CA2200513A1 - A method for manufacturing an impregnated cathode - Google Patents
A method for manufacturing an impregnated cathodeInfo
- Publication number
- CA2200513A1 CA2200513A1 CA 2200513 CA2200513A CA2200513A1 CA 2200513 A1 CA2200513 A1 CA 2200513A1 CA 2200513 CA2200513 CA 2200513 CA 2200513 A CA2200513 A CA 2200513A CA 2200513 A1 CA2200513 A1 CA 2200513A1
- Authority
- CA
- Canada
- Prior art keywords
- plate
- support
- cathode
- soldering
- metal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/13—Solid thermionic cathodes
- H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
- H01J1/28—Dispenser-type cathodes, e.g. L-cathode
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/02—Manufacture of electrodes or electrode systems
- H01J9/04—Manufacture of electrodes or electrode systems of thermionic cathodes
- H01J9/042—Manufacture, activation of the emissive part
- H01J9/047—Cathodes having impregnated bodies
Abstract
A procedure for manufacturing an impregnated cathode whose upper part includes an emitting plate of refractory material arranged in a support dish, wherein the soldering of the dish to its support is carried out by melting a metal material arranged between the plate and its support. The material has a melting point between the operating temperature of the cathode and the melting point of the components constituting the emitting plate.
Description
RCA 88,153 A METHOD FOR MANUFACTURING AN IMPREGNATED CATHODE
The present invention relates to a method for manufacturing impregnated cathodes, especially for equipping electron guns for - 5 cathode ray tubes.
An impregnated cathode contains a porous emitting plate of refractory material (tungsten, molybdenum, rhenium, etc.) impregnated with emitting material (barium, strontium, calcium, aluminum, cesium, etc.). This plate is arranged on a support 10 generally in the form of a small refractory metal dish (tantalum, molybdenum, etc.). The plate and dish unit forms the upper part of the cathode.
The emitting plate and its support are assembled so as to form a- mechanical unit capable of standing up under the various 15 phases of manufacture of the cathode and the high operating temperatures of the cathode. Morever, the contact between the plate and its support should be as good as possible in order to guarantee the performance of the cathode.
Various methods have been used to make the upper part of 2 0 an impregnated cathode. One method consists of depositing a coating on the back surface of the emitting plate to facilitate soldering with the support. The coating is, in general, based on powders of molybdenum and rhenium. The major disadvantages are the high price of this coating; difficulty in storing due to high 2 5 degrees of evaporation and sedimentation; difficulty in controlling and reproducing the quantity deposited on the support, which causes a variable thickness of the interface; the impossibility of depositing on small size cathodes (less than 2 mm); and the required alignment of the surface of the plate covered with 30 coating to make the weld.
A second method, as indicated in U.S. Patent No. 5,218,263, issued to L. R. Falce et al. on June 8, 1993, consists of mechanically blocking the emitting plate of the cathode on the support by a cap or a piece covering the latter in part. The cap has an opening to 35 permit the emission of the plate into the tube. This cap is soldered with the support and thus forms a single piece with the 2 RCA 88,153 upper part of the cathode. The major disadvantages are an increase of the weight of the cathode in making this structure, which is to the detriment of the arcing time of the cathode; low efficiency thermal conduction from the plate to the rest of the 5 cathode, to the detriment of the overall performance of the cathode; a risk of assembling the plate at a bias or with a high degree of freedom; the presence of a metal piece between the electrode of the gun situated in front of the cathode and the surface of the plate, which piece modifies the conformation of the 10 applied electrical field; and a subsequent deposit of the material on the surface of the plate at the outlet of the cathode that lowers the output from the cathode.
