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High Temperature Materials Characterization and Sensor Application
Title
High Temperature Materials Characterization and Sensor Application.
Creator
Ren, Xinhua, Gong, Xun, Wahid, Parveen, Wu, Xinzhang, An, Linan, University of Central Florida
Abstract / Description
This dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate...
Show moreThis dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate characterization of both dielectric constant and loss tangent of the material. The dielectric properties of Silicon Carbonitride (SiCN) and Silicoboron Carbonitride (SiBCN) ceramics, developed at UCF Advanced Materials Processing and Analysis Center (AMPC) are characterized from 25 to 1300oC. It is observed that the dielectric constant and loss tangent of SiCN and SiBCN materials increase monotonously with temperature. This temperature dependency provides the valuable basis for development of wireless passive temperature sensors for high-temperature applications. Second, wireless temperature sensors are designed based on the aforementioned high-temperature ceramic materials. The dielectric constant of high-temperature ceramics increases monotonically with temperature and as a result changes the resonant frequency of the resonator. Therefore, the temperature can be extracted by measuring the change of the resonant frequency of the resonator. In order for the resonator to operate wirelessly, antennas need to be included in the design. Three different types of sensors, corresponding to different antenna configurations, are designed and the prototypes are fabricated and tested. All of the sensors successfully perform at temperatures over 1000oC. These wireless passive sensor designs will significantly benefit turbine engines in need of sensors operating at harsh environments.
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Date Issued
2012
Identifier
CFE0004791, ucf:49727
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004791
VACANCY ENGINEERED DOPED AND UNDOPED NANOCRYSTALLINE RARE EARTH OXIDE PARTICLES FOR HIGH TEMPERATURE OXIDATION RESISTANT COATINGS
Title
VACANCY ENGINEERED DOPED AND UNDOPED NANOCRYSTALLINE RARE EARTH OXIDE PARTICLES FOR HIGH TEMPERATURE OXIDATION RESISTANT COATINGS.
Creator
THANNEERU, RANJITH, SEAL, SUDIPTA, University of Central Florida
Abstract / Description
Rare earth oxides with trivalent lattice dopants have been of great interest to researchers in the recent years due to its potential applications in catalysis and high temperature protective coatings. The ability to store oxygen in rare earths is the basis for catalysis because of the ability to change valence states which causes the presence of intrinsic oxygen vacancies in the crystal lattice. Although, several doped-rare earth oxide systems in micron scale have been investigated, the...
Show moreRare earth oxides with trivalent lattice dopants have been of great interest to researchers in the recent years due to its potential applications in catalysis and high temperature protective coatings. The ability to store oxygen in rare earths is the basis for catalysis because of the ability to change valence states which causes the presence of intrinsic oxygen vacancies in the crystal lattice. Although, several doped-rare earth oxide systems in micron scale have been investigated, the doping effect in cerium oxide nanoparticles with well characterized particle size has not been studied. The doping of ceria at that small size can be very beneficial to further improve its catalytic properties and alter the high temperature phases in alloy systems. Cost effective room temperature chemical methods are used in the current work to synthesize uniformly distributed undoped and doped (dopants: La, Nd, Sm, Gd, Y and Yb) rare earth oxide nanoparticles. In the present study, the variation of the properties in nanocrystalline ceria (NC) synthesized by microemulsion method is studied as a function of dopant size and its concentration. To further understand, the role of dopant (cation) size on the oxygen vacancy concentration, doped nanocrystalline oxide powders were analyzed by Raman Spectroscopy, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). XRD studies showed that lattice parameter change in nanocrystalline oxide by doping trivalent rare earth elements is largely depending on size of trivalent ions. It showed that by doping larger cations (Gd3+ and Y3+) compare to Ce3+ causes lattice expansion where as smaller cations (Yb3+) leads to lattice contraction. It also showed that the lattice expansion or contraction is directly proportional to dopant concentration. The results of Raman Spectroscopy showed that the correlation length decreases resulting in increase in oxygen vacancies for larger trivalent dopants (Sm3+, Gd3+ and Y3+). However, the correlation length increases resulting in decrease in oxygen vacancies for smaller trivalent dopants (Yb3+) compare to nanocrystalline ceria. These nanostructured oxides are further applied to develop high temperature oxidation resistance coatings for austenitic steels. The present study investigates the role of oxygen vacancies in the performance of high temperature oxidation resistance as a function of various trivalent dopants and dopant concentration. NC and La3+ doped nanocrystalline ceria (LDN) particles were coated on AISI 304 stainless steels (SS) and exposed to 1243K in dry air for longer duration and subjected to cycling. The results are further compared with that of micro-ceria (MC) coatings. The coated samples showed 90% improvement in oxidation resistance compared to uncoated and MC coated steels as seen from the SEM cross-sectional studies. XRD analysis showed the presence of chromia in both NC and 20 LDN samples which is absent in uncoated steels. From SIMS depth profiles, Fe, Ni depletion zones are observed in presence of LDN coated sample indicating diffusion through the oxide layer. The role of oxygen vacancies in the nanoceria coatings on the early formation of protective chromia layer is discussed and compared to its micron counterpart. This study helps in understanding the role of oxygen vacancies to protect austenitic stainless steel at high temperature and confirms the oxygen inward diffusion rather cation outward diffusion in rare earth oxide coatings. It also gives an idea to identify the type of dopant and its concentration in nanocrystalline cerium oxide which supplies the critical oxygen partial pressure required at high temperature to form primarily impervious chromia layer.
