US 1244217 A
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v l. LANGMUIR. 'ngcmow o'rscmume AEPARATUS AND METHOD OF OPERATING THE SAME.
AP PLICATION FILED OCT. 28. 1915- Patented Oct. 23, 1917.
Inventor-:- lr'ving L. y
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ELEUI'BON DIBCEABGB mmros AND METHOD 0! ormrme em Specification of letters latent.
Patented Oct. 23, 1917.
Application filed October 88, 1915. Serial H0. 58,877.
To all'whom it may concern:
Be it known that I, Invmc Lanonum, a citizen of the United States, residing at SchenectagTy, in the county of Schenectad State of ew York, have invented certain new and useful Improvements in Electron- Discharge A paratus and Methods of Op of which the following 1s e'presen't invention relates to electrical devices having an -electrode consisting atleast in part of thorium and having at a given temperature. an electron emission per unit surface materially. greater than the emission of a refractory metal such as tun sten at the same temperature-independent y of and .,in the absence of positive ionization. These devices are described and claimed in acopending application, Serial No. 851,095,
.and also'rendered easier. the preparation of the same by providing in the envelop a quantity of avaporizable reagent of low vapor pressure capable of preventing the oxidation of thorium. I refer to use for this purpose an alkali meta, such for example, as po- The accompanying drawing" illustrates one particular form of a paratus to which my invention is applicab e, namely, an incandescent cathode discharge device provided with means for'introducing the desired reagent. 7
The device shown in the drawing which may be used for rectifying alternating current, comprises an envelop 1 conslstin of a glam not chemically attacked by a ali metal provided with 'a cathode 2 consisting for example of thoriated tungsten, and a cylindrical or on shaped anode 3, also conslsting of a hlg ly refractory metal, such for exam 1e, as tungsten. A heating curconveyed to the-cathode by leading-in conductors 4, 5, sealed into a stem 6 in the usual manner and connected to a threaded socket 7 similar to an incandescent lamp socket. The anode stem 8 is also sealed into a glass stem 9 and attached to an external metal cap 10.
The cathode 2 is prepared by adding a thoria compound, sue as nitrate of thorium to the oxid of tungsten before reduction of the metal, or by adding either thorium nitrate or thoria to the metal'powder after reduction, but before consolidation of the metal powder by sintering and mechanical working to thesolid state as described, for example by reference to thoriated tungsten atent #:3082333. The proportion of thoria in t e ally varies from to 10% but in some cases may be even greater. The proportion of thorium compound within the above limits makes little difference in' the maximum electron emission that may be obtained under the best conditions but the favorable conditions will be more easily attained with a greater than with a lesser amount.
The preliminary evacuation of the envelo is carried out by the usual methods of p ucing a non-striking high vacuum, which includes bakingrplut the envelop to remove water vapor. e final stage of the evacuation is preferably but not necessarily carried out by a Gaede molecular pump to the highest possible vacuum obtainable by this means, that is, to about .001 micron. While the apparatus is still on the pump the cathode 2 is eated to a tem erature of about 2900 K. (2727 C.) for a s ort time and the envelop 1 is baked out in an oven at a temperature of about 360 to 450 C.
The substance to be distilled into the envelop, for example, potassium, is indicated at 12 in a small side chamber 13, a small quantity of glass particles, or glass wool, 14 being preferably placed in front of the reducing material. As already indicated all glasses (including the glass wool) used in t e apparatus should be unattacked by alkali metal. When the envelop isbaked out care should be exercised not to heat the chamber 13 to too high a temperature. The potassium, or other material, is transferred by meltin into a communicating chamber 15. after w ich the chamber 13 may be sealed off. Thereupon, the material is distilled into a second communicating chamber 16 and into the main envelop 1, both the chambers cathode maybe operate 15 1,6 being successively seaed ofi. The re-.
distillation of the reducin material serves to purify it. Although al ali metals have been indicated as preferable tor the purposes of m invention, other reducing materials may .used, for exam 1e, hydrocarbon compounds. The bulb is nally sealed from the vacuum system at the contraction 1.1. The thoriated cathode 2 is now heated to about 2900 K. for about one minute. The
treatment of the filament at. this temperature appears to be desirable for purifying the suriace of the cathode. The cathode is then incandesced within the range of about 20Q0 to 2400 K. and by this temperature treatment some change is produced in the cathode which enormously increases its electronemitting rop-prty under the condition described. he greatest activity is obtained between about 2200 to 2300 K.and the treatment at this temperature is usually continue for about one minute. Apparently -a concentration ofmetallic thorium or of some other oxidizable' thorium material takes place on the surface of the filament. The filament 2 may now be used as a cathode at or below this forrningtemperature.
