Specific Features of the Anticorrosive Action of a Mixture of Nontoxic Pigments in an Epoxy Coating on Steel

We investigate capacitance-resistance characteristics of epoxy coatings on low-carbon steel that contain a strontium crown or a mixture of phosphate and calcium-containing pigments in a primer. Tests were carried out in a medium simulating acid atmospheric precipitation. The protective action of chromate-free pigments hinders the diffusion of an acid medium into a polymeric coating and improves its insulating properties. The swelling of free films and the capacitance of coatings with chromate-free pigments are lower than those of epoxy and epoxychromate coatings. We establish the existence of an incubation period in the protective action of pigmented coatings. In both pigmented coatings, an increase in both the active resistance and frequency dependence is observed. The results of impedance tests show that the anticorrosive efficiency of epoxy coatings with a mixture of nontoxic pigments is on a par with the anticorrosive efficiency of epoxychromate coatings.