Les Céramiques Ultra-Haute Température (UHTC) sont des matériaux prometteurs dans le cadre d'applications en conditions extrêmes comme les parties proéminentes de véhicules à rentrée atmosphérique ou les chambres de combustion de moteurs aéronautiques. La compréhension des mécanismes d'oxydation à haute température présente donc un intérêt majeur, car les réactions en milieu oxydant limitent fortement leur durée de vie. Les matériaux ZrB2-SiC, HfB2-SiC et HfB2-SiC-Y2O3 ont été soumis pendant des durées et températures variables (jusqu'à 2400°C) à des environnements contrôlés contenant de la vapeur d'eau. Les microstructures formées ont été décrites, et les mécanismes et cinétiques d'oxydation régissant leur comportement ont été analysés. L'importance de la stabilité et de la nature de la phase vitreuse formée durant l'oxydation a été soulignée. En complément de ces analyses microstructurales, une campagne d'essais utilisant la Fluorescence Induite par Laser (LIF) a permis, via la détection in situ de la molécule BO2, de comprendre plus finement la dynamique de la phase vitreuse lors de l'oxydation. Enfin, une modélisation de la croissance de couches oxydées sur un matériau monophasé a été effectuée. / Ultra-High Temperature Ceramics (UHTC) are promising materials for applications in extreme environments such as prominent parts of atmospheric re-entry vehicles or the combustion chambers of aeronautic engines. The understanding of oxidation mechanisms at high temperature is of great interest, because reactions in oxidizing atmosphere strongly shorten their lifetime. ZrB2-SiC, HfB2-SiC and HfB2-SiC-Y2O3 materials have been subjected to controlled water vapor-containing environments for different durations and temperatures (up to 2400°C). The microstructures developed by the oxidized materials have been described, and oxidation mechanisms and kinetics governing their behavior have been analyzed. The importance of the stability and nature of the vitreous phase formed during the oxidation has been emphasized. In order to complement these microstructural analyses, tests using Light-Induced Fluorescence (LIF) have been performed, allowing us to finely understand the dynamics of the vitreous phase during oxidation thanks to the in situ detection of the BO2 molecule. Finally, a modelling of the growth of oxidized layers on a single-phased material has been performed.

Tungsten (W) based materials can be used in fusion reactors due to several advantages. Different fabrication routes can be applied to develop tungsten materials with intended microstructure and properties for specific application including nanostructured grades. Therein, innovative chemical routes are unique in their approach owing numerous benefits. This thesis summarizes the development of W-based composites dispersed-strengthened by rare earth (RE) oxides and their evaluation for potential application as plasma facing armour material to be used in fusion reactor. Final material development was carried out in two steps; a) fabrication of nanostructured metallic tungsten powder dispersed with RE-oxides and b) powder sintering into bulk oxide-dispersed strengthened (ODS) composite by spark plasma process. With the help of advanced characterization tools applied at intermediate and final stages of the material development, powder fabrication and sintering conditions were optimized. The aim was to achieve a final material with a homogenous fine microstructure and improved properties, which can withstand under extreme conditions of high temperature plasma. Two groups of starting materials, synthesized via novel chemical methods, having different compositions were investigated. In the first group, APT-based powders doped with La or Y elements in similar ways, had identical particles’ morphology (up to 70 μm). The powders were processed into nanostructured composite powders under different reducing conditions and were characterized to investigate the effects on powder morphology and composition. The properties of sintered tungsten materials were improved with dispersion of La2O3 and Y2O3 in the respective order. The oxide dispersion was less homogeneous due to the fact that La or Y was not doped into APT particles. The second group, Ydoped tungstic acid-based powders synthesized through entirely different chemistry, contained nanocrystalline particles and highly uniform morphology. Hydrogen reduction of doped-tungstic acid compounds is complex, affecting the morphology and composition of the final powder. Hence, processing conditions are presented here which enable the separation of Y2O3 phase from Y-doped tungstic acid. Nevertheless, the oxide dispersion reduces the sinterability of tungsten powders, the fabricated nanostructured W-Y2O3 powders were sinterable into ultrafine ODS composites at temperatures as low as 1100 °C with highly homogeneous nano-oxide dispersion at W grain boundaries as well as inside the grain. The SPS parameters were investigated to achieve higher density with optimum finer microstructure and higher hardness. The elastic and fracture properties of the developed ODS-W have been investigated by micro-mechanical testing to estimate the materials’ mechanical response with respect to varying density and grain size. In contrast from some literature results, coarse grained ODS-W material demonstrated better properties. The developed ODS material with 1.2 Y2O3 dispersion were finally subjected to high heat flux tests in the electron beam facility “JUDITH-1”. The samples were loaded under ELM-like thermal-shocks at varying base temperatures up to an absorbed power density of 1.13 GW/m2, for armour material evaluation. Post mortem characterizations and comparison with other reference W grades, suggest lowering the oxide contents below 0.3 wt. % Y2O3. As an overview of the study conducted, it can be concluded that innovative chemical routes can be potential replacement to produce tungsten based materials of various composition and microstructure, for fusion reactor applications. The methods being cheap and reproducible, are also easy to handle for large production at industrial scale. / <p>QC 20120827</p>

