EP0157634B1 - Wolfram und Iridium enthaltende Vorratskathode - Google Patents
Wolfram und Iridium enthaltende Vorratskathode Download PDFInfo
- Publication number
- EP0157634B1 EP0157634B1 EP19850302311 EP85302311A EP0157634B1 EP 0157634 B1 EP0157634 B1 EP 0157634B1 EP 19850302311 EP19850302311 EP 19850302311 EP 85302311 A EP85302311 A EP 85302311A EP 0157634 B1 EP0157634 B1 EP 0157634B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- cathode
- agglomerates
- tungsten
- particles
- porous
- 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.)
- Expired
Links
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Classifications
-
- 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
-
- 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
Definitions
- the invention pertains to thermionic cathodes in which a porous body of refractory metal is impregnated with a molten oxide containing an alkali- earth.
- U.S. Patent No. 3,373,307 issued November 12, 1964 describes an improved impregnated cathode in which the emissive surface is coated with iridium or other metals of its group.
- the coating improves the electron emission, but it has been found that the improvement is often short-lived.
- a principal problem seems to be that, in an electron tube where high current density is drawn from the cathode at high voltage, ions are formed from the residual gas. They are accelerated back to the cathode and sputter away a thin layer from its surface, removing the iridium.
- U.S. Patent No. 4,165,473 issued August 21,1979 to Louis R. Falce and assigned to the assignee of the present invention discloses a cathode in which particles of iridium orthe like are dispersed among the tungsten particles of the matrix. During sintering the iridium partially alloys with the tungsten. This dispersed cathode solved the problem of surface sputtering. It has been found, however, that the sintering is a very delicate process. If the time and temperature are enough to get a lot of alloying, the emission is often poor.
- the emission is initially good, but interdiffusion of iridium and tungsten occurs at operating temperature to form unreactive alloy. This in turn causes the barium supply to the surface to fall off with a resultant decay in emission. Also, shrinkage of the cathode button can take place with the distortion of the emitting surface, which impacts adversely on the electron optics of the gun.
- An object of the invention is to provide a cathode with improved emission over a long life span.
- Another object is to provide a cathode which is tolerant of the exact parameters of manufacture and operation.
- thermoionic cathode comprising:
- an emitting surface which has a low work-function. This is provided by a thin (sometimes monatomic) layer of an alkaline earth metal such as barium, strontium, calcium or mixtures thereof and often containing oxygen as well.
- an alkaline earth metal such as barium, strontium, calcium or mixtures thereof and often containing oxygen as well.
- the second requirement is a means for replenishing the active layer as it is removed in operation by evaporation or sputtering.
- tungsten to include molybdenum.
- barium as an example of an alkaline earth metal, which may additionally include calcium, strontium, and alloys thereof as well.
- the emitting layer is on the surface of the porous tungsten. It has a moderately low work function and thus give emission capability of a few amperes per square centimeter. The life is very good however, because the surfaces of the tungsten matrix in contact with the barium aluminate impregnant are chemically reducing at the operating temperature of around 1000°C, sufficient to react with the oxide and product free barium atoms. This barium can then be transported to the active surface to re-activate it as fast as surface material was removed.
- the iridium provides tighter bonding of the barium atoms, reducing evaporation as well as work function. Iridium, however, has low reducing power. When it is added to the matrix as taught by U.S. Patent No. 4,165,473 it alloys with the tungsten, perhaps more as a surface coating than a bulk alloy. This will decrease the reducing power of the tungsten and slow the replenishment of lost barium.
- This embodiment of the invention has been found to provide emission current densities equal or superior to, and lives exceeding those of, the best examples of the prior art.
- this cathode can be reproducibly manufactured. Cathodes capable of 8 amperes per square centimeter below 1050°C brightness have been produced with greater than 90% yield. Running temperatures for a given current density were within 10°C of each other. The performance was very stable with operating time. Cathodes have passed 4,000 hours at 8 Alcm 2 with practically no change.
- Fig. 2 illustrates the incorporation of the emitting element (the "cathode” proper) in a cathode structure as used in a linear-beam microwave tube.
- Cathode 10' is machined to have a smooth concave emitting surface 20' (usually spherical). Its base is fitted onto a cylindrical support 22, as of molybdenum or tantalum and attached thereto as by welding at junction 23.
- a radiant heater 24, as of tungsten wire in a bifilar spiral is supported by its legs 25 by the support means (not shown) of cylinder 22.
- the proportions of the various components can cover a wide range. For example, we believe the ratio of iridium to tungsten may vary from about 20% to about 80%.
- the "barium” may also include calcium, and/or strontium, or mixtures thereof.
- the "tungsten” may be molybdenum, tungsten, or their alloys.
- the "iridium” may be osmium, ruthenium, rhenium, iridium or alloys thereof.
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Solid Thermionic Cathode (AREA)
- Powder Metallurgy (AREA)
Claims (15)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US59578984A | 1984-04-02 | 1984-04-02 | |
US595789 | 1984-04-02 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0157634A2 EP0157634A2 (de) | 1985-10-09 |
EP0157634A3 EP0157634A3 (en) | 1986-01-08 |
EP0157634B1 true EP0157634B1 (de) | 1988-08-17 |
Family
ID=24384685
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19850302311 Expired EP0157634B1 (de) | 1984-04-02 | 1985-04-02 | Wolfram und Iridium enthaltende Vorratskathode |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0157634B1 (de) |
JP (1) | JPH0630214B2 (de) |
DE (1) | DE3564511D1 (de) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CH678671A5 (de) * | 1989-08-22 | 1991-10-15 | Asea Brown Boveri | |
KR0161381B1 (ko) * | 1994-12-28 | 1998-12-01 | 윤종용 | 직열형 음극 구조체 |
KR100195167B1 (ko) * | 1994-12-29 | 1999-06-15 | 손욱 | 직열형 음극 구조체 및 그 제조방법 |
JP3596453B2 (ja) | 2000-09-28 | 2004-12-02 | ウシオ電機株式会社 | ショートアーク放電ランプ |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4165473A (en) * | 1976-06-21 | 1979-08-21 | Varian Associates, Inc. | Electron tube with dispenser cathode |
DE2909958A1 (de) * | 1979-03-14 | 1980-09-25 | Licentia Gmbh | Sinterwerkstoff |
FR2469792A1 (fr) * | 1979-11-09 | 1981-05-22 | Thomson Csf | Cathode thermo-ionique, son procede de fabrication et tube electronique incorporant une telle cathode |
-
1985
- 1985-03-11 JP JP4668985A patent/JPH0630214B2/ja not_active Expired - Lifetime
- 1985-04-02 EP EP19850302311 patent/EP0157634B1/de not_active Expired
- 1985-04-02 DE DE8585302311T patent/DE3564511D1/de not_active Expired
Also Published As
Publication number | Publication date |
---|---|
EP0157634A3 (en) | 1986-01-08 |
EP0157634A2 (de) | 1985-10-09 |
DE3564511D1 (en) | 1988-09-22 |
JPH0630214B2 (ja) | 1994-04-20 |
JPS60220529A (ja) | 1985-11-05 |
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