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Abstract
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.
Highlights
Aluminium alloys represent today a primary choice for the manufacturing of structural components, due to their peculiar characteristics such as high mechanical properties, low specific weight and the ease of manufacturing [1,2]
Thermophoretic deposition of the flame-formed nano-TiO2 particles is based on a rotating disk system that allows metal substrates to be inserted in the flame by a fast insertion procedure that maintains the substrate at room temperature
This paper presented a technology based on a one-step method for the coating of aluminium alloy surfaces with nanostructured coating layers of TiO2 using a combination of aerosol flame synthesis and direct thermophoretic deposition
Summary
Aluminium alloys represent today a primary choice for the manufacturing of structural components, due to their peculiar characteristics such as high mechanical properties (damage tolerance and tensile strength), low specific weight and the ease of manufacturing [1,2]. A key point in designing structural components made of aluminium alloys is the protection from corrosion, since aluminium alloys could be very sensitive to corrosion [3]. To this aim, surface treatments are widely used since they could lead to an improvement of the electrochemical properties of aluminium-made surfaces without significant mechanical performance losses [4]. Coatings made by TiO2 nanoparticle are highly attractive due to the excellent chemical stability and low toxicity of titania even in the form of nanoparticles and the high compatibility with aluminium alloys [5,6,7,8,9]. Conversion coating processes, such as chromate conversion and anodic oxidation, involve the use of hexavalent chromium compounds, which are very toxic and dangerous for both the environment and human health [10]
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