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

Investigations of the mechanism of the protective action of strontium chromate pigment in an epoxy primer were carried out with electrochemical impedance spectroscopy (EIS), atomic absorption spectroscopy (AAS), scanning reference electrode techniques (SRET) and water uptake measurements. Epoxy primers applied to galvanized steel were studied in a corrosion environment which models the atmospheric precipitation of European countries. Corrosion and 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 polymer coating. It is suggested that the process of leaching of chromate ions from epoxy primer into the environment takes place because the decrease in pH at anodic defect sites causes the destruction of the primer film and accelerates the dissolution of the chromate pigment.