Kinetics of β‐Si 3 N 4 Grain Growth in Si 3 N 4 Ceramics Sintered under High Nitrogen Pressure

The kinetics of anisotropic β‐Si 3 N 4 grain growth in silicon nitride ceramics were studied. Specimens were sintered at temperatures ranging from 1600° to 1900°C under 10 atm of nitrogen pressure for various lengths of time. The results demonstrate that the grain growth behavior of β‐Si 3 N 4 grains follows the empirical growth law D n – D 0 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 β‐Si 3 N 4 growth during isothermal grain growth. The resultant aspect ratio of these elongated grains increases with sintering temperature and time.