Corrosion Resistance of Titanium Alloy on the Overpack for High-level Radioactive Waste Disposal

Abstract

Crevice corrosion of titanium and its alloys were investigated in 10% sodium chloride at 100 °C simulating the environment of the overpack near the seaside. The pH and Chloride ion concentration inside the crevice were monitored by using W/WO₃ and Ag/AgCl microelectrode, respectively. The pH and Cl^- concentration within the crevice were calculated from the standard potential-pH and potential-log [Cl^-] calibration curves. The effect of Mo on the crevice corrosion of titanium was mainly studied. The passivation behavior of the titanium and Ti-15% Mo alloy were also studied using electrochemical impedance studies. A marginal decrease in pH and increase in Cl^- ion concentration were observed for pure titanium at 100 °C, where there was large increase of the crevice current. On other hand, there was no apparent change in pH and Cl^- ion activity inside the crevice for Ti-15% Mo alloy, where there was no increase of the crevice current. Based on the results, it has been documented that the Ti-15%Mo alloy was not susceptible to crevice corrosion in 10% NaCl solutions at 100 °C. The corrosion reaction resistance (R_t) was found to increase with addition of Mo as an alloying element and also increase with applied anodic potential. Hence, Mo is able to be an effective alloying element, which enhanced the crevice corrosion resistance of titanium under the environment simulating the overpack near the seaside.