EP0907960B1 - Cold electrode for gas discharges - Google Patents

Cold electrode for gas discharges Download PDF

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Publication number
EP0907960B1
EP0907960B1 EP98916816A EP98916816A EP0907960B1 EP 0907960 B1 EP0907960 B1 EP 0907960B1 EP 98916816 A EP98916816 A EP 98916816A EP 98916816 A EP98916816 A EP 98916816A EP 0907960 B1 EP0907960 B1 EP 0907960B1
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EP
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Prior art keywords
electrode
electrode according
emission coating
work function
coating
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EP98916816A
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German (de)
French (fr)
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EP0907960A2 (en
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Marcus Thielen
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    • 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
    • H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
    • 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
    • H01J1/025—Hollow cathodes
    • 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
    • H01J61/067—Main electrodes for low-pressure discharge lamps
    • H01J61/0672—Main electrodes for low-pressure discharge lamps characterised by the construction of the electrode
    • 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
    • H01J61/067—Main electrodes for low-pressure discharge lamps
    • H01J61/0675—Main electrodes for low-pressure discharge lamps characterised by the material of the electrode
    • H01J61/0677—Main electrodes for low-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
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/04—Electrodes; Screens; Shields
    • H01J61/06—Main electrodes
    • H01J61/09—Hollow cathodes

Definitions

  • the present invention relates to an electrode for gas discharges with an electrically conductive material.
  • Cold electrodes are usually on the inside with a coating consisting of mixtures of alkaline earth oxides -after activation called-, provided to reduce the work function (principle of Wehnelt i.J. 1907). Since the oxides are not stable under normal ambient conditions, the carbonaceous emission liners are applied to the electrode base material at low pressure and high temperature, e.g. under annealing of the support material, converted into the corresponding oxides.
  • an electrode of tungsten is known whose emission coating may contain yttrium.
  • US-A-3474280 From the US-A-3474280 is the use of yttrium known as a coating material.
  • the US-A-3474280 but specifies a spectral hollow cathode lamp in which the operating temperature of the cardboard material is so high that the material evaporates and thereby the spectral lines are excited in the steam in front of the cathode.
  • the operating temperatures of hollow cathode vapor lamps are sometimes close to the melting point.
  • the US-A-2943226 discloses that only a small portion of the inner electrode surface may be coated with the active metal throughout the lifetime of the electrode. Thus, the largest part of the electrode surface has a high work function. This low active surface thus also causes a lower surface current carrying capacity of the electrode.
  • the EP-A-0741402 In addition to the explicit field emission as a functional principle, only forms that are not hollow bodies are disclosed. These are only low-temperature cathodes, which can be pump cathodes or wire cathodes according to their type. Furthermore, a nanostructure of the emission layer is described.
  • Object of the present invention is therefore to provide an electrode which is insensitive to the boundary conditions during processing and during the entire life of the gas discharge device low electrical losses - and thus a lower heating - has.
  • the essence of the solution according to the invention is therefore that the coating of the electrode which emits the electrons ("emission coating") is chosen in a special way with regard to their photoelectric work function.
  • This work function should be less than that of the support material of the electrode in the operating temperature range of the electrode, which is typically between 260 and 450 K. Irrespective of the carrier material, the photoelectric work function in the temperature range from 0 to 500 K should be less than 5.6 * 10 -19 Joule / electron.
  • Concretely usable coating materials are yttrium, praseodymium or cerium or mixtures thereof.
  • the photoelectric work function is defined as the photoelectric quantum energy that must be applied per electron to dissolve it out of the electrode (measured in eV / electron or Joule / electron).
  • the electron-emitting layer may consist of metallic or semiconducting substances with lower photo-exiting work than the substrate, instead of the oxides having high photo-exiting activity at low temperatures, often with simultaneous utilization of the hollow-cathode effect known in principle.
  • the electrode is almost independent of the gas atmosphere during fabrication and conditioning; Neither the activating mass can be poisoned nor can an incompletely carried out reaction in the reaction at a later time release reaction products into the atmosphere of the gas discharge space.
  • the electrode of the present invention is substantially safe from mistreatment in preparation and conditioning by e.g. untrained staff. Also, the avoidance of the hitherto necessary, production-technically very complicated preparation process for carbonate mixtures can lead to considerable cost advantages.
  • Oxide mixtures have, thermally stimulated, a low photo-exiting work.
  • thermal electron emission from inhomogeneous, multicomponent, insulating solids whose electronic band structure has indirect transitions lattice vibrations (phonons) are involved in the excitation of the transitions' in the minimum of the band gap (Lit .: eg Joseph Eichmeier, "Modern Vacuum Electronics”; Springer Verlag, Berlin 1981 ).
  • the photo-exiting work could be found as the decisive variable for the losses; it differs from the thermally determined work function under certain circumstances. Since the phonon energy in cold electrodes is considerably lower than in thermally emitting electrodes, no indirect band transitions can be excited with cold electrodes.
  • Coating materials according to the invention have only almost direct band transitions and a small band gap, which make it unnecessary to involve phonons of high energy in the excitation process.
  • the electrode according to the invention is designed as a hollow body, in particular cup-shaped, and the emission coating (3) is located on the inside of the hollow body.
  • the hollow cathode effect can be positively utilized.
  • the hollow body may in particular have the shape of a cup and the emission coating is located on the inside of the hollow body, where the emission of the electrons takes place.
  • the emission coating (3) has a lower photoelectric work function than the remaining surface of the electrode, in particular the outer surface of the hollow body. As a result, a concentration of the electron emission is achieved on the emission coating.
  • the carrier material (1) is provided on the outside of the hollow body with a coating (4), preferably made of nickel or platinum, which has a high photo-exiting work, preferably higher than 8.0 * 10 -19 joule / electron.
  • a coating (4) preferably made of nickel or platinum, which has a high photo-exiting work, preferably higher than 8.0 * 10 -19 joule / electron.
  • the support material may preferably contain metal, in particular iron.
  • the content is particularly preferred that the carrier material consists of the metal.
  • the emission coating (3) may further contain dopants for reducing the photo-exiting work compared to the pure substance, preferably with the dopants, for example calcium, cesium or barium in the concentrations 10 -5 at% to 1 at%. This allows a further reduction of the work function and thus the losses can be achieved by reducing the band gap in the electronic band structure compared to the use of pure substances.
  • dopants for example calcium, cesium or barium in the concentrations 10 -5 at% to 1 at%.
  • a part of the surface of the carrier material (1) is provided with an electrically insulating coating (4) for suppressing an electron or ion current. This has the advantage of completely suppressing electron flow from the outside of the substrate and thereby increasing the life of the electrode.
  • the parts of the electrode which are directed towards the gas discharge can be coated with an electrically insulating, temperature and vacuum-resistant material, preferably ceramic. This has the advantageous effect of preventing the sputtering of the active or supporting material of the electrode from the edge facing the gas discharge.
  • an electrically insulating sleeve (9) which is provided with a collar can also be arranged in the opening of the cavity formed by the electrode such that the collar covers the edges of the opening in the direction of the gas discharge.
  • the gas discharge facing edge of the opening of the cavity formed by the electrode may also be formed such that the electric field gradient is reduced at the opening, preferably by bending or crimping. As a result, a partial reduction of the sputtering rate can be achieved without requiring a further manufacturing element.
  • the electrode may be surrounded by a glass body (8), which may preferably be cylindrical.
  • centering of the electrode in a cylindrical glass body can be achieved to avoid breakage of the glass under mechanical stress (e.g., impact, impact) or unilateral thermal stress, such as e.g. could occur during conditioning of the electrode.
  • the at least partially feldfireie space is formed inside a metallic cup, hollow cylinder or hollow cone.
  • the device according to the invention for the use of existing manufacturing tools for the production of the carrier body in a known per se is suitable.
  • the device according to the invention can furthermore be equipped in such a way that at least on a part of the surface of the carrier material (1) a reactive gas-binding substance (getter) is applied, which is activated, for example, during the conditioning of the electrodes.
  • a reactive gas-binding substance getter
  • the inside of the carrier body (1) is provided with a layer (3) of a material having a low photoelectric work function, e.g. Yttrium, which has been applied by mechanical, chemical and / or physical coating techniques (e.g., press-on, roller, vapor deposition, sputtering, plating, spraying), while the outer surface (4) is exemplified by high photoelectric work function material, e.g. Nickel or platinum, coated.
  • a material having a low photoelectric work function e.g. Yttrium
  • high photoelectric work function material e.g. Nickel or platinum
  • the power supply wires (5) At the closed end of the support body (1), here in the form of a spherical cap, the power supply wires (5) in a conventional manner, e.g. by spot welding, attached.
  • FIG. 2 shows exemplarily a longitudinal section through an electrode according to the invention, installed in a cylindrical glass body (8) in a known per se, as part of a gas discharge vessel, for use in high-voltage fluorescent tubes.
  • the power supply wires (5) in the pinch (6) are fusibly sealed to the glass body (8) fused.
  • An additionally in the squeeze (6) melted glass tube (7) can be used to evacuate the -in Fig. 2 not shown- serve gas discharge vessel.
  • the electrode is usually attached to the gas discharge vessel by means of the glass body (8).
  • FIG. 2 the opening (2) of the carrier body (1) with an insulating guard ring (9), for example made of ceramic, which in a known manner on the carrier body (1) by squeezing, curling, knurling, rolling, etc. is attached.
  • an insulating guard ring (9) for example made of ceramic, which in a known manner on the carrier body (1) by squeezing, curling, knurling, rolling, etc. is attached.
  • guard ring (9) and support body (1) an additional centering ring (10), for example made of mica.
  • the centering ring (10) may deviate from the circular ring shape, for example with notches or similar. be prepared to enter aerodynamically favorable evacuation of the gas discharge vessel through the neck tube (7) to allow.
  • FIG. 3 shows comparative results of measurements of the photoelectric work function of various commercially available electrodes over an embodiment of the invention.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Discharge Lamp (AREA)
  • Gas-Filled Discharge Tubes (AREA)
  • Glass Compositions (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)

