Random closed sets and random marked closed sets present an important general concept for the description of random objects appearing in a topological space, particularly in the Euclidean space. This thesis deals with two major tasks. At first, it is the dimension reduction problem where dependence of a random closed set on underlying spatial variables is studied. Solving this problem allows to find the most significant regressors or, possibly, to identify the redundant ones. This work achieves both theoretical results, based on extending the inverse regression techniques from classical to spatial statistics, and numerical justification of the methods via simulation studies. The second topic is estimation of characteristics of random marked closed sets which is primarily motivated by an application in the microstructural research. Random marked closed sets present a mathematical model for the description of ultrafine-grained microstructures of metals. Methods for statistical estimation of their selected characteristics are developed in the thesis. Correct quantitative characterization of microstructure of metals allows to better understand their macroscopic properties.

Cette thèse porte sur le comportement hydromécanique d’un mélange de poudre et pellets de bentonite MX80 avec une proportion 80/20 en masse sèche. Il s’agit d’un matériau étudié par l’Institut de Radioprotection et de Sûreté Nucléaire (IRSN) dans le cadre du projet SEALEX qui a pour objectif principal la vérification de l’efficacité des dispositifs de scellement ou des barrières ouvragées dans le system du stockage géologique des déchets radioactifs. Le comportement hydromécanique du matériau à différentes échelles a été étudié par différents essais en laboratoire. Premièrement, les changements à l’échelle microstructurale d’un seul pellet de bentonite durant l’hydratation a été abordée à l’aide de deux techniques : la porosimétrie au mercure et la tomographie aux rayons-X. Les résultats ont montré que le gonflement d’un pellet peut être expliqué par deux mécanismes : la création des fissures surtout à des succions entre 38 et 9 MPa, et le gonflement des grains de bentonite, correspondant à l’hydratation des smectites à l’échelle nano. A des succions inférieures à 9 MPa, une diminution de l’épaisseur des feuillets d’argile et une augmentation du désordre des ceux-ci sont observées. Des essais de rétention d’eau, de pression de gonflement et de compression à l’odomètre à succion contrôlée ont été effectués sur le mélange de poudre et pellets. Les propriétés de rétention d’eau sous conditions de volume constant et pour un seul pellet sous conditions de gonflement libre apparaissent similaires pour des valeurs de succion supérieures à 4 MPa. Cela implique que la succion physico-chimique est prédominante devant la succion capillaire. Pour des valeurs de succions plus basses, une capacité de rétention plus faible a été observée sous conditions de volume constant, à relier à la disparition des macro-pores par le gonflement des grains de bentonite. Des valeurs de pression de préconsolidation plus petites que celles des mélanges de bentonite pure ont été obtenues pour des succions non-nulles, montrant l’effet granulaire des pellets dans le mélange. Deux colonnes d’infiltration ont été réalisés afin d’étudier deux cas extrêmes avec une densité sèche globale identique (1.49 Mg/m3). Avec la première colonne, un mélange de poudre et pellets relativement homogène, fabriqué en suivant un protocole spécial a été étudié. En revanche, un mélange fortement hétérogène a été fabriqué dans la deuxième colonne d’infiltration. Les résultats montrent que la pression de gonflement radiale dépend fortement de la distribution des pellets et de la poudre ainsi que de l’évolution du front d’hydratation. Une anisotropie de gonflement a été observée dans les deux cas, avec la pression de gonflement axiale inférieure à celle radiale. De plus, la valeur finale de pression de gonflement axiale est différente pour les deux colonnes, bien que les deux échantillons aient fabriquées avec la même densité sèche globale. En parallèle, plusieurs observations à la tomographie aux rayons-X ont été réalisées sur le mélange de pellets et poudre pendant l’hydratation. Un mélange complètement homogène a été observé après 100 jours d’hydratation à l’échelle étudiée (50 μm/voxel). Un nouveau modèle d’endommagement qui prend en compte des fissures observées au sein du pellet pendant hydratation a été développé en adaptant le Barcelona Expansive Model (BExM). L’essai d’infiltration sur l’échantillon relativement homogène a été simulé avec succès en utilisant le modèle développé. L’hétérogénéité initiale de la porosité a été aussi considérée dans la simulation afin de reproduire l’anisotropie de gonflement. Les résultats expérimentaux obtenus dans le cadre de cette étude permettent de mieux comprendre la réponse des ouvrages de scellement avec le mélange de pellets et poudre de bentonite dans le projet SEALEX. De plus, le modèle développé, qui prend en compte des fissures observées au sein du pellet et l’hétérogénéité initiale du matériau, permettra d’améliorer / The present investigation deals with the hydro-mechanical