Thermal conductivity of self-reinforced silicon nitride containing large grains aligned by extrusion pressing

beta-Si3N4 containing 0.5 mol%Y2O3 and 0.5 mol%Nd2O3 was seeded with 5 mass% beta-Si3N4 whisker with high aspect ratio and extruded to align the whiskers. Self-reinforced microstructure composed of well-aligned large elongated grains in smaller matrix grains was developed by the grain growth of seeded whiskers during gas-pressure sintering at 2000 degrees C in 30 MPa N-2 for 4h and heat treatment at 2200 degrees C in 30 MPa N-2 for 4h. Room-temperature thermal conductivity was anisotropic; 140 W.m(-1).K-1 for parallel to the grain alignment, and 84 W.m(-1).K-1 for perpendicular to the alignment.