Effect of lemon juice as an eco-friendly additive on the microstructure and corrosion properties of anodized alumina layers

Abstract

The challenge of anodizing processes is to decrease the chromate compounds or other poisonous materials from the anodizing bath in a way that the performance of oxide layers does not change. Therefore, in this study, a new anodizing bath was developed to create the alumina layers. The new bath contained an H2SO4 solution with an eco-friendly additive. This additive was lemon juice (which contained natural citric acid) at various concentrations (0.3 to 2.5 vol%). Field-emission scanning electron microscopy (FESEM) was used to investigate the microstructural evaluations. Tafel polarization and electrochemical impedance spectroscopy (EIS) were also utilized to study the corrosion behavior of the alumina layers on aluminum substrates. The obtained results depicted that the presence of the bio-additive in the anodizing bath caused a reduction in corrosion rates of alumina layers by approximately 90.2 to 100% compared to the layer manufactured without additive. EIS measurements showed an increase in impedance of modified alumina layers by approximately 46%–71% in 0.6 M NaCl solution. Optimum corrosion properties were related to the modified alumina layer when the additive concentration in the anodizing bath was approximately 1.8 vol%. Since it contained low porosity with a value of 3.8% and a thick barrier layer with a thickness of 21 nm.