Electrochemical Study On The Corrosion Inhibition Effect Of The FLiNaK-CrF₃/CrF₂ Redox Buffering Salt System On 316L Stainless Steel

In this paper,it is proposed that CrF₃ and CrF₂ were introduced into LiF-NaF-KF?FLiNaK?molten salt to form FLiNaK-CrF₃/CrF₂ redox buffering molten salt to inhibit the corrosion of 316L stainless steel?316LSS?in the molten salt environment.And it is expected that the corrosion rate of the 316LSS could be quickly obtained by the traditional Tafel extrapolation method.However,experimental results indicated that the corrosion current obtained by the traditional Tafel method cannot reflect the real corrosion condition of 316LSS.The reason is proved to be the existing of the non-corrosion related interfering current when traditional Tafel method performed in the redox buffering system.Thus,a modified Tafel method is proposed in this paper by introducing an inert comparison electrode to eliminate the interference of non-corrosion-related currents in the polarization current of the alloy material in the redox buffering system.Investigations were performed in the following two systems:FLiNaK-CrF₃ system?FLiNaK molten salt containing 500ppm CrF₃?and FLiNaK-CrF₃/CrF₂ system?FLiNaK molten salt containing 1000ppm CrF₃ and 1500ppmCrF₂?.Polarization curve tests and immersion corrosion tests were performed on 316LSS,pure Fe wire and nickel-based alloy Hastelloy C-276 in these two systems.Through the comparative analysis of the experimental results and the verification of the immersion corrosion test,the accuracy of the corrosion current of the material obtained by the modified Tafel method in the FLiNaK-CrF₃/CrF₂ redox buffering molten salt was demonstrated.Based on the quick corrosion evaluation method established above,the effect of the molten salt potential on the corrosion rate of 316LSS in the FLiNaK molten salt was examined.The results of this study show that when the experimental temperature is 873K and 823K,the molten salt potential is lower than-0.741V and-0.770V,respectively,the corrosion of 316LSS in the FLiNaK molten salt can be effectively inhibited.This conclusion was verified by the immersion corrosion tests.