Studies all transport and magnetic properties of nano particle doped MgB2 superconductor for technological applications

This thesis Entitled Studies on transport and magnetic properties of nano particle doped mgb2 superconductor for technological applications.The thesis ahead focuses on the establishment of enhanced superconducting properties in bulk MgB2 via nano particle doping and its conversion into mono/multifilamentary wires. Further, an attempt has also been made to develop prototypes of MgB2 coil and conduction cooled current lead for technological applications. The thesis is configured into 6 chapters. The opening chapter gives an idea on the phenomenon of superconductivity, the various types of superconductors and its applications in different fields. The second chapter is an introduction on MgB2 superconductor and its relevance which includes crystal and electronic structure, superconducting mechanism, basic superconducting properties along with its present international status. The third chapter provides details on the preparation and characterization techniques followed through out the study on MgB2. Fourth chapter discusses the effect of processing temperature and chemical doping using nano sized dopants on the superconducting properties of MgB2• Fifth chapter deals with the optimization of processing parameters and novel preparation techniques for wire fabrication. Sixth chapter furnishes the preparation of multifilamentary wires with various filament configurations, their electromechanical properties and it also incorporates the development of an MgB2 coil and a general purpose conduction cooled current lead.

Hydrothermally formed functional niobium oxide doped tungsten nanorods

Nanorod forms of metal oxides is recognised as one of the most remarkable morphologies. Their structure and functionality have driven important advancements in a vast range of electronic devices and applications. In this work, we postulate a novel concept to explain how numerous localised surface states can be engineered into the bandgap of niobium oxide nanorods using tungsten. We discuss their contributions as local state surface charges for the modulation of a Schottky barrier height, relative dielectric constant and their respective conduction mechanisms. Their effect on the hydrogen gas molecule interactions mechanisms are also examined herein. We synthesised niobium tungsten oxide (Nb17W2O25) nanorods via a hydrothermal growth method and evaluated the Schottky barrier height, ideality factor, dielectric constant and trap energy level from the measured I-V vs temperature characteristics in the presence of air and hydrogen to show the validity of our postulations.

Tungsten oxide doped N,N-'-di(naphthalen-1-yl)-N,N-'-diphenyl-benzidine as hole injection layer for high performance organic light-emitting diodes

By introducing tungsten oxide (WO3) doped N,N-'-di(naphthalen-1-yl)-N,N-'-diphenyl-benzidine (NPB) hole injection layer, the great improvement in device efficiency and the organic film morphology stability at high temperature were realized for organic light-emitting diodes (OLEDs). The detailed investigations on the improvement mechanism by optical, electric, and film morphology properties were presented. The experimental results clearly demonstrated that using WO3 doped NPB as the hole injection layer in OLEDs not only reduced the hole injection barrier and enhanced the transport property, leading to low operational voltage and high efficiency, but also improved organic film morphology stability, which should be related to the device stability. It could be seen that due to the utilization of WO3 doped NPB hole injection layer in NPB/tris (8-quinolinolato) aluminum (Alq(3))-based device, the maximum efficiency reached 6.1 cd A(-1) and 4.8 lm W-1, which were much higher than 4.5 cd A(-1) and 1.1 lm W-1 of NPB/Alq(3) device without hole injection layer. The device with WO3 doped NPB hole injection layer yet gave high efficiency of 6.1 cd A(-1) (2.9 lm W-1) even though the device was fabricated at substrate temperature of 80 degrees C.

Study of Densification Process and Microstructure for Highly Dense Doped MgB2 Bulk Samples

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Alumina and Silica based Epoxy Nano-composites for Electrical Insulation

Plain epoxy resins or resin impregnated cellulose have found application as electrical insulation in power equipment. In the past, their performance was improved by the use of inorganic oxide fillers of microscopic dimensions. In the recent past nano-particle doped epoxy insulation came into use with a view to further enhance the dielectric properties. This paper reports dielectric investigations into epoxy nano-composites based on a class of metal oxides, Al2O3 and SiO2. In particular, consideration has been given to the partial discharge performance and electrical breakdown under different voltage profiles as a function of the volumetric composition of the nano-particles in epoxy resin.

Phase transformation in the surface region of zirconia and doped zirconia detected by UV Raman spectroscopy

The phase evolution of yttrium oxide and lanthanum oxide doped zirconia (Y2O3-ZrO2 and La2O3-ZrO2, respectively) from their tetragonal to monoclinic phase has been studied using UV Raman spectroscopy, visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD mainly give the bulk information. For Y2O3-ZrO2 and La2O3-ZrO2, the transformation of the bulk phase from the tetragonal to the monoclinic is significantly retarded by the presence of yttrium oxide and lanthanum oxide. However, the tetragonal phase in the surface region is difficult to stabilize, particularly when the stabilizer's content is low. The phase in the surface region can be more effectively stabilized by lanthanum oxide than yttrium oxide even though zirconia seemed to provide more enrichment in the surface region of the La2O3-ZrO2 sample than the Y2O3-ZrO2 sample, based on XPS analysis. The surface structural tension and the enrichment of the ZrO2, component in the surface region of ZrO2-Y2O3 and ZrO2-La2O3 might be the reasons for the striking difference between the phase change in the surface region and the bulk. Accordingly, the stabilized tetragonal surface region can significantly prevent the phase transition from developing into the bulk when the stabilizer's content is high.

