Abstract:

Electrochemical methods including polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were used to characterize and investigate the electrochemical behavior of rusted carbon steel immersed in seawater. Results indicate that the inner rust layer that forms on the surface of the carbon steel after long-term immersion greatly affects the electrode process. Polarization resistance (Rp), determined by LPR and EIS, increases during the initial immersion period. After long-term immersion, it decreases. Rp initially increases and then decreases gradually with immersion time. The electrochemical characteristics of the rusted carbon steel were studied by removing the outer and inner rust layers. The materials were analyzed by Fourier transform infrared (FTIR) spectroscopy and their cross-sectional morphologies were obtained to determine the cause. The results show that the β-FeOOH, which exists in the inner rust layer, has high electrochemical activity. Its content increases with the growth of the inner rust layer. In the electrochemical tests, even a small amount of polarization allows β-FeOOH to participate in the cathodic reduction reaction. Besides the anodic dissolution of iron and the cathodic reduction of oxygen, rust reduction is also possible. For this reason, the cathodic reaction rate is promoted and Rp decreases.

Key words: Electrochemical behavior, Rust layer, Polarization resistance, Cathodic reduction, Fourier transforminfrared spectroscopy