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Re: the cathode materials; the information I find is the currently used mixture is 56% BaCO3, 31% SrCO3, and 13% CaCO3 by weight. Then mixed with nitrocellulose lacquer in the proportion of 44% carbonates and 56% lacquer. In the past it was usually Ba and Sr carbonate; the Ca was added later because it was found to improve emission current.
What happens when a tube loses vacuum is the oxides combine with water vapor in the air and form hydroxides, The reaction is reversible under vacuum and with heat, but does not result in a working cathode again for some reason.
During activation, the carbonate compounds reduce to oxides, giving off carbon dioxide, plus whatever gases the lacquer breaks down into. Ideally this process is carried out while still under pumpdown to get those gases out of the tube prior to sealing and getter flashing.
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Erich Loepke
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