O Titânio e suas ligas possuem uma grande aplicação na área biomédica devido à combinação de suas propriedades mecânicas, físicas e químicas, como baixa densidade, alta resistência mecânica, baixo módulo de elasticidade, alta resistência à corrosão e boa biocompatibilidade. O presente trabalho estudou o processo de metalurgia do pó, descrevendo suas ferramentas, máquinas e processos. Pesquisa bibliográfica e análises experimentais foram feitos para obtenção de materiais biocompatíveis, através da mistura de pós metálicos, compactação e sinterização. Foram realizadas mistura dos pós de titânio (Ti) e nióbio (Nb) em proporções distintas para viabilizar a aplicação deste produto na área da medicina. Foram feitos testes para obter as características mecânicas do material, já compactado e sinterizado, com o objetivo principal de aplicar este material em implantes humanos. Além dos implantes a liga de Ti-Nb também pode ser usada na fabricação de prótese de reabilitação e testes de implantes em animais. A compactação da mistura dos pós metálicos foi realizada em uma prensa hidráulica ferramentada com dois punções e uma matriz fechada, dando origem a um material denominado compactado verde. Com os materiais já compactados, a próxima etapa foi levá-los ao forno para sinterização, de acordo com as respectivas temperaturas para cada grupo de corpo de prova. Os resultados mostraram que as amostras, sinterizadas pelo processo da metalurgia do pó, levaram à obtenção de peças de alta porosidade (de acordo com a densidade teórica). A microestrutura predominante encontrada em amostras sinterizadas a 1450 ºC consiste em partículas de titânio e nióbio bastante irregulares e com tamanhos desproporcionais, devido à diferença do tamanho das partículas dos pós, como mostrou o ensaio metalográfico. O ensaio de compressão mostrou um baixo módulo de elasticidade em função da porosidade alta, e os resultados foram considerados baixos se comparados à resistência óssea. A dureza também não foi considerada ideal, em função da alta porosidade. / Titanium and its alloys have a wide application in biomedical field due to the combination of its mechanical, physical and chemical properties such as low density, high mechanical strength, low elasticity modulus, high corrosion resistance and good biocompatibility. This work studied the process of powder metallurgy, describing their tools, machines and processes. Bibliographical research and experimental analyses were made to obtain biocompatible materials, by mixing metal powders, compacting and sintering. Titanium (Ti) powder mixtures with Niobium (Nb) powder were performed in distinct proportions to enable the application of this product in medical field. Tests were made to obtain the mechanical characteristics of the material, already compacted and sintered, with the main objective of applying this material in human implants. Besides the implants Ti-Nb alloy can also be used in the manufacture of prosthetic rehabilitation and testing of implant in animals. The compaction of the metal powders mixture was performed in a hydraulic press with two punctures and a closed die giving rise to a material called compacted green. With the materials already compressed, the next step was to take them to the oven for sintering, in accordance with their respective temperatures for each group of specimen. The results showed that the samples, sintered by powder metallurgy process, led to obtain parts of high porosity (according to the theoretical density). The predominant microstructure found in samples sintered at 1450 ºC consist in particles of Titanium and Niobium very irregulars and disproportionate in size, due to powders particles size difference, as shown by metallographic test. The compression test showed a low elasticity modulus due to high porosity and the results were considered low when compared to bone resistance. The hardness was not considered ideal, due to the high porosity.

