US2813220A - Indirectly heated cathode - Google Patents

Indirectly heated cathode Download PDF

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Publication number
US2813220A
US2813220A US473386A US47338654A US2813220A US 2813220 A US2813220 A US 2813220A US 473386 A US473386 A US 473386A US 47338654 A US47338654 A US 47338654A US 2813220 A US2813220 A US 2813220A
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US
United States
Prior art keywords
refractory metal
molybdenum
sintered
layer
alkaline earth
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 - Lifetime
Application number
US473386A
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English (en)
Inventor
Patrick P Coppola
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Philips North America LLC
US Philips Corp
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US Philips Corp
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Filing date
Publication date
Priority to BE543391D priority Critical patent/BE543391A/xx
Priority to NL94233D priority patent/NL94233C/xx
Priority to US473386A priority patent/US2813220A/en
Application filed by US Philips Corp filed Critical US Philips Corp
Priority to DEN11529A priority patent/DE1039141B/de
Priority to GB34563/55A priority patent/GB793726A/en
Priority to ES0225387A priority patent/ES225387A1/es
Priority to CH336905D priority patent/CH336905A/de
Priority to FR1143215D priority patent/FR1143215A/fr
Application granted granted Critical
Publication of US2813220A publication Critical patent/US2813220A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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

  • my invention relates to an indirectly heated dispenser cathode in which an alkaline earth material is dispersed within the pores of a refractory metal matrix and that matrix incorporated in a refractory metal sleeve.
  • a barrier is sometimes interposed between the emissive portion and the heater to prevent even the minutest passage of alkaline earth metal, or compound giving rise to emission in the heater zone.
  • a principal object of my invention is to provide a novel indirectly heated dispenser cathode in which back-emission between the cathode and heater is substantially eliminated.
  • a further object of my invention is to provide a simpler and less expensive method of manufacturing an indirectly heated dispenser cathode.
  • the cathode comprises a tube of refractory metal having a refractory metal partition dividing the tube into two separate chambers, one of which houses a heating element and the other an emissive body which comprises a porous sintered refractory metal matrix, e. g. molybdenum, tungsten, hafnium, tantalum, zirconium and alloys of those metals in the pores of which there is dispersed an emissive alkaline earth material.
  • a porous sintered refractory metal matrix e. g. molybdenum, tungsten, hafnium, tantalum, zirconium and alloys of those metals in the pores of which there is dispersed an emissive alkaline earth material.
  • the two chambers are tightly sealed from one. another by a special seal which comprises a very dense layer of sintered refractory metal of lower reactivity than the refractory metal matrix bonding the partition to the inner walls of the tube; and below this layer on the side facing the heating zone there is a layer of a sintered mixture of a refractory metal and a refractory metal oxide, bonded to the walls of the tube.
  • This layer can combine chemically with any alkaline earth material which might seep through the sintered refractory metal layer, thus effectively preventing any leakage of alkaline earth material into the heater zone which might give rise to back-emission.
  • I employ a rolled molybdenum sleeve overlapped along its edges to serve as the tubular housing. Dividing this housing into the two chambers is a molybdenum disc of smaller diameter than the inside diameter of the sleeve. This disc is sealed to the inner walls of the sleeve by a dense layer of sintered molybdenum underneath which there is a layer of a sintered mixture of molybdenum and aluminum oxide.
  • a drawn tube of molybdenum or other suitable refractory metal could be employed instead of a rolled sleeve; and instead of the molybdenum disc a continuous layer of sintered molybdenum or other refractory metal can serve as the partition.
  • This layer of a sintered refractory metal is then backed-up with a layer of a sintered mixture of refractory metal and a refractory metal oxide.
  • refractory metal oxide As a suitable refractory metal oxide, I prefer A1203, but other refractory metal oxides such as BeO, ZrOz, SiOz,
  • molybdenum as the refractory metal and prefer to use a mixture of about 90% by weight of molybdenum and 10% by weight of A1203 in the underlayer. It is essential however, that the A1203 be of a high degree of purity and in particular he alkali-free.
