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[ES] El presente trabajo de investigación está centrado en la valorización y la mejora del bioetanol, empleando catalizadores heterogéneos, en un reactor de flujo continuo a escala de laboratorio. En primer lugar, en los laboratorios del Departamento de Química Industrial de la Universidad de Bolonia (Unibo), se ha estudiado la conversión catalítica del etanol en fase gaseosa sobre catalizadores basados en hidroxiapatitas (HAP). Los ensayos catalíticos se llevaron a cabo alimentando un reactor de lecho fijo a escala de laboratorio, empleando el catalizador en forma de pellets y una mezcla de etanol/He, en el rango de temperatura de 300-600 ºC. El interés se focalizó en la formación de productos de alta condensación, con el fin de obtener una mezcla orgánica que pueda ser empleada como bio-combustible. Tras seleccionar las condiciones de reacción, se sintetizaron y probaron diferentes hidroxiapatitas con capacidad de intercambio iónico que poseen metales de transición (Fe, Cu) y metales alcalinotérreos (Sr) en su composición. Mientras que las HAP conteniendo metales de transición actúan esencialmente como catalizadores ácidos, produciendo principalmente el producto de la deshidratación del etanol, el etileno, el catalizador de Sr-HAP permite la formación de una mezcla de reacción compleja, la cual necesita de una mayor optimización para cumplir con los requisitos adecuados para su posterior empleo como biofuel. A continuación, en los laboratorios del Instituto de Tecnología Química (ITQ) de la Universidad Politécnica de Valencia (UPV), el estudio se centró en dos materiales catalíticos diferentes, el óxido de zirconio y la sepiolita, una arcilla natural abundante en España. Ambos materiales se han probados para la transformación de etanol, en el rango de temperatura de 300-450 ºC, empleando un reactor de lecho fijo a escala laboratorio, con el catalizador en forma de pellets, y usando una mezcla de etanol/N2. Los catalizadores con óxido de zirconio se prepararon mediante dos métodos diferentes, precipitación e hidrotermal, variando algunos de los parámetros de síntesis (pH, naturaleza de la base), y empleando algunos metales de transición como elementos dopantes (Ti, Y). La presencia de un elemento dopante en la estructura de la zirconia favorece la estabilización de las fases tetragonal y cúbica frente a fase monoclínica. Todas las muestras exhibieron un comportamiento ácido. Resulta interesante que la zirconia dopada con 5%mol de Ti exhibe un comportamiento catalítico diferente, produciendo el dietiléter como principal producto a 300ºC, mientras que los otros catalizadores producen principalmente etileno, ambos, productos de la deshidratación del etanol. Por otra parte, se ha estudiado el efecto de las propiedades ácido-base de la sepiolita, modificada con metales alcalinos (Na, K, Cs) y cargas de metal variables (2, 4, 5, 7, 14 wt%), y de las propiedades redox de la sepiolita, como soporte de CuO o NiO, sobre la conversión catalítica de etanol a n-butanol. Las sepiolitas tratadas térmicamente actúan principalmente como catalizadores ácidos, produciendo preferentemente productos de deshidratación del etanol (etileno y dietiléter). Mientras que la presencia de un metal de transición no favorece la producción de n-butanol, la presencia de un metal alcalino en el sistema catalítico parece ser crucial para la formación de n-butanol. Los mejores resultados en términos de actividad (conversión de etanol, 59%) y selectividad (30%) de n-butanol se han obtenido a 400 ºC y un tiempo de contacto, W/F, de 2 g/mL·s, con el catalizador basado en sepiolita calcinada a 500 ºC, y modificada con 7 wt% de cesio, mediante impregnación en fase acuosa. / [CA] El present treball de recerca està centrat en la valorització i la millora del bioetanol, emprant catalitzadors heterogenis, en un reactor de flux continu a escala de laboratori. En primer lloc, en els laboratoris del Departament de Química Industrial de la Universitat de Bolonya (Unibo), s'ha estudiat la conversió catalítica de l'etanol en fase gasosa sobre catalitzadors basats en hidroxiapatitas (HAP). Els assajos catalítics es van dur a terme alimentant un reactor de llit fix, a escala de laboratori, contenint el catalitzador en forma de pèl·lets amb una mescla d'etanol/He, en el rang de temperatura de 300-600 °C. L'interés es va focalitzar en la formació de productes d'alta condensació, amb la finalitat d'obtindre una mescla orgànica que puga ser emprada com a bio-combustible. Després de seleccionar les condicions de reacció, es