US3273970A

US3273970A - Gettering device

Info

Publication number: US3273970A
Application number: US245249A
Authority: US
Inventors: John C Priscu; Linden E Snyder
Original assignee: Titanium Metals Corp
Current assignee: Titanium Metals Corp
Priority date: 1962-12-17
Filing date: 1962-12-17
Publication date: 1966-09-20
Anticipated expiration: 1983-09-20

Description

p 1966 J. c. PRISCU ET AL 3,273,970

GETTERING DEVICE Filed Dec. 17, 1962 INVENTORS. JOHN c. PRISCU LINDEN E. SNYDER '8 20b BY Agent United States Patent 3,273,970 GETTERING DEVICE John C. Priscu and Linden E. Snyder, Las Vegas, Nev., assignors to Titanium Metals Corporation of America, New York, N .Y., a corporation of Delaware Filed Dec. 17, 1962, Ser. No. 245,249 Claims. (Cl. 23277) This invention relates to a gettering device particularly useful for removing oxygen and to some extent nitrogen from inert gases.

Reactive metals at elevated temperatures react readily with atmospheric gases, particularly oxygen and to some extent nitrogen. This characteristic has made them adapted for use as so-called getters. Inert gases such as helium and argon are often required to be purified by removal of as much as possible of their oxygen and nitrogen content. Treatment of such gases with a reactive metal getter has therefore proved to be a convenient way of conducting this purification process.

Gettering dvices heretofore proposed and used have generally comprised a body of reactive metal, such as titanium, which is maintained at an elevated temperature of between 800 and 1000 C. At this temperature, the titanium will absorb substantial quantities of oxygen and to some lesser degree nitrogen, but the absorption reaction takes place on the surface of the heated metal and the efficiency of such a gettering unit is therefore limited The reactive metal getter must be frequently replaced when the surface reaction has proceeded to a point where its gettering efliciency has been materially reduced. Moreover, apparatus for containing and also heating the reactive metal getter is necessarily diffioult to construct and maintain because of the elevated temperatures involved and the critical requirements for strength and corrosion resistance of structural materials at such temperatures. In operation, the reactive metal getter is often heated by induction or resistance heating and inasmuch as the entire body must be so heated while only its available surface is useful for gettering action, the power required for maintaining the required temperature is unduly great.

A principal object of this invention is to provide an improved gettering device. Another object of this invention is to provide a more eflicient gettering device for gettering oxygen from a gas or atmosphere. Another object of this invention is to provide a simple yet efiicient gettering device employing a molten get-tering metal. These and other objects of this invention will be apparent from the following description thereof and from the annexed drawings in which:

FIG. 1 shows a side view partially broken out of apparatus embodying features of this invention.

FIG. 2 shows a top view of the apparatus of FIG. 1.

FIG. 3 illustrates a modified form, somewhat reduced, of apparatus embodying features of this invention in which the .getering device is employed in a side arm organization for gettering gas in a containing vessel.

Referring now particularly to FIGS. 1 and 2, the gettering device comprises a metal shell '10 conveniently fabricated of steel whose side 12 is cooled by provision of surrounding coils 14 through which a suitable cooling fluid such as water may be circulated. The bot-tom 16 of container is also provided with attached cooling coils 18. Side arms 20 communicate with the interior of container 10 and are prefer-ably arranged on opposite sides thereof, as shown. Side arms 20 are employed for connecting the get-tering device in a circuit through which gas to be gettered is circulated, one of side arms 20 providing an inlet for unpurified gas and the other side arm 20 providing an outlet for gettered gas.

"ice

The top of container 10 is closed by provision of top 22 which is preferably also cooled by attached cooling coils 24. Top 22 is attached in sealing engagement with the flanged top of side '12 by means of bolts 26, a gas-tight seal being maintained by provision of O-ring gasket 28. Top 22 is provided with a suitable sighting device such as intruding tube 30 having a top sealed viewing glass 32.

A central opening 34 is provided in container top 22 around which is fixedly attached bellows member 36 fabricated of flexible insulating material such as neoprene. The top of bellows member 36 is closed by plate 38 through which slidab-ly passes electrode 40. Passage of electrode 40 through plate 38 is sealed by provision of seal 42. Electrode 40 is hollow and provided with an inner tube 44 through which :a cooling fluid such as water may be circulated. The water inlet connection 46 may be connected to a suitable supply of water, not shown, and water outlet 48 may be connected toa suitable drain, not shown. At the top of plate 38 is attached upstanding bearing bracket 50 and opposite to this is attached clamp bracket 52 provided with adjustable thumb screw 54 by means of which the electrode 40 may be securely clamped against bearing bracket 50 to maintain it in any adjusted position vertically with respect to the interior of container 10. Electrode 40 is also provided with a bottom tungsten tip 56. An electrical connector 58 is attached to electrode 40 and a similar connector 60 is attached .to one of bolts 26 to wall 12 of container 10.

