Thesis (MSc)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (Ph.D.) - University of Queensland, 2003. / Includes bibliography.

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

Thesis (M.S.)--State University of New York at Binghamton, Department of Biological Sciences, 2008. / Includes bibliographical references (leaves 45-47)

Thesis submitted in fulfilment of the requirements for the degree Doctor of Technology: Chemical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / This study investigated water-in-oil (W/O) super-concentrated emulsions used as pumpable explosives. The aqueous phase of the emulsions is a supersaturated nitrate salt solution (at room temperature), with a volume fraction of approximately 0.9. Instability of such emulsions arises either from crystallization of the dispersed phase in the system during ageing or under high shear conditions. Here, we report an alternative approach to stabilize this highly concentrated W/O emulsion by adding colloidal particles in combination with short amphiphilic molecules. Thus, the primary goal of this research concerned a phenomenological study of the dependence of surfactant-to-particle ratio as well as the particle hydrophobicity index on stability under high shear in the emulsification process, rheological properties and stability against initiation of crystallization of an internal phase both with ageing and under high shear with a view to optimize the time to the start of crystallization of the emulsion both with ageing and under high shear; to elucidate the mechanism of initiation of crystallization of an internal phase (homogeneous or heterogeneous) and shed light in the stabilization mechanism of the emulsion; to determine how the emulsion formulation content affect pumping characteristics as measured by characteristic rheological parameters. A series of five fumed silica nanoparticles, each with a different hydrophobicity index (HI) in the range of 0.60 – 3, were used in the form of single types of particles as well as binary mixtures. These particles were combined with a low molecular weight conventional surfactant, Sorbitan MonoOleate (SMO), into the oil phase prior to emulsification. It has been found that regardless of the particle hydrophobicity, fumed nanosilica alone cannot form highly concentrated W/O emulsion up to 90 vol%. Moreover, Pickering emulsions are unstable under shear conditions and thus it is difficult to make highly concentrated W/O pumpable emulsion explosives using only fumed nanosilica. The correlation between the refinement time and SMO-to-particle ratio showed a deflection point/transitional point in the stabilization mechanism. Below the transitional point the silica content dominates over SMO. Conversely, above the transitional point the particles have little effect and the SMO dominates. A thermodynamic consideration revealed that in this region only SMO is likely to adsorb at the W/O interface and controls the emulsifying process. As with refinement time, the correlation between the shear modulus and SMO/particle ratio shows a deflection /transitional point which, as before, mark the transition point between regions of particle or SMO domination. Interestingly, it was found that for each HI, the initiation of crystallization is the most delayed, both on shelf life and under high shear, when the emulsion is prepared with an SMO-to-particle ratio equaling exactly the value at this transitional point. Moreover, the research demonstrated that a drastic change in mechanism of initiation of crystallization of the dispersed droplets occurs at the transitional point. Homogeneous nucleation within the droplets is the dominating mechanism of initiation of crystallization of an internal phase for SMO/particle ratios below and at the transitional point. In this case, the relationship between the zero modulus of particle dispersions in oil and the SMO-to-particle ratio demonstrated that the most stable emulsions are formed from the most unstable dispersions, indicating that less repulsion between particles is required to delay the onset of crystallization. This was further corroborated by the linear correlation between the time to the onset of crystallization and the shear modulus of the emulsion. On the contrary, it was found that for SMO/particle ratios above the critical point, heterogeneous nucleation catalyzed at the surface of droplets is the dominating mechanism of initiation of crystallization of nitrate salts in the super-cooled droplets This was found to be consistent with SMO-only system. That is the change in the mechanism of initiation of crystallization originates from a drastic change in the emulsion structure due to excess surfactant was highlighted by the drastic change in the linear correlation between the time to the start of crystallization and the strength of the emulsion structure as measured by the shear modulus. The optimum time to the start of crystallization (onset of crystallization associated with optimum SMO-to-particle ratio) is sensitive to the particle HI; increasing with increase of particle HI. A general correlation between the particle HI and optimum time to the onset of crystallization has been identified and formulated for the whole family of single types and mixtures of fumed nanosilica used in this study.

Orientador: Theo Guenter Kieckbusch / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-15T23:02:38Z (GMT). No. of bitstreams: 1 Queiroz_MariseBonifacio_D.pdf: 2421839 bytes, checksum: 864f367f1ae8ca6c17e48aa7cc7fa709 (MD5) Previous issue date: 2010 / Resumo: Sob o ponto de vista termodinamico, fondant e uma solucao supersaturada de sacarose e a qualidade da textura (cristalizacao) e controlada pela adicao de xarope de glicose e pelo 'batimento' da mistura. As formulacoes conhecidas de fondant usam xarope de milho e essa tese avaliou o uso de xarope de mandioca produzido com materia-prima e tecnologia nacionais. Inicialmente realizou-se a determinacao experimental de curvas de equilibrio solido-liquido para misturas de sacarose com os dois xaropes (milho e mandioca) em temperaturas de 25 e 30º C. De acordo com os resultados encontrados no estudo de solubilidade dos sistemas a 30º C, o xarope de milho normalmente utilizado na industria de confeitos com o objetivo de retardar a cristalizacao da sacarose, pode ser substituido pelo xarope de mandioca no mesmo nivel de adicao, O estudo da cristalizacao foi feito em dois sistemas distintos. Inicialmente a producao de fondant foi em batelada, em escala de laboratorio e serviu para estabelecer parametros de processo, formulacoes indicativas e condicoes previas para a otimizacao do batimento em sistema continuo. Um batedor continuo em escala planta-piloto foi entao projetado, construido em aco inoxidavel e posto a funcionar. Para a otimizacao do batimento em sistema continuo utilizou-se o delineamento experimental com um planejamento fatorial completo 23 com pontos axiais e centrais. As variaveis estudadas foram a porcentagem de xarope de mandioca na formulacao, a velocidade de rotacao da rosca e a temperatura de cristalizacao/batimento. Como resposta mediu-se a atividade de agua e a textura (resistencia da massa cristalizada a compressao) do fondant. A caracterizacao da microestrutura do fondant foi baseada na determinacao da Distribuicao do Tamanho de Cristais (DTC) pela analise de imagem gerada por microscopia otica e por espalhamento de luz. O estudo indica que Fondant produzido com xarope de mandioca, com uma atividade de agua apropriada (garantia de estabilidade microbiologica) e textura adequada pode ser obtido usando teores de xarope de glicose superiores a 20% (minima atividade de agua), temperatura inicial de batimento de 60 ºC e uma velocidade de rotacao da rosca de 110 rpm / Abstract: From the thermodynamic point of view, fondant is a supersaturated solution of sucrose and the quality of the texture (crystallization) is controlled through addition of glucose syrup and by the 'beating' intensity of the mixture. Fondant is usually manufactured with corn syrup. In this research its replacement by cassava syrup, recently introduced in the Brazilian market, and produced with national technology was evaluated. Initially the solid-liquid equilibrium condition for the mixtures of sucrose and both syrups (corn and cassava), at 25 and 30 ºC was experimentally determined. The similar saturation conditions at 30 ºC, indicated that corn syrup normally used in the candy industry with the objective to delay the crystallization of sucrose could be substituted by the cassava syrup at the same addition level. The investigation considered two systems for the production of fondant. Initially, using a lab-scale batch system for the beating, the process parameters, indicative formulations and previous conditions for the optimization of a continuous beating conditions were established. A continuous pilot-plant scale beating system was then design, built in stainless steel and the limiting operating conditions established. For the optimization of the continuous system parameters an experimental design based on a 23 complete factorial design with axial and central points was setup. The percentage of cassava syrup in the formulation, the rotation of the screw (impeller) and the crystallization/beating temperature were the independent variables. The water activity and the texture (resistance of the crystalline mass to compression) of the fondant were used as responses variables. The microstructure of the crystalline system was characterized in terms of the Crystal Size Distribution (CSD) using optic microscopy analysis and light scattering. Fondant manufactured with cassava syrup showed appropriate water activity (microbiological stability) and adequate texture parameters when formulations with at least 20% of cassava syrup (for lower water activity) at an initial beating temperature of 60 ºC were submitted to screw rotation speed of 110 rpm / Doutorado / Engenharia de Processos / Doutor em Engenharia Química

Magister Scientiae - MSc / This work examined the systematic approach to protein crystallization, exploring some of the techniques that have been developed to enhance the success rate of crystallization. The work was centered on two proteins; namely Vaccinia virus complement control protein (VCP) and glutamate dehydrogenase (GDH) from Bacteriodes fragilis. The crystal structures of the full lengthe native VCP and VCP bound to heparin had already been determined. In the same way, the structure of GDH from Bacteriodes fragilis is not known, even though structures of other GDHs from different organisms have been determined. / South Africa

The crystallization kinetics of sodium sulphate from 9N sulphuric acid was studied under cooling conditions. The crystal growth and nucleation rates were determined using the Population Balance concept in a continuous mixed-suspension mixed-product-removal (MSMPR) crystallizer. The effects of supersaturation, crystal suspension density and temperature on the crystallization kinetics were all investigated. The study was conducted at crystallizer temperatures of 45, 50, 55, and 60 °C. The crystal growth rate data were correlated to the supersaturation with a power-law, G = KGSg. The crystal nucleation rate data were fitted to both primary (B° = KBSb) and secondary (B° = KNMTjSu) nucleation models. Growth and nucleation rate data were correlated according to the primary (B° = KbGi) and secondary (B° = KnMTjGv) relative kinetic models. The study determined that the growth rate data fit the expression, (G = KGS⁰‧⁸⁷ ), and that secondary nucleation was the dominant mode of nuclei generation (B° = KNMT⁰‧⁸⁴S¹‧²⁷). The sodium sulphate crystallizes from solution as the acid salt, sodium sesqui-sulphate (Na₃HSO₄) . The rate constants, KG and KN, were both functions of temperature and were fitted to Arrhenius type expressions : [formula omitted] / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate