WO2001097247A1 - Cathode a oxydes amelioree et son procede de fabrication - Google Patents
Cathode a oxydes amelioree et son procede de fabrication Download PDFInfo
- Publication number
- WO2001097247A1 WO2001097247A1 PCT/FR2001/001762 FR0101762W WO0197247A1 WO 2001097247 A1 WO2001097247 A1 WO 2001097247A1 FR 0101762 W FR0101762 W FR 0101762W WO 0197247 A1 WO0197247 A1 WO 0197247A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- support
- grains
- cathode
- layer
- oxide
- Prior art date
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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
- H01J1/14—Solid thermionic cathodes characterised by the material
-
- 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
Definitions
- the present invention relates to the field of electronic tubes, and in particular to cathodes which have the role in these tubes of emitting electrons and thus constituting the source of an electronic current.
- the invention is intended for so-called oxide cathodes.
- These cathodes which are the most commonly used, include a layer of highly electron-emitting oxides on one side of a metal support.
- the support is connected to a negative electrical potential relative to the surrounding potential, allowing the emission of a flow of electrons from the oxide layer.
- FIG. 1 is a simplified sectional view showing a section of a conventional oxide cathode 2.
- the support 1 consists of a thin nickel plate forming a patch, which has a face 1a covered with a layer of oxides 3 in the form of a whitewash.
- Whitewash is a deposit consisting of a charge of active compound and a binder.
- the active compound is generally based on barium carbonates (BaCO3) and other elements, which are subsequently transformed into barium oxides (BaO) and other elements.
- the oxide layer normally needs to be at a relatively high temperature to emit.
- a heat source such as a filament is provided near the support, connected to a low voltage current source.
- an electronic current flows through the thickness of the oxide layer 3 (arrow I) under the effect of the surrounding electric field.
- the electric field is created by establishing a potential difference between the support 1 and an electrode 5 located near the outer surface 3a of the layer 3.
- the support is referenced to a ground voltage while the electrode 5 is polarized at a positive voltage high + V.
- the electronic flux obtained by cathode 2 is proportional to the intensity of this electronic current I.
- Figure 2 shows the same section of cathode 2 after a change in time thereof. It can be seen that a resistive layer 6, called the interface layer, develops between the metal support 1 and the whitewash layer 3.
- a resistive layer 6 called the interface layer
- cathode ray tubes for "multimedia” and “high resolution” display screens, as well as for video projectors, and other types of electronic tubes, such as those used in the microwave field.
- the insufficient electrical conductivity of the oxide cathode is due to two parameters: the fact that the emissive whitewash 3 is based on oxides which are by nature not very conductive, and the fact that the interface layer 6 is resistive develops between the metal of support 1 and the whitewash.
- FIG. 3 is an equivalent electrical diagram of the components R1 and R2 of the electrical resistivity of the oxide cathode originating respectively from the emissive whitewash layer 3 and from the layer interface interface 6. These two layers being superimposed, the components R1 and R2 combine as resistors in series.
- the contribution to the electrical resistivity of the whitewash layer 3 changes over the lifetime of the cathode. In fact, it is created in this layer of metallic barium by the reaction between the barium oxides BaO and the reducing elements which diffuse from the nickel. This metallic barium, the primary purpose of which is to move to the surface of the whitewash to allow the emission of electrons, provides electrical conductivity in the whitewash. But its quantity decreases for two reasons:
- the interface layer 6 itself acts as a diffusion barrier with respect to these reducing elements.
- the contribution to the electrical resistivity of the interface layer 6 evolves during the lifetime because this interface develops.
- the development of this interface is due to chemical reactions between the whitewash and the reducing elements contained in nickel (such as Mg, Si, Al, Zr, W, ...) which accumulate compounds in this interface.
- These compounds are not very conductive, because they are mainly oxides such as MgO, AI 2 O 3 , SiO 2 , Ba 2 SiO 4 , BaZrO 3 , Ba 3 WO 6 , etc.
