Effectiveness of some diquaternary ammonium surfactants as corrosion inhibitors for carbon steel in 0.5 M HCl solution N.A. Negm a, * , A.M. Al Sabagh a , M.A. Migahed a , H.M. Abdel Bary b , H.M. El Din c a Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt b Faculty of Science, Al Azhar University, Cairo, Egypt c Cairo Company for Petroleum Refining, Cairo, Egypt article info Article history: Received 17 November 2009 Accepted 25 February 2010 Available online 3 March 2010 Keywords: A. Carbon steel alloy B. Polarization B. EIS C. Interfacial and acid corrosion abstract Four Gemini surfactants were synthesized and characterized using elemental analysis, FTIR and 1 H NMR spectroscopy. The synthesized compounds were evaluated as corrosion inhibitors for carbon steel in 0.5 M HCl solution. The inhibition efficiencies of the tested inhibitors were depended on the hydrophobic chain length and the used doses of the inhibitors. The polarization measurements showed that these inhibitors are acting as mixed inhibitors for both anodic and cathodic reactions. The results showed that the inhibition efficiencies were increased by increasing the inhibitor doses and the hydrophobic chain length and reached the maximum at 500 ppm by weight for stearyl derivative. The efficiencies obtained from the impedance measurements were in good agreement with those obtained from the gravimetrical and polarization techniques which prove the validity of these tolls in the measurements of the tested inhibitors. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Acid solutions are widely used for industrial cleaning, oil well acidification and in the petrochemical processes [1]. Hydrochloric acid is generally used in the pickling processes of metals and alloys. The corrosion of steel in such environments and its inhibition consti- tute a complex problem of processes [2]. Corrosion inhibitors are used to prevent metal dissolution as well as acid consumption [3,4]. Most organic inhibitors are substances with at least one func- tional group, which considered as the reaction center for the adsorp- tion process. The adsorption of inhibitors is related to the presence of heteroatom as nitrogen [5–11], phosphorus and sulfur [12–14]. Sur- factants are special type of organic compounds and exhibit unique properties due to their amphiphilic molecule. This is the reason of their wide application in the field of inhibition of metals against cor- rosion. A molecular layer of surfactants is formed as a result of this attraction with the construction of a hydrophobic barrier, which pre- vent the contact of the metal surface with the environment. The sur- factant inhibitors have many advantages such as high inhibition efficiency, low price, low toxicity and easy production [15–20]. The adsorption of the surfactant on the metal surface can markedly change the corrosion-resisting property of the metal [21,22], and so the study of the relationship between the adsorption and corro- sion inhibition is of great importance. Ionic surfactants have been used for the corrosion inhibition of iron [23–30], copper [31–34], aluminum [35–38] and other metals [39,40] in different corroding media. Recently, many nonionic surfactants have been widely used as corrosion inhibitors for iron in acidic media [41–43]. The molecu- lar layer formed on the protected metal surface may consist of mul- tilayer. The first molecular layer formed may be strongly bonded, perhaps by an electrical charge exchange analogous to a chemical reaction. Such strong bonding is called chemisorption [1]. The appli- cation of surfactants as inhibitors has been studied by many authors [30,44–52]. The role of surfactants as corrosion inhibitors in forma- tion water was also investigated in order to install a wide and vari- able usage for these compounds [53,54]. 2. Experimental 2.1. Preparation of triethanolamine monoester Triethanolamine (0.1 mol) and lauric, palmetic and stearic acid (0.1 mol) were esterified individually in toluene as a solvent and in presence of 0.01% p-toluene sulphonic acid as a catalyst at 109 °C under nitrogen atmosphere. The reaction was stopped when the theoretical amount of water was removed (1.8 mL). Subsequent purification (two times) was done by means of vacuum distillation to remove the excess and unreacted and residual materials [55]. The produced compounds were triethanolamine monolaurate (ML), triethanolamine monopalmitate (MP) and triethanolamine monostearate (MS). 0010-938X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2010.02.044 * Corresponding author. E-mail address: nabelnegm@hotmail.com (N.A. Negm). Corrosion Science 52 (2010) 2122–2132 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci