US3919581A - Thoria-yttria emission mixture for discharge lamps - Google Patents

Thoria-yttria emission mixture for discharge lamps Download PDF

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Publication number
US3919581A
US3919581A US488109A US48810974A US3919581A US 3919581 A US3919581 A US 3919581A US 488109 A US488109 A US 488109A US 48810974 A US48810974 A US 48810974A US 3919581 A US3919581 A US 3919581A
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Prior art keywords
lamp
tho2
mole percent
range
proportion
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Expired - Lifetime
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US488109A
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English (en)
Inventor
Ranajit K Datta
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General Electric Co
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General Electric Co
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Publication date
Application filed by General Electric Co filed Critical General Electric Co
Priority to US488109A priority Critical patent/US3919581A/en
Priority to GB21483/75A priority patent/GB1508827A/en
Priority to JP7213375A priority patent/JPS548995B2/ja
Priority to DE2530076A priority patent/DE2530076C3/de
Application granted granted Critical
Publication of US3919581A publication Critical patent/US3919581A/en
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    • 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
    • H01J61/0737—Main electrodes for high-pressure discharge lamps characterised by the material of the electrode characterised by the electron emissive material

Definitions

  • ABSTRACT An improved emission material particularly useful as a coating on the metallic electrodes of metal halide lamps consists of a solid solution of yttrium oxide in the thorium oxide lattice. Enhanced maintenance including less shifting of color rendition with life is achieved. Preferred proportions are 5 to 20 mole percent of Y O in Th0; prefired into a single-phase solid solution.
  • Rare earth oxides including ThO and Y O have been used separately or together as emission mix'in high intensity discharge lamps on account of their low work function, low vapor pressure and chemical compatibility withfthe lamp components and are materials.
  • Such emission mix containing six oxides mechanically mixed was unsatisfactoryfin fact less satisfactory than ThO' alonei According to U.S. Pat. No.
  • rare earth oxides are most useful in-hi gh -i-nten'sity discharge lamps in which the halides of the same rare earths are used as are materials, that is, as the materialsthrough whose vapors the are discharge takes place.
  • a rareeai'th'oxide or a mechanical mixture of one or more of theseoxides was used asemission mix.
  • the object of my invention is to provide a new emission material having improved characteristics and in particular better maintenance than what has been available up to now.
  • I provide a solid solution of yttrium oxide Y O in the thorium oxide ThO lattice, such material forming an improved electron emission material having enhanced maintenance and constancy of color rendition when used for electrode activation in metal halide lamps.
  • the amount of Y O can range from a small amount effective to improve emission characteristics up to about 50 mole percent. I have found the range from 5 to mole percent of Y O dissolved in ThO to be optimum.
  • FIG. 1 is a side view of a metal halide lamp in which the arc tube electrodes are activated with emission mix according to the invention.
  • FIG. 2 is a graph comparing the maintenance of tion.
  • lamps embodying theinvention with that of lamps using a mechanical mixture of six oxides
  • T heemission material of-the present invention is a solid solution of Y O in-the Th0, prepared asfollows:
  • Th(NO );.4H O is soluble in water at room temperature, whereas Y- O dissolves in warm dilute ni-' tric acid.
  • These two materials 'may be dissolved separately and the solutions mixed together later; The mixed solution 'should be chilled in a refrigerator for several hours.
  • the metal ions (Th,Y) nowcan be precipitated as oxalates by slowly adding a supersaturated solution of oxalic acid to the chilled'nitrate solution kept in an ice bath. The nitrate solution should be con stantly stirred to keep oxalates fromforming lumps.
  • the precipitate is now filtered, thoroughly washed and dried at C for several hours.
  • the fine precipitate contained in a platinum'crucible is ignited to oxides at 900C for several hours.
  • the cooled oxide mixture is new ground, blended and reheated at [500C for 3 4 hours; I
  • the material resulting from the foregoing preparation shows only one phase. namely ThO solid solution, u'iider X-ray diffraction analysis. It is well known that the solubility of Y- O in the Th O lattice increases with the final sintering temperature (V. Subbarao et al., J. AmerJ'Ceramic Soc'., Vol. 48, No. 9, 1965). Thus at l500.and 1600C, aboutl2 and 2 0 mole percent of Y Qgre spectively can be dissolved in the ThO lattice.
