E. V. Nikitina, E. A. Karfidov, Yu. P. Zaikov, K. E. Seliverstov.
ABSTRACT
Even though alkali metal fluorides are among the most aggressive salts in terms of degradation of structural material used in reactor engineering, these salt melts have huge advantages due to high thermal conductivity, low viscosity, high boiling points, the highest heat capacity per unit volume and insensitivity to radiation.
In most high-temperature technologies using molten salts, alloys containing high concentrations of chromium, silicon or aluminum are used, since these elements easily form passive oxide films. However, in molten halide salts, these oxides either do not form or are unstable due to the very low oxygen activity in the molten salts. In this regard, experiments were carried out to determine the corrosion rate of the Hastelloy C2000 alloy with different concentrations of O2- (by adding lithium oxide to the melt in the concentration range from 0 to 5 wt %) in a fluoride melt. The formation of a protective oxygen-containing layer with a thickness of 10 microns has been established. The corrosion rate decreases by an order of magnitude at the concentration of oxygen anions in the melt from 0.14 to 0.28 wt %, which may indicate the detection of the phenomenon of high-temperature passivation of the material due to modification of the composition of the fluoride melt and reduction of its corrosion activity. In addition, for the Hastelloy C2000 alloy, the depth of corrosion damage in fluoride melts decreases when lithium oxide is introduced into the melt due to the formation of oxygen-containing compounds of sufficient thickness on the surface.
KEYWORDS
corrosion, candidate materials for LSR, alkali metal halide melt, high-temperature passivation, spinel-type oxides
DOI: 10.31857/S0235010622060093