US1244216A - Electron-discharge apparatus and method of preparation. - Google Patents

Electron-discharge apparatus and method of preparation. Download PDF

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Publication number
US1244216A
US1244216A US17692617A US17692617A US1244216A US 1244216 A US1244216 A US 1244216A US 17692617 A US17692617 A US 17692617A US 17692617 A US17692617 A US 17692617A US 1244216 A US1244216 A US 1244216A
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cathode
temperature
thorium
electron
tungsten
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US17692617A
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English (en)
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Irving Langmuir
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General Electric Co
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General Electric Co
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/14—Solid thermionic cathodes characterised by the material

Definitions

  • the present invention relates to electrical devices operating with a pure electron discharge and comprises a novel cathode material and the method of its preparation.
  • the electron emissivity of pure thorium is of an entirely different order of magnitude than the emissivity of refracto materials heretofore used in electron dlscharge devices. It is not necessary that the electrode should. consist entirely 'of thorium.
  • a thorium compound such as the oxid
  • the highly refractory metals for example, tungsten, and the metaL
  • Fig. 2 is a device operable as a rectifier having a thoriated cathode and plate-shaped anodes; and Fig. 3 illustrates a modification in which active. thorium material may be transferred to the cathode from an independent thoriated conductor. v
  • envelop 1 consistin of glass, quartz or the like provided wit two filamentary conductors 2, 3, of highly refractory metal, such for example as tungsten, at least one of which, say filament 2, is thoriated. They are connected to leading-in wires 4, 5, sealed into a stem 6 in the well-known manner.
  • the envelop is connected to a vacuum sys tem by a tube 7, containing a trap -8 which may be surrounded by a freezing bath, such as liquid air, contained in a Dewar flask 9 or even an ice and salt mixture. It is the function of the freezing bath to prevent mercury, or other vapors, from the vacuum pumps from reaching the envelop 1.
  • the preliminary evacuation of the envelop is carried out by the usual methods of producing high vacuum, which includes baking out the envelop to remove water vapor.
  • the final stage of the evacuation is preferably but not necessarily carried out by a Gaede molecular pum to the highest possible vacuum obtainable y this means,- that is, to about .001 micron.
  • the filaments 2, 3 are heated to a temperature of about 2900 K. (absolute) for a short time and the envelop 1 is baked out in an oven at a temperature of about 360 to 450 K.
  • the apparatus may then be sealed from the vacuum system at the contraction 10. It is then preferably immersed in liquid air and both filaments 2, 3 aged by heating for about A hourto .a temperature of 2400 to 2500 K.
  • filament 3 is then incandesced by a passage of current to a temperature of about 3000 K. which causes rapid vaporization of the metal, thereby producing a gas-free conducting deposit or coating 11 which has been shown on the inner surface of the envelop.
  • Conductors 12, 13 sealed into the envelo make contact with this coating and enable 1t to be used as an anode for an electrical dis-.
  • the cathode conductor 2 is prepared by introducing a thorium compound, such as the nitrate of thorium to the oxid of the refractory metal before reductron emission that may be obtained under the best conditions but with a greater roportion of thorium compound the deslred active condition of the filament may be reached and maintained with greater case than with a lesser amount.
  • a thorium compound such as the nitrate of thorium
  • the thoriated cathode 2 is now heated to about 2900 K. for about one minute.
  • the treatment. of the filament at a temperature of 2900 has no marked effect on the subsequent electron emission of the cathode when at lower temperature but appears to be desirable for purifying the surface of the cathode.
  • the cathode is then incandesced within the range of about 2000 to 2400 K. and by this temperature treatment Some change is produced in the cathode wh ch enormously increases its electron-emitting property under the condition described.
  • the greatest activity is obtained between about 2200 to 2300 K. and the treatment at this temperature is usually continued for about one minute, but even outside of this range a marked change is produced.
  • a concentration of metallic thorium or of some other oxidizable thorium material takes lace on the surface of the filament.
  • lament 2 may now be used as a cathode at a temperature below this forming tempera- With a filament thus prepared I have obtained at a temperature of about 1300 to 1380 K. substantially the same electron emission per sq. cm. as with a pure tungsten filament at about 2000 K., that is, about three milliamperes per sq. cm.
  • a thoriated cathode is operated around 17 00 to 1800 K., at which temperatures its life is indefinitely long.
  • the filament is heated to a higher temperature, for example, to 2800 K., causes some change, apparently a distillatlon of the film of thorium from the surcandescence.
  • the active thorium material may be transferred by distillation to an adj acent surface.
  • the heating of the cathode to a temperature above 2300 after the preparation of the surface film results in the distillation of some of the thorium material to conductor 3 so that when the conductor 3 is used as a cathode with respect to the anode 11, it is found that its electron emission has been greatly increased.
  • %athodes containin only a small amount of thorium compoun are deleteriously affected by disintegration of the surface produced by positive ion bombardment and in this respect may be extremely sensitive. In this case, it is necessary when using voltages high enough to cause ionization of residual gases to carry the vacuum far beyond the point at which a disruptive discharge no onger takes place, which ordinarily is about of a thoriated cathode even in the presence of pressures of gasup to atmospheric pressure.
  • the active thorium is slowly diffusing to the surface from the interior of the metal. As the temperature is raised a point is reached where the distillation of thorium from the surface exceeds the rate at which the metal difluses to the surfaces. It is possible, however, to operate a refractory thoriated cathode at a temperature between 2000 and 2200 K. for a long time without destroying its high electron emission, but operation at a higher temperature is not advisable. A sufficiently great electron emission can be secured through the indicated temperature range with an accompanying saving of energy necessary for heat paratus shown in Fig. 1.
  • the envelop 17 is baked out and-evacuated as already described in connection with Fig. 1.
  • the ionizable gas should be removed from the anodes during the final stages of the exhaust after the pressure has been reduced below about of a micron of mercury by subjecting the anodes to an electron discharge from the cathode 18 whereby ionizable gas is evolved, as disclosed in my co-pendingapplication, Serial No. 795,610 of October 16, 1913.
  • This gas should be removed as fast as liberated and the discharge voltage progressively increased, care being taken'fnot to materially exceed the voltage at which blue glow takes place so as to avoid injury to the cathode.
  • the final stage of the evacuation is produced by vaporizin a tungsten conductor in a side chamber %not shown in the drawing), thereby producing the very hi h vacuum necessary for the operation 0 the thoriated cathode.
  • the anodes 15, 16 may be both connected to one terminal of a secondary of the transformer 19, by conductors 20, 21, the cathode being connected to the other terminal by conductor 22, including a load circuit 23.
  • the cathode 18 has been merely indicated by dotted lines as being a V-shaped filament supported by terminal wires 24, 25, and maintained taut at its bight by a spring .26, but it is to be understood that it may have any convenient form.
  • Thorium compound, for example, the oxid is introduced during the process of manufacture as already described.
  • the apparatus here shown is suitable for the rectification of alternating current when the cathode is maintained at incandescence by a battery 27, preferably at a temperature of 1700 to 1800 K.
  • a cathode 28 located opposite an anode 29 is provided with a film of active thorium material vaporized from the coiled filamentary cathode 30 heated by a battery 31.
  • the cathode 30 may consist either of a thoriated cathode prepared as already described, or of metallic thorium.
  • the coil 30 consists of thori'ated wire it is first rendered active by heat treatment at a temperature of 2200 to 2300 K., as already described, and is then heated to a, temperature of about 2900 K. to distil ofi' active material, some of which is condensed on the cathode 28.
  • the coil 30 consists of metallic thorium, it should be heated to a temperature near its melting point to distil some of the thorium over on to the surface of the cathode 28.
  • an inert gas at a pressure of say .01 micron when the volta e impressed between the cathode and anode does not arise above the ionizing potential of the gas.
  • Advantage can be taken of this fact .to use an electron discharge device containing a thoriated cathode as a voltage sensitive cut-out device. Below the voltage at which disintegration of the surface begins, a device such as shown in Fig. 1 may be used to pass a current of about of an ampere per sq. cm.
  • an electrode comprising in part at least oxidizable thorium ma rial said electrode having at a temperature of about 1300 to 1380 absolute an electron emission substantially equal to that of tungsten at about 2000 absolute.
  • an electrode comprising in part at least oxidizable thorium and having when at incandescence in a vacuum so highly attenuated that positive ionization is substantially absent, an electron emission materially greater per unit of surface than tungsten at the same temperature.
  • a cathode for electron-discharge ap- -paratus consisting largely 'of a highly refractory metal and a surface layer of material having an electron emissivity at a given temperature materially greater per unit surface than said refractory metal independ.
  • a conductor comprising a refractory meta and a surface film of thorium material vaporizable at a temperature above about 2300 K. and having a greater electron emission when at incandescence in a non-striking vacuum than said refractory metal.
  • an electrode comprising metallic tungsten and a surface film of thorium material vaporizable at a temperature above about 2300 K. removable from said surface by positive ionization and having an electron emission per unit surface many times greater than pure tungsten at the same temperature.
  • an electrode comprising metallic tungsten and thoria said electrode having been subjected to a temperature of about 2200 to 2350 K. and having an electron emission a thousand times as great per unit of surface as tungsten in a vacuum too high to permit of positive ionization.
  • a cathode comprisin metallic tungsten and thoria, said electrode having received a heat treatment at about 2000 to 2350 K, and having an electron emission when at incandescence at a given temperature of a higher order of magnitude than pure tungsten at the same temperature.
  • a cathode for electron discharge apparatus consisting largely of tungsten and containing thorium, said cathode having an electron emissivity, independently of and in the absence of positive ionization, at a given temperature materially greater per-unit surface than tungsten at the same temperature.
  • an electrode comprising a highly refractory metal and containin oxidizabl'e thorium material,'said electrode aving an electron emissivity per unit surface many times greater than said refractor metal alone at the same temperature, the e ectron emissivity of said cathode being lowered by the presence of oxygen and by positive ionization.

