US2640945A - Introduction of active materials into evacuated envelopes - Google Patents

Description

June 1953 w. HARBAUGH ElAL. 2,640,945

INTRODUCTION OF ACTIVE MATERIALS INTO EVACUATED ENVELOPES Filed Feb. 1, 1950 2 Sheets-Sheet 1 Z2 4 INVENTORS WILLIS E. HARBAUGH LLOYD P- GARNER 0 WA RNEY June 2, 1953' 2,640Q945 INTRODUCTION OF ACTIVE MATERIALS INTO EVACUATED ENVELOPES Filed Feb. 1, 1950 W. E. HARBAUGH ET AL 2 Sheets-Sheet 2 A g RNEY Patented June 2, 1953 UNITED STATES PiAiT EfNT OFFICE,

INTRODUCTION OF ACTIVE MATERIALS INTO EVACUATED ENVELOPES' Willis E. Harbaugh, Bareville, and Lloyd P. Garner, Lancaster, Pa., assignors: to Radio Corporation of America, a: corporation of Delaware Application February 1, 1950; Serial No. 141,648

8" Claims; 1

This invention relates to electron discharge devices and more particularly to gettering such devices and improved gettering means for cleaning. up gases during processing of the same as Well as gases which are evolved'during their life.

It is known to be desirable to provide means for'effecting a continuing gettering action during the useful life of an electron discharge device. However, methods and means heretofore provided" for carrying this out have not been entirely successful for various reasons. One of the difficulties encountered was the fact that in connection with flash type getters a material which is usually a good emitter of electrons is introduced into the active regions of the electron discharge device and is" evaporated on or migrates to insulators, grids or anodes and subsequently interferes with the operation of the device' Thus, it has been necessary to limit the quantity of getter material in spite of the fact that after the electron discharge device has been carefully outgassed some gasis liberated during processing, aging and normal operation. Another type of getter commonly utilized is an electrode or other part in an electron discharge device which is made of or coated with getter material. This lattertype of getter has the disadvantage, as heretofore utilized, in operating at its most appropriate gettering temperature and consequently effecting most of its gettering Whenthe largest u amount of gas is present during processing of the device on exhaust thereby utilizing all or almost all of the gettering action available in the active material at a time when it is Ieastneeded; In the case of high power electron discharge de-- vicesthe difficulties attending the introduction of sufficient quantities of active gettering material have been such that in many instances it has been expeditious to operate the high powerelectron discharge deviceonly'while connected to ex"- haust apparatus. In particular in high power tubes having multiple element electrodes and large expansesof parts which evolve residual gas during operation of the tube it has been necessary to operate the tube only While connected to exhaust apparatus.

We have found that the foregoing as well as other disadvantages may be eliminated and that.

not only may the getter action be substantially improved but that an active gettering material maybe available in any desired quantity during 2: tortuous path and" which is preferably connected to and a direct continuation of the exhaust tubulation.

It is, therefore, a principal object ofour inven- 'tion to provide agetter by means of which active getter material may be exposed to the interior of a vacuum envelope at any desired time Without liberating quantities of gas;

Another object isthe provision of such a getter which does not require additional leads through the vacuum envelope and by means'o'f which large quantities of active gettering' material may be eX-- posed to the interior of'avacuum envelope-while at the same time keeping the active material in a placewhere it cannot affectthe operation of the device.

Yet another objectis theprovision of'a getter in a region of an electron discharge device where the deposition of even large quantities of active gettering material on surrounding parts isharmless, which region is inaccessible to alternating induction heating currents without requiring ad dit'ional' leads-through the vacuum envelope.

A mor'especific object is the provision of' a get f ter capsule containing" a substantial" amount of activated getter-mg material; which capsule may be readily inserted in a region of'a'n electron dischargedevioe'and"which if'desired, may be readily withdrawn and replaced.

A further specific object is the provision of a getter which" is not exposed t'o high temperatures during processing of the electron discharge deviceand which is heated to' optimum gettering temperature duringthe useful life of an electron discharge device by the filament or'heater voltage without the requirement of separate leads through the vacuum envelope.

In accordance-with an important aspect of our invention, we prov'ide'a sealed getter capsule having at least onereadily'frangible portion and containing activated getter material which requires no'further treatment other than exposure to the interior ofthe electron discharge device in order for getteringto commence.

