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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Mixed ionic-electronic conductors in gas separation applications

Chen, Guannan January 2016 (has links)
Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and SrCo0.48Fe0.12Ti0.4O3-delta (SCFT) were synthesised by co-precipitation. BSCF was pressed and sintered at 1100℃ for 10 hours to pellets (relative density: 93%) from which X-ray diffraction (XRD) revealed single Pm-3m phase (a=3.9782 A). Scanning electron microscopy (SEM) revealed clear equiaxed grains (grain size 33 ± 16 micro metre). The pellets were decomposed in 7 ± 1 % CO2/N2 at 800℃ for 1 to 30 minutes. XRD confirmed secondary phases: R-3mH phase (a=b=5.1397 A, c=9.4847 A) and Fm-3m phase (a=4.2490 A). Electron backscattered diffraction (EBSD) ascribed R-3mH and Fm-3m phases to the surface and part of the cross-section precipitates, respectively as revealed by SEM. Energy dispersive X-ray spectroscopy (EDX) revealed the compositions of R-3mH and Fm-3m phases to be Ba0.65±0.03Sr0.35±0.03CO3 (BSC) and CoO, respectively. Transmission electron microscopy (TEM) and EDX revealed the structure (15R, R3m and R-3mH) and composition (Ba0.20Sr0.10Co0.59Fe0.10Ox) of lamellar precipitates in cross-section, suggesting Ba and Sr diffuse from the lamellae to BSC. A unique orientation relation (BSCF {111} // BSC {0001}) was uncovered by EBSD. TEM revealed high symmetry contact planes of lamellae and BSCF, suggesting nucleation energy governs decomposition. Fresh BSCF pellets were decomposed in N2 at 800℃. Fm-3m and P63/mmc phases were confirmed by XRD and lamellae were observed by SEM, followed by decomposition in 7±1 % N2/CO2 at 800℃. XRD revealed higher weight % of BSC and CoO. SEM revealed BSC preferring lamellae, hence hexagonal phases accelerated BSC formation. BSCF pellets were dip coated in SCFT propan-2-ol suspension (3:10), followed by sintering at 1165℃ for 10 hours. XRD revealed a Pm-3m phase (a=3.885 A) and SEM revealed a grain size of 65 ± 9 micro metre and open porosity of 1.6 ± 1 %. They were annealed in 7 ± 1 % CO2/N2 at 800℃. XRD revealed no secondary phases, suggesting enhanced stability. However, oxygen permeability was reduced (1.2 ml/cm2 to 0.8 ml/cm2) because the coating composition changed to Ba0.20Sr0.27Co0.40Fe0.10Ti0.04Ox; this was revealed by EDX.
42

Kvantitativní korelace texturních dat získaných metodou CIP a EBSD / Quantitative correlation of textural data obtained with CIP and EBSD method

Slunská, Petra January 2012 (has links)
Since 2011, the Institute of Petrology and Structural Geology, Charles University in Prague, worked with CIP - Computer Integrated Polarization microscopy as fast, inexpensive measurement of c-axis orientation of uniaxial minerals, mostly quartz in high definition. CIP method is developed from the early nineties in Switzerland (Heilbronner & Pauli 1993) and later in many other workplaces. The aim of this work was testing and calibration of optical and camera equipment to verify the accuracy and reliability of data obtained. Served as an independent measurement of EBSD (Electron Backscatter Diffraction) data obtained from the same part of the studied thinsections. The data obtained were analyzed by quantitative analysis of microstructures (PolyLX - MATLABTM toolbox; Lexa 2003). The samples used for testing the methodology mentioned were taken on the profile of Hvězdná and Zdobnice near Rokytnice in the Eagle Mountains by contact orlica-snieznik complex and its mantle. Field studies showed the existence of west dipping shear zone along the said contact and deformed orthogneiss show a macroscopic superposition of several deformation events. The resulting frequency histograms similarities and differences of angles c-axes and angles misorientace grains have a high consensus in the azimuthal criterion, axes...
43

Study on texture and mechanical properties of electrodeposited Ni and NiFe alloys

Yi, Lian-Hao 16 June 2011 (has links)
Nanoindentation has been widely used for measuring mechanical behavior of nanocrystalline (nc) metals that cannot be measured by tensile and compressive test. The hardness and elastic modulus are usually obtained by Oliver and Pharr method. However, this may not be true for materials showing viscoelastic characteristics. This study aims at clarifying the effect of testing parameters, especially loading rate and holding time, on the hardness and elastic modulus of a nanocrystalline Fe-51Ni coating obtained in nanoindentation tests as the material exhibits anelastic and creep characteristics. An analytical method based on the correspondence principle for linear viscoelasticity was developed. The holding displacement-time data obtained in indentation creep tests at a high loading rate of 20 mN/s were analyzed and material parameters related to the elastic, anelastic and creep characteristic were derived using a model containing one Maxwell unit and two Kelvin units. The anelastic deformation thus contains at least two relaxation processes having relaxation times of 0.37 s and 6.8 s, respectively and the creep deformation is described by a viscosity value of 4.2x104 GPa.s for the alloy in an as-deposited state. Moreover, electrodeposited (ED) Ni was analyzed by electron backscatter diffraction. Results indicated that the ED Ni exhibits a bimodal distribution of grain size. The grains having sizes larger than 2 £gm shows a strong fiber texture of <100>//ND, whereas the small grains (<2 £gm) are mainly randomly oriented.
44