  • the emissive body may be prepared either by forming a mixture of a refractory metal and an emissive alkaline earth material and sintering that mixture into a coherent body or by forming a porous refractory metal body, preferably by sintering, and impregnating the pores of that body with an emissive alkaline earth material.
  • alkaline earth material I prefer to use one of those disclosed in co-pending application Ser. No. 258,892 filed November 29, 1951, by R. C. Hughes et al., now U. S. Patent 2,700,118. These materials comprise fused mixtures of an alkaline earth metal oxide such as barium oxide and one or more refractory metal oxides. In addition, I may add to the fused mixture of the alkaline earth oxide and the refractory metal oxide, one or more alkaline earth oxides such as calcium oxide, magnesium oxide and strontium oxide as disclosed in co-pending application Ser. No. 444,323 filed July 19, 1954, by R. Levi.
  • I may use as the emissive material an alkaline earth tungstate mixed with thorium as disclosed in U. S. application Ser. No. 331,874 filed January 19, 1953, by O. G. Koppius.
  • Fig. 1 is a sectional view showing a suitable die for forming the cathode according to the invention
  • Fig. 2 is a sectional view showing another die for forming the cathode according to the invention.
  • Fig. 3 is a sectional view showing a cathode made in accordance with the invention.
  • Fig. 4 is a sectional view of another cathode made in accordance with the invention.
  • Fig. 5 is a sectional view of still another cathode made in accordance with the invention.
  • a sleeve 1 prepared by rolling and overlapping the edges of a sheet of molybdenum and slightly bevelling at one end with India stone, is positioned in a cylindrical hardened steel die 2.
  • the sleeve is partly filled with an emitter mixture 3 composed of about 90% by weight of a -25% tungsten-molybdenum alloy and about 10% by weight of an emissive alkaline earth material.
  • This alkaline earth material preferably consists of a prefired mixture of about 5 moles of BaO and 2 moles of A1203 to which one or more of the oxides CaO, 810, Mg() may be added.
  • a molybdenum disc 4 having a diameter smaller than the inside diameter of the sleeve is inserted into the sleeve.
  • a measured amount of molybdenum powder, first fired in a reducing atmosphere to remove all oxides, and having an average particle size of about 2 is introduced into the sleeve to cover the disc and fill the space between the disc and the sleeve, forming layer 5.
  • a measured quantity of a mixture of about by weight of molybdenum powder having an avera e particle size of about and about 10% by weight of aluminum oxide is introduced into the sleeve to form a second layer 6.
  • a second molybdenum disc 7 is inserted into the sleeve. After the second disc is inserted, the mass within the sleeve is compacted by applying pressure to pin 8 positioned in the die against pressing pin 9 outside the die.
  • Pin 9 is provided with a special cup-like cavity 10 bevelled at an angle of about 38 in order to crimp over the ends of the molybdenum tube and hold the emitter mixture in place. In the event a heavy wall tube is used, the crimping may be omitted.
  • a cup-shaped female die member 11, shown in Fig. 2 may be used.
  • the assembly is ejected from the die and the mass in the tube sintered to form a coherent structure.
  • the assembly is placed in a furnace (vacuum or inert atmosphere) and heated rapidly to a temperature of about 1700-1900 C. for about seconds in order to sinter the compact and bond the molybdenum disc 4, and layers 5 and 6 to the inner walls of the tube 1.
  • a furnace vacuum or inert atmosphere
  • the alkaline earth material is melted and dispersed throughout the refractory metal matrix and evolves entrapped gas.
  • the molybdenum disc 4 which is sealed by the molybdenum layer 5, serves to prevent the alkaline earth material in the emitter compact 3 from being drawn into the layers 5 and 6.
  • the molybdenum disc 4 may be omitted provided that there are continuous layers 5 and 6 underlying the emitter body and tightly sealed to the sleeve.
  • a heating element 14 is positioned in the lower chamber 13 as shown in Fig. 3 and the cathode assembled in an evacuated envelope.
  • the refractory metal layer 5 and the layer of a mixture of refractory metal and refractory metal oxide need only surround the joint between the disc 4 and the inner wall of tube 1.
  • disc 4 may be eliminated and the partition formed solely by the layer 5 of sintered refractory metal backed up by layer 6 as shown in Fig. 5.
  • the emissive body 3 be preformed, e. g., that it comprise a porous refractory metal body whose pores have been impregnated with an emissive alkaline earth material.
  • the novel seal according to my invention in each of the embodiments illustrated effectively impedes the flow of alkaline earth material and decomposition products into the heater zone and thereby effectively prevents backemission to the heater which is usually at a potential dif ferent thanthat of the cathode.
