Abstract
The oxidation of carbothermally synthesised β′-sialon powder (z=2.45) was found by X-ray powder diffraction and solid-state 29 Si and 27 Al MAS NMR spectroscopies to result in the initial formation of amorphous SiO 2 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 29 Si in the SiO 2 to 29 Si in the mullite oxidation products is about 4, consistent with the formation of Al 2 O 3 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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