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Elaboration de phases hydroxydes doubles lamellaires intercalant des anions sulfates: étude de leur évolution structurale, thermique et hygrométrique

Abstract : This thesis presents the elaboration and a thermal, hygrometric and structural study of Layered Double Hydroxides (LDH's) based on [Zn-Cr], [Zn-Al] and [Cu-Cr] main layers intercalating sulphate anions. In the first part, we optimized the procedures allowing to prepare these compounds in large quantities and in a reproducible way. Two varieties were obtained. The first is characterized by a basal distance of 11Å and has a surstructure which makes it an analogue of the mineral shigaite. The second variety, characterized by a basal distance from 8,9Å, is obtained by washing the first one with water. By a synthesis carried out under original conditions, we were able to highlight that the sulphate LDH could intercalate the interlayer cations Na+, Li+, Mg2+, Ca2+ and Al3+. The study of the interlayer evolution of the prepared phases was undertaken in the second part in an isothermal way; either by setting progressive vacuum which showed an important contraction which corresponds to the removal of interlayer water and is accompanied by a change of stacking sequence, or by control the of water vapour pressure. This study allows to specify the pressures at which the transformation occurs and to establish their reversibility under increasing PH2O. The linked gravimetric study is in agreement with the observed structural transformations. In the third part we carried out an isobar study at constant water vapour pressure by modifying the temperature of the sample. These measurements lead us to develop original experimental devices to work under PH2O only. This study has shown cycles of dehydration/rehydration with fast kinetics of transformation without deterioration of the crystalline quality. A higher temperatures where the deshydroxylation of the structure reaches notable proportions the transformations becomes irreversible. In the case of the sulphate LDH, these irreversible transformations are accompanied by a strong contraction of the interlayer distance which can only correspond to the grafting of the sulphate anions on the oxy-hydroxylated layers.
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  • HAL Id : tel-00691964, version 1

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Rachid Mostarih. Elaboration de phases hydroxydes doubles lamellaires intercalant des anions sulfates: étude de leur évolution structurale, thermique et hygrométrique. Chimie organique. Université Blaise Pascal - Clermont-Ferrand II, 2006. Français. ⟨NNT : 2006CLF21657⟩. ⟨tel-00691964⟩

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