Optimized silica-based hybrid coatings for the protection of aluminum against chloride-rich environment

Sol–gel hybrid coatings have become one of the dominant platforms intended for anticorrosion applications. In this study, hybrid (silica/epoxy) ceramic coatings were designed and prepared using the sol–gel technique. 3-Glycidyloxypropyl trimethoxysilane and diglycidyl ether of bisphenol A (epoxy) were used as the main precursors, while 3-Aminopropyl triethoxysilane was involved as a coupling agent (linker) in different ratios along with diethylenetriamine as a tertiary hardener responsible for the hybrids curing. The formation of the silica as an inorganic network, epoxy as an organic network, and the interconnection between them was confirmed using FTIR. The scanning electron microscopy was utilized for investigating the morphology of the processed coatings. Moreover, the adhesion and the hardness of the formed coatings were evaluated as critical features for epoxy. Besides, thermogravimetric analysis was used to assess the thermal properties in order to overcome one of the disadvantages of epoxy coatings. Electrochemical Impedance Spectroscopy was performed in order to measure the capability of each combination for protection against corrosion. It was proven that the morphology of the product would vary in a great deal depending on the silica content, which plays a vital role in determining the mechanical and thermal properties of these coatings. Improvements could be witnessed by increasing the silica content up to a specific limit (ranging from 15 to 20%). However, a further increase in the silica content will lead to a noticeable drop in the corrosion resistance capability.