EIS study of the corrosion behaviour of zinc-based coatings on steel in quiescent 3% NaCl solution. Part 1: directly exposed coatings V. Barranco, S. Feliu Jr. * , S. Feliu Centro Nacional de Investigaciones Metal urgicas, Avda. Gregorio del Amo, 8, 28040 Madrid, Spain Received 11 March 2003; accepted 26 September 2003 Available online 21 January 2004 Abstract The possibilities offered by the EIS technique for studying the progress of corrosion in several types of galvanised coatings were investigated. Corrosion tests were performed in a 3 wt.% NaCl aqueous solution, at approximately neutral pH, without stirring and in contact with the air. A tendency was seen towards an electrochemical overestimation of the corrosion values of essentially pure zinc and Zn–5%Al (Galfan) coatings compared with the gravimetric reference values. In contrast, the opposite tendence was revealed with the Zn–10%Fe (Galv- anneal) coating. These deviations have made it necessary to use empirical values of the con- stant B of the Stern–Geary equation. The approximately linear progress of the attack with immersion time suggests a slight barrier effect of the corrosion products layer. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: A. Metal coatings; A. Zinc; B. EIS; B. Electrochemical correlation 1. Introduction Electrochemical methods, and in particular the electrochemical impedance spec- troscopy (EIS) technique, have been shown in numerous studies to be an efficient and convincing tool for analysing the corrosion behaviour of metals. Their most out- standing and well known advantages are that they allow continuous monitoring of the progress of corrosion, with instantaneous corrosion rate measurements, and that * Corresponding author. Fax: +34-91-534-7425. E-mail address: sfeliu@cenim.csic.es (S. Feliu Jr.). 0010-938X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2003.09.032 www.elsevier.com/locate/corsci Corrosion Science 46 (2004) 2203–2220