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1
Janasi, Suzilene Real [UNESP]. "Ferrita de bário: preparação de fases dopadas com cobalto, titânio e estanho". Universidade Estadual Paulista (UNESP), 1997. http://hdl.handle.net/11449/102592.
Testo completoAbstract (sommario):
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janasi_sr_dr_araiq.pdf: 2566763 bytes, checksum: e10173459cbf62287b0478669d7c6ed0 (MD5)A substituição parcial de íons Fe3+ por pares de íons (Co2+-Ti4+ ou Co2+-Sn4+) na ferrita de bário hexagonal (BaFe12O19) leva a uma substancial diminuição no campo coercitivo (Hc) com uma pequena mudança na magnetização de saturação (Ms), permitindo seu uso em gravação magnética e magneto-óptica de alta densidade. Os diferentes métodos de preparação de ferritas de bário resultam em produtos com propriedades distintas. Neste trabalho, preparou-se BaFe12-2xCoxTixO19 e BaFe12-2xCoxSnxO19 (0,25 £ x £ 1) por coprecipitação, utilizando cloretos dos metais precursores e solução de KOH/K2CO3 como precipitante. Após a secagem, o produto obtido foi calcinado a 950oC por 3h, lavado e seco. Os difratogramas de raios X indicaram a formação da ferrita de bário. As micrografias eletrônicas de varredura mostraram que os pós obtidos apresentam-se na forma de plaquetas hexagonais de 1 a 2mm. As curvas de magnetização das ferritas de bário dopadas mostraram que o campo coercitivo e a remanência diminuem em função do aumento da razão de substituição x. A curva de magnetização da amostra dopada com Co-Ti, com x = 1 é característica de uma ferrita mole, com Hc = 13,5 kA.m-1 (0,17 kOe), Ms = 46,1 emu.g-1 e Mr = 11,0 emu.g-1. Para a amostra dopada com Co-Sn a diminuição de Mr não é significante. Estes resultados mostraram que as propriedades magnéticas das ferritas de bário dopadas obtidas por coprecipitação foram melhoradas, em relação aos dados da literatura para ferrita de bário pura ou dopada.
The partial substitution of Fe3+ ions with pairs of ions (Co2+-Ti4+ or Co2+-Sn4+) in hexagonal barium ferrite (BaFe12O19) leads to a substantial reduction on coercivity (Hc) with only a low change in saturation magnetization (Ms), allowing its use in high density magnetic and magneto-optical recording. Different preparative methods result in barium ferrites with distinguished properties. In this work, BaFe12-2xCoxTixO19 and BaFe12-2xCoxSnxO19 (0.25 £ x £ 1) were prepared by the coprecipitation method using chloride salt precursors and KOH/K2CO3 solution. After drying, the powder was calcinated at 950oC by 3 h, washed and dried. The X ray diffraction patterns indicated the barium ferrite phase formation. The scanning electron micrographs showed that the particles are hexagonal platelike with diameter size ranging from 1 to 2 mm. The magnetization curves of substituted barium ferrites showed that the values of Hc and Mr decrease with the increase of the substitution ratio x. The magnetization curve profile for Co-Ti substituted sample with x =1 is characteristic of a soft ferrite with Hc = 13.5kA.m-1 (0.17 kOe), Ms = 46.1 emu.g-1 and Mr = 11.0 emu.g-1. These results indicated that the magnetic properties of substituted barium ferrites obtained by coprecipitation were improved when compared with the literature data for pure and substituted barium ferrite.
2
Liu, Fanmao. "Photoresponse of ferroelectric BaTiO3 thin films". Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/458535.
Testo completoAbstract (sommario):
BaTiO3 es un material de óxido ferroeléctrico sin plomo. BaTiO3 películas delgadas han sido ampliamente estudiados para aplicaciones de memoria debido a su efecto de memoria de carga resultante de su naturaleza ferroeléctrica. Hoy en día, la comunidad científica ha renovado su interés en BaTiO3, ya que posee características que son interesantes para áreas de rápido desarrollo como la fotovoltaica, la detección fotoeléctrica y la fotocatálisis. El objetivo principal de la presente tesis es estudiar los efectos fotoeléctricos de las películas delgadas BaTiO3 y dar luz sobre los mecanismos relevantes que las controlan.
Los materiales ferroeléctricos muestran campos eléctricos internos intrínsecos, inevitables y exclusivos: campo eléctrico de impresión (Eimp) y campo eléctrico de despolarización (Edep). Así se pueden obtener distintos efectos fotoeléctricos debido a Eimp y Edep. En la presente tesis hemos estudiado en detalle el papel de Eimp y Edep en los efectos fotoeléctricos de películas BaTiO3. En particular, se muestra que se puede usar una configuración de medición apropiada para revelar y aislar su contribución. Como resultado, pueden obtenerse diferentes foto respuestas transitorias y constantes según se desee. De igual modo, se analiza su contribución a la dinámica de conmutación ferroeléctrica. La foto respuesta transitorio tiene su origen en el cribado de la carga superficial (fotograbado). Para modular su magnitud se ha realizado una caracterización detallada. Se concluye que la polarización de las fotos se rige por la presencia de agua adsorbida en la superficie, lo que permite su control. Sin embargo, se ha encontrado que la eficiencia fotoeléctrica está limitada por la baja generación de portadores por la luz, por lo que el efecto de O sustituido por N en la red BaTiO3, lo que debería dar lugar a un estrechamiento de banda, mejorando así la eficiencia fotoeléctrica , ha sido estudiado. Curiosamente, se encuentra que los tratamientos de amoníaco son eficientes para mejorar las respuestas fotoeléctricas, sin tener ninguna evidencia clara de la sustitución de N.BaTiO3 is a lead-free ferroelectric oxide material. BaTiO3 thin films have been widely studied for memory applications due to its charge memory effect resulting from its ferroelectric nature. Nowadays, the scientific community has renewed its interest on BaTiO3, because it holds characteristics that is interesting for rapidly developing areas such as photovoltaics, photoelectric sensing and photocatalysis. The main goal of the present thesis is to study the photoelectric effects on BaTiO3 thin films and to give light on the relevant mechanisms that control them. Ferroelectric materials show intrinsic, unavoidable and exclusive internal electric fields: imprint electric field (Eimp) and depolarization electric field (Edep). Thus distinct photoelectric effects can be obtained due to Eimp and Edep. In the present thesis we have studied in detail the role of Eimp and Edep on photoelectric effects of BaTiO3 films. In particular, it is shown that appropriate measurement configuration can be used to disclose and isolate their contribution. As a result, different transient and constant photoresponses can be obtained as wish. By the same token, their contribution to the ferroelectric switching dynamics are also analyzed. The transient photoresponse finds its origin on the screening of surface charge (photoscreening). In order to modulate its magnitude detailed characterization has been performed. It is concluded that the polarization photoscreening is governed by the presence of water adsorbed at the surface, allowing it to be controlled. However, the photoelectric efficiency has been found to be limited by the low generation of carriers by light, that is the reason why the effect of O substituted by N in BaTiO3 lattice, which should result in band-gap narrowing, hence improving the photoelectric efficiency, has been studied. Interestingly, it is found that ammonia treatments are efficient to improve photoelectric responses, without having any clear evidence of N substitution.
3
ALMEIDA, JUNIOR Airton Tavares De. "Caracterização da barita e do vidro cristal como atenuadores na blindagem das radiações X e Gama". Universidade Federal de Pernambuco, 2005. https://repositorio.ufpe.br/handle/123456789/9904.
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Previous issue date: 2005Com objetivo de determinar as características de atenuação do minério sulfato de bário (BaSO4) e do vidro cristal utilizados como blindagem contra as radiações ionizantes X e gama, em instalações radiográficas, foi realizado um estudo de atenuação com argamassa e concreto de barita, usados, respectivamente, no revestimento de paredes e em blocos; e com o vidro cristal usado em biombos e janelas. Para isso, foram analisadas 10 placas de argamassa de barita, 3 placas de concreto de barita, com área média útil de 900 cm2 e espessura média de 1 a 5 cm, e 3 placas de vidro cristal, com área útil de 323 cm2, com espessuras de 1, 2 e 4 cm. As amostras foram irradiadas com raios-X, com potenciais de 60, 80,110 e 150 quilovolts, e raios gama do 60Co. As respostas de atenuação (mGy/mAmin) e (mGy/h) ambos a 1 metro, em função da espessura, resultaram na obtenção das curvas de atenuação e de transmissão. Além disso, foram determinadas as espessuras equivalentes das camadas semi e deciredutoras, tanto para o vidro cristal, como para a argamassa e o concreto de barita
4
Gondim, Priscylla Cinthia Alves. "Desenvolvimento de bloco de veda??o com barita na composi??o de partida para blindagem de radia??o X". Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12744.
