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<p> An investigation is reported of oxygen diffusion in monoclinic zirconia at elevated temperatures. </p> <p> A method was developed for production of solid zirconia spheres of a quality suitable for diffusion measurements. The spheres, 60μ and 90μ diameter were subsequently used for the determination of the coefficient of self-diffusion of oxygen in stoichiometric zirconia at 800°C, 850°C, 900°C, 950°C and 1000°C. Oxygen O18 isotope exchange using mass spectrometry for the gas analysis was employed for this investigation. </p> <p> The oxygen self-diffusion coefficent was found to conform to the Arrhenius equation (see online text for equation) Theoretical considerations indicate that this diffusivity represents virtually the lattice diffusion of oxygen in zirconia. </p> <p> Diffusivities of oxygen in zirconia scale calculated from zirconium oxidation studies are 104 times higher and are believed to be due to short-circuit diffusion through line defects. To substantiate this hypothesis, "slabs" of stoichiometric zirconia scale and irregular, but equiaxed particles of the same material were used for oxygen diffusion experiments employing the same method. The diffusivities for the slabs were 10^3 times higher than those for spheres, supporting the validity of the short-circuit diffusion theory for zirconia scale. </p> <p> Oxygen concentration drop across zirconia scale on metal, during its formation by parabolic kinetics was calculated for 600°C and 850°C, and was found to be 0.04 g/cm3 approximately, while the concentration drop across the interface between the oxide and the oxygen-saturated metal was about 1.07 g/cm3. </p> / Thesis / Doctor of Philosophy (PhD)

Measurements of the high temperature dielectric properties of ceramic materials at microwave frequencies have been made using two different experimental techniques.Data has been collected at frequencies from O.2GHz to 4.0GHz and for sample temperatures up to 1200°C. Detailed cross checking of the high temperature dielectric data obtained by the two techniques has been carried out with the help of other laboratories worldwide. An investigation of the applicability of dielectric mixture equations to practical measurement techniques is reported. The most reliabl~ estimates of permittivity were given by the Landau-Lifshitz, Looyenga equation or by a cube root extrapolation technique.Permittivity data obtained for a series of yttria stabilised zirconia samples, three differently processed silicon nitride samples and ten related glass compositions are presented. Analysis of the frequency and temperature dependence of both components of complex permittivity has been undertaken· in an attempt to identify the physical origins of the dielectric loss mechanisms. For the yttria doped zirconia samples results indicate two distinct loss mechanisms dominant over different temperature ranges. Below approximately 950K a hopping model involving short range motion of oxygen vacancies around fixed dopant ions is proposed. Above 950K thermally activated quantum mechanical tunneling of electrons is suggested as the dominant mechanism. A single loss mechanism for the entire temperature range involving the lattice loss of the silicon nitride network itself is indicated from the measurements of the hot pressed and pressureless sintered silicon nitride samples. For the reaction bonded silicon nitride samples there is evidence of a second loss mechanism due to additional ion impurities above 1410K. The measurements on the oxide glass systems add support to the belief that + 1 charged metal ions will dominate the dielectric properties of glass systems when present. The loss process has an increasing activation energy with increasing temperature which is seen to be consistent with ionic motion within the previously proposed random potential energy model. Differences in the complex permittivity with composition are attributed to variation in ionic size and metal ion-oxygen ion bond strength.

