US1729888A - Getter for vacuum devices - Google Patents

Description

Oct. 1, 1929.. L. McCULLOCH 1,729,888

GETTER FOR VACUUM DEVICES Filed Oct. 14, 1924 F/ aZ.

WITNESSES: INVENTOR Lea/7 M CW/Och BY I q: I

Patented Oct. 1, 1929 UNITED STATES PATENT iaFFlfi-E LEON MCCULLOCH, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA GETTER FOR VACUUM DEVICES Application filed October 14, 1924. Serial No. 743,546.

My invention relates to thermionic discharge devices, and particularly to means for maintaining a suitable vacuum therein.

An object of my invention is to produce an im roved etter for vacuum devices.

Another object of my invention is to produce a gas absorbent of greater absorptive power.

Another object of my invention is to produce a gas absorbent of great absorptive power which is produced in situ.

Another object of my invention is to produce a gas-absorbent means, by the use of which the pumping and evacuating opera: tions required in the manufacture of vacuum devices may be simplified.

Another object of my invention is to produce a gas-absorbent means which will maintain a suitable vacuum in a thermionic discharge device for a longer time than is now possible.

Another object of my invention is to produce a gas-absorbent means of sufiicient capacity to obviate the need of diffusion pumps and liquid-air cooling in the process of evacuation of thermionic discharge devices.

In the prior art, in the manufacture of thermionic devices, various means have been devised for producing a suitable high degree of vacuum and for maintaining the vacuum therein. Most of these means have fallen short, in various ways, of the desired qualities, as the required very elaborate heat treating an evacuation by a complicated exhausting ystem before such devices are closed by sealing oil.

The exhausting system usually employed comprises a rough pump or backing pump, which may be of a mechanical type, for producing a relatively poor vacuum. This is supplemented by a diflusion pump which is connected to the device to be evacuated through a liquid air trap, to prevent mercury and other gases working backward into the device and to produce a higher degree of vacuum. This system is complicated, difficult to operate on a, production scale, and is expensive to install and to operate.

In the application of Sutherlin and Freeman, filed on Februar 8, 1923, No. 617,876 and assigned to the estinghouse Electric and Manufacturing Company, is disclosed the use of a compound comprising calcium oxide within a thermionic discharge device for maintaining a suitable degree of vacuum. In my application filed Oct. 14,1924, Serial No. 743,545, and assigned to the Westinghouse Electric and Manufacturing Company,

I have disclosed means for maintaining a suitable pressure of water vapor within a thermionic discharge device. In the prepara tion of devices by these means, it has been found essential to evacuate the devices very thoroughly by careful pumping and heat treating before sealing off, in order to produce the desired functions.

My invention provides adequate absorbent means, placed within the device to be evacuated which will absorb and retain a relatively large quantity of residual gas, and thereby make it possible, first, to evacuate the'device by a simple evacuation system to a relatively poor vacuum, and then to produce a good vacuum by the action of the absorbent means.

My invention comprises essentially the use of pyrophoric metals placed within the evacuated space of the device for the purpose of reducing the residual pressure to a suitable low value.

Other objects and structural details of my invention Will be apparent from the following description, when read in connection With the accompanying drawing, wherein:

Figure 1 is a view partially in elevation and partially in section, of a thermionic discharge device comprising a form of my invention, a portion of the container being broken away, and

Fig. 2 is a side elevation of a mount of a thermionic discharge device showing an embodiment of my invention.

It is well known among chemists that, by heating such compounds as the formate,

oxalate, acitate or other organic acid salt.

of such metals as iron, cobalt or nickel, the metal is liberated from the compound in the form of very finely divided free metal which is chemica ly very reactive. The liberation reaction which occurs very readily at a low vapor pressure, with slightly elevated temperature, results in the formation of a finely divided free metal, and the liberation 5 of the organic acid portion of the compound in a volatile form, as carbon dioxide, or as mixtures of carbon dioxide, carbon monoxide,

water, etc.

In the practice of my invention, I produce a mixture of an organic acid compound of some one of the metals previously mentioned. with a similar organic acid compound of magnesium or similar metals, or with some convenient compound of calcium, such as lime, to which mixture magnesium may be added also as a compound. This mixture is combined with water to form a paste which is then spread upon the mount of the discharge device as shown at 1 in the drawing. If desired, the lime absorbent may be spread upon another portion of the mount, as shown at 2 in the drawing.

The mount may then be assembled within the container 3 and the interior of the device may be connected, by the customary tube, to a vacuum pump, and provision made for heating, and partially exhausting the device, as is well known in the art.

The operation of baking and exhausting simultaneously, reduces the vapor pressure within the device and also causes the pre viously mentioned chemical reaction to occur, whereby the pyrophoric metal is liberated within the device, the lime and magnesium compounds prepared for their functions, as

disclosed in the previously mentioned applications, and the volatile reaction products removed.

The device may then be sealed off from the pump. After standing a short time, which is known in the art as aging, the pyrophoric metal removes a large portion of the residual gases which may not have been removed by the pump. By this means it is possible to evacuate the device roughly, upon the pump, and to depend upon the pyrophoric metal as agetter to complete the evacuation and the reduction of the pressure within the device to the value required for satisfactory operation.

By this means, I am able to simplify greatly the operations required in the evacuation of a thermionic discharge device and thereby to cheapen the cost of manufacture and to facilitate the production of better devices of this character.

While I have shown only one embodiment of my invention in the accompanying drawings, it is capable of various changes and modifications without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be imposed thereon as are indicated in the prior art or in the appended claims.

I claim as my invention;

1. A device comprising an evacuated container, electrodes and a gas-absorbent means therein, said means comprising a mixture of a metal oxide and another metal in the finely divided state which results from chemically liberating it from an organic compound thereof.

2. A device comprising an evacuated container, electrodes and a gas-absorbent means therein, said means comprising the product obtained by baking a mixture of organic acid compounds with a base metal and an alkaliearth metal.

3. A device comprising an evacuated container, electrodes and a gas-absorbent means therein, said means comprising a mixture of finely divided metallic nickel and magnesium oxide.

4. A thermionic discharge device comprising an evacuated container, electrodes and a gas-absorbent means therein, said means comprising the combination of the product obtained by baking a calcium compound and the product obtained by baking a mixture of the organic-acid compounds of an alkaliearth metal and a base metal.

5. A thermionic discharge device compris- LEON MCCULLOCH.

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