Dissertations / Theses on the topic 'Carbides Effect of high temperatures on'
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Wingbrant, Helena. "Development of high temperature SiC based field effect sensors for internal combustion engine exhaust gas monitoring." Licentiate thesis, Linköping University, Linköping University, Applied Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-4673.
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While the car fleet becomes increasingly larger it is important to lower the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from high NOx emissions and particulates, in the case when diesel is utilized, and emissions at cold start from gasoline engines. One way of treating the high NOx levels is to introduce ammonia in the diesel exhausts and let it react with the NOx to form nitrogen gas and water, which is called SCR (Selective Catalytic Reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose.
This thesis presents the efforts made to test the SiC-based field effect transistor (SiC-FET) sensor technology both as an ammonia sensor for SCR systems and as a cold start lambda sensor. The SiC-FET sensor has been shown to be highly sensitive to ammonia both in laboratory and engine measurements. As a lambda sensor it has proven to be both sensitive and selective, and its properties have been studied in lambda stairs both in engine exhausts and in the laboratory. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application.
On the day of the public defence of the doctoral thesis, the status of article III was: in press. Report code: LiU-Tek-Lic-2003:50.
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Mellin, Hannu Kaarlo Olavi. "The effect of high temperatures (30 degrees Celsius) on biological nutrient removal performance." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/21729.
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The main objective of this investigation was to evaluate activated sludge biological nutrient removal (BNR) performance at elevated temperatures for possible application of nitrification denitrification (ND) and ND biological excess phosphorus removal (NDBEPR) systems to municipal wastewater treatment in the equatorial and tropical regions or to combined treatment of municipal and anaerobically (thermophilic) pretreated paper and pulp industry wastewaters in the very cold northern forested regions. To accomplish this objective, a ND Modified Ludzack Ettinger (MLE) system and a NDBEPR University of Cape Town (UCT) system were operated at 30°C and 10 days sludge age for a period of 582 days. During the investigation 41 sewage batches, each lasting about two weeks, of real sewage from the Mitchells Plain municipal wastewater treatment plant (Western Cape, South Africa) were fed to the systems. The two systems were sampled and tested ,almost daily for Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), Free and Saline Ammonia (FSA), nitrate, nitrite, Total Phosphorus, Volatile Settleable Solids (VSS), Total Settleable Solids (TSS), pH, Oxygen Utilization Rate (OUR) and diluted sludge volume index (DSVI) in the influent, anaerobic, anoxic and aerobic reactors and effluent as appropriate. Also, in order to determine the kinetic rates of nitrification, denitrification and readily biodegradable COD (RBCOD) conversion to Volatile Fatty Acids (VF A), aerobic, anoxic and anaerobic batch tests were conducted at 30°C on sludge harvested from the two systems and microscopic examination of the sludges was undertaken every four weeks to identify the filamentous organisms in the systems.
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Krishnamoorthy, Vijay. "Effect of gas density on corrosion in horizontal multiphase slug flow at high temperatures and pressures." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177096097.
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Fry, J. C. "A study of the cooling effect of water sprays on steel strip at high temperatures." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637015.
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To meet customers' demands for increased quality and product consistency, together with the production of a wider range of steels there is a need for accurate temperature control throughout the whole cooling path on the hot Strip Mill. This requires a cooling system that couples the required cooling rate with the heat transfer capabilities of the water spray system and the production speed and line length, however, information on the heat transfer characteristics of water sprays is sparse. Therefore, the project described in this thesis has investigated the heat transfer characteristics of water sprays. The project has been two fold. Initially a steady state test apparatus has been designed, built and commissioned which allows the heat transfer coefficient of a single pressure atomised water spray to be evaluated under various operating conditions. Secondly, the apparatus has been used to conduct experiments on two commercially available spray nozzles with the aim of determining the relationship between the spray operating conditions and the heat transfer coefficient. The work has demonstrated that a steady state technique can be used to determine the heat transfer coefficient of a spray at surface temperatures between 650°C and 950°C. The experimental work has shown that the heat transfer coefficient increases with increasing surface temperature, increasing flow rate and decreasing stand off distance. For the two nozzles tested correlation equations have been derived which allow the heat transfer coefficient to be evaluated in terms of the surface temperature, flow rate and stand off distance. Finally, the application of the correlation equations to the design and improvement of water cooling lines has been considered.
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Peng, Yucheng. "EFFECT OF HIGH TEMPERATURES ON ADHESIVE BOND DURABILITY AND TOXIC CHEMICAL PRODUCTION FOR ENGINEERED WOOD PRODUCTS." MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-07082008-153319/.
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The objectives of this research were to investigate the heat resistant performance of a structural adhesive and to analyze the contribution of the adhesive to the chemical emissions from the glued wood products affected by the elevated temperatures. Phenol-resorcinol-formaldehyde (PRF) and two wood species, southern pine (Pinus palustris) and Douglas-fir (Pseudotsuga menziesii), were investigated. The dynamic mechanical analysis (DMA) test results showed that the heat durability performance of cured PRF resin was better than that of the two wood species used in this study. The results indicated that the fire safety of PRF bonded wood products should be comparable to solid wood products. The pyroysis products obtained from pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) system showed that most of the pyrolysis products of glued wood samples were same as those of wood and adhesive samples at the same temperature level except a few compounds, such as carbon disulfide, Cyclopropyl carbinol, acetaldehyde, furfural and others.
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Lindsay, John Christopher. "Stress corrosion cracking and internal oxidation of alloy 600 in high temperature hydrogenated steam and water." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/stress-corrosion-cracking-and-internal-oxidation-of-alloy-600-in-high-temperature-hydrogenated-steam-and-water(1d6b037c-baf1-4397-a6c9-43835e7bb39a).html.
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In this study, the possibility of using low pressure hydrogenated steam to simulate primary water reactor conditions is examined. The oxides formed on Alloy 600 (WF675) between 350 Celsius and 500 Celsius in low pressure hydrogenated steam (with a ratio of oxygen at the Ni/NiO to oxygen in the system of 20) have been characterised using analytical electron microscopy (AEM) and compared to oxide that formed in a high pressure water in a autoclave at 350 Celsius with 30 cc/kg of hydrogen. Preferential oxidation of grain boundaries and bulk internal oxidation were observed on samples prepared by oxide polishing suspension (OPS). Conversely, samples mechanically ground to 600 grit produced a continuous, protective oxide film which suppressed the preferential and internal oxidation. The surface preparation changed the form of the oxides in both steam and autoclave tests. The preferential oxidation rate has been determined to be K_{oxide} = Aexp{-Q/RT}with A = 2.27×10^(−3) m^(2)s^(−1) and Q = 221 kJ.mol^(−1) (activation energy) for WF675 and A = 5.04 × 10^(−7) m^(2)s^(−1) and Q = 171 kJ.mol^(−1) for 15% cold worked WF675. These values are consistent with the activation energy of primary water stress corrosion cracking (PWSCC) initiation. Bulk oxygen diffusivities were calculated from the internal oxidation after 500 h exposures. At 500 Celsius the oxygen diffusivity was determined to be 1.79×10^(−20) m^(2)s^(−1) for WF675 and 1.21×10^(−20) m^(2)s^(−1) for 15% cold worked WF675, the oxygen diffusivity at 400 Celsius in 15% cold worked WF675 was calculated to be 1.49×10^(−22) m^(2)s^(−1).The Cr-depletion associated with preferential oxidation has been assessed by AEM. The Cr-depletion was asymmetric and it could not be accounted for by local variations in the diffusion rate. Chemically induced grain boundary migration is suggested as a possible explanation. Constant load SCC tests conducted in hydrogenated steam at 400 Celsius have shown a similar trend to the classical dependency of PWSCC as a function of potential. The SCC samples were also prepared with two surface finishes, OPS and 600 grit. In all SCC tests, significantly more cracking was observed on the OPS surface and all failures initiated from this surface.
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Karkhanis, Shalmira. "Macroscopic and microscopic changes in incinerated deciduous teeth." University of Western Australia. Centre for Forensic Science, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0170.
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The teeth are amongst the most resilient elements of the human skeleton and are thus often utilised in routine forensic investigation involving the identification of unknown remains. The teeth, however, also have other practical forensic applications. Teeth exposed to thermal stress have the potential to not only aid in identification but also in understanding the circumstances surrounding the fire. Previous investigations have drawn conclusions that if a fire flares up suddenly and intensively, the teeth burst and enamel is lost. If the blaze commences gently and burns slowly, then the first observable morphologic change is the colour. The teeth subsequently are difficult to handle, thus changes in teeth can indicate the history of exposure to thermal conditions. Children are twice as likely to become victims of house fire because of an inability to safely evacuate from areas of danger. The literature demonstrates, however, that research on the effects of incineration on teeth is mostly restricted to the permanent teeth. The apparent lack of knowledge on the effects of incineration on deciduous teeth thus necessitates further research in this area. This research project primarily aims at understanding the effect of extreme temperatures on deciduous teeth. It also aims to relate colour changes that occur post heating with fragility to aid in proper handling of samples in a forensic scenario and to determine the possibility of identifying incineration temperature based on tooth condition. The samples analysed composed of 90 deciduous teeth (45 molars and 45 anteriors) extracted as a part of clinical treatment were used for the study. The project involved exposing extracted deciduous teeth to temperatures ranging from 100°C to 1100°C for 30 minutes using a laboratory Gallenkamp oven. Unheated deciduous teeth were used as controls for the project. Post-incineration the teeth were then analysed under a stereomicroscope and SEM for morphological changes. A colorimetric analysis was also undertaken to evaluate the colour changes induced in the primary teeth due to the thermal stress. It was found that it was possible to identify the incineration temperature based on the tooth condition when the colour changes, stereomicroscopic findings and SEM images were utilised collectively. It was also concluded that the thermally induced changes observed in primary teeth occur at lower temperatures in comparison to the permanent teeth. It was also established that post-incineration deciduous teeth are fragile and show a tendency to fragment after minimal exposure to thermal stress as compared to the permanent teeth. Moreover enamel and dentin remained identifiable in primary teeth even after exposure to 1100°C for 30 minutes while cementum lost its structural morphology at 900°C.
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Laurent, Véronique. "Mouillabilité et réactivité dans les systèmes composites métal/céramique : étude du couple Al/SiC." Grenoble INPG, 1988. http://www.theses.fr/1988INPG0115.
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Etude experimentale du mouillage par la methode de la goutte posee et par une methode tensiometrique d'immersion-emersion. Analyse chimique et structurale des interfaces par spectrometrie auger, microsonde, microscopie electronique a balayage et en transmission. Influence de la temperature (973-1173k), de la composition de la phase metallique(additions de si, ti, cu et sn) et des traitements de surface de sic (recouvrement par des couches de silice ou carbure sur la cinetique de mouillage. Interpretation et generalisation des resultats par une approche thermodymique
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Pearson, Stephen R. "The effect of nitriding on the fretting wear of a high strength steel at ambient and elevated temperatures." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/29004/.
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This work is an experimental evaluation of the wear and friction of a high strength alloy steel (super-CMV (SCMV» in its as heat treated and plasma nitrided states under fretting conditions in air, at both ambient and elevated temperatures. In order to conduct the experimental programme, a new test rig and associated data processing and assessment capability was developed. Wearing couples in homogeneous and heterogeneous arrangements were tested to assess the effectiveness of the nitriding process as a fretting palliative-the heterogeneous mating is particularly representative of configurations found in aerospace transmission assemblies. A range of test conditions were examined with a line contact, including normal loads from 25 to 65Nmm-1, displacement amplitudes from 10 to 100 µm and temperatures from 24 to 450°C. At ambient temperatures, the wear behaviour was assessed using an energy-wear analysis, whereupon it was demonstrated that the wear volume was a linear function of the dissipated frictional energy (over the range of loading conditions) with a significant energy threshold before the onset of wear. Accordingly, the fretting wear over the full range of loading conditions could be described by a single wear rate and threshold value. The wear rate for homogeneous couples of nitrided super-CMV (SCMVN) was found to be 12 % lower than that for comparable SCMV pairings, although the lower threshold energy for the SCMVN case would lead to them suffering greater wear at < 2.5 kJ of dissipated energy (in the configuration examined). In heterogeneous couples, the harder SCMVN specimen was found to wear preferentially; while the SCMV specimen suffered severe plastic damage of the surface, a protective oxide debris bed was seen to form, which protected the underlying SCMV from wear and abraded the SCMVN specimen. At elevated temperatures, the tribology (of both SCMV and SCMVN) was dominated by the formation of a glaze-layer. The progressive formation of the glaze, with increasing temperature, led to a critical transition temperature (TT) above which a significant reduction in both the wear and friction of the materials was observed. For SCMV, after only a modest increase in temperature to 85 °C, the overall loss of material from the contact had become negative. At temperatures greater than 85°C, negative wear was maintained, with the coefficient of friction dropping monotonically until a slight minimum at 300°C. The behaviour for the SCMVN couples was very similar; the transition to negative wear occurred at a higher temperature of 150°C but the friction minimum was also found at 300°C. It is proposed that the changes in wear rate and friction coefficient were due to changes in the way that the oxide particles sintered to form a protective debris bed, with sintering of the oxide debris particles at these low temperatures being promoted by the nano-scale at which the oxide debris is formed.
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Tripp, David William. "The thermal regime during electron beam hearth remelting." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26748.
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Electron beam hearth remelting is extensively used in refining of superalloys, titanium alloys and the recycling of these materials. The removal of impurities and exhogenous particles during the hearth melting operation depends primarily on the time at temperature relationship developed within a pool of molten metal. In the past hearth melters have acted largely on empirical evidence to specify such parameters as melt rates, power levels and skull sizes. This work describes a mathematical model which could be used to predict certain parameters (such as pool volume or alloy element evaporation rates) when given skull geometry, power input and melt rate.
A three dimensional steady state heat transfer model of both the skull and water cooled copper mould during electron beam hearth remelting has been developed. The model has been used to investigate the effects of surface temperature, liquid motion, power input, skull geometry, presence of the hearth mould and melt rate on parameters such as pool volume during skull melting.
In general the choice of any combination of operating parameters depends on a balance between the refining capacity of the process (i.e. liquid volume) and the loss of alloy elements by evaporation. In the case of melting pure materials (e.g. CP titanium) the balance is between refining capacity and efficient energy use.
It was found that forced convection is significantly more effective in increasing the volume of the liquid pool than any other single parameter. Increasing the power input to the skull, increasing the skull width and removing the water cooled copper mould from around the skull also increase the pool volume. The evaporation rates of alloy elements within the skull were most effected by changes in the power distribution and the degree of liquid motion.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Abdallah, Zakaria. "Creep lifing methods for components under high temperature creep." Thesis, Swansea University, 2010. https://cronfa.swan.ac.uk/Record/cronfa43065.
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Acquaye, Lucy. "Effect of high curing temperatures on the strength, durability and potential of delayed ettringite formation in mass concrete structures." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013837.
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Tsantrizos, Panayotis G. "The characteristics of titanium tetrachloride plasmas in a transferred-arc systems /." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75670.
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A stable transferred arc was produced with plasmagas containing up to 20 percent molar TiCl$ sb4$ in argon, helium and argon/hydrogen mixtures. This was achieved by replacing the commonly-used thoriated tungsten cathode tip with a tantalum carbide tip. Thus, corrosive reactions at the cathode surface, which were shown to be the cause of the observed instability, were prevented. This allowed the characteristics of stable titanium tetrachloride plasmas in a transferred arc reactor to be investigated.Furthermore, an investigation was conducted into the feasibility of collecting titanium metal from the dissociated TiCl$ sb4$ molecule in the plasmagas. The titanium metal was collected in a molten bath, which also served as the anode in the transferred arc system. Three anode bath compositions were used in this study. Two of them, namely titanium and zirconium, were not able to reduce recombined titanium subchlorides in the bath. The third aluminum, was a reducing bath. When aluminum was used, about 60 percent of all titanium fed into the reactor was collected.
Finally, phenomena occurring on the surface of a thoriated tungsten cathode were studied in a transferred-arc reactor using argon or helium as the plasmagas. The effect of cathode geometry on the rate and mechanisms of cathode erosion were investigated. It was shown that the surface temperature of flat-tip cathodes operating in argon is near the melting point of tungsten. On the other hand, the surface temperature of flat-tip cathodes operating in helium and pointed-tip cathodes operating in either helium or argon are near the boiling point of tungsten. Some of the material vapourized from the cathode was redeposited on the cathode surface, forming crystals whose morphology and composition depended on their distance from the arc root and the plasmagas composition.
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Havn, Torgeir Børresen. "The Effect of Catch and Release Angling at High Water Temperatures on Behavior and Survival of Atlantic Salmon (Salmo salar L.)." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for biologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23960.
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Many wild Atlantic salmon (Salmo salar L.) populations have declined during the last decades. A multitude of restrictions on riverine fisheries have been initiated to preserve spawning populations, including increased use of catch-and-release (C&R) angling. As a result, more than half of all Atlantic salmon caught in the north Atlantic region during the recent years have been released. Previous studies have shown that the majority of the caught and released Atlantic salmon angled at temperatures below 15 °C survived and participated in spawning, while the mortality seemed to increase at higher water temperatures. However, the survival of caught and released salmon at water temperatures above 15 °C has so far not been well examined under natural conditions. In this study, I investigated behavior and survival following C&R for wild Atlantic salmon (n = 52) angled on regular sport fishing gear in the River Otra in southern Norway at water temperatures ranging between 16.3-19.7 °C (mean 17.3 °C). The fish were tagged externally with radio transmitters without being anaesthetized and immediately released back into the river to simulate a realistic C&R situation. The results showed that a large proportion survived C&R (92%, n = 48) and that all salmon present in the River Otra during the spawning period 3-4 months later were located at known spawning grounds. Downstream movements during the first four days after release were recorded for 74% of the fish, and this was regarded as unusual behavior caused by C&R. Unusual behavior in the form of downstream movements during the first four days after release were recorded for 74% of the fish, and were assumed to have been caused by C&R. The salmon spent on average 24 days before commencing their first upstream movement after release and 41 days before they returned to or were located above their release site. The results suggest that C&R at these water temperatures may be a viable management tool as most fish survived and were present on the spawning grounds. However, it is not known if the physiological strain inflicted by C&R and the altered behavior affected reproductive success for caught and released fish compared to non-angled fish.
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McDonald, Teaghan. "Investigating the effect of high temperatures and substrates on the detection of human blood using the ABAcard® Hematrace® kit." Thesis, McDonald, Teaghan (2017) Investigating the effect of high temperatures and substrates on the detection of human blood using the ABAcard® Hematrace® kit. Masters by Coursework thesis, Murdoch University, 2017. https://researchrepository.murdoch.edu.au/id/eprint/37532/.
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Blood is one of the most commonly encountered types of evidence at a crime scene. The first step to begin processing is observation and documentation, followed by presumptive testing which analyses if the substance is likely blood, and if the blood comes from human origin. This procedure ensures less time and resource wastage of items of evidence which have little or no forensic value. However this process can be hindered when the presumptive test in vulnerable to false negative results.
There are many degradative agents which blood can be exposed to at crime scenes. This ranges from high temperatures, UV light or chemicals such as bleach. This review will focus on how high temperatures affect blood and more specifically haemoglobin. The ABAcard® HemaTrace® Kit is an immunochromatographic assay test which relies on antibodies imbedded within a test strip to detect the presence of human haemoglobin. It is currently unknown in the literature to what degree haemoglobin is affected by high temperatures and how this affects the outcome of the HemaTrace® Kit. Denaturation of haemoglobin can cause structural damage to the protein making is unrecognisable to the antibodies within the test and therefore producing a false negative result.
The aim of this literature review is to determine the effects of high temperatures on human haemoglobin as a degradative agent and the effect on the outcome of the HemaTrace® Kit. The purpose is to assist in future research designing and should hopefully be able to answer questions regarding further investigations.
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Kandasamy, Sasikaran, and s3003480@student rmit edu au. "Investigation of SiC Based Field Effect Sensors with Gas Sensitive Metal Oxide Layers for Hydrogen and Hydrocarbon Gas Sensing at High Temperatures." RMIT University. Electrical and Computer Engineering, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080724.142015.
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This PhD thesis sets out to investigate novel Silicon Carbide (SiC) based field effect devices (Schottky and transistor structures), with gas sensitive layers for monitoring hydrogen and propene gases at high temperatures. The devices developed by the author were shown to exhibit sensitivities at least 1~2 orders of magnitude (voltage shift, ¢V) higher than those reported in literature. Not only did the author seek to investigate the gas sensing potential of such devices, but also he set out to study, analyse and establish the gas interaction mechanism of these novel sensors. High temperature tolerant hydrogen and hydrocarbon sensors are required in numerous applications such as: aerospace, nuclear power plant, space exploration and exhaust monitoring in automobiles. Monitoring these gases in a reliable and efficient manner is of great value in these applications, not only from a safety point of view but also for economical reasons. Hence there is an absolute necessity for simple, efficient and high performance sensors not only for monitoring and leak detection but also to function as part of a safety device to prevent accidents. The proposed sensor structure of combining SiC with gas sensitive oxide layers allow them to be operated at high temperatures, making them extremely appealing for direct or in-situ monitoring applications. The microstructural analysis performed using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Rutherford Backscattering Spectroscopy (RBS) provides no evidence of inter-diffusion between different layers, in spite of the sensors being annealing at 650 in O2, H2 and C3H6 atmospheres for approximately 50hrs. Samples in different conditions (as deposited, annealed and tested) were compared. The electrical properties of the MROSiC (current-voltage, I-V and capacitance-voltage, C-V characteristics) and MESFET (drain current-source drain voltage (ID-VSD) and transfer, (ãID-H2 concentration) characteristics) devices were measured in the presence and absence of H2 and C3H6. Several parameters such as barrier height, saturation currents, pinch-off voltages and channel conductance were determined from the electrical characteristics, and their influence on the device performance was studied. The authorfs proposed gas interaction model based on energy band diagram is well supported by the experimental data obtained.
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Duan, Runrun. "Investigation of xBi(B')O₃-(1 -- x)PbTiO₃ and xBi(B',B")O3-(1 -- x)PbTiO3 perovskite solid solutions with high transition temperatures." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/24688.
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he extent of BiInO₃ substitution in the perovskite system xBiInO(₃)-(1 - x)PbTiO₃ and the corresponding raise in the transition temperature were investigated using thermal analysis, dielectric measurements, x-ray diffraction, and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x = 0.20, with a corresponding Curie temperature of 582°C. Phase-pure tetragonal perovskite was obtained for x less than or equal to 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD). Niobium-modified BIPT ceramics with PT contents of 80% and 85% were found to possess significantly lower dielectric loss at elevated temperatures, making it possible to polarize the materials. Piezoelectric properties were measured for a 1.5 mol% Nb -0.15BI-0.85PT composition with a transition temperature of 542°C; the longitudinal piezoelectric coefficient and coercive field were found to be 60 pC/N and 125 kV/cm, respectively.
Compositions of xBiLaO₃-(1 − x)PbTiO₃ over the range 0 < x < 0.225 were calcined and sintered. Dielectric constant with temperature and differential scanning calorimetry measurements were in excellent agreement with respect to a Curie-like tetragonal to cubic transformations starting at 495°C for pure PbTiO₃, shifting to lower temperatures with increasing x. For compositions of x > 0.05, a second higher-temperature (∼600°C) endotherm, and matching dielectric anomaly, were consistently observed, for which there were no structural changes indicated by hot-stage x-ray diffraction. This transformation was interpreted to be similar to a Curie transformation in relaxor ferroelectrics in which localized segregation of B-site cations (below the resolution limit of x-ray diffraction) facilitated ferroelectric behavior.
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Falahi, Khalil El. "Contribution à la conception de driver en technologie CMOS SOI pour la commande de transistors JFET SiC pour un environnement de haute température." Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0056/document.
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Dans le domaine aéronautique, les systèmes électriques remplacement progressivement les systèmes de contrôle mécaniques ou hydrauliques. Les bénéfices immédiats sont la réduction de la masse embarquée et des performances accrues à condition que l’électronique supporte l’absence de système de refroidissement. Si la haute température de fonctionnement n’empêche pas d’atteindre une fiabilité suffisante, il y aura réduction des coûts opérationnels. Des étapes clefs ont été franchies en introduisant des systèmes à commande électriques dans les aéronefs en lieu et place de systèmes conventionnels : freins électriques, inverseur de poussée, vérins électriques de commandes de vol… Toutes ces avancées se sont accélérées ces dernières années grâce entre autre à l’utilisation de nouveaux matériaux semiconducteurs, dit à grand gap (SiC, GaN…), opérant à haute température et palliant ainsi une faiblesse des dispositifs classiques en silicium (Si). Des composants de puissance haute température, diode Schottky ou transistor JFET SiC, sont ainsi disponibles commercialement et peuvent supporter des ambiantes de plus de 220°C. Des modules de puissances (onduleur) à base de transistor JFET SiC ont été réalisés et validés à haute température. Finalement la partie « commande » de ces modules de puissance reste à concevoir pour les environnements sévères pour permettre leur introduction dans le module de puissance. C’est dans ce contexte de faiblesse concernant l’étage de commande rapprochée qu’a été construit le projet FNRAE COTECH, et où s’inscrivent les travaux de cette thèse, Dans un premier temps, un état de l’art sur les drivers et leurs technologies nous a permis de souligner le lien complexe entre électronique et température ainsi que le potentiel de la technologie CMOS sur Silicium sur Isolant (SOI) pour des applications hautes températures. La caractérisation en température de drivers SOI disponibles dans le commerce nous a fourni des données d’entrée sur le comportement de tels dispositifs. Ces caractérisations sont essentielles pour visualiser et interpréter l’effet de la température sur les caractéristiques du dispositif. Ces mesures mettent aussi en avant les limites pratiques des technologies employées. La partie principale de cette thèse concerne la conception et la caractérisation de blocs ou IPs pour le cœur d’un driver haute température de JFET SiC. Elle est articulée autour de deux runs SOI (TFSmart1). Les blocs développés incluent entre autres des étages de sortie et leurs buffers associés et des fonctions de protection. Les drivers ainsi constitués ont été testés sur un intervalle de température allant de -50°C à plus de 250°C sans défaillance constatée. Une fonction originale de protection des JFETs contre les courts-circuits a été démontrée. Cette fonction permet de surmonter la principale limitation de ces transistors normalement passant (Normaly-ON). Finalement, un module de bras d’onduleur a été conçu pour tester ces driver in-situIn aeronautics, electrical systems progressively replace mechanical and hydraulic control systems. If the electronics can stand the absence of cooling, the immediate advantages will be the reduction of mass, increased performances, admissible reliability and thus reduction of costs. In aircraft, some important steps have already been performed successfully when substituting standard systems by electrical control system such as electrical brakes, thrust reverser, electrical actuators for flight control… Large band gap semiconductors (SiC, GaN…) have eased the operation in high temperature over the last decade and let overcome a weakness of conventional silicon systems (Si). High temperature power components such as Schottky diodes or JFET transistors, are already commercially available for a use up to 220°C, limited by package. Moreover inverters based on SiC JFET transistors have been realized and characterized at high temperature. Finally the control part of these power systems needs to be designed for harsh environment. It is in this context of lack of integrated control part that the FNRAE COTECH project and my doctoral research have been built. Based on a state of the art about drivers, the complex link between electronic and temperature and the potentialities of CMOS Silicon-On-Insulator technology (SOI) for high temperature applications have been underlined. The characterization of commercial SOI drivers gives essential data on these systems and their behavior at high temperature. These measurements also highlight the practical limitations of SOI technologies. The main part of this manuscript concerns the design and characterization of functions or IPs for high temperature JFET SiC driver. Two SOI runs in TFSmart1 have been realized. The developed functions include the driver output stage, associated buffers and protection functions. The drivers have been tested from -50°C up to 250°C without failure under short time-range. Moreover, an original protection function has been demonstrated against the short-circuit of an inverter leg. This function allows overcoming the main limitation of the normally on JFET transistor. Finally, an inverter module has been built for in-situ test of these new drivers
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Shortlidge, Erin Elizabeth. "Testing the Ecological and Physiological Factors Influencing Reproductive Success in Mosses." PDXScholar, 2014. http://pdxscholar.library.pdx.edu/open_access_etds/1951.
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As non-vascular, early land plants with an aquatic ancestry, mosses do not regulate internal water conditions separate from that of their environment and as a result, evolved mechanisms to survive in a terrestrial world out of water. Yet, there is a widely accepted dogma that moss reproductive success is solely dependent on rainfall events carrying swimming, bi-flagellate sperm across the landscape to reproductively mature and receptive female mosses--but this classic view of moss reproduction may be too simplistic. In this dissertation I test the assumptions of reproductive limitation in mosses and present novel findings in a basal, yet understudied terrestrial plant mating system.
I find evidence of environmental desiccation tolerance in moss sperm, thus offering the potential for stress-tolerant gametes on the landscape possibly suited for various transport vectors, reminiscent of a pollen grain. To investigate the broad evolutionary implications of this newfound complexity in moss sexual reproduction, I tested classic tenets of plant-pollinator theory on the ancient mosses and their ubiquitous microarthropod inhabitants. Experimental results show that mosses and microarthropods are engaged in a "pollination-like" syndrome guided by sex-specific volatile cues that differentially affect microarthropod behavior. These data indicate an existing complex mutualistic relationship and provides new evidence of sexually dimorphic investment by male and female mosses into reproductive success. Further, these data put forth the idea that female mosses challenge an inherent mate limitation by investing into reproductive assurance via maintaining a relationship with microarthropods.
Experimental work further confirms a role for invertebrates in moss reproductive success and tests mutualism theory through ongoing experiments. Such experiments include an assessment of moss genetic diversity, paternity, and male fitness traits as it relates to mosses with or without the presence of microarthropods, thereby testing for fitness benefits gained by mosses possibly engaged in a transport mutualism with microarthropods.
I further tested mutualism, community ecology and moss sexual reproduction concepts in extreme geothermal moss populations living at the edges of inhabitable Earth, and results show that even geothermal moss canopies are diverse and host differential and abundant life. In a first field test of mutualism I found that although extreme heat stress may constrain sexual reproduction in mosses, a correlation between within-population moss genetic diversity and microarthropod abundances exists. To further examine mosses in extreme environments, and how these environments may constrain sexual reproductive success, I evaluated the effects of simulated warming on Antarctic moss physiology and reproductive biology. Data indicates that simulated warming relieves mosses of physiological stress, and results in a greater investment into primary productivity and sexual reproduction. These data support the hypothesis that with less stress, sexual reproduction is increased. Mosses are an ideal system by which to understand organisms that exist in environments ranging from the mesic to the extreme, in the laboratory and the field and even in the classroom, where the small functioning ecosystem of mosses can be used for discovery-based biology education as described in the Mosscosms curriculum.
This work contributes significantly to the field of bryophyte and plant biology by revealing novel insights into the biotic and abiotic drivers of sexual reproduction in mosses.
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Sabbah, Wissam. "Contribution à l’étude des assemblages et connexions nécessaires à la réalisation d’un module de puissance haute température à base de jfet en carbure de silicium (SiC)." Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR12013/document.
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Le développement de composants de puissance à base de carbure de silicium (SiC) permet la réalisation d’interrupteurs pouvant fonctionner au-delà de 200°C. Le silicium présente plus de limitations au niveau physique du matériau qu’au niveau des technologies d’assemblages. Le SiC est un matériau semi-conducteur grand gap ce qui permet d’obtenir des courants de fuite inverse qui restent faibles à haute température ; d’où un fort intérêt pour des applications haute température. Mise à part son utilisation à des températures pouvant dépasser les 300°C, c’est un matériau qui permet aussi d’augmenter les fréquences de commutation ainsi que la densité de puissance par rapport à des composants à technologie silicium. Ceci en fait un candidat idéal pour des applications forte puissance dans le domaine de la traction, des protections de réseaux électriques ou de la transmission et de la distribution d’énergie. L’utilisation du SiC pour une application haute température pose le problème de son packaging, des choix de matériaux et de sa configuration. Cette thèse a pour but d’effectuer une étude de fiabilité et de durée de vie des briques technologiques d’assemblage et de connexions nécessaires à la réalisation d’un cœur de puissance haute température à base de JFET SiC. Une étude des différentes technologies d’assemblages de convertisseurs de puissance haute température est effectuée afin de définir différentes briques technologiques constitutives de ces systèmes. Cette première étude nous permet de procéder à une sélection de certaines technologies d’assemblages comme le frittage de pâtes d’argent pour la technologie de report de puces. Ces briques technologiques feront l’objet d’études plus approfondies allant de la réalisation de véhicules tests jusqu’à la mise au point des essais de cyclages associés aux techniques d’analyse nécessaires à l’étude de leur défaillance.Les études expérimentales concernent des essais de cyclage passif et de stockage thermique, l’apparition de délaminages en cours de cyclage thermique (scan acoustique, RX), le report par frittage de pâtes d’argent nano et microscopiques et la caractérisation électrique et thermique (Rth, I[V])The development of power components based on silicon carbide (SiC) allows for the design of power converter operating at high temperature (above 200 or 300°C). SiC is a semiconductor material with a large band gap that not only can operate in temperatures exceeding 300°C but also offers fast switching speed, high voltage blocking capability and higher thermal conductivity compared to silicon technology components. The classical die attach technology uses high temperature solder alloys which melt at around 300°C. However, even a soldered die attach with such high melting point can only operate up to a much lower temperature. Alternative die attach solutions have recently been proposed: Transient Liquid Phase Bonding, soldering with higher melting point alloys such as ZnSn, or silver sintering.Silver sintering is a very interesting technology, as silver offers very good thermal conductivity (429W/m.K, better than copper), relatively inexpensive (compared to alternative solutions which often use gold), and has a very high melting point (961°C).The implementation of two silver-sintering processes is made: one based on micrometer-scale silver particles, and one on nano-meter-scale particles. Two substrate technologies are investigated: Al2O3 DBC and Si3N4 AMB. After the process optimization, tests vehicles are assembled using nano and micro silver particles paste and a more classical high-temperature die attach technology: AuGe soldering. Multiple analyses are performed, such as thermal resistance measurement, shear tests and micro-sections to follow the evolution of the joint during thermal cycling and high-temperature storage ageing
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Wilcox, Edward. "Silicon-germanium devices and circuits for cryogenic and high-radiation space environments." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33850.
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This work represents several years' research into the field of radiation hardening by design. The unique characteristics of a SiGe HBT, described in Chapter 1, make it ideally suitable for use in extreme environment applications.
Chapter 2 describes the total ionizing dose effects experienced by a SiGe HBT, particularly those experienced on an Earth-orbital or lunar-surface mission. In addition, the effects of total dose are evaluated on passive devices.
As opposed to the TID-hardness of SiGe transistors, a clear vulnerability to single-event effects does exist. This field is divided into three chapters. First, the very nature of single-event transients present in SiGe HBTs is explored in Chapter 3 using a heavy-ion microbeam with both bulk and SOI platforms [31]. Then, in Chapter 4, a new device-level SEU-hardening technique is presented along with circuit-design techniques necessarily for its implementation. In Chapter 5, the circuit-level radiation-hardening techniques necessarily to mitigate the effects shown in Chapter 3 are developed and tested [32].
Finally, in Chapter 6, the performance of the SiGe HBT in a cryogenic testing environment is characterized to understand how the widely-varying temperatures of outer space may affect device performance.
Ultimately, the built-in performance, TID-tolerance, and now-developing SEU-hardness of the SiGe HBT make a compelling case for extreme environment electronics. The low-cost, high-yield, and maturity of Si manufacturing combine with modern bandgap engineering and modern CMOS to produce a high-quality, high-performance BiCMOS platform suitable for space-borne systems.
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Gupta, Niraj. "First Principles Study of Metastable Beta Titanium Alloys." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc804949/.
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The high temperature BCC phase (b) of titanium undergoes a martensitic transformation to HCP phase (a) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed b phase separates into a + b upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in as-quenched b microstructure creates nanoscale precipitates of a new simple hexagonal w phase, which considerably reduces ductility. These phase transformation reactions have been extensively studied experimentally, yet several significant questions remain: (i) The mechanism by which the alloying element stabilizes the b phase, thwarts its transformation to w, and how these processes vary as a function of the concentration of the stabilizing element is unclear. (ii) What is the atomistic mechanism responsible for the non-Arrhenius, anomalous diffusion widely observed in experiments, and how does it extend to low temperatures? How does the concentration of the stabilizing elements alter this behavior? There are many other w forming alloys that such exhibit anomalous diffusion behavior. (iii) A lack of clarity remains on whether w can transform to a -phase in the crystal bulk or if it occurs only at high-energy regions such as grain boundaries. Furthermore, what is the nature of the a phase embryo? (iv) Although previous computational results discovered a new wa transformation mechanism in pure Ti with activation energy lower than the classical Silcock pathway, it is at odds with the a / b / w orientation relationship seen in experiments. First principles calculations based on density functional theory provide an accurate approach to study such nanoscale behavior with full atomistic resolution, allowing investigation of the complex structural and chemical effects inherent in the alloyed state. In the present work, a model Ti-Mo system is investigated to resolve these fundamental questions. Particular attention is paid to how Mo- (i) influences the bonding in Ti, (ii) distorts the local structure in the Ti lattice, (iii) impacts the point and interfacial defect formation and migration energies, and (iv) affects the mechanism and energetics of b w and wa transformations. Our results are correlated with appropriate experimental results of our collaborators and those in open literature. The modification of Ti bonding by Mo solutes and the attendant distortion of the lattice hold the key to answering the diverse questions listed above. The solutes enhance electron charge density in the <111> directions and, consequently, stiffen the lattice against the displacements necessary for b w transformation. However, Ti atoms uncoordinated by Mo remain relatively mobile, and locally displace towards w lattice positions. This effect was further studied in a metastable Ti-8.3 at.% Mo system with an alternate cell geometry which allows for either b w or $\betaa transformation, and it was found that after minimization Ti atoms possessed either a or w coordination environments. The creation of this microstructure is attributed to both the disruption of uniform b w transformation by the Mo atoms and the overlap of Ti-Mo bond contractions facilitating atomic displacements to the relatively stable a or w structures in Mo-free regions. The vacancy migration behavior in such a microstructure was then explored. Additionally, several minimized configurations were created with planar interfaces between Mo-stabilized b region and its adjacent a- or w- phases, and it was found that the positioning of Mo at the interface strongly dictates the structure of the adjacent Mo depleted region.
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Mogniotte, Jean-François. "Conception d'un circuit intégré en SiC appliqué aux convertisseur de moyenne puissance." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0004/document.
