Aqueous root extract of Salvadora persica (ARESP) was studied as a new green corrosion inhibitor for mild steel (MS) in 1.0 N sulfamic acid solutions by using mass loss and electrochemical techniques at temperatures ranging from 303 to 333 K. Appropriate equivalent circuit model was used to calculate the impedance parameters. The electrochemical impedance spectroscopy (EIS) measurements showed that the charge transfer resistance increases with an increase in the concentration of ARESP. The results obtained from the new technique electrochemical frequency modulation (EFM) indicated that ARESP acts as mixed type of inhibitor. The protection efficiency increases with the increase in inhibitor concentration and decreases with temperature. The results of the study revealed that ARESP inhibits the corrosion of MS through adsorption process following Temkin adsorption isotherm model. The apparent activation energy (Ea) and the equilibrium constant of adsorption (Kads) were calculated. Scanning electron microscopy (SEM) was used to investigate the adsorbed film of ARESP on the steel surface.
Acid cleaning, Sulfamic acid, Corrosion inhibition, Mass loss, EIS, EFM