EP0416535A2 - Cathode pour tube électronique - Google Patents

Cathode pour tube électronique Download PDF

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Publication number
EP0416535A2
EP0416535A2 EP90116972A EP90116972A EP0416535A2 EP 0416535 A2 EP0416535 A2 EP 0416535A2 EP 90116972 A EP90116972 A EP 90116972A EP 90116972 A EP90116972 A EP 90116972A EP 0416535 A2 EP0416535 A2 EP 0416535A2
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EP
European Patent Office
Prior art keywords
alkaline earth
cathode
earth metal
carbonate
layer
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.)
Granted
Application number
EP90116972A
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German (de)
English (en)
Other versions
EP0416535A3 (en
EP0416535B1 (fr
Inventor
Yukio C/O Sony Corporation Hara
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.)
Sony Corp
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Sony Corp
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Publication date
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Publication of EP0416535A2 publication Critical patent/EP0416535A2/fr
Publication of EP0416535A3 publication Critical patent/EP0416535A3/en
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Publication of EP0416535B1 publication Critical patent/EP0416535B1/fr
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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
    • 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
    • H01J1/142—Solid thermionic cathodes characterised by the material with alkaline-earth metal oxides, or such oxides used in conjunction with reducing agents, as an emissive material
    • 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
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/04—Manufacture of electrodes or electrode systems of thermionic cathodes
    • H01J9/042—Manufacture, activation of the emissive part