behavior of a mixture composed of pellets and powder of MX80 bentonite with a proportion of 80/20 in dry mass. This is one of the studied materials by the French Institute for Radiation protection and Nuclear Safety (IRSN) within the SEALEX project, which aims at investigating the long-term performance of swelling clay-based sealing systems in the context of geological high-level radioactive waste disposal. This study has been conducted by following an experimental program covering different scales. Firstly, the microstructure changes while wetting of a single pellet was investigated by combining MIP results with μ-CT observations. Results revealed that swelling of a pellet is due to the development of cracks, with significant development between 38 and 9 MPa of suction, combined to swelling of bentonite grains, which is governed by the hydration mechanisms of smectite at nano-scale. The application of suctions below 9 MPa leads to a significant decrease of the platelet thickness and to an increase in the disorder of the platelet assembly. Water retention tests, swelling pressure tests and suction controlled oedometer tests on the pellet/powder mixture were performed. Similar water retention properties were observed for the mixture under constant-volume condition and pellet under free swelling condition under suctions higher than 4 MPa, suggesting that physico-chemical suction prevails on capillary suction. At lower suctions, constant-volume condition defined a lower water retention capacity because of the disappearance of macro-pores. Lower yield stress values than the common pure bentonite mixtures were found for the pellet/powder mixture for non-zero suctions, showing that the volume change behavior is governed by the rearrangement and crushing of pellets, and the loss of the granular structure in the case of zero suction. Two mock-up tests were performed, aiming at studying two extreme cases at a global dry density of 1.49 Mg/m3: a homogeneous pellet/powder mixture fabricated by following a special protocol, and a strong heterogeneous sample. Results revealed that the radial swelling pressure depends strongly on the local pellet/powder distribution combined with the evolution of the hydration front. An anisotropy swelling was found in both cases, being the axial swelling pressure lower than the radial one. Moreover, different values of axial pressure were found between the two tests, even though they have the same global dry density of samples. In parallel, μ-CT observations were carried out on the mixture while wetting, revealing a homogeneous sealed sample after 100 days of hydration. No density gradients were identified at the investigated resolution (50 μm/voxel) after this long time of hydration. A new damage model, which takes into account the development of fissures within a pellet while wetting, was proposed an included to the well-IVknown double porosity Barcelona Expansive Model (BExM) to carry out numerical simulations of one mock-up test. The initial heterogeneous porosity distribution was also considered to reproduce the anisotropy swelling. The experimental results obtained in this study will greatly help well understand the response of seals made up of pellets/powder bentonite mixture in the SEALEX in situ experiment. Moreover, the constitutive model developed taking into account the pellet cracking damage and the initial sample heterogeneity allows significantly improving the prediction of hydomechanical behavior of seals/plugs made up of this mixture, constituting thus an useful tool for the safety assessment of the nuclear waste disposal system

[pt] Nos últimos anos muitos esforços foram realizados para obtenção de materiais capazes de explorar eficientemente a conversão de energia solar. Em particular, a geração de combustíveis por fotocatálise retém grande interesse devido às suas propriedades intrínsecas de promover reações com variação de energia positiva, possibilitando seu armazenamento em compostos químicos. A eficiência desses processos, entretanto, é limitada pela fotoativação dos principais fotocatalisadores no espectro UV, desperdiçando grande parte da energia solar presente no Visível. Neste trabalho foi investigada a influência no desempenho de fotoativação de heteroestruturas de titanatos de Fe e Cu crescidos sobre TiO2 para produção de gás H2 por fotólise da água utilizando luz Visível. As amostras foram preparadas segundo rota por impregnação via úmida e pós-tratamento térmico, em que óxidos metálicos foram formados na superfície de partículas de TiO2 com posterior interdifusão e formação de fases ternárias de Fe2TiO5 e Cu3TiO4. Realizou-se a caracterização dos materiais por meio das técnicas de DRX, DSC, TGA, MEV/EDS, DRS, PLS e Fisissorção de N2. Os resultados obtidos confirmaram a formação dos materiais, sugerindo a criação de heteroestruturas do tipo PN para as amostras contendo Fe e a formação de fase dopada rutilo Cu para as contendo Cu. A atividade fotocatalítica foi avaliada em teste de desempenho realizado em sistema reacional construído na execução do trabalho. Os testes permitiram identificar resultados preliminares promissores de atividade fotocatalítica para as amostras contendo Fe em sua estrutura, que demonstraram uma significativa atividade fotocatalítica no espectro Visível. / [en] In recent years many efforts have been made to obtain materials capable of efficiently exploiting the potential of solar energy conversion. In particular, the generation of fuels by photocatalysis retains great interest due to its intrinsic properties of promoting up-hill reactions, with a positive free energy variation, allowing its storage in chemical compounds. The efficiency of these processes, however, is usually limited by the photoactivation of main photocatalysts in UV spectrum, wasting much of the solar energy present in visible spectrum. This work investigates the influence on photoactivation performance of heterojunctions with Fe and Cu titanate grown on TiO2 for H2 gas production under Visible light by water-splitting. The samples were prepared according route by wet impregnation followed by post-heating treatment, where metal oxides were formed on TiO2 particles surface with subsequent interdiffusion and formation of ternary phases of Fe2TiO5 e Cu3TiO4. The materials were characterized by DRX, DSC, TGA, MEV / EDS, DRS, PLS and N2 Physisorption techniques. The results confirmed the materials sucessful preparation, suggesting the formation of PN-type heterostructures for Fe-containing samples and a rutile-Cu doped phase for Cu-containing samples. The photocatalytic activity was evaluated in a performance test using a photoreactor system built in as part of this work. The tests allowed to identify promising preliminary results for Fe-containing samples, which demonstrated a significant photocatalytic activity in the Visible spectrum.

[pt] Pelotas de minério de ferro são formadas a partir da aglomeração de finos de minério e constituem o principal insumo para o processo de redução na indústria siderúrgica. As frações de fases sólidas e de poros afetam propriedades tais como resistência à compressão, permeabilidade a gases durante o processo de redução, e redutibilidade. No presente trabalho desenvolveu-se um método automático para a identificação e a quantificação automáticas das fases sólidas e poros presentes em pelotas de minério de ferro, mediante a correlação de imagens obtidas por duas técnicas diferentes – microscopia ótica (MO) e eletrônica de varredura (MEV). Imagens em mosaico cobrindo completamente uma seção transversal equatorial da pelota foram capturadas em MO e MEV. Utilizando técnicas de processamento de imagens, as fases e os poros foram identificados e quantificados em cada tipo de imagem. No entanto, cada técnica apresenta limitações na discriminação de certas fases, impedindo uma quantificação completa. Por outro lado, a combinação de imagens dos dois tipos permite discriminar todas as fases. Para isso as imagens de MO e MEV foram automaticamente registradas utilizando pontos de referência homólogos obtidos pela técnica SIFT – Scale Invariant Feature Transform. Após o registro, fases e poros foram individualmente identificadas e quantificadas, levando a resultados muito mais precisos do que os obtidos separadamente. Comparou-se também o resultado de porosidade com o obtido por microtomografia de raios-x (MicroCT). Para isso, um procedimento de correlação identificou a camada de uma tomografia 3D mais similar às imagens de MO ou MEV, foi realizado o registro e mediu-se a fração de área de poros. O valor encontrado foi muito menor na imagem de MicroCT, fato atribuído à pior resolução espacial desta técnica. / [en] Iron ore pellets are formed by an agglomeration process and currently constitute the main source for the reduction process in steel making. The fractions of solid phases and pores directly affect pellets´ properties such as compression resistance, gas permeability during the reduction process, and reducibility. In this work a method for the automatic identification and quantification of phases and pores in iron ore pellets was developed, based on the correlation between images obtained with two different techniques – optical microscopy (OM) and scanning electron microscopy (SEM). Mosaic images covering the full equatorial cross section of a pellet were acquired with OM and SEM. Employing digital image processing techniques the phases and pores were identified and quantified in each type of image. However, each imaging technique has limitations in the discrimination of certain phases, preventing a full quantification. On the other hand, the combination of the two types of images allows discriminating all phases. For that, OM and SEM images were automatically registered using homologous reference points obtained with the SIFT – Scale Invariant Feature Transform technique. After registration, phases and pores were individually identified and quantified, leading to much more accurate results than those provided separately by OM or SEM. The porosity was also compared with that provided by x-ray MicroCT. For that, a correlation procedure identified the closest matching MicroCT layer to the OM or SEM images, the image was registered and the pore fraction was measured. The obtained value is much lower for the MicroCT image, what was attributed to the worse spatial resolution of the technique.

