferred growth direction in parallel with the stacking fault planes) and inclined faults (preferred growth direction neither perpendicular to nor in parallel with the stacking fault planes). Simple structure models describing the characteristics of TF-TF, AF-TF, AF-AF kinked nanowires are constructed in SolidWorks, which help to differentiate the kinked nanowires viewed from the zone

  11. Studies on the equation of state of mixed carbide fuel

    NASA Astrophysics Data System (ADS)

    Joseph, M.; Mathews, C. K.; Rao, P. Bhaskar

    1989-12-01

    The equation of state of reactor fuels is required up to very high temperatures in order to assess the energy release in hypothetical core disruptive accidents (HCM). Though the mixed carbide of uranium and plutonium is a candidate fuel material for fast breeder reactors, much information is not available on its equation of state. This paper reports the results of our studies to obtain the equilibrium vapour pressures of uranium carbide and uranium-plutonium mixed carbide of varying compositions in the temperature range of 1300-9000 K. An extrapolation method based on the principles of equilibrium thermodynamics has been used as also the principle of corresponding states. The agreement between the different results are discussed and their implications in HCDA calculations brought out.

  12. Elastic and piezoresistive properties of nickel carbides from first principles

    NASA Astrophysics Data System (ADS)

    Kelling, Jeffrey; Zahn, Peter; Schuster, Jörg; Gemming, Sibylle

    2017-01-01

    The nickel-carbon system has received increased attention over the past years due to the relevance of nickel as a catalyst for carbon nanotube and graphene growth, where nickel carbide intermediates may be involved or carbide interface layers form in the end. Nickel-carbon composite thin films comprising Ni3C are especially interesting in mechanical sensing applications. Due to the metastability of nickel carbides, formation conditions and the coupling between mechanical and electrical properties are not yet well understood. Using first-principles electronic structure methods, we calculated the elastic properties of Ni3C ,Ni2C , and NiC , as well as changes in electronic properties under mechanical strain. We observe that the electronic density of states around the Fermi level does not change under the considered strains of up to 1%, which correspond to stresses up to 3 GPa . Relative changes in conductivity of Ni3C range up to maximum values of about 10%.

  13. New process of silicon carbide purification intended for silicon passivation

    NASA Astrophysics Data System (ADS)

    Barbouche, M.; Zaghouani, R. Benabderrahmane; Benammar, N. E.; Aglieri, V.; Mosca, M.; Macaluso, R.; Khirouni, K.; Ezzaouia, H.

    2017-01-01

    In this work, we report on a new, efficient and low cost process of silicon carbide (SiC) powder purification intended to be used in photovoltaic applications. This process consists on the preparation of porous silicon carbide layers followed by a photo-thermal annealing under oxygen atmosphere and chemical treatment. The effect of etching time on impurities removal efficiency was studied. Inductively coupled plasma atomic emission spectrometry (ICP-AES) results showed that the best result was achieved for an etching time of 10 min followed by gettering at 900 °C during 1 h. SiC purity is improved from 3N (99.9771%) to 4N (99.9946%). Silicon carbide thin films were deposited onto silicon substrates by pulsed laser deposition technique (PLD) using purified SiC powder as target. Significant improvement of the minority carrier lifetime was obtained encouraging the use of SiC as a passivation layer for silicon.

  14. A study of silicon carbide synthesis from waste serpentine.

    PubMed

    Cheng, T W; Hsu, C W

    2006-06-01

    There are 60000 tons of serpentine wastes produced in year 2004 in Taiwan. This is due to the well-developed joints in the serpentine ore body as well as the stringent requirements of the particle size and chemical composition of serpentine by iron making company. The waste also creates considerable environmental problems. The purpose of this study is reutilization of waste serpentine to produce a high value silica powder after acid leaching. These siliceous microstructure products obtained from serpentine would be responsible for high reactivity and characteristic molecular sieving effect. In this study, the amorphous silica powder was then synthesized to silicon carbide with the C/SiO(2) molar ratio of 3. The experiment results show that silicon carbide can be synthesized in 1550 degrees C. The formed silicon carbide was whisker beta type SiC which can be used as raw materials for industry.

  15. Pulsed energy synthesis and doping of silicon carbide

    DOEpatents

    Truher, J.B.; Kaschmitter, J.L.; Thompson, J.B.; Sigmon, T.W.

    1995-06-20

    A method for producing beta silicon carbide thin films by co-depositing thin films of amorphous silicon and carbon onto a substrate is disclosed, whereafter the films are irradiated by exposure to a pulsed energy source (e.g. excimer laser) to cause formation of the beta-SiC compound. Doped beta-SiC may be produced by introducing dopant gases during irradiation. Single layers up to a thickness of 0.5-1 micron have been produced, with thicker layers being produced by multiple processing steps. Since the electron transport properties of beta silicon carbide over a wide temperature range of 27--730 C is better than these properties of alpha silicon carbide, they have wide application, such as in high temperature semiconductors, including HETEROJUNCTION-junction bipolar transistors and power devices, as well as in high bandgap solar arrays, ultra-hard coatings, light emitting diodes, sensors, etc.

  16. Pulsed energy synthesis and doping of silicon carbide

    DOEpatents

    Truher, Joel B.; Kaschmitter, James L.; Thompson, Jesse B.; Sigmon, Thomas W.

    1995-01-01

    A method for producing beta silicon carbide thin films by co-depositing thin films of amorphous silicon and carbon onto a substrate, whereafter the films are irradiated by exposure to a pulsed energy source (e.g. excimer laser) to cause formation of the beta-SiC compound. Doped beta-SiC may be produced by introducing dopant gases during irradiation. Single layers up to a thickness of 0.5-1 micron have been produced, with thicker layers being produced by multiple processing steps. Since the electron transport properties of beta silicon carbide over a wide temperature range of 27.degree.-730.degree. C. is better than these properties of alpha silicon carbide, they have wide application, such as in high temperature semiconductors, including hetero-junction bipolar transistors and power devices, as well as in high bandgap solar arrays, ultra-hard coatings, light emitting diodes, sensors, etc.

  17. On Some Features of Chromium Carbide Diffusion Layer Formation

    NASA Astrophysics Data System (ADS)

    Glowacki, Z.; Kaluba, W.

    1982-05-01

    The formation of chromium carbide diffusion layers on iron-carbon alloys was studied in this investigation. The investigation was carried out on graphite, plain carbon steels, gray cast iron, and white cast iron. The carbide layers were obtained by the powder pack method. To distinguish the effect of iron from the chromizing medium on the layer morphology, high purity iron and chromium powders were used as the components of the powder mixture. The samples were chromized in the temperature range of 870 to 1373 K for five to 1500 minutes. Phase composition of the layers was examined by X-ray diffraction method. To assess chromium and iron distribution in the layers, an electron micro-probe was employed. Microstructure of the layers was examined with the aid of light and electron microscopes. Both replica and thin foil methods were used in this work. The original method of thin foil preparation was used to show the M7C3 layer substructure and to define its crystallographic orientation. It was found that formation of the carbide layer began at temperatures below A1 transformation, when the samples were heated to a normal chromizing temperature. It was proved that M3C appearance in the layer depends on both chromizing temperature and amount of carbon in the alloy. The Fe : Cr ratio in the chromized medium was found to affect the microstructure and thickness of the layers strongly. The needle-shaped grains of the M7C3 layer showed particular crystallographic orientation, i.e., [0001] M7C3 crystallographic direction was perpendicular to the diffusion front. The new data on microstructure of the carbide layers were obtained by thin foil method. The growth direction of the carbide layer was defined, which allowed the suggestion of the diffusion model for the carbide layer formation.

  18. Evolution of carbides in cold-work tool steels

    SciTech Connect

    Kim, Hoyoung; Kang, Jun-Yun; Son, Dongmin; Lee, Tae-Ho; Cho, Kyung-Mox

    2015-09-15

    This study aimed to present the complete history of carbide evolution in a cold-work tool steel along its full processing route for fabrication and application. A sequence of processes from cast to final hardening heat treatment was conducted on an 8% Cr-steel to reproduce a typical commercial processing route in a small scale. The carbides found at each process step were then identified by electron diffraction with energy dispersive spectroscopy in a scanning or transmission electron microscope. After solidification, MC, M{sub 7}C{sub 3} and M{sub 2}C carbides were identified and the last one dissolved during hot compression at 1180 °C. In a subsequent annealing at 870 °C followed by slow cooling, M{sub 6}C and M{sub 23}C{sub 6} were added, while they were dissolved in the following austenitization at 1030 °C. After the final tempering at 520 °C, fine M{sub 23}C{sub 6} precipitated again, thus the final microstructure was the tempered martensite with MC, M{sub 7}C{sub 3} and M{sub 23}C{sub 6} carbide. The transient M{sub 2}C and M{sub 6}C originated from the segregation of Mo and finally disappeared due to attenuated segregation and the consequent thermodynamic instability. - Highlights: • The full processing route of a cold-work tool steel was simulated in a small scale. • The carbides in the tool steel were identified by chemical–crystallographic analyses. • MC, M{sub 7}C{sub 3}, M{sub 2}C, M{sub 6}C and M{sub 23}C{sub 6} carbides were found during the processing of the steel. • M{sub 2}C and M{sub 6}C finally disappeared due to thermodynamic instability.

  19. Ultrathin fiber poly-3-hydroxybutyrate, modified by silicon carbide nanoparticles

    NASA Astrophysics Data System (ADS)

    Olkhov, A. A.; Krutikova, A. A.; Goldshtrakh, M. A.; Staroverova, O. V.; Iordanskii, A. L.; Ischenko, A. A.

    2016-11-01

    The article presents the results of studies the composite fibrous material based on poly-3-hydroxybutyrate (PHB) and nano-size silicon carbide obtained by the electrospinning method. Size distribution of the silicon carbide nanoparticles in the fiber was estimated by X-ray diffraction technique. It is shown that immobilization of the SiC nanoparticles to the PHB fibers contributes to obtaining essentially smaller diameter of fibers, high physical-mechanical characteristics and increasing resistance to degradation in comparison with the fibers of PHB.

  20. Catalytic carbide formation at aluminium-carbon interfaces

    NASA Technical Reports Server (NTRS)

    Maruyama, B.; Rabenberg, L.; Ohuchi, F. S.

    1990-01-01

    X-ray photoelectron spectroscopy investigations of the reaction of several monolayer-thick films of aluminum with glassy carbon substrates are presented. The influence of molecular oxygen and water vapor on the rate of reaction is examined. It is concluded that water vapor catalyzed the formation of aluminum carbide from aluminum and carbon by forming active sites which weakened carbon-carbon bonds at the glassy carbon surface, thus assisting their cleavage. The rate of carbide formation for undosed and molecular oxygen-dosed examples was less as neither metallic aluminum nor oxygen-formed alumina could bond to the carbon atom with sufficient strength to dissociate it quickly.

  1. Effects of laser ablation on cemented tungsten carbide surface quality

    NASA Astrophysics Data System (ADS)

    Tan, J. L.; Butler, D. L.; Sim, L. M.; Jarfors, A. E. W.

    2010-11-01

    Although laser micromachining has been touted as being the most promising way to fabricate micro tools, there has been no proper evaluation of the effects of laser ablation on bulk material properties. The current work demonstrates the effects of laser ablation on the properties of a cemented tungsten carbide surface. Of particular interest is the resultant increase in compressive residual stresses in the ablated surface. From this study it is seen that there are no adverse effects from laser ablation of cemented tungsten carbide that would preclude its use for the fabrication of micro-tools but a finishing process may not be avoidable.

  2. Process for forming silicon carbide films and microcomponents

    DOEpatents

    Hamza, A.V.; Balooch, M.; Moalem, M.

    1999-01-19

    Silicon carbide films and microcomponents are grown on silicon substrates at surface temperatures between 900 K and 1700 K via C{sub 60} precursors in a hydrogen-free environment. Selective crystalline silicon carbide growth can be achieved on patterned silicon-silicon oxide samples. Patterned SiC films are produced by making use of the high reaction probability of C{sub 60} with silicon at surface temperatures greater than 900 K and the negligible reaction probability for C{sub 60} on silicon dioxide at surface temperatures less than 1250 K. 5 figs.

  3. Process for forming silicon carbide films and microcomponents

    DOEpatents

    Hamza, Alex V.; Balooch, Mehdi; Moalem, Mehran

    1999-01-01

    Silicon carbide films and microcomponents are grown on silicon substrates at surface temperatures between 900 K and 1700 K via C.sub.60 precursors in a hydrogen-free environment. Selective crystalline silicon carbide growth can be achieved on patterned silicon-silicon oxide samples. Patterned SiC films are produced by making use of the high reaction probability of C.sub.60 with silicon at surface temperatures greater than 900 K and the negligible reaction probability for C.sub.60 on silicon dioxide at surface temperatures less than 1250 K.

  4. Wear particles of single-crystal silicon carbide in vacuum

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    Sliding friction experiments, conducted in vacuum with silicon carbide /000/ surface in contact with iron based binary alloys are described. Multiangular and spherical wear particles of silicon carbide are observed as a result of multipass sliding. The multiangular particles are produced by primary and secondary cracking of cleavage planes /000/, /10(-1)0/, and /11(-2)0/ under the Hertzian stress field or local inelastic deformation zone. The spherical particles may be produced by two mechanisms: (1) a penny shaped fracture along the circular stress trajectories under the local inelastic deformation zone, and (2) attrition of wear particles.

  5. Comparative sinterability of combustion synthesized and commercial titanium carbides

    SciTech Connect

    Manley, B.W.

    1984-11-01

    The influence of various parameters on the sinterability of combustion synthesized titanium carbide was investigaged. Titanium carbide powders, prepared by the combustion synthesis process, were sintered in the temperature range 1150 to 1600/sup 0/C. Incomplete combustion and high oxygen contents were found to be the cause of reduced shrinkage during sintering of the combustion syntheized powders when compared to the shrinkage of commercial TiC. Free carbon was shown to inhibit shrinkage. The activation energy for sintering was found to depend on stoichiometry (C/Ti). With decreasing C/Ti, the rate of sintering increased. 29 references, 16 figures, 13 tables.

  6. Process for synthesizing titanium carbide, titanium nitride and titanium carbonitride

    DOEpatents

    Koc, Rasit; Glatzmaier, Gregory C.

    1995-01-01

    A process for synthesizing titanium carbide, titanium nitride or titanium carbonitride. The process comprises placing particles of titanium, a titanium salt or titanium dioxide within a vessel and providing a carbon-containing atmosphere within the vessel. The vessel is heated to a pyrolysis temperature sufficient to pyrolyze the carbon to thereby coat the particles with a carbon coating. Thereafter, the carbon-coated particles are heated in an inert atmosphere to produce titanium carbide, or in a nitrogen atmosphere to produce titanium nitride or titanium carbonitride, with the heating being of a temperature and time sufficient to produce a substantially complete solid solution.

  7. Process for synthesizing titanium carbide, titanium nitride and titanium carbonitride

    DOEpatents

    Koc, R.; Glatzmaier, G.C.

    1995-05-23

    A process is disclosed for synthesizing titanium carbide, titanium nitride or titanium carbonitride. The process comprises placing particles of titanium, a titanium salt or titanium dioxide within a vessel and providing a carbon-containing atmosphere within the vessel. The vessel is heated to a pyrolysis temperature sufficient to pyrolyze the carbon to thereby coat the particles with a carbon coating. Thereafter, the carbon-coated particles are heated in an inert atmosphere to produce titanium carbide, or in a nitrogen atmosphere to produce titanium nitride or titanium carbonitride, with the heating being of a temperature and time sufficient to produce a substantially complete solid solution.

  8. Process for preparing fine grain titanium carbide powder

    DOEpatents

    Janney, M.A.

    1985-03-12

    A method for preparing finely divided titanium carbide powder in which an organotitanate is reacted with a carbon precursor polymer to provide an admixture of the titanium and the polymer at a molecular level due to a crosslinking reaction between the organotitanate and the polymer. The resulting gel is dried, pyrolyzed to drive off volatile components and provide carbon. The resulting solids are then heated at an elevated temperature to convert the titanium and carbon to high-purity titanium carbide powder in a submicron size range.

  9. Process for preparing fine grain titanium carbide powder

    DOEpatents

    Janey, Mark A.

    1986-01-01

    A method for preparing finely divided titanium carbide powder in which an organotitanate is reacted with a carbon precursor polymer to provide an admixture of the titanium and the polymer at a molecular-level due to a crosslinking reaction between the organotitanate and the polymer. The resulting gel is dried, pyrolyzed to drive off volatile components and provide carbon. The resulting solids are then heated at an elevated temperature to convert the titanium and carbon to high-purity titanium carbide powder in a submicron size range.

  10. Method for forming fibrous silicon carbide insulating material

    DOEpatents

    Wei, George C.

    1984-01-01

    A method whereby silicon carbide-bonded SiC fiber composites are prepared from carbon-bonded C fiber composites is disclosed. Carbon-bonded C fiber composite material is treated with gaseous silicon monoxide generated from the reaction of a mixture of colloidal silica and carbon black at an elevated temperature in an argon atmosphere. The carbon in the carbon bond and fiber is thus chemically converted to SiC resulting in a silicon carbide-bonded SiC fiber composite that can be used for fabricating dense, high-strength high-toughness SiC composites or as thermal insulating materials in oxidizing environments.

  11. Method for forming fibrous silicon carbide insulating material

    DOEpatents

    Wei, G.C.

    1983-10-12

    A method whereby silicon carbide-bonded SiC fiber composites are prepared from carbon-bonded C fiber composites is disclosed. Carbon-bonded C fiber composite material is treated with gaseous silicon monoxide generated from the reaction of a mixture of colloidal silica and carbon black at an elevated temperature in an argon atmosphere. The carbon in the carbon bond and fiber is thus chemically converted to SiC resulting in a silicon carbide-bonded SiC fiber composite that can be used for fabricating dense, high-strength high-toughness SiC composites or as thermal insulating materials in oxidizing environments.

  12. High-Q silicon carbide photonic-crystal cavities

    SciTech Connect

    Lee, Jonathan Y.; Lu, Xiyuan; Lin, Qiang

    2015-01-26

    We demonstrate one-dimensional photonic-crystal nanobeam cavities in amorphous silicon carbide. The fundamental mode exhibits intrinsic optical quality factor as high as 7.69 × 10{sup 4} with mode volume ∼0.60(λ/n){sup 3} at wavelength 1.5 μm. A corresponding Purcell factor value of ∼10{sup 4} is the highest reported to date in silicon carbide optical cavities. The device exhibits great potential for integrated nonlinear photonics and cavity nano-optomechanics.

  13. The thermal conductivity of carbon coated silicon carbide fibers embedded in a silicon carbide matrix

    SciTech Connect

    Beecher, S.C.; Dinwiddie, R.B.; Lowden, R.A.

    1993-12-31

    The room temperature thermal conductivity has been measured for a series of composite materials composed of carbon coated silicon carbide (SiC) fibers embedded in a SiC matrix. The composite samples consisted of 0/30{degree} bi-directional plain weave Nicalon fibers coated with varying thicknesses of pyrolitic carbon and infiltrated with SiC by the forced flow chemical vapor infiltration process to form the matrix. The fiber volume fraction was held constant at 0.423 {plus_minus} 0.012 and the from 0.03 {mu}m to 0.983 {mu}m, with the fibers of one sample left uncoated. Results transverse to fiber direction show significant differences with the introduction and subsequent increase in the carbon coating thickness. The thermal conductivity decreased for all the coated samples compared to the uncoated sample coating thickness compared to the sample with the thinnest carbon coating.

  14. Boron-carbide-aluminum and boron-carbide-reactive metal cermets. [B/sub 4/C-Al

    DOEpatents

    Halverson, D.C.; Pyzik, A.J.; Aksay, I.A.

    1985-05-06

    Hard, tough, lighweight boron-carbide-reactive metal composites, particularly boron-carbide-aluminum composites, are produced. These composites have compositions with a plurality of phases. A method is provided, including the steps of wetting and reacting the starting materials, by which the microstructures in the resulting composites can be controllably selected. Starting compositions, reaction temperatures, reaction times, and reaction atmospheres are parameters for controlling the process and resulting compositions. The ceramic phases are homogeneously distributed in the metal phases and adhesive forces at ceramic-metal interfaces are maximized. An initial consolidated step is used to achieve fully dense composites. Microstructures of boron-carbide-aluminum cermets have been produced with modules of rupture exceeding 110 ksi and fracture toughness exceeding 12 ksi..sqrt..in. These composites and methods can be used to form a variety of structural elements.

  15. Method for homogenizing alloys susceptible to the formation of carbide stringers and alloys prepared thereby

    DOEpatents

    Braski, David N.; Leitnaker, James M.

    1980-01-01

    A novel fabrication procedure prevents or eliminates the reprecipitation of segregated metal carbides such as stringers in Ti-modified Hastelloy N and stainless steels to provide a novel alloy having carbides uniformly dispersed throughout the matrix. The fabrication procedure is applicable to other alloys prone to the formation of carbide stringers. The process comprises first annealing the alloy at a temperature above the single phase temperature for sufficient time to completely dissolve carbides and then annealing the single phase alloy for an additional time to prevent the formation of carbide stringers upon subsequent aging or thermomechanical treatment.

  16. The Kinetics of Formation and Decomposition of Austenite in Relation to Carbide Morphology

    NASA Astrophysics Data System (ADS)

    Alvarenga, Henrique Duarte; Van Steenberge, Nele; Sietsma, Jilt; Terryn, Herman

    2017-02-01

    The effect of the carbide morphology on the kinetics of austenite formation and its decomposition was investigated by a combination of measurements of austenite fraction by dilatometry and metallography. These measurements show that coarse carbide morphology is generated by fast cooling through the early stages of eutectoid transformation, enabling fast precipitation of pro-eutectoid ferrite, followed by slow cooling during the final stages of transformation, during the precipitation of carbides. Additionally, a strong influence of the morphology of carbides on the kinetics of austenite formation is observed. The presence of coarse carbides can determine the rate of austenite formation during intercritical annealing as a result of its slow dissolution kinetics.

  17. Process for preparing metal-carbide-containing microspheres from metal-loaded resin beads

    DOEpatents

    Beatty, Ronald L.

    1976-01-01

    An improved method for treating metal-loaded resin microspheres is described which comprises heating a metal-loaded resin charge in an inert atmosphere at a pre-carbide-forming temperature under such conditions as to produce a microsphere composition having sufficient carbon as to create a substantially continuous carbon matrix and a metal-carbide or an oxide-carbide mixture as a dispersed phase(s) during carbide-forming conditions, and then heating the thus treated charge to a carbide-forming temperature.

  18. Research and Development on Advanced Silicon Carbide Thin Film Growth Techniques and Fabrication of High Power and Microwave Frequency Silicon Carbide-Based Device Structures

    DTIC Science & Technology

    1990-12-01

    0W " -Annual Letter Report- N,4 Research and Developmen. on Advanced Silicon Carbide Thin Film Growth Techniques and Fabrication of High Power and...Microwave Frequency Silicon Carbide -Based Device Structures Supported under Grant #N00014-88-K-0341/P00002 Office of the Chief of Naval Research Report...SUBTITLE Research and Development on Advanced S. FUNDING NUMBERS Silicon Carbide Thin Filn.Growth Technl.ques and R&T:212k003---03 Fabrication of High

  19. Growth characteristics of primary M7C3 carbide in hypereutectic Fe-Cr-C alloy

    PubMed Central

    Liu, Sha; Zhou, Yefei; Xing, Xiaolei; Wang, Jibo; Ren, Xuejun; Yang, Qingxiang

    2016-01-01

    The microstructure of the hypereutectic Fe-Cr-C alloy is observed by optical microscopy (OM). The initial growth morphology, the crystallographic structure, the semi-molten morphology and the stacking faults of the primary M7C3 carbide are observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The in-suit growth process of the primary M7C3 carbide was observed by confocal laser microscope (CLM). It is found that the primary M7C3 carbide in hypereutectic Fe-Cr-C alloy is irregular polygonal shape with several hollows in the center and gaps on the edge. Some primary M7C3 carbides are formed by layers of shell or/and consist of multiple parts. In the initial growth period, the primary M7C3 carbide forms protrusion parallel to {} crystal planes. The extending and revolving protrusion forms the carbide shell. The electron backscattered diffraction (EBSD) maps show that the primary M7C3 carbide consists of multiple parts. The semi-molten M7C3 carbide contains unmelted shell and several small-scale carbides inside, which further proves that the primary M7C3 carbide is not an overall block. It is believed that the coalescence of the primary M7C3 carbides is ascribed to the growing condition of the protrusion and the gap filling process. PMID:27596718

  20. Raman spectroscopic characterization of the core-rim structure in reaction bonded boron carbide ceramics

    SciTech Connect

    Jannotti, Phillip; Subhash, Ghatu; Zheng, James Q.; Halls, Virginia; Karandikar, Prashant G.; Salamone, S.; Aghajanian, Michael K.

    2015-01-26

    Raman spectroscopy was used to characterize the microstructure of reaction bonded boron carbide ceramics. Compositional and structural gradation in the silicon-doped boron carbide phase (rim), which develops around the parent boron carbide region (core) due to the reaction between silicon and boron carbide, was evaluated using changes in Raman peak position and intensity. Peak shifting and intensity variation from the core to the rim region was attributed to changes in the boron carbide crystal structure based on experimental Raman observations and ab initio calculations reported in literature. The results were consistent with compositional analysis determined by energy dispersive spectroscopy. The Raman analysis revealed the substitution of silicon atoms first into the linear 3-atom chain, and then into icosahedral units of the boron carbide structure. Thus, micro-Raman spectroscopy provided a non-destructive means of identifying the preferential positions of Si atoms in the boron carbide lattice.

  1. Carbide-fluoride-silver self-lubricating composite

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E. (Inventor)

    1987-01-01

    A self-lubricating, friction and wear reducing composite material is described for use over a wide temperature spectrum from cryogenic temperature to about 900 C in a chemically reactive environment comprising silver, barium fluoride/calcium fluoride eutectic, and metal bonded chromium carbide.

  2. Carbide/fluoride/silver self-lubricating composite

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E. (Inventor)

    1988-01-01

    A self-lubricating, friction and wear reducing composite material for use over a wide temperature spectrum from cryogenic temperature to about 900.degree. C. in a chemically reactive environment comprising silver, barium fluoride/calcium fluoride eutectic, and metal bonded chromium carbide.

  3. Sintered silicon carbide molded body and method for its production

    NASA Technical Reports Server (NTRS)

    Omori, M.; Sendai, M.; Ohira, K.

    1984-01-01

    Sintered silicon carbide shapes are described. They are produced by using a composition containing an oxide of at least one element chosen from the group: Li, Be, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Nb, Mo, Ba, Tc, Ta, W and Th as a supplement to known sintering aids.

  4. Carbon, carbides, and methane in an apollo 12 sample.

    PubMed

    Chang, S; Kvenvolden, K; Lawless, J; Ponnamperuma, C; Kaplan, I R

    1971-02-05

    Total carbon in the Apollo 12 sample 12023 fines was 110 micrograms per gram of sample with a carbon isotopic abundance delta(13)C (relative to the Pee Dee belemnite standard) of +12 per mil. Hydrolysis of the fines with deuterium chloride yielded undeuterated methane along with deuterated hydrocarbons, thus confirming the presence of 7 to 21 micrograms of carbon per gram of sample as carbide and about 2 micrograms of carbon per gram of sample as indigenous methane. After vacuum pyrolysis of the fines to 1100 degrees C the following gases were detected in the relative abundance: carbon monoxide carbon dioxide methane. Variations of the delta(13)C value with the pyrolysis temperature indicated the presence of carbon with more than one range of isotopic values. The observed delta(13)C value of +14 per mil for lunar carbide is much higher than that of carbide in meteorites. These results suggest that lunar carbide is either indigenous to the moon or a meteoritic contribution that has been highly fractionated isotopically.

