Effect of oxidizing ions on the corrosion behavior of SiN stainless steel in high-temperature nitric acid solution

The oxidizing ions, abundantly existing in spent fuel reprocessing process, play a vital role in the corrosion behavior of stainless steels due to the inherently high electrode potential. However, the systematic research on the effect of these ions on the corrosion mechanism of stainless steels in high-temperature nitric acid media is rarely reported. Herein, the electrochemical behavior and the passive film characteristics of SiN stainless steel in hot nitric acid solution containing different ions with various concentrations were investigated. The oxidizing Cr6+, V5+ and Ce4+ affected both the anodic and the cathodic reactions, while the non-oxidizing Fe3+ only changed the cathodic reactions. Meanwhile, the passive film characteristics of SiN stainless steel are partly altered with the change in ion concentration, and the passive film primarily consisted of Fe2O3, Cr2O3, Cr(OH)3 and silicate. The existence of silicate with high chemical stability improved the protection of passive film, displaying a high resistance to intergranular corrosion in the transpassive domain. In addition, a critical concentration phenomenon was observed in nitric acid with oxidizing ions, and the deposition theory was proposed to reveal the mechanism of critical concentration phenomenon.