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Publication numberUS3833494 A
Publication typeGrant
Publication dateSep 3, 1974
Filing dateMay 2, 1973
Priority dateMay 30, 1972
Also published asCA994280A, CA994280A1, DE2325273A1, DE2325273B2, DE2325273C3
Publication numberUS 3833494 A, US 3833494A, US-A-3833494, US3833494 A, US3833494A
InventorsMitra N, Van Stratum A
Original AssigneePhilips Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of manufacturing a lanthanum hexaboride-activated cathode for an electric discharge tube
US 3833494 A
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.
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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 [75] Inventors: Antonius Johannes Alberta Van I Stratum, Emmasingel, Eindhoven; Nira'njan Kumar Mitra, Best, both of Netherlands [73] Assignee: U. S. Philips Corporation, New

York, NY.

[22] Filed: May 2, 1973 211 App]. No.: 356,620

[30] Foreign Application Priority Data May 30, 1972 Netherlands 7207275 [52] US. Cl. 204/181, 313/346 R [51] Int. Cl C231! 13/00 [58] 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.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3312856 *Mar 26, 1963Apr 4, 1967Gen ElectricRhenium supported metallic boride cathode emitters
US3498897 *Jul 25, 1967Mar 3, 1970Ford Motor CoMethod for manufacturing multilayered product
US3630770 *Apr 30, 1969Dec 28, 1971Gen ElectricMethod for fabricating lanthanum boride cathodes
Non-Patent Citations
Reference
1 *L. Favreau, Cataphoretic Coating Lanthanum Boride on Rhenium Filaments, Rev. Sci. Inst., Vol. 36, pages 856 857, (1965).
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4019081 *Oct 6, 1975Apr 19, 1977Bbc Brown Boveri & Company LimitedReaction cathode
US4054946 *Sep 28, 1976Oct 18, 1977Bell Telephone Laboratories, IncorporatedElectron source of a single crystal of lanthanum hexaboride emitting surface of (110) crystal plane
US4055780 *Apr 12, 1976Oct 25, 1977National Institute For Researches In Inorganic MaterialsThermionic emission cathode having a tip of a single crystal of lanthanum hexaboride
US4482839 *Jan 20, 1982Nov 13, 1984Denki Kagaku Kogyo Kabushiki KaishaThermionic emission cathode and preparation thereof
US5142652 *Aug 1, 1991Aug 25, 1992Siemens AktiengesellschaftX-ray arrangement comprising an x-ray radiator having an elongated cathode
US5170422 *Aug 1, 1991Dec 8, 1992Siemens AktiengesellschaftElectron emitter for an x-ray tube
US8456076 *Jul 11, 2008Jun 4, 2013Denki Kagaku Kogyo Kabushiki KaishaElectron emitting source and manufacturing method of electron emitting source
US8952605 *Jun 26, 2013Feb 10, 2015National Institute For Materials ScienceMetal hexaboride cold field emitter, method of fabricating same, and electron gun
US20100301736 *Jul 11, 2008Dec 2, 2010Toshiyuki MorishitaElectron emitting source and manufacturing method of electron emitting source
US20150002009 *Jun 26, 2013Jan 1, 2015National Institute For Materials ScienceMetal hexaboride cold field emitter, method of fabricating same, and electron gun
EP1983546A1 *Apr 20, 2007Oct 22, 2008PANalytical B.V.X-ray cathode and tube
Classifications
U.S. Classification204/484, 204/491, 313/346.00R
International ClassificationH01J17/04, H01J9/04, H01J17/06
Cooperative ClassificationH01J9/042
European ClassificationH01J9/04B