ORNL-1771 - Oak Ridge National Laboratory

PERIOD ENDING SEPTEMBER 70, 1954
TABLE 5.9. DECOMPOSITION POTENTlALS OF VARIOUS CHLORIDES IN KCI AT 850'C
Concentration of
Salt Salt in Solute
(mole %)
Electrodes Blanketing Potential 0 bserved
Cathode Anode Atmosphere (V)
_I l-__l_________...._l________
K CI 100.0 Ni Cr He 1 .so
UCI3 33.3
33.3
u CI, 33.3
33.3
33.3
3.0
3.0
3.0
FeCI2 33.3
33.3
2.0
1.0
10.0
Pt Zr He Spontaneous
Pt Cr He 0.40
PI C H2 0.95, 0.83, (0.75)
Pt C He 0.83, 0.95
Pt Ni He 0.60 to 0.80
Pt C He 1.84 to 1.87
Pt C H2 (1.15)
Pt Ni He 0.34
Ni C He 0.80 to 0.83
Ni Ni He 0.35 to 0.45
Ni C He 1.45
Ni C He 1.50
Ni C He 1.00
NiCI, 33.3 Ni C He 0.93, 0.82
3.0 Ni C He 1.13 to 1.17
1 .o Ni C He 1.20
little evidence for this behavior in fluoride melts.
Dilute solutions of UCI, decompose into U and
CI, at inert electrodes upon passage of current.
Since the measured E's are somewhat less than
the theoretical estimate of 1.99 v, it is believed
that either some depolarization occurs or that the
estimate is too high, or that both are responsible.
Concentrated UCI, solutions may undergo the folio
wing electrochemical tran sformati on s at platinumgraphite
e I ectrodes:
(1) 2UC14 - 2UCI, + a,, Eo 7 1.18 v,
( 2)
(3)
UCI, = u i- 2c4, Eo = 1.9 V,
5UCI, = 4UCI, t- U ~ E
O = 1.6 v,
Uranium metal is deposited on the cathode; so the
first reaction does not occur alone. I f this process
takes place in coniunction with the transformation
(4) 4uc1, = 3UC14 + u , Eo := 0.85 v,
a continuous depletion in the UCI, concentration,
which is low initially, would result (more UCI,
would be oxidized io UCI, than would be replaced
at the cathode). With low concentrations of UCI,
_1_-- _I-___
the reaction
(5) 2UCI, = 2U + 3CI,, E O = 2.2 v,
has been found to predominate. The high value of
E' for reaction 2 eliminates its consideration at
these voltages, The decomposition potential of
reaction 3 is high also but may be accounted for
by an activity ratio of (UCI,)/(UC1,)5'4 that is
approximately equal to if the estimated AFD's
of -191 and -183 kcal for UCI, and UCI,, respectively,
are correct. The reaction of dilute and
concentrated UCI, solutions and nickel anodes may
be attributed to
2UCI, t Ni -: 2UC1, -t NiCI,, Eo L- 0.36 v.
Dilute UCI, solutions seem to show signs of reduction
in a hydrogen atmosphere.
concentrated and dilute FeCI, solutions also
undergo different reactions at. inert electrodes. In
concentrated solutions FeCI, is oxidized to Feci3
at the onode (E" : 0.35 v), whereas in dilute solutions
decomposition into the elements occurs
(E" = 1.11 v). With nickel anodes, both the fol-
1 owing reactions probably occu r si ni u I t aneou s I y :
E" = 0.30 v,
FeCI, t Ni = NiCI, + Fe,
69