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Previous issue date: 2009-08-21Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
This work main objective is to study the use of bricks in barium X-rays rooms in order to contribute to the optimization of shielding rooms diagnosis. The work was based on experimental measurements of X-ray attenuation (40 to 150 kV), using ceramic seal bearing the incorporation of barium sulfat (BaSO4). Different formulations were studied in three different firing temperatures and evaluated for incorporation in the ceramic body. The composition of 20% of barite processed at a temperature of 950 ? C showed better physical and mechanical properties, is considered the most suitable for the purpose of this work. Were produced bricks sealing composition formulated based on that presented the best technological features. These blocks were tested physically as a building material and wall protective barrier. Properties such as visual, deviation from the square, face flatness, water absorption and compressive strength were evaluated for all the blocks produced. The behavior of this material as attenuator for X-rays was investigated by experimental results which take into account mortar manufacturers barium through the different strains and compared with the reference material (Pb). The simulation results indicated that the ceramic block barium shows excellent properties of attenuation equivalence lead taking into account the energy used in diagnostic X-ray
Este trabalho tem por finalidade principal estudar a utiliza??o de blocos cer?micos baritados em salas de radia??o X, visando contribuir para a otimiza??o da blindagem de salas de diagn?stico. O trabalho foi baseado em medidas experimentais de atenua??o da radia??o X (40 a 150 kV), empregando material cer?mico de veda??o contendo a incorpora??o de sulfato de b?rio (BaSO4). Diferentes formula??es foram estudadas em tr?s temperaturas de queima diferentes e avaliadas as incorpora??es na massa cer?mica. A composi??o de 20% de barita processada a temperatura de 950?C, apresentou melhores propriedades f?sicas e mec?nicas, sendo considerada a mais adequada para a proposta deste trabalho. Foram produzidos blocos cer?micos de veda??o baseados na composi??o formulada que apresentou melhores caracter?sticas tecnol?gicas. Estes blocos foram testados fisicamente como material construtivo de parede e barreira protetora. Propriedades como caracter?sticas visuais, desvio com rela??o ao esquadro, planeza das faces, absor??o de ?gua e resist?ncia ? compress?o foram avaliadas para todos os blocos produzidos. O comportamento deste material como atenuador para a radia??o X foi investigado por meio de resultados experimentais que levaram em considera??o fabricantes de argamassas baritadas atrav?s das diferentes tens?es e comparado com o material de refer?ncia (Pb). Os resultados obtidos nas simula??es indicaram que o bloco cer?mico baritado demonstra ?timas propriedades de atenua??o em equival?ncia ao chumbo levando-se em conta as energias usadas em raios X diagn?stico
5
Zhong, Zhimin. "Combustion syntheses and characterization of Barium Titanate, Barium Tetratitanate and Lead substituted Barium Tetratitanate /". The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487861396027028.
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6
Kudelová, Barbora. "Prekonavani barier". Master's thesis, Vysoké učení technické v Brně. Fakulta architektury, 2017. http://www.nusl.cz/ntk/nusl-316300.
Testo completoAbstract (sommario):
Showing the barriers in the city, which inhibit a human in its movement along the landscape. Bunch of barriers at one place can signify a problem for a human to overcome. Marking these places is also showed below the prize map which illustrates from the economic point of view the problem exists at that place and the place is not that permeable as it should be. After marking the problematic spaces and their overlook in the real world there follows a choice of one place and its particular solution. Verifying the reasons why overcoming especially this place, what are the reasons for connecting it, analysing the areas on both sides, pointing out the place of connection and the way to solve the pedestrian bridge and finding the conceptual principle which is the support for the construction principle.
7
Almeida, Jademir Jesus Pirapora de. "Ação da radiação de alta energia nas propriedades mecânicas de compostos elastoméricos a base de SBR carregados com barita". Universidade Presbiteriana Mackenzie, 2012. http://tede.mackenzie.br/jspui/handle/tede/1329.
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Previous issue date: 2012-03-30Universidade Presbiteriana Mackenzie
In this work were studied the action of ionizing radiation on the physical-mechanical properties in elastomeric compounds based on styrene-butadiene rubber (SBR) filled with barite, opening way for application of these composites in the protection and shield against high-energy radiation, in the form of aprons. These aprons come to substitute the elastomeric ones with lead filler in ergonomic and economically advantageous conditions. The effect of high-energy radiation was studied on SBR compounds filled with barite at 50, 75, 100, 125, and 150phr (phr = parts per hundred rubber) of barite concentrations, exposed to ionizing radiation at 0, 100, 200, 500 and 1000kGy doses. The samples were characterized by physic-mechanical tests as rheometry, tensile strength, resilience, hardness, wear resistance, oil absorption, permanent deformation under compression (compression set) and dynamic mechanical thermal analysis. The morphological characteristics were determined by scanning electron microscopy. The results showed that the radiation causes an increase in tensile strength and elongation, the tear strength and hardness, and a decrease in fluid absorção and deformation under compression.
Neste trabalho foi estudada a ação da radiação ionizante nas propriedades físico-mecânicas nos compostos elastoméricos a base de estireno-butadieno (SBR) carregados com barita, abrindo caminho para aplicação destes compostos na proteção e blindagem contra a radiação alta energia, na forma de aventais, vindo substituir os aventais a base de elastômero carregado com chumbo em condições ergonômicas e economicamente vantajosas. Foi estudado o efeito da radiação ionizante em compostos a base de SBR carregado com barita nas concentrações de 50, 75, 100, 125, e 150phr (phr = partes por cem de borracha) de barita expostos à radiação ionizante nas doses de 0, 100, 200, 500 e 1000kGy. As amostras foram caracterizadas por meio de ensaios físico-mecânicos de reometria, de resistência à tração, resiliência, dureza, resistência ao rasgo, absorção de óleo, deformação permanente sob compressão (compression set) e ensaios de análise térmica dinâmico-mecânica. As características morfológicas dos compositos foram determinadas por meio de microscopia eletrônica de varredura. Os resultados mostraram que a radiação provoca um aumento da resistência à tração, do alongamento sob tração, da resistência ao rasgamento e da dureza; e um decréscimo na absorção de fluido e na deformação sob compressão.
8
FRIMAIO, AUDREW. "Desenvolvimento de um material cerâmico para utilização em proteção radiológica diagnóstica". reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11414.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
9
Rai, Maha. "Molecular dynamics modelling of barium silicate and barium fluorozirconate glasses". Thesis, University of Kent, 2018. https://kar.kent.ac.uk/66702/.
Testo completoAbstract (sommario):
Advancement in science and technology has profoundly depended on new types of glass innovation. The glasses that were studied in this project are binary barium silicate glasses, binary barium fluorozirconate glasses, ZBLAN glasses and 〖Eu〗^(3+) doped ZBLAN glass (the ZBLAN glasses are based on binary barium fluorozirconate glass). The high atomic number of barium in the barium silicate glasses provides high mass and high electron density providing its applications for heat and X-ray shielding. The phenomena such as phase separation in the barium silicate glass will affect its properties of durability and electrical conductivity. On the other hand, ZBLAN glasses have a broad infrared optical transmission window due to the weaker bonding/interaction of F^- ions. Due to the presence of lanthanum in the composition ZBLAN glass can be easily doped with rare-earth ions such as 〖Eu〗^(3+) giving it many optical applications such as optical amplifier and fibre lasers. Hence, it's essential to study the structure of these glasses to understand their properties for applications. This thesis used the classical molecular dynamics modelling technique to study the static atomic structure of glass. Generally, fluoride glasses can be formed by totally replacing oxygen atoms in oxide glasses by fluorine atoms. The oxide silicate glasses are common glasses that follow the Zachriasen rules of glass formation but the fluorozirconate glasses do not and lack fixed structural units. The structure analysis was performed at short-range order (e.g. coordination number, bond length and bond angle), medium-range order (e.g. network connectivity) and long- range order (e.g. phase separation). The related crystals were also simulated in similar conditions to the glasses to compare their atomic structure. Normally at short-range order glass structure is similar to its related crystal but the differences between them starts from the position and number of next nearest neighbours and increases thereafter. Additionally, the new methods such as rotational invariants and grid analysis were used to scrutinise structural units and phase separation respectively. The model of barium silicate glass shows good agreement with experimental diffraction data. The typical bond length and coordination number for Ba were 2.97 Å and approximately 7 respectively. The model did not show any phase separation at low Ba content and hence for further investigation very large models of alkaline earth silicate glasses were studied to see how Ba, Ca and Mg are distributed in the glass. The grid analysis was used to see the distributions which show homogeneity for Ba and Ca and inhomogeneity for Mg cation. The structural units of fluorozirconate glasses were carefully studied as they do not follow the Zachriasen glass model. The coordination number for Zr was mixture of 7 and 8. The rotational invariant analysis shows that the structural units of ZrF_n polyhedra for coordination number 7 and 8 were similar to Augmented Triangular Prism and Biaugmented Triangular Prism respectively. However, rotational invariant values for BaF_n polyhedra tend more towards random. The large complex model of 〖Eu〗^(3+) doped ZBLAN glass was made as it is studied for optical applications. The initial analysis was to observe whether Zr and Ba has similar structural roles as in binary fluorozirconate glass system which they do. Considering the extra elements in ZBLAN glass, Al behaves like a network former and has octahedra structural units whereas La and Na behave like modifiers. In the glass Eu was uniformly distributed with predominantly coordination number of 8 and does not have well defined structural units.
