Inhibitory power of N,N´-(1,4-phenylene)bis(1-(4- nitrophenyl)methanimine) and the effect of the addition of potassium iodide on the corrosion inhibition of XC70 steel in HCl medium: Theoretical and experimental studies

Abstract

The inhibitory efficacy of N,N´-(1,4-phenylene)bis(1-(4-nitrophenyl)methanimine) (PNM) and its synergistic effect with KI on corrosion of XC70 steel in 1.0 M HCl solution have been studied by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The results show that the percentage of inhibition of XC70 steel in 1.0 M HCl solution increases with the increase of the concentration of PNM and reaches 84% at 1.0∙10–4 M PNM as an optimal concentration of this inhibitor. It was found that the percentage of inhibition of XC70 steel increases with the addition of KI to the optimal concentration of PNM in 1.0 M HCl solution, reaching 94% with a concentration of 7.5 mM of KI. This inhibitor N,N´-(1,4- phenylene)bis(1-(4-nitrophenyl)methanimine) (PNM) may form a film which acts as a barrier decreasing the contact area between the XC70 surface and the HCl solution. PNM acts as cathodic inhibitor in HCl solution without modifying the mechanism of hydrogen evolution. From the EIS examination, we notice that with an increase in the concentration of PNM, the double layer capacitance decreased, but the charge transfer resistance increased. Thermodynamic parameters of activation and adsorption were calculated and explained. The sign of the free energy of adsorption implies that the adsorption process is spontaneous. The surface morphology of XC70 was examined by employing the SEM technique. Finally, the quantum chemical parameters were calculated by the Density Functional Theory (DFT) method and a Monte Carlo simulation was used to find the equilibrium configurations of the inhibitor/Fe(110) adsorption systems in the presence of water molecules. The results obtained by all the methods are in good harmony.