L'obtenció de precursors de lactones i d'alcohols asimètrics té gran valor ensíntesi orgànica ja que són intermediaris clau per a la preparació de moltscompostos bioactius, com medicaments, agroquímics i additius alimentaris. Toti que es disposa d'un gran nombre de reaccions selectives per a moltesnecessitats sintètiques, és encara necessari millorar i trobar nous processos quanes vol disposar de productes amb una estereoquímica definida, a més de trobarnous sistemes més respectuosos amb el medi ambient i la salut humana.En aquesta tesi es presenten diferents aproximacions per a l'obtenció d'alcoholsquirals i de precursors de lactones. Una de les aproximacions consisteix en unmètode quimio-enzimàtic, amb un primer pas de síntesi d'èsters α-funcionalitzats seguit d'una hidròlisi estereoselectiva d'aquests èsters amblipases per a l'obtenció d'halohidrines quirals. Es va estudiar l'aplicabilitat delslíquids iònics, l'ús de reactius poc contaminants i l'ús d'enzims comercials iresting-cells d'origen fúngic. Aquesta aproximació ha permès l'obtenció del S-1-cloro-2-octanol i el S-1-bromo-2-octanol. La segona aproximació consisteixen la utilització d'oxidoreductases per a la biotransformació de cetonesproquirals. Aquestes estan presents en cèl·lules en creixement de noves soquesfúngiques aïllades com a endòfits de plantes. S'ha trobat una soca de Rhizopusoryzae amb activitat biocatalítica per a l'obtenció d'alcohols quirals. / La obtención de precursores de lactonas y de alcoholes asimétricos tiene granvalor en síntesis orgánica ya que son intermedios clave para la preparación demuchos compuestos bioactivos, como medicamentos, agroquímicos y aditivosalimentarios. Aunque se dispone de un gran número de reacciones selectivaspara muchas necesidades sintéticas, aún es necesario mejorar y encontrar nuevosprocesos cuando se quiere disponer de productos con una estereoquímicadefinida, además de encontrar nuevos procesos más respetuosos con el medioambiente y la salud humana.En la presente tesis se describen varias aproximaciones para la obtención dealcoholes quirales y precursores de lactonas. Una de las aproximaciones consisteen un método quimio-enzimático, con una primera etapa de síntesis de ésteres α-funcionalizados seguida de una hidrólisis estereoselectiva de estos ésteres conlipasas para la obtención de halohidrinas quirales. Se estudió la aplicabilidad delos líquidos iónicos, el uso de reactivos poco contaminantes y el uso de enzimascomerciales y resting-cells de origen fúngico. Esta aproximación ha permitido laobtención del S-1-cloro-2-octanol y el S-1-bromo-2-octanol. La segundaaproximación consiste en la utilización de oxidoreductasas para labiotransformación de cetonas proquirales. Dichas enzimas están presentes encélulas en crecimiento de nuevos microorganismos aislados como hongosendófitos de plantas. Se ha encontrado una cepa de Rhizopus oryzae conactividad biocatalítica para la obtención de alcoholes quirales. / Asymmetric lactones and alcohols are valuable building blocks in organicchemistry applicable to the synthesis of many bioactive compounds such asdrugs, agrochemicals and food additives. There are a large range of selectiveorganic reactions available for most synthetic needs, but there is still one weakarea in organic chemical synthesis where stereochemistry is involved. Inaddition, there is a need to develop new syntheses and processes less hazardousto human health and the environment.This thesis reports diverse approaches to prepare chiral alcohols and lactonesprecursors. The first one consists of a chemo-enzymatic method to synthesisechiral halohydrins. This process implies a first step of synthesis of α-functionalesters followed by a stereoselective hydrolysis by lipases. The suitability ofionic liquids as reaction media, the use of less polluting reagents, and theapplication of commercial enzymes and resting-cells from fungus were studied.This methodology permits the preparation of S-1-chloro-2-octanol and S-1-bromo-2-octanol. The second approach consists of the biotransformation ofprochiral ketones by oxidoreductases from new endophytic fungus strainsisolated from diverse plants. One Rhizopus oryzae strain was found to be aputative biocatalyst to provide chiral alcohols.

