EP0298558A1 - Method of manufacturing a scandat cathode - Google Patents

Method of manufacturing a scandat cathode Download PDF

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Publication number
EP0298558A1
EP0298558A1 EP88201392A EP88201392A EP0298558A1 EP 0298558 A1 EP0298558 A1 EP 0298558A1 EP 88201392 A EP88201392 A EP 88201392A EP 88201392 A EP88201392 A EP 88201392A EP 0298558 A1 EP0298558 A1 EP 0298558A1
Authority
EP
European Patent Office
Prior art keywords
cathode
scandium
approximately
hydride
manufacturing
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
EP88201392A
Other languages
German (de)
French (fr)
Other versions
EP0298558B1 (en
Inventor
Johannes Van Esdonk
Jan Hasker
Josef Johannes Van Lith
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.)
Koninklijke Philips NV
Original Assignee
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
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
Application filed by Philips Gloeilampenfabrieken NV, Koninklijke Philips Electronics NV filed Critical Philips Gloeilampenfabrieken NV
Publication of EP0298558A1 publication Critical patent/EP0298558A1/en
Application granted granted Critical
Publication of EP0298558B1 publication Critical patent/EP0298558B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • 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
    • 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
    • H01J9/047—Cathodes having impregnated bodies
    • 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
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
    • H01J1/28—Dispenser-type cathodes, e.g. L-cathode

Definitions

  • the invention relates to a method of manufacturing a dispenser cathode comprising a barium compound for dispensing barium to an emissive surface of a porous cathode body substantially comprising a metal melting at a high temperature.
  • the invention also relates to a dispenser cathode manufactured by means of such a method and to an electron tube provided with such a cathode.
  • a characteristic feature of dispenser cathodes is that there is a functional separation between the electron emissive surface on the one hand and a store of the emitter material for realizing a sufficiently low work function on the emissive surface on the other hand.
  • the emitter material is present in the pores of the porous metal cathode body.
  • European Patent Specification No. 0,091,161 describes how such cathodes can be improved on sensitivity to and recovery after ion bombardment by compressing the cathode body (notably the top layer) from a mixture of tungsten powder and scandium oxide and by subsequently sintering it.
  • the compressing operation is generally performed in two steps. Firstly, the tungsten portion of the cathode body is slightly pre­compressed. Subsequently, the top layer powder is evenly distributed over a surface of the tungsten portion whereafter the definitive compressing operation is performed.
  • a method according to the invention is characterized in that the cathode body is compressed from a quantity of metal powder which is mixed with scandium or scandium hydride whereafter the body is sintered and the cathode is provided with emitter material.
  • the quantity of scandium or scandium hydride in the quantity of metal powder is preferably 0.3-0.7% by weight.
  • this sintering operation is preferably performed at a temperature which is lower than the melting point of scandium (1539°C).
  • the sintering temperature must be chosen to be as high as possible in order to obtain a sufficiently robust cathode body.
  • a preferred embodiment of a method according to the invention is therefore characterized in that the sintering temperature is between 1430°C and 1500°C.
  • Figure 1 is a longitudinal cross-section of a cathode according to the invention.
  • the cathode body 1 is compressed from a mixture of tungsten powder and approximately 0.5% by weight of scandium or scandium-hydride. After compressing at a pressure of approximately 3.5 atmosphere and sintering in hydrogen for approximately one hour at 1450°, the cathode body of scandium and tungsten has a porosity of approximately 20%.
  • the cathode body 1 now has, for example, a thickness of 0.5 mm and a diameter of approximately 1.8 mm.
  • the cathode body 1 is impregnated in a hydrogen atmosphere with barium calcium aluminate (for example, 5BaO; 2Al2O3; 3CaO or 4BaO; 1Al2O3; 1CaO), compressed in a holder 2 and welded onto the cathode shank 3.
  • barium calcium aluminate for example, 5BaO; 2Al2O3; 3CaO or 4BaO; 1Al2O3; 1CaO
  • the cathode shank 3 accommodates a coiled cathode filament 4 comprising a helically wound metal core 5 and an aluminium oxide insulating layer 6.
  • the emission of the emissive surface 7 of such a cathode was approximately 100 A/cm2 at 950°C obtained at a pulse load at 1000 V in a diode with a cathode-anode distance of 0.3 mm.
  • Such an emission is comparable to that of a cathode with a top layer of tungsten and scandium oxide as described in European Patent Application No. 0,178,716 (PHN 11,169) which is more difficult to manufacture.
  • the recovery after ion bombardment was comparable to that of the cathode described in that Application with a cathode body sintered at approximately 1900°C (approximately 65%). In a cathode according to the invention, sintered at 1500°C this recovery was poorer and was approximately 58%.
  • the impregnant absorption was approximately 4.5%.
  • this absorption decreased to approximately 2% which shortens the life time of the cathode.
  • the quantity of absorbed impregnant is sufficient; the recovery after ion bombardment did not show any significant change in this range.
  • a cylinder 20 with an emissive surface 21 in which a heating element is provided and which is shown in an elevational view in Figure 2 can also be turned from a tungsten body compressed in accordance with the method as described hereinbefore.
  • the cathodes according to the invention may be used in electron tubes such as, for example magnetrons, transmitter tubes, etc., but also in cathode-ray tubes for e.g. television applications and electron microscopy.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Solid Thermionic Cathode (AREA)
  • Powder Metallurgy (AREA)

Abstract

A cathode body for an impregnated scandate cathode is obtained by compressing and sintering a mixture of tungsten powder with approximately 0.5% by weight of scandium, whereafter the body is impregnated.

Description

  • The invention relates to a method of manufacturing a dispenser cathode comprising a barium compound for dispensing barium to an emissive surface of a porous cathode body substantially comprising a metal melting at a high temperature.
  • The invention also relates to a dispenser cathode manufactured by means of such a method and to an electron tube provided with such a cathode.
  • A characteristic feature of dispenser cathodes is that there is a functional separation between the electron emissive surface on the one hand and a store of the emitter material for realizing a sufficiently low work function on the emissive surface on the other hand. The emitter material is present in the pores of the porous metal cathode body.
  • A method of the type mentioned in the opening paragraph is described in United States Patent No. 4,077,393. This patent describes how a cathode body with a porosity of approximately 20% compressed from tungsten powder and subsequently sintered is impregnated with a mixture which comprises calcium oxide, aluminium oxide and scandium oxide in addition to barium oxide.
  • European Patent Specification No. 0,091,161 describes how such cathodes can be improved on sensitivity to and recovery after ion bombardment by compressing the cathode body (notably the top layer) from a mixture of tungsten powder and scandium oxide and by subsequently sintering it. To obtain a cathode body with a thin top layer (approximately 0.1 mm) which is as homogeneous as possible the compressing operation is generally performed in two steps. Firstly, the tungsten portion of the cathode body is slightly pre­compressed. Subsequently, the top layer powder is evenly distributed over a surface of the tungsten portion whereafter the definitive compressing operation is performed.
  • It is an object of the invention to provide a different method of manufacturing such a dispenser cathode, which method is simpler and leads to similar results as regards current density and lifetime.
  • To this end a method according to the invention is characterized in that the cathode body is compressed from a quantity of metal powder which is mixed with scandium or scandium hydride whereafter the body is sintered and the cathode is provided with emitter material. The quantity of scandium or scandium hydride in the quantity of metal powder is preferably 0.3-0.7% by weight.
  • From a manufacturing technical point of view such a method is more advantageous because compressing is only to be performed in one operation and the distribution of the top-­layer powder is no longer necessary. After the introduction of the impregnant the cathode bodies manufactured by means of such a method can undergo mechanical treatments such as turning or other types of shaping without any detrimental effects.
  • In order to prevent as much as possible that scandium is lost during sintering which is preferably performed in a hydrogen atmosphere, this sintering operation is preferably performed at a temperature which is lower than the melting point of scandium (1539°C). However, on the other hand the sintering temperature must be chosen to be as high as possible in order to obtain a sufficiently robust cathode body.
  • A preferred embodiment of a method according to the invention is therefore characterized in that the sintering temperature is between 1430°C and 1500°C.
  • The invention will now be described in greater detail by way of example with reference to the accompanying drawing, in which:
    • Figure 1 is a longitudinal cross-section of a cathode according to the invention and
    • Figure 2 is an elevational view of a cylindrical cathode according to the invention.
  • Figure 1 is a longitudinal cross-section of a cathode according to the invention. The cathode body 1 is compressed from a mixture of tungsten powder and approximately 0.5% by weight of scandium or scandium-hydride. After compressing at a pressure of approximately 3.5 atmosphere and sintering in hydrogen for approximately one hour at 1450°, the cathode body of scandium and tungsten has a porosity of approximately 20%. The cathode body 1 now has, for example, a thickness of 0.5 mm and a diameter of approximately 1.8 mm.
  • Subsequently, the cathode body 1 is impregnated in a hydrogen atmosphere with barium calcium aluminate (for example, 5BaO; 2Al₂O₃; 3CaO or 4BaO; 1Al₂O₃; 1CaO), compressed in a holder 2 and welded onto the cathode shank 3. The cathode shank 3 accommodates a coiled cathode filament 4 comprising a helically wound metal core 5 and an aluminium oxide insulating layer 6. The emission of the emissive surface 7 of such a cathode was approximately 100 A/cm² at 950°C obtained at a pulse load at 1000 V in a diode with a cathode-anode distance of 0.3 mm. Such an emission is comparable to that of a cathode with a top layer of tungsten and scandium oxide as described in European Patent Application No. 0,178,716 (PHN 11,169) which is more difficult to manufacture. The recovery after ion bombardment was comparable to that of the cathode described in that Application with a cathode body sintered at approximately 1900°C (approximately 65%). In a cathode according to the invention, sintered at 1500°C this recovery was poorer and was approximately 58%. For the significance of the recovery percentages and the way in which they have been determined reference is made to the European Patent Application No. 0,178,716 or to the magazine Article "Properties and manufacture of top layer scandate cathodes" in Applied Surface Science 26 (1986), pages 173-195.
  • In the above-mentioned example the impregnant absorption was approximately 4.5%. Upon raising the quantity of scandium (hydride) in the mixture to be compressed to 1 percent by weight this absorption decreased to approximately 2% which shortens the life time of the cathode. For a quantity of 0.3-0.7% by weight of scandium (hydride) the quantity of absorbed impregnant is sufficient; the recovery after ion bombardment did not show any significant change in this range.
  • A cylinder 20 with an emissive surface 21 in which a heating element is provided and which is shown in an elevational view in Figure 2 can also be turned from a tungsten body compressed in accordance with the method as described hereinbefore.
  • The cathodes according to the invention may be used in electron tubes such as, for example magnetrons, transmitter tubes, etc., but also in cathode-ray tubes for e.g. television applications and electron microscopy.

Claims (7)

1. A method of manufacturing a dispenser cathode comprising a barium compound for dispensing barium to an emissive surface of a porous cathode body substantially comprising a metal melting at a high temperature, characterized in that the cathode body is compressed from a quantity of metal powder which is mixed with scandium or scandium hydride whereafter the body is sintered and the cathode is provided with emitter material.
2. A method as claimed in Claim 1, characterized in that the quantity of scandium or scandium hydride in the mixture of metal powder and scandium or scandium hydride is approximately between 0.3 and 0.7% by weight.
3. A method as claimed in Claim 1 or 2, characterized in that the sintering temperature is lower than the melting point of scandium.
4. A method as claimed in Claim 3, characterized in that the sintering temperature is between 1430°C and 1500°C.
5. A method as claimed in any one of the preceding Claims, characterized in that the cathode body is definitively shaped after it has been provided with emitter material.
6. A dispenser cathode manufactured by means of a method as claimed in any one of Claims 1 to 5.
7. An electron tube provided with a cathode as claimed in Claim 6.
EP88201392A 1987-07-06 1988-07-04 Method of manufacturing a scandat cathode Expired - Lifetime EP0298558B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL8701583A NL8701583A (en) 1987-07-06 1987-07-06 SCANDAT CATHOD.
NL8701583 1987-07-06

Publications (2)

Publication Number Publication Date
EP0298558A1 true EP0298558A1 (en) 1989-01-11
EP0298558B1 EP0298558B1 (en) 1994-05-25

Family

ID=19850259

Family Applications (1)

Application Number Title Priority Date Filing Date
EP88201392A Expired - Lifetime EP0298558B1 (en) 1987-07-06 1988-07-04 Method of manufacturing a scandat cathode

Country Status (5)

