abstract: Lithium metal is a promising anode for the next generation lithium batteries owing to its high capacity (3860 mAh g-1) and the lowest negative reduction potential (-3.04 V). Commercial produced lithium anodes have a native rough surface which deteriorates the cycling performance of the battery. Here, an attempt has been made to deposit lithium on copper from an electrolytic cell consisting of simple electrolyte of pyridine and lithium chloride at room temperature. Water is known to react aggressively with the lithium metal, however in the electrochemical plating process, it has a significant beneficial effect in catalyzing the electrochemical reactions. The effect of trace amounts of water was investigated in air as well as in controlled atmosphere of argon, nitrogen, breathing grade dry air and ultra-zero dry air. The electrochemical products examined by Fourier transform infrared spectroscopy revealed the deposition might require the reduction of pyridine to facilitate the reduction of the lithium salt. Purity of the lithium film was determined by inductively coupled plasma mass spectrometry. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2019

A novel room temperature bonding method is used to package the micro-component. The bonding method utilizes metal microcap to package the micro-component under room temperature status, which not only can provide micro-component mechanical support also can prevent micro-component from contamination. The bonding condition under room temperature is the most conventional method can not achieve, which characteristic is the most significant effect factor to drive the wafer-level packaging process to improve in today. Utilizing ASTM standard, which was used as a macroscopic standard to evaluate and analyze the bonding shear strength relationship between the ASTM standard specimen and the metal microcap. The carrier wafer has been oxidized before photolithography process; the diameter of cavity and the contact area between the metal microcap and glass substrate were controlled by the photomask design and the accuracy of the photoresist exposure. The passivation treatment was developed to separate the microcap from the carrier wafer more easily. In this thesis, the metal microcap was fabricated by using electroforming process, which can control the thickness of metal microcap. The advantages of microcap are superior to the thin film poly-silicon made by the surface micromachining technique on the quality and mechanical properties. A glass is used as substrate of the metal microcap, and its transparent characteristic is a feature how we perform UV curing process. The adhesive can be cured under room temperature and the results exhibit the adhesive has excellent bonding strength. SEM is used to analyze the passivation result, the increasing rate of electroforming thickness. The shear stress-strain relationship between the metal microcap and the ASTM standard specimen is also discussed and analyzed in this thesis.

With the increasing requirements for higher strength materials with high electrical conductivity, a lot of interest has been paid to develop Cu-based composites in the last 25 years. These composites have superior tensile strength, combined with good electrical conductivity, to that exhibited by pure Cu and conventional Cu alloys. To date, much of the research carried out on this composite has focused on the mechanical and electrical properties of the as processed material. However, there is a basic lack of understanding of the way in which the properties may change or degrade during service. Without this knowledge, these composites cannot be fully and safely exploited. Thus the objective of this study was to investigate the thermo-mechanical behaviour of a Cu-Cr composite, and the nature and extent of any damage mechanisms occurring within the composite over a wide range of experimental conditions. Neutron diffraction was used to investigate the deformation behaviour of the individual phases in the composite and their interaction through elastic and plastic loading at room temperature. For the composite, a fairly good agreement was observed in the phase strains predicted by the Eshelby theory and measured by neutron diffraction. In-situ tensile tests in the SEM were also performed to study the damage mechanism of the composite. Tensile and creep tests were carried out in air and in vacuum over a wide range of temperatures. To provide data for comparison with the composite material, pure Cu specimens were tested whenever possible. Creep resistance increases significantly with the introduction of Cr fibres into Cu. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. Damage characteristics and distributions were found to be similar during tensile and creep testing.

