GB788655A - Improvements in electric discharge lamps - Google Patents

Abstract

788,655. Glass-metal seals. BRITISH THOMSON-HOUSTON CO., Ltd. April 29, 1954 [April 29, 1953], No. 12487/54. Class 36. [Also in Group XL (a)] A high-pressure mercury vapour discharge lamp has a palladium disc or tube sealed in the wall of an outer glass envelope sealed around the discharge tube to allow diffusion of hydrogen therethrough. The glass of the outer envelope is substantially impervious to hydrogen at the operating temperature of the lamp and may be hard or heat-resistant type glass, or soft or lead or soda-lime type glass. In the construction shown in Fig. 3, an ironnickel-cobalt or chromium-iron ferrule 30 is heated in a hydrogen furnace, or by induction heating, and the palladium disc 32 brazed thereto through a copper ring 33. The brazed assembly is then sealed to a glass tubulation 34, the temperature coefficient of expansion of which matches that of the ferrule 30, and that of the outer glass envelope. The complete assembly is then sealed into a re-entrant part of the outer glass envelope, and the tubulation 34 removed. In a modification the palladium disc and ferrule is sealed to the flared end of a glass tube passing through the outer glass envelope and having its outer end open to the atmosphere. In a further modification a palladium tube, one end of which is closed, is sealed through a graded seal to the outer envelope. Specifications 484,629 and 494,192, [Group XL], are referred to.