O material Y2O3:Eu3+ vem sendo usado comercialmente como luminóforo vermelho desde da década de 1960, em uma grande variedade de aplicações devido ao seu elevado rendimento quântico (próximo de 100 %), elevada pureza de cor e boa estabilidade. Portanto, este trabalho propõe um novo método de síntese baseado nos complexos benzenotricarboxilatos (BTC) de terras raras trivalentes (RE3+) dopados com íons Eu3+. O objetivo principal é produzir materiais luminescente RE2O3:Eu3+ a temperatura mais baixa (500 °C) e em escala nanométrica. Os complexos precursores [RE(BTC):Eu3+] e [RE(TLA)·n(H2O):Eu3+], onde RE3+: Y, Gd e Lu; BTC: ácido trimésico (TMA) e ácido trimelítico (TLA) foram calcinados em diferentes temperaturas de 500 a 1000 °C, a fim de obter os materiais luminescentes RE2O3:Eu3+. Os complexos foram caracterizados por análise elementar de carbono e hidrogênio, analise térmica (TG), espectroscopia de absorção no infravermelho (FTIR), difração de raios-X - método do pó (XPD) e microscopia eletrônica de varredura (SEM). Todos os complexos são cristalinos e termo estáveis até 460 °C. Dados de fosforescência dos complexos de Y, Gd e Lu mostram que o nível T1 do aníon BTC3- tem energia acima do nível emissor 5D0 do íon Eu3+, indicando que os ligantes podem atuar como sensibilizadores de energia intramolecular. O estudo das propriedades fotoluminescentes dos complexos dopados foi baseado nos espectros de excitação e emissão e curvas de decaimento de luminescência. Ademais, foram determinados os parâmetros de intensidades experimentais (&#937;&#955;), tempos de vida (&#964;), taxas de decaimentos radiativo (Arad) e não-radiativo (Anrad). Os materiais luminescentes RE2O3:Eu3+ foram sintetizados de forma bem sucedida por meio do método benzenotricarboxilatos calcinados a 500, 600, 700, 800, 900 e 1000 °C, apresentando alta homogeneidade química e controle de tamanho de cristalito. Os nanomateriais foram caracterizados pelas técnicas de FTIR, XPD SEM e TEM revelando a obtenção dos materiais C-RE2O3:Eu3+ mesmo a 500 °C. Os dados de XPD dos materiais confirmaram um aumento do tamanho dos cristalitos de 5 até 52 nm (equação de Scherrer) de em função da temperatura de calcinação de 500 a 1000 °C, respectivamente, corroborados pelas técnicas de SEM e TEM. Os espectros de emissão de RE2O3:Eu3+ mostram uma banda larga atribuída a transição interconfiguracional de transferência de carga ligante-metal (LMCT) em 260 nm, i.e. O2-(2p)&#8594Eu3+(4f6). Além disso, foram observadas linhas finas de absorção devido as transições intraconfiguracionais 4f do íon európio (7F0,1&#85945LJ; J: 0, 1, 2, 3 e 4), como esperado. As propriedades fotoluminescentes dos luminóforos foram baseadas nos espectros (excitação e emissão) e curvas de decaimento luminescente. Os parâmetros de intensidade experimental, tempos de vida, assim como as taxas de decaimentos radiativos e não radiativos foram calculados. As propriedades fotônicas dos nanomateriais são consistentes com o sítio de baixa simetria C2 ocupado pelo íon Eu3+ no C-RE2O3:Eu3+, produzindo emissão vermelha dominada pela transição hipersensível 5D0&#85947F2 do íon Eu3+ no sitio C2, ao invés do sítio centrossimétrico S6. Além disso, os nanomateriais Y2O3:Eu3+ exibem características espectroscópicas semelhantes e elevados valores de eficiência quântica (&#951;~91 %), compatível com os luminóforos comerciais disponíveis no mercado. Este novo método pode ser utilizado para o desenvolvimento de novos nanomateriais contendo íons terras raras, assim como outros íons metálicos. / Y2O3:Eu3+ has been used as luminophore since the early 1960s, despite the large variety of potential substitute materials tested so far, this luminophore still be used as commercial red-emission luminescent material in large range of applications due excellent quantum efficiency (close to 100 %), high color purity and good stability. Consequently, This work propose a new benzenetricarboxylate (BTC) method, which use Eu3+ ion doped in the trivalent rare earths (RE3+) complexes to produce RE2O3:Eu3+ luminescent materials at lower temperature (500 °C) and nanoscale. The [RE(BTC):Eu3+] and [RE(TLA)·n(H2O):Eu3+] complexes where RE3+: Y, Gd and Lu; BTC: trimesic acid (TMA) and trimellitic acid (TLA) and annealed materials (500, 600, 700, 800, 900 and 1000 °C) can be obtained without the need of intricate experimental setup. The complexes were characterized by carbon and hydrogen elemental analysis, thermal analyses (TG), infrared absorption spectroscopy (FTIR), X-ray powder diffraction (XPD) and scanning electron microscopy (SEM). The complexes are crystalline and thermostable up to 460°C. Phosphorescence data of the complexes with Y, Gd and Lu show that the T1 state of the BTC3- anion has energy higher than the 5D0 emitting level of the Eu3+ ion, indicating that the ligands can act as an intramolecular energy sensitizer. The photoluminescence properties of the doped complexes were studied based on the excitation and emission spectra and luminescence decay curves. The experimental intensity parameters (&#937;&#955;), lifetimes (&#964;), radiative (Arad) and non-radiative (Anrad) decay rates were determined and discussed. In addition, the RE2O3:Eu3+ nanomaterials were successfully synthesized with this unprecedented method using the benzenetricarboxylate precursor complexes annealed at 500, 600, 700, 800, 900 and 1000 °C, with