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Solid state NMR as a new approach for the structural characterization of rare-earth doped lead lanthanum zirconate titanate laser ceramics

MOHR, Daniel; CAMARGO, Andrea Simone Stucchi de; SCHNEIDER, Jose Fabian; QUEIROZ, Thiago B.; ECKERT, Hellmut; BOTERO, Eriton R.; GARCIA, Ducinei; EIRAS, Jose A.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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To facilitate the design of laser host materials with optimized emission properties, detailed structural information at the atomic level is essential, regarding the local bonding environment of the active ions (distribution over distinct lattice sites) and their extent of local clustering as well as their population distribution over separate micro- or nanophases. The present study explores the potential of solid state NMR spectroscopy to provide such understanding for rare-earth doped lead lanthanum zirconate titanate (PLZT) ceramics. As the NMR signals of the paramagnetic dopant species cannot be observed directly, two complementary approaches are utilized: (1) direct observation of diamagnetic mimics using Sc-45 NMR and (2) study of the paramagnetic interaction of the constituent host lattice nuclei with the rare-earth dopant, using Pb-207 NMR lineshape analysis. Sc-45 MAS NMR spectra of scandium-doped PLZT samples unambiguously reveal scandium to be six-coordinated, suggesting that this rare-earth ion substitutes in the B site. Static Pb-207 spin echo NMR spectra of a series of Tm-doped PLZT samples reveal a clear influence of paramagnetic rare-earth dopant concentration on the NMR lineshape. In the latter case high-fidelity spectra can be obtained by spin echo mapping under systematic incrementation of the excitation frequency...

Síntese, caracterização e estudo termoanalítico de etanossulfonatos de terras raras; Synthesis, characterization and study of thermal decomposition of rare earth ethanessulfonates

Gomes, Ana Carolina Ribeiro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/04/2007 PT
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Este trabalho consiste na síntese, caracterização e estudo da decomposição térmica de etanossulfonatos de terras raras, abordando aspectos relativos à etapa de desidratação e decomposição térmica dos sais anidros. As reações entre o ácido etanossulfônico e os óxidos de terras raras, em meio aquoso, permitiram obter os etanossulfonatos de terras raras, com fórmula geral mínima TR(C2H5SO3)3.xH2O, sendo TR = La ao Lu e Y, exceto o Ce, com x variando de 1,3 a 5. Esta estequiometria foi proposta a partir dos resultados de O estudo do comportamento térmico dos compostos foi realizado empregando a TG/DTG sob atmosfera dinâmica de N2 e ar, com razão de aquecimento de 5ºC.min-1 para a etapa de desidratação e 10ºC.min-1 para a etapa de decomposição térmica dos sais anidros. Os eventos térmicos foram evidenciados nas curvas DSC (etapa de desidratação) por picos no sentido endotérmico e estão em concordância com as variações de massa indicadas na TG/DTG. As curvas TG/DTG mostraram eventos sobrepostos, característicos da saída simultânea de vários voláteis durante a decomposição térmica das espécies anidras. Na etapa de desidratação, os resultados de análise térmica indicaram que ao longo da série as moléculas de água apresentam diferentes formas de ligação. A técnica de espectroscopia de absorção na região do infravermelho permitiu verificar uma grande similaridade entre os compostos e que as espécies são hidratadas. Os desdobramentos e deslocamentos de algumas bandas de absorção são indicativas da alteração na forma de interação da espécie etanossulfonato com os íons TR3+ em relação à espécie no ácido livre. A técnica de difração de raios X indicou que os compostos são cristalinos e permitiu separá-los em sete classes isomorfas. A caracterização dos produtos intermediários da decomposição térmica dos sais anidros permitiu inferir a presença de espécies sulfatos...

Caracterização magneto-óptica de terras raras (Nd3+ and Yb3+) em LiNbO3.; Magneto-optical characterization of rare-earth ions (Nd3+ and Yb3+) in LiNbO3 crystals.

