EP0143222B1 - Thermionic cathode capable of high emission for an electron tube, and method of manufacture - Google Patents

Thermionic cathode capable of high emission for an electron tube, and method of manufacture Download PDF

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Publication number
EP0143222B1
EP0143222B1 EP84110730A EP84110730A EP0143222B1 EP 0143222 B1 EP0143222 B1 EP 0143222B1 EP 84110730 A EP84110730 A EP 84110730A EP 84110730 A EP84110730 A EP 84110730A EP 0143222 B1 EP0143222 B1 EP 0143222B1
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Prior art keywords
carrier
activation substance
thermionic cathode
alloy
activation
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French (fr)
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EP0143222A1 (en
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Charley Dr. Buxbaum
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BBC Brown Boveri AG Switzerland
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BBC Brown Boveri AG Switzerland
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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
    • H01J9/04—Manufacture of electrodes or electrode systems of thermionic cathodes
    • H01J9/042—Manufacture, activation of the emissive part
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/14—Solid thermionic cathodes characterised by the material

Definitions

  • the invention relates to a hot cathode for an electron tube according to the preamble of claim 1 and to a method for its production according to the preamble of claim 9.
  • Glow cathodes for electron tubes are known in numerous types of functions and material combinations. Barium oxide cathodes with good yield were frequently used for small outputs.
  • the thoraxed tungsten cathodes (system Th0 2 / W 2 C / W) with or without additional additives are used as high-performance cathodes.
  • cathodes delivering high emission current densities (thoriated tungsten cathode, lanthanum hexaboride cathode) operate at high operating temperatures (1700 to 2000 K), which leads to the limits of the permissible mechanical stresses. Since the heat resistance of the materials used can no longer be increased significantly, the design and process engineering involved in the production of hot cathode vessels is considerable. Because of its brittleness, lanthanum hexaboride in particular cannot be given any desired and desirable geometric shape.
  • the invention has for its object to provide a hot cathode with high emissivity and a method for its production, which has a long life and high heat resistance at high emission current density in continuous operation, consists of the most ductile material that can be easily processed, does not tend to embrittlement and is simple Can be produced in any geometrically appropriate form.
  • the hot cathode is said to be executable, in particular in the form of thin wires and wire meshes, as a shockproof structure.
  • the operating temperature should be as low as possible.
  • the basic characteristic of the new hot cathode is that the activation substance which promotes electron emission, contains an alloy or intermetallic compound, has a metallic character both as a supply and as an emissive surface layer and can in principle be present on any support. So there are no chemical reactions or thermal decomposition of a non-metallic substance. This allows a practically unlimited amount of activating substance to be accommodated on the carrier or in the carrier. In addition, in the case of a metallic carrier, this material allows for practically unproblematic further processing into thin wires, strips and sheets. In contrast, however, the proposed system also allows the activation substance to be accommodated on or in a ceramic carrier, if this results in particular advantages. In this case, the carrier must of course be brought into its final form beforehand.
  • An alloy of barium and platinum was used as the activation substance.
  • it is the barium platinum Ba Pt s .
  • Weighed amounts of barium and platinum were melted down in the correct stoichiometric ratio in an arc furnace under an inert gas atmosphere of argon.
  • the melt was cooled, solidified and crushed in a mortar.
  • the fragments were ground in a ball mill with a tungsten carbide lining and tungsten carbide balls to a powder with a particle size of at most 1 ⁇ m.
  • the powder was mixed with nitrocellulose and amyl acetate to form a thin slurry. This suspension was applied to a tungsten wire of 0.5 mm diameter by rolling in a layer thickness of 100 ⁇ m and dried.
  • the 100 mm long coated wire was clamped by means of the cathode holder in a Glühkathodengefäss and the latter to a residual gas pressure of less than 10- 4 m evacuated bar.
  • the wire was slowly heated to a temperature of about 800 K, the nitrocellulose being decomposed and the decomposition products leaving the reaction space. After a holding time of 20 minutes, the vacuum was brought to a residual gas pressure of less than 10-5 m bar and the wire was further heated to a temperature of 1400 K. After a 15 min lasting formation time, the full stationary emission current density of 4 A / cm 2 was reached and maintained.
  • the cathode was not very sensitive to vacuum.
  • the emission current density of 4 A / cm 2 could be kept unchanged in continuous operation even if the vacuum deteriorated to a residual gas pressure of approx. 3 ⁇ 10 -4 m bar.
  • the formation of the barium-rich platinum Ba Pt 2 together with free platinum was found on the cathode surface. Hence, a new chemical-thermodynamic equilibrium occurred, which then remained unchanged over the entire operating period until the activation substance was exhausted. The achievable emission current density was not affected by this.
  • Example I an alloy corresponding to the intermetallic compound Ba Pt 2 was first melted, cooled, solidified, crushed in a mortar and ground in a ball mill to a fine-grained powder. This powder was then slurried finely in a suitable bath and cataphoretically applied to a molybdenum wire with a diameter of 0.5 mm in a layer thickness of 50 ⁇ m. The coated wire was subsequently subjected to an annealing treatment at a temperature of 1400 ° C. for 10 minutes under an argon atmosphere, the Ba Ptz particles being firmly connected to the support and to one another by sintering. By alternately cataphoretic deposition and sintering treatment, surface layers of any thickness can be achieved.
