Understanding of benzimidazole based ionic liquid as an efficient corrosion inhibitor for carbon steel: Experimental and theoretical studies

Abstract

This work is focused on corrosion inhibition of N,N’-bis(carboxilic methyl)benzimidazolium based ionic liquid (IL) for carbon steel. Electrochemical polarization Tafel lines are nearly constant, generating H2 at electrode (M + HCl → Mn+ + H2 + Cl); however, the reaction has been largely inhibited by Imidazole (IMD), Benzimidazole (BMD) and N,N’-bis(carboxilic methyl) benzimidazolium catio (IL) since the blank current density (3.86 × 10-3 A/cm2) was reduced significantly to 1.95 × 10-5 A/cm2 for IL (5.0 mM), following as IMD (∼50%) < BMD (∼80%) < IL (∼95%). In impedance spectroscopy, the solution resistance (Rsol, 20 Ω-cm2 for blank) was increased to 23.54 Ω-cm2 for IMD, 23.6 for BMD and 28.43 Ω-cm2 for IL since the loop diameter was augmented greatly if the IL concentration was increased. A greater charge transfer resistance (Rct, 831.1 Ω-cm2) was obtained for IL at 0.5 mM as compared to IMD (134.8 Ω-cm2) and BMD (127.2 Ω-cm2), reaching a maximum of 1347 Ω-cm2. The corrosion inhibition of IL on the electrode was analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy Dispersive X-ray spectrometer (EDS), revealing that the corrosion-holes caused by HCl were covered neatly by IL, consisting with the EDS as Fe (60.2 %, O 22.9% for blank) was improved to 76.0, 80.5, and 87.3% %, for IMD and BMD and IL, respectively. The interaction of IL with iron surface was studied theoretically, observing the delocalization of imidazoline in IL, corroborating with Natural Transition Orbitals (NTOs), Electron density contour, molecular orbital and Density of Sates (DOS) studies.