Inhibition effects of thiosemicarbazide derivatives on the corrosion of mild steel in 1.0 m hcl: Theoretical and experimental studies

The inhibition of mild steel corrosion in 1.0 M HCl by TSC, 4FPhTSC, 4ClPhTSC, 3FPhTSC and 2,4ClPhTSC has been investigated using weight loss, electrochemical measurements and quantum chemical calculations. The results showed that 2,4ClPhTSC is the best corrosion inhibitor among the four compounds studied and the inhibition efficiency increases with increase in concentration for all the inhibitors. The adsorption of inhibitor molecules on mild steel surface was found to be spontaneous and obeyed the Langmuir adsorption isotherm. Potentiodynamic polarization investigations indicated that the studied inhibitors were mixed type inhibitors. EIS shows that increasing the concentration of the inhibitor leads to an increase of the polarisation resistance and reducing the double layer capacitance. The quantum chemical parameters were calculated with the DFT method at the B3LYP/6-31++G(2d,2p) level of theory and CBS. the calculated parameters such as EHOMO, ELUMO, Energy Gap, Electronegativity (χ), Hardness (η), Softness (S), Chemical Potential, Electophilicity, Electrofugality, Nucleofugality, Polarizibility and Hyperpolarizability. The theoretical and experimental results were in good agreement.