Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology Subjects: Materials Science >> Ceramics submitted time 2024-03-20
Abstract： The long-term structural stability of high-level radioactive wastes was the key for deep geological disposal under irradiation. In this work, 500 keV He2+ ion beams irradiation of zirconolite-2M, zirconolite-3O and zirconolite-4M three-type solid solutions were performed to study the structure damage from α decay in long-term deep geological disposal. All samples were synthesized through conventional high-temperature solid-state reaction at 1400℃ sintered twice 48h. The grazing incidence x-ray diffraction (GIXRD), Raman and x-ray photoelectron spectroscopy (XPS) results indicated that zirconlite-2M sample experienced crystalline phase evolution from zirconolite-2M to zirconolite-4M to disorder pyrochlore and amorphous with irradiation dose increased. For zirconolite-3O sample, the phase transformed to perovskite at 5×1015 ions/cm2 dose, and perovskite quickly transformed to disorder pyrochlore at higher dose. Disorder pyrochlore became major crystal structure when dose increased to 1×1017 ions/cm2. Zirconolite-4M remained with disorder pyrochlore or defect fluorite second phase under 1×1017 ions/cm2 irradiation. Summarily, the irradiation damage resistance of zirconolite-2M was similar with zirconolite-3O, and lower than zirconolite-4M.
Subjects: Materials Science >> Ceramics submitted time 2023-02-01
Abstract： The study deals with the use of different amounts of MgO or tetraethyl orthosilicate (C8H20O4Si, TEOS), from 0.04 wt %, 0.06 wt %, 0.08 wt %, 0.4 wt %, 0.6 wt % to 0.8 wt %, respectively, as additional sintering aids during the vacuum sintering of transparent Ce3+ doped Y3Al5O12 (Ce:YAG) ceramics to investigate their effect on microstructure and luminescence properties. A comparative study was carried out by using X - ray diffraction, scanning electron microscopy/energy dispersive X - ray spectroscopy, optical and photo-luminesce spectra, as well as electroluminescent spectra. The dominant garnet phase was obtained even when adding 0.8 wt % of MgO or TEOS, while adding MgO led to finer average grain size (~ 5 - 10 μm) and more homogenous distribution compared to TEOS (~ 20 - 25 μm) in Ce:YAG ceramics. Adding a large amount of MgO was found to result in the segregation of MgO in Ce:YAG ceramics, while an excess of TEOS led to the segregation of Al2O3. A strong absorption peak at 308 nm was observed in Ce:YAG ceramics with MgO sintering aids, which was ascribed to the existence of Ce4+ induced by a charge compensation effect of Mg2+. The optimum transmittance reached 80% @ 800 nm in Ce:YAG ceramics when adding 0.6 wt % TEOS, which also exhibited a maximum luminous efficacy of 106 lm/W. Si4+ was experimentally proved to have a better optimization effect on luminous efficacy compared to Mg2+.
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