Les propriétés structurales et de luminescence de couches minces de TiO2 et Y2O3 dopées terres rares (thulium, terbium et ytterbium) ont été étudiées en vue de les intégrer dans une cellule photovoltaïque comme couche de conversion spectrale du proche UV vers l'infrarouge afin d'en améliorer l'efficacité. Ces couches minces ont été synthétisées par dépôt chimique en phase vapeur à pression atmosphérique à l'aide de précurseurs organo-métalliques et assisté par aérosol (aerosol assisted MOCVD). Les couches minces sont partiellement cristallisées dès la synthèse (400°C pour le TiO2 en phase anatase, 540°C pour Y2O3 en phase cubique). Après traitement thermique la cristallisation est largement améliorée et la luminescence des ions dopant terres rares est obtenue dans les deux matrices oxydes. Le thulium émet dans une large bande située vers 800 nm et l'ytterbium vers 980 nm. Le terbium quand à lui émet dans une gamme située principalement dans le visible. Les spectres d'excitation ont montré que l'absorption des photons se fait via la matrice. En matrice TiO2 une efficacité de transfert d'énergie du Tm3+ vers l'Yb3+ de l'ordre de 20 % a été déterminée pour des teneurs de 0,8 % des deux dopants, ce qui correspond à la limite d'auto-extinction. Le rendement global mesuré est faible, nous avons montré que les causes probables de cette faible valeur sont le manque d'absorption des couches minces pour obtenir l'excitation de l'ion sensibilisateur ainsi que des processus de luminescence et de down conversion pas assez efficaces.

Ce travail de thèse porte sur la synthèse et la caractérisation de matériaux amorphes et cristallin sous forme de poudres et de couche minces du systhème Er2O3-Y2O3-Al2O3-B2O3. L'objectif principal du travail a été de préparer des couches minces amorphes dopées erbium dont la composition est proche de YAl3(BO3)4 (YAB), en vue de la réalisation d'amplificateurs pour l'optique guidée. Pour la synthèse des échantillons, les méthodes des précurseurs polymériques et sol-gel ont été utilisées. Les caractérisations thermiques, structurales et optiques des échantillons, sous forme de poudre et de couches minces, ont été réalisées par l'analyse thermogravimétrique, microcalorimétrie différentielle, diffraction des rayons X, spectroscopie infrarouge à transformé de Fourier, spectroscopie Raman, microscopie électronique à balayage, microscopie à force atomique, spectroscopie “m-line”, et de luminescence. L'ensemble de ces résultats nous a permis de parfaitement contrôler l'élaboration de couches minces vitreuses de compositions Y1-xErxAl3(BO3)4 (x = 0,02; 0,05; 0,1; 0,3 et 0,5) qui présentent une très bonne homogénéité chimiques et de bonnes propriétés optiques. Les couches minces recuites à des températures comprises entre Tg et Tc, présentent les meilleures conditions pour obtenir des dépôts très denses et homogènes, conduisant à de bonnes efficacité de guidage, d'émission de luminescente et de durées de vie. Les couches vitreuses de composition Y0,9Er0,1Al3(BO3)4 et d'épaisseurs comprises entre 500 et 800 nm sont des guides d'onde monomodes qui présentent durées de vie comparables à d'autres systèmes borates amorphes. Ces résultats confirment la possibilité d'utilisation de ces couches amorphes comme amplificateurs pour l'optique guidée.