Cruz, Cláudia Bonardi Kniphoff da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/04/2001 PT
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Neste trabalho, apresentamos resultados da caracterização Magneto-Óptica de íons terras-raras (Nd3+ e Yb3+) em monocristais de niobato de lítio (LiNbO3). Medidas de Dicroísmo Circular Magnético (MCD) e de Emissão Circularmente Polarizada em Presença de Campo Magnético (MCPE) foram realizadas pela primeira vez nesses sistemas. Os resultados foram obtidos à temperatura de 2K, e em campos magnéticos de até 5 T. Através desses estudos, foi possível identificar os números quânticos cristalinos (μ) dos subníveis Zeeman desses íons. A partir da dependência do sinal de MCD com a intensidade de campo magnético, determinou¬se o fator giromagnético efetivo g// do estado fundamental de cada íon, obtendo-se os valores: g//Nd = (1,4 ± 0,1) e g//Yb = (4,7 ± 0,1). Esses valores foram confirmados através de medidas de espectroscopia de Ressonância Paramagnética Eletrônica (EPR), realizadas a baixa temperatura (4-8 K), em banda X. Os espectros de EPR foram tomados em função da orientação relativa do campo magnético externo com o eixo c cristalino dos cristais, em 3 planos perpendiculares entre si. Os espectros de EPR mostram a existência de diferentes sítios ocupados pelos íons terras-raras. O sítio mais populado tem simetria axial...

Preparação e caracterização de eletrocatalisadores PtSn/C - terras raras e PtRu/C - terra raras para a eletro- oxidação do etanol; Preparation and characterization of PtSn/C-rare earth and PtRu/C-rare earth using an alcohol reduction process for ethanol electro-oxidation

Rodrigues, Rita Maria de Sousa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/11/2011 PT
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Os eletrocatalisadores PtRu/C-terras raras e PtSn/C-terras raras (20% em massa) foram preparados pelo método da redução por álcool utilizando H2PtCl6.6H2O RuCl3·xH2O, SnCl2.2H2O como fonte de metais, 85 % Vulcan - 15 % de terras raras como suporte e, por último, etileno glicol como agente redutor. Os eletrocatalisadores obtidos foram caracterizados fisicamente por difração de raios-X (DRX), energia dispersiva de raios X (EDX) e microscopia eletrônica de transmissão (MET). As análises por EDX mostraram que as razões atômicas dos diferentes eletrocatalisadores, preparados pelo método da redução por álcool, são similares às composições nominais de partida indicando que esta metodologia é promissora para a preparação destes eletrocatalisadores. Em todos os difratogramas para os eletrocatalisadores preparados observa-se um pico largo em aproximadamente 2θ = 25o, o qual é associado ao suporte de carbono e quatro outros picos de difração em aproximadamente 2θ = 40o, 47o, 67o e 82o, que por sua vez são associados aos planos (111), (200), (220) e (311), respectivamente, da estrutura cúbica de face centrada (CFC) de platina. Os resultados de difração de raios X também mostraram tamanhos médios de cristalitos entre 2...

Vidros de germanato com nanopartículas metálicas e semicondutoras dopados com terras-raras para aplicações em fotônica.; Germanate glasses containing metalic an semiconductor nanoparticles dopes with rare-earth ions for photonic aplicattions.

Silva, Diego Silvério da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 01/09/2010 PT
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Neste trabalho é apresentado um estudo espectroscópico sobre vidros de germanato contendo nanopartículas (NPs) metálicas e semicondutoras dopados com íons de terras-raras (TRs) Eu3+, Nd3+ e Er3+ visando o desenvolvimento de novos materiais para aplicações em fotônica. Estes vidros apresentam larga janela de transmissão (400-4500 nm), alto índice de refração (~ 1,9), baixa energia de fônon (700 cm-1), alta resistência mecânica e durabilidade química. Com a finalidade de verificar a nucleação das NPs metálicas e semicondutoras, foram realizadas análises por Microscopia Eletrônica de Transmissão (MET) que indicaram a presença de NPs metálicas e semicondutoras. As técnicas de espectroscopia de fluorescência de raios X por energia dispersiva (EDS energy dispersive spectroscopy) e difração de elétrons comprovaram a natureza química das NPs. As medidas de absorção óptica evidenciaram a incorporação dos íons de TRs na forma trivalente, fenômeno responsável pela luminescência nos vidros, e permitiram as medidas das bandas de absorção relacionadas à ressonância dos plasmons superficiais e das bandas de absorção características de NPs de natureza semicondutora. Medidas de emissão foram realizadas através de diferentes procedimentos...

Síntese, caracterização e estudo termoanalítico dos nitrilotriacetatos de terras raras; Synthesis, characterization and thermoanalytical study of the rare earth nitrilotriacetates

Silva, Ademir Oliveira da
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/03/2000 PT
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Este trabalho consiste da preparação, caracterização e estudo do comportamento térmico dos nitrilotriacetatos de terras raras hidratados. A reação entre o cloreto de terra rara e o sal Na2HNTA, em meio aquoso, produziu compostos de fórmula geral mínima TRNTA.xH2O, onde x=2,5 para La e Ce; x=3 para Pr ao Gd (exceto o Pm) e x=4 para TR=Tb ao Lu, incluso Y. A estequiometria desses compostos foi proposta com base nos teores da terra rara, obtidos a partir das curvas TG/DTG, e nos teores de carbono, nitrogênio e hidrogênio por obtidos por análise elementar. Os difratogramas de raios X permitiram identificar três séries isomorfas, que são concordantes com a similaridade no grau de hidratação das espécies, com os espectros de absorção na região do infravermelho e com as curvas TG/DTG e DSC. Os espectros de absorção na região do infravermelho indicaram a formação dos sais, devido ao deslocamento das banda do grupo carboxilato (vCOO- de 1724 cm-1 no ácido livre, para 1670-1560 cm-1 nos sais. Os espectros de emissão do sal de EuNTA.3H2O no estado sólido, evidenciaram que o íon Eu3+ encontra-se numa microssimetria C. O comportamento térmico dos sais foi estudado por TG/DTG em atmosfera dinâmica de ar, N2 e da mistura gasosa (ar + CO2)...

Optical emission and electron capture of rare-earth trivalent ions located at distinct sites in SnO(2) thin films

Morais, Evandro A.; Scalvi, Luis V. A.; Ravaro, Leandro P.; Boulon, G; Dujardin, C; Jurdyc, A. M.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 353-364
ENG
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We present photoluminescence and decay of photo excited conductivity data for sol-gel SnO(2) thin films doped with rare earth ions Eu(3+) and Er(3+), a material with nanoscopic crystallites. Photoluminescence spectra are obtained under excitation with several monochromatic light sources, such as Kr(+) and Ar(+) lasers, Xe lamp plus a selective monochromator with UV grating, and the fourth harmonic of a Nd: YAG laser (4.65eV), which assures band-to-band transition and energy transfer to the ion located at matrix sites, substitutional to Sn(4+). The luminescence structure is rather different depending on the location of the rare-earth doping, at lattice symmetric sites or segregated at grain boundary layer, where it is placed in asymmetric sites. The decay of photo-excited conductivity also shows different trapping rate depending on the rare-earth concentration. For Er-doped films, above the saturation limit, the evaluated capture energy is higher than for films with concentration below the limit, in good agreement with the different behaviour obtained from luminescence data. For Eu-doped films, the difference between capture energy and grain boundary barrier is not so evident, even though the luminescence spectra are rather distinct.

Optical and transport properties of rare-earth trivalent ions located at different sites in sol-gel SnO2

Morais, E. A.; Scalvi, L. V A; Ravaro, L. P.; Li, Siu M.; Floriano, E. A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
ENG
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Photoluminescence and photo-excited conductivity data as well as structural analysis are presented for sol-gel SnO2 thin films doped with rare earth ions Eu3+ and Er3+, deposited by sol-gel-dip-coating technique. Photoluminescence spectra are obtained under excitation with various types of monochromatic light sources, such as Kr+, Ar+ and Nd:YAG lasers, besides a Xe lamp plus a selective monochromator with UV grating. The luminescence fine structure is rather different depending on the location of the rare-earth doping, at lattice symmetric sites or segregated at the asymmetric grain boundary layer sites. The decay of photo-excited conductivity also shows different trapping rate depending on the rare-earth concentration. For Er-doped films, above the saturation limit, the evaluated capture energy is higher than for films with concentration below the limit, in good agreement with the different behaviour obtained from luminescence data. For Eu-doped films, the difference in the capture energy is not so evident in these materials with nanoscocopic crystallites, even though the luminescence spectra are rather distinct. It seems that grain boundary scattering plays a major role in Eu-doped SnO2 films. Structural evaluation helps to interpret the electro-optical data. © 2010 IOP Publishing Ltd.

