Evaluation of protection performances of novel synthesized bis-oxindole-based derivatives for the corrosion of aluminum in acidic environment

Three bis(3-schiff base-indoline-2-one) derivatives, 3(a-c), and two bis-spirotriazole-indole derivatives, 5(a,b), were synthesized and were evaluated as inhibitors for the corrosion of Al in 1.0 M HCl at 303 K. Weight loss (WL) method was applied for evaluation of the inhibition efficiencies (% IEs) of all synthesized compounds while WL in addition to potentodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were employed in case of the compound that has the highest% IE values. The collected results illuminated that the synthesized compounds were discovered to be efficient inhibitors and their% IEs were set to vary with their concentrations, structures, and the corrosive medium concentration. WL outcomes revealed that, the order of% IEs of the synthesized compounds was: 5a approximate to 5b > 3a > 3b >= 3c. The acquired high% IEs of such compounds were attributed to their potent adsorption on the Al surface and production of a protective film, and this adsorption was agreed with Langmuir adsorption isotherm. The kinetics of corrosion inhibition by the synthesized compounds appeared a negative-first order process confirming the gained higher values of% IEs of such compounds. PDP results indicated that the compound 5a behaves as a mixed inhibitor with a cathodic majority. The results acquired from the three utilized tools were set to be in a good agreement with each other's confirming the validity of the obtained results.