controllable particle size and high chemical homogeneity, crystallite size from 6 to 52 nm (Scherrer\'s equation), confirmed by SEM and TEM images. The nanomaterials characterized by the FTIR, XPD, SEM and TEM techniques revealed that the C-RE2O3:Eu3+ materials were obtained even at 500 °C. The RE2O3:Eu3+ excitation spectra show a broad absorption band assigned to interconfigurational ligand-to-metal charge-transfer (LMCT) band at 260 nm, i.e. O2-(2p)&#8594;Eu3+(4f6). Besides, it is observed the narrow absorption lines arising from the 4f intraconfigurational transitions of the Eu3+ ion (7F0,1&#8594;5LJ; J : 0, 1, 2, 3 and 4), as expected. The characterization of the photoluminescence properties of the luminophores was also based on the analysis of the emission spectra and luminescence decay curves. The experimental intensity parameters (&#937;&#955;), lifetimes (&#964;), as well as radiative (Arad) and non-radiative (Anrad) decay rates were calculated and discussed. The photonic properties of the luminophores are consistent with the low C2 symmetry site occupied by the Eu3+ ion in the cubic C-type RE2O3:Eu3+, yielding the red emission color, which is dominated by the hypersensitive 5D0&#8594;7F2 transition of the Eu3+ ion in the C2 instead of the centrosymmetric S6 sites. Furthermore, the Y2<O3:Eu3+ nanomaterials prepared by this new method exhibit similar emissions spectral features and high values of emission quantum efficiency (&#951;~91 %), compatible with the commercial phosphors currently available in the market. This novel synthetic method can be used to produce large range of rare earth nanophotonic materials, as well as other metal ions.

Metabólitos secundários produzidos por actinobactérias são uma inesgotável fonte de compostos com potentes atividades biológicas e estruturas intrínsecas. O desenvolvimento em instrumentação analítica tem contribuído significantemente para acelerar o processo de identificação e caracterização desses metabólitos bioativos. Sem dúvida alguma, a espectrometria de massas (MS) e o seu acoplamento com técnicas de separação, especialmente a cromatografia líquida (UHPLC-MS), tem sido reconhecida como a técnica mais eficiente em análises de produtos naturais. Nesta dissertação foi explorado o potencial da espectrometria de massas como ferramenta analítica para a identificação e caracterização estrutural de fitotoxinas produzidas por actinobactérias isoladas da rizosfera de plantas da caatinga. Foram produzidos noventa extratos de actinobactérias, dos quais quinze apresentaram alguma atividade para o bioensaio da Lemna minor e seis apresentaram atividade para o bioensaio da Chlorella vulgaris. Os extratos brutos ativos das actinobactérias Caat 7-38, Caat 8-6 e Caat 5-29 foram selecionados para caracterização dos compostos ativos, os quais foram isolados empregando o fracionamento guiado por bioensaios. No extrato bruto Caat 7-38, a actinomicina D foi identificada como fitotoxina, ao passo que para o extrato bruto Caat 8-6, foi possível inferir a atividade fitotóxica à presença do griseorhodin A. Já para o extrato bruto Caat 5-29, o composto identificado com atividade fitotóxica apresenta uma estrutura inédita, provavelmente pertencente à classe das anguciclinonas. Foi realizado ainda um estudo para avaliar o efeito da adição de terras raras ao meio de cultivo da actinobacteria Caat 7-38. Para os meios de cultivos contendo neodímio e, principalmente, lantânio ocorreu uma superprodução da actinomicina D, indicando assim, o grande potencial da aplicação das terras raras nos estudos de micro-organismos. / Secondary metabolites produced by actinomycetes are an inexhaustible source of compounds with potent biological activities and intrinsic structures. The development analytical instrumentation has contributed significantly to accelerate the identification and characterization of these bioactive metabolites. Undoubtedly, mass spectrometry (MS) and its coupling with separation techniques, especially liquid chromatography (UHPLC-MS) has been recognized as the most \"efficient\" technique in natural product analysis. In this work was explored the potential of mass spectrometry as an analytical tool for identification and structural characterization of phytotoxins produced by actinomycetes isolated from the rhizosphere of plants from the Caatinga biome. Ninety actinomycetes extracts were produced, of which fifteen showed some activity for the bioassay with Lemna minor and six showed activity for the bioassay with Chlorella vulgaris. The crude active extract of actinomycetes Caat 7-38, Caat 8-6 and Caat 5-29 were selected to characterize the active compounds, which were isolated using bioassay-guided fractionation. In the crude extract Caat 7-38, actinomycin D was identified as phytotoxin, while for crude extract Caat 8-6, it was possible to infer phytotoxic activity to the presence of griseorhodin A. For the crude extract Caat 5-29, the compound identified with phytotoxic activity presents a new structure, probably belonging to the class of anguciclinones. A study to evaluate the effect of addition of rare earths to the culture medium of actinobacteria Caat 7-38 was also carried out. To the culture medium containing neodymium and especially lanthanum occurred overproduction of actinomycin D, thus indicating the great potential of application of rare earths in the studies of microorganisms.