Piezoresponse force microscopy characterization of rare-earth doped BiFeO3 thin films grown by the soft chemical method

Foschini, C. R.; Ramirez, M. A.; Simões, S. R.; Varela, José Arana; Longo, Elson; Simões, A. Z.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Revisão Formato: 2185-2195
ENG
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The multiferroic behavior with ion modification using rare-earth cations on crystal structures, along with the insulating properties of BiFeO3 (BFO) thin films was investigated using piezoresponse force microscopy. Rare-earth-substituted BFO films with chemical compositions of (Bi 1.00-xRExFe1.00O3 (x=0; 0.15), RE=La and Nd were fabricated on Pt (111)/Ti/SiO2/Si substrates using a chemical solution deposition technique. A crystalline phase of tetragonal BFO was obtained by heat treatment in ambient atmosphere at 500 °C for 2 h. Ion modification using La3+ and Nd3+ cations lowered the leakage current density of the BFO films at room temperature from approximately 10-6 down to 10-8 A/cm2. The observed improved magnetism of the Nd3+ substituted BFO thin films can be related to the plate-like morphology in a nanometer scale. We observed that various types of domain behavior such as 71° and 180° domain switching, and pinned domain formation occurred. The maximum magnetoelectric coefficient in the longitudinal direction was close to 12 V/cm Oe. © 2012 Elsevier Ltd and Techna Group S.r.l.

Effect of surface deposited rare earth oxide gel characteristics on cyclic oxidation behavior of Fe20-Cr alloys

Fernandes,Stela Maria Cristina; Ramanathan,Lalgudi Venkataraman
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2006 EN
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Rare earths have been used to increase high temperature oxidation resistance of many chromium dioxide and alumina forming alloys. These rare earths can be added as elements (or as oxide dispersions) to the alloys or applied as an oxide coating to the alloy surface. The sol-gel technique is considered to be very efficient to apply fine oxide particle coatings. Oxide gel coatings of various rare earths such as lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, dysprosium, yttrium, erbium and ytterbium have been applied to an iron-chromium alloy to determine their influence on the cyclic oxidation behavior (RT-900 °C) of the alloy. The morphology and coverage of the rare earth oxide gels varied with the type of rare earth. The cyclic oxidation resistance of the alloy increased with increase in time at temperature required to reach a specific chromium dioxide layer thickness and this in turn was influenced by the rare earth ion radius and characteristics of the rare earth oxide coating such as morphology, stability, coverage, resistance to thermal stresses and consequently adhesion.

Effect of rare earth oxide additions on oxidation behavior of AISI 304L stainless steel

Pillis,Marina Fuser; Araújo,Edval Gonçalves de; Ramanathan,Lalgudi Venkataraman
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2006 EN
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AISI 304L stainless steel powder compacts containing 2 vol% high purity rare earth oxides were prepared by mixing the different powders in a vibratory mill followed by pressing. The compacts thus obtained were sintered in a vacuum furnace and isothermal oxidation measurements were carried out in a muffle furnace, in air, up to 200 hours at 900 °C. The oxidized surfaces were examined in a scanning electron microscope and micro regions of the reaction products were studied using energy dispersive analysis. The addition of rare earth oxides decreased the oxidation rate of the stainless steel. Further evidence of predominant oxygen ion diffusion controlling the overall oxidation process in rare earth containing chromium oxide forming alloys has been observed.

