US2043724A - Vacuum tube - Google Patents

Description

June 9, 1936. G. ANDERSON YIVACULDIM TUBE Filed Oct 25, 1932 INVENTOR AHOMER G. ANDERSON 84M %M Arron/Ex Patented June 9, 1936 UNITED STATES 2,043,724 VACUUM TUBE Homer G. Anderson, Waltham,

Raytheon Production Corporation,

a corporation of Delaware Mass,

Mass, assignor to Newton,

Application October 25, 1932, Serial No. 639,435

7 Claims.

This invention relates to vacuum tubes, and particularly to gett'ers therefor. Gettering material for vacuum tubes is ordinarily made up in the form of small pellets which are supported within a getter cup. This getter cup together with the pellet therein are heated to a high temperature, usually by high frequency induction, at which temperature the getteris vaporized or fiashedf, and "cleans up the residual gases Within the tube. I have found that barium oxide and aluminum, when finely divided and mixed together, form a very efiicient getter. This mixture can be very easily flashed, and the portion of the envelope upon which the barium condenses may be easily regulated. I-Iowever, when attem ts are made to compress this powdered mixture into a pellet form, I have found that the pellets swell up and finally disintegrate within a comparatively short period of time; This is prob- 20 ably due to the fact that the pressure causes the barium oxide to change tothe hydroxide orperoxide. These latter compounds are very difficult to flash, and are practically useless as a getter.

In order to use the above getter in the form of a pellet, sucli pellets must be put into the tube and flashed within such a very short period after they have been made up that their use as a getter is entirely impracticable. In accordance with my invention I am able to avoid this difficulty by so placing the mixture in its original powdered form within a; special getter cup without exerting any pressure on the mixture. In this manner my powdered getter may be prepared and placed in the getter cups, or not, for considerable periods' of time before being utilized in a vacuum tube without impairing the effectiveness thereof to-any appreciable degree. p

My invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing, wherein:

Fig. l is a cross sectional view of a getter cup partially completed;

Fig. 2 is a similar cross-sectional view thereof after the getter has been placed in the cup and the cup has been completed; and

Fig. 3 shows a portion of a vacuum tube structure with my novel getter cup supported thereon.

In preparing my getter I heat barium peroxide in powdered form to a comparatively high temperature to reduce it to barium oxide. This temperature is usually above 800 C. After obtaining the oxide in powdered form, I mix it thoroughly with sufficient powdered aluminum to reduce the barium oxide to barium. An excess of aluminum over that theoretically required is desirable. I prefer to use a mixture of four parts by weight of barium oxide to one part of aluminum. In some cases I add powdered magnesium to the above mixture.

In forming my getter cup, I first form a cup blank I, preferably of thinflnickel and having a cylindrical upper portion 2. open at its upper end and closed by a wall 3 at its lower end. The cylindrical portion 2 in its original form is provided with perfectly straight cylindrical walls.

The lower wall 3 is then embossed to provide a pocket 4 in the middle thereof, leaving anannular ledge 3' around said pocket. In assembling the getter within said cup, I first of all place a quantity of the getter mixture 5 within the pocket 4. In order to retain the powdered material 5 in the pocket 4, .I place a retaining member 6 above said material. This retaining member is formed of a disk of wire mesh 1, preferably of nickel, to the lower side of which is pasted a disk of metal foil 8. This foil is preferably of aluminum, although any other suitable metal, such as magnesium, could be used. This foil is pasted to the wire mesh 1 by some suitable material, such as nitro-cellulose. Of course the foil 8 and the mesh 7 could be inserted into the cup I separately, in which case pasting would be unnecessary. However, I prefer to insert these elements as a unit. In order to retain the powdered mixture and the retaining member 6 within the cup, I spin a groove in the side walls of the cylindrical portion 2 of said cup immediately above the annular ledge 3'. This forms an annular projection 9 within said cylindrical member 2. The edge of this retaining member 6 is thereby firmly retained between said projection l and the ledge 3', whereby said member 6 together the materials under it are retained within the getter cup. In filling the pocket 4 with the powdered getter, it is desirable to take care that the level of the powder is below the level of the annular ledge 3, and also that none of the powder is deposited on said ledge. This is to insure that none of the pressure exerted on the retaining member 6 when fastening it in the getter cup is transmitted to the powdered getter. In order to support the getter cup Within a vacuum tube, I preferably weld asupporting wire I 0 to the side of the cylindrical portion 2 of said cup. This wire I 0 may be Welded to any suitable part of the vacuum tube structure, and preferably to a supporting standard I l sealed in the usual glass press l2 of a vacuum tube, said standard ll being one of .the standards supporting the usual electrode structure l3.