  • the coated molybdenum wire was tested as a hot cathode and, at a temperature of 1400 K, gave a stationary emission current density of 4 A / cm 2 .
  • Example I Based on Example I, an alloy of lanthanum and platinum was used. It was the lanthanum platinum La Pt 2 . Corresponding stoichiometric amounts of lanthanum and platinum were melted together in an arc furnace under an argon atmosphere and, after the melt had solidified, crushed in a mortar and ground to a fine-grained powder. The application to a tungsten wire with the aid of nitrocellulose and amyl acetate was carried out in exactly the same way as described in Example I. The coated wire was degassed at a temperature of approx. 800 K and a residual gas pressure of less than 10- 4 m bar for 20 minutes.
  • the activating substance was an alloy of barium and palladium, which corresponded approximately to the composition of the intermetallic compound Ba Pd 5 . It was melted by mixing the components in an arc furnace under an argon atmosphere. An open-pore round rod with a diameter of 10 mm was made from molybdenum with a pore volume of 25% by powder metallurgy. The molybdenum body, together with the molten Ba / Pd alloy, was placed in a vacuum-tight casting device and brought to a temperature of 1700 ° C. After a dwell time of 15 min under vacuum, the casting device was flooded with argon at a pressure of 10 bar and the temperature was maintained for 30 min.
  • the Ba / Pd alloy infiltrated the porous molybdenum body and completely filled its pores. After cooling, the rod was turned over and heated again to 1100 ° C. Now a series of hot-forming operations with intermediate annealing was carried out under a protective gas atmosphere, which consisted of round hammering and drawing into a wire with a diameter of 0.8 mm.
  • the finished molybdenum wire doped with the Ba / Pd alloy was inserted into a hot cathode vessel and operated at a temperature of 1350 K under vacuum with a residual gas pressure of 10- 4 m bar.
  • the measured emission current density was 2 A / cm 2 in steady-state operation. After a while, the formation of Ba Pd 2 was observed on the cathode surface.
  • An alloy of barium and ruthenium was chosen as the activation substance, which roughly corresponded to the intermetallic compound Ba R U2 .
  • the alloy was melted from the components in a vacuum in an induction furnace and solidified.
  • the carrier consisted of a porous hollow cylinder made of sintered zirconium oxide stabilized with yttrium oxide and having an outside diameter of 12 mm and an inside diameter of 6 mm.
  • the pore volume of the open-pore sintered body was 30%.
  • Last The other was packed into the powdered activation substance on all sides and the whole thing was placed in a vacuum vessel and inductively heated to 2,000 ° C.
  • the Ba / Ru alloy melted and penetrated into the pores of the sintered body.
  • the vessel was additionally flooded with argon under a pressure of 10 bar for 20 minutes. After the infiltrated sintered body had cooled, it was slightly turned on the outside and inside to remove adhering alloy residues. A 5 ⁇ m thick ruthenium layer was additionally electroplated on the outer surface to bridge the non-metallic surface areas delimited by the sintered body. The whole was then annealed under vacuum at a temperature of 1,500 ° C. for 1 h. The provided with a tungsten coil for heating in the interior cathode was installed in an electron tube and operated under vacuum with 10- 5 mbar residual gas pressure at a temperature of 1500 K. The measured emission current density in steady operation was 10 Alcm 2 .
  • the carrier can consist of a heat-resistant metallic or ceramic body with a pore volume of 10 to 50%, the pores of which are completely filled with the activating substance.
  • Particularly suitable are the high-melting metals W, Mo, Ta. Nb or alloys of at least two of these metals. They have the advantage of being ductile and can be used as framework materials in any shape, e.g. B. to be processed as wire, tape, sheet metal, etc. Ceramic materials with a high melting point, such as ZrO 2 stabilized with Y 2 O 3 , can also be used. Alloys of the metals of the VIII.
  • the activation substance used as an alloy and / or intermetallic compound is applied to the carrier either by wet mechanical means (application as a paste with suitable chemical substances or cataphoresis) or by chemical means (e.g. electroless deposition, co-precipitation etc.) and then forms the edge zone of the hot cathode body.
  • Another method is to infiltrate the activating substance by melt metallurgy, ie in the liquid state, in the porous support (open-pore body), a body having the same structure over the entire cross section being obtained as the hot cathode.
  • the infiltrated body can subsequently be subjected to hot deformation by extrusion, rotary hammering, drawing or rolling, provided that a ductile material is used as the carrier.
  • the two methods can also be used in combination.
  • the advantages lie in the comparatively simple production method and in the low operating temperature of the cathode (in particular for barium alloys as an activating substance) and, at the same time, in the long service life compared to conventional cathodes (large supply of activating substance).

Abstract

A reactionless thermionic cathode for electronic tubes consists of a metallic or ceramic support and an alloy, preferably an intermetallic compound, containing the actual emission-promoting element, with a metal from the group comprising those of the VIIIth vertical row of the periodic table and rhenium. The preferred activation substances are platinides of the elements having a low electron work function, predominantly Ba and La. The cathode is manufactured by wet-mechanical, cataphoretic or electroplating application of the activation substance to the support or by infiltration of the porous support having a pore volume of at least 10%. High emission current densities are obtained at relatively low operating temperatures.