- - US-A-4 369 392 proposes incorporating nickel powder in the whitewash, which is in this case produced by pressing and then sintering;
- - US-A-4,797,593 provides a solution which includes the addition of scandium oxide or yttrium oxide in the whitewash, one of the effects of which is to improve the electrical conductivity;
- - US-A-4 273 683 is in the case of an interface formed mainly of Ba 3 W0 6 .
- a layer of nickel powder is deposited on the nickel support prior to painting, and in addition a concentration gradient of barium carbonate is produced in the thickness of the painting.
- the concentration of BaCO 3 is lower in the region touching the interface, so that less BasWO ⁇ compound is created;
- cathodes There are also other types of cathodes, called impregnated cathodes, which allow a sustained regime with an important electronic current, even if this current is temporally constant. These cathodes comprise a porous metallic pellet impregnated with an emissive material. However, they are complex and their manufacturing costs exclude them from numerous applications, in particular in cathode ray tubes intended for the general public.
- the subject of the present invention is an oxide cathode comprising a support and a layer of oxides on the support. It also comprises grains of conductive material having a first end incorporated in the support and a second end housed in the oxide layer, so as to constitute bridges conductors passing through an interface layer forming between the support and the oxide layer.
- the grain-conducting material is a carbide of one or more metals, for example: - Group IV B metals, and preferably at least one metal from: titanium (Ti), zirconium (Zr) and hafnium (Hf);
- V B metals and preferably at least one metal from: vanadium (V), niobium (Nb) and tantalum (Ta);
- Group VI B metals and preferably at least one metal from: chromium (Cr), molybdenum (Mo) and tungsten (W).
- the support can be made of metal, preferably based on nickel.
- the invention also relates to an electronic tube, for example a cathode ray tube, comprising an oxide cathode of the aforementioned type.
- the cathode ray tube can be intended for so-called "multimedia" television applications.
- the invention also relates to a method for manufacturing an oxide cathode in which an oxide layer is deposited on a support, this method comprising the steps consisting in: - lining the surface of the support intended to receive the oxide layer grains of conductive material so that the grains have a first end incorporated in the support and a second end exposed, and
- the step of lining grains of conductive material consists in spreading the grains on said surface and in applying a force on the grains to encrust the first end of the grains in the support.
- the step of lining grains of conductive material consists in incorporating the grains in the support and in removing the second end of the grains by a surface treatment, for example by means of a selective chemical attack. .
- the grains can be incorporated into the support during the metallurgical preparation of the latter.
- FIG. 1 is a partial sectional view and simplified of a conventional oxide cathode and an electrode for creating an electric field conducive to the emission of electrons;
- - Figure 2 already described, is a simplified partial sectional view of a conventional oxide cathode in which an interface layer has formed;
- - Figure 3 is a theoretical electrical diagram showing the contribution of the oxide layer and the interface layer to the electrical resistivity of the cathode of Figure 2;
- - Figure 4 is a partial and simplified sectional view of an oxide cathode according to the present invention
- - Figure 4a is a magnifying glass showing in detail the nesting of a grain of conductive material in the cathode of Figure 4
- FIG. 5 is a theoretical electrical diagram showing the components at the electrical resistivity of the cathode of Figure 4; - Figures 6a to 6c show different stages in the development of a cathode according to a first manufacturing method according to the present invention.
- FIG. 7a to 7d show different stages in the development of a cathode according to a second manufacturing method according to the present invention.
- FIG. 4 The basic structure of a cathode 2 according to the invention is shown diagrammatically by the sectional view in FIG. 4. This representation is similar to that of Figure 2 and the common parts of these two figures have the same references.
- a conductive support 1 based on nickel on a surface 1a of which is deposited a layer of oxides 3 in the form of whitewash.
- an interface layer 6 is formed between the aforementioned surface 1a and the oxide layer 3, as described above with reference to FIG. 2.
- the cathode 2 includes grains 8 of conductive material located at the junction of the support 1 and the oxide layer 3.
- the grains 8 are distributed substantially uniformly over the entire surface (or at least a part) occupied by the oxide layer 3.
- each grain 8 has a first end 8a which penetrates the aforementioned surface 1a of the support 1 so as to be embedded in the support and a second end 8b which is housed in the thickness of the oxide layer 3.
- These two ends 8a and 8b are, within the limit of the irregularity of shape of the grain, mutually opposite on an axis A perpendicular to the surface 1a of the support.
- An intermediate portion 8c of the grain crosses the entire thickness of the interface layer 6.
- the grain 8 constitutes a conductive bridge which establishes an electrically conductive connection connecting the body of the support 1 to the end point of the second end 8b, that is to say within the oxide layer 3.
- the average size of the grains relative to the thickness of the oxide layer 3 can be adapted so that the projection P in the aforementioned axis A of the part of a grain 8 housed in the oxide layer 3 occupies a greater or lesser proportion of the thickness E of this layer depending on the characteristics sought.
- the resistivity R4 of the part of the cathode 2 containing the interface layer 6 appears to be negligible. Indeed, the grains 8 being good conductors, this layer is effectively short-circuited by the conductive bridge effect that each grain 8 provides. Furthermore, the set of grains 8 constitutes a set of parallel connections distributed over the entire active surface of the oxide layers.
- the electrical resistivity R3 of the part of the cathode 2 containing the oxide layer 3 is reduced compared to the resistivity R1 of a conventional cathode without grain material. Indeed, the penetration of the grains 8 in a certain proportion of the layer 3 also creates a conductive bridge effect within the latter. The electrical resistivity is improved in this proportion.
- this single means a reduction in the resistivity of both the interface layer 6 (the latter becoming substantially zero) and the oxide layer 3.
- a material which satisfies several criteria is chosen for the grains 8: to be hard enough to be able to be embedded in the nickel (or other metal) of the support 1, not to be a poison from the emission of the cathode 2, to be electrical conductor, resist oxidation (in particular that caused by the conversion of carbonates into oxides), be chemically stable and in particular do not react with the elements of the cathode, and do not evaporate too much or diffuse too much under the conditions of operation of the cathode.
- Metals with a relatively high melting point oxidize more than nickel and therefore do not offer the best solution, and metal oxides can be insufficiently conductive of electricity.
- an optimal realization can be obtained with metallic carbides.
- one or more can advantageously be chosen from:
- Group IV B carbides and in particular titanium (Ti), zirconium (Zr), hafnium (Hf);
- V B carbides and in particular vanadium (V), niobium (Nb), tantalum (Ta); and
- Group VI B carbides and in particular chromium (Cr) molybdenum (Mo), tungsten (W).
- the metal carbides listed above meet all the criteria: a) they are very hard (Vickers hardness> 1000 HV), b) they are chemically stable and even inert, and therefore cannot be poisons of the cathode emission, c) they are good electrical conductors (electrical resistivity ⁇ 100 ⁇ ohms.cm), d) they resist oxidation very well (for example (tantalum carbides (TaC), niobium (Nb) and zirconium (ZrC) resist oxidation in air up to approximately 800 ° C), and e) they evaporate very little, because they are very thermally stable due to their high melting point (for example, carbides of hafnium (HfC), niobium (NbC), tantalum (TaC), titanium ( TiC) and zirconium (ZrC) have melting points above 3000 ° C, which are among the highest of all materials.
- a first method of manufacturing oxide cathodes according to the invention will now be described with reference to FIGS. 6a to 6c.
- a cathode preform simply comprising the conductive support 1.
- it is a continuous strip of nickel-based material 1 which will be cut and stamped to form the support in its final dimensions.
- a powder composed of grains 8 of one or more metal carbides is spread over a surface 1a of this strip according to the composition described above.
- the part 8a of the grains 8 forming the end in contact with the surface 1a is embedded in the material of the support 1 by applying a compressive force to the opposite end 8b of the grains in the direction of the arrow F (FIG. 6b ).
- a compressive force to the opposite end 8b of the grains in the direction of the arrow F (FIG. 6b ).
- Several techniques can be used to apply this overlay pressure. In the example illustrated, it is obtained by means of a vertical press 10 positioned above the grains, controlled to obtain the desired degree of incrustation. It is also possible to pass the strip 1 with its powder deposit on the surface between a pair of compressing rollers to obtain the same technical effect. If necessary, the support 1 can be heated to allow better penetration of the grains 8.
- the oxide layer 3 is deposited so as to cover the exposed portions of the surface 1a of the strip and of the grains 8. In the example, the layer completely drowns the exposed parts of the grains.
- the grains therefore have an end 8a incorporated in the nickel, and an end 8b in the whitewash, and thus form conductive bridges as explained above.
- Layer 3 is prepared in the form of a whitewash consisting of carbonate (s) and a binder. Typically, carbonates are used, barium carbonates, strontium, and optionally calcium.
- the interface layer 6 is not shown in the figure, because it only appears and develops during aging of the cathode 2, by transformation of the part of the oxide layer near the surface 1a of the support. It is possible to know in advance the thickness of this interface layer and to provide consequently that the height of the non-encrusted parts of the grains 8 is large enough to cross all this thickness and thus ensure its function as a conductive bridge.
- FIGS. 7a to 7d Another method of manufacturing the cathode 2 in accordance with the present invention will now be described with reference to FIGS. 7a to 7d, according to which the grains 8 are incorporated into the material constituting the support 1 during the metallurgical preparation of the latter.
- the support is based on nickel.
- the support 1 is in the form of a metallic ribbon during the phase of incorporation of the grains 8. This ribbon will then be cut and stamped to obtain the support in its final form.
- the ribbon 1 is moved in the direction of the arrow G by means of rollers 12 so that its surface 1 intended to receive the oxide layer passes successively past a heat source 14 and a barrel 16 which pulverizes the grains 8.
- the grain composition used for this technique can be the same as for the first manufacturing method.
- the function of the heat source 14 is to raise the temperature at the surface 1a enough for the metal of the strip to be softened (plastic phase).
- the heat source can be an eddy current induction device in the metal strip 1.
- the barrel 16 projects the grains 8 with force against the surface 1a of the ribbon. This surface having been softened, the grains penetrate almost entirely into the mass of the strip and are therefore found immersed in it, near the surface 1a, as shown in more detail in Figure 7b.
- the strip 1 is subjected to a selective chemical attack aimed at removing the material constituting this strip at its surface 1a without altering the constitution of the grains.
- this attack is carried out by depositing an acid 18 in the liquid phase on the surface 1a of the ribbon (FIG. 7b).
- Other techniques can be envisaged, such as a vapor phase or plasma attack.
- a layer of whitewash 3 containing the carbonates, and in particular the barium carbonate, forming the emissive part of the cathode is deposited on the surface 1a and the parts of the projecting grains 8.
- the exposed parts of the grains 8 after the chemical attack are sufficiently protruding from the surface 1a to pass through a possible interface layer and penetrate into the oxide layer of the cathode.
- the strip thus prepared is cut into cathode support preforms and then stamped to obtain the body of the cathode.
- the aforementioned cutting and optionally stamping are carried out before the chemical etching or similar step.
- the end 8b of the grains 8 is brought out once the support 1 is in the preform state or in its final form.
- the oxide cathode according to the present invention has very wide applications, comprising all the fields where the oxide cathodes are normally used: display tubes (TRC), microwave tubes, grid tubes, etc.
