Thermoelectric materials are the only known materials capable of direct conversion of a heat gradient into electricity (Seebeck effect) or vice-versa (Peltier effect). Thermoelectric (TE) devices are comprised of solid-state p-type and n-type semiconductors paired in an electrical circuit and exposed to a temperature gradient. The effectiveness of the materials is evaluated based on the mathematical term ZT=T∙S^2 σ/κ: S represents the Seebeck coefficient; σ represents the electrical conductivity; κ is the thermal conductivity; and T is the average of the coldest and hottest regions of the applied gradient. This ZT term is larger for better materials; most modern devices in use to-date display ZT values on the order of one. A large temperature gradient combined with a large Z term will lead to a high-performance TE material that involves no waste, no side product, and no requirement for moving parts. Discovery and optimization of new thermoelectric materials is a critical component of current thermoelectric research. As such, researchers are constantly searching for a new material that has the following properties: the ability to withstand higher temperatures, thus maximizing the T term; exhibit a large Seebeck coefficient and electrical conductivity through doping techniques; and present minimal thermal conductivity, κ. In recent years, research attention has moved from S^2σ to κ, which can be optimized through a variety of techniques including complex crystal structure, heavy element inclusion, and introduction of structural defects such as nanodomains/nanostructuring. Due to their tendency to form complex crystal structures and bonding, Te-based materials have become popular targets for TE research and optimization. Compounds with Te anions that also include other heavy elements such as alkali (A) metals, alkaline earth (R) elements, or heavy p-block elements including the triels (Tr), tetrels (Tt), or pnictogens (Pn) have become a principal source of new and ground-breaking thermoelectric materials. Likewise, optimization of existing TE materials with these aforementioned compositions has led to ZT values twice those of the materials' original reports. Of the known TE materials, Bi2Te3 is one of the staples in the field. It shows narrow band-gap semiconducting properties that can be tuned to p- or n-type values based on the impurities introduced, and its κ values are inherently low due to the presence of heavy elements and their structural layering motifs. A series of compounds, (SnTe)x(Bi2Te3)y, based on this idea can be produced via the alteration of x:y. In this work, several of these compounds are introduced and studied as potentially useful thermoelectric materials: SnBi2Te4, SnBi4Te7, and SnBi6Te10 are the major targets because of their systematic layering motifs and complex structures. Phase range studies, crystal structure (Rietveld) refinements, and synthesis optimizations were commenced to ensure that the materials were well-characterized and produced phase-pure before the attempted ZT improvements. By altering the quantity of active charge carriers in these systems, changes in ZT can be observed – this is achieved through doping with, primarily, heavy Tr elements Ga, In, and Tl. Thusly, the physical properties are measured and compared for a number of series: [Tr]xSn1-xBi2Te4, [Tr]xSnBi2-xTe4, [Tr]xSn1-xBi4Te7, [Tr]xSnBi4-xTe7, [Tr]xSn1 xBi6Te10, and [Tr]xSnBi6-xTe10. Of the triels, Tl is the largest useful element in the group and is known for showing both Tl+ and Tl3+ cationic states and, in thermoelectric applications, for possessing uniquely low κ values. Thallium telluride compounds such as Tl5Te3 are therefore quite relevant to this field. The family of compounds includes Tl9BiTe6 – one of the better materials with ZT = 1.2 (500 K) using a hot-pressed pellet. Herein, the system is expanded to include Tl10-xSnxTe6 which shows good TE potential with ZT(Tl7.8Sn2.2Te6) = 0.6 (617 K) with a cold-pressed pellet. The incorporation of tetrel elements is investigated through measurements on Tl10-x-ySnxBiyTe6 and also applies to the lesser-studied Tl9SbTe6 compound via research on the systems Tl9SnxSb1 xTe6 and Tl9PbxSb1 xTe6. Tl is studied in three concentrations with Tl10 x ySnxBiyTe6: Tl9…, Tl8.67…, and Tl8.33…, with varying Sn:Bi at each increment. Tt elements are systematically added to the Tl9[Tt]xSb1 xTe6 structure with 0.0 ≤ x ≤ 0.7. Crystallographic studies, electronic structure calculations, and physical properties are explored for each series. Due to Te’s ability to form complex Te–Te interactions in certain environments, the combination of alkaline earth metals, namely R = Ba, with the coinage metals (Cg = Cu, Ag), chalcogenides (Q = S, Se), and Te, form a plethora of previously unknown crystal structures. Many of these are Zintl-phase narrow-band gap semiconductors with complex Cg–Cg and Q–Q bonding schemes – combined with their heavy element incorporation, the family is of great interest to the thermoelectrics community. Within this thesis, three new crystal systems are presented: Ba3Cu17-x(Se,Te)11; Ba3Cu17-x(S,Te)11 and Ba3Cu17-x(S,Te)11.5; and Ba2Cu7-xTe6. All structures show Cu-deficiencies in their crystal structures with d10–d10 interactions and 3-dimensional networks of the Cg metal. The chalcogenide elements in the structures display unique Q–Q or Te–Te bonding of varying dimensionality. The electronic structures and bonding calculations are reported for each compound, as are the single crystal studies. The first two of the aforementioned compounds are narrow-band gap semiconductors, whereas the latter two display metallic behaviour.

