EP0081270A2 - Procédé de fabrication d'une cathode thermoionique et cathode thermoionique fabriqué selon ce procédé - Google Patents

Procédé de fabrication d'une cathode thermoionique et cathode thermoionique fabriqué selon ce procédé Download PDF

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Publication number
EP0081270A2
EP0081270A2 EP82201538A EP82201538A EP0081270A2 EP 0081270 A2 EP0081270 A2 EP 0081270A2 EP 82201538 A EP82201538 A EP 82201538A EP 82201538 A EP82201538 A EP 82201538A EP 0081270 A2 EP0081270 A2 EP 0081270A2
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Prior art keywords
layer
cathode
base
deposited
layers
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German (de)
English (en)
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EP0081270B1 (fr
EP0081270A3 (en
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Berthold Dr. Frank
Georg Dr. Gärtner
Hans Dr. Lydtin
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Koninklijke Philips NV
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Philips Patentverwaltung GmbH
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
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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
    • 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 method for producing a thermionic cathode with a polycrystalline cover layer made of a high-melting metal, which is deposited on layers underneath.
  • the invention further relates to a thermionic cathode which has been produced by this method.
  • a refractory metal is a metal that melts at a high temperature, e.g. W, Mo, Ta, Nb, Re, Hf, Ir, Os; Pt, Rh, Ru, Th, Ti, V, Yb, Zr.
  • a method of the aforementioned type is known from DE-OS 14 39 890.
  • thermionic cathodes with a support made of pyrolytic graphite and an electron-emitting body arranged thereon are problematic in three respects and are not very suitable for commercial use.
  • the main problem is the different coefficients of thermal expansion of the support and the emitting cathode part.
  • pyrolytic graphite has a linear thermal expansion coefficient of 10 -6 K -1 with respect to its layer structure in a direction referred to as the a direction.
  • the c direction perpendicular to it it is 20 to 30 . 10 -6 k -1
  • for tungsten at 4.5. 10 -6 K -1 and for thorium at 12 . 10 -6 K -1 lies.
  • an adhesive layer between the support and the emitting cathode part in which, for example, the coefficient of thermal expansion is an average of Coefficient of the substrate and the emitting cathode part, does not create a permanent connection at the usual operating temperatures of 2000 K.
  • the second disadvantage is the diffusion of carbon into the crystal structure of the emitting cathode part, against which there are no suitable diffusion barriers at an operating temperature of 2000 K.
  • tungsten carbide W 2 C and WC
  • W 2 C and WC tungsten carbide
  • ThC thorium carbide
  • the usual manufacturing processes e.g. Powder metallurgy, cathodes made of polycrystalline surfaces with statistically oriented crystallites. Accordingly, a few crystallites or monolayer-covered crystallites with a correspondingly favorable orientation emit very strongly, but the far larger part of the crystallites hardly contributes to the emission.
  • This layer can either consist of a pure, high-melting metal such as W, Mo, Ta, Nb, Re, Hf, Ir, Os, Pt, Rh, Ru, Th, Ti, V, Yb, Zr or C. and should have a suitable preferred orientation or it can be a high emission substance, preferably a rare earth oxide, ZrC, ThC, UC 2 , UN, LaB 6 or N dB 6 .
  • a pure, high-melting metal such as W, Mo, Ta, Nb, Re, Hf, Ir, Os, Pt, Rh, Ru, Th, Ti, V, Yb, Zr or C. and should have a suitable preferred orientation or it can be a high emission substance, preferably a rare earth oxide, ZrC, ThC, UC 2 , UN, LaB 6 or N dB 6 .
  • the monoatomic emitter layer formed thereon by diffusion from the inside of the cathode or by adsorption from the vapor preferably consists of Th, Ba or Cs and, together with the preferred orientation, has a lower work function than that of the respective pure materials or monolayers on unoriented tungsten.
  • the cathodes produced in this way also have a number of disadvantages.
  • An important disadvantage is, for example, that conventional cathodes must first be manufactured using the usual powder metallurgical methods, which are then additionally coated with the preferred oriented CVD layer, with a number of surface processing steps also having to be inserted to achieve the preferred orientation.
  • the production of such cathodes is therefore very complex.
  • the cathode shaping is very restricted due to the powder metallurgical production of the substrates.
  • thoriated wires are coated with ⁇ 111> -oriented tungsten, which in turn can be used to produce a mesh cathode, but the method does not allow the production of a cylindrical unipotential cathode made of thoriated tungsten, since the correspondingly shaped substrate cathode is not can be produced by powder metallurgy if it is also to be heated directly and effectively at the same time.
