EP0639848B1 - Cathode à oxyde pour tube à électrons - Google Patents

Cathode à oxyde pour tube à électrons Download PDF

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Publication number
EP0639848B1
EP0639848B1 EP19930310036 EP93310036A EP0639848B1 EP 0639848 B1 EP0639848 B1 EP 0639848B1 EP 19930310036 EP19930310036 EP 19930310036 EP 93310036 A EP93310036 A EP 93310036A EP 0639848 B1 EP0639848 B1 EP 0639848B1
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EP
European Patent Office
Prior art keywords
oxide
electron emissive
emissive material
cathode
metal base
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
EP19930310036
Other languages
German (de)
English (en)
Other versions
EP0639848A1 (fr
Inventor
Jong-Seo Choi
Kyung-Cheon Shon
Kwi-Seok Choi
Gyu-Nam Ju
Sang-Won Lee
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.)
Samsung SDI Co Ltd
Original Assignee
Samsung Display Devices Co Ltd
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 claimed from KR1019930021670A external-priority patent/KR950006911A/ko
Priority claimed from KR1019930022490A external-priority patent/KR100271484B1/ko
Application filed by Samsung Display Devices Co Ltd filed Critical Samsung Display Devices Co Ltd
Publication of EP0639848A1 publication Critical patent/EP0639848A1/fr
Application granted granted Critical
Publication of EP0639848B1 publication Critical patent/EP0639848B1/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
    • H01J1/144—Solid thermionic cathodes characterised by the material with other metal oxides as an emissive material

Definitions

  • the present invention relates to an oxide cathode such as a cathode ray tube or image pickup tube, and more particularly, to a novel oxide cathode for an electron tube having a long lifetime.
  • oxide cathode For a conventional thermoelectron emitting cathode for an electron tube, there is an “oxide cathode” which includes an alkaline earth metal carbonate layer formed on a metal base containing Ni as a main component. Such an alkaline earth metal carbonate is converted into oxide during an evacuating process and is therefore termed an oxide cathode.
  • An oxide cathode works at relatively low temperatures (700-800°C), since its work function is low.
  • oxide cathodes have the problem of relatively short lifetimes.
  • FIG.1 is a schematic sectional view illustrating a structure of a conventional oxide cathode.
  • a conventional oxide cathode comprises a disk-shaped metal base 2, a cylindrical sleeve 3 supporting the metal base 2, a heater 4 for heating the cathode, and an electron emissive material layer 1 which is formed on the metal base 2 and is made of an alkaline earth metal oxide as a main component.
  • Such a conventional oxide cathode is manufactured by closing up one end of the cylindrical sleeve 3 with the metal base 2, inserting the heater 4 in the sleeve 3, and forming the electron emissive material layer 1 which is made of a mixture of at least two alkaline earth metal oxides on the surface of the metal base 2.
  • the metal base 2 is located on the sleeve 3 and supports the electron emissive material layer 1. It is made of a refractory metal, such as nickel (Ni) or platinum (Pt), and contains a reducing element to facilitate the reduction of an alkaline earth metal oxide.
  • a reducing element is typically used a reducing metal, such as tungsten (W), magnesium (Mg), silicon (Si) or zirconium (Zr).
  • W tungsten
  • Mg magnesium
  • Si silicon
  • the reducing metals are generally used in combination with each other.
  • the sleeve 3, which supports the metal base 2 and has a heater 4 therein, is typically made of a refractory metal, such as molybdenum (Mo), tantalum (Ta), tungsten (W) or stainless steel.
  • Mo molybdenum
  • Ta tantalum
  • W tungsten
  • the heater 4 which is located inside the sleeve 3, heats an electron emissive material layer 1 through the metal base 2. It is made of a tungsten wire coated with alumina et al.
  • the electron emissive material layer 1, which emits thermoelectrons, is formed on the metal base 2 as an alkaline earth metal oxide layer.
  • a suspension of a carbonate of an alkaline earth metal (Ba, Sr, Ca etc.) is sprayed on the metal base 2. After the coating layer is heated by the heater 4 in a vacuum, the alkaline earth metal carbonate is converted to oxides.
  • the alkaline earth metal oxide is partially reduced at a high temperature of 900 to 1000°C, so that it is activated to have semiconductive properties.
  • the reducing element such as Si or Mg
  • the metal base 2 diffuses to move toward the interface between the electron emissive material layer 1 composed of the alkaline earth metal oxide and the metal base 2, and then reacts with the alkaline earth metal oxide.
  • barium oxide is reduced by the reducing element to give free barium.
  • the free barium derived from BaO becomes a semiconductor of an oxygen vacancy type. Consequently, an emission current of 0.5 to 0.8A/cm 2 is obtained under the normal condition at an operation temperature of 700 to 800°C.
  • an oxide cathode operates at high temperature over 750°C, so free Ba, Sr or Ca vaporizes due to the high vapor pressure and an electron emissive surface reduces while operating.
  • an intermediate layer of an oxide such as MgO or Ba 2 SiO 4 , is formed in the interface region between the electron emissive material layer and the metal base and serves as a barrier. The barrier so formed prevents the reducing element Mg or Si from diffusing into the electron emissive layer, so that a sufficient amount of a free Ba cannot be generated and the vaporized Ba, Sr or Ca is hard to be refilled.
  • electron emissive current is also limited by a high resistance of the intermediate layer. Therefore, the intermediate layer contributes to the shortening of the cathode lifetime and other undesirable results. On the other hand, an excessive supply of the reducing element results in excessive reduction of BaO, so that stable emission cannot be achieved.
  • a conventional oxide cathode has disadvantages in that its operation temperature becomes higher during use, so the emission efficiency decreases to about 75% of initial characteristic, and the exhaustion of electron emissive material shortens its lifetime.
  • An impregnated-type cathode known to have a high current density and a long lifetime, is manufactured by a complicated process and the operation temperature is 1100°C or higher, which is as much as 300-400°C higher than that of an oxide cathode. Therefore, continuous efforts have been made to lengthen the lifetime of an oxide cathode, which can be manufactured easily and operates at low temperature.
  • German Patent No. 1592502 discloses an electron emissive material for a discharge lamp in which BeO and Y 2 O 3 are added to Ba 2-x Sr x CaWO 6 (where x is from 0.0 to 0.5).
