ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORT
Oxidetioar-[Reduction Titrations in Fused Salts
A. S. Meyer, Jr.
.4nalytical Chemistry Division
Experiments were carried out to determine whether
the equivalence point of a titration in which UF,
dissolved in a molten fluoride fuel solvent is re-
duced by the addition of small increments of an
electrodeposition metal could be observed by one
of the conventional electrametric techniques. The
first system studied involved the reduction of UF,
in NaZrF, by zirconium metal according to the
proposed reaction
4UF, + Zio.----+ 4UF, t ZrF, .
Since no insulating material which is compatible
with molten NaZrF, was available, it was not
possible to devise a reference electrode for meas-
urement of the potentials of the solutions. Accord-
ingly, polarized platinum electrodes were selected
CIS indicating clectrodes. In order to obtain more
inlgrmation about the nature of the polarization
phenomena, the area of one of the electrodes was
made approximately 80 times that of the other.
TAiis, since the current density at die smaller
electrode WQS 80 times as great ns that at the
larger, the potential difference between the elec-
trodes was approximately equal to that of the
smaller electrode. By reversing the direction of
the polarizing current, it was possible to determine
the potential at the cathode and at the anode.
The solution of UF, in NaZrF, was contained in
a 25-ml platinum crucible whish was placed in the
helium-filled quartz liner of a pot furnace, Agi-
tation was accotnplished by means af a mechani-
contained 1.25 mole % UF, the potential of both
electrodes wets approximately 300 mv, with no
significant difference between the potentials of the
cathode and anode.
During the early part of the titration of the molten
fluoride mixture with zirconium metal, the potential
of the cathode decreased to values less than 10 mv
and remained constant throughout the titration. At
the same time the potential of the anode increased
rapidly and attained potentials in excess of 1 v
before the end point of the titrution was reached.
When an equivalence point was reached, the poteti-
tial of the anode decreased rapidly to about SQ mv
and then decreased gradually on further addition of
reductant. Only one break in the potential vs
titrant curve wa5 observed, The curve is shown
Fig. 10.2.
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p 0 ~-
0 O! 02 03 04 05 06
1
EQUIVALENTS OF ZlRCOYlUM PER MOLE 0' UF4
09 io
Fig. 10.2. Titration of UF, in Molten NaZrF,
with Zirconiun1 Metal.
cally driven platinum stirrer which was constructed
of 0,05in.-dia platinum wire, Additions to the Theobserved end points of two titrations occurred
solution were made through a quartz tube which at a weight of titrant which corresponded to oneextended
from the top of the liner to a point about half an equivalent of zirconium metal per mole of
1 in. abave the nie!t. UF,. This stoichiometry indicates the reduction of
In pure NaZrF, the anode was inore strongly UF, to a mixed oxidation state that corresponds
polarized than the cathode. At polarizing currents to the postulated formula U,F,.
of 80 pa the potential of both electrodes exceeded
1 v. Approximately \ hr was required for the
electrodes to reach equilibrium. Platinum electrodes
could not be appreciably polarized in NaF-
KF-LiF-base fuels.
When UF, was added to he molten NaZrF5, the
potential decreased rapidly. For solution which
2E. L. Colichmno, Polaro raphy in Molten Ammonium
Fomzate, LRL-117 (April 1959).
150
Poiarogaaphic Studies in Fused Ammonium Formate
A. S. Meyer, Jr. D. L. Manning
Analytical Chemistry Division
CoIichmun2 reported that when solutions of UCI,
in molten ammonium formate were reduced at the
droppingmercury electrode, three we1 I-defined re-
duction waves with half-wave potentials of -0.1 to
-0.2, 4,75 to -0.80, and -0.95 v (vs pool) were