High-Temperature Raman Spectroscopy Study of the in situ Interaction Between Lanthanum Oxide and FLiNaK Fluoride Melt

Abstract

An in situ Raman spectroscopy study has established a chemical mechanism for the interaction of lanthanum oxide with a molten fluoride mixture, FLiNaK, which holds promise for use in molten salt nuclear reactors. Hightemperature spectral studies along with the use of x-ray phase analysis and thermodynamic modeling have indicated an irreversible heterogeneous reaction La₂O_3s + 2LiF_sol → 2LaOF_s + Li₂O_sol. The reaction product in this fluoride system (lanthanum oxyfluoride, LaOF) has been shown to form hexagonal (R3m) and tetragonal (P4/nmm) crystal modifications. Data were obtained on the thermal behavior of the vibrational modes of lanthanum oxide La₂O₃ in the range 20–600oC and its interaction with atmospheric water vapor.