Corrosion inhibiting performance and mechanism of protic ionic liquids as green brass inhibitors in nitric acid

Abstract

Four protic ionic liquids (ILs) were synthesized via a one-step method by using benzotriazole (BTA) and benzimidazole as cations, and benzenesulfonic acid and 2-naphthalenesulfonic acid (NSA) as anions. These ILs were used as green corrosion inhibitors for brass specimens in a nitric acid solution. The structure of the protic ILs was characterized by 1H-NMR, 13C-NMR, and FT-IR spectroscopy. The effects of the IL structure, IL concentration, acid concentration, and corrosion time on the surface morphology of brass specimens and the inhibition efficiency (η%) of ILs were investigated by the weight loss method combined with SEM and EDS spectroscopy. Polarization curves and impedance spectroscopy were used to analyze the electrochemical corrosion inhibition mechanism of ILs. Results showed that IL synthesis was a proton transfer process, and the proton of the –SO3H group on NSA was deprived by BTA. IL [BTA][NSA], which had a high charge density and large conjugate π band, was the most effective inhibitor for brass corrosion. The η% of [BTA][NSA] decreased with the increase in acid concentration and corrosion time, which showed an increment with the increase in [BTA][NSA] concentration. The higher the η% of [BTA][NSA] is, the smoother the surface of the brass specimens is, and the smaller the undistributed area of Cu element will be. Corrosion inhibiting mechanism from electrochemical analysis indicated that the addition of [BTA][NSA] increased the polarization resistance of the brass electrode significantly and suppressed both anodic and cathodic reactions.