The present study aims to increase understanding of the physical processes that govern thermoelectric efficiency in Na-containing group 14 type II clathrates. This has been achieved through structural characterization and physical property measurements. Local and electronic structures of Si clathrates with the formula NaxSi136, where x = 0, 1.3, 5.5, 7.2, 8.8, 14.1, 20 and 21.5 were studied using x-ray absorption spectroscopy. Thermoelectric properties, namely Seebeck coefficient, electrical conductivity and thermal conductivity were measured from 2.5 K to 400 K. Low Na content samples, x < 8, showed reduced thermal conductivity compared to the empty clathrate, x = 0. For x > 8, increased Na content led to increased charge transfer, increased thermal conductivity and decreased magnitude of Seebeck voltages. The heat capacities of the NaxSi136 materials were measured from 2.5 K to 300 K. Analysis of the heat capacity data showed that the vibrational modes associated with Na in the Si28 cages are of sufficiently low energies to interact with heat transporting acoustic phonons, leading to reduced thermal conductivity as x is increased up to ~ 8. Increasing Na content beyond x = 8 introduces Na into the Si20 cages. This stiffens the lattice, increasing (or maintaining) phononic contributions to thermal conductivity, and increasing electronic contributions. Electronic thermal conductivity is responsible for upwards of 50 % of heat conduction when x = 21.5. Na containing type II Ge clathrates were produced using an ionic liquid reaction medium. Seebeck coefficients observed in Na9Ge136 materials, were negative but larger in magnitude than those of the NaxSi136 materials and thermal conductivities of Na9Ge136 were lower than those of the NaxSi136 materials. While both Si and Ge type II clathrates showed modest figures of merit, with maximum ZT values of 2.5 × 10-6 and 2.8 × 10-5 observed in Na20Si136 and Na¬9Ge136, of the two framework elements, type II Ge clathrates have been shown to have more favourable thermoelectric properties.

The A2Mo3O12 family, where A3+ is a large trivalent cation, can show interesting thermal properties such as negative thermal expansion, also known as thermomiotic behavior, where the overall volume of the material contracts with increasing temperature. A selection of compounds in this family, namely HfMgMo3O12, In2Mo3O12, Y2Mo3O12, Al2Mo3O12, In(HfMg)0.5Mo3O12, and In1.5(HfMg)0.25Mo3O12, have been synthesized using solid-state and mechanical activation techniques as well as a simplified sol-gel approach (Al2Mo3O12). Coefficients of thermal expansion were found to range from large-negative to low-positive in the orthorhombic phase, including near-zero in In(HfMg)0.5Mo3O12 and In1.5(HfMg)0.25Mo3O12. This set of materials provided insight into the role of low-frequency phonon modes in open-framework materials. Low-temperature heat capacity and thermal conductivity measurements confirmed that low-frequency modes were active in thermomiotic materials, and also present to some extent in all members of the open-framework A2Mo3O12 family examined. A clear correlation exists between the magnitude and sign of the coefficient of thermal expansion in the orthorhombic phase and the contribution of low-energy modes to the low-temperature heat capacity, with negative thermal expansion materials having a larger contribution. The low-frequency phonon modes result in low thermal conductivity and reduced phonon mean free paths when compared to conventional ceramics and indicate that these low values are characteristic of open-framework materials in NTE families even if the materials in the families are not thermomiotic themselves.

The objective of this research was to design aluminum powder metallurgy (PM) alloys and processing strategies that yielded sintered products with thermal properties that rivaled those of the cast and wrought aluminum alloys traditionally employed in heat sink manufacture. Research has emphasized PM alloys within the Al-Mg-Sn system. In one sub-theme of research the general processing response of each PM alloy was investigated through a combination of sintering trials, sintered density measurements, and microstructural assessments. In a second, the thermal properties of sintered products were studied. Thermal conductivity was first determined using a calculated approach through discrete measurements of specific heat capacity, thermal diffusivity and density and subsequently verified using a transient plane source technique on larger specimens. Experimental PM alloys achieved >99% theoretical density and exhibited thermal conductivity that ranged from 179 Wm-1K-1 to 225 Wm-1K-1. Thermal performance was largely dominated by the amount of magnesium present within the aluminum grains and in turn, bulk alloy chemistry. Data confirmed that the novel PM alloys were highly competitive with even the most advanced heat sink materials such as wrought 6063 and 6061. Two methods of thermal analysis were employed in order to determine the thermal conductivity of each alloy. This first consisted of individual analysis of the specific heat capacity (Cp), thermal diffusivity (?) and density (?) as a function of temperature for each alloy. The thermal conductivity (K) was subsequently determined through the relationship: K=C_p ??. The second means of thermal analysis was a direct thermal conductivity measure using a transient plane source (TPS). The thermal diffusivity and density of samples were both found to decrease with temperature in a linear fashion. Conversely, the specific heat capacity was found to increase with temperature. The only measured thermal property that appeared to be influenced by the alloy chemistry was the thermal diffusivity (and subsequently the calculated thermal conductivity). Both means of thermal analysis showed high thermal conductivity in alloys with low concentrations of magnesium, demonstrating the significance of having alloying elements in solid solution with aluminum. Overall, several alloys were developed using a press and sinter approach that produced higher levels of thermal conductivity than conventional aluminum heat sink materials. The highest thermal conductivity was achieved by alloy Al-0.6Mg-1.5Sn with a calculated value of 225.4 Wm-1K-1. This novel aluminum PM alloy was found to exceed both wrought 6061 and 6063 (195 and 217 Wm-1K-1 respectively). Furthermore, PM alloy Al-0.6Mg-1.5Sn was found to have a significant advantage over die-cast A390 (142 Wm-1K-1).

The results of photoluminescence (PL) spectra of TlGaS2 single crystal were reported in the 500-1400 nm wavelength and in the 15-115 K temperature range. Three broad PL bands with an asymmetric Gaussian lineshapes were observed to be centered at 568 nm (A-band), 718 nm (B-band) and 1102 nm (C-band). The shift of the emission band peak energy as well as the change of the half-width of the emission band with temperature and excitation laser intensity were also studied. We analyzed the observed results using the configurational coordinate (CC) model. The powder diffraction patterns of TlInS2 and TlGaS2 crystals were obtained and the diffraction data were indexed using CRYSFIRE computer program packet. TlInS2 has hexagonal system with parameters a = 3.83 and c = 14.88 Ao. TlGaS2 has monoclinic system with parameters a = 9.62, b = 4.01 and c = 7.52 Ao with &amp / #946 / = 96.30o. Our diffraction studies at low temperatures did not reveal any phase transition for TlInS2 as reported in the literature. The specific heat capacities of both TlInS2 and TlGaS2 crystals calculated from Differential Scanning Calorimetry (DSC) measurements at low temperatures are reported in the thesis.

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.

