The search of materials relevant for thermoelectric and magnetocaloric applications, as well as materials that interact with light, is an important aspect of the materials science. Such materials can be used for solid-state power generation and refrigeration, as light sources, detectors, or controllers. Intermetallic clathrates have long been of interest for the materials science research. The promise these materials hold for useful applications ranges from thermoelectrics to photovoltaics and optoelectronics to potentially ultra-hard materials and magnetic cooling applications. Their unique physical properties are intimately related to their intriguing structural properties. Thus a fundamental understanding of the chemistry and physics of inorganic clathrates offers the possibility to assess their potential for use in the various applications mentioned above. In this work the selective, phase pure, single-crystal growth of AxSi46 and AySi136 (A = Na, K) intermetallic clathrates by the new vapor-phase intercalation method is presented. The approach appears promising for accessing regions of the equilibrium diagrams for Na-Si and K-Si clathrates that can be otherwise difficult to reach due to the greatly differing properties of the constituent elements. Physical properties of these materials were investigated in terms of single-crystal diffraction, electrical and thermal properties measurements. The synthesis and structural properties of single crystals of NaxSi136 are presented. A two-step synthetic approach was employed for the synthesis of NaxSi136 which also allowed for low temperature transport measurements of polycrystalline NaxSi136. The potential of the Eu8Ga16Ge30 type-I and VIII - EuO composites for magnetocaloric applications is discussed. The type-I clathrate - EuO composites hold promise for active magnetic refrigeration around 70 K.

Acacia holosericea A. Cunn. Ex G. Don (Velvet Leaf Wattle, Family Mimosaceae) is indigenous to Australia and holds promise as a novel cut foliage crop due to its silvery green silky phyllodes. Insufficient water uptake, possibly due to low stem hydraulic conductivity (Kh), is potentially responsible for early wilting and desiccation of phyllodes and limiting vase life. This study aimed to characterize the anatomy of stem xylem conduits and determine cation (K+ and Ca2+) mediated stem Kh. Differential localization of Ca2+ in xylem vessels and the effects of KCl and CaCl2 salts as cation contributors in vase solutions were also evaluated for their effects on cut foliage longevity. Anatomical characteristics of stem xylem conduits were studied using light, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Tracheids and vessels with simple perforation plates were the principal water conducting cells. SEM and TEM revealed bordered vestured intervessel pits in xylem conduits. Vestures were branched and coralloid-like structures. Xylem conduit lengths were assessed by ink perfusion. The majority of conduits (89%) were short (1 to 5 cm), and only ~ 2% were long (15 to 16 cm). Mean conduit diameter was 77 ± 0.9 µm, with 29% of conduits in the range 70 to 80 µm. Effects of S-carvone (0, 0.318, and 0.636 mM), a monoterpene inhibitor of wound-healing enzyme inhibitor found in caraway (Carum carvi) and dill (Anethum graveoleus) seeds, on several native Australian, non-proteaceous cut flower and foliage species including A. holosericea (Mimosaceae), Baeckea frutescens (Myrtaceae), Chamelaucium uncinatum cv. ‘Mullering Brook’ (Myrtaceae), and the non-native Chrysanthemum sp. cv. ‘Dark Splendid Reagan’ (Asteraceae) were examined. As comparator treatments regular recutting of stem ends and use of standard tap water (STW: 0.7 mM CaCl2, 1.5 mM NaHCO3, and 0.05 mM CuSO4 in vases) were tested. S-Carvone treatments significantly (P≤0.05) extended the vase life of B. frutescens and C. uncinatum, constituting the first report of positive S-carvone effects on the vase life of Myrtaceous species. S-Carvone at 0.318 and 0.636 mM did not have antibacterial effects against Bacillus cereus (the main vase solution microbe) either in vitro or in the vase solution. Regular recutting of stem ends consistently improved all vase life parameters [viz. relative fresh weight (RFW), solution uptake, and vase life] in the three native species examined. STW had a positive effect on RFW and solution uptake only for A. holosericea cut foliage. Effects of di- and monovalent cations (Ca2+ as CaCl2 and K+ as KCl) on stem Kh of cut stem segments were studied. Abundance of Ca2+ on pit membranes versus xylem lumen wall surfaces was investigated using a novel low vacuum (LV) SEM plus energy dispersive X-ray (EDX) microanalysis technique. Both salts (0.1, 1, 10, and 100 mM KCl or CaCl2) did not significantly increase stem Kh compared to the corresponding deionised (DI) water controls (experiment 1). Highest increase in Kh was with KCl and CaCl2 at 10 and 1 mM, respectively. Increases in Kh with 100 