EP1104005B1 - Gas discharge lamp having an oxide emitter electrode - Google Patents

Gas discharge lamp having an oxide emitter electrode Download PDF

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Publication number
EP1104005B1
EP1104005B1 EP00204015A EP00204015A EP1104005B1 EP 1104005 B1 EP1104005 B1 EP 1104005B1 EP 00204015 A EP00204015 A EP 00204015A EP 00204015 A EP00204015 A EP 00204015A EP 1104005 B1 EP1104005 B1 EP 1104005B1
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EP
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Prior art keywords
gas discharge
metal
discharge lamp
electrode
oxide
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EP00204015A
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German (de)
French (fr)
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EP1104005A1 (en
Inventor
Georg Dr. Philips Corp. Int. Prop. GmbH Gärtner
Willem Dr. Van Den Hoek
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Philips Intellectual Property and Standards GmbH
Koninklijke Philips NV
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Philips Intellectual Property and Standards GmbH
Koninklijke Philips Electronics NV
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    • 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
    • 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
    • H01J61/067—Main electrodes for low-pressure discharge lamps
    • H01J61/0675—Main electrodes for low-pressure discharge lamps characterised by the material 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
    • H01J61/073—Main electrodes for high-pressure discharge lamps
    • H01J61/0735—Main electrodes for high-pressure discharge lamps characterised by the material 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
    • H01J61/073—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

