Viscosity Determination of Boron Oxide and Binary Borates

Abstract

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...

Thermal Conductivity of Molten Li2O–B2O3 and K2O–B2O3 Systems

“…This effect of cations on the physical properties has been reported for the alkali borate system . The viscosity and electrical conductivity are in the hierarchy order of Li 2 O–B 2 O 3 > Na 2 O–B 2 O 3 > K 2 O–B 2 O 3 for the relative systems, and the opposite order can be observed for the apparent specific volume and the coefficient of thermal expansion .…”

Composition and temperature dependence of cesium-borate glasses by molecular dynamics

“…For example, the viscosity-composition isotherms have been discussed in terms of the field strength of the alkali metal ion, and it has been suggested that for a given M 2 O content the concentration of NBOs increases from Li to Cs. 9 This trend is consistent with the alkali dependence of other physical properties, [10][11][12][13][14] including sound velocities and elastic constants which decrease systematically as the alkali changes from Li to Cs. 15 Such a disagreement for the role of metal ions, resulted from parallel studies of the structure and properties of alkali borate glasses, appeared to be resolved in more recent NMR investigations of Zhong and Bray 16 and Bray.…”

“…In addition to the strong influence of the metal oxide content, studies of physical properties of borate glasses have shown a clear dependence on the type of alkali modifier as well. This is demonstrated by viscosity, 9 absorption edge, 10 optical basicity, 11,12 glass transition temperature, and thermal-expansion coefficient 13,14 data of alkali borate glasses. It is possible that this dependence on the type of M 2 O oxide originates from structural variations, although less pronounced than those induced by the increasing M 2 O modifier content.…”

A model to calculate the viscosity of silicate melts

“…The viscosity of Na 2 O-B 2 O 3 melts was reported by Li et al [10], Leedecke and Bergeron [11], Shartsis et al [12], Kaiura and Toguri [13], Nakashima et al [14] and Zhang and Reddy [15]. As can be seen from Fig.…”