Classifications

• • 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
• • 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
  • H10N60/0661—Processes performed after copper oxide formation, e.g. patterning

Definitions

• the invention relates to a method for tempering a superconductor material, the tempered, only one grain or a few grains or one or more magnetic
• the aim is to produce the highest possible superconducting and magnetic properties.
• High-temperature superconductors are non-contact, self-stabilizing magnetic bearings. Such bearings contain arrangements of permanent magnets and high-temperature superconducting moldings:
• a high-temperature superconducting molded body If a high-temperature superconducting molded body is above its transition temperature T c in the field of a permanent magnet, it is penetrated by a magnetic flux. If the superconductor is cooled to temperatures below the transition temperature, part of the magnetic flux in the superconductor material remains frozen. A displacement of the high-temperature superconducting molded body is only possible in this state with the application of force. The stability of such a bearing is greater, the more magnetic flux can be frozen in the superconductor material, that is, the higher the maximum value of the remanent induction.
• Improved magnetic properties such as higher values of the remanence induction and the levitation force enable, for example, the construction of magnetic bearings with a larger gap between the superconducting components and the permanent or electromagnets. In this way, for example in the case of motors with superconducting components, larger imbalances or deviations from the ideal running of the rotors can be permitted.
• the safety reserves can be increased by increasing the gap, or simpler, geometrically and economically less complex bearing geometries can be accepted.
• Enlargement of the magnetic domains without enlargement of the shaped bodies can also occur in shaped bodies provided with cracks and / or other imperfections by the healing of such imperfections according to that in German
• Patent application 198 41 925.2 method described can be achieved. This The patent application is considered to be fully included in this application by name.
• Remanence induction is not even half as large as that of the molded body based on SmBaCuO.
• the object was therefore to propose a method with which such superconductor materials with high remanence induction, high levitation force and / or high critical transport current density can be produced. It is also advantageous if these moldings can be manufactured as simply and reliably as possible.
• the object is achieved with a method for tempering molded articles made of a superconducting material based on (Y / SE) BaCuO, which is characterized in that a coating made of an applied material is applied to at least part of the surface of the molded article, the applied material being at least partially melts at a lower temperature than the molded body material and / or is flowable at a lower temperature than that material and possibly flows out on the surface of the molded body, the molded body with the applied application material being heated to a temperature at which the molded body material has not yet melts or / and is not yet flowable, but in which the application material is in the at least partially melted and / or flowable state and wherein at least part of a region of the molded body near the surface at this temperature or / and a subsequent one
• Cooling is modified and in which the shaped body treated in this way Cooling or / and in a subsequent heat treatment is enriched with oxygen, the modification contributing to increasing the remanence induction and / or the critical current density of the shaped body enriched with oxygen.
• the superconductor material contains at least one superconducting or superconducting phase, the superconducting phase becoming a superconducting phase when appropriately enriched with oxygen. It preferably contains at least one rare earth element (including lanthanum and yttrium) and at least barium, copper and oxygen and optionally also elements from the group of Be, Mg, Ca, Sr, Zn, Cd, Sc, Zr, Hf, Pt, Pd, Os , Ir, Ru, Ag, Cu, Au, Hg, Ag, Tl, Pb, Bi and S.
• the trivalent elements are preferably used as a replacement for yttrium and the divalent elements preferably for modulating the electronic structure or for partially replacing barium.
• Rare earth elements SE in the sense of this application also include lanthanum and yttrium. Among the rare earth elements are Y,
• La, Ce, Nd, Sm, Pr, Eu, Gd, Yb, Dy, Er are preferred, with Ce, Pr and Sm being preferred only as a proportion of mixed crystals in addition to other rare earth elements.
• Cerium can be used to refine the particles of the 211 phase and similar pinning centers.
• Y, Yb, Dy, Er and Nd are particularly preferred.
• a material of the molded body or / and an application material is preferably selected from the group of materials based on Y-Ea-Cu-O, (Y, SE) -Ea- Cu-O, SE-Ea-Cu-O, where proportions these chemical elements can be substituted by other, not mentioned and where Ea stands for at least one alkaline earth element.
• Suitable high-temperature superconducting materials for the process according to the invention are those in which the superconducting material to be modified or the modified shaped body and / or the application material contains phases which are selected from the group of phases with an approximate
• Sm or / and Nd can also be partially substituted by other lanthanides including Y and where Ag, Ag0 2 and / or other related chemical elements can occur.
• the untreated and / or the treated shaped body of the superconductor material, the application material and / or the layer material can additionally have calcium or / and other cations which change the band structure of the electrons and contribute to higher critical transport current densities.
• Superconductor material and / or the application material can also have at least one gradient with regard to the chemical composition, the structure or / and the peritectic, flow or melting temperature.
• the magnetic domains do not necessarily correspond to regions of aligned magnetic moments, as is usual with permanent magnets, but are used depending on the conditions of the magnetization used Field oriented. In this application, the magnetic domains are referred to hereinafter only as "domains".
• the aim of the further development and optimization of such shaped articles is to produce the highest possible values of the remanent induction and the critical transport current density, which, with the same technical application, enables the use of smaller shaped articles modified according to the invention. If, after texturing, the shaped body has an inhomogeneous distribution of superconducting properties, in particular towards the edge regions, then the shaped body is to be modified more or in particular in the edge region according to the inventive method in order to achieve a homogenization of the distribution of the superconducting properties.
• Shaped bodies as a precursor material for the process according to the invention which are provided with only one grain or with a few grains or with only one magnetic domain or with a few magnetic domains, are preferably produced in a modified melt texture growth process, e.g. the melt-textured-growth process, in a top-seeded-melt-growth process with a germ on top, in a zone melting process such as the vertical gradient freeze process or in a single crystal growing process such as e.g. the modified Bridgeman process. Shaped bodies that were produced in one of these processes sometimes have only one to six magnetic domains. If such samples have cracks and / or contaminated or structurally disturbed areas, these defects can be filled in and / or healed, and the split magnetic domains can also be healed.
• a modified melt texture growth process e.g. the melt-textured-growth process
• a top-seeded-melt-growth process with a germ on top in a zone melting process such as the vertical gradient freeze process or in a single crystal growing process such as e.
• the pre-sintered moldings based on (Y / SE) BaCuO are heated to a temperature above the peritectic temperature or Melting temperature of the corresponding precursor material is. This temperature is maintained until the entire precursor material has changed into the partially molten state, in which, for example, the Y 2 Ba ⁇ C ⁇ u0 phase is in equilibrium with a Ba- and Cu-rich melt.
• the subsequent process section can be the actual texturing step. He determines that
• the cooling which is common to all processes, takes place, in which the temperature is returned to room temperature.
• This cooling can be enriched with oxygen, especially with slow cooling in the temperature range from about 500 to 350 ° C. or with a holding time in this temperature range using a flowing oxygen-rich gas stream. Otherwise, after texturing, the shaped body must be enriched with oxygen in at least one further heat treatment.
• the microstructure of the moldings produced in this way is formed from one or more grains, depending on the process. These grains, in turn, are composed of plates that are separated by small-angle grain boundaries of less than 1 °.
• spherical or needle-shaped particles of phase 211 with diameters of approximately 100 nm to 100 ⁇ m are distributed throughout the molded body.
• the characteristic process steps and features of the most important texturing processes are shown below:
• This method is a non-directional texturing method without spatial temperature gradients.
• the texturing takes place above all by slowly cooling the molded body out of the partially molten state to temperatures below the peritectic or melting temperature.
• VVF Vertical gradient freeze process
• This process is a directional melt texturing process.
• Eight individually controllable zones of a stationary furnace are activated in such a way that a temperature profile is passed through the sample, which is also held stationary.
• the vertical temperature gradient can e.g. 25 K / cm.
• cooling is often carried out at about 1 K / h.
• the resulting melt-textured moldings contain several grains in the first melted area due to the irregular nucleation. In the grain growth following the nucleation, such grains prevail whose c-axes are aligned essentially parallel to the temperature gradient prevailing during production.
• the difference in orientation between such preferably growing grains can be up to about 15 °.
• the sample can preferably be moved vertically in relation to a stationary, often three-zone furnace.
• the sample can either be made using a suitable support structure, e.g. supported by a crucible or hung on a traction device.
• the temperature in the upper zone is typically around 850 ° C, that in the middle around
• the cylindrical samples are often about 12 cm long and often have a diameter of about 6 mm. Below an approximately 2 to 3 cm long nucleation zone in which differently oriented grains compete in growth, the samples are usually one-domain and then necessarily have only one grain. The c-axis in this one-domain area is often inclined by about 45 ° to the sample axis.
• This method enables the production of crystallographically single-domain shaped bodies with a crystallographic orientation which is suitable by the orientation of the one to be applied to the surface of the precursor material
• Seed crystal can be specified.
• the seed crystal must consist of a material which is still in crystalline form even at temperatures above the peritectic or melting temperature of the material to be textured.
• the lattice parameters of the seed material must correspond approximately to those of the material to be textured.
• the germ can be applied before the actual texturing step by pressing, sintering or simply by placing it on, and during the texturing process by placing it on the already heated sample.
• the precursor material thus provided with a germ is converted into a partially melt-liquid state and rapidly cooled to a temperature below the peritectic or melting temperature of the material to be textured, at which, in direct contact with the seed crystal, nucleation and growth, in particular of the grains of the phase (Y, SE) ⁇ Ba 2 Cu 3 0 7 .
• x uses, the subcooling in other areas of the molded body is not sufficient for nucleation and grain growth.
• a holding time is often chosen in the temperature profile in order to stabilize the growth of the central grain.
• the subsequent temperature control must primarily aim to remove the heat of crystallization and to maintain the stable growth of the central grain and to suppress the growth of further grains.
• the samples produced in this way consist of a single grain with an orientation which essentially corresponds to that prescribed by the seed crystal.
• an orientation of the c-axis perpendicular to one of the surfaces of the geometry of the shaped body is preferred.
• the substructure of these grains is formed, like in the other methods for forming a precursor material, essentially from plate-shaped grains which are separated from one another by small-angle grain boundaries of less than 1 °.
• Shaped body spreads.
• T means the respective peritectic or melting temperature and where the use of a germ only serves to produce a suitable precursor material for the remuneration process according to the invention:
• Table 1 basically gives guidelines for the selection of suitable pairings of elements. Mixtures of various elements, the use of pressure or negative pressure, contents of substances which lower the melting point or the peritectic temperature, and in particular the oxygen partial pressure, can, however, cause a significant change in the temperature value and possibly also a change in the sequence listed in Table 1.
• the table does not take into account that the superconductor material before the treatment with a germ can have a slightly different composition and different properties than after the germination.
• the superconductor material before the treatment with a germ can have a slightly different composition and different properties than after the germination.
• the application material is preferably applied in a layer thickness in the range from 1 ⁇ m and 5 mm, particularly preferably in the range from 10 ⁇ m to 3 mm, very particularly preferably in the range from 50 ⁇ m and 2 mm.
• a powder, a molded body and / or a coating can be applied as the application material which is provided for coating at least part of the surface of the molded body to be modified; preferably a pressed, calcined, sintered or melted, possibly textured or melt-textured shaped body as the shaped body and preferably a physically and / or chemically deposited coating, produced essentially by precipitation, decomposition reaction, spraying or spray pyrolysis, such as e.g. Laser ablation, vapor deposition, sputtering, vapor deposition, atomization, CVD, PVD, sol-gel processes.
• oxides, hydroxides, carbonates, nitrates and similar precursor materials such as citrates and oxalates can be used, but also materials for lowering the melting point such as halides, in particular fluorides.
• materials for lowering the melting point such as halides, in particular fluorides.
• halides in particular fluorides.
• a powdered application material which also includes a single-phase or multi-phase powder, a powder mixture and / or a granulate, can be sprinkled on or spread on, among other things; a molded body of the application material can be placed or glued to the corresponding surface of the molded body of the superconductor material; eg from the gas phase or with a
• Aerosol can be used to coat the molded body to be modified.
• the coated shaped body of the superconductor material can be kept at a temperature for so long at which the shaped body material has not yet melted and / or is not yet flowable, but at which the application material is in the at least partially melted and / or flowable state, and at least part of one Area near the surface of the molded body is modified at this temperature and / or a subsequent cooling, so that part of the application material can diffuse or penetrate into the superconductor material to be modified.
• Surface defects e.g. Pores, cracks and microcracks, which may be present in the surface area to be modified, are closed and a tight interlocking can occur due to chemical or physicochemical reactions at the interfaces.
• certain elements can also diffuse deeper into the superconductor material to be modified.
• the order material may possibly diffuse in as far as possible, penetrate and, if necessary, evaporate subordinate, so that with thinner coatings only a very thin remaining layer or no remaining layer may remain on the modified molded article after the fire.
• the layer material which is in the form of a very flat Pyramid-grown crystal surfaces and / or the unevenness of the molded body are then preferably removed mechanically, for example by sawing, grinding, lapping or / and polishing, and if necessary subsequently subjected to a heat treatment which can serve to oxygenate and / or to heal the material.
• the molded body to be modified preferably has a relative density of at least 80%, particularly preferably at least 95%, but in exceptional cases, less dense molded bodies can also offer advantages if they are treated according to the invention.
• the shaped body of the superconductor material can be set during the fires and heat treatments such that, apart from the application material, it is only in direct contact with a material based on (Y / SE) BaCuO, preferably with a material based on phases based on Y 2 BaCuOs. This helps to avoid contact reactions and partial flow of the superconducting molded body in the event of fire or the occurrence of mechanical stresses. Lightweight bricks and kiln furniture based on MgO or Al 2 0 3 are therefore less suitable.
• the cooling after or when modifying the superconductor material and after a subsequent heat treatment is carried out as slowly as possible in order to avoid the formation of cracks, microcracks and flaking, preferably slower than 30 K.
• the shaped body can during cooling or / and during a renewed
• Heat treatment can be enriched with oxygen in order to produce and / or improve the superconducting properties.
• the modification of the superconductor material can lead to the formation of defects in the crystal lattice of the shaped body, which contribute to increasing the magnetic properties. This can be point defects, in particular defects due to the
• a crack which may be present, a grain boundary or / and a contaminated or structurally disturbed one are removed area, in particular by sawing, the removed area is then treated in the further inventive method analogous to an area to be modified. This makes it possible to completely heal and modify defective moldings or to produce particularly large moldings with better properties than is currently technically possible.
• the method according to the invention can advantageously be carried out in such a way that the flowable application material at high temperature at least partially into a crack and / or into a e.g. penetrates through the saw cut area of the molded body, which are present in the surface area to be modified.
• the shaped body of the superconductor material preferably has only one to one hundred grains and / or one to one hundred before the modification and heat treatment
• the shaped body of the superconductor material preferably has only one to one hundred grains or / and one to one hundred domains, in particular up to 50, particularly preferably only one to 20, very particularly preferably only one to eight grains or Domains or even just one grain and up to four domains.
• all geometries of moldings are suitable for use in the process according to the invention or, after modification in these molds, for technical use.
• Panels can have a square or rhombic layout.
• a large-sized shaped body of the superconductor material can have a plurality of seeds spaced from one another, the crystal orientations of the c-axes advantageously either being essentially parallel to one of the main directions of the geometry of the shaped body, for example essentially parallel to the cylinder axis of a cylinder, or essentially perpendicular to it .
• This has the advantage that the preferred orientation of the c-axis, to which the plane of particularly good superconductivity is perpendicular, is arranged so that a higher critical transport current density is achieved by the alignment in the direction of flow of the electrical current, a high current can flow and a strong magnetization is achieved.
• the crystal orientation in the shaped body to be modified can be controlled.
• a large-sized shaped body of the superconductor material can advantageously be produced in several segments, which may be matched to one another or even better joined together.
• the joining can in particular be carried out by heat treatment at a temperature at which the molding material has not yet melted and / or is not yet flowable, but at which
• Application material is in the at least partially melted and / or flowable state and at least a part of a region of the molded body near the surface is modified at this temperature and / or subsequent cooling - if necessary under pressure and possibly with the addition of an application material towards one another joining interfaces, but also e.g. through a simple
• a shaped body made of a superconducting material based on (Y / SE) BaCuO which is obtainable by a process according to at least one of claims 1 to 17 and which has at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu contains and which has a maximum value of the remanence induction at 77 K and 0 T of at least 1100 mT, preferably of at least 1200 mT, very particularly preferably of at least 1300 mT, especially more than 1400 mT.
• the shaped body is preferably a cylinder, a ring, a tube or a disk consisting essentially of one or more segments, the one Alignment of the c-axes of the grains or of one grain has essentially in the direction of the cylinder axis / plate axis or another main direction of the shaped body or perpendicular to it.
