Easily prepared system, consisting of matrix of hollow zirconia microspheres containing dispersed tungsten powder, produces minimum-cost, prototype test specimen. Combination represents basic concept of highly reflective dispersed phase in low density insulative matrix and is stable at 2200 K. Other combinations of materials are suggested

Carpenter, H. W.

English

NASA Technical Reports Server

August 1971
	 Brief 71-10290 
S NASA TECH BRIEF
	 ____ 
NASA Pasadena Office 
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 Off ice, NASA, Code KT, Washington, D. f. 20546. 
Granular Two-Phase Insulation Systems 
A new insulation system, consisting of a matrix 
of loosely packed, hollow zirconia microspheres 
containing a small amount of dispersed tungsten 
powder, can be used to produce a minimum-cost, 
prototype test specimen. The combination specified 
was chosen because: (1) it represents the basic 
concept of a highly reflective dispersed phase in 
a low-density insulative matrix; (2) the materials 
are stable at 2200 K (3500° F); (3) the raw materials 
are readily available and reasonably inexpensive; 
and (4) the system can be easily prepared without 
a developmental effort. Screening tests at 2200 K 
showed this system to be better than all other 
candidate systems. Shrinkage was 5% or less, out-
gassing was negligible, and there was no reaction 
with the molybdenum can. 
Any effective high-temperature insulation system 
must contain a means of dispersing or back-re-
flecting radiation. Reflective surfaces reduce radiation 
heat transfer, the dominant mode at higher tempera-
tures, particularly above 1366 K (2000° F). The two 
essential ways of forming a system with a high 
proportion of reflective surfaces are: (1) Use multi-
layer system, alternating reflective foils with layers 
of low thermal conductivity materials; and (2) 
disperse reflective particles throughout a stable 
matrix. 
Reflective surfaces can be suspended or formed 
in a refractory powder matrix by vapor deposition, 
precipitation, or decomposition. The most promis-
ing method involves coating the particles in a manner 
similar to that used to apply decorative films 
on ceramic pottery and dinnerware. The metal
phase, a refractory or precious metal, is dissolved 
in an appropriate organic liquid. The solution is 
then mixed with the ceramic particles, and the 
excess solution is poured off for reuse. The film 
that remains on each particle is converted to 
the pure metal phase by thermal treatment. The 
refractory metals require a second heat treatment 
in hydrogen to reduce the oxide in the metal phase. 
The thickness is very small so that relatively little 
material is required. 
Another method involves suspending a refractory 
metal powder in a phenolic resin that can be molded 
or extruded into various shapes. The phenolic is 
pyrolyzed to form a strong, yet porous, structure, 
or. an
 organic-based paint containing suspended 
refractory or precious metal powder is successively 
applied as discrete layers on a fugitive mandrel. 
More metal powder is attached on the wet surface 
after each coating. The multilayered composite is 
pyrolyzed to form poorly bonded multilayers of 
a low-density carbon structure impregnated with 
refractory metal-oxide powder. A reduction reaction 
is required, provided that the refractory metal is 
oxidized during the pyrolyzation operation. Al-
though both molybdenum and tantalum will car-
burize, the refractory metal carbide particles will 
still have a reflectance value of about 5% or more. 
Several other combinations of materials are 
potentially useful. The ceramic matrix can be 
zirconia, thoria, carbon, or graphite, and the re-
flective powder can be tungsten, tantalum, colum-
bium, molybdenum, rhenium, iridium, or ruthen-
ium. The use of precious metals should not be 
(csnsliriued os erIci1) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person 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 such use 
will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19710000289 2020-03-17T02:20:33+00:00Z
excluded, because these metals can be painted or de-
posited as very thin layers so that only a relatively 
small amount of material would actually be required. 
Notes: 
1. Related information concerning wrapped multi-
layer insulations can be found in NASA Tech 
Brief B71-10289. 
2. Requests for further information may be 
directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP7I-10290
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code 1 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: H. W. Carpenter of

Rocketdyne Division

North American Rockwell Corp.

under contract to

NASA Pasadena Office

(N PO-12068) 
Brief 71-10290	 Category 04


Granular two-phase insulation systems

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