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.

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.

Masters of Science / Rare-earth (RE) compounds have been an attractive subject, based on the unique electronic structures of the rare-earth elements. In particular, the RETX (RE = rare-earth, T = 3d/4d/5d, transition metals, and X = p – block elements) series is a large family of intermetallic compounds which crystallizes in different crystal structure depending on the constituents. Most of these compounds crystalize in the hexagonal, orthorhombic, and tetragonal crystal structure. On the other hand, the family of compounds RET2X2 adopted the tetragonal crystal structure of the ThCr2Si2 or the CaBe2Be2 with different space groups. Owing to the different crystal structure, these compounds show versatile magnetic and electrical properties such as Kondo effect, complex magnetic behaviour, valence fluctuation, unconventional and conventional superconductivity, heavy fermion behaviour, Fermi and non – Fermi liquid behaviour, metamagnetism, spin – glass, memory effect, crystal electric field (CEF), magnetoresistance and magnetocaloric effect. The history of magnetism reveals that it is closely related to practical applications and magnetic materials from the most vital components in many applications. These are memory devices, permanent magnets, transformer cores, magneto-mechanical devices and magneto-electronic devices. Recent additions to this list include magnetic refrigeration through the studies of magnetocaloric effect as well as spintronics. Magnetic refrigeration (MR) is an emerging technology and shows real potential to enter conventional markets and the principles of MR obeys the magnetocaloric effect (MCE), which is based on the effect caused by a magnetic field on the materials that accept the property of varying the magnetic entropy, as well as its temperature when varying the magnetic field. In this thesis, we report giant magnetocaloric effect and magnetic properties of NdPd2Al2 and RECuGa (RE = Nd, Dy, and Ho) compounds. These investigations were done through measurements of X – ray diffraction (XRD), magnetic susceptibility, ((T)), magnetization, (M(H)), isothermal magnetization, (M(H, T)), heat capacity, (Cp(T)) and electrical resistivity, ((T)). MCE has been studied from the isothermal magnetization and heat capacity measurements.The first chapter of the thesis describes the theoretical background from which the experimental results have been analyzed and interpreted. This is followed by the chapter which presents experimental details and methodology carried out in this thesis. Chapter three presents the results and discussion of the transport, magnetic and magnetocaloric properties of NdPd2Al2 compounds. XRD studies confirm the tetragonal CaBe2Ge2 – type structure with space group P4/nmm (No. 129). The results of (T), (T) and Cp(T) indicate a putative antiferromagnetic (AFM) phase transition at low temperature at, TN = 3 K. On the other hand, (T) data at high temperatures follow the Curie – Weiss relationship giving an effective magnetic moment close to that expected for the trivalent Nd3+ ion. The magnetization results indicate metamagnetic – like transition at a low field that bears a first-order character which corroborates with the Below – Arrott plots. Giant MCE was obtained for the NdPd2Al2 compound similar to those reported for potential magnetic refrigerant materials. Chapter four discusses the magnetic and thermodynamic properties of the series of compounds RECuGa where RE = Nd, Dy, and Ho. XRD studies indicate the orthorhombic CeCu2 – type crystal structure with space group Imma (No. 74) for all three compounds. Magnetic measurements indicate a putative AFM phase transition below 𝑇𝑁 = 7.1, 8.5, and 3.7 K for Nd, Dy, and Ho compounds, respectively. The high-temperature (T) data for all three compounds follow the Curie – Weiss relationship giving an effective magnetic moment close to that expected for the trivalent rare-earth ion. Again, large MCE were obtained for all three compounds similar to those reported for materials that can be used as magnetic refrigerant materials.

The thermodynamics of disorder have been studied for hundreds of years, with physicists using entropy to quantitatively connect the macroscopic properties of a system to its microscopic multiplicity (disorder). Here, we consider the effect of disorder in magnetic materials. The pyrochlore oxides (A2B2O7), comprised of a bipartite lattice of corner-sharing tetrahedra, have been central to the study of geometric frustration for the past several decades. Pyrochlores, in which the A-site is occupied by the magnetic cation dysprosium, tend to exhibit spin ice ordering down to low temperatures, in spite of chemical perturbations to the B-site lattice. With the motivation of this study being the investigation of how adding B-site disorder to the traditional Dy2ScNbO7 form of Dy-pyrochlores, a stoichiometric mixture of Sc-3+ and Nb-5+ was used to synthesize Dy2ScNbO7, the pyrochlore material that is central to this thesis work. We show using magnetometry, heat capacity, muon spin relaxation, and inelastic neutron scattering that the mixed B-site pyrochlore Dy2ScNbO7, does not adopt the spin ice ground state. The low temperature spin dynamics are much faster than other analogous dysprosium pyrochlores, the residual entropy is significantly smaller than that predicted for a spin ice and there are low-lying crystal field excitations. These results all indicate that the B-site disorder appears to destroy the predicted Ising anisotropy of dysprosium. / Thesis / Master of Science (MSc)

No description available.

A small-scale adiabatic calorimeter has been constructed as part of a larger project to study nano-particles and to facilitate specific heat measurements on samples where it is difficult to obtain enough material to run on the current large-scale adiabatic apparatus. This calorimeter is designed to measure sample sizes of less than 0.8 cc over a temperature range from 13 K to 350 K. Specific heat results on copper, sapphire, and benzoic acid show the accuracy of the measurements to be better than ±0.4% for temperatures higher than 50 K. The reproducibility of these measurements is generally better than ±0.25%. Experimental specific heat data was collected on this new apparatus for synthetic akaganeite, β-FeOOH, for samples with varying degrees of hydration. Our results yield values for Δ_0^298.15S°m of 79.94 ±0.20 J•K^-1•mol^-1 and 85.33 ±0.021 J•K^-1•mol^-1 for samples of β-FeOOH0.551H2O and β-FeOOH0.652H2O, respectively. From this data, we were able to determine the standard molar entropy for bare β-FeOOH, as Δ_0^298.15S°m = 53.8 ±3.3 J•K^-1•mol^-1, based on subtractions of the estimated contribution of water from the hydrated species. Additionally, the specific heats of α-uranium, titanium diboride, and lithium flouride have been measured on a low-temperature, semi-adiabatic calorimeter down to 0.5 K. For the α-uranium, the specific heat of a polycrystalline sample was compared to that of a single crystal, and it was found that there was a significant difference in the specific heats, which has been attributed to microstrain in the polycrystal. The third law entropy for the polycrystal at 298.15 K, Δ_0^298.15S°m, calculated from these heat capacities is 50.21 ±0.1 J•K^-1•mol^-1, which is good in agreement with previously published values of polycrystal samples. For the single crystal Δ_0^298.15S°m, calculated using the thermodynamic microstrain model, is 49.02 ±0.2 J•K^-1•mol^-1. The low-temperature specific heats of titanium diboride and lithium fluoride have been measured from 0.5 K to 30 K as part of a larger project in the construction of a neutron spectrometer. For this application, the measured specific heats were used to extrapolate the specific heats down to 0.1 K with lattice, electronic, and Schottky equations for the respective samples. The resultant specific heat values at 0.1 K for TiB2 and 6LiF are 4.08E-4 ±0.27E-4 J•K^-1•mol^-1 and 9.19E-9 ±0.15E-9 J•K^-1•mol^-1, respectively.

Adiabatic calorimetry provides accurate and precise specific heat (Cp) data. From this data, thermodynamic functions may be calculated. Cu2OCl2, melanothallite, became of interest as part of a study of a particular thermochemical cycle. The experimental specific heat data and the calculated thermodynamic functions are reported here. Free energies of formation, calculated from the thermodynamic functions, suggest the particular cycle of interest with this compound as an intermediate is not feasible; uncertainty as to the accuracy of CuO and CuCl2 data used in the calculations indicate further study may be necessary. Upon collection of the specific heat data, an antiferromagnetic transition was observed at 70 K; this led to examination of the magnetic heat capacity and entropy of the transition in melanothallite. The entropy of the transition was estimated to be 18.1 % and 7.5 % of 2Rln2 by two methods. A theoretical calculation using an Ising model produced a result of 39 %. This is consistently low when compared to the entropies of the antiferromagnetic transitions of CuO and CuCl2. This suggests geometric frustration. This thesis reports the thermodynamic functions calculated from the specific heat; the examination of the magnetic entropy; and repairs to an adiabatic apparatus involved in the collection of this data.