• the molded body can have a critical transport current density of at least 4 10 4 A / cm 2 in the external field of 1 T at 77 K, preferably of at least 6 10 4 A / cm 2 , particularly preferably of at least 8 10 4 A / cm 2 and in particular of at least 9.7 ⁇ 10 4 A / cm 2 . It can also determine a fracture toughness from the
• Crack system to have hardness impressions of at least 1 MPa m, preferably of at least 1.5 MPa Vm. Furthermore, it can have a bending strength of at least 300 MPa, preferably of at least 400 MPa.
• the molded body produced according to the invention can be used, for example, for transformers, circuit breakers, power supplies, magnetic
• FIG. 1 shows the measurement results of the precursor material
• FIG. 2 shows the measurement results of the superconductor material which has been coated according to the invention.
• the PTFE bracket was connected to an SD positioning system using a stainless steel rod.
• the control unit of the 3D positioning system was a CNC controller C116-4 from Isel, which could be controlled by a PC via an RS 232 interface.
• the stepper motors could be positioned reproducibly with a minimum step size of 10 ⁇ m.
• a permanent magnet was lowered from a height of 100 mm in steps of 0.5 mm onto the surface of the shaped body cooled to 77 K and back into it
• the magnet used was a cylindrical SmCo magnet with a diameter of 25 mm, a height of 15 mm and a remanence on the surface B z (0) of 0 according to the standardization of the "Superconducting Materials” committee of the German Society for Material Science (DGM) , 4 T. The positioning took place with the in the procedure for
• the fracture toughness could be measured by evaluating the crack pattern generated by a Vickers hardness test specimen. With this only with brittle
• the length and the configuration of the cracks resulting from the hardness test procedure were related to the methods used for materials, the test load used and the determined hardness of the material.
• the hardness impressions were generated with a Leitz Durimed 2 low-load hardness tester with loads between 10 g and 500 g with a dwell time of the test specimen on the surface of 15 s. ' The
• the critical transport stream densities were determined using the conventional Vie ⁇ unkt method. Currents up to a strength of 400 A are passed through the sample (cross-sectional area 0.25 mm 2 ) in pulse mode with a pulse duration of 1 ms. Low-resistance silver contacts (0.04 mOhm) were burned into the sample for contacting.
• Y ⁇ Ba 2 Cu 3 0. x which additionally contained 25 mol% Y 2 0 3 and 1 wt.% Ce0 2 , at temperatures up to 1045 ° C by a melt growth process with top-sitting germ (top-seeded-melt-growth TSMG).
• the structure consisted of YBCO 123 with a high density of fine particles of YBCO 211.
• the dimensions of the finished textured plate-shaped body were 34 x 34 x 12 mm. After texturing, the molded body had no macroscopic cracks near the surface.
• the distribution of the remanent induction measured after the texturing gave a maximum value of the remanent induction B z, max of 820 mT (FIG. 1).
• the cone-shaped geometry of this distribution shows the magnetic uniqueness of the molded body.
• This shaped body was then coated and coated according to the invention by infiltration: First, an application material, also known as an infiltrate, which
• Example 1 a textured molded body with dimensions 38 ⁇ 38 ⁇ 12 mm 3 was produced. Unlike in Example 1, Er-123 was used as order material. The distribution of the remanent induction measured after the texturing gave a maximum value of the remanent induction B z, max of 902 mT.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Superconductor Devices And Manufacturing Methods Thereof (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Hard Magnetic Materials (AREA)
• Oxygen, Ozone, And Oxides In General (AREA)

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• 1999
  • 1999-02-27 DE DE19908597A patent/DE19908597A1/de not_active Ceased
  • 1999-09-10 JP JP2000603103A patent/JP2002538071A/ja active Pending
  • 1999-09-10 EP EP99973753A patent/EP1159767B1/de not_active Expired - Lifetime
  • 1999-09-10 WO PCT/EP1999/006680 patent/WO2000052768A1/de not_active Ceased
  • 1999-09-10 DK DK99973753T patent/DK1159767T3/da active
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  • 1999-09-10 DE DE59914891T patent/DE59914891D1/de not_active Expired - Lifetime
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  • 2001-08-24 NO NO20014121A patent/NO20014121L/no unknown
• 2003
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