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Gu, Jingjing. "Ternary Oxide Structures for High Temperature Lubrication." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc804963/.
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In this research, a temperature dependent tribological investigation of selected ternary oxides was undertaken. Based on the promising results of previous studies on silver based ternary oxides, copper based ternary oxides were selected to conduct a comparative study since both copper and silver are located in the same group in the periodic table of the elements. Two methods were used to create ternary oxides: (i) solid chemical synthesis to create powders and (ii) sputtering to produce thin films. X-ray diffraction was used to explore the evolution of phases, chemical properties, and structural properties of the coatings before and after tribotesting. Scanning electron microscopy, Auger scanning nanoprobe spectroscopy, and X-ray photoelectron spectroscopy were used to investigate the chemical and morphological properties of these materials after sliding tests. These techniques revealed that chameleon coatings of copper ternary oxides produce a friction coefficient of 0.23 when wear tested at 430 °C. The low friction is due to the formation of copper tantalate phase and copper in the coatings. All sputtering coatings showed similar tribological properties up to 430 °C.
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Beck, Michael Peter. "Thermal conductivity of metal oxide nanofluids." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26488.
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Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Teja, Amyn S.; Committee Member: Abdel-Khalik, Said I.; Committee Member: Meredith, Carson; Committee Member: Nair, Sankar; Committee Member: Skandan, Ganesh. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Liu, Hao. "Modified thermal reduction of graphene oxide." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/14024/.
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As a strictly two-dimensional carbon material, graphene has attracted great interest in recent years due to its unique mechanical, electrical and optical properties. Currently, the principal methods for mass production of graphene are focused on the solution-based chemical redox reaction. The oxidation of graphite introduces a large amount of oxygen functional groups attached onto its basal plane or edges, which makes graphene oxide (GO) sheets hydrophilic to form stable aqueous colloids. However, the raw material graphite gradually becomes an insulator during the oxidation process as part of planar sp2-hybridized geometry transformed to distorted sp3-hybridized geometry, which loses its excellent electronic properties. As a result, reduction of GO is definitely necessary to recover its “lost” electrical conductivity for practical applications. In addition, the hydrophilic property of GO sheets allows metal oxide (MO) nanoparticles (NPs) anchoring on reduced graphene oxide (rGO) plane to fabricate MO/rGO composites with excellent electrochemical performance. However, the current preparation methods for the electrical conductive MO/rGO composites are very complicated which might have negative effects on the properties and hinder mass production. The objective of this project is to synthesize aluminium oxide (Al2O3)/rGO nanocomposites via oxygen annealing without using an Al2O3 precursor. This method establishes a very simple and efficient way to yield Al2O3 NPs on rGO plane by filtering GO dispersion through an Anodisc membrane filter with oxygen annealing, which is named oxygenally reduced graphene oxide (OrGO). The characterizations reveal that the Al2O3 NPs are formed exclusively on the edges of defective regions with uniform particle size less than 10 nm. As for the electronic properties, OrGO has a higher electrical conductivity at 7250 S m−1 with a narrower range of the electrical conductivity mostly between 6500 and 7250 S m−1, which can be due to the increase of the sp2/sp3 carbon ratio caused by the formation of Al2O3 NPs at the edges of defective regions in OrGO plane. Moreover, the formation of Al2O3 NPs maintains OrGO sheets with good hydrophilic property with a contact angle around 71.5°. The electrochemical performance of OrGO paper fabricated as electrode materials for lithium-ion batteries (LIBs) is also investigated. OrGO electrodes exhibit a high specific charge and discharge capacity at 1328 and 1364 mAh g−1. The cyclic voltammograms (CV) performance reveal that the insertion of Li+ ions begins at a very low potential around 0 V vs. Li+/Li while the extraction process begins in the range of 0.2–0.3 V. In addition, the OrGO electrode has excellent rate capability and cycling performance. The average coulombic efficiency (CE) was measured at 99.608% for 30 cycles, indicating a superior reversibility of the Li+ ion insertion/extraction process.
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James, Amy Frances. "Tin-oxide thin films by thermal oxidation." University of Western Cape, 2021. http://hdl.handle.net/11394/8239.
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>Magister Scientiae - MScTin dioxide (SnO2) thin films are a worthy candidate for an electron transport layer (ETL) in perovskite solar cells, due to its suitable energy level, high electron mobility of 240 cm2 v-1 s- 1, desirable band gap of 3.6 - 4.0 eV, and ultimately proves to be suited for a low temperature thermal oxidation technique for ETL production. A variety of methods are available to prepare SnO2 thin films such as spin and dip coating and chemical bath deposition. However, the customary solid-state method, which incorporates thermal decomposition and oxidation of a metallic Sn precursor compound in an oxygen abundant atmosphere prevails to be low in cost, is repeatable and allows for large-scale processing.
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Sun, Baoguo. "Thermal Cycling of Solid Oxide Fuel Cells." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486561.
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Solid-oxide fuel cells (SOFCs) are energy conversion devices that theoretically have the capability of producing electrical- energy for as long as the fuel and oxidant are supplied to the electrodes and perfonnance is expected for at least 40,000 hours. However, it is observed that perfonnance degrades under repeated thennal cycling conditions, which limits the practicaI.operating life of these SOFCs. Therefore, the mechanism of damage to planar and integrated planar SOFCs (IPt' SOFCs) on thennal cycling is the subject of this thesis. A detailed literature review has been carried out and a mechanical and thennal properties database of the key materials used in these SOFCs has been built up. Extensive work has been done on the residual ~tress analysis of anode-supported and inert substrate supported SOFCs. Analytical model, surface profile measurement (Talysurf) and XRD stress analysis were used to detennine t4e residual stresses in the components. From this study, it was found that the difference of thennal expansion coefficients between components in the SOFCs is the dominant source of stress during thennal cycling in the absence of significant temperature gradient. For the integrated planar SOFCs, it was found tha~ the cells degraded due to the failure of the sealing materials during cooling. For anode supported planar SOFCs, the electrolyte (YSZ) is under high compressive stress when cooling from sintering or operating temperature to room temperature and the anode is under very small tensile stress. The results from theoretical analysis, XRD stress measurement and literature were compared and found that they agreed with each other quite well.
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Dong, Shuhong. "Effects of Thermal Gradient and Cyclic Oxidation on the Delamination and Lifetime of High Temperature Protective Coatings." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38334.
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Thermal barrier coatings have been widely used to provide thermal protection to components in the hot section of gas turbines. This research focuses on two influencing factors on coating behavior: thermal gradient and cyclic oxidation.
The delamination mechanics under thermal gradient is analyzed, taking thermally grown oxide into consideration. Coatings experience thermal gradients at different stages during actual service flight. One is due to engine power shut down when landing and the other due to internal cooling of the substrate. Thermally grown oxide (TGO) also acts as a critical factor in delamination mechanics. The induced stress gradient and corresponding energy release rate for interface delamination and shallower delamination are presented. Mechanism maps that explain the criteria for preventing delamination from developing and propagating are established. Three cooling trajectories are envisaged to analyze the variation in the possibility of delamination.
Multilayer coatings used in components of the hot section of aero turbine engines also experience cyclic temperature variation during flight cycles. As experiment conditions vary and coating performance is improved, the time required to run through the test of coating failure can be both time-consuming and prohibitive. Therefore, protocols providing prediction of quantified coating behavior are in demand to shorten life-time tests. Curves of mass change are obtained from quantifying scale growth and loss by different models such as Cyclic Oxidation Spall Program (COSP). A modification is made by combining COSP and a mechanic based model to obtain critical parameters for lifetime prediction from short time experiment. The time for coatings to reach peak temperature during cycling is discovered to influence prominently on modeling results. Predictions for several coating compositions and cycling conditions are consistent with the data from the existing experiments of the coating system.
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Tang, Xiaoli Dong Jianjun. "Theoretical study of thermal properties and thermal conductivities of crystals." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Physics/Dissertation/Tang_Xiaoli_9.pdf.
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Zhou, Linghe. "Non-thermal plasma technology for nitric oxide removal." Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29440.
