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

Hajime Kiyono, Shiro Shimada, K. J.D. MacKenzie

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12 Citations (Scopus)

Abstract

Wet oxidation of α-Si3N4 and β-sialon (Si6 zAlzOzN8 z, z = 1, 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, 26Si and 17O 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 Ar/O2 (80/20 kPa). The oxide product phase was composed of very tine acicular mullite grains and amorphous SiO2. 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 OH ̇, When the z = 3 sialon was oxidized in either Ar/H217O or Ar/O2/H217O atmospheres, 17O was detected by MAS-NMR in the SiO2 and mullite oxidation products, indicating that the oxygen atoms from the water vapor contribute in nearly equal amounts to the formation of mullite and SiO2

Original languageEnglish
Pages (from-to)B86-B91
JournalJournal of the Electrochemical Society
Volume148
Issue number2
DOIs
Publication statusPublished - 2001 Dec 1

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry

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