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Détection in-situ de la réactivité à l'interface métal-peinture : exemple de revêtements anti-corrosion en base zinc peints

Abstract : Conversion coatings are used to enhance paint adherence and protect metals in numerous industrial applications from construction to aeronautics. The degradation mechanism of buried metal-oxide-polymer interface is difficult to elucidate, especially on rough metallic substrates. All the more so, the challenges reside in: (1) the distinction between the interface and the polymer degradation, (2) the localization of the underpaint reactivity initiation and (3) the survey of local degradation kinetics.The main objective of this work was to propose a methodological approach able to describe in-situ the effect of thin conversion coatings on the stability of buried metal-oxide-polymer interface, under stable intact polymer, in immersion condition. The approach is based on the combination of model epoxy coating and adapted electrochemical ageing procedure. The stability of the polymer coating was verified by infrared spectroscopy and electrochemical methods. The degradation mode of the interface was studied by combined local electrochemical impedance mapping and time lapse microscopy. This approach allowed an intelligent screening and fast-ranking of conversion coatings in function of their ability to form stable metal-oxide-polymer interfaces. It also permitted to localize the degradation initiation and to quantify its lateral propagation.A secondary objective of the PhD was to allow in-depth chemical characterization of nanometric conversion coatings on rough substrates. Low energy argon plasma sputtering in GD-OES was used to perform homogeneous nanometric thinning (model craters) of the conversion coating on millimetric areas; near metal-oxide interface chemical description was achieved by XPS and Auger nanoprobe.The combination of the two proposed approaches permitted to demonstrate the effect of nanometric thinning in conversion coatings on the local reactivity at metal-oxide-polymer interface. The effect of the size and distribution of nanometric defects was also discussed.The PhD was performed on the example of epoxy coated electrodeposited zinc-based alloy with trivalent chromium conversion coating.
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Thomas Sanchez. Détection in-situ de la réactivité à l'interface métal-peinture : exemple de revêtements anti-corrosion en base zinc peints. Chimie théorique et/ou physique. Université Paris sciences et lettres, 2020. Français. ⟨NNT : 2020UPSLC030⟩. ⟨tel-03648428⟩

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