Effect of Concentrations of Fe 2+ and Fe 3+ on the Corrosion Behavior of Carbon Steel in Cl − and SO 4 2− Aqueous Environments

The concentration of metal ions in aqueous environments significantly affects the formation of corrosion products and further metal corrosion. In this paper, the electrochemical behavior of carbon steel in the presence of Fe 2+ or Fe 3+ concentration in Cl − and SO 4 2− aqueous environments have been investigated using conventional electrochemical methods such as linear polarization and alternating current impedance spectroscopy. The morphology and composition of carbon steel corrosion products were studied using scanning electron microscopy and laser Raman spectroscopy. The effects of corrosion products and iron ions concentration on the corrosion of carbon steel were discussed. Corrosion products of carbon steel in aqueous environments were γ-FeOOH, γ-Fe 2 O 3 and a small amount of α-Fe 2 O 3 . The addition of Fe 2+ affected the cathode reaction of the electrode reaction, and promotes the formation of γ-FeOOH and Fe 3 O 4 . And with the increase of Fe 2+ concentration in the solution, the anode process of electrode reaction was suppressed. The addition of Fe 3+ promoted the formation of γ-Fe 2 O 3 and Fe 3 O 4 . Fe 3+ affected the ionization of water, causing the pH of the solution to drop. Fe 3+ undergoes a redox reaction with the matrix. Addition of Fe 3+ ions promoted the formation of FeOOH, an intermediate product, which reacts with the anode product Fe 2+ . These factors all accelerated the corrosion process. Graphic Abstract