  • the maintenance of the ThO emission mix begins to improve as soon as the minutest'amountof Y O is incorporated into the lattice.
  • the amount of Y O can rangefrom a small amount effective to improve emission characteristics up to about 50 mole percent which is the largest amount which can be incorporated into Th0 in practice.
  • the thoroughness of mixing and the reaction time and temperature less than all of the Y O may go into solid solution in the ThO
  • the resultant material is a mixture of Y 0 and solid solution of Y O in ThO It is the latter material that has the im proved characteristics. I have found the range from 5 to 20 mole percent of Y O dissolved in ThO as a single phase solid solution to be optimum.
  • the sintered material is mixed with acetone, alcohol or some other organic binder into a slurry and milled for several hours to form a homogeneous suspension of appropriate particle size.
  • the metallic electrode is coated with the emission material by dipping it into the suspension up to a predetermined level; it is then allowed to dry and any loose emission material is brushed off.
  • the amount of the emission material on the electrode surface varies according to the sizes of the lamp (wattage), arc cham- FIG. 3 is a graph comparing the maintenance of lattice which may be her, cathode etc., and can be adjusted by controlling such factors as the density of the suspension and the particle size.
  • the organic binder is burned off and the electrode degassed by thoroughly baking and sintering in the temperature range from 1200 to 1900C in a vacuum environment prior to incorporation into the arc tube.
  • FIG. I shows an otherwise conventional metal halide lamp 1 of 400 watt size in which my improved emission material may be used. It comprises an outer glass envelope 2 containing a quartz arc tube 3 having electrodes 4, 5 sealed into opposite ends.
  • the are tube contains an ionizable filling comprising mercury, sodium iodide, thallium iodide, indium iodide and an inert starting gas such as argon.
  • the electrodes may consist of two layers of tungsten wire turns wound over tungsten shanks 6, 7 which are connected through the usual molybdenum foils to inleads 8, 9.
  • the electrodes are coated with the ThO 0 emission mix which also desirably fills the interstices between turns in the two layers.
  • the are tube inleads are connected to outer leads 10, ll sealed through press 12 of stem 13 of outer envelope 2.
  • the outer leads in turn are connected externally to the contact surfaces of screw base 14 attached to the neck end of the envelope.
  • the lamp according to the invention has less shift in color from to 4000 hours, and less reversal in color from 4000 to 8000 hours.
  • the change in the lamp according to the invention also tends to parallel the black body locus which is a desirable characteristic.
  • An electrode for an arc discharge device comprising a refractory metal substrate and an electron emissive material carried thereon comprising a solid solution of Y O in ThO wherein the proportion of Y O is in the range from a small amount effective to improve emission characteristics up to about 50 mole percent in ThO 2.
  • a high pressure electric discharge lamp comprising a light-transmitting envelope having refractory metal electrodes sealed into opposite ends and containing an ionizable medium including mercury, metal halide and an inert gas at low pressure, and an electron emissive material carried on said electrodes comprising a solid solution of Y O in ThO wherein the proportion of Y Q is in the range from a small amount effective to improve emission characteristics up to about 50 mole percent in ThO 4.
  • the proportion of Y O is inthe range from 5 to 20 mole percent in ThO 5.
  • the refractory metal electrodes comprise turns of tungsten wire wound around a tungsten shank and the electron emissive material'is coated on said turns and lodged in the interstices between turns.

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  • Discharge Lamp (AREA)
US488109A 1974-07-12 1974-07-12 Thoria-yttria emission mixture for discharge lamps Expired - Lifetime US3919581A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US488109A US3919581A (en) 1974-07-12 1974-07-12 Thoria-yttria emission mixture for discharge lamps
GB21483/75A GB1508827A (en) 1974-07-12 1975-05-20 Emission mixtures for discharge lamps
JP7213375A JPS548995B2 (enrdf_load_stackoverflow) 1974-07-12 1975-06-16
DE2530076A DE2530076C3 (de) 1974-07-12 1975-07-05 Elektrode für Hochdruck-Entladungslampen

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US488109A US3919581A (en) 1974-07-12 1974-07-12 Thoria-yttria emission mixture for discharge lamps

Publications (1)

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US3919581A true US3919581A (en) 1975-11-11

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US488109A Expired - Lifetime US3919581A (en) 1974-07-12 1974-07-12 Thoria-yttria emission mixture for discharge lamps

Country Status (4)

