DE1050457B - X-ray tube with preferably rotating the high-temperature-resistant anode - Google Patents

Description

GERMAN

PATENT OFFICE

kl. 21 g 17/02

INTERNAT. KL. H 01 j

C 14416 VIIIc / 21g

REGISTRATION DATE: FEBRUARY 20, 1957

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EDITORIAL: FEBRUARY 12, 1959

The invention relates to an X-ray tube with a preferably rotating high-temperature-resistant anode, in which the focal point of an electron beam emanating from the cathode is limited Surface part of the anode made using tungsten is highly heated.

With X-ray tubes in which a more or less limited surface part of the anode passes through Electron impact on the focal spot is highly heated, the most difficult problem is to achieve the most effective possible heat dissipation from the anode, since almost the entire tube is in the Electrical energy supplied to operation when the electrons emitted by the cathode collide is converted into heat on the anode. In particular, the cooling rate of the anode decisive for the chronological sequence of a series of X-rays or the connection a recording of a previous direct observation of a screen image. With an X-ray tube with rotating anode, which is used as an exemplary embodiment for the explanation of the present invention is selected, the heat is dissipated from the generally as a solid tungsten disk executed anode essentially by heat radiation.

When an X-ray tube is switched on for the purpose of producing an X-ray image, the temperature T _{F of} the focal point on the anode suddenly rises from an initial value T ₀ to a value T ₁ and then increases during the X-ray emission from time t ₀ to time t ₁ lasts, from the temperature value T ₁ to the temperature value T ₂ . This slower increase in the focal point temperature also corresponds approximately to the increase in the temperature T _{c of} the focal point path, which increases from the value T ₀ to the value T ₃ during the same time. Finally, the temperature T _{D of} the anode disk itself also increases during the operation of the tube; it comes from the initial value T ₀ to the value T ₄ , T _{4 being} less than Tg (see FIG. 1). When such an X-ray tube is operated, the anode "ages", which leads to a reduction in the X-ray emission. The aging depends on the temperature of the focal point attachment point on the anode. There is therefore an interest in always starting from an initial temperature T ₀ that is as low as possible when the tube is put into operation again. However, it is often necessary to take several recordings in quick succession or to take a photograph of an X-ray image after viewing a screen image. These possibilities depend on the cooling speed of the anode, as it is an X-ray tube

with preferably rotating, high temperature resistant anode

Applicant:

Compagnie Generale de Radiologie, Paris

Representative: Dipl.-Ing. R. Beetz, patent attorney, Munich 22, Steinsdorfstr. 10

Claimed priority: France of March 15, 1956

Roger Griffoul, Sevres,

and Antoine Joseph Schräm, Monigeron (France), have been named as inventors

a certain temperature limit must not be exceeded.

The invention relates to X-ray tubes in which the cooling rate is reduced by the special design of the anode is significantly increased.

For a given anode, which is cooled down practically solely by its heat radiation, the cooling rate is very approximated by the Stephan-Boltzmann law of heat radiation "

conditional. In this formula, W means the radiated heat energy in watts, ε the total radiation coefficient (or the absorption ratio) of the heat-emitting surface at the temperature T ₁ C the radiation constant = 5.67 · ICH ¹² W / cm ^{2 0} K ⁴ , T the temperature the surface in ⁰ K, T ₀ the ambient temperature in ⁰ K and 5 "the radiating surface in cm ² (effective surface).

At the temperatures in question here, the value To can be neglected ^{compared to the value T 4.} If T and S are given, one has to increase ε if one takes the total heat

809 749/313

3 4

W radiation will increase. Now, with tungsten ε, the significantly higher temperatures than nickel have approximately the following values: withstand anodizing and should also radiate correspondingly higher amounts of heat at 1000 ° K 0 114. In the USA.-

at 1500 ° K o'l92 patents 1,862,138 and 2,641,555 are

at 1700 ° K "o'222 ^{5 aTt} ^ S ^e experiments mentioned; but at the same time it is given attached at 2000 ° K"o'26O that tungsten is very much in the carburization

at 2500 ° K θ'3Ο3 becomes brittle and, as a result, carburized tungsten

'anodes are unsuitable for practice. In these

A comparison with the theoretical maximum patent specifications is recommended as a remedy value ε = 1, as it is for the completely black 10 anode consisting of tungsten Body «applies, shows without further ado that a tungsten with nickel has to be plated thinly and then the nickel surface to carburize the layer with regard to its heat radiation, so that the high temperature out is not ideal. solid, unchanged tungsten only supports the

In order to increase the heat radiation, the support for the softening nickel was formed, 15 Such an anode can, however, be enlarged in an X-ray. So the anode surface through the tube cannot be used, because on the one hand the emis sands roughened or inadequate on the purely chemical or ionic properties of the nickel plating attacked electrochemically. On these and also the nickel plating on the high ones Way, ε can be increased within certain limits. Temperatures that an X-ray tube anode is exposed to

