2005 Volume 113 Issue 1318 Pages 394-399
Silicon nitride ceramics were fabricated by dry pressing of a raw α-Si3N4 powder with Y2O3-SiO2 and Y2O3-Al2O3 as sintering aids, following by gas-pressured sintering at a temperature of 2123 K for 2 h under a nitrogen gas pressure of 1.0 MPa with Si3N4/BN packing powder. Subsequently, these specimens were heat-treated at a temperature up to 2223 K for 8 h under a nitrogen gas pressure of 1.0 MPa without any packing powder. Mass loss, density, oxygen content and thermal conductivity of the specimens before and after the post-sintering heat-treatment were measured. Due to the heat-treatment, the reduction of oxygen content, via the reaction of Si3N4 and SiO2, without decrease of relative density was found to be effective in improving thermal conductivity of the Si3N4 ceramics sintered with Y2O3-SiO2 additives. The effect of post-sintering heat-treatment was not significant for the Si3N4 specimen sintered with Y2O3-Al2O3 additives due to formation of SiAlON. Thermal conductivity of one of the former specimens reached 84 W/m•K at room temperature.