| Description du poste : |
1. Context: Inorganic salt hydrates are a well-studied and promising class of Phase Change Materials (PCMs) for thermal energy storage, offering relatively high thermal conductivity, high volumetric latent heat, and cost-effectiveness. The performance of these materials is hindered by low thermodynamic stability during repeated melting, i.e., dehydration cycles, and solidification, i.e., re-hydration cycles. The major problems are their uneven melting, separation of components, freezing at much lower temperatures than expected during rehydration, resulting loss of their ability to store heat over time. These performance limitations are fundamentally linked with their intrinsic crystallographic and structural dynamics mechanisms during these phase transition hydration/dehydration cycles. Therefore, a fundamental understanding of the structure-property relationships is crucial for optimizing the reaction conditions and designing these improved PCMs' inorganic salt hydrates. 2. Objective and Tasks: The objective of the internship is to understand the structure-property relationship in selected inorganic salt hydrates during phase transition hydration/dehydration cycles. This will be achieved by powder X-ray Diffraction (XRD), and possibly Raman and IR spectroscopy. X-ray Diffraction analysis: The core of this internship will be to monitor crystallographic changes during thermal cycling by temperature-dependent in situ X-ray Diffraction (XRD) analysis. This will involve the identification of phases, followed by quantification of the crystalline phase transitions during dehydration/rehydration of possibly all intermediates through extensive Rietveld refinement, yielding the structures of reaction intermediates at each step. Changes in lattice parameters and crystallinity as a function of temperature and cycle number. Raman and IR spectroscopy techniques: will be used to complement the phase changes observed by XRD. The O-H stretching and bending vibrations of water molecules in the hydrate have very strong and characteristic signals in both IR and Raman. This will help to directly monitor the loss of water molecules during heating (dehydration) and their re-incorporation during cooling (rehydration). |
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