  5. 81. Photocopied August 1978. 'CARBIDE' OR SECOND FLOOR LOOKING WEST, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    81. Photocopied August 1978. 'CARBIDE' OR SECOND FLOOR LOOKING WEST, OCTOBER 24, 1902. THE TABLES ARE SET IN PREPARATION FOR THE GRAND OPENING CELEBRATION WHICH WAS HELD, IN PART, IN THE QUARTER-MILE LONG ROOM. (438) - Michigan Lake Superior Power Company, Portage Street, Sault Ste. Marie, Chippewa County, MI

  6. Surface Coating of Tungsten Carbide by Electric Exploding of Contact

    SciTech Connect

    Grigoryev, Evgeny G.

    2011-01-17

    Electric exploding of a tungsten carbide--cobalt material near-by high-speed steel surface forms on it a hardening coating. The essential structure properties of the formed coatings are determined by parameters of contact exploding electrode at the pulse current amplitude from above 106 A/cm2 and duration less than 10-4 s. The metallographic investigations of coating structures were done by microscope 'Neophot-24'. They have shown that the contact electric exploding caused the transfer of tungsten carbide and cobalt on the surface of high-speed steel. The breakdown of tungsten carbide--cobalt material took place during electrical exploding. The hardening layers of tungsten carbide and pure nanocrystalline tungsten have been formed upon the surface of high-speed steel as a result of electric exploding. Crystalline grains of tungsten have an almost spherical form and their characteristic size less than 400 nanometers. Micro hardness of the coating layers and high-speed steel structures was measured.

  7. Silicon carbide and other films and method of deposition

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

    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.

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

    SciTech Connect

    Z. Zak Fang, H. Y. Sohn

    2009-03-10

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

  9. High Temperature Slow Crack Growth in Silicon Carbide.

    DTIC Science & Technology

    1978-12-18

    The purpose of this investigation was to identify by survey the probable maximum use temperatures and stress levels for Sintered Alpha Silicon ... Carbide in expected marine (salt containing) and oxidizing environments as a function of sample surface condition. The results of this survey should be

  10. Silicon carbide and other films and method of deposition

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  11. The synthesis of titanium carbide-reinforced carbon nanofibers.

    PubMed

    Zhu, Pinwen; Hong, Youliang; Liu, Bingbing; Zou, Guangtian

    2009-06-24

    Tailoring hard materials into nanoscale building blocks can greatly extend the applications of hard materials and, at the same time, also represents a significant challenge in the field of nanoscale science. This work reports a novel process for the preparation of carbon-based one-dimensional hard nanomaterials. The titanium carbide-carbon composite nanofibers with an average diameter of 90 nm are prepared by an electrospinning technique and a high temperature pyrolysis process. A composite solution containing polyacrylonitrile and titanium sources is first electrospun into the composite nanofibers, which are subsequently pyrolyzed to produce the desired products. The x-ray diffraction pattern and transmission electron microscopy results show that the main phase of the as-synthesized nanofibers is titanium carbide. The Raman analyses show that the composite nanofibers have low graphite clusters in comparison with the pure carbon nanofibers originating from the electrospun polyacrylonitrile nanofibers. The mechanical property tests demonstrate that the titanium carbide-carbon nanofiber membranes have four times higher tensile strength than the carbon nanofiber membranes, and the Young's modulus of the titanium carbide-carbon nanofiber membranes increases in direct proportion to the titanium quantity.

  12. Tungsten-yttria carbide coating for conveying copper

    DOEpatents

    Rothman, Albert J.

    1993-01-01

    A method is provided for providing a carbided-tungsten-yttria coating on the interior surface of a copper vapor laser. The surface serves as a wick for the condensation of liquid copper to return the condensate to the interior of the laser for revolatilization.

  13. The development of silicon carbide-based power electronics devices

    NASA Astrophysics Data System (ADS)

    Hopkins, Richard H.; Perkins, John F.

    1995-01-01

    In 1989 Westinghouse created an internally funded initiative to develop silicon carbide materials and device technology for a variety of potential commercial and military applications. Westinghouse saw silicon carbide as having the potential for dual use. For space applications, size and weight reductions could be achieved, together with increased reliability. Terrestrially, uses in harsh-temperature environments would be enabled. Theoretically, the physical and electrical properties of silicon carbide were highly promising for high-power, high-temperature, radiation-hardened electronics. However, bulk material with the requisite electronic qualities was not available, and the methods needed to produce a silicon carbide wafer—to fabricate high-quality devices—and to transition these technologies into a commercial product were considered to be a high-risk investment. It was recognized that through a collaborative effort, the CCDS could provide scientific expertise in several areas, thus reducing this risk. These included modeling of structures, electrical contacts, dielectrics, and epitaxial growth. This collaboration has been very successful, with developed technologies being transferred to Westinghouse.

  14. Nuclear breeder reactor fuel element with silicon carbide getter

    DOEpatents

    Christiansen, David W.; Karnesky, Richard A.

    1987-01-01

    An improved cesium getter 28 is provided in a breeder reactor fuel element or pin in the form of an extended surface area, low density element formed in one embodiment as a helically wound foil 30 located with silicon carbide, and located at the upper end of the fertile material upper blanket 20.

  15. Low Temperature Hall Measurements of Neutron Irradiated Silicon Carbide

    DTIC Science & Technology

    2004-03-01

    general programming interface bus (GPIB). Table 3: Equipment List for Keithley System 110 Make Model Name Keithley 617 Electrometer Keithley 196 Voltmeter...concentration with temperature as measured by the S110 system . Theory models the temperature dependence of carrier concentration as an exponential. 44 y = 8E+16x...Penney Model of Conduction ........................................................................ 7 Silicon Carbide

  16. High-hardness ceramics based on boron carbide fullerite derivatives

    NASA Astrophysics Data System (ADS)

    Ovsyannikov, D. A.; Popov, M. Yu.; Perfilov, S. A.; Prokhorov, V. M.; Kulnitskiy, B. A.; Perezhogin, I. A.; Blank, V. D.

    2017-02-01

    A new type of ceramics based on the phases of fullerite derivatives and boron carbide B4C is obtained. The material is synthesized at a temperature of 1500 K and a relatively low pressure of 4 GPa; it has a high hardness of 45 GPa and fracture toughness of 15 MPa m1/2.

  17. An Exploration of Neutron Detection in Semiconducting Boron Carbide

    NASA Astrophysics Data System (ADS)

    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

  18. Sputtering and codeposition of silicon carbide with deuterium

    NASA Astrophysics Data System (ADS)

    Causey, Rion A.

    2003-03-01

    Due to its excellent thermal properties, silicon carbide is being considered as a possible plasma-facing material for fusion devices. If used as a plasma-facing material, the energetic hydrogen isotope ions and charge-exchanged neutrals escaping from the plasma will sputter the silicon carbide. To assess the tritium inventory problems that will be generated by the use of this material, it is necessary that we know the codeposition properties of the redeposited silicon carbide. To determine the codeposition properties, the deuterium plasma experiment at Sandia National Laboratories in Livermore, California has been used to directly compare the deuterium sputtering and codeposition of silicon carbide with that of graphite. A Penning discharge at a flux of 6×10 19 D/m 2 and an energy of ≈300 eV was used to sputter silicon and carbon from a pair of 0.05 m diameter silicon carbide disks. The removal rate of deuterium gas from the fixed volume of the system isolated from all other sources and sinks was used to measure the codeposition probability (probability that a hydrogen isotope atom will be removed through codeposition per ion striking the sample surface). A small catcher plate used to capture a fraction of the codeposited film was analyzed using Auger spectroscopy. This analysis showed the film to begin with a high carbon to silicon ratio due to preferential sputtering of the carbon. As the film became thicker, the ratio of the depositing material changed over to the (1:1) value that must eventually be attained.

  19. Tungsten carbide encapsulated in nitrogen-doped carbon with iron/cobalt carbides electrocatalyst for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Chen, Jinwei; Jiang, Yiwu; Zhou, Feilong; Wang, Gang; Wang, Ruilin

    2016-12-01

    This work presents a type of hybrid catalyst prepared through an environmental and simple method, combining a pyrolysis of transition metal precursors, a nitrogen-containing material, and a tungsten source to achieve a one-pot synthesis of N-doping carbon, tungsten carbides, and iron/cobalt carbides (Fe/Co/WC@NC). The obtained Fe/Co/WC@NC consists of uniform Fe3C and Co3C nanoparticles encapsulated in graphitized carbon with surface nitrogen doping, closely wrapped around a plate-like tungsten carbide (WC) that functions as an efficient oxygen reduction reaction (ORR) catalyst. The introduction of WC is found to promote the ORR activity of Fe/Co-based carbide electrocatalysts, which is attributed to the synergistic catalysts of WC, Fe3C, and Co3C. Results suggest that the composite exhibits comparable electrocatalytic activity, higher durability, and ability for methanol tolerance compared with commercial Pt/C for ORR in alkaline electrolyte. These advantages make Fe/Co/WC@NC a promising ORR electrocatalyst and a cost-effective alternative to Pt/C for practical application as fuel cell.

  20. The Active Oxidation of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Myers, Dwight L.

    2009-01-01

    The high temperature oxidation of silicon carbide occurs in two very different modes. Passive oxidation forms a protective oxide film which limits further attack of the SiC: SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g) Active oxidation forms a volatile oxide and may lead to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g) Generally passive oxidation occurs at higher oxidant pressures and active oxidation occurs at lower oxidant pressures and elevated temperatures. Active oxidation is a concern for reentry, where the flight trajectory involves the latter conditions. Thus the transition points and rates of active oxidation are a major concern. Passive/active transitions have been studied by a number of investigators. An examination of the literature indicates many questions remain regarding the effect of impurity, the hysteresis of the transition (i.e. the difference between active-to-passive and passive-toactive), and the effect of total pressure. In this study we systematically investigate each of these effects. Experiments were done in both an alumina furnace tube and a quartz furnace tube. It is known that alumina tubes release impurities such as sodium and increase the kinetics in the passive region [1]. We have observed that the active-to-passive transition occurs at a lower oxygen pressure when the experiment is conducted in alumina tubes and the resultant passive silica scale contains sodium. Thus the tests in this study are conducted in quartz tubes. The hysteresis of the transition has been discussed in the detail in the original theoretical treatise of this problem for pure silicon by Wagner [2], yet there is little mention of it in subsequent literature. Essentially Wagner points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. A series of experiments were conducted for active-to-passive and passive

  1. Spark plasma sintering of tantalum carbide and graphene reinforced tantalum carbide composites

    NASA Astrophysics Data System (ADS)

    Kalluri, Ajith Kumar

    Tantalum carbide (TaC), an ultra-high temperature ceramic (UHTC), is well known for its exceptional properties such as high hardness (15-19 GPa), melting point (3950 °C), elastic modulus (537 GPa), chemical resistance, and thermal shock resistance. To make TaC to be the future material for hypersonic vehicles, it is required to improve its thermal conductivity, strength, and fracture toughness. Researchers have previously reinforced TaC ceramic with carbides of silicon and boron as well as carbon nanotubes (CNTs), however, these reinforcements either undergo chemical changes or induce defects in the matrix during processing. In addition, these reinforcements exhibit a very minimal improvement in the properties. In the present work, we attempted to improve TaC fracture toughness by reinforcing with graphene nano-platelets (GNPs) and processing through spark plasma sintering at high temperature of 2000 °C, pressure of 70 MPa, and soaking time of 10 min. In addition, we investigated the active densification mechanism during SPS of TaC powder and the effect of ball milling time on mechanical properties of sintered TaC. A relative density of >96% was achieved using SPS of monolithic TaC (<3 μm). Ball milling improved the sintering kinetics and improved the mechanical properties (microhardness, bi-axial flexural strength, and indentation fracture toughness). Activation energy (100 kJ/mol) and stress exponent (1.2) were obtained using the analytical model developed for power-law creep. Grain boundary sliding is proposed as active densification mechanism based on these calculations. Reinforcing GNPs (2-6 vol.% ) in the TaC matrix improved relative density (99.8% for TaC-6 vol.% GNP). Also ˜150% and ˜180% increase in flexural strength and fracture toughness, respectively, was observed for TaC-6 vol.% GNP composite. The significant improvement in these properties is attributed to improved densification and toughening mechanisms such as sheet pull-out and crack

  2. STATUS OF HIGH FLUX ISOTOPE REACTOR IRRADIATION OF SILICON CARBIDE/SILICON CARBIDE JOINTS

    SciTech Connect

    Katoh, Yutai; Koyanagi, Takaaki; Kiggans, Jim; Cetiner, Nesrin; McDuffee, Joel

    2014-09-01

    Development of silicon carbide (SiC) joints that retain adequate structural and functional properties in the anticipated service conditions is a critical milestone toward establishment of advanced SiC composite technology for the accident-tolerant light water reactor (LWR) fuels and core structures. Neutron irradiation is among the most critical factors that define the harsh service condition of LWR fuel during the normal operation. The overarching goal of the present joining and irradiation studies is to establish technologies for joining SiC-based materials for use as the LWR fuel cladding. The purpose of this work is to fabricate SiC joint specimens, characterize those joints in an unirradiated condition, and prepare rabbit capsules for neutron irradiation study on the fabricated specimens in the High Flux Isotope Reactor (HFIR). Torsional shear test specimens of chemically vapor-deposited SiC were prepared by seven different joining methods either at Oak Ridge National Laboratory or by industrial partners. The joint test specimens were characterized for shear strength and microstructures in an unirradiated condition. Rabbit irradiation capsules were designed and fabricated for neutron irradiation of these joint specimens at an LWR-relevant temperature. These rabbit capsules, already started irradiation in HFIR, are scheduled to complete irradiation to an LWR-relevant dose level in early 2015.

  3. Normal spectral emittance of crystalline transition metal carbides

    SciTech Connect

    Mackie, W.A.; Carleson, P.; Filion, J.; Hinrichs, C.H. )

    1991-05-15

    We report on experiments to determine the normal spectral emittance of crystalline forms of five transition metal carbides: hafnium carbide, niobium carbide, tantalum carbide, titanium carbide, and zirconium carbide. These emittance measurements were taken at the commonly used pyrometer wavelength of 0.65 {mu}m. The specimens were cylindrical with 0.10-cm-diameter blackbody holes drilled axially to a depth of 1.0 cm. The crystalline specimens were prepared from sintered stock by floating zone arc refinement and then centerless ground to the desired diameter. Measurements were made in vacuum in the temperature range 1200{lt}T{lt}2400 K. The emittance of HfC tends to increase slightly with temperature ({epsilon}{sub HfC}=0.4322+1.065{times}10{sup {minus}4} {ital T}) while those of NbC, TaC, TiC, and ZrC decrease ({epsilon}{sub NbC}=0.4913{minus}6.6{times}10{sup {minus}5} {ital T}, {epsilon}{sub TaC}=0.4662{minus}5.084{times}10{sup {minus}5} {ital T}, {epsilon}{sub TiC}=0.8192{minus}1.66{times}10{sup {minus}4} {ital T}, and {epsilon}{sub ZrC}=0.715{minus}1.174{times}10{sup {minus}4} {ital T}). Bulk stoichiometries of the samples were C/Hf=0.86{plus minus}0.03, C/Nb=0.833{plus minus}0.014, C/Ta=0.79{plus minus}0.05, C/Ti=0.955{plus minus}0.005, and C/Zr=0.917{plus minus}0.015. As a check on the accuracy of the method and procedure, normal spectral emittance measurements were taken on molybdenum yielding values consistent with those accepted. The normal spectral emittance was determined to be isotropic with respect to crystal orientation within the uncertainty of our measurements.

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

    NASA Astrophysics Data System (ADS)

    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

  5. Development and Processing of Nickel Aluminide-Carbide Alloys

    NASA Technical Reports Server (NTRS)

    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

  6. SILICON CARBIDE CERAMICS FOR COMPACT HEAT EXCHANGERS

    SciTech Connect

    DR. DENNIS NAGLE; DR. DAJIE ZHANG

    2009-03-26

    Silicon carbide (SiC) materials are prime candidates for high temperature heat exchangers for next generation nuclear reactors due to their refractory nature and high thermal conductivity at elevated temperatures. This research has focused on demonstrating the potential of liquid silicon infiltration (LSI) for making SiC to achieve this goal. The major advantage of this method over other ceramic processing techniques is the enhanced capability of making high dense, high purity SiC materials in complex net shapes. For successful formation of net shape SiC using LSI techniques, the carbon preform reactivity and pore structure must be controlled to allow the complete infiltration of the porous carbon structure which allows complete conversion of the carbon to SiC. We have established a procedure for achieving desirable carbon properties by using carbon precursors consisting of two readily available high purity organic materials, crystalline cellulose and phenolic resin. Phenolic resin yields a glassy carbon with low chemical reactivity and porosity while the cellulose carbon is highly reactive and porous. By adjusting the ratio of these two materials in the precursor mixtures, the properties of the carbons produced can be controlled. We have identified the most favorable carbon precursor composition to be a cellulose resin mass ratio of 6:4 for LSI formation of SiC. The optimum reaction conditions are a temperature of 1800 C, a pressure of 0.5 Torr of argon, and a time of 120 minutes. The fully dense net shape SiC material produced has a density of 2.96 g cm{sup -3} (about 92% of pure SiC) and a SiC volume fraction of over 0.82. Kinetics of the LSI SiC formation process was studied by optical microscopy and quantitative digital image analysis. This study identified six reaction stages and provided important understanding of the process. Although the thermal conductivity of pure SiC at elevated temperatures is very high, thermal conductivities of most commercial Si

  7. Carbon-rich icosahedral boron carbide designed from first principles

    SciTech Connect

    Jay, Antoine; Vast, Nathalie; Sjakste, Jelena; Duparc, Olivier Hardouin

    2014-07-21

    The carbon-rich boron-carbide (B{sub 11}C)C-C has been designed from first principles within the density functional theory. With respect to the most common boron carbide at 20% carbon concentration B{sub 4}C, the structural modification consists in removing boron atoms from the chains linking (B{sub 11}C) icosahedra. With C-C instead of C-B-C chains, the formation of vacancies is shown to be hindered, leading to enhanced mechanical strength with respect to B{sub 4}C. The phonon frequencies and elastic constants turn out to prove the stability of the carbon-rich phase, and important fingerprints for its characterization have been identified.

  8. Electrical transport and thermoelectric properties of boron carbide nanowires.

    PubMed

    Kirihara, Kazuhiro; Mukaida, Masakazu; Shimizu, Yoshiki

    2017-04-07

    The electrical transport and thermoelectric property of boron carbide nanowires synthesized by a carbothermal method are reported. It is demonstrated that the nanowires achieve a higher Seebeck coefficient and power factor than those of the bulk samples. The conduction mechanism of the nanowires at low temperatures below 300 K is different from that of the sintered-polycrystalline and single-crystal bulk samples. In a temperature range of 200-450 K, there is a crossover between electrical conduction by variable-range hopping and phonon-assisted hopping. The inhomogeneous carbon concentration and planar defects, such as twins and stacking faults, in the nanowires are thought to modify the bonding nature and electronic structure of the boron carbide crystal substantially, causing differences in the electrical conductivity and Seebeck coefficient. The effect of boundary scattering of phonon at nanostructured surface on the thermal conductivity reduction is discussed.

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

    PubMed

    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.

  10. Scalable Quantum Photonics with Single Color Centers in Silicon Carbide.

    PubMed

    Radulaski, Marina; Widmann, Matthias; Niethammer, Matthias; Zhang, Jingyuan Linda; Lee, Sang-Yun; Rendler, Torsten; Lagoudakis, Konstantinos G; Son, Nguyen Tien; Janzén, Erik; Ohshima, Takeshi; Wrachtrup, Jörg; Vučković, Jelena

    2017-02-24

    Silicon carbide is a promising platform for single photon sources, quantum bits (qubits), and nanoscale sensors based on individual color centers. Toward this goal, we develop a scalable array of nanopillars incorporating single silicon vacancy centers in 4H-SiC, readily available for efficient interfacing with free-space objective and lensed-fibers. A commercially obtained substrate is irradiated with 2 MeV electron beams to create vacancies. Subsequent lithographic process forms 800 nm tall nanopillars with 400-1400 nm diameters. We obtain high collection efficiency of up to 22 kcounts/s optical saturation rates from a single silicon vacancy center while preserving the single photon emission and the optically induced electron-spin polarization properties. Our study demonstrates silicon carbide as a readily available platform for scalable quantum photonics architecture relying on single photon sources and qubits.

  11. Diamond-Silicon Carbide Composite And Method For Preparation Thereof

    DOEpatents

    Qian, Jiang; Zhao, Yusheng

    2005-09-06

    Fully dense, diamond-silicon carbide composites are prepared from ball-milled microcrystalline diamond/amorphous silicon powder mixture. The ball-milled powder is sintered (P=5-8 GPa, T=1400K-2300K) to form composites having high fracture toughness. A composite made at 5 GPa/1673K had a measured fracture toughness of 12 MPa.multidot.m.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. X-ray diffraction patterns and Raman spectra indicate that amorphous silicon is partially transformed into nanocrystalline silicon at 5 GPa/873K, and nanocrystalline silicon carbide forms at higher temperatures.

  12. Diffusion Bonding of Silicon Carbide Ceramics using Titanium Interlayers

    NASA Technical Reports Server (NTRS)

    Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, James D.

    2006-01-01

    Robust joining approaches for silicon carbide ceramics are critically needed to fabricate leak free joints with high temperature mechanical capability. In this study, titanium foils and physical vapor deposited (PVD) titanium coatings were used to form diffusion bonds between SiC ceramics using hot pressing. Silicon carbide substrate materials used for bonding include sintered SiC and two types of CVD SiC. Microscopy results show the formation of well adhered diffusion bonds. The bond strengths as determined from pull tests are on the order of several ksi, which is much higher than required for a proposed application. Microprobe results show the distribution of silicon, carbon, titanium, and other minor elements across the diffusion bond. Compositions of several phases formed in the joint region were identified. Potential issues of material compatibility and optimal bond formation will also be discussed.

  13. Infrared absorption spectra of metal carbides, nitrides and sulfides

    NASA Technical Reports Server (NTRS)

    Kammori, O.; Sato, K.; Kurosawa, F.

    1981-01-01

    The infrared absorption spectra of 12 kinds of metal carbides, 11 kinds of nitrides, and 7 kinds of sulfides, a total of 30 materials, were measured and the application of the infrared spectra of these materials to analytical chemistry was discussed. The measurements were done in the frequency (wave length) range of (1400 to 400/cm (7 to 25 mu). The carbides Al4C3, B4C, the nitrides AlN, BN, Si3N4, WB, and the sulfides Al2S3, FeS2, MnS, NiS and PbS were noted to have specific absorptions in the measured region. The sensitivity of Boron nitride was especially good and could be detected at 2 to 3 micrograms in 300 mg of potassium bromide.

  14. Laser-induced phase separation of silicon carbide.

    PubMed

    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

    2016-11-30

    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.

  15. Carbide and carbonitride surface treatment method for refractory metals

    DOEpatents

    Meyer, G.A.; Schildbach, M.A.

    1996-12-03

    A carbide and carbonitride surface treatment method for refractory metals is provided, in steps including, heating a part formed of boron, chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten or zirconium, or alloys thereof, in an evacuated chamber and then introducing reaction gases including nitrogen and hydrogen, either in elemental or water vapor form, which react with a source of elemental carbon to form carbon-containing gaseous reactants which then react with the metal part to form the desired surface layer. Apparatus for practicing the method is also provided, in the form of a carbide and carbonitride surface treatment system including a reaction chamber, a source of elemental carbon, a heating subassembly and a source of reaction gases. Alternative methods of providing the elemental carbon and the reaction gases are provided, as well as methods of supporting the metal part, evacuating the chamber with a vacuum subassembly and heating all of the components to the desired temperature. 5 figs.

  16. Atomic-Level Understanding of "Asymmetric Twins" in Boron Carbide.

    PubMed

    Xie, Kelvin Y; An, Qi; Toksoy, M Fatih; McCauley, James W; Haber, Richard A; Goddard, William A; Hemker, Kevin J

    2015-10-23

    Recent observations of planar defects in boron carbide have been shown to deviate from perfect mirror symmetry and are referred to as "asymmetric twins." Here, we demonstrate that these asymmetric twins are really phase boundaries that form in stoichiometric B(4)C (i.e., B(12)C(3)) but not in B(13)C(2). TEM observations and ab initio simulations have been coupled to show that these planar defects result from an interplay of stoichiometry, atomic positioning, icosahedral twinning, and structural hierarchy. The composition of icosahedra in B(4)C is B(11)C and translation of the carbon atom from a polar to equatorial site leads to a shift in bonding and a slight distortion of the lattice. No such distortion is observed in boron-rich B(13)C(2) because the icosahedra do not contain carbon. Implications for tailoring boron carbide with stoichiometry and extrapolations to other hierarchical crystalline materials are discussed.

  17. Preferential killing of cancer cells using silicon carbide quantum dots.

    PubMed

    Mognetti, Barbara; Barberis, Alessandro; Marino, Silvia; Di Carlo, Francesco; Lysenko, Vladimir; Marty, Olivier; Géloën, Alain

    2010-12-01

    Silicon carbide quantum dots are highly luminescent biocompatible nanoparticles whose properties might be of particular interest for biomedical applications. In this study we investigated Silicon Carbide Quantum Dots (3C-SiC QDs) cellular localisation and influence on viability and proliferation on oral squamous carcinoma (AT-84 and HSC) and immortalized cell lines (S-G). They clearly localize into the nuclei, but the presence of 3C-SiC QDs in culture medium provoke morphological changes in cultured cells. We demonstrate that 3C-SiC QDs display dose- and time-dependent selective cytotoxicity on cancer versus immortalized cells in vitro. Since one of the limitations of classical antineoplastic drugs is their lack of selectivity, these results open a new way in the search for antiproliferative drugs.

  18. Laser-induced phase separation of silicon carbide

    PubMed Central

    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

    2016-01-01

    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. PMID:27901015

  19. Protective coating for alumina-silicon carbide whisker composites

    DOEpatents

    Tiegs, Terry N.

    1989-01-01

    Ceramic composites formed of an alumina matrix reinforced with silicon carbide whiskers homogenously dispersed therein are provided with a protective coating for preventing fracture strength degradation of the composite by oxidation during exposure to high temperatures in oxygen-containing atmospheres. The coating prevents oxidation of the silicon carbide whiskers within the matrix by sealing off the exterior of the matrix so as to prevent oxygen transport into the interior of the matrix. The coating is formed of mullite or mullite plus silicon oxide and alumina and is formed in place by heating the composite in air to a temperature greater than 1200.degree. C. This coating is less than about 100 microns thick and adequately protects the underlying composite from fracture strength degradation due to oxidation.

  20. Colloidal characterization of silicon nitride and silicon carbide

    NASA Technical Reports Server (NTRS)

    Feke, Donald L.

