US3313974A - High pressure electric discharge device having electrodes with thorium on the exposed surface thereof - Google Patents

High pressure electric discharge device having electrodes with thorium on the exposed surface thereof Download PDF

Info

Publication number
US3313974A
US3313974A US277634A US27763463A US3313974A US 3313974 A US3313974 A US 3313974A US 277634 A US277634 A US 277634A US 27763463 A US27763463 A US 27763463A US 3313974 A US3313974 A US 3313974A
Authority
US
United States
Prior art keywords
thorium
electrodes
arc
arc tube
iodine
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US277634A
Other languages
English (en)
Inventor
Koury Frederic
John F Waymouth
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
GTE Sylvania Inc
Original Assignee
Sylvania Electric Products Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GB1051170D priority Critical patent/GB1051170A/en
Application filed by Sylvania Electric Products Inc filed Critical Sylvania Electric Products Inc
Priority to US277634A priority patent/US3313974A/en
Priority to US588851A priority patent/US3427087A/en
Application granted granted Critical
Publication of US3313974A publication Critical patent/US3313974A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/38—Exhausting, degassing, filling, or cleaning vessels
    • H01J9/395—Filling vessels
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/073—Main electrodes for high-pressure discharge lamps
    • H01J61/0735—Main electrodes for high-pressure discharge lamps characterised by the material of the electrode

