Corrosion Behavior of Sn-Bearing Steel under Wet/Dry Cyclic Environments Containing Cl⁻

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The corrosion potential and corrosion rate of steel under wet/dry transitions were investigated using the Kelvin probe/pressure difference measurement system in order to elucidate the effect of Sn on the corrosion of steel covered by a thin electrolyte film in wet/dry environments containing chloride ions (Cl⁻). The corrosion rate in the case of an electrolyte containing Cl⁻ during the drying stage was higher than that in the case of an electrolyte containing sulfate ions (SO₄²⁻). Cl⁻ accelerate the hydrolysis of Fe³⁺ and lead to the acidification of the anode site in the thin electrolyte film, while also contributing to corrosion during the drying stage. The Sn-bearing steel showed a lower corrosion rate during the drying stage than that of the mild steel. This was because the Sn ions from the steel can exist stably in the acidic thin electrolyte film and inhibit the anodic reaction during the drying stage. Thus, the superior corrosion resistance of the Sn-bearing steel under atmospheric conditions is attributable to the retardation of the anodic reaction during drying by Sn ions.