Investigation of the inhibitive effect of ortho -substituted anilines on corrosion of iron in 1 M HCl solutions K.F. Khaled *, N. Hackerman Chemistry Department, Rice University, Houston, TX 77005, USA Received 22 November 2002; received in revised form 8 March 2003; accepted 2 May 2003 Abstract The inhibitory activity of some o -substituted anilines on iron corrosion in hydrochloric acid (HCl) was studied in relation to inhibitor concentration using potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements. O -substituted anilines were found to act as mixed type inhibitors. The results showed that o -substituted anilines suppressed both cathodic and anodic processes of iron corrosion in 1 M HCl by its adsorption on the iron surface according to Langmuir adsorption isotherm. Potentiodynamic and EIS measurements reveal that these compounds inhibit the iron corrosion in 1 M HCl and that the efficiency increases with increasing of the inhibitor concentration. Data obtained from EIS are analyzed to model the corrosion inhibition process through equivalent circuit. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Iron; Polarization; EIS; Acid inhibition 1. Introduction The study of corrosion of iron is a matter of tremendous theoretical and practical concern as such has received a considerable amount of interest [1]. Hydrochloric acid (HCl) solutions are widely used for pickling, cleaning, descaling, etc. of iron. Corrosion inhibitors are needed to reduce the corrosion rates of metallic materials in this acid media. Most acid corro- sion inhibitors are nitrogen-, sulfur- or oxygen-contain- ing compounds [2]. In research on organic corrosion inhibitors, attention is paid to the relationship of inhibitor structure to its inhibition efficiency [3,4], to its adsorption and to the mechanism of adsorption. It has been observed that the adsorption depends mainly on certain physicochemical properties of the inhibitor molecule such as functional groups, steric factors, aromaticity, electron density at the donor atoms and p orbital character of donating electrons [5  /7], and also on the electronic structure of the molecules [8,9]. In continuation of the work on acid corrosion inhibitors [10  /12], 2-chloroaniline, 2-fluoroaniline, 2- aminophenetole, 2-ethylaniline, o -aminoanisole and o - toluidine were investigated by potentiodynamic and electrochemical impedance spectroscopy (EIS) measure- ments. An equivalent circuit to the system has been suggested. 2. Experimental details Fig. 1 shows chemical structure of the studied compounds. All of these compounds obtained from (Aldrich chemical co.). Corrosion tests have been carried out on electrodes cut from iron (Puratronic 99.9999%) from Johnson Mattey Ltd. Iron rods were mounted in Teflon (surface area 0.28 cm 2 ). The surface preparation of the specimens was carried out using emery papers, grit 2, 000 and 0000, rinsed with redis- tilled water, degreased with acetone and dried at room temperature before use. HCl solutions were prepared from concentrated acid and redistilled water. All experi- ments were conducted in aerated solutions at 25 8C. The solutions were prepared by mixing HCl (Fisher Scien- tific) with the inhibitor (Aldrich chemical co.), which * Corresponding author. Tel.:  /1-713-348-3276; fax:  /1-713-348- 5155. E-mail address: khaledf@rice.edu (K.F. Khaled). Electrochimica Acta 48 (2003) 2715  /2723 www.elsevier.com/locate/electacta 0013-4686/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0013-4686(03)00318-9