Transformation induced plasticity was investigated in a model ceramic. The effect upon toughness of the martensitic transformation from the cubic (paraelectric) to the tetragonal ( ferroelectric) phase in BaTiO3 was determined. The K1C fracture toughness, as measured by the hardness indentation technique, exhibits a maximum within a temperature range approximately 50°C above the stress-free transformation temperature. Unlike the martensitic transformation associated with partially stabilized zirconia, there is no volume change during the cubic-to-tetragonal phase change in BaTi03. In addition, no evidence of microcracking was observed. The enhanced toughness in the vicinity of the transition temperature was attributed to limited plasticity at crack tips provided by the transformation shear strains. The effective strains at the crack tips required to produce the observed fracture toughness values are consistent with transformation strains calculated using the phenomenological theory of martensite. / Master of Science

The sintering of (Ca_0.6,Mg_0.4)Zr₄(PO₄)₆ powder (CMZP) synthesized via a new solid-state reaction method was investigated for application as a thermal barrier in next generation internal combustion engines. Specifically, CMZP is being considered as a potential material for the manufacture of exhaust port liners to increase the overall performance of diesel engines. The effects of firing time, firing temperature, and amount of ZnO sintering aid on modulus of rupture (MOR), bulk density, and coefficient of thermal expansion (CTE) were determined for both dry pressed and slip cast samples to optimize the physical properties for this application. For both processing methods, suppressing the formation of secondary interparticle phases (grain boundaries) was found to be the controlling factor for obtaining high strength and positive thermal expansion. For a given ZnO level, increases in firing time and/or temperature resulted in improved density but a degradation in microstructure (undesirable grain growth, formation of a liquid phase, and intra-/trans- granular microcracking), accompanied by a reduction in MOR and negative CTE values. Therefore, optimizing bulk density was determined to be counter-productive for improving strength when ZnO is used as a sintering aid. / Master of Science

The excellent particulate removal efficiency of ceramic candle filters has prompted efforts to develop a more durable and economical alternative to existing ceramic candle filters. Porous ceramic candle filter elements were successfully fabricated from calcium aluminate cement, calcined fireclay aggregate, and organic pore formers using refractory concrete casting techniques. Methods used to characterize the porous ceramic filter elements included determination of pore size and distribution, permeability, resistance to alkali attack, and mechanical strength. Various pore formers and casting, curing, and sintering conditions were examined to produce highly permeable and structurally sound filter elements. The optimized fabrication procedure produced porous ceramic candle filter elements with pore diameters between 20.3 to 43.1 tlm, porosities of 38 to 60%, and pressure drops of 3 to 24 mbars at a face velocity of 100 mjh. These characteristics are comparable to existing ceramic filters which are noted for their > 99% collection efficiencies of submicrometer-sized particles, but short-term durability in advanced coal combustion clean-up systems. Test specimens of the alumino silicate refractory concrete proved more durable by showing no severe attack following exposures to alkali-containing atmospheres at 700-1000°C. The strength of the cast samples ranged from 200 to 1139 psi depending on the relative densities and pore formers. Porous fliter elements with different porous structures, permeabilities, and shapes can be easily produced with this technique. / Master of Science

The strain induced into isotropic flat plates by surface bonded and embedded piezoceramic patches was investigated. The free piezoceramic patch voltage/strain response was characterized using moire interferometry and Twyman-Green interferometry techniques. Moire interferometry experiments were conducted to investigate the induced strain of actuation in a flat plate with two surface bonded piezoceramic patches and a flat plate with one embedded patch. Three-dimensional finite element models of these two specimens were constructed and analyzed. The measured in-plane voltage/strain response of a free piezoceramic patch was found to be nearly linear and of a much higher magnitude than the published data. Similarly, the out-of-plane voltage/strain response was found to be much higher in magnitude than the published data as well as being non-linear. Correlation between the moire experiment concerning the surface bonded patch specimen and the corresponding finite element model was good, indicating the validity of the modeling technique. Possible depoling damage of the embedded patch caused the correlation between the experiment and analysis of this specimen to be poor. Both finite element models predicted stresses that are not statically significant but may represent problems over many loading cycles. / 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

