Dynamic analysis of chloride-induced passive film breakdown mechanisms in carbon steel within simulated concrete pore solution

The erosion of chloride ions is a significant factor that causes the fracture of the passive film of steel bars in reinforced concrete. To investigate the time-dependent growth and fracture mechanism of the passive film on steel bars under the influence of chloride ions, open circuit potential method and Mott-Schottky measurements were employed to analyze its evolving electronic characteristics. Additionally, X-ray Photoelectron Spectroscopy(XPS) analysis was employed to characterize the progressive changes in physical and chemical properties of the passive film at the microscopic level. Then, a temporal growth and fracture model for the passive film under the influence of chloride ions erosion was developed. The research indicates that the growth and fracture process of passive films follows a distinct temporal sequence, specifically divided into formation, stabilization, binding, and fracture stages. The progression of structural variation in the passive film is determined by the concentration of chloride ions in the solution. When the concentration of chloride ions is less than the threshold value, the passive film undergoes limited bonding with chloride atoms. However, once the concentration surpasses the threshold, chloride ions progressively react with the outer layer of the passive film, initiating a dissolution and fracture process. This work provides new insights into the temporal evolution of chloride-induced depassivation of steel bars and establishes a time-based framework for understanding the breakdown mechanism.