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Compréhension des mécanismes d’élaboration de revêtements de zinc électrolytiques composites (nano et microparticules) pour la protection vis-à-vis de la corrosion de l’acier et les propriétés d’adhésion

Abstract : Electrodeposited zinc nickel alloy coatings are widely used for steel protection against corrosion and for assembly by rubber to metal bonding. However, ZnNi technologies cost and the possible restriction for its use due to European legislation strengthening are serious drawbacks. This work proposes particles codeposition of silica and polymethyl methacrylate together with zinc, of respectively nanometric and submicronic size. If silica particles are available on the market, polymer particles are not in a reasonable cost. Thus, a synthesis protocol had been developed. It consists in emulsifying monomer into water by sonication of the mixture with successive sonications of increasing frequencies. After polymerization, monodisperse PMMA spherical particles of 100 to 300 nm in diameter are obtained. Moreover, the proposed synthesis allows the choice of particles charge signs. This parameter is a key one in particles codeposition in electrodeposited matrix. After a preliminary study with conductive polymers, particles are dispersed into the electrolytes and then characterized by electrochemistry. It appears that PMMA particles interact with the steel substrate if polarized as a cathode. Composite coatings are elaborated, under mechanical steering or ultrasound irradiation, with convection intensity near the cathode previously homogenized to compare the contribution of the different kinds of convection, thanks to the concept of equivalent velocity. The influence off the particles’ incorporation on the morphology and the microstructure off the coatings are evaluated, related to the hydrodynamic conditions and the type of particle incorporated. PMMA particles incorporation leads to the refinement of the coating, the opposite being observed for silica particles. Ultrasound as well as the surface charge sign of PMMA particles influenced significantly morphology and microstructure off the coatings. The scale up off the plating process is led in a pilot cell of 50L. An exposure to Neutral Salt Spray test showed that Zn/PMMA composite coatings exhibit the best corrosion properties, while the better adhesion results are obtained with Zn/SiO2 composite.
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Lucas Baissac. Compréhension des mécanismes d’élaboration de revêtements de zinc électrolytiques composites (nano et microparticules) pour la protection vis-à-vis de la corrosion de l’acier et les propriétés d’adhésion. Matériaux. Université Bourgogne Franche-Comté, 2019. Français. ⟨NNT : 2019UBFCD005⟩. ⟨tel-02549685⟩

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