Nanostructuration par séparation de phases et cristallisation à faible température dans des oxydes amorphes massifs élaborés par voie sol-gel

Abstract : This PhD work deals with the development of nanostructured oxide materials and the control of the formation of tin oxide nanocrystals in an amorphous silica matrix obtained by sol-gel process. Prior to the structural and microstructural study of xerogels, a first part of this work concerns the sol-gel process. Washing the gels with hydroalcoholic solutions allows to extract a significant quantity of hydrochloric acid after gelation. Thus, if the washing solutions are renewed, 50% of the acid introduced can be removed. This washing, combined with improvement of the drying process, allowed to reduce the drying duration and finally to obtain bulk xerogels exhibiting a centimetric size.The second part of this work focuses on the structural and microstructural evolution of xerogels through thermal treatments. The results of this second part are obtained through ex situ measurements of X-ray diffraction or coupled small angle X-ray scattering and X-ray diffraction experiments realized in situ as a function of temperature. In both cases the measurements have been performed on synchrotron beamlines. We show that in xerogels containing 10% tin, the amount of nanosized tin oxide crystals can continuously increases without increasing the average size of these crystals. The lowest average size is obtained after a phase separation thermal pretreatment before crystallization and the longer this treatment is, the smaller the size of the crystals. This study is completed by heat treatments carried out in situ in order to simultaneously evidence phase separation and crystallization. These measurements allow to observe the phenomenon of phase separation by small angle X-ray scattering in xerogels containing 10% tin and whose crystallized quantity obtained during a thermal treatment at 350 °C is the highest compared to other heat treatment temperatures and tin concentrations.
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Benjamin Costille. Nanostructuration par séparation de phases et cristallisation à faible température dans des oxydes amorphes massifs élaborés par voie sol-gel. Autre. Université de Limoges, 2019. Français. ⟨NNT : 2019LIMO0044⟩. ⟨tel-02335159⟩

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