Electrochemical and Quantum Chemical Studies on Adsorption and Corrosion Inhibition Performance of Quinoline -Thiazole Derivatives on Mild Steel in Hydrochloric Acid Solution

In the present study two quinoline-thiazole derivatives namely, {4-[1-aza-2-(phenyl) vinyl]-3-phenyl-2-thioxo(1,3-thiazoline-5-yl)}-N-[1-aza-2-(2-chloro(3-quinolyl)) vinyl] (Inh I) and {4-[1-aza-2-(4-methoxyphenyl) vinyl]-3-phenyl-2-thioxo(1,3-thiazoline-5-yl)}-N-[1-aza-2-(2 chloro (3-quinolyl)) vinyl] (Inh II) were synthesized and investigated as an inhibitor for mild steel corrosion in 15% HCl solution by using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibitors Inh I and Inh II show corrosion inhibition efficiencies of 81.5% and 84.0% at a 20 ppm concentration and 95.0% and 96.3% at a 200 ppm concentration, respectively, at 333 K. It was found that the inhibition efficiency of both the inhibitors increases with an increase in temperature and concentration of inhibitors. Polarization studies show that both the studied inhibitors are of mixed type in nature. The adsorption of inhibitors on the mild steel surface obeys the Langmuir adsorption isotherm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were performed for the surface study of uninhibited and inhibited mild steel samples. The semi-empirical AM1 method was employed for theoretical calculations.