Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/12—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on oxides
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/45—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides
  • C04B35/4504—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides containing rare earth oxides
  • C04B35/4508—Type 1-2-3
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0268—Manufacture or treatment of devices comprising copper oxide
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0912—Manufacture or treatment of Josephson-effect devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/20—Permanent superconducting devices
  • H10N60/203—Permanent superconducting devices comprising high-Tc ceramic materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/80—Constructional details
  • H10N60/85—Superconducting active materials
  • H10N60/855—Ceramic superconductors
  • H10N60/857—Ceramic superconductors comprising copper oxide

Definitions

• This invention relates generally to a bulk , composite superconductor material which can more easily be fabricated into articles of manufacture than pure ceramic superconductor and more particularly the invention relates to fabricating metal oxide ceramic superconductors in a manner which preserves the superconductivity while providing improved thermal conductivity, higher strength, and improved machine workability, possibly including malleability and ductility in a resulting material which is considerably less brittle than pure ceramic superconductor.
• superconductive materials exhibit a high thermal conductivity so that the heat from local heating generated by flux motion can be conducted away from the superconductor to minimize quenching.
• the new ceramic superconductor materials do exhibit excellent superconductivity, unfortunately they exhibit the poor thermal and mechanical properties which are characteristic of ceramics.
• Superconducting ceramics have low thermal conductivity, are brittle and do not exhibit high strength. Instead, they break and chip easily and therefore cannot be conveniently machined and cannot be shaped by applying stress forces to cause plastic deformation of them into desired shapes. Thus, the ceramic superconducting materials have thermal and mechanical properties which are quite unsuitable for many superconductor applications. A variety of lamination techniques have been suggested to enable superconducting ceramics to be formed into useful shapes.
• a cylindrical, silver tube has been filled with a superconductor ceramic powder before the powder was heat treated and then swaged or drawn into a wire.
• a superconductor ceramic powder forms a fine pipe containing a core of ceramic superconductor powder.
• This wire can be formed into a desired shape and then heat treated to fuse the particles and make it superconductive.
• Another solution is the formation of laminates or tapes.
• a superconductor powder, before heat treatment, is placed on a layer of metal which is then wound or otherwise formed into a laminate and then shaped into the desired structure. Following shaping, the entire structure is then heat treated to fuse the particles and initiate superconductivity.
• Yet another way of making superconductive wires is to pack a superconductive powder in among long microscopic chains of a suitable polymer. This mixture is then formed into the desired shape and heat treated to fuse the particles.
• One major problem with all these prior art solutions is that, following the sintering which fuses the ceramic particles, the structures cannot be further shaped, as by bending, drawing, or machining. Any significant change in their mechanical shape cracks and separates the fused ceramic material causing loss of continuity.
• the invention is essentially a solid, composite consisting of a dispersion of ceramic superconductor particles distributed in a matrix of connected, non- ferromagnetic metal which is nondestructive of superconductivity.
• the volume fraction of ceramic superconductor equals or exceeds the percolation fraction for the ceramic particles, but is not greater than one minus the percolation fraction for the metal. Within that range both the metal and the ceramic particles form a continuously connected matrix, each in effect an infinite cluster.
• a superconductor material results which will have enhanced, metal-like thermal conductivity and strength and can be machined considerably more effectively and accurately than pure ceramic material itself and yet the material will still exhibit superconductivity through the ceramic particle matrix.
• the volume fraction of superconductor particles is within a range so that it is less than the percolation fraction for the superconductor particles, but greater than a minimum which is needed to maintain the spacing between the ceramic particles within their tunnelling distance so that tunneling can be maintained through the metal and the interfaces between neighboring ceramic particles.
• a composite material in which the ceramic superconducting particles do not contact each other permits metal-like deformation, strength and thermal conductivity and yet the superconductivity can be maintained throughout the material by tunnelling.
• Fig. 1 is a graphical illustration of the properties of composites embodying the present invention over the range of relative metal and ceramic concentrations. The ranges shown are appropriate for spherical particles. Elongated powder particles would result in different ranges.
• Fig. 2 is a graphical plot of resistance vs. temperature data for one embodiment of the invention.
• Fig. 3 is a graphical plot like Fig. 2, but for a second embodiment of the invention.
• Suitable superconductor material includes the metal oxide ceramics which have recently been developed, including all copper oxide based superconductors.
• the superconducting ceramics contains yttrium, barium, and copper oxide such as YBa Cu O may be used. These have a layered, oxygen deficient crystal structure derived from the perovskite structure.
• Other such superconductors, including ones yet to be developed, can advantageously be used with the present invention if they have the mechanical and thermal deficiencies described above.
• the ceramic powder or particles are micron size, for example in the range of 1 to 100 microns. Particles having a diameter of 10 microns and 50 microns have been used.
• the ceramic particles are then dispersed randomly and as homogeneously as possible, in a matrix of continuously connected, nonferromagnetic metal which is nondestructive of the superconductivity of the ceramic particles.
• a dispersion may be prepared by homogeneously mixing the ceramic superconductor particles with metallic particles preferably within the same size range. The mixture is then compacted and subsequently sintered.
• the percolation fraction for a mixture of solid particles is the minimum volume fraction of the mixture which is necessary for a constituent to be formed into an infinite cluster which is ' a continuously connected network extending throughout the composite.
• a volume fraction of metal particles of at least approximately 16% is necessary to provide such a matrix of continuously connected metal.
• the percolation fraction for the ceramic is approximately 16% so that if the volume fraction of the ceramic is at least 16%, the ceramic particles will also form such a continuously connected network extending throughout the composite.
• a continuously connected network of metal is formed extending throughout the composite.
• the minimum volume fraction of metal is that volume which will give such a continuously connected matrix. If the composite is formed by mixing ceramic and metal particles, the volume fraction of the metal particles must be at least equal to the percolation fraction. For a perfectly random distribution of spherical metal particles a minimum of approximately 16% volume fraction of metal is required to receive the desired metallic correctedness. The existence of this continuous metal matrix provides the bulk material with the desired metal-like thermal and mechanical properties described above.
• the ceramic superconductor phase also percolates throughout the composite to provide a continuously connected matrix or infinite cluster.
• This range of metal concentration is illustrated as range A in Fig. 1. Sintering of a compressed composite in range A fuses the ceramic particles into a solid superconductor network within the metal matrix. The metal matrix provides the mechanical strength and thermal conductivity which are desired, while the superconductor phase provides the superconductivity.
• the metal matrix holds the ceramic material together and prevents the migration of cracks, thus permitting more accurate machining.
• the relative volume fractions or concentrations of the metal and ceramic superconductor can be adjusted within the range A to thereby adjust the mechanical properties of the composite between the more metal-like properties for higher metal concentrations and a more ceramic like properties for the lower metal concentration.
• a material made within range A, after being sintered, can be machined but still cannot be significantly mechanically deformed as by drawing, forging, or bending because such deformation would be destructive of the fused ceramic matrix.
• the volume fraction of ceramic superconductor particles is less than the percolation fraction but at least as great as the minimum volume fraction which is necessary to maintain the randomly distributed ceramic particles separated by a distance which does not exceed the tunnelling distance, then proximity coupling will be maintained through the metal between neighboring ceramic particles.
• the superconducting proximity effect causes superconductivity to be induced into a normal metal conductor in the region immediately adjacent to the superconductor because the wave function extends beyond the superconductor out into the metal.
• a distance which is the coherence length, from each superconducting grain in the composite through which superconductivity may be induced into the metal matrix between neighboring superconducting particles.
• a material formulated in range B may be mechanically deformed after the ceramic has been heat treated to allow the manufacture of and bending of superconducting component parts.
• a composite material embodying the invention in the range B will have flow or deformation characteristics which are metal-like and yet superconductivity can be maintained principally by the proximity effect or Josephson coupling.
• Embodiments of the invention may utilize any of several types of tunnelling to maintain continuous superconductivity throughout the entire composite material. As described above, superconductivity will extend into the metal by a distance on the order of the coherence length if there is a direct metal to ceramic interface with no intervening barrier. In that circumstance proximity effect or Josephson coupling will maintain the superconductivity.
• tunnelling distance depends upon the particular tunnelling effect being utilized to maintain superconductivity. Tunnelling distance is typically in the range from approximately 5 to 30 Angstroms to 1 micron or so.
• the metals which may be used as the metal constituent in embodiments of the present invention do not include ferromagnetic metals since it is well known that ferromagnetic materials destroy superconductivity in a nearby superconductor.
• Other metals e.g., silver, which exhibit the typical metal-like properties can be used.
• some metals, such as copper share electrons with the superconductor material and this chemical reaction destroys the superconductivity.
• reactive metals may be coated with more inert metals, such as platinum or palladium, and still be used.
• Bi-phase random composites embodying the invention may also be formed by mixing the ceramic particles in a liquid metal melt and then freezing the melt. In this case, the ceramic particles are heat treated to make them superconductive before being mixed with the melt. The heat treatments of the ceramic metal composite may be done in the other embodiments of the invention either before or after mixing with the metal.
• the relative proportion of the two phases of the composite govern the electrical and mechanical properties of the material embodying the invention as illustrated in -Fig. 1»
• the metal matrix essentially governs the mechanical properties of the material reducing its brittleness, providing tensile strength, and machinability.
• the metal phase also provides the high thermal conductivity, which is characteristic of metals, to enable efficient cooling of superconductive material.
• the high thermal conductivity of the metal as compared to the pure ceramic, serves to dissipate local heating of the superconductor resulting from flux motion, contributing to the stability of the composites and minimizing the possibility of quenching in high current density application.
• the high thermal conductivity of the metal matrix in the composite also allows the material to reach thermal equilibrium more rapidly than possible in a pure ceramic material.
• the regions of metal in the composite serve to trap lines of magnetic flux, thus stabilizing the composite in the presence of strong, magnetic fields.
• a composite embodying the present invention in range B utilizes principally proximity effect or Josephson coupling to allow metal bridges to exist between the superconductor particle in which superconductivity may be induced.
• These metal bridges in the geometrical connected of the superconducting phase allow the simultaneous coexistence of the metal-like mechanical and thermal properties with the continuous superconductivity throughout the material.
• the composite material is considerably more immune to microscopic flexing, mechanical defects introduced by other deformations than is single phase ceramic superconductors.
• Figs. 2 and 3 illustrate composite superconductors embodying the present invention.
• Fig. 2 a mixture of 18% volume fraction of palladium with YBa Cu_ O _. sllows
• Fig. 3 illustrates a composite embodying the present invention having a 19% volume fraction of platinum and 81% ceramic superconductor. It demonstrates that superconductivity at a Tc of approximately 63 degrees K. Other materials may be added to the composite to obtain other characteristics and features.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Structural Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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• 1988
  • 1988-06-22 EP EP19880908848 patent/EP0376981A4/en not_active Withdrawn
  • 1988-06-22 JP JP63508069A patent/JPH03502212A/ja active Pending
  • 1988-06-22 WO PCT/US1988/002071 patent/WO1989001706A1/en not_active Application Discontinuation

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