  • a Another difficulty is that the recrystallization or crystal growth at longer operating times and normal operating temperatures (2000 K for Th- [W] cathodes) leads to an increasing destruction of the preferred orientation, whereby the emission naturally drops.
  • dispenser cathodes with porous sintered bodies are known, which are built up in layers such that layers with high-melting metal such as tungsten or molybdenum and layers with emission-promoting material such as thorium or thorium compounds or Alternate barium aluminate with the top layer of tungsten or molybdenum of the emitting surface is somewhat pronounced thicker and the pad is composed of the layer structure made of W ungsten molybdenum or carbon. It is important for the function of these cathodes that they are porous and that the emitting substance can easily reach the surface.
  • the layer-by-layer production only has the task of achieving a uniform distribution of the emitting substance in the storage area; the layers should even overlap or be interlocked by means of a coarse-grained structure.
  • Such cathodes are produced by sintering powder layers onto the support or also by (physical) vapor deposition of the support.
  • the present invention has the task of creating a thermionic cathode which is suitable as a unipotential cathode for use in UHF and microwave tubes, and which has the advantages of a large-area cathode with largely freely selectable geometric shape, high emission current and stable high-frequency behavior over a long service life gets away.
  • the layers are preferably applied by reactive deposition, e.g. CVD processes, pyrolysis, cathode sputtering, vacuum condensation or plasma sputtering.
  • reactive deposition e.g. CVD processes, pyrolysis, cathode sputtering, vacuum condensation or plasma sputtering.
  • W, Mo, Ta, Nb, Re and / or C are preferably used as the base material, the composition of the base material being the same or different in the individual layers.
  • the method according to the invention which can be used in particular for the production of thermionic monolayer cathodes with a high electron emission density, accordingly a layer structure, at least consisting of a high-melting metal and a substance with high electron emission as a monolayer, successively deposited in a continuous process, for example by reactive deposition from the gas phase (CVD process) of at least two components on a base, the base being removed after the deposition so that a self-supporting whole CVD cathode is obtained.
  • a cathode - designed as a cylindrical unipotential cathode - is particularly suitable for transmitter and amplifier tubes at high frequencies and / or high powers.
  • the thermionic cathode produced according to the invention - the material of which is essentially high-melting metal, such as W, Mo, Ta, Nb and / or Re and / or carbon - consists of a very finely crystalline, mechanically stable support or base layer, a layer sequence which is highly enriched with emitting substance and an optionally preferred oriented top layer, wherein all layers have been applied via the gas phase, preferably by CVD method, and the base has been removed after the deposition has ended.
  • a finely crystalline carrier layer made of high-melting metal with good mechanical properties and grain growth suppressed by doping is applied to a suitable (and suitably shaped) base, for example by reactive deposition from the gas phase (CVD method).
  • a layer or a sequence of layers of alternating electron-emissive substance and base material the layer composition being controlled by varying the gas flows, for example in CVD deposition.
  • a top layer preferred-oriented columnar layer made of a high-melting metal, which is protected by additives against grain growth and destruction of the preferred orientation.
  • the substrate or substrate preform is detached from the positive (ie the layer structure) and a self-supporting cathode with the desired properties is obtained, for example in the form of a cylindrical, self-supporting, directly heated unipotential cathode with high emission and long service life.
  • the base preferably consists of an easily and precisely mouldable material which has little adhesion to the cathode material deposited thereon.
  • the substrate is removed according to the invention either by selective etching, mechanically or by evaporation when heated in vacuo, e.g. in a vacuum oven, or in a suitable gas atmosphere, e.g. Hydrogen, by burning off or by a combination of the methods mentioned, depending on the material used for the base.
  • the base is, for example, a body made of graphite, in particular pyrolytic graphite, or vitreous carbon, which is removed by mechanical processing, burning and / or mechanical-chemical micropolishing, or the base consists of copper, nickel, iron, molybdenum or one Alloy with a predominant proportion of these metals and is removed by selective etching or initially in its predominant mass mechanically and in the remaining residues by evaporation with heating in a vacuum, for example in a vacuum oven, or under a suitable gas atmosphere, for example under hydrogen.
  • the base used for the method according to the invention must be made with the layer material, ie the material from which the supporting parts of the cathode are made are produced, as little compatible as possible, ie easily removable from it.
  • Graphite advantageously fulfills this requirement.
  • Graphite for example polycrystalline electrographite, is easy to machine mechanically, so that even complicated moldings can be produced easily.
  • electrographite is porous, a thin layer of pyrolytic graphite is deposited on the preforms made from it, which is practically non-porous and is a good base for the deposition of the cathode material.
  • the cathode can be pulled off the graphite shaped body very simply and with only a small force by pulling or pushing in the direction of the layering axis (a-axis) of the pyrolytic graphite.