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The use of plasma sprayed ceramic coats as thermal barrier coatings (TBCs) for the protection of metallic structures and equipment from severe thermal, abrasive and corrosive conditions has been documented extensively in the last two decades. The state-of-the-art TBCs consist of a double layer coat. a top ceramic layer and an intermediate bond coat (MCrAIY, M=Ni, Co, Fe) deposited on the alloy substrate. Zirconia, both stabilized and partially stabilized with different oxides has been used as the ceramic top coat due to its low thermal conductivity and low thermal expansion coefficient. Studies of the microstructure of the TBCs have shown aspects that can help the understanding of the properties of the coating. The ternary system ZrOz-Y203-TiCz is believed to offer improved properties when it is compared to Zr02-Y203. However, the use of &02-Y203-Ti02 as TBCs, a major part of this work, is not widely reported in the literature. The purpose of this thesis was to study the microstructure of a plasma sprayed ZrOrY203-TiO2 TBC using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Transmission Electron Microscopy (TEM). The evolution of the Zr41_phase distribution in the ceramic coat was followed by XRD after different heat treatments, with the finding that the cooling rate plays a decisive role in the final Zr42 phase composition. SEM studies allowed a description of the lamellae structure of the Zr02-Y203-TiOz coating. The evolution of the morphology, porosity and crack distribution in the coat after different thermal treatments were followed by SEM. Evidence of incipient sintering is observed in Zr02-Y203-Ti02 coats heated at temperatures higher than 1200 °C. This should lead to poor coating performance. EDS analysis revealed an heterogeneous distribution of titanium through the oating. A detailed microstructural characterization of the as-sprayed coating was done using TEM. Microstructural features such as micro-twins, antiphase-boundaries and mottled morphology associated with "non-transformable" tetragonal ZrO2 phase were identified. It is believed that these microstructural elements promote toughening and thermal stress relief mechanisms that provide the coating with the erosion and thermal shock resistance required for a TBC. The presence of TiO2 is linked to a higher proportion of tetragonal ZrO2 in the Zr02-Y203-Ti02 coating, therefore improved properties of the coating are expected. The addition of TiO2 promotes grain growth and decreases the final density in pressed and sintered Zr02-Y203-TiO2 powders. The results obtained are a contribution to the understanding of the microstructure of TBCs and to the sparse knowledge base of the ZrOrY2O3-TiO2 coatings. Further work should be done in the characterization of the ZrO2-Y2O3-Ti42 coatings and the study of its stability under different conditions in order to determine the real potential of this material offers as an alternative to the better known ZrOrY203 TBC.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: With the improvement of CAD/CAM technology and translucency of zirconia material, the full contour zirconia crown was introduced to offer dentists a metal free, high strength, and acceptable esthetic prosthesis option. In addition, it is claimed that it is possible to make a full contour high translucent zirconia crown close to natural tooth color by using coloring liquid. However, there is little information in the literature regarding the effect of coloring techniques and cement color on the optical properties of high translucent zirconia. Objective :1) To evaluate the effect of the coloring liquid technique on the resulting optical properties of a monolithic high translucent zirconia 2) To evaluate the cumulative effect of the cement color on the resulting optical properties of a monolithic high translucent zirconia. Alternative hypothesis: There is a significant difference in optical properties between the high translucent monolithic zirconia ceramics with different color staining technique. In addition, the use of shaded resin cement has an effect on the final optical properties of high translucent monolithic zirconia ceramics. Materials and methods: 35 specimens of high translucent zirconia (11mm x11mm) with thickness 1mm was divided into 5 groups according coloring technique, as follows: no color, submerge, two layers of painting, four layers of painting, and six layers of painting. All specimens were measured for the Δ E, transparent parameter (TP), and opalescence parameter(OP) by spectrophotometer (CM-2600D) after firing. Forty-two specimens of high translucent zirconia (11mm x11mm) with thickness 1mm were divided into three groups according to cement color, as follows: clear, opaque, and A2. After firing and cementing with ND4 resin Block. The Δ E, TP and OP will be measured by spectrophotometer. Statistics: The data were analyzed with significant level set at 0.05 one way ANOVA followed by pair-wise group comparisons using Fisher’s Protected Least Significant Differences. Result: 1) The shade of cement significantly affected the mean value of ΔE of E-max CAD and BruxZir high translucent zirconia restoration. Using opaque cement combined with E-max CAD resulted in color difference that was above the clinically perceptible level (ΔE> 3.7). 2) With more layers of staining liquid application, the ΔE and value decreased. The six-layered group showed lowest mean delta ΔE value of 22 (0.78). ΔE was significantly different among groups (p<0.0001). The submerged group showed higher ΔE than the all painting groups. Conclusions: Based on the results of the study, the colors of BruxZir high translucent zirconia and E-max CAD restorations were affected by the shade of cement, whereas white opaque resin cement resulted in BruxZir high translucent zirconia more yellowish. The results of the study demonstrated that the staining technique has an influence on value and final color of Lava-Plus high translucent. Therefore, it is recommended to consider staining technique as one of the influential factors on the final color of zirconia crowns.

This thesis describes the processing and testing of homogeneous nickel and fully yttria stabilized cubic zirconia interpenetrating phase composites. This work was part of a research program investigating step graded Functionally Gradient Materials. This work was focused on understanding the deformation behaviour of the interpenetrating composites near the percolation threshold of the ceramic phase. The composite grades selected for this study included the pure materials, nickel and zirconia, as well as composites with volume fractions of zirconia of 5%, 10%, 15%, 20% and 25%. These compositions were selected to provide data near the zirconia percolation threshold. Processing of the composites involved tape casting, lamination, organic removal, reduction, and hot pressing. All composites except the 5% volume fraction achieved densities greater than 98% of theoretical. Tensile testing was performed on composite grades up to and including the 20% zirconia material, and flexural testing was carried out on the 25% material and pure zirconia. The maximum tensile strength of 530 MPa was obtained in the 10% material resulting from load transfer to the zirconia phase. Ductility decreased as the volume fraction of zirconia increased, with no macroscopic plasticity above 15% volume fraction zirconia. Hardness tests and compression tests were carried out on all composite grades and the yield stress was determined.The compressive yield stress was found to be related to the hardness by the equation: H=6σy This relationship is a result of the constraint imposed on the nickel phase by the zirconia network. Measurements of damage in one pure nickel sample were also performed. The area fraction of voids as a function of local strain was found to follow an exponential relationship. The Young’s modulus of each material was determined ultrasonically and found to be uniform as expected. Modeling of the tensile specimens indicated that materials above the zirconia percolation threshold work harden more rapidly than those below it. This is not accounted for in the model by Ravichandran. / Thesis / Master of Engineering (ME)

