Wang C, Chen X, Gong Y. On the Structures of Thorium Fluoride and Oxyfluoride Anions in Molten FLiBe and FLiNaK.
J Phys Chem B 2021;
125:1640-1646. [PMID:
33533620 DOI:
10.1021/acs.jpcb.0c10197]
[Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The structures of thorium fluoride and oxyfluoride ions in molten FLiBe-ThF4 and FLiNaK-ThF4 were investigated by Raman spectroscopy and density functional theory calculations. Thorium fluorides are present in the form of ThF62- (Oh) and ThF73- (C2v) in molten FLiNaK-ThF4. Similar speciation was identified in FLiBe-ThF4, and the thorium fluoride anions are in equilibrium with free F- ions and beryllium fluoride anions, which are responsible for the red shift of the beryllium fluoride bands in the Raman spectra. With the addition of Li2O into the FLiNaK-ThF4 and FLiBe-ThF4 melts, the Th2OF104- anion with a linear Th-O-Th geometry was formed at the expense of thorium fluoride anions. The beryllium fluoride bands in the Raman spectra of FLiBe-ThF4 exhibit a blue shift upon Th2OF104- formation, which results from the release of free F- ions that can further react with beryllium fluoride. Insoluble thorium oxides were found in the FLiNaK and FLiBe melts at a Li2O concentration of 15 mol %, and the Th2OF104- anion is, therefore, a bridge connecting the soluble thorium fluorides and insoluble thorium oxides in molten fluorides.
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