The effect of surface treatment of titanium on hydrogen absorption was investigated.Surface treated titanium specimens prepared by polishing, anodizing and air oxidizing were immersed in 0.5-6%HCl solutions at the temperature range of 70C to 250C. After immersion, the weight loss, hydrogen content and oxide film thickness of three specimens were measured. As a result, it became clear that anodizing did not reduce hydrogen absorption of titanium because titanium oxide film formed by anodizing had dissolved away in dilute HCl solutions for short time but air oxidizing specimen was stable in this solution for long time and so prevented to hydrogen absorption of titanium.These results of laboratory tests corresponded to the results of field tests conducted in hot molten urea and reducing acid solution at high temperature.

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In the crevice corrosion of commercially pure titanium in hot saline water, the effect of gasket materials and the coupling with dissimilar metals, e. g. with copper alloy or mild steel, has been studied and the mechanism of crevice corrosion was discussed. Titanium crevice specimen with the gasket of dimethacrylate resin was more susceptible to crevice corrosion compared with specimens with PTFE and rubber or without gasket. A role of dimethacrylate in crevice corrosion seems to be attributable to the formation of more tight crevice. The results of potentiostatic electrolysis for titanium crevice specimens revealed that the crevice corrosion occurred at potential more noble than about-0.4V (SCE). Therefore, titanium crevice specimen coupled with copper alloy and mild steel were immune to crevice corrosion because corrosion potentials of these couples are less noble than-0.4V. It was clarified that passive film thickness of titanium decreased markedly with lowering solution pH to the depassivation pH of titanium. On the other hand, pitting potential of titanium was about 5 volts (SCE), regardless of the solution pH and so titanium would be hardly subject to pitting corrosion even in low pH solution. These results suggest that crevice corrosion of titanium is caused by not pitting corrosion but by active corrosion in the crevice.

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