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Date Issued
2007
Identifier
CFE0001711, ucf:47306
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001711
TERAHERTZ RADIATION FROM HIGH-TEMPERATURE SUPERCONDUCTING BSCCO MESAS OF VARIOUS GEOMETRIES
Title
TERAHERTZ RADIATION FROM HIGH-TEMPERATURE SUPERCONDUCTING BSCCO MESAS OF VARIOUS GEOMETRIES.
Creator
Cerkoney, Daniel, Klemm, Richard, University of Central Florida
Abstract / Description
The purpose of this thesis is to examine the radiation from high-temperature superconducting mesas of Bi2Sr2CaCu2O8+d (BSCCO). This is motivated by the need for coherent sources of continuous wave terahertz (THz) emission capable of radiating practically in the THz frequency band. As BSCCO has been shown to be tunable from 0.5-2.4 THz (i.e., through the entire so-called terahertz gap centered about 1 THz), and has a higher peak operating temperature near 1 THz than most alternative sources,...
Show moreThe purpose of this thesis is to examine the radiation from high-temperature superconducting mesas of Bi2Sr2CaCu2O8+d (BSCCO). This is motivated by the need for coherent sources of continuous wave terahertz (THz) emission capable of radiating practically in the THz frequency band. As BSCCO has been shown to be tunable from 0.5-2.4 THz (i.e., through the entire so-called terahertz gap centered about 1 THz), and has a higher peak operating temperature near 1 THz than most alternative sources, it is a good candidate for imaging and spectroscopy device applications. When a static DC voltage is applied to a BSCCO mesa, the stack of Josephson junctions intrinsic to this type-II layered superconductor synchronously radiate. Adjustment of the bath temperature and applied voltage allows for the high degree of tunability observed for such an emitter. To determine the angular dependence of radiation from BSCCO mesas, the dual source model from antenna theory is employed, and Love's equivalence principle is used to simplify this framework. The total emission power obtained in this manner for the pie-shaped wedge is then fit to experimental results for a thin isosceles triangular mesa using the method of least squares, resulting in a standard deviation of 0.4657. Additionally, symmetry is shown to play a significant role in the emissions for the transverse magnetic (TM) cavity modes of the equilateral triangular mesa. When the full group symmetry is imposed, the density of allowed modes is heavily diminished, and the original first excited even mode becomes the C3v symmetric ground state. These results for the equilateral triangle suggest, along with earlier experiments on the regular pentagonal mesa, that symmetry breaking effects can be used for purposes of tuning the characteristic frequency and angular dependence of the power radiated from BSCCO mesas with a high degree of symmetry.
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Date Issued
2015
Identifier
CFH0004898, ucf:45429
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH0004898
WIRELESSLY SENSING RESONATE FREQUENCY OF PASSIVE RESONATORS WITH DIFFERENT Q VALUES
Title
WIRELESSLY SENSING RESONATE FREQUENCY OF PASSIVE RESONATORS WITH DIFFERENT Q VALUES.
Creator
Lukacs, Mathew, Gong, Xun, University of Central Florida
Abstract / Description
Numerous techniques exist for measuring temperature using passive devices such as SAW filters. However, SAW filters have a significant limitation regarding high temperature environments exceeding 1000C. There are several applications for a high temperature sensor in this range, most notably heat flux or temperature in turbine engines. For these environments, an alternative to SAW filters is to use a passive resonator. The resonate frequency will vary depending on the environment temperature....
Show moreNumerous techniques exist for measuring temperature using passive devices such as SAW filters. However, SAW filters have a significant limitation regarding high temperature environments exceeding 1000C. There are several applications for a high temperature sensor in this range, most notably heat flux or temperature in turbine engines. For these environments, an alternative to SAW filters is to use a passive resonator. The resonate frequency will vary depending on the environment temperature. Understanding how the frequency changes with temperature will allow us to determine the environmental temperature. In order for this approach to work, it is necessary to induce resonance in the device and measure the resonance frequency. However, the extreme high temperature makes wired connections impractical, therefore wireless interrogation is necessary. To be practical a system of wireless interrogation of up to 20cm is desired.
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Date Issued
2011
Identifier
CFE0003709, ucf:48828
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003709
MULTICOMPONENT INTERDIFFUSION IN AUSTENITIC NI-, FE-NI-BASE ALLOYS AND L12-NI3AL INTERMETALLIC FOR HIGH-TEMPERATURE APPLICATIONS
Title
MULTICOMPONENT INTERDIFFUSION IN AUSTENITIC NI-, FE-NI-BASE ALLOYS AND L12-NI3AL INTERMETALLIC FOR HIGH-TEMPERATURE APPLICATIONS.
Creator
Garimella, Narayana, Sohn, Yong-ho, University of Central Florida
Abstract / Description
Interdiffusion in multicomponent-multiphase alloys is commonly encountered in many materials systems. The developments of multicomponent-multiphase alloys require control of microstructure through appropriate heat treatment, involving solid-state transformations, precipitation processes, and surface modification, where the interdiffusion processes play a major role. In addition, interdiffusion processes often control degradation and failure of these materials systems. Enhanced performance and...