O Escândio é um elemento terra rara, utilizado principalmente em ligas de alumínio, células combustíveis de óxido sólido e na produção de lâmpadas de haletos metálicos. Apesar de ser o 31° elemento mais abundante na crosta terrestre, raramente é encontrado concentrado na crosta terrestre, e sua produção é sempre associada ao processamento de outros minerais na forma de um subproduto, ou a recuperação de sucata. Minérios de Níquel podem conter teores de Sc variando de 50 a 350ppm e resíduos gerados durante seu processamento pode concentrar o Sc acima de 1000ppm. A recuperação do Escândio de um resíduo da cadeia de produção do Níquel foi estudada, de modo a obter um óxido com pureza acima de 99,0% para aplicações industriais. O resíduo utilizado é um precipitado, na forma de hidróxido, e contém principalmente Fe, Cu, Ni e Co, sendo o teor de Escândio em base seca aproximadamente 1000ppm. O processo de recuperação proposto consiste na lixiviação atmosférica do resíduo, precipitação seletiva para concentração do escândio e extração por solventes. A lixiviação atmosférica em meio sulfúrico 2,0mol.L-1 a 70°C permitiu a recuperação de 92,5% do Escândio contido no resíduo. Entretanto, não foi seletiva, lixiviando também parte dos demais metais presentes. Após a lixiviação para concentrar o Escândio, antes da extração por solventes, foi realizada uma precipitação com NaOH. O intuito foi precipitar o Fe, principal contaminante presente no lixiviado, entretanto ocorreu a co-precipitação de 95,5% do Sc junto a 65,6% Fe em pH 2,0. O precipitado representou uma concentração do Escândio do resíduo em 5,6 vezes. Esse concentrado de Escândio obtido foi dissolvido em solução de H2SO4 para recuperação do Escândio por extração por solventes. O extrante escolhido foi o Cyanex 923, uma mistura de óxidos alquil-fósfinicos. O mecanismo de extração do Sc pelo Cyanex 923 observado foi a solvatação e a estequiometria da reação 1:2. Foi observado um aumento na extração do Sc com o aumento da concentração de H+. O processo de extração do Sc com o Cyanex 923 é exotérmico, sendo favorecido a temperatura ambiente. O teor de Fe na solução aquosa antes da extração é 35 vezes maior que o Escândio, e apesar do Cyanex 923 ser mais seletivo para o Sc do que para o Fe, parte do Fe é co-extraído. O Fe co-extraído foi removido da fase orgânica por meio de uma lavagem com H2SO4 3mol.L-1 com uma perda de Sc de 1,3%. A reextração do Sc na fase orgânica não foi efetiva utilizando ácidos fortes devido a formação de um complexo estável. Foi utilizado ácido oxálico, técnica consolidada para reextração de terras raras, para recuperação do Sc da solução orgânica e a recuperação do Sc foi de 84,3% para uma solução com 4,0% de ácido oxálico. O oxalato de Sc precipitado foi recuperado por filtração e calcinado a 600°C. O óxido obtido apresentou pureza mínima de 99,0%. / Scandium is a rare earth element, used mainly in special aluminum alloys, SOFC\'s and metal halide lamps production. Despite of being the 31st element more abundant in Earth\'s Crust, it is rarely found concentrated in ores, and its production is always related to other minerals processing as a by-product or scrap recovering. Scandium content in Nickel ore may vary between 50 and 350ppm and residues produced during its processing can concentrate Sc above 1000ppm. Scandium recovery from a residue of Nickel processing was studied in order to obtain an oxide with purity higher than 99,0% for industrial applications. The residue used is a hydroxide precipitate, which contains mainly Fe, Cu, Ni and Co, Sc content is around 1000ppm (dry basis). The recovery process proposed consists in atmospheric leaching of the residue, selective precipitation to concentrate the Scandium and solvent extraction. The atmospheric leaching in sulfuric acid 2,0mol.L-1 at 70°C allowed the recovery of 92,5% of the Scandium present in the residue. However it was not selective and part of the other metals present in the residue were also leached. After leaching, in order to concentrate the Sc before solvent extraction, a precipitation with NaOH was performed. The initial aim was to precipitate the Iron - main contaminant present in the leach liquor - nevertheless it occurred the co-precipitation of 95,5% of the Sc besides 65,6% of Fe in pH 2,0. The precipitantion represented a concentration of the Sc in the residue of 5,6 times. The Scandium concentrate obtained was dissolved in a sulfuric acid solution to Sc recovery by solvent extraction. The extractant selected was Cyanex 923, a mixture of alkyl-phosphinic oxides. The mechanism of extraction of Scandium observed was solvation and reaction stechiometry was 1:2. It was observed an increase in Sc extraction rates by increasing the concentration of H+. The extraction of Scandium with Cyanex 923 is exothermic, and favorable at room temperature. The Iron content in aqueous solution before extraction is 35 times higher than that of Scandium, and even though Cyanex 923 being more selective for Sc than Fe, part of the Fe is co-extracted. The Fe co-extracted was removed of the organic phase by H2SO4 3mol.L-1 scrubbing with a Sc loss of 1,3%. The stripping of Scandium from organic phase was not accomplished by using strong acids due to formation of a stable complex. Afterwards, it was used oxalic acid - a technique consolidated for rare earths stripping - and the Sc recovery of organic phase was 84,3% with a solution of 4,0% oxalic acid. The Scandium oxalate precipitated was recovered by filtration and calcinated at 600°C. The Scandium oxide obtained presented 99,0% minimum purity.