mM KCl and CaCl2 were significant over DI water (experiment 2) for long (10 and 20 cm) and short (2 and 5 cm) stem segments, respectively. Increases in Kh of 1.2- and 2.4-fold for 100 mM KCl over DI water were found with increasing stem length from 2 to 20 cm. Kh decreased as stem segment length increased from 5 to 20 cm. However, contrasting results were found with 100 mM CaCl2, where ΔKh was larger in shorter (2 cm) than longer (20 cm) segments. To prevent dislocation of ions and distortion damage to the specimens, stem pieces were first LV freeze-dried, and then carbon-coated, viewed under SEM, and analysed for elemental composition and distribution by EDX. However, the method could not identify specific calcium peaks in xylem vessels perhaps because background signals were too high, and tissue topography interfered with signal detection. Effects of KCl and CaCl2 on vase life were also tested. RFW, solution uptake, and vase life were higher with 10 mM KCl and CaCl2 in the vase solution than with 0, 1, and 100 mM. STW had a significant (P≤0.05) positive effect on RFW and solution uptake rate when tested against deionised water, 10 mM KCl and 10 mM CaCl2. Different combinations of 0.05 mM CuSO4, 10 mM CaCl2, and 10 mM KCl were also tested as vase solutions. A significant positive effect on RFW and vase life was obtained with CuSO4 alone, CaCl2 alone, and CuSO4 plus KCl. Only CuSO4 and CaCl2 gave a significant positive effect on solution uptake rate. None of the eight treatments tested showed a consistent effect on stomatal conductance or stem Kh. Overall, the research revealed that tracheids and vessels with simple perforation plates and bordered vestured intervessel pits are the principal water conducting cells in A. holosericea. LV-SEM-EDX technique was unable to assess the spatial distribution of Ca2+ on xylem vessels, but this was the first attempt to apply this technique. Also, this is the first report on the extension of vase life of B. frutescens and C. uncinatum (Myrtaceous species) using S-carvone. In vase solutions, 0.05 mM CuSO4, 10 mM KCl plus 0.05 mM CuSO4 and 10 mM CaCl2 should have positive influences on the water balance of A. holosericea cut foliage stems.

Semiconducting properties and related defect disorder for well defined TiO2 single crystal were studies. Semiconducting properties have been determined using simultaneous measurements of two independent electrical properties, including electrical conductivity, ??, and thermoelectric power, S, at elevated temperatures (1073-1323 K) in the gas phase of controlled oxygen activity (10-10 Pa &lt p(O2) &lt 75 kPa). Measurements of s and S were conducted (i) in the gas/solid equilibrium and (ii) during equilibration. Oxygen vacancies have been identified as the predominant defects in TiO2 over a wide range of p(O2). Individual conductivity components related to electrons, electron holes and ions, were determined from the obtained ?? data. The effect of p(O2) on these individual components was considered in the form of a diagram. This work led to the discovery of the formation and diffusion of Ti vacancies. However, the obtained diffusion data indicate that, in the temperature ranges commonly used in studies of semiconducting properties (1000-1400K), the Ti vacancies concentration is quenched and may thus be assumed constant. In addition it was shown that Ti vacancies in appreciable concentrations form only during prolonged oxidation. It was determined that the discrepancies in the reported n-p transition point are related to the concentration and spectrum of impurities as well as the concentration of Ti vacancies. It has been shown that the n-p transition point in high-purity TiO2 is determined by the Ti vacancy concentration. A well defined chemical diffusion coefficient, Dchem, was determined using kinetic data obtained during equilibration. A complex relationship between p(O2) and Dchem was observed. These data showed a good agreement between the obtained diffusion data and defect disorder. Examination of the determined equilibration kinetics, led to the discovery of two kinetic regimes, the result of the transport of defects at different mobilities. The determined data are considered well defined due to the following reasons: 1. The studied specimen was of exceptionally high purity and free of grain boundaries (single crystal) 2. The specimen was studied in the gas phase of controlled and well defined oxygen activity which was continuously monitored. 3. Whenever the experimental data were measured in equilibrium, the gas/solid equilibrium has been verified experimentally. 4. A good agreement between the two, self-confirmatory, electrical properties, including ?? and S has been determined simultaneously and independently. The defect disorder model derived in the present work may be used for tailoring controlled semiconducting properties through the selection of annealing conditions involving the temperature and oxygen activity.

Titanium dioxide, TiO2, has potential applications as a photoelectrode for photoelectrochemical generation of hydrogen by splitting water using solar energy and as a photocatalyst for water purification. This study is part of the UNSW research program to process TiO2-based oxide semiconductors as high-performance photoelectrodes and photocatalysts. This study investigates the effect of defect disorder on semiconducting properties of polycrystalline TiO2. This study involved the processing of high-purity polycrystalline TiO2 and determination of its semiconducting properties through measurement of electrical conductivity and thermoelectric power at elevated temperatures (1073-1323K) in controlled oxygen activities [1x10-13 Pa < p(O2) < 75 kPa]. The study included two types of experiments: Determination of electrical properties under conditions of gas/solid equilibrium. The data obtained was used to derive defect disorder and related semiconducting properties Monitoring of electrical properties during equilibration. This data was used to determine the chemical diffusion coefficient. The data obtained under equilibrium conditions indicates that oxygen may be used as a dopant to impose controlled semiconducting properties. In reduced conditions TiO2 is an n-type semiconductor and under oxidizing conditions TiO2 is a p-type semiconductor. The n-type behaviour is associated with oxygen vacancies as the predominant defects and titanium interstitials as the minority defects. The p-type behaviour is closely related to titanium vacancies that are formed during prolonged oxidation. Charge transport at elevated temperature was shown to involve substantial contribution from ions. Analysis of electrical properties enabled determination of several defect-related quantities including the activation enthalpy for oxygen vacancy formation, and the activation energy of the electrical conductivity components related to electrons, holes and ions. The kinetic data obtained during gas/solid equilibration enabled determination of the chemical diffusion coefficient which exhibited a complex dependence on nonstoichiometry. In addition, prolonged oxidation showed that equilibration occurred in two kinetic regimes. One for highly mobile oxygen vacancies and titanium interstitials which quickly reached an ??operational equilibrium?? within hours and another slow kinetic regime for equilibration of titanium vacancies over many thousand hours. The determined chemical diffusion coefficient data may be used to select the processing conditions required to impose uniform concentration of defects within a TiO2.

We conduct a comprehensive and systematic study of the Fermi-Pasta-Ulam (FPU) model using both equilibrium and non-equilibrium molecular dynamics simulations, with the aim being to explain the cause of the anomalous energy-transport behaviour in the model. In the equilibrium scenario, our motivation stems from the lack of a complete understanding of the effects of initial conditions on the energy dissipation among Fourier modes. We also critically reconsider the ????probes' that had been widely used to quantitatively describe the types of energy sharing in a system, and then decide on a preferred choice to be used in our equilibrium study. We establish, from strong numerical evidence, that there exists a critical energy density of approximately 0:1, above which the energy dissipation among the modes becomes independent of initial conditions and system parameters, and that the full equipartition of mode energy is never attained in the FPU model. We report, for the first time, the violation of particle positions in the FPU model at high energies, where the particles are found to pass through one another. In the non-equilibrium scenario, we critically review the Nos???Se-Hoover algorithm thermostatting method largely used by other works, and identify its weaknesses. We also review some other alternative methods and decide on the most appropriate one to be implemented throughout our work. We confirm the divergence of the thermal conductivity of the FPU model as the chain length increases, and that kfpu [symbol] No.41, in agreement with other works. Our study further shows that there exists an upper limit of the anharmonicity in the FPU model, and that any attempt to increase the strength of this anharmonicity will not succeed. We also introduce elastic collisions into the original FPU model and find that the Modified model (FPUC) still exhibits anomalous thermal conductivity. We conclude that a one-dimensional FPU-type model with ????only' nearest-neighbour interaction, regardless of being soft or hard, does not exhibit a finite thermal conductivity as the system size increases, due to the non-chaotic nature of its microscopic dynamics, the origin of which we are unable to account for. Finally, we briefly outline possible research directions.