Definitions

  • the invention relates to a gas discharge lamp, in particular a low-pressure gas discharge lamp, equipped with an electrode comprising an electrode made of an electrode metal and an electrode coating of an electron-emitting material containing a metal powder and at least one alkaline earth oxide selected from the group consisting of calcium oxide, strontium oxide and barium oxide ,
  • the generation of light in a gas discharge lamp is based on the ionization and the resulting electrical discharge of the atoms of the filling gas of the lamp when an electric current flows through the lamp. From the electrodes of the lamp, electrons are emitted which are accelerated so much by the electric field between the electrodes that they can excite and ionise them upon collision with the gas atoms. When the gas atoms return to their ground state and the recombination of electrons and ions, a more or less large part of the potential energy is converted into radiation.
  • the amount of electrons that can be emitted by the electrodes depends on the work function of the electrodes for electrons.
  • Tungsten which is typically used as the electrode metal, has a relatively high work function by itself. Therefore, the electrode metal is usually coated with a material whose main purpose is to improve the electron-emitting properties of the electrode metal.
  • Characteristic of the electron-emitting coating materials of electrodes in gas discharge lamps is that they contain an alkaline earth metal, either in the form of the alkaline earth metal oxide or an alkaline earth metal-containing precursor for the alkaline earth metal oxide.
  • Low-pressure gas discharge lamps of conventional type are thus generally equipped with electrodes consisting of tungsten wires with an electron-emitting coating containing oxides of the alkaline earth metals calcium, strontium and barium.
  • a tungsten wire is coated, for example, with the carbonates of the alkaline earth metals in a binder formulation.
  • the carbonates are converted at temperatures of about 1000 ° C in the oxides.
  • This burning of the electrode it already provides a noticeable emission current, which is not yet stable.
  • This activation process turns the originally non-conducting ion lattice of the alkaline earth oxides into an electronic semiconductor by incorporating donor-type impurities into the crystal lattice of the oxides.
  • These impurities consist essentially of elemental alkaline earth metal, z. As calcium, strontium or barium.
  • the electron emission of such electrodes is based on this impurity mechanism.
  • the purpose of the activation process is to provide a sufficient amount of excess elemental alkaline earth metal that allows the oxides in the electron-emitting coating to deliver the maximum emission current at a prescribed heat output.
  • the electrode coating constantly loses alkaline earth metal during the lifetime of the lamp, because the electrode coating as a whole evaporates partly slowly and is partly spattered by the ion current in the lamp.
  • the elemental alkaline earth metal is initially replenished by reduction of the alkaline earth oxide on the tungsten wire during operation of the lamp.
  • this replenishment comes to a standstill when the tungsten wire is passivated over time by a high-resistance interface of tungsten oxide, alkaline earth silicate or alkaline earth tungstate.
  • the electron-emitting substance in addition to Erdalkalimischcarbonat zirconium and further 3 to 15 wt .-% of a reducing metal powder having a high melting point, wherein the reducing metal powder of at least one of tantalum, niobium, tungsten and molybdenum existing group is selected, and the electron-emitting substance is distributed so that it fills the entire winding core of the coil up to the two end turns of the multi-filament filament.
  • the metal powders of tantalum, niobium, tungsten or molybdenum also surround themselves over time, just like the electrode carrier wire, with a passivating separating layer of tungsten oxide, alkaline earth silicate or alkaline earth tungstate, or of the corresponding niobium, tantalum or molybdenum compounds.
  • a gas discharge lamp equipped with an electrode comprising a support of an electrode metal and a first electrode coating of an electron-emitting material comprising a metal powder preparation of a powder of a reducing metal selected from the group consisting of aluminum, silicon, titanium, zirconium, Hafnium, tantalum, molybdenum, tungsten and their alloys, with a powder coating with a precious metal selected from the group of rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium and platinum and their alloys, and at least one alkaline earth metal oxide selected from the group of calcium oxide Strontium oxide and barium oxide.
  • a metal powder preparation of a powder of a reducing metal selected from the group consisting of aluminum, silicon, titanium, zirconium, Hafnium, tantalum, molybdenum, tungsten and their alloys with a powder coating with a precious metal selected from the group of rhenium, cobalt, nickel, ruthen
  • Gas discharge lamps with such electrodes have a uniform electron emission over a long period of time because the powder coating of the metal powder with a noble metal avoids a reaction of the alkaline earth oxide with the reducing metal during the activation phase in the process of manufacturing the gas discharge lamp. Only during operation of the gas discharge lamp does the reducing metal diffuse through the powder coating of a noble metal and reduces the alkaline earth oxide to elemental alkaline earth metal. Due to the continuous alkaline earth tracking a depletion of the electron emission is avoided and ensures that sufficient metallic alkaline earth is released during the whole operation of the lamp. The emission current is uniform and uniform and extends the life of the gas discharge lamp.
  • the electrodes in these gas discharge lamps are also resistant to poisoning.
  • the reject rate in the production is low because these electrodes can be easily reproduced produced.
  • a second electrode coating of a noble metal selected from the group of rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum is arranged between the support and the first electrode coating.
  • a noble metal selected from the group of rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum is arranged between the support and the first electrode coating.
  • the metal powder formulation consists of a powder of a tungsten-iridium alloy with a powder coating of iridium.
  • the electron-emitting material additionally contains zirconium oxide.
  • the metal powder preparation has a mean grain size d of 2.0 microns ⁇ d ⁇ 3.0 microns.
  • Fig. 1 shows schematically the light generation in a fluorescent lamp.
  • Gas discharge lamps can be divided into low pressure lamps and high pressure lamps. Distinguish yourself in the way of stabilizing the discharge.
  • Fig. 1 shows an example of a low-pressure discharge lamp with mercury filling, ie a fluorescent lamp.
  • a gas discharge lamp consists of a glass tube 1 in rod, ring or U-shape.
  • the electrodes 2 are located at the ends of the tube.
  • Two-pin bases 3 serve as connection.
  • the inside of the glass tube is provided with a phosphor layer 4 whose chemical composition is the spectrum of the light or its color certainly.
  • the glass tube contains, in addition to a noble gas filling of argon, a small amount of mercury or mercury vapor, which excites under operating conditions to glow, emitting the Hg resonance line at a wavelength of 253.7 nm in the ultraviolet range.
  • the emitted UV radiation excites the phosphors in the phosphor layer to emit light in the visible region 5.
  • the lamp further comprises means for igniting and operating, e.g. B. a choke coil and a starter.
  • a gas discharge lamp includes an electron-emitting electrode comprising a support of an electrode metal and a first electrode coating of an electron-emitting material.
  • the carrier of an electrode metal is usually made of tungsten or a tungsten alloy, optionally with a molybdenum, molybdenum, niobium, tantalum and their alloys. It can also consist of nickel, platinum, silicon, magnesium, aluminum or their alloys.
  • the carrier may be formed as a wire, helix, spiral, corrugated wire, tube, ring, plate or band. It is usually heated directly by the current flow.
  • the raw material for the electron-emitting material is applied.
  • the carbonates of the alkaline earth metals calcium, strontium and barium are ground and optionally mixed with each other and with zirconium metal powder.
  • the weight ratio of calcium carbonate: strontium carbonate: barium carbonate: zirconium equal to 25.2: 31.5: 40.3: 3.
  • a metal powder having an average particle size of 2-3 microns is used with a 0.1 to 0.2 micron thick powder coating.
  • CVD methods such as fluid Bed CVD can be used. This coated metal powder is added to the raw mass.
  • the raw mass can still be mixed with a binder. It is then applied to the support by brushing, dipping, cataphoretic deposition or spraying.
  • the coated electrodes are melted into the lamp ends. During evacuation and filling of the lamp, the electrodes are formed.
  • the electrode wire is heated by direct current passage to a temperature of 1000 ° C to 1200 ° C. At this temperature, the alkaline earth carbonates are converted to the alkaline earth oxides to release CO and CO 2 and then form a porous sintered body. After this "burning off" of the electrodes activation takes place, which has the purpose to provide excess, embedded in the oxides, elemental alkaline earth metal.
  • the excess alkaline earth metal is formed by reduction of alkaline earth metal oxide. During the actual reduction activation, the alkaline earth oxide is reduced by the liberated CO or the carrier metal.
  • there is a current activation which reaches the required free alkaline earth metal by electrolytic processes at high temperatures.
  • the finished-forming electron-emitting material may preferably contain 2 to 20% by weight of a metal powder preparation.
  • the zirconia content can be between zero and 10 wt .-%.
  • a three-coiled tungsten wire is coated with rhenium with a layer thickness of 1 micron.
  • tungsten powder is coated with a mean grain size of 3 .mu.m in fluid Bed CVD process with a rhenium layer with a layer thickness of 0.1 microns.
  • Tripelcarbonat consisting of Calcium carbonate, strontium carbonate and barium carbonate in the weight ratio 1: 1.25: 1.6 is mixed with 3% by weight of zirconium metal powder and 10% by weight of the rhenium-coated tungsten powder and a binder preparation of nitrocellulose and butyl acetate.
  • the rhenium-coated tungsten wire is coated with this emission compound, then placed in a lamp envelope and heated to 1000 ° C.
  • the electrode is baked, the carbonates of the alkaline earth metals are converted into their oxides and the zirconium metal powder is converted into zirconium oxide.
  • This burn-in process may be followed by activation by means of reduction activation or current activation.
  • Such a lamp has a short ignition phase, the emitter electrode a low work function of 1.42 eV and a conductivity improved by a factor of 2.
  • a three-coiled tungsten wire is coated with rhenium with a layer thickness of 1 micron.
  • tungsten powder is coated with a mean grain size of 3 .mu.m in fluid Bed CVD process with a rhenium layer with a layer thickness of 0.1 microns.
  • Tripelcarbonate consisting of calcium carbonate, strontium carbonate and barium carbonate in a weight ratio of 1: 1.25: 1.6 is mixed with 3% by weight zirconium metal powder and 10% by weight of the rhenium-coated tungsten powder and a binder preparation of nitrocellulose and butyl acetate.
  • the rhenium-coated tungsten wire is coated with this emission compound, then placed in a lamp envelope and heated to 1000 ° C.
  • the electrode is baked, the carbonates of the alkaline earth metals are converted into their oxides and the zirconium metal powder is converted into zirconium oxide.
  • Such a lamp has a short ignition phase, the emitter electrode a low work function of 1.42 eV and a conductivity improved by a factor of 2.

