PRODUCTION OF SUBMICRON SIC PARTICLES BY DC THERMAL PLASMA - A SYSTEMATIC-APPROACH BASED ON INJECTION PARAMETERS

Aiming at producing high temperature structural ceramics, ultra-fine SiC powders were synthesized by the gas phase reaction of silicon tetrachloride with methane in a d.c. thermal plasma. The influence of parameters as the SiCl4 feeding rate, C/Si and H-2/C molar ratios and internal pressure on the powder properties were investigated. The SiC powders were characterized by chemical analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electronic microscopy. The experimental set-up allows the production of beta-SiC powders at a rate of 200 g h-1 with particle size around 0.1-mu-m. The main impurities in the as-produced powder handled at ambient atmosphere are: oxygen (1.8-2.5%) and free carbon (3-4%). Interesting relationships were found between the SiCl4 feeding rate and the H-2/C molar ratio and between the C/Si molar ratio and the internal pressure. The internal pressure plays a major role in controlling the particle size.