van sintetitzar i van provar diferents hidroxiapatitas amb capacitat d'intercanvi iònic que posseeixen metalls de transició (Fe, Cu) i metalls alcalinotérreos (Sr) en la seua composició. Mentre que les HAP contenint metalls de transició actuen essencialment com a catalitzadors àcids produint principalment el producte de la deshidratació de l'etanol, l'etilé, el catalitzador de Sr-HAP permet la formació d'una mescla de reacció complexa, la qual necessita d'una major optimització per a complir amb els requisits adequats per a la seua posterior ocupació com biofuel. A continuació, en els laboratoris de l'Institut de Tecnologia Química (ITQ) de la Universitat Politècnica de València (UPV), l'estudi es va centrar en dos materials catalítics diferents, l'òxid de zirconio i sepiolita, una argila natural abundant a Espanya. Tots dos materials s'han provats per a la transformació d'etanol en el rang de temperatura de 300-450 °C, emprant un reactor de llit fix a escala laboratori, contenint el catalitzador en forma de pèl·lets, i usant una mescla d'etanol/N2 Els catalitzadors amb òxid de zirconio es van preparar mitjançant dos mètodes diferents, precipitació i hidrotermal, variant alguns dels paràmetres de síntesis (pH, naturalesa de la base), i emprant alguns metalls de transició com a elements dopants (Ti, Y). La presència d'un element dopant en l'estructura de la zircònia afavoreix l'estabilització de les fases tetragonal i cúbica enfront de fase monoclínica Totes les mostres van exhibir un comportament àcid. Resulta interessant que la zircònia dopada amb 5%mol de Ti exhibisca un comportament catalític diferent, produint el dietiléter com a principal producte a 300 °C, mentre que les altres mostres produeixen principalment etilé, tots dos, productes de la deshidratació de l'etanol. D'altra banda s'ha estudiat l'efecte de les propietats àcid-base de la sepiolita, modificada amb metalls alcalins (Na, K, Cs) i càrregues de metall variables (2, 4, 5, 7, 14 wt%), i de les propietats redox de la sepiolita, com a suport de CuO o NiO, sobre la conversió catalítica d'etanol a n-butanol. Les sepiolites tractades tèrmicament actuen principalment com a catalitzadors àcids, produint principalment productes de deshidratació de l'etanol (etilé i dietiléter). Mentre que la presència d'un metall de transició no afavoreix la producció de n-butanol, la presència d'un metall alcalí en el sistema catalític sembla ser crucial per a la formació del n-butanol. Els millors resultats en termes d'activitat (conversió d'etanol, 59%) i selectivitat (30%) de n-butanol s'han obtingut a 400°C i un temps de contacte, W/F, de 2 g/ml·s amb el catalitzador compost de sepiolita calcinada a 500 °C, i modificada amb 7 wt% de Cs. / [EN] The present research work focused on the valorisation and upgrading of bio-ethanol over heterogeneous catalysts in a lab-scale continuous gas-flow system. Firstly, in the laboratories of the Department of Industrial Chemistry of the University of Bologna (Unibo), the catalytic ethanol gas-phase conversion was studied over hydroxyapatite (HAP) based catalysts. Catalytic tests have been carried out in the temperature range 300-600°C by feeding an ethanol/He mixture into a quartz lab-scale fixed bed reactor of pelletized catalyst. The focus was placed on enhancing the formation of higher condensation products in order to obtain an organic mixture with application as bio-fuel. After choosing the reaction conditions, ion-exchanged hydroxyapatite with transition metals (i.e., Fe, Cu) and alkaline earth metal (i.e., Sr) have been synthesized and tested. While the transition metal-exchanged HAP acted essentially as acid catalysts, yielding mainly the dehydration product of ethanol, ethylene, the Sr-HAP catalyst led to the formation of a complex reaction mixture the composition of which need further optimization in order to fill the requisite to be used as fuel-blend. Then, in the laboratories of the Institute of Chemical Technology (ITQ) of the Polytechnic University of Valencia (UPV), the study focused on two different catalytic materials, zirconium oxide and the natural clay sepiolite. Both the materials have been tested into the ethanol transformation carrying out the catalytic tests in the temperature range 300-450 °C by feeding an ethanol/N2 mixture into a quartz lab-scale fixed bed reactor of pelletized catalyst. Zirconium-oxide based catalysts have been prepared through two different methods, precipitation and hydrothermal, by varying some synthetic parameters (i.e., pH, the nature of the base) and by adding a transition metal as dopant agent (i.e., Ti and Y). The presence of a dopant into the zirconia structure favoured the stabilization of the tetragonal or cubic phase against the monoclinic one. All samples exhibited acidic behaviour. Interestingly, 5%mol Ti-doped zirconia exhibited a different catalytic behaviour yielding diethyl ether as major product at 300°C, while all the others samples produced mainly ethylene, both dehydration products of ethanol. The effect of acid-base properties of sepiolite, using alkali metals (i.e., Na, K, Cs) with different metal loading (i.e., 2, 4, 5, 7, 14 wt%) as promoters, and of the redox properties of sepiolite-supported CuO or NiO, on the catalytic conversion of ethanol into n-butanol has been investigated. Thermal treated sepiolite samples mainly acted as acid catalyst, yielding preferentially the dehydration products of ethanol (ethylene and diethyl ether). While the presence of a transition metal did not favour n-butanol production, the presence of an alkali metal into the catalytic system appeared to be crucial for n-butanol formation. Best results in terms of activity (ethanol conversion, 59%) and n-butanol selectivity (30%) where obtained at 400ºC and a contact time, W/F, of 2 g/mL·s over the catalyst consisting of sepiolite calcined at 500ºC modified with 7 wt% of cesium. / Balestra, G. (2022). Valorization of Bio-Alcohols into Added Value Chemicals [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/184991

Tesis por compendio / [ES] Debido a los rápidos avances tecnológicos de las últimas décadas han surgido nuevas necesidades que requieren la generación de nuevos materiales a la carta que cumplan con ciertas funcionalidades o que adquieran características concretas. A este diseño de materiales a la carta hay que sumar la problemática de los procesos de conformado, que en el caso de los materiales cerámicos son procesos largos que requieren altas temperaturas y conllevan un gran consumo energético. Materiales cerámicos como la circona (ZrO2) han atraído la atención de los investigadores debido a sus excelentes propiedades mecánicas, térmicas y de alta resistencia química. Además, hay que mencionar que se trata de un material altamente biocompatible y que no reacciona en ambientes húmedos, lo cual hace que pueda utilizarse en una amplia gama de sectores transversales, que van desde el aeroespacial hasta la medicina protésica. Una de las características importantes de la circona, dada su naturaleza de sólido cristalino blanco, es que sea sencilla de colorear, pudiendo obtener tonalidades muy similares a las de la dentina humana con pequeños dopajes de óxidos metálicos, es por ello que su uso se ha extendido ampliamente en la odontología. Otra de las propiedades significativas que hacen de esta cerámica un material excepcional es su alta conductividad iónica, que le permite ser utilizada como electrolito en las pilas de combustible de óxido sólido (SOFC). El conjunto de todas las propiedades mencionadas hace de la circona un material muy versátil con un amplio abanico de posibles aplicaciones, que abarca desde celdas de combustible sólido, recubrimientos para hélices de turbinas, intercambiadores de calor, así como para medicina protésica, odontología y otras aplicaciones. El propósito de esta tesis doctoral es la obtención de materiales cerámicos nanoestructurados basados en circona que puedan ser empleados en la fabricación de nuevos composites con propiedades a carta para los diversos sectores anteriormente mencionados. Para ello, se utilizará la tecnología de sinterización no convencional basada en microondas, la cual nos permite consolidar materiales altamente densificados a temperaturas relativamente bajas y ciclos muy cortos de tiempo, a la vez de que se trata de un procesado limpio, ecológico y medioambientalmente sostenible. En esta investigación se ha planteado el estudio de distintos composites base circona estabilizada con ytria: circona dopada con óxido de hierro (Fe2O3), composites de circona con manganita de lantano dopada con estroncio (LSM) y composites circona-circón (ZrSiO4). Los resultados obtenidos de esta investigación permitirán, por una parte, determinar si la técnica de sinterización rápida no-convencional empleada mejora las propiedades tanto mecánicas, eléctricas, magnéticas y químicas de los materiales en comparación con la sinterización convencional, y por otra parte, avanzar en el diseño y fabricación de materiales cerámicos avanzados. / [CA] A causa dels ràpids avanços tecnològics de les últimes dècades han sorgit noves necessitats que requereixen la generació de nous