Powder silicon carbides

A trivalent hard chromium bath has recently been described . The bath contains potassium formate as a complexing agent, and thicknesses in excess of 20 m can be deposited. Hardnesses of up to l650Hy can be obtained by heat treatment at 700°C. The deposits contain 1.6-4.8% carbon, and the bath is suitable for the deposition of composite deposits containing diamond or silicon carbide powder. 

Wu, H. D., and Ready, D. W., Silicon Carbide Powders by Gaseous Pyrolysis of Tetramethylsilane, mSilicon Carbide 87, Ceramic Transactions, 2 35-46 (1987)... 

V. Venkateswaran, J. M. Halstead, and B. Mehosky, "Synthesis of High-Purity Sinterable Silicon Carbide Powders," in Proceedings of the 23rd... 

Other linear polysilanes can also be used as ceramic precursors. Solid objects of silicon carbide are manufactured by Nippon Soda Co. from polysilastyrene and finely divided silicon carbide powder.133 These materials are blended, injection molded to the... 

A considerable amount of subsequent research and process development has been carried out to produce silicon carbide with a reduced level of excess carbon via processes that allow more facile cross-linking.2 -32 Several hundred papers and patents on this topic exist in the literature, and only a few examples will be mentioned here. One process development involves the slurry spinning of fibers in place of melt spinning.33 In this process, silicon carbide powder, made by a conventional industrial process, is dispersed in a solution of carbosilanes in toluene. The syrupy paste is spun into fibers and then pyrolyzed to silicon carbide. These fibers are reported to be stable at 1,500 °C for 120 hours. 

Docekal B., Broekaert J. A. C., Graule T., Tschopel P. and Tolg G. (1992) Determination of impurities in silicon carbide powders, Fresenius J Anal Chem 342 113-117. 

Liden, E. et al.. Surface modification and dispersion of silicon nitride and silicon carbide powders, J. Eur. Ceram. Soc., 7, 361, 1991. 

Acceptor dopants are introduced in the crucible either in elemental form or in the form of carbides. If a dopant is introduced in elemental form, it is placed in a special internal crucible with carbon or silicon carbide powder. This is required to prevent the dissolution of the crucible, in the case of aluminium doping, and to reduce the boron vapour pressure to the equilibrium value for the SiC-C system, in the case of boron doping. If elemental boron is placed in the vicinity of the substrate, this results in the formation of boron carbide on the crystal faces of SiC [46]. For moderate doping of crystals, grown at high temperatures, doped SiC sources also can be employed. 

HP Martin, R Ecke, and E Muller, Synthesis of nanocrystalline silicon carbide powder by carbothermal reduction, J. Ear Ceram. Soc.,18,1737-1742(1998). 

As the volume fraction of powder in a feedstock is increased, the viscosity of the feedstock rises exponentially until a critical volume fraction of powder is reached. Figure 2 shows the mixer torque (which is directly proportional to the viscosity of the feedstock) as a function of silicon carbide powder concentration in a polyethylene/wax binder system [Cle 05]. It is assume that by extrapolating the data to zero reciprocal torque, the maximum powder loading for the feedstock formulations can be determined. 

G. Zaray, F. Leis, T. Kantor, J. Hassler, and G. Tolg, Analysis of silicon carbide powder by ETV-ICP-AES, Fres. J. Anal. Chem. 1993, 346, 1042-1046. 

The samples generated for this paper were all produced in the following fashion. Firstly, a slip was developed with silicon carbide powder and a carbon based binder. The SiC powder type, 6H or 3C, and carbon content were systematically varied in the slip formulation. Secondly, a preform was cast from this slip. Finally, the preform was subjected to a reactive infiltration step in which the preform was brought into contact with a molten silicon bath under vacuum. 

Three different sets of samples were made with varying types of SiC. Two of the silicon carbide powders used to make the samples were primarily the 6H polytype. The third silicon carbide powder used was primarily of the 3C polytype. Of the two powders with the 6H... 

P.A. Kistler-De Coppi and W. Richarz, Phase Transformation and Grain Growth in Silicon Carbide Powders, Int. J. High Technol. Ceram., 2, 99-113 (1986). 

Figurf 16.15. Making a silicon carbide laminate, (a) Silicon carbide powder, (b) twin roll mflled into poiyrmer. solution, (c) printed with graphite ink, (d) stacked and fired.

Kim, E. S. Lee, T. H. Shin, S. H. Yoon, J.-S., Effect of Incorporation of Carbon Fiber and Silicon Carbide Powders Into Silicone Rubber on the Ablation and Mechanical Properties of the Silicone Rubber-Based Ablation Material. 

The formulation selected is a high-surface-area silicon carbide powder that can be sintered in a reducing atmosphere or a neutral atmosphere. The binder burnout has to be done in an oxidizing atmosphere below the oxidation point for the SiC. The powder had a surface area of > 15 mVg. 

Ultrafme refractory carbide and nitride powders can be produced in an inductively coupled radio-frequency (rf) plasma torch.a schematic drawing of a plasma torch for the production of silicon carbide powder is shown in Fig. 14.1. 

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