Abstract
A kinetic analysis of the isothermal nitridation of high-purity oxide-free silicon powder is described. The kinetic analysis suggests that theα andβ polymorphs of Si3N4 are formed by separate and parallel reaction paths. This analysis provides for the decoupling and quantitative kinetic interpretation ofα- andβ-Si3N4 formation reactions. Consistent with existing microstructural and thermodynamic evidence, theα-forming reaction is shown to obey a first-order rate law, whereas a phase-boundary controlled rate law describes theβ-forming reaction. A kinetic model employing these rate laws is developed and is used to predict theα/β phase ratio as a function of isothermal reaction temperature and extent of reaction. Theα/β phase ratios so obtained are shown to be in good agreement with experimental observations made under a variety of reaction conditions.
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