Abstract

Cold electrodes for gas discharges have an electrically conductive carrier material on which an emission coating is disposed. The photoelectric output work of the material of the emission coating is less than that of the carrier material or less than 5.6*10-19 joule/electron. The emission coating can, in particular, contain yttrium. The electrode preferably has the form of a hollow body and can be embedded in a glass body.

Description

Die vorliegende Erfindung betrifft eine Elektrode für Gasentladungen mit einem elektrisch leitenden Material.The present invention relates to an electrode for gas discharges with an electrically conductive material.

Kalte Elektroden für Gasentladungen unter Ausnutzung des Hohlkathodeneffektes sind in der Technik für z.B. Elektronenröhren oder Beleuchtungszwecke seit langer Zeit bekannt und in Gebrauch. ( U.S. Pat. 1 125 476 ; Hohlkathodeneffekt siehe Literatur, z.B. Manfred von Ardenne (Hrsg); "Effekte der Physik und ihre Anwendungen"; Verlag Harri Deutsch; Thun, Frankfurt/Main, 1990 ) Cold electrodes for gas discharges utilizing the hollow cathode effect have been known and used in the art for, for example, electron tubes or lighting for a long time. ( US Pat. No. 1,125,476 ; Hollow cathode effect see literature, eg Manfred von Ardenne (eds); "Effects of Physics and its Applications"; Publisher Harri German; Thun, Frankfurt / Main, 1990 )

Kalte Elektroden sind meist auf der Innenseite mit einem Belag, bestehend aus Gemischen von Erdalkalioxiden -nachstehend Aktivierung genannt-, versehen zur Verringerung der Austrittsarbeit (Prinzip von Wehnelt i.J. 1907). Da die Oxide unter normalen Umgebungsbedingungen nicht stabil sind, werden die Emissionsbeläge in Form von Karbonaten auf das Trägermaterial der Elektrode aufgebracht und bei niedrigen Drucken und hoher Temperatur, z.B. unter Ausglühen des Trägermaterials, in die entsprechenden Oxide überführt.Cold electrodes are usually on the inside with a coating consisting of mixtures of alkaline earth oxides -after activation called-, provided to reduce the work function (principle of Wehnelt i.J. 1907). Since the oxides are not stable under normal ambient conditions, the carbonaceous emission liners are applied to the electrode base material at low pressure and high temperature, e.g. under annealing of the support material, converted into the corresponding oxides.

Die elektrischen Verluste an vorstehend beschriebenen Elektroden mit den damit verbundenen Nachteilen hängen empfindlich von den Randbedingungen während der Umsetzung der Karbonate bei der Konditionierung ab sowie von Restgasen im Entladungsraum während des Betriebes, welche die Emissionsfähigkeit herabsetzen ("Vergiftung der Aktivierung").The electrical losses on electrodes described above, with the disadvantages associated with them, depend sensitively on the boundary conditions during the reaction of the carbonates in the conditioning and of residual gases in the discharge space during operation, which reduce the emissivity ("poisoning of the activation").

Aus der US-A-4620128 ist eine Elektrode aus Wolfram bekannt, deren Emissionsbeschichtung Yttrium enthalten kann. Es handelt sich hier jedoch um thermisch emittierende Elektroden, die hohe Arbeitstemperaturen erfordern.From the US-A-4620128 For example, an electrode of tungsten is known whose emission coating may contain yttrium. However, these are thermally emitting electrodes that require high working temperatures.

Aus der US-A-4117374 ist darüber hinaus eine ähnliche Elektrode bekannt. Diese erfordert z. B. eine Arbeitstemperatur ab 1.000° C.From the US-A-4117374 In addition, a similar electrode is known. This requires z. B. a working temperature from 1,000 ° C.

Aus der GB-A-438727 sind Emissionsbeschichtungen aus metallischem Barium bekannt. Solche Beschichtungen sind für die Verwendung in technischen Gasentladungslampen jedoch nicht einsetzbar. Dies liegt in erster Linie daran, dass Alkali- und Erdalkalimetalle in der Atmosphäre nicht stabil sind, also nicht in metallischer Form in die Elektrode eingebracht werden können. Die Alkali- und Erdalkalimetalle müssen vielmehr erst in der Röhre unter besonderen Bedingungen durch chemische Reaktion oder physikalische Vorgänge erzeugt werden.From the GB-A-438727 Emission coatings are known from metallic barium. However, such coatings are not suitable for use in technical gas discharge lamps. This is primarily due to the fact that alkali and alkaline earth metals are not stable in the atmosphere, so can not be introduced into the electrode in metallic form. The alkali and alkaline earth metals must rather be produced in the tube under special conditions by chemical reaction or physical processes.

Aus der GB-A-378076 ist ebenfalls der Einsatz von Alkali- und Erdalkalimetallen bekannt. Auch in dieser Entgegenhaltung wird beschrieben, dass die Emissionsschicht erst in der Gasentladungslampe erzeugt werden muss. Auch hier ergeben sich bei der Herstellung somit Schwierigkeiten.From the GB-A-378076 is also the use of alkali and alkaline earth metals known. Also in this citation is described that the emission layer must be generated only in the gas discharge lamp. Again, there are difficulties in the production thus.

Aus der US-A-3474280 ist die Verwendung von Yttrium als Beschichtungsmaterial bekannt. Die US-A-3474280 spezifiziert aber eine Spektral-Hohlkathodenlampe, bei der die Betriebstemperatur des Kartonmaterials derart hoch ist, dass das Material verdampft und dadurch die Spektrallinien im Dampf vor der Kathode angeregt werden. Die Betriebstemperaturen von Hohlkathoden-Dampflampen liegen teilweise nahe dem Schmelzpunkt.From the US-A-3474280 is the use of yttrium known as a coating material. The US-A-3474280 but specifies a spectral hollow cathode lamp in which the operating temperature of the cardboard material is so high that the material evaporates and thereby the spectral lines are excited in the steam in front of the cathode. The operating temperatures of hollow cathode vapor lamps are sometimes close to the melting point.

Die US-A-2943226 offenbart, dass während der gesamten Lebensdauer der Elektrode nur ein geringer Teil der inneren Elektrodenfläche mit dem aktiven Metall beschichtet sein darf. Damit weist der größte Teil der Elektrodenfläche eine hohe Austrittsarbeit auf. Diese geringe aktive Oberfläche bewirkt damit auch eine geringere Flächen-Strombelastbarkeit der Elektrode.The US-A-2943226 discloses that only a small portion of the inner electrode surface may be coated with the active metal throughout the lifetime of the electrode. Thus, the largest part of the electrode surface has a high work function. This low active surface thus also causes a lower surface current carrying capacity of the electrode.

Die EP-A-0741402 offenbart neben der expliziten Feldemission als Funktionsprinzip lediglich Formen, die keine Hohlkörper sind. Es handelt sich hier nur um Niedertemperaturkathoden, die nach ihrer Bauart Pumpkathoden oder Drahtkathoden sein können. Ferner wird eine Nanostruktur der Emissionsschicht beschrieben.The EP-A-0741402 In addition to the explicit field emission as a functional principle, only forms that are not hollow bodies are disclosed. These are only low-temperature cathodes, which can be pump cathodes or wire cathodes according to their type. Furthermore, a nanostructure of the emission layer is described.