Connectors

58 and 60 are connected to a suitable source of direct electric current which may be supplied as illustrated diagrammatically by transformer 62 operating from an alternating current supply line with the output thereof being rectified Iby rectifier 64.

In FIG. 1, the gettering device is shown in operation with a [body 66 of reactive metal such as titanium contained in the bottom of container 10 and a pool of molten titanium 68 being maintained molten by the action of electric are indicated at 70, playing between it and tip 56 of electrode 40 suspended above. 7

Referring now particularly to FIG. 3, the gettering device is essentially the same as that as shown in FIGS. 1 and 2 except that side arms 20a and 20b are arranged at a higher and lower level respectively in side wall 12. These side arms, 20 and 20b, functioning as outlet and inlet means, may be connected respectively to an upper portion and a lower portion of a vessel 72 containing gas which it is desired to getter. It will be seen that the gettering device of this invention is arranged in a side arm organization so that cooler gas will be drawn in through side arm 20b and will become heated in container 10 and will flow upwardly out of side arm 20a into the top of vessel 72. This will provide a circulating flow of gas through the gettering device resulting after a period of time in efiicient removal of the oxygen from the gas contained in vessel 72. It will be appreciated that under these conditions, the gettering device performs a dual function in that the molten reactive metal contained therein efiiciently removes oxygen from the gas circulated through container 10 and the heat generated by the melting arc provides a convection flow insuring circulation of gas through the gettering chamber.

In operation of the device of this invention, and particularly the embodiment illustrated in FIGS. 1 and 2, connection is made to a source of inert gas to the purified as by connecting side arms 20 as inlet and outlet in a system through which the inert gas is circulated. Such connection will provide an inflow of unpurified gas through the inlet side arm, the gas then flowing through container 10 and out of the outlet arm 20 after having been gettered.

Container 10 is then opened by lossening bolt 26, top

22 is then removed and a suitable charge of gettering metal such as titanium is placed in the bottom of container 10. The titanium gettering metal may be in any convenient form at this stage and may comprise compacted titanium sponge, or scrap titanium metal as solid bodies of convenient dimensions. Sufficient gettering metal should be placed in container so that the level thereof in the bottom during the melting operation will not rise above the bottoms of side arms 20. Top 22 is then replaced. Cooling fluid such as water is then connected to

cooling coils

14, 18 and 24 which cool respectives the side, bottom and top of container 10. Power connections are then made to

connectors

58 and 60, and the are 70 is struck between the tungsten tip 56 of electrode 40 and the gettering metal in the bottom of container 10.

Initally the electrode 40 is moved manually over the surface of the gettering metal in the bottom of container 10 to melt it down into a more or less unitary body. Flexibility in bellows 36 will provide for lateral, vertical and rotary motion of the end of electrode 40 so that this can readily be accomplished. Thumb screw 54 should be loosened at this time so that the tip 56 of electrode 40 can be placed in best position to maintain an efficient melting iarc.

After the gettering metal in the bottom of container 10 has been suitably melted down, the vertical adjustment of electrode 40 is carefully set to maintain an electric are between the tip 56 of electrode 40 and the gettering metal of intensity sufiicient to maintain a pool of molten metal 68 which will be formed inside a skull of solid gettering metal 66. It will be appreciated that the heat of the are 70 will maintain the molten metal pool 68 while the skull 66 will be maintained solid by reason of its contact with the cooled side wall 12 and bottom 16 of container 10.

The effect of actuation and adjustment of electrode 40 is readily determined by sighting through sight glass 32 and when the adjustment of electrode 40 has satisfactorily been set, then thumb screw 54 is tightened to fix it in this position.

