Electrochemical coating of zinc carboxylate: A new protection for zinc in atmospheric conditions

Abstract

To prevent the premature tarnishing of zinc-coated products in moist atmosphere or during wet-dry climatic cycles, new surface treatments of zinc are developed in this study. For that, electrochemical behaviour of pure zinc in this media was studied versus pH and potential by using electrochemical impedance spectroscopy and potentiodynamic techniques. Then, different coatings constituted by zinc heptanoate or zinc hydroxyheptanoate were synthesized by electrochemical oxidation on zinc-coated steel and tested in climatic chamber. The coatings mainly constituted by zinc heptanoate trap the OH − anions and delay the alkalinisation of the zinc surface during the wet-dry cycle. This coating constitutes an environmentally friendly alternative to the usual conversion treatments, to inhibit the formation of hydrozincite (white rust) in atmospheric corrosion. • Zinc soap layer can be formed by electrochemical oxidation of zinc in aqueous medium. • The electrochemical conversion of zinc is more efficient in slightly acid medium. • Crystalline zinc heptanoate constitutes a temporary protection against zinc tarnishing. • Zinc soaps inhibit the formation of powdery white rust on zinc