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This research is concerned with identifying and characterizing four solid-state precipitation reactions in the W-Ni-Fe system that can be induced by appropriate heat treatments. Previous work in this area is reviewed, and a general overview of the research on this system that may, directly or indirectly, further the understanding of microstructure/mechanical property relationships in the W-Ni-Fe heavy alloy is presented. The many metallographic and analytical techniques that have been employed in the course of this investigation are also briefly reviewed. The specific precipitation reactions studied in the 90W-5Ni-5Fe heavy alloy are listed and briefly described. Interfacial precipitation - interfacial precipitates at the W-andgamma; and andgamma;-andgamma; boundaries were found to be andeta;-carbides. This morphology is expected to severely embrittle the alloy. Matrix-phase precipitation - discontinuous precipitation of W was observed in the matrix region. W-W grain boundary precipitation - W-W grain boundary allotriomorphs (andgamma;-phase) were identified and characterized. W-phase precipitation hardening - fine scale precipitation in the W-phase was found to strengthen the alloy. Deformation prior to aging significantly increased the rate of precipitate nucleation. TEM contrast analysis showed the precipitates to be plate-like with a {100} habit plane, and the strain in the W lattice normal to the precipitates was found to be tensile in nature. Matrix-composition alloys were manufactured to simulate the andgamma;-phase in the 90W-5Ni-5Fe alloy. Metallographic observations of these alloys furthered the understanding of reactions 1) and 2) above. These results are discussed in terms of (a) current theories of solid-state precipitation and (b) the influence of the various morphologies on mechanical properties.

Thesis (Ph.D)--Murdoch University, 2004. / Thesis submitted to the Division of Science and Engineering. Includes bibliographical references (leaves 136-144).

Thesis (Ph. D.)--University of Pennsylvania, 1903. / Includes bibliographical references.

Thesis (Ph. D.)--University of Pennsylvania, 1903. / Includes bibliographical references.

Thesis (Ph. D.)--University of Pennsylvania, 1942. / Reproduced from type-written copy. Bibliography: p. 44.

