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Synthesis and characterization of cobalt ferrite spinel nanoparticles doped with erbiumCripps, Chala Ann 05 1900 (has links)
No description available.
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Composites at micro- and nano-scale and a new approach to the problem of a concentrated force on a half-planeJordan, Jeff 05 1900 (has links)
No description available.
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Mechanochemically synthesized nanomaterials for intermediate temperature solid oxide fuel cell membranesHos, James Pieter January 2005 (has links)
[Truncated abstract] In this dissertation an investigation into the utility of mechanochemically synthesized nanopowders for intermediate temperature solid oxide fuel cell components is reported. The results are presented in the following parts: the synthesis and characterisation of precursors for ceramic and cermet components for the fuel cell; the physical and electrical characterisation of the electrolyte and electrodes; and the fabrication, operation and analysis of the resulting fuel cells. Samarium-doped (20 mol%) ceria (SDC) nanopowder was fabricated by the solid-state mechanochemical reaction between SmCl3 with NaOH and Ce(OH)4 in 85 vol% dilution with NaCl. A milling time of 4 hours and heat treatment for 2 hours at 700°C yielded a material with equivalent particle and crystallite sizes of 17 nm. The existence of a complete solid solution was affirmed by electron energy loss spectroscopy and x-ray diffraction analysis. Doped-ceria compacts were sintered for 4 hours at 1350°C forming ceramics of 88% theoretical density. The ionic conductivity in flowing air was 0.009 S/cm, superior to commercially supplied nanoscale SDC. Anode precursor composite NiO-SDC nanopowder was synthesized by milling Ni(OH)2 with the previously defined SDC formulation ... Anode-supported fuel cells were fabricated on a substrate of at least 500 'm 55wt%NiO-SDC with 17vol% graphite pore formers. Suspensions of SDC were deposited by aerosol on the sintered bilayer at a thickness around 5 'm. A cathode of 10% SDC (SmSr)0.5CoO3 was deposited onto the sintered electrolyte and after firing had a thickness of around 25 'm. Operation of fuel cells in single-chamber mixtures of CH4 and air diluted in argon were successful and gave power outputs of 483 'W/cm2. Operation in undiluted 25 vol% CH4:air gave a power output of 5.5 mW/cm2. It was shown that a large polarisation resistance of 4.1 Ω.cm2 existed and this was assigned to losses in the anode, namely mass transport limitation associated with the catalytic combustion of methane and insufficient porosity. The large surface area of Ni appeared to allow more methane to combust and hence prevented its electrochemical reaction from occurring, thus limiting the performance of the cell. The synthesis procedures, ceramic processing and fabrication techniques and testing methods are discussed and contribute significant understanding to the fields of ceramic science and fuel cell technology.
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Water-based suspension of polymer nanoclay composite prepared via miniemulsion polymerizationTong, Zhaohui 19 December 2007 (has links)
The polymer-clay nanocomposites, when applied as coating materials, are expected to improve the barrier properties without sacrificing mechanical and thermal properties, and thus solve one of the most challenging problems existing in current food and beverage packaging using paper barrier coating. Furthermore, a stable polymer composite suspension in an aqueous form has many other advantages such as better environmental concern, easier manipulation and better energy saving. However, the research in this area is quite limited in the literature. In this research, a stable water-based suspension of polymer-encapsulated nanoclay composite has been successfully synthesized. The polymer nanocomposites, which encapsulate the exfoliated and well-dispersed nanoclay inside the polymer matrix, can dramatically improve almost all the aspects of mechanical properties and thermal stability in comparison with that of pure polystyrene (PS) and polystyrene butyl acrylate (PSBA) films. The particle size of nanoclay and the surface modification method are two important factors for emulsion stability, the encapsulation and intercalation (or exfoliated) degree of nanoclay. Furthermore, the impact of nanoclay on miniemulsion kinetics has been extensively investigated and the results show the hindrance of nanoclay on styrene miniemulsion polymerization kinetics.
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The synthesis and characterisation of polyhedral oligosilsesquioxane based dendrimers and nanomaterials /Neumann, Daniel. Unknown Date (has links)
Thesis (PhDApSc)--University of South Australia, 2002.
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Low Field Microwave Absorption in Nano-Magnetic Participle - incorporated YBa2Cu3O7-z Superconducting MaterialsNemangwele, Fhulufhelo 21 September 2018 (has links)
PhD (Physics) / Department of Physics / Understanding how and why superconductivity (SC) occurs in a given material has been
very challenging for physicists for more than a hundred years, notwithstanding the major
milestones, such as the London theory, the Landau-Ginzburg theory, and the BCS theory.