Definitions

  • This invention relates to the fabrication of high pres sure discharge devices and particularly to the fabrica tion of iodine-containing high pressure discharge devices.
  • the core of thorium is an emitter of a copious flow of electrons which initiates an arc discharge between the electrodes.
  • the problem of thoriums gettering hydrogen during sealing was not too troublesome.
  • certatin disadvantages when they are used with iodide-containing high pressure discharge devices. As we have explained, the main disadvantage is due to the extremely high hydrogen gettering ability of thorium.
  • the arc tube is formed of a quartz or similar glass having a pair of thoriated refractory metal electrodes, generally fabricated of tungsten, supported on lead-in wire-s and sealed into either end thereof.
  • the scaling is performed by heating the glass to softening with gas burners and then urging softened sides of the glass together upon the electrode support such as disclosed in the prior art or in the copending application of Loughridge, Ser. No. 256,049, filed February 4, 1963 and assigned to the same assignee as the instant application.
  • Loughridge Ser. No. 256,049
  • the thorium core contained in the electrodes is also quite near. As the hydrogen containing gas passes through the wall and over the thorium, it is quickly gettered by the thorium and hence included in the envelope. After sealing the arc tube and striking an arc, the hydrogen is expelled from the thorium sliver due to the heat.
  • the thorium sliver should not be disposed within the cathode during sealing. Rather we have discovered that a non-thoriated cathode, that is a cathode containing no thorium sliver, should be sealed within the arc tube, and after the sealing is completed, the requisite thorium should be dropped into the arc tube through an appended exhaust tube together with other ingredients'which are necessary such as mercury, iodine and/or mercuric iodide. After inclusion of such material and filling the envelope with an inert gas of suitable 'pressure, an arc may be struck in the tube. The are will act upon the thorium metal and cause it to plate out upon the outside of the cathodes through the-cooperative action of the iodine.
  • the primary object of our invention is to reduce the amount of hydrogen which is trapped within an arc tube.
  • Another object of our invention is to reduce starting voltages of white light-emitting high pressure electric discharge devices containing iodine.
  • Another object of our invention is to eliminate hydrogen gettering by thorium during arc tube sealing.
  • a feature of our invention is the inclusion of a quantity of thorium metal within the arc tube after the electrodes have been sealed therein.
  • Yet another feature of our invention is dropping a quantity of thorium metal into the arc tube while the arc tube is under a vacuum through an appended exhaust tube disposed on the side of the envelope.
  • FIG. 1 is a crosssectional view of'a' high pressure discharge device which can be fabricated according to our invention.
  • the practice of our invention involves the fabrication of non-thoriated electrodes for use in the arc tube.
  • Non-thoriated electrodes are quite similar to those generally used by the art since they are fabricated of a shank of tungsten surrounded at one end with a tungsten wire helix, however they differ because they contain no sliver of thorium. At the other end of the shank, a small sheet of molybdenum is attached which in turn is Welded to a lead-in wire.
  • This non-thoriated electrode is then positioned Within the end portion of a tubular envelope usually prepared of a silica glass, such as quartz or Vycor. In order to seal the electrodes into the envelope we then heat the glass to softening at the end in which the electrode is disposed and when soft, a press-seal is made. Conventionally, a stream of a suitable inert gas is directed into the envelope through an exhaust tube during heating so that an inert blanket is provided over all metal parts to prevent their oxidation. When the seal is made, the electrode is rigidly disposed in the envelope.
  • the hot sealed end is cooled and a similar non-thoriated electrode is disposed at the other end of the envelope and then sealed in a manner such as described above.
  • the arc tube is ready to be cleaned and then filled with are forming ingredients and gases.
  • the operation can be repeated again if desired and the arc tube is then in condition for the addition of thori um, mercury and iodine, it being possible to add the latter two materials either as elements, the corresponding compound or as a mixture of the elements and the corresponding compound.
  • thori um, mercury and iodine it being possible to add the latter two materials either as elements, the corresponding compound or as a mixture of the elements and the corresponding compound.
  • other metals or chemicals may be added similarly if desired.
  • the arc tube may then be fully fabricated merely by sealing off the exhaust tube as is conventional in the art. At this point however, the thorium must be transferred to the cathodes since its disposition there is required.
  • the arc tube is fabricated according to techniques set forth in the abovementioned Loughridge application. We then pump down the arc tube to a partial vacuum and fill with argon, which operation is generally repeated two times.
  • the :argon may be added to a pressure of 300 mm. of Hg pres- ;sure.
  • the purpose for these flush and fill steps is to remove any water and other gases which accidently may be included in the arc tube.
  • the arc tube When the arc tube has been flushed and filled with :argon it is then placed under a vacuum and baked at temperatures of 750 to 1200 C. for about minutes until there is no evidence of outgassing in either electrodes or the glass envelope.
  • a convenient measure of outgassing is watching a pressure gauge which indicates the pressure in the arc tube. If outgassing is occurring, the vacuum pump will not be able to maintain a constant vacuum and this inability will be indicated upon the associated pressure gauge. When the gauge is constant, outgassing has ceased.
  • the arc tube can be flushed with argon a few times, four for example, to insure the removal of the outgassed gases.
  • a current in the order of microamperes is developed together with a frequency in the order of a megacycle while producing up to five to ten thousand volts. It is generally desirable to keep the are formed for a minimum time at high electrode operating temperatures (2000 to 250-0 C.) to prevent inordinate volitization of the tungsten onto the walls of the envelope.
