US2677873A - Method of making nickel sponge cathodes - Google Patents

Description

IN My y 11, 1954 J. G. BUCK 2,677,873

METHOD OF MAKING NICKEL SPONGE CATHODES Filed Jan. 10, 1946 FIG.2

INVENTOR JAMES G. BUCK ATTORNEY Patented May 11, 1954 UNITED STATES TENT OFFICE METHOD OF MAKING NI CATHODE James G. Buck, Meriden,

assignments, to the Un as represented by the This invention relate tubes, and more particu of cathodes therein.

Considerable research ha production or" cathod and with long life un s to electronic vacuum larly to the construction s been done on the es which will operate stably der pulsed operation in magnsmitting tubes.

pulsed performance.

One of the principal requiremen magnetron cathode is that it have good sparking properties. Sparking can be loose1y defined as the boilin of cathode material to the anode.

ts for a pulsed a prescribed Improvement are: (1) the impe cathode sleeve and of the coatin 3 oh the sparking may possibly be due to e of, or a combination of, the following:

electron path means drop, with a resulting discharge similar to that of a dielectric breakdown It is questionable whether the mechanism involved in (1) and (2) immediately above are actually difierent. In any event, concern is with the cause and not the method.

Of the several impedances it appears that. 86

N. H., assignor,

Secretary of Application January 10, 1946, Serial No.

5 Claims. (Cl.

SCKEL SPONGE by mesne of America the Navy ited States when the cathode is sub tion, the impedance at the interface of the oathode sleeve and its coating is most important.

his interfaci jected to pulsed operaover, the heat dis ture are improved It is, accordingly, the object of the present invention to improve the physical structure of cathodes.

It is another which will have good sparking properties.

her object to constr rial can be impregnated.

In the present embodiment sisting of flat flakes of nickel powder con- 200 mesh size was substituted for being non-criti the nickel, cal. Similarly, inder, the ments being that it b due, and has a high 111 principal requiree volatile, will leave no resielting point. r

This homogeneous mixture was pressed into a steel collar-shaped die or mold, labeled Ill on the accompanying drawings, which die is fitted onto object to construct a cathode supporting nickel sleeve II, this sleeve becoming part of the finished cathode structure. The metal chosen for the sleeve is the same as that used for the mixture to avoid, among Other things, trouble arising from different coefficients of expansion. The mixture is fired in a hydrogen furnace to volatilize the stearic acid and to sinter the flat nickel flakes together and to the nickel sleeve. Die IE is then removed to leave the sintered structure forming a porous metal collar on sleeve l I.

The sintcred structure, as seen underv a low power microscope, consists of layers of the flat nickel flakes l2 tightly bonded together as shown in Fig. 2. The discontinuities-in. the arrangemerit of the flakes, as shown atlitof Fig. 2 are eliminated by machining the sintered structure to a desirable thickness. In the present embodiment the thickness of the porous structure after the mold was removed was approximately .020

inch, this being machined down to .010 inch in the final product.

The porous structure has a large free volume and a large interracial area, resulting in high electrical and thermal conductivity. The use of the fiat nickel flakes allows for a larger interfacial area of contact between metal and coating. 11 similarly porous structure can be prepared by utilizing flakes which'have random shapes, and the volatile binder may be omitted. These changes of method are made, however, at a sacriflce of interfacial area;

The porous structure so prepared is impregnated with the ordinarily used alkaline earth carbonates such as barium, calcium, or a strontium carbonate, the coating being-applied with a brush in the present case, and heat-treated as a conventional cathode.

In summary, the novel features, as sought to be outlined in the following claims, are the construction of a porous metal sponge having a larger interracial area than the previously used screen type of cathode. The structure, there-- fore, provides for higher electrical andv thermal conductivity, with resulting sparking properties which are more desirable for pulsed operation.

What is claimed is:

1. The method of constructing a cathode, which method includes-mixing particles of metal with a volatile binder molding the mixture to form a hollow tube fitted onto a supporting sleeve, holding the molded mixture in contact with the sleeve while heating the mixture thereby removing the volatile substance and sintering said particles or metal together and to said supporting sleeve, machining the outer surface of the composite structure so formed to remove discontinuities in the arrangement of particles, impregnating the composite structure so prepared with an alkaline earth carbonate, and heating until predetermined emission characteristics are obtained.

2. The method of constructing a base structure for a cathode, said method including the steps of mixing particles of metal with a mouldable, volatile binder, molding the mixture to form a molded hollow tube fitted onto a metallic sleeve, heating said mixture while supported in intimate contact with said sleeve thereby. removing the volatile binder and sintering said particles of metal together and to said metallic sleeve, and machining the outer surface of the base structure so formed to remove the outermost layer of particles.

3. The method of constructing a base structure for a cathode, said method including the steps of mixing flat flakes of nickel or 100-200 mesh size with stearic acid, pressing the mixture into a collar-shaped mould fitted onto the supporting sleeve to give a thickness of the mixture of approximately .020 inch on said sleeve, heating said mixture with said mould in place thereby removing the stearic acid, sintering said nickel flakes together and to said supporting sleeve with said mould in place, and machining said sintered nickel flakes with said mould removed to leave a thickness of approximately .010 inch of sintered flakes on said supporting sleeve.

l. The method of manufacturing a cathode comprising the steps of mixing flat flakes of metalwitha volatile binder, molding the mixture to form a hollow tube covering a metallic sleeve, supporting the molded mixture in place while heatingthe tube and sleeve to remove the volatile binder and to sinter the metallic flakes togethcr and to said supporting sleeve, machining said composite structure to remove particles at the outer surface, and impregnating the machined structure with an electron emitting material.

5. The method of producing a porous nickel base structure for a cathode comprising the steps of mixing flat flakes of nickel powder with stearic acid, the proportions being determined by the desired free volume in the final porous structure, molding the mixture to form a hollow tube covering a nickel sleeve, supporting the molded m'ixture in place while heating the tube and sleeve to remove the volatile binder and to sinter the nickel flakes together and to said nickel sleeve, and machining said composite structure to remove particles at the outer surface.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,051,814 Lowendahl Jan. 28, 1913 1,902,478 Wiegand Mar. 21, 1933 2,172,207 Kolligs Sept. 5, 1939 2,289,658 Koehring July 14, 1942 2,337,588 Calkins I Dec. 28, 1943

Claims (1)

1. 2. THE METHOD OF CONSTRUCTING A BASE STRUCTURE FOR A CATHODE, SAID METHOD INCLUDING THE STEPS OF MIXING PARTICLES OF METAL WITH A MOULDABLE, VOLATILE BINDER, MOLDING THE MIXTURE TO FORM A MOLDED HOLLOW TUBE FITTED ONTO A METALLIC SLEEVE, HEATING SAID MIXTURE WHILE SUPPORTED IN INTIMATE CONTACT WITH SAID SLEEVE THEREBY REMOVING THE VOLATILE BINDER AND SINTERING SAID PARTICLES OF METAL TOGETHER AND TO SAID METALLIC SLEEVE, AND MACHINING THE OUTER SURFACE OF THE BASE STRUCTURE SO FORMED TO REMOVE THE OUTERMOST LAYER OF PARTICLES.

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