Description

Die Erfindung betrifft eine Gasentladungslampe, insbesondere eine Niederdruckgasentladungslampe, ausgerüstet mit einer Elektrode, die einen Träger aus einem Elektrodenmetall und eine Elektrodenbeschichtung aus einem elektronenemittierenden Material, das ein Metallpulver und mindestens ein Erdalkalioxid, ausgewählt aus der Gruppe Calciumoxid, Strontiumoxid und Bariumoxid, enthält, umfaßt.The invention relates to a gas discharge lamp, in particular a low-pressure gas discharge lamp, equipped with an electrode comprising an electrode made of an electrode metal and an electrode coating of an electron-emitting material containing a metal powder and at least one alkaline earth oxide selected from the group consisting of calcium oxide, strontium oxide and barium oxide ,

Die Lichterzeugung in einer Gasentladungslampe beruht auf der Ionisation und der resultierenden elektrischen Entladung der Atome des Füllgases der Lampe, wenn ein elektrischer Strom die Lampe durchfließt. Von den Elektroden der Lampe werden Elektronen emittiert, die durch das elektrische Feld zwischen den Elektroden so stark beschleunigt, dass sie beim Zusammenstoß mit den Gasatomen diese anregen und ionisieren können. Bei der Rückkehr der Gasatome in ihren Grundzustand sowie bei der Rekombination von Elektronen und Ionen wird ein mehr oder weniger großer Teil der potentiellen Energie in Strahlung umgewandelt.The generation of light in a gas discharge lamp is based on the ionization and the resulting electrical discharge of the atoms of the filling gas of the lamp when an electric current flows through the lamp. From the electrodes of the lamp, electrons are emitted which are accelerated so much by the electric field between the electrodes that they can excite and ionise them upon collision with the gas atoms. When the gas atoms return to their ground state and the recombination of electrons and ions, a more or less large part of the potential energy is converted into radiation.

Die Menge der Elektronen, die von den Elektroden emittiert werden können, hängt von der Austrittsarbeit (work function) der Elektroden für Elektronen ab. Wolfram, das in der Regel als Elektrodenmetall verwendet wird, hat selbst eine relativ hohe Austrittsarbeit. Deshalb wird das Elektrodenmetall üblicherweise noch mit einem Material beschichtet, dessen Hauptaufgabe es ist, die elektronenemittierenden Eigenschaften des Elektrodenmetalls zu verbessern. Charakteristisch für die elektronenemittierenden Beschichtungsmaterialien von Elektroden in Gasentladungslampen ist es, dass sie ein Erdalkalimetall enthalten, entweder in der Form des Erdalkalimetalloxids oder einer erdalkalimetallhaltigen Ausgangsverbindung (precursor) für das Erdalkalimetalloxid.The amount of electrons that can be emitted by the electrodes depends on the work function of the electrodes for electrons. Tungsten, which is typically used as the electrode metal, has a relatively high work function by itself. Therefore, the electrode metal is usually coated with a material whose main purpose is to improve the electron-emitting properties of the electrode metal. Characteristic of the electron-emitting coating materials of electrodes in gas discharge lamps is that they contain an alkaline earth metal, either in the form of the alkaline earth metal oxide or an alkaline earth metal-containing precursor for the alkaline earth metal oxide.

Niederdruckgasentladungslampen konventioneller Art sind somit in der Regel mit Elektroden ausgestattet, die aus Wolframdrähten mit einer elektronenemittierenden Beschichtung, die Oxide der Erdalkalimetalle Calcium, Strontium und Barium enthält, bestehen.Low-pressure gas discharge lamps of conventional type are thus generally equipped with electrodes consisting of tungsten wires with an electron-emitting coating containing oxides of the alkaline earth metals calcium, strontium and barium.

