|Publication number||US3833494 A|
|Publication date||Sep 3, 1974|
|Filing date||May 2, 1973|
|Priority date||May 30, 1972|
|Also published as||CA994280A, CA994280A1, DE2325273A1, DE2325273B2, DE2325273C3|
|Publication number||US 3833494 A, US 3833494A, US-A-3833494, US3833494 A, US3833494A|
|Inventors||Mitra N, Van Stratum A|
|Original Assignee||Philips Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Non-Patent Citations (1), Referenced by (11), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Unite States Patent [1 1 Van Stratum et al.
[111 3,833,494 14 1 Sept. 3, 1974 METHOD OF MANUFACTURING A LANTHANUM HEXABORIDE-ACTIVATED CATHODE FOR AN ELECTRIC DISCHARGE TUBE  Inventors: Antonius Johannes Alberta Van I Stratum, Emmasingel, Eindhoven; Nira'njan Kumar Mitra, Best, both of Netherlands  Assignee: U. S. Philips Corporation, New
 Filed: May 2, 1973 211 App]. No.: 356,620
 Foreign Application Priority Data May 30, 1972 Netherlands 7207275  US. Cl. 204/181, 313/346 R  Int. Cl C231! 13/00  Field of Search 204/181; 313/346 R L. Favreau, Cataphoretic Coating Lanthanum Boride on Rhenium Filaments, Rev. Sci. In'st., Vol. 36, pages 856-857, (1965). I
Primary Examiner-John l-l. Mack Assistant Examiner-Aaron Weisstuch Attorney, Agent, or Firm-Frank R. Trifari; Carl P.
' Steinhauser [5 7 ABSTRACT A layer of lanthanum hexaboride is applied cataphoretically to a rhenium wire and then sintered. The process is repeated. In this manner a cathode with small evaporation and long life is obtained.
1 Claim, l Drawing Figure METHOD OF MANUFACTURING A LANTI-IANUM I-IEXABORIDE-ACTIVATED CATHODE FOR AN ELECTRIC DISCHARGE TUBE The invention relates to a method of manufacturing a cathode for an electric discharge tube in which a layer of lanthanum hexaboride is cataphoretically provided on a rhenium support and is sintered. The invention furthermore relates to a cathode manufactured in this manner.
The method described above is known from Rev.Sci. Inst. 36, 856-7, 1965.
It is found in practice that lives of only approximately 1,000 hours are obtained with such cathodes. The rhenium wire on which the lanthanum hexaboride is sintered then usually breaks. If the boride is not yet very pure, that is to say free from free boron and boron oxide, the life is still considerably shorter. This'is the result of the fact that in the presence of the said contaminations borides of rhenium are formed in an uncontrol- 20 lable manner. The reaction between the rhenium and the lanthanum hexaborideis then subject to considerable fluctuations and the operation of the cathodejis not satisfactory. Should lanthanum tetraboride also be present in the lanthanum hexaboride, a considerable evaporation of lanthanum occurs because the tetrabo ride first decomposes to hexaboride rather rapidly. The hexaboride reacts slowly with the rhenium and evaporates only slowly. Perhaps the lanthanum released from the tetraboride could'also react with the rhenium.
It is the object of the invention to provide a method by which cathodes of the indicated composition can be obtained with a long life.
According to the invention, in a method of manufacturing a cathode for an electric discharge tube in which a layer of lanthanum hexaboride is cataphoretically provided on a rhenium support and is sintered, the cataphoretically provided layer is slowly heated to a temperature of l,500 to l,550C and maintained at said final temperature for maximum 30 seconds until a smooth and shining surface is obtained, after which a second layer of lanthanum hexaboride is cataphoretically provided and also heated to a temperature of 1,500 to l,550C and maintained at said temperature for maximum 2 minutes.
Upon heating the first layer of hexaboride which need not be very pure, a layer of rhenium boride is formed all over the surface of the rhenium wire and rhenium wire as a result of excessive boride formation ing example.
is prevented and a long life of many thousands of hours can be achieved. At the normal operating temperature of the lanthanum hexaboride cathodes, good emission densities are achieved. If the second layer contains no lanthanum tetraboride, littleevaporation occurs.
The invention will be described in greater detail, also with reference to the FIGURE, by means of the follow- In the FIGURE, 1 denotes a part of a hard glass bottom in which two wires 2 and 3 of an iron-nickel-cobalt alloy are present.
A rhenium wire 4 of 0.18 mm diameter is welded to the lead-in wires 2 and 3. After firing the rhenium wire in hydrogen gas at 1,600C for 2 minutes, it is covered from a lanthanum boride suspension (unpurified LaB with a 50 p. thick layer. Said layer is heated for 5 minutes and sintered in hydrogen at 1,530C for 15 seconds. The layer becomes smooth and shining. A 20 microns thick layer of lanthanum hexaboride is then cataphoretically provided, said layer being sintered in hydrogen at l,550C for 2 minutes.
After sealing the bottom 1 in a tube and after evacuation thereof, the cathode is degassed at 1,600C for a few seconds. The cathode is then activated at 1,500C for 5 to 30 minutes.
At a temperature of l,400C the saturation emission (measured with pulses) is 10 Alcm The life at said temperature is more than 8,000 hours.
Like all the hexaboridecathodes, the cathodes according to the invention are suitable for use in high voltage apparatus such as X-ray tubes, rectifier tubes and also in electron beam welding apparatus, electron microscopes and the like, in which comparatively poor vacuum conditions occur and which cathodes are exposed to air repeated times. In apparatus in which layers have to be locally activated by means of electron beams or be worked differently, said cathodes are also suitable.
What is claimed is:
1. A method of manufacturing a cathode for an electric discharge tube in which a layer of lanthanum hexaboride is cataphoretically provided on a rhenium support and sintered, characterized in that the cataphoretically provided layer is slowly heated to a temperature of l,500 to l,550C and maintained at said final temperature formaximum 30 seconds until a smooth and shining surface is obtained, after which a second layer of lanthanum hexaboride is cataphoretically provided and also heated to a temperature of l,500 to l,550C and maintained at said temperature for maximum 2 minutes.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3312856 *||Mar 26, 1963||Apr 4, 1967||Gen Electric||Rhenium supported metallic boride cathode emitters|
|US3498897 *||Jul 25, 1967||Mar 3, 1970||Ford Motor Co||Method for manufacturing multilayered product|
|US3630770 *||Apr 30, 1969||Dec 28, 1971||Gen Electric||Method for fabricating lanthanum boride cathodes|
|1||*||L. Favreau, Cataphoretic Coating Lanthanum Boride on Rhenium Filaments, Rev. Sci. Inst., Vol. 36, pages 856 857, (1965).|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US4019081 *||Oct 6, 1975||Apr 19, 1977||Bbc Brown Boveri & Company Limited||Reaction cathode|
|US4054946 *||Sep 28, 1976||Oct 18, 1977||Bell Telephone Laboratories, Incorporated||Electron source of a single crystal of lanthanum hexaboride emitting surface of (110) crystal plane|
|US4055780 *||Apr 12, 1976||Oct 25, 1977||National Institute For Researches In Inorganic Materials||Thermionic emission cathode having a tip of a single crystal of lanthanum hexaboride|
|US4482839 *||Jan 20, 1982||Nov 13, 1984||Denki Kagaku Kogyo Kabushiki Kaisha||Thermionic emission cathode and preparation thereof|
|US5142652 *||Aug 1, 1991||Aug 25, 1992||Siemens Aktiengesellschaft||X-ray arrangement comprising an x-ray radiator having an elongated cathode|
|US5170422 *||Aug 1, 1991||Dec 8, 1992||Siemens Aktiengesellschaft||Electron emitter for an x-ray tube|
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|US8952605 *||Jun 26, 2013||Feb 10, 2015||National Institute For Materials Science||Metal hexaboride cold field emitter, method of fabricating same, and electron gun|
|US20100301736 *||Jul 11, 2008||Dec 2, 2010||Toshiyuki Morishita||Electron emitting source and manufacturing method of electron emitting source|
|US20150002009 *||Jun 26, 2013||Jan 1, 2015||National Institute For Materials Science||Metal hexaboride cold field emitter, method of fabricating same, and electron gun|
|EP1983546A1 *||Apr 20, 2007||Oct 22, 2008||PANalytical B.V.||X-ray cathode and tube|
|U.S. Classification||204/484, 204/491, 313/346.00R|
|International Classification||H01J17/04, H01J9/04, H01J17/06|