Experimental studies on the corrosion inhibition performance of 2-(2-aminophenyl)benzimidazole for mild steel protection in HCl solution

Abstract

BackgroundMild steel is one of the most widely used material in industry. However, this metal easily corrodes specifically in acidic solutions. Therefore, protection of this metal in this solutions is essential. There are many protection methods. The use of corrosion inhibitors is one of the widely them, which is a rapid, relatively easy and economical method. The choice of 2-(2-aminophenyl)benzimidazole (APBI) for this aim was based on its molecular structure, which bringing three N atoms and conjugated bonds as adsorption centers, and being a friendly compound. MethodsThe corrosion inhibition and adsorption properties of APBI on mild steel (MS) in 1 M HCI were studied by potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The MS surface was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The potential of zero charge (Epzc) of the steel in the presence of the inhibitor was determined by EIS method and an adsorption process was discussed. The effects of temperature and exposure time on the corrosion of MS were also reported. Significant findingsIt was found that the average inhibition efficiency of ABPI on the corrosion of MS determined from three electrochemical techniques is 98.8% in 1 M HCl solution. The high inhibition efficiency was assigned to its adsorption on the steel surface and forming a protective organic film. The PP studies showed that the corrosion current densitiy reduced almost 99% and open circuit potential moved from -0.48 V to -0.439 V in the presence of 10 mM inhibitor, which indicates a mixed type corrosion inhibition effect. SEM images showed good surface coverage of the inhibitor. The average percentage ratios of N and CI− on the metal which exposed to the inhibited solution were 0.97 % and 2.44 %, respectively. EDX mapping images indicated that the inhibitor distributed very homogenously. The adsorption of APBI on the mild steel surface in the corrosive solution was found to obey the Langmuir adsorption isotherm. The average value of equilibrium constant (Kads) and standard free energy of adsorption of the inhibitor (∆Goads) were found as 20.58 M−1 and -34.56 kJ mol−1, respectively. The activation energy (Ea) values are 77.28 kJ mol−1 and 78.00 kJ mol−1 for the corrosion process in the presence and absence of APBI, respectively. The CA and CV results clearly show that the inhibitor molecules are tightly adsorbed on the steel surface and form a very stable film.