Influence of purification process on incipient material corrosion in molten FLiNaK salts

This study investigated the incipient corrosion characteristics on Ni based and Mo based alloys at 600 degrees C in FLiNaK molten salts regarding to different purification processes of FLiNaK molten salts. Ni based Hastelloys-N alloys exhibited relatively better corrosion resistances, while Mo based TZM alloys showed the poorest corrosion resistance. The mass loss of the tested alloys was strongly dependent on purification process of the FLiNaK molten salts; through preheating and stirring the FLiNaK salts at higher temperature during the purification process, impurities and residual moisture of the FLiNaK salts could be effectively removed, leading to the improvement of mass loss of the tested alloys. The results of microstructural characterisation revealed that Hastelloy-N tended to exhibit intergranular corrosion, whereas grains of Hastelloy-B3 were also attacked by the corrosive medium in addition to grain boundaries. The results of EDX mapping showed that both Cr and Mo were found to be dissolved into FLiNaK salts for Hastelloy-N and Hastelloy-B3. The Mo based TZM alloys exhibited general corrosion pattern.