US3136907A

US3136907A - Anticathodes for X-ray tubes

Info

Publication number: US3136907A
Application number: US81216A
Authority: US
Inventors: Kieffer Richard; Sedlatschek Karl
Original assignee: Metallwerk Plansee GmbH
Current assignee: Metallwerk Plansee AG; Metallwerk Plansee GmbH
Priority date: 1961-01-05
Filing date: 1961-01-05
Publication date: 1964-06-09
Anticipated expiration: 1981-06-09

Description

Ju 9, 1964 R. KIEFFER ETAL 3,136,907

I ANTICATHODES FOR X-RAY TUBES Filed Jan. 5,1961

INVENTORS AW 664/4 0 K/FFFE/P BY X/I/PL 5501475095? United States Patent M 3,136,907 ANTICATHODES FOR X-RAY TUBES Richard Kiefier and Karl Sedlatschek, Reutte, Tirol, Austria, assignors to Metfllwerk Plansee Aktiengesellschaft, Tirol, Austria, a corporation of Austria Filed Jan. 5, 1961, Ser. No. 81,216 4 Claims. (Cl. 313-55) This invention relates to X-ray or Roentgen tubes which operate with fixed or rotary anodes for use in medical applications, determining the crystal structure of various substances, and other services. Such X-ray tubes operate as a rule with an anticathode or anode of pure tungsten. There are many applications wherein it is of utmost importance to operate such X-ray tubes with a very high load factor. However, the level of the load factor to which such X-ray tubes may be subjected is limited by the fact that the beam-impinged target area of the tungsten cathode develops cracks because of high thermal loading thereof, thereby making it impossible to increase the anticathode load of such tube above a limited level.

Among the objects of the invention is an X-ray tube which will permit loading of its anticathode by the electron beam to a materially higher extent than heretofore possible. In accordance with the invention, the anticathode or anode of X-ray tubes which are to be subjected to high electron-beam load, are provided at least in the region of their electron-beam target area, with a target-area layer formed of an alloy consisting of 10% to 35% rhenium and as balance the base metal tungsten.

. (Throughout the specification and claims, all proportions are given by weight unless otherwise specifically stated.)

The foregoing and other objects of the invention will best be understood from thefollowing description of exemplifications thereof reference being had to the accompanying drawings wherein FIG. 1 is a partially diagrammatic elevational view of an X-ray tube having a rotary anode exemplifying the invention; and

FIG. 2 is a partially cross-sectional and partially elevational view of the bottom part of the anode of FIG. 1 on a greatly enlarged scale.

FIGS. 1 and 2 show partially diagrammatically an example of an X-ray tube operating with a rotary anode exemplifying theinvention. A glass envelope 1 contains in its highly evacuated interior space a cathode structure 2 carrying filament 3 and an electron concentrating element 4 located opposite a narrow portion of the conical target layer 5 of rotary anode disk 6. The anode disk 6 has central anode shaft 7 which is rotated by a motor 8.

Under application of high tension voltage a concentrated electron beam emitted by the negative cathode filament 3 will bombard a facing portion of the positive anode target area 5 and cause it to emit X-rays. The energy of the electron beam impinging upon the anode target area 5 is transformed almost entirely into heat which is transmitted to and heats the entire mass of the anode 6. Under excessive heat the metal of the target area 5 of anode6 develops cracks which reduce the X-ray emission therefrom.

In accordance with the invention at least the target surface layer 5 of the anti cathode or anode 6 of the X-ray tube is formed of an alloy consisting of 10% to 25% of rhenium and as balance of a base metal alloyed with the 3,136,907 Patented. June 9, 1964 rhenium and selected from the group consisting of tungsten alloyed with up to 14% of tantalum or niobium or a mixture of tantalum and niobium. Furthermore, such rhenium alloyed target layer 5 of the anode should be at least about inch thick.