Silicon nitride (Si₃N₄) has the potential for use in various high-performance applications. However, surface defects such as voids/pits are commonly present on as processed Si₃N₄. When subjected to external forces, fracture originates at such flaws. To reduce or eliminate surface flaws, machining operations are required which constitute a major proportion of production costs. In order to offer an inexpensive alternative to machining and also to enhance the room temperature flexural strength of as fired Si₃N₄, low expansion glaze coatings of lithium aluminosilicate (LAS) and magnesium aluminosilicate (MAS) compositions were developed. Homogeneous and crack-free glaze coatings were successfully formed on as processed Si₃N₄. This ensured formation of compressive surface stresses on the as fired Si₃N₄ which, in turn, led to the reduction of the effects of surface flaws. When compared to the uncoated as fired Si₃N₄, both the glaze coatings helped achieve greater flexural strength. Analyses of the two glazes indicated better strength for the MAS coating compared to the LAS. Wear tests revealed that the MAS glaze exhibited higher wear resistance than the LAS glaze. These differences were attributed to the ability of the magnesium aluminosilicate glaze to achieve greater surface smoothness and better adherence to the substrate than the lithium aluminosilicate. / Master of Science

Room-temperature ionic liquids (RTILs) and their derivatives are promising electrolytes for electrochemical devices including supercapacitors. Understanding the behavior of RTILs in these devices is critical for improving their performance. The energy density of supercapacitors can be improved greatly by using RTILs as electrolytes and nanoporous carbon as electrodes, but the mechanism of the charge storage using these materials is not well understood. In this dissertation, the diffusion and charging dynamics of RTILs in nanopores are studied. The results show that ion packing typically plays the most important role in ion diffusion. The study also demonstrates that the cyclic charging and discharging of a pore can exhibit a number of interesting features (e.g., sloshing of ionic charge along the pores during cyclic scans), which help explain experimental observations such as the negligible contribution of co-ions to charge storage at high scan rates. Solid electrolytes with both high ionic conductivities and excellent mechanical strength are needed in many electrochemical devices. The invention of ion gels featuring aligned polyanions immersed inside RTILs has shown promise in meeting this demand, but the mechanism behind their superior mechanical strength remains elusive. Using molecular simulations, it is discovered that the high elastic moduli of model PBDT ion gels originate from the RTIL-mediated interactions between the polyanions. This insight is useful for future design of ion gels to improve their transport and mechanical properties. / Ph. D. / Room-temperature ionic liquids (RTILs) and their derivatives are promising electrolytes for electrochemical devices including supercapacitors. Understanding the behavior of RTILs in these devices is critical for improving their performance. The energy density of supercapacitors can be improved greatly by using RTILs as electrolytes and nanoporous carbon as electrodes, but the mechanism of the charge storage using these materials is not well understood. In this dissertation, the diffusion and charging dynamics of RTILs in nanopores are studied. The results show that ion packing typically plays the most important role in ion diffusion. The study also demonstrates that the cyclic charging and discharging of a pore can exhibit a number of interesting features (e.g., sloshing of ionic charge along the pores during cyclic scans), which help explain experimental observations such as the negligible contribution of co-ions to charge storage at high scan rates. Solid electrolytes with both high ionic conductivities and excellent mechanical strength are needed in many electrochemical devices. The invention of ion gels featuring aligned polyanions immersed inside RTILs has shown promise in meeting this demand, but the mechanism behind their superior mechanical strength remains elusive. Using molecular simulations, it is discovered that the high elastic moduli of model PBDT ion gels originate from the RTIL-mediated interactions between the polyanions. This insight is useful for future design of ion gels to improve their transport and mechanical properties.

No description available.

