Study of corrosion of AA2024-T3 protected by sol-gel coating with Electrochemical Impedance Spectroscopy and Ellipsometry in liquid cell
Résumé
Aluminum alloy 2024 T3 is widely used in the aeronautical field thanks to its high weight to strength ratio. However, it is particularly sensitive to corrosion due to its heterogeneous structure. To protect these alloys against corrosion, the actual strategy is to use a three layer stacking doped with CrVI based corrosion inhibitors. Nevertheless, those substances are highly toxic so their replacement has become a critical issue for the aircraft industry. In this context, sol-gel based coating are good candidate. Indeed, the huge quantity of precursors allows tunable properties and can provide good adhesion on the substrate. Moreover they are easy to deposit and they can incorporate corrosion inhibitors less toxic than chromate1,2.
One objective of this PhD is to use sol-gel chemistry to develop new anticorrosion coatings. On one hand, work has been done on hybrid hydrophobic layers to enhance barrier properties. On the other, mesostructured layers, potential matrix for anticorrosion inhibitors has been studied. The final goal is to couple those two material in a multi-layer system in order to optimize anticorrosion properties.
Development and optimization of those system requires particular techniques to analyze in-situ anticorrosion properties as well as coating structural evolution (porosity, swelling, resistance to hydrolysis …). For this purpose we developed a new analytical approach based on Electrochemical Impedance Spectroscopy3 (EIS) and environmental ellipsometry4 that can be used for different coating deposited on the alloy.