Thesis (Ph.D.) -- McMaster University, 2001. / Includes bibliographical references. Also available via World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Orientador: Maria Helena Andrade Santana / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-17T20:18:08Z (GMT). No. of bitstreams: 1 Bicudo_RafaelaCostaSouza_M.pdf: 3349678 bytes, checksum: 109d86456a55f4f24183d31d45bc6b81 (MD5) Previous issue date: 2011 / Resumo: O ácido hialurônico (AH) é um mucopolissacarídeo natural, hidrofílico, composto de unidades alternadas de N-acetil-D-glicosamina e ácido D-glucurônico, unidas por ligações ?- 1,3 e ?-1,4. Ele possui diversas aplicações médicas, farmacêuticas e cosméticas, nas quais ele é usado na sua forma nativa ou reticulado, formando hidrogéis de alta viscosidade ou nanopartículas para encapsulação e/ou liberação modificada de bioativos. A produção de partículas de AH é geralmente feita por emulsificação água/óleo, envolvendo tensoativos e reticulação química. Todavia, as partículas produzidas possuem alta polidispersidade e necessitam da posterior remoção do óleo. Portanto, processos livres de óleo e de tensoativos são vantajosos, embora ainda pouco estudados. Neste trabalho, nanopartículas de AH foram produzidas por nanoprecipitação e reticulação química com dihidrazida adípica (ADH) e cloridrato de carbodiimida (EDCl), em processos descontínuo e contínuo, na ausência de óleo e tensoativos. O processo descontínuo foi conduzido em tanque agitado, em escoamento turbulento no seio da solução. Já o processo contínuo foi realizado em um sistema de microcanais de fluxo cruzado, no qual uma solução aquosa de AH, com ADH e EDCl, fluiu no canal principal e a solução orgânica nos dois canais laterais, simultaneamente. Nesse caso, a nanoprecipitação ocorreu em escoamento laminar no interior do microcanal principal, na interface formada entre o solvente orgânico e a água. Em ambos os casos foi estudada a influência dos solventes etanol, álcool isopropílico e acetona nos processos e nas propriedades finais das partículas. Nanopartículas estáveis de AH foram produzidas com os três solventes orgânicos utilizados e em ambos os processos. Todavia, no processo descontínuo, o tamanho das partículas dependeu da tensão superficial do sistema, enquanto no contínuo o tamanho foi dependente da afinidade água-solvente orgânico. Além disso, no processo descontínuo, foi demonstrado que a quantidade usada de solvente orgânico e a ordem e o momento de sua adição influenciam no tamanho final das nanopartículas, que a adição de ADH e EDCl no início do processo não modificou o tamanho das partículas e que o pH influencia na formação dos núcleos de precipitação e na velocidade da reação de reticulação. Já no processo contínuo, além de se analisar a influência do tipo de solvente orgânico, analisou-se a vazão da solução orgânica e a concentração de AH. Ambos os processos são simples, reprodutíveis e produzem, em uma única etapa, nanopartículas de AH livres de óleo e de tensoativos, ampliando suas aplicações médicas, farmacêuticas e cosméticas / Abstract: Hyaluronic acid (HA) is a natural, hydrophilic mucopolisaccharide composed of alternating units of D-glucuronic acid and N-acetylglucosamine joined by ?-1,3 and ?-1,4 linkages. It has several medical, pharmaceutical and cosmetics applications, in which it is used in its native form or reticulated, forming hydrogels of high viscosity or nanoparticles for encapsulation and controlled delivery of bioactives. The production of HA nanoparticles is usually made by emulsification water/oil, involving surfactants and crosslinking reaction. However, the particles produced have high polydispersity and require the subsequent oil removal. Therefore, processes free of oil and surfactants are advantageous, although still poorly studied. In this study, HA nanoparticles were produced by nanoprecipitation and chemical crosslinking with adipic dihydrazide (ADH) and chloride carbodiimide (EDCl), in discontinuous and continuous processes, in the absence of oil and surfactants. The discontinuous process was conducted in a stirred tank, in a turbulent flow within the solution. The continuous process was conducted in a cross-flow microchannel, in which a HA aqueous solution with ADH and EDCl flowed into the main channel and the organic solution flowed simultaneously in the two side channels. Nanoprecipitation occurred in laminar flow inside the microchannels, formed at the interface between the organic solvent and water. In both cases it was studied the influence of the solvents ethanol, isopropyl alcohol and acetone on the processes and on the final properties of the particles. Stable HA nanoparticles were produced with the three organic solvents used and in both processes. However, in the discontinuous process, the particle size depended on the surface tension of the system, while in the continuous process it was dependent on the affinity water-organic solvent. Besides, in the discontinuous process, it was demonstrated that the quantity of organic solvent used and the order and time of addition influenced on HA nanoparticles final size, that the addition of ADH and EDCl at the beginning of the process did not modify the final particles size, and that the pH influenced on coil globules formation and on the velocity of the crosslinking reaction. In the continuous process, besides analyzing the influence of the organic solvent used, it was analyzed the influence of the organic solvent flow and of HA concentration. Both processes are simple, reproducible and produce, in a single step, HA nanoparticles free of oil and surfactants, extending their medical, pharmaceutical and cosmetic applications / Mestrado / Desenvolvimento de Processos Biotecnologicos / Mestre em Engenharia Química

The growth of strontium sulfate precipitate by diffusion in various gels was studied by using optical transmission and confocal microscopies, scanning and transmission electron microscopies, and energy dispersive X ray fluorescence. Pure silica gel, pure agarose gel and the silica/agarose mixed gel at pH 7 - 10 were used throughout the present study. Precipitate morphology is sensitive to pH and to the nature of the growth medium. The morphology was observed as a function of time. The lack of change is presumably because of rapid depletion of the limiting reagent after the very beginning of precipitation. The problem of separating strontium sulfate precipitate from the gel medium is discussed.