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Depuis les années 80, l’élaboration de couches minces de silice, SiO2 à partir d’orthosilicate de tétraéthyle ((Si(OC2H5)4, TEOS) par dépôt chimique en phase vapeur (CVD) a été largement étudiée pour répondre aux problématiques de la microélectronique. Récemment, l’élargissement de l’éventail d’applications pour les revêtements à base de SiO2 pour l’optique, l’agroalimentaire, le biomédical, l’emballage ou la séparation des gaz, induit une modification des cahiers des charges tant pour les matériaux que les procédés. Il est souvent mis en avant les besoins de : (a) réduire le budget thermique lors de l’élaboration, (b) éliminer la formation de poudres, induites par exemple par une réactivité élevée en présence d’ozone, (c) revêtir des structures complexes, ce qui diminue l’intérêt des procédés plasma. En réponse à ces besoins, cette étude s’intéresse à la structure de couches de SiO2 amorphe élaborées à partir de TEOS et oxygène à pression atmosphérique à des températures Td comprises entre 400°C et 550°C, et corrèle ces caractéristiques à leur résistance à l’abrasion chimique.

International audience; An apparent kinetic model for the chemical vapor deposition of SiO 2 from tetraethyl orthosilicate (TEOS) and O 2 was developed in a poorly investigated range of operating conditions, that is, at atmospheric pressure and between 350 and 500 C, based on literature survey and experimental results obtained in a hot wall tubular reactor. The kinetic model was implemented into the computational fluid dynamics code FLUENT and validated both in shape and value by comparison with experimental deposition rate profiles. It reveals that for the conditions tested, a possible mechanism of SiO 2 deposition involves two intermediate species formed from TEOS homogeneous decomposition, the first one being active from 300 C and the second one contributing to deposition for temperatures higher than 370 C. The calculated local profiles of gas flow, gas temperature, species mass fraction, and silica deposition rate indicate that the first intermediate species leads to marked film thickness gradients, the second one being more stable as producing uniform thicknesses.

Producing alumina catalysts containing high amounts of penta-coordinated aluminum sites ([5]Al) is of main interest to develop a green production of olefins from biomass. Inspired from an original process developed on planar substrates at low pressure, a Fluidized Bed Chemical Vapor Deposition (CVD) process coupled to a DLI (Direct Liquid Injection) system has been studied at atmospheric pressure to deposit amorphous alumina on soluble NaCl powders, using dimethyl aluminum isopropoxide (DMAI) as precursor. A set of experiments has been performed at 310°C, showing the good reproducibility of the deposition process in terms of deposit morphology, mass and chemical composition. Nuclear Magnetic Resonance of aluminum-27 probing the structure at atomic scale of the deposit indicates the presence of high contents of penta-coordinated aluminum, as it was the case on planar substrates. This demonstrates that this DLI-CVD route from DMAI is robust. Coupled with a fluidized bed, it could lead to massive production of high specific surface area amorphous alumina with high content of penta-coordinated aluminum environments.

Chemical vapor deposited SiO2 films from tetraethyl orthosilicate (TEOS) is a key enabling material in numerous applications. Among the several pathways for the CVD of SiO2 films from TEOS, the poorly investigated medium temperature process involving oxygen ensures a compromise between the high thermal load of the surface reaction of the TEOS pyrolysis process, and the strong activation of gas phase reactions in the ozone assisted decomposition of TEOS. It is a promising route towards conformal coverage of complex-in-shape structures, growth rate control, and appropriate physical & chemical properties of the coating. SiOx films are obtained from TEOS+O2 in a horizontal CVD reactor operating at atmospheric pressure between 350 and 500°C. FTIR operating under normal and 55° incidence angle is used for the investigation of the structure, namely density, strain, oxygen content and stoichiometry of the films, by probing vibrational modes in the 900-1300 cm-1 region with well-resolved TO-LO phonon splitting. Complementary density values obtained by ellipsometry allow estimating the porosity of the films. Their corrosion resistance is investigated by the P-Etch test through thickness loss and is correlated with their composition, porosity and density.

International audience; We present first experimental results obtained with a newly patented high-temperature resistivity measurement apparatus. This technique is of great interest for monitoring the behaviour of a surface layer submitted to high temperature, either during its processing or while the functional surface is used. The innovation resides in the combination of features that are available commercially or have previously been reported by research groups worldwide, but isolated. Resistivity measurements can be performed under vacuumor controlled atmosphere, fromroomtemperature to 1250°C, on samples as low as 10*10mm2 in size. Technical details about the apparatus are presented. Then, we show that high-temperature resistivity measurements performed on a platinum sheet compare well with available data, and validate the prototype measurement head. Finally, we explore the monitoring of phase transitions occurring in an Al/Cu bilayer processed by metallorganic chemical vapour deposition, while a temperature ramp is applied. The high-temperature resistivity plot is very well explained by the following sequence of phase formation: Al + Cu!θ-Al2Cu+ Cu+ Al!d-Al2Cu3 + g-Al4Cu9+Cu!d-Al2Cu3 + g-Al4Cu9+Cu+a-(Cu), as determined by hightemperature X-ray diffraction.

The corrosion resistance of MOCVD Al2O3 coating system was investigated to protect a TA6V Alloy under hot salt corrosion conditions: This coating was corroded with a salt deposit without mechanical loading at 480°C during 100 h. Corrosion products formed in salted areas were studied by Energy Dispersive Spectroscopy (EDS). Although all coated specimens were damaged with corrosion products presence in salted area, Al2O3 coatings showed the lowest salt damage on titanium substrate after a metallographic cross section observation compared to uncoated ones. As well as these interesting experimental results, coated specimens exhibit a good adherence on titanium substrate.