Galvanic corrosion behavior of bi-metal couples, all consisting of commercially pure (CP) titanium, in 3.5 wt% NaCl solution was investigated. The roles of dissolved oxygen in the solution, cathode/anode area ratio and the anodized oxide on titanium surface of titanium were explored in terms of the changes of electrochemical polarity and the magnitude of galvanic current. The presence of dissolved oxygen caused an increase in galvanic current for the titanium-carbon steel couple compared with that measured in de-aerated solution. However, a reverse case was found for the titanium-brass couple. By increasing cathode/anode area ratio, an increase in galvanic current was found for the titanium/carbon steel couple, while a reversion of electrochemical polarity was observed for the titanium/brass couple. At a higher titanium/brass area ratio, titanium acted as anode, while it became cathode due to rapid passivation at a lower area ratio (titanium/brass area ratio 1:10). The composition of the surface film on the each electrode at different cathode/anode area ratios were investigated thoroughly by XPS. It was found that the corrosion product layer formed on the carbon steel at titanium/carbon steel area ratio 1:1 and 10:1 were composed mainly of FeOOH and Fe3O4. As decreased titanium/carbon steel area ratio 0.1:1, however, corrosion product of Fe3O4 was not detected. On the other hand, with increasing titanium/carbon steel area ratio increased the signals of Fe3O4, indicating increased the dissolution rate of the carbon steel. Moreover, the XPS results for titanium coupled to brass at different area ratio implies that with increasing brass area ratio increased the signals of Cu2O and the concentration of ZnO increased from 29.5% to 70.3%. This XPS results confirm that the role of area ratio in affecting the polarity reversal of titanium/brass couples. In addition, SEM was used to analyse the morphology of each electrodes after coupling at different cathode/anode area ratio. In the latter case, a progressive change in electrochemical polarity during coupling with brass was also observed. The formation of an artificial oxide film made the anodized titanium acting as the cathode when coupled with brass.

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