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Studies of the dehydroxylated-rehydroxylated montmorillonite : Structure of the layers and intercalation of water molecules

Abstract : Dioctahedral micas and smectites are phyllosilicates in which only two of the three octahedral sites of the half unit cell are occupied, which leads to tv layers (vacant sites in trans position) or cv layers (vacant sites in cis positions). Micas and smectites differ essentially by the layer charge. For illite (mica family), the powder XRD pattern modeling shows that the layers of the natural sample are cv ones, and become tv ones after a dehydroxylation-rehydroxylation cycle. The thermo-gravimetric analysis (TGA) shows a change in the dehydroxylation temperature from 700°C for the natural specimen to 550°C in the rehydroxylated one. Such a shift can be correlated with the cv → tv transformation which modifies the OH-OH distance. For montmorillonite (smectite family), the powder XRD patterns are poorly resolved due to the disorder in the stacking of the layers. The dehydroxylation temperature, which is 700°C for the natural sample, is 540°C for the rehydroxylated one. Then, the TGA indicates a cv → tv transformation during the dehydroxylation-rehydroxylation process. The XRD patterns recorded from oriented samples give prominence to the 00l reflections and show that the intercalation of water molecules is not influenced by the cv / tv nature of the layers.
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Submitted on : Tuesday, November 3, 2020 - 9:20:26 AM
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Fabrice Muller, Alain Plançon, V.A. Drits. Studies of the dehydroxylated-rehydroxylated montmorillonite : Structure of the layers and intercalation of water molecules. Journal de Physique 4, EDP Sciences, 2000, 10 (PR10), pp.Pr10-481-Pr10-487. ⟨10.1051/jp4:20001051⟩. ⟨insu-02986504⟩

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