Minimising the Decoherence of Rare Earth Ion Solid State Spin Qubits

Fraval, Elliot
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD); Doctor of Philosophy (PhD)
EN
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This work has demonstrated that hyperfine decoherence times sufficiently long for QIP and quantum optics applications are achievable in rare earth ion centres. Prior to this work there were several QIP proposals using rare earth hyperfine states for long term coherent storage of optical interactions. The very long T_1 (~weeks ) observed for rare-earth hyperfine transitions appears promising but hyperfine T_2s were only a few ms, comparable to rare earth optical transitions and therefore the usefulness of such proposals was doubtful. ¶ This work demonstrated an increase in hyperfine T_2 by a factor of 7 × 10^4 compared to the previously reported hyperfine T_2 for Pr^[3+]:Y_2SiO_5 through the application of static and dynamic magnetic field techniques. This increase in T_2 makes previous QIP proposals useful and provides the first solid state optically active Lamda system with very long hyperfine T_2 for quantum optics applications. ¶ ...; yes

Evaluation of a stoichiometric rare earth crystal for quantum computing

Ahlefeldt, Rose
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD)
EN
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This thesis presents a spectroscopic study of the 7F0 ---t5D0 transition of Eu3+ in EuC13 ·6H2 0, which is used to evaluate the potential performance of a quantum com­ puting system implemented in EuCla·6H2 0 and, more generally, in stoichiometric rare earth crystals. EuC13 ·6H2 0 has one of the narrowest optical inhomogeneous linewidths of any solid but this linewidth is shown to be still much larger than that required for practical quantum computing in a rare earth crystal. To assess the possibility of reducing the linwidth, the contributions of isotopic impurities to both the optical linewidth and line structure were investigated, and ligand isotopes were identified as a major source of both inhomogeneous broadening and structure on the optical transition, suggesting that the linewidth could be substantially reduced by isotopi­ cally purifying EuC13 ·6H20. The effect of ligand isotopes on the optical lifetime and coherence time was also investigated. It was found that fully deuterating the crystal to EuC13·6D20 substantially improves both the lifetime and coherence time. The satellite lines formed in the optical spectrum of a rare earth crystal when it is doped with another rare earth are proposed as qubits. A crucial step in char­ acterising EuCla ·6H20 for quantum computing is associating these satellite lines in EuC13 ·6H2 0 with crystallographic sites. A new method for associating sites with lines...

Experimental studies on the behaviour of rare earth elements and tin in granitic systems; Eine experimentelle Studie über das Verhalten von Seltenen Erden und von Zinn in Granit-Systemen

Tin, Quach Duc
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
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In this thesis, the behavior of rare earth elements and of tin during the crystallization of a granitic magma and the release of hydrothermal fluids has been studied in two series of experiments in hydrothermal cold seal bombs. Part I: Monazite and xenotime solubility in haplogranitic melts Crystals of pure rare earth phosphates were synthesized for each rare earth element (except Pm) by the reaction of rare earth oxides with aqueous solutions of phosphoric acids at 800 oC and 2 kbar. The light rare earths from La to Gd formed crystals of monazite, while the heavy rare earths from Gd to Lu formed xenotime. The GdPO4 samples were a mixture of the monazite and xenotime polymorph. The solubility of the rare earth phosphates in hydrous (6 wt. % H2O) haplogranitic melts with aluminum saturation index ranging from 0.7 to 1.2 was investigated at 2 kbar and 800 oC with run durations between one and two months. The influence of phosphorus and fluorine rare earth phosphate solubility was also studied under the same conditions. One additional series of experiments was carried out at 1100 °C and 2 kbar. Run products were investigated by electron microprobe. Equilibrium rare earth concentrations were estimated both from average microprobe analyses and from the extrapolation of measured diffusion profiles around dissolving crystals to the crystal-melt interface. To demonstrate equilibrium...

