US1931647A - Process for introducing active metal into alpha vacuum tube - Google Patents

Description

Oct. 24, 1933. H. DE BQER ET AL 1,931,647

PROCESS FOR INTRODUCING ACTIVE METAL INTO A VACUUM TUBE Filed Nov. 13, 1931 INVENTOR J-HDE BOER J.L.H. JONKEK &: K. VA ESSEL /P Q W ATTOR EY cit Patented a. 24, 1933 PROCESS PATENT 0mm 1',931',647' V Fox INTRODUCING Ao T I v METAL-INTOA VACUUM'TUBE JanHendrikde-Boer, .njh llodewijk Hendrik Junker, and Karel Marinus van Gessel, Eindhoven, Netherlands, assignors to Radio Gorporation of America, a corporationof Delaware Application November 13, 1931; Serial No. 574,810, 5 and intheNetherlands November 15,1930.

* 7Clai1ns. (Gretn -27.5) f

This invention relates to a process for intro ducing a chemicallyactive-metal into an electron discharge tube, Among "such metals the alkaline earth metals andthejalkali metals play a prominent part, and 'are frequently used for producing an electron emitting layer on a cathode, and alsofor'binding residual gases orgaseous impurities. l

' Owing to the great-affinity of 'these metalsffor oxygen they cannot be exposed to'the open air.

For this reason various methods have already been proposed for introducingthese metals into a vacuum tube without running therisk of the metals being attacked by'the oxygen of the air. 'It has already-been proposed to introduce the active metal into the discharge tube by introducing compounds of the metal from which the metal maybe liberated by heating and which themselves are not attacked by the air, the compounds being heated and decomposed after evacuation of the tube.

line earth metals use has been made, for example, of compounds such as azides 'of these metals." Instead of decomposable compounds use has been made of alloys for example, magnesium and aluminum alloys'of the active alkaline earth and alkali metals. panying metal protects against oxidation the whilst the accompanying metal either volatilizes when the alloy is heated and decomposed in the discharge tube, or stays behind at the point at which the decomposition takes place.

nium into a discharge tube and to heat this mixture after exhaustion of the tube to such'a' temperature that the caesium or barium is produced in the form of vapour.

' 7 When using these methods the substances to be introduced into the discharge tube are often shaped as pellets and fixed in this form to one of the metal members of the discharge tube. 59 Though excellent results have been obtained with some of the methods above referred to, it 1 has been found that they do 'not always give perfectly satisfactory results. the cathode of a triode is coated with a layer of barium introduced in the triode by means of For introducing 'alka-- In these alloys the accomactive metal 170,138 introduced into the tube- Furthermore it has been proposed to intro- If, for example,

such a pellet, then the use of this triode is-often attended with disturbances in the discharge "manifested for example, by cracking'noises ina loudspeaker connected to the triode.

Accordingto, the invention these difficulties are avoided by introducing into thetube the active metal, or a compound or alloy from which this metal may be produced, admixed with such a quantity of insulating material that the introduced mixture is electrically insulating even after it is heated to produce the active metal. In fact, it hasbeen found that the said disturbances' are due to coherent particles of the compound introduced into the tube and from which the active" metal is produced. On heating the compound and volatilizing the produced metal particles of theintroduced mass or compound seem to scale oif. These particles may lodge,

for example, betweenthe electrodes of the tube must be substantially an insulator, i. e. it must have such' a high resistance that the voltages present in the vacuum' tubes do not cause an appreciable current to flow thru the material.

The invention Will be more clearly understood by reference to the accompanying drawing which represents byway of example an electron discharge'tube embodying the invention.

The triode shown on the drawing has a vitreous envelope 1, in which an anode 2, a grid 3 and an electron emitting cathode 4 are enclosed. The anode has an aperture in front of which 5 a receptacle 5 is fixed on the anode. If desired, the side of this receptacle facing the interior of the anode may be covered by a netting or mesh screen. The receptacle contains a mixture of the active metal and an insulating material, 109 such as barium'mixedwith magnesium oxide or zirconium oxide preferably finely divided or powdered; The percentage of oxide is so chosen that the mixture which is preferably, and by the aid of a binder, if necessary, brought into a 00- herent formfor example, that of a pellet, is electrically insulating. After .the exhaustion of the tube the receptacle 5 is heated, which may be done by means of a-high frequencymagnetio field until the barium is expelled from the mix- 110 ture. Part of this expelled bariumdeposits on the cathode 4, where it forms a layer which after being oxidized, if desired, is electron emitting.

The mixture introduced into the receptacle 5 may be prepared by mixing barium azide with a sufiicient quantity of magnesium oxide or zirconium oxide and by heating. this mixture in a vacuum or in an inert atmosphere to such a temperature that the barium azide decomposes leaving barium and liberating nitrogen How ever, the temperature to which the mixture is heated is kept so low that all or at least a largepart of the barium produced stays behind in'theq mixture. In this wayv there is obtained amix ture of magnesium oxide or zirconium oxide in timately admixed with finely dividedmetallic.

barium. As has been'stated the starting'mixture is so proportioned that the prepared mixture is electrically insulating. Goodresults'have been obtained, for example, from a starting mixture of 'barium; azide and' magnesiumoxide or zirconium oxide, in which the ratio by weight between the barium azide and themagnesium oxide or zirconium oxide is 1 to 15.

It is also. possible to decompose the barium azide after the mixture has been introduced into the discharge tube. In this case the nitrogen is liberated in the discharge tube and must be removed by a vacuum pump.

This mixture to be introduced into the vacuum tube may be conserved in a vacuum or under a protecting liquid. It is possible to expose the mixture to the open air-for a short time without the active metal contained in the mixture being materially attacked by the oxygen of the air,

The barium oxideproduced in the mixture by exposure to the .air does not unfavorably affect the conductivity of the mixture introduced into the tube, since barium oxide is practically an in sulator under these conditions.

In preparing this mixture one may also start with barium oxide and areducing agent, provided care be taken that asufficient. excess of bariumoxide is present in which case the'prepared mixture will contain free barium, barium oxide and the oxide of the reducing agent. I a I We claim: 7 1. The method of introducing a chemically ac tive metal into an evacuated electric discharge device which consists in providing within said device a mixture of the active metal and a refractory insulating material sufficient in amount to render said mixture electricallyv insulating, and heating said mixture to vaporize some of said metal.

2. An electric discharge device containing a mixture of a chemically active metal and a refractory insulating material sufficient in amount to render saidmixture electrically insulating,

and means whereby said mixture may be heated to vaporize some of said metal.

I 3. The method of introducing barium intoan evacuated electron discharge device which consists in placing withinsaid device in position to be heated a mixture of barium in finely divided form and a powdered zirconium oxide suflicient in amount to render said mixture electrically insulating, and heating said mixture to vaporize some of said barium.

, 4. The method of introducing barium into an evacuated electric discharge device which con,- sists in placing within said device in position to be heateda mixture of barium in finely divided {form and powdered magnesium oxide sufficient material.

6,. A clean up agent for electron discharge de-,

vices comprising a pellet-of a mixture of an alkaline earth metaland an insulating oxide suflicientin amountto make said mixture substantially an electrical insulator.

'7.. A clean up agent consisting of an electrically insulating mixture of a finely divided barium compoundv and powdered magnesium oxide the ratio'by weight being 1 of the former to 15 of the latter. 1 1

I JAN .HENDRIK'DE BOER.

' JOHAN YLODEWIJK HENDRIK JONKER. KAREL MARINUS VAN GESSEL.

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