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ANP PROJECT PROGRESS REPORT
MF2*ZrF4
TABLE 2.2.12. FREE ENERGY OF FORMATION OF MFZ*frF,
Saturation Free Energy of Free Energy of
Temperature
(OC)
Solubility, N
(mole fraction)
Activity
Coefficient, y
Complexing, A
(kca I/mo le)
F ~ Formation, ~ bo ~ ~
(kcal/mole)
600
700
'600
700
0.007 1
0.0550
0.00331 1900
0.0 180 1100
GF2* Zr F, 600 0.0210 1.15 -8.8 -545
3.28
2.20
-8.8
-8.3
+0.9
+ 1.6
-530
-520 -
700 0.183 0.87 -7.8 -535
solid complex is no3 stable with respect to solid
NiF, and ZrF,.
The activities of MF, in the saturated solution
were obtained by combining solubility and activity
coefficient measurements. Henry's law is expected
to hold quite well for dilute solutions in molten
electrolytes because the environment of a solute
ion is not significantly influenced by the presence
of other solute ions unless appreciable concentra-
tions are present. This has been demonstrated for
FeF, in NaF-ZrF, (53-47 mole %) over a range of
concentrations from 0.03 to 0.06 mole % by meas-
urements of the activity coefficient based on equi-
librium studies at 600 to 800°C.17 The values of
the activity coefficients for FeF, (y at 600OC is
3.28; y at 700OC is 2.20) were combined with
elertrometrically determined activity coefficient
ratiosl8 (from bimetallic couples) to give the
activ-ity coefficients of CrF, and NiF, shown in
Table 2.2.12. Previously published measurements1
showing a twofold change in yFeF with concen-
tration in the range'0.06 to l.5mofe % FeF, are
tentatively regarded as in need of reinterpretation.
The saturation concentrations listed in Table
2.2.12 were obtained from the equations presented
in the preceding section on "Solubility Determina-
tions by Measurement of Electromotive Forces of
Concen trot ion Ce I Is."
The activities of ZrF, were computed from vapor
pressures by using the expression
17C. M. Blood and G M. Watson, ANP Qum. Ptog.
Rep. March 10, 1956, ORNL-2061, p 84
'*L. E. Topol, ANP Quar. Prog. Rep. Dec. 10, 1955,
ORNL-2012, p 97.
106
-510
-500
where p is the vapor pressure of ZrF, in NaF-ZrF,
(53-47 mole %) and po is the vapor pressure of
solid ZrF,. Since
and
log P = 9.243 -
9.252 x lo3
T
12.376 x lo3
log Po = 13.400 - I
T
P 3.124 x lo3
log- = -4.157 +
T
PO
where T is temperature in OK, which gives
P
log - = -0.578 at 600OC ,
PO
= -0.945 at 7OOOC .
The equation for po was obtained from the work of
Sense et The activity of ZrF, in the satu-
rated solution was assumed to be the same as the
activity in the pure solvent NaF-ZrF, (53-47
mole 76). This assumption is probably valid in all
cases except that of CrF, at 700OC; here the solu-
tion is too concentrated for much reliance to be
placed on the calculation. If the saturating phase
were simple NiF, in the NiF, experiments, then
19K. A Sense et aL, Vapor Pressures o/ the Sodium
Fluoride-Zirconium Fluoride System and Derived In-
formation, BMI-1064 (Jan. 9, 1956).
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