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Microstructure and Composition of Synroc Samples Crystallized From a CaCeTi2O7 Chemical System: HRTEM/EELS Investigation

Published online by Cambridge University Press:  10 February 2011

Huifang Xu ,
Yifeng Wang ,
Robert L. Putnam ,
Jose Gutierriez  and
Alexandra Navrosky
Huifang Xu
Affiliation:
Transmission Electron Microscopy Laboratory, Department of Earth and Planetary Sciences, The University of New Mexico, Albuquerque, New Mexico 87131. E-mail: hfxu@unm.edu
Yifeng Wang
Affiliation:
Sandia National Laboratories, 115 North Main Street, Carlsbad, New Mexico 88220 E-mail: ywang@sandia.gov
Robert L. Putnam
Affiliation:
Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Jose Gutierriez
Affiliation:
Dept. of Chemical Engineering and Materials Science, University of California at Davis, One Shields Avenue, Davis, CA 95616-8779
Alexandra Navrosky
Affiliation:
Dept. of Chemical Engineering and Materials Science, University of California at Davis, One Shields Avenue, Davis, CA 95616-8779
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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 Cepyrochlore, 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 CeO2and 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

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 461
Copyright
Copyright © Materials Research Society 2000

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References

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