US2424294A - Graphite outgassing - Google Patents

Description

July 22, 1947- J. E. WHITE l GRAPHITE AOU'J'GSSING Filed March 1,' 1945 van.

INVENTOR J'. E VH/7'5" BY MAM l l u ATTORNEY heated in use.

-release of further gas from the anode.

Patented July V22, 1947 UNITED A STAT Corporation, ion of Pennsylvania Westinghouse Electric burg'h, Pa., av corporat assigner toVlr East Pitts# Application Marchi, 1945, serial No'. sossrffv 4 claims. (ci. siczii- This invention relates to graphite outg'assin and has particular application to the electronic art and outgassing of such graphite 'partsas an'- cdes, baies and the like, which are used Within an evacuated electronic device.

It is well appreciated in the electronic art that graphite parts have a tendency to'release gas therefrom into an evacuated. container in which situated particularly when vsaid part becomes Presence of gas in an electronic device will not only change its characteristics but in most instances renders the device inoperative for its intended purposes. For instance, an ignitron utilizes aV graphite anode, and in use may be subjected to intense heat atsome spot from an arc back. If the heat at that spot liberates gas from the anode, the gaswill result in greater ionization in the ignitron, which in turn encourages further arc backs' with the probability of Thus the Vice iS 0u tbefpumpszbeing`evacuated. VSince the ignitron `musty of necessityV contain parts having ignitron becomes progressively Worse and soon is useless for its intended purpose.l

Broadly considered, therefore,`the invention has for an object the more perfect outgassing of graphite parts.

Likewise, from its most general aspect, the invention proposes the outgassing of graphite parts at temperatrues exceeding any encountered in use.

A further object of the invention is to protect the graphite part after it is outgassed and' until incorporated in the electronic device so it may` be then nally and adequately outgassed by normal procedure with other parts of the device.

Still further objects of the invention will Aappear to those skilled inthe art to which it appertains as the description progresses, bothI by direct recitation thereof and by implication from the context.

In the accompanying drawing:

Figure 1 illustrates an ignitron having an anode of the character treated in accordance with the present invention; and

Figure 2 is a sectional view of anv apparatus forl carrying out the outgassing of graphite parts in accordance With the invention.

By way of example, an ignitron is shown in l Figure 1 having a graphite anode I0 suspended in a sealed envelope Ilv on the bottom header l2 ofA which is a mercury pool cathode I3 into which a starter electrode or ignitor I4 is dipped. During manufacture of the ignitron, the same is sub-v jected to as high a temperature as the character of its parts and joints will permit, for purposes of freeing gas from internal parts and While the devite part,- Vand :in v the presv 4lower mel-tingftemp e'ratures than 'thoseof the anode or. its envelopether.efis a'practicallix'nitatin on heat .which'can befsafel-'nl applied to tlieanode after it -is mounted"A in "tl'iel ignitron'. Unfortu.- nately, thelimitation-i's tooiowtopermit'heat ing the'anode .to sufficiently high temperature to :Attempts'havlesbe'enhere 1 the-anode",be1`or`e iritroducf ing it into thel ignitronpbut-ithasbeeri'fund thatA when exposed toairmfmak ing transfer to the ignitrcn-,pabsorbs gasses frofmf the air, wh'ich again socontannnatethe anode jj;

that normal outgassirigirifthe' 'gniton envelope thoroughly outgas -it .tofore Iliade to 'ontgaathe outg'a'ssed anode does not suiilce. 4 According to the prese I0 as representativefof su the envelope. An e1ectric"furnace` "Seis-shown inFi'gure 2 forfthe purpose, 'jsaid'frnacel having I Y eral walls of the shell are heat shields t9 serving to confine the greater part o f the developed heat to the-oven. The part, such as anode lfllto be outgassed is placedin the oven. Leadein co'nne'c'- tions 20'pass current to the heating element or oven and by it a temperature Within the range of 180D" .C. to 2000 C. isf developed inl the oven n Y and effective upon partfl.

Shell lli has apipe connection 2l to its interior from the exterior, and duringthe heating periodabove related, thisl pipe connection is joined,fas.

through a valve'22y to a vacuumpump or system by which the oven is evacuated. The partfican be considered degassed when the pressure goes down to .'75 micron at 1800 C. and when-fthe pumps can be shut off for one hour at i800 C. without the pressure rising above '3 microns.

