In-situ X-ray Diffraction Study of Inorganic Salt Hydrates for Thermal Energy Storage

Laboratoire Georges Friedel
(LGF) UMR5307 CNRS

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 1. The performance of these materials is hindered by low thermodynamic stability
during repeated melting ie, dehydration cycles, and solidification ie, 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 2. These
performance limitations are fundamentally linked with their intrinsic crystallographic and structural
dynamics mechanisms during these phase transition hydration/de-hydration cycles. Therefore, a
fundamental understanding of the structure-property relationships3,4 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/de-hydration 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
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 OH 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).

This project is primarily experimental and analytical. The candidate is expected to have skills in
materials characterization and solid-state chemistry. Prior experience with X-ray Diffraction is a plus
but not mandatory. Interested candidate should be enrolled in Master 2 and enrolled Final year of
Materials Science, Chemistry, Physics, engineering or a related field. The work will be carried out
completely within the laboratory.