GAS-PRESSURE SINTERING OF BETA-SILICON NITRIDE

The sintering behaviour of beta-Si3N4 powder was investigated in 980 kPa (10 atm) nitrogen at 1800-2000-degrees-C. It is shown that beta-Si3N4 has a higher sinterability than the finer alpha-Si3N4. The solution of small grains and reprecipitation on large grains occurred during sintering at > 1600-degrees-C. The rate-determining step in the liquid-phase sintering is believed to be the diffusion of material through the liquid phase at grain boundaries. There was no abnormal grain growth during gas pressure sintering of beta-Si3N4. The microstructures of gas pressure sintered materials from beta-Si3N4 were more uniform than those from alpha-Si3N4. The densification mechanism of beta-Si3N4 is discussed in relation to that of alpha-Si3N4.