Abstract
The inclusion of zirconium precursors in the preparation of organosilane sol-gel coatings has been acknowledged to improve the corrosion protection performance of such coatings on aluminium and steel. Due to the inherent differences in the hydrolysis rates of the silane and zirconium precursors, various ligands were used to control the hydrolysis by decreasing the number of reactive alkoxide group. Hybrid sols were synthesised using 3-(trimethoxysilyl) propylmethacrylate (MAPTMS) and zirconium n-propoxide which was chelated with organic ligands. The selection of ligands included different organic acids, acetyl acetone and 2 2' bipyridyl. The effects of zirconia inclusion on the properties of the coatings were compared on the aerospace alloy AA 2024-T3. Dynamic light scattering (DLS) was used to measure the sol-gel particle diameter, while differential scanning calorimetry (DSC) and atomic force microscopy (AFM) were used to study thermal network stability and the surface morphology of the coating respectively. Potentiodynamic scan (PDS) and electrochemical impedance spectroscopy (EIS) were used to characterize the protective properties of the coatings, while neutral salt spray (NSS) tests were used to evaluate the coatings in an aggressive corrosive environment. The results indicate that acid chelated systems possess better corrosion protection when compared to the other ligands, due to smaller zirconium nanoparticles being formed thereby leading to improved film formation. In particular superior performance was displayed by the coatings involving 3,4 diaminobenzoic acid (DABA) due to inherent anticorrosive properties
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