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Development of Glass-Ceramic Composites by One-Step Synthesis Methods



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High level nuclear waste can potentially be separated from the environment using glassceramic composite materials. These materials are usually synthesized using a two-step synthesis method where the ceramic and glass phases are made separately followed by mixing and annealing to form the composite material. This thesis work aims to investigate possible one-step synthesis methods (using both dry and wet chemical methods) where all precursors are mixed together and annealed only once. Additionally, the crystallization behaviour of a Pu surrogate (Ce) was investigated under different annealing temperatures, ceramic loading in the composite material, and oxidation state of the Ce precursor. Rare-earth phosphate-borosilicate glass composites were synthesized for this work and the local and long-range order was investigated as well as the morphology. This was performed using powder X-ray diffraction, X-ray absorption near-edge spectroscopy, and electron microscopy along with energy dispersive X-ray spectroscopy. It was observed that the long-range order and local chemical environment of both glass forming ions and ceramic forming ions is similar in the one-step ceramic method to the two-step ceramic method. The shape and size of the crystallites were different depending on synthesis method and was attributed to the mechanism in which the crystallites form. Differences in solubility of LaPO4 and YPO4 in borosilicate glass was observed and suggested to be caused by the difference in the structural roles of La3+ and Y3+. The one-step solution-based method was found to possess differences compared to the one-step ceramic method. These differences include the temperature at which the glass partially crystallized, the size of the crystallites, and the ordering of the Si network in the glass. These changes were all suggested to be caused by the intimate mixing of precursors the solution-based method provides. Finally, Ce was found to potentially crystalize as CePO4, CeO2, or Na3Ce(PO4)2. The crystal phases present were dependant on the annealing temperature, ceramic loading, and oxidation state of the Ce precursor. Higher ceramic loading and higher annealing temperature are among the synthesis conditions which favoured the formation of CePO4.



Glass-ceramic, XANES, Rare-earth phosphates, Borosilicate glass, Synchrotron Radiation



Master of Science (M.Sc.)






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