US2890367A - Getter material - Google Patents

Description

June 9, 1959 l. s, HmscHHoRN ETAL 2,890,367

' GETTER MATERIAL Filed July 2, 1957 United States Patent O i GETTER MATERIAL Isidor S. Hirschhorn, West Grange, N J and Thomas H. Briggs, Norristown, Pa., assignors to New Process Metals, Inc., Newark, NJ., a corporation of New Jersey Application July 2, 1957, Serial No. 669,615

3 Claims. (Cl. 313-308) This invention relates to the production of getters for use, in particular, in electron tubes, such as high vacuum tubes and voltage regulator tubes, wherein the getters are to remove residual quantities of undesirable active gases, and in other Vessels of similar type.

Heretofore gettering material was composed of refractory metals, such as titanium, zirconium, tantalum, thorium, etc., either sintered onto or bonded directly to a vital part of the aforesaid vessels.

It is one of the objects of the invention to provide means facilitating the manufacture of gettering material in a desirable precise quantity, configuration or crosssection and gauge as required for optimum and uniform performance of electron tubes.

It is another object of the invention -to provide means conducive to increase of efficiency of gas clean up by the gettering materials contemplated by the invention.

Yet a further object of the invention resides in the pron vision of means affording continuous removal of active gaseous impurities from rare gases present in gaseous discharge tubes and the like.

Still another object of the invention is to provide means contributing to stable tube performance and long life thereof by virtue of the continuous clean up of gases during the operation of electron tubes.

It is still another object of the present invention to provide getters, which are to continuously or otherwise permanently eliminate gaseous impurities over a wide range of practical tube operating temperatures without adversely affecting uniformity of cathode emission, without creating electrically conducting or metallic films across insulators in thermionic tubes, which would cause noise and leakage currents and without causing alteration of interelectrode capacitance.

The invention will be more fully and comprehensively understood from a consideration of the following detailed description with the understanding, that the improvement is capable of extended application and is not confined to the precise disclosure, suggested changes and modifications may be made herein which do not affect the spirit of the invention nor exceed the scope thereof as expressed in the appended claims.

In the attached drawing:

A gaseous discharge tube is shown partly in section, somewhat schematically disclosing a cylindrical cathode and an anode wire both having associated therewith respective materials for gettering and other functions.

The invention will now be described in greater details with reference to certain examples, where were found in practice to give most favorable results in eliminating any damaging effects of undesirable gases developed during cathode emission and during the life of the active tube parts.

Example I About by weight of cerium (mischmetal) together with 5% by weight of aluminum and 80% by weight of thorium are mixed and then sintered in the 2,890,367 Patented June 9, 1959 2 form ofa coating onto predetermined electron tube parts made of a base metal, such as stainless steel, nickel or copper alloy at a temperature ranging from about 600"v to 1000 C.

It has beenffound that tubes containing such alloyed getter materials retain a continually high vacuum and their operative powers are considerably lengthened as compared with tubes having getter materials of heretofore known composition. The temperature according to the invention for obtaining optimum gas removal by these novel getters ranges from about to 900 C. The

special addition of alloy of mischmetal to thorium reduces the active threshold to about 100 C.

The aforesaid coating has the advantage, that no loose' particles of the compound are created by flashing.

The black surface created upon application of the: aforesaid getter material improves heat radiation. More-4 over, the material operates eliciently at temperatures: normally occurring in electron tubes, thus making un necessary auxiliary heating means for the getter activa*- tion.

The aforesaid coating may be applied to a metal strip) which is subsequently cut to size and bonded to mount structures, such as grid radiators, plates, etc.

The temperature range of the gettering material is from about 100 C. to about 900 C. Undesirable deposits in the form of coatings condensed onto cool portions of the electron tubes or loose getter particles may be effectively avoided. Therefore, the aforesaid getter material is particularly attractive for micro-wave and special tubes requiring a high degree of reliability and long life at high ambient temperature.

Example 1I It was further found that cerium (mschmetal) con` taining about 15% to 25% by Weight of iron and 1% to 2% by weight of magnesium is particularly efficient for scavenging active gaseous impurities from rare gases pres-- ent in gaeous discharge tubes or for absorbing gases from vacuum tubes, thereby creating and maintaining a high` degree of vacuum therein.

