Journal
CERAMICS INTERNATIONAL
Volume 44, Issue 12, Pages 13572-13579Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ceramint.2018.04.191
Keywords
Zirconolite; Pyrochlore; Nuclear waste immobilization; Phase evolution; Chemical stability
Categories
Funding
- National Natural Science Foundation of China [11705153]
- Foundation of Laboratory of National Defense Key Discipline for Nuclear Waste and Environmental Safety, Southwest University of Science and Technology [17kfhk05]
- Longshan Academic Talent Research Supporting Program of SWUST [17LZX653]
- Postgraduate Innovation Fund Project of Southwest University of Science and Technology [17ycx020, 17ycx022]
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In order to ascertain the structural relationship of zirconolite and pyrochlore for their potential application in HLW immobilization, the Gd-doped zirconolite-pyrochlore composite ceramics (Ca1-xZr1-xGd2xTi2O7) were systematically synthesized with x = 0.0-1.0 by traditional solid-phase reaction method. The phase evolution and microstructure of the as-prepared samples have been elucidated by XRD and Rietveld refinement, Raman spectroscopy, BSE-EDS and HRTEM analysis. The results showed that zirconolite-2M, zirconolite-4M, perovskite and pyrochlore, four phases were identified in Ca1-xZr1-xGd2xTi2O7 system and could be coexisted at x = 0.4 composition. With the increase of Gd3+ substitution, the phase evolution was followed by zirconolite-2M -> zirconolite-4M -> pyrochlore. It is illustrated that the phase transformation from zirconolite-2M to zirconolite-4M was promoted by the preferential substitution of Gd3+ for Ca2+. And the solubility of Gd3+ in zirconolite-2M, zirconolite-4M and pyrochlore increased in sequence. The chemical stability test was also measured by the PCT leaching method. The normalized elemental release rates of Ca, Zr, Ti and Gd in Ca1-xZr1-xGd2xTi2O7 system were fairly low and in the range of 10(-6) - 10(-8) g m(-2) d(-1), which indicated a potential ceramics composite ensemble of CaZrTi2O7-Gd2Ti2O7 system for nuclear HLW immobilization.
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