US2542348A

US2542348A - Electrode structure

Info

Publication number: US2542348A
Application number: US116028A
Authority: US
Inventors: Edward B Noel; Ernest C Martt
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1949-09-16
Filing date: 1949-09-16
Publication date: 1951-02-20
Anticipated expiration: 1968-02-20

Description

Feb, 20, 1951 NOEL ETAL 2,542,348

ELECTRODE STRUCTURE Filed Sept. 16, 1949 Irwvervkovs: Edward B. NoeL, Ernesi: C. Mav'bk, 5 W

Theh" A-t-lror'ne Patented Feb. 20, 1951 ELEC IRODE STRUCTURE Edward B. Noel, Cleveland Heights, and Ernest O Martt, Cleveland, Ohio, assignors to General Electric Company, a corporation of New York Application September 16, 1949, Serial No. 116,028

3 Claims. (Cl. 176-126) The present invention relates generally to gaseous electric discharge devices or lamps of the gaseous conduction type and more particularly to electrode structures useful in such devices.

In the copending applications Serial N 0. 553,531 01' Lyman B. Johnson, filed September 11, 1944, now Patent #2,499,506, issued March '7, 1950, and Serial No. 725,031, now abandoned, of Paul D. Cargill, filed January 29, 1947, both of which applications are assigned to the assignee of this application, unactivated self-heating electrode structures are disclosed and claimed. As disclosed in the copending applications, self-heating electrodes without activation material thereon, that is, without material of low work function, such as thoria or the alkaline earth oxides, on their discharge-supporting surfaces must operate hotter than activated ones because electron emission corresponding to the discharge current must be obtained from them thermionically. Such self-heating unactivated electrodes thus require a greater amount of energy for heating them which usually entails a higher cathode drop and a lower efficiency of operation.

The electrodes disclosed and claimed in the c'opending applications, however, are of such structure that they are maintained at the required high operating temperature by the use of energy inherent in the discharge without need for cathode drop in excess of that required to ionize the gaseous atmosphere. Lamps employing the unactivated electrodes of the copending applicationsapproach or substantially equal the efliciencies of commercial lamps having activated electrodes, start easily and do not show rapid electrode disintegration or envelope blackening for a commercially useful life.

The principal object of the present invention is to provide an electrode structure embodying the inventive concepts of the aforesaid copending applications but which is more easily manufactored and less expensive to make than the specific electrode structures disclosed in said applications. Further objects and advantages attaching to the invention will appear from the following detailed description of a species thereof and from the accompanying drawing in which Fig. 1 is a side elevational view of one end of a tubular vitreous envelope of an electric discharge lamp showing an electrode structure of my invention mounted therein; Fig. 2 is a similar view partly in section and on an enlarged scale of the electrode structure shown in Fig. 1; Fig. 3 is a back plan view of a reflector disc plate of the electrode structure; and Fig. 4 is a front plan view of the electrode structure.

Referring to Fig. 1 of the drawing, the end of the tubular vitreous envelope 1 shown is of radiation-transmitting material, such as glass or quartz, and has an unactivated self-heating main discharge supporting electrode structure 2 mounted on a current inlead 3, such as a tungsten wire, passing through the wall of the envelope I. When the envelope is of quartz, a molybdenum foil seal or a graded glass seal may be used between the envelope l and the inlead 3. The opposite end of the envelope is of similar structure and may include in addition to the main discharge-supporting electrode structure 2 a starting electrode in the well known manner. The envelope I of the completed lamp is sealed and contains a starting gas, such as argon, and a quantity of mercury, the vapor of which is luminosity producing duringthe operation of the lamp. The quantity of mercury may be selected so as to produce at the operating temperature of the envelope either a saturated or an unsaturated vapor atmosphere at a vapor pressure high enough to constrict the gaseous discharge in the lamp in the form of a luminous chord spaced from the wall of the tubular envelope. Lamps of the high pressure mercury vapor discharge type are well known commercially and further description of their operating characteristics is not necessary for a complete understanding of my invention which has to do with the electrode structure 2.

As shown in Figs. 2, 3, and 4, the electrode structure 2 comprises a support wire 5, preferably of tantalum, one end of which is welded to the current inlead 3 of the lamp to support the electrode structure 2. The support wire 5 thus constitutes an extension of the current inlead 3. The opposite end portion of the support wire 5 is transversely bent substantially at right angles to the length of the wire 5 to provide a leg 6 for the attachment of the part I, 8 of the electrode structure 2 whereon the discharge terminates. A reflector plate 9 for reflecting heat back to the part 1, 8 and for facilitating starting of the lamp by supporting an end glow with the part 1, l engages the leg 6. The part 1, 8 of the electrode structure whereon the discharge terminates is called the electrode element hereinafter to distinguish it from the reflector plate 9.

The electrode element 1, 8 includes a discshaped body portion 1 having thereon shallow convoluted ridges 8 providin transversely opposed surfaces for minimizing heat loss by radiation and for increasing the electron-emitting surface of the electrode element I, 8 with minimum increase in depth and with minimum increase in dimension or projected area of the electrode element 1, 9 transverse to the are discharge path. The shallow ridges 9 also reduce the blackening of the envelope by evaporated electrode material by reducing the evaporating area of the electrode element 1, 9 as compared to a flat disc of the same total area. Ridges 8 are preferably constituted by a strip of tantalum formed into a spiral and spot welded to the discshaped body portion 1 of the electrode element which portion is also preferably of tantalum. The body portion I is spot welded to the front of the leg 6 of the support wire 5 and is transverse to the length of the wire 5.

The reflector plate 9 is a disc-shaped member preferably of tantalum having a slot l therein (Fig. 3) wide enough to receive the wire support which passes through the plate 9. The slot I0 is made by cutting the plate 9 along parallel lines extending inward from the edge tobeyond the center of. the plate and spaced equally from its center. The portion of the plate 9 between the cuts constitutes a tab H which is bent at right angles to leave a slot of sufllcient width to receive the support wire 5 and of suillcient length so that the reflector plate 9 is coaxial with the body portion 1 of the electrode element 2 when the plate 9 is mounted on the support wire 5 as shown in Fig. 2. In mounting the reflector plate 9 on the support wire 5 the disc portion thereof is held against the back of the leg 5 of the support wire 5'with the tab I I against the straight portion of the wire 5. The tab II is then spot welded to the wire 5 to firmly secure the reflector plate 9 and the wire 5 together and complete the assembly of the electrode struc ture 2.

The straight end portion of the support wire 5 is then welded to an end portion of the current inlead 3 which may be provided with a glass bead in the usual manner. The current inlead wire 5 is then hermetically united with the vitreous envelope by fusing the bead and the envelope together with the electrode structure 2 within the envelope I as shown in Fig. 1. The other usual steps in the manufacture of the lamp are then performed to complete the lamp.

The above-described electrode structure 2 is easily made and assembled in the small sizes required for unactivated electrodes for mercury lamps operating in the pressure range of, for example, from to 2 atmospheres and with operating currents of from 2 to amperes, with an optimum range of 3 to 7 amperes.

As illustrative of the small size of the electrode structure 2 and by way of example a particular electrode structure for an ultraviolet emitting high pressure mercury vapor discharge lamp rated at 3000 watts and having a hard glass envelope approximately 55 inches long and about 1%. inches in diameter will be described. The disc-shaped body portion 1 and the reflector plate 9 have a diameter of 3.57 millimeters and a thickness of about 0.25 mm. The strip forming the ridges 8 has rounded edges, is approximately mm. long, about 0.25 mm. thick and about 0.42 mm. wide. The strip is wound as a spiral of about 2 turns and has an edge spot welded to the body portion 1 with a separation of about 0.25 mm. between adjacent turns. The tab II is about 0.5 mm. wide and the greatest projected distance from the surface of the tab welded to the support wire 5 to the edge of the plate 9 in back of the tab ii is 1% mm. The bent support wire 5 is about 0.5 mm. in diameter and has a projected length of 6 mm. in one direction and a projected length of 1.5 to 2.0 mm. in a direction normal thereto.

The simplicity of the electrode structure described above greatly facilitates the manufacture thereof in the small sizes required for unactivated electrodes.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electrode structure for an electric discharge device of the high pressure type comprising a refractory metal support wire having a transversely bent end, an electrode element of refractory metal having a disc-shaped body portion secured to the bent end of said wire and transverse to the length of said wire and having a convoluted ridge on the surface thereof facing away from said wire, and a refractory metal reflector plate of-disc-shape also secured to said wire coaxially with said electrode element to minimize heat losses from the latter, the bent end of said support wire being interposed between and spacing apart said electrode element and said reflector plate.

2. An electrode structure for an electric discharge device of. the high pressure type comprising a refractory metal support wire having an end bent at right angles, an electrode element of refractory metal havinga disc-shaped body ortion secured to the bent end of said wire and transverse to the length of said wire and having a convoluted ridge on the surface thereof facing away from said wire, and a refractory metal reflector plate of disc-shape also secured to said wire coaxially with said electrode element to minimize heat losses from the latter. said support wire extending through said reflector plate with its bent end interposed between and spacing apart said electrode element and said reflecting plate.

3.- An electrode structure for an electric discharge device of the high pressure type comprising a refractory metal support wire having an end bent at right angles, an electrode element of refractory metal having a disc-shaped body portion secured to the bent end of said wire and transverse to the length of said wire and having a convoluted ridge on'the surface thereof facing away from said wire, and a refractory metal reflector plate of disc-shape also secured to said wire coaxially with said electrode element to minimize heat losses from the latter, said reflector plate having an opening through which said support wire passes and an outwardly extending tab juxtaposed to said opening and secured to said wire, the bent end of said wire being interposed between and spacing apart said electrode element and said reflector plate.

EDWARD B. NOEL. ERNEST C. MARTT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,008,066 Ende July 16, 1935 2,249,094 Seitz July 15, 1941 2,499,506 Johnson Mar. 7, 1950 FOREIGN PATENTS Number Country Date 482,807 Great Britain Apr. 5, 1938