Insights on the adsorption and corrosion inhibition behavior of Alstonia scholaris leaf extract for aluminium in acidic and basic medium

In recent years, natural extracts have been presented as effective and environment-friendly inhibitors for the corrosion of metals and alloys.This work, for the first time, reports the application of Alstonia scholaris leaf extract (ALE) on the corrosion inhibition behaviour of aluminium in HCl and NaOH solutions.A detailed corrosion evaluation was undertaken employing gravimetric, impedance analyses, polarization studies, and surface analytical measurements.The inhibition efficiency (%) increased with increasing inhibitor concentration, and the maximum efficiencies achieved were 93.1% and 59.7% at 1.2 gL -1 of ALE in HCl and NaOH, respectively.A considerable decrease in the corrosion rates was observed with the introduction of successive additions of various concentrations of ALE.Energy of activation increased in the presence of the inhibitor, revealing an increase in the energy barrier required to be overcome for the corrosion process to occur in the presence of inhibitor ALE.EIS studies revealed the existence of inductive loops in the Nyquist plots with two time constants in HCl and three in NaOH solutions.Potentiodynamic polarization curves justified the mixed mode of inhibition in both media and cathodic predominance in HCl.Inhibitor adsorption was in accordance with the Langmuir isotherm.Surface morphological analyses corroborated the electrochemical testing by revealing a protected surface of aluminium in both the media.These results validate the applicability of ALE as a green corrosion inhibitor for aluminium in acidic as well as alkaline environment.