  • the refractory metal bond actually serves the additional purpose of reducing the flow into the heater zone of alkaline earth metal and alkaline earth metal oxide decomposition products available after the cathode has been activated. The small amount that may traverse this barrier is absorbed by the aluminum oxide'which has a strong affinity for such products thus effectively sealing off the heater chamber to the flow of those products.
  • a thermionic cathode comprising a tubular refractory metal housing having a partition therein forming two chambers, heating means disposed in one of said chambers, a porous sintered bdy with an emissive alkaline earth material dispersed in the pores thereof disposed in the other of said chambers, a dense layer of sintered refractory metal bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered refractory metal and comprising a sintered mixture of a refractory metal and a refractory metal oxide.
  • a thermionic cathode comprising a tubular refractory metal housing having a partition therein forming two chambers, heating means disposed in one' of said chambers, a porous sintered tungsten body with an emissive alkaline earth material dispersed in the pores thereof disposed in the other of said chambers, a dense layer of sintered refractory metal bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered refractory metal and comprising a sintered mixture of a refractory metal and a refractory metal oxide.
  • a thermionic cathode comprising a tubular refractory metal housing having a partition therein forming two chambers, heating means disposed in one of said chambers, a porous sintered body with an emissive alkaline earth material dispersed in the pores thereof disposed in the other of said chambers, a dense layer of sintered refractory metal bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered refractory metal and comprising a sintered mixture of a refractory metal and aluminum oxide.
  • a thermionic cathode comprising a tubular refractory metal housing having a partition therein forming two chambers, heating means disposed in one of said chambers, a porous sintered body with an emissive alkaline earth material'dispersed in the pores thereof disposed in the other of said chambers, a dense sintered layer ofthe same refractory metal as that of said housing bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered refractory metal and comprising a sintered mixture of the same refractory metal as that of said housing and a refractory metal oxide.
  • a thermionic cathode comprising a tubular molybdenum housing having a partition therein forming two chambers, heating means disposed in one of said chambers, a porous sintered body of an alloy of about 75% tungsten and 25% molybdenum with an emissive alkaline earth material dispersed in the pores thereof disposed in the other of said chambers, a dense layer of sintered molybdenum bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered molybdenum and comprising a sintered mixture of molybdenum and aluminum oxide.
  • a thermionic cathode comprising a tubular molybdenum housing having a partition therein forming two chambers, heating means disposed in one of said chambers, a porous sintered refractory metal body with an emissive alkaline earth material consisting of a fused mixture of an alkaline earth oxide and aluminum oxide dispersed in the pores thereof disposed in the other of said chambers, a dense layer of sintered molybdenum bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered molybdenum and comprising a sintered mixture of molybdenum and aluminum oxide.
  • a thermionic cathode comprising a tubular molybdenum housing having a partition therein forming two chambers, heating means disposed in one of said chambers, a porous sintered body with an emissive alkaline earth material dispersed in the pores thereof disposed in the other of said chambers, a dense layer of sintered molybdenum bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered molybdenum and comprising a sintered mixture of about molybdenum and 10% aluminum oxide.
  • a thermionic cathode comprising a tubular molybdenum housing having a partition therein forming two chambers, heating means disposed in one of said chambers, a porous sintered body of an alloy of 75% tungsten and 25% molybdenum with an emissive alkaline earth material dispersed in the pores thereof disposed in the other of said chambers, said alkaline earth material consisting of a fused mixture of an alkaline earth oxide and aluminum oxide, a dense layer of sintered molybdenum bonding the partition to the inner wall of the tube, and a second layer below said layer of sintered molybdenum and comprising a sintered mixture of about 90% molybdenum and 10% of aluminum oxide.