Une part importante de la détérioration des réseaux d’assainissement en matériau cimentaire est d’origine biologique. Dans ce contexte, les matériaux à base de ciment alumineux ont montré une meilleure durabilité que ceux à base de ciment Portland ordinaire, couramment utilisés. Les hypothèses de la littérature qui expliqueraient cette meilleure résistance sont centré sur l’aluminium (présent à plus de 50% dans les ciments alumineux pour seulement 5% dans les ciments Portland). L’objectif de cette thèse est de caractériser et hiérarchiser les mécanismes de résistance des matériaux cimentaires lors de la biodétérioration. Cela permettra de comprendre le rôle de l’aluminium dans les interactions entre les microorganismes et les matériaux cimentaires. Après des études en réacteur et des tests de biodétérioration de pâte de ciments en laboratoire, il semblerait que la principale cause de résistance est due à la réactivité des matrices cimentaires plus qu’à un effet inhibiteur de l’aluminium ou du matériau sur les microorganismes. / An important part of the deterioration observed in concrete sewer networks is due to biological activity. In this context, calcium aluminate cement (CAC) based material has shown a better durability than ordinary Portland cement, usually used in such context. In literature, hypothesis explaining the better resistance are focused on aluminium. The aim of the project is to characterize the role of aluminium in the interactions between cementitious material and microorganisms. Reactor study and Lab scale aggressive biodeterioration protocol of cementitious material revealed that the better resistance of CAC is due to their lower reactivity and not to a bacteriostatic effect of the material on the microorganisms.

Orientador: Juno Gallego / Resumo: A cavitação ocorre inerente ao processo de produção de energia elétrica nas Usinas Hidrelétricas, ocasionando perda progressiva de massa, afetando o desempenho e potência obtidos das turbinas hidráulicas, sendo necessário o seu reparo. Visando minimizar desgaste utiliza-se uma técnica de engenharia de superfície que é aplicar uma camada de material resistente a cavitação. Dentre esses materiais destacam-se os aços inoxidáveis com cobalto, por causa de sua dureza, baixa energia de falha de empilhamento e capacidade de endurecimento por deformação. As deposições desses materiais são realizadas por processos de soldagem, como a soldagem a arco elétrico com atmosfera gasosa ou por soldagem com arame tubular, devido ao baixo custo, elevada taxa de deposição, qualidade de acabamento superficial e baixa taxa de diluição. Diante deste contexto, esse trabalho foi realizado para analisar a camada de aço inoxidável austenítico com cobalto e verificar a influência da camada de amanteigamento. Sendo assim, foram produzidas duas séries de amostra, cada uma composta por três corpos de provas, sendo diferenciadas pela energia de soldagem utilizadas no processo, obtidas pela variação da corrente de soldagem, 98 A, 143 A e 198 A. Na primeira série foi simulado uma condição de reparo das turbinas hidráulicas, utilizando como metal base o aço ASTM A36, sendo depositado sobre ele o arame AWS E70-S6, como camada de preenchimento, posteriormente foi aplicado o arame AWS E309-T1, camada de amanteiga... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Cavitation occurs inherently to the process of production of electric power in the Hydroelectric Power Plants, causing progressive loss of mass, affecting the performance and power obtained from the hydraulic turbines, being necessary its repair. In order to minimize wear, a surface engineering technique is used to apply a layer of cavitation resistant material. Among these materials stand out the cobalt stainless steels, because of their hardness, low stacking failure energy and strain hardenability. The depositions of these materials are carried out by welding processes, such as Gas Metal Arc Welding or by Flux Cored Arc Welding, due to the low cost, high deposition rate, surface finish quality and low dilution rate. Considering this context, this work was carried out to analyze the austenitic stainless steel layer with cobalt and to verify the influence of the buttery layer. Therefore, two series of samples, each composed of three test bodies, were differentiated by the welding energy used in the process, obtained by the variation of the welding current, 98 A, 143 A and 198 A. In the first group, a hydraulic turbine repair condition was simulated using ASTM A36 steel as the base metal. The AWS E70-S6 wire was deposited on it as a fill layer, after which the AWS E309-T1 wire was applied. and finally the austenitic stainless steel with cobalt was deposited as a coating. In the second group of samples were produced without the buttery layer. The microstructure was analyzed by... (Complete abstract click electronic access below) / Mestre

O presente trabalho teve como objetivo a caracterização mecânica, microestrutural e inspeção fratográfica do compósito de matriz de alumínio Al-1100 reforçado com partículas de carbeto de silício-SiC (40 μm) fabricados por meio de laminação acumulativa (ARB- do inglês Accumulative Roll Bonding), assim como, para efeito comparativo, foram estudados o Al-1100 processado por ARB sem adição de partículas e Al-1100 como recebido. Ensaio de desgaste microadesivo com esfera fixa e ensaio de tração unidirecional quase estático que foram realizados em amostras sem entalhes e em amostras contendo diferentes geometrias de entalhe. Microscopia óptica, microscopia eletrônica de varredura nos modos: elétrons secundários, elétrons retroespalhados, espectroscopia de energia dispersiva por raios-X e difração de elétrons retroespalhados, difração de raios-X e microtomografia computadorizada foram utilizados para caracterizar as amostras. Os resultados obtidos mostraram êxito da incorporação de partículas de SiC na matriz de Alumínio por meio do processo ARB. Houve ganhos relevantes na resistência máxima à tração, na rigidez e na deformação máxima no momento da ruptura, devido à incorporação de SiCp. Essas propriedades foram bastante influenciadas na presença de concentradores de tensão (entalhes). A resistência ao desgaste do compósito foi excepcionalmente incrementada comparativamente aos demais materiais. Todos os resultados foram corroborados pelas análises microetrutural e fratográficas. / The present study aims to characterize mechanical, microstructural and through fractographic inspection laminates Al-1100 aluminum matrix composite reinforced with silicon carbide particles, SiCp (40 μm), manufactured by accumulative roll bonding (ARB), as well as, for comparative effect, were studied Al-1100 processed by ARB without the addition of particles and Al-1100 received. Micro-adhesive wear test with fixed ball and test almost static unidirectional traction were performed on samples without scoring, and in samples containing different geometries notches. Optical microscopy, scanning electron microscopy modes: secondary electrons, backscattered electrons, energy dispersive X-ray and electron backscatter diffraction, X-ray diffraction and computed microtomography, these were used to characterize the samples. The results indicated successful incorporation of SiC particles in the aluminum matrix by ARB process. There have been significant gains in maximum tensile strength, stiffness and maximum deformation at the time of rupture, due to incorporation of SiCp. These properties were strongly influenced in the presence of stress concentrators (notches). The resistance of the composite wear was exceptionally increased compared to Al-1100 ARB. All results were corroborated by microstructural and fractographics analysis.

