Dissolved valence state of iron fluorides and their effect on Ni-based alloy in FLiNaK salt

Abstract In this study, the stable dissolved valence state of iron fluorides in molten LiF - NaF - KF (FLiNaK) salt and their effect on GH3535 alloy were systematically investigated. Results of in situ ultraviolet–visible (UV–Vis) absorption spectroscopy and electrochemical analysis indicated that Fe (II) in molten FLiNaK salt is unstable and gets converted to more stable Fe (III) through the disproportionation reaction: 3 Fe (II) = 2 Fe (III) + Fe. Thus, the corrosion of GH3535 alloy is aggravated by the addition of iron fluorides due to the redox reaction: Fe (III) + Cr = Fe + Cr (III), resulting in the formation of the Cr-depletion layer and Fe-rich layer.