GB1136949A - Improvements in electric incandescent lamp and filament - Google Patents

Abstract

1,136,949. Electric incandescent lamps. GENERAL ELECTRIC CO. 13 June, 1966 [2 July, 1965], No. 26214/66. Heading H1F. An incandescent lamp filament consists of a coil or coiled-coil of tungsten wire, substantially free from surface layer impurities of carbon, iron or molybdenum but containing tantalum diffused into the surface layer in an amount materially less than 300 parts per million. The content of tantalum is preferably less than 100 parts per million and is effective as a getter for oxygen and hydrogen that may be present in the lamp bulb or filament. The filament may be made by winding tungsten wire 8 from a spool 10 on to a mandrel 9 of tantalum either as a continuous coil or as a series of sections 12, immersing the wire and mandrel in hot hydrochloric acid to remove iron and nickel impurities, annealing them in an inert atmosphere between 900‹ C. and 1500‹ C. and cutting the sections apart at the lines A. The sections are again immersed in hot hydrochloric acid, sintered in a vacuum furnace at between 1000‹ C. and 2500‹ C., the mandrels removed in a bath of hot hydrofluoric acid and the sections rinsed in distilled water and stored in glass containers. For making coiled-coils, the annealed filament wire and mandrel are coiled on a secondary mandrel also of tantalum before cutting into lengths. The filaments are particularly suitable for use in microminiature lamps having a bulb diameter of, for example, # inch.