As cerâmicas a base de carbeto de silício, SiC, tem muitas aplicações na engenharia devido às suas excelentes propriedade mecânicas, térmicas e químicas. Para a produção de cerâmicas de SiC com propriedades específicas, seu processamento deve ser escolhido de maneira a se produzirem microestruturas adequadas para cada aplicação. Para isso, na maioria das vezes, essas cerâmicas são sinterizadas via fase líquida, usando como aditivos formadores dessa fase misturas de óxidos de alumínio e algumas terras raras. Esta dissertação tem dois objetivos principais: implantar o método SEVNB no Departamento de Engenharia de Materiais (DEMAR), na Escola de Engenharia de Lorena (EEL), para medida de KIC, propriedades mecânicas que, muitas vezes, limita aplicações das cerâmicas, e introduzir mais dois óxidos de terras raras para formação da fase líquida na sinterização do SiC, os óxidos de disprósio e itérbio. Após a mistura e secagem das matérias primas, os pós foram prensados com dupla ação de pistões e isostaticamente, e em seguida foram sinterizados em atmosfera de argônio utilizando seis ciclos diferentes para cada sistema de aditivos. Após sinterização as amostras foram caracterizadas e entalhadas com lâmina de barbear utilizando pastas diamantadas de 6 e 0,25 ?m e flexionadas em 4 pontos. Os resultados mostraram uma maior densificação para o sistema de aditivos Al2O3/ Yb2O3, de aproximadamente 97% da densidade teórica, prensados a 400 MPa e sinterizados na temperatura de 1950ºC por 1 hora, com formação de ?-SiC, DyAG e YbAG em todas as temperaturas estudadas. A máquina fabricada para entalhamento das amostras se mostrou eficiente, produzindo raios de entalhes atendendo a norma ISSO 23146:2008. Quanto as propriedades mecânicas, o sistema com itérbia possui os maiores valores de módulo de elasticidade e dureza, porém menor tenacidade à fratura em relação a cada ciclo de sinterização, resultado que sugere a influência do raio catiônico das terras raras formadoras da fase secundária nas cerâmicas a base de SiC. / The silicon carbide, SiC, has many applications in engineering due to its excellent mechanical, thermal and chemical properties. For the production of SiC ceramics with specific properties, the processing should be chosen to produce microstructures suitable for each application. For this reason, in most cases, these ceramics are liquid phase sintered using additives such as formers of this phase mixed oxides of aluminum and certain rare-earths. This dissertation has two main objectives: to implement the method SEVNB at Department of Materials Engineering (DEMAR), Engineering School of Lorena (EEL), to measure KIC, mechanical propertie, which often limits the ceramic\'s applications, and introduce two more rare-earth oxides for the formation of liquid phase sintering SiC, dysprosium and ytterbium oxide . After mixing and drying, the powders were pressed with a double acting piston and isostatically, and then sintered in an argon atmosphere using six different cycles for each additive system. After sintered, samples were characterized and V-notched using a razor blade and diamond pastes of 6 and 0.25 ?m and four-point flexured. The results showed a higher densification for the system Al2O3 / Yb2O3, approximately 97% , pressed at 400 MPa and sintered at a temperature of 1950 ° C for 1 hour, with formation of ?-SiC, DyAG and YbAG at all temperatures studied. The machine used to notched the samples proved to be effective, producing notch root according to the standard ISO 23146:2008. As for the mechanical properties, the system with ytterbium oxide has higher values of elastic modulus and hardness, but lower fracture toughness for each sintering cycle studied, result that suggests the influence of the rare-earth\'s cationic radius that forming the secondary phase in the SiC.

Sistemas de células a combustível alimentadas por etanol (DEFC - Direct Ethanol Fuel Cell) são vistos como candidatos para ajudar preencher a lacuna entre a demanda e oferta de energia elétrica. Entretanto, as DEFC ainda não apresentam desempenho tão elevado, que incentivem a comercialização. Um dos principais esforços para elevar o desempenho é obter catalisadores anódicos mais eletroativos e estáveis para reação de oxidação de etanol (ROE). Neste trabalho, visou-se obter e avaliar catalisadores Pt-Sn-Terras raras (La, Ce, Pr e Eu) para ROE. Os catalisadores foram sintetizados a partir de algumas modificações do método do poliol; caracterizados fisicamente, por técnicas de EDX, ICP, ATG, DRX, TEM, XPS e XAS; e caracterizados eletroquimicamente em células de três eletrodos e em células unitárias. O método de síntese promoveu tamanhos médios de partícula entre 3,0 a 4,5 nm para catalisadores PtSnTR/C (TR: La, Ce, Pr e Eu), um dos menores valores reportados para esse tipo de material. Por DRX, foi possível verificar que a síntese promoveu um certo grau de liga Pt-Sn. Por XPS, confirmou-se a presença de Pt e Sn metálicos, óxidos de estanho e de platina, e terras raras em forma de óxidos mistos. Por XAS, observou-se que os metais adicionados promoveram um preenchimento da banda 5d da Pt. As caracterizações eletroquímicas indicaram maior densidade de corrente na ROE para os materiais ternários PtSnTR/C 75:20:05 do que os catalisadores Pt/C, e que PtSn/C 60:40, na maioria dos casos. Os testes de envelhecimento acelerado indicaram que, mesmo com a alteração dos perfis voltamétricos, os catalisadores ternários apresentaram menores perdas na atividade que os catalisadores Pt/C e PtSn/C. Ao caracterizar os produtos da oxidação dos catalisadores por FTIR e HPLC, observou-se que os produtos majoritários foram acetaldeído e ácido acético; e apenas uma pequena formação de CO2 foi detectada . A adição de terras raras, em baixas concentrações, aumentou a atividade eletrocatalítica dos catalisadores Pt/C e PtSn/C provavelmente por disponibilizar espécies oxidadas a baixos potenciais, favorecendo a oxidação de intermediários da ROE, e contribuiu para a estabilidade dos catalisadores PtSn/C. / Direct ethanol fuel cell (DEFC) systems are seen as candidates to fill the gap between demand and supply of electric electricity. However, the DEFC\'s performance does not encourage its large commercialization yet. One of the main efforts to increase the performance is obtaining more electroactive and stable anodic catalysts for the ethanol oxidation reaction (EOR). In this work, Pt-Sn-Rare Earth catalysts (La, Ce, Pr and Eu) were obtained and evaluated for EOR. The catalysts were synthesized using polyol method with some modifications; physically characterized by XDS, ICP, TGA, XRD, TEM, XPS and XAS techniques; the electrochemical characterization involved tests on three electrodes cell and on unit cell systems. The synthesis method promoted mean particle sizes between 3.0 and 4.5 nm for PtSnRE/C catalysts (RE: La, Ce, Pr and Eu), one of the smallest values reported for this type of material. By XRD, it was observed some degree of Pt-Sn alloy. The presence of Pt and Sn metallic, tin and platinum oxides, and rare earths in the form of mixed oxides were confirmed by XPS. The added metals promoted a fill of the Pt 5d band, as observed by XAS. Electrochemical characterizations indicated higher current density in the EOR for the ternary materials than Pt/C catalysts and PtSn/C 60:40, in most of cases. The accelerated aging tests indicated that, even with voltammetric profiles changes, the ternary catalysts had lower losses in the activity than the Pt/C and PtSn/C catalysts. By FTIR and HPLC, it was observed that the main products were acetaldehyde and acetic acid; and small concentration of CO2 was detected. The low addition of rare earths increased the electrocatalytic activity of Pt/C and PtSn/C catalysts probably because they promoted more oxidized species at low potentials, favoring the intermediates oxidation of the EOR, and contributed to PtSn/C catalysts stability.