Ceramics are more than merely the most common artifact type in the archaeological record of most parts of the world. While they have long served as chronological markers, they also provide insights into the daily lives of the people who made, used, and exchanged them. In this dissertation I present a study of three ceramic assemblages from the Tlajinga district of Classic period (AD 100 – 650) Teotihuacan, Mexico. I focus on consumption practices and temporal changes by evaluating the ceramics recovered through excavations at two multifamily apartment compounds and a neighborhood center. I first compare the assemblages from each area, then assess how they changed over time. Given that the composition of ceramic assemblages results from different use and depositional practices, one of the main issues addressed is the importance of contextual information for their analysis. Thus, I analyzed primary deposits in relation to stratigraphic data; this way, I provide a basis for the relative dating of the three sites and the refinement of the existing ceramic chronology. Absolute dates came from the largest number of radiocarbon dates analyzed thus far for a residential sector at Teotihuacan. I also employed three analytical techniques: chemical residue analysis to identify vessel contents, and petrographic and neutron activation analysis to identify clay sources. Even though Tlajinga’s inhabitants used most of their utilitarian wares for cooking, storing, and serving purposes, the chemical residue analysis suggests other uses and possible reuses that challenge what we believed was the sole function of certain ceramic vessels. Petrographic and compositional studies group locally manufactured ceramics and distinguish imports into clear provenance clusters, allowing us to better understand interregional exchange and ceramic consumption in Tlajinga. Results illustrate that there is a uniformity in the ceramic assemblages of the two domestic areas but they differ significantly from those recovered from the neighborhood center, of a presumed more public function. This study uses a multidisciplinary approach to demonstrate a clear difference between the private and the public spheres at Tlajinga. This has important implications for understanding urban lifeways and the organization of domestic and neighborhood space at Teotihuacan. / 2025-07-01T00:00:00Z

In order to increase the efficiency and economic viability of solid oxide fuel cells (SOFCs), new materials for the cathode, anode, and electrolyte of the cells must be found. SOFCs have a ceramic electrolyte, which is commonly made of fully stabilized zirconia. Due to increased material degradation rates at elevated temperatures ( ~ 1000°C) of current SOFCs, materials for the manufacture of intermediate temperature SOFCs, which operate in the range of 700-800°C, are currently under study. In this study, the manufacturing process for scandia-ceria stabilized zirconia powder (1 0mol¾ Sc2O3, lmol¾ CeO2, 89mol% ZrO2), from Daiichi Kigenso Kagaku Kogyo (DKKK) is developed, including tape casting and sintering procedures to result in pellets of high enough quality to produce single button cells. It is found that a slip prepared with about 44 wt% zirconia powder and increased proportions of solvents, dispersant, binder and plasticizers produces a favorable viscosity of about 7 40cP after deairing, and will produce tapes that are reasonably smooth and of stable thickness. Since the single cell will be structurally based upon this electrolyte material, the physical properties of the pellets are important, in addition to the electrochemical properties of the constituent materials. Tapes cast at 500µm, at 50% feed rate with a 50°C drying temperature, laminated and sintered at 1500°C on setter plates will produce flat, smooth, stiff pellets for the production of single buttons for use as the electrolyte. Cathode (50-50 mixture of La0.6Sr0_4Fe0_8Co0.2O3 + 20mol% Gd2O3 80mol% CeO2) and Anode (35 wt% DKKK powder, 65 wt% NiO) materials were hand-painted on to either side of the electrolyte and sintered to create a complete SOFC cell consisting of cathode, electrolyte, and anode.

Experimental results of damage development in and mechanical response of heat-treated NicaloniCAS-II laminates subjected to monotonic flexure and axial loading and to cyclic tensile loading are reported. The specimens were subjected to post-processing heat treatments at 900°, 1000°, and l100°C in air for 100 hours. Changes at the fiber/matrix interface/interphase due to post-processing heat treatments were also characterized. The combined effect of fiber debonding and transverse matrix cracking in both 90° and 0° plies plays an important role in damage development in [0/90]₄₅ Nicalon/CAS-II laminates, especially in developing the secondary damage modes such as longitudinal matrix cracking and delamination. Frictional wear effects found in cyclically loaded specimens may be responsible for the observed temperature profiles during the intermediate stage of fatigue life. It is also believed that frictional wear is critical to the failure of notch sensitive fibers. Different damage modes such as "brittle" matrix crack propagation and "quasi-brittle" matrix crack propagation were observed in heat-treated specimens. Results obtained from microanalysis using an analytical scanning transmission electron microscope equipped with an energy dispersive spectrometer, and microindentation indicated that the changes of damage and failure modes were directly related to the changes of characteristics at the fiber/matreix interface/interphase. / Ph. D.

