Etude structurale d'un hydrate 10 Å instable de kaolinite

The treatment of KGa-1 kaolinite with dimethyl sulfoxide and ammonium fluoride heated at 383 K provides an unstable hydrated phase characterized by a 10 A basal distance. When air-dried, this hydrate gives a dehydrated phase at 7.15 A. The aim of this work is to determine the structural characteristics of this hydrate. The method used to characterize this hydrate is based on the comparison between experimental and calculated X-ray diffraction profiles. This study is achieved in two steps: the study of 00l reflections enabled the determination of the number of intercalated water molecules, their positions and the stacking mode along the normal to the (a, b) plane; and the study of the hkl reflections with h and/or k ≠ 0 enabled the determination of the stacking mode and the positions of water molecules in the (a, b) plane. The unstable hydrate is characterized by two water molecules per Al2Si2O5(OH)4 unit situated at z1 = z2 = 7.57 A. Two adjacent layers are translated with respect to each other with TI = −0.155a + 0.13b + 10n.