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Oblique ion texturing of yttria-stabilized zirconia: The {l_brace}211{r_brace}<111> structure

Description: Amorphous (Zr,Y)O{sub x} films were synthesized by reactive magnetron sputtering and subsequently crystallized by oblique ion bombardment. Crystalline texture nucleated by the ion beam was replicated by solid-phase epitaxial growth throughout the formerly amorphous yttria-stabilized zirconia (YSZ) film. The resulting YSZ films have (211) orientation normal to the substrate with in-plane directions (111), parallel, and (110), transverse, to the azimuth of the ion beam. We hypothesize that the texture mechanism involves ion-induced film compression and shear. The results, taken together with prior work, show that oblique ion texturing of amorphous films is a general phenomenon that can be used to fabricate substrates with more than one type of crystallographic orientation.
Date: July 1, 2002
Creator: Berdahl, Paul; Reade, Ronald P.; Liu, Jinping; Russo, Richard E.; Fritzemeier, Les; Buczek, David et al.
Partner: UNT Libraries Government Documents Department

Microwave Processing of Simulated Advanced Nuclear Fuel Pellets

Description: Throughout the three-year project funded by the Department of Energy (DOE) and lead by Virginia Tech (VT), project tasks were modified by consensus to fit the changing needs of the DOE with respect to developing new inert matrix fuel processing techniques. The focus throughout the project was on the use of microwave energy to sinter fully stabilized zirconia pellets using microwave energy and to evaluate the effectiveness of techniques that were developed. Additionally, the research team was to propose fundamental concepts as to processing radioactive fuels based on the effectiveness of the microwave process in sintering the simulated matrix material.
Date: August 29, 2010
Creator: Clark, D.E. & Folz, D.C.
Partner: UNT Libraries Government Documents Department

Dynamic response of physisorbed hydrogen molecules on lanthanide-modified zirconia nanoparticles

Description: We investigated the microstructure and surface properties of ultrafine Ce- and Nd-modified zirconia powders by a joint adsorption-isotherm and neutron-scattering study. While the average pore size distribution and specific surface area can be determined by BET analysis of nitrogen adsorption, neutron inelastic scattering from surface adsorbed hydrogen provides additional information about the modulation of local potential energies over the substrate surfaces and distinguishes subtle differences in the microporous and mesoporous structure of the two samples.
Date: December 31, 1996
Creator: Loong, C.K.; Trouw; Ozawa, Masakuni & Suzuke, Suguru
Partner: UNT Libraries Government Documents Department

Stability of eutectic interface during directional solidification

Description: Directional solidification of eutectic alloys shows different types of eutectic morphologies. These include lamellar, rod, oscillating and tilting modes. The growth of these morphologies occurs with a macroscopically planar interface. However, under certain conditions, the planar eutectic front becomes unstable and gives rise to a cellular or a dendritic structure. This instability leads to the cellular/dendritic structure of either a primary phase or a two-phase structure. The objective of this work is to develop a fundamental understanding of the instability of eutectic structure into cellular/dendritic structures of a single phase and of two-phases. Experimental studies have been carried out to examine the transition from a planar to two-phase cellular and dendritic structures in a ceramic system of Alumina-Zirconia (Al{sub 2}O{sub 3}-ZrO{sub 2}) and in a transparent organic system of carbon tetrabromide and hexachloroethane (CBr{sub 4}-C{sub 2}Cl{sub 6}). Several aspects of eutectic interface stability have been examined.
Date: April 23, 1996
Creator: Han, S.H.
Partner: UNT Libraries Government Documents Department

Development of high performance refractory fibers with enhanced insulating properties and longer service lifetimes: Phase 2, Improved refractory fiber and industrial benefit development. Final report