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L’émergence d’interrupteurs de puissance en SiC permet d’envisager des convertisseurs de puissance capables de fonctionner au sein des environnements sévères tels que la haute tension (> 10 kV ) et la haute température (> 300 °C). Aucune solution de commande spécifique à ces environnements n’existe pour le moment. Le développement de fonctions élémentaires en SiC (comparateur, oscillateur) est une étape préliminaire à la réalisation d’un premier démonstrateur. Plusieurs laboratoires ont développé des fonctions basées sur des transistors bipolaires, MOSFETs ou JFETs. Cependant les recherches ont principalement portées sur la conception de fonctions logiques et non sur l’intégration de drivers de puissance. Le laboratoire AMPERE (INSA de Lyon) et le Centre National de Microélectronique de Barcelone (Espagne) ont conçu un MESFET latéral double grille en SiC. Ce composant élémentaire sera à la base des différentes fonctions intégrées envisagées. L’objectif de ces recherches est la réalisation d’un convertisseur élévateur de tension "boost" monolithique et de sa commande en SiC. La démarche scientifique a consisté à définir dans un premier temps un modèle de simulation SPICE du MESFET SiC à partir de caractérisations électriques statique et dynamique. En se basant sur ce modèle, des circuits analogiques tels que des amplificateurs, oscillateurs, paires différentielles, trigger de Schmitt ont été conçus pour élaborer le circuit de commande (driver). La conception de ces fonctions s’avère complexe puisqu’il n’existe pas de MESFETs de type P et une polarisation négative de -15 V est nécessaire au blocage des MESFETs SiC. Une structure constituée d’un pont redresseur, d’un boost régulé avec sa commande basée sur ces différentes fonctions a été réalisée et simulée sous SPICE. L’ensemble de cette structure a été fabriqué au CNM de Barcelone sur un même substrat SiC semi-isolant. L’intégration des éléments passifs n’a pas été envisagée de façon monolithique (mais pourrait être considérée pour les inductances et capacités dans la mesure où les valeurs des composants intégrés sont compatibles avec les processus de réalisation). Le convertisseur a été dimensionné pour délivrer une de puissance de 2.2 W pour une surface de 0.27 cm2, soit 8.14 W/cm2. Les caractérisations électriques des différents composants latéraux (résistances, diodes, transistors) valident la conception, le dimensionnement et le procédé de fabrication de ces structures élémentaires, mais aussi de la majorité des fonctions analogiques. Les résultats obtenus permettent d’envisager la réalisation d’un driver monolithique de composants Grand Gap. La perspective des travaux porte désormais sur la réalisation complète du démonstrateur et sur l’étude de son comportement en environnement sévère notamment en haute température (> 300 °C). Des analyses des mécanismes de dégradation et de fiabilité des convertisseurs intégrés devront alors être envisagéesThe new SiC power switches is able to consider power converters, which could operate in harsh environments as in High Voltage (> 10kV) and High Temperature (> 300 °C). Currently, they are no specific solutions for controlling these devices in harsh environments. The development of elementary functions in SiC is a preliminary step toward the realization of a first demonstrator for these fields of applications. AMPERE laboratory (France) and the National Center of Microelectronic of Barcelona (Spain) have elaborated an elementary electrical compound, which is a lateral dual gate MESFET in Silicon Carbide (SiC). The purpose of this research is to conceive a monolithic power converter and its driver in SiC. The scientific approach has consisted of defining in a first time a SPICE model of the elementary MESFET from electric characterizations (fitting). Analog functions as : comparator, ring oscillator, Schmitt’s trigger . . . have been designed thanks to this SPICE’s model. A device based on a bridge rectifier, a regulated "boost" and its driver has been established and simulated with the SPICE Simulator. The converter has been sized for supplying 2.2 W for an area of 0.27 cm2. This device has been fabricated at CNM of Barcelona on semi-insulating SiC substrate. The electrical characterizations of the lateral compounds (resistors, diodes, MESFETs) checked the design, the "sizing" and the manufacturing process of these elementary devices and analog functions. The experimental results is able to considerer a monolithic driver in Wide Band Gap. The prospects of this research is now to realize a fully integrated power converter in SiC and study its behavior in harsh environments (especially in high temperature > 300 °C). Analysis of degradation mechanisms and reliability of the power converters would be so considerer in the future
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Hamieh, Youness. "Caractérisation et modélisation du transistor JFET en SiC à haute température." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00665817.
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Dans le domaine de l'électronique de puissance, les dispositifs en carbure de silicium (SiC) sont bien adaptés pour fonctionner dans des environnements à haute température, haute puissance, haute tension et haute radiation. Le carbure de silicium (SiC) est un matériau semi-conducteur à large bande d'énergie interdite. Ce matériau possède des caractéristiques en température et une tenue aux champs électriques bien supérieure à celles de silicium. Ces caractéristiques permettent des améliorations significatives dans une grande variété d'applications et de systèmes. Parmi les interrupteurs existants, le JFET en SiC est l'interrupteur le plus avancé dans son développement technologique, et il est au stade de la pré-commercialisation. Le travail réalisé au cours de cette thèse consiste à caractériser électriquement des JFET- SiC de SiCED en fonction de la température (25°C-300°C). Des mesures ont été réalisé en statique (courant-tension), en dynamique (capacité-tension) et en commutation sur charge R-L (résistive-inductives) et dans un bras d'onduleur. Un modèle multi-physique du transistor VJFET de SiCED à un canal latéral a été présenté. Le modèle a été développé en langage MAST et validé aussi bien en mode de fonctionnement statique que dynamique en utilisant le simulateur SABER. Ce modèle inclut une représentation asymétrique du canal latéral et les capacités de jonction de la structure. La validation du modèle montre une bonne concordance entre les mesures et la simulation.
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Smith, Benjamin Daniel. "Microstructure-sensitive plasticity and fatigue of three titanium alloy microstructures." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49237.
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Titanium alloys are employed in many advanced engineering applications due to their exceptional properties, i.e., a high strength-to-weight ratio, corrosion resistance, and high temperature strength. The performance of titanium alloys is known to be strongly affected by its inherent microstructure, which forms as a result of its thermo-mechanical processing. These microstructures produce compromise relationships between beneficial and detrimental effects on the alloy's performance. To study these structure-property relationships, two distinct crystal plasticity algorithms have been calibrated to data acquired from cyclic deformation experiments performed on three different Ti microstructures: (1) Ti-6Al-4V beta-annealed , (2) Ti-18 solution-treated, age-hardened (STA), and (3) Ti-18 beta-annealed, slow-cooled, age-hardened (BASCA). The calibrated models have been utilized to simulate fatigue loading of variant microstructures to investigate the influence of mean grain size, crystallographic texture, and phase volume fraction. The driving force for fatigue crack nucleation and propagation is quantified through the calculation of relevant fatigue indicator parameters (FIPs) and radial correlation functions are employed to study the correlation between favorably oriented slip systems and the extreme value FIP locations. The computed results are utilized to observe fatigue performance trends associated with changes to key microstructural attributes.
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Narang, Vikas A. "Heat Transfer Analysis In Steel Structures." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-050405-133533/.
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Sylvestre, Alain. "Evolution des proprietes electriques et physiques aux basses temperatures de transistors a effet de champ a heterojonction a grille courte sur substrat inp." Paris 11, 1996. http://www.theses.fr/1996PA112020.
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Cette these presente une etude experimentale a temperature ambiante et aux temperatures cryogeniques de transistors a effet de champ a heterojonctions (hemts) inalas/ingaas/inalas en accord de maille et pseudomorphiques sur substrat inp, de longueur de grille submicronique. Malgre des performances microondes a l'etat de l'art, ces composants souffrent d'une technologie encore immature qui rend difficile une bonne reproductibilite de transistors performants. L'analyse des potentialites microondes sur la frequence de coupure du gain en courant de ces transistors revele que ces derniers s'ameliorent significativement avec la reduction de la longueur de grille et dans une moindre mesure avec l'abaissement de la temperature. L'absence d'evolution significative des capacites intrinseques avec la temperature confirme un bon confinement des porteurs dans le canal aux temperatures cryogeniques. Par ailleurs, la frequence maximale d'oscillation s'ameliore avec l'augmentation de la tension de drain, neanmoins l'utilisation des composants dans ces regimes de fonctionnement est limitee par la faible tenue au claquage des hemts sur inp. L'obtention de fortes densites de porteurs et des tensions de claquage elevees constituent les deux facteurs clef pour une montee en frequence encore plus importante. Les causes du claquage precoce de ces hemts sont etudiees de facon originale a partir de mesures d'electroluminescence. Celles-ci ont revele l'apparition d'un processus d'ionisation par choc dans le canal ingaas pour expliquer le claquage du composant. Par ailleurs, des anomalies ont ete observees sur les caracteristiques courant-tension. Ces anomalies sont la consequence de mecanismes de piegeage/depiegeage de porteurs dans les couches inalas et aux differentes interfaces. En conclusion, l'evolution des performances avec la temperature nous a permis de mieux comprendre les phenomenes physiques qui regissent le fonctionnement des hemts sur substrat inp a grille courte. L'etude a temperature variable s'est averee etre un outil precieux de caracterisation de l'ensemble de ces phenomenes
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Lokvenc, Martin. "Testování lomové houževnatosti za vysokých teplot s využitím miniaturních CT těles." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231784.
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This thesis deals with a high temperature testing of fracture toughness and studies the size effect on measured values using miniature size CT specimen. Two types of specimen geometry were manufactured from P91 steel, the standard size and the quarter size specimen. J-R curves were obtained in the temperature range from 23°C to 600°C. No specimen size effect was observed at room temperature tests. The realized experiments together with fractography analysis demonstrated the drop of toughness at 400°C caused by the effect of dynamic strain aging.
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Arakelian, Andrea Katherine. "Strength analysis of bolted shear connections under fire conditions using the finite element approach." Worcester, Mass. : Worcester Polytechnic Institute, 2008. http://www.wpi.edu/Pubs/ETD/Available/etd-122208-145717/.
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Lin, Shih-Min, and 林士民. "Microstructures of Silicon Carbides Sintered at High- temperatures and Their Significance of Sintering." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/42135353544183578327.
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碩士國立成功大學
地球科學系
83
Silicon carbides sintered at high temperatures including refractory bricks, refractory plates, kiln furniture and heating elements have been collected and analyzed for their microstructures in the present study. On the basis of microstructures, the following four different types of sintered silicon carbides have been recognized: clay-bonded, sialon- bonded, self-bonded and recrystallized silicon carbides. In the clay-bonded silicon carbides, the silicon carbide grains are surrounded by fine-grained cristobalites, mullites of needle form, small amounts of Al2O3- and SiO2-rich amorphous phases, Fe-Si alloy of chondritic form and whiskers of β-silicon carbide. In the sialon-bonded silicon carbides, the silicon carbide grains were surrounded by frame-worked β'-sialon crystals and corundums. In the sintering process, Si3N4 and Al2 O3 were used as sintering agents and were sintered in nitrogen atmosphere. In the self-bonded silicon carbides, the silicon carbide grains were necked among one another and the surface of the grains were coated with thin films of cristbalites. In the recrystallized silicon carbides, in addition to the necking, the silicon carbide crystals have grown well and penetrated each other.
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Hu, Guixing. "Oxygen isotope salt effect at high pressure and high temperature /." 2000. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:9990561.
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許邦聖. "Effect of different storage temperatures on the quality of high oleic peanut(Arachis hypogaea L.)." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/fm6455.
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Cadell, Seth R. "Development of a binary mixture gas composition instrument for use in a confined high temperature environment." Thesis, 2012. http://hdl.handle.net/1957/36206.
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With recent advancements in material science, industrial operations are being conducted at higher and higher temperatures. This is apparent in the nuclear industry where a division of the field is working to develop the High Temperature Gas Reactor and the Very High Temperature Gas Reactor concurrently. Both of these facilities will have outlet gas temperatures that are at significantly higher temperatures than the typical water cooled reactor. These increased temperatures provide improved efficiency for the production of hydrogen, provide direct heating for oil refineries, or more efficient electricity generation. As high temperature operations are being developed, instruments capable of measuring the operating parameters must be developed concurrently. Within the gas reactor community there is a need to measure the impurities within the primary coolant. Current devices will not survive the temperature and radiation environments of a nuclear reactor. An instrument is needed to measure the impurities within the coolant while living inside the reactor, where this instrument would measure the amount of the impurity within the coolant.
There are many industrial applications that need to measure the ratio of two components, whether it be the amount of particulate in air that is typical to pneumatic pumping, or the liquid to gas ratio in natural gas as it flows through a pipeline. All of the measurements in these applications can be met using a capacitance sensor. Current capacitance sensors are built to operate at ambient temperatures with only one company producing a product that will handle a temperature of up to 400 °C. This maximum operating temperature is much too low to measure the gas characteristics in the High Temperature Gas Reactor. If this measurement technique were to be improved to operate at the expected temperatures, the coolant within the primary loop could be monitored for water leaks in the steam generator, carbon dust buildup entrained in the flow, or used to measure the purity of the coolant itself.
This work details the efforts conducted to develop such an instrument. While the concept of designing a capacitance sensor to measure a gas mixture is not unique, the application of using a capacitance sensor within a nuclear reactor is a new application. This application requires the development of an instrument that will survive a high temperature nuclear reactor environment and operate at a sensitivity not found in current applications. To prove this technique, instrument prototypes were built and tested in confined
environments and at high temperatures. This work discusses the proof of concept testing and outlines an application in the High Temperature Test Facility to increase the operational understanding of the instrument. This work is the first step toward the ultimate outcome of this work, which is to provide a new tool to the gas reactor community allowing real-time measurements of coolant properties within the core.Graduation date: 2013
34
Peng, Min-Ru, and 彭敏茹. "Electrical Characteristics and Hot-Carrier Effect of Stacked High-k/Metal-Gate nMOSFETs under Nitridation Annealing Temperatures." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/qvz6gd.
Full textAbstract:
碩士國立臺北科技大學
機電整合研究所
101
Since 45nm process generation and beyond, high-k/metal-gate (HK/MG) combining strain engineering technology for nano-scale MOSFETs incorporated into the conventional CMOS process is available and promising to increase the drive current. In the past, after gate dielectric deposition, the annealing process with nitrogen gas was commonly adopted to repair the existence of defects in gate dielectric and therefore improve the quality of interfacial layer in MOSFETs. However, few published researches discussed the nitridation effect of decoupled plasma nitridation (DPN) process with the hot-carrier effect and electrical characteristics at different annealing temperatures. In this study, I focus on these points and try to establish these relationships. In this work, the tested 28nm wafers came from UMC. The hafnium-based gate dielectric with a profile of HfOx/ZrOy/HfOz (HZH) was deposited with atomic layer deposition (ALD) technology. The experimental parameters include the different channel lengths and stress temperatures. Consequently, through the statistical and analytical analysis of experimental data, the nitridation effect with annealing temperatures reflecting the various results of device electrical characteristics are exposed in this thesis. After the analysis, the annealing temperatures after DPN treatments do not obviously impact the device performance. Owing to the stronger horizontal electrical field, the degradation of short channel nMOSFETs with L=0.03?m in channel hot-carrier (CHC) stress is more serious than that with L=1?m. Additionally, for the identical L, the worst degradation of nMOSFETs with CHC test is the samples of 8% N2 concentration and 900℃ annealing temperature stressed at 125℃. This may attribute to the formation of thicker oxide interfacial layer (IL) and was annealed cause crystallization.
35
吳宛蓉. "Characterization and Analysis of Impact Ionization Effect of Sb-based High Electron Mobility Transistors at Low Temperatures." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/63049703207314832450.
Full textAbstract:
碩士國立彰化師範大學
電子工程學系
102
Sb-based high electron mobility transistors (HEMTs) with InAs as the channel layer have excellent electron mobility, making them very suitable for ultra-high-speed, low-power electronic devices. However, the narrow energy band gap of InAs is inherently accompanied with strong impact ionization. In this thesis, we measure the low-temperature characteristics of Sb-based HEMTs and analyze the effect of impact ionization on the device characteristics at various temperatures. To explore the impact ionization effect in depth, we establish a simplified modal theory to fit the experimental current-voltage curves so that the ideal current and the impact ionization current can be extracted. Our study clearly shows that the impact ionization effect in the HEMTs with the channel layer of small band gap can be significant even under low electric field. Besides, the current contributed by impact ionization becomes larger at lower temperatures.
36
Morudu, Kholo Veronica. "Influence of temperature on the metal dusting of alloy 800." Thesis, 2018. https://hdl.handle.net/10539/27004.
Full textAbstract:
A research report submitted in fulfilment of the requirements for the degree of Master of Science in Engineering (50/50) to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, 2018Metal dusting (MD) is a severe form of corrosion in which iron, steels, and nickel (Ni) and cobalt (Co) based alloys disintegrate into a metal or carbide powder with a coke deposit when exposed to strongly carburising gases (carbon activity, ac>1) at elevated temperatures (400800°C). Temperature affects both the driving force and rate of the reaction, represented by gas phase supersaturation with carbon, and the rates of the various processes involved in converting that energy difference into the dusting process. Therefore, process streams such as reformer gas can be benign when hot, but becomes aggressive below critical temperatures. There are different views in literature about the effect of temperature on metal dusting of different materials and alloys. Alloy 800 experiences metal dusting (MD) at 525°C, which is the temperature of the tube sheet of reformers in petrochemical industry. This alloy is specifically used for tube ferrules in the reformers. The reformer trains can reach a critical (highest) internal temperature of 650°C. Therefore, these two temperatures were compared. The effect of temperature and exposure time on the metal dusting of Alloy 800 were investigated in terms of the form of attack and the degradation mechanism. From the results obtained, it was observed that the longer exposure periods result in more carbon deposition and the carbon filaments in the coke become finer as compared to the nanotubes obtained after shorter exposure periods. The alloy suffered metal dusting attack after a relatively short exposure period of three days (72 hours) at both temperatures of 525°C and 650°C, with very little coking.
TL2019
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Tao, Ju Zhou. "Theory of negative thermal expansion." Thesis, 2002. http://hdl.handle.net/1957/31094.
Full textAbstract:
Two framework oxide materials of the MO��� network type have been
synthesized and structurally characterized by synchrotron and X-ray powder
diffraction and the Rietveld method in the temperature range 25~500 K. The results
show one of them to be a low thermal expansion material.
Theoretical studies of negative thermal expansion (NTE) in framework oxides
were conducted with two methods, geometrical modeling by Rigid Unit Mode
(RUM) method and lattice dynamic calculations by free energy minimization
(FEM) method, the results are compared with each other as well as with
experimental observations.
RUM analysis of all five types of framework oxide structures negates any
simple and direct correlation between presence or absence of RUMs in a structure
and the sign of its thermal expansion. Instead, results suggest that NTE of a
crystalline solid can not be explained by pure geometrical considerations over its
structure alone, and for a better understanding of structure-relationship in negative
thermal expansion structures, specific interatomic interactions present in each one
must be brought in explicitly.
FEM calculation of two negative thermal expansion structures indicates on a
structure by structure basis NTE could be predicted and understood within the
Gruneisen model, which attributes NTE of a structure to special vibration modes in
a structure that softens when the lattice shrinks. The soft NTE modes are, however,
not necessarily RUM or RUM like vibration motions.Graduation date: 2003
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Krejci, Michael. "Development of a New Flame Speed Vessel to Measure the Effect of Steam Dilution on Laminar Flame Speeds of Syngas Fuel Blends at Elevated Pressures and Temperatures." Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-05-10978.
Full textAbstract:
Synthetic gas, syngas, is a popular alternative fuel for the gas turbine industry, but the composition of syngas can contain different types and amounts of contaminants, such as carbon dioxide, methane, moisture, and nitrogen, depending on the industrial process involved in its manufacturing. The presence of steam in syngas blends is of particular interest from a thermo-chemical perspective as there is limited information available in the literature. This study investigates the effect of moisture content (0 ? 15% by volume), temperature (323 ? 423 K), and pressure (1 ? 10 atm) on syngas mixtures by measuring the laminar flame speed in a newly developed constant-volume, heated experimental facility. This heated vessel also broadens the experimental field of study in the authors? laboratory to low vapor pressure fuels and other vaporized liquids. The new facility is capable of performing flame speed experiments at an initial pressure as high as 30 atm and an initial temperature up to 600 K. Several validation experiments were performed to demonstrate the complete functionality of the flame speed facility. Additionally, a design-of-experiments methodology was used to study the mentioned syngas conditions that are relevant to the gas turbine industry. The design-of-experiments methodology provided the capability to identify the most influential factor on the laminar flame speed of the conditions studied. The experimental flame speed data are compared to the most up-to-date C4 mechanism developed through collaboration between Texas A&M and the National University of Ireland Galway. Along with good model agreement shown with all presented data, a rigorous uncertainty analysis of the flame speed has been performed showing an extensive range of values from 4.0 cm/s to 16.7 cm/s. The amount of carbon monoxide dilution in the fuel was shown to be the most influential factor on the laminar flame speed from fuel lean to fuel rich. This is verified by comparing the laminar flame speed of the atmospheric mixtures. Also, the measured Markstein lengths of the atmospheric mixtures are compared and do not demonstrate a strong impact from any one factor but the ratio of hydrogen and carbon monoxide plays a key role. Mixtures with high levels of CO appear to stabilize the flame structure of thermal-diffusive instability. The increase of steam dilution has only a small effect on the laminar flame speed of high-CO mixtures, while more hydrogen-dominated mixtures demonstrate a much larger and negative effect of increasing water content on the laminar flame speed.
