Effects of dissolved oxygen on the electrochemical corrosion behavior of pure titanium in fluoride-containing weakly acidic solutions

The effects of dissolved oxygen (DO) on the electrochemical behavior of titanium in fluoride-containing weakly acidic solutions (pH = 5.0) were evaluated quantitatively by electrochemical methods, such as open circuit potential (OCP) measurements and potentiodynamic polarization tests, combined with corrosion morphology observation. The results showed that the electrochemical behavior changed from spontaneously passive to active-passive behavior with increasing the fluoride concentration irrespective of the DO content. DO was found to increase the critical fluoride concentration for the corrosion of titanium due to the increased limiting diffusion current density of oxygen reduction reaction and decreased maximum anodic current density caused by DO. But the corrosion rate of titanium would be accelerated by DO once the fluoride concentration exceeded the critical value. Moreover, corrosion products were observed on the surface when the fluoride concentrations were high enough and titanium was in the active state, which altered the electrochemical behavior of titanium further, such as facilitating the occurrence of OCP oscillation.