US3307063A - Grid electrode made of pyrolytic graphite - Google Patents

Grid electrode made of pyrolytic graphite Download PDF

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Publication number
US3307063A
US3307063A US269919A US26991963A US3307063A US 3307063 A US3307063 A US 3307063A US 269919 A US269919 A US 269919A US 26991963 A US26991963 A US 26991963A US 3307063 A US3307063 A US 3307063A
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Prior art keywords
grid
graphite
electrode
grid electrode
oriented graphite
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Expired - Lifetime
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US269919A
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English (en)
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Sarrois Jean Marcel
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Compagnie Francaise Thomson Houston SA
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Compagnie Francaise Thomson Houston SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J19/00—Details of vacuum tubes of the types covered by group H01J21/00
    • H01J19/28—Non-electron-emitting electrodes; Screens
    • H01J19/30—Non-electron-emitting electrodes; Screens characterised by the material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2893/00—Discharge tubes and lamps
    • H01J2893/0001—Electrodes and electrode systems suitable for discharge tubes or lamps
    • H01J2893/0012—Constructional arrangements
    • H01J2893/0019—Chemical composition and manufacture
    • H01J2893/002—Chemical composition and manufacture chemical
    • H01J2893/0021—Chemical composition and manufacture chemical carbon

Definitions

  • This invention relates to grid electrodes for electron discharge devices, and has among its objects the provision of an improved grid electrode possessing very low values of primary and secondary emission, high thermal conductivity and high mechanical strength and dimensional stability.
  • grid electrodes designed for operation under high power and heat loading conditions were almost exclusively made from metals such as molybdenum, tantalum and tungsten, having high mechanical strength at elevated temperatures.
  • These metallic materials however have certain definite drawbacks for such use. They are poor conductors of heat, so that the heat received by the grid cannot be dissipated as fast as it is supplied through electron bombardment and a considerable amount of forced cooling becomes necessary.
  • the aforesaid metals when coated with a thin film of cathodic deposits as mentioned above greatly increase the primary emission rate of the grid. This emission rate is increased by the temperature elevation which results from the poor heat conductivity just mentioned. Secondary emission effects are simultaneously increased, the secondary emis sion factor assuming a value greater than unity as the electron accelerating voltage exceeds a certain threshold value within the range of from 150 to 250 volts.
  • Objects of this invention are to eliminate these drawbacks and the consequent limitations on the power rating and other operating characteristics of the electron discharge devices in which grid electrodes are incorporated.
  • a grid electrode characterized in that it comprises, at least at the surface thereof, oriented graphite so applied that its maximal thermal conductivity is directed substantially parallel to the surface of the electrode.
  • the grid electrode is composed throughout its full depth of oriented graphite applied as just specified.
  • Molecularly oriented graphite also sometimes known as pyrolytic graphite, is known in the art. It is a form of crystalline carbon obtainable through thermal decomposition of a gaseous carbon compound such as a gaseous hydrocarbon, on the surface of a supporting base carried to a suitable high temperaure, e.g. of the order of 2000" C. It deposits on the surface of the base in the form of successive layers or strata which can be built up to considerable depths. Each layer is of extremely high mechanical strength and due to the oriented crystalline buildup of the layers the resulting sheet of graphite exhibits a very high degree of anisotropy in its physical characteristics. This is especially true in regard to its heat con ductivity.
  • the heat conductivity of such a foliated layer of oriented graphite when measured at a temperature below about 1000 C. in a direction parallel to the general surface of the layer is very high, being about the same as that of copper sheet, about three times higher than that of ordinary commercial graphite as obtained e.g. by recrystallization from a conglomerate of microcrystalline carbon.
  • the heat conductivity of oriented graphite is considerably less than that of ordinary graphite.
  • the secondary emission factor of oriented graphite is substantially equal to that of ordinary graphite, and is therefore less than unity regardless of the velocity of the impinging elec trons. Its primary emission properties are also satisfactory in that it acts greatly to reduce the primary emission of cathodic substances deposited thereover just as would a sub layer of ordinary graphite or carbon, as earlier mentioned.
  • the oriented graphite constituting at least a surface layer of the electrode is just as favourable in eliminating unwanted secondary electron emission as the best coatings known for a similar purpose in prior-art electrodes.
  • the inherent rate of heat dissipation is much increased so that, under comparable conditions of external forced cooling (if any), the operating temperature of the grid is lowered, thereby providing an additional factor for reducing the rate of primary emission from the grid surface, besides the normal reduction in primary emission due to the properties of carbon in general as earlier mentioned.
  • the individual grid elements such as strips or bars, exposed to heating from electron bombardment, are rapidly cooled by dissipation of their heat content in directions parallel to the layers or folia of oriented graphite towards the supporting elements of the electrode. Due to the extraordinarily high value of heat conductivity of oriented graphite in the aforementioned directions, this heat dissipating effect is highly effective even in cases where only a relatively thin surface layer of the grid structure is formed from the oriented graphite material; it is substantially more effective still where the grid electrode structure is composed of oriented graphite throughout its depth in accordance with the aforementioned preferred embodiment of the invention.
  • the mechanical strength characteristics of the electrode of the invention are also remarkably good, owing to the high mechanical strength of the elementary layers or folia of the oriented graphite especially in regard to tensile stresses in directions parallel to the general surface of the folia.
  • the improved electrode wherein the. oriented graphite is applied as a coating overlying electrode elements made of some other material, such as molybdenum or tantalum, there is provided in effect a tough, compact sheath around the grid elements, which greatly increases their resistance to impacts and vibrations.
  • the over-all mechanical strength is even better, and is generally considerably higher than that of comparable electrodes made of conventional metallic materials such as molybdenum and tantalum.
  • Grid electrodes according to the invention can be provided in a great variety of over-all geometrical shape, including fiat, cylindrical, spherical, etc.
  • the individual grid elements such as wires or strips, may also be made to a wide diversity of forms and dimensions.
  • an electrode in the form of a skew-slotted tubular cylindrical element wherein the slots are conveniently provided as elliptical curves defined by the intersection of the cylindrical surface with angularly spaced planes inclined at a common angle to the generatrices of the cylinder.
  • Such a form of electrode is especially suitable when made entirely from oriented graphite in accordance with a preferred aspect of the present invention.
  • Another suitable shape is that of a cup-shaped element having a flat end or bottom wall in which slots in the form of equispaced circular arcs are cut, as disclosed in said application 261,461.
  • a tubular or flat blank made from oriented graphite may first be prepared by known techniques as by depositing the oriented graphite over a core, which may conveniently comprise ordinary commercial graphite, through heating the core in a suitable carbon containing gaseous atmosphere as earlier indicated, and then separating the deposited coating of oriented graphite from the core, an operation easily performed where the core comprises ordinary graphite.
  • the electrode shown is generally similar in form with that illustrated in copending application No. 261,461 mentioned above, and comprises a part in the form of a surface of revolution including a frustoconical base section 1, a cylindrical main body section 2 and a flat top 3.
  • the cylindrical body section 2 is formed with a series of slots 4 angled with respect to the generatrices of the cylindrical surface.
  • the slots 4 and hence also the mid-lines of the inter-slot strips 6 forming the elements of the grid electrode are elliptical arcs defined by the intersection with the cylinder 2 of a family of angularly-spaced planes inclined at a common angle to the axis of the cylinder.
  • both the angle of inclination of the slots, indicated at 7, and the pitch spacing between them, are shown larger than would actually be used in most practical applications.
  • the average inclination of the slots with respect to the generattrices of the cylinder may advantageously be selected within the range of from 10 to 30.
  • the electrode shown is entirely constituted of a sheet of oriented graphite and is prepared by depositing carbon from a gaseous compound upon a suitably shaped core, made e.g. of ordinary commercial graphite, at a suitable temperature of the order of 2000 C. After the deposited oriented graphite has built up to the desired depth, the assembly is allowed to cool and the deposited layer is separated from the underlying graphite core. The resulting oriented graphite element is then machined to provide the inclined slots 4 in its cylindrical body part 2, e.g. by the procedure described in the aforementioned application No.
  • the resulting slotted electrode can then be mounted on a support 8, e.g. of ordinary graphite, as by brazing the periphery of base section 1 to the support 8 by means of a suitable brazing medium such as titanium carbide, zirconium carbide, or pure titanium, as shown at 9.
  • cylindrical body section 2 0.20 to 0.25 mm. Diameter of cylindrical body section 2 40 mm. Axial height of body section 2 30 mm.
  • the slots 4 extended over about 20 mm.
  • Such an electrode can be machined without having to introduce any support or core within the blank, and this makes it possible to machine two similar grid electrodes in a single operation.
  • the resulting electrodes will have their slots and inter-slot strips aligned with a high degree of accuracy, especially where the angle of the slots is comparatively low. In this way assemblies including e.g. a grid electrode and a screen electrode for incorporation into a common electron discharge tube can be simultaneously prepared.
  • an electrode according to an alternative embodiment of the invention can be produced by providing a coating of oriented graphite over the surfaces of a base grid structure of any suitable material and shape.
  • the apparatus used may comprise a casing made of ordinary graphite, formed with an inlet and an outlet for a suitable carbon containing gas, such for example as methane, acetylene, benzene or other hydrocarbon.
  • the casing is positioned within an electric heating device such as a cage of closely-spaced heating resistors.
  • an electric heating device such as a cage of closely-spaced heating resistors.
  • Within the casing and adjacent to the gas inlet is a gas diffuser member.
  • the electrode structure to be coated and having any suitable shape as earlier indicated, is mounted centrally within the casing. When the gas is circulated through the casing and the heater is operated to bring the internal temperature to a value of about 1500 C.
  • fol iated layers of oriented graphite deposit over the surfaces of the electrode elements and build up to a depth depending on the time the process is continued.
  • the oriented graphite layer is found to settle with great uniformity, even if the underlying support includes irre gular areas such as spots of solder or the like, so that there are practically no reasonable restrictions on the shape and structure of the electrodes achievable by this method.
  • a grid electrode having low secondary emission said grid electrode having a configuration to define a surface and comprising at least in a surface area thereof, a layer of pyrolytic graphite having a direction of maximum thermal and electrical conductivity thereof directed substantially parallel to the general surface of said area.
  • a grid electrode having low secondary emission which comprises a sheet element defining a surface of pyrolytic graphite having its maximum thermal and electrical conductivity directed substantially parallel to the surface of the sheet, and spaced perforations formed in said sheet element.
  • a grid electrode having low secondary emission which comprises a tubular cylindrical body portion defining a cylindrical surface and slots formed through the wall of said body and inclined with respect to the 'generatrices of the cylindrical surface thereof, said body comprising at least in the surface area thereof a layer of pyrolytic graphite having its maximum thermal and electrical conductivity directed parallel to the general surface of said area.
  • a grid electrode having low secondary emission which comprises a cup-shaped element with a flat end Wall defining an end surface, and regularly spaced slots formed in said end wall, said end Wall comprising at least in the surface area thereof a layer of pyrolytic graphite having its maximum thermal and electrical conductivity directed parallel to the general plane of said end wall.

