Inhibitive action of moringa oleifera seed pod extract for the corrosion of aluminium in 1.0 m hydrochloric acid (HCl) solution
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Date
2018-06
Authors
Kisheelah Rakavan
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Abstract
Aluminium is most widely used metal after iron in the industries like construction, aerospace, chemical, mechanical and others. However, it showed corrosion behaviour in aggressive environments such as highly acidic or alkaline media. There are numerous methods that have been explored to prevent corrosion of aluminium in aggressive media. One of the most environmental friendly methods is using natural products like plant extracts to inhibit corrosion. In this research study, the inhibitive action of M. oleifera seed pod extract on aluminium corrosion in 1.0 M hydrochloric acid (HCl) solution was studied using weight loss technique. The percentage of inhibition efficiency was found to be increasing with the increasing inhibitor concentration. M. oleifera seed pod extract exhibited the maximum inhibition efficiency, η (%) of 96.4% at 1.8g/L (optimum concentration) under room temperature (289 K). The effect of temperature on the corrosion behaviour of aluminium in HCl solution with addition of optimum extract concentration was also studied. The result revealed that the percentage of inhibition efficiency decreases as the temperature increases in the range of 303 K – 343 K. The characterization study of M. oleifera seed pod extract was carried out using Gas Chromatography Mass Spectrometry (GCMS) and Fourier Transform Infrared Spectroscopy (FTIR). The results depicts that the compound responsible for the inhibitive action is fatty acid compounds. In addition, the inhibition occurred via adsorption of the inhibitor molecules on the aluminium surface obeying the Langmuir adsorption isotherm. Besides, thermodynamic parameters such as activation energy (Ea), enthalpy (∆H ∗ ) and entropy (∆S ∗ ) of activation for corrosion process as well as free energy of adsorption value (ΔG°ads) were calculated and discussed. The value of Ea, ∆H ∗ and ∆S ∗ and ΔG°ads obtained in the presence of inhibitor was 101.27 kJ/mol, 98.63 kJ/mol, 101.48 kJ/mol and -19.01 kJ/mol respectively. These calculated values revealed that the adsorption process are endothermic, spontaneous and the inhibitor molecules were adsorbed on the aluminium surface through physisorption. Thus, it can be concluded that the seed pod extract of M. oleifera could serve as an effective inhibitor of the corrosion of aluminium in HCl solution.