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US3681644A - Indirectly heated dispenser cathode - Google Patents

Indirectly heated dispenser cathode Download PDF

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Publication number
US3681644A
US3681644A US76669A US3681644DA US3681644A US 3681644 A US3681644 A US 3681644A US 76669 A US76669 A US 76669A US 3681644D A US3681644D A US 3681644DA US 3681644 A US3681644 A US 3681644A
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Prior art keywords
mask member
organic polymer
polymer material
storage chamber
cathode
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US76669A
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Horst Hofmann
Erwin Huebner
Helmut Katz
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Siemens AG
Siemens Corp
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Siemens Corp
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Priority claimed from DE19691951603 external-priority patent/DE1951603C3/en
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    • 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
    • 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

  • ABSTRACT A dispenser MK-type cathode structure adapted for storage and/or handling with subsequent activation and a method of producing the same whereby a supply source material of an emission-promoting substance is positioned in an open-ended storage chamber of a plug-like cathode insert member and sealed within the chamber by a fluid impermeable pore-free mask member.
  • a porously sintered tungsten disc member sits above the mask member so as to have an undersurface thereof in fluid communication with the supply source material upon rupture of the mask member.
  • the mask member is sealed to the boundaries of the storage chamber by a self-sticking organic polymer material which is thermally decomposable without residue at operational temperatures of such dispenser cathodes.
  • the mask member comprises a unitary structure composed of a high melting metal foil having at least one surface thereof coated with the organic polymer material, a lamina of a film forming organic material having a layer of the self-thicking organic polymer material along a surface thereof or a self supporting film of the organic polymer material.
  • the mask member is provided in a controlled thickness of sufficient dimension to resist rupture until the environment around the sealed storage chamber is subjected to cathode vacuum conditions.
  • Prior Art Metal capillary cathodes i.e., MK cathodes
  • MK cathodes comprise a confining metal cup member having a supply substance for an emission-promoting material therein (i.e., one yielding an emission-promoting material, such as barium, at a high temperature) and a porous disc welded to the rim of the cup member, the upper surface of which defines an emission surface.
  • a heating means heats both the cup member and the disc causing the supply substance to evaporate and the emission-promoting material to migrate by capillary action through the porous discs and to the emission surface.
  • the emission-promoting material forms a film on the free surface of the disc and acts to reduce the work function of the material forming the disc.
  • modified structures have been prepared wherein relatively thin metal foils are positioned between the supply materials yielding an emission promoting substance and the porous disc.
  • the supply material is surrounded with an inert atmosphere and the thin metal foil tightly seals this atmosphere within the storage chamber.
  • the assembled dispenser cathode structure can be handled and/or stored with a subsequent activation by rupturing the foil with subjection of the environment around the field chamber to cathode vacuum operating conditions.
  • Such modified structures function relatively reliably providing that the thickness of the metal foil is relatively thin.
  • other high melting metals such as molybdenum, are extremely difficult to manufacture into foils of precisely controlled thickness.
  • the instant invention provides a cathode structure and a method of producing the same which avoids the aforesaid difficulties and provides novel masks or foil members of easily controlled thicknesses.
  • the invention provides a novel dispenser cathode structure of the MK indirectly heated type and a method of producing the same where a supply material yielding an emission promoting substance is stored in an open-ended storage chamber of a plug-like cathode insert member and sealed in an inert atmosphere and from the surrounding environment by a fluid impermeable mask member composed of a unitary structure including a thermally decomposable organic polymer material, a combination of a relatively dense high melting metal foil and a layer of such organic polymer material along at least one surface of the metal foil and/or a combination of a lamina of a film-forming organic material and a layer of such organic polymer material along one surface of the lamina.
  • plurality of such plug-like cathode insert members are spaced about a relatively large dimension ring-shaped cathode body and each insert member is machined to mate or lock with a portion of such body and the mask member sealingly cooperates with the peripheral surfaces of the storage chamber to confine the inert atmosphere and the supply material therein and out of communication with the environment surrounding the chamber, including the cathode emission surface.
  • the thickness of the mask member is readily controlled by liquid or semi-liquid coating techniques.
  • the organic material utilized forms a self-sticking film which is readily united with a relatively high melting metal foil or an organic material lamina and readily forms a fluid impermeable seal on the peripheral boundaries of the storage chamber. Additionally, the organic polymer material thermally decomposes at normal cathode operating temperature without producing any harmful reaction product or other undesirable residue.