Study on epitaxial growth of Ni on polycrystalline Cu by electrodeposition

Liu, Ying-chen 06 September 2011 (has links)
The present study aims at clarifying the effects of processing parameters and substrate orientation on the epitaxial growth of Ni on polycrystalline Cu by electrodeposition from a sulfamate solution. The deposits were analyzed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), auger electron spectroscopy (AES) and transmission electron microscopy (TEM). Two morphologies: rough and smooth, of the substrate surface were introduced by electropolishing. Auger electron spectroscopy showed that Ni was deposited on both areas without preference. However, the deposition rate for the rough area was slightly higher at a low current density of 0.01 A/dm2. At higher current densities, both areas possessed the same rate of deposition. In-plane TEM results demonstrated that Ni deposited on Cu epitaxially regardless the orientation of the Cu grains, electrolyte temperature and current density. EBSD analysis indicated that the Ni epilayer with an orientation of <001>//ND grew epitaxially to as thick as 12 £gm, whereas randomly oriented Ni nucleated on the epilayer having orientations of <011>//ND or <-111>//ND on prolonging deposition at current of 10 A/dm2. In other words, the epitaxial growth of Ni on Cu cannot be sustained to a thickness of hundreds of micrometers without a <001>//ND orientation.
45

Microtexture and Mechanical Properties of Electron Beam or Tungsten Inert Gas Arc Welded Mg Alloys

Wu, Hsin-Hui 13 August 2003 (has links)
none
46

Deformation characteristics of ultrafine-grained AZ31 Mg alloy

Hsiao, Chun-i 13 August 2009 (has links)
none
47

Lattice Strain and Texture of Plastically Deformed Zircaloy-2 at 77K

Judge, COLIN 07 December 2009 (has links)
Zircaloy-2 is used extensively in the nuclear industry as a structural material for the reactor core in both light and heavy water reactors. The intergranular strains and texture greatly affect the mechanical properties of the material while in operation. Understanding the plastic deformation of Zircaloy-2 will improve on current plastic deformation models, particularly for twinning mechanisms, which are more active at lower temperatures, and are not yet well understood. For this study, neutron diffraction was used to track the lattice spacing and peak intensity in warm-rolled and recrystallized Zircaloy-2 slab for various crystallographic orientations at 77 K. Tests were performed in all three principle directions under tension and compression. The texture was measured for the deformed samples to help interpret the dominant deformation systems and then Electron Back Scattering Diffraction was used to identify and image the active twinning modes. Prism <a> slip, basal <a> slip, {10-12} and {11-2 1} tensile twinning, and {11-2 2} compression twinning were found to be contributing deformation systems in Zircaloy-2 at 77K. In this study, the diffraction elastic constants for Zircaloy-2 at room temperature and 77K are reported for the first time in open literature. These values will be useful in future experimental work by allowing a conversion between lattice spacing and residual stress. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-09-24 13:41:25.371
48

Development of advanced ferritic steels for high efficiency power generation plant

Qin, Guixiang January 2009 (has links)
E911 creep samples exposed to temperatures of 600˚C, 625˚C and 650˚C at differing stress levels were supplied by CORUS. The hardness of the gauge length that experienced both creep strain and temperature was found to be lower than that of the head where thermal softening only can be assumed. The changes in the morphology and size of precipitates were observed qualitatively by optical microscopy and Scanning Electron Microscopy. A creep fracture mechanism map of E911 steel was constructed with two modes of creep (transgranular and intergranular ). A fitted ellipse shape was used to characterise the irregular block shape by Electron Backscattered Diffraction (EBSD). It showed that the width of the block inside a prior austenite grain increases more rapidly in the gauge length than in the head; subgrain growth was also observed by EBSD. Transmission Electron Microscopy studies indicate that at 600°C E911 steel can reach up to 75647 hours creep rupture life (108MPa), which is due to the relatively small size of M23C6, Laves and M2X phases. However, Z phase precipitation results in a drop in creep resistance owing to the dissolution of fine MX phase and the transformation of M2X phase. At 625°C and 650°C, the creep rupture life decreases owing to the coarsening of Laves, M23C6 and M2X phases. Four experimental steel casts were prepared with varying levels of Ni and Cr to investigate the effect of these elements on Z phase formation. After 10,000 hours exposure, there was little evidence of Z phase in the samples studied and therefore it is difficult to draw definitive conclusions about the role of Ni or Cr in promoting Z phase formation. It is possible that the casts studied here will allow better conclusions to be drawn after exposing the samples to longer durations.
49

Combined nanostructural and isotopic analysis of baddeleyite : new horizons in solar system chronology

White, Lee Francis January 2017 (has links)
Baddeleyite (monoclinic-ZrO2) is an exceptionally common accessory phase in many of the mafic and ultra-mafic rocks prevalent throughout the Solar System. This study presents the first ground-truthing efforts in the development of this robust mineral into a diagnostic indicator, discrete barometer, and precise U-Pb geochronometer of shock metamorphism by combining electron backscatter diffraction and atom probe tomography to generate unique chemical and structural datasets. Microstructural analysis of variably shocked baddeleyite grains around the Sudbury impact structure (Ontario, Canada) highlights a series of crystallographic structures that can be correlated with discrete variations in formative pressure-temperature conditions. Decompression at high temperatures generates a series of interlocking reversion twinned structures, while quenching forms a quasi-amorphous matrix. These features are comparable to those observed in extra-terrestrial samples, where they can be directly linked with the severity and extent of lead loss and age resetting. This finding facilitates the application of baddeleyite as a shock indicator, barometer (>5 GPa) and chronometer in a wide range of planetary materials. This structural variability is also observable on the nanometre scale. Analysis of the most highly shocked Sudbury baddeleyite using atom probe tomography reveals planar and curvi-planar fractures, trace element enriched subgrain boundaries, and solid-state diffusion clusters. These micrometre and nanometre scale features encourage localised diffusion of lead, with whole-microtip U-Pb analyses yielding complex partially reset ages. The application of atom probe tomography allows these features to be spatially resolved on the nanometre scale, yielding highly accurate ages for protolith crystallization and impact metamorphism within a single grain. These results have significant implications for the isotopic analysis of baddeleyite-bearing planetary materials, where the mechanisms of U-Pb age resetting have until now been poorly understood.
50

Aspectos Microestruturais e Cristalográficos da Ferrita Acicular Obtida Por Meio de Sequencias Termomecânicas Em Aço Api 5l X-80

Castro, Renato Soares de 08 1900 (has links)
Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-10T14:51:17Z No. of bitstreams: 2 TESE COMPLETA Renato Castro_ biblioteca.pdf: 5223231 bytes, checksum: 9faaba65fe169b6609c1ee3b1c65d60c (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-10T14:51:17Z (GMT). No. of bitstreams: 2 TESE COMPLETA Renato Castro_ biblioteca.pdf: 5223231 bytes, checksum: 9faaba65fe169b6609c1ee3b1c65d60c (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-08 / FACEPE / Aços de alta resistência e baixa liga (ARBL) têm sido melhorados por meio do desenvolvimento de composição química e, principalmente, pelo uso de processos de manufatura avançados. Neste trabalho, sequências termomecânicas foram aplicadas em um aço tipo API 5L X-80, a fim de se obter microestrutura com predominância de ferrita acicular. Após aquecimento até 950 ºC por 15 min., as amostras foram laminadas, em temperatura de não recristalização da austenita, alcançando redução de espessura de 10% a 35%. Em seguida foram resfriadas bruscamente em água ou mantidas em banho de chumbo para a decomposição isotérmica a diferentes temperaturas (400 - 600 ºC). Imagens obtidas por microscopia eletrônica revelaram que a microestrutura de ferrita acicular, caracterizada pela excelente combinação de resistência e tenacidade, foi obtida predominantemente em condições de resfriamento contínuo. Os tratamentos isotérmicos resultaram em uma microestrutura complexa, com presença de ferrita poligonal, ferrita granular e constituinte M-A, além da ferrita acicular. Por meio de análises de EBSD estudou-se o efeito do tratamento termomecânico nos aspectos microestruturais e cristalográficos do material, sendo possível relacionar a modificação do perfil de desorientação dos contornos com aspectos morfológicos da ferrita acicular. Esta microestrutura apresentou elevada frequência de grau de desorientação de baixo ângulo, elevado nível de discordâncias e alto grau de desorientação local. Verificou-se, também, que a formação de fronteiras CSL (coincident site lattice) pode ser estimulada por meio de tratamento termomecânico, especialmente as do tipo Ʃ3 cuja presença é favorável ao aumento da resistência no material. Foi possível relacionar a modificação do perfil de desorientação com o aumento da quantidade de fronteiras CSL e identificar que a deformação tem um papel relevante no desenvolvimento ou inibição dessas fronteiras, no entanto são necessários mais estudos para esclarecer os mecanismos de sua formação.

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