Thermocouple tubing of thoriated tungsten with a very fine grain structure produces a small-diameter sheath capable of operating up to 5000 degrees R in a hydrogen and graphite environment. This tubing remains ductile and resists both grain growth and carbiding even after prolonged exposure to temperature

Zellner, G. J.

English

NASA Technical Reports Server

December 1967	 Brief 67-10627 
AEC-NASA TECH BRIEF 
TES
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. 
Thoriated Tungsten Tube Provides Improved High Temperature

Thermocouple Sheath 
The problem: 
To produce asmall-diameter tungsten thermocouple 
sheath that is capable of operating up to 5000°R 
in a hydrogen and graphite environment. Pure 
tungsten and pure tantalum have the temperature 
capability. However, in this temperature range, 
tungsten embrittles severely from grain growth and 
tantalum hydrides and carbides are formed too 
readily. The result is that both materials become 
structurally unsound and are therefore useless in this 
application. 
The solution: 
Utilize thermocouple tubing, nominally 0.095-inch 
diameter, made of thoriated tungsten with a very fine 
grain structure. 
How it's done: 
By adding 2 percent thoria (Th02) to pure tungs-
ten, a sintered tubing billet can be made that will 
produce a fine-grain hot-extruded tungsten tube. The 
2 percent thoria acts as a grain growth inhibitor by 
creating barriers to grain growth at the grain bound-
aries. This property has been recognized and utilized 
in the manufacture of filament wire for vacuum tubes 
and light bulbs. Under vacuum, however, thoria de-
composes rapidly above ahiit 40000R. 
At moderate positive hydrogen pressures the thoria 
does not undergo decomposition and therefore re-
mains as an effective deterrent to grain growth. Car-
bon attacks the tungsten, but the resultant carbide 
is of finer grain size which is less likely to cause 
structural failure of the thermocouple sheath. 
This tubing remains ductile above 40000
 R and re-
sists both grain growth and carbiding at tempera-
tures extending up to 5000 0
 R for 1 hour. Even after 
prolonged exposure to temperature, the microstruc-
ture of the thoriated tube is superior to that of pure 
tungsten. Hydrogen does not react chemically with the 
tungsten or thoria. 
Note: 
Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
AEC—NASA Space Nuclear Propulsion 
Office 
U.S. Atomic Energy Commission 
Washington, D. C. 20545 
Reference: B67-10627 
Patent status: 
No patent action is contemplated by-AEC or 
NASA.
Source: G. J. Zellner
of Westinghouse Astronuclear Laboratory

under contract to

AEC—NASA Space Nuclear Propulsion Office

(NUC-10145) 
Category 03 
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=19670000626 2020-03-11T21:34:52+00:00Z



Thoriated tungsten tube provides improved high temperature thermocouple sheath

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