Vol. 114, No. 9
ACTIVITIES
j
o o: ~J
oo~
t DATAWITHPREGISiONINDIGATEO
as 9 1o0,982NA.- P_366NA
2.
'
o~
- - APPARENT(SEE
TEXTS
I TRUCTURALEFFEGT
o~.
GOLD MO~E FRACTION (n 2)
o~
FROM EMF
937
its corollary t e m p e r a t u r e dependence, there seemed
little reason to test the t e m p e r a t u r e dependence f u r ther. Instead we chose to make extensive studies of
S n - H g and A u - C d solutions as will be reported later.
~ - a s , , 9 I-NA.+b
~ f "
~ ~ ~
. ~
OF TIN ALLOYS
olo
Fig. 4. Dundee plot for tin with gold data (see text)
v e n t activity with solute mole fraction. The bars show
the e x p e r i m e n t a l u n c e r t a i n t y .
For the corrections we have used the emf for the
m e a s u r e m e n t s of "pure" t i n vs. "pure" tin except for
the copper w h e r e a piece fell i n too early, s I n this
case we have corrected the first emf to the Raoult's
law value.
Conclusions
As can be seen i n the figures, w i t h i n the accuracy of
the measurements, Raoult's law is approached for all
three of these systems.
For the C u - S n system the solvent behavior is ideal
over the whole range of composition measured.
For the A g - S n system a correction t e r m is r e q u i r e d
which follows NAg2. Such terms are sometimes ascribed
to i m p o r t a n t solute-solute interactions.
For the A u S n system, i n addition to the presence of
a n NAu2 term, there is a n indication of a change of
behavior at NAu = 0.01. S i m i l a r a b r u p t changes have
been observed b y the authors and co-workers i n cont i n u i n g vapor pressure studies of cad.mium alloys w i t h
gold (9), lead (10), and copper.
Since the dilute solution behavior in these systems
proved to be so ideal i n satisfying Raoult's law with
a Several factors could contribute to this required correction such
a s s m a l l d i f f e r e n c e s i n i m p u r i t i e s i n t h e p u r i f i e d t i n as a d d e d ,
trace i m p u r i t i e s in the electrolyte s c a v e n g e d more by one tin bath
t h a n b y t h e o t h e r , or t e m p e r a t u r e d i f f e r e n c e s o f 0.01~ o r less b e t w e e n t h e legs.
Acknowledg ment
The authors wish to t h a n k Dr. D. R. C o n a n t for his
interest and suggestions regarding this work.
Manuscript received March 9, 1967; revised m a n u script received May 20, 1967.
A n y discussion of this paper will appear in a Discussion Section to be published in the J u n e 1968 JOURNAL.
REFERENCES
1. G. R. B. Elliott, J. F. Lemons, and H. S. Swofford,
Jr., J. Phys. Chem., 69, 933 (1965)
2. G. R. B. Elliott, J. F. Lemons, and "H. S. Swofford,
Jr., "An A l t e r n a t i v e T r e a t m e n t of Solvent Activity in the Raoult's Law Region. The G a l l i u m C a d m i u m System," Los Alamos Scientific Laboratory Report, LA-2997 ( J u l y 1964).
3. J. A. Yanko, A. E. Drake, and F. Hovorka, Trans.
Electrochen~. Soc., 89, 357 (1946).
4. H. J. McDonald, ibid., 89, 371 (1946).
5. R. O. F r a n t i k and H. J. McDonald, ibid., 88, 243
(1945) ; ibid., 253.
6. J. D. Corbett a n d S. von Winbush, J. Am. Chem.
Soc., 77, 3964 (1955).
7. A. A. Kolotnii, Sb. Tr. Tsentr. Nauchn.--Issled.
Inst. Chern. Met., No. 34, 34 (1963).
8. G. R. B. Elliott and J. F. Lemons, J. Phys. Chem.,
64, 137 (1960).
9. G. R. B. Elliott, C. C. Herrick, J. F. Lemons, and
P. C. Nordine, " S t r u c t u r e in Liquid A u - C d and
Ce-Cd Solutions. Vapor Pressure a n d Electrical
Resistivity. Liquid Compounds, T w o - L i q u i d Regions, P r e m o n i t o r y P h e n o m e n a , and Freezing,"
Los Alamos Scientific Laboratory Report, L A 3526 (March 1966).
10. H. S. Swofford, Jr., G. R. B. Elliott, and D. R. Conant, " F u r t h e r Tests of Dilute Solution Equations
a n d T h e r m o d y n a m i c Relationships: The Vapor
Pressure of C a d m i u m over Liquid Alloys cont a i n i n g Small A m o u n t s of Lead," Los Alamos
Scientific Laboratory Report, LA-3657 (October
1965).
Solvent Properties of Molten NAN02 Using a
Freezing Point Technique
Theodore R. Kozlowski and Roger F. Bartholomew
Tech~ica~ Staffs Division, Coming Glass Works, Coming, New York
The physical a n d chemical properties of m o l t e n
alkali metal nitrates have been studied extensively
because of their low m e l t i n g points and ease of
handling. I n comparison there has been v e r y little
work reported on the properties of m o l t e n nitrites.
Protsenko and co-workers (1-5) have published bin a r y a n d t e r n a r y phase diagrams i n v o l v i n g alkali
and alkaline earth metal nitrites, a n d the electrochemical reduction of sodium n i t r i t e has b e e n discussed i n recent papers (6-7). However, the experim e n t a l difficulties i n w o r k i n g with m o l t e n nitrites,
such as the ease of oxidation to nitrate, and the p r o b lems of d r y i n g the materials have resulted i n the a b sence of data on these compounds. This work was
u n d e r t a k e n as a p r e l i m i n a r y investigation on the solv e n t properties of m o l t e n sodium n i t r i t e using a
freezing point technique.
E x p e r i m e n t a l conditions were constrained to permit
use of the following equation for t e m p e r a t u r e change
as a function of concentration
AT _-- ~K/m
[1]
Here AT is the t e m p e r a t u r e depression TI - - T, Tf
being the m e l t i n g point (~
of the pure solvent, and
T that of the solution; v represents the n u m b e r of e n tities dissolved i n the melt that are distinguishable
from the solvent; m is the molality of the solute, defined as moles of solute per 1000g solvent; and Kf is
the molal cryoscopic constant in deg/mole. In der i v i n g Eq. [1], Kf was defined as
RTI 2
Ks
hH f n l
[2]
where hH t is the heat of fusion of the solvent at TI
and n l the moles of solvent i n 1000g.
Experimental
Freezing points for the melts were obtained using
the cooling curve technique. The essential details
of the design a n d operation of the cryoscopic assembly
w e r e similar to systems previously described in the
l i t e r a t u r e (8, 9). One m i n o r modification involved the
938
J. Electrochem. Soc.: ELECTROCHEMICAL S C I E N C E
September
1967
O
G
--
|
v= ~
_
u=3
O
v=]
o
--%
-it
Fig. 1. Apparatus for water solubility measurements: A, solenoid;
B, glass enclosed iron cylinder; C, cryoscope head; D, chromel-alumel thermocouple; E, nitrogen-water vapor delivery tube; F, small
nichrome wound furnace; G, stirrer; H, melt; I, sand for support;
J, vacuum stopcocks; K, water heating coils; L, water reservoir;
M, nitrogen inlet; N, to vacuum pump; 1-4, numbers refer to
the operation of the apparatus.
use of a m o t o r - d r i v e n propellor-type stirrer, r a t h e r
t h a n a reciprocating magnetic stirrer, to achieve the
necessary agitation for solid-liquid e q u i l i b r i u m at the
m e l t i n g point. A small gap b e t w e e n the cryoscope
head and the stirrer shaft provided an exit port for
the dry nitrogen continuously swept over the melt. A
small window cut into the furnace insulation allowed
continuous visual inspection and m o n i t o r i n g of the
molten sodium nitrite. A p p r o x i m a t e l y 100g of salt
were used in each trial.
Diagrammed in Fig. 1 is a closed apparatus, h a v i n g
a capacity of 30g of molten sodium nitrite, which was
constructed for w a t e r solubility measurements. With
reference to Fig. 1, the initial operation consisted of
evacuation, followed b y immediate filling of the assembly with n i t r o g e n at 1 atm pressure, 1. A w a t e r
reservoir at k n o w n temperature, 2, was opened to the
system, and the n i t r o g e n - w a t e r vapor m i x t u r e was
b u b b l e d through the melt, 3, passing out t h r o u g h an
opening, 4. A control r u n utilizing a Hygrodynamics
Inc. Line operated Electric Hygrometer Indicator, No.
15-3000, established the vapor pressure of water prior
to e n t e r i n g the melt. The simple expedient of elevating
the water reservoir t e m p e r a t u r e increased the a m o u n t
of water passing through the molten sodium nitrite.
Cooling curves were obtained after at least an hour
of b u b b l i n g n i t r o g e n - w a t e r vapor through the melt.
C h r o m e l - a l u m e l thermocouples, referenced to a
distilled water-ice cold junction, served as t e m p e r a ture sensors for all measurements. A S a r g e n t Model
MR recorder performed the f u n c t i o n of b u c k i n g all
b u t 2 m y of thermocouple output, a m p l i f y i n g and presenting the r e m a i n d e r as a cooling curve (8, 9) on a
10-in. time-voltage chart. Three cooling curves for
given concentrations of solute were generally sufficient to a t t a i n a precision of •176
in the m e l t i n g
point. The melt t e m p e r a t u r e was kept below 320~
a n d the cooling rate was m a i n t a i n e d at 3 deg/min.
Super cooling was especially small, n e v e r exceeding
,
0
I
2
,
I
4
,
I
,
i
6
8I
MOLALITY x 0 2
,
I
,
I0
I
12
Fig. 2. Change in NAN02 freezing points (Tf--T) with added
solutes: Q , NaC2H302; ~,, Na2S04; ITI, Ba(CI03)2; e, NaSCN;
X, Na2COs; *, NaCI.
Results
The average m e l t i n g point for sodium n i t r i t e was
found to be 281.5~ which is in good agreement with
the value of 281~ reported by F r a m e e t a l . (10). Because there was no available value in the l i t e r a t u r e
for the heat of fusion of sodium nitrite, it was not
possible to construct the ideal freezing point curves
for the solutes added. Figure 2 presents the experim e n t a l points given i n Table I. The solid lines shown
for v = 1, 2, and 3 were d r a w n using the heat of
fusion obtained by l e a s t - m e a n - s q u a r e s analyses on the
data obtained for the solutes Na2SO4, NaSCN, and
Na2CO3. The reasons for this are discussed later. The
slope of the AT vs. m plot (i.e., Ks) for the three
solutes t a k e n together gave a value of 17.0 deg/mole
with a standard deviation of ___0.5 deg/mole. The heat
of fusion calculated from Eq. [2], was f o u n d to
be 2.48 • 0.07 kcal/mole. The entropy of fusion,
~Sf, was calculated as 4.47 • 0.13 eu.
The solubility of w a t e r in molten sodium nitrite
was determined b y v a r y i n g the vapor pressure of
water above the melt and o b t a i n i n g the freezing-point
depression at a k n o w n vapor pressure. By assuming
that water behaves in the same m a n n e r i n sodium n i trite as has been found in sodium n i t r a t e (11), Le., that
w a t e r dissolves as a monomer, the folIowing concentrations of water i n the melt were obtained; 0.63 x
10-2M at 7 m m Hg, 2.86 x 10-2M at 19.5 m m Hg, and
Table I. Experimental data for freezing point depressions
in NAN02
AT, ~
Molality
• 10~
Solute
AT, ~
Molality
• 10~
Solute
0.25~
The following Baker's "Analyzed" reagent grade
chemicals were used: NaNO~, Na2SO4, NaC1, NaC2H802,
NaSCN, Na2CO3, Ba(C1Os)2, and BaSO4. NaNO2,
Ba(C1Os)2, and NaSCN were dried to constant weight
in a National Appliance Company, Model 5830-4,
v a c u u m oven at l l 0 ~ for 7 to 10 days. S i m i l a r t r e a t m e n t e x t e n d i n g I-2 days sufficed for the r e m a i n i n g
chemicals. Concentration changes for the melt were
effected by dropping pieces weighing a p p r o x i m a t e l y
0.1g into the melt. After each concentration change, a
cooling curve was obtained only after the added, solute
was observed to totally dissolve.
0.14
0.40
0.59
0.73
1.22
1.40
1.65
1.80
0.903
1.991
3.070
4.197
6.488
8.046
9.765
11.425
Na~SO~
0.21
1.189
Na.~CO~
0.27
0.39
0.58
0.89
1.09
-- 0.46
-- 1.23
1.159
2.402
3.240
5.223
6.379
2.202
4.805
NaSCN
NaC1
0.21
0.89
1.68
2,13
3.35
3.75
4.90
1.702
3.30,1
5.044
6.872
8.632
10.381
11.747
NaC2H~02
0.52
0.'/7
1.61
0.596
1.192
3.071
Ba(CIOa)2
Vol. 114, No. 9
SOLVENT
PROPERTIES
4.54 x 10-2M at 37.9 m m Hg. This last v a l u e was obtained by e x t r a p o l a t i o n from the first two because, for
two pressures above 37.9 m m Hg, the depression of the
freezing point b e c a m e i n d e p e n d e n t of the v a p o r p r essure of water. This represents the m a x i m u m solubility
of w a t e r in the m e l t at its freezing point, w h i c h corresponds to a concentration of 31.4 x 10 -4 moles w a t e r /
mole sodium nitrite. A n a p p r o x i m a t e v a l u e of 8 x 10 -5
moles w a t e r / m o l e sodium n i t r i t e - m m Hg was obtained for K, the H e n r y ' s l a w constant.
Discussion
Fusion of the dried m a t e r i a l resulted in a clear
yellow liquid w h i c h displayed no b u b b l i n g at atmospheric pressure u n d e r nitrogen. This condition could
be m a i n t a i n e d for weeks if the t e m p e r a t u r e of the
melt was not allowed to exceed 325~
A b o v e this
t e m p e r a t u r e , an increasing a m o u n t of fine sodium
oxide precipitate (12) appeared in the melt. With continued overheating, no gas evolution was noted in or
on the melt, although the flowing purge gas w o u l d
have p r e v e n t e d the buildup of n i t r o g e n dioxide and
nitrous oxide r e p o r t e d to a c c o m p a n y the decomposition (12-14). Cooling c u r v e s obtained on pure sodium
nitrite b e f o r e and after decomposition displayed no
change in the m e lt in g point, indicating that solubility
of the Na20 was less t h a n 1 x 10-3M.
The choice of solutes for freezing point m e a s u r e ments in sodium n it r it e is li m it e d because of double
decomposition reactions w h ic h f o r m unstable m et al
nitrites (15). A t t e m p t s to use c a d m i u m and lead
salts w e r e unsuccessful because of this reason. This
limits the choice of solutes to alkali or alkaline earth
metal salts. Within this range of compounds, f u r t h e r
limitations are imposed by th e f o r m a t i o n of solid solutions b e t w e e n sodium nitrite and salts containing potassium (16), n i t ri te (16), and chloride ions. I n the case
of BaSO4 v e r y low solubility was found, since no d epression of the freezing point could be detected in a
saturated solution.
The b e s t - b e h a v e d solute w a s sodium sulfate, since
clear solutions w i t h no bubbling w e r e obtained up to
the highest concentration studied, 11.4 x 10-2/YF. Only
one point was obtained for Na2COs, because attempts
to go to higher concentrations resulted in b u b b l i n g
and t h e f o r m a t i o n of a fiocculent precipitate, p r e s u m ably sodium oxide. Additions of sodium th io c y an at e
gave w e l l - b e h a v e d melts up to concentrations of 6.4 x
10 -2 M. A b o v e these concentrations slight evolution of
gas was observed; therefore, only results in w e l l - b e h a v e d melts are reported. These t h r e e solutes should
all introduce one foreign particle in the melt, and, as
can be seen in Fig. 2, they all fall on the same line.
Because of this good a g r e e m e n t w i t h expected behavior, these data w e r e used to calculate • s for sodium n i t r i t e wh i c h was then used to describe the
other solute systems. The v a l u e of 2.48 --+_ 0.07 k c a l /
mole obtained is not directly c o m p a r a b l e with p u b lished data. Estimates w e r e m a d e f r o m the h e a t capacity data of Voskresenskaya et al. (17) and f r o m
the phase diagrams r e p o r t e d by P r o t s e n k o and his cow o rk er s (2, 4). In the f o r m e r case the heat of fusion
was estimated to be in the range 2.1 to 2.9 k c a l / m o l e
at 282~
F r o m the phase diagrams (Li +, N a + ) ,
(NO~-) and (Sr 2+, Na+), (NO2-) values of 4.3 and
9.5 kcal/mole at 284~ were calculated. Our value falls
toward the middle of the value obtained from the
heat-capacity data, which ]ends good support to its
accuracy. A value of 6 _ I kcal/mole was reported
by Rapoport (18) in his work on the effect of pressure on the melting point of sodium nitrite. However,
it was pointed out (19) that this method of obtaining
thermodynamic data does involve considerable extrapolation, which can greatly affect the final value.
Solutions with sodium acetate gave unexpected results. Freezing-point depressions characteristic of
v ----- 2 rather than the expected v ~ 1 were found. As
can be seen from Fig. 2, there is considerable scatter
OF MOLTEN
NaNO2
939
in the points; the lowest co n cen t r at i o n fell on the ~ ---- 1
line, but at higher concentrations the data tended to
fall on the v -~ 2 line. R e c e n t w o r k by Hazlewood
et al. (20) on t h e properties of m o l t e n alkali m e t a l
acetates indicated that sodium acetate was t h e r m a l l y
stable iust above its m el t i n ~ uoint of 329~
This is
4~ higher than the highest t e m p e r a t u r e used in our
work. T h e y also pointed out that the t h e r m a l stability
of m o l t e n acetate~ is enhanced bv the absence of o x y gen above the melt. Therefore, the freezing point r e sults found f o r sodium acetate cannot be ex p l ai ne d on
the basis of t h e r m a l instability. The concentration of
acetate was kept below 11.7 x 10-2M in this work,
and, despite t h e care used in co n t r o l l i n g the t e m p e r a ture, slight bubbling did occur. The b e h a v i o r of alkali
acetates in m o l t e n alkali m e t a l nitrates has been e x a m i n e d in this l a b o r a t o r y using freezing point m e a surements, infrared, polarography, and mass spectra
(21). Reactions do occur, the products b ei n g alkali
nitrites, carbonates, oxides, and gases. On the basis
of the results for the n i t r at e systems, it is suggested
that the v a l u e of ~ ~ 2, found for sodium acetate in
sodium nitrite, occurs because of a chemical reaction
b e t w e e n the solute and solvent. F u r t h e r study is r e q u i r e d in order to elucidate the reaction mechanisms and products in m o l t e n nitrites. The small
a m o u n t of nitrite w h i ch m a y be r e m o v e d f r o m the
solvent because of the reaction w o u l d not significantly alter the concentration t e r m defined in Eq. [1].
Only t h r ee concentrations are shown on Fig. 2 for the
addition of Ba(C10~)2 because, at concentrations in
excess of 3.1 x 10-2M, slight evolution of gas was noted.
H o w e v e r , the data obtained fell on the calculated ~ ~ 3
line within e x p e r i m e n t a l error. This indicates that at
the l o w er concentrations any reaction taking place is
negligible, since the e x p e c t e d t h r e e - p a r t i c l e depression
was found. The addition of NaC1 gave an increase
in the freezing point of NaNO2, indicative of solidsolution formation.
The m a x i m u m w a t e r solubility of 31.4 x 10 -4 moles
w a t e r / m o l e sodium nitrite can be c o m p a r e d w i t h 14.1
x 10 -4 and 3.9 x 10 -4 moles w a t e r / m o l e m e l t at 20
m m Hg of w a t e r for sodium n i t r at e and potassium ni trate, respectively, r e p o r t e d by F r a m e et al. (11). A l l
of these values are for the melts at their freezing
points. A H e n r y ' s l aw constant of 7 x 10 -5 for sod i u m nitrate, calculated f r o m their data, is v e r y n e a r
the v al u e found for sodium nitrite. The presence of a
reaction or some unusual dissolution mechanism, e.g.,
the passage of w a t e r into the melt as ( H 2 0 ) 2 , w oul d
h a v e resulted in different values of K. It is suggested that the p l a c e m e n t of w a t e r molecules in the
sodium nitrite m e l t n e a r its m e l t i n g point proceeds
w i t h the same m e c h a n i s m postulated for the nitrate,
viz., "interstitial dissolution." In retrospect, this conclusion could h a v e been implied f r o m the structural
similarity of n i t r i t e and n i t r a t e melts, as w e l l as t he
low solubilities of w a t e r f o u n d in t h e course of the
investigation.
F r o m the p r eced i n g discussion it is ev i d en t that
sodium nitrite is not as good a solvent for cryoscopic
w o r k as sodium n i t r at e (22, 23). The g r e a t e r chemical
r e a c t i v i t y of the melt to added solutes and the ease
with which solid solutions are f o r m e d restrict its use.
Acknowledgment
The authors wish to express their appreciation for
the assistance of Mr. Dale E r d m a n in obtaining t he
cooling curves used in this work.
Manuscript r e c e i v e d May 2, 1967; revised m a n u script received J u n e 12, 1967.
A n y discussion of this paper will appear in a Discussion Section to be published in the J u n e 1968 JOURNAL.
REFERENCES
1. P. I. Protsenko and B. S. Medvedev, Russ. J. Inorg.
Chem., 8, 1434 (1963).
2. P. I. P r o t sen k o and R. P. Shisholina, ibid., 8, 1436
(1963).
September I967
J. Electrochem. Soc.: ELECTROCHEMICAL S C I E N C E
940
3. P. I. Protsenko and R. P. Shisholina, ibid., 8, 1438
(1963).
4. P. I. Protsenko and G. K. Shurdumov, ibid., 9, 916
(1964).
5. P. I. Protsenko and N. A. Brykova, ibid., 10, 659
(1965).
6. A. J. Calandra and A. J. Arvia, Electrochim. Acta,
10, 474 (1965).
7. H. E. Bartlett and K. E. Johnson, This Journal, 114,
64 (1967).
8. A. G. K e e n a n , J. Phys. Chem., 60, 1356 (1956).
9. C. Solomons a n d G. J. Janz, Rev. Sci. Instrs., 29,
302 (1958).
10. ft. P. Frame, E. Rhodes, A. R. Ubbelohde, Trans.
Faraday Soc., 55, 2039 (1959).
11. J. P. Frame, E. Rhodes, A. R. Ubbelohde, ibid.,
57, 1075 (1961).
12. T. M. Oza, J. Indian Chem. Soc., 22, 173 (1945).
13. T. M. Oza and B. R. Walarwalkar, ibid., 22, 243
(1945).
14. A. Peneloux, Comp. rend., 237, 1082 (1953).
15. N. V. Sidgwick, "The Chemical Elements and Their
Compounds," p. 695, Clarendon Press (1950).
16. "Phase Diagrams for Ceramists," E. M. Levin, C. R.
Robbins, and H. F. McMurdie, Editors, pp. 339340, A m e r i c a n Ceramic Society (1964).
17. N. K. Voskresenskaya, G. N . Yankovskaya, a n d
V. Ya. Anosov, Zhur. Priklad Khim., 21, 18 (1948).
18. E. Rapoport, J. Chem. Phys., 45, 2721 (1966).
19. C. W. F. T. Pistorius, ibid., 45, 3513 (1966).
20. F. J. Hazlewood, E. Rhodes, and A. R. Ubbelohde,
Trans. Faraday Soc., 62, 3101 (1966).
21. T. R. Kozlowski and R. F. Bartholomew, Data being prepared for publication.
22. E. R. Van Artsdalen, J. Tenn. Acad. Sci., 29, 122
(1954).
23. G. J. Janz a n d T. R. Kozlowski, J. Phys. Chem., 67,
2857 (1963).
Nitrosyl Fluoride Electrolytes
Madeline S. Toy and William A. Cannon
Astropower Laboratory, Missile and Space Systems Division,
Douglas Aircraft Company, Inc., Newport Beach, California
There is a growing interest in the field of l o w - t e m p e r a t u r e electrolytes which m a y be utilized i n electrochemical energy conversion devices for operation
at well below --60~ As part of a study of l o w - t e m p e r a t u r e electrolytes, we have measured the electrical
conductivities of solutions of Lewis acid fluorides in
nitrosyl fluoride. The electrical conductivity of pure
nitrosyl fluoride has been reported b y Christe a n d
G u e r t i n as 5.4 x 10 -5 ohm -1 cm -1 at --79~ (1). This
value indicates a relatively high degree of self-ionization which p r o b a b l y occurs in the following m a n n e r
-60
~o-:-
Temperature
-70
(~
-80
I
[
t
J
I
I
I
t
-90
I:
I-
-
NOF ~ NO + + FToy and C a n n o n (2, 3) have reported the large increase of electrical conductivity of a self-ionizing
solvent (bromine trifluoride) on addition of a Lewis
acid fluoride (boron trifluoride). This paper describes
the self-ionizing properties of nitrosyl fluoride (bp
--59.9 ~ and m p --137.5 ~ in the presence of fluoride ion
acceptors (boron trifluoride, phosphorus pentafluoride,
and arsenic pentafluoride) leading to lormat,on of
moderately conductive low-temperature electrolytic
solutions below --60~
A n electrochemical energy
conversion system using halogen fluoride electrolytes
has been reported to be applicable at room temperature to as low as --40~ (4). This paper suggests that
an electrochemical energy conversion system using
nitrosy] fluoride electrolytes is capable of reaching
even lower temperatures.
Experimental
Materials.--Nitrosyl
fluoride and arsenic p e n t a fluoride were obtained from O z a r k - M a h o n i n g Company. Boron trifluoride a n d phosphorus pentafluoride
were obtained from Matheson Company. All materials
were purified by l o w - t e m p e r a t u r e distillations. The
p u r i t y of the samples was checked b y i n f r a r e d analysis
of the vapor. The specific conductivities of boron t r i fluoride, phosphorous pentafluoride and arsenic p e n t a fluoride in the liquid phase were less t h a n 10 -9 ohm -1
cm -1. The specific conductivity of liquid nitrosyl
fluoride reported by Christe and G u e r t i n as 5.4 x 10 -2
ohm -1 cm -1 at --79~ (1) falls on the specific conductivity vs. t e m p e r a t u r e curve of p u r e n i t r o s y l
fluoride given in Fig. I. All electrodes were h i g h - p u r ity commercial materials of 99.9% p u r i t y or better,
~
,
1
j
I
l:
o
:
~
I
I
I:
t-
I
ure
s
PF 5
10-5.
4.5
[
4,7
Mole Solute
P e r 1000 g N O F
II ,
4.9
5,1
1000/Temperature
(~
F
1-
I
t
t
J
5.3
5,5
Fig. 1. Specific conductivity of NOF and NOF solutions as o
function of temperature.
Apparatus.--The conductivity cell (Fig. 2) was
made of stainless steel w i t h a Teflon l i n e r and
equipped with two smooth p l a t i n u m electrodes. The
leads passed t h r o u g h Teflon plugs a n d were compressed b e t w e e n m e t a l fittings to effect a v a c u u m a n d
pressure tight seal. T e m p e r a t u r e s were m e a s u r e d b y a
thermocouple inserted into a hole drilled in the wall
of the conductivity cell. Cell constants r a n g i n g from
0.2 to 0.5 cm -1 were used. Cell constants were determ i n e d by m e a s u r i n g the resistance of s t a n d a r d potassium chloride solutions i n the cell. I n a conductivity
cell of this design, the cell constant varies slightly
with the volume of solution due to the v a r i a b l e i m -