materials a la carta que complisquen amb unes certes funcionalitats o que adquirisquen característiques concretes. A aquest disseny de materials a la carta cal sumar la problemàtica dels processos de conformat, que en el cas dels materials ceràmics són processos llargs que requereixen altes temperatures i comporten un gran consum energètic. Materials ceràmics com la circona (ZrO2) han atret l'atenció dels investigadors a causa de les seues excel·lents propietats mecàniques, tèrmiques i d'alta resistència química. A més, cal esmentar que es tracta d'un material altament biocompatible i que no reacciona en ambients humits, la qual cosa fa que puga utilitzar-se en una àmplia gamma de sectors transversals, que van des de l'aeroespacial fins a la medicina protètica. Una de les característiques importants de la circona, donada la seua naturalesa de sòlid cristal·lí blanc, és que siga senzilla d'acolorir, podent obtindre tonalitats molt similars a les de la dentina humana amb xicotets dopatges d'òxids metàl·lics, és per això que el seu ús s'ha estés àmpliament en l'odontologia. Una altra de les propietats significatives que fan d'aquesta ceràmica un material excepcional és la seua alta conductivitat iònica, que li permet ser utilitzada com a electròlit en les piles de combustible d'òxid sòlid (SOFC). El conjunt de totes les propietats esmentades fa de la circona un material molt versàtil amb un ampli ventall de possibles aplicacions, que abasta des de cel·les de combustible sòlid, recobriments per a hèlices de turbines, bescanviadors de calor, així com per a medicina protètica, odontologia i altres aplicacions. El propòsit d'aquesta tesi doctoral és l'obtenció de materials ceràmics nanoestructurats basats en circona que puguen ser emprats en la fabricació de nous compòsits amb propietats a carta per als diversos sectors anteriorment esmentats. Per a això, s'utilitzarà la tecnologia de sinterització no convencional basada en microones, la qual ens permet consolidar materials altament densificats a temperatures relativament baixes i cicles molt curts de temps, alhora de què es tracta d'un processament net, ecològic i mediambientalment sostenible. En aquesta investigació s'ha plantejat l'estudi de diferents compòsits base circona estabilitzada amb ytria: circona dopada amb òxid de ferro (Fe2O3), compòsits de circona amb manganita de lantani dopada amb estronci (LSM) i compòsits circona-circón (ZrSiO4). Els resultats obtinguts d'aquesta investigació permetran, d'una banda, determinar si la tècnica de sinterització ràpida no-convencional empleada millora les propietats tant mecàniques, elèctriques, magnètiques i químiques dels materials en comparació amb la sinterització convencional, i d'altra banda, avançar en el disseny i fabricació de materials ceràmics avançats. / [EN] Due to the rapid technological advances of recent decades, new needs have arisen that require the generation of new on demand materials that meet certain functionalities or acquire specific characteristics. In addition to the design of tailor-made materials, there is the problem of forming processes, which in the case of ceramic materials are long processes that require high temperatures and entail high energy consumption. Ceramic materials such as zirconia (ZrO2) have attracted the attention of researchers due to their excellent mechanical, thermal and high chemical resistance properties. In addition, it should be mentioned that it is a highly biocompatible material that does not react in humid environments, which makes it suitable for use in a wide range of cross-cutting sectors, ranging from aerospace to prosthetic medicine. One of the important characteristics of zirconia, given its nature as a white crystalline solid, is that it is easy to color, being able to obtain shades very similar to those of human dentin with small doping of metal oxides, which is why its use has been widely extended in dentistry. Another significant property that makes this ceramic an exceptional material is its high ionic conductivity, which allows it to be used as an electrolyte in solid oxide fuel cells (SOFC). All these properties together make zirconia a very versatile material with a wide range of possible applications, ranging from solid fuel cells, coatings for turbine propellers, heat exchangers, as well as for prosthetic medicine, dentistry and other applications. The purpose of this doctoral thesis is to obtain zirconia-based nanostructured ceramic materials that can be used in the fabrication of new composites with tailored properties for the various sectors mentioned above. For