  • FIG. 1 is an overall diagrammatic sectional view of an embodiment of a ring-shaped cathode structure and includes a cross-sectional view through an embodiment of an insert member constructed in accordance with the principles of the invention
  • FIG. 2 is a somewhat enlarged cross-sectional view of another embodiment of an insert member constructed in accordance with the principle of the invention.
  • This invention provides an indirectly heated dispenser cathode structure of the MK-type.
  • cathode structure includes a ringshaped emission surface supported on an appropriately shaped cathode body member wherein a supply material (i.e., an alkali earth metal oxide) for an emissionpromoting substance (i.e., an alkali earth metal) is spaced away from the emission surface within the cathode body member and distributed around the perimeter thereof.
  • a supply material i.e., an alkali earth metal oxide
  • an emissionpromoting substance i.e., an alkali earth metal
  • the porous cover member defines the cathode emission surface and the emission-promoting substance forms a thin film thereat to reduce the work function of such emission surface.
  • the porous disc is composed of a porously sintered tungsten and the supply source material is i.e., an alkali earth metal oxide, and particularly barium oxide.
  • the ring-shaped cathode structures are provided with a relatively large emission surface composed of a porously sintered tungsten or other emission base material supported along peripheral portions thereof by a body member.
  • the body member is composed of a relatively high melting metal, such as molybdenum, and is provided with a plurality of axial bores extending toward the emission surface so as to be in fluid communication therewith. These axial bores are generally uniformly spaced around the perimeter of the body member.
  • One or more plug-like insert members are provided for insertion into a desired number of axial bores.
  • Each insert member is also composed of a relatively high melting metal, such as molybdenum, and has an open-ended storage chamber at an upper axial end thereof for containing a desired amount of a supply material for an emission-promoting substance.
  • the insert members are adapted to mechanically mate or lock with the axial bore walls, as by suitably provided screw threads or the like.
  • the supply material (i.e., BaO) for an emissionpromoting substance (i.e., Ba) is formed into appropriately sized tablets or the like for ease of usage and insertion into the storage chamber of the insert member.
  • the supply material can be used in powdered form, if desired.
  • a suitable amount of such supply material is placed within a storage chamber, surrounded or blanketed with an inert atmosphere and sealed.
  • a dry inert gas is pumped or injected at about ambient pressures into the partially filled storage chamber so as to completely surround and blanket the supply material.
  • There after the chamber is sealed by a mask member so as to maintain the supply material under a blanket of such inert gas at such ambient (i.e., atmospheric) pressure.
  • the mask member is provided with a self-sticking coating which forms a fluid (i.e., water or gas) impervious seal between the upper boundaries of the storage chamber and the mask member independently of the cathode body member.
  • a fluid i.e., water or gas
  • the sealed insert members are stored or handled as desired without danger of any chemical reaction or the like from occurring with the supply material.
  • the seal insert members are locked into the axial bores within the cathode body and the assembled unit is stored or handled as desired until activation.
  • Activation or operational condition is achieved by positioning an assembled cathode body member, i.e., one having sealed insert members locked in place, into a suitable envelope or tube device or some other device utilizing a cathode, and evacuating the tube device to provide an operational vacuum state for such device.
  • the inert gas atmosphere at atmospheric pressures sealed within the storage chamber will rupture and/or destroy mask member and provide a free path of travel for the emission-promoting material to the emission surface of the porously sintered covered member.
  • the cathode structure is then indirectly heated, as by an electrically operating heating coil, to the normal operating temperatures thereof, i.e., between about 800 to l ,300" C. depending upon the characteristics of the material of the structure and the supply material.
  • the mask member is a relatively dense foil or film and includes a self-sticking organic polymer material which thermally decomposes without any objectionable residue at the operating temperatures of a dispenser cathode.
  • the self-sticking organic polymer materials are preferably selected from the group consisting essentially of paraffin, acetic acid esters, polyacrylic acid esters, phthalic acid esters and mixtures thereof.
  • the mask member comprises a composite film structure comprised of a combination of a high melting metal (i.e., Ta or Mo) foil and a layer of the self-sticking organic polymer material along at least one surface of a metal foil; a combination of a lamina of a film-forming organic material and a layer of the self-sticking organic polymer material along a surface of the lamina; and a self-supporting film of the self-sticking organic polymer material.
  • the composite film structure is provided in accurately controlled thicknesses, and preferably in a thickness of not more than about l20 micrometers (i.e., am). The thickness is accurately controlled to insure that the mask member will rupture at the operating conditions of a cathode.
