Corrosion inhibition study of pure Al and some of its alloys in 1.0 M HCl solution by impedance technique Sayed S. Abd El Rehim * , Hamdi H. Hassan, Mohammed A. Amin Department of Chemistry, Faculty of Science, Ain Shams University, Abbassia, Cairo, Egypt Received 7 September 2001; accepted 29 May 2003 Abstract This paper describes the use of the potentiodynamic polarization and electrochemical im- pedance spectroscopy technique (EIS) in order to study the corrosion inhibition process of pure Al, (Al + 6%Cu) and (Al + 6%Si) alloys in 1.0 M HCl solution at the open circuit po- tential (OCP) in the temperature range 10–60 °C. Dodecyl phenol ethoxidate as a non-ionic surfactant (NS) inhibitor has been examined. The Nyquist diagrams consisted of a capacitive semicircle at high frequencies followed by a well defined inductive loop at low frequency values. The impedance measurements were interpreted according to a suitable equivalent circuit. The results obtained showed that the addition of the surfactant inhibits the hydro- chloric acid corrosion of the three Al samples. The inhibition occurs through adsorption of the surfactant on the metal surface without modifying the mechanism of corrosion process. Po- tentiodynamic polarization measurements showed that the surfactant acts predominately as anodic inhibitor. The inhibition efficiency increases with an increase in the surfactant con- centration, but decreases with an increase in temperature. Maximum inhibition is observed around its critical micelle concentration (CMC). The inhibition efficiency for the three Al samples decreases in the order: (Al + 6%Si) > (Al + 6%Cu) > Al. Kinetic-model and Frumkin adsorption isotherm fit well the experimental data. Thermodynamic functions for both dis- solution and adsorption processes were determined. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Corrosion; Inhibition; Protection efficiency; Pure Al; (Al + 6%Cu) alloy; (Al + 6%Si) alloy; Anionic surfactant; EIS * Corresponding author. Fax: +20-283-1836. 0010-938X/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0010-938X(03)00133-1 www.elsevier.com/locate/corsci Corrosion Science 46 (2004) 5–25