EFFECTS OF NITRITE ANIONS ON SURFACE PASSIVE FILM PROPERTIES FOR Q235 CARBON STEELS

Abstract

In this paper, for Q235 carbon steels in NaNO 2 solutions with different concentrations of NO[Formula: see text], a passive film composed of mainly Fe 2 O 3 was formed on the Q235 surface, and the effects of NO[Formula: see text] 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[Formula: see text] concentration until the NO[Formula: see text] concentration was up to 0.01[Formula: see text]M, which was the critical NO[Formula: see text] concentration of stable passivation for the Q235 surface. The relation between the electrochemical behavior and the passive film was also discussed in detail.