Description

Die Erfindung geht aus von einer Glühkathode für eine Elektronenröhre nach der Gattung des Oberbegriffs des Anspruchs 1 und von einem Verfahren zu deren Herstellung nach der Gattung des Oberbegriffs des Anspruchs 9.The invention relates to a hot cathode for an electron tube according to the preamble of claim 1 and to a method for its production according to the preamble of claim 9.

Glühkathoden für Elektronenröhren sind in zahlreichen Funktionsarten und Werkstoffkombinationen bekannt. Für kleine Leistungen wurden vielfach Bariumoxydkathoden mit guter Ausbeute verwendet. Als Hochleistungskathoden werden vor allem die dem Reduktions-Nachlieferungs-Typ angehörenden thorierten Wolframkathoden (System Th02/W2C/W) mit oder ohne weitere Zusätze eingesetzt. Unter den homogenen einphasigen Kathoden kann man die Untergruppen Einkomponenten- und Mehrkomponenten-Kathoden unterscheiden. Zu letzteren gehören unter anderem die aus einer chemischen Verbindung bestehenden Kathoden, z. B. TiC, ZrC, TiSi, LaB6, sowie die Legierungskathoden. Sie « Tungsten-Osmium Alloys for Improved Cathodes •, Platinum Metals Review, Vol. 26, January 1982, No. 1 ; « Thermoemissive Properties of (100) Faces of Single Crystals of Solie Solutions of Iridium, Osmium, and Rhenium in Tungsten •, N. B. Smirnova, B. G. Smirnov, S. M. Mikahilov, and G. B. Shuppe, Soviet Physics - Solid State, Vol. 12, No. 4, October 1976 ; « Thermionic Emission Properties of Metal Alloys (Survey)., T. L. Matskevich, Soviet Physics - Technical Physics, Vol. 13, No. 3, Sept. 1968 ; « Austrittsarbeit von Legierungen Nb-Ta, Ti-Re, Ta-Re •, Radiotechnika : Elektronika No. 11, 1964, Moskau.Glow cathodes for electron tubes are known in numerous types of functions and material combinations. Barium oxide cathodes with good yield were frequently used for small outputs. The thoraxed tungsten cathodes (system Th0 2 / W 2 C / W) with or without additional additives are used as high-performance cathodes. A distinction can be made between the subgroups of one-component and multi-component cathodes among the homogeneous single-phase cathodes. The latter include the cathodes consisting of a chemical compound, e.g. B. TiC, ZrC, TiSi, LaB 6 , and the alloy cathodes. "Tungsten-Osmium Alloys for Improved Cathodes," Platinum Metals Review, Vol. 26, January 1982, No. 1 ; «Thermoemissive Properties of (100) Faces of Single Crystals of Solie Solutions of Iridium, Osmium, and Rhenium in Tungsten •, NB Smirnova, BG Smirnov, SM Mikahilov, and GB Shuppe, Soviet Physics - Solid State, Vol. 12, No. 4, October 1976; "Thermionic Emission Properties of Metal Alloys (Survey)., TL Matskevich, Soviet Physics - Technical Physics, Vol. 13, No. 3, Sept. 1968; «Work function of alloys Nb-Ta, Ti-Re, Ta-Re •, radio technology: Elektronika No. 11, 1964, Moscow.

Alle hohe Emissionsstromdichten liefernden Kathoden (thorierte Wolframkathode, Lanthanhexaborid-Kathode) arbeiten bei hohen Betriebstemperaturen (1700 bis 2000 K), wodurch man an die Grenzen der zulässigen mechanischen Beanspruchungen kommt. Da sich die Warmfestigkeit der verwendeten Werkstoffe nicht mehr wesentlich steigern lässt, ist der konstruktive und verfahrenstechnische Aufwand bei der Herstellung von Glühkathodengefässen beträchtlich. Insbesondere das Lanthanhexaborid lässt sich zufolge seiner Sprödigkeit nicht in jede beliebige und wünschenswerte geometrische Form bringen.All cathodes delivering high emission current densities (thoriated tungsten cathode, lanthanum hexaboride cathode) operate at high operating temperatures (1700 to 2000 K), which leads to the limits of the permissible mechanical stresses. Since the heat resistance of the materials used can no longer be increased significantly, the design and process engineering involved in the production of hot cathode vessels is considerable. Because of its brittleness, lanthanum hexaboride in particular cannot be given any desired and desirable geometric shape.

Es besteht daher ein Bedürfnis nach Verbesserung der herkömmlichen Glühkathoden und nach Erhöhung der Betriebssicherheit und Lebensdauer bei gleichzeitiger Verringerung der Betriebstemperatur.There is therefore a need to improve the conventional hot cathodes and to increase the operational reliability and service life while reducing the operating temperature.

Der Erfindung liegt die Aufgabe zugrunde, eine Glühkathode mit hohem Emissionsvermögen sowie ein Verfahren zu deren Herstellung anzugeben, welche bei hoher Emissionsstromdichte im Dauerbetrieb eine lange Lebensdauer und hohe Warmfestigkeit besitzt, aus möglichst duktilem leicht verarbeitbarem Material besteht, nicht zur Versprödung neigt und sich auf einfache Weise in jeder geometrisch zweckmässigen Form herstellen lässt. Die Glühkathode soll insbesondere in Form dünner Drähte und Drahtgeflechte als stossichere Struktur ausführbar sein. Dabei soll die Betriebstemperatur möglichst tief liegen.The invention has for its object to provide a hot cathode with high emissivity and a method for its production, which has a long life and high heat resistance at high emission current density in continuous operation, consists of the most ductile material that can be easily processed, does not tend to embrittlement and is simple Can be produced in any geometrically appropriate form. The hot cathode is said to be executable, in particular in the form of thin wires and wire meshes, as a shockproof structure. The operating temperature should be as low as possible.