Further objects and advan-tges of our inven-- tion'will become apparent as the following description proceeds'reference being had to the accompanying drawing in which:

Figure-1 is asectional view of one embodiment ofour invention with parts of an electron discharge device shown partly in section with the remainder indicated schematically;

Figure 2 is a sectional view through the" line 2 2 ofFigure' 1;"

Fi'gureE is a sectionalview' similar to Figure l with a portion cut away for convenience and illustrating one modification thereof;

Figure 4 is a similar view of another embodiment of our invention;

Figure 5 is an elevational view of a modification of the construction of Figure 4; and

Figure 6 is a sectional view of still another embodiment of our invention.

Referring now to the drawings and in particular to Figures 1 and 2, a superhigh power electron discharge device I indicated schematically may be such a device as is disclosed and described in detail in our copending joint application with W. N. Parker, Serial No. 81,932, filed March 1'7, 1949, which is capable of a continuous output of approximately 750,000 watts or more at 80 per cent efiiciency. As pointed out in said copending application said tube has 48 cathode elements, 48 grid elements and a reentrant anode all arranged in concentric cylindric arrays. The active grid and cathode elements are approximately 8 inches long which serves to indicate the approximate size of the tube, which though large is exceedingly compact and is even smaller than high power tubes heretofore made which are capable of comparatively small output.

Such devices have considerable areas of metal which require out-gassing and which under certain conditions evolve a substantial quantity of residual gas during the life thereof. It is apparent that in connection with such a device an effective getter must have a substantial quantity of active gettering material which is preferably available over the entire life of the device.

Getter capsule or tube I I comprises a vacuumtight tubular envelope I2 having hollow extensions I3 each of which communicates with the interior of envelope I2 and is formed by relatively thin frangible glass. The interior wall of envelope I2 is coated with a highly active gettering material I4. Such a getter tube is preferably made by spot welding a plurality of conventional getter loops I5 containing a getter material such as barium berylliate plus titanium to a rod I6 which in the embodiment shown is nickel. The ends of rod I6 have resilient members such as springs I! of high speed steel welded thereto and the assembly is placed inside of a glass tube open at one end and having extensions I3 spaced 120 degrees apart. Springs I'I frictionally engage the wall of the tube and maintain the getter tab assembly in place. A tube having a constricted opening is then sealed to the open end of the tube containing the getter tab assembly and the whole is then connected to an exhaust system.

The system is then pumped down and glass envelope I2 containing the getter tab assembly baked out. The metal parts are out-gassed as well as the getters which are heated to a dull red. On completion of the out-gassing the getters are flashed -by means of heat induced in the metal loops by radio frequency coils positioned about the envelope and active getter material becomes deposited in the form of a coating I4 on the inside wall of envelope I2. We have found that a substantially improved active material is obtained if the getter flashing is carried out in an inert atmosphere, preferably argon gas under a pressure of about to 20 mm. of mercury. In this instance the argon is removed and then envelope I2 is sealed off and removed from the exhaust system.

We provide clamps I8 adjacent each end of envelope l2 for maintaining the same in position in an electron discharge device. One preferred location for our improved getter is such that at least a part of envelope I2 carrying extensions I3 extends into soft metal exhaust tubulation I9 which in the embodiment illustrated in Figure 1 is sealed to one end of tubular lead-in conductor and support 20 which communicates with the active electron region of tube I0 by means of the upper end thereof (Figure 6). Lead-in conductor and support 29 corresponds to the central tubular conducting support of the tube described in said copending application referred to hereinabove. Clamps I8 carry high temperature spring fingers 2I which frictionally engage the inner wall of lead-in conductor and support 20 and maintain envelope I2 in the desired position with extensions I3 extending well down into soft metal tubulations I9 Which may be copper or other suitable metal. Electron discharge device ID is then connected to an exhaust system and completely processed. On completion of the processing of device In exhaust tube or tubulation I9 is squeezed as indicated by dotted lines I9 causing one or more of extensions I3 to fracture and thereby expose active getter material I4 to the interior of device I0. The fractured portions of extensions I3 fall to a harmless area below the pinch-off and the exhaust tubulation pinched off as at 22 by squeezing the same under sufficient pressure to cause plastic flow of the metal as is now well known. On the other hand, the pinch oil may, if desired, be effected prior to opening of getter tube II, it only being necessary to provide a sufficient length of exhaust tubulations I9 so that when the same is squeezed at I9 the pinch off at 22 will not be ruptured. A clean fracture of extensions I3 may be insured by providing score lines as at 23.

