Influence of HSO₃^- on passive film composition and corrosion resistance of 2205 duplex stainless steel in simulated seawater

Corrosion behavior of 2205 duplex stainless steel in simulated seawater containing different concentration of NaHSO₃ has been systemically investigated by means of potentiodynamic polarization and electrochemical impedance spectrum (EIS) measurements. While the defects and the compositions of the formed passive films on the steel were characterized by Mott-Schottky and XPS respectively. The results demonstrate that the existence of HSO₃^- in the simulated seawater contributes to the increase of metal oxide content in the passive film formed on 2205 stainless steel. In the simulated seawater containing 0.01 mol/L HSO₃^-, 2205 duplex stainless steel presents the worst corrosion resistant performance, correspondingly the calculated defect concentration for the formed passive film is consistent to the electrochemical test results. The oxidation of HSO₃^- induces the formation of HSO₄^- in aqueous solution, which will give rise to the releasing of hydrogen ions, leading to the increase of acidity of the solution and thus induces the damage of the passive film on 2205 stainless steel. However, when the concentration of HSO₃^- in simulated seawater is less than 0.01 mol/L, the corrosion resistance of the steel will rise again. This is because the competitive adsorption between HSO₃^- and Cl^- on the 2205 stainless steel surface can inhibit the adsorption of Cl^-, which then results in the decline of the pitting corrosion probability.