GB957597A - Improvements in metallic carbide filament lamps - Google Patents

Abstract

957,597. Incandescent electric lamps. GENERAL ELECTRIC CO. Nov. 9, 1962 [Nov. 29, 1961], No. 42408/62. Heading H1F. An incandescent lamp comprises a sealed light-transmitting envelope containing a filament of carbide of a metal of the group comprising tantalum, hafnium, niobium and zirconium or mixtures thereof, a source of hydrogen and a quantity of uncombined solid carbon which is located in effective range of the atomic hydrogen formed in the vicinity of the filament so that a carbon bearing gas, e.g. a gaseous hydrocarbon is formed which is thermally decomposed at the filament so as to maintain the carbon content thereof at a fixed value and to release hydrogen for continuation of the cycle. The lamp may contain hydrogen and a rare gas at a total pressure approximating to atmospheric pressure. Methane alone or mixed with hydrogen may be used. The source of carbon may be a pellet on the envelope wall or a layer of soot. In one form, the lamp has a small spherical envelope with a punch seal, a pellet of carbon being provided on the envelope wall. In another form, the filament 2a is supported by lead-in wires 3a within a tubular envelope 1a. A metallic screen 6 coated with finely-divided carbon is carried by a support 7 from one of the lead-in wires so that atomic hydrogen formed by dissociation of the filament is carried by convection into contact with the screen where it combines with the carbon to form a hydrocarbon which returns to and is dissociated at the filament. In a third form, a layer of soot is coated on the upper end of the envelope. The lead-in wires may, in this case, be partly coated with glass to minimize the deposition of carbon thereon. The filling may also contain nitrogen or a source of nitrogen such as hydrogen cyanide or ammonia.