In this thesis, the feasibility of employing organometallic single-source precursors in the preparation of advanced transition metal pnictide materials such as colloidal nanoparticles and films has been investigated. In particular, the ternary FeMnP phase was targeted as a model for preparing advanced heterobimetallic phosphide materials, and the iron-rich Fe 3 P phase was targeted due to its favorable ferromagnetic properties as well as the fact that the preparation of advanced Fe 3 P materials has been elusive by commonly used methods. Progress towards the synthesis of advanced Fe 2-x Mn x P nanomaterials and films was facilitated by the synthesis of the novel heterobimetallic complexes FeMn(CO) 8 (μ-PR 1 R 2 ) (R 1 = H, R 2 = H or R 1 = H, R 2 = Ph), which contain the relatively rare μ-PH2 and μ-PPhH functionalities. Iron rich Fe 2-x Mn x P nanoparticles were obtained by thermal decomposition of FeMn(CO) 8 (μ-PH 2 ) using solution-based synthetic methods, and empirical evidence suggested that oleic acid was responsible for manganese depletion. Films containing Fe, Mn, and P with the desired stoichiometric ratio of 1:1:1 were prepared using FeMn(CO) 8 (μ-PH 2 ) in a simple low-pressure metal-organic chemical vapor deposition (MOCVD) apparatus. Although the elemental composition of the precursor was conserved in the deposited film material, spectroscopic evidence indicated that the films were not composed of pure-phase FeMnP, but were actually mixtures of crystalline FeMnP and amorphous FeP and Mn x O y . A new method for the preparation of phase-pure ferromagnetic Fe 3 P films on quartz substrates has also been developed. This approach involved the thermal decomposition of the single-source precursors H 2 Fe 3 (CO) 9 PR (R = t Bu or Ph) at 400 °C. The films were deposited using a simple home-built MOCVD apparatus and were characterized using a variety of analytical methods. The films exhibited excellent phase purity, as evidenced by X-ray diffraction, X-ray photoelectron spectroscopy, and field-dependent magnetization measurements, the results of which were all in good agreement with measurements obtained from bulk Fe 3 P. As-deposited Fe 3 P films were found to be amorphous, and little or no magnetic hysteresis was observed in plots of magnetization versus applied field. Annealing the Fe 3 P films at 550 °C resulted in improved crystallinity as well as the observation of magnetic hysteresis.

Many Canadian water treatment plants supplied by surface waters of the Canadian Prairie and Shield have elevated concentrations of trihalomethanes (THMs), which exceed the provincial standards. These water sources are characterized by elevated levels of dissolved organic carbon (DOC) and varying levels of calcium hardness, which causes a challenge for the removal of THMs precursors. The objective of this study was to investigate the effect of two treatment methods: chemical coagulation and pre-ozonation-coagulation on the removal of DOC as the main THMs precursor. Surface waters typical for the Canadian Prairie and Canadian Shield were used in the experiments which includes Assiniboine River, Red River, and Rainy River. The effects of different experimental conditions such as coagulant dose, coagulant type, and solution pH as well as ozone dosage on THMs removal were investigated. The structural and chemical characteristics of natural organic matter and isolated humic substances, before and after the reaction with ozone, were studied using spectroscopic techniques. The results illustrated that the quality of source water (DOC characteristics, concentration of water DOC and Calcium) has a significant impact on THMs reduction by chemical coagulation and ozonation. Coagulation results showed that reduction of total DOC does not guarantee THMFP reduction and chemical coagulation should be optimized to remove the hydrophobic acid fraction which forms most THMs. The removal of DOC by aluminum-based coagulants was affected more by the concentration of polymeric and colloidal aluminum speciation. This finding is especially important for plants supplied by high alkalinity waters where pH adjustment is a serious challenge. The effect of pre-ozonation on coagulation varies depending on the concentration of calcium, which has the ability to form complexes with DOC compounds promoting their removal in coagulation. For the surface water with high levels of organic carbon and calcium hardness, ozonation prior to coagulation was beneficial in terms of DOC reduction. However, it showed the opposite effect on water with high levels of DOC accompanied with low level of calcium hardness. Spectroscopic results showed that ozonation of NOM and humic substances cause a significant reduction of aromatic and highly conjugated compounds (constituting primarily the hydrophobic acid fraction). / February 2016

Thesis (Ph. D.)--University of Missouri--Columbia, 1998. / "July 1998." Typescript. Vita. Includes bibliographical references (leaves 215-225). Also available on the Internet.

The dramatic change in properties of water near its critical point (i.e. T = 374 °C and p = 22.1 MPa, note: 100 MPa = 0.1 GPa = 1 kbar ≈ 1000 atm) has been a subject of numerous studies and also lead to the development of various applications (e.g. in waste destruction, biomass processing, and the synthesis of advanced ceramic materials). However, comparatively little is known about the behavior of water at gigapascal pressures. The present study attempts to explore catalytical properties and reactivity of extreme water with respect to several oxide systems: SiO2, TiO2 and LiAlSiO4. “Extreme water” here is defined as existing at p,T conditions of 0.25–10 GPa and 200–1000 °C, thus considering both supercritical fluid and hot compressed ice. The study shows that extreme water can make high pressure mineral phases accessible at relatively mild T conditions. At the same time, high pressure aqueous environments appear efficient in stabilizing novel metastable structures and may be considered as a general route for synthesizing new materials. The hydrothermal treatment of SiO2 glass at 10 GPa and 300–550 °C yielded an unusual ultrahydrous form of stishovite with up to 3% of structural water. At the same time, the extreme water environment enhanced notably the kinetics of stishovite formation, making it accessible at unprecedentedly low temperatures. Thus, for the SiO2–H2O system water acts as both catalyst and reactant. For TiO2 a hydrothermal high pressure treatment proved to be of high importance for overcoming the kinetical hindrance of the rutile – TiO2-II transformation. 6 GPa and 650 °C were established as the mildest conditions for synthesizing pure TiO2-II phase in less than two hours. The crystallization of LiAlSiO4 glass in an extreme water environment yielded a number of different phases. In the low pressure region (0.25 – 2 GPa) mainly a zeolite (Li-ABW) and a dense anhydrous aluminosilicate (α-eucryptite) were obtained. At pressures above 5 GPa the formation of novel pyroxene-like structures with crystallographic amounts of structural water was observed. The overall conclusion of this study is that extreme water environments show a great potential for catalyzing phase transitions in oxide systems and for stabilizing novel structures via structural water incorporation. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

xx, 153 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / In the research area of Group 13 hydroxide clusters, progress is often hampered by difficult and inefficient synthetic procedures. This has greatly limited the numerous potential applications of Group 13 hydroxide compounds, many of which require large amounts of material. Most relevant to this dissertation is their application as precursors for high quality amorphous metal oxide thin films. Addressing this issue, this dissertation presents a series of Group 13 containing hydroxide compounds of general formula [M 13 (μ 3 -OH) 6 (μ-OH) 18 (H 2 O) 24 ](NO 3 ) 15 which are generated through an efficient, scalable synthetic procedure. Throughout this dissertation, the compounds are generally referred to by their metal content, i.e. [Ga 13 (μ 3 -OH) 6 (μ-OH) 18 (H 2 O) 24 ](NO 3 ) 15 is designated as Ga 13 . Chapter I reviews the literature of inorganic and ligand-supported Group 13 hydroxide compounds with the aim of identifying common structural trends in metal composition and coordinating ligands. This summary is limited to clusters of aluminum, gallium, and indium. Chapter II describes in detail the synthesis and characterization of one such cluster, Al 13 . Following this in Chapter III is the description of the first heterometallic Group 13 hydroxide compound, Ga 7 In 6 , which along with Ga 13 was used as a precursor material for metal oxide thin films in collaboration with Professor Doug Keszler at Oregon State University. Chapter IV describes a series of six Ga/In compounds, as well as two Al/In compounds. Included in this chapter is an analysis of the heat-induced decomposition properties of the Ga/In clusters. Understanding such thermal decomposition is particularly relevant for the use of these compounds as precursor materials, as an annealing step is used to condense the films. Chapter V addresses the potential for post-synthetic modification of the compounds through metal and ligand exchange reactions, an area that also addresses the issue of solution stability of the structures Chapter VI describes the synthesis and characterization of related Group 13 compounds, including two infinite chain structures and additional heterometallic compounds. Lastly, Chapter VII concludes this dissertation and discusses potential areas of future research. This dissertation includes co-authored material and previously published results. / Committee in charge: Victoria DeRose, Chairperson, Chemistry; Darren Johnson, Member, Chemistry; James Hutchison, Member, Chemistry; Michael Haley, Member, Chemistry; Raghuveer Parthasarathy, Outside Member, Physics

