Thesis (M.S.)--University of Michigan, 1965.

Thesis (Ph. D.)--University of Iowa, 2000. / Supervisor: Clark M. Stanford. Title-page, preliminaries, Certificate of approval, Table of contents and Project summary issued in paper (xii, 13 leaves ; 28 cm.). Includes bibliographical references. Also issued on CD-ROM (144 files, 33.7 megabytes).

Submitted in full compliance with the requirements for the Master of Health Science Degree: Dental Technology, Durban University of Technology, Durban, South Africa, 2017. / Background Shade matching is a challenging aspect of aesthetic dentistry (Vichi et al., 2011). For a long time, aesthetically pleasing prostheses have been achieved using the porcelain-fused-to-metal crown whereby the metal is masked with an opaque layer and then consecutive layers of veneering ceramic are built up (McLean, 1979). The growing popularity of all-ceramic restorations has created a need for an understanding of its colour characteristics in preference to porcelain fused to metal restorations. The study aims to assist dental technicians in making a more informed decision when choosing an all-ceramic system in terms of colour stability. Objectives The objectives were to identify colour changes of the zirconia after each firing cycle and defining if there are any microstructural changes in the zirconia cores after subsequent firing. Methods This is a quantitative study with a sample size of eighteen which was used for each experimental group. Green state zirconia blocks from Cercon (Dentsply DeguDent, USA), Lava (3M ESPE,USA), and Zirkon Zahn (Zirkonzahn Gmbh, Bruneck, Italy) were trimmed, finished and sintered to a final thickness of 0.5mm according to the manufacturers’ instructions. Each sample group was obtained directly from the manufacturer. In each group, nine specimens were shaded and nine were unshaded. The colour of each specimen was recorded before being exposed to firing cycles. This data formed the control group. All specimens were subjected to three firings and spectrophotometer reading. After each firing, SEM analysis was done after one and three firings. There was a total of thirty six specimens x three firings; n = 108. The raw data for the statistical analysis was obtained from the spectrophotometer readings recorded after the firings (n=108). The data of the study was analyzed using the SPSS version 22.0. The data were compared among the three groups using Pearsons chi square tests, where the data of the firings were measured as a binary or nominal variable, and using t-tests where a measured normally distributed variable was compared. The general linear model (GLM) looked at combinations of the variables and their effects on the dependant variable. The Multivariate tests table indicates the actual result of the one-way MANOVA. Results The Cercon results for both the control and experimental groups reveal the same result patterns and was maintained before and after firing. Lava also revealed the same results before and after firing, however, the cores in the control group differed in colour. The Zirkon Zahn system proved to be the least stable in colour. Conclusion This study supports the hypothesis that colour differences would occur relative to the number of firings for shaded zirconia. It can be concluded that Cercon displayed the most stable results in terms of colour. The acumen gained in this study may better assist dental technicians in their selection of an all-ceramic zirconia system. / M

A transmission electron microscopy study involving direct and replicating techniques is directed to a definition of the microstructure of radio frequency-sputtered, thin lead-dielectric cermet films. Once defined, this microstructure is used to obtain theoretical film refractive indices. The Maxwell Garnet theory provides a basis for the theoretical results. Measurements of film transmission and reflectivity are used to obtain rough experimental values for film refractive indices by the Tekucheva method. More exact values are obtained via ellipsometry. The rough Tekucheva values are used to determine the range over which computer calculations interpreting the ellipsometric results must be made. This technique yields accurate values for the film refractive indices. The films are radio-frequency-sputtered from lead glass targets with varying amounts of lead attached to their faces. Three different targets are used, resulting in three sets of films, each containing a different percentage of lead. The lead content of the films is measured by microprobe analysis as well as visual inspection of micrographs. The lower content lead films are seen to consist of tiny balls of lead embedded in the dielectric, as are the intermediate lead content films; but the higher lead content films form metallic networks throughout the dielectric. The lower and intermediate lead content films have indices which agree with the predictions of the Maxwell Garnett theory; but the higher lead content films, whose structure fails to conform to the Maxwell Garnett configuration, have indices whose values diverge from the Maxwell Garnett predictions. It is thus shown that the theory of Maxwell Garnett is valid for thin cermet films whose structure consists of tiny metal balls embedded in a dielectric medium. / Ph. D.

Thesis (Ph.D.) -- McMaster University, 2002. / Adviser: Anthony Petric. Includes bibliographical referernces. Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 2002. / Adviser: Anthony Petric. Includes bibliographical referernces. Also available via World Wide Web.

Thesis (M.S.)--University of Michigan, 1977.

Thesis (M.S.)--University of Michigan, 1977.

Ultra-high temperature (i.e., greater than 2500°C) engineering applications present continued materials challenges. Refractory metal/ceramic composites have great potential to satisfy the demands of extreme environments (e.g., the environments found in solid rocket motors upon ignition), though general scalable processing techniques to fabricate complex shaped parts are lacking. The work embodied in this dissertation advances scientific knowledge in the development of processing techniques to form complex, near net-shape, near net-dimension, near fully-dense refractory metal/ceramic composites with controlled phase contents and microstructure. Three research thrusts are detailed in this document. First, the utilization of rapid prototyping techniques, such as computer numerical controlled machining and three dimensional printing, for the fabrication of porous tungsten carbide preforms and their application with the Displacive Compensation of Porosity process is demonstrated. Second, carbon substrates and preforms have been reactively converted to porous tungsten/tungsten carbide replicas via a novel gas-solid displacement reaction. Lastly, non-oxide ceramic solid solutions have been internally reduced to create intragranular metal/ceramic micro/nanocomposites. All three techniques combined have the potential to produce nanostructured refractory metal/ceramic composite materials with tailorable microstructure for ultra-high temperature applications.

Porous ceramic-metal composites, or cermets, such as nickel zirconia (Ni-YSZ), are widely used as the anode material in solid oxide fuel cells (SOFC). These materials need to enable electrochemical reactions and provide the mechanical support for the layered cell structure. Thus, for the anode supported planar cells, the thermomechanical behavior of the porous cermet directly affects the reliability of the cell. Porous cermets can be viewed as three-phase composites with a random heterogeneous microstructure. While random in nature, the effective properties and overall behavior of such composites can still be linked to specific stochastic functions that describe the microstructure. The main objective of this research was to develop the relationship between the thermomechanical behavior of porous cermets and their random microstructure. The research consists of three components. First, a stochastic reconstruction scheme was developed for the three-phase composite. From this multiple realizations with identical statistical descriptors were constructed for analysis. Secondly, a finite element model was implemented to obtain the effective properties of interest including thermal expansion coefficient, thermal conductivity, and elastic modulus. Lastly, nonlinear material behaviors were investigated, such as damage, plasticity, and creep behavior. It was shown that the computational model linked the statistical features of the microstructure to its overall properties and behavior. Such a predictive computational tool will enable the design of SOFCs with higher reliability and lower costs.