Submitted by Marta Toyoda (1144061@mackenzie.br) on 2018-09-04T17:03:54Z No. of bitstreams: 2 Dênison Angelotti Moraes.pdf: 4087093 bytes, checksum: 92e8923c2697fbf1a44b31c6c7fb05d1 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Paola Damato (repositorio@mackenzie.br) on 2018-09-19T18:27:52Z (GMT) No. of bitstreams: 2 Dênison Angelotti Moraes.pdf: 4087093 bytes, checksum: 92e8923c2697fbf1a44b31c6c7fb05d1 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-09-19T18:27:52Z (GMT). No. of bitstreams: 2 Dênison Angelotti Moraes.pdf: 4087093 bytes, checksum: 92e8923c2697fbf1a44b31c6c7fb05d1 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-06-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Automotive components are always in development, aiming to improve performance and quality, either by reducing costs, market need, increased sales and productivity or some new environmental or safety legislation. In the last years the environmental theme has gained interest and has become central to vehicles that use fossil fuels, especially Diesel oil, and must comply with new emission laws. For this, new engines and exhaust systems and gas filtration have been developed, such as catalytic converters. The upcoming legislation, called PROCONVE P8, restricts the values of nitrous oxides (NOx) and particulate matter to very low values. In order to achieve these values, the post-treatment system called the ATS (After Treatment System) was developed. In order for the process to reduce pollutants to be made within the ATS, the exhaust gases burned in the combustion process inside the engine must be between 450 and 550 ºC. The burned gases, or exhaust gases, are piped to the catalyst by metal tubing. In this work was proposed the use of 8% by weight (ZrO2-Y2O3) stabilized Zirconia oxide ceramic, known as YSZ (Ytria Stabilized Zirconia), or 8YSZ, known as TBC (Thermal Barrier Coating). The TBC was studied as a coating of exhaust pipe, through analytical calculation and CFD (Computer Fluid Dynamics). The results showed that the YSZ is a potential material for the studied application, as well as for applications where the thermal barrier theme is relevant. / Componentes automotivos estão sempre em desenvolvimento, seja objetivando a melhoria de performance e qualidade, seja pela redução de custos, necessidade de mercado, aumento de vendas e produtividade ou alguma nova legislação ambiental ou de segurança. Nos últimos anos o tema ambiental ganhou corpo e passou a ser central para os veículos que utilizam combustíveis fósseis, em especial o óleo Diesel, devendo atender a novas legislações de emissão. Para isso, novos motores e sistemas de exaustão e filtragem dos gases foram desenvolvidos, como os conversores catalíticos. A próxima legislação que entrará em vigor, chamada de PROCONVE P8 restringe os valores de óxidos nitrosos (NOx) e material particulado a valores muito baixos. Para que esses valores sejam atingidos foi desenvolvido o sistema de pós-tratamento de gases chamado de ATS (After Treatment System). Para que o processo de redução dos agentes poluidores seja feito dentro do ATS, os gases de escapamento queimados no processo de combustão dentro do motor devem estar a temperatura entre 450 e 550ºC. Os gases queimados, ou gases de exaustão, são conduzidos por tubulação metálica até o catalisador. Neste trabalho foi proposta a utilização de revestimento cerâmico de óxido de Zircônia estabilizado com Ítria a 8% em peso (ZrO2-Y2O3), conhecido como YSZ (Ytria Stabilized Zirconia), ou ainda 8YSZ, conhecido como TBC (Thermal Barrier Coating). Foi estudado o TBC como revestimento de tubulação de escapamento, por meio de cálculo analítico e por CFD (Computer Fluid Dynamics). Os resultados mostraram que o YSZ é um material de potencial para a aplicação estudada, bem como para aplicações onde o tema barreira térmica seja relevante.

Alumino-silicate systems are of great interest for materials scientists and geochemists. Thermodynamic knowledge of these systems is useful in steel and ceramic industries, and for understanding geochemical processes. A popular and efficient approach used to obtain a self-consistent thermodynamic dataset is called CALPHAD. It couples phase diagram information and thermochemical data with the assistance of computer models. The CALPHAD approach is applied in this thesis to the thermodynamic modelling and assessments of the CaO-Al2O3-SiO2, MgO-Al2O3-SiO2 and Y2O3-Al2O3-SiO2 systems and their subsystems. The compound energy formalism is used for all the solution phases including mullite, YAM, spinel and halite. In particular, the ionic two sub-lattice model is applied to the liquid solution phase. Based both on recent experimental investigations and theoretical studies, a new species, AlO2-1, is introduced to model liquid Al2O3. Thus, the liquid model corresponding for a ternary Al2O3-SiO2-M2Om system has the formula (Al+3,M+m)P (AlO2-1,O-2, SiO4-4,SiO20)Q, where M+m stands for Ca+2, Mg+2 or Y+3. This model overcomes the long-existing difficulty of suppressing the liquid miscibility gap in the ternary systems originating from the Al2O3-free side during the assessments. All the available and updated experimental information in these systems are critically evaluated and finally a self-consistent thermodynamic dataset is achieved. The database can be used along with software for Gibbs energy minimization to calculate any type of phase diagram and all thermodynamic properties. Various phase diagrams, isothermal and isoplethal sections, and thermochemical properties are presented and compared with the experimental data. Model calculated site fractions of species are also discussed. All optimization processes and calculations are performed using the Thermo-Calc software package. / QC 20100607