VACUUM COMPATIBILITY OF MACHINABLE GLASS-CERAMICS

The thermal outgassing and helium permeation characteristics of Code 9658 machinable glass-ceramic are discussed. It is found that up to 600 degree C, this material can be treated like glass vacuum system components. The quantities of outgassing constituents under vacuum conditions are given and the need for vacuum baking freshly machined material is demonstrated. Although the material can be used up to 1000 degree C, between 600 degree and 1000 degree C some fluorine evolution from the material takes place and could present a corrosion problem to some systems. Helium permeability of this material is an order of magnitude lower than for Code 7740 glass.