Corrosion Inhibition of Aluminium Alloy by Eco-Friendly Biosurfactants

摘要

Rhamnolipids are a class of glycolipid derived from pseudomonas aeruginosa bacteria and are amongst the best characterised of the bio-surfactant materials. The influence of this substance on the corrosion of an aerospace Al-Cu-Mg alloy (D16T, equivalent to AA2024) using electrochemical methods supported by quantum-chemical calculations was studied. It was established that the rhamnolipid biosurfactant and its complex with polysacharide effectively inhibit corrosion of the alloy in synthetic acid rainwater. The efficiency of inhibition becomes stronger with the increase of biosurfactant concentration however above the critical micelle concentration further improvement in inhibition is minor. It is believed that the mechanism of corrosion inhibition is related to the adsorption of the biosurfactant molecule on the aluminium alloy surface and the formation of a barrier film however, the formation of a complex compound (salt film) between aluminium ions and rhamnolipid on anodic sites of the alloy is not ruled out. In the case of surface mechanical activation of the alloy, the biosurfactant molecule effectively prevents corrosion. Furthermore, addition of the biosurfactant to the corrosion environment increases the re-passivation kinetics of the alloy by 2-4 times as compared with an uninhibited environment. The biosurfactant can form synergistic inhibiting compositions with some inorganic compounds.