O objetivo desta dissertação foi estudar a produção de pós de titanato de alumínio - tialita - pelo processo sol-gel associado à aspersão térmica por plasma. Foram investigados 3 tipos de solventes (etilenoglicol, álcool etílico e água) para a obtenção de um pó com características adequadas para a aplicação por aspersão ténnica a plasma. Os pós foram preparados por co-precipitação de sais inorgânicos de titânio e alumínio através da desestabilização das soluções com uma base forte. Os produtos obtidos foram então secos, calcinados em diferentes temperaturas, observando a evolução das fases. Alternativamente, pós pré-calcinados foram submetidos à aspersão térmica a plasma contra um recipiente com água, e contra um substrato de aço baixo carbono, proporcionando um resfriamento rápido. Os pós obtidos foram caracterizados por análises terrnodiferenciais (ATD) e termogravimétricas (ATG), análise granulométrica por difração de laser, análise da evolução de fases em função da temperatura de calcinação (e após aspersão térmica) por difração de raios X, análise da homogeneidade química e morfologia das partículas utilizando microscopia eletrônica de varredura (MEV) com o auxílio de espectrômetro de energia dispersiva (EDS). Os resultados mostraram que é possível obter, via sol-gel, matérias-primas adequadas para a formação da fase tialita após calcinação a temperaturas acima de 1300°C ou calcinando-se a cerca de 600°C e aspergindo em chama plásmica. Os diferentes solventes utilizados proporcionaram a produção de pós com diferentes morfologias e graus de homogeneidade química. Os pós apresentaram uma distribuição de titânio e alumínio na mesma partícula, sendo que a utilização de etilenoglicol corno solvente levou à maior homogeneidade. Com menores taxas de aquecimento nas calcinações (150Kfh), em temperaturas entre 800 e 1200°C, ocorre a segregação desses elementos com formação e crescimento de grãos de rutila e coríndon. Já com o rápido aquecimento e resfriamento, característicos da aspersão térmica por chama plásmica, a fase final preponderante é a tialita, tanto com resfriamento em água quanto no resfriamento sobre um substrato. / This work has the purpose of studying the production of a ceramic powder of aluminurn titanate - tialita - by sol-gel process associated with plasma spraying. Three kinds of solvents (ethyleneglicol, ethyl alcohol, and distillated water) were investigated in order to obtain a powder with adequate characteristics to be used as feedstock in plasma spray technique. The powders were made by co-prectpttation of inorganic salts of titanium and aluminurn through destabilization of the solutions using a strong base. The products obtained were dried, calcinated at different temperatures with attention to the phase evolution. Alternately, powders pré-calcinated were submitted to plasma thermal spraying in water and in a low-carbon steel substrate, providing an intense cooling rate. The powders obtained were characterized by differential thermal analysis (DT A) and thermogravimetric analysis (TGA), particle size analysis by laser diffraction, phase evaluation in function of calcinations temperature by X ray diffraction, chemical homogeneity and particle morphology using scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The results showed that is possible obtain, by sol-gel, adequate feedstock to formation of tialita phase after calcinations at temperatures above 1300°C, or calcining at temperatures near 600°C followed by thermal spraying with plasma flame. The different kinds of solvents used, propitiated the production of powders with different morphologies and degrees of chemical homogeneity. With low heating rates in calcinations (150Kih), at temperatures between 800°C and 1200°C, occurs the segregation of aluminum and titaniurn with formation and growing of corundum and rutile phases. Since with fast heating and cooling propitiate by plasma spraying, the preponderant final phase is tialite in the substrate (water or metallic) aspersion.

