Dissertations / Theses on the topic 'Thermal stability'
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Luecke, Katherine J. Bell Leonard N. "Thermal stability of Tagatose." Auburn, Ala, 2009. http://hdl.handle.net/10415/1770.
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Rashidian, Mahla. "Thermal degradation study by continuous thermal stability rig." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemisk prosessteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22913.
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This investigation was done at NTNU and together with Statoil research and development department in Rotvoll, Trondheim to facilitate a new semi dynamic amine thermal degradation rig.This study was an initial attempt to investigate semi dynamic thermal stability rig as an alternative to thermal degradation study. The major purposes are: (1) to study MEA and MDEA thermal degradation by thermal stability rig apparatus which is designed by Statoil. (2) to demonstrate the result differences between the new and conventional experimental method. MEA and MDEA were selected in this study due to have more available literature data in amine based absorption process. The loaded liquid was circulated through the pipe from the cold stream to the hot stream. There is no analytical method was connected to the rig therefore a regular sample was taken every week and sent to SINTEF analytical lab to identify degradation products.Residence time of solution in high temperature zone also was calculated as an important factor in thermal degradation investigation. Different authors have been provided to understand: the background, the experimental set up, the analytical method to describe the degradation products, data interpretation and the mechanism of the degradation.Based on analytical results, it seems that only small portion of MEA and MDEA were degraded. It showed that the elapsed time was not enough to observe degradation in a significant amount. Metal qualification tests showed low metal concentration in solutions and generally very little corrosiveness effect. However, few degradation products were reported in this study the most probably degradation mechanism is estimated similar to suggested degradation pathway by Davis (2009). More works are required in future to better interpret the new thermal stability rig.
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McGuffey, Matthew Kenneth. "Thermal Stability of alpha-Lactalbumin." NCSU, 2004. http://www.lib.ncsu.edu/theses/available/etd-05212004-155321/.
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The objective of this research was to quantitatively describe the the denaturation and aggregation processes of a-lactalbumin at neutral pH in order to understand their interrelationship and effect on solution stability. Three different preparations of a-La had similar denaturation temperatures, enthalpies and % reversibility as measured by differential scanning calorimetry. However, Native PAGE reveled three non-native monomer bands that corresponded to three distinct dimer bands indicating specific intramolecular disulfide bond shuffling leads to formation of disulfide-specific dimers. The apo protein was the most thermostable to turbidity development. The Ca-La was the most thermostable holo- preparation. Turbidity development at 95 degreesC (95 degrees C) indicated pure preparations intensely associate through hydrophobic interactions through bridging by divalent phosphate and this effect was mitigated by decreasing the ionic strength, decreasing the phosphate charge to ¡V1 (at pH 6.6) or decreasing the temperature. The aggregation behavior of a commercial a-La was investigated at neutral pH and 95?aC in a complex mineral salt environment to understand general stability factors involved in a nutritional beverage. The objective was to understand the effect of a-La lot variation, relative b-lactoglobulin concentration and excess calcium on the aggregate size development as measured by light scattering and turbidity development. The lot of holo-a-La possessing a higher intrinsic b-Lg concentration had higher solubility at pH 6.80, evolved more reactive thiol groups, had a 25% faster first order rate constant, dissociated only slightly with cooling and formed spherical aggregates with a much higher molecular weight. Aggregates intrinsic to the protein powder may play a role in aggregate growth and shape. Adding increasing quantities of b-Lg generally decreased solubility. The highest b-Lg concentrations investigated demonstrated a net thiol oxidation and, subsequently, had a diminished ability to aggregate through hydrophobic interactions. Adding excess calcium caused a dramatic loss of solubility at pH 7.0 and required an increase in pH to 7.5 to regain solubility.
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Nevell, Roger Thomas. "Scaling the thermal stability test." Thesis, University of Portsmouth, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310467.
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Hedderich, Johannes. "Thermal stability in machine tools." Thesis, KTH, Industriell produktion, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185117.
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Reliable and stable processes allowing precision manufacturing are a core demand in today’s production. To achieve stable processes several influences on machine tools have to be controlled. Beside the other factors, thermal influences are among the most important factors infecting the production system.In this work two problems that are caused by thermal deviations are considered: Firstly the positioning error of machine tools, and secondly possible changes in the elastic behaviour of a machine tool due to changes in stiffness.Positioning problems due to thermal changes are widely examined in research and the focus in this thesis is laid to a machine tool control program, developed and used by “Company A”, which will be explained and evaluated. This program is used both to evaluate new machine tools but also machine tools used in daily production. Also the standard method of Company A to compensate for thermal deviations in production is shortly evaluated.The connection between thermal deviations and changes in stiffness of a machine tool is a fairly new field in research. In this work tests were done using the Loaded Double Ball Bar (LDBB), a tool to measure the elastic behaviour of machine tools during movement. The changes observed in the machine tool are documented over time and different thermal states. A couple of machine tools of the same type but with different specifications are compared and differences and similarities are highlighted and evaluated.Dagens produktion, som är sträver mot allt snävre toleranser och bättre precision kräver stabila och pålitliga processer. Flera faktorer som påverkar verktygsmaskiner måste kontrolleras för att nå en stabil process. Bredvid andra fakrorer har termiska förändringar en väldigt stor påverkan på produktions systemet.Det här arbetet undersökte två olika problem som framkallas av förändringen av termiska tillståndet, positionerings fel i verktygsmaskiner samt möjliga ändringar i maskinens styvhet.Termisk påverkan på positionerings felet av verktygsmaskiner är ett ämne som underöks av många forskare. Det här arbetet fokusserades därför på att undersöka ett program för att testa och kontrollera förändringar i verktygsmaskiner, framtagen av ett företag som kallas för ”Company A”. Själva programmet undersöktes och värderades. Programmet används av företaget både för att värdera nya maskina samt maskiner som används i daglig produktion. Dessutom undersöktes metoden av ”Company A” som används för termisk kompensering i daglig produktion.Sammanhanget mellan termiska förändringar och styvhet av en verktygsmaskin är ett någorlunda nytt forskningsämne. I det här arbetet utfördes tester med en Loaded Double Ball Bar (LDBB), ett verktyg som mätar elastiska egenskaper av en maskin under rörelse. Skillnader i maskinen som dokumenterades sattes i relation till tid och termiska förändringar. Några stycken maskiner av samma typ men med olika konfigurationer jämfördes och skillnader som likheter analyserades.
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Syed, Muhammad Bilal. "Thermal Stability of Arc Evaporated ZrCrAlN." Thesis, Linköpings universitet, Nanostrukturerade material, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-84769.
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This research explores the thermal stability of ZrCrAlN material system. For this purpose fourteen different compositions of ZrCrAlN coatings were deposited onto tungsten carbide substrates by using reactive cathodic arc evaporation. These compositions were further annealed at 800oC, 900oC, 1000oC and 1100oC temperatures. EDS was employed to specify the compositions. The crystal structure of the coatings were analysed by XRD, and the hardness of these coatings was determined by Nanoindentation. The experimental findings reported a significant age hardening of Zr0.16Cr0.12Al0.72N and a delayed h-AlN formation in Zr0.07Cr0.40Al0.52N. ZrCrAlN was thus proved to be thermally stable.Multifilms,A4:2 Growth and characterization of Multicomponent Nitrides by Magnetron Sputtering and Arc evaporation
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Chen, Yun-Chu. "Ensilication and thermal stability of proteins." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760953.
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Stability of biological substances based on proteins, including vaccines, antibodies, and enzymes, is critically linked to its thermal environment. Temperature stress over time results in protein denaturation. Denaturation is a loss of structure and function in proteins. Their storage and distribution therefore relies on a “cold chain” of continuous refrigeration, which is costly and not always effective in medical and biological applications. Due to this issue, access to insulin for treating diabetes is still beyond the reach of millions of people around the world [1]. Diabetes is predicted to be the 7th leading cause of death in the next decade [2].This project therefore sought to develop an innovative protocol of “ensilication” ef- fectively enclosing protein in a deposited silica “cage” to protect the protein from the denaturing process. To evaluate this aim, a release protocol involving treatment with a dilute solution of acidified NaF was designed to release the ensilicated proteins into solution. As test subject, covalently bonded sol-gel silica network was first exam- ined to surround lysozyme, then applied to haemoglobin, a heterotetrameric protein with a complex tertiary and quaternary structure. Remarkably, insulin is profitably ensilicated (80%) here along with a mediator, chitosan. The mechanism for the formation of protein ensilication was investigated using Syn- chrotron SAXS and DLS. The structures of ensilicated protein were confirmed using multiple microscopy and spectrometry methods. In order to test the product’s stabil- ity, the ensilicated protein was subjected to heating at 100 ◦C for hours or long-term ambient temperature storage. Analysis of the proteins released from their ensilica- tion with a wide range of methods including SAXS, ELISA, CD and FT-IR revealed that even after exposure to such extreme temperatures, the protein structure remains consistent with that of the native protein. The results demonstrate that the process produces a storable solid protein-loaded material directly from solution, and may thus be suitable for use with proteins that do not tolerate lyophilisation. Ensilication offers the prospect of a solution to the “cold chain” problem for biological materials, such as insulin.
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Heron, Andrew David. "The stability of monoclonal antibodies." Thesis, University of Glasgow, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252169.
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Jones, R. H. "Interpretation and sensitivity of thermal stability measurements." Thesis, London South Bank University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618641.
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COELHO, MARIANNA ANSILIERO DE OLIVEIRA. "STABILITY OF BURIED PIPES UNDER THERMAL LOADS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14132@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONeste trabalho é realizado um estudo da estabilidade de dutos enterrados submetidos a cargas térmicas. As cargas térmicas são devidas ao aquecimento do fluido com o objetivo de facilitar o transporte dos óleos que são escoados nos dutos. O duto expande devido a estas cargas térmicas. Como o duto está restringido em suas extremidades e devido à expansão são causadas forças axiais de compressão no duto. Para a análise destes dutos submetidos à variação da carga térmica foram utilizados modelos teóricos e numéricos para o problema de flambagem vertical e lateral, considerando o duto perfeito e com imperfeição. Os modelos numéricos foram desenvolvidos utilizando o programa ABAQUS. Para estes modelos numéricos o duto foi considerado como uma viga e a o solo como elementos de interface e elementos de mola. Foi desenvolvido também um modelo de viga-casca onde parte do duto é modelada como uma casca cilíndirca para permitir a análise de enrugamento e da deformação da seção transversal. São realizados estudos paramétricos numéricos para investigar o efeito do recobrimento do duto da forma e amplitude da imperfeição e da rigidez do solo na temperatura crítica de flambagem do duto.
In this work a study of the stability of buried pipelines subjected to thermal loads is developed. The thermal loads are due to the heated fluid that flows through the pipe. Fluid heating is for ease of oil transportation. The pipe expands due to the thermal loading. Axial forces are developed in the pipe due to the expansion since the pipe is restricted on its ends. The analysis of pipes subject to thermal loadas were carried out with use of theoretical and numerical methods for upheaval and snaking buckling problems considering perfect pipes and pipes with imperfection. The numerical models were developed with the support of the ABAQUS software. The pipe was modeled as a beam and the soil is represented by interface elements and alternatively by spring elements. A beam-shell model was also developed where part of the pipe was modeled as a shell to allow a wrinkling analysis. Parametric studies were also carried out to investigate the effects of the soil stiffness, shape and amplitude or the imperfection and internal pressure on the critical temperature of the pipe.
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Kaplan, Maciej. "Thermal Stability of Amorphous MoSiZr Thin Films." Thesis, Uppsala universitet, Materialfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-298165.
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Metallic glass is a class of materials which have a disordered structure of atoms, due to this, glasses lack grains and grain boundaries, which are present in their crystalline counterparts. Metallic glasses have many interesting properties worth investigating, such as high corrosion resistance or high mechanical strength. However, metallic glasses are metastable and will therefore crystallise if heated above the crystallisation temperature. MoSiZr alloys have been studied and to gain knowledge of how the composition affects the crystallisation temperature, which enables further improvement of thermal stability. Crystallisation temperatures of the MoSiZr alloys were investigated by heat treatments in vacuum and ex-situ X-ray diffraction and X-ray reflectivity analysis. The highest thermal stability of the alloys was exhibited by M48Si48Zr4, Mo43Si50Zr7, Mo50Si40Zr10 and Mo45Si43Zr12, they remained amorphous after heat treatment at 1073 K. The resulting crystalline phases are Mo3Si, Mo5Si3 and ZrO2. Oxidation of Zr in the alloys is present only when the Zr content is at least 10 at%, crystallisation is otherwise mainly driven by formation of Mo3Si. Further improvement of the thermal stability is possible by introducing new alloying elements at the cost of those that promote crystallisation. Keeping the content of Zr below 10 at% is of great importance to prevent oxidation.
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Hulme-Smith, Christopher. "The thermal stability of bulk nanocrystalline steels." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/261814.
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Nanocrystalline bainite, commonly known as “superbainite”, is a novel class of steel that utilises careful alloy design to reduce the bainite transformation temperature to below 300℃. This results in grains that are tens of nanometres in width, which make steel strong and tough. The structure can be produced in large volumes without the need for rapid cooling or severe deformation. The presence of austenite in nanocrystalline bainite is largely responsible for the toughness. Unfortunately, the austenite is metastable and previous work has shown that it decomposes into cementite and ferrite upon heating. This decomposition makes the material weak and brittle. The present work aims to develop new alloys that form nanocrystalline bainite, but which are able to survive heating. Previous work has shown that cementite precipitation is the first stage in the decomposition process and so the first alloys developed aimed to suppress cementite precipitation. This resulted in a noticeable improvement in thermal stability, although the austenite does eventually decompose at higher temperatures. Subsequent work led to an alloy which was designed not to resist cementite precipitation, but to tolerate it without the associated loss of austenite. This was achieved by the addition of large quantities of nickel to stabilise the austenite even if its carbon content is depleted. This alloy is able to survive exposure to elevated temperatures with the majority of austenite being retained. The thermal stability of the alloys was assessed using time-resolved synchrotron X-ray diffractometry at both the Deutsches Elektronen Synchrotron (DESY) and Diamond Light Source. The high-quality data that were collected allowed the symmetry of the ferrite lattice to be investigated and it was found that the lattice was best-described using a body-centred tetragonal crystal structure. This is the first evidence of its kind. Mechanical properties were investigated in the as-transformed condition at ambient temperature and at a temperature representative of aeronautic applications. The alloys developed in this project have comparable strength, toughness and fatigue performance to existing nanocrystalline bainitic steels. Mechanical properties were also measured after heating at 480℃ for 8 d and this was found to reduce strength and toughness, consistent with the measured loss of austenite.
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Darnbrough, J. E. "Thermal stability and deformation of nanocrystalline nickel." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683939.
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This work is conducted on nanocrystalline nickel using a range of novel techniques in order to investigate the thermal stability of the microstructure and the mechanical properties of subsequent microstructures. Work is focused on two sources of nanocrystalline nickel produced via electrodeposition with varying levels of impurity sulphur. Impurity sulphur alters the thermal stability of the material; a low sulphur system is stable up to a temperature of 400°C and then coarsens normally to produce a micro-polycrystalline structure, a high sulphur material coarsens at 300°C and the coarsening quickly stagnates leaving a stable microstructure of rv550nm grains. Above 485°C, the high sulphur material is observed to undergo abnormal growth of large planar faceted grains. Observation of the growth post heat treatment via standard electron microscopy techniques gave statistical data complemented by in-situ heat treatment scanning electron microscopy and high temperature resistivity measurement tests to elucidate the stages of growth. A range of macro and micro scale tests were undertaken to investigate the physical properties of the materials; from Vickers hardness and four point bend, to novel in-situ micro-cantilever bend tests. The effect of the increased grain size from heat treatment leads to a reduction in the hardness and yield strength of the materials and in the case of the high sulphur material, segregation of the impurity to the grain boundary led to a ductile to brittle transition.
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Villarraga, Díaz Claudia Juliana. "Effect of thermal cycles on rock massif stability." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/462250.
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The environmental conditions may play a relevant role in the stability of rock slopes. In fact, weathering can contribute to the reduction of strength of the material, while atmospheric actions may increase internal stresses in the rock massif. This Ph.D. thesis deals with the effect of atmospheric thermal cycles in rocks, from both experimental and numerical point of view.
This research is focused on the real case of La Roque Gageac, a small town located in the south-west of France, which experiences rock fall risks. Installed instrumentation evidenced the main role played by thermal variations in rock falls occurrence.
With the aim of isolating the effect of thermal cycles in the La Roque Gageac limestone, an experimental study is performed. Samples were obtained from blocks felt and intact cores drilled from the cliff face. These samples were submitted to thermal cycles between 10ºC and 50ºC, in order to mimic natural variations.
The damage induced in the samples is evaluated through measurements of strains, elastic wave propagation velocities and uniaxial compressive strength. It is observed that samples experience an accumulation in strains and reduction in the elastic wave propagation velocity and material strength during the imposition of thermal cycles. The response depends moreover on the mineralogical composition of the rock, which varies from sample to sample, as the cliff presents a large heterogeneity.
Based on the results obtained in the experimental program, principal characteristics of thermal damage have been evaluated, proposing a constitutive model capable to reproduce the macroscopic mechanical response of the rock under the applied thermal cycles.
With this purpose, a constitutive model based on the concept of composite material defined by Vaunat & Gens (2003) is developed. This model considers the material as composed of two different components endowed with their own behavior and interacting each other. This constitutive model has been implemented in the finite elements code CODE_BRIGHT and validated with the experimental results. It allows a better understanding of the internal stresses developed in the material under thermal loading.Las condiciones ambientales juegan un papel relevante en la estabilidad de taludes de roca, de hecho, las variaciones climáticas pueden afectar tanto la resistencia del material como el nivel de esfuerzos internos a los que el macizo está sometido. Esta tesis doctoral se enfoca en el efecto de los ciclos térmicos atmosféricos en las rocas, desde un punto de vista experimental y numérico. Esta investigación se centra el caso de La Roque Gageac, un pequeño pueblo localizado en el Sur de Francia, que se ha visto afectado por importantes caídas de rocas, las cuales, de acuerdo con registros de instrumentación parecen estar ligadas a las variaciones de temperatura registradas en el sitio. Con el objetivo de aislar el efecto de los ciclos térmicos en la caliza de la Roque Gageac un estudio experimental es llevado a cabo, para esto se consideran muestras obtenidas de bloques caídos en eventos anteriores y de núcleos intactos obtenidos de la cara del acantilado. Dichas muestras han sido sometidas a ciclos de temperatura entre 10ºC y 50ºC con el fin de imitar las variaciones naturales. El daño inducido en las muestras es evaluado a través de medidas de deformación, velocidad de propagación de ondas elásticas y resistencia a la compresión uniaxial. Se observa una acumulación de deformaciones, así como la reducción en la velocidad de propagación de onda y la resistencia del material con la imposición de los ciclos térmicos. Adicionalmente, la respuesta obtenida depende de la composición mineralógica de la roca que varía entre muestras, debido a la heterogeneidad del acantilado. Con base en los resultados obtenidos en el programa experimental se definen las principales características del fenómeno de daño térmico, con lo cual es posible proponer un modelo numérico capaz de reproducir la respuesta mecánica a nivel macroscópico de la roca cuando es sometida a ciclos térmicos. Para esto se desarrolla un modelo constitutivo basado en el concepto de material compuesto definido por Vaunat & Gens (2003). Dicho modelo considera que el material bajo estudio está compuesto por dos componentes diferentes con comportamientos establecidos para cada uno y que interactúan entre ellos. Este modelo constitutivo es implementado en el código de elementos finitos CODE_BRIGHT y validado con los resultados experimentales, permitiendo un mejor entendimiento de la generación de tensiones internas en la roca cuando esta es sometida a cargas térmicas.
Les conditions environnementales jouent un rôle important dans la stabilité des massifs rocheux. De fait, les variations climatiques peuvent affecter la résistance du matériau et également augmenter les contraintes internes dans le massif. Cette thèse étudie les effets des cycles thermiques atmosphériques sur les roches, dans une approche expérimentale puis numérique. Cette recherche est centrée sur le cas de la falaise de La Roque Gageac, un village du sudouest de la France, situé au pied d’une falaise qui présente une caverne à mi-hauteur. Cette commune a été affectée par plusieurs éboulements. Les données issues de l’instrumentation du massif montrent que ces instabilités sont liées aux cycles thermiques. Afin d’isoler l’effet des cycles thermiques dans la roche calcaire de La Roque Gageac, un programme expérimental a été mis en place. Des échantillons ont été prélevés sur deux sites de la falaise (blocs éboulés à l’intérieur de la caverne et carottés dans la face de la falaise). Ces échantillons ont été soumis à des cycles thermiques entre 10ºC et 50ºC afin de simuler les conditions enregistrées sur le site. L’endommagement de la roche est évalué en laboratoire par le suivi de mesures de déformations, de vitesses de propagation d’ondes élastiques et par l’évolution de la résistance à la compression uniaxial. Une réduction de la vitesse de propagation des ondes élastiques de compression et de cisaillement ainsi que de la résistance à la compression du matériau sont observées. De la même façon, les échantillons enregistrent une accumulation de déformations. De plus, la réponse des échantillons est influencée par la composition minéralogique de la roche. Celle-ci est liée au lieu de prélèvement, le calcaire de la falaise montrant une importante hétérogénéité. Les résultats du programme expérimental ont permis la détermination des caractéristiques principales du phénomène d’endommagement thermique. Une loi de comportement modélisant l’effet des cycles thermiques sur la roche calcaire de La Roque Gageac d’un point de vue macroscopique a été proposée. À cette fin, une loi de comportement sur la base de matériau composite présentée par Vaunat & Gens (2003) est suggérée. Ce modèle prend en compte un matériau formé de deux constituants au fonctionnement distinct dont l’interaction décrit le comportement de la roche. Le modèle a été introduit dans le programme aux éléments finis « CODE_BRIGHT » et est évalué en simulant la réponse observée sur les échantillons pendant le programme expérimental.
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Chen, Yu-Hsiang. "Mechanical and thermal stability of hard nitride coatings." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/665071.
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Hard coating 's thermal stability is essential due to the high temperature environment of high-speed cutting applications, while the induced phase and microstructure evolution affects the mechanical properties. In this thesis, the mechanical stability of arc-evaporated hard nitride coatings annealed at high temperature is analyzed and connected to the phase evolution. In addition to hardness, fracture toughness is evaluated by surface and cross-sectional investigations by scanning/transmission electron microscopy of damage events by mechanical tests.
The crack resistance of Ti1-xAixN with a range of Al content (x = 0.23-0.82) is studied by contact fatigue tests, where the difference in the microstructure plays a major role. Superior mechanical properties are found in annealed Ti0.63AI0.37N at 900 oC due to the spinodal decomposition.
The mechanical and high-temperature properties of hard coatings can be enhanced by alloying or multi-layering. Quaternary Ti-Al-X-N (X = Cr, Nb and V) alloys are studied, and superior toughness is found in TiAI(Nb )N in both the as-deposited and annealed (1100 oC) states. The h-AIN formation in TixAI0.37Cr1-0.37-xN (x = 0.03 and 0.16) is analyzed by in-situ x-ray scattering during annealing. The kinetic energy for h-AIN formation is found to be dependent on the microstructure evolution during annealing, which varies with coating composition.
High Al content h-ZrAIN/c-TiN and h-ZrAIN/c-ZrN multilayers are investigated through scratch tests followed by focused ion-beam analysis of the crack propagation. A c-Ti(Zr)N phase forms in h-ZrAIN/c-TiN multilayers at high temperatures and that contributes to enhanced hardness and fracture toughness by keeping the semi-coherency at the sub-interfaces.
Finally, an in-situ analysis of coatings by x-ray scattering during a turning process is carried out. lt demonstrates the possibility of observation of stress evolution and thermal expansion of the coatings or the work piece material during machining. This experiment provides real-time information on the coating behavior during cutting.La estabilidad térmica del recubrimiento es esencial debido a que estos recubrimientos durante su aplicación son utilizados a elevada temperatura y a alta velocidad. Durante dicho proceso, la evolución microestructural afecta a las propiedades mecánicas. En dicha tesis, la estabilidad mecánica de los recubimientos duros base nitruro producidos mediante arco y recocidos a elevada temperatura son analizados y se correlacionado con su transformación de fase. La dureza, la resistencia a la fractura son evaluados mediante la observación tanto superficial como transversal mediante microscopia electrónica de barrido. La resistencia a la propagación de grieta de Ti1−xAlxN con un contenido en Al que fluctúa entre 0.23-0.82 se estudia mediante ensayos de fatiga por contacto, donde la diferencia microstructural juega un papel importante. Las mejores propiedades mecánicas se encentran en las muestras con un 0.63 de Ti donde se ha realizado un proceso de recocido a 900o C debido a la descomposición espinoidal. Las características mecánicas y de alta temperatura de recubrimientos duros pueden ser mejoradas si tenemos un recubrimiento multicapa. Aleaciones cuaternarias de Ti-Al-X-N (X = Cr, Nb y V) son estudiada, y una mejor tenacidad de fractura se encuentra para la muestra TiAl(Nb)N sin tratamiento de recocido como recocida a 1000ºC. La formación del AlN con una estructura hexagonal en la muestra TixAl0.37Cr1−0.37−xN (x = 0.03 y 0.16) son analizadas mediante ensayos in-situ de difracción de rayos X durante el proceso de recocido. Cabe mencionar que la energía cinética para la formación de la AlN con una estructura hexagonal depende del proceso de recocido, la cual hace variar la composición química del recubrimiento. Multicapas de h (hexagonal)-ZrAlN/c (cúbica)-TiN con un elevado contenido de Al son estudiadas mediante ensayos de rayado y la generación de daño es observado mediante la técnica del haz de iones focalizados. Las formas de la fase de c-Ti(Zr)N en las multicapas de (h)-ZrAlN/c-TiN formadas a elevadas temperaturas contribuyen a mejorar la dureza y la tenacidad de fractura manteniendo la semicoherencia en las intercaras entre cada capa. Finalmente, se realiza un análisis in-situ de los diferentes recubrimientos me diante dispersión de rayos X durante un proceso de torneado. En este caso, se demuestra la posibilidad de observar la evolución de las tensiones residuales y de la expansión térmica durante el proceso de conformado. Dicho experimentos proporciona información en tiempo real sobre el comportamiento del recubrimiento en condiciones de servicio.
