Corrosion resistance of molybdenum, tantalum, and nickel-based alloys was studied in molten salt systems based on LiF–NaF–KF mixture in the temperature range 550–750°C. The rates of corrosion of these materials were determined, the nature of the degradation of the surface of materials established, and the effect of the salt medium and temperature on the corrosive properties of metals and nickel-based alloys considered.

Corrosion resistance of ceramic and carbon materials was studied in molten salt systems based on LiF–NaF–KF mixture in the temperature range 550–750°C. The rates of corrosion of silicon nitride, boron nitride, carbon-carbon composites, and high density graphite in the fluoride electrolyte were determined. The mechanisms of materials degradation after the contact with molten FLiNaK are proposed, and the effect of the salt media and the temperature on the mechanical properties of ceramic and carbon materials is considered.

Corrosion of nickel alloys in molten salts is a complex process dependent on many factors. The paper describes the influence of microstructural changes in several nickel-based alloys (Hastelloy^® G-35^®, VDM^® Alloy 59, KhN62M-VI, Hastelloy^® B-3^®) on the mechanism of their corrosion in molten fluoride salts. The corrosion experiments were performed in LiF–NaF–KF and (LiF–NaF–KF) + UF₄ melts at 550–750 °C. Formation of excess secondary phases along the grain boundaries of the alloys led to heterogeneity of the alloy microstructure. As a result of these changes, microgalvanic couples formed on the surface of the alloys, leading to the development of intergranular corrosion upon contact with molten electrolytes. Secondary phases acted as microanodes or microcathodes depending on a number of factors. Formation and composition of the secondary phases affected the depth and extent of the corrosion damage to nickel alloys.

Bismuth–lithium alloys are considered primary candidates for the reductive extraction step in the on-line reprocessing of molten salt reactor fuel. The corrosion behavior of molybdenum-based alloys and Hastelloy^® B-3 alloy (taken for comparison) was examined here in a liquid Bi–Li (5 mol.%) alloy at 650 °C. MoW10, MoW30, and TZM corrosion-resistant alloys were studied as prospective construction materials for holding liquid bismuth–lithium alloy. Rates of corrosion were determined by the gravimetric method as well as by chemical analysis of corrosion products formed in liquid-phase Bi–Li alloy. The microstructure and chemical composition of samples of the materials and Bi–Li alloys containing the corrosion products after the tests were determined using inductively coupled plasma–atomic emission spectroscopy, X-ray fluorescence analysis, scanning electron microscopy, and energy dispersive spectroscopy. TZM molybdenum-based alloy corrodes in the bismuth-lithium alloy due to the formation of a zirconium–bismuth intermetallic compound, which passes into the liquid phase. The corrosion rates of MoW10, MoW30, and TZM alloys at 650 °C were 16, 16, and 23 µm/year, respectively. Hastelloy^® B-3 alloy, despite its high molybdenum content, was subjected to severe corrosion in liquid Bi–Li alloys due to dissolution of nickel in liquid bismuth. The corrosion rate of this alloy was 14 mm/year.

Bismuth–lithium alloys are considered as primary candidates for the reductive extraction step of on-line reprocessing of a molten salt reactor fuel. The corrosion behavior of pure metals and nickel-based alloys was studied in a liquid Bi–Li (5 mol.%) alloy at 650 °C. The tantalum, molybdenum, and corrosion-resistant alloys VDM^® Alloy C-4, Hastelloy^® G-35^®, KhN62M, VDM^® Alloy 59 were studied as prospective materials for this liquid metal media. The corrosion rates were determined by gravimetric method as well as chemical analysis of corrosion products in Bi–Li alloy. Microstructure and chemical composition of samples of the materials and Bi–Li alloys containing the corrosion products after the tests were evaluated using inductively coupled plasma–atomic emission spectroscopy, X-ray fluorescence analysis, scanning electron microscopy, and energy dispersive spectroscopy. Metallic tantalum and molybdenum do not chemically interact with liquid Bi–Li alloy; the corrosion rate of these metals is determined only by the solubility in this medium. The corrosion rates of Ta and Mo at 650 °C were 0.09 and 0.07 mm/year, respectively. Nickel alloys are subjected to severe corrosion in liquid Bi–Li alloys due to dissolution of nickel in liquid bismuth. Alloys of this type cannot be used in such an environment.