Electrical conductance and activation energy measurements on mixtures of calcium and potassium nitrate show the hydrated form to be a new class of molten salt. The theoretical glass transition temperature of the hydrate varied in a manner opposite to that of the anhydrous system

Angell, C. A.

English

NASA Technical Reports Server

March 1967	 Brief 67-10033 
•
Icy C
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Hydrated Multivalent Cations Are New Class of Molten Salt Mixtures 
The problem: 
To establish that aqueous mixtures of polyvalent 
ions, whose water content is insufficient to satisfy 
more than a first coordination sheath for the cations, 
are molten salt mixtures of weak-field cations. (Such 
mixtures consist of hydrated molten salts having inde-
pendent, hydrated cations. These hydrated molten 
salts dissolve unhydrated salts in the same way that 
unhydrated molten salts usually dissolve each other.) 
If the mixed nitrate—hydrate melt Ca(NO3)2.4H20 
+KNO3 is an aqueous molten salt mixture of weak-
field cations, it should behave as follows: (1) its electri-
cal conductivity should be completely analogous to 
that of other molten salt mixtures, (2) its theoretical 
glass transition temperature should vary in a manner 
opposite to that of the anhydrous system Ca(NO3)2 
+KNO3 and should increase with KNO3 content 
(since the theoretical glass transition temperature for 
molten KNO3 is greater than the experimental value 
for Ca(NO3)2.4H 20 , and (3) its activation energy 
(Arrhenius coefficient) at a given temperature should 
increase with KNO3 content. 
The solution: 
Electrical transport is exponentially dependent on 
1/(T—T0) in accord with the general equation for 
electrical conductance 
A = ATI/2exp(TkTO) 
where A is equivalent conductance, To is the theoreti-
cal glass transition temperature, and k and A are 
constants. Since the value of k for the hydrated molten 
salt Ca(NO3)2.4H20 is virtually the same as for the 
anhydrous molten salt mixture Ca(NO3)2+ KNO 3, the 
same value of k is assumed for the mixed nitrate—
hydrate melt Ca(NO3)2.4H20+KNO3. 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any
A.R. grade Ca(NO3)2 .4H20 is fused without loss of 
water. Then the composition is changed by adding 
A.R. grade KNO3, and the specific conductance is 
measured after each addition. 
The activation energies increase rapidly with falling 
temperature. This increase occurs because the proba-
bility of ionic movement approaches zero at the 
theoretical glass transition temperature, rather than 
at 00K as required by Arrhenius. The general equa-
tion for electrical conductance reduces to almost a 
single straight-line plot of activation energies for the 
systems Ca(NO3)2 . 4H20+ KNO3 and Ca(NO3)2 
+KNO3. 
The theoretical glass transition temperature To of 
the mixed nitrate—hydrate melt Ca(NO3)2.4l-120 
+KNO3 increases with KNO3 content, but the theore-
tical glass transition temperature of the anhydrous 
system Ca(NO3)2+KNO3 decreases with KNO3 
content. 
The activation energy of the mixed nitrate—hydrate 
melt increases with KNO3 content. 
Since the change in electrical conductance with con-
centration of KNO3 is the same for both the mixed 
nitrate—hydrate melt ECa(NO3)2 .4H20 + K NO31 and 
the anhydrous mixture [Ca(NO3)2+KNO3], the mixed 
nitrate—hydrate melt closely resembles a molten salt 
mixture. 
Notes: 
The mixed nitrate—hydrate melt Ca(NO3)2.4H20 
+KNO3 is a representative hydrated mixture. It 
was selected because its anhydrous salt analogue, 
Ca(NO3)2+KNO3, has been studied in some 
detail and because the electrical conductance of 
molten Ca(NO3)2 . 4H20 has been measured 
recently.
CUiIIIIlUCU U'tI (Cdl? 
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000033 2020-03-11T20:18:12+00:00Z
2. The temperature of the melt is measured by a 
precision mercury thermometer and checked by a 
fine-gage Cr/Al thermocouple attached to the 
conductance cell. 
3. The resistance of the melt is measured at 3 kc and 
I kc with a silica dip-type cell with platinized elec-
trodes, in conjunction with a precision conductance 
bridge. Calculations are based on the 3-kc readings, 
because the polarization errors are not sufficient to 
detectably affect results when resistance is greater 
than 1000 ohms. 
4. Because of the low tiquidus temperatures of the 
melt, this new class of molten salt mixtures may be 
useful for physicochemical investigations of molten 
salt behavior in a temperature range otherwise not 
readily accessible. 
5. The general coherence of the experimental observa-
tions indicates that binary systems with hydrate 
components such as those of the system studied 
may be useful for investigating free volume-de-
termined properties of ionic liquids.
Additional details are contained in: Journal of the 
Electrochemical Societ y, December 1965, vol. 112, 
no. 12, p. 1224-1227. 
Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B67-10033
Source: C. A. Angell
Chemistry Division

(ARG-2l 1) 
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 67-10033	 Category 03


Hydrated multivalent cations are new class of molten salt mixtures

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