REACTION-BONDED SILICON-NITRIDE SYNTHESIS - EXPERIMENTS AND MODEL

A mathematical model to describe the reaction-bonded synthesis of sili con nitride is described. The process involves formation of a network of whiskers and flakes that progressively detach from the reacting sol id silicon particles and cause product densification and macropore fil ling. In turn, this hinders nitrogen diffusion into the bulk of the co mpact and slows the nitridation rate at higher conversion levels. Base d on the particle-pellet concept for noncatalytic gas-solid reactions, the model accounts for diffusion in both the individual particles and the macropores, as well as fracture of product layer from volume expa nsion. A comparison between model predictions and experimental data fo r different reaction conditions is made. This comparison leads to a be tter understanding of the structural changes (porosity and pore size) that occur during the silicon nitridation process. (C) 1998 Elsevier S cience Ltd. All rights reserved.