Corrosion inhibition of aluminum by coatings formulated with Al-Zn-vanadate hydrotalcite

The hydrotalcite structure is an ionic lamellar solid with positively charged layers incorporating two kinds of metallic cations and hydrated gallery anions. The ability of these compounds to retain aggressive ions and simultaneously release a corrosion inhibitor is the main reason for the development of hydrotalcite compounds to replace hexavalent chromium compounds (chromates) as inhibitive pigments. In this study, alkyd coatings formulated with Al-Zn-vanadate hydrotalcite, at different pigment concentrations were applied on aluminum specimens. The painted panels were subjected to different accelerated tests (condensing humidity, salt spray and Kesternich) and atmospheric exposure in atmospheres of different aggressiveness. Corrosion performance was evaluated by electrochemical impedance spectroscopy (EIS). A traditional zinc chromate pigment was also tested for comparative purposes. The obtained results confirm that hydrotalcite compounds achieve corrosion inhibition of the underlying aluminum substrate. It has been shown that an increase of anticorrosive pigment content (for a constant pigment volume concentration) does not always improve the primer behavior, but a larger amount of vanadates released from Al-Zn-vanadate hydrotalcite particles does improve anticorrosive behavior. (C) 2010 Elsevier B.V. All rights reserved.