The formation of single phase Si-Al-O-N ceramics.

Abstract

(1) “Balanced” powder mixture of Si3N4, AlN and Al2O3 for sialon (Si6-zAlzOzN8-z with z=1, 2, 3 or 4) was hot pressed at 1750°C for 1h under 200kg/cm2. The densification was incomplete in a sialon with z=1. Other sialons were pore free.(2) The reactions included in the process of β-sialon formation were inferred to be, (a) the formation of 15 R-sialon, x-phase and β-sialon with z=2.3-2.5 at low temperature (equations (2) and (3)), (b) steep densification at higher temperature than 1600°C by “transient liquid phase sintering” with x-phase as a liquid, (c) the final step to approach z value of β-sialon into predicted one (equations (5) and (6)).(3) Density measurement and chemical etching with diluted HF+HNO3 of fracture surface of sialon revealed that there was unreacted materials in sialons with z=3 and 4. A single phase and fully dense sialon was obtained in the composition z=2 with very small amount of grain boundary phase, if any.(4) Small amount of excess oxide (about 3 wt%) in a sialon with z=2, which existed as grain boundary phase, was detected by chemical etching.