GB271401A - Improvements in and relating to thermionic valves and methods of manufacturing the same - Google Patents

Abstract

271,401. Just, A. May 21, 1926, [Convention date]. Vacuum tubes.-Electron-emitting cathodes for thermionic valves comprise a metal or alloy melting above 1000‹ C. and containing or coated with one or more sulphides of zinc or the alkaline earth metals, calcium, barium and strontium, or rare earth metals such as cerium, erbium, yttrium lanthanum, thorium, zirconium, neodymium and praseodymium. The metal melting above 1000‹ C. may be copper or platinum or molybdenum or their alloys such as platinum-iridium or platinumnickel. Phosphorescent sulphides may be used or formed, such sulphides containing traces of sulphides of heavy metals such as copper, cadmium, bismuth, thallium, uranium, tin, manganese, silver and lead. A sulphide coating may be applied to a metal wire and fixed by heating to incandescence. Known oxide cathodes may be heated in sulphur vapour or sulphuretted hydrogen, or a calcium coating containing traces of copper or bismuth on a platinum or platinumiridium core may be converted into sulphide by heating similarly. In modifications, the cathode consists of a homogeneous mixture of metal and sulphide, for instance, a mixture of molybdenum and calcium containing 2-5 per cent of sulphide. Platinum black, or finely powdered amorphous molybdenum obtained by the reduction of molybdenum trioxide with hydrogen, may be mixed with ordinary or phosphorescent calcium sulphide or sulphides of rare earth metals and the mixture pressed into a bar, sintered, hammered and drawn into a wire. Alternatively, powdered platinum or other precious metal may be mixed with calcium powder or oxide or with other alkaline earth or rare earth metals or mixtures or oxides thereof, with or without a small quantity of heavy metal such as copper or a compound thereof, and, after forming into wire, the wire is heated by current or otherwise in an atmosphere of sulphur vapour or sulphuretted hydrogen together with free hydrogen to form sulphides of all the metals except the precious metal. Molten metal such as platinum or platinum nickel may be used instead of powdered metals, the sulphides or metals, with or without a trace of heavy metal, being added to the molten metal.