A third method, divulged in U.S. Patent No. 5,171,180, issued to K. S. Lee on December 15, 1992, consists of directly assembling 15 the plate onto its support without soldering, then treating the assemby of parts in a high temperature hydrogen furnace to cause a chemical reaction of the emitting products contained in the plate with the support, in order to make a bond. The major disadvantages are the loss of emitting materials contained in the 20 plate, to be able to make the bond with the support, which reduces the service life of the cathode; the treatment in a hydrogen furnace, necessitating having only one pile of many small size parts; the correct positioning of the plate not being guaranteed during the handling in the furnace or by the 2 5 movements caused to the plate in its positioning during the chemical reaction; a positioning stability not being guaranteed for the plate during the use; and the possibility of delamination of the products .
A fourth method, divulged by U.S. Patent No. 5,128,584, 30 issued to J. Choi on July 7, 1992, consists of soldering the cathode plate directly with its support, with a preliminary treatment roughening the two surfaces to be joined. The soldering is carried out by electrical resistance and is facilitated by the good contact made between the two components. The greatest disadvantages 3 5 are the power necessary for soldering the refractory material, which causes a high increase in temperature modifying or ~ ~ n ~ ~ 3 3 RCA 88,153 destroying in part the emission products contained in the plate;
the fragility of the solder, because the latter remains weak and fragile during the assembly of the cathodes into the electron gun;
the obligation to align the face of the plate made rough to make 5 the solder; and the difficulty of aligning the surface of a plate of small size (less than 2 mm).
Thus, there is need for a procedure for manufacturing an impregnated cathode and, more particularly, a procedure for assembling the emitting plate to its support, which does not have 10 the disadvantages of the state of the art, which is simple to put into operation and economical, and whose effects are neutral, relative to the emissivity of the plate, while guaranteeing a reliable and repeatable positioning of the plate onto its support.
A method of manufacturing an impregnated cathode, 15 according to the invention, includes soldering a porous emitting plate of refractory material inside a support of refractory metal, wherein, to facilitate the soldering, a purely metallic transport material is arranged between the emitting plate and its support.
In a particularly advantageous form of implementation, the 20 transport material is a thin metal tab inserted between the emitting plate and its support.
In the drawings:
Figure 1 is a cut-away side view of an impregnated cathode according to the state of the art;
Figure 2 is a side view of a cathode, in accordance with the present invention, showing the upper part of the cathode in exploded view; and Figure 3 is a top view, and Figure 4 is a cut-away side view, illustrating a preferential mode of implementation of the present 30 invention.
As indicated in Figure 1, an impregnated cathode generally includes a cylindrical body 2 at the end of which is an upper part of the cathode consisting of an emitting plate 1, most often containing tungsten as a basic material, arranged on a support 13, 3 5 most often of tantalum or molybdenum. Inside the body 2 is inserted a heating element 5. A cylinder 4 forms the outer skirt 4 RCA 88,153 of the cathode and serves as a heat shield to prevent losses of the heat created by the heating element 5, thus increasing the thermal efficiency of the assembly. The body of the cathode 2 is kept in position inside the shield by strips 3 soldered to the body 2 (e.g., 5 at points 6, as shown in Figure 2) and to the outer skirt 4.
One of the difficulties concerning the assembly of the various elements of the cathode involves the connection of the plate 1 to its support 13. This connection should be mechanically strong, offer an excellent thermal transmission, and be neutral 10 toward the emission properties of the plate, all at high operating temperatures which may exceed 1200~C.
The parameters of stability during emission, service life, arcing time, and stability of the emission threshold depend essentially on the mechanical strength of the plate with the rest of 15 the cathode structure.
Because the emitting plate and its support are of refractory materials, it is extremely difficult to make, by soldering, the direct connection of the two components. The numerous solutions divulged in the state of the art do not offer a simple, reliable, and 2 0 cheap solution with the characteristics of repeatability necessary for mass producing a key component of cathode ray tubes.
To obtain a superior contact between the refractory metal support 13 and the emitting plate 1, which contact makes it possible to optimize the thermal conduction between the heating 25 element 5 and the plate, it is necessary to join by soldering the materials together without destroying the porosity of the plate and without modifying the emission characteristics, which prohibits a soldering at a temperature which is too high.
