US1733809A - Means for gettering electrical discharge devices - Google Patents

Description

Oct; 29, 1929. 1,733,809

MEANS FOR GETTERING ELECTRICAL DISQHARG'E DEYIGHS a A; LEDEYRER Filed June 26, 1928 [MENTOR BY EJLLEIDEBEE ATTORNEY Patented Oct. 29, 1929- UNITED STATES PATENT orrlcr.

1' ANTON WEBER, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAM]? COMPANY, A CORPORATION OF PENNSYLVANIA MEANS FOR GETTERING ELECTRICAL DISCHARGE DEVICES Application filed June 26,

This invention relates to electrical dislamps and rectifiers, to create a metallic vapor in the device, or for a number of other purposes.

The getters ordinarily employed in such devices are magnesium or other alkaline earth metal, aluminum, misch metal or one or more of the alkali metals. It has been the usual practice in the gettering of such devices to introduce a quantity of one of these getter materials into the device by application thereof to one of the electrodes or to a metallic carrier suitably supported in the device so as to be heated by high frequency induction currents.

This process has proven successful in many types of devices, the operation of which is not extremely sensitive to small quantifies of gases liberated from the electrodes or the getter carrier at the time the carrier is heated to vaporize the material.

In certain of devices, however, dilficulty has been experienced due to the gas liberated from the metal parts of'the devices upon vaporization of the getter material. For instance, in the manufacture of electron discharge devices employing thermionically active cathodes, the thermal emission of which is imparted thereto by the presence of an alkali metal, such as caesium or rubidium, difiiculty has been experienced due to loss of emission caused by liberation of gas from the electrodes or from the getter carrier during activation of the getter. It is in connection with devices of this nature that the invention has been found particular- 1928. Serial No. 288,347.

1y advantageous, although it applies to the gettering of other types of devices.

' ()ne of the objects of the present invention is, therefore, to produce a means for introducing getter material into evacuated devices and vaporizing the same therein without the liberation of appreciable quantities of deleterious gases or vapors.

Another object is to provide a means for gettering electrical discharge devices in which the amount of metal necessarily heatcd during vaporization of the getter will be small.

Another object is to produce a novel means of supporting the getter material Within the device and allowing thesameto be heated by high frequency inductipn currents.

Other objects and advantages will hereinafter appear.

The invention will be described with particular reference to the introduction of alkali metals, such as caesium, intovan electron discharge device employing a caesiated cathode. ther embodiments of the invention will be apparent therefrom.

In the, manufacture of caesiated cathode devices it is a practice to preliminarily de- -'gasify electrodes 'prior to introduction of these parts into the envelope and after these metal electrodes have been scaled into the envelope,-to heat them to a high temperature by high frequency induction currents, to further degasify the same. The cathode is then heated to a high temperaturein the- After the oxidation of the cathode the caesium is liberated in the envelope, preferably by' heating a compound of caesiumsuch gases may exert a reducing action members for securing the several electrodes upon the very sensitive monotomic oxygen layer formed on the cathode.

accordance with the present invention, the getter material is supported in the envelope out of contact with the electrodes and in such position that it may be heatedby positioning the-primary coil of a. high frequency induction heating apparatus e.x-'

ternal to the envelope and with its axis so arranged that the electrodes of the tube do not form any closed loops of appreciable 512 within the active field of the induction CO1 Preferably, the getter material, which in the case of the caesiated cathode type of tube is caesium, is prepared in the form of a compound of the alkali metal mixed with a reducing agent in powdered form and pressed into pellets of convenient size. The preferred caesium compounds are non-hydroscopic materials, such as caesium dichromate or caesium permanganate mixed with a reducing agent, as silicon. Such pellets upon being heated in the device, liberate the alkali metal by the reducing action of the silicon upon the caesium compounds. The pellets may be supported by a metallic bond or ribbon partially encircling the same-and in good thermal contact therewith, such ribbon forming a portion of a closed electrical loop capable of being heated by high frequency induction.

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In order that the invention may be more fully. understood, reference will be had to the accompanying drawing, in which Figure 1 shows a thermionic tubeof the caesiated cathode type embodying the present invention;

Figure 2 is a schematic view showing. the relative positioning of the electrodes and getter carrier in position to be heated by high frequency induction currents; and

Fig. 3 is a perspective view of the getter .support on an enlarged scale.

'The discharge device shown in the figure comprises a bulb 10 having a flare tube 11 provided with the usual press 12. Extending from the press are a plurality of supporting in position. The electrode assembly includes a filament 13, a control electrode or grid 14 and a plate electrode or anode 15. The anode 15 is composed of two plate members 16 and 17 disposed upon opposite sides of the control electrode 14. I

' .The electrodes are secured to the support wires 18 and constitute the mount. The mount is sealed into the bulb at the junction 19 and the bulb may be exhausted through an appropriate exhaust tube 20 which'extends from the interior of the flare tube.

The filament .13 is'supported at its upper;

the loop, a small metallic strip 30 and 25 which ext-end upwardly from the press 12 and are welded to the side members 26 of the grid.

In order to provide a supply of alkali metal in the device, a pellet 27, which may be composed of a compound of the alkali metal and reducing agent, is supported by a loop 28 intermediate the ends of a thin metallic strip or ribbon 29 welded at each end to the grid support 25. The loop 28 is formed of a refractory material, such as molybdenum, and is of sufficient resiliency to tightlygrip the peripheral edge of the getter pellet 27 so as to form a good thermal contact therewith. In order to prevent the getterpellet from becoming detached from may be welded'to the loop 28 and extended across the face of the pellet.

The ribbon 29 forms with the grid support 25 a closed electrical loop, which is arranged in a plane at right angles to the plane of the plate 15 so that current may be induced in this loop comprising the ribbon 29 by dispos ing a high frequency induction coil 31 with its axis horizontal and. normal to the planeof the loop in the position A shown-in Figheated to the reaction temperature without.

inducing heating currents in the plate electrode 16 or the grid electrode 14. Prior to of the getter material, however,

the heating the plate electrode 15 may be heated to free it of gases by disposing the high'frequency coil with its axis at right angles to the plane of the plate in position B. In this position the high frequency coil will exert no heating action on the getter carrier 28.: The grid or control electrode 14 in this particular type of device, is composed of two sets of slats or lattice members 32 and 33 disposed on opposite sides of the cathode andthese lattice members form closed loops arranged in a horizontal plane so that the control electrode may be heated by high frequency induction current by disposing the high frequency induction coil about the envelope with its axis vertical in position C; With the high he I quency. heating coil in this position the grid electrode may be'heat-ed to d-egasify the same without introducing any heating currents in the getter carrier 28. The paths of the induced currents in the anode, control electrode and getter carrier are indicated bythe arrow in Figure 2. Each of these elements provides a closed electric circuit for the high frequency induction currents, each of said circuits being confined to a plane at right ioo angles to'the plane of each '(if the other circuits.

It will be evident from the above that both the grid electrode and the plate electrode may be separately heated to degasify the same prior to the oxidation of the filament Without exerting any heating effect upon the getter capsule 28 and after such degasification and subsequent oxidation of the cathode, the getter may be heated by high frequency induction currents to liberate the alkali metal without setting up heating currents in any of the metal parts of the devices except the getter carrier 28.

The loop formed by the getter carrier and the grid support is relatively large and, therefore, enables good coupling to be obtained with the high frequency induction current so that efficient heating of the getter is obtainable. The getter carrier is formed of very thin material, as for instance, 25 mil molybdenum ribbon, so that it becomes highly heated with a current flow which is not sufficient- 1y large to heat the grid support 25 appreciably.

It will be understood, of course, that numerous modifications. may be made in the means for supporting and heating getter capsules described herein and I do not desire to be limited to the specific details shown except in accordance with the appended claims.

What is claimed is:

1. A support for a getter material in an electrical discharge device, comprising a metallic member forming a closed electrical circuit adapted to, have high frequency cur-. rents induced therein and including a resilient portion of thin refractory metal encircling the getter material in close thermal contact therewith, said thin refractory metal having a smaller cross sectional area than the remainder of the closed electrical circuit.

.2. A support for a-getter material, comprising a metallic member formin a closed electrical loop adapted to have high frequency currents induced therein and including a portion'of materially smaller cross section than the remainder'and disposed in close thermal contact with the getter material to heat the same by said induced currents.

3. A support for a getter materialcomprising a strip of thin refractory metal having intermediate its ends a looped portion in which the getter material is positioned.

4. An electron discharge device comprising an electrode assembly and a getter support associated with said electrode assembly, said getter support including a thin metallic band disposed out of contact with the electrodes and having a looped portion intermediate its ends in which the is positioned. I

5. An electrical discharge device'comprising an electrode, a support therefor, an

getter material elongated metallic member secured at'each end to said support and forming therewith aclosed electrical circuit, and a getter material carried by said elongated member.

6. An electrical discharge device comprising an envelope having a'ieentrant stem, a wire sealed to the stem and extending into said envelope, a metallic ribbon of smaller cross section than said wire secured at each end to spaced points on said wire and a getter material supported intermediate the ends of said ribbon. 1

7. An electrical discharge device comprising a cathode, an anode, a control electrode and a getter material, said anode being disposed so as to be heated by a high frequency induction coil disposed in-a definite relationship to the device, said control electrode being constructed and disposed sov as to be heated by a high frequency induction coil disposed at substantially right angles to the position required for heating the anode, and

disposed so as to be heated by a high frequency coil disposed at substantially right a metallic support for said getter material I angles, to the positions required for heating both the anode and control electrode.

8. An electrical discharge device comprising at least two electrodes arranged so that each electrode is heated by a high frequency induction coil disposed in a different angular position with respect to the device, and a metallic support for a getter material disposed with relation to said electrode so as to be heated by a high frequency induction coil disposed in a difierent angle position with respect to the device.

In testimony whereof, I have hereunto subscribed my name this 25th day of June, 1928.

' ERNEST ANTON LEDERER.

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