Effects of Calcium Modification on the Electrochemical and Corrosion Properties of Weathering Steel

The effect of Ca modification on the corrosion properties of weathering steel was investigated by pH measurement, electrochemical impedance spectroscopy (EIS), and cyclic corrosion testing. The pH measurement and EIS were performed with a thin water film covering the steel. Test results showed that the addition of Ca to the steel (in a range from 50 ppm to 70 ppm) increased the pH value of the thin distilled water film covering on the steel. From the pH measurement and EIS test results, the Ca-modified steel showed good corrosion resistance in distilled water or a mild solution containing ≤0.01 M sodium chloride (NaCl), but it was not very effective in the solution containing 0.1 M NaCl. During cyclic corrosion testing in a chamber simulating a marine environment, formation of α-FeOOH on the Ca-modified weathering steel was promoted as the corrosion cycles were increased. In the rust layer that formed on the Ca-modified weathering steel, α-FeOOH and γ-FeOOH were located mainly in the inner rust layer having a dense and compact structure, whereas γ-FeOOH and β-FeOOH were located in the outer rust layer having porous structures.