Synthèse en milieu fluoré et caractérisation de phyllosilicates de type montmorillonite. Etude structurale par spectroscopies d'Absorption des Rayons X et de Résonance Magnétique Nucléaire.

Abstract : The aim of this work is to synthesize and characterise montmorillonite type phyllosilicates and to study the distribution of the metal elements in the structure.
First, generalities about phyllosilicates are introduced. A particular attention is given to (2:1) dioctahedral phyllosilicates and especially to montmorillonite. The different methods of the synthesis of this mineral are reviewed. The method of hydrothermal synthesis in fluoride medium and the techniques used to characterise the materials (XRD, TGA-DTA, chemical analyses) are then described. The descriptions of solid state NMR and EXAFS are particularly developed. Next, a systematic study of the synthetic products is realised for two systems MO-Al2O3-SiO2 (M = Mg or Zn). The compositions of hydrogel are based on a theoretical formula of montmorillonite : Na2x[Al2(1-x)M2x]Si4O10OH2 (x represents the octahedral layer charge). A montmorillonite type phyllosilicate is obtained for 0.10 < x < 0.25 in the MgO-Al2O3-SiO2 system and for x = 0.10 in the ZnO-Al2O3-SiO2 system. Besides the Mg/Al substitutions in the octahedral sheet, Al/Si substitutions in the tetrahedral sheet are observed by 29Si and 27Al NMR. The 19F NMR shows a clustering of the octahedral elements in (Mg)phyllosilicate. Then, the parameters of the synthesis of (Mg)phyllosilicate are introduced. Kaolinite is observed as an intermediary phase during the crystallisation. The optimal pH is found between 5.0 and 5.5. The presence of a little amount of F- is necessary (0.05 < F/SiO2 < 0.10). Tetrahedral substitutions are fewer with the use of Na+ as compensating cation. Finally, Zn and Mg K-edges EXAFS show a distortion of the layer and a clustering of the octahedral elements for the (Zn)phyllosilicate. A quantitative 27Al MAS-NMR method is elaborated which allows to determine both total amount of aluminium in the structure and AlVI/AlIV ratio.
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Marc X. Reinholdt. Synthèse en milieu fluoré et caractérisation de phyllosilicates de type montmorillonite. Etude structurale par spectroscopies d'Absorption des Rayons X et de Résonance Magnétique Nucléaire.. Matériaux. Université de Haute Alsace - Mulhouse, 2001. Français. ⟨tel-00072356⟩

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