Aufgabe der vorliegenden Erfindung ist es daher, eine Elektrode zu schaffen, die unempfindlich gegenüber den Randbedingungen während der Verarbeitung ist und während der gesamten Lebensdauer der Gasentladungseinrichtung niedrige elektrische Verluste -und damit eine geringere Erwärmung- aufweist.Object of the present invention is therefore to provide an electrode which is insensitive to the boundary conditions during processing and during the entire life of the gas discharge device low electrical losses - and thus a lower heating - has.

Dieses Problem wird durch eine Kalte Elektrode für Gasentladungen mit einem elektrisch leitenden Trägermaterial auf welchem eine Emissionsbeschichtung angeordnet ist, gelöst, dadurch gekennzeichnet, dass

  • die Elektrode zumindest teilweise als Hohlkörper ausgebildet ist,
  • die Emissionsbeschichtung sich auf der Innenseite des Hohlkörpers befindet,
  • die Emissionsbeschichtung aus metallischem Material besteht,
  • die Emissionsbeschichtung Yttrium, Praseodym, Cer oder Gemische hiervon enthält,
  • die Außenseite des Hohlkörpers mit einem Belag vorzugsweise aus Nickel oder Platin, versehen ist, der eine hohe Photoaustrittsarbeit, vorzugsweise höher als 8,0x10-19 Joule/Elektron aufweist, und
  • die kalte Elektrode für den Betrieb im Temperaturbereich unter 570 K, vorzugsweise unter 420 K, geeignet ist und die photoelektrische Austrittsarbeit des Materials der Emissionsbeschichtung in diesem Bereich geringer ist als die des Trägermaterials.
This problem is solved by a cold electrode for gas discharges with an electrically conductive carrier material on which an emission coating is arranged, characterized in that
  • the electrode is at least partially formed as a hollow body,
  • the emission coating is on the inside of the hollow body,
  • the emission coating consists of metallic material,
  • the emission coating contains yttrium, praseodymium, cerium or mixtures thereof,
  • the outside of the hollow body is provided with a coating, preferably of nickel or platinum, which has a high photo-exiting work, preferably higher than 8.0 × 10 -19 Joule / electron, and
  • the cold electrode is suitable for operation in the temperature range below 570 K, preferably below 420 K, and the photoelectric work function of the material of the emission coating in this area is lower than that of the support material.

Der Kern der erfindungsgemäßen Lösung besteht demnach darin, daß die Beschichtung der Elektrode, welche die Elektronen emittiert ("Emissionsbeschichtung"), in besonderer Weise in Hinblick auf ihre photoelektrische Austrittsarbeit gewählt wird.The essence of the solution according to the invention is therefore that the coating of the electrode which emits the electrons ("emission coating") is chosen in a special way with regard to their photoelectric work function.

Diese Austrittsarbeit sollte im Arbeitstemperaturbereich der Elektrode, der typischerweise zwischen 260 und 450 K liegt, geringer sein als die des Trägermaterials der Elektrode. Unabhängig vom Trägermaterial sollte die photoelektrische Austrittsarbeit im Temperaturbereich von 0 bis 500 K kleiner als 5.6*10-19 Joule/Elektron sein. Konkret verwendbare Beschichtungsmaterialien sind Yttrium, Praseodym oder Cer oder Gemische hiervon.This work function should be less than that of the support material of the electrode in the operating temperature range of the electrode, which is typically between 260 and 450 K. Irrespective of the carrier material, the photoelectric work function in the temperature range from 0 to 500 K should be less than 5.6 * 10 -19 Joule / electron. Concretely usable coating materials are yttrium, praseodymium or cerium or mixtures thereof.

Die photoelektrische Austrittsarbeit ist definiert als die lichtelektrische Quantenenergie, die pro Elektron aufgewendet werden muß, um dieses aus der Elektrode herauszulösen (gemessen in eV/Elektron oder Joule/Elektron).The photoelectric work function is defined as the photoelectric quantum energy that must be applied per electron to dissolve it out of the electrode (measured in eV / electron or Joule / electron).

Nach der Erfindung werden Oberflächen mit niedriger und hoher Photoaustrittsarbeit kombiniert. Die elektronenemittierende Schicht kann dabei aus metallischen oder halbleitenden Stoffen mit gegenüber dem Trägermaterial niedrigerer Photoaustrittsarbeit bestehen anstelle der bei niedrigen Temperaturen eine hohe Photoaustrittsarbeit aufweisenden Oxide, oft unter gleichzeitiger Ausnutzung des im Prinzip bekannten Hohlkathodeneffektes.According to the invention surfaces are combined with low and high Photoaustrittsarbeit. The electron-emitting layer may consist of metallic or semiconducting substances with lower photo-exiting work than the substrate, instead of the oxides having high photo-exiting activity at low temperatures, often with simultaneous utilization of the hollow-cathode effect known in principle.

Vorteil der Erfindung ist die Vermeidung einer unerwünschten chemischen Umsetzung auf der Elektrodenoberfläche. Dadurch ist die Elektrode nahezu unabhängig von der Gasatmosphäre während Fertigung und Konditionierung; es kann weder die Aktivierungsmasse vergiftet werden noch kann eine unvollständig ausgeführte Reaktion bei der Umsetzung zu einem späteren Zeitpunkt Reaktionsprodukte in die Atmosphäre des Gasentladungsraumes freisetzen.Advantage of the invention is the avoidance of unwanted chemical reaction on the electrode surface. As a result, the electrode is almost independent of the gas atmosphere during fabrication and conditioning; Neither the activating mass can be poisoned nor can an incompletely carried out reaction in the reaction at a later time release reaction products into the atmosphere of the gas discharge space.