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- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Electrodes For Cathode-Ray Tubes (AREA)
- Solid Thermionic Cathode (AREA)
- Cold Cathode And The Manufacture (AREA)
- Inert Electrodes (AREA)
Abstract
Description
Claims
Priority Applications (7)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP01945372A EP1200973B1 (fr) | 2000-06-14 | 2001-06-07 | Cathode a oxydes amelioree et son procede de fabrication |
MXPA02001603A MXPA02001603A (es) | 2000-06-14 | 2001-06-07 | Catodo de oxido mejorado y su metodo de fabricacion. |
DE60102648T DE60102648T2 (de) | 2000-06-14 | 2001-06-07 | Oxidkathode und zugehöriges herstellungsverfahren |
JP2002511357A JP2004503905A (ja) | 2000-06-14 | 2001-06-07 | 改善された酸化物被覆陰極及びその製造方法 |
KR1020027001926A KR20020019981A (ko) | 2000-06-14 | 2001-06-07 | 개량된 산화물 피복 캐소드 및 그것의 제조 방법 |
AU67610/01A AU6761001A (en) | 2000-06-14 | 2001-06-07 | Improved oxide-coated cathode and method for making same |
US10/049,453 US6759799B2 (en) | 2000-06-14 | 2001-06-07 | Oxide-coated cathode and method for making same |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR0007540A FR2810446A1 (fr) | 2000-06-14 | 2000-06-14 | Cathodes a oxyde amelioree et son procede de fabrication |
FR00/07540 | 2000-06-14 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2001097247A1 true WO2001097247A1 (fr) | 2001-12-20 |
Family
ID=8851229
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/FR2001/001762 WO2001097247A1 (fr) | 2000-06-14 | 2001-06-07 | Cathode a oxydes amelioree et son procede de fabrication |
Country Status (10)
Country | Link |
---|---|
US (1) | US6759799B2 (fr) |
EP (1) | EP1200973B1 (fr) |
JP (1) | JP2004503905A (fr) |
KR (1) | KR20020019981A (fr) |
CN (1) | CN1214436C (fr) |
AU (1) | AU6761001A (fr) |
DE (1) | DE60102648T2 (fr) |
FR (1) | FR2810446A1 (fr) |
MX (1) | MXPA02001603A (fr) |
WO (1) | WO2001097247A1 (fr) |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8385506B2 (en) | 2010-02-02 | 2013-02-26 | General Electric Company | X-ray cathode and method of manufacture thereof |
US8938050B2 (en) | 2010-04-14 | 2015-01-20 | General Electric Company | Low bias mA modulation for X-ray tubes |
CN102254766B (zh) * | 2010-05-19 | 2013-03-06 | 中国科学院电子学研究所 | 一种制备稀土贮存式氧化物阴极的方法 |
KR20180062812A (ko) * | 2016-12-01 | 2018-06-11 | 삼성전자주식회사 | 이종의 메모리 소자들을 포함하는 집적회로 소자 및 그 제조 방법 |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR1107589A (fr) * | 1954-06-18 | 1956-01-03 | Csf | Perfectionnements aux supports de cathodes à oxydes |
US3257703A (en) * | 1961-09-29 | 1966-06-28 | Texas Instruments Inc | Composite electrode materials, articles made therefrom and methods of making the same |
US4313854A (en) * | 1978-11-15 | 1982-02-02 | Hitachi, Ltd. | Oxide-coated cathode for electron tube |
Family Cites Families (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4273683A (en) * | 1977-12-16 | 1981-06-16 | Hitachi, Ltd. | Oxide cathode and process for production thereof |
JPS5596531A (en) * | 1979-01-19 | 1980-07-22 | Hitachi Ltd | Directly heated cathode for electron tube |