  • a reliable detachment is achieved by taking advantage of the different thermal expansion coefficients of the graphite base and the cathode formed, for example, from tungsten. As tungsten expands more than graphite in the heat, the finished cathode is split by heating to e.g. 300 ° C above the separation temperature.
  • the desired cleavage is obtained in an even simpler manner by cooling to room temperature.
  • Another simple method for removing graphite, for example in inaccessible places, is by burning it off. Micropolishing results in particularly clean and uniform surfaces.
  • Underlay molded articles made of copper or nickel are also easy to machine and can be removed. Copper will initially mostly removed mechanically, e.g. by machining. Copper residues can be removed in a vacuum furnace by evaporation at 1800 to 1900 ° C or, like nickel, by selective etching or micropolishing. A mixture of HN03, H 2 0 and H 2 O 2 in a mixing ratio of 6: 3: 1 parts by volume or an aqueous solution of 220 g Ce (NH 4 ) 2 (NO 3 ) 6 and 110 is used as the etchant, in particular for nickel ml HN0 3 to 1 1 H 2 0 used.
  • Copper supports can be removed in a solution of 200 g FeC1 3 each 1 1 H 2 0 at a working temperature of 50 ° C.
  • Molybdenum substrates are preferably etched away by immersing them in a boiling solution from one part each of HN0 3 , HC1 and H 2 0.
  • a thermionic cathode produced by the method according to the invention is self-supporting and flat and has a thickness of 50 / um to 500 / um, preferably 100 to 150 / um, and even larger thicknesses can be realized without problems.
  • the second possibility of structural stabilization is the deposition of wafer-thin crystallite growth-inhibiting intermediate layers.
  • tungsten is again to be used, the deposition of which from the gas phase is repeatedly interrupted by throttling the WF 6 + H 2 gas stream.
  • carrier gas is alternately introduced with, for example, an organometallic thorium compound from a saturator, so that, for example, a ThO 2 intermediate layer is deposited.
  • a similar effect can be achieved by carbon deposition in the intermediate layer at a very high saturator temperature.
  • the thickness of the tungsten layers is of the order of 1 / um, that of the intermediate layers containing thorium or carbon is significantly less (about 0.2 / um).
  • the third method is based on the fact that the base material is deposited together with a doping material which has a negligibly low solubility in solid in the crystal lattice of the base material. For example, tungsten is deposited with 2% Th0 2 to produce the layers. Such a separation from the gas phase (multi-component CVD process) results in an extremely fine and uniform distribution of the admixture in the layer material.
  • the cathodes according to the invention achieve a lifespan of 10 4 hours due to the addition mentioned, in fact under normal operating conditions and with increased emission rates.
  • the backing layer i.e. the load-bearing base layer
  • the mechanical strength is about three times greater than that of the pure CVD material.
  • the dopants which are practically insoluble in the base metal, are either finely dispersed simultaneously or alternately in a high-frequency layer sequence by CVD, excessive germ growth is interrupted again and again. In particular, this foreign doping strongly inhibits grain growth under normal operating temperatures, so that the mechanical stability is also guaranteed over a longer service life.
  • the stabilization of the base material is achieved by the addition of Th0 2 in tungsten, which is mentioned by way of example, also by other substances, provided that they have a small or negligible solid solubility in tungsten (e.g. scandium, yttrium) and their melting point is above 2000 K.
  • These substances include in particular Zr, Zr0 2 , Ru, U0 2 , Sc 2 0 3 and Y203, which moreover can advantageously be separated from the gas phase simultaneously with the layer material.
  • Structural stabilization of the carrier layer that is to say the base, can only be brought about by correspondingly small additions, which as a rule do not have to be identical to the emitting substance.
  • additional layers with a significantly higher doping concentration of emitting substance are required.
  • a supply and subsequent delivery layer with a high doping concentration of emissive substance is therefore applied to the structure-stabilized base.
  • This subsequent delivery area expediently consists of a high-frequency layer sequence, layers with emitting material alternating with layers of base material in such a way that these layers are still mechanically sufficiently stable and adhere well to the CVD carrier layer and at the same time have a high mean emitter concentration in the subsequent delivery area of preferably 10 to 20% by weight.
  • This layer sequence is produced according to the invention by reactive deposition from the gas phase with temporal variation of the parameters, in particular the flow rates of the gases involved in the reaction and / or the substrate temperature.
  • the variation in time of the CVD parameters is preferably periodic, in particular alternating between the optimal parameters for deposition of the emitting substance and those for CVD of the base material.
  • a corresponding change in the respective gas flow rates is usually sufficient; in some cases, however, the substrate temperature must also be lowered and raised appropriately.
