Depassivation behavior of titanium alloys in strong alkaline aqueous solutions

The depassivation behavior of titanium alloys in highly alkaline aqueous environments was investigated based on the self-passivation concept. The depassivation pH values, pH(d), defined as the critical pH values at that the free corrosion potential started to shift in the less noble direction, showed a good correlation with the inverse of the test temperatures although no remarkable difference existed with respect to alloy species on pH(d). The less-noblement behavior of the free corrosion potential was analyzed based on the polarization curves, and was concluded to be reasonable kinetically. However, no weight losses of test specimen were observed in the immersion tests conducted at 25 C even in the region above pH(d). Some possible reasons for the disagreement were investigated and some future items to be investigated were proposed.