US3697798A

US3697798A - Rotating x-ray target

Info

Publication number: US3697798A
Application number: US127507A
Authority: US
Inventors: Rudolf Machenschalk; Herbert Wagner
Original assignee: Schwarzkopf Technologies Corp
Current assignee: Schwarzkopf Technologies Corp
Priority date: 1970-03-25
Filing date: 1971-03-24
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10
Also published as: GB1285426A; AT300971B; NL152704B; FR2083554B1; DE2106277A1; FR2083554A1; NL7103827A; DE2106277C3; DE2106277B2

Abstract

This invention relates to a rotating X-ray target made up of three metallic components, i.e., a molybdenum body, a focal track of an alloy of tungsten with one or more metal additives and a component present in the surface not exposed to electrons comprising tungsten alone or a tungsten alloy having a lesser amount of the additive metals.

Description

United States Patent Machenschalk et al.

154] ROTATING X-RAY TARGET [72] Inventors: Rudolf Machenschalk; Herbert Wagner, both of Reutte, Austria [73] Assignee: Schwarzkopf Development Corporation, New York, NY.

221 Filed: March 24, 1971 211 App1.No.: 127,507

[30] Foreign Application Priority Data March 25, 1970 Austria ..2792/70 [52] US. Cl. ..313/330, 313/55, 313/311,

313/352 [51] Int. Cl ..H0lj 35/10, HOlj 1/05, l-lOlj 1/38 [58] Field of Search ..313/55, 311, 330, 352

[56] References Cited UNITED STATES PATENTS Atlee ..313/311 X 1 Oct. 10, 1972 2,863,083 12/1958 Schram ..3l3/330 FOREIGN PATENTS OR APPLICATIONS 1,464,251 7/ 1969 Germany ..313/55 Primary Examiner-David Schonberg Assistant Examiner-Paul A. Sacher Attorney-Morgan, Finnegan, Durham & Pine [57] ABSTRACT This invention relates to a rotating X-ray target made up of three metallic components, i.e., a molybdenum body, a focal track of an alloy of tungsten with one or more metal additives and a component present in the surface not exposed to electrons comprising tungsten alone or a tungsten alloy having a lesser amount of the additive metals.

11 Claims, 3 Drawing Figures P'A'IENTEDHBI 10 I912 13. 697; 7 98 2 I Q @EI 1 (PRIOR ART) FIG. I

I I 2 Q /3 @w 1 1 FIG. 2

FIG. 3

INVENTORS RUDOLF MACHENSCHALK ATTO R NEYS ROTATING X-RAY TARGET X-ray equipment is in wide use for a variety of purposes. Various means are employed to bombard electrons onto a positively charged surface which is conveniently referred to either as an anode or as an X-ray target. There are various types of targets available on the market. These include stationary targets and rotating targets. In general, the X-rays are produced when the electrons hit the surface of the anode or target under appropriate X-ray generating conditions.

The portion of the surface of the target that is bombarded by electrons can be referred to as the focal track.

The material of which the target surface area or focal track is produced is quite important. The material must be of the proper type to both withstand the temperatures of operation and to be an X-ray emitter of sufficient intensity. In addition, the material must have sufficient ductility to withstand conditions of repeated operation. One of the problems frequently encountered with X-ray targets is the roughening of the surface thereby diminishing the efficiency of X-ray emission and rendering emission erratic.

Tungsten is a material commonly used in X-ray targets either alone or as an alloy with small amounts of one or more metal alloying additives. Rhenium is a preferred alloying additive but other alloying additives include osmium, iridium, platinum, technetium, ruthenium, rhodium and palladium.

The alloying additions to the tungsten serve to a large extent to prevent surface roughening during prolonged operation and also tend to reduce the tendency to form cracks on the surface of the focal track.

Since the alloying elements are relatively expensive and some of them are in short supply, attempts have been made to use the tungsten alloys only on the surface of the target and to use other materials, such as molybdenum or molybdenum alloys, i.e., materials with lower specific gravity, as the material for the body of the target. Attempts have also been made to limit the tungsten alloy to just the focal track with the remainder of the surface of the target containing the same material as the body, e.g., molybdenum. Such X-ray targets create considerable difficulty because the different surface zones are subject to different shrinkages, both during formation by powder metallurgical methods and because of heat build-up on the focal track and surrounding areas during electron bombardment of the target. The consequence is the formation of cracks at the transitions between the zones, i.e., between the tungsten alloy and the molybdenum.

