Effect of grain growth on the thermal conductivity of liquid-phase sintered silicon carbide ceramics

The effect of grain growth on the thermal conductivity of SiC ceramics sintered with 3 vol% equimolar Gd2O3-Y2O3 was investigated. During prolonged sintering at 2000 °C in an argon or nitrogen atmosphere, the β → α phase transformation, grain growth, and reduction in lattice oxygen content occurs in the ceramics. The effects of these parameters on the thermal conductivity of liquid-phase sintered SiC ceramics were investigated. The results suggest that (1) grain growth achieved by prolonged sintering at 2000 °C accompanies the decrease of lattice oxygen content and the occurrence of the β → α phase transformation; (2) the reduction of lattice oxygen content plays the most important role in enhancing the thermal conductivity; and (3) the thermal conductivity of the SiC ceramic was insensitive to the occurrence of the β → α phase transformation. The highest thermal conductivity obtained was 225 W(m K)−1 after 12 h sintering at 2000 °C under an applied pressure of 40 MPa in argon.