10
Kinsey-Nielsen, Susan Mary. "HIGH-RESOLUTION LASER SPECTROSCOPY OF BARIUM-MONOHYDROXIDE AND BARIUM-MONODEUTEROXIDE". Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/292080.
Testo completo
11
Kirby, Nigel Matthew. "Barium zirconate ceramics for melt processing of barium cuprate superconductors". Thesis, Curtin University, 2003. http://hdl.handle.net/20.500.11937/1364.
Testo completoAbstract (sommario):
The widespread use of high temperature superconductors through improved understanding of their underlying physics is in part dependent on the synthesis of large, high quality single crystals for physical research. Crucible corrosion is an important factor hindering the routine synthesis of large, high purity rare-earth barium cuprate superconductor single crystals. Molten BaCuO2-CuO fluxes required for the growth of such crystals are highly corrosive to substrate materials, and corrosion products may lead to chemical contamination of crystals and other practical difficulties. BaZrO3 is known to be inert to BaCuO2-CuO melts, but its use has remained restricted to a very small number of laboratories worldwide because it is very sensitive to the effects of off- stoichiometric or residual secondary phases which degrade its performance. BaZrO3 suitable for sustained melt containment is difficult to produce due to kinetic limitations of phase purity, difficulty in sintering to adequate density, and very narrow stoichiometry tolerances of finished ceramics. The existing literature provided a guide to the production of high quality BaZrO3, but was not sufficiently complete to readily allow production of crucibles suitable for this application. The two basic aims of this project were: To provide a comprehensive and quantitative description of the necessary attributes of crucibles for barium cuprate melt processing and to expand the knowledge of solid-state BaZrO3 processing to encourage its widespread application to crucible manufacture; To explore the application of solution chemical processes whose potential benefits could lead to routine application of BaZrO3 through improved ceramic quality and processing properties.Based primarily on solid-state processing research, the optimal stoichiometry for corrosion resistant crucibles was observed over the narrow range of 1.003±0.003 Ba : (Zr + Ht) mole ratio. Residual ZrO2 must be strictly avoided even at very low levels because severe localized expansion of Z a grains during reaction with the melt severely reduces corrosion resistance. Although the effect of Ba-rich phases are less severe, their abundance must be suppressed as much as allowed by the production process. Solid-state derived crucibles with a large barium excess were unstable and readily attacked by water. TEM analysis clearly showed residual Zr02 was present as discrete grains and not as grain boundary films, and also the prevalence of intragranular defects in Ba-rich ceramics. Quantitative knowledge of the narrow range of required stoichiometry is critical for developing successful solid-state and solution chemical processes. Reliably achieving the required stoichiometry and phase purity is experimentally challenging and beyond the capability of many processing systems. Systematic investigation revealed sharp changes in physical properties of processed powders across the phase boundary. The resistance of BaZrO3, of the desired stoichiometry to grain growth during powder processing has not previously been reported in the available literature. At the desired stoichiometry for corrosion resistance, powder grain growth resistance combined with very precise control over stoichiometry makes the solid-state process more competitive with solution-based processes than previously acknowledged in the literature. The development of solution processes for BaZr03 precursors is complicated by aqueous chemistry of zirconium compounds.This project developed the first chemically derived precursor process demonstrated to produce a ceramic of adequate quality for sustained barium cuprate melt containment. The barium acetate / zirconium oxychloride / ammonium oxalate system provided control over stoichiometry without requiring elevated solution temperatures, a large excess of barium reagents, or reagents containing alkalis. Despite showing the capability to supersede the solid-state process, the oxalate process still requires further refinement to more reliably achieve high sintered densities. Although the attributes required for sustained barium cuprate melt containment are now clear, its routine mass production remains reliant on further development of solution chemical techniques or improvements to the kinetics of solid-state processing. This project advanced ceramic design and processing technology in the BaZrO3 system and provided new approaches in meeting the challenging analytical needs of research and process control for high quality production of this compound.
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Kirby, Nigel Matthew. "Barium zirconate ceramics for melt processing of barium cuprate superconductors". Curtin University of Technology, Department of Applied Physics, 2003. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16216.
Testo completoAbstract (sommario):
The widespread use of high temperature superconductors through improved understanding of their underlying physics is in part dependent on the synthesis of large, high quality single crystals for physical research. Crucible corrosion is an important factor hindering the routine synthesis of large, high purity rare-earth barium cuprate superconductor single crystals. Molten BaCuO2-CuO fluxes required for the growth of such crystals are highly corrosive to substrate materials, and corrosion products may lead to chemical contamination of crystals and other practical difficulties. BaZrO3 is known to be inert to BaCuO2-CuO melts, but its use has remained restricted to a very small number of laboratories worldwide because it is very sensitive to the effects of off- stoichiometric or residual secondary phases which degrade its performance. BaZrO3 suitable for sustained melt containment is difficult to produce due to kinetic limitations of phase purity, difficulty in sintering to adequate density, and very narrow stoichiometry tolerances of finished ceramics. The existing literature provided a guide to the production of high quality BaZrO3, but was not sufficiently complete to readily allow production of crucibles suitable for this application. The two basic aims of this project were: To provide a comprehensive and quantitative description of the necessary attributes of crucibles for barium cuprate melt processing and to expand the knowledge of solid-state BaZrO3 processing to encourage its widespread application to crucible manufacture; To explore the application of solution chemical processes whose potential benefits could lead to routine application of BaZrO3 through improved ceramic quality and processing properties.Based primarily on solid-state processing research, the optimal stoichiometry for corrosion resistant crucibles was observed over the narrow range of 1.003±0.003 Ba : (Zr + Ht) mole ratio. Residual ZrO2 must be strictly avoided even at very low levels because severe localized expansion of Z a grains during reaction with the melt severely reduces corrosion resistance. Although the effect of Ba-rich phases are less severe, their abundance must be suppressed as much as allowed by the production process. Solid-state derived crucibles with a large barium excess were unstable and readily attacked by water. TEM analysis clearly showed residual Zr02 was present as discrete grains and not as grain boundary films, and also the prevalence of intragranular defects in Ba-rich ceramics. Quantitative knowledge of the narrow range of required stoichiometry is critical for developing successful solid-state and solution chemical processes. Reliably achieving the required stoichiometry and phase purity is experimentally challenging and beyond the capability of many processing systems. Systematic investigation revealed sharp changes in physical properties of processed powders across the phase boundary. The resistance of BaZrO3, of the desired stoichiometry to grain growth during powder processing has not previously been reported in the available literature. At the desired stoichiometry for corrosion resistance, powder grain growth resistance combined with very precise control over stoichiometry makes the solid-state process more competitive with solution-based processes than previously acknowledged in the literature. The development of solution processes for BaZr03 precursors is complicated by aqueous chemistry of zirconium compounds.
