Nano-TiO2 Coating Layers with Improved Anticorrosive Properties by Aerosol Flame Synthesis and Thermophoretic Deposition on Aluminium Surfaces.

TiO2 in the form of nanoparticles is characterized by high photocatalytic activity and high resistance to oxidation, making it an excellent candidate to realize coatings for improving the corrosion resistance of aluminium surfaces. Different coating technologies have been proposed over the years, which often involve the use of toxic compounds and very high temperatures. In this work, an alternative and novel one-step method for the coating of aluminium alloy surfaces with titania nanoparticles is presented. The method is based on the combination of aerosol flame synthesis and direct thermophoretic deposition and allows to produce nanostructured thin coating layers of titania with different features. Specifically, 3.5 nm anatase nanoparticles were synthesized and deposited onto aluminium alloy AA2024 samples. The thickness of the coating was changed by modifying the total deposition time. A thermal annealing treatment was developed to improve the adhesion of nano-titania on the substrates, and the morphology and structures of the coatings were characterized using (ultra violet) UV-vis absorption, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The corrosion resistance behavior of the coatings was evaluated by means of electrochemical polarization measurements, coupled with a numerical analysis using COMSOL software. Both the experimental and numerical electrochemical polarization curves showed a significant increase in the corrosion potential of coated substrates with respect to the bare aluminium and a decrease in the current density. The coatings obtained with higher deposition time and greater thickness showed the best performances in terms of the resistance of the aluminium surfaces to corrosion.