Inhibition of stainless steel pitting corrosion in acidic medium by 2-mercaptobenzoxazole S.A.M. Refaey * , F. Taha, A.M. Abd El-Malak Chemistry Department, Faculty of Science, Minia University, Minia 61519, Egypt Received in revised form 15 April 2004; accepted 15 April 2004 Available online 28 July 2004 Abstract The corrosion behavior of stainless steel samples (304L and 316L) in HCl and H 2 SO 4 solution has been studied using potentiodynamic, cyclic voltammogram, EDX and scanning electron microscope (SEM) techniques. The inhibition character- istics of 2-mercaptobenzoxazole (MBO) on 316L stainless steel (316L SS) in HCl solutions were investigated at different temperatures (25, 40, 50 and 60 8C). MBO compound has proven to be efficient inhibitors for general and pitting corrosion of 316L SS in HCl solution. The inhibitive property of MBO may be argued to the formation of very low soluble bis-benzoxazolyl disulfide (BBOD) layer and a compact Fe–MBO complex film on the electrode surface. Some samples were examined by scanning electron microscope. The inhibition efficiencies increased with the increasing of MBO concentration but decreased with increasing temperature. The activation energy and thermodynamic parameters were calculated. # 2004 Elsevier B.V. All rights reserved. Keywords: Corrosion; Inhibition; 2-Mercaptobenzoxazole; 304L and 316L stainless steels; Thermodynamic parameters 1. Introduction Stainless steel (SS) derives their corrosion resis- tance by forming thin passive films on their surfaces that give protection to the base alloy. Breakdown of these protective films leads to localized corrosion failures such as pitting corrosion. The ability of the SS to repassivate after breakdown determines its resistance against localized failures. The inhibition efficiency of organic compounds is strongly depen- dent on the structure and chemical properties of the layer formed on the metal surface under particular experimental conditions. The adsorption of the nitro- genous compounds is ascribed to the effects of the functional groups connected with aromatic rings. It has been reported that the adsorption of nitrogenous compounds occurs with aromatic rings parallel to the metal surface [1]. Since aggressive acid solutions are widely used for industrial purposes, inhibitors are commonly used to reduce the corrosive attack on metallic materials. 2-Mercaptobenzoxazole (MBO) was used previously [1–6] in the inhibition of the corrosion of Cu and Fe. It has been shown that the MBO was able to reduce the corrosion rate, a marked bacteriostatic and fungicidal activity. The coordina- tion of MBO to transition metal ions is of special interest because of the efficiency of this ligand as a corrosion inhibitor [3]. Faltermeier [7] has used MBO to prevent the conversation of nantokit (CuCl) into paratacamite (CuCl 2 ), which causes major damage in Applied Surface Science 236 (2004) 175–185 * Corresponding author. Tel.: þ20-2-3771-406; fax: þ20-2-3771-406. E-mail address: saeed_refaey@hotmail.com (S.A.M. Refaey). 0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.04.016