Show moreInterdiffusion in multicomponent-multiphase alloys is commonly encountered in many materials systems. The developments of multicomponent-multiphase alloys require control of microstructure through appropriate heat treatment, involving solid-state transformations, precipitation processes, and surface modification, where the interdiffusion processes play a major role. In addition, interdiffusion processes often control degradation and failure of these materials systems. Enhanced performance and reliable durability always requires a detailed understanding of interdiffusion. In this study, ternary and quaternary interdiffusion in Ni-Cr-X (X = Al, Si, Ge, Pd) at 900C and 700C, Fe-Ni-Cr-X (X = Si, Ge) at 900C, and Ni3Al alloyed with Ir, Ta and Re at 1200C were examined using solid-to-solid diffusion couples. Interdiffusion fluxes of individual components were calculated directly from experimental concentration profiles determined by electron probe microanalysis. Moments of interdiffusion fluxes were examined to calculate main and cross interdiffusion coefficients averaged over selected composition ranges from single diffusion couple experiments. Consistency in the magnitude and sign of ternary and quaternary interdiffusion coefficient were verified with interdiffusion coefficients determined by Boltzmann-Matano analysis that requires multiple diffusion couples with intersecting compositions. Effects of alloying additions, Al, Si, Ge and Pd, on the interdiffusion in Ni-Cr-X and Fe-Ni-Cr-X alloys were examined with respect to Cr2O3-forming ability at high temperature. Effects of Ir, Ta and Re additions on interdiffusion in Ni3Al were examined with respect to phase stability and site-preference. In addition, a numerically refined approach to determine average ternary interdiffusion coefficients were developed. Concentrations and moments of interdiffusion fluxes are employed to generate multiple combinations of multicomponent interdiffusion coefficient as a function of moments. The matrix of multicomponent interdiffusion coefficients corresponds to the lowest order of the moment. It yields real and positive eigen values which provides reliable average interdiffusion coefficients for the selected composition range.
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Date Issued
2009
Identifier
CFE0002521, ucf:47639
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002521
MECHANICAL AND THERMAL CHARACTERIZATION OF CONTINUOUS FIBER-REINFORCED PYROLYSIS-DERIVED CARBON-MATRIX COMPOSITES
Title
MECHANICAL AND THERMAL CHARACTERIZATION OF CONTINUOUS FIBER-REINFORCED PYROLYSIS-DERIVED CARBON-MATRIX COMPOSITES.
Creator
Lui, Donovan, Gou, Jihua, Raghavan, Seetha, Lin, Kuo-Chi, University of Central Florida
Abstract / Description
Maturity of high-temperature polymer-reinforced composites defer to conventionally expensive and intensive methods in both material and manufacturing aspects. Even traditional carbon-carbon, aerogel, and ceramic approaches are highly limited by difficult manufacturing techniques and are subject to sensitive handling throughout their processing and lifetime. Despite their utility in extreme environments, the high costs of existing high-temperature composites find limited practical...
Show moreMaturity of high-temperature polymer-reinforced composites defer to conventionally expensive and intensive methods in both material and manufacturing aspects. Even traditional carbon-carbon, aerogel, and ceramic approaches are highly limited by difficult manufacturing techniques and are subject to sensitive handling throughout their processing and lifetime. Despite their utility in extreme environments, the high costs of existing high-temperature composites find limited practical applicability under high-performance applications. The development of continuous fiber-reinforced pyrolysis-derived carbon-matrix composites aim to circumvent the issues surrounding the manufacturing and handling of conventional high-temperature composites.Polymer matrix composites (PMCs) have a number of attractive properties including light weight, high stiffness-to-weight and strength-to-weight ratios, ease of installation on the field, potential lower system-level cost, high overall durability and less susceptibility to environmental deterioration than conventional materials. However, since PMCs contain the polymer matrix, their applications are limited to lower temperatures. In this study, a pyrolysis approach was used to convert the matrix material of phenolic resin into carbon-matrix to improve the mechanical and thermal properties of the composites. Composite material consisting of basalt fiber and phenolic resin was pyrolyzed to produce basalt-carbon composites through a novel method in which the pyrolysis promoted in-situ carbon nanotube growth to form (")fuzzy fibers("). The carbon phenolic composites were pyrolyzed to produce carbon-carbon composites. Several types of composites are examined and compared, including conventional phenolic and carbon-matrix composites. Through Raman spectroscopy and scanning electron microscopy, the composition of materials are verified before testing. Investigation into the improvements from in-situ carbon growth was conducted with an open-flame oxyacetylene test (ASTM-E285), to establish high-temperature thermal behavior, in addition to mechanical testing by three-point bending (ASTM-D790), to evaluate the mechanical and thermal properties of the pyrolyzed composites.
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Date Issued
2014
Identifier
CFE0005654, ucf:50196
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005654
INVESTIGATION OF REACTIVELY SPUTTERED SILICON CARBON BORON NITRIDE (SICBN) THIN FILMS FOR HIGH TEMPERATURE APPLICATIONS
Title
INVESTIGATION OF REACTIVELY SPUTTERED SILICON CARBON BORON NITRIDE (SICBN) THIN FILMS FOR HIGH TEMPERATURE APPLICATIONS.
Creator
Vijayakumar, Arun, Sundaram, Kalpathy, University of Central Florida
Abstract / Description
The increasing demand for efficient energy systems in the last decade has brought about the development of advanced sensor systems that utilize advance detection methods to help in preventive maintenance of these essential systems. These usually are needed in hard to access environments where conditions are extreme and unfit for human interaction. Thin film based sensors deposited directly on the surfaces exposed to harsh environments can serve as ideal means of measuring the temperature of...