  • the above-mentioned cathodes do not make a considerable improvement in the short lifetime of an oxide cathode. Further, the manufacturing processes of the above cathode is not always interchangeable with those of the typical oxide cathode. Especially, changing the activation process of the cathode is required.
  • the rare earth metal oxide needs to be subjected to a heat treatment at a high temperature in a reducing atmosphere before mixing with an alkaline earth metal oxide.
  • An object of the present invention considering the above-mentioned problems of the conventional oxide cathodes is to provide an oxide cathode in which a stable electron emissive characteristic is maintained for a longer time by suppressing an excessive Ba vaporization, so that the lifetime has been greatly improved, and the manufacturing process is interchangeable with a conventional one.
  • an oxide cathode comprising:
  • the metal base is subjected to a heat treatment at a temperature over 900°C and under a vacuum of over 133 ⁇ 3x10 -6 Pa (10 -6 Torr), the heat treatment being effected prior to providing the layer of electron emissive material.
  • an electron emissive material layer on a metal base further contains a lanthanum oxide and/or a terbium oxide, and the electron emissive material layer forms a needle-shaped crystal structure, or the metal base is subject to a heat treatment under vacuum, so that the electron emissive characteristic becomes stable and the emission stability is maintained longer than that of conventional ones.
  • an adequate supply of a reducing metal has been considered in order to lengthen the lifetime of an oxide cathode.
  • Such an adequate supply of a reducing metal may be achieved according to the following two methods. The first is to form a needle-shaped crystal structure of the electron emissive material layer, and the second is a heat treatment of the metal base. If an electron emissive material layer forms a needle-shape crystal, a reducing metal may diffuse at an adequate speed, so that a current density may be kept up with an enhanced value for a long time.
  • a metal base containing a reducing metal is subject to the heat treatment under vacuum, the excessive supply of the reducing metal may be prevented, so that stable BaO produced by the lanthanum oxide and/or terbium oxide may keep its stable condition over a long period of time. In this manner, an electron emission may be stabilized for a long time and the lifetime of the oxide cathode may be increased.
  • an electron emissive material may be used a triple carbonate, such as (Ba,Sr,Ca)CO 3 , or a double carbonate, such as (Ba,Sr)CO 3 .
  • a triple carbonate such as (Ba,Sr,Ca)CO 3
  • a double carbonate such as (Ba,Sr)CO 3 .
  • any lanthanum compound or terbium compound which can be converted to oxide by heating may be used as well as lanthanum oxide or terbium oxide itself.
  • the amount of lanthanum oxide or terbium oxide contained in an electron emissive material is in the range of 0.0001% to 5% by weight, based on the total amount of the electron emissive material.
  • Lanthanum oxide or terbium oxide of less than 0.0001% by weight cannot achieve the effect of forming the stable BaO, and so does not lengthen the lifetime.
  • lanthanum oxide or terbium oxide of more than 5% by weight may aggravate the already poor condition of the initial emission characteristic and thus decrease the effect of lengthening the lifetime.
  • Lanthanum oxide or terbium oxide, or both is contained in, for example, a co-precipitated triple carbonate of (Ba,Sr,Ca)CO 3 as an electron emissive material.
  • the co-precipitated triple carbonate is conventionally manufactured by dissolving nitrates such as Ba(NO 3 ) 2 , Sr(NO 3 ) 2 or Ca(NO 3 ) 2 in pure water, and adding Na 2 CO 3 or (NH 4 ) 2 CO 3 as a precipitant to the nitrate solution to co-precipitate as a carbonate of Ba, Sr and Ca.
  • the obtained carbonate crystal structures vary.
  • the above factors should be controlled to form a needle-shaped crystal structure.
  • the suspension may be applied onto a metal base by means of dipping, spraying or sputtering to give an oxide cathode according to one embodiment of the present invention.
  • a metal base is preferred to be subjected to heat treatment at a temperature over 900°C, under a vacuum of over 133 ⁇ 3 x 10 -6 Pa (10 -6 torr).
  • lanthanum oxide and/or terbium oxide is contained in, for example, a co-precipitated triple carbonate of (Ba,Sr,Ca)CO 3 as an electron emissive material.
  • the oxide cathode of the present invention is inserted and fixed in an electron gun, and a heater is inserted and fixed in a sleeve. After the electron gun is sealed into a bulb for an electron tube, the carbonate of the electron emissive material layer is decomposed to the oxide by the heater during an evacuating process. Thereafter, an activation process is carried out by a conventional manufacturing process for an electron tube.
  • the reaction condition was controlled as follows: the concentration of the triple nitrates was above 0.6M; pH was controlled to be above 8 with ammonium hydroxide; and, when (NH 4 ) 2 CO 3 was used as a precipitant, the temperature of the nitrate solution was above 60°C, and the solution of precipitant was dropped at the speed of 30ml per minute.
