Thermal Conductivity of Gas‐Pressure‐Sintered Silicon Nitride

Abstract

Si 3 N 4 with high thermal conductivity (120 W/(m . K)) was developed by promoting grain growth and selecting a suitable additive system in terms of composition and amount. β‐Si 3 N 4 doped with Y 2 O 3 ‐Nd 2 O 3 (YN system) or Y 2 O 3 ‐A1 2 O 3 (YA system) was sintered at 1700°‐2000°C. Thermal conductivity increased with increased sintering temperature because of decreased two‐grain junctions, as a result of grain growth. The effect of the additive amount on thermal conductivity with the YN system was rather small because increased additive formed multigrain junctions. On the other hand, with the YA system, thermal conductivity considerably decreased with increased additive amount because the aluminum and oxygen in the YA system dissolved into β‐Si 3 N 4 grains to form a β‐SiAlON solid solution, which acted as a point defect for phonon scattering. The key processsing parameters for high thermal conductivity of Si 3 N 4 were the sintering temperature and additive composition.