Some amino acids as corrosion inhibitors for copper in nitric acid solution K. Barouni a , L. Bazzi a , R. Salghi b , M. Mihit a , B. Hammouti c, ⁎, A. Albourine a , S. El Issami a a L. M. E., Faculté des Sciences, BP 8106, 80 000 Agadir, Morocco b L.I.P.E.E, ENSA, BP 1136, 80 000 Agadir, Morocco c L.C.A.E, Faculté des Sciences, BP717, 60 000 Oujda, Morocco article info abstract Article history: Received 6 November 2007 Accepted 19 February 2008 Available online 2 March 2008 The inhibition effect of five amino acids (AA) on the corrosion of copper in molar nitric solution was studied by using weight loss and electrochemical polarization measurements. Valine (Val) and Glycine (Gly) accelerate the corrosion process; but Arginine (Arg), Lysine (Lys) and Cysteine (Cys) inhibit the corrosion phenomenon. Cysteine is the best inhibitor. Its efficiency increases with the concentration to attain 61% at 10 - 3 M. Correlation between the quantum chemical calculations and inhibition efficiency was discussed using semi- empirical methods (AM1 and MNDO). © 2008 Elsevier B.V. All rights reserved. Keywords: Corrosion Inhibition Copper Amino acids 1. Introduction Copper is a very widely used material for its excellent electrical and thermal conductivities in many industrial applications; its corrosion resistance becomes less while the aggressive solution concentration increases [1–3]. The use of chemical inhibitors is the most practical method for the protection against corrosion in acidic solutions [4–7]. Several works have been performed on the use of organic compounds as inhibitors for the corrosion of metals in aggressive acidic media. Many studies have examined the behaviour of copper and copper alloys in various corrosive environments [8–12]. Thus, we have already studied the inhibitive effect of triazolic compounds for copper corro- sion in 0.5 M HCl [8]. The results revealed that 3-amino-1,2,4-triazole (ATA) and 3,5-amino-1,2,4-triazole (DTA) effectively reduce the corro- sion rate of copper. This implies that corrosion inhibition is due to the presence of amino groups in the molecular structure. In the same medium, Gasparac et al. [9,10] have been examined the effect of addition of imidzole and its derivative on the corrosion of copper. Kertit et al. [11] have studied the effect of some tetrazolic compounds on the corrosion of 70Cu30Zn in 0.1 M H 2 SO 4 and reported that PMT has a much significant effect. However, the use of these compounds was limited by their degree of toxicity. Amino acids were reported as good toxic corrosion inhibitors for many metals in various aggressive media [13–17]. The choice of an inhibitor is generally based not only on the electron cloud of the heteroatom (S, N, Se, O, P). On the other hand, the consideration is rarely made on the toxicity degree of the tested compounds. In this focus, we mentioned that some studies are report- ed on non-toxic products as amino acids, amino-ester and peptides compounds [18–23]. In this study, we tested the amino acids (AA) compounds such as Arginine (Arg), Cysteine (Cys), Glycine (Gly), Lysine (Lys) and Valine (Val) on the corrosion behaviour of copper in 1 M HNO 3 using weight loss and electrochemical polarization measurements. Theoretical calculations provide an explanation of the differences between the tested inhibitors. Among these quantum parameters, we can mention the energies of HOMO, LUMO and energy gap (ΔE = E LUMO - E HOMO ). 2. Experimental The potentiodynamic current–voltage characteristics are recorded with a potentiostat PGP 201, piloted by ordinate, at a scan rate of 60 mV min - 1 . The potential started from cathodic to anodic potential. Before recording each curve, the working electrode is maintained with its free potential of corrosion for 30 min. We used for all electro- chemical tests a cell with three electrodes thermostats with double wall (Tacussel Standard CEC/TH). Saturated calomel electrode (SCE) and platinum electrode are used as reference and Auxiliary electrodes, respectively. The working electrode is in the form of a disc from pure copper of the surface 0.35 cm 2 . Prior to each gravimetric or electro- chemical experiment, the surface of the specimens was abraded suc- cessively with emery paper. The specimens are then rinsed with acetone and bidistilled water. Gravimetric methods were conducted on copper test samples of a total surface of 12 cm 2 . All experiments were carried out under total immersion in 75 ml of test solutions. Mass loss was recorded by an analytical balance. Prior to each gravimetric or electrochemical Materials Letters 62 (2008) 3325–3327 ⁎ Corresponding author. Tel.: +212 36 500 602; fax: +212 36 500 603. E-mail address: hammoutib@yahoo.fr (B. Hammouti). 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.02.068 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet