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 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 hightemperature 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

Ceramics membranes are made in a wide variety of different techniques using a wide variety of different materials. However, many of the common techniques utilize a slurry of ceramic particles, additives, and either organic solvent or water that is shaped into a membrane, left to dry, and then sintered together. Drying is a time consuming process, often requiring several hours for the liquid medium to evaporate. Defect formation caused by development of partial pressures across the drying membrane, including cracks and warpage, also typically occurs during the drying process. To address this, slurries of ceramic particles made with a low viscosity UV-curable resin, which can cure in the span of a few seconds, eliminating the need for drying and any defects associated with drying. Slurries were made with different particle sizes and volume fractions and made into thin membranes using an Autodesk Ember 3D printer. Curing of UV resin and slurries were examined with FTIR. Pyrolytic behavior of resin was examined using isothermal TGA. Cure depth profiles were determined using the modified Beer-Lambert Law and compared against models in literature. Results showed contrasting curing behavior based on volume fraction and particle size due to differences in UV light exposure methods.

Long wave infrared (LWIR) optics that transmit in the 8 to 14 m wavelength range and, additionally, can withstand severe physical and thermal stresses are needed for advanced remote sensing, guidance and communication-based applications. However, most non-oxide transparent LWIR optics do not have the wider transmission range, nor the hardness and resistance to thermal shock needed for extreme environments. Because of these limitations, research is circling back to a promising material, calcium lanthanum sulfide (CLS), that could meet LWIR needs for extreme environments. In this thesis, we will demonstrate the abilities of x-ray photoelectron spectroscopy (XPS) as a technique for characterizing CLS powders and ceramics for elemental analysis, valence state and stoichiometry evaluation. Three preliminary studies were conducted - a binary metal sulfide evaluation of lanthanum sulfide (La2S3) and calcium sulfide (CaS), and a calibration curve of mixtures of the two binary metal sulfide powders from a known concentration matrix. Based on these results, a methodology was developed to evaluate CLS powder and ceramics via XPS. We showcase the power of XPS to reliably determine CLS stoichiometry, identify impurities and defects as related to the presence of carbon and oxygen during processing, and predict the bonding environment of sulfur which can lead to better quality CLS ceramics. This thesis demonstrates the use of XPS as a potential characterization tool in CLS to identify contaminants, determine if stoichiometry is met, and identify the bonding environments to assist in processing improvements for producing higher-quality ceramics.

Coral reefs are an important element of marine ecosystem that are critical to maintain a healthy environment. Unfortunately, in recent years coral reefs are doing poorly and many in parts of the ocean are simply dying. Therefore, study of coral’s structural response to external loads could answer what will happen with their structures, while they exhibit different types of loading. Therefore, the proposition of using in-situ micro-Raman spectroscopy to study skeletons of Acropora cervicornis was used. Coral skeleton samples I subjected to mechanical loading studied their vibrational properties by exciting the material with 532nm visible light. A uniaxial compressive load I applied using a MTS universal testing machine and then using the Raman Spectroscopy to study the vibrational response of coral skeletons. Indentations used Vickers Hardness tester and performed 2D mapping of the coral structure around the indentation. If it’s expected that as a result of the proposed research the better understanding of structural stability of the Acropora Cervicornis coral skeletons will be achieved.

Electrochemical conversion devices are a developing technology that prove to be a viable and more efficient alternative to current environmentally friendly generation devices. As such, constant research has been done in the last few decades to increase their applications and reliability. One of these systems, and the focus of this research, is the single cell Solid Oxide Fuel Cell (SOFC). These systems are a developing technology which main caveat is the need of high operating temperatures and costs. As such, most multidisciplinary research has been focused on researching materials and/or processes that help mitigate the costs or lower the operating temperature. The research presented in this paper focused on the manufacturing of a cubic stabilized zirconia (CSZ) electrolyte thin membrane for a single cell SOFC through tape casting. Thus, the process was divided into slurry preparation, tape casting, further processing, and analysis of samples. First the tape was produced reaching optimal viscosity (between 500 to 6000 cP) and minimizing impurities. Then, the slurry was poured into the doctor's blade with a 200 micrometers gap and allowed to dry. Samples were punched from the green tape with a diameter of 28 inches. Afterwards, these samples were pressed and sintered with a force of 218016 N and temperature of 1550 degrees celsius, respectively. These steps are done to maximize density and grain growth and minimize porosity. Lastly, the tape went further analysis and it was stated that further research should be done to determine this tape viability for stationary SOFC application.

