Characterization of thin water-based silane pre-treatments on aluminium with the incorporation of nano-dispersed CeO2 particles

Thin silane films with the incorporation of nano-dispersed CeO2 particles have been deposited by dip-coating over aluminium substrates. The silane molecule under investigation is bis-1,2-(triethoxysilyl)ethane (BTSE), which has been used as a water-based solution in order to fulfill the industry need for reducing the impact on human health and environment. The influence of the nano-oxides on the silane was first analyzed in the solution by means of 29Si NMR, which showed that the ageing and stability of BTSE are not affected by the presence of CeO2 nanoparticles in the silane matrix. The chemical interactions between CeO2 nanoparticles and the BTSE in the cured coating were investigated by XPS, and the results pointed to the possible formation of a bond between Ce and Si. Field emission scanning electron microscopy (FE-SEM), field emission Auger electron spectroscopy (FE-AES) and focused ion beam coupled with transmission electron microscope (FIB–TEM) were used to investigate the film structure and surface morphology. A major challenge in the formation of thin layers with the incorporation of nano-oxides is to avoid the formation of particles agglomeration, which affects the film uniformity and might create preferential paths for corrosion attack. This issue has been overcome and the resulting films appear uniform and homogeneous, with the nanoparticles well embedded in the silane matrix and always covered by a thin silane layer. Electrochemical impedance spectroscopy (EIS) measurements have been performed on the samples and the results show how the barrier properties of the thin silane films are improved by the addition of CeO2 nano-dispersed particles.