US3780501A

US3780501A - Getter pumps

Info

Publication number: US3780501A
Application number: US00197819A
Authority: US
Inventors: P Porta; M Zucchinelli; C Pisani
Original assignee: SAES Getters SpA
Current assignee: SAES Getters SpA
Priority date: 1968-08-10
Filing date: 1971-11-11
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25
Also published as: DE1940137A1; NL163054B; DE1940137B2; DE1940137C3; NL163054C; FR2016916A1; NL6911978A; GB1280891A

Abstract

A getter pump comprising a circular pleated strip of metal having a non-vaporative getter material attached to its surface and a heater coaxially disposed within said circular strip.

Description

[ Dec. 25, 1973 References Cited UNITED STATES PATENTS 1/1963 Griessel............................ 417/51 X 3/1967 Hemstreet et a1. 55/389 X 1/1961 Buckman.. 210/493 X 1/1967 Gabbrielli 3/1967 Hetherington........................

ABSTRACT 14 Claims, 5 Drawing Figures 3,167,678 3,309,844 2,968,361 2,984,314 5/1961 Denton 2,778,485 3,309,010

Primary Examiner-John Adee AttorneyDavid R. Murphy A getter pump comprising a circular pleated strip of metal having a non-vaporative getter material attached to its surface and a heater coaxially disposed within said circular strip.

wOOOOOOOO M 0 OOOQ OO ooooodoo if OOOOOOOOOOO Q B0ld 53/04 55/208, 387, 389,

Zucchinelli, both of Milan; Cesare Pisani, Turin, all of Italy Assignee: S.A.E.S. Getters S.p.A., Milan, Italy Nov. 11, 1971 Related US. Application Data Continuation of Ser. No. 761,161, Sept. 20, 1968, abandoned.

Foreign Application Priority Data Aug. 10, 1968 U.S. 55/208, 55/387, 417/51 [58] Field of Search....

United States Patent [1 1 Porta et a1.

[ GETTER PUMPS [75] Inventors: Paolo Della Porta; Mario [22] Filed:

[2]] Appl. No.: 197,819 I INVENTORS PAOLO dELLA PORTA MARIO ZUCCHINELU CESARE PISANI THE'IR AT'roRNEYs mm O O PATENTED UEC25 I975 SHEEI 1 OF 2 PAIENTEBUECZS ms SHEU 2 BF 2 INVENTORS PAOLO dELLA PORTA MARIO ZUCCHINELLI CESARE PISANI BY "1% 0M! 304, 00

FIG .5

THEIR ATroRNsys GETTER PUMPS This is a continuation of application Ser. No. 761,161 filed Sept. 20, 1968 and now abandoned.

Sublimation pumps operating by evaporation of a gas reactive metal such as titanium are commonly used to produce or maintain vacuum in vessels such as electronic tubes. However, such sublimation pumps suffer from a number of disadvantages such as their low rate of gas sorption and the danger of creating short circuits within the electronic tube by depositing the active metal on insulating surfaces. These sublimation pumps require elaborate control units, especially at high gas adsorption rates. Additionally, the reactive metal film which deposits on the inside walls of the vessels is prone to peel off, leaving loose particles in the vessel, which may cause short circuits and other problems.

Accordingly, it is an object of the present invention to provide novel getter pumps substantially free of one or more of the disadvantages of sublimation pumps. Another object is to provide getter pumps capable of sorbing gases at high rates. A further object is to provide getter pumps which do not require complicated control systems. Yet another object is to provide a novel pleated strip carrying a getter material which is especially useful in the getter pumps of the present invention. A still further object is to provide getter pumps which do not require the evaporation of an active metal.

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

FIG. 1 is a partially cutaway view of a getter pump of the present invention;

FIG. 2 is a section taken along line 2-2 of FIG. 1;

FIG. 3 is a section taken along line 3-3 of FIG. 1;

FIG. 4 is a drawing illustrating the method of folding or pleating the strips employed in the present invention to carry a non-vaporable getter material;

FIG. 5 is a section taken along line 5-5 of FIG. 4.

The above and other objects are accomplished according to the present invention by a getter pump comprising a circular strip of metal which is preferably pleated and which has a non-vaporative getter material attached to its surface and a heater coaxially disposed within the circular strip.

Referring now to the drawing, and in particular to FIGS. 1 and 2 there is shown a getter pump comprising a cylindrical housing 11 having therein a plurality of gas passages in the form of holes 12. Attached to the housing 11 by any convenient means, is a base 13, in the center of which is a hole through which passes a shaft 14. The shaft 14 also passes through an electrical and thermal insulator 15 upon which is wound a helical coil of a wire 16 of high electrical resistance, such as tungsten or tantalum. The wire 16 and insulator 15 together serve as a heater, the wire 16 being connected to a suitable source of power, not shown. The insulator 15 is fixedly held coaxially within the housing 11 by means of nut 17 and insulator 18. Attached to the outside of the housing 11 are a plurality of rods 19 each of which is threaded throughout its length and carries

nuts

20 and 21, which fixedly hold an arm 22 which is attached to retainer 23, the purpose and function of which is described below. Each rod 19 also carries

nuts

24 and 25 which fixedly hold spacer 26 annular shield 27 and flat shield 28 by means of a support 29.