  • the self-sticking organic polymer material is suitably prepared for application by mixing with a suitable solvent (for example a relatively volatile low molecular weight alcohol) so that the resultant liquid or semi-liquid mixture is amenable to coating techniques and can be applied in a layer of a desired thickness on a base source to provide a substantially pore-free mask member.
  • a suitable solvent for example a relatively volatile low molecular weight alcohol
  • a self-sticking organic polymer material of the invention is formulated into a self-supporting film suitable for use as a M member per se by preparing a substantially homogeneous paste-like material comprised of about 4.0 milliliters (i.e., ml) of Plexisol P-SSO (a registered trademark of Roehm & Haas Co. for polyacrylic acid ester materials), 1.0 ml of butyl acetate and 0.1 gram of phthalic acid ester (phthalic acid ester-bis-Z-ethyl ester) and a suitable solvent.
  • a substantially homogeneous paste-like material comprised of about 4.0 milliliters (i.e., ml) of Plexisol P-SSO (a registered trademark of Roehm & Haas Co. for polyacrylic acid ester materials), 1.0 ml of butyl acetate and 0.1 gram of phthalic acid ester (phthalic acid ester-bis-Z-ethy
  • This paste-like material is transferred to a draw ring having a slit width of about 200 micrometers (i.e., pm) and then drawn through the slit onto a smooth base surface.
  • the solvent used is removed, as by evaporation, and a selfsupporting film is formed which is tacky or selfsticking.
  • the finished film has a thickness of about l20 um and forms an excellent mask member which is ruptured at operational cathode vacuum conditions and is thermally decomposed, without residue, at the operational temperatures of indirectly heated dispenser cathode structure.
  • FIG. 1 is an overall diagrammatic sectional view of an indirectly heated dispenser cathode structure which has a relatively large diameter ring-shape, and those elements thereof which do not materially aid a better understanding of the principles of the invention are left out or are merely not given a reference numeral.
  • a ring-shaped cathode body member 1 supports and carries a ring-shaped disc member along peripheral portions thereof so that its upper surface defines an emission surface 20.
  • the disc member 2 and the emission surface 24 are composed of the same material, such as porously sintered tungsten.
  • the cathode body member 1 is provided with a plurality of axial apertures or bores 3, generally uniformly spaced about the perimeter of body number 1.
  • the axial bores 3 extend generally toward the emission surface Za so as to be in fluid communication therewith but are somewhat spaced away from disc member 2.
  • An insert member 4 is adapted to mechanically mate or lock with the peripheral walls of the axial bores 3.
  • the insert member 4 is provided with an open-ended storage chamber 5 opening toward said disc member 2.
  • a passageway means 11 is provided along the upper surface of the bores 3 so as to provide uniform communication with the exposed underside of the disc member 2.
  • the plug-like insert member 4 is formed somewhat in the shape of a hollow set screw or the like having an open ended storage chamber 5.
  • a supply material for an emission-promoting substance is pre-formed into tablets 6 and a suitable number of such tablets 6 are positioned within the chamber 5 and a dry inert atmosphere is injected within the remaining hollow space of the chamber so as to completely surround or blanket the supply material.
  • the inert atmosphere is maintained at about ambient pressure, although a slightly positive pressure can be utilized if desired. Thereafter, the storage chamber 5 is tightly sealed from the surrounding environment by a mask member 8.
  • the mask member 8 is a composite film structure having a relatively high density and is porefree so as to be impervious to fluids and particularly water and CO in the embodiment shown at FIG. 1, the mask member 8 comprises a lamina 9 of an organic filmforming material having a layer 90 of the self-sticking organic polymer material along a surface of the lamina.
  • the lamina 9 may be composed of the self-sticking organic polymer material per se or of another organic film forming material.
  • the assembled unit, such as shown in FIG. 1, can be stored or handled as desired without any danger of a chemical reaction occurring with the supply material within chamber 5.
  • the passageway 11 which may be somewhat ringshaped, provides fluid communication around the entire periphery of the body member I so that the emission-promoting substance can uniformly contact the entire underside of the disc member 2.
  • FIG. 2 illustrates another embodiment of the mask member 8 constructed in accordance with the invention. ln this embodiment, the structure is essentially similar to that explained in conjunction with FIG. 1 except that the supply of material is utilized in powdered form 60.
  • the mask member 8 is composed of a unitary structure having a relatively high melting metal foil 13 and a layer 9! of the self-sticking organic polymer material along a surface of the foil.
  • the metal foil 13 can be sandwiched between a pair of such layers 9b, if desired.
  • the invention provides a novel indirectly heated dispenser cathode structure comprising a shaped porous disc member having an emission surface with a cathode body member supporting and carrying the disc member along a surface thereof opposed the emission surface.
  • the cathode body member has a plurality of axial bores distributed about the perimeter of the body member and extending toward the emission surface.
  • a plurality of insert members are provided which are adapted to mechanically lock with the walls of the axial bores and each insert member has an openended storage chamber extending toward the disc member with a supply material for an emission-promoting substance sealed within the chamber and surrounded by an inert atmosphere.
  • a fluid impermeable mask member is positioned between the storage chamber and a passage means within the cathode body member that provides communication between the storage chamber and the disc member to block travel of the emission-promoting substance to the disc member.
  • the mask member is provided with a selfsticking organic polymer material along a surface thereof or sealing the storage chamber independently of the body member.
  • An indirectly heated dispenser cathode structure comprising, a shaped porous disc member having an emission surface, a cathode body member positioned to support said disc member along a surface thereof opposite said emission surface, said body member having a plurality of axial bores spaced about the periphery thereof and extending toward said disc member and in fluid communication with the supported surface thereof, a plurality of insert members adapted to mechanically lock with peripheral side walls of said axial bores, each of said plurality of inset members having an open-ended storage chamber facing toward said disc member, a passageway means positioned within the cathode body member providing fluid communication between said storage chamber and the support surface of said disc member, a supply material for an emission-promoting substance positioned within said storage chamber and surrounded by an inert atmosphere, and a fluid impermeable mask member positioned on upper peripheral walls of said storage chamber so as to seal the interior thereof from surrounding environment, said mask member including a self-sticking organic polymer material thermally decomposable without residue at operating temperatures of a dispenser cath
  • organic polymer material is selected from the group consisting essentially of paraffin, nitro-cellulose, acetic acid esters, polyacrylic acid esters, phthalic acid esters, and mixtures thereof.
  • An indirectly heated dispenser MK cathode structure comprising, a ring-shaped porously sintered tungsten disc member having a free surface thereof defining an emission surface for such cathode structure, a cathode body member positioned to support said disc member along a portion of an undersurface thereof, said cathode body member having a plurality of axial bores substantially uniformly spaced about the perimeter thereof and in fluid communication with said undersurface of the disc member, said bores having a crossmask member positioned on upper peripheral boundaries of said storage chamber so as to seal the interior thereof from fluid communication with the unsupported undersurfaces of said disc member until the rupture of said mask member, said mask member including a self-sticking organic polymer material selected from the group consisting essentially of paraffin, nitrocellulose, acetic acid ester. polyacrylic acid ester, phthalic acid ester and mixtures thereof.

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Abstract

A dispenser MK-type cathode structure adapted for storage and/or handling with subsequent activation and a method of producing the same whereby a supply source material of an emission-promoting substance is positioned in an open-ended storage chamber of a plug-like cathode insert member and sealed within the chamber by a fluid impermeable pore-free mask member. A porously sintered tungsten disc member sits above the mask member so as to have an undersurface thereof in fluid communication with the supply source material upon rupture of the mask member. The mask member is sealed to the boundaries of the storage chamber by a selfsticking organic polymer material which is thermally decomposable without residue at operational temperatures of such dispenser cathodes. The mask member comprises a unitary structure composed of a high melting metal foil having at least one surface thereof coated with the organic polymer material, a lamina of a film forming organic material having a layer of the self-thicking organic polymer material along a surface thereof or a self supporting film of the organic polymer material. The mask member is provided in a controlled thickness of sufficient dimension to resist rupture until the environment around the sealed storage chamber is subjected to cathode vacuum conditions.

Description

United States Patent Hoimann et al.
[4 1 Aug. 1,1972
[54] INDIRECTLY HEATED DISPENSER CATHODE [72] Inventors: Horst l-lotmann; Erwin Huebner;
Helrnut Katz, all of Munich, Germany [73] Assignee: Siemens Aktlengesellschaft, Berlin and Munich, Germany [22] Filed: Sept. 30, 1970 [211 App]. No.: 76,669
[30] Foreign Application Priority Date FOREIGN PATENTS OR APPLICATIONS Primary Examiner-David Schonbcrg Assistant Examiner-Paul A. Sacher Attorney-Hill, Sherman, Meroni, Gross & Simpson 10/ l 968 Canada ..3 13/346 [57] ABSTRACT A dispenser MK-type cathode structure adapted for storage and/or handling with subsequent activation and a method of producing the same whereby a supply source material of an emission-promoting substance is positioned in an open-ended storage chamber of a plug-like cathode insert member and sealed within the chamber by a fluid impermeable pore-free mask member. A porously sintered tungsten disc member sits above the mask member so as to have an undersurface thereof in fluid communication with the supply source material upon rupture of the mask member. The mask member is sealed to the boundaries of the storage chamber by a self-sticking organic polymer material which is thermally decomposable without residue at operational temperatures of such dispenser cathodes. The mask member comprises a unitary structure composed of a high melting metal foil having at least one surface thereof coated with the organic polymer material, a lamina of a film forming organic material having a layer of the self-thicking organic polymer material along a surface thereof or a self supporting film of the organic polymer material. The mask member is provided in a controlled thickness of sufficient dimension to resist rupture until the environment around the sealed storage chamber is subjected to cathode vacuum conditions.
5 Claim, 2 Drawing Figures INDIREC'I'LY HEATED DISPENSER CATI-IODE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the dispenser cathodes and more particularly to MK-type indirectly heated dispenser cathode structures and a method of producing the same.
2. Prior Art Metal capillary cathodes (i.e., MK cathodes) are known. Generally, such cathodes comprise a confining metal cup member having a supply substance for an emission-promoting material therein (i.e., one yielding an emission-promoting material, such as barium, at a high temperature) and a porous disc welded to the rim of the cup member, the upper surface of which defines an emission surface. A heating means heats both the cup member and the disc causing the supply substance to evaporate and the emission-promoting material to migrate by capillary action through the porous discs and to the emission surface. The emission-promoting material forms a film on the free surface of the disc and acts to reduce the work function of the material forming the disc.
In certain more recent developments relating to this type of dispenser cathode, modified structures have been prepared wherein relatively thin metal foils are positioned between the supply materials yielding an emission promoting substance and the porous disc. The supply material is surrounded with an inert atmosphere and the thin metal foil tightly seals this atmosphere within the storage chamber. In this manner, the assembled dispenser cathode structure can be handled and/or stored with a subsequent activation by rupturing the foil with subjection of the environment around the field chamber to cathode vacuum operating conditions. Such modified structures function relatively reliably providing that the thickness of the metal foil is relatively thin. However, it is extremely difficult to economically produce a sufficiently thin and pore-free foil of a high melting metal, such as tantalum. Further, other high melting metals, such as molybdenum, are extremely difficult to manufacture into foils of precisely controlled thickness.
The instant invention provides a cathode structure and a method of producing the same which avoids the aforesaid difficulties and provides novel masks or foil members of easily controlled thicknesses.
SUMMARY OF THE INVENTION The invention provides a novel dispenser cathode structure of the MK indirectly heated type and a method of producing the same where a supply material yielding an emission promoting substance is stored in an open-ended storage chamber of a plug-like cathode insert member and sealed in an inert atmosphere and from the surrounding environment by a fluid impermeable mask member composed of a unitary structure including a thermally decomposable organic polymer material, a combination of a relatively dense high melting metal foil and a layer of such organic polymer material along at least one surface of the metal foil and/or a combination of a lamina of a film-forming organic material and a layer of such organic polymer material along one surface of the lamina. In one embodiment, plurality of such plug-like cathode insert members are spaced about a relatively large dimension ring-shaped cathode body and each insert member is machined to mate or lock with a portion of such body and the mask member sealingly cooperates with the peripheral surfaces of the storage chamber to confine the inert atmosphere and the supply material therein and out of communication with the environment surrounding the chamber, including the cathode emission surface. The thickness of the mask member is readily controlled by liquid or semi-liquid coating techniques. The organic material utilized forms a self-sticking film which is readily united with a relatively high melting metal foil or an organic material lamina and readily forms a fluid impermeable seal on the peripheral boundaries of the storage chamber. Additionally, the organic polymer material thermally decomposes at normal cathode operating temperature without producing any harmful reaction product or other undesirable residue.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall diagrammatic sectional view of an embodiment of a ring-shaped cathode structure and includes a cross-sectional view through an embodiment of an insert member constructed in accordance with the principles of the invention; and
FIG. 2 is a somewhat enlarged cross-sectional view of another embodiment of an insert member constructed in accordance with the principle of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention provides an indirectly heated dispenser cathode structure of the MK-type. One embodiment of such cathode structure includes a ringshaped emission surface supported on an appropriately shaped cathode body member wherein a supply material (i.e., an alkali earth metal oxide) for an emissionpromoting substance (i.e., an alkali earth metal) is spaced away from the emission surface within the cathode body member and distributed around the perimeter thereof. The emission-promoting substance migrates or travels from a storage chamber and through a porously sintered cover member positioned above such storage chamber. The upper free surface of the porous cover member defines the cathode emission surface and the emission-promoting substance forms a thin film thereat to reduce the work function of such emission surface. Preferably, the porous disc is composed of a porously sintered tungsten and the supply source material is i.e., an alkali earth metal oxide, and particularly barium oxide.