Neste trabalho foi estudado o efeito da presença do cério em catalisadores de Pt/C e PtSn/C para eletro-oxidação de etanol visando aumentar a eficiência da reação, entender o motivo das variações na atividade catalítica e avaliar a estabilidade destes catalisadores nas condições de operação da célula. Todos os catalisadores foram preparados pelo método do ácido fórmico, os dados de espectroscopia XPS confirmaram as porcentagens nas composições dos catalisadores de PtCe/C e PtSnCe/C. Através das técnicas de TEM e XRD verificou-se que, com exceção da proporção PtCe/C 50:50, todos os outros catalisadores apresentaram tamanho de partícula próximos ao tamanho de cristalito. Os dados de XRD não indicam a presença de liga nos catalisadores de PtCe/C e de PtSnCe/C, mas mesmo em forma de óxido, o estanho apresentou um efeito eletrônico, como informado pelos dados de XAS. A adição de cério promove a oxidação do etanol em menores potenciais que a platina. A adição de estanho ao catalisador PtCe/C teve um efeito benéfico na atividade catalítica promovendo a oxidação em potenciais inferiores aos catalisadores de PtCe/C. A interação de Pt-Sn promove a dissociação da água para formar Sn-OHad próximo a espécies de monóxido de carbono adsorvidas na Pt, facilitando a rápida oxidação de etanol. Os testes de estabilidade indicaram que ao comparar os catalisadores PtSnCe/C com um catalisador comercial de PtSn/C, é possível aferir que a adição de cério promove uma melhora da estabilidade do catalisador. / In this work, the effect of the cerium presence in Pt/C and PtSn/C catalysts for ethanol electro-oxidation was studied to increase the efficiency of the reaction, to understand the variations in catalytic activity and to evaluate the catalysts stability at the cell operating conditions. All catalysts were prepared by the formic acid method, and the XPS data confirmed the percentages in the compositions of the catalyst PtCe/C and PtSnCe/C. The XRD and TEM data showed that, with the exception of the proportion PtCe/C 50:50, all other catalysts showed particle size close to the crystallite size. The XRD data does not indicate the presence of alloy in the PtCe/C and PtSnCe/C catalysts, but even in the form of oxide, tin presented an electronic effect, as reported by the XAS data. The addition of cerium promotes oxidation of ethanol in lower potential than platinum. The addition of tin in this catalyst had a beneficial effect on the catalytic activity, promoting the oxidation in lower potential than the PtCe/C catalysts. The interaction of Pt-Sn promotes the dissociation of water to form Sn-OHad near species of carbon monoxide adsorbed on Pt, facilitating the rapid ethanol oxidation. Stability tests showed when comparing PtSnCe/C catalyst with commercial catalyst PtSn/C, it was possible to determine that the addition of cerium provides an improvement of the catalyst stability.

