Materials Chemistry and Physics 131 (2012) 621–633 Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics j ourna l ho me pag e: www.elsevier.com/locate/matchemphys Green approach to corrosion inhibition of mild steel in two acidic solutions by the extract of Punica granatum peel and main constituents M. Behpour a,∗ , S.M. Ghoreishi a , M. Khayatkashani a , N. Soltani b a Department of Analytical Chemistry, Faculty of Chemistry, University of Kashan, Kashan, I.R. 87317-51167, Islamic Republic of Iran b Department of Chemistry, Payame Noor University (PNU), 19395-4697 Tehran, Islamic Republic of Iran a r t i c l e i n f o Article history: Received 28 November 2010 Received in revised form 28 June 2011 Accepted 22 October 2011 Keywords: Mild steel Inhibition EIS D. Corrosion a b s t r a c t The effect of the extract of Punica granatum (PG) and their main constituents involve ellagic acid (EA) and tannic acid (TA), as mild steel corrosion inhibitor in 2 M HCl and 1 M H 2 SO 4 solutions was investigated by weight loss measurements. The results obtained from the weight loss measurements show that the inhibition efficiency of TA even in high concentration is very low. Thus, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) investigations were used for different concentrations of PG and EA and best concentration of TA. Potentiodynamic polarization curves indicated that PG and EA behave as mixed-type inhibitors. EIS measurements show an increase of the transfer resistance with increasing inhibitor concentration. The temperature effect on the corrosion behavior of steel without and with the PG extract was studied. The inhibition action of the extract was discussed in view of Langmuir adsorption isotherm. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Acid solutions are commonly used for the removal of undesir- able scale and rust in metal finishing industries, cleaning of boilers and heat exchangers. To prevent unexpected metal dissolution and excess acid consumption in the process of cleaning, there- fore, inhibitors will be inevitable to be put into use [1]. Most of the well-known acid inhibitors are organic compounds especially those with N, O and S showed an effective corrosion inhibition [2,3]. Nevertheless, most of these compounds are not only expensive but also toxic for live beings. Recently, good results were obtained when lanthanide salts, which have a low toxicity, were employed as corrosion inhibitors [4,5]. Unfortunately, these compounds are very expensive. So development of a novel corrosion inhibitor of plant extracts has attracted some attention as eco-friendly corro- sion inhibitor for many decades [6]. Plant extracts are an incredibly rich source of natural chemical compounds that can be extracted by simple procedures with low cost and are biodegradable in nature. Corrosion inhibition of the extracts of Azaricta indica [7], Ferula gammosa [8], Black pepper [9], Chamomile, Halfabar [10], Strych- nos nux vomica [11], Ferula assa-foetida and Dorema ammoniacum [12] were studied as corrosion inhibitors in HCl and H 2 SO 4 medium. Punica granatum (PG) peels are widely used in the treatment of respiratory diseases and in the preparation of tinctures, cosmet- ics and other therapeutic formulae [13]. PG peels are very rich in ∗ Corresponding author. Tel.: +98 3615912375; fax: +98 3615552935. E-mail address: m.behpour@kashanu.ac.ir (M. Behpour). ellagitannins, which are water-soluble phenolic compounds with high molecular weight. Hydrolysis of ellagitannins produces hexahydroxydiphenic acid, which spontaneously rearranges into ellagic acid (EA) [14,15]. EA (Fig. 1) is a highly thermodynamically stable molecule with four rings representing the lipophilic domain, four phenolic (hydroxyl) and two lactone groups (which can act as hydrogen bond donor or acceptor) representing the hydrophilic part. PG peels contain a substantial amount of polyphenols such as sugar-bound flavonoids, quercetin, kaempferol [16], flavonoid diglycosid [17], ellagic acid, ellagic tannin [18] and organic acids [19]. On the other hand, there were some reports that the PG extracts contain steroid hormones including estrone [20], estra- diol [21] and testosterone [22]. Tannic acid (TA) (Fig. 1) is the typical hydrolyzable tannin which consists of a mixture of differ- ent gallic acid (GA) esters of glucose. TA occurs in the bark and fruits of many plants involve PG, chelates iron due to its ten gal- loyl groups and it diminishes intestinal non-heme iron absorption [23,24]. The objective of the present work is to study the inhibitive action of PG peel extract as a cheap, green and naturally occur- ring substance on corrosion behavior of mild steel in 2 M HCl and 1 M H 2 SO 4 solutions. A comparative study of PG peels extract and its two main constituents, involving EA and TA, were investigated. The study is conducted by weight loss, potentiodynamic polariza- tion and electrochemical impedance spectroscopy methods. The main constituent responsible for corrosion inhibition characteris- tic of PG peel extract is found to be EA. Polarization curves indicate that PG peel extract and EA act as mixed type inhibitor in two acid solutions. The effect of temperature on the corrosion reaction rate 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.10.027