Les principaux objectifs de ces travaux de thèse sont d'une part d'optimiser le protocole d'élaboration des barrières thermiques (BT) issues de la voie sol-gel et d'autre part de caractériser l'adhérence de ces barrières thermiques mais aussi de proposer des pistes en vue d'augmenter la durée de vie de celles-ci. Tout d'abord, une première étude a porté sur le choix et la validation d'un nouvel agent dispersant pour optimiser la formulation du sol chargé permettant la mise en forme des barrières thermiques. Ainsi, ce changement de dispersant a généré une microstructure conduisant à une augmentation significative de la durée de vie du système en oxydation cyclique mais a aussi permis de simplifier le protocole d'élaboration puisque l'étape de colmatage, jusqu'alors nécessaire, a été supprimée. L'étude paramétrique de la microstructure surfacique des barrières thermiques a montré que le réseau de microfissures formé initialement restait stable en fonction du vieillissement avec la création d'un sous-réseau microfissuré. Pour comprendre les mécanismes d'endommagement des barrières thermiques sol-gel et les confronter à ceux des barrières thermiques industrielles EB-PVD, la méthode d'indentation interfaciale a été retenue pour sonder l'interface revêtement/substrat. Ainsi des valeurs de ténacités apparentes ont pu être déterminées afin de comparer les adhérences des BTSG et des BTEB-PVD. A partir de ces résultats, des modèles phénoménologiques d'endommagement ont été imaginés. Pour les BTEB-PVD, l'initiation et la propagation de fissures restent localisées à l'interface barrière thermique/sous-couche de liaison, d'un coté ou de l'autre de l'oxyde de croissance selon les conditions, alors que pour les BTSG, l'endommagement est induit par la libération d'énergie élastique stockée dans le système qui augmente en fonction du vieillissement. / The main objectives of this PhD are first to improve and optimise the elaboration protocol of thermal barrier coatings (TBC) manufactured by the sol-gel route and then to characterise their adhesion and investigate the possibility to enhance their lifetime. A preliminary study is focused on the selection and validation of a new dispersing agent to optimise the composite sol formulation before shaping TBC. Indeed, the new dispersant induced a microstructure allowing to significantly increase the cyclic oxidation lifetime of the system but also to simplify the elaboration process as the reinforcement step was suppressed. The parametric study of TBC surface microstructure proved that the initial micro-cracks network remained stable during ageing including the formation of a crack sub-network. To understand the damage mechanisms of sol-gel TBC and to compare them to those corresponding to industrial EB-PVD TBC, the method of interfacial indentation was developed to investigate the subtrate/top-coat interface. The apparent toughness values were determined to compare both BTSG and BTEB-PVD adhesions. From these results, phenomenological models for damage mechanisms were proposed. For BTEB-PVD, crack initiation and propagation are located at the top-coat/bond-coat interface, either on one side or the other side of the thermally grown oxide (TGO) depending of the conditions. For BTSG, the damage is a consequence of the release of the elastic strain energy stored in the system, increasing with the ageing temperature.

Cette étude a pour finalité le développement d'une nouvelle famille de catalyseurs pour la combustion des suies Diesel afin de produire des filtres à particules (FAP) à régénération continue basse température. En effet, les régénérations périodiques des FAP actuellement commercialisés, engendrent une surconsommation plus ou moins élevée en carburant. Les catalyseurs étudiés sont des céramiques conductrices par les ions oxygènes et exempts de métal noble. L'ensemble de ces études a permis d'aboutir à plusieurs conclusions majeures. Les oxygènes actifs pour oxyder les particules de suies à basse température sont les oxygènes contenus dans le catalyseur. L'oxydation de la suie a donc lieu à l'interface solide/solide : suie/catalyseur. Un mécanisme de type électrochimique comme dans une pile à combustible mais à l'échelle nanométrique a été proposé : l'oxydation de la suie représente la réaction anodique qui se déroule aux points de contact suie / 8-YSZ, les électrons produits diffusent à travers les particules de suie vers les point triples entre les particules de suie (conductrices électroniques), la phase gaz (présence d'oxygène) et 8-YSZ (conducteur ionique) où se déroule la réaction cathodique d'incorporation de l'oxygène gazeux dans le matériau. Les paramètres clés qui gouvernent l'activité catalytique sont la surface de contact suie/catalyseur et donc la granulométrie de la poudre de catalyseur ainsi que la pression partielle d'oxygène dans la phase gaz et la mobilité de l'oxygène dans le catalyseur / This study aims to develop a new family of catalysts for diesel soot combustion to produce and optimize self-DPFs, based on ionic conducting ceramics, able to continuously burn soot particulates at low temperatures without fuel overconsumption and without the use of noble metals. The investigated catalysts are oxygen ionically conducting ceramics. Yttria stabilized Zirconia (8-YSZ containing 8 mol% of yttria) was chosen as the reference catalyst due to its high thermal and chemical stability and good ionic conductivity. A set of experiments was implemented to vary different parameters that can influence the reactivity of the reference catalyst. All of these studies have resulted in several major conclusions. Oxygen species active to oxidize soot particles at low temperature are those contained in the catalyst. An electrochemical type mechanism as in a fuel cell but at the nanoscale was proposed: the soot oxidation represents the anodic reaction which occurs at the contact points soot / 8-YSZ/O2 (gas) electrons are diffused through soot particles to triple points between the soot particles (electronic conductor), the gas phase (presence of oxygen) and 8-YSZ (ion conductor) where the cathodic reaction takes place with the incorporation of gaseous oxygen into the ceramic. The key parameters that influence the catalytic activity of 8-YSZ are soot / catalyst contact and thus the agglomerates size of the catalyst powder, the oxygen partial pressure in the gas phase and the mobility of oxygen in the catalyst

Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC applications. The desire to achieve a higher engine efficiency of agas turbine engine by increasing the turbine inlet temperature has pushed YSZ toits upper limit. Above 1200°C, issues such as poor phase stability, high sinteringrates, and susceptibility to CMAS (calcium magnesium alumino silicates) degradation have been reported for YSZ based TBCs. Among the new materials,gadolinium zirconate (GZ) is an interesting alternative since it has shown attractive properties including resistance to CMAS attack. However, GZ has a poor thermo-chemical compatibility with the thermally grown oxide leading to poor thermal cyclic performance of GZ TBCs and that is why a multi-layered coating design seems feasible.This work presents a new approach of depositing GZ/YSZ multi-layered TBCs by the suspension plasma spray (SPS) process. Single layer YSZ TBCs were also deposited by SPS and used as a reference.The primary aim of the work was to compare the thermal conductivity and thermal cyclic life of the two coating designs. Thermal diffusivity of the YSZ single layer and GZ based multi-layered TBCs was measured using laser flash analysis (LFA). Thermal cyclic life of as sprayed coatings was evaluated at 1100°C, 1200°C and 1300°C respectively. It was shown that GZ based multi-layered TBCs had a lower thermal conductivity and higher thermal cyclic life compared to the single layer YSZ at all test temperatures. The second aim was to investigate the isothermal oxidation behaviour and erosion resistance of the two coating designs. The as sprayed TBCs were subjected toisothermal oxidation test at 1150°C. The GZ based multi-layered TBCs showed a lower weight gain than the single layer YSZ TBC. However, in the erosion test,the GZ based TBCs showed lower erosion resistance compared to the YSZ singlelayer TBC. In this work, it was shown that SPS is a promising production technique and that GZ is a promising material for TBCs.