Referring now to FIG. 3, there is shown the retainer 23 generally in the form of a sinusoidally curved strip, which holds in place a pleated strip in the form of an annular ring 30. Since the heater wire 16 is positioned coaxially with respect to the ring 30 even heating of the ring 30 is ensured.

The particular structure of the ring 30 is an important feature of the present invention and is best appreciated by reference to FIGS. 4 and 5, wherein a preferred method of formation of the ring 30 from a strip 31 is shown. The strip 31 has a flat portion 32 and a pleated portion 33. As can be seen by reference to the flat portion 32 a powdered getter material 34 is attached to the central portion of the strip 31 and extends towards but terminates short of the

edges

35 and 36 of the strip 31, leaving a margin of the strip 31 free of getter material 34.

The strip 31 contains a plurality of slits 37 which extend transversely across the strip 31 and into the getter free margin. As shown in FIGS. 4 and 5 the annular ring 30 is formed by bending the flat portion 32 as shown in the pleated portion 33 to provide an annular ring 30 having a plurality of generally radially extending planar portions 38 with their adjacent outer extremities attached to one another via a small bridging attachment 39, which is free of getter material. Likewise, the inner extremities of alternate adjacent planar portions 38 are attached to each other via a similar bridging attachment. The above described structure of the strip 31 permits pleating without bending any portion of the strip coated with getter material which might otherwise fall off in the form of undesirable particles. The ring 30 composed of a pleated strip is an especially useful means of confirming a very large surface area for gas sorption to a relatively small volume. The strip 31 can be of any suitable material, but is preferably a metal such as iron or stainless steel, which is softer than the getter material 34. The getter material 34 can be any well known non-vaporative getter material, examples of which include, among others, zirconium, titanium, tantalum or niobium, as well as alloys of two or more of the above. The preferred getter material 31 is an alloy of zirconium and aluminium containing the l to 40% Al, balance Zr and most preferably 84% Zr and 16% Al, available commercially as StlOl. The getter material 34 is employed as a powder in order to have a high surface area to mass ratio facilitating gas sorption. The powder is preferably one which passes through a US. standard screen of 270 mesh/inch. The powder is attached to the strip 31 by any suitable means such as rolling or pressing which does not materially reduce the total surface area of the powder.

In operation, the pump 10 is placed in the tube or vessel to be evacuated and the wire 16 connected in series with a switch and a source of power not shown,

preferably outside the vessel. The vessel is then evacuated to the extent possible by any suitable means, such as a mechanical pump, a vac-ion pump, or a diffusion pump in order to conserve the pumping capacity of the pump 10. To active the pump 10 and cause it to getter residual gases, the switch is closed, causing the wire 16 to heat. This heat is radiated to the strip 31 and the getter material 34 activating the getter material in -a known manner by driving previously adsorbed gases to the center of each particle of getter material leaving a fresh gas adsorptive surface. Power is supplied to the wire 16 such that the temperature of the getter material 34 is held at 600 to 900 and preferably 700 to 800C. At temperatures below the broad range activation is too slow to be practical whereas at temperatures above, the broad range sinterization of the particles of the getter material 34 begins to occur together with diffusion of the metal of the strip 31 both of which tend to reduce the gas adsorptive capacity of the getter material 34.

Once activation is accomplished the getter material 34 is gas adsorptive at room temperature but the rate of gas adsorption can be increased by heating the getter material 34 as described above or more preferably at temperatures of 300 to 450 C to avoid the evolution of hydrogen, which is present in the getter material as a solid solution. The getter material 34 remains gas adsorptive after heating is terminated and continues to sorb gases evolved during the life of the tube. Should an undesirable increase in gas pressure in the tube occur, it is only necessary to supply power to the wire 16 in order to reactivate the getter material 34. In this manner, a very high vacuum can be maintained in a vessel or tube throughout its life until thegetter material 34 becomes saturated with gases.

The getter pumps of the present invention find utility as supplements to vac-ion pumps and diffusion pumps and can be used to create and maintain a vacuum in continuously pumped vacuum syytems and in sorbed vacuum systems. These pumps can be permanently installed in klystron tubes and image intensifier tubes as so called appendage pumps. 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:

l. A getter pump comprising a heater and a metallic strip having a particulate non-vaporable getter metal embedded in its surface, said strip being coaxially disposed around said heater.

2. A getter pump comprising a circular pleated strip of metal having a particulate non-vaporable getter metal embedded in its surface and a heater coaxially disposed within said circular strip.