Hårda skikts högtemperaturstabilitet är viktig på grund av den höga temperaturskikten utsätts för under skärande bearbetning, och den utveckling av faser och mikrostruktur som då sker påverkar skiktets mekaniska egenskaper. I den här avhandlingen har den mekaniska stabiliteten hos arcförångade, hårda metallnitridskikt som värmebehandlats vid höga temperaturer studerats. Förutom hårdhet har även skiktens seghet utvärderats genom yt- och tvärsnittsstudier av den sprickbildning som uppstår vid mekanisk provning med hjälp av svep- och transmissionselektronmikroskopi. Segheten hos Ti1−xAlxN skikt med varierande Al-halt (x = 0.23-0.82) studerades genom utmattningsprovning och resultaten visar att förändringar i mikrostrukturen spelar en stor roll. Ti0.63Al0.37N skikten hade överlägsna mekaniska egenskaper; på grund av en fördelaktig kornstorlek i de obehandlade skikten och efter värmebehandling som ett resultat av det spinodala sönderfall som skett. De mekaniska egenskaperna och högtemperaturegenskaperna hos hårda skikt kan förbättras genom legering eller genom multilagring. I den här avhandlingen har kvarternära Ti-Al-X-N (X = Cr, Nb eller V) skikt studerats och TiAl(Nb)N skikten hade en överlägsen seghet i både obehandlat och värmebehandlat (1100oC) tillstånd. Bildandet av h-AlN i TixAl0.37Cr1−0.37−xN (x = 0.03 and 0.16) skikt studerades genom in situ röntgenspridning under värmebehandling. Den energi som krävs för att bilda h-AlN beror av mikrostrukturutvecklingen under värmebehandling vilken i sin tur beror av skiktens kemiska sammansättning. h-ZrAlN/c-TiN och h-ZrAlN/c-ZrN multilager med hög Al-halt undersöktes genom reptester följda av tvärsnittsstudier av sprickbildningen genom en analys med en fokuserad jonstråle (FIB). En c-Ti(Zr)N fas bildas vid höga temperaturer i h-ZrAlN/c-TiN multilagren och det bidrar till förhöjd hårdhet och förbättrad seghet på grund av en bibehållen koherens mellan lagren. Slutligen har in situ röntgenspridningsstudier av ytskikt utförts vid svarvning. Studien visar på möjligheten att observera spänning och värmeutvidgning av skikten eller arbetsmaterialet under bearbetning. Experimenten ger information om skiktens beteende under bearbetning i realtid.
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Varsani, Laxman M. "Protein engineering of glucose isomerase for thermal stability." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46592.
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Wong, Wai-leung Nelson, and 王韋良. "Thermal stability of luminescence signals relevant to dating." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31220137.
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Alston, Angus. "Thermal stability and degradation of some polyacrylate salts." Thesis, University of Glasgow, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318195.
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Hobson, Anthony James. "The thermal stability of aluminium-lithium alloy 8090." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287033.
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Villarraga, Diaz Claudia Juliana. "Effect of thermal cycles on rock massif stability." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30029.
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Les conditions environnementales jouent un rôle important dans la stabilité des massifs rocheux. De fait, les variations climatiques peuvent affecter la résistance du matériau et également augmenter les contraintes internes dans le massif. Cette thèse étudie les effets des cycles thermiques atmosphériques sur les roches, dans une approche expérimentale puis numérique. Cette recherche est centrée sur le cas de la falaise de La Roque Gageac, un village du sud-ouest de la France, situé au pied d'une falaise qui présente une caverne à mi-hauteur. Cette commune a été affectée par plusieurs éboulements. Les données issues de l'instrumentation du massif montrent que ces instabilités sont liées aux cycles thermiques. Afin d'isoler l'effet des cycles thermiques dans la roche calcaire de La Roque Gageac, un programme expérimental a été mis en place. Des échantillons ont été prélevés sur deux sites de la falaise (blocs éboulés à l'intérieur de la caverne et carottés dans la face de la falaise). Ces échantillons ont été soumis à des cycles thermiques entre 10ºC et 50ºC afin de simuler les conditions enregistrées sur le site. L'endommagement de la roche est évalué en laboratoire par le suivi de mesures de déformations, de vitesses de propagation d'ondes élastiques et par l'évolution de la résistance à la compression uniaxial. Une réduction de la vitesse de propagation des ondes élastiques de compression et de cisaillement ainsi que de la résistance à la compression du matériau sont observées. De la même façon, les échantillons enregistrent une accumulation de déformations. De plus, la réponse des échantillons est influencée par la composition minéralogique de la roche. Celle-ci est liée au lieu de prélèvement, le calcaire de la falaise montrant une importante hétérogénéité. Les résultats du programme expérimental ont permis la détermination des caractéristiques principales du phénomène d'endommagement thermique. Une loi de comportement modélisant l'effet des cycles thermiques sur la roche calcaire de La Roque Gageac d'un point de vue macroscopique a été proposée. À cette fin, une loi de comportement a été développée. Elle considère la roche comme un matériau composite constitué par de deux composantes, chacune dotée de sa propre loi de comportement thermo-mécanique. Le modèle a été ensuite implémenté dans le code Éléments Finis Code_bright et utilisé pour simuler les essais de laboratoire. Les résultats fournissent, d'une part, une validation du modèle par les mesures expérimentales et, d'autre part, des éléments pour une meilleure compréhension du développement des contraintes internes et de l'endommagement des échantillons pendant les cycles thermiquesThe environmental conditions may play a relevant role in the stability of rock slopes. In fact, weathering can contribute to the reduction of strength of the material, while hydro-mechanical loading actions may induce and eventually concentrate internal stresses in the rock massif. This Ph.D. thesis deals with the effect of atmospheric thermal cycles in rocks, from both experimental and numerical point of view. This research is focused on the real case of La Roque Gageac, a small town located in the south-west of France, which experiences rock fall risk. Installed instrumentation evidenced the main role played by thermal variations in rock falls occurrence. With the aim of isolating the effect of thermal cycles in the La Roque Gageac limestone, an experimental study is performed. Samples were obtained from blocks felt and intact cores drilled from the cliff face. These samples were submitted to thermal cycles between 10ºC and 50ºC, in order to mimic natural variations. The damage induced in the samples is evaluated through measurements of strains, elastic wave propagation velocities and uniaxial compressive strength. It is observed that samples experience an accumulation in strains and a reduction in the elastic wave propagation velocity and material strength during the imposition of thermal cycles. The response depends moreover on the mineralogical composition of the rock, which varies from sample to sample, as the cliff presents a large heterogeneity. Based on the results obtained in the experimental program, principal characteristics of thermal damage have been evaluated, proposing a constitutive model capable to reproduce the macroscopic mechanical response of the rock under the applied thermal cycles. With this purpose, a constitutive model has been developed. It considers the rock as a composite material made of two components endowed each with its own thermo-mechanical behavior. The model has been further implemented in the Finite element Code_Bright and used to model laboratory tests. Results provide, on the one hand, a validation of the model by the measurements and, on the other hand, insights into a better understanding of the development of internal stress and damage inside the samples during thermal cycles
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Clough, Matthew Thomas. "Ionic liquid thermal stability : implications for cellulose regeneration." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/25394.
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During the course of the past twenty years, the applications of contemporary ionic liquids have become increasingly widespread and varied; as solvents or catalysts for sustainable synthetic processes, as battery electrolytes, and for the dissolution and deconstruction of lignocellulosic biomass. These ionic liquid-assisted procedures frequently operate at high temperatures, therefore a comprehensive understanding of ionic liquid thermal stability is of great practical value. It has been demonstrated that ionic liquids incorporating carboxylate anions are capable of dissolving a substantial quantity of cellulose, the world's most abundant bio-renewable resource. The thermal stabilities of carboxylate ionic liquids are thoroughly characterised in this contribution, employing a broad range of experimental and computational methods. The impact of structural modification of the cation/anion on thermal stability is evaluated, and the prevailing thermal decomposition mechanisms are elucidated. Subsequently, the reactivity and decomposition pathways of cellulose and carbohydrate model compounds, dissolved in carboxylate ionic liquids, are uncovered. Thermal stabilities of carboxylate ionic liquids are found to be highly sensitive to relatively modest changes in the ion chemical structure (e.g. via fluorination or substitution of sulfur into the carboxylate group), and the experimental conditions. Furthermore, the prevailing thermal decomposition mechanisms are dependant on the electronic and steric properties of the ions. Crucially, the prototypical carboxylate ionic liquid 1-ethyl-3-methylimidazolium acetate is susceptible to transient and reversible formation of an N-Heterocyclic Carbene species through abstraction of the ring C2 proton, enabled by the basicity of the anion. This 'non-innocent' behaviour of carboxylate ionic liquids is critical in initiating a sequence of undesirable degradation pathways with dissolved carbohydrates, yielding imidazolium-derived adducts bearing hydroxyalkyl substituents. Strikingly, the analogous ionic liquid 1-butyl-3-methylimidazolium chloride does not initiate the unwanted series of reactions, yet is capable of dissolving a significant quantity of cellulose.
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Stahl, Brian James. "Thermal Stability and Performance of Foil Thrust Bearings." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1333722754.
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Zi, Aikaterini. "Thermal stability of severely deformed aluminium and copper." Clausthal-Zellerfeld Papierflieger, 2008. http://d-nb.info/992301130/04.
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Wong, Wai-leung Nelson. "Thermal stability of luminescence signals relevant to dating /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19471129.
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Chureemart, Jessada. "Orientation and thermal stability of advanced recording media." Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/4532/.
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This study is focused on the characterisation of advanced perpendicular recording media. In particular, the distribution of the effective easy axis orientation and the effect of silica (SiO2) content on the magnetic properties have been investigated via magnetic measurements. The variation of coercivity (HC) as a function of angle has been used to determine the easy axis distribution. Due to the efficiency of the SiO2 segregation at the grain boundaries leading to intergranular exchange decoupling, the magnetisation reversal of each single domain particle can be described by a numerical simulation using Stoner Wohlfarth theory. The standard deviation of a Gaussian distribution of easy axis orientations in the calculations replicates the magnetic easy axis distribution in thin film media. Three types of media; granular, exchange coupled composite (ECC) and the combination of exchange coupled composite and a coupled granular continuous (CGC) film have been studied. The crystallographic orientation was also measured via X-ray rocking curves for a comparison to be made. It was found that the ECC media which have their grains almost completely segregated by SiO2 give an excellent fit to the simulation with σ = 5 degree. The results for granular and ECC/CGC media do not fit to the same level of accuracy. In-plane and cross-section TEM analysis of both samples show far from perfect segregation leading to intergranular exchange coupling. The activation volume has been used to study the effect of SiO2 content in ECC media. Vact and the physical grain volume have been investigated for identical structures with three different levels of SiO2. Time dependence measurements have been used to determine Vact. TEM analysis has been also carried out to investigate the grain size distribution and to examine the grain boundaries. Vact and the single grain volume are in excellent agreement for the sample with the highest SiO2 content, indicating complete exchange decoupling.
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Martinez, Vilarino Sofia. "Thermal and transport properties of layered silicate nanomaterials subjected to extreme thermal cycling." ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/556.
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There is a raising need to design a safe and efficient cryogenic fuel tank for the new generation of reusable launch vehicles. The new tank design focuses on composite materials that can achieve the drastic reduction of empty/non-payload and structural weight. In addition to the materials to be compatible with cryogenic temperatures, interior components of the vehicle may be subjected to significantly elevated temperatures due to heat conduction from the vehicle surfaces during and after atmospheric re-entry. Therefore, there is the need to understand the performance of the composites after experiencing extreme thermal environments. Polymer-layered nanocomposites were studied to determine if they can reduce the permeation to the liquid nitrogen used as fuel in the next generation of space vehicles. Due to the non-permeable nature of the silicates and the exfoliated structure they adopt into the polymer matrix the addition of nanoclays into a polymer is expected to reduce the permeation to several gases without sacrificing the mechanical strength of the nanocomposite as well as providing additional improvements such as increase of thermal stability of the nanocomposite. Several types of matrixes modified with different types and content of nanoclays were tested and their permeability coefficient was calculated. The permeability values obtained for the different formulations assisted to understand the transport properties of nanoclay modified composites. In addition to this, thermal characterization was performed with the help of dynamic mechanical analysis, thermogravimetric analyses and differential scanning calorimetry studies. To determine if the nanoclay modified nanocomposites were affected by extreme temperatures the samples were subjected to thermal cycling. Comparison of the transport and thermal properties before and after cycling helped to analyze the effect of the addition of the nanoclays in the nanocomposites. Positron annihilation spectroscopy (PAS) was utilized to comprehend how the distribution of the free volume was affected by the presence of the nanoclays and by the thermal cycling applied. Different permeability models were utilized in an attempt to validate the experimental results of the different nanocomposite structures. This analysis was used to provide additional insight into many aspects of the experimental results obtained in this study.
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Mirmohammadi, Seyed Aliakbar, and Mohammadreza Behi. "Investigation on Thermal Conductivity, Viscosity and Stability of Nanofluids." Thesis, KTH, Tillämpad termodynamik och kylteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103801.
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In this thesis, two important thermo-physical properties of nanofluids: thermal conductivity and viscosity together with shelf stability of them are investigated. Nanofluids are defined as colloidal suspension of solid particles with the size of lower than 100 nanometer. Thermal conductivity, viscosity and stability of nanofluids were measured by means of TPS method, rotational method and sedimentation balance method, respectively. TPS analyzer and viscometer were calibrated in the early stage and all measured data were in the reasonable range. Effect of some parameters including temperature, concentration, size, shape, alcohol addition and sonication time has been studied on thermal conductivity and viscosity of nanofluids. It has been concluded that increasing temperature, concentration and sonication time can lead to thermal conductivity enhancement while increasing amount of alcohol can decrease thermal conductivity of nanofluids. Generally, tests relating viscosity of nanofluids revealed that increasing concentration increases viscosity; however, increasing other investigated parameters such as temperature, sonication time and amount of alcohol decrease viscosity. In both cases, increasing size of nanofluid results in thermal conductivity and viscosity reduction up to specific size (250 nm) while big particle size (800 nm) increases thermal conductivity and viscosity, drastically. In addition, silver nanofluid with fiber shaped nanoparticles showed higher thermal conductivity and viscosity compared to one with spherical shape nanoparticles. Furthermore, effect of concentration and sonication time have been inspected on stability of nanofluids. Test results indicated that increasing concentration speeds up sedimentation of nanoparticles while bath sonication of nanofluid brings about lower weight for settled particles. Considering relative thermal conductivity to relative viscosity of some nanofluids exposes that ascending or descending behavior of graph can result in some preliminary evaluation regarding applicability of nanofluids as coolant. It can be stated that ascending trend shows better applicability of the sample in higher temperatures while it is opposite for descending trend. Meanwhile, it can be declared that higher value for this factor shows more applicable nanofluid with higher thermal conductivity and less viscosity. Finally, it has been shown that sedimentation causes reduction of thermal conductivity as well as viscosity. For further research activities, it would be suggested to focus more on microscopic investigation regarding behavior of nanofluids besides macroscopic study.
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Acharya, Ananta R. "Indium Nitride Surface Structure, Desorption Kinetics and Thermal Stability." Digital Archive @ GSU, 2013. http://digitalarchive.gsu.edu/phy_astr_diss/62.
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Unique physical properties such as small effective mass, high electron drift velocities, high electron mobility and small band gap energy make InN a candidate for applications in high-speed microelectronic and optoelectronic devices. The aim of this research is to understand the surface properties, desorption kinetics and thermal stability of InN epilayers that affect the growth processes and determine film quality as well as device performance and life time. We have investigated the structural properties, the surface desorption kinetics, and the thermal stability using Auger electron spectroscopy (AES), x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). Investigations on high pressure chemical vapor deposition (HPCVD)-grown InN samples revealed the presence of tilted crystallites, which were attributed to high group V/III flux ratio and lattice mismatch. A study of the thermal stability of HPCVD-grown InN epilayers revealed that the activation energy for nitrogen desorption was 1.6±0.2 eV, independent of the group V/III flux ratio. Initial investigations on the ternary alloy In0.96Ga0.04N showed single-phase, N-polar epilayers using XRD and HREELS, while a thermal desorption study revealed an activation energy for nitrogen desorption of 1.14 ± 0.06 eV.
HREELS investigations of atomic layer epitaxy (ALE)-grown InN revealed vibrational modes assigned to N-N vibrations. The atomic hydrogen cleaned InN surface also exhibited modes assigned to surface N-H without showing In-H species, which indicated N-polar InN. Complete desorption of hydrogen from the InN surface was best described by the first-order desorption kinetics with an activation energy of 0.88 ± 0.06 eV and pre-exponential factor of (1.5 ± 0.5) ×105 s-1.
Overall, we have used a number of techniques to characterize the structure, surface bonding configuration, thermal stability and hydrogen desorption kinetics of InN and In0.96Ga0.04N epilayers grown by HPCVD and ALE. High group V/III precursors ratio and lattice mismatch have a crucial influence on the film orientation. The effects of hydrogen on the decomposition add to the wide variation in the activation energy of nitrogen desorption. Presence of surface defects lowers the activation energy for hydrogen desorption from the surface.
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Saleem, Hassan. "Thermal Stability of cubic and nanocrystalline arcevaporated TiCrAlN coatings." Thesis, Linköpings universitet, Nanostrukturerade material, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-106139.
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(TixCryAlz)N coatings were deposited on WC-Co substrate using cathodic arc evaporation technique to investigate phase transformation, thermal stability, and high temperature mechanical properties. Two compositions Ti0.34Cr0.33Al0.33N and Ti0.24Cr0.02Al0.74N were studied and compared with industrial standard hard TiAlN coating. These compositions were annealed at 800 oC up to 1100 oC. X-ray diffractogram showed a mixture of cubical and hexagonal phases in as-deposited state for high Al content composition. Differential scanning calorimetry showed that spinodal decomposition starts late compared to TiAlN coating. The results from nanoindentation did not show age hardening in Ti0.34Cr0.33Al0.33N composition while composition Ti0.24Cr0.02Al0.74N showed a significant increase in hardness compared with TiAlN coating. Also the Ti0.24Cr0.02Al0.74N retains its hardness over a wide temperature range while TiAlN coating hardness decreases after annealing at 900 oC. Upon annealing at 1400 oC, the coating decomposes into equilibrium phases i.e., c-TiN and h-AlN while Cr found to be in oxides form. HRTEM results revealed that the coating consists of nanocrystalline grains with defects rich regions.
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Regonini, Domenico. "Anodised TiO2 nanotubes : synthesis, growth mechanism and thermal stability." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492286.
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Anodised titanium dioxide (titania, TiO2) nanotubes have been widely studied over the last few years, following the discovery in 1999 of nanoporous TiO2 films prepared via anodisation in aqueous solution containing small quantities of hydrofluoric acid. The synthesis of nanotubular titania by anodisation, a relatively simple and low cost technique, represents a motivation for scientists, considering the impact that such a material could have on a variety of applications, including gas-sensing, biomedical, photocatalysis, and photovoltaics. This research project has focused on the optimisation of the growth process of anodic titania nanotubes, both in an aqueous (NaF/Na2SO4) and an organic (Glycerol/NaF) electrolyte containing fluorine ions. Reproducibility and the ability to generate anodic films having a thickness of several micrometers are fundamental steps to be achieved before investigating any possible application of the nanotubes. To characterise the anodic specimens and build upon the general lack of information on the growth mechanism, a comprehensive study of the different stages of the process has been performed, using Scanning and Transmission Electronic Microscopy (SEM and TEM). Among the questions to be addressed in this thesis, is to establish whether the anodic film undergoes a transition from pores to tubes or develops a tubular morphology from the beginning of its growth. Additional characterisation of the anodisation process includes the study of current-time curves, and chemical composition analysis of the anodic layers using X-ray Photo-Electron Spectroscopy (XPS). The thermal stability of the nanotubes and structural/morphological changes as a result of heat treatment at different temperatures were also studied, again using SEM, TEM, XPS and Raman spectroscopy. The final part of the thesis is dedicated to preliminary work on the use of anodised TiO2 nanotubes in Dye Sensitized Solar Cells (DSSCs), along with suggestions for future works and general conclusions.
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Landström, Anton. "Thermal Stability of Carbon Nanotubes and Role of Intercalation." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-61074.
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Research in carbon nanotubes (CNTs) has become a very active field in the past decades, with much interest in their electronic and mechanical properties. However, the thermal properties of CNTs are still not well understood, in particular the process of annealing; i.e. purification of samples by desorption of internal and external impurities. Understanding the response of carbon nanotubes to high temperatures is critical for proper characterization of CNTs and CNT-based materials; especially because purportedly non-destructive characterization techniques such as Raman spectroscopy can induce high temperatures through laser heating. This thesis delineates an experiment aimed at elucidating the annealing and destruction process of carbon nanotubes. The experiment consists of heat treatments of single-walled nanotubes (SWNTs), monitoring nanotube abundance and purity by Raman spectroscopy. The samples are HiPCO-produced SWNTs of very high purity, separated in open and closed (end-capped) tubes. They are wetted with H2O in order to fill the open tubes, but are otherwise kept in their raw (as-produced) form of flakes of bundled tubes. This means that they have a low thermal conductivity as compared to dispersed CNTs, making them sensitive to overheating. The samples are heated in both air and argon environments in order to study the effect of oxidation. It is found that all tubes exhibit some annealing after heat treatment at temperatures as low as 100 °C. Temperatures higher than that are sufficient to degrade the samples in the case of closed tubes, which are found to be more thermally sensitive than open tubes, especially in air environments as oxidation is found to be a major component of the destructive mechanisms of CNTs. With higher temperature heat treatments at 500 °C, some of the open tubes exhibit a further step of annealing. This correlates with tube diameter, thus indicating that this annealing step can be associated with the desorption water from the CNTs' interior. A transition is found after heat treatment at 600 °C, although the new phase is not conclusively established, with evidence pointing to either charge transfer (by way of intercalation of dopant atoms in CNTs) or graphitization.
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Silwana, Nothemba. "Structure and thermal stability of selected organic inclusion compounds." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/2618.
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Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2012.Crystal engineering is the synthesis of new crystalline materials with specific chemical and physical properties which allows the comprehensive understanding of the non covalent interactions that occur between molecules in the crystalline state. This has lead to extensive work being done in terms of host design. The study of non-covalent interactions formed by - these materials is crucial to understanding many biological processes. This study focuses on the inclusion compounds of 1, 4-bis (diphenylhydroxymethyl) benzene H, a host compound engineered by EWeber, that conforms to Weber's rules for host design as it is bulky, rigid, and has hydroxyl moieties that act as hydrogen-bonding donors. A Cambridge Structural Database (CSDversion 5.33) search has revealed that no research has been conducted on this host compound. Characterization of the compounds were conducted using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), hot stage microscopy (HS), gas chromatography (GC), powder X-ray diffraction(PXRD) and single X -ray diffraction. Host: guest ratios determined from TG analysis were correlated with structural analysis results. We have successfully prepared inclusion compounds with N, N- dimethylformamide(DMF) N, N- dimethylacetamide (DMA), N-methylformamide (NMF) and N-methylacetamide (NMA), 2-picoline, 3-picoline, 4-picoline, pyridine and morpholine. Following which a series of competition experiments were conducted to establish the selectivity profile of the host by dissolving the host in an excess of two guests pairs, between DMF: DMA, DMF: NMF, DMF: NMA, DMA: NMF, DMA: NMA and NMF: NMA. The results of the competition experiment showed that the host had high selectivity for DMF and the selectivity profile follows a trend as follows DMF>NMA>NMF>DMA. The results for the competition experiments between the picolines, pyridine and morpholine were inconclusive.
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Tang, Alvin Chiu Tak. "Activation and thermal stability of ion implanted gallium arsenide." Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/844401/.
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Results on the activation characteristics of Be, Be+P, Zn and Zn+P implants In GaAs have been presented. It is found that the in-diffusion of zinc and the out-diffusion of beryllium atoms has been prevented through the co-implantation of phosphorus. High hole concentrations of the order of 6x1019/cm3 have been obtained for the Zn+P Implanted samples. It has also been demonstrated for the first time that by performing the co-implantation of phosphorus and rapid thermal annealing, an effective way of preventing the out-diffusion of beryllium at annealing temperatures up to 950°C for 10s has been achieved. The Influence of heat treatment on the rapid thermally annealed, ion-implanted samples has also been investigated. It is found that the temperature at which the electrical properties change significantly is at 600°c for the Be, Mg and Zn Implanted samples and at 700°C for the selenium implanted samples respectively. These changes in the sheet carrier concentration are observed to be reversible for the selenium and zinc implanted samples after further annealing at high temperatures. This phenomenon is not observed for the beryllium and magnesium Implanted samples. A value In the range of 1.5-2.5eV has been identified as the energy which characterises the rate dependent step for the reversible processes for the zinc and selenium implanted samples. This energy value is thought to correspond to the diffusion of gallium atom/vacancy. Similarly, an energy of about 1eV has been identified for the beryllium Implanted samples. It is concluded that the decrease in the sheet hole concentration for the beryllium implanted samples is due to the out-diffusion of the beryllium atoms. The value of 1ev is thought to be the energy which characterises the diffusion of beryllium.
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Agulov, A. V., V. A. Turchenko, S. A. Goncharova, U. V. Kudelin, A. A. Goncharov, A. I. Bazhin, and V. A. Stupak. "Thermal stability of film nanostructure of high-melting compounds." Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20656.
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Janjic, Nikolina. "Structures and thermal stability of selected organic inclusion compounds." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/14968.
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Includes bibliographical references.The crystal structures of 1,1 ,6,6-Tetraphenyl-hexa-2,4-diyne-1 ,6-diol and 5-(3,5- Dicarboxyphenylethynyl)-isophthalic acid hosts with various guests have been elucidated. Depending on their structural properties and the way in which the host components pack, the guests may become trapped in spaces or voids, stacked in channels or sandwiched between layers of hosts. The crystal structures are stabilised by hydrogen bonding networks created by host-guest intermolecular interactions. The host hydroxy moieties adopt a trans conformation in 1,1 ,6,6-Tetraphenyl-hexa-2,4-diyne-1 ,6- diol host-guest inclusion componds. Host-guest hydrogen bonding in 5-(3,5- Dicarboxyphenylethynyl)-isophthalic acid salts occurs via the carboxylate group of the host anion. Hydrogen bond formation was the directing force determining the form of a host-guest array. The crystal structures of four inclusion compounds with 1,1 ,6,6-Tetraphenyl-hexa-2,4- diyne-1 ,6-diol host and six hydrated salt structures with 5-(3,5-Dicarboxyphenylethynyl)isophthalic acid host were solved using the single crystal X-ray diffraction technique. In addition the thermal stability and the structural properties of all compounds were investigated by thermal analysis techniques, including differential scanning calorimetry, thermogravimetry and hot-stage microscopy.
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Celer, Ewa B. "Thermal and Hydrothermal Stability of Polymer-Templated Siliceous Mesostructures." Kent State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=kent1185232734.
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Uzzell, Jamar. "STRUCTURAL BASIS FOR THERMAL STABILITY OF THERMOPHILIC TRMD PROTEINS." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2539.
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Thermal stability of theG37 tRNA methyltransferase proteins from Thermotoga maritima and Aquifex aeolicus have been compared using Differential Scanning Calorimetry. It was shown that the Thermotoga protein is remarkably stable and is denatured at temperatures in excess of 100 degrees Centigrade. The Aquifex aeolicus protein was less stable, denaturing broadly at temperatures between 55oC and 100oC. In contrast, the mesophilic E. coli protein was completely denatured at 55oC. Enzymatic activity of the proteins was measured at various temperatures. Both the Thermotoga and Aquifex enzymes are active at ambient temperatures, and display a significant decrease in activity when the temperature is raised above 50oC. This may relate to subtle changes in protein structure causing an effect on the tRNA based assay. Both enzymes contain inter subunit disulfide bonds which might contribute to thermal stability. Assays of the enzymes in the presence of high concentrations of Dithiothreitol (DTT) did not significantly reduce activity at higher temperatures, but did stimulate activity at lower temperatures. Site directed mutagenesis of non -conserved protein sequences within Thermotoga maritima were initiated in order to determine what structures might confer heat stability on the protein. Alanine mutagenesis of lysine residues 103,104 led to reduced catalytic activity, but did increased activity at higher temperatures. Aspartate is the most common residue at the relative position 166 in the variable loop of most TrmD genes. It has been shown that in E. coli this is essential for catalytic activity and possibly the residue which carries out N1 deprotonation on residue G37 in tRNA. In Thermotoga glutamate is present at this position. Alanine mutagenesis of this residue did not eliminate activity suggesting another nearby residue may function in this capacity in the Thermotoga TrmD protein.
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Hattori, Tae. "Investigation into Stability, Transition and Turbulence of Thermal Plumes." Thesis, The University of Sydney, 2012. http://hdl.handle.net/2123/9338.
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In this thesis, the stability, transition and turbulence of thermal plumes were investigated by numerical simulation. Experiments were also conducted, but only for the validation of the simulation code being used. The effect of variable transport properties on a large eddy simulation of a turbulent axisymmetric plume was examined, and it was shown that an in-house incompressible Navier-Stokes solver, which is based on a standard Smagorinsky LES model, with the effects of variable properties incorporated using a modified Sutherlands law, predicts the correct statistical behaviours of the turbulent plume. The near-field puffing instability in thermal planar plumes, which had received little attention in the literature, was investigated by direct numerical simulation. The associated lapping flow instability, forming bulge structures over a heated floor section, was studied using a channel flow model, which allows the lapping flow velocity to be varied. The parametric dependencies were found for the bulge formation and the oscillation frequencies in the lapping flow. Further, the Prandtl number dependent transitional behaviours in the near-field were investigated, and direct stability analysis was conducted to study the lapping flow and stem instabilities. Experiments using a shadowgraph technique and an in-house, two-dimensional, two-component particle image velocimetry, with water as the working fluid, provided validations for the near-field unsteady behaviours of thermal plumes. A ventilated filling box flow with a transitional planar plume was also investigated by direct numerical simulation. A mapping of transitional flow behaviours was obtained, and the parametric dependencies of turbulence statistics and mean flow characteristics were investigated. The three-dimensionality was shown to have only minor effects on the transitional ventilated filling box flows being considered.
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Bocchetti, Virgile. "Melting, Surface Relaxation and Thermal Stability of Crystalline Solids." Phd thesis, Université de Cergy Pontoise, 2013. http://tel.archives-ouvertes.fr/tel-00949404.
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In this thesis we study thermal properties and melting behavior of crystals using Monte Carlo simulations. The Monte Carlo method is very difficult to implementfor melting investigation, unlike for problems where particles (such as spins) are localized on lattice sites. However, once it is well conceived, it is among themost efficient numerical techniques, to be able to study melting.We have created a high-performance algorithm based on an optimized Verlet procedure, which allowed us to investigate thermalproperties up to the melting. This optimization was necessary for treating an important number of atoms in very long runsto have good statistics, without prohibitive CPU time.We applied our algorithm to rare-gas crystals using the Lennard-Jones potential with parameters given by Bernardes which are widely used in the literature since 1958.Our results, thanks to their precision, show that we should modify these parameters in order to have a good agreement with experimental data.We studied melting of bulk semiconductors and metals by considering the case of Si and Ag. These materials have been chosen to serve our project about Silicene. Silicon has a diamond structure, and silver has the FCC lattice structure, both of them have been well experimentallystudied with well-known experimental melting temperatures. In spite of this, no good simulations have been done. For Si, one of the major problems is thechoice of a potential which stabilizes the diamond structure at finite temperatures. We have applied our algorithm to these materials using the multi-body Stillinger-Weber and Tersoff potentials for Si and the Gupta and EAM(embedded atom method) potentials for Ag. We obtained results much more precise than in early simulations and in good agreement with experiments.We also studied the Ag(111) surface trying to elucidate the long-standing controversy whether or not there is the ''anomalous'' thermal expansion whichhappens, for certain metals, when the inter-layer distances between the topmost atomic planes changes from a contracted situation to an expansion with respect tothe bulk distance. We showed that, depending on the potential, the anomalous crossover exists and the surface melting can occur at a temperature very far belowthat of the bulk melting. This is the case of EAM potential, but not the Gupta potential where surface melting occurs just belowbulk the melting.Finally, we studied the thermal stability of a stand-alone silicene sheet. Silicene is the Si counterpart of 2D carbon sheet called ''graphene". Siliceneattracts the attention of many researchers, because of its electronic and thermal properties which seem to be comparable to those of graphene which is actually oneof the most studied materials, due to its unusual properties susceptible for revolutionary device applications. Furthermore, because it is a Si-based material, thecompatibility, with the actual Si-based electronic industry, is expected to be better than for graphene. We show that, using the Tersoff potential with twosets of parameters (the original and the modified ones), the silicene 2D honeycomb structure is stable up to high temperatures without buckling. We have tested the Stillinger-Weberpotential: it yields a buckled honeycomb sheet at low temperatures but the 2D structure is destroyed in favor of a tri-dimensional structureat the melting. Discussion on this point is given.A general conclusion with some open perspectives is given at the end.
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RONCALLO, GIACOMO. "Thermal Barrier Coatings phase stability and in service degradation." Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1046720.
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This thesis work is the result of a collaboration between Ansaldo Energia's Materials Laboratory and the Department of Chemistry and Industrial Chemistry of the University of Genoa.
The study developed from the industrial need to better understand the degradation processes of the turbine blade thermal barriers coating already used in Ansaldo Energia gas turbines and to test new materials that could be used in the future.
The material mostly used as a protective coating is 7YSZ (ZrO2 with 7 wt% of Y2O3) which has excellent characteristics and has been used inside turbines for land use and on aircraft engines since the 1960s.
The need to increase the operating temperature of the machines, with a consequent increase in efficiency, makes it necessary to modify this material, as it tends to degrade when it works at temperatures above 1300°C.
With cooling from high temperatures, the 7YSZ tends to modify its crystallographic structure until the formation of the monoclinic phase, extremely harmful because it is a source of mechanical fragility and an increase in thermal conductivity.
A new material has been proposed by Ansaldo Energia, consisting of a double layer, with the upper layer formed by 14YSZ (ZrO2 with 14% of Y2O3), while the lower one remains 7YSZ for better compatibility with the metal substrate.
The new material is crystallographically stable but its properties must be characterized before being used in gas turbines. Starting from their precursor powders and reacting long exposure time at high temperature of sprayed material.
In addition, the TBC modifications due to interactions with CMAS (Calcium-Magresium-Alluminium-Silicates) have been investigated. Several tests have been performed for times up to 10000h and temperatures between 1100 and 1400°C. The samples have been examined mainly to evaluate the effect of the interaction on the formation of the monoclinic and other secondary phases, the modification of the microstructure and the variation of physical properties.
Finally, to better study the interaction phenomena between oxides, a multicomponent thermodynamic database (Al-Ca-Si-Mg-Si-Y-Zr-O) has been implemented using the CALPHAD method.
The thesis work has been divided into an experimental part, carried out at the Ansaldo Energia laboratories and a thermodynamic modeling part, conducted at the Department of Chemistry and Industrial Chemistry. The thermodynamic database for oxides has been also implemented through the experimental study of the MgO-Y2O3-ZrO2 system at the University of Freiberg in Germany, in the group of Prof.Olga Fabrichnaya.
The experimental part focused on the analysis of thermal barrier specimens exposed at high temperature and examined with usual materials characterization techniques.
For this purpose, quantitative analysis of the detected phases has been carried out using Xray diffraction with quantification using the Rietveld method. The microstructural analyzes have been done using optical microscope and FEG-SEM (Field Emission Gun-Scanning Electron Microscope) equipped with EDS (Energy- dispersive detector) and EBSD (Electron Back Scattered Diffraction) to evaluate microstructure variations, phase compositions, grain shapes and dispersion of the phases within the sample.
Furthermore, thermal conductivity tests have been carried out, using thermography technique, thank to the collaboration with the group of Dr. Paolo Bison and Dr. Giovanni Ferrarini of the ITC-CNR of Padua.