Um eine solche Elektrode herzustellen, wird ein Wolframdraht beispielsweise mit den Carbonaten der Erdalkalimetalle in einer Bindemittelzubereitung beschichtet. Während des Auspumpens und Ausheizens der Lampe werden die Carbonate bei Temperaturen von etwa 1000°C in die Oxide umgewandelt. Nach diesem Abbrennen der Elektrode liefert sie bereits einen merklichen Emissionsstrom, der allerdings noch nicht stabil ist. Es folgt noch ein Aktivierungsprozess. Durch diesen Aktivierungsprozess wird das ursprünglich nichtleitende Ionengitter der Erdalkalioxide in einen elektronischen Halbleiter verwandelt, indem Störstellen vom Donator-Typ in das Kristallgitter der Oxide eingebaut werden. Diese Störstellen bestehen im wesentlichen aus elementarem Erdalkalimetall, z. B. Calcium, Strontium oder Barium. Die Elektronenemission derartiger Elektroden basiert auf diesem Störstellenmechanismus. Der Aktivierungsprozess hat den Zweck, eine genügende Menge von überschüssigem, elementarem Erdalkalimetall zu schaffen, durch das die Oxide in der elektronenemittierenden Beschichtung bei einer vorgeschriebenen Heizleistung den maximalen Emissionsstrom liefern können.To produce such an electrode, a tungsten wire is coated, for example, with the carbonates of the alkaline earth metals in a binder formulation. During the pumping out and heating of the lamp, the carbonates are converted at temperatures of about 1000 ° C in the oxides. After this burning of the electrode, it already provides a noticeable emission current, which is not yet stable. There is still an activation process. This activation process turns the originally non-conducting ion lattice of the alkaline earth oxides into an electronic semiconductor by incorporating donor-type impurities into the crystal lattice of the oxides. These impurities consist essentially of elemental alkaline earth metal, z. As calcium, strontium or barium. The electron emission of such electrodes is based on this impurity mechanism. The purpose of the activation process is to provide a sufficient amount of excess elemental alkaline earth metal that allows the oxides in the electron-emitting coating to deliver the maximum emission current at a prescribed heat output.

Wichtig für die Funktion dieser Elektroden und die Lebensdauer der Lampe ist es, dass immer wieder erneut elementares Erdalkalimetall zur Verfügung steht. Die Elektrodenbeschichtung verliert nämlich während der Lebensdauer der Lampe ständig Erdalkalimetall, weil die Elektrodenbeschichtung insgesamt teils langsam verdampft, teils durch den Ionenstrom in der Lampe abgesputtert wird.Important for the function of these electrodes and the life of the lamp is that again and again elemental alkaline earth metal is available. Namely, the electrode coating constantly loses alkaline earth metal during the lifetime of the lamp, because the electrode coating as a whole evaporates partly slowly and is partly spattered by the ion current in the lamp.

Das elementare Erdalkalimetall wird durch Reduktion des Erdalkalioxids am Wolframdraht während des Betriebs der Lampe zunächst immer wieder nachgeliefert. Diese Nachlieferung kommt jedoch zum Stillstand, wenn der Wolframdraht mit der Zeit durch eine hochohmige Trennschicht (interface) aus Wolframoxid, Erdalkalisilikat oder Erdalkaliwolframat passiviert wird.The elemental alkaline earth metal is initially replenished by reduction of the alkaline earth oxide on the tungsten wire during operation of the lamp. However, this replenishment comes to a standstill when the tungsten wire is passivated over time by a high-resistance interface of tungsten oxide, alkaline earth silicate or alkaline earth tungstate.

Um in einer Leuchtstofflampe die Reduktion von Bariumoxid zu elementarem Barium zu verbessern, ist es aus DE 44 15 748 bereits bekannt, dass die elektronenemittierende Substanz neben Erdalkalimischcarbonat und Zirkonoxid weiterhin 3 bis 15 Gew.-% eines reduzierenden Metallpulvers mit einem hohen Schmelzpunkt enthält, wobei das reduzierende Metallpulver aus wenigstens einem Metall der aus Tantal, Niob, Wolfram und Molybdän bestehenden Gruppe ausgewählt ist, und die elektronenemittierende Substanz so verteilt ist, dass sie den gesamten Wicklungskern der Wendel bis hin zu den beiden Abschlusswindungen der Mehrfachwendel aus Glühdraht ausfüllt.In order to improve the reduction of barium oxide to elemental barium in a fluorescent lamp, it is already known from DE 44 15 748 that the electron-emitting substance in addition to Erdalkalimischcarbonat zirconium and further 3 to 15 wt .-% of a reducing metal powder having a high melting point, wherein the reducing metal powder of at least one of tantalum, niobium, tungsten and molybdenum existing group is selected, and the electron-emitting substance is distributed so that it fills the entire winding core of the coil up to the two end turns of the multi-filament filament.

Die Metallpulver aus Tantal, Niob, Wolfram oder Molybdän umgeben sich aber auch - eben so wie der Elektrodenträgerdraht - mit der Zeit mit einer passivierenden Trennschicht aus Wolframoxid, Erdalkalisilikat oder Erdalkaliwolframat, bzw. aus den entsprechenden Niob-, Tantal- oder Molybdänverbindungen.However, the metal powders of tantalum, niobium, tungsten or molybdenum also surround themselves over time, just like the electrode carrier wire, with a passivating separating layer of tungsten oxide, alkaline earth silicate or alkaline earth tungstate, or of the corresponding niobium, tantalum or molybdenum compounds.

Es ist die Aufgabe der vorliegenden Erfindung, eine Gasentladungslampe, die eine verlängerte Lebensdauer und einen verbesserten Emissionsstrom hat, zu schaffen.It is the object of the present invention to provide a gas discharge lamp having a prolonged life and an improved emission current.

Erfindungsgemäß wird die Aufgabe gelöst durch eine Gasentladungslampe ausgerüstet mit einer Elektrode, die einen Träger aus einem Elektrodenmetall und eine erste Elektrodenbeschichtung aus einem elektronenemittierenden Material, das eine Metallpulverzubereitung aus einem Pulver eines reduzierenden Metalls, ausgewählt aus der Gruppe Aluminium, Silicium, Titan, Zirkon, Hafnium, Tantal, Molybdän, Wolfram und deren Legierungen, mit einer Pulverbeschichtung mit einem Edelmetall ausgewählt aus der Gruppe Rhenium, Kobalt, Nickel, Ruthenium, Palladium, Rhodium, Iridium und Platin und deren Legierungen, und mindestens ein Erdalkalimetalloxid, ausgewählt aus der Gruppe Calciumoxid, Strontiumoxid und Bariumoxid, umfaßt.According to the invention the object is achieved by a gas discharge lamp equipped with an electrode comprising a support of an electrode metal and a first electrode coating of an electron-emitting material comprising a metal powder preparation of a powder of a reducing metal selected from the group consisting of aluminum, silicon, titanium, zirconium, Hafnium, tantalum, molybdenum, tungsten and their alloys, with a powder coating with a precious metal selected from the group of rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium and platinum and their alloys, and at least one alkaline earth metal oxide selected from the group of calcium oxide Strontium oxide and barium oxide.

Gasentladungslampen mit derartigen Elektroden haben über eine langen Zeitraum hin eine gleichmäßige Elektronenemission, weil durch die Pulverbeschichtung des Metallpulvers mit einem Edelmetall wird eine Reaktion des Erdalkalioxids mit dem reduzierenden Metall während der Aktivierungsphase beim Herstellungsprozeß der Gasentladungslampe vermieden. Erst während des Betriebs der Gasentladungslampe diffundiert das reduzierende Metall durch die Pulverbeschichtung aus einem Edelmetall und reduziert das Erdalkalioxid zu elementarem Erdalkalimetall. Durch die kontinuierliche Erdalkali-Nachführung wird eine Erschöpfung der Elektronenemission vermieden und gewährleistet, dass während des ganzen Betriebes der Lampe ausreichend metallisches Erdalkali freigesetzt wird. Der Emissionsstrom ist einheitlich und gleichförmig und die Lebensdauer der Gasentladungslampe verlängert.Gas discharge lamps with such electrodes have a uniform electron emission over a long period of time because the powder coating of the metal powder with a noble metal avoids a reaction of the alkaline earth oxide with the reducing metal during the activation phase in the process of manufacturing the gas discharge lamp. Only during operation of the gas discharge lamp does the reducing metal diffuse through the powder coating of a noble metal and reduces the alkaline earth oxide to elemental alkaline earth metal. Due to the continuous alkaline earth tracking a depletion of the electron emission is avoided and ensures that sufficient metallic alkaline earth is released during the whole operation of the lamp. The emission current is uniform and uniform and extends the life of the gas discharge lamp.

Die Elektroden in diesen Gasentladungslampen sind auch widerstandsfähig gegen Vergiftung. Die Ausschußrate in der Fertigung ist gering, da sich diese Elektroden leicht reproduzierbar herstellen lassen.The electrodes in these gas discharge lamps are also resistant to poisoning. The reject rate in the production is low because these electrodes can be easily reproduced produced.

Nach einer bevorzugten Ausführungsform der Gasentladungslampe ist zwischen dem Träger und der ersten Elektrodenbeschichtung eine zweite Elektrodenbeschichtung aus einem Edelmetall ausgewählt aus der Gruppe Rhenium, Kobalt, Nickel, Ruthenium, Palladium, Rhodium, Iridium, Platin, angeordnet. Eine derartige Gasentladungslampe hat eine verkürzte Zündphase, die darin enthaltene Elektrode eine niedrige Austrittsarbeit und eine verbesserte elektrische Leitfähigkeit.According to a preferred embodiment of the gas discharge lamp, a second electrode coating of a noble metal selected from the group of rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum is arranged between the support and the first electrode coating. Such a gas discharge lamp has a shortened ignition phase, the electrode contained therein a low work function and improved electrical conductivity.

Es kann bevorzugt sein, dass die Metallpulverzubereitung aus einem Pulver aus einer Wolfram-Iridium-Legierung mit einer Pulverbeschichtung aus Iridium besteht.It may be preferred that the metal powder formulation consists of a powder of a tungsten-iridium alloy with a powder coating of iridium.

Es kann auch bevorzugt sein, dass das elektronenemittierende Material zusätzlich Zirkonoxid enthält.It may also be preferred that the electron-emitting material additionally contains zirconium oxide.

Nach einer anderen bevorzugten Ausführungsform hat die Metallpulverzubereitung eine mittlere Korngröße d von 2.0 µm ≤ d ≤ 3.0 µm.According to another preferred embodiment, the metal powder preparation has a mean grain size d of 2.0 microns ≤ d ≤ 3.0 microns.

Nachfolgend wird die Erfindung anhand einer Figur und zweier Ausführungsbeispiele weiter erläutert.The invention will be further explained with reference to a figure and two embodiments.

Fig. 1 zeigt schematisch die Lichterzeugung in einer Leuchtstofflampe.Fig. 1 shows schematically the light generation in a fluorescent lamp.