3. A getter pump of claim 1 comprising:

a. A cylindrical housing having therein a plurality of gas passages.

b. At least one resistance heater axially positioned in said housing.

c. A circular pleated strip of metal having a nonvaporable getter material attached to at least one of its surface, said circular pleated strip surrounding said heater.

4. A getter pump comprising:

a. a pleated metallic strip having a particulate nonvaporable getter metal on at least one surface of the strip, said pleated strip being in the form of an annular ring having a plurality of generally radially extending planar portions wherein the outer extremities of adjacent planar portions are attached to each another and wherein the inner extremities of alternate adjacent planar portions are attached to each other.

b. a heater coaxially disposed within said ring.

5. Apparatus for use in a getter pump comprising:

a. a support b. a pleated metallic strip carried by said support,

said strip having a particulate non-vaporable getter metal on at least one surface of the strip, said getter metal terminating short of the edge, leaving a portion of the strip free of getter metal, said pleated strip being in the form of an annular ring having a plurality of generally radially extending planar portions wherein the outer extremities of adjacent planar portions are attached to each another via that portion of the strip free of getter metal and wherein the inner extremities of alternate adjacent planar portions are attached to each other via that portion of the strip free of getter metal.

b. a heater carried by said support, said heater being coaxially disposed within said ring.

6. A pleated metallicstrip for use in a getter pump having a particulate non-vaporable getter metal on at least one surface thereof, said getter metal terminating short of the edge leaving one portion of the strip free of getter metal, said pleated strip being in the form of an annular ring having a plurality of generally radially extending planar portions wherein the outer extremities of adjacent planar portions are attached to each another via that portion of the strip free of getter metal and wherein the inner extremities of alternate adjacent planar portions are attached to each other via that portion of the strip free of getter metal.

7. The getter pump of claim 1 wherein said heater is a wire of high electrical resistance.

8. The getter pump of claim 1 wherein said heater is a helically wound ceramic insulated wire of high electrical resistance.

9. The getter pump of claim 8 wherein the wire is tungsten.

10. The getter pump of claim 1 wherein the nonvaporable getter metal is harder than the strip and is partially embedded therein.

11. The getter pump of claim 10 wherein said getter metal is a Zr-Al alloy.

12. The getter pump of claim 10 wherein said getter metal is an alloy of 1 to 40% Al balance Zr.

13. A getter pump comprising a heater and a stationary strip of a first metal; particles of a non-vaporable getter metal embedded in the strip; wherein the getter metal is harder than the strip, said strip being axially disposed around the heater.

14. A getter pump comprising a heater and a metallic strip having a particulate non-vaporable getter metal embedded in its surface, said strip being folded along lines which are perpendicular to its length, said strip being formed into a ring the axis of which is parallel to the lines along which the strip is folded, said ring being coaxially disposed around said heater.

Claims

1. A getter pump comprising a heater and a metallic strip having a particulate non-vaporable getter metal embedded in its surface, said strip being coaxially disposed around said heater.

3. A getter pump of claim 1 comprising: a. A cylindrical housing having therein a plurality of gas passages. b. At least one resistance heater axially positioned in said housing. c. A circular pleated strip of metal having a non-vaporable getter material attached to at least one of its surface, said circular pleated strip surrounding said heater.

4. A getter pump comprising: a. a pleated metallic strip having a particulate non-vaporable getter metal on at least one surface of the strip, said pleated strip being in the form of an annular ring having a plurality of generally radially extending planar portions wherein the outer extremities of adjacent planar portions are attached to each another and wherein the inner extremities of alternate adjacent planar portions are attached to each other. b. a heater coaxially disposed within said ring.

5. Apparatus for use in a getter pump comprising: a. a support b. a pleated metallic strip carried by said support, said strip having a particulate non-vaporable getter metal on at least one surface of the strip, said getter metal terminating short of the edge, leaving a portion of the strip free of getter metal, said pleated strip being in the form of an annular ring having a plurality of generally radially extending planar portions wherein the outer extremities of adjacent planar portions are attached to each another via that portion of the strip free of getter metal and wherein the inner extremities of alternate adjacent planar portions are attached to each other via that portion of the strip free of getter metal. b. a heater carried by said support, said heater being coaxially disposed within said ring.

6. A pleated metallic strip for use in a getter pumP having a particulate non-vaporable getter metal on at least one surface thereof, said getter metal terminating short of the edge leaving one portion of the strip free of getter metal, said pleated strip being in the form of an annular ring having a plurality of generally radially extending planar portions wherein the outer extremities of adjacent planar portions are attached to each another via that portion of the strip free of getter metal and wherein the inner extremities of alternate adjacent planar portions are attached to each other via that portion of the strip free of getter metal.

9. The getter pump of claim 8 wherein the wire is tungsten.

10. The getter pump of claim 1 wherein the non-vaporable getter metal is harder than the strip and is partially embedded therein.

11. The getter pump of claim 10 wherein said getter metal is a Zr-Al alloy.