GB1184691A - Improvements in or relating to the manufacture of Electric Discharge Lamps - Google Patents

Abstract

1,184,691. Metal-vapour lamps. CLAUDE PAZ & VISSEAUX. 18 April, 1967 [18 April, 1966; 16 Nov., 1966], No. 17842/67. Heading H1D. A process for the manufacture of an electric discharge lamp comprising a discharge tube having an ionizable atmosphere containing a rare gas and the vapour of a metal or alloy or compound of a metal includes the step of introducing into the discharge tube a hydrocarbon or halohydrocarbon which will produce, during the operation of the lamp with the temperature of the coolest internal surface of the discharge tube at least 500‹ C., an organometallic compound whose saturated vapour pressure is higher than that of said metal or alloy or compound of a metal. The emission of low-volatility elements, e.g. alkali metals, is thus increased at low lamp loadings and extends over the whole discharge path with no formation of opaque deposits. The lamp is also suitable for pulse operation, e.g. for pumping lasers. Saturated or unsaturated aliphatic hydrocarbons, e.g. ethylene or acetylene, may be introduced under a partial pressure of 0À1 to 10 mm. Hg. Halohydrocarbons may be introduced under a partial pressure of 0À1 to 50 mm. Hg. The metal vapour may be that of indium, mercury, the alkali metals, the alkaline earth metals, the rare earth metals, or the transition metals Y and Sc. Two methods of carrying out the process are described. In the first method, the discharge tube is sealed before operation. Examples of suitable fillings are (a) a drop of mercury alloyed with indium, argon at a pressure of 20 mm. Hg and ethylene bromide at a pressure of 10 mm. Hg and (b) mercury, thallium iodide, indium iodide, sodium iodide, argon at 20 mm. Hg and ethylene at 0À25 mm. Hg. In the second method, a discharge is maintained in the tube for about 1 min. before it is sealed off. The tube containing mercury, iodides, argon and a hydrocarbon is connected to a vacuum duct through a stem surrounded by a cold trap (Fig. 2, not shown). Following the discharge the tube is allowed to cool until the volatilized products have completely condensed and the gaseous atmosphere is pumped out. The tube is then filled with argon at a pressure of 20 mm. Hg. Finally, the cold trap is heated to drive condensed products back into the tube which is then sealed off. In this method hydrogen may be introduced with the original filling to prevent the formation of carbonaceous deposits during the discharge treatment.