An Experimental and Theoretical Investigation of Adsorption Characteristics of a Quinoxaline Compound as Corrosion Inhibitor at Carbon Steel/Hydrochloric Acid Interface

摘要

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 wereapplied to study adsorption of Q3 at metal/solution interface. Some quantum chemical parameters andthe optimized structure of Q3 were calculated using the B3LYP/6-31G (d,p) basis. Results revealedthat Q3 is an excellent inhibitor for carbon steel corrosion in 1.0 M HCl; showing a maximum-3 efficiency 97.4% at concentration of 10 M. Values of inhibition efficiency obtained from weight loss,potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) are in goodagreement. 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 withthe inhibitor concentration, confirming the adsorption process mechanism. Its was shown thatadsorption is consistent with the Langmuir isotherm for 308K. The negative free energy of adsorptionin the presence of Q3 suggests chemisorption of quinoxaline molecules on the steel surface. Resultsobtained from theoretical study were found to confirm experimental findings.