Review Films formed on copper surface in chloride media in the presence of azoles Milan M. Antonijevic ´ * , Snez ˇana M. Milic ´ , Marija B. Petrovic ´ University of Belgrade, Technical Faculty Bor, VJ 12, P.O. Box 50, 19210 Bor, Serbia article info Article history: Received 10 February 2009 Accepted 20 March 2009 Available online 28 March 2009 Keywords: A. Copper A. Azole C. Corrosion inhibition C. Chloride media C. Protective ﬁlms abstract The literature dealing with copper behaviour in chloride media in the presence of azoles is studied in order to improve understanding of their action mechanism, protective ﬁlms formed, and the possibility of their application according to the inhibition efﬁciency achieved. The corrosion inhibition effect results from inhibitor molecule adsorption on copper surface and formation of the protective complex coating. According to the results summarised, copper corrosion may be successfully inhibited by benzotriazole, phenyl derivatives of tetrazole, bypyrazoles and 2-methyl-5-mercapto-1,3,4-thiadiazole in NaCl solu- tions, and in HCl solutions by 5-chloro benzotriazole, 3,5-diamino-1,2,4-triazole, and 4-methylimidazole. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Copper and its alloys are known for plenty of favourable prop- erties such as conductivity, workability, resistance, making them suitable for a wide range of applications. Hence, they are used in electronic industry, for production of wires, sheets, tubes, and also for formation of alloys. Copper is resistant to the inﬂuence of atmo- sphere and many chemicals. However, the corrosion susceptibility is conﬁrmed when the chloride ions are present in atmosphere, aqueous or soil media [1,2]. Investigation of the initial stages of localized copper corrosion is conducted by Van Ingelgem et al. [3]. In the ﬁrst stage there is the growth of a general and uniform oxide layer. It is pierced when local attack starts to occur. The sec- ond stage is the consequent activation and de-activation of differ- ent places on the surface, located at the grain boundaries. In this third stage almost all locally attacked sites are repassivated and the oxide has thickened. Only a few active sites remain on the sur- face. Local attack and general oxide forming reactions take place in parallel on the surface. Also an in-depth evolution of the surface composition show that at the surface of the oxide, chlorine con- taining compounds are formed, but they are not built in into the layer. The results of Van Ingelgem et al. [4] indicate that two types of surface ﬁlms are formed, the thicker layer, consisting almost exclusively of Cu 2 O and the thinner less protective layer containing more chloride ions. The pitting corrosion of copper in chloride solution has been observed [5,6]. It is already seen that in dilute chloride solutions Cu 2 O ﬁlm is formed on the copper surface and where CuCl is trapped [5] or the protective layer is damaged [6] the initiation of the pits occurs. The mechanism of copper electro- dissolution in chloride media has been investigated by many researchers whose results are reviewed in the paper published by Kear et al. [7]. The proposed mechanisms are: ðIÞ Cu þ 2Cl  $ CuCl  2 þ e  ð1Þ ðIIÞ Cu $ Cu þ þ e  ð2Þ Cu þ þ 2Cl  $ CuCl  2 ð3Þ ðIIIÞ Cu þ Cl  $ CuCl þ e  ð4Þ CuCl þ Cl  $ CuCl  2 ð5Þ Cases I and III present the direct formation of a cuprous chloride species from copper, and II involves the dissolution to cuprous ion. CuCl 2  is believed to control the kinetics of anodic dissolution of copper in inhibitor free solutions, whereas at chloride concentra- tions higher than 1 M complexes CuCl 3 2 and CuCl 4 3 may be formed. Under some circumstances the formation of cuprous oxide may be favoured over chloride complexes formation and the pres- ence of surface ﬁlms diminish the aggressive chloride ions attack. Even back in 1940, Asselin and Rohrman [8] observed the maximum value of weight loss of copper, whereas at lower chloride ions con- centration copper tarnish and above the dissolution is faster than ﬁlm formation. The passivation-like phenomenon is observed by Zhang et al. [9]. The highest corrosion rate occurs when the concen- tration of chloride ion is approximately 0.1 M. The increase in chlo- ride ion concentration leads to the attack on the insoluble CuCl layer, which transforms into a soluble CuCl 2  complex, whereas, 0010-938X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2009.03.026 * Corresponding author. Tel.: +381 30 424 555; fax: +381 30 421 021. E-mail addresses: mantonijevic@tf.bor.ac.rs (M.M. Antonijevic ´), smilic@tf.bor. ac.rs (S.M. Milic ´), mpetrovic@tf.bor.ac.rs (M.B. Petrovic ´). Corrosion Science 51 (2009) 1228–1237 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci