Aqueous Extract of Vitex negundo Leaves as Green Corrosion Inhibitor for the Protection of Carbon Steel in 1N HCl Solution

The corrosion inhibition of carbon steel in 1N HCl containing aqueous extract of Vitex negundo leaves (VNL) has been studied using chemical techniques (Weight loss and gasometric methods) and electrochemical techniques (Electrochemical Polarization and electrochemical impedance studies). At the best concentration of 800 ppm of VNL extract provides 79.2% of the inhibition efficiency on carbon steel. The effect of acid concentration on the corrosion reaction showing first order without changing the reaction mechanism, and the results showed that when the concentration of VNL extract increased the rate of carbon steel corrosion is decreased, which indicates that the inhibition of the corrosion process is produced. Electrochemical impedance analysis results showed that the corrosion inhibition of carbon steel occurred mainly by charge transfer. The electrochemical results of polarization showed that the extract of VNL plant act as a mixed type inhibitor and they retarded both anodic and cathodic reactions. The experimental results from chemical and electrochemical studies were fit Langmuir isotherm. Values of the equilibrium constant of adsorption and the standard free energy of adsorption for the extracts are also calculated.