Narrow Results

In this paper, for Q235 carbon steels in NaNO₂ solutions with different concentrations of NO${}_2^{-}$, a passive film composed of mainly Fe₂O₃ was formed on the Q235 surface, and the effects of NO${}_2^{-}$ concentrations on the properties of passive film were studied by electrochemical methods and microstructural analyses. The applications of electrochemical impedance spectroscopy (EIS), Mott–Schottky (MS) plot, scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) were carried out to characterize the resistance, defect, morphology and composition of passive film, respectively. The passive film resistance and defect, respectively, increased and decreased with the increase of NO${}_2^{-}$ concentration until the NO${}_2^{-}$ concentration was up to 0.01M, which was the critical NO${}_2^{-}$ concentration of stable passivation for the Q235 surface. The relation between the electrochemical behavior and the passive film was also discussed in detail.