Activation energies for the oxidation of iron by oxygen gas and water vapour

The low temperature (<150 °C) activation energy (E) for the reaction of iron (Fe) with oxygen gas (O2) and water vapour (H2O vapour) was calculated using the Eley-Wilkinson kinetic model for metal oxidation. From these calculations, previous statements indicating that the rate-determining step during the oxidation of Fe in both environments was place exchange were confirmed. The increase in activation free energy with increasing thickness of the oxide film (γ) was also calculated and used to discuss the difficulty in forming thick oxide films.