EIS and noise study of zirconia-alumina- benzotriazole nano-composite coating applied on Al2024 by the sol-gel method

Abstract

Nano-composite coatings containing corrosion inhibitors increase the protection against corrosion and wear of aluminum and aluminum alloys. Although zirconia-alumina coatings have commercial applications because of the high corrosion resistance and appropriate mechanical properties; their performance is undermined by defects such as holes, pores, and micro-cracks. Corrosion inhibitors can reduce the amounts of defects in the coatings by repairing them with the aid of corrosion products. In this work, zirconia-alumina-benzotriazole coatings are deposited on Al2024 substrates by the sol-gel technique and the phase, structure, and morphology of the homogenous and crack-free coatings with a thickness of 950 nm and surface roughness of 0.276 nm are investigated in details. The corrosion properties are evaluated by electrochemical noise, potentiodynamic test and electrochemical impedance spectroscopy after immersion in 0.05 M NaCl solutions for 1, 2, 3, 4, 5, and 6 h. The open circuit potential variation observed from the zirconia-alumina-benzotriazole coating is less than that of the zirconia-alumina coating due to the more effective protection layer. And also the changes in the current as well as potential at different frequencies before and after the polarization test indicating that the release rate of benzotriazole shows the same healing behavior which is affected by the extent of the corrosion reactions. Benzotriazole decreases icorr by more than 31% and 84% compared to zirconia-alumina and Al2024, respectively. Benzotriazole enhances the corrosion resistance by reacting with oxygen to form corrosion products consequently delaying the cathodic reactions and improving the properties of the double layer.