THERMAL PLASMA CHEMICAL VAPOR-DEPOSITION FOR SIC POWDERS FROM SICH3CL3-H2

Ultrafine beta-SiC powders were synthesized by introducing trichloromethylsilane and hydrogen into the high temperature RF thermal plasma argon gas. Powders were characterized by XRD, TEM, TGA, FT-IR and wet chemical analysis. Two different positions of reactant gas injection, i.e., upstream and downstream of the plasma flame, were compared in terms of the powder characteristics. The optimum concentration of hydrogen was found out to be about 3 to 4 mol% for the upstream injection. Amorphous SiC with free carbon was formed when the hydrogen concentration was lower than optimum and beta-SiC with free silicon was formed when it was higher than the optimum. For the downstream injection, free silicon formation was not significant and free carbon formation was suppressed when the hydrogen concentration was higher than 7 mol%. Chemical reaction pathways were suggested which could explain these observations.X118sciescopu