The presence of the reducing agent in the main receptacle maintains the thorium reduced in s its of traces of watervapor ay any event the high electron emissivity of the thoriated cathode is more easily secured and maintained in the presence'of the reducing agent than without it.
With a filament thus 'pre ared I have obtained at a temperature 0 about 1300 to 1380* K. substantially the same electron emission per sq. cm. as with a pure tu sten filament at about 2000 'K., that is, a ut three milliamperes per s cm. A thoriated around 17009 to 1800 K., at which temperatures its life is long, and thermionic current may be obtained many thousands oi times greater than obtainable with pure tungsten at the same temperature.
Subsequently heating the filament to a higher temperature, for example, to 2800 K. causes some change, apparently a distillation of the film of thorium the sur fiace, as the electron emitting power of the cathode falls to the same order of magnitude as pure tun sten. When the cathode after being thus eated is re-subjected to a temperature of 2200 to 2300 K. the active liberated 'from the glam. In Y within said envelop,
the beneficial efi'ect of the alkaline metal is exerted upon thoria content of the filament and is not due to some ionization phenomena.
Under carefully controlled conditions the benefit oi the increased electron'emission ot a thorium-containin cathode may be securedin a device tied with an 'inert gas, such, i or example, as argon' or other monatomic' ases, at pressures ranging from 'a few millimeters oi mercury pressure upward, in the presence ofpotassium orequivalent material for preventing the oxidation of thorium. Care must be exercised to have the cathode at a high enough temperature with reference to the current transmitted so that the vicinity of the cathode is surrounded by free. electrons. In other wor&, the electron emission should be greater than necessary to convey the current thereby preventing a removal of the active thorium material on the surface of the cathode bya bombardment of positive ions.
What I claim 'as new and desire to secure by Letters Patent of the United States, is:
1. An electrical discharge device comprising electrodes, one of which contains thorium, an inclosing envelop the space within which is evacuated to a ressure so low that positive ionization is su antialily absent, and a quantity of a va 4 rizable'rea ent capable of preventing t oxidation 0 thorium in communication with the space within said envelop.
2. In an electrical discharge devi an inclosing envelop, a quantity of alkali metal and electrodes therein, one of which comprises in part at least, oxidizable thorium material, said electrodes having at a temperature of about 1300 to 1380" absolute an electron emission substan-. tially equal 'to that of tungsten at about 2000 absolute.
3. In an electrical discharge device, an inclosing envelop, a quantity of potassium within said envelop, and electrodes therein, one of which consists largely of tungsten and containing thorium, said electrode having an electron emissivity at a given temperature materially greater per unit surface than tungsten at the same temperature.
t. An electrical discharge device compris ingelectrodes, one of which consists of me tallic tungsten and a thorium material'in an oxidizable state, an inclosin envelop, and a quantity of a vaporizab e reagent within said envelop capable of preventing the oxidation of thorium at an elevated temperature. I
5. The process of improving the operation of an electron discharge apparatus containing an electrode operating at. incandescence com rising a hi h y refractory metal and a thorium materia which consists in bringing into contact with said electrode the vapor of a reagent preventing the oxidation of thorium at an elevated temperature.
6. The process of improvingthe' operation of an electron discharge apparatus containing an electrode of tungsten and thorium operating at incandescence in a nonstriking vacuum, which consists in bringing into contact with said electrode the vapor of an alkali metal at a pressure too low to .cause appreciable positive ionization phenomena.,
7. An electrical device comprising the combination of a sealed evacuated envelop a refractory cathode, means for heating said cathode to incandescence, a cooperating anode and a quantity of potassium within said envelop.
8. An electrical device comprising the combination of an evacuated envelo a cathode, an anodeand a quantity of a kali metal mclosed within said envelop and means for heating said cathode to moandescenoe.
-In witness whereof, I have hereunto set my hand this 27th day of October, 1915.