published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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The first part of this thesis intends to create a fuel processor model capable of generating 1kW power as output through the use of a solid oxide fuel cell system. The fuel processor system consists of a reformer, heat exchanger network, desulphurizer and an afterburner. Modelled in VMGSimTM, inlet diesel gas is provided at the mass flow rate of 0.2596kg/hour, with the oxygen to carbon ratio calculated at 0.31 and the steam to carbon ratio arbitrarily set to be 2.25. The diesel fuel is preheated and mixed with air and steam and then fed to the auto-thermal reformer. The higher hydrocarbons are broken down and converted into hydrogen. The outlet of the reformer is fed into the SOFC where H2 is converted to generate energy which, in this case is approximately 1200W. The off gas is fed to the afterburner; where the remaining H2 is burnt and the energy is used to provide for steam generation and pre-heating through the heat exchangers. The project also focuses upon performing basic sizing calculations on components of the system. The fuel cell efficiency was found to be 62% and the system efficiency was calculated to be approximately 41%, which falls within the range given in literature. For the second part of this work, a ceramic porous tail-gas burner using a non-premixed feed of anode exhaust and air was modeled using COMSOL™. The reaction kinetics were experimentally assessed on the basis of COMSOL™ limitations and accuracy of the comparative results. Three performance metrics were evaluated in the analysis: i) velocity profile, ii) temperature profile, and iii) concentration profile. These metrics confirm the combustion reaction at the outer boundary of the porous ceramic in the burner. The spike of temperature and decrease of mass fraction of hydrogen, carbon monoxide and methane to approximately zero in the outlet exhaust confirms this study. This study was further validated by comparing results with the experimental data collected at NRC-IFCI. The results of COMSOL™ model agreed with the experimental results of NRC-IFCI. / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-10-29 17:49:32.266

Given the long history of research within the Aegean, the Middle Bronze Age (MBA) of the Cyclades is surprisingly poorly understood. This region is often considered within the context of other ‘worlds’, particularly in the quest to understand ‘Minoanisation’. Prominent Middle Cycladic sites such as Ayia Irini (Kea), Phylakopi (Melos) and Akrotiri (Thera) have played a dominant role towards informing the perceived Cycladic ‘response’ to growing Minoan influence within the Aegean sphere, often at the expense of considering the interactions between these important settlements. However, the recent 2000-2001 pillar pit excavations at Akrotiri have allowed a whole new phasing for the MBA ceramic deposits and offer great potential for characterising these neglected interactions. The ceramic material studied here, from Phases B and C of the MBA assemblage at Akrotiri, corresponds to the introduction of imported and ‘Minoanised’ material traits, both compositional and technological, to the local ceramic repertoire. This material is contextualised within previous research in the Cyclades, including Phylakopi, Ayia Irini and Mikre Vigla. Scale is considered an important theme and provides a key structure throughout this thesis. Three scales were defined for considering all aspects of the ceramic assemblage at Akrotiri: a) the potters at Akrotiri, the technological choices they make, the social practices they participate in and perpetuate and the character of the local ceramic production sequence (the micro-scale of individuals); b) the character and significance of the Akrotiri ceramic assemblage within the Cyclades (the meso-scale of group interaction); c) the role that Akrotiri played as a node within larger social and exchange networks throughout the Aegean (the macro-scale of community interactions). From a theoretical standpoint, four explanatory frameworks are employed to tackle and integrate these various scales: the chaîne opératoire, dynamic systems framework, network theory and communities of practice. In combination, these frameworks have the potential to bridge the structure-agency divide, by acknowledging the fundamentally social nature of artefact production and consumption, and to integrate recent considerations of human and non-human agency within dynamic processes. Ultimately, by considering the socially constituted processes that drive the learning and practice of a craft or technique, and how these processes contribute to and perpetuate communities of practice, archaeologists can begin to meaningfully characterise the contact between different groups of people in the past. Therefore, this technological study of the late Middle Cycladic ceramic assemblage of Akrotiri, integrates macroscopic, petrographic and QEMSCAN analyses to characterise and explore the interactions within and between the many communities of practice operating within the late MBA Cyclades. In addition, this methodology allows a better understanding of the choices the communities in the Cyclades were making in the lead up to ‘Minoanisation’ so we can approach these material phenomena from a more localised, site-based perspective rather than a traditional Creto-centric viewpoint.

