US2379397A - Anode structure - Google Patents

Description

June 26, 1945. J. ZUMCK 2,379,397

ANODE STRUCTURE Filed Nov. 16, 1942 (a? :w- Z

I N V EN TOR.''

Patented June 26, 1945 AN ODE STRUCTURE Michael J. Zunick, Columbus, Ohio, assignor to General Electric X- Ray Corporation, Chicago,

111., a corporation of New York Application November 16, 1942, Serial No. 465,715

15 Claims.

My invention relates in general to electronics and has more particular reference to an improved electrode construction particularly well suited for anodes of X-ray generators.

An X-ray generator comprises an electron emitting cathode and an anode at which X- rays are generated by impingement, upon a suitable target at the anode, of electrons emitted by the cathode. Among materials commonly used for anode targets are tungsten, nickel, copper, cobalt, iron, chromium, molybdenum, and other metals. Electron impingement on the target surface of the anode during operation of the tube results in grain growth in the target material at the target surface due to heat, liberated in the anode through electron impingementthereon.

Such. grain growth results in deformation or curling of the anode at the targetsurface and consequent reduction in the X-ray output of the generator; and an important. objectof the present invention is to minimize such target deformation or curling through the provision of an improved anode structure presenting the anode material at the target surface in dense'condition having a grain structure and. other characteristics particularlywell' adapted to'res'ist target'deformation or curling. v

Another object is to minimize target deterioration by employing atarget of pure metal;ja further object being to utilize pure electrolytic Cops Another important object is to provide an anode ior an X-ray generator having a target surface comprising material in which the grain structure extends in'a direction intersecting the plane of th 'target surface preferably at right angles; a further object being to utilize as an X-ray anode target a button in which the metallic grain structure extends in a direction normal to the target face of the button; a still further object being to form target buttons by first rolling a bar of suitable metallic target-material longitudinall to impart a grain-structure extending lengthwise of the bar and-then cutting discs from the bar to provide buttons in which the grain structur comprises grains having ends extendingatthe cut. face of the. button.

The foregoing andnumerous. other important objects, advantages, and inherent functionsof the invention will be. fully understood. from the following, description,v which, taken in connection with the accompanying. drawing. discloses a preierred embodiment of the invention.

j Referring to the drawing: g i Figure 1 is a sectional view taken through; an

showing a modified anode structure embodying the invention.

To illustrate the invention the drawing. shows an X-ray generator H comprising a sealed envelope 13. containing an. anode l5 and a cathode ll embodying an. electron emitting filament 19, the cathode and anode beingmounted incoaxial .spaced and facing relationship within. the envelope Iii. Suitable conductors for energizing the filament. t9 and for applying operating potential between the filament and the: anode from anelectrical power source outwardly of the. envelope,-of course, are. provided.

While the invention. is not necessarily limited to. any particular type or form. of generator, the X-ray generator H, as shown in. Figure 1, come prises a generator of the short particularly well suited: for producing X-rays for the analysis of materials by X-ray diffraction. To. this end the surface of. the anode facing, the electron emitting element l9 forms, a. target, surface 2|, and the generator operates to produce X-rays at said target surface as a. result of theimpingement, on said surface, of electrons emitted at the filament 19 when electrically energized, said emitted electrons being impelled. toward and caused to impinge upon the. target surface 2| under the influence of generator operating electrical. potential, applied between the filament and the anode. The target surface 2! may, of course, comprise any suitable metallic material, suchas tungstenjmolybdenum, copper, nickel, cobalt, iron,

chromium or other preferred target material.

X-rays generated as a resultv of electron impingement on the target surface 21 pass outward- 1y of. the envelope through transmitting windows 23. formed. in the envelope walls opposite the anodetarget. If. desired, the. envelope of the generator may be enclosed in a casing, or a sleeve 25 fX -ray opaquev material, and. may b assembledaround the X-ray transmitting portions of. the) envelope. and provided with openings 21 in line with the windows 23for the purpose of blocking exit. of X-rays' from the tube except at said openings 21.

When. anX-ray generator is in operation for production of X-rays at the? target 21, a considerable amount of heat is developed at the target surface as a result of electron impingement, such heat being dissipated through the body of the anode and thence outwardly of the envelope. The temperature at the target surface of the anode, however, may be of the order of the melting temperature of the target. material, it bein usual, in the interests of operating efilciency, to oper:- ate the generator so that its anode at the target surface functions at a temperature just short of the softening temperature of the anode material. When operated at such temperature there is a tendency for grain growth to occur in the anode material, such growth being evidencedby the bulging or curling of the anode material at the target surface and the consequent deformation of said surface from a desirable flat condition. Such deformation or curl, to some extent, impairs the production of X-rays at the target of the device.

According to the present invention, the tendency of the target surface to becom raised or curled in service is minimized by providing a target comprising substantially pure metal; To this end, where the target is formed of copper, pure electrolytic copper is preferably employed as the target material. Likewise, where other target material, such as tungsten, chromium, nickel, cobalt, iron, molybdenum or other metal is employed, appreciable improvement is obtained in the abilityof th target to resist deterioration in service, when the target material is applied and maintained in substantially pure form.

