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DOI: 10.1039/A604354B (Paper) Reference Section for: J. Mater. Chem., 1997, 7, 527-530

Thermal oxidation of carbothermal β′-sialon powder: reaction sequence and kinetics

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Kenneth J. D. MacKenzie, Shiro Shimada and Takenori Aoki

Abstract

The oxidation of carbothermally synthesised β′-sialon powder (z=2.45) was found by X-ray powder diffraction and solid-state 29Si and 27Al MAS NMR spectroscopies to result in the initial formation of amorphous SiO2 and a non-crystalline mullite-like aluminosilicate which becomes crystalline at higher temperatures. The evolution of crystalline mullite is accompanied by a decrease in both the sialon z value and in the proportion of tetrahedral Al. The ratio of 29Si in the SiO2 to 29Si in the mullite oxidation products is about 4, consistent with the formation of Al2O3 as an additional oxidation product. The oxidation kinetics at 1100–1300 °C are described by a parabolic rate law with an activation enthalpy of 161 kJ mol-1 , suggesting the rate-determining step to be the permeation of oxygen through the oxidised layer coating the sialon grains.

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