SURFACE PASSIVE FILM CHARACTERISTIC OF Q235 CARBON STEEL IN PURE MOLYBDATE SOLUTION

In pure Na2MoO4 solutions with different concentrations of MoO[Formula: see text] (0.01, 0.04, 0.06, 0.08 and 0.10 mmol/L), a passive film was formed on the surface of Q235 carbon steel spontaneously, and the influences of MoO[Formula: see text] concentrations on the passive film characteristics were investigated. The electrochemical and microstructural techniques of electrochemical impedance spectroscopy (EIS), Mott–Schottky plot (MSP), scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) were applied to characterize the passive film characteristics, including resistance, defect, microstructure and composition. The resistance and defect of passive film respectively increased and decreased with increased MoO[Formula: see text] concentration up to 0.08[Formula: see text]mmol/L, which was the critical MoO[Formula: see text] concentration of complete passivation for the Q235 surface. The passive film formed in the 0.08[Formula: see text]mmol/L Na2MoO4 solution showed a dense microstructure and was composed of Fe2(MoO[Formula: see text] mainly. Further, in this work, the relation between characteristic and anti-corrosion of passive film was also discussed.