Adsorption and corrosion inhibition effect of 2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol Schiff base on mild steel

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Abstract

In this study, the inhibition effect of 2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol Schiff base (MTMP) on mild steel corrosion in 0.5 M HCl solution was studied. For this aim, electrochemical techniques such as potentiodynamic polarization curves, weight loss (WL), electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) were used. It was shown that, the MTMP Schiff base has remarkable inhibition efficiency on the corrosion of mild steel in 0.5 M HCl solution. Polarization measurements indicated that, the studied inhibitor acts as mixed type corrosion inhibitor with predominantly control of cathodic reaction. The inhibition efficiency depends on the concentration of inhibitor and reaches 97% at 1.0 mM MTMP. The remarkable inhibition efficiency of MTMP was discussed in terms of blocking of electrode surface by adsorption of inhibitor molecules through active centers. The adsorption of MTMP molecules on the mild steel surface obeys Langmuir adsorption isotherm.

Introduction

The investigation of adsorption of surfactants at solid/liquid interfaces is extremely important in electrochemical studies [1]. Their adsorption on the metal surface can markedly change the corrosion resisting properties of metals [2]. The study of relationship between adsorption and corrosion inhibition is of great importance; since the corrosion inhibition is a surface process and the degree of protection of metal is a function of adsorption [2], [3].

Corrosion in mineral acids represents a terrible waste of both resources and money [4]. Corrosion prevention systems favour the use of environmental chemicals with low or zero environmental impacts. The use of organic molecules as corrosion inhibitor is one of the most practical methods for protecting against the corrosion and it is becoming increasingly popular. The existing data show that organic inhibitors act by the adsorption on the metal surface and protective film formation. The adsorption of organic inhibitors at the metal/solution interface takes place through the replacement of water molecules by organic inhibitor molecules according to following process [5].Org(sol) + xH2O(ads)  Org(ads) + xH2O(sol)where Org(sol) and Org(ads) are organic molecules in the solution and adsorbed on the metal surface, respectively. x is the number of water molecules replaced by the organic molecules.

It was shown that organic compounds containing heteroatoms with high electron density such as phosphorus, nitrogen, sulphur, oxygen as well as those containing multiple bonds which are considered as adsorption centers, are effective as corrosion inhibitor [6], [7], [8], [9]. It has been also found that the molecules contain both nitrogen and sulphur in their molecular structure have exhibited greater corrosion inhibition efficiency in comparison with those contain only one of these atoms [10], [11], [12], [13], [14]. Recently, Schiff base compounds have been of interest in order to obtain efficient corrosion inhibitors since they provide much greater inhibition compared to corresponding amines and aldehydes [15], [16], [17], [18], [19]. The presence of –Cdouble bondN– group in Schiff base molecules enhances their adsorption ability and corrosion inhibition efficiency [20], [21].

We have recently reported 2-amino-5-mercapto-1,3,4-thiadiazole (2A5MT) as corrosion inhibitor for mild steel [22]. In this study, we have further improved inhibition efficiency of 2A5MT by preparing its Schiff base using salicylaldehyde (SA). The synthesized Schiff base molecule has additional п bonds as well as a phenyl group which are assumed to be active centre of adsorption. Therefore the molecule is expected to show better adsorption ability and corrosion inhibition efficiency. The aim of this study is to investigate inhibition effect of MTMP on the mild steel corrosion in 0.5 M HCl solution. For this purpose, potentiodynamic polarization, WL, EIS and LPR techniques were used.

Section snippets

Preparation of electrodes

The working electrode was a cylindrical disc cut from a mild steel specimen with following chemical composition (wt); C (0.21%), Si (0.36%), Mn (1.25%), P (0.025%), S (0.046%), Cr (0.16%), Ni (0.16%), Cu (0.41%), Mo (0.017%), Sn (0.017%), Al (0.003%), V (0.081%) and Fe (remainder). The steel disc was mounted in polyester in such a way that only 0.50 cm2 surface area was in contact with the electrolyte. The mild steel specimen was purchased from Technical Metals Co., Adana, Turkey. The surface of

Weight loss measurements

The WL of mild steel specimens after exposure to 0.5 M HCl solution with and without addition of various concentrations of MTMP was calculated in g m−2 h−1 and the data obtained were given in Table 1. It is clear from Table 1 that, the addition of inhibitor to the aggressive solution reduces dissolution rate of mild steel efficiently. The WL was reduced with increasing Schiff base concentration indicates that the inhibitor molecules act by adsorption on the metal surface.

Potentiodynamic polarization measurements

The potentiodynamic

Conclusions

The Schiff base of 2A5MT with SA was synthesized and tested as possible corrosion inhibitor for mild steel in 0.5 M HCl solution. According to results obtained, the following points can be emphasized:

  • 1.

    The MTMP Schiff base has better corrosion inhibition efficiency than the corresponding amine group. The inhibition efficiency of Schiff base studied depends on its concentration. The excellent inhibition efficiency was attributed to the adsorption of inhibitor molecules and protective film formation

Acknowledgements

The authors are greatly thankful to Çukurova University Research Found for its financial support.

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