US3513349A - Discharge tube - Google Patents

Discharge tube Download PDF

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Publication number
US3513349A
US3513349A US605327A US3513349DA US3513349A US 3513349 A US3513349 A US 3513349A US 605327 A US605327 A US 605327A US 3513349D A US3513349D A US 3513349DA US 3513349 A US3513349 A US 3513349A
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US
United States
Prior art keywords
cathode
iron boride
discharge tube
carbonate
powder
Prior art date
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Expired - Lifetime
Application number
US605327A
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English (en)
Inventor
Hideo Mizuno
Hidezo Akutsu
Eiziro Moriguchi
Katsuyuki Yamashita
Shigeru Kamiya
Koshi Iwata
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.)
Panasonic Holdings Corp
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Matsushita Electronics Corp
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Publication date
Application filed by Matsushita Electronics Corp filed Critical Matsushita Electronics Corp
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Publication of US3513349A publication Critical patent/US3513349A/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
    • H01J61/067—Main electrodes for low-pressure discharge lamps

Definitions

  • a coating for electrodes of discharge tubes including iron boride, a high-melting reducing metal such as zirconium, hafnium, niobium or tantalum, and electron emissive materials.
  • the coating reduces R.F. emission in the 535-1605 kHz. range and is particularly adapted for lowpressure mercury-vapor discharge tubes.
  • This invention relates to discharge tubes and more particularly to improvements in low-pressure mercury-vapor discharge tubes such as fluorescent discharge lamps.
  • oxide-coated cathodes employed heretofore as the electrodes of low-pressure mercury-vapor discharge tubes, such as fluorescent lamps, have been made with a double coil of tungsten or the so-called triple coil made by further winding a fine wire of tungsten around the above-mentioned tungsten double coil.
  • a triple carbonate consisting of barium carbonate, strontium carbonate and calcium carbonate, is coated on the double coil or the triple coil electrode.
  • the electrodes are enclosed in a discharge tube, and during the step of exhausting the tube, this carbonate is thermally decomposed into oxides of barium, strontium and calcium and thus forms a socalled oxide-coated cathode.
  • the conventional oxide coating made in the manner described above, has a high specific resistance and a poor thermal conductivity, resulting in the appearance of local high temperature cathode spots when the discharge tube is energized. These cathode spots act as emission centers. Due to thermal inertia, the temperature of a cathode spot hardly varies at the time of reignition and extinction of the arc, on each cycle of the alternating current, and remains high throughout the energized state of the discharge tube.
  • the thermionic emission current I becomes greater than the discharge current I during the reignition and extinction of the arc on the cathode so that a negative field is formed in front of the cathode and causes cathode oscillation, which results in reignition noises and extinction noises.
  • This cathode oscillation has been a major cause of severe radio interference.
  • Japanese patent publication No. 1581/ 1964 discloses a method according to which the thickness of an oxide coating is reduced to a value of less than 30 microns thereby resulting in a substantial improvement of the thermal conductivity of such oxide coating and enlargement of the cathode spot to reduce the temperature thereof. This method, however, is undesirable because the absolute quantity of the oxide emitter is inevitably reduced and this leads to a short life for the discharge tubes.
  • Japanese patent publication No. 1581/ 1964 discloses a method according to which the thickness of an oxide coating is reduced to a value of less than 30 microns thereby resulting in a substantial improvement of the thermal conductivity of such oxide coating and enlargement of the cathode spot to reduce the temperature thereof.
  • This method is undesirable because the absolute quantity of the oxide emitter is inevitably reduced and this leads to a short life for the discharge tubes.
  • the cathode material discovered by the present inventors consists essentially of iron boride powder which has a high melting point and a remarkably high thermal conductivity when compared with conventional ionic crystals, reducing metal powders such as zirconium, hafnium, niobium and tantalum, and emitters such as barium, strontium and calcium oxide.
  • the above-described reducing metal powders, such as zirconium, hafnium, niobium and tantalum effectively prevent the oxidation of iron boride during thermal decomposition of the carbonate during the step of exhausting the discharge tube.
  • a very excellent noise suppression effect could be obtained with a discharge tube provided with the inventive cathode material including iron boride (either FeB or Fe B) in an amount of 2 percent by weight, oxides of barium, strontium and calcium, and metallic zirconium, in an amount of 3 percent by weight of the oxides.
  • this discharge tube performed in such an excellent fashion that a noise intensity of less than 15 decibels was attained, as shown by curve 2 in the figure, throughout a frequency range of from 535 kilocycles to 1605 kilocycles.
  • the excellent performance of the inventive discharge tube is self evident through comparison with a corresponding performance of a conventional discharge tube, as shown by curve 1 in the figure.
  • iron boride powder added to the oxides is highly resistant to heat, is chemically stable even at elevated temperatures, does not develop such phenomena as evaporation and sputtering, and does not cause any brittleness f the coil resulting from reaction with tungsten. Therefore, it is unlikely that undesirable conditions, such as extreme blackening and short lamp life, will be brought forth by inclusion of iron boride in the cathode oxide coating.
  • Iron boride is normally represented by two chemical formulas, FeB and Fe B, which are both effective for use in the cathode material for the inventive electrode.
  • the amount of boron required in the iron boride employed in the invention is not as strict as that defined by the chemical formulas.
  • the boron content may lie in a wide range of from to 30 percent by weight.
  • the addition of iron boride powder in an amount of more than 0.05 percent by weight exhibits a substantial effect for the prevention of radio interference, but an amount of the order of 0.5 to 3 percent is especially desirable to avoid possible content fluctuation in the manufacturing process and to obtain a cathode of good quality.
  • Addition of iron boride in an amount of more than 3 percent by weight is still effective to attain the effect of noise suppression.
  • the addition in an amount in excess of percent by weight is objectionable since addition of such a large amount results in reduction of the amount of oxides of barium, strontium, and calcium and in a shortened service life of the discharge tube.
  • powders of at least one metal of a high-melting and reducing nature selected from the group consisting of zirconium, hafnium, niobium and tantalum, should be added in an amount in the order of 1 to 8 percent to the oxide cathode material. Addition of these additives in a total amount of less than 1 percent is undesirable in view of the insufficient effect achieved while addition in a total amount in excess of 8 percent is also undesirable due to the fact that electron emission is lowered.
  • composition of the inventive cathode coating material will be described hereunder:
  • Radio interferences of all the fluorescent lamps having the cathodes made in the above-described manner were less than 15 decibels in a radio frequency range of 535 to 1605 kilocycles, and the fluorescent lamps had a service life comparable to that of conventional fluorescent lamps.
  • substantially perfectly noisless fluorescent lamps can be provided by the present invention.
  • a coating material for electrodes which substantially reduces radio interferences produces in electron discharge tubes consisting essentially of the mixture of iron boride powder in an amount of 0.05 to 10 percent by weight, at least one metal powder in an amount of 1 to 8 percent by weight, said metal being selected from the high-melting reducing metal group consisting of zirconium, hafnium, niobium and tantalum, and the balance being electron emissive material powders consisting of barium oxide, strontium oxide, calcium oxide or mixtures thereof.
  • a coating material for electrodes according to claim 11 which said iron boride has the chemical formula
  • An electrode for an electron discharge tube which has substantially no radiointerference consisting essentially of a wound coil of tungsten wire, a coating on said coil consisting of the mixture of iron boride powder in an amount of 0.05 to 10 percent by weight of said coating, at least one metal powder in an amount of 1 to 8 percent by weight of said coating, said metal being selected from the high-melting reducing metal group consisting of zirconium, hafnium, niobium and tantalum, and the bal- UNITED STATES PATENTS 2,737,607 3/1956 Lemmens et al. 313-346 3,312,856 4/1967 Lafferty et al. 313346 J. DAVID WELSH, Primary Examiner US. Cl. X.R.