At the same time, by means of thermodynamic modeling according to the CALPHAD method, the development of a thermodynamic database has been started. It includes the seven main oxides relevant to the CMAS-TBC interaction and our work was mainly focused on the definition of thermodynamic models for the description of the phases present in the system and the assessment of a series of pseudo-binary and pseudo-ternary subsystems .
The results obtained allow the definition of the critical conditions of the tested materials in service, to better understand their evolution and the degradation and to define the range of use.
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Mores, S. "Development of instrumentation and modelling in accelerating rate calorimetry." Thesis, London South Bank University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357315.
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Conley, Mark Lewis. "Mechanistic investigations and optimizations of thermal stability in polyethylene and polyvinyl chloride blends." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53938.
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The thermal stability of two distinct blended polymer systems was examined. A model for polyethylene was used to investigate the vulnerability of polyethylene to premature crosslinking in industrial crosslinking conditions. Careful experiments were conducted to gather evidence of the interaction between a peroxide crosslinking agent and a specific antioxidant additive. Multiple lines of evidence were combined to propose a complete mechanism of interaction between the two species. The mechanism was further tested and a hypothesis was proposed for the reduction in premature crosslinking exhibited when the two species are present in polyethylene blends. A specific aspect of the proposed mechanism warranted further investigation on its own. The acid-catalyzed degradation of the peroxide initiator was thoroughly investigated.
The thermal degradation of polyvinyl chloride was also studied. Model compounds were reacted with carboxylates to determine the relative rates of stabilization at various polymer defect sites. These model studies were combined with weight loss and color change investigations of bulk polymer systems. The knowledge gained from the model and polymer studies allowed for the proposal and examination of two novel stabilizing salt systems. The efficacy of the new stabilizers is presented.
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Melane, Babalwa Blossom. "Thermal and photostability studies of furosemide and its cyclodextrin mixtures." Thesis, Rhodes University, 2002. http://hdl.handle.net/10962/d1007625.
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Furosemide (Lasix®), abbreviated as FR and also known as frusemide, is a drug used for renal problems and treatment of cardiac edema. Various polymorphic forms of furosemide, dependent upon the method of preparation and thermal treatment, have been reported. The main thermal decomposition product of furosemide has been identified as saluamine. The dissolution properties of furosemide have also been reported to be improved by complexation with beta-cyclodextrin. Photostabilities of the different crystal forms have been studied. Differential scanning calorimetry (DSC) and thermogravimetry (TG) have been used to examine the thermal behaviour of furosemide itself and of its physical and kneaded mixtures with betacyclodextrin (BCD) and gamma-cyclodextrin (GCD). There is strong evidence from DSC that complex formation between FR and GCD occurs. This is supported by IR and XRD data. Decreases in the intensity and broadening of the characteristic carbonyl (1660 cm'l) and amine (1588 cm⁻¹) bands in the kneaded mixture, compared to the physical mixture, were observed with IR. X-ray diffraction results for the 1:3 molar ratio FR/GCD kneaded mixture showed a halo diffraction pattern characteristic. of an amorphous solid and did not resemble patterns from the drug, or the gamma, cyclodextrin, or the physical mixture. Photostability studies have been conducted on solid furosemide and its mixtures with GCD or BCD. An HPLC method was developed to determine the amount of drug remaining after exposure and the presence of any degradants. Results indicated that about 10% degradation of the drug occurred during exposure for 16 hours at 550 W/m², with the appearance of polar degradants. Although IR and DSC results for the 1:3 molar ratio FR/GCD kneaded mixture showed a probable strong interaction between FR and GCD, the photostability of FR was decreased. The 1 :3 molar ratio FR/BCD kneaded mixture showed less photo-degradation than the 1:3 molar ratio FR/GCD mixture under similar conditions, suggesting that inclusion of the drug molecule (FR) is different in the two cyclodextrins.
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Bolander, Michael John. "Thermal instability with radiation by the method of energy." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/19150.
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Jia, Zichen. "Stability, aggregation kinetics and aggregates thermal restructuring of polymer colloids /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16913.
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Ku, Nai-Yuan. "Thermal Stability of Zr-Si-N Nanocomposite Hard Thin Films." Thesis, Linköping University, Linköping University, Department of Physics, Chemistry and Biology, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-58622.
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Mechanical property and thermal stability of Zr-Si-N films of varying silicon contents deposited on Al2O3 (0001) substrates are characterized. All films provided for characterization were deposited by reactive DC magnetron sputter deposition technique from elemental Zr and Si targets in a N2/Ar plasma at 800 oC. The hardness and microstructures of the as deposited films and post-annealed films up to 1100 oC are evaluated by means of nanoindentation, X-ray diffractometry and transmission electron microscopy. The Zr-Si-N films with 9.4 at.% Si exhibit hardness as high as 34 GPa and a strong (002) texture within which vertically elongated ZrN crystallites are embedded in a Si3N4 matrix. The hardness of these two dimensional nanocomposite films remains stable up to 1000 oC annealing temperatures which is in contrast to ZrN films where hardness degradation occurs already above 800 oC. The enhanced thermal stability is attributed to the presence of Si3N4 grain boundaries which act as efficient barriers to hinder the oxygen diffusion. X-ray amorphous or nanocrystalline structures are observed in Zr-Si-N films with silicon contents > 13.4 at.%. After the annealing treatments, crystalline phases such as ZrSi2, ZrO2 and Zr2O are formed above 1000 oC in the Si-containing films while only zirconia crystallites are observed at 800 oC in pure ZrN films because oxygen acts as artifacts in the vacuum furnace. The structural, compositional and hardness comparison of as-deposited and annealed films reveal that the addition of silicon enhances the thermal stability compared to pure ZrN films and the hardness degradation stems from the formation of oxides at elevated temperatures.
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Motaung, David Edmond. "Structure property relationship and thermal stability of organic photovoltaic cells." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6331_1307942460.
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In this thesis, regioregularpoly( 3-hexylthiophene) (rr-P3HT) polymer was used as a light absorption and electron donating material, while the C60 fullerene and its derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used as electron acceptor materials. The effect of solvent to control the degree of mixing of the polymer and fullerene components, as well as the domain size and charge transport properties of the blends were investigated in detail using P3HT:C60 films. The photo-physical, structural and electrical transport properties of the polymer blends were carried out according to their ratios. A distinctive photoluminescence (PL) quenching effect was observed indicating a photo-induced electron transfer. In this thesis, the effect of solvents on the crystallization and interchain interaction of P3HT and C60 fullerene films were studied using XRD, UV-vis, PL, Raman and FTIR spectroscopy. The polymer blends formed with non-aromatic solvents exhibited an improved crystallinity and polymer morphology than that formed with aromatic solvents. An improved ordering was demonstrated in the polymer films spin coated from non-aromatic solvents. This indicates that the limited solubility of rr P3HT in a marginal solvent such as non-aromatic solvents can offer a strategy to obtain highly ordered crystal structures and lead directly to optimal morphologies on the films.
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Tomicki, Piotr. "Thermal stability and color change of myoglobin in model systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ27548.pdf.
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Velazquez, Alberto. "Microstructure and thermal stability of PVC and chemically modified PVC." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74243.
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This thesis describes a study of the effect of microstructure on the thermal stability of poly(vinyl chloride), PVC, vinyl chloride-ethylene, VC-E, and vinyl chloride-propylene, VC-P, copolymers obtained by chemical modification of PVC. The VC-E copolymers, with an ethylene content between 1.1 and 21 mole %, are random copolymers with approximately the same degree of polymerization as the original PVC. A decrease in the number of defect sites is observed with extent of reaction. Concomitantly, the syndiotacticity increases. The VC-P copolymers, with propylene content of ca. 0.1%, also have less labile chlorines than the homopolymer since these react preferentially.The thermal stability of solid state samples was studied, at temperatures between 150 and 190$ sp circ$C under a nitrogen atmosphere, using a conductimetric method to measure evolved HCl. The thermal stability of the modified samples is improved relative to that of the initial homopolymers. For the VC-E copolymers, a linear relationship is observed between the rates of degradation and the number of labile chlorines, total double bonds and the degree of syndiotacticity. The role of syndiotacticity on the thermal degradation behavior is confirmed in results obtained with two unmodified PVC samples, with a similar number of defect sites but different syndiotacticity. The more syndiotactic resin shows a higher thermal stability. The average polyene sequence length is independent of the ethylene concentration. Thus, the ethylene units do not interfere in the development of polyene sequences.
The VC-P copolymers also show improved thermal stability as compared to that of PVC. However, the improvement is less than that of the VC-E copolymers, due to a lower extent of substitution of labile sites.
PVC previously saturated with HCl shows a markedly increased rate of degradation reflecting the autocatalytic role of HCl. For the PVC coated samples, a decrease in the degradation rates with decreasing PVC film thickness is observed due to more efficient removal of HCl. The PVC mixtures with Chromosorb W or silica gel exhibit a decrease in the dehydrochlorination rate constants with decreasing PVC content. The inert substrate acts as a diluent and avoids agglomeration of the samples and thus facilitates the removal of HCl.
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Pattenden, Caroline Sarah. "The effect of radiation on the thermal stability of polyisobutylene." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366649.
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