In heterogeneous catalysis, promoting the activity of the catalytic metals is long known as an important method to make a process more efficient and viable. Noble metals have been promoted classically by a chemical coverage of an ionic solution on the surface of the catalyst or using inert support, e.g., silica or alumina, allowing an increase of the dispersion of the catalyst. Therefore, new methods of promotion needed to be better explored to improve the efficiency of metal and metal oxide catalysts. One way of enhancing the catalyst’s activity is to disperse the noble metal at the nanoscale using an active type of support that is ion-conducting. Not only lattice ions can be exchanged with the surface of the nanoparticles but it can also engage in the oxidation reaction on the surface, resulting in what is known as metal-support interaction (MSI). Another method of improving the catalytic activity is to polarize the catalyst, allowing ions to migrate from a solid electrolyte to the gas-exposed surface, in a phenomenon known as electrochemical promotion of catalysis (EPOC). The change in the ions concentration on the surface would change the adsorption energy of the gaseous reactants and enhance or supress the catalytic rate. In this thesis, the effect of supporting nanoparticles of noble and non-noble metal (oxides) (Pt, Ru, Ir, Ni) was studied for the case of ionic and ionic-electronic conducting supports (CeO2, TiO2, YSZ). The enhancement in their catalytic rate was found and correlated to an electrochemical property, the exchange current density. Then, using isotopically-labeled oxygen, the oxygen exchange ability of the conductive oxides was evaluated when supporting Ir and Ru nanoparticles and correlated with the results from C3H8 isotopic oxidation reaction, which showed the extent of involvement of oxygen from the support as carried by the isotopically-labeled CO2 produced. Following this, electrochemical promotion of catalysis experiments were performed for different reactant/catalyst systems (C2H4 - Pt, Ru; C3H8 - Pt; CH4 - Pd, Ni9Pd). In the first system, the main outcome was the functional equivalence found for the MSI and EPOC effect in promoting the catalysts as experiments were performed at different temperatures, reactants partial pressures and polarization values. In the case of C3H8/Pt, the novel dispersion of Pt on an intermediate supporting layer (LSM/GDC) was found as a feasible method to obtain long stability of the catalyst while electrochemically promoting the rate of reaction. For CH4 oxidation, the polarization of the Pd nanoparticles showed continuous oxidation of the bulk of the catalyst resulting in a continuous increase of the catalytic rate. The Ni9Pd synthesized in a way to form a core/double-shell layer of Ni/Pd resulted in an enhanced catalytic rate and enhanced stability compared to stand-alone Pd. And lastly, to comprehend the ions’ effect in the electrochemical promotion and the non-Faradaic nature of the phenomena, density-functional theory (DFT) modeling was used to demonstrate the increase of the heat of adsorption of reactants depending on their electronegative/positive nature.

Reducing the heat losses in heavy-duty diesel engines is of importance for improving engine efficiency and reducing CO2 emissions. Depositing thermal barrier coatings (TBCs) onto engine components has been demonstrated to have great potential to reduce heat loss from the combustion chamber as well as from exhaust components. The overall aim of this thesis is to evaluate the thermal cycling lifetime and thermal insulation properties of TBCs for the purpose of reducing heat losses and thermal fatigue in heavy-duty diesel engines. In the thermal cycling test inside exhaust manifolds, nanostructured yttria-stabilized zirconia (YSZ) performed best, followed by YSZ with conventional microstructure and then La2Zr2O7. Forsterite and mullite could not withstand the thermal cycling conditions and displayed large cracks or spallation. Two sol-gel composite coatings displayed promising thermal cycling performance results in a furnace test under similar conditions. Thermal cycling testing of YSZ coatings having different types of microstructure, in a furnace at temperatures up to 800°C, indicated that the type of microstructure exerted a great influence. For the atmospheric plasma sprayed coatings, a segmented microstructure resulted in the longest thermal cycling lifetime. An even longer lifetime was seen for a plasma spray–physical vapour deposition (PS-PVD) coating. In situ heat flux measurements inside the combustion chamber indicated that plasma-sprayed Gd2Zr2O7 was the TBC material providing the largest heat flux reduction. This is explained by a combination of low thermal conductivity and high reflectance. The plasma-sprayed YSZ and La2Zr2O7 coatings provided very small heat flux reductions. Long-term testing indicated a running-in behaviour of YSZ and Gd2Zr2O7, with a reduction in heat flux due to the growth of microcracks in YSZ and the growth of macrocracks in Gd2Zr2O7. / <p>QC 20170821</p>

Background: The influence of typical manufacturing regimes for producing fixed dental prostheses (FDPs) from yttria partly-stabilized zirconia polycrystals (3Y/4Y/5Y-TZP) on the phase composition is quantified. Methods: Fixed dental prostheses (FDPs) were designed using a CAD process and machined from different Y-TZP blanks from two manufacturers differing in yttria contents. Subsequent to sintering, the FDPs were glaze fired and air-blasted using alumina particles. Phase composition was determined with X-ray diffraction and quantified with Rietveld refinement. Results: The blanks from VITA Zahnfabrik (VITA YZ HT, VITA YZ ST, VITA YZ XT) and Dental Direct (DD Bio ZX2, DD cube ONE, DD cube X2) featured a rhombohedral portion with rather small crystallites and a small monoclinic portion for 3Y/4Y-TZPs, which increased after machining and disappeared after sintering. Glaze firing and air-blasting with alumina particles had no significant influence on the phase composition. Conclusion: The phase history of dental zirconia is revealed, which may have implications on further processing and aging of the FDP (e.g. low temperature degradation) in mouth.

