Effects of pH and Chloride Ion on the Corrosion Behavior of TiCode-12

Effects of pH and chloride ion on the corrosion behavior of TiCode-12 in deaerated 0.5M Na2SO4 supporting electrolyte have been studied by potentiodynamic anodic polarization and galvanostatic anodic oxidation techniques. In all tested chloride ion-free solutions, corrosion potential of the alloy specimens lay in the passive region of the polarization curve except in pH 0.37 solution where it was in the active region. Only in the latter solution was observed so-called active nose in the polarization curve. The potential of the Ticode-12 specimen increased linearly with time in the most part of the galvanostatic anodic oxidation curve, which was deviated from the linearity at the reversible oxygen evolution potential. The slope of the linear portion in the potential-time curve increased with increase in pH and applied current density. These behaviors in acidic solutions were explained in terms of the defect structure and non-stoichiometric nature of titanium oxides passive film formed on the alloy specimen. In pH 1.33, chloride ion-containing solutions, potentiodynamic anodic polarization measurements indicated that a critical chloride ion concentration exists below which the polarized currents at each potentials increase with its increment but beyond which the currents decrease on the contrary. In the potential decay curves examined after the galvanostatic anodic oxidation experiments in chloride ion-containing solutions, two potential arrests were observed, which indicates the passive film formed during anodic oxidation may be comprised of two stratifications: an oxide layer and a chloride layer. Auger electron spectroscopy was used to detect the existence of chloride layer in the passive film, but the expected chlorine peak appeared ambiguously