Oxydation des quasi-cristaux pour applications industrielles

Abstract : The oxidation behavior of quasicrystalline and approximant compounds has been studied in near industrial environnement, together with the subsequent evolution of their wetting properties. Two alloys have been selected: the icosahedral phase of the AlCuFe system and the O1 orthorhombic approximant of the decagonal phase in the AlCuFeCr system. Samples were either sintered pins or powders. Caracterisation techniques include X-ray diffraction, transmission electron microscopy, photoelectrons spectroscopy and laser ellipsometry, carried on specimens after just the surface preparation, i.e. polishing, and atter oxidation cycles. It has been shown that the alloy chemistry prevail on the structure regarding the oxidation behavior. Because these intermetallics are Al-based, amorphous alumina is always formed on the surface. Depending on the oxidation conditions, the other chemical species can also oxidize. ln the studied temperature and atmosphere ranges, depassivation is experienced either above 300°C and in boiling water. When oxidizing the icosahedral phase, a reservoir effect is proposed to explain occurring phase transformations. Non-wetting behavior was also studied just atter surface preparation and atter oxidation. Non- wetting properties are related to the complete surface system being the intermetallic substrate, the oxide(e) layer(s) it promotes and the extreme surface -carbon layers, hydroxides and hydroxyles bonds-. During cycles at 500°C, a reversible behavior is experienced.
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Gaëtan Bonhomme. Oxydation des quasi-cristaux pour applications industrielles. Autre [cond-mat.other]. Institut National Polytechnique de Lorraine, 2003. Français. ⟨NNT : 2003INPL053N⟩. ⟨tel-01749698⟩

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