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EP0421521B1 - X-ray tube anode with oxide layer - Google Patents

X-ray tube anode with oxide layer Download PDF

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Publication number
EP0421521B1
EP0421521B1 EP90202558A EP90202558A EP0421521B1 EP 0421521 B1 EP0421521 B1 EP 0421521B1 EP 90202558 A EP90202558 A EP 90202558A EP 90202558 A EP90202558 A EP 90202558A EP 0421521 B1 EP0421521 B1 EP 0421521B1
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EP
European Patent Office
Prior art keywords
oxide
weight
coating
ray anode
ray
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EP90202558A
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German (de)
French (fr)
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EP0421521A3 (en
EP0421521A2 (en
Inventor
Wolfgang Hohenauer
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Metallwerk Plansee GmbH
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Metallwerk Plansee GmbH
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • H01J35/08—Anodes; Anti cathodes
    • H01J35/10—Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes
    • H01J35/105—Cooling of rotating anodes, e.g. heat emitting layers or structures

Definitions

  • the invention relates to an X-ray anode, in particular a rotating anode, with high heat emissivity, with a base body made of refractory metal or its alloys and a focal spot or focal path region made of refractory metal which may differ from the base body, the X-ray anode at least on parts of the surface outside the focal path essentially has the metals titanium, zirconium and optionally aluminum-containing oxidic coating.
  • X-ray tube anodes only emit a fraction of the radiated energy in the form of X-rays. The rest is transferred to heat and has to leave the anode in the form of heat radiation. It has therefore been known for many years to improve the heat emissivity of X-ray anodes from refractory metals by means of an oxidic coating (AT-A-337 314, DE-A-22 01 979, DE-A-24 43 354). These prior publications claim to increase the adhesion of the oxide layer on the surface of the base metal compared to the prior art by means of different oxide materials and production processes and to increase the thermal emissivity of the anode surface. It has been shown that the performance of layers produced in this way is limited in view of the continuously increasing requirements for X-ray anodes with regard to layer aging, heat radiation capability and the resistance to degassing (avoidance of electrical flashovers).
  • EP-A-0 172 491 describes in a further development an X-ray anode made of a molybdenum alloy with an oxide coating from a mixture of 40% - 70% titanium oxide, the rest of the stabilizing oxides from the group ZrO2, HfO, MgO, CeO2, La2O3 and SrO.
  • this prior publication has in particular the task of melting the oxides into smooth, shiny, shimmering layers by means of economical processes.
  • EP-A-0 244 776 relates essentially to the same subject matter of the invention.
  • the invention relates to the pretreatment of the oxidic material before application to the X-ray anode by means of conventional spraying techniques.
  • a mixture of 77% - 85% titanium dioxide with 15 - 23% by weight calcium oxide is processed in a first process step to a powder with a homogeneous phase and then optionally mixed with other oxide powders by known spraying methods.
  • Plasma spraying, sputtering processes, chemical and physical deposition processes from the gas phase or also the electron beam process are mentioned as coating processes for the oxide coating on the X-ray anodes made of refractory metals.
  • An X-ray anode made of refractory metal is usually subjected to a degassing annealing at the end of the manufacturing process.
  • the degassing annealing of the anode serves to avoid gas leaks and consequently highly undesirable flashovers between the electrodes when they are used in an X-ray tube in a high vacuum.
  • the inventive teaching of this prior publication includes an advantageous coordination of the material composition of the oxide layer with regard to the annealing treatment after the coating of the X-ray anodes.
  • These degassing anneals simultaneously serve for the final formation and melting of the oxide phase, ie the conversion into a state which cannot be achieved by an oxide application process such as the plasma spraying process alone.
  • the layer composition according to the prior publication and the processes for their production do not meet the requirements sufficiently. Rather, when annealing the oxide layers according to this prior publication, there is the risk that at an annealing temperature at which the oxides melt into smooth, well-adhering layers, they are already so thin that the contour between coated and uncoated parts of the X-ray anode surface is undesirable in Area of the focal track disappears to an intolerable extent. In addition, such oxide layers have an annoying gas phase formation at the required annealing temperatures.
  • the object of the present invention is therefore to give the oxide surface layer such a composition that, when it is produced by customary application processes, including annealing treatment, on the one hand, the good adhesion properties between the oxide layer and the substrate which have been achieved to date, and the good thermal emissivity properties of the layer, are at least maintained if not be surpassed.
  • the structural structure and the composition of the oxide layer should allow easier technical handling in the production of the layer, in particular with regard to smooth melting without annoying evaporation and undesirable flow of the oxide during the annealing treatment of the X-ray anode.
  • the object is achieved in that the oxidic coating on the X-ray anode contains 1 to 20% by weight of silicon oxide and is a homogeneously melted phase.
  • the oxide layer according to the invention applied to an X-ray anode made of high-melting metals has excellent adhesion, smooth surfaces and a high thermal heat coefficient ⁇ ⁇ 0.80.
  • the oxidic layer has the decisive advantage over the prior art that it is less liquid under otherwise comparable conditions during the required annealing treatment of the anode. ie the melt toughness is higher in comparison with similar oxide layers without the addition of silicon oxide when melting during the annealing treatment.
  • the contours between surface parts with and without oxide coating do not melt. There is only a comparatively small amount of evaporation and undesirable precipitation of oxide components on uncoated surface parts during the annealing process.
  • layers with a desired surface roughness of approx. 20 ⁇ m (R T ) and the appearance of an orange peel can be achieved.
  • X-ray rotary anodes are currently usually made from the refractory metals tungsten, molybdenum or molybdenum alloys, in particular the carbon-containing alloy TZM.
  • the oxidic coating has the previously preferred oxide components zirconium oxide, calcium oxide and / or titanium oxide, for example in a ratio of 70: 10: 20.
  • the calcium oxide can be partially or completely replaced by other stabilizing oxides known for such applications and can also be supplemented by small proportions of other, thermally stable compounds, such as borides and / or nitrides.
  • the aforementioned oxide mixture can contain up to 10% by weight of aluminum oxide, primarily for reducing or controlling the melting temperature.
  • the remainder of the composition of the oxidic coating is, according to the invention, silicon oxide with a weight fraction of 1-20%, preferably 4-7%.
  • the thickness of the oxide layer can vary between a few and a few thousand micrometers depending on the deposition process.
  • PVD and CVD processes in particular plasma CVD processes and sputtering processes, as well as flame spraying, plasma spraying and electron beam processes have proven themselves as deposition processes.
  • a homogeneous phase is to be understood as a finely divided oxide mixture in the oxidic coating.
  • the desired oxide layer structure and surface roughness can be achieved with good adhesion between the layer and the base material by means of annealing at temperatures between 1550 ° C and 1680 ° C and a glow time between 30 minutes and 1.5 hours achieve advantageous.
  • the evaporation of oxide components begins to become noticeable at temperatures above approx. 1550 ° C. In the worst cases, it is therefore advisable to cover the focal path area during the glow treatment or to carry out a final cleaning, for example also grinding treatment of the focal path after the glow treatment.
  • the molybdenum alloy TZM with low carbon content tends to release carbon at temperatures above 1550 ° C.
  • the released carbon forms volatile CO or CO2 with the oxygen components of the oxide in the oxide layer and results in premature aging of the layer.
  • An X-ray rotating anode consisting of the alloy Mo 5% by weight W has an approx. 2 mm thick W-Re layer in the focal path area.
  • this anode surface is provided with an oxide layer according to the invention.
  • a completely sintered and mechanically shaped X-ray anode on the back of the anode to be coated is cleaned and roughened by means of sandblasting and, if possible, subsequently coated under the usual process conditions by means of plasma spraying of oxide powder.
  • the applied oxide powder has the following composition: 89% by weight of an oxide mixture of 72% by weight ZrO2, 8% by weight CaO, 20% by weight TiO2, further 5% by weight Al2O3 and 6% by weight Si-O2.
  • the rotating anode coated in this way must be subjected to an annealing treatment in order to make it usable for use in X-ray tubes.
  • the rotating anode both the base material and the layer material, is largely freed of gas inclusions and of contaminants which are volatile at higher temperatures, in order to prevent electrical flashovers as a result of the release of gas inclusions when the rotating anode is later used in the high-vacuum X-ray tube.
  • the degassing annealing takes place within a narrow temperature and time range, matched to the anode base material, in order to avoid undesired structural changes in the base material.
  • the applied layer must also be treated within a very specific temperature and time range in order to achieve melting in the desired homogeneous phase and with a slightly nubbed surface structure (orange peel layer).
  • the annealing is carried out at 1620 ° C. for 65 minutes.
  • the melted layer has the desired degree of blackening and the desired surface structure (orange peel).
  • There is no uncontrolled flow of the melting oxide layer especially not in the transition area between coated and uncoated parts of the rotating anode surface. Insofar as gaseous oxides evaporate from the layer surface during the annealing process, these do not form a disturbing layer coating in the originally uncoated focal path area of the rotating anode.
  • the rotating anode was then tested in an X-ray tube arrangement under practical conditions. It ran there for several days without any problems within the required limit load.
  • An X-ray rotating anode consisting of the alloy TZM, has an approx. 2 mm thick W / Re layer in the focal path area. To increase the heat radiation capability, this anode surface is provided with an oxide layer according to the invention.
  • a completely sintered and mechanically shaped X-ray anode is cleaned and roughened by means of sandblasting and, if possible, coated immediately afterwards under the usual process conditions by means of plasma spraying outside the focal path area.
  • a molybdenum layer acting as a carbon barrier is applied and subjected to a reduction annealing in hydrogen at 1350 ° C. for 2 hours.
  • a first oxide coating based on aluminum oxide-titanium oxide It is only this oxide layer that enables the blackening oxidic coating to be melted in the required quality.
  • the final oxidic coating has the composition: 94% by weight of an oxide mixture of 72% zirconium oxide, 8% calcium oxide, 20% titanium oxide, and also 6% silicon oxide.
  • the rotating anode coated in this way must be subjected to an annealing treatment in accordance with Example 1.
  • Example 1 The rotating anode was then tested according to Example 1 in an X-ray tube test arrangement under practical conditions. There it ran trouble-free within the required limit load.

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  • Coating By Spraying Or Casting (AREA)

Description

Die Erfindung betrifft eine Röntgenanode, insbesondere Drehanode, hoher Wärmeemissivität, mit einem Grundkörper aus hochschmelzendem Metall oder dessen Legierungen sowie einem Brennfleck- bzw. Brennbahnbereich aus ggf. vom Grundkörper verschiedenem hochschmelzenden Metall, wobei die Röntgenanode zumindest auf Teilen der Oberfläche außerhalb der Brennbahn einen im wesentlichen die Metalle Titan, Zirkonium und Wahlweise Aluminium aufweisenden oxidischen Überzug besitzt.The invention relates to an X-ray anode, in particular a rotating anode, with high heat emissivity, with a base body made of refractory metal or its alloys and a focal spot or focal path region made of refractory metal which may differ from the base body, the X-ray anode at least on parts of the surface outside the focal path essentially has the metals titanium, zirconium and optionally aluminum-containing oxidic coating.

Röntgenröhrenanoden senden nur einen Bruchteil der eingestrahlten Energie in Form von Röntgenstrahlung aus. Der Rest wird in Wärme überführt und muß die Anode in Form von Wärmestrahlung verlassen.
Es ist daher seit vielen Jahren bekannt, die Wärmeemissivität von Röntgenanoden aus hochschmelzenden Metallen mittels eines oxidischen Überzuges zu verbessern (AT-A-337 314, DE-A-22 01 979, DE-A-24 43 354). Diese Vorveröffentlichungen nehmen für sich in Anspruch, mittels unterschiedlicher Oxidwerkstoffe und Fertigungsverfahren die Haftung der Oxidschicht auf der Oberfläche des Grundmetalles gegenüber dem Stand der Technik zu erhöhen und die thermische Emissivität der Anodenoberfläche zu steigern.
Dabei hat sich gezeigt, daß die Leistungsfähigkeit derart hergestellter Schichten angesichts der laufend zunehmenden Anforderungen an Röntgenanoden hinsichtlich Schichtalterung, Wärmeabstrahlfähigkeit sowie die Beständigkeit gegen Entgasung (Vermeidung elektrischer Überschläge) begrenzt ist.X-ray tube anodes only emit a fraction of the radiated energy in the form of X-rays. The rest is transferred to heat and has to leave the anode in the form of heat radiation.
It has therefore been known for many years to improve the heat emissivity of X-ray anodes from refractory metals by means of an oxidic coating (AT-A-337 314, DE-A-22 01 979, DE-A-24 43 354). These prior publications claim to increase the adhesion of the oxide layer on the surface of the base metal compared to the prior art by means of different oxide materials and production processes and to increase the thermal emissivity of the anode surface.
It has been shown that the performance of layers produced in this way is limited in view of the continuously increasing requirements for X-ray anodes with regard to layer aging, heat radiation capability and the resistance to degassing (avoidance of electrical flashovers).

Die EP-A-0 172 491 beschreibt in einer Weiterentwicklung eine Röntgenanode aus einer Molybdänlegierung mit einem Oxidüberzug aus einer Mischung von 40 % - 70 % Titanoxid, der Rest stabilisierende Oxide aus der Gruppe ZrO₂, HfO, MgO, CeO₂, La₂O₃ und SrO. Zur besseren Realisierung der obengenannten Anforderungen an derartige Schichten stellt sich diese Vorveröffentlichung insbesondere die Aufgabe der Aufschmelzung der Oxide zu glatten, glänzend schimmernden Schichten mittels wirtschaftlicher Verfahren.EP-A-0 172 491 describes in a further development an X-ray anode made of a molybdenum alloy with an oxide coating from a mixture of 40% - 70% titanium oxide, the rest of the stabilizing oxides from the group ZrO₂, HfO, MgO, CeO₂, La₂O₃ and SrO. In order to better meet the above-mentioned requirements for such layers, this prior publication has in particular the task of melting the oxides into smooth, shiny, shimmering layers by means of economical processes.

Die EP-A-0 244 776 betrifft im wesentlichen den gleichen Erfindungsgegenstand. Die Erfindung zieht sich auf die Vorbehandlung des oxidischen Materials vor der Auftragung auf die Röntgenanode mittels üblicher Spritztechniken. Dabei wird eine Mischung aus 77 % - 85 % Titandioxid mit 15 - 23 Gew.% Calciumoxid in einem ersten Verfahrensschritt zu einem Pulver mit homogener Phase verarbeitet und dann ggf. in Mischung mit anderen Oxidpulvern nach bekannten Spritzverfahren aufgetragen. Als Beschichtungsprozesse für die Oxidbeschichtung auf den Röntgenanoden aus hochschmelzenden Metallen werden Plasmaspritzen, Sputteringverfahren, chemische und physikalische Abscheideverfahren aus der Gasphase oder auch das Elektronenstrahlverfahren genannt. Üblicherweise wird eine Röntgenanode aus hochschmelzendem Metall zum Abschluß des Herstellungsprozesses einer Entgasungsglühung unterzogen. Die Entgasungsglühung der Anode dient der Vermeidung von Gasaustritten und in deren Folge von höchst unerwünschten Plasma-Überschlägen zwischen den Elektroden beim Einsatz derselben in einer Röntgenröhre im Hochvakuum.
Die erfinderische Lehre dieser Vorveröffentlichung beinhaltet eine vorteilhafte Abstimmung der Materialzusammensetzung der Oxidschicht im Hinblick auf die Glühbehandlung nach der Beschichtung der Röntgenanoden. Diese Entgasungsglühungen dienen gleichzeitig der endgültigen Formation und Aufschmelzung der Oxidphase, d.h. der Umwandlung in einen Zustand, der alleine durch ein Oxidauftrageverfahren, wie das Plasmaspritzverfahren, nicht erreichbar ist. Die Schichtzusammensetzung gemäß Vorveröffentlichung und die Verfahren zu ihrer Herstellung werden jedoch den gestellten Anforderungen nur ungenügend gerecht. Vielmehr besteht beim Glühen der Oxidschichten nach dieser Vorveröffentlichung die Gefahr, daß bei einer Glühtemperatur, bei der die Oxide zu glatten, guthaftenden Schichten aufschmelzen, diese bereits so dünnflüssig sind, daß die Kontur zwischen beschichteten und unbeschichteten Teilen der Röntgenanoden-Oberfläche in unerwünschtem, im Bereich der Brennbahn nicht tolerierbarem Ausmaße verfließt.
Zudem weisen derartige Oxidschichten bei den erforderlichen Glühtemperaturen eine störende Gasphasenbildung auf.EP-A-0 244 776 relates essentially to the same subject matter of the invention. The invention relates to the pretreatment of the oxidic material before application to the X-ray anode by means of conventional spraying techniques. A mixture of 77% - 85% titanium dioxide with 15 - 23% by weight calcium oxide is processed in a first process step to a powder with a homogeneous phase and then optionally mixed with other oxide powders by known spraying methods. Plasma spraying, sputtering processes, chemical and physical deposition processes from the gas phase or also the electron beam process are mentioned as coating processes for the oxide coating on the X-ray anodes made of refractory metals. An X-ray anode made of refractory metal is usually subjected to a degassing annealing at the end of the manufacturing process. The degassing annealing of the anode serves to avoid gas leaks and consequently highly undesirable flashovers between the electrodes when they are used in an X-ray tube in a high vacuum.
The inventive teaching of this prior publication includes an advantageous coordination of the material composition of the oxide layer with regard to the annealing treatment after the coating of the X-ray anodes. These degassing anneals simultaneously serve for the final formation and melting of the oxide phase, ie the conversion into a state which cannot be achieved by an oxide application process such as the plasma spraying process alone. The layer composition according to the prior publication and the processes for their production, however, do not meet the requirements sufficiently. Rather, when annealing the oxide layers according to this prior publication, there is the risk that at an annealing temperature at which the oxides melt into smooth, well-adhering layers, they are already so thin that the contour between coated and uncoated parts of the X-ray anode surface is undesirable in Area of the focal track disappears to an intolerable extent.
In addition, such oxide layers have an annoying gas phase formation at the required annealing temperatures.

Die Aufgabe vorliegender Erfindung besteht demnach darin, der oxidischen Oberflächenschicht eine solche Zusammensetzung zu geben, daß bei seiner Herstellung nach gebräuchlichen Auftrageverfahren, einschließlich der Glühbehandlung, einerseits die bisher erzielbaren guten Haftungseigenschaften zwischen Oxidschicht und Substrat sowie die guten thermischen Emissivitätseigenschaften der Schicht zumindest beibehalten, wenn nicht übertroffen werden. Daneben soll der strukturelle Aufbau und die Zusammensetzung der Oxidschicht eine einfachere technische Handhabung bei der Schichtherstellung erlauben, insbesondere hinsichtlich einer glatten Aufschmelzung ohne störendes Abdampfen und unerwünschtes Fließen des Oxides während der Glühbehandlung der Röntgenanode.The object of the present invention is therefore to give the oxide surface layer such a composition that, when it is produced by customary application processes, including annealing treatment, on the one hand, the good adhesion properties between the oxide layer and the substrate which have been achieved to date, and the good thermal emissivity properties of the layer, are at least maintained if not be surpassed. In addition, the structural structure and the composition of the oxide layer should allow easier technical handling in the production of the layer, in particular with regard to smooth melting without annoying evaporation and undesirable flow of the oxide during the annealing treatment of the X-ray anode.

Die Aufgabe wird erfindungsgemäß dadurch gelöst, daß der oxidische Überzug auf der Röntgenanode 1 - 20 Gew.% Siliziumoxid enthält und eine homogen aufgeschmolzene Phase ist.The object is achieved in that the oxidic coating on the X-ray anode contains 1 to 20% by weight of silicon oxide and is a homogeneously melted phase.

Die Oxidschicht gemäß Erfindung auf eine Röntgenanode aus hochschmelzenden Metallen aufgetragen weist hervorragend Haftung, glatte Oberflächen und einen hohen thermischen Wärmekoeffizient ε ≈ 0,80 auf. Die oxidische Schicht hat gegenüber dem Stand der Technik jedoch den entscheidenden Vorteil, daß sie bei sonst vergleichbaren Bedingungen während der erforderlichen Glühbehandlung der Anode weniger flüssig ist, d. h. die Schmelzzähigkeit ist im Vergleich mit gleichartigen Oxidschichten ohne den Siliziumoxidzusatz beim Aufschmelzen während der Glühbehandlung höher. Die Konturen zwischen Oberflächenteilen mit und ohne Oxidbeschichtung verfließen nicht. Es kommt nur in vergleichsweise geringem Ausmaß zur Abdampfung und zum unerwünschten Niederschlag von Oxidanteilen auf nicht beschichteten Oberflächenteilen während des Glühvorganges. Mittels Abstimmung von Oxidzusammensetzung und Temperatur der Glühbehandlung lassen sich Schichten mit einer angestrebten Oberflächenrauhigkeit von ca. 20µm (RT) und dem Aussehen einer Orangenhaut erzielen.The oxide layer according to the invention applied to an X-ray anode made of high-melting metals has excellent adhesion, smooth surfaces and a high thermal heat coefficient ε ≈ 0.80. However, the oxidic layer has the decisive advantage over the prior art that it is less liquid under otherwise comparable conditions during the required annealing treatment of the anode. ie the melt toughness is higher in comparison with similar oxide layers without the addition of silicon oxide when melting during the annealing treatment. The contours between surface parts with and without oxide coating do not melt. There is only a comparatively small amount of evaporation and undesirable precipitation of oxide components on uncoated surface parts during the annealing process. By matching the oxide composition and the temperature of the annealing treatment, layers with a desired surface roughness of approx. 20µm (R T ) and the appearance of an orange peel can be achieved.

Röntgendrehanoden werden heute üblicherweise aus den hochschmelzenden Metallen Wolfram, Molybdän oder Molybdänlegierungen, insbesondere der kohlenstoffhaltigen Legierung TZM, hergestellt.X-ray rotary anodes are currently usually made from the refractory metals tungsten, molybdenum or molybdenum alloys, in particular the carbon-containing alloy TZM.

Der oxidische Überzug weist einmal die schon bisher bevorzugten Oxidkomponenten Zirkonoxid, Calciumoxid und/oder Titanoxid, beispielsweise im Verhältnis 70 : 10 : 20 auf. Das Calciumoxid kann durch andere für derartige Anwendungen bekannte stabilisierende Oxide teilweise oder ganz ersetzt und weiters um geringe Anteile anderer, thermisch stabiler Verbindungen, wie Boride und/oder Nitride ergänzt werden. Daneben kann das vorgenannte Oxidgemisch bis zu 10 Gew.% Aluminiumoxid-Anteile vornehmlich zur Herabsetzung bzw. Steuerung der Aufschmelztemperatur enthalten.
Der restliche Anteil an der Zusammensetzung des oxidischen Überzuges ist erfindungsgemäß Siliziumoxid mit einem Gewichtsanteil von 1 - 20 %, vorzugsweise 4 - 7 %.
Die Dicke der Oxidschicht kann je nach Abscheideverfahren zwischen einigen wenigen und einigen tausend Mikrometern variieren.The oxidic coating has the previously preferred oxide components zirconium oxide, calcium oxide and / or titanium oxide, for example in a ratio of 70: 10: 20. The calcium oxide can be partially or completely replaced by other stabilizing oxides known for such applications and can also be supplemented by small proportions of other, thermally stable compounds, such as borides and / or nitrides. In addition, the aforementioned oxide mixture can contain up to 10% by weight of aluminum oxide, primarily for reducing or controlling the melting temperature.
The remainder of the composition of the oxidic coating is, according to the invention, silicon oxide with a weight fraction of 1-20%, preferably 4-7%.
The thickness of the oxide layer can vary between a few and a few thousand micrometers depending on the deposition process.

Als Abscheideverfahren haben sich die bekannten PVD- und CVD-Verfahren, insbesondere Plasma-CVD-Verfahren und Sputterverfahren ebenso bewährt wie Flammspritz-, Plasmaspritz- und Elektronenstrahlverfahren. Unter homogener Phase ist bei dem oxidischen Überzug ein feinverteiltes Oxidgemisch zu verstehen.The known PVD and CVD processes, in particular plasma CVD processes and sputtering processes, as well as flame spraying, plasma spraying and electron beam processes have proven themselves as deposition processes. A homogeneous phase is to be understood as a finely divided oxide mixture in the oxidic coating.

Bei Röntgenanoden aus Molybdän und üblichen Molybdänlegierungen, wie TZM, läßt sich die gewünschte Oxidschichtstruktur und Oberflächenrauhigkeit bei gleichzeitig bleibend guter Haftung zwischen Schicht und Grundmaterial mittels Glühungen bei Temperaturen zwischen 1550°C und 1680°C sowie einer Glühzeit zwischen 30 Minuten und 1,5 Stunden vorteilhaft erreichen. Die Abdampfung von Oxidanteilen beginnt bei Temperaturen oberhalb ca. 1550°C praktisch bemerkbar zu werden. In ungünstigsten Fällen ist daher eine Abdeckung des Brennbahnbereiches während der Glühbehandlung oder eine abschließende Reinigungs-, beispielsweise auch Schleifbehandlung der Brennbahn im Anschluß an die Glühbehandlung empfehlenswert.With X-ray anodes made of molybdenum and conventional molybdenum alloys, such as TZM, the desired oxide layer structure and surface roughness can be achieved with good adhesion between the layer and the base material by means of annealing at temperatures between 1550 ° C and 1680 ° C and a glow time between 30 minutes and 1.5 hours achieve advantageous. The evaporation of oxide components begins to become noticeable at temperatures above approx. 1550 ° C. In the worst cases, it is therefore advisable to cover the focal path area during the glow treatment or to carry out a final cleaning, for example also grinding treatment of the focal path after the glow treatment.

Die Molybdänlegierung TZM mit geringen Kohlenstoffanteilen neigt zur Kohlenstoff-Freisetzung bei Temperaturen oberhalb 1550°C. Der freigesetzte Kohlenstoff bildet mit den Sauerstoff-Komponenten des Oxids in der Oxidschicht flüchtiges CO bzw. CO₂ und hat eine vorzeitige Alterung der Schicht zur Folge. Es ist daher bei der Verwendung von TZM als Grundmaterial in einzelnen Ausgestaltungen der Erfindung vorteilhaft, zwischen Grundmaterial und Oxidschicht eine Diffusionsbarriere einer Schichtdicke von wenigen Mikrometern bis in den Bereich von Millimetern aus reinem Molybdän bzw. aus einem Mo / Oxid Verbundmaterial einzubringen.The molybdenum alloy TZM with low carbon content tends to release carbon at temperatures above 1550 ° C. The released carbon forms volatile CO or CO₂ with the oxygen components of the oxide in the oxide layer and results in premature aging of the layer. When using TZM as the base material in individual embodiments of the invention, it is therefore advantageous to introduce a diffusion barrier with a layer thickness of a few micrometers to a range of millimeters from pure molybdenum or from a Mo / oxide composite material between base material and oxide layer.

Die Erfindung wird anhand der nachfolgenden Ausführungsbeispiele näher erläutert.The invention is explained in more detail using the following exemplary embodiments.

Beispiel 1example 1

Eine Röntgendrehanode, bestehend aus der Legierung Mo 5 Gew.% W besitzt im Brennbahnbereich eine ca. 2 mm dicke W-Re-Schicht. Zur Erhöhung der Wärmeabstrahlfähigkeit wird diese Anodenoberfläche mit einer Oxidschicht gemäß Erfindung versehen.
Dazu wird eine fertig gesinterte und mechanisch umgeformte Röntgenanode auf der zu beschichtenden Anoden-Rückseite mittels Sandstrahlen gereinigt und aufgerauht und möglichst gleich anschließend unter den üblichen Verfahrensbedingungen mittels Plasmaspritzens von Oxidpulver beschichtet. Das aufgetragene Oxidpulver weist folgende Zusammensetzung auf: 89 Gew.% einer Oxidmischung aus 72 Gew.% ZrO₂, 8 Gew.% CaO, 20 Gew.% TiO₂, ferner 5 Gew.% Al₂O₃ und 6 Gew.% Si-O₂.
Die so beschichtete Drehanode muß einer Glühbehandlung unterworfen werden, um sie für den Einsatz in Röntgenröhren brauchbar zu machen. Durch die Glühung wird die Drehanode, und zwar sowohl das Grundmaterial als auch das Schichtmaterial von Gaseinschlüssen sowie von bei höheren Temperaturen flüchtigen Verunreinigungen weitgehend befreit, um beim späteren Einsatz der Drehanode in der Hochvakuum-Röntgenröhre elektrische Überschläge als Folge der Freisetzung von Gaseinschlüssen auszuschalten. Die Entgasungsglühung erfolgt, abgestimmt auf das Anoden-Grundmaterial, innerhalb eines engen Temperatur- und Zeitbereiches, um unerwünschte Strukturänderungen des Grundmaterials zu vermeiden. Andererseits muß die aufgetragene Schicht in Abhängigkeit von deren Zusammensetzung ebenfalls innerhalb eines sehr spezifischen Temperatur- und Zeitbereiches behandelt werden, um ein Aufschmelzen in der gewünschten homogenen Phase und mit einer leicht genoppten Oberflächenstruktur (Orangenhautschicht) zu erzielen.An X-ray rotating anode consisting of the alloy Mo 5% by weight W has an approx. 2 mm thick W-Re layer in the focal path area. To increase the heat radiation capability, this anode surface is provided with an oxide layer according to the invention.
For this purpose, a completely sintered and mechanically shaped X-ray anode on the back of the anode to be coated is cleaned and roughened by means of sandblasting and, if possible, subsequently coated under the usual process conditions by means of plasma spraying of oxide powder. The applied oxide powder has the following composition: 89% by weight of an oxide mixture of 72% by weight ZrO₂, 8% by weight CaO, 20% by weight TiO₂, further 5% by weight Al₂O₃ and 6% by weight Si-O₂.
The rotating anode coated in this way must be subjected to an annealing treatment in order to make it usable for use in X-ray tubes. As a result of the annealing, the rotating anode, both the base material and the layer material, is largely freed of gas inclusions and of contaminants which are volatile at higher temperatures, in order to prevent electrical flashovers as a result of the release of gas inclusions when the rotating anode is later used in the high-vacuum X-ray tube. The degassing annealing takes place within a narrow temperature and time range, matched to the anode base material, in order to avoid undesired structural changes in the base material. On the other hand, depending on its composition, the applied layer must also be treated within a very specific temperature and time range in order to achieve melting in the desired homogeneous phase and with a slightly nubbed surface structure (orange peel layer).

Die Glühung erfolgt im vorliegenden Fall bei 1620°C während 65 Minuten. Die aufgeschmolzene Schicht weist den gewünschten Schwärzungsgrad sowie die angestrebte Oberflächenstruktur (Orangenhaut) auf. Es kommt zu keinem unkontrollierten Fließen der aufschmelzenden Oxidschicht, insbesondere nicht im Übergangsbereich zwischen beschichteten und unbeschichteten Teilen der Drehanodenoberfläche. Soweit während des Glühvorganges gasförmige Oxide von der Schichtoberfläche abdampfen, schlagen sich diese nicht als störender Schichtbelag im ursprünglich nicht beschichteten Brennbahnbereich der Drehanode nieder.In the present case, the annealing is carried out at 1620 ° C. for 65 minutes. The melted layer has the desired degree of blackening and the desired surface structure (orange peel). There is no uncontrolled flow of the melting oxide layer, especially not in the transition area between coated and uncoated parts of the rotating anode surface. Insofar as gaseous oxides evaporate from the layer surface during the annealing process, these do not form a disturbing layer coating in the originally uncoated focal path area of the rotating anode.

Die Drehanode wurde anschließend in einer Röntgenröhren-Versuchsanordnung unter praxisnahen Bedingungen erprobt. Sie lief dort über mehrere Tage störungsfrei innerhalb der geforderten Grenzbelastung.The rotating anode was then tested in an X-ray tube arrangement under practical conditions. It ran there for several days without any problems within the required limit load.

Beispiel 2Example 2 TZM Anode mit Kohlenstoff-BarriereTZM anode with carbon barrier

Eine Röntgendrehanode, bestehend aus der Legierung TZM besitzt im Brennbahnbereich eine ca. 2 mm dicke W/Re-Schicht. Zur Erhöhung der Wärmeabstrahlfähigkeit wird diese Anodenoberfläche mit einer Oxidschicht gemäß Erfindung versehen.An X-ray rotating anode, consisting of the alloy TZM, has an approx. 2 mm thick W / Re layer in the focal path area. To increase the heat radiation capability, this anode surface is provided with an oxide layer according to the invention.

