US3187885A

US3187885A - Getter

Info

Publication number: US3187885A
Application number: US239024A
Authority: US
Inventors: Hansen Norbert Ernst Fritz; Flunkert Horst
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1961-11-21
Filing date: 1962-11-20
Publication date: 1965-06-08
Anticipated expiration: 1982-06-08
Also published as: DK108584C; GB1011259A; CH423002A; BE625037A; DE1224845B; NL285519A

Description

June 8, 1965 Filed Nov. 20, 1962 N. E. F. HANSEN ETAL GETTER 2 Sheets-Sheet l INVENTOR HORBERT E.F. HANSEN HORST FLUNKERT lhple' HAG Ea June 8, 1965 N. E. F. HANSEN E TAL 3,

7 GETTER Filed Nov. 20, 1962 2 Sheets-Sh eet 2 INVENTOR HORBERT E.E HANSEN HORST FLUNKERT United States Patent Filed Nov. 20, 1962, Ser. No. 239,024 Claims priority, applicgtigai Ge1rmany,'Nov. 21, 1961,

15 Claims. b1. 206-.4)

This invention relates to a getter for electric discharge tubes and other vacuum vessels which contain zirconium, hafnium, titanium, thorium or an alloy thereof as the activemetal. By a getter is understood in the scope of this application both the active getter in an evacuated vacuum envelope and the not yet activated getter which contains the gettering metal or the hydride of this metal in a nonactivated form, oxide layers being present at the surface.

Known getters consist of compressed tablets, pills, or powder compressed in holders. The starting material usually is obtained by granulating a larger compressed piece which contains the hydride of the gettering metal into grains having diameters smaller than 5 microns, mixed with tungsten grains of a considerably smaller diameter to prevent sintering. A rather coarse sieve fraction of the granulated material then is compressed into getters. The fine powder, as such, is not suitable for being processed directly to getters.

For many uses, the gas absorption rate of the known compressed getters is too small, although the absorption capacity is sufiiciently large. This condition results in the use of many pills, or tablets, or larger holders containing compressed material which, however, is unsuitable for various reasons. I

In accordance with our invention, the getter is a compact but uncompressed mass composed of a plurality of granules, hereinafter referred to as secondary grains arranged in an abrasion resistant manner, preferably in a partially perforated container. Each granule is constituted of an agglomeration of grains each consisting of an active metal such as zirconium, hafnium, titanium, thorium, or an alloy thereof mixed with a refractory metal, such as tungsten or molybdenum, which prevents particles of the active metal from sintering together. The latter grains, hereinafter referred to as primary grains, have a specific surface area as large as possible.

In the getter according to the invention, an assembly is obtained in which the large specific surface area of the primary grains can be reached through short micropores in the secondary grains. The secondary grains can be reached through macropores between these grains. With this assembly, a gas absorption rate is obtained which is higher by at least an order of magnitude as compared with the known getters in which the grains are compressed and in which micropores are hardly present.

In the known compressed getter, substantially only a volume reaction can be operative which corresponds to the so far general conception about gettering. However, such a reaction proceeds very slowly, In the getter according to the invention, the whole surface area can be reached by the gases to be absorbed which are bound in a surface reaction. By the device according to the invention, this surface area can be reached with a pore diffusion of great velocity which can be determined by the combination of micropores and macropores. The experimentally determined diffusion velocities are in good agreement with the theory and the associated calculations. In the known getters, the micropores possibly present, offer no possibility of sufficient diffusion.

In the getter according to the invention, it is necessary for obtaining a gas absorption rate which is as large as 3,187,885 Patented June 8, 1965 possible not to compress the secondary grains, but a small pie-tension of the holder is permissible to ensure an abrasion-resistant location of the grains.

The minimum value for the specific surface area of the grains of the gettering material according to the invention may be about 1 to 2 m? per gram, but considerably better absorption rates are obtained with powder having a specific surface area of from 25 to 30 m per gram. The specific surface area is indicated for the material which is not yet activated. As a result of the activation, a decrease by approximately 30% occurs. The grains of the metal which prevents the sintering together preferably have approximately the same specific area and are present in approximately the same quantities by weight.

