Study on passivation and erosion-enhanced corrosion resistance by Mott-Schottky analysis

The erosion-enhanced corrosion of carbon steel A1045 was investigated by electrochemical methods in three borate buffer solutions with different concentrations, and the resistance of material to erosion-enhanced corrosion was discussed from the passive film growth kinetics. In polarization tests, the carbon steel exhibited comparable passive behavior in the three solutions. However, the dependence of passive current density on sand concentration became more significant with a decrease in borate concentration. The scratching simulation tests showed that after the passive film was damaged the peak current and decay constant were higher in the dilute solution, indicating a slower film growth rate. Based on point defect model (PDM), the key parameters for passive film growth are the diffusivity and density of the defects within the film. Mott-Schottky analysis in conjunction with PDM was performed and the results indicated that the diffusivities of defects were comparable in the films while the donor density increased with solution concentration. The higher donor density could result in higher diffusion flux and thus higher film growth rate, which could explain the better erosion-enhanced corrosion resistance in the concentrated solution.