  • the iodine is added in the form of mercury iodide with additional mercury metal being-added later to bring the quantity to a point which is adequate for high pressure discharge device arc formation.
  • the two stage addition is preferable since the thorium and particularly mercury iodide tend to absorb small quantities of water which are deleterious to are formation. Such water can be removed easily by flaming the materials while they are disposed in the arc tube and under vacuum and thus causing the mixture to be distilled off and drawn from the envelope. When the flaming is finished, a vacuum can again be formed at which time the remaining quantity of mercury can be added. This amount should be sufficient to form a ratio of iodine to mercury of 0.10 to 0.85 atom iodine per atom of mercury.
  • the final steps in the process are to flush the envelope with argon or a similar gas which is inert to the ingredients of the lamp, then filled with argon at a pressure of about 23 millimeters of mercury and immediately sealed from the atmosphere by tipping off the exhaust tubulation.
  • the thorium Since at least a part of the thorium must be deposited upon the electrodes of the arc tube in order to perform its function, we then start the are at which time the thorium reacts with the iodine and forms ThL, The ThI, then evaporates into the arc and some will dissociate in the vicinity of the electrodes. When such dissociation occurs the thorium metal will plate out upon the electrodes and will eventually form an ever-renewing coating. After operation of the are for about a half hour,
  • the are tube, fully fabricated, is shown in the figure wherein a pair of non-thoriated electrodes are sealed through the ends 12 and 14 of the tube 16.
  • These electrodes may be of any of the typical designs, however we prefer to use ones having a shank of tungsten metal surrounded at their inner ends by a helical winding of tungsten.
  • tungsten shanks 1 and 4 having windings 2 and 3 are sealed into the ends 12 and 14 of the arc tube 16 and attached to one end of molybdenum foil sections 5 and 9.
  • lead-in wires 6 and 11 Disposed on the other ends of the foil sections 5 and 9 and extending outside of the arc tube are lead-in wires 6 and 11 which can be connected to a source of current.
  • a residual fused tip 15 which remains after the inclusion of the arc-forming ingredients is disposed upon the outside of the arc tube.
  • a thin coating of thorium metal (not shown) is formed upon the electrodes and generally a small ball 17 of thorium will occur at the distal ends.
  • the ball is formed by the dissociation of thorium iodide (ThI in the high temperature arc stream.
  • ThI thorium iodide
  • the thorium reacts with the iodine to form thorium iodide.
  • the thorium iodide dissociates and deposits thorium metal upon the hottest place on the electrode.
  • the electrode When fabricating the electrode, it should be designed so that the thorium reacts with the iodine and hence is removed from the wall and deposited upon the electrode. Hence the point of minimum vapor pressure of the thorium or its iodine compounds should be on the electrode. In order to attain such minimum vapor pressure it is necessary to take both the vapor pressure and the stability of thorium iodide into consideration. When plotting the partial pressure of thorium or thorium compounds over metallic thorium in an atmosphere of iodine vapor as a function of temperature, a three component curve results.
  • the partial pressure of the Th1; atoms increases with increasing temperature.
  • the rate-limiting process is the rate of arrival of iodine atoms at the surface, and the pressure of ThL; becomes a constant, independent of temperaturre.
  • the Thl is unstable and the effective partial pressure of the ThI will decrease.
  • evaporation of the thorium metal atoms will take place and the vapor pressure of thorium will increase with increasing temperature.
  • the range of operating electrode temperature for our lamp is in the first, second or third temperature ranges noted above and hence there is a tendency for the thorium to deposit at the point of highest temperature on the electrode, provided that the partial pressure of thorium corresponding to the operating temperature is less than the partial pressure of the ThI at the arc tube wall.
  • the iodine will pick thorium in the arc tube and gradually deposit it during operation as a ball on the tip of the electrode.
  • a high pressure electric discharge device comprising an arc tube; a filling in said are tube comprising mercury atoms and iodine atoms; a pair of electrodes disposed at either end of said are tube, said electrodes having a coating of thorium metal disposed upon the exposed surface thereof in order to supply thorium atoms to the are discharge.
  • a high pressure electric discharge device comprising: an arc tube, an electrode disposed at either end thereof, each of said electrodes having a central shank portion surrounded'by helical Winding at the inner ends, a filling in said are tube of mercury and a iodine and coating of thorium metal disposed upon the exposed surfaces of said electrodes in order to supply thorium atoms to the arc discharge.
  • a high pressure electric discharge device comprising: an arc tube; an electrode disposed at either end thereof, each of said electrodes having a coating of thorium metal disposed upon the exposed surfaces thereof and a ball of thorium disposed on upon at least one of the distal ends in order to supply thorium atoms to the arc discharge, a filling in said are tube of mercury and iodine.
  • a high pressure electric discharge device comprising: an arc tube; an electrode disposed at either end thereof, each of said electrodes having a coating of thorium metal disposed at the exposed point of maximum temperature in order to supply thorium atoms to the arc discharge; a filling in said arc tube of iodine and mercury.
  • part of the thorium coating is in the shape of a ball disposed at the distal end of at least one of the electrodes.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Discharge Lamp (AREA)
US277634A 1963-05-02 1963-05-02 High pressure electric discharge device having electrodes with thorium on the exposed surface thereof Expired - Lifetime US3313974A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB1051170D GB1051170A (enrdf_load_stackoverflow) 1963-05-02
US277634A US3313974A (en) 1963-05-02 1963-05-02 High pressure electric discharge device having electrodes with thorium on the exposed surface thereof
US588851A US3427087A (en) 1963-05-02 1966-10-24 Arc tubes and process for their fabrication

