Protective properties of new inhibitors based on substituted 1,2,4-thiadiazoles in hydrochloric acid solutions

The paper presents the results of a study of thiadiazole derivatives as corrosion inhibitors of mild steel in a solution of 1 M hydrochloric acid.2-Amino-5-styryl-1,3,4-thiadiazole and 2amino-5-heptyl-1,3,4-thiadiazole were studied.The semi-empirical GFN2-xTB Grimme method was used to calculate the protonation of the studied molecules in hydrochloric acid medium.Weight loss tests were carried out on C1018 steel at a temperature of 293 K, the exposure time of the samples was 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.The case of the greatest inhibitory effect by the studied compounds was not distinguished, since at a concentration equal to or more than 100 mg/L, they all exhibit the same protective effect, taking into account the statistical error.A similar degree of protection of the metal surface by the studied inhibitors is associated with the same order of protonation of molecules in acidic solutions.Using the potentiodynamic polarization method, it was found that the studied compounds are inhibitors of the mixed (2amino-5-styryl-1,3,4-thiadiazole) and cathodic (2-amino-5-heptyl-1,3,4-thiadiazole) types.The preservation of a high protective effect for inhibitors over the entire temperature range under study is associated with the process of chemical adsorption of inhibitor molecules on the metal surface, this fact is confirmed by the calculation of the activation energy of the corrosion process.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.The results of this work point to the prospects of searching for potential inhibitors of acid corrosion in the series of thiadiazole derivatives.