Investigation of glass-ceramic composites containing CeTi2O6 and CaZrTi2O7 for immobilization of nuclear waste

Glass-ceramic composite materials are being investigated for numerous applications (i.e. textile, energy storage, nuclear waste immobilization applications, etc.) due to the chemical durability and flexibility of these materials. The objective of this thesis was to understand the interaction of brannerite or zirconolite-type crystallites within the glass matrix and to investigate how the local structure of these composite materials changed with changing synthesis conditions as well as to study the structural stability of these materials upon irradiation. Borosilicate and Fe-Al-borosilicate glass-ceramic composites containing brannerite (CeTi2O6) or zirconolite (CaZrTi2O7) crystallites were synthesized at different annealing temperatures. Powder X-ray diffraction (XRD) and Backscattered electron (BSE) microprobe images have been used to study how the ceramic crystallites dispersed in the glass matrix. X-ray absorption near edge spectroscopy (XANES) spectra were also collected from all glass-ceramic composite materials. Examination of XANES spectra from the glass-ceramic composites have shown that the annealing temperature, glass composition, and the loading of the ceramic crystallites in the glass matrix can affect the local environment of the glass-ceramic composite materials. Radiation induced structural damage has been simulated by bombarding (implanting) the glass-ceramic materials using 2 MeV Au- to understand how the structure of a composite wasteform responds to the radioactive decay of incorporated nuclear waste elements. A combination of ion implantation and GA-XANES has been used to investigate the structural stability of glass-ceramic composite materials. Surface sensitive glancing angle XANES (GA-XANES) spectra were collected to selectively probe the damaged surface layer of the ion implanted materials. Examination of Ti K-edge GA-XANES spectra from ion implanted glass-ceramic composite materials have shown that ion implantation damaged the structure of the ceramics in the composite materials. However, the study of Si L2,3-edge XANES spectra from the ion implanted composite materials showed that ion implantation does not appear to damage the glass structure in these composite materials. A comparison of the glass-ceramic composites containing brannerite or zirconolite crystallites has shown that similar changes in the long-range and local structure of these composite materials occur when the synthesis conditions to form these materials are changed and/or after ion implantation