GB937391A - Cold-cathode glow-discharge tubes - Google Patents

Abstract

937,391. Cathode materials and processing. MULLARD Ltd. Feb. 14, 1962, No. 5666/62. Class 39 (1). The cathode of a glow-discharge tube has a surface layer containing gold, CsAu and an oxide of caesium. The cathode may comprise a cylinder 5 of molybdenum or nickel, or a glass support coated with molybdenum or tin oxide, or a gold strip. As shown, a gold wire filament 9 is wound on a platinum-coated molybdenum wire 7 which may constitute the anode. Alternatively, the anode may comprise a rod 10 alone, or a ring 17 supported on rod 10. During manufacture, the tube is heated to 350‹ C. and exhausted through stem 4. The electrodes are outgassed by passing a current through filament 7 and inductively heating cathode 5. A further tube, containing a compressed powder mixture of 2 parts silicon to 1 part of caesium dichromate, or 1 part silicon to 1 part of caesium chromate, is joined to stem 3, and the mixture is heated to cause caesium to be deposited on the walls of this tube. The gold 9 is then evaporated in vacuo or in neon at low pressure and deposited on the cathode 5. After exhaustion, caesium is distilled from the further tube so as to react with the gold cathode layer, by heating at 100 ‹ C. until photo-emission from the cathode reaches a maximum, e.g. about 1¢ hours. After sealing off stem 3, and admitting neon at 10 mm. of Hg, a discharge current of 10 mA. is passed between cathode 5 and anode 17 and pure oxygen is slowly admitted until the maintaining voltage of the discharge is a minimum, e.g. 31 to 33 v., or until thermionic emission from the cathode at 100‹ C. in the absence of neon is a maximum. Finally the tube is again exhausted and refilled with neon at 5 to 20 e.g. 10, mm. of Hg, or with helium at 3 to 20 mm. of Hg.