Ce Component Research Articles

Effect of Hydrolysis Conditions on the Direct Formation of Nanoparticles of Ceria–Zirconia Solid Solutions from Acidic Aqueous Solutions

The effect of the cation concentration, hydrolysis temperature, and composition in the CeO2–ZrO2 system on the direct precipitation of ceria–zirconia solid solutions and the structure of the precipitates from acidic aqueous solutions of (NH4)2Ce(NO3)6 and ZrOCl2 by hydrolysis under hydrothermal conditions were investigated. Nanometer-sized (8–10 nm) ceria–zirconia solid solution particles in a composition range of 0 to 60 mol% ZrO2 were directly precipitated from the solutions with total metal cation concentration less than 0.2 mol/dm3 by simultaneous thermal hydrolysis at 150–240°C. The crystalline phase of the precipitates gradually changed from cubic and/or tetragonal to monoclinic with increasing the cation concentration of the solution from 0.2 to 0.8 mol/dm3 at the starting composition of 50 mol% ZrO2 under hydrolysis condition of 150°C for 48 h, which was attributed to decrease in the supply of hydrolyzed Ce component caused by decrease in the hydrolysis ratio of (NH4)2Ce(NO3)6. Ceria–zirconia solid solutions containing large amount of ZrO2 maintained high specific surface area and small-sized crystallite after heat-treatment at 900–1000°C for 1 h.

Absolute Cross Sections for Fast Electron Ejection by Swift Highly Charged Ions and Evidence for “Fermi Shuttle” Acceleration

We report the results of recent experiments performed at the CS (Catania) and GANIL (Caen) cyclotron accelerators, with 45 A MeV 19+ and 28+ 58Ni and 95 A MeV 18+ 36Ar pulsed beams, respectively. Electron velocity spectra were measured in a large angular range with different target foils (C, Al, Ni, Ag, Au). Besides electrons with the beam velocity (convoy electrons, CE) and two times the beam velocity (binary encounter electrons, BE), we observe also a high velocity tail in the case of the Au target only, which can be explained by a “Fermi-shuttle” mechanism. We also give absolute BE and CE production cross-sections. As a preliminary result of the recent GANIL experiment, we observe the lack of the CE component at the most forward angles in the case of the carbon target. For the other targets the CE yield increases as a function of the target atomic number.

Process of solid state reaction between doped ceria and zirconia

Solid state reaction at an interface between doped zirconia and ceria has been analyzed by X-ray diffraction and EDX. The solid state reaction between Y-doped ceria and Y-stabilized zirconia occurred on heating at 1300°C or higher temperatures to form a single cubic fluorite Y-doped ceria–zirconia phase. The reaction proceeded by preferential migration of the Ce component to the zirconia lattice. The reaction significantly lowered the electrical conductivity. The reaction between Sm-doped ceria and Y-stabilized zirconia, on the other hand, proceeded by migration of every component equally, i.e. preferential migration of a specific component was hardly observed.

Analysis of solid state reaction at the interface of yttria-doped ceria/yttria-stabilized zirconia

Interfacial reaction between yttria-stabilized zirconia (YSZ) and yttria-doped ceria (YDC) phases was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis after heating at 1300°C indicated that the solid state reaction between YDC and YSZ accompanied a significant shift of the zirconia lines to lower angle. The lines from the ceria phase were only weakened with the reaction. The reaction completed to give a single cubic fluorite phase of Y-doped zirconia–ceria (YCZ) solid solution after heating at 1300°C or higher temperatures. A Pt marker was inserted at the original interface between YSZ and YDC to observe the process of the solid state reaction. From SEM and EDX analyses, the gradated compositional changes were observed in the zirconia side from the Pt marker after heating at 1700°C. Sintered pellets of YDC and YSZ couple showed Kirkendall-void along the interface of the YDC side because of the preferential migration of the Ce component to the zirconia side.

Preparation of non-aggregation YAG-Ce phosphor particles by spray pyrolysis

Yttrium Aluminum Garnet(Y,AISOlz, YAG) materials have been widely studied in the application of fluorescent and solid state lasers(Schol1 and Trimmier, 1986; Robbins, 1982) YAG is a hard material which does not damage easily under conditions of high irradiance with an electron beam. Therefore, rare earth doped YAG materials are promising phosphor candidates in cathode-ray tubes (CRTs), field emission display (FED), scintillation, vacuum fluorescent displays (VFDs), and electroluminescent (EL). Recently, spray pyrolysis was successfully applied to the preparation of phosphor materials(Kang et al., 1997a, b). In this work, we prepared YAG:Ce green phosphors by spray pyrolysis using ultrasonic and FEAG process. In the system of YAG phosphors, the directly prepared particles in spray pyrolysis have amorphous phase, and activation of doping component was not occurred because of short residence time of particles inside hot wall reactor as several seconds. Therefore, anriealing process at high temperatures is required for the crystallization and activation of ceriuum-doped YAG particles. The peaks of cubic structure YAG appeared after annealing from 800 “C, and high crystallinity YAG was formed above 1000 “C. In all samples, small peak of CeO, was appeared, and intensity of peak was increased with increasing doping concentrations of dopant. Fig. 1 shows the SEM photographs of particles prepared by different processes. The overall solution concentration was 0.4M. The prepared particles have spherical morphology and submicron size in both processes. Additionally, the particles had nonaggregation and sphericity after annealing at high temperatures. The YAG:Ce particles prepared at low flow rate of carrier gas had more solid morphology and sphericity than those of high flow rate of carrier gas. The photoluminescence characteristics of YAG:Ce particles with spherical morphology were investigated. The all particles for the measurements of PL were prepared by ultrasonic spray pyrolysis at the conditions of 2 Nmin and 900 “C. The excitation spectra of YAG:Ce particles have maximum peak at wavelength of 465 nm. The emission spectra have a maximum intensity at 527 nm. The optimum brightness was obtained at doping concentration of lat.%. The effect of calcination temperature on the luminous intensities of particles at constant doping concentration( 1 at.%) was shown in Fig.2. The luminescence of particles was increased with increasing annealing temperatures because of good activation of Ce component into YAG matrix. In the XRD spectra, the peak intensity of CeO, was decreased with increasing annealing temperatures.