The extreme challenge to predict the occurrence of SC is symbolized by the long string
of unanticipated but breathtaking advances, i.e., the unexpected discoveries of cuprates
and Fe-pnictides being the dramatic modern examples. Because of their incompatibility,
the nucleation of SC near a ferromagnet is di cult and has never been realized except for
the case that another superconductor provides proximity-boosted Cooper pairs.
This perceived necessity to start with another superconductor is engrained in the exten-
sive study of the proximity e ect in superconductor/ferromagnet (S/F) powder sample,
where all the structures involve a superconductor with either stable or metastable struc-
ture.
Compounding the di culty, it is also generally recognized that SC with substantial
Tc is favourable in low dimensionality because of strong quantum
uctuation. In this
thesis, we report a serendipitous nding of SC that emerges under the most implausible
circumstances in low eld microwave absorption measurement. This new revelation may
lead to unconventional avenues to explore novel SC for applications in superconducting
spintronics.
By means of a varienty of techniques, including EPR, SEM, FTIR, PPMS/VSM and
XRD, nanonickel incorporated YBCO in di erent weighting factors have been studied.
With its complex chemical structure and magnetic properties, Ni-YBCO is far from well
understood and the magentic behavior of the system under di erent conditions is investi-
gated. From the dilute mixture of nanonickel particles, it is found that groups of normal
Josephson junctions (JJs) and JJs due to YBCO-nickel-YBCO interparticle weaklinks
form as nickel is ferromagnetic. We experimentally show, for the rst time multiple phase
reversals in the non-resonant microwave absorption (NRMA) spectra from Ni-YBCO pos-
sibly, due to the formation of JJs. We also show that these multiple phase reversals then
vii
depend on microwave power and temperature. We argue that microwave power induced
coherence among some groups of JJs and breaking of some of the weaker JJs can then
lead to the disappearance of multiple phase reversals at higher microwave power levels.
Further, we also report a role of pair breaking e ects that shall give a linear eld de-
pendence of the derivative microwave absorption signal, which is essentially the NRMA
signal. This pair-breaking e ect dominates at temperatures closer to Tc as expected
thermodynamically.
The presence of two peaks in the system, results in high permeability ferromagnet
which acts as a magnetic short circuit for magnetic
ux density and creates low reluctance
path. A transition from normal to anomalous does not occur in this work, because of the
possibility of junction in the sample.
As predictable at the region around the origin where the weaklinks are supposed to
be very strong for a very low doping or low nanonickel addition ( 0.5 % wt), not much
e ect was observed. However, when the nanonickel addition is increased to 2 % and 3%
we see a signi cant change in the magnetization and the associated hysteresis, indicating
ux pinning. / NRF
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Strengthening Mechanisms in Nanostructured MaterialsYailuth Alexandra Loaiza Lopera (13176354) 29 July 2022 (has links)
<p>Understanding the behavior of materials with nanoscale features is important because of both the size of engineering devices and the internal microstructure of more bulk materials. Many electronic components have been miniaturized in recent years to attend the high demand of technology development. Similarly, new stronger bulk metallic materials use nm-scale grain sizes or precipitates to increase their strength over more conventionally processed alloys. Nanoscale testing also offers a route for mechanical behavior understanding at the microscale. Nanoindentation has been used to find structure-properties relationships of nanostructured materials due to its high load-depth resolution and versatility of the test. Nanoindentation can be used to find hardness and modulus of the materials, important characteristics to evaluate mechanical performance. An introduction to strengthening mechanism and generalities of nanoindentation is shown in Chapter 1.</p>
<p>This thesis explores how traditional strengthening mechanisms for bulk materials, can be applied to nanomaterials and how the microstructure could be tailored to achieve the desired outcomes on the specific materials studied. The first one is the study of mechanical properties of Nanometallic Foams (NMF) and its relationship with the nanostructure. NMFs of pure copper, CuNi and CuZn alloys were fabricated and tested to find the predominant structural and chemical parameters of the mechanical properties. Research on how to control and tailor the structural parameters of NMF with viscosity of the precursors is shown in Chapter 2. The relative density was the most predominant parameter among the structural parameters studied. However, when relative density parameter is isolated, NMF are more susceptible to strengthen by second phase precipitation instead of solid solution. The solid solution strengthening mechanism was validated with MD simulation and agrees with the experimental findings that showed the addition of Ni atoms to Cu have a moderate effect on the mechanical properties. Chapter 3 presents these findings The second example presented shows the strengthening effect of precipitates in nanometallic multilayer. The precipitation was achieved by aging treatment. High temperature nanomechanical testing is also presented in Chapter 4. The third and final example, presented in chapter 5, shows how the second phase precipitation and dispersion strengthening of lead-free solder SAC 305 compares between samples aged for nine years at body temperature and an accelerated aging treatments.</p>
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Nanopartículas metálicas anisotrópicas : mecanismos de formação e aplicações ópticas / Anisotropic metal nanoparticles : formation mechanisms and optical applicationsRocha, Tulio Costa Rizuti da 03 December 2008 (has links)
