Patented Mar. 15', 1932 1,849,598 UNITED STATES‘ OFFICE-j" FRIT? SCHIRbTER, 0F BERLIN, GERMANY, ASSIGNOR-TO‘ T'ELEFUNKEN‘ G-ESELLSGHAFT FUR DRAH'I‘LOSE TELEGRAPHIE M. B. H., OF» BERLIN,‘ GERMANY, A CORPORATION OF GERMANY OXIDE GATE-015E No Drawing. Application ?led June 12, 1929, Serial No. 370,469, and in Germany June 9, 1928. It has been known in the prior art to make high emission cathodes or ?laments by caus or cerium, are added so that there results a of metallic vapors of different kinds, ing the vapors of highly reducing metals to mixture and this mixture is caused to act on an oxide cs: act upon metal ?lament suitably'oxidized su containing ?lament body. per?cially. For instance, thermionic tubes It is also’ possible to proceed in the fol are manufactured by causing barium azid to lowing manner : decompose by heating while the tube is being To the metal of the carrier ?lament, say, exhausted, and then the ensuing vapors of ba tungsten, there are added oxides of cerium, rium are caused to act upon an oxidiferous lanthanum, etc., in ?ne division and of the (oxide-containing) tungsten ?lament provid requisite concentration in the course of the a It is very likely that: ed with a coat of oxide. 1.3 manufacture of the ?lament, and the resultant the ?lament thus obtained is endowed with body is subjected to the vaporizing process high electron emitting powers because the ba in which only an azid of the alkaline earth rium more or less combines with the oxide of the ?lament metals with the incidental pro metal is employed. What results in either upon the surface of the carrier wire is duction of ?nely divided barium oxide acase mixture of the oxide of the alkaline earth (baryta) . It has likewise been known in the prior 'art metal and of such of the said other oxides as to obtain pronounced maxima of emissivity have been used. At all events, the working 1- in oxide cathodes by using mixtures of ox conditions are so chosen that there is obtaine ides of alkaline earth metal and the metallic an optimum composition of the ?nely divided oxide mixture for maximum electron emis oxides of other groups, such as ceria or Ian sion. thanum oxide, in certain proportions. Such 60 In case the addition of lanthanum oxide, a marked maxima of emitting powers is ceria, or other equivalent oxides or oxid'e found, for instance, in a mixture of 90% mixtures to the carrier metal, say, tungsten, baryta and 10% lanthanum oxide or a mix should be inadvisable in the course of its be ture of 10% baryta and 90% lanthanum ox~ ing shaped into a ductile body, then the said ide. The process of manufacturing cath oxldes or oxide mixtures in small quantities odes of this kind according to previous prac— and in extremely ?ne division are subsequent tice has been to apply the mixtures in ques tion inthe form of a layer of oxide upon the ‘?ly brought upon the surface of the tungsten 75 lament, whereupon the cathode thus 'pre carrier ?lament or substratum. pared is subjected to the vaporizing process, The present invention has for its object to say, by the use of barium azid. combine the advantages of the said two meth Having invention, what ods, namely, of the metal oxide method and I claim is:now' described my ' 80 the oxide mixture method. For this purpose, 1. The method of producing an electron by the aid of the vaporizing method, a mix emitting cathode which comprises exposing in ture comprising a most favorable proportion to a vapor of an alkaline earth metal of metallic oxides of the alkaline earth group avacuo carrier consisting principally of a refrac with such other groups of oxide mixtures as tory metal with oxide of cerium incor orated 85 hereinbefore mentioned, ‘is applied upon the in and thru it, and there y pro surface of the bearerlor carrier metal used ducing disseminated an adherent highly emissive coating u as a substratum. For instance barium'azid carrier. is decomposed by heating, and other metals of on2.said The method of making an electron emit the kind under consideration, e. g., lanthanum ting cathode comprising a carrier of tung 1,849,594 2 sten in which oxide of cerium is incorporated which comprises placing said carrier in an envelope containing barium azide, evacuating said envelope, and heating said barium azide in vacuo to decompose it and thereby produce on said carrier an adherent coating of high electron emissivity. 3. An electron emitting cathode comprising a carrier of refractory metal in which oxides 10 of cerium and lanthanum are incorporated and an electron emissive coating on said car rier comprising an alkaline earth. 4:. An electron emitting cathode compris ing a carrier of tungsten intimately admixed with oxide of cerium, and an adherent coat ing of a compound of barium on said carrier. 15 FRITZ soHRoTEB. 20 CO U! 43 50 65