Concentration cell, based upon a thermally regenerative cell principle, produces electrical energy from any large heat source. This experimental bimetallic EMF cell uses a sodium-bismuth alloy cathode and a pure liquid sodium anode. The cell exhibits reliability, corrosion resistance, and high current density performance

Hesson, J. C.

Shimotake, H.

English

NASA Technical Reports Server

November 1968	 Brief 68-10415 
.	
ttlicy CO
AEC—NASA TECH BRIEF 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
New Bimetallic EMF Cell Shows Promise in Direct Energy Conversion 
Electrical 
Insulators
Insulation 
Silicone Rubber 
	
Vacuum Seals	 Sodium /	 I 
'N,	 Electrolyte	 1	 Reservoir For Charging 
	
/	 Sodium-Bismuth 
Alloy 
:	
-
othusmiy/fl 
Frozen Electrolyte	 _____________________________ 
Insulator Seal	 Q ° ° (4 \	 00 
	
Alumina	 Electric Heaters Spacer 
The problem: 
To develop a system capable of economically and 
effectively converting thermal energy into electrical 
energy. The system would be coupled with a nuclear 
reactor or isotropic heat source. At the present time, 
nuclear power is used to produce steam, which is con-
verted to electricity via conventional turbogenerators. 
A direct energy conversion process would eliminate 
the expensive, bulky, and inefficient steam interface. 
The solution: 
A concentration cell, based upon a thermally regen-
erative cell principle, which can produce electrical
energy from any large heat source. This experimental 
bimetallic EMF cell (without a thermal regenerator) 
uses a sodium—bismuth alloy cathode and a pure 
liquid sodium anode. The cell has been operated for 
17 months without failure, exhibiting reliability, cor-
rosion resistance, and a high current density perform-
ance. Although there are presently material problems 
related to the regenerator, when these are solved, the 
regenerative bimetallic EMF cell system should be a 
promising direct energy conversion device. 
How it's done: 
The experimental bimetallic EMF cell for a Na—Bi 
system, shown in the figure, is constructed of type 
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
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=19680000415 2020-03-12T05:55:13+00:00Z
18-8 stainless steel. The electrodes are cylindrical and 
have a 76.2 mm i.d. Spikes 2 mm in diameter on the 
anode act as electron collectors. 
The anode and cathode are electrically insulated 
by a high purity alumina disc. A portion of the molten 
salt penetrates into gaps between the alumina spacer 
and the stainless steel flange and freezes. This frozen 
electrolyte, together with a silicone rubber gasket, 
provides a vacuum and pressure seal. Nichrome heater 
wires, insulated with alumina powder and sheathed by 
stainless steel, are used for the heaters. A high tem-
perature insulating material covers the heaters. 
The cell is charged under an inert gas atmosphere 
since the sodium alloys are highly reactive and the 
salt mixtures are hygroscopic. To charge the cell, first 
the cathode material, 20 at/o Na-Bi alloy, is charged 
into the cell under argon atmosphere and melted. 
After freezing the alloy (the electrolyte) a eutectic 
mixture of Nal-NaCI-NaF, is charged. The alloy and 
salt mixture are then melted in an argon atmosphere. 
At each step, the liquid levels, of metal and salt must 
be checked, since bismuth expands upon freezing, 
which raises the metal level and may short-circuit the 
cell. 
The cell was electrically charged every 48 hours. The 
cell temperature was varied up to 650 1 C, however, a 
major portion of the time, the temperature was kept at 
approximately 550°C. The melting point of the salt is 
535°C. The cell current was varied by external resist-
ance and loaded up to 10 amperes and the charging 
current ranged from I to 2 amperes. 
Cell discharge current densities of 90 and 110 
ma/cm 2 at 0.5 and 0.45 V, respectively, were achieved 
at an anode fuel efficiency of approximately 87. The 
internal resistance was about 0.05 Q at 550°C, which 
decreases with increasing temperature and increases 
very rapidly when cooled to near the melting point.
After 17 months of operation, the cell, including the 
frozen electrolyte insulator seal, showed no signs of 
failure. An interior inspection revealed little corrosion, 
with only 0.05 mm dissolution of stainless steel at the 
electrodes. X-ray analysis of the molten salt showed 
no signs of dissociation. 
Notes: 
I. This information may be of interest to gas and 
power utility suppliers. 
2. Users and producers of electricity may develop or 
employ sufficiently inexpensive heat sources and 
suitable use conditions to permit further develop-
ment in this area. 
3. The significance of this item is dependent upon the 
further development of regeneration system ma-
terials to withstand the boiling sodium and molten 
sodium-bismuth alloy environment. 
4. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B68-104I5 
Source: H. Shimotake and J. C. Hesson 
of the Chemical Engineering Division

(ARG-10l83) 
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 68-10415	 Category 01


New bimetallic EMF cell shows promise in direct energy conversion

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