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  • Solid Thermionic Cathode (AREA)
  • Powder Metallurgy (AREA)
US473386A 1954-12-06 1954-12-06 Indirectly heated cathode Expired - Lifetime US2813220A (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
BE543391D BE543391A (en。) 1954-12-06
NL94233D NL94233C (en。) 1954-12-06
US473386A US2813220A (en) 1954-12-06 1954-12-06 Indirectly heated cathode
GB34563/55A GB793726A (en) 1954-12-06 1955-12-02 Improvements in or relating to dispenser cathodes
DEN11529A DE1039141B (de) 1954-12-06 1955-12-02 Vorratskathode mit einer Trennwand zwischen dem poroesen Koerper und dem Heizkoerper und Verfahren zur Herstellung einer Kathode
ES0225387A ES225387A1 (es) 1954-12-06 1955-12-03 MEJORAS INTRODUCIDAS EN LA FABRICACIoN DE CáTODOS
CH336905D CH336905A (de) 1954-12-06 1955-12-05 Vorratskathode und Verfahren zur Herstellung einer solchen Kathode
FR1143215D FR1143215A (fr) 1954-12-06 1955-12-05 Cathode à réserve et son procédé de fabrication

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US473386A US2813220A (en) 1954-12-06 1954-12-06 Indirectly heated cathode

Publications (1)

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US2813220A true US2813220A (en) 1957-11-12

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US473386A Expired - Lifetime US2813220A (en) 1954-12-06 1954-12-06 Indirectly heated cathode

Country Status (8)

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US (1) US2813220A (en。)
BE (1) BE543391A (en。)
CH (1) CH336905A (en。)
DE (1) DE1039141B (en。)
ES (1) ES225387A1 (en。)
FR (1) FR1143215A (en。)
GB (1) GB793726A (en。)
NL (1) NL94233C (en。)

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2912611A (en) * 1953-08-14 1959-11-10 Int Standard Electric Corp Thermionic cathodes
US2945150A (en) * 1958-12-11 1960-07-12 Gen Electric Thermionic cathodes and methods of making
US2945295A (en) * 1957-12-20 1960-07-19 Westinghouse Electric Corp High temperature metallic joint
US2975322A (en) * 1958-12-29 1961-03-14 Raytheon Co Indirectly heated cathodes
US2975320A (en) * 1958-12-03 1961-03-14 Rca Corp Low-temperature plasma source
US3018404A (en) * 1958-03-27 1962-01-23 Raytheon Co Electron tube cathodes
US3117249A (en) * 1960-02-16 1964-01-07 Sperry Rand Corp Embedded heater cathode
US3134924A (en) * 1960-07-05 1964-05-26 Monsanto Co Emissive materials of a metal matrix with molecularly dispersed additives
US3201639A (en) * 1955-02-09 1965-08-17 Philips Corp Thermionic dispenser cathode
US3229147A (en) * 1961-09-01 1966-01-11 Gen Electric Thermionic emitter and method of making same
US3373307A (en) * 1963-11-21 1968-03-12 Philips Corp Dispenser cathode
EP0009261A1 (de) * 1978-09-27 1980-04-02 Siemens Aktiengesellschaft Vorratskathode, insbesondere Metall-Kapillar-Kathode
US4400648A (en) * 1979-10-01 1983-08-23 Hitachi, Ltd. Impregnated cathode
US4494035A (en) * 1980-11-07 1985-01-15 Thomson-Csf Thermoelectric cathode for a hyperfrequency valve and valves incorporating such cathodes
US5171180A (en) * 1991-04-23 1992-12-15 Gold Star Co., Ltd. Method for manufacturing impregnated cathodes
FR2683090A1 (fr) * 1991-10-25 1993-04-30 Europ Composants Electron Cathode a reserve et procede de fabrication d'une telle cathode.
US20060076871A1 (en) * 2002-11-23 2006-04-13 Koninlijke Philips Electronics N.V. Vacuum tube with oxide cathode
CN114340124A (zh) * 2021-12-30 2022-04-12 中国科学院合肥物质科学研究院 一种钠离子发射体及其制备方法

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1257980B (de) 1966-05-20 1968-01-04 Telefunken Patent Vorratskathode und Verfahren zu deren Herstellung
KR930014673A (ko) * 1991-12-20 1993-07-23 김정배 함침형 음극 구조체 및 그 제조방법

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2698913A (en) * 1951-11-29 1955-01-04 Philips Corp Cathode structure
US2700118A (en) * 1951-11-29 1955-01-18 Philips Corp Incandescible cathode
US2716716A (en) * 1951-11-29 1955-08-30 Philips Corp Cathode containing a supply of an electron-emissive material

