Quinol-2-thione compounds as corrosion inhibitors for mild steel in acid solution

The corrosion inhibition effect of 3-[(E)-(phenylimino)methyl]quinoline-2-thione (PMQT), 3{(E)-[(4-chlorophenyl)imino]methyl}quinoline-2-thione (CPMQT) and 3{(E)-[(4-fluorophenyl)imino]methyl}quinoline-2-thione (FPMQT) on mild steel in 1 mol dm−3 HCl has been determined by mass loss, polarization and impedance (EIS) methods at 300 K. The investigated results showed that the corrosion rate decreased significantly with increase in the concentration of inhibitors. The shape of polarization profiles of all the three compounds indicated their mixed-type nature of inhibition. The inhibition efficiencies decreased in the order FPMQT > CPMQT > PMQT. The adsorption of the compounds on the mild steel surface obeys Langmuir's adsorption isotherm. The surface morphology of the tested mild steel specimens in the presence and absence of inhibitors was studied by using the respective images of SEM. FTIR studies were undertaken to confirm the interaction of molecules with surface atoms of the mild steel and established the adsorption process.