Nióbio e suas ligas são utilizados atualmente em muitas aplicações industriais por oferecerem excelente resistência à degradação em diversos meios corrosivos. Estes meios incluem atmosferas gasosas em temperaturas elevadas, como as encontradas em plantas de gaseificação de carvão existentes em usinas termelétricas para geração de energia. As atmosferas encontradas nestes meios são misturas gasosas complexasque contêm, entre outros compostos, oxigênio e enxofre. Os sulfetos são compostos menos estáveis, possuem pontos de fusão mais baixos e apresentam, freqüentemente, maiores desvios de estequiometria em relação ao óxido correspondente. Apesar de existirem estudos relacionados à aplicação de metais refratários em atmosferas sulfetantes a temperaturas elevadas, o uso de compostos de nióbio ainda não foi devidamente avaliado como revestimento protetor, havendo poucos dados disponíveis na literatura. O objetivo deste trabalho foi avaliar o efeito proporcionado por um filme de nióbio, obtido por pulverização catódica,sobre o comportamento de sulfetação isotérmica das ligas Fe-20Cr e Fe-20Cr-1Y.Os testes de sulfetação foram realizados a 500, 600 e 700°C pelo período de 2h em atmosfera H2/2%H2S. A avaliação da resistência à sulfetação foi feita por meio do ganho de massa por unidade de área exposta. Observou-se que o comportamento de sulfetação a 500ºC das ligas FeCr e FeCrY sem e com revestimento é similar. Nesta condição, nenhuma das ligas sofreu escamação. A 700ºC a liga FeCr sofreu leve escamação na forma de um pó fino, enquanto que o produto de reação formado sobre a liga FeCrY escamou na forma de placas. O efeito do nióbio se torna pronunciado a 700ºC. A camada de produto de reação formada sobre as ligas revestidas é mais fina e plástica que na liga sem revestimento. O ganho de massa por unidade de área diminuiu sensivelmente para as ligas recobertas, que não sofreram escamação. / Niobium and niobium based alloys are currently used in many industrial applications because they offer excellent resistance to degradation in various corrosive environments. These media include gaseous atmospheres at high temperatures such as those found in existing coal gasifying plants in power plants for energy generation. These atmospheres are complex gas mixtures that contain sulfur and oxygen, among other compounds. Sulphides are thermodynamically less stable, have lower melting points and often have larger deviations from stoichiometry compared to the corresponding oxides. Although there are studies regarding the use of refractory metals in high temperature sulphidizing atmospheres, the use of niobium compounds has not been adequately evaluated and there is very little studies available in the literature about its use as a protective coating. The aim of this study was to evaluate the effect of a niobium film, deposited by magnetron sputtering on the isothermal sulphidation behavior of Fe-20Cr and Fe-20Cr-1Y alloys. The sulphidation tests were carried out at 500, 600 and 700° C for 2h in H2/2% H2S atmosphere. The sulphidation resistance was determined by mass gain per unit area. The sulphidation behavior of the coated and uncoated alloys was similar at 500ºC, and none of the alloys spalled. At 700ºC FeCr alloy scalled in the form of a fine powder, while the reaction product formed on the alloy FeCrY scalled in the form of plates. The effect of niobium became pronounced at 700°C. The reaction product layer formed on the coated alloy was thinner andmore plastic than that formed on the uncoated alloy. The mass gain per unit area of the coated alloys decreased significantly and they did not scaled.

