Internal surfaces of the glass component of a vacuum system are exposed to cesium in gaseous form to reduce helium permeation. The cesium gas is derived from decomposition of cesium nitrate through heating. Several minutes of exposure of the internal surfaces of the glass vessel are sufficient to complete the treatment

Bryant, P. J.

Gosselin, C. M.

English

NASA Technical Reports Server

August 1966	
- Brief 66-10372 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Special Treatment Reduces Helium Permeation

of Glass in Vacuum Systems 
The problem: 
Permeation of helium through glass has become an 
important consideration in the design and construc-
tion of ultrahigh vacuum equipment. The helium atom 
is sufficiently small to penetrate the silicon dioxide 
lattice of a glass vessel used in a high vacuum system, 
thereby limiting the minimum pressure obtainable. 
The solution: 
The internal surfaces of the glass component of the 
vacuum system are exposed to cesium in gaseous form 
derived from decomposition of cesium nitrate through 
heating. 
How it's done: 
The cesium nitrate is placed in a glass vessel con-
nected by tubing to the primary pressure vessel to be 
treated. Pressure in both vessels is lowered by means 
of a vacuum pump. After a high vacuum has been ob-
tained, heat is applied to the vessel containing the 
cesium nitrate until its decomposition temperature 
level has been reached at which point cesium gas is 
produced. Due to the extremely low pressure, the 
cesium atoms have high mobility and readily travel
throughout the system. Several minutes of exposure 
of the internal surfaces of the glass vessel are sufficient 
to complete the treatment. 
Notes: 
1. The vessel containing the cesium nitrate must be 
raised to a temperature above 414°C, the melting 
point of cesium nitrate. A vessel of quartz glass or 
special laboratory glass is used to prevent distor-
tion due to the pressure differential across its wall. 
2. This treatment would be useful during fabrication 
of dewar vacuum glass jackets in order to increase 
their efficiency. 
Patent status: 
Title to this invention has been waived under the

provisions of the National Aeronautics and Space Act

(42 U.S.C. 2457 (f)) to Midwest Research Institute,

50th and Cherry Streets, Kansas City, Missouri 64110.

Source: Paul J. Bryant

and Charles M. Gosselin

of Midwest Research Institute 
under contract to NASA
(HQ-25) 
Category 02 
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 owned rights.
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Special treatment reduces helium permeation of glass in vacuum systems

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