The work presented in this thesis involves the use of room temperature ionic liquids (RTILs) as solvents in electrochemical experiments for the detection of hydrogen sulfide. The fundamentals of electrochemistry are presented, followed by an overview of RTILs in terms of their properties, applications and their behaviour as electrochemical solvents compared to conventional solvents. This is followed by an outline of electrochemical detection of various gases in aqueous, organic and ionic solvents. The results of 8 original studies are then presented as follows: <ul><li>The study of the electrochemical window of twelve different room temperature ionic liquids using cyclic voltammetry vs. an internal redox couple for two defined current densities, and observation of water uptake of different ionic liquids under different conditions using a Karl Fischer titrator.</li><li>The reduction of hydrogen sulfide in various room temperature ionic liquids at a platinum electrode, measured using cyclic voltammetry. Also, solubilities and diffusion coefficients of hydrogen sulfide determined by potential step chronoamperometry.</li><li>The oxidation of hydrogen sulfide in various room temperature ionic liquids at a platinum electrode measured using cyclic voltammetry and the simulation of the electrochemical signal using experimentally defined parameters.</li><li>The disproportionation of N,N-dimethyl-p-phenylenediamine (DMPD) in room temperature ionic liquids using cyclic voltammetry, and computational simulation of the voltammetry of DMPD using experimentally defined parameters to elucidate kinetic and thermodynamic data. DMPD was examined as a mediating species for hydrogen sulfide detection.</li><li>The oxidation of catechol and dopamine in ionic liquids using cyclic voltammetry and observing adsorption effects when varying solvent anion. Catechol was examined as a mediating species for hydrogen sulfide detection.</li><li>The electrochemical oxidation of NADH in ionic liquids using cyclic voltammetry and observing the ”switching on or off” of the electrochemical signal when varying the solvent anion. NADH was examined as a mediating species for hydrogen sulfide detection.</li><li>The mediated detection of hydrogen sulfide utilizing various mediating species in several ionic liquids using cyclic voltammetry, and the elucidation of the mediating mechanism of hydrogen sulfide in 3,5-tert-butyl-o-benzoquinone.</li><li>The observation of the diffusion of ferrocene in an ionic liquid at ring-recessed disc microelectrode arrays in generator-collector mode using potential step chronoamperometry.</li><ul> The results presented show that room temperature ionic liquids perform well as solvents in gas sensors, and could be viable alternatives to traditional organic solvents. Ionic liquids have also been observed to be tuneable in their reactions with analytes depending on the constituent cations and, in particular, anions. This tuneability is advantageous as specific combinations of cations and anions can be chosen to suit particular experiments.

