Dee., 1959
SOLUBILITY OF HYDROGEN FLUORIDE IN NAF-ZRF~MIXTURES
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in the molar heat of vaporization is estimated to be 10 cal./mole. To smooth the data, they were fitted to the equation
measurements, reporting 3412 and 3431 cal./mole, respectively. The first value is in good agreement with the value reported here considering the uncertainty in the two values. Wirth and Palmer calculated a value of the heat of vaporization a t the L, = 546.2 ( T o - T)O.39cal. mole-' (3) normal boiling point from their vapor pressure where T , = 289.7"K. Table 11gives the values of measurements, estimating the gas imperfection L,, calculated using eq. 3, and ASv, the entropy of using the Bertholet equation. Their value is 3413 cal./mole and is in exceptional agreement with the vaporization. There have been several previous determinations other two. (4) John T. Clarke, E. B. Rifkin and H. L. Johnston, J . Am. Chem. of the heat of vaporization of diborane at the nor- Soc., 76, 781 (1953). mal boiling p ~ i n t . ~Clarke, ,~ et al., determined it 60, 911 (5) Henry E. Wirth and Emiel D. Palmer, THIS JOURNAL, both calorimetrically and from their vapor pressure (1956).
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SOLUBILITY OF HYDROGEN FLUORIDE I N MOLTEN FLUORIDES. I. I N MIXTURES OF NaF-ZrF4 BY J. H. SHAFFER, W. R. GRIMESA N D G. M. WATSON Oak Ridge National Laboratory,l Oak Ridge, Tennessee Received March 6 , 1968
Solubilities of H F have been determined a t pressures from 0.5 to 3 atmospheres over a temperature range 550 to 800" NaF. Henry's law is obeyed and the solubility decreases with inin NaF-ZrF4 mixtures containing 45 to 80.5 mole creasing temperature. The solubility of HF increases approximately tenfold as the mole % of NaF in the solvent is increased from 45 to 80.5 mole yo. Henry's law constants in moles H F per cc. of solution per atmosphere at 600, 700 and 800" are (1.23 f0.04) x 10-6 and (0.03 0.02) X !0-6 and (0.73 0.01) X 10-6 in NaF-ZrF4 (53 mole % NaF). The enthalpies of solution in kcal. per mole also increase in magnitude from -3.85 to -9.70 as the mole % of NaF is changed from 45 to 80.5. The entropies of solution vary from -5.2 to -6.5 e.u. over the same range of solvent compositions.
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Introduction This investigation constitutes part of a systematic study of the solubilities of gases in molten salts. In this study an attempt is being made to elucidate the solvent characteristics which have an effect on gas solubility. The results of measurements on the solubility of H F in various mixtures of NaF-ZrF4 at pressures from 0.5 to 3 atmospheres over the temperature range 550 to 800" are presented here. Solubilities of gases in liquids have been studied by many investigators; reGews covering much of this work are Solubilities of noble gases in molten fluoride mixtures have been rep ~ r t e d . Burkhard ~ and Corbett6 recently determined the solubility of water in molten LiC1-KC1 mixtures and presented an approximate value of the solubility of HC1 a t 480" in a mixture containing 60% LiC1. No information regarding the solubilities of HF in molten fluorides in the range of pressures, temperatures and solvent compositions presented here has been found in the literature. Related investigations 011 some of the properties and phase behavior of acid fluorides of LiF,' (1) Operated for the United States Atomic Energy Commission by the Union Carbide Corporation. (2) A. E . Markham and K. A. Kobe, Chem. Reus., 28, 519 (1941). (3) J. H. Hildebrand and R. L. Scott, "The Solubility of NonElectrolytes," Chapter XV, 3rd Ed.. Reinhold Publ. Corp., New York. N. Y . , 1950. (4) M. W. Cook, U. S. Atomic Energy Commission, UCRL-2459 (1954). ( 5 ) (a) W. R. Grimes, N. V. Smith and G. M. Watson, THIS JOURNAL. 62. 862 (1958); (b) M. Blander, W. R. Grimes, N. V. Smith and G . M. Watson, ibid., 63, 1164 (1959). (6) W. J. Burkhard and J. D. Corbett, J . A m . Chem. SOL, 79, 63F1 ( 1 957).
NaF,+1° KF," RbF,12CsFi3and NHI FI4have been reported. Information on liquid-liquid solubilities and liquid-vapor equilibrium of HF-UFe mixtures is available.15p16 Mixtures of NaF and ZrF4 were chosen for this investigation because of their value in nuclear fuel element r e p r o c e s ~ i n g ~and ~ - ~ their ~ use (with added UF,) as fuel for an experimental nuclear reactor. 22 (7) H. V. Wartenberg and 0. Bosse, Z . Eleklvochem., 28, 386 (1922). (8) J. F. Froning, M. K. Richards, T. W. Stricklin and S. G. Turnbull, Ind. Eng. Chem., 39, 275 (1947). (9) D. G. Hill, unpublished work, Oak Ridge National Laboratory, Oak Ridge, Tennessee. (10) W. Davis, Jr., KLI-2552, "Vapor Pressure-Temperature Relations in the System NaF-HF," Union Carbide Nuclear Company, Oak Ridge Gaseous Diffusion Plant. ( 1 1 ) G. H. Cady, J . Am. Chem. SOC.,66, 1431 (1934). (12) E. B. R. Prideaux and I
