Abstract
The electrochemical behavior of Fe(III) in molten LiF–NaF–KF [46.5:11.5:42 (mol%)] [FLINAK] salt was studied by cyclic voltammetry (CV), chronopotentiometry (CP) and square wave voltammetry (SWV) at 600°C. It was found that Fe(III) was initially reduced to Fe(II) at +2.0 V (vs. alkalis) followed by reduction of Fe(II) to Fe at +1.4 V (vs. alkalis) and both reduction processes were controlled by ion diffusion. Diffusion coefficients of Fe(III) in molten FLINAK were calculated through CV and CP. The reduction peak of Fe(III)/Fe(II) was still observed in SWVs even though only FeF2 was added to FLINAK. This result showed that Fe(II) was converted to Fe(III), which exists stably in FLINAK melts.
Highlights
Molten fluorides are suitable for use as coolants of molten salt reactors because these materials present excellent heat transfer properties [1,2,3]
According to the investigations described by Oak Ridge National Laboratory (ORNL) [11], the corrosion valence state of Fe in molten fluorides is determined by the acid-base properties of the molten fluoride employed; here, a Lewis acid is defined as a fluoride ion acceptor, and a Lewis base is a fluoride ion donor
According to the theory of non-electric transfer described by Ozeryanaya [12], Fe may firstly dissolve in FLINAK melts as a form of Fe(II), which would further convert to Fe(III)
Summary
Molten fluorides are suitable for use as coolants of molten salt reactors because these materials present excellent heat transfer properties [1,2,3]. According to the investigations described by Oak Ridge National Laboratory (ORNL) [11], the corrosion valence state of Fe in molten fluorides is determined by the acid-base properties of the molten fluoride employed; here, a Lewis acid is defined as a fluoride ion acceptor, and a Lewis base is a fluoride ion donor. Pure FLINAK consisting of LiF, NaF, and KF [LiF:NaF:KF, 46.5:11.5:42 (mol%)] is known to be a strongly basic solvent that tends to stabilize the Fe(III) valence state [11]. According to the theory of non-electric transfer described by Ozeryanaya [12], Fe may firstly dissolve in FLINAK melts as a form of Fe(II), which would further convert to Fe(III). No relevant studies have yet been published to prove this conversion
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