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Étude et mise en œuvre du couple de diffusion La2SiO5 / SiO2 pour l’élaboration de couches texturées et optimisées d’oxyapatite silicatée pour le domaine de l’énergie

Abstract : This thesis work is focused on the study of different shaping processes in order to obtain a polycrystalline, dense and textured oxyapatite material (La9,33+x/3(SiO4)6O2+x/2). Due to their ionic conduction properties, these materials have potential applications as SOFC fuel cell electrolyte. A preferential orientation along the c-axis of oxyapatite crystallites considerably improves the conduction performances. This material is obtained by reactive sintering between layers of precursors: La2SiO5 and SiO2. The La2SiO5 precursor was synthesized by solid-state reaction, using La2O3 and SiO2 as raw materials. This synthesis route was optimized evaluating the influence of the crystalline nature and the particle size of silica. Thus, the reaction mechanisms involved in the formation of the different lanthanum silicates from the La2O3-SiO2 phase diagram in relation with the silica characteristics were identified. Several shaping processes were studied (tape casting, uniaxial pressing and electrophoretic deposition) for the fabrication of bi-layer and multi-layer materials using the diffusion couple La2SiO5 / SiO2. The influence of different reactive sintering parameters (temperature and holding time) and the porosity of layers on the mechanisms of oxyapatite crystal growth were studied. This work also made it possible to evaluate the feasibility of tape casting and electrophoretic deposition for the elaboration of thin layers of reagents in order to obtain textured materials by reactive diffusion. The results of these studies show that the mechanism of oxyapatite crystal growth is conditioned by the appearance of a liquid phase at the La2SiO5 / SiO2 interface (on the silica grains), which enables the diffusion of lanthanum La+III, and leads to the precipitation of a La2Si2O7 layer, that is the basis for the oxyapatite crystal growth.
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Lizeth Arbelaez Morales. Étude et mise en œuvre du couple de diffusion La2SiO5 / SiO2 pour l’élaboration de couches texturées et optimisées d’oxyapatite silicatée pour le domaine de l’énergie. Matériaux. Université de Limoges, 2021. Français. ⟨NNT : 2021LIMO0104⟩. ⟨tel-03563124⟩

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