STABILITY AND OPEN CIRCUIT BREAKDOWN OF THE PASSIVE OXIDE FILM ON TITANIUM

Titanium electrodes that have been passivated by forming an anodic oxide film in acid solution are known to undergo a spontaneous passive - active transition at open circuit after a delay period that depends on the experimental conditions. In this work, the reactivation of the electrode has been investigated, and it has been shown that it arises as the result of uniform chemical dissolution of the oxide film. The rate of dissolution, and hence the stability of the oxide, was found to depend on the rate at which the oxide film had been formed as well as on solution composition and temperature. The rate of film dissolution in sulphuric acid showed a first order dependence on proton concentration, but high dissolution rates were also measured in alkaline solution (pH 14).