This project developed the first chemically derived precursor process demonstrated to produce a ceramic of adequate quality for sustained barium cuprate melt containment. The barium acetate / zirconium oxychloride / ammonium oxalate system provided control over stoichiometry without requiring elevated solution temperatures, a large excess of barium reagents, or reagents containing alkalis. Despite showing the capability to supersede the solid-state process, the oxalate process still requires further refinement to more reliably achieve high sintered densities. Although the attributes required for sustained barium cuprate melt containment are now clear, its routine mass production remains reliant on further development of solution chemical techniques or improvements to the kinetics of solid-state processing. This project advanced ceramic design and processing technology in the BaZrO3 system and provided new approaches in meeting the challenging analytical needs of research and process control for high quality production of this compound.
13
Cure, Barbie. "Baring It All". ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1909.
Testo completoAbstract (sommario):
This collection of creative nonfiction encapsulates the author’s career as a burlesque performer in New Orleans. The goal of this thesis is to tell her story using the techniques of creative nonfiction – specifically, the memoir. This is not merely a story of her career – it is a piece about her relationships, the author conquering her fears, and how she rises up to meet her goals. Part I tells of how the author discovers this new world and how she finds her place in it. Part II is the author’s personal narrative of her revelation to her family. This story will introduce those who are unfamiliar with burlesque to a world of theatrics, sparkle, erotic subtexts, and this story needs the techniques of creative nonfiction to do it justice.
14
Lehnen, Peer. "Relaxoreigenschaften von Strontium-Barium-Niobat - Relaxor Properties of Strontium-Barium-Niobate". Gerhard-Mercator-Universitaet Duisburg, 2001. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-12132001-102821/.
Testo completoAbstract (sommario):
In the present thesis the relaxor properties of the tungsten-bronze ferroelectric material strontium-barium niobate Sr1-wBawNb2O6 (SBN) are investigated. SBN is a very good experimental realization of the three-dimensional random-field Ising model (3d RFIM). The quenched random fields (RF) originate from charge disorder and can be enhanced by doping with Ce3+. They are responsible for the formation of polar nanoclusters in the paraelectric phase. In order to study the critical behavior of SBN, linear birefringence (LB) and second harmonic generation (SHG) have been measured as a function of temperature. Within an Ornstein-Zernike analysis of the LB data the autocorrelation function, <P2>, was determined, whereas the dipolar correlation length was obtained from the SHG data. They suggest that, due to its intrinsic disorder, pure SBN does not belong to the 3d Ising universality class. Doping with Ce3+ions, which seem to generate RFs, enhances the relaxor properties. The critical exponents v and y of SBN:Ce shift against those of the 3d RFIM. The domain morphology of SBN:Ce has been investigated by piezoelectric force microscopy (PFM). Fractal-like shaped zero-field cooled nanodomains are observed. Their size distribution can be described by a power law with exponential cutoff in accordance with prediction for the RFIM. It was measured for the first time in a RF system. The temperature and field induced evolution of natural and written domains has been studied with PFM, LB and SHG measurements. It reveals a very slow relaxation from a macrodomain into a depolarized multidomain state (and vice versa) even above TC. This hints at strong pinning forces due to quenched RFs. They are also responsible for the observed aging in poled SBN and the field induced cluster percolation above TC measured with SH-hysteresis. The domains can be considered as a "thick" phase grating for SH-diffraction. The Bragg-regime diffraction efficiency reflects the temperature and field induced change of the averaged domain sizes in the system.
15
Warren, Davis Morgan. "Molecular dynamics simulation of barite and celestite ion-pairs". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41177.
Testo completoAbstract (sommario):
The presence of ion-pairs in electrolyte solutions affects the activity of dissolved species as well as the solubility of minerals. The extent of ion-pairing in a system is predicted by an association constant, K[subscript A], which for sparingly soluble salts are frequently determined experimentally in binary or ternary systems. This introduces complex activity coefficient calculations that often require unavailable parameters. Barite (BaSO₄) and celestite (SrSO₄) are sparingly soluble minerals with interest in the oil and mining industry, yet the values of K[subscript A] for the ion-pairs BaSO₄(aq.) and SrSO₄(aq.) are still uncertain. Molecular dynamics simulations are used to obtain the K[subscript A] values for these two salts through potential of mean force (PMF) calculations. The molecular mechanisms involved in the association reactions are also explored, in particular the role of the association intermediates in the overall reaction as described by the Eigen mechanism. Additionally, the kinetics of water exchange around the free and paired ions is examined and the residence time of a water coordinated to the free and paired cation is calculated.
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Roach, Dan. "Barite bodies west of Hemlo, Ontario petrofabric and geochemical study". Thesis, University of Ottawa (Canada), 1987. http://hdl.handle.net/10393/5312.
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Maie, Hiroki. "Synthesis and dielectric properties of nanocrystalline barium titanate and silver/barium titanate particles". Connect to this title online, 2008. http://etd.lib.clemson.edu/documents/1211387100/.
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Nabasenja, Caroline. "Radiation doses for barium meals and barium enemas in the Western Cape South Africa". Thesis, Cape Peninsula University of Technology, 2009. http://hdl.handle.net/20.500.11838/1560.
Testo completoAbstract (sommario):
Thesis submitted in fulfilment of the requirements for the award of the
degree of
Master of Technology Radiography (Diagnostic)
in the Faculty of Health and Wellness Sciences
at the Cape Peninsula University of Technology
2009Since their discovery in 1895, the use of x-rays is continuously evolving in medicine making the diagnosis of injuries and diseases more practicable. It is therefore not surprising that x-rays contribute 90% of the radiation dose to the population from manmade sources (DWP, 1992). Moreover, these radiation doses are associated with both fatal and non-fatal cancer risk that is detrimental to adults between 20 to 60 years (Wall, 1996). Radiation dose to individuals therefore needs to be actively monitored in order to minimise such risk. Barium contrast examinations were characterised as one of the radiological examinations that contributed enormously to the collective dose to the patients in the radiology department (DWP, 1992). Determining the diagnostic reference levels of such examinations would reduce the over-exposure of individuals to ionising radiation. Currently in South Africa (SA), there are no diagnostic dose reference levels for barium meal (BaM) and barium enema (BaE) examinations. This study therefore investigated the radiation doses delivered to patients referred for BaM and BaE, obtained potential regional reference doses for these examinations, compared the radiation doses obtained with those from similar dosimetry studies and investigated sources of dose variation among the study sites. A total of 25 BaM and 30 BaE patients in the age range 18 to 85 years, weighing 50 kg to 90 kg, at 3 hospitals in the Western Cape, SA were investigated. The radiation dose to the patients was measured using Dose Area Product (DAP) meters that were permanently fitted onto fixed fluoroscopy units at these 3 hospitals. The third quartile DAP values were 20.1 Gycm2 and 36.5 Gycm2 for BaM and BaE respectively. The median DAP values were 13.6 Gycm2 and 27.8 Gycm2 for BaM and BaE respectively. The median values were recommended as the potential Diagnostic Reference Levels for BaM and BaE as they are less affected by outlying values of under or over- weight (Yakoumakis, Tsalafoutas, Sandilos, Koulentianos et al, 1999). The weights of the patients, fluoroscopy time, the number of images obtained, the use of digital or conventional fluoroscopy equipment and the level of training of the radiologists were the factors considered for dose variation among the 3 hospitals.
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Amaral, Graziella Ferecini Bueno. "Utilização de compostos elastoméricos à base de SBR carregados com barita em aventais isolantes de raios X". Universidade Presbiteriana Mackenzie, 2011. http://tede.mackenzie.br/jspui/handle/tede/2741.
Testo completoAbstract (sommario):
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Previous issue date: 2011-03-17Fundo Mackenzie de Pesquisa
In this study it was studied the physical-mechanical properties of elastomers based on styrenebutadiene rubber (SBR) with the addition of barite, for application of these compounds in protecting in the shielding against radiation X, for the substitution of aprons form based on elastomer fillered with lead in ergonomic and economically advantageous conditions. Elastomeric compounds were studied with different barite concentrations [50, 75, 100, 125 and 150 phr (parts for hundred of rubber)]. The studied properties were: tensile strength, tensile modulus, tear strength, permanent deformation in compression, hardness, absorption of fluid, resilience, measure of rheology, morphological analysis and characterization of attenuating materials to radiation X. Results showed that all compositions exhibit good dispersion of the filler in the matrix. It was observed that with the increase barite concentration there is an increase in hardness beyond not causing significant alteration in the tensile strenght, in the elasticity, as well as in the resistance to the tearing of the material.