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US (1) US3919581A (enrdf_load_stackoverflow)
JP (1) JPS548995B2 (enrdf_load_stackoverflow)
DE (1) DE2530076C3 (enrdf_load_stackoverflow)
GB (1) GB1508827A (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4052634A (en) * 1975-06-20 1977-10-04 U.S. Philips Corporation High-pressure gas discharge lamp and electron emissive electrode structure therefor
US4136227A (en) * 1976-11-30 1979-01-23 Mitsubishi Denki Kabushiki Kaisha Electrode of discharge lamp
US4992700A (en) * 1989-03-10 1991-02-12 General Electric Company Reprographic metal halide lamps having high blue emission
US5013968A (en) * 1989-03-10 1991-05-07 General Electric Company Reprographic metal halide lamps having long life and maintenance
US5111108A (en) * 1990-12-14 1992-05-05 Gte Products Corporation Vapor discharge device with electron emissive material
US6157132A (en) * 1998-08-19 2000-12-05 General Electric Company Discharge lamp emission material

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5822856B2 (ja) * 1975-12-16 1983-05-11 松下電子工業株式会社 メタルハライドランプ
JPS549833Y1 (enrdf_load_stackoverflow) * 1976-02-07 1979-05-09
JPS53128172A (en) * 1977-04-14 1978-11-08 Toshiba Corp Metal vapor discharge lamp
US4123685A (en) * 1977-10-21 1978-10-31 Westinghouse Electric Corp. HID lamp electrode comprising solid solution of dibarium calcium molybdate and tungstate
DE2951741C2 (de) * 1978-12-29 1984-05-30 Mitsubishi Denki K.K., Tokio/Tokyo Elektrode für eine Entladungslampe
JPS5761238A (en) * 1980-09-30 1982-04-13 Mitsubishi Electric Corp Electron emission substance and production

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2460739A (en) * 1946-04-17 1949-02-01 Gen Electric Electrode construction
US3364375A (en) * 1963-10-25 1968-01-16 Gen Electric Metal vapor lamp thorium coated electrode
US3372297A (en) * 1964-09-28 1968-03-05 Varian Associates High frequency electron discharge devices and thermionic cathodes having improved (cvd) refractory insulation coated heater wires
US3485343A (en) * 1967-08-28 1969-12-23 Gen Electric Oxygen getter for high pressure sodium vapor lamp
US3530327A (en) * 1968-03-11 1970-09-22 Westinghouse Electric Corp Metal halide discharge lamps with rare-earth metal oxide used as electrode emission material

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2460739A (en) * 1946-04-17 1949-02-01 Gen Electric Electrode construction
US3364375A (en) * 1963-10-25 1968-01-16 Gen Electric Metal vapor lamp thorium coated electrode
US3372297A (en) * 1964-09-28 1968-03-05 Varian Associates High frequency electron discharge devices and thermionic cathodes having improved (cvd) refractory insulation coated heater wires
US3485343A (en) * 1967-08-28 1969-12-23 Gen Electric Oxygen getter for high pressure sodium vapor lamp
US3530327A (en) * 1968-03-11 1970-09-22 Westinghouse Electric Corp Metal halide discharge lamps with rare-earth metal oxide used as electrode emission material

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4052634A (en) * 1975-06-20 1977-10-04 U.S. Philips Corporation High-pressure gas discharge lamp and electron emissive electrode structure therefor
US4136227A (en) * 1976-11-30 1979-01-23 Mitsubishi Denki Kabushiki Kaisha Electrode of discharge lamp
US4992700A (en) * 1989-03-10 1991-02-12 General Electric Company Reprographic metal halide lamps having high blue emission
US5013968A (en) * 1989-03-10 1991-05-07 General Electric Company Reprographic metal halide lamps having long life and maintenance
US5111108A (en) * 1990-12-14 1992-05-05 Gte Products Corporation Vapor discharge device with electron emissive material
US6157132A (en) * 1998-08-19 2000-12-05 General Electric Company Discharge lamp emission material

Also Published As

Publication number Publication date
JPS548995B2 (enrdf_load_stackoverflow) 1979-04-20
GB1508827A (en) 1978-04-26
JPS5114779A (enrdf_load_stackoverflow) 1976-02-05
DE2530076C3 (de) 1979-03-29
DE2530076A1 (de) 1976-02-12
DE2530076B2 (de) 1978-07-27

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