US3920355A

US3920355A - Gettering

Info

Publication number: US3920355A
Application number: US447307A
Authority: US
Inventors: Mario Zucchinelli
Original assignee: SAES Getters SpA
Current assignee: SAES Getters SpA
Priority date: 1974-02-28
Filing date: 1974-03-01
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18
Also published as: IT1016466B

Abstract

A getter device for releasing an evaporable getter metal such as barium in a vacuum tube comprising a ring and a getter metal releasing material attached to the ring. The getter metal releasing material has a zone of high density adjacent to the ring. It also has a zone of low density adjacent to the zone of high density. In getter devices of the present invention, upon release of the getter metal, the getter metal releasing material remains attached to the ring.

Description

United States Patent [191 Zucchinelli Nov. 18, 1975 GETTERING Mario Zucchinelli, Milan, Italy S.A.E.S. Getters S.p.A., Milan, Italy Filed: Mar. 1, 1974 Appl. No.: 447,307

Foreign Application Priority Data Feb. 28, 1974 Italy ..862l7A/74 US. Cl 417/49; 313/174 Int. Cl. F04B 37/02; FO4F 11/00 Field of Search 417/48, 49; 313/174;

Inventor:

Assignee:

References Cited UNITED STATES PATENTS 3,820,919 6/1974 Katz 417/48 Primary Examiner-C. J. Husar Assistant ExaminerG. P. LaPointe Attorney, Agent, or FirmLittlepage, Quaintance, Murphy & Dobyns [57] ABSTRACT A getter device for releasing an evaporable getter metal such as barium in a vacuum tube comprising a ring and a getter metal releasing material attached to the ring. The getter metal releasing material has a zone of high density adjacent to the ring. It also has a zone of low density adjacent to the Zone of high density. In getter devices of the present invention, upon release of the getter metal, the getter metal releasing material remains attached to the ring.

14 Claims, 4 Drawing Figures 1 ll ll U.S. Patent Nov. 18, 1975 GETTERING Getter devices which release an evaporable getter metal in a vacuum tube are well known. These getter devices generally comprise a ring and a getter metal releasing material attached to the ring. The getter metal is released from the getter metal releasing material by subjecting the ring to radio frequency currents. These radio frequency currents induce heating in the ring and in the getter metal releasing material causing the getter metal releasing material to release its getter metal. Upon release of the getter metal, there is a tendency for the getter metal releasing material to become detached from the ring. This propensity to become detached is true of all getter devices, and is also true of getter devices having a high exposed surface area to mass ratio such as those described and claimed in della Porta US. Pat. No. 3,385,420. Numerous attempts have been made to reduce the tendency of the getter metal releasing material to become detached from the ring. See, for example, Reash US. Pat. No. 3,428,168 which describes the use of a reinforcing member imbedded in .the getter metal releasing material." Unfortunately,

prior attempts to reduce the propensity of the getter metal releasing material to detach itself from the ring have met with only. limited success. Furthermore, detachment of the getter metal releasing material from the ring frequently results in the production of loose particles. These loose particles can cause short circuits and other problems within the vacuum tube.

Accordingly, it is an object of the present invention to provide an improved getter device substantially free of one or more of the disadvantages of prior getter devices.

Another object is to provide an improved getter de- I ing to the present invention, it has been found that the getter metal releasing material remains attached to the ring after release of its getter metal.

Any evaporable getter metal can be employed in the devices of the present invention such as the alkali or alkaline earth metals, examples of which include among towards air and are easier to handle. The preferred getvice in which separation of the getter material from'the ring is minimized.

A further object is to provide an improved getter device which has a reduced tendency to release loose particles.

A still further object of the present invention is to provide an improved getter device accomplishing the above objects without adversely affecting other properties, such as the amount of getter metal released.

Yet another object of the present invention is to provide an improved process for producing a getter device.

Additional objects and advantages of the present invention will be apparent to those skilled in the art by ,reference to the following detailed description and drawings wherein:

FIG. 1 is a partially cut-away plan view of a getter device of the present invention;

FIG. 2 is a sectional view of the getter device of FIG.

'1 taken along line 2 2 of FIG. 1;

-The getter metal releasing material has a zone of high density adjacent to the ring and a zone of lower density adjacent to the zone of high density. In apreferred embodiment of the present invention, the getter device further comprises a third zone of high density. Accordter alloys are those of barium and aluminum, generally in weight ratio of about 10:5 to 10:20, and especially binary alloys containing about 50 to 56% barium, balance aluminum. The getter metals and getter alloys can be employed alone or in admixture with other substances. When employed alone so-called endothermic getter devices are produced. These devices rely upon induction heating in order to provide the heat of vaporization of the getter metal. More preferably the getter alloy is employed admixed with nickel to create an exothermic getter device wherein a portion of the heat of vaporization of the getter metal is supplied by an exothermic reaction between the nickel and the bariumaluminum alloy.

The'getter metal-releasing materials of the present invention preferably contain a small amount of a gasreleasing material as described for example in US. Pat. Nos. 3,389,288 and 3,669,567.

The particulate getter metal releasing material is em ployed in the present invention in the same particle sizes as employed in the prior art. The particulate material generally passes through a US. standard screen of 100 mesh per inch and preferably passes through a US. standard screen of 200 mesh per inch.

In the broadest aspects of the present invention, the

' ring can have any of a variety of forms as long as it retains the getter metal releasing material at least prior to getter metal release. One preferred embodiment of a ring is an annular ring having a bottom wall attached to an inner wall which is substantially vertical and also attached to an outer wall which is also substantially vertical. The bottom wall can have a plurality of holes therein, in order to increase the exposed surface area to mass ratio. The exposed surface area to mass ratio of the getter metal releasing material is generally greater than 0.45 mm lmg and is preferably between 0.6 and 0.8 mm /mg. The ring is preferably constructed of a material which can be heated by radio frequency currents. Examplesof such an inductively-heatable material include among others iron, nickel and stainless steel.

Referring now to the drawings and in particular to FIGS. 1 and 2, there is shown a getter device 10 of the present invention comprising an annular ring 11 and a getter metal releasing material l2attached to the ring 11. The ring 11 comprises a bottom wall 14 attached to an outer wall 15 and an inner wall 16. The bottom wall I 14 is provided with a plurality of

holes

18, 19. The getpressed free-flowing state is placed in the ring 11. A plate 30 is placed underneath the ring 11 in order to keep the material 12 from flowing out of the ring 11 through the hole 18. The upper surface 32 of the uncompressed material 12 is substantially planar. A die 33 having a first flat annular surface 34 and a second flat annular surface 35 and having an annular depression 36 between the

surfaces

34 and 35 is placed above the material 12. The die 33 is then moved downwardly causing the material 12 to be compressed unevenly. The zones of the material 12 underneath the

flat surfaces

34 and 35 will becompressed to a greater degree than the zone of the material 12 underlying the depression 36. The greater degree of compression is caused by a reduction in the amount of free space in the material which gives zones of different bulk densities in the compressed material 12. The compression in all zones is sufficient to cause the particles of the material 12 to adhere to one another.

As shown in FIG. 4, the getter device produced by the above described process has an annular zone 40 of high density adjacent to the outer wall 15. The device 10 also has an annular zone 41 of high density adjacent to the inner wall 16. Between these

zones

40 and 41 is an intermediate zone 42 which has a density less than that of

zones

40 and 41. The upper surface 43 of the getter metal releasing material 12 has an elevated annular ridge 44 which is substantially concentric with the annular ring 11. The ridge 44 has a radius of curvature, R, which is greater than the depth of the getter metal releasing material 12.

The instant invention is further illustrated by the following nonlimiting example intended to described the best mode contempated for practicing the invention.

EXAMPLE A getter device 10 as shown in FIGS. 1 and 2 having a ridge 44 is produced by pressing into an annular ring 11, 460mg of an alloy containing 56 weight percent barium, balance aluminum; 516mg nickel; and 24mg Fe N, in the manner described herein with reference to FIGS. 4 and 5. A number of such getter devices 10 are each placed in a vacuum tube and heated by a radio frequency induction coil until the barium is evaporated. Identical tests are conducted with prior art getter devices identical to the getter device 10 but having no ridge 44. Fewer of the getter devices of the present invention exhibit undesirable separation of the getter metal releasing material 12 from the ring 11 than do the prior art getter devices.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.

What is claimed is:

1. A getter device for releasing an evaporable getter metal in a vacuum tube, said device comprising:

A. a ring,

B. a compressed, particulate getter metal releasing material attached to the ring, said getter metal releasing material having a zone of high density adjacent to the ring and a zone of lower density adjacent to the zone of high density;

whereby upon release of the getter metal, the getter metal releasing material remains attached to the ring.

2. The getter device of claim 1 wherein the ring is an annular ring having a bottom wall attached to an inner and an outer wall, wherein the getter metal releasing material is in particulate form, the particles of which are compressed to different densities within the annular ring, wherein said different densities are achieved by reducing the amount of free space in the getter metal releasing material, said getter metal releasing material having a first annular zone of high density adjacent to the outer wall of the annular ring and a second annular zone of high density adjacent to the inner wall of the annular ring and an intermediate annular zone of density lower than the density in either the first or the second zone, said intermediate zone lying between the first and second zones being contiguous thereto.

3. The getter device of claim 2 wherein the upper surface of the getter material is non-planar and comprises an elevated annular ridge spaced from both the inner and the outer walls of the ring.

4. The getter device of claim 1 wherein the surface of the getter metal releasing material has a first planar portion adjacent to the outer wall of the ring and substantially perpendicular thereto and a second planar portion adjacent to the inner wall of the annular ring and substantially perpendicular, thereto said first and second surfaces being contiguous with a third surface which is curved above the first and second surfaces.

5. The getter device of claim 1 wherein the particulate getter metal releasing material in its uncompressed state has a particle size such that it passes through a US. standard screen of mesh per inch.

