EFFECT OF GRAIN-GROWTH ON THE THERMAL-CON DUCTIVITY OF SILICON-NITRIDE

Thermal conductivity of sintered silicon nitride has been improved by grain growth of beta-Si3N4. beta-Si3N4 containing 0.5 mol% Y2O3 and 0. 5 mol% Nd2O3 was gas-pressure sintered at 1973 to 2473 K and the micro structures and the thermal conductivities were investigated. The mater ials sintered at temperatures higher than 2173 K had a microstructure of ''in-situ composite'' with smaller beta-Si3N4 matrix grains and a s mall amount of elongated beta-Si3N4 grains, The grain size increased w ith increasing sintering temperature. Room temperature thermal conduct ivity increased with increasing sintering temperature; 122 W . m(-1). K-1 was produced by sintering at 2473 K-this value was about two times higher than the values reported up to this time, Higher thermal condu ctivities were established by growth of Si3N4 grains and decrease in t he amount of two-grain junctions.