EP0487144A1 - X-ray tube anode with oxide layer - Google Patents
X-ray tube anode with oxide layer Download PDFInfo
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- EP0487144A1 EP0487144A1 EP91202965A EP91202965A EP0487144A1 EP 0487144 A1 EP0487144 A1 EP 0487144A1 EP 91202965 A EP91202965 A EP 91202965A EP 91202965 A EP91202965 A EP 91202965A EP 0487144 A1 EP0487144 A1 EP 0487144A1
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- 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 a high-melting metal or its alloys and a focal spot or focal path region made of a high-melting metal or its alloys, which directly or above at least on parts of the surface outside the focal path has an underlayer on the base body applied oxidic coating as a homogeneous, melted phase, which contains oxides of the metals Ti, Zr and Al and is optionally stabilized by another oxide.
- 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 high-melting metals by means of an oxidic coating (AT-PS 337 314, DE-OS 22 01 979, DE-OS 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 and to increase the thermal emissivity of the anode surface by means of different oxide materials and production processes. 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).
- DE-OS 22 01 979 describes in particular an oxide layer which consists of the heating product of a mixture which contains titanium dioxide and additives of at least one other meltable oxide.
- Aluminum oxide, calcium oxide, magnesium oxide and zirconium oxide are mentioned as other, equally suitable oxides. Particular advantages of a very special oxide combination are not mentioned.
- As a preferred oxide mixture a mixture of approximately equal proportions of aluminum oxide and titanium dioxide can be found in the examples and the subclaims. Furthermore, it can be seen from the description that it is important that the titanium dioxide content does not drop below 20%.
- the EU A2 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.
- EU A2 0 244 776 relates essentially to the same subject 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 into a powder with a homogeneous phase and then optionally mixed with other oxide powders by known spraying methods.
- coating processes for the oxide coating on the X-ray anodes made of refractory metals are called plasma spraying, sputtering processes, chemical and physical deposition processes from the gas phase or the electron beam process.
- 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 its production do not adequately meet the requirements. 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, these 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 path disappears to an intolerable extent. In addition, such oxide layers have an annoying gas phase formation at the required annealing temperatures.
- the US-PS 4 870 672 describes an oxidic coating for X-ray anodes, consisting of a mixture of Al2O3, ZrO2 and TiO2.
- the preferred composition of the coating consists of 40 - 70 wt.% TiO2, 20 - 40 wt.% ZrO2 and 10 - 20 wt.% Al2O3.
- the Limit compositions of the coating are given with 10 - 80 wt.% TiO2, 10 - 60 wt.% ZrO2 and 5 - 30 wt.% Al2O3.
- a disadvantage of this coating is that if the composition is chosen in an unfavorable manner, the coating evaporates and thus fogging and flashover may occur in the X-ray anode.
- the object of the present invention is therefore to give the oxidic surface layer such a composition that, on its one hand, at least maintain the good adhesion properties between the oxide layer and the substrate and the good thermal emissivity properties of the layer which have been achievable so far when it is produced by customary application methods, including annealing treatment 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 unwanted flow of the oxide during the annealing treatment of the X-ray anode.
- the composition is also intended to prevent fogging or electrical flashovers in the X-ray tube.
- the object is achieved in that the coating 1-20% by weight of aluminum oxide, less than 20% by weight of titanium dioxide and more than 60% by weight. Contains zirconium oxide.
- 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, under otherwise comparable conditions, during the required annealing treatment of the Anode is less liquid, ie the melt toughness is higher compared to previously known oxide layers 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 unwanted precipitation of oxide components on uncoated surface parts during the annealing process.
- layers with a desired surface roughness R T of approx. 20 ⁇ m 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 titanium dioxide, for example in a ratio of 75: 10: 15, it being essential that the titanium dioxide always contains less than 20% by weight and the zirconium oxide contains more than 60%. is present in the oxide mixture.
- 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 remaining part of the composition of the oxidic coating is, according to the invention, aluminum 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.
- the known PVD and CVD processes in particular plasma CVD processes and sputtering processes, as well as thermal coating processes such as e.g. B. plasma spraying.
- the homogeneous phase in the oxidic coating is to be understood as a finely divided oxide mixture.
- 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 o C and 1680 o C and a glow time between 30 minutes and 1.5 hours achieve advantageous.
- the molybdenum alloy TZM with low carbon content tends to release carbon at higher temperatures.
- 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.
- TZM as the base material in individual embodiments of the invention to arrange a diffusion barrier between the base material and the oxide layer with a layer thickness of a few micrometers up to the millimeter range in the form of a single-layer molybdenum layer or a two-layer Mo / oxide composite layer.
- An X-ray rotary anode consisting of an alloy of molybdenum to which 5% by weight of tungsten has been added, has an approx. 2 mm in the focal path area thick W-Re layer.
- this anode surface is provided with an oxide layer according to the invention.
- a completely sintered and mechanically formed X-ray anode on the back of the anode to be coated is cleaned and roughened by means of sandblasting and, if possible, immediately afterwards coated with oxide powder under the usual process conditions by plasma spraying.
- the oxide powder applied has the following composition: 89% by weight of an oxide mixture of 72% by weight of ZrO2, 8% by weight of CaO, 20% by weight of TiO2; further 11 wt.% Al2O3.
- 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 subsequently 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).
- annealing takes place at 1620 o 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. So far during the annealing process vaporize gaseous oxides from the surface of the layer, these do not form a disruptive layer 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 smoothly for several days within the required limit load.
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Abstract
Description
Die Erfindung betrifft eine Röntgenanode, insbesondere Drehanode, hoher Wärmeemissivität, mit einem Grundkörper aus einem hochschmelzenden Metall oder dessen Legierungen sowie einem Brennfleck- bzw. Brennbahnbereich aus einem hochschmelzenden Metall oder dessen Legierungen, die zumindest auf Teilen der Oberfläche außerhalb der Brennbahn einen unmittelbar oder über eine Unterlagsschicht auf dem Grundkörper aufgebrachten oxidischen Überzug als homogene, aufgeschmolzene Phase aufweist, welcher Oxide der Metalle Ti, Zr und Al enthält und wahlweise durch ein weiteres Oxid stabilisiert ist.The invention relates to an X-ray anode, in particular a rotating anode, with high heat emissivity, with a base body made of a high-melting metal or its alloys and a focal spot or focal path region made of a high-melting metal or its alloys, which directly or above at least on parts of the surface outside the focal path has an underlayer on the base body applied oxidic coating as a homogeneous, melted phase, which contains oxides of the metals Ti, Zr and Al and is optionally stabilized by another oxide.
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-PS 337 314, DE-OS 22 01 979, DE-OS 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 high-melting metals by means of an oxidic coating (AT-PS 337 314, DE-OS 22 01 979, DE-OS 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 and to increase the thermal emissivity of the anode surface by means of different oxide materials and production processes.
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 DE-OS 22 01 979 beschreibt im speziellen eine Oxidschicht, die aus dem Erhitzungsprodukt eines Gemisches besteht, welches Titandioxid und Zusätze wenigstens eines anderen, schwerschmelzbaren Oxides enthält. Als andere, gleichermaßen geeignete Oxide sind dabei Aluminiumoxid, Kalziumoxid, Magnesiumoxid und Zirkonoxid genannt. Besondere Vorteile einer ganz speziellen Oxidkombination sind nicht genannt. Als bevorzugtes Oxidgemisch ist aus den Beispielen und den Unteransprüchen eine Mischung aus etwa gleichen Anteilen Aluminiumoxid und Titandioxid zu entnehmen. Darüberhinaus ist der Beschreibung zu entnehmen, daß es wichtig ist, daß der Titandioxidgehalt nicht unter 20 % absinkt.DE-OS 22 01 979 describes in particular an oxide layer which consists of the heating product of a mixture which contains titanium dioxide and additives of at least one other meltable oxide. Aluminum oxide, calcium oxide, magnesium oxide and zirconium oxide are mentioned as other, equally suitable oxides. Particular advantages of a very special oxide combination are not mentioned. As a preferred oxide mixture, a mixture of approximately equal proportions of aluminum oxide and titanium dioxide can be found in the examples and the subclaims. Furthermore, it can be seen from the description that it is important that the titanium dioxide content does not drop below 20%.
Die EU A2 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.The EU A2 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 EU A2 0 244 776 betrifft im wesentlichen den gleichen Erfindungsgegenstand. Die Erfindung bezieht 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.% Kalziumoxid 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.EU A2 0 244 776 relates essentially to the same subject 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. In this process, a mixture of 77% -85% titanium dioxide with 15-23% by weight calcium oxide is processed in a first process step into a powder with a homogeneous phase and then optionally mixed with other oxide powders by known spraying methods. As coating processes for the oxide coating on the X-ray anodes made of refractory metals are called plasma spraying, sputtering processes, chemical and physical deposition processes from the gas phase or the electron beam process. 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. However, the layer composition according to the prior publication and the processes for its production do not adequately meet the requirements. 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, these 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 path disappears to an intolerable extent.
In addition, such oxide layers have an annoying gas phase formation at the required annealing temperatures.
Die US-PS 4 870 672 beschreibt eine oxidische Beschichtung für Röntgenanoden, bestehend aus einer Mischung von Al₂O₃, ZrO₂ und TiO₂. Die bevorzugte Zusammensetzung der Beschichtung besteht aus 40 - 70 Gew.% TiO₂, 20 - 40 Gew.% ZrO₂ und 10 - 20 Gew.% Al₂O₃. Die Grenzzusammensetzungen der Beschichtung werden mit 10 - 80 Gew.% TiO₂, 10 - 60 Gew.% ZrO₂ und 5 - 30 Gew.% Al₂O₃ angegeben.
Nachteilig bei dieser Beschichtung ist, daß es bei ungünstig gewählter Zusammensetzung zu einem Abdampfen der Beschichtung und damit zu einem Beschlagen und überschlag in der Röntgenanode kommen kann.The US-PS 4 870 672 describes an oxidic coating for X-ray anodes, consisting of a mixture of Al₂O₃, ZrO₂ and TiO₂. The preferred composition of the coating consists of 40 - 70 wt.% TiO₂, 20 - 40 wt.% ZrO₂ and 10 - 20 wt.% Al₂O₃. The Limit compositions of the coating are given with 10 - 80 wt.% TiO₂, 10 - 60 wt.% ZrO₂ and 5 - 30 wt.% Al₂O₃.
A disadvantage of this coating is that if the composition is chosen in an unfavorable manner, the coating evaporates and thus fogging and flashover may occur in the X-ray anode.
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. Ebenso soll durch die Zusammensetzung ein Beschlagen oder elektrische Überschläge in der Röntgenröhre verhindert werden.The object of the present invention is therefore to give the oxidic surface layer such a composition that, on its one hand, at least maintain the good adhesion properties between the oxide layer and the substrate and the good thermal emissivity properties of the layer which have been achievable so far when it is produced by customary application methods, including annealing treatment 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 unwanted flow of the oxide during the annealing treatment of the X-ray anode. The composition is also intended to prevent fogging or electrical flashovers in the X-ray tube.
Die Aufgabe wird erfindungsgemäß dadurch gelöst, daß der Überzug 1 - 20 Gew.% Aluminiumoxid, weniger als 20 Gew.% Titandioxid sowie mehr als 60 Gew.%. Zirkonoxid enthält.The object is achieved in that the coating 1-20% by weight of aluminum oxide, less than 20% by weight of titanium dioxide and more than 60% by weight. Contains zirconium oxide.
Die Oxidschicht gemäß Erfindung, auf eine Röntgenanode aus hochschmelzenden Metallen aufgetragen, weist hervorragende 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 bisher bekannten Oxidschichten 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, Temperatur und Dauer der Glühbehandlung lassen sich Schichten mit einer angestrebten Oberflächenrauhigkeit RT von ca. 20 µm 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, under otherwise comparable conditions, during the required annealing treatment of the Anode is less liquid, ie the melt toughness is higher compared to previously known oxide layers 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 unwanted precipitation of oxide components on uncoated surface parts during the annealing process. By matching the oxide composition, temperature and duration of the annealing treatment, layers with a desired surface roughness R T of approx. 20 µm 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, Kalziumoxid und Titandioxid, beispielsweise im Verhältnis 75 : 10 : 15 auf, wobei es wesentlich ist, daß das Titandioxid immer mit Anteilen unter 20 Gew.% und das Zirkonoxid mit Anteilen über 60 % in der Oxidmischung vorhanden ist. Das Kalziumoxid 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.
Der restliche Anteil an der Zusammensetzung des oxidischen Überzuges ist erfindungsgemäß Aluminiumoxid 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 titanium dioxide, for example in a ratio of 75: 10: 15, it being essential that the titanium dioxide always contains less than 20% by weight and the zirconium oxide contains more than 60%. is present in the oxide mixture. 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 remaining part of the composition of the oxidic coating is, according to the invention, aluminum 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 thermische Beschichtungsverfahren, wie z. B. Plasmaspritzen.
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 thermal coating processes such as e.g. B. plasma spraying.
The homogeneous phase in the oxidic coating is to be understood as a finely divided oxide mixture.
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 1550oC und 1680oC sowie einer Glühzeit zwischen 30 Minuten und 1,5 Stunden vorteilhaft erreichen.
Die Molybdänlegierung TZM mit geringen Kohlenstoffanteilen neigt zur Kohlenstoff-Freisetzung bei höheren Temperaturen. 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 in Form einer einlagigen Molybdänschicht bzw. einer zweilagigen Mo / Oxid Verbundschicht anzuordnen.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 o C and 1680 o C and a glow time between 30 minutes and 1.5 hours achieve advantageous.
The molybdenum alloy TZM with low carbon content tends to release carbon at higher temperatures. 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. It is therefore advantageous when using TZM as the base material in individual embodiments of the invention to arrange a diffusion barrier between the base material and the oxide layer with a layer thickness of a few micrometers up to the millimeter range in the form of a single-layer molybdenum layer or a two-layer Mo / oxide composite layer.
Die Erfindung wird anhand des nachfolgenden Ausführungsbeispieles näher erläutert.The invention is explained in more detail using the following exemplary embodiment.
Eine Röntgendrehanode, bestehend aus einer Legierung von Molybdän, der 5 Gew.% Wolfram zugesetzt sind, 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 11 Gew.% Al₂O₃.
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.
Die Glühung erfolgt im vorliegenden Fall bei 1620oC 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 Schichtoberflache abdampfen, schlagen sich diese nicht als störender Schichtbelag im ursprünglich nicht beschichteten Brennbahnbereich der Drehanode nieder.An X-ray rotary anode, consisting of an alloy of molybdenum to which 5% by weight of tungsten has been added, has an approx. 2 mm in the focal path area thick W-Re layer. 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 formed X-ray anode on the back of the anode to be coated is cleaned and roughened by means of sandblasting and, if possible, immediately afterwards coated with oxide powder under the usual process conditions by plasma spraying. The oxide powder applied has the following composition: 89% by weight of an oxide mixture of 72% by weight of ZrO₂, 8% by weight of CaO, 20% by weight of TiO₂; further 11 wt.% Al₂O₃.
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 subsequently 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).
In the present case, annealing takes place at 1620 o 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. So far during the annealing process vaporize gaseous oxides from the surface of the layer, these do not form a disruptive layer 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 smoothly for several days within the required limit load.
Claims (4)
dadurch gekennzeichnet,
daß der Überzug 1 - 20 Gew.% Aluminiumoxid < 20 Gew.% Titandioxid sowie > 60 Gew.% Zirkonoxid enthält.X-ray anode, in particular rotating anode, high heat emissivity, with a base body made of a high-melting metal or its alloys as well as a focal spot or focal track area made of a high-melting metal or its alloys, which, at least on parts of the surface outside the focal track, directly or via an underlayer on the Basic body applied oxidic coating as a homogeneous, melted phase, which contains oxides of the metals Ti, Zr and Al and is optionally stabilized by a further oxide,
characterized,
that the coating contains 1-20% by weight of aluminum oxide <20% by weight of titanium dioxide and> 60% by weight of zirconium oxide.
89 Gew.% einer Oxidmischung aus 72 Gew.% ZrO₂, 8 Gew.% CaO und 20 Gew.% TiO₂; zusätzlich 11 Gew.% Al₂O₃.X-ray anode according to Claims 1-2, characterized in that the oxide coating has the following composition:
89% by weight of an oxide mixture of 72% by weight of ZrO₂, 8% by weight of CaO and 20% by weight of TiO₂; additionally 11 wt.% Al₂O₃.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT236790 | 1990-11-22 | ||
| AT2367/90 | 1990-11-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| EP0487144A1 true EP0487144A1 (en) | 1992-05-27 |
Family
ID=3533054
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP91202965A Withdrawn EP0487144A1 (en) | 1990-11-22 | 1991-11-14 | X-ray tube anode with oxide layer |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US5199059A (en) |
| EP (1) | EP0487144A1 (en) |
| JP (1) | JPH04267040A (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7180981B2 (en) * | 2002-04-08 | 2007-02-20 | Nanodynamics-88, Inc. | High quantum energy efficiency X-ray tube and targets |
| DE102010040407A1 (en) | 2010-09-08 | 2012-03-08 | Siemens Aktiengesellschaft | X-ray tube, has anode partially comprising surface coatings provided outside stopping area of focal spot, where surface coatings are made of material with nuclear charge number less than nuclear charge number of material of anode |
| CN102437000B (en) * | 2011-12-06 | 2014-12-31 | 肖李鹏 | Medical X-ray tube rotating anode high-heat radiation ceramic coat and production method thereof |
| RU2653508C1 (en) * | 2017-05-30 | 2018-05-10 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Рязанский государственный радиотехнический университет" | Through-type microfocus x-ray tube with high level of power dispersed on anode |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2381834A1 (en) * | 1977-02-16 | 1978-09-22 | Gen Electric | ADVANCED ANODE FOR X-RAY TUBE |
| US4870672A (en) * | 1987-08-26 | 1989-09-26 | General Electric Company | Thermal emittance coating for x-ray tube target |
| EP0421521A2 (en) * | 1989-10-02 | 1991-04-10 | Metallwerk Plansee Gesellschaft M.B.H. | X-ray tube anode with oxide layer |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2201979C3 (en) * | 1972-01-17 | 1979-05-03 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Process for the production of a blackened layer on rotating anodes of X-ray tubes |
| NL7312945A (en) * | 1973-09-20 | 1975-03-24 | Philips Nv | TURNTABLE FOR A ROSE TUBE AND METHOD FOR MANUFACTURE OF SUCH ANODE. |
| AT337314B (en) * | 1975-06-23 | 1977-06-27 | Plansee Metallwerk | X-ray anode |
| AT376064B (en) * | 1982-02-18 | 1984-10-10 | Plansee Metallwerk | X-RAY TUBE ROTATING ANODE |
| US4600659A (en) * | 1984-08-24 | 1986-07-15 | General Electric Company | Emissive coating on alloy x-ray tube target |
| US4840850A (en) * | 1986-05-09 | 1989-06-20 | General Electric Company | Emissive coating for X-ray target |
| US4953190A (en) * | 1989-06-29 | 1990-08-28 | General Electric Company | Thermal emissive coating for x-ray targets |
-
1991
- 1991-11-14 EP EP91202965A patent/EP0487144A1/en not_active Withdrawn
- 1991-11-15 JP JP3326632A patent/JPH04267040A/en not_active Withdrawn
- 1991-11-21 US US07/795,760 patent/US5199059A/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2381834A1 (en) * | 1977-02-16 | 1978-09-22 | Gen Electric | ADVANCED ANODE FOR X-RAY TUBE |
| US4870672A (en) * | 1987-08-26 | 1989-09-26 | General Electric Company | Thermal emittance coating for x-ray tube target |
| EP0421521A2 (en) * | 1989-10-02 | 1991-04-10 | Metallwerk Plansee Gesellschaft M.B.H. | X-ray tube anode with oxide layer |
Also Published As
| Publication number | Publication date |
|---|---|
| US5199059A (en) | 1993-03-30 |
| JPH04267040A (en) | 1992-09-22 |
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