6. The getter device of claim 1 wherein the particulate getter metal releasing material in its uncompressed state has a particle size such that it passes through a US. standard screen of 200 mesh per inch.

7. The getter device of claim 1 wherein the getter metal releasing material is a mixture of an alloy of barium with aluminum in particulate form mixed with particulate nickel.

8. The getter device of claim 1 further comprising a ceramic heat insulating base attached to the ring and extending substantially completely underneath the ring.

9. The getter device of claim 1 wherein the ring is constructed of an inductively heatable material.

10. The getter device of claim 1 wherein the exposed surface area to mass ratio of the getter metal releasing material is greater than 0.45 mm /mg.

11. The getter device of claim 1 wherein the exposed surface area to mass ratio of the getter metal releasing material is between 0.6 and 0.8 mm /mg.

12. A getter device for releasing a evaporable getter metal in a vacuum tube, said device comprising:

A. an annular ring having a vertical outside wall, a bottom wall attached to the vertical outside wall and an inner wall attached to the bottom wall, said bottom wall having a plurality of openings therein; B. a particulate getter metal releasing material, the particles of which adhere to one another within the annular ring, wherein the exposed surface area to mass ratio of the material is greater than 0.45 mm /mg; said getter metal releasing material having a first annular zone wherein the particles are highly compressed said first annular zone being adjacent to the outer wall;

said getter metal releasing material having a second annular zone wherein the particles are highly compressed said second annular zone being adjacent to the inside wall,

said getter metal releasing material having a third zone of compression sufficient to make the particles adhere to one another but less than the compression of the first and second zones, said third zone lying between said first and second zones; whereby upon release of the getter metal, the getter metal releasing material remains attached to the annular ring. 13. A getter device for releasing an evaporable getter metal in a vacuum tube, said device comprising:

A. a ring; B. a compressed, particulate getter metal releasing material attached to the ring wherein the upper surface of the getter metal releasing material has an annular ridge substantially concentric with the annular ring. 1

14. A process for producing a getter device comprising an annular ring and a getter metal releasing material within the annular ring wherein said getter metal releasing material has a reduced tendency to separate from the annular ring during heating by radio frequency currents, said process comprising the steps of:

- l. placing a particulate getter metal releasing material in the annular ring;

ll. compacting the particulate getter metal releasing material to a greater degree in a zone adjacent to the outer wall and in a zone adjacent to the inner wall than in a zone intermediate between the zone adjacent to the outer wall and the zone adjacent to the inner wall.

Claims

1. A getter device for releasing an evaporable getter metal in a vacuum tube, said device comprising: A. a ring, B. a compressed, particulate getter metal releasing material attached to the ring, said getter metal releasing material having a zone of high density adjacent to the ring and a zone of lower density adjacent to the zone of high density; whereby upon release of the getter metal, the getter metal releasing material remains attached to the ring.

5. The getter device of claim 1 wherein the particulate getter metal releasing material in its uncompressed state has a particle size such that it passes through a U.S. standard screen of 100 mesh per inch.

6. The getter device of claim 1 wherein the particulate getter metal releasing material in its uncompressed state has a particle size such that it passes through a U.S. standard screen of 200 mesh per inch.

10. The getter device of claim 1 wherein the exposed surface area to mass ratio of the getter metal releasing material is greater than 0.45 mm2/mg.

11. The getter device of claim 1 wherein the exposed surface area to mass ratio of the getter metal releasing material is between 0.6 and 0.8 mm2/mg.

12. A getter device for releasing a evaporable getter metal in a vacuum tube, said device comprising: A. an annular ring having a vertical outside wall, a bottom wall attached to the vertical outside wall and an inner wall attached to the bottom wall, said bottom wall having a plurality of openings therein; B. a particulate getter metal releasing material, the particles of which adhere to one another within the annular ring, wherein the exposed surface area to mass ratio of the material is greater than 0.45 mm2/mg; said getter metal releasing material having a first annular zone wherein the particles are highly compressed said first annular zone being adjacent to the outer wall; said getter metal releasing material having a second annular zone wherein the particles are highly compressed said second annular zone being adjacent to the inside wall; said getter metal releasing material having a third zone of compression sufficient to make the particles adhere to one another but less than the compression of the first and second zones, said third zone lying between said first and second zones; whereby upon release of the getter metal, the getter metal releasing material remains attached to the annular ring.

13. A getter device for releasing an evaporable getter metal in a vacuum tube, said device comprising: A. a ring; B. a compressed, particulate getter metal releasing material attached to the ring wherein the upper surface of the getter metal releasing material has an annular ridge substantially concentric with the annular ring.

14. A process for producing a getter device comprising an annular ring and a getter metal releasing material within the annular ring wherein said getter metal releasing material has a reduced tendency to separate from the annular ring during heating by radio frequency currents, said process comprising the steps of: I. placing a particulate getter metal releasing material iN the annular ring; II. compacting the particulate getter metal releasing material to a greater degree in a zone adjacent to the outer wall and in a zone adjacent to the inner wall than in a zone intermediate between the zone adjacent to the outer wall and the zone adjacent to the inner wall.