Passivation and repassivation behavior of titanium in hot concentrated nitric acid solution containing fluoride ions

The effect of F − on the passivation and repassivation of titanium in a simulated spent fuel reprocessing environment was examined using a custom-designed scratching electrode device. Electrochemical experiments and characterization of the passive film revealed that F − accelerates both cathodic and anodic reactions of titanium. The critical concentration phenomenon of F − on intact and scratched titanium surfaces in hot HNO 3 solutions can be attributed to competitive adsorption between F − and NO 3 − . Below the critical concentration, F − primarily affects the outer layer of the passive film, while above it, F − penetrates the entire passive film, significantly reducing corrosion resistance. The lower critical concentration on scratched surfaces (0.5 mmol/L) compared to intact surfaces (1 mmol/L) is due to enhanced F − adsorption caused by the presence of scratches. It is indicated that regular monitoring of F − concentrations and minimizing scratches on titanium surfaces to prevent corrosion failure are imperative during the spent fuel reprocessing process.