JP6359937B2 - RE oxide superconducting wire manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a tape-shaped RE-based oxide superconducting wire useful for superconducting application equipment such as a superconducting magnet, a superconducting cable, a current limiter, a generator, a motor, and a transformer.

Oxide superconductors have a higher critical temperature Tc than liquid metal superconductors such as conventional Nb ₃ Sn and Nb ₃ Al and exceed the liquid nitrogen temperature, so superconducting applications such as power cables, transformers, motors, etc. Equipment and devices can be operated at liquid nitrogen temperatures.

In order to apply the oxide superconductor to the above field, the critical current density Jc [MA / cm ² ] (hereinafter “Jc”) is high and the critical current Ic value (hereinafter “Ic”) [A / cm] is high. It is necessary to manufacture a long tape-shaped wire having the following properties, and research into making the wire is energetically performed.

  As a method for producing a tape-shaped RE-based oxide superconducting wire, for example, a method (TFA-MOD method) of forming a film with a solution using an organic acid salt containing fluorine (TFA salt: trifluoroacetate) as a starting material is used. The production used is known. In this method for producing an oxide superconducting wire, the grain boundary characteristics and crystallinity of the oxide superconductor are improved by controlling the composition and material of the solution to be deposited, and the self-magnetic field, that is, 77 [K], 0 It has been confirmed that Jc in [T (Tesla)] is improved.

  By the way, in the oxide superconductor, as the applied magnetic field increases, the density of the quantized magnetic flux penetrating into the oxide superconductor increases, and the superconducting state (critical current density Jc · The critical current Ic value) decreases. In addition, due to the crystal structure, the oxide superconductor has a lower Jc · Ic when a magnetic field is applied in the c-axis direction of the crystal axis than Jc · Ic when a magnetic field is applied in the a-axis direction of the crystal axis. It has the characteristic.

  For this reason, in order to use it for the apparatus used under an applied magnetic field, as shown in Patent Document 1, for example, a magnetic flux pinning point is introduced in the oxide superconductor so as not to be affected by the applied magnetic field angle dependency. Technology to do is considered.

  In Patent Document 1, isotropic shape nano-size magnetic flux pinning points that are effective in any magnetic field direction are uniformly introduced into the oxide superconductor at nanometer intervals to move the quantized magnetic flux in the oxide superconductor. This greatly improves Jc. According to the oxide superconducting wire formed as described above, very excellent superconducting characteristics could be obtained in a magnetic field of about 77 [K] and 1 [T]. Ic was remarkably lowered, and the desired superconducting properties could not be obtained.

  This is because the conventional method for manufacturing an oxide superconducting wire cannot control the size of the magnetic flux pinning point formed in the superconducting layer, resulting in the generation of coarse particles. Has proposed the technique shown in Patent Document 2.

  In this technique, in the MOD method, between the pre-baking process after applying the superconducting raw material solution to the substrate and the main baking process after the pre-baking process, In the baking treatment, intermediate baking is performed at a low temperature. Thereby, the size of the magnetic flux pinning point formed in the superconducting layer is controlled, and the superconducting wire has stable superconducting characteristics (20 [A / cm] in a magnetic field of 3T greater than 77K and 1T) in a magnetic field environment. Manufactured.

JP 2009-164010 A JP 2012-181963 A

  However, in recent years, an oxide superconducting wire having excellent characteristics in a magnetic field environment compared to the oxide superconducting wire manufactured in Patent Document 2, for example, a current of 50 [A / cm] or more can flow at 3 [T]. Production of oxide superconducting wires is desired.

  An object of the present invention is to provide a method for producing a tape-shaped RE-based oxide superconducting wire capable of ensuring stable and high superconducting characteristics in a magnetic field application environment.

One aspect of the method for producing a RE-based oxide superconducting wire according to the present invention is to apply a superconducting raw material solution on an intermediate layer formed on a substrate, and then perform a temporary baking treatment to form a superconducting precursor. By subjecting the superconducting precursor to a main firing treatment, REBayCu3Oz-based RE (represents at least one element selected from Y, Nd, Sm, Eu, Gd, and Ho) tape-like RE. In a manufacturing method for manufacturing a system oxide superconducting wire,
The superconducting raw material solution contains RE, Ba and Cu, and Zr, Sn, Ce, Ti, Hf, Nb which forms a magnetic flux pinning point in a mixed solution in which the molar ratio of Ba is in the range of y <2. A solution containing at least one additive element,
After the temporary baking treatment and before the main baking treatment, an intermediate for baking the superconducting precursor while maintaining a temperature higher than the baking temperature in the temporary baking treatment and lower than the baking temperature in the main baking treatment. Heat treatment,
In the intermediate heat treatment, the time for rapid cooling from the firing temperature held for the superconducting precursor to room temperature is within one hour .

  According to the present invention, the non-superconducting oxide particles that serve as the magnetic flux pinning point are nucleated during the temperature rise, and the condition during the firing, particularly during the temperature rise, is used as the above means, so that the magnetic flux pinning point can be made extremely fine and It is possible to produce an RE-based oxide superconducting wire that is uniformized and can ensure stable and high superconducting characteristics in a magnetic field application environment.

Schematic which shows the cross section perpendicular | vertical to the axial direction of the tape of the oxide superconducting wire manufactured with the manufacturing method of RE type oxide superconducting wire of embodiment of this invention. Schematic diagram for explaining the manufacturing method of the RE-based oxide superconducting wire of the same embodiment Schematic sectional view showing the main configuration of a heat treatment apparatus used in the method for producing an RE-based oxide superconducting wire according to the present embodiment Schematic showing the rotating body of the heat treatment equipment The figure which shows the profile of the process in the heat processing apparatus

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The tape-shaped RE-based oxide superconducting wire manufacturing method according to the embodiment of the present invention is a tape-shaped REBa _y Cu ₃ O _z- based (RE is selected from Y, Nd, Sm, Eu, Gd, and Ho) An oxide superconducting wire (herein referred to as a YBCO superconducting wire) of at least one element is produced.

<Oxide superconducting wire>
First, an example of a tape-shaped oxide superconducting wire manufactured in the present embodiment will be described.

  FIG. 1 is a schematic view showing a cross section perpendicular to the axial direction of a tape of an oxide superconducting wire manufactured by a method for manufacturing a tape-shaped RE-based oxide superconducting wire according to an embodiment of the present invention.

  The oxide superconducting wire 10 is formed by laminating an intermediate layer 12, a tape-shaped oxide superconducting layer (hereinafter referred to as “superconducting layer”) 13, and a stabilization layer 14 on a tape-shaped metal substrate 11. It is formed. Here, the intermediate layer 12 includes a first intermediate layer 12a, a first intermediate layer 12b, a third intermediate layer 12c, and a fourth intermediate layer 12d.

  The tape-shaped metal substrate 11 is, for example, nickel (Ni), nickel alloy, stainless steel, or silver (Ag). Here, the metal substrate 11 is a crystal grain non-oriented, heat-resistant, high-strength metal substrate, and is Ni-Cr-based (specifically, Ni-Cr-Fe-Mo-based Hastelloy (registered trademark) B, C, X). Etc.), W-Mo series, Fe-Cr series (for example, austenitic stainless steel), Fe-Ni series (for example, non-magnetic composition type) and other materials such as cubic Vickers hardness (Hv ) = 150 or more nonmagnetic alloy. The thickness of the metal substrate 11 is 0.1 mm or less, for example.

The first intermediate layer 12a is a layer made of Gd ₂ Zr ₂ O ₇ (GZO), yttrium stabilized zirconia (YSZ), or the like formed on the tape-shaped metal substrate 11 by a sputtering method. Here, the first intermediate layer 12a _is configured as an intermediate layer for all axes oriented depositing the _{Gd 2 Zr 2 O 7 (GZO} ). The thickness of the first intermediate layer 12a is about 1000 [nm]. A second intermediate layer 12b made of MgO is formed on the uniaxially oriented first intermediate layer 12a by the IBAD method. A third intermediate layer 12c made of LaMnO ₃ is formed on the second intermediate layer 12b by sputtering. Furthermore, here, CeO ₂ is vapor-deposited by a sputtering method (or a PLD method), and a fourth intermediate layer 12d is formed as an omniaxially oriented cap layer. The thickness of the fourth intermediate layer 12d is about 1000 [nm]. In addition, when the fourth intermediate layer 12d is a Ce-Gd-O film in which Gd is added to a CeO ₂ film, in order to obtain good orientation when a YBCO superconducting layer is formed as the superconducting layer 13, a film is used. The amount of Gd added is preferably 50 at% or less. A superconducting layer 13 is formed on the fourth intermediate layer 12d by the MOD method.

  In the oxide superconducting wire 10, the intermediate layer 12 is formed by the first intermediate layer 12a to the fourth intermediate layer 12d. The intermediate layer 12 is formed on the metal substrate 11 to constitute the composite substrate 15. The composite substrate 15 is a substrate on which the superconducting layer 13 is formed. Even if the composite substrate 15 has biaxial orientation, the intermediate layer 12 having biaxial orientation is formed on the metal substrate 11 having no orientation. You may have done. The intermediate layer 12 may be formed of one to three layers or five layers or more.

  On the superconducting layer 13 is provided a stabilizing layer 14 which is a noble metal such as silver, gold or platinum, or an alloy thereof and is a low resistance metal. The stabilization layer 14 is formed immediately above the superconducting layer 13 to prevent the superconducting layer 13 from deteriorating in performance caused by reaction due to direct contact with materials other than noble metals such as gold and silver or alloys thereof. To do. In addition to this, the stabilization layer 14 disperses heat generated by an accident current or alternating current to prevent destruction and performance degradation due to heat generation. The thickness of the stabilization layer 14 is 10-30 [micrometers] here.

The superconducting layer 13 is an REBa _y Cu ₃ O _z system (RE represents one or more elements selected from Y, Nd, Sm, Eu, Gd, and Ho, and y ≦ 2 and z = 6.2 to 7 It is a layer of a high-temperature superconducting thin film. Here, the superconducting layer 13 is an yttrium oxide superconductor (also referred to as a YBCO superconducting layer).

  Here, the superconducting layer 13 is obtained by adding an additive element M to a raw material solution composition RE: Ba: Cu = 1: 1.5: 3 used in a normal low Ba composition method in which the stoichiometric composition of Ba is smaller than 2. It has an artificial pin particle (hereinafter referred to as “magnetic flux pinning point”) 13a which is an effective oxide particle formed. The superconducting raw material solution composition at this time is set in consideration of the composition of the magnetic flux pinning points (Ba: Zr = 1: 1 in the case of Zr).

  The magnetic flux pinning point (artificial pin particle) 13a has a particle size of 50 nm or less including at least one additive element M among Zr, Sn, Ce, Ti, Hf, and Nb, which is uniformly dispersed in the superconducting layer 13. It is. Here, the magnetic flux pinning point 13a in the superconducting layer 13 is an oxide particle as a compound controlled to have a particle size of 10 [nm] or less. The particle diameter of the magnetic flux pinning point 13a is more effective when it is closer to the magnetic flux line size.

Note that the number n of the magnetic flux pinning points is preferably included in the superconducting layer 13 by 1.0 × 10 ³ ≦ n <1.0 × 10 ⁷ per [μm ³ ]. A large number of particles is effective because more magnetic flux can be pinned, but if it exceeds the above range, the effect of reducing the volume of the superconductor is increased, which inhibits the superconducting current and eventually superconducting properties. Will be reduced. For example, when 1.0 × 10 ⁷ or more per 1 [μm ³ ] exists, even if the particle size of the oxide particles is 5 [nm], the volume fraction will exceed 60%, Reduce superconducting properties.

  The addition amount of the additive element M needs to be 30 [wt%] or less, and is preferably 1 [wt%] to 10 [wt%] with respect to the entire superconducting layer. A reason why 1 [wt%] to 10 [wt%] is desirable is that, in order to improve the characteristics in the magnetic field, a larger amount of the additive element can effectively pin more magnetic flux. However, if it exceeds 10 [wt%], that is, the volume fraction is 30 [vol%], the effect of reducing the volume of the superconductor is increased and the criticality that particles can exist alone is exceeded. This is because the current is inhibited. Furthermore, when the above range is exceeded, the precipitates aggregate to inhibit the superconducting current. In addition, when the additive element M is at least one of Zr, Sn, Ce, Ti, and Hf, the ratio with Ba is Ba: M = 1: 1.

When the additive element M is Zr, the compound formed by dispersing in the superconductor as the magnetic flux pinning point 13a is BaZrO ₃ . When the additive element M is Ti, the compound