This thesis deals with certain aspects of the solution chemistry of the simple dicarboxylate anions: oxalate, malonate and succinate, up to high concentrations. These ions are either significant impurities in the concentrated alkaline aluminate solutions used in the Bayer process for the purification of alumina, or are useful models for degraded organic matter in industrial Bayer liquors. Such impurities are known to have important effects on the operation of the Bayer process. To develop a better understanding of the speciation of oxalate (the major organic impurity in Bayer liquors) in concentrated electrolyte solutions, the formation constant (Log£]) of the extremely weak ion pair formed between sodium (Na+) and oxalate (Ox2ƒ{) ions was determined at 25 oC as a function if ionic strength in TMACl media by titration using a Na+ ion selective electrode. Attempts to measure this constant in CsCl media were unsuccessful probably because of competition for Ox2ƒ{ by Cs+. Aqueous solutions of sodium malonate (Na2Mal) and sodium succinate (Na2Suc) were studied up to high (saturation) concentrations at 25 oC by dielectric relaxation spectroscopy (DRS) over the approximate frequency range 0.1 „T £h/GHz „T 89. To complement a previous study of Na2Ox, formation constants of the Na+-dicarboxylate ion pairs were determined and they were shown to be of the solvent-shared type. Both the Mal2ƒ{ and Suc2ƒ{ ions, in contrast to Ox2ƒ{, were also shown to possess large secondary hydration shells Apparent molal volumes (Vf) and heat capacities at constant pressure (Cpf) of aqueous solutions of Na2Ox, Na2Suc, Na2Mal and K2Ox were determined at 25 oC up to their saturation limits using vibrating tube densitometry and flow calorimetry. These data were fitted using a Pitzer model. The adherence of Vf and Cpf of various Na+ and K+ salts to Young¡¦s rule was examined up to high concentrations using the present and literature data. Young¡¦s rule was then used to estimate hypothetical values of Cpf and Vf for the sparingly soluble Na2Ox at high ionic strengths, which are required for the thermodynamic modelling of Bayer liquors. The solubility of Na2Ox in various concentrated electrolytes was measured, at temperatures from 25 oC to 70 oC in media both with (NaCl, NaClO4, NaOH) and without a common ion (KCl, CsCl, TMACl). The common ion effect was found to dominate the solubility of Na2Ox. The solubility of calcium oxalate monohydrate (CaOx„ªH2O) was also determined. The solubilities of both Na2Ox and CaOx„ªH2O in media without a common ion increased with increasing electrolyte concentration, except in TMACl media, where they decreased. The solubility of Na2Ox was modelled using a Pitzer model assuming the Pitzer parameters for Na2SO4 and minimising the free energy of the system. The data were modelled successfully over the full concentration and temperature range of all the electrolytes, including ternary (mixed electrolyte) solutions.

Orientador: Marcio Francisco Colombo / Banca: Flávio Augusto Vicente Seixas / Banca: Richard John Ward / Banca: Gustavo Orlando Bonilla-Rodriguez / Banca: Marinômio Cornélio Lopes / Resumo: A hemoglobina (Hb) e uma proteina tetramerica cuja principal funcao e o transporte de oxigenio. As moleculas de O2 se ligam cooperativamente a proteina, com afinidade crescente com a saturacao. O favorecimento a energia de ligacao se deve a mudanca da estrutura quaternaria da proteina, ou seja, da conformacao T de baixa afinidade para a conformacao R de alta afinidade, induzida pela ligacao do ligante. Decorrente desta mudanca conformacional ha um aumento da area de superficie proteica acessivel ao solvente (ASA), na transicao do estado totalmente desoxigenado (T) para o estado totalmente oxigenado (R). Esta variacao de ASA pode ser medida, em solucao, utilizando-se o metodo de estresse osmotico (COLOMBO et al., 1992). Neste trabalho, determinamos o numero de moleculas de agua ( nw) que se liga a diferentes especies de Hb na transicao desoxiHboxiHb. Este valor varia de especie para especie, e dentro de cada especie e maior na presenca de NaCl do que na ausencia deste sal. A ligacao preferencial do anion cloreto a conformacao T da Hb altera sua estrutura terciaria, o que reflete em mudancas no valor de nw de oxigenacao medidos na ausencia e na presenca deste anion. Como referenciado, os valores de nw de oxigenacao foram determinados em solucao pelo metodo de estresse osmotico, isto e, a partir da determinacao da dependencia de P50 com a atividade de agua (aw). Mostramos que diferentes especies de Hb, em diferentes condicoes de solucao, alem de terem valores de nw de oxigenacao distintos, apresentam valores diferentes de H de oxigenacao ( Hobservado). Os valores de nw e de Hobservado, determinados para as especies de Hb Equina adulta (HbEq), Bovina adulta (HbBovad) e fetal (HbBovfet) em diferentes condicoes experimentais, em conjunto com valores de nw e Hobservado para as hemoglobinas das especies Humana (HbA0) e do molusco Scapharca inaequivalvis (HbI)...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Hemoglobin (Hb) is a tetrameric protein whose main function is oxygen transport. Four O2 molecules bind cooperatively to the protein. The cooperative stepwise increasing in O2-affinity with protein saturation is bound to the change in the protein's quaternary structure from the low O2- affinity conformation (T-state) to the high O2-affinity conformation (R-state) induced by ligand binding. Upon the T'R transition, the water accessible surface area (ASA) of the protein increase, with a consequent binding of extra water molecules to the protein. The change in hydration associated with the ASA can be determined in solution using the osmotic stress method (COLOMBO et al., 1992). In this work, we determined the number of water molecules ( nw) that bind to different Hb specie in the T'R transition. This value changes from specie to specie, and is larger in presence of NaCl than in absence for all specie. In this work we had also determined the enthalpy change of Hb oxygenation ( Hobs) for the different specie and at varied conditions where the value of nw of oxygenation were observed to vary. nw and Hobs values determined for the Equine adult (HbEq), Bovine adult (HbBovad) and fetal (HbBovfet) Hb in different experimental conditions, and nw and Hobs values previously determined for Human (HbA0) and for the mollusk Scapharca inaequivalvis (HbI) hemoglobins, we correlated and analyzed in order to determine the enthalpy and entropy changes associated with the binding of extra water molecules to the newly exposed protein surface upon oxygenation. We have found that 'ÂHsol, the heat change of protein hydration, is approximately -0,57Kcal/mol.H2O. This parameter represents the enthalpic cost of protein hydration in aqueous solution. The entropic cost, ÂSsol, was estimated as approximately -2,89cal/mol.K.H2O. At 298K, the free energy...(Complete abstract click electronic access below) / Doutor