Os revestimentos eletrozincados empregados como proteção galvânica ativa sobre os aços são utilizados industrialmente há longo tempo. Entretanto, como o zinco é um elemento muito reativo, o tratamento da sua superfície é necessário para aumentar sua vida útil. O tratamento mais utilizado consiste em imersão em solução de conversão contendo cromo hexavalente, o qual vem sendo banido por gerar substâncias tóxicas e carcinogênicas, tendo sua utilização proibida pelas normas europeias. Neste trabalho, foram estudados tratamentos alternativos ao cromato para o aço eletrozincado que não geram resíduos tóxicos. O tratamento escolhido foi desenvolvido em etapas. A primeira etapa envolveu o uso de um composto orgânico, o 2 butino-1,4 diol propoxilato, em solução com sais oxidantes e com nitrato de cério como aditivo. A etapa seguinte consistiu em imersão da superfície tratada pela etapa anterior, em um agente oxidante, o peróxido de hidrogênio. A terceira etapa consistiu na imersão em solução com 2 butino-1,4 diol propoxilato e oxalato de nióbio amoniacal (ANO). As superfícies tratadas, após cada uma das etapas, foram caracterizadas por microscopia óptica e eletrônica de varredura (MEV), difração de raios X (DRX), espectroscopia por infravermelho (FTIR) e espectroscopia fotoeletrônica de raios X (XPS). A caracterização quanto à corrosão das superfícies tratadas foi feita por ensaios de névoa salina e espectroscopia de impedância eletroquímica (EIE). Os resultados mostraram que cada uma das etapas teve uma contribuição no aumento da resistência à corrosão e esta foi dependente do tempo de tratamento em cada uma das três etapas. A composição química das camadas obtidas foi caracterizada por FTIR e XPS. Esta última técnica permitiu analisar a distribuição dos elementos nas camadas formadas ao longo da espessura da mesma, usando a técnica de desbaste (sputtering), obtendo perfis de profundidade. A presença de ácido carboxílico ligado ao substrato metálico (zinco) foi observada. Os resultados mostraram que ocorreu formação de camada orgânica e a incorporação de cério e de nióbio a esta camada. Estes se apresentam distribuídos em toda a extensão da camada, na forma de óxidos em dois estados de oxidação, III e IV, no caso do cério, e IV e V, no caso do nióbio. As camadas formadas após as várias etapas adotadas contêm uma estrutura polimérica formada por filme orgânico e uma mistura de óxidos, particularmente óxido e hidróxido de zinco, os quais ficam retidos na estrutura da camada e conferem proteção à corrosão do substrato metálico por períodos prolongados de imersão. Os resultados quanto a proteção à corrosão mostraram que o tratamento com o melhor desempenho (T10_10_10) proporcionou proteção ao substrato por longos períodos de tempo e esta foi superior em comparação à promovida por camada de cromato, tanto pelo ensaio de névoa salina como o de EIE. Este tratamento mostrou-se, portanto, uma alternativa promissora para substituição de camada de cromato na proteção de aço eletrozincado, tanto do ponto de vista ambiental, por não gerar resíduos tóxicos, como de resistência à corrosão. / Electrogalvanized coatings are employed as active galvanic protection to steel and its applications have been used industrially for a long time. However, as zinc is a very reactive element, the treatment of the surface is necessary to increase its lifespan. The most common treatment consisted of a conversion treatment in solution containing hexavalent chromium, which has been banned by generating toxic and carcinogenic substances, and its use prohibited by European standards. In this work, surface treatments alternative to chromating for electrogalvanized steel that do not generate toxic waste were studied. The chosen treatment was developed in stages. The first stage involved the use of an organic compound, 2 butyne 1,4 diol propoxylate in solution with oxidizing salts and cerium nitrate as an additive. The next step involved immersing the treated surface by the previous step in an oxidizing agent, hydrogen peroxide. The third step consisted of immersion in solution with 2-butyne 1,4 diol propoxylate and ammonium niobium oxalate (ANO). Treated surfaces after each step were characterized by optical microscopy and scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR) and photoelectron spectroscopy X- ray (XPS). The characterization for corrosion of the treated surfaces was made by salt spray tests and electrochemical impedance spectroscopy (EIS). The results showed that each step has a contribution in increasing the corrosion resistance and this was dependent on the treatment time adopted in each of the three stages. The chemical composition of the layers obtained was characterized by FTIR and XPS. This last technique allowed to analyze the distribution of the elements in the layer formed along its thickness, by sputtering the surface to obtain depth profiling. The presence of carboxylic acid bonded to the metal substrate (zinc) was observed. The results showed that there was formation of organic layer and the incorporation of cerium and niobium this layer. These elements were distributed throughout the length of the layer in the form of oxides in two oxidation states; in the case of cerium, as III and IV, and IV and V, in the case of niobium. The layers formed after the various steps contain a polymeric structure and a mixture of oxides/hydroxide, particularly of zinc, which are retained in the structure of the layer and provide corrosion protection to the metal substrate for prolonged periods. The corrosion results showed that the best treatment (T10_10_10) provided protection to the substrate for long periods of time and that was higher compared to that promoted by the chromate layer, either by the salt spray test as the EIS test. Therefore, this treatment proved a promising replacement to chromate layer in the corrosion protection of electrogalvanised steel, either from its corrosion properties or from an environmental point of view.

The present project has made a comprehensive assessment of the effect of Nb doping on various charge-transfer related properties of TiO2. Of particular focus, the electrical properties of Nb-doped TiO2 (0.65 at %) have been investigated using the simultaneous measurement of electrical conductivity and thermoelectric power. This investigation was undertaken at elevated temperatures (1073 K -- 1298 K) in equilibrium with a gas phase of controlled oxygen activity (10-10 Pa < p(O2) < 75 kPa). In addition, the effect of segregation on the surface versus bulk composition of Nb-doped TiO2 was also investigated at a function of temperature and oxygen activity. Specifically, the following determinations were undertaken: The effect of oxygen activity, p(O2) and temperature on both electrical conductivity and thermoelectric power The effect of Nb on the defect disorder and related electrical properties of TiO2 The determination of equilibration kinetics and the associated chemical diffusion data for Nb-doped TiO2 The determination of Nb bulk diffusion in TiO2 The effect of p(O2), temperature and dopant content on Nb segregation and the related surface composition of Nb-doped TiO2 The obtained electrical properties enable the determination of a defect disorder model for Nb-doped TiO2, which may be considered within the following p(O2) regimes: Strongly Reduced Regime. In this regime, the predominant ionic defect was anticipated to be oxygen vacancies compensated electronically by electrons. While the transition to this regime (from higher p(O2)) was clearly observed, the predominant defect disorder existing beyond this transition was not confirmed due to an inability to obtain sufficiently low oxygen activity. Metallic-type conductivity behaviour was observed within this transition region. Reduced Regime I. In this regime, the predominate defect disorder defined by the electronic compensation of incorporated Nb ions by electrons was clearly observed. Reduced Regime II. In this regime, the predominate defect disorder defined by the ionic compensation of incorporated Nb ions by quadruply-charged titanium vacancies, was clearly observed. The present project included the determination of diffusion data which included: Temperature dependence of 93Nb tracer diffusion in single crystal TiO2 over the temperature range 1073 K -- 1573 K Chemical diffusion coefficient over the temperature range 1073 K -- 1298 K and oxygen activity range, 10-10 Pa < p(O2) < 75 kPa These pioneering studies are significant as they enable the prediction of the processing conditions required to reliably 1) incorporate Nb into the TiO2 lattice, and 2) achieve equilibrium with the gas phase. Finally, the present project included investigations on the effect of Nb segregation on the surface composition of Nb-doped TiO2, with the following outcomes: Due to segregation, the surface can be significantly enriched in Nb compared to the bulk The extent of enrichment increases as the bulk Nb content or the oxygen activity is decreased Following enrichment, the surface Nb concentration could be sufficiently high to assume a unique surface phase The outcomes of the present project are significant as they can enable the processing of TiO2 with enhanced charge transport and controlled surface properties.

Des poudres de LiNbO₃ ou de LiTaO₃ ont été préparées par la méthode sol-gel à partir d'alcoolates de lithium et de niobium ou de tantale. Des céramiques de bonne compacité ont été frittées à des températures de 1075 et 1150°C respectivement. Divers paramètres ont été considérés : structure, état d'association et concentration du précurseur, rapport eau/alcoolate, nature du solvant. Leur influence sur la compacité, la microstructure des céramiques et sur les propriétés diélectriques et ferroélectriques a été déterminée.

