OBJECTIVES: To evaluate the mechanical and physical properties of three glass-ceramic CAD/CAM systems; Vita Suprinity PC (Vita ZahnFabrik), Cerrec Tessera (Dentsply-Sirona), and IPS e.max CAD (Ivoclar Vivadent). MATERIALS AND METHODS: For each material, CAD/CAM blocks were sectioned into a total of N=108 (n=12 per group) test discs with a diameter of 11.3 mm core drill and used the precision saw machine. Specimens were divided into three groups (1) glaze control, (2) polish only, and (3) ground after manufacturer glaze. Specimens were randomly assigned for the biaxial flexural strength test then each group was tested under three conditions post-treatment: (1) static, (2) thermal cycling for 5000 cycles, and (3) cyclic loading at 200,000 cycles. The biaxial flexural strength test was preformed according to ISO 6872-2015 using an Instron universal testing machine. Thermal artificial aging cycling was from 5° to 55°C, while fatigue was used for about 20% of the static failure load for 200,000 cycles. Vickers indentation was performed to test microhardness and fracture toughness. Also, surface roughness was measured for each group using a stylus contact profilometer. Additionally, surface topography and crystal microstructure analysis by SEM and crystallographic structural analysis by X-ray diffraction were done. Data were analyzed using one-way ANOVA test or least square regression (α = 0.05) and the post hoc Tukey HSD test. RESULTS: Significant differences were observed in the mean of biaxial flexural strength between the three glass-ceramics materials. The highest mean flexural strength for static was IPS e.max CAD 385.91 ± 46.23 MPa, then Vita Suprinity PC glazed 355.72 ± 72.44 MPa, followed by CEREC Tessera glazed 323.40 ± 61.01 MPa. After thermal cycling and fatiguing, there were no significant effects in flexural strength for CEREC Tessera; however, there was an increase in flexural strength for IPS e.max CAD and Vita Suprinity PC. Vickers Hardness was highest for CEREC Tessera with 7.19 ± 0.47 GPa, then Vita Suprinity PC at 7.05 ± 0.73 GPa, followed by IPS e.max CAD 5.79 ± 0.77 GPa. The fracture toughness for IPS e.max CAD was the highest with 1.97 ± 0.12 MPa.m1/2, CEREC Tessera 0.93 ± 0.05 MPa.m1/2, and Vita Suprinity PC 0.85 ± 0.08 MPa.m1/2. CONCLUSIONS: IPS e.max CAD polished outperformed Vita Suprinity PC and CEREC Tessera with respect to flexural strength under different aging conditions. In contrast, Vita Suprinity PC had the highest strength in every aging condition among the glazing group. Clinically Significant: Although all three materials might be suitable for single restorations, caution is needed when choosing material, especially as the rough surface from clinical adjustments may reduce its strength.

This project studies the generation of crystalline mesoporous structured titanium dioxide (TiO2) using cellulose nanocrystal (CNC) aerogel hard templates for photocatalytic and biomaterial applications. Suspensions of CNCs in water varying in solid loading from 20 mg/mL to 100 mg/mL were prepared and frozen at three different temperatures (-20 °C, -40 °C, or -80 °C) using four combinations of hollow cylindrical molds and mold plates with different thermal conductivities (stainless-steel or glass) placed on different heat conductive and insulative substrates (aluminum, polystyrene foam and cardboard). Frozen samples were then freeze dried to sublimate the ice and render a multiscale and mesoporous structure with a variety of microstructural features, including lamellar sheeting, flakes, ribbons, or striations. Ceramic green bodies are then produced by reacting Titanium isopropoxide with water through several different processes to generate amorphous TiO2 either in-situ in the CNC aerogel or as a suspension for infiltration under varying pressure. Green bodies are dried at room temperature, and the extent of ceramic coating of the template is visually determined using SEM imaging. Once dried, crystalline TiO2 are produced through a two-step heat treatment with a CNC burnout at 270 °C and crystallization and sintering at 500 °C, 600 °C, or 1000 °C. The final crystallinity and phase composition is examined using XRD, and the final porosity is determined using BET. Results have shown the ability to satisfactorily coat aerogels under 10 mm in one dimension with TiO2. These samples have been successfully heat-treated to produce both anatase and rutile phase TiO2 while maintaining the macrostructure of the CNC aerogel. Multiscale porosity has been achieved, and samples heat treated at 1000 °C have achieved structural integrity. / Master of Science / Titanium Dioxide (TiO2) is a common material in today's world used in a range of applications including pigments, sunscreens, and thin films. It is a chemically and physically stable material, making it ideal for some biomedical applications including bone and cell growth scaffolds. TiO2 is also photocatalytic and has been used in photovoltaic cells and water decontamination systems to take advantage of this property. While TiO2 has been effectively implemented in these applications, the multiscale, controllable porous structure required for these applications has proven complicated to generate. To help improve this process, cellulose nanocrystal (CNC) aerogels were investigated as tunable hard templates for porous TiO2. Controlled ice templating through alteration of the freezing conditions followed by freeze drying provided a reliable method for the production CNC aerogels with repeatable micro and macrostructures. Testing multiple methods for coating the template in TiO2 led to the successful replication of the template in a ceramic part. The final TiO2 exhibited multiscale porosity with micro and macrostructures matching those of the CNC aerogel template. These parts can be tailored to fit a desired application by controlling the structure of the aerogel.

M.S.

Calcium lanthanum sulfide (CLS) has been identified as a candidate material for various optical applications due to its wide transmission range, high refractive index, desirable thermo-optic properties, and refractory behavior. Implementation of CLS in optical systems has remained unrealized due to various difficulties in the synthesis and bulk fabrication of this material. The key challenge facing the development of CLS is the incorporation of oxygen and the presence of unwanted secondary phases related to the lack of control of stoichiometric variations across the ternary phase diagram. Though these difficulties have been previously discussed in the processing of CLS, the exact form, mechanisms of formation and impact of these attributes have not been systematically evaluated. Each of these problems must be meticulously elaborated upon to understand what processing conditions are needed to avoid these common pitfalls which have been shown to degrade the ultimate optical quality of the resulting ceramic. This thesis investigated the role of oxygen in CLS ceramics as it applies to the resulting optical quality of the processed ceramic. The research done specifically examined ceramic materials with high La- content, prepared by hot pressing and hot isostatic pressing. The materials chosen for this work displayed varying levels of optical quality and phase purity. Determination of the desired cubic crystal structure as the main phase present was confirmed using x-ray diffraction and transmission electron microscopy. Through the correlation of data from multiple material metrology tools, the concentration and bond environment of oxygen in the ceramics and starting powders has been determined. It has been shown that the role of oxygen does not necessarily induce local phase transformation in the crystalline material, but rather can be dissolved into the CLS crystal lattice in low levels. Raman spectroscopy has been identified as a simple, useful tool that can be used to aid future synthesis routes due to its ability to differentiate the different types of O present. This thesis demonstrates how low levels of oxygen impurities can be incorporated into the CLS lattice utilizing simple IR and Raman spectroscopy techniques.

No

No / Although some limited consideration has been given to the possibility of links between the early medieval ceramic traditions of the Western Isles and the souterrain ware of north-east Ireland, these have tended to be framed in the context of supposed Dalriadic cultural infl uence fl owing from Ireland to Scotland. A re-evaluation of the possible relationships between these pottery styles suggests that souterrain ware might instead be seen as part of a regional expansion of western Scottish pottery styles in the seventh¿eighth centuries AD. This raises the question of what social processes might underlie the cross-regional patterning evident in what remains a vernacular, rather than a high-status, technology.

No description available.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 166-212).