  • the electron-emitting substance is preferably selected from the scandium group (Sc, Y, La, Ac, lanthanides, actinides) and in metal, oxide, boride and / or carbide form with the base material, preferably W, Mo, Nb, Ta, Re , separated from the gas phase.
  • the following combinations of substances serve in particular as emitting substance + base material: Th / Th0 2 + W, Th / Th0 2 + Nb, ThB 4 + Re, Y / Y 2 0 3 + Ta, Y 2 0 3 + Nb, or Sc 2 0 31 Y 2 0 3 or La 2 0 3 in combination with molybdenum or tungsten as the base material are deposited as emitting substances.
  • ThB 4 is preferably applied by pyrolysis of Th (BH 4 ) 4 , enriched in, for example, argon as the carrier gas, on a layer of rhenium with an underlying structurally stabilized tungsten carrier at substrate temperatures greater than or equal to 300 ° C.
  • a further improvement in the cathode properties can be achieved by additionally using an activator component, preferably boron or carbon, to release the emitter in atomic form, and also a diffusion-enhancing component are also deposited using the CVD method.
  • an activator component preferably boron or carbon
  • a diffusion-enhancing component are also deposited using the CVD method.
  • Pt, Os, Ru, Rh, Re, Ir or Pd in concentrations of 0.1 to 1% by weight are preferably used as diffusion-promoting or reinforcing constituents for the emitting substance.
  • Tungsten and thorium or Th0 2 are preferably allowed to alternate or simultaneously from WF 6 + H 2 and Th-diketonate, in particular Th-acetylacetonate, preferably Th-trifluoroacetylacetonate or Th-hexafluoroacetylacetonate, but also Th-heptafluorodimethyloctanedione or Th-dipivaloylmethane, at temperatures grow between 400 ° C and 650 ° C by reactive deposition from the gas phase, the organometallic Th starting compound being in powder form in a saturator which is heated to a temperature close to the respective melting point and by an inert gas, in particular argon, as Carrier gas is flowed through.
  • Th-acetylacetonate preferably Th-trifluoroacetylacetonate or Th-hexafluoroacetylacetonate, but also Th-heptafluorodimethyloctanedi
  • the layer structure of Nachêts Kunststoffs is typically formed such that the layer thicknesses of the base material layers is about 1 to 10 / um and that of the emissive material about 0.1 to 1 / um, respectively.
  • 100 of Nachêts Kunststoff with emissive material in the form of a layer sequence by CVD method on a structure-stabilized doped CVD carrier layer of 30 to 300 / um thickness to thickness is applied, in which one layer alternates from high-melting metal with small admixtures of electron-emissive material and optionally stabilizing doping with one with high concentrations of electron-emissive material, which is somewhat thinner, the layer spacings being of the order of the grain sizes.
  • the individual layer thickness is 0.5 to 10 / ⁇ m at a concentration of the emitting substance of up to 5% by weight and 0.1 to 2 / ⁇ m at a concentration of the emitting substance of 5 to 50% by weight.
  • the average concentration of emissive substance is preferably 15 to 20% by weight.
  • the grain size increases too much due to recrystallization during operation of the cathode, this finally causes a drop in the emission current and thus a shorter service life due to the decrease in the monoatomic coverage.
  • the same stability requirement also applies to the texture, ie the preferred orientation set on the surface must be maintained.
  • This recrystallization is prevented analogously to the mechanical stabilization of the support layer by adding a substance which is insoluble in the crystal lattice of the cover layer material and which is simultaneously separated from the gas phase.
  • doping with Th, Th0 2 , Zr, Zr0 2 , U0 2 , Y, Sc, Y 2 0 3 , Sc 2 0 3 and Ru are suitable because of their low solubility in tungsten. If one assumes a working temperature of 2000 K (ie the melting point of the doping must be higher) and demands easy handling, Th0 2 , Zr0 2 , Y 2 0 3 , Sc 2 O 3 and Ru remain as preferred CVD doping.
  • the doping can in particular also be identical to the emitting substance if Th, Y or Sc form the emitter monolayer.
  • the prevention of crystallite growth also means a stabilization of the texture, which in the majority of cases is destroyed without doping in the activation phase of the cathode.
  • the destruction of the texture at higher operating temperatures is probably caused in pure materials by the fact that minority crystallites grow strongly at the expense of the preference-oriented majority, or that crystallite growth starts from the unoriented base.
  • cathodes with a preferred cover layer - which also means a higher emission than conventional cathodes - can be produced, which also have a correspondingly long service life.
