Chemical Papers 68 (3) 362–371 (2014) DOI: 10.2478/s11696-013-0458-x ORIGINAL PAPER Inhibition of copper corrosion in acidic sulphate media by eco-friendly amino acid compound Ana T. Simonovi´ c, Marija B. Petrovi´ c, Milan B. Radovanovi´ c, Snežana M. Mili´ c, Milan M. Antonijevi´ c* Technical Faculty in Bor, University of Belgrade, VJ 12, P.O. Box 50, 19210 Bor, Serbia Received 27 February 2013; Revised 7 June 2013; Accepted 11 June 2013 This investigation aimed to study a “green” non-toxic biodegradable copper corrosion inhibitor in an acidic sodium sulphate solution. The methods used in the investigation of cysteine as a copper corrosion inhibitor in an acidic sodium sulphate solution were: potentiodynamic measurements, open circuit potential measurements, and chronoamperometric measurements. Optical microscopy was used in addition to electrochemical methods. Potentiodynamic measurements show that cysteine has good inhibitory properties in an acidic medium. Polarisation curves indicate that the presence of cysteine in a sulphate solution decreases the current density and that using various cysteine concentrations results in the formation of a protective film on the surface of the electrode due to the formation of the Cu(I)–cys complex. These results are confirmed by chronoamperometric measurements. Furthermore, it is clear from microphotographs that a protective film does form on copper electrode in the presence of cysteine. The Langmuir adsorption isotherm indicates that cysteine is chemisorbed on the surface of the electrode. c  2013 Institute of Chemistry, Slovak Academy of Sciences Keywords: copper, cysteine, polarisation, anodic dissolution, corrosion inhibition Introduction Copper has many industrial uses in everyday life due to its superior qualities. Despite its considerable resistance to various chemical reagents, it corrodes in certain media. In order to reduce dissolution of the metal, a wide range of corrosion inhibitors is used. Previous studies of copper corrosion have shown that, in alkaline solutions, passivation occurs on the metal surface as a result of the formation of copper oxide (Milošev et al., 2006). Considerable attention has been directed towards investigation of chloride ions as the cause of corro- sion of copper and its alloys (Antonijevic et al., 2005, 2009a; Mili´ c & Antonijevi´ c, 2009). In order to prevent corrosion and avoid damage to the metal, a large num- ber of potential corrosion inhibitors have been inves- tigated. Good copper corrosion-inhibiting properties have been exhibited by organic compounds. Extraor- dinary results have been achieved using benzotriazole as an inhibitor of the corrosion of copper and its al- loys (Frignani et al., 1999a, 1999b; Antonijevic et al., 2005, 2009b, 2009c). In addition to these organic com- pounds, good inhibiting properties were also exhibited by other organic molecules such as triazoles (Sherif et al., 2007), tetrazoles (El Issami et al., 2007; Sz¨ocs et al., 2005), as well as organic heterocyclic compounds containing the mercapto group (Ye et al., 1998; Zucchi et al., 1996). Sulphate ions were found to exert a stronger cor- rosion effect than chloride ions (Duthil et al., 1996; Souissi & Triki, 2008). One of the inhibitors used to prevent copper dissolution in 0.5 M Na 2 SO 4 solution is bis-[4H-5-hydroxy-1,2,4-triazole-3-yl]methane (BH- TAM) (El-Naggar, 2000). Many inhibitors have also shown a good inhibitory effect in acidic sulphate so- lutions (Benali et al., 2010; Gomma, 1998). How- ever, azoles are toxic compounds and are considered *Corresponding author, e-mail: mantonijevic@tf.bor.ac.rs