Fabrication of Si3N4–SiC nano-composite ceramics through temperature-induced gelation and liquid phase sintering

This paper describes the fabrication of Si3N4–SiC nano-composite ceramics through a novel direct casting method (temperature-induced gelation) followed by liquid-phase sintering. A kind of polyester/polyamine condensation copolymer (hypermer KD1) was used as dispersant and gelling agent. At room temperature (≈20 °C), it plays the role of a steric dispersant, allowing the preparation of stable homogeneous and high concentrated suspension (57.5 vol.% solids) consisting of Si3N4, Y2O3, Al2O3 and 20 wt.% nano-SiC. At low temperature it acts as gelling agent, inducing incipient flocculation due to the collapse of adsorbed layer. The low values of viscosity and elastic modulus at room temperature, increased dramatically within a moderate decrease of temperature from 20 to 5 °C. A completely solidified green body with precise dimensions, smooth surface, high strength and homogeneous density has been obtained, which could be gas-pressure sintered to near theoretical density at 1850 °C.