New inhibitors based on substituted 1,2,4-triazoles for mild steel in hydrochloric acid solutions

• M.D. Plotnikova, A.D. Solovyev, A.B. Shein, A.N. Bakiev and A.S. Sofronov

Perm State National Research University, st. Bukireva 15, 614068 Perm, Russian Federation

Abstract: The article presents the results of studies on triazole derivatives as corrosion inhibitors for mild steel in hydrochloric acid solutions of various concentrations, namely, 1 M and 5 M. 5-Heptyl-1,2,4-triazole-3,4-diamine and 4,5-diphenyl-4H-1,2,4-triazole-3-thiol were studied. Grimme´s semi-empirical GFN2-xTB method was used to calculate the protonation of the investigated molecules in hydrochloric acid media. Weight loss tests were carried out on steel C1018 at a temperature of 293 K with an exposure time of 24 h. The polarization curves in the temperature range of 293–353 K were recorded in the potentiodynamic mode in a three-electrode cell from the cathodic to the anodic potentials at a potential sweep rate of 0.5 mV/s, using a SOLARTRON 1280C electrochemical measuring complex. It was found that 5-heptyl-1,2,4-triazole-3,4-diamine at a concentration of 200 mg/L has the greatest inhibition effect in 1 M HCl, whereas 4,5-diphenyl-4H-1,2,4-triazole-3-thiol is most efficient in 5 M HCl at the same concentration. It was determined by the potentiodynamic polarization method that the investigated compounds are cathodic-type inhibitors. The effective activation energy of the corrosion process in the presence of 4,5-diphenyl-4H-1,2,4-triazole-3-thiol decreases, which indicates that chemosorption on the electrode surface occurs. The degrees of surface coverage of the steel with triazole molecules were calculated based on the results of electrochemical impedance spectroscopy at the corrosion potential. It was found that the adsorption process obeys the Freundlich equation for an energetically inhomogeneous surface.

Keywords: mild steel, acid corrosion, triazole, inhibitor, potentiodynamic polarization, activation energy, electrochemical impedance spectroscopy, adsorption

Int. J. Corros. Scale Inhib., 2021, 10, no. 3, 1230-1244
doi: 10.17675/2305-6894-2021-10-3-23

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