US3189397A - Method of getter flashing - Google Patents

Description

June 15, 1965 .1.B. Fl'rzPATRlcK Erl-Al.y g 3,189,397

METHOD 0F GETTER FLASHING Filed Feb. 28. 1961 United States Patent O 3,189,397 METHOD OF GETTER FLASHWG John B. Fitzpatrick, Essex County, NJ., and William O. Zvonik, Flushing, FLY., assignors to Radio Corporation of America, a corporation of Delaware Filed Feb. 23, 1961, Ser. No. 92,245 2 Claims. (Cl. Sid-25) This invention relates to electron tube mounts in which space allocations are relatively limited, and to a novel method of flashing a getter for increased yield of active getter material.

One type of electron tube in which the invention iinds particular utility is generally known as a pencil tube. This tube comprises an elongated envelope including two metallic end portions. In one of the metallic end portions is housed a complement of cylindrical electrodes displosed concentric relation, and in the other end portion are located a getter structure as well as getter and heater supports in the form of lead-in wires or conductors.

One of the problems involved in housing the supports for the heater and getter structure, as well ash the getter structure itself, in their associated tube end portion, concerns the space available for this purpose. Since the inner diameter of this portion is only about three-sixteenths of an inch, suitable space allocation for the several supports and the getter structure, with assurance of freedom from undesirable electrical shorts therebetween, presents a serious diliiculty. t

Another problem is related to the getter structure. Due to the relatively large amount of metal used in the construction of a pencil type tube, an appreciable amount of residual gas remain occluded in the metal after tube seal-off. The getter is relied on to take up such gas during the life-time of the tube. Consequently a relatively large amount of active getter material is needed to produce a tube having a desired long service life. In some applications, Such as use in satellites, it is desirable that the tube have an operating life as long as twenty-flve thousand hours.

One known way of evolving a relatively large amount of gas absorbing material from a getter ilash is by reliance on an exothermic reaction of the material of which the getter is composed. However, such exothermic reaction occurs only when the getter material is raised to a relatively high temperature.

Heretofore, in tubes of the type discussed, it has not been feasible to heat a getter having the desired amount of` active getter material for the long life indicated, to a required tlashing temperature, for several reasons. The getter structure for a pencil tube must necessarily be of a type heated by electrical power fed to it directly by electrical conductors. This is a consequence of the metallic enclosure of the region in which the getter is located, which makes it impossible to heat the getter by induction from an exterior source. Sincethe region referred to is hermetically sealed from the ambient, it is necessary for the electrical conductors to be hermetically sealed through the wall of the enclosure. The seal is effected through the insulating header aforementioned.

The relatively small diameter of the insulated header requires the use of conductors of relatively small cross section. Such small cross section of the conductors limits the amount of electrical power that can be carried safely thereby preserving the seals through the header from damage. This limit in power carrying ability is below that required for ashing a getter having the desired amount of active getter material for relatively long tube life.

Accordingly it is an object of the invention to provide an improved electron tube.

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A further purpose is to provide an improved method of flashing a getter.

Briefly considered, a getter mount according to the in-` vention comprises lead-in conductors sealed through an insulating header and connected to spaced portions of a` getter structure. The cross-sectional area of the getter structure is relatively large in order to contain a sutiicient amount of active getter material for relatively long tube life. The cross-sectional area of the conductors is relatively small to avoid the development of objectionable strains in the header, and to conserve space within the tube envelope. Thus, the relationship between the cross-Sectional areas of the getter structure and the conductors is unfavorable to seal preservation during the passage through the conductors of electrical power suflicient to flash the getter.

According to one aspect of the invention a novel method of dashing the getter is provided which renders the aforementioned relationship between the cross-sectional areas of the conductors and getter structure, favorable with respect to seal preservation. This makes it feasible to house conveniently a relatively large getter structure within a relatively small space provided in the tube. An important contribution to this feasibility resides in the fact that the lead-in conductors do not require enlargement of their cross-sections, Consequently, the conductors do not impose an added accommodation burden on the relativeiy small space aforementioned.

