Influence of Anticorrosion Pigments on Protective Properties of Epoxy Coatings

We investigated the impedance characteristics of epoxy coatings which contain chromate pigment or a mixture of phosphate and calcium-containing pigments in their primer layer. The coatings were applied on low-carbon and zinc-coated steels. The studies were performed in a corrosive medium which simulated the acidic atmospheric precipitation. We found that chromate pigment provides a greater passivation effect without significant improvement of the insulating properties of the epoxy coating. The introduction of a chromate-free pigment mixture increases the barrier characteristics of the epoxy coating. As can be concluded from the impedance dependences, the combination of two chromate-free pigments can be regarded as a promising alternative to toxic chromates in epoxy protective coatings, their use being more efficient on a normal steel as compared with a zinc-coated steel.