The ring-shaped cathode structures are provided with a relatively large emission surface composed of a porously sintered tungsten or other emission base material supported along peripheral portions thereof by a body member. The body member is composed of a relatively high melting metal, such as molybdenum, and is provided with a plurality of axial bores extending toward the emission surface so as to be in fluid communication therewith. These axial bores are generally uniformly spaced around the perimeter of the body member. One or more plug-like insert members are provided for insertion into a desired number of axial bores. Each insert member is also composed of a relatively high melting metal, such as molybdenum, and has an open-ended storage chamber at an upper axial end thereof for containing a desired amount of a supply material for an emission-promoting substance. The insert members are adapted to mechanically mate or lock with the axial bore walls, as by suitably provided screw threads or the like.
The supply material (i.e., BaO) for an emissionpromoting substance (i.e., Ba) is formed into appropriately sized tablets or the like for ease of usage and insertion into the storage chamber of the insert member. Of course, the supply material can be used in powdered form, if desired. A suitable amount of such supply material is placed within a storage chamber, surrounded or blanketed with an inert atmosphere and sealed. Preferably, a dry inert gas is pumped or injected at about ambient pressures into the partially filled storage chamber so as to completely surround and blanket the supply material. There after the chamber is sealed by a mask member so as to maintain the supply material under a blanket of such inert gas at such ambient (i.e., atmospheric) pressure. The mask member is provided with a self-sticking coating which forms a fluid (i.e., water or gas) impervious seal between the upper boundaries of the storage chamber and the mask member independently of the cathode body member. In this form, the sealed insert members are stored or handled as desired without danger of any chemical reaction or the like from occurring with the supply material. Alternatively, the seal insert members are locked into the axial bores within the cathode body and the assembled unit is stored or handled as desired until activation.
Activation or operational condition is achieved by positioning an assembled cathode body member, i.e., one having sealed insert members locked in place, into a suitable envelope or tube device or some other device utilizing a cathode, and evacuating the tube device to provide an operational vacuum state for such device. The inert gas atmosphere at atmospheric pressures sealed within the storage chamber will rupture and/or destroy mask member and provide a free path of travel for the emission-promoting material to the emission surface of the porously sintered covered member. The cathode structure is then indirectly heated, as by an electrically operating heating coil, to the normal operating temperatures thereof, i.e., between about 800 to l ,300" C. depending upon the characteristics of the material of the structure and the supply material.
The mask member is a relatively dense foil or film and includes a self-sticking organic polymer material which thermally decomposes without any objectionable residue at the operating temperatures of a dispenser cathode. The self-sticking organic polymer materials are preferably selected from the group consisting essentially of paraffin, acetic acid esters, polyacrylic acid esters, phthalic acid esters and mixtures thereof. The mask member comprises a composite film structure comprised of a combination of a high melting metal (i.e., Ta or Mo) foil and a layer of the self-sticking organic polymer material along at least one surface of a metal foil; a combination of a lamina of a film-forming organic material and a layer of the self-sticking organic polymer material along a surface of the lamina; and a self-supporting film of the self-sticking organic polymer material. The composite film structure is provided in accurately controlled thicknesses, and preferably in a thickness of not more than about l20 micrometers (i.e., am). The thickness is accurately controlled to insure that the mask member will rupture at the operating conditions of a cathode. The self-sticking organic polymer material is suitably prepared for application by mixing with a suitable solvent (for example a relatively volatile low molecular weight alcohol) so that the resultant liquid or semi-liquid mixture is amenable to coating techniques and can be applied in a layer of a desired thickness on a base source to provide a substantially pore-free mask member.
In order to more clearly demonstrate one embodiment of a mask member produced in accordance with the principle of the invention, the following example is set forth. It will be understood that this example is for purposes of demonstration only and does not limit the invention in any way.