As indicated in Figure 2, the invention proposes inserting 30 between the emitting plate 1 and its support 13, a metal transport material 8, which is chemically neutral and which permits soldering the two components at a sufficiently low temperature so as not to deteriorate the emission characteristics of the plate. For this, the material chosen should have a melting point between the 3 5 operating temperature of the cathode and that of the metals constituting the plate.
RCA 88,153 The transport material, placed as an interface between the plate and its support, may be in the form of metal powder, flat ribbon, or wire.
Because it is necessary to minimi7e the amount of transport 5 material, in order to reduce the weight and/or size of the cathode particularly for heat output reasons, the transport material may, in one advantageous mode of implementation, be deposited by vaporization in a vacuum directly upon the support 13. In this way, the thickness of the layer of material 8 may be controlled, 10 preferably to between 1 and 25 microns, a thickness permitting good solderability of the components 1 and 13 without affecting the heat output characteristics of the cathode.
In another preferential mode of implementation, the transport material is in the form of a thin metal tab with a 15 thickness chosen between 1 and 25 microns. Advantageously, the tab is cut so as not to occupy the whole contact surface between the support 13 and the plate 1, in order to reduce the weight of the transport material. To reliably perform the soldering between the plate and its support, it is necessary, however, that the surface 20 covered by the transport material be sufficient, taking into account the small dimensions of the components to be soldered.
Experience has shown that a tab surface area ranging between 0.4 and 0.7 times the surface area of the face of the plate, generally of a rounded shape, would make it possible to ensure the soldering 2 5 of the components under good conditions of reliability.
As illustrated in Figure 3, showing a view of the inside of the support 13, the tab 10 is, for example, cut in the form of a rectangle with rounded corners, which shape has the advantage of automatic centering during its insertion into the support 13, 30 generally in the form of a dish. In this way, there is moreover ensured the soldering of the plate 1 to its support 13 by situating the soldering points 9 in the center part of the plate. For a circularly cylindrical emitting plate with a diameter of 1.27 mm, there is chosen, by way of example, a metal tab 1.1 mm long by 35 0.6 mm wide with a metal thickness which can be selected from l to 25 microns.
5 ~ ~
The present invention relates to a method for manufacturing impregnated cathodes, especially for equipping electron guns for - 5 cathode ray tubes.
An impregnated cathode contains a porous emitting plate of refractory material (tungsten, molybdenum, rhenium, etc.) impregnated with emitting material (barium, strontium, calcium, aluminum, cesium, etc.). This plate is arranged on a support 10 generally in the form of a small refractory metal dish (tantalum, molybdenum, etc.). The plate and dish unit forms the upper part of the cathode.
The emitting plate and its support are assembled so as to form a- mechanical unit capable of standing up under the various 15 phases of manufacture of the cathode and the high operating temperatures of the cathode. Morever, the contact between the plate and its support should be as good as possible in order to guarantee the performance of the cathode.
Various methods have been used to make the upper part of 2 0 an impregnated cathode. One method consists of depositing a coating on the back surface of the emitting plate to facilitate soldering with the support. The coating is, in general, based on powders of molybdenum and rhenium. The major disadvantages are the high price of this coating; difficulty in storing due to high 2 5 degrees of evaporation and sedimentation; difficulty in controlling and reproducing the quantity deposited on the support, which causes a variable thickness of the interface; the impossibility of depositing on small size cathodes (less than 2 mm); and the required alignment of the surface of the plate covered with 30 coating to make the weld.
