CVD IN POWDER APPLICATION

The preparation of ceramic powders by CVD is a promising and growing field. These powders are used as precursors for the processing of advanced ceramics, or directly as powder for such applications as abrasives. 

If the temperature and supersaturation are sufficiently high in a CVD reaction, the product is primarily powder precipitated from the gas phase (see Ch. 2). Such powders have few impurities provided that the CVD precursors are carefully purified. Their small diameter and great uniformity are important factors in the production of high quality hot-pressed or sintered ceramic bodies with good mechanical and electrical properties. In addition, the sintering temperatures required for CVD powders are lower than those for conventional powders. 

The following powders are made experimentally or on a production basis. 

Beta SiC powder from the decomposition of methyl-trichlorosilane (MTS) in the presence of hydrogen in an argon plasma. Also from the gaseous thermal decomposition of tetramethylsilane, Si(CH3)4, in a flowthrough reactor between 850 and 1500°CP 1 and by the reaction of acetylene and silane. 

Submicron pSiC powder by reacting silane and acetylene in a 10-50 W continuous-wave CO2 laser beam.P l 

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