Trigona Sp. And Apis Sp. Honey As Natural Corrosion Inhibitor For Aluminium Alloy In 1 M Phosphoric Acid
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Date
2016-09
Authors
Sulaiman, Nur Izzana
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Abstract
Two types of honey samples, stingless bee honey (Trigona sp.) and natural honey (Apis sp.) were selected and studied as aluminium alloy corrosion inhibitor in 1 M phosphoric acid (H3PO4). The characterization studies have been conducted to determine the heteroatoms in honey that are responsible for inhibition process. Fourier transform infrared (FTIR) spectroscopy results suggest the presence of important functional groups that fulfilled the requirement as a potent organic corrosion inhibitor. The analysis of both honeys by liquid chromatography mass spectrometry with a reversed phase C18 column was done and the analysis showed evidence on the presence of p-coumaric acid, one of the phenolic compounds that has the highest antioxidant capacity. The phenolic content and antioxidant capacity showed stingless bee honey have the highest content compared to natural honey. The percentage inhibition efficiency (IE %) of the honeys were investigated in 1 M H3PO4 by means of weight loss method, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurement. These analysis showed IE % for both honeys increased with the increasing of the concentration of honeys. Potentiodynamic polarization method gave the highest IE %, which were 78.6 % for stingless bee honey and 73.9 % for natural honey at optimum concentration (1500 ppm). Potentiodynamic polarization measurement indicated that the inhibitors act as mixed type inhibitors with predominant anodic inhibition. EIS measurement showed that the corrosion of aluminium alloy with and without inhibitors was mainly
controlled by a charge transfer process. Pitting corrosion was investigated by using cyclic polarization, which revealed that the area of the hysteresis loop of the 1 M H3PO4 solution without inhibitors was larger than that of the inhibitors. Thus, it indicated that the intensity of pitting corrosion was smaller in the 1 M H3PO4 with honeys when compared to the aluminium alloy without honeys. Weight loss measurements at different temperatures showed that the inhibition efficiencies for stingless bee honey and natural honey decreased as the temperature increased. The adsorption isotherm study revealed that the inhibitor follows Langmuir adsorption model. Based on the potential zero charges (PZC) it indicated that the adsorption on the aluminium alloy surface was by physical adsorption. The scanning electron micrographs showed that the surface of the aluminium alloy had improvement in the presence of the stingless bee honey.
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The heteroatoms in honey that are responsible , for inhibition process.