Winter cropping often does not realise its full potential in south-western Victoria, where waterlogging is a major problem on the poorly drained soils of conventional cultivation (CC) systems. Consequently, cropping has been undertaken on raised beds (RB) to reduce the risk of waterlogging. Initial reports on the yields of RB were encouraging. It was hypothesized that an improvement in soil properties of RB may account for their better performance compared to CC systems. / The aim of the thesis was to evaluate selected soil physical properties of RB and to make comparisons with other treatments (CC and pasture). The specific objectives were to: 1) evaluate plant growth and crop yield; 2) quantify soil water dynamics; 3) assess changes in the soil water retention characteristic (SWRC), soil strength and soil hydraulic properties; 4) describe pore pathways from solute transport; and 5) quantify soil macropore structure. / Measurements of volumetric water content (θv) were taken at 20, 40, 60 and 80 cm and at the soil surface. These data allowed the determination of the profile soil water deficit (SWD), which was found to be greater under the RB than the CC, although at times the pasture had the largest SWD. The RB mostly remained drier than the CC, but the response to rainfall in the surface θv was similar between treatments. Below average rainfall was received during the whole study period which resulted in drier than normal conditions. / There was no consistent difference in plant growth between crops on the RB and CC; e.g. in 2004 periods of waterlogging resulted in greater dry matter production on the RB; while drier conditions in 2003 saw better crop growth on the CC. Grain yield varied annually according to rainfall, and overall the treatment yields were similar. Analysis of regional yield data showed that there was no yield difference in years with average or below average rainfall, but years with higher rainfall favoured RB. / Little difference was found in the laboratory-derived SWRC, but in the field the RB were consistently drier at all depths and at 60 cm depth the CC had a saturated zone. The RB were found to have a lower soil strength characteristic within the surface 24 cm compared to the CC. The air-filled porosity (AFP) was higher in the RB while for long periods the CC were <10 per cent AFP. There was no significant difference between the treatments in unsaturated hydraulic conductivity (Kus) in the soil surface. Saturated hydraulic conductivity (Ks) in the subsoil was very small, although the RB had significantly greater Ks than the CC. / A solute transport experiment investigated the movement of a solute in large soil cores of the RB and CC treatments. Derived parameters from a transfer function model were used to assess the solute transport characteristics. This showed that under nearly saturated conditions the CC had significantly greater solute spreading than the RB. Furthermore, the transport volume (θst) to θv ratio was smaller in the RB which indicated a greater proportion of preferential flow. These and other data suggested that the RB had a better connected and more stable pore network. / Soil macropore structure was quantified using image analysis of resin-impregnated soil. Samples were taken twice; the first samples showed that the RB had improved pore connectivity, slightly greater porosity and a pore network with smaller sized pore components than the CC. In comparison, at the second sampling time the structural parameters of the two treatments were similar. / Uncertainty exists in the scenario of higher rainfall or of the longer-term changes of soil properties under RB cropping. Nevertheless after three years of measurements, this thesis concludes that most soil physical properties of RB are distinctly better for cropping than under CC systems.

Magister Scientiae - MSc (Physics) / Rare-earth intermetallic compounds continue to draw considerable attention, due to their fundamental importance in understanding physical properties and potential applications based on a variety of phenomena. The focus of this project is to employ two family of rare-earth intermetallic compounds: RE2Pt2In (RE = Pr, Nd) and RE8Pd24Ga (RE = Gd, Tb, Dy) ternary intermetallic systems as a model candidate to uncover the underlying ground state properties that result in a strong coupling between the conduction electron and the 4f-electron of the rare-earth ions.