Observações diretas das propriedades do interior da Terra são muito restritas. A maior parte das informações advém de estudos indiretos ligados à geofísica, os quais necessitam ser relacionados a estudos de materiais em laboratório para serem corretamente interpretados. Experimentos de laboratório, no entanto, precisam ser realizados em condições extremas de pressão e temperatura, o que constitui uma tarefa muito difícil de ser alcançada. Nesse contexto, estudos teóricos são fundamentais no suporte à elaboração de modelos sobre a estrutura e a composição interna da Terra. O objetivo de nosso trabalho é utilizar métodos de primeiros princípios para ajudar a elucidar o comportamento dos silicatos (MgSiO3 e CaSiO3) e dos carbonatos (MgCO3 e CaCO3) de magnésio e cálcio nas condições termodinâmicas extremas do manto. O estudo da estabilidade energética desses silicatos e carbonatos, bem como o de outros minerais que compõem o manto, fornece novas evidências sobre a melhor forma de o cálcio ser incorporado nessa região profunda, além de determinar qual carbonato é o principal hospedeiro de carbono nas profundezas da Terra. As propriedades dos sistemas foram obtidas através da teoria do funcional da densidade, considerando diversas aproximações para a energia de troca e correlação, e o método PAW (Projector Augmented Wave). As propriedades termodinâmicas foram investigadas usando a aproximação quase harmônica e a teoria de perturbação do funcional da densidade. As simulações computacionais foram efetuadas utilizando o código Quantum ESPRESSO. Observamos que a decomposição dos silicatos em seus respectivos óxidos alcalinos terrosos, MgO e CaO, mais SiO2 não é favorável. Além disso, a coexistência dos silicatos MgSiO3 e CaSiO 3 é mais estável do que a formação de ligas do tipo Mg1xCaxSiO3. Dessa forma, concluímos que o cálcio, no manto, existe numa fase independente, fazendo parte de um silicato (CaSiO3). Nossos resultados mostraram que a decomposição dos carbonatos em seus respectivos óxidos alcalinos terrosos, MgO e CaO, mais CO2 também é desfavorável, indicando que deve existir uma baixa concentração de CO 2 livre no manto, e que o carbonato de magnésio é mais estável do que o carbonato de cálcio. Portanto, nossa investigação propõe que o MgCO3 é o principal hospedeiro de carbono, na forma oxidada, no manto. Por fim, notamos que as propriedades estruturais e termodinâmicas são melhores descritas quando a energia de van der Walls é adicionada à energia de troca e correlação, indicando que esses cálculos mais precisos constituem um passo importante para melhorar a construção de modelos teóricos sobre as propriedades e a composição do manto. / Direct observations of the Earths interior properties are very restricted. Most of the information comes from indirect studies related to geophysics, which need to be related to materials studies in the laboratory to be correctly interpreted. Laboratory experiments, however, need to be performed under extreme pressure and temperature conditions, which is a very difficult task to achieve. In this context, theoretical studies are fundamental in supporting the elaboration of models on the structure and internal composition of the Earth. The purpose of our work is to use first principles methods to help elucidate the behavior of magnesium and calcium silicates (MgSiO3 and CaSiO3) and carbonates (MgCO3 and CaCO3) under the extreme thermodynamic conditions of the lower mantle. The study of the energy stability of these carbonates and silicates, as well as of other mantle minerals, provides new evidence on how calcium can best be incorporated into the mantle and to determine which carbonate is the main carbon host in the Earths deep mantle. The properties of the systems were obtained within the density functional theory, using several approximations for the exchange and correlation energy, and the PAW (Projector Augmented Wave) method. The thermodynamic properties were investigated using the quasi-harmonic approximation and the density functional perturbation theory. The computational simulations were performed using the Quantum ESPRESSO code. We observe that the decomposition of the silicates in their respective alkali earth oxides, MgO and CaO, plus SiO2 is not favorable. In addition, the coexistence of silicates MgSiO3 and CaSiO3 is more stable than the formation of alloys like Mg1xCaxSiO3. Thus, we conclude that the calcium in the lower mantle exists in an independent phase, being part of a silicate (CaSiO3). Our results also indicate that the decomposition of the carbonates into their respective alkali earth oxides, MgO and CaO plus CO2 is unfavorable, showing that there should be a low concentration of free CO2 in the mantle and that the magnesium carbonate is more stable than calcium carbonate. Therefore, our investigation proposes that MgCO3 is the main oxidized carbon host in the lower mantle. Finally, we note that the structural and thermodynamic properties are best described when the van der Walls interactions are taken into account in the exchange and correlation energy, indicating that these more accurate calculations constitute an important step to improve the construction of theoretical models on the properties and composition of the mantle.