Processing of Bulk Metastable Oxide Ceramics Oxide ceramic materials are extensively used in various modern application domains which require properties such as high temperature stability or creep resistance, wear resistance, chemical stability, useful electronic, optical and magnetic properties. In the diverse arena of materials technology that interlinks processing, structure, properties and performance, the advancement of new processing techniques to develop oxide ceramics facilitates the extension and refinement of their desirable properties and also mitigate their limitation in terms of application. Progress in processing science/technology offers a real impetus to the development of metastable ceramics with novel, non-equilibrium structures that exhibit scientifically interesting properties and have the potential to cater to the requirements of modern application areas. In the absence of the equilibrium state of a material system, metastable states can be formed with amorphous phases, extended solid solutions, metastable crystal structures and nanocrystallinity. Such metastable states can be retained by imposing kinetic constraints, which means that under the conditions of temperature and pressure, atomic mobilities are inadequate for the transformation. Metastable ceramics that are produced using non-equilibrium processing routes, such as rapid solidification, vapour deposition, spray pyrolysis, sol-gel technique etc., have been known to possess potentially useful properties, such as hard and soft magnetic characteristics, semiconductivity, varistor action, optical transmittivity and superconductivity. Apart from possessing attractive properties, a metastable phase may also serve as a precursor to a desired microstructure; for instance, controlled crystallization of an amorphous phase is a possible way enroute to nanocrystalline structure. It was well recognized that the comprehensive study and use of nanostructured and other metastable ceramics requires consolidation of the fine discontinuous forms (powders or flakes) produced from non-equilibrium processing routes, into bulk shapes with greater control on the fine scale of the structure. Such efforts have not been entirely successful. Non-equilibrium processing techniques do not produce the metastable materials in bulk form. Consolidation of metastable ceramics into dense forms needs high temperatures, mechanical activation (in the form of static pressures or shock waves), or a combination of both. Such activation may trigger the transformation of the desired metastable phase into a more stable phase with concurrent grain growth. Conversely, conditions that allow the desired metastable phase to be retained may not be adequate for complete densification. The subject of the present thesis is two-fold: (i) processing of dense amorphous Al2O3-Y2O3 materials through a novel densification route involving hot pressing of amorphous powders, produced by co-precipitation, at low temperatures and moderately high pressures, (ii) detail study of possible deformation mechanisms of the amorphous phase from mechanical testing at elevated temperatures. Unusual deformation behavior of the bulk amorphous material has been related to the densification process. Development of Pressure Consolidation Technique Amorphous powder of composition Al2O3-15 mol% Y2O3 (A15Y) was synthesized by co-precipitating a hydroxide from metal nitrate precursor’s solution by using ammonium hydroxide. Chemical homogeneity was ensured by a molecular level mixing of precursors of aluminium and yttrium at room temperature. The as-precipitated powder undergoes thermal decomposition (pyrolysis) to an amorphous oxide by ~770-800o C. The crystallization temperature was found from thermal analysis to be ~900o C, with γ-Al2O3 as the initial product of crystallization. The true density of the amorphous A15Y phase was measured to be only 2.69 g cm-3 by pycnometry, which is ~2/3 of the assemblage of equilibrium crystalline phases consisted of Al2O3 and YAG. Uniaxial hot pressing was performed with decomposed, classified powders (large agglomerates with sizes more than 10 µm were removed by sedimentation technique) at low temperature of about 630-640o C and moderately high pressure of 710-750 MPa. Pressure was held constant for 30-45 minutes. Cold compaction at pressures of 50-65 MPa for 8-10 minutes was carried out prior to hot pressing to ensure green strength of the compacts. All hot-pressed compacts revealed significant densification (95-96% relative densities) with uniformly distributed fine porosity. X-ray diffraction, electron microscopy analysis, Raman spectroscopy and differential thermal analysis established the amorphous nature of the dense, hot-pressed pellets. The amorphous phase displays an elastic modulus of ~ 50-60 GPa and a hardness of 4-5 GPa, which are considerably lower than those of the crystalline counterpart. Deformation Behavior of Amorphous Al2O3-Y2O3 The experiments described above clearly demonstrated the feasibility of producing bulk metastable ceramics in the Al2O3-Y2O3 system by a novel consolidation (viz., low temperature-high pressure) route of amorphous powders. This section of the thesis concentrates on studying the deformation mechanisms of the amorphous phase, which are found to be characteristic of the temperature domain of the experiment. Uniaxial compression tests at temperatures of 650-850o C with constant engineering strain rates of ~3-4 X 10-4 s-1 were conducted on dense amorphous samples made from the hot-pressed compacts. At a temperature of 850o C, i.e., close to the crystallization temperature, the amorphous phase was characterized by homogeneous deformation with continuous work hardening after yielding, accompanied by an increase in the true density of this glass by 10-12%. X-ray and electron microscopy analysis confirmed that the density increase was not due to the formation of nano-crystals at this high temperature. Raman spectroscopy and differential thermal analysis further corroborates that the glass was amorphous even after deformation. No shear instabilities were formed at the side surfaces due to the deformation. Significantly large compressive longitudinal strains up to about 28% were observed before unloading. Moreover, an interrupted loading-unloading test established that the bulk density increase was monotonic with the existence of multiple amorphous states enroute to a succession of denser structures. A simultaneous increase in both hardness (H) and modulus (E) of the amorphous phase of up to 100% after deformation bolstered this experimental observation of bulk density increment at constant porosity. The above evidence clearly points towards significant structural changes of the amorphous phase during high temperature deformation process and therefore a phenomenon of molecular densification of the amorphous structure through a hierarchy of dense amorphous phases was hypothesized, analogous to density or entropy driven amorphous-to-amorphous phase transitions (polyamorphism). Note that the densification described here does not refer to the conventional removal of porosity in a ceramics. At an intermediate temperature of 725o C, which is significantly (~200o C) below the crystallization temperature, plastic deformation commences at a stress (yield stress) of 700-780 MPa (considerably higher compared to the yield stress at 850o C) and continued to deform plastically with a slowly decreasing flow stress before reaching a plateau. Thus, the glass exhibited flow softening, in contrast to flow hardening observed at 850oC. Plastic deformation of this glass is largely non-viscous through shear instabilities (akin to the low temperature deformation behavior of metallic glass) and resulted in 8% increment in bulk density after deformation. Once again, the amorphous nature of the glass after deformation was confirmed by X-ray and electron microscopy analysis. Therefore, this intermediate temperature domain was characterized by both densification and shear. Deformation at even lower temperature, viz., at the temperature of hot pressing (650o C), was also characterized by elastic-plastic behavior (similar to flow softening described above), with immediate yield drop after yielding and resulted in a fairly large amount of plasticity of about 17% before unloading. The bulk density was found to be increased only by 2%. Another very interesting experimental finding from the present investigation is the time-dependent deformation (viz., creep densification) exhibited by this glass. It was established from the result of longer term creep experiment at 850o C that the glass revealed large uniaxial compression of about 15% with 5.5% densification to a density of 3.02 g cm-3. Strain rate sensitivity of the A15Y glass was revealed by another stress jump test. To summarize, the present thesis elucidates the discovery of a new class of ceramics with unusual physical properties in an amorphous mixture of Al2O3-Y2O3, which is in contrast to the conventional brittle ceramics. This new class of ceramics deforms plastically without any hydrostatic containment, like ductile metal, at temperatures about 1000o C below those at which their crystalline counterpart would deform. The behavior of this amorphous ceramics under stress that leads to unusually large change in shape, density, hardness and modulus with hierarchies of amorphous structures is demonstrated in detail with experimental evidence.

