Abstract
This study investigates the effect of a quinoxaline namely ethyl 2-(4-(2-ethoxy-2-oxoethyl)-2-p-tolylquinoxalin-1(4H)-yl) acetate (Q3), on corrosion inhibition of carbon steel in 1.0 M HCl. Electrochemical impedance measurement, potentiodynamic polarization and weight loss methods were applied to study adsorption of Q3 at metal/solution interface. Some quantum chemical parameters and the optimized structure of Q3 were calculated using the B3LYP/6-31G (d,p) basis. Results revealed that Q3 is an excellent inhibitor for carbon steel corrosion in 1.0 M HCl; showing a maximum efficiency 97.4% at concentration of 10-3M. Values of inhibition efficiency obtained from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) are in good agreement. Polarization curves show that Q3 behaves as a mixed-type inhibitor in hydrochloric acid. EIS shows that charge-transfer resistance increase and the capacitance of double layer decreases with the inhibitor concentration, confirming the adsorption process mechanism. Its was shown that adsorption is consistent with the Langmuir isotherm for 308K. The negative free energy of adsorption in the presence of Q3 suggests chemisorption of quinoxaline molecules on the steel surface. Results obtained from theoretical study were found to confirm experimental findings.