Effect of Grain Growth on the Thermal Conductivity of Silicon Nitride

Abstract

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.