ORNL-1816 - the Molten Salt Energy Technologies Web Site

AN P QUARTERLY PROGRESS R €PO RT
to cause oxidation of the hydrogen from the NaOH-
Ni reaction to water.
Addition of 2 mole % Na20 also resulted in
oxidation of the hydrogen to water. At 8OOOC the
pressure with this addition was found to be only
33 mm, while the hydrogen pressure of the NaOH-Ni
system was 126 mm at this temperature.
A 2 mole % addition of an equimolar mixture of
Na20 and NiO to NaOH gave a pressure of 33 mm
at 800OC. Evidence indicates that a substantial
fraction of this pressure is due to water vapor.
FUNDAMENTAL CHEMISTRY OF FUSED SALTS
Solubility of Xenon in Fused Salts
R. F. Newton
esearch Director’s Department
e t tive values for the solubility of
X in the NaF-KF-LiF eutectic and in the
eutectic were reported,24 experi-
ments have shown that leakage of xenon through
the frozen seal was possible. To minimize this
possibility the apparatus was redesigned to have
at least 10 cm of liquid above the frozen section
on the xenon side and to be about 6 cm long. The
new design also permits returning the fused salt
by adjusting the pressure difference and melting
the frozen seal.
While the metallic apparatus for use with the
fluoride eutectic was being rebuilt, the KN0,-
NaNO, eutectic was reinvestigated in a glass
apparatus that incorporated the new design features
described above. The nitrate mixture can be used
without significant decomposition up to about
450OC; in 6 hr, at temperature,about 0.01% of the
nitrate was decomposed at 41OOC and about 0.3%
was decomposed at 500OC.
With the new apparatus, values of 8 x and
9.3 x 10-8 mole of xenon per milliliter of melt
at 260°C and 8.9 x and 9.6 x at
45OOC were obtained. These values are essentially
in agreement with the previous ones, namely
8.5 x at 28OOC and 10 x lo-* at 360OC.
The change in solubility with temperature appears
ay Diffraction Studies in Salt Systems
P. A. Agron M. A. Bredig
Chemistry Division
MF-XF, Binary Systems. The renewed interest
in the binary systems of alkali fluorides with
uranium trifluorides was emphasized this past
quarter. In studying these systems, difficulties
arise from partial oxidation of U(III) to U(IV)
and/or through disproportionation of the uranium
in solution in the molten alkali fluorides. It thus
appeared to be worth while first to obtain un-
equivocal x-ray data on the corresponding binary
fluoride complexes of some of the “4f rare earth”
especially of lanthanum, which may be
considered as a good “stand-in” for U(III).
Zachariasen reported2‘ several trifluorides of the
“5f rare earth” group as having the same “tysonite”
structure as those of the “4f” group, previously
determined by Oftedc11.~~ For the trifluorides,
the average La-F and U-F distances are given as
2.50 and 2.56 A, respectively. The lattice di-
mensions of these hexagonal cells differ by only
0.05%. Thus it is not surprising to discover in
samples prepared here2* that the structure of the
double fluorides25 of NaLaF, and KLaF, had
their counterpart in analogous NaUF4 and KUF,
structures.
According to Derg~nov,~ in MF-LaF3 systems
all alkali fluorides, with the possible exception
of CsF, form 1:l compounds, and only CsF forms
a 3:1, Cs,LaF,, congruently melting compound.
These data were obtained by visual observation
of crystallization from melts. Compounds below
the eutectic that are stable and polymorphous
transitions would not have been discerned.
In the present work, fused mixtures of the binary
systems MF-LaF, (except 3NaF-LaF3 and LiF
mixtures) of the molar compositions 3:l and 1:l
were made available from thermal-halt measurements.
29 X-ray diffractometer patterns were obtained
on these melts, The phases found in the
NaF and KF systems are indicated in Table 5.7
and are the phases expected for these binary compositions.
Excellent agreement is shown for the
24R. F. Newton and D. G. Hill, ANP Quar. Prog. Rep.
Sept. IO. 1954, ORNL-1771, p 70.
25W. H. Zachariasen, Acta Cryst. 1, 265 (1948); J.
Am. Chem. SOC. 70, 2147 (1948).
26W. H. Zachariasen, Fluorides of Uranium and Thorium
with the LaF Type of Structure, MDDC-1 153 (date
3
of manuscript, June 1946; date of declassification,
July 18, 1947).
271. Oftedal, 2. psysik. Chem. 5B, 272-291 (1929).
28V. S. Coleman, W. C. Whitley, and C. J. Barton,
Materia Is Chemistry D ivis ion.
29L. M. Bratcher and C. J. Barton, Materials Chemistry
D i vis ion.
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