Description: This is Phase II of a three-phase study for the development of high performance refractory fibers with enhanced insulating properties and longer service lifetimes, for use in the aluminum, glass, cement, and iron and steel industries. Fiberization of 24 out of 25 compositions in the Al{sub 2}O{sub 3}-Si0{sub 2}-Zr0{sub 2} system were achieved. These 24 and three existing fiber compositions were evaluated: The shrinkage and the crystalline and vitreous phases were determined vs heat treatment time and temperature. Four theoretical models were developed: Shrinkage, devitrification kinetics, density change, and fiberization. Although some of the fibers formed during Phase II had properties as good as the reference ASZ fiber, no fiber had a significantly improved performance. This work, although not entirely successful, did produce significant benefits to refractory insulating fiber manufacturers and users: Mechanisms of both linear and thickness shrinkage for vitreous refractory fibers were determined, devitrification kinetics were quantified and used in models to predict shrinkage during service, and the mechanism of fiber formation in the melt spinning process was studied.
Date: May 1, 1995
Creator: Cai, Yifang; Curtis, J.M.; DePoorter, G.L.; Martin, P.C. & Munoz, D.R.
Partner: UNT Libraries Government Documents Department

Synthesis and microstructure of powder and porous ZrO{sub 2} from hydrolysis process

Description: Powder and porous ceramics of ZrO{sub 2} are useful as starting materials for composites, catalytic supports, and absorbates. ZrO{sub 2} is, in practice, used as promoter composition in automotive catalyst. Hydrolysis results in advantage on possible control of primary particle size and its dispersion/aggregate state. This study focuses on crystal structure, microstructure, and porous structure in powder and porous ceramics of ZrO{sub 2}. The agglomeration reaction was controlled by pH in a solution resulting from hydrolysis of aqueous ZrOCl{sub 2}. We used neutron diffraction, small angle neutron scattering, and BET adsorption. Results clarify some factors in the well-controlled processing using hydrolysis for porous ZrO{sub 2} ceramics.
Date: March 1, 1997
Creator: Ozawa, M.; Suzuki, S.; Loong, C.K. & Thiyagarajan, P.
Partner: UNT Libraries Government Documents Department

An investigation of particle trajectories and melting in an air plasma sprayed zirconia

Description: The partially stabilized zirconia powders used to plasma spray thermal barrier coatings typically exhibit broad particle-size distributions. There are conflicting reports in the literature about the extent of injection-induced particle-sizing effects in air plasma-sprayed materials. If significant spatial separation of finer and coarser particles in the jet occurs, then one would expect it to play an important role in determining the microstructure and properties of deposits made from powders containing a wide range of particle sizes. This paper presents the results of a study in which a commercially available zirconia powder was fractionated into fine, medium, and coarse cuts and sprayed at the same torch conditions used for the ensemble powder. Diagnostic measurements of particle surface temperature, velocity, and number-density distributions in the plume for each size-cut and for the ensemble powder are reported. Deposits produced by traversing the torch back and forth to produce a raised bead were examined metallographically to study their shape and location with respect to the torch centerline and to look at their internal microstructure. The results show that, for the torch conditions used in this study, the fine, medium, and coarse size-cuts all followed the same mean trajectory. No measureable particle segregation effects were observed. Considerable differences in coatings microstructure were observed. These differences can be explained by the different particle properties measured in the plume.
Date: December 31, 1996
Creator: Neiser, R.A. & Roemer, T.J.
Partner: UNT Libraries Government Documents Department

In situ ion-beam analysis and modification of sol-gel zirconia thin films

Description: We report the investigation of ion-beam-induced densification of sol-gel zirconia thin films via in situ ion backscattering spectrometry. We have irradiated three regions of a sample with neon, argon, and krypton ions. For each ion species, a series of irradiation and analysis steps were performed using an interconnected 3 MV tandem accelerator. The technique offers the advantages of minimizing the variation of experimental parameters and sequentially monitoring the densification phenomenon with increasing ion dose.
Date: May 1, 1995
Creator: Levine, T.E.; Yu, Ning; Kodali, P.; Walter, K.C.; Nastasi, M.; Tesmer, J.R. et al.
Partner: UNT Libraries Government Documents Department

Vibrational Raman and Optical Studies of Cm in Zirconia-Based Pyrochlores and Related Oxides Matrices

