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

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 boras 0.1 mol l(-1) and NaOH 0.01 mol l(-1) + sodium silicate (500 ppm SiO2). A charge density balance has also been performed in order to discuss mechanisms already propossed in the literature. Among several models proposed for the kinetics of passive firm 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 SiO2). The results showed that the model is suitable to explain the electrochemical behaviour of iron under these conditions. (C) 2001 Elsevier Science Ltd. All rights reserved.