Aluminum Corrosion Inhibition by 7-(Ethylthiobenzimidazolyl) Theophylline in 1M Hydrochloric Acid: Experimental and DFT Studies

Inhibitive properties of 7-(ethylthiobenzimidazolyl) theophylline (7-ETBT) molecule for the corrosion of aluminum (Al) in one molar hydrochloric acid medium have been investigated using mass loss and Tafel polarization methods. The results suggest spontaneous and predominant physical adsorption of 7-ETBT on the metal surface which obeys Langmuir isotherm model. The studied inhibitor showed excellent inhibition efficiency up to 94.07 % at 298 K for its optimum concentration (2 mM). Moreover, Tafel polarization method revealed that 7-ETBT is a cathodic-type inhibitor. Further investigation on the morphology using scanning electron microscopy (SEM) has confirmed the existence of a protective film of inhibitor molecules on aluminum surface. Theoretical approach for the performance of 7-ETBT as Al corrosion inhibitor is also done using Density Functional Theory (DFT) level with B3LYP exchange correlation functional for 6-31G (d, p) basis set. The results provided by this theoretical study are consistent with the experimental data. All the results have shown an evidence of the effectiveness of the inhibitive effect of 7-ETBT on Al.