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The CaO-TiO2-ZrO2 System at 1200 °C and the Solubilities of Hf and Gd in Zirconolite

Published online by Cambridge University Press:  15 February 2011

D. Swenson ,
T. G. Nieh  and
J. H. Fournelle
D. Swenson
Affiliation:
Chemistry and Materials Science, Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551
T. G. Nieh
Affiliation:
Chemistry and Materials Science, Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551
J. H. Fournelle
Affiliation:
Department of Geology and Geophysics, University of Wisconsin, 1215 Dayton St., Madison, WI 53706
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Abstract

Phase equilibria are established in the CaO-TiO2-ZrO2 system at 1200 °C, using X-ray diffraction and electron probe microanalysis. The existence of two previously reported ternary phases, zirconolite (CaZrTi2O7) and calzirtite (Ca2Zr5Ti2O16), is confirmed. Each of these phases exhibits a significant range of homogeneity between TiO2 and ZrO2 while maintaining a nearly constant concentration of CaO. The ternary solubilities of the constituent binary phases are found to be negligible, with the exceptions of the perovskites, which display mutual solubility of at least 22 mol.% and may in fact form a series of continuous solid solutions. The solubilities of Hf and Gd in zirconolite are also investigated. While Hf-bearing samples did not reach thermodynamic equilibrium under the experimental conditions employed, the existence of a Hf analog to zirconolite, CaHfTi2O7, is conclusively demonstrated. The phase is stable at the stoichiometric composition, and its lattice parameters are very close to those reported in the literature for stoichiometric zirconolite. A Gd-bearing sample of the composition Ca0.88Zr0.88Gd0.24Ti2O7 is found to be essentially single phase zirconolite, in agreement with previous investigations at higher temperatures.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 412: Symposium V – Scientific Basis for Nuclear Waste Management XIX , 1995 , 337
Copyright
Copyright © Materials Research Society 1996

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