GB2059676B (en) * | 1979-09-12 | 1983-07-20 | Hitachi Ltd | Oxide-coated cathodes |
JPS5641636A (en) * | 1979-09-12 | 1981-04-18 | Hitachi Ltd | Directly heated type oxide cathode |
US4369392A (en) * | 1979-09-20 | 1983-01-18 | Matsushita Electric Industrial Co., Ltd. | Oxide-coated cathode and method of producing the same |
CA1270890A (fr) * | 1985-07-19 | 1990-06-26 | Keiji Watanabe | Cathode de tube electronique |
KR910009660B1 (ko) * | 1988-02-23 | 1991-11-25 | 미쓰비시전기 주식회사 | 전자관용 산화물피복음극 |
DE4207220A1 (de) * | 1992-03-07 | 1993-09-09 | Philips Patentverwaltung | Festkoerperelement fuer eine thermionische kathode |
KR100294485B1 (ko) * | 1993-08-24 | 2001-09-17 | 김순택 | 산화물음극 |
US5925976A (en) * | 1996-11-12 | 1999-07-20 | Matsushita Electronics Corporation | Cathode for electron tube having specific emissive material |
KR100247820B1 (ko) * | 1997-08-07 | 2000-03-15 | 손욱 | 전자관용 음극 |
KR100249714B1 (ko) * | 1997-12-30 | 2000-03-15 | 손욱 | 전자총용 음극 |
KR20000038644A (ko) * | 1998-12-08 | 2000-07-05 | 김순택 | 전자총용 음극 |
-
2000
- 2000-06-14 FR FR0007540A patent/FR2810446A1/fr active Pending
-
2001
- 2001-06-07 CN CNB018024106A patent/CN1214436C/zh not_active Expired - Fee Related
- 2001-06-07 US US10/049,453 patent/US6759799B2/en not_active Expired - Fee Related
- 2001-06-07 DE DE60102648T patent/DE60102648T2/de not_active Expired - Fee Related
- 2001-06-07 AU AU67610/01A patent/AU6761001A/en not_active Abandoned
- 2001-06-07 JP JP2002511357A patent/JP2004503905A/ja not_active Withdrawn
- 2001-06-07 KR KR1020027001926A patent/KR20020019981A/ko active IP Right Grant
- 2001-06-07 EP EP01945372A patent/EP1200973B1/fr not_active Expired - Lifetime
- 2001-06-07 MX MXPA02001603A patent/MXPA02001603A/es active IP Right Grant
- 2001-06-07 WO PCT/FR2001/001762 patent/WO2001097247A1/fr active IP Right Grant
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR1107589A (fr) * | 1954-06-18 | 1956-01-03 | Csf | Perfectionnements aux supports de cathodes à oxydes |
US3257703A (en) * | 1961-09-29 | 1966-06-28 | Texas Instruments Inc | Composite electrode materials, articles made therefrom and methods of making the same |
US4313854A (en) * | 1978-11-15 | 1982-02-02 | Hitachi, Ltd. | Oxide-coated cathode for electron tube |
Non-Patent Citations (1)
Title |
---|
OHIRA T ET AL: "AN ANALYSIS OF THE SURFACE OF THE NI-W LAYER OF A TUNGSTEN FILM COATING CATHODE", APPLIED SURFACE SCIENCE,ELSEVIER, AMSTERDAM,NL, VOL. 146, PAGE(S) 47-50, ISSN: 0169-4332, XP000912107 * |
Also Published As
Publication number | Publication date |
---|---|
EP1200973A1 (fr) | 2002-05-02 |
US20040000854A1 (en) | 2004-01-01 |
MXPA02001603A (es) | 2002-07-02 |
CN1214436C (zh) | 2005-08-10 |
FR2810446A1 (fr) | 2001-12-21 |
CN1388979A (zh) | 2003-01-01 |
EP1200973B1 (fr) | 2004-04-07 |
JP2004503905A (ja) | 2004-02-05 |
US6759799B2 (en) | 2004-07-06 |
DE60102648D1 (de) | 2004-05-13 |
DE60102648T2 (de) | 2005-03-24 |
AU6761001A (en) | 2001-12-24 |
KR20020019981A (ko) | 2002-03-13 |
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