Orientadores: Daniela Zanchet, Jose Antonio Brum / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-10T04:28:03Z (GMT). No. of bitstreams: 1
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Previous issue date: 2008 / Resumo: Nanopartículas de metais nobres têm atraído uma renovada atenção nos últimos anos devido às novas aplicações científicas e tecnológicas explorando suas propriedades ópticas únicas. No regime nanométrico, é bem conhecido que a resposta óptica de metais, associada aos plásmons de superfície, depende fortemente do tamanho e também da forma. De fato, grande parte das aplicações ópticas de nanopartículas de ouro e prata baseia-se na exploração dos efeitos de forma. Porém, apesar dos esforços realizados, os processos que levam à formação de morfologias anisotrópicas ainda não são bem compreendidos e a formulação de um mecanismo geral ainda é um desafio. Nesse trabalho, foram abordados os mecanismos de formação e crescimento de nanoprismas triangulares de prata produzidos por métodos de síntese coloidal. Uma combinação de diferentes técnicas experimentais foi utilizada para estudar diversos aspectos da síntese fotoquímica, dentre eles, a evolução morfológica, a cinética da reação e a estrutura cristalina das nanopartículas. As sólidas evidências experimentais obtidas associadas a outras observações da literatura foram utilizadas na formulação de um modelo fenomenológico para explicar a formação e crescimento dos nanoprismas de prata em métodos fotoquímicos. Esse modelo baseia-se na influência dos defeitos cristalográficos, que induzem a formação dos nanoprismas nos momentos iniciais da síntese, e na excitação de plásmons de superfície, que ocorre em estágios avançados, sendo responsável pela definição do tamanho final dos nanoprismas. Adicionalmente, cálculos teóricos indicaram que aspectos energéticos podem ter um papel ativo nesse sistema, favorecendo o crescimento dos nanoprismas em relação às nanopartículas esféricas durante os estágios iniciais da síntese. Finalmente, os nanoprismas triangulares de prata produzidos foram aplicados ao estudo de efeitos de intensificação do espalhamento Raman de moléculas. Medidas espectroscópicas de moléculas depositadas na superfície de nanoprismas com diferentes tamanhos foram realizadas e a comparação quantitativa dos resultados indicou a presença de um tamanho ótimo, que é determinado por processos de perda de energia dos plásmons de superfície / Abstract: Noble metal nanoparticles have attracted a recent renewed interest due to the new scientific and technological applications exploiting their unique optical properties. At nanometric scale, it is well known that the optical response of metals, related to the excitation of surface plasmons, strongly depends not only on the size of the particles but also on their shape. Several methodologies to produce silver and gold nanoparticles with different shapes are available in the literature. However, notwithstanding the efforts that have been made, the process that lead to the formation of anisotropic morphologies has not been fully understood yet and a general mechanism is still a challenge. In this work, we address the formation and growth mechanisms of silver triangular nanoprisms produced by photochemical methods. A set of characterization tools was used to study different aspects of the photochemical synthesis, namely, the morphological evolution, the reaction kinetics and the crystalline structure of the nanoprisms. The solid experimental evidences obtained here were used to build a phenomenological model that explains the formation and growth of silver triangular nanoplates in photochemical methods. This model was based on the influence of crystallographic defects, which induce the formation of the nanoprismas in the initial stages of the synthesis, and on the excitation of surface plasmons, which occurs in advanced stages and it is responsible for the definition of the final size of the nanoprismas. Additionally, theoretical calculations indicate that energetics might play an important role in this system, favoring the growth of nanoprismas relative to spheres. Finally, the silver triangular nanoprisms were used to study enhancement effects in the Raman scattering of molecules. We performed spectroscopic measurements for nanoplates with different sizes and the quantitative comparison of the curves indicated the existence of an optimum size that is dictated by surface plasmon energy losses / Doutorado / Física da Matéria Condensada / Doutor em Ciências
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Crescimento e caraterização de estruturas de baixa dimensionalidade para aplicações no espectro vísivel / Growth and characterization of low dimensional structures for applications in the visible spectrumChiaramonte, Thalita 26 April 2007 (has links)
Orientadores: Lisandro Pavie Cardoso, Marco Sacilotti / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T18:38:56Z (GMT). No. of bitstreams: 1
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Previous issue date: 2007 / Resumo: Os nitretos (Ga, Al, In)N assim como os compostos GaInP, GaCuO2, representam um sistema de materiais muito importante para as aplicações em opto-eletrônica e dispositivos tais como os diodos emissores de luz (LEDs), lasers e nanosensores. Entretanto, o requisito essencial para as aplicações industriais desses materiais é a redução em seus tamanhos. Neste trabalho foram crescidos materiais metálicos formados por nitretos de gálio e também de semicondutores do tipo GaInP, GaCuO2 na forma de estruturas 3D, pela técnica de deposição química de organometálicos em fase vapor (MOCVD). Foi utilizado como precursor organometálico (OM) o trimetil gálio Ga(CH3)3e o nitrogênio N2 como gás portador. A temperatura e a pressão foram controladas durante o crescimento variando entre 500 e 750 o C e 100 a 760 Torr, respectivamente.