Geopolymers are a relatively new class of material that has many broad applications, including use as a substitute for Ordinary Portland Cement (OPC), use in soil stabilisation, fire resistant panels, refractory cements, and inorganic adhesives. The synthetic alkali aluminosilicate structure of geopolymer results in a highly versatile material that can be synthesised en masse, cost competitively and from a wide varietyof aluminosilicate bearing raw materials. / Despite the commercial promise and technical viability of the technology, the fundamental understanding of the chemical structure and characteristics of geopolymeric materials, and to some degree the academic rigor of some aspects of the science related to geopolymers, leave a lot to be desired. In particular, the understanding of the effects of Si/Al ratio and alkali cation type on the molecular structure of the binder, and how these relate to the microstructure and mechanical and thermal properties are poorly understood. / The thesis explores the structure and characteristics of a systematic multi-dimensional matrix of geopolymers derived from metakaolin, a relatively pure aluminosilicate source. The thesis addresses the determination of the core molecular structure of geopolymers by solid-state NMR spectroscopy, and how this is altered by the nominal Si/Al ratio and alkali cation type. The chemical ordering is observed to reduce with Si/Al ratio and with inclusion of potassium over sodium. Most significantly, the presence of Al-O-Al linkages is identified for the first time in specimens with Si/Al ratios close to unity, by the application of 17O NMR techniques on geopolymers. The role of molecular structure and gel chemistry of geopolymers is elucidated, and links are drawn to understand the development of the microstructure and physical properties of the material. The thermal evolution of geopolymeric gels derived from metakaolin is investigated in terms of physical and structural development when exposed to temperatures up to 1000°C. The response of geopolymers to heating is characterised into four regions regardless of the extent of shrinkage or crystallisation. Several critical material performance relationships exist that are related to both the microstructure and chemical composition. / The thesis presents an updated structural model of geopolymers to include new insights obtained from application of solid-state NMR techniques and thermal analysis. The improvements in structural understanding described in the thesis have the potential to affect all aspects of geopolymer science.

Theoretical models for the electrokinetics of weakly permeable porous colloidal particles are absent from the literature. The understanding of this topic will be advanced through a systematic analysis of the standard electrokinetic equations, resulting in a theory for the electrophoretic mobility of weakly permeable porous colloidal particles. / The standard electrokinetic equations are employed to model the flux of solvent and ions outside the porous particle. To be consistent with this approach, the flux of solvent and ions in the pores must also be governed by the standard electrokinetic equations. However, in practice, only transport phenomena on the particle scale are observed and it is sufficient for information regarding pore-scale behaviour to be retained purely in the form of averaged quantities. To complete the theoretical description, the standard electrokinetic equations outside the particle must be coupled to particle-scale transport equations inside the particle via boundary conditions at the porous/free-fluid interface. / It has been shown experimentally and theoretically for coupled Stokes and Darcy flows, that the correct interfacial boundary condition for the tangential external flow is given by the Beavers-Joseph-Saffman (BJS) condition. The effect of the BJS boundary condition on the hydrodynamic drag on an oscillating porous particle is investigated. It is found that the particle may be regarded as impermeable with a slip length independent of frequency, and the resulting drag is significantly reduced in comparison with an equivalent impermeable particle that does not exhibit a slip length. / The transport of a general electrolyte solution through a rigid porous body subjected to a static (d.c.) electric field is studied. The pore-scale description is given by the standard electrokinetic equations, including the effects of ion diffusion, electromigration and convection. Homogenization theory is used to derive transport equations that capture the particle-scale behaviour. It is proven that the transport coefficient tensors obey Onsager’s reciprocal relations and the diagonal coefficient tensors are positive definite. / New interfacial boundary conditions are derived using conservation arguments supplemented by Stern-layer theory. When combined with the particle-scale transport equations, these boundary conditions incorporate four principal effects into the standard electrokinetic model: solvent slip and Stern-layer ionic conduction at the interface, and macroscopic ionic conduction together with the electroosmotic flow of solvent through the particle. / The method of matched asymptotic expansions is then used to construct an approximate solution to the aforementioned system, in the thin double-layer limit. An expression for the electrophoretic mobility of a weakly permeable colloidal sphere is produced that consists of a generalization of Smoluchowski’s formula to encompass porous particles, and a next order correction. For the first time, the effects of solvent slip and Stern-layer ionic conduction within the porous/free-fluid interface, in conjunction with macroscopic ionic conduction and electroosmosis through the particle, are exhibited. It is shown that solvent slip at the porous interface is overwhelmingly the dominant effect on the mobility of weakly permeable porous colloidal particles.