When the degassing has thus been accomplished,: the temperature inthe ovenV is reduced to 200 C. or less, to be Within a temperature range wherein an appropriate gas to be used, such-as hydrogen, or one ofthe noble gases such as helium, argon, neon. and so forth,`is practically insoluble in solids. For brevity, the selected gas will be referred to as the protective gas. At that temperature condition of the oven,the valve 22 (which forthe purpose is preferably a, threec h partgds treated pri-or I',

-to being appliedinintended'place-j offuse withinvv instance.

way valve) is turned toadmit the said protective gas to the oven and ll the same to atmospheric pressure. The protective gas at this temperature and pressure enters the surface pores oi the part I outgassed. The protective gas does not seem to penetrate to any considerable depth, and

yet by surface absorption or impregnation thereofin the anode, it constitutes a protection against extraneous gases being absorbed when the anode is next exposed to air. This surface penetration of the protective -gas is readily removedrby subsequent normal outgassing procedure applied to the ignitron after transfer of the anode to its appointed lplace therein. As indicated above, hydrogen and the noble gases are not dissolved in graphite to any objectionable extent, and those gases are therefore readily removed at moderate temperatures. as may have dissolved in the graphite, on being released during the higher temperature periods during exhaust, has a beneficial effect in removing traces of injurious oxides which may have been left in the tube inadvertently.

Consequently, after the hydrogen or other protectiveras has been introduced into the oven as above cited, the protective gas supply is shut offA and the furnace shell opened. The graphite part or anode I0 is then promptly'transferred to its appointed place, as in the ignitron envelope, and that envelope, with its contents, then subjected to the usual outgassing procedure. In this stage of operation, temperatures from` about 800 C. and not exceeding 1200 C. are usually employed while the device is on the pump for evacuating said device or ignition in the present The protective surface infiltration of hydrogen or other protective gas present in the graphite part due to the pre-mounting and outgassing procedure outlined above, is readily drawn from the anode at this lower temperature; approximating 800 C. to 1200 C., and thus the anode is to all intents and purposes devoid of releasable gas. As a result, arc-back spots in use on the anode,Y whichr are at a. lower temperature 'than the primary outgassing temperature of 1800o C. to 20,00" C.,have no gas-releasing effect, and the ignitron remains in good evacuated condition free of evolved gas from the are back.

While the foregoing description has utilized graphite as an exemplary material being out-V gassed and has referred to the part as an anode and as used in an ignitron as the device in which used, the invention is to be understood as also applicable to other materials, parts and devices.

Such small amount of hydrogen I claim:

1. An outgassing method for a part to be used in an evacuated envelope, comprising outgassing the part at a temperature approximating 1800 C., applying a surface impregnation of a protective gas to the outgassed part, enclosing said part in an envelope, and outgassing said part in said envelope at a less temperature than before.

2. An outgassing method for a part to be used in an evacuated envelope, comprising outgassing the part at a temperature in the approximate range of 1800` C. to 2000 C., reducing the temperature to approximately a tenth of the said outgassing temperature, yapplying a protective gas toY the vpart at its reduced temperature, enclosing said part in an envelope and outgassing said part in said envelope at a less temperature than the first used outgassing temperature,

3. An outgassing method for a part to be used in an evacuated envelope, comprising outgassing the part before introduction into said envelope at a temperature in the approximate range of 1800 C. to 2000 C., reducing the temperature to approximately 200 C., applying vhydrogen as a protective surface impregnation to said part at its reduced temperature, transferring Vsaid part to and mounting it in an envelope for use,

' and again outgassing said part and in its final position in said envelope and at a temperature less than the said range of 1800 C. to 2000"v C. and more than the approximate said temperature of' 200, C. at which the hydrogen was applied.

4. Anoutgassingmethod for a part 4to'be used in an evacuated envelope, comprising heating the part in vacuum toa temperature less than l its melting `point and'sirnultaneously outgassing the same beforeintroduction into said envelope, cooling said part while still in vacuum, and after cooling of said part admitting a protecting gas thereto, transferring said part to said envelope, and again heating, but at' a. lower temperature than the first said heating, and simultaneously outgassing said part in the envelope.

JOHN E. WHITE.

REFERENCES CITED UNITED STATES PATENTS Name Date Spanner Dec. 26, 1939 Number

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