The CaO-TiO{sub 2}-ZrO{sub 2} system at 1200 C and the solubilities of Hf and Gd in zirconolite

Book · Thu Aug 01 04:00:00 EDT 1996

OSTI ID:264439

Swenson, D; Nieh, T G ^[1]; Fournelle, J H ^[2]

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1. Lawrence Livermore National Lab., CA (United States). Chemistry and Materials Science
2. Univ. of Wisconsin, Madison, WI (United States). Dept. of Geology and Geophysics

Phase equilibria are established in the CaO-TiO{sub 2}-ZrO{sub 2} system at 1,200 C, using X-ray diffraction and electron probe microanalysis. The existence of two previously reported ternary phases, zirconolite (CaZrTi{sub 2}O{sub 7}) and calzirtite (Ca{sub 2}Zr{sub 5}Ti{sub 2}O{sub 16}), is confirmed. Each of these phases exhibits a significant range of homogeneity between TiO{sub 2} and ZrO{sub 2} 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, CaHfTi{sub 2}O{sub 7}, 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 Ca{sub 0.88}Zr{sub 0.88}Gd{sub 0.24}Ti{sub 2}O{sub 7} is found to be essentially single phase zirconolite, in agreement with previous investigations at higher temperatures.

• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 264439
• Report Number(s): CONF-951155--; ISBN 1-55899-315-0
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
36 MATERIALS SCIENCE
CALCIUM OXIDES
CHEMICAL COMPOSITION
CRITICALITY
EXPERIMENTAL DATA
GADOLINIUM
HAFNIUM
NUCLEAR POISONS
PHASE DIAGRAMS
PHASE STUDIES
RADIOACTIVE WASTE DISPOSAL
RADIOACTIVE WASTE FACILITIES
SCANNING ELECTRON MICROSCOPY
SOLUBILITY
SORPTIVE PROPERTIES
SYNROC PROCESS
SYNTHETIC ROCKS
TITANIUM OXIDES
WASTE FORMS
ZIRCONIUM OXIDES
ZIRCONOLITE