Dazu wird eine fertig gesinterte und mechanisch umgeformte Röntgenanode mittels Sandstrahlen oberflächlich gereinigt und aufgerauht und möglichst gleich anschließend unter den üblichen Verfahrensbedingungen mittels Plasmaspritzen außerhalb des Brennbahnbereiches beschichtet. Zunächst wird eine als Kohlenstoff-Barriere wirkende Molybdän-Schicht aufgebracht und einer Reduktionsglühung in Wasserstoff bei 1350°C über 2 Stunden unterzogen. Anschließend erfolgt eine erste Oxidbeschichtung auf der Basis Aluminiumoxid-Titanoxid. Erst diese Oxidschicht ermöglicht das Aufschmelzen des schwärzungsfähigen oxidischen Überzuges in der erforderlichen Qualität. Der abschließend aufgebrachte oxidische Überzug weist die Zusammensetzung auf: 94 Gew.% einer Oxidmischung aus 72 % Zirkonoxid, 8 % Kalziumoxid, 20 % Titanoxid, ferner 6 % Siliziumoxid.For this purpose, a completely sintered and mechanically shaped X-ray anode is cleaned and roughened by means of sandblasting and, if possible, coated immediately afterwards under the usual process conditions by means of plasma spraying outside the focal path area. First, a molybdenum layer acting as a carbon barrier is applied and subjected to a reduction annealing in hydrogen at 1350 ° C. for 2 hours. This is followed by a first oxide coating based on aluminum oxide-titanium oxide. It is only this oxide layer that enables the blackening oxidic coating to be melted in the required quality. The final oxidic coating has the composition: 94% by weight of an oxide mixture of 72% zirconium oxide, 8% calcium oxide, 20% titanium oxide, and also 6% silicon oxide.

Die so beschichtete Drehanode muß einer Glühbehandlung entsprechend Beispiel 1 unterworfen werden.
Die Glühbedingungen lauten: T = 1580°C, h = 45 min.The rotating anode coated in this way must be subjected to an annealing treatment in accordance with Example 1.
The annealing conditions are: T = 1580 ° C, h = 45 min.

Die Drehanode wurde anschließend entsprechend Beispiel 1 in einer Röntgenröhren-Versuchsanordnung unter praxisnahen Bedingungen erprobt. Sie lief dort störungsfrei innerhalb der geforderten Grenzbelastung.The rotating anode was then tested according to Example 1 in an X-ray tube test arrangement under practical conditions. There it ran trouble-free within the required limit load.

Claims (6)

  1. X-ray anode, in particular rotary anode, with a high heat emissivity, having a base body composed of a metal with a high melting point or its alloys and having a cathode spot or strip region optionally of a different metal with a high melting point from the base body, the X-ray anode having an oxidic coating comprising essentially the metals Ti, Zr and optionally Al at least on parts of the surface outside the cathode strip, characterised in that the coating contains 1 - 20 % by weight silicon oxide and is a homogeneously molten phase.
  2. X-ray anode according to claim 1, characterised in that the oxidic coating contains stabilising oxide additives.
  3. X-ray anode according to claim 2, characterised in that the stabilising additive is CaO.
  4. X-ray anode according to claim 1-3, characterised in that between the base body composed of a Mo alloy and the oxidic coating, a two-ply middle layer having a thickness of between 10 and 1000µm is provided, the first layer consisting of Mo and the second layer of an oxide composed of TiO₂ and/or Al₂O₃.
  5. X-ray anode according to claim 1-4, characterised in that the oxide coating has the following composition: 89 % by weight of an oxide mixture composed of 72 % by weight ZrO₂, 8 % by weight CaO, and 20 % by weight TiO₂; additionally 5 % by weight Al₂O₃ and 6 % by weight SiO₂.
  6. Method of manufacturing an X-ray anode according to one of claims 1-5, characterised in that the oxidic coating is applied by the plasma sputtering of oxide powders, and simultaneously with degassing and cleaning of the substrate, in a subsequent annealing process at temperatures of between 1550 and 1680°C, the coating is melted for an annealing time of between 0.5 and 1.5 hours to form a homogeneous phase with a structured surface.
EP90202558A 1989-10-02 1990-09-27 X-ray tube anode with oxide layer Expired - Lifetime EP0421521B1 (en)

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AT0227689A AT394643B (en) 1989-10-02 1989-10-02 X-RAY TUBE ANODE WITH OXIDE COATING
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US6749337B1 (en) 2000-01-26 2004-06-15 Varian Medical Systems, Inc. X-ray tube and method of manufacture
US6456692B1 (en) * 2000-09-28 2002-09-24 Varian Medical Systems, Inc. High emissive coatings on x-ray tube components
AU2001296611A1 (en) * 2000-10-23 2002-05-06 Varian Medical Systems, Inc. X-ray tube and method of manufacture
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JPH03127439A (en) 1991-05-30
EP0421521A2 (en) 1991-04-10
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ATA227689A (en) 1991-10-15
US5157705A (en) 1992-10-20
AT394643B (en) 1992-05-25

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