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GB2173944A - Construction of porous impregnated cathodes for discharge tubes - Google Patents

Construction of porous impregnated cathodes for discharge tubes Download PDF

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Publication number
GB2173944A
GB2173944A GB08510003A GB8510003A GB2173944A GB 2173944 A GB2173944 A GB 2173944A GB 08510003 A GB08510003 A GB 08510003A GB 8510003 A GB8510003 A GB 8510003A GB 2173944 A GB2173944 A GB 2173944A
Authority
GB
United Kingdom
Prior art keywords
impregnated
work function
lower work
porous
function material
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.)
Withdrawn
Application number
GB08510003A
Other versions
GB8510003D0 (en
Inventor
Richard Mole Bretherton
John Francis Littlechild
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.)
Excelitas Noblelight Ltd
Original Assignee
Noblelight 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
Application filed by Noblelight Ltd filed Critical Noblelight Ltd
Priority to GB08510003A priority Critical patent/GB2173944A/en
Publication of GB8510003D0 publication Critical patent/GB8510003D0/en
Publication of GB2173944A publication Critical patent/GB2173944A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • 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

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)

Abstract

A cathode for a gas discharge lamp is produced by impregnating a porous conductive material with the lower work function material. After impregnation, the cathode is treated to prevent the lower work function material from being exposed on the surface of the impregnated material. This treatment can either be carried out by removing some of the lower work function material from the exposed faces of the cathode, or by covering the material which is exposed on the exterior of the cathode by another material which has a higher work function.

Description

SPECIFICATION Construction of porous impregnated cathodes for discharge tubes Field of invention This invention concerns the method of construction of porous impregnated cathodes for gas discharge tubes.
Background to the invention It is known to impregnate porous material such as porous tungsten with a lower work function material such as a derivative of barium as barium strontium oxide so as to improve the arc discharge characteristics of the cathode.
It is an object of the present invention to provide an improved method of construction which provides an improved cathode from an impregnated material.
Summary of the invention According to the present invention a method of forming a cathode for a gas discharge lamp comprises the steps of impregnating a porous conductive material with a lower work function material and after impregnation removing the lower work function material from at least part of the surface of the impregnated material.
In the case of porous tungsten impregnated by a derivative of barium, this is most simply achieved by immersing the impregnated material or a region of the surface thereof in boiling water for a controlled period of time. It is found that dependent on the length of time the surface of the impregnated material is exposed to the boiling water, so a smaller or greater depth of the surface of the impregnated material becomes deficient of the impregnating material, the latter being washed or dissolved away by the boiling water.
In the case of tungsten impregnated with a barium derivative, it is found that boiling the impregnated material for periods of time between five and ten minutes produces a depletion layer of sufficient depth to achieve the advantages of the invention.
According to another aspect of the invention, the depletion layer may be achieved alternatively by impregnating the porous conductive material with a lower work function material such as a barium derivative and thereafter coating some or all of the surface of the impregnated material with a higher work function material which is also porous and admits the release of electrons from the lower work function material embedded therein.
The layer of material applied to the surface of the impregnated material need only be very thin and may for example be applied by spraying or sputtering or vacuum deposition or dipping.
The outer coating material may be of the same chemical composition as that of the material impregnated by the lower work function material or may be different therefrom.
1. A method of forming a cathode for a gas discharge lamp, comprising the steps of impregnating a porous conductive material with a lower work function material and, after impregnation, treating the impregnated material to prevent the lower work function material from being exposed on the surface of the im impregnated material.
2. A method as claimed in Claim 1, wherein the conductive material is porous tungsten and the lower work function material is a derivative of barium.
3. A method as claimed in Claim 1, wherein the lower work function material is removed from at least part of the surface of the impregnated material.
4. A method as claimed in Claim 3, wherein the lower work function material is removed by immersing the impregnated material or a region of the surface thereof in boiling water.
5. A method as claimed in Claim 4, wherein the impregnated material is immersed for a period of time between five and ten minutes.
6. A method as claimed in Claim 1 or Claim 2, wherein the impregnated material is coated on some or all of its surface with a higher work function material which is also porous and admits the release of electrons from the lower work function material embedded therein.
7. A method as claimed in Claim 6, wherein said higher work function material is applied by spraying or sputtering or vacuum deposition or dipping.
8. A method as claimed in Claim 6 or Claim 7, wherein the outer coating material is of the same chemical composition as that of the material impregnated by the lower work function material.
9. A method as claimed in Claim 6 or Claim 7, wherein the outer coating material is of a different chemical composition to that of the impregnated material.
10. A method of forming a cathode for a gas discharge lamp, substantially as herein described.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Construction of porous impregnated cathodes for discharge tubes Field of invention This invention concerns the method of construction of porous impregnated cathodes for gas discharge tubes. Background to the invention It is known to impregnate porous material such as porous tungsten with a lower work function material such as a derivative of barium as barium strontium oxide so as to improve the arc discharge characteristics of the cathode. It is an object of the present invention to provide an improved method of construction which provides an improved cathode from an impregnated material. Summary of the invention According to the present invention a method of forming a cathode for a gas discharge lamp comprises the steps of impregnating a porous conductive material with a lower work function material and after impregnation removing the lower work function material from at least part of the surface of the impregnated material. In the case of porous tungsten impregnated by a derivative of barium, this is most simply achieved by immersing the impregnated material or a region of the surface thereof in boiling water for a controlled period of time. It is found that dependent on the length of time the surface of the impregnated material is exposed to the boiling water, so a smaller or greater depth of the surface of the impregnated material becomes deficient of the impregnating material, the latter being washed or dissolved away by the boiling water. In the case of tungsten impregnated with a barium derivative, it is found that boiling the impregnated material for periods of time between five and ten minutes produces a depletion layer of sufficient depth to achieve the advantages of the invention. According to another aspect of the invention, the depletion layer may be achieved alternatively by impregnating the porous conductive material with a lower work function material such as a barium derivative and thereafter coating some or all of the surface of the impregnated material with a higher work function material which is also porous and admits the release of electrons from the lower work function material embedded therein. The layer of material applied to the surface of the impregnated material need only be very thin and may for example be applied by spraying or sputtering or vacuum deposition or dipping. The outer coating material may be of the same chemical composition as that of the material impregnated by the lower work function material or may be different therefrom. CLAIMS
1. A method of forming a cathode for a gas discharge lamp, comprising the steps of impregnating a porous conductive material with a lower work function material and, after impregnation, treating the impregnated material to prevent the lower work function material from being exposed on the surface of the im impregnated material.
2. A method as claimed in Claim 1, wherein the conductive material is porous tungsten and the lower work function material is a derivative of barium.
3. A method as claimed in Claim 1, wherein the lower work function material is removed from at least part of the surface of the impregnated material.
4. A method as claimed in Claim 3, wherein the lower work function material is removed by immersing the impregnated material or a region of the surface thereof in boiling water.
5. A method as claimed in Claim 4, wherein the impregnated material is immersed for a period of time between five and ten minutes.
6. A method as claimed in Claim 1 or Claim 2, wherein the impregnated material is coated on some or all of its surface with a higher work function material which is also porous and admits the release of electrons from the lower work function material embedded therein.
7. A method as claimed in Claim 6, wherein said higher work function material is applied by spraying or sputtering or vacuum deposition or dipping.
8. A method as claimed in Claim 6 or Claim 7, wherein the outer coating material is of the same chemical composition as that of the material impregnated by the lower work function material.
9. A method as claimed in Claim 6 or Claim 7, wherein the outer coating material is of a different chemical composition to that of the impregnated material.
10. A method of forming a cathode for a gas discharge lamp, substantially as herein described.
GB08510003A 1985-04-18 1985-04-18 Construction of porous impregnated cathodes for discharge tubes Withdrawn GB2173944A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB08510003A GB2173944A (en) 1985-04-18 1985-04-18 Construction of porous impregnated cathodes for discharge tubes

