ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORT
of 0.5 and agrees closely with the slruiyht line
calculated from Brewer’s value of AFa for the
reaction.
The values obtained for Kx and for Y F ~ on F ~ the
assumption that the activities of HF and W, are
proportional to their partial pressures at 8OOOC and
that
and
Al:OFeF2 - -45.4 kcal per atom of F
LIFO,, = -65.8 kcal per atom of F
are shown in Table 5,7, The QgiYXment of the
values obtained over CI fourfold concentration runge
of FeF, is extremely good. It appears that FeF,
in molten NaF-ZrFd is in nearly ideal solution.
TABLE 5,s. EQUlLlBRlUM CONSTANTS AND
ACTiVlTY COEFFICIENTS AT 800OC IN MQLTEN
NcsF-ZrF4 (53-47 mole X) FOR THE REACTiOW
H2 t FeF2eFeo + 2HF
1598
1513
1458
1372
1318
1233
1122
1067
983
900
8 57
760
606
5.50
48 1
2.15
2.15
2.17
1.98
1.91
2.37
2.07
2.00
2.11
2.18
2.11
2.17
2.19
2.24
2.19
Av 2.13 f 0.22
1.47
1.47
1.48
1.36
1.3 1
1.62
1.38
1.37
1.44
1.49
1.45
1.49
1.50
1.S4
1.50
1.46 f 0.16
Equilibration Method. Since it was doubtful that
the lowest flow rate found to be practicable (9
ml/min) actually represented equil ibriurn condi-
tions, an attempt was rnode to determine the equi-
librium conditions directly. A mixture of HF and
H2 was bubbled through a melt containing Fao and
FeF, until the influent HF concentration matched
66
thot of the effluent. At that time a sample was
drown through a sintered nickel filter and analyzed
to determine the FeF, concentration.
Since the decomposition pressures of molten
KFaHF saturated with KF depend only on temperature,19
definite mixtures of H, and HF could be
obtained while hydrogen gas WQP passed over such
mixtures held at a constant temperature. The
mixtures of H, thus obtained were used as influent
for the reactor containing the salt mixture.
In a typical experiment in which this method was
used, a batch (“3 kg) of previously purified NaF-
ZrF, (53-47 mole %) mixture WQS loaded into a
clean nickel reactor. The mixture was heated to
80OoC and further puiified with hydrogen until a
very low HF concentration (“3 x mote/Iiter)
in the effluen* gas denoted high purity of the melt.
The mixture vias allowed to cool to roam temperature,
and FeF, and iron wire wereadded to the cold,
frozen mixture under un atmosphere of argon. The
mixture was then heated, melted, and brought up to
temperature while it was sparged with helium gas.
The reactor containing the KF*HF or HF generator
SVQS heated separately to a convenient initial
temperature and connected to the system. Pure
hydrogen was passed in parallel through both
reactors - the HF geiuerator and the equilibration
reactor - in order to clean out any NiF, films on
vmlls and to precipitate nickel impurities. After
1 to 2 hr of parallel operation, the reactors were
connected in series, and the inlet on$ effluent
gas streams were continuously sampled and analyzed.
The temperature of the furnace of the
generator was then adjusted until the analyzer
showed H,-HF mixtures of the desired composition.
The gas mixture was allowed to bubble through the
system for extended periods of time, and samples
were taken intermittently for analysis. When it was
considered that the system had approached equilibrium,
as indicated by a convergence of the influent
and effluent compositions, the HF generator
was removed from thz systern and helium was substituted
for the influent gas mixture. A filtering
tube was introduced into the melt under an additional
argon atmosphere and a filtrate was obtained.
The filtering tubs with the frozen filtrate was removed
and analyzed for iron. This procedure was
repeated with appropriate variation of the temperaturf:
of the HF generator and consequent variation
of the influent gas composition,
19G. H. Cndy, /. Am. Chern. SOC. 56, 1432 (1934).