A second method, as indicated in U.S. Patent No. 5,218,263, issued to L. R. Falce et al. on June 8, 1993, consists of mechanically blocking the emitting plate of the cathode on the support by a cap or a piece covering the latter in part. The cap has an opening to 35 permit the emission of the plate into the tube. This cap is soldered with the support and thus forms a single piece with the 2 RCA 88,153 upper part of the cathode. The major disadvantages are an increase of the weight of the cathode in making this structure, which is to the detriment of the arcing time of the cathode; low efficiency thermal conduction from the plate to the rest of the 5 cathode, to the detriment of the overall performance of the cathode; a risk of assembling the plate at a bias or with a high degree of freedom; the presence of a metal piece between the electrode of the gun situated in front of the cathode and the surface of the plate, which piece modifies the conformation of the 10 applied electrical field; and a subsequent deposit of the material on the surface of the plate at the outlet of the cathode that lowers the output from the cathode.
A third method, divulged in U.S. Patent No. 5,171,180, issued to K. S. Lee on December 15, 1992, consists of directly assembling 15 the plate onto its support without soldering, then treating the assemby of parts in a high temperature hydrogen furnace to cause a chemical reaction of the emitting products contained in the plate with the support, in order to make a bond. The major disadvantages are the loss of emitting materials contained in the 20 plate, to be able to make the bond with the support, which reduces the service life of the cathode; the treatment in a hydrogen furnace, necessitating having only one pile of many small size parts; the correct positioning of the plate not being guaranteed during the handling in the furnace or by the 2 5 movements caused to the plate in its positioning during the chemical reaction; a positioning stability not being guaranteed for the plate during the use; and the possibility of delamination of the products .
A fourth method, divulged by U.S. Patent No. 5,128,584, 30 issued to J. Choi on July 7, 1992, consists of soldering the cathode plate directly with its support, with a preliminary treatment roughening the two surfaces to be joined. The soldering is carried out by electrical resistance and is facilitated by the good contact made between the two components. The greatest disadvantages 3 5 are the power necessary for soldering the refractory material, which causes a high increase in temperature modifying or ~ ~ n ~ ~ 3 3 RCA 88,153 destroying in part the emission products contained in the plate;
the fragility of the solder, because the latter remains weak and fragile during the assembly of the cathodes into the electron gun;
the obligation to align the face of the plate made rough to make 5 the solder; and the difficulty of aligning the surface of a plate of small size (less than 2 mm).
Thus, there is need for a procedure for manufacturing an impregnated cathode and, more particularly, a procedure for assembling the emitting plate to its support, which does not have 10 the disadvantages of the state of the art, which is simple to put into operation and economical, and whose effects are neutral, relative to the emissivity of the plate, while guaranteeing a reliable and repeatable positioning of the plate onto its support.
A method of manufacturing an impregnated cathode, 15 according to the invention, includes soldering a porous emitting plate of refractory material inside a support of refractory metal, wherein, to facilitate the soldering, a purely metallic transport material is arranged between the emitting plate and its support.
In a particularly advantageous form of implementation, the 20 transport material is a thin metal tab inserted between the emitting plate and its support.
In the drawings:
Figure 1 is a cut-away side view of an impregnated cathode according to the state of the art;
Figure 2 is a side view of a cathode, in accordance with the present invention, showing the upper part of the cathode in exploded view; and Figure 3 is a top view, and Figure 4 is a cut-away side view, illustrating a preferential mode of implementation of the present 30 invention.
As indicated in Figure 1, an impregnated cathode generally includes a cylindrical body 2 at the end of which is an upper part of the cathode consisting of an emitting plate 1, most often containing tungsten as a basic material, arranged on a support 13, 3 5 most often of tantalum or molybdenum. Inside the body 2 is inserted a heating element 5. A cylinder 4 forms the outer skirt 4 RCA 88,153 of the cathode and serves as a heat shield to prevent losses of the heat created by the heating element 5, thus increasing the thermal efficiency of the assembly. The body of the cathode 2 is kept in position inside the shield by strips 3 soldered to the body 2 (e.g., 5 at points 6, as shown in Figure 2) and to the outer skirt 4.
One of the difficulties concerning the assembly of the various elements of the cathode involves the connection of the plate 1 to its support 13. This connection should be mechanically strong, offer an excellent thermal transmission, and be neutral 10 toward the emission properties of the plate, all at high operating temperatures which may exceed 1200~C.
