US1883174A - Discharge tube fabrication - Google Patents

Description

Oct. 18, 1932. c. J. R. H. VON WEDEL 1,883,174

I DISCHARGE TUBE FABRICATION Fild Dec. 12 1927 gm; ATTORNEY INVENTOR 631m. JRH row/V5051.

. Patented on. 18,1932

= in the functionin UNITED STATES PATENT OFFICE CARL J, R. H. V0! WEDEL, O1 BERLIILGW, ASSIGNOR, BY MESNE ASSIGRIM;

'10 ELECTRONS, INC, A CORPORATION OF DELAWARE DISCHARGE TUBE FABRICATION.

Application Med December 12, 1927. Serial No. 239,417.

This invention relates generally'to the fabrication of discharge tubes, and particularly to those discharge tubes including in final form a smal quantity of a chosen gas to aid of the tube.

A particular 0 ject of my invention is to speed up that part of the fabrication of discharge tubes involving the de-gasing of the included electrodes and disposal of the undesired expelled electrode gases, and to use the same'period for other 0 erations necessary to the production of the final successful discharge device.

Mfy invention contemplates in particular the abrication of a tube having one or more cathodes of the ty e depending for efi'ective electron emission pen the aid of chemical compounds spread upon the surface of a suitable support adapted to be heated in a convenient way, and which com ounds do not take on final form for best aid in the emission function until subjected to proper treatment within the tube. 'And it further contemplates in particular a type of such cathode that will r. not be injured by controlled ionic bombardmeat, but may be of such character that ionic bombardment can materially assist in securing an emissive surface having advantageous characteristics.

Another object is to employ ionic bombardment to aid in the conversion of chemical compounds and to bring about particular atomic arrangements within the molecules of such compounds.

Certain cathode compounds or coatings, such as the amphoteric compounds, having advantageous characteristics both in the matter of emission and preservation, are derived from diiferent chemical compounds, or mixtures of them, cemented in raw form to the coating support, and do not take on final chemical composition and/or atomic disposition within the molecules to give the desired results until treated by heat and ionic bombardment in a highly evacuated tube, or in the presence of a small uantity of gas inert with respect to the partlcular cathode coating; that is, non-absorbable by the coating. There may however be deliberately present a quantity of selected gas intended for composi-- good electron emission cannot be arrived at by ordinary chemical compounding, but only through conversion from certain selected com ounds of diiferent character with the aid of t e processes herein outlined. The amphoteric compounds referred to are thesalts of the combination of the oxides of the highly 'electro-positive metals, as for exam le, the "alkaline and alkaline earth metal oxi es with those oxygen compounds which may, by chemical conversion, be produced from amphoteric compounds, the resultant combinations being for example, aluminates, zincates,

chromites, zirconates, etc. of the highly electro-positive metals.

One of the severest of the problems in the fabrication of discharge tubes is to so de-gas the included electrodes and di o se of the expelled gases that subsequently in use additional occluded or getter bound gas is not freed in sufiicient amount to chan the composition of the inert gas to detrimental degree if the tube is a-so-called gas filled tube,-

or to alter the desired high degree of vacuum if the tube is a so-calle'd hard tube.

This problem of subsequent. gas appearance arises quite severely in the case of the employ ,ment of cathodes coated with the usual simple compounds, such as oxides of barium and the like, which cannot be formed in the usual brief period of the fabrication process usually employed with these simple compounds into final and permanent compounds, as is done in the case of the amphoteric compound cathode coatings with the process herein contemplate-d. and'which incompletely formed cathodestherefore continue to change chem ically during use with resultant gas freeing, The undesired freed gases have in general the detrimental effect of increasing the otential drop of the discharge path, resulting in a. loss that reduces the eiliciency of the device. A further bad result is a premature destruction of the electrodes.

of accomplishing the same result with the aid of heat produced in the electrodes by eddy currents generated under the influence of high frequency current fields. These prior methods however are time consumin and have other disadvanta es, in particu ar in the matter of treating t e cathode to obviate subsequent gas generation or freein I Accordin to the present invention tubes can be free so thoroughly of undesired gas during the fabrication process, and the cathode at the same time so formed that it will thereafter not yield gas to a disturbing degree, that the characteristics of the tube wi 1 remain substantially constant over extended use, and if a gas-filled tube it can be expected to function in accordance with the degree and kind of gas used in the original filling. The rocess also provides for activating the cat ode com ound or compounds for good and uniforme ectron emission over the entire surface after the desired chemical compound or compounds have been formed by the process.

