Deflocculation of SiC Slips with a Cationic Cellulose Derivative and Its Effects on the Sintered Density

Casting slips of silicon carbide without sintering additives were prepared by the use of a cationic cellulose derivative (CCD) as a deflocculant. The effects of CCD addition on the degree of dispersion, flow behaviors and moldability of the slips along with those on the sintered bodies were investigated. The optimum amounts of CCD for good dispersion based on the mechanisms both of steric stabilization and positive electrification by the adsorbed layer of CCD increased with increasing pH values, because CCD molecules bond electrostatically to the negatively charged sites formed by ionization of the surface silanol groups of SiC. The slips well-dispersed in the presence of CCD exhibited flow curves close to Newtonian and/or pseudoplastic flow with a low viscosity and were found to be 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 were shaped by the use of high solid content slips without CCD, indicating that not only the interparticle structures formed in the slips but also the presence of CCD affects the sintering stages.