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  • Discharge Lamp (AREA)
US605327A 1966-01-08 1966-12-28 Discharge tube Expired - Lifetime US3513349A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP140866 1966-01-08

Publications (1)

Publication Number Publication Date
US3513349A true US3513349A (en) 1970-05-19

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Application Number Title Priority Date Filing Date
US605327A Expired - Lifetime US3513349A (en) 1966-01-08 1966-12-28 Discharge tube

Country Status (6)

Country Link
US (1) US3513349A (ja)
BE (1) BE692297A (ja)
DE (1) DE1589227B2 (ja)
FR (1) FR1507611A (ja)
GB (1) GB1167157A (ja)
NL (1) NL6618407A (ja)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4044276A (en) * 1976-04-09 1977-08-23 Gte Sylvania Incorporated High pressure mercury vapor discharge lamp having improved electrodes
DE4415748C2 (de) * 1994-05-04 1998-08-13 Matsushita Electric Works Ltd Elektrode für eine Leuchtstofflampe

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2737607A (en) * 1951-07-17 1956-03-06 Hartford Nat Bank & Trust Co Incandescible cathode
US3312856A (en) * 1963-03-26 1967-04-04 Gen Electric Rhenium supported metallic boride cathode emitters

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2737607A (en) * 1951-07-17 1956-03-06 Hartford Nat Bank & Trust Co Incandescible cathode
US3312856A (en) * 1963-03-26 1967-04-04 Gen Electric Rhenium supported metallic boride cathode emitters

Also Published As

Publication number Publication date
DE1589227A1 (de) 1970-03-05
GB1167157A (en) 1969-10-15
BE692297A (ja) 1967-06-16
DE1589227B2 (de) 1971-06-16
FR1507611A (fr) 1967-12-29
NL6618407A (ja) 1967-07-10

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