GRAIN-GROWTH KINETICS OF SI3N4 DURING ALPHA-BETA-TRANSFORMATION

The growth of beta-Si3N4 particles, highly diluted in an oxynitride glass, was analysed by SEM and the growth features of individual crystals were discussed. The observed linear time law for the length growth during alpha/beta-transformation was correlated with results of a theoretical analysis taking into account the diffusion in the liquid phase as well as the interface reaction at alpha- and beta-crystals. The number of initial nuclei was found to be important for a linear time law of growth. Finally, the considerations of the dilute particle system were applied to a Si3N4 ceramic. The opposing influence of growth anisotropy of beta-Si3N4 in the presence of a melt and the packing requirements demanding a reduction of the specific surface area is discussed.