The invention and its procedure will be I best understood by a descri tion accompanied by reference to the gures of the drawing.

Fig. 1 illustrates the invention used in connection with the fabrication of a rectifying discharge tube provide with a single cathode and two anodes for ordinary so-called full-wave rectification.

Figs. 2, 3 and 4 illustrate modes of extension and modification of the processes as carried out in Fig. 1.

In Fig. 1 VT is an ordinary glass or like container provided with the usual stem N for carrying the connecting wires and supporting the included electrodes. The electrodes are a filament F and two cooperating anodes A and A,, which combination of electrodes, properly connected to a source of alternating current, will produce in the completed tube so-called double wave rectification. The tube is shown connected through a communicating stem E to a vacuum ump onone side and a source of inert or ot er desirable gas intended as afinal gas filling if the tube is to be a so-called gas filled tube, the two-way cock V providing for connecting either the vacuum pump or gas source to the tube as desired. The tube will be sealed off at the point J when the pumping and gas filling features are completed. p

There is shown attached to each of the anodes a getter substance K and K respectively, such as magnesium, which substance may be attached to the anode surface in any convenient way, such as welding. These Leeann getter substances are preferably provided with roJect' ns P and P extending in the direction of he filament, the reason for for disconnecting the filament from a? source. Arrangement is also made for supplying a potential between anodes A and A from secondary winding S of a transformer. the switch WV: providing for applying this potential as desired. A potential between the filament and both of the anodes is secured by means 0 the connection incudin the variable resistance R, the potential or degree of current being controlled by varying this resistance as required.

The filament F, or cathode, comprises a p suitable support for a raw chemical compound, or mixture of raw chemical compounds, cemented or bound to the support in any suitable way, as by means of a cement or binder included in the mixture. Thus the chemical com ounds may be in the form of a powder inclu ing gum-arabic or like bindna material in sufiicient quantity to cause the owder to securely adhere to the support, it

eing understood that this binder is of temorary character, it being usually intended in the forming of the typegof cathode herein contemplated that this binder will be expelled during the processes when the forming of the final compounds results in a change of state of the raw compounds that includes a film adherence of the final compound to the support. Usually some material, not origina 1y a. binder, is included in the raw compound, which material has the property of transposin the final compounds into a more or less har firmly adhering coating on the surface of the support. It is usual to choose this material of such character as .toeither aid in producing the final desired compounds, or at least not to interfere with the electron emitting characteristics of them.

Proceeding with an outline of the process a tube, such as VT, would normally be connected to the vacuum pump through cock V and pumped while the filament F is heated by closing the switch W the tube being at the same time heated in some suitable way to a temperature safely below that of softening of the-glass or like material of the walls. This step therefore provides for expelling some of the occluded gases of the tube walls, filament and other physical elements while pumping is in progress, and ordinarily requires about 20 minutes before the desired exhaustion is arrived at. It should be pointed out that during this step the formation of the filament coating begins, this because the filament is heated as before stated. The heat is sutficient to volatilize thebinding material of the assen raw compounds, and the raw chemical compounds change over into an approximation of the final chemical compounds of the coating,

which step also involves freeing of a large percentag of gases of conversion, but does not result in producing the final state of the coating necessary to active electron emission, which seems to be one of atomic arrangement within the molecules of the compounds. '11; is further pointed out that the coating does not arrive at a condition of being substantially non-ga'sing until this final condition of the compounds is arrived at.

