Electrochemical and Theoretical Studies of Novel Quinoxaline Derivatives as Corrosion Inhibitor for Mild Steel in HCl Solution

Two substituted quinoxaline derivatives, namely diethyl 2,2-(2,3-dioxo-2,3- dihydroquinoxaline-1,4-diyl)diacetate (QX-H) and diethyl 2,2-(6-methyl-2,3-dioxo-2,3- dihydroquinoxaline-1,4-diyl)diacetate (QX-CH3), were tested as a corrosion inhibitor for mild steel in 1.0 M HCl solution using weight loss, Tafel polarization and electrochemical impedance spectroscopy (EIS). The experimental results reveal that the studied compounds have good inhibiting effects of mild steel corrosion in 1.0 M HCl medium. It is found that their inhibition efficiency increases with their concentration to reach a maximum at 10-3 M and they are acting as mixed type inhibitors. So, the inhibition efficiency was increased with inhibitor concentration in the order QX-CH3>QX-H which depended on their molecular structures. It has been determined that the adsorption of these compounds on mild steel surface complies with the Langmuir adsorption isotherm. However, in order to get information on bonding mechanism of mild steel surface/ inhibitors/1.0 M HCl solution system, the corrosion protection was also investigated by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS). Finally, the experimental obtained results were confirmed by the theoretical study.