It is important to note that since heat is supplied to the pool of molten metal 68 by are 70, and heat is abstracted thereform through skull 66 to cooled container wall 12 and bottom 16, an equilibrium is established very quickly and the size of the pool of molten metal 68 will remain substantially constant. After initial adjustment of electrode 40, equilibrium conditions will automatically be maintained for a long period of time. An occasional re-adjustment of electrode 40 may be required but other than this, the device needs no attention and will operate efliciently until the reactive metal of molten pool 68 has combined with such amount of oxygen and nitrogen that its melting point has been substantially raised and absorptive capacity has become impaired. When this has occurred, the units is shut down, the reactive metal in container 10 is all-owed to cool and solidify and is removed. A fresh charge is then placed in container 10 and the operation as described above repeated for another cycle.

Operation of the embodiment illustrated in FIG. 3 is basically the same as that described above. Container 10 is connected by upper side arm 20a and lower side arm 20b to a vessel 72 containing gas to be gettered. Charging and adjustment of the arcing electrode is the same as for the embodiment of FIGS. 1 and 2. When the gettering device is in operation, the gas to be gettered becomes heated in container 10 to induce a convection and circulation in side arm 20b and out side arm 20a. A flow of gas is thereby automatically maintained through the gettering device so that the contents of vessel 72 may be progressively gettered.

As an example of the type of operation to be expected from the apparatus described, an 18-inch diameter container was loaded with massive scrap titanium. An arc was struck by contacting the titanium with the electrode and then withdrawing the electrode until a stable are requiring 28 to 38 volts was established. The amperage from the power supply was adjusted to provide between 200 and 300 amperes which resulted in sufficient intensity in the arc to maintain a pool of molten titanium within a skull of solid titanium. Helium containing about 1% air was circulated through inlet and outlet arms 20, the helium passing over the body of molten titanium at a rate of about 30 cubic feet per minute. The molten titanium efficiently gettered the helium gas removing oxygen down to a level of less than 200 parts per million. The gettering device operated without more than occasional adjustment of electrode 40 for a period of about 20 hours, at which time the oxygen and nitrogen combined with the metal of the molten pool raised the melting point so that it was difiicult to maintain it in a molten condition. At this time, power was shut off to the gettering device, the body of titanium metal in the bottom of the container was allowed to cool and was replaced with a fresh charge of scrap titanium.

The gettering device of this invention may be constructed principally of low cost and readily available materials such as carbon steel. The bellows member 36 is preferably fabricated of neoprene to provide flexibility, electrical insulation, and this material has been found also to be impervious to gas passage. Electrode 40 may be constructed of steel tubing, and the tip 56 is preferably of tungsten which will provide long life under arcing conditions. If corrosive conditions are encountered, electrode 40 may advantageously be fabricated of stainless steel. Cooling coils 14, 18 and 24 are preferably constructed of copper tubing to provide advantageous heat transfer. The apparatus may be constructed in any suit-able size depending on the service required, the rate of gas flow therethrough and the degree of gettering necessary.

Any suitable type power supply may be employed and it has been found preferable to employ a direct current power input to the electrode. Power supply characteristics may vary considerably depending on the amperage and voltage required and these may be of the order of from 20 to 40 volts and from a few hundred to a thousand or more amperes, depending on the heat input required and the size of the pool of molten metal to be maintained. A DC. welding power unit has been found to provide a convenient source of such power.

Any reactive metal which possess the characteristic of rapidly reacting with atmospheric gases such as oxygen and nitrogen at elevated temperature may be employed as the getter metal. Metals of the class of aluminum and magnesium may be used, magnesium having been found to be particularly reactive. Titanium or zirconium are, however, preferred since these are extremely reactive with oxygen and nitrogen at elevated temperatures, titanium being preferred because of its somewhat lower cost.

Additionally, titanium dissolves its own oxide and while such dissolution is slow in solid metal, it is extremely rapid when titanium is molten. Therefore, employment of titanium in a gettering device as described herein has the unique advantage that the pool of molten titanium will absorb a very large amount of oxygen and nitrogen compared to absorption on a solid surface, even maintained at red heat. While absorption of oxygen and nitrogen by molten titanium is a surface phenomenon, as soon as these elements are absorbed, they are immediately dispersed and dissolved throughout the pool of molten titanium. Thus, a relatively large body of reactive metal in molten form is available for oxygen and nitrogen absorption and for this reason, the gettering device of this invention employing titanium as a gettering metal will operate efficiently for an extended period of time and will absorb large quantities of atmospheric gases.

The gettering device of this invention is extremely efficient because the reactivity of the gettering metal is molten form is substantially higher than such metal in a solid state, Passage of inert gas to be gettered over the surface of the molten reactive metal provides adequate contact for eificient gettering action.

