Principle heat absorption of silica-reinforced plastic ablative materials occurs from the in-depth reaction of silica with carbon to form silicon monoxide and carbon monoxide. The higher the degree of completion of this reaction, the higher the capacity of the ablative material to absorb heat

Burns, E. A.

Jones, J. F.

Lubowitz, H. R.

English

NASA Technical Reports Server

NASA TECH BRIEF 
July 1970
	
Brief 70-10300 
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 Clearinghouse for Federal Scientific and Technical 
Information, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Polyimide Polymers Provide Improved Ablative Materials 
fl
Continuing research has been directed towards im-
proving the capability of ablative materials to with-
stand more severe engine combustion environments. 
Results from this research indicate that these ma-
terials have application in supersonic aircraft struc-
tures, circuit boards, and adhesive formulations. 
Silica-reinforced plastic ablative materials have 
been studied recently, and it has been shown that the 
principal heat absorption occurs from the in-depth 
reaction of silica with carbon to form silicon monoxide 
and carbon monoxide, e.g., Si0 2 + C - SiO + CO 
(heat absorbed is 2.06 Kcal/gm of reactants). Thus, 
the higher the degree of completion of this highly 
endothermic chemical reaction per unit weight, the 
higher the capacity of the ablative material to absorb 
heat. 
Current silica-reinforced plastic ablative materials 
are formulated from phenolic resins. The resultant 
ablative composite contains approximately 30% resin, 
which, during ablative pyrolysis, yields about 50% 
conversion to char (15% char absolute). By substitut-
ing a higher-charring resin for the conventional phe-
nolic resin, the ablative capacity of the resultant com-
posite material can be enhanced. 
Polyimide polymers are such high-char resin sys-
tems. During pyrolysis, these polymers convert to 
about 80 weight percent char. By preparing a com-
posite material composed of 20% polyimide resin, the 
product obtained after pyrolysis consists of 16% char. 
The 16% char (carbon) and 80% silica represent equal 
molar quantities and result in more reactants being 
available for the Si0 2-C endothermic reaction. Con-
sequently, this polyimide ablative composite has a 
significantly higher capacity to absorb heat.
Theoretical ablative reaction capacity for any resin-
silica system is not totally achieved because of kinetic 
limitations. A solid state reaction is involved and the 
carbon and silica must diffuse together to provide 
contact of unreacted materials as the reaction pro-
ceeds. Silica is present in glass fiber form and probably 
never comes in total contact with the available car-
bon in the system. Therefore, by using finer diameter 
silica filaments, which provide considerably more 
surface area per unit volume, the silica-carbon reac 
tion is significantly improved. It is not advised that 
powdered silica be used because it would be blown 
from the ablator combustion gas interface. Thus, the 
finer diameter silica fiber is recommended. 
Notes: 
1. The new polyimide polymers, their properties and 
other applications, are.described in NASA Tech 
Brief 69-10118. 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B70-10300 
Patent status: 
No patent action is contemplated by NASA. 
Source: E. Burns, J. Jones and H. Lubowitz of 
TRW Systems Group 
under contract to 
Lewis Research Center 
(LEW- 10861) 
Category 04 
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 owned .rights.
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Polyimide polymers provide improved ablative materials

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