Gas pressure sintering of β-silicon nitride

The sintering behaviour of beta-Si3N4 powder was investigated in 980 kPa (10 atm) nitrogen at 1800-2000 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 greater than 1600 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 that those from alpha-Si3N4. The densification mechanism of beta-Si3N4 is discussed in relation to that of alpha-Si3N4. 22 refs.