Mixture Of Silicon Carbide Research Articles

ＩＩＩ族元素および窒素を共添加した炭化ケイ素セラミックスのピエゾ抵抗効果

Evaluation samples of p-type α-silicon carbide ceramics were first fabricated by glass capsule HIP method using powder mixture of silicon carbide with boron, aluminum, or gallium at various ratios. The resultant p-type silicon carbide ceramics were doped with nitrogen by changing the post-HIP nitrogen gas pressure. The lattice parameter decreased with nitrogen doping pressure indicating that the incorporated nitrogen were dissolved into silicon carbide. In the case of boron and aluminum doped samples, the piezoresistive coefficient decreased with the nitrogen doping pressure, while gallium doped one remained almost constant with doping pressure.

Crystal structure and growth of carbon–silicon mixture film prepared by ion sputtering

Si (10–50%)-containing carbon (C–Si) films were prepared by ion sputtering of carbon and silicon carbide mixture pellets. The C–Si film was composed of a solid-solution phase of carbon and silicon with a diamond structure. The film showed a higher transparency than a simultaneously evaporated C–Si mixture film. Diamond crystals 100 nm in diameter were also produced by vacuum heating of C–Si film at 800 ∘ C . The infrared spectrum showed significant absorption features at 9.5 and 21 μ m , in contrast to the 11 and 12 μ m of SiC. The 21 μ m feature is one of the candidate unidentified infrared bands on the spectra of carbon-rich post-asymptotic giant branch stars.

Effect of Heat Treatment on Microstructure and Mechanical Properties of Stoichiometric SiC/SiC Composites

Polymer impregnation and pyrolysis (PIP) is one of the most attractive fabrication processes for silicon carbide (SiC) composites due to the shape flexibility, mass production and relatively low cost. In particular, advanced PIP SiC/SiC composite with high-crystallinity and near-stoichiometric composition is expected to have superior thermo-mechanical properties including good oxidation resistance, due to the reduction of impurities and well-organized crystal structure. Additionally, by applying a thin carbon interphase by chemical vapor infiltration (CVI), control of the crack propagation and oxidation resistance are also achieved. In this study, a CVI + PIP hybrid process based on the recently developed stoichiometric PIP process was performed. Specifically, matrix crystallization was enhanced by heat treatment in Ar, and its effect on microstructures and mechanical properties were evaluated. Stoichiometric SiC/SiC composites exhibit superior flexural strength up to 1573 K in Ar and 1273 K in air. This is because the stoichiometric composition in PIP-SiC matrix reduces inner oxidation by impurities. Also, the thin pyrolytic carbon interphase tailored by CVI process effectively controls crack propagation at fiber and matrix interphase. In a similar manner, the microstructure of the stoichiometric PIP-SiC matrix, constructed by the mixture of amorphous SiC and highly crystalline SiC, was stable against the high-temperature heat exposure up to 1773 K in Ar. In particular, stoichiometric SiC/SiC composites heated at 1773 K in Ar provides superior stability of mechanical properties up to 1573 K even in air atmosphere, although extensive crystallization, in the case of heat treatment at 1973 K in Ar, caused brittle composite fracture.

Band gap engineering of SiCN film grown by pulsed laser deposition

The band gap tuning of amorphous silicon carbon nitride thin (a-SiCN) film was demonstrated in the range of 2.3–3.0 eV by pulsed laser deposition using mixed targets. a-SiCN films were grown on silicon and quartz glass substrates at room temperature in a vacuum. Targets were fabricated by compacting a mixture of silicon carbide and silicon nitride powders. The stoichiometry of the film could be varied by the mixing ratio of the target. Ternary phase SiCN films were deposited at 30– 70 wt. % SiC in a target and their band gaps were controlled by appropriate adjustment of the carbon content. These findings indicate that the growth of a-SiCN films with a mixed target and their subsequent use as optoelectronic materials is a possibility.

Structural and Mechanical Properties of Silicon Carbide Mixtures Based on Boroethyl Silicate Binders

The rheologic properties of silicon carbide plastic mixtures with varying contents, in both concentration and type, of molding binders are analyzed. Ranges of binder concentrations, optimum for semi-dry pressing technology, are specified.

