Crystal-chemical investigation of the "cubic Al-Si spinel" issued from the thermal transformation of kaolinite and halloysite - Archive ouverte HAL Access content directly
Journal Articles Journal of the American Ceramic Society Year : 2022

Crystal-chemical investigation of the "cubic Al-Si spinel" issued from the thermal transformation of kaolinite and halloysite

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Abstract

Since its discovery in 1959 as a transient nanocrystalline product of the thermal transformation of aluminum-rich clays, the so-called "Al-Si spinel" has been the object of numerous studies aimed at determining its composition. In this work, samples obtained from fired kaolinite-and halloysite-containing clays were analyzed using X-ray diffraction, leading to conclude in a single cubic (space group Fd-3m) form, with an unvarying size of crystallites of 5 nm and a constant cell volume, typical of a transition alumina form. Trial-and-error Rietveld fitting procedure revealed a crystal structure consisting in an oxygen close packing and a disordered cation sublattice that differs from the known forms of spinel alumina. Rietveld quantitative phase analysis based on this model was successfully implemented on a series of fired halloysite clays, giving a first quantitative insight on the transformations in the 980-1260 °C range.
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Dates and versions

hal-03624522 , version 1 (30-03-2022)

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Christelle Chauffeton, Gilles Wallez. Crystal-chemical investigation of the "cubic Al-Si spinel" issued from the thermal transformation of kaolinite and halloysite. Journal of the American Ceramic Society, 2022, 105 (7), pp.4986-4993. ⟨10.1111/jace.18439⟩. ⟨hal-03624522⟩
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