The experiments performed for this research were completed to produce solid cerium oxide microspheres by an internal gelation sol-gel process. The motivation for this work was to develop a process that would enable the fabrication of a storage or transmutation form for the plutonium and transuranics (TRU) from the Uranium Extraction Plus (UREX ) used fuel reprocessing process. This process is being investigated by the Department of Energy (DOE) and the Advanced Fuel Cycles Initiative (AFCI) through the Nuclear Energy Research Initiative. The internal gelation production of cerium oxide involves the combination of hexamethylenetetramine (HMTA), urea, and cerium nitrate solutions at ~100oC. Microspheres were produced by injection of a broth solution into a flowing stream of hot silicone oil. The captured microspheres were aged, washed, and then underwent Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and XRay Diffraction (XRD) analysis. The process variables examined in this study include the concentrations of HMTA, urea and cerium nitrate, the process temperature, the postgelation aging time, and the product washing conditions. Over a series of 70 experiments, it was determined that a broth solution containing a mixture of 1.45 M cerium nitrate and 1.65 M HMTA and urea (1:1 ratio) solutions produced the best cerium oxide microspheres. The spheres were aged for 30 to 60 minutes and then washed in hexane to remove the silicone oil and a subsequent series of ammonium hydroxide washes to remove unreacted product and to fully gel the microspheres. Through DSC analysis it was determined that excess wash or unreacted product may be removed by an exothermic reaction at approximately 200oC. The XRD analysis of unheated spheres showed the presence of cerium oxide with additional cerium-bearing organics. Following heating, the microspheres were completely converted to cerium oxide.

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The research in this project was directed, firstly towards gaining an understanding of the effect excited-state absorption (ESA) has on gain and lasing in broadly tunable Ce:LiLuF lasers and secondly towards the development of Ce:LiLuF lasers suitable for spectroscopic applications. Detailed measurements of the single-pass, small-signal gain in Ce:LiLuF were undertaken, with a gain coefficient as high as 30±1 cm^-1 at 309 nm, with an absorbed pump fluence of 0.46 Jcm^-2. Further, the ESA in Ce:LiLuF at 261 nm and 349 nm was measured. Using both the gain and ESA results in a computer model, the effective gain cross-sections at 309 nm and 327 nm and the ESA cross-sections at 261 nm, 309 nm, 327 nm and 349 nm were determined. The ESA cross-sections were found to be of the order of 10^-18 cm². The effective gain cross-section in Ce:LiLuF was found to increase with decreasing temperature. This was proposed to arise from a decrease in the ESA cross-section with decreasing temperature in the Ce:LiLuF. An in-depth parametric study of Ce:LiLuF laser operation and tunability was undertaken. The results of these studies, together with computer modelling, enabled the importance of ESA and other effects on lasing to be established. In particular, the gain competition effects and ESA were found to lead to inefficient laser operation unless σ-polarised lasing was suppressed. With polarisation selection, efficient operation was obtained, with continuous tunability between 305 nm - 335 nm. Narrow bandwidth operation of Ce:LiLuF for use in OH radical detection in the atmosphere was investigated. Narrow bandwidth operation was achieved for the first time in Ce:LiLuF using a Eittrow grating with a telescopic and prism beam expansion system. Tunable lasing between 306.5 nm and 311.5 nm was obtained, with a spectral bandwidth of 0.7 cm^-1. Finally, highly efficient Ce:LiLuF lasing was achieved with a new all-solid-state, 289 nm frequency-quadrupled Raman-shifted Nd:YAG laser. Slope efficiencies as high as 62±3% were achieved. This slope is believed to be the highest obtained in any cerium laser to date. The IR-to-UV conversion efficiency was 0.41% and the UV-to-UV conversion efficiency was 41%. These high efficiencies were attributed to high pump beam quality and good mode matching.

No description available.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.

AN ABSTRACT OF THE THESIS OF James Morrow, for the Master of Science degree in Mechanical Engineering, presented on November 3, 2017, at Southern Illinois University Carbondale. TITLE: INVESTIGATION OF THE MATERIAL PROPERTIES OF CERIUM OXIDE WITH DOPANTS FOR AN OXYGEN TRANSPORT MEMBRANE MAJOR PROFESSOR: Dr. Kanchan Mondal Many physical properties of cerium oxide both undoped and doped have been studied herein. These properties include electrical conductivity, hardness, sintered density, and microstructure. These will be used to help determine a cerium oxide compound to use as an oxygen transport membrane in a combustion system. These compounds have been readily studied beforehand with exception to compounds with multiple dopants. Along with single doped cerium oxide, dual doped was investigated as well. The samples to be tested were created using co-precipitation and the subsequent powders were sintered at 1500°C to generate solid pellets. Once the pellets were formed the physical properties were tested. It was found that hardness and sintered density had little to no effect on electrical conductivity and the microstructures of the samples were shown to be favorable. As far as single or dual dopants were concerned, it was found that by including a second dopant along with zirconium that the electrical conductivity was reduced. Except for in the case where iron was doped along with zirconium, where the conductivity was increased. It was suggested to use samarium as the second dopant along with zirconium for the membrane.

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In this work the performance of cerium-based oxygen carriers is investigated in a simulated chemical looping dry reforming system using methane and carbon dioxide as fuel and oxidizing gas respectively. The samples to be studied are pure cerium oxide and cerium oxide doped with zirconium, yttrium, samarium, and scandium more specifically: CeO2, Ce0.8Y0.2O1.9, Ce0.85Y0.05Zr0.1O1.975, Ce0.95Zr0.05O2, Ce0.9Sm0.05Zr0.05O1.975, and Ce0.9Sc0.05Zr0.05O1.975. Characteristics such as crystallography including lattice parameter and particle size of the samples are evaluated using X-ray diffraction (XRD) and particle size analysis. The oxygen transport capacity will also be measured using a thermogravimetric analyzer (TGA). This method of measurement also allowed for insight on oxygen release temperatures as well as recyclability of the samples. The particle size analysis showed that the synthesis method of precipitation-agglomeration resulted in samples with consistent particle size distribution indicating the method can be scaled up. The X-ray analysis of samples before and after the TGA tests show that all the materials tested had a cubic fluorite crystal structure which was maintained through the oxidation reduction cycles. The lattice parameter was found to increase slightly with a loss in oxygen content in the samples. The addition of trivalent dopants resulted in a decrease in the temperature of initiation of reduction in methane. While reduction of commercial ceria initiated near 800 oC. the addition of trivalent dopants resulted in a lowering of the initialization temperature between of 150 – 200oC. The activation energy of commercial ceria was 248.42 kJ/mol for reduction in methane, indicating that the rate controlling mechanism is chemical reaction rather than diffusion. The addition of trivalent dopants resulted in a significant lowering in the activation energy. The activation energies obtained in this study show that the addition of dopant increased the significance of diffusion through the solid and the controlling mechanisms were both diffusion and chemical reaction. Overall, the addition of trivalent dopants enhanced the extent of oxygen exchange in CLDR process.