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CERIUM AND PLUTONIUM DIOXIDE--NOTES ON REDUCTION TO MASSIVE METAL

Description: In reduction reactions of CeO/sub 2/, with calcium and a CaCl/sub 2/ flux, the use of vibrational energy was shown to have a marked effect on the yield of coalesced metal. Buttons of 40 to 50% theoretical yield were obtained from the vibrated reductions. As the flux concentration is decreased, the slag becomes more viscous containing undissolved CaO. The undissolved CaO present prevents the metal from completely coalescing, but the metal can be recovered from the slag and coalesced under CaCl/sub 2/ containing a small amount of calcium to reduce any oxide skin present. Cerium pellet yields of 50 to 60% metal were obtained by the procedure and were not difficult to handle in air. Cerium was used as a stand-in material for plutonium. (B.O.G.)
Date: February 13, 1956
Creator: Tolley, W. B.
Partner: UNT Libraries Government Documents Department

Determination of Ideal Broth Formulations Needed to Prepare Hydrous Cerium Oxide Microspheres via the Internal Gelation Process

Description: A simple test tube methodology was used to determine optimum process parameters for preparing hydrous cerium oxide microspheres via the internal gelation process.1 Broth formulations of cerium ammonium nitrate [(NH4)2Ce(NO3)6], hexamethylenetetramine, and urea were found that can be used to prepare hydrous cerium oxide gel spheres in the temperature range of 60 to 90 C. A few gel-forming runs were made in which microspheres were prepared with some of these formulations to be able to equate the test-tube gelation times to actual gelation times. These preparations confirmed that the test-tube methodology is reliable for determining the ideal broth formulations.
Date: February 1, 2009
Creator: Collins, Jack Lee & Chi, Anthony
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

Morphology and microstructure of (111) crystalline CeO{sub 2} films grown on amorphous SiO{sub 2} substrates by pulsed-laser ablation

Description: The surface morphology and microstructure of (111)-oriented CeO{sub 2} thin films, grown on amorphous fused silica (SiO{sub 2} substrates by low-energy-ion-beam assisted pulsed laser ablation, have been studied by atomic force microscopy (AFM) and x-ray diffraction (XRD). These CeO{sub 2} films are aligned with respect to a single in-plane axis despite being deposited on an amorphous substrate. There is a honeycomb-like growth morphology to the films and island-growth can be observed in thicker films. These islands, inside of which are high density of honeycomb-like clusters, are separated by a void network with {approximately}700 nm width. However, on the surface of the thinnest film ({approximately}3 nm), only very small clusters (diameter <60 nm) appear, and the boundaries of the void network are undefined, which implies that the film is just beginning to coalesce into clusters (grains). The combined AFM images and XRD pattern suggest these clusters probably are the initial seeds for the subsequent island growth. Based on these results, the growth mechanism of oriented CeO{sub 2} films on amorphous fused silica substrates is discussed.
Date: November 1, 1994
Creator: Zhu, S.; Lowndes, D.H.; Budai, J.D.; Thundat, T.; Norton, D.P. & Warmack, R.J.
Partner: UNT Libraries Government Documents Department

Characterization of ceria-based SOFCs

Description: Solid Oxide Fuel Cells (SOFCs) operating at low temperatures (500-700 C) offer many advantages over conventional zirconia-based fuel cells operating at higher temperatures. Cathode performance is being improved by using better materials and/or microstructures. Fabrication of thin dense electrolytes is also necessary to achieve high cell performances.
Date: December 31, 1996
Creator: Doshi, R.; Roubort, J. & Krumpelt, M.
Partner: UNT Libraries Government Documents Department

Isobutanol-methanol mixtures from synthesis gas. Quarterly technical progress report, October 1, 1996--December 30, 1996

Description: A series of MgO-based Cu catalysts have been prepared by coprecipitating the corresponding metal nitrates with a mixed solution of potassium carbonate and potassium hydroxide. The bulk composition of the catalyst has been measured by atomic absorption (AA) analysis and the Cu dispersion has been determined by N{sub 2}O titration at 363 K. Kinetic studies of ethanol coupling reactions on Cu{sub 0.5}Mg{sub 5}CeO{sub x} and 1.0 wt % K-Cu{sub 0.5}Mg{sub 5}CeO{sub x} catalyst indicates that at similar steady-state acetaldehyde concentrations, the presence of K increases the rates of base-catalyzed aldol coupling reactions to acetone and butyraldehyde. Aldol coupling chain growth reaction rates on 1.2 wt % K-Cu{sub 7.5}Mg{sub 5}CeO{sub x} are higher than on 1.0 wt % K-Cu{sub 0.5}Mg{sub 5}CeO{sub x} even though basic site densities are similar on both samples, suggesting that Cu metal sites are also involved in rate-determining steps required for condensation reactions. Cu appears to enhance the desorption of H{sub 2} via the migration of H species from basic to Cu sites and makes the basic sites available for subsequent C-H bond activation steps. Addition of CO{sub 2} decreases the rate of base-catalyzed chain growth reaction to acetone, but does not affect the rate of ethanol dehydrogenation reaction on Cu metal sites
Date: March 1, 1997
Partner: UNT Libraries Government Documents Department

Superconductive articles including cerium oxide layer

Description: A ceramic superconductor comprising a metal oxide substrate, a ceramic high temperature superconductive material, and a intermediate layer of a material having a cubic crystal structure, said layer situated between the substrate and the superconductive material is provided, and a structure for supporting a ceramic superconducting material is provided, said structure comprising a metal oxide substrate, and a layer situated over the surface of the substrate to substantially inhibit interdiffusion between the substrate and a ceramic superconducting material deposited upon said structure.
Date: December 1991
Creator: Wu, X. D. & Muenchausen, R. E.
Partner: UNT Libraries Government Documents Department

RELATIVE HUMIDITY TESTS IN SUPPORT OF THE 3013 STORAGE AND SURVEILLANCE PROGRAM

Description: Techniques to control the initial relative humidity over oxide/salt mixtures have been developed using cerium oxide as a surrogate for plutonium oxide. Such control is required to validate certain assumptions in the Department of Energy Standard DOE-STD-3013, and to provide essential information to support field surveillance at the storage sites for excess plutonium oxides. Concern over the validity of the assumption that corrosion induced degradation in 3013 containers could be controlled by assuring that the moisture content of any stored oxide/salt mixture was below 0.5 w t% arose when stress corrosion cracks were found in test samples exposed at room temperature to plutonium oxide/salt mixtures having a moisture content only marginally above 0.5 wt %. Additionally, analysis of the stress corrosion cracking observations suggests that the initial relative humidity over the oxide/salt mixture may play a major role in the cracking process. The investigations summarized in this report provide the procedures necessary to control the initial relative humidity to selected values within the range of 16 to 50% by controlling the loading relative humidity (18 to 60%) and the oxide/salt mixture water content (0.05 to 0.45 wt %). The studies also demonstrated that the initial relative humidity may be estimated by calculations using software EQ3/6. Cerium oxide/salt mixtures were used in this study because qualification tests with non-radioactive materials will reduce costs while increasing the breadth of the test programs required to support field surveillances of stored 3013 containers.
Date: August 1, 2011
Creator: Mickalonis, J. & Duffey, J.
Partner: UNT Libraries Government Documents Department

Effect of rogue particles on the sub-surface damage of fused silica during grinding/polishing

Description: The distribution and characteristics of surface cracks (i.e., sub-surface damage or scratching) on fused silica formed during grinding/polishing resulting from the addition of rogue particles in the base slurry has been investigated. Fused silica samples (10 cm diameter x 1 cm thick) were: (1) ground by loose abrasive grinding (alumina particles 9-30 {micro}m) on a glass lap with the addition of larger alumina particles at various concentrations with mean sizes ranging from 15-30 {micro}m, or (2) polished (using 0.5 {micro}m cerium oxide slurry) on various laps (polyurethanes pads or pitch) with the addition of larger rogue particles (diamond (4-45 {micro}m), pitch, dust, or dried Ceria slurry agglomerates) at various concentrations. For the resulting ground samples, the crack distributions of the as-prepared surfaces were determined using a polished taper technique. The crack depth was observed to: (1) increase at small concentrations (&gt;10{sup -4} fraction) of rogue particles; and (2) increase with rogue particle concentration to crack depths consistent with that observed when grinding with particles the size of the rogue particles alone. For the polished samples, which were subsequently etched in HF:NH{sub 4}F to expose the surface damage, the resulting scratch properties (type, number density, width, and length) were characterized. The number density of scratches increased exponentially with the size of the rogue diamond at a fixed rogue diamond concentration suggesting that larger particles are more likely to lead to scratching. The length of the scratch was found to increase with rogue particle size, increase with lap viscosity, and decrease with applied load. At high diamond concentrations, the type of scratch transitioned from brittle to ductile and the length of the scratches dramatically increased and extended to the edge of the optic. The observed trends can explained semi-quantitatively in terms of the time needed for a rogue particle to penetrate into ...
Date: May 2, 2007
Creator: Suratwala, T I; Steele, R; Feit, M D; Wong, L; Miller, P E; Menapace, J A et al.
Partner: UNT Libraries Government Documents Department

High-Temperature Heat Contents and Entropies of Cerium Dioxide and Columbium Dioxide

Description: Experimentally determined heat content and corresponding entropy increment data for cerium and niobium dioxides in the temperature range from 298 to 1800 deg K are presented in tabular form. Equations were derived to represent the heat contents and heat capacities. The data for n dioxide showed two previously unreported anomalies a 1090 and 1200 deg K. (auth)
Date: October 1, 1960
Creator: King, E. G. & Christensen, A. U.
Partner: UNT Libraries Government Documents Department

Development of pair distribution function analysis

Description: This is the final report of a 3-year LDRD project at LANL. It has become more and more evident that structural coherence in the CuO{sub 2} planes of high-{Tc} superconducting materials over some intermediate length scale (nm range) is important to superconductivity. In recent years, the pair distribution function (PDF) analysis of powder diffraction data has been developed for extracting structural information on these length scales. This project sought to expand and develop this technique, use it to analyze neutron powder diffraction data, and apply it to problems. In particular, interest is in the area of high-{Tc} superconductors, although we planned to extend the study to the closely related perovskite ferroelectric materials andother materials where the local structure affects the properties where detailed knowledge of the local and intermediate range structure is important. In addition, we planned to carry out single crystal experiments to look for diffuse scattering. This information augments the information from the PDF.
Date: September 1, 1996
Creator: Vondreele, R.; Billinge, S.; Kwei, G. & Lawson, A.
Partner: UNT Libraries Government Documents Department

Influence of stoichiometry on the electrochromiccerium-titanium oxide compounds

Description: CeO<sub>2</sub>-TiO<sub>2</sub> finds use as passive counter-electrode in electrochromic devices. Thin films were produced by de-sputtering in a wide range of compositions. Influence of total pressure and oxygen partial pressure on the optical constants of TiO<sub>2</sub> was investigated. Slightly substoichiometric Ti0<sub>2</sub> films exhibit a red-shift of the bandgap. The Ti0<sub>2</sub> content in the compound essentially determines the degree of cathodical coloring upon Li<sup>+</sup> intercalation [1]. However, pure TiO<sub>2</sub> films with comparable visible transmittance in the clear state behave differently during electrochemical cycling depending on oxygen stoichiometry. Films that are deposited at higher total pressure are more oxygen rich and require initial formatting until current voltage cycles become stable. CeO<sub>2</sub>-Ti0<sub>2</sub> films of intermediate compositions have the relatively highest charge capacity. Comparison with atomic force microscopy indicates a correlation of small grain size with high charge capacity.
Date: November 1, 1997
Creator: Kullman, L.; Richardson, T.; Rubin, M.; Slack, J. & von Rottkay, K.
Partner: UNT Libraries Government Documents Department

Advanced sulfur control concepts in hot-gas desulfurization technology: Phase 2. Exploratory studies on the direct production of elemental sulfur during the regeneration of high temperature desulfurization sorbents. Topical report

