Zirconium Incorporation into CaTiO3 Perovskite Prepared from Xerogels and Implication for the Fate of (Ca,Sr)TiO3 Nuclear Waste Ceramics

Authors

  • Nissim U. Navi,

    1. Department of Nuclear Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
    2. Nuclear Research Center–Negev (NRCN), Beer-Sheva, Israel
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  • Giora Kimmel,

    1. Institutes for Applied Research, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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  • Guy Yardeni,

    1. Nuclear Research Center–Negev (NRCN), Beer-Sheva, Israel
    2. Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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  • Jacob Zabicky,

    1. Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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  • Roni Z. Shneck,

    1. Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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  • Moshe H. Mintz,

    1. Department of Nuclear Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
    2. Nuclear Research Center–Negev (NRCN), Beer-Sheva, Israel
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  • Alexandra Navrotsky

    Corresponding author
    1. Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California at Davis, Davis, California
    • Department of Nuclear Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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    • Member, The American Ceramic Society.

Author to whom correspondence should be addressed. e-mail: anavrotsky@ucdavis.edu

Abstract

CaTiO3 perovskite has been proposed as a ceramic waste form for immobilization of 90Sr. Nonradioactive coprecipitated xerogel powders with nominal atomic ratios of Ca:Zr:Ti = 0.75:0.25:1.00 were synthesized to mimic the fate of (Ca0.7590Sr0.25)TiO3 solid solution after complete decay of the Sr and its intermediate product Y to stable Zr when an excess B4+ (Ti and 90Zr) cations will present. Ca:Ti = 1.00:1.00 samples were used as a reference. The powders were heated to various conditions to explore the thermodynamic stability of its oxides. The heated Ca:Zr:Ti = 0.75:0.25:1.00 samples formed a major orthorhombic Ca(Zr1−xTix)O3 perovskite phase. The Ti/(Ti + Zr) ratio of the perovskite preserves its nominal ratio at 600°C. The Zr rejects from the Ca(Zr1−xTix)O3 with further increasing the temperature, following the formation of CaTiZrO secondary phases. This study indicates a tendency of the Zr to segregate from an original (Ca,Sr)TiO3 waste form when the stoichiometry is controlled by the conversion of Sr to Zr (in normal oxidation states).

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