  • the preferred oriented cover layer ensures a very low electron work function from the surface dipole layer and also thanks to its fine crystalline structure for good coverage with the monoatomic emitter film. It is also texture stabilized by low insoluble doping.
  • an inner coating of a suitable hollow body can also be carried out.
  • the layers are applied in reverse order, i.e. one separates the preferred oriented cover layer first, then the subsequent delivery zone and finally the mechanically stable load-bearing base, i.e. the carrier layer.
  • the finished cathode body is finally provided with power supplies for direct heating.
  • the advantages of the invention are that large-area thermionic cathodes with high emission currents, stable high-frequency behavior and freely selectable geometric shape and long service life are available, which are suitable for automated large-scale production with low manufacturing costs without the many time-consuming process steps as with mesh cathodes.
  • CVD process the complex and difficult mechanical processing of the known high-melting and very hard cathode materials, for example tungsten, is avoided and at the same time an almost arbitrary layer structure can be produced.
  • the layer structure is applied in such a way that the three layers ⁇ , ⁇ and y mentioned above are identical. This ensures that a single layer takes over the functions of the layers ⁇ , ⁇ and y.
  • This single layer has a suitable texture and a high emitter and doping concentration; due to the finely divided doping, it is also texture stabilized, microstructure stabilized and mechanically stable under thermal stress.
  • the cathodes produced according to the invention are distinguished by the combination of a long service life, high emitter concentration and great mechanical stability.
  • a hollow cylinder 1 serving as a base made of pyrolytic graphite with an inner diameter of 12 mm, a length of 95 mm and a wall thickness of approximately 200 ⁇ m is surrounded over its entire length by a heating coil 3 made of tungsten wire and at its ends also made of heat-resistant material Cover plates 2 held.
  • the pyrolytic graphite of the base 1 is layered parallel to the inner surface, i.e. the crystallographic c-axis lies in the direction of the surface normal of the lateral surface.
  • the graphite cylinder can also be heated by direct current passage through the cylinder.
  • the cathode 4 is formed in the CVD process by growing on the inner circumferential surface of the base 1 in the reverse order of the layers of the cathode, i.e. the later surface layer of the cathode is deposited first and finally the later inner support layer of the cathode.
  • the base 1 is heated to a temperature of 550 to 600 ° C, the reaction gases are introduced at a pressure of about 50 mbar.
  • FIG. 2 shows the grown layers of the cathode in a section transverse to the longitudinal axis of the underlay hollow cylinder 1.
  • a fine-crystalline (grain sizes 1 / um and%) Based on the underlay surface in the ⁇ 1,1,1> direction is first placed on the substrate smaller) and deposited with 1% Th0 2 to stabilize the crystal structure W layer 7 in a thickness of 5 / um.
  • the reaction gases WF 6 with a flow rate of 30 to 50 cm 3 / min
  • H 2 with a flow rate of 400 to 500 cm3 / min
  • Ar saturated with thorium acetylacetonate with a flow rate of 100 cm 3 / min as a mixture about 3 passed over the pad for up to 5 minutes.
  • the hydrogen serves as a reducing gas for the metal compounds.
  • the thorium acetylacetonate is in powder form in a saturation vessel, which is kept at a temperature of 160 ° C and is flushed out by the Ar serving as the carrier gas.
  • the reaction gases are mixed in a mixing chamber, which is heated to a temperature of approximately 180 ° C., and passed through a nozzle onto the surface of the substrates.
  • the saturator temperature of 160 ° C must be strictly observed, since below + 150 ° C the Th (AcAc) 4 vapor pressure for one Coating is too low and premature decomposition of this compound already occurs in the saturation vessel at + 170 ° C.
  • the subsequent delivery layer 6 enriched with electron-emissive material is deposited.
  • an argon flow rate of about 85 cm 3 / min is set at flow rates of about 15 cm 3 / min for WF 6 or 150 cm / min for H 2 .
  • a W layer is formed with an admixture of about 20% Th0 2 - possibly with the help of an additional oxidizing gas such as C0 2 .
  • the layer After a deposition time of approximately 100 minutes, the layer reaches a thickness of approximately 40 ⁇ m .
  • a carburization as with conventional thoriated tungsten cathodes is not necessary because enough carbon from Th C 20 B 28 O 8 is already deposited.
  • Another solution also practiced for the subsequent delivery area is to grow Th (Th0 2 ) and W layers alternately, in particular the WF 6 flow rate between 10 and 60 cm 3 / min and the Ar rate between 85 and 30 cm 3 / min changes.
  • the H 2 rate is usually ten times the WF 6 rate and the intervals are 1 min for W and about 5 min for Th layers, which are then about 4 or 1 / um thick.
  • the cathode-supporting member 5 is formed with a layer thickness of about 50 to 100 / um.