Show moreThe increasing demand for efficient energy systems in the last decade has brought about the development of advanced sensor systems that utilize advance detection methods to help in preventive maintenance of these essential systems. These usually are needed in hard to access environments where conditions are extreme and unfit for human interaction. Thin film based sensors deposited directly on the surfaces exposed to harsh environments can serve as ideal means of measuring the temperature of the component during operation. They provide the basic advantage of proximity to the surface and hence accurate measurement of the surface temperature. The low mass size ratio provides the additional advantage of least interference to system operation. The four elements consisting of Si, C, B, and N can be used to form binary, ternary and quaternary compounds like carbides, nitrides, which are chemically and thermally stable with extreme hardness, thermal conductivity and can be doped n- and p-type. Hence these compounds can be potential candidates for high temperature applications. This research is focused on studying sputtering as a candidate to obtain thin SiCBN films. The deposition and characterization of amorphous thin films of silicon boron carbon nitride (SiCBN) is reported. The SiCBN thin films were deposited in a radio frequency (rf) magnetron sputtering system using reactive co-sputtering of silicon carbide (SiC) and boron nitride (BN) targets. Films of different compositions were deposited by varying the ratios of argon and nitrogen gas in the sputtering ambient. Investigation of the oxidation kinetics of these materials was performed to study high temperature compatibility of the material. Surface characterization of the deposited films was performed using X-ray photoelectron spectroscopy and optical profilometry. Studies reveal that the chemical state of the films is highly sensitive to nitrogen flow ratios during sputtering. Surface analysis shows that smooth and uniform SiCBN films can be produced using this technique. Carbon and nitrogen content in the films seem to be sensitive to annealing temperatures. However depth profile studies reveal certain stoichiometric compositions to be stable after high temperature anneal up to 900ºC. Electrical and optical characteristics are also investigated with interesting results. Finally a metal semiconductor metal structure based optoelectronic device is demonstrated with excellent performance improvement over standard silicon based devices under higher temperature conditions.
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Date Issued
2007
Identifier
CFE0001914, ucf:47490
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001914
HIGH TEMPERATURE PACKAGING FOR WIDE BANDGAP SEMICONDUCTOR DEVICES
Title
HIGH TEMPERATURE PACKAGING FOR WIDE BANDGAP SEMICONDUCTOR DEVICES.
Creator
Grummel, Brian, Shen, Z. John, University of Central Florida
Abstract / Description
Currently, wide bandgap semiconductor devices feature increased efficiency, higher current handling capabilities, and higher reverse blocking voltages than silicon devices while recent fabrication advances have them drawing near to the marketplace. However these new semiconductors are in need of new packaging that will allow for their application in several important uses including hybrid electrical vehicles, new and existing energy sources, and increased efficiency in multiple new and...
Show moreCurrently, wide bandgap semiconductor devices feature increased efficiency, higher current handling capabilities, and higher reverse blocking voltages than silicon devices while recent fabrication advances have them drawing near to the marketplace. However these new semiconductors are in need of new packaging that will allow for their application in several important uses including hybrid electrical vehicles, new and existing energy sources, and increased efficiency in multiple new and existing technologies. Also, current power module designs for silicon devices are rife with problems that must be enhanced to improve reliability. This thesis introduces new packaging that is thermally resilient and has reduced mechanical stress from temperature rise that also provides increased circuit lifetime and greater reliability for continued use to 300°C which is within operation ratings of these new semiconductors. The new module is also without problematic wirebonds that lead to a majority of traditional module failures which also introduce parasitic inductance and increase thermal resistance. Resultantly, the module also features a severely reduced form factor in mass and volume.
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Date Issued
2008
Identifier
CFE0002482, ucf:47690
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002482
Development of Polymer Derived SiAlCN Ceramic and Its Applications for High-Temperature Sensors
Title
Development of Polymer Derived SiAlCN Ceramic and Its Applications for High-Temperature Sensors.
Creator
Shao, Gang, An, Linan, Fang, Jiyu, Xu, Chengying, Chow, Lee, Deng, Weiwei, University of Central Florida
Abstract / Description
Polymer-derived ceramic (PDC) is the name for a class of materials synthesized by thermal decomposition of polymeric precursors which excellent thermomechanical properties, such as high thermal stability, high oxidation/corrosion resistance and high temperature multifunctionalities. Direct polymer-to-ceramic processing routes of PDCs allow easier fabrication into various components/devices with complex shapes/structures. Due to these unique properties, PDCs are considered as promising...
Show morePolymer-derived ceramic (PDC) is the name for a class of materials synthesized by thermal decomposition of polymeric precursors which excellent thermomechanical properties, such as high thermal stability, high oxidation/corrosion resistance and high temperature multifunctionalities. Direct polymer-to-ceramic processing routes of PDCs allow easier fabrication into various components/devices with complex shapes/structures. Due to these unique properties, PDCs are considered as promising candidates for making high-temperature sensors for harsh environment applications, including high temperatures, high stress, corrosive species and/or radiation. The SiAlCN ceramics were synthesized using the liquid precursor of polysilazane (HTT1800) and aluminum-sec-tri-butoxide (ASB) as starting materials and dicumyl peroxide (DP) as thermal initiator. The as-received SiAlCN ceramics have very good thermal-mechanical properties and no detectable weight loss and large scale crystallization. Solid-state NMR indicates that SiAlCN ceramics have the SiN4, SiO4, SiCN3, and AlN5/AlN6 units. Raman spectra reveals that SiAlCN ceramics contain (")free carbon(") phase with two specific Raman peaks of (")D(") band and (")G(") band at 1350 cm-1 and 1600 cm-1, respectively. The (")free carbon(") becomes more and more ordered with increasing the pyrolysis temperature. EPR results show that the defects in SiAlCN ceramics are carbon-related with a g-factor of 2.0016(&)#177;0.0006. Meanwhile, the defect concentration decreases with increasing sintered temperature, which is consistent with the results obtained from Raman spectra.Electric and dielectric properties of SiAlCN ceramics were characterized. The D.C. conductivity of SiAlCN ceramics increases with increasing sintered temperature and the activation energy is about 5.1 eV which higher than that of SiCN ceramics due to the presence of oxygen. The temperature dependent conductivity indicates that the conducting mechanism is a semiconducting band-gap model and follows the Arrhenius equation with two different sections of activation energy of 0.57 eVand 0.23 eV, respectively. The temperature dependent conductivity makes SiAlCN ceramics suit able for high temperature sensor applications. The dielectric properties were carried out by the Agilent 4298A LRC meter. The results reveal an increase in both dielectric constant and loss with increasing temperature (both pyrolysis and tested). Dielectric loss is dominated by the increasing of conductivity of SiAlCN ceramics at high sintered temperatures.SiAlCN ceramic sensors were fabricated by using the micro-machining method. High temperature wire bonding issues were solved by the integrity embedded method (IEM). It's found that the micro-machining method is a promising and cost-effective way to fabricate PDC high temperature sensors. Moreover IEM is a good method to solve the high temperature wire bonding problems with clear bonding interface between the SiAlCN sensor head and Pt wires. The Wheatstone bridge circuit is well designed by considering the resistance relationship between the matching resistor and the SiAlCN sensor resistor. It was found that the maximum sensitivity can be achieved when the resistance of matching resistor is equal to that of the SiAlCN sensor. The as-received SiAlCN ceramic sensor was tested up to 600 degree C with the relative output voltage changing from -3.932 V to 1.153 V. The results indicate that the relationship between output voltage and test temperature is nonlinear. The tested sensor output voltage agrees well with the simulated results. The durability test was carried out at 510 degree C for more than two hours. It was found that the output voltage remained constant for the first 30 min and then decreased gradually afterward by 0.02, 0.04 and 0.07 V for 1, 1.5 and 2 hours.
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Date Issued
2013
Identifier
CFE0004937, ucf:49602
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004937
High Temperature Mechanics of Aerospace Ceramic Composites Characterized via Synchrotron Radiation
Title
High Temperature Mechanics of Aerospace Ceramic Composites Characterized via Synchrotron Radiation.
Creator
Manero, Albert, Raghavan, Seetha, Kauffman, Jeffrey L., Gou, Jihua, University of Central Florida
Abstract / Description
This research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine...
Show moreThis research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine inlet temperatures exceeding 1100(&)deg;C; and ii) ceramic matrix composites that have shown capability and promise for hypersonic applications beyond 1300(&)deg;C. Understanding the mechanical and material properties of these materials as they evolve with temperature and load requires in-situ measurements under realistic representative environments, and from these measurements life expectancy and failure mechanisms can be more completely elucidated.In this work, TBCs representative of typical jet engine turbine blade coatings, comprised of a Yttria-stabilized zirconia top coat and NiCoCrAlY bond coat deposited on an IN 100 superalloy substrate were studied. Particular interest was given to the thermally grown oxide (TGO) that develops between the top layer and the bond coat that has a major influence on TBC durability. The oxide scale's development is linked to the typical failure mechanisms observed in application for aircraft engines, and the influence of internal cooling has been shown to vary the behavior and evolution over its lifetime. Tubular specimens coated via electron beam physical vapor deposition (EB-PVD) were investigated with hard synchrotron X-rays at Argonne National Laboratory's Advanced Photon Source, while subjected to realistic mechanical and thermal loading representative of the engine environment. A multi-variable investigation was conducted to determine the influence and magnitude of internal flow cooling, external applied force loading, and thermal exposure in cyclical application. The superposition of all these variables together creates variation spatially across in service turbine blades. Lattice strains for the axial and radial directions were resolved for the YSZ top coat layer and the internal thermally grown oxide scale. The findings revealed that during sufficiently high axial loading the strain condition for both the thermally grown oxide and top coat layers may be reversed in direction, and demonstrated how the internal flow and applied mechanical loading produce opposing effects while showing the magnitude of each variable. This reversal of the strain direction is known to contribute to the failure mechanics in the system. This discovery shows that with increased internal cooling to critical zones that experience higher mechanical loads, it is possible to tune the response of the system and prevent the reversal from compressive to tensile strains (in the axial direction). The impact of the results has the potential to be used in design for enhanced durability of the multi-layer coatings.Ceramic matrix composites are identified to comprise the next generation of turbine blades and high temperature parts. All oxide ceramic matrix composites were investigated for the influence of micro-structure variations and processing on the mechanics of the system. Isolation techniques of the all alumina composite by means of synchrotron diffraction and tomography presented a novel non-destructive method for evaluating the constituent's properties and evolution. The study successfully revealed how variations in grain size and elastic modulus result in a complex strain states. Further tomographical analysis identified system mechanics influenced by porosity and processing effects. CMCs with an yttria based environmental barrier coating were investigated for comparison to uncoated parts to further capture the in service condition, and revealed considerations for how to improve the durability of the inter-laminar strength of environmental barrier coatings interface. Together the research conducted has contributed to the high temperature aerospace materials' community, and the experimental work taken strides to provide validation and support future numerical simulation for developing better lifetime modeling. Resulting high temperature mechanics' information has the potential to enhance the design of aerospace components for substantial increases in durability. The outcomes from this work can be leveraged to continue advancing material characterization for aerospace material systems under complex and extreme environments.
