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 ter ms of composition and amount. beta-Si3N4 doped with Y2O3-Nd2O3 (YN sys tem) or Y2O3-Al2O3 (iii system) was sintered at 1700 degrees-2000 degr ees C. Thermal conductivity increased with increased sintering tempera ture because of decreased two-grain junctions, as a result of grain gr owth. The effect of the additive amount on thermal conductivity with t he YN system was rather small because increased additive formed multig rain junctions. On the other hand, with the YA system, thermal conduct ivity considerably decreased with increased additive amount because th e aluminum and oxygen in the YA system dissolved into beta-Si3N4 grain s 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 com position.