Improvements relating to thermionic cathodes

1,070,503. Thermionic cathodes. ELECTRIC & MUSICAL INDUSTRIES Ltd. Dec. 13, 1963 [Dec. 13, 1962], No. 47093/02. Heading H1D. A thermionic cathode comprises a metallic cap formed at its closed end into a re-entrant recess which contains sintered powdered electron-emissive material held in the recess by an inwardly-projecting lip at the mouth of the recess. As shown, a recess 1, Fig. 1d, in a nickel cathode cap is filled with emissive material, the assembly then being subjected to pressure, and activated and sintered at 1050‹ C., to form the cathode shown in Fig. 1e. Alternatively the sides (4), Fig. 2c (not shown), of the cathode cup may be deformed inwardly to produce a lip overhanging the recess, or the overhang may be produced by securing a stainless steel ring or flange over the mouth of the recess. In addition, a conical, stainless steel member (5), Fig. 3 (not shown), with or without a central aperture, may be pressed into the emissive matrix. The cathode may be used in cathode-ray tubes which may be dismountable. The emissive matrix may comprise carbonyl nickel, a triple carbonate mixture, zirconium hydride, boron, stearic acid and acetone, a specific composition being given.