Neste trabalho foram estudadas as propriedades físico-mecânicas de elastômeros a base de borracha de estireno-butadieno (SBR) com a adição de barita, para aplicação destes compostos na proteção de blindagem contra a radiação X, para a substituição de aventais a base de elastômeros carregados com chumbo em condições ergonômicas e economicamente vantajosas. Foram estudados compostos elastoméricos com diferentes concentrações de barita [50, 75, 100, 125 e 150 phr (partes por cem de borracha)]. Entre as propriedades estudadas destacam-se: resistência à tração, módulo sob tração, resistência ao rasgo, deformação permanente à compressão, dureza, absorção de fluido, resiliência, medida de reologia, análise morfológica e caracterização de materiais atenuadores à radiação X. Os resultados mostraram que todas as composições apresentam uma boa dispersão da carga na matriz. Observou-se que com o aumento da concentração de barita há um aumento na dureza além de não causar alteração significativa na resistência à tração, na elasticidade, bem como na resistência ao rasgamento do material.
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BOTERO, ANA ELISA CASAS. "BIOFLOTATION OF MAGNESITE, CALCITE AND BARITE USING RHODOCOCCUS OPACUS AS BIOREAGENT". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=10515@1.
Testo completoAbstract (sommario):
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORA bactéria Rhodococcus opacus foi avaliada como biorreagente para a flotação dos minerais da magnesita calcita e barita. As análises para determinar a conformação de parede o R. opacus estabelecem que é constituída por macromoléculas com características anfipáticas. O balanço entre grupos catiônicos e aniônicos da parede atribui um ponto isoelétrico equivalente de 3,2. Os resultados dos testes de aderência indicam que a bactéria R. opacus tem uma forte afinidade por superfícies de características ácido - base. Medidas dos minerais antes e após da interação com o R. opacus revelaram que embora fossem observadas modificações sobre todas as superfícies dos minerais, a bactéria R. opacus apresentou uma melhor afinidade pela superfície da magnesita. A capacidade de adsorção das células sobre as superfícies foi fortemente dependente dos valores de pH e a velocidade de adsorção atingiu a máxima concentração de células nos primeiros 5 minutos. As isotermas para a adsorção da bactéria sobre os minerais poderiam ser categorizadas do tipo Lagmuir (L) , II. A melhor flotabilidade foi observada em pH 7. Para a magnesita, a porcentagem foi de 92% usando uma concentração de R. opacus de 100 ppm. Para calcita os melhores resultados apresentaram flotabilidade de 55% para uma concentração de 250 ppm. Em relação à barita, os melhores valores de flotabilidade (60%) foram obtidos para uma concentração de R. opacus de 350 ppm. A aproximação termodinâmica determinou que a energia de adesão era negativa para todos os sistemas, sugerindo assim uma adsorção espontânea da bactéria sobre as superfícies minerais. Para magnesita e calcita as teorias DLVO confirmam os resultados experimentais, as atrações eletrostáticas entre as partículas determinaram as forças de interação. Já para barita, a teoria de XDLVO poderia predizer o comportamento das células sobre o mineral. Neste caso as interações ácido-base seriam as responsáveis pela adesão.
Rhodococcus opacus micro-organism was evaluated as a biocollector for flotation of calcite and magnesite and barite. Analyses of R. opacus cell wall indicated the macromolecules configurationl. The IEP value of R. opacus was around 3.2,. The acidic IEP value of R. opacus could be due to the presence of anionic groups on the wall that dominate over the cationic groups. The adherence test showed the R. opacus affinity for acid-base surfaces.The behavior of the minerals, before and after R. opacus interaction, was evaluated and showed that the cells adhesion shifted both the minerals zeta potential curves and the reversal charges in comparison to their original isoelectric points. Adhesion tests suggested a higher affinity of the bacteria for magnesite than calcite and barite. The experiments of the adsorption rate of the R. opacus on the minerals surfaces showed fast behavior, achieving a maximum of cell adsorption after 5 minutes. Adsorption isotherm curves for the minerals could be categorized as Lagmuir (L) type II. The best bioflotability results for the minerals were achieved for pH 7. Magnesite reached values around 93% for a R. opacus concentration of 100 ppm. For calcite the best flotability was of 55% for a R. opacus concentration of 220 ppm. For barite, the best flotability achieved 70% for a bacterial concentration of 350 ppm. Using the thermodynamic approach of the minerals systems, the adhesion energy of R. opacus on the surfaces was negative. The result suggested a spontaneous adsorption of R. opacus on to the all minerals. For magnesite and calcite, the DLVO theory can predict the cell behavior on the minerals surfaces. The electrostatic attractions determine the interaction forces. For barite and pH 7, the X- DLVO theory predicted the R. opacus adhesion on the surface by acid base interactions.
21
Hosler, Carrie E. "Fluid flow, heat, and mass transfer of barite mineralization in Missouri /". free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1421142.
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Jakubek, Zygmunt J. (Zygmunt Jerzy). "Rydberg spectroscopy of barium monofluoride". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32154.
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Barath, Aljosha [Verfasser]. "Kommerzialisierung der Sportlerpersönlichkeit / Aljosha Barath". Baden-Baden : Nomos Verlagsgesellschaft mbH & Co. KG, 2018. http://d-nb.info/1160309469/34.
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Yang, Yaodong. "Barium Titanate-Based Magnetoelectric Nanocomposites". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/38666.
Testo completoAbstract (sommario):
Barium Titanate (BaTiO3 or BTO) has attracted an ever increasing research interest because of its wide range of potential applications. Nano-sized or nanostructured BTO has found applications in new, useful smart devices, such as sensors and piezoelectric devices. Not only limited to one material, multi-layers or multi-phases can lead to multifunctional applications; for example, nanocomposites can be fabricated with ferrite or metal phase with BTO. In this study, I synthesized various BTO-ferrites, ranging from nanoparticles, nanowires to thin films. BTO-ferrite coaxial nanotubes, BTO-ferrite self-assemble thin films, and BTO single phase films were prepared by pulsed laser deposition (PLD) and sol-gel process. BTO-ferrite nanocomposites were grown by solid state reaction. Furthermore, BTO-metal nanostructures were also synthesized by solid state reaction under hydrogen gas which gave us a great inspiration to fabricate metal-ceramic composites.
To understand the relationship between metal and BTO ceramic phase, I also deposited BTO film on Au buffered substrates. A metal layer can affect the grain size and orientation in BTO film which can further help us to control the distribution of dielectric properties of BTO films.
After obtaining different nanomaterials, I am interested in the applications of these materials. Recently, many interesting electric devices are developed based on nanotechnology, e.g.: memristor. Memristor is a resistor with memory, which is very important in the computer memory. I believe these newly-synthesized BTO based nanostructures are useful for development of memristor, sensors and other devices to fit increasing needs.Ph. D.
25
Boleslavská, Yvona. "Pracovní (výrobní) prostředí bez bariér". Doctoral thesis, Vysoké učení technické v Brně. Fakulta architektury, 2014. http://www.nusl.cz/ntk/nusl-233272.
Testo completoAbstract (sommario):
This dissertation Barrier-free Work Environment examines and emphasizes some elements, which are projected and will be projected even more into architectural production – architect’s work. Buildings designed specially to create a working environment accessible for disabled people are of a current interest and they will become a very prominent subject of social development in the future, because it will be necessary to react sensitively to the disproportions in human abilities and in the society’s capability to create new workplaces, implement progressive technologies, computer systems, and last but not least, to react to new possibilities of people’s creative invention. This thesis is based on the key definitions for this topic – the terms health and handicap. It is aimed at the ethics of communication in a society and its perception by a person with some kind of disability – handicap. This thesis also analyzes the limits of human possibilities in the context of contemporary and future progressive technologies. The topic of accessible workplaces necessarily derives from the historical development of workplaces, and it indicates the future trends of development. An important part of this thesis is concerned with the conditions for creating a friendly working environment, not only from the aspect of the construction itself, but mainly by the interior design, its flexible furniture, and special work tools not only for the handicapped. This dissertation and its contribution to the scholarly research are based on evaluation of an opinion survey, whose respondents were companies employing handicapped people. The analysis and consequent synthesis of the answers given by the employers of the disadvantaged people brought pieces of information, which are summarized in conclusions and recommendations.
