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2.2. CHEMICAL REACTIONS IN MOLTEN SALTS
F. F. Blankenship
R. F. Newton
ACTIVITY OF CHROMIUM IN CHROMIUM-NICKEL
ALLOYS
M. B. Panish
Further measurements were made of the electro-
motive forces of electrode concentration cells in
in order to determine the activity of chromium-nickel
alloys. The cells used were the same as those
described previously,' and they contained as an
electrolyte a eutectic mixture of sodium chloride
and rubidium chloride with about 0.2 to 0.5 wt %
chromous chloride added.
Activity determinations were made for alloys
containing from 11.2 to 53.0 mole % chromium. It
was found that there was a marked tendency for
the electromotive forces of the cells to drift down-
ward because of the reaction
Ni + CrCI,+NiCI, + Cr
This effect was reduced markedly by packing the
lower end of the cell with crushed quartz in order
to prevent the transfer of nickel by convection and
diffusion. For several cells in which the quartz
packing was not used, the equilibrium electromotive
force was approximated by extrapolating the steadily
drifting electromotive force to zero time.
With cells in which the alloy electrode contained
over 35 mole % chromium, erratic results were ob
tained after raising and lowering the cell tempera-
ture, whereas the electromotive forces obtained
should be reproducible. The reasons for this be-
havior have not yet been ascertained, but it is
highly probable that the diffusion rate in these elec-
trodes is very low and that surface effects play a
very important role. It should also be noted that ac-
tivity values for the high-activity region will be
approximations because of the low electromotive
force produced by cells containing these electrodes
vs a pure chromium electrode. If the activity of the
chromium in the alloy electrode of such a cell is
0.90, then the electromotive force will be about
0.004. The nonreproducibility of the cells in this
region is of the same order of magnitude as the
electromotive forces measured.
'M. B. Panirh, ANP Quar. Prog. Rep. March 10, 1956,
ORNL-2061, p 92.
L. G. Overholser
G. M. Watson
PERIOD ENDING JUNE IO, 1956
The activities obtained for various chromium-
nickel alloys at 750OC are shown in Fig. 2.2.1,
along with the curve obtained by Gube and Flad2
at llOO°C. The two curves are not inconsistent, in
that it is quite possible that the differences are
due entirely to the difference in the temperatures at
which the measurements were made.
!.oo
0.75
>.
c
2 0.50
5
0.25
0
TWO PHASE REGION
UNCLASSIFIED
ORNL-LR- DWG (4633
/ .f
TWO PHASE REGION 1
f-0 THE WORK AT 750OC
- (ELECTROCHEMICAL) I
o DATA OF GRUBE AND FLAD AT
f!OO°C (2Cr203+3H2 f 3H20+2Crl
I I
I I
Ni 25 50 75 Cr
CHROMIUM (at. 70)
Fig. 2.2.1. Activity of Chromium in Nickel-
Chromium Alloys at 750 and llOO°C.
It should be noted that the chromium activity in
the region near 15% chromium is slightly below the
ideal activity which would have been predicted for
a perfect solid solution. This is considerably
lower than the activity which might have been ex-
pected from an inspection of the chromium-nickel
phase diagram, and it justifies the assumption of
near "ideal" activity for chromium in Inconel.
This assumption is usually made in discussions
regarding the chemical equilibria involved in the
corrosion of Inconel by molten salts.
,G. Grube and M. Flad, Z. Elektrochem. 48, 377 (1942).
93