  • La 2 O 3 was added in the amount of 1% by weight of the electron emissive material calculated as oxide. Further, a nitrocellulose and an organic solvent were dispersed to make a suspension of the electron emissive material.
  • a Ni-metal base containing Si and Mg was washed. Then, the above manufactured suspension of the electron emissive material was spray-coated on the base, dried to obtain an oxide cathode according to an embodiment of the present invention.
  • Example 2 The same procedure as in Example 1 was repeated, except that Tb 4 O 7 was added to the co-precipitated triple carbonate solution in the amount of 5% by weight of the electron emissive material calculated as oxide, to obtain an oxide cathode according to an embodiment of the present invention.
  • Example 2 The same procedure as in Example 1 was repeated, except that La 2 O 3 was added to the co-precipitated triple carbonate solution in the amount of 0.0001% by weight of the electron emissive material calculated as oxide, to obtain an oxide cathode according to an embodiment of the present invention.
  • Example 2 The same procedure as in Example 1 was repeated, except that Tb 4 O 7 was added to the co-precipitated triple carbonate solution in the amount of 0.001 % by weight of the electron emissive material calculated as oxide, to obtain an oxide cathode according to an embodiment of the present invention.
  • Example 2 The same procedure as in Example 1 was repeated, except that the mixture of La 2 O 3 and Tb 4 O 7 was added to the co-precipitated triple carbonate solution in the amount of 0.01% by weight of the electron emissive material calculated as oxide, to obtain an oxide cathode according to an embodiment of the present invention.
  • a Ni-metal base containing Si and Mg was subjected to heat treatment at 1000°C, under a vacuum of over 133 ⁇ 3 x 10 -6 Pa (10 -6 torr).
  • La 2 O 3 was added in the amount of 1% by weight of the electron emissive material calculated as oxide. Further, a nitrocellulose and an organic solvent were dispersed to make a suspension of an electron emissive material.
  • the above suspension was spray-coated on the heat-treated metal base, and dried to obtain an oxide cathode according to another embodiment of the present invention.
  • Example 6 The same procedure as in Example 6 was repeated, except that La 2 O 3 was added to the co-precipitated triple carbonate solution in the amount of 0.0001 % by weight of the electron emissive material calculated as oxide, to obtain an oxide cathode according to another embodiment of the present invention.
  • Example 6 The same procedure as in Example 6 was repeated, except that La 2 O 3 was added to the co-precipitated triple carbonate solution in the amount of 5% by weight of the electron emissive material calculated as oxide, to obtain an oxide cathode according to another embodiment of the present invention.
  • FIG.2 is an enlarged schematic view illustrating an electron emissive material layer of an oxide cathode manufactured according to Example 1.
  • FIG.2 shows that the electron emissive material manufactured in Example 1 forms a needle-shaped crystal structure.
  • the oxide cathode manufactured according to the above is inserted and fixed in an electron gun, and a heater is inserted and fixed in a sleeve.
  • the electron gun is sealed into a bulb for an electron tube, the carbonate of the electron emissive material layer is decomposed to the oxide by the heater during an evacuating process.
  • an activation process is carried out by a conventional manufacturing process for an electron tube, and its electron emissive characteristic is measured.
  • MIK maximum cathode current
  • MIK maximum cathode current
  • a lifetime characteristic is evaluated by the amount of decrease in the current when a cathode installed in an electron tube is operated continuously for a ccertain length of time under constant conditions. That is, it is evaluated in terms of MIK consistency for a constant period.
  • FIG.3 is a graph showing MIK change with respect to the time of the oxide cathode manufactured according to Example 1 (a) and a conventional oxide cathode (b).
  • an oxide cathode according to an embodiment of the present invention has an effect on lengthening lifetime by 20% more than a conventional one.
  • the oxide cathodes manufactured according to Examples 2 through 5 also show that they have equal effects on the lifetime.
  • FIG.4 is a graph showing MIK change with respect to the time of an oxide cathode manufactured according to Example 6 (a) and a conventional oxide cathode (b).
  • an oxide cathode according to another embodiment of the present invention has an effect on lengthening lifetime by 20% more than a conventional one.
  • the oxide cathodes manufactured according to Examples 7 and 8 also show that they have equal effects on the lifetime.
  • the oxide cathode according to the present invention which is characterized in that the electron emissive material layer contains a lanthanum oxide and/or a terbium oxide and forms a needle-shaped crystal structure, or which is characterized in that the electron emissive material layer contains a lanthanum oxide and/or a terbium oxide and that the metal base is subject to a heat treatment under vacuum, has an effect on lengthening the lifetime, and has a manufacturing procedure interchangeable with a conventional one.