Dispersion, slip casting and reaction nitridation of silicon–silicon carbide mixtures

The dispersing behaviour of silicon, silicon carbide and their mixtures in aqueous media were monitored by particle size, sedimentation, viscosity and zeta potential analyses as a function of pH of the slurry. The pH values for optimum dispersion were found to be 4 and 8 for silicon, 10 for SiC and 9 for Si+SiC mixtures. Optimum slips of Si+SiC mixtures were slip cast to obtain green compacts which were nitrided once at 1450°C for 2 or 4 h or successively and cumulatively for 8 (2+6) and 10 (4+6) h in a resistively heated graphite furnace. The binding phases in the nitrided products were found to be fibrous/needle like α-Si 3N 4, flaky grains of β-Si 3N 4 and Si 2ON 2. The products containing 19–47% of silicon nitride as bond/matrix possessed flexural strength (three-point bending) values of 50–85 MPa. ©

Simulation of Pressure Filtrating Process for Making Porosity Graded Silicon Carbide Evaporator Tubes

Porous silicon carbide (SiC) ceramics are promising materials for liquid fuel evaporator tubes in gas turbine combustors Previous finite element method (FEM) calculations show that a tailored porosity gradient is necessary to meet the local stress/ strength requirements. For tubes with such porosity gradients a processing route based on pressure filtration was developed. The formation of one- and more dimensional wax concentration gradients in the filter cake (corresponding to porosity gradients after sintering) is adjusted by controlling the composition of a mixture of SiC- and SiC-wax slurries and the filtration pressure The design concept of a laboratory casting apparatus which uses this concept is presented An experimental/ numerical method for the derivation of the process parameters will also be treated in the paper.

Inorganic Solid-State Chemistry with Main Group Element Carbodiimides

Organosilicon carbodiimides have been successfully applied as single-source precursor compounds for the synthesis of novel ternary Si-, C-, and N-containing solid phases. Their thermally induced decomposition gives either amorphous silicon carbonitrides or polycrystalline silicon nitride and silicon carbide mixtures, materials that are presently of technological interest for their exceptional hardness, strength, toughness, and high temperature resistance even in corrosive environments. This review is concerned with the synthesis, characterization, and thermal stability of element carbodiimides. The main part of this paper is focused on polymeric silicon-based carbodiimides obtained by the reaction of chloro(organo)silanes with bis(trimethylsilyl)carbodiimide. In the case of RSiCl3, novel poly(silylcarbodiimide) gels are formed. Starting from silicon tetrachloride, new crystalline SiCN phases (namely, SiC2N4 and Si2CN4), have been isolated. Their crystal structures as well as their thermal behavior in the range between room temperature and 1600 °C are discussed. Moreover, preliminary results on the synthesis of germanium- and boron-containing carbodiimides are reported. It is also shown that carbon-based carbodiimides can be obtained by the reaction of cyanuric halides with bis(trimethylsilyl)carbodiimide. These materials are investigated as precursors for the synthesis of new carbon nitrides with high hardness.

Bias-enhanced nucleation of diamond on silicon dioxide

Characterization of amorphous SiO2 surfaces after biasing pretreatments, which induce nucleation of diamond, has been carried out using x-ray photoelectron spectroscopy and Raman spectroscopy. A mixture of silicon carbide, silicon oxycarbide, and diamond are formed upon exposure of biased SiO2 surfaces to a CH4+H2 plasma used for diamond deposition. It is concluded that nucleation of diamond on amorphous SiO2 surfaces is promoted by formation of a SiC surface layer. Textured diamond films have been fabricated on bulk SiO2 substrates using biasing pretreatments to induce diamond nucleation.

Dispersion of three ceramic powders in a slurry. The Al 2O 3AlNSiC mixture

This work presents, in a first stage the influence of aluminium nitride (AlN) addition to a well dispersed α-alumina slurry, and in a second stage the influence of silicon carbide (SiC) phase to a Al 2O 3 AlN slurry. We have shown that the acid-basic character of polymer dispersants and powder surface play a major role in the adsorption phenomena of dispersant onto a surface: an acidic polymer will have a better affinity with a basic powder surface than with an acidic surface and vice versa. This study has allowed to determine the dispersion conditions of each powder in an azeotrope medium (methyl ethyl ketone-ethanol) with phosphoric ester (PE) on Al 2O 3 powder and polyvinylpyrrolidone (PVP) on SiC and AlN powders. If, for two components (Al 2O 3AlN) the best conditions of dispersion lead to a homogeneous material, it is not the same for three-powder mixtures (Al 2O 3AlNSiC).

