Aluminium adalah salah satu logam yang kerap digunakan dalam industri pembinaan, aeroangkasa, mekanikal, kimia dan sebagainya. Namun begitu, aluminium menunjukkan sifat kekakisannya apabila didedahkan kepada bahantara agresif seperti media yang sangat berasid atau beralkali. Terdapat pelbagai cara yang diteroka untuk mencegah kakisan aluminium dalam bahantara agresif. Antara cara yang mesra alam untuk merencat kakisan aluminium adalah menggunakan produk semulajadi iaitu ekstrak dari tumbuh-tumbuhan. Dalam kajian ini, pencegahan kakisan aluminium dalam 1.0 M larutan asid hidroklorik (HCl) dengan ekstrak pod benih Moringa oleifera telah dikaji dengan menggunakan kaedah penurunan berat. Kajian ini menunjukkan bahawa peratusan kecekapan perencatan meningkat dengan peningkatan kepekatan ekstrak. Ekstrak pod benih M. oleifera mempamerkan kecekapan perencatan, η (%) yang maksima sebanyak 96.4 % pada 1.8 g/L dalam suhu bilik (289K) yang merupakan kepekatan ekstrak yang optimum. Selain itu, kesan suhu ke atas tingkah laku kakisan aluminium dalam 1.0 M HCl dengan penambahan kepekatan ekstrak optimum juga dikaji. Hasil kajian ini mendedahkan bahawa peratusan kecekapan perencatan menurun dengan peningkatan suhu dari 303K hingga 343K. Filem terjerap pada permukaan aluminium yang mengandungi M. oleifera daun ekstrak juga diukur oleh Kromatografi Gas – Spektrometri Jisim (GCMS) dan Spektroskopi Transformasi Fourier Infra Merah (FTIR). Keputusan yang diperolehi menunjukkan bahawa sebatian yang bertanggungjawab bagi perencatan kakisan ialah sebatian asid lemak. Tambahan pula, penjerapan ekstrak pod benih M.oleifera di atas permukaan aluminium mematuhi isoterma penjerapan Langmuir. Parameter termodinamik untuk proses perencatan tersebut seperti tenaga pengaktifan bagi penjeratan (Ea), entalpi (ΔH∗) dan entropi (ΔS∗) pengaktifan, tenaga bebas Gibbs (ΔG°ads) telah dikira and dianalisiskan. Nilai Ea, ΔH∗, ΔS∗ dan ΔG°ads yang diperolehi adalah 101.27 kJ/mol, 98.63 kJ/mol, 101.48 kJ/mol dan -19.01 kJ/mol masing-masing. Nilai tersebut menunjukkan bahawa proses penjerapan ini adalah tindak balas serap haba, spontan dan molekul perencat telah terjerap di atas permukaan aluminium melalui penjerapan fizikal. Dengan ini, kajian ini membuktikan bahawa ekstrak pod benih M. oleifera boleh menjadi perencat berkesan daripada kakisan aluminium dalam media larutan asid hidroklorik.
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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 (ΔH∗) and entropy (ΔS∗) of activation for corrosion process as well as free energy of adsorption value (ΔG°ads) were calculated and discussed. The value of Ea, ΔH∗ and ΔS∗ 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.
Inhibitive action of moringa oleifera seed pod extract for the corrosion of aluminium in 1.0 m hydrochloric acid (HCl) solution / Kisheelah Rakavan