Method of preparing silicon carbide powders from the gas phase

Cubic SiC powders for sintering with a submicron particle size were prepared from methylsilane CH3SiH3 by chemical gas-phase deposition with argon as a carrier gas. The process was carried out in a flow reactor in the temperature range between 1,000 and 1,8000C. The preparation of the initial product methylsilane by lithium alanate reduction of technical methyl trichlorosilane and the apparatus used are described. The test plant for powder preparation consists of an induction-heated graphite reactor with a deposition chamber with a filter and a gas supply system connected with it. The SiC yield increases with temperature and reaches values up to 98%. The powders are studied by radiographic, chemical, and physical methods. They are characterized by small crystallite sizes, large specific surface, high purity, and low oxygen content. Sintering with 1 weight percent each of boron and carbon additives in a high-temperature dilatometer is illustrated by the example of a powder charge. At a sintering temperature of 2,0800C, a relative density of 96.5% was reached under argon. (orig.)