Definitions

  • This invention relates to a cathode for electron tube employed in image receiving tubes and image pickup tubes more particularly, to a so-called oxide coated cathode for electron tubes.
  • the invention also relates to a method for fabricating a cathode of the type mentioned above.
  • cathode or cathodes Ordinarily employed oxide coated cathodes (hereinafter referred to simply as cathode or cathodes) mostly include metal substrate mainly composed of nickel (Ni) and several percent of tungsten (W) and the like used as a reducing agent and a coating formed on the substrate and made of a ternary alkaline earth metal oxide consisting of barium (Ba), strontium (Sr) and calcium (Ca).
  • a lower working temperature is more advantageous not only saving the consumption power for heaters for the cathode, but also in the improvement of the life characteristic of the cathode. More particularly, it is known that the life characteristic is greatly influenced by the intermediate layer formed owing to the thermal reaction between the oxide and the coated metal substrate during operation. The lowering of the working temperature of the cathode brings about a prolonged life by suppressing the formation of the intermediate layer.
  • indium (In) in the form of indium oxide (In2O3) is adapted for improving the capability of electron radiation with a working temperature for the same level of radiation current being reduced. This is disclosed in Japanese Patent Publication No. 38-2334.
  • In2O3 has a sublimation temperature of about 850°C which is lower than the thermal decomposition temperature of alkaline earth metal carbonates. Accordingly, most In2O3 which has been added to the alkaline earth metal carbonates will be lost from the cathode layer during a step where the carbonates are heated at 1000 to 1100°C and decomposed into oxides during evacuation under vacuum or during the so-called thermal decomposition activation step for the cathode.
  • the results of the analysis on the composition of the oxide cathode prior to and after the thermal decomposition and activation reveal, as shown in Tables 1 and 2, that the oxide cathode layer prior to the thermal decomposition and activation contains 2 to 3 atomic percent of In3+ whereas the oxide cathode layer after the thermal decomposition and activation has a considerably reduced content of In3+ of not larger than 0.005 atomic percent.
  • the small amount of remaining In contributes to good electron radiation characteistics of the cathode. Too large particles of In or In compounds existing prior to the activation step may cause their neighboring regions to be molten depending on the thermal decomposition and activation conditions, resulting in bad influences on the electron radiation characteristics.
  • the amount of an additive element necessary for improving the electron radiation capability should be small sufficient to have it incorporated in the crystals of alkaline earth metal carbonates and that particles of an additional element or its compound not incorporated in the crystals should be preliminarily removed from the carbonate composition prior to the activation, which is important for obtaining the stable capability of electron radiation.
  • An object of the invention is to provide a cathode for electron tubes which has high capability of electron radiation and is stable by removing an additional additive element or its compound from carbonate crystals.
  • Another object of the invention to provide a cathode for electron tubes wherein an element capable of producing an amphoteric compound is used as an additive element.
  • a further object of the invention is to provide a method for fabricating the cathode mentioned above.
  • a cathode for electron tubes which comprises a substrate metal mainly composed of nickel and a reducing agent and a coating layer of a composition comprising alkaline earth metal carbonates and formed on the substrate metal, the alkaline earth metal carbonates in the coating layer being converted into corresponding metal oxides, characterized in that the alkaline earth metal carbonates contain at least one of zinc (Zn) and aluminium (Al).
  • a method for fabricating a cathode for electron tubes which comprises the steps of: adding at least one element of Zn and Al or its compound to a solution of water-soluble salts of alkaline earth metals; adding a carbonate precipitant to the solution thereby causing co-precipitation to obtain a powder mainly composed of a multi-component alkaline earth metal carbonate; immersing the powder in an alkaline aqueous solution and subjecting the resulting mixture to filtration to obtain an alkaline earth metal carbonate containing Al and/or Zn from which the element in excess is removed by dissolution; applying, onto a substrate metal, a cathodic material composition obtained by mixing the alkaline earth metal carbonate and a binder therefor to form a layer of the cathodic material composition; and heating the thus formed layer in an evacuated closed system to convert the layer into an oxide layer.
  • the cathode obtained above has not only high capability of electron radiation as in the case where In is added, but also more stable characteristics than in the case of adding In. This is considered for the reason that the addition of Zn or Al in small amounts has the effect of enhancing the capability of electron radiation as in the case where In is added and that the additive element is incorporated in the crystals of the alkaline earth metal carbonate prior to activation of the cathode.
  • An additional additive element or its compound which is not incorporated in the crystals and which is amphoteric in nature is dissolved by the use of an alkaline solution and removed sufficiently.
  • the cathode has a heater 1 for heating the cathode to a working temperature and a cathode sleeve 2 in which the heater is built, and a substrate metal 3 provided at one end of the sleeve 2 and made primarily of nickel. On the substrate metal 2 is further formed an oxide layer 4 mainly compose of alkaline earth metal oxides and serving to emit electrons.
  • a cathode is used as an electron gun according to an ordinary arrangement and is built in an electron tube.
  • Fig. 2 is a flow chart showing a fabrication procedure of a cathode according to the invention. This fabrication procedure is illustrated in more detail.
  • Barium carbonate (BaCO3), strontium carbonate (SrCO3) and calcium carbonate (CaCO3) are weighed at ratios by weight of 62:35.5:2.5 and dissolved in and mixed with a dilute nitric acid aqueous solution, to which ZnO is added for dissolution in amounts of from 1 to 3 wt% based on the total amount of the alkaline earth metal carbonates.
  • an ammonium carbonate ((NH4)2CO3) aqueous solution (about 1.5 mols/l) while sufficiently agitating, thereby causing a precipitate mainly composed of a quaternary carbonate of Ba, Sr, C and Zn and containing Zn or a Zn compound, followed by filtration.
  • the thus obtained precipitate is immersed in an ammonium hydroxide ((NH4OH) aqueous solution (about 3 mols/l) or ammonium carbonate ((NH4)2CO3) aqueous solution (about 3 mols/l), sufficiently agitated and filtered.
  • an ammonium hydroxide (NH4OH) aqueous solution (about 3 mols/l) or ammonium carbonate ((NH4)2CO3) aqueous solution (about 3 mols/l)
  • quaternary carbonate crystals have such an irregular structure on the surface thereof as is schematically shown in Fig. 3, which is considered to result from the incorporation of Zn in the alkaline earth metal carbonate crystals.
  • the crystals of a ternary carbonate of Ba. Sr and Ca obtained without addition of any Zn for comparison have a smooth surface as is schematically shown in Fig. 4.
  • the thus obtained quaternary carbonate powder and nitro cellulose used as a binder are added to and mixed with a mixed organic solvent of ethyl acetate and isoamyl acetate to prepare a paste composition for cathode material.
  • the above cathode material composition is spray coated, n a thickness of 100 ⁇ m at a density of 0.8 g/cm3, on a substrate metal; which consists of nickel containing 4 wt% of tungsten as a reducing agent and which is provided at one end of the cathode sleeve to form a coating layer of the cathode material.
  • an electron gun is assembled using the cathode and built in an electron tube.
  • the electron tube is evacuated and subjected to thermal decomposition and activation treatment at a temperature of 1000 to 1100°C.
  • thermal decomposition and activation treatment the quaternary carbonate contained in the cathode material coated layer is converted into oxides, thereby producing an oxide layer having good capability of electron emission.
  • Thirty cathodes are fabricated in this manner and are subjected to measurement of a pulse emission characteristic.
  • a single pulse with a pulse width of 45 microseconds and a voltage of EpV is passed between the cathode and an electrode at the high voltage side, after which the voltage Ep is changed to measure a current density at the cathode.
  • Fig. 5 shows a typical pulse emission characteristic curve among the results of the measurement.
  • a cathode to which In is added according to a known technique is fabricated according to the flow chart shown Fig. 7. The fabrication procedure is described in detail.
  • BaCO3, SrCO3 and CaCO3 are weighed at ratios of 62:35.5:2.5 and dissolved in and mixed with a dilute nitric acid aqueous solution.
  • a dilute nitric acid aqueous solution To the resultant ternary nitrate aqueous solution (about 0.4 mols/l) is gradually added an (NH4)2CO3 aqueous solution (about 1.5 mols/l) while sufficiently agitating, thereby causing a precipitate of a ternary carbonate of Ba, Sr and Ca, followed by filtration. This ternary carbonate is washed with hot pure water and dried.
  • the addition of Zn and/or Al is effective in improving he electron radiation capability to an extent equal to that conventionally attained by the addition of In.
  • the best use is made of characteristic features of Zn and Al which are elements capable of producing amphoteric compounds, i.e. additive elements or compounds thereof, which are considered as harmful and have not been incorporated in alkaline earth metal carbonates, can be sufficiently removed, ensuring the characteristics to be readily stabilized.
  • the improvement in the electron radiation capability will bring about a reduced working temperature of the cathode and a prolonged life of the cathode.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
EP90116972A 1989-09-05 1990-09-04 Cathode pour tube électronique Expired - Lifetime EP0416535B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP1228433A JPH0393126A (ja) 1989-09-05 1989-09-05 電子管用陰極
JP228433/89 1989-09-05