EXAMPLE 1 A self-sticking organic polymer material of the invention is formulated into a self-supporting film suitable for use as a M member per se by preparing a substantially homogeneous paste-like material comprised of about 4.0 milliliters (i.e., ml) of Plexisol P-SSO (a registered trademark of Roehm & Haas Co. for polyacrylic acid ester materials), 1.0 ml of butyl acetate and 0.1 gram of phthalic acid ester (phthalic acid ester-bis-Z-ethyl ester) and a suitable solvent. This paste-like material is transferred to a draw ring having a slit width of about 200 micrometers (i.e., pm) and then drawn through the slit onto a smooth base surface. The solvent used is removed, as by evaporation, and a selfsupporting film is formed which is tacky or selfsticking. The finished film has a thickness of about l20 um and forms an excellent mask member which is ruptured at operational cathode vacuum conditions and is thermally decomposed, without residue, at the operational temperatures of indirectly heated dispenser cathode structure.
Referring now to the drawings, it will be noted that FIG. 1 is an overall diagrammatic sectional view of an indirectly heated dispenser cathode structure which has a relatively large diameter ring-shape, and those elements thereof which do not materially aid a better understanding of the principles of the invention are left out or are merely not given a reference numeral.
As shown, a ring-shaped cathode body member 1 supports and carries a ring-shaped disc member along peripheral portions thereof so that its upper surface defines an emission surface 20. Preferably, the disc member 2 and the emission surface 24 are composed of the same material, such as porously sintered tungsten. The cathode body member 1 is provided with a plurality of axial apertures or bores 3, generally uniformly spaced about the perimeter of body number 1. The axial bores 3 extend generally toward the emission surface Za so as to be in fluid communication therewith but are somewhat spaced away from disc member 2. An insert member 4 is adapted to mechanically mate or lock with the peripheral walls of the axial bores 3. The insert member 4 is provided with an open-ended storage chamber 5 opening toward said disc member 2. A passageway means 11 is provided along the upper surface of the bores 3 so as to provide uniform communication with the exposed underside of the disc member 2.
The plug-like insert member 4 is formed somewhat in the shape of a hollow set screw or the like having an open ended storage chamber 5. A supply material for an emission-promoting substance is pre-formed into tablets 6 and a suitable number of such tablets 6 are positioned within the chamber 5 and a dry inert atmosphere is injected within the remaining hollow space of the chamber so as to completely surround or blanket the supply material. The inert atmosphere is maintained at about ambient pressure, although a slightly positive pressure can be utilized if desired. Thereafter, the storage chamber 5 is tightly sealed from the surrounding environment by a mask member 8.
Preferably, the mask member 8 is a composite film structure having a relatively high density and is porefree so as to be impervious to fluids and particularly water and CO in the embodiment shown at FIG. 1, the mask member 8 comprises a lamina 9 of an organic filmforming material having a layer 90 of the self-sticking organic polymer material along a surface of the lamina. As will be appreciated, the lamina 9 may be composed of the self-sticking organic polymer material per se or of another organic film forming material. The assembled unit, such as shown in FIG. 1, can be stored or handled as desired without any danger of a chemical reaction occurring with the supply material within chamber 5. When such an assembled unit is inserted into an envelope or tube device (not shown) and the environment surrounding the cathode is evacuated, the gas pressure within the chamber 5 will burst the mask member 8 and provide a path of communication between the chamber 5 and the adjacent disc member 2. The passageway 11, which may be somewhat ringshaped, provides fluid communication around the entire periphery of the body member I so that the emission-promoting substance can uniformly contact the entire underside of the disc member 2.
FIG. 2 illustrates another embodiment of the mask member 8 constructed in accordance with the invention. ln this embodiment, the structure is essentially similar to that explained in conjunction with FIG. 1 except that the supply of material is utilized in powdered form 60. The mask member 8 is composed of a unitary structure having a relatively high melting metal foil 13 and a layer 9!) of the self-sticking organic polymer material along a surface of the foil. Of course, it will be appreciated, the metal foil 13 can be sandwiched between a pair of such layers 9b, if desired.
Thus, the invention provides a novel indirectly heated dispenser cathode structure comprising a shaped porous disc member having an emission surface with a cathode body member supporting and carrying the disc member along a surface thereof opposed the emission surface. The cathode body member has a plurality of axial bores distributed about the perimeter of the body member and extending toward the emission surface. A plurality of insert members are provided which are adapted to mechanically lock with the walls of the axial bores and each insert member has an openended storage chamber extending toward the disc member with a supply material for an emission-promoting substance sealed within the chamber and surrounded by an inert atmosphere. A fluid impermeable mask member is positioned between the storage chamber and a passage means within the cathode body member that provides communication between the storage chamber and the disc member to block travel of the emission-promoting substance to the disc member. The mask member is provided with a selfsticking organic polymer material along a surface thereof or sealing the storage chamber independently of the body member.
