Synthesis of beta silicon carbide powders using carbon coated fumed silica

The synthesis of beta silicon carbide (beta-SiC) powders by carbothermic reduction of carbon coated silica and silica mixed with carbon black was investigated. The production of beta-SiC powders by using carbon coated silica consists of two steps. The first step is to prepare the carbon coated silica precursor by coating fumed silica particles with carbon by pyrolytic cracking of a hydrocarbon gas (C3H6) This provides intimate contact between the reactants and yields a better distribution of carbon within the fumed silica. Fumed silica was also mechanically mixed with carbon black for comparison. Both starting mixtures were reacted in a tube furnace for 2 h at temperatures of 1300 degrees C to 1600 degrees C in 1 l min(-1) flowing argon. The reaction products were characterized using weight loss data, X-ray diffraction (XRD), a BET surface area analyser, oxygen and free carbon analysis and transmission electron microscopy (TEM). The carbon coating process resulted in a more complete reaction, purer product and high yield SIC powders with very little agglomeration at temperatures of 1500 degrees C and 1600 degrees C. The beta-SiC powders produced at 1600 degrees C for 2 h in argon gas flow have oxygen content of 0.3 wt %, a very fine particle size 0.1-0.3 mu m and uniform shape. (C) 1998 Chapman & Hall.