The Virginia Museum of Fine Arts (VMFA) has in its collection eleven ancient West Mexican ceramic sculptures. Given that the VMFA's West Mexican Ceramic figure collection has not been included in any extensive study, this thesis serves to provide a critical analysis of these figures through a formal and stylistic approach. These analyses are preceded by a brief history of the West Mexican cultures and highlight the artistic similarities and differences between each region. The primary regions under discussion are Colima, Nayarit, and Jalisco which correspond to modern geopolitical boundaries. Primary sources for these discussions are the figures themselves, while various published catalogues serve as comparative sources. Where applicable, iconographical theories are introduced and discussed in conjunction with the formal and stylistic analysis.

My love of learning, teaching, and providing creative spaces for people to connect informs my work and my life. For me, art is like life: messy, physical, and, if done with intent, beautiful. It is more about the process than the result; it is about recognizing that although we make choices, there are many things we cannot control; it is about being so present in the moment that everything else fades away. How I live, what I do, what I believe, and my art are all the same.

“Truth happens only by establishing itself in the strife and the free space opened up by truth itself. Because truth is the opposition of clearing and concealing, there belongs to it what is here called establishing.”[i]—Martin Heidegger All things contain their own individual existence. When I look at objects I notice material, tradition, individual history. These are starting points for my imagination to seed and germinate. My ideas are fragmented, nonlinear and nonsensical to others but they hold honesty to me. Honesty is powerful and is worth sharing. This document is an examination of my work during my graduate studies. I will explain the importance of my relationship with: the imagination, jokes, materials, traditions and process as these are constant variables of my art practice. [i] Martin Heidegger, “The Origin of the Works of Art” in Tanke, Joseph J., and Colin McQuillan. The Bloomsbury Anthology of Aesthetics. 394. New York: Bloomsbury Publishing Plc, 2012

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Solid oxide fuel cells (SOFCs) are the most efficient electrochemical devices to directly convert stored chemical energy to usable electrical energy. The infiltration of ceramic conductors and catalytic metals (e.g. Ni, Pt and Pd) into porous scaffolds that had been pre-sintered onto the electrolyte is regarded as an effective way of promoting the electrode performance via producing nano-scale particles by in-situ sintering at relatively low temperatures. Large-scale fuel cells (5 cm x 5 cm) are prepared with this method and tested to demonstrate its scalability so as to achieve industrial applications. Four configurations are examined in respect of variation in the thickness of cathode, anode and electrolyte to investigate their effect on the infiltration process and electrochemical losses. To further improve infiltration as a method of fabricating high-performance electrodes, much effort is also devoted to optimising and understanding the microstructure of pre-sintered scaffold and its effect on infiltration using image analysis and electrochemical impedance. First, we have prepared the nano-structured electrodes on the 200-μm thick electrolyte-supported planar fuel cell with a 5 x 5 cm dimension. The 8YSZ scaffold is impregnated with La₀.₈Sr₀.₂Cr₀.₅Mn₀.₅O₃ (LSCM) for the anode and La₀.₈Sr₀.₂FeO₃ (LSF) for the cathode. The large planar cell achieved a maximum power density of 116 mWcm⁻² at 700°C and 223 mWcm⁻² at 800°C in humidified hydrogen. Moreover, with the addition of catalyst of 10 wt.% CeO₂ and 1 wt.% Pd, the cell performance reached 209 mWcm⁻² at 700°C and 406 mWcm⁻² at 800°C. Compared to the cell without catalysts, ceria and Pd are efficient in decreasing the electrochemical reaction resistance but making the diffusion resistance more obvious. Second, supported thin electrolytes are prepared by scalable tape casting to reduce the ohmic losses as that in electrolyte-supported cell. The cell with thick LSF-infiltrated support is very efficient in decreasing the ohmic loss thanks to the high solubility of its nitrate precursors in water and fairly high electric conductivity, but the thick cathode causes higher diffusional losses, especially at 800°C. Even though with thinner electrolyte, the ohmic loss from the cell with thick infiltrated anode is comparable to that of 200-μm electrolyte supported cell. The extra ohmic loss can be attributed to the compositional segregation of La₀.₇Sr₀.₃VO₃ (LSV) in the infiltration process in the anode, and lower loading, ca. 25 wt %. A trade-off between the diffusional loss from the cathode and the extra ohmic loss from the thick anode can be achieved by sandwiching the electrolyte between electrodes with identical thickness. A flat large area cell prepared with this method can achieve a high performance of 300 mW cm⁻² and 489 mW cm⁻² at 700°C and 800°C, respectively, if Pd-ceria is added to the anode LSV as catalyst. Third, image analyses and modelling are performed on the constrained sintering of porous thin film on a rigid substrate to study the evolution of pores at different stages. Result shows that both the anisotropy of the pore former/pores in the green body and transport of materials during the sintering process have effect on the orientation of the final microstructure. Specifically, the in-plane orientation of large-scale pores will be intensified during the constrained sintering process, while those small pores whose shape are subjected to materials transport during sintering tend to erect during the constrained sintering process at 1300°C. Fourth, image analyses and semi-quantification are used to predict the correlation between the microstructure and performance of the LSF-infiltrated electrode. Two types of YSZ powders, Unitec 1-μm powder with a broad particle-size distribution having two maxima at ~ 0.1 μm and 0.8 μm, and Unitec 2-μm powder with only one at ~1 μm are selected to fabricate the porous scaffold for infiltration. The porous structure using Unitec 2-μm powder shows finer YSZ grains and a higher boundary length than the 2-μm powder. Ac impedance on symmetrical cells was used to evaluate the performance of the electrode impregnated with 35-wt.% La₀.₈Sr₀.₂FeO₃. At 700°C, the electrode from Unitec 2-μm powder shows a polarization resistance (Rp) of 0.21 Ω cm², and series resistance (Rs) of 8.5 Ω cm², lower than the electrode from Unitec 1-μm powder does. The quantitative study on image indicates that Unitec 2-μm powder is better in producing architecture of high porosity or long triple phase boundary (TPB), which is attributed as the reason for the higher performance of the LSF-impregnated electrode. Finally, oxides of transition metals are doped into the YSZ-infiltrated LSF electrode and the impedances of symmetrical cells are tested to evaluate their effect on the ohmic and polarization resistance. Cobalt oxides are able to reduce the ohmic resistance and polarization resistance only when it is calcined at 700°C, but nickel oxide can reduce both the ohmic and polarization resistance if it is well-mixed and fully reacted with the previously infiltrated LSF. Doping of manganese oxide into LSF-YSZ electrode slightly changes the ohmic resistance but significantly increases the polarization resistance. Detailed analyses of the impact of infiltration process on the impedance data and oxygen reduction process are also presented.