26
Gross, Timothy M. "[Beta]-barium borate thin film formation on silicon through metal organic decomposition of two novel precursors, barium dimesitylborinate and barium (18-crown-6) cyclotriboroxane /". Online version of thesis, 2004. http://hdl.handle.net/1850/11802.
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Smith, Esther Jane. "The biogeochemical behaviour of trace-metals in seasonally anoxic lake". Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266804.
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Thomas, Gilberto Lima. "A interação bárion-bárion na aproximação de estado ligado ao modelo de Skyrme". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2000. http://hdl.handle.net/10183/31456.
Testo completoAbstract (sommario):
Estudamos, neste trabalho, em uma das extensões do modelo de Skyrme a SU(3) - a aproximação de estado ligado - o setor estranho de número bariOnico igual a 2. Analisamos situações em que os dois bárions envolvidos são ligados, constituindo o que conhecemos como dibárions, e em que dois bárions livres são simplesmente espalhados. No primeiro caso o espectro dos dibárions é calculado com o uso da configuração axialmente simétrica generalizada, sendo comparado com o obtido no modelo não relativístico de quarks. É feita, também, uma predição sobre a existência da partícula H. No segundo caso desenvolvemos, com o uso da configuração produto, um formalismo para o estudo da interação bárion-bárion, calculando o potencial correspondente. Expressões detalhadas e resultados numéricos são apresentados para a interação AN, com as componentes central, spin-spin e tensorial do potencial sendo obtidas e comparadas com outros resultados fenomenológicos.In this work we study, in the framework of the bound state approach to the SU(3) Skyrme model, the baryonic number—two strange sector. We analyze situations where the two baryons involved are bound to forni the so called dibaryons and where two free baryons are simply scattered. In the first case, with the help of the generalized axially symmetric ansatz, the dibaryon spectrum is calculated and compared with the one obtained in the non relativistic quark model. A prediction about the existente of the H—particle is also made. In the second case we have used the product ansatz to develop a formalism to study the baryon—baryon interaction, calculating the corresponding potential. Detailed expressions and numeric results are presented for the AN interaction, with the central, spin—spin and tensor components of the potential being obtained and compared with other phenomenological results.
29
Lee, Chung-Kook. "Crystallization of Nano-sized barium ferrite". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19920.
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Cannell, David Stuart. "The electric strength of barium titanate". Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.237676.
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Quadros, da Cunha Feteira AntoÌnio Manuel AndreÌ. "Characterisation of barium titanate based ceramics". Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407525.
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Abdulla, Sarah Ahmed Eltayed. "Barium sulphate : problems, solutions and applications". Thesis, University of Surrey, 2010. http://epubs.surrey.ac.uk/848627/.
Testo completoAbstract (sommario):
The main aim of this work is to synthesise barium sulphate (BaS04) that are tiny in size (nanoparticles). BaS04 scaling is a known problem in the context of offshore oil recovery. Different methods of scale control have been suggested in the literature, none has solved the BaS04 scaling problem dramatically. In this work several methods were assessed, but only one of them seemed to work well. The methods studied were: 1) Formation of colloidal BaS04 in an aqueous alcohol medium using BaCh and Na2S04 as precursors. The precursors were mixed rapidly forming rhombohedral BaS04 and by tubular reactor forming dendrite-like particles. 2) Inhibition of Ba2+ using phosphino (carboxylic acids)prior to the sol- addition induced the formation of broom-stick-like BaS04 particles. 3)Formation of BaS04 microemulsions using different surfactants. Cationic surfactants (sodium bis-2-thylhexylsulfosuccinate) (AOT) induced the formation of BaS04 platelets and nanofilaments. While non-ionic surfactants (polyoxyethylene-4-dodecyl ether)(C12E04) and SEs different HLB values (2,6,15 and 16), induced the formation of BaS04 platelets with the former and BaS04 nanobaguettes with HLB 2 and platelet-like particles,defined nanorods and interconnected nanoparticles with HLB 6, 15 and 16 respectively. TX-lOO (polyethylene glycol p(1,1,3,3-tetramethylbutyl)- phenylether) formed small BaS04 nanoparticles. Anionic didodecyldimethylammonium bromide (DDAB) formed cylindrical BaS04 nanoparticles. 4) (SOl) in H20 was added to Ba2+ adsorbed on Stober silica producing spherical BaS04 nanoparticles in StOber silica spheres. 5) Ba2 + in H20 was added to (SOl)/AIO(OH). This is a new method to the best of our knowledge. It formed small BaS04 nanoparticles at 2 and 4 J.lmol (BaCh and Na2S04) and big bow-tie structured BaS04 particles at 6 J.lmol concentration per 5cm3 of AIO(OH). Since BaSOJAIO(OH) produced with SOlIAIO(OH)(aq) + Ba2+(aq) showed higher yields its scaling inhibition efficiency was studied in detail at three different concentrations of Ba2+ (64, 90 and 121 ppm) at 298 K and 320 K. This novel approach to scale control using chaperoning AIO(OH) is promising. A comparison study using 2-D imaging took place in BaS04 in AIOOH and BaS04 in H20 showed that the former remained longer as a sol. This suggests that BaS04 based in AIOOH can be used in medical diagnosis. BaS04 in AIOOH was used as a catalyst (prior to freeze drying) in an exhaust engine to test its efficiency in detoxifying the exhaust engine from CO, HC and NO" under stoichiometric conditions. Catalytic activates were also investigated after activation with Pt and Au.
33
Johnston, Diane E. "Characterisation of lanthanum-doped barium titanate". Thesis, University of Aberdeen, 1993. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU554634.
Testo completoAbstract (sommario):
One significant application of donor doped barium titanate (BaTiO3) is in the manufacture of Positive Temperature Coefficient of Resistance (PTCR) thermistors. Combined synthesis, phase diagram and electrical studies were undertaken on donor doped barium titanate with a view to understanding the factors responsible for PTCR phenomena. A range of materials, both commercial PTCR devices and in-house lanthanum-doped barium titanate samples, have been studied. All three commercial PTCR samples measured were found to be electrically inhomogeneous with two PTCR-exhibiting regions and a conductive grain core. The conductive core resistance had a characteristic temperature dependence, with a minimum occurring in the vicinity of the tetragonal to cubic phase transition (Tc) of barium titanate. The phase relations and electrical behaviour of two joins in the lanthanum-doped BaTiO3 system, join A (Ba4-4xLa4xTi4-xO12) and join B (Ba1-yLayTiO3+), were also studied. Compositions on joins A and B for 0x0.195 and 0y0.1 respectively, crystallised as single phase barium titanate. Charge compensation on both joins (at these concentrations) was achieved by a mixture of both titanium vacancies and free electrons. The electron compensation mechanism, Ba_1-yLa_yTi. 4+_1-yTi. 3+O_3, significantly complicates determination of phase relations in this system, since it occurs off the BaO-TiO_2-La_2O_3 ternary phase diagram. Ac impedance measurements indicated that samples on join A were electrically inhomogeneous resulting in the presence of different regions with variable Tx values; furthermore, the phase transitions in each region were themselves complex. The tetragonal to cubic phase transition was studied by a combination of x-ray diffraction, ac impedance and by varying dopant concentration. The resulting behaviour was complex, with both first order and continuous transitions occurring. There was also evidence of a two phase, (i.e. both cubic and tetragonal barium titanate) region associated with a distribution in particle size: small particles (&60 2m) were cubic; larger ones were tetragonal. It is apparent that the combined, complicating effects of grain size and segregation phenomena make it inappropriate to give an explanation for the phase relations and electrical behaviour of lanthanum-doped barium titanate in terms of classical phase equilibria and phase transition theories.
34
Smetana, Volodymyr. "Subnitride im System Alkalimetall-Barium-Stickstoff". [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-36312.
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De, Palatis Michael V. "Production of cold barium monohalide ions". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50251.
Testo completoAbstract (sommario):
Ion traps are an incredibly versatile tool which have many applications throughout the physical sciences, including such diverse topics as mass spectrometry, precision frequency metrology, tests of fundamental physics, and quantum computing. In this thesis, experiments are presented which involve trapping and measuring properties of Th³⁺. Th³⁺ ions are of unique interest in part because they are a promising platform for studying an unusually low-lying nuclear transition in the 229Th nucleus which could eventually be used as an exceptional optical clock. Here, experiments to measure electronic lifetimes of Th³⁺ are described. A second experimental topic explores the production of sympathetically cooled molecular ions. The study of cold molecular ions has a number of applications, some of which include spectroscopy to aid the study of astrophysical objects, precision tests of quantum electrodynamics predictions, and the study of chemical reactions in the quantum regime. The experiments presented here involve the production of barium monohalide ions, BaX⁺ (X = F, Cl, Br). This type of molecular ion proves to be particularly promising for cooling to the rovibrational ground state. The method used for producing BaX⁺ ions involves reactions between cold, trapped Ba⁺ ions and neutral gas phase reactants at room temperature. The Ba⁺ ion reaction experiments presented in this thesis characterize these reactions for producing Coulomb crystals composed of laser cooled Ba⁺ ions and sympathetically cooled BaX⁺ ions.
