TiOx self-assembled networks prepared by templating approach as nanostructured reservoirs for self-healing anticorrosion pre-treatments

The development of new effective anticorrosion pre-treatments for metallic substrates is an issue of primer importance for corrosion science due to the fact that chromates must be banned. Removal of hexavalent chromium from the industry opens a significant gap in the corrosion protection technologies. This work presents a new approach for design of self-healing anticorrosion pre-treatments for the 2024 aluminium alloy. A TiOx porous layer obtained by templating synthesis was used as nanostructured reservoir for an organic corrosion inhibitor. This provides active corrosion protection and self-healing ability of the coating system. The reservoir is composed by titania nanoparticles which are self-assembled forming a cellular network that replicates the surface structure of the etched alloy. The nanoreservoir layer was coated with a sol-gel based thin hybrid film to provide additional barrier effect. The morphology of the titania-based film was characterized with scanning electron microscopy and atomic force microscopy. Electrochemical impedance spectroscopy and the scanning vibrating electrode technique were used to study the anticorrosion behavior of the developed pre-treatments. The novel pre-treatments show enhanced corrosion protection when compared with undoped sol-gel films, or films doped directly introducing inhibitor in the sol gel matrix. The pre-treatment formed by the nanostructured titania reservoir layer covered with the hybrid film demonstrates well-defined self-healing ability leading to effective long-term active corrosion protection. The nanostructured porous character of the titania layer provides a very high effective surface area for the adsorption of the inhibitor. The developed surface formed by the self-assembled layer offers also the good adhesion between the oxide and the sol-gel film due to the high contact area between the two phases. Moreover, employment of the nanoreservoir approach avoids negative effects of the inhibitor on the stability of the sol-gel matrix and improves the release of the inhibitor in the places where defects start to develop. The present work shows for the first time, the promising ability on the use of nanostructured porous oxide films doped with organic inhibitors as effective environmental-friendly corrosion protective pre-treatments for metallic substrates. (c) 2006 Elsevier B.V. All rights reserved.