The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs. / <p>QC 20111014</p>

Os filmes cerâmicos de manganito de lantânio dopado com estrôncio (LSM) e de manganito de lantânio dopado com estrôncio/zircônia estabilizada com ítria (LSM/YSZ) são utilizados como catodos das células a combustível de óxido sólido de temperatura alta (CaCOSTA). Estes filmes cerâmicos porosos foram depositados sobre o substrato cerâmico denso de YSZ, utilizado como eletrólito, componente estrutural do módulo, assim conferindo uma configuração de meia-célula denominada auto-suporte. O estudo da meia-célula é fundamental, pois na interface catodo/eletrólito ocorre a reação de redução do oxigênio, conseqüentemente influenciando no desempenho da CaCOSTA. Neste sentido, o presente trabalho contribui para a síntese de pós de LSM e LSM/YSZ e para o processamento de filmes finos, utilizando a técnica de pulverização de pó úmido, adotada para a conformação dos filmes cerâmicos por permitir a obtenção de camadas porosas com espessuras variadas na ordem de micrômetros. Os pós de LSM foram sintetizados pela técnica de citratos e os pós de LSM/YSZ pela técnica de mistura de sólidos. Na etapa de conformação foram preparadas suspensões orgânicas de LSM e LSM/YSZ alimentada por gravidade em um aerógrafo manual. Para a conformação do substrato de YSZ utilizou-se uma prensa uniaxial hidráulica. Foram possíveis a obtenção das meia-células de óxido sólido catodo/eletrólito de estruturas cristalinas hexagonal para a fase LSM e cúbica para a fase YSZ. E as micrografias das meia-células mostram que o substrato YSZ é denso, suficiente para ser utilizado como eletrólito sólido, e os filmes de LSM e LSM/YSZ apresentam-se porosos com espessura de aproximadamente 30 &mu;m e com boa aderência entre os catodos e o eletrólito. A presença do catodo compósito entre o catodo LSM e o substrato YSZ, possibilitou um aumento no desempenho eletroquímico na reação de redução do oxigênio. / The ceramic films of strontium-doped lanthanum manganite (LSM) and strontiumdoped lanthanum manganite/yttria-stabilized zirconia (LSM/YSZ) are used as cathodes of the high temperature solid oxide fuel cells (HTSOFC). These porous ceramic films had been deposited on the YSZ dense ceramic substrate, used as electrolyte, structural component of the module, thus conferring a configuration of half-cell called auto-support. The study of the half-cell it is basic, therefore in the interface cathode/electrolyte occurs the oxygen reduction reaction, consequently influencing in the performance of the HTSOFC. In this direction, the present work contributes for the processing of thin films, using the wet powder spraying technique, adopted for the conformation of the ceramic films for allowing the attainment of porous layers with thicknesses varied in the order of micrometers. The LSM powders were synthesized by the citrate technique and the LSM/YSZ powders synthesized by the solid mixture technique. In the stage of formation were prepared organic suspensions of LSM and LSM/YSZ fed by gravity in a manual aerograph. For the formation of the YSZ substrate was used a hydraulical uniaxial press. The attainment of solid oxide half-cells cathode/electrolyte was possible of crystalline structures hexagonal for phase LSM and cubic for phase YSZ. The half-cells micrographs show that the YSZ substrate is dense, enough to be used as solid electrolyte, and the LSM and LSM/YSZ films are presented porous with approximately 30 &mu;m of thickness and good adherence between the cathodes and the electrolyte. The presence of composite cathode between the LSM cathode and YSZ substrate, presented an increase in the electrochemical performance in the oxygen reduction reaction.

