Peculiarities of corrosion inhibition by mixture of phosphate and calcium containing pigments

Abstract

Several possible alternatives to toxic chromate pigments have been considered for a variety of inhibitive applications. One of the more promising pigment combinations involves mixtures of phosphate and calcium ion-exchange pigments for inhibition of corrosion on organic coated galvanized steel. This paper presents recent work on a detailed study of the mechanisms of action of this mixture which has been established as effective in cut edge and zinc inhibition, but as less effective for inhibition of steel. The use of the blend of inhibitors is shown to result in the development of an adsorbed phosphate film on the metal which plays an important role in the development of anodic and cathodic inhibitive control. Zinc ions also appear to have an important synergistic effect on the film composition and structure increasing its coherence and decreasing its porosity. Traditional and localised electrochemical methods (EIS and SVET) were used in this study of corrosion of coated galvanized steel in artificial acid rain solution. The data confirms the anticorrosion efficiency of the pigment blend dispersed in organic coating on galvanized steel and reveals the peculiarities of their inhibiting action at coating defects.