Orientador: Fernando Aparecido Sigoli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-23T08:20:03Z (GMT). No. of bitstreams: 1 Rodrigues_EmilleMartinazzo_M.pdf: 7026453 bytes, checksum: 919cfa3fb9a89e5e72f429d675b89d74 (MD5) Previous issue date: 2013 / Resumo: Neste trabalho, foram estudadas as propriedades espectroscópicas de membranas de polidimetilsiloxano (pdms) contendo nanopartículas de fluoreto de lantânio (LaF3) dopadas com íons lantanídeos. Para isso, em um primeiro momento foi feita a caracterização e o estudo espectroscópico de nanopartículas de LaF3 dopadas com o íon Eu(III) e estabilizadas com N,Ndimetilacetamida, N,N-dimetilformamida, oleilamina ou oleilamina/ácido oleico, a fim de escolher o melhor sistema para a co-dopagem com os íons Er(III) e Yb(III) e posterior dispersão no polidimetilsiloxano. As nanopartículas estabilizadas com oleilamina apresentaram os melhores resultados espectroscópicos e de dispersão no pdms e, portanto, foi o sistema escolhido para co-dopagem com Er(III) e Yb(III). Em seguida, foi feito o estudo espectroscópico dessas nanopartículas co-dopadas com Er(III) e Yb(III) a fim de verificar se as mesmas apresentavam propriedades luminescentes desejáveis para aplicação em fotônica. Tanto as nanopartículas dopadas com Eu(III) quanto as nanopartículas co-dopadas com Er(III) e Yb(III) estabilizadas com oleilamina foram dispersas em polidimetilsiloxano. A reticulação da cadeia de pdms foi feita utilizando diferentes proporções entre dois reticulantes: tetravinilsilano e divinilbenzeno, permitindo assim o ajuste do valor do índice de refração do material híbrido obtido. As nanopartículas apresentaram boa dispersibilidade no pdms resultando em membranas transparentes, termicamente estáveis até aproximadamente 300 °C e com índice de refração variável dependendo das proporções entre os reticulantes utilizados. Por fim realizou-se um estudo sistemático de luminescência compreendendo emissão Stokes e anti-Stokes desses materiais / Abstract: In the present work the spectroscopic properties of polydimethilsiloxane (pdms) membranes containing lanthanide-doped lanthanum fluoride (LaF3) nanoparticles were studied. In a first moment, Eu(III)-doped LaF3 nanoparticles stabilized with N,N-dimethylacetamide, N,Ndimethylformamide, oleylamine or oleylamine/oleic acid were prepared and their spectroscopic properties were studied in order to find out the best system for subsequent co-doping with Er(III)/Yb(III) and dispersion in pdms. The oleylamine-stabilized nanoparticles show the best spectroscopic and dispersion results, and therefore they were chosen for co-doping with Er(III) and Yb(III) ions. The Er(III)/Yb(III) co-doped nanoparticles were studied in order to analyze their potential use as a material for photonic applications. Eu(III)-doped and Er(III)/Yb(III) co-doped LaF3 nanoparticles stabilized with oleylamine were dispersed in pdms. The crosslinking of pdms network was done using different ratios between two types of crosslink molecules: tetravinylsilane (tvs) and divinylbenzene (dvb) allowing thecontrol of the resulting material refractive index. The nanoparticles were well dispersed into the pdms matrix and the resulting hybrid membranes were transparent and thermically stable up to 300 °C with variable refractive index depending on the ratio of used crosslink molecules. A systematic luminescence spectroscopy was done including Stokes and anti-Stokes emissions of these materials / Mestrado / Quimica Inorganica / Mestra em Química

L’objectif de cette thèse était d’étudier les propriétés de conversion de photons des ions terres rares insérées dans des matrices d’oxydes transparents en vue d’application photovoltaïques. En particulier, le but était de fonctionnaliser des couches minces déjà utilisées dans les cellules solaires comme couches antireflet ou oxydes transparents conducteurs. Nous avons donc sélectionné deux matériaux (ZnO et CeO2) compatibles avec les cellules solaires au silicium.Ce travail a montré que les couches minces dopes aux terres rares peuvent être utilisées pour convertir les photons dans des applications photovoltaïques, mais qu’il n’est pas facile d’obtenir des rendements élevés.Cependant, nous avons obtenu des informations très importantes sur l’influence de la matrice sur les propriétés de conversion des terres rares et sur les mécanismes de transfert d’énergie entre la matrice et la terre rare. / The objective of this thesis was to investigate the photon converting properties of rare earths (RE) ions embedded in transparent oxide hosts in view of potential application on silicon solar cells. In particular, the goal was to functionalize thin films that are already used in solar cells such as anti-Reflection coatings or transparent conductive oxides.Two host materials (ZnO and CeO2) have been selected, which are compatible with silicon solar cells.This work shows that RE-Doped transparent oxide films are a viable low-Cost solution for obtaining photon-Converting layers that can be applied on solar cells, but that achieving high efficiencies is much more difficult than it might appear in theory. Nevertheless, very valuable information has been obtained on the effect of the host material on the photon management properties and on the energy transfer mechanisms in these systems. In particular, the energy level diagram of some of the rare earth ions in the specific matrices has been reconstructed.

Ce travail est consacré au développement de luminophores de type orthophosphates GdPO4 et ultraphosphates YP5O14 activés par les ions Yb3+, Er3+ et Tm3+, synthétisés sous forme de poudres par voie solvothermale (orthophosphates) et par méthode de flux (ultraphosphates), aptes à émettre une lumière blanche par up-conversion IR-visible. Des orthophosphates GdPO4 : Eu3+ ont également été élaborés par chimie douce afin d’établir le lien entre propriétés optiques et propriétés morphologiques. Les conditions opératoires optimales ont été déterminées. La caractérisation des matériaux obtenus a été menée d’un point de vue structural, par DRX et IR, et morphologique, par MEB. Les orthophosphates GdPO4 ont été obtenu sous forme de nanobâtonnets en condition acide et nanodisques en milieu basique. L’étude des propriétés de luminescence des orthophosphates GdPO4 : Eu3+ a montré que les nanodisques présentent de meilleures performances que les nanofils. L’utilisation de la théorie de Judd et Ofelt a permis de relier les propriétés optiques, structurales et morphologiques de ces orthophosphates. Sous excitation IR, un processus de up-conversion est mis en évidence dans les phosphates YP5O14 : Yb3+, Er3+, Tm3+ et GdPO4 : Yb3+, Er3+, Tm3+. Les processus de transfert d’énergie Yb3+ → Er3+, Tm3+, présidant à l’émission d’une lumière blanche, ont été étudiés. La morphologie des matrices phosphatées a une influence notable sur les propriétés de up-conversion. Ainsi, l’orthophosphate GdPO4 : Yb3+, Er3+, Tm3+ obtenu sous forme de nanobâtonnets en milieu acide est un candidat prometteur pour la lutte anti-contrefaçon. / This work deals with the development of polycrystalline Yb3+/Er3+/Tm3+ activated phosphate phosphors of formula GdPO4 (orthophosphates) and YP5O14 (ultraphosphates) elaborated by a solvothermal method (GdPO4) and by a flux method (YP5O14), able to emit a white light by a IR-visible up-conversion process. Eu3+ doped GdPO 4 samples were also elaborated by soft chemistry in order to establish the relation between optical and morphological properties. The elaborating conditions were determined. The characterization of these materials has been carried out using X-ray diffraction, IR spectroscopy and SEM analysis. GdPO4 orthophosphates were obtained as nanorods and nanoparticles under acidic and basic media respectively. GdPO4 : Eu3+ orthophosphate nanoparticles show better optical performances than nanorods. Moreover, the optical, structural and morphological properties of orthophosphate materials were corroborated by the Judd and Ofelt theory. Under an IR excitation, an up-conversion mechanism is evidenced in YP5O14 : Yb3+, Er3+, Tm3+ and GdPO4 : Yb3+, Er3+, Tm3+ activated phosphates. Yb3+ → Er3+, Tm3+ energy transfer processes leading to a white light emission are investigated. The up-conversion properties are considerably influenced by the morphology of the phosphates. The GdPO4 : Yb3+, Er3+, Tm3+ orthophosphate obtained as nanorods in an acidic medium is a promising candidate for anticounterfeit labels.