Gasentladungslampen können in Niederdrucklampen und in Hochdrucklampen eingeteilt werden. Unterscheiden tun sie sich in der Art der Stabilisierung der Entladung. Fig. 1 zeigt beispielhaft eine Niederdruck-Entladungslampe mit Quecksilberfüllung, d.h. eine Leuchtstofflampe. Eine solche Gasentladungslampe besteht aus einem Glasrohr 1 in Stab-, Ring oder U-Form. An den Enden des Rohrs befinden sich die Elektroden 2. Als Anschluß dienen Zweistiftsockel 3. Die Innenseite des Glasrohrs ist mit einer Leuchtstoffschicht 4 versehen, deren chemische Zusammensetzung das Spektrum des Lichts bzw. dessen Farbton bestimmt. Das Glasrohr enthält neben einer Edelgasfüllung aus Argon eine geringe Menge Quecksilber bzw. Quecksilberdampf, der unter Betriebsbedingungen zum Leuchten angeregt, die Hg-Resonanzlinie bei einer Wellenlänge von 253,7 nm im Ultraviolettbereich emittiert. Die ausgesendete UV-Strahlung regt die Leuchtstoffe in der Leuchtstoffschicht zur Emission von Licht im sichtbaren Bereich 5 an.Gas discharge lamps can be divided into low pressure lamps and high pressure lamps. Distinguish yourself in the way of stabilizing the discharge. Fig. 1 shows an example of a low-pressure discharge lamp with mercury filling, ie a fluorescent lamp. Such a gas discharge lamp consists of a glass tube 1 in rod, ring or U-shape. The electrodes 2 are located at the ends of the tube. Two-pin bases 3 serve as connection. The inside of the glass tube is provided with a phosphor layer 4 whose chemical composition is the spectrum of the light or its color certainly. The glass tube contains, in addition to a noble gas filling of argon, a small amount of mercury or mercury vapor, which excites under operating conditions to glow, emitting the Hg resonance line at a wavelength of 253.7 nm in the ultraviolet range. The emitted UV radiation excites the phosphors in the phosphor layer to emit light in the visible region 5.

Die Lampe umfaßt weiterhin Mittel zum Zünden und zum Betreiben, z. B. eine Drosselspule und einen Starter.The lamp further comprises means for igniting and operating, e.g. B. a choke coil and a starter.

Eine Gasentladungslampe enthält eine elektronenemittierende Elektrode, die einen Träger aus einem Elektrodenmetall und eine erste Elektrodenbeschichtung aus einem elektronenemittierenden Material umfaßt.A gas discharge lamp includes an electron-emitting electrode comprising a support of an electrode metal and a first electrode coating of an electron-emitting material.

Der Träger aus einem Elektrodenmetall besteht üblicherweise aus Wolfram oder einer Wolframlegierung, gegebenenfalls mit einer Molybdänseele, Molybdän, Niob, Tantal und deren Legierungen. Er kann auch aus Nickel, Platin, Silicium, Magnesium, Aluminium oder deren Legierungen bestehen. Der Träger kann als Draht, Wendel, Spirale, als Welldraht, Rohr, Ring, Platte oder Band geformt sein. Er wird üblicherweise direkt durch den Stromfluß geheizt.The carrier of an electrode metal is usually made of tungsten or a tungsten alloy, optionally with a molybdenum, molybdenum, niobium, tantalum and their alloys. It can also consist of nickel, platinum, silicon, magnesium, aluminum or their alloys. The carrier may be formed as a wire, helix, spiral, corrugated wire, tube, ring, plate or band. It is usually heated directly by the current flow.

Auf dem Träger aus einem Elektrodenmetall kann eine Beschichtung aus einem Edelmetall ausgewählt aus der Gruppe Rhenium, Kobalt, Nickel, Ruthenium, Palladium, Rhodium, Iridium, Platin, angeordnet sein. Bevorzugt besteht sie aus einer 0.1 bis 2 µm dicken Iridium- oder Rheniumschicht.On the support of an electrode metal, a coating of a noble metal selected from the group rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum, be arranged. It preferably consists of a 0.1 to 2 .mu.m thick iridium or rhenium layer.

Auf diesen Träger wird die Rohmasse für das elektronenemittierende Material aufgebracht. Zur Herstellung der Rohmasse werden die Carbonate der Erdalkalimetalle Calcium, Strontium und Barium gemahlen und gegebenenfalls miteinander und mit Zirkonmetallpulver gemischt. Typischerweise beträgt das Gewichtsverhältnis von Calciumcarbonat : Strontiumcarbonat : Bariumcarbonat : Zirkon gleich 25,2 : 31,5 : 40,3 : 3. Weiterhin wird ein Metallpulver der Metalle aus der Gruppe Aluminium, Silicium, Titan, Zirkon, Hafnium, Tantal, Molybdän, Wolfram und deren Legierungen mit einem Metall aus der Gruppe Rhenium, Rhodium, Palladium, Iridium und Platin mit einer Pulverbeschichtung aus einem Edelmetall wie Rhenium, Nickel, Kobalt, Ruthenium, Palladium, Rhodium, Iridium oder Platin versehen. Bevorzugt wird ein Metallpulver mit einer mittleren Korngröße von 2-3 µm mit einer 0.1 bis 0.2 µm dicken Pulverbeschichtung verwendet.On this carrier, the raw material for the electron-emitting material is applied. To produce the raw mass, the carbonates of the alkaline earth metals calcium, strontium and barium are ground and optionally mixed with each other and with zirconium metal powder. Typically, the weight ratio of calcium carbonate: strontium carbonate: barium carbonate: zirconium equal to 25.2: 31.5: 40.3: 3. Furthermore, a metal powder of the metals from the group aluminum, silicon, titanium, zirconium, hafnium, tantalum, molybdenum, Tungsten and its alloys with a metal from the Group rhenium, rhodium, palladium, iridium and platinum with a powder coating of a noble metal such as rhenium, nickel, cobalt, ruthenium, palladium, rhodium, iridium or platinum provided. Preferably, a metal powder having an average particle size of 2-3 microns is used with a 0.1 to 0.2 micron thick powder coating.

Als Pulverbeschichtungsverfahren können CVD-Verfahren wie Fluid-Bed-CVD eingesetzt werden. Dieses beschichtete Metallpulver wird der Rohmasse beigefügt.As a powder coating method, CVD methods such as fluid Bed CVD can be used. This coated metal powder is added to the raw mass.

Die Rohmasse kann noch mit einem Bindemittel gemischt werden. Sie wird dann durch Pinseln, Tauchen, kataphoretische Abscheidung oder Sprühen auf den Träger aufgebracht.The raw mass can still be mixed with a binder. It is then applied to the support by brushing, dipping, cataphoretic deposition or spraying.

Die beschichteten Elektroden werden in die Lampenenden ein geschmolzen. Während des Evakuierens und Füllens der Lampe werden die Elektroden formiert. Der Elektrodendraht wird durch direkten Stromdurchgang auf eine Temperatur von 1000°C bis 1200°C erhitzt. Bei dieser Temperatur werden die Erdalkalicarbonate zu den Erdalkalioxiden unter Freisetzung von CO und CO2 umgesetzt und bilden dann einen porösen Sinterkörper. Nach diesem "Abbrennen" der Elektroden erfolgt die Aktivierung, die den Zweck hat, überschüssiges, in die Oxide eingelagertes, elementares Erdalkalimetall zu liefern. Das überschüssige Erdalkalimetall entsteht durch Reduktion von Erdalkalimetalloxid. Bei der eigentlichen Reduktionsaktivierung wird das Erdalkalioxid durch das freigesetzte CO oder das Trägermetall reduziert. Hinzu kommt eine Stromaktivierung, die das erforderliche freien Erdalkalimetall durch elektrolytische Vorgänge bei hohen Temperaturen erreicht.The coated electrodes are melted into the lamp ends. During evacuation and filling of the lamp, the electrodes are formed. The electrode wire is heated by direct current passage to a temperature of 1000 ° C to 1200 ° C. At this temperature, the alkaline earth carbonates are converted to the alkaline earth oxides to release CO and CO 2 and then form a porous sintered body. After this "burning off" of the electrodes activation takes place, which has the purpose to provide excess, embedded in the oxides, elemental alkaline earth metal. The excess alkaline earth metal is formed by reduction of alkaline earth metal oxide. During the actual reduction activation, the alkaline earth oxide is reduced by the liberated CO or the carrier metal. In addition, there is a current activation, which reaches the required free alkaline earth metal by electrolytic processes at high temperatures.

Das fertig formierte elektronenemittierende Material kann bevorzugt 2 bis 20 Gewichtsprozent einer Metallpulverzubereitung enthalten. Der Zirkonoxidgehalt kann zwischen Null und 10 Gew.-% liegen.The finished-forming electron-emitting material may preferably contain 2 to 20% by weight of a metal powder preparation. The zirconia content can be between zero and 10 wt .-%.

Ausführungsbeispiel 1Embodiment 1

Ein dreifach gewendelter Wolframdraht wird mit Rhenium mit einer Schichtdicke von 1 µm beschichtet. Für die elektronenemittierende Beschichtung wird Wolframpulver mit einer mittleren Korngröße von 3µm im Fluid-Bed-CVD-Verfahren mit einer Rheniumschicht mit einer Schichtdicke von 0.1 µm überzogen. Tripelcarbonat bestehend aus Calciumcarbonat, Strontiumcarbonat und Bariumcarbonat im Gewichtsverhältnis 1 : 1.25 : 1.6 wird mit 3 Gew.-% Zirkonmetallpulver und 10 Gew.-% des mit Rhenium beschichteten Wolframpulvers und einer Bindemittelzubereitung aus Nitrocellulose und Butylacetat gemischt. Der mit Rhenium beschichtete Wolframdraht wird mit dieser Emissionsmasse bestrichen, dann in einen Lampenkolben eingesetzt und auf 1000°C erhitzt. Beim Ausheizen der Elektrode wandeln sich die Carbonate der Erdalkalimetalle in deren Oxide und das Zirkonmetallpulver in Zirkonoxid um. Diesem Einbrennprozess kann sich noch eine Aktivierung mittels Reduktionsaktivierung oder Stromaktivierung anschließen.
Eine derartige Lampe hat eine kurze Zündphase, die Emitterelektrode eine niedrige Austrittsarbeit von 1.42 eV und eine um den Faktor 2 verbesserte Leitfähigkeit.A three-coiled tungsten wire is coated with rhenium with a layer thickness of 1 micron. For the electron-emitting coating tungsten powder is coated with a mean grain size of 3 .mu.m in fluid Bed CVD process with a rhenium layer with a layer thickness of 0.1 microns. Tripelcarbonat consisting of Calcium carbonate, strontium carbonate and barium carbonate in the weight ratio 1: 1.25: 1.6 is mixed with 3% by weight of zirconium metal powder and 10% by weight of the rhenium-coated tungsten powder and a binder preparation of nitrocellulose and butyl acetate. The rhenium-coated tungsten wire is coated with this emission compound, then placed in a lamp envelope and heated to 1000 ° C. When the electrode is baked, the carbonates of the alkaline earth metals are converted into their oxides and the zirconium metal powder is converted into zirconium oxide. This burn-in process may be followed by activation by means of reduction activation or current activation.
Such a lamp has a short ignition phase, the emitter electrode a low work function of 1.42 eV and a conductivity improved by a factor of 2.