Masters Research - Master of Philosophy (Engineering) / Thermal conduction properties are of major concern for those metal/ceramic composite materials having applications in semiconductor devices and electronic packaging materials. A higher thermal conductivity to coefficient of thermal expansion ratio is an advantage for such materials employed in electronic devices due to the subjective high thermal loads. It is well known that the shape, size and distribution of the insulating phase have an effect on the overall thermal conductivity properties. But the details are lacking and well deserving of study. Metal/ceramic oxide interfaces are important in the strengthening mechanisms of dispersion strengthened materials. Accordingly, considerable attention has been given to recent investigations of oxygen diffusion characteristics and the bonding mechanisms at such interfaces. Susceptibility to oxidation can be studied by analysing several thicknesses of material. As an example, studying a thin film and a semi-infinite material subjected to a high oxygen partial pressure environment and a vacuum condition would help to determine the oxidation (in-diffusion) and de-oxidation (out-diffusion) processes respectively. Since metal/ceramic internal interfaces play a very important role in controlling the mechanical, thermal and electrical properties, it is timely to consider these diffusion processes for detailed study. In this Thesis, the two areas mentioned above were selected for detailed investigation. The Thesis also addresses the further development of a method for solving complex phenomenological diffusion problems. This method makes use of lattice-based random walks of virtual particles, directed according to the Monte Carlo method (the Lattice Monte Carlo method) which is then used to address various mass and thermal diffusion processes. Chapter 2 is concerned with using this method to determine the thermal conductivity of model composites. In that chapter, the Lattice Monte Carlo method is used to calculate the effective thermal conductivity of several models of a composite, where inclusions are arranged in square planar and cubic arrangements with periodic boundary conditions. Excellent agreement is found of the effective thermal conductivity with the century-old Maxwell-Garnett Equation. Chapter 3 is concerned with a phenomenological representation of oxygen diffusion and segregation in a model composite based on Ag/MgO. The Lattice Monte Carlo method is employed to address mass diffusion in this composite. Square and randomly distributed multiple inclusions were considered as shapes of the MgO inclusion phase. The time-dependence of oxygen concentration depth profiles and contour maps were determined. First, oxygen in-diffusion is considered from a constant surface source solely into the Ag metal matrix: oxygen depth profiles were in excellent agreement with exact results. Next, oxygen in-diffusion/segregation is simulated in the composite by permitting and restricting the mobility of oxygen in different scenarios involving the Ag-MgO interface. The (higher temperature) out-diffusion of oxygen from the composite was also simulated and corresponding results obtained for the oxygen depth profiles. In both cases, very good agreement was found between the results from the Lattice Monte Carlo method and analytical expressions.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007. / Committee Chair: Mizaikoff, Boris; Committee Member: Bottomley, Lawrence; Committee Member: Hunt, William; Committee Member: Janata, Jiri; Committee Member: Josowicz, Miroslawa.

Progischrift--Amsterdam. / Includes bibliographical references.