Kinetic and Magic Angle Spinning-Nuclear Magnetic Resonance Studies of Wet Oxidation of Beta-Sialon Powders

Abstract

Wet oxidation of and β-sialon 2, and 3) powders was carried out at 1000-1300°C in atmospheres containing 0-20 kPa water vapor. The oxidation was monitored by XRD, and magic-angle spinning-nuclear magnetic resonance (MAS-NMR), transmission electron microscopy, and thermogravimetric analysis. The kinetic results were compared with those of our previous dry oxidation studies in The oxide product phase was composed of very fine acicular mullite grains and amorphous The early-stage oxidation is described by a two-stage linear kinetic law, the first stage operating at 0-5% reaction, the second at 5-20% reaction. From 20-80% reaction, the kinetics follow a parabolic law represented by the Ginstling-Brounshtein equation. The diffusion rates for wet oxidation were 2-11 times greater than for dry oxidation. The dependence of the diffusion rate on water vapor pressure over the range 0-20 kPa was approximately parabolic, indicating the diffusion of When the sialon was oxidized in either or atmospheres, was detected by MAS-NMR in the and mullite oxidation products, indicating that the oxygen atoms from the water vapor contribute in nearly equal amounts to the formation of mullite and © 2001 The Electrochemical Society. All rights reserved.