Durch Verwendung entsprechend chemisch inerter Materialien mit niedriger Photoaustrittsarbeit (z.B. Yttrium) ist die erfindungsgemäße Elektrode weitgehend sicher vor Fehlbehandlungen bei Herstellung und Konditionierung durch z.B. ungeschultes Personal. Auch kann die Vermeidung des bisher notwendigen, fertigungstechnisch sehr aufwendigen Präparationsverfahrens für Karbonatmischungen zu erheblichen Kostenvorteiten führen.By using appropriately chemically inert materials with low photo-exiting work (e.g., yttrium), the electrode of the present invention is substantially safe from mistreatment in preparation and conditioning by e.g. untrained staff. Also, the avoidance of the hitherto necessary, production-technically very complicated preparation process for carbonate mixtures can lead to considerable cost advantages.

Darüber hinaus ergaben Messungen eine erheblich geringere Erwärmung beim Betrieb der erfindungsgemäßen Elektrode verglichen mit Elektroden gleicher Dimension und Bauart, welche mit Oxidmischungen aktiviert wurden.In addition, measurements showed a significantly lower heating during operation of the electrode according to the invention compared with electrodes of the same dimension and design, which were activated with oxide mixtures.

Messungen der Photoaustrittsarbeit bei verschiedenen Temperaturen belegen die erheblich niedrigere photoelektrische Austrittsarbeit der erfindungsgemäßen Elektrode bei einer Betriebstemperatur von T= 300 K (siehe Figur 3).Measurements of the photo-exiting work at different temperatures prove the considerably lower photoelectric work function of the electrode according to the invention at an operating temperature of T = 300 K (see FIG. 3 ).

Oxidmischungen weisen, thermisch angeregt, eine niedrige Photoaustrittsarbeit auf. Bei der thermischen Elektronenemission aus inhomogenen, mehrkomponentigen, isolierenden Festkörpern, deren elektronische Bandstruktur indirekte Übergänge aufweist, sind Gitterschwingungen (Phononen) an der Anregung der übergänge' im Minimum der Bandlücke beteiligt (Lit.: z.B. Joseph Eichmeier, "Moderne Vakuumelektronik"; Springer Verlag, Berlin 1981 ). Oxide mixtures have, thermally stimulated, a low photo-exiting work. In the case of thermal electron emission from inhomogeneous, multicomponent, insulating solids whose electronic band structure has indirect transitions, lattice vibrations (phonons) are involved in the excitation of the transitions' in the minimum of the band gap (Lit .: eg Joseph Eichmeier, "Modern Vacuum Electronics"; Springer Verlag, Berlin 1981 ).

Für Gasentladungen mit kalten Elektroden konnte die Photoaustrittsarbeit als die für die Verluste maßgebliche Größe gefunden werden; sie unterscheidet sich unter bestimmten Umständen von der thermisch bestimmten Austrittsarbeit. Da die Phononenenergie in kalten Elektroden erheblich geringer ist als in thermisch emittierenden Elektroden, können bei kalten Elektroden keine indirekten Bandübergänge angeregt werden.For gas discharges with cold electrodes, the photo-exiting work could be found as the decisive variable for the losses; it differs from the thermally determined work function under certain circumstances. Since the phonon energy in cold electrodes is considerably lower than in thermally emitting electrodes, no indirect band transitions can be excited with cold electrodes.

Erfindungsgemäße Beschichtungsmaterialien weisen nur nahezu direkte Bandübergänge und eine kleine Bandlücke auf, die eine Beteiligung von Phononen hoher Energie am Anregungsvorgang entbehrlich machen.Coating materials according to the invention have only almost direct band transitions and a small band gap, which make it unnecessary to involve phonons of high energy in the excitation process.

Die erfindungsgemäße Elektrode ist als Hohlkörper ausgebildet insbesondere becherförmig, und die Emissionsbeschichtung (3) befindet sich auf der Innenseite des Hohlkörpers. Damit kann zusätzlich zu den Vorteilen der erfindungsgemäßen Beschichtung der Hohlkathodeneffekt positiv ausgenutzt werden. Der Hohlkörper kann insbesondere die Form eines Bechers haben und die Emissionsbeschichtung befindet sich auf der Innenseite des Hohlkörpers, wo die Emission der Elektronen stattfindet.The electrode according to the invention is designed as a hollow body, in particular cup-shaped, and the emission coating (3) is located on the inside of the hollow body. Thus, in addition to the advantages of the coating according to the invention, the hollow cathode effect can be positively utilized. The hollow body may in particular have the shape of a cup and the emission coating is located on the inside of the hollow body, where the emission of the electrons takes place.

Bei der Hohlkörperelektrode weist die Emissionsbeschichtung (3) eine geringere photoelektrische Austrittsarbeit als die übrige Oberfläche der Elektrode, insbesondere die äußere Oberfläche des Hohlkörpers, auf. Hierdurch wird eine Konzentration der Elektronenemission auf die Emissionsbeschichtung erreicht.In the case of the hollow-body electrode, the emission coating (3) has a lower photoelectric work function than the remaining surface of the electrode, in particular the outer surface of the hollow body. As a result, a concentration of the electron emission is achieved on the emission coating.

Nach der Erfindung ist das Trägermaterial (1) auf der Außenseite des Hohlkörpers mit einem Belag (4), vorzugsweise aus Nickel oder Platin, versehen, der eine hohe Photoaustrittsarbeit aufweist, vorzugsweise höher als 8.0*10-19 Joule/Elektron. Dies erlaubt vorteilhafterweise die Erhöhung der Lebensdauer der Elektrode im Betrieb durch Verhinderung eines Übergreifens der Entladung auf die Außenseite des Trägerkörpers und damit dessen Zerstörung.According to the invention, the carrier material (1) is provided on the outside of the hollow body with a coating (4), preferably made of nickel or platinum, which has a high photo-exiting work, preferably higher than 8.0 * 10 -19 joule / electron. This advantageously allows the life of the electrode to be increased during operation by preventing the discharge from spreading to the outside of the carrier body and thus destroying it.

Das Trägermaterial kann vorzugsweise Metall enthalten, insbesondere Eisen. Besonders bevorzugt ist inhaltlich, daß das Trägermaterial aus dem Metall besteht.The support material may preferably contain metal, in particular iron. The content is particularly preferred that the carrier material consists of the metal.

Die Emissionsbeschichtung (3) kann ferner Dotierungen zur Reduzierung der Photoaustrittsarbeit gegenüber dem Reinstoff, vorzugsweise mit den Dotierungsstoffen, z.B. Calcium, Cäsium oder Barium in den Konzentrationen 10-5 at% bis 1 at% enthalten. Hierdurch kann eine weitere Reduktion der Austrittsarbeit und damit der Verluste durch Verkleinerung der Bandlücke in der elektronischen Bandstruktur gegenüber der Verwendung von Reinstoffen erreicht werden.The emission coating (3) may further contain dopants for reducing the photo-exiting work compared to the pure substance, preferably with the dopants, for example calcium, cesium or barium in the concentrations 10 -5 at% to 1 at%. This allows a further reduction of the work function and thus the losses can be achieved by reducing the band gap in the electronic band structure compared to the use of pure substances.

Weiter bevorzugt ist, daß ein Teil der Oberfläche des Trägermaterials (1) mit einem elektrisch isolierenden Belag (4) zur Unterdrückung eines Elektronen- oder Ionenstromes versehen wird. Dies hat den Vorteil der vollständigen Unterdrückung eines Elektronenstromes von der Außenseite des Trägermaterials und erhöht dadurch die Lebensdauer der Elektrode.It is further preferred that a part of the surface of the carrier material (1) is provided with an electrically insulating coating (4) for suppressing an electron or ion current. This has the advantage of completely suppressing electron flow from the outside of the substrate and thereby increasing the life of the electrode.

Die zur Gasentladung gerichteten Teile der Elektrode können mit einem elektrisch isolierenden, temperatur- und vakuumbeständigen Material, vorzugsweise Keramik, beschichtet sein. Dies hat den vorteilhaften Effekt, daß die Zerstäubung des aktiven oder des Trägermaterials der Elektrode -ausgehend von der der Gasentladung zugewandten Kante- verhindert wird.The parts of the electrode which are directed towards the gas discharge can be coated with an electrically insulating, temperature and vacuum-resistant material, preferably ceramic. This has the advantageous effect of preventing the sputtering of the active or supporting material of the electrode from the edge facing the gas discharge.

Erfindungsgemäß kann auch eine elektrisch isolierende Hülse (9), welche mit einem Kragen versehen ist, in der Öffnung des von der Elektrode gebildeten Hohlraumes derart angeordnet sein, daß der Kragen die Kanten der Öffnung in Richtung der Gasentladung bedeckt. Dadurch läßt sich -insbesondere gleichzeitig mit der beschriebenen Verhinderung der Zerstäubung- eine Ausbildung eines z.B. ringförmigen Kanales bei Verwendung der Elektrode in zylindrischen Mänteln aus Isolierstoff erzielen. Es verhindert ein schädliches und deshalb unerwünschtes Übergreifen der Entladung auf die Außenseite des Trägerkörpers und die Stromzuführungsdrähte.According to the invention, an electrically insulating sleeve (9) which is provided with a collar can also be arranged in the opening of the cavity formed by the electrode such that the collar covers the edges of the opening in the direction of the gas discharge. As a result, in particular simultaneously with the described prevention of sputtering, it is possible to form a ring-shaped channel, for example, when the electrode is used in cylindrical jackets made of insulating material achieve. It prevents a harmful and therefore undesirable spreading of the discharge on the outside of the carrier body and the power supply wires.

Die der Gasentladung zugewandte Kante der Öffnung des von der Elektrode gebildeten Hohlraumes kann darüber hinaus derart ausgeformt sein, daß der elektrische Feldgradient an der Öffnung reduziert wird, vorzugsweise durch Umbiegen oder Umbördeln. Hierdurch läßt sich eine teilweise Reduktion der Zerstäubungsrate ohne Erfordernis eines weiteren fertigungstechnischen Elementes erreichen.The gas discharge facing edge of the opening of the cavity formed by the electrode may also be formed such that the electric field gradient is reduced at the opening, preferably by bending or crimping. As a result, a partial reduction of the sputtering rate can be achieved without requiring a further manufacturing element.

Ferner kann die Elektrode von einem Glaskörper (8) umgeben sein, der vorzugsweise zylinderförmig ausgebildet sein kann. In einer anderen vorzugsweisen Ausgestaltung der Erfindung kann die Elektrode in dem Glaskörper (8) mit einem Ring (10) aus schlecht wärmeleitendem Isolierstoff, vorzugsweise Keramik oder Glimmer, zentriert sein. Dadurch läßt sich eine Zentrierung der Elektrode in einem zylinderförmigen Glaskörper zur Vermeidung von Glasbruch bei mechanischer Beanspruchung (z.B. Stoß, Schlag) oder einseitiger thermischer Belastung erreichen, wie sie z.B. beim Konditionieren der Elektrode entstehen könnte.Furthermore, the electrode may be surrounded by a glass body (8), which may preferably be cylindrical. In another preferred embodiment of the invention, the electrode in the glass body (8) with a ring (10) made of poor thermal conductivity insulating material, preferably ceramic or mica, be centered. As a result, centering of the electrode in a cylindrical glass body can be achieved to avoid breakage of the glass under mechanical stress (e.g., impact, impact) or unilateral thermal stress, such as e.g. could occur during conditioning of the electrode.

Bevorzugt ist ferner, daß der mindestens teilweise feldfireie Raum im inneren eines metallischen Bechers, Hohlzylinders oder Hohlkegels entsteht. Damit ist die erfindungsgemäße Vorrichtung für die Verwendung vorhandener Fertigungswerkzeuge zur Herstellung der Trägerkörper in an sich bekannter Bauart geeignet.It is further preferred that the at least partially feldfireie space is formed inside a metallic cup, hollow cylinder or hollow cone. Thus, the device according to the invention for the use of existing manufacturing tools for the production of the carrier body in a known per se is suitable.

