Inhibition of stainless steel pitting corrosion in acidic medium by 2-mercaptobenzoxazole

doi:10.1016/j.apsusc.2004.04.016

Applied Surface Science

Volume 236, Issues 1–4, 15 September 2004, Pages 175-185

https://doi.org/10.1016/j.apsusc.2004.04.016 Get rights and content

Abstract

The corrosion behavior of stainless steel samples (304L and 316L) in HCl and H₂SO₄ solution has been studied using potentiodynamic, cyclic voltammogram, EDX and scanning electron microscope (SEM) techniques. The inhibition characteristics of 2-mercaptobenzoxazole (MBO) on 316L stainless steel (316L SS) in HCl solutions were investigated at different temperatures (25, 40, 50 and 60 °C). 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.

Introduction

Stainless steel (SS) derives their corrosion resistance 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 dependent on the structure and chemical properties of the layer formed on the metal surface under particular experimental conditions. The adsorption of the nitrogenous 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], [2], [3], [4], [5], [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 coordination 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 (CuCl₂), which causes major damage in archaeological copper artifacts. The present work aims to establish the role of MBO in the improving the passive films’ resistance towards general and pitting corrosion of 316L SS caused in acidic medium (HCl). The thermodynamic feasibility of MBO inhibitor via coverage of the 316L SS surface by adsorbed MBO molecules was also aimed.

Section snippets

Experimental

The composition (wt.%) of 304L SS is 0.03% C, 2.0% Mn, 0.10% Si, 0.45% P, 18–20% Cr, 8–12% Ni and 0.03% S. The composition of 316L SS is 0.03% C, 2.0% Mn, 0.10% Si, 0.45% P, 16–18% Cr, 10–14% Ni, 0.03% S, 2–3% Mo and the remainder being iron. The ingot samples were machined in the form of short rods. Experiments were carried out in HCl and H₂SO₄ solutions in absence and presence of different concentrations of MBO solutions. MBO (Fluka) was used as received. All solutions were prepared from

Results and discussion

The polarization curves for 304L SS and 316L SS in different concentrations of each solution of HCl and H₂SO₄ at scan rate 20 mV s⁻¹ in the potential range from −500 to 1700 mV (SCE) are shown in Fig. 1 (as example). The scans have the same general features and characterized by the appearance of active, passive and transpassive regions before oxygen evolution. After the corrosion potential (zero current), the anodic current density starts to increase to form the active region. The increase of the

Conclusions

MBO compound has proven to be efficient inhibitor for general and pitting corrosion of 316L SS in HCl solution. The MBO inhibition efficiency increases by increasing of the inhibitor concentration, but decreases with the increasing of temperature. The inhibitive property of MBO may be argued to the formation of very low soluble bis-benzoxazolyl disulfide layer and a compact Fe–MBO complex film on the electrode surface. The inhibition of 316L SS in HCl solution at different temperatures was

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Inhibition of stainless steel pitting corrosion in acidic medium by 2-mercaptobenzoxazole

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Desalination

Electrochim. Acta

J. Inorg. Nucl. Chem.

Russ. J. Electrochem.

Stud. Conserv.

Appl. Surf. Sci.