US1946603A - Cathode for electrical discharge devices - Google Patents

Description

Feb. 13, 1934. c, J. R. H. voN wl-:DEL ,1,945,603

Y CATHODE FOR ELECTRICAL DISCHARGE DEVICES "gmx Filed May 9, 1929 Patented Feb.` 13, 1934 UNITED STATES PATENT i OFFICE CATHODE FOR ELECTRICAL DISCHARGE DEVICES Carl J. `R. H. von Wedel, Berlin, Germany, as-

signor to Electrons, Inc., a` corporation of Delaware Application May 9, 1929. Serial No. 361,652 19 Claims. (Cl. Z50-27.5)

substance is used, and moreliparticularly to fla- Figure 1 is a perspective view of a segment of mentary or directly heated cathjdes for electric my improved CathOde,

5 discharge tubes. The features of the invention Figures 2, 3 and 4 illustrate the manner in 60 oiier particular advantages connection with Which the 0016 0f my impIOVed CahOde iS Conlarge current and high potential discharge de- Structed, and vices, as in heavy duty rectifier tubes, but may Figure 5 illustrates the action of my improved be applied with advantage to tubesehaving those cathode flo-operating with an anode in a recti- 10 characteristics usual for radio receiving and like fier tube. 65 amplifying systems. Referring to Figure 1, the cathode comprises since the beneficial results of my invention are a core 1 having a helical rib 2 between the spaced better emphasized in Connection with a, heavy turns of which is embedded a filling 3 of an elecduty gas-filled rectiiier tube I hereinafter detrOn @missive 'COmDound preferably 011e 0f the Heretofore in the prolonged use of discharge the favorable influence of the core materials on 75 In addition to the causes pointed out in said mi Zirc0nium`Barium z irconate; 85 patent for the waning of space current with use 9T Wlth these c ompounds smgly or as mlXPues I have found that when operating with high cur interchanged wlthlthe metals or those emlsslve rents and high potentials the emissive coatings ggugsag; glllzlfthtebrlllyalmlarsngtlrsl rg; undergo severe physlcal disturbances even to the those emissive double metal compounds in which 90 emissive coating from its support; and also that talle elerfent oxx'genpas ben replaced .by sul arcing effects may occur and be most destructive p mi m regen uorme Car on or arsemo' to the coating and its support.

It is the object of the present invention to materially eliminate any loosening of the coating 4 pounds less acid than titanic acid, and another 100 quick destruction of the cathode due to increased core 4 of sumcient Size to carry the heating cur 105 come electromcally inert so that further destrucwith a surface 5 of another metal such as nickel tion at the point will not occur. by any of the usual electro-plating or other Further objects w1l1 appear as the description processes. Upon this coated core, I wind a helix 110 having preferably a pitch equal to one and onehalf times the diameter of the wire 6 of the same or a similar metal, the resultant product being shown in Figure 3. I then treat the structure of 5 Figure 3 in an electrolytic or other bath containing one of the above mentioned metals, such as nickel, so that there is produced a. coating or plating over the entire structure, with the result that the turns of the helix 6 are metallically and i conductively connected to the surface 5 as shown at 'l in Figure 4. (See Figs. 1 and 5.) In this manner I have produced a helical dove-ta groove about the core in which I place the filling of emissive compound 3, for example, barium l aluminate, filling the dove-tail groove substantially to the outer diameter of the helix 6.

When this type of cathode is used with a closely associated anode 8 having high potential, the emissive coating being securely held within the "dove-tail groove of the cathode, there is little possibility of the coating being loosened and torn from the core.

This type of cathode has particular advantages in gas lled rectifier tubes. The electron cloud around the cathode neutralizes the ions of the discharge to prevent ionic bombardment, and the neutralizing is most effective because such a cathode arrangement has a very large effective emitting surface, enhanced by the fact that the emissive coating continuously creeps over the surface of the helix 6 maintaining an undulated eiective emissive surface.

Further, should an arc occur between the anode and the cathode, Fig. 5, such arcing will 85 occur between the helix 6 and the anode 8 with the result for instance that, a portion of the helix 6 will be burned away as illustrated at 9. Even though the cross-section of the cathode proper at this point is reduced by this action, it is still greater than the cross-section of the core proper at a point between the turns of the helix 6, so that no hot-spot is produced on the cathode by reason of reduction of current carrying cross-sectional area. The creeping characteristic of the emissive coating during operation soon covers over the injured spot so that the original characteristic emission from this portion ensues. Should the arcing continue for a sufficient length of time that a portion of the cathode is pitted as shown at 10 sufciently deep to penetrate to the core 4, the ionic bombardment of the gas upon the exposed core metal, together with the creeping of the emissive coating thereover, will form a non-emitting coating at 11 for 5i the reasons set forth in the aforementioned patent, so that at the temperature at which such a cathode is designed to operate, usually about 800 C., emission at this point stops even though this point is relatively hotter than the rest of the cathode. In this manner the destruction of the cathode at this point is stopped. Since in general these spots, ii occurring, are of small area d t the rest oi the cathode the reas compare 0 maining emissive surface will easily pfovle necessary emission iordco'isneugsgacem. thihlitl): Iviltigvteusibecherein a Specific @pist-1 sive cathode structure in which I have mme the metals d prefer to tungsten and nickel, an

bstances cereon as electron emissive su tlntilnpounds such as compounds of the high 1y electropositive metals in the form of zincatels, materia. s

s .and zirconiates or other s:iiflz'laima;@the iiuorides of these metals and those previously mentioned, and specically barium aluminate, it is to be understood that other metals and other emissive compounds, such as those proposed by Wehnelt, or barium oxide, strontium oxide and calcium oxide, or mixtures thereof, may be used without departing from the spirit of my invention as defined in the claims appended hereto. f

Having thus described my invention what I claim is:

1. In a cathode structure, the combination of a cylindrical core, a helix of wire wound upon said core, a metallic junction between the wire and said core whereby said wire is incorporated integrally upon said core, and an electron emissive substance between the turns of said helix.

