GB491176A - Improvements in high-pressure metal-vapour electric discharge devices - Google Patents

Abstract

491,176. Discharge-lamp electrodes. GENERAL ELECTRIC CO., Ltd., FRANCIS, V. J., and PIRANI, M. May 20, 1937, No. 14069. [Class 39 (i)] In high-pressure metal vapour discharge devices wherein the main discharge commences on a starting electrode and transfers to an associated running electrode such as described in Specifications 444,545 and 472,658 the running electrode of tungsten has a supply of thoria to improve its thermionic emissivity the starting electrode being coated or constructed with a supply of alkaline earth oxide ; at least one of the main electrodes is so formed and if the supply is A.C. both are constructed in this manner. An auxiliary discharge electrode may be used to start the discharge. The starting electrode 2 is a rod 3 of alkaline earth silicate surrounded by two tungsten helices 4, 5 ; the running electrode consists of the turns 1 of tungsten coated with a suspension made by ball-milling thoria and water with tungsten powder. The electrodes are degassed by external heating both when the envelope is evacuated and afterwards in a hydrogen filling and by bombardment, the tungsten and thoria coating sintering together. In a modification the running electrode is a rod coated with a suspension as described above the rod being enclosed by helices in which a rod of alkaline earth silicate is held. In a further construction a tungsten helix at one end surrounds the alkaline earth silicate rod to form the starting electrode and its other turns have wound thereon a fine wire helix these turns being coated with the thoria tungsten suspension ; the ends of the main helix are led out of the envelope so that a current for degassing may be passed through the helix. The dimensions are given of tubes in which the three electrode constructions as set out can be used. When the device is on a D.C. supply the anode may have a thoria supply to keep the electrode at lower temperature than if tungsten only were used. Specifications 482,012 and 486,138 also are referred to.