Electrochemical behaviour of titanium in H₂SO₄-MnSO₄ electrolytes

The corrosion of titanium in H₂SO₄ electrolytes (0.001–1.0 M) at temperatures from ambient to 98°C has been investigated using steady-state polarization measurements. Four distinct regions of behaviour were identified, namely active corrosion, the active–passive transition, passive region and the dielectric breakdown region. The active corrosion and active–passive transition were characterized by anodic peak current (im) and voltage (Em), which in turn were found to vary with the experimental conditions, i.e., d(log(im))/dpH=−0.8±0.1 and dEm/dpH which was −71 mV at 98°C, −58 mV at 80°C and −28 mV at 60°C. The activation energy for titanium corrosion, determined from temperature studies, was found to be 67.7 kJ mol⁻¹ in 0.1 M H₂SO₄ and 56.7 kJ mol⁻¹ in 1.0 M H₂SO₄. The dielectric breakdown voltage (Ed) of the passive TiO₂ film was found to vary depending on how much TiO₂ was present. The inclusion of Mn²⁺ into the H₂SO₄ electrolyte, as is done during the commercial electrodeposition of manganese dioxide, resulted in a decrease in titanium corrosion current, possibly due to Mn²⁺ adsorption limiting electrolyte access to the substrate.