this purpose, the non-conventional microwave-based sintering technology will be used, which allows us to consolidate highly densified materials at relatively low temperatures and very short cycle times, as well as being a clean, ecological and environmentally sustainable process. In this research, the study of different zirconia-based composites stabilized with yttria has been proposed: zirconia doped with iron oxide (Fe2O3), zirconia composites with lanthanum manganite doped with strontium (LSM) and zirconia-zirconia composites (ZrSiO4). The results obtained from this research will allow, on the one hand, to determine if the non-conventional fast sintering technique used improves the mechanical, electrical, magnetic and chemical properties of the materials in comparison with conventional sintering, and on the other hand, to advance in the design and fabrication of advanced ceramic materials. / Moratal Ruiz, S. (2023). Desarrollo de cerámicas mediante tecnología de microondas basadas en circona y manganitas de lantano [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/200904 / Compendio

Les composites Carbone/Carbone (C/C), largement utilisés à hautes températures dans des environnements oxydants, sont sensibles à l'oxydation dès 400°C. Deux voies sont envisagées pour accroître la tenue à l'oxydation de ces matériaux. La première est de renforcer la force de la liaison fibre/matrice en modifiant les propriétés de surface des fibres de carbone. La seconde voie d 'étude consiste à remplacer une partie de la matrice carbone par un oxyde. L'introduction d'une nouvelle phase conduit à la création de nouvelles interfaces dans les matériaux. L'ensemble des résultats obtenus à partir des caractérisations physico-chimiques et macroscopiques des matériaux élaborés permettent alors de répondre à la problématique qui est de connaître le rôle des interfaces dans les propriétés macroscopiques de composites C/C. / C/C composites are widely used as structural parts in oxiding environment. Yet, they become very sensitive to air oxidation for temperature higher than 400°C. This work proposed two methods to improve their oxidation resistance :(i) the fiber/matrix bond is increased by modifying the properties of the carbon fiber surface, and (ii) a fraction of the carbon matrix is substitued by an oxide phase.Introduction of new constituants leads to the creation of new material interfaces. Thus, the influence of the interfaces on the macroscopic properties of the composite is evaluated by physico-chemical and macroscopic characterizations.

The effects of metastable tetragonal zirconia on the properties of Ordinary Portland Cement were observed during which the effect of crystallite size pH on the preparation solution, precursor salt, and the presence of co-precipitates, Fe(OH)3, SnO2 and SiO2 on the crystallization temperature, enthalpy and crystal structure, immediately following the crystallization exothermic burst phenomenon in ZrO2 were measured. Thermal analysis and x-ray methods were used to determine crystallite sizes and structures immediately following the exothermic burst. Comparisons were made for zirconias prepared from oxychloride, chloride and nitrate solutions. The existence of tetrameric hydroxidecontaining ions in oxychloride precursor is used to rationalise low values of crystallization enthalpy. The position of the crystallization temperature, Tmax was not dependent on crystallite size alone but also on the pH at which the gel was made, the surface pH after washing, and the presence of diluent oxides. Enthalpy v r1/2 and Tmax v (diluent vol)1/3 relationships indicate that surface coverage effects dominate a surface nucleated phenomenon. The data established for ZrO2 systems was used to develop tetragonal-ZrO2-SnO2 powders capable of improving the mechanical properties of Ordinary Portland Cement discs. The ZrO2-OPC discs were prepared by powder mixing, water hydration and uniaxial pressing. Vicat needle tests showed that tetragonal-ZrO2 increases the initial setting rate. Microscopy indicated that porosity distribution changes near to ZrO2 particles. Zirconia has also been introduced into OPC discs by vacuum infiltration methods developed for solutions and colloidal suspensions. Comparisons between OPC discs and the OPCtetragonal ZrO2 composites have been made on the basis of diametral compression strength, Young’s modulus, hardness and toughness (K1c), as estimated by the cracked indentation method. Bell-shaped curves are found for the way the mechanical properties are changed as a function of Zirconia content.

