Abstract
The corrosion protection of Hastelloy-N alloy in LiF-NaF-KF (commonly referred to as FLiNaK) molten salt has been developed by pure Ni and Co coatings using the laser cladding technique. An immersion experiment with samples was performed in molten FLiNaK salt at 900 °C for 100 h. It was found that the corrosion rates of the pure Ni-coated specimen and the pure Co-coated specimen are 39.9% and 35.7% of that of Hastelloy-N alloy, respectively. A careful microstructural characterization indicates that a selective dissolution of the elemental Cr occurred in the surface of bare Hastelloy-N alloy, showing a severe intergranular corrosion. For pure metal-coated specimens, in contrast, only metal oxide formed during the laser cladding process dissolved into the molten fluoride salt. The dense pure metal (Ni or Co) coatings exhibit a slightly general corrosion and protect the Hastelloy-N substrate effectively. The possible corrosion mechanism for both coated and uncoated Hastelloy-N under the current experimental condition are discussed in this work.
Highlights
Ternary LiF-KF-NaF (FLiNaK, with molar ratio of 46.5:11.5:42.0) molten salt, one of the most promising candidate fluids for the high-temperature heat transfer, exhibits a series of advantages including high-temperature stability (>1000 ◦ C), high thermal conductivity, high specific heat, high boiling point, and low viscosity [1,2,3,4]
The results show that the corrosion rates corrosion testing in molten salt at corrosion testing in FLiNaK molten salt at 900 °C for 100 h
This study has developed the laser-cladded pure metallic coatings (Ni and Co) to improve the
Summary
Ternary LiF-KF-NaF (FLiNaK, with molar ratio of 46.5:11.5:42.0) molten salt, one of the most promising candidate fluids for the high-temperature heat transfer, exhibits a series of advantages including high-temperature stability (>1000 ◦ C), high thermal conductivity, high specific heat, high boiling point, and low viscosity [1,2,3,4]. FLiNaK molten salt can be used as a secondary coolant and a primary simulation coolant in molten salt reactors [5,6], and as a primary coolant in advanced high-temperature reactors and heat transfer fluid in next-generation concentrated solar power systems [7]. One critical limitation for the FLiNaK molten salt is of intrinsically extremely corrosive at high temperatures [8]. The corrosion will be aggravated due to the presence of impurities in the FLiNaK molten salt [8]. The corrosion control has been a main concern for the materials applied in molten fluoride salts.
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