Patent GB-827487-A (GB)
Title: Improvements in or relating to electric discharge devices
IPC: H01J61/067
Filed: 1957-06-05
Abstract: 827,487. Discharge lamps ; electrode materials. WESTINGHOUSE ELECTRIC CORPORATION. June 5, 1957 [June 13, 1956], No. 17843/57. Class 39(1). [Also in Group XXXVI] A low pressure mercury vapour-inert gas discharge lamp 10, which may be fluorescent, has lead conductors 18 projecting within the envelope 12 and refractory metal, e.g. tungsten, electrode coils 20 coated with alkaline earthoxide materials, including at least barium oxide, and supported by the lead conductors 18 at either end of the envelope, the electrode coils 20 serving primarily as cathodes and portions of the lead conductors serving as anodes, and the surfaces of at least the lead conductor portions serving as anodes being of a dull dark colour, e.g. black or grey, and roughened or etched, the surfaces being stable and adherent to the lead conductor portions and rendering them highly thermally emissive. The dull dark and roughened lead conductor surfaces are preferably stable and adherent under partial vacuum conditions at temperatures of at least approximately 750‹C. The surfaces can be of a black chromium-vanadium-complex plating, about 0À05 mils thick, comprising from 100 to 9À5 parts by weight of chromium per part of vanadium, applied to a core of iron or nickel for example. The vanadium can be essentially in the form vanadium oxide and the chromium can be partially oxidised, the ratio of total chromium atoms to total oxygen atoms combined with chromium being from 2 : 1 to 100 : 1. In other constructions the surfaces can be a coating of aluminium-iron alloy which may be coated on iron, a coating of carbonized nickel, of iron heat-reacted with a small amount of molybdenum, or of a coating of evaporated aluminium on iron. Apparatus for filating the chromium-vanadium-complex on wire is shown in Fig. 3. The wire is drawn from a reel 30 over rollers into a tank 36 containing an alkaline solution in which the wire is anodically cleaned, and then passed between a water spray 44, and a drain tray 50 carrying rubber squeegee blades into an acid cleaning solution in tank 48 in which it is again anodically cleaned. The alkaline solution may be sodium hydroxide in water and the acid solution a 50% aqueous solution of concentrated sulphuric acid. The wire then passes between a water spray 56 and a drain tray 62 carrying rubber squeegee blades into an electro-plating bath 60 containing chromium trioxide, ammonium, metavanadate and glacial acetic, formic or citric acid. The current density in the bath 60 is 750-1200 amps. per sq. ft. of wire surface, electrical contact with the wire being made by the roller 58 and bar 66. The wire is then passed between the water jets 74 and a sponge 70 on a drain tray 72 and then under the heat lamps 76. The iron wire coated with an alloy of aluminium and iron can be formed by wiping the wire with powdered aluminium and heating to 800‹C. in hydrogen. Alternatively the aluminium can be applied by cladding or plating. The coating of aluminium-iron alloy can be 0À001-0À0005 in. thick. The alkaline earth-oxide coating on the coils 20 can be of BaO, of BaO and SrO, of BaO and CaO or of 60% BaO, 30% CaO, and 10% SrO, by weight. The lamp filling can consist of argon at a pressure of 4mms. together with mercury. In the construction shown in Fig. 4 the lead conductors 18 have anode portions 78 positioned parallel to the coil 20 and preferably lying therewith in a plane perpendicular to the envelope axis.