Synthesis of beta silicon carbide powders using carbon coated fumed silica

The synthesis of beta silicon carbide (beta-SiC) powders by carbothermic re duction of carbon coated silica and silica mixed with carbon black was inve stigated. The production of beta-SiC powders by using carbon coated silica consists of two steps. The first step is to prepare the carbon coated silic a precursor by coating fumed silica particles with carbon by pyrolytic crac king of a hydrocarbon gas (C3H6) This provides intimate contact between the reactants and yields a better distribution of carbon within the fumed sili ca. Fumed silica was also mechanically mixed with carbon black for comparis on. Both starting mixtures were reacted in a tube furnace for 2 h at temper atures of 1300 degrees C to 1600 degrees C in 1 l min(-1) flowing argon. Th e reaction products were characterized using weight loss data, X-ray diffra ction (XRD), a BET surface area analyser, oxygen and free carbon analysis a nd transmission electron microscopy (TEM). The carbon coating process resul ted in a more complete reaction, purer product and high yield SIC powders w ith very little agglomeration at temperatures of 1500 degrees C and 1600 de grees C. The beta-SiC powders produced at 1600 degrees C for 2 h in argon g as 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.