Les aciers inoxydables ferritiques sont actuellement les meilleurs candidats pour répondre au cahier des charges des matériaux destinés aux interconnexions de piles à combustibles à oxyde solide (SOFC acronyme anglo-saxon pour Solid Oxide Fuel Cell). Cependant, du coté du compartiment cathodique de ces piles, le phénomène de sublimation du chrome à haute température conduit à des dégradations importantes, réduisant ainsi la durée de vie en service des SOFC. Les objectifs de ce travail de thèse sont (i) d'étudier le phénomène de sublimation du chrome sur l'acier inoxydable ferritique AISI 441 et (ii) de rechercher le ou les moyen(s) d'atténuer cette même sublimation. Sur le deuxième point, des méthodes de protection ont été mises en œuvre, en particulier avec le dépôt de films minces de spinelle Mn-Co obtenues via un procédé de galvanoplastie ou bien encore en procédant à des pré-oxydations des alliages dans des atmosphères contrôlées de type argon impur ou mélanges gazeux équimolaires CO / CO2 (250 ° C et 850 ° C, pour une durée totale de 3 h).Concernant l'étude de la sublimation du chrome, des essais d'oxydation simulant les conditions de service ont été conduites dans des mélanges gazeux : 5% de O2 dans H2O à 800 °C pendant 96 h. A vitesse de gaz oxydants faible, de 1 à 3 cm / s, la sublimation du chrome est limitée par un phénomène de diffusion dans la phase gazeuse de l'espèce volatile oxo-hydroxyde de chrome. A vitesse plus élevée, de 3 à 10 cm / s, la sublimation du chrome semble limitée par un phénomène interfacial. La vitesse de sublimation apparait indépendante de la rugosité de surface des échantillons, elle même variant selon la préparation des échantillons. Du point de vue de la caractérisation morphologique des couches d'oxydation thermiques obtenues, sur les surfaces de plus forte rugosité (surface industrielle), nous avons noté le développement de nodules riches en titane et en niobium avec une partie externe et une autre interne. Dans le substrat, des phases de lave de type Fe2Nb ont été observées le long des joints de grain métalliques.Dans une deuxième partie, la sublimation du chrome a été étudiée sur échantillons revêtus ou pré-oxydés. Les films minces de spinelle Mn-Co ne conduisent pas à l'abaissement de la vitesse de sublimation du chrome et sont donc pas protecteurs. L'adhérence de ces revêtements est de mauvaise qualité. Les couches présentent de nombreuses fissures. La pré-oxydation conduit quant à elle à une réduction considérable (jusqu'à un facteur 10) de la vitesse de sublimation du chrome (sauf dans le cas de la pré-oxydation dans l'argon à 850 °C). La formation d'un film riche en fer obtenu à basse température (250 °C) peut expliquer cette réduction par l'établissement d'une barrière de diffusion. Cette même réduction est cependant surprenante sur les films riches en chrome obtenus par pré-oxydation à 850 °C dans CO / CO2. Nous proposons dans ce travail une interprétation originale basée sur les différences de nature semi-conductrice des films de chromine formées à haute pression d'oxygène (proche de l'atmosphère) et identifiés comme étant de type p par rapport à ceux obtenus à basse pression (dans CO/CO2) qui sont connu pour être de type n. Après l'oxydation à haute température de 96 heures, tous les échantillons préalablement pré-oxydés ont été observés comme étant composés d'oxyde de chrome et d'un spinelle Mn-Cr.Au terme de ce travail de thèse, il peut être conclu que la pré-oxydation de l'alliage 441 à basse température (250 °C) dans l'argon ou le mélange CO/CO2 ou encore à plus haute température (850 °C) dans le mélange CO/CO2 sont des traitements qui conduisent à l'abaissement de la vitesse de sublimation du chrome et par voie de conséquence à l'amélioration de la tenue de cet alliage en condition d'oxydation dans le compartiment cathodique des SOFC. / Ferritic stainless steels are the most attractive materials that are able to fulfil SOFC(Solid Oxide Fuel Cell) interconnect properties. However, in cathodic SOFC condition, Crvolatilisation from ferritic steels leads to degradations of interconnect and cathode materialsand shorter service lifetime of SOFC. The objectives of this work are (i) to study Crvolatilisation from AISI 441 ferritic stainless steel and (ii) to find the way out to suppress Crvolatilisation. The Cr volatilisation protective methods used in this work were coating withMn-Co spinel by an electroplating method and preoxidation in the condition of Ar or CO/CO2at either 250°C or 850°C, for 3 h. Cr volatilisation experiments were performed in 5%H2O inO2 at 800°C for 96 h. According to the results, it can be concluded that the preoxidation ofthe AISI 441 in Ar or CO/CO2 at low temperature (250°C) or in the CO/CO2 at a highertemperature (850°C) are treatments that lead to lowering the sublimation rate of the Cr andimprovement in the oxidation resistance of this alloy in the cathodic compartment of theSOFC.

