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Dike, Shweta SrikantDynamic Deformation of Materials at Elevated Temperatures
Master of Sciences (Engineering), Case Western Reserve University, 2010, EMC - Mechanical Engineering
High Strength Low Alloy steel, grade 65 (HSLA-65) plates used by the US Navy for ship building are to be joined by Friction Stir Welding (FSW) which subjects the work-piece material to high strain rates at high temperatures. The strength of materials varies with the strain-rate and temperature to which they are subjected. Development of constitutive models to get the optimum FSW weld parameters requires experimental determination of the dynamic behaviour of a material at different strain-rates and temperatures. In the current study, experiments using the Split Hopkinson Pressure Bar (SHPB) were conducted on HSLA-65 at high temperatures to generate the true stress-strain curves in compression. In addition, two other materials, which are used in practical applications where high strain rate loading occurs at high temperatures, namely Inconel-718 superalloy (precipitation hardened and annealed) and Aluminum alloy 7075-T6 were also tested using the SHPB.

Committee:

Vikas Prakash (Advisor); John Lewandowski (Advisor); Joseph Mansour (Committee Member)

Subjects:

Engineering; Experiments; Mechanical Engineering; Mechanics; Metallurgy

Keywords:

Dynamic compressive response of HSLA-65 steel at high temperature; Dynamic compressive response of Inconel-718 at high temperature; High temperature SHPB experiments

Yu, XinyuHigh-temperature Bulk CMOS Integrated Circuits for Data Acquisition
Doctor of Philosophy, Case Western Reserve University, 2006, Electrical Engineering

In this research, a monolithic, high-temperature bulk CMOS data acquisition system for Wheatstone-bridge sensors has been developed. The main design challenges were 1) excess leakage current, 2) decreased carrier mobility, and 3) unstable threshold voltage. Design techniques were developed to overcome these high-temperature effects and allow the bulk CMOS IC to operate at temperatures > 250 degree C. Two generations of data acquisition ICs have been designed and characterized: an instrumentation amplifier and a sigma-delta modulator. Both were fabricated using the AMI 1.5-µm bulk CMOS process.

The Instrumentation Amplifier IC features a fully-differential, adjustable-gain amplifier with digitally programmable offset cancellation, and features a constant-gm biasing circuit, a fully monolithic oscillator, internal thermometer circuit and RTD sensor interface. The thermometer and RTD sensor interface perform well at temperatures for T < 225 degree C. The oscillator demonstrates a temperature stability of ~97 ppm/degree C for T < 290 degree C at the fast clock setting. The instrumentation amplifier shows excellent stability for T < 300 degree C. With GA = 6 and GD = 8, gain stability is 128 ppm/degree C for 25 degree C < T < 300 degree C.

The Sigma-Delta IC includes a sigma-delta modulator with correlated double-sampling (CDS) pre-amplifier, a stand-alone sigma-delta modulator, constant-gm biasing circuit, oscillator and internal thermometer circuit. The CDS pre-amplifier has an adjustable gain and digitally programmable offset cancellation. The stand-alone sigma-delta modulator has a peak SNR and SNDR of 94 dB and 90 dB, respectively, at 25 degree C, and 94 dB and 87 dB at 300 degree C. The gain stability of the CDS pre-amplifier for GA = 6, 12 and 24 is 62, 66 and 95 ppm/degree C, respectively, for 25 degree C < T < 300 degree C. At 300 degree C, the modulator with CDS pre-amplifier achieves a dynamic range of 110 dB including the stand-alone modulator range.

Committee:

Steven Garverick (Advisor); Mehran Mehregany (Other); Christian Zoraman (Other); Darrin Young (Other); Chung-Chiun Liu (Other)

Keywords:

High-temperature; Temperature Stability; Mixed-signal; Analog-to-digital converter; High-temperature electronics; Sensor interface; Delta modulator; Sigma-delta modulator; ADC; Correlated double-sampling; High resolution; Temperature sensor

Stebner, Aaron P.Development, Characterization, and Application of Ni19.5Ti50.5Pd25Pt5 High-Temperature Shape Memory Alloy Helical Actuators
Master of Science, University of Akron, 2007, Mechanical Engineering
Shape memory alloys (SMAs) have been used as actuators in many different industries since the discovery of the shape memory effect. These include, but are not limited to, applications in the automobile industry, medical devices, commercial plumbing, and robotics. The use of SMAs as actuation devices in aeronautics has been limited due to the temperature constraints of commercially available materials. Consequently, work is being done at NASA’s Glenn Research Center to develop new SMAs capable of being used in high temperature environments. One of the more promising high-temperature shape memory alloys (HTSMAs) is Ni19.5Ti50.5Pd25Pt5. Recent work has shown that this material is capable of being used in operating environments of up to 250°C. This material has also been shown to have very useful actuation capabilities, demonstrating repeatable strain recoveries up to 2.5% in the presence of an externally applied load. Based on these findings, further work has been initiated to explore potential applications and alternative forms of this alloy, such as springs. Thus, characterization of Ni19.5Ti50.5Pd25Pt5 springs, including their mechanical response (e.g. stroke capabilities, load carrying capabilities, and work outputs) and how variations in this response correlate to changes in geometric parameters (e. g. wire diameter, coil diameter, wire-to-coil diameter ratio, and number of coils) are discussed. The effects of loading history, or training, on spring behavior were also investigated. A comparison of the springs with wire actuators is made and the benefits of using one actuator form as opposed to the other discussed. These findings are used to discuss design considerations for a surge-control mechanism used in the centrifugal compressor of a T-700 helicopter engine. The mechanical response observed during testing is then compared with responses predicted using current SMA spring design methodology. The deficiencies in predictions using this current design methodology are discussed in terms of future work needed to develop a model for HTSMA springs that can accurately guide engineering design.

Committee:

D. Quinn (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Shape Memory Alloy; Shape Memory Alloy Spring; SMA; High Temperature Shape Memory Alloy; High Temperature Shape Memory Alloy Spring; HTSMA; Spring; Helical Actuator; Adaptive Structure; Active Structure; Flight Structure; Actuator; Actuation Device

Bai, HeHigh temperature proton-exchange and fuel processing membranes for fuel cells and other applications
Doctor of Philosophy, The Ohio State University, 2008, Chemical Engineering

Proton-exchange membrane fuel cells (PEMFCs) have become a very active research area for both mobile and stationary applications, particularly for fuel cell vehicles. Compared to inner combustion engines, PEMFCs can decrease pollution and increase the energy efficiency. New proton-exchange membrane (PEM) materials and new technologies for fuel processing are the most important and challenging parts in this research field.

Nafion® and other perfluorinated sulfonic acid membranes are still the only commercial PEM materials so far. However, their high cost and low performance at high temperatures significantly limit their applications. In this research, new five-member ring and six-member ring soft segment-containing sulfonated polyimide (SPI)-based membranes and new sulfonated polybenzimidazole (SPBI)-based membranes were successfully synthesized. The resulting membranes could outperform Nafion® at various conditions, particularly at high temperatures and low relative humidities (RHs). Moreover, the new membrane materials should be much more cost-effective since the starting materials are more than two orders of magnitude less expensive than those for Nafion® membranes.

In the research on fuel processing, amine carriers were successfully incorporated into the SPBI copolymer or the crosslinked poly(vinyl alcohol) (PVA) matrix, which could react reversibly with acid gases, such as CO2. Thus, the resulting membranes have shown very promising CO2 selectivity vs. the other gas molecules, such as H2 and CH4, by the facilitated transport mechanism. These newly synthesized membranes have many applications in the field of gas separations, including the low pressure synthesis gas purification for fuel cell applications, the high pressure synthesis gas purification for refinery industrial applications, and the high pressure natural gas purification to obtain high purity CH4.

Committee:

W.S. Winston Ho, PhD (Advisor); L. James Lee, PhD (Committee Member); Kurt Koelling, PhD (Committee Member); Isil Erel, PhD (Committee Member)

Subjects:

Chemical Engineering; Energy; Polymers

Keywords:

fuel cell; proton-exchange membrane; high temperature; carbon dioxide removal; hydrogen purification; gas separation

Martone, Anthony MDevelopment of Iron-Rich (Fe1-x-yNixCoy)88Zr7B4Cu1 Nanocrystalline Magnetic Materials to Minimize Magnetostriction for High Current Inductor Cores
Master of Sciences (Engineering), Case Western Reserve University, 2017, Materials Science and Engineering
Advanced power electronic systems, with increased switching frequencies, demand greater efficiency and higher operating temperature inductors. This demand can be met by developing a new magnetic core material. Nanocrystalline magnetic materials, in particular, Fe77Co5.5Ni5.5Zr7B4Cu1, have been developed for use at elevated temperatures. While this nanocrystalline alloy having iron substituted with equal atomic percentages of cobalt and nickel has resulted in small coercivity, 10 A/m, and high Curie temperature, 220°C, magnetostriction persists as the main source of losses. Coercivity in this alloy system has proven to have a strong dependence on the magnetostriction. Through alloy development, low coercivities and high Curie temperatures can be achieved while minimizing magnetostrictive losses. This thesis focuses on varying the magnetic element content in the iron-rich (Fe1-x-yNixCoy)88Zr7B4Cu1 alloy system to minimize magnetostriction. Fe77Ni8.25Co2.75Zr7B4Cu1 has shown the best results with a coercivity of 10 A/m, magnetostrictive coefficient of 4.8 ppm, and Curie temperature of 218°C.

Committee:

Matthew Willard, Prof. (Advisor); David Matthiesen, Prof. (Committee Member); Alp Sehirlioglu, Prof. (Committee Member)

Subjects:

Energy; Engineering; Materials Science; Nanoscience

Keywords:

magnetic material; nanocrystalline; magnetostriction; soft magnetic material; inductor core; low coercivity; high temperature magnet; FeCoNi magnetic material

Casalena, LeeMultimodal Nanoscale Characterization of Transformation and Deformation Mechanisms in Several Nickel Titanium Based Shape Memory Alloys
Doctor of Philosophy, The Ohio State University, 2017, Materials Science and Engineering
The development of viable high-temperature shape memory alloys (HTSMAs) demands a coordinated multimodal characterization effort linking nanoscale crystal structure to macroscale thermomechanical properties. In this work, several high performance NiTi-based shape memory alloys are comprehensively explored with the goal of gaining insight into the complex transformation and deformation mechanisms responsible for their remarkable behavior. Through precise control of alloying and aging parameters, microstructures are optimized to enhance properties such as high-temperature strength and stability. These are crucial requirements for the development of advanced applications such as actuators and adaptive components that operate in demanding automotive and aerospace environments. An array of NiTiHf and NiTiAu alloys are at the core of this effort, offering the possibility of increased capability over traditional pneumatic and hydraulic systems, while simultaneously reducing weight and energy requirements. NiTi-20Hf alloys exhibit a favorable balance of properties, including high strength, stability, and work output at temperatures in excess of 150 °C. The raw material cost of Hf is also much lower compared with Pt, Pd, and Au containing counterparts. Advanced scanning transmission electron microscopy (STEM) and synchrotron X-ray characterization techniques are used to explore unusual nanoscale effects of precipitate-matrix interactions, coherency strain, and dislocation activity in these alloys. Novel use of the 4D STEM strain mapping technique is used to quantify strain fields associated with precipitates, which are being coupled with new phase field modeling approaches to particle/defect interactions. Volume fractions of nanoscale precipitates are measured using STEM-based tomography techniques, atom probe tomography, and synchrotron diffraction of bulk samples. Plastic deformation of the HTSMA austenite phase is shown to occur through <100>B2 type slip for the first time. NiTiAu alloys are shown to demonstrate work output at extremely high temperatures - above 400 °C - where the potential benefits may offset material cost. Crystal structures and chemical effects of previously undocumented secondary phases are extensively examined using STEM and X-ray energy dispersive spectroscopy (XEDS). These insights are combined with mechanical test data to develop an understanding of the critical microstructure-property relationships involved. In addition to the native corrosion resistance common to all these alloys, a nickel rich NiTi-1Hf alloy is shown to demonstrate extremely high strength and wear resistance, making it an ideal candidate for tribological applications such as bearings used in corrosive environments. Details of the stress-induced martensite phase are revealed in this alloy system using synchrotron radiation and aberration-corrected STEM. Finally, post mortem Transmission Kikuchi Diffraction (TKD) and in situ High Energy Diffraction Microscopy (HEDM) are used to explore the remarkable grain refinement process that occurs in NiTi and related alloys through load-biased thermal cycling. Microstructural changes in the form of defect generation and subgrain development are key mechanistic insights sought to further understand the processes resulting in unrecovered strain accumulation, which lead to detrimental functional fatigue in these alloys.

Committee:

Michael Mills (Advisor); Yunzhi Wang (Committee Member); Peter Anderson (Committee Member); Ronald Noebe (Committee Member); David Wood (Committee Member)

Subjects:

Materials Science; Metallurgy

Keywords:

high-temperature shape memory alloys; NiTiHf; NiTiAu; NiTi; actuator; STEM; HEDM; TKD; structural characterization; precipitate phases; load-biased thermal cycling; work output; strain mapping; H-phase; martensite

Blunt, Rory Alexander FabianA Study of the Effects of Turning Angle on Particle Deposition in Gas Turbine Combustor Liner Effusion Cooling Holes
Master of Science, The Ohio State University, 2016, Mechanical Engineering
The deposition of particulate in gas turbine cooling systems with a focus on single wall effusion holes was investigated. This study focused on the effect that flow turning angle into the cooling hole has on the blockage of these holes. The test hardware is based on a single walled combustor liner with angled effusion holes. By allowing the mass flow through the test system to decrease as deposition occurred the pressure drop across the test coupon was held at 3% of the discharge pressure. The mean flow turning angle was varied between favorable (10°) and adverse (130°) by mounting the plate in different orientations on a stalled plenum. The dust used was 0-10 µm Arizona Road Dust (ARD). These tests were run with a coupon temperature of 870 °C; this was achieved by use of an electric kiln. Flow reduction of the adverse test plates was around twice as much as the favorable condition; however both conditions had very similar capture efficiencies. 3D scans and sectioned test plates were used to investigate the different structures of the deposition that formed on the test plates and in the effusion holes. It is seen that turning angle does not influence the amount of captured mass but just the location of where that mass is captured and so its effect on the flow. A companion CFD study was also performed to explore the ability of computational models to predict the impact location and deposition depending on the impingement angle. This model was a simplified case and modeled a single effusion hole with the same geometry as the test plate. The inlet conditions were held constant and based on the experimental data. Particles were tracked with an Eulerian-Lagrangian method and it was seen that the predicted first impact locations closely matched the deposition seen in the experimental setup. Additionally a sticking model was used to predict deposition. It was seen that under the simulated conditions this model predicted deposition similar to the experimental results.

Committee:

Jeffrey Bons, Dr. (Advisor); Randall Mathison, Dr. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

Turning Angle; Deposition; Turbine; Combustor Liner; Effusion; Cooling Holes; CFD; Sticking; Computational; High Temperature; Validate; Engine; Modeling;

Wellman, William EdwardI. High temperature oxidation of hydrocabons in the chemical shock tube ; II. Synthetic analogs of actinomycin D /
Doctor of Philosophy, The Ohio State University, 1960, Graduate School

Committee:

Not Provided (Other)

Subjects:

Chemistry

Keywords:

Hydrocarbons;High temperature chemistry;Actinomycin

SONG, HYO-JINPROCESSING PHASE TRANS
MS, University of Cincinnati, 2005, Engineering : Materials Science
Recently, there has been a great interest in niobium-based alloys having a multiphase microstructure composed of Nb-silicides in a softer β matrix for high temperature structural applications, owing to their good combination of properties like high strength at elevated temperatures, high stiffness, low density, etc. Selection of alloying elements is a critical issue as the additions that improve high temperature oxidation resistance generally degrade the mechanical properties of the alloys. Therefore, after a preliminary investigation, the multi component Nb-Si-Ti-Al-Cr-X system was selected with the aim of developing new alloys that have the potential to meet the required properties for high temperature applications.

Committee:

Dr. Vijay Vasudevan (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

Nb composite alloy; intermetallic; high temperature materials

Jin, PengMechanism of Corrosion by Naphthenic Acids and Organosulfur Compounds at High Temperatures
Doctor of Philosophy (PhD), Ohio University, 2013, Chemical Engineering (Engineering and Technology)
Due to the law of supply and demand, the last decade has witnessed a skyrocketing in the price of light sweet crude oil. Therefore, refineries are increasingly interested in "opportunity crudes", characterized by their discounted price and relative ease of procurement. However, the attractive economics of opportunity crudes come with the disadvantage of high acid/organosulfur compound content, which could lead to corrosion and even failure of facilities in refineries. However, it is generally accepted that organosulfur compounds may form protective iron sulfide layers on the metal surface and decrease the corrosion rate. Therefore, it is necessary to investigate the corrosive property of crudes at high temperatures, the mechanism of corrosion by acids (naphthenic acids) in the presence of organosulfur compounds, and methods to mitigate its corrosive effect. In 2004, an industrial project was initiated at the Institute for Corrosion and Multiphase Technology to investigate the corrosion by naphthenic acids and organosulfur compounds. In this project, for each experiment there were two experimentation phases: pretreatment and challenge. In the first pretreatment phase, a stirred autoclave was filled with a real crude oil fraction or model oil of different acidity and organosulfur compound concentration. Then, the stirred autoclave was heated to high temperatures to examine the corrosivity of the oil to different materials (specimens made from CS and 5% Cr containing steel were used). During the pretreatment, corrosion product layers were formed on the metal surface. In the second challenge phase, the steel specimens pretreated in the first phase were inserted into a rotating cylinder autoclave, called High Velocity Rig (HVR). The HVR was fed with a high-temperature oil solution of naphthenic acids to attack the iron sulfide layers. Based on the difference of specimen weight loss between the two steps, the net corrosion rate could be calculated and the protectiveness of corrosion product layer against naphthenic acid corrosion could be assessed. Routinely, the layers generated in pretreatment and challenge phases were investigated with SEM/EDS (Scanning Electron Microscopy/Energy Dispersive Spectroscopy). Selectively, some thin layers formed in the first or second phase were analyzed with FIB-TEM (Focused Ion Beam - Transmission Electron Microscopy). FIB-TEM analysis revealed that there was an iron oxide layer beneath the iron sulfide layer. Experimental results showed that the iron oxide layer was closely related to the layer protectiveness against naphthenic acid corrosion and its formation was due to the presence of naphthenic acids in the fluid. Finally, a new mechanism of naphthenic acid/organosulfur compound corrosion was proposed based on properties of crudes, results of corrosion experimentation, and microscopic analysis of developed surface layers.

Committee:

Srdjan Nesic (Committee Chair); Martin Kordesch (Committee Member); Valerie Young (Committee Member); Eric Masson (Committee Member); Monica Burdick (Committee Member)

Subjects:

Chemical Engineering; Materials Science; Petroleum Engineering

Keywords:

naphthenic acids; high temperature corrosion; organosulfur compound; magnetite; crude fractions; TEM