In the present invention, use is made of a transition layer between the focal track and the body member which can be of molybdenum or molybdenum alloy. In essence, the X-ray target of this invention comprises a body and a surface layer, the body being comprised of molybdenum or an alloy of molybdenum. The portion of the surface comprising the focal track, the area in which the electrons are intended to impinge, is made of an alloy of tungsten containing a total of from about 0.05 to 25 percent by weight of one or more of metal alloying additives selected from the group consisting of rhenium, osmium, iridium, platinum, technetium, palladium, ruthenium and rhodium. The remainder of the surface, i.e., the portion of the surface not intended for electron impingement, will also be made of a tungsten alloy but it will be a tungsten alloy having a smaller quantity of metal alloying additives than will the tungsten alloy of the focal track. Thus, depending on the alloying additive content of the focal track, this additional surface will contain a total of from about 0.01 to about 4 percent by weight of one or more of the foregoing alloying additives. Alternatively, the surface other than the focal track can be composed of tungsten alone.

The invention is more fully described in connection with the annexed drawings in which:

FIG. 1 shows a section of a prior art type rotating X- ray target;

FIG. 2 is a section of the rotating target of this invention; and

FIG. 3 is a section of a rotating target of an alternate embodiment of this invention.

In the prior art target of FIG. 1, the body 1 is made of molybdenum and the circular focal track, where the electrons impinge on the target, is formed of a tungsten alloy containing 10 percent rhenium. Particularly when this type of target is made by powder metallurgical methods, cracks tend to form at the transition of

zones

1 and 2. It will be noted that the surface areas other than the focal track 2 are made of molybdenum.

In FIG. 2, focal track 2 is made of a tungsten-rhenium alloy containing 10 percent rhenium, and body 1 is made of molybdenum. However, there is an additional layer 3 on the surface of the target not exposed to electron impingement. That surface 3 is made of tungsten or a tungsten-rhenium alloy containing 2 percent rheni- FIG. 3 differs from FIG. 2 in that the alloy zone ex: tends slightly beyond the electron impact area in order to shift the transition between

zones

2 and 3 to the flat area of the target, a convenience which aids in manufacture.

The thickness of the layer comprising the focal track can generally be between about 0.1 mm and 2 mm. The remainder of the surface can also have a thickness within this range. The thickness of the body is not critical and will depend upon the requirements of the equipment in which the target is to be installed. A body of from about 4 to 20 mm in thickness is satisfactory.

The body can be made of molybdenum or a suitable alloy of molybdenum such as those used conventionally as bodies for X-ray targets. Suitable alloys include molybdenum alloys containing from about 2 to 10 percent by weight of tungsten or tantalum, molybdenum alloys containing from about 0.05 to 1.5 percent by weight of titanium, and molybdenum alloys containing from about 0.05 to 0.5 percent by weight of zirconium.

Bodies other than molybdenum may also be employed in the X-ray targets of this invention. For example, graphite may be employed.

The alloy comprising the focal track in the preferred embodiment of this invention should be tungsten alloyed with at least about 1 percent by weight up to about 25 percent by weight of rhenium and, optionally, small amounts, i.e., 0.1 to 5 percent by weight, of osmium, and 0.05 to 2 percent by weight, of iridium. Additionally, the presence of from about 0.05 to 5 percent by weight of platinum also is useful. In the preferred embodiment, the total metal alloying additive content will not exceed about 25 percent by weight of the alloy composition. Most preferably, the rhenium content will be at least about 5 percent by weight of the alloy composition while the amount of any additional additives in total will not exceed the weight of rhenium present.

The remaining part of the surface layer in the preferred embodiment will be composed of tungsten metal alone or of tungsten with a lesser amount of one or more of the alloying additives, preferably from about 0.01 to 4 percent by weight of one of the metal alloying additives. Rhenium is the preferred alloying additive for the surface layer not exposed to electron impact.

A convenient target for use in an X-ray tube can be made, for example, by preparing a die and filling it to a predetermined level with molybdenum powder of particle size range 2 to microns, i.e., where a molybdenum body is desired for the target. By means of a suitable template, the alloy powder for the focal track 2 in particle size 2 to 6 microns is then added. Finally, the remaining space is filled with the powder composition desired to form the zone 3, again in the particle size of from 2 to 10 microns. Thereupon a pressure of about 4 tons per square centimeter is employed to compact the powder in the die. The green compacts thus formed are then sintered under a high degree of vacuum or in an inert or reducing atmosphere such as hydrogen, helium or argon, at a temperature of at least 2,000 C. for 2 hours, and thereupon cooled under the protective atmosphere. The anode is then given its final shape by forging and grinding.

it is found that the products of this invention made in this manner do not suffer from the tendency to crack.