This master thesis deals with characterization of two black and white products based on ethylene-propylene-diene rubber (EPDM) used for skating rink. Products marked with A and are different in their diameter of circular tubes trough which cooling medium passes and also in the distance of these tubes. Both of materials were characterized in order to determine whether it is the EPDM and how are they different. The characterization methods were used: differential scanning calorimetry, thermogravimetric analysis, attenuated total reflectance Fourier transform infrared spectroscopy, tensile test, swelling test, thermooxidative test. The composition of both materials, including fillers and others additives is almost the same but difference is in structure of EPDM and probably also in interaction with fillers, what exhibits different mechanical properties, thermooxidative stability and thermal capacity. These differences which have been found are essential for long-term use properties of both materials.

Target of the master´ thesis is a design of heat exchanger air-water with the air flowing inside the pipes and with staggered pipe configuration, based on the engaged and chosen values. Next target is to determine heat exchanger with cross parallel flow and cross countercurrent flow of mediums, pressure drop on both sides air and water and dimensions of intake and outgoing gate on both sides air and water.

Title: Magnetic excitations in cerium compounds Author: Kristina Vlášková Department: Department of Condensed Matter Physic Supervisor: doc. Mgr Pavel Javorský, Dr., Department of Condensed Matter Physics Abstract: Thanks to presence of only one electron in 4f shell of cerium ion, Ce based compounds reveal wide range of exceptional magnetic properties like valence fluctuations, magnetic ordering or spin glass behavior. In present thesis we mainly focus on tetragonal CeCuxAl4-x system and its magnetic behavior. Former results of inelastic neutron experiments opened discussion about energy levels of cerium ions in CeCuAl3. Except two crystal field excitations also one additional energy level was present, phenomenon of vibron quasi-bound state was proposed to explain observed energy structure. Measurement and analysis of specific heat and neutron inelastic scattering on compounds with various Cu content should help to understand phenomenon of vibron state and also its development with Cu/Al concentration. Another two types of cerium compounds will be investigated in means of specific heat and resistivity measurement, polycrystalline sample of CePt4Al and single crystal of Ce3Ru4Al12. Preparation, characterization and measurement of low temperature properties are subjects of this work. Results will be discussed...