Composition, structure and morphology of hybrid acrylate-based sol-gel coatings containing Si and Zr composed for protective applications

The role is reported of zirconium tetrapropoxide (ZTP) and methacrylic acid (MAA), following their combination with sol synthesized from tetraethyl orthosilicate (TEOS) and 3-methacryloxypropyl trimethoxysilane (MAPTMS). The molar content of ZTP was varied between 0.06 and 0.96 and that of MAA between 0.12 and 1.92. The synthesized sols were deposited as coatings on aluminium substrates. The effects of ageing of sols and curing of the coatings were examined. The composition of the sol, ageing process and size distribution of the particles, the thermal stability of the sols and coatings, the phase composition and microstructure of the coatings and contact angle of the water drop at the coating surface were all investigated. Comparison of sols, using Fourier transform infrared spectroscopy, confirmed important differences in terms of the presence of Si-O-Zr and chelated ZTP-MAA bonds. The three sols studied differ significantly in their ageing behaviour, as shown by dynamic light scattering. Thermogravimetric analysis and analysis of vapour side products during the curing process confirmed the effect of sol composition on the mass loss at elevated temperatures. Morphology, phase composition and structure of the coating were analysed with scanning and transmission electron microscopy, atomic force microscopy and X-ray diffraction analysis. The coatings possess a homogeneous and amorphous structure, without the formation of nanoparticles. Synthesized coatings offer high corrosion protection of aluminium under simulating aircraft conditions. (C) 2015 Elsevier B.V. All rights reserved.