GB245147A - Improved manufacture of oxide cathodes for discharge tubes - Google Patents

Abstract

245,147. Naamlooze Vennootschap Philips' Gloeilampenfabrieken. Dec. 27, 1924, [Convention date]. Drawings to Specification. Vacuum tubes; R÷ntgen-ray tubes.-A process of making an oxide cathode consists in oxidizing at least part of the surface of a metal core, and surrounding the oxidized core by alkaline earth metal vapour so that oxide of the alkaline earth metal is formed on the surface. The core is preferably tungsten wire, heated in air to about 600‹ C. to oxidize the surface, but may consist of molybdenum, nickel, or alloys. Barium azide is provided on the anode, which is heated in a bulb to a temperature of 1100-1200‹ C. to expel occluded gas, and to reduce and volatilize barium, which is precipitated on the cathode and oxidized, the bulb being evacuated during the heating operation; or the azide may be applied elsewhere inside the bulb. The cathode may be aged by gradually heating the wire to a high temperature and maintaining it at that temperature. Specifications 209,730, 214,262, and 229,622 are referred to. The Specification as open to inspection under Sect. 91 (3) (a) comprises also (a) a process in which the barium compound is applied to the oxidized surface of the core and heated, and (b) a process in which the electrodes, mounted on the usual stem, are immersed in barium azide, and barium is brought into contact with the oxidized surface during the subsequent evacuating and heating operation, both by decomposition of the azide on the cathode, and by volatilization from the other electrodes. This subject-matter does not appear in the Specification as accepted.