Dynamic Variation in the Semiconductive Tendency of the Passive Film on Duplex Stainless Steel in Corrosion Environments

Duplex stainless steels, known for their excellent corrosion resistance, are employed in a variety of chloride solutions-acidic, neutral, and alkaline-due to a stable passive film that forms on their surfaces. This study involved polarization tests, EIS (Electrochemical Impedance Spectroscopy) measurements, Mott-Schottky plots, and XPS (X-Ray Photoelectron Spectroscopy) analyses in both static and dynamic conditions across acidic (1NaCl + 0.1N HCl, pH 1.0), neutral (1N NaCl, pH 6.7), and alkaline (1N NaCl + 0.1N NaOH, pH 13.2) chloride solutions to confirm that duplex stainless steels exhibit similar passivation behavior (0.79 μA/cm² > i_p > 0.2 μA/cm² and 590 kΩ·cm² < R_p < 651 kΩ·cm²). Regardless of the pH of the solution, p-type and n-type semiconductive properties were observed, but the balance of the semiconductive tendencies was different. Comparing passive films formed under dynamic conditions, through real-time HCl injection into a neutral chloride solution, with those formed under static conditions, revealed that both conditions yield similar structural and property characteristics in the films, as well as comparable electrochemical behaviors. These findings suggest that the passive film on the stainless steel surface adjusts to the environment and can be spontaneously repassivated in response to environmental changes.