An attempt of experimental separation of the potentiodynamic anodic peaks of iron in alkaline solutions and application of the ohmic model for passive film growth

Abstract The composition of the oxide film formed on iron during potentiodynamic experiments as well as the formation mechanism are still under much discussion. In the present study an experimental separation of anodic peaks was performed from the first voltammetric scan obtained for iron in borax 0.1 mol l −1 and NaOH 0.01 mol l −1 +sodium silicate (500 ppm SiO 2 ). A charge density balance has also been performed in order to discuss mechanisms already proposed in the literature. Among several models proposed for the kinetics of passive film growth, the ohmic model is recent and was applied to the study of the second potentiodynamic anodic peak obtained for iron in borate 0.1 mol l −1 and to the third potentiodynamic anodic peak obtained for iron in NaOH 0.01 mol l −1 +sodium silicate (500 ppm SiO 2 ). The results showed that the model is suitable to explain the electrochemical behaviour of iron under these conditions.