Peltier effect, Thomson effect, and Seeback effect are utilized in design of thermal control coating that serves as versatile means for controlling heat absorbed and radiated by surface. Coatings may be useful in extreme temperature environment enclosures or as heat shields

Clemons, J. M.

Krupnick, A. C.

English

NASA Technical Reports Server

May 1973	 B73-10153 
NASA TECH BRIEF S	 Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Thin Film Thermoelectric Devices as 
Thermal Control Coatings: A Study 
. 
Base	 Aluminum 
J
Electrical Insulation	 __________	 N Type Semiconductor 
Ii	 I	 I	 I	 I I P-Type Semiconductor	 Outer Layer of Aluminum 
Thin-Film Thermoelectric Device
.
The problem: 
Thermal control coatings are used to control the heat 
absorbed or reflected by a surface. They help regulate 
the temperature of spacecraft cabins, but may also be 
useful in other enclosures in extreme temperature en-
vironments, or as heat shields. Most thermal control 
coatings are passive and are chosen for their reflectance 
or absorbance, which cannot be controlled. Passive coat- 
ings are also subject to degradation by radiation and 
contamination. 
The solution: 
A thin film of thermoelectric devices is not easily 
degraded and can be used to vary the heat absorbed 
by a surface. 
How it's done: 
Thermoelectric devices are constructed by connecting 
n- and p-type semiconductor bar materials through a
good electrical conductor to form a single heat transfer 
element (see figure). These elements may be connected 
in series or parallel based upon the desired electrical 
and heat transfer factors, with, the circuit ends in con-
tact with the electrical energy source. As current flows 
through the entire device, the metal conductors will 
either heat or cool, depending upon the direction of the 
current flow. In addition, if the opposite metal ends 
of thermoelectric devices are exposed to a temperature 
gradient, current will flow from one semiconductor bar 
through an external circuit into a second bar, and the 
circuit will act as a generator. 
These phenomena are the result of the interaction 
of three thermoelectric parameters: the Peltier effect 
which states that as current is driven across the junction 
of two metals, the contact either heats or cools depend-
ing upon the direction of current flow; the Thomson 
effect which states that when different parts of the 
(continued overleaf) 
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same metallic conductor are maintained at different 
temperatures, a potential difference may be observed 
in the conductor; and the Seebeck effect which states 
that if two wires of dissimilar metal are joined at their 
ends, and these ends are maintained at different temper-
atures, a current may be observed in the wires of the 
circuit. These effects are utilized in the design of a 
thermal control coating that serves as a versatile means 
for controlling the heat absorbed and radiated by a 
surface. 
Selection of the semiconductor materials to be used 
is based upon a term called "figure of merit". It is 
related to the thermoelectric power, conductivity, and 
resistivity of the material. Based upon present-day 
technology, it appears that bismuth telluride (Bi2Te3) 
compounds, when suitably doped, offer the maximum 
"figure of merit". 
The optimal ratio of n- to p-type semiconductor and 
film thickness can be calculated. The proper choice has 
a significant effect on the 'efficiency of the coating. 
The coating could be deposited on a mechanically 
attachable surface or directly on a metal surface. Two 
forms of deposition are discussed briefly: . (1) the flash 
evaporation method in which individual grains of semi-
conductor material are sublimated, and (2) the close-
spaced method which employs a chemical transport 
agent.
Notes: 
1. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: TMX-64570 (N71-19733) "The 
Application of Thermoelectric Devices as Space-
craft Thermal Control Coatings" 
Technical questions may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B73-10153 
Patent status: 
NASA has decided not to apply for a patent. 
Source: J. M. Clemons and
A. C. Krupnick
Marshall Space Flight Center
(MFS-2 1384)
. 
B73-10153	 Category 04, 02


Thin film thermoelectric devices as thermal control coatings: A study

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