Die erfindungsgemäße Vorrichtung kann weiterhin derart ausgestattet sein, daß zumindest auf einem Teil der Oberfläche des Trägermaterials (1) eine reaktive Gase bindende Substanz (Getter) angebracht wird, welche beispielsweise beim Konditionieren der Elektroden aktiviert wird. Dies hat den Vorteil, daß die Edelgasatmosphäre einer Gasentladung im Betrieb durch chemische und/oder physikalische Bindung von eventuell aus Entladungsgefäß oder Elektrodenkörper freigesetzten reaktiven Gasen oder Dämpfen reingehalten wird.The device according to the invention can furthermore be equipped in such a way that at least on a part of the surface of the carrier material (1) a reactive gas-binding substance (getter) is applied, which is activated, for example, during the conditioning of the electrodes. This has the advantage that the inert gas atmosphere of a gas discharge during operation is kept pure by chemical and / or physical binding of possibly released from the discharge vessel or electrode body reactive gases or vapors.

Die Materialien zur Beschichtung des Trägermaterials (1) können in Form von Hydriden, vorzugsweise als Yttriumhydrid, aufgebracht werden. Die Hydride werden beim Konditionieren der Elektroden in die metallische Form umgewandelt unter Freisetzung von Wasserstoff. Vorteilthaft ist dies deshalb, weil die Oxidation von im Entladungsraum befindlichen reaktiven Substanzen beim Ausheiz- und Glühvorgang vermieden wird, wie sie bei der Regenerierung von quecksilberhaltigen Entladungslampen, z.B. Hochspannungsleuchtröhren, vorzufinden sind. Im folgenden wird die Erfindung unter Bezugnahme auf die Beispiele näher beschrieben:

  • Fig. 1 zeigt eine beispielhafte Ausführung der Erfindung. Dabei ist die Elektrode im Längsschnitt dargestellt. Die Schichtdicken sind zur Verdeutlichung in der Zeichnung nicht maßstäblich dargestellt.
  • Die erfindungsgemäße Elektrode besteht aus dem Trägerkörper (1), hergestellt z.B. aus Eisen und beispielhaft in Becherform ausgeführt, mit einer der Gasentladung zugewandten Öffnung (2).
The materials for coating the support material (1) can be applied in the form of hydrides, preferably as yttrium hydride. The hydrides are converted to the metallic form during the conditioning of the electrodes with liberation of hydrogen. This is advantageous because the oxidation of reactive substances located in the discharge space during the annealing and annealing process is avoided, as can be found in the regeneration of mercury-containing discharge lamps, for example high-voltage light tubes. In the following the invention will be described in more detail with reference to the examples:
  • Fig. 1 shows an exemplary embodiment of the invention. The electrode is shown in longitudinal section. The layer thicknesses are not shown to scale in the drawing for clarity.
  • The electrode according to the invention consists of the carrier body (1), made, for example, of iron and designed, for example, in the form of a cup, with an opening (2) facing the gas discharge.

Die Innenseite des Trägerkörpers (1) ist mit einer Schicht (3) eines Materials mit niedriger photoelektrischer Austrittsarbeit versehen, z.B. Yttrium, welches durch mechanische, chemische und/oder physikalische Beschichtungsverfahren (z.B. Aufpressen, Aufwalzen, Aufdampfen, Sputtern, Galvanisieren, Spritzen) aufgebracht wurde, während die Außenfläche (4) beispielhaft mit Material hoher photoelektrischer Austrittsarbeit, z.B. Nickel oder Platin, beschichtet ist.The inside of the carrier body (1) is provided with a layer (3) of a material having a low photoelectric work function, e.g. Yttrium, which has been applied by mechanical, chemical and / or physical coating techniques (e.g., press-on, roller, vapor deposition, sputtering, plating, spraying), while the outer surface (4) is exemplified by high photoelectric work function material, e.g. Nickel or platinum, coated.

Am verschlossenen Ende des Trägerkörpers (1), hier in Form einer Kugelkalotte, sind die Stromzuführungsdrähte (5) in an sich bekannter Weise, z.B. durch Punktschweißung, befestigt.At the closed end of the support body (1), here in the form of a spherical cap, the power supply wires (5) in a conventional manner, e.g. by spot welding, attached.

Figur 2 zeigt bespielhaft einen Längsschnitt durch eine erfindungsgemäße Elektrode, eingebaut in einen zylinderförmigen Glaskörper (8) in an sich bekannter Bauart, als Teil eines Gasentladungsgefäßes, zur Verwendung z.B. in Hochspannungs- Leuchtröhren. Dabei sind die Stromzuführungsdrähte (5) im Quetschfuß (6) vakuumdicht mit dem Glaskörper (8) verschmolzen.
Ein zusätzlich im Quetschfuß (6) eingeschmolzenes Glasrohr (7) kann zum Evakuieren des -in Fig. 2 nicht dargestellten- Gasentladungsgefäßes dienen. Die Elektrode wird üblicherweise mittels des Glaskörpers (8) am Gasentladungsgefäß angebracht. FIG. 2 shows exemplarily a longitudinal section through an electrode according to the invention, installed in a cylindrical glass body (8) in a known per se, as part of a gas discharge vessel, for use in high-voltage fluorescent tubes. In this case, the power supply wires (5) in the pinch (6) are fusibly sealed to the glass body (8) fused.
An additionally in the squeeze (6) melted glass tube (7) can be used to evacuate the -in Fig. 2 not shown- serve gas discharge vessel. The electrode is usually attached to the gas discharge vessel by means of the glass body (8).