Os filmes cerâmicos de manganito de lantânio dopado com estrôncio (LSM) e de manganito de lantânio dopado com estrôncio/zircônia estabilizada com ítria (LSM/YSZ) são utilizados como catodos das células a combustível de óxido sólido de temperatura alta (CaCOSTA). Estes filmes cerâmicos porosos foram depositados sobre o substrato cerâmico denso de YSZ, utilizado como eletrólito, componente estrutural do módulo, assim conferindo uma configuração de meia-célula denominada auto-suporte. O estudo da meia-célula é fundamental, pois na interface catodo/eletrólito ocorre a reação de redução do oxigênio, conseqüentemente influenciando no desempenho da CaCOSTA. Neste sentido, o presente trabalho contribui para a síntese de pós de LSM e LSM/YSZ e para o processamento de filmes finos, utilizando a técnica de pulverização de pó úmido, adotada para a conformação dos filmes cerâmicos por permitir a obtenção de camadas porosas com espessuras variadas na ordem de micrômetros. Os pós de LSM foram sintetizados pela técnica de citratos e os pós de LSM/YSZ pela técnica de mistura de sólidos. Na etapa de conformação foram preparadas suspensões orgânicas de LSM e LSM/YSZ alimentada por gravidade em um aerógrafo manual. Para a conformação do substrato de YSZ utilizou-se uma prensa uniaxial hidráulica. Foram possíveis a obtenção das meia-células de óxido sólido catodo/eletrólito de estruturas cristalinas hexagonal para a fase LSM e cúbica para a fase YSZ. E as micrografias das meia-células mostram que o substrato YSZ é denso, suficiente para ser utilizado como eletrólito sólido, e os filmes de LSM e LSM/YSZ apresentam-se porosos com espessura de aproximadamente 30 &mu;m e com boa aderência entre os catodos e o eletrólito. A presença do catodo compósito entre o catodo LSM e o substrato YSZ, possibilitou um aumento no desempenho eletroquímico na reação de redução do oxigênio. / The ceramic films of strontium-doped lanthanum manganite (LSM) and strontiumdoped lanthanum manganite/yttria-stabilized zirconia (LSM/YSZ) are used as cathodes of the high temperature solid oxide fuel cells (HTSOFC). These porous ceramic films had been deposited on the YSZ dense ceramic substrate, used as electrolyte, structural component of the module, thus conferring a configuration of half-cell called auto-support. The study of the half-cell it is basic, therefore in the interface cathode/electrolyte occurs the oxygen reduction reaction, consequently influencing in the performance of the HTSOFC. In this direction, the present work contributes for the processing of thin films, using the wet powder spraying technique, adopted for the conformation of the ceramic films for allowing the attainment of porous layers with thicknesses varied in the order of micrometers. The LSM powders were synthesized by the citrate technique and the LSM/YSZ powders synthesized by the solid mixture technique. In the stage of formation were prepared organic suspensions of LSM and LSM/YSZ fed by gravity in a manual aerograph. For the formation of the YSZ substrate was used a hydraulical uniaxial press. The attainment of solid oxide half-cells cathode/electrolyte was possible of crystalline structures hexagonal for phase LSM and cubic for phase YSZ. The half-cells micrographs show that the YSZ substrate is dense, enough to be used as solid electrolyte, and the LSM and LSM/YSZ films are presented porous with approximately 30 &mu;m of thickness and good adherence between the cathodes and the electrolyte. The presence of composite cathode between the LSM cathode and YSZ substrate, presented an increase in the electrochemical performance in the oxygen reduction reaction.

Les dépôts de YSZ, élaborés par projection plasma, sont des céramiques réfractaires généralement utilisées pour les applications de barrières thermiques (TBC). Sa faible conductivité thermique associée à sa bonne résistance mécanique assure aux TBC de hautes performances et de bons rendements. La structure et la microstructure complexe sont à l'origine de ces propriétés mécaniques, et celles doivent être contrôlées. Tout comme les céramiques denses la YSZ se dégrade en température et sous vapeur d'eau.La dégradation des propriétés mécaniques dans le temps (module d'élasticité et contrainte à rupture)est accélérée par la température. Pour cette étude les propriétés ont été évaluées en flexion 3 points à température ambiante. Les observations structurales et microstructurales ont été réalisées respectivement par DRX et microscopie électronique à balayage au cours du vieillissement. Un model analytique a pu être proposé pour prédire le comportement du matériau dans le temps sous humidité. / Yttria Stabilized Zirconia (YSZ) coatings, deposited by plasma sprayed process, are refractory ceramics mostly used as the Thermal Barrier Coating (TBC) applications. The low YSZ thermal conductivity associated to the good mechanical resistance ensures a high performances and efficiencies of these TBC. The structure and the complex microstructure are responsible for the mechanical properties and must be controlled. Like brittle ceramic materials, the YSZ is affected by degradation at low temperature due to water vapor. Material ageing results from the progressive degradation of the mechanical properties (such as fracture strength and Young’s modulus), which seem to decrease in time and accelerate depending on temperature. In this study, the mechanical properties have been evaluated by means of three-point bending tests at room temperature. The observations of the structure and the microstructure are respectively investigated by X-ray diffraction and SEM-technique with material ageing. An analytical model is suggested in order to predict the evolution of the properties under humidity atmosphere.