Landscapes

  • Solid Thermionic Cathode (AREA)
  • Carbon And Carbon Compounds (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Inert Electrodes (AREA)
US269919A 1962-03-02 1963-04-02 Grid electrode made of pyrolytic graphite Expired - Lifetime US3307063A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR889759A FR1344220A (fr) 1962-03-02 1962-03-02 Grille pour tubes électroniques

Publications (1)

Publication Number Publication Date
US3307063A true US3307063A (en) 1967-02-28

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ID=8773876

Family Applications (1)

Application Number Title Priority Date Filing Date
US269919A Expired - Lifetime US3307063A (en) 1962-03-02 1963-04-02 Grid electrode made of pyrolytic graphite

Country Status (7)

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US (1) US3307063A (fr)
CH (1) CH415872A (fr)
DE (1) DE1194988C2 (fr)
ES (1) ES285347A1 (fr)
FR (1) FR1344220A (fr)
GB (1) GB1011587A (fr)
NL (1) NL139841B (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3535758A (en) * 1967-03-07 1970-10-27 Thomson Houston Comp Francaise Method of machining perforate electrodes from pyrolytic graphite
US3591822A (en) * 1967-12-13 1971-07-06 Siemens Ag Electric discharge vessel electrode structure of pyrolytic carbon discs
FR2469794A1 (fr) * 1979-11-07 1981-05-22 Varian Associates Tube electronique modulaire a grille de carbone
DE3205075A1 (de) * 1981-02-13 1982-09-09 Stanislav M. Šatalov Gitterfoermige elektrode fuer elektronengeraete und verfahren zu ihrer herstellung
US4387320A (en) * 1978-07-27 1983-06-07 Thomson - Csf Electron tube with cylindrical grid of pyrolytic graphite
US4975617A (en) * 1983-01-19 1990-12-04 U.S. Philips Corporation Electric discharge tube

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2450261C3 (de) * 1974-10-23 1980-06-26 Philips Patentverwaltung Gmbh, 2000 Hamburg Verfahren zur Herstellung von Gitterelektroden für Elektronenröhren
DE2623828A1 (de) * 1976-05-28 1977-12-08 Philips Patentverwaltung Elektrode, insbesondere gitterfoermige elektrode fuer elektronenroehren, und verfahren zu deren herstellung
DE2613170B2 (de) * 1976-03-27 1978-10-12 Philips Patentverwaltung Gmbh, 2000 Hamburg Verfahren zur Herstellung von Gitterelektroden für Elektronenröhren
DE2838020C3 (de) * 1978-08-31 1987-06-19 Siemens AG, 1000 Berlin und 8000 München Direkt geheizte Kathode für Senderöhren mit koaxialem Aufbau der Elektroden
FR2437060A1 (fr) * 1978-09-19 1980-04-18 Thomson Csf Procede de fabrication de grilles planes en graphite pyrolytique pour tubes electroniques
CS224267B1 (en) * 1980-12-24 1984-01-16 Slavomir Ing Zizka Power tube grid
NL8500220A (nl) * 1985-01-28 1986-08-18 Philips Nv Elektronenbuis.

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1612835A (en) * 1917-01-23 1927-01-04 Siemens Ag Intermediate electrode in incandescent cathode tube
US1985087A (en) * 1931-11-09 1934-12-18 Gen Electric Arc discharge apparatus
US2054234A (en) * 1933-07-29 1936-09-15 Hygrade Sylvania Corp Electric discharge device
GB830532A (en) * 1957-07-12 1960-03-16 Standard Telephones Cables Ltd Improvements in or relating to electron discharge tubes
GB918880A (en) * 1959-12-23 1963-02-20 Du Pont Improvements in carbon products and in their production
FR1323676A (fr) * 1962-02-28 1963-04-12 Thomson Houston Comp Francaise électrode pour tubes électroniques et procédé de sa fabrication
US3138434A (en) * 1961-04-26 1964-06-23 Gen Electric Deposition method of forming a pyrolytic graphite article
US3172774A (en) * 1965-03-09 Method of forming composite graphite coated article
US3187502A (en) * 1961-01-23 1965-06-08 Gen Electric Rocket nozzle

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2101462A (en) * 1935-03-13 1937-12-07 Farnsworth Television Inc Grid
US2193600A (en) * 1935-04-10 1940-03-12 Westinghouse Electric & Mfg Co Carbon grid for transmitting vacuum tubes

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3172774A (en) * 1965-03-09 Method of forming composite graphite coated article
US1612835A (en) * 1917-01-23 1927-01-04 Siemens Ag Intermediate electrode in incandescent cathode tube
US1985087A (en) * 1931-11-09 1934-12-18 Gen Electric Arc discharge apparatus
US2054234A (en) * 1933-07-29 1936-09-15 Hygrade Sylvania Corp Electric discharge device
GB830532A (en) * 1957-07-12 1960-03-16 Standard Telephones Cables Ltd Improvements in or relating to electron discharge tubes
GB918880A (en) * 1959-12-23 1963-02-20 Du Pont Improvements in carbon products and in their production
US3187502A (en) * 1961-01-23 1965-06-08 Gen Electric Rocket nozzle
US3138434A (en) * 1961-04-26 1964-06-23 Gen Electric Deposition method of forming a pyrolytic graphite article
FR1323676A (fr) * 1962-02-28 1963-04-12 Thomson Houston Comp Francaise électrode pour tubes électroniques et procédé de sa fabrication

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3535758A (en) * 1967-03-07 1970-10-27 Thomson Houston Comp Francaise Method of machining perforate electrodes from pyrolytic graphite
US3591822A (en) * 1967-12-13 1971-07-06 Siemens Ag Electric discharge vessel electrode structure of pyrolytic carbon discs
US4387320A (en) * 1978-07-27 1983-06-07 Thomson - Csf Electron tube with cylindrical grid of pyrolytic graphite
FR2469794A1 (fr) * 1979-11-07 1981-05-22 Varian Associates Tube electronique modulaire a grille de carbone
US4277718A (en) * 1979-11-07 1981-07-07 Varian Associates, Inc. Modular electron tube with carbon grid
DE3041113A1 (de) * 1979-11-07 1981-08-27 Varian Associates, Inc., Palo Alto, Calif. Elektronenroehre
DE3205075A1 (de) * 1981-02-13 1982-09-09 Stanislav M. Šatalov Gitterfoermige elektrode fuer elektronengeraete und verfahren zu ihrer herstellung
US4469984A (en) * 1981-02-13 1984-09-04 Sergeev Jury S Grid-like electrode for electronic components and process for making same
US4975617A (en) * 1983-01-19 1990-12-04 U.S. Philips Corporation Electric discharge tube

Also Published As

Publication number Publication date
FR1344220A (fr) 1963-11-29
ES285347A1 (es) 1963-06-16
DE1194988B (de) 1965-06-16
DE1194988C2 (de) 1976-01-15
GB1011587A (en) 1965-12-01
NL139841B (nl) 1973-09-17
CH415872A (fr) 1966-06-30

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