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. Me 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-modifted steel showed good corrosion resistance In distilled water or a mild solution containing less than or equal to0.01 M sodium chloride (NaCl), but it was not very effective in the solution containing 0.1 Al NaCl. During cyclic corrosion testing in a chamber simulating a marine environment, formation of alpha-FeOOH on the Ca-modifted weathering steel was promoted as the corrosion cycles were increased. In the rust layer that formed on the Ca-modifted weathering steel, alpha-FeOOH and FeOOH were located mainly in the inner rust layer having a dense and compact structure, whereas gamma-FeOOH and beta-FeOOH were located in the outer rust layer having porous structures.