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Date Issued
2016
Identifier
CFE0006836, ucf:51794
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006836
NOVEL CONCEPTUAL DESIGN AND ANLYSIS OF POLYMER DERIVED CERAMIC MEMS SENSORS FOR GAS TURBINE ENVIRONMENT
Title
NOVEL CONCEPTUAL DESIGN AND ANLYSIS OF POLYMER DERIVED CERAMIC MEMS SENSORS FOR GAS TURBINE ENVIRONMENT.
Creator
Nagaiah, Narasimha, Kapat, Jay, University of Central Florida
Abstract / Description
Technical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are...
Show moreTechnical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are currently underdeveloped for measuring these parameters in turbine engines. One of them is an optical-based non-contact technology. However, these nondirective measuring technologies lack the necessary accuracy, at least at present state. An alternative way to measure these parameters without disturbing the working environments is using MEMS type sensors. Currently, the techniques under development for such harsh environment applications are silicon carbide (SiC) and silicon nitrite (Si3N4) –based ceramic MEMS sensors. But those technologies present some limitation such as narrow processing method, high cost (materials and processing cost), and limited using temperatures (typically < 800 C). In this research we propose to develop two sensors based on recently developed polymer-derived ceramics (PDCs): Constant Temperature Hot wire Anemometer, temperature/heat-flux sensor for turbine applications. PDC is a new class of high temperature ceramics. As we shall describe below, many unique features of PDCs make them particularly suitable for the proposed sensors, including: excellent thermo-mechanical properties at high temperatures, enable high temperature operation of the devices; various well-developed processing technologies, such as injection molding,photolithography, embossing, DRIE etching and precise machining, can be used for the fabrication of the devices; and tunable electric conductivity, enable the proposed sensors fabricated from similar materials, thus reliability considerations associated with thermal mismatch, which is a big concern when using MEMS-based sensors at elevated temperatures, will be minimized.
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Date Issued
2006
Identifier
CFE0001285, ucf:46892
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001285
ENVIRONMENTAL DEGRADATION OF OXIDATION RESISTANT AND THERMAL BARRIER COATINGS FOR FUEL-FLEXIBLE GAS TURBINE APPLICATIONS
Title
ENVIRONMENTAL DEGRADATION OF OXIDATION RESISTANT AND THERMAL BARRIER COATINGS FOR FUEL-FLEXIBLE GAS TURBINE APPLICATIONS.
Creator
Mohan, Prabhakar, Sohn, Yongho, University of Central Florida
Abstract / Description
The development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature...
Show moreThe development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature protective coatings, one critical challenge that received greater attention in recent years is their resistance to high-temperature degradation due to corrosive deposits arising from fuel impurities and CMAS (calcium-magnesium-alumino-silicate) sand deposits from air ingestion. The presence of vanadium, sulfur, phosphorus, sodium and calcium impurities in alternative fuels warrants a clear understanding of high-temperature materials degradation for the development of fuel-flexible gas turbine engines. Degradation due to CMAS is a critical problem for gas turbine components operating in a dust-laden environment. In this study, high-temperature degradation due to aggressive deposits such as V2O5, P2O5, Na2SO4, NaVO3, CaSO4 and a laboratory-synthesized CMAS sand for free-standing air plasma sprayed (APS) yttria stabilized zirconia (YSZ), the topcoat of the TBC system, and APS CoNiCrAlY, the bond coat of the TBC system or a stand-alone ORC, is examined. Phase transformations and microstructural development were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. This study demonstrated that the V2O5 melt degrades the APS YSZ through the formation of ZrV2O7 and YVO4 at temperatures below 747°C and above 747°C, respectively. Formation of YVO4 leads to the depletion of the Y2O3 stabilizer and the deleterious transformation of the YSZ to the monoclinic ZrO2 phase. The investigation on the YSZ degradation by Na2SO4 and a Na2SO4 + V2O5 mixture (50-50 mol. %) demonstrated that Na2SO4 itself did not degrade the YSZ, however, in the presence of V2O5, Na2SO4 formed vanadates such as NaVO3 that degraded the YSZ through YVO4 formation at temperature as low as 700°C. The APS YSZ was found to react with the P2O5 melt by forming ZrP2O7 at all temperatures. This interaction led to the depletion of ZrO2 in the YSZ (i.e., enrichment of Y2O3 in tÂÂ'-YSZ) and promoted the formation of the fluorite-cubic ZrO2 phase. Above 1250°C, CMAS deposits were observed to readily infiltrate and significantly dissolve the YSZ coating via thermochemical interactions. Upon cooling, zirconia reprecipitated with a spherical morphology and a composition that depended on the local melt chemistry. The molten CMAS attack destabilized the YSZ through the detrimental phase transformation (tÂÂ' -> t -> f + m). Free standing APS CoNiCrAlY was also prone to degradation by corrosive molten deposits. The V2O5 melt degraded the APS CoNiCrAlY through various reactions involving acidic dissolution of the protective oxide scale, which yielded substitutional-solid solution vanadates such as (Co,Ni)3(VO4)2 and (Cr,Al)VO4. The molten P2O5, on the other hand, was found to consume the bond coat constituents significantly via reactions that formed both Ni/Co rich phosphates and Cr/Al rich phosphates. Sulfate deposits such as Na2SO4, when tested in encapsulation, damaged the CoNiCrAlY by Type I acidic fluxing hot corrosion mechanisms at 1000°C that resulted in accelerated oxidation and sulfidation. The formation of a protective continuous Al2O3 oxide scale by preoxidation treatment significantly delayed the hot corrosion of CoNiCrAlY by sulfates. However, CoNiCrAlY in both as-sprayed and preoxidized condition suffered a significant damage by CaSO4 deposits via a basic fluxing mechanism that yielded CaCrO4 and CaAl2O4. The CMAS melt also dissolved the protective Al2O3 oxide scale developed on CoNiCrAlY by forming anorthite platelets and spinel oxides. Based on the detailed investigation on degradation of the APS YSZ and CoNiCrAlY by various corrosive deposits, an experimental attempt was carried out to mitigate the melt-induced deposit attack. Experimental results from this study demonstrate, for the first time, that an oxide overlay produced by electrophoretic deposition (EPD) can effectively perform as an environmental barrier overlay for APS TBCs. The EPD protective overlay has a uniform and easily-controllable thickness, uniformly distributed closed pores and tailored chemistry. The EPD Al2O3 and MgO overlays were successful in protecting the APS YSZ TBCs against CMAS attack and hot corrosion attack (e.g., sulfate and vanadate), respectively. Furnace thermal cyclic oxidation testing of overlay-modified TBCs on bond-coated superalloy also demonstrated the good adhesive durability of the EPD Al2O3 overlay.
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Date Issued
2010
Identifier
CFE0003099, ucf:48315
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003099
REFRACTIVE INDICES OF LIQUID CRYSTALS AND THEIR APPLICATIONS IN DISPLAY AND PHOTONIC DEVICES
Title
REFRACTIVE INDICES OF LIQUID CRYSTALS AND THEIR APPLICATIONS IN DISPLAY AND PHOTONIC DEVICES.
Creator
Li, Jun, Wu, Shin-Tson, University of Central Florida
Abstract / Description
Liquid crystals (LCs) are important materials for flat panel display and photonic devices. Most LC devices use electrical field-, magnetic field-, or temperature-induced refractive index change to modulate the incident light. Molecular constituents, wavelength, and temperature are the three primary factors determining the liquid crystal refractive indices: ne and no for the extraordinary and ordinary rays, respectively. In this dissertation, we derive several physical models for describing...
Show moreLiquid crystals (LCs) are important materials for flat panel display and photonic devices. Most LC devices use electrical field-, magnetic field-, or temperature-induced refractive index change to modulate the incident light. Molecular constituents, wavelength, and temperature are the three primary factors determining the liquid crystal refractive indices: ne and no for the extraordinary and ordinary rays, respectively. In this dissertation, we derive several physical models for describing the wavelength and temperature effects on liquid crystal refractive indices, average refractive index, and birefringence. Based on these models, we develop some high temperature gradient refractive index LC mixtures for photonic applications, such as thermal tunable liquid crystal photonic crystal fibers and thermal solitons. Liquid crystal refractive indices decrease as the wavelength increase. Both ne and no saturate in the infrared region. Wavelength effect on LC refractive indices is important for the design of direct-view displays. In Chapter 2, we derive the extended Cauchy models for describing the wavelength effect on liquid crystal refractive indices in the visible and infrared spectral regions based on the three-band model. The three-coefficient Cauchy model could be used for describing the refractive indices of liquid crystals with low, medium, and high birefringence, whereas the two-coefficient Cauchy model is more suitable for low birefringence liquid crystals. The critical value of the birefringence is deltan~0.12. Temperature is another important factor affecting the LC refractive indices. The thermal effect originated from the lamp of projection display would affect the performance of the employed liquid crystal. In Chapter 3, we derive the four-parameter and three-parameter parabolic models for describing the temperature effect on the LC refractive indices based on Vuks model and Haller equation. We validate the empirical Haller equation quantitatively. We also validate that the average refractive index of liquid crystal decreases linearly as the temperature increases. Liquid crystals exhibit a large thermal nonlinearity which is attractive for new photonic applications using photonic crystal fibers. We derive the physical models for describing the temperature gradient of the LC refractive indices, ne and no, based on the four-parameter model. We find that LC exhibits a crossover temperature To at which dno/dT is equal to zero. The physical models of the temperature gradient indicate that ne, the extraordinary refractive index, always decreases as the temperature increases since dne/dT is always negative, whereas no, the ordinary refractive index, decreases as the temperature increases when the temperature is lower than the crossover temperature (dno/dT<0 when the temperature is lower than To) and increases as the temperature increases when the temperature is higher than the crossover temperature (dno/dT>0 when the temperature is higher than To ). Measurements of LC refractive indices play an important role for validating the physical models and the device design. Liquid crystal is anisotropic and the incident linearly polarized light encounters two different refractive indices when the polarization is parallel or perpendicular to the optic axis. The measurement is more complicated than that for an isotropic medium. In Chapter 4, we use a multi-wavelength Abbe refractometer to measure the LC refractive indices in the visible light region. We measured the LC refractive indices at six wavelengths, lamda=450, 486, 546, 589, 633 and 656 nm by changing the filters. We use a circulating constant temperature bath to control the temperature of the sample. The temperature range is from 10 to 55 oC. The refractive index data measured include five low-birefringence liquid crystals, MLC-9200-000, MLC-9200-100, MLC-6608 (delta_epsilon=-4.2), MLC-6241-000, and UCF-280 (delta_epsilon=-4); four middle-birefringence liquid crystals, 5CB, 5PCH, E7, E48 and BL003; four high-birefringence liquid crystals, BL006, BL038, E44 and UCF-35, and two liquid crystals with high dno/dT at room temperature, UCF-1 and UCF-2. The refractive indices of E7 at two infrared wavelengths lamda=1.55 and 10.6 um are measured by the wedged-cell refractometer method. The UV absorption spectra of several liquid crystals, MLC-9200-000, MLC-9200-100, MLC-6608 and TL-216 are measured, too. In section 6.5, we also measure the refractive index of cured optical films of NOA65 and NOA81 using the multi-wavelength Abbe refractometer. In Chapter 5, we use the experimental data measured in Chapter 4 to validate the physical models we derived, the extended three-coefficient and two-coefficient Cauchy models, the four-parameter and three-parameter parabolic models. For the first time, we validate the Vuks model using the experimental data of liquid crystals directly. We also validate the empirical Haller equation for the LC birefringence delta_n and the linear equation for the LC average refractive index . The study of the LC refractive indices explores several new photonic applications for liquid crystals such as high temperature gradient liquid