EFFECT OF ALIGNMENT OF LARGE GRAINS ON TH E THERMAL-CONDUCTIVITY OF SELF-REINFORCED BETA-SILICON NITRIDE

Thermal conductivity of sintered silicon nitride has been improved by the alignment of large beta-Si3N4 grains, Beta-Si3N4 containing 0.5 mo l% Y2O3 and 0.5 mol% Nd2O3 was seeded with rodlike beta-Si3N4 grains a nd tape-cast to align the seed grains. In-situ composite microstructur e of the aligned large grains in smaller matrix grains was developed b y the grain growth of seed grains during gas-pressure sintering at 220 0 degrees C for 4 h. Room-temperature thermal conductivity was anisotr opic: 137 W . m(-1) . K-1 in the direction of tape-easting, 97 W . m(- 1) . K-1 of seet width, and 12 W . m(-1) . K-1 in the direction of see t stack. The thermal conductivity in the direction parallel to the tap e-casting direction was high because of the aligned large grains.