Tungsten-rhenium alloy thermocouples, specifically, insulated, sheathed W/W plus 26Re and W plus 5 Re/W plus 26 Re thermocouples, are effective for temperature measurement in excess of 2920 degrees C. These thermocouples have a high thermoelectric output and excellent relationship to temperatures up to 2760 degrees C

Brooks, E. J.

Kramer, W. C.

English

NASA Technical Reports Server

April 1968
	 Brief 68-10109 
co
AEC-NASA TECH BRIEF 
TES
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
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the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Tungsten—Rhenium Alloy Thermocouples Effective
for High-Temperature Measurement
TIG Weld 
I Insulation W-5% Re Conductor  
W-26% Re Conductor
Sheath	 Seal Plug (W) 
Swaged Junction 
The problem: 
To measure temperatures in the range of 27600C 
(the temperature reached on the thermocouple rods 
of a UO2-fueled reactor under maximum design 
power). In existing high-temperature thermocouples, 
a reaction occurs between the BeO insulation and the 
tantalum sheathing at approximately 2200°C. BeO it-
self melts at about 2550°C. Both of these tempera-
tures are below the desired temperature measurement 
range. Improved sensors are needed which are chemi-
cally, metallurgically, and electrically stable above 
2760°C. 
The solution: 
Tungsten—rhenium alloy thermocouples, speci-
fically, insulated, sheathed W/W+26Re and W+5Re/ 
W+26Re thermocouples, are effective for temperature 
measurement in excess of 2920°C. These thermo-
couples have a high thermoelectric output, excellent 
sensitivity, and a reasonably linear emf-temperature 
relationship to temperatures up to 27600C. 
How it's done: 
The thermocouple developed for high temperature 
measurement is shown. When selecting materials for
this measurement device, a W/W+26Re thermo-
couple was first fabricated, but an extreme brittleness 
was present in the tungsten leg. A leg of tungsten+5Re 
has been used to replace the tungsten leg since it is 
less brittle and easier to fabricate. 
Thorium oxide is used as the insulating material. 
Of the refractory oxides, only Th02 has a melting 
point high enough to permit use as an insulating 
material in the 2760° C thermocouple. The only other 
possibilities were MgO and Hf02, with melting 
points of 28000 and 2777°C, respectively; both of 
these melting points are too close to the desired 
maximum service temperature. 
Tungsten, rhenium, tantalum, and their alloys were 
considered for reference sheathing, since their melt-
ing points are above 2760 0 C. Tantalum was eliminated 
because of its high affinity for oxygen; tungsten be-
cause of its brittleness after exposure to high tempera-
ture; and rhenium because of its high cost. Since the 
alloy W+26Re is workable and more ductile than 
tungsten, it serves as the reference sheathing. 
Hot-junction construction, using a tungsten seal 
plug, was incorporated into the design of these 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 	 liability resulting from the use of the information contained in this 
Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, 
Administration. Neither the United States Government nor any per- 	 method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000109 2020-03-12T05:25:42+00:00Z
44 
40 
36 
32 
0 
>
28 
24 
0 
w 
0-	 20 D 
0 
0
16
Standard Calibration 
Curve for W/W+26 Re
Experimental Results 
12 
4 
0
600	 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 
Temperature. C 
CALIBRATION OF W/W+26 Re THERMOCOUPLES 
thermocouples to obviate a welded junction which 
would have been brittle and fragile. This fabrication 
should aid in preventing premature failures during 
installation or low-temperature operation. 
The thermocouples have been tested and calibrated 
to 30000 C in two separate test series. Each calibra-
tion point required approximately 15 to 20 minutes 
to ensure temperature stability. No apparent chemical 
interaction takes place between the thermocouple 
components. Typical results of this calibration are 
shown in the graph. 
Notes: 
1. Radial and longitudinal cracks, in the thermo-
couple legs, believed to be introduced during 
fabrication, are found in varying degrees. 
2. This information should be of interest to manu-
facturers of high-temperature furnaces and to those 
engaged in high temperature research. 
3. Complete details are contained in: Tungsten—
Rhenium Alloy Thermocouples and Their Use in a 
UO2-Fueled Reactor, by E. J. Brooks and W. C. 
Kramer, ANL-6981, Argonne National Labora-
tory, Argonne, Illinois, November 1965. The report 
is available from the Clearinghouse for Federal 
Scientific and Technical Information, Springfield,
Virginia 22151; price $3.00, microfiche $0.65. The 
report includes information on design and testing 
of the thermocouples, experimental measurements, 
difficulties in use, and suggestions for improve-
ments for further research. 
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: B68-10109
Source: E. J. Brooks, 
Idaho Division
and W. C. Kramer,
Metallurgy Division 
(ARG- 10059) 
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 68-10109	 Category 03


Tungsten-rhenium alloy thermocouples effective for high-temperature measurement

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