If in the getter according to the invention secondary grains of considerably larger diameters are chosen, the micropores are larger also it is true, but the micropores, via which a larger part of the active surface area of the primary grains can be reached, become longer, so that the gas absorption rate is decreased. Therefore, the diameter of the secondary grains should be between a few times 10 microns and a few tenths of a millimeter. The diameter of the largest granules, preferably, should not exceed twice the diameter of the smallest granules. The most favorable dimensions lie between to 200 microns. The secondary grains may be obtained by granulating a larger compressed piece which is obtained with pressure below 5 tons/cm. preferably 1 ton/cm.

The getter, according to the invention, gives not only a higher gas absorption rate, but the degasification and also the removal of the hydrogen, if during the activation a hydride is decomposed, is much easier so that also at higher operating temperatures no noticeable hydrogen pressure is to be feared in contrast with the known devices.

The invention will be described with reference to the accompanying drawing, in which FIGURES 1, 2 and 3 show getters according to the invention.

FIGURE 4 shows the location of the grains; and

FIGURE 5 shows a few gas absorption curves.

Referring now to FIGURE 1, a nickel cylinder 1 of 4 mms. diameter and 4 mms. height is closed at both ends by wire gauze 2 and 3 respectively of chromium-nickel steel, the wire gauze consisting of crossed wires of 30 microns diameter and 30 microns spacing. The cylinder 1 contains secondary grains of a sieve fraction of 100 to 200 microns diameter which is obtained as follows: Zirconium hydride powder having a specific surface area of from 2 to 30 m? per g. is mixed with tungsten powder having approximately the same specific surface area in a weight ratio of 60:40. The whole is compressed under a pressure of 1 ton/cm. and then granulatedn Of this granulate, the sieve fraction stated is used.

In FIGURE 2, the same secondary grains 4 are provided between two wire nets 5 and 6 welded at the edge 7 as a result of which a better access to the grains is obtained. In order to promote heating during the activation, the holder also includes a nickel ring 8 which can be heated by eddy currents. Further, a metal plate laid in the holder may be used.

FIG. 3 shows a cross-section at right angles to the axis of the getter which consists of two

gauze wire rings

9 and 10 of approximately 22 mms. diameter and 12 mms. height which are welded above and below and, in addition, are formed into eight bags by eight axial parallel welds, which bags contain the grains 4.

In FIG. 4 the secondary grains 4 are shown on an exaggerated scale as compared with FIG. 1. The primary grains of zirconium hydride are designated by 12 and the primary grains of tungsten by 13. Although the figure does not show the ratios on a real scale, it is easy to see that the micropores 14 are considerably smaller than the macropores l5.

In FIG. 5, the horizontal axis indicates the quantity of absorbed gas in mm./l while the vertical axis indicates the gas absorption rate in liters/sec. All measurements were carried out with carbon monoxide as a test gas, because this gas forms a large part of the residual gases in cathode-ray tubes and is in addition rather harmful. Curve I relates to a device shown in FIG. 1, in which 50 mgs. of grains were used. Curve II relates to a device shown in FIG. 2, in which the bag of gauze wire'had a diameter of 14 mms. It is relatively easy to see from the two curves that the same quantity of gas is absorbed, but that for the curve 11 the absorption rate through a larger area of the capacity is approximately an order of magnitude larger, which may be explained by the better access to the secondary grains. Curve II relates to the same powder weight as curve 1. Curve III relates to two bags shown in FIG. 2 each filled with 50 mgs. of powder. Curve IV relates to a getter shown in FIG. 3 filled with 500 mgs. of powder. It is easy to see from the four curves that they approach more or les an ideal rectangular curve, that is to say an ideal getter behaves so that the gas absorption rate 5 remains constant up to the entire use of the absorption capacity Q. All the curves relate to starting powder having a specific surface area of 25 m?/ g.

For comparison, curve V is shown which relates to a 'known device in which 26 mgs. of the same powder as for the determination of the other curves was used and in which a tablet of 3.5 mms. diameter and approximately 1 mm. thickness was pressed into a metal strip. FIG. 5 clearly shows that the difference in gas absorption rate between the curves I and V is larger by more than one order of magnitude than was to be expected from the difference between the quantity of powder. The highest gas absorption rate which could be reached with this device for curve V was 3X10 1/ see. with a quantity of 5 X l mm./ 1.

