US3427492A - Discharge tube satisfactorily low in radio-interfering noise - Google Patents

Discharge tube satisfactorily low in radio-interfering noise Download PDF

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Publication number
US3427492A
US3427492A US631258A US3427492DA US3427492A US 3427492 A US3427492 A US 3427492A US 631258 A US631258 A US 631258A US 3427492D A US3427492D A US 3427492DA US 3427492 A US3427492 A US 3427492A
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United States
Prior art keywords
radio
borides
discharge tube
cathodes
oxides
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US631258A
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English (en)
Inventor
Hideo Mizuno
Hidezo Akutsu
Eijiro Moriguchi
Katsuyuki Yamashita
Shigeru Kamiya
Koshi Iwata
Yoshio Tawara
Atsushi Iga
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Panasonic Holdings Corp
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Matsushita Electronics Corp
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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

  • a discharge tube satisfactorily low in radio-interfering noise and equipped with cathodes coated with a cathode emitter consisting principally of oxides of barium, strontium and calcium and containing 0.05 to by Weight of a substance selected from the group consisting of cobalt boride and iron boride and further containing 1 to 8% by weight of a reducing metal having a high melting point and selected from the group consisting of zirconium, hafnium and tantalum, whereby a discharge tube low in noise intensity in the broadcasting frequency band is obtained.
  • the present invention relates to an improvement of discharge tubes, and more particularly to an improvement in low pressure mercury discharge tubes such as fluorescent lamps.
  • Oxide cathodes of the prior art utilized as electrodes in low pressure mercury vapor type discharge tubes such as fluorescent lamps were formed by coating double coils or so-called triple coils having a fine filament wound around said double coils with a compound carbonate consisting of barium carbonate, strontium carbonate and calcium carbonate, enclosing the coated structures in a discharge tube, thereafter subjecting these carbonates to thermal decomposition during the process of exhausting gas from said tube, thereby producing oxides of barium, strontium and calcium.
  • the oxide layers thus produced were of high resistivity and poor thermal conductivity.
  • a discharge tube incorporating cathodes led, when lighted, to the development of cathode spots locally having a high temperature and such cathode spots constituted the centers of thermionic emission.
  • this temperature of the cathode spots did not make any substantial change due to their thermal inertia, either during the re-ignition or extinction of the arc of the cathodes in all AC cycles, but rather the cathode spots continued to have a high temperature.
  • Japanese patent publication No. 1,5 81/ 1964 proposes lowering the temperature of the cathode spots by restricting the thickness of the oxide layers to 30;; or less to substantially enhance the thermal conductivity of cathodes and 3,427,492 Patented Feb. 11, 1969 to thereby enlarge the cathode spots.
  • this prior method is not desirable because it inevitably reduces the absolute volume of the electron-emitting oxides, and this, in turn, reduces the life of the discharge tube.
  • Another attempt has been reported in Japanese patent publication No.
  • a fluorescent lamp whose interference with radio receivers is restricted to 15 db or less and which, when used for practical purposes, is almost perfectly free from interfering noise and which is free from the development of blackening can be obtained by the use of a cathode emitter comprised of oxides of barium, strontium and calcium containing iron-cobalt borides having high melting points and having a markedly superior thermal conductivity as compared with that of an ordinary ionic crystal and also containing powder of a reducing metal selected from the group consisting of zirconium, hafnium, niobium and tantalum.
  • Said powders of reducing metals namely, zirconium, hafnium, niobium and tantalum satisfactorily prevent the metal borides from being oxidized during the thermal decomposition of the carbonates which is carried out during the process of exhausting gas from the discharge tubes.
  • a discharge tube according to the present invention which is equipped with oxide cathodes comprised of a mixture consisting of oxides of barium, strontium and calcium and containing, in a proportion of 1% by weight relative to said oxides, iron-cobalt borides corresponding to the composition formula of and further containing 3% by weight of zirconium relative to said oxides, showed a markedly superior effect of minimizing interfering noise.
  • oxide cathodes comprised of a mixture consisting of oxides of barium, strontium and calcium and containing, in a proportion of 1% by weight relative to said oxides, iron-cobalt borides corresponding to the composition formula of and further containing 3% by weight of zirconium relative to said oxides
  • the drawing shows a comparison between the magnitudes of noise imparted to a radio-receiver by a fluorescent lamp embodying the present invention, curve 2, and by a conventional fluorescent lamp, curve 1.
  • the metal borides according to the present invention point to such iron-cobalt borides as those corresponding to the composition formula of ⁇ (1x)Fe-xCo ⁇ B
  • These metal borides are mixed with carbonates of barium, strontium and calcium and this mixture is applied to the electrode coils.
  • the resulting coated electrodes are then heated to 1200 C. during the process of exhausting gas from the fluorescent lamps. During this heating, the aforesaid carbonates are decomposed by the heat to form the so-called oxide cathodes. For this reason, it is necessary that the added metal borides have melting points of 1300 C. or higher and that they do not become oxidized when heated to the order of 1200 C. in a carbon dioxide gas atmosphere.
  • Iron boride includes those having two different composition ratios, namely, Fe B and FeB.
  • Cobalt boride includes those having two different composition ratios, namely, Co B and CoB. Their melting points are 1389 C., 1550 C., 1265 C. and 1350 C., respectively.
  • Fe B and Co B have melting points which are somewhat lower than those of FeB and CoB.
  • metal borides containing boron in a large proportion as in FeB and CoB reduce the life duration of the cathode emitter.
  • a fluorescent lamp employing an emitter containing 5% by weight of FeB has a life duration of about 2000 hours. In case 5% by weight of Fe B is added to the emitter, the life duration is in the order of 5000 hours.
  • the desirable iron-cobalt borides are represented by those having the composition formula of (Fe-Co) B.
  • Co B has a superior oxidation resistivity at high temperature to Fe B, there occurs hardly any blackening of this type in case C0 3 is added to the cathode emitter. In view of the fact, however, that Co B has a melting point of 1265" C., the use of Co B as a simple substance leads to the appearance of yellowish brown blackening in the terminal portions of the tube behind the electrodes after lighting for 1000 hours.
  • the fluorescent lamp using the composition formula ⁇ (1-x)Fe-xCo ⁇ B wherein 0.15 x0.6 and wherein to 60% of the iron of Fe B has been substituted with cobalt shows a great improvement in both the end-band and the blackening in the terminal portions of the tube as compared with the fluorescent lamp using Fe B or C0 B as a simple substance.
  • x 0.15 an end-band type blackening is apt to occur similarly as in the case of Fe B, while when x 0.6, the tube easily develops a blackening in the terminal portions as in the case of Co B.
  • the effect of minimizing the noise interference is noted when the cathodes contain 0.05% or more by weight of the borides.
  • the borides in a proportion of the order of from 0.1 to 2%. While the effect of minimizing the noise interference can be equally obtained from the addition of borides of more than 2% by weight, the addition of borides in excess of 10% by weight means a reduced proportion of oxides of barium, strontium and calcium, and results in a reduced duration of life of the lamp, and therefore, the addition of borides in such excess proportion is not desirable.
  • an additive consisting of powder of one or more of the reducing metals having high melting points selected from the group consisting of zirconium, hafnium, niobium and tantalum which is to be contained in a proportion of the order of from 1 to 8% by weight in the oxides of the cathodes of the present invention is mandatory for the prevention of blackening of the lamp during lighting and also for the purpose of obtaining a prolonged duration of life of the lamp.
  • EXAMPLE 1 Grams Barium carbonate 35 Strontium carbonate 35 Calcium carbonate 29 (0.8Fe-0.2Co) B 1 Zirconium 3
  • EXAMPLE 2 Grams Barium carbonate 35 Strontium carbonate 35 Calcium carbonate 29 (0.5Fe-0.5Co) B 1 Zirconium 3
  • EXAMPLE 3 Grams Barium carbonate 35 Strontium carbonate 35 Calcium carbonate 29 Iron-cobalt borides, (0.5Fe-0.5Co) B 1 Zirconium 2 Hafnium 1
  • EXAMPLE 4 Grams Barium carbonate 35 Strontium carbonate 35 Calcium carbonate 29 Iron-cobalt borides (0.7Fe-0.3Co) B 1 Zirconium 2 Niobium 1
  • EXAMPLE 5 Grams Barium carbonate 35 Strontium carbonate 35 Calcium carbonate 29 Iron-cobalt borides (O.5Fe'0.5Co) B 1 Zirconium 2 Tantalum 3

