Fabrication techniques for high temperature thermocouples bind all components so that differential thermal expansion and contraction do not result in mechanical slippage and localized stress concentrations. Installation space is reduced or larger thermoelements and thicker insulation can be used to improve temperature measurement accuracy

Remley, G. A.

Zellner, G. J.

English

NASA Technical Reports Server

December 1967
	 Brief 67-10616 
ICY CO
.AEC-NASA TECH BRIEF 
TIES
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. 
Vapor Deposition Process Provides New Method for Fabricating 
High Temperature Thermocouples 
W26% Re Tube (-) 
Tungsten	 +)
 Thermocouple Bead 
BeO Insulation 
FIRST TECHNIQUE
Hf02 
Thermocouple Bead 
";W260%1. Re Wire (-) 
Sheath	 Tungsten Tube (+) 
SECOND TECHNIQUE 
The problem: 
Thermocouple temperature measurements in con-
fined spaces present physical problems that interfere 
with the achievement of a high degree of accuracy. In 
addition, mechanical problems become substantial 
where the thermocouple is required to operate over a 
wide range of temperatures. In conventionally designed 
two-wire thermocouples having hard-fired insulators 
and a metal sheath capable of temperatures above 
3000°F, approximately 30 0 of the available space may 
be used to provide the minimum required mechanical 
clearances. This requires the use of smaller diameter 
wires which results in a reduction in temperature 
measurement accuracy because of insulator shunting 
at high temperatures.
The solution: 
Fabrication techniques which bind all components 
so that differential thermal expansion and contrac-
tion do not result in mechanical slippage and local-
ized stress concentrations. The space required for 
installation is greatly reduced or given the same avail-
able space: larger thermoelements and thicker insula-
tion can be used to improve temperature measurement 
accuracy. 
How it's done: 
Two separate deposition techniques are used, vary-
ing materials as required, to form coaxial-type ther-
mocouples with the conducting metal components in-
sulated from each other by vapor-deposited refractory 
oxides.
(continued over(eaF) 
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=19670000615 2020-03-11T21:26:49+00:00Z
The first technique uses a vapor-deposited W 26% 
Re tube on which a layer of BeO is deposited, fol-
lowed by a vapor-deposited layer of tungsten over 
the BeO to form two concentric tubular thermoele-
ments. 
The second technique uses a tungsten or tungsten—
rhenium alloy thermocouple wire, followed by de-
posits of (I) a layer of Hf02 insulation, (2) a tubular 
thermoelement of opposite polarity over the Hf02, 
(3) another layer of l-1f02 on top of the tubular ther-
moelement, and, finally (4) a protective sheath over 
all. The resultant thermocouple is a high density co-
axial design complete with outer electrical insulation 
and a protective sheath. 
The hot junction is formed during the vapor de-
position process by allowing one end to have de-
posited metal between the wire and element. Ther-
mocouple fabrication by this method results in a 
tightly packed material .which is resistant to slippage 
and resultant stress concentrations during heatup and 
cooldown. The Hf02 was selected for its high tem-
perature capabilities and its relative freedom from 
toxicity problems. 
Test results have indicated duration times of about 
two hours at temperatures above 35000
 F. Based upon 
achieved results it appears that these types of thermo-
couples can be made to withstand a temperature of 
4600° R for one hour.
Notes: 
A number of design variations are possible for 
both techniques, yielding tradeoffs between me-
chanical complexity, performance, and monitoring 
flexibility. 
Although several practical laboratory versions of 
these thermocouples have been constructed, pro-
duction versions have not been fabricated. 
Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
AEC—NASA Space Nuclear Propulsion 
Office 
U.S. Atomic Energy Commission 
Washington, D.C. 20545 
Reference: B67-10616 
Patent status: 
Inquiries about obtaining rights for the commer-
cial use of this invention may be made to NASA, 
Code GP, Washington, D.C. 20546. 
Source: G. J. Zellner, G. A. Remley 
of Westinghouse Astronuclear Laboratory, 
and R. A. HoIzi 
of the San Fernando Laboratories 
under contract to 
AEC—NASA Space Nuclear Propulsion Office 
(NUC-10152) 
Brief 67-10616.	 Category 01


Vapor deposition process provides new method for fabricating high temperature thermocouples

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