Nitridation in the Processing and Preparation of Metals and Ceramics

The formation and separation of metal nitrides from a variety of materials including ferroalloys, oxides, natural materials and minerals is an important component in current materials processing practice. Ferroalloys like ferroniobium and ferrovanadium undergo nitridation by ammonia yielding a mixture of iron nitrides and the refractory metal nitride. Acid leaching effectively separates the iron nitride from the mixture. Niobium nitride thus obtained is used to produce niobium metal by pyrovacuum treatment. Vanadium nitride converts to metal when pyrovacuum treatment is followed by electrorefining. Nitride suitable for decomposition to metal can be obtained from niobium pentoxide by reacting ammonia or by reacting a mixture of carbon and nitrogen. Rice husk is a ready-made intimate mixture of silica and carbon. It can be converted to silicon nitride or to a mixture of silicon carbide and silicon nitride by carbonitrothermic reduction. β sialon can be directly prepared from kaolinite by carbonitrothermic reduction. Ilmenite is another mineral amenable to nitridation processing. It yields after reaction with nitrogen in presence of carbon, a separable titanium nitride-iron mixture. All these attractive features of nitridation have been discussed in this paper. The possibility of incorporating nitridation into the process flowsheets has been highlighted.

Comparison of the Pyrolysis Products of Dichlorodimethylsilane in the Chemical Vapor Deposition of Silicon Carbide on Silica in Hydrogen or Argon

A chemical analysis of the pyrolysis gases and solids formed during the deposition of silicon carbide from the decomposition of dichlorodimethylsilane in argon and hydrogen is reported. Depositions were performed at 1 atm pressure, temperatures from 700° to 1100°C, and a mean residence time of approximately 1 min. The chemical analysis shows that, under reactor conditions, the gases formed were mainly methane, hydrogen, silicon tetrachloride, trichloro‐silane, and trichloromethylsilane. The presence of hydrogen chloride was not examined. The use of hydrogen, as a carrier gas, decreased the trichloromethylsilane and solid aerosol (smoke) in the reaction products, compared to that present in the argon system, and increased methane, trichlorosilane, and silicon production. Primarily, silicon and silicon carbide were deposited when hydrogen was used as the carrier gas. When argon was used, a complex mixture of silicon carbide and organosilicon compounds was formed. It is hypothesized that, when hydrogen was used as the carrier gas, silicon carbide formed from chlorosilanes and methane, which were products from the decomposition of dichlorodimethylsilane. These products subsequently reacted to form silicon, which then reacted with methane to form silicon carbide. In argon, however, it is hypothesized that silicon carbide can be formed in two ways: (1) from the pyrolysis of solid organosilicon compounds which are products from the pyrolysis of dichlorodimethylsilane in argon and (2) as the reduction of dichlorodimethylsilane to chlorosilanes and methane, caused by the hydrogen produced from the pyrolysis of dichlorodimethylsilane in argon.

Characterization of nanophase powders prepared by laser synthesis

AbstractSibased (SiCN and SiCAl) nanopowders prepared by laser synthesis process have been studied by XPS and XAES analyses.The changes of the silicon coordination as a function of the carbon fraction in SiCN powders have been investigated by a detailed analysis of Si 2p and Si KLL lines and the measurements of the Auger parameter Ek(Si KLL) + Eb(Si 2p). The non‐linear dependence of the Auger parameter on the carbon fraction has been interpreted as due to the formation of a carbonitride nanophase, indicating that the ternary powders are not merely a mixture of silicon carbide and silicon nitride.In SiCAl powders it has been found that the incorporation of aluminium results in a modified structure of the silicon carbide, as shown by the variation of the different spectral features.

Hydrodynamic compressibility of silicon carbide through shock compression of metal-ceramic mixtures

Shock-compression experiments were performed on 50% by volume ceramic-metal mixtures of silicon carbide and copper at pressures of 15–30 GPa. The objective of these experiments was to determine the hydrodynamic compressibility (dynamic pressure-volume response) of silicon carbide through shock measurements on the ceramic-metal composite and the application of analytic mixture theory. Compression states inferred for silicon carbide above 20 GPa appear consistent with hydrodynamic behavior and are in agreement with compression curves extrapolated from ultrasonic data. Dynamic strength or viscosity effects apparently complicate shock compression of the ceramic-metal composite at the lower shock pressures. Shock release experiments on the composites provide further high-pressure equation-of-state data for the ceramic-metal mixture.

