A novel class of inorganic/ organic hybrid materials referred to as CERAMERs have been successfully prepared by a sol-gel process using a polymeric acid catalyst, poly(styrene sulfonic acid), to form a network from tetraethylorthosilicate (TEOS) and triethoxysilane end capped oligomers of poly( tetramethylene oxide) (PTMO). The structure-property relationships were determined for these hybrid networks from their dynamic mechanical behavior, mechanical properties, and SAXS behavior. Thermal gravimetric data coupled with FfIR analysis were used to obtain a qualitative measure of the extent of conversion of the metal alkoxides as a function of acid catalyst. Another new class of CERAMERs was successfully developed by the sol-gel processing of three different metal alkoxides in conjuction with the triethoxy silane end capped PTMO oligomers. The first novel hybrid is based upon complexes of aluminum tri-n-butoxide with ethyl acetoacetonate or titanium tetra-iso-propoxide with ethyl acetoacetate reacted with the triethoxysilane end capped PTMO. The hybrid networks were optically clear and could be easily formed as relatively large monoliths. A novel method of preparation of stable sols without the use of ethyl acetoacetate, developed by Dr. Bing Wang in this laboratory, led to more stable CERAMERS of titanium tetra-iso-propoxide (TiOPr) reacted with the functionalized P'TMO as well as a fourth inorganic/organic hybrid material based upon zirconium tetra-n-propoxide and PTMO. Indeed, the mechanical properties of the TiOPr/P'TMO CERAMERs and ZrOPr/P'TMO CERAMERs were significantly enhanced over the TEOS/PTMO CERAMERs in terms of both Young's modulus and stress at break. The structure-property relationships of these materials were adequately described by the morphological model originally developed for the CERAMERs based upon TEOS/PTMO. / Ph. D.

Superplasticity and superionic conductivity (SIC), both thermally activated processes, have been independently observed in certain materials with a high diffusion coefficient in high temperature ranges. Intuitively, this observation leads one to the idea that both types of behavior may be inter-related with one another. Therefore, it is the purpose of this research to investigate, specifically, the deformation characteristics of two SIC's, Bi₂O₃ and YSZ (yttria-stabilized zirconia), and to attempt a correlation of their behavior. Compressive deformation of these two materials was conducted over a wide range of temperatures and at various strain rates in an effort to characterize the temperature and/or strain-rate dependences of any observed superplasticity. Steady-state flow stress values were utilized to calculate the strain-rate sensitivity, m, of the materials, as well as the activation energies (Q_C) of superplasticity. Next, the obtained values of Q_C. were compared to SIC activation energies from the literature. Bi₂O₃ exhibited structural superplasticity within the range of test conditions utilized. However, published values of SIC activation energy were lower than experimentally derived Q_C by a factor of four. Therefore, one is not able to state whether or not there is any correlation between the two behaviors. Unfortunately, YSZ exhibited brittle behavior over the entire temperature and strain-rate ranges, so the same analysis could not be performed. Furthermore, SEM micrographs showed that YSZ samples, as processed, did not possess the proper microstructure required for superplasticity. Hence, no final conclusions on YSZ can be drawn from this study. / Master of Science

Over the last twenty years, substantial emphasis has been placed on the development of a new class of inorganic glasses using the sol-gel approach. This technique utilizes metal alkoxide precursors such as tetraethylorthosilcate (TEOS) to build an inorganic glass matrix out of solution by a two step poly(hydrolysis-condensation) reaction mechanism. The benefits of making ceramics by this method include considerable energy savings due to the lower sintering temperatures required to form the densified glass and the ability to produce multi-component amorphous materials that can not be made through the traditional firing processes. As a result of this last possibility, polymer researchers have sought to develop spin-off hybrid inorganic-organic network systems that can be prepared by the sol-gel method using reactively functionalized oligomers and/or monomers along with the metal alkoxide precursors. These types of organically modified multi-component glasses could have enormous potential from an applications standpoint because the system's mechanical and physical features can be tailored in accordance to the organic and polymeric materials chosen. One such inorganic-organic system prepared by this procedure is the new PEK/TEOS glasses. The PEK represents the bisphenol-A polyarylene ether either ketone thermoplastic polymer endcapped with triethoxysilane functional groups. By mixing the PEK and TEOS components at different weight compositions in the starting sol-gel reaction solution, change in the mechanical properties is observed as the TEOS content is increased for the final, thin film glasses. Also, a poor extent of reaction or degree of incorporation of the PEK oligomer is revealed which has been attributed to the vitrification of the glass before the PEK endgroups have a chance to react. To alleviate this problem, thermal treatments are employed to further the sol-gel reaction and to complete the network formation in the PEK/TEOS glasses. After the thermal treatments, the change in the mechanical and physical properties are monitored, and the data reflects systematic trends in regards to the TEOS content and the temperature of the thermal treatment utilized. In addition to these results, some speculative information is provided on the temperature sensitivity and the rate of curing of the PEK/TEOS glasses during the thermal treatments. / Master of Science

This research was undertaken as a contribution to the study of light weight ceramic materials. Specifically the relationship of bulk density and strength was investigated and an empirical equation for the type Y=aX^b, where Y represents unit crushing strength and X represents bulk specific gravity, was found to agree with the data. It was found that a rational theory for the strength of light weight ceramic materials is possible of attainment. / Master of Science