Diese Aufgabe wird durch die im kennzeichnenden Teil der Ansprüche 1 und 9 angegebenen Merkmale gelöst.This object is achieved by the features specified in the characterizing part of claims 1 and 9.

Das grundlegende Kennzeichen der neuen Glühkathode besteht darin, dass die die Elektronenemission fördernde, eine Legierung oder intermetallische Verbindung enthaltende Aktivierungssubstanz sowohl als Vorrat wie als emissive Oberflächenschicht metallischen Charakter hat und prinzipiell auf einem beliebigen Träger vorhanden sein kann. Es finden also keinerlei chemische Reaktionen oder thermische Zersetzungen eines nichtmetallischen Stoffes statt. Dies gestattet, eine praktisch unbegrenzte Menge von Aktivierungssubstanz auf dem Träger bzw. im Träger unterzubringen. Ausserdem erlaubt dieser Werkstoff im Falle eines metallischen Trägers die praktisch unproblematische Weiterverarbeitung zu dünnen Drähten, Bändern und Blechen. Im Gegensatz dazu gestattet jedoch das vorgeschlagene System ebenfalls die Unterbringung der Aktivierungssubstanz auf oder in einem keramischen Träger, falls dadurch besondere Vorteile erwachsen. In diesem Falle muss der Träger selbstverständlich zuvor in die endgültige Form gebracht werden.The basic characteristic of the new hot cathode is that the activation substance which promotes electron emission, contains an alloy or intermetallic compound, has a metallic character both as a supply and as an emissive surface layer and can in principle be present on any support. So there are no chemical reactions or thermal decomposition of a non-metallic substance. This allows a practically unlimited amount of activating substance to be accommodated on the carrier or in the carrier. In addition, in the case of a metallic carrier, this material allows for practically unproblematic further processing into thin wires, strips and sheets. In contrast, however, the proposed system also allows the activation substance to be accommodated on or in a ceramic carrier, if this results in particular advantages. In this case, the carrier must of course be brought into its final form beforehand.

Die Erfindung wird anhand der nachfolgenden Ausführungsbeispiele beschrieben.The invention is described using the following exemplary embodiments.

Ausführungsbeispiel IEmbodiment I

Als Aktivierungssubstanz wurde eine Legierung von Barium und Platin verwendet. Im vorliegenden Fall handelt es sich um das Bariumplatinid Ba Pts. Abgewogene Mengen Barium und Platin wurden im richtigen stöchiometrischen Verhältnis im Lichtbogenofen unter einer Schutzgasatmosphäre von Argon eingeschmolzen. Die Schmelze wurde abgekühlt, zur Erstarrung gebracht und im Mörser zerkleinert. Die Bruchstücke wurden in einer Kugelmühle mit Wolframkarbid-Auskleidung und Wolframkarbid-Kugeln zu einem Pulver mit einer Partikelgrösse von höchstens 1 µm zermahlen. Dann wurde das Pulver mit Nitrozellulose und Amylazetat zu einem dünnflüssigen Brei verrührt. Diese Suspension wurde durch Aufrollen in einer Schichtdicke von 100 µm auf einen Wolframdraht von 0,5 mm Durchmesser aufgetragen und getrocknet. Der 100 mm lange beschichtete Draht wurde mittels Kathodenhalter in ein Glühkathodengefäss eingespannt und letzteres bis auf einen Restgasdruck von weniger als 10-4 m bar evakuiert. Der Draht wurde langsam auf eine Temperatur von ca. 800 K aufgeheizt, wobei die Nitrozellulose zersetzt wurde und die Zersetzungsprodukte den Reaktionsraum verliessen. Nach 20 min Haltezeit wurde das Vakuum auf einen Restgasdruck von weniger als 10-5 m bar gebracht und der Draht weiter auf eine Temperatur von 1400 K aufgeheizt. Nach einer 15 min dauernden Formierungszeit wurde die volle stationäre Emissionsstromdichte von 4 A/cm2 erreicht und gehalten. Die Kathode erwies sich als wenig vakuumempfindlich. Die Emissionsstromdichte von 4 A/cm2 konnte auch bei einer Verschlechterung des Vakuums auf einen Restgasdruck von ca. 3·10-4 m bar unverändert im Dauerbetrieb gehalten werden. Im Verlaufe der ersten Betriebszeit konnte an der Kathodenoberfläche die Bildung des bariumreicheren Platinids Ba Pt2 nebst freiem Platin festgestellt werden. Offenbar stellte sich ein neuer chemisch-thermodynamischer Gleichgewichtszustand ein, der dann über die ganze Betriebsdauer bis zur Erschöpfung der Aktivierungssubstanz unverändert anhielt. Die erzielbare Emissionsstromdichte wurde dadurch nicht beeinflusst.An alloy of barium and platinum was used as the activation substance. In the present case, it is the barium platinum Ba Pt s . Weighed amounts of barium and platinum were melted down in the correct stoichiometric ratio in an arc furnace under an inert gas atmosphere of argon. The melt was cooled, solidified and crushed in a mortar. The fragments were ground in a ball mill with a tungsten carbide lining and tungsten carbide balls to a powder with a particle size of at most 1 μm. Then the powder was mixed with nitrocellulose and amyl acetate to form a thin slurry. This suspension was applied to a tungsten wire of 0.5 mm diameter by rolling in a layer thickness of 100 μm and dried. The 100 mm long coated wire was clamped by means of the cathode holder in a Glühkathodengefäss and the latter to a residual gas pressure of less than 10- 4 m evacuated bar. The wire was slowly heated to a temperature of about 800 K, the nitrocellulose being decomposed and the decomposition products leaving the reaction space. After a holding time of 20 minutes, the vacuum was brought to a residual gas pressure of less than 10-5 m bar and the wire was further heated to a temperature of 1400 K. After a 15 min lasting formation time, the full stationary emission current density of 4 A / cm 2 was reached and maintained. The cathode was not very sensitive to vacuum. The emission current density of 4 A / cm 2 could be kept unchanged in continuous operation even if the vacuum deteriorated to a residual gas pressure of approx. 3 · 10 -4 m bar. In the course of the first operating time, the formation of the barium-rich platinum Ba Pt 2 together with free platinum was found on the cathode surface. Apparently, a new chemical-thermodynamic equilibrium occurred, which then remained unchanged over the entire operating period until the activation substance was exhausted. The achievable emission current density was not affected by this.

Ausführungsbeispiel IIEmbodiment II

Gemäss Beispiel I wurde zunächst eine der intermetallischen Verbindung Ba Pt2 entsprechende Legierung erschmolzen, abgekühlt, zur Erstarrung gebracht, im Mörser zerstossen und in einer Kugelmühle zu einem feinkörnigen Pulver vermahlen. Dieses Pulver wurde dann in einem geeigneten Bad feindispers aufgeschlämmt und kataphoretisch auf einen Molybdändraht von 0,5 mm Durchmesser in einer Schichtdicke von 50 µm aufgebracht. Der beschichtete Draht wurde nachher unter Argonatmosphäre während 10 min einer Glühbehandlung bei einer Temperatur von 1400 °C unterworfen, wobei die Ba Ptz-Partikel durch Sintern fest mit dem Träger und unter sich verbunden wurden. Durch abwechslungsweise kataphoretische Abscheidung und Sinterbehandlung lassen sich Oberflächenschichten beliebiger Dicke erzielen. Wesentlich ist dabei, dass der Kontakt mit der Luft möglichst vermieden wird, da Ba Pt2 nicht korrosionsbeständig ist und in BaO + Pt zerfällt. Der beschichtete Molybdändraht wurde als Glühkathode geprüft und ergab bei einer Temperatur von 1400 K eine stationäre Emissionsstromdichte von 4 A/cm2.According to Example I, an alloy corresponding to the intermetallic compound Ba Pt 2 was first melted, cooled, solidified, crushed in a mortar and ground in a ball mill to a fine-grained powder. This powder was then slurried finely in a suitable bath and cataphoretically applied to a molybdenum wire with a diameter of 0.5 mm in a layer thickness of 50 μm. The coated wire was subsequently subjected to an annealing treatment at a temperature of 1400 ° C. for 10 minutes under an argon atmosphere, the Ba Ptz particles being firmly connected to the support and to one another by sintering. By alternately cataphoretic deposition and sintering treatment, surface layers of any thickness can be achieved. It is essential that contact with the air is avoided as far as possible, since Ba Pt 2 is not corrosion-resistant and breaks down into BaO + Pt. The coated molybdenum wire was tested as a hot cathode and, at a temperature of 1400 K, gave a stationary emission current density of 4 A / cm 2 .

Ausführungsbeispiel 111Embodiment 111

In Anlehnung an Beispiel I wurde eine Legierung von Lanthan und Platin verwendet. Es handelte sich hier um das Lanthanplatinid La Pt2. Entsprechende stöchiometrische Mengen von Lanthan und Platin wurden im Lichtbogenofen unter Argonatmosphäre zusammengeschmolzen und nach der Erstarrung der Schmelze im Mörser zerkleinert und zu einem feinkörnigen Pulver zermahlen. Die Auftragung auf einen Wolframdraht mit Hilfe von Nitrozellulose und Amylazetat erfolgte in genau gleicher Weise wie in Beispiel I beschrieben. Der beschichtete Draht wurde bei einer Temperatur von ca. 800 K und einem Restgasdruck von weniger als 10-4 m bar während 20 min entgast. Daraufhin wurde der Restgasdruck des Vakuums auf einen Wert von weniger als 10-5 m bar gesenkt und die Temperatur des Drahtes auf 1850 K erhöht. Nach einer Formierungszeit von 10 min wurde im Glühkathodengefäss eine Emissionsstromdichte von 5,5 A/cm2 erreicht. Dieser Wert wurde auch im stationären Dauerbetrieb ohne Abfall gehalten.Based on Example I, an alloy of lanthanum and platinum was used. It was the lanthanum platinum La Pt 2 . Corresponding stoichiometric amounts of lanthanum and platinum were melted together in an arc furnace under an argon atmosphere and, after the melt had solidified, crushed in a mortar and ground to a fine-grained powder. The application to a tungsten wire with the aid of nitrocellulose and amyl acetate was carried out in exactly the same way as described in Example I. The coated wire was degassed at a temperature of approx. 800 K and a residual gas pressure of less than 10- 4 m bar for 20 minutes. Thereupon, the residual gas pressure of the vacuum to a value of less than 10- 5 m bar was lowered, and increases the temperature of the wire at 1850 K. After a formation time of 10 minutes, an emission current density of 5.5 A / cm 2 was achieved in the hot cathode vessel. This value was also kept in steady-state operation without waste.

