ORNL-1771 - Oak Ridge National Laboratory

Hydrogen Used
(I iters)
PERIOD ENDING SEPTEMBER 70, 1954
TABLE 5.11. COMPARISON OF HYDROGEN AND ZIRCONIUM METAL FOR REMQViNG
REDUCIBLE IMPURITIES FROM NaF-KF-LiF MIXTURES
Zircon i urn
Contaminants Found in Product
Metal Added -- ___-
Zr (wt %) Fe (ppm) Ni Ippd Cr (wm) -
(31) -
500 None 0.0 2100 7 25
600 None 0.0 725 6 30
300 57 1.3 70 8 20
None 30 1.4 65 9 20
. _I_-___ I_
zirconium introduced wi I1 have a negligible effect
on the physical properties of the melt. However,
in these experiments at 800T some alkali metal
was detected in cold regions of the equipment and
some attack on the gaskets and flanges was ob-
served. If large-scale purifications were attempted,
it would probably be necessary to use a lower tem-
perature for this treatment,
Purification of NaF-ErF, Mixtures by Electrolysis
C. M. Blood
H. A. Friedman
F. P. Boody
F. W. Miles
6. M. Watson
Materials Chemistry Division
In the effort to obtain improved fuel purification
procedures it was shown that electrolysis in NaF-
Zrf, melts at 8OOOC with graphite anodes and
nickel cathodes reduces dissolved iron and nickel
to relatively low concentration in a much shorter
time than is required for the customary reduction
with hydrogen, Furthermore, the reduced impurities
were collected on a removable cathode that could
easily be withdrawn from pots with welded lids.
This feature promises to be of marked advantage in
processing large batches in equipment of a current
design which allows the reduced metal from each
batch io recontaminate subsequent batches and
thereby multiply the amount of reduction required,
Careful attention was given to current-voltage
curves at all stages during the electrolysis in the
hope that “breaks” and apparent decomposition
potentials would permit the progress of the reduc-
tion to be followed. Filtered samples were removed
during various stages and analyzed for iron and
nickel to determine the actual amount present. To
facilitate analysis of the current-voltage curves, the
electrolysis pot was fitted with “floating” anode
and cathode probes, which were used to determine
__
the potential between the melt and the “working”
anode or cathode. The probes were made of k-in.
nickel rod; their potentials with respect to each
other and to both electrodes were followed through
many cycles of increasing and decreasing applied
voltage, but the results have not been completely
interpreted.
J. A. McLaren of the Chemical Technology
Division is of the opinion that measurements with
the reference electrodes have shown that the depo-
sition of iron takes place with very little over-
voltage, At a current of 1 amp, iron was deposited
with a difference of potential between the cathode
and the nickel reference electrode of only 15 mv.
After depletion of the iron, the cathode potential
increased to 75 rnv.
The anode potential was found to have a marked
discontinuity in the graph of current density and
voltage, At some critical current density the anode
voltage would increase suddenly. At the beginning
of the electrolysis the jump was found only at high
current densities, but as electrolysis continued,
it was found at lower current densities. The anode
lump was on the order of 0.2 to 2 v, an order of
magnitude greater than the increase found on the
cathode.
All the electrolyses were carried out in NaF-
ZrF, (47-53 mole %) mixtures in nickel containers.
The electrodes were suspended from the lid of a
3-kg capacity purification reactor (4 x 17 in.) with
modified spark plugs as insulating connectors; the
electrodes were immersed to a depth of about 4 in.
The anode was a $-in,-dia C-18 graphite bar
threaded to a short length of nickel rod which was
welded to the spark plug. Direct current was
supplied from a Dresser Electric Co. 26.v 25amp
selenium rectifier; measurements were made with
the use of sui table potentiometers, voltmeters,
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