Quote:
Originally Posted by Winky Dink
I don’t know what the white substance is, but it apparently coats the filament to insulate it from the cathode and the cathode is covered to insulate it from the screens. When I touched the white powdery stuff with an instrument, it released an invisible gas. Really! I could see nothing in the air, but it was extremely noxious--caused instant cough if I inhaled at all in the vicinity. I sealed it in a plastic bag, opened the windows and let the room ventilate for two hours before I reentered. I looked at a 50B5, and it has the same white coating on the filament. I waited 24 hours to be sure I was still alive before I posted this.
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Two different materials with two different purposes... the white coating on the heater is alumina, applied to insulate the heater from the cathode... the white material on the cathode is barium carbonate which is applied to emit electrons. I don't recall any particular noxious fumes from either substance, when taking apart cathode assemblies.
jr
note: during processing on the pumping station, co and co2 are given off and mostly barium oxide is left on the cathode nickel surface.