Briefly stated, the novel method. of the invention involves cooling the lead-in conductors and the header while the getter structure is energized to flashing temperature, the cooling being continued for a short time after v flashing to remove residual heat from the getter structure.

One way, by way of example of the invention, in which the cooling may be accomplished is by immersing the entire tube including the exterior portions of its leadin conductors, in a relatively cool insulating liquid such as deionized water, during the liashing operation.

The cooling step aforementioned prevents the lead-in conductors from reaching a temperature at the seal regions high enough to harm the seals. In the absence of such cooling the relatively large amount of power conducted by the lead-ins to, and as required for flashing by, the relatively large getter structure, would raise the conductors to a temperature adverse to the seals.

Further objects and features of the invention will become apparent as the present description continues.

Reference to the drawing for a more detailed considera tion of an example embodying the invention, will reveal that:

FIG. l is a fragmentary elevational view, partly in section, of an electron tube having a getter mount incorporating the invention;

FIG. 2 is a transverse sectional View taken along the line 2 2 of FIG. 1;

FIG. 3 shows an enlarged cross-section of the getter, taken along the line 3--3 of FIG. l; and

FIG. 4 shows an elevation partlyl in section, of apparatus useful in practicing the method aspect Iof the invention.

There are two known complementary techniques for removing gases from the envelopes of electron tubes. One is by pumping the gases out through an exhaust tubulation communicating with the interior of the tube. The other is by the action of a getter within the tube envelope, which, after sealing the exhaust tabulation, is heated to release a material, such as barium, for chemically combining with any gas remaining or evolved within the envelope.

To perform its function of reacting with gases within the tube envelope, it is necessary that the getter be heated mais? to a hashing temperature, at which it releases its gas absorbing material. Where the getter is disposed in an envelope having a glass portion surrounding the getter, it is customary to raise the getter to its hashing temperature by inducing radio frequency energy therein by a coil positioned exteriorly of the envelope. However, where the envelope portion surrounding the getter is made of a metal that shields the getter from exteriorly applied radio frequency energy, it is customary to connect spaced portions of the getter structure to electrical conductors that are sealed through the tube envelope, and to subject the conductors to a potential difference. in this way, electrical current is fed through the getter structure and as a consequence of the dissipation of electrical energy therein, the getter structure is raised to the desired flashing temperature.

The amount of getter material in the getter structure is a significant factor in the life duration of an electron tube. If a relatively small amount of getter material is provided, its full depletion will occur within a relatively short time, and the subsequently evolved gases will be free to adversely affect tube operation.

One tube type that is particularly adapted for use in satellites by virtue of its relatively rugged structure, is the so-called pencil tube. This type of tube, an example of which is shown in FIG. 4, includes a metal end portion or sleeve 12 housing the getter structure 14. The getter structure is supported on lead-in conductors 15, 18 passing through a disc shaped header 20 made of soft glass or ceramic (FIG. 1). For reasons of economy, most pencilV tube types employ headers of soft glass, such as Corning Glass No. 0120. The lead-in conductors 16, 18

Vare of a type known as Dumet which comprises a structure including a core of an alloy of iron and nickel and a sheath Iof copper.

As a consequence of the metallicenclosure of the getter structure by the sleeve 12, which may be made of steel, it is necessary to heat the getter 14 to flashing temperature by passing electrical current therethrough by means of the conductors 16, 18. Heretofore, the amount of current that could be passed through the conductors 16, 1% was limited to a value sufficiently low to preserve from harm the seals formed between the header 20 and the conductors 16, 18. This current value was 4.2 amperes at 2 volts. This limitation restricted the getter to a cross-section of relatively small size, in order to produce the required characteristic resistance of about 10 ohms per meter, required for getter flashing. A tantalum ribbon having the aforementioned resistance and cut to the specific length required was capable of containing only from 0.4 to 0.6 milligram of getter material such as barium berylliate.

