Effects of solution temperature on electronic properties of passive film formed on Fe in pH 8.5 borate buffer solution

Effects of solution temperature on the electronic properties of passive film formed on Fe in pH 8.5 borate buffer solution were investigated to clarify why the passive current density of Fe increases with solution temperature. The Mott-Schottky analysis and photocurrent measurement were employed to determine the electronic properties of the film. The Mott-Schottky analysis and photocurrent measurement revealed that as solution temperature increased, the concentration of oxygen vacancy in the passive film increased accompanying with an increase in the concentration of Fe²⁺ ion in the γ-Fe₂O₃ passive film due to a charge neutrality reaction in the film. Further, the increase in passive current density of Fe with solution temperature was found due primarily to the increase in the concentration of oxygen vacancy in the passive film, which is well explained by the point defect model (PDM).