C.J. Barton

Phase relations in fluoroborate systems—I: Material preparation and the systems NaFNaBF4 and KFKBF4☆☆☆

Abstract High-purity NaBF4 and KBF4 having higher melting points than any previously reported were prepared. These preparations were used in a reinvestigation of phase relations in the systems NaFNaBF4 and KFKBF4 by means of differential thermal analysis (D.T.A.) and gradient quenching techniques. Both were found to be simple eutectic systems with eutectics melting at 384±2°C for the NaFNaBF4 system and 460±2°C for the KFKBF4 system.

Phase equilibria in the systems NaFPuF3 and NaFCeF3

Abstract Phase equilibrium relations in the system NaFPuF 3 were determined by thermal analysis and microscopic examination of the slowly-cooled fused mixtures. This system was investigated because of interest in possible use of mixtures in the systems NaFBeF 2 PuF 3 and NaFLiFBeF 2 PuF 3 to fuel a molten fluoride power reactor. Previous studies indicated that the solubility of PuF 3 in such mixtures at proposed reactor operating temperatures is adequate for reactor designs currently under consideration. A similar study of the NaFCeF 3 system carried out in conjunction with the NaFPuF 3 study served to test high-temperature thermal analysis apparatus, discussed in this paper, before it was used with plutonium mixtures in the glove box. It also provided data needed to complete a phase diagram based on earlier studies of the system in this Laboratory. The NaFPuF 3 system was found to have one eutectic composition containing about 24 mole % PuF 3 melting at 727 ± 3°C and one compound, NaF·PuF 3 , melting incongruently at 842 ± 3°C. Similarly, the NaFCeF 3 system was found to have one eutectic composition containing about 28 mole % CeF 3 melting at 726 ± 3°C and one compound, NaF·CeF 3 , melting incongruently at 810 ± 10°C.

Phase relations in fluoroborate systems—II: The system NaFKFBF3

Abstract Two quasi-binary systems were identified in the system formed by the compounds NaF, NaBF 4 , KBF 4 , and KF. The only part of the NaFKFBF 3 system that can be studied at atmospheric pressure contains a maximum of 50 mole % BF 3 . Differential thermal analysis and quenching data indicate that the high-temperature polymorphs of NaBF 4 and KBF 4 form a continuous series of solid solutions with a very shallow minimum, melting at 398°C, near the 90 mole % NaBF 4 composition. There is some evidence for the existence of a sub-solidus compound, 3NaBF 4 ·KBF 4 , which is stable between approximately 193° and 280°C. The compounds NaF and KBF 4 form a simple eutectic system containing 94 ± 1 mole % KBF 4 which melts at 539±2°C. The ternary system is dominated by a large NaF primary phase field. There is a shallow ternary minimum, corresponding to the NaBF 4 KBF 4 quasi-binary minimum, containing 3·5±1 mole % KF and 48±1 mole % BF 3 which has a liquidus temperature of 377±2°C. The ternary eutectic composition in the NaFKBF 4 KF triangle is very close to the KFKBF 4 binary eutectic in composition and it melts at 458°C only about 2° lower in temperature.

Phase relations in the system KFCeF3

Abstract The system KFCeF 3 was investigated as a function of temperature and composition by thermal analysis, differential thermal analysis, and gradient quenching. Crystalline phases in the quenched samples were identified principally by use of the polarizing microscope, but selected samples were examined by X-ray powder diffraction. Three compounds were identified: 3KF·CeF 3 , KF·CeF 3 , and KF·2CeF 3 which melt incongruently at 675±10°C, 755±5°C, and 1135±15°C, respectively. Of these only KF·CeF 3 is stable below 585°C. Three peritectic equilibria were observed corresponding to these incongruent melting points at 24, 32, and 63 mole % CeF 3 . The αKF·2CeF 3 phase exhibits a substantial solid solubility for KF at temperatures above 795°C which results in a region of cubic solid solution whose properties vary over the composition range from 50 to 66- 2 3 mole % CeF 3 .

Phase equilibria in the systems BeF2CeF3, LiFCeF3 and LiFBeF2CeF3

Abstract A tentative phase diagram for the system BeF 2 CeF 3 is presented that shows it to be a simple eutectic system with a eutectic composition containing 4 ± 1 mole % CeF 3 which melts at 540±3°C. Additional thermal analysis and visual observation data are reported to support a phase diagram of the system LiFCeF 3 that has been in the literature. The ternary system LiFBeF 2 CeF 3 is dominated by the CeF 3 primary phase field. Three ternary invariant points are all estimated to contain approximately 0·1 mole % CeF 3 . They have melting points about 0·5°C lower than the corresponding LiFBeF 2 invariant points.

Phase relations in fluoroborate systems—III: The system RbF-RbBF4☆

Abstract Differential thermal analysis and quenching techniques were used to demonstrate that the compounds RbF and RbBF 4 form a simple eutectic system. The eutectic composition contains 68·5 mole % RbBF 4 and melts at 442° ± 2°C.