Kinetics of phase transformations in SiAlON ceramics: II. Reaction paths

Kinetics of various alpha/beta-Si3N4-->alpha'/beta'-SiAlON transformations were investigated for SiAlON ceramics with additions of rare-earth cations. It was determined that alpha-Si3N4 starting powders lead to faster Si3N4-->alpha'/beta'-SiAlON transformations than beta-Si3N4 powders. In reactions with a two-phase alpha'/beta'-SiAlON product, the formation of a SiAlON that is structurally similar to the majority starting powders is initially favored, and such SiAlON has a solute composition leaner than the final equilibrium composition. These results suggest that the transformation kinetics is largely governed by the heterogeneous nucleation that is strongly sensitive to the driving force, dictated by the majority phase of the starting powders, and that coherent nucleation is often favored when abundent isostructural nucleation sites are available. (C) 1999 Elsevier Science Ltd. All rights reserved.