    1986-01-01

    The colloidal behavior of aqueous ceramic slips strongly affects the forming and sintering behavior and the ultimate mechanical strength of the final ceramic product. The colloidal behavior of these materials, which is dominated by electrical interactions between the particles, is complex due to the strong interaction of the solids with the processing fluids. A surface titration methodology, modified to account for this interaction, was developed and used to provide fundamental insights into the interfacial chemistry of these systems. Various powder pretreatment strategies were explored to differentiate between true surface chemistry and artifacts due to exposure history. The colloidal behavior of both silicon nitride and carbide is dominated by silanol groups on the powder surfaces. However, the colloid chemistry of silicon nitride is apparently influenced by an additional amine group. With the proper powder treatments, silicon nitride and carbide powder can be made to appear colloidally equivalent. The impact of these results on processing control will be discussed.

  1. Thermal shock as a carbide grade development tool

    SciTech Connect

    Merten, C.W.; von Turkovich, B.F.

    1984-01-01

    Objective improvement of quality through the maximization of signal to noise ratios is discussed. It is proposed that the signal to noise ratio concept also be applied to grade development of carbide tools for intermittent cutting. Thermal shock resistance is identified as a tool material property which might serve as a practical indicator of tool life for certain cutting conditions. Carbide specimens were subjected to single cycle thermal shock and statistical methods for the analysis of the resulting data are presented. Parameters for monitoring signal shift and signal to noise ratio are identified for the Weibull distribution. These parameters are then utilized for grade selection or grade prediction according to a proposed grade development strategy.

  2. Heteroepitaxial growth of highly oriented diamond on cubic silicon carbide

    SciTech Connect

    Kawarada, H.; Wild, C.; Herres, N.; Locher, R.; Koidl, P.; Nagasawa, H.

    1997-04-01

    We have deposited epitaxial diamond films with very low angular spread on epitaxial {beta}-phase silicon carbide layers on silicon (001) substrates. From x-ray rocking curve measurements, half-widths of the angular spread of the crystal orientation as low as 0.6{degree} have been determined, which is the smallest value ever reported in heteroepitaxial diamond films and appears to be smaller than those of the {beta}-phase silicon carbide underlayers. The film surface exhibits a roughness of about 100 nm with very few discernible boundaries due to misorientation. The optimization of the bias-enhanced nucleation process and the control of selective growth are the main factors for the improvement of the crystallinity. {copyright} {ital 1997 American Institute of Physics.}

  3. Process for coating an object with silicon carbide

    NASA Technical Reports Server (NTRS)

    Levin, Harry (Inventor)

    1989-01-01

    A process for coating a carbon or graphite object with silicon carbide by contacting it with silicon liquid and vapor over various lengths of contact time. In the process, a stream of silicon-containing precursor material in gaseous phase below the decomposition temperature of said gas and a co-reactant, carrier or diluent gas such as hydrogen is passed through a hole within a high emissivity, thin, insulating septum into a reaction chamber above the melting point of silicon. The thin septum has one face below the decomposition temperature of the gas and an opposite face exposed to the reaction chamber. The precursor gas is decomposed directly to silicon in the reaction chamber. A stream of any decomposition gas and any unreacted precursor gas from said reaction chamber is removed. The object within the reaction chamber is then contacted with silicon, and recovered after it has been coated with silicon carbide.

  4. Laser-induced phase separation of silicon carbide

    NASA Astrophysics Data System (ADS)

    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.

  5. Carbide coated fibers in graphite-aluminum composites

    NASA Technical Reports Server (NTRS)

    Imprescia, R. J.; Levinson, L. S.; Reiswig, R. D.; Wallace, T. C.; Williams, J. M.

    1975-01-01

    Thin, uniform coats of titanium carbide, deposited on graphite fibers by chemical vapor deposition with thicknesses up to approximately 0.1 microns were shown to improve fiber strength significantly. For greater thicknesses, strength was degraded. The coats promote wetting of the fibers and infiltration of the fiber yarns with aluminum alloys, and act as protective barriers to inhibit reaction between the fibers and the alloys. Chemical vapor deposition was used to produce silicon carbide coats on graphite fibers. In general, the coats were nonuniform and were characterized by numerous surface irregularities. Despite these irregularities, infiltration of these fibers with aluminum alloys was good. Small graphite-aluminum composite samples were produced by vacuum hot-pressing of aluminum-infiltrated graphite yarn at temperatures above the metal liquidus.

  6. Friction, deformation and fracture of single-crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1977-01-01

    Friction experiments were conducted with hemispherical and conical diamond riders sliding on the basal plane of silicon carbide. The results indicate that, when deformation is primarily elastic, the friction does not depend on crystallographic orientation and there is no detectable fracture or cracking. When, however, plastic deformation occurs, silicon carbide exhibits anisotropic friction and deformation behavior. Surface fracture crack patterns surrounding wear tracks are observed to be of three types. The crack-geometries of two types are generally independent of orientation, the third crack, however, depends on the orientation. All surface cracks extend into subsurface. Anisotropic friction, deformation and fracture on the basal plane are primarily controlled by the slip system and cleavage.

  7. Pairwise cobalt doping of boron carbides with cobaltocene

    SciTech Connect

    Ignatov, A. Yu.; Losovyj, Ya. B.; Carlson, L.; LaGraffe, D.; Brand, J. I.; Dowben, P. A.

    2007-10-15

    We have performed Co K-edge x-ray absorption fine structure and x-ray absorption near edge structure measurements of Co-doped plasma enhanced chemical vapor phase deposition (PECVD) grown 'C{sub 2}B{sub 10}H{sub x}' semiconducting boron carbides, using cobaltocene. Cobalt does not dope PECVD grown boron carbides as a random fragment of the cobaltocene source gas. The Co atoms are fivefold boron coordinated (R=2.10{+-}0.02 A) and are chemically bonded to the icosahedral cages of B{sub 10}CH{sub x} or B{sub 9}C{sub 2}H{sub y}. Pairwise Co doping occurs, with the cobalt atoms favoring sites some 5.28{+-}0.02 A apart.

  8. Diffusion Bonding of Silicon Carbide for MEMS-LDI Applications

    NASA Technical Reports Server (NTRS)

    Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, J. Douglas

    2007-01-01

    A robust joining approach is critically needed for a Micro-Electro-Mechanical Systems-Lean Direct Injector (MEMS-LDI) application which requires leak free joints with high temperature mechanical capability. Diffusion bonding is well suited for the MEMS-LDI application. Diffusion bonds were fabricated using titanium interlayers between silicon carbide substrates during hot pressing. The interlayers consisted of either alloyed titanium foil or physically vapor deposited (PVD) titanium coatings. Microscopy shows that well adhered, crack free diffusion bonds are formed under optimal conditions. Under less than optimal conditions, microcracks are present in the bond layer due to the formation of intermetallic phases. Electron microprobe analysis was used to identify the reaction formed phases in the diffusion bond. Various compatibility issues among the phases in the interlayer and substrate are discussed. Also, the effects of temperature, pressure, time, silicon carbide substrate type, and type of titanium interlayer and thickness on the microstructure and composition of joints are discussed.

  9. Electrical transport and thermoelectric properties of boron carbide nanowires

    NASA Astrophysics Data System (ADS)

    Kirihara, Kazuhiro; Mukaida, Masakazu; Shimizu, Yoshiki

    2017-04-01

    The electrical transport and thermoelectric property of boron carbide nanowires synthesized by a carbothermal method are reported. It is demonstrated that the nanowires achieve a higher Seebeck coefficient and power factor than those of the bulk samples. The conduction mechanism of the nanowires at low temperatures below 300 K is different from that of the sintered-polycrystalline and single-crystal bulk samples. In a temperature range of 200–450 K, there is a crossover between electrical conduction by variable-range hopping and phonon-assisted hopping. The inhomogeneous carbon concentration and planar defects, such as twins and stacking faults, in the nanowires are thought to modify the bonding nature and electronic structure of the boron carbide crystal substantially, causing differences in the electrical conductivity and Seebeck coefficient. The effect of boundary scattering of phonon at nanostructured surface on the thermal conductivity reduction is discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Mechanisms of Superplastic Deformation of Nanocrystalline Silicon Carbide Ceramics

    DTIC Science & Technology

    2012-08-01

    These included the following: standard hot isostatic pressing (HIP), spark plasma sintering , ultra-high pressure HIP, and a multianvil pressure...96.8 2270 Multianvil apparatus 1200 3000 94.8 1130 Note: SPS = spark plasma sintering . 2 Figure 1. Ultra-high pressure HIP; 1600 °C, 980...strain rate sensitivity and flow stress. 15. SUBJECT TERMS silicon carbide, nanostructure, sintering , hot isostatic pressing, hardness 16. SECURITY

  13. Method of making carbide/fluoride/silver composites

    NASA Technical Reports Server (NTRS)

    Sliney, Harold E. (Inventor); Dellacorte, Christopher (Inventor)

    1991-01-01

    A composition containing 30 to 70 percent chromium carbide, 5 to 20 percent soft noble metal, 5 to 20 percent metal fluorides, and 20 to 60 percent metal binder is used in a powdered metallurgy process for the production of self-lubricating components, such as bearings. The use of the material allows the self-lubricating bearing to maintain its low friction properties over an extended range of operating temperatures.

  14. Microstructure and properties of IN SITU toughened silicon carbide

    SciTech Connect

    De Jonghe, Lutgard C.; Ritchie, Robert O.; Zhang, Xiao Feng

    2003-05-01

    A silicon carbide with a fracture toughness as high as 9.1 MPa.m1/2 has been developed by hot pressing b-SiC powder with aluminum, boron, and carbon additions (ABC-SiC). Central in this material development has been systematic transmission electron microscopy (TEM) and mechanical characterizations. In particular, atomic-resolution electron microscopy and nanoprobe composition quantification were combined in analyzing grain boundary structure and nanoscale structural features.

  15. Synthesis of multifilament silicon carbide fibers by chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Revankar, Vithal; Hlavacek, Vladimir

    1991-01-01

    A process for development of clean silicon carbide fiber with a small diameter and high reliability is presented. An experimental evaluation of operating conditions for SiC fibers of good mechanical properties and devising an efficient technique which will prevent welding together of individual filaments are discussed. The thermodynamic analysis of a different precursor system was analyzed vigorously. Thermodynamically optimum conditions for stoichiometric SiC deposit were obtained.

  16. Final design review of boron carbide safety rod

    SciTech Connect

    Lutz, R.N.

    1991-09-24

    The object of this paper discusses the design review of the boron carbide safety rod for the Westinghouse Savannah River Company. This paper reviewed information presented by personnel of the Savannah River Laboratory (SRL) Equipment Engineering Section, SRL Materials Technology Section and Reactor Materials Engineering and Technology. From this report, views, opinions and recommendations were made on the safety rod from materials testing to production.

  17. Wear Resistant Coating on Tungsten Carbide Hard Alloy

    NASA Astrophysics Data System (ADS)

    Oskolkova, T. N.

    2015-09-01

    The article reveals new knowledge about the role of zirconium in the composition of (Ti, Zr)N ion-plasma coating applied on WC10KS alloy. It is determined that when zirconium is introduced into ion-plasma coating TiN (50%) wear resistance and adhesion strength grow, nanohardness increases by 23% (up to 38500MPa), Yung's modulus rises by 67%, friction coefficient reduces to p = 0.07 and performance characteristics of a carbide alloy improve.

  18. 6H Silicon Carbide Photoconductive Switches for High Power Applications

    DTIC Science & Technology

    2006-11-01

    6H SILICON CARBIDE PHOTOCONDUCTIVE SWITCHES FOR HIGH POWER APPLICATIONS W. C. Nunnally*, N. Islam, K. Kelkar & C. Fessler Photonics for Radars...PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Photonics for Radars and Optical Systems...switches. Additional work by the UMC Photonics for Radar and Optical Systems (PROS) group has demonstrated that the relatively new material of

  19. Boron Carbide Aluminum Cermets for External Pressure Housing Applications

    DTIC Science & Technology

    1992-09-01

    TABLES 1. Phase chemistry of B4C/A1 composites as a function of baking temperature (by stereology) .................. ...... 10 2. Summary of the...diffractometer using CuKo radiation and a scan rate of 2° per minute. The chemistry of all phases was determined from electron microprobe analysis of... a change in the chemistry of the boron carbide. The depth of the ESCA beam into the surface is only about 50A. Further analysis of the BC powders

  20. Corrosion Characteristics of Silicon Carbide and Silicon Nitride

    PubMed Central

    Munro, R. G.; Dapkunas, S. J.

    1993-01-01

    The present work is a review of the substantial effort that has been made to measure and understand the effects of corrosion with respect to the properties, performance, and durability of various forms of silicon carbide and silicon nitride. The review encompasses corrosion in diverse environments, usually at temperatures of 1000 °C or higher. The environments include dry and moist oxygen, mixtures of hot gaseous vapors, molten salts, molten metals, and complex environments pertaining to coal ashes and slags. PMID:28053489

  1. Steam Reforming on Transition-metal Carbides from Density-functional Theory

    SciTech Connect

    Vojvodic, Aleksandra

    2012-05-11

    A screening study of the steam reforming reaction on clean and oxygen covered early transition-metal carbides surfaces is performed by means of density-functional theory calculations. It is found that carbides provide a wide spectrum of reactivities, from too reactive via suitable to too inert. Several molybdenum-based systems are identified as possible steam reforming catalysts. The findings suggest that carbides provide a playground for reactivity tuning, comparable to the one for pure metals.

  2. Extreme-Environment Silicon-Carbide (SiC) Wireless Sensor Suite

    NASA Technical Reports Server (NTRS)

    Yang, Jie

    2015-01-01

    Phase II objectives: Develop an integrated silicon-carbide wireless sensor suite capable of in situ measurements of critical characteristics of NTP engine; Compose silicon-carbide wireless sensor suite of: Extreme-environment sensors center, Dedicated high-temperature (450 deg C) silicon-carbide electronics that provide power and signal conditioning capabilities as well as radio frequency modulation and wireless data transmission capabilities center, An onboard energy harvesting system as a power source.

  3. Single Molecule Source Reagents for Chemical Vapor Deposition of B- Silicon Carbide

    DTIC Science & Technology

    1992-12-10

    vapor deposition of stoichiometric Beta silicon carbide . Four single molecule sources were synthesized, their decomposition pathways studied, and their...utility in Beta- silicon carbide CVD investigated. Dramatic differences in the CVD process resulted from small changes in the reagent structure. A...strained cyclic molecule, 1,3-disilacyclobutane, allowed growth of a Beta- silicon carbide film at a temperature >300 deg C lower than was possible with a

  4. Tensile Strengths of Silicon Carbide (SiC) Under Shock Loading

    DTIC Science & Technology

    2001-03-01

    The present work was initiated to measure and compare tensile strengths (i.e., spall thresholds) of five different types/varieties of silicon carbide materials...France. Spall strengths of these five different silicon carbide materials were measured by performing plane shock wave experiments to a maximum impact...investigation is that spall strength of silicon carbide , irrespective of its manufacturing process, improves initially to a certain impact stress level

  5. Nanosized Borides and Carbides for Electroplating. Metal-Matrix Coatings: Specifications, Performance Evaluation

    NASA Astrophysics Data System (ADS)

    Galevskiy, G. V.; Rudneva, V. V.; Galevskiy, S. G.; Il'yashchenko, D. P.; Kartsev, D. S.

    2016-04-01

    This paper summarizes experience of application of nano-sized carbides and borides of titanium and chromium, silicon carbide as components of electro-depositable coating compositions based on nickel, zinc, and chromium. Basic physical and mechanical properties of the coatings are determined. Technological and economic evaluation is completed; practicability of high-cost nano-diamonds substitution for nano-sized borides and carbides is justified.

  6. Silicon carbide-silicon composite having improved oxidation resistance and method of making

    NASA Technical Reports Server (NTRS)

    Luthra, Krishan Lal (Inventor); Wang, Hongyu (Inventor)

    1999-01-01

    A Silicon carbide-silicon matrix composite having improved oxidation resistance at high temperatures in dry or water-containing environments is provided. A method is given for sealing matrix cracks in situ in melt infiltrated silicon carbide-silicon matrix composites. The composite cracks are sealed by the addition of various additives, such as boron compounds, into the melt infiltrated silicon carbide-silicon matrix.

  7. Method of making silicon carbide-silicon composite having improved oxidation resistance

    NASA Technical Reports Server (NTRS)

    Luthra, Krishan Lal (Inventor); Wang, Hongyu (Inventor)

    2002-01-01

    A Silicon carbide-silicon matrix composite having improved oxidation resistance at high temperatures in dry or water-containing environments is provided. A method is given for sealing matrix cracks in situ in melt infiltrated silicon carbide-silicon matrix composites. The composite cracks are sealed by the addition of various additives, such as boron compounds, into the melt infiltrated silicon carbide-silicon matrix.

  8. Effect of carbide distribution on rolling-element fatigue life of AMS 5749

    NASA Technical Reports Server (NTRS)

    Parker, R. J.; Bamberger, E. N.

    1983-01-01

    Endurance tests with ball bearings made of corrosion resistant bearing steel which resulted in fatigue lives much lower than were predicted are discussed. Metallurgical analysis revealed an undesirable carbide distribution in the races. It was shown in accelerated fatigue tests in the RC rig that large, banded carbides can reduce rolling element fatigue life by a factor of approximately four. The early spalling failures on the bearing raceways are attributed to the large carbide size and banded distribution.

  9. Review on Sintering Process of WC-Co Cemented Carbide in Metal Injection Molding Technology

    NASA Astrophysics Data System (ADS)

    Prathabrao, M.; Amin, Sri Yulis M.; Ibrahim, M. H. I.

    2017-01-01

    The objective of this paper is to give an overview on sintering process of WC-Co cemented carbides in metal injection molding technology. Metal injection molding is an advanced and promising technology in producing cemented nanostructured carbides. Cemented tungsten carbide (WC-Co) hard metal is known for its high hardness and wear resistance in various applications. Moreover, areas include fine grained materials, alternative binders, and alternative sintering techniques has been discussed in this paper.

  10. Effect of carbide size, area, density on rolling-element fatigue

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    A carbide parameter that can be used to predict rolling element fatigue life was developed.The parameter is based on a statistical life analysis and incorporates the total number of particles per unit area, particle size, and percent carbide area. These were determined from quantimet image analyzing computer examinations of random samples selected from eight lots of material previously tested in rolling fatigue. The carbide parameter is independent of chemical composition, heat treatment, and hardening mechanism of the materials investigated.

  11. Refining the pathway of carbide insertion into the nitrogenase M-cluster

    PubMed Central

    Wiig, Jared A.; Hu, Yilin; Ribbe, Markus W.

    2015-01-01

    Carbide insertion plays a pivotal role in the biosynthesis of M-cluster, the cofactor of nitrogenase. Previously, we proposed a carbide insertion pathway involving methyltransfer from SAM to a FeS precursor and hydrogen abstraction from this methyl group that initiates the radical-based precursor maturation. Here we demonstrate that the methyl group is transferred to a precursor-associated sulfur before hydrogen abstraction, thereby refining the initial steps of the carbide insertion pathway. PMID:26259825

  12. Reactively sputtered titanium carbide thin films: Preparation and properties

    NASA Astrophysics Data System (ADS)

    Eizenberg, M.; Murarka, S. P.

    1983-06-01

    The low resistivity and refractory nature of titanium carbide makes it potentially useful as a diffusion barrier in thin film metallization schemes. In the present investigation, deposition and properties of thin titanium carbide films have been investigated. The films were deposited by reactive radio frequency sputtering in methane-argon mixtures on a variety of substrates. The effects of methane to argon ratio, total sputtering pressure, and power on the film deposition rate, composition and properties were determined. There were interactive effects of these parameters on the composition and properties of these films. Resistivity increased with carbon content; for Ti/C≥1 it was ˜200 μΩ cm. Stress that was compressive was maximum in the nearly stoichiometric TiC film. Grain size was small in all films, especially so in carbon rich films. All stoichiometric titanium carbide films were resistant to HF solutions. Films with TiC/≥1 dissolved easily in ethylene dinitrilo tetra acetric acid (EDTA) solution.

  13. Fabrication of Carbon Nanotube - Chromium Carbide Composite Through Laser Sintering

    NASA Astrophysics Data System (ADS)

    Liu, Ze; Gao, Yibo; Liang, Fei; Wu, Benxin; Gou, Jihua; Detrois, Martin; Tin, Sammy; Yin, Ming; Nash, Philip; Tang, Xiaoduan; Wang, Xinwei

    2016-03-01

    Ceramics often have high hardness and strength, and good wear and corrosion resistance, and hence have many important applications, which, however, are often limited by their poor fracture toughness. Carbon nanotubes (CNTs) may enhance ceramic fracture toughness, but hot pressing (which is one typical approach of fabricating CNT-ceramic composites) is difficult to apply for applications that require localized heat input, such as fabricating composites as surface coatings. Laser beam may realize localized material sintering with little thermal effect on the surrounding regions. However, for the typical ceramics for hard coating applications (as listed in Ref.[1]), previous work on laser sintering of CNT-ceramic composites with mechanical property characterizations has been very limited. In this paper, research work has been reported on the fabrication and characterization of CNT-ceramic composites through laser sintering of mixtures of CNTs and chromium carbide powders. Under the studied conditions, it has been found that laser-sintered composites have a much higher hardness than that for plasma-sprayed composites reported in the literature. It has also been found that the composites obtained by laser sintering of CNTs and chromium carbide powder mixtures have a fracture toughness that is ~23 % higher than the material obtained by laser sintering of chromium carbide powders without CNTs.

  14. Ceramic composites reinforced with modified silicon carbide whiskers

    DOEpatents

    Tiegs, Terry N.; Lindemer, Terrence B.

    1990-01-01

    Silicon carbide whisker-reinforced ceramic composites are fabricated in a highly reproducible manner by beneficating the surfaces of the silicon carbide whiskers prior to their usage in the ceramic composites. The silicon carbide whiskers which contain considerable concentrations of surface oxides and other impurities which interact with the ceramic composite material to form a chemical bond are significantly reduced so that only a relatively weak chemical bond is formed between the whisker and the ceramic material. Thus, when the whiskers interact with a crack propagating into the composite the crack is diverted or deflected along the whisker-matrix interface due to the weak chemical bonding so as to deter the crack propagation through the composite. The depletion of the oxygen-containing compounds and other impurities on the whisker surfaces and near surface region is effected by heat treating the whiskers in a suitable oxygen sparaging atmosphere at elevated temperatures. Additionally, a sedimentation technique may be utilized to remove whiskers which suffer structural and physical anomalies which render them undesirable for use in the composite. Also, a layer of carbon may be provided on the surface of the whiskers to further inhibit chemical bonding of the whiskers to the ceramic composite material.

  15. Predicted boron-carbide compounds: A first-principles study

    SciTech Connect

    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 B{sub 5}C indicates its high stability. The density of states of B{sub 5}C show that it is p-type semiconducting. The calculated theoretical Vickers hardnesses of B-C exceed 40 GPa except B{sub 4}C, BC, and BC{sub 4}, 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.

  16. Carbide-Derived Carbon Films for Integrated Electrochemical Energy Storage

    NASA Astrophysics Data System (ADS)

    Heon, Min

    Active RFID tags, which can communicate over tens or even hundreds of meters, MEMS devices of several microns in size, which are designed for the medical and pharmaceutical purposes, and sensors working in wireless monitoring systems, require microscale power sources that are able to provide enough energy and to satisfy the peak power demands in those applications. Supercapacitors have not been an attractive candidate for micro-scale energy storage, since most nanoporous carbon electrode materials are not compatible with micro-fabrication techniques and have failed to meet the requirements of high volumetric energy density and small form factor for power supplies for integrated circuits or microelectronic devices or sensors. However, supercapacitors can provide high power density, because of fast charging/discharging, which can enable self-sustaining micro-modules when combined with energy-harvesting devices, such as solar cell, piezoelectric or thermoelectric micro-generators. In this study, carbide-derived carbon (CDC) films were synthesized via vacuum decomposition of carbide substrates and gas etching of sputtered carbide thin films. This approach allowed manufacturing of porous carbon films on SiC and silicon substrates. CDC films were studied for micro-supercapacitor electrodes, and showed good double layer capacitance. Since the gas etching technique is compatible with conventional micro-device fabrication processes, it can be implemented to manufacture integrated on-chip supercapacitors on silicon wafers.

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

    PubMed

    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. Disorder and defects are not intrinsic to boron carbide

    PubMed Central

    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. PMID:26777140

  19. Visible-blind ultraviolet photodetectors on porous silicon carbide substrates

    SciTech Connect

    Naderi, N.; Hashim, M.R.

    2013-06-01

    Highlights: • Highly reliable UV detectors are fabricated on porous silicon carbide substrates. • The optical properties of samples are enhanced by increasing the current density. • The optimized sample exhibits enhanced sensitivity to the incident UV radiation. - Abstract: Highly reliable visible-blind ultraviolet (UV) photodetectors were successfully fabricated on porous silicon carbide (PSC) substrates. High responsivity and high photoconductive gain were observed in a metal–semiconductor–metal ultraviolet photodetector that was fabricated on an optimized PSC substrate. The PSC samples were prepared via the UV-assisted photo-electrochemical etching of an n-type hexagonal silicon carbide (6H-SiC) substrate using different etching current densities. The optical results showed that the current density is an outstanding etching parameter that controls the porosity and uniformity of PSC substrates. A highly porous substrate was synthesized using a suitable etching current density to enhance its light absorption, thereby improving the sensitivity of UV detector with this substrate. The electrical characteristics of fabricated devices on optimized PSC substrates exhibited enhanced sensitivity and responsivity to the incident radiation.

  20. Method for removing oxide contamination from silicon carbide powders

    DOEpatents

    Brynestad, J.; Bamberger, C.E.

    1984-08-01

    The described invention is directed to a method for removing oxide contamination in the form of oxygen-containing compounds such as SiO/sub 2/ and B/sub 2/O/sub 3/ from a charge of finely divided silicon carbide. The silicon carbide charge is contacted with a stream of hydrogen fluoride mixed with an inert gas carrier such as argon at a temperature in the range of about 200/sup 0/ to 650/sup 0/C. The oxides in the charge react with the heated hydrogen fluoride to form volatile gaseous fluorides such as SiF/sub 4/ and BF/sub 3/ which pass through the charge along with unreacted hydrogen fluoride and the carrier gas. Any residual gaseous reaction products and hydrogen fluoride remaining in the charge are removed by contacting the charge with the stream of inert gas which also cools the powder to room temperature. The removal of the oxygen contamination by practicing the present method provides silicon carbide powders with desirable pressing and sintering characteristics. 1 tab.

  1. Characterization of a boron carbide-based polymer neutron sensor

    NASA Astrophysics Data System (ADS)

    Tan, Chuting; James, Robinson; Dong, Bin; Driver, M. Sky; Kelber, Jeffry A.; Downing, Greg; Cao, Lei R.

    2015-12-01

    Boron is used widely in thin-film solid-state devices for neutron detection. The film thickness and boron concentration are important parameters that relate to a device's detection efficiency and capacitance. Neutron depth profiling was used to determine the film thicknesses and boron-concentration profiles of boron carbide-based polymers grown by plasma enhanced chemical vapor deposition (PECVD) of ortho-carborane (1,2-B10C2H12), resulting in a pure boron carbide film, or of meta-carborane (1,7-B10C2H12) and pyridine (C5H5N), resulting in a pyridine composite film, or of pyrimidine (C4H4N2) resulting in a pure pyrimidine film. The pure boron carbide film had a uniform surface appearance and a constant thickness of 250 nm, whereas the thickness of the composite film was 250-350 nm, measured at three different locations. In the meta-carborane and pyridine composite film the boron concentration was found to increase with depth, which correlated with X-ray photoelectron spectroscopy (XPS)-derived atomic ratios. A proton peak from 14N (n,p)14C reaction was observed in the pure pyrimidine film, indicating an additional neutron sensitivity to nonthermal neutrons from the N atoms in the pyrimidine.

