Effect of the experimental setup in the behaviour of sol-gel coatings

Electrochemical behaviour of the sol-gel-coated AA2024-T3 samples was evaluated using electrochemical impedance spectroscopy (EIS) in a three-electrode arrangement cell using Na2SO4 0.1 M solution as electrolyte. The effect of the reference electrode leakage was examined using as reference a low-leakage Ag/AgCl electrode and a platinum wire. The results show that very low-chloride, concentrations in solution are able to induce heavy dissolution of intermetallic precipitates. That corrosion process masks information on the barrier properties of sol-get coatings otherwise available through EIS measurements. Thus, the use chloride containing reference electrodes shall be avoided in studies on sol-gel-coated aluminium alloys in mild media. (C) 2008 Elsevier B.V. All rights reserved.