Electrochemical and quantum chemical studies of 2-amino-4-methyl-thiazole as corrosion inhibitor for mild steel in HCl solution
Introduction
The carrier systems such as oil pipelines, gas distribution networks, steam boilers, central air conditioning systems are indispensable materials for the industry. In these industrial facilities, the steel is widely used as a construction material. Due to the low installation costs, mild steel is especially preferred. However, the main problem with the use of mild steel is its low resistance to corrosion. Therefore, it must be protected against corrosion in especially aggressive media. The use of organic inhibitors is one of the most practical and effective methods for protection of the mild steel. The selection of appropriate molecules as an inhibitor depends absolutely on structure and formulation. Generally, molecules containing nitrogen, sulfur, oxygen and aromatic rings are preferred. The efficiency of these molecules depends mainly on their abilities to adhere onto the metal surfaces [1], [2], [3], [4]. The researches show that these molecules adsorb on the metal surface by displacing water molecules on the surface and forming a protective film [4], [5], [6]. Especially, the studies show that chloride containing acidic medium plays an important role, because chloride ions easily adsorb on the inner Helmholtz plane [7]. Furthermore, in industrial applications, HCl(aq) is one of the most-used acid for degreasing, descaling, pickling, etc. [8], [9]. Therefore, the protection efficiency of inhibitors in this medium is very important. In recent studies, the quantum calculation methods are used for detailed explanation of the inhibition efficiency mechanism. In this approach, the electronic properties relevant to the inhibiting action are calculated [10], [11], [12].
Döner et al. [13] investigated the possible application of 2-amino-5-mercapto-1,3,4-thiadiazole (2A5MT) and 2-mercaptothiazoline (2MT) as an inhibitor for protecting MS in 1.0 M H2SO4. The experimental analysis shows that 2A5MT has better performance than 2MT, which is supported by the theoretical calculations [13]. Ghailane et al. determined the inhibition effects of 2-aryl-benzothiazin-3-one (P1) and 3-arylbenzothiazin-2-one (P2) on mild steel corrosion in 1 M HCl with experimental and theoretical investigations [14]. The quantum parameters show that the P2 molecule was more distorted than P1. Therefore, P1 had higher inhibition efficiency than P2. It was in a good agreement with experimental results [14]. In this study, thermodynamic, kinetic and theoretical parameters and the inhibitive properties of 2-amino-4-methyl-thiadiazole (2A4MT) for MS protection in 0.5 M HCl(aq) were determined. The electrochemical measurements were performed, the adsorption mechanism was clarified, and the potential of zero charge and the surface charge were determined. The surface morphology of the MS was examined with SEM in the presence and absence of 2A4MT. The energy of the highest occupied molecular orbital (EHOMO), the energy of the lowest unoccupied molecular orbital (ELUMO), the energy gap (ΔE), Mulliken charges and NBO charges on the backbone atoms were calculated. Finally our findings are discussed along with the studies reported in the literature.
Section snippets
Experimental
The working electrode was a MS specimen. Thin MS disk with surface area of 0.5 cm2 was cut from the MS sheet (wt.%): 0.17 C, 0.59 Si, 1.60 Mn, 0.04 P and Fe (remainder). After connecting it through a copper wire for electrical conductivity, the specimens were mounted to a polyester block. The exposed surface of working electrode was polished using emery paper up to 1200 grade prior to the experiments. Then, it was cleaned with distilled water and dried with a filter paper.
The electrochemical tests
Corrosion performance
Electrochemical impedance spectroscopy (EIS) is commonly used technique in corrosion researches to explain the mechanisms and adsorption phenomena [18], [19]. Especially, in inhibition studies, a single semi-circular shape is observed for MS in acidic media [20], [21], [22], [23], [24]. As in previous studies [20], [21], [22], [23], [24], the parallel results were detected in EIS data. The EIS results and equivalent circuit were presented in Fig. 2, Fig. 3, respectively. In this equivalent
Conclusions
The inhibition behavior of 2A4MT on MS in 0.5 M HCl was investigated using different techniques. The following points can be highlighted;
- 1.
The obtained results indicate that, 2A4MT performs excellent inhibition activity against the corrosion of MS in 0.5 M HCl solution. The determined high inhibition efficiency is attributed to the adherent adsorption of the 2A4MT.
- 2.
The potentiodynamic polarization curves show that 2A4MT prevents metal dissolution and also hydrogen evolution reactions.
- 3.
The adsorption
Acknowledgement
The authors are greatly thankful to Cukurova University research fund (Project No. FEF2013BAP10) for financial support.
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