Inhibition of corrosion by a mixture of nonchromate pigments in organic coatings on galvanized steel

We consider several possible substitutes for toxic chromate pigments. Among the most promising compositions for the corrosion inhibition of galvanized steel with a protective organic coating we should mention a mixture of phosphate- and calcium-containing pigments. As was shown earlier such a mixture possesses a high efficiency under conditions of the corrosion of zinc and galvanized steel sheet; however it is less efficient for the protection of carbon steels. This pigment mixture forms an adsorbed phosphate film on the metal and hinders the course of anodic and cathodic reactions. Zinc ions play an important role for obtaining a synergistic protective effect increasing the coherence and decreasing the porosity of the deposited film. Traditional and local electrochemical methods (EIS and SVE) were used for studying the corrosion of galvanized steel with coatings in acid rain solution. The data obtained corroborated the high anticorrosive efficiency of a pigment mixture in an organic coating on galvanized steel. In addition we established some specific features of its inhibiting action near defects in the coating. © 2004 Springer Science+Business Media, Inc.