GB702615A - Improvements in or relating to thermionic cathodes - Google Patents

Abstract

702,615. Cathode materials. GENERAL ELECTRIC CO., Ltd., and MILES, E. E. Sept. 29, 1952 [Sept. 28, 1951], No. 22724/51. Class 39(1) A thermionic cathode for a gas or vapour filled discharge tube consists of a carrier of refractory metal, such as tungsten, carrying electron emissive material which consists at least partly of one or more alkaline earth metal germanates. The proportion of germanate is preferably in the range of 2.5-20 per cent, and is preferably 7 per cent, of the alkaline earth metal oxide and not more than 10 per cent of calcium oxide should be present in the barium and calcium oxides. The germanate may be mixed with the oxides or germanium or the oxide or other compound thereof, preferably of particle size of ¢-5 microns, may be ball-milled with the alkaline metal carbonate suspended in a solution of nitrocellulose in butyl acetate which is applied by dipping or spraying the carrier such as a coiled coil which is dried and then heated to 1200-1300‹C preferably during the manufacture of the discharge device. The barium and strontium carbonates are preferably in equimolecular proportions and when used in a fluorescent discharge lamp the germanium is within the range of 2-15 per cent, preferably 5 per cent, of the carbonates. The material may be shaped into pellets with the use of gum tragacanth which may be enclosed within the metal carrier.