Effect of henna at low concentration in methanol for the inhibition of aluminium in seawater

Abstract

Aluminium alloy type AA5083 shows excellent corrosion resistance mostly in seawater and industrial chemical environment. Nowadays, corrosion is entrenched in maritime industry where the ship plate undergoes corrosion and corrosion rate varies with different environment. As a remedy, natural inhibitor was used to overcome this problem. This study is used plant extract which is henna (Lawsonia Inermis).Henna was used in this study as an inhibitor towards AA5083. Henna was extracted with methanol as solvent by using rotary evaporator (Rotavap). Low concentration of henna which is lOOppm, 200ppm, 300ppm, 400ppm and 500ppm was used. While for immersion test, the powder form of henna was dissolved in the seawater with different concentration in separate tank. The samples were hang in the test solution for 60 days. The characterization of the corrosion was performed by using potentiodynamic polarization (PP), weight loss (WL), electrochemical impedance spectroscopy (EIS), fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The percentage of inhibition efficiency (%) and corrosion rate (CR) was calculated and this study showed that the corrosion rate increase by decreasing concentration of the henna extract. The value for charge transfer resistance, (Re,) increase as a result increase the degree of protection of AA5083 in test solution and double layer capacitance, (Cdt) decrease indicates that a layer was form indicating the formation of a surface film. This reflects the inhibitor does retard the corrosion rate. Extract Lawsone which is the main constituent of henna able to protect AA5083 for this experiment.