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  • Discharge Lamp (AREA)
US631258A 1966-04-20 1967-04-17 Discharge tube satisfactorily low in radio-interfering noise Expired - Lifetime US3427492A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2563166 1966-04-20

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US3427492A true US3427492A (en) 1969-02-11

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US (1) US3427492A (cs)
BE (1) BE697244A (cs)
DE (1) DE1589231B2 (cs)
GB (1) GB1178052A (cs)
NL (1) NL146637B (cs)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3505553A (en) * 1966-05-12 1970-04-07 Philips Corp Radio-interference-free low-pressure mercury-vapor lamp
US5757130A (en) * 1990-10-25 1998-05-26 Fusion Lighting, Inc. Lamp with electrodes for increased longevity

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2473358A (en) * 1946-08-23 1949-06-14 Raytheon Mfg Co Cathode coating for electron discharge devices
US2724070A (en) * 1953-02-09 1955-11-15 Westinghouse Electric Corp Cathode coating for electrical discharge devices and method for making the same
US2820920A (en) * 1952-09-17 1958-01-21 Claude Ets Manufacture of coated electrodes
US2849637A (en) * 1956-02-02 1958-08-26 Weiss Harry Electrode for fluorescent lamp
US3312856A (en) * 1963-03-26 1967-04-04 Gen Electric Rhenium supported metallic boride cathode emitters

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2473358A (en) * 1946-08-23 1949-06-14 Raytheon Mfg Co Cathode coating for electron discharge devices
US2820920A (en) * 1952-09-17 1958-01-21 Claude Ets Manufacture of coated electrodes
US2724070A (en) * 1953-02-09 1955-11-15 Westinghouse Electric Corp Cathode coating for electrical discharge devices and method for making the same
US2849637A (en) * 1956-02-02 1958-08-26 Weiss Harry Electrode for fluorescent lamp
US3312856A (en) * 1963-03-26 1967-04-04 Gen Electric Rhenium supported metallic boride cathode emitters

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3505553A (en) * 1966-05-12 1970-04-07 Philips Corp Radio-interference-free low-pressure mercury-vapor lamp
US5757130A (en) * 1990-10-25 1998-05-26 Fusion Lighting, Inc. Lamp with electrodes for increased longevity

Also Published As

Publication number Publication date
NL146637B (nl) 1975-07-15
NL6705394A (cs) 1967-10-23
DE1589231B2 (de) 1971-09-30
BE697244A (cs) 1967-10-02
GB1178052A (en) 1970-01-14
DE1589231A1 (de) 1970-09-10

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