Abstract
Concerning the development of new alternatives for replacement of the toxic chromate surface treatments, the aim of the present study is to design and produce new electrochemically active sol-gel thin films of different composition in the ZrO2-SiO2 system, to act as first chemically active layer for pre-treatments of metallic painted surfaces. For its evaluation, a new methodology combining accelerated test, and global and localised electrochemical impedance spectroscopy (EIS) is proposed. For the localised measurements, a new mini-cell system (MCS) is introduced. An active protection mechanism at the cathodic sites underneath the sol-gel thin film was observed. This inhibitor effect is associated with a self-sealing mechanism by the hydrolysis of Zr4+-ions chemically incorporated in the sol-gel network. After the accelerated test, these Zr4+-ions tend to form links different from Si-O-Zr (i.e. zirconium hydroxides and/or oxides). Such new insoluble compounds plug the pores and defects in the sol-gel coatings increasing the low frequency impedance during immersion in NaCl aqueous solutions.
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