Acenaphtho[1,2-b]quinoxaline and acenaphtho[1,2-b]pyrazine as corrosion inhibitors for mild steel in acid medium

• AQ and AP are effective mixed type (cathodic/anodic) inhibitors in 1 M H2SO4.
• Inhibition efficiency of the compounds increases with increasing concentration.
• Adsorption of compounds on mild steel surface obeys Langmuir’s isotherm.
• Examination of surface morphology by SEM and AFM methods.
• Theoretical calculations provide good support to experimental results.

The corrosion inhibition of mild steel in 1 M H2SO4 using acenaphtho[1,2-b]quinoxaline and acenaphtho[1,2-b]pyrazine at 303–333 K have been investigated. The study was performed using weight loss method, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Polarization measurements proved that the inhibitors behave as mixed-type. EIS data showed that the charge transfer resistance of mild steel increases in acid solution containing inhibitors. The surface morphology was evaluated using scanning electron microscope (SEM), atomic force microscopy (AFM) techniques. Density functional theory (DFT) at the B3LYP/6-311G(d,p) basis set level was performed. Excellent correlation was found between experimental and theoretical results.