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Non-thermal plasma, as a potential nitric oxide (NO) removal technology, has been researched for more than one decade. The advantage of direct non-thermal plasma treatment is that it is able to generate reactive species from the existing components in the flue gas without additional catalyst, oxidant or reductant, so any NO removal system based upon this technology is simple and easy to operate. However, the energy efficiency of non-thermal plasma technology is lower than the most commonly used selective catalytic reduction system for NO removal. In order to understand the possible reasons, it is important to investigate the mechanism of NO removal by direct non-thermal plasma treatment. Two of the most commonly used non-thermal plasma sources, dielectric barrier discharge (DBD) and corona discharge, are investigated. The most important reactive species include oxygen atom (O), ozone (O3) and hydroxyl radical (OH). Different reactive species lead to different chemical reaction pathways for NO removal. Under different NO concentration and discharge configurations, the dominant reactive species was found to change from one to another. For dielectric barrier discharge, when the initial NO concentration was higher than 420 ppm under dry condition, it was found that O was the dominant reactive species for NO oxidation and NO oxidation was independent on O2 concentration. When initial NO concentration was lower than 100 ppm under dry condition, it was found that O3 was the dominant reactive species and NO oxidation was dependent on O2 concentration. When NO concentration was in the range of 120 ppm to 190 ppm, there was a synergistic effect of O and O3 on NO oxidation. NO removal depended on the initial NO concentration. However, no matter what the initial NO concentration was, the NO removal energy efficiency was lower than 25g/kWh. When water vapour (H2O) was introduced into the gas mixture, reactive species OH was generated and provided an alternative chemical reaction pathway for NO removal. When initial NO concentration was 1000 ppm, NO removal was in the range of 150 ppm to 200 ppm, but the energy efficiency was in the range of 7 to 12 g/kWh. With an increase of temperature in DBD reactor, the effect of OH on NO removal was promoted. To further investigate the OH effect, a novel pin to water corona discharge configuration was used. The effect of discharge modes from Trichel pulse, pulseless and arc discharge was investigated. Under arc discharge mode, 200 ppm NO was generated at 6W discharge power. Under Trichel and pulseless discharge modes, NO removal increased with increasing discharge power. When initial NO concentration was 1000 ppm, the highest NO removal achieved was 715 ppm with 5.5 g/kWh energy efficiency. In addition, it was found that the energy efficiency did not reduce with increasing discharge power. In order to increase the possibility of chemical reaction between NO and reactive species, higher initial NO concentration was used. To obtain higher NO concentration a process of NO absorption by activated carbon and thermal desorption was used. This increased the NO concentration from 1000 ppm up to 6%. It is found that at 6% level, NO could be partially oxidized by oxygen molecule (O2) and higher O2 concentration would obtain higher NO oxidation rate. Direct non-thermal plasma treatment can be used for NO removal but the energy efficiency (less than 30g/kWh) is too low to compete with the mature technologies including selective catalytic reduction (SCR) and low temperature oxidation (LoTOx) whose energy efficiencies are higher than 60 g/kWh. Although the energy efficiency is not improved in this research, the mechanism and chemical reaction pathways of NO removal are quantitatively analysed under different initial NO concentration levels by two different non-thermal plasma technologies (DBD and corona discharge). The dominant reactive species for NO removal can shift from O, O3 to OH. In addition, a novel technology which is a combination of non-thermal plasma, NO absorption and desorption processes is developed in this research. It offers a new mechanism for NO removal, because increasing the concentration of NO from ppm level to a few percentages creates a regime where NO removal can be effectively done by O2 rather than strong oxidants like O and O3. As the formation of O and O3 is more expensive than that of O2, this is a promising research direction for NO removal. However, based on the investigation in this research, some challenges are found. One is the poor selection between NO and H2O for activated carbon and the other one is high energy consumption for the desorption process.
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Yeandel, Stephen. "Atomistic simulation of thermal transport in oxide nanomaterials." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687351.
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The aim of this work has been to use atomistic computer simulation methods to calculate the thermal conductivity and investigate factors that will modify the behaviour when applied to three different oxide materials: MgO, SiO2 and SrTiO3. These were chosen as they represent distinct classes of materials and are substrates for thermoelectric devices, where one of the primary goals is to tailor the system to reduce the thermal conductivity. Chapter 1 introduces thermoelectric concepts, gives a background of the theory and a review of various important thermoelectric materials. In Chapter 2 an overview of the interatomic interactions is presented along with details on the implementation of these interactions in a simulation of a 3D periodic crystal. Chapter 3 outlines the importance of phonon processes in crystals and several approaches to the calculation of thermal conductivity are presented. MgO results are given in Chapter 4. Both the Green-Kubo and Boltzmann transport equation (BTE) methods of calculating thermal conductivity were used. The effect on thermal conductivity of two different grain boundary systems are then compared and finally extended to MgO nanostructures, thus identifying the role of surfaces and complex nanostructure architectures on thermal conductivity. In Chapter 5 two different materials with the formula unit SiO2 are considered. The two materials are quartz and silicalite which show interesting negative thermal expansion behaviour which may impact upon the thermal transport within the material. Chapter 6 presents results on the promising thermoelectric material STO. Once again the results from both Green-Kubo and BTE calculations are compared. Grain boundaries are also studied and the effect of inter-boundary distance and boundary type on the thermal conductivity is explored. Finally, a nanostructured STO system (assembled nanocubes) with promising thermoelectric applications is studied. Chapter 7 outlines the conclusions made from this work and suggests areas for future study.
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Curran, J. A. "Thermal and mechanical properties of plasma electrolytic oxide coatings." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598226.
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A critical review of the current knowledge of PEO coating characteristics and properties is made, and several areas requiring more accurate or more detailed investigations are identified. A leading commercial product – the KeroniteTM coating for aluminium alloys – is the used as a basis for the investigation of the microstructure and properties of PEO coatings. Coating structure and morphology are studied quantitatively to investigate their growth mechanism. Composition is accurately determined for the first time, allowing predictions of physical, mechanical and thermal properties to be made. Particular attention is also paid to the presence of amorphous material and fine-scale porosity – properties which had previously been neglected. The latter is critical to the understanding of coating formation and the capacity for coating impregnation, and is measured and characterised using numerous porosimetry techniques. Mechanical properties of the coatings are characterised using indentation and macroscopic techniques such as beam bending. Correlations are established between the observed structure and measured physical properties such as hardness, local modulus and global stiffness. It is found that wear resistance can also be explained on the basis of the measured mechanical properties and structure. The discovery of low coating stiffness means that high-temperature applications, which had previously been dismissed on the basis of thermal expansion mismatch between the coating and substrate, may indeed be possible. The thermal stability of the coatings is therefore investigated and their stability up to 800°C is demonstrated. Residual stresses are measured and explained in terms of the postulated coating growth mechanism.
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Poston, Michael Joseph. "Thermal and non-thermal processes involving water on Apollo lunar samples and metal oxide powders." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52223.
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Water is of interest for understanding the formation history and habitability of past and present solar system environments. It also has potential as a resource - when split to its constituent oxygen and hydrogen - both in space and on the Earth. Determining the sources, evolution, and eventual fate of water on bodies easily reachable from Earth, especially Earth's moon, is thus of high scientific and exploration value to the private sector and government space agencies. Understanding how to efficiently split water with solar energy has potential to launch a hydrogen economy here on Earth and to power spacecraft more sustainably to far away destinations. To address the fundamental interactions of water with important surfaces relevant to space exploration and technology development, temperature programmed desorption (TPD) and water photolysis experiments under well controlled adsorbate coverages have been carried out and are described in detail in this thesis.
TPD experiments under ultra-high vacuum (UHV) conditions were conducted on lunar surrogate materials and genuine lunar samples brought to Earth by the Apollo program. The TPD's were conducted to determine the desorption activation energies of water chemisorbed directly to the powder surfaces, knowledge of which can improve existing models of water evolution on Earth's moon and aid in interpreting data collected by spacecraft-based investigations at the Moon.
