Electrochemical and quantum chemical studies of some Schiff bases on the corrosion of steel in H2SO4 solution

doi:10.1016/j.apsusc.2006.08.025

Applied Surface Science

Volume 253, Issue 8, 15 February 2007, Pages 3913-3921

https://doi.org/10.1016/j.apsusc.2006.08.025 Get rights and content

Abstract

The efficiency, as steel-corrosion inhibitors in 0.1 M and 1 M H₂SO₄, of two Schiff bases, 2-{[(4-methoxyphenyl)imino]methyl}phenol and 1-{[(4-methoxyphenyl)imino]methyl}-2-naphthol, (abbreviated SB-1 and SB-2, respectively) was investigated by Tafel extrapolation and linear polarization methods. Corrosion parameters and adsorption isotherms were determined from current–potential curves. It was found that the percent inhibition efficiencies (η%) and surface coverage (θ) increase with an increases in the concentrations of inhibitors. The results showed that these compounds act as good corrosion inhibitors especially at high concentrations. The adsorption of used compounds on the steel surface obeys Langmuir's isotherm. Obvious correlation was found between corrosion inhibition efficiency and quantum chemical parameters obtained by B3LYP/6-31g(d) method. The obtained theoretical results have been compared with the experimental findings.

Introduction

Being the major structural material in industry, the protection of steel against corrosion has attracted much attention. As most steels are generally stable in neutral and alkaline media, acidic environments are the major concern [1]. Handling of fairly acidic solutions in the beverage and food industries generally require steel vessels, for example [2], [3], [4]. Besides, steel materials in use for various purposes are subjected to surface regeneration procedures like descaling, pickling, etc. and acidic solutions of pH values below 1 are in common use for these applications [5], [6]. Sulphuric acid is generally the choice in the steel surface treatment basically due to its lower cost, minimal fumes and noncorrosive nature of the SO₄²⁻ ion.

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. In acidic media, the adsorption process of the nitrogenous compounds is ascribed to the effects of the functional groups connected to aromatic rings [7], [8]. It has been reported that the adsorption of nitrogenous compounds occurs with aromatic rings parallel to metal surface. It has also been observed that the adsorption appears to depend mainly on the electronic structure of the molecule and that the inhibition efficiency increases with an increase in the number of aromatic rings [9].

The main focus of several research topics with Schiff bases has been the use of these compounds as inhibitors in preventing corrosion in metals and alloys [10], [11], [12], [13], [14], [15], [16], [17], [18]. A study on the steel-corrosion inhibition of 2-hydrazino-6-methylbenzothiazole is reported to have led the conclusion that in steel corrosion, the presence of an aromatic ring and functional groups containing nitrogen and oxygen are likely to induce a greater adsorption of the compound on the metal surface promoting effective inhibition [19]. Theoretical approaches provide means of analyzing these interactions and there have been several studies on this issue [12], [16], [17], [20], [21], [22]. The aim of this study is to investigate the inhibition effects of two Schiff base compounds on the corrosion of steel in both 0.1 and 1 M H₂SO₄ solutions. The relation between the inhibition efficiency of the Schiff bases studied and some quantum chemical parameters such as frontier orbital energies, Mulliken charges of possible adsorption centers and dipole moments (μ) have also been presented.

The most aggressive acidic medium to be used in the treatment of the surfaces of steel materials can tentatively be suggested to be H₂SO₄ solutions of concentrations not more than 1 M. We therefore decided to investigate the corrosion of steel samples in 0.1 and 1 M H₂SO₄ media. The use of an inhibitor in these studies is a general practice, and we tried two novel Schiff bases for this purpose.

Section snippets

Experimental

The chemical structures, the names and the abbreviations of the studied Schiff bases are given in Table 1.

The concentration range of inhibitors was varied from 5 × 10⁻⁴ to 2 × 10⁻² M. The composition of the steel used in experiments is shown in Table 2.

Salicylaldehyde and p-methoxyaniline were purchased from Sigma and used without further purification. 2-hydroxy-1-naphtaldehyde was purchased from Fluka. All other chemical substances used were regaent-grade commercial products.

Experimental results

Fig. 1, Fig. 2 give the anodic and cathodic polarization curves in 0.1 M H₂SO₄ in the absence and presence of various concentrations of SB-1 and SB-2, respectively. Fig. 3, Fig. 4 represent the anodic and cathodic polarization curves in 1 M H₂SO₄ for SB-1 and SB-2, respectively at various concentrations.

Corrosion parameters such as corrosion potentials, anodic and cathodic Tafel slopes, polarization resistance, current densities, percentage inhibition efficiencies and degrees of surface coverage

Conclusion

The following results can be drawn from this study:

1.
The inhibition efficiencies are comparable to other Schiff bases that have been tried in similar media for similar steel materials.
2.
Inhibition efficiencies increase with the increasing concentration of inhibitors.
3.
In determining the corrosion rates, Tafel extrapolation and linear polarization methods give similar results.
4.
The inhibitor-effect of the Schiff bases are apparently based on the adsorption of the molecules on the steel surface.
5.

Acknowledgements

The authors are indebted to The Scientific and Technical Research Council of Turkey (TUBITAK) for the scholarship (NATO-PC-A1) granted to Rovshan Hasanov. The authors also acknowledge Dr. Selçuk Aktürk, from Physics Department, Kırıkkale University for taking the SEM images in the study and Hacı Özışık from Physics Department of Gazi University for his technical assistance.

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Electrochemical and quantum chemical studies of some Schiff bases on the corrosion of steel in H2SO4 solution

Abstract

Introduction

Section snippets

Experimental

Experimental results

Conclusion

Acknowledgements

Biochem. J.

Postharvest Biol. Technol.

Corros. Sci.

Corros. Sci.

Mater. Chem. Phys.

Mater. Chem. Phys.

Electrochim. Acta

Appl. Surf. Sci.

Corros. Sci.

Corros. Sci.

Corros. Sci.

Mater. Chem. Phys.

Corros. Sci.

Corros. Sci.

J. Agricult. Food Chem.

Br. Corros. J.

Electrochemical and quantum chemical studies of some Schiff bases on the corrosion of steel in H₂SO₄ solution