Os compostos semicondutores com alto número atômico e energia de banda proibida larga vêm sendo pesquisados como detectores de radiação X e gama, com alta resolução energética, operando à temperatura ambiente. O denominador comum dos materiais semicondutores, que operam à temperatura ambiente, é a dificuldade em crescer cristais com pureza química elevada e boa estequiometria. O desenvolvimento deste tipo de detectores semicondutores de radiação é ainda um desafio tecnológico e tem deparado com muitos fatores limitantes, tais como: material de partida com qualidade compatível para o uso no crescimento de cristal, baixa estabilidade do detector ao longo do tempo, oxidação superficial e outras dificuldades relatadas na literatura, que limitam o seu uso. Neste trabalho, estabeleceu-se a metodologia de transporte físico de vapor (PVT) para a purificação e crescimento do cristal semicondutor de Iodeto de Mercúrio (HgI2). Cristais de HgI2 com orientação cristalina, estequiometria e morfologia da superfície adequadas foram obtidos por essa técnica. Uma redução nítida de impurezas após a purificação pode ser observada e o nível de impureza presente nos cristais não interferiu nas suas estruturas cristalinas. Uma boa morfologia com uniformidade nas camadas da superfície foi encontrada nos cristais, indicando uma boa orientação na estrutura cristalina. Um estudo inédito foi realizado no Laboratório da University of Freiburg, sob a coordenação do Prof. Michael Fiederle, com o intuito de aumentar a estabilidade do detector de HgI2 ao longo do tempo. A aplicação de diferentes tipos de resina polimérica para encapsulamento dos detectores HgI2 foi realizada e estudada, no intuito de proteger o cristal de HgI2 das reações com os gases atmosféricos e isolar eletricamente a superfície dos cristais. Quatro resinas poliméricas foram analisadas, cujas composições são: Resina n 1: 50% - 100% de heptano, 10% - 25% metilcicloexano, <1% de ciclo-hexano; Resina n2: 25% - 50% de etanol, 25% - 50% de acetona, <2,5% de acetato de etilo; Resina n3: 50% - 100% de acetato de metilo, 5% - 10% de n-butilo e Resina 4: 50% - 100% de etil-2- cianoacrilato. A influência dos tipos de resina polimérica utilizada na espectroscopia de desempenho do detector semicondutor HgI2 é, claramente, demonstrada. O melhor resultado foi encontrado para o detector encapsulado com resina n3. Um aumento de até 26 vezes no tempo de estabilidade, como detector de radiação, foi observado para os detectores encapsulados com resina em comparação com o detector não encapsulado, exposto à atmosfera. / The semiconductor compounds with high atomic number and wide band gap energy have been investigated as X and gamma range radiation detectors, with high energy resolution, operating at room temperature. The common denominator of semiconductor materials, which operate at room temperature, is the difficulty to grow crystals with high chemical purity and good stoichiometry. The development of this type of radiation semiconductor detectors is still a technological challenge and it has faced many limiting factors, such as: starting material quality compatible for use in crystal growth, low stability of the detector over the time, surface oxidation and other difficulties reported in the literature, which limit their use. In this work, the Physical vapor transport (PVT) methodology for purification and growth of the Iodide Mercury (HgI2) semiconductor crystals was established. HgI2 crystals with crystalline orientation and suitable surface stoichiometry and morphology were obtained by this technique. A significant reduction of impurities after purification could be observed and the impurity levels present in crystals did not interfere in their crystal structures. A good morphology with uniformity in the surface layers of the crystals was found, indicating a good orientation in the crystal structure. A novel study was conducted at the Laboratory of the University of Freiburg, under the guidance of Prof. Michael Fiederle, in order to increase the stability of the HgI2 detector over the time. The application of different types of polymer resins for encapsulation of HgI2 detectors was carried out and studied, in order to protect the HgI2 crystal of reactions with the atmospheric gases and to isolate, electrically, the surface of these crystals. Four types of polymeric resins were evaluated, and each composition is : (a) Resin n1: 50% - 100% heptane 10% - 25% methyl cyclohexane, <1% cyclohexane; (b) Resin n2: 25% - 50% ethanol, 25% - 50% acetone <2.5% ethyl acetate; (c) Resin n3: 50% - 100% methyl acetate, 5% - 10% n-butyl and (d) Resin n 4: 50% - 100% ethyl-2- cyanoacrylate. The influence of the different types of polymer resins composition, used in the HgI2 detector encapsulation, is clearly demonstrated by the results of the gamma ray spectroscopy. The best results were found for the detector encapsulated with resin n3. An increase of up to 26 times in the stability period was observed for the detectors encapsulated with resin, compared to those which were not encapsulated and, therefore, had been exposed to the atmosphere.

In today’s world the significance of bio-based materials are increasing rapidly because ofthe environmental concern. Material scientists are nowadays engaged in development ofsuch materials which have natural origin and degrade in its environment. Several workshave already been reported in area of thermoplastic biocomposites. However biocompositesbased on thermosets is comparatively new area of research. In this work biobasedcomposites have been developed from two different bio-based thermoset resins.The main objective of the work was room temperature curing of poly lactic acid basedresin (POLLIT™) and AESO, acrylated epoxidized soy-bean oil (TRIBEST®). These tworesin systems were impregnated with different natural fibre mats. Cure behavior wascharacterized by means of DSC (Differential Scanning Calorimeter) and results showsthat the resins have been cured at room temperature. The mechanical properties ofprepared composites were assessed by the means of flexural testing and charpy impacttesting. The viability of using these composites in structural applications are also beendiscussed. / Uppsatsnivå: D

