Effect of NaCl-MgCl₂ complex on the corrosion behavior of carbon steel in wet/dry environment

The iron rust phase has been analyzed by using the in-situ XRD and the alternating current (AC) impedance methods after wet/dry corrosion test using NaCl-MgCl₂ complex which is main composition of airborne saline particles. The corrosion mass gain of the carbon steel depends on the concentration of Cl ion from environment in the test chamber, and it does not depend on the type of cations (NaCl or MgCl₂). As the concentration of Cl ion increases, the content of β-FeOOH increases in iron rust phases. The transition of β-FeOOH from the green rust I (G.R.I) was observed directly by the in-situ XRD. The amount of G.R.I depends on the concentration of Cl ion, and β-FeOOH is transformed from G.R.I automatically in drying process, where there is no dependence of type of cations on the iron rust phase whichever cation Cl bonds with. It was found by the AC impedance that the resistance of the rust (R_rust) increases with the number of cycles in the corrosion test, and that the structural factor of the rust becomes predominant in R_rust. With the increase of the amount of rust, the resistance corresponding to corrosion rate (R_t) decreases, which is related to the reduction of β-FeOOH in rust phase.