It has been found that with a reasonable gas flow through a gettering device as described, oxygen can be absorbed quantitatively and substantially all the nitrogen removed from an inert gas such as helium or argon.

Since operation of the gettering device of this invention is essentially automatic, requiring little attention during long periods of use, its operating cost is relatively low. The power requirements are not high, sufi icient heat only need be provided by the arc to maintain the pool of reactive metal in molten condition under the equilibrium conditions established.

We claim:

1. A gettering device comprising;

(a) a cooled container,

(b) a body of reactive metal in said container,

(c) an electrode suspended above the said reactive metal body in said container,

((1) means for maintaining the bottom of said electrode spaced arcing distance above the top of the said body of reactive metal in said container,

(e) mean for supplying electric current between said electrode and said body of reactive metal in said container in amount to maintain an electric are therebetween of intensity sufficient to maintain a pool of said reactive metal molten within a skull of solid reactive metal in said container, and,

(f) means for contacting the surface of the molten portion of said reactive metal with gas to be gettered.

2. A gettering device comprising;

(a) a cooled container,

(b) a body of reactive metal in said container,

(0) an inert tungsten tipped electrode suspended above said reactive metal in said container,

(d) means for maintaining the bottom of said electrode spaced arcing distance above the top of the said body of reactive metal in said container,

(e) means for supplying electric current between said electrode and said body of reactive metal in said container in amount to maintain an electric are therebetween of intensity sufiicient to maintain a pool of said reactive metal molten within a skull of solid reactive metal in said container, and,

3. A gettering device comprising;

(a) a cooled container,

(b) a body of titanium metal in said container,

(c) an electrode suspended above the said titanium metal body in said container,

(d) means for maintaining the bottom of said electrode spaced arcing distance above the top of the said body of titanium metal in said container,

(e) means for supplying electric current between said electrode and said body of titanium metal in said container in amount to maintain an electric are therebetween of intensity sufficient to maintain a pool of said titanium metal molten within a skull of solid titanium metal in said container, and,

(f) means for contacting the surface of the molten portion of said titanium metal with gas to be gettered.

4. A gettering device comprising;

(a) a cooled container,

(b) a body of reactive metal in said container,

(d) means for maintaing the bottom of said electrode spaced arcing distance above the top of the said body of reactive metal in said container,

(e) means for supplying electric current between said electrode and said body of reactive metal in said container in amount to maintain an electric are there between of intensity sufficiently to maintain a pool of said reactive metal molten within a skull of solid reactive metal in said container, and,

(f) side arm inlet and outlet means for passage of a gas to be gettered through said container to provide contact of said gas with the surface of the molten portion of said reactive metal in said container.

5. A gettering device comprising;

(a) a cooled container,

(b) a body of reactive metal in said container,

(e) means for supplying electric current between said electrode and said body of reactive metal in said container in amount to maintain an electric are therebetween of intensity sufficiently to maintain a pool of said reactive metal molten within a skull of solid reactive metal in said container, and,

(f) inlet means communicating with a lower portion of said container and outlet means communicating with said container at a higher level than said inlet means for passage of gas to be gettered through said container contacting the surface of the molten portion of the reactive metal in said container.

References Cited by the Examiner UNITED STATES PATENTS 4/1898 Eldridge et al 1314 X 1/1964 Herb 313- X

Claims

1. A GETTERING DEVICE COMPRISING; (A) A COOLED CONTAINER, (B) A BODY OF REACTIVE METAL IN SAID CONTAINER, (C) AN ELECTRODE SUSPENDED ABOVE THE SAID REACTIVE METAL BODY IN SAID CONTAINER, (D) MEANS FOR MAINTAINING THE BOTTOM OF SAID ELECTRODE SPACED ARCING DISTANCE ABOVE THE TOP OF THE SAID BODY OF REACTIVE METAL IN SAID CONTAINER, (E) MEANS FOR SUPPLYING ELECTRIC CURRENT BETWEEN SAID ELECTRODE AND SAID BODY OF REACTIVE METAL IN SAID CONTAINER IN AMOUNT TO MAINTAIN AN ELECTRIC ARC THEREBETWEEN OF INTENSITY SUFFICIENT TO MAINTAIN A POOL OF SAID REACTIVE METAL MOLTEN WITHIN A SKULL OF SOLID REACTIVE METAL IN SAID CONTAINER, AND, (F) MEANS FOR CONTACTING THE SURFACE OF THE MOLTEN PORTION OF SAID REACTIVE METAL WITH GAS TO BE GETTERED.