The mode of action of chromate inhibitor in epoxy primer on galvanized steel

Investigations of the mechanism of the protective action of strontium chrom ate pigment in an epoxy primer were carried out with electrochemical impeda nce spectroscopy (EIS), atomic absorption spectroscopy (AAS), scanning refe rence electrode techniques (SRET) and water uptake measurements. Epoxy prim ers applied to galvanized steel were studied in a corrosion environment whi ch models the atmospheric precipitation of European countries. Corrosion an d electrochemical properties of samples of bare galvanized steel and coated galvanized steel were investigated It was established that the protective function of the chromate in the primer is primarily due to a cathodic/mixed inhibition of the surface of galvanized steel in defect areas of the polym er coating. It is suggested that the process of leaching of chromate ions f rom epoxy primer into the environment takes place because the decrease in p H at anodic defect sites causes the destruction of the primer film and acce lerates the dissolution of the chromate pigment. (C) 1998 Elsevier Science S.A. All rights reserved.