Electrochemical and theoretical study of the inhibition effect of two synthesized thiosemicarbazide derivatives on carbon steel corrosion in hydrochloric acid solution

Abstract

In this work, two thiosemicarbazide derivatives, 2-carbamothioyl-N-phenylhydrazine carboxamide (TSC1) and N-[(2-carbamothioylhydrazino)carbonothioyl]benzamide (TSC2) are synthesized and used as carbon steel corrosion inhibitors in 1.0 M HCl. Weight loss measurements indicate that the studied compounds reduce the corrosion rate of carbon steel in acidic solution and the inhibition effect increases with the inhibitors concentration. It was also shown that the adsorption of TSC1 and TSC2 followed a Langmuir adsorption isotherm. The Tafel polarization method reveals that the organic compounds act as mixed type corrosion inhibitors with a predominantly anodic effect. Electrochemical Impedance Spectroscopic measurements show that the inhibitors form an adsorptive layer on the metallic surface and increase the polarization resistance of the corrosion reaction. Fast Fourier Transform Continuous Cyclic Voltammetry is used to continuously monitor the inhibitors adsorption behavior on the carbon steel surface. The results indicate that TSC2 can better inhibit the carbon steel corrosion rather than TSC1. Some of the inhibitors' quantum chemical parameters are calculated with the DFT method at the B3LYP/6-31g(d,p) level of theory. Among the calculated parameters, the LUMO energy, energy gap between the HOMO and LUMO and the hardness could well describe the experimental observations.