Electrochemical Behavior of Rust Formed on Carbon Steel in a Wet/Dry Environment Containing Chloride Ions

The iron rust phase was analyzed by using the in-situ x-ray diffraction (XRD) and alternating current (AC) impedance methods after a wet/dry corrosion test using sodium chloride (NaCl) solution, which is the main composition of airborne saline particles. The corrosion content of the carbon steel depended on the concentration of Cl ions in the environment of the test chamber. As the concentration of Cl ions increased, the content of β-FeOOH increased in iron rust phases. The transition of β-FeOOH from the green rust I (GRI) was observed directly by in-situ XRD. The amount of GRI depended on the concentration of Cl ions, and β-FeOOH was transformed from GRI automatically in the dry process of the test. AC impedance showed that the resistance of the rust (R_rust) increased with the number of cycles in the corrosion test, and that the structural factor of the rust became predominant in R_rust. With the increase of the amount of rust, the resistance corresponding to the corrosion rate (R_t decreased, which was related to the reduction of β-FeOOH in the rust phase.