US1873730A - Electron emitting material - Google Patents

Description

Aug. 23, 1932. E. WIEGAND 1,873,730

ELECTRON EMITTING MATERIAL Filed Oct. 2. 1928 I I I 2 INVENTOR ATTORNEY Patented Aug. 23, 1932 Enron or ogan nnunnnonr, GERMANY, Assrenon. T .ALLGEMEINE nLEK- r ucrrnrz ensnnnsonnrrgou mm, enmvmnxn conronnmron 0F GERMANY l hppli cation filed octoberfi, 1 928, Serial N 'o.

the productionof dischargetubes, with.

or without rare gas filling, such asreceiver or transmitter tubes for wireless: telegraphy, rec'tifiertubes and the like, the metals of the alkaline earths are customarilyemployed for many purposes. They are employedfor instance for the production of highly emitting 1 oxide cathodes,@in thatthey are. developed in the form i of vapor in the tubes, are then del o posited on a carrierflbody' and there; for in'-: stance, converted a into oxide, afterwhaving been alloyed with the metalof the carrier bodyfthrough conversion with substances a giving oflf oxygeni a 3 They are further employedvfor. improving 325 and specifically, the salts of the nitrogen-hydrogen acids, which are constant, in the air at ordinary temperature, but which, at higher temperatures, decompose,forming metal of alkaline earth. This process has, however, disadvantages, which interfere considerably with its utility.

Apart fromthe high price of the acids and their explosiveness, which render the accumulation of great quantities of the same at one point inadvisable, above allother considerations, the fact carries weight, that the pump ing time of the tubes is very considerably prolonged by the great quantities of gas -(Il1t10 gen) freed by the decomposition of the acids. Furthermore, the output of metal is comparatively small, since, on decomposition, in addition to metals, other alkaline earth combinations are formed in great quantities. Thus from barium acid, for instance, upto 75% of barium nitride results. A very particular disturbance in connection with the use of tubes of this kind, is the deterioration of the vacuum, which occurs for no apparent reason and which renders the utility of the tubes questionable.

" LELECTRON EMITTING MATERIAL 309,892, and in Germany November 2, 1927. V

v N ow [it has been. found, contrary to the general expectation, that the reason for this phenomenon is to be sought in the process of the generation ofthe alkaline earth metal from acid.; If now, in contradistinction to this process, the metal is produced in the tube in such away that certain alkaline earth combinations evolving no gases at the glow temperature, such as oxides, aluminates etc. are heated with reducing agents which do not noticeably volatilize at the converting temperature, such as beryllium, aluminum or the metals of the rareearths, then, a deteoriation of the vacuum during the working will no longer be noticed. a

his effect, by far more favorable, as compared with that of the acids, may perhaps be explained by the fact that when the alkaline earthmetals are generated according to the oldprocess, certain alkaline earth combinations result, addition to metal, such as the nitride,which are more, or less of unstable character. Now it is decidedly possible, that these substances decompose under the influence of electrical discharges, and produce a deterioration of the vacuum, owing to the gases freed. on the other hand, the combine tions produced by the generation of the metal of alkaline earth according to the novel process, suchasthe oxides of beryllium, aluminum and of the rare earths are known as substances, extremelydifiicult to decompose and as non-volatile, even when glowed. Thus theydo not deteriorate the vacuum. It is however possible,that the diiferent behavior of the tubes produced by both processes may be due to other reasons.

The reduction of the alkaline earth combinations according to the novel process is at times accompanied by an intense generation of heat, for instance when aluminum is used as a reducing medium, so that there is danger that together with'the alkaline earthmetal, noticeable quantities of the reducing medium also mayvaporize. In these cases, it is ad- 9 vantageous to add to the mixture, suitable dilutingmeans, such as berylliumoxide, aluminum oxide, as also metals ,volatilized with difliculty, such as tungstemmolybdenum, etc., and thus to avoid excessive heating during the operation and a too rapid development of the vapor of the alkaline earth metal. Under circumstances, the diluting agents can even be added in excess. c

The reaction can also be prolonged by employing mixtures of such substances, on which the reducing agents take'effectin different degrees of intensity. For many purposes, good results have been attainedby the employment, as diluting means, of metals which form alloys with the alkaline earth metals, such as aluminum, copper; etc. q From.

the alloy formed during the reaction, the al kaline earth metal, does not escape 0n glow ing so quickly as it does from thepure mixture, in this manner, a current of metal vapor is attainedof longer duration, which is of great advantage, for instance, for the production of oxide cathodes; according to the alloying process mentioned in the introduc tion.

When employing oxides ofalkaline earths,

it has proved advantageous, to consolidate the mixtureinto blocks by pressure, and to protect the compressed blocks against the effect of water and-carbonic acid by coating and saturating them with parafin oil or simi lar liquids of suificient viscosity,'which have no efiect on the mixture and which become volatile at a high temperature, These blocks are attached to the electrodes or to special carriers in suitable manner and the tubes sealed in, in known manner. The invention may be better understood by reference to the accompanying drawing in which the single figure is 'a side view partly in section'of a radio tube adapted to be treated in accordance with the invention.

line earth metals are selected as initial substances, for instance those of barium and strontium.

The new process enables an extremely rapid pumping out of the tubes, since, with the exception ofthe alkaline earth vapor, no

gases are freed-from the mixture introduced. The residue can have no deteriorating efiect on the vacuum since it contains, no decompos- "able substances; 'The'metail of'the alkaline earth devel'oped, isofthe highest purity and as-asurface inthe discharge tubes, it exceeds by far the gasclean-up efiects of those metal surfaceswhich are produced by the ,old process.

Also in"connection with tubes filled with V rare gas, forinst'ance theargon filledglow rectifiers in which theefiect is soon deteri orated owingto the contentsof nitrogen, thei presentj process can be employed with advantage; v

. Vhat I claim as new anddesire to secure by LettersPatent ofthe United States, is:

. Y The method of treating an. electron dis-1 charge device having an evacuated envelope enclosing: an anode and cathode which com-*- prises placing adjacent said cathode a'mix ture of an alkaline earth oxide, powdered aluminum, and a powderedrefractory oxide non-reducible by aluminum, andsuflici'ent in amount 'to prolong: the "exothermic" reaction between said-alkaline earth oxide and aluminum','and heating 531d. mixture to' cause sald reaction. 7

-' ERICH WIEGAND.

' The radio tube comprisesabulb'or envelope pressed" blocks, advantageously by heating the same, for instance by high frequency or radiation heating to about 500 C. By slowly increasing the temperature to 700 to 800 C. the alkaline earth metalis vaporized and precipitated onto thewalls or onto the oathodes. The furthertreatment takes place in the known manner. 1 i

In manycases. it is usual toemploy mixtures of oxides for oxide cathodes. I According to the novel process such mixtures ican'be readily'obtained, if, in the original mixture, the corresponding combinations of the alka- After the tubes have been pumped out, the gas is extracted fromrthe

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