GB1014340A - Improvements in or relating to electrodes for gaseous discharge lamps - Google Patents

Abstract

1,014,340. Making electrodes. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Aug. 18, 1964 [Aug. 21, 1963], No. 33694/64. Heading B3A. [Also in Division H1] An electrode containing electron emissive material for a gas-discharge lamp of the kind which is ignited by means of a glow discharge comprises a coil 2 of coiled tungsten wire surrounding and supported by a central core wire 1 which projects from the coil at the end 3 thereof facing the discharge, the wire of the coil being thin with respect to the core wire 1 and the turns of the first winding of the coil being arranged so that they do not contact one another, and the electron - emissive material being located for the greater part within the first winding. Preferably the coil wire diameter is less than <SP>1</SP>/ 3 of the core wire diameter and the pitch of the first winding of the coil is greater than 1À5 times the thickness of the coil wire. A second coil similar to the first coil may be wound over the outside of the first coil (Fig. 2, not shown). The first winding is formed by winding tungsten wire around a molybdenum mandrel (or a tungsten mandrel of a diameter preferably less than <SP>1</SP>/ 3 the diameter of the first winding together with molybdenum mandrels) and winding the first winding about a steel mandrel to form the second winding. The steel mandrel is then pulled out and the molybdenum etched away. The coil is then dipped in a suspension of carbonates of the emissive material, which may be barium, calcium, strontium or thorium, the coil is then fitted on tungsten core wire and the carbonates converted into the emissive material, i.e. the oxides by heating. A specific example with dimensions is given.