After the getter cup has been assembled within the vacuum tube, as described above, the tube is evacuated and sealed in accordance with the usual practice. The getter cup I, together with the mixture therein, are then heated to a comparatively high temperature by some suitable means, such as high frequency induction, at which temperature the aluminum powder reacts with the barium oxide to reduce it and liberate pure vaporized barium. Said vaporized barium passes out into the vacuum tube and is deposited upon the walls thereof. In this manner the barium performs the well-known gettering function. During the reaction which takes place between the barium oxide and the aluminum, the foil either partakes of this reaction or else is easily fused, so that the continuity of the foil is destroyed and the barium is free to escape through the interstices of the wire mesh I. However, before this reaction takes place, the foil efiectively prevents any of the powdered material from escaping from the cup. In absence of this foil, however, it will be seen that the powdered mixture would readily sift out through the interstices of the wire mesh 1.

Of course it is to be understoodthat this invention is not limited to the particular details of construction, materials or processes as described above, as many equivalents will suggest themselves to those skilled in the art. For example, the foil '6 could be sealed to the annular ledge 3' so as to make the connection hermetically tight. This would prevent the possibility of water vapor and other impurities from contaminating the getter. Instead of having the member I in the form of a wire mesh, it could be a perforated metal disk or any other form which would retain the foil 6 and the powdered mixture beneath it within the cup. Also the getter cup which I have described could be used to hold other getters than those I have described. Such getters could be either in powdered or in pellet form. If pellets are used, it is usually unnecessary to utilize the foil 8, and the wire mesh 1 alone is used. Various other changes in my device will readily suggest themselves.

It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is: V

1. In combination, a hollow metal cup closed at one end and open at the other end, a pocket in said closed end, a mixture of powdered barium oxide and powdered aluminum in said pocket, an aluminum foil covering said mixture, a perforated member covering said foil, and means for retaining said perforated member within said cup to retain said foil and mixture therein.

2. In combination, a hollow metal cup closed at one end and open at the other end, a pocket in said closed end, a powdered getter in said pocket, a metal foil covering said getter, a perforated member covering said foil, and means for retaining said perforated member within said cup to retain said foil and getter therein.

3. In combination, a hollow metal cup closed at one end and open at the other end, a pocket in said closed end, an annular ledge surrounding said pocket, a powdered getter in said pocket, a metal foil covering said getter and resting on said annular ledge, a perforated member covering said foil, and means engaging the outer side of said perforated member to hold said perforated member and'said foil firmly against said ledge, whereby said getter is retained in said pocket.

4. In combination, a hollow metal cup closed at one end and open at the other end, a pocket in said closed end, a getter in said pocket, a metal foil covering said getter, a perforated member covering said foil, and means for retaining said perforated member within said cup to retain said foil and getter therein.

5. In combination, a hollow getter cup having an opening for the escape of vaporized getter material, a finely-powdered getter within said hollow cup, closure means comprising an imperforate foil covering said getter material and preventing the escape of the particles thereof from said cup, the foil being made of a material of which the continuity is readily destroyed by the flashing of the getter material, said cup being constructed to retain its continuity during said flashing.

6. In combination, a hollow getter cup having an opening for the escape of vaporized getter material, a finely-powdered getter within said hollow cup, and imperforate closure means covering said getter material and preventing the escape of the particles thereof from said cup, said closure means comprising a material of which the continuity is readily destroyed by the flashing of the getter material, said cup being constructed to retain its continuity during said flashing.

7. In combination, a hollow getter cup having an opening for the escape of vaporized getter material, a finely-powdered getter within said cup, and closure means covering said getter material and preventing the escape of particles thereof from said cup, said closure means being constructed to have its continuity destroyed by the flashing of the getter material, said cup being constructed to retain its continuity during said flashing.

HOMER G. ANDERSON.

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