Ausführungsbeispiel IVEmbodiment IV

Die Aktivierungssubstanz war eine Legierung von Barium und Palladium, welche ungefähr der Zusammensetzung der intermetallischen Verbindung Ba Pd5 entsprach. Sie wurde durch Mischen der Komponenten im Lichtbogenofen unter Argonatmosphäre erschmolzen. Auf pulvermetallurgischem Weg wurde ein offenporiger Rundstab von 10 mm Durchmesser aus Molybdän mit einem Porenvolumen von 25 % hergestellt. Der Molybdänkörper wurde mitsamt der schmelzflüssigen Ba/Pd-Legierung in eine vakuumdichte Giessvorrichtung gegeben und auf eine Temperatur von 1700 °C gebracht. Nach einer Verweilzeit von 15 min unter Vakuum wurde die Giessvorrichtung mit Argon von 10 bar Druck geflutet und die Temperatur während 30 min gehalten. Dabei infiltrierte die Ba/Pd-Legierung den porösen Molybdänkörper und füllte seine Poren vollständig aus. Nach dem Abkühlen wurde der Stab überdreht und erneut auf 1100 °C erhitzt. Nun wurde unter Schutzgasatmosphäre eine Reihe von Warmverformungsoperationen mit Zwischenglühungen durchgeführt, die in einem Rundhämmern und Ziehen zu einem Draht von 0,8 mn Durchmesser bestanden. Der fertige, mit der Ba/Pd-Legierung dotierte Molybdändraht wurde in ein Glühkathodengefäss eingesetzt und bei einer Temperatur von 1350 K unter Vakuum mit einem Restgasdruck von 10-4 m bar betrieben. Die gemessene Emissionsstromdichte betrug im Dauerbetrieb stationär 2 A/cm2. Nach einiger Zeit konnte an der Kathodenoberfläche die Bildung von Ba Pd2 beobachtet werden. Diese chemische Veränderung blieb ohne Einfluss auf die Emissionsstromdichte. Da das Ba Pd2 jedoch einen wesentlich tieferen Schmelzpunkt als das Ba Pd5 aufweist, ist zu beachten, dass in Anbetracht der grossen relativen Menge der Aktivierungssubstanz die Elektronenröhre nicht bei einer zu hohen Kathodentemperatur betrieben wird. Andererseits zeichnet sich eine derartige Glühkathode durch einen beträchtlichen Vorrat an Aktivierungssubstanz und eine dementsprechend lange Lebensdauer aus.The activating substance was an alloy of barium and palladium, which corresponded approximately to the composition of the intermetallic compound Ba Pd 5 . It was melted by mixing the components in an arc furnace under an argon atmosphere. An open-pore round rod with a diameter of 10 mm was made from molybdenum with a pore volume of 25% by powder metallurgy. The molybdenum body, together with the molten Ba / Pd alloy, was placed in a vacuum-tight casting device and brought to a temperature of 1700 ° C. After a dwell time of 15 min under vacuum, the casting device was flooded with argon at a pressure of 10 bar and the temperature was maintained for 30 min. The Ba / Pd alloy infiltrated the porous molybdenum body and completely filled its pores. After cooling, the rod was turned over and heated again to 1100 ° C. Now a series of hot-forming operations with intermediate annealing was carried out under a protective gas atmosphere, which consisted of round hammering and drawing into a wire with a diameter of 0.8 mm. The finished molybdenum wire doped with the Ba / Pd alloy was inserted into a hot cathode vessel and operated at a temperature of 1350 K under vacuum with a residual gas pressure of 10- 4 m bar. The measured emission current density was 2 A / cm 2 in steady-state operation. After a while, the formation of Ba Pd 2 was observed on the cathode surface. This chemical change had no effect on the emission current density. However, since the Ba Pd 2 has a much lower melting point than the Ba Pd 5 , it should be noted that, in view of the large relative amount of the activation substance, the electron tube is not operated at too high a cathode temperature. On the other hand, such a hot cathode is characterized by a considerable supply of activating substance and a correspondingly long service life.

