EIS Studies of Anionic Surfactants Inhibiting Effect of Al-2017 Corrosion in HCl Aqueous Solutions

This paper describes the use of the EIS (electrochemical impedance spectroscopy) technique and potentiodynamic polarization in order to study the corrosion inhibition process of aluminium in hydrochloric acid solution. Three anionic surfactants: GOS (gasoil sulfonate), KES (kerosene sulfonate) and HSS (heavy solvent sulfonate) have been synthesized from petroleum fractions and tested during corrosion of aluminium in 1 M HCl solution at 25 °C. 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 surfactants inhibits the hydrochloric acid corrosion of aluminium. The inhibition occurs through adsorption of the surfactant on the metal surface without modifying the mechanism of corrosion process. Potentiodynamic polarization measurements showed that the surfactant acts predominately as cathodic inhibitor. The inhibition efficiency increases with rising of the inhibitor concentration and decreases in the order: GOS > KES > HSS. The corrosion inhibiting mechanism is thought to proceed via an adsorption of the surfactant molecules on the aluminium surface, generating a film and hindering the active sites. Our experimental adsorption data were found to obey the Langmuir adsorption isotherm. Optical images of the treated specimens, revealing the likely formation of a protective film, demonstrated the inhibiting capacity of the petroleum surfactants.