Thesis (M.F.A.)--Rochester Institute of Technology, 1981. / Typescript. Includes bibliographical references (leaf 28).

Thesis (M.Arch.)--University of Hong Kong, 1994. / Includes special report study entitled : Technology of glass and glass constructions. Includes bibliographical references. Also available in print.

Thesis (M. Sc.)(Geology)--University of Pretoria, 2006. / Includes bibliographical references. Available on the Internet via the World Wide Web.

No description available.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 167-175).

No description available.

published_or_final_version / Architecture / Master / Master of Architecture

A viability study was undertaken on a farm Zandrivierspoort 210 JP, in the Pilanesberg Alkaline Complex to investigate the red syenite deposit. The red syenite deposit of interest is located in the south-western quadrant of the Pilanesberg. It is a potential source of nepheline, which is used as a flux in glass and ceramics industry. The study was aimed at establishing the demand for the material in South Africa and the market logistics related to its exploitation. Glass and ceramics manufacturers have different specifications as far as the quality and the product form is concerned. A market study conducted indicated that glass manufacturers require already beneficiated material with a low Fe content, depending on the kind of glass being manufactured. Ceramics manufactures also want material with low Fe content, but the material can be unbeneficiated as most of these factories already have facilities to remove Fe and other gangue. The common requirement is that material must be crushed and milled to a specific size. Red Syenite complies with the specifications of the ceramics manufacturer and did not comply directly with the specification of the glass manufacturer. The main reason for not non-compliance with glass specifications can be attributed to the fact that the material supplied was unbeneficiated. A major concern from the industry is the continuity of production from the deposit and an assurance of constant quality. It was also established that the availability of substitutes such as feldspar at a lower cost than nepheline results in an unwillingness of potential users to source nepheline despite its advantages. It is recommended that extensive geological studies be undertaken to confirm the resources and reserves of the entire nepheline-bearing deposits in the Pilanesberg. The mining of the deposit will be undertaken by employing a quarrying method, which will be followed by opencast to a depth of 50m. The Run-Of-Mine (ROM) will be crushed and milled to sizes specified by clients and the beneficiation process will follow. A financial investigation based on the known facts about the deposit established that capital, production rate, and selling price have the highest influence on the viability of the project. Transport and operating costs in this case showed a less significant influence on the viability of the project. / Dissertation (MSc (ESPM))--University of Pretoria, 2007. / Geology / unrestricted

We propose new theoretical models, which generalize the classical Avrami-Nakamura models. These models are suitable to describe the kinetics of nucleation and growth in transient regime, and/or with overlapping of nucleation and growth. Simulations and predictions were performed for lithium disilicate based on data reported in the literature. One re-examined the limitations of the models currently used to interpret DTA or DSC results, and to extract the relevant kinetic parameters. Glasses and glass-ceramics with molar formulation 0.45SiO2? (0.45-x)MgO?xK2O?0.1(3CaO.P2O5) (0?x?0.090) were prepared, crystallized and studied as potential materials for biomedical applications. Substitution of K+ for Mg2+ were used to prevent devritification on cooling, to adjust the kinetics of crystallization and to modify the in vitro behaviour of resulting biomaterials. The crystallization of the glass frits was studied by DTA, XRD and SEM. Exothermic peaks were detected corresponding to bulk crystallization of whitlockite-type phosphate, Ca9MgK(PO4)7, at approximately 900ºC, and surface crystallization of a predominant forsterite phase (Mg2SiO4) at higher temperatures. XRD also revealed the presence of diopside (CaMgSi2O6 in some samples. The predominant microstructure of the phosphate phase is of the plate-type, seemingly crystallizing by a 2-dimensional growth mechanism. Impedance spectroscopy revealed significant changes in electrical behaviour, associated to crystallization of the phosphate phase. This showed that electrical measurements can be used to study the kinetics of crystallization for cases when DTA or DSC experiments reveal limitations, and to extract estimates of relevant parameters from the dependence of crystallization peak temperature, and its width at half height. In vitro studies of glasses and glass-ceramics in acelular SBF media showed bioactivity and the development of apatite layers The morphology, composition and adhesion of the apatite layer could be changed by substitution of Mg2+ by K+. Apatite layers were deposited on the surface of glass-ceramics of the nominal compositions with x=0 and 0.09, in contact with SBF at 37ºC. The adhesion of the apatite layer was quantified by the scratch test technique, having been related with SBF?s immersion time, with composition and structure of the glass phase, and with the morphology of the crystalline phase of the glass-ceramics. The structure of three glasses (x=0, 0.045 and 0.090) were investigated by MAS-NMR ( 29Si and 31P), showing that the fraction of Q3 structural units increases with the contents of Mg, and that the structure of these glasses includes orthophosphate groups (PO43-) preferentially connected to Ca2+ ions. Mg2+ ions show preference towards the silicate network. Substitution of Mg2+ by K+ allowed one to change the bioactivity. FTIR data revealed octacalcium phosphate precipitation (Ca8H2(PO4)6.5H2O) in the glass without K, while the morphology of the layer acquires the shape of partially superimposed hemispheres, spread over the surface. The glasses with K present a layer of acicular hidroxyapatite, whose crystallinity and needles thickness tend to increase along with K content. / São propostos novos modelos teóricos, que generalizam o modelo clássico de Avrami-Nakamura, apropriados para a cinética de nucleação e de crescimento em regime transiente, e/ou com sobreposição entre o estágio de nucleação e o de crescimento. Foram efectuadas simulações com base em resultados da literatura, reportados para o dissilicato de lítio. Foram examinadas as limitações dos métodos correntemente usados para obter estimativas de parâmetros cinéticos, com base em resultados de ATD. Desenvolveram-se e investigaram-se vidros e materiais vitrocerâmicos susceptíveis de aplicação biomédica com a formulação molar 0.45SiO2?(0.45-x)MgO?xK2O?0.1(3CaO.P2O5) (0?x?0.090), preparados mediante a substituição de Mg2+ por K+. A cristalização das fritas de vidro foi estudada por ATD, DRX e SEM. Foram detectados picos exotérmicos correspondentes à cristalização de fosfato (cristalização em volume) do tipo whitlockite Ca9MgK(PO4)7 a aproximadamente 900ºC, e de forsterite (Mg2SiO4) acompanhada de alguma diopside (CaMgSi2O6; cristalização superficial) a temperaturas superiores. A microestrutura predominante da fase fosfato é do tipo placa, aparentando cristalizar por um mecanismo de crescimento bidimensional. Foi usada espectroscopia de impedâncias para monitorizar a cristalização em condições em que os ensaios de ATD ou de DSC revelam limitações, recorrendo a alterações significativas de propriedades eléctricas associadas à cristalização da fase de fosfato. Os vidros e vidros cerâmicos desenvolvidos revelaram bioactividade em meio acelular in vitro, desenvolvendo camadas apatíticas em SBF. A morfologia, composição e aderência da camada de apatite pôde ser modulada com base na substituição parcial de Mg2+ por K+. Foram depositadas camadas de apatite sobre vidros ceramizados (x=0 e 0.09), em SBF a 37ºC. A adesão da camada de apatite foi quantificada pela técnica de indentação deslizante tendo sido relacionada com o tempo de imersão em SBF, com a composição e estrutura da fase vítrea, e com a morfologia da fase cristalina dos vidros cerâmicos. Foi investigada a estrutura de três vidros (x=0, 0.045 e 0.090) por MAS-RMN (29Si e 31P), verificando-se que nos vidros mais ricos em Mg, a participação da unidade estrutural Q3 é mais significativa, e que a estrutura dos vidros inclui grupos ortofosfato (PO43-) mais próximos de iões Ca2+ do que dos iões Mg2+, sendo estes incorporados preferencialmente na rede de silicato. A substituição parcial de Mg2+ por K+ permitiu ajustar a cristalização dos materiais vitrocerâmicos e modular a bioactividade pretendida. Resultados de FTIR revelaram precipitação de fosfato octacálcico (Ca8H2(PO4)6.5H2O) no vidro sem K, enquanto que a morfologia da camada adquire a forma de hemisférios parcialmente sobrepostos, espalhados sobre a superfície. Os vidros com K apresentam uma camada de hidroxiapatite acicular, cuja cristalinidade e espessura de agulhas tende a aumentar com o teor de K.

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