What is claimed is:

l. A rotating X-ray target comprising a body and a surface layer, the body being comprised of a substance selected from the group consisting of graphite, molybdenum and alloys of molybdenum, the portion of the surface comprising a focal track being comprised of an alloy of tungsten and a metal alloying additive selected from the group consisting of rhenium, osmium, iridium, platinum, palladium, technetium, rhodium and ruthenium, and the surface of the target not containing the focal track being comprised of a metal selected from the group consisting of tungsten and tungsten alloys having a smaller amount of metal alloying additive than in the alloy of the focal track surface.

2. A rotating X-ray target as in claim 1 in which the body is comprised of molybdenum.

3. A rotating X-ray target as in claim 1 in which the body is comprised of an alloy of molybdenum.

4. A rotating X-ray target as in claim 1 in which the body is comprised of graphite.

5. A rotating X-ray target as in claim 1 wherein the focal track comprises an alloy of tungsten with about from 1 to 25 percent by weight of rhenium with the remainder of said surface being comprised of a metal selected from the group consisting of tungsten and tungsten alloys with a lesser amount, up to 4 percent by weight, of rhenium.

6. A rotating X-ray target as in claim 1 in which the focal track comprises tungsten, from 1 to 25 percent by weight of rhenium and up to a total of 5 percent by weight of at least one metal selected from the group consisting of osmium, iriditun and platinum.

7. A rotating anode as in claim 1 wherein the alloy in the focal track is an alloy of tungsten with about 10 perent b wei t of rhenium. c 8. X rotefii ng X-ray target comprising a body and a surface layer, the body being comprised of a substance selected form the group consisting of molybdenum and alloys of molybdenum, the portion of the surface comprising a focal track being comprised of an alloy of tungsten with at least one metal alloying additive selected from the group consisting of rhenium, osmiurn, iridium, platinum, palladium, technetium, rhodium and ruthenium, and the remainder of the surface layer being comprised of a metal selected from the group consisting of tungsten and tungsten alloys in which the alloying additive metal is present in smaller amount by weight than in the alloy of the focal track.

9. An X-ray target as in claim 8 in which the metals and alloys are present in the form of sintered metallic material.

10. An X-ray target as in claim 8 in which tungsten alloys are present in both the focal track and the surface layer adjacent thereto.

11. A rotating X-ray target as in claim 8 in which rhenium is alloyed with tungsten in both the focal track and said remainder of the surface area.

Claims

2. A rotating X-ray target as in claim 1 in which the body is comprised of molybdenum.
3. A rotating X-ray target as in claim 1 in which the body is comprised of an alloy of molybdenum.
4. A rotating X-ray target as in claim 1 in which the body is comprised of graphite.
5. A rotating X-ray target as in claim 1 wherein the focal track comprises an alloy of tungsten with about from 1 to 25 percent by weight of rhenium with the remainder of said surface being comprised of a metal selected from the group consisting of tungsten and tungsten alloys with a lesser amount, up to 4 percent by weight, of rhenium.
6. A rotating X-ray target as in claim 1 in which the focal track comprises tungsten, from 1 to 25 percent by weight of rhenium and up to a total of 5 percent by weight of at least one metal selected from the group consisting of osmium, iridium and platinum.
7. A rotating anode as in claim 1 wherein the alloy in the focal track is an alloy of tungsten with about 10 percent by weight of rhenium.
8. A rotating X-ray target comprising a body and a surface layer, the body being comprised of a substance selected form the group consisting of molybdenum and alloys of molybdenum, the portion of the surface comprising a focal track being comprised of an alloy of tungsten with at least one metal alloying additive selected from the group consisting of rhenium, osmium, iridium, platinum, palladium, technetium, rhodium and ruthenium, and the remainder of the surface layer being comprised of a metal selected from the group consisting of tungsten and tungsten alloys in which the alloying additive metal is present in smaller amount by weight than in the alloy of the focal track.
9. An X-ray target as in claim 8 in which the metals anD alloys are present in the form of sintered metallic material.
10. An X-ray target as in claim 8 in which tungsten alloys are present in both the focal track and the surface layer adjacent thereto.
11. A rotating X-ray target as in claim 8 in which rhenium is alloyed with tungsten in both the focal track and said remainder of the surface area.