JPH023263B2 - - Google Patents

Abstract

1. A rotary anode for an X-ray tube which is formed by a base body of which at least a part of the surface referred to as the "active" surface is covered by a layer of an emissive material, characterised in that the base body is made of aluminium nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to anodes used in X-ray tubes, particularly rotating anodes.

X-ray tubes, which are mainly used in the radiology field, have a disc-shaped anode or pair that has the function of emitting X-rays from a surface area that is affected by a flux of electrons with a sufficiently high level of kinetic energy generated from the cathode. The provision of a cathode is well known to those skilled in the art.

It is also known that in an X-ray tube, only about 1% of the kinetic energy of electrons is converted into X-ray energy, and most of the electron energy is converted into heat.

Initially, such anodes were therefore initially composed only of materials which, in addition to good properties with respect to X-ray radiation, had a very high melting point, such as tungsten and tungsten alloys, in particular alloys of tungsten and rhenium. Eventually, concerned about the high cost and weight of such anodes, engineers realized that the use of tungsten alone was sufficient to create the electron-receiving portion, the "active zone" or "focal track" of the anode. We found that. Development subsequently turned to composite anodes comprising a substrate made of a material more suitable than tungsten and having an active zone obtained from a coating of tungsten or its alloys attached to the substrate.

In order for the anode to function properly, the substrate had to have a high melting point, high specific heat level and good thermal conductivity. At first molybdenum was used, but then interest turned to graphite because it had a significantly higher level of specific heat and was also significantly lighter, making it easier to rotate when used as a rotating anode. However, problems subsequently arose of cracking in the active zone due to reactions occurring between the tungsten layer and the graphite, weakening the intermediate layer, and due to expansion differences between the materials used. To solve this problem, for example, French Patent No. 1575111
It has been proposed to deposit a barrier layer consisting of pure rhenium as taught in No. Further advances in the radiation field have led material designers to consider increasing the rotational speed of the anode, working to reach speeds that can significantly exceed 10,000 rotations per minute. At such speeds the mechanical properties of the substrate must be high and the substrate must have a low specific gravity, a high level of specific heat and good thermal conductivity.

The applicant focused on the advantages obtained by a composite anode whose substrate density is lower than that of molybdenum, and it meets the above criteria, does not require a barrier layer unlike graphite, and due to its high mechanical properties, it can be used up to 10,000 times. Efforts have been made to discover materials capable of reaching rotational speeds that can exceed 1/2 min.

As a result of research conducted by the present applicant, an anode characterized in that the substrate is made of aluminum nitride has been developed.

The substance is a nitrogen compound of aluminum with the chemical formula AlN, obtained in powder form, has thermal and mechanical properties such that it can be shaped by conventional sintering methods, and has a specific gravity of approximately 3.26, i.e. graphite. It can form solids with a specific gravity slightly larger than that of molybdenum but significantly lower than that of molybdenum. This material also has a relatively high melting point and good thermal conductivity, such that in particular the significant heat flux generated in the active zone can be conducted into and discharged into the electrode. It is these properties that make the material useful for anode production, but it is important to note that it is not until the applicant discovered that the material could be directly coated with radioactive materials without the need for a bonding or barrier layer. , and if the material did not have mechanical properties that allowed it to be used at high rotational speeds, it would not have been sufficient to compete against graphite or solid metal anodes.

The applicant has in fact discovered that, irrespective of the nature of the metal or alloy constituting the active zone and the method of depositing it on the substrate, perfect adhesion is obtained between the composite elements thus produced; It was confirmed that the quality was economically maintained even under the action of electron fluxes with very high levels of kinetic energy.

Thus, a wide variety of methods, such as molten salt bath electrolysis, physical or chemical vapor deposition, brazing fixing, or even after long-term use in high-power tubes used in modern radiation technology, can reduce adhesion or deterioration. Tungsten, using any other method for fixing the sintered metal element in the form of a ring or as part of a ring on a flat surface or on the surface of a hollow structure without admitting
A 0.5-2 mm thick deposit of rhenium, iridium, osmium and their alloys or their compounds in the carbide, nitride or boride type was formed.

By way of example, the anode of the present invention was used to replace certain conventional anodes that were used under power and time conditions such that the active zone temperature was between 2500 and 3000<0>C. When used under the same conditions, the temperature of the active zone decreased to 200-400°C, indicating the good thermal conductivity properties of aluminum nitride.

The anode of the present invention has high power level and 10000 times/
It is used in all X-ray tubes, including the latest models, which use rotational speeds that can exceed minutes.

Claims (1)

[Scope of Claims] 1. A rotating anode for an X-ray tube constituted by a substrate whose so-called "active" surface is at least partially coated with a layer of radioactive material, the substrate being formed from aluminum nitride. The anode characterized by: 2. The anode according to claim 1, wherein the substrate is formed by sintering particles. 3. The anode according to claim 1, wherein the radioactive material is in direct contact with the substrate. 4 The radioactive material is tungsten, rhenium, osmium and iridium metals, alloys thereof,
2. An anode according to claim 1, characterized in that it belongs to the group consisting of compounds of these metals, such as carbides, nitrides and borides. 5. characterized in that the radioactive material is obtained by a method belonging to the group consisting of molten bath electrolysis, aqueous phase chemical vapor deposition, vapor phase physical vapor deposition, brazing fixing and any other method of fixing the sintered metal element. An anode according to claim 1. 6. The anode according to claim 1, wherein the thickness of the radioactive material is in the range of 0.5 to 2 mm.