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  • Solid Thermionic Cathode (AREA)
  • Cold Cathode And The Manufacture (AREA)
US17692617A 1914-07-15 1917-06-25 Electron-discharge apparatus and method of preparation. Expired - Lifetime US1244216A (en)

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DE (1) DE311102C (fr)
FR (1) FR507198A (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2525263A (en) * 1950-08-25 1950-10-10 Michel E Macksoud Method of producing highly emissive electrodes
US2525262A (en) * 1948-02-18 1950-10-10 Cooper Hewitt Electric Co Method of producing highly emissive electrodes
US2675498A (en) * 1948-12-07 1954-04-13 Raytheon Mfg Co Cathode for electron discharge devices
US3134924A (en) * 1960-07-05 1964-05-26 Monsanto Co Emissive materials of a metal matrix with molecularly dispersed additives

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2525262A (en) * 1948-02-18 1950-10-10 Cooper Hewitt Electric Co Method of producing highly emissive electrodes
US2675498A (en) * 1948-12-07 1954-04-13 Raytheon Mfg Co Cathode for electron discharge devices
US2525263A (en) * 1950-08-25 1950-10-10 Michel E Macksoud Method of producing highly emissive electrodes
US3134924A (en) * 1960-07-05 1964-05-26 Monsanto Co Emissive materials of a metal matrix with molecularly dispersed additives

Also Published As

Publication number Publication date
DE311102C (fr) 1919-02-25
FR507198A (fr) 1920-09-07

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