Viscosity Determination of Boron Oxide and Binary Borates 83times contained glassy material in addition to crystalline phases since the compounds BeF2 or 2LiF.BeF2 failed t o crystallize. This nonequilibrium condition occurred during thc cooling period after the purification process. A thermal gradient or a filtration study of such a sample would not indicate thc equilibrium crystallization path; therefore, all melts containing glassy material after purification were discarded. The probability of the formation of glassy material predominated in those compositions which had been heated to teinpcratures 200OC or more above their liquidus temperature. This probability was minimized when the temperatures during the purification process were limited to 5O0C above the liquidus temperature. A metastable phase found in some samples quenched from above the solidus temperature in the lithium fluoride-uranium tetrafluoride system had been reported by Barton et aL3 with a probable composition of 3LiF.UF4. The same phase was found in ternary compositions which had been quenched from above the solidus temperature near the 3LiF.UF4 composition point. I n several instances, this phase was found in slowly cooled ternary compositions which covered a wider composition range than the range from which the phase was formed during the quenching process. IV. ConclusionsThe addition of BeF2 to the binary system LiF-UF4 yields two low-melting ternary eutectics. T h e BeF2 shows no tendency to form compounds or enter into solid solution with UF4 or lithium-uranium fluoride compounds. Suitable compositions for a molten-salt nuclear-reactor fuel could be chosen from a wide range of ternary compositions with low liquidus temperatures. AcknowledgmentsThe writers acknowledge with gratitude the assistance of L. L.Bentz, D. L. Roesch, and J. J. Dauby, who performed the chemical analyses required for this study.The anomalous behavior of rubidium and cesium borate glass and the boron coordination in alkali borate liquids are discussed. The viscositycomposition isotherms of rubidium and cesium borates have been found to follow the same trend as those of other alkali borates. For boron oxide at temperatures between 500" and 775"C, the activation energy for viscous flow, Evis = (4.213 X lo4) (1/T) -22.15 and for temperatures above 775"C, &is = (1.121 X lo4) (1/T) + 7.40, in which T is in OK. The activation energies for viscous flow, I L S , in kcal per mole, increase with all molten alkali borates in the order Li > Na > K > Rb > Cs to about 20 mole yo of akali oxide. This phenomenon is explained on the basis of Douglas's hole theory.T investigations on t h e behavior of alkali (Li, Na, K)2 and allialine-earth borate9 were conducted, however, within the Presented a t the Sixty-Third Annual Meeting, The American Ccramic Society, last decade. The purpose of this paper is to present some new information on rubidium and cesium borates and to discuss the anomalous behavior of alkali borates and the boron coordination in borate liquids. Previous investigatio...
Density determinations of pure Bz03 and binary rubidium and cesium borates have been made in the temperature ranges 450" to 13OO0C and 500" to ll0O'C respectively. The density of BZO3 can be represented between 600' and 1000°C as d = 1.3388 + 228 (l/T) and for temperatures above 1000°C as d = 1.3947 + 157.9(l/T), where d is in grams per milliliter and T is in O K . The volume expansion ( d V / d T ) in the alkali borate systems at 800°C increases with an increase of alkali oxide when the alkali concentration is more than 18 mole yo. This increase in the volume expansion follows the order Cs > Rb > K > Na > Li. In the range 15 to 20 mole yo alkali oxide a break in the volume expansion was observed. This break suggests a possible change in the structural configuration of the alkali borates.
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