Electrochemical and XPS studies of the corrosion inhibition of carbon steel in hydrochloric acid pickling solutions by 3,5-bis(2-thienylmethyl)-4-amino-1,2,4-triazole

•2-TMAT is good organic corrosion inhibitor for carbon steel in 1M HCl.•Polarization and EIS methods are in reasonable agreement.•2-TMAT adsorption is well described by Langmuir isotherm.•XPS analyses were used to explain the 2-TMAT mechanism of carbon steel corrosion inhibition. Corrosion inhibition of carbon steel in normal hydrochloric acid solution at 30°C by new 4-amino-1,2,4-triazole derivative, namely 3,5-bis(2-thienylmethyl)-4-amino-1,2,4-triazole (2-TMAT) has been studied by electrochemical impedance spectroscopy (EIS) and polarization techniques. The experimental results have showed that this organic compound revealed a good corrosion inhibition and that the inhibition efficiency is increased with the inhibitor concentration. Two time constants determined by the charge-transfer and the adsorption of the inhibitor, respectively, can be readily outlined. Potentiodynamic polarization showed that 2-TMAT is a mixed type of inhibitor. The adsorption of 2-TMAT on the carbon steel surface in 1M HCl solution obeyed to the Langmuir isotherm with a very high negative value of the standard Gibbs free energy of adsorption ΔGads° (chemisorption). X-ray photoelectron spectroscopy (XPS) analyses were carried out to establish the mechanism of corrosion inhibition of carbon steel in 1M HCl medium by 3,5-bis(2-thienylmethyl)-4-amino-1,2,4-triazole (2-TMAT).