US2080925A - Electric discharge device - Google Patents

Description

May 18, 1937-v P. MIDDLETN ET AL 2,080,925

ELECTRIC DISCHARGE DEVICE Filed April 9, 1935 Patented May 18, 1.937V

ELECTRIC DISCHARGE DEV-ICE Percy Middleton, Kew, and Vivian Gillies Myatt, deceased, late of North Wembley, England, by Marie Louise Myatt, executrix, North Wembley, England, assignors to 'The General Electric Company Limited, London, England Application April 9, 1935, Serial No. 15,484 In Great Britain April 9, 1934 2 claims. (ci. 17e- 2) 'Ihis invention relates-to electrical discharge If oxides, instead of silicates, are enclosed by devices of the type having at least one thermionic the tungsten spiral, the treatment may have to cathode of which one part at least consists of a be modified in order to avoid their reduction. refractory metal whose oxide is appreciably vola- The use of silicates in place of oxides is described tile at any temperature reached during manuin British patent speciiication Nos. 384,067 and facture or operation of the device. Tungsten is 411,266. an example of such-a metal. More particularly In the drawing accompanying and forming it relates to luminous electrical discharge tubes part of this specification a gaseous electric dishaving thermionic cathodes consisting of bodies charge lamp having electrodes treated by the of alkaline earth compounds surrounded by tungprocess described above is shown in a front elesten spirals. vational, partly sectional view.

When the cathode is sealed into a tube of the Referring to the drawing the lamp comprises type specified, the tungsten is often oxidized aninternal envelope of glass I having approxisupercially. During subsequent manufacture mately spherical ends 2 into which are sealed and/or during operation this oxide is deposited the leading-in Wires 3. To these leads are spoton the walls of the tube forming a dark deposit welded the thermionic electrodes each consisting which intercepts some of the light from the disof a short refractory rod 5 composed of alkaline charge. The purpose of the invention is to overmetal silicates surrounded by a tungsten spiral come this objection. 4; two turns 6 of the spiral, free of the rod, are

According to the invention, the manufacture of used as the curved part of the leads for preventan electric discharge tube of the type specied ing the conduction of excessive heat to the seals. includes the step of introducing a reducing gas The electrodes are mounted very close to the into the tube with the cathode sealed in and spherical ends of the tube, being not more than heating the refractory metal in this gas, so that l0 mm. from the wall. its oxide is reduced. Since the reduced metal is The internal envelope I is arranged within not volatile, there is then less blackenlng of the an outer envelope 'l (shown as partly cut away in tube during subsequent manufacture and life. the drawing) having a foot-tube 8 and a stand- Thus in one manner of manufacture of a. highard form of lamp cap I2 at one end. The leads pressure mercury vapour discharge lamp, ac- 0 for the discharge tube are brought through the cording to the invention, the tube, furnished with foot-tube in the ordinary way, and connected to electrodes consisting of tungsten spirals enclosthe leads 3 sealed into the inner envelope; these ing alkaline metal silicates, is sealed to the pump leads 9 may conveniently carry wire rings I3 and exhausted. During the making of the tubes, which bear against the inside of the outer enthe tungsten will probably have become oxidized, velope and serve as supports for the inner enespecially if, as is usual in such lamps, the elec' velope. The outer envelope is exhausted after trodes are near the end of the tube. The tube is assembly and sealed oil. then lled to about 700 mm. with a mixture of The internal envelope contains enough mercury 40% hydrogen and 60% nitrogen, and the tungto give a pressure of about l atmosphere when sten spirals are heated to 1100 C. for about 3 operating on acurrent 0f from 21/. to S'amperesminutes. The gas is then pumped out; if the in the case of a tube about l'l cm. long by 3 cm. tungsten is much oxidized, it may be desirable to diameter, for example, about 0.2 to 0.25 gm. of rell with the same mixture and repeat the mercury are adequate-together with a few mm. treatment at the same temperature. But in any of argon to facilitate starting. Furthermore, to case, the tube is refilled with the same gas, and render the tube self-striking, a wire I0 is carried the spirals heated at l3001500 C. for about 5 from one of the leads along the outside of the minutes. The gas is then pumped out, and the inner envelope to a point near the other elecelectrodes degassed at about l500 C. Manutrode of the tube and there wound round the facture then proceeds in the normal way. outside of the inner envelope to form a con- A similar process may be usefully employed in ductive ring II. I vthe manufacture of sodium vapor discharge After the electrodes 4. 6 are mounted in the lamps, inner tube I in the manufacture of the lamp but Pure hydrogen may be used in piace of the before the tube I is sealed ofi from the exhaust mixture. Ii' the mixture is used, its freedom system the electrodes l, 6 are treated by the from oxidizing impurities become more improcess disclosed above after which the other portant, the lower the hydrogen content. steps in the manufacture of the lamp are perl0 trodes sealed therein, filling the envelope to about 700 mm. with a mixture of 40% hydrogen and 60% nitrogen, and heating the tungsten spirals to 1100 C. for about 3 minutes.

2. In the manufacture of a high pressure mer- 15 cury vapour discharge lamp having an envelope containing electrodes comprising tungsten spirals enclosing alkaline metal silicates, the steps which comprise exhausting the envelope with the electrodes sealed therein, filling the envelope to about 700 mm. with a mixture of 40% hydrogen and 60% nitrogen, heating the tungsten spirals to 1100 C. for about 3 minutes, exhausting the envelope of said gas mixture, refilling the envelope with the same gas mixture to the same pressure, heating the tungsten spirals to a temperature of from 1300 C. to 1500 C. for about 5 minutes, exhausting the envelope and degassing the electrodes.

PERCY MIDDLETON.

MARIE LOUISE MYAT'I', Executria: of the Estate of Vivian Gillies Myatt,

Deceased.

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