36
Souza, João Geraldo Martins de. "Argamassa baritada : teste da proporção e da espessura do revestimento, para uso como barreira de proteção para raios-x de 30K e V de energia efetiva, em clinicas odontologicas". [s.n.], 1992. http://repositorio.unicamp.br/jspui/handle/REPOSIP/288884.
Testo completoAbstract (sommario):
Orientador: Frab Norberto BoscoloDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba
Made available in DSpace on 2018-07-14T02:20:12Z (GMT). No. of bitstreams: 1 Souza_JoaoGeraldoMartinsde_M.pdf: 1939298 bytes, checksum: db33f1f8c25e3f28983e120355828c46 (MD5) Previous issue date: 1992
Resumo: O presente estudo teve o propósito de determinar a proporção ideal do mineral barita em argamassa de revestimento. E a espessura necessária e equivalente à espessura de chumbo para barrar ou absorver raios-X de aproximadamente 30keV de energia efetiva, para blindagens em clinicas de radiologia odontológica. Foram confeccionados blocos de argamassa baritada com 150x150mm e espessuras de 1.4 a 15.1mm. Foi utilizado como fonte de radiação um a aparelho GE 100 modelo A0061. Os feixes incidentes e emergentes de radiação, foram medidos por meio de dosimetros termoluminescentes de Fluoreto de Litio 700, e por câmara de ionização e eletrometro Victoreen modelos 600-4 e 600 respectivamente, e ainda foi feito um cálculo teórico a partir dos elementos componentes da argamassa, para uma comparação com os resultados nos testes. Os resultados evidenciaram que a barita, numa proporção de 60%, em relação aos demais componentes da argamassa estudada, para raios-X de aproximadamente 30keV de energia efetiva (93.7 kVp), foi obtido por meio de um fator de conversão de 5.6 da espessura da argamassa para espessura necessária de chumbo. A camada semi-redutora (HVL) da argamassa baritada foi de 1.24mm e a camada semi-redutora (HVL) do chumbo foi de O.22mm. Assim sendo, para cada milímetro de chumbo seria necessário 5.6mm da argamassa de revestimento para uma proteção eficiente
Abstract: The present paper has the aim of determine the ideal portion of baryte mineral in plaster and the necessary equivalent thickness of plumbum to absorb or stop x-rays in nearly 30keV effective energy, in isolating odontological clinics. Baryte plaster boards were made at 150x150mm and from 1.4 to 15.1mm of thick. As a radiation source, a GE 100, model A0061 device was used. The incidental and emergent radiadion beams were measured with Lithium Fluoride 700 dosimeter and ionization chamber and Victoreen electrometer models 600-4 and 600 respectively. A theo cal calculus was also done from the plaster compound elements for a testing result comparison. The results highlighted that baryte in 60% portion related to the other studied plaster compounds for x-rays nearly 30keV effective energy (93.7kVp) was obtained through a convertion factor of 5.6 in the plaster thickness for the plumbum necessary thickness. The baryte plaster half-value-layer (HVL) was 1.24mm and the plumbum half-value-layer was 0.22mm. Hence, for each plumbum milimeter it would be necessary 5.6mm of plaster for an efficient protection
Mestrado
Radiologia
Mestre em Odontologia
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Kaur, Mehar. "The Terrestrial Biogeochemical Cycle of barium: A proposed study to examine barium flux in Mojave Desert dust". Scholarship @ Claremont, 2013. http://scholarship.claremont.edu/scripps_theses/150.
Testo completoAbstract (sommario):
Barium is a relatively abundant element in the crustal environments, Ba quantities can range from anywhere between 200ppm to 900ppm. Most common forms of Ba-minerals found in the environment are barite (BaSO4), witherite (BaCO3) and hollandite (Ba2Mn8O16). Ba is a useful element; it is used in various industries as a component in drilling fluids, in medical research and in manufacturing of various substances such as glass, ceramics, printing paper etc. However high quantity of Ba can be potentially toxic for the human body and can impair plant growth. It is therefore, important to review the terrestrial biogeochemical cycle of Ba, which is less studied and less understood than the oceanic biogeochemical cycle of Ba. Additionally, terrestrial systems face a diverse climate and are not as stable as the oceanic systems. Due to this the terrestrial biogeochemical cycle of barium is continuously changing and is more dynamic than the oceanic cycle. By studying one part of the cycle, i.e. the interaction of Ba in the atmosphere with the geosphere in the Mojave desert, NV, I propose a study to test the hypothesis that occurrence of, Ba-mineral, barite, in desert soils is mainly driven by dust flux. The proposal includes methodology for dust collection, sample analysis using XRF, XRD and SEM.EDS techniques and potential budget and timeline. Evidence supporting this claim would suggest that dust transports such minerals, affects the soil chemistry of desert soils and the interaction of various terrestrial systems.
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Gurav, Ankita B. "Investigating Heterogeneous Nucleation of Barite using Hydrothermal Atomic Force Microscopy and Optical Microscopy". Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1610403323603442.
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Niggli, Stefan. "Klassische und laser-spektroskopische Untersuchungen an Barium /". [S.l.] : [s.n.], 1987. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=8416.
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Wu, Wenzhong. "Low Temperature Sintering Semiconductive Barium Strontium Titanate". FIU Digital Commons, 2007. http://digitalcommons.fiu.edu/etd/76.
Testo completoAbstract (sommario):
Low temperature sintering has become a very important research area in ceramics processing and sintering as a promising process to obtain grain size below 100nm. For electronic ceramics, low temperature sintering is particularly difficult, because not only the required microstructure but also the desired electronic properties should be obtained. In this dissertation, the effect of liquid sintering aids and particle size (micrometer and nanometer) on sintering temperature and Positive Temperature Coefficient Resistivity (PTCR) property are investigated for Ba1-xSrxTiO3 (BST) doped with 0.2-0.3mol% Sb3+ (x = 0.1,0.2,0.3,0.4 and 0.5). Different sintering aids with low melting point are used as sintering aids to decrease the sintering temperature for micrometer size BST particles. Micrometer size and nanometer size Ba1-xSrxTiO3 (BST) particles are used to demonstrate the particle size effect on the sintering temperature for semiconducting BST. To reduce the sintering temperature, three processes are developed, i.e. 1 using sol-gel nanometer size Sb3+ doped powders with a sintering aid; 2 using micrometer size powders plus a sintering aid; and 3 using nanometer size Sb3+ doped powders with sintering aids. Grain size effect on PTCR characteristics is investigated through comparison between micrometer size powder sintered pellets and nanometer size powder sintered pellets. The former has lower resistivity at temperatures below the Curie temperature (Tc) and high resistivity at temperatures above the Curie temperature (Tc) along with higher ñmax/ñmin ratio (ñmax is the highest resistivity at temperatures above Tc, ñmin is the lowest resistivity at temperatures below Tc), whereas the latter has both higher ñmax and ñmin. Also, ñmax/ñmin is smaller than that of pellets with larger grain size. The reason is that the solid with small grain size has more grain boundaries than the solid with large grain size. The contribution z at room temperature and high temperature and a lower ñmax/ñmin ratio value.
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Gallagher, Andrew James. "Modelling barium isotopes in metal-poor stars". Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/9224.
