Conditions Extrêmes et Matériaux : Haute Température et Irradiation

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L.Maksoud, M.Gobet, D.Zanghi, H.Matsuura, M.Numakura, O.Pauvert, C.Bessada., 'NMR and EXAFS Investigations of Lanthanum Fluoride Solubility in Molten LiF-ZrF4-LaF3 mixture: Application in Molten Salts Reactor', Proceeding of the 9th International Symposium on Molten Salts Chemistry and Technology (2011)

Our original approach consists in coupling, in situ at high temperature, NMR and EXAFS techniques, both sensitive to the local environment of a selected element and able to follow evolution of ionic species in the melt with composition and temperature. We focused on the study of rare earth fluorides solubility, starting with LaF3, in molten LiF-ZrF4 mixtures. We studied the NMR signal evolution of 19F, 139La and 91Zr in situ in the melt at high temperature. Compared to the binary LiF-ZrF4, NMR experiments do not show any difference in 19F chemical shift evolution. The NMR signal of Zirconium is only slightly shifted. This corresponds to a weak evolution of the average coordination around Zr. This is confirmed by in situ EXAFS experiments at the Zr K-edge. In LiF-ZrF4-LaF3 with 5 mol % of LaF3, 139La chemical shift strongly increases with ZrF4 content. This evolution is associated with an important modification of the local environment around the lanthanum. It can be correlated to an important increase of its coordination number or to the influence of Zirconium atoms in its second sphere of coordination