Resistance spot welding is the main welding method used in the automotive industry to weld thin sheet metal. Today adaptive control systems have been developed for RSW, which means it can adjust the parameters in the weld process automatically during welding. The control systems can register the parameters and properties of the weld in real-time and from that calculate with algorithms how to adjust to give optimal weld conditions. This project is performed at Scania CV AB, Oskarshamn. Conducted in the part of body in white, where an adaptive control system called HCC is used in all weld processes. In this project, HCC was compared to the fixed control system CCR and another adaptive control system named Master mode. First step in the comparison was to create a weld schedule for each control system and test them on two different material combinations. The aim was to quantify gains and benefits that adaptive resistance spot welding systems have on the welding process. Benefits are quantified by examining the parameters and factors such as: weld time, expulsion, robustness, electrode wear and parameters in the control system. The tests were performed by welding as many approved spot welds as possible without tip-dressing the electrode. The experiment followed the requirements from international standards and the Scania standard for resistance spot welding.  The results from the experiment showed that HCC was the most robust process and the spot welds never decreased in size, which CCR and Master mode did. It is possible to weld several different material combinations with HCC, it increases flexibility in production and reduces the time needed to develop new weld schedules. The same schedule can handle many combinations with the same thickness. HCC allows the process to use several pulses and each pulse adds in time. Therefore, the weld schedule should be well developed and optimized to avoid waste in terms of long weld times. The results will give Scania knowledge about the processes and how to further optimize the welding processes in production. The result can also be used as foundation for selection of products or future investments. / Motståndspunktsvetsning är den huvudsakliga svetsmetoden som används inom fordonsindustrin för att svetsa tunn plåt. Idag har adaptiva styrsystem utvecklats för RSW vilket innebär att de automatiskt kan justera parametrarna i svetsprocessen under svetsning. Styrsystemen kan registrera parametrarna och egenskaperna hos svetsen i realtid och därmed beräkna med algoritmer hur de bör justeras för att ge optimala svetsförhållanden. Detta projekt är resultatet av ett examensarbete på Scania CV AB, Oskarshamn. Det utfördes i den nya karossfabriken, där ett adaptivt styrsystem som heter HCC används i alla svetsprocesser. I projektet jämfördes HCC med ett konstantströms styrsystem CCR samt ett annat adaptivt styrsystem kallat Master mode. Den primära metoden var att skapa ett svetsschema för varje styrsystem och testa dem på två olika materialkombinationer. Syftet var att kvantifiera vinster och fördelar som adaptiva punktsvetssystem har på svetsprocessen. Testerna utfördes genom att svetsa så många godkända punkter som möjligt utan att formera elektroden. Fördelarna kvantifieras genom att man undersökte parametrarna och faktorerna svetstid, sprut, robusthet, elektrodslitage och parametrar i styrsystemen. Experimentet följde kraven i enighet med internationella standarder och Scania-standarden för punktsvetsning. Resultaten från experimentet visade att HCC var den mest robusta processen och punkterna minskade aldrig i storlek, vilket CCR och Master mode gjorde. Det är möjligt att svetsa flera olika materialkombinationer med HCC, det ökar flexibiliteten i produktionen och minskar den tid som krävs för att utveckla nya svetsscheman eftersom samma schema kan hantera många kombinationer med samma tjocklek. HCC tillåter processen att använda flera pulser, och varje puls adderar tid och svetsschemat bör därför vara välutvecklat och optimerat för att undvika slöseri med avseende på långa svetstider. Resultaten kommer att ge Scania mer kunskap om processerna och hur man kan optimera processerna ytterligare i produktionen. Resultatet kan också användas som grund för val av produkter eller framtida investeringar.