Description: The topical report describes the results of Phase 2 research to determine the feasibility of the direct production of elemental sulfur during the regeneration of high temperature desulfurization sorbents. Many of the contaminants present in coal emerge from the gasification process in the product gas. Much effort has gone into the development of high temperature metal oxide sorbents for removal of H{sub 2}S from coal gas. The oxides of zinc, iron, manganese, and others have been studied. In order for high temperature desulfurization to be economical it is necessary that the sorbents be regenerated to permit multicycle operation. Current methods of sorbent regeneration involve oxidation of the metal sulfide to reform the metal oxide and free the sulfur as SO{sub 2}. An alternate regeneration process in which the sulfur is liberated in elemental form is desired. Elemental sulfur, which is the typical feed to sulfuric acid plants, may be easily separated, stored, and transported. Although research to convert SO{sub 2} produced during sorbent regeneration to elemental sulfur is on-going, additional processing steps are required and the overall process will be more complex. Clearly, the direct production of elemental sulfur is preferred. Desulfurization utilizing a cerium oxide based sorbent is discussed.
Date: July 1, 1997
Creator: Lopez, A.; Huang, W. & White, J.
Partner: UNT Libraries Government Documents Department

An assessment of the validity of cerium oxide as a surrogate for plutonium oxide gallium removal studies

Description: Methods for purifying plutonium metal have long been established. These methods use acid solutions to dissolve and concentrate the metal. However, these methods can produce significant mixed waste, that is, waste containing both radioactive and chemical hazards. The volume of waste produced from the aqueous purification of thousands of weapons would be expensive to treat and dispose. Therefore, a dry method of purification is highly desirable. Recently, a dry gallium removal research program commenced. Based on initial calculations, it appeared that a particular form of gallium (gallium suboxide, Ga{sub 2}O) could be evaporated from plutonium oxide in the presence of a reducing agent, such as small amounts of hydrogen dry gas within an inert environment. Initial tests using ceria-based material (as a surrogate for PuO{sub 2}) showed that thermally-induced gallium removal (TIGR) from small samples (on the order of one gram) was indeed viable. Because of the expense and difficulty of optimizing TIGR from plutonium dioxide, TIGR optimization tests using ceria have continued. This document details the relationship between the ceria surrogate tests and those conducted using plutonia.
Date: March 1, 1999
Creator: Kolman, D.G.; Park, Y.; Stan, M.; Hanrahan, R.J. Jr. & Butt, D.P.
Partner: UNT Libraries Government Documents Department

Investigation of Mixed Metal Sorbent/Catalysts for the Simultaneous Removal of Sulfur and Nitrogen Oxides

Description: Simultaneous removal of SO{sub 2} and NO{sub x} using a regenerable solid sorbent will constitute an important improvement over the use of separate processes for the removal of these two pollutants from stack gases and possibly eliminate several shortcomings of the individual SO{sub 2} and NO{sub x} removal operations. The work done at PETC and the DOE-funded investigation of the investigators on the sulfation and regeneration of alumina-supported cerium oxide sorbents have shown that they can perform well at relatively high temperatures (823-900 K) as regenerable desulfurization sorbents. Survey of the recent literature shows that addition of copper oxide to ceria lowers the sulfation temperature of ceria down to 773 K, sulfated ceria-based sorbents can function as selective SCR catalysts even at elevated temperatures, SO{sub 2} can be directly reduced to sulfur by CO on CuO-ceria catalysts, and ceria-based catalysts may have a potential for selective catalytic reduction of NO{sub x} by methane. These observations indicate a possibility of developing a ceria-based sorbent/catalyst which can remove both SO{sub 2} and NO{sub x} from flue gases within a relatively wide temperature window, produce significant amounts of elemental sulfur during regeneration, and use methane for the selective catalytic reduction of NO{sub x}.
Date: August 1, 2001
Creator: Akyurtlu, Ates & Akyurtle, Jale F.
Partner: UNT Libraries Government Documents Department

Development of proton-conducting membranes for hydrogen separation

Description: The objective of this project is to develop dense ceramic membranes that can efficiently and economically separate hydrogen from gaseous mixtures (e.g., syngas, coal gas, etc.). Toward this end, materials with suitable electronic and protonic conductivities will be identified, and methods for fabricating thin, dense ceramic membranes from such materials will be developed. The chemical and mechanical stability of the membranes will be determined to estimate the expected lifetime of the membranes. Scoping-level evaluations will be performed to identify potential applications of proton membrane technology. Areas that will be evaluated include overall market scale, typical site operating scale, process integration opportunities and issues, and alternative-source economics. The literature on mixed electronic/protonic conductors was surveyed to identify suitable candidate materials. SrCe{sub 1{minus}x}M{sub x}O{sub 3{minus}{delta}} and BaCe{sub 1{minus}x}M{sub x}O{sub 3{minus}{delta}} (where M is a fixed-valent dopant such as Ca, Y, Yb, In, Nd, or Gd) were selected for further investigation on the basis of their reported total conductivities and proton transference numbers.
Date: July 1, 1998
Creator: Balachandran, U.; Guan, J. & Dorris, S.E.
Partner: UNT Libraries Government Documents Department