Landscapes

  • Solid Thermionic Cathode (AREA)
  • Discharge Lamp (AREA)

Claims (2)

  1. Cathode à oxyde comprenant :
    une base en métal (2) contenant un élément réducteur afin de faciliter la réduction d'oxyde de baryum ;
    une couche en matériau émetteur d'électrons (1) qui forme une structure cristalline en forme d'aiguille formée sur la base en métal (2) et contient au moins Ba et au moins un oxyde de lanthane ou un oxyde de terbium dans une proportion en poids allant de 0,0001 % à 5 %, en se basant sur la quantité totale du matériau émetteur d'électrons ; et
    des moyens (4) permettant de chauffer la couche en matériau émetteur d'électrons.
  2. Cathode à oxyde selon la revendication 1, dans laquelle la base en métal (2) est soumise à un traitement thermique à une température supérieure à 900°C et sous un vide dépassant 133,3 x 10-6 Pa (10-6 Torr) avant de mettre à disposition la couche en matériau émetteur d'électrons (1).
EP19930310036 1993-08-20 1993-12-13 Cathode à oxyde pour tube à électrons Expired - Lifetime EP0639848B1 (fr)

Applications Claiming Priority (8)

Application Number Priority Date Filing Date Title
KR9316231 1993-08-20
KR930016231 1993-08-20
KR9321670 1993-10-19
KR1019930021670A KR950006911A (ko) 1993-08-20 1993-10-19 전자관용 산화물 음극
KR9322124 1993-10-23
KR930022124 1993-10-23
KR1019930022490A KR100271484B1 (ko) 1993-10-23 1993-10-27 산화물 음극
KR9322490 1993-10-27

Publications (2)

Publication Number Publication Date
EP0639848A1 EP0639848A1 (fr) 1995-02-22
EP0639848B1 true EP0639848B1 (fr) 1997-09-10

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Application Number Title Priority Date Filing Date
EP19930310036 Expired - Lifetime EP0639848B1 (fr) 1993-08-20 1993-12-13 Cathode à oxyde pour tube à électrons

Country Status (6)

Country Link
EP (1) EP0639848B1 (fr)
JP (1) JPH0765692A (fr)
CN (1) CN1061462C (fr)
DE (1) DE69313845T2 (fr)
SG (1) SG44617A1 (fr)
TW (1) TW259877B (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100200661B1 (ko) * 1994-10-12 1999-06-15 손욱 전자관용 음극
CN100336154C (zh) * 2000-09-19 2007-09-05 皇家菲利浦电子有限公司 包括氧化物阴极的阴极射线管
JP2007305438A (ja) * 2006-05-12 2007-11-22 New Japan Radio Co Ltd 酸化物陰極及びその製造方法並びにそれに用いる酸化物陰極用炭酸塩の製造方法

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB182817A (en) * 1921-07-11 1923-08-09 Drahtlose Telegraphie Gmbh Improvements in the cathodes of electric discharge tubes
US1794298A (en) * 1926-09-21 1931-02-24 Gen Electric Thermionic cathode
CA1270890A (fr) * 1985-07-19 1990-06-26 Keiji Watanabe Cathode de tube electronique

Also Published As

Publication number Publication date
SG44617A1 (en) 1997-12-19
CN1061462C (zh) 2001-01-31
DE69313845T2 (de) 1998-04-02
DE69313845D1 (de) 1997-10-16
TW259877B (fr) 1995-10-11
CN1099185A (zh) 1995-02-22
EP0639848A1 (fr) 1995-02-22
JPH0765692A (ja) 1995-03-10

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