In the embodiment of Figure 3, as in the following figures, similar parts have been identified with identical numbers. I-Iere, envelope I2 instead of hollow extensions is provided with a small pinch 23 which has embedded therein a loop of refractory metal wire 24 such as tungsten connected at its ends to copper leads 25. Prior to the pinch-off of tube I0, leads 25 are spaced apart and are connected to a source of electrical current through a switch (not shown). Just before the pinch-off is effected the switch is closed and the high current passing through lead 24 causes pinch 23 to fracture from thermal shock. The switch is then opened to interrupt the flow of current and the pinch-off effected in the usual way, the soft copp r lead 25 becoming sealed in the pinch at 22 and the portion therebelow being cut off. If desired, leads 25 may be pulled clear from below prior to the pinch-off. It is apparent that in this embodiment the exhaust tube may also be glass as well as metal. In such a case, leads 25 are either pulled clear prior to the tip off or constituted 'of good glass sealing metal or alloy at the area of the tip off to permit the formation of a vacuumtight seal between the leads and the glass in the well known manner.

We have found that in such a device as electron discharge device In having a tubular conducting lead-in and support 20 which is connected to the active electron region of the device by a substantially tortuous or indirect path a substantial deposit or coating of active gettering material may be conveniently located in conducting support 20 without in any way impairing the :efiiciency of the device operation while in fact improving the same.

Inq-the embodiment of Figure. 4., wire or ribbon 2.6 from. which active getter materiai may be evolved is stretched between 'two condncting tabs.

or leads 2'1, 28; lead 21 being connected to conducting lead-inandi support: while lead 28* extends down through the middle of, soft copper tube 19 prior to the pinch-oil and is connected to one side oiv a current. supply :(tnot showni. Just before pinching oil of. device l0 conducting support 20 is connected to the other side of the current source, the resulting high temperature heating of getter wire 26 causes. the getter material to form and evaporate and. deposit active getter material in the. form of coating 29 directly on the interior wall of conducting sup.- port 20. Pinch-off oi device Ht is then carried out as described hereinabove.

In certain applications as where a relatively long expanse of getter wire 26 is used, it isdesirable to keep the voltage along the same below the are level of an alkali metal such as barium. In that case we connect getter wire 26 between two conducting wires or rods 29, 30 as at 3]., 3.2 as well as at a plurality of spaced points as shown in Figure 5.. Instead of every loop of wire 26, we also connect spaced loops such as every fifth one alternately to rod 29 or rod .30 in accordance with the. voltage. used and the resistance of the component materials. We then connect rod 29 to lead 21 while rod 30 may be connected to lead 28 or may replace the same and itself extend down through tube l9.

As pointed out hereinabove, it has long been desired to provide a continuing gettering. action during the useful life of an electron discharge device. Such is now possible in accordance with our invention; the getter itself being located in.- side of a tubular conducting lead-in and support with the means for heating the same arranged in such manner that the getter is not excessively heated at any time. In particular the getter is not excessively heated during tube processing as was the case heretofore, but is maintained at an optimum temperature during tube operation throughout the life of the tube. Such a getter is of the high temperature type. It utilizes a coating or body of a material such as zirconium, thorium or the like which has desirable gettering action when heated. If the temperature of the getter is maintained at an optimum point in accordance with the material utilized therein gcttering proceeds at the preferred rate. However, if the getter is excessively heated the gettering action may cease and at still higher temperatures the getter may even evolve gas or evaporate. This not only resulted in loss of the desired gettering action but also in impairment of the functioning of the electron discharge device.

In Figure 6 is illustrated a getter in accordance with our invention which is capable of gettering action over the entire useful life of the electron discharge device. A strip of getter material or a conducting rod 32 coated with such material 33 is mounted in lead-in and support 29 and connected at one end to lead 34 which in turn is connected to conducting lead-in support or beam former 35 which is connected to one side of the filament, heating voltage source (not shown) for the tube. Rod 32 is connected at its other end to lead 28 which after pinch-off of device ID is electrically connected to copper tubulation I9 which is in turn connected to lead-in and support 29. Lead-in 20 is connected to the other side or the filament; heating voltage source. As

pointed out in said copending application the cathode elements. are cemented at: one end to beam former 35 and at their other end to: conducting support 20. to complete the filament heating circuit. With the: connections as shown in Figure 6? it is apparent: then that by proper selection of resistance a desired proportion of the current supplied tov members, 20 and 35 may be shunted through getter32 In practice the resistances are so arranged that the getter is maintained: at. the desired temperature. by current flowing through it at the normal filament. voltagev of the tube.

Before pinch-off leadv 28 is connected to the. heating current source. whereby degassing and processing of getter 33 may be executed at a stage of tube processing when it will not be exposed to high. gas pressures or other deleterious conditions.

