LOW-TEMPERATURE EQUILIBRIA AMONG ZrO$sub 2$, ThO$sub 2$, AND UO$sub 2$
Studies made on low-hafnium-content ZrO/sub 2/ show that the monoclinic- tetragonal inversion temperature is 1170 deg C, and it is raised to approximately 1190 deg C in the "natural" ZrO/sub 2/ which contains approximately 2% HfO/sub 2/. No explanation oould be found for the known marked hysteresis during cooling, when the reverse polymorphic transformation takes place at 1040 deg C. In the System ZrO/sub 2/-- ThO/sub 2/ the monoclinic-tetragonal ZrO/sub 2/ inve rsion temperature is lowered to 1000 deg C, although the maximum solid solution extent of ZrO/sub 2/ in ThO/sub 2/ and vice versa is approximately only 2% at this temperature. Relow about 400 deg C. under hydrothermal conditions it was possible to prepare a continuous, although metastable, series of solid solutions with the fluorite structure with compositions varying from ThO/sub 2/ to nearly pure ZrO/sub 2/. Contrary to earlier work only 8 mole% ZrO/sub 2/ dissolves in UO/sub 2/ and less than 4 mole% of UO/sub 2/ in ZrO/sub 2/ at temperatures up to 1300 deg C. A continuous series of solid solutions could be made between ThO/sub 2/ and UO/sub 2/ at 1300 deg C, and extensive defect fluorite solid solutions could be prepared between ThO/sub 2/ and U/sub 3/O/sub 8/; there is some evidence for exsolution into uranium-rich and thorium-rich members at low temperatures. (auth)
- Research Organization:
- Pennsylvania State Univ., University Park
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-14-014085
- OSTI ID:
- 4189444
- Journal Information:
- Journal of the American Ceramic Society (U.S.), Vol. Vol: 43; Other Information: Orig. Receipt Date: 31-DEC-60
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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