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Synthèse de matériaux composites à base d'oxydes préformés : de la compréhension des mécanismes de déstabilisation de sols multiconstituants à l'étude des propriétés des hétéroagrégats

Abstract : Since lots of years, aggregation conditions of charged colloids in suspension have been studied in order to control the structure of aggregates [KIM 2003] or the porosity [SNO 2005] of dried materials. We have focused this work on the understanding of the formation and the growth mechanism of heteroaggregates composed of different nature oxide nanoparticles. After validating the proof of heteroaggregation concept with amorphous silica spheres and goethite nanorods, our study has concerned crystalline system in order to show the exposed crystallographic facets of the used particles role in the heteroaggregation mechanism. In a second time, we interested us to the properties generated by the heteroaggregation of oxide nanoparticles. Four families of model particles, isotropic particles of brookite (TiO2) and silica (SiO2), and anisotropic particles of goethite (α-FeO(OH)) and boehmite (γ-AlO(OH), have been synthetized and characterized to know their size, morphology and surface charge. To generate some heteroaggregation, we have developed and adapted to each system a mixing and in situ following methodology by using a Dynamic Light Scattering (DLS) and laser-diffraction. We have identified pH conditions which favored particles heteroaggregation instead of homoagrégation. In this case, the heteroaggregates growth mechanism followed bridging process of the two kinds of particles. Their relative proportions adjustment allows controlling the size and the structure of the heteroaggregates. The reversibility of the heteroaggregation process is limited notably by the aging time of the aggregate in suspension due to the evolution of the interaction nature of the two oxides interface and also due to a critical aggregate size. The heteroaggregates present a specific porosity significantly different from the one kind of particles powders which pores diameters could be controlled by the size and the number of coating particles. Finally, for the mixed systems of heteroaggregated silica - alumina, we have highlighted the possibility to generate some acidic sites to the interface and we have related it to the heteroaggregates catalytic activity according to the m-xylene isomerization.
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  • HAL Id : tel-00827971, version 1

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Loïc André. Synthèse de matériaux composites à base d'oxydes préformés : de la compréhension des mécanismes de déstabilisation de sols multiconstituants à l'étude des propriétés des hétéroagrégats. Science des matériaux [cond-mat.mtrl-sci]. Université Pierre et Marie Curie - Paris VI, 2012. Français. ⟨NNT : 2012PA066136⟩. ⟨tel-00827971⟩

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