  2. Silicon Carbide Mounts for Fabry-Perot Interferometers

    NASA Technical Reports Server (NTRS)

    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.

  3. Calcium Carbide: A Unique Reagent for Organic Synthesis and Nanotechnology.

    PubMed

    Rodygin, Konstantin S; Werner, Georg; Kucherov, Fedor A; Ananikov, Valentine P

    2016-04-05

    Acetylene, HC≡CH, is one of the primary building blocks in synthetic organic and industrial chemistry. Several highly valuable processes have been developed based on this simplest alkyne and the development of acetylene chemistry has had a paramount impact on chemical science over the last few decades. However, in spite of numerous useful possible reactions, the application of gaseous acetylene in everyday research practice is rather limited. Moreover, the practical implementation of high-pressure acetylene chemistry can be very challenging, owing to the risk of explosion and the requirement for complex equipment; special safety precautions need to be taken to store and handle acetylene under high pressure, which limit its routine use in a standard laboratory setup. Amazingly, recent studies have revealed that calcium carbide, CaC2 , can be used as an easy-to-handle and efficient source of acetylene for in situ chemical transformations. Thus, calcium carbide is a stable and inexpensive acetylene precursor that is available on the ton scale and it can be handled with standard laboratory equipment. The application of calcium carbide in organic synthesis will bring a new dimension to the powerful acetylene chemistry.

  4. Fatigue of alumina-based ceramics and chrome carbide composites

    NASA Astrophysics Data System (ADS)

    Kireitseu, Maksim V.; Yerakhavets, Liudmila; Nemerenco, Ion; Basenuk, Vladimir L.

    2003-10-01

    The paper was revealed a fatigue in the alumina-chrome carbide composite. The trapped crack front resembles a collinear array of microcracks interspersed by grains rich in transformable precipitates. This micromechanical model provides a reasonable explanation for the observed fatigue crack growth. A numerical procedure similar to the one used in the analysis of the array of collinear cracks, based on complex potentials and dislocation formalism is also used to simulate fatigue of composite coatings based on oxide ceramics and chrome carbide. Assuming power-law crack growth, it is found that the crack growth rate decreases with the applied stress intensity factor in the initial stage of fatigue crack growth. Depending on the applied load and the amount of transformation, the growth rate either goes through a minimum before increasing to the normal crack regime, or the rate continues to decrease until the crack is arrested. A detailed parametric study of the phenomenon of fatigue crack arrest in composite coatings based on oxide ceramics and chrome carbide reveals that the combination of transformation strength parameter and applied load determines whether or not crack arrest will occur, irrespective of the initial crack length. Based on the parametric study a simple linear relationship between the applied load and the minimum transformation strength parameter necessary to cause crack arrest has been developed. it will be found useful in the design against fatigue by predicting the maximum toad at which crack arrest can be expected.

  5. Numerical Simulation of the Detonation Propagation in Silicon Carbide Shell

    NASA Astrophysics Data System (ADS)

    Balagansky, Igor; Terechov, Anton

    2013-06-01

    Last years it was experimentally shown that in condensed high explosive charges (HE) placed in silicon carbide shell with sound velocity greater than the detonation velocity in HE, there may be observed interesting phenomena. Depending on the conditions, as an increase or decrease of the detonation velocity and pressure on the detonation front can be observed. There is also the distortion of the detonation front until the formation of a concave front. For a detailed explanation of the physical nature of the phenomenon we have provided numerical simulation of detonation wave propagation in Composition B HE charge, which was placed in silicon carbide shell. Modeling was performed with Ansys Autodyn in 2D-axis symmetry posting on an Eulerian mesh. Special attention was paid to selection of the parameters values in Lee-Tarver kinetic equation for HE and choice of constants to describe behavior of the ceramics. For comparison, also we have carried out the modeling of propagation of detonation in a completely similar assembly with brass shell. The simulation results agree well with the experimental data. In particular, in silicon carbide shell distortion of the detonation front was observed. A characteristic feature of the process is the pressure waves propagating in the direction of the axis of symmetry on the back surface of the detonation front.

  6. Carbide coated fibers in graphite-aluminum composites

    NASA Technical Reports Server (NTRS)

    Imprescia, R. J.; Levinson, L. S.; Reiswig, R. D.; Wallace, T. C.; Williams, J. M.

    1975-01-01

    The NASA-supported program at the Los Alamos Scientific Laboratory (LASL) to develop carbon fiber-aluminum matrix composites is described. Chemical vapor deposition (CVD) was used to uniformly deposit thin, smooth, continuous coats of TiC on the fibers of graphite tows. Wet chemical coating of fibers, followed by high-temperature treatment, was also used, but showed little promise as an alternative coating method. Strength measurements on CVD coated fiber tows showed that thin carbide coats can add to fiber strength. The ability of aluminum alloys to wet TiC was successfully demonstrated using TiC-coated graphite surfaces. Pressure-infiltration of TiC- and ZrC-coated fiber tows with aluminum alloys was only partially successful. Experiments were performed to evaluate the effectiveness of carbide coats on carbon as barriers to prevent reaction between alluminum alloys and carbon. Initial results indicate that composites of aluminum and carbide-coated graphite are stable for long periods of time at temperatures near the alloy solidus.

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

    PubMed

    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.

  8. Bonding and Integration Technologies for Silicon Carbide Based Injector Components

    NASA Technical Reports Server (NTRS)

    Halbig, Michael C.; Singh, Mrityunjay

    2008-01-01

    Advanced ceramic bonding and integration technologies play a critical role in the fabrication and application of silicon carbide based components for a number of aerospace and ground based applications. One such application is a lean direct injector for a turbine engine to achieve low NOx emissions. Ceramic to ceramic diffusion bonding and ceramic to metal brazing technologies are being developed for this injector application. For the diffusion bonding, titanium interlayers (PVD and foils) were used to aid in the joining of silicon carbide (SiC) substrates. The influence of such variables as surface finish, interlayer thickness (10, 20, and 50 microns), processing time and temperature, and cooling rates were investigated. Microprobe analysis was used to identify the phases in the bonded region. For bonds that were not fully reacted an intermediate phase, Ti5Si3Cx, formed that is thermally incompatible in its thermal expansion and caused thermal stresses and cracking during the processing cool-down. Thinner titanium interlayers and/or longer processing times resulted in stable and compatible phases that did not contribute to microcracking and resulted in an optimized microstructure. Tensile tests on the joined materials resulted in strengths of 13-28 MPa depending on the SiC substrate material. Non-destructive evaluation using ultrasonic immersion showed well formed bonds. For the joining technology of brazing Kovar fuel tubes to silicon carbide, preliminary development of the joining approach has begun. Various technical issues and requirements for the injector application are addressed.

  9. Parallel microwave chemistry in silicon carbide microtiter platforms: a review.

    PubMed

    Kappe, C Oliver; Damm, Markus

    2012-02-01

    In this review, applications of silicon carbide-based microtiter platforms designed for use in combination with dedicated multimode microwave reactors are described. These platforms are employed not only for the efficient parallel synthesis of compound libraries, but also in the context of high-throughput reaction screening/optimization and a number of other (bio)analytical and biomedical applications. Since the semiconducting plate material (silicon carbide) is strongly microwave absorbing and possesses high thermal conductivity, no temperature gradients across the microtiter plate exist. Therefore, many of the disadvantages experienced in attempting to perform microtiter plate chemistry under conventional microwave conditions can be eliminated. In general, the silicon carbide-based microtiter platforms allow sealed vessel processing (either directly in the well or in glass vials placed into the wells) of volumes ranging from 0.02-3.0 mL at a maximum temperature/pressure limit of 200°C/20 bar. Depending on the specific plate and rotor configuration, a maximum of 80-192 transformations can be carried out in parallel in a single microwave irradiation experiment under strict temperature control. A platform type utilizing HPLC/GC vials as reaction vessels allows analysis directly from the reaction vessel eliminating the need for a transfer step from the reaction to the analysis vial. The latter system is particularly useful for analytical applications as well as reaction optimization/screening.

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

    PubMed

    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.

  11. Properties of Alloys of Zirconium and Niobium Carbides in Their Homogeneity Domain,

    DTIC Science & Technology

    ZIRCONIUM COMPOUNDS, ELECTRICAL PROPERTIES), (*NIOBIUM COMPOUNDS, ELECTRICAL PROPERTIES), (*REFRACTORY MATERIALS, CARBIDES), ELECTRICAL RESISTANCE, HALL EFFECT, MAGNETIC PROPERTIES, THERMAL PROPERTIES, SEEBECK EFFECT , USSR

  12. Formation Energies and Electronic Properties of Vanadium Carbides Found in High Strength Steel Alloys

    NASA Astrophysics Data System (ADS)

    Limmer, Krista; Medvedeva, Julia

    2013-03-01

    Carbide formation and stabilization in steels is of great interest owing to its effect on the microstructure and properties of the Fe-based alloys. The appearance of carbides with different metal/C ratios strongly depends on the carbon concentration, alloy composition as well as the heat treatment. Strong carbide-forming elements such as Ti, V, and Nb have been used in microalloyed steels; with VC showing an increased solubility in the iron matrix as compared with TiC and NbC. This allows for dissolution of the VC into the steel during heating and fine precipitation during cooling. In addition to VC, the primary vanadium carbide with cubic structure, a wide range of non-stoichiometric compositions VCy with y varying from 0.72 to 0.88, has been observed. This range includes two ordered compounds, V8C7 and V6C5. In this study, first-principles density functional theory (DFT) is employed to examine the stability of the binary carbides by calculating their formation energies. We compare the local structures (atomic coordination, bond distances and angles) and the density of states in optimized geometries of the carbides. Further, the effect of alloying additions, such as niobium and titanium, on the carbide stabilization is investigated. We determine the energetically preferable substitutional atom location in each carbide and study the impurity distribution as well as its role in the carbide formation energy and electronic structure.

  13. Influence of the matrix structure and properties on the crack resistance of sintered carbides

    SciTech Connect

    Novikov, N.V.; Devin, L.N.; Mitlikin, M.D.; Ul'yanenko, A.P.

    1985-05-01

    This paper presents the results of an automatic analysis of the structure of tungsten-cobalt sintered carbides with 6-25% weight of the binder phase and shows the possibility of their practical use for improvement of the mechanical properties of the materials. The authors conclude that accurate determination of the structural parameters of sintered carbides has made it possible to establish the yield strengths of the matrix material of different types of tungsten-cobalt sintered carbides and to determine those for which an increase in crack resistance is possible. The effect of the increase in fracture toughness of sintered carbides with an increase in loading rate is also explained.

  14. Tunable carbon nanotube-tungsten carbide nanoparticles heterostructures by vapor deposition

    SciTech Connect

    Xia, Min; Guo, Hongyan; Ge, Changchun; Yan, Qingzhi Lang, Shaoting

    2014-05-14

    A simple, versatile route for the synthesis of carbon nanotube (CNT)-tungsten carbide nanoparticles heterostructures was set up via vapor deposition process. For the first time, amorphous CNTs (α-CNTs) were used to immobilized tungsten carbide nanoparticles. By adjusting the synthesis and annealing temperature, α-CNTs/amorphous tungsten carbide, α-CNTs/W{sub 2}C, and CNTs/W{sub 2}C/WC heterostructures were prepared. This approach provides an efficient method to attach other metal carbides and other nanoparticles to carbon nanotubes with tunable properties.

  15. Research and Development on Advanced Silicon Carbide Thin Film Growth Techniques and Fabrication of High Power and Microwave Frequency Silicon Carbide-Based Device Structures

    DTIC Science & Technology

    1991-12-01

    AD-A243 531IIII!IIHUHllAlll| DTIC Annual Letter Report EL Vr DECA S C Research and Development on Advanced Silicon Carbide Thin Film Growth...Techniques and Fabrication of High Power and Microwave Frequency Silicon Carbide -Based Device Structures Supported under Grant #N00014-88-K-0341/P00002 Office...Letter l/,1- 2 3 lj9 l 4. TITLE AND SUBTITLE Research and Develp~nt on Advanced S. FUNDING NUMBERS Silicon Carbide Thin Film .Growth Techniques and R&T

  16. Tungsten Carbide-Cobalt with Nano-Crystalline Tungsten Carbide Platelets ---Synthesis, Processing, Sintering and Properties

    NASA Astrophysics Data System (ADS)

    Zhong, Yang

    Tungsten Carbide --- Cobalt (WC-Co) is one of the most important ceramic-metal composites, which has been used in variety areas of different industries. Future applications of WC-Co in more areas of industries require higher hardness and fracture toughness. Current technology of synthesis, processing and sintering of WC-Co barely enhances the hardness and fracture toughness of WC-Co simultaneously (including nanostructured WC-Co). Within this project, a new approach of effectively controlling the structure of WC to lead to the simultaneous enhancement of hardness and fracture toughness has been investigated. The nano-WC platelet is proposed to be promising for the simultaneous enhancement. Several different aspects related to the formation of nano-WC platelets are studied. A new and effective method to produce nanostructured WC-Co powder is established in this study. This method is a combination of high energy milling and carbothermic reduction of the mixture of tungsten oxide (WO 3) and cobalt oxide (Co3O4). The condition to remove the free carbon without decarburization of WC has been achieved by thermodynamic analysis and coupled experiments. By the utilization of density functional theory simulations and Wulff construction, the equilibrium shape of WC crystals inside WC-Co is predicted to be bulky structure instead of platelet structure. The growth mechanisms for the WC in commercial coarse grained WC-Co under different heating conditions are observed. It is found that the heating temperature is a critical factor affecting the structure of WC inside WC-Co. Higher temperature will lead to the layer-by-layer structure formation due to higher thermodynamic driving force. The in situ formation of nano-WC platelet is achieved using different W containing sources. The formation mechanism has been studied. Bulk WC-Co samples with nano-WC platelets are obtained through sintering of WC-Co nano-powder at relatively low sintering temperatures. The mechanical properties of

  17. First Principle Calculations of a Family of Noble Metal Nitrides and Carbides

    NASA Astrophysics Data System (ADS)

    Li, Linyan

    The structural and electronic properties of selected noble metal nitrides and carbides are studied using the local density approximation and the generalized gradient approximation. The zinc-blende and rock-salt structures are employed. The nitride and carbide of palladium have high bulk modulus. From the DOS, the MX (M = Pd, Ag, Au; X = N, C) compound display metallic nature.

  18. Development of a Robust Tri-Carbide Fueled Reactor for Multimegawatt Space Power and Propulsion Applications

    SciTech Connect

    Samim Anghaie; Travis W. Knight; Johann Plancher; Reza Gouw

    2004-08-11

    An innovative reactor core design based on advanced, mixed carbide fuels was analyzed for nuclear space power applications. Solid solution, mixed carbide fuels such as (U,Zr,Nb)c and (U,Zr, Ta)C offer great promise as an advanced high temperature fuel for space power reactors.

  19. Decoupling of silicon carbide optical sensor response for temperature and pressure measurements

    NASA Astrophysics Data System (ADS)

    Chakravarty, A.; Quick, N. R.; Kar, A.

    2007-10-01

    Single crystal silicon carbide is a chemically inert transparent material with superior oxidation-resistant properties at elevated temperatures compared to black polycrystalline silicon carbide substrates. These improved properties make crystalline silicon carbide a good optical sensor material for harsh environments such as combustion chambers and turbine systems. Interferometric optical sensors are orders of magnitude more sensitive than electrical sensors and are proposed for these applications. Silicon carbide itself behaves as a Fabry-Pérot etalon eliminating the need for an external interferometer for any measurement using this silicon carbide as a sensor. The principle of the optical sensor in this study is the temperature- and pressure-dependent refractive index of silicon carbide, which can be used to determine the temperatures and pressures of gases that are in contact with silicon carbide. Interference patterns produced by a silicon carbide (4H-SiC) wafer due to multiple reflections of a helium-neon laser beam of wavelength of 632.8nm have been obtained at temperatures up to 500°C and pressures up to 600psi. The pattern changes for the same gas at different temperatures and pressures and for different gases at the same temperature and pressure. The refractive index at the wafer-gas interface is calculated from the interference pattern and the refractive index gradients with respect to temperature and pressure, respectively, are also determined. Decoupling temperature and pressure using these gradients and the measured reflectivity data are discussed in this paper.

  20. Molecular dynamics investigation of the interaction of dislocations with carbides in BCC Fe

    NASA Astrophysics Data System (ADS)

    Granberg, F.; Terentyev, D.; Nordlund, K.

    2015-06-01

    Different types of carbides are present in many steels used as structural materials. To safely use steel in demanding environments, like nuclear power plants, it is important to know how defects will affect the mechanical properties of the material. In this study, the effect of carbide precipitates on the edge dislocation movement is investigated. Three different types of carbides were investigated by means of molecular dynamics, with a Tersoff-like bond order interatomic potential by Henriksson et al. The obstacles were 4 nm in diameter and were of Fe3C- (cementite-), Fe23C6- and Cr23C6-type. The critical unpinning stress was calculated for each type at different temperatures, to get the temperature-dependent obstacle strength. The results showed a decreasing critical stress with increasing temperature, consistent with previous studies. The critical unpinning stress was seen to be dependent on the type of carbide, but the differences were small. A difference was also observed between the obstacles with the same structure, but with different composition. This study shows the relation between the existing Cr23C6 carbide and the experimentally non-existing Fe23C6 carbide, which needs to be used as a model system for investigations with interatomic potentials not able to describe the interaction of Cr in the Fe-C-system. We found the difference to be a between 7% and 10% higher critical unpinning stress for the chromium carbide, than for the iron carbide of the same type.

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

    NASA Astrophysics Data System (ADS)

    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. .

  2. Preparation of molybdenum carbides with multiple morphologies using surfactants as carbon sources

    SciTech Connect

    Wang, Hongfen; Wang, Zhiqi; Chen, Shougang

    2012-10-15

    Molybdenum carbides with surfactants as carbon sources were prepared using the carbothermal reduction of the appropriate precursors (molybdenum oxides deposited on surfactant micelles) at 1023 K under hydrogen gas. The carburized products were characterized using scanning electron microscopy (SEM), X-ray diffraction and BET surface area measurements. From the SEM images, hollow microspherical and rod-like molybdenum carbides were observed. X-ray diffraction patterns showed that the annealing time of carburization had a large effect on the conversion of molybdenum oxides to molybdenum carbides. And BET surface area measurements indicated that the difference of carbon sources brought a big difference in specific surface areas of molybdenum carbides. - Graphical abstract: Molybdenum carbides having hollow microspherical and hollow rod-like morphologies that are different from the conventional monodipersed platelet-like morphologies. Highlights: Black-Right-Pointing-Pointer Molybdenum carbides were prepared using surfactants as carbon sources. Black-Right-Pointing-Pointer The kinds of surfactants affected the morphologies of molybdenum carbides. Black-Right-Pointing-Pointer The time of heat preservation at 1023 K affected the carburization process. Black-Right-Pointing-Pointer Molybdenum carbides with hollow structures had larger specific surface areas.

  3. Method of enhanced lithiation of doped silicon carbide via high temperature annealing in an inert atmosphere

    DOEpatents

    Hersam, Mark C.; Lipson, Albert L.; Bandyopadhyay, Sudeshna; Karmel, Hunter J; Bedzyk, Michael J

    2014-05-27

    A method for enhancing the lithium-ion capacity of a doped silicon carbide is disclosed. The method utilizes heat treating the silicon carbide in an inert atmosphere. Also disclosed are anodes for lithium-ion batteries prepared by the method.

  4. A universal method to synthesize nanoscale carbides as electrocatalyst supports towards oxygen reduction reaction.

    PubMed

    He, Guoqiang; Yan, Zaoxue; Ma, Xueming; Meng, Hui; Shen, Pei Kang; Wang, Chengxin

    2011-09-01

    We have developed a general ion-exchange method of preparing a composite of low nanometre size carbide particles with controllable size less than 10 nm on carbon foams. The nanoarchitectures of the carbide nanoparticles on carbon foam are used to load Pt nanoparticles as electrocatalysts which show enhanced activity for the oxygen reduction reaction.

  5. Synthesis of nanocrystalline molybdenum carbide (Mo{sub 2}C) by solution route

    SciTech Connect

    Patel, Manish Subrahmanyam, J.

    2008-08-04

    Nanocrystalline molybdenum carbide (Mo{sub 2}C) of less than 10 nm size was synthesized by solution route. The process temperature and composition of raw materials were optimized by thermodynamic equilibrium calculation. The raw materials as well as synthesized nanocrystalline molybdenum carbide were characterized by X-ray diffraction (XRD) and thermogravimetric analysis/differential thermal analysis (TGA/DTA)

  6. PREPARATION OF B-MODIFICATION SILICON CARBIDE ALLOYED WITH VARIOUS IMPURITIES,

    DTIC Science & Technology

    The beta-modification of silicon carbide can be obtained by any of the following methods: (1) synthesis from silicon and carbon (graphite) at 1400...certain metals, a process based on the substantial temperature variation of the solubility of silicon carbide in fused metals; beta-SiC is obtained in

  7. THE CRYSTAL STRUCTURE OF THE NEW SILICON CARBIDE POLYMORPH 69R,

    DTIC Science & Technology

    The 69R polymorph is one of the 32 silicon carbide polymorphs recently discovered by us. The space group is R3m and the unit cell is hexagonal with...and in two industrial silicon carbide crystal plates. They all pair with the fundamental type 6H. The five ways of pairing are: 6H + 69R + 87R, 6H

  8. Process for preparing metal-carbide-containing microspheres from metal-loaded resin beads

    DOEpatents

    Beatty, Ronald L.

    1977-01-01

    An improved process for producing porous spheroidal particles consisting of a metal carbide phase dispersed within a carbon matrix is described. According to the invention metal-loaded ion-exchange resin microspheres which have been carbonized are coated with a buffer carbon layer prior to conversion of the oxide to carbide in order to maintain porosity and avoid other adverse sintering effects.

  9. Silicon nitride/silicon carbide composite densified materials prepared using composite powders

    DOEpatents

    Dunmead, S.D.; Weimer, A.W.; Carroll, D.F.; Eisman, G.A.; Cochran, G.A.; Susnitzky, D.W.; Beaman, D.R.; Nilsen, K.J.

    1997-07-01

    Prepare silicon nitride-silicon carbide composite powders by carbothermal reduction of crystalline silica powder, carbon powder and, optionally, crystalline silicon nitride powder. The crystalline silicon carbide portion of the composite powders has a mean number diameter less than about 700 nanometers and contains nitrogen. The composite powders may be used to prepare sintered ceramic bodies and self-reinforced silicon nitride ceramic bodies.

  10. Effect of an atmosphere on the wetting of titanium carbide with liquid low-carbon steel

    NASA Astrophysics Data System (ADS)

    Chumanov, I. V.; Anikeev, A. N.

    2016-12-01

    The methodology and the experimental studies of the influence of an atmosphere on the wetting of titanium carbide with liquid low-carbon steel in various atmospheres are presented. The wetting of titanium carbide in an oxidizing atmosphere is found to be limited (the wetting angle is 97°-110°), while complete wetting takes place in vacuum and in an argon atmosphere.

  11. Zirconium carbide as an electrocatalyst for the chromous-chromic redox couple

    NASA Technical Reports Server (NTRS)

    Gahn, R. F.; Reid, M. A.; Yang, C. Y. (Inventor)

    1981-01-01

    Zirconium carbide is used as a catalyst in a REDOX cell for the oxidation of chromous ions to chromic ions and for the reduction of chromic ions to chromous ions. The zirconium carbide is coated on an inert electronically conductive electrode which is present in the anode fluid of the cell.

  12. WETTABILITY OF ALUMINUM OXIDE AND CARBIDES BY METALS OF THE IRON GROUP,

    DTIC Science & Technology

    There was obtained the dependency of surface ten sion, the contact angle of wetting, the work of adhesion, and the interphase tensions of the alloys...cobalt. Titanium carbide is not com pletely wetted by nickel. The dependency of the contact angle of wetting by nickel of carbides of the system TiC-WC

  13. The Effects of Carbide Characteristics on the Performance of Tungsten Carbide-Based Composite Overlays, Deposited by Plasma-Transferred Arc Welding

    NASA Astrophysics Data System (ADS)

    Fisher, G.; Wolfe, T.; Meszaros, K.

    2013-06-01

    In Alberta, there are huge quantities of ore processed to remove bitumen from oil sands deposits. The scale of production generates very aggressive tribocorrosive conditions during the mining, extraction, and upgrading processes. It is common to apply tungsten carbide-based composite overlays to improve the reliability and extend service lives of equipment and components. The performance of the applied overlays is largely dependent on the selection of the carbide type and the wear environment. This paper will evaluate overlays containing macrocrystalline, angular eutectic, and spherical eutectic tungsten carbides and discuss the performance of the overlays with a focus on carbide properties and the interactions between the service conditions and the composite material. This discussion will demonstrate how effective selection of protective materials can improve the reliability of oil sands equipment.

  14. Nuclear transformation of Chlamydomonas reinhardtii with silicon carbide fibers

    SciTech Connect

    Dunahay, T.G. )

    1992-01-01

    Efficient nuclear transformation of cell wall-deficient strains of the green alga Chlamydomonas reinhardtii can be accomplished by vortexing the cells in the presence of glass beads and polyethylene glycol (Kindle 1990 PNAS 87:1228). Intact (walled) cells can also be transformed using this protocol, but at very low efficiencies. Two recent reports have described the use of silicon carbide fibers to mediate DNA entry into plant suspension cells (Kaeppler et al. 1990 Plant Cell Rep. 9:414; Asano et al. 1991 Plant Sci. 79:247). The author has found that nuclear transformation efficiencies of walled cells of C. reinhardtii can be increased 3 to 10 fold by vortexing the cells in the presence of silicon carbide fibers and PEG. Using a modification of the glass bead transformation procedure, the wild-type nitrate reductase structural gene was used to complement a NR-deficient mutant of C. reinhardtii, nit-1-305. The transformation efficiency increased with longer vortexing times, although the absolute number of transformants varied between experiments, ranging from 10 to 40 transformants per 10[sup 7] cells. In contrast to vortexing with glass beads, cell viability was very high, with greater than 80% cell survival even after vortexing for 10 minutes. Neither cell death nor transformation efficiency increased when cell wall-deficient mutants (cw15 nit-1-305) were used as compared to intact cells. Experiments are in progress to test the applicability of silicon carbide-mediated transformation to other algal strains for which cell wall mutants or protoplasting procedures are unavailabile.

  15. Irradiation and annealing of p-type silicon carbide

    SciTech Connect

    Lebedev, Alexander A.; Bogdanova, Elena V.; Grigor'eva, Maria V.; Lebedev, Sergey P.; Kozlovski, Vitaly V.

    2014-02-21

    The development of the technology of semiconductor devices based on silicon carbide and the beginning of their industrial manufacture have made increasingly topical studies of the radiation hardness of this material on the one hand and of the proton irradiation to form high-receptivity regions on the other hand. This paper reports on a study of the carrier removal rate (V{sub d}) in p-6H-SiC under irradiation with 8 MeV protons and of the conductivity restoration in radiation- compensated epitaxial layers of various p-type silicon carbide polytypes. V{sub d} was determined by analysis of capacitance-voltage characteristics and from results of Hall effect measurements. It was found that the complete compensation of samples with the initial value of Na - Nd ≈ 1.5 × 10{sup 18} cm{sup −3} occurs at an irradiation dose of ∼1.1 × 10{sup 16} cm{sup −2}. It is shown that specific features of the sublimation layer SiC (compared to CVD layers) are clearly manifested upon the gamma and electron irradiation and are hardly noticeable under the proton and neutron irradiation. It was also found that the radiation-induced compensation of SiC is retained after its annealing at ≤1000°C. The conductivity is almost completely restored at T ≥ 1200°C. This character of annealing of the radiation compensation is independent of a silicon carbide polytype and the starting doping level of the epitaxial layer. The complete annealing temperatures considerably exceed the working temperatures of SiC-based devices. It is shown that the radiation compensation is a promising method in the technology of high-temperature devices based on SiC.

