Chemical and Biomolecular Engineering - Theses
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ItemThe extensional properties of food emulsions(University of Melbourne, 2006)
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ItemThe extensional properties of food emulsions(University of Melbourne, 2006)
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ItemEffect of modifiers on the kinetics of solvent extraction(University of Melbourne, 2006)
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ItemEffect of modifiers on the kinetics of solvent extraction(University of Melbourne, 2006)
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ItemA conceptual model of geopolymerisation( 2006-10)The discovery of geopolymers is a breakthrough which provides a cleaner and environmentally-friendlier alternative to Ordinary Portland Cement (OPC). Since the pioneering days, the understanding of the chemistry, synthesis, and practical application of geopolymers has improved to the extent that commercialisation of geopolymers on a large scale is possible in the near future. However, the fundamental breakthroughs and understanding to date are based on investigations of ‘pure’ raw materials, like metakaolinite. The utilisation of metakaolinite has been useful in a research setting, but will be impractical for widespread application. Therefore, the thesis attempts to do a more detailed study on geopolymers synthesised from waste materials, such as fly ash. The motivation for using fly ash as the main raw material is driven by various factors: (1) it is cheap and available in bulk quantities, (2) it is currently under-utilised, except for its use as an additive in OPC, (3) it has high workability, and (4) it requires less water (or solution) for activation.
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ItemThe structure and thermal evolution of metakaolin geopolymers( 2006-02)Geopolymers are a relatively new class of material that has many broad applications, including use as a substitute for Ordinary Portland Cement (OPC), use in soil stabilisation, fire resistant panels, refractory cements, and inorganic adhesives. The synthetic alkali aluminosilicate structure of geopolymer results in a highly versatile material that can be synthesised en masse, cost competitively and from a wide varietyof aluminosilicate bearing raw materials. Despite the commercial promise and technical viability of the technology, the fundamental understanding of the chemical structure and characteristics of geopolymeric materials, and to some degree the academic rigor of some aspects of the science related to geopolymers, leave a lot to be desired. In particular, the understanding of the effects of Si/Al ratio and alkali cation type on the molecular structure of the binder, and how these relate to the microstructure and mechanical and thermal properties are poorly understood. The thesis explores the structure and characteristics of a systematic multi-dimensional matrix of geopolymers derived from metakaolin, a relatively pure aluminosilicate source. The thesis addresses the determination of the core molecular structure of geopolymers by solid-state NMR spectroscopy, and how this is altered by the nominal Si/Al ratio and alkali cation type. The chemical ordering is observed to reduce with Si/Al ratio and with inclusion of potassium over sodium. Most significantly, the presence of Al-O-Al linkages is identified for the first time in specimens with Si/Al ratios close to unity, by the application of 17O NMR techniques on geopolymers. The role of molecular structure and gel chemistry of geopolymers is elucidated, and links are drawn to understand the development of the microstructure and physical properties of the material. The thermal evolution of geopolymeric gels derived from metakaolin is investigated in terms of physical and structural development when exposed to temperatures up to 1000°C. The response of geopolymers to heating is characterised into four regions regardless of the extent of shrinkage or crystallisation. Several critical material performance relationships exist that are related to both the microstructure and chemical composition. The thesis presents an updated structural model of geopolymers to include new insights obtained from application of solid-state NMR techniques and thermal analysis. The improvements in structural understanding described in the thesis have the potential to affect all aspects of geopolymer science.
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ItemModelling the formation of geopolymers( 2006-03)Geopolymers, a class of largely X-ray amorphous aluminosilicate binder materials, have been studied extensively over the past several decades, but largely from an empirical standpoint. The primary aim of this investigation has been to apply a more science-based approach to the study of geopolymers, including introducing a variety of mathematical modelling techniques to the field. The nanostructure of geopolymers is analysed via an extensive literature review, and conclusions regarding the presence and role of crystallinity within the geopolymer structure are drawn. Si/Al ordering within the tetrahedral aluminosilicate gel framework is described by a statistical thermodynamic model, which provides an accurate representation of the distribution of Si and Al sites within the framework as well as physically reasonable values for the energy penalty associated with ordering violation. Framework and extraframework structure within the geopolymer binder are also described by the pair distribution function (PDF) technique, whereby synchrotron X-ray scattering data are converted via a Fourier transform-based method into real-space structural data on an Ångstrom length scale. Real-space Rietveld analysis of geopolymers crystallised at high temperature is used to back-calculate and analyse the original geopolymer structure, and the primary change in very short-range structure from the as-synthesised geopolymer to the high-temperature crystalline product is observed to be a shift in the location of the extraframework charge-balancing cation.