Mechanical properties of Nb-Ti composite superconducting wires were tested at room temperature. The results were analysed using simple composite theory, the rule of mixtures. The objective is to predict the mechanical properties of Nb-Ti superconducting composite wires as a function of volume ratio and geometry of the components, the composite wire size and the effect of heat treatment at final drawing wire sizes. To understand the mechanical behaviors of the Nb-Ti composite, mechanical testing of the individual composite components, Nb-Ti filament and copper matrix, was performed, and the geometry of the composite was also studied. The results indicate that for the monofilamentary composite simple composite theory with two components, Nb-Ti filament and copper matrix, can be used as the prediction of the UTS of the composite. For the multifilamentary composite three components make up the composites; a high strength Nb-Ti fiber, a low strength, high ductility bulk copper matrix and a mid-strength (between the Nb-Ti fiber's and bulk copper matrix's) interfilamentary copper matrix. After heavy cold work the UTS of Nb-Ti filaments and bulk copper matrix in the composite saturate, while the UTS of the interfilamentary copper increases as the interfilamentary spacing decreases. The UTS of the interfilamentary copper matrix as a linear function of the reciprocal of interfilamentary spacing is found. The controlling parameters in the manufacturing which determine the mechanical properties of Nb-Ti composite superconducting wires include superconductor to composite ratio, UTS of the Nb-Ti filament and copper matrix, wire final drawing size, and geometry of the composite such as size and number of the filaments, interfilamentary spacing, volume fraction of fringe and core bulk copper in multifilamentary composites. / Graduation date: 1991

Thin-film niobium mechanically controlled break junctions and resistively shunted niobium mechanically-controlled break junctions were developed and successfully microfabricated. Using these devices, high-stability atomic size contacts were routinely produced and investigated both in the normal and superconducting states. Investigations of the two-level conductance fluctuations in the smallest contacts allowed the calculation of their specific atomic structure. Embedding resistive shunts close to the superconducting atomic-sized junctions affected the coherence of the electronic transport. Finally, point contact spectroscopy measurements provide evidence of the interaction of conduction electrons with the mechanical degrees of freedom of the atomic-size niobium contacts.

La première partie de cette étude concerne la distribution de Nb et Ta à l'échelle microscopique dans les roches mantelliques. On a mesuré à la microsonde électronique leurs concentrations dans des microphases titanifères (rutile), afin d'étudier le rôle de ces phases dans le fractionnement des deux éléments.<br />La seconde partie concerne la distribution de Nb et Ta dans les différentes enveloppes terrestres. A partir d'analyses en roche totale par ICP-MS, on a étudié les variations des rapports Nb/Ta, Nb/Th et Ta/La dans les grands réservoirs géochimiques représentant la Terre Silicatée. La plupart ont un rapport Nb/Ta moyen infrachondritique (< 17,5). Seule la couche lithosphérique située à l'interface croûte-manteau se distingue par des rapports Nb/Ta suprachondritiques, attribués à la migration de faibles fractions de liquides enrichis en volatiles. Cependant, cette couche, peu épaisse et faiblement concentrée en Nb et Ta, ne peut contrebalancer les valeurs infrachondritiques des autres réservoirs.<br />Trois raisons nous conduisent à réfuter l'hypothèse d'un réservoir à Nb/Ta élevé « caché » dans le manteau convectif et alimenté par les zones de subduction, proposée pour contrebalancer ces valeurs infrachondritiques: (1) la valeur moyenne de Nb/Ta dans les arcs n'est pas significativement inférieure à celle des basaltes océaniques, (2) les valeurs faibles de Nb/Ta dans la croûte continentale ne sont pas un héritage de la subduction mais l'aboutissement de la différenciation intracrustale et (3) l'étude des basaltes océaniques n'a pas révélé de composant mantellique à Nb/Ta élevé dans leur source.<br />Finalement, l'inversion des données de Nb, Ta, Th et La à l'échelle de la planète montre qu'une incorporation de Nb dans le noyau peut expliquer le rapport infrachondritique de la Terre Silicatée. Les résultats fournissent une estimation du coefficient de partage de Nb entre noyau et manteau primitif de 0,25 ± 0.08, en accord avec les données expérimentales récentes.

Thèse doctorat : Matériaux : Villeurbanne, INSA : 2005. / Titre provenant de l'écran-titre. Bibliogr. à la fin de chaque chapitre.

Reproduction de : Thèse de doctorat : Structure et dynamique des systèmes réactifs : Lille 1 : 2005. / N° d'ordre (Lille 1) : 3712. Titre provenant de la page de titre du document numérisé. Bibliogr. à la suite de chaque chapitre.