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>

Les réfractaires électrofondus, qui constituent l’objet de ce travail, appartiennent au système alumine-zircone-silice. Ils sont obtenus par coulée dans des moules à des températures supérieures à 2000°C, rendant très difficile toute instrumentation. De nombreux phénomènes intrinsèques au matériau interviennent lors du refroidissement qui suit la coulée. Parmi ces derniers, cette recherche a essentiellement porté sur la transformation de phase (de tétragonale à monoclinique) de la zircone et aux phénomènes associés (gonflement, plasticité,…).A partir d’essais mécaniques à haute température réalisés en laboratoire, les lois de comportements thermiques et mécaniques ont été caractérisées et modélisées en cours de transformation de la zircone. La plasticité à très bas seuil de contrainte observée a, en particulier, été décrite par une vitesse de déformation dérivée du modèle de Leblond, une fonction de rendement de type Cam-clay sans consolidation et une fonction de rendement définissant l’avancement de la transformation en fonction de la température. Après implémentation dans un code de calcul par éléments finis et validation par confrontation avec des résultats d’essais sous contraintes multiaxiales, ce modèle a été assemblé aux autres composantes du comportement mécanique (fluage, élasticité,…), pour décrire l’ensemble des phénomènes thermomécaniques observés lors du refroidissement.Parallèlement, des coulées de blocs en laboratoire, instrumentées par des thermocouples et des capteurs d’émission acoustique, ont permis de reconstruire par simulation numérique l’évolution du champ de température à l’intérieur de la dalle au cours du refroidissement. L’enthalpie de solidification et celle associée à la transformation de phase, préalablement quantifiée par ATD, ont été prises en compte. L’application du modèle mécanique complet, associant toutes les composantes du comportement, a permis de calculer l’évolution du champ de contraintes généré par les gradients thermiques en fonction du temps et, en particulier, de mettre en évidence le rôle essentiel joué par la transformation de phase sur la relaxation des contraintes. / Fused-cast refractories, which are concerned by this work, belong to the alumina-zirconia-silica system. They are obtained by casting in molds at temperatures higher than 2000°C, that make very difficult any instrumentation. Many phenomena intrinsic to the material occur during cooling-down after casting. Among these latter, this research essentially focused on the phase transformation (from tetragonal to monoclinic) of zirconia and the associated phenomena (swelling, plasticity,...).From high temperature mechanical tests performed in laboratory, the thermal and mechanical behavior laws were characterized and modeled during the zirconia transformation. Plasticity at very low stress threshold was observed. A Leblond type model has been extended by introducing a Cam-clay yield function without consolidation. In this model, the progress of the transformation is controlled by the evolution of the temperature. This model was complemented by other components of the mechanical behavior (creep, elasticity, ...). It has been validated by experimental tests under multiaxial loadings that replicate the main thermomechanical phenomena observed during cooling.In parallel, blocks casted in laboratory conditions, instrumented with thermocouples and acoustic emission sensors, allowed a numerical simulation of the change in temperature field within the block during cooling-down. This simulation took into account the solidification enthalpy and the enthalpy associated to the phase transformation, previously quantified by DTA. The implementation of the complete mechanical model integrating all the behavior components led to a calculation of the stress field changes generated by thermal gradients as a function of time and, in particular, to highlight the essential role played by the phase transformation on stress relaxation.

OBJETIVOS: comparar dois sistemas CAD-CAM de diferentes gerações quanto ao grau de adaptação de infraestruturas estéticas de próteses fixas de três elementos para verificar se existe alguma evolução no quesito diminuição do gap marginal e se existe diferença de contração entre blocos de conformações diferentes que podem afetar diretamente a adaptação das mesmas. MATERIAL E MÉTODOS: para isso foi confeccionado um preparo de prótese fixa de três elementos em manequim odontológico simulando a ausência do elemento dental 25; posteriormente aos preparos foi reproduzido um modelo mestre em liga metálica Co-Cr para serem realizados os testes. O modelo mestre foi submetido a escaneamento em cada sistema comercial para a infraestrutura ser desenhada e fresada. Para serem confrontados, em cada sistema CAD/CAM foi confeccionado cinco infraestruturas em Y-TZP (n=5), sendo