At this point the tube is ready to be sealed oil at the oint J if it is not to have a gastilling, or t e necessary desired gas for a gasfilled tube is admitted through cock V, the

ressures of such fillings ranging in practice rom fractions-of one millimeter to a number of millimeters mercury, this depending u on the purposes and manner of use of the tu as, as well as their design.

If the tube is not to'have a gas filling, but is tobe a so-called hard tube, the next step in the process may be carried outwith a gas filling and the tube later pumped to the desired degree of hardness before sealing off. However, thenext step involves the use of ion bombardment in the presence of getter, or

getter alloy, materials which in themselves may be sufiicient to produce the necessary ionic conditions to carry on the bombardment process without a gas filling. The "absence of a gas filling however, introduces some difiiculty in the matter of starting the discharge,

it being first necessary to heat the getter substance to produce vapors at required pressures to sustain such a discharge; A further difficulty, in the absence of a gas filling, is that there does not exist a predetermined pressure around which to determine the necessary discharge potentials, and the initially low getter vapor pressures that might be created require undesirably high starting potentials, which high starting potentials may produce some destructive effects, particularly on the cathode, before they can be altered after the discharge is underway. Further, in depending upon getter vapor alone, precautions must be taken that there does not result an immediate condensing of the early production of getter vapors on cold walls and other parts of the .tube, one precaution being to heat the tube and another being to produce the vapor quickly and in large quantities.

Though there are difficulties connected with producing the process with getter vapors alone these may be overcome in a manner to be later described.

If the process is to be continued ina manare made for heating the filament by winding S and a plying potentials between the anodes, an between suchanode and the filament, by winding S2.

At the beginning of the application of the discharge potentials the projections P and P of the getter substances K and K receive the brunt of the bombardment, and therefore commence to heat and vaporize before the anodes A and A have reached sufiicient temperature to commence to expel their occluded gases, as they later do. Immediately the getter vapors are produced they take part in the ionic discharge and, being ionized, are

process arrangementearly in the bombardment stage.

This requirement accounts for placing the getter substance between the cathode and anode. and making a projection thereon extending well towards the cathode.

The active bombardment in which the getter 'vapor partakes, once created, includes bombardment of the cathode coating with the result that the incomplete formation of the coating left over from the initial heating and pumping process is completed, including finally freeing the coating of all gases, which gases are immediatelybound by the getter vapors. The bombardment also acts to activate the coating, that is, produce that final atomic arrangement within the molecules of the compounds necessary to final successful electron emissive characteristics.

A further advantage of the bombardment process is that in the formation of certain types of coating compounds there may be included in the gas filling a quantity of a gas or gases having elements needed to produce the final compound, so that during the bombardment process these elements may be conveyed thereby to the cathode coating to take their places in the final compound.

Another advantage of the bombardment process is that the bombardment results in avoiding heating other parts of the cathode structure to the same high temperatures requiredat the particular points in the coating. For example, if reliance should be had upon passing a current through the filament core to produce the necessary high heat at the surface of the coating to bring about the desired results in coating formation, it is before mentioned. The walls of a glass contuiner form a good surface to which molecules of undesired gas cling, and do not readily leave under suction of the vacuum pump. The ions of getter vapors in depositing on the walls also capture and bind a large part of these clinging molecules, and so occlude them in the condensation process, along with the gas molecules brought from other parts of the tube, that the occluded molecules are not thereafter free for later diffusion throughout the spaces of the tube.

. A further advantageous result of the process is that during the condensation of the getter vapors the stem N, electrodes. shields and leads are electrically charged by the discharge producing potentials in such way as to produce about them fields which divert the getter vapor ions, or are of such temperature that they do not invite condensation as readily as do the cool walls. The result is that when theprocess is discontinued these parts of the tube are substantially free from the getter deposit, or mirror, thus avoiding short-circuiting paths with resulting possible flash over damages if these deposits were permitted to take place at. these points of the tubes which must later withstand operating differences of potential. For this reason the discharge process is maintained until the getter condensation and deposition is com"- pleted, which completion is nicely indicated by a readily discernible change in the color of the discharge readily recognized by an experienced operator of the process.

The electrodes, including the cathode, of the tube must be designed so that the discharge can beincrea-sed until each electrode is heated sullieiently, and so maintained for a sufficientlylong time, that the expulsion of the occluded gases is substantially complete. I For this reason the cathode must be able towithstand without undue injury a greater current than is ordinarily employed during the norcess current. 'The other electrodes of the tube should be so designed that they remain relatively cool under normal 0 rating load con.-

ditions, but are sulficient y heated by the above mentioned overload for the expulsion of occluded gases during the gas expulsion process. 3

Fig. 2 shows'a tube intended for the same serviceas the tube of Fig. 1, except that it includes a design and arrangement of electrodes particularly suitable for operating with high potential currents, and for which reason there is included a shield B between the anodes, which shield includes projections or extensions B B and B for lengthening and directing the discharge paths. The arrangement of the electrodes is shown in perspective, so that there is intended a second anode corresponding to anode A located on the opposite side of shield B. It will be noted that the projection B of the shield lengthens the path between the two anodes around the righthand side of the shield, that the same results from the extension 13, around the left-hand side of the shield, and that the double extension l5, lengthens the paths between the filament F and the two anodes;

In a tube so designed for hi'gh voltage operation special precautions are desirable in the matter of starting the bombardment operation, this because higher starting voltages are necessary and since it cannot be expected that the gas li ling will be entirely free from foreign gasesstlll higher starting voltages may be necessary unless special arrangements are -made to overcome;the requirement. The

danger of a high starting voltage is that there may be concentrated on the cathode a severe bombardment that will do injury before the discharge can be controlled after starting takes place. This can be overcome by proper arrangement for having the necessary amount of getter vapor present at the time the discharge commences.

fT here is shown attached to anode A a piece 0 or ess extend in the curved axis of the (lischarge path between the filament F and the anode A which curved path is compelled in part by the projection B but which is also due to the fact that the electron emission from the filament F flies out in all directions with theresult that a part of the field occupies the upper regions of the tube beyond the limits of the projection 13,. It will be noted that with this long. curved discharge path between the filament F and the anode A it is difiicult to project the getter substance K far enough to make as lar a difference of potential between the on of the projecting getter and the anode as can be had in an arrangement such as shown in Fig. 1, so that there may not he suflicient concentration of the bombardment on the getter substance to the exclusion of the anode at'the beginning of the discharge to free enough advance getter vapor to properly sa feguard the operation against foreign gases 1 getter substance K so formed as to more eeann either initially included in the gas filling or prematurely expelled from the electrodes,

particularly the cathode which is highly sensitive to high voltage bombardment in the matter of gas expulsion.

For these reasons another source of getter vapor is illustrated, which is shown to m-' clude'the getter substance K interwoven or otherwise associated with a heating wire F which is connected to the outside of the tube in such way that heating from the secondary winding S can be commenced before applying the discharge potential to the electrodes, thus making possible an adequate supply of getter vapor at the commencement of the dischar e. Once the discharge is properly and saf ely under way, the getter substance K attached to the anode insures a further continued supply of getter vapor for the operation. After the tube is finished the outside connection to the heating wire F; can be cut off or otherwise dis osed of.

Both the filament F an the heating wire F are connected at one side to the shield B, so that a single leading in wire to this shield serves as one outside connection for both of these elements. The other ends of these elements have independent connections leading to. the two branc es of switch W which'two branches may be closed independently to first start the getter vaporizing process and then to heat the filament at the commencement of the discharge. The discharge potentials are applied through switch W from secondary winding S as in Fi '1.

The springs D an D, of conductin material, are shown connected between eac side of the shield B and the'wall of the tube, and therefore make a conductive connection between the shield, which is of a potential different from the anodes, and the metallic getter mirror deposited on the tube walls which connection is a (path for relieving the charge constantly ten ing to collect on the walls by reason of the electron or ion dis ersion in the tube. Without such leak pat it is possible for the tube walls to collect such a high charge that it will interrupt the discharge operation of the tube, and this eifect is enhanced by placing the hand or otherobject against the tube. Such interruption cannot occur with the leak paths rovided by these springs, thus making the tu he proof against interruption of operation by handling.

The contact made by such a spring with the getter surface is one of more or less high resistance, so that the relief of the tube wall charge is in the form of a leak, thus maintaining somecharge on the walls, but preventing an overload, and it may be found that in some types of tubes this maintainedlower charge on the walls is of value.

The potential of the-spring at its point 5 of contact with the walls during the bomneighborhood of the spring, and this accounts for the automatically produced hi h resistance-of this connection. Also, the" eposit within the limits of the end turnof the sprin is very thin, which thereziore leaves what mig t be termed a peephole through which internal parts of the tube can afterwards be observed.

While one. spring may be all that is nee essary for providing the leak path between the shield and the walls,it is preferable to place a spring on opposite sides of the shield as shown to aid in supporting or centering the electrode structure in the tube, as opposed to a tendency of one spring to push this structure to one side. i

Fig. 3 principally differs fromv Fig. 2 in the arran ement of the getter substance K intended for early vaporizing. In this arrangement the getter substance is shown supported above the electrode structure in a position to be easily heated by edd current effects from a high frequenc coil capped over the tube, which coil is suitably energized with high frequency currents from a suitable source Y. ThlS arrangement provides for producing in the tube suficient getter vapor in advance of starting the discharge to satisfy the precautions outlined in connection with Fig. 2.

Fig.. 4 shows another arrangement for early vaporization of an auxiliary getter substance K This auxiliary getter substance is shown positioned bymeans of a support quite close to the cathode F, and S witc W, provides for independently producing a d1soharge potential between getter substance K and the filament in advance of applylng the main discharge potentials, so that getter sub stance K can be va orized by means of an auxilia discharge etween it and the oathode. T ere is also shown another getter substance K located in close proximit to the cathode F, which will be va orize by the heat of radiation from the. ament at such times as may be helpful to the operation.

In tubes so designed as to produce cathode rays, it isalso possible to bring about the vaporization of the getter material by so d1sposing the material in the tube as to be adequate y under the influence of. such rays.

' Wh1le I have illustrated and explained my invention in connection with the fabrication of discharge tubes, and the formation of cathment, and the inclusion of elements in the discharge gas which, by reason of the bombardment action, finally become constituent elements of the desired compounds, whlch features have general application obvious to those skilled in the art in chemical processes and production of desired atomic arrangements in such compounds.

Having thus described my invention, what I claim is:

1. A discharge tube comprising an anode and an electron emissive cathode, terminals for said anode and cathode including termi- ,nals for sugplying heating current for the tween said anode and cathode alongthe'nor mal discharge path therebetween.

3. The combination of a discharge tube a cathode structure in said tube, a getter ee by chemical conversion, assembling ath posit-on an internal wallof said tube, and a flexible conductor connected to said structure and in contact with said deposit, the deposit being less dense near the area of contact than on the remainder of said wall, thereby formmg a high resistance contact between said deposit and said conductor.

4. The process of manufacture of thermionic discharge tubes, comprising the steps of coating the cathode with a mixture of the raw materials to form an emissive coatin by chemical conversion, assemblin said cat ode with other electrodes of said tu sealing the assembled electrodes within an envelo substantially evacuating said envelope, eating and envelope and said cathode while continumg said step of evacuation, producing a getter vapor within said envelope, ene gi l the electrodes whereby a discharge occurs rebetween and ions are produced within said discharge path and the electrodes are bombarded thereby, concentrating said bombardment at the commencement of the discha upona getter substance so located and electrically charged as to attract said bombardment whereby said last mentioned getter substance is heated to avaporizing temperature. and continuing-the step" of energization of said electrodes until substantially all of said gtbugfilmaterial sublimates out. of said dis-. d

e process of manufacture of thermlomc d1 tubes, comprising the'stens of coating the cathode with a mixture of the raw materials to' form an emissive coating said cathode with other electrodes of said tube,

electrodes withinanenproduced within said dischar velope, substantially .evacuatin said cn velope, heatin said envelope an said cathv ode while continuing said ste of evacuation. introducing an inert gas 0 predetermined pressure within said envelo producing a getter vapor within said enve o ener 'zmg theelectrodes whereby a discharge 0 overload intensity occurs therebetween and ions are produced within said discharge path and the electrodes are bombarded thereby, concentrating said bombardment at the commencement of thedischarge upon a getter substance so located and electrically charged as to'attract said bombardment whereby sair: last mentioned getter substance is heated to a vaporizing temperature; and continuing the step of energization of said electrodes until substantially all of said getter material sublimates out of said discharge.

