Metastable and stable pitting corrosion of titanium in halide solutions

Stable and metastable pitting corrosion of Ti was investigated in neutral and acidic halide solutions. In agreement with earlier findings by others, Br- were found to be significantly more aggressive in triggering pitting corrosion of Ti than Cl-. In Br--containing solutions, the major factors influencing the occurrence of stable pitting are the Br- concentration and the purity of Ti; solution pH influences the pitting potential in a much lesser extent. Repassivation of growing pits takes place at significantly lower potentials than the onset of stable pitting. Current transients were observed in the passive range in Br--containing solutions indicating that metastable pitting takes place. The current transient activity depends on the electrolyte, but moreover very significantly on the purity of Ti. Hence. pit initiation on Ti is connected to the presence of impurities in the bulk material.