The foregoing limitation on the amount of getter material yield was accounted for in the case of tubes having headers of soft glass of the type described, by the strainpoint temperature of such glass and its coefficient of expansion. The strain-point temperature of the glass described is about 395 C. At this temperature strains may be introduced into the glass body of the header. Some of such strains may be harmful to header stability. The coeicient ofV expansion of Corning Glass No. 0120 is about S9 10-'l inches per inch per degree centigrade, while the longitudinal coecient of expansion of the Dumet conductors is 65 l0*7 inches per inch per degree centigrade. This difference in expansion characteristics between the header and conductors is harmful to the seals between the conductors and the header, when the conductors are heated to an appreciable temperature.

According to the invention there is provided a getter structure adapted to yield 5 milligrams of free barium for a pencil type tube, and to use a power input of from 20 to watts, involving a current of 13 amperes without enlarging the cross-section of the conductors 16, 18. This represents an increase in getter material yield of about 2,500 percent above that heretofore obtainable, and conl ributes to the attainment of a tube life of the order of 25,000 hours.

The getter mount according to the invention includes a header 20, which may be made of Corning Glass No. 0120 for example, through which Dumet leads 16, 1S, 22 and Z4 are sealed (FIGS. 1 and 2). The Dumet leads are of a size heretofore used, Le., 20 mils in diameter. The header 20 has a diameter of about 0.2 inch and is about 0.08 inch thick. Lead-in conductor 16 serves exclusively as a conductor and support for the getter structure 14. Lead-in 13 serves the dual function of conductor and support for the getter structure and as a conductor for the heater 26. lead-in 22 is connected only to the heater 26. Lead-in 24 (FG. 2) serves the sole function of providing a symmetric array of lead-ins in the header to balance any strains in the glass of the header produced by the other lead-ins. lts inner end terminates ush with the upper surface of header 20 (FIG. 1). its outwardly extending portion 28 is cut off prior to the completion of the tube. Lead-in 24 serves to preserve a predetermined strain pattern in the header, thereby conditioning the header to withstand without harm, mechanical and temperature shocks.

Lead-in 18 serves as the common conductor for the getter structure 14 and header 26 in the interests of space economy within the sleeve 12. Such economy is mandatory in View of the relatively large size of the getter structure 14. If the lead-in 24 were elongated to engage the upper end of the getter structure as viewed in FlG. 1, to provide independent leads for the heater and getter, it would render the region within the sleeve 12 so cramped that electrical shorts between the several conductors therein might occur.

The getter structure 14 (FIG. 3) includes a sheath 30, which may be made of iron and within which is disposed a body 32 comprising a matrix of nickel impregnated with a barium yielding material such as a barium-aluminum alloy, which contributes to an exotherrnic reaction, or the material may be barium alone. Any other active source of barium may be used.

The getter sheath 30 includes a thinned down portion 34 extending between shoulders 36, 3S formed in the sheath. The thickness of the thinned down portion 34 is about 0.002 inch, while the thickness of the other portions of the sheath 30 is about from 0.010 to 0.015 inch.

The thinned down portion 341 of the getter sheath constitutes a zone of weakness which ruptures during getter flashing. Such rupture occurs partly as a consequence of volatilization of the material of the thinned down portion in response to heat generated therein by the flashing current, and partly in response to pressures created by the getter body 32 when heated by the sheath. The shoulders 36, 3S constitute effective means for properly directing the flash of the appreciably increased volume of active getter material, to a region in which it is harmless to tube operation. lt is preferred that the getter structure 14 be disposed substantially parallel to the axis of sleeve 12. In this way the getter material expelled by the ash will impinge on the inner wall of the sleeve 12 and assure absence of getter material on the inner surface of header 20 and on the lower surface, as viewed in FIG. l, of a spacing disc 40, made of mica for example, and Serving to space heater leads 18 and 22 from each other. Such absence of getter material on the surfaces referred to precludes current leakage thereacross between conductors having different potentials.