While we have described our invention with reference to specific examples and embodiments thereof, other modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A getter for an electric discharge device comprising a porous body composed of a plurality of separate contacting granules, each of said granules being constituted of a porous agglomeration of grain of an active metal and a refractory metal, said grains having a specific surface area larger than'l m. g.

2. A getter assembly for an electric'discharge device comprising a perforated container, a porous body disposed within said container and composed of a plurality of separate contacting granules, each of said granules being constituted of a porou agglomeration of grains of anactive metal and a refractory metal, said grains having a specific surface area larger than 1 mP/g.

3. A getter for an electric discharge device comprising a porous body composed of a plurality of separate contacting granules, each of said granules being constituted of a porous agglomeration of grains of an active metal and grains of a refractory metal which prevent sintering together of said grain of active metal, said grains of active metal and said grains of refractory metal being present in substantially equal quantitie by weight and having a surface area larger than 1 m. g.

4. A getter as defined in claim .3 in which the surface area of the grains is between about 25 and 30 m?/ g.

5. A getter for an electric discharge device comprising a porous body composed of a plurality of separate contacting granules, each of said granules being constituted of a porous agglomeration of grains of an active metal and a refractory metal, said grains having a specific surface area larger than 1 m. /g., said granules having a a diameter between a few times 10,41 and a few tenths of a millimeter.

6. A getter for an electric discharge device comprising a porou body composed of a plurality of separate contacting granules, each of said granules being constituted of a porous agglomeration of grains of an active metal and a refractory metal, said grains having a specific surface area larger than 1 m. /g., the largest granules having a diameter not exceeding twice the diameter of smaller granules.

7. A getter for an electric discharge device comprising a porous body composed of a plurality of separate contacting granules, each of said granules being constituted of a porous agglomeration of grains of an active metal and a refractory metal, said grains having a specific surface arealarger than 1 m. /g., the diameters of the granules being between about 100 and ZOO/1..

8. A getter for an electric discharge device comprising a porous body composed of a plurality of separate contacting granules, each of said granules being constituted of a porous compressed agglomeration of grains of an active metal and a refractory metal, said grains having a specific surface area larger than 1 m. g. i

A getter asdefined in claim 8 in which the grains have been compressed into granules at a pressure of less than 5 tons/cm.

it A getter as defined in claim 9 in which the grains have been compressed into granules at a pressure of about 1 ton/cm.

11. A getter assembly for anelectric discharge device comprising a cylindrical container closed at both ends with a grid-like member, a getter disposed within said container and engaging said grid-like end-closing members under tension, said getter being composed of a plurality of separate contacting granules, each of said granules being constituted of a porous agglomeration of grains of an active metal and a refractory metal, said grains having a specific surface area larger than 1 m. g.

12.. A getter assembly for an electric discharge device comprising a porous pliable container, a porous getter disposed within said container under slight compression, said getter being composed of a plurality of separate contacting granules, each of said granules being constituted of a porous agglomeration of grains of an active metal and a refractory metal, said grains having a specific surface area larger than 1 m. g.

13. A getter assembly as claimed in claim 12 in which a metal plate is disposed within said container with said granules.

References Cited by the Examiner UNITED STATES PATENTS 2,404,803 7/46 Stafford 206-04 x 2,855,368 10/58 Perdijk etal. 252-l81.6 3,082,174 3/63 Perdijk et al. 252--18l.6

7O FOREIGN PATENTS 886,788 10/53 Germany.

1,178,495 12/58 France.

' THERON E. CONDON, Primary Examiner.

EARLE I. DRUMMOND, Examiner.

14. A getter assembly as claimed in claim 12 in which

Claims

12. A GETTER ASSEMBLY FOR AN ELECTRIC DISCHARGE DEVICE COMPRISING A POROUS PLIABLE CONTAINER, A POROUS GETTER DISPOSED WITHIN SAID CONTAINER UNDER SLIGHT COMPRESSION, SAID GETTER BEING COMPOSED OF A PLURALITY OF SEPARATE CONTACTING GRANULES, EACH OF SAID GRANULES BEIN CONSTITUTED OF A POROUS AGGLOMERATION OF GRAINS OF NAN ACTIVE METAL AND A REFRACTORY METAL, SAID GRAINS HAVING A SPECIFIC SURFACE AREA LARGER THAN 1 M.2/G.