Investigation of adsorption, corrosion inhibition, synergistic inhibition effect and stability studies of Rheum ribes leaf extract on mild steel in 1 M HCl solution

Due to high cost, toxicity of conventional inhibitors and environmental regulations, corrosion scientists have directed toward plant extracts as alternatives to conventional inhibitors. In this study, leaf extracts of Rheum ribes (RR leaf) were prepared, and their adsorption and protective effects on mild steel (MS) corrosion were investigated in 1.0 M HCl solution. The synergistic inhibition effect of iodide ions and the stability of surface inhibitor film were also studied. The protection ability of extract was investigated using electrochemical techniques. The stability of surface film was evaluated by potentiodynamic and potentiostatic studies. After being exposed to the corrosive medium, the surface of metal was examined using SEM, EDX, AFM and contact angle measurements. The extract molecules formed an adherent and homogenous protective film on the MS surface. When the RR leaf extract concentration increased, a stronger inhibition effect against corrosive attack was obtained. At 1000 ppm extract concentration, the protection efficiency of RR leaf extract increased from 91.8% to 94.9% when 1000 ppm KI was added to the inhibited acid solution. The extract molecules adsorbed to the metal surface via physical and chemical interactions. The surface extract film was very stable under potentiostatic or potentiodynamic conditions.