Titania and tungsten doped titania thin films on glass; active photocatalysts

Acidification of an isopropanol solution containing mixtures of [Ti(OPri)(4)] and [W(OEt)(5)] produced solutions from which various TiO2, WO3 and TiO2/WO3 thin films could be obtained by dip coating and annealing. The films were analysed by X-ray diffraction, SEM/EDAX, Raman, electronic spectra, contact angle and photoactivity with respect to destruction of an over layer of stearic acid. The TiO2/WO3 films were shown to be mixtures of two phases TiO2 and WO3 rather than a solid solution TixWyO2. The 2% tungsten oxide doped titania films were shown to be the most effective photocatalysts. All of the TiO2 and TiO2/WO3 films showed light induced superhydrophillicity. (C) 2002 Elsevier Science Ltd. All rights reserved.

Influence of rare earth doping on the structural and catalytic properties of nanostructured tin oxide

Nanoparticles of tin oxide, doped with Ce and Y, were prepared using the polymeric precursor method. The structural variations of the tin oxide nanoparticles were characterized by means of nitrogen physisorption, carbon dioxide chemisorption, X-ray diffraction, and X-ray photoelectron spectroscopy. The synthesized samples, undoped and doped with the rare earths, were used to promote the ethanol steam reforming reaction. The SnO2-based nanoparticles were shown to be active catalysts for the ethanol steam reforming. The surface properties, such as surface area, basicity/base strength distribution, and catalytic activity/selectivity, were influenced by the rare earth doping of SnO2 and also by the annealing temperatures. Doping led to chemical and micro-structural variations at the surface of the SnO2 particles. Changes in the catalytic properties of the samples, such as selectivity toward ethylene, may be ascribed to different dopings and annealing temperatures.

FABRICATION, CHARACTERIZATION, AND IRRADIATION OF AN AUSTENITIC OXIDE DISPERSION STRENGTHENED STEEL SUITED FOR NEXT GENERATION NUCLEAR APPLICATIONS

As nuclear energy systems become more advanced, the materials encompassing them need to perform at higher temperatures for longer periods of time. In this Master’s thesis we experiment with an oxide dispersion strengthened (ODS) austenitic steel that has been recently developed. ODS materials have a small concentration of nano oxide particles dispersed in their matrix, and typically have higher strength and better extreme temperature creep resistance characteristics than ordinary steels. However, no ODS materials have ever been installed in a commercial power reactor to date. Being a newer research material, there are many unanswered phenomena that need to be addressed regarding the performance under irradiation. Furthermore, due to the ODS material traditionally needing to follow a powder metallurgy fabrication route, there are many processing parameters that need to be optimized before achieving a nuclear grade material specification. In this Master’s thesis we explore the development of a novel ODS processing technology conducted in Beijing, China, to produce solutionized bulk ODS samples with ~97% theoretical density. This is done using relatively low temperatures and ultra high pressure (UHP) equipment, to compact the mechanically alloyed (MA) steel powder into bulk samples without any thermal phase change influence or oxide precipitation. By having solutionized bulk ODS samples, transmission electron microscopy (TEM) observation of nano oxide precipitation within the steel material can be studied by applying post heat treatments. These types of samples will be very useful to the science and engineering community, to answer questions regarding material powder compacting, oxide synthesis, and performance. Subsequent analysis performed at Queen’s University included X-ray diffraction (XRD) and inductively coupled plasma optical emission spectrometry (ICP-OES). Additional TEM in-situ 1MeV Kr2+ irradiation experiments coupled with energy dispersive X-ray (EDX) techniques, were also performed on large (200nm+) non-stoichiometric oxides embedded within the austenite steel grains, in an attempt to quantify the elemental compositional changes during high temperature (520oC) heavy ion irradiation.

The influence of dislocations on the nonlinearity of ZnO:Cu varistors

Zinc Oxide doped only with Cu shows highly nonlinear I–V characteristics. Microstructural observations of these ceramics reveal the presence of extensive dislocation network. The transmission electron microscopy (TEM) indicates that the dislocations are impurity decorated which arise as a result of limited solubility of CuO in ZnO. It is envisaged that the depletion region is generated in the region containing the dislocations because of the presence of acceptor type traps.

Growth and characterization of new transparent conductive oxides single crystals beta-Ga2O(3): Sn

Tin oxide doped beta-Ga2O3 single crystals are recognized as transparent conductive oxides (TCOs) materials. They have a larger band gap (4.8 eV) than any other TCOs, thus can be transparent in UV region. This property shows that they have the potential to make the optoelectronic device used in even shorter wavelength than usual TCOs. beta-Ga2O3 single crystals doped with different Sn4+ concentrations were grown by the floating zone technique. Their optical properties and electrical conductivities were systematically studied. It has been found that their conductivities and optical properties were influenced by the Sn4+ concentrations and annealing. (c) 2006 Elsevier Ltd. All rights reserved.

Preparo de óxidos de manganês em presença de biomassa e avaliação catalítica em reações de oxidação de hidrocarbonetos e remoção catalítica de SOx

Os riscos de poluição ao meio ambiente envolvendo petróleo envolvem, não só o seu transporte, como também seu refino. O prejuízo causado por um derramamento de petróleo vai além de danos à fauna e flora, pois envolvem também questões sociais. A emissão de óxidos de enxofre, denominadas SOx, durante o refino de petróleo através do craqueamento catalítico em leito fluidizado (FCC) também é uma das preocupações ambientais, já que esses óxidos estão relacionados com o a formação de chuva ácida e problemas respiratórios. Os hidrocarbonetos provenientes de um derramamento podem ser degradados em produtos menos agressivos ao meio ambiente, por oxidação química, por exemplo. Já as emissões de enxofre na unidade de FCC podem ser minimizadas por diversos processos, como por exemplo, o uso de aditivos nas unidades de FCC. Nesse trabalho óxidos de manganês dos tipos OMS-1 e OMS-2 foram sintetizados em presença e ausência de biomassa e óxidos OMS-2 foram dopados com os metais cobre, vanádio e ferro. Possíveis alterações em suas propriedades, suas atividades catalíticas em oxidação de hidrocarbonetos e em testes de captura de enxofre em condições de temperatura similares à unidade de FCC foram investigadas. Constatou-se uma diminuição na área superficial, tamanho e volume de poros nos óxidos sintetizados em presença de biomassa, através de uma análise de adsorção e dessorção de N2 (ASAP), porém seus difratogramas em uma análise de difração de raio X de pó (DRX) revelaram a obtenção de estruturas do criptomelano em todos os OMS-2. Os óxidos OMS-2 testados na oxidação do cicloexano, não sofreram modificações em sua estrutura após seu uso como catalisador, mas a presença da biomassa na síntese não aumentou sua atividade catalítica. Nos testes DeSOx, o óxido dopado com ferro apresentou o melhor desempenho e testes em ciclos mostraram ser possível sua reutilização

Estudo da formação de sub-produtos da degradação de clorobenzeno e 1,2-dicloroetano a partir da reação com reagente de Fenton em solução aquosa utilizando diferentes fontes de ferro

Poluições da água e do solo são duas das cinco categorias básicas de poluição ambiental. As outras três são do ar, ruído e luz. Poluição ocorre quando um material/produto químico é adicionado ao meio ambiente afetando-o adversamente. Uma vez que a poluição existe, retornar a matriz impactada para o seu estado anteriormente não poluído torna-se muito difícil ou até mesmo impossível em alguns casos. Os compostos organoclorados (OC) representam um importante grupo de poluentes orgânicos persistentes (POP), devido à sua toxicidade e elevada persistência no ambiente. Diferentes técnicas de remediação de solo e água subterrânea têm sido desenvolvidas com o objetivo de reparar as áreas contaminadas em menor tempo e custo possíveis e, assim, a oxidação química in situ tem se mostrado uma técnica cada vez mais atraente devido sua simplicidade e baixo custo. A degradação de dois compostos organoclorados via oxidação química por reagente de Fenton em solução aquosa é o objeto do presente trabalho. Para tanto, foram selecionados dois compostos, sendo um alifático e outro aromático. Assim, foram avaliadas as condições de degradação dos compostos organoclorados em relação às concentrações do oxidante em diferentes tempos reacionais, diferentes fontes de catalisador e, de forma qualitativa, quais foram os principais subprodutos formados. Os ensaios oxidativos foram realizados em meio aquoso com temperatura controlada a 25 C e em 3 configurações de [Fe2+] e [H2O2]. A extração dos compostos de interesse para a fase orgânica também foi estudada. A análise dos extratos revelou que o acetato de etila foi o solvente que melhor extraiu os compostos de interesse da fase aquosa. Além destes ensaios, foram avaliadas outras duas fontes de Fe(II), sendo 11 óxidos de manganês dopados com ferro e a classe de solo predominante no território nacional, que é caracterizada pela sua alta concentração de ferro endógeno (latossolo). O ensaio entre as fontes de ferro revelou que tanto o óxido de Mn quanto o latossolo produziram menos subprodutos em relação à reação com a solução de sulfato Fe(II). Entretanto, em termos quantitativos, a redução na concentração de clorobenzeno foi mais efetiva na reação com a solução de Fe(II) (cerca de 63%). A identificação dos sobprodutos foi realizada a partir da análise em cromatógrafo a gás acoplado a espectrômetro de massas e em análise comparativa dos espectros com a biblioteca NIST. Os ensaios oxidativos revelaram que em baixas concentrações de oxidante, há a possibilidade de geração de subprodutos mais tóxicos que os reagentes, sendo produzido bifenilas policloradas e hexaclorociclohexano nas reações com clorobenzeno e 1,2-dicloroetano, respectivamente