Thermal conductivity of gas-pressure-sintered silicon nitride

Si3N4 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. beta-Si3N4 doped with Y2O3-Nd2O3 (YN system) or Y2O3-Al2O3 (iii system) was sintered at 1700 degrees-2000 degrees 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 beta-Si3N4 grains to form a beta-SiAlON solid solution, which acted as a point defect for phonon scattering. The key processsing parameters for high thermal conductivity of Si3N4 mere the sintering temperature and additive composition.