Zuev, Yuri L.Studies of thermal phase fluctuations in severely underdoped YBCO films
Doctor of Philosophy, The Ohio State University, 2005, Chemical Physics
One of the central problems in the area of high-T C superconductivity is the origin of the so-called pseudogap , its relationship to superconductivity and peculiar normal state properties of cuprates. One point of view, very popular in the field, is that opening of the pseudogap is caused by thermal phase fluctuations (i.e. thermal fluctuations of the phase of the superconducting order parameter). In this work I have attempted to address the role of thermal phase fluctuations experimentally by studying their effect on superfluid density. The experimental challenge in this area is to produce samples homogeneous enough that most of superfluid density temperature dependence is unobscured by inhomogeneities. This is very difficult because in the interesting regime, i.e. heavily underdoped samples with transition temperatures 40K and below, T C varies rapidly with carrier concentration, and minute oxygen inhomogeneities cause severe variations of T C across a given sample. This challenge has been successfully met and I was able to produce homogeneous enough sample, such that it was possible to draw quantitative conclusions from our data. Carrier doping in CuO 2 planes could be varied by two techniques: changing number of oxygen atoms in the CuO chains (therefore changing the chemical composition of the sample), or changing the degree of order within chains (without overall change in composition). The results of this work prove to be insensitive to a particular way of carrier concentration adjustment. I see no evidence of strong role of thermal phase fluctuations in my thin films. Individual CuO 2 layers are coupled strongly almost all the way to T C , and the suppression of the transition temperature by fluctuations is by a few degrees at most. There is no evidence of T C suppression by several hundred degrees as is envisioned by fluctuation-mediated pseudogap model. Transition temperature is not proportional to T C , rather it is proportional to T C 2.3 . This is also contrary to the picture of superconducting transition in HTSC as phase-ordering transition. Magnetic field was applied parallel to the layers as a way to decouple them. The dependence of the films inductance on the magnetic field indicate very strong effect of the vortices located between CuO 2 planes. The experimental findings are compared to theory and shortcomings of the experiment and analysis are considered.

Committee:

Gregory Lafyatis (Advisor)

Subjects:

Physics, Condensed Matter

Keywords:

High-Temperature superconductivity; cuprates; YBCO; Phase Fluctuations; Kosterlitz-Thouless-Berezinskii transition; Parallel Magnetic Field

Shi, ShuRepair weldability of heat-resistant stainless steel casings-HP45NB, HP50NB and 20-32NB alloys
Doctor of Philosophy, The Ohio State University, 2006, Welding Engineering
The repair weldability of two types of heat-resistant austenitic stainless castings, HP-Nb modified alloys and 20-32Nb alloys, is studied in the present work. This investigation has focused on the microstructure evolution and hot ductility behavior of the two types of alloys. The microstructure evolution starting from the as-cast condition, to the condition after service exposure, as well as the condition after simulated repair welding (HAZ simulation) is discussed in the present work. After service exposure, Ni-Nb silicide and Cr-rich M23C6 were identified in both types of alloys. However, the HP-Nb alloys have a much higher total volume fraction of microconstituents than the 20-32Nb alloys. The M23C6 phase is more prevalent than Ni-Nb silicide in the HP alloys; while in the 20-32Nb alloys the Ni-Nb silicide is dominant. The 20-32Nb alloys have a much coarser dendritic structure than the HP alloys. The nature of the service-exposed microstructure evolution directly affected the microstructure and hot ductility behavior during simulated HAZ testing conducted with a Gleeble 3800™ thermo-mechanical simulator. For the HP-Nb alloys the results revealed a good metallurgical stability and on-cooling ductility, which can be related to good repair weldability of these alloys. In contrast, service-exposed 20-32Nb alloys showed a severe susceptibility to liquation cracking and significant loss in on-cooling ductility. The liquation cracking is the combination effect of high-silicon concentration at the dendrite boundaries resulting from the dissolution of the Ni-Nb silicide and a NbC constitutional liquation mechanism. The loss in on-cooling ductility that resulted from these two liquation mechanisms persisted from peak HAZ temperature to below 1000°C. The liquation cracking mechanism is discussed in detail relative to the microstructure evolution during HAZ simulation. The high temperature embrittlement (HTE) and strengthening mechanisms are also proposed. Based on these studies, recommendations on repair welding are proposed from the perspective of controlling microstructure. Control of phase balance appears to be very important in avoiding cracking during repair welding and involves manipulating the relative amounts of species among the element Nb, C and Si. Controlling dendrite size is also important from the standpoint of controlling silicon concentration in the interdendritic regions during repair welding.

Committee:

John Lippold (Advisor)

Subjects:

Engineering, Metallurgy

Keywords:

Repair weldability; Heat-resistant stainless steel casting; Microstructure evolution; High temperature embrittlement; Hot ductility behavior

Pigott, Jeff S.The Viscosity of Water at High Pressures and High Temperatures: A Random Walk through a Subduction Zone
Master of Science, The Ohio State University, 2011, Geological Sciences
The viscosity of water is a first-order constraint on the transport of material from a subducting plate to the mantle wedge. The viscosity of fluids that are released during the dehydration of hydrous minerals during subduction can vary by more than 9 orders of magnitude between the limits of pure liquid water and silicate melts. Accurate determination of low viscosities (<1 mPa·s) for liquids at simultaneous high pressures (>1 GPa) and high temperatures (>373 K) is hindered by the geometry and sample size of high-pressure devices. Here the viscosity of water at pressures representative of the deep crust and upper mantle through use of Brownian motion in the hydrothermal diamond anvil cell (HDAC) is reported. By tracking the Brownian motion of 2.8 and 3.1 micron polystyrene spheres suspended in H2O, the viscosity of the water at high pressure and high temperature can be determined in situ using Einstein’s relation. Accuracies of 3-10% are achieved and measurements are extended to pressures relevant to fluid release from subducting slabs and temperatures up to 150% of the melting temperature. Unhampered by wall effects of previous methods, the results from this study are consistent with a homologous temperature dependence of water viscosity in which the viscosity is a function of the ratio of the temperature to the melting temperature at a given pressure. Based on the homologous temperature dependence of water, transport times for fluids released from subducted plates inferred from geochemical proxies are too short for transport via porous flow alone, and suggest transport through a combination of channel-flow and porous flow implying hydrofracturing at 50-150 km depth.

Committee:

Wendy Panero (Advisor); Michael Barton (Committee Member); David Cole (Committee Member)

Subjects:

Geophysics

Keywords:

Viscosity; High Pressure;Water; Diamond Anvil Cell; Subduction Zones; Brownian Motion; High Temperature

Standish, Evan C.Design of a Molten Materials Handling Device for Support of Molten Regolith Electrolysis
Master of Science, The Ohio State University, 2010, Materials Science and Engineering
This study was performed to develop a method of removing molten process fluids, namely a ferrosilicon alloy and a complex silicate melt, from an electrolysis cell. The device was designed as a component of equipment used for an in situ lunar oxygen generating process under development. This work focuses on developing a system for integration into a molten regolith electrolysis cell, the products of which are highly reactive, making materials compatibility a primary concern of a materials handling system. This paper describes the design and operation of a mechanism utilizing a pressure differential to pull molten material from a furnace into a mold. The results of several different materials choices for equipment hardware are described and suggestions for modification of the device for improvement and lunar compatibility are made.

