ORNL-1771 - Oak Ridge National Laboratory

Stability of Chrorni lam Compounds in
Molten IF! uor ides
J. D. Redinan C. F. Weaver
Mater i al s Chem i s try Divi s ion
It was shown in previous experiments that CrF,
or some complex compound of divalent chromium
was fhe corrosion product in the ZrFdobase fluoride
melts of interest. However, when NaF-KF-LiF
mixtures, with and without UF,, were tested in
equipment prepared from al ley s containing chromium,
the reaction products found were complex com-
pounds of CrF,. Since films that were apparently
NaK,CrF, or similar materials have been observed
in some experiments, attempts have been made to
observe the stability and soluLility of CrF, and
CrF, in typical salt mixtures of the two types.
In the temperature range 600 to 8RQ°C, CrF, is
not stable in NaZrF, solution in contact with
equipment of nickel. Examination of filtered speci-
mens shows that the reaction
2CrF, + Ni ,A NiF, + XrF,
proceeds to essential completion, The solubility
of 6rF2 in the NaZrF, solvent seems to exceed
6000 parts of Cr per million parts of salt at 600%;
solubility at 800°C seems ta be at least 15,000 ppm
and may be consideratly higher.
In the NaF-KF-LiF system it appears that CPF,
is not stable. Whether the disproportionution re-
action
3CrF,-dCr0 i 2CrF,
or some other mechanism is involved 15 not evident
from the data available. It appears from preliminary
evidence, however, that the solubility of Cr3' is
several thousand parts per million at 600OC.
Reduction of NiF, by H, in NaF-ZrF, Systems
C. M. Blood H. A. Friedman
G. M. Watson
Materials Chemistry Division
The use of hydrogen as a reducing agent in the
removal of oxidizing impurities from fluoride melts
has been routine for almost two years. One of the
principal impurities removed is the Ni +' introduced
as a result of treating the melts with hydrogen
fluoride in nickel containers at 80OoC, Since
hydrogen was first employed in this fashion, kinetic
studies have been under way in order to supply data
on which improved fluoride production procedures
PERIOD ENDING SEPTEMBER 70, I954
could be based. The Ni" was found to reduce so
rapidly that the controlling step was the rate of
removal of hydrogen fluoride from the melt; hence
the chemistry of the process presents no problem of
consequence from an engineering standpoint. With
the completion of measurements at 800'C during the
past quarter, these studies have been di scontinued.
The experimentol method used for the measure-
ments at 800°C was the same as that used in
previously described experiments at 600 and
?Oo°C.'8 Figure 5.5 shows a comparison of the
effect of temperature on the rates of reduction for
four concentrations. The slopes of the curves show
that the apparent activation energy for the rate de-
termining step is about 7800 cal, This energy of
activation is in accord with the hypothesis that
the reaction is heterogeneous and is catalyzed by
nickei surfaces.
18G. M. Wutsan, C. M. Blood, F. F. Rlankenship, ANP
Quar, Prog, Reg). MUT. 10, 1954, QRNL-7692, p 62.
____ ................. ...... ~-
J .... .I ......... '
fl~
............. -
~~ ..............
A.-
Fig. 5.5. Effect of Temperature and Concentra-
tion on the Rate of Reduction of Nif, by H, in
Molten NaF-ZrF1 (53-47 mole %).
63