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Sujet de stage / Master 2 Internship

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Reactivity in confined media

Contact: LE CAER Sophie, , sophie.le-caer@cea.fr, +33 1 69 08 15 58
Summary:
Reactivity under irradiation in layered or nanotubular clay minerals will be studied as a function of the water amount. Reaction mechanisms will be proposed.
Possibility of continuation in PhD: Oui
Deadline for application:20/04/2018

Full description:
The influence of ionizing radiation on clay minerals is poorly known, in spite of their use as a major component of the engineered barrier in High Level Nuclear Waste Repositories (HLNWR). In this context, the production of H2 by clay minerals under ionizing radiation could be a real issue. It can, e.g., lead to the loss of radionuclide retention properties by creating cracks in the engineered barrier. It is thus important to determine H2 formation reaction mechanisms and to understand the role of several parameters on this production, such as the water amount and the geometry of the confining material. Indeed, the confinement of water molecules play a crucial role in their behavior under ionizing radiation.
We propose here, during this internship, to work on different model clay minerals systems: nanometric talc and imogolite. Nanometric talc has a layered structure, is hydrophilic and the amount of water molecules can be precisely controlled. Another system of interest is imogolite which has a completely different confining geometry : it consists of aluminosilicate nanotubes with a monodisperse diameter and whose chemical groups at the surface of the tubes (-OH, -CH3) can be tuned while maintaining a well-defined geometry. It is then possible to control the hydrophilicity of imogolites.
The purpose of the internship is to measure the H2 production under irradiation by gas chromatography for these two types of samples (nanometric talc and imogolite) as a function of the water content and to try to decipher the role played by the amount of water and by the confining geometry. Electron Paramagnetic Resonance (EPR) experiments will be performed to identify the defects formed in the material after irradiation. These experiments will help proposing reaction mechanisms in both cases. Moreover, in the case of imogolite samples, it is possible to synthesize transparent and thick samples, making picosecond pulse radiolysis experiments possible. We will then follow the decay kinetic of the electron at the picosecond-nanosecond timescale and thus evidence the specificities of reactions occuring in confined media. Other experimental techniques used for the characterization of materials include thermogravimetric analysis, infrared spectroscopy and X-ray diffraction. From all these measurements, reaction mechanisms, taking place in confined media, will be proposed according to the geometry of the confininig material and to the water amount.
Technics/methods used during the internship:
Gas phase chromatography, EPR (electron paramagnetic resonance), thermogravimetric analysis, infrared spectroscopy, X-ray diffraction, picosecond pulse radiolysis.

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