Investigation of high concentration of benzotriazole on corrosion behaviour of titania–benzotriazole hybrid nanostructured coating applied on Al 7075 by the sol–gel method

Abstract

Nowadays, surface modification with self-healing ability is a valuable technique to improve chemical stability, oxidation behaviour and corrosion resistance of materials without interference with its physical, chemical or mechanical properties of bulk material underneath. In this paper, hybrid organic amorphous titania coatings are deposited on 7075 aluminium alloy substrates by using the sol–gel method. A titania–benzotriazole (BTA) nanostructured hybrid sol–gel coating is impregnated with three different high concentrations of BTA, 1.4, 2.8 and 4.2%. The bonds existing in the hybrid coating, structure and morphology and coating corrosion behaviour have been studied using the FTIR, GIXRD, field emission scanning electron microscopy and electrochemical impedance spectroscopy (EIS) test in a 3.5 wt-% NaCl solution during different immersion times, 24, 48, 72, 96 and 120 h. EIS studies indicated that a higher coating resistance value was gained for titania–4.2% BTA even after 120 h of immersion and BTA acted mainly on the amorphous titania coating as a corrosion inhibitor and a healing agent that acts by two mechanisms: first, release of a healing agent to the formation of corrosion products, then finally blocking surface defects; second, release of a healing agent during 48 h of immersion and its adsorption to produce an insulating layer on the surface of the coating in contact with the solution.