Various modifications and alterations can, of course, be effected without departing from the novel concepts of the invention.
We claim as our invention:
1. An indirectly heated dispenser cathode structure comprising, a shaped porous disc member having an emission surface, a cathode body member positioned to support said disc member along a surface thereof opposite said emission surface, said body member having a plurality of axial bores spaced about the periphery thereof and extending toward said disc member and in fluid communication with the supported surface thereof, a plurality of insert members adapted to mechanically lock with peripheral side walls of said axial bores, each of said plurality of inset members having an open-ended storage chamber facing toward said disc member, a passageway means positioned within the cathode body member providing fluid communication between said storage chamber and the support surface of said disc member, a supply material for an emission-promoting substance positioned within said storage chamber and surrounded by an inert atmosphere, and a fluid impermeable mask member positioned on upper peripheral walls of said storage chamber so as to seal the interior thereof from surrounding environment, said mask member including a self-sticking organic polymer material thermally decomposable without residue at operating temperatures of a dispenser cathode structure.
2. An indirectly heated dispenser cathode structure as defined in claim 1 wherein the organic polymer material is selected from the group consisting essentially of paraffin, nitro-cellulose, acetic acid esters, polyacrylic acid esters, phthalic acid esters, and mixtures thereof.
3. An indirectly heated dispenser cathode structure as defined in claim 1 wherein the mask member comprises a composite structure of a relatively high melting metal foil and a layer of the organic polymer material on at least one surface of said metal foil.
4. An indirectly heated dispenser cathode structure as defined in claim 1 wherein the mask member comprises a self-supporting film of the organic polymer material having a thickness of about 1 20 micrometers.
5. An indirectly heated dispenser MK cathode structure comprising, a ring-shaped porously sintered tungsten disc member having a free surface thereof defining an emission surface for such cathode structure, a cathode body member positioned to support said disc member along a portion of an undersurface thereof, said cathode body member having a plurality of axial bores substantially uniformly spaced about the perimeter thereof and in fluid communication with said undersurface of the disc member, said bores having a crossmask member positioned on upper peripheral boundaries of said storage chamber so as to seal the interior thereof from fluid communication with the unsupported undersurfaces of said disc member until the rupture of said mask member, said mask member including a self-sticking organic polymer material selected from the group consisting essentially of paraffin, nitrocellulose, acetic acid ester. polyacrylic acid ester, phthalic acid ester and mixtures thereof.
t t I I i

Claims (4)

  1. 2. An indirectly heated dispenser cathode structure as defined in claim 1 wherein the organic polymer material is selected from the group consisting essentially of paraffin, nitro-cellulose, acetic acid esters, polyacrylic acid esters, phthalic acid esters, and mixtures thereof.
  2. 3. An indirectly heated dispenser cathode structure as defined in claim 1 wherein the mask member comprises a composite structure of a relatively high melting metal foil and a layer of the organic polymer material on at least one surface of said metal foil.
  3. 4. An indirectly heated dispenser cathode structure as defined in claim 1 wherein the mask member comprises a self-supporting film of the organic polymer material having a thickness of about 120 micrometers.
  4. 5. An indirectly heated dispenser MK cathode structure comprising, a ring-shaped porously sintered tungsten disc member having a free surface thereof defining an emission surface for such cathode structure, a cathode body member positioned to support said disc member along a portion of an undersurface thereof, said cathode body member having a plurality of axial bores substantially uniformly spaced about the perimeter thereof and in fluid communication with said undersurface of the disc member, said bores having a cross-axial passageway along the upper boundaries thereof providing fluid communication with each other and with an unsupported portion of the undersurface of said disc member, a plurality of insert members adapted to mechanically lock with peripheral side walls of said axial bores, each of said insert members having an open-ended storage chamber facing toward said disc member, a supply material for an emission-promoting substance positioned within said storage chamber and surrounded by an inert atmosphere at substantially ambient pressures, and a fluid impermeable pore-free mask member positioned on upper peripheral boundaries of said storage chamber so as to seal the interior thereof from fluid communication with the unsupported undersurfaces of said disc member until the rupture of said mask member, said mask member including a self-sticking organic polymer material selected from the group consisting essentially of paraffin, nitrocellulose, acetic acid ester, polyacrylic acid ester, phthalic acid ester and mixtures thereof.
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