The aforesaid getter material may be readily extruded; at Ia temperature of about 400 to 450 C. at an extrusion pressure of about 7500 to less than 12,000 kg./' cm.2 whereby an extruded strip having typically a crosssection of .090 inch by .155 inch may be obtained.

The dimensions of strips produced by extrusion can: be readily controlled within one thousandth of one inch,l

making possible production of pellets of uniform dimensions.

cylindrical bodies for a purpose later described.

A rod body of this type may be extruded with a V-V This rod may subsequently beI shaped sectorial cut-out. cut to the required length forming a pellet, which may,

then be forged around an anode wire at an approxi mate temperature of 450 C. and at a pressure of about.. 10,000 kg./cm.2 exerted against the peripheral surface.- of said pellet, causing it to finally unite with said wire: for a purpose, as hereinafter set forth.

This strip or rod material offers also the advantage that the same may be extruded through a die of suchconfiguration that the iinal shape of the strip materialk is conformed to the dimensions of a receptacle, for instance, a rectangular-shaped receptacle made from nickel or similar sheet metal into which the respective preshapedfI alloy pellet lits and which is applied to and located withirs the space of a cylindrical cathode of a voltage regulator tube.

Example III As a further getter material a mischmetal alloy is proposed containing preferably 25% by weight of manganese, the manganese addition varying from 1% to 35% by weight." This getter material may preferably be shaped through ay suitable die in an extrusion press at an 'extrusion temperature of about 400'to 450or C. and at an extrusion pressure of about 5000'to 7500 kg./cm.2, a desired profiled rod form being thus obtained.

Referring now more particularly to `the drawing, there is disclosed schematicallya voltage regulator tube of known construction in which getter material has been incorporated.

Inorder to reduce the work function of the cylindrical cathode surface 15 and thereby to lower the resistance to the ow of electrons with respect to said cathode, an anode pellet V is cut from an extruded rod of preshaped 'configuration as aforesaid,4 and is employed for anchorage on the anode wire 11, for instance of'a voltage regulator tube 12. This pellet 10 may have a diameter of about .155 inch, the length thereof varying from .125 tol .250 inch. The anode wire 11 nay have a diameter of.041 inch. Upon application ofsuitable heat and pressure to the peripheral surface of this pellet having a V-shaped sectorial cutout 10a, said pellet 10 may be intimately united with the anode wire 11.

Thereafter a sputtering action is initiated between the inner surface 14 of the cathode cylinder 15 from which a nickel or iron wire 13 extends, and said pellet of getter material, constituting the anode by applying a voltage of the order of about 500 to 1,000 volts. The extruded cylindrical' body 10 made of a material according to Example Il or III will be vaporized on account of such sputtering action on the inner surface 14 of the cathode cylinder as a coating 15a.Y Y

Thereafter this coating 15a as well as other parts of the vacuum tube will be subjected to a gettering action by vaporizing a pellet of getter material placed in getter box 16 made from sheet metal, such as nickel, which box is squareor rectangular in cross-section and whose abutting box edges 18 remain open to permit escape offvapors therethrough. ByVV placing in this getter box 16 one or more pellets 17 of an alloy as hereinabove disclosed in Example II andupon subjecting said getter box to high frequencyheating current or other known heating means the pellet material after vaporization will be deposited on partsof the tube, such as the colder inner surface-19 of itsV glass envelope 20. The

deposited gettering material may be recognized as a silvery coating-20a and contributes effectively to the desired getter action.

The aforementioned getter materials may act on any active residual or evolved gases not only in vacuum tubes but also in fluorescent lamps whether gas filledA or not. The getter material as indicated'in Example I was found to have extraordinary gas absorptioncapacity vbetween approximately' 100 C. and 900"C. and may be readily applied inthe form of a black and conductive paste coating to be sintcrcd to the supporter mount metal. This getter coating is particularly useful for micro-wave and magnetron tubes requiring a high degree of reliability and long life at high ambient and electrode dissipation temperatures. The addition of cerium (mischmetal)aluminum to thorium creates an alloy which absorbs gases such as O2, H2, N2, CO2, etc. at a far lower temperature (upward of 100 C.) than thorium alone.