In Japan, ceramics has long been considered a medium associated with elevated aesthetic expression and high cultural capital. However, the late nineteenth and twentieth centuries saw transformations of its epistemological underpinnings. The collapse of the feudal system gave rise to the multivalenced concept of "art craft" (bijutsu kôgei) that included "art ceramics." For individual artists like Tomimoto Kenkichi (1886-1963), ceramics traversed a parallel path with other mediums of modern art that emphasized self-expression and hybridizations of multiple geo-historical sources. Ultimately, these ceramics became significant state-supported symbols of the nation. An analysis of the art, praxis, and theories of Tomimoto Kenkichi presents an ideal case study for illuminating the central mechanisms responsible for the emergence and development of modern Japanese art ceramics. With a wide angle yet critical perspective lacking in previous studies, this dissertation not only reveals Tomimoto's complex individual role in the history of modern ceramics, but also sheds light on the ontology of modern Japanese craft itself. By considering Tomimoto's entire oeuvre-- including calligraphy, ceramics, design goods, painting, and prints--we may track the development of his modernist embrace of the direct observation of nature, abstract form, and original expression. His praxis, synergistically modeled on William Morris and Ogata Kenzan, reveals a modernist stance towards Japanese literati culture in which ceramics became a medium negotiating between British Arts and Crafts design; modernist European sculpture; and Chinese, Korean, and Japanese historical ceramics. The dissertation's diachronic structure charts artistic concepts, ideologies, and creative works from the late Meiji to the mid-Shôwa eras, relying on formal analysis as well as organizational analysis of pedagogical systems, art organizations, and exhibition structures. Chapter One considers Tomimoto's lineal inheritances, university education, and self-study. Chapter Two explores Tomimoto's discourse of self-expression and the equivalency of artistic mediums. Chapter Three deconstructs the image of the ceramic vessel and Tomimoto's discourse of ceramic form according to respective engagements with Joseon porcelain and modernist sculpture. Chapter Four analyzes the sinophilic and modernist aspects of his overglaze enamel porcelain. Finally, Chapter Five surveys the role of exhibitions and preservation efforts in positioning ceramics as art and national tradition.