US2913077A - Gas seal - Google Patents

Gas seal Download PDF

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Publication number
US2913077A
US2913077A US760460A US76046058A US2913077A US 2913077 A US2913077 A US 2913077A US 760460 A US760460 A US 760460A US 76046058 A US76046058 A US 76046058A US 2913077 A US2913077 A US 2913077A
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Prior art keywords
ceramic
palladium
brazing
seal
tube
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US760460A
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English (en)
Inventor
Altroy Frederick A D
Pat R Pondy
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AT&T Corp
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Bell Telephone Laboratories Inc
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Priority to US760460A priority Critical patent/US2913077A/en
Priority to BE576451A priority patent/BE576451A/fr
Priority to GB24469/59A priority patent/GB928523A/en
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    • C04B37/00—Joining burned ceramic articles with other burned ceramic articles or other articles by heating
    • C04B37/02—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles
    • C04B37/023—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles characterised by the interlayer used
    • C04B37/026—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles characterised by the interlayer used consisting of metals or metal salts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
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    • C04B2235/658—Atmosphere during thermal treatment
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    • C04B2237/66—Forming laminates or joined articles showing high dimensional accuracy, e.g. indicated by the warpage
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    • C04B2237/76—Forming laminates or joined articles comprising at least one member in the form other than a sheet or disc, e.g. two tubes or a tube and a sheet or disc
    • C04B2237/765—Forming laminates or joined articles comprising at least one member in the form other than a sheet or disc, e.g. two tubes or a tube and a sheet or disc at least one member being a tube
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    • C04B2237/84—Joining of a first substrate with a second substrate at least partially inside the first substrate, where the bonding area is at the inside of the first substrate, e.g. one tube inside another tube
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
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    • Y10T428/12076—Next to each other
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y10T428/12931—Co-, Fe-, or Ni-base components, alternative to each other

Definitions

  • This invention relates to a gas-tight ceramic-to-metal seal.
  • the seal of this invention is particularly applicable to gas and vacuum electron tube structures.
  • the desirability of ceramic details due to their refractory nature and excellent dielectric properties and the requirement of metal conducting parts in electrical devices have resulted in a considerable amount of development time being directed to sealing these materials one to the other.
  • the first phase of this development program was directed to the design of metallic alloy materials of the requisite refractory nature and having temperature coefficients of expansion making them compatible with the desirable ceramic compositions. This resulted in the development of Kovar and similar compositions.
  • Figs. la through 1 are perspective views of tube com ponents and a tube structure depicting various stages of manufacture of a device utilizing the inventive process described herein;
  • Fig. 2 is a cross section elevational view of a tube structure utilizing a ceramic-to-metal seal of this invention.
  • Fig. 1a depicts a ceramic body 1 to be bonded.
  • Ceramic materials suitable for the instant processes and seal should have a softening point above the brazing temperatures of the brazed material to be .used in the seal (from l300-l400 C.) and are generally aluminum oxide containing. Examples of suitable ceramic materials will be. discussed herein. These include such materials as alumina, zircon, fosterite and steatite.
  • ceramic body 1' has been metallized on both flat surfaces.
  • the metallizing layer '2 may consist'of a mixture of molybdenum andtitanium producedby spraying the surface with, for example, a 95-.-5 weight percent mixture of elemental molybdenum and titanium hydride, followed by sintering at a temperature of the order of 1560-1606? C. in a manner to be described.
  • cathode holder 3 which may be made of molybdenum
  • base plate 4 which may be made of Kovar or other material hav-' ing suitable refractory and physical properties
  • brazing ring 5 desirably made of a palladium-nickel alloy
  • top plate 6 which may be made of Kovar
  • brazing washer 7 which in accordance with this invention is constructed of palladium-nickel or palladium-cobalt to be used for bond- I ing top plate 6 to the uppermost metallized surface 2 of bonded thereto on its uppermost surface through brazing layer 7, and having bottom plate 4 attached to the lowermost metallized surface 2 of ceramic body 1 through; palladium-nickel brazing layer 8.
  • the structure .shojwnf is completed by molybdenum cathode holder 3 attachedi Fig. 1d depicts the structure after bonding of the elements shown in Fig. 10.
  • ceramic body 1 having metallized surfaces 2, having top plate 6 I tobase plate 4 by means of palladium-nickel brazing ring may be made of palladium-nickel, and tubulation 13, consisting of glass tube 14 and Kovartube 15, the latter tobe sealed to tube member 11 of cap 10.
  • cap has been bonded to the tube structure of view 1d. These two parts may be joined by conventional resistance welding means. Tubulation 13 is shown sealed to tube structure 11 of cap 10 by means of brazing layer 12..
  • tubulation 13 is attached to a pumping means, not shown, the entire tube structure 16 is heated to the desired degassing temperature, and pumping is commenced. After degassing is completed, tube 16 is filled with a gaseous atmosphere such as neon-helium and is then sealed off from tube 13. This completes the tube.
  • a gaseous atmosphere such as neon-helium
  • Fig. 2 depicts a gastube diode structure similar to that produced in accordance with the process of Figs. la through If.
  • This structure consists of hollow cathode 20, which may be made of niobium orother suitable cathode material contained in molybdenum holder 30, plate 21, which may be made of zirconium or other suitable material, the latter supported in fixed position relative to cathode 20 by structural member 22, which may be made of molybdenum, and welding tabs 23, which may conveniently be made of Kovar.
  • the cathode and anode elements are enclosed within cap 24, which may be Kovar, ceramic member 29, and Kovar bottom plate 25, which latter is part of the cathode structure.
  • Seals 27 and 28 are composite seals consisting of a molybdenum-titanium metallizing layer on-the .bonded surfaces of ceramic member 29 and a palladium-nickel or palladium-cobalt brazing layer in intimate contact with both the metallized and Kovar surfaces, which are bonded.
  • the ceramic surface to' be bonded is first coated with the components which produce metallizing.
  • Application of these materials may be by spraying, by silkscreen technique, by painting, or by any other suitable means.
  • these materials are applied in a carrier, such carrier, which may be.
  • a nitrocellulose-amyl acetate mixture to be suitable should be decomposable to gaseous. components which leave the system prior to sintering. These materials should leave no carbonaceous or other residue.
  • Suitable ceramic materials must be capable of withstanding the higher brazing temperatures used in this process. For this reason, such ceramic materials having softening points below about 1400 C. are unsuitable.
  • the best known ceramic materials having therequisite softening points are based on the aluminum oxide system. Such aluminum oxide ceramics tobe useful should have a purity range of from about 90% to about 99%. Purer materials do not appear to, adhere properly to the metallized bond. Less pure materials may have a softening point below. the brazing temperature of the process, generally resulting from the larger inclusion of silica. Ceramic materials meeting the above requirementsinclude alumina, zircon, fosterite and steatite.
  • cial materials which have been used in preferred embodiments herein are: Coors, AI-200, Almonox 4462 and Diamonite, made by Coors Porcelain Company, Golden, Colorado, Frenchtown Porcelain, Frenchtown, New Jersey, and U5. Ceramic Tile Company, Canton, Ohio, respectively. All of these materials contain of the order of 95 weight percent of aluminum oxide, the remainder primarily silica. The temperature coefficient of expansion of such ceramic materials is typically'of the order of, 83x10" cm./cm./C. at 600 C. p p
  • Thesprayed or otherwise deposited surface is next sin? tered.
  • Sintering may be carried out over a temperature range of from about 1550 C. to about 1 600.C. for a period of from about 5-60 minutes.
  • the specific examples herein were produced by sintering for 30 minutes.
  • sintering at temperatures higher than the indicated maximum results in devitrification.
  • this upper limit may be slightly extended for certain of the materials in the described class.
  • sintering time must be extended. This lower limit is chosen in accordance with conventional practice in which sintering is carried out at about two-thirds of the meltingjpoint of the prey dominant metallizing component.
  • the brazing material palladium-nickel or palladiumcobalt
  • the brazing material palladium-nickel or palladiumcobalt
  • the brazing material is either an alloy of palladium-nickel or palladium-cobalt.
  • the composition: of'the brazing material is not critical except with respect to the brazing temperature which may be tolerated by the other tube components present duringthis step. Since a lower brazing temperature for either of' the brazing compositions designated does not in any way impair the operating characteristics of the tube, it is generallydesirable to choose a lower melting corn position of either system in accordance with their composition diagrams. In general, since the Kovar elements to be included have a melting point of about 1450 C., any brazing alloy having a melting point at or below about 1400 C. is suitable.
  • a 1400 C. maximum indicates a range of from -20 to 10-90 palladium-nickel, with the lowest melting composition occurring at about 60 40+5%; for palladium-cobalt the included range is from 12-88 to 92-8 palladium cobalt, with the lowest melting composition occurring at about65-35 (all composittions based onweight pen cent).
  • the brazing material may be applied in the form 033 Commerpalladium-cobalt.
  • a powder or a solid body such as a washer, wire or other configuration.
  • a slight compressive force being desirable to effect intimate contact, the metallized ceramic, brazing material and metallic body to be bonded thereto are generally brazed in a jig.
  • the jig is next placed in an oven which is maintained at the brazing temperature of the chosen material.
  • the oven temperature may exceed the brazing temperature, it should not be higher than either the softening point of the ceramic or the melting point of the metallic body.
  • Heating is carried out in a wet hydrogen or wet forming gas atmosphere as described above. Time of heating is not critical, a range of from 5 minutes to 60 minutes having been found suitable.
  • the jigged structure is gradually cooled to avoid thermal shock. Cooling is carried out in the same atmosphere of wet hydrogen or wet forming gas. Minimum cooling time is dependent upon the dimensions of the structure. For the structure shown in Fig. 1d, of overall dimensions of the order of A by in diameter, a cooling time of the order of 15 minutes to cool the structure from the melting point of 60-40 palladium-nickel (1227-l237 C.) to room temperature has been found suitable.
  • Tube structures made in the above manner have been found to be vacuum-tight by conventional leak detection methods carried out under vacuum of the order of millimeters of mercury. Such structures have been outgassed at temperatures as high as 1000 C. to 1050 C. under vacuum of the order of 10- millimeters of mercury.
  • the avoidance of contamination in structures so produced is evidenced by visual inspection as compared, for example, with the copper deposit left by use of 73-27 copper-nickel brazing material and by manifestation of sustained voltages almost identical with those inherent for the cathode material and structure used.
  • Example 1 A Coors AI-200 ceramic aluminum oxide ceramic manufactured by Coors Porcelain Company) ring of approximate dimensions mils x 275 mils ID. by 375 mils CD. was coated with a 95-5 weight percent mixture of elemental molybdenum and titanium hydride powders by spraying to a thickness of about 0.002" on both flat surfaces. The ceramic ring so coated was then sintered in an alundum core-type furnace at a temperature of l550 C.:20 C. for a period of 30 minutes in an atmosphere of wet hydrogen having a dew point of +20 C.i-5 C.
  • the ceramic ring so metallized was placed in a jig with two rings of 60-40 palladium-nickel of a thickness of .003 and Kovar details to be joined thereto (details 4 and 6 of Fig. 1c).
  • the jig was placed under slight compression, the assembly was placed in a nickel boat which was pushed into an oven maintained at 1275 C.- -10 C. having a moving atmosphere of wet forming gas of a +20 C.i5 C. dew point.
  • the assembly was left in the oven at the said temperature for a period of about 15 minutes, after which the boat was gradually moved into successively cooler zones in the furnace at the rate of about one-half inch per minute, resulting in attainment of room temperature in a period of about 15 minutes.
  • the seal so produced was determined to be vacuum-tight at a vacuum of 10' millimeters of mercury in an atmosphere of helium on a mass spectrometer.
  • the tube structure was then completed in the general manner depicted in Figs. 1a through 1 and was outgassed in a vacuum of about 10- millimeters of mercury at a temperature of about 1025 C., local heating being produced by an R. F. furnace.
  • the tube structure was then filled with an atmosphere of helium and neon gas.
  • the resultant structure resembling that shown in Fig. 2 had a sustained voltage of 98.7105 volts. This value was compared with the sustained voltage measured on the same structure contained in a sealed glass tube, which latter was found to be 98.8:05 volts.
  • Example 2 A Coors AI-200 ceramic ring of the same approximate dimensions as in Example 1 was coated with a 95-5 weight percent mixture of elemental molybdenum and titanium hydride powders by spraying to a thickness of about 0.002" on both flat surfaces. The ceramic ring so coated was then sintered at a temperature of 1550 C.i20 C. for a period of 30 minutes in an atmosphere of wet hydrogen having a dew point of +20 C.:L5 C. The ceramic ring so metallized was placed in a jig with two rings of 65-35 palladium-cobalt of a thickness of .003" and Kovar details to be joined thereto (details 4 and 6 of Fig. 1c).
  • the jig was held under slight compression, the assembly was placed in a nickel boat which was pushed into an oven maintained at 1265 0:10 C. having a moving atmosphere of wet forming gas of a +20i5 C. dew point.
  • the assembly was left in the oven at the said temperature for a period of about 15 minutes, after which the boat was gradually moved into successively cooler zones in the furnace at the rate of about one-half inch per minute, resulting in attainment of room temperature in a period of about 15 minutes.
  • the seal so produced was determined to be vacuum-tight at a vacuum of 10- millimeters of mercury in an atmosphere of helium on a mass spectrometer.
  • the tube structure was then completed in the general manner depicted in Figs.
  • seal and process of this invention were developed primarily .for use inelectron tube structures. For this reason the above description isprimarily in such terms. It is Well known, however, that ceramic -to-metal seals are required in other types of structures. Wherever it is desirable t0. make such a seal, to subsequently process a structure containing such a seal, or to, operate such structure, at temperatures substantially above the order of .600. C., the seal and process of this invention may be used, to advantage. Certain processing steps and conditions have been described in specific terms. It is-intended that these be consideredvas exemplary only and'thatrthe claimed invention not be solimited.
  • a gas-tight ceramic-to-metal seal comprising successively a ceramic surface, a metallizing layer'comprising t least one metal selected from the group consisting of molydbenum and tungsten, together with up to weight percent, of at least one metal selected from the group consisting of titanium and zirconium, a brazing material comprising palladium together: with; at least one metal selected from the group consisting of nickel and cobalt, and a metallic surface.
  • the gas-tight sealiof c1aimy1 in: which the ceramic body is aluminum oxide of a purity'of between 90% and 99% by. weight and in which the said metallic surface is an alloy of the approximate compositionexpressed in weight percent 53.7% iron, 29% nickel, 17% Cobalt, 0.3% manganese.v