que no grupo CT1 foi utilizado um disco (ronde) com dimensões de 98x20 mm capaz de ser fresada até seis infraestruturas de uma só vez enquanto que no grupo CT2 cada infraestrutura foi confeccionada individualmente em um bloco com dimensões de 40x15x19 mm. Uma vez concluídas as infraestruturas, as mesmas foram submetidas a teste de adaptação com a técnica do dedal de silicone e posteriormente em cada preparo, tanto do molar quanto do pré-molar, foi retirada uma fatia de 2 mm de espessura em cada face (mesial, distal, lingual e vestibular) para se analisar a espessura de desadaptação na região de término através da análise de imagem (fotografia das fatias realizado por estereomicroscópio e medição com o software ImageJ). Os resultados foram submetidos aos testes de Normalidade e Homocedasticidade (p=0,05) e posteriormente analisados por ANOVA e Tukey (p=0,05). RESULTADOS: as medições foram divididas em dois grupos: 1. Adaptação geral ( medidas por face) e 2. Adaptação circunferencial (média das medidas das quatro faces). Em ambas as medições não houve diferenças estatisticamente significantes, permanecendo o gap marginal de ambos os materiais com resultados estatisticamente uniformes. CONCLUSÕES: ambos os sistemas CAD/CAM testados apresentaram resultados semelhantes e satisfatórios, dentro dos padrões clínicos aceitáveis e não houve diferença de contração de sinterização entre o disco (ronde) e o bloco. / OBJECTIVES: compare two CAD-CAM systems of different generations according to the adaptation level of three elements aesthetic FPD to discover if there are any changes in the item \"gap marginal decrease\" and if there is contraction differences between blocks of different conformations that may directly affect the adaptation. MATERIAL AND METHODS: it was made a FPD preparation (total crown preparation in each pillar tooth) in a dental mannequin, simulating the absence of the tooth 25; later was made a master template in Co-Cr alloy to be performed the tests, according to the mannequin preparations. The master model was subjected to scanning in each trading system to be designed the infrastructure and posteriorly milled. It was made five infrastructure in Y-TZP (n = 5) to be compared in every CAD / CAM system, and in the CT1 group was used a disc (ronde) with dimensions of 98x20 millimeters, where it can be milled up to six infrastructure of a once, while in the group CT2 each structure was fabricated into a single block with dimensions of 40x15x19 millimeters. After the infrastructure was milled, they were subjected to the adaptive technique of \"silicone replica\" and subsequently in each preparation (molar and premolar) was withdrawn from a 2 mm thickness slice on each side (mesial, distal, lingual and buccal) to analyze the mismatch thickness in the end region via image analysis (slices photography performed by a stereomicroscope and measured by the ImageJ software). The results were submited by Normality and Homoscedasticity test (p=0.05) and subsequently analyzed by ANOVA and Tukey test (p=0.05). RESULTS: the measurements were divided into two groups: 1. General adaptation (measures per side) and 2. Circumferential adaptation (average measure of the four faces). In both measurements there were no statistically significant differences, remaining both materials with statistically uniform marginal gap. CONCLUSIONS: both CAD / CAM systems tested showed similar and satisfactory results within the acceptable clinical standards and there was no sintering contraction difference between the disk (ronde) and block.

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.

Este estudo teve como objetivo principal desenvolver uma técnica para síntese de um nanocompósito de Y-TZP/MWCNT-COOH (Zircônia estabilizada por 3 mol% de ítria reforçada por nanotubos de carbono funcionalizado em -COOH) com propriedades mecânicas e ópticas que permitam a sua futura utilização como infraestrutura de próteses fixas dentárias e pilares protéticos para implantes. Assim, foram avaliados a microestrutura, resistência à flexão, tenacidade à fratura, limite de fadiga e propriedades ópticas do nanocompósito e comparada àquelas medidas para Y-TZP convencional (controle). O material Y-TZP/MWCNT-COOH foi desenvolvido pelo processo de co-precipitação de hidróxidos mistos associado ao tratamento hidrotérmico/solvotérmico e prensagem uniaxial em formato de blocos para sistemas CAD/CAM. O pó de MWCNT-COOH foi caracterizado por meio de MEV-FEG, TEM, TGA, DRX e FRX previamente a sua utilização para desenvolvimento do nanocompósito. Espécimes foram obtidos a partir do material Y-TZP/MWCNT-COOH para caracterização por meio de DRX, MEV-FEG e TEM, e comparação de suas propriedades estruturais (densidade e contração), ópticas, resistência à flexão, tenacidade à fratura e limite de fadiga com a Y-TZP convencional. O MWCNT-COOH apresentou-se em feixes de nanotubos de carbono