CONICET | Buscador de Institutos y Recursos Humanos

Chromates are among the most common substances used as corrosion inhibitors. However, these compounds are highly toxic and an intense effort is being undertaken to replace them. Cerium compounds seem to fulfil the basic requirements for consideration as alternative corrosion inhibitors. On the other hand, epoxy-based hybrid organic-inorganic sol-gel coatings with low-temperature sintering treatments are being developed to protect metal substrates susceptible of degradation, as aluminium alloy AA 2024. The aim of this work was to study the influence of the incorporation of cerium ions in silica-methacrylate sol-gel coatings on AA 2024 as potential replacement of chromate treatments. The idea was to combine the barrier effect of silica-methacrylate coatings with the corrosion inhibitor effect of the cerium inside the coatings. The coatings have been prepared using tetraethyl orthosilicate (TEOS), 3-methacryloxypropyl trimethoxysilane (MPS), silica nanoparticles (Levasil 200S, Bayer) and Ce(NO3)3∙6H2O. Multilayer coatings with and without cerium have been obtained by dip-coating. After thermal treatment at 120°C, single coatings are homogeneous and crack-free and around 4 µm thick. Polarisation curves and Electrochemical Impedance Spectroscopy (EIS) in NaCl 0.05 M showed good barrier properties at initial immersion times, with passive current densities of 6 ∙ 10-8 A/cm2 and a passive region of 900 mV. The increase of the immersion time leads to a gradual reduction of the impedance associated with the sol-gel coating as a consequence of the deterioration of the protection system. An increase of the impedance modulus at 0.01 Hz after an initial reduction and precipitation of yellow deposits with significant relative increase of Ce content (EDX analysis) can be associated to self-healing behaviour