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Ceramic Products (AREA)
US760460A 1958-09-11 1958-09-11 Gas seal Expired - Lifetime US2913077A (en)

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US760460A US2913077A (en) 1958-09-11 1958-09-11 Gas seal
BE576451A BE576451A (fr) 1958-09-11 1959-03-07 Joint étanche au gaz et procede pour sa fabrication.
GB24469/59A GB928523A (en) 1958-09-11 1959-07-16 Ceramic-to-metal seals submersible pressure vessels

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3187083A (en) * 1963-06-17 1965-06-01 Rca Corp Container for an electrical component
DE1273404B (de) * 1964-07-30 1968-07-18 Bertold Berberich Dipl Ing Ausbildung einer ultrahochvakuumdicht hartzuverloetenden Oberflaeche eines Keramikteiles

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2644907A (en) * 1951-05-07 1953-07-07 Eitel Mccullough Inc Electron tube
US2773570A (en) * 1952-11-29 1956-12-11 Gen Electric Combined vacuum seal and electrode terminal
US2842699A (en) * 1956-07-24 1958-07-08 Edgerton Germeshausen & Grier Gaseous seal and method

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2644907A (en) * 1951-05-07 1953-07-07 Eitel Mccullough Inc Electron tube
US2773570A (en) * 1952-11-29 1956-12-11 Gen Electric Combined vacuum seal and electrode terminal
US2842699A (en) * 1956-07-24 1958-07-08 Edgerton Germeshausen & Grier Gaseous seal and method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3187083A (en) * 1963-06-17 1965-06-01 Rca Corp Container for an electrical component
DE1273404B (de) * 1964-07-30 1968-07-18 Bertold Berberich Dipl Ing Ausbildung einer ultrahochvakuumdicht hartzuverloetenden Oberflaeche eines Keramikteiles

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GB928523A (en) 1963-06-12

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