PHASE EQUILIBRIUM DIAGRAMS OF SYSTEMS UO$sub 2$-ZrO$sub 2$ AND ThO$sub 2$- ZrO$sub 2$

Technical Report · Sat Oct 31 04:00:00 EST 1959

OSTI ID:4290613

Voronov, N M; Voitekhova, E A; Danilin, A S

Phase equilibrium diagrams of the systems UO/sub 2/ZrO/sub 2/ and ThO/ sub 2/ -- ZrO/sub 2/ were plotted. The diagram of the ously only by a decrease of the single-phase region at low temperatures, while the diagram of the ThO/sub 2/--ZrO/sub 2/ system hardly corresponds to the findings published about it by previous investigators. It follows from the diagrams of UO/sub 2/--ZrO/sub 2/ and ThO/sub 2/ --ZrO/sub 2/ that the tendency of the components in both systems to form eutectic mixture which is preconditioned by a substantial differrence in the cation sizes is not realized, and the transition from the liquid state to a solid one terminates by the formation of solid solutions: continuous in the case of UO/sub 2/--ZrO/sub 2/ and containing from 0 to 87 mole% of ZrO/sub 2/ in the case of the ThO/sub 2/--ZrO/sub 2/ system. However, the difference in the sizes of the cations entails in both systems a discontinuity of solubility in a solid state. Because of difference in the sizes of the ions of zirconium and thorium, which is bigger than the difference between the ions of zirconium and uranium, the disintegration of the ThO/sub 2/-ZrO/sub 2/ solid solution begins at a higher temperature than the disintegration of the solid solution of UO/sub 2/--ZrO/sub 2/ . The greater difference in the sizes of Zr/sup 4+/ and Th/sup 4+/ than between Zr/sup 4+/ and U/sup 4+/- explains also the fact that in the case of the UO/sub 2/ --ZrO/sub 2/ system the transition from a cubic UO/sub 2/ solid solution to a tetragonal ZrO/sub 2/ one is continuous while the same transition (of a ThO/sub 2/ solid solution) in the ThO,--ZrO/sub 2/ gystem takes place through an intermediate, although a narrow two-phase region. The stability of the tetragonal solid solution in the UO/sub 2/-ZrO/sub 2/ system to lower temperatures than of the ThO/sub 2/--ZrO/sub 2/ system may be also explained by the difference in the cation sizes. (auth)

• Research Organization: U.S.S.R.
• NSA Number: NSA-13-006420
• OSTI ID: 4290613
• Report Number(s): A/CONF.15/P/2490
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

CATIONS
CERAMICS
CHEMISTRY
CONFIGURATION
DECOMPOSITION
DIAGRAMS
ELECTRONS
EUTECTICS
FUELS
GRAIN SIZE
IONS
LOW TEMPERATURE
MEASURED VALUES
MIXING
PHASE DIAGRAMS
QUANTITY RATIO
SOLID SOLUTIONS
SOLIDS
SOLUBILITY
TABLES
TEMPERATURE
THORIUM
THORIUM COMPOUNDS
THORIUM OXIDES
URANIUM
URANIUM COMPOUNDS
URANIUM DIOXIDE
VALENCE
ZIRCONIUM
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES