LIMITATIONS OF POTENTIOSTATIC REPASSIVATION TECHNIQUES AND THEIR RELATIONSHIP TO THE APPLICABILITY OF THE HIGH-FIELD APPROXIMATION TO THE REPASSIVATION OF TITANIUM

Bare surface and oxide repassivation kinetics are critical to the understanding of environmental cracking of titanium. Various potentiostatic repassivation techniques have been used by previous researchers to obtain this information. However, the apparent repassivation kinetics are a function of depassivation speed, solution resistance, potentiostat response, etc. The effect of each of these limitations on repassivation behavior is examined. The applicability of the high field approximation to potentiostatic repassivation tests on titanium in chloride solutions is also discussed. The above experimental limitations, as well as a significant difference between the total measured current (90% of which is due to anodic dissolution) and the oxide formation current, render the high field approximation to oxide growth an ineffective model of the current decay observed on titanium and explains the wide range of high field parameters that have been reported in the literature for this material.