Spent Nuclear Fuel (SNF) is a by-product of existing nuclear reactors; SNF consists of long-lived radioactive actinides which have an average half-life of several thousand years (e.g. Plutonium-239 with a half-life of 24,000 years, and Americium-243 with a half-life of 7,360 years). Several multinational organizations are making an attempt to extract the energetic value out of these nuclear stockpiles in order to minimize the risk of nuclear proliferation and reduce waste volume. The Inert Matrix Fuel (IMF) concept is being considered as an option to reuse the radioactive actinides present in spent nuclear fuel by means of a transmutation process. Due to the volatile nature of these radioactive actinides, it is expected that the high-temperature conventional processing of IMFs will result in a significant loss of material. This study investigates microwave sintering of inert matrix material (excluding actinide fuel) as an alternative route to conventional processing. It was observed that microwave sintering showed a reduction of 300°C in temperature required for full densification when compared to conventional sintering. The reduction in sintering temperatures did not show any significant variation in the resulting properties (hardness and grain size). While these results satisfy the need for the application, it is important to understand why microwaves enhance the sintering phenomena. It is speculated (by many researchers) that the electric field associated with microwave energy is enhancing flux leading to accelerated densification during microwave sintering. This study has observed a decrease in the activation energy (for sintering 8YZ) with the increase in the magnitude of the applied electric field. / Ph. D.

Aim: The aim is to evaluate the fracture strength and fracture type of long-term water-stored monolithic 3-unit multilayered zirconia fixed dental prostheses (FDPs) depending on connector dimension and placement in disc. Material and method: Thirty-two 3-unit FDPs (212223) of KATANATM Zirconia Yttria Multilayered (YML) were divided into four groups (n=8/group). The EB-groups were placed in Enamel layer/Body layer 1 in the disc, with connector dimensions of 12 mm2 (EB12), or 7 mm2 (EB7). The BB-groups were placed in Body layer 2/Body layer 3, with connector dimensions 12 mm2 or 7 mm2 (BB12 and BB7). All FDPs were long-term water-stored (37° C, one year). They were cemented on die models, cyclic mechanical preloaded (10,000 cycles), followed by fracture strength test. The results were analyzed with one-way ANOVA, Tukey's test, significance level α = 0.05. Fracture type analysis was performed visually and presented descriptively. Result: Group BB12 showed significantly higher strength (2660 N) compared to EB7 with the lowest mean value (1044 N) (p &lt; 0.05). There was no significant difference between the remaining groups. Conclusion: Design and placement of monolithic 3-unit FDPs in multilayered zirconia affects the fracture strength and fracture type.With increased connector dimension the location can be in the upper layer of the disc, and with reduced connector dimension, the location can be in the lower layer. The fractures occur in the connectors of the pontic. With an increased connector dimension and the FDP located in the lower layer, a total fracture will occur / Syfte: Syftet med föreliggande studie är att utvärdera brotthållfastheten och frakturtyp på långtidsvattenförvarade monolitiska 3-leds-broar som framställts i flerskiktad zirkonia med olika konnektordimensioner och placering i disk. Material och metod: Trettiotvå 3-leds-broar med två preparerade tänder, 212223 delades in i fyragrupper (n=8/grupp) beroende på dimensionering av konnektorn och placering i KATANATM Zirconia Yttria Multilayered (YML)-disk. Grupperna EB var placerade i Enamel layer/Body layer 1 i disken,med konnektordimension på antingen 12 mm2 för grupp EB12, eller 7 mm2 för grupp EB7. Grupperna BB var placerade i Body layer 2/Body layer 3 i disken, med konnektordimensionerna 12 mm2 för grupp BB12 respektive 7 mm2 förBB7. Samtliga broar förvarades i vatten, 37° C under ett år. Broarnacementerades på stansmodeller. Efter 24 h genomfördes cyklisk mekanisk förbelastning, 10 000 cykler, följt av ett brotthållfasthetstest. Resultaten analyserades med one-way ANOVA, Tukey’s test,signifikansnivå α = 0,05. Frakturtypsanalys genomfördes visuellt och resultaten presenterades deskriptivt. Resultat: Grupp BB12 hade signifikant högre brotthållfasthet (2660 N) jämfört med EB7 som hade lägst medelvärde (1044 N) (p ≤ 0,05). Mellan övriga grupper fanns det ingen signifikant skillnad.Majoriteten av frakturerna skedde i det hängande ledet. Även totalfrakturer förekom. Slutsats: Utformning och placering av monolitiska 3-leds-broar i ett flerskiktat zirkoniamaterial påverkar brotthållfastheten och frakturtyp. Vid ökad konnektordimension kan placeringen vara i det övre skiktet i disken. Vid minskad konnektordimension kan placering vara i nedre skikt. Frakturerna sker vid det hängande ledet, och vid ökad konnektordimensionering och placering i nedre skikt sker totalfraktur