Committee:

Doru Stefanescu, PhD (Advisor); Yogeshwar Sahai, PhD (Committee Member)

Subjects:

Aerospace Materials; Engineering; Geotechnology; Materials Science; Mining

Keywords:

In Situ Resource Utilization; Molten Regolith Electrolysis; Molten Silicate Electrolysis; electrowinning cell equipment; lunar oxygen process; high temperature fluid handling

Barnes, Matthew A.Integrating High Temperature Superconducting Yttrium Barium Copper Oxide with Silicon-on-Sapphire Electronics
MS, University of Cincinnati, 2012, Engineering and Applied Science: Electrical Engineering
High temperature superconductors (HTSC) offer near zero loss performance when operated below the critical temperature which – at this point in the evolution of HTSCs – ranges from 77K to well over 100K, meaning that they can be cooled by readily available and relatively cheap liquid nitrogen. Silicon-on-insulator (SOI) electronics have proven advantageous with very low parasitics, very low power consumption, and easy integration to high yield CMOS processes [1]. It also enjoys a much lower cost than the more exotic III-V semiconductors that are their best competitors performance-wise. This research develops and validates processes to develop silicon-on-sapphire (SOS) electronics and YBCO electronics, side-by-side, on the same wafer, without degrading either respective material, or the electrical performance of devices fabricated on either material.

Committee:

Altan Ferendeci, PhD (Committee Chair); Joseph Thomas Boyd, PhD (Committee Member); Peter Kosel, PhD (Committee Member)

Subjects:

Electrical Engineering

Keywords:

High Temperature Superconductors;Resonator;Silicon;Processing;;;

Wiacek, Kevin JohnSYNTHESIS AND ELECTRICAL PROPERTIES OF FLUORENYL POLYESTERS INCORPORATING DIAMOND FRAGMENTS
Master of Science (MS), Wright State University, 2007, Chemistry
Based on the paradigm of diamond as a wide band-gap electrical insulator, molecular counterparts to crystalline diamond (cyclohexane, adamantane, and diamantane) were incorporated into a high-temperature fluorenyl polyester (FPE) with the intent of increasing the breakdown strength. The effect of incorporating a CycloteneTM thermoset as a crosslinking agent to increase the dielectric strength and the self-healing phenomena of these polymers were also investigated. Polymers were synthesized using 9,9-bis(4-hydroxyphenyl)fluorene and the diacid chloride of cyclohexane, adamantane, and diamantane. Thin films of the polymers were cast from chloroform and the electrical properties were investigated. The polyester incorporating the largest diamond fragment had the highest breakdown strength (543V/μm). When the thermoset (CycloteneTM) was added and cured, the breakdown strength increased to (650V/μm). The self-healing phenomenon was investigated by clearing the defects from the polymer films and quantifying the loss of capacitance.

Committee:

William Feld (Advisor)

Keywords:

Capacitor; Energy Storage; High temperature polymer; Diamondoid; Adamantane; Diamantane; Self-healing; Cyclotene

Erdem, Haci BayramSynthesis and Characterization of Thermoplastic Polyphenoxyquinoxalines
Doctor of Philosophy, University of Akron, 2008, Polymer Science
This research was divided into two main parts. In the first part, a new facile route to relatively inexpensive thermoplastic polyphenoxyquinoxalines was developed. The synthetic route involves the aromatic nucleophilic substitution reaction of bisphenols with 2,3-dichloroquinoxaline. The dichloro monomer was prepared in two steps. In the first step, oxalic acid was condensed with o-phenylenediamine to give 2,3-dihydroxyquinoxaline. In the second step, 2,3-dihydroxyquinoxaline was treated with thionyl chloride to give 2,3-dichloroquinoxaline. This monomer was successfully polymerized with bisphenol-A, bisphenol-S, hexafluorobisphenol-A and 9,9-bis(4-hydroxyphenyl)fluorenone. Hydroquinone and biphenol, however, can not be polymerized to high molecular weight polymers because of the premature precipitation of crystalline oligomers. The glass transition temperatures of the high molecular weight polymers prepared from a series of bisphenols range from 191 °C to 279 °C, and their thermal decomposition temperatures are around 500 °C. The polymers are soluble in a wide range of solvents and can be solution-cast into thin films that are colorless and transparent. The polymers have tensile strengths ranging from 61 to 107 MPa, and tensile moduli ranging from 3.5 to 2.3 GPa. The synthesis of polymer obtained from 2,3-dichloroquinoxaline and bisphenol-A was scaled up to afford 500 g of material. This polymer is a thermoplastic with a melt-viscosity less than 1000 Pa.s. at 300 °C. The notched Izod impact strength of injection-molded samples of this polymer is 40.7 J/m. In the second part of this research, the synthetic method has been modified to allow the preparation of quinoxaline containing polyimides. Thus, 2,3-dichloroquinoxaline was treated either with p-nitrophenol followed by reduction of nitro groups, or with p-aminophenols to directly obtain the desired 2,3-(4-aminophenoxy)quinoxaline. This diamine was polymerized with 3,3',4,4'-biphenyldianhydride, 4,4'-oxydiphthalic anhydride and 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride. The polymerizations were carried out by the two step method. The poly(amic acid) intermediates were thermally imidized. Although they have high molecular weights judged by their inherent viscosities ranging from 0.51 to 1.01, thin films of all these polyimides were brittle. The glass transition temperatures of the polyimides range from 259 °C to 282 °C with thermal decomposition temperatures around 550 °C. The polyimide obtained from 2,3-(4-aminophenoxy)quinoxaline and 3,3',4,4'-biphenyldianhydride was found to be semi-crystalline.

Committee:

Frank Harris, Ph.D. (Advisor); Judit Puskas, Ph.D. (Committee Chair); Stephen Cheng, Ph.D. (Committee Member); Roderic Quirk, Ph.D. (Committee Member); David Modarelli, Ph.D. (Committee Member)

Subjects:

Polymers

Keywords:

Condensation Polymerization; High Temperature Polymers; Quinoxaline; Polyquinoxaline; Polyphenoxyquinoxaline

