Surface analysis of inhibitor films formed by imidazolines and amides on mild steel in an acidic environment O. Olivares-Xometl a,b , N.V. Likhanova b , M.A. Domı ´nguez-Aguilar b , J.M. Hallen a , L.S. Zamudio b , E. Arce a, * a Instituto Polite ´cnico Nacional-ESIQIE, Departamento de Ingenierı ´a Metalu ´rgica, Apdo. Postal 75-876, Me ´xico D.F. 07300, Mexico b Programa de Ingenierı ´a Molecular, Competencia de Quı ´mica Aplicada, Instituto Mexicano del Petro ´leo, Eje Central La ´zaro Ca ´rdenas No. 152, San Bartolo Atepehuacan, Me ´xico D.F. 07730, Mexico Received 13 December 2004; received in revised form 19 March 2005; accepted 26 March 2005 Available online 31 August 2005 Abstract Imidazolines and amidic precursors were synthesized with good yields through an optimized process. These compounds were evaluated as corrosion inhibitors in an aqueous solution of 1.0 M HCl by gravimetric and polarization techniques. AISI 1018 carbon steel displayed a corrosion rate dependent on the molecular structure and concentration of inhibitor in the testing environment. Adsorption of inhibitors was found to follow the Langmuir’s isotherm, this concept together with Gibbs’ free energy provided the basis to arrange corrosion inhibitors according to efficiency and stability. The surface analysis by AFM displayed that the damage on the metallic surface was considerably reduced in the presence of certain inhibitors. XPS determined the presence of a layer of inhibitor on the metal surface with protective properties. # 2005 Published by Elsevier B.V. Keywords: Carbon steel; Corrosion inhibitor (CI); Polarization scan; Acidic medium; Atomic force microscopy (AFM); X-ray photoelectron spectroscopy (XPS) 1. Introduction The petroleum industry is affected by strong economic losses derived from the serious damages caused by the metallic corrosion on piping and plant systems. Statistical data show that failures by corrosion in the oil and gas industry oscillate between 25 and 30% of the total losses [1–3]. There are many methods available to prevent the corrosion of piping and plants in aggressive environments, but one of the most economic methods is the application of corrosion inhibitors (CIs) [4–7]. A CI can be defined as ‘‘any www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 2139–2152 * Corresponding author. Tel.: +525 5729 6000x54212; fax: +525 5729 6000x55270. E-mail address: earce@imp.mx (E. Arce). 0169-4332/$ – see front matter # 2005 Published by Elsevier B.V. doi:10.1016/j.apsusc.2005.03.178