  16. GEN IV: Carbide Fuel Elaboration for the 'Futurix Concepts' experiment

    SciTech Connect

    Vaudez, Stephane; Riglet-Martial, Chantal; Paret, Laurent; Abonneau, Eric

    2007-07-01

    In order to collect information on the behaviour of the future GFR (Gas Fast Reactor) fuel under fast neutron irradiation, an experimental irradiation program, called 'Futurix-concepts' has been launched at the CEA. The considered concept is a composite material made of a fissile fuel embedded in an inert matrix. Fissile fuel pellets are made of UPuN or UPuC while matrices are SiC for the carbide fuel and TiN for the nitride fuel. This paper focuses on the description of the carbide composite fabrication. The UPuC pellets are manufactured using a metallurgical powder process. Fabrication and handling of the fuels are carried out in gloveboxes under a nitrogen atmosphere. Carbide fuel is synthesized by carbothermic reduction under vacuum of a mixture of actinide oxide and graphite carbon up to 1550 deg. C. After ball milling, the powder is pressed to create hexagonal or spherical compacts. They are then sintered up to 1750 deg. C in order to obtain a density of 85 % of the theoretical one. The sintered pellets are inserted into an inert and tight capsule of SiC. In order to control the gap between the fuel and the matrix precisely, the pellets are abraded. The inert matrix is then filled with the pellets and the whole system is sealed by a BRASiC{sup R} process at high temperature under a helium atmosphere. Fabrication of the sample to be irradiated was done in 2006 and the irradiation began in May 2007 in the PHENIX reactor. This presentation will detail and discuss the results obtained during this fabrication phase. (authors)

  17. Promotion of the Growth of Boron-Carbide Nanowires

    NASA Astrophysics Data System (ADS)

    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

  18. Arc Synthesis of Fullerenes from the Carbide of Waste Cloths

    NASA Astrophysics Data System (ADS)

    Hayashi, Koichiro; Mieno, Tetsu

    2000-09-01

    A great many scraps of cotton cloth are disposed of as industrial waste through making clothes. The purpose of this study is to transform the waste into very valuable carbon compounds, that is, fullerenes. The scraps were piled and carbonized in air at 1050°C. By carbonization, the weight of the scraps decreased to 16-18%. Carbide from the scraps was used as the raw material for synthesizing fullerenes with the \\mbi{J}×\\mbi{B} arc discharge method. The soot that was deposited on the inside of the vacuum chamber contained C60 (>0.05 wt%), C70 and higher fullerenes.

  19. Tungsten carbide laser alloying of a low alloyed steel

    NASA Astrophysics Data System (ADS)

    Cojocaru, Mihai; Taca, Mihaela

    1996-10-01

    Laser alloying is a way to change the composition of metal surfaces in order to improve their corrosion-resistance, high-temperature strength and hardness. The results of a structural and phase analysis of a tungsten carbide based surface layer prepared by laser alloying of a low carbon steel substrate are presented. Structure, phase composition and microhardness of surface alloyed layers have been investigated. The surface of the samples exhibited a thin layer with a different chemical and phase composition. An increase in alloyed surface hardness and wear-resistance was observed.

  20. Crystallization of silicon carbide thin films by pulsed laser irradiation

    NASA Astrophysics Data System (ADS)

    De Cesare, G.; La Monica, S.; Maiello, G.; Masini, G.; Proverbio, E.; Ferrari, A.; Chitica, N.; Dinescu, M.; Alexandrescu, R.; Morjan, I.; Rotiu, E.

    1996-10-01

    Pulsed laser irradiation at low incident fluences was demonstrated to be effective for the crystallization of amorphous hydrogenated silicon carbide (a-SiC:H) films deposited on Si wafers. The amorphous films, with a carbon content in the range 30-50%, were deposited on (100) Si wafers by low temperature plasma enhanced chemical vapor deposition (PECVD). The crystallization treatment was carried out by a multipulse KrF excimer laser. The crystallinity modifications induced by the laser treatment were evidenced by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. An important increase of the microhardness was evidenced as an effect of the laser treatment.

  1. Improvement of contact resistances on plasma-exposed silicon carbide

    NASA Astrophysics Data System (ADS)

    Cheung, R.; Hay, J.; van der Drift, E.; Gao, W.

    2000-11-01

    We demonstrate improvements in the specific contact resistance of unannealed ohmic contacts by at least one order of magnitude on undoped 6H-SiC (silicon carbide, SiC). The improved contacts with a specific resistance of 0.3 Ω cm 2 have been fabricated on SiC surfaces exposed to an argon plasma at -80 V for 2.5 min. Under these plasma conditions, the top monolayers of the plasma-exposed SiC surface is silicon rich as revealed by X-ray photoelectron spectroscopy, and the surface roughness is decreased by a factor of 2 from atomic force microscopy analysis.

  2. Formation of titanium carbide coating with micro-porous structure

    NASA Astrophysics Data System (ADS)

    Luo, Yong; Ge, Shirong; Jin, Zhongmin; Fisher, John

    2010-03-01

    Micro-porous titanium carbide coating was successfully synthesized in a vacuum gas carburizing furnace by using a sequential diffusion technology. The composition and structure of the as-synthesized TiC were examined by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and glow discharge mass spectrometry (GDMS), and scanning electron microscopy (SEM). All of the XRD, XPS and GDMS analysis results indicate that carbon atoms effectively diffused into the titanium alloys and formed a uniform acicular TiC coating with micro-porous structure.

  3. Synthesis of functional acetylene derivatives from calcium carbide.

    PubMed

    Lin, Zhewang; Yu, Dingyi; Sum, Yin Ngai; Zhang, Yugen

    2012-04-01

    AHA Erlebnis: CaC(2), used to produce acetylene until several decades ago, is re-emerging as a cheap, sustainable resource synthesized from coal and lignocellulosic biomass. We report efficient catalytic protocols for the synthesis of functional acetylene derivatives from CaC(2) through aldehyde, alkyne, and amine (AAA) as well as alkyne, haloalkane, and amine (AHA) couplings, and in addition demonstrate its use in click and Sonogashira chemistry, showing that calcium carbide is a sustainable and cost-efficient carbon source.

  4. Silicon carbide alloys: Research reports in materials science

    SciTech Connect

    Dobson, M.M.

    1986-01-01

    The book draws from work done on other silicon materials, silicon nitrides and sialons, to emphasize the importance of the SiC system. A comprehensive treatment of non-oxide silicon ceramics, this work is of special interest to researchers involved in ceramics, materials science, and high-temperature technology. This book covers the alloys of silicon carbide with aluminum nitride. Crystallography and experimental methods including sample preparation, furnace methods, X-ray and electron diffraction, optical and electron microscopy and chemical analysis are covered.

  5. First-principles study of transition metal carbides

    NASA Astrophysics Data System (ADS)

    Connétable, Damien

    2016-12-01

    This study investigates the physical properties of transition metal carbides compounds associated with the Nb-C, Ti-C, Mo-C and W-C alloys systems using first-principles calculations. The ground-state properties (lattice parameters, cohesive energies and magnetism) were analyzed and compared to the experimental and theoretical literature. The simulations are in excellent agreement with experimental findings concerning atomic positions and structures. Elastic properties, computed using a finite-differences approach, are then discussed in detail. To complete the work, their lattice dynamics properties (phonon spectra) were investigated. These results serve to establish that some structures, which are mechanically stable, are dynamically unstable.

  6. Process for preparing fine grain silicon carbide powder

    DOEpatents

    Wei, G.C.

    Finely divided silicon carbide powder is obtained by mixing colloidal silica and unreacted phenolic resin in either acetone or methanol, evaporating solvent from the obtained solution to form a gel, drying and calcining the gel to polymerize the phenolic resin therein, pyrolyzing the dried and calcined gel at a temperature in the range of 500 to 1000/sup 0/C, and reacting silicon and carbon in the pyrolyzed gel at a temperature in the range of 1550 to 1700/sup 0/C to form the powder.

  7. Synthesis of silicon carbide nanocrystals from waste polytetrafluoroethylene.

    PubMed

    Wang, Liangbiao; Cheng, Qinglin; Qin, Hengfei; Li, Zhongchun; Lou, Zhengsong; Lu, Juanjuan; Zhang, Junhao; Zhou, Quanfa

    2017-02-28

    Resource utilization of waste plastic could solve the problem of environmental pollution and simultaneously relieve energy shortages, achieving sustainable development. In this study, the conversion of waste polytetrafluoroethylene (PTFE) to cubic silicon carbide (SiC) nanoparticles has been described. The structures and morphologies of the obtained SiC were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, the FTIR spectrum of the obtained SiC sample suggests that the waste PTFE was completely converted into SiC in our approach.

  8. Method of fabricating silicon carbide coatings on graphite surfaces

    DOEpatents

    Varacalle, Jr., Dominic J.; Herman, Herbert; Burchell, Timothy D.

    1994-01-01

    The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1600.degree.C. which transforms the coating to silicon carbide.

  9. Method of fabricating silicon carbide coatings on graphite surfaces

    DOEpatents

    Varacalle, D.J. Jr.; Herman, H.; Burchell, T.D.

    1994-07-26

    The vacuum plasma spray process produces well-bonded, dense, stress-free coatings for a variety of materials on a wide range of substrates. The process is used in many industries to provide for the excellent wear, corrosion resistance, and high temperature behavior of the fabricated coatings. In this application, silicon metal is deposited on graphite. This invention discloses the optimum processing parameters for as-sprayed coating qualities. The method also discloses the effect of thermal cycling on silicon samples in an inert helium atmosphere at about 1,600 C which transforms the coating to silicon carbide. 3 figs.

  10. Temperature Induced Voltage Offset Drifts in Silicon Carbide Pressure Sensors

    NASA Technical Reports Server (NTRS)

    Okojie, Robert S.; Lukco, Dorothy; Nguyen, Vu; Savrun, Ender

    2012-01-01

    We report the reduction of transient drifts in the zero pressure offset voltage in silicon carbide (SiC) pressure sensors when operating at 600 C. The previously observed maximum drift of +/- 10 mV of the reference offset voltage at 600 C was reduced to within +/- 5 mV. The offset voltage drifts and bridge resistance changes over time at test temperature are explained in terms of the microstructure and phase changes occurring within the contact metallization, as analyzed by Auger electron spectroscopy and field emission scanning electron microscopy. The results have helped to identify the upper temperature reliable operational limit of this particular metallization scheme to be 605 C.

  11. PROCESS OF COATING GRAPHITE WITH NIOBIUM-TITANIUM CARBIDE

    DOEpatents

    Halden, F.A.; Smiley, W.D.; Hruz, F.M.

    1961-07-01

    A process of coating graphite with niobium - titanium carbide is described. It is found that the addition of more than ten percent by weight of titanium to niobium results in much greater wetting of the graphite by the niobium and a much more adherent coating. The preferred embodiment comprises contacting the graphite with a powdered alloy or mixture, degassing simultaneously the powder and the graphite, and then heating them to a high temperature to cause melting, wetting, spreading, and carburization of the niobium-titanium powder.

  12. Enhanced magnetic anisotropy in cobalt-carbide nanoparticles

    SciTech Connect

    El-Gendy, AA; Qian, MC; Huba, ZJ; Khanna, SN; Carpenter, EE

    2014-01-13

    An outstanding problem in nano-magnetism is to stabilize the magnetic order in nanoparticles at room temperatures. For ordinary ferromagnetic materials, reduction in size leads to a decrease in the magnetic anisotropy resulting in superparamagnetic relaxations at nanoscopic sizes. In this work, we demonstrate that using wet chemical synthesis, it is possible to stabilize cobalt carbide nanoparticles which have blocking temperatures exceeding 570 K even for particles with magnetic domains of 8 nm. First principles theoretical investigations show that the observed behavior is rooted in the giant magnetocrystalline anisotropies due to controlled mixing between C p- and Co d-states. (C) 2014 AIP Publishing LLC.

  13. Diamond Growth on Carbide Surfaces Using a Selective Etching Technique

    DTIC Science & Technology

    1993-07-01

    nucleation when utilizing hexafluoroethane (C2F6 ) (b), perfluoropropane ( C3F8 ) (c), and octafluorocyclobutane (C4F8 ) (d). Carbon-fluorine atomic ratios...and roughen WC particles SiC: No modification Feed Gases: CF 4, C2F6, C3F8 , or C4F8 all at 1/2% - 3%, 1% 02, balance H2 Total Flow Rate: 200 sccm...1/2% CF 4, (b) 1/2% C2F6, (c) 1/2% C3F8 , and (d) 1/2% C4F8. Figure 6. Growth of diamond on tungsten carbide / 6% cobalt using various fluorocarbon

  14. The Oxidation of CVD Silicon Carbide in Carbon Dioxide

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Nguyen, QuynchGiao N.

    1997-01-01

    Chemically-vapor-deposited silicon carbide (CVD SiC) was oxidized in carbon dioxide (CO2) at temperatures of 1200-1400 C for times between 100 and 500 hours at several gas flow rates. Oxidation weight gains were monitored by thermogravimetric analysis (TGA) and were found to be very small and independent of temperature. Possible rate limiting kinetic laws are discussed. Oxidation of SiC by CO2 is negligible compared to the rates measured for other oxidants typically found in combustion environments: oxygen and water vapor.

  15. ε-Iron carbide as a low-temperature Fischer-Tropsch synthesis catalyst.

    PubMed

    Xu, Ke; Sun, Bo; Lin, Jun; Wen, Wen; Pei, Yan; Yan, Shirun; Qiao, Minghua; Zhang, Xiaoxin; Zong, Baoning

    2014-12-12

    ε-Iron carbide has been predicted to be promising for low-temperature Fischer-Tropsch synthesis (LTFTS) targeting liquid fuel production. However, directional carbidation of metallic iron to ε-iron carbide is challenging due to kinetic hindrance. Here we show how rapidly quenched skeletal iron featuring nanocrystalline dimensions, low coordination number and an expanded lattice may solve this problem. We find that the carbidation of rapidly quenched skeletal iron occurs readily in situ during LTFTS at 423-473 K, giving an ε-iron carbide-dominant catalyst that exhibits superior activity to literature iron and cobalt catalysts, and comparable to more expensive noble ruthenium catalyst, coupled with high selectivity to liquid fuels and robustness without the aid of electronic or structural promoters. This finding may permit the development of an advanced energy-efficient and clean fuel-oriented FTS process on the basis of a cost-effective iron catalyst.

  16. Accelerated carbide spheroidisation of 1.2343 tool steel by induction heating

    NASA Astrophysics Data System (ADS)

    Dlouhý, J.; Kövér, M.

    2015-12-01

    Tool steels undergo spheroidisation or soft annealing to enhance machinability and cold formability. Conventional soft annealing takes several hours. The final microstructure is composed of globular carbides in a ferritic matrix. We present an alternative process of carbide spheroidisation and steel softening. Accelerated carbide spheroidisation and refinement (ASR) was achieved by induction heating at temperatures close to the A1 temperature. The spheroidised structure was obtained in less than 5 minutes. The carbide particles that formed during the ASR were significantly finer than for the conventional soft annealing. The hardness after ASR was higher than the hardness after soft annealing because of the dispersion strengthening by finer and more densely distributed carbide particles. On the other hand, the fine structure is favourable for hardening. It enables smaller austenite grains and martensite laths to be obtained.

  17. Carbides in iron-rich Fe-Mn-Cr-Mo-Al-Si-C systems

    NASA Technical Reports Server (NTRS)

    Lemkey, F. D.; Gupta, H.; Nowotny, H.; Wayne, S. F.

    1984-01-01

    The optimization of high carbon iron-base superalloy properties with duplex microstructure gamma + M7C3 carbide requires analysis in the context of a seven-component system. Data are first provided here for the Fe-Mn-Cr-Mo-C quinary system, at 30 at. pct carbon. A characterization of competing carbides, according to a pseudoternary phase diagram at 35 wt pct iron, is made from isothermal sections. It is noted that while M7C3 and M3C carbides' occurrences are respectively favored at the Cr and Mn corners, the M2C carbide and molybdenum cementite are predominant with increasing amounts of Mo. Lattice parameters are reported for the various carbides.

  18. Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica

    NASA Astrophysics Data System (ADS)

    Luo, Xiaogang; Ma, Wenhui; Zhou, Yang; Liu, Dachun; Yang, Bin; Dai, Yongnian

    2010-11-01

    Silicon carbide nanowires have been synthesized at 1400 °C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core-shell structure and grow along <111> direction. The diameter of silicon carbide nanowires is about 50-200 nm and the length from tens to hundreds of micrometers. The vapor-solid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough core-shell interface.

  19. Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica.

    PubMed

    Luo, Xiaogang; Ma, Wenhui; Zhou, Yang; Liu, Dachun; Yang, Bin; Dai, Yongnian

    2009-11-11

    Silicon carbide nanowires have been synthesized at 1400 degrees C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core-shell structure and grow along <111> direction. The diameter of silicon carbide nanowires is about 50-200 nm and the length from tens to hundreds of micrometers. The vapor-solid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough core-shell interface.

  20. Development of refractory armored silicon carbide by infrared transient liquid phase processing

    NASA Astrophysics Data System (ADS)

    Hinoki, Tatsuya; Snead, Lance L.; Blue, Craig A.

    2005-12-01

    Tungsten (W) and molybdenum (Mo) were coated on silicon carbide (SiC) for use as a refractory armor using a high power plasma arc lamp at powers up to 23.5 MW/m 2 in an argon flow environment. Both tungsten powder and molybdenum powder melted and formed coating layers on silicon carbide within a few seconds. The effect of substrate pre-treatment (vapor deposition of titanium (Ti) and tungsten, and annealing) and sample heating conditions on microstructure of the coating and coating/substrate interface were investigated. The microstructure was observed by scanning electron microscopy (SEM) and optical microscopy (OM). The mechanical properties of the coated materials were evaluated by four-point flexural tests. A strong tungsten coating was successfully applied to the silicon carbide substrate. Tungsten vapor deposition and pre-heating at 5.2 MW/m 2 made for a refractory layer containing no cracks propagating into the silicon carbide substrate. The tungsten coating was formed without the thick reaction layer. For this study, small tungsten carbide grains were observed adjacent to the interface in all conditions. In addition, relatively large, widely scattered tungsten carbide grains and a eutectic structure of tungsten and silicon were observed through the thickness in the coatings formed at lower powers and longer heating times. The strength of the silicon carbide substrate was somewhat decreased as a result of the processing. Vapor deposition of tungsten prior to powder coating helped prevent this degradation. In contrast, molybdenum coating was more challenging than tungsten coating due to the larger coefficient of thermal expansion (CTE) mismatch as compared to tungsten and silicon carbide. From this work it is concluded that refractory armoring of silicon carbide by Infrared Transient Liquid Phase Processing is possible. The tungsten armored silicon carbide samples proved uniform, strong, and capable of withstanding thermal fatigue testing.

  1. Replacing precious metals with carbide catalysts for hydrogenation reactions

    SciTech Connect

    Ruijun, Hou; Chen, Jingguang G.; Chang, Kuan; Wang, Tiefeng

    2015-03-03

    Molybdenum carbide (Mo₂C and Ni/Mo₂C) catalysts were compared with Pd/SiO₂ for the hydrogenation of several diene molecules, 1,3- butadiene, 1,3- and 1,4-cyclohexadiene (CHD). Compared to Pd/SiO₂, Mo₂C showed similar hydrogenation rate for 1,3-butadiene and 1,3-CHD and even higher rate for 1,4-CHD, but with significant deactivation rate for 1,3-CHD hydrogenation. However, the hydrogenation activity of Mo₂C could be completely regenerated by H₂ treatment at 723 K for the three molecules. The Ni modified Mo₂C catalysts retained similar activity for 1,3-butadiene hydrogenation with significantly enhanced selectivity for 1-butene production. The 1-butene selectivity increased with increasing Ni loading below 15%. Among the Ni modified Mo₂C catalysts, 8.6%Ni/Mo₂C showed the highest selectivity to 1-butene, which was even higher selectivity than that over Pd/SiO₂. Compared to Pd/SiO₂, both Mo₂C and Ni/Mo₂C showed combined advantages in hydrogenation activity and catalyst cost reduction, demonstrating the potential to use less expensive carbide catalysts to replace precious metals for hydrogenation reactions.

  2. Preparation and characterization of zirconium carbide field emitters

    SciTech Connect

    Mackie, W.A.; Hinrichs, C.H. ); Davis, P.R. )

    1989-11-01

    The authors' report on experiments to determine the feasibility of using the refractory transition metal carbide ZrC as a stable field-emission cathode. Applications of such cathodes could include radiation-immune microcircuitry, flat-panel displays, e-beam lithography, and other uses where the need is for very high-density, small spot size electron sources. The primary emphasis of this paper is the preparation and analysis of methods needed to obtain stable electron emission from a cold field-emission cathode. CrC single-crystal specimens were prepared by arc floating zone refinement from sintered stock, yielding an average bulk stoichiometry of C/Zr = 0.913. Due to its brittle nature and the high temperatures required for cleaning of this carbide, new mounting methods were developed and are described. Emitter etching procedures are reported for ZrC, as well as {ital in situ} tip sharpening techniques of neon-ion bombardment and temperatures required for thermal cleaning. A temperature of 1500{degrees}C is required to remove adsorbates including oxygen. A clean ZrC field-emission pattern is shown. Ordering of work functions of various crystal planes is reported through field-emission microscopy and comparisons made with thermionic projection microscopy. Effective thermionic work functions are presented for clean surfaces to further support the ordering obtained. The ability of ZrC field emitters to operate at pressures far above those commonly found for field-emission cathodes is demonstrated.

  3. High Input Voltage, Silicon Carbide Power Processing Unit Performance Demonstration

    NASA Technical Reports Server (NTRS)

    Bozak, Karin E.; Pinero, Luis R.; Scheidegger, Robert J.; Aulisio, Michael V.; Gonzalez, Marcelo C.; Birchenough, Arthur G.

    2015-01-01

    A silicon carbide brassboard power processing unit has been developed by the NASA Glenn Research Center in Cleveland, Ohio. The power processing unit operates from two sources - a nominal 300-Volt high voltage input bus and a nominal 28-Volt low voltage input bus. The design of the power processing unit includes four low voltage, low power supplies that provide power to the thruster auxiliary supplies, and two parallel 7.5 kilowatt power supplies that are capable of providing up to 15 kilowatts of total power at 300-Volts to 500-Volts to the thruster discharge supply. Additionally, the unit contains a housekeeping supply, high voltage input filter, low voltage input filter, and master control board, such that the complete brassboard unit is capable of operating a 12.5 kilowatt Hall Effect Thruster. The performance of unit was characterized under both ambient and thermal vacuum test conditions, and the results demonstrate the exceptional performance with full power efficiencies exceeding 97. With a space-qualified silicon carbide or similar high voltage, high efficiency power device, this design could evolve into a flight design for future missions that require high power electric propulsion systems.

  4. High Input Voltage, Silicon Carbide Power Processing Unit Performance Demonstration

    NASA Technical Reports Server (NTRS)

    Bozak, Karin E.; Pinero, Luis R.; Scheidegger, Robert J.; Aulisio, Michael V.; Gonzalez, Marcelo C.; Birchenough, Arthur G.

    2015-01-01

    A silicon carbide brassboard power processing unit has been developed by the NASA Glenn Research Center in Cleveland, Ohio. The power processing unit operates from two sources: a nominal 300 Volt high voltage input bus and a nominal 28 Volt low voltage input bus. The design of the power processing unit includes four low voltage, low power auxiliary supplies, and two parallel 7.5 kilowatt (kW) discharge power supplies that are capable of providing up to 15 kilowatts of total power at 300 to 500 Volts (V) to the thruster. Additionally, the unit contains a housekeeping supply, high voltage input filter, low voltage input filter, and master control board, such that the complete brassboard unit is capable of operating a 12.5 kilowatt Hall effect thruster. The performance of the unit was characterized under both ambient and thermal vacuum test conditions, and the results demonstrate exceptional performance with full power efficiencies exceeding 97%. The unit was also tested with a 12.5kW Hall effect thruster to verify compatibility and output filter specifications. With space-qualified silicon carbide or similar high voltage, high efficiency power devices, this would provide a design solution to address the need for high power electric propulsion systems.

  5. High-strength silicon carbides by hot isostatic pressing

    NASA Technical Reports Server (NTRS)

    Dutta, Sunil

    1989-01-01

    Silicon carbide has strong potential for heat engine hardware and other high-temperature applications because of its low density, good strength, high oxidation resistance, and good high-temperature creep resistance. Hot isostatic pressing (HIP) was used for producing alpha and beta silicon carbide (SiC) bodies with near-theoretical density, ultrafine grain size, and high strength at processing temperatures of 1900 to 2000 C. The HIPed materials exhibited ultrafine grain size. Furthermore, no phase transformation from beta to alpha was observed in HIPed beta-SiC. Both materials exhibited very high average flexural strength. It was also shown that alpha-SiC bodies without any sintering aids, when HIPed to high final density, can exhibit very high strength. Fracture toughness K (sub C) values were determined to be 3.6 to 4.0 MPa m (sup 1/2) for HIPed alpha-SiC and 3.7 to 4.1 MPa m (sup 1/2) for HIPed beta-SiC. In the HIPed specimens strength-controlling flaws were typically surface related. In spite of improvements in material properties such as strength and fracture toughness by elimination of the larger strength-limiting flaws and by grain size refinement, HIPing has no effect on the Weibull modulus.

  6. High capacitance of coarse-grained carbide derived carbon electrodes

    DOE PAGES

    Dyatkin, Boris; Gogotsi, Oleksiy; Malinovskiy, Bohdan; ...

    2016-01-01

    Here, we report exceptional electrochemical properties of supercapacitor electrodes composed of large, granular carbide-derived carbon (CDC) particles. We synthesized 70–250 μm sized particles with high surface area and a narrow pore size distribution, using a titanium carbide (TiC) precursor. 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. Moreover, 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 withmore » 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.« less

  7. High capacitance of coarse-grained carbide derived carbon electrodes

    SciTech Connect

    Dyatkin, Boris; Gogotsi, Oleksiy; Malinovskiy, Bohdan; Zozulya, Yuliya; Simon, Patrice; Gogotsi, Yury

    2016-01-01

    Here, we report exceptional electrochemical properties of supercapacitor electrodes composed of large, granular carbide-derived carbon (CDC) particles. We synthesized 70–250 μm sized particles with high surface area and a narrow pore size distribution, using a titanium carbide (TiC) precursor. 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. Moreover, 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.

  8. High capacitance of coarse-grained carbide derived carbon electrodes

    NASA Astrophysics Data System (ADS)

    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.

  9. Oxidation Behavior of Carbon Fiber Reinforced Silicon Carbide Composites

    NASA Technical Reports Server (NTRS)

    Valentin, Victor M.