This dissertation culminates a three year research program investigating the properties and performance of a tubular, ceramic composite component. Eight test specimens were fabricated using an injection molding process with a borosilicate glass matrix reinforced with chopped graphite fibers. These specimens were then tested under quasi-static and cyclic loading at room temperature. Due to the infancy of CMC materials and, especially, CMC components, the program included a very broad-based investigation into many areas which are considered well-established for more conventional materials, and a very extensive and diverse set of achievements were realized. A tubular CMC test specimen representing an engineering component was designed and fabricated. A high temperature multiaxial test facility for ceramic matrix composite components was developed and installed at Virginia Tech. Nondestructive and destructive test methods for CMC components were developed, and a thorough investigation of the failure mechanisms in injection molded CMC tubes subjected to room temperature, quasi-static and cyclic loading was conducted in spite of a very limited quantity of material. As a result of this investigation, performance limiting defects in the injection molded tubes were identified. In addition, a generalized modeling approach was investigated for the analysis of complex, composite components which includes the effects of damage development under static and cyclic loading. All of these topics are discussed in detail in this dissertation. / Ph. D.

The corrosion resistance of chemically modified β-eucryptite (Li_0.41Mg_0.035AlP_0.52Si_0.480₄) having low expansion anisotropy and a near zero coefficient of thennal expansion was evaluated. Samples were exposed to aqueous hydrochloride acid at temperatures up to 100°C and environments containing sodium sulfate up to l000°C. The corrosion resistance was characterized by dilatometry, scanning electron microscopy, X-ray diffraction, energy dispersive x-ray analysis, weight variations, and mechanical properties variations. The results show that modified β-eucryptite is more severely corroded than commercial lithium-alumina-silicate glass-ceramics when exposed to these environments. Aqueous HCI removes AIP04 from modified β-eucryptite leaving a very porous structure. Molten salt corrodes modified β-eucryptite by penetration of sodium and sulfur which form an alkali melt under the surface. The modulus of rupture and the Young's modulus are reduced by both types of corrosion. / Master of Science

High Temperature Superconductors (HTS) materials are ideal for many electrical applications. These applications include high speed interconnects, microwave structures and transmission lines, as well as electronic devices that utilize the unique electrical and magnetic properties of these materials. To date, the use of high temperature superconductors has been limited to a narrow range of substrate materials, due to the reactive nature of these superconductors. Chemical reactions between the substrate and the superconductor cause decomposition of the superconductor into an insulator. The researcher has developed a thick film system that allows the production of high quality HTS films on reactive substrates, such as alumina (Al203). This system utilizes a thick film buffer layer of pure silver in combination with thick film superconductors composed of Y1Ba2~CU30X. The silver buffer layer is designed to prevent contact between the substrate and the superconductor, thereby eliminating chemical reactions between the two materials. The development as well as the comprehensive characterization of these films is described in this work. / Master of Science

The corrosion resistance of two commercially available SiC filter materials coated with Mg-doped Al₂ TiO₅ and (Ca _0.6.6' Mg_0.52) Zr₄P₆O₂₄ (CMZP) was investigated in high-temperature high pressure (HTHP) alkali-steam environments. Coated specimen properties, including cold and hot compressive strengths, bulk density, apparent porosity, permeability, and weight change, detected after exposure to 92% air-S% steam 10 ppm Na at 8OO°C and 1.8 MPs for 500 h were compared with those of uncoated specimens. Procedures for applying homogeneous coatings of Mg-doped Al₂ TiO₅ and CMZP to porous SiC filters were established and coating of the materials was successfully accomplished. Efforts to stabilize the Al₂ TiO₅ coating composition at elevated temperature were successful. Coatings show promise for providing improved corrosion resistance of the materials in pressurized fluidized bed combustion (PFBC) environments as evidenced by higher compressive strengths exhibited by coated SiC specimens than by uncoated SiC specimens following HTHP alkali-steam exposure. / Master of Science

The goal of this dissertation consists of improving the efficiency of energy harvesting using pyroelectric and piezoelectric materials in a system by the proper characterization of electrical parameters, widening frequency, and coupling of both effects with the appropriate parameters. A new simple stand-alone method of characterizing the impedance of a pyroelectric cell has been demonstrated. This method utilizes a Pyroelectric single pole low pass filter technique, PSLPF. Utilizing the properties of a PSLPF, where a known input voltage is applied and capacitance Cp and resistance Rp can be calculated at a frequency of 1 mHz to 1 Hz. This method demonstrates that for pyroelectric materials the impedance depends on two major factors: average working temperature, and the heating rate. Design and implementation of a hybrid approach using multiple piezoelectric cantilevers is presented. This is done to achieve mechanical and electrical tuning, along with bandwidth widening. In addition, a hybrid tuning technique with an improved adjusting capacitor method was applied. An toroid inductor of 700 mH is shunted in to the load resistance and shunt capacitance. Results show an extended frequency range up to 12 resonance frequencies (300% improvement) with improved power up to 197%. Finally, a hybrid piezoelectric and pyroelectric system is designed and tested. Using a voltage doubler, circuit for rectifying and collecting pyroelectric and piezoelectric voltages individually is proposed. The investigation showed that the hybrid energy is possible using the voltage doubler circuit from two independent sources for pyroelectrictity and piezoelectricity due to marked differences of optimal performance.