Electrochemical characterisation of multilayer organic coatings

The protective properties of eight high performance commercial multilayer organic coatings for aeronautical use (based on polyurethane, epoxy and polyurethane-compatible epoxy resins) on anodised 2024-T3 Al alloy were evaluated in neutral aerated 3.5% NaCl aqueous solution using the electrochemical impedance spectroscopy (EIS) technique. The investigation was performed on specimens supplied and prepared from Alenia in accordance with their technical specifications. Results obtained in this paper show that all coating systems exhibit excellent protective properties even after prolonged immersion in the test solution (one year). Although the dielectric properties of all multilayer coatings are quite similar, EIS was proved to be able to discriminate among them, making possible a rank of these protective systems to prevent or to reduce corrosion. Capacitance measurements performed on the same coatings allow their behaviour to be forecasted.