La première partie de ce travail porte sur l’élaboration et la caractérisation de nouvelles nanoparticules (NPs) multifonctionnelles de silice à architectures complexes. L’enjeu est de répondre à la demande croissante d’élaboration de nouveaux systèmes colloïdaux non toxiques, magnétiques et/ou luminescents dans la région NIR pour des applications potentielles en biotechnologie. Cet objectif a été atteint en associant intimement des composés à clusters de molybdène avec des nanocristaux de maghémite et/ou d’or dans une NPs de silice de 50 nm. Une évaluation de la cytotoxicité des NPs contenant des clusters d’éléments de transition Cs2Mo6Br14 ainsi qu’un suivi par microscopie de fluorescence en temps retardé des NPs Cs2Mo6I8(C2F5COO)6@SiO2 incorporées dans des cellules cancéreuses sont présentés. Dans la deuxième partie, des poudres microcristallines de composés hétéronucléaires de polymères de coordination à base de terres rares de formule chimique générale [Ln2-2xLn’2x(bdc)3,4H2O]∞ avec 0 ≤ x ≤ 1 ont été nanométrisées dans du glycérol. Ces NPs présentent des propriétés luminescentes identiques à celles du matériau massif. Une étude détaillée de cette nouvelle voie de synthèse répondant aux principes de la chimie verte ainsi qu’une étude de la stabilité en fonction du temps et de la dilution des colloïdes obtenus ont été réalisées. / The first part of this work involves the development and characterization ofnovel nanoparticles (NPs) of multifunctional silica with complex architectures.The challenge is to meet the increasing demand for development of newnon-toxic colloidal systems, magnetic and/or luminescent in the NIR regionfor potential applications in biotechnology. This objective was achievedby closely associating molybdenum clusters compounds with maghemitenanocrystals and/or gold in 50 nm silica NPs. An evaluation of thecytotoxicity of NPs containing clusters of transition elements of Cs2Mo6Br14and a time-gated fluorescence microscopy of Cs2Mo6I8(C2F5COO)6@SiO2NPs incorporated in cancer cells are presented.In the second part, microcrystalline powders of heteronuclear lanthanidebasedcoordination polymers with general chemical formula [Ln2-2xLn’2x(bdc)3,4H2O] ∞ 0 ≤ x ≤ 1 were dissolved in glycerol . These NPsexhibit luminescent properties identical to that of the bulk material.A detailed study of this new green synthetic route and a study of thestability over time and a dilution of the obtained colloids were performed.