Orientador: Jacinta Enzweiler / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências / Made available in DSpace on 2018-08-25T06:48:42Z (GMT). No. of bitstreams: 1 Campos_FranciscoFerreirade_M.pdf: 4411120 bytes, checksum: 0ec78e552f133054bf849333f9d8386f (MD5) Previous issue date: 2014 / Resumo: A composição de águas naturais, que inclui íons principais e muitos constituintes traço, resulta da interação da água com a litosfera, atmosfera e biosfera. Dentre os elementos-traço presentes encontram-se os elementos terras raras (ETR). Na sociedade contemporânea, os ETR possuem uma ampla gama de usos, dentre eles o gadolínio (Gd) em reagentes de contraste usados em exames de imagem de ressonância magnética, e diversos ETR em produtos eletrônicos, dentre outras aplicações. Consequentemente, os ETR vem sendo introduzidos no ambiente sem que se conheça a sua distribuição natural e a sua toxicidade. O objetivo deste trabalho foi caracterizar a distribuição natural e a presença de anomalias antrópicas de ETR dissolvidos nas águas superficiais do Rio Atibaia, Ribeirão Anhumas e alguns tributários, localizados no estado de São Paulo. Esses cursos d¿água atravessam áreas com elevada densidade populacional e a região abriga importantes complexos médico-hospitalares e industriais, em especial do ramo petroquímico. O trabalho consistiu de duas etapas: testes laboratoriais de procedimentos descritos de pré-concentração, e trabalho de campo e analítico, onde as águas superficiais da área de estudo foram amostradas e analisadas e determinadas as concentrações de ETR (fração dissolvida e material particulado). Três métodos de pré-concentração de ETR foram testados sob condições variáveis: co-precipitação com Fe(OH)3, extração em fase sólida com resina Ln-Spec e extração em fase sólida com éster de fosfato adsorvido em cartucho com C18. Com base nos resultados obtidos, a extração em fase sólida com éster de fosfato foi utilizada na análise das amostras de água. Além do Rio Atibaia, do Ribeirão Anhumas e alguns tributários, a amostragem compreendeu os efluentes de duas estações de tratamento de efluentes (ETE) e uma amostra do Rio Jaguari, totalizando 28 amostras. A análise das amostras de água foram realizadas por cromatografia de íons (constituintes maiores), titulação acidimétrica (alcalinidade) e ICP-MS (ETR e outros elementos-traço). O material particulado retido nas membranas usadas na filtração das amostras foi digerido e analisado por ICP-MS. Os resultados obtidos para os ETR foram normalizados pelo PAAS (Folhelho Australiano Pós-Arqueano) e a presença de anomalias de Gd antrópico nos padrões das águas foi constatada nos diagramas e pela extrapolação do Gd background (Gd*) usando elementos vizinhos, com razões Gd/Gd* chegando a 87. O Gd antrópico só ocorre na fase dissolvida, e foi mostrado que as amostras com anomalias também podem ser identificadas através do diagramas de correlação entre o Gd e os demais ETR, sem necessidade de normalização. A fonte do Gd antrópico foi atribuída aos efluentes lançados nos rios, principalmente os das ETEs, que contêm quelatos de Gd utilizados em exames médicos. Constatou-se que a distribuição dos ETR nas amostras filtradas está significativamente associada com partículas de tamanho coloidal o que resulta num enriquecimento em ETR leves. A normalização dos resultados de ETR obtidos na água filtrada pelos valores de ETR obtidos no material particulado de cada amostra é proposto como artifício para superar a influência das partículas coloidais na distribuição dos ETR da fração verdadeiramente dissolvida / Abstract: The composition of natural water includes majors ions and many trace constituents and results from the interaction of water with the lithosphere, atmosphere, and biosphere. The rare earth elements (REE) are part of the trace elements. In modern society, REE have a wide spectrum of uses, as gadolinium (Gd) in contrast agents used in magnetic resonance imaging, and many REE in electronic products. Due to their use, the REE are being released to the environment before their natural distribution and toxicity are known. The objective of this work was to characterize the natural distribution and anthropogenic anomalies of dissolved REE in the surface waters of Atibaia River, Anhumas Creek and some tributaries, located in the state of São Paulo (Brazil). These water courses flow through areas of high population density and the region has important medical and industrial facilities, including petrochemical units. The work was done in two steps: the laboratorial tests of described REE pre-concentration procedures, and the field and analytical work, where the surface waters of the study area were sampled and analyzed and the REE concentrations determined (in the dissolved fraction and particulate matter). Three REE pre-concentration methods were tested under variable conditions: co-precipitation with Fe(OH)3, solid phase extraction with Ln-Spec resin, and solid phase extraction with phosphate ester adsorbed on C18 cartridge. Based on the obtained results the solid phase extraction with phosphate ester was used to determine the REE in the water samples. Besides Atibaia River, Anhumas Creek, and some tributaries, the sampling comprised the effluents of two wastewater treatment plants (WWTP) and one sample of Jaguari River, in a total of 28 samples. The water samples analysis was accomplished by ion chromatography (major constituents), acidimetric titration (alkalinity), and ICP-MS (REE and other trace elements). The particulate matter retained in the membranes during filtration of water samples was digested and analyzed by ICP-MS. The results obtained for the REE were normalized to PAAS (Post-Archean Australian Shale) and the presence of anthropogenic Gd anomalies in the patterns of the waters was observed in the plots and by extrapolation of background Gd (Gd*) by neighboring elements, with Gd/Gd* ratios reaching 87. The anthropogenic Gd only occurs in the dissolved phase, and it was shown that samples with anomalies can also be identified by correlation plots of Gd and the other REE, without the need of normalization. The source of anthropogenic Gd was attributed to the discharge of effluents in the rivers, mainly from the WWTP, which contains Gd chelates used in medical exams. It was observed that REE distribution in the filtered samples are significantly associated with particles of colloidal size that results in a light REE enrichment. The normalization of the REE results obtained in the filtered water by the REE values obtained for the particulate matter of each sample is proposed as a way to overcome the influence of the colloidal particles in the distribution of the REE in the truly dissolved fraction / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

Dans le contexte actuel, l’approvisionnement en terres rares est un enjeu capital, et le recyclage des déchets produits par les sociétés industrialisées apparaît comme une solution extrêmement pertinente d’un point de vue écologique. Dans ce travail, nous nous sommes intéressés aux aimants permanents Nd-Fe-B, car ils constituent un gisement potentiel important pour le néodyme, mais aussi pour le dysprosium et le praséodyme, éléments également critiques. Plus précisément, les aimants présents au sein des disques durs d’ordinateur ont été étudiés en vue de leur recyclage. L’intérêt est donc de mettre en place des solutions permettant le retraitement et la valorisation de ces aimants, présentant non seulement un impact environnemental faible, mais également un coût bas. Nous avons décidé de nous intéresser au traitement hydrothermal des aimants permanents Nd-Fe-B en vue de leur recyclage. L’étude du traitement thermique des aimants Nd-Fe-B en présence d’une solution saline pour des températures avoisinant les 225°C, permet la mise en évidence d’une dégradation complète du matériau. La poudre récupérée à l’issue du procédé est donc constituée de cristaux octaédriques, correspondant à la magnétite, et de cristaux aciculaires correspondant aux hydroxydes de néodyme, mais également aux différentes terres rares présentes en tant que dopants dans la phase intergranulaire. A l’issue du traitement hydrothermal, les fragments de revêtement peuvent être retirés par tamisage, en raison de leur dimension millimétrique, et les ocydes de fer séparés des hydroxydes de terres rares par séparation magnétique. Afin de valoriser les aimants Nd-Fe-B comme matière première magnétique permettant la fabrication de nouveaux aimants permanents, le broyage a également été envisagé. Des échantillons d’alliage Nd2Fe14B ont été broyés à haute énergie sous atmosphère protectrice, et nous avons réalisé l’étude microstructurale et magnétique de ces poudres. Les échantillons ont été analysés par magnétométrie SQUID, par spectrométrie Mössbauer, ainsi que par Sonde Atomique Tomographique. Ainsi, nous avons pu mettre en évidence un phénomène couplé de décomposition et de nanostructuration à l’échelle moléculaire de la phase Nd2Fe14B. L’ensemble de ce travail a donc permis d’étudier le comportement et les transformations des aimants Nd-Fe-B au cours de deux procédés très différents : le traitement hydrothermal et le broyage mécanique. Les résultats obtenus lors du traitement hydrothermal sont très prometteurs en vue du recyclage des terres rares à grande échelle. / Rare earth supplying is a very current topic, linked to the rare earth crisis of 2010. « Urban mining » is a promising path for recycling rare earths included in waste daily generated by industralized countries. In this work, we focus on recycling Nd-Fe-B permanent magnets, because they are a very interesting deposit for Neodymium, but also for Dysprosium and Praseodymium. More precisely, permanent magnets included in hard disks drives have been considered. The objective of this work is to set up environmentally friendly and low cost recycling processes for rare earths. First, we investigated hydrothermal treatment of Nd-Fe-B permanent magnets, We developed a new and environmentally friendly approach for recycling Ni−Cu coated Nd-Fe−B permanent magnets included in computer hard disk drives. In a closed reactor, the coated magnets are heated at 250 °C in water mixed with sodium chloride for up to 18 h. First, the hydrothermal treatment induces the removal of the metallic coating that can be recovered by sieving. Then, the Nd-rich phase reacts with water, leading to the formation of Nd(OH)3. Atomic hydrogen is absorbed by the Nd2Fe14B phase, leading to the formation of Nd2Fe14BHx. The volume expansion of the intergranular phase, in relation to the formation of Nd(OH)3, together with the lattice expansion of the Nd2Fe14BHx phase causes the disintegration of the magnets. Finally, Nd2Fe14BHx is oxidized by water into Fe3O4 and Nd(OH)3. The Nd(OH)3 crystals can be isolated from the Fe3O4 crystals by magnetic separation. This process is thus an easy way to extract rare earths from permanent magnets found in WEEE. It uses green chemistry design principles and can be applied to large amounts of magnetic wastes. Mechanical milling of Nd-Fe-B permanent magnets has also been investigated, and, in the study presented here, the milling effect on the magnetic properties of the Nd2Fe14B intermetallic was investigated using SQUID measurements, Mössbauer spectrometry and atom probe tomography (APT). Mechanical milling of the Nd2Fe14B alloy leads to its decomposition and its nanostructuration. This transformation induces first the formation of an amorphous, disordered phase Nd-Fe-B, with an enrichment in Neodymium; then to the formation of a mixture of -Fe and Nd-rich regions. The corresponding microstructure is very characteristic, with the formation of pure iron particles, with a hundred of nanometers in size, surrounded by an amorphous shell enriched in Neodymium and in Boron. Finally, intermixing of these phases is observed. Thanks to this work, we determine the behavior and the transformations of Nd-Fe-B permanent magnets during two very different processes: hydrothermal treatment and mechanical milling. Results obtained with hydrothermal treatment are very promising for recycling rare earths at the industrial scale.

On a global scale, the deployment of wind power plants is soaring. However, the availability of their construction materials could be a potential bottleneck, a problem rarely discussed in literature so far. Rare earth elements represent the most critical materials in terms of high economic importance, supply risk and environmental risk. This study therefore provides a market analysis of rare earths, ascertaining that geological scarcity is not the main problem. Instead, four kinds of market failure are identified: market power, co-production, by-production and negative externalities. Altogether, the market for rare earth metals is in a state of severe disequilibrium. Subsequently, an estimate of future rare earth demand patterns based on the wind power industry by 2050 reveals that the current level of supply is unlikely to be sufficient in the long run. To allow for a more elaborate analysis, two options of including a rare earth side condition in an integrated assessment model are finally suggested.

The subject of this thesis are channel waveguide lasers in epitaxial garnet films grown by liquid phase epitaxy. Results of this thesis include: The feasibility of a waveguide laser with erbium-doped YIG as the active material is discussed. Nonlinear rate equations that describe the behavior of this laser are formulated and solved numerically. The material parameters that are needed as the input are taken from literature. The simulations reveal that the performance of the laser depends critically on the magnitude of the upconversion parameter W22. A thorough analysis shows, however, that the values of W22 that are found in literature are most likely too small. The other parameter of importance is the background loss of the waveguide. Our results indicate that, unless the absorption losses of the LPE grown iron garnet films can be significantly reduced, the chances to realize such a device are only minimal. The mechanisms behind the absorption losses in LPE grown YIG films are investigated. During the LPE growth process, lead, platinum and other non-trivalent impurities are incorporated into the films in high concentrations. While platinum is tetravalent only, lead can be both di- and tetravalent. Depending on the ratio of the lead and the platinum concentrations, the near infrared absorption can be caused by three entirely different mechanisms. In case the tetravalent impurities are the majority, charge compensation is achieved by the formation of Fe2+ and the absorption is caused by crystal field transitions between the 5E and the 5T2 states of the Fe2+-ion. If the divalent impurities are in the majority, the absorption is due to crystal field transitions between the 5T2 and the 5E states of the Fe4-ion. In LPE-grown iron garnets, however, the impurity with the highest concentration is usually lead. We prove that lead performs self-compensation as it is incorporated in Pb2+/4+ pairs on neighboring lattice sites, and that the optical absorption is caused entirely by a charge transfer transition between the two neighboring lead ions. The electrical conductivity is measured in a temperature range from 300 to 800 K. It is demonstrated that in this temperature range the so-called impurity conduction is the predominant conduction mechanism in all types of films. Around room temperature, the conductivity shows an abnormal temperature behavior as the measured Bohr radius of the impurity ions almost doubles between 295 and 370 K. This can be explained by the fact that film and substrate have different temperature expansion coefficients. As the temperature increases, the stress in the film changes from tensile to compressive. When that happens, the {Pb2+} and the [Pb4+] ions counteract the strain in that they interchange their lattice sites. Also, Fe4+, if present, switches from the tetrahedral to the octahedral site which reduces the lattice constant of the film. This interpretation finds support in the results on the optical absorption, in the lattice mismatch, and in MCD spectra that were previously measured by Milani and Paroli. Based on the above findings, an easy way to eliminate the growth induced absorption in LPE iron garnet films is presented. By co-doping the films with other di- and tetravalent ions like Mg and Ge in high concentrations, the concentration of absorbing Pb2+/Pb4+ centers is greatly reduced due to the formation of non-absorbing Pb2+/Ge4+ and Ca2+/Pb4+ centers. As a result, absorption losses as low as 0.05 cm-1 at 1.3 µm wavelength have been achieved. In the second part of this thesis the fabrication of a channel waveguide laser in epitaxial Nd:GGG films is described. The films are grown by LPE on [111] oriented GGG substrates from a PbO/B2O3 flux. To increase the index contrast between film and substrate, Bi is added to the melt. Initially, the films showed strong brown discoloration and a high defect density. Luminescence lifetime measurements revealed severe quenching problems. The chemical analysis of the films by EPMA shows that platinum from the crucible enters the films but no lead from the flux. It is found that the platinum in GGG, similar to the lead in YIG, forms Pt2+/Pt4+ centers in order to achieve charge compensation. The quenching is caused by the charge transfer transition between the two platinum ions. To eliminate the quenching, MgO is added to the melt. As a result, the brown discoloration, the quenching and the growth defects disappear. From the planar film rib waveguides are fabricated using ion beam etching. The unclad waveguides are cut and the endfaces are polished to couple light in and out. Both endfaces are perpendicular to the waveguide within 0.1°. The losses are derived from the Fabry-Perot interferences. Losses as low as 0.2 dB/cm are achieved for both TE and TM modes. Laser oscillation starts at a launched pump power of 5 mW. The resonator is formed by the polished endfaces of the waveguide, no dielectric mirrors have been applied. Thus, the facet reflectivity is only about 10%. The launched pump power is measured precisely using a novel technique at which the luminescence intensity emitted through the surface is spatially resolved with a beam profile analyzer. Coupling efficiencies of over 90% are measured. The slope efficiency is found to be 48%.

