Corrosion of iron under alternating wet and dry conditions

In-situ alternating current (AC) and direct current (DC) electrochemical techniques were used to determine the corrosion rate and corrosion potential of high-purity iron under alternate wet and dry conditions. Comparisons between DC electrochemical measurements and weight loss were conducted to verify the validity of the corrosion rate measurements. Identification of the corrosion products was performed using Raman spectroscopy. Corrosion products contained layers of iron oxides and oxyhydroxides. At Low Cl- concentrations, corrosion products consisted of lepidocrocite (gamma-FeOOH) and magnetite (Fe3O4). At higher Cl- concentrations, the formation of akaganeite (beta-FeOOH) was observed. Corrosion rates and corrosion potentials fluctuated throughout the wet cycles depending on electrolyte layer thickness, ionic strength, and wetting cycle. Accelerated corrosion rates of high-purity iron, up to three times those observed under continuously immersed conditions, were the result of Fe(III) reduction in the corrosion product layer, increased Cl- concentration during evaporation, and accelerated oxygen transport across the thin electrolyte layer.