EFFECT OF FREE CARBON CONTAINED IN SiC RAW POWDERS ON SLIP CASTING AND SINTERING PROCESSES

SiC powders were pre-heated to evaluate the effect of the amount of free carbon and the oxygen content on the surface of the particles on the fluidity of the slurries and the sintered density. The amount of free carbon decreased and the oxygen content on the surface of the particles increased by heating at > 300 C, and the fluidity of the slurries was enhanced. On the other hand, the fluidity of the carbon slurries was effectively enhanced by the addition of aqueous ammonium 2-naphthalene sulphonate formaldehyde condensate (DEMOL-AS) solution. Green bodies were obtained through slip casting the slurries with carbon and B4C and were then fired in Ar atmosphere at 2150 C. The sintered bodies, formed from powders pre-heated at 300 and 400 C, exhibited densities of about 98% of theoretical by the addition of 1 and 2.5 wt% of carbon, respectively. A SiC body with the highest sintered density was produced by controlling the addition of carbon, taking into account the oxygen content on the surface of the particles and the amount of free carbon. 3 refs.