Shear-elasticity anomaly in Ce/Fe multilayers

Brillouin light-scattering experiments have been performed at room temperature to determine the shear modulus C{sub 44} of Ce/Fe multilayers (in their reference frame) as a function of the modulation wavelength {Lambda}. The study is complementary to a previous investigation of the flexural modulus E{sub F} of this system in the sense that, while E{sub F} is dominated by the Fe layers, C{sub 44} largely reflects the elasticity of the more compliant Ce component. In the heterostructures, the Ce layers exhibit a laminated two-phase structure composed of low-volume {alpha} and high-volume {gamma}-like Ce, with a thickness-dependent relative fraction. Furthermore, structural transitions occur from an amorphous phase to the crystalline phases of bcc Fe and fcc Ce, for Fe abruptly within the entire sublayer volume at a critical thickness near 20 {Angstrom}, for Ce more gradually with increasing layer thickness starting near 40 {Angstrom}. These structures and phase transitions are reflected in the variation of C{sub 44} with {Lambda}. A large portion of this variation can be ascribed to the {Lambda}-dependent {alpha}-{gamma}-like composite structure of the Ce layers. A superposed softening of C{sub 44} is essentially the signature of the amorphous-to-crystalline transition in the Ce sublayers. {copyright} {ital 1997} {ital The Americanmore » Physical Society}« less

TEM Observation of Reaction at the Interface between Yttria-Doped Ceria and Yttria-Stabilized Zirconia

Interfacial reaction between yttria-stabilized zirconia (YSZ) and yttria-doped ceria (YDC) phases was analyzed by X-ray diffraction and high-resolution transmission electron microscopy. An X-ray diffraction pattern indicated that the mixture of YSZ and YDC consisted of their original phases after heating at 1100°C, whereas a solid state reaction occurred between them at higher temperatures. The solid state reaction proceeded as the Ce component was dissolved into the cubic YSZ phase, with an expense in the amount of the cubic YDC phase. The completion of the reaction gave a single cubic fluorite phase of Y-doped zirconia–ceria (YCZ) solid solution at 1500°C or high temperatures. A high-resolution transmission electron microscopic analysis supported this reaction process. No solid state reaction was observable at the interface of the ceria and zirconia particles on heating at 1100°C. Although the YDC and YSZ particles are tightly combined at the interface, the lattice kept its original array and orientation. The sample heated at 1300°C contained particles undergoing solid state reaction. The YDC phase was observed in the interface region of the zirconia side. The surface region of YCZ which faced the ceria particle contained a number of defects. The formation of defects is accompanied by the dissolution of ceria in the zirconia lattice and the lattice of zirconia was distorted to fit to the orientation of the ceria lattice. After heating at 1500°C the sample consisted of a homogeneous YCZ phase.

Physico-chemical and electrochemical characterization of Ru-based ternary oxides containing Ti and Ce

The effect of mixing Ru and Ce has been investigated by systematically substituting Ce for Ti in 30 mol% RuO 2 + 70 mol% TiO 2. A set of ternary oxide electrodes with the general formula Ru 0.3 Ti (0.7− x Ce x O 2 has been prepared from x = 0 to x = 0.7 at 10 mol% intervals by thermal decomposition of aqueous acid solutions of the chlorides as precursors using Ti as a support. Ex situ characterization included TGA, XRD and SEM. Electrodes were characterized in acid solution as a function of composition by determining the open-circuit potential, the voltammetric curve and the voltammetric charge. Variables were temperature, time and atmosphere of calcination. The electrodes showed variation of the voltammetric charge and of the voltammetric features dependent on the potential window and the number of cycles. The main reason for instability appears to be the cathodic dissolution of the Ce component, which has been confirmed by analysing the solution by ICPES. Ways of minimizing this inconvenience have been explored. Preliminary results in alkali indicate excellent stability.

Technology-transfer strategies of DOE's conservation programs

This paper examines the process by which R&D results funded by the Office of Conservation and Renewable Energy (CE) of the US Department of Energy (DOE) have generated commercial applications. It looks at examples of technology-transfer procedures and activitees across three of CE's component offices that correspond to the major energy end-use sectors: transportation, buildings, and industry. On the surface, the conservation programs would appear to have little strategic consistency and, therefore, lack the clear leadership many seek in a technology-transfer program. However, as an alternative to strategic consistency, one may tailor the technology-transfer approach of each program to its unique circumstances. This paper presents case studies of such tailoring, in which the diversity of approaches mirrors the complexity of the energy end-use markets and the private-public interests that must be negotiated to successfully commercialize energy-saving innovations. The paper discusses the lessons learned about the conditions requiring adaptive design and the structures and practices that have been proven effective.