Microstructure and composition of synroc samples crystallized from a CaCeTi2O7 chemical system: HRTEM/EELS investigation

Huifang Xu, Yifeng Wang, Robert L. Putnam, Jose Gutierriez, Alexandra Navrosky

Research output: Contribution to journalConference articlepeer-review

4 Scopus citations

Abstract

Ce-pyrochlore, CaCeTi2O7 is a chemical analogue for CaPuTi2O7, which is a proposed ceramic endmember waste form for the disposition of excess weapon-usable plutonium in geological repositories. Ce-pyrochlore was synthesized by firing and annealing in air a mixture of CeO2, TiO2, and CaCO3 with a stoichiometry of CaCeTi2O7. The annealed products contain Ce-pyrochlore, Ce-bearing perovskite, CeO2, and minor CaO. The mixture annealed at a temperature of 1140 °C contains more pyrochlore phase than that annealed at a higher temperature (1300 °C), indicating that a low temperature condition favors the formation of the Ce-pyrochlore. The Ca/Ce ratio of the pyrochlore is slightly lower than the ideal ratio (one). Electron energy-loss spectroscopy results show that there is a small fraction of Ce3+ present in the pyrochlore. Ce present in perovskite is dominated by Ce3+. High-resolution TEM images show that the boundary between pyrochlore and perovskite is semi-coherent. No glassy phases were observed at the grain boundary between pyrochlore and perovskite, nor between CeO2 and pyrochlore. It is postulated, based on the presence of trivalent Ce in the Ce-pyrochlore, that neutron poisons such as trivalent cation Gd would be incorporated into the CaPuTi2O7 phase.

Original languageEnglish (US)
Pages (from-to)461-466
Number of pages6
JournalMaterials Research Society Symposium - Proceedings
Volume608
StatePublished - 2000
Externally publishedYes
EventScientific Basis for Nuclear Waste Management XXIII - Boston, MA, USA
Duration: Nov 29 1999Dec 2 1999

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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