Cette thèse de doctorat se fixe tout particulièrement pour objectif d’apporter un éclairage sur la problématique de la production des éléments de terres rares aux États-Unis. Ces minéraux, aux qualités nucléaire très particulières, constituent des intrants cruciaux dans certaines technologies et industries stratégiques : technologies « vertes », technologies d’information et de communication, ainsi que dans les technologies militaires. Ces minéraux stratégiques constituent aujourd’hui un enjeu géoéconomique mais aussi géopolitique et environnemental majeur. En 2011, 97 % des éléments de terres rares dans le monde proviennent de la Chine (qui dispose donc d’un monopole), selon l’United States Geological Survey. Cette position de la Chine a soulevé des inquiétudes chez les responsables américains concernant l’accès à ces ressources minérales, de manière évidente depuis 2010. Cette recherche questionne le rôle crucial joué par les acteurs au sein des agences étatsuniennes dans l’objectif d’élaborer une politique solide pour faire face au risque géopolitique lié à la vulnérabilité des États-Unis face au risque de ruptures d’approvisionnement de ces minéraux stratégiques. Ces minéraux sont donc une source de conflit international, surtout en raison de la montée de la Chine comme un nouveau joueur sur la scène internationale, dotée d’un quasi monopole sur les terres rares. Situé à la croisée des préoccupations géoéconomiques et géopolitiques et environnementales, il a semblé nécessaire de comprendre quels enjeux essentiels soulèvent ces minéraux stratégiques : enjeux géoéconomiques, défis géopolitique ou danger écologique ? C’est donc en ces termes que nous examinerons la question des minéraux de terres rares par les États-Unis. / This doctoral dissertation particularly aims at shedding light on the issue of U.S. rare earth production, a group of minerals with very special qualities nuclear, which are vital inputs in certain strategic industries and technologies: green technologies, information and communication technologies, as well as in military technologies. These strategic minerals constitute nowadays one of the major challenges associated with geo-economic, geopolitical and environmental issues. In 2011, China has provided approximately 97 percent of the world’s rare earth minerals (near-monopoly) according to U.S. Geological Survey data. This position of China has raised concerns about access to these mineral resources among American officials, obviously since 2010. This research discuss the crucial role played by actors within the U.S. Agencies to develop a robust policy to deal with the geopolitical risks about U.S. vulnerability to a supply disruption of these critical strategic minerals, as part of a source of international conflict, especially with the rise of China as a new player on the international stage. Located at the crossroads of geo-economic, geopolitical, and environmental concerns, it seems necessary to understand what key impasses constitute rare earths strategic minerals, economic power or geopolitical challenges or ecological danger? It is in these terms that we will deal with the issue of rare earths as considered by the United States.

This thesis studies different Eu optical centers in MgS:Eu and CaS:Eu thin films produced by Chemically Controlled Pulse Laser Deposition (CCPLD) and evaluates their suitability for the development of spectral storage devices of the future. The produced thin films consist of one or more optically active layer(s), MgS:Eu, CaS:Eu or a similar material, and a corresponding ZnS capping layer that functions as a protecting barrier for the other layers and preserves their composition and integrity. Given that the synthesis of the materials used to produce the multilayer structures in this work proved a great challenge, careful attention was given to the optimization of all fabrication parameters. Mass Spectrometry was used during the deposition of the thin films and the data obtained resulted on improvements and optimization of the deposition process. Scanning electron microscopy studies of these thin films were conducted to study degradation upon long-term storage. Microscopy results show that the morphology of the produced thin films is correlated to the growth environment during deposition and deterioration of the deposited materials could be initiated by nano-gaps and cracks in the capping layer of the thin films. In addition to optical centers in MgS:Eu and CaS:Eu, new centers were created by changing the thin film growth environment inside a hi-vacuum chamber, modifying the composition of the ablation target material, or both. For example, introducing O2, or alternatively HCl, inside the CCPLD chamber while producing MgS:Eu thin films results in the formation of impurity associated centers across lattice sites throughout the deposited structures. In another method of impurity doping studied, Cl- and Na+ were introduced into the MgS:Eu and CaS:Eu lattices by mixing trace amounts of the impurity ions into these materials in polycrystalline form and making this mixture a deposition target by hi-pressure cold compression technique. The introduction of these impurity ions will alter the crystal field environment around the Eu ions thus creating new optical centers with a shift in energy of their characteristic Zero Phonon Line. After extensive characterization of the optical properties of the thin films produced, laser-induced fluorescence spectroscopy and absorption spectroscopy measurements confirm that they are suitable candidates to be used in conjunction with power-gated spectral holeburning technique and could potentially provide ultrahigh, terabits per square inch, storage densities. / Physics