X-ray techniques were used extensively in this work to examine ceramic samples. The well known techniques including : (1) identification of phases and chemical species, (2) peak separation, (3) quantitative phase analysis, (4) intensity band simulation, and (5) line shape analysis, were applied to ceramic materials of silicon nitride, zirconia toughened alumina, fully and partially stabilized zirconia. A theoretical derivation of the x-ray intensity from a rough sample based on a statistical roughness model was carried out. The statistical model was then combined with the intensity band simulation technique to simulate the intensity band from a rough sample. The modified technique for intensity band simulation was used to determine the strain profile in the near surface regions of a flat and a rough fully stabilized zirconia samples. The results show that a compressive zone is present in the near surface region of each sample. A partially stabilized zirconia disk was examined using symmetrical and asymmetrical diffraction optics after a prolonged pin on disk wear test. The different diffraction optics provided different probe depths and revealed a depth gradient of the phase distribution. A general picture of the wearing process of ceramic components is described based on the examinations carried out in this work. / Ph. D.

Solid-state reaction and sol-gel processing methods were used to prepare samples of (Ca_{1 - X,}Mg_X)Zr₄(PO₄)₆(CZP-CMZP) where x = 0.0-0.4. CMZP is a member of the NaZr₂(PO₄)₃ (NZP) class of ceramics and is being investigated for heat engine applications. Linear thermal expansion was determined with a dual push rod dilatometer and axial thermal expansion by high temperature X-ray diffraction and least squares refinement. Thermal diffusivity was determined with the laser flash method and specific heat by differential scanning calorimetry. Thermal conductivity was found by the product of the thermal diffusivity, specific heat, and bulk density of each sample. Results indicate that CMZP samples exhibit very low α̅_L values which become more positive as Mg²⁺ content is increased. Thermal expansion anisotropy (from room temperature to 1000°C) is significantly reduced by the addition of Mg²⁺. Samples where x = 0.4 exhibit the lowest anisotropy with α_a being essentially zero (hexagonal system). The thermal conductivity of CMZP samples is very low (0.56 W/m K at 200°C). Thermal conductivity values were observed to decrease with increasing Mg²⁺ content. The materials structure and cation site selection are discussed in relation to the observed properties. / Master of Science

Piezoelectric actuators frequently exhibit a time-dependent behavioral phenomenon known as hysteresis, resulting in a lag in the deformation of the actuator compared to linear models. The presence of hysteresis complicates control systems involving piezoelectric actuators. However, traditional modeling methods for piezoelectric actuated smart structures often treat the piezoelectric patches as linear actuators without considering hysteresis, leading to suboptimal controller performance. This thesis aims to establish a comprehensive model by integrating the Euler-Bernoulli beam bending model with the hysteresis dynamics induced by two opposing piezoelectric patches attached to a beam. A model expansion method is employed to transform the partial differential equations describing beam vibration into a set of ordinary differential equations in the modal coordinate frame. These equations are then coupled with the Bouc-Wen model describing the hysteresis of piezoelectric materials. Model parameters are identified using a genetic algorithm tested against experimental data across varied excitation frequencies. The experimental dataset is divided into two sets: a training set for the genetic algorithm and a validation set to verify the identified model. Results demonstrate that the inclusion of hysteresis in a nonlinear model provides better agreement with experimental results than the linear model, thereby enhancing the predictive capability of piezoelectric actuator behavior. This thesis has laid the foundation for future work on advanced control methods to mitigate beam vibration under external excitation, thus optimizing smart structure performance.

The gaseous alkali corrosion kinetics of silicon carbide, silicon nitride, alumina, mullite, cordierite, transformation toughened zirconia, and aluminum titanate were systematically investigated from 950°C to 1100°C in dry air containing 1.0 +/- 0.1 vol% alkali. The linear reaction rates observed at all temperatures indicate that the alkali corrosion of Si,N, and SiC is interfaced-controlled with an activation energy of 199 and 104 kJ/mol, respectively. The overall reaction in these materials involves a complex absorption-dissolution-oxidation process and the rate-controlling step appears to be the interfacial oxidation of Si,N, or SiC to SiO,. Linear alkali reaction rates were observed for alumina, resulting in the formation of sodium aluminate which occurs in a relatively planar fashion at low temperatures and in beta-alumina at higher temperatures with an experimental activation energy of 200 kJ/mol. The beta alumina forms in laths along the grain boundaries such that the fast ion conduction plane is perpendicular to the sample surface. Linear reaction rates were also observed for mullite at all temperatures with an experimental activation energy of 182 kJ/mol, resulting in the formation of sodium aluminate and carnegieite. The alkali reaction rate of cordierite is linear at low temperatures and parabolic at higher temperatures, apparently due to the change in reaction layer morphology from a highly porous to a more dense structure. The observed alkali reaction rate of transformation toughened zirconia is linear at all temperatures with an experimental activation energy of 229 kJ/mol. The fragile alkali reaction layer which formed on aluminum titanate resulted in a very large dimensional change (approximately 25%) for short times at 950°C. The reaction products which formed from long isothermal heat treatments of cordierite, zirconia, and calcia stabilized zirconia powders mixed with sodium or potassium carbonate were investigated. Observed phases as a function of composition, temperature and time are presented. Subsolidus phase equilibria in the soda-alumina-titania system were investigated and a tentative subsolidus ternary phase diagram for the low soda portion of this system is presented. / Ph. D.

No description available.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 164-176).