Submitted by ALEXSANDER LOURENÇO PESSOA null (alexsander.pessoa@gmail.com) on 2016-05-25T13:56:43Z No. of bitstreams: 1 Síntese dos supercondutores Y123 e Y358 pelo método dos precursores poliméricos modificado utilizando fornos convencionais e de micro-ondas (Alexsander Lourenço Pessoa).pdf: 79622456 bytes, checksum: 34f39ae01a459719e274bac2d98b0ab7 (MD5) / Rejected by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br), reason: Foram realizadas duas submissões Por favor realize uma nova e única submissão contendo o arquivo correto. on 2016-05-30T20:24:48Z (GMT) / Submitted by ALEXSANDER LOURENÇO PESSOA (alexsander.pessoa@gmail.com) on 2016-07-27T12:31:13Z No. of bitstreams: 1 Síntese dos supercondutores Y123 e Y358 pelo método dos precursores poliméricos modificado utilizando fornos convencionais e de micro-ondas (Alexsander Lourenço Pessoa).pdf: 79622456 bytes, checksum: 34f39ae01a459719e274bac2d98b0ab7 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-07-28T14:05:39Z (GMT) No. of bitstreams: 1 pessoa_al_me_ilha.pdf: 79622456 bytes, checksum: 34f39ae01a459719e274bac2d98b0ab7 (MD5) / Made available in DSpace on 2016-07-28T14:05:39Z (GMT). No. of bitstreams: 1 pessoa_al_me_ilha.pdf: 79622456 bytes, checksum: 34f39ae01a459719e274bac2d98b0ab7 (MD5) Previous issue date: 2016-03-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Do ponto de vista energético e de sustentabilidade, o estudo de materiais supercondutores se torna atraente pelo fato de possuírem resistividade elétrica nula. Dentre tais materiais, os mais adequados para aplicações como transporte eletrônico, limitadores de corrente entre outros, são os cerâmicos. Os supercondutores cerâmicos se destacam pelo fato de possuírem temperaturas críticas acima da temperatura do nitrogênio líquido, deixando assim, o processo de resfriamento mais viável economicamente. Em geral, a supercondutividade desses materiais reside nos planos de CuO. Dessa forma, pode-se supor que suas propriedades, tais como Tc e Jc, melhorarão com o aumento do número desses planos. Neste ínterim, no presente trabalho foram estudadas amostras de YBa2Cu3O7− X e Y3Ba5Cu8O18 sintetizadas pelo Método de Precursores Poliméricos Modificados e tratadas termicamente em diferentes temperaturas usando tanto forno convencional quanto forno de micro-ondas. O uso deste último se deve a dois motivos principais: (i) tentativa de diminuir o tempo de síntese e, consequentemente, o gasto com energia elétrica e (ii) o fato de que o CuO ser um excelente absorvedor de radiação de micro-ondas, o que provoca um aquecimento interno do material. Posteriormente, as amostras foram caracterizadas por DRX, MEV/EDX, TGA e transporte elétrico. Por tais resultados podemos concluir que o uso do forno de micro-ondas nos processos de calcinação é adequado, mas que as altas taxas de aquecimento e diminuto tempo de sinterização podem comprometer a formação da fase desejada. / In the energetic and sustainability point of view, the superconductors are atractive materials mainly due to the fact that their resistivity is zero. The most adequate materials for applications in electronic transport, fault current limiters and so on are ceramic ones. They present critical temperatures above to that of the liquid nitrogen, which makes the cooling process much more reliable economically speaking. In general, is believed that the superconductivity resides on the CuO planes then, we can think that if the number of such planes were increased some of the properties of the material, as Tc and Jc, will increase too. In this interim, in the present work we produced samples of Y Ba2Cu3O7−X and Y3Ba5Cu8O18 following the Modified Polymeric Precursors method. They were heat treated at several temperatures using a conventional furnace and a domestic microwave oven. This last one was used due to two main reasons: (i) the decrease of the time of the calcination processes and, consequently, avoiding the electrical energy consumption and (ii) the fact that the CuO is an excelent microwave absorber assisting the internal heating of the material. The samples were characterized by XRD, SEM/DEX, TGA and electrical transport. With the results we can conclude that the microwave oven is suitable for calcination processes. However, due to the great heat rate and very small time for the sinterization process, the desired superconducting phase could not be formed.