Cette thèse de doctorat traite du comportement géochimique de Zr, Hf et Terres Rares dans des environnements aqueux extrêmes. Les études ont été effectuées dans les eaux hyper-salines long de la faille de la Mer Morte (Israël), les eaux hyper-acides dans le système volcanique hydrothermal du Nevado del Ruiz (Colombie) et les eaux riches en CO2 du système volcanique hydrothermal de l'île de Pantelleria, en comprenant le lac alcalin “Specchio di Venere”. Haute appauvrissement en Terres Rares légères a été trouvé dans les eaux acides dominées par le sulfate où on a reconnu la formation d’alunite et jarosite. Certaines eaux long de la faille de la Mer Morte montrent des enrichissements en Terres Rares intermédiaires, causés par la dissolution des minéraux évaporitiques. Les grandes variations redox et de pH observées dans ces systèmes hydrothermaux sont la cause des anomalies de Eu et Ce. Les eaux sulfates acides (1 < pH < 3.6) se caractérisent par des relations de Zr/Hf sous-condritiques et des relations condritiques de Y/Ho. Les rapports de Zr/Hf augment à l'augmentation du rapport Cl/SO4 en suggérant un comportement différent de Zr et Hf. Contrairement aux eaux acides, les relations de Y/Ho et Zr/Hf dans les eaux proches de la neutralité avec valeurs de Eh positives augmentent vers des valeurs super-condritiques, en raison de l'élimination préférentielle par les oxyhydroxydes de fer, de l'Hf et Ho que de Zr et Y. Le distribution des Terres Rares, avec les rapports de Y/Ho et Zr/Hf du “Specchio di Venere” montrent l’interaction entre les particules atmosphériques qui viennent du désert du Sahara et le lac “Specchio di Venere”, démontrent qu’ils sont de traceurs géochimiques. / This thesis concerns the geochemistry of Zr, Hf and REE (Rare Earth Elements) in extreme water environments. The investigations were carried out in hypersaline waters covering a wide range of Eh values along Dead Sea Fault (Israel), in hyperacid waters circulating in Nevado del Ruiz volcano-hydrothermal system (Colombia) and in CO2-rich waters in Pantelleria volcano-hydrothermal system (Italy), including the alkaline lake “Specchio di Venere” within a calderic depression. The acidic sulphates waters characterized by the precipitation of alunite and jarosite show a strong LREE depletion. The REE in waters along Dead Sea Fault show MREE enrichments in waters with relative high Ca and SO4 concentrations due to the water interaction with MREE-enriched salt minerals. In the natural waters, changing of pH and Eh induce variations of Ce and Eu anomalies, due to the different behaviour of these elements with respect to the neighbours REE. In sulphate acidic waters, Zr/Hf ratios are very low down to 4.7, while quite constant Y/Ho ratio (close to the local rock value) indicates the lack of decoupling. Zr/Hf ratio increases as Cl/SO4 ratio increases. On the contrary, Zr/Hf and Y/Ho ratios in near-neutral pH waters with positive Eh values change from near-chondritic to super-chondritic. The precipitation of Fe-oxyhydroxides removes preferentially Hf and Ho with respect to Zr and Y. The interaction of atmospheric fallout from the nearby Sahara Desert with the water of the lake “Specchio di Venere” was recognized by the Zr, Hf and REE distribution. Zr, Hf and REE show the capability to trace the interaction process between open water bodies and atmospheric fallout.

The Guano-Guayes property, in the Pelly Mountains of the Yukon Territory, covers a rare earth element (REE) bearing contact metamorphic aureole which developed around a syenite stock during Mississippian time (319 ± 10 Ma phlogopite K-Ar date, 333 ± 10 Ma Rb-Sr skarn mineral isochron). Sedimentary rocks consist of several hundred metres of Ordovician dark gray shale which are faulted upward adjacent to 450 m of Silurian interbedded impure calcite and dolomite marbles and quartzites overlain by at least 500 m of Silurain quartzite. Sedimentary rocks are on the steeply, west-dipping limb of a regional anticline (the axis bears 162 degrees and plunges 24 degrees south). The syenite, at the southeast end of a northwest-trending belt of syenite stocks and associated volcanic rocks, consists of 40 to 90 percent orthoclase in laths up to several cm long, and of up to 60 percent mafic minerals now mostly altered to biotite. Rare earth element values of syenite, when normalized to chondritic values, have a crustal pattern with magnitude slightly higher than that of crustal rocks. Dikes, believed to be cogenetic with syenite, intrude sedimentary rocks within and inear the contact metamorphic aureole. These dikes are dark-coloured and originally contained up to 25 percent zircon (now partly altered to secondary minerals). Zircon is enriched in total REE and relatively