Nano-Tio2 Coatings of Aluminum Surfaces Produced by Aerosol Flame Synthesis

This work reports the development of a one-step method for the coating of aluminum surfaces with titania nanoparticles. Monodisperse, ultra-fine TiO2 nanoparticles were synthesized by Flame Aerosol Synthesis and directly deposited by thermophoresis onto cylindrical samples of aluminum alloy AA2024. Submicron coatings of different thickness and porosity were produced by varying the total time of deposition. Two flame synthesis conditions were investigated in order to study the effect of titania particle dimension and phase composition on the characteristics of coatings. Pure anatase nanoparticles of 3.5 nm diameter were produced in fuel-lean synthesis condition, while fuel-rich non-sooting condition was used to synthesize a mixture of rutile and anatase nanoparticle of 22 nm in diameter, rutile being the predominant phase. Confocal Microscopy measurements allowed to calculate coatings thickness. The electrochemical behavior of the coatings was characterized by means of Electrochemical Impedance Spectroscopy by analyzing the impedance phase angle and modulus, which is an index of the capability of the coating to protect the aluminum substrate. The results obtained show an improvement of the electrochemical behavior of the AA2024 substrate when TiO2 nanoparticles are deposited. Specifically, processed samples have a capacitive behavior with a higher impedance modulus in a larger range of frequencies. Substrates processed with rutile phase nanoparticles of 3.5 nm in diameter and with a lower exposure time showed better results with respect to all the other operating parameters.