Effect of additives on the extract of henna by shellac coating for aluminium protection in seawater

Abstract

The effect of additives on corrosion behavior of Aluminium Alloy 5083 (AA5083) by using henna extract with shellac coating has been investigate with modified henna by using 1,3-propanediamine and glycerol at 5%, 10% and 15% of henna extract by using salt-spray test for 30 days. Start from surface preparation, produce the coating, coating process, laboratory work, weighing and collect data lastly the laboratory analysis. AA5083 was cut into 25mm x 25mm x 3mm and was polished manually using 600, 800 and 1200 grit of emery papers. Henna was extracted with ethanol as a solvent by using rotary evaporator (Rotavap). To investigate the content of extraction, a Fourier Transform Infrared Spectroscopy (FTIR) device was used. Six type of coating was produce which is coating with 5%, 10% and 15% of native henna and modified henna. The specimens were coated by immerse into each coating for 10 second and was dried. Specimen was coating by 5% of native henna was set for experiment control. The corrosion behavior was investigated using several methods which were weight loss measurement, potentiodynamic polarization measurement, Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscope (SEM). Calculations of inhibition efficiency for weight loss shows that the results indicates that the henna extract using ethanol solvent have good inhibition efficiency, IE(%). 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, (Cd,) decrease indicates that a layer was form indicating the formation of a surface film. This reflects the inhibitor does retard the corrosion rate. Image from SEM show when percentage of modified henna was increase, the corrosion was decrease because the particle of henna extract where acts as anti-oxidant was protecting the AA5083 surface. Extract Lawsone which is the main constituent of henna able to protect AA5083 for this experiment.