Description: Raman spectroscopy has been employed to follow the phase behavior of Cm-Zr oxide materials as a function of Cm:Zr ratio. Three different structural phases, monoclinic, cubic and pyrochlore, are formed when the Cm:Zr ratio is varied from &gt;0 to 1. Each phase produces a distinct Raman profile in the 100-700 cm{sup -1} spectral region. Up to 10 atom % Cm, the Raman spectra indicate that the monoclinic structure is dominant. Raman bands corresponding to the monoclinic phase are absent in samples containing 20 - 40 atom % Cm. Concomitantly, a band at -600 cm' broadens and increases in intensity with increasing curium content, indicating that the cubic phase is dominant in this concentration range. The pyrochlore oxide structure, which forms at 50 atom % Cm, generates three Raman bands (the center of mass are at 283, 387,495 cm-') out of six bands predicted by nuclear site group analyses. The strongest of these is at 283 cm-', and corresponds to the O-Cm-O bending mode. Details of these studies will be compared and discussed with data obtained for comparable systems containing selected analogous 4f-elements.
Date: November 2, 2001
Creator: Assefa, Z.
Partner: UNT Libraries Government Documents Department

Superplasticity and joining of zirconia-based ceramics

Description: Steady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1,250 and 1,350 C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1,200 C.
Date: December 10, 1999
Creator: Dominguez-Rodriguez, A.; Gutierrez-Mora, F.; Jimenez-Melendo, M.; Chaim, R. & Routbort, J. L.
Partner: UNT Libraries Government Documents Department

Characterization of intergranular phases in tetragonal and cubic yttria-stabilized zirconia

Description: Achieving superplasticity in fine grained ceramics is a potential method to lower energy costs associated with ceramic manufacturing via net shape forming. Superplasticity is intrinsic in 3-mol%- yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP); and can be enhanced by addition of glass to form intergranular phases which are thought to both limit grain growth and promote grain boundary sliding during processing (sintering and hot isostatic pressing). This permits processing at lower temperatures. However, superplasticity has not been observed in 8-mol%-yttria-stabilized cubic zirconia (8Y-CSZ), ostensibly due to its larger grain size and high grain growth rates. As part of a larger study, high-spatial-resolution energy-dispersive X-ray spectrometry (EDS) has been performed on 3Y-TZP and 8Y-CSZ specimens doped with various glassy phases to characterize intergranular compositions.
Date: March 1, 1998
Creator: Evans, N.D.; Imamura, P.H.; Mecartney, M.L. & Bentley, J.
Partner: UNT Libraries Government Documents Department

A model for residual stress evolution in air-plasma-sprayed zirconia thermal barrier coatings

Description: Ruby fluorescence spectroscopy indicates that residual stress in air-plasma-sprayed zirconia thermal barrier coatings is a function of the local interface geometry. The stress profile of a simulated rough interface characterized by ``peaks'' and ``valleys'' was modeled with a finite-element approach that accounted for thermal mismatch, oxide scale growth, and top coat sintering. Dependence of the stress profile on interface geometry and microstructure was investigated, and the results were compared with measured stresses.
Date: February 28, 2000
Creator: Nair, B. G.; Singh, J. P. & Grimsditch, M.
Partner: UNT Libraries Government Documents Department

Technical Status Report: Preliminary Glass Formulation Report for INEEL HAW. Revision 1

Description: Preliminary glass formulation work has been initiated at Pacific Northwest National Laboratory (PNNL) and the Savannah River Technology Center (SRTC) to support immobilization efforts of Idaho National Engineering and Environmental Laboratory (INEEL) high activity waste (HAW). Based on current pretreatment flow sheet assumptions, several glasses were fabricated and tested using an average `All Blend` waste stream composition which is dominated by the presence of ZrO{sub 2} (i.e., approximately 80 wt percent). The results of this initial work show that immobilization via vitrification is a viable option for a specific INEEL HAW waste stream. Waste loadings of at least 19 wt percent can be achieved for the `All Blend` stream while maintaining targeted processing and product performance criteria. This waste loading translates into a ZrO{sub 2} content in excess of 15 wt percent in the final glass waste form. Frits developed for this work are based in the alkali borosilicate system. Although the results indicate that vitrification can be used to immobilize the `All Blend` waste stream, the glass compositions are by no means optimized.
Date: March 1998
Creator: Peeler, D.; Reamer, I.; Vienna, J. & Crum, J. A.
Partner: UNT Libraries Government Documents Department