Testo completoAbstract (sommario):
The principal theory concerning the origin of the elements heavier than the Fe-peak, such as Ba, strongly suggest that for old, metal-poor environments, the rapid (r-) process is the most likely path taken in their synthesis, while the slow (s-) process becomes more substantial in younger, more metal-rich stellar populations. In this work I test this theory by evaluating the isotope ratios of Ba. It is understood that Ba consists of seven stable isotopes, five of which are synthesised by the two neutron-capture processes. The two odd isotopes, 135,137Ba, as well as 138Ba are synthesised via both the r- and s-processes while two of the even isotopes, 134,136Ba are synthesised via the s-process only. The relative contribution of the r- and s-process to these isotopes can be understood via nucleosynthesis calculations and is described using the parameter fodd, where fodd = [N (135Ba) + N (137Ba)] /N (Ba). Low values of fodd (~0.11) indicate an s-process regime, while high values of fodd (~0.46) indicate an r-process regime. In the Ba II 4554 A line the even isotopes lie close to the line centre, while the odd isotopes, which are hyperfine split because of their non-zero nuclear spin, lie in the wings of the line. From an analysis of the line profile shape, one can determine whether Ba has been synthesised primarily through the r-process or s-process; a broad, asymmetric line would indicate a high r-process contribution, while a line with a deeper core and shallower wings would indicate a high s-process contribution. Using the radiative transfer code ATLAS, which assumes local thermodynamic equilibrium (LTE) and employs 1-dimensional (1D) KURUCZ06 model atmospheres, I synthesised line profiles for six metal-poor stars: HD140283, HD122563, HD88609, HD84937, BD-04 3208 and BD+26 3578 - for a range of isotope ratios. All six are of sufficiently low metallicity that Ba was expected to have an r-process origin. These were fit to high resolution (R\equiv \lamda/\Delta\lamda = 90 000 - 95 000), high signal-to-noise to the Ba II 4554 A line which has multiple components. In the first test, synthetic spectra were computed using the non local thermodynamic equilibrium (NLTE) radiative transfer code MULTI. The synthetic line profiles were fit to a number of lines in HD140283. Although this technique might have improved the fit in the line core, it was found that such a treatment did not improve upon fitting errors associated with the best fit 1D LTE synthetic profiles. The second test used a 3-dimensional (3D) radiative transfer code (LINFOR3D) that employed 3D, time-dependent atmospheres produced with CO5BOLD. The 3D synthetic pro les were fit to a selection of Fe lines and improvements over the poor fits produced by the 1D LTE synthesis were seen. It was found that the 3D synthesis could almost completely reproduce the line asymmetries seen in the observed stellar spectrum. This result suggests that further work to refine the 3D calculations and synthesis code would be valuable.
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Wegmann, Markus Rolf. "Microextrusion of barium titanate for PTCR applications". Thesis, University of Strathclyde, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248863.
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Cui, Yongfei. "Ferroelectric barium titanate for semiconductor photocatalytic application". Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9530.
Testo completoAbstract (sommario):
Semiconductor photocatalysis has received extensive attention due to its wide applications in water and indoor air purification, solar fuel production, etc. Charge carrier separation is a crucial step in semiconductor photocatalysis and influences the overall efficiency. It has been demonstrated that internal depolarisiation field of ferroelectric materials can drive spatial separation of charge carriers, which results in spatial separation of reduction and oxidation reactions, and improved charge carrier separation. In this thesis, ferroelectric barium titanate was chosen and its photocatalytic performance in decolourisation of organic dye molecules was investigated. Photodeposition method was adopted to deposite silver nanoparticles on the surface of barium titanate. Silver modified barium titanate showed increased photodecolourisation rate compared with bare barium titanate due to its role of electron traps and hindered charge carrier recombination. A simple thermal treatment was used to alter the phase composition of the as-received barium titanate. Samples which contained more ferroelectric tetragonal phase were found to possess higher photocatalytic activity compared with non-ferroelectric samples. This was associated with stronger ferroelectricity after thermal treatment, which enhanced dye molecule adsorption and aid charge carrier separation. The mechanism and intermediates generated in photodegradation of Rhodamine B with silver modified ferroelectric barium titanate were studied. Cleavage of chromophore was demonstrated to dominate in the initial process. Benzoic acid was identified as the main intermediate and no siginificant discrepancy in intermediates distribution between ferroelectric photocatalytic system and non-ferroelectric system was observed. The influence of ferroelectric dipole of barium titanate on photocatalytic activity of heterostructured barium titanate/hematite was also studied. The synthesised heterostructured barium titanate/hematite showed higher photodcolourisation rate than both barium titanate and hematite. This phenomenon was attributed to the improved charge carrier separation and extended charge carrier lifetime arising from heterojunction and an interaction between the ferroelectric dipole and the carriers in the hematite.
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Lea, David Wallace. "Foraminiferal and coralline barium as paleoceanographic tracers". Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/54332.
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Jette, Bruce Donald. "Feasibility of electrodeposition of yttrium and barium". Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/79452.
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Fallon, Joseph John. "Multiscale theory and simulation of barium titanate". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/28089.
Testo completoAbstract (sommario):
Although barium titanate is one of the most widely studied ferroelectric materials, questions about the nature of its phase transition remain. There are two competing models for this transition (displacive and order-disorder) and experiments detect signs of both types of transition. To study this issue computationally requires the simulation of large, disordered systems on the atomic scale. In this PhD I have developed a new classical force field for BaTiO3 which, in essence, is an ionic model. The free parameters within this force field were fitted to data generated from density-functional theory (DFT) simulations. Properties that were not used in the fitting procedure calculated with the resulting force field were found to be in excellent agreement with those calculated via DFT. The potential energy surface of BaTiO3 has been explored in detail using DFT and the force field, enabling both sublattice and single ion displacements to be studied, and highlighting in particular the important role played by the oxygen ions. Dynamical simulations show behaviour compatible both with experiments that have been interpreted as evidence for displacive transitions and with experiments interpreted as evidence for order-disorder transitions. In particular, when the local structure of the phases was studied, the locations of the ions were found to be consistent with a displacive model, whereas the calculated distribution of polarisation densities was more characteristic of an order-disorder model. The direction of the local relative displacements of titanium and oxygen ions was also considered. The deviation of this displacement from the < 111 > directions produced excellent agreement with experimental measurements of the tetragonal phase, and a similar effect was found in the orthorhombic phase. These dynamical simulations were found to be very sensitive to a range of factors such as supercell size.
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Jech, David. "Příprava a strukturní stabilita nanokrystalických tepelných bariér". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-391813.
Testo completoAbstract (sommario):
Complex thermal barrier coating systems are one the most efficient high-temperature surface treatments which open up practical applications in land-based turbines and air jet engines. In the case of most exposed rotor and stator jet engine components, the combination of thermal barrier coatings together with the inner cooling system made it possible to increase working temperature by several tens of degrees of Celsius. Nevertheless, it is very difficult to achieve any further increase in working temperature by using the conventional thermal barrier coatings based on the ZrO2-Y2O3 ceramic top coat and the MCrAlY metallic bond coat, which currently work at their material limits. The working temperature inside the combustion chamber of the jet engine is proportional to engine’s efficiency and inversely proportional to fuel consumption and production of undesirable CO2 emission. Therefore, a considerable effort has recently been devoted to research and development of new types of ceramic coatings that can withstand long term extreme working conditions. New design approaches of multi-layer composite thermal barrier coating systems can sustain the required trend of increasing working temperature of jet engines mainly because of possibility of optimization of high-temperature durability and long lifetime. The theoretical part of thesis provides a fundamental overview of thermal barrier coatings, their properties, deposition technologies and testing methods. The experimental part is focused on optimization of deposition parameters of conventional ZrO2-Y2O3 / MCrAlY thermal barrier coatings prepared by means of atmospheric plasma spraying. Furthermore, a novel multi-layer thermal barrier coating system based on ZrO2-Y2O3-Al2O3-SiO2 / ZrO2-Y2O3 / MCrAlY, which contains amorphous and/or nanocrystalline regions, is developed, tested and characterized as well. Structural stability, phase transformations and growth of the thermally grown oxide in both conventional and experimental systems after high-temperature isothermal oxidation, cyclic oxidation and burner-rig tests were evaluated by means light microscopy, scanning electron microscopy with energy-dispersive microanalysis and X-ray diffraction. In comparison with the conventional thermal barrier coatings, the novel multi-layered systems have lower thermal conductivity, slower thermally grown oxide kinetic, better structural stability, and generally higher lifetime in all high-temperature tests.
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Fathi, Ariya Reza. "Barium Solidification/Stabilization of Legacy Fly Ash". University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1523014706886586.
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Fung, Sing Chor. "Conductivity fluctuations in yttrium barium cooper oxides". HKBU Institutional Repository, 1994. http://repository.hkbu.edu.hk/etd_ra/34.
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Austin, Peter Evans. "Baring Brothers and the panic of 1837 /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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