Electrochimica Acta 54 (2009) 6892–6895 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Electrochemical behavior of organic and inorganic complexes of Zn(II) as corrosion inhibitors for mild steel: Solution phase study R. Naderi, M. Mahdavian, M.M. Attar ∗ Polymer Engineering Department, Amirkabir University of Technology, P.O. Box: 15875-4413, Tehran, Iran article info Article history: Received 27 February 2009 Received in revised form 25 June 2009 Accepted 25 June 2009 Available online 4 July 2009 Keywords: Mild steel Electrochemical impedance spectroscopy SEM Polarization Neutral inhibition abstract This work intends to study inhibitive performance of organic and inorganic complexes of Zn(II) using electrochemical techniques along with surface analysis. In this regard, inorganic zinc aluminum polyphosphate pigment as modified zinc phosphate and zinc acetylacetonate and benzimidazole mix- ture representing organic replacement of zinc phosphate were employed. Through taking advantage of electrochemical impedance spectroscopy and DC polarization, two mentioned approaches were indicated to be efficient. Charge transfer resistance and corrosion current density values exhibited superiority of zinc aluminum polyphosphate and mixture of zinc acetylacetonate and benzimidazole compared to zinc phosphate and also zinc acetylacetonate and benzimidazole as individual inhibitors. Corrosion inhibi- tion efficiencies calculated based on charge transfer resistance in consistent with those calculated from corrosion current density showed the following sequence; zinc aluminum polyphosphate > mixture of zinc acetylacetonate and benzimidazole > zinc acetylacetonate > zinc phosphate > benzimidazole. Show- ing film formation, surface analysis SEM/EDX confirmed the results obtained by electrochemical methods. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Chromate compounds as powerful inhibitors have been used to prevent corrosion for many years. It is well-known that chro- mates, functioning as passivating agents, can form intact thin film on the metal surface even at the absence of oxygen [1]. However, their use has been restricted due to adverse effects on environ- ment as well as human safety. Among abundant suggestions for chromates replacement, ZP has gained attractions. According to lit- erature, undesirable inhibitive characteristics of ZP revealed need for further modification or other alternatives [2–7]. A variety of methods [8–12], including modification of anionic part and cationic constitution as well, could be employed to improve zinc phosphate (ZP) inhibitive behavior. The mentioned approaches have significant effects on the solubility of inhibitors and film formation properties. Furthermore, conventional ZP anti- corrosion pigments could be totally replaced with organic modified compounds. Thanks to improved release of inhibiting species and film forma- tion properties, anticorrosion pigments based on polyphosphates were introduced through modification of anionic part and cationic constitution as well [9,13]. Polyphosphates, as the names suggest, contain more than one phosphorus atom in the molecule or ion ∗ Corresponding author. Tel.: +98 21 64542404; fax: +98 21 66468243. E-mail address: attar@cic.aut.ac.ir (M.M. Attar). connected to each other through an oxygen bridge. In the pres- ence of these compounds, positively charged colloidal complexes are formed and migrate to the cathode forming an amorphous polymeric film [14,15]. Furthermore, the polyphosphate could be considered as a reservoir of potential orthophosphate by reversion process [16–18]. Although one could find no publication about combination of imidazole derivatives and zinc acetylacetonate used as corrosion inhibitor, their individual impact on corrosion inhibition is shown by some authors [19,20]. It is suggested that imidazole derivatives can act as corrosion inhibitor in the formulation of an antifreeze composition for cooling systems [19]. Corrosion inhibition of some metal acetylacetonate complexes including zinc acetylacetonate was evaluated using electrochemical impedance spectroscopy (EIS) in 3.5% NaCl for mild steel [20]. It is shown that a complex protective film is formed in presence of zinc acetylacetonate. EIS, providing useful electrochemical qualitative and quantita- tive parameters, is a powerful nondestructive technique [13,20–23]. Through taking advantage of EIS, electrochemical behavior of anti- corrosive compounds could be evaluated. The objective of the present study is to compare inhibitive behavior of zinc aluminum polyphosphate (ZAPP) as inorganically modified ZP to that of zinc acetylacetonate and benzimidazole mixture (ZBM), an organic com- plex of Zn, serving as replacement of ZP using electrochemical techniques along with surface analysis. 0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2009.06.073