method for manufacture of thermionic cathode for electric entladungsgefaesse

摘要

741,369. Cathode materials and processing. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 14, 1953 [Oct. 22, 1952], No. 26525/52. Class 39 (1). Between the base metal (e.g. tungsten) and the emissive layer an intermediate layer is provided consisting of a silicide of the base metal, to prevent the formation of undesirable reaction products and interface compounds between the base and emissive materials. In an example a tungsten coil is heated with powdered silicon in a stream of equal parts of hydrogen and hydrochloric acid gas at 700‹- 950‹-1400‹ C., to form the tungsten silicide or disilicide. Additionally metal grains which have been similarly coated with silicide are mixed with the emissive material. The cathodes are particularly useful in fluorescent mercury discharge lamps, where they reduce blackening.