Target deformation and curling in service also is minimized by using compact, dense metal having a uniform grain structure characterized, preferably, in that the grains of the material extend vertically with respect to the targetsurface of the anode. Electrons impinging on such a surface strike the ends of the crystals of material forming the anode target, which, because of the compact parallel grain structure, tends to'avoid grain growth. The structure of material having parallel grain arrangement, with the grain ends presented at the target surface, may conveniently be designated by the term end grain.

While the entire anode may be formed of material having the desired grain structure, including grains ending or terminating at the target surface, it is not necessary to make the entire anode of the relatively expensive end grain material, and it is preferable to form the. body 29 of the anode in any suitable or convenient manner, as by forming the same as a casting, preferably comprising vacuum melting copper.

The body of the anode, however, is formed with a pocket 31' in the surface thereof which faces the cathode and a. target button is fixed in said pocket, as by soldering the same in place. The button 33, in the illustrated embodiment, comprises a suitable metallic target material, such as pure electrolytic copper, or other metallic target material, in which the grains extend in a direction normal to the target surface 2Iof the button. Such granular structure may be accomplished by rolling .or otherwise working a bar of the selected target material in order to accomplish the desired parallel grain structure in a direction longitudinally of the bar, and then'cutting the bar in sections at right angles to the grain direction in order to provide the target button 33, having the so-called end grain structure.

The button 33 may be'secured' inthe'pocket 3| by solderin the same in place, as with eutectic ployment of an anode embodying end grain target material materially improves the curl-resisting ability of the target. At the same time, it is equally important, if not more important, to employ a target material comprising pure metal. In making a copper target, pure electrolytic copper should be used as the target material. Commercial Vacuum melted copper of the sort ordinarily employed in X-ray tube anodes is appreciably contaminated with foreign material and shows a very definite tendency to blister or curl when used as a target material, even if treated to provide vertical grain structure. Pure electrolytic copper, however, even in the absence of the desirable end grain arrangement, provides a sat- .isfactory substantially non-bulging target, the

same being true where other target materials are used in substantially pure condition for target purposes. The end grain arrangement, however, is of appreciable value in producing satisfactory anodes and consequently the same forms a val-' uable phase of the present invention.

When in operation at high temperature there is a tendency for the solder 35 to flow along and between the parallel grains of the button 33, and solder may, in this way undesirably reach the face of the target.

In order to exclude the possibility of solder flow along and between the crystals of a soldered end grain target button, the same may be directly united with a backing disc 31 of like material in which the grains extend crosswise of the disc, as shown in Figure 4. The composite backed button thus produced may besoldered in the pocket 3| without any possibility of solder flow therethrough to the face of the target.

X-ray tube anodes made in accordance with the teachings of the present invention are characterized in that they are substantially immune to target surface deformation in service.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. An anode structure comprising a body of pure electrolytic copper forming a target surface, said body having an internal grain structure normal to the target surface.

2. An anode structure comprising a body of metal forming a target surface, said body having an internal grain structure normal to the target surface.

3. An anode structure comprising a body" of metal forming a target surface, said body being in substantially pure condition without contamination and having an internal grain structure substantially normal to the target surface.

4. An anode structure comprising'a copper base having a pocket and a body of metal forming a target button secured in said pocket, said button said button providing a target surface and having an end grain structure at said surface.

6. An anode structure comprising a copper base having a pocket and a body of pure electrolytic copper forming a target button secured in said pocket, said button forming a target surface and having an internal grain structure normal to the target surface.

7. An anode structure comprising a base of vacuum cast copper formed with a pocket and a target button of pure electrolytic copper secured in said pocket, said button forming a target surface and having an internal grain structure normal to the target surface.

8. An anode structure comprising a base having a pocket, a metal target button having end grain structure secured'in the pocket, and a backing disc of metal in the pocket behind said target button.

9. An anode structure comprising a base having a pocket, a metal target button having end grain structure secured in the pocket, and a backing disc of metal in the pocket behind said target button, said backing disc having cross grain structure.

10. An anode structure comprising a metallic base having a pocket, a metal target button having end grain structure in said pocket, and a backing disc of metal in the pocket behind said target button and directly bonded to said target button, said backing disc having internal cross grain structure and being soldered in place in the pocket whereby to prevent contamination of the target button by the solder.

11. An anode structure comprising a base having a pocket, and a target button secured in said pocket and having a target surface, said target button comprising metal having an internal grain structure substantially normal to the target surface.

12. An anode structure comprising a copper base having a pocket, and a target button secured in said pocket and providing a target surface, said target button comprising metal in substantially pure condition without contamination and having an internal grain structure substantially normal to the target surface.

13. An anode structure comprising a base of vacuum cast copper formed with a pocket, and a target button secured in said pocket and providing a target surface, said target button comprising metal in substantially pure condition without contamination and having an end grain structure at said surface.

14. An anode structure comprising a base having a pocket, a target button secured in said pocket and providing a target surface, said button comprising metal in substantially pure condition without contamination and having an end grain structure at said surface, and a backing disc of metal in the pocket behind said target button.

15. An anode structure comprising a base having a pocket, 2. target button secured in said pocket and providing a target surface, said button comprising metal in substantially pure condition without contamination and having an end grain structure at said surface, and a backing disc of metal in the pocket behind said target button, said backing disc having cross grain structure.

MICHAEL J. ZUNICK.

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