Spectroscopic constraints on the properties of dust in active galactic nuclei

The lack of a significant silicate or silicon carbide emission feature in bright active galactic nuclei (AGNs) is used to constrain models in which the IR continuum is emitted by dust. We consider two models for the dust, a graphite + silicate grain mixture and a graphite + silicon carbide mixture. The optical properties of the grains are calculated using Mie theory, the Rayleigh-Gans approximation and geometric optics, for grains in the 0.005-10 micron size range, over the 1000 micron-I A wavelength range. We use these grain models to calculate the emission of optically thin and of optically thick dust, with various grain compositions, incorporating both absorption and scattering in the detailed radiative transfer. We find that ~1:1 mixtures of graphite + silicate grains of a < 3 microns in any configuration which is optically thin at 10 microns produce a very strong emission feature and are clearly ruled out. Optically thin dust must either be depleted of silicates by at least a factor of 5, or be composed mostly of grains as large as 10 microns. Dust with a large optical depth at 10 microns produces a significantly weaker emission feature, but its amplitude is still larger than the observational limits in most objects. This feature is washed out if the dust composition or grain size distribution are somewhat modified, or possibly if another heat source (e.g., stars) exists at a large optical depth inside the clouds. Similar results are obtained for a graphite + silicon carbide mixture. The different solutions to the absence of a silicate or silicon carbide emission feature can be further constrained using high S/N IR spectroscopy at 10 microns, X-ray spectroscopy, near-IR variability, and by looking for high ionization lines, or molecular lines from the associated gas. The constraints on the dust configuration and composition imply the following: (1) the observed broad emission lines and continuum are unlikely to be noticeably reddened in most objects. (2) Dust cannot exist in the broad-line region clouds if their distance from the continuum source is smaller than 0.2L_46_^1/2^ pc as recently indicated in a few objects. (3) Dust can exist in the narrow-line region clouds, and will have a strong effect on the narrow line flux if the ionization parameter U ~> 0.01. (4) If the IR emission originates in clouds which are optically thick at 10 microns, then U ~> 0.1 at the cloud surface. We finally note that physical and dynamical arguments lead to similar constraints: small grains in an optically thin dust configuration are likely to be destroyed on a short time scale, while very large grains and grains in an optically thick cloud, both of which do not produce a pronounced emission feature, or reddening, are likely to survive longer.

Preceramic organoboron–silicon polymers

AbstractSeveral boron‐containing organosilicon polymers were synthesized from a sodium‐coupling reaction of silicon and boron halides with and without alkyl halide in hydrocarbon solvents. The B–Si preceramic polymers were characterized using techniques such as IR, UV, and NMR spectrometry, gel permeation chromatography, elemental analysis, molecular weight measurement, and thermal analyses (TGA, DSC, DTA, and TMA). The chemical structures of the preceramic polymers were postulated based on the analytical results. Black ceramic materials were obtained from the precursor polymers upon thermal degradation at temperatures above 1000°C in an inert atmosphere. The precursor polymers had a ceramic yield of up to 70%. Thermogravimetric analysis of the ceramic material in air at a flow rate of 100 mL/min showed it was stable up to 1000°C with little weight gain or loss. Several methods were used to characterize the ceramic materials: XRD, solid NMR, high‐temperature DTA, elemental analysis, and acid digestion. The analyses indicated that the ceramic materials comprised a mixture of silicon carbide (SiC), silicon borides (SiB4, SiB6), and amorphous Si–B–C ceramics, with small amounts of silica and free silicon.

Concentration of silicon carbide with a density separation process

During the production of silicon carbide, a byproduct is generated that contains a mixture of crystalline and amorphous silicon carbide. Utilizing the difference in density, shape, and surface properties of the crystalline and amorphous silicon carbide, separation tests were carried out with gravity concentration. The processing of the coarse fraction of the silicon carbide mixture by jigs resulted in a high grade crystalline SiC concentrate with the desired specifications. The separation was largely influenced by the shape factor. A jig with a newly designed hydraulic drive was used to carry out the test program.

Phase composition of silicon-nitride-bonded carborundum refractories

Using electron-microscopic study, we confirmed the presence ofα-Si3N4,Β-Si3N4 andΒ-SiC in specimens of a mixture of silicon carbide and silicon after they had been fired in a coke charge in an oil furnace.

THE PREPARATION AND PROPERTIES OF SELF-BONDED SILICON CARBIDE

Dense self-bonded silicon carbide, prepared by impregnating with silicon pressed mixtures of silicon carbide and graphite, has been improved by attention to grading and composition. Treatment at 2000°C for ½ h has given a much greater degree of self-bonding. Porous self-bonded silicon carbide with a dense surface has also been prepared.

炭化珪素及び塩化アンモニウム混合剤による珪素拡散について

This siliconizing experiment is carried out by packing the low carbon steel or high carbon chromium steel in a mixture of silicon carbide and ammonium chloride at the temperature of 800∼1100°.In this siliconizing experiment, the rate of diffusion depends on the temperature, the time and the amount of the ammonium chloride.The exact mechanism of this reaction is not clear.But it is believed that the decomposition of ammonium chloride liberates the silicon chlorides from the silicon carbide in the gassy form, and the silicon chloride into the steel to be treated.