Preparation of silicon carbide powders by chemical vapour deposition of the SiH4-CH4-H2 system

Chemical vapour deposition (CVD) of the SiH₄ + CH₄ + H₂ system was applied to synthesize-silicon carbide powders in the temperature range 1523 to 1673 K. The powders obtained at 1673 K were single-phase-SiC containing neither free silicon nor free carbon. The powders obtained below 1623 K were composite powders containing free silicon. The carburization ratio (SiC/(SiC + Si)) increased with increasing reaction temperature and total gas flow rate, and with decreasing reactant concentration. The average particle sizes measured by TEM ranged from 46 to 114nm, The particle size increased with the reaction temperature and gas concentration but decreased with gas flow rate. The-SiC particles obtained below 1623 K consisted of a silicon core and a-SiC shell, as opposed to the-SiC particles obtained at 1673 K which were hollow. Infrared absorption peaks were observed at 940 and 810 cm^–1 for particles containing a silicon core; whereas a single peak at about 830 cm^–1 with a shoulder at about 930 cm^–1 was observed for the-SiC hollow particles. The lattice parameter of-SiC having a carburization ratio lower than 70 wt%, was larger than that of bulk-SiC and decreased with the increasing carburization ratio. However, when the carburization ratio exceeded 70 wt%, the lattice parameter became approximately equal to that of bulk-SiC.