  • the initial flow rates are set again, this time at a temperature of 500 ° C, or the parameters of the layer sequence of the subsequent delivery area are switched over in quick succession, the duration of the W intervals being 20 s each and that of the Th intervals being about 1 min is.
  • the uppermost layer nor a pure W layer can then addition of about 10 / um can be deposited.
  • a high-frequency modulation of all flow rates is recommended, in particular, in order to achieve uniformly thick layers within the graphite tube.
  • the substrate and cathode are slowly cooled to room temperature. Due to the different thermal expansion coefficients of both materials, and by the poor adhesion of the tungsten to the pyrolytic graphite, the thoriated tungsten cathode 4 shrinks on cooling to about 500 ° C in diameter by approximately 10 / um stronger than the documents hollow cylinder 1 and separates from it . Because of the gap 10 formed, the tungsten-thorium cathode is pulled out of the underlay cylinder with ease. Since the inner cylinder surface of the base consists of pyrolytic graphite with a very smooth, uniform surface, the outer surface of the finished cathode has a high surface quality without polishing, which is also not influenced by irregularities in the deposited layers.
  • the finished tubular cathode body is cut into several short tube sections perpendicular to its longitudinal axis, e.g. with a laser beam. Each of the sections then forms the cathode of a tube.
  • the top layer 7 is one ⁇ 111> -oriented, polycrystalline W layer with average grain sizes of about 1 to 2 / um. It has a thickness of about 10 / um and is doped with about 1% finely dispersed Th0 2 . Among them is of about 50 / um thick Nachwoods Suite 6, the micrometers of individual layers 9 2 1% thoriated W, with intermediate layers 8 of 0.2 / um with about 20 to 40 mole% Th0 2 and a carbon enrichment of the same order .
  • the high-frequency layer sequence serves to stabilize the grain structure and to preserve grain sizes from 1 to 2 ⁇ m.
  • the intermediate layers mentioned consists consistently of W with 1% ThO 2 .
  • 1% Th0 2 but also 1% Zr0 2 or 1% Sc 2 O 3 is used for mechanical and structural stabilization against thermal stress.
  • All layers 5 to 9 are produced by deposition from the gas phase on a base made of Mo or graphite. The underlay is removed again after the coating.
  • Fig. 3b shows in addition to Fig. 3a again the Th0 2 - and C concentration profile over the cathode cross section.
  • Ar is the carrier gas for thorium acetylacetonate Th (C 5 H 7 0 2 ) 4 , with which it has accumulated after flowing through a saturator which is heated to a temperature of 160 ° C.
  • the other gases that flow through the reactor are H 2 , the flow rate of which is about 10 times higher than that of WF 6 , and N 2 , which serves as a purge gas for an observation window.
  • the substrate temperature is measured using a radiation pyrometer through the observation window measured and kept constant at a value of around 500 ° C.
  • the average pressure in the reactor is in the range from 10 to 100 mbar, preferably 40 mbar.
  • the reactor itself is at a temperature of approximately 180 ° C.
  • Fluorinated thorium acetylacetonate is even more suitable for Th - CVD than T h (C 5 H 7 0 2 ) 4 .
  • Other special organometallic compounds with higher vapor pressure such as Th-dipivaloylmethane or Th-heptafluorodimethyloctanedione, are also suitable.
  • Th0 2 as an emitter material can be replaced without significant changes by rare earth metals, preferably by Ce0 2 , Sm 2 0 3 , E u 2 0 3 , Y 2 O 3 , while Th0 2 or Zr0 2 continues as doping of W for mechanical-thermal stabilization or Sc 2 0 3 can be used.
  • the re-deposition is through Slow reduction of the gas flow from ReF 6 and H 2 ended until after 2 minutes the inflow of these gases has been completely prevented. Simultaneously with this reduction in the gas inflow, the substrate temperature is set to 400 ° C. and Th (BH 4 ) 4 is fed to the substrate with Ar as the carrier gas, the Ar flow rate being approximately 90 cm 3 / min. Th (BH 4 ) 4 is in powder form in a saturator heated to about 190 ° C. The reactor temperature during the deposition should be 2C0 to 210 ° C.
  • pyrolytic decomposition layer Re-7 is deposited on the course of about 40 min a 30 / um thick layer 6 of ThB 4 from.
  • the conclusion is formed by a 100 / um thick layer 5 made of tungsten doped with 1% Th0 2 , which uses the process parameters listed in Example 1 for layers 5 at one time of 25 min at a substrate temperature of 600 ° C; this layer 5 forms the supporting layer of the cathode.
  • the base and cathode are slowly cooled to room temperature, the entire cathode shrinking away from the base 1 and a gap 16 forming, as described in Example 1.