For best results, at least the target surface layer of the anticathode or anode of the X-ray tube, consists of 10% to 25% rhenium, and as balance the base metal tungsten. It has also been found that the base metal of such anticathode or anode of the invention may be formed of an alloy of tungsten with one or more of the metals of the group consisting of niobium and tantalum, thereby yielding a target anticathode body formed of a ternary alloy, such as consisting of tungsten, 10% tantalum, and 30% rhenium, which case, the base metal consists of about 86% tungsten and 14% of tantalum. The entire anticathode or anode of an X-ray tube may be formed of such alloys of tungsten with rhenium, or such tungsten alloys with rhenium. Since rhenium is scarce and costly, only a surface layer of the anticathode which constitutes the target for the electron beams, is formed of such basemetal rhenium alloy, the balance of the anticathode being formed of the base metal tungsten.

Anticathodes for X-ray tubes of the invention may be formed by mixing powder particles of tungsten and rhenium in the specified proportions, and compacting such metal-powder mixture in a die cavity having the shape of the anticathode, followed by sintering and forging of the sintered metal powder body to give it high density and the desired final shape. For producing an anticathode or anode for an X-ray tube wherein only the target area layer of the anticathode is formed of the rhenium basemetal alloy, a layer section of the die cavity in which the anticathode is to be formed, for instance ,4 in thickness, is filled with the alloy powder mixture consisting of rhenium particles and base-metal particles in the abovespecified proportions, with the balance of the die-cavity filled with the base metal only. After so compacting the powder body in the die into a green, self-supporting compact, it is sintered, for instance under protective atmosphere or under vacuum, at temperatures in the range between 2300 C. and 2800 0., followed by forging or coining to final shape at a temperature range between 1400 C. and 1600 C. FIG. 2 shows in partial crosssection an example of such X-ray anode 6 of the invention.

The main body of the anode disk 6 is made of a refractory metal such as tungsten or an alloy of tungsten with tantalum and/or niobium, as described above. To increase its load factor the anode target layer 5 is at least A inch thick and consists of 10% to 25% rhenium alloyed with the base metal thereof consisting of tungsten or tungsten alloyed with up to 14% of tantalum and/ or niobium. Rhenium being scarce, only the target layer 5 of the anode 6 is shown formed of the rhenium containing base metal alloy.

It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific exemplifications thereof, will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims, they shall not be limited to the specific exemplifications of the invention described above.

We claim:

1. In an X-ray tube, the combination of a metallic anode having an exposed target area and beam means including an electron source for producing an electron beam impinging on said exposed target area and causing said exposed target area to emit X-rays,

a metal layer of said anode having said exposed target area and being at least about of an inch thick consisting essentially of 10% to 25% rhenium and as balance of a base metal alloyed with said rhenium, said base metal being selected from the group consisting of tungsten, tungsten alloyed with up to 14% tantalum, tungsten alloyed with upto 14% niobium and tungsten alloyed with up to 14% of tantalum and niobium. a

2. In an X-ray tube as claimed in claim 1, said base metal consisting essentially of tungsten.

3. In an X-ray tube as claimed in claim 1, said metal alloy containing 5% to 25 of Re, said base metal consisting essentially of tungsten, body parts of said anode other than said surface layer consisting essentially of tungsten.

4. In antX-ray tube as claimed in claim 1, said base metal consisting essentially of tungsten, body parts of said anticathode other than said surface layer consisting essentially of tungsten alloyed with tantalum.

References Cited in the file of this patent UNITED STATES PATENTS 2,863,083 Schram Dec. 2, 1915 8

Claims

1. IN AN X-RAY TUBE, THE COMBINATION OF A MEALLIC ANODE HAVING AN EXPOSED TARGET AREA AND BEAM MEANS INCLUDING AN ELECTRON SOURCE FOR PRODUCING AN ELECTRON BEAM IMPINGING ON SAID EXPOSED TARGET AREA AND CAUSING SAID EXPOSED TARGBET AREA TO EMIT X-RAYS, A METAL LAYER OF SAID HAVING SAID EXPOSED TARGET AREA AND BEING AT LEAST ABOUT 1/18 OF AN INCH THICK CONSISTING ESSENTIALLY OF 10% TO 25% RHENIUM AND AS BALANCE OF A BASE METAL ALLOYED WITH SAID RHENIUM, SAID BASE METAL BEING SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN, TUNGSTEN ALLOYED WITH UP TO 14% TANTALUM, TUNGSTEN ALLOYED WITH UP TO 14% NIOBIUM AND TUNGSTEN ALLOYED WITH UP TO 14% OF TANTALUM AND NIOBIUM.