The parameters of stability during emission, service life, arcing time, and stability of the emission threshold depend essentially on the mechanical strength of the plate with the rest of 15 the cathode structure.
Because the emitting plate and its support are of refractory materials, it is extremely difficult to make, by soldering, the direct connection of the two components. The numerous solutions divulged in the state of the art do not offer a simple, reliable, and 2 0 cheap solution with the characteristics of repeatability necessary for mass producing a key component of cathode ray tubes.
To obtain a superior contact between the refractory metal support 13 and the emitting plate 1, which contact makes it possible to optimize the thermal conduction between the heating 25 element 5 and the plate, it is necessary to join by soldering the materials together without destroying the porosity of the plate and without modifying the emission characteristics, which prohibits a soldering at a temperature which is too high.
As indicated in Figure 2, the invention proposes inserting 30 between the emitting plate 1 and its support 13, a metal transport material 8, which is chemically neutral and which permits soldering the two components at a sufficiently low temperature so as not to deteriorate the emission characteristics of the plate. For this, the material chosen should have a melting point between the 3 5 operating temperature of the cathode and that of the metals constituting the plate.
RCA 88,153 The transport material, placed as an interface between the plate and its support, may be in the form of metal powder, flat ribbon, or wire.
Because it is necessary to minimi7e the amount of transport 5 material, in order to reduce the weight and/or size of the cathode particularly for heat output reasons, the transport material may, in one advantageous mode of implementation, be deposited by vaporization in a vacuum directly upon the support 13. In this way, the thickness of the layer of material 8 may be controlled, 10 preferably to between 1 and 25 microns, a thickness permitting good solderability of the components 1 and 13 without affecting the heat output characteristics of the cathode.
In another preferential mode of implementation, the transport material is in the form of a thin metal tab with a 15 thickness chosen between 1 and 25 microns. Advantageously, the tab is cut so as not to occupy the whole contact surface between the support 13 and the plate 1, in order to reduce the weight of the transport material. To reliably perform the soldering between the plate and its support, it is necessary, however, that the surface 20 covered by the transport material be sufficient, taking into account the small dimensions of the components to be soldered.
Experience has shown that a tab surface area ranging between 0.4 and 0.7 times the surface area of the face of the plate, generally of a rounded shape, would make it possible to ensure the soldering 2 5 of the components under good conditions of reliability.
As illustrated in Figure 3, showing a view of the inside of the support 13, the tab 10 is, for example, cut in the form of a rectangle with rounded corners, which shape has the advantage of automatic centering during its insertion into the support 13, 30 generally in the form of a dish. In this way, there is moreover ensured the soldering of the plate 1 to its support 13 by situating the soldering points 9 in the center part of the plate. For a circularly cylindrical emitting plate with a diameter of 1.27 mm, there is chosen, by way of example, a metal tab 1.1 mm long by 35 0.6 mm wide with a metal thickness which can be selected from l to 25 microns.
5 ~ ~
6 RCA 88,153 The metal of the interface material 8 should be chosen so as not to have a chemical reaction at high temperature, while making it possible to ensure a good mechanical connection between the plate and its support. Likewise, its melting point should be S sufficiently low so as not to reduce the emissivity characteristics of the plate.
Various metals may be used, whether pure or in the form of alloys, to implement the invention: nickel, chromium, vanadium, and rhenium, for example, have given excellent results, both from 10 a mechanical standpoint, as well as from a standpoint of neutrality toward the emissivity properties of the emitting plate.
In one advantageous mode of implementation, pure nickel was selected to make the tab 10. This metal has a melting point of 1453~C, between the operating temperature of the cathode, l S around 1200~C, and the melting point of the tungsten plate, of the order of 3410~C; and it exhibits a good thermal conductivity and a very good solderability with tungsten and tantalum. Moreover, nickel offers the additional advantage of being a magnetic material; thus, it permits considering an automated deposit by 20 electromagnet of the tab on the dish, which deposit would be very difficult manually, taking into account the small dimensions of the - components constituting the cathode.