In electron tubes of conventional type which is exposed to electron drivingly 20 melt, or gegetroden not emit X-rays, are used ^to:; if necessary it would even evaporate. Improvement of the operating properties, especially the risk of the tungsten becoming brittle

to increase the heat radiation that is not emitted by carburizing, is in the case of highly stressed X-ray patients Electrodes or anodes, using tubular anodes - especially preferably flat ones different processes on the electrodes - 25 plate-shaped rotating anodes - of those substances applied that should not underestimate the effective surface, since the sudden onset increase and at the same time their specific heat and also very unevenly distributed thermal increase radiation. So one has z. B. hochtempe- stresses on the anode as a result of occurrence temperature-resistant carbides can easily be cracked directly by electrophoresis at high material stresses the anode knocked down; there was also formation and - especially in the case of rapidly rotating ones already recommended to apply a metal oxide and anodes - encourage tearing of the anode it would then have to do with chemical or thermal effects.

subject to treatment. Furthermore, it is now despite the prevailing in professional circles

knows, on the anode for X-ray tubes a prejudice carried out tests with carburier mixture tungsten anodes for X-ray tubes made from carbides and metal oxides have shown strike. Attempts have also been made to make mixtures that reduce the abovementioned risks of embrittlement made of zirconium carbide and metallic zirconium and / or the anode material through the carburization apparently Mixtures of certain high temperature resistances have been far overestimated and that are in the Carbides and tungsten powder or a powdery practice with X-ray tubes did not cause any problems other high-temperature-resistant metal on the 40, if you according to the invention at least one To frit anode. thin anode carbu- surface layer of tungsten

The application of this known method on riert.

Anodes of X-ray tubes have greater disadvantages. Perhaps the opposite of the carbu-

with it, from which it can be explained that most of the grooved surface layer has a relatively large thickness this method only matters on normal electron tubes 45 anode; that lying in deeper layers with non-emissive anodes remained limited to tungsten metals that are through the surface carburies. tion is not influenced, is evidently able to

Electrophoresis deposited precipitates not just the sudden voltage changes in show with X-ray tubes because of the very high absorption of the anode body without cracking, Temperatures and the extraordinarily strong elec- 5 ° but even cracking of the surface layer Irish fields which largely prevent this rainfall on the.

Exposed to the anode, insufficient adhesion. Carburizing the anode according to the invention

It also creates difficulties, the low (anticathode) of an X-ray tube is relatively simple, hit the one that does not emit x-rays but brings about an increase in heat radiation Part of the anode surface to be restricted to the 55 on the order of about 100%. You can X-ray generation efficiency not including the entire surface of the anode to affect. Another disadvantage of most focal point raceways is carburizing; an essential such coatings consist in that they emerge when the X-ray radiation produced is reduced high temperatures did not include significant amounts of occluded. This can perhaps be explained by this Gases are released which are the working of the X-ray 60 that the focal point path during operation of the affect the genröhre. X-ray tube heated to very high temperatures

In normal vacuum tubes one has already been given a partial or complete Carburized nickel anodes used, experienced during decarburization.

for whom the carburization of the outer nickel layer is important, however, that the carburization

Heat radiation of the anode increased; Nickel anodes 65 process is performed in such a way that the carburized ones cannot be used in X-ray tubes because of the low tungsten surface layer of the anode, which is essentially temperature resistance of the nickel. made of tungsten carbide with the composition W ₂ C. Attempts have also been made to produce the non-emitting buried tungsten carbide WC at high levels and only very small amounts of the more heavily car-loaded electron tubes. Anodes have to be designed as carburized tungsten anodes, 70 taking this condition into account as an

moderately proven, the carburization by thermal decomposition of a hydrocarbon compound (e.g. Hexane) on the tungsten anode, which is only heated to temperatures between 800 and 1400 ° C, under negative pressure or at normal atmospheric pressure in the presence of an inert gas to carry out the Partial pressure of the fission products of the hydrocarbon is reduced accordingly.

The preparation of the anode before it is carburized does not require any special effort; you can use the known methods such. B. sanding, chemical or electrochemical roughening, etc. use. An examination of the surface layer by means of X-rays has shown that the weakly carburized tungsten carbide W ₂ C is essentially formed in the process. However, it is possible that a small amount of carbon is not chemically bonded to tungsten or that, in addition to the W ₂ C, the particularly hard tungsten carbide WC is also formed.

FIG. 2 shows the improvement in the achievable using the present invention Cooling by heat radiation. Curve 1 is a cooling curve of a conventional X-ray tube anode and curve 2 shows a cooling curve of a tungsten anode which is carburized according to the invention has been.

Claims (4)

Patent claims: 1. X-ray tube with preferably rotating, high-temperature-resistant anode, in which the combustion spot of an electron beam emanating from the cathode highly heated a surface portion of the anode made using tungsten, characterized in that at least a thin tungsten surface layer of the anode is carburized. 2. X-ray tube according to claim 1, characterized in that the entire thin tungsten surface layer of the anode consists essentially of tungsten carbide of the composition W ₂ C. 3. Process for the production of a carburized tungsten surface layer on anodes for X-ray tubes according to claim 1 or 2, characterized in that the carburization by thermal Decomposition of a pure hydrocarbon, z. B. of hexane, on the heated to temperatures between 800 and 1400 ° C tungsten anode takes place at reduced pressure or at atmospheric pressure in the presence of an inert gas. 4. The method according to claim 3, characterized in that that one known the tungsten surface of the anode before its carburization by per se Measures - e.g. B. sanding, chemical or electrochemical attacks - roughened. Considered publications:
U.S. Patent Nos. 1,862,138, 2,641,555;
Steyshal: "Working methods and material science of high vacuum technology", Physik Verlag Mosbach / Baden, 1955, p. 123. 1 sheet of drawings