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB08510003A GB2173944A (en) 1985-04-18 1985-04-18 Construction of porous impregnated cathodes for discharge tubes

Publications (2)

Publication Number Publication Date
GB8510003D0 GB8510003D0 (en) 1985-05-30
GB2173944A true GB2173944A (en) 1986-10-22

Family

ID=10577878

Family Applications (1)

Application Number Title Priority Date Filing Date
GB08510003A Withdrawn GB2173944A (en) 1985-04-18 1985-04-18 Construction of porous impregnated cathodes for discharge tubes

Country Status (1)

Country Link
GB (1) GB2173944A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2225158A (en) * 1988-11-12 1990-05-23 Samsung Electronic Devices Manufacturing dispenser cathodes of electron guns

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB364583A (en) * 1929-09-05 1932-01-04 Lampes Fotos Soc D Improvements in or relating to the cathodes of vacuum tubes
GB462500A (en) * 1935-02-26 1937-03-10 British Thomson Houston Co Ltd Improvements in and relating to electric discharge devices

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB364583A (en) * 1929-09-05 1932-01-04 Lampes Fotos Soc D Improvements in or relating to the cathodes of vacuum tubes
GB462500A (en) * 1935-02-26 1937-03-10 British Thomson Houston Co Ltd Improvements in and relating to electric discharge devices

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2225158A (en) * 1988-11-12 1990-05-23 Samsung Electronic Devices Manufacturing dispenser cathodes of electron guns
GB2225158B (en) * 1988-11-12 1993-01-13 Samsung Electronic Devices Manufacturing method for dispenser cathode of an electron gun

Also Published As

Publication number Publication date
GB8510003D0 (en) 1985-05-30

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Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)