Abstract
A concept of repassivation potential, ER, for crevice corrosion had been developed for stainless steels. Applicability of the ER concept to C. P. Ti was confirmed through the corrosion test in 25% NaCl solution at 100°C. ER for growing crevice with penetration depth deeper than a critical depth, h* (≅12 μm), was found to be a well reproducible electrochemical parameter which coincides with the critical potential, VCREV, below which the growing crevice does not initiate.
The repassivation method was also applied to determine critical conditions in terms of NaCl concentration and temperature for crevice corrosion of specimens kept at -0.2V, SCE which was more noble than ER and was included in the spontaneous potential range of passivated Ti in deaerated NaCl solutions measured previously. Crevice corrosion which had been initiated in 25% NaCl solution at 100°C continued to grow in successively diluted NaCl solutions not lower than 0.75% in NaCl concentration and to grow at successively lowered temperatures not lower than 50, 70, and 90°C in 25, 3, and 1% NaC1 solutions, respectively. Critical conditions in terms of temperature and NaCl concentration determined as above were confirmed to agree with the reported results obtained by immersion tests for crevice corrosion resistance of C. P. Ti.