Submitted by LUIZIANA APARECIDA GONZAGA null (lugonzaga@outlook.com) on 2017-10-17T01:17:58Z No. of bitstreams: 1 Dissertação de Mestrado - Luiziana Gonzaga.pdf: 3098359 bytes, checksum: d7f683fd9ec29fe64f0d8885301dc5ca (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-10-18T18:59:58Z (GMT) No. of bitstreams: 1 gonzaga_la_me_rcla.pdf: 3098359 bytes, checksum: d7f683fd9ec29fe64f0d8885301dc5ca (MD5) / Made available in DSpace on 2017-10-18T18:59:58Z (GMT). No. of bitstreams: 1 gonzaga_la_me_rcla.pdf: 3098359 bytes, checksum: d7f683fd9ec29fe64f0d8885301dc5ca (MD5) Previous issue date: 2017-07-25 / Nos últimos anos, o estudo de materiais cerâmicos vem evoluindo muito rapidamente, principalmente os estudos relacionados com cerâmicas avançadas. As diversas aplicações envolvendo esses materiais, tais como pigmentos cerâmicos com partículas nanométricas, justificam cada vez mais a necessidade de uma melhor compreensão da influência da adição de dopantes nas propriedades finais dos materiais. No presente trabalho propõe-se analisar e estudar as propriedades estruturais e morfológicas de pigmentos cerâmicos a base de óxido de cério (CeO2) e dopados com diferentes porcentagens molares de lantânio (5 e 10%) e praseodímio (1%). Um dos principais objetivos foi obter pigmentos cerâmicos com tamanho de partícula nanométrico de baixa toxicidade. O processo químico adotado para a obtenção dos pós foi o método dos precursores poliméricos. As nanopartículas foram estruturalmente caracterizadas por difração de raios X (DRX), espectroscopia Raman e espectroscopia de absorção de raios X (XAS). A forma e o tamanho das nanopartículas foram observados por intermédio da microscopia eletrônica de varredura (MEV). A caracterização óptica foi realizada utlizando-se dos resultados de reflectância difusa para obtenção das coordenadas colorimétricas. Os padrões de DRX e espectros Raman indicam a formação de soluções sólidas cristalinas monofásicas com estrutura cúbica do tipo fluorita, pertencentes ao grupo espacial Fm3m. O tamanho dos grãos foi da ordem de 20 a 30 nanômetros, como estimado por MEV. Por reflectância difusa e coordenadas colorimétricas foi determinado que as amostras de CeO2 e CL (óxido de cério dopado com lantânio) possuem coloração amarela enquanto as amostras CLP (óxido de cério dopado com lantânio e praseodímio) e CP (óxido de cério dopado com praseodímio) possuem coloração que varia do magenta-alaranjado ao vermelho-amarronzado. Tonalidades mais intensas foram obtidas nos pigmentos dopados com praseodímio submetidos a tratamento térmico a 800 ºC. / In the last few years, the study of ceramic materials has increased very fast, mainly studies related to advanced ceramics. The several applications of these materials as ceramic pigments in nanometric scale justify more and more the need for a better understanding of the influence of the dopant addition on the final properties of the materials. In this present work, it was studied structural and morphological properties of ceramic pigments based on cerium oxide (CeO2) and doped with differents molar percentages of lanthanum (5 and 10%) and praseodymium (1%). The goal of this work was to obtain nanosized ceramic pigments with a low-toxicity. The chemical route adopted to obtain materials was the polymeric precursor method. The nanoparticles were structurally characterized by X-Ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and X-Ray absorption spectroscopy (XAS). Optical characterization was carried out using the results of diffuse reflectance to obtain the colorimetric coordinates. The XRD patterns and Raman spectra indicate the formation of crystalline solid solutions with