EIS evaluation on the degradation behavior of rust-preventive oil coating exposure to NaCl electrolyte

The traditional evaluation on anti-corrosion performance of a rust-preventive oil is often time-consuming and of high cost. In this investigation, electrochemical impedance spectroscopy (EIS) has been employed to understand the degradation behavior of rust-preventive oil in contact with NaCl electrolyte, with a focus on analyzing the electrochemical responses that correspond to a different frequency range in the obtained EIS spectra. The results indicate that the obtained EIS spectra can be generally divided into four frequency ranges. The high-frequency range is influenced by the continuous seepage of NaCl electrolyte, and the sub-high frequency range can reflect the presence of reversed micelle formed by corrosion inhibitor molecules and water molecules. Besides, the mid-frequency range is associated with the adsorption process of corrosion inhibitor molecules at the oil-film/metal interface, and the low-frequency range is associated with the diffusion process of dissolved ferrous ions. An extended immersion will result in a continuous seepage of electrolyte into rust-preventive oil coating and degrade the adsorption of corrosion inhibitor molecules, leading to a poor corrosion protection performance of the oil coating. Therefore, it is believed that the proposed design can provide a method in evaluating the degradation behavior and corrosion protection performance of rust-preventive oil to underlying steel substrate by EIS measurement under a lower amplitude.