Physicochemical performance of FeCO3 films influenced by anions

Abstract

The corrosion film plays an important role in the further electrochemical processes of steel in CO₂ corrosion. Thus, the physicochemical performance of an FeCO₃ film was investigated using the Mott–Schottky electrochemical technique, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The performance of the FeCO₃ film was dependent on the aqueous solution. In 0.5 mol L⁻¹ NaHCO₃ solution, an n-type semiconducting behavior was found for the FeCO₃ film. The dense microstructure and lower interstitial cation or anion vacancy doping was in favor of strong corrosion resistance of the film. On the contrary, a p-type semiconducting behavior of the FeCO₃ film was exhibited in both 0.5 mol L⁻¹ NaCl solution and 0.5 mol L⁻¹ Na₂SO₄ solution. Higher cation vacancy doping was found, and the integrity of the microstructure was damaged, which decreased the transfer resistance of electron and mass. As a result, the protective ability of the FeCO₃ film was decreased. The physicochemical mechanism for the semiconducting properties of the FeCO₃ film was explained using the Point Defect Model (PDM).