Chemical and Biomolecular Engineering - Theses
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ItemAn investigation of the compression moulding and extrusion of polyethylene foam( 1979)The processes of compression moulding and extrusion of polyethylene foam using chemical blowing agents were investigated. Both high and low density polyethylenes together with the chemical blowing agents azodicarbonamide, Porofor S-44, 4,4'-oxybis(benzenesulphonyl hydrazide) and N,N'-dinitrosopentamethylenetetramine were used. The same mechanisms were found to be operative in both processes. The nucleation of cells was related to the decomposition of the chemical blowing agent used. Secondary nucleation of the diffusing gas was effected by the use of a very fine particle size silica. The processes of gas diffusion and gas dissolution in the melt were shown to be important in explaining the cell structure obtained. These were related to gas sorption studies. Very fine cellular structures could be obtained by compression moulding by using fast heating and cooling cycles. This reduced diffusion resulting in low foam density and fine cell size. The dielectric constant of the foam was related to foam density by the use of mixture formulae. Tensile properties were found to be dependent on cell size and, foam density.
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ItemSplashing due to gas injection( 1993)The splash event produced by a falling drop impinging on a bath of liquid was studied to enable a more fundamental understanding of the mechanisms of splash formation. An experimental method involving the use of a high speed photographic technique was developed to enable discrete splash events to be recorded at different time intervals. The effect of varying impact velocity, liquid viscosity and surface tension on the splash event was studied. The aspects of the splash mechanism that pertained to the projection of liquid above the liquid surface were monitored as a function of the experimental variables. Such aspects included the cavity depth, the Rayleigh jet behaviour and the extruded crown behaviour. Depending on the impact velocity of the falling drop, different shaped Rayleigh jets formed which varied in their manner of break up. Such changes in the Rayleigh jet behaviour could be related to the curvature of the interfacial cavity produced by the impact of the falling drop. As the impact velocity increased, the maximum height of the extruded crown increased. If the impact velocity exceeded a critical value, break up of the crown occurred. Increasing liquid viscosity had the effect of dissipating the energy of the system and hence producing less splash. Such viscous dissipating effects were quantified by the use of an energy balance. For liquids of a lower surface tension, there was evidence to suggest that a greater proportion of the incoming energy to the splash event was transferred to the extruded crown rather than to the cavity. Consequently, the splash produced from the break up and extrusion of the crown became more significant. A knowledge of the size of the bubbles reaching the liquid surface would assist in predicting the splashing behaviour of an industrial process which utilised gas injection.
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ItemSlag-cleaning reactions in the KNS flash smelting furnace( 1991)The increasing cost of mining and concentrate production, together with the shift from traditional reverberatory smelting furnaces to more energy efficient smelting processes such as flash smelting, has made the slag cleaning step an indispensable part of current smelting technology. At the Kalgoorlie Nickel Smelter (KNS), slag cleaning is performed in an "appendage" to the flash smelting furnace. The aim of this project was to study the slag-cleaning reactions through plant measurements, thermodynamic modelling and laboratory experiments. Measurements taken at KNS showed that the slag and matte in the furnace were not in equilibrium. This was also predicted by the thermodynamic model and subsequently confirmed by laboratory experiments. The slag was over-oxidised relative to the matte and during equilibration iron in matte acted as a reductant for nickel oxide and magnetite in the slag. Thermodynamic modelling of the carbon-free slag-matte system indicated that the equilibrium concentration of nickel and magnetite in slag matte was about 0.4 and 7.5%, respectively. This is in good agreement with the results of the laboratory experiments in which samples of slag and matte from the smelting section of the furnace were allowed to come to equilibrium. The thermodynamic model also showed that further reduction of nickel from slag required the addition of carbon and that excessive reduction of slag would result in the reduction of FeO from slag and led to a decrease in matte grade. The latter was confirmed in a laboratory experiment performed in a graphite crucible. There was no difference between the performance of the various types of carbonaceous reductants at low N2 injection rates (0.2 to 0.4 l/min) in the laboratory experin1ents. In these experiments, the reduction rate of nickel and magnetite was relatively slow. When the experiments were repeated at a higher N2 injection rate of 2.0 l/min, the nickel and magnetite reduction rate increased significantly and it was found that the more reactive forms of carbon performed better than the less reactive carbon. The results suggest that with gentle stirring, reduction is controlled by mass transfer but with more vigorous stirring the reactivity of carbon is in1portant. The results of the laboratory experiments also found that the rate of reduction nickel and magnetite increased at higher temperatures. Injection of powdered carbonaceous reductants into slag in the laboratory experiments was more effective than lump addition of reductants in reducing nickel and magnetite from slag. Injection of reductants also resulted in greater utilisation of the volatiles in the reductants. The results suggest that the current practice at KNS could be made more efficient by lowering the nickel and magnetite concentration in slag before it enters the slag cleaning section. This could be achieved by injecting N2 to promote mixing and increase the rate of attainment of equilibrium between the matte and slag and/or by injection of powdered reductant, before the slag enters the appendage.
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ItemShrinkage behaviour of geopolymer( 2009)Geopolymer cements offer an alternative to, and potential replacement for, ordinary Portland cement (OPC). Geopolymer technology also has the potential to reduce global greenhouse emissions caused by OPC production. There is already a considerable amount of work and research conducted on geopolymers in the past decades, and it is now possible to implement this technology commercially. However, to ensure that geopolymer becomes commercially available and able to be used in the world, further understanding of its ability to provide durable and long lasting materials is required. One main property which is still relatively unexplored compared to other properties is its shrinkage properties. The objective of this thesis is therefore to examine the shrinkage of geopolymers and factors which might influence it. The factors which influence geopolymer strength were investigated as being the factors which may influence shrinkage. The selection of the activating solution is an important factor in forming the final product of a geopolymer. Activating solution SiO2/Na2O ratio is determined to be an important influence on the shrinkage of geopolymer. SEM images of the samples enable observation of the sample topology and microstructure. An important observation was the existence of a ‘knee point’ which also occurs in OPC shrinkage. The ‘knee point’ is the point where the shrinkage goes from rapid shrinkage to slow shrinkage. From SEMs it is noted that the samples past the knee point are shown to have a smoother topology which means it is more reacted. Autogenous shrinkage is an important issue for OPC containing a high amount of silica, and is also a key factor in geopolymer shrinkage. Autogenous shrinkage is tested by keeping samples in a sealed environment where water lost to drying is kept to a minimum. It is noted that sealing and bagging the samples reduces the shrinkage considerably. The water to cement ratio, which is an important factor in OPC shrinkage, is also explored for the case of geopolymers. Water content plays an important role in determining early stage shrinkage, and has little to no effect on the later stage shrinkage. The water loss from the samples during drying on exposure to environment is noted and compared. The addition of more water did not necessary means that more water was lost. Addition of slag is known to be beneficial to geopolymers by giving early structural strength and faster setting time. Commercial geopolymer concrete will also include the use of slag. However, the addition of slag up to a certain extent gives a deleterious affect on shrinkage. A different type of Class F fly ash source with different composition data was used to see its effect on shrinkage, with only a slight influence observed between the two ashes tested. Fly ash was also ground for different lengths of time before use in geopolymerization, with grinding for less than 12 hours giving higher shrinkage than an unground sample, but shrinkage the decreasing with grinding for 18 or 24 hours. This initial higher shrinkage has been attributed to the mechanism of grinding which resulted in unevenly shaped fly ash particles taking up a larger initial volume resulting in higher shrinkage. The sample grinded for 24 hours showed higher shrinkage due to the particle size to be so fine that agglomerates may have form during mixing which would result in a lower reaction rate which increases the shrinkage. Elevated curing temperatures also reduce geopolymer shrinkage. Thus, it is clear that the shrinkage of geopolymers is influenced by a wide range of variables, and more notably by a few important variables: activating solution ratio, addition of water, grinding and bagging. The shrinkage of geopolymers can be correlated to the strength to a certain extent. However, the understanding of the shrinkage of geopolymers is still at a very initial phase, and further research is required.
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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.