Effect of Iron Rust on Hydrogen Uptake during Steel Corrosion under an Aqueous NaCl Droplet

The effect of iron rust on hydrogen uptake into steel during corrosion under an aqueous NaCl droplet was investigated. Pre-rusted steel was obtained by exposing a steel coupon to natural environmental conditions for 1 month at the Choshi site of the Japan Weathering Test Center. The iron rust that formed on the coupon was partly removed, and model rust/steel samples differing in the area ratios of rusted and bare steel were prepared. The hydrogen permeation current and the corrosion potential were simultaneously measured by Devanathan-Stachurski (DS) method and the Kelvin probe technique, respectively. As the applied droplet of aqueous NaCl dried, the corrosion potential shifted in the negative direction and the hydrogen permeation current slightly increased in all model samples. However, the corrosion potential and hydrogen permeation current did not differ substantially among the model samples once the rusted area of the model sample exceeded 50%. These results indicate that iron rust cause a positive shift in the corrosion potential, and hydrogen uptake was significantly suppressed due to the inhibition of the hydrogen evolution reaction. The hydrogen uptake behavior of the model sample is discussed with consideration of the cathodic reduction reaction of iron rust.