While the current carrying capacity of the getter conductors 16, 18 is adequate for a getter structure of relatively small size and containing from 0.4 to 0.6 milligram of getter material, it presents a serious problem in connection with a getter adapted to yield 5 milligrams of getter material, and requiring appreciably more electrical current for hashing.

This problem arises because as indicated before herein,

the conductors in each case are restricted to a diameter of mils. in order to avoid an undesirable strain pattern in the header, and in the interests of space economy within the sleeve 12. Prior getter structures yielding relatively small amount of getter material referred to, comprised a tantalum ribbon or trough having a relatively small cross-section characterized by a resistance of about 10 ohms per meter and were limited to a power input of from 2 to 10 watts. The getter structure according to the invention, on the other hand, comprises a sheath of material such as iron and having a relatively large cross-section involving a resistance of only 1.3 ohms per meter. Since the conductors for both getter structures are required to be of the same size, as pointed out above, it is obvious that the dissipation of electrical energy must be greater for getter flashing, in the conductors serving the larger getter than in those serving the smaller getter. It was found that the energy dissipated in the conductors associated with the smaller getter were such as to heat the conductors to a temperature below 395 C., the strain-point temperature of the glass header. However, the energy dissipated in the conductors serving the larger getter required a power input resulting in a temperature in the conductors as high as 800 C. Such high temperature was harmful to the seals between the conductors and the header through which they pass and could not be tolerated in the manufacture of electron tubes.

According to a method aspect of the invention, the foregoing difficulty is avoided. According to this method aspect, the tube 10 (FIG. 4) is evacuated to a desired degree by a suitable pumping system (not shown) and an exhaust tubulation 42, made of copper for example. After exhaust, the exhaust tubulation is sealed ohc by urging together opposite wall portions thereof with sucient force to produce a weld therebetween without the deliberate application of heat. Thereafter the tube l0 is suspended in a beaker 44 made of glass for example, and containing a cooling liquid 46. The suspension of the tube in the beaker is effected by engagements between clamps 48, S0 and conductors 1S, 15 respectively. The clamps 48, 50 are xed to conducting rods S2, 54 respectively. The rods are adjustably mounted on an insulating support 56, and according to one example, are connected to a power supply (not shown) of 11 amperes at 2 volts. A switch 58 is adapted to selectively connect and disconnect the conducting rods 52, 54 from the power source aforementioned.

A getter dashing operation according to the invention is effected by closing switch 58 for about six seconds, with the tube 10 suspended in the cooling liquid as aforementioned. It is found that this interval of time is long enough to tiash the getter, whether it be of the exothermic type or of the endothermic kind. lt is further found that during this period, the leads 16, 18 do not heat up to a temperature adverse to the conductor seals.

Since the energization of the getter structure 14 (FIG. 1) to ashing temperature involves heating the sheath 30 thereof (FIG. 3) to a temperature sufciently high to fuse the thinned down portion 34 thereof and vaporize the active getter material 32, it is found necessary to allow the tube 10 to remain in the cooling fluid 46 for about a minute after the switch 58 is opened, to allow residual heat in the sheath to become dissipated by conduction through the conductors 16, 18 to the cooling fluid. Without such dissipation of the residual heat in the sheath 30, there is danger that this residual heat might harm the conductor seals aforementioned.

The cooling liquid 46 should be non-electrolytic and possess good thermal capacity. Deionized water is preferred. While methanol can be used, its use involves undesirable hazards. Oil can also be used, but it involves a re-cleaning problem.

The liquid 46 should be kept at a cool temperature. Room temperature has been found to be adequate, but temperatures from appreciably below room temperature to as high as C. are tolerable. However, a temperature of 75 C. is about the upper limit of the temperature range that can be used for good results.