Advanced sulfur control concepts in hot-gas desulfurization technology. Quarterly report, April 1--June 30, 1998

Description: Twenty-five reduction/sulfidation tests plus one sulfidation/regeneration test were completed during the quarter. The reduction/sulfidation tests examined the behavior of six cerium oxide sorbents from different sources with reaction variables of temperature, pressure, gas composition and flow rate. Most significantly, steam was added to the sulfidation feed gas for the first time. Tests using pre-reduced sorbents and tests in which reduction and sulfidation occurred simultaneously were performed. Prebreakthrough H{sub 2}S concentrations less than 10 ppmv were obtained over a range of reaction conditions with prebreakthrough concentrations as low as 1 ppmv achieved at the most favorable conditions. The general response to reaction variables was as expected except when feed rate was varied. In some of these cases the FPD breakthrough time did not correspond to expectation. The single regeneration run was conducted at 600 C and 2 atm using 12% SO{sub 2} in N{sub 2} at a feet rate of 400 sccm. This was the first regeneration test at other than 1 atm pressure; favorable results were obtained. The only experimental objective remaining is additional high pressure regeneration testing.
Date: September 1, 1998
Creator: Harrison, D.P.
Partner: UNT Libraries Government Documents Department

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

Description: Ultrafine lanthanide (Ln = Ce and Nd)-modified zirconia powders synthesized by a coprecipitation method exhibit high surface areas and adsorption sites that are essential for catalytic applications. We report a study of the surface chemistry of Ce{sub 0.1}Zr{sub 0.9}O{sub 2} and Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} powders. First, the specific surface area and porosity are characterized by nitrogen isotherm-adsorption measurements. Second, the motion of hydrogen molecules physisorbed on Ce- and Nd-doped zirconias is studied by inelastic neutron scattering. Nitrogen adsorption-desorption isotherm measurements yield a BET surface area (26.1 m{sup 2}/g) and mesopore size ({approximately}5 nm radius) in Ce{sub 0.1}Zr{sub 0.9}O{sub 2} as compared to those (72.3 m{sup 2}/g and {approximately}3 nm) in Nd{sub 0.1}Zr{sub 0.9} O{sub 1.95}. The vibrational densities of states of H{sub 2} on Ce{sub 0.1}Zr{sub 0.9}O{sub 2} and Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} were measured at 20 K over the 0-200 meV energy range for three hydrogen coverage. The spectra for both samples consist of two parts: a sharp peak at {approximately}14.5 meV and a broad component extending beyond 200 meV. The sharp peak corresponds to transitions from the J=0 to J=1 rotational states of bulk hydrogen molecules, and its intensity decreases with decreasing H{sub 2} coverage. The broad component corresponds to overdamped motion of surface adsorbed hydrogen molecules. The major difference in the latter component between the Ce- and Nd-doped samples is an excess of intensities in the 5-14 meV region in Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95}. The confined motion of adsorbed H{sub 2} on the different micropore and mesopore surfaces of Ce{sub 0.1}Zr{sub 0.9}O{sub 2} and Nd{sub 0.1}Zr{sub 0.9}O{sub 1.95} is discussed.
Date: October 1, 1997
Creator: Loong, C.K.; Trouw, F.; Ozawa, Masakuni & Suzuki, Suguru
Partner: UNT Libraries Government Documents Department

Effective medium approximation of the optical properties of electrochromic cerium-titanium oxide compounds

