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Phase Equilibria in the Alkali Fluoride‐Uranium Tetrafluoride Fused Salt Systems: I, The Systems LiF‐UF 4 and NaF‐UF 4
Author(s) -
BARTON C. J.,
FRIEDMAN H. A.,
GRIMES W. R.,
INSLEY H.,
MOORE R. E.,
THOMA R. E.
Publication year - 1958
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1958.tb13520.x
Subject(s) - eutectic system , liquidus , chemistry , mole fraction , analytical chemistry (journal) , phase diagram , phase (matter) , differential thermal analysis , mole , crystallography , chromatography , diffraction , microstructure , physics , organic chemistry , optics , biochemistry
Detailed phase diagrams, and a description of the techniques which were employed, are presented for the systems LiF‐UF 4 and NaF‐UF 4 . The phase diagrams are complete with respect to the stable phase boundaries from the liquidus to 300°C. and are accurate to within 5°C. with respect to temperatures. The data were obtained from thermal analysis, equilibration followed by quenching, differential thermal analysis, and visual observation methods closely coupled with examination by X‐ray diffraction techniques and optical identification of the cooled melts from all these procedures. The system LiF‐UF 4 contains only incongruently melting compounds with the following peritectic liquid compositions and temperatures: 4LiF. UF 4 , 26 mole % UF 4 , 500° C.; 7LiF.6UF 4 , 40 mole % UF 4 , 610°C.; and LiF‐4UF 4 , 57 mole % UF 4 , 775° C. A single eutectic occurs at 27 mole % UF 4 and 490°C. The compound 4LiF.UF 4 has a lower limit of stability at 470° C., whereas 3LiF.UF 4 is metastable. Five compounds occur in the system NaF‐UF 4 Congruent melting points were found for 3NaF.UF 4 at 629°C. and 7NaF.6UF 4 at 718°C. Peritectic liquids occur at 32.5 mole % UF 4 and 648° C. for 2NaF UF 4 and at 37 mole % UF 4 and 673° C. for 5NaF.3UF 4 . NaF‐2UF 4 has a subsolidus upper limit of stability at 660° C. Eutectic liquids appear at 21.5 mole % UF 4 and 618°C., 28 mole % UF 4 and 623°C., and 56 mole % UF 4 and 680°C. The compound 3NaF.UF 4 has a transition at 528°C. and is unstable below 497°C.; the compound 5NaF‐3UF 4 is not stable below 63O° C. The only stable modification of 2NaF.UF 4 above 273°C. is a hexagonal form not previously reported. The “α‐2NaF.UF 4 ” phase reported by Zachariasen apparently is 5NaF.3UF 4 , and the γ‐2NaF. UF 4 which he described is metastable.