Study of mild steel corrosion in H2SO4: effect of sulfate ion addition

The corrosion behavior and mechanism of mild steel/H2SO4 systems were examined using hydrogen gas evolution, HE, and weight loss, WL, as chemical measurements and electrochemical impedance spectroscopy, EIS, and potentiodynamic polarization, PDP, as electrochemical measurements at 30oC. From the chemical results, the corrosion rate of mild steel increased as well as increasing acid concentration, with a reaction constant of 0.70 and 0.60 for HE and WL, respectively. Different features including general and pitting corrosion can be shown on the mild steel surface after dipping in different concentrations of H2SO4, and the latter became more distinct at higher acid concentrations. EIS results showed that the Rp value decreases while the Cdl value increases along with increasing acid concentration. PDP results clearly revealed that the dissolution of mild steel undergoes anodic control. The chemical and electrochemical method suggested that the dissolution mechanism of mild steel is the same at different H2SO4 concentrations. Based on the results and observations, the mechanism of mild steel corrosion in H2SO4 can be explained based on the role of anions, the main corrosive agent in aqueous H2SO4 solutions, which partake directly in anodic dissolution and cathodic reaction during corrosion.