Wilson, Brandon AugustusEvaluation of Optical Fiber Sensors in High Temperature and Nuclear Reactor Environments
Doctor of Philosophy, The Ohio State University, 2017, Nuclear Engineering
The Department of Energy and Idaho National Laboratory are restarting the TREAT reactor and are interested in updating the reactor’s instrumentation regarding the analysis of the test fuel. Optical fibers’ ability to make distributed temperature measurements coupled with its small footprint makes optical fiber a viable candidate to monitor fuel performance in the TREAT reactor. In addition to TREAT reactor, the U.S. Department of Energy and nuclear reactor companies like TerraPower have shown interest in using distributed optically based instrumentation for nuclear instrumentation in Next-gen reactors. The performance and evaluation of optical fiber based instrumentation in high temperature and radiation environments is the main goal of this work. A feasibility study to determine the viability of extending this technology to the nuclear field was made. In addition to the performance testing of commercial optical fiber based instrumentation, I was able to modify and innovate various aspects of the optical fiber based instrumentation, so that it could survive the high temperature and radiation environments of a Next-Gen reactor. Distributed temperature sensing using optical fiber based methods in silica optical fibers was found to have a temperature limit of around 700 C. Above the 700 C mark, various effects, from annealing of the glass to environmental effects from the atmosphere, start to cause sensing failure in the fiber. This temperature limit can be extended to 1000 C if the silica optical fiber is placed in an inert environment with a micro capillary tube or high temperature coating to support it mechanically. Distributed temperature sensing with commercial optical fibers was also tested in a reactor environment and was found to incur a sensing failure after a neutron fluence of around 1018 n/cm2. Radiation hardness can be added to the distributed sensing ability of optical fibers by placing Bragg gratings into the fiber. The high reflective signature off of the Bragg gratings in the fiber allows the distributed temperature sensing to continue to provide accurate measurements, even when the noise floor from radiation damage is increased in the fiber. Femtosecond Bragg gratings have the most potential for long term use in a nuclear reactor, since they were shown to survive long periods of high temperature and radiation fluences without much degradation. Sapphire fiber was also analyzed in this work for its suitability as optical instrumentation in Next-Gen reactors. Sapphire fiber has a temperature limit of 1300 C for light transmission in the fiber. Above 1300 C, aluminum oxyhydroxide forms on the surface of the fiber, causing massive light attenuation in the fiber. An inert atmosphere can extend the temperature range of sapphire optical fibers and sapphire instrumentation above 1300 C. Distributed temperature sensing with sapphire fiber was also achieved in this work by creating an internal reflective cladding using, high energy ion implantation in the fiber. This internal reflective cladding creates a graded index in the sapphire fiber creating a near single mode fiber. The sapphire cladded fiber has tremendous promise and should be further researched in the future.

Committee:

Thomas Blue (Advisor); Raymond Cao (Committee Member); Marat Khafizov (Committee Member)

Subjects:

Nuclear Engineering

Keywords:

Optical Fiber Sensors, High Temperature and Nuclear Reactor Environments

Mullen, Max RobertsonElectrochemical Sensing for a Rapidly Evolving World
Doctor of Philosophy, The Ohio State University, 2015, Chemistry
This dissertation focuses on three projects involving the development of harsh environment gas sensors. The first project discusses the development of a multipurpose oxygen sensor electrode for use in sealing with the common electrolyte yttria stabilized zirconia. The purpose of the sealing function is to produce an internal reference environment maintained by a metal/metal oxide mixture, a criteria for miniaturization of potentiometric oxygen sensing technology. This sensor measures a potential between the internal reference and a sensing environment. The second project discusses the miniaturization of an oxygen sensor and the fabrication of a more generalized electrochemical sensing platform. The third project discusses the discovery of a new mechanism in the electrochemical sensing of ammonia through molecular recognition and the utilization of a sensor taking advantage of the new mechanism. An initial study involving the development of a microwave synthesized La0.8Sr0.2Al0.9Mn0.1O3 sensor electrode material illustrates the ability of the material developed to meet ionic and electronic conducting requirements for effective and Nernstian oxygen sensing. In addition the material deforms plastically under hot isostatic pressing conditions in a similar temperature and pressure regime with yttria stabilized zirconia to produce a seal and survive temperatures up to 1350 oC. In the second project we show novel methods to seal an oxygen environment inside a device cavity to produce an electrochemical sensor body using room temperature plasma-activated bonding and low temperature and pressure assisted plasma-activated bonding with silicon bodies, both in a clean room environment. The evolution from isostatic hot pressing methods towards room temperature complementary metal oxide semiconductor (CMOS) compatible technologies using single crystal silicon substrates in the clean room allows the sealing of devices on a much larger scale. Through this evolution in bonding technology we move from performing non-scalable experiments to produce one sensor at a time to scalable experiments producing six. The bonding methods we use are compatible with wafer scale processing. Practically speaking this means that the oxygen sensor design is scalable to produce thousands of sensors from one single bond. Using this bonding technology we develop a generalized sensing platform that could be used for a variety of sensing applications, including oxygen sensing, but also potentially involving CO2 or NOx as well. Future efforts will involve completing of O2 sensor construction and adaption of the design for CO2 and NOx sensing. The final project focuses on a novel ammonia sensor and sensing mechanism in Ag loaded zeolite Y. The sensor resistance changes upon exposure to ammonia due to the molecular recognition of Ag+ and ammonia, producing Ag(NH3)x+ species. The sensing mechanism is a Grothuss like mechanism based on the hoping of Ag+ centers. The hopping frequency of Ag+ changes upon introduction of ammonia due to the reduced electrostatic interactions between Ag+ and the negatively charged zeolite framework upon formation of Ag(NH3)x+. The change in hopping frequency results in a measurable change in impedance.

Committee:

Prabir Dutta (Advisor)

Subjects:

Chemistry; Materials Science

Keywords:

electrochemical sensor; oxygen; oxygen sensor; ammonia; nitric oxide; NOx; emissions; high temperature; harsh environment; MEMS; zirconia; hydrophilic bonding; direct bonding

Chen, MinghuiDESIGN, FABRICATION, TESTING, AND MODELING OF A HIGH-TEMPERATURE PRINTED CIRCUIT HEAT EXCHANGER
Master of Science, The Ohio State University, 2015, Nuclear Engineering
One of the very-high-temperature reactor (VHTR) missions is to produce electricity and/or to provide process heat for applications with high efficiency. The electricity generation or process heat applications of these advanced reactors greatly rely on an effective intermediate heat exchanger (IHX) that transfers heat from the primary fluid (i.e., helium) to the secondary fluid, which can be helium, molten salt, water/steam, or supercritical carbon dioxide. The IHX performance is directly related to the efficiency and safety of the overall nuclear system. A printed circuit heat exchanger (PCHE) is one of the leading IHX candidates due to its high effectiveness and compactness, as well as its robustness. In the current study, a scaled-down PCHE was fabricated using Alloy 617 plates and Alloy 800H headers. The PCHE fabrication processes, i.e., photochemical etching, diffusion bonding and brazing, are described. This PCHE has eight hot and eight cold plates with 11 semicircular wavy (zigzag) channels in each plate with the following channel dimensions: 1.2 mm hydraulic diameter, 24.6 mm pitch in the flow (stream-wise) direction, 2.5 mm pitch in the span-wise direction, and 15º wavy pitch angle. The thermal-hydraulic performance of the PCHE is investigated experimentally in the high-temperature helium test facility (HTHF) at The Ohio State University. The PCHE inlet temperatures and pressures are varied up to 350 ºC/2 MPa for the cold side and 700 ºC/2 MPa for the hot side, respectively, while the maximum mass flow rate of helium reaches 30 kg/h. The corresponding maximum channel Reynolds number for both the hot and cold sides is about 3,000, including the laminar flow and laminar-to-turbulent transitional flow regimes. Comparisons between the obtained experimental data and available empirical correlations in the literature have been carried out. Both hot-side and cold-side friction characteristics of the PCHE with the wavy channels follow the trend established in the empirical model well, while large deviation is presented in the low Reynolds number region. Heat transfer characteristics obtained from model available in the literature show a discrepancy from the experimental results. Large deviation appears in the low Reynolds number region as well. A new heat transfer correlation based on experimental data has been subsequently proposed for the current wavy-channel PCHE. Finally, transients that involve variations of the mass flow rate and temperature on the hot and cold sides of the scaled-down PCHE are investigated by numerical method. A dynamic model has been verified using a commercial software DYNSIM and validated using the experimental data. The model predicts the dynamic trends well and is available for use in the future.