The TPD experiments of molecular water interacting with two lunar surrogates (micronized JSC-1A and albite) in ultra-high vacuum revealed water desorption during initial heating to 750 K under ultra-high vacuum. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) indicated possible water formation during the initial heating via recombinative desorption of native hydroxyls above 425 ± 25K. Dissociative chemisorption of water (i.e., formation of surface hydroxyl sites) was not observed on laboratory time scales after controlled dosing of samples (initially heated above 750 K) with 0.2 - 500 L exposures of water. However, pre-heated samples of both types of surrogates were found to have a distribution of molecular water chemisorption sites, with albite having at least twice as many as the JSC-1A samples by mass. A fit to the TPD data yields a distribution function of desorption activation energies ranging from ~0.45 eV to 1.2 eV. Using the fitted distribution function as an initial condition, the TPD process was simulated on the timescale of a lunation. A preview of these results and their context was published in Icarus (2011) 213, 64, doi: 10.1016/j.icarus.2011.02.015 by lead author Charles Hibbitts and the full treatment of the results from the TPD on lunar surrogates (presented here in Chapter 2) has been published in the Journal of Geophysical Research – Planets (2013) 118, 105, doi: 10.1002/jgre.20025 by lead author Michael J Poston.
The desorption activation energies for water molecules chemisorbed to Apollo lunar samples 72501 and 12001 were determined by temperature programmed desorption (TPD) experiments in ultra-high vacuum. A significant difference in both the energies and abundance of chemisorption sites was observed, with 72501 retaining up to 40 times more water (by mass) and with much stronger interactions, possibly approaching 1.5 eV. The dramatic difference between the samples may be due to differences in mineralogy, surface exposure age, and contamination of sample 12001 with oxygen and water vapor before it arrived at the lunar sample storage facility. The distribution function of water desorption activation energies for sample 72501 was used as an initial condition to mathematically simulate a TPD experiment with the temperature program matching the lunar day. The full treatment of the TPD results from these two lunar samples (presented here in Chapter 3) has been submitted with the title "Water chemisorption interactions with Apollo lunar samples 72501 and 12001 by ultra-high vacuum temperature programmed desorption experiments" to Icarus for publication in the special issue on lunar volatiles by lead author Michael J Poston.
A new ultra-high vacuum system (described in Chapter 4) was designed and constructed for planned experiments examining the possible formation of hydrated species, including water, from interaction of solar wind hydrogen with oxygen in the lunar regolith and to examine the effects of the active radiation environment on water adsorption and desorption behavior on lunar materials. This system has been designed in close collaboration with Dr. Chris J Bennett.
An examination of a unique system for water photolysis - zirconia nanoparticles for hydrogen production from water with ultra-violet photons - was performed to better understand the mechanism and efficiency of water splitting on this catalyst. Specifically, formation of H₂ from photolysis of water adsorbed on zirconia (ZrO₂) nanoparticles using 254 nm (4.9 eV) and 185 nm (6.7 eV) photon irradiation was examined. The H₂ yield was approximately an order of magnitude higher using monoclinic versus cubic phase nanoparticles. For monoclinic particles containing 2 monolayers (ML) of water, the maximum H₂ production rate was ~0.4 µmole hr⁻¹ m⁻² using 185 + 254 nm excitation and a factor of 10 lower using only 254 nm. UV reflectance reveals that monoclinic nanoparticles contain fewer defects than cubic nanoparticles. A H₂O coverage dependence study of the H₂ yield is best fit by a sum of interactions involving at least two types of adsorbate-surface complexes. The first dominates up to ~0.06 ML and is attributed to H₂O chemisorbed at surface defect sites. The second dominates at coverages up to a bilayer. H₂ formation is maximum within this bilayer and likely results from efficient energy transfer from the particle to the interface. Energy transfer is more efficient for the monoclinic ZrO₂ nanoparticles and likely involves mobile excitons. These results (presented in Chapter 5) have been submitted with the title "UV Photon-Induced Water Decomposition on Zirconia Nanoparticles" for publication in the Journal of Physical Chemistry C by lead author Michael J Poston. This paper has been reviewed and will be accepted after minor modification.
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Vasquez, Cristal Jeanette. "Oxide-coated vertically aligned carbon nanotube forests as thermal interface materials." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52237.
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Carbon nanotube (CNT) forests have outstanding thermal, electrical, and mechanical properties, which have generated significant interest as thermal interface materials (TIMs). Some drawbacks to using CNTs as TIMs include poor substrate adhesion, high interface resistances inhibiting thermal transport, and lack of electrical insulation in electronic component applications. It is thus useful to be able to modify CNTs to reduce their electrical conductivity while maintaining high thermal conductivity and interface conductance, and high mechanical compliance. A recent report suggests that nanoscale oxide coatings could be applied to CNTs in forests without changing the mechanical deformation behavior of the forests. Oxide coatings could also provide environmental stability as well as better adhesion to the substrate compared to pristine CNT forests.
In this study, we investigated thermal and electrical resistance of CNT forests with an oxide coating. Low-pressure chemical vapor deposition (LPCVD) was used to produce CNTs on high-conductivity Si substrates. Plasma-enhanced atomic layer deposition (PALD) was used to deposit Al2O3 on individual CNTs in forests. This process was facilitated by O2 plasma pretreatment to functionalize the surface of the CNTs and nucleate oxide growth. Several analytical techniques were used to characterize the CNT-oxide composites, including scanning electron microscopy, Raman and X-ray photoelectron spectroscopy. Thermal conductivity and thermal interface resistance were measured using a modified photoacoustic technique. The oxide coating had no significant effect on the effective thermal conductivity of the forests, in contrast to expectations of increased phonon scattering. Electrical resistivity measurements were made and a threefold increase was observed for the oxide-coated forests. This approach could emerge as a promising route to create a viable TIM for thermally conductive and electrically insulating applications.
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LeMasters, Jason Augustine. "Thermal Stress Analysis of LCA-based Solid Oxide Fuel Cells." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5220.
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This research characterizes the thermal stress resulting from temperature gradients in hybrid solid oxide fuel cells that are processed using a novel oxide powder slurry technology developed at Georgia Tech. The hybrid solid oxide fuel cell is composed of metallic interconnect and ceramic electrolyte constituents with integral mechanical bonds formed during high temperature processing steps. A combined thermo-mechanical analysis approach must be implemented to evaluate a range of designs for power output and structural integrity. As an alternative to costly CFD analysis, approximate finite difference techniques that are more useful in preliminary design are developed to analyze the temperature distributions resulting from a range of fuel cell geometries and materials. The corresponding thermal stresses are then calculated from the temperature fields using ABAQUS. This model analyzes the manufacturing, start-up, and steady state operating conditions of the hybrid solid oxide fuel cell.
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Sen, Firat. "Thermal Management Of Solid Oxide Fuel Cells By Flow Arrangement." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614496/index.pdf.
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Solid oxide fuel cell (SOFC) is a device that converts the chemical energy of the fuel into the electricity by the chemical reactions at high temperatures (600-1000oC). Heat is also produced besides the electricity as a result of the electrochemical reactions. Heat produced in the electrochemical reactions causes the thermal stresses, which is one of the most important problems of the SOFC systems. Another important problem of SOFCs is the low fuel utilization ratio. In this study, the effect of the flow arrangement on the temperature distribution, which causes the thermal stresses, and the method to increase the fuel utilization, is investigated.
An SOFC single cell experimental setup is developed for Cross-Flow arrangement design. This setup and experimental conditions are modeled with Fluent®. The experimental results are used in order to validate and verify the model. The model results are found to capture with the experimental results closely. The validated model is used as a reference to develop the models for different flow arrangements and to investigate the effect of the flow arrangement on the temperature distribution. A method to increase the SOFC fuel utilization ratio is suggested. Models for different flow arrangements are developed and the simulation results are compared to determine the most advantageous arrangement.
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Damm, David L. "Radiative and transient thermal modeling of solid oxide fuel cells." Thesis, Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-11162005-155659/.
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Singh, Virendra. "Rare Earth Oxide Coating with Controlled Chemistry Using Thermal Spray." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5503.
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Cerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent consolidation, specially using thermal spray. This dissertation aims to develop a scientific understanding towards the development of pure and doped ceria- based coating for a variety of technological applications, from SOFC applications to corrosion resistant coating. Atmospheric plasma spray (APS) and solution precursor plasma spray (SPPS) techniques for the fabrication of nano ceria coating were investigated. For feedstock powder preparation, a spray drying technique was used for the agglomeration of cerium oxide nano particles to achieve high density coating. Deposition efficiencies and coating porosity as a function of processing parameters were analyzed and optimized using a statistical design of experiment model. The coating deposition efficiency was dependent on the plasma temperature and vaporization pressure of the ceria nanoparticles. However, low standoff distance and high carrier gas flow rate were responsible for the improved density upto 86 [plus or minus] 3%.An alternative novel SPPS technique was studied for a thin film of cerium oxide deposition from various cerium salt precursors in doped and undoped conditions. The SPPS process allows controlling the chemistry of coating at a molecular level. The deposition mechanism by single scan experiments and the effect of various factors on coating microstructure evolution were studied in terms of splats formation. It was found that the precursor salt (nitrate of cerium) with lower thermal decomposition temperatures was suitable for a high density coating. The high concentration and low spray distance significantly improve the splat morphology and reduced porosity (upto 20%). The feasibility of the trivalent cations (Sm 3+ and Gd 3+) doping into cerium oxide lattice in high temperature plasma was discussed and experimentally studied. XRD analysis revealed the nano crystalline characteristic of the coating and lattice expansion due to doping. The extensive transmission electron microscopy, Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric were conducted to evaluate the precursors, and coating microstructure. Due to facial switching between Ce4+ and Ce3+ oxidation state, the cerium oxide surface becomes catalytically active. Thus, the APS ceria coatings were investigated for their applicability under extreme environmental conditions (high pressure and temperature). The air plasma sprayed coated 17-4PH steel was subjected to high pressure (10 Kpsi) and temperature (300 oF) corrosive environment. The coated steel showed continuous improvement in the corrosion resistance at 3.5 wt% NaCl at ambient temperature for three months study whereas, high pressure did not reveal a significant role in the corrosion process, and however, one needs to do further research. The ceria coated steel also revealed the improvement in corrosion protection (by 4 times) compared to the bare steel at low pH, 300 oF and 4000 Psi environment. This study projects the importance of cerium oxide coatings, their fabrication, optimization and applications.ID: 031001377; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Sudipta Seal.; Title from PDF title page (viewed May 21, 2013).; Thesis (Ph.D.)--University of Central Florida, 2012.; Includes bibliographical references (p. 171-182).
Ph.D.
Doctorate
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Chang, Cliff Cheng-Shiou. "Thermal reactions of freshly generated coal tar over calcium oxide." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15046.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Bibliography: leaves 351-363.
by Cliff Cheng-Shiou Chang.
Ph.D.
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Schwartz, Brian. "Analysis of the potential for thermal radiation promotion within solid oxide fuel cells." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53909.
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Solid oxide fuel cell (SOFC) systems have the potential to provide highly efficient power generation systems capable of utilizing readily available hydrocarbons. It is hoped that these systems will be capable of replacing some of the conventional power systems and act to reduce overall emissions and increase energy efficiency. SOFC technology faces many challenges such as high cost, lifetime uncertainties, and long startup times; and these challenges have prevented SOFC technology from being widely adopted.
Established methods for providing SOFC stack thermal management are either very costly, work against system design goals, or are unreliable. If SOFC thermal management needs could be reduced, it is possible that SOFC cost and lifetime could be improved. It is thought that promotion of thermal radiation within a SOFC stack may add thermal control which will reduce the need for stack thermal management. Radiation may be promoted by decreasing the length: hydraulic diameter ratio of cathode flow channels and by increasing the manifold size to create a larger stack radiation enclosure. Full thermal tests of a SOFC stack are difficult and expensive, and due to this simulations of a SOFC are widely used to analyze stack thermal behavior.
In this work, a model of a SOFC “unit cell” is adjusted to represent modern SOFC stacks. The proposed methods for radiation promotion are tested with simulations using this model, and conclusions of radiation promotion in SOFC stacks are provided. Additionally, radiative properties of commonly used materials are obtained through experiments, and future work for reducing stack reliance on active thermal management is proposed.
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Yiu, Wing-ching James. "Synthesis of one-dimensional tungsten oxide nano-structures by thermal evaporation." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B32047770.
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Cerezo, Frances Therese, and francestherese_cerezo@hotmail com. "Thermal stability and mechanical property of polymer layered graphite oxide composites." RMIT University. Applied Sciences, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080627.161157.
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Polymer composites formed from layered fillers with high surface volume ratio show enhanced reinforcement. Graphite oxide is a high modulus material that can be separated into thin layers with high surface area. The aim of this study is to prepare polymer layered graphite oxide composites using functionalised polyolefin to enhance compatibility with various forms of layered graphite oxide in varying concentration. Functionalised polyolefins reinforced with layered graphite oxides and expanded graphite oxides were prepared using solution blending and melt blending methods. Three different mixing methods with varying shear intensity were employed to prepare polymer layered graphite oxide composites. The crystalline structure, thermal and mechanical properties of the prepared polymer layered graphite oxide composites was studied. Oxidised graphite prepared from the Staudenmaier method and its exfoliated form were dispersed in poly(ethylene-co-methyl acrylate-co-acrylic acid) (EMAA) via solution blending to prepare EMAA layered composites. The thermal stability was determined using thermogravimetric analysis. The EMAA layered composites showed higher thermal stability in comparison with pure EMAA. The mechanical properties of these EMAA layered composites were determined through dynamic mechanical analysis. Shear modulus, yield stress and storage modulus of EMAA in the presence of graphite oxide fillers decreased. A solution blending method was used to prepare poly(propylene-grafted-maleic anhydride) layered expanded graphite oxide composites (PPMA-EGO). Two types of PPMA-EGO were prepared using different mixing methods - low and high shear were employed. The effects of preparative mixing methods on the PPMA-EGO properties were investigated. The mechanical properties of PPMA-EGO obtained from dynamic mechanical analysis indicated that EGO had a reinforcing effect on the elastic behaviour of PPMA-EGO. This is due to strong interfacial adhesion between PPMA and EGO as a result of hydrogen bonding. The elastic behaviour of PPMA-EGO was affected by the surface area of graphite flakes. Low sheared PPMA-EGO elastic behaviour was found to be higher compared with that of high sheared PPMA-EGO. A melt blending method was used to prepare PPMA-EGO with varying EGO concentration. The interconnected network structure of EGO in the PPMA-EGO was not observed as shown by its scanning electron microscopy images. Thermogravimetric analysis of PPMA-EGO indicates increased decomposition temperature of the PPMA matrix. Dynamic mechanical analysis showed enhanced storage modulus of PPMA-EGO. The maximum elastic modulus of PPMA-EGO was observed at 3 %wt of EGO. The electrical conductivity of PPMA-EGO was measured only for EGO concentrations above 2 %wt. The EGO concentration was found to be the most critical factor in the enhancement of the electrical conductivity of PPMA-EGO. Wide angle X-ray diffraction analysis of all polymer layered graphite oxide composites revealed no change in interlayer spacing of graphite layers, indicating the absence of EMAA intercalation in the graphite layers. The crystallisation temperature and crystallinity of all polymer layered graphite oxide composites were determined using differential scanning calorimetry. The results indicated that graphite oxide and expanded graphite oxides acted as nucleating agents in inducing the crystallisation of functionalised polyolefin in the layered composites. However, the degree of crystallinity of functionalised polyolefin decreased in the layered composites.
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Zhao, Qiang. "The thermal stability and catalytic application of MnOx-ZrO2 oxide powders /." Philadelphia, Pa. : Drexel University, 2004. http://dspace.library.drexel.edu/handle/1860/286.
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Lai, Chiu-Kin Steven. "Thermal reactions of aromatic hydrocarbons and m-cresol over calcium oxide." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15044.
Full textAbstract:
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Bibliography: leaves 284-290.
by Chiu-Kin Steven Lai.
Sc.D.
23
Spackman, Jesse. "Characterization of the Thermal Resistance of Grain Boundaries of Cerium Oxide." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6427.
Full textAbstract:
Many materials are made up of small crystals, or grains. Grain boundaries are the interfaces between two grains and affect the flow of heat through the material. These interfaces serve to interfere with the energy carriers by scattering or disrupting them. Because of the negative effect these interfaces have on these energy carriers, they inhibit heat flow and act as thermal resistors. The thermal boundary resistance between two grains of the same material is sometimes referred to as the Kapitza resistance, although this term is also used to describe the thermal resistance between solid/solid interfaces of different materials or solid/liquid interfaces. A better understanding of the heat transport process on a micro-scale is especially relevant to nuclear energy applications. Nuclear fuels are polycrystalline materials that experience large heat differences over small distances. An improved understanding of these grain boundaries and the role they play in transferring heat can help better predict nuclear fuel performance and improve nuclear reactor efficiency and safety.
The study of the thermal resistance across crystal interfaces and their potential influence on nuclear fuels is a topic that has received relatively little attention. While the thermal resistance across a single grain boundary is rather small, the total resistance generated from many grain boundaries can have a big impact on the material. Smaller grains mean there are more interfaces, which will result in a lower overall thermal conductivity.
For this study, Kapitza resistance across individual grain boundaries was measured using a laser-based measurement technique. The sample material was Cerium Oxide. It was used because of its similar properties to Uranium Oxide, which is a popular material used in nuclear fuel. The average interfacial thermal resistance measured at room temperature in this thesis study was 9.88∙10-9 �2�/�. The average measured value fit in an accepted range from other results found in similar studies.
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Fischer, Patrick. "Numerical Simulation of Microwave Sintering of Zinc Oxide." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/36596.
Full textAbstract:
Experiments at the University of Maryland Plasma Physics
Laboratory have discovered an unusual temperature
response in the form of a "thermal wave" which begins at
the center and propagates towards the surface of a zinc
oxide sample, when heated in a microwave cavity without
the presence of oxygen. This effect is believed to be
caused by the irregular temperature dependence of the
dielectric properties of zinc oxide, particularly dielectric
loss. Two thermocouple probes were used to measure the
temperature response in a small cylindrical sample of zinc
oxide packed in powder insulation, and heated in a
microwave oven. In order to determine if the unusual
response is caused by the dielectric properties, this work
uses a finite-difference mathematical model to simulate the
experiments, both for the case of zinc oxide heated in
ordinary air, as well as for the case of zinc oxide heated in
nitrogen. A revised version of the model is used to
determine if the thermocouple probe has any effect on the
temperature of the sample. The spatial and temporal
temperature distribution results from the model indicate
that the thermocouple probe has a negligible effect on the
results and that the "thermal wave" can be attributed to the
irregular temperature dependence of the dielectric loss of
the material.Master of Science
25
Manisha. "Evaluation of thermal stresses in planar solid oxide fuel cells as a function of thermo-mechanical properties of component materials." Texas A&M University, 2008. http://hdl.handle.net/1969.1/86039.
Full textAbstract:
Fuel cells are the direct energy conversion devices which convert the chemical energy of a
fuel to electrical energy with much greater efficiency than conventional devices. Solid Oxide
Fuel Cell (SOFC) is one of the various types of available fuel cells; wherein the major
components are made of inherently brittle ceramics. Planar SOFC have the advantages of
high power density and design flexibility over its counterpart tubular configuration.
However, structural integrity, mechanical reliability, and durability are of great concern for
commercial applications of these cells. The stress distribution in a cell is a function of
geometry of fuel cell, temperature distribution, external mechanical loading and a mismatch
of thermo-mechanical properties of the materials in contact. The mismatch of coefficient of
thermal expansion and elastic moduli of the materials in direct contact results in the
evolution of thermal stresses in the positive electrode/electrolyte/negative electrode (PEN)
assembly during manufacturing and operating conditions (repeated start up and shut down
steps) as well. It has long been realized and demonstrated that the durability and reliability of
SOFCs is not only determined by the degradation in electrochemical performance but also
by the ability of its component materials to withstand the thermal stresses.
In the present work, an attempt has been made to evaluate the thermal stresses as a function
of thermal and mechanical properties of the component materials assuming contribution
from other factors such as thermal gradient, mechanical loading and in-service loading
conditions is insignificant. Materials used in the present study include the state of art anode (Ni-YSZ), electrolyte(YSZ) and cathode materials(LM and LSM) of high temperature SOFC
and also the ones being suggested for intermediate temperature SOFC Ni-SCZ as an anode,
GDC and SCZ as electrolyte and LSCF as the cathode. Variation of thermo-mechanical
properties namely coefficient of thermal expansion, and elastic and shear moduli were
studied using thermo-mechanical analyzer and resonant ultrasound spectroscope respectively
in 25-900°C temperature range. A non-linear variation in elastic and shear moduli- indicative
of the structural changes in the studied temperature range was observed for most of the
above mentioned materials. Coefficient of thermal expansion (CTE) was also found to
increase non-linearly with temperature and sensitive to the phase transformations occurring
in the materials. Above a certain temperature (high temperature region- above 600°C), a
significant contribution from chemical expansion of the materials was also observed.
In order to determine thermal stress distribution in the positive electrode, electrolyte,
negative electrode (PEN) assembly, CTE and elastic and shear moduli of the component
materials were incorporated in finite element analysis at temperature of concern. For the
finite element analysis, anode supported configuration of PEN assembly (of 100mm x
100mm) was considered with 1mm thick anode, 10μm electrolyte and 30μm cathode. The
results have indicated that cathode and anode layer adjacent to cathode/electrolyte and
electrolyte/anode interface respectively are subjected to tensile stresses at the operating
temperature of HT-SOFC (900°C) and IT-SOFC (600°C). However, the magnitude of
stresses is much higher in the former case (500MPa tensile stress in cathode layer) when
compared with the stress level in IT-SOFC (178MPa tensile stress in cathode layer). These
high stresses might have been resulted from the higher CTE of cathode when compared with
the adjacent electrolyte. However, it is worth mentioning here that in the present work, we
have not considered any contribution from the residual stresses arising from fabrication and
the stress relaxation from softening of the glass sealant.
26
Roy, Nirmita. "Electrical, Optical and Thermal Investigations of Cobalt Oxide-Antimony Doped Tin Oxide (CoO-ATO) Thin Films and Nanofiber Membranes." Scholar Commons, 2017. https://scholarcommons.usf.edu/etd/7441.
Full textAbstract:
The main aim of this thesis work is to investigate the electrical, optical and thermal impact characteristics of cobalt oxide doped antimony tin oxide (CoO-ATO) in the form of thin films and nanofiber membranes. CoO-ATO is a novel composite material that has the potential to be used as reinforced aircraft coatings, military garment coatings, or more specifically as an anti-reflective (AR) top coating for photovoltaic (PV) cells. This work will be critical in determining the effectiveness of using a CoO-ATO layer in these applications. Electrospun nanofibers and spin coated thin films consisting of a polymeric solution of CoO-ATO will be used. Thin films are created using spin coating techniques, and nanofiber membranes are created using an electrospinning technique. Polystyrene (PS) will be used as a solute, and chloroform as a solvent, to create the solution. It is hypothesized that coatings of this material will have improved optical characteristics as compared to traditional ATO coatings and minimum impact from thermal cycling making it a favorable candidate for PV cells. This work will do an electrical, optical and thermal cycling impact characterization of CoO-ATO thin films and nanofiber membranes for a doping range of x% CoO where x ranged from 0.2
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Vazquez, Calnacasco Daniel. "All-Oxide Ceramic Matrix Composites : Thermal Stability during Tribological Interactions with Superalloys." Thesis, Luleå tekniska universitet, Materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-85513.
Full textAbstract:
The challenges faced in today’s industry require materials capable of working in chemically aggressive environments at elevated temperature, which has fueled the development of oxidation resistant materials. All-Oxide Ceramic Matrix Composites (OCMC) are a promising material family due to their inherent chemical stability, moderate mechanical properties, and low weight. However, limited information exists regarding their behavior when in contact with other high-temperature materials such as superalloys. In this work three sets of tribological tests were performed: two at room temperature and one at elevated temperature (650 °C). The tests were performed in a pin-on-disk configuration testing Inconel 718 (IN-718) pins against disks made with an aluminosilicate geopolymeric matrix composite reinforced with alumina fibers (N610/GP). Two different loads were tested (85 and 425 kPa) to characterize the damage on both materials. Results showed that the pins experienced ~ 100 % wear increase when high temperature was involved, while their microstructure was not noticeably affected near the contact surface. After high temperature testing the OCMC exhibited mass losses two orders of magnitude higher than the pins and a sintering effect under its wear track, that led to brittle behavior. The debris generated consists of alumina and suggests a possible crystallization of the originally amorphous matrix which may destabilize the system. The data suggests that while the composite’s matrix is stable, wear will not develop uncontrollably. However, as soon as a critical load/temperature combination is attained the matrix is the first component to fail exposing the reinforcement to damage which drastically deteriorates the integrity of the component.
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Riyad, M. Faisal. "Simultaneous analysis of Lattice Expansion and Thermal Conductivity in Defected Oxide Ceramics." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492737800363063.
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Arbuzov, A. A., V. E. Muradyan, and B. P. Tarasov. "Synthesis of Few-layer Graphene Sheets via Chemical and Thermal Reduction of Graphite Oxide." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35063.
Full textAbstract:
Few-layer graphene sheets were produced from graphite oxide (GO) chemical and thermal reduction.
For the chemical reduction of GO as reducing agents were used hydrazine hydrate, hydroxylammonium
chloride, sodium borohydride and sodium sulfite. The reduced material was characterized by elemental
analysis, thermo-gravimetric analysis, scanning electron microscopy, X-ray diffraction, Fourier transform
infrared and Raman spectroscopy. A comparison of the deoxygenation efficiency of graphene oxide suspension by different method or reductants has been made, revealing that the highest degree of reduction was
achieved by thermal reduction and using hydrazine hydrate and hydroxylammonium chloride as a reducing agents.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35063
30
Rooker, William E. "Enhancing the thermal design and optimization of SOFC technology." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/18881.
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Church, Benjamin Cortright. "Fabrication and Characterization of Solid Oxide Fuel Cell Interconnect Alloys." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4829.
Full textAbstract:
Metal alloy honeycomb structures were fabricated using a paste extrusion technique and characterized for potential application as interconnects in solid oxide fuel cells. Thermal expansion characteristics of Fe-Cr, Fe-Ni, Ni-Cr, Fe-Ni-Cr, and similar alloys containing an oxide dispersion were determined and compared with the thermal expansion behavior of yttria-stabilized zirconia (YSZ). A method was developed to calculate thermal expansion mismatch between two materials under a variety of heating and cooling conditions. It was shown that Fe 20 wt% Cr and Fe 47.5 wt% Ni alloys have low expansion mismatch with YSZ under a wide range of heating and cooling conditions. Oxidation experiments showed that Fe-Cr alloys have superior oxidation resistance in air at 700℃compared with Fe-Ni-Cr alloys with similar chromium contents. The inclusion of oxide dispersions (Y₂O₃ and CaO) into an alloy honeycomb was shown to improve oxidation resistance without affecting thermal expansion behavior. The honeycomb extrusion process provides a method by which experimental alloys can be produced and characterized rapidly to develop an alloy suitable for use as an interconnect in a solid oxide fuel cell.
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Johnson, Samuel C. "Scanning Optical Probe Thermometry Using an Optically Trapped Erbium Oxide Nanoparticle." Ohio University Honors Tutorial College / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1429811168.
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Gupta, Mohit Kumar. "Design of Thermal Barrier Coatings : A modelling approach." Doctoral thesis, Högskolan Väst, Avd för maskinteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-7181.
Full textAbstract:
Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating's final thermal and mechanical properties, and the service lives of the coatings. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.
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Schunk, Lothar Oliver. "Solar thermal dissociation of zinc oxide : reaction kinetics, reactor design, experimentation, and modeling /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18041.
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Perkins, Christopher Michael. "Solar thermal decomposition of zinc oxide in aerosol flow for renewable hydrogen production." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3239400.
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Koh, A. "Investigation of thermal oxidation on silicon carbide for power metal-oxide-semiconductor devices." Thesis, Swansea University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637818.
Full textAbstract:
The rapid progress in the semiconductors technology and the increasing demand in performance for the high power and high frequency semiconductor devices have prompt for the search of a new semi-conducting material to meet the needs in the new millennium. Silicon Carbide (SiC), a wide band gap compound semiconductor is deemed to be the most likely candidate for its unique ability to thermally oxidise, forming Silicon Dioxide (SiO2). This advantage allows the fabrication of Metal-Oxide-Semiconductor (MOS) devices on SiC, thus has been a focus in the semiconductor research arena with a drastic increase in world-wide research activities particularly during the last two years. The research work in this thesis focuses on the basics of the thermal oxidation on Silicon Carbide, investigating on the physics behind the problems hampering the ability to grow oxide of acceptable quality of MOS device application. This is achieved by providing experimental results supporting initial hypothetical "Carbon Cluster Model" phenomenon described by Bassler et, al. observed in SiC/SiO2 interface. This is of vital importance as the success of fabricating a SiC MOS device would ultimately depends on the ability to produce high quality oxide with low SiC/SiO2 interface states density and other oxide trap charges. The work also includes a comparative study on the different methods of thermal oxidation on SiC such as conventional wet and dry thermal oxidation on SiC, and Sacrificial Silicon Oxidation (SSO) and SiC, which utilises the advantage of temperature differences between thermally oxidising Silicon (Si) and SiC. This has yield promising results. Consequently the results also suggest that the SSO technique, when optimised can be further utilised as a form of surface preparation of SiC.
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Salehi, Alireza. "Radiation and thermal treatment of indium tin oxide (ITO) films and rectifying contacts." Thesis, Cardiff University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388426.
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Luo, Lan, Hao Zhang, Jie Liu, and Keyong Tang. "Effect of graphene oxide on the thermal properties of bovine hide powders - 214." Verein für Gerberei-Chemie und -Technik e. V, 2019. https://slub.qucosa.de/id/qucosa%3A34316.
Full textAbstract:
Content:
Graphene oxide (GO) is one of the most interesting nanomaterials in recent years. In order to explore its potential application in leather making process, a study on evaluating the effects of GO on the thermal
stability and decomposition kinetics of bovine hide powders (HP) was performed by thermogravimetry. It was shown that the GO-doped hide powders (GO-HP) exhibit better thermal stability than those of raw hide powders. The kinetic and mechanism analysis of the decomposition stage used an integrated procedure involving model-free methods and universal master-plots method. Various methods were employed to calculate the activation energy of the fibers, including the Flynn-Wall-Ozawa (FWO), Modified Kissinger-Akahira-Sunose (MKAS) and Friedman methods. The activation energy values of GO-HP and raw hide powder were found to be 240.5 and 184.7 kJ/mol, respectively. Comparison of the experimental and theoretical master plots of various reaction mechanisms showed that when the conversion values are below 0.5, the most probable decomposition mechanism for HP and GO-HP is D1. Above 0.5, the decomposition mechanisms of HP and GO-HP are most probably described by A3 and R3 models,
respectively.
Take-Away:
Graphene oxide (GO) doped hide powders (GO-HP) exhibit better thermal stability than those of raw hide powders.
The activation energy values of GO-HP and raw hide powder were found to be 240.5 and 184.7 kJ/mol, respectively.
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Gerlach, Gerald, and Karl Maser. "A Self-Consistent Model for Thermal Oxidation of Silicon at Low Oxide Thickness." Hindawi, 2016. https://tud.qucosa.de/id/qucosa%3A29979.
Full textAbstract:
Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model) for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship is the basis of many similar investigations. However, measurement results show that the DG-model does not apply to very thin oxides in the range of a few nm. Additionally, it is inherently not self-consistent. The aim of this paper is to develop a self-consistent model that is based on the continuity equation instead of Fick’s law as the DG-model is. As literature data show, the relationship between silicon oxide thickness and oxidation time is governed—down to oxide thicknesses of just a few nm—by a power-of-time law. Given by the time-independent surface concentration of oxidants at the oxide surface, Fickian diffusion seems to be neglectable for oxidant migration. The oxidant flux has been revealed to be carried by non-Fickian flux processes depending on sites being able to lodge dopants (oxidants), the so-called DOCC-sites, as well as on the dopant jump rate.
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Gerlach, Gerald, and Karl Maser. "A Self-Consistent Model for Thermal Oxidation of Silicon at Low Oxide Thickness." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-214263.
Full textAbstract:
Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model) for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship is the basis of many similar investigations. However, measurement results show that the DG-model does not apply to very thin oxides in the range of a few nm. Additionally, it is inherently not self-consistent. The aim of this paper is to develop a self-consistent model that is based on the continuity equation instead of Fick’s law as the DG-model is. As literature data show, the relationship between silicon oxide thickness and oxidation time is governed—down to oxide thicknesses of just a few nm—by a power-of-time law. Given by the time-independent surface concentration of oxidants at the oxide surface, Fickian diffusion seems to be neglectable for oxidant migration. The oxidant flux has been revealed to be carried by non-Fickian flux processes depending on sites being able to lodge dopants (oxidants), the so-called DOCC-sites, as well as on the dopant jump rate.
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Ludford, Nicholas Philip. "An investigation into the thermal aging of an all oxide ceramic matrix composite." Thesis, University of Surrey, 2005. http://epubs.surrey.ac.uk/843476/.
Full textAbstract:
The effect of thermal aging in air on a Nextel(TM) 720 aluminosilicate fibre reinforced alumina matrix material (N72O/AI2O3) has been investigated. Samples were aged at 1100oC for up to 4000 hours as well as for 200 hours at 1100°C, 1200°C, 1300°C, 1400°C and 1480°C. On completion of the thermal aging treatments, the microstructures of the samples were characterised, principally using scanning and transmission electron microscopy. The mechanical properties of the material, flexural strength, Young's modulus and relative toughness, after aging were investigated using three point flexural testing. The as-received material was found to contain many voids and a large quantity of cracking that are believed to arise from in-complete matrix infiltration and green body production, respectively, during manufacture. It was found that the material does not meet the original proposed design criteria for this class of material. Initial results indicate that the 1100°C thermal aging treatment for up to 2000 hours has no detectable effect on the microstructure or properties of the material. After aging at 1100°C for 4000 hours, changes were detected in the material suggesting that prolonged thermal exposure of the material does have an effect on its properties, specifically a reduction in sample thickness indicating that the matrix may have densified slightly and a small increase in modulus and loss of aluminium from the fibre. In contrast, much shorter exposures to higher temperatures lead to significant changes to the microstructure, principally in terms of the reduction in porosity and grain growth in the matrix regions and an embrittlement of the material from an aging temperature of 1300°C, such that the material behaved as a monolithic ceramic after aging at 1480°C. Aging at 1200°C and above was found to cause a progressive decrease in the material thickness indicating a densification of the material. The fibre architecture was found to restrict densification in the plane of the fibre reinforcement. The mechanical properties of the material aged for 200 hours at 1200°C appear unaffected by the thermal aging. The aging of material at 1300°C was found to increase the Young's modulus to a maximum value after aging at 1400°C. Aging at 1480°C appeared to cause a slight decrease in the Young's modulus of the material. Aging of the material at 1300°C and above was found to cause a continuing reduction in the flexural strength of the material until a minimum value was reached after aging at 1480°C. A change in the microstructure of the fibre was initially observed after aging at 1300°C and was more pronounced after aging at 1400°C and 1480"C. A progressive growth of elongated alumina grains in the fibres was observed to occur as the meta-stable aluminium-rich mullite transformed to a silicon-rich mullite within the fibre. After aging at 1480°C the fibre was also observed to contain significant quantities of porosity. Furthermore, the fibre reinforcement appears to have lost aluminium, possibly to the matrix. The results of this investigation have found that the material is stable for aging periods of 2000 hours at 1100°C and for up to 200 hours at 1200°C. Whilst aging regimes of over 2000 hours at 1100°C may be acceptable, evidence has been found to suggest that the material is changing.
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Osborne, Daniel Josiah. "A Nanoengineering Approach to Oxide Thermoelectrics For Energy Harvesting Applications." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/36133.
Full textAbstract:
The ability of uniquely functional thermoelectric materials to convert waste heat directly into electricity is critical considering the global energy economy. Profitable, energy-efficient thermoelectrics possess thermoelectric figures of merit ZT â ¥ 1. We examined the effect of metal nanoparticle â oxide film interfaces on the thermal conductivity κ and Seebeck coefficient α in bilayer and multilayer thin film oxide thermoelectrics in an effort to improve the dimensionless figure of merit ZT. Since a thermoelectricâ s figure of merit ZT is inversely proportional to κ and directly proportional to α, reducing κ and increasing α are key strategies to optimize ZT.
We aim to reduce κ by phonon scattering due to the inclusion of metal nanoparticles in the bulk of thermoelectric thin films deposited by Pulsed Laser Deposition. XRD, AFM, XPS, and TEM analyses were carried out for structural and compositional characterization. The electrical conductivities of the samples were measured by a four-point probe apparatus. The Seebeck coefficients were measured in-plane, varying the temperature from 100K to 310K. The thermal conductivities were measured at room temperature using Time Domain Thermoreflectance.Master of Science
43
Ford, James Christopher. "An Enhanced Transient Solid Oxide Fuel Cell Performance Model." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14052.
Full textAbstract:
In order to facilitate the application of solid oxide fuel cells, in conjunction with reduced research and development costs, there is a need for accurate performance models to aid scientists and engineers in component and process design. To this end, an enhanced transient performance model has been developed. The present thesis enhances transient modeling and simulation via characterization of two important transient phenomena. They are bimodal stimuli (i.e., simultaneous changes in reactant supply and load demand) electrical transients, inclusive of the simulation of electrolysis, and the electrochemical light off phenomenon. One key result of the electrochemical light off simulations was that the realization that electrochemical parameters such as cell potential may be used as dynamic control variables during transitional heating of the cell. Reflective of the state-of-the-art in controls and dynamic simulation development, the modeling efforts are completed in the MATLAB computing environment. There is then a tangible software development that accompanies the modeling and simulation exercises and transient insights resolved.
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Hamie, Houssam. "Morphology and Thermal Behavior of Single Crystals of Polystyrene-Poly(ethylene oxide) Block Copolymers." Phd thesis, Université de Haute Alsace - Mulhouse, 2010. http://tel.archives-ouvertes.fr/tel-00560051.
Full textAbstract:
In the present work, we have undertaken a structural study of PS-b-PEO single crystals to elucidate the influence of the state of the PS block on crystallization from dilute solution and on subsequent thermal annealing at elevated temperature. It is noteworthy that the interest in these systems has been recently renewed in the perspective of using them as a model of grafted amorphous brushes with variable grafting density. Indeed, during crystallization of PEO, the amorphous block, i.e. PS, is rejected from the crystal accumulating on its basal surfaces. Since the crystal thickness formed during isothermal crystallization is a sharply selected value, the grafting density of the resulting PS brush is also well defined. Therefore by varying the crystal thickness one can obtain the PS brushes with grafting density varying in a broad range.In our study, a combination of reciprocal and direct-space techniques such as SAXS/WAXS and AFM was employed. While AFM experiments were performed on isolated single crystals, the SAXS investigation was carried out on oriented mats of single crystals slowly sedimented from the "mother" solution. In this case, the one-dimensional two-phase system model was used for the data interpretation where the thickness of the amorphous (La) and crystalline (Lc) layers are conventionally determined following the correlation fonction and interface distribution fonction approaches.
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Richard, Brandon Demar. "Thermal Infrared Reflective Metal Oxide Sol-Gel Coatings for Carbon Fiber Reinforced Composite Structures." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4569.
Full textAbstract:
Recent trends in composite research include the development of structural materials with multiple functionalities. In new studies, novel materials are being designed, developed, modified, and implemented into composite designs. Typically, an increase in functionality requires additional material phases within one system. The presence of excessive phases can result in deterioration of individual or overall properties. True multi-functional materials must maintain all properties at or above the minimum operating limit. In this project, samples of antimony and cobalt-doped tin oxide (ATO(Co2O3)) sol-gel solutions are used to coat carbon fibers and are heat treated at a temperature range of 200 - 500 °C. Results from this research are used to model the implementation of sol-gel coatings into carbon fiber reinforced multifunctional composite systems. This research presents a novel thermo-responsive sol-gel/ (dopant) combination and evaluation of the actuating responses (reflectivity and surface heat dissipation) due to various heat treatment temperatures. While ATO is a well-known transparent conductive material, the implementation of ATO on carbon fibers for infrared thermal reflectivity has not been examined. These coatings serve as actuators capable of reflecting thermal infrared radiation in the near infrared wavelengths of 0.7-1.2 μm. By altering the level of Co2O3 and heat treatment temperatures, optimal optical properties are obtained. While scanning electron microscopy (SEM) is used for imaging, electron diffraction
spectroscopy (EDS) is used to verify the compounds present in the coatings. Fourier transform infrared (FT-IR) spectroscopy was performed to analyze the chemical bonds and reflectivity in the infrared spectra after the heat treatments. Total reflection and angle-dependent reflectivity measurements were performed on the coatings in the wavelengths of 0.7-2 μm. Laser induced damage threshold testing was done to investigate the dielectric breakdown and used to calculate surface temperatures.
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Tao, Zhaojun. "Experimental Study and Modelling of Mechanical Features in an Oxide Layer under Thermal Loadings." Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0003.
Full textAbstract:
La qualité des couches protectrices d’oxyde thermiques se développant à haute température à la surface des matériaux métalliques dépend des niveaux de contraintes générées et de leurs mécanismes de relaxation. Dans ce travail, un modèle et un outil d'identification ont été développés afin d'étudier l'évolution des contraintes dans les systèmes métal / oxyde sous charge thermique, ainsi que l'identification du mécanisme et des propriétés des matériaux. Le modèle est appliqué en utilisant les données expérimentales fournies par la littérature pour le système NiAl / Al2O3. La valeur de l'énergie d'activation est comparée à celle des publications, afin de valider notre méthode. L'évolution des contraintes des couches de chromine formées sur Ni30Cr et Ni28Cr ont pu être mesuré par diffraction in situ à haute température sur rayonnement Synchrotron, en découplant les effets liés à l’activation thermique de ceux liés à la taille de grain. La valeur de l’énergie d’activation associée (environ 1,4 ev) a montré, par comparaison avec les données de la littérature, que ce mode non destructeur de relaxation est gouverné par le transport des anions d’oxygène aux joints de grains de l’oxyde. Lorsque l'élément réactif Y2O3 a été ajouté au substrat métallique Ni28Cr, un changement linéaire de l'énergie d'activation a été noté lors de l'augmentation de la quantité d'élément introduit. Pour autant que nous le sachions, c'est la première fois qu'une influence linéaire est trouvéeThe quality of protective oxide scales developing at the metallic alloys surface at high temperature depends on the stress generation and relaxation mechanisms. In this work, a model and a related identification tool have been developed in order to investigate the stress evolution in the metal/oxide systems under thermal cycling loadings, along with the identification of mechanism and materials properties. The model is applied using the experimental data providing from literature for the system NiAl/Al2O3. The value of activation energy is compared with that in the publications, in order to valid our method. In situ high temperature oxidation coupled with Synchrotron X-rays diffraction was used to measure the stress evolution of chromia scales grown on Ni30Cr and Ni28Cr, with dissociating the effects related to thermal activation and grain size. Confrontation of the obtained activation energy (around 1.4ev) with literature results has shown that the creep was likely governed by grain boundary transport of oxygen species. When the reactive element Y2O3 was added to the metallic substrate Ni28Cr, a linear change of the activation energy was noted when increasing the amount of introduced element. As far as we know, this is the first time that a linear influence is found
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He, Yao-Tsung, and 何耀棕. "Study on thermal evolution of tungsten oxide." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/68377215613454716755.
Full textAbstract:
碩士中國文化大學
應用化學研究所
96
In recent years tungstic acid were studied very common and tungstic acid were used widespread. In this work, we investigated the changes in morphology and structure in the tungsten oxide of the high-temperature sintering. The experiment has use the high temperature sintering tungstic acid powder that to process tungsten oxide powder and we have use TG to discuss tungstic acid and tungsten oxide between the association. In the sintering temperature above that is choice of 300 ℃, 400 ℃, 500 ℃, 600 ℃ to compare, then we have use the FTIR, XRD and SEM to conduct research different temperature of tungsten oxide structural change.
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Wu, Cheng Tao, and 吳政道. "Thermal contraction behavior of cuprous oxide nanoparticles." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/28ee53.
Full textAbstract:
碩士國立中央大學
物理研究所
97
The sample Cu071227 was formed by natural oxidation of Cu nanoparticles for eight months, which are fabricated by the thermal evaporation method. X-ray diffraction and energy dispersive spectrometer indicate that the chemical composition of sample is Cu2O0.88. The mean particle diameter is 14.3nm determined using scanning electron microscopy image and X-ray diffraction patterns. Temperature dependence of the X-ray diffraction patterns are measured to study the thermal evolution of lattice parameters. The results reveal a negative thermal expansion in the temperature region of 190 to 230 K. We perform the Raman scattering experiment at selective temperature and used Lorentzian functions to fit the Raman spectra. The Raman shift of the phonon mode (out-of-phase in-plane vibrations of Cu) increases with increasing temperature region of 190 to 230 K. The phenomenon may be understood by the reduction of the distance between Cu ions in that temperature region. Magnetic properties were studied by Physical Property Measurement System. The M-H curve of the cuprous oxide nanoparticles can be described by a Langevin function plus a diamagnetic term. The mean particle moment rapidly increases in the temperature region of 210 to 230 K, followed by progressing decreases between 230-280 K. This indicates the change in particle moment and the thermal contraction behavior of cuprous oxide nanoparticle are indeed related.
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Lin, Sheng-da, and 林聖達. "The phenomenon of thermal contraction of cuprous oxide and cupric oxide nanoparticles." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/68878682658490946519.
Full textAbstract:
碩士國立中央大學
物理研究所
99
The copper nanoparticles were manufactured by the thermal evaporation method. We got the sample of cuprous oxide from a process that heated the copper in a condition in which not enough oxygen, and got the sample of cupric oxide from the process that heated in air. The chemical composition of the sample were pure Cu2O and CuO by X-ray diffraction and General Structure Analysis System. The mean particle diameter of Cu2O and CuO nanoparticles were 5.5 nm and 3.6 nm that determined respectively by X-ray diffraction patterns. Magnetic properties of nanoparticles were measured by Physical Property Measurement System. The M(H) of Cu2O in various temperature were observed, then fitted the M(H) curve by a Langevin function, a Brillouin function and a diamagnetic term. From a result of fitting curve at all temperature, there were three effect in the system, spin polarization, Zeeman effect, diamagnetic term. At low temperature, the M(H) of Cu2O could be represented by spin polarization and Zeeman effect, then at high temperature, M(H) could be predominated by spin polarization and diamagnetic term. Looking the M(H) curve of CuO, it showed there were two components in the system at low temperature, spin polarization and Zeeman effect. M(H) was risen with magnetic field increasing at high temperature, there was other term in the system. By fitting Ms(T) and M(T),we observed that it had spin wave in the nanoparticle system. By the XRD patterns, we observed that Cu2O had a property of the negative thermal expansion at 150~180 K, and it had a relation with charge density transition.
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"Thermal Processing and Microwave Processing of Mixed-Oxide Thin Films." Doctoral diss., 2011. http://hdl.handle.net/2286/R.I.9343.
Full textAbstract:
abstract: Amorphous oxide semiconductors are promising new materials for various optoelectronic applications. In this study, improved electrical and optical properties upon thermal and microwave processing of mixed-oxide semiconductors are reported. First, arsenic-doped silicon was used as a model system to understand susceptor-assisted microwave annealing. Mixed oxide semiconductor films of indium zinc oxide (IZO) and indium gallium zinc oxide (IGZO) were deposited by room-temperature RF sputtering on flexible polymer substrates. Thermal annealing in different environments - air, vacuum and oxygen was done. Electrical and optical characterization was carried out before and after annealing. The degree of reversal in the degradation in electrical properties of the thin films upon annealing in oxygen was assessed by subjecting samples to subsequent vacuum anneals. To further increase the conductivity of the IGZO films, Ag layers of various thicknesses were embedded between two IGZO layers. Optical performance of the multilayer structures was improved by susceptor-assisted microwave annealing and furnace-annealing in oxygen environment without compromising on their electrical conductivity. The post-processing of the films in different environments was used to develop an understanding of mechanisms of carrier generation, transport and optical absorption. This study establishes IGZO as a viable transparent conductor, which can be deposited at room-temperature and processed by thermal and microwave annealing to improve electrical and optical performance for applications in flexible electronics and optoelectronics.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2011