The effects of aging time on the sol-gel properties and its relationship with the anti-corrosive performance of coatings prepared by sol-gel dip coating

This work evaluated the changes in the physicochemical properties (viscosity, surface tension, and zeta potential) of both alumina sol and boehmite solution at different aging times and their relationship with the corrosion resistance (in a saline solution) of the alumina film/boehmite conversion coating/carbon steel substrate systems prepared by sol-gel dip coating. The boehmite solution did not show significant changes in physicochemical properties throughout the studied time. As a result, the electrochemical behavior of the coating systems was independent of the aging time used to pretreat the substrate with the boehmite solutions. On the other hand, the changes in the physicochemical properties of the alumina sol with age were observed since the second week, causing an increase in the thickness (from 3.06 to 5.10 μm) and a decrease in the charge transfer resistance (from 138 to 30 kΩ cm2) of the systems. The most intense solvent evaporation effect and the macromolecules formed due to hydrolysis and condensation reactions during the studied aging period affected the properties of the alumina sol, leading to more heterogeneous and defective films when produced from sols with longer aging times.