# Reaction of Rubidium with vacuum system viewport

I have a vacuum system ($<1\times10^{-7}$ mbar) filled with Rubidium ($^{87}$Rb) vapour, at room temperature.

We also have a viewport near the Rubidium source, made of a stainless steel flange and a glass substrate, connected with a Kovar alloy.

We are seeing potential degradation of the seal, which we do not see on other parts of the system. The only difference is the Nickel and Cobalt based Kovar alloy, not present anywhere else.

What are the reaction rates of Nickel and/or Cobalt with Rubidium?

• Please, check the mark of the glass and if it is suited for work with rubidium in this particular settings. In general, glasses are oxides that can potentially react with alkali metals in right circumstances. I see no reason for them to react with nickel/cobalt alloy. However, rubidium might react with oxide layer on the surfaces of this alloy and/or any dirt left on the seal (and glass, and any dirt left on the glass) and any passing air if the seal is... not good enough. – permeakra Aug 21 '17 at 18:04
• btw, thanks to ability of rubidium to form suboxides even tiniest amount of oxygen may bind a lot of rubidium. – permeakra Aug 21 '17 at 18:05