crystals, high thermal tunable liquid crystal photonic crystal fibers, the laser induced 2D+1 thermal solitons in nematic crystals, determination for the infrared refractive indices of liquid crystals, comparative study for refractive index between liquid crystals and photopolymers for polymer dispersed liquid crystal (PDLC) applications, and so on. In Chapter 6, we introduce these applications one by one. First, we formulate two novel liquid crystals, UCF-1 and UCF-2, with high dno/dT at room temperature. The dno/dT of UCF-1 is about 4X higher than that of 5CB at room temperature. Second, we infiltrate UCF-1 into the micro holes around the silica core of a section of three-rod core PCF and set up a highly thermal tunable liquid crystal photonic crystal fiber. The guided mode has an effective area of 440 ƒÝm2 with an insertion loss of less than 0.5dB. The loss is mainly attributed to coupling losses between the index-guided section and the bandgap-guided section. The thermal tuning sensitivity of the spectral position of the bandgap was measured to be 27 nm/degree around room temperature, which is 4.6 times higher than that using the commercial E7 LC mixture operated at a temperature above 50 degree C. Third, the novel liquid crystals UCF-1 and UCF-2 are preferred to trigger the laser-induced thermal solitons in nematic liquid crystal confined in a capillary because of the high positive temperature gradient at room temperature. Fourth, we extrapolate the refractive index data measured at the visible light region to the near and far infrared region basing on the extended Cauchy model and four-parameter model. The extrapolation method is validated by the experimental data measured at the visible light and infrared light regions. Knowing the LC refractive indices at the infrared region is important for some photonic devices operated in this light region. Finally, we make a completely comparative study for refractive index between two photocurable polymers (NOA65 and NOA81) and two series of Merck liquid crystals, E-series (E44, E48, and E7) and BL-series (BL038, BL003 and BL006) in order to optimize the performance of polymer dispersed liquid crystals (PDLC). Among the LC materials we studied, BL038 and E48 are good candidates for making PDLC system incorporating NOA65. The BL038 PDLC cell shows a higher contrast ratio than the E48 cell because BL038 has a better matched ordinary refractive index, higher birefringence, and similar miscibility as compared to E48. Liquid crystals having a good miscibility with polymer, matched ordinary refractive index, and higher birefringence help to improve the PDLC contrast ratio for display applications. In Chapter 7, we give a general summary for the dissertation.
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Date Issued
2005
Identifier
CFE0000808, ucf:46677
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000808
Design and Characterization of High Temperature Packaging for Wide-Bandgap Semiconductor Devices
Title
Design and Characterization of High Temperature Packaging for Wide-Bandgap Semiconductor Devices.
Creator
Grummel, Brian, Shen, Zheng, Sundaram, Kalpathy, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description
Advances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor...
Show moreAdvances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor device packaging with high reliability at high temperatures is necessary. Transient liquid phase (TLP) die-attach has shown in literature to be a promising bonding technique for this packaging need. In this work TLP has been comprehensively investigated and characterized to assess its viability for high-temperature power electronics applications. The reliability and durability of TLP die-attach was extensively investigated utilizing electrical resistivity measurement as an indicator of material diffusion in gold-indium TLP samples. Criteria of ensuring diffusive stability were also developed. Samples were fabricated by material deposition on glass substrates with variant Au(-)In compositions but identical barrier layers. They were stressed with thermal cycling to simulate their operating conditions then characterized and compared. Excess indium content in the die-attach was shown to have poor reliability due to material diffusion through barrier layers while samples containing suitable indium content proved reliable throughout the thermal cycling process. This was confirmed by electrical resistivity measurement, EDS, FIB, and SEM characterization. Thermal and mechanical characterization of TLP die-attached samples was also performed to gain a newfound understanding of the relationship between TLP design parameters and die-attach properties. Samples with a SiC diode chip TLP bonded to a copper metalized silicon nitride substrate were made using several different values of fabrication parameters such as gold and indium thickness, Au(-)In ratio, and bonding pressure. The TLP bonds were then characterized for die-attach voiding, shear strength, and thermal impedance. It was found that TLP die-attach offers high average shear force strength of 22.0 kgf and a low average thermal impedance of 0.35 K/W from the device junction to the substrate. The influence of various fabrication parameters on the bond characteristics were also compared, providing information necessary for implementing TLP die-attach into power electronic modules for high-temperature applications. The outcome of the investigation on TLP bonding techniques was incorporated into a new power module design utilizing TLP bonding. A full half-bridge inverter power module for low-power space applications has been designed and analyzed with extensive finite element thermo-mechanical modeling. In summary, TLP die-attach has investigated to confirm its reliability and to understand how to design effective TLP bonds, this information has been used to design a new high-temperature power electronic module.
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Date Issued
2012
Identifier
CFE0004499, ucf:49276
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004499