Silicone-rubber adhesive is applied externally to seal hair-line cracks in sections of high vacuum system while system is partially evacuated. No pretreatment of surface is required since adhesive will be drawn into crack while diffusion or ion pump is off

Christian, J. D.

Gilbreath, W. P.

English

NASA Technical Reports Server

September 1974	 B74-10175 
NASA TECH BRIEF 
Ames Research Center	 4W 
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. 2046. 
Semipermanent Sealing of Leaks in High Vacuum Systems 
.
The problem: 
To seal hair-line cracks in sections of a high vac-
uum system which are subject to mechanical or ther-
mal stresses. 
The solution: 
Apply a silicone-rubber adhesive externally to the 
leak area while the system is partially evacuated. 
How It's done: 
No pretreatment of the surface is required; the ad-
hesive will be drawn into the crack while the diffusion 
or ion pump is off. The adhesive is cured by gently 
heating the treated area, for example, with a 75-watt 
reflector lamp for a few hours; alternatively, the ad-
hesive is allowed to cure overnight at room tempera-
ture. A second application may be required for 
troublesome leaks. When a permanent repair can be 
made, the cured adhesive can be easily peeled from 
the surface. 
The silicone sealant has been used effectively with 
systems operating at 1 x 10-7 torr to seal leaks as 
large as 200 standard cm3 sec-1 (net pumping speed 
of 8 liters per second at the leak); no troublesome 
outgassing has been detected after the curing period. 
The sealant appears equallly useful for glass, ceramic,
metal, or plastic systems; because of the flexibility of 
the rubber adhesive, cracks do not reopen or enlarge 
under mechanical or thermal stresses as they might 
when an epoxy sealant is used. 
Reference: 
Christian, J. D. and Gilbreath, W. P.: Sealing of 
large leaks in high-vacuum systems subject to mech-
anical and thermal stresses. Journal of Vacuum 
Science and Technology, vol. 11, no. 4, July/August 
1974. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B74-10175 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Jerry D. Christian

and William P. Gilbreath

Ames Research Center

(ARC-10881) 
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
	
wilt be tree from privately owned rights.
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Semipermanent sealing of leaks in high vacuum systems

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