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT174993B (de) * 1951-02-08 1953-05-26 Philips Nv Elektrische Entladungsröhre mit einer aus einem porösen Körper aus hochschmelzendem Metall bestehenden Kathode und Verfahren zur Herstellung einer solchen Kathode
AT176924B (de) * 1951-03-22 1953-12-10 Philips Nv Verfahren zur Herstellung einer Kathode für eine elektrische Entladungsröhre, die im Inneren einen Vorrat Erdalkalimetallverbindungen enthält und deren Wand wenigstens teilweise aus einem durch Pressen und Sintern hergestellten porösen Körper besteht, und durch dieses Verfahren hergestellte Kathode
DE890390C (de) * 1951-07-12 1953-09-17 Siemens Ag Kathode fuer elektrische Entladungsgefaesse
AT180338B (de) * 1952-02-27 1954-11-25 Philips Nv Kathode für eine elektrische Entladungsröhre und Verfahren zur Herstellung dieser Kathode
AT183488B (de) * 1953-06-11 1955-10-10 Philips Nv Verfahren zur Herstellung eines Kathodenkörpers für eine elektrische Entladungsröhre

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2698913A (en) * 1951-11-29 1955-01-04 Philips Corp Cathode structure
US2700118A (en) * 1951-11-29 1955-01-18 Philips Corp Incandescible cathode
US2716716A (en) * 1951-11-29 1955-08-30 Philips Corp Cathode containing a supply of an electron-emissive material

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2912611A (en) * 1953-08-14 1959-11-10 Int Standard Electric Corp Thermionic cathodes
US3201639A (en) * 1955-02-09 1965-08-17 Philips Corp Thermionic dispenser cathode
US2945295A (en) * 1957-12-20 1960-07-19 Westinghouse Electric Corp High temperature metallic joint
US3018404A (en) * 1958-03-27 1962-01-23 Raytheon Co Electron tube cathodes
US2975320A (en) * 1958-12-03 1961-03-14 Rca Corp Low-temperature plasma source
US2945150A (en) * 1958-12-11 1960-07-12 Gen Electric Thermionic cathodes and methods of making
US2975322A (en) * 1958-12-29 1961-03-14 Raytheon Co Indirectly heated cathodes
US3117249A (en) * 1960-02-16 1964-01-07 Sperry Rand Corp Embedded heater cathode
US3134924A (en) * 1960-07-05 1964-05-26 Monsanto Co Emissive materials of a metal matrix with molecularly dispersed additives
US3229147A (en) * 1961-09-01 1966-01-11 Gen Electric Thermionic emitter and method of making same
US3373307A (en) * 1963-11-21 1968-03-12 Philips Corp Dispenser cathode
EP0009261A1 (de) * 1978-09-27 1980-04-02 Siemens Aktiengesellschaft Vorratskathode, insbesondere Metall-Kapillar-Kathode
US4400648A (en) * 1979-10-01 1983-08-23 Hitachi, Ltd. Impregnated cathode
US4494035A (en) * 1980-11-07 1985-01-15 Thomson-Csf Thermoelectric cathode for a hyperfrequency valve and valves incorporating such cathodes
US5171180A (en) * 1991-04-23 1992-12-15 Gold Star Co., Ltd. Method for manufacturing impregnated cathodes
FR2683090A1 (fr) * 1991-10-25 1993-04-30 Europ Composants Electron Cathode a reserve et procede de fabrication d'une telle cathode.
US20060076871A1 (en) * 2002-11-23 2006-04-13 Koninlijke Philips Electronics N.V. Vacuum tube with oxide cathode
CN114340124A (zh) * 2021-12-30 2022-04-12 中国科学院合肥物质科学研究院 一种钠离子发射体及其制备方法
CN114340124B (zh) * 2021-12-30 2024-02-27 中国科学院合肥物质科学研究院 一种钠离子发射体及其制备方法

Also Published As

Publication number Publication date
BE543391A (en。)
CH336905A (de) 1959-03-15
GB793726A (en) 1958-04-23
FR1143215A (fr) 1957-09-27
DE1039141B (de) 1958-09-18
ES225387A1 (es) 1956-02-01
NL94233C (en。)

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