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Theses

Étude de la solubilité de l'oxyde de zirconium et de sa réactivité de surface en milieux aqueux

Abstract : Zirconium dioxide is a promising ceramic for the specific immobilization of actinides in a geological disposal vault. An appropriate knowledge of the solubility controlling solid phases confining radioactive waste is necessary if one wants to assess the stability of ZrO2 in a disposal environmental conditions. The solubility of zirconium oxide is very low at neutral pH (<10-8M), but increases at highly acidic and alkaline pH. Solubility values may differ by more than 6 orders of magnitude at a given pH, indicating high uncertainties. The objective of this work is to understand processes governing the equilibrium between zirconium oxide and water, and to study the surface reactivity of the material in contact with aqueous solutions. The solubility of monoclinic and of cubic ZrO2 in aqueous solutions were investigated, approaching equilibrium from under-saturated conditions.The low solubility of zirconia makes its measurement a challenging task. A reliable experimental procedure was developed to measure low concentrations of zirconium (limit of quantitation[Zr] ~10-11M). In order to examine the surface reactivity, solid phases were further characterized by BET, XRD, SAXS, HR-TEM and STEM-HAADFbefore and after reaching equilibrium. In order to understand the reaction mechanism taking place at the zirconia/water interface as well as the low solubility in aqueous phase, hydrolysis of Zr-O-Zr bonds by a single and multiple water molecule were studied using the periodic DFT code, with Vienna ab initio simulation package (VASP). This study led to the proposal of a dissolution mechanism whose limiting step, in the neutral pH range, is the difficulty of formation of an activated complex.
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Submitted on : Thursday, December 23, 2021 - 1:01:09 AM
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  • HAL Id : tel-03501102, version 1

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Wiem Zouari. Étude de la solubilité de l'oxyde de zirconium et de sa réactivité de surface en milieux aqueux. Matériaux. Ecole nationale supérieure Mines-Télécom Atlantique, 2018. Français. ⟨NNT : 2018IMTA0117⟩. ⟨tel-03501102⟩

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