Etude structurale par diffraction des RX et spectroscopie IR des hydrates 10 et 8.4 Å de kaolinite

Two hydrated kaolinites, characterized by 10 and 8.4 Å basal distances, were synthesized by treating the kaolinite KGa-1 with dimethyl sulfoxide (DMSO) and ammonium fluoride (NH₄F). The X-ray diffraction study was based on a comparison between the experimental and calculated profiles. This study was conducted in two steps: firstly, the study of the 00l reflections enabled the determination of the stacking mode along c*, the number of water molecules and their positions along the normal to the plane of the sheet structure; secondly, the study of the hk bands, with h and/or k ≠ 0, enabled the determination of the stacking mode and the positions of the water molecules in the (a,b) plane. The 10 Å hydrated kaolinite is characterized by two water molecules per Al₂Si₂O₅(OH)₄ unit, situated at 3 and 3.4 Å from the hydroxyl surface, over the octahedral sites. Two adjacent layers are translated with respect to each other, with T₁₁ = −0.38a − 0.37b + 10n. The 8.4 Å hydrated kaolinite is characterized by one water molecule per Al₂Si₂O₅(OH)₄ unit, situated at 2.4 Å from the hydroxyl surface and inserted between the vacant octahedral site and the ditrigonal cavity of the tetrahedral sheet. The corresponding interlayer shift is T₁₁ = −0.355a + 0.35b + 8.4n.