ORNL-1771 - Oak Ridge National Laboratory

values were given for the "equilibrium constants"
obtained with UF, and the metal as starting ma-
terials. During the past quarter, the values have
been checked with various ratios of UF, to UF, as
starting materials in the NaZrF, solution. The
apparatus and details of the experimental technique
were the same as in previous experiments. The
results of the recent series of experirnents in which
2 g of hydrogen-fired (120QOC) Cro and various
UF,-to-UF, ratios were used are shown in Table
5.4. In the table
with the concentrations expressed as mole fractions
by using the formula weight NaZrF, = 2 moles.
Pt was necessary to calculate the final UF, concentration,
since accurate analyses for u3+ in the
presence of Crft could not be made; any error
arising from this calculation would be important
only at low UF, concentrations.
The data show that at both 600 and 800°C the
PERIOD ENDlNG SEPTEMBER 70, 1954
values of Kx remain constant at low UF,-to-UF,
ratios but increase rapidiy as this ratio rises above
3. This rapid increase in Kn may be due to in-
complete removal by filtration of small amounts of
chromium metal or to uncertainties in analysis of
these trace quantities. Since, as shown above, the
UF,-to-UF, ratio in NaZrF, solution in equilibrium
with uranium metal is about 9 at 800"C, it is not
likely that disproportionation of the UF, is re-
sponsible for the increase in Kx.
In any case, the agreement between the mean of
four values of the constant ut each temperature
with previously published values is extremely good.
Agreement among the various initial UF,-to-UF,
ratios seems to show that a state of equilibrium is
reached in these experiments.
When equilibrium data for the reaction
Fe" t 2UF4&2UF, i FeF,
were obtained by the addition of UF, UF, and
FeF, to NaZrF, in the same way as for the chra-
mium reaction, the results obtained were not so
reproducible. The data obtained are shown in
Table 5.5. The mean of the values obtained at
TABLE 5.4. EQUILIBRIUM DATA FOR THE REACTION Cr" t 2UF,f==! CrF2 + 2UF3 IN MOLTEN NoZrF5
Experimental Cond it ion s
Equi I i bri um*
Concentroti or?
Temperature
UF, Added UF3 Added of Cr++
("C) (moles/kg of melt) (moles/kg of melt)
(PP4
600
0.358
0.267
0.178
0.089
0.035
0.029
0.078
0.158
0.238
0.287
0.318
800
0.360
2660
7.4 io-,
0.280
0.08 1
1 I25
6.1 IO-,
0.194
0.165
210
3.3 lo-,
0.111
0.244
55
4.2 x lo-'
0.064
0.295
30
1.8
0.032
0.325
35
7.9 10-3
+t
*Values shown ore mean of closely agreeing values from duplicate experiments. Blank contained 200 ppm of Cr .
**Kk values previously obtained: at 6OO0C, Kx = 4.2 4 W4, at 8OO0C, Kx - 4.1 x lo-,.
K calculated from -l\P= RT InK by uslng Brewer's values for AP: at 6Q0°C,Kcq - 1; at 800"C,Keq:
eq "4
0.1.
2080
9 50
150
35
50
40
3.0 x
5.1
2.7 x
KX**
4.4 10-4
5.7 lo-,
1.1 x 10-2
61