The Inhibition Effect and Mechnism of a Thiadiazole Derivative on Q235 Carbon Steel in 1 M HCl Solution

Abstract

N,N-dihydroxyethyl-(5-methyl-[1,3,4] thiadiazol-2-sulfur)-carbonyl acetamide was synthesized and used as an inhibitor to protect Q235 carbon steel in a 1 M HCl solution. The results showed an increased inhibition efficiency with the increase in the concentration of this inhibitor, and an inhibition efficiency higher than 96% at 40 mg/L can be obtained from weight loss, electrochemical impedance spectroscopy, and potentiodynamic polarization results. The inhibition effect was determined by the adsorption film according to the surface morphology and elemental distribution of the carbon steel surface. The adsorption consists of physical adsorption and chemical adsorption in view of the free adsorption energy of −40.64 kJ/mol derived from the Langmuir adsorption isotherm line. The lone pair electrons of N, O and S and π electronics of double bonds in molecules form stable covalent coordination bonds with the empty d orbitals of iron atoms, which is beneficial to chemical adsorption of the inhibitor. The high inhibiton efficiency of this inhibitor is important for the potential application in pickling field.