Orientador: Edson Alves de Campos / Resumo: O objetivo deste estudo é investigar e comparar, por meio de três diferentes protocolos de pesquisa, o comportamento de diferentes materiais cerâmicos utilizados para fabricação de restaurações em CAD/CAM. No Estudo 1, o objetivo foi determinar quais dos materiais possui a melhor usinabilidade, ou seja, a facilidade de corte. Os blocos para CAD/CAM selecionados foram: IPS e.max CAD, IPS Empress CAD, Vitablocs Mark II e LAVA Ultimate, estes cortados em uma máquina de corte (Isomet 4000, Buehler, Lake Bluff, IL, USA) e levados ao microdurômetro. Através das medidas da identação e trincas geradas pela leitura, foi determinado qual dos materiais utilizados em restaurações de CAD/CAM possui a melhor usinabilidade por meio do cálculo do índice de fragilidade. O LAVA Ultimate apresentou a melhor usinabilidade seguido pelo IPS Empress CAD. O IPS e.max CAD e o Vitablocs Mark II não apresentaram diferenças estatisticamente significantes. Para os estudos 2 e 3 os materiais selecionados foram IPS e.max CAD, Vitablocs Mark II, LAVA Ultimate e Enamic. No Estudo 2, o objetivo foi determinar qual dos materiais possui maior resistência à fratura após serem submetidos a diversas condições de termociclagem. Os blocos de cerâmicas de CAD/CAM foram cortados em várias fases até atingirem as dimensões finais de 14mm x 3mm x 2,5mm, no formato de barra, foram confeccionados um total de 144 corpos de prova. A resistência à fratura foi determinada por meio do teste de três pontos com um entalhe realiza... (Resumo completo, clicar acesso eletrônico abaixo) / The aim of this study was to investigate and compare, through three different research protocols, the behavior of different ceramic materials used to manufacture CAD/CAM restorations. In Study 1, the objective was to determine which material has better machinability, i.e., ease of cutting. The blocks for CAD/CAM selected were: IPS e.max CAD IPS Empress CAD, VITABLOCS Mark II and LAVA Ultimate, these were cut on a cutting machine and taken to microhardness. From the measurements of the indentation and crack generated by the readings was determined which of the materials used for CAD/CAM restorations has the better machinability by calculating the Brittleness index. The LAVA Ultimate showed the best machinability followed by IPS Empress CAD. The IPS e.max CAD and VITABLOCS Mark II showed no statistically significant differences. For studies 2 and 3 the selected materials were IPS e.max CAD, VITABLOCS Mark II, LAVA Ultimate and Enamic. In Study 2, the goal was to determine which of the materials have greater fracture toughness after being subjected to various conditions of thermal cycling. Ceramic CAD/CAM blocks were cut in several stages until got the final dimensions of 14mm x 3mm x 2.5mm on bar formats, in total 144 specimens were made. The fracture toughness was determined by the three-point bending test with a notch made in the specimens. Later fractures were analyzed in scanning electron microscope and classified how the fractures occurred. The best performance was shown by the IPS e.max CAD material, where a statistically significant increase was observed after 120,000 cycles term. The LAVA Ultimate and Enamic materials showed reduction in their fracture toughness after thermal cycling. In Study 3, the objective was to determine the best performance among the materials on flexural strength and flexural modulus. The specimens had the same measures of the study 2, but without the notch...(Complete electronic access below) / Doutor

This study examines the effects of cryogenic temperatures on the mechanical properties of carbon, aramid, and poly(p-phenylene-2, 6-benzobisoxazole) (PBO) fibers. Although the mechanical properties are documented for these fibers at ambient and elevated temperatures, there is an absence of data in the open literature for how these fibers behave at very low temperatures. To evaluate the mechanical properties, the ASTM standard method for testing at ambient temperature was used as a baseline. The low temperature tests were conducted inside a double walled cryogenic chamber to evaluate the fiber performance at 100K. Fiber properties at low temperatures displayed differences from room temperature properties in the form of increased ultimate tensile strength (UTS), decreased in elongation to failure, and increased Young’s Modulus. The change in properties due to the effect of temperature was more pronounced in fibers with a higher degree of crystallinity.

<p dir="ltr">Adhesives surround us on a daily basis without us even being aware. They are the unsung heroes of most commercial products we use. Whether it be the car you drive, the shoes you wear, or the furniture you sit on, glue is keeping everything together. Adhesives have been used since the cavemen utilizing tar for keeping stone tools together. Over time, adhesives have exploded in the scientific landscape through a multitude of chemical pathways. Current products are comprised of epoxies, cyanoacrylates, polyurethanes, and many others. The need for adhesives in the manufacturing of products is consistently increasing over the years in the goal of light weighting without compromising on performance of the final material. However, this comes at the cost of glues being both toxic and nonrecyclable. With this in mind an improvement was needed to address both augmenting the glue strength and improving the sustainability of the adhesive.</p><p dir="ltr">Hierarchical structures can be observed on the micro scale in natural materials. Tree limbs are able to withstand a tremendous amount of force applied from winds, human machinery, and animal life. Why they are so resistant lies in the fact there is an ordered structure of multiple length scales working in tandem upholding the integrity of the limb. The question to ask then relating this to adhesives is if there is a way to create a glue that can disperse the forces amongst the overall material without catastrophic failure. The use of fillers such as calcium carbonate and different adhesive strain rates can be used to mimic this interaction.</p><p dir="ltr">Addressing the sustainability factor of current glues, the need was set to create a more bio-based alternative using widely available materials that are cost effective and do not compromise on overall performance. Competing with or outperforming the current market adhesives was a goal in mind. Two generations of bio-based adhesives were generated through multiple formulations using epoxidized soybean oil as the common factor. Soybean oil is one of the most widely produced vegetable oils in the country. Utilizing the oil in a functionalized way through epoxide rings, the replacement of current epoxy technology was achieved.</p>

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