US2112855A - Electrode for discharge lamps - Google Patents

Description

April 5, 1938. J. w. MARDEN ET AL ELECTRODE FOR DISCHARGE LAMPS Filed June 30, 1954 INVENTOR J 14 MflFDE/V 6- MEI-572" ATTORNEY Z Patented Apr. 5, 1938 UNITED STATES PATENT OFFICE ELECTRODE FOR DISCHARGE LAMPS facturing Company, E corporation of Pennsyl ast Pittsburgh, Pa., a

vania Application June 30, 1934, Serial No. 733,168

16 Claims. -(Cl. 176-126) This invention relates to discharge devices and more particularly to an improved form of electrode therefor.

Although an electrode constructed in accordance with the present invention may find use in various forms of electrical devices it is especially advantageous in connection with discharge lamps of the type employing a metallic vapor. A lamp of this character may include an inner and an outer bulb. The inner bulb contains the electrodes and one or more rare gases as well as asmall quantity of vaporizable metal such as mercury, sodium, cadmium, or mixtures of the same. The outer bulb or envelope may be exhausted, or gas or air filled to provide a heat insulative enclosure for the inner bulb or discharge chamber.

Heretofore electrodes used in the above devices have been made of cores of alkaline earth oxides, hydroxides, or silicates, with or without metal mixtures, supported in spirals of tungsten wire. The oxides were activated by heating the tungsten coil to a sufiiciently high temperature by the passage of electrical energy therethrough. Two lead wires were employed for this purpose. After activation, however, the leads were connected to make a single lead. Other electrode constructions have been used-such as a mesh disk of nickel or other metal coated with an oxide to serve as an electron emission source, in which case only a single lead was employed and the oxides were activated by high frequency induction heating.

In both types of electrodes the decomposition of the oxides resulted in a deposit of emission material over the entire effective surface of the electrode which surface served to emit electrons and maintain a discharge during operation.

When electrical energy is applied for the operation of the above device, the initial discharge takes place by reason of the initial ionization of the rare gases and by reason of the electron emission of the material at relatively low temperature and voltage. As the bulb heats up the mercury is volatilized and its pressure rises with the result that the discharge contracts and takes the form of an attenuated column between the two electrodes.

It has been found that devices operating with electrodes contructed as above described are subject to certain disadvantages as for example the oxides which, during operation, must withstand high temperature and ionic bombardment, vaporire and sputter, thus shortening the life of the device and causing blackening of the bulb, or the high temperature causes the nickel to melt with detrimental results. v

It is an object of the present invention to provide an electrode surface capable of supplying a copious flow of electrons to provide the necessary 5 low voltage drop for ionizing the gas for starting and for preventing destruction of the electrode surface during operation.

Another object of the invention is to provide an electrode having a low temperature electron 1 source and a high temperature electron source.

A further object of the invention is to provide a compound electrode for a discharge lamp, said electrode having one portion of low electrode drop and another portion electron emissive at high temperature.

A still further object of the invention is to provide an electrode composed of an electron emissive oxide and an electron emissive metal.

Another object of the invention is to provide a 20 discharge device with an electrode which is elec tron emissive at relatively low temperature and in preventing said electrode from being heated to high temperature during the operation of the device.

A further object of the invention is to provide a discharge device with a compound electrode consisting of a body which is electron emissive at relatively low temperature and a second electrode arranged to protect said first electrode against heating to a relatively high temperature during operation of the device.

Other objects and advantages of the invention will be more clearly understood from the following description together with the accompanying drawing in which Fig. 1 is a side elevational view of a discharge device having electrodes constructed in accordance with the present invention;

Fig. 2 is an enlarged sectional view taken on 4 line 11-11 inFig. 1;

Fig. 3 is an enlarged side view of one of the. electrodes shown in Fig. 1;

Fig. 4 is a perspective view of a modified form of the electrode;

Fig. 5 is a perspective view of another modified form of the electrode and Fig. 6 shows the electrode made in the form of a plate with raised portions extending above the thermionically active material.

The outer chamber may be provided with a reentrant stem l4 having leading-in conductors l5 and I6 sealed in the press I! thereof. An exhaust tube I8 may be provided for evacuating the chamber In, if desired. The inner chamber ll may be provided with the electrodes l2 and it of similar construction and a filling of any suitable ionizable medium. The inner chamber may be supported in the outer chamber by means of spring strips ll extending from a metallic collar Ii clamped or tightly fitting the tubular portion I! of the stem.

A conductive support rod 28 sealed through a wall at one end of the chamber II is electrically connected to lead wire It. The electrode i2 is mounted on rod 23 at the end of the chamber and a connector piece 24 electrically connects with a strip ii, the strips being electrically connected by the collar II. The electrode II is mounted at one end of a support rod 2| sealed to the wall at the other end of the chamber II. The other end of the support rod II is electrically connected with a conductor 28 which is electrically connected with the lead wire I.

The spring strips II, which serve to hold the chamber II in spaced relation to the wall of the outer chamber I. also serve to provide a short gap between the electrodes for starting.

A lamp constructed for operation with electrodes made in accordance with the present invention and operable on 110-volt circuit may have the electrodes spaced about 12.5 centimeters apart; that is, to give a discharge length of about 12.5 centimeters. The diameter of the discharge chamber may be 4.3! centimeters and a suitable impedance may be employed to give an operating voltage of 63.5 volts at 6.35 amperes. The chamber may have a filling of argon of about 5 millimeters pressure for low starting and mercury vapor at a pressure of about 200 millimeters or more.

The gaseous filling for the discharge chamber may be mercury as mentioned but other metallic vapors such ascadmium, sodium, or a combination of such vapors may be employed. The rare gas may not always be necessary but it has been found advantageous in starting at low voltage.

With a lamp of the above type it is important to have electrodes which will provide a copious supply of electrons for initiating a discharge. It is, therefore, advantageous to provide electrode surfaces of electron active materials such as barium oxide, strontium oxide or other alkaline earth compounds. These compounds may be decomposed to the oxides and activated by high frequency heating in a manner well known in this art.

An electrode constructed in accordance with the present invention may be considered as a dual or compound electrode and may consist of a plate or disk 21 and a member 20. The disk 21 serves as the supporting body for material capable of giving copious electron emission at relatively low temperature and in practice foraminous disks have been used consisting of nickel wire mesh which serves to hold the electron emissive material.

The material may be applied by spraying with the apertures or interstices arefilled or the disk may be dipped in a bath to eflect the required deposit of electron emissive material. After the disk or other supporting body has been given a deposit of electron material, the material, in

accordance with the present invention. is removed from the surface of the body so that the portions of the mesh material around the apertures are free of said material. It is to be understood that although good results have been obtained by using a metallic mesh to hold the electron emission material, such material may be in the form of a solid body as a disk or rod. When the electron emissive material is in such form, the high temperature electron emissive body may be secured in spaced relation to the material, care said member it is soon dissipated when said member reaches the temperature at which it emits electrons and carries the discharge.

It has been found that when constructing an electrode as for a lamp made in accordance with the above description, which operates at about 400 watts, the bridge piece may be made of 16 mil tungsten wire and the disk may be made of about 60 mesh nickel about one-half inch in diameter. Good results have been had when using four layers of mesh to provide apertures or interstices to receive and hold the electron emissive material. Although tungsten wire is satisfactory it is to be understood that other metals or refractory materials may be used for example thorium, vanadium or molybdenum. The bridge piece may be varied in its dimensions in accordance with the character of material employed.

Heretofore in devices of the character to which the present invention relates, the electrode, either of a wire woven or wound construction, was eniirely covered with the electron emissive material and served to support a discharge during the operation of the device.

In devices of the high intensity metal vapor type the discharge, as above mentioned, instead of being widely diffused throughout the bulb, contracts into what is termed a pencil" form of discharge of high current density. The coated surfaces of the electrodes are subjected to ionic bombardment to the extent that they become heated to an excessively high temperature and the nature of the coating is such that it vaporizes or breaks away and spots or sputters with the result that the portions of the walls adjacent to the electrodes become blackened. Therefore, in addition to the disintegration of the electrodes which shortens the life of the device, the light output is reduced by an obstructing light absorbing coatins.

It is the purpose of the present invention to provide a voltage-activated electrode which will operate to give a low electrode drop and at the same time remove the detrimental'efl'ects above pointed out. This may be accomplished by diverting the discharge away from the coated electrode surface after it has served its purpose in initiating a discharge. The present electrode is,

therefore, provided with means capable of supporting the discharge to the substantial exclusion of the highly emitting material. It has been found possible to accomplish this result by constructing what may be termed a compound or dual function electrode. I

The disk 21 may be permitted to operate in the usual manner as a starting electrode. 0n the discharge side of the disk, however, is mounted the member 28 preferably of tungsten or other metal which becomeseflectively electron emissive at high temperatures and serves as an operating electrode. When the discharge starts the member 28 or secondary electrode is heated by bombardment. It has been found in practice when operating a lamp, as above described, that the said member reaches a temperature of about 2500 degrees centigrade, at which it is sufficiently electron emissive In the electrode construction shown in Figs. 1 to 3 the member 28 is provided with connector arms 3! integral with the said member and electrically connected to the support rod 23. Thus when the' discharge is in full operation, the current between members 28 on opposite electrodes. is bypassed withrespect to the coated disks 21 and the disks are therefore, not subjected to any action detrimental to their useful life. In fact the coating on the disk is kept substantially \intact ready to perform its starting function when necessary.

It is obvious that the present electrode may be made in various forms and the dimensions of its component parts varied since the invention in its broad aspects is to provide a starting electrode and an operating electrode; the starting electrode being emissive at low temperature and protected by the operating electrode which latter is electron emissive at a relatively high temperaelectrode .in which a. coated mesh disk 32 is mounted on a support disk -33 one end 34 extending through the rod and serving as the thermionically active secondary or operating electrode. The end 34 may be of the same material as the rod 33, as for example, nickel in certain types of lamps or'it may consist of a tip of tungsten or other material of high melting point which is sufliciently electron emissive at the opcrating temperature of the device.

If desired, the electrode may be constructed, as shown in Figs. and 6. In Fig. 5 a bridge member 35 is provided with a plurality of turns 36 to give a plurality of points to receive the discharge. In Fig. 6 a disk 31 is made from sheet metal with projections 38 and so formed as to provide cavities, 39. for the deposit of the electron emissive material 40. The projections may be free of such material and serve as the operating electrode to carry the discharge when the device is in full operation.

The member 28 is so arranged with respectto the electron emissive material of the disk that the discharge during operation is spaced from the said material. For the purpose of centering the discharge column in the envelope, the member 28 is formed as above described, with a point or relatively small efiective area disposed on the longitudinal axis of the envelope. With this construction the discharge does not shift from side to side as would occur if the member were divided as for example if one member projected from each side of the disk. As shown in Figs. 5 and 6, the discharge is carried by a plurality of points and although the discharge may move from one point to the other or be divided between all the points, it is held spaced from the electron emissive material and the possibility of the discharge current taking a path through the discharge material is remote.

It has been found that, when operating a discharge lamp provided with electrodes constructed in accordance with the present invention,

during the operation of the device the body of 4 electron emissive material remains comparatively cool and inactive,'whi le the metallic member which becomes electron emissive and sup,- ports the discharge reaches the high temperature mentioned above. In devices as heretofore constructed, the electron emissive material and its supporting structureconstituting an electrode operated-at such a high temperature that vaporization was comparatively rapid and since such electrode was required to give electron emission at low temperature for starting and to also operate at an excessively high temperatureduring operation, the useful life of the device was short compared to the present device in which the starting electrode is protected and only functions for its intended purpose.

It will be'evident that a device provided with electrodes constructed in accordance with the present invention will not only operate at the required starting potential but that the starting means will be conserved. The device, therefore, which is provided with a more durable and lastingelectrode for actual operation will give longor life and by reason of the removal of theabove mentioned defects, will be more practical and eflicient.

Although a preferred embodiment of the invention is shown and described herein, it is to be understood that modifications may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A discharge device comprising a sealed envelope, a conductor sealed through a wall of said envelope, a plate mounted at one end of said conductor and within said envelope, a deposit of electron emissive material on portions of said plate, other portions of said plate being without a deposit of said material, and a member electron emissive at relatively high temperature extending from said plate and disposed in the discharge path.

2. A discharge device comprising a sealed en velope, a conductor sealed through a wall of said envelope, a plate mounted at one end of said conductor and within said envelope, a deposit of electron emissive material on portions of said plate, other portions of said plate being without a deposit of said material, a member extending across said plate and spaced therefrom, and arms electrically connecting said member to said conductor.

3. An electrode for a discharge device comprising a mesh disk, a conductive lead wire extending.

from one side of said disk, a coating of electron emissive material-on said disk, and a metallic bridge member extending across the other side of said disk.

4. An electrode for a discharge device comprisjing a mesh d sk, a conductive support member extending from'one side of said disk, a deposit of electron emissive material disposed between the wires of said mesh and a metallic bridge member on the other side of said disk and extending outwardly from said emissive material.

6. A voltage-activated electrode fora discharge device comprising a body having apertures to receive electron emissive material, the surrounding edges adjacent to the perimeters of said apertures being free from said material, and a metallic member electron emissive at high temperature extending above the surface of said material and disposed in the path of discharge of said electron emissive material. I

7. A voltage-activated electrode for a discharge device comprising a body having apertures to receive' electron emissive material, the surrounding edges adjacent to the perimeters of said apertures being free from said material, and a metallic member spaced from said body and disposed in the discharge path to receive the discharge and serve as an operating electrode, said member being electrically connected with said body.

8. A voltage-activated electrode for a discharge device comprising a metallic member, a conductive lead wire extending from one side of said member, a deposit of electron emissive material on said member, another member on the other side of said metallic member electrically connected with said lead wire and free from said emissive material, said last mentioned member being positioned to serve as an operating electrode to the substantial exclusion of the member having the deposit of electron emissive material..

9. Adischarge device comprising a sealed envelope, a mesh disk support for electron emission material, a conductor member sealed through the wall of said envelope and connected to one side of said support, a deposit of electron emissive material on portions of the other side of said support,

other portions of said support being free of said electron emissive material, and a metallic member extending from said other side of said support and electrically connected with said conduc-- material on portions of the surface of the other side of said support, other portions of said support being free of said electron emissive material, and a metallic member spaced from said surface and connected with said conductor member, in order to serve as an operating electrode taking the main discharge.

11. A discharge device comprising a sealed enveiope, a conductor sealed through a wall of said envelope, a plate having one side thereof secured to one end of said conductor and within said envelope, a deposit of electron emissive material on portions of the other side of said plate, other portions of said plate being without a deposit of said material, a metallic member extending from said other side of said plate, and means for electrically connecting said member with said conductor.

12. A discharge device comprising a sealed envelope, a conductor sealed through a wall of said envelope, a voltage-activated starting electrode having one side thereof secured to one end of said conductor and within said envelope, a deposit of electron emissive material onsaid electrode, an operating electrode extending above said material and across said starting electrode and spaced aliases therefrom, and means for electrically connecting said operating electrode with said conductor.

13. A ,high intensity vapor lamp comprising a sealed envelope, an ionizable medium in said-envelope, a conductor sealed through the wall of. said envelope, a cold duplex electrode connected to said conductor, said electrode including a mesh support holding material electron emissive at a relatively low temperature and a given voltage,

sealed bulb, an ionizable vapor within said bulb.

' a conductor sealed through the wall at each end of said bulb, a cold electrode connected with each conductor, each of said electrodes having a mesh portion coated with an electron emissive material to ionize said vapor when said electrodes are subjected to a difierence of potential, each of said electrodes having an extended portion positioned in the discharge path, said extended portions being electron emissive when heated by the discharge and so positioned with respect to said coated portions that the discharge continues between said extended portions subs'tantially to the exclusion of said coated portions.

15. A high intensity vapor lamp comprising a sealed tubular bulb, an ionizable metallic vapor within said bulb, a small quantity of more readily ionizable gas in said bulb. a conductor sealed through the wall at each end of said bulb, a cold electrode connected with each conductor and disposed in close proximity to the ends of said bulb, each of said electrodes having a mesh portion coated with a material electron emissive at a given voltage when cold to ionize said gas when said electrodes are subjected to a difference of potential, each of said electrodes having a portion extending from said emissive portion and disposed inthe path of discharge, said'extended portion being electron emissive when heated by the discharge and so positioned with respect to its coated portion that the discharge is carried by said extended portions to the substantial exclusion of said emissive material when the lamp is in operation.

' 16. A compound electrode having a non-metallic portion electronemissive when subjected to agiven voltage when cold and held on a metallic mesh portion, and another metallic portion electron emissive at a higher voltage when cold and so positioned with respect to said first portion as to be heated during the operation of said first portion, said high voltage portion being so positioned with respect to said first mentioned portion as to become electron emissive for operation to the substantial exclusion of said first portion. as

JOHN W. MARDEN. GEORGE MEISTER.

Images