Inhibitory performance of some pyrazole derivatives against corrosion of mild steel in 1.0 M HCl: Electrochemical, MEB and theoretical studies

• S.A. Mrani¹, S. El Arrouji¹, K. Karrouchi², F. El Hajjaji¹, K.I. Alaoui¹, Z. Rais¹ and M. Taleb¹

¹ Laboratoire d’Ingénierie d’Electrochimie de Modélisation et d’Environnement (LIEME) FSDM Fès, Morocco
² Laboratoire National de Contrôle des Médicaments, D M P, Ministère de la Santé, Madinat Al Irnane, BP 6206, Rabat, Morocco

Abstract: In this study, we discussed the inhibition properties of three new Pyrazole derivatives (DPA, DPM and DPF) against the corrosion of mild steel in 1.0 M HCl, using the weight loss technique, the stationary method and the transitional method. The experimental results show that the inhibition properties increase with the concentration and can reach a limit value of 97% for the inhibitor DPA at 10^–3 M. The curves of polarization show that the Pyrazole derivatives were a mixed inhibitor. The data obtained by electrochemical impedance spectroscopy were analyzed to be modeled by appropriate equivalent circuit models. The evolution of the temperature leads to a decrease in the inhibition efficiency of the Pyrazole compounds. Several adsorption isotherms have been modeled such as Langmuir, Temkin, Frumkin, Flory–Huggins, Freundlich and the kinetic thermodynamic model of El-Awady, in order to provide additional information on the inhibitory properties of the compounds studied. The coefficient of determination values of all the isotherms are very high, from the two models of Flory–Huggins and El-Awady we find that the adsorption of molecules on the surface of the steel moves more than a single molecule of water which is at odds with the Langmuir isotherm. Whereas the isotherms of Temkin and Frumkin suggest the existence of the lateral interactions between the adsorbed species. Scanning electron microscopy (SEM) and EDX analyzes were used to characterize the chemical composition of the film formed on the surface of the steel. Surface studies have shown that the inhibitory layer consists of an iron oxide/hydroxide mixture in which the N, F atoms are incorporated. The DFT studies have also been carried out for protonated form of the inhibitor molecules by considering that in acidic medium the heteroatoms of organic inhibitors easily undergo protonation. The experimental and density functional theory (DFT) studies were in good agreement.

Keywords: pyrazole, mild steel, corrosion inhibition, surface, adsorption, DFT

Int. J. Corros. Scale Inhib., 2018, 7, no. 4, 542-569 PDF (1 608 K)
doi: 10.17675/2305-6894-2018-7-4-5

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