An Electrochemical Investigation of Localized Corrosion on Titanium in Chloride Environments

Electrochemical methods have been used to study the crevice and pitting corrosion behavior of unalloyed titanium in chloride solutions at elevated temperatures (maximum 150 C). The investigation was focused primarily on crevice corrosion. The techniques which were used included simultaneous measurement of the corrosion potential-time behavior of plain and creviced specimens, controlled anodic polarization of creviced specimens (both potentiostatic and potentiodynamic methods), and the measurement of the current and the potential of galvanic cells formed between creviced specimens and large uncreviced areas of titanium. The data obtained under both controlled and freely corroding conditions were interpreted using an electrochemical mechanism of crevice corrosion on titanium in chloride solutions. The degree of anodic polarization in the crevice, produced either potentiostatically or naturally by galvanic coupling, was shown to have a major effect on the kinetics of crevice corrosion initiation and propagation. The distribution of the cathodic reaction between reduction of O₂ on the external surface and H⁺ reduction in the crevice was evaluated. The concept of a critical crevice pH for initiation of crevice corrosion was used to explain the differences between these results and those of other published studies for the critical temperatures and chloride concentrations necessary for initiation of crevice corrosion on unalloyed titanium.