Within this work a study of the vibrations of laminated composite cantilevers exhibiting structural uncertainties and damage is accomplished. The study is performed within both the Classical Lamination (CLT) and the First-order Transverse Shear Deformation Theories (FSDT). Upon comparing the natural frequencies and mode shapes obtained by both theories, the effects of transverse shear deformation will be emphasized. Other nonclassical effects as e.g. the bending-twist coupling and the warping restraint on the cantilevered structure are also considered. As passive techniques of vibration control, structural tailoring and optimization are implemented. To deal with structural uncertainties, a probabilistic discretization technique for the governing system is developed. Statistical properties of natural frequencies are obtained by means of a second-moment method and a first-order perturbation technique. Structural tailoring is reconsidered to reduce the sensitivity of the dynamic behavior to parameter uncertainties. Next, the damage effect on the structure is considered in the design process. As a result, the problem of the robustness of structures in the presence of damage is addressed. This work also deals with the active feedback control of cantilevered structural systems. An efficient control technique for continuous structures, namely modal control, is adopted and the control gain is obtained by an optimal control law. The comparison of controlled and uncontrolled dynamic responses is made between two models based on CLT and FSDT with emphasis on the influence played by transverse shear deformation and warping restraint. / Ph. D.

The lubrication of ceramic materials is a difficult problem; conventional lubrication techniques are limited or often ineffective. Therefore, the concept of tribopolymerization -- originally proposed by Furey and later modified by Furey and Kajdas -- is used as a new approach to boundary lubrication of ceramics. In this approach, potential polymer-forming compounds are used in minor concentrations in a carrier fluid, which polymerize at the contact region under the sliding action to form a protective layer at the contact. Selected monomers -- including one condensation type, C₃₆ dimer acid/ ethylene glycol monoester, and five addition type, i.e., lauryl methacrylate, diallyl phthalate, vinyloctadecyl ether, vinyl acetate and methyl-2-acrylamido-2- methoxy acetate, were used at 1% concentration in hexadecane in pin-on-disk tests with sliding alumina and zirconia ceramic systems. Results showed that wear reductions of alumina by up to 80% were achieved at room temperature. At elevated temperatures (up to 150°C), the monomers were also effective; one of the monomers reduced wear by over 90% at higher temperatures. In the zirconia system, the monomers in general were also effective in reducing wear, but not to the same extent as with alumina. There was no significant effect of the monomers on friction. Detailed surface analytical studies of the worn surfaces lubricated with the monomer solutions using Fourier transform infrared microspectroscopy, X-ray photoelectron spectroscopy and mass spectrometry showed the complex nature of tribochemistry involved in the antiwear action of these monomers. In addition to the polymerization, evidence of chemical reactions of the monomers with the ceramic substrate was found. Using an advanced infrared microscope system, surface temperatures at the lubricated contacts of alumina-on-sapphireand zirconia-on-sapphiresystems were measured for selected monomers. In general the temperatures were very low. Theoretical estimations of surface temperatures using Vick’s model were also carried out for several systems (including the ones studied in the past) and the role of surface temperature in the anti-wear action of the monomers was examined. The relationship is complex; but the general trend suggests that temperatures are important for tribopolymerization of the monoester, whereas not so much so for the addition monomers. A molecular modeling software -- CHEM-X -- was also used to obtain additional insight into the mechanisms of anti-wear action of the monomers. In this exploratory study, 3-dimensional shapes of the monomers, their polymerization mechanisms, and possible orientation of a selected monomer on polymerization mechanisms, and possible orientation of a selected monomer on a ceramic surface was examined. Possible mechanisms of anti-wear action of these monomers are proposed. For the monoester, the mechanism involves (a) an initial adsorption of the carboxylic end of the molecules on the surface, (b) chemical reaction with the surface to form a soap, and (c) the formation and outward growth of oligomer/polymer chains somewhat similar in structure to a Langmuir-Blodgett multi-layer. The mechanism of anti-wear action of the addition monomers is believed to be connected to the negative-ion radical action mechanism (NIRAM) as proposed by Kajdas. According to this mechanism, exoelectron emitted during sliding initiate tribopolymerization of vinyl monomers, and monomers polymerizing only by anionic or free radical mechanisms are capable of tribopolymerization on the ceramic surfaces. It is proposed that the formed polymeric products act as a binding medium for fine wear debris particles generated during sliding. As a result, a strongly bonded debris layer -- somewhat similar to a ceramic powder reinforced polymer composite -- forms on the surface. This layer provides protection to the sliding surfaces against wear. / Ph. D.