Potassium silicate-treated zinc oxide paint stabilizes pigment against ultraviolet-induced, bleachable degradation in infrared region, and permits use of ZnO as pigment in ultraviolet-stable coatings based upon polymethyl siloxane elastomers and resins. Material has low absorptance/emittance ratio

Gates, D. W.

Roger, F. O.

Zerlaut, G. A.

English

NASA Technical Reports Server

June 1971	 Brief 71-10180 
S
NASA TECH BRIEF 
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. f. 20546. 
Improved Thermal Paint Formulation 
The problem: 
To develop a stable thermal-control coating with 
low solar energy absorption. Zinc oxide (ZnO) based 
silicone coatings were thought to be the best avail-
able in terms of hemispherical spectral reflectance 
stability to ultraviolet radiation. However, when 
tested, they were considerably less stable than pre-
dicted. This discrepancy was attributed to the fact 
that ZnO exhibits bleachable degradation in the 
infrared absorption region. 
The solution: 
The S-13G formulation, a potassium silicate-treated 
ZnO paint, which effectively stabilizes the pigment 
against ultraviolet-induced, bleachable degradation 
in the infrared region of the solar spectrum. This 
formulation provides the most satisfactory optical 
and physical characteristics, and permits the use 
of ZnO as a pigment in ultraviolet-stable coatings 
based upon polymethylsiloxane elastomers and 
resins. An emittance of 0.88 appears to be average 
compared to many black or colored paint systems, 
but slightly higher than most white systems. The 
low absorptance of 0.19 makes the low absorptance/ 
emittance ratio of the material especially attractive. 
How it's done: 
Factors considered in developing S-13G in-
cluded: (I) initial ZnO-silicate reaction parameters; (2) 
pigment filtration and silicate extraction (washing) 
procedure; (3) pigment drying and grinding procedures; 
(4) silicone paint manufacturing procedure; and (5) 
optimization of paint formula relative to pigment 
volume concentration, solvents employed, and catalyst 
concentration. 
S-13G is prepared from SP500 zinc oxide, which 
is slurried with PS-7 potassium silicate at —196K
(77°C) for 20 minutes. The slurry is diluted with 
distilled water, vacuum filtered, wrapped in aluminum 
foil, and allowed to sweat for 16 hours. The sweated 
pigment is then redispersed in distilled water and 
filtered two more times. The resulting cake is spread 
out to dry in an oven at —173K (100°C) for 16 hours, 
after which it is hand-mulled, sieved (80 mesh), and 
packaged, ready for manufacture into paint. 
The RTV-602 silicone-based S-13G coating is 
prepared at 30% pigment-to-volume concentration 
by milling for 3 1/2 hours in a porcelain ball 
mill with a minimum of grinding media. The 
solvent system currently used is 50% toluene, 25% 
xylene, 15% isopropanol, and 10% n-butanol. 
Paints, catalyzed with SRC-05 catalyst at 0.4% 
by weight based on RTV-602 solids, cure to the 
touch in 4 to 6 hours and can be handled in 16 
hours. The uncured paint possesses a shelf life 
of over 3 months. 
The engineering values of solar absorptance, a, 
and hemispherical emittance, E, currently quoted 
for 2.03 mm (8 mil) films of S-13G are 0.19±0.02 
and 0.88 1 0.05, respectively. (To prevent heat 
buildup under radiation, a should be low and 
should be high.) The engineering value currently 
quoted for Aa is 0.03 for 1000 equivalent sun hours 
(ESH) of simulated space ultraviolet radiation em-
ploying in situ postexposure reflectance measurements 
and AH-6 lamp irradiation. 
Notes: 
1. Possible applications include coatings for optical 
instruments to minimize dimensional varia-
tions, and coatings to keep structures in the 
tropics cooler during sunlit hours. 
-.	
(continued 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19710000179 2020-03-17T02:24:45+00:00Z
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Code A&TS-TU 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B71-10180
Patent status: 
No patent action is contemplated by NASA. 
Source: D. W. Gates

Marshall Space Flight Center

and F. 0. Roger and G. A. Zerlaut of

LIT Research Institute

under contract to

Marshall Space Flight Center

(MFS- 14706)
. 
Brief 71-10180	 Category 03


Improved thermal paint formulation

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