Method of fabricating cathodes for electron discharge devices
United States Patent 1191 Kerstetter METHOD OF FABRICATING CATHODES FOR ELECTRON DISCHARGE DEVICES [75] Inventor: Donald R. Kerstetter, Emporium,  
 [73] Assignee: GTE Sylvania Incorporated,  
 Stamford, Conn.  
 [22] Filed: May 18, 1973 [21] Appl. No.: 361,831  
 [52] U.S. C1. 29/25.14; 29/494; 29/504 [51] Int. Cl. H0lj 9/00; B23k 31/02 158] Field of Search 29/25.]3, 25.14, 25.15,  
  313/270 [56] References Cited UNlTED STATES PATENTS 2,641,727 6/1953 Pohle 313/270 X 2,708,249 5/1955 Pryslak 29/2516 X 2,945,295 7/1960 Feaster 29/25.]4 X 3,085,175 4/1963 Knauf, Jr. 313/270 3,214,626 10/1965 Larson 313/270 3,333,141 7/1967 Lemmens et a1 313/346 R 3,656,226 4/1972 Burne 29/502 3,667,110 6/1972 Gwyn, Jr.... 3,675,311 7/1972 Wells 29/501 Apr. 8, 1975 10/1973 Woodward 29/484 OTHER PUBLICATIONS B. R. Garrett et a1., Broad Applications of Diffusion Bonding,&#34; NASA CR-409, March, 1966, pp. 84-89.  
 [57} ABSTRACT A cathode assembly comprised of stack or body and a cup-shaped top cap is fabricated by forming the stack, which is generally tubular, from a suitable material such as nickel. The top cap is then formed. also from a suitable material such as nickel. One end of the stack is coated with a slurry comprised of nickel or nickel oxide particles in an organic binder and the top cap is fitted thereover. The stack and assembled top cap are then first fired at a temperature of about 500-600C, in air, to remove the organic binder. This assembly is then second fired at 1,100C in H for at least 1 minute to achieve a bond between the stack and cap via the nickel or the now reduced nickel oxide layer therebetween.  
 3 Claims, 6 Drawing Figures METHOD OF FABRICATING CATHODES FOR ELECTRON DISCHARGE DEVICES BACKGROUND OF THE INVENTION This invention relates to cathodes for electron discharge devices and more particularly to a method of fabricating such cathodes which have particular usefulness in cathode ray tubes.  
  The typical cathode ray tube cathode comprises a tubular stack of nickel or nickel alloy provided at one end thereof with a substantially cup-shaped top cap of a similar nickel material. The top cap, on its upper surface, is provided with an electron emissive material and a heater is generally provided within the stack. In the past it has been the practice to weld the top cap to the stack to achieve affixation. This practice is time consuming and costly in an extremely competitive industry where cost is an important factor.  
 OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of this invention to obviate the disadvantages of the prior art.  
  It is another object of this invention to enhance cathode manufacture.  
  Yet another object of the invention is the enhancement of cathode ray tube cathodes.  
  Still another object of the invention is the creation of a method of fabricating cathodes which can easily be automated.  
  These objects are accomplished in one aspect of the invention by the provision of a method which eliminates the welding of the top cap to the stack. Bonding instead is achieved by using a metal particle containing slurry which is coated upon one end of the stack. The top cap is then placed thereover and the assembly so formed is fired at a temperature sufficiently high to achieve bonding.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an exploded perspective view of a cathode with which this invention is concerned:  
  FIG. 2 is an elevational view of an alternate shape of a top cap;  
  FIGS. 3 and 4 are diagrammatic representations of one method by which the stack can have a layer of slurry applied thereto;  
  FIG. 5 is a view of a stack with the layer or coating of slurry applied; and  
  FIG. 6 is a perspective view of a completed cathode assembly.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in conjunction with the above-described drawings.  
  Referring now to the drawings with greater particularity, there is shown in FIG. 1 a typical cathode ray tube cathode l comprised of a body or stack 12 and a top cap 14 which is substantially cup-shaped and is formed to fit over one end of stack 12. The stack I2 and top cap 14 can be formed by known processes of suitable materials, preferably nickel or nickel alloys containing at least 95 percent nickel.  
  To aid in fitting the top cap 14 to the stack 12 the open end 16 of cap 14 can be flared outwardly as is shown in FIG. 2.  
  To achieve the desired bond between cap 14 and stack 12 a bonding material such as a slurry 18 comprised of nickel or nickel oxide particles suspended in an organic binder is applied to one end of stack 12 and cap 14 is fitted thereover to form cathode I0 which is then fired at a temperature sufficiently high to remove the organic binder and to achieve the desired bond. This temperature is in the neighborhood of greater than 800C and must be in a wet reducing atmosphere to first burn off the organics and second sinter the nickel particles to each other and to any metal in contact with them.  
  For best results particularly in the case of chromium bearing materials, the firing can be accomplished in two steps; a first firing in an oxidizing atmosphere to remove the volatile organic binder at a temperature of about 500600C; and a second firing in a dry reduc ing atmosphere, preferably H at a temperature of about IC. After the firing, the top cap 14 is securely bonded to stack 12 and the cathode 10 is ready to have emissive material applied thereto.  
  While the slurry 18 can be applied to stack 12 in a number of ways, such as by brushing it on directly, a more suitable and novel technique for applying consistent amounts is illustrated in FIGS. 3, 4 and 5. Herein, the slurry 18 is first applied to the interior surface 20 of a tubular sleeve 21 which has an inside diameter slightly larger than the outside diameter of stack 12. Surface 20 can be coated with a brush as shown in FIG. 3. One end of stack 12 is inserted into the interior of sleeve 21 and relative rotation between the pieces is caused to occur. Upon withdrawal of stack 12 a coating of the slurry 18 will have been applied thereto, as shown in FIG. 5 and top cap 14 can be applied thereto. Processing is as described above to produce the cathode 10 shown in FIG. 6.  
  It will be seen that use of this process obviates many of the disadvantages of the prior art. Complicated welding procedures with the consequent contamination possibilities are eliminated. No burrs or rough spots are introduced which could cause arcing under high voltage applications and the process is readily automated, thus providing a cost saving.  
  While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.  
 What is claimed is:  
  l. A method of fabricating cathodes for electron discharge devices, said cathodes comprising a hollow tubular stack and a substantially cup-shaped top cap fitted over one end of said stack and affixed thereto, said method comprising the steps of: forming said stack from a suitable material; forming said top cap from a suitable material; applying a bonding slurry composed of an organic binder containing nickel or nickel oxide particles to one end of said stack; fitting said top cap onto said one end of said stack; and first firing said stack and top cap in air at a temperature between about 500-600C to remove the volatile components of said binder and second firing said stack and top cap in H with said slurry by first coating with said slurry the interior surface of a tubular sleeve having an inside diameter slightly larger than said stack; and inserting said stack into said sleeve whereby said slurry is transferred to said stack.