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U- and Hf-Bearing Pyrochlore and Zirconolite and their Leached Layers Formed in Acidic Solution: Tem Investigation

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Abstract

Transmission electron microscopy results from a sintered ceramics with stoichiometry of Ca(U0.5Ce0.25Hf0.25)Ti2O7 show the material contains both pyrochlore and zirconolite phases and structural intergrowth of zirconolite lamellae within pyrochlore. (001) plane of zirconolite is parallel to (111) plane of pyrochlore because of their structural similarities. The pyrochlore is relatively rich in U, Ce, and Ca with respect to the coexisting zirconolite. Average compositions for the coexisting pyrochlore and zirconolite at 1350 °C are Ca1.01(Ce3+ 0.13Ce4+ 0.19U0.52Hf0.18)(Ti1.95Hf0.05)O7 (with U/(U+Hf) = 0.72) and (Ca0.91Ce0.09)(Ce3+ 0.08U0.26Hf0.66Ti0.01)Ti2.00O7 (with U/(U+Hf) = 0.28) respectively. A single pyrochlore (Ca(U,Hf)Ti2O7) phase may be synthesized at 1350 °C if the ratio of U/(U+Hf) is greater than 0.72, and a single zirconolite (Ca(Hf,U)Ti2O7) phase may be synthesized at 1350 °C if the ratio of U/(U+Hf) is less than 0.28. An amorphous leached layer that is rich in Ti and Hf forms on the surface after the ceramics has been leached in pH 4 buffered solution. The thickness of the layer ranges from 5 nm to 15 nm. The leached layer functions as a protective layer and therefore reduces the leaching rate.

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Authors and Affiliations

  1. Transmission Electron Microscopy Laboratory, Department of Earth and Planetary Sciences, The University of New Mexico, 87131, Albuquerque, New Mexico, USA

    Huifang Xu & Yifeng Wang

  2. Sandia National Laboratories, 88220, Carlsbad, NM, USA

    Huifang Xu

  3. Lawrence Livermore National Laboratory, L-219, 94550, Livermore, CA, USA

    Pihong Zhao, William L. Bourcier, Richard Van Konynenburg & Henry F. Shaw

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  1. Huifang Xu
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  2. Yifeng Wang
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Correspondence to Huifang Xu.

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Xu, H., Wang, Y., Zhao, P. et al. U- and Hf-Bearing Pyrochlore and Zirconolite and their Leached Layers Formed in Acidic Solution: Tem Investigation. MRS Online Proceedings Library 757, 62 (2002). https://doi.org/10.1557/PROC-757-II6.2

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  • DOI: https://doi.org/10.1557/PROC-757-II6.2

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