Fabrication of Si_3N_4-SiC nano-composite ceramics through temperature-induced gelation and liquid phase sintering

摘要

This paper describes the fabrication of Si_3N_4-SiC nano-composite ceramics through a novel direct casting method (temperature-induced gelation) followed by liquid-phase sintering. A kind of polyester/poly amine condensation copolymer (hypermer KD1) was used as dispersant and gelling agent. At room temperature (approx = 20 deg C), it plays the role of a steric dispersant, allowing the preparation of stable homogeneous and high concentrated suspension (57.5 vol. percent solids) consisting of Si_3N_4, Y_2O_3, Al_2O_3 and 20 wt. percent 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 deg 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 deg C.