Experimental and quantum chemical characterization of the adsorption of some Schiff base compounds of phthaloyl thiocarbohydrazide on the mild steel in acid solutions

Three derivatives of 2-[2-(hydrazinecarbonothioyl)hydrazinecarbonyl]benzoic acid (IL1) have been evaluated as new corrosion inhibitors for the corrosion of mild steel in 1 M HCl solutions using weight loss, polarization and electrochemical impedance spectroscopy (EIS) techniques. The adsorption of these compounds has been tested thermodynamically which was found to be of neither a typical physisorption nor a typical chemisorption mode. The thermodynamic functions (such as Ea, ΔH°ads, ΔS°ads and ΔG°ads) of dissolution and adsorption processes have been evaluated. The polarization measurements indicated that the inhibitors are of mixed type. The adsorption of the compounds was found to obey Langmuir's adsorption isotherm. In addition, quantum chemical calculations have been made to correlate inhibition efficiencies determined experimentally.