    1995-01-01

    Carbon fiber reinforced Silicon Carbide (C-SiC) composites offer high strength at high temperatures and good oxidation resistance. However, these composites present some matrix microcracks which allow the path of oxygen to the fiber. The aim of this research was to study the effectiveness of a new Silicon Carbide (SiC) coating developed by DUPONT-LANXIDE to enhance the oxidation resistance of C-SiC composites. A thermogravimetric analysis was used to determine the oxidation rate of the samples at different temperatures and pressures. The Dupont coat proved to be a good protection for the SiC matrix at temperatures lower than 1240 C at low and high pressures. On the other hand, at temperatures above 1340 C the Dupont coat did not seem to give good protection to the composite fiber and matrix. Even though some results of the tests have been discussed, because of time restraints, only a small portion of the desired tests could be completed. Therefore, no major conclusions or results about the effectiveness of the coat are available at this time.

  10. Energy loss mechanics in the erosion of cemented tungsten carbide

    SciTech Connect

    Freinkel, D.M. ); Luyckx, S.B. )

    1989-05-01

    The erosion of tungsten carbide has been studied by several researchers under various conditions: the cobalt content of the cemented carbide has been varied from 4.5 to 11.3 wt % Co, the size of the WC grains varied from 0.9 to 5.1 {mu}m, the size of the erodant particles varied from 30 to 630 {mu}m, the velocity of the particles varied from 30 to 507 m/s, and particle incidence angle varied from 15{degrees} to 90{degrees}. While it is generally agreed that with increasing cobalt content and increasing particle velocity the erosion rate of WC-Co increases, there is disagreement on the effect of grain size and angle of incidence. More work was clearly required to explain this disagreement, thus the present investigation was undertaken. The present work differs from previous experimental work in that the erodant particles are 4 mm average diameter and that the present investigation does not neglect the role of plastic deformation in the erosion process and the energy lost in damage to the erodant particles. These two additional energy loss mechanisms have been found to contribute significantly to the interpretation of the present results and of the results previously reported in the literature.

  11. Hydrogen adsorption in metal-decorated silicon carbide nanotubes

    NASA Astrophysics Data System (ADS)

    Singh, Ram Sevak; Solanki, Ankit

    2016-09-01

    Hydrogen storage for fuel cell is an active area of research and appropriate materials with excellent hydrogen adsorption properties are highly demanded. Nanotubes, having high surface to volume ratio, are promising storage materials for hydrogen. Recently, silicon carbide nanotubes have been predicted as potential materials for future hydrogen storage application, and studies in this area are ongoing. Here, we report a systematic study on hydrogen adsorption properties in metal (Pt, Ni and Al) decorated silicon carbide nanotubes (SiCNTs) using first principles calculations based on density functional theory. The hydrogen adsorption properties are investigated by calculations of adsorption energy, electronic band structure, density of states (DOS) and Mulliken charge population analysis. Our findings show that hydrogen adsorptions on Pt, Ni and Al-decorated SiCNTs undergo spontaneous exothermic reactions with significant modulation of electronic structure of SiCNTs in all cases. Importantly, according to the Mulliken charge population analysis, dipole-dipole interaction causes chemisorptions of hydrogen in Pt, Ni and Al decorated SiCNTs with formation of chemical bonds. The study is a platform for the development of metal decorated SiCNTs for hydrogen adsorption or hydrogen storage application.

  12. Influence of radiation damage on krypton diffusion in silicon carbide

    NASA Astrophysics Data System (ADS)

    Friedland, E.; Hlatshwayo, T. T.; van der Berg, N. G.; Mabena, M. C.

    2015-07-01

    Diffusion of krypton in poly and single crystalline silicon carbide is investigated and compared with the previously obtained results for xenon, which pointed to a different diffusion mechanism than observed for chemically active elements. For this purpose 360 keV krypton ions were implanted in commercial 6H-SiC and CVD-SiC wafers at room temperature, 350 °C and 600 °C. Width broadening of the implantation profiles and krypton retention during isochronal and isothermal annealing up to temperatures of 1400 °C was determined by RBS-analysis, whilst in the case of 6H-SiC damage profiles were simultaneously obtained by α-particle channeling. Little diffusion and no krypton loss was detected in the initially amorphized and eventually recrystallized surface layer of cold implanted 6H-SiC during annealing up to 1200 °C. Above that temperature thermal etching of the implanted surface became increasingly important. No diffusion or krypton loss is detected in the hot implanted 6H-SiC samples during annealing up to 1400 °C. Radiation damage dependent grain boundary diffusion is observed at 1300 °C in CVD-SiC. The results seem to indicate, that the chemically inert noble gas atoms do not form defect-impurity complexes, which strongly influence the diffusion behavior of other diffusors in silicon carbide.

  13. Carbide and carbonitride surface treatment method for refractory metals

    DOEpatents

    Meyer, Glenn A.; Schildbach, Marcus A.

    1996-01-01

    A carbide and carbonitride surface treatment method for refractory metals is provided, in steps including, heating a part formed of boron, chromium, hafnium, molybdenum, niobium, tantalum, titanium, tungsten or zirconium, or alloys thereof, in an evacuated chamber and then introducing reaction gases including nitrogen and hydrogen, either in elemental or water vapor form, which react with a source of elemental carbon to form carbon-containing gaseous reactants which then react with the metal part to form the desired surface layer. Apparatus for practicing the method is also provided, in the form of a carbide and carbonitride surface treatment system (10) including a reaction chamber (14), a source of elemental carbon (17), a heating subassembly (20) and a source of reaction gases (23). Alternative methods of providing the elemental carbon (17) and the reaction gases (23) are provided, as well as methods of supporting the metal part (12), evacuating the chamber (14) with a vacuum subassembly (18) and heating all of the components to the desired temperature.

  14. Development of the SOFIA silicon carbide secondary mirror

    NASA Astrophysics Data System (ADS)

    Fruit, Michel; Antoine, Pascal; Varin, Jean-Luc; Bittner, Hermann; Erdmann, Matthias

    2003-02-01

    The SOFIA telescope is ajoint NASA-DLR project for a 2.5 m airborne Stratospheric Observatory for IR Astronomy to be flown in a specially adapted Boeing 747 SP plane, Kayser-Threde being resopinsible for the development of the Telescope Optics. The φ 352 mm Secondary Mirror is mounted ona chopping mechanism to allow avoidance of background noise during IR observations. Stiffness associated to lightness is a major demand for such a mirror to achieve high frequency chopping. This leads to select SIlicon Carbide for the mirror blank. Its development has been run by the ASTRIUM/BOOSTEC joint venture SiCSPACE, taking full benefit of the instrinsic properties of the BOOSTEC SiC-100 sintered material, associated to qualified processes specifically developed for space borne mirrors by ASTRIUM. Achieved performances include a low mass of 1.97 kg, a very high stiffness with a first resonant frequency of 1865 Hz and a measured optical surface accuracy of 39 nm rms, using Ion Beam Figuring. It is proposed here to present the major design features of the SOFIA Secondary Mirror, highlighting the main advantages of using Silicon Carbide, the main steps of its development and the achieved optomechanical performances of the developed mirror.

  15. Replacing precious metals with carbide catalysts for hydrogenation reactions

    DOE PAGES

    Ruijun, Hou; Chen, Jingguang G.; Chang, Kuan; ...

    2015-03-03

    Molybdenum carbide (Mo₂C and Ni/Mo₂C) catalysts were compared with Pd/SiO₂ for the hydrogenation of several diene molecules, 1,3- butadiene, 1,3- and 1,4-cyclohexadiene (CHD). Compared to Pd/SiO₂, Mo₂C showed similar hydrogenation rate for 1,3-butadiene and 1,3-CHD and even higher rate for 1,4-CHD, but with significant deactivation rate for 1,3-CHD hydrogenation. However, the hydrogenation activity of Mo₂C could be completely regenerated by H₂ treatment at 723 K for the three molecules. The Ni modified Mo₂C catalysts retained similar activity for 1,3-butadiene hydrogenation with significantly enhanced selectivity for 1-butene production. The 1-butene selectivity increased with increasing Ni loading below 15%. Among the Nimore » modified Mo₂C catalysts, 8.6%Ni/Mo₂C showed the highest selectivity to 1-butene, which was even higher selectivity than that over Pd/SiO₂. Compared to Pd/SiO₂, both Mo₂C and Ni/Mo₂C showed combined advantages in hydrogenation activity and catalyst cost reduction, demonstrating the potential to use less expensive carbide catalysts to replace precious metals for hydrogenation reactions.« less

  16. High-strength silicon carbides by hot isostatic pressing

    NASA Technical Reports Server (NTRS)

    Dutta, Sunil

    1988-01-01

    Silicon carbide has strong potential for heat engine hardware and other high-temperature applications because of its low density, good strength, high oxidation resistance, and good high-temperature creep resistance. Hot isostatic pressing (HIP) was used for producing alpha and beta silicon carbide (SiC) bodies with near-theoretical density, ultrafine grain size, and high strength at processing temperatures of 1900 to 2000 C. The HIPed materials exhibited ultrafine grain size. Furthermore, no phase transformation from beta to alpha was observed in HIPed beta-SiC. Both materials exhibited very high average flexural strength. It was also shown that alpha-SiC bodies without any sintering aids, when HIPed to high final density, can exhibit very high strength. Fracture toughness K (sub C) values were determined to be 3.6 to 4.0 MPa m (sup 1/2) for HIPed alpha-SiC and 3.7 to 4.1 MPa m (sup 1/2) for HIPed beta-SiC. In the HIPed specimens strength-controlling flaws were typically surface related. In spite of improvements in material properties such as strength and fracture toughness by elimination of the larger strength-limiting flaws and by grain size refinement, HIPing has no effect on the Weibull modulus.

  17. Cavity-Enhanced Measurements of Defect Spins in Silicon Carbide

    NASA Astrophysics Data System (ADS)

    Calusine, Greg; Politi, Alberto; Awschalom, David D.

    2016-07-01

    The identification of new solid-state defect-qubit candidates in widely used semiconductors has the potential to enable the use of nanofabricated devices for enhanced qubit measurement and control operations. In particular, the recent discovery of optically active spin states in silicon carbide thin films offers a scalable route for incorporating defect qubits into on-chip photonic devices. Here, we demonstrate the use of 3C silicon carbide photonic crystal cavities for enhanced excitation of color-center defect spin ensembles in order to increase measured photoluminescence signal count rates, optically detected magnetic-resonance signal intensities, and optical spin initialization rates. We observe an up to a factor of 30 increase in the photoluminescence and optically detected magnetic-resonance signals from Ky5 color centers excited by cavity-resonant excitation and increase the rate of ground-state spin initialization by approximately a factor of 2. Furthermore, we show that the 705-fold reduction in excitation mode volume and enhanced excitation and collection efficiencies provided by the structures can be used to overcome inhomogenous broadening in order to facilitate the study of defect-qubit subensemble properties. These results highlight some of the benefits that nanofabricated devices offer for engineering the local photonic environment of color-center defect qubits to enable applications in quantum information and sensing.

  18. Thermal conductivity and emissivity measurements of uranium carbides

    NASA Astrophysics Data System (ADS)

    Corradetti, S.; Manzolaro, M.; Andrighetto, A.; Zanonato, P.; Tusseau-Nenez, S.

    2015-10-01

    Thermal conductivity and emissivity measurements on different types of uranium carbide are presented, in the context of the ActiLab Work Package in ENSAR, a project within the 7th Framework Program of the European Commission. Two specific techniques were used to carry out the measurements, both taking place in a laboratory dedicated to the research and development of materials for the SPES (Selective Production of Exotic Species) target. In the case of thermal conductivity, estimation of the dependence of this property on temperature was obtained using the inverse parameter estimation method, taking as a reference temperature and emissivity measurements. Emissivity at different temperatures was obtained for several types of uranium carbide using a dual frequency infrared pyrometer. Differences between the analyzed materials are discussed according to their compositional and microstructural properties. The obtainment of this type of information can help to carefully design materials to be capable of working under extreme conditions in next-generation ISOL (Isotope Separation On-Line) facilities for the generation of radioactive ion beams.

  19. Iron aluminide-titanium carbide composites: Microstructure and mechanical properties

    SciTech Connect

    Subramanian, R.; Schneibel, J.H.; Alexander, K.B.

    1996-09-01

    Composites of intermetallics and carbides (with binder contents less that 50 vol.%) are considered as potential candidates for applications requiring high wear resistance in corrosive environments. Intermetallics, especially aluminides, provide the corrosion resistance, and the high hardness of the carbide phase contributes to increased wear resistance of the composites. In this study, cost effective and simple processing techniques to obtain FeAl-TiC composites, over a wide range of binder volume fractions, are demonstrated. Binder volume fractions range from 0.15 to 0.7 (18 to 75 wt. % binder). Two techniques - liquid phase sintering of mixed powders and pressureless melt infiltration of TiC preforms was found to be very successful for obtaining fully dense composites with binder volume fractions from 0.15 to 0.3 (18 to 34 wt. %), whereas for higher binder contents liquid phase sintering of mixed powders was the best approach. Mechanical properties of these composites including the 3-point bend strength, fracture toughness and hardness are presented.

  20. Microstructural Evolution of Chloride-Cleaned Silicon Carbide Aluminum Composites

    NASA Astrophysics Data System (ADS)

    Adeosun, S. O.; Akpan, E. I.; Gbenebor, O. P.; Balogun, S. A.

    2016-02-01

    This study examines the synergy between reinforcement surface modifications on the evolution of microstructures of AA6011-silicon carbide particle (SiCp) composites in multidirectional solidification. Silicon carbide particles (SiCp) were cleaned with ammonium chloride, tin(II) chloride, sodium chloride, and palladium(II) chloride and used as reinforcement to cast AA6011-SiCp composites by applying the stir casting method. A scanning electron microscope and x-ray diffractometer were used to investigate the morphology and phases present, respectively, in the composite material. Results show that wetting agents were effective as they inhibited the formation of Al4C3 in all modified composites. The modified SiCp was found to have varying effects on the morphology, dendrite arm size and direction, size and configuration of AlFeSi, and the amount of eutectic silicon depending on the concentration of the reagent and cleaning time. The highest effect was shown by the use of 40 g/L of tin(II) chloride. The composites had short dendritic arms, good interfacial interaction, and only a few crystals of AlFeSi.

  1. Demonstration of Minimally Machined Honeycomb Silicon Carbide Mirrors

    NASA Technical Reports Server (NTRS)

    Goodman, William

    2012-01-01

    Honeycomb silicon carbide composite mirrors are made from a carbon fiber preform that is molded into a honeycomb shape using a rigid mold. The carbon fiber honeycomb is densified by using polymer infiltration pyrolysis, or through a reaction with liquid silicon. A chemical vapor deposit, or chemical vapor composite (CVC), process is used to deposit a polishable silicon or silicon carbide cladding on the honeycomb structure. Alternatively, the cladding may be replaced by a freestanding, replicated CVC SiC facesheet that is bonded to the honeycomb. The resulting carbon fiber-reinforced silicon carbide honeycomb structure is a ceramic matrix composite material with high stiffness and mechanical strength, high thermal conductivity, and low CTE (coefficient of thermal expansion). This innovation enables rapid, inexpensive manufacturing. The web thickness of the new material is less than 1 millimeter, and core geometries tailored. These parameters are based on precursor carbon-carbon honeycomb material made and patented by Ultracor. It is estimated at the time of this reporting that the HoneySiC(Trademark) will have a net production cost on the order of $38,000 per square meter. This includes an Ultracor raw material cost of about $97,000 per square meter, and a Trex silicon carbide deposition cost of $27,000 per square meter. Even at double this price, HoneySiC would beat NASA's goal of $100,000 per square meter. Cost savings are estimated to be 40 to 100 times that of current mirror technologies. The organic, rich prepreg material has a density of 56 kilograms per cubic meter. A charred carbon-carbon panel (volatile organics burnt off) has a density of 270 kilograms per cubic meter. Therefore, it is estimated that a HoneySiC panel would have a density of no more than 900 kilograms per cubic meter, which is about half that of beryllium and about onethird the density of bulk silicon carbide. It is also estimated that larger mirrors could be produced in a matter of weeks

  2. Growth mode of carbide from C 2H 4 or CO on Ni( 1 1 1 )

    NASA Astrophysics Data System (ADS)

    Nakano, H.; Ogawa, J.; Nakamura, J.

    2002-08-01

    The growth of carbide on a Ni(1 1 1) surface by the decomposition of C 2H 4 and the Boudouard reaction (2CO g→C a+CO 2,g) was studied using scanning tunneling microscopy (STM), Auger electron spectroscopy and low energy electron diffraction. STM results showed that the carbide growth by the Boudouard reaction started at step edges on Ni(1 1 1), while for the C 2H 4 decomposition the carbide was formed preferentially at terrace sites with very low concentration of carbide at the step edge. The different behavior for the carbide growth was ascribed to the difference in the dissociation sites of CO and C 2H 4. As for the Boudouard reaction, CO was dissociated at the step edge and then carbon migrated into the bulk at a reaction temperature of 500 K. The carbon was then segregated at room temperature to the surface from the bulk to form a single domain of the ( 39× 39) R16.1° structure at the step edge. On the other hand, the C 2H 4 decomposition took place on the terrace leading to an isolated carbide unit or carbide short strings on the terrace.

  3. Effect of electroslag remelting on carbides in 8Cr13MoV martensitic stainless steel

    NASA Astrophysics Data System (ADS)

    Zhu, Qin-tian; Li, Jing; Shi, Cheng-bin; Yu, Wen-tao

    2015-11-01

    The effect of electroslag remelting (ESR) on carbides in 8Cr13MoV martensitic stainless steel was experimentally studied. Phases precipitated from liquid steel during solidification were calculated using the Thermo-Calc software. The carbon segregation was analyzed by original position analysis (OPA), and the carbides were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy- dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results indicated that more uniform carbon distribution and less segregation were obtained in the case of samples subjected to the ESR process. After ESR, the amount of netty carbides decreased significantly, and the chromium and vanadium contents in the grain-boundary carbides was reduced. The total area and average size of carbides were obviously smaller after the ESR process. In the sample subjected to ESR, the morphology of carbides changed from lamellar and angular to globular or lump, whereas the types of carbides did not change; both M23C6 and M7C3 were present before and after the ESR process.

  4. Characterization of M23C6 Carbides Precipitating at Grain Boundaries in 100Mn13 Steel

    NASA Astrophysics Data System (ADS)

    Xu, Zhenfeng; Ding, Zhimin; Dong, Linnan; Liang, Bo

    2016-10-01

    Characteristics of the formation, the interfacial structure, and the defects of M23C6 carbides in 100Mn13 steel after 1323 K (1050 °C) solution treatment and subsequent aging treatment were investigated by transmission electron microscope (TEM). The results show that M23C6 carbides precipitated on both sides of the grain boundaries. Each M23C6 carbide particle possesses a coherent interface and the cube-cube orientation relationship with the one austenite grain which M23C6 precipitated from. The orientation relationships between the M23C6 carbides and the austenite matrix were determined as follows: (1) [211]γ allel [211]M23C6, ( 1bar{1}bar{1} )γ allel ( 1bar{1}bar{1} )M23C6, (02 bar{2} )γ allel (02 bar{2} )M23C6, (2) [110]γ allel [110]M23C6, ( bar{1}1bar{1} )γ allel ( bar{1}1bar{1} )M23C6, ( bar{1} 11)γ allel ( bar{1} 11)M23C6. The M23C6 carbide also possesses an incoherent interface with the other austenite grain which the M23C6 carbide grew into by ledge mechanism. The precipitation of the M23C6 carbides along the boundaries can improve the hardness of the high-manganese steel to some extent. Besides, twinning and stacking faults were observed in M23C6 carbides. The reports about twinning and stacking faults in the M23C6 carbides have not been found.

  5. SOLID SOLUTION CARBIDES ARE THE KEY FUELS FOR FUTURE NUCLEAR THERMAL PROPULSION

    NASA Technical Reports Server (NTRS)

    Panda, Binayak; Hickman, Robert R.; Shah, Sandeep

    2005-01-01

    Nuclear thermal propulsion uses nuclear energy to directly heat a propellant (such as liquid hydrogen) to generate thrust for space transportation. In the 1960 s, the early Rover/Nuclear Engine for Rocket Propulsion Application (NERVA) program showed very encouraging test results for space nuclear propulsion but, in recent years, fuel research has been dismal. With NASA s renewed interest in long-term space exploration, fuel researchers are now revisiting the RoverMERVA findings, which indicated several problems with such fuels (such as erosion, chemical reaction of the fuel with propellant, fuel cracking, and cladding issues) that must be addressed. It is also well known that the higher the temperature reached by a propellant, the larger the thrust generated from the same weight of propellant. Better use of fuel and propellant requires development of fuels capable of reaching very high temperatures. Carbides have the highest melting points of any known material. Efforts are underway to develop carbide mixtures and solid solutions that contain uranium carbide, in order to achieve very high fuel temperatures. Binary solid solution carbides (U, Zr)C have proven to be very effective in this regard. Ternary carbides such as (U, Zr, X) carbides (where X represents Nb, Ta, W, and Hf) also hold great promise as fuel material, since the carbide mixtures in solid solution generate a very hard and tough compact material. This paper highlights past experience with early fuel materials and bi-carbides, technical problems associated with consolidation of the ingredients, and current techniques being developed to consolidate ternary carbides as fuel materials.

  6. Priority compositions of boron carbide crystals obtained by self-propagating high-temperature synthesis

    NASA Astrophysics Data System (ADS)

    Ponomarev, V. I.; Konovalikhin, S. V.; Kovalev, I. D.; Vershinnikov, V. I.

    2015-09-01

    Splitting of reflections from boron carbide has been found for the first time by an X-ray diffraction study of polycrystalline mixture of boron carbide В15- х С х , (1.5 ≤ x ≤ 3) and its magnesium derivative C4B25Mg1.42. An analysis of reflection profiles shows that this splitting is due to the presence of boron carbide phases of different compositions in the sample, which are formed during crystal growth. The composition changes from В12.9С2.1 to В12.4С2.6.

  7. Formation of Iron Carbide Nanorod by Pulsed Plasma Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Yooyen, S.; Kawamura, T.; Kotake, S.; Suzuki, Y.

    2010-11-01

    Iron carbide nanorods were produced on the surface of pure iron sheet by means of pulsed plasma chemical vapor deposition. Hydrogen plasma was used in the initial state, varied from 10 to 60 minute, for the purpose of cleaning and preparing nanoparticles. The formation was done under methane atmosphere, varied from 2 to 30 minute. X-ray diffraction (XRD) patterns analysis showed that iron carbide was found on all of these experiment conditions. By field emission scanning electron micro spectroscopy (FESEM) observation, iron carbide nanorods, however, were found neatly only on the methane plasma treating at 10 minute.

  8. A New Approach to Joining of Silicon Carbide-Based Materials for High Temperature Applications

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay

    1998-01-01

    Ceramic joining is recognized as one of the enabling technologies for the application of silicon carbide-based materials in a number of high temperature applications. An affordable, robust technique for the joining of silicon carbide-based ceramics has been developed. This technique is capable of producing joints with tailorable thickness and composition. Microstructure and mechanical properties of reaction formed joints in a reaction bonded silicon carbide have been reported. These joints maintain their mechanical strengths at high temperatures (up to 1350 C) in air. This technique is capable of joining large and complex shaped ceramic components.

  9. Method for silicon carbide production by reacting silica with hydrocarbon gas

    DOEpatents

    Glatzmaier, G.C.

    1994-06-28

    A method is described for producing silicon carbide particles using a silicon source material and a hydrocarbon. The method is efficient and is characterized by high yield. Finely divided silicon source material is contacted with hydrocarbon at a temperature of 400 C to 1000 C where the hydrocarbon pyrolyzes and coats the particles with carbon. The particles are then heated to 1100 C to 1600 C to cause a reaction between the ingredients to form silicon carbide of very small particle size. No grinding of silicon carbide is required to obtain small particles. The method may be carried out as a batch process or as a continuous process. 5 figures.

  10. Method for silicon carbide production by reacting silica with hydrocarbon gas

    DOEpatents

    Glatzmaier, Gregory C.

    1994-01-01

    A method is described for producing silicon carbide particles using a silicon source material and a hydrocarbon. The method is efficient and is characterized by high yield. Finely divided silicon source material is contacted with hydrocarbon at a temperature of 400.degree. C. to 1000.degree. C. where the hydrocarbon pyrolyzes and coats the particles with carbon. The particles are then heated to 1100.degree. C. to 1600.degree. C. to cause a reaction between the ingredients to form silicon carbide of very small particle size. No grinding of silicon carbide is required to obtain small particles. The method may be carried out as a batch process or as a continuous process.

  11. SANS and TEM studies of carbide precipitation and creep damage in type 304 stainless steel

    SciTech Connect

    Yoo, M.H.; Ogle, J.C.; Schneibel, J.H.; Swindeman, R.W.

    1984-01-01

    Small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) studies were performed to characterize the carbide (M/sub 23/C/sub 6/) precipitation and creep damage induced in type 304 stainless steel in the primary creep stage. The size distribution of matrix carbides evaluated from SANS analyses was consistent with TEM data, and the expected accelerated kinetics of precipitation under applied stress was confirmed. Additional SANS measurements after the postcreep solution annealing were made in order to differentiate cavities from the carbides. Potential advantages and difficulties associated with characterization of creep-induced cavitation by the SANS techniques are discussed.

  12. Role of silicon dangling bonds in the electronic properties of epitaxial graphene on silicon carbide.

    PubMed

    Ridene, Mohamed; Kha, Calvin S; Flipse, Cees F J

    2016-03-29

    In this paper, we study the electronic properties of epitaxial graphene (EG) on silicon carbide by means of ab initio calculations based on the local spin density approximation + U method taking into account the Coulomb interaction between Si localized electrons. We show that this interaction is not completely suppressed but is screened by carbon layers grown on-top of silicon carbide. This finding leads to a good qualitative understanding of the experimental results reported on EG on silicon carbide. Our results highlight the presence of the Si localized states and might explain the anomalous Hanle curve and the high values of spin relaxation time in EG.

  13. Structural and phase changes in carbides of the high-speed steel upon heat treatment

    NASA Astrophysics Data System (ADS)

    Chaus, A. S.

    2016-07-01

    The effect of austenitizing temperature on structural and phase changes in carbides of the tungsten-molybdenum high-speed steel has been studied. The results of metallographic analysis and energy dispersive microanalysis have been discussed. It has been shown that an increase in austenitizing temperature from 1180 to 1260°C causes structural transformations in carbide particles of eutectic origin crushed upon hot plastic deformation, which are related to their dissolution and coalescence, and changes in the phase composition of the carbides themselves.

  14. Affordable Fabrication and Properties of Silicon Carbide-Based Interpenetrating Phase Composites

    NASA Technical Reports Server (NTRS)

    Singh, Mrityunjay

    1998-01-01

    An affordable processing technique for the fabrication of silicon carbide-based interpenetrating phase composites (IPCs) is presented. This process consists of the production of microporous carbon preforms and subsequent infiltration with liquid silicon or silicon-refractory metal alloys. The microporous preforms are made by the pyrolysis of a polymerized resin mixture for which methods to control pore volume and pore size have been established. The process gives good control of microstructure and morphology of silicon carbide-based composite materials. Room and high temperature mechanical properties (flexural strength, compressive strength, and flexural creep) of low and high silicon-silicon carbide composites will be discussed.

  15. Molecular dynamics simulations of nanoindentation and nanoscratching of silicon carbide

    NASA Astrophysics Data System (ADS)

    Noreyan, Alisa A.

