Physicochemical performance of FeCO3 films influenced by anions

摘要

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).