Experimental and Theoretical Studies on Corrosion Inhibition Effect of Synthesized Benzothiazole Derivatives on Mild Steel in 15% HCl Solution

Two benzothiazole derivatives, namely, (Z)-5-(4-chlorobenzylidene)-3-(benzo[d]thiazol-2-yl)-2-(4-methoxyphenyl)thiazolidine-4-one (CBTMT) and (Z)-5-(4-methoxybenzylidene)-3-(benzo[d]thiazol-2-yl)-2-(4-methoxyphenyl)thiazolidine-4-one (MBTMT) were synthesized in the laboratory and their corrosion inhibition performance on mild steel in 15% HCl solution was studied by means of weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency of each inhibitor increased with increasing the concentration of inhibitor. According to weight loss measurements, the inhibitors CBTMT and MBTMT show corrosion inhibition efficiency of 95.8 and 97.5% respectively, in 150 ppm concentration, at 303 K. Polarization studies showed that corrosion current density decreased in presence of both the inhibitors in comperision to in absence of inhibitors. The thermodynamic adsorption and activation parameters were evaluated for corrosion inhibition process.The adsorption of inhibitors on the mild steel surface obey Langmuir adsorption isotherm. The surface analysis of uninhibited and inhibited mild steel samples was performed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). Quantum chemical parameters calculated by Density functional theory (DFT) were correlated with the experimental results.