recobertos por sílica tendo comprimento médio de 5,10 ± 1,34 ?m, com 90% dos comprimentos medidos (D90) estando abaixo de 6,9 ?m. Foi verificado a não possibilidade da utilização de líquidos orgânicos em nenhum passo da fabricação dos compósito Y-TZP/MWCNT-COOH por levar ao escurecimento do compósito, inviabilizando sua futura aplicação clínica. O tratamento hidrotérmico sem uso de líquidos orgânicos mostrou-se eficaz em proporcionar o revestimento do nanotubo de carbono por partículas de óxido de zircônio e ítrio. Entretanto, ocasionou a formação de aglomerados e partículas de Y-TZP com tamanho maiores que 5 ?m. Uma densidade relativa de 97,4% foi alcançada para o compósito experimental de Y-TZP contendo MWCNT-COOH, tendo uma razão de contraste de 0.9929 ± 0.0012 e um valor de diferença de cor da Y-TZP convencional de 6,1 ± 3,1 ( ?E). As propriedades mecânicas da Y-TZP/MWCNT-COOH, dureza Vickers (10,14 ± 1,27 GPa; p=0,25) e tenacidade à fratura (4,98 ± 0,30 MPa.m1/2; p=0,39), não apresentaram diferença significativa da Y-TZP convencional (dureza: 8,87 ± 0,89; tenacidade à fratura: 4,98 ± 0,30 MPa.m1/2). Entretanto, para a resistência à flexão (p=0,003) e limite de fadiga cíclica (LFC) foram obtidos valores inferiores para o material experimental Y-TZP/MWCNT-COOH (resistência à flexão: 299,4 ± 30,5 MPa; LFC: 179,4 ± 22,5 MPa) quando comparado à Y-TZP controle (resistência à flexão: 623,7 ± 108,8 MPa; LFC: 439,0 ± 56,4 MPa). Com base nos resultados apresentados, é possível concluir que a síntese de um nanocompósito de Y-TZP/MWCNT-COOH com propriedades ópticas adequadas para aplicação na odontologia restauradora foi possível por meio dos métodos descritos, entretanto algumas adequações nos métodos de síntese e processamento para criação do nanocompósito devem ser realizadas para se evitar a acentuada diminuição de importantes propriedades mecânicas do material. / This study aim was to develop a technique for synthetize nanocomposite of Y-TZP/MWCNT-COOH (3 mol% Yttria-Stabilized Tetragonal Zirconia reinforced with COOH functionalized carbon nanotubes) with mechanical and optical properties that allow their future use as fixed dental prosthesis infrastructure and implant abutments. Thus, the following properties of the nanocomposite were investigated and compared to those measured for conventional Y-TZP (control): microstructure, flexural strength, fracture toughness, fatigue limit and optical properties. Y-TZP/MWCNT-COOH material was developed by the co-precipitation of mixed hydroxides associated with the hydrothermal/solvothermal treatment and uniaxial pressing to form blocks for CAD/CAM systems. The MWCNT-COOH powder was characterized by SEM-FEG, TEM, TGA, XRD and XRF prior to its use for the development of nanocomposite. Specimens were obtained from the Y-TZP/MWCNT-COOH material and characterized by XRD, SEM-FEG and TEM. After characterization, the material had their structural properties (density and contraction), optical, flexural strength, fracture toughness and fatigue limit compared to a conventional Y-TZP. The MWCNT-COOH material was observed to be a bundle formation of carbon nanotube covered with silica with an average length of 5.10 ± 1.34 ?m, with 90% of the measured lengths (D90) being below 6.9 ?m. It has been found to be not possible to use organic liquids on any step of the Y-TZP/MWCNT-COOH manufacturing process due to darkening of the composite, making it unfeasible to future clinical application. The hydrothermal treatment without the use of organic liquids was effective in providing the carbon nanotube coating by zirconium and yttrium oxide particles. However, this treatment led to the formation of agglomerates and particles of Y-TZP with larger than 5 ?m. A relative density of 97.4% was achieved for the Y-TZP/MWCNT-COOH composite, having a contrast ratio of 0.9929 ± 0.0012, and a color difference value from the conventional Y-TZP of 6.1 ± 3.1 (?E). The mechanical properties of Y-TZP/MWCNT-COOH, Vickers hardness (10.14 ± 1.27 GPa; p = 0.25) and fracture toughness (4.98 ± 0.30 MPa.m1/2; p = 0.39), showed no significant difference from the conventional Y-TZP (hardness: 8.87 ± 0.89; fracture toughness: 4.98 ± 0.30 MPa.m1/2). However, flexural strength (p = 0.003) and cyclic fatigue limit (CFL) showed lower values for the experimental material Y-TZP/MWCNT-COOH (flexural strength: 299.4 ± 30.5 MPa; CFL: 179.4 ± 22.5 MPa) compared to Y-TZP control (flexural strength: 623.7 ± 108.8 MPa; CFL: 439.0 ± 56.4 MPa). Based on the results presented, it could be conclude that the synthesis of a nanocomposite of Y-TZP/MWCNT-COOH with optical properties suitable for application in restorative dentistry was made possible by the described methods, however some adjustments in synthesis and processing methods for the nanocomposite creation should be taken; to avoid the sharp decrease of important mechanical properties of the material.