Submitted by Danilo Gomide (gomidedanilo@gmail.com) on 2018-09-25T01:29:16Z No. of bitstreams: 1 Dissertação-Danilo Gomide.pdf: 5902894 bytes, checksum: 200b6aa57360f837a89107b0b9e766f0 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-09-25T18:54:18Z (GMT) No. of bitstreams: 1 gomide_da_me_ilha.pdf: 5902894 bytes, checksum: 200b6aa57360f837a89107b0b9e766f0 (MD5) / Made available in DSpace on 2018-09-25T18:54:18Z (GMT). No. of bitstreams: 1 gomide_da_me_ilha.pdf: 5902894 bytes, checksum: 200b6aa57360f837a89107b0b9e766f0 (MD5) Previous issue date: 2018-07-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A cavitação ocorre inerente ao processo de produção de energia elétrica nas Usinas Hidrelétricas, ocasionando perda progressiva de massa, afetando o desempenho e potência obtidos das turbinas hidráulicas, sendo necessário o seu reparo. Visando minimizar desgaste utiliza-se uma técnica de engenharia de superfície que é aplicar uma camada de material resistente a cavitação. Dentre esses materiais destacam-se os aços inoxidáveis com cobalto, por causa de sua dureza, baixa energia de falha de empilhamento e capacidade de endurecimento por deformação. As deposições desses materiais são realizadas por processos de soldagem, como a soldagem a arco elétrico com atmosfera gasosa ou por soldagem com arame tubular, devido ao baixo custo, elevada taxa de deposição, qualidade de acabamento superficial e baixa taxa de diluição. Diante deste contexto, esse trabalho foi realizado para analisar a camada de aço inoxidável austenítico com cobalto e verificar a influência da camada de amanteigamento. Sendo assim, foram produzidas duas séries de amostra, cada uma composta por três corpos de provas, sendo diferenciadas pela energia de soldagem utilizadas no processo, obtidas pela variação da corrente de soldagem, 98 A, 143 A e 198 A. Na primeira série foi simulado uma condição de reparo das turbinas hidráulicas, utilizando como metal base o aço ASTM A36, sendo depositado sobre ele o arame AWS E70-S6, como camada de preenchimento, posteriormente foi aplicado o arame AWS E309-T1, camada de amanteigamento, e por último foi depositado o aço inoxidável austenítico com cobalto, como revestimento. Na segunda série as amostras foram produzidas sem a camada de amanteigamento. A microestrutura foi analisada por macrografia e microscopia eletrônica de varredura. Os resultados mostraram boa interação metalúrgica entre as diferentes camadas e microconstituintes correspondentes aos investigados na literatura. A microanálise por EDS demonstra a baixa diluição do processo de soldagem utilizado. Os ensaios de difração de raio-X foram capazes de identificar as estruturas de cada camada, como a estrutura CFC no material resistente a cavitação. O ensaio de microdureza instrumentado demostra a capacidade de o revestimento com cobalto resistir à cavitação e que é dispensável a camada de amanteigamento. / Cavitation occurs inherently to the process of production of electric power in the Hydroelectric Power Plants, causing progressive loss of mass, affecting the performance and power obtained from the hydraulic turbines, being necessary its repair. In order to minimize wear, a surface engineering technique is used to apply a layer of cavitation resistant material. Among these materials stand out the cobalt stainless steels, because of their hardness, low stacking failure energy and strain hardenability. The depositions of these materials are carried out by welding processes, such as Gas Metal Arc Welding or by Flux Cored Arc Welding, due to the low cost, high deposition rate, surface finish quality and low dilution rate. Considering this context, this work was carried out to analyze the austenitic stainless steel layer with cobalt and to verify the influence of the buttery layer. Therefore, two series of samples, each composed of three test bodies, were differentiated by the welding energy used in the process, obtained by the variation of the welding current, 98 A, 143 A and 198 A. In the first group, a hydraulic turbine repair condition was simulated using ASTM A36 steel as the base metal. The AWS E70-S6 wire was deposited on it as a fill layer, after which the AWS E309-T1 wire was applied. and finally the austenitic stainless steel with cobalt was deposited as a coating. In the second group of samples were produced without the buttery layer. The microstructure was analyzed by macrography and scanning electron microscopy. The results showed good metallurgical interaction between the different layers and microconstituents corresponding to those investigated in the literature. Microanalysis by EDS demonstrates the low dilution of the welding process used. The X-ray diffraction tests were able to identify the structures of each layer, such as the CFC structure in the cavitation resistant material. The instrumented microhardness test demonstrates the ability of the cobalt coating to withstand cavitation and that the buttery layer is dispensable.

