Phase structure evolution and chemical durability studies of Ce-doped zirconolite–pyrochlore synroc for radioactive waste storage
Source abstract
Abstract
The Ca1−x Zr1−x Ce2x Ti2O7+δ (0 ≤ x ≤ 0.4) series is synthesized via chemical routes, with microstructure/phase structure characterized by XPS, XRD, HRTEM, and SEM as well. The partial reduction of Ce4+ in Ce3+ in Ca1−x Zr1−x Ce2x Ti2O7+δ ceramics is observed from the Ce 3d XPS spectra. The XRD investigations and Rietveld refinements show that there are three crystal structures, namely monoclinic zirconolite-2M or zirconolite-4M, tetragonal perovskite, and cubic pyrochlore. The Ca and Zr sites of zirconolite structure are occupied by Ce3+ and Ce4+ ions, respectively. The zirconolite-2M → zirconolite-4M → pyrochlore transformation is based on the extent of Ce3+ and Ce4+ substitution. The zirconolite-4M phase tends to form at slightly higher substitution levels of Ce3+ and Ce4+ ions. At high substitution levels of Ce3+ and Ce4+ ions, cation rearrangement occurs resulting in the formation of pyrochlore structure. The chemical durability test is measured by the ASTM Product Consistency Test leaching method, and the normalized mass loss (NL Ce) of Ce in the Ca1−x Zr1−x Ce2x Ti2O7+δ ceramics is shown in the order of 10−6–10−7 g/m2.
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Research context
OpenAlex topics: Nuclear materials and radiation effects · Radioactive element chemistry and processing · Nuclear Materials and Properties
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