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EP (1) EP0298558B1 (en)
JP (1) JP2685232B2 (en)
KR (1) KR890002949A (en)
DE (1) DE3889696T2 (en)
NL (1) NL8701583A (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5264757A (en) * 1989-11-13 1993-11-23 U.S. Philips Corporation Scandate cathode and methods of making it
EP0651419A1 (en) * 1993-10-28 1995-05-03 Koninklijke Philips Electronics N.V. Dispenser cathode and method of manufacturing a dispenser cathode
BE1007676A3 (en) * 1993-10-28 1995-09-12 Philips Electronics Nv Method for manufacturing a dispenser cathode
BE1007677A3 (en) * 1993-10-28 1995-09-12 Philips Electronics Nv Method for manufacturing a dispenser cathode
WO1995025337A1 (en) * 1994-03-15 1995-09-21 Philips Electronics N.V. Dispenser cathode and method of manufacturing a dispenser cathode

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6281626B1 (en) * 1998-03-24 2001-08-28 Casio Computer Co., Ltd. Cold emission electrode method of manufacturing the same and display device using the same

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4007393A (en) * 1975-02-21 1977-02-08 U.S. Philips Corporation Barium-aluminum-scandate dispenser cathode
EP0091161A1 (en) * 1982-04-01 1983-10-12 Koninklijke Philips Electronics N.V. Methods of manufacturing a dispenser cathode and dispenser cathode manufactured according to the method
EP0178716A1 (en) * 1984-10-05 1986-04-23 Koninklijke Philips Electronics N.V. Method of manufacturing a scandate dispenser cathode and scandate dispenser cathode manufactured according to the method
EP0179513A1 (en) * 1984-10-05 1986-04-30 Koninklijke Philips Electronics N.V. Method of manufacturing a scandate dispenser cathode and dispenser cathode manufactured by means of the method

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58154131A (en) * 1982-03-10 1983-09-13 Hitachi Ltd Impregnation type cathode
JPS63254636A (en) * 1987-04-10 1988-10-21 Hitachi Ltd Impregnated cathode

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4007393A (en) * 1975-02-21 1977-02-08 U.S. Philips Corporation Barium-aluminum-scandate dispenser cathode
EP0091161A1 (en) * 1982-04-01 1983-10-12 Koninklijke Philips Electronics N.V. Methods of manufacturing a dispenser cathode and dispenser cathode manufactured according to the method
EP0178716A1 (en) * 1984-10-05 1986-04-23 Koninklijke Philips Electronics N.V. Method of manufacturing a scandate dispenser cathode and scandate dispenser cathode manufactured according to the method
EP0179513A1 (en) * 1984-10-05 1986-04-30 Koninklijke Philips Electronics N.V. Method of manufacturing a scandate dispenser cathode and dispenser cathode manufactured by means of the method

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, vol. 8, no. 190 (E-263)[1627], 31st August 1984; & JP-A-59 79 934 (HITACHI SEISAKUSHO K.K.) 09-05-1984 *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5264757A (en) * 1989-11-13 1993-11-23 U.S. Philips Corporation Scandate cathode and methods of making it
US5314364A (en) * 1989-11-13 1994-05-24 U.S. Philips Corporation Scandate cathode and methods of making it
CN1036165C (en) * 1989-11-13 1997-10-15 菲利浦光灯制造公司 Scandate cathode
EP0651419A1 (en) * 1993-10-28 1995-05-03 Koninklijke Philips Electronics N.V. Dispenser cathode and method of manufacturing a dispenser cathode
BE1007676A3 (en) * 1993-10-28 1995-09-12 Philips Electronics Nv Method for manufacturing a dispenser cathode
BE1007677A3 (en) * 1993-10-28 1995-09-12 Philips Electronics Nv Method for manufacturing a dispenser cathode
US5666022A (en) * 1993-10-28 1997-09-09 U.S. Philips Corporation Dispenser cathode and method of manufacturing a dispenser cathode
WO1995025337A1 (en) * 1994-03-15 1995-09-21 Philips Electronics N.V. Dispenser cathode and method of manufacturing a dispenser cathode

Also Published As

Publication number Publication date
DE3889696T2 (en) 1994-12-08
DE3889696D1 (en) 1994-06-30
EP0298558B1 (en) 1994-05-25
JP2685232B2 (en) 1997-12-03
KR890002949A (en) 1989-04-12
JPH01163941A (en) 1989-06-28
NL8701583A (en) 1989-02-01

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