I describe an experimental apparatus used to perform deformation experiments relevant to volcanology. The apparatus supports low-load, high-temperature deformation experiments under dry and wet conditions on natural and synthetic samples. The experiments recover the transient rheology of complex (melt ± porosity ± solids) volcanic materials during uniaxial deformation. The key component to this apparatus is a steel cell designed for high-temperature deformation experiments under controlled water pressure. Experiments are run under constant displacement rates or constant loads; the range of accessible experimental conditions include: 25 - 1100 °C, load stresses 0 to 150 MPa, strain rates 10⁻⁶ to 10⁻² s⁻¹, and fluid pressures 0-150 MPa. I present a suite of high-temperature, uniaxial deformation experiments performed on 25 by 50 mm unjacketed cores of porous Φ∼0.8) sintered rhyolitic ash. The experiments were performed at, both, atmospheric (dry) and elevated water pressure conditions (wet). Dry experiments were conducted mainly at 900 °C, but also included a suite of lower temperature experiments at 850, 800 and 750 °C. Wet experiments were performed at ∼650 °C under water pressures of 1, 2.5, 3, and 5 MPa, and at a fixed PH2O of ∼2.5 MPa for temperatures of ∼385, 450, and 550 °C. During deformation, strain is manifest by shortening of the cores, reduction of porosity, flattening of ash particles, and radial bulging of the cores. The continuous reduction of porosity leads to a dynamic transient strain-dependent rheology and requires strain to be partitioned between a volume (porosity loss) and a shear (radial bulging) component. The effect of increasing porosity is to expand the window for viscous deformation for dry melts by delaying the onset of brittle deformation by ∼50 °C (875 °C to 825 °C). The effect is more pronounced in hydrous melts (∼0.67 — 0.78 wt. % H₂0) where the viscous to brittle transition is depressed by ∼140 to 150 °C. Increasing water pressure also delays the onset of strain hardening due to compaction-driven porosity reduction. These rheological data are pertinent to volcanic processes where high-temperature porous magmas I liquids are encountered (e.g., magma flow in conduits, welding of pyroclastic materials). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Rheological characterization of pharmaceutical semisolids is of importance as it provides fundamental information required for the assessment of some of the final properties of a product such as viscosity, elasticity, quality and storage stability. The effect of formulation variables on product characteristics such as consistency and correlation of consumer evaluation of consistency can also be attained. (Ramachandran et al., 1999) This study focussed on using rheological techniques to fully characterize the properties of various semisolid formulations being developed or produced at a South African-based generic pharmaceutical company. Various tests were employed to characterize the semisolid dosage forms (creams and ointments), including continuous shear tests such as flow and viscosity curves and yield point measurements, oscillatory tests such as amplitude and frequency sweeps, as well as step and temperature ramp tests. A method to determine justifiable and meaningful viscosity specifications was developed, where excellent reproducibility of results were obtained when compared to the single-point viscosity determinations usually used. An evaluation as to whether rheology can be utilized as an assessment tool for product stability revealed varying results, with the oscillation-frequency sweep test displaying modest predictive capabilities. Observable differences in rheological character were found when evaluating ointment formulations exhibiting deviating quality characteristics. When analysing the effect of varying processing parameters, namely, cooling rate and mixing speed, during the manufacture of a cream, statistically significant rheological differences were obtained, while a thorough characterization of a scale-up procedure was also achieved upon analysis of various rheological properties.

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This work is the subject of an EPSRC-Tioxide Industrial CASE Award, the principal area of study being factors affecting the achievable steady state permeate flux during the crossflow microfiltration of concentrated titania dispersions. The performance of this continuous thickening process is of particular interest to Tioxide as a potential alternative to current batch filtration processes, which delay the manufacturing process.

Results of forced vibration tests in longitudinal and transverse modes on three different rocks are presented. The experimental investigation leads to evaluation of solid viscosity parameters as a function of frequency and logarithmic decrement. Linear viscoelasticity theory is applied to the test results within the frequency range studied. The test results indicate that the rheological parameter viscosity of the rocks tested, quartzite, granodiorite and an argilite, is of the order of 10⁸ to 10⁹ poises. Methods of predicting solid viscosity parameters from forced vibration resonance tests by linear viscoelastic theories are derived. The correspondence principle, which is based on the solution to steady state sinusoidal oscillation is not strictly applicable, but does yield results which are of the same order as the measured relationships. The behaviour of rocks to idealized rheological models has been examined. Measurements of the viscosity and complex moduli are described and from a consideration of the results obtained the type of mechanical model most respresentative of the behaviour of rocks is suggested. A method for predicting directional properties of rocks using photo-elastic studies for different loading conditions is examined. This enables allowances to be made for the wide variation in dynamic test results on rocks. However, it is felt that the dynamic method of determining viscosity may have more application in the examination of rock structure, since a comparison of the laboratory and field test results at the same temperature and pressure yields a method for structural design involving rocks. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

This thesis concerns design of two pieces of suspension dewatering equipment (i.e. transient batch settlers and steady state continuous gravity thickeners). In a transient batch settler, very slow densification of aggregates within the suspension is considered whilst the drag on the solids in the suspension is assumed to be negligible. The interface of the suspension is then determined by a balance between gravity and the gradient of the compressive yield stress of the gelled suspension. The compressive yield stress functional form in general could be either a weakly gelled formula, or a strongly gelled formula. These formulae differ in the way they behave for solids concentrations in the neighbourhood of the suspension gel point. The effects of the above two gel formulae, the evolution of the compressive yield stress functional form over time during aggregate densification, different initial suspension heights, and different initial feed solids volume fractions upon the predictions of consolidated bed structures and solids volume fractions obtained at the bottom of a batch settler, and upon the evolution of the heights of the suspension and the consolidated bed have been explored. A sufficiently tall initial suspension height might lead to insignificant increases in the solids volume fractions obtained at the bottom of batch settlers after time-dependent aggregate densification. The interfaces of the suspension and the consolidation zone coincide after aggregate densification if the gel point, which increases with time, is larger than the initial feed solids volume fractions. Moreover, the maximum permitted underflow solids fluxes predicted from steady state thickeners have been investigated and compared. Pre-shearing of aggregates which densifies aggregates to have smaller diameters upon entering the thickener is necessary if large underflow solids fluxes and small underflow solids volume fractions are specified. The solids volume fraction at the top of the consolidated bed which is the densified gel point is influenced by the extent of pre-shearing of aggregates. An algorithm for determining this densified gel point has also been developed. In reality, thickeners contain not just a consolidating bed, but also a hindered settling region above it. When the hindered settling region is considered in a thickener, the effects of the extent of aggregate densification that has occurred in the hindered settling region and how that impacts upon thickener performance and sludge rheological properties have been explored in this thesis. A new algorithm for predicting the densified gel point obtained at the top of the consolidated bed has been developed when the hindered settling region is present. The effects of underflow solids volume fractions, aggregate densification rate parameters and pre-shearing of aggregates upon the predictions of maximum permitted underflow solids fluxes, sludge rheological properties, and thickener performance have been explored. The predictions of thickener performance using both the weakly and strongly gelled formulae have also been achieved. In cases where it is possible to neglect the hindered settling region, substantial increases in the maximum permitted underflow solids fluxes, and substantial decreases in the consolidated bed heights and the total solids residence times have been achieved after aggregate densification for a comparatively small underflow solids volume fraction. The benefits arising from aggregate densification are more modest if the underflow solids volume fraction is larger. On the other hand, when the hindered settling region is included, more densification of aggregates occurring in the hindered settling region might lead to taller consolidated bed heights for a specified suspension flux and a specified aggregate densification rate parameter due to higher underflow solids volume fractions.

Aqueous dispersions of xanthan and locust bean gum, in combination, show a synergistic increase in viscosity. At sufficiently high concentrations, firm gels are formed, although neither component forms true gels when alone. The actual molecular processes resulting in this phenomenon are still incompletely understood and Theological studies can provide some clues to the mechanism of the interaction. Rheological properties of the polysaccharide blend were therefore investigated. Moisture, ash and inorganic elements and protein content as well as the intrinsic viscosity of the individual polysaccharides were determined. Dynamic viscoelastic properties of dispersions prepared from the polysaccharide blend were evaluated in four solvent treatments capable of disrupting weak intermolecular bonds. The effect of polysaccharide concentration, temperature, ionic strength, pH, ratio of mixing of the two gums and urea concentration on steady shear rheological properties were evaluated in a fractional factorial experiment. More detailed studies were carried out on the effects of temperature at two levels of concentration and ionic strength. Solvent treatments significantly affected the viscoelastic properties of xanthan-locust bean gum solutions. At 20°C and under the conditions used, dipole interactions appeared to be the primary force responsible for stabilizing the xanthan-1ocust bean gum interacting system. Hydrogen bonding and hydrophobic interactions seemed to play less important roles. Under conditions of low ionic strength and increased temperature, the interactions were lost and polysaccharide solution behavior passed from that of a viscoelastic solid to that of a viscoelastic liquid. At 60°C and at high ionic strengths, hydrophobic interactions may become important in the stabilization of the three dimensional gel network. Temperature effects on steady shear viscosity of xanthan-locust bean gum solutions were dependent on the concentration and ionic strength of the system. In general, steady flow properties were comparable to the reported behavior of xanthan solutions and so reflected the weakness of the interaction (dipole interactions) between the two polysaccharides. / Land and Food Systems, Faculty of / Graduate

No description available.

No description available.

No description available.