US1952717A - Means for producing high vacuum - Google Patents

Description

Patented Mar. 27, 1934 UNiTa stares 1,952,717 MEAN S FOR PRODUCING HIGH VACUUM Ernest Anton Lederer,

East Orange, N. J., as-

signcr, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware No Drawing. Application January 8, 1932, Serial No. 585,635

12 Claims.

This invention relates to an improved form of getter material such as customarily employed as a clean-up agent during the process of evacuating electron devices.

I have heretofore employed a method of cleaning up residual gases of an electron device by introducing into the envelope thereof a getter material comprising an alloy consisting essentially of aluminum and an alkaline earth metal, more particularly barium. The aluminum functions primarily as a protective'carrier (in the sense that it affords chemical rather than physical protection) for the barium.

The getter is introduced into the device in a 15 solid form at the time of sealing the mount into the envelope and may be supported by the electrode structure or secured independently thereof.

After the usual mechanical evacuation of theenvelope, the alloy is flashed at a temperature not substantially higher than the volatilization point of the barium.

Previous to the aforesaid practice it had been proposed to employ an alloy of magnesium and barium containing a preponderance of magnesium as a getter material, but because of the comparative low volatilization point of the magnesium it was difficult to determine when the barium was flashed because the magnesium flash predominated, which quickly manifested itself in the form of an opaque depositupon the interior of the envelope, thus making it impossible to observe when the. barium Was flashed.

Since barium, due to its chemical activity, is

probablythe best clean-up agent which'can be 5 usedfor vacuum tubes and similar devices, it is It is an objectof my invention to preserve all of the advantages obtained by a barium flash without introducing undesirable complications. It is another object of my invention to provide a method of cleaning up the residual gases of an electron device by reducing or eliminating :heat losses due to convection prior'to flashing the principal clean-up agent of the getter material.

Other objects having to do with the employment of a superior getter material of which barium is the most effective clean-up constituent, will manifest themselves upon a reading of the following specification.

The specific improvement of the present invention over the above mentioned prior practice is the addition of a small percentage of metallic magnesium to a getter material, comprising an alloy of aluminum and an alkaline earth metal such as barium. This percentage of magnesium may vary from about 1% to about 10% but I have obtained excellent results with about 5% of magnesium added to an alloy consisting of aluminum and barium, the barium constituting about 45% of the alloy. However, the barium content may be varied fromabout 5% to about 60%, depending upon the desired stabilityv of the getter material, which in turn depends upon the time required to process a receiving tube or the like under existing factory conditions, it being obvious that the longer the period required to complete the processing, a corresponding decrease in the percentage of barium should be used.

The magnesium in powdered form may be added to the powdered barium-aluminum alloy and the mixture pressed up into pellets. Or by using a suitable binder as a vehicle for the powdered alloy and the magnesium a mixture is obtained which can be used as a paste getter" for application to the electrodes or to a special holder designed to carry the getter. If the getter material is in pellet form, the pellets may be attached They are quite stable in air and can successfully resist oxidation or contamination by moisture for a substantial period of time.

In heating up the getter material by any suitable means, such as with a given high frequency source: the temperature of the getter material is considerably aifected by a small amount of gas. The reduction of the gas pressure by a few microns increases the temperature of the getter carrier considerably. The magnesium metal, being the first constituent of the clean-up agent to flash, will lower the gas pressure. Thus the temperature of the getter carrier can easily be brought up to about 930 C. at which point the barium-aluminum alloy will melt and the barium metal will readily volatilize. The percentage of the magnesium is low enough to avoid any serious discoloration of the interior of the envelope so that it is possible to observe without difficulty the barium flash, making possible to judge the quality of the getter flash by the eye.

While I have oifered a theory of explanation as to the functioning of the magnesium to prevent heat losses, I do not wish to be held strictly thereto. Irrespective of any explanation, I have found it to be a fact that improved results are obtained, particularly from the standpoint of processing vacuum tubes under existing factory conditions, if

to one of the electrodes or to a special support.

the getter material employed is composed of the elementsv aluminum, barium and magnesium in the percentages specified. This composition may take the form of a true alloy of the several substances involved or an alloy of barium and alum inum with the magnesium unalloyed.- In any event the aluminum and barium will always take the form of an alloy while the-magnesium may be alloyed or unalloyed therewith. Forthis reason the resulting composition may be a true alloy or merely a mixture. However, in certain of the claims in attempting to employ a term sufiiciently comprehensive to include both these forms I have designated the composition as a getter material or a getter in the form of powdered material" and I wish it iuiderstood that these terms be interpreted to be inclusive of both a true alloy or a mixture.

