Changes in the properties of anodic oxide films formed on titanium during long-term immersion in deaerated neutral solutions

Abstract The changes in immersion potential and impedance of Ti specimens mechanically polished and with or without a pre-formed anodic oxide film were traced during immersion up to 20 weeks at 298 or 353 K in deaerated borate and carbonate solutions and in aqueous solutions in contact with a bentonite suspension in the pH range from neutral to weakly alkaline. A continuous rise in the immersion potential and increase in reciprocal capacitance were observed in the case of polished specimens immersed at 298 K, indicating that a surface oxide film grows during immersion. The drop in immersion potential and decrease in charge transfer resistance observed in the case of specimens immersed at 353 K suggested that the surface oxide film was rather unstable, especially in a bentonite-contact solution. AFM observation revealed the presence of pits and grooves with deposition of corrosion products around them.