A thesis submitted to the Faculty of engineering. University of Witwatersrand. Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy Pretoria, 1995 / This thesis describes a study of the friction and wear characteristics of a range of oxide and silicon-based ceramics sliding against AlSI 440C stainless steel, as well as various sliding combinations of two types of De Beers polycrystalline diamond (PCD), namely Syndite and Syndax, To facilitate the former work, a high-speed reciprocating sliding test machine with computerized data acquisition and control was developed. It was confirmed that under water-lubricated sliding, the oxide ceramics (alumina, PSZ, 3YTZP, and Ce-TZP) showed higher friction coefficients and Weal' rates than the silicon-based ceramics (Sialon and silicon nitride). This was related to different levels of adhesion and the formation of metallic transfer films. For the zirconia ceramics, increased transformation toughening was associated with increased surface fracture damage and metallic film formation. In general, the metallic transfer films were beneficial, protecting the underlying ceramic and dominating the friction and wear behaviour. The superior performance of the silicon-based ceramics was related to the formation of lubricious tribofilms containing silicon oxides and hydroxides. Experiments with synthetic mine water as lubricant demonstrated that the presence of significant amounts of chloride and sulphate in the water generally reduced friction and wear. This was tentatively explained in terms of reduced adhesion and the promotion of iron oxide and hydroxide formation. It is suggested that the influence of sulphate may be more important in thi'3 regard than that of chloride. The tribological behaviour of self-mated Syndite PCD sliding couples is dominated by the formation of Co-rich trlbofilms, which nrc associated with increased friction coefficients and reduced load carrying capacity (LCC). Syndax, which employs silicon as the binder phase, shows lower friction coefficients anti higher LCe under both dry and water-lubricated sliding conditions. Mixed Syndax/Syndite couples show superior performance to self-mated Synditc tinder dry sliding conditions, but 110 improvements in the presence of water. The former effect is related to the preferential removal of Co 11'0111 the Syndite surface to the Syndax / GR 2017