NEW HYBRID SOL-GEL Coatings for Aluminium Alloys CORROSION Protection

Sol–gel films are actively investigated from the last decade as possible candidates for environmentally friendly pre-treatments on metals [1-2].

However, the main drawback is the lack of active corrosion protection compared to chromate conversion coatings, particularly on aluminium alloys [3]. However, the environmental laws in many countries have imposed severe restrictions on chromate use due to its high toxicity and environmental hazards.

A new promising approach consists to use sol-gel process to prepare hybrid coatings containing cerium on aluminium substrates [4-5]. In this work cerium nitrate was used as additive to the hybrid sol–gel formulations in order to confer active corrosion protection without damaging the coating. The cerium nitrate was added at different ratios in the synthesis process to understand the role of possible interaction of the inhibitor with components of the sol–gel system. A series of microstructural and physico-chemical characterizations (X-ray photoelectrons and Auger spectroscopies, EIS) were performed on the coatings to understand the role of cerium, its spatial distribution (depth profiling) and an important focusing was made on the accurate characterization of oxidation degree of Ce (+III, +IV) within the solgel matrix as a function of the doping level and the composition of the solgel.

The results demonstrate that first, cerium nitrate do not affect the stability of sol-gel films and second, that this inhibitor plays two roles in the coating: first, an active role in corrosion resistance and second, an increase of polymeric network cohesion leading to a best adhesion on the metallic substrate due to a well-defined bond at the aluminium alloy/ solgel interface.

Present work belongs to SOLGREEN-Aerospace Valley consortium.

[1] K.A. Yasakau; M.L. Zheludkevich; O.V. Karavai; M.G.S. Ferreira; Progress in Organic Coatings, 2008, 63, 352.

[2] M.L. Zheludkevich; R. Serra; M.F. Montemor; I.M. Miranda Salvado; M.G.S. Ferreira; Surface and Coatings Technology, 2006, 200, 3084.

[3] M.L. Zheludkevich; R. Serra; M.F. Montemor; I.M. Miranda Salvado; M.G.S. Ferreira; Surface and Coatings Technology, 2006, 200, 3084.

[4] V. Moutarlier; B. Neveu; M.P. Gigandet; Surface and Coatings Technology, 2008, 202, 2052.

[5] A. Conde; A. Durán; J. J. de Damborenea; Progress in Organic Coatings, 2003, 46, 288.