DEFLOCCULATION OF SIC SLIPS WITH A CATION IC CELLULOSE DERIVATIVE ANDITS EFFECTS ON THE SINTERED DENSITY

Casting slips of silicon carbide without sintering additives were prep ared by the use of a cationic cellulose derivative (CCD) as a defloccu lant. The effects of CCD addition on the degree Of dispersion, dow beh aviors and moldability of the slips along with those on the sintered b odies were investigated. The optimum amounts of CCD for good dispersio n based on the mechanisms both of steric stabilization and positive el ectrification by the adsorbed layer of CCD increased with increasing p H values, because CCD molecules bond electrostatically to the negative ly charged sites formed by ionization of the surface silanol groups of SIC. The slips well-dispersed in the presence of CCD exhibited dow cu rves close to Newtonian and/or pseudoplastic flow with a low viscosity and were found to he satisfied both in moldability and mold release, while the SiC slips deflocculated without CCD show the intrinsic flow of dilatancy. The resulting fired bodies proved to have the values of apparent density much lower than those of the sintered bodies of which green bodies mere shaped by the use of high solid content slips witho ut CCD, indicating that not only the interparticle structures formed i n the slips but also the presence of CCD affects the sintering stages.