    Parallel molecular dynamics simulations were carried out to investigate the interaction between a diamond indenter and silicon carbide during nanoindentation and nanoscratching. The dependence of the critical depth and pressure for the elastic-to-plastic transition on indentation velocity, tip size, and workpiece temperature was studied along with the nature of the deformation due to indentation and scratching. The two most widely used polytypes---cubic silicon carbide (3C-SiC) and hexagonal silicon carbide (6H-SiC)---were considered while the Si-terminated (001) ((0001)) surface was used in each case. Simulations were implemented using the Tersoff SiC potential, which accurately reproduces the lattice and elastic constants of 3C-SiC and 6H-SiC. Nanoindentation experiments were also carried out for 6H-SiC. For the 3C polytype, both the critical pressure and indentation depth for the elastic-to-plastic transition were found to decrease with increasing indenter size over the nanoscale range of indenter sizes used in our simulations. As a result, the measured hardness was found to be significantly higher than obtained experimentally for significantly larger indenter sizes. In addition, for indentation depths beyond the critical depth a phase transition to the rocksalt structure was observed. A similar phase transition was observed for the 6H polytype, but the transition pressure was found to be somewhat higher than for 3C-SiC. Both of these results are in good agreement with experimental results for bulk SiC. Thus, for nanoscale indentation of 3C and 6H-SiC, the onset of plastic behavior is related to the existence of a phase transition under the indenter tip. For the 6H case a weak dependence on indentation velocity was also observed. This claim was also confirmed by nanoindentation experiments, in which the strain rate sensitivity of mono-crystal 6H was investigated. Simulations of the nanoscratching of 3C-SiC were also carried out. Significant anisotropy in the

  16. Rapid Fabrication of Carbide Matrix/Carbon Fiber Composites

    NASA Technical Reports Server (NTRS)

    Williams, Brian E.; Bernander, Robert E.

    2007-01-01

    Composites of zirconium carbide matrix material reinforced with carbon fibers can be fabricated relatively rapidly in a process that includes a melt infiltration step. Heretofore, these and other ceramic matrix composites have been made in a chemical vapor infiltration (CVI) process that takes months. The finished products of the CVI process are highly porous and cannot withstand temperatures above 3,000 F (approx.1,600 C). In contrast, the melt-infiltration-based process takes only a few days, and the composite products are more nearly fully dense and have withstood temperatures as high as 4,350 F (approx.2,400 C) in a highly oxidizing thrust chamber environment. Moreover, because the melt- infiltration-based process takes much less time, the finished products are expected to cost much less. Fabrication begins with the preparation of a carbon fiber preform that, typically, is of the size and shape of a part to be fabricated. By use of low-temperature ultraviolet-enhanced chemical vapor deposition, the carbon fibers in the preform are coated with one or more interfacial material(s), which could include oxides. The interfacial material helps to protect the fibers against chemical attack during the remainder of the fabrication process and against oxidation during subsequent use; it also enables slippage between the fibers and the matrix material, thereby helping to deflect cracks and distribute loads. Once the fibers have been coated with the interfacial material, the fiber preform is further infiltrated with a controlled amount of additional carbon, which serves as a reactant for the formation of the carbide matrix material. The next step is melt infiltration. The preform is exposed to molten zirconium, which wicks into the preform, drawn by capillary action. The molten metal fills most of the interstices of the preform and reacts with the added carbon to form the zirconium carbide matrix material. The zirconium does not react with the underlying fibers because they

  17. A review on single photon sources in silicon carbide

    NASA Astrophysics Data System (ADS)

    Lohrmann, A.; Johnson, B. C.; McCallum, J. C.; Castelletto, S.

    2017-03-01

    This paper summarizes key findings in single-photon generation from deep level defects in silicon carbide (SiC) and highlights the significance of these individually addressable centers for emerging quantum applications. Single photon emission from various defect centers in both bulk and nanostructured SiC are discussed as well as their formation and possible integration into optical and electrical devices. The related measurement protocols, the building blocks of quantum communication and computation network architectures in solid state systems, are also summarized. This includes experimental methodologies developed for spin control of different paramagnetic defects, including the measurement of spin coherence times. Well established doping, and micro- and nanofabrication procedures for SiC may allow the quantum properties of paramagnetic defects to be electrically and mechanically controlled efficiently. The integration of single defects into SiC devices is crucial for applications in quantum technologies and we will review progress in this direction.

  18. Hydrothermal corrosion of silicon carbide joints without radiation

    DOE PAGES

    Koyanagi, Takaaki; Katoh, Yutai; Terrani, Kurt A.; ...

    2016-09-28

    In this paper, hydrothermal corrosion of four types of the silicon carbide (SiC) to SiC plate joints were investigated under pressurized water reactor and boiling water reactor relevant chemical conditions without irradiation. The joints were formed by metal diffusion bonding using molybdenum or titanium interlayer, reaction sintering using Ti—Si—C system, and SiC nanopowder sintering. Most of the joints withstood the corrosion tests for five weeks. The recession of the SiC substrates was limited. Based on the recession of the bonding layers, it was concluded that all the joints except for the molybdenum diffusion bond are promising under the reducing environmentsmore » without radiation. Finally, the SiC nanopowder sintered joint was the most corrosion tolerant under the oxidizing environment among the four joints.« less

  19. Deposition of tantalum carbide coatings on graphite by laser interactions

    NASA Technical Reports Server (NTRS)

    Veligdan, James; Branch, D.; Vanier, P. E.; Barietta, R. E.

    1994-01-01

    Graphite surfaces can be hardened and protected from erosion by hydrogen at high temperatures by refractory metal carbide coatings, which are usually prepared by chemical vapor deposition (CVD) or chemical vapor reaction (CVR) methods. These techniques rely on heating the substrate to a temperature where a volatile metal halide decomposes and reacts with either a hydrocarbon gas or with carbon from the substrate. For CVR techniques, deposition temperatures must be in excess of 2000 C in order to achieve favorable deposition kinetics. In an effort to lower the bulk substrate deposition temperature, the use of laser interactions with both the substrate and the metal halide deposition gas has been employed. Initial testing involved the use of a CO2 laser to heat the surface of a graphite substrate and a KrF excimer laser to accomplish a photodecomposition of TaCl5 gas near the substrate. The results of preliminary experiments using these techniques are described.

  20. Dispersion of nonresonant third-order nonlinearities in Silicon Carbide

    PubMed Central

    De Leonardis, Francesco; Soref, Richard A.; Passaro, Vittorio M. N.

    2017-01-01

    In this paper we present a physical discussion of the indirect two-photon absorption (TPA) occuring in silicon carbide with either cubic or wurtzite structure. Phonon-electron interaction is analyzed by finding the phonon features involved in the process as depending upon the crystal symmetry. Consistent physical assumptions about the phonon-electron scattering mechanisms are proposed in order to give a mathematical formulation to predict the wavelength dispersion of TPA and the Kerr nonlinear refractive index n2. The TPA spectrum is investigated including the effects of band nonparabolicity and the influence of the continuum exciton. Moreover, a parametric analysis is presented in order to fit the experimental measurements. Finally, we have estimated the n2 in a large wavelength range spanning the visible to the mid-IR region. PMID:28098223

  1. Computer Simulation of Displacement Damage in Silicon Carbide

    SciTech Connect

    Devanathan, Ram; Gao, Fei; Weber, William J.; M. Chipara, D. L. Edwards, S. Phillips, and R. Benson

    2005-07-01

    We have performed molecular dynamics simulation of displacement events on silicon and carbon sublattices in silicon carbide for displacement doses ranging from 0.005 to 0.5 displacements per atom. Our results indicate that the displacement threshold energy is about 21 eV for C and 35 eV for Si, and amorphization can occur by accumulation of displacement damage regardless of whether Si or C is displaced. In addition, we have simulated defect production in high-energy cascades as a function of the primary knock-on atom energy and observed features that are different from the case of damage accumulation in Si. These systematic studies shed light on the phenomenon of non-ionizing energy loss that is relevant to understanding space radiation effects in semiconductor devices.

  2. Magnesium carbide monolayer: A novel quasi-planar semiconductor

    NASA Astrophysics Data System (ADS)

    Naseri, Mosayeb

    2017-02-01

    By using the first principles calculations in the framework of the density functional theory, a new quasi-planer semiconductor material, namely Magnesium Carbide Monolayer (Mg2C) is predicted. The stability of the proposed structure is confirmed by cohesive energy calculation. According to our simulation, Mg2C monolayer is a semiconductor material with an indirect band gap of 0.68 eV, which is tunable under external biaxial stress. Optical properties calculation indicates considerable sharp absorption peaks in ultra violet (UV) energy range. As a semiconductor with an indirect tunable band gap, Mg2C monolayer is a promising 2D material for application in future optoelectronic technology especially in designing ultraviolet (UV) light filters.

  3. A review of oxide, silicon nitride, and silicon carbide brazing

    SciTech Connect

    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.

  4. Silicon Carbide-Based Hydrogen and Hydrocarbon Gas Detection

    NASA Technical Reports Server (NTRS)

    Hunter, Gary W.; Neudeck, Philip G.; Chen, Liang-Yu; Knight, D.; Liu, C. C.; Wu, Q. H.R

    1995-01-01

    Hydrogen and hydrocarbon detection in aeronautical applications is important for reasons of safety and emissions control. The use of silicon carbide as a semiconductor in a metal-semiconductor or metal-insulator-semiconductor structure opens opportunities to measure hydrogen and hydrocarbons in high temperature environments beyond the capabilities of silicon-based devices. The purpose of this paper is to explore the response and stability of Pd-SiC Schottky diodes as gas sensors in the temperature range from 100 to 400 C. The effect of heat treating on the diode properties as measured at 100 C is explored. Subsequent operation at 400 C demonstrates the diodes' sensitivity to hydrogen and hydrocarbons. It is concluded that the Pd-SiC Schottky diode has potential as a hydrogen and hydrocarbon sensor over a wide range of temperatures but further studies are necessary to determine the diodes' long term stability.

  5. Hydrothermal corrosion of silicon carbide joints without radiation

    NASA Astrophysics Data System (ADS)

    Koyanagi, Takaaki; Katoh, Yutai; Terrani, Kurt A.; Kim, Young-Jin; Kiggans, James O.; Hinoki, Tatsuya

    2016-12-01

    Hydrothermal corrosion of four types of the silicon carbide (SiC) to SiC plate joints were investigated under pressurized water reactor and boiling water reactor relevant chemical conditions without irradiation. The joints were formed by metal diffusion bonding using molybdenum or titanium interlayer, reaction sintering using Ti-Si-C system, and SiC nanopowder sintering. Most of the joints withstood the corrosion tests for five weeks. The recession of the SiC substrates was limited. Based on the recession of the bonding layers, it was concluded that all the joints except for the molybdenum diffusion bond are promising under the reducing environments without radiation. The SiC nanopowder sintered joint was the most corrosion tolerant under the oxidizing environment among the four joints.

  6. Surface wave accelerator based on silicon carbide: theoretical study

    NASA Astrophysics Data System (ADS)

    Kalmykov, S.; Korobkin, D.; Neuner, B.; Shvets, G.

    2009-01-01

    Compact near-field solid-state accelerating structure powered by a carbon dioxide (CO2) laser is considered. The accelerating luminous transverse magnetic mode is excited in a few-micron wide evacuated planar channel between two silicon carbide (SiC) films grown on silicon (Si) wafers. Laser coupling to this mode is accomplished through the properly designed Si gratings. Operating wavelength is dictated by the frequency-dependent dielectric permittivity of SiC and the channel width. The geometric loss factor κ of the accelerating mode is computed. It is found that the unwanted excitation of the guided modes in Si wafers reduces the laser coupling efficiency and increases the fields inside the Si wafer.

  7. Surface wave accelerator based on silicon carbide: theoretical study

    SciTech Connect

    Kalmykov, S.; Korobkin, D.; Neuner, B.; Shvets, G.

    2009-01-22

    Compact near-field solid-state accelerating structure powered by a carbon dioxide (CO{sub 2}) laser is considered. The accelerating luminous transverse magnetic mode is excited in a few-micron wide evacuated planar channel between two silicon carbide (SiC) films grown on silicon (Si) wafers. Laser coupling to this mode is accomplished through the properly designed Si gratings. Operating wavelength is dictated by the frequency-dependent dielectric permittivity of SiC and the channel width. The geometric loss factor {kappa} of the accelerating mode is computed. It is found that the unwanted excitation of the guided modes in Si wafers reduces the laser coupling efficiency and increases the fields inside the Si wafer.

  8. Porous silicon carbide (SiC) semiconductor device

    NASA Technical Reports Server (NTRS)

    Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

    1994-01-01

    A semiconductor device employs at least one layer of semiconducting porous silicon carbide (SiC). The porous SiC layer has a monocrystalline structure wherein the pore sizes, shapes, and spacing are determined by the processing conditions. In one embodiment, the semiconductor device is a p-n junction diode in which a layer of n-type SiC is positioned on a p-type layer of SiC, with the p-type layer positioned on a layer of silicon dioxide. Because of the UV luminescent properties of the semiconducting porous SiC layer, it may also be utilized for other devices such as LEDs and optoelectronic devices.

  9. Method of producing novel silicon carbide articles. [Patent application

    DOEpatents

    Milewski, J.V.

    1982-06-18

    A method of producing articles comprising reaction-bonded silicon carbide (SiC) and graphite (and/or carbon) is given. The process converts the graphite (and/or carbon) in situ to SiC, thus providing the capability of economically obtaining articles made up wholly or partially of SiC having any size and shape in which graphite (and/or carbon) can be found or made. When the produced articles are made of an inner graphite (and/or carbon) substrate to which SiC is reaction bonded, these articles distinguish SiC-coated graphite articles found in the prior art by the feature of a strong bond having a gradual (as opposed to a sharply defined) interface which extends over a distance of mils. A method for forming SiC whisker-reinforced ceramic matrices is also given. The whisker-reinforced articles comprise SiC whiskers which substantially retain their structural integrity.

  10. Silicon Carbide Sensors and Electronics for Harsh Environment Applications

    NASA Technical Reports Server (NTRS)

    Evans, Laura J.

    2007-01-01

    Silicon carbide (SiC) semiconductor has been studied for electronic and sensing applications in extreme environment (high temperature, extreme vibration, harsh chemical media, and high radiation) that is beyond the capability of conventional semiconductors such as silicon. This is due to its near inert chemistry, superior thermomechanical and electronic properties that include high breakdown voltage and wide bandgap. An overview of SiC sensors and electronics work ongoing at NASA Glenn Research Center (NASA GRC) will be presented. The main focus will be two technologies currently being investigated: 1) harsh environment SiC pressure transducers and 2) high temperature SiC electronics. Work highlighted will include the design, fabrication, and application of SiC sensors and electronics, with recent advancements in state-of-the-art discussed as well. These combined technologies are studied for the goal of developing advanced capabilities for measurement and control of aeropropulsion systems, as well as enhancing tools for exploration systems.

  11. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    PubMed Central

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-01-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I−V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane. PMID:26548439

  12. In situ electrochemical dilatometry of carbide-derived carbons

    SciTech Connect

    Hantel, M M; Presser, Volker; Gogotsi, Yury

    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.

  13. Development of silicon carbide semiconductor devices for high temperature applications

    NASA Technical Reports Server (NTRS)

    Matus, Lawrence G.; Powell, J. Anthony; Petit, Jeremy B.

    1991-01-01

    The semiconducting properties of electronic grade silicon carbide crystals, such as wide energy bandgap, make it particularly attractive for high temperature applications. Applications for high temperature electronic devices include instrumentation for engines under development, engine control and condition monitoring systems, and power conditioning and control systems for space platforms and satellites. Discrete prototype SiC devices were fabricated and tested at elevated temperatures. Grown p-n junction diodes demonstrated very good rectification characteristics at 870 K. A depletion-mode metal-oxide-semiconductor field-effect transistor was also successfully fabricated and tested at 770 K. While optimization of SiC fabrication processes remain, it is believed that SiC is an enabling high temperature electronic technology.

  14. Incidence of cancer among workers producing calcium carbide.

    PubMed Central

    Kjuus, H; Andersen, A; Langård, S

    1986-01-01

    The overall mortality and the incidence of cancer have been studied among male employees at a plant producing calcium carbide. The cohort was defined as all men employed at the plant for at least 18 months in the period 1953 to 1970 and was classified according to 10 occupational categories. The 790 men have been observed from 1953 to 1983 and the incidence of cancer in the cohort has been compared with national incidence rates. A significant excess of colonic cancer (standardised incidence ratio, SIR = 2.09) and of prostatic cancer (SIR = 1.78) was found, and also a slight excess of lung cancer among furnace and maintenance workers (SIR = 1.56). The possible exposure of the workers to polycyclic aromatic hydrocarbons, asbestos, and cadmium is discussed. PMID:3964572

  15. Spin-photon entanglement interfaces in silicon carbide defect centers

    NASA Astrophysics Data System (ADS)

    Economou, Sophia E.; Dev, Pratibha

    2016-12-01

    Optically active spins in solid-state systems can be engineered to emit photons that are entangled with the spin in the solid. This allows for applications such as quantum communications, quantum key distribution, and distributed quantum computing. Recently, there has been a strong interest in silicon carbide defects, as they emit very close to the telecommunication wavelength, making them excellent candidates for long range quantum communications. In this work we develop explicit schemes for spin-photon entanglement in several SiC defects: the silicon monovacancy, the silicon divacancy, and the NV center in SiC. Distinct approaches are given for (i) single-photon and spin entanglement and (ii) the generation of long strings of entangled photons. The latter are known as cluster states and comprise a resource for measurement-based quantum information processing.

  16. Ion Beam Synthesis Of Metal - Silicon Carbide - Si Multilayer Structures

    NASA Astrophysics Data System (ADS)

    Lindner, J. K. N.; Tsang, W. M.; Stritzker, B.; Wong, S. P.

    2003-08-01

    High doses of Ti, Ni, Mo, or W ions were implanted at elevated temperatures either conventionally or using a MEVVA ion source into ion beam synthesized Si/SiC/Si or SiC/Si layer structures in order to create metallic layers contacting the SiC. The depth distribution of metal atoms and the formation of silicide and carbide phases as well as the formation of cavities at the lower SiC/Si interface are studied by Rutherford backscattering spectroscopy (RBS) and cross-sectional transmission electron microscopy (XTEM). A brief survey of the effects ocurring in the ion beam metallization of SiC films is given and the benefit of using ion beams for metallization of thin films is elucidated.

  17. Silicon carbide: a versatile material for biosensor applications.

    PubMed

    Oliveros, Alexandra; Guiseppi-Elie, Anthony; Saddow, Stephen E

    2013-04-01

    Silicon carbide (SiC) has been around for more than 100 years as an industrial material and has found wide and varied applications because of its unique electrical and thermal properties. In recent years there has been increased attention to SiC as a viable material for biomedical applications. Of particular interest in this review is its potential for application as a biotransducer in biosensors. Among these applications are those where SiC is used as a substrate material, taking advantage of its surface chemical, tribological and electrical properties. In addition, its potential for integration as system on a chip and those applications where SiC is used as an active material make it a suitable substrate for micro-device fabrication. This review highlights the critical properties of SiC for application as a biosensor and reviews recent work reported on using SiC as an active or passive material in biotransducers and biosensors.

  18. A review on single photon sources in silicon carbide.

    PubMed

    Lohrmann, A; Johnson, B C; McCallum, J C; Castelletto, S

    2017-03-01

    This paper summarizes key findings in single-photon generation from deep level defects in silicon carbide (SiC) and highlights the significance of these individually addressable centers for emerging quantum applications. Single photon emission from various defect centers in both bulk and nanostructured SiC are discussed as well as their formation and possible integration into optical and electrical devices. The related measurement protocols, the building blocks of quantum communication and computation network architectures in solid state systems, are also summarized. This includes experimental methodologies developed for spin control of different paramagnetic defects, including the measurement of spin coherence times. Well established doping, and micro- and nanofabrication procedures for SiC may allow the quantum properties of paramagnetic defects to be electrically and mechanically controlled efficiently. The integration of single defects into SiC devices is crucial for applications in quantum technologies and we will review progress in this direction.

  19. Optical thermometry based on level anticrossing in silicon carbide.

    PubMed

    Anisimov, A N; Simin, D; Soltamov, V A; Lebedev, S P; Baranov, P G; Astakhov, G V; Dyakonov, V

    2016-09-14

    We report a giant thermal shift of 2.1 MHz/K related to the excited-state zero-field splitting in the silicon vacancy centers in 4H silicon carbide. It is obtained from the indirect observation of the optically detected magnetic resonance in the excited state using the ground state as an ancilla. Alternatively, relative variations of the zero-field splitting for small temperature differences can be detected without application of radiofrequency fields, by simply monitoring the photoluminescence intensity in the vicinity of the level anticrossing. This effect results in an all-optical thermometry technique with temperature sensitivity of 100 mK/Hz(1/2) for a detection volume of approximately 10(-6) mm(3). In contrast, the zero-field splitting in the ground state does not reveal detectable temperature shift. Using these properties, an integrated magnetic field and temperature sensor can be implemented on the same center.

  20. Dispersion of nonresonant third-order nonlinearities in Silicon Carbide.

    PubMed

    De Leonardis, Francesco; Soref, Richard A; Passaro, Vittorio M N

    2017-01-18

    In this paper we present a physical discussion of the indirect two-photon absorption (TPA) occuring in silicon carbide with either cubic or wurtzite structure. Phonon-electron interaction is analyzed by finding the phonon features involved in the process as depending upon the crystal symmetry. Consistent physical assumptions about the phonon-electron scattering mechanisms are proposed in order to give a mathematical formulation to predict the wavelength dispersion of TPA and the Kerr nonlinear refractive index n2. The TPA spectrum is investigated including the effects of band nonparabolicity and the influence of the continuum exciton. Moreover, a parametric analysis is presented in order to fit the experimental measurements. Finally, we have estimated the n2 in a large wavelength range spanning the visible to the mid-IR region.

  1. Dispersion of nonresonant third-order nonlinearities in Silicon Carbide

    NASA Astrophysics Data System (ADS)

    de Leonardis, Francesco; Soref, Richard A.; Passaro, Vittorio M. N.

    2017-01-01

    In this paper we present a physical discussion of the indirect two-photon absorption (TPA) occuring in silicon carbide with either cubic or wurtzite structure. Phonon-electron interaction is analyzed by finding the phonon features involved in the process as depending upon the crystal symmetry. Consistent physical assumptions about the phonon-electron scattering mechanisms are proposed in order to give a mathematical formulation to predict the wavelength dispersion of TPA and the Kerr nonlinear refractive index n2. The TPA spectrum is investigated including the effects of band nonparabolicity and the influence of the continuum exciton. Moreover, a parametric analysis is presented in order to fit the experimental measurements. Finally, we have estimated the n2 in a large wavelength range spanning the visible to the mid-IR region.

  2. Optical limiting effects in nanostructured silicon carbide thin films

    SciTech Connect

    Borshch, A A; Starkov, V N; Volkov, V I; Rudenko, V I; Boyarchuk, A Yu; Semenov, A V

    2013-12-31

    We present the results of experiments on the interaction of nanosecond laser radiation at 532 and 1064 nm with nanostructured silicon carbide thin films of different polytypes. We have found the effect of optical intensity limiting at both wavelengths. The intensity of optical limiting at λ = 532 nm (I{sub cl} ∼ 10{sup 6} W cm{sup -2}) is shown to be an order of magnitude less than that at λ = 1064 nm (I{sub cl} ∼ 10{sup 7} W cm{sup -2}). We discuss the nature of the nonlinearity, leading to the optical limiting effect. We have proposed a method for determining the amount of linear and two-photon absorption in material media. (nonlinear optical phenomena)

  3. Correlative microscopy of a carbide-free bainitic steel.

    PubMed

    Hofer, Christina; Bliznuk, Vitaliy; Verdiere, An; Petrov, Roumen; Winkelhofer, Florian; Clemens, Helmut; Primig, Sophie

    2016-02-01

    In this work a carbide-free bainitic steel was examined by a novel correlative microscopy approach using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). The individual microstructural constituents could be identified by TKD based on their different crystal structure for bainitic ferrite and retained austenite and by image quality for the martensite-austenite (M-A) constituent. Subsequently, the same area was investigated in the TEM and a good match of these two techniques regarding the identification of the area position and crystal orientation could be proven. Additionally, the M-A constituent was examined in the TEM for the first time after preceded unambiguous identification using a correlative microscopy approach. The selected area diffraction pattern showed satellites around the main reflexes which might indicate a structural modulation.

  4. Joining of Silicon Carbide Through the Diffusion Bonding Approach

    NASA Technical Reports Server (NTRS)

    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.

  5. Cryogenic Performance of a Lightweight Silicon Carbide Mirror

    NASA Technical Reports Server (NTRS)

    Eng, Ron; Carpenter, James; Haight, Harlan; Hogue, William; Kegley, Jeff; Stahl, H. Philip; Wright, Ernie; Kane, Dave; Hadaway, James

    2005-01-01

    Low cost, high performance lightweight Silicon Carbide (SiC) mirrors provide an alternative to Beryllium mirrors. A Trex Enterprises 0.25m diameter lightweight SiC mirror using its patented Chemical Vapor Composites (CVC) technology was evaluated for its optical performance. CVC SiC is chemically pure, thermally stable, and mechanically stiff. CVC technology yields higher growth rate than that of CVD SiC. NASA has funded lightweight optical materials technology development efforts involving SiC mirrors for future space based telescope programs. As part of these efforts, a Trex SiC was measured interferometrically from room temperature to 30 degrees Kelvin. This paper will discuss the test goals, the test instrumentation, test results, and lessons learned.

  6. Silicon carbide, a semiconductor for space power electronics

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony; Matus, Lawrence G.

    1991-01-01

    After many years of promise as a high temperature semiconductor, silicon carbide (SiC) is finally emerging as a useful electronic material. Recent significant progress that has led to this emergence has been in the areas of crystal growth and device fabrication technology. High quality single-crystal SiC wafers, up to 25 mm in diameter, can now be produced routinely from boules grown by a high temperature (2700 K) sublimation process. Device fabrication processes, including chemical vapor deposition (CVD), in situ doping during CVD, reactive ion etching, oxidation, metallization, etc. have been used to fabricate p-n junction diodes and MOSFETs. The diode was operated to 870 K and the MOSFET to 770 K.

  7. Silicon carbide, a semiconductor for space power electronics

    NASA Technical Reports Server (NTRS)

    Powell, J. A.; Matus, Lawrence G.

    1991-01-01

    After many years of promise as a high temperature semiconductor, silicon carbide (SiC) is finally emerging as a useful electronic material. Recent significant progress that has led to this emergence has been in the area of crystal growth and device fabrication technology. High quality of single-crystal SiC wafers, up to 25 mm in diameter, can now be produced routinely from boules grown by a high temperature (2700 K) sublimation process. Device fabrication processes, including chemical vapor deposition (CVD), in situ doping during CVD, reactive ion etching, oxidation, metallization, etc. have been used to fabricate p-n junction diodes and MOSFETs. The diode was operated to 870 K and the MOSFET to 770 K.

