Corrosion Inhibition of Aluminum in Acidic Medium by Bamboo Leaves Extract
The inhibitive effects of bamboo leaves extracts (BLE) on the corrosion
of aluminum in 1M HCl were studied using weight loss, adsorption, thermodynamics and kinetic studies. The phytochemical constituents of the BLE were tannins, polyphenols, flavonols, terpenoids, sterols and alkaloids. BLE was noted to contain more of the polyphenols and terpenoids which were largely responsible for the inhibitive action of the extracts. Results obtained from the experiments carried out at 303K and 333K revealed that, the corrosion rate decreased as the concentration of BLE increased. The inhibition efficiency increased as the concentration of BLE increased at 333K. As the temperature increased from 303K to 333K, the corrosion rate increased significantly. The adsorption parameters showed that the adsorption of the BLE conformed perfectly to the Langmuir, Temkin and Freundlich adsorption isotherms, with the Langmuir isotherm being the best model with R2 = 0.992. The negative values of Gibbs free energy indicated that the reaction was spontaneous and the mechanism of adsorption was electrostatic (physical) adsorption mechanism since the negative values of ΔG°ads were lower than -20 kJ/mol. The values of activation energy, Ea, being lower than 80 kJ/mol, also confirmed a physical adsorption mechanism. The values of heat of adsorption being lower than 40 kJ/mol, also confirmed that the adsorption mechanism was physisorption. The positive values of heat of adsorption, Qads indicated that the reaction was endothermic. The small values of adsorption equilibrium constant, Kads indicated low interaction between the adsorbed molecules and the metal surfaces and thus the extracts were physically adsorbed on the metal surfaces. The reaction showed a first order kinetics, since the plots of log Wf vs Time were linear for all the concentrations of the extracts. The increase in half-life as the concentration of the extract increased indicated more protection of the metals by the BLE.