Committee:

XIAODONG SUN (Advisor); RICHARD CHRISTENSEN (Committee Member); PIYUSH SABHARWALL (Committee Member)

Subjects:

Energy; Engineering; Mechanical Engineering; Nuclear Engineering

Keywords:

PCHE, thermal-hydraulic performance, compact heat exchangers, high-temperature helium facility, VHTR, dynamic response

Ngan, TiffanyEvaluation of the Response of Armor Alloys to High Temperature Deformation
Master of Science, The Ohio State University, 2014, Welding Engineering
High strength alloys, such as titanium alloys and steels have been widely used for armor applications. However, high strength materials have poor formability at room temperature and are prone to cracking during welding. It is necessary to develop alternative manufacturing methods that can replace conventional welding technologies. The main objectives of this project are: 1) development of a testing procedure for evaluation of the response of high strength alloys to hot induction bending, and 2) development of optimal process control windows for hot induction bending of three high strength materials: alloy Ti-6Al-4V and armor steels Armox 440 and ARL XXX. A testing procedure has been developed that combines hot ductility testing, high temperature straining using a GleebleTM thermo-mechanical simulator, high temperature straining followed by room temperature tensile testing, evaluation of response to tempering, phase transformation analysis, thermodynamic simulations, and metallurgical characterization. Hot ductility testing indicates a gradual increase in ductility of the three tested alloys as temperature increases. Strain rate has no significant effect on hot ductility of alloy Ti-6Al-4V and ARL XXX steel. During hot ductility testing, extensive void formation is observed in alloy Ti-6Al-4V between the starting temperatures of alpha and beta transformation and the recrystallization temperature, and in Armox 440 steel between the A1 and A3 temperatures. No voids were found above beta solvus temperature in Ti-6Al-4V and above the A3 temperature in Armox 440. Limited void formation occurs below the start of alpha and beta transformation in Ti-6Al-4V and below the A1 temperature in Armox 440. High temperature straining tests show that strain-induced porosity in Ti-6Al-4V can be avoided if strain is limited below 24% at 430 degrees Celsius and below 7% at 650 degrees Celsius. In Armox 440 and ARL XXX steels, voids were only observed in samples strained to failure. High temperature straining followed by room temperature tensile testing shows that in class 2 Ti-6Al-4V alloy highest ultimate tensile strength is obtained after 11% straining at 430 degrees Celsius. For the two armor alloys, straining above the A3 temperature provides room temperature mechanical properties that are closest to the original properties of two armor steels. Holloman-Jaffe parameters have been developed for evaluation of the effect of hot induction bending on hardness in Armox 440 and ARL XXX steels. A continuous cooling transformation diagram has been developed for the coarse grained heat affected zone of ARL XXX steel. The liquidus, solidus, A1 and A3 temperatures in this steel have been determined using single sensor differential thermal analysis. The reasons for solidification cracking in fillet welds of ARLXXX steel have been investigated using metallurgical characterization and thermodynamic simulations. The presented approach allows developing optimized processing windows for hot bending of high strength alloys. Process parameters developed in this research, in terms of optimal bending temperatures and strain ranges, can be applied to avoid defect formation and minimize loss of properties during hot induction bending of the three tested alloys.

Committee:

John Lippold (Advisor); Boian Alexandrov (Committee Member); David Phillips (Committee Member)

Subjects:

Engineering; Metallurgy

Keywords:

Armor alloys; High strength alloys; Ti-6Al-4V; Armox 440; ARL XXX; Hot induction bending; High temperature; Deformation; Strain-induced porosity; Void formation

Ramamurti, RahulSynthesis of Diamond Thin Films for Applications in High Temperature Electronics
PhD, University of Cincinnati, 2006, Engineering : Materials Science

High-temperature electronics and MEMS (Micro-Electro-Mechanical Systems) based on polycrystalline diamond (PCD) are promising because of its wide band gap, high thermal conductivity, and large carrier mobility. To take advantage of this opportunity, research was undertaken to develop techniques for the synthesis of both undoped and doped high quality PCD films with good surface flatness suitable for the fabrication of high temperature electronics and MEMS devices. One way to fabricate smooth films is to decrease the grain size because diamond films with large grain size bring forth problems in contact formation and device fabrication due to the large surface roughness. Consequently, there is a need to fabricate nanocrystalline films with small grain size and good smoothness. In addition, the electrical properties and conduction mechanisms in nanocrystalline diamond (NCD) films have not been sufficiently analyzed. This study also aims at achieving high resistivity nanocrystalline diamond films and to study the electrical conduction mechanism.

Several approaches have been used in our research to achieve these goals. Initially microcrystalline diamond (MCD) films were grown on silicon (100) substrates by the microwave plasma enhanced chemical vapor deposition (MPCVD) method using methane in a hydrogen plasma environment. Introduction of small amounts of argon into the Argon / Hydrogen plasma was used to deposit diamond films with a range of microstructures from microcrystalline to nanocrystalline grains. A detailed quantitative study of the sp3, sp2 content in the films grown with varying amounts of argon in the plasma was done using Raman spectroscopy. The optimum gas composition that gave the best quality diamond film consisting of 1.6 µm grains was 60% Ar/ 39% H2/ 1% CH4. The optimum gas composition that gave nanocrystalline grains of size in the order of <50 nm was 95% Ar/ 4% H2/ 1% CH4. A change in the cross-sectional microstructure from the columnar to grain-like (equiaxed) morphology was observed. The change was attributed to different plasma chemistry with the C2 dimer as the primary growth species in the Ar-rich plasma. Varying concentrations of N2 gas were also used to decrease the grain size of the diamond films. The growth species in this case was C2 at low nitrogen content and CN at high nitrogen content. This can also be used to dope the films n-type, when added in small quantities in order to increase the conductivity of the PCD. Small quantities of nitrogen (<0.1%) gave ultrananocrystalline diamond (UNCD) of grain size less than 10 nm. For N2 concentrations between 0.1% and 2% diamond films of grain sizes in the range of 100-200 nm were obtained. The addition of boron in small concentrations was used to dope the films p-type. These were useful in making electronic devices.

