ORNL-1771 - Oak Ridge National Laboratory

handled melts and pure chromium metal. Itappears,
therefore, that impurities were predominantly re-
sponsible for the amounts of corrosion measured.
The most likely impurity is HF, which can result
from hydrolysis of adsorbed water or hydrated water
in salts containing Na3Zr4F,, or from inadequate
pur if ication.
If HF were responsible, the ascending portion of
the curve could be due to an increasing rate of
reaction with increasing temperature. (There is
little reason to believe that equilibrium conditions
are reached in static capsules in 100 hr.) The
descending portion of the curve may be ascribed to
a marked decrease in corrosiveness of HF at
increasing temperatures.
Standard free energy e~timates'~ show that Ai:'
for the reaction of HF with Ni to form NiF, becomes
positive near 5OO0C, with Fe to form FeF, at
800°C, and with Cr to form CrF, at 1400°C. In
the experiments under discussion here, the melt at
+t
the end of a 100-hr test contains mostly Cr , with
very little Fe" and Ni".
There is some evidence that at the lower temper-
ature a11 three elements are attacked rather slowly
and indiscriminately by HF and that the resulting
Fe" and Ni" are replaced by Crt+ in a fast
secondary reaction. The effect of increasing
temperature is to increase the degree of approach
to eqoilibrium in 100 hr in a static capsule; how-
ever, at higher temperatures the effect of a more
unfavorable equil ibrirrm constant becomes manifest.
Iron and nickel are relatively unreactive toward HF
at IOOO"C, and the amount of Cr++ pickup in 100 hr
could well be less than that noted at 800°C for
three reasons: the free energy change for the
reaction of chromium with HF is smaller, fewer
Fef+ and Nit' ions are present for reaction with
Cr", and there is mechanical interference by the
unreacted nickel and iron. In other words, chromium
is most readily oxidized from an alloy by HF if the
accompanying alloy constituents are also attacked.
Corrosion by Fission Products
H. J. Buttram R. E. Meadows
Materia Is Chemis try D i v is ion
In Q previously reported experiment," a fuel
mixture containing simulated fission products at
1000 times the concentration expected in the AWE
"L. Brewer et (21." 7'?ie Tbeririodynamic Properties wtd
Equilibria at Nigh Temperatures of Vrunium Ualides,
Oxides, Nitrides, rrnd Curbzdrs, MDDC-1543 (Sept. 20,
'1945, rev. Apr. 1, 1947).
PERIOD ENDING SEPTEMBER IO, 7954
was Corrosion tested. Very heavy attack was
observed; this was expected, not because normal
amounts of fission products are particularly cor-
rosive but because oxidizing agents such as RuF4,
MoBr,, and elemental tellurium were used in suffi-
cient concentration to cause excessive corrosion
in any case.
Additional experiments were performed with the
use of the same additives, individually, in amounts
as small as possible in an attempt to measure the
relative activities as corrosive agents. Preliminary
results, such as those previously reported which
showed YF, to be extremely corrosive, and addi-
tional trials during the past quarter, which showed
that such compounds as CsF were also very cor-
rosive, made it obvious that the techniques em-
ployed were unsuitable and that very misleading
indications were being obtained. Free energy
considerations, as well as general experience with
fluoride systems in closed capsules, make it ap-
parent that impurities such as HF and water were
responsible for the effects noted. Hence it must
be concluded that none of the experiments per-
formed to date on corrosion by simulated fission
products have been satisfactory for the intended
purpose.
Controlled-veiocity Corrosion Testing Apparatus
N. '4. Smith F. A. Knox
Materials Chemistry Division
In order to more nearly simulate corrosion con-
ditions of molten fluorides circulating through
reactor components, a control led-velocity corrosion
testing apparatus has been constructed. This ap-
paratus, similar to one previously described,16 al-
lows the rapid transfer of molten fluorides through
both heated and cooled test sections. The apparatus
consists of two 4-in.-ID, 24-in.-high lnconel cylin-
drical pots connected by means of three sections of
fh-in. inconel tubing with a WQII thickness of 0.035
in, The two outside sections are 5 ft long and the
center section, which was initially 3 ft long, WQS
later increased to 3'/, ft, The center section is
cooled by either air or water. Suitable furnaces
and heaters permit holding the pots and transfer
lines at desired temperatures. Each inconel pot
has a gas inlet which allows application of helium
109