Chemical and Biomolecular Engineering - Theses
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ItemInterfacial tension study and rheological characterisation of water-in-oil emulsion explosives( 2007)Highly concentrated emulsion explosives are complex colloidal systems that remain robust for very many years after production. In this work a poly-isobutyl succinic anhydride (PIBSA) derived emulsions have been studied to understand the extraordinary nature of the stability and flow of these emulsions. In this study a model sodium oleate emulsion system is developed to further confirmation of the nature emulsion explosives. Two PIBSA based emulsifiers were used to prepare the emulsions. The main emulsifier of interest was comprised of an amide, ester and imide head group attached to a PIBSA chain, the second was entirely comprised of an imide head group attached to a PIBSA chain. The pendant drop method was used to obtain dynamic interfacial tension measurements for an interface between of paraffin oil/PIBSA-imide and ammonium nitrate, and dodecane/sodium oleate and sodium nitrate. The IsoFit-WardTordai computer package that incorporated Langmuir, Frumkin, Reorientation and Aggregation adsorption isotherms was used to calculate diffusion coefficients for total time adsorption. Diffusion coefficients for short time adsorption with Langmuir and Frumkin isotherms were determined and long time adsorption with the Langmuir isotherm were calculated. All of the diffusion coefficients results suggested that direct diffusion controlled adsorption was not the mechanism these surface active agents employed, rather, the results suggested that an activation barrier controlled adsorption process dominated the kinetics of the interfacial adsorption. There is much evidence to suggest that rheological properties of highly concentrated emulsions have not been characterised correctly for some time. This is mainly due to wall depletion or wall slip effect phenomenon inherent to rheological investigations performed on smooth stainless steel surfaces. The effect of wall slip was eliminated through physical means by performing rheological investigations with a sand blasted cone and plate, and the use of the vane geometry as a rheomter. Another method to eliminate wall slip effects in steady shear for highly concentrated emulsions was formulated and established in this investigation. A two-stage Tikhonov regularisation procedure that converts steady shear data into rheological property functions has been developed. The two-stage method is able to obtain not only the shear-stress shear-rate function but also the slip velocity as a function of wall shear- stress. The method is such that it obtains the rheological functions over the maximum range of shear-rate covered by the data. The results obtained using the new method were compared to those obtained using the sand blasted cone and plate and vane geometry with good agreement being observed. Over a 17 month period, a PIBSA based emulsion was observed in order to determine if any dramatic rheological changes were taking place with time, the results obtained in both shear and dynamic analysis effectively concluded that the PIBSA emulsion explosive was extremely stable and the minor changes observed were within experimental uncertainty of the measurements. Various microscopy techniques were used to determine the droplet structure and size distribution within various emulsions. Optical microscopy, Qualitative Phase Imaging, Differential Interference Contrast imaging were employed, and it was found that the PIBSA and PIBSA-imide emulsions had a spherical shape rather than a hexagonal close packed structure that was previously assumed for these emulsion explosives. Images of the sodium oleate emulsion indicated that there were obvious destabilising mechanisms at work, affecting the longevity of the emulsion.
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ItemCharacterisation of xanthan based, polymer solutions, physical gels and permanent networks( 2001)Gels and the gel transition are topics that have been the subject of extensive and widespread academic and industrial interest. Polymer gels and particularly those involving biopolymers are extensively applied in the food, pharmaceutical, agricultural, photographic, oil recovery and paper industries. Such widespread commercial application is responsible for the academic and industrial interest in gaining a greater understanding of the intrinsic physics governing the behaviour of these systems. Rheological analysis of biopolymer based gelling systems is an invaluable tool for investigating fundamental properties as well as replicating processing and application conditions. Through combination of careful rheological analysis with techniques capable of probing molecular structure and dynamics, such as static and dynamic light scattering (LS), it is possible to develop structure-function relations that are considered critical in understanding and controlling gels and gelation of biopolymer systems. This thesis utilises the biopolymer xanthan gum, to investigate both rheologically and optically, polymer solutions, physical gels and permanent networks. A physical gel is one in which the interactions between molecules, responsible for the gel like properties, are not permanent, that is they have a finite timescale. Subsequently, on long enough time scales, a physical gel will flow. Alternatively, a permanent network, as the name suggests, is one in which the interactions (or crosslinks) are thermodynamically stable, and the system will therefore never flow. Aqueous xanthan solutions in the presence of mono or divalent cations will produce a solution with 'weak-gel' physical properties. A 'weak-gel' is a term commonly applied to structured fluids that on short time-scales possess properties allowing them to appear more 'gel like', however on longer timescales, they will flow. Conversely, on the addition of trivalent metal ions (and for the purposes of this work, aluminum ions Al(III)) , xanthan will form a strong thermally stable permanent network. Using rheological and light scattering (LS) techniques, this thesis, will consider the similarities and differences of xanthan based physical gels and permanent networks. (From Abstract)
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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.