Various metals may be used, whether pure or in the form of alloys, to implement the invention: nickel, chromium, vanadium, and rhenium, for example, have given excellent results, both from 10 a mechanical standpoint, as well as from a standpoint of neutrality toward the emissivity properties of the emitting plate.
In one advantageous mode of implementation, pure nickel was selected to make the tab 10. This metal has a melting point of 1453~C, between the operating temperature of the cathode, l S around 1200~C, and the melting point of the tungsten plate, of the order of 3410~C; and it exhibits a good thermal conductivity and a very good solderability with tungsten and tantalum. Moreover, nickel offers the additional advantage of being a magnetic material; thus, it permits considering an automated deposit by 20 electromagnet of the tab on the dish, which deposit would be very difficult manually, taking into account the small dimensions of the - components constituting the cathode.
Claims (6)
1. A method for manufacturing an impregnated cathode, including soldering a porous emitting plate of refractory material inside a refractory metal support, wherein, to facilitate the soldering, a purely metal transport material is arranged between the plate and its support.
2. A method according to claim 1, wherein the support material has a melting point between the operating temperature of the cathode and the melting point of the metals constituting the emitting plate.
3. A method according to claim 1 or 2, wherein the transport material is deposited in a vacuum on the support for the emitting plate.
4. A method according to claim 1 or 2, wherein the transport material is in the form of a thin metal tab.
5. A method according to claim 4, wherein the metal tab is essentially rectangular.
6. A method according to claim 1 or 2, wherein the transport material is in the form of metal powder.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP96400659A EP0798758A1 (en) | 1996-03-28 | 1996-03-28 | Method of fabricating or impregnated cathode for a cathode ray tube |
| EPEP96400659.7 | 1996-03-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2200513A1 true CA2200513A1 (en) | 1997-09-28 |
Family
ID=8225241
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2200513 Abandoned CA2200513A1 (en) | 1996-03-28 | 1997-03-20 | A method for manufacturing an impregnated cathode |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0798758A1 (en) |
| JP (1) | JPH103846A (en) |
| KR (1) | KR970067448A (en) |
| CA (1) | CA2200513A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106328468B (en) * | 2016-08-21 | 2018-04-17 | 北京工业大学 | The preparation method of magnetron La2O3 doping Mo cathode materials |
| CN106206216B (en) * | 2016-08-26 | 2018-04-17 | 北京工业大学 | Be carbonized La2O3 and the composite mixed Mo cathode materials of Lu2O3 and preparation method thereof |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1050519A (en) * | 1951-01-08 | 1954-01-08 | English Electric Valve Co Ltd | Emissive Cathode Improvements for Electron Discharge Tubes |
| JPS62213031A (en) * | 1986-03-14 | 1987-09-18 | Hitachi Ltd | Impregnated type cathode structure |
| JPH04141928A (en) * | 1990-10-01 | 1992-05-15 | Toshiba Corp | Impregnation-type cathode structural body |
| JPH04322029A (en) * | 1991-04-19 | 1992-11-12 | New Japan Radio Co Ltd | Impregnated type cathode and manufacture thereof |
| KR930007461B1 (en) * | 1991-04-23 | 1993-08-11 | 주식회사 금성사 | Method of making a dispenser type cathode |
-
1996
- 1996-03-28 EP EP96400659A patent/EP0798758A1/en not_active Withdrawn
-
1997
- 1997-01-08 KR KR1019970000225A patent/KR970067448A/en not_active Application Discontinuation
- 1997-03-20 CA CA 2200513 patent/CA2200513A1/en not_active Abandoned
- 1997-03-21 JP JP6844897A patent/JPH103846A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| KR970067448A (en) | 1997-10-13 |
| EP0798758A1 (en) | 1997-10-01 |
| JPH103846A (en) | 1998-01-06 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Dead |