US3397338A - Rotary anode plate for X-ray tubes - Google Patents

Description

Aug. 13, 1968 A. F. ELSAS 3,397,338

ROTARY ANODE PLATE FOR X-RAY TUBES Filed Feb. 25, 1965 11 70 7 /Z 12 Q I 8 J5ZZ/67Zf0r. Jd0/f/?[5@5.

llnited States Patent 3,397,338 ROTARY ANODE PLATE FOR X-RAY TUBES Adolf Friedrich Elsas, Erlangen, Germany, assignor to Siemens Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Filed Feb. 25, 1965, Ser. No. 435,178

' 3 Claims. (Cl. 313-330) ABSTRACT OF THE DISCLOSURE A rotary anode plate for X-ray tubes in which at least the electron impact surface is formed of a high melting alloy which consists of tungsten, osmium, and another high melting metal, such as rhenium.

The invention is concerned with a rotary anode plate for X-ray tubes in which, at least, the electron impact surface consists of an alloy of refractory metals.

It was found that when rotary anode plates of tungsten are used, the electron impact surface is gradually roughened owing to the load to which the tube is subjected while radiation is generated and that the roughening of the impact surface reduces the radiation output. The roughening of the impact surface was largely reduced by providing the electron impact surface with rhenium and its alloys which are softer and more ductile than tungsten. However, rhenium is very expensive so that its use in sufiicient quantities proves prohibitive for reasons of economy. Consequently rhenium is being used as an alloy with tungsten and with a rhenium content of 1 up to 35% adequate alloys were obtained. Moreover, 5 up to 25% of the tungsten content of these alloys were replaced by high-melting metals such as niobium or tantalum. Such alloys, however, still prove to be relatively expensive. Hence, it was decided to apply them by layers which form at least the anode plate surface hit by the electrons. Anode plates provided with a layer which contains rhenium still turned out to be rather expensive.

According to the invention a reduction of costs for anode plates in which at least the electron impact surface is formed by an alloy of high-melting ;metals was obtained by using an alloy of tungsten-osmium containing at least a tungsten content of 65%, an osmium content of up to approximately, and a content of 0 up to 25% of one or several high-melting metals.

Starting from the known finding that with tungsten alloys containing additives to increase ductility a portion of up to 25% of the tungsten content can be replaced by one or several other high-melting metals and that in accordance with the invention the osmium content shall amount to about 10%, a tungsten content of up to 65% is attained.

By using a tungsten-osmium alloy a metal of greater hardness is produced as compared with tungsten-rhenium alloys. According to the opinion on the effect of the tungsten-rhenium alloy an impairment of the anode plate would develop when osmium is used as alloy ingredient. Moreover, an unfavourable reduction of the usability of the alloy would be brought about because of the lower melting point of osmium as compared with rhenium. However, it is surprising to see that already 1% of osmium suflices to obtain the effect which is achieved by adding 5 to 10% rhenium. For instance, a tube whose anode plate is provided with an electron impact surface made of a tungsten-osmium alloy, osmium accounting for 1%, shows after 10,000 loadings a decrease of the radiation output which is also found in tubes whose electron impact surface is formed by a rhenium-tungsten alloy, the rhenium content accounting for 10%. A cost reduction is obtained for the anode plates made in accordance with 3,397,338 Patented Aug. 13, 1968 the invention by the possibility of lessening by factor 5 to 10 the quantity of osmium required for the improvement and the alloy without experiencing an impairment of the properties. The osmium content can be limited to 10% because this percentage allows the desired improvement to be obtained to such an extent that increasing the osmium content would no longer prove rewarding economically. Apart from this, if the osmium content is increased considerably in excess of 10%, this would lower the melting point and the heat conductivity, two factors tending to lessen the tube rating. When the limit of 10% of the osmium content is exceeded slightly, this would still fall within the scope of the invention.

Also with tungsten-rhenium alloys an addition of osmium proves to be advantageous. Such alloys may have a composition with tungsten accoun ing for with osmium accounting up to about 10%, and with a portion of other metals, let us say rhenium, ranging from 0 to about 10%. An osmium content of 1% can also replace the elfect of 5 up to 10% rhenium. When the rhenium content ranges from 1 to 10%, the additional osmium portion may amount to 0.1 up to about 10%. As mentioned in the foregoing example, even in this case the costs of the tube can be reduced because a substantial quantity of the more expensive rhenium content is replaced by a small portion of osmium.

Moreover it proves to be of advantage that because of the smaller quantity of the required osmium content and the resulting cost reduction of the material the whole anode is made of the alloyed material. In this manner the necessity of applying a compound layer is eliminated.

When the osmium alloy covered by the invention is used in a so-called compound anode, a surface layer, usually 0.1 to 2 mm. thick, is applied to a base of tungsten or molybdenum or an alloy of these metals. Here again the share of expensive additives is smaller than with known tubes so that a reduction of cost is ensured.

The illustration shows an example of a rotary anode tube 1 embodying the inventive idea and representing a sectional view with a cut-away envelope and rotary anode plate. The glass envelope 2 embraces cathode 3 fitted at one envelope end with leads 4 and the rotary anode 5 fitted at the other end. Both envelopes 2 and cathode 3 as well as rotary anode 5, consisting of rotor 6 and anode plate 7, are arranged and supported in a known manner. Plate 7 is provided with carrier 8 made of molybdenum and tungsten alloy which contains 5% tungsten and molybdenum and the unavoidable impurities. Electron impact surfaces 10 and 11, which are differently inclined with respect to plate spindle 9, are formed of an 1 mm. thick layer 12 of tungsten alloy with osmium accounting for 1%. In order to obtain, in accordance with the inventive idea, an improved loadability, it is also possible to provide stationary anodes of X-ray tubes with an impact surface containing osmium.

I claim:

1. An X-ray tube, having an anode body with an exposed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom;

said electron impact surface consisting of a tungstenosrnium alloy containing up to 10% osmium.

2. An X-ray tube, having an anode body with an exposed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom;

said electron impact surface consisting of a tungstenrhenium-osmium alloy containing up to 25% rhenium, up to 10% osmium and the remainder of tungsten.

3. An X-ray tube, having an anode body with an ex- 3 posed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom;

said electron impact surface consisting of a tungstenrhenium-osmium alloy containing from 1 to 10% rhenium, .1 to 10% osmium and the remainder of tungsten.

References Cited UNITED STATES PATENTS 3,328,626 6/ 1967 Natter et al 75176 X 4 648,660 5/1900 Fessenden 313330 2,863,083 12/1958 Schram 313330 3,136,907 6/1964 Kieffer et a1 313-330 X OTHER REFERENCES Journal of the Less Common Metals, vol. 1, 1959, Kieffer et al., February 1959, p. 26.

X-Rays, Kaye, 2nd ed., Pub. by Longmans Green and Co., New York, p. 39.

5/1967 K hl 75.476 X 10 CHARLES N. LOVELL, Primary Examiner.

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