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Article Dans Une Revue The American Mineralogist Année : 2006

Evolution of product phase assemblages during thermal decomposition of muscovite under strong disequilibrium conditions

Résumé

We investigated the thermal decomposition of muscovite in natural granite powders heated to 1175°C for durations from 5 min to 68 h, at 1 bar, paying special attention to the early stages of decomposition. This study shows that muscovite is completely transformed after 5 min. Muscovite pseudomorphs consist of glass, mullite, and Al-rich oxides. For short durations (5 and 40 min), the Al-rich phase was identiÞ ed by XRD, electron diffraction, and TEM microanalysis as γ-Al2O3 containing 4.8 wt% FeO (total Fe), probably a few weight percents of MgO, and possibly up to 10 wt% SiO2. Faint superstructure spots and diffuse streaks observed in electron-diffraction patterns suggest vacancy or trace elements ordering in the γ-Al2O3 defect spinel structure. γ-Al2O3 displays an unexpected acicular morphology, elongated along three directions at 120° in the basal (001)musc planes and parallel to lateral faces of the former muscovite. Mullite forms rods elongated in the basal (001)musc planes along a direction at 90° from one set of γ-Al2O3 needles. The γ-Al2O3 structure appears to be a metastable phase that is replaced by corundum for longer durations.
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Dates et versions

hal-00089971 , version 1 (25-08-2006)

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Karine Devineau, Bertrand Devouard, Frédéric Villiéras, François Faure, Jean-Luc Devidal, et al.. Evolution of product phase assemblages during thermal decomposition of muscovite under strong disequilibrium conditions. The American Mineralogist, 2006, 91, pp.413-424. ⟨10.2138/am.2006.1933⟩. ⟨hal-00089971⟩
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