Study of Synergistic Effect of Some Pyrazole Derivatives as Corrosion Inhibitors for Mild Steel in 1 M H 2 SO 4
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tudy of Synergistic Effect of Some Pyrazole Derivatives as Corrosion Inhibitors for Mild Steel in 1 M H2SO4 Zahraa Talib Khudhaira and Mehdi Salih Shihaba, * a
Department of Chemistry, College of Science, Al-Nahrain University, Baghdad, 64021 Iraq *e-mail: [email protected] Received May 13, 2019; revised May 23, 2019; accepted May 23, 2019
Abstract– Six new pyrazole derivatives were successfully prepared and investigated as corrosion inhibitors for mild steel in 1 M H2SO4 solution by weight loss measurements for 24 h at 30°C. It was observed that at higher inhibitor concentrations, the rate of corrosion decreases, the inhibition efficiency increases as well as the surface coverage degree. The values of the standard free energy of adsorption showed that all prepared pyrazole derivatives afford physisorption effects. The correlation between experimental results and theoretical data could be concluded by using semiempirical molecular orbital calculations for the six studied inhibitors. Theoretical calculations were used to understand the interaction nature between the metal surface and the organic molecules as a corrosion inhibitors. Keywords: corrosion inhibitor, inhibition efficiencies, physisorption DOI: 10.3103/S1068375520050142
INTRODUCTION A highly corrosive nature of some strong acid solutions has a significant effect on the steel surface. The organic corrosion inhibitors are regarded as solid available means to prevent or reduce the loss of steel [1–4]. The triazene ligands with aryl groups like 1,3-substituents (Ar′–NH–N=N–Ar′′) have coordination properties. Coordination of N1-monodentate, N1,N3-chelating or N1,N3-bridging ligand with a wide range of metals is applied to obtain metal complexes [5–8]. Corrosion inhibition of iron using pyrazole derivatives in acidic medium is also reported [9–11]. These compounds could be coordinated with steel as well by the lone pair electrons of nitrogen and the π electrons of the aromatic ring [12]. In the present work, the corrosion rate and corrosion inhibition of mild steel in 1M H2SO4 solutions without and with prepared six pyrazole derivatives were investigated by weight loss measurements for 24 h at 30°C. EXPERIMENTAL Materials Used and Their Preparation Disc-shaped sheets of mild steel were used, with the composition percentage as follows: 0.002% P, 0.288% Mn, 0.03% C, 0.0154% S, 0.0199% Cr, 0.002% Mo, 0.065% Cu, 0.0005% V, and the remainder iron. Those sheets were mechanically press-cut with a diameter of 2.5 cm and thickness 0.05 cm. Next, they were polished with emery papers ranging from
500 to 1200 grades to obtain a highly smooth surface. After that, they were washed with distilled water, absolute ethanol, and finally with acetone. The treated specimens were then stored in a moisture-free desiccator before being tested by the weight loss method. New pyrazole derivatives designated as inhibitors (1), (2), (3), (4), (5), and (6) were synthesized as follows: 1-(4-acetophenyl)-3-phenyltriazene was synthesized by two steps. Firstly, a primary aromatic amine (
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