KINETICS OF BETA-SI3N4 GRAIN-GROWTH IN SI3N4 CERAMICS SINTERED UNDER HIGH-NITROGEN PRESSURE

The kinetics of anisotropic beta-Si3N4 grain growth in silicon nitride ceramics were studied. Specimens were sintered at temperatures ranging from 1600-degrees to 1900-degrees-C under 10 atm of nitrogen pressure for various lengths of time. The results demonstrate that the grain growth behavior of beta-Si3N4 grains follows the empirical growth law D(n) - D(o)n = kt, with the exponents equaling 3 and 5 for length [001] and width [210] directions, respectively. Activation energies for grain growth were 686 kJ/mol for length and 772 kJ/mol for width. These differences in growth rate constants and exponents for length and width directions are responsible for the anisotropy of beta-Si3N4 growth during isothermal grain growth. The resultant aspect ratio of these elongated grains increases with sintering temperature and time.