2. In a cathode structure, the combination of a core of highly refractory metal, a coating of a metal upon said core, capable by chemical conversion of forming an amphoteric compound less acid than titanic acid, a helical rib of said metal integral with said coating and surrounding said core, and an electron emissive material between the tunis of said helical rib.

3. In a cathode structure, the combination of a core of highly refractory metal, a coating of nickel upon said core, and a helical rib of nickel metallically joined to said coating.

4. In a cathode structure, the combination of a core of highly refractory metal, a coating of nickel upon said core, and a nickel wire helically wound over said coating and metallically integral therewith, said nickel wire forming a helical dove-tail groove around said core.

5. In a cathode structure, the combination of a core of tungsten, a plating of nickel upon said core, a nickel wire helically wound upon said core and metallically joined to said plating, and an electron emissive compound between the turns of said helix.

`6. In a cathode structure, the combination of a core of highly refractory metal, a nickel Wire helically woundupon said core and metallically integral therewith, an electron emissive material including barium nickelate between the turns of said helix.

7. The process of production of a cathode structure which comprises plating a core of tungsten with metallic nickel, Winding a helix of nickel wire upon said plating, immersing said core and said helix in a bath containing nickel, by electrolysis metallically joining said helix to said plating and filling in the space between the turns or said helix with an electron emissive material which reacts with said nickel to form barium nickelate.

8. In a cathode structure, the combination of a refractory metal core, a coating of metal upon said core which by chemical conversion forms an amphoteric compound less acid than titanic acid, and a helical rib of a similar metal upon said 135 coating and metallically joined thereto.

9. In a cathode structure, the combination of a core of refractory metal,i a coat'iig o said core capable of orming y 0 e me@ a maar trattasse 14 eica ri a. or highly electroposltwemetal ailleenetal comby chemical -conversion atalcfhe Said Compound pound with said coating me id helix. beg pohloewstirutlr griabination of 1 a f metal 0 metal, a' Plat-'mg o cifedrnetai being capable by Clgg 5o ical conversion of forming an amphftenc 1 pound less acid than titanic acid, a helical Wire of said metal wound upon said plating and electrically joined thereto, and an electron emissive compound containing a metal capable of forming by chemical conversion an amphoteric compound less acid than titanic acid, said emissive compound being disposed between the turns of said helix.

ll. In a cathode structure, the combination of a core containing, at leaston itssurface, a metal capable of forming by chemicalf. .cnversion an amphoteric compound less acid than titanic acid, a helical wire of said metal wound upon said core and electrolytically joined thereto forming a helical dove-tail groove around said core, and an electron emissive compound, capable of forming a double-metal compound with said metal on the core surface, disposed within said dove-tail groove.

12. The method for making a cathode structure which comprises coating a metal core with another metal, winding a helix of wire over said coating, electrically joining said helix to said metal coating, and applying a thin coating of electron emissive material to lthe outer portions of the helix and athick coating thereof to the corey coating and helix between turns of the latter.

13. 'I'he method for making a cathode structure which comprises plating a refractory core with a metal, winding a helix of wire upon said plating, and electrically joining said helix to said plating with an additional plating of said metal on both core and helix.

14. In a lamentary cathode structure, the combination of a metallic core, a series of metal ribs upon said core, a metallic junction between the ribs and the core whereby said ribs are incorporated integrally upon the core, and an electron emissive substance between said ribs.

15. In a cathode structure, the combination oi' a refractory core, a coating of nickel on said core, a metal wire helically wound on the said core, means for maintaining a metal to metal contact between each turn of the wound wire and said coating, and a substance of electron emitting capacity applied to the said wire.

16. In a cathode structure, the combination of a core at least the outer surface of which is nickel, a metal Wire helically wound on said core with each turn of the wire forming with the nickel surface a permanent metallic contact having a lo'wer electrical resistance than a turn of the wound wire, and a substance of electron emitting capacity applied to the said wire.

17. In a cathode structure, the combination of i a core of a metal capable of forming by chemical conversion an amphoterio compound less acid than titanic acid, a wire of a similar metal helically wound on the said core and metallically joined thereto for at least a portion of each turn of the Wound wire, and a substance of electron emitting capacity applied to the wire.

18. In a cathode structure, the combination of a lamentary core having a surface of nickel, a series of nickel ribs upon said surface and metalically joined thereto, and an electron emissive substance between said ribs.

19. In a cathode structure the combination of a core having a metal layer for its outer portion, said metal being capable of forming by chemical conversion an amphoteric compound less acid than titane acid, a metal wire helically wound on said metal layer, means for metallically connecting the turns of said wire to the surface of said metal layer, and a substance of electron emitting capacity applied to said wire.

CARL J. R. H. VON WEDEL.

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