Synergistic Inhibition of MoO42- and NO2- on Pitting Corrosion of Mild Steel postprint

Abstract: The synergistic inhibition effect of MoO42- and NO2- on pitting corrosion of mild steel was studied by polarization curve, electrochemical impedance spectroscopy (EIS), Mott-Schottky plot, and X-ray photoelectron spectroscopy (XPS). The results showed that the metastable pitting potential (Em) and the pitting breakdown potential (Eb) of the mild steel shift significantly to much positive and the value of (Eb-Em) increased markedly when MoO42- and NO2- were applied at the same time, indicating that the combined application of MoO42- and NO2- not only restrained the initiation of metastable pits but also prevented the transition from metastable pits to stable pits, correspondingly where a composite passive film Fe2O3+Fe2(MoO4)3 could form on the mild steel surface. The impedance of the composite passive film Fe2O3+Fe2(MoO4)3 formed in the solution containing MoO42- and NO2- was larger than that of the single passive films formed in the solutions with individual MoO42- or NO2-, while the defects of the former was less than that of the later one, therefore, the composite passive film could provide better protectiveness for the mild steel.