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investigation of the oxidation of fuel
mixtures contained in nickel has been
complicated by the corrosion of the
nickel containers. The corrosion has
been studied in a series of experi-
ments
In each experiment, 5 to 10 g of
fluoride, in a nickel boat, was placed
in a “combustion tube” consisting of a
horizontal 1 1/2-in.-OD stainless
steel tube heated by a tube furnace.
The inner surface of the steel tube
was protected by a sleeve of 5 - m i l
nickel sheet. The tube was evacuated
and heated to the desired temperature;
dry air was then admitted and passed
through at a rate of about 40 cm3/miri
for about 4 hours. The solid product,s
were examined by x-ray diffraction.
No gaseous products were observed.
In summary, nickel is oxidized
severely by dry air when in contact
with fused fluorides. The oxidation
is accompanied by creeping of the melt
over the entire heated surface of the
nickel container. Uranium, when
present in the fluoride mixture, reacts
to form a yellow product that probably
contains oxygen but has not yet been
completely identified.
It 1s suggested that the oxidation
orcurs because the fused fluorides
d is so 1 ve the ad her en t p r o t e c t i ve s c a 1 e
of nickel oxide, which forms in the
,.
absence of the melt.
1he formation of the greenish-gray
nickel oxide observed in several of
the experiments appears to be associated
with the presence of moisture in the
salt employed.
EMF Measurements in Fused Fluorides
(L. E. Topol, L. G. Overholser,
Materials ChemistryDivision). Previous
studies, (’) involving the determination
of the decomposition potential of NiF,
in molten KF, suggested that a thermal
decomposition of NiF, occurred during
the experiments and led to a study of
the decomposition of NiF,, NiO, and
K,?JiF, at temperatures from 700 to
.__I
(9)L. E. Topol and L. G. Overholser, ANP Quar.
Prog. Rep. Sept. 10. 1952, ORNL-1375, p. 123.
PERIOD EBBING DECEMBER 10, 1952
900°C in a purified helium atmosphere.
The study has been continued and
extended to include the possibility of
decomposition under vacuum. An attempt
has been made to measure the decompo-
sition potential of KF on Ki at 890°C
in a nickel container.
Repeated attempts to prevent the
decomposition of NiO and NiF, at 750
to 900°C under a purified helium
atmosphere were unsuccessful, even
when all the rubber tubing was re-
placed with glass or copper tubing.
In some caseb, the weight losses were
apparently greater than could be
explained hy complete decomposition of
the NiF, or hi0. An attempt is being
made to measure the dissociation of
NiF, and NiO in vacuum at various
temperatures. A vacuum system has
been constructed, and a preliminary
experiment showed that no apparerlt
decomposition of the NiO occurred, even
though it had been heated to 1020°C.
This absence of dissociation is in
agreement with the findings of Johnson
and Marshall,(’o) who measured the
vapor pressure of NiO at temperatures
from 1440 to 1566°K. Studies of the
behavior of NiO in vacuurn are con-
t inuing.
Decomposition potentials have heen
determined in KF at 890°C with nickel
electrodes invarious vessels. Measure-
ments were made in Norton stabilized-
zirconia crucibles (TZ-5601) and in
Norton thoria crucibles (LT-7010),
although these materials are somewhat
permeable to the KF. Subsequent runs
were made with a nickel cup as both
container and cathode and a 1/16-in.-
dia nickel rod as the anode. In every
case except one, a decomposition
potential was observed at 0.7 to 0.9
volt. These values agree with earlier
values(’) and wit,h those determined by
Neumann and Richter( on graphite.
In one run in which higher potentials
(lo)H. L. Johnson and A. L. Marshall, J. Am.
Chern. SOC. 62, 1382 (1940).
(‘“B. Neurnann and H. Richter. Z. Elektrochem,
31, 296 (1925).