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Water has been introduced experimentally into sealed-off pentode electron tubes by decomposition of calcium hydroxide, so that any reaction products are retained within a sealed-off tube. The calcium hydroxide is carried through normal tube processing in a sealed glass capsule. Subsequent to processing, the glass capsule is broken, and water is liberated by gentle heating.
Mass spectrometric analyses show that within seconds water is reduced to hydrogen; in fact, water ordinarily cannot be detected. In addition the emission of an oxide-coated cathode based on pure nickel is improved by as much as an order of magnitude when water is liberated within an electron tube to give a pressure of 10−3 torr. The increase of emission appears to be greater than that observed when hydrogen is introduced to give the same total pressure. Smaller increases in emission are observed when water is introduced into tubes with more active cathodes.
Small amounts of water within an electron tube apparently are not deleterious to oxide cathodes, so long as the total pressure remains below 1 × 10−4 torr. Consequently, rigorous processing to remove all possible water from the internal parts of an electron tube might not be justifiable for cathode protection alone, although such processing might be desirable if gas would interfere with electron-tube operation in other ways.
Frost, H. B.
Bell Telephone Laboratories, Inc., Murray Hill, N. J.