6. The process of manufacture of thermionic discharge tubes, comprising the ste s of coating the cathode with a mixture of t 1e raw materials to form an emissive coating by chemical conversion, assemblin said cathode with other electrodes of said tu e, sealing the assembled electrodes within an envelo substantially evacuating said envelope, eating said envelo and said cathode while continuing sai step of evacuation, producing a getter vapor within said envelo e, energizmg the electrodes whereby a ischarge occurs therebetween and ions are within said discharge ath and the e ectrodes are bombarded there y, concentrating said bombardment at the commencement of the discharge upon a tter substance so located and electrically c arged as to attract said bombardment whereby said last mentioned getter substance is heated to a vaporizing temperature, and continuing the step of energization of said electrodes until chemical conversion of the raw materials upon the cathode and activation of the resultant product are completed.

7. The process of manufacture of thermionic discharge tubes, comprising the ste s of coating the cathode with a mixture of t e raw materials to form an emissive coatin by chemical conversion, assemblin sai cathode with other electrodes of sai tube,

reduced sealing the assembled electrodes within an envelope, substantially evacuating said en velope, heating said envelope and 'said cathode while continuing said step of evacuation, producing a getter vapor within said envelo energizing the electrodes whereby a isc ar'ge' occurstherebetween and ions are electrodes are bombarded t ereby, concentratjng said bombardment at the commence-v ment of the discharge upon a getter substance so located and electrically charged as to attract said bombardment whereby said last mentioned getter substance is heated to a vaporizing temperature, continuing the path and the lee step of energization of said electrodes until the chemical conversion of the raw materials upon the cathode and activation of the resultant product are completed and further extending and continuing the step of energization of said electrodes until substantially n therein, termina s for said all of said getter material sublimates out of said discharge.

8. A dischar e tube having electrodes electrodes, a getter substance attached to one of: said electrodes and projecting along the discharge path between said electrodes to be subjected to a discharge therebetween, whereby the initial discharge path is substantially shorter than the normal discharge path between said electrodes, additional getter substance in said tube independent of said electrodes, and

- means for heating said additional getter substance independently of a discharge between said electrodes.

9. 'A process for the capture by getter vapors of undesired gases from the electrodes of a discharge device, the method of assuring a supply of ionized getter vapor at the commencement of ionic bombardment from a discharge, and the method of supplying a getter vapor for participation in the discharge which consists of heating a getter substance to vaporizing temperature in advance of initiating a discharge, initiating the discharge and concentrating thebombardment at the commencement of the discharge upon a getter substance so located as 3 to produce such concentration, whereby the last mentioned getter substance is first heated to a vaporizing temperature.

10. A process for the capture by getter vapor of undesired gases from the electrodes of a discharge device one of which is a heatable electron-emissive cathode which has been partially degased, which consists in first heating the cathode, then initiating a discharge between the hot cathode. and another of said electrodes, concentrating the bombardment at the commencement of the discharge upon a getter substance so located as to produce such concentration, whereby the getter substance is first heated to vaporizing temperature, and continuing the discharge with continued vaporization of the getter substance co-incident with the evolution of gases from the electrodes.

11. A discharge tube having an anode and a cathode therein, terminals for said elecmeans trodes, a getter substance disposed between said anode and cathode and adapted to be vaporized by a discharge therebetween, ad-

ditional getter substance in said tube independent of said anode and cathode, and

for heating said additional getter substance independently of a discharge between said anode and cathode.

CARL J. R. H. VON WEDEL.

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