enriched in light REE compared to syenite, probably due to selective partitioning of REE. REE patterns in skarn and sedimentary rocks suggest that fluids circulated through syenite and carried trace amounts of REE from it into the skarn. There was no significant movement of REE from dikes into skarn or sedimentary rocks. Contact metamorphic rocks can be divided into three units: quartz-muscovite hornfels, dark green diopsade-calcite-phlogopite-tremdlite-sphene skarn, and light green diopside-calcite-phlogopite skarn. Depth at time of intrusion of syenite, as estimated from regional geologic contraints, was around 1 to 2 km (circa 500 bars). Parageneses and textures observed in thin section in contact metamorphic rocks indicate that prograde metamorphism at this pressure reached a maximum temperature of 450 to 540 degrees C, with heat being transferred from the intrusive dominantly by fluids. The mole fraction of CO₂ in metamorphic fluids, increased By the liberation of CO₂ during prograde metamorphic reactions, was moderate. Large amounts of Fe, Mg, and possibly Si0₂, were added to the skarn. Retrograde metamorphism involved significant addition of water to the system, proven by the appearance of secondary epidote, chlorite, and, later, serpentine. Extensive retrograde metamorphism accompanied by large-scale migration of elements through syenite ended 206 ±15 Ma ago (syenite whole-rock isochron) and the last resetting event took place between 156 ± 5 Ma (K-Ar date on biotite-altered arfvedsonite) and 128 ± 25 Ma (syenite mineral isochron). Petrology, geochronometry, and rare earth element studies presented here have contributed to an understanding of the genesis of syenite, skarn, and mineralized dikes within the Guano-Guayes area. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Unknown

O trabalho tem como objetivo abordar e investigar a viabilidade técnica e econômica da proposta de substituição de um motor de corrente continua, por um motor síncrono com imãs permanentes. O passo inicial foi a análise de dados referentes à manutenção preventiva do motor em operação comparado ao motor de indução e o resultado foi que se teria grande vantagens. Foi observado que o mercado oferecia uma solução inovadora, que mudou a trajetória dos estudos. Esta solução é o motor síncrono de imã permanentes, que é um motor brushless de corrente alternada, com dimensões reduzidas para a mesma potência de um motor indução trifásico. As perdas por efeito Joule no rotor que praticamente são as maiores, neste caso são desprezíveis, pois o rotor é equipado internamente com imãs de Terras Raras, o Neodímio Ferro Boro de alta energia, que desta forma minimizam também a temperatura no motor aumentando sua vida útil. Além disso, para aplicações onde se tem a necessidade de controle de torque com velocidades baixas é a melhor solução. Estas e outras qualidades fizeram a diferença na escolha deste motor para a aplicação, onde é necessário o controle de torque com a velocidade baixa. Neste trabalho se descreve todas as etapas do retrofiting, incluindo as comparações do sistema atual com duas propostas, através de simulações no software MATLAB, que demonstraram que as expectativas iniciais foram alcançadas, identificando o motor síncrono de imãs permanentes mais indicado nos dias de hoje para a substituição. / The work had as objective approach and investigate the technical and economic viability of the proposed replacement of a DC motor, by a permanent magnets synchronous motor. The initial step was the analysis of data on preventive maintenance of the motor in operation compared to the induction motor and the result was that it would have great advantages. It was observed that the market offered an innovative solution, which changed the course of the studies. This solution is permanent magnet synchronous motor, which is a brushless AC motor with reduced dimensions at the same power of a three phase induction motor. The Joule losses in the rotor which practically are the biggest. this case are not important, because the rotor is fitted internally with Rare Earths Magnets Neodymium Iron Boron the high energy, which thus also minimize the temperature in the motor increasing its lifetime. Also, for application where there is the need to control torque at low speeds is the best solution. These and other qualities made the difference in the choice of this motor to the application, where it is necessary to control torque with low speed. We describe all stages of Retrofitting, including comparisons of the current system with two proposals, through simulations in MATLAB, which have shown that initial expectations were met, identifying the permanent magnet synchronous motor best suited these days for the replacement.