Neue Verbindungen der Selten-Erd-Carbodiimide.Synthesen und Strukturen; New compounds of the rare-earth-carbodiimides. Synthesis and structures

Unverfehrt, Leonid
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
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Die Fortführung der Untersuchungen der Synthese von Selten-Erd-Carbodiimiden durch das präparative Instrument der Festkörpermetathesereaktion führte zu zahlreichen noch unbekannten Verbindungen der Selten-Erd-Carbodiimiden. Durch die Synthese von Eu2(CN2)3 konnte die Reihe der Seltenerdcarbodiimide vervollständigt werden, und Untersuchungen über das dimorphe Verhalten von Tm2(CN2)3 wurden durchgeführt. Die Synthese und Struktur eines gemischt valenten Europiumfluoridcarbodiimids der Zusammensetzung Eu4F5(CN2)2 konnte durch Kristallstrukturanalyse, Mößbauer-Spektroskopie und magnetische Messungen geklärt werden. Neue Verbindungen des Typs LiLa(CN2)2 konnten synthetisiert und strukturell aufgeklärt werden. Die thermischen Zersetzungen von LiSE(CN2)2 (La, Ce) führten zu den ersten Selten-Erd-Carbodiimid-Nitriden mit der Zusammensetzung SE3(CN2)3N deren Strukturen durch Kristallstrukturanalyse bestimmt werden konnten. In dieser Arbeit soll auch die neue Verbindungsklasse der homoleptischen Tetracyanamidoaluminate mit der Zusammensetzung LiM2[Al(CN2)4] (M = Eu , Sr) vorgestellt werden. Für die beiden ersten Vertreter LiEu2[Al(CN2)4] und LiSr2[Al(CN2)4] konnten Synthesewege gezeigt und die Struktur aufgeklärt werden. Als erster Vertreter der heteroleptischen Cyanamidoaluminate konnte die Verbindung Eu3[AlF2(CN2)3(CN)] synthetisiert werden. Die strukturellen Untersuchungsmethoden waren hier Kristallstrukturanalyse...

Impact of rare earth element added filters on the X-ray beam spectra: a Monte Carlo approach

Eskandarlou, A.; Jafari, A.A.B.; Mohammadi, M.; Zehtabian, M.; Faghihi, R.; Shokri, A.; Pourolajal, J.
Fonte: IOS Press Publicador: IOS Press
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
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The effectiveness of added filters including conventional and rare earth materials for dental radiography tasks was investigated using a simulation approach. Current study focuses on the combination of a range of various filters to investigate the reduction of radiation absorbed dose and improving the quality of a radiography image. To simulate the X-ray beam spectrum, a MCNP5 code was applied. Relative intensity, beam quality, and mean energy were investigated for a typical dental radiography machine. The impact of different rare-earth materials with different thicknesses and tube voltages on the X-ray spectrum was investigated. For Aluminum as a conventional filter, the modeled X-ray spectra and HVL values were in a good agreement with those reported by IPEM. The results showed that for a 70 kVp voltage, with an increase of the thickness and atomic number of a given added filters, an increase of HVL values were observed. However, with the increase of the attenuator thickness, X-ray beam intensity decreases. For mean energy, different results were observed. It was also found that rare earth made filters reduce high energy X-ray radiation due to k-edge absorption. This leads to an ideal beam for intra-oral radiography tasks. However...

China's rare earth policies: economic statecraft or interdependence?

Smith, Robert K.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
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Approved for public release; distribution is unlimited.; This study is about discovering to what extent China uses its rare earth element policies as a tool of economic statecraft. With Chinas virtual monopoly on this resource and the United States increasingly growing demand, it is necessary to examine how China intends on using its economic power. The study builds a comparative framework using both structural realism and neoliberal institutionalism, by identifying theory predictions in terms of Chinas strategic intent and the specific policies it might employ in the rare earth element sector. Specifically, the study finds that Beijing has and will continue to use its rare earth policies as a tool of economic statecraft, but with restraint. Despite its present reliance on economic interdependence with the United States, as China continues to modernize the structure of its economy, more statecraft interventions will likely occur. Beijing was successful in utilizing its rare earth policies as a tool of economic statecraft both by influencing the behavior of its international and its domestic commercial actors. China will leverage its near-monopoly on the rare earths industry by continuing to aggressively employ policies that meet its long-term strategic objectives.; Lieutenant Commander...