Publications (3)

Publication Number Publication Date
EP0416535A2 true EP0416535A2 (fr) 1991-03-13
EP0416535A3 EP0416535A3 (en) 1991-05-08
EP0416535B1 EP0416535B1 (fr) 1994-03-16

Family

ID=16876413

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90116972A Expired - Lifetime EP0416535B1 (fr) 1989-09-05 1990-09-04 Cathode pour tube électronique

Country Status (4)

Country Link
EP (1) EP0416535B1 (fr)
JP (1) JPH0393126A (fr)
KR (1) KR100198909B1 (fr)
DE (1) DE69007383T2 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9201450A (nl) * 1991-10-24 1993-05-17 Samsung Electronic Devices Werkwijze voor het vervaardigen van een geimpregneerde kathodestruktuur.
EP0847071A4 (fr) * 1996-02-29 2000-03-01 Matsushita Electronics Corp Cathode de tube electronique
CN102543617A (zh) * 2011-12-15 2012-07-04 宁波盈旺通信设备有限公司 金属陶瓷气体放电管的电子发射材料

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR911627A (fr) * 1945-01-19 1946-07-16 Sadir Carpentier Perfectionnement aux cathodes des tubes à décharge électronique
FR1274476A (fr) * 1959-08-06 1961-10-27 Philips Nv Procédé pour la fabrication d'une cathode à oxydes et cathode ainsi fabriquée
US3625759A (en) * 1967-04-03 1971-12-07 Varian Associates Process for making oxide cathodes having improved thermal emissivity

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9201450A (nl) * 1991-10-24 1993-05-17 Samsung Electronic Devices Werkwijze voor het vervaardigen van een geimpregneerde kathodestruktuur.
EP0847071A4 (fr) * 1996-02-29 2000-03-01 Matsushita Electronics Corp Cathode de tube electronique
CN102543617A (zh) * 2011-12-15 2012-07-04 宁波盈旺通信设备有限公司 金属陶瓷气体放电管的电子发射材料

Also Published As

Publication number Publication date
DE69007383D1 (de) 1994-04-21
JPH0393126A (ja) 1991-04-18
EP0416535A3 (en) 1991-05-08
EP0416535B1 (fr) 1994-03-16
DE69007383T2 (de) 1994-10-06
KR100198909B1 (ko) 1999-06-15
KR910007027A (ko) 1991-04-30

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