  • Fig. 6 shows a finished cathode according to this embodiment.
  • the cylindrical one manufactured in the CVD system Cathode body 4 is divided into several sections perpendicular to its longitudinal axis with a laser beam.
  • a circular disk 18 of the same diameter made of tungsten or molybdenum is attached to the edge 17 of one of these sections 4 by spot welding.
  • This circular disk carries in its center a pin 19, also made of tungsten or molybdenum, which is used for supplying the heating current and which is aligned in such a way that its longitudinal axis coincides with the cylinder axis.
  • the heating current is dissipated again via the edge 20 of the cylinder jacket 4 facing away from the disk 18.
  • the cathode is etched for about 30 s in a solution of 0.1 1 H 2 0 + 10 g potassium ferricyanide + 10 g potassium hydroxide and the outer layer 15 made of tungsten is thereby removed.
  • the (preferred-oriented) re-layer 7 is also optionally removed.
  • an essentially monoatomic, electron-emitting layer of Th is formed on the surface of the exposed ThB 4 layer (or on the Re layer) by diffusion of the Th.
  • the base is formed by a hollow cylinder made of nickel 21, which is closed off in the direction of flow and which is heated via a central power supply pin and a current discharge via the cylinder jacket, is heated directly or indirectly via a W coil 22 and on the outer surface of which the cylindrical cathode body 4 is deposited.
  • On the base 5 of tungsten is deposited as a first layer, which is doped with 1% Th0 2 and 5 is prepared in Example 1 by the same method as the innermost layer, with in 20 minutes growth time at 600 ° C a 80 / um thick Layer forms.
  • ReF 6 the flow rate of which is increased to the same extent as that of the WF 6 is reduced, until after 2 minutes only ReF 6 in the same amount as before the WF 6 is introduced, with the substrate temperature of 600 at the same time ° C is increased to 800 ° C and the supply of Th (C 5 H 7 O 2 ) 4 saturated Ar carrier gas is stopped.
  • the cathode substrate is heated directly by a central power supply 19 and a lead 20, only Ni is etched away under the emitting cathode jacket, which can be ensured, for example, by an Mo supply pin and an Mo cover plate, which are not attacked during the etching.
  • the Re layer usually remains on the cathode surface.
  • Example 1 The device described in Example 1 is used.
  • a cathode is produced in which the layer 7 extends over the entire cathode body.
  • the pad 1 is heated to 650 ° C; the total pressure in the reaction chamber is 67 mbar.
  • the corresponding flow rates of the supplied gases are 20 cm 3 / min for W g 6 , 150 cm 3 / min for H 2 and 100 cm 3 / min for Ar saturated with Th-diketonate, the saturator being at a temperature just below the melting point of the organometallic Th compound is held.
  • the dopant Th0 2 serves as an emissive substance and at the same time ensures the microstructural and mechanical stabilization of the cathode.
  • the invention thus provides a cathode which has hitherto only had singular advantages in known cathode types unites, whose layer sequence is produced entirely via the gas phase in a single operation with variation of the parameters, which is self-supporting, has a continuous and large surface (without intentionally created holes, such as mesh cathodes) and is therefore suitable as a unipotential cathode and at which, as a result of the substrate detachment after the deposition, avoids the mostly harmful interaction with the substrate.
  • the cantilever design is made possible by simultaneously with deposited structure-stabilizing (insoluble) additives, which additives in a similar form also stabilize the texture of the preferred oriented top layer and make the advantage of high electron emission with a suitably adjusted preferred orientation available even for long lifetimes or operating times.
  • the high emission and long lifespan are also due in particular to the high doping concentration with emissive substance in the subsequent delivery and storage area, which has not previously been possible with powder metallurgy methods for any substrate shape, as well as the finely crystalline structure of the top layer with average grain diameters 9 1 / um, which good subsequent delivery of the emissive substance by grain boundary diffusion to the surface, good monoatomic surface coverage even at higher temperatures and low desorption rates guaranteed.