Duas classes de estruturas 3D foram obtidas a partir da decomposição total ou parcial do gás pre-cursor, devido a interação entre o OM e o substrato que gera diferentes morfologias: i) as ligas metálicas (Ga, Al, In) formando estruturas semelhantes a balões, cetros (hastes com terminações esféricas) e neurônios, todos apresentando uma fina membrana de carbono amorfo que reveste a estrutura. Após o crescimento, estas estruturas foram submetidas ao processo de nitretação sob atmosfera de NH3 para transformá-las em micro/nanocristais de GaN; ii) os fios semicondutores micro/nanométricos com uma esfera metálica em sua terminação (bambus e cetros) .
Na formação de ambas as estruturas, os precursores OM são como moléculas catalisadoras do crescimento. Este crescimento é considerado como um método alternativo e original para se obter estruturas 3D. Uma possível associação com o modelo apresentado pelo mecanismo de crescimento Vapor-Líquido-Sólido (VLS), que utiliza uma partícula metálica para promover os nanotubos de carbono e os nanofios semicondutores, ainda está em discussão. Informações estruturais e ópticas dessas novas estruturas crescidas sobre substratos de Cu (grade de difração), Si (001), InP (policristalino) e Al/SiO2/Si (fotolitografia) foram obtidas através da caracterização por difração de raios-X, microscopia eletrônica de varredura e de transmissão em alta resolução, espectroscopia por energia disper-siva, catodoluminescência e a espectroscopia de excitação por dois fótons. Nas amostras nitretadas, micro/nano cristais de GaN obtidos da liga de Ga aparecem impregnados no carbono turbostrático (folhas de carbono sem orientação obtidas do amorfo) que revestem as estruturas, e emitem na região do espectro l £ 365 nm, devido às suas dimensões quânticas. As hastes das estruturas do tipo bambus apresentam nódulos formados por discos monocristalinos de GaInP rotacionados de 60 o um em relação ao outro. Óxidos CuGaO2 e CuGa2O4compondo nanofios, denominados cetros, também foram obtidos / Abstract: Nitride (Ga, Al, In)N as well as GaInP, GaCu O2 compounds represent a very important class of materials to be used in the opto-electronic and devices applications such as light emission diodes (LEDs) lasers and nanosensors. However, the essential requirement to the industrial applications of these materials is the reduction in theirs sizes. In this work 3D structures based on gallium nitride and also GaInP, GaCuO2 semiconductors were grown by metalorganic chemical vapor deposition (MOCVD) technique. Trimethyl-gallium Ga(CH3) was used as the metal-organic (MO) precursor and nitrogen N2as carrier gas. During the growth to the temperature and pressure intervals of 500 - 700 oC and 100 - 760 Torr, respectively.
Two 3D material classes were obtained from the total or partial precursor gas decomposition, since the interaction between the MO compound and the substrate gives rise to different morphologies: i) (Ga,In,Al) metallic alloys form ballons, scepters (wires with spherical ends) and neurons like structures, all involved by a thin carbon amorphous membrane. After growth, these structures were turned into GaN micro/nanocrystals by nitridation process under NH3 atmosphere; ii) micro/nanometer semiconductor wires with a metallic sphere at its end (bamboos and scepters). In order to form both structures, the MO precursors are taken as a catalyst molecule of the growth process. This is an alternative and original method to obtain 3D structures and a possible association to the model used in the vapour-liquid-solid (VLS) growth mechanism, in which a metallic particle promotes the carbon nanotubes and semiconductors nanowires is still under discussion. Structural and optical informations on these new structures grown on Cu (diffraction grid), Si(001), InP (polycrystalline) and Si/Al (photolithography) substrates were obtained through the characterization by X-ray diffraction, scanning electron microscope, high resolution transmission electron microscopy, en-ergy dispersive x-rays, cathodoluminescence and two photon excitation. In the nitrided samples, GaN micro/nanocrystals obtained from Ga alloy appear embedded in the turbostratic carbon (C sheets at random obtained from the amorphous) which involves the structures and, they emit in the l £ 365 nm region specter, due to their quantum dimensions. The bamboo rods present nodes consisting of GaInP single crystal discs turned by 60o one with respect to the other. The CuGaO2 and CuGa2O4 oxides compounding nanowires, called scepters, also were obtained. / Doutorado / Física / Doutor em Ciências
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