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Mantyi, Hadio Caprice. "High temperature oxidation and corrosion behaviour of titanium aluminide alloy Ti-52.5AI-10.0Ni-0.2Ru (at.%)." Thesis, 2016. http://hdl.handle.net/10539/22671.
Full textAbstract:
A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering
15 October 2016The alloys Ti-52.5Al-10.0Ni (at.%) and Ti-52.5Al-10.0Ni-0.2Ru (at.%) were made by mixing, and melting their powders in a button arc furnace under an argon atmosphere. The high temperature oxidation and room temperature corrosion of behaviour of the alloys was investigated. Isothermal oxidation in air at 950°C for 120 hours and 720 hours was done. Cyclic oxidation behaviour of the alloys was also investigated in air and in a hot salt (Na2SO4) environment. The corrosion tests were conducted in 5 wt% and 25 wt% HCl. All the samples were characterised using scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffraction and hardness measurements. On solidification, the Ti-52.5Al-10.0Ni (at.%) alloy formed dendrites of γ-TiAl (~55 at.% Al) surrounded by a eutectic of γ-TiAl + Ti2NiAl3 (τ3) phases. Most of the nickel was found in the Ti2NiAl3 (τ3) phase (~12 at.%) with trace amounts in the dendrites (~0.5 at.%). The Ti-52.5Al-10.0Ni-0.2Ru (at.%) alloy formed dendrites of γ-TiAl (~53 at.% Al) surrounded by a eutectic of γ-TiAl + Ti2NiAl3 (τ3). Most of the nickel (~15 at.%) and ruthenium (~0.3 at.%) were in solid solution in the Ti2NiAl3 (τ3) phase, although small amounts of both metals were present in the dendrites (~1 at.% Ni and 0.1 at.% Ru). Under isothermal oxidation conditions, both alloys showed good oxidation resistance with a low mass gain (< 2%). The alloys formed a continuous scale of TiO2 and Al2O3 with good adherence to the substrate, but as exposure time increased, the scale was severely degraded and exfoliated from the surface. Cyclic oxidation conditions were more aggressive for both alloys. The Ti-52.5Al-10.0Ni-0.2Ru (at.%) alloy was more resistant and formed a nickel-rich sub-surface zone between the substrate and intermixed oxide layer. Both alloys had a fairly good corrosion resistance in HCl due to the presence of nickel. They formed a thin and non-continuous Al2O3 oxide scale on the surface of the γ-TiAl dendrites, with Ti3NiAl2O on the γ-TiAl + Ti2NiAl3 (τ3) eutectic regions. The acid mainly corroded the τ3 phase, thus attacking the eutectic and leaving the γ-TiAl dendrites exposed.
MT2017
40
Keller, Nicole Simone. "Metals and volatiles in melts : an experimental and field study." Phd thesis, 2008. http://hdl.handle.net/1885/150923.
Full text
41
Malwela, Thomas. "The study of bionanocomposite thin films and their crystal growth behaviour." Thesis, 2014. http://hdl.handle.net/10210/12337.
Full textAbstract:
Ph.D. (Chemistry)This study focuses on the morphology and crystal-growth behaviour of polyactide (PLA)-based blends and blends modified with organoclay thin films. The study further examined the effect of blending and the incorporation of organoclays on the enzymatic degradation behaviour. Thin films of unmodified and nanoclay-modified PLA/poly(butylene succinate) (PBS) blends were cast on a glass substrate by a spin coater, while thin films of biodegradable PLA/poly[(butylene succinate)-coadipate] PBSA blends and blends containing organoclays were cast on a silicon (100) wafer substrate. The morphology and crystal growth behaviour of the thin films crystallized at different temperatures were examined with an atomic force microscopy (AFM) equipped with a hot-stage scanner. In PLA/PBS blend thin films, AFM images showed that the size of the dispersed PBS phase was influenced by C30B clay loading on the blends. The dispersed size reduced on the addition of C30B clay up to 2 wt%, beyond which, dispersed size began to increase. Transmission electron microscopy studies indicated that this behaviour was due to the preferential location of silicates in the PBS phase than in the PLA phase. For thin films annealed at 60 °C, the additi on of organoclays to the blend quenched the growth of edge-on lamellae. The crystalline morphologies at 120 °C were dominated by edge-on lamellae grown, around the PBS phase to form spherulites. Morphologies of thin films crystallized at 120 °C from melt were dominated by the flat-on lamellae, while those crystallized at 70 °C from melt were dominated by the edge-on lamellae. In the case of PLA/PBSA blend thin films, the results indicated that the size and distribution of the dispersed phase were directly related to the blend composition. The crystal growth behaviours indicated the presence of homogeneous and heterogeneous nucleations, and the nature of nucleation was directly related to the blend ratio and the temperature at which crystallization occurred. Therefore, this study will facilitate the understanding of crystal growth behaviour in a confined environment and will enable the modulation of the blend properties.
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Ramalall, Dawlall Shahil. "The relationship between the metal dusting mechanism and the synthesis of carbon nanofilaments using toluene and a nickel based alloy." Thesis, 2016. http://hdl.handle.net/10539/21729.
Full textAbstract:
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016.Metal dusting (MD) is a severe type of corrosion that occurs mainly in petrochemical industries. The occurrence of MD is mainly due to syngas attacking Fe-, Ni- and Co-based alloys at elevated temperatures. More recently, literature has shown that apart from syngas, liquid hydrocarbon sources have been causing problems on platformer units in refineries. In the first part of this study a highly corrosion resistant Ni-based alloy (Hastelloy C276), in its polished form, was subjected to MD conditions at 800 °C using a liquid hydrocarbon (toluene) and helium (carrier gas) for 1 h. Exposure to these conditions revealed the formation of carbon nanofilaments and graphite layers which were confirmed by laser Raman spectroscopy, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Burning off the carbon nanofilaments and the graphite layers in laboratory air for 1 h at 800 °C revealed that pits were formed on the Hastelloy C276. These same pits were not evident when Hastelloy C276 was exposed to either the carrier gas (helium) or laboratory air alone. Besides MD being a continuous problem in industry, this mechanism has been shown to be beneficial in the synthesis of carbon nanofilaments viz., carbon nanofibers (CNTs) and nanotubes (CNFs). In the second part of this study, unpolished Hastelloy C276 blocks (as opposed to polished blocks) were used to synthesize carbon nanofilaments. This was done as prior studies had shown that carbon nanofilaments were produced with better quality and greater yields this way. Here the flow rate (80, 160 and 240 mL/min) and reaction duration (10, 15, 30, 45, 60, 120 and 240 min) were studied using toluene (a liquid hydrocarbon). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to assess the quality and quantity of the carbon nanofilaments synthesized. Besides the formation of carbon nanofilaments, a less important material known as graphite particle structures (GPSs) were also synthesized. These studies collectively showed that MD had taken place on the surface of Hastelloy C276 when exposed to toluene at 800 °C.
TG2016
43
Kim, Hyeong Jun. "Thermal effects on modular maglev steel guideways." Thesis, 2007. http://hdl.handle.net/2152/3282.
Full textAbstract:
Current research on thermal effects on guideways has addressed many aspects of the behavior of guideways using two-dimensional models. The two-dimensional models are acceptable for existing guideway designs, in which cross sectional shapes are uniform along the length of the guideway. However, three-dimensional models are necessary for a modular design, in which the track structures that interact with Maglev vehicles are made separately and are assembled into the support structure, and in which the cross sectional shapes are not uniform. A three-dimensional numerical model of the thermal environment, in which the effect of partial shading is taken into account, is implemented for the study of guideway behavior under various thermal environments. The numerical model of the thermal environment is calibrated to the experimental results under the thermal environment at Austin, Texas, and is extrapolated to predict the behaviors of guideways under the thermal environment in Las Vegas, Nevada, which is one of the candidate sites for the implementation and deployment of the high speed Maglev transportation system. This study addresses the suitability of a modular steel guideway design under such a thermal environment. Characteristics of the behavior of guideways under various thermal environments are identified, and the behavior of guideways under the effect of partial shading is summarized.text
44
Liang, YUAN-MING, and 梁原銘. "Application of Failure Mode and Effect Analysis in Risk Assessment and Management of Equipment Used in High-operating Temperatures for Production Processes – A Case Study of a Semiconductor Factory." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/59w9qh.