Description: Cerium titanium oxide samples derived from a solution have been compared against sputtered films over a wide range of different compositions. X-ray diffraction was used to investigate the structural properties of the compound material existing in a two-phase mixture M{sub A}O{sub 2}-M{sub B}O{sub 2}. The optical properties were evaluated over the whole solar spectrum by variable angle spectroscopic ellipsometry combined with spectrophotometry. The spectral complex refractive index was determined for CeO{sub 2} and TiO{sub 2}, as well as for their compounds. To reduce the large number of permutations in composition of multi-component oxides it would be useful to be able to predict the properties of the mixtures from the pure oxide components. Therefore these results were compared to those obtained by effective medium theory utilizing the optical constants of CeO{sub 2} and TiO{sub 2}. In order to investigate the performance as passive counter-electrode in Li{sup +} based electrochromic devices the films were tested by cyclic voltammetry with in-situ transmission control. Chemical composition was measured by Rutherford backscattering spectrometry. Surface morphology was analyzed by atomic force microscopy.
Date: July 1, 1997
Creator: von Rottkay, K.; Richardson, T.; Rubin, M. & Slack, J.
Partner: UNT Libraries Government Documents Department

Electrochemical synthesis of CeO2 and CeO2/montmorillonite nanocomposites.

Description: Nanocrystalline cerium oxide thin films on metal and semiconductor substrates have been fabricated with a novel electrodeposition approach - anodic oxidation. X-ray diffraction analysis indicated that as-produced cerium oxide films are characteristic face-centered cubic fluorite structure with 5 ~ 20 nm crystal sizes. X-ray photoelectron spectroscopy study probes the non-stoichiometry property of as-produced films. Raman spectroscopy and Scanning Electron Microscopy have been applied to analyze the films as well. Deposition mode, current density, reaction temperature and pH have also been investigated and the deposition condition has been optimized for preferred oriented film formation: galvanostatic deposition with current density of -0.06 mA/cm2, T > 50oC and 7 < pH < 10. Generally, potentiostatic deposition results in random structured cerium oxide films. Sintering of potentiostatic deposited cerium oxide films leads to crystal growth and reach nearly full density at 1100oC. It is demonstrated that in-air heating favors the 1:2 stoichiometry of CeO2. Nanocrystalline cerium oxide powders (4 ~ 10 nm) have been produced with anodic electrochemical synthesis. X-ray diffraction and Raman spectroscopy were employed to investigate lattice expansion phenomenon related to the nanoscale cerium oxide particles. The pH of reaction solution plays an important role in electrochemical synthesis of cerium oxide films and powder. Cyclic voltammetry and rotation disk electrode voltammetry have been used to study the reaction mechanisms. The results indicate that the film deposition and powder formation follow different reaction schemes. Ce(III)-L complexation is a reversible process, Ce3+ at medium basic pH region (7~10) is electrochemically oxidized to and then CeO2 film is deposited on the substrate. CE mechanism is suggested to be involved in the formation of films, free Ce3+ species is coordinated with OH- at high basic pH region (>10) to Ce2O3 immediately prior to electrochemically oxidation Ce2O3 to CeO2. CeO2 / montmorillonite nanocomposites were electrochemically produced. X-ray ...
Date: December 2003
Creator: Wang, Qi
Partner: UNT Libraries

Mechanical properties of Ce{sub 0.9}Gd{sub 0.1}O{sub 2-x} and Ce{sub 0.9}Gd{sub 0.1}O{sub 2-x} + Al{sub 2}O{sub 3} composites.

Description: The room-temperature elastic moduli, fracture strength, and fracture toughness of dense, fine-grained, pure Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} and composites containing 1.3 and 9.1 wt. % Al{sub 2}O{sub 3} were investigated. Addition of 9.1 wt.% Al{sub 2}O{sub 3} to Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} changed the fracture mode from intergranular to transgranular and increased room-temperature fracture strength from 65 to 125 MPa and fracture toughness from 1.3 to 1.6 MPam{sup 1/2}. In addition, steady-state compressive creep was measured for Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} and the Ce{sub 0.9}Gd{sub 0.1}O{sub 2{minus}x} + 9.1 wt.% Al{sub 2}O{sub 3} composite. The stress exponent {approx}1.3 and the activation energy {approx}480 kJ/mole for Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} suggested diffusional flow controlled by the cations. There was no difference in creep rate between Ce{sub 0.9}Gd{sub 0.1}O{sub 2{minus}x} and the composite.
Date: January 12, 1998
Creator: Routbort, J. L.
Partner: UNT Libraries Government Documents Department