NMR and EXAFS Investigations of Lanthanum Fluoride Solubility in Molten LiF-ZrF4-LaF3 Mixture: Application in Molten Salts Reactor (original) (raw)

Gaune-Escard/Molten Salts Chemistry and Technology, 2014

Abstract

ABSTRACT Our original approach consists in coupling, in situ at high temperature, NMR (nuclear magnetic resonance) and EXAFS (extended X-ray absorption fine structure) techniques, both sensitive to the local environment of a selected element and able to follow the evolution of ionic species in the melt with composition and temperature. We focussed on the study of rare earth fluoride 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 K-edge of Zr. 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.

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