Vitreous bond CBN high speed and high material removal rate grinding of ceramics

Description: High speed (up to 127 m/s) and high material removal rate (up to 10 mm{sup 3}/s/mm) grinding experiments using a vitreous bond CBN wheel were conducted to investigate the effects of material removal rate, wheel speed, dwell time and truing speed ratio on cylindrical grinding of silicon nitride and zirconia. Experimental results show that the high grinding wheel surface speed can reduce the effective chip thickness, lower grinding forces, enable high material removal rate grinding and achieve a higher G-ratio. The radial feed rate was increased to as high as 0.34 {micro}m/s for zirconia and 0.25 {micro}m/s for silicon nitride grinding to explore the advantage of using high wheel speed for cost-effective high material removal rate grinding of ceramics.
Date: August 1, 1998
Creator: Shih, A.J.; Grant, M.B.; Yonushonis, T.M.; Morris, T.O. & McSpadden, S.B.
Partner: UNT Libraries Government Documents Department

Technical Status Report: Preliminary Glass Formulation Report for INEEL HAW

Description: This study was performed by a team comprising experts in glass chemistry, glass technology, and statistics at both SRTC and PNNL. This joint effort combined the strengths of each discipline and site to quickly develop a glass formulation for specific INEEL HAW.
Date: March 1998
Creator: Peeler, D.; Reamer, I.; Vienna, J. & Crum, J. A.
Partner: UNT Libraries Government Documents Department

Tribological properties of hard carbon films on zirconia ceramics

Description: This study investigated the tribological properties of hard diamondlike carbon (DLC) films on magnesia-partially-stabilized zirconia (MgO-PSZ) substrates over a wide range of loads, speeds, temperatures, and counterface materials. The films were 2 {micro}m-thick and produced on by ion-beam deposition at room temperature. Tribological tests were conducted on a ball-on-disk machine in open air of 30 to 50% relative humidity under contact loads of 1 to 50 N, at sliding velocities of 0.1 to 6 m/s, and at temperatures to 400{degrees}C. A1{sub 2}O{sub 3} and Si{sub 3}N{sub 4} balls were also used and rubbed against the DLC-coated MgO-PSZ disks, primarily to assess and compare their friction and wear performance to that of MgO-PSZ balls. A series of long-duration lifetime tests was run at speeds of 1, 2, and 6 m/s under a 5-N load to assess the durability of these DLC films. Test results showed that the friction coefficients of MgO-PSZ balls sliding against MgO-PSZ disks were in the range of 0.5-0.8, and the average specific wear rates of MgO-PSZ balls ranged from 10{sup {minus}5} to 5 {times} 10{sup {minus}4} mm{sup 3}/N.m, depending on sliding velocity, contact load and ambient temperature. The friction coefficients of MgO-PSZ balls sliding against the DLC-coated-MgO-PSZ disks varied between 0.03 to 0.1. The average specific wear rates of MgO-PSZ balls were reduced by factors of three to four orders of magnitude when rubbed against the DLC coated disks. These DLC films could last 1.5 million to 4 million cycles, depending on sliding velocity. Scanning electron microscopy and micro-laser Raman Spectroscopy were used to elucidate the microstructural and chemical nature of DLC films and worn surfaces.
Date: December 31, 1995
Creator: Erdemir, A.; Bindal, C.; Fenske, G.R. & Wilbur, P.
Partner: UNT Libraries Government Documents Department

A laser spectroscopic study of Nd-doped Zirconia

Description: High-surface-area rare-earth (RE) modified zirconia powders prepared by solution methods can be used as catalytic support of noble metals and as electrolyte oxygen sensors in automobile exhaust-emission- control systems. Previous neutron-scattering study showed that substituting Zr with trivalent RE ions not only stabilizes the cubic and tetrgonal phases over a wide range of temperatures but also creates oxygen vacancies in the RE-Zr oxide solid solution. This work focuses on Nd fluorescence in Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} powders under laser excitation of the Nd{sup 3+} ground state to the {sup 4}G{sub 7.2} states. Distinct features were found at 8K in the {sup 4}I{sub 9/2}{r_arrow}{sup 4}G{sub 7/2} excitation and {sup 4}F{sub 3.2}{r_arrow}{sup 4}I{sub 9/2} emission spectra using two sets of incident and emission frequencies, respectively. Results are discussed in terms of site-sensitive local structures surrounding the Nd ions in the two-phased oxide structure.
Date: June 1, 1996
Creator: Loong, C.-K.; Liu, G.K.; Ozawa, M. & Suzuki, S.
Partner: UNT Libraries Government Documents Department