Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 138-154). Also available via the Internet.

Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Thesis (Ph.D.)--Drexel University, 2010. / Includes abstract and vita. Includes bibliographical references (leaves 188-200).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 111-115). Also available in electronic version.

GaInAsP and GaInAs epitaxial layers grown on Fe-doped InP substrates of {100} orientation have been studied using cross-sectional and plan-view transmission electron microscopy. Studies of the epilayer surface regions of LPE Ga[0.03]In[0.97] As[0.07]P[0.93] heavily doped with Mn or Mn and Ge have revealed at least seven precipitate types when classification is made according to precipitate morphology, configurations and associated strain fields. The origin of some of these second phase particles is shown to be iron-phosphide precipitation resulting from iron diffusion from the substrate. Furthermore, in a LPE Ga[0.47]In[0.53]As layer co-doped with Mn and Ge four distinct precipitate types were observed. Speckle and long wavelength microstructures in GalnAs grown by LPE, MOCVD and MBE have been studied. A long wavelength microstructure lying along directions which is observed in some MBE GalnAs layers is associated with reduced electron mobilities. In MOCVD GalnAs a long wavelength microstructure lying along directions was seen to vary as a function of distance from the interface. The presence and wavelength of the speckle contrast is shown to be independent of the growth technique employed. Some MBE GalnAs layers also reveal an island contrast along orthogonal directions. Undoped MOCVD GalnAs epilayers with large compositional fluctuations approximately half way through the thickness of the epilayer or small compositional fluctuations near the epilayer surface have been studied. These perturbations in composition are associated with a dislocation cell structure and a cross-hatch of dislocations along directions respectively. A variety of defects have been identified and the microstructure correlated with Sputter Auger profiles and depth-resolved Hall profiles. Cliff-Lorimer k-factors have been determined experimentally and theoretically for Ga, As and P relative to In and extinction distances for GalnAs and InP calculated.

A study of the constitution, transformation and precipitation effects in ternary Fe-Cr-Ni alloys and quaternary Fe-Cr-Ni-X alloys containing Mo, Nb, Ti, and Si was carried out. A systematic approach was adopted so that the microstructural effects observed as a result of ageing the selected iron base ternary alloys could be directly compared to the quaternary alloys. A series of ageing curves were plotted for the six ternary alloys over the temperature range 400°-900°C and for the ten quaternary alloys in the temperature range 650°-850°C. Optical and electron metallography were used to study the transformation and precipitation of intermetallic phases and carbides in the aged microstructures. The transformation of delta ferrite to sigma phase in a duplex (gamma+delta) ternary alloy was studied. The transformation was preceded by the precipitation of a cellular structure which formed on the delta/gamma grain boundaries and consisted of M23C6 and new austenite. A complex transformation product, which resembled a region of imiscibility, then formed at the delta/(gamma + M23C6) interface, this product consumed the delta ferrite grain, eventually transforming to sigma phase and new austenite. The alpha' phase, more commonly referred to as 475°C embrittlement, was also observed precipitating in the delta ferrite grains in two of the iron based ternary alloys in the temperature region 400°-500°C. Overageing of the alpha' precipitates after 1000 hours at 500°G was accompanied by the precipitation of a rod like austenite. The elements 2%Mo, 1%Nb, 1/4%Ti and 1% and 2%Si were added totwo Fe-Ni-Cr base alloys. One alloy was an austenitic (20Cr,23Ni) and the other was a transformable alloy (18Cr, 7Ni). The quaternary element additions had no effect on the constitution of the austenitic ternary alloy. However the addition of Mo to the 18Cr, 7Ni ternary alloy caused the transformation of delta ferrite to sigma phase over ageing temperature range 650°-850°C. The addition of Si moved the constitution of the ternary alloy further into the gamma+delta phase field, a small amount of sigma phase was observed in the 2%Si quaternary alloy on ageing at 650°C for 1000 hours. Irradiation damage studies were performed using High Voltage Electron Microscope and Variable Energy Cyclotron. The effect ofthe quaternary alloying additions Mo, Si, and Nb on the voidswelling behaviour of a 20Cr, 23Ni alloy were studied using 46MeV Ni6 ions in the Variable Energy Cyclotron, irradiating to a total dose of 10dpa at 550°C. All additions reduced void swelling, the largest reduction was observed in the Si containing allov. The Insert A Thermal ageing showed the presence of M23C6 the amount of which increased with increasing ageing temperature. No delta ferrite was observed in these alloys.

This thesis is concerned with the derivation, development, and validation of a model for the dynamic behaviour of gas bubbles in molten instant coffee, in response to changes in pressure and temperature. Initially, the material properties of molten instant coffee were investigated. The primary technique used was capillary rheometry, as the viscous behaviour of molten instant coffee is a major contributor to the behaviour of bubbles within the fluid. The experimental technique was supplemented by analytical and computational modelling of the pressure losses in the system, to improve data processing accuracy. Additional thermal and mechanical tests were performed to obtain as much of the necessary material information as possible for the system. The modelling of bubble behaviour was performed using a combination of analytical and computational methods. The relationship between the pressure driving force for bubble growth or shrinkage and the rate of change of bubble size was derived analytically for a number of common generalised Newtonian fluid models. Heat and mass transfer between the bubble and the surrounding fluid was calculated using a finite difference approximation of the governing partial differential equations. The model was written in MATLAB and initial validation was carried out by comparison with existing models for bubble dynamics. Experimental observations of bubble dynamics in flows of molten instant coffee were recorded and used for an extended validation of the model. Bubbles were exposed to step changes in pressure and oscillatory pressure profiles at a range of temperatures, and the observations of 130 individual bubbles were used to validate the model using the same material parameters for each. A final case study in using the bubble model to predict the bubble size and pressure distribution created by an extrusion process is presented as an example of the use of the model, and highlights the additional information about a process that is required to effectively use the model.

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