Synergistic Effect of Phosphate and Calcium-Containing Pigments on the Corrosion Resistance of Galvanized Steel

We studied the corrosion inhibition of galvanized steel in artificial acid rain solution by chromate-free pigments containing phosphate and calcium ions. We used the methods of electrochemical impedance spectroscopy, potentiodynamic polarization, electron microscopy, and X-ray microspectrum analysis. It was established that the combination of modified zinc phosphate and ion-exchange-type calcium-containing pigment provides a significant synergistic anticorrosion effect on galvanized steel as compared with the same inhibiting pigments used separately. The charge-transfer resistance of the metal in acid rain solution saturated with this pigment composition approaches that in the same solution with a chromate inhibitor and is significantly higher as compared with the solutions of separate pigments. Owing to the combination of nonchromate pigments, a protective film is formed on galvanized steel, which represents a complex mixture of calcium and zinc phosphates and guarantees the corrosion inhibition of galvanized steel under mixed cathodic-anodic control.