Comparative study of the effect of an acidic anion on the mild steel corrosion inhibition using Rhus Coriaria plant extract and its quercetin component

The use of plant extracts as corrosion inhibitors has been increasing greatly in recent studies. The inhibitive effect of sumac, Rhus Coriaria (RC), a Lebanese plant, and Quercetin, one of its chemical constituents, on mild steel corrosion, in 0.5 M HCl and 0.5 M H2SO4 solutions, was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force spectroscopy (AFM) and Fourier infrared spectroscopy (FTIR) techniques. Potentiodynamic polarization curves indicated that both RC and its chemical constituent, Quercetin, behave as a mixed type inhibitor in both acidic media. The dissolution process of RC and Quercetin occured under activation control, as showed by EIS measurements, and the corrosion inhibition is the result of the inhibitor adsorption onto the metal surface. Inhibition by RC extract was found to be greater in 0.5 M HCl than in 0.5 M H2SO4 solutions; RC extract also proved to be a better inhibitor than its chemical constituent, Quercetin, in both acids. Thermodynamic parameters indicate that the inhibition process on the steel surface was due to spontaneous physical adsorption of RC and Quercetin onto it. The adsorption model was found to obey thermodynamic-kinetic model and Flory-Huggins model. Surface analysis by AFM spectroscopy investigated the formation of the adsorbed protective film onto the mild steel surface.