Weiterhin zeigt Fig. 2 die Öffnung (2) des Trägerkörpers (1) mit einem isolierenden Schutzring (9), beispielsweise aus Keramik, welcher in an sich bekannter Weise am Trägerkörper (1) durch Quetschen, Einrollen, Rändeln, Walzen etc. befestigt ist.Further shows Fig. 2 the opening (2) of the carrier body (1) with an insulating guard ring (9), for example made of ceramic, which in a known manner on the carrier body (1) by squeezing, curling, knurling, rolling, etc. is attached.

Ebenso beispielhaft dargestellt ist zwischen Schutzring (9) und Trägerkörper (1) ein zusätzlicher Zentrierring (10), z.B. aus Glimmer. Dieser garantiert einen zentrischen Sitz der Elektrode im zylinderförmigen Glaskörper (8). Der Zentrierring (10) kann abweichend von der Kreisringform z.B. mit Einkerbungen o.ä. versehen sein, um ein strömungstechnisch günstiges Evakuieren des Gasentladungsgefäßes durch das Ansatzrohr (7) zu ermöglichen.Likewise shown by way of example between guard ring (9) and support body (1) an additional centering ring (10), for example made of mica. This guarantees a centric seat of the electrode in the cylindrical glass body (8). The centering ring (10) may deviate from the circular ring shape, for example with notches or similar. be prepared to enter aerodynamically favorable evacuation of the gas discharge vessel through the neck tube (7) to allow.

Figur 3 zeigt vergleichend Ergebnisse von Messungen der photoelektrischen Austrittsarbeit verschiedener handelsüblicher Elektroden gegenüber einer erfindungsgemäßen Ausführung. FIG. 3 shows comparative results of measurements of the photoelectric work function of various commercially available electrodes over an embodiment of the invention.

Es bedeuten: Nr. der Elektrode Bauart der Elektrode (Trägermaterial: Eisen) 1 Ohne Aktivierungsmasse 2...4 Handelsübliche Elektroden verschiedener Hersteller mit Aktivierungsmasse aus Erdalkalioxiden 5 Erfindungsgemäße Elektrode mit Aktivierungsmasse aus Yttrium It means: No. of the electrode Type of electrode (carrier material: iron) 1 Without activation mass 2 ... 4 Commercially available electrodes of various manufacturers with activating compound of alkaline earth oxides 5 Inventive electrode with activation mass of yttrium

Claims (14)

  1. Cold electrode for gas discharges comprising an electrically conductive support material (19) on which an emission coating is present, characterized in that
    - the electrode is at least partly configured as a hollow body,
    - the emission coating (3) is located on the inside of the hollow body,
    - the emission coating (3) comprises metallic material,
    - the emission coating (3) contains yttrium, praseodymium, cerium or mixtures thereof,
    - the outside of the hollow body is provided with a coat (4), preferably of nickel or platinum, which has a high photoelectric work function, preferably greater than 8.0 × 10-19 joule/electron, and
    - the cold electrode is suitable for operation in the temperature range below 570 k, preferably below 420 K, and the photoelectric work function of the material of the emission coating (3) in this range is lower than that of the support material (1).
  2. Electrode according to Claim 1, characterized in that the photoelectric work function of the material of the emission coating (3) in the temperature range from 200 to 500 K, preferably from 260 to 450 K, is < 5.6*10-19 joule/electron.
  3. Electrode according to either of the preceding claims, characterized in that it is cup-shaped or has the shape of a hollow cylinder or a hollow cone.
  4. Electrode according to any of the preceding claims, characterized in that the emission coating (3) has a lower photoelectric work function than the remaining surface of the electrode.
  5. Electrode according to any of the preceding claims, characterized in that the support material (1) is a metal, preferably iron.
  6. Electrode according to any of the preceding claims, characterized in that the emission coating (3) contains dopants to reduce the photoelectric work function relative to the pure material, preferably caesium, calcium or barium or mixtures thereof as dopants in concentrations of from 10-5 at% to 1 at%.
  7. Electrode according to any of the preceding claims, characterized in that part of the surface of the support material (1) is provided with an electrically insulating coat (4) to suppress the electron or ion current.
  8. Electrode according to any of the preceding claims, characterized in that the parts of the electrode designed for gas discharge are coated with an electrically insulating, heat- and vacuum-resistant material, preferably ceramic.
  9. Electrode according to any of the preceding claims, characterized in that an electrically insulating tube (9) which is provided with a collar is arranged in the opening of the hollow space formed by the electrode in such a way that the collar covers the edges of the opening in the direction of the gas discharge.
  10. Electrode according to any of the preceding claims, characterized in that the edge of the opening of the hollow space formed by the electrode which faces the gas discharge is shaped so that the electric field gradient at the opening is reduced, preferably by bending over or flanging.
  11. Electrode according to any of the preceding claims, characterized in that the electrode is surrounded by a glass body (8) which is preferably cylindrical.
  12. Electrode according to any of the preceding claims, characterized in that the electrode is centred in the glass body (8) by means of a ring (10) composed of insulating material which does not conduct heat well, preferably ceramic or mica.
  13. Electrode according to any of the preceding claims, characterized in that a substance which binds reactive gases is applied to at least part of the surface of the support material (1).
  14. Process for producing an electrode according to any of the preceding claims, characterized in that the materials for coating the support material (1) are applied in the form of hydrides, preferably yttrium hydride, which on conditioning of the electrodes are converted into the metallic form with liberation of hydrogen.
EP98916816A 1997-03-05 1998-02-28 Cold electrode for gas discharges Expired - Lifetime EP0907960B1 (en)

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DE29703990U DE29703990U1 (en) 1997-03-05 1997-03-05 Cold electrode for gas discharges
PCT/DE1998/000595 WO1998039791A2 (en) 1997-03-05 1998-02-28 Cold electrode for gas discharges

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DE29703990U1 (en) 1997-04-17
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US6417607B1 (en) 2002-07-09
JP4510941B2 (en) 2010-07-28
ATE387008T1 (en) 2008-03-15
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WO1998039791A2 (en) 1998-09-11
BR9805925A (en) 2000-04-25

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