Ausführungsbeispiel 2Embodiment 2

Ein dreifach gewendelter Wolframdraht wird mit Rhenium mit einer Schichtdicke von 1 µm beschichtet. Für die elektronenemittierende Beschichtung wird Wolframpulver mit einer mittleren Korngröße von 3µm im Fluid-Bed-CVD-Verfahren mit einer Rheniumschicht mit einer Schichtdicke von 0.1 µm überzogen. Tripelcarbonat bestehend aus Calciumcarbonat, Strontiumcarbonat und Bariumcarbonat im Gewichtsverhältnis 1 : 1.25 : 1.6 wird mit 3 Gew.-% Zirkonmetallpulver und 10 Gew.-% des mit Rhenium beschichteten Wolframpulvers und einer Bindemittelzubereitung aus Nitrocellulose und Butylacetat gemischt. Der mit Rhenium beschichtete Wolframdraht wird mit dieser Emissionsmasse bestrichen, dann in einen Lampenkolben eingesetzt und auf 1000°C erhitzt. Beim Ausheizen der Elektrode wandeln sich die Carbonate der Erdalkalimetalle in deren Oxide und das Zirkonmetallpulver in Zirkonoxid um.
Eine derartige Lampe hat eine kurze Zündphase, die Emitterelektrode eine niedrige Austrittsarbeit von 1.42 eV und eine um den Faktor 2 verbesserte Leitfähigkeit.A three-coiled tungsten wire is coated with rhenium with a layer thickness of 1 micron. For the electron-emitting coating tungsten powder is coated with a mean grain size of 3 .mu.m in fluid Bed CVD process with a rhenium layer with a layer thickness of 0.1 microns. Tripelcarbonate consisting of calcium carbonate, strontium carbonate and barium carbonate in a weight ratio of 1: 1.25: 1.6 is mixed with 3% by weight zirconium metal powder and 10% by weight of the rhenium-coated tungsten powder and a binder preparation of nitrocellulose and butyl acetate. The rhenium-coated tungsten wire is coated with this emission compound, then placed in a lamp envelope and heated to 1000 ° C. When the electrode is baked, the carbonates of the alkaline earth metals are converted into their oxides and the zirconium metal powder is converted into zirconium oxide.
Such a lamp has a short ignition phase, the emitter electrode a low work function of 1.42 eV and a conductivity improved by a factor of 2.

Obwohl die Erfindung anhand eines Leuchtstofflampe beschrieben wurde, ist ihre Verwendung nicht auf diesen Typ der Gasentladungslampen beschränkt, sondern kann beispielsweise auch für andere Niederdruckgasentladungslampen verwendet werden.Although the invention has been described with reference to a fluorescent lamp, its use is not limited to this type of gas discharge lamps, but may be used, for example, for other low-pressure gas discharge lamps.

Claims (5)

  1. A gas discharge lamp comprising an electrode including a carrier of an electrode metal and a first electrode coating of an electron-emitting material, which material comprises a metal powder preparation of a powder of a reducing metal selected from the group formed by aluminum, silicon, titanium, zirconium, hafnium, tantalum, molybdenum, tungsten and the alloys thereof, which metal powder preparation is provided with a powder coating containing a noble metal selected from the group formed by rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium and platinum, and the alloys thereof, and said material comprising at least one alkaline earth metal oxide selected from the group formed by calcium oxide, strontium oxide and barium oxide.
  2. A gas discharge lamp as claimed in claim 1, characterized in that a second electrode coating of a noble metal selected from the group formed by rhenium, cobalt, nickel, ruthenium, palladium, rhodium, iridium, platinum is arranged between the carrier and the first electrode coating.
  3. A gas discharge lamp as claimed in claim 1, characterized in that the metal powder preparation is made from a powder of a tungsten-iridium alloy and a powder coating of iridium.
  4. A gas discharge lamp as claimed in claim 1, characterized in that the metal powder preparation has an average grain size d in the range from 2.0 µm ≤ d ≤ 3.0 µm.
  5. A gas discharge lamp as claimed in claim 1, characterized in that the electron-emitting material additionally comprises zirconium oxide.
EP00204015A 1999-11-23 2000-11-14 Gas discharge lamp having an oxide emitter electrode Expired - Lifetime EP1104005B1 (en)

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DE10242241A1 (en) * 2002-09-12 2004-03-25 Philips Intellectual Property & Standards Gmbh Low pressure discharge lamp comprises a gas discharge vessel containing a noble gas filling, electrodes and devices for producing and maintaining a low pressure gas discharge, and an electron emitter substance
CN101297452A (en) * 2005-09-14 2008-10-29 力特保险丝有限公司 Gas-filled surge arrester, activating compound, ignition stripes and method therefore
US7633226B2 (en) * 2005-11-30 2009-12-15 General Electric Company Electrode materials for electric lamps and methods of manufacture thereof
JP2008060056A (en) * 2006-08-04 2008-03-13 Sumitomo Electric Ind Ltd Electrode for cold-cathode fluorescent lamp
US20100301746A1 (en) * 2007-05-10 2010-12-02 Koninklijke Philips Electronics N.V. Gas discharge lamp with a gas filling comprising chalcogen
DE102013215056A1 (en) * 2013-07-31 2015-02-19 Osram Gmbh Low-pressure discharge lamp with discharge vessel and electrode

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JPS5574052A (en) * 1978-11-29 1980-06-04 Toshiba Corp Gas discharge lamp
DE4415748C2 (en) * 1994-05-04 1998-08-13 Matsushita Electric Works Ltd Electrode for a fluorescent lamp
JP3762434B2 (en) * 1994-11-08 2006-04-05 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ Low pressure discharge lamp
US5847498A (en) * 1994-12-23 1998-12-08 Philips Electronics North America Corporation Multiple layer composite electrodes for discharge lamps
JP2876591B2 (en) * 1996-11-29 1999-03-31 三菱電機株式会社 Cathode for electron tube
DE69912937T2 (en) * 1998-03-20 2004-09-02 Hamamatsu Photonics K.K., Hamamatsu Discharge tube for use as a light source

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DE50013884D1 (en) 2007-02-01

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