  8. Method of Assembling a Silicon Carbide High Temperature Anemometer

    NASA Technical Reports Server (NTRS)

    Okojie, Robert S. (Inventor); Fralick, Gustave C. (Inventor); Saad, George J. (Inventor)

    2004-01-01

    A high temperature anemometer includes a pair of substrates. One of the substrates has a plurality of electrodes on a facing surface, while the other of the substrates has a sensor cavity on a facing surface. A sensor is received in the sensor cavity, wherein the sensor has a plurality of bondpads, and wherein the bondpads contact the plurality of electrodes when the facing surfaces are mated with one another. The anemometer further includes a plurality of plug-in pins, wherein the substrate with the cavity has a plurality of trenches with each one receiving a plurality of plug-in pins. The plurality of plug-in pins contact the plurality of electrodes when the substrates are mated with one another. The sensor cavity is at an end of one of the substrates such that the sensor partially extends from the substrate. The sensor and the substrates are preferably made of silicon carbide.

  9. Transition Metal Carbides and Nitrides in Energy Storage and Conversion.

    PubMed

    Zhong, Yu; Xia, Xinhui; Shi, Fan; Zhan, Jiye; Tu, Jiangping; Fan, Hong Jin

    2016-05-01

    High-performance electrode materials are the key to advances in the areas of energy conversion and storage (e.g., fuel cells and batteries). In this Review, recent progress in the synthesis and electrochemical application of transition metal carbides (TMCs) and nitrides (TMNs) for energy storage and conversion is summarized. Their electrochemical properties in Li-ion and Na-ion batteries as well as in supercapacitors, and electrocatalytic reactions (oxygen evolution and reduction reactions, and hydrogen evolution reaction) are discussed in association with their crystal structure/morphology/composition. Advantages and benefits of nanostructuring (e.g., 2D MXenes) are highlighted. Prospects of future research trends in rational design of high-performance TMCs and TMNs electrodes are provided at the end.

  10. Electromechanical computing at 500 degrees C with silicon carbide.

    PubMed

    Lee, Te-Hao; Bhunia, Swarup; Mehregany, Mehran

    2010-09-10

    Logic circuits capable of operating at high temperatures can alleviate expensive heat-sinking and thermal-management requirements of modern electronics and are enabling for advanced propulsion systems. Replacing existing complementary metal-oxide semiconductor field-effect transistors with silicon carbide (SiC) nanoelectromechanical system (NEMS) switches is a promising approach for low-power, high-performance logic operation at temperatures higher than 300 degrees C, beyond the capability of conventional silicon technology. These switches are capable of achieving virtually zero off-state current, microwave operating frequencies, radiation hardness, and nanoscale dimensions. Here, we report a microfabricated electromechanical inverter with SiC complementary NEMS switches capable of operating at 500 degrees C with ultralow leakage current.

  11. Dynamic SEM wear studies of tungsten carbide cermets

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Buckley, D. H.

    1975-01-01

    Dynamic friction and wear experiments were conducted in a scanning electron microscope. The wear behavior of pure tungsten carbide and composite with 6 and 15 weight percent cobalt binder was examined. Etching of the binder was done to selectively determine the role of the binder in the wear process. Dynamic experiments were conducted as the WC and bonded WC cermet surfaces were transversed by a 50 micron radiused diamond stylus. These studies show that the predominant wear process in WC is fracture initiated by plastic deformation. The wear of the etched cermets is similar to pure WC. The presence of the cobalt binder reduces both friction and wear. The cementing action of the cobalt reduces granular separation and promotes a dense polished layer because of its low shear strength film-forming properties. The wear debris generated from unetched surface is approximately the same composition as the bulk.

  12. New method for synthesis of metal carbides, nitrides and carbonitrides

    SciTech Connect

    Koc, R.; Folmer, J.S.; Kodambaka, S.K.

    1997-04-01

    The purpose of this work is to develop a novel synthesis method using a carbothermic reduction reaction of carbon coated precursors for producing high purity, submicron, non-agglomerated powders of metal carbide, metal nitride and metal boride systems. The authors also want to demonstrate the advantages of the process and provide information on the applicability of the process for synthesizing related advanced ceramic powders (e.g. SiC, WC, TiN, TiB{sub 2}, Si{sub 3}N{sub 4}). During the FY96 of the project, steps are taken to investigate the reaction mechanisms and phase evolution during the formation of TiC from carbon coated titania precursors and to produce submicron TiC powders with desired stoichiometries. Depending on the carbon content in the coated titania precursor, TiC powder was produced with different stoichiometries (different amount of oxygen and free carbon).

  13. Aligned silicon carbide nanowire crossed nets with high superhydrophobicity.

    PubMed

    Niu, Jun Jie; Wang, Jian Nong; Xu, Qian Feng

    2008-06-01

    Aligned silicon carbide nanowire crossed nets (a-SiCNWNs) were directly synthesized by using a vapor-solid reaction at 1100 degrees C. Zinc sulfide was used as catalyst to assist the growth of a-SiCNWNs with small size and crystal structure. After functionalization with perfluoroalkysilane, a-SiCNWNs showed excellent superhydrophobic property with a high water contact angle more than 156 +/- 2 degrees , compared to random nanowires (147 +/- 2 degrees ) and pure silicon wafers (101 +/- 2 degrees ). The topographic roughness and chemical modification with CF 2/CF 3 groups contributed the better superhydrophobicity. Furthermore, the as-grown SiCNWNs can be scraped off and coated on other substrates such as pure silicon wafers. The novel nanowire coating with good superhydrophobicity displays extensive applications in silicon-related fields such as solar cells, radar, etc.

  14. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    NASA Astrophysics Data System (ADS)

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  15. Electromagnetic interference shielding with 2D transition metal carbides (MXenes)

    NASA Astrophysics Data System (ADS)

    Shahzad, Faisal; Alhabeb, Mohamed; Hatter, Christine B.; Anasori, Babak; Man Hong, Soon; Koo, Chong Min; Gogotsi, Yury

    2016-09-01

    Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.

  16. Joining and Integration of Silicon Carbide for Turbine Engine Applications

    NASA Technical Reports Server (NTRS)

    Halbig, Michael C.; Singh, Mrityunjay; Coddington, Bryan; Asthana, Rajiv

    2010-01-01

    The critical need for ceramic joining and integration technologies is becoming better appreciated as the maturity level increases for turbine engine components fabricated from ceramic and ceramic matrix composite materials. Ceramic components offer higher operating temperatures and reduced cooling requirements. This translates into higher efficiencies and lower emissions. For fabricating complex shapes, diffusion bonding of silicon carbide (SiC) to SiC is being developed. For the integration of ceramic parts to the surrounding metallic engine system, brazing of SiC to metals is being developed. Overcoming the chemical, thermal, and mechanical incompatibilities between dissimilar materials is very challenging. This presentation will discuss the types of ceramic components being developed by researchers and industry and the benefits of using ceramic components. Also, the development of strong, crack-free, stable bonds will be discussed. The challenges and progress in developing joining and integration approaches for a specific application, i.e. a SiC injector, will be presented.

  17. Monolithic Carbide-Derived Carbon Films for Micro-Supercapacitors

    NASA Astrophysics Data System (ADS)

    Chmiola, John; Largeot, Celine; Taberna, Pierre-Louis; Simon, Patrice; Gogotsi, Yury

    2010-04-01

    Microbatteries with dimensions of tens to hundreds of micrometers that are produced by common microfabrication techniques are poised to provide integration of power sources onto electronic devices, but they still suffer from poor cycle lifetime, as well as power and temperature range of operation issues that are alleviated with the use of supercapacitors. There have been a few reports on thin-film and other micro-supercapacitors, but they are either too thin to provide sufficient energy or the technology is not scalable. By etching supercapacitor electrodes into conductive titanium carbide substrates, we demonstrate that monolithic carbon films lead to a volumetric capacity exceeding that of micro- and macroscale supercapacitors reported thus far, by a factor of 2. This study also provides the framework for integration of high-performance micro-supercapacitors onto a variety of devices.

  18. First-principles study of point defects in thorium carbide

    NASA Astrophysics Data System (ADS)

    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.

  19. Spin-photon entanglement interfaces in silicon carbide defect centers.

    PubMed

    Economou, Sophia E; Dev, Pratibha

    2016-12-16

    Optically active spins in solid-state systems can be engineered to emit photons that are entangled with the spin in the solid. This allows for applications such as quantum communications, quantum key distribution, and distributed quantum computing. Recently, there has been a strong interest in silicon carbide defects, as they emit very close to the telecommunication wavelength, making them excellent candidates for long range quantum communications. In this work we develop explicit schemes for spin-photon entanglement in several SiC defects: the silicon monovacancy, the silicon divacancy, and the NV center in SiC. Distinct approaches are given for (i) single-photon and spin entanglement and (ii) the generation of long strings of entangled photons. The latter are known as cluster states and comprise a resource for measurement-based quantum information processing.

  20. Transition Metal Carbides and Nitrides in Energy Storage and Conversion

    PubMed Central

    Zhong, Yu; Shi, Fan; Zhan, Jiye; Tu, Jiangping

    2016-01-01

    High‐performance electrode materials are the key to advances in the areas of energy conversion and storage (e.g., fuel cells and batteries). In this Review, recent progress in the synthesis and electrochemical application of transition metal carbides (TMCs) and nitrides (TMNs) for energy storage and conversion is summarized. Their electrochemical properties in Li‐ion and Na‐ion batteries as well as in supercapacitors, and electrocatalytic reactions (oxygen evolution and reduction reactions, and hydrogen evolution reaction) are discussed in association with their crystal structure/morphology/composition. Advantages and benefits of nanostructuring (e.g., 2D MXenes) are highlighted. Prospects of future research trends in rational design of high‐performance TMCs and TMNs electrodes are provided at the end. PMID:27812464

  1. Microstructural optimization of solid-state sintered silicon carbide

    NASA Astrophysics Data System (ADS)

    Vargas-Gonzalez, Lionel R.

    Silicon carbide armor, manufactured through solid-state sintering, liquid-phase sintering, and hot-pressing, is being used by the United States Armed Forces for personal and vehicle protection. There is a lack of consensus, however, on which process results in the best-performing ballistic armor. Previous studies have shown that hot-pressed ceramics processed with secondary oxide and/or rare earth oxides, which exhibit high fracture toughness, perform well in handling and under ballistic impact. This high toughness is due to the intergranular nature of the fracture, creating a tortuous path for cracks and facilitating crack deflection and bridging. However, it has also been shown that higher-hardness sintered SiC materials might perform similarly or better to hot-pressed armor, in spite of the large fracture toughness deficit, if the microstructure (density, grain size, purity) of these materials are improved. In this work, the development of theoretically-dense, clean grain boundary, high hardness solid-state sintered silicon carbide (SiC) armor was pursued. Boron carbide and graphite (added as phenolic resin to ensure the carbon is finely dispersed throughout the microstructure) were used as the sintering aids. SiC batches between 0.25--4.00 wt.% carbon were mixed and spray dried. Cylindrical pellets were pressed at 13.7 MPa, cold-isostatically pressed (CIP) at 344 MPa, sintered under varying sintering soaking temperatures and heating rates, and varying post hot-isostatic pressing (HIP) parameters. Carbon additive amounts between 2.0--2.5 wt.% (based on the resin source), a 0.36 wt.% B4C addition, and a 2050°C sintering soak yielded parts with high sintering densities (˜95.5--96.5%) and a fine, equiaxed microstructure (d50 = 2.525 mum). A slow ramp rate (10°C/min) prevented any occurrence of abnormal grain growth. Post-HIPing at 1900°C removed the remaining closed porosity to yield a theoretically-dense part (3.175 g/cm3, according to rule of mixtures). These

  2. High surface area silicon carbide-coated carbon aerogel

    DOEpatents

    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.

  3. Radiation damage of transition metal carbides. Final technical report

    SciTech Connect

    Dixon, G.

    1991-12-31

    In this grant period we have investigated electrical properties of transition metal carbides and radiation-induced defects produced by low-temperature electron irradiation in them. Special attention has been given to the composition VC{sub 0.88} in which the vacancies on the carbon sublattice of this fcc crystal order to produce a V{sub 8}C{sub 7} superlattice. The existence of this superlattice structure was found to make the crystal somewhat resistant to radiation damage at low doses and/or at ambient temperature. At larger doses significant changes in the resistivity are produced. Annealing effects were observed which we believe to be connected with the reconstitution of the superlattice structure.

  4. Anisotropic electronic conduction in stacked two-dimensional titanium carbide.

    PubMed

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-09

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  5. Hydrothermal corrosion of silicon carbide joints without radiation

    SciTech Connect

    Koyanagi, Takaaki; Katoh, Yutai; Terrani, Kurt A.; Kim, Young-Jin; Kiggans, James O.; Hinoki, Tatsuya

    2016-09-28

    In this paper, hydrothermal corrosion of four types of the silicon carbide (SiC) to SiC plate joints were investigated under pressurized water reactor and boiling water reactor relevant chemical conditions without irradiation. The joints were formed by metal diffusion bonding using molybdenum or titanium interlayer, reaction sintering using Ti—Si—C system, and SiC nanopowder sintering. Most of the joints withstood the corrosion tests for five weeks. The recession of the SiC substrates was limited. Based on the recession of the bonding layers, it was concluded that all the joints except for the molybdenum diffusion bond are promising under the reducing environments without radiation. Finally, the SiC nanopowder sintered joint was the most corrosion tolerant under the oxidizing environment among the four joints.

  6. Size Dependence of Nanoscale Wear of Silicon Carbide.

    PubMed

    Tangpatjaroen, Chaiyapat; Grierson, David; Shannon, Steve; Jakes, Joseph E; Szlufarska, Izabela

    2017-01-18

    Nanoscale, single-asperity wear of single-crystal silicon carbide (sc-SiC) and nanocrystalline silicon carbide (nc-SiC) is investigated using single-crystal diamond nanoindenter tips and nanocrystalline diamond atomic force microscopy (AFM) tips under dry conditions, and the wear behavior is compared to that of single-crystal silicon with both thin and thick native oxide layers. We discovered a transition in the relative wear resistance of the SiC samples compared to that of Si as a function of contact size. With larger nanoindenter tips (tip radius ≈ 370 nm), the wear resistances of both sc-SiC and nc-SiC are higher than that of Si. This result is expected from the Archard's equation because SiC is harder than Si. However, with the smaller AFM tips (tip radius ≈ 20 nm), the wear resistances of sc-SiC and nc-SiC are lower than that of Si, despite the fact that the contact pressures are comparable to those applied with the nanoindenter tips, and the plastic zones are well-developed in both sets of wear experiments. We attribute the decrease in the relative wear resistance of SiC compared to that of Si to a transition from a wear regime dominated by the materials' resistance to plastic deformation (i.e., hardness) to a regime dominated by the materials' resistance to interfacial shear. This conclusion is supported by our AFM studies of wearless friction, which reveal that the interfacial shear strength of SiC is higher than that of Si. The contributions of surface roughness and surface chemistry to differences in interfacial shear strength are also discussed.

  7. The 11 micron Silicon Carbide Feature in Carbon Star Shells

    NASA Technical Reports Server (NTRS)

    Speck, A. K.; Barlow, M. J.; Skinner, C. J.

    1996-01-01

    Silicon carbide (SiC) is known to form in circumstellar shells around carbon stars. SiC can come in two basic types - hexagonal alpha-SiC or cubic beta-SiC. Laboratory studies have shown that both types of SiC exhibit an emission feature in the 11-11.5 micron region, the size and shape of the feature varying with type, size and shape of the SiC grains. Such a feature can be seen in the spectra of carbon stars. Silicon carbide grains have also been found in meteorites. The aim of the current work is to identity the type(s) of SiC found in circumstellar shells and how they might relate to meteoritic SiC samples. We have used the CGS3 spectrometer at the 3.8 m UKIRT to obtain 7.5-13.5 micron spectra of 31 definite or proposed carbon stars. After flux-calibration, each spectrum was fitted using a chi(exp 2)-minimisation routine equipped with the published laboratory optical constants of six different samples of small SiC particles, together with the ability to fit the underlying continuum using a range of grain emissivity laws. It was found that the majority of observed SiC emission features could only be fitted by alpha-SiC grains. The lack of beta-SiC is surprising, as this is the form most commonly found in meteorites. Included in the sample were four sources, all of which have been proposed to be carbon stars, that appear to show the SiC feature in absorption.

  8. New catalysts for coal processing: Metal carbides and nitrides

    SciTech Connect

    S. Ted Oyama; David F. Cox

    1999-12-03

    The subject of this research project was to investigate the catalytic properties of a new class of materials, transition metal carbides and nitrides, for treatment of coal liquid and petroleum feedstocks. The main objectives were: (1) preparation of catalysts in unsupported and supported form; (2) characterization of the materials; (3) evaluation of their catalytic properties in HDS and HDN; (4) measurement of the surface properties; and (5) observation of adsorbed species. All of the objectives were substantially carried out and the results will be described in detail below. The catalysts were transition metal carbides and nitrides spanning Groups 4--6 in the Periodic Table. They were chosen for study because initial work had shown they were promising materials for hydrotreating. The basic strategy was first to prepare the materials in unsupported form to identify the most promising catalyst, and then to synthesize a supported form of the material. Already work had been carried out on the synthesis of the Group VI compounds Mo{sub 2}C, Mo{sub 2}N, and WC, and new methods were developed for the Group V compounds VC and NbC. All the catalysts were then evaluated in a hydrotreating test at realistic conditions. It was found that the most active catalyst was Mo{sub 2}C, and further investigations of the material were carried out in supported form. A new technique was employed for the study of the bulk and surface properties of the catalysts, near edge x-ray absorption spectroscopy (NEXAFS), that fingerprinted the electronic structure of the materials. Finally, two new research direction were explored. Bimetallic alloys formed between two transition metals were prepared, resulting in catalysts having even higher activity than Mo{sub 2}C. The performance of the catalysts in hydrodechloration was also investigated.

  9. Electronic and vibrational properties of vanadium-carbide nanowires

    NASA Astrophysics Data System (ADS)

    Singh, Poorva; Nautiyal, Tashi; Auluck, Sushil

    2012-09-01

    We have made an effort to understand the properties of transition metal carbide nanowires (NWs) and studied vanadium-carbide (VC) nanowires as a specific case. Different structures have been considered and their electronic and vibrational properties studied employing density functional theory. The effect of dimensionality is very well brought forth by these NWs, narrow/thinner structures have clear preference for magnetic state with sizeable magnetic moment at the V sites. As the thickness/width increases, the margin decreases and the magnetic moment disappears altogether for structures like square and rectangular NWs. The cohesive energy per atom increases with the increase in lateral dimensions of the NW, and it is about 88% of the bulk value for the rectangular NW, while it is only 50% for the linear chain. All the wires are conducting in nature, with the linear and zigzag wires having half-metallic character. Our calculations show that the V atoms decide the electronic and magnetic properties in these while compressibility, a mechanical property, is governed by the C atoms. The electron localization function beautifully illustrates the closeness of thicker/wider NWs to the bulk. It also reveals that electrons are highly localized around C atoms; however, the amount of charge transferred depends strongly on the structure of wire. The optical properties unfurl the impact of different spatial expanse in the cross section of NW in a nice way, e.g., ɛ2xx > ɛ2yy (ɛ2 is imaginary part of dielectric function) for all those with a larger expanse along X compared to Y and vice-versa. Thicker nanowires seem to be more suitable for optical applications. Site-resolved phonon density of states shows that presence of C atoms is responsible for high frequency branches. The heat capacity variation for various structures closely follows the magnitude of respective phonon density of states.

  10. Advanced Measurements of Silicon Carbide Ceramic Matrix Composites

    SciTech Connect

    Farhad Farzbod; Stephen J. Reese; Zilong Hua; Marat Khafizov; David H. Hurley

    2012-08-01

    Silicon carbide (SiC) is being considered as a fuel cladding material for accident tolerant fuel under the Light Water Reactor Sustainability (LWRS) Program sponsored by the Nuclear Energy Division of the Department of Energy. Silicon carbide has many potential advantages over traditional zirconium based cladding systems. These include high melting point, low susceptibility to corrosion, and low degradation of mechanical properties under neutron irradiation. In addition, ceramic matrix composites (CMCs) made from SiC have high mechanical toughness enabling these materials to withstand thermal and mechanical shock loading. However, many of the fundamental mechanical and thermal properties of SiC CMCs depend strongly on the fabrication process. As a result, extrapolating current materials science databases for these materials to nuclear applications is not possible. The “Advanced Measurements” work package under the LWRS fuels pathway is tasked with the development of measurement techniques that can characterize fundamental thermal and mechanical properties of SiC CMCs. An emphasis is being placed on development of characterization tools that can used for examination of fresh as well as irradiated samples. The work discuss in this report can be divided into two broad categories. The first involves the development of laser ultrasonic techniques to measure the elastic and yield properties and the second involves the development of laser-based techniques to measurement thermal transport properties. Emphasis has been placed on understanding the anisotropic and heterogeneous nature of SiC CMCs in regards to thermal and mechanical properties. The material properties characterized within this work package will be used as validation of advanced materials physics models of SiC CMCs developed under the LWRS fuels pathway. In addition, it is envisioned that similar measurement techniques can be used to provide process control and quality assurance as well as measurement of

  11. Expanding the versatility of silicon carbide thin films and nanowires

    NASA Astrophysics Data System (ADS)

    Luna, Lunet

    Silicon carbide (SiC) based electronics and sensors hold promise for pushing past the limits of current technology to achieve small, durable devices that can function in high-temperature, high-voltage, corrosive, and biological environments. SiC is an ideal material for such conditions due to its high mechanical strength, excellent chemical stability, and its biocompatibility. Consequently, SiC thin films and nanowires have attracted interest in applications such as micro- and nano-electromechanical systems, biological sensors, field emission cathodes, and energy storage devices. However to fully realize SiC in such technologies, the reliability of metal contacts to SiC at high temperatures must be improved and the nanowire growth mechanism must be understood to enable strict control of nanowire crystal structure and orientation. Here, we present a novel metallization scheme, utilizing solid-state graphitization of SiC, to improve the long-term reliability of Pt/Ti contacts to polycrystalline n-type SiC films at high temperature. The metallization scheme includes an alumina protection layer and exhibits low, stable contact resistivity even after long-term (500 hr) testing in air at 450 ºC. We also report the crystal structure and growth mechanism of Ni-assisted silicon carbide nanowires using single-source precursor, methyltrichlorosilane. The effects of growth parameters, such as substrate and temperature, on the structure and morphology of the resulting nanowires will also be presented. Overall, this study provides new insights towards the realization of novel SiC technologies, enabled by advanced electron microscopy techniques located in the user facilities at the Molecular Foundry in Berkeley, California. This work was performed in part at the Molecular Foundry, supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

  12. Structural evolution of molybdenum carbides in hot aqueous environments and impact on low-temperature hydroprocessing of acetic acid

    DOE PAGES

    Choi, Jae -Soon; Schwartz, Viviane; Santillan-Jimenez, Eduardo; ...

    2015-03-13

    In this paper, 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 themore » 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. Finally, 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.« less

  13. Structural evolution of molybdenum carbides in hot aqueous environments and impact on low-temperature hydroprocessing of acetic acid

    SciTech Connect

    Choi, Jae -Soon; Schwartz, Viviane; Santillan-Jimenez, Eduardo; Crocker, Mark; Lewis, Sr., Samuel A.; Lance, Michael J.; Meyer, III, Harry M.; More, Karren L.

    2015-03-13

    In this paper, 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. Finally, 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.

  14. Silicon-Carbide Power MOSFET Performance in High Efficiency Boost Power Processing Unit for Extreme Environments

    NASA Technical Reports Server (NTRS)

    Ikpe, Stanley A.; Lauenstein, Jean-Marie; Carr, Gregory A.; Hunter, Don; Ludwig, Lawrence L.; Wood, William; Del Castillo, Linda Y.; Fitzpatrick, Fred; Chen, Yuan

    2016-01-01

    Silicon-Carbide device technology has generated much interest in recent years. With superior thermal performance, power ratings and potential switching frequencies over its Silicon counterpart, Silicon-Carbide offers a greater possibility for high powered switching applications in extreme environment. In particular, Silicon-Carbide Metal-Oxide- Semiconductor Field-Effect Transistors' (MOSFETs) maturing process technology has produced a plethora of commercially available power dense, low on-state resistance devices capable of switching at high frequencies. A novel hard-switched power processing unit (PPU) is implemented utilizing Silicon-Carbide power devices. Accelerated life data is captured and assessed in conjunction with a damage accumulation model of gate oxide and drain-source junction lifetime to evaluate potential system performance at high temperature environments.

  15. Silyl-acetylene polymers for use as precursors to silicon carbide fibers

    SciTech Connect

    Meyer, M.K.

    1991-12-20

    The steps involved in production of silicon carbide fiber using silyl acetylene polymer precursors can be separated into four processing steps: polymer synthesis, fiber spinning, fiber crosslinking, and pyrolysis. Practical experimental considerations in each step are discussed.

  16. Surface roughness analysis after machining of direct laser deposited tungsten carbide

    NASA Astrophysics Data System (ADS)

    Wojciechowski, S.; Twardowski, P.; Chwalczuk, T.

    2014-03-01

    In this paper, an experimental surface roughness analysis in machining of tungsten carbide is presented. The tungsten carbide was received using direct laser deposition technology (DLD). Experiments carried out included milling of tungsten carbide samples using monolithic torus cubic boron nitride (CBN) tool and grinding with the diamond cup wheel. The effect of machining method on the generated surface topography was analysed. The 3D surface topographies were measured using optical surface profiler. The research revealed, that surface roughness generated after the machining of tungsten carbide is affected by feed per tooth (fz) value related to kinematic-geometric projection only in a minor extent. The main factor affecting machined surface roughness is the occurrence of micro grooves and protuberances on the machined surface, as well as other phenomena connected, inter alia, with the mechanism for material removal.

  17. CHARACTERIZATION OF PRECIPITATES IN CUBIC SILICON CARBIDE IMPLANTED WITH 25Mg+ IONS

    SciTech Connect

    Jiang, Weilin; Spurgeon, Steven R.; Liu, Jia; Edwards, Danny J.; Schreiber, Daniel K.; Henager, Charles H.; Kurtz, Richard J.; Wang, Yongqiang

    2016-09-26

    The aim of this study is to characterize precipitates in Mg+ ion implanted and high-temperature annealed cubic silicon carbide using scanning transmission electron microscopy, electron energy loss spectroscopy and atom probe tomography.

  18. Single-Event Effects in Silicon and Silicon Carbide Power Devices

    NASA Technical Reports Server (NTRS)

    Lauenstein, Jean-Marie; Casey, Megan C.; LaBel, Kenneth A.; Topper, Alyson D.; Wilcox, Edward P.; Kim, Hak; Phan, Anthony M.

    2014-01-01

    NASA Electronics Parts and Packaging program-funded activities over the past year on single-event effects in silicon and silicon carbide power devices are presented, with focus on SiC device failure signatures.

  19. Raman and FTIR Studies of Silicon Carbide Surface Damage from Palladium Implantation in Presence of Hydrogen

    NASA Technical Reports Server (NTRS)

    Muntele, I.; Ila, D.; Muntele, C. J.; Poker, D. B.; Hensley, D. K.; Larkin, David (Technical Monitor)

    2001-01-01

    The ion implantation in a crystal such as silicon carbide will cause both damage in the ion track and in the substrate at the end of the ion track. We used both keV, and MeV Pd ions in fabricating electronic chemical sensors in silicon carbide, which can operate at elevated temperatures. In order to study the feasibility of fabricating an optical chemical sensor (litmus sensor), we need to understand the optical behavior of the embedded damage in the presence of hydrogen, as well as the potential chemical interaction of silicon carbide broken lattice bonds with the hydrogen dissociated from gas by palladium. Implanted samples of silicon carbide were studied using both Raman spectroscopy and FTIR (Fourier Transform-Infrared). The results of this work will be presented during the meeting.

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

    SciTech Connect

    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.