Preparation of new Schiff bases based on thiosemicarbazide and evaluation of their inhibitory properties on corrosion of carbon steel in acidic environment

In this work, two Schiff bases named 1-(2-hydroxybenzylidene)-4-phenylthiosemicarbazide (2-HTSC) and 1-(3-hydroxybenzylidene)-4-phenylthiosemicarbazide (3-HTSC) were synthesized and evaluated their inhibitory properties on corrosion of carbon steel in 15% HCl environment. Inhibitory effect of compounds were investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), polarization, Scanning electron microscopy (SEM) analysis, X-ray diffraction (EDX) spectroscopy and absorption isotherms. Concentrations of 0.5, 1, 1.5 and 2 mM of the inhibitor were evaluated and the best result was obtained at a concentration of 1.5 mM. The results showed that the 3-HTSC Schiff base has a better inhibitory percentage than the Schiff base 2-HTSC. Adsorption of inhibitors on the steel surface follows all Langmuir adsorption isotherm and the results of thermodynamic parameters indicate physico-chemical adsorption. In the presence of inhibitor, the adsorption rate of chloride ions on the metal substrate decreased by 26% and 74% for inhibitors 2-HTSC and 3-HTSC, respectively, due to the predominance of better interactions of 3-HTSC with the metal substrate in Comparison with 2-HTSC inhibitor.