Since the coating is conductive, it may be applied to the inside of'an anode without appreciably affecting current drain or it may be painted ona ceramic wafer as stacked in metal-cerarnic tube assemblies to thus become the anode itself.` 1

It is further proposed according to the invention to 4 activate a bulk or coating getter according to Example I immediately subsequent to the manufacture of the tube when the same is to be placed into immediate operation.

if the tube is to be stored for a long period of time prior to its use the getter according to Example i may be easily activated as hereinafter described, enabling the tube to give optimum performance regardless of the length of time elapsed since its manufacture.

For example a magnetron tube may be subjected to high vacuum pumping action and heat for a predetermined period of time of much less than 24 hours, thereby liberating depth gases from its metal parts. However, generation of further gases during ensuing shelf life of the tube has been found to occur. if such tubes must be stored prior to use at relatively low temperatures, as they prevail in arctic regions, such tubes may be further gettered after their storage and immediately prior to use by activation of the aforementioned coating getter. This activation is carried out by placing the tubes in an oven or oil bath at relatively moderate temperatures ranging from 400 C. to 500 C. whereby the coating getter will be activated for several hours. This activating process can be performed at relatively low expense.

A further advantage resides in the use of a similar process during manufacture of these tubes with the result that considerable simplification of conventional large tube processing schedules is obtained.

The getter material according to Example I may be inserted in a micro-wave or magnetron tube at a location where its temperature may be kept low enough to prevent activation during the manufacturing process steps of sealing and tip-off. The advantage of this coating material is that prolonged use of mechanical and diffusion pumps may be dispensed with, and the coating itself will function as a built-in pump before operation of the tube and at any time after storage.

Although preferred embodiments of the invention have been described, it will be understood that modifications may be made within the spirit and scope of the appended claims. It will, however, be understood that there is no intention to include unmentioned ingredients other than minor impurities.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

l. An electron tube comprising a cathode, a grid and .an anode, and respective gettering materials in said tube at predetermined locations thereof, one of said gettering materials being an instantaneous fiash getter for activation during manufacture of said tube, the other getter material being a continuous, coating getter for activation prior to usel and after storage, said one gettering material being an alloy body comprising mischmetal and manganese extruded in rod formation and cut to predetermined length and attached to said anode, said other getter material being a coating comprising mischmetal and aluminum with thorium.

2. A gas discharge tube comprising a cylindrical cathode and an anode wire, a first gettering material united with said anode'wire, a second gettering material, a receptacle associated with said cathode, said second gettering material being disposed in said receptacle and being in the form of a pellet obtained through extrusion of an alloy consisting of mischmetal, iron and magnesium and having a configuration conforming to the shape of said receptacle to tit same, said first gettering material comprising mischmetal and manganese extruded in rod formation and cut to predetermined length, and means in said tube to cause activation of said gettering material for said anode through sputtering.

3. A gas discharge tube comprising an envelope having a cylindrical cathode and an anode wire therein, a first gettering material united with said anode wire, a

second gettering material, a receptacle made of sheet metal and xed to the inner surface of said cylindrical cathode remote from said anode wire, said second gettering material being disposed in said receptacle, said second gettering material comprising an extruded alloy consisting of mischmetal, iron and magnesium in pellet form to correspond to the inner dimensions defined by the walls of said receptacle, said second gettering material being vaporizable by application of high frequency heat within said receptacle whence vapors escape from the latter for deposit as a lm on the inner wall surface of said envelope, the rst gettering material comprising an alloy body of mischmetal and manganese having a V-shaped groove and attached to said anode Wire, and

References Cited in the file of this patent UNITED STATES PATENTS Rentschler Afug. 9, 1932 Atlee Apr. 1, 1947 OTHER REFERENCES Dushman: Scientic Foundations of Vacuum Technique, .lohn Wiley & Sons, New York, 1949, pp. 663 to means on said inner surface of said cathode and extend- 15 666.

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