ORNL-1816 - the Molten Salt Energy Technologies Web Site

In the electrolyses of KCI the variable in the
two experiments was the insertion of a “dia-
phragm” between the electrodes in one of the runs.
The diaphragm could produce the following effects:
first, although the surface areas of the electrodes
involved were the same in both runs, the interpo-
sition of an insulat crucible with a small hole
through which all the current must flow could
result in a smaller effective surface area for the
cathode. Thus, despite the maximum current in
each cell being the same (1 amp), the current
density of the unseparated cell might not have
been large enough to extrapolate to a true value
of E, the decomposition potential. Second, and
more likely, the lower voltages obtained in the
cell without the diaphragm were due to interaction
of the electrode products at one of the electrodes.
It should be no so that the decomposition
potentials measu this case decreased with
time. In other runs with KCI for which small
cathodes were used, for example, rods or wires,
decomposition potentials of around 3.25 v were
found, with or without the use of a diaphragm,
This anomaly may be due to a greater evolution
of gaseous potassium at an electrode of small
surface area, whereas a thin layer of potassium
formed over a large area may go into solution more
read i I y.
The chlorides of chromium may undergo the fol-
lowing electrochemical reactions at inert elec-
t rodes :
(1) CrCI, = Cr + CI, , Eo = 1.36~~
(2) 3CrCI, = 2CrCI, + Cr , Eo = 0.84 V,
(3) 2CrCI, = 2Cr + 3CI,, Eo = 1.08 V,
PERIOD ENDING DECEMBER 70, 7954
sealed containers for several days. Although there
are differences in the measured decomposition
potentials, it is difficult to explain them ond the
wide ranges of values found. There is no evidence
of dilute solutions of CrCI, undergoing reaction
2 electrolytically, although thermal disproportion-
ation cannot be ruled out, There are similar varied
and divergent values of E for both dilute and
concentrated CrCI, solutions in an inert atmos-
phere. In this case there is evidence of reaction
4 occurring in solutions of various concentrations.
At the end of most of the runs, current-voltage
curves intersected the origin and indicated the
anode and cathode reactions to be equal and
opposite:
cr3+ + e- = Cr+* .
In every case a deposit of metallic chromium was
found on the cathode.
Although decomposition potential measurements
have been terminated, electrochemical studies in
fused salts are to be continued and will include
emf measurements, primarily in fused fluorides,
with speciat emphasis to be placed on finding a
reversible fluoride electrode.
Stability of Chromous and Ferrous Fluorides
in Molten Fluorides
J. D. Redman C. F. Weaver
Materials Chemi stry Division
The compound CrF, or some complex compound
of divalent chromium is quite stable in NaZrF,
melts. When CrF, is added to such melts, it is
reduced to the divalent state even by metals as
noble as nickel; this reduction is, apptrrently,
”L. G, Overholser, J. D. Redman, and C. F. Weaver,
ANP Quar. Prog. Rep. Mar. 10, 1954, ORNL-1692, p 56.
63