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

The changes in immersion potential and impedance of Ti specimens mechanical ly 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 berate and car bonate solutions and in aqueous solutions in contact with a bentonite suspe nsion in the pH range from neutral to weakly alkaline. A continuous rise in the immersion potential and increase in reciprocal capacitance were observ ed in the case of polished specimens immersed at 298 KI indicating that a s urface oxide film grows during immersion. The drop in immersion potential a nd decrease in charge transfer resistance observed in the case of specimens immersed at 353 K suggested that the surface oxide film was rather unstabl e, especially in a bentonite-contact solution. AFM observation revealed the presence of pits and grooves with deposition of corrosion products around them. (C) 2000 Elsevier Science Ltd. All rights reserved.