Experimental and theoretical evaluation of semicarbazones and thiosemicarbazones as organic corrosion inhibitors

The inhibition ability of four thiosemicarbazones (1A–D) and two semicarbazones (2A–B) towards carbon steel corrosion in 1.0 M HCl was evaluated by molecular modeling, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) at different inhibitor concentrations. Polarization curves showed that all of the evaluated compounds acted as mixed inhibitors. EIS plots indicated that the presence of the inhibitors increases the charge transfer resistance of the corrosion process, increasing the inhibition efficiency. The adsorption of the evaluated inhibitors obeys the Langmuir adsorption isotherm. The theoretical results were corroborated by experimental data, with both the experimental and theoretical data showing that the thiosemicarbazones are better corrosion inhibitors than the semicarbazones.

► We evaluated the corrosion inhibition of carbon steel by thio- and semicarbazones.
► We studied by molecular modeling using semiempirical methods.
► The potentiodynamic polarization was used to study the corrosion inhibitory effect.
► The EIS was used to evaluate the corrosion inhibitory effect.