Modifications of the invention will suggest themselves to those skilled in theart but it is my intention to'cover all such modifications as come within the terinsof the appended claims.

What is claimed is:

1; The method of cleaning up the residual gases of an electron device,comprising introducing into the envelope thereoi a getter material in the form 0': a powder consisting of aluminum, barium and magnesium, the barium constituting from about 5% to about 60% and the magnesium constituting from about 1% to about 10% of the material, mechanically exhausting the envelope and first flashing the getter at the volatilization point of the magnesium,'thereby lowering the gas "pressure within the envelope and reducing heat losses 'due' to'"convection during the completion of'the flashing operation.

2. In an electron device, a clean-up agent in the form of apellet of powdered material consisting of aluminum, barium and magnesium, the barium constituting from about 5% to about 60% and the'magnes'ium"constituting from about 1% to about 10% of thematerial.

' 3. In an electron device, a clean-up agent in the form of a'pellet of powdered material consisting 'of alum'inum, barium and magnesium, the aluminur'n'and barium being alloyed and the latter constituting from about 5% to about 60%, the magnesium being unalloyed and constituting from about1% to about 10% of the material.

4. In an electron device, a clean-up agent comprising a mixture consisting of powdered alloy of aluminum and bariurn'having added thereto me talliomagnesium'in powdered form, the barium constituting from about 5% to about60% and the magnesium constituting from about 1% to about 10% offthe material. g p

5. The method of cleaning up the residual gases of an electron device, comprising introducinginto the envelope thereof a getter material 1 in the form of a pellet or paste and consisting of pellet or paste form and consisting of aluminum, barium and magnesium, the aluminum being alloyed with the barium and present in suflioient quantity to afford stability to the barium when exposed to atmospheric conditions for a period of time necessary to process a given electron device under general factory conditions, mechanically exhausting the envelope, and first heating the getter sufficiently to flash only the magnesium to effect a preliminary clean-up and then heating the aluminum and barium alloy sufficiently to flash the barium only and thereby effect a final clean-up action.

7. The method of cleaning up the residual gases of an electron device, comprising introducing into the envelope a'getter material either'in pellet or paste form andconsistingof aluminum, bariumand magnesium, the aluminum beingalloyed with the barium in sufiicient quantity to afford stability to the barium when exposed to atmospheric conditions for a period of time necessary to process a given electron device under gen-' eral factory conditions, the amount of the magnesium being suflicient to -reduce substantially the gas pressure in the envelope but'insufficien't to cause any serious discoloration of the interior of the envelope so that it is possible to observe;

without difficulty, the barium fiash, and the bar-*- ium constituting from about 5% to about 60% of said aluminum barium alloy.

8. The method of cleaning up the residual gases inthe envelope of an electron discharge de-' vice which comprises introducing into the en-- velope in the form of a pellet orpaste a getter material.consisting of magnesium mechanically mxed with a greater amount of an alloy of b'arium and aluminum; flashing the magnesium to effect a preliminary clean up, and then flashing only the barium from said alloy to effect a final clean up action.

9; The method of cleaning up residual gas" in the'exhausted envelope ofan electron discharge" tube whioh comprises introducing intothe envelope a powdered getter material of Which'the major part isan alloy of barium and aluminum stable in air andthe remainder is uncombined" magnesium,nieohanically' exhausting the env lope, heatng the getter mixture 'until'magnesium from said' alloy and complete the'clean' up.

10. iAgetter material capable when fiashed'of cleaning up residual gas in the envelope of an electron discharge tube-and consisting of an al-'- loy of bar'um and'aluminum stable in air and intimately associated with a lesser amount by weight of magnesium.

11. A getter material stable for use in electron discharge tubes and consisting of magnesium, barium and aluminum, the --ba.-- rium and aluminum being alloyed and-constitutingthe major part of said material.

1-2. A getter material for use in electron discharge tubes comprising, a mixture of 11%, to

about 10% magnesium with 90% to 99% of analloy of aluminum and .barium, the barium con-m stituting from about 5% to about -60% of said. alloy.

in air and adapted.

V ,145 ERNEST ANTON LEDERER.