Investigation of corrosion inhibition mechanism and stability of Vitamin B1 on mild steel in 0.5 M HCl solution Ramazan Solmaz ⇑ Bingöl University, Science and Letters Faculty, Chemistry Department, 12000 Bingöl, Turkey article info Article history: Received 22 July 2013 Accepted 9 December 2013 Available online 15 December 2013 Keywords: A. Mild steel B. EIS B. SEM C. Acid corrosion abstract The corrosion inhibition mechanism and the stability of Vitamin B1 (VitB1) on mild steel in 0.5 M HCl solution were investigated. Surface of the steel after exposing to test solutions were examined by scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDX). The stability of the inhibitor film was investigated by electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and cyclic voltammetry (CV) techniques. It was found that VitB1 acts by adsorption on mild steel via physical and chemical interactions and a protective film for- mation. The inhibitor film evenly distributes over the steel surface and is stable. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The use of organic inhibitors is one of the most practical met- hods for protection of metals against corrosion, and is becoming increasingly popular according to recent studies. The inhibitory efficiency of organic molecules mainly depends on their adsorption ability on metal surface, which can markedly change the corrosion resisting properties of metals [1]. Therefore, the determination of relation between adsorption and corrosion inhibition is very important. Their adsorption at the metal/solution interface takes place through the replacement of water molecules according to the following equation [2]: Org ðsolÞ þ xH 2 O ðadsÞ $ Org ðadsÞ þ xH 2 O ðsolÞ ð1Þ In this equation, Org (sol) and Org (ads) are organic molecules in the solution and adsorbed on metal surface, respectively. x is the num- ber of water molecules replaced by organic molecules. The adsorption of organic molecules on metals surfaces de- pends mainly on the nature and the surface charge of metals, the chemical structure of organic molecule (functional groups, steric factors, electron density, etc.) and the type of solution [3–6]. The existing data show that organic compounds having heteroatoms with high electron density such as phosphorus, sulfur, nitrogen, oxygen or those containing multiple bonds are effective inhibitors for the corrosion of metals [7–14]. The presence of such atoms with high electron density and multiple bonds in molecular structure enhance the adsorption ability of organic compounds. The usage of some of the inhibitors has been restricted due to the toxicity, and their insufficient inhibitory efficiencies at low dosages [15–17]. Corrosion prevention systems favor the usage of chemicals with low or no environmental impacts. Therefore, the studies have begun to focus on finding novel, cheap, non-toxic, healthy and effective corrosion inhibitors. In this content, we have recently focused on the inhibitory efficiencies of some rhodanine and barbiturate derivatives, which are not toxic and have a variety of biological applications [18–24]. VitB1 is a non-toxic compound and could be easily extracted from natural foods [25]. VitB1 molecule contains many p electrons as well as one oxygen, one sul- fur, and four nitrogen atoms. The presence of such adsorption centers in the molecular structure is expected to cause an easier electron transfer from the functional groups to the mild steel surface which provides greater adsorption ability and inhibitory efficiency. The large size and high molecular weight of VitB1 mo- lecule could also contribute to its inhibitory efficiency. The good water solubility is another advantage for its practical applications. Vitamins B and their derivatives have also been reported as good corrosion inhibitors for various metals in different corrosive media [25–30]. Ju et al. [25] studied the inhibition effect of envi- ronmental-friendly corrosion inhibitors-Vitamins B for hot dipping Zn coated steel in diluted HCl solution using weight loss measure- ments and quantum chemical calculations. The authors reported that Vitamins B have a number of active centers, and good corro- sion inhibition efficiency. Qiao et al. [26] studied synergistic inhibi- tion effect of Lysozyme and VitB1 on corrosion of carbon steel in 0.5 M H 2 SO 4 solution with the help of potentiodynamic polariza- tion and EIS methods. It was found that carbon steel is more efficiently protected by mixture of Lysozyme and VitB1 than 0010-938X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.corsci.2013.12.006 ⇑ Tel.: +90 426 216 0012; fax: +90 426 215 0877. E-mail addresses: rsolmaz01@gmail.com, rsolmaz@bingol.edu.tr Corrosion Science 81 (2014) 75–84 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci