US1894946A - Method for activating glowing cathodes or the like - Google Patents

Description

Patented Jan. 24, 1933 UNITED STATES PATENT OFFICE WERNER ESPE, OI IBERLIN-CHARLOTT-ENBUBG, GERMANY, ASSIGNOB TO SIEMENS 86 HALSKE .AKTIENGESELLSCHAFT, OF SIEMENSSTADT NEAR BERLIN, GERMANY, A

GERMAN COMPANY METHOD FOR Ao'rIvA'rINe GLOWING CATHODES on THE LIKE No Drawing. Application filed August 14, 1930, Serial No. 475,400, and in Germany August 19, 1929.

The invention relates to a method for activating glowing cathodes or the like by means of metals of the alkaline earth group which are formed from chemical compounds of these metals in the tube.

The oxide paste cathode which, as well known, is produced from a paste consisting of alkaline earth oxides applied to the core has the advantage of possessing an extraordinarily long life (5000 hours and more) but shows however a relatively low activity (40 milliampere per watt). This is due to the fact that during the formation process a thin layer of pure alkaline earth metal is produced on the surface of the cathode by electrolysis which displaces itself automatically from the oxide base in the course of operation. Recently one has gone over to distilling over the earth alkaline metal in metallic form on the core from an electrode whereby a complete coating of the cathode surface with alkaline earth metal and a very high activity (about 120 milliampere per watt) is obtained. In view of the fact however that the layers distilled on are very thin, the life of a cathode of this kind is considerably shorter than that of the squirted or paste cathode (about 800 to 1000 hours).

An object of this invention is the making of glowing cathodes or the like which have both the high activity of distillation cathodes and the long life of squirted or paste cathodes.

In accordance with the invention one of the alkaline earth metals, is in the well known manner, applied to the oxide paste cathode, said metal being obtained froma compound which only decomposes above the maximum temperature occurring in the tube during the formation process of the oxide paste cathode.

It was observed however that an unformed squirted cathode could not be coated with an alkaline earth metal, as on subsequent formation so much gas escaped from the oathode that the alkaline earth metal distilled on was oxidized again and its effect was thereby nullified. If, however, the oxide cathode is formed first, a high heating of the cathode and a high anode potential are necessary so that the other electrode on which the alkaline earth metal source is situated glows highly Before, however, completely terminating the formation this source must not be closed. F or this reason it is not possi ble to use, for instance, azides of alkaline earth metals whichdeoompose at-approximately 180 centigrade.

For appropriate reasons a mixture is used, 1

which consists of a compound of a metal of the alkaline earth group, for instance, barium oxide and aluminium oran equivalent metal, for instance, magnesium and which reacts only at temperatures over 1000 whereby metallic barium forms.

For forming a glowing cathode in accordance with the invention one may proceed in the following manner.

After evacuation, the squirted cathode ishighly heated and any available carbonate decomposed into the oxide. The forming is thereupon effected with anode potential in that gradually increasing anode potentials are one after the other applied to the grid or grids and the anode, whereby simultaneously with the formation of the cathode both electrodes and the reaction mixture are raised to temperatures up to 1000 centigradeand can be well de-gassed. If the emission of the cathode has attained the desired degree the formation is terminated. After cooling of the tube has been effected, the mixture applied to the anode or situated in a special container is ignited by heating for a short time at 1100 to 1200 centi grade, in any well known manner, as by highfrequency light or heat rays which are concentrated through mirrors or lenses, whereupon the reaction proceeds further automatically, until all the 700 C. The gradually evaporated alkaline earth metal is ionized by the electrons of the oxide cathode and the positive alkaline earth metal ions fly .directively to the negative cathode and accumulate thereon to a greater extent than by ordinary temperature distillation Where the major portion of the alkaline earth metal would go to the cold glass *wall'ofthetubm; I .r The method in: accordance with the inven'@ tion oflers this advantage that the reaction temperature is substantially higher than the temperature employed for de-gassing the metal parts and forming the cathodes so that thegasescohtained'in the metal parts of the electrodes and resulting on the formation of theioxide'paste cathode are removed by the long before the metal formed the evacuating said enclosing vessel, heating said cathode to completely decompose said first compound to form the oxide of said metal, simultaneously applying a potential between said cathodeoand said electrode whereby said electrodeand said mixture are out-gassed by electron bombardment, removing the liberated gases from said vessel, removing said potent'ial, heating-f saidatmixture to; liberate-the free alkaline: earth: .therefnom, applying a negative potentialtoisaid: cathode, and 7 simultaneously heating said electrode to complletely transferisaid metal tosaid oxide cathiIn'witness whereof, I hereunto subscribe my name, this, 5th day of August, 1930. V

" p 1' WERNER ESPE.

reaction mixture. is over-distilled to thed formed cathode;

What is claimed is: '1'. In the manufacture of electron dischargefde vices comprising a cathode having a coating. of-barium carbonate, an electrode adjacent said cathode, and'a mixture includ-.

ing barium oxide, and a reducing agent upon said electrode, the. method which comprises heating, said carbonate to form barium oxde, applyinga potential between saidcathode I and said eleetrodewhereby said electrode and said mixture are out-gassed by electron i bombardment, producing a reaction in said mixture to form metallic barium, applying a y a barium on said cathode.

V negative potentialto said cathode and'simultaneously heating said electrode to 1on- ,l izefsaidbarium, anddepositmg said lOlllZed 21 In the manufacture of electrode disi- I charge devlcescomprlsing a cathode having a U I coating of decomposable compoundsv of'alkaline earth metal, an electrode adjacent said 'cathOdeQand a reactionmixture having a reaction temperature hi ghe'r than that atwhi ch said" compound is decomposable carried by said electrode, the methodfwhich comprises decomposing saidcompound to form the oxline earth metal'thereon, lsaid compound 'beingydeeomposableto form the oxide offsaid metalhan electrode adjacent said cathode,

andia mixture including a compound of an alkaline earthmetalupon saidelectrode, said mixture havinga reaction temperature high- I 1 er than that 1 at which said first'compoundis decomposable, the method Whichcomprises