Abstract

In the present work the influence of the two organic inhibitors, namely : phenyl (2- (3,4,5 trimethoxyphenyl) -1H-benzo [d] imidazol-1-yl) methanone (P3) and ( 2- (4 -methoxyphenyl) -1H-benzo [d] imidazol-1-yl) (phenyl) methanone (P4) on the ordinary steel corrosion in 5.0 M HCl solution was investigated by using electrochemical measurements, scanning electron spectroscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDX), UV-visible spectroscopy and theoretical study. The obtained results showed that these compounds act as mixed inhibitors. It is obtained that the inhibition efficiency increases with their concentrations and reaches 97.0% and 91.3% at 10⁻³ M of P3 and P4, respectively. These findings were confirmed by the electrochemical impedance spectroscopy measurements, where the transfer resistance values increase with the concentrations. In addition, the effect of temperature range from 298 K to 328 K was investigated and indicated that P3 and P4 keep their performance at height temperature. Moreover, density functional theory explained the relationship between the molecular structure of imidazole derivatives and inhibition performance obtained experimentally. Additionally, the morphological surface and EDX analyses indicated that these compounds act by the formation of a protective layer on the ordinary steel surface. In order to confirm the possibility of the formation of P3-Fe and P4-Fe complexes, the UV–Visible absorption spectra was used. The obtained results indicated the formation of a complex between Fe²⁺ and molecules inhibitors.

Keywords:
Imidazole derivatives; Ordinary steel; Corrosion inhibition; 5 M HCl; DFT calculations; SEM/EDX analyse; UV–visible spectroscopy