Células a combustível de óxido sólido suportadas no eletrólito de zircônia estabilizada com ítria (YSZ) foram fabricadas usando a técnica do recobrimento por rotação (spin-coating) para deposição de catodos de manganita de lantânio dopada com estrôncio (LSM) e anodos compósitos de níquel e YSZ (Ni-YSZ). Parâmetros microestruturais dos eletrodos, tais como espessura, tamanho médio de partículas e temperatura de sinterização foram otimizados, visando reduzir a resistência de polarização da célula e melhorar o seu desempenho. Estes estudos serviram de base para a fabricação de células com camada catalítica para uso com etanol direto. Sobre o anodo Ni-YSZ da célula foi depositada uma camada catalítica de céria dopada com gadolínia (CGO) com 0,1% em peso de irídio (Ir-CGO). A camada catalítica visa reformar o etanol antes do seu contato com o anodo Ni-YSZ, evitando o depósito de carbono na superfície do Ni que inviabiliza o uso de combustíveis primários contendo carbono nestas células a combustível. Inicialmente, a célula a combustível foi testada com etanol e as melhores condições de operação foram determinadas. Em seguida, as células unitárias foram testadas com etanol sem adição de água por períodos de tempo de até 390 horas. As células a combustível a etanol direto com camada catalítica operam no modo de reforma interna gradual, apresentando boa estabilidade e densidades de corrente similares às obtidas na operação com hidrogênio. Após a operação das células a combustível a etanol direto, análises de microscopia eletrônica de varredura mostraram que não houve formação significativa de depósitos de carbono na superfície do Ni, indicando que a camada catalítica de Ir-CGO foi efetiva para operação com o etanol. Testes de células a combustível a etanol direto sem a camada catalítica revelaram uma rápida degradação nas horas iniciais de operação com formação de grandes quantidades de depósitos de carbono identificados visualmente. Considerando-se a operação estável com etanol a seco por tempos relativamente longos de operação, os resultados alcançados representam um avanço significativo e apontam para o desenvolvimento de células a combustível a etanol direto usando-se os componentes tradicionais com a adição de uma camada catalítica. / Yttria-stabilized zirconia (YSZ) electrolyte supported solid oxide fuel cells were fabricated with spin-coated strontium-doped lanthanum manganite (LSM) cathodes and Ni-YSZ cermet anodes. The microstructural parameters of the electrodes such as thickness, average particle size, and sintering temperature were optimized to decrease the polarization resistance of the single cells and to improve their electrochemical performance. These preliminar studies provided the basis for the fabrication of single fuel cells with a catalytic layer of gadolinia-doped ceria (CGO) and 0.1 wt% iridium (Ir-CGO) deposited onto the anode. The catalytic layer aims at the stable operation with dry (direct) ethanol; it avoids the contact of the alcohol with the anode, preventing the anode degradation by carbon deposition. Initially, the single cells were tested with ethanol and optimized operating parameters were determined. Then, the single cells were operated with anhydrous ethanol for periods of time up to 390 hours. The single cells with catalytic layer operate by the gradual internal reforming of ethanol, with good stability and delivering similar electric current densities as the ones measured using hydrogen as fuel. After single cell operation on direct ethanol, scanning electron microscopy analyses identified no significant carbon deposition on the surface of Ni, indicating that the Ir-CGO catalytic layer was effective for the reforming of ethanol. Such results were compared to the ones of standard single cells operating on dry ethanol, which showed a fast degradation and the formation of large amounts of carbon deposits. Considering the rather stable performance of single cells running on dry ethanol for relatively long times, such results represent a significant advance towards the development of direct ethanol solid oxide fuel cells using the standard components and a catalytic layer.