JPS61143929A - Rotary positive electrode for x ray tube - 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 radiation field, have a disk-shaped anode or It is well known to those skilled in the art that there is a difference between self and other.

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 regard to X-ray radiation, had very high melting points, such as tungsten and tungsten alloys, in particular tungsten and rheum alloys. Eventually, considering the high cost and heavy weight of such anodes, engineers decided to use tungsten alone to create the part that received the electrons, the "active zone" or "focal track" of the anode. We found that it is sufficient. 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, after that,
Problems were raised of cracking in the active zone due to reactions occurring between the tungsten layer and the graphite, weakening the interlayer, and due to expansion differences between the materials used. To solve this problem, it has been proposed to deposit a barrier layer between graphite and tungsten consisting of pure rhenium, as taught for example in FR 1,575,111. Furthermore, with advances in the field of radiation, material inventors have considered increasing the rotation speed of the anode, increasing the number of times per
Research has begun to reach speeds that can significantly exceed minutes.

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 of the present application focused on the advantages obtained by a composite anode whose base density is lower than that of molybdenum, and it meets the above criteria and does not require a barrier layer unlike graphite.
Moreover, due to its high mechanical properties, we have made great efforts to discover a material that can reach rotational speeds exceeding 1000 revolutions per minute.

As a result of the applicant's research, an anode characterized in that the base is made of aluminum nitride has been developed.

The substance is a nitrogen compound of aluminum with the chemical formula AIN, obtained in powder form, has thermal and mechanical properties such that it can be shaped by conventional sintering methods, has a specific gravity of about 3.26, and has a specific gravity of about 3.26. can form a solid with a specific gravity slightly larger than graphite but significantly lower than 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 removed from 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 shown that perfect adhesion can be obtained between these C-manufactured composite elements, regardless of the nature of the metal or alloy constituting the active zone and the method of depositing the metal or alloy onto the substrate. , and confirmed that the quality is maintained over time even under the action of electron fluxes of 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, reduces the loss of adhesion or deterioration. tungsten, rhenium, iridium, osmium and their alloys, 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 Alternatively, deposits of 0.5 to 2111 #I thick were formed consisting of these compounds of the carbide, nitride or boride type.

By way of example, an anode of the invention was used to replace a conventional anode in a scale that was 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 was 200-400℃
and improved the good properties of aluminum nitride thermal conductivity.

The anode of the present invention is used in all Xa tubes, including the latest types, which use high power levels and rotational speeds that can exceed 10,000 revolutions per minute.

Claims (6)

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