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Fusion, structure et diagramme de phases des glaces d’eau et d’ammoniac sous conditions extrêmes de pression et de température

Abstract : The objective of this thesis is to explore melting curves, structures and phase diagrams of H2O and NH3 at high pressure and high temperature. Despite the several studies on these compounds, there are significant uncertainties in their phase diagrams. In this work, new experimental approaches of X-ray diffraction and Raman scattering resulted in new data on phase diagrams, melting and chemical stability of NH3 and H2O in a wide range of P-T (P<70 GPa, T<3000 K). For NH3, we have determined the melting curve up to 40 GPa and 2300 K. The melting temperature increases monotonically with pressure, contrary to a previous study but in accordance with theoretical predictions. We observe a chemical decomposition of NH3 into N2 and H2 at high temperature, the importance of this decomposition varies with pressure. Exploration of the phase diagram made it possible to constrain the position of the triple point NH3-III/superionic/fluid. We also present the first data on the evolution of the structure and density of NH3 liquid with variable pressure at 800 K. For H2O, we have determined the melting curve up to 45 GPa and 1500 K. We note a slope failure towards 15 GPa and a higher melting temperature than predicted by the extrapolation of the low pressure data, in better agreement with the "upper limit" of the melting curves of the literature. In addition, we observe indications of a phase transition beyond 25 GPa and 1000 K towards a cubic phase centred that is different of phase VII. The possibility of this phase being superionic is discussed.
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  • HAL Id : tel-02415212, version 2

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Jean-Antoine Queyroux. Fusion, structure et diagramme de phases des glaces d’eau et d’ammoniac sous conditions extrêmes de pression et de température. Matériaux. Université Pierre et Marie Curie - Paris VI, 2017. Français. ⟨NNT : 2017PA066514⟩. ⟨tel-02415212v2⟩

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