Os compostos semicondutores com alto número atômico e energia de banda proibida larga vêm sendo pesquisados como detectores de radiação X e gama, com alta resolução energética, operando à temperatura ambiente. O denominador comum dos materiais semicondutores, que operam à temperatura ambiente, é a dificuldade em crescer cristais com pureza química elevada e boa estequiometria. O desenvolvimento deste tipo de detectores semicondutores de radiação é ainda um desafio tecnológico e tem deparado com muitos fatores limitantes, tais como: material de partida com qualidade compatível para o uso no crescimento de cristal, baixa estabilidade do detector ao longo do tempo, oxidação superficial e outras dificuldades relatadas na literatura, que limitam o seu uso. Neste trabalho, estabeleceu-se a metodologia de transporte físico de vapor (PVT) para a purificação e crescimento do cristal semicondutor de Iodeto de Mercúrio (HgI2). Cristais de HgI2 com orientação cristalina, estequiometria e morfologia da superfície adequadas foram obtidos por essa técnica. Uma redução nítida de impurezas após a purificação pode ser observada e o nível de impureza presente nos cristais não interferiu nas suas estruturas cristalinas. Uma boa morfologia com uniformidade nas camadas da superfície foi encontrada nos cristais, indicando uma boa orientação na estrutura cristalina. Um estudo inédito foi realizado no Laboratório da University of Freiburg, sob a coordenação do Prof. Michael Fiederle, com o intuito de aumentar a estabilidade do detector de HgI2 ao longo do tempo. A aplicação de diferentes tipos de resina polimérica para encapsulamento dos detectores HgI2 foi realizada e estudada, no intuito de proteger o cristal de HgI2 das reações com os gases atmosféricos e isolar eletricamente a superfície dos cristais. Quatro resinas poliméricas foram analisadas, cujas composições são: Resina n 1: 50% - 100% de heptano, 10% - 25% metilcicloexano, <1% de ciclo-hexano; Resina n2: 25% - 50% de etanol, 25% - 50% de acetona, <2,5% de acetato de etilo; Resina n3: 50% - 100% de acetato de metilo, 5% - 10% de n-butilo e Resina 4: 50% - 100% de etil-2- cianoacrilato. A influência dos tipos de resina polimérica utilizada na espectroscopia de desempenho do detector semicondutor HgI2 é, claramente, demonstrada. O melhor resultado foi encontrado para o detector encapsulado com resina n3. Um aumento de até 26 vezes no tempo de estabilidade, como detector de radiação, foi observado para os detectores encapsulados com resina em comparação com o detector não encapsulado, exposto à atmosfera. / The semiconductor compounds with high atomic number and wide band gap energy have been investigated as X and gamma range radiation detectors, with high energy resolution, operating at room temperature. The common denominator of semiconductor materials, which operate at room temperature, is the difficulty to grow crystals with high chemical purity and good stoichiometry. The development of this type of radiation semiconductor detectors is still a technological challenge and it has faced many limiting factors, such as: starting material quality compatible for use in crystal growth, low stability of the detector over the time, surface oxidation and other difficulties reported in the literature, which limit their use. In this work, the Physical vapor transport (PVT) methodology for purification and growth of the Iodide Mercury (HgI2) semiconductor crystals was established. HgI2 crystals with crystalline orientation and suitable surface stoichiometry and morphology were obtained by this technique. A significant reduction of impurities after purification could be observed and the impurity levels present in crystals did not interfere in their crystal structures. A good morphology with uniformity in the surface layers of the crystals was found, indicating a good orientation in the crystal structure. A novel study was conducted at the Laboratory of the University of Freiburg, under the guidance of Prof. Michael Fiederle, in order to increase the stability of the HgI2 detector over the time. The application of different types of polymer resins for encapsulation of HgI2 detectors was carried out and studied, in order to protect the HgI2 crystal of reactions with the atmospheric gases and to isolate, electrically, the surface of these crystals. Four types of polymeric resins were evaluated, and each composition is : (a) Resin n1: 50% - 100% heptane 10% - 25% methyl cyclohexane, <1% cyclohexane; (b) Resin n2: 25% - 50% ethanol, 25% - 50% acetone <2.5% ethyl acetate; (c) Resin n3: 50% - 100% methyl acetate, 5% - 10% n-butyl and (d) Resin n 4: 50% - 100% ethyl-2- cyanoacrylate. The influence of the different types of polymer resins composition, used in the HgI2 detector encapsulation, is clearly demonstrated by the results of the gamma ray spectroscopy. The best results were found for the detector encapsulated with resin n3. An increase of up to 26 times in the stability period was observed for the detectors encapsulated with resin, compared to those which were not encapsulated and, therefore, had been exposed to the atmosphere.