Though we have described our invention in connection with certain specific embodiments illustrated, we do not desire to be limited thereto since various modifications within the spirit and scope of our invention may be made thereto. As for example, other getter materials or materials which on processing, such as zirconium hydride, form materials with desirable gettering properties may be utilized. Therefore, while our invention is subject to obvious modifications by those skilled in the art, it is intended to cover all such modifications as come within the scope of the appended claims.

We claim:

1. An electron discharge device, comprising an evacuated envelope, a tubular lead-in sealed, through said envelope and extending into the same with its interior in communication with the interior of said envelope, an exhaust tubulation. connectedto the outer end of said lead-in andsealing the same to. the external atmosphere, a container in said lead-in. and having, a portion thereof extending into said exhaust tubulation, and an active getter material in said container.

2. An electron discharge device, comprising an evacuated envelope, a tubular lead-in support sealed through said envelope and extending into the same with its interior in communication with the interior of said envelope, a, soft metallic exhaust tubulation connected to the outer end of said lead-in support at one end thereof and sealed to the external atmosphere at its other end, a getter container in said lead-in and having at least one fractured portion extending into said exhaust tubulation.

3. An electron discharge device, comprising an evacuated envelope, a tubular conducting leadin sealed through said envelope and extending into the same with its interior in communication with the interior of said envelope, 9. soft metallic exhaust tubulation connected to the outer end of said lead-in, a normally gastight getter container in said lead-in and having a plurality of frangible portions, said frangible portions extending into said. exhaust tubulation for a substantial distance whereby at least one of said frangible portions is broken when said exhaust tubulation is deformed intermediate its ends.

4. A preprocessed getter assembly adapted to be mounted in an electron discharge device, comprising an evacuated gas-tight elongated envelope having frangible fingers extending from one end thereof, said fingers being hollow and having an interior communicating with the interior of said envelope, and activated getter material in said 7. envelope, whereby fracture of at least one of said frangible fingers releases said getter material to the interior of said device with reduced residue of fractured material.

5. A preprocessed getter assembly according to claim 4, and wherein said getter material is in the form of a coating on the interior wall of said envelope.

6. An electron discharge device comprising an evacuated envelope, a tubular lead-in sealed through said envelope and extending into the same with its interior in communication with the interior of said envelope and having a free end extending outwardly from said envelope, an exhaust tubulation having predetermined transverse dimensions connected to said free end of said lead-in and sealing the same to the external atmosphere, an' elongated container in said leadin in coaxial relation therewith, said container including a body portion, on end of said body portion extending into said exhaust tubulation, said body portion having a fractured finger extending from said one end thereof, and an active getter material in said container, said fractured finger having a hollow interior providing a passage for said getter material from said container to the interior of said exhaust tubulation, said one end of said body portion having transverse dimensions sufliciently smaller than said predetermined dimensions for forming an annular passageway for said getter material from said exhaust tubulation-to the interior of said envelope while blocking the transfer of fractured finger material detached from said finger, for preventing contamination of the interior of said envelope.

7. An electron discharge device including an evacuated envelope, a closed metallic exhaust tubulation sealed to said envelope and having an interior in communication with the interior of said envelope, a container mounted in said envelope and having an end portion extending into said tubulation, and an active getter material in 8. said container, said container having a fractured finger extending from said portion thereof and into said tubulation, said finger having a hollow interior communicating with the interior of said container and said tubulation, whereby said getter material is free to pass from said container to the interior of said tubulation, said end portion having transverse dimensions for providing a path for getter material between the interior of said tubulation and the interior of said envelope, and for blocking transfer of fractured finger material to the interior of the envelope.

8. An electron discharge device including an evacuated envelope, a metallic exhaust tubulation closed at one end and open at the other, the open end of said tubulation being sealed to said envelope and having an interior in communication with the interior of said envelope, a container mounted in said envelope, and an active getter material in said container, said container having a fractured finger extending into said tubulation, said finger having a hollow interior communicating with the interiors of said envelope and said tubulation, one end of said container extending into said open end of the tubulation to partly close the same for providing a passageway for said getter material from said tubulation to the interior of said envelope, and for blocking transit to the interior of said envelope of fractured finger material deposited in said tubulation when said finger was fractured.

WILLIS E. HARBAUGH. LLOYD GARNER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,188,186 Kling Jan. 23, 1940 2,408,234 Spencer Sept. 24, 1946 2,412,302 Spencer Dec. 10, 1946 2,499,197 Posey Feb. 28, 1950

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