Ausführungsbeispiel VEmbodiment V

Als Aktivierungssubstanz wurde eine Legierung von Barium und Ruthenium gewählt, welche etwa der intermetallischen Verbindung Ba RU2 entsprach. Die Legierung wurde aus den Komponenten unter Vakuum im Induktionsofen erschmolzen und zur Erstarrung gebracht. Der Träger bestand aus einem mit Yttriumoxyd stabilisierten porösen Hohlzylinder aus gesintertem Zirkonoxyd mit einem Aussendurchmesser von 12 mm und einem Innendurchmesser von 6 mm. Das Porenvolumen des offenporigen Sinterkörpers betrug 30 %. Letzterer wurde allseitig in die pulverisierte Aktivierungssubstanz eingepackt und das Ganze in ein Vakuumgefäss gebracht und induktiv auf 2 000 °C erhitzt. Dabei schmolz die Ba/Ru-Legierung und drang in die Poren des Sinterkörpers ein. Zur Verbesserung des Eindringens wurde das Gefäss zusätzlich mit Argon unter einem Druck von 10 bar während 20 min geflutet. Nach dem Abkühlen des infiltrierten Sinterkörpers wurde dieser zwecks Entfernung von anhaftenden Legierungsresten aussen und innen leicht überdreht. Auf die äussere Oberfläche wurde zusätzlich eine 5 µm dicke Rutheniumschicht galvanisch aufgebracht zur Ueberbrückung der vom Sinterkörper begrenzten nichtmetallischen Oberflächenpartien. Daraufhin wurde das Ganze während 1 h bei einer Temperatur von 1 500 °C unter Vakuum geglüht. Die mit einem Wolframwendel zur Heizung im Innern versehene Kathode wurde in eine Elektronenröhre eingebaut und unter Vakuum mit 10-5 m bar Restgasdruck bei einer Temperatur von 1 500 K betrieben. Die dabei gemessene Emissionsstromdichte betrug im Dauerbetrieb stationär 10 Alcm2.An alloy of barium and ruthenium was chosen as the activation substance, which roughly corresponded to the intermetallic compound Ba R U2 . The alloy was melted from the components in a vacuum in an induction furnace and solidified. The carrier consisted of a porous hollow cylinder made of sintered zirconium oxide stabilized with yttrium oxide and having an outside diameter of 12 mm and an inside diameter of 6 mm. The pore volume of the open-pore sintered body was 30%. Last The other was packed into the powdered activation substance on all sides and the whole thing was placed in a vacuum vessel and inductively heated to 2,000 ° C. The Ba / Ru alloy melted and penetrated into the pores of the sintered body. In order to improve the penetration, the vessel was additionally flooded with argon under a pressure of 10 bar for 20 minutes. After the infiltrated sintered body had cooled, it was slightly turned on the outside and inside to remove adhering alloy residues. A 5 µm thick ruthenium layer was additionally electroplated on the outer surface to bridge the non-metallic surface areas delimited by the sintered body. The whole was then annealed under vacuum at a temperature of 1,500 ° C. for 1 h. The provided with a tungsten coil for heating in the interior cathode was installed in an electron tube and operated under vacuum with 10- 5 mbar residual gas pressure at a temperature of 1500 K. The measured emission current density in steady operation was 10 Alcm 2 .

Die Erfindung ist nicht auf die Ausführungsbeispiele beschränkt. Grundsätzlich kann der Träger aus einem warmfesten metallischen oder keramischen Körper mit einem Porenvolumen von 10 bis 50 % bestehen, dessen Poren vollständig von der Aktivierungssubstanz ausgefüllt sind. Als Träger eignen sich insbesondere die hochschmelzenden Metalle W, Mo, Ta. Nb oder Legierungen von mindestens zweien dieser Metalle. Sie haben den Vorteil, duktil zu sein und sich als Gerüstwerkstoffe in beliebige Formen, z. B. als Draht, Band, Blech etc. weiterverarbeiten zu lassen. Des weiteren können keramische Materialien mit hohem Schmelzpunkt wie beispielsweise mit Y203 stabilisiertes Zr02 verwendet werden. Als Aktivierungssubstanz können Legierungen der Metalle der VIII. Vertikalreihe des periodischen Systems, Platinmetalle, Eisenmetalle, vorab Nickel sowie Rhenium mit einem Element ausgewählt aus der Gruppe von Ba, Ca, La, Y, Gd, Ce, Th, U oder intermetallische Verbindungen derselben Elemente Verwendung finden. Besonders vorteilhaft erweisen sich Platinide des Ba und/oder La, darunter Ba Pt5 und/oder Ba Pt2 bzw. La Pt5 und/oder La Pt3 und/oder La Pt2. Die betreffenden Legierungen bzw. intermetallischen Verbindungen können auch gemischt sein, also in der Mehrzahl auftreten. Es soll jedoch mindestens eine der vorgenannten Legierungen und/oder intermetallischen Verbindungen als Aktivierungssubstanz vorliegen. Die als Legierung und/oder intermetallische Verbindung verwendete Aktivierungssubstanz wird entweder auf nassmechanischem Weg (Auftragen als Paste mit geeigneten chemischen Substanzen oder Kataphorese) oder auf chemischem Weg (z. B. stromlose Abscheidung, Co-Präzipitation etc.) oder galvanisch auf den Träger aufgebracht und bildet dann die Randzone des Glühkathodenkörpers. Eine andere Methode besteht darin, die Aktivierungssubstanz schmelzmetallurgisch, d. h. im flüssigen Zustand in den porösen Träger (offenporiger Körper) zu infiltrieren, wobei als Glühkathode ein über den ganzen Querschnitt gleichartig aufgebauter Körper erhalten wird. Der infiltrierte Körper kann nachträglich einer Warmverformung durch Strangpressen, Rundhämmern, Ziehen oder Walzen unterworfen werden, sofern als Träger ein duktiles Material verwendet wird. Die beiden Methoden können auch in Kombination angewendet werden.The invention is not restricted to the exemplary embodiments. In principle, the carrier can consist of a heat-resistant metallic or ceramic body with a pore volume of 10 to 50%, the pores of which are completely filled with the activating substance. Particularly suitable are the high-melting metals W, Mo, Ta. Nb or alloys of at least two of these metals. They have the advantage of being ductile and can be used as framework materials in any shape, e.g. B. to be processed as wire, tape, sheet metal, etc. Ceramic materials with a high melting point, such as ZrO 2 stabilized with Y 2 O 3 , can also be used. Alloys of the metals of the VIII. Vertical series of the periodic system, platinum metals, iron metals, in advance nickel and rhenium with an element selected from the group of Ba, Ca, La, Y, Gd, Ce, Th, U or intermetallic compounds of the same elements can be used as the activation substance Find use. Platinides of Ba and / or La have proven particularly advantageous, including Ba Pt 5 and / or Ba Pt 2 or La Pt 5 and / or La Pt 3 and / or La Pt 2 . The alloys or intermetallic compounds in question can also be mixed, that is to say they occur in the majority. However, at least one of the aforementioned alloys and / or intermetallic compounds should be present as an activation substance. The activation substance used as an alloy and / or intermetallic compound is applied to the carrier either by wet mechanical means (application as a paste with suitable chemical substances or cataphoresis) or by chemical means (e.g. electroless deposition, co-precipitation etc.) and then forms the edge zone of the hot cathode body. Another method is to infiltrate the activating substance by melt metallurgy, ie in the liquid state, in the porous support (open-pore body), a body having the same structure over the entire cross section being obtained as the hot cathode. The infiltrated body can subsequently be subjected to hot deformation by extrusion, rotary hammering, drawing or rolling, provided that a ductile material is used as the carrier. The two methods can also be used in combination.

Die Vorteile liegen in der vergleichsweise einfachen Herstellungsart und in der niedrigen Betriebstemperatur der Kathode (insbesondere für Bariumlegierungen als Aktivierungssubstanz) sowie gleichzeitig in der gegenüber herkömmlichen Kathoden hohen Lebensdauer (grosser Vorrat an Aktivierungssubstanz).The advantages lie in the comparatively simple production method and in the low operating temperature of the cathode (in particular for barium alloys as an activating substance) and, at the same time, in the long service life compared to conventional cathodes (large supply of activating substance).

Claims (12)

1. Thermionic cathode with high emissive power for an electron tube consisting of a heat-resistant metallic or ceramic body serving as carrier and of a metallic activation substance promoting electron emission which contains an alloy, characterized in that the alloy consists of a metal of the Vlllth vertical row of the periodic system and also rhenium and an element selected from the group comprising Ba, Ca, La, Y, Gd, Ce, Th, and U or is replaced by an intermetallic compound of the same elements, and in that the activation substance covers the entire surface of the carrier and fills at least 10% of the total volume of the cathode body.
2. Thermionic cathode according to Claim 1, characterized in that the carrier consists of a cohesive porous skeleton which has a pore volume of 10 to 50 % and whose pores are completely filled with the activation substance.
3. Thermionic cathode according to Claim 1, characterized in that the activation substance contains at least one intermetallic compound of a platinum metal with at least one of the elements Ba and La.
4. Thermionic cathode according to Claim 3, characterized in that the activation substance contains a platinide of the elements Ba and/or La.
5. Thermionic cathode according to Claim 4, characterized in that the activation substance contains Ba Pt5 and/or Ba Pt2.
6. Thermionic cathode according to Claim 4, characterized in that the activation substance contains at least one compound selected from the group comprising La Pt5, La Pt3 and La Pt2.
7. Thermionic cathode according to Claim 1, characterized in that the carrier consists of at least one high-melting metal selected from the elements W, Mo, Ta, Nb.
8. Thermionic cathode according to Claim 1, characterized in that the carrier consists of Zr02 doped with Y203.
9. Method for manufacturing a thermionic cathode with high emissive power for an electron tube, in which a heat-resistant metallic or ceramic body serving as carrier and also a metallic activation substance which contains an alloy are provided, characterized in that an alloy is produced from a metal of the Vlllth vertical row of the periodic system and also rhenium and an element selected from the group comprising Ba, Ca, La, Y, Gd, Ce, Th, and U or an intermetallic compound of the same elements as activation substance by smelting metallurgy or by powder metallurgy and is deposited on and/or in the carrier by a wet- mechanical, chemical, electroplating or smelting- metallurgy method.
10. Method according to Claim 9, characterized in that the activation substance is deposited on a compact body serving as carrier by brushing on or cataphoresis.
11. Method according to Claim 9, characterized in that the activation substance is introduced by infiltration in the liquid state into an open-pore body with a pore volume of 10 to 50 % serving as carrier and forming a skeleton.
12. Method according to Claim 9, characterized in that the heat-resistant body serving as carrier is manufactured from at least one of the high-melting metals W, Mo, Ta, Nb or an alloy of at least two of these metals and in that the activation substance is manufactured from a platinide of barium or lanthanum.
EP84110730A 1983-09-30 1984-09-08 Thermionic cathode capable of high emission for an electron tube, and method of manufacture Expired EP0143222B1 (en)

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