Inhibition of mild steel corrosion in 0.5 M sulfuric acid by an aqueous extract of leaves of Tectona grandis L. plant

Inhibition of corrosion of mild steel in 0.5 M sulfuric acid by an aqueous extract of leaves of Tectona grandis L. plant has been investigated by weight loss method. The mechanistic aspects of corrosion inhibition have been studied by electrochemical studies such as potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). It is observed that as the concentration of the inhibitor increases the corrosion rate decreases and the inhibition efficiency increases. This is due to adsorption of the molecules of the active ingredients of the extract on the metal surface. A maximum inhibition efficiency of 96.70% is achieved by this inhibitor system. Potentiodynamic polarization technique reveals that the inhibitor system functions as a mixed type of inhibitor, controlling anodic reaction and cathodic reaction to an equal extent. It is noted that, in presence of inhibitor, linear polarization resistance value increases, and corrosion current decreases. Electrochemical impedance studies reveal that a protective film (blanket effect) is formed on the metal surface, since in the presence of inhibitor system the charge transfer resistance value increases and double layer capacitance value decreases. The surface morphology of the protective film has been studied by SEM and AFM. The outcome of the study can be used in pickling industry, where sulfuric acid is used to remove the rust on the mild steel surface.