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US277634A US3313974A (en) 1963-05-02 1963-05-02 High pressure electric discharge device having electrodes with thorium on the exposed surface thereof

Publications (1)

Publication Number Publication Date
US3313974A true US3313974A (en) 1967-04-11

Family

ID=23061731

Family Applications (1)

Application Number Title Priority Date Filing Date
US277634A Expired - Lifetime US3313974A (en) 1963-05-02 1963-05-02 High pressure electric discharge device having electrodes with thorium on the exposed surface thereof

Country Status (2)

Country Link
US (1) US3313974A (enrdf_load_stackoverflow)
GB (1) GB1051170A (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3364375A (en) * 1963-10-25 1968-01-16 Gen Electric Metal vapor lamp thorium coated electrode
US3937996A (en) * 1974-10-07 1976-02-10 General Electric Company Metal halide lamp using loop electrodes
US4105908A (en) * 1976-04-30 1978-08-08 General Electric Company Metal halide lamp having open tungsten coil electrodes
US4360756A (en) * 1979-11-13 1982-11-23 General Electric Company Metal halide lamp containing ThI4 with added elemental cadmium or zinc
US5357167A (en) * 1992-07-08 1994-10-18 General Electric Company High pressure discharge lamp with a thermally improved anode

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2691853A (en) * 1951-09-29 1954-10-19 Gen Electric Tubular lamp manufacture
US2740186A (en) * 1951-07-17 1956-04-03 Sylvania Electric Prod Gas tube assembling method
US2916653A (en) * 1957-04-01 1959-12-08 Duro Test Corp Electron emissive electrode
US3153169A (en) * 1961-06-02 1964-10-13 Patent Treuhand Ges Fuer Elektrische Gluehlampen Mbh Discharge lamp
US3170081A (en) * 1962-06-05 1965-02-16 Westinghouse Electric Corp Discharge lamp electrode
US3234421A (en) * 1961-01-23 1966-02-08 Gen Electric Metallic halide electric discharge lamps

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2740186A (en) * 1951-07-17 1956-04-03 Sylvania Electric Prod Gas tube assembling method
US2691853A (en) * 1951-09-29 1954-10-19 Gen Electric Tubular lamp manufacture
US2916653A (en) * 1957-04-01 1959-12-08 Duro Test Corp Electron emissive electrode
US3234421A (en) * 1961-01-23 1966-02-08 Gen Electric Metallic halide electric discharge lamps
US3153169A (en) * 1961-06-02 1964-10-13 Patent Treuhand Ges Fuer Elektrische Gluehlampen Mbh Discharge lamp
US3170081A (en) * 1962-06-05 1965-02-16 Westinghouse Electric Corp Discharge lamp electrode

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3364375A (en) * 1963-10-25 1968-01-16 Gen Electric Metal vapor lamp thorium coated electrode
US3937996A (en) * 1974-10-07 1976-02-10 General Electric Company Metal halide lamp using loop electrodes
US4105908A (en) * 1976-04-30 1978-08-08 General Electric Company Metal halide lamp having open tungsten coil electrodes
US4360756A (en) * 1979-11-13 1982-11-23 General Electric Company Metal halide lamp containing ThI4 with added elemental cadmium or zinc
US5357167A (en) * 1992-07-08 1994-10-18 General Electric Company High pressure discharge lamp with a thermally improved anode

Also Published As

Publication number Publication date
GB1051170A (enrdf_load_stackoverflow)

Similar Documents

Publication Publication Date Title
US3259777A (en) Metal halide vapor discharge lamp with near molten tip electrodes
US3334261A (en) High pressure discharge device having a fill including iodine mercury and at least one rare earth metal
US5363007A (en) Low-power, high-pressure discharge lamp, particularly for general service illumination use
US3514660A (en) Electric discharge flicker lamp
US3350598A (en) High pressure electric discharge device containing a fill of mercury, halogen and an alkali metal and barrier refractory oxide layers
US3521110A (en) Mercury-metallic halide vapor lamp with regenerative cycle
US3067357A (en) Electric discharge lamp electrode
US4321504A (en) Low wattage metal halide arc discharge lamp
US3377498A (en) In a high pressure lamp, protective metal oxide layers on the inner wall of the quartz envelope
US3405303A (en) Arc discharge tube having an electrode which contains a light-emitting metal
US2419902A (en) Fluorescent electric discharge lamp
US3714493A (en) Compact metal halide arc lamp containing primarily mercury iodide
US3313974A (en) High pressure electric discharge device having electrodes with thorium on the exposed surface thereof
US3563797A (en) Method of making air stable cathode for discharge device
US2769112A (en) Discharge lamp, mount therefor, and method
US3331982A (en) High pressure electric discharge device having a fill including vanadium
US4836816A (en) Method of treating tungsten cathodes
US3427087A (en) Arc tubes and process for their fabrication
US2438181A (en) Fluorescent and/or cathode glow lamp and method
US3324332A (en) Discharge tube having its electrodes recessed in wells
US3577029A (en) High-pressure electric discharge device containing mercury, halogen, scandium and samarium
US2657325A (en) Electrode for electric discharge lamps
US2728871A (en) Electric discharge lamp
US4910433A (en) Emitterless SDN electrode
US2906905A (en) Fluorescent lamp