The beaker 44, in one example had a capacity of 2 liters. This permitted use of a sufficient quantity of cooling liquid for successively fiashing a relatively large number of electron tubes without raising the liquid to an intolerably high temperature. To keep the liquid cool it may be replaced at intervals or the liquid may be circulated from a relatively large reservoir. Cooling means may also be used for cooling the liquid. If desired, a trough may be used instead of a beaker to permit the simultaneous ilashing of a plurality of electron tubes.

What is claimed is:

1. Method of dashing a getter structure, wherein the getter structure is disposed within an envelope having a glass portion and two lead-in conductors sealed through said glass portion in glass-to-metal seals are connected to spaced portions of said getter structure and have legs extending exteriorly of said envelope, said method comprising suspending a portion of said legs in a relatively 'i cool non-electrolytic liquid while engaging said two lead in conductors only, passing electrical power through said conductors of a magnitude normally accompanied by heat harmful to said glass-to-metal seals of said conductors through said envelope in the absence of cooling by said liquid, said liquid serving to cool said conductors at the regions of said seals to a temperature harmless to said seals, stopping the passage of electric power through said conductors after said getter has dashed, continuing the immersion in said liquid of said leg portions after said stoppage of said electrical power through said conductors, for dissipating residual heat in said getter structure, and removing said legs from said liquid after said residual heat has been dissipated.

2. Method of ilashing within a metal envelope of an electron tube, a getter having two getter leads connected thereto and whose flashing temperature is as high as the temperature which can be achieved only by electric current of a value sufficiently high to heat a portion of said getter leads adjacent to said envelope to a temperature adversely atfecting the subsequent operation of said tube, said method comprising suspending said electron tube by said two getter leads only, in a dielectric liquid at substantially room temperature, at a depth to dispose a portion of said leads adjacent to said envelope in said liquid, applying electric current to said getter leads of a value to generate suilicient heat to raise the temperature of said getter to said flashing temperature while said portion of said leads is immersed in said liquid, stopping the application of electric current to said leads, and then removing said tube from said liquid prior to said subsequent operation of the tube and after residual heat in said getter has been dissipated by conduction through said leads to said liquid.

References Cited by the Exaer RALPH NEILSON, Examiner.

Claims (1)

1. METHOD OF FLASHING A GETTER STRUCTURE, WHEREIN THE GETTER STRUCTURE IS DISPOSED WITHIN AN ENVELOPE HAVING A GLASS PORTION AND TWO LEAD-IN CONDUCTORS SEALED THROUGH SAID GLASS PORTION IN GLASS-TO-METAL SEALS ARE CONNECTED TO SPACED PORTIONS OF SAID GETTER STRUCTURE AND HAVE LEGS EXTENDING EXTERIORLY OF SAID ENVELOPE, SAID METHOD COMPRISING SUSPENDING A PORTION OF SAID LEGS IN A RELATIVELY COOL NON-ELECTROLYTIC LIQUID WHILE ENGAGING SAID TWO LEAD IN CONDUCTORS ONLY, PASSING ELECTRICAL POWER THROUGH SAID CONDUCTORS OF A MAGNITUDE NORMALLY ACCOMPANIED BY HEAT HARMFUL TO SAID GLASS-TO-METAL SEALS OF SAID CONDUCTORS THROUGH SAID ENVELOPE IN THE ABSENCE OF COOLING BY SAID LIQUID, SAID LIQUID SERVING TO COOL SAID CONDUCTORS AT THE REGIONS OF SAID SEALS TO A TEMPERATURE HARMLESS TO SAID SEALS, STOPPING THE PASSAGE OF ELECTRIC POWER THROUGH SAID CONDUCTORS AFTER SAID GETTER HAS FLASHED, CONTINUING THE IMMERSION IN SAID LIQUID OF SAID LEG PORTIONS AFTER SAID STOPPAGE OF SAID ELECTRICAL POWER THROUGH SAID CONDUCTORS, FOR DISSIPATING RESIDUAL HEAT IN SAID GETTER STRUCTURE, AND REMOVING SAID LEGS FROM SAID LIQUID AFTER SAID RESIDUAL HEAT HAS BEEN DISSIPATED.

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