Exploratory synthesis: crystal chemistry and physical properties of binary, ternary and quaternary alkaline-, rare-earth and group 12 metal tetrelides

Suen, Nian-Tzu
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
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Bobev, Svilen; The relationship between crystal structures, compositions and physical properties, together with the reasons determining the formation of one phase among others, still remains as an open question in the realm of solid-state chemistry. The crystal structures and bonding patterns within compounds hold the key to further understanding the physical properties of the compounds in question. Therefore this inspires us to embark on a series of exploratory synthesis of binary, ternary and even quarternary intermetallic compounds containing lanthanide f -block metals (Rare-Earth metals; denote RE hereafter), alkaline-earth metals (Mg, Ca, Sr; denote AE hereafter) or group 12 (Zn) and group 14 elements (Ge, Sn and Pb; group 14 elements are also known as tetrel elements, which we denote Tt hereafter). The compositions and crystal structures of those phases were determined by using different kinds of techniques, such as single-crystal/ powder X-ray diffractions and elemental analysis. The physical properties including magnetic susceptibilities and electrical resistivities of the compounds were reported and discussed herein. In this work, the results can be separated into four chapters including: 1) The binary RE -Ge system: RE 5Ge3 (RE = La and Ce; Pu 5 Rh3 structure type). It was confirmed that RE 5Ge3 could adopt two different structure types depending on the synthesis temperature. It crystalized with Pu 5 Rh3 structure type of low temperature (<600 ??C)...

Allanite: thorium and light rare earth element carrier in subducted crust

Hermann, Joerg
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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The investigation of deeply subducted eclogites from the Dora-Maira massif, Western Alps reveals that accessory minerals are important hosts for trace elements. Rutile contains most of the bulk rock Ti, Nb and Ta while zircon hosts nearly all Zr and Hf. More than 90% of the bulk rock light rare earth elements (LREE) and Th and about 75% of U are incorporated in accessory allanite. Phengite is the most interesting major mineral because it hosts more than 95% of Rb, Ba and Cs. Synthesis piston cylinder experiments in a model crustal composition in the range 2.0-4.5 GPa, 680-1150 °C doped with trace elements demonstrate that accessory allanite forms at the expense of the major mineral zoisite at temperatures above 700 °C and 2.0 GPa. Allanite is stabilised by the incorporation of light rare earth elements and was found up to temperatures of 1050 °C and to pressures of at least 4.5 GPa. Disappearance of allanite is caused by dissolution in a coexisting hydrous granitic melt and is not related to the breakdown of any major phase. Experimentally determined element partitioning between allanite and a hydrous granitic melt at 900 °C, 2.0 GPa yield DLREEall/melt of about 200, DThall/melt of 60 and DUall/melt of 20. These results, combined with literature data...

Leaching of rare earth elements from bentonite clay

van der Watt,J.G; Waanders,F.B
Fonte: Journal of the Southern African Institute of Mining and Metallurgy Publicador: Journal of the Southern African Institute of Mining and Metallurgy
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2012 EN
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Due to increasing concerns of global rare earth element shortfalls in the near future, possible alternative sources of rare earth elements have recently become of economic interest. One such alternative is decanting acid mine water originating primarily from abandoned old mines in the Witwatersrand region of the Republic of South Africa. In this study, a novel way of rare earth element removal from the acid mine drainage was employed, making use of bentonite clay, which has very good adsorbent properties, as a rare earth element carrier material. The process can be economically viable only, if the elements can be selectively removed from the bentonite clay carrier material so as to yield reusable clay. Acid leaching was proposed to liberate the adsorbed rare earth elements from the bentonite clay. Accordingly, acid leaching experiments were performed to study the desorption of three commonly-found rare earth elements, namely neodymium, samarium, and dysprosium, from bentonite clay in the presence of sulphuric and hydrochloric acid. It was established that the three rare earth element species could be selectively removed as a group from iron, magnesium, and manganese metals through the careful manipulation of the pH. An investigation into the kinetic aspects of the rare earth element desorption process from the bentonite clay was also undertaken. The applicability of various kinetic models such as zero-order...