US2731581A - Electrode for gaseous discharge lamps - Google Patents

Description

Jan. 17, 1956 H. E. KREFFT ELECTRODE FOR GASEOUS DISCHARGE LAMPS Filed Dec. 18 1950 INVENTOR. f/ mm Foz/A/w/(REFF M MUM z ATTORNEY United States Patent ELECTRODE FOR GASEOUS DISCHARGE LAMPS Hermann Eduard Kreift, Buenos Aire's, Argentina Application December 18, 1950, SerialN 201,331

4 Claims. (Cl. 313-343) The present invention relates to electrodes for electrical gas discharge lamps and more particularly to activated electrodes for high pressureand super high pressure lamps.

The terms high pressure lamp and super high pressure lamp in accordance with the present invention refer to electrical discharge lamps which operateunder pressures of from about one atmosphere and above about ten atmospheres respectively, and which contain, under operating conditions, a metal vapor, e. g. mercury vapor, to which is added an inert gas, or which may contain a mixture of metal vapors or a mixture of metal vapors and rare gases, e. g. krypton and xenon.

In such lamps, as it is known, the discharge forms an arc of high temperature which, owing to the high current density, is limited to a very small area of the electrode. Consequently, the electrodes are exposed locally to very high temperatures which cause evaporation of electrode material. Through this process, electrode life is limited, and the bulb of the lamp is blackened. Electrodes for high pressure or super high pressure lamps are, therefore, mostly made of tungsten, and they are provided with a certain amount of activating materials through which their temperature is lowered. These activating materials are also required in order to improve starting of the discharge. Such activating materials are the metals barium, calcium, strontium, thorium, or the oxides thereof and the dioxides of thorium and zirconium. However, these activating materials, although they lower the temperature of the electrodes, may produce considerable blackening of the bulb as they evaporate rather easily. It is, therefore, very important to limit their quantity, and to add them to the electrode in such a way that they produce sufiicient activation without being excessively exposed to the action of the discharge are.

It is, therefore, one object of my invention to provide an activated electrode for high pressure and super high pressure lamps which does not blacken' the wall' of the discharge vessel; another object is to provide an electrode which starts easily and without sputtering; still another object is an electrode of the coiled coil type; a further object is a novel electrode of the storage type; another object is an electrode of the self heating type. Other objects and advantages of this invention will become apparent from the description hereinafter following and the drawings forming part hereof in which:

Figure 1 is a transverse, partly sectional view of a coil, provided with a core, according to the invention;

Figure 2 is a longitudinal sectional view of a coil, taken on the line 22 of Figure 1 illustrating the structure of the core;

Figure 3 is another transverse, partly sectional view of a coil according to Figure 1, illustrating the positions of a gas absorbing wire and of the activating material;

Figure 4 illustrates a modification of the arrangement of the core wires;

Figure 5 is a diagrammatic, partly sectional view of a coiled coil electrode according to the present invention;

2,731,581 Patented Jan. 17, 1956 Figure 6 is another schematic representation of a coiled coil electrode according to the present invention.

According to the present invention an activated solid incandescent electrode of the storage type is formed by a tungsten wire coilcontaining, in its interior, a core composed of a plurality of metallic wires which are preferably twisted, and thus form a rigid supporting structure for the coil which, inthe spaces existing between the core wires, and between the core and the coil, also contains the activating materials. This coil is preferably coiled by which means an electrode of the coiled coil type is produced which possesses a mechanically strong structure, and which is provided, in a particularly convenient way, with a storage of activating materials. Owing to this structure, this novelelectrode isadvantageously used in high pressure, and super high pressure lamps which are started without pre-heating of the electrodes, but it can be used also in other .gaseous discharge lamps which are started with cold electrodes.

As shown in Figure 1,- which is a transverse partly sectional view of a coil, the core contained in its interior consists of four metallic wires 1', 2, 3, and 4,: on which the coil 5 is firmly connected. The interior of the coil is not entirely occupied by the core wires which form, with the coil, and between themselves, channels 6, and 7. In Figure 2' which is a longitudinal sectional view of the same coil, takenon the line 2-2 of Figure l, the core wires 2, and 4-, and the central channel 7, and transverse sections of the coil 5-, are shown.

Preferably, the coil 5 consists of a tungsten wire, while the core is composed of tungsten, molybdenum, tantalum, or thorium,- or of a combination of wires consisting of these metals. A preferred combination of the core consists of three tungsten wires and one tantalum or thorium wire. The invention, however, is not limited to the use of four core wires which quantity is indicated by way of example only. As shown in Figure 3, a centrally located fifth core wire 9 may be added to the structure already described. This central wire may be made either of tantalum or thorium, while the others, 1, 2, 3,. and 4, are tungsten wires, or at leastpartly consist of tungsten, and partly of the other metals mentioned. The spaces which are formed between the core wires and the coil, are filled with activating materials 8 composed, for example, of

. the oxides of barium, calcium, strontium, or thorium, or

of zirconium-dioxide, or of mixtures of these materials the particle size of which should be chosen as small as possible.

This electrode structure olfers many advantages as it combines several properties required by high pressure lamps, or other lamps which start with cold electrodes. In the first place,the coilprovided with a core is an element with considerable mechanical strength which can be utilized for the construction of other electrode structures; furthermore, the pockets or channels which exist in the interior of the coil, are excellent places for the activating materials which must be protected from the direct action of the discharge arc, but should be well distributed all over the electrode, and close to its surface; another advantage is the use of gas absorbing or activating metals as a component of the core. These advantages would not exist if a solid core were used instead of a plurality of core wires which form a flexible core.

Since a core, composed according to the present invention, is flexible, the coil, or primary coil, which I have described may be coiled up to form a secondary coil. To this end, however, it is convenient to twist the core wires, as shown in Figure 4 which illustrates a coil assembly composed of four twisted core wires 1, 2, 3, and 4, and a coil 5. According to Figure 5, an electrode embodying my invention consists of a secondary coil 10 which forms a hollow cylindrical body, supported by a coaxial wire or rod 11 which fits accurately into the interior of the coil 10. This secondary coil is composed oxides of barium, calcium, strontium, or thorium, or of zirconium dioxide, or of mixtures of these materials. The wire or rod 11 consists of tungsten, tantalum or molybdenum, and it may form simultaneously the inner lead of the lead wire contained in the seals of'the lamp. However, this electrode supporting wire 11 must not consist of a single wire or rod, as shown in Figure 5, but it may be also composed of a plurality of wires forming a secondary core which has the same structure as the primary core previously described. According to another embodiment of my invention, illustrated by Figure 6, the coiled coil electrode structure is self supporting, and does not contain a coaxial supporting wire or secondary core. The electrode shown in Figure 6, is composed of a secondary coil which is formed by a primary coil assembly consisting of twisted primary core wires 1, 2, 3, and 4, a fifth axial core Wire 9, and a primary tungsten coil 5. As already described, the free spaces existing between the core wires, and between these wires and the coil 5, are filled out with activating materials.

The degree of activation of an electrode according to the present invention naturally depends on the choice and proportion of the activating materials already mentioned, and on the spaces existing between the turns of the primary coil. Therefore, the pitch which is given this coil during manufacture, which pitch depends on the nature and composition of the activating materials, is an important means of control of electrode performance. Electrode life also depends on the quantity of activating materials contained in the electrode which is determined by the volume of the channels existing in the interior of the primary coil assembly. Obviously, a desired volume is obtained by properly choosing size and number of the primary core wires, and the total length of the primary coil assembly.

As it is known, electrode performance and lamp life, particularly in super high pressure lamps, are considerably improved by the use of gas absorbing materials like tantalum, zirconium, and thorium. According to the present invention, these materials form part of the primary or secondarycore of the electrode where they are exposed, under operating conditions, to temperatures which lie within a convenient range for optimum gas absorption.

During manufacture of the electrode, the primary coil is produced in a continuous process which is carried out by a customary coiling machine utilizing the primary core, which is composed of a plurality of core wires, as mandrel wire. After annealing, the second coil is produced on steel mandrel pins, or on the wire or rod which is used as secondary core, and given another heat treatment at high annealing temperatures, by which means it obtains a definite shape. Finally, the activating materials are introduced into the interior of the primary coil, which is done in the usual Way by dipping the electrode into a suspension of these materials prepared with a suitable solvent and binder, like amyl-acetate and nitrocellulose.

What I claim is:

1. An activated electrode for high pressure and super high pressure gaseous electric discharge'devices comprising a core composed of a plurality of refractory metal wires, which are twisted with respect to the axis of said core, a tungsten wire coil helically wound about said core and in contact therewith throughout its length, the pitch of the coil being very low and constant throughout the length thereof, and the individual convolutions of said coil being closely adjacent one another whereby said coil forms a protecting wall about'said core and whereby small pockets are formed between the coil and the core wires and among the core wires themselves throughout the length thereof, saidelectrode being in the form ofa coiled coil, an activating material selected from the group consisting of barium, calcium, strontium, thorium, and zirconium, deposited in said pockets to form a continuous tortuous path of activated material and wherein said coil serves to shield, said core wires and activating materials against rapid deterioration by the high pressure discharge.

2. The electrode of claim 1, wherein said core is comprised of a plurality of tungsten wires.

3. The electrode of claim 1, wherein said core is com- 7 prised of a plurality of tungsten wires and at least one wire selected from the group consisting of thorium and tantalum.

4. The electrode of claim 1, including a supporting metal wire element located within said coiled coil and about which said coiled coil is wound, said supporting element being taken from the group consisting of tungsten,

tantalum, and molybdenum.

I References Cited in the file of vthis patent UNITED STATES PATENTS

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