single phase and cubic structure (fluorite), all belongs to the space group Fm3m. The obtained grain size was in nanoscale range, 20 to 30 nm, according to MEV. By diffuse reflectance tecnique and colorimetric coordinates were verified that the CeO2 and CL (cerium oxide doped with lanthanum) samples possess yellow coloration and the CLP (cerium oxide doped with lanthanum and praseodymium) and CP (cerium oxide doped with praseodymium) samples present coloration that varies from magenta-orange to red-brown. More intense shades were obtained in pigments doped with praseodymium at 800 ºC temperature.

Orientador: Rafael Zadorosny / Resumo: Do ponto de vista energético e de sustentabilidade, o estudo de materiais supercondutores se torna atraente pelo fato de possuírem resistividade elétrica nula. Dentre tais materiais, os mais adequados para aplicações como transporte eletrônico, limitadores de corrente entre outros, são os cerâmicos. Os supercondutores cerâmicos se destacam pelo fato de possuírem temperaturas críticas acima da temperatura do nitrogênio líquido, deixando assim, o processo de resfriamento mais viável economicamente. Em geral, a supercondutividade desses materiais reside nos planos de CuO. Dessa forma, pode-se supor que suas propriedades, tais como Tc e Jc, melhorarão com o aumento do número desses planos. Neste ínterim, no presente trabalho foram estudadas amostras de YBa2Cu3O7− X e Y3Ba5Cu8O18 sintetizadas pelo Método de Precursores Poliméricos Modificados e tratadas termicamente em diferentes temperaturas usando tanto forno convencional quanto forno de micro-ondas. O uso deste último se deve a dois motivos principais: (i) tentativa de diminuir o tempo de síntese e, consequentemente, o gasto com energia elétrica e (ii) o fato de que o CuO ser um excelente absorvedor de radiação de micro-ondas, o que provoca um aquecimento interno do material. Posteriormente, as amostras foram caracterizadas por DRX, MEV/EDX, TGA e transporte elétrico. Por tais resultados podemos concluir que o uso do forno de micro-ondas nos processos de calcinação é adequado, mas que as altas taxas de aquecimento e diminuto te... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In the energetic and sustainability point of view, the superconductors are atractive materials mainly due to the fact that their resistivity is zero. The most adequate materials for applications in electronic transport, fault current limiters and so on are ceramic ones. They present critical temperatures above to that of the liquid nitrogen, which makes the cooling process much more reliable economically speaking. In general, is believed that the superconductivity resides on the CuO planes then, we can think that if the number of such planes were increased some of the properties of the material, as Tc and Jc, will increase too. In this interim, in the present work we produced samples of Y Ba2Cu3O7−X and Y3Ba5Cu8O18 following the Modified Polymeric Precursors method. They were heat treated at several temperatures using a conventional furnace and a domestic microwave oven. This last one was used due to two main reasons: (i) the decrease of the time of the calcination processes and, consequently, avoiding the electrical energy consumption and (ii) the fact that the CuO is an excelent microwave absorber assisting the internal heating of the material. The samples were characterized by XRD, SEM/DEX, TGA and electrical transport. With the results we can conclude that the microwave oven is suitable for calcination processes. However, due to the great heat rate and very small time for the sinterization process, the desired superconducting phase could not be formed. / Mestre