Electrical properties of the microcrystalline and nanocrystalline diamond films were measured over a range of temperatures by fabricating capacitors using a metal-insulator-metal (MIM) configuration that could withstand temperatures up to 600 °C. Typical electrical resistivities of MCD were ∼1012 Ω.cm while the dielectric constant was near 5.6, which was representative of natural diamond. For NCD, the electrical resistivities were of ∼1011 Ω.cm was obtained, which was eight orders of magnitude higher than values reported by other researchers. A lower dielectric constant of 5.2 was obtained for the NCD. The electrical conduction mechanisms in undoped MCD, NCD, and nitrogen-doped films were studied. The Hill’s conduction mechanism was dominant in MCD and NCD films due to the deep-level traps present, which contributed to grain-boundary conduction. The average distances between the trap sites were found to be 11 nm for the MCD, and 5 nm for the NCD were estimated. These related to the hopping conduction across impurities present in the grain boundaries. These impurities were attributed to graphite in the PCD films. The nitrogen-doped diamond films were processed to fabricate a metal-insulator-semiconductor (MIS) structure. The resistivity of a 1% nitrogen-doped diamond was 2.8x107 Ω.cm. The space-charge-limited-conduction mechanism was suggested for the nitrogen-doped diamond films due to holes injected from the p-type silicon into the n-type diamond layer, and the injected holes played a role of the current carriers.

Committee:

Dr. Raj Singh (Advisor)

Subjects:

Engineering, Materials Science

Keywords:

chemical vapor deposition; microwave plasma; high temperature electronics; nanocrystalline diamond; silicon substrate; argon/ hydrogen plasma; Raman spectroscopy; quantitative analysis; nitrogen doping; boron doping; metal-insulator-metal configuraion

Brenneman, James WAn Experimental Study on the Scuffing Performance of High-Power Spur Gears at Elevated Oil Temperatures
Master of Science, The Ohio State University, 2013, Mechanical Engineering
In this study, a number of spur gear tests were performed under high-power and high-temperature conditions representative of certain aerospace gearing applications. As the first type of tests, long cycle tests of 100 million cycles were performed at set operating speed, load, and temperature conditions. The second type of tests, load-staged scuffing tests, implemented an incrementally increased torque schedule under constant speed and oil temperature conditions. Two different gear tooth surfaces were considered in these tests: hard ground surfaces representative of rough, as machined gear surfaces and chemically polished gear surfaces that were an order of magnitude smoother than the ground surfaces. The primary failure mode of concern was scuffing of the contact surfaces due to temperature build up. The impact of surface roughness amplitudes, contact stress, and oil inlet temperature on scuffing failures were investigated. Effects of ramp up procedures for the speed and torque, as well as the introduction of a break-in test stage were also investigated to show that they are critical to the scuffing performance of gears.

Committee:

Ahmet Kahraman (Advisor); Brian Harper (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

gears; scuffing; high temperature;contact fatigue

KARKI, BHISHMA R.SURFACE RESISTANCE OF HIGH TEMPERATURE SUPERCONDUCTOR BY THE RESONANT CAVITY METHOD
MS, University of Cincinnati, 2004, Engineering : Electrical Engineering
The cavities of high temperature superconductor were prepared and oxygenated Q measurements made.TM 010 modes were chosen for the measurements since they are independent of the cavity height. Resonant frequencies of the cavities were theoretically calculated and the corresponding S 11 parameters were measured by sweeping the Network Analyzer over the corresponding frequency range. Measurements were taken at a range of temperature from 10 K to 90 K in step of 10 K. Both unloaded Q-factor (Q 11 ) and loaded Q–factor (Q L ) were then calculated using the experimental data. A series of plots of Q vs. T are included in the thesis. Theoretical calculations were done to establish the relation between Q values and surface resistance of YBCO superconductor cavities based on the mode excitation. The surface resistances were then evaluated for the corresponding of YBCO cavities using the Q 0 values found from the measured data.

Committee:

Dr. Altan Ferendeci (Advisor)

Keywords:

Superconductor; High Temperature Superconductor; Surface Resistance; TM 010 modes

Chung, SeungjoonDual-phase Inorganic Membrane for High Temperature Carbon Dioxide Separation
MS, University of Cincinnati, 2004, Engineering : Chemical Engineering
2 separation from the hot flue gas is a key technology to reduce green house gas. However, there are no efficient methods of separating carbon dioxide available at high temperature so far. This research is aimed at synthesis of a new inorganic dual-phase carbonate membrane for high temperature (>400 °C) CO2 separation.

It is well known that molten carbonate has high CO32- ion conducting properties from the research on the molten carbonate fuel cell (MCFC). From the extension of MCFC, the concept of dual-phase membrane was introduced in this research. This membrane consists of a porous solid phase and a molten carbonate phase. The solid phase serves as an electronic conductor and molten carbonate phase serves as an ionic transport channel. Metal-carbonate dual-phase membranes were prepared by the direct infiltration method with Li/Na/K (42.5/31.5/25 mol.%) carbonate mixture and porous stainless steel support. The surface of the membrane was characterized by SEM/EDS and XRD. Gas tightness was checked with helium permeation at room temperature. Permeance for different gases was measured at different temperature (450~750 °C).

SEM with EDS results show that the pores in the support were successfully filled with molten carbonate. The membrane is gas-tight with helium permeance about six orders of magnitude lower than that for the metal support. Gas permeance of CO2, N2, and CO2 with O2 were measured at various temperatures (450~750 °C). Permeance of carbon dioxide with oxygen tends to increase with temperature while others show only a slight change. Permeance of CO2, N2, and CO2 with O2 was in the range of 3~5 x 10-9, 1~3 x 10-9, and 7~25 x 10-9 mol/s.m2.Pa, respectively at 450~650 °C. At 650 °C, permeance of carbon dioxide with oxygen reached maximum, which was 16 times higher than that of nitrogen. Temperature dependence of the CO2 with O2 flux was described by modified Wagner equation and Arrhenius relationship. At high temperature the permeance of CO2 with O2 decrease dramatically with time due to the oxidation of metal and molten carbonate. XRD analysis showed that iron oxides and lithium-iron oxides were formed after CO2 with O2 permeation experiment.

The ultimate goal of this study is to prepare a stable metal-carbonate dual phase membrane and to have a better understanding of this type of the membrane in the application of CO2 separation at high temperature. Experimental results were used to study the characteristic of the membrane and its permeation properties.

Committee:

Dr. Jerry Lin (Advisor)

Subjects:

Engineering, Chemical

Keywords:

dual phase membrane; CO2 separation; high temperature molten carbonate

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