Full textAbstract:
碩士國立中央大學
環境工程研究所在職專班
106
In the semiconductor packaging and testing industry, many raw materials (such as flammable chemicals, strong acids, strong alkalis, strong oxidizing substances and flammable gases) are used in various processes equipment operated at high temperatures according to the process requirements. While the products are regulated by the relevant laws and regulations, these laws and regulations are not as clear and specific as the standards that can be followed in foreign countries, resulting in that enterprises can only rely on the experience to set up their equipment procurement specifications. In this case, it is easy to derive the fire caused by poor equipment safety design and improper on-site management. In addition, the design of the plant is mostly in a closed environment, which leads to the difficulty of people evacuation and disaster relief when the fire occurs. In this study, the Failure Mode and Effect Analysis (FMEA) and EMI S10 risk assessment method are used to analyze the hazards that can be caused in the process of equipment with high-temperature operation (i.e., High Temperature Equipment) by the functional failure of apparatus components, exhaust system and the safety interlock devices, and study the improvement countermeasures according to the risk assessment results. Using a semiconductor packaging and testing industry as a case, the failure analysis of the fire project caused by the process of High Temperature Equipment reveals that (i) among the Equipment Components, the highest risk priority number is when the element material is carbonated (RPN was 320); (ii) in the Exhaust System, when the pipeline full of internal condensation, the highest risk priority number is scored 392; (iii) among the Safety interlock System, the highest risk priority number of the safety interlock devices and the temperature detection devices are scored 336. According to the analysis of various failure items, it was found that the reason of the high risk priority, apart from causality, the general problems are lack of existing prevention and detection deficiencies, which leads to the failure to prevent the occurrence. This study also takes how to early prevention of failures as an improvement strategy to compare the differences between before and after improvement that is made. It is found that the abnormity of the equipment components is carbonated by the element material, the RPN scored is reduced to 128; the RPN scored of the safety interlock system is reduced to 96, and the RPN scored of the temperature detection system is reduced to 144; in exhaust pipe, the abnormal internal condensation in the pipeline which RPN scored fell from 392 to 112. From the outcome of the improvement, it is known that the Standards should be set up early in the stage of equipment planning and evaluation to reduce the failure rate of process equipment during operation. According to the above results, the risk value of internal condensation of exhaust pipeline is the highest, resulting in condensation phenomenon caused when a high temperature gas contacting with cold surfaces. The second high risk value is the safety interlock system, because the equipment machine is not connected with the safety interlock devices. The element material carbonation ranks the third place, because the component temperature exceeds the circuit insulation temperature. Hence. the above projects in the management control should be strengthened via personnel routine testing, cleaning frequency and regular infrared thermal imaging instrument to measure temperature; further, in engineering control, a condensation collecting plate and the exhaust flow detector can be set up inside the exhaust pipe and safety interlock system should controlled by double and double loop protection devices; lastly, the material carbonation of the circuit material should be replaced with a heat-resistant material.
45
Thirunavukarasu, Balamurugesh. "A study of solidification dynamics with liquid mass influx." Thesis, 2003. http://hdl.handle.net/1957/31591.
Full textAbstract:
A computational model is developed to study the effects of alumina layer formation
on an ablative surface when exposed to high temperature particle laden gas
flow. The solidification dynamics i.e., the solid and liquid alumina layer growth rate,
and the heat transferred to the ablative surface are investigated. A one-dimensional
model is developed taking into consideration the thermal loading, particle loading
and the temperature dependence of the thermo-physical properties of alumina. A
fully implicit finite volume method is used to solve the coupled set of non-linear heat
conduction equations. The solidification interface is tracked using the Lagrangian
interpolation technique. The particle mass flux was found to be the major factor
affecting the solid layer growth rate. The gas heat flux also has a major effect on
the solid growth rate and the heat transferred to the ablative surface, but only for
lower particle mass fluxes. On other hand the particle temperature has a linear
effect on the solidification dynamics and the heat transferred to the ablative surface
for all particle mass fluxes. The heat transferred to the ablative surface is reduced
by approximately 39% to 88%, depending on the mass fluxes, due to the formation
of the alumina layer.Graduation date: 2003
46
"Simulation study on the effects of heat and ash on a frequently burnt soil in Hong Kong." 2005. http://library.cuhk.edu.hk/record=b5892332.
Full textAbstract:
Lam Lai-yee.Thesis submitted in: November 2004.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references (leaves 124-140).
Abstracts in English and Chinese.
Abstract --- p.i
Acknowledgement --- p.vii
Table of contents --- p.viii
List of Tables --- p.xi
List of Figures --- p.xiii
List of Plates --- p.xiv
Chapter CHAPTER ONE --- Introduction
Chapter 1.1 --- Introduction --- p.1
Chapter 1.2 --- Background and ecological impact of hill fires in Hong Kong --- p.2
Chapter 1.3 --- Conceptual framework of study --- p.4
Chapter 1.4 --- Objectives of the study --- p.10
Chapter 1.5 --- Significance --- p.11
Chapter 1.6 --- Organization of the thesis --- p.12
Chapter CHAPTER TWO --- The study area
Chapter 2.1 --- Introduction --- p.14
Chapter 2.2 --- Geographical setting of Hong Kong --- p.14
Chapter 2.2.1 --- Climate of Hong Kong --- p.14
Chapter 2.2.2 --- Geology of Hong Kong --- p.15
Chapter 2.2.3 --- Soils of Hong Kong --- p.16
Chapter 2.2.4 --- Vegetation of Hong Kong --- p.17
Chapter 2.3 --- Site selection --- p.18
Chapter 2.4 --- Grassy Hill --- p.20
Chapter CHAPTER THREE --- Heating effect on the properties of ash
Chapter 3.1 --- Introduction --- p.23
Chapter 3.2 --- Experimental design and methodology
Chapter 3.2.1 --- Selection of simulation heating --- p.26
Chapter 3.2.2 --- "Heating intensity at 200°-600°C for 1,5 and 15 minutes" --- p.27
Chapter 3.2.3 --- Field work --- p.27
Chapter 3.2.4 --- Heating method --- p.28
Chapter 3.2.5 --- Chemical analysis --- p.28
Chapter 3.2.6 --- Analysis of data --- p.32
Chapter 3.3 --- Results and Discussion
Chapter 3.3.1 --- Heating effect on ash weight and pH --- p.33
Chapter 3.3.2 --- "Heating effect on ash organic C, N and P" --- p.33
Chapter 3.3.3 --- Heating effect on ash available cations --- p.40
Chapter 3.4 --- Conclusion --- p.42
Chapter CHAPTER FOUR --- The effect of heat and ash on soil
Chapter 4.1 --- Introduction --- p.44
Chapter 4.2 --- Methodology
Chapter 4.2.1 --- Field work --- p.48
Chapter 4.2.2 --- Soil heating methods --- p.48
Chapter 4.2.3 --- Chemical analysis --- p.49
Chapter 4.2.4 --- Statistical analysis --- p.52
Chapter 4.3 --- Results and Discussion
Chapter 4.3.1 --- The effect of heat and ash on soil pH --- p.53
Chapter 4.3.2 --- "The effect of heat and ash on soil organic matter, N and P" --- p.55
Chapter 4.3.3 --- The effect of heat and ash on soil cations --- p.62
Chapter 4.4 --- Conclusion --- p.65
Chapter CHAPTER FIVE --- Nitrogen and phosphorus mineralization after heating
Chapter 5.1 --- Introduction --- p.67
Chapter 5.2 --- Methodology
Chapter 5.2.1 --- Heating and incubation method --- p.70
Chapter 5.2.2 --- Laboratory methods --- p.72
Chapter 5.2.3 --- Statistical analysis --- p.72
Chapter 5.3 --- Results and discussion
Chapter 5.3.1 --- Temporal changes of N mineralization in heated bare soils --- p.72
Chapter 5.3.2 --- The effect of ash on N mineralization --- p.78
Chapter 5.3.3 --- Comparison of N mineralization with other studies --- p.79
Chapter 5.3.4 --- Temporal changes of P mineralization in the heated bare soils --- p.81
Chapter 5.3.5 --- The effect of ash on P mineralization --- p.83
Chapter 5.3.6 --- Comparison of P mineralization to other studies --- p.84
Chapter 5.4 --- Conclusion --- p.85
Chapter CHAPTER SIX --- Vertical movement of mineral N in ash-covered soil columns
Chapter 6.1 --- Introduction --- p.87
Chapter 6.2 --- Methodology
Chapter 6.2.1 --- Package of soil columns --- p.89
Chapter 6.2.2 --- Water addition and extraction of pore water --- p.90
Chapter 6.2.3 --- Statistical analysis --- p.92
Chapter 6.3 --- Results and Discussion
Chapter 6.3.1 --- Mineral N in the pore water --- p.92
Chapter 6.3.2 --- The effect of ash on mineral N in pore water --- p.97
Chapter 6.3.3 --- The leaching loss of mineral N --- p.98
Chapter 6.3.4 --- Comparisons with other studies --- p.103
Chapter 6.4 --- Conclusion --- p.105
Chapter CHAPTER SEVEN --- Integrative discussion
Chapter 7.1 --- Summary of major findings --- p.107
Chapter 7.2 --- Clarifying some misconceptions about the effect of fire --- p.110
Chapter 7.3 --- Estimated losses of N and P from heating --- p.112
Chapter 7.4 --- Nutrient supplying capacity of soils after heating --- p.115
Chapter 7.5 --- Why are repeatedly burnt areas reduced to grassland? --- p.118
Chapter 7.6 --- Implication on the restoration of fire-affected areas --- p.119
Chapter 7.7 --- Limitations of the study --- p.121
Chapter 7.8 --- Suggestions for future research --- p.122
References --- p.124
Appendices --- p.141
47
Kunc, Jan. "Dvourozměrný elektronový plyn v kvantových jamách CdTE: studie ve vysokých magnetických polích." Doctoral thesis, 2011. http://www.nusl.cz/ntk/nusl-296138.
Full textAbstract:
KurHigh mobility two-dimensional electron gas in CdTe quantum wells: High magnetic field studies Experimental studies of two-dimensional electron gases confined in CdTe and CdMnTe quantum wells are presented. The data analysis is supported by numerical calcula- tions of the band structure of confined states, using the local density and envelope func- tion approximations. Four by four, k.p calculations have been performed to justify the parabolic approximation of valence bands. Samples were characterized by Raman scatter- ing spectroscopy and far infrared cyclotron resonance absorption measurements. Low-field magneto-transport shows the dominant contribution of the semi-classical Drude conduc- tivity and three orders of magnitude weaker contributions of weak localization, electron- electron interaction and Shubnikov-de Haas oscillations. The contribution of electron- electron interactions is explained within a semi-classical model of circling electrons. The shape of Landau levels, broadening, transport and quantum lifetimes and dominant long- range scattering mechanism have been determined. High-field magneto-transport displays fractional quantum Hall states at Landau levels N = 0 and N = 1. The ground states 5/3 and 4/3 have been determined to be fully spin polarized, in agreement with the approach of composite...