GB289763A - An improved method for the production of cathodes for electric discharge tubes - Google Patents

Abstract

289,763. Vereinigte Gl³hlampen-und Elektricitõts Akt.-Ges. April 30, 1927. [Convention date]. Vacuum tubes.-Cathodes for discharge tubes are coated with electron emitting alkaline earth metals by introducing into the tube an oxide of the metal and a reducing agent such as magnesium or calcium and heating in vacuo to reduce and vaporize the metal and deposit it on the core wire of the cathode. A mixture of barium oxide or hydroxide with finely ground magnesium may be formed into a rod, compressed and attached to the side of the anode facing the cathode; a small trough for the rod may be formed in the anode. After evacuating the tube but before sealing it from the pump, the anode is heated by high-frequency induction to form and vaporize barium. The cathode core is of platinum, nickel, copper, chrome-nickel, &c. In a modification, an aqueous colloidal solution of barium or strontium hydroxide is coated on the anode and reduced by vaporization of a fragment of magnesium in the vicinity. When the anode cannot be directly heated sufficiently to vaporize the emissive metal, the necessary heat is supplied by an exothermic reaction giving products of low vapour-pressure, for example, the reduction of iron oxide by aluminium or magnesium. An excess of magnesium and iron oxide may be added to the compressed rod or colloidal solution in the above process. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following:- The emissive metals may be reduced from their halides, and may include thorium. A tungsten or molybdenum wire is preferably used as a core to receive thorium. This subject-matter does not appear in the Specification as accepted.