US2715691A - Vapor discharge lamp - Google Patents

Description

Aug. 16, 1955 G. MEISTER I2,715,691

VAPOR DISCHARGE LAMP Filed June 29, 1951 ATTORNEY United States Patent O vAPoR DISCHARGE LAMP George Meister, Newark, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corpora tion of Pennsylvania Application June 29, 1951, Serial No. 234,395

1 Claim. (Cl. 313-25) This invention relates to lamps and, more particularly, to improved metal vapor discharge lamps.

In metal vapor discharge lamps, particularly those containing alkali metals, which operate at relatively high temperatures, that is, above 200 C., the making of metal glass seals which are impervious to attack by the vaporized metal has presented a real problem. The metal glass seals in such tubes usually consist of a refractory metal leading-in conductor, suitably tungsten, and have. an oxide layer at the metal-glass interface.` This oxide layer fails to withstand the attack of the reducing metal vapor, such as cesium vapor, at about 200 C.

Some improvement has been obtained through the use of molybdenum leading-in conductors in lamps which operate up to approximately 250 C. However,y even these molybdenum glass seals fail above 280 C. when the cesium vapor attains suicient pressure to, force its way into contact with the protective intermediate layer of oxide in the metal glass seal, thereby combining with the oxygen of said layer to form, in the case of cesium, cesium oxide within the tube and to produce a leakage path along the leading-in conductors.

Hence, it has been found advantageous,l according to my invention, to make the metal-glass seal in alkaliY metal vapor lamps, such as cesium, with a degasified borosilicate glass and a refractory metal leading-in conductor which remains metallic and has no intermediate oxide layer at the interface between the glass and the said conductors which the cesium vapor can attack. Duringy the sealing of said conductor to said degasitied borosilicate glass, I' prevent the formation of the intermediate oxide layer on the glass metal interface by holding the refractory metal leading-in conductor in or at the tip of the reducing part of an Oxy-hydrogen flame so that no oxide can form or, if such an oxide is formed, it is immediately vaporized from the conductor by the hot llame.

In its general aspect, the present invention has the object of overcoming the aforementioned, disadvantages of the prior art in metal vapor discharge tubes.

Specifically, an object of the present invention is an alkali metal vapor lamp having a seal between a refractory metal leading-in conductor and a degasified borosilicate glass which will withstand action by said metal vapor.

Another and specific object is an alkali metal vapor lamp having a seal between a refractory metal leading-in conductor and a degasified borosilicater glass without formation of an intermediate oxide layer at the glass interface.

An additional object is a method of sealing a refractory metal leading-in conductor to a degasified borosilicate glass of an alkali metal vapor lamp comprising heating said conductor in or at the tip of the reducing part of an Oxy-hydrogen ame so that no oxide forms at the glass metal interface, or if said' oxide is formed thereat, it is immediately vaporized by the hot llame during the sealing of said conductor to said glass.

Another object of the invention is a metal vapor lamp 2,7 1 5 ,6 91 Patented Aug. 16, 1955.

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operating at temperatures at which said metal vapor will reduce any oxide of refractory metal used in effecting a seal and having a seal between a refractory metal leadingin conductor and a degasiied borosilicate glass which is impervious to reduction by the metal vapor and resultant early life leakage failures through the seal along the conductor.

Other objects and advantages will appear to those skilled in the art to which it appertains as the description thereof proceeds, both by direct recitation thereof, and by implication from the context.

Referring to the accompanying drawing, in which like numerals of reference indicate similar parts throughout:

Fig. 1 is an elevational view of a metal vapor lamp embodying my invention;

Fig. 2 is an enlarged fragmentary axial sectional View of one end of the lamp of Fig. 1;

Fig. 3 is an elevational view of a seal between a refractory leading-in conductor of the lamp of Fig. 1 and a degasified borosilicate glass bead.

Referring to the drawing in detail, the reference numeral 10 designates an alkali metal vapor lamp comprising an inner envelope or arc tube 12, an outer evacuated envelope 14 desirably enclosing a gettering device 16, and oppositely disposed electrode mounts 18 and 20.

The generally cylindrical arc tube 12 is desirably of alkali-resistant vitreous material, such as glass No. 1, a soda-aluminum borosil'icate glass with a. small percentage of alumina, and is desirably coated on its interior with a. glaze composed largely of boric oxide. This glass is designated as a tungsten sealing glass. It has a softening point at 703 C., an annealing point of 496 C., a strain point of 461 C., a coeihcient of expansion of 46 l07 between 0 and 300 C., and a density of 2.23. The login of its resistivity at 350' C. is 6.77. lts power factor is .0033' (expressed as a decimal and not asV percent), its dielectric constant 4.9 andv its loss factor .0161 (expressed as a decimal and not as percent). This glass has the following approximate composition:

This tube 12 contains an inert gaseous filling, such as argon at about 20 cm. pressure, for initiating and sustaining a discharge, and a small quantity of a metal, such as cesium, which is readily vaporizable. While a cesium vapor lamp has been selected as an embodiment of this invention, it will be understood that other alkali metal vapor lamps or vapor lamps employing metals which readily reduce refractory metal oxides at their operating temperatures are contemplated. To each end of tube 12 is attached a hollow extension 22 of reduced diameter. To these extensions are axially sealed, as hereinafter explained, refractory leading-in conductors 23 of electrode mounts 18 and 20.

The electrode mount 18 comprises a fllamentary electrode 24 having an oxide coated helix 25 surrounding a straight return portion 26. It is secured to the inner extremities of conductors 23 as by welding. Near the outer portion of one conductor 23 is the gettering means 16 mounted by means of a connector 27 in close proximity to the outer bulb 14. The outer ends of conductors 23 are connected by flexible, desirably semicircular connectors 28 to outer leads 30, which in turn are sealed through a stem 31 to the outer envelope 14.

The electrode mount 20 differs from mount 18 only in the addition of a cup-like anode 32 surrounding the electrode 24 and electrically joined by connector 34 to one of the leading-in conductors 23. ThisV anode is em- -ployed for direct current operation of the lamp 10. The outer extremities of conductors V23 of mount 20 are joined by flexible connectors 34V to outer leads 36. The l leads 36 in turn are secured, as by welding, to hollow `cup-like outer pins 37. These pins 37 are sealed to dishf like projections 35 at one end of the envelope 14. A About each of the above-mentioned extensions 22 of 1 arc tube 12 are two suitable resilient supporting collars 38, each having a semi-circular bodyr 39 clamped to g each other and about the extensions 22k by bolts and j nuts, and spring arm extensions 40 projecting outwardly perpendicular from the plane of the body 39 to the inner vWall of outer envelope 14. A heat resistant tape, such V`Vas'glass tape, is desirably employed between said'collars "l 38 and the extensions 22.` i

' YInV outer Yvitreous envelope 14, employed for conserving 7* the heat of operation, there is provided an exhaust tubulation 41 for evacuation purposes.` A suitable base 42 is axedat the end opposite pins 37'for making a connection to the outer leads 30 of mount 18. v

According to my invention, theY metal vapor lamp V10 is `provided with an oxide-free seal which Vthe metal f vapor will vnot spoil at operating temperatures above 300or C., that is,V between 307 and 325 C., between the leading-in conductors 23 of electrode mounts 18 and 20 and the extensions 22 of arc tube 12.V This approxi# mately 300 C. operating temperature corresponds to 2 watts input per cm2 of the surface of arc tube 12 when the lamp is operated within an outer euvelope'14.

Y First, the refractory leading-in conductors 23, suitably tungsten or molybdenum, are chemically cleaned electrolytically to remove any oxide thereon and Vproduce a clean, bright, metallic surface. The clean Vconductors 23 are then heated in or at the tip or inner cone of an l Y Oxy-hydrogen flame and hermetically sealed to or coated with a'beadV 44 of a degasied borosilicate glass, such as glass No. 2, as shown in Fig. 3. Y Y This glass No. 2, a soda aluminum borosilicate glass, is designated H. R. Clear Chemical. It has Ya softening point at 820i1 10'7 between 0 and 300 C., an approximate working pointV of 1220 C. and a density of 2.23. The login of its resistivity at 350 C. is 6.68. Its power factor is .0046 (expressed as a decimaland not as percent); its/dielectric constant 4.6 and its loss factorr.021- (expressed as a decimal and not asY percent); Y

.This glass has the following approximate composition:

Per cent SiOz 80 f B203 i3 A12O3- 2 Naz'O-l-KzO 41/2 Miscellaneous Y 1/2 The degasilied borosilicate glass No. 2is obtained Vby heating vsaid glass to a temperature of about l700 C. Vto remove the gases therefrom. The intermediate oxide elayer'which normally forms atV the metal glass interface,

is avoided bythe use of the degasiied borosilicate glass, andthe reducing action of the Oxy-hydrogen sealing ame, which prevents formation of the refractory metal oxide on conductors 23, or if the oxide is formed thereon,

immediately'vaporizes said oxidev from said conductors.

YEmploying a suitable jig (not shown) Vaftixed to one Vend of conductors 23 the iilamentary electrode24 is mounted on the opposite extremities of conductors 23. VThese conductors 23, still aligned in the fixture, are sealed together at the beads 44 by a button 46 of dey Y gasitied boro/silicate glass, such as glass No. 2, the same glass employed for the beads 44.,

The mount Y18, so formed, is in turn sealedV by means of the button 46 to the extension 2.2 of arc tube 12. In

like manner, the mount Y20 is sealed to the oppositelydisposedextension 22 of arc tube 12. Y Y Y After a suitable exhaust, which may consist of a bake, lamentary electrode treatment, evacuation and final gas and metal ll, the arc tube 12'is tipped off as at 47.

Tne oppositely disposed electrode mounts 18 and 20 are joined by connectors 28 and 34 to the outer leads 30 and 36 respectively. The support collars 38 are secured about extensions `22 of arc tube 12, and the outer ening means 16 is vaporized on to the interior wall'of Y' envelope 14 and a base 42 is applied, thereby completing the'lamp 10. Y Y

' Thus it Will be seen from the foregoing'description that I have constructed a metal vapor lamp 10 having a seal between refractory metal leading-in conductors 23 and a degasiiied borosilicate glass bead 44 which will withstand metal vapor at operating temperatures of the lamp where. said metal vapor normally would reduce any oxide of a Y refractory metal conductor. This seal between therefrractory metal leading-in conductors 23 and the degasiiied borosilicate glass bead 44 'ismade without the formation of an intermediate oxide layerV at the metal-glass interface.

In addition, the above-mentioned sealbeing impervious to the metal vapor at the operating temperatures in the lamp 10, a resultant'early leakage failure through the seal along said conductors 23 are eliminated, as well'as seals cracked g from overheating. I Y Y Although a preferred embodiment of my invention has been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claim.

I claim: A cesium vapor lamp adapted to'operate at about 2 watts yper square centimeter of the inner envelope sur.-V face area to maintain said cesium as `a vapor at atemperature at aboutf300 C. and comprising an inner vitreousV .r light transmitting envelope, oppositely disposed Yelectrode Vmounts in said inner envelope and each having rat least'` Y two tungsten leading-in conductors'and a lila'mentaryV elec- Vtrode'thereon, an hermetic seal between said conductors Y and said inner envelope, withA said conductors being oxide-V "j free at least along substantially the length of said hermetic Y seal thereon, said seal having degasified borosilicate 'glass Vhermetically fused directly to said oxide-free tungsten con-V Y.

ductors without an oxide bond at the metal-glass interfaceY and througha degasitied borosilicate glass button to said inner envelope, an ionizable medium in said inner envelope for initiating and sustaining a discharge admixed' with small quantity of Ycesium which is readily Vaporizable and an outer evacuated vitreous light transmitting enf velope enclosing said Vinner envelope for conserving the heat of operation. Y

References Cited in the le of this patent UNITED VSTATES PATENTS Spinnler Nov. 4, 1952 Y

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