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Vapour Deposition (AREA)
  • Solid Thermionic Cathode (AREA)
EP82201538A 1981-12-08 1982-12-03 Procédé de fabrication d'une cathode thermoionique et cathode thermoionique fabriqué selon ce procédé Expired EP0081270B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3148441 1981-12-08
DE19813148441 DE3148441A1 (de) 1981-12-08 1981-12-08 Verfahren zur herstellung einer thermionischen kathode

Publications (3)

Publication Number Publication Date
EP0081270A2 true EP0081270A2 (fr) 1983-06-15
EP0081270A3 EP0081270A3 (en) 1984-06-06
EP0081270B1 EP0081270B1 (fr) 1986-12-03

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EP82201538A Expired EP0081270B1 (fr) 1981-12-08 1982-12-03 Procédé de fabrication d'une cathode thermoionique et cathode thermoionique fabriqué selon ce procédé

Country Status (7)

Country Link
US (1) US4533852A (fr)
EP (1) EP0081270B1 (fr)
JP (1) JPS58106735A (fr)
CA (1) CA1211737A (fr)
DE (2) DE3148441A1 (fr)
ES (1) ES517938A0 (fr)
HU (1) HU194646B (fr)

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DE3446334A1 (de) * 1984-12-19 1986-06-19 Philips Patentverwaltung Gmbh, 2000 Hamburg Verfahren zur herstellung von <111>-vorzugsorientiertem wolfram
DE3622614A1 (de) * 1986-07-05 1988-01-14 Philips Patentverwaltung Verfahren zur herstellung von elektrisch leitenden formkoerpern durch plasmaaktivierte chemische abscheidung aus der gasphase
GB2202865A (en) * 1987-03-26 1988-10-05 Plessey Co Plc Thin film deposition process
DE3919724A1 (de) * 1989-06-16 1990-12-20 Philips Patentverwaltung Verfahren zur herstellung von erdalkalimetallhaltigen und/oder erdalkalimetalloxidhaltigen materialien
DE4113085A1 (de) * 1991-04-22 1992-10-29 Philips Patentverwaltung Verfahren zur herstellung eines gluehkathodenelements
DE4305558A1 (de) * 1993-02-24 1994-08-25 Asea Brown Boveri Verfahren zur Herstellung von Drähten, welche insbesondere für Kathoden von Elektronenröhren geeignet sind
US5391523A (en) * 1993-10-27 1995-02-21 Marlor; Richard C. Electric lamp with lead free glass
DE4421793A1 (de) * 1994-06-22 1996-01-04 Siemens Ag Thermionischer Elektronenemitter für eine Elektronenröhre
US6071595A (en) * 1994-10-26 2000-06-06 The United States Of America As Represented By The National Aeronautics And Space Administration Substrate with low secondary emissions
FR2745951B1 (fr) * 1996-03-05 1998-06-05 Thomson Csf Cathode thermoionique et son procede de fabrication
US5856726A (en) * 1996-03-15 1999-01-05 Osram Sylvania Inc. Electric lamp with a threaded electrode
TW398003B (en) * 1998-06-25 2000-07-11 Koninkl Philips Electronics Nv Electron tube comprising a semiconductor cathode
US6815876B1 (en) * 1999-06-23 2004-11-09 Agere Systems Inc. Cathode with improved work function and method for making the same
US6559582B2 (en) * 2000-08-31 2003-05-06 New Japan Radio Co., Ltd. Cathode and process for producing the same
KR20020068644A (ko) * 2001-02-21 2002-08-28 삼성에스디아이 주식회사 금속 음극 및 이를 구비한 방열형 음극구조체
FR2863769B1 (fr) * 2003-12-12 2006-03-24 Ge Med Sys Global Tech Co Llc Procede de fabrication d'un filament de cathode d'un tube a rayons x et tube a rayons x
US7795792B2 (en) * 2006-02-08 2010-09-14 Varian Medical Systems, Inc. Cathode structures for X-ray tubes
DE102008020164A1 (de) * 2008-04-22 2009-10-29 Siemens Aktiengesellschaft Kathode mit einem Flachemitter
US20090284124A1 (en) * 2008-04-22 2009-11-19 Wolfgang Kutschera Cathode composed of materials with different electron works functions
JP2017107816A (ja) * 2015-12-11 2017-06-15 株式会社堀場エステック 熱電子放出用フィラメント、四重極質量分析計、及び残留ガス分析方法
JP7176121B2 (ja) * 2019-08-06 2022-11-21 株式会社東芝 放電ランプ用カソード部品および放電ランプ

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US8183756B2 (en) 2007-07-24 2012-05-22 Koninklijke Philips Electronics Nv Thermionic electron emitter, method for preparing same and X-ray source including same

Also Published As

Publication number Publication date
CA1211737A (fr) 1986-09-23
ES8308449A1 (es) 1983-08-16
DE3148441A1 (de) 1983-07-21
JPS58106735A (ja) 1983-06-25
EP0081270B1 (fr) 1986-12-03
DE3274598D1 (en) 1987-01-15
HU194646B (en) 1988-02-29
EP0081270A3 (en) 1984-06-06
ES517938A0 (es) 1983-08-16
JPH0354415B2 (fr) 1991-08-20
US4533852A (en) 1985-08-06

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