Thermal conductivity of sintered silicon nitride has been improved by grain growth of β-Si3N4. β-Si3N4 containing 0.5mol% Y2O3 and 0.5mol% Nd2O3 was gas-pressure sintered at 1973 to 2473K and the microstructures and the thermal conductivities were investigated. The materials sintered at temperatures higher than 2173K had a microstructure of “in-situ composite” with smaller β-Si3N4 matrix grains and a small amount of elongated β-Si3N4 grains. The grain size increased with increasing sintering temperature. Room temperature thermal conductivity increased with increasing sintering temperature; 122W·m-1·K-1 was produced by sintering at 2473K-this value was about two times higher than the values reported up to this time. Higher thermal conductivities were established by growth of Si3N4 grains and decrease in the amount of two-grain junctions.
