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±0.1d(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.