US2469626A - High vacuum getter - Google Patents

Description

May 10, 1949. J. BEERS I 2,469,626

HIGH VACUUM GETTER Filed June 20, 1946 INVENTOR JOHN /P. EE'RD BY ATTORNEY.

Patented May 10, 1949 HIGH VACUUM GETTER John R. Beers, Briarclifl Manor, N. Y., assignor, by mesne assignments, to Philips Laboratories, Inc., Irvington on Hudson, N. Y., a corporation of Delaware Application June 20, 1946, Serial No. 678,120

8 Claims. 1

My invention relates to electron discharge tubes and more particularly to a getter means capable of maintaining a high degree of vacuum in such tubes.

Cathode ray tubes employing magnetic beam deflection generally sufier from the disadvantage that in operation they develop a so called ion spot. This ion spot has been found to be chiefly due to the presence of minute quantities of gas. Notwithstanding careful evacuation and aging of the tube, it has been diflicult to evacuate it to the extent that the gas is reduced to an amount below that at which ion spots occur, and in some instances it has been necessary to employ an ion trap in the tube whereby the ions formed are directed towards portions of the tube other than the fluorescent screen.

It is an object of my invention to provide a novel structure for vacuum tubes whereby gas retained after evacuation is substantially completely absorbed.

Another object of my invention is to provide a novel structure for cathode ray tubes whereby the gas remaining after evacuation is substantially completely absorbed, thereby precluding the necesslty for an ion trap in tubes which are to be operated with magnetic deflection.

A further object of my invention is to provide a getter for absorbing gas which getter is eifective throughout the life of the vacuum tube.

These and further objects of the invention will appear as the specification progresses.

In accordance with the invention, these objects are achieved by means of a novel getter arrangement. I have found that at temperatures in the region of 400 C. zirconium readily absorbs hydrogen forming a solid solution of the gas in the metal. At still higher temperatures, zirconium absorbs other gases, and may release some hydrogen absorbed at lower temperatures. For example, increasing the temperature to approximately 1000 C. causes the zirconium to release some of the hydrogen previously absorbed while absorbing the nitrogen and oxygen gases present in the atmosphere of the tube. I utilize these properties of zirconium most effectively in removing the residual gases in electron discharge tubes requiring a high degree of vacuum by maintaining portions of the zirconium at different temperatures during the operation of the tube.

I- continuous zirconium getter is shown mounted within a vacuum tube heater-cathode structure.

Referring now to the figure, a heater wire II is wound in a re-entrant helix around a cylinder l2 of a refractory insulating material such as ceramic. A thin zirconium strip formed into a cylinder I3 is inserted into cylinder I2. A stem I8 of the zirconium cylinder I3 extends slightly below cylinder I2 and is welded to a support wire it which is mounted in the press of the base I! p of the tube. The lower end of the zirconium cylinder I3 is open to permit the residual gases in the tube to enter the cylindrical enclosure and allow the zirconium to absorb these gases. The heater wire II is connected to the tube electrodes through, lead-in wires I5 and I6 respectively. The heater structure is enclosed within a cathode structure I!) such for example, as those customarily employed in cathode ray tubes having its upper end I 0 coated with an electron emissive substance, as shown. The evacuated envelope 20, which may be made of glass or the like and within which the cathode assembly and other elements are enclosed, is shown broken away near the base 2| of the tube. The remaining structure of the tube is not shown as it is not necessary for an understanding of the invention.

If a portion of the zirconium is exposed directly to the heater II, I have found that some of the zirconium may contact or be evaporated onto the heater element, particularly during processing, with deleterious 'efi'ects. Therefore, I have afforded complete protection andseparation of the zirconium from the heater wire by not only surrounding the zirconium cylinder I3 with a cylinder I2 of refractory insulating material, but also by sealing the top of the cylinder I2 with a sealing material such as ceramic cement.

The zirconium is heated to a temperature in the the the base thereof is operating at normal tube In order that the invention may be more clearly understood and readily carried into effect, it will now be described with reference to the accompanying drawing in which the sole figure shows a preferred embodiment of my invention wherein a temperature. The temperature gradient thus afforded offers a unique advantage in that the lower surface of the zirconium absorbs and retains the hydrogen in the atmosphere of the tube while the upper surface absorbs other gases such as nitrogen and oxygen. I have found that exposure of a portion of the zirconium below the ceramic cylinder I2, and thus out of the heater structure, is a particularly advantageous and emcient means for affording a continuous temperature gradient along the zirconium. The exposed portion may be flattened as shown, to permit easy connection, for example, by welding to a support of metal on the inner surface of cylinder l2. In

the latter form, a substantial thickness of metal. say several microns thick, is desirable in order that the zirconium may function effectively to clean up the residual atmosphere in the tube,

It will be understood that the term cylinder as used in the specification may include other than circular cylinders. Likewise, various other shapes, such as a rod, a corrugated strip, or a ribbon of zirconium may be employed supported within a cylinder of refractory insulating material, particularly if space is allowed for the residual gases in the tube to have access to the zirconium.

While I have described my invention with specific examples and applications, other variations will suggest themselves to those skilled in the art without departing from the spirit and- I refractory insulating member having at least two surface portions in heat exchange relationship, electrical heating means adjacent to one said surface portion of said member for heating the other surface to a given temperature, and heat responsive gas absorbing means non-volatile at said temperature adjacent to said other surface portion.

.2. An electron discharge device comprising a tubular refractory insulating member having an inner surface and an outer surface in heat exchange relationship, electrical heating means adjacent to said outer surface for heating said inner surface to a given temperature, and heat responsive gas absorbing means non-volatile at said temperature adjacent to said inner surface.

3. An electron discharge device comprising a tubular refractory insulating member, an electrical wire element wound on said tubular member, and a tubular gas absorbent member responsive to heat within said insulating member.

4. An electron discharge device comprising a heat responsive gas absorbing member, means to heat said gas absorbing member non-uniformly over the length of said member, said means comprising an electrical heating wire element surrounding a portion of said gas absorbing member, and a cathode in heat transfer relationship with said heating wire element.

5. An electron discharge device having a cathode assembly comprising a tubular zirconium member, a tubular refractory insulating member surrounding said zirconium member, an electrical heater wire element surrounding a portion of said zirconium member, and a cathode in heat transfer relationship with said heating wire element.

6. An electron discharge device comprising an evacuated envelope and, within said envelope, a tubular zirconium member to absorb residual gas, a refractory insulating. tubular member surrounding a portion of said zirconium member, electrical heating means disposed around said insulating member, and a cathode in heat transfer relationship with said heating means.

7. An electron discharge device comprising a tubular zirconium member, a tubular refractory insulating member surrounding a portion of said zirconium member, means to heat said zirconium member non-uniformly over the length thereof comprising an electrical wire element surrounding said refractory member. and a cathode in heat transfer relationship with said heating wire element.

8. An electron discharge device comprising an evacuated envelope a cathode structure mounted within said envelope, a refractory insulating tubular member mounted within said cathode structure, cathode heater means disposed between said structure and said tubular member, and a tubular zirconium member disposed within said refractory member, a portion of said zirconium member extending out of said refractory member.

JOHN R. BEERS.

REFERENCES CITED UNITED STATES PATENTS Number Name I Date McQuade Nov. 21, 1939

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