Silicon carbide ceramics through temperature-induced gelation and pressureless sintering

Temperature-induced gelation is a novel near-net-shape method for forming ceramic green bodies from homogeneous high-solids-loaded suspensions. It is based on the change of the solubility of dispersant in solvent with changing temperature. Stable and low-viscosity suspensions of SiC, Y2O3 and Al2O3 powder mixtures were prepared in methyl ethyl keton (MEK)/ ethanol (E) solvent with solid loading as high as 60 vol.% using hypermer KD1 (a polyester/polyamine condensation polymer) as dispersant. The solubility of the dispersant in MEK/E decreased dramatically on cooling. Thus, the suspension displayed a reversible temperature-induced gelation process, being a stable and free flowing fluid at 20 °C, and being completely solidified at 5 °C. The obtained green body showed uniform microstructure, and it was possible to obtain almost theoretical density (≥0.98) upon pressureless sintering without special dispersant burn-out procedure. The possibilities of fabricating homogeneous and complex SiC green parts that can achieve high sintered densities by pressureless sintering are demonstrated.