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ItemMass transfer enhancement of supercritical fluid extraction from a model herb( 2006)The use of supercritical fluids to separate natural materials from foods has attracted much attention recently. However, the commercial success of supercritical carbon dioxide for this application has been limited because it can only separate non-polar substances and the use of high pressure requires a high capital investment. The current study has explored two different methods to enhance the extraction yield and thereby widen the applicability of supercritical fluid extraction. These methods are 1. The effect of the natural moisture content of the substrate 2. The concurrent use of ultrasonic vibration Ginger (Zingiber Officinale Roscoe), which belongs to the Zingerberceae family is used as a model herb in this work. It is found that the use of a new season high moisture content fresh ginger (96 wt % substrate moisture content) for supercritical extraction provides a greater yield than the use of a dried ginger feed (. 1 wt% moisture content) as is currently employed commercially. However, when more fibrous low moisture content old season ginger is employed (. 85 wt % moisture content), the fresh ginger provides lower yield. This variation is considered to be due to differences in the structure and moisture content of the ginger matrix. Mathematical modeling of the new season high moisture content fresh ginger data shows that the effective diffusivity is higher than that of freeze-dried ginger. However, in the case of old season low moisture content ginger batches, the effective diffusivity is higher in the freeze-dried sample. This shows that when a ginger sample of high moisture content (96% moisture) is used, the high water content acts as a swelling agent to enhance the extraction rate and yield. The solubility parameter is comparable across different ginger batches, which indicates that the entraining effect of moisture is negligible. For further work, it may be possible to consider pre-soaking the old season ginger to increase the moisture content to > 95% (wt %) in order to improve the yield. High Performance Liquid Chromatography (HPLC) and Gas Chromatography — Mass Spectrometry (GC-MS) analyses are performed on the fresh, freeze-dried and oven-dried ginger extracts. This analysis shows that the fresh and freeze-dried ginger extracts contain more natural characteristic flavor and pungency than the oven-dried feed which is commonly used in industry. Under the influence of ultrasound, the extraction yield is increased by up to 30%. This higher extraction yield is attributed to disruption of the cell structure and an increase in the accessibility of the solvent to the internal particle structure, which enhances the intra-particle diffusivity. FESEM images of the surface of different ginger particles shows clear evidence of cellular disruption. While such effects are usually attributed to acoustic cavitation in ambient systems, the absence of phase boundaries in a supercritical system should preclude such a phenomenon. In spite of this, the possibility of cavitational collapse as one of the mechanisms for mass transfer enhancement in supercritical extraction due to ultrasonication is considered. Although, experimental results to prove this phenomenon are inconclusive, the formation of cavitation remains a possible cause of the cellular damage. Rapid changes in density (associated with the pressure fluctuations induced by the ultrasonic wave), sonoporation and acoustic streaming are other possible mechanisms that could be responsible for this mass transfer enhancement. It is recommended that further work is conducted using a high pressuer vessel with a direct viewing port to confirm the presence of cavitation. Chromatographic analysis of the extract from experiments conducted both with and without the influence of ultrasound is also performed. This analysis shows that the proportion of all extracted compounds incleased and that no new degradation products were formed as a result of ultrasonication.
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ItemRheological characterisation of nickel laterite slurry in processing environments( 2006)With China’s continuing economic boom, the demand for nickel has seen unprecedented growth over the past 10 years. Most of the world’s nickel is present in nickel laterite deposits. These high volume, low grade deposits are now being exploited and processed. An understanding of nickel laterite rheology and the ability to obtain meaningful rheological data is essential to process intensification and stability. The properties and physical characteristics of 8 industrial nickel laterite slurries as well as two alumina slurries were examined using various rheological techniques. The samples chosen covered a wide range of physical conditions such as differing pH, particle size distributions, solids densities and mineralogy as well as country and deposit of origin. The rheological parameters investigated were the yield stress and shear stress vs. shear rate of the particulate slurries. Considerable attention was focused on the techniques used in shear stress vs. shear rate characterisation, including capillary rheometry, smooth and roughened cup and bob rheometry and the vane in infinite medium technique. This work confirmed the finding of previous works, showing nickel laterite slurry rheological behaviour ranging from time independent to thixotropic to rheopectic. It found the vane in infinite medium technique highly suitable for testing nickel laterites at process relevant yield stresses. This technique gave data that correlated well with vane yield stresses and capillary rheometry data. Cup and bob tests showed significant slip at lower shear rates. In a number of cases, the cup and bob techniques also showed erroneously high stresses at higher shear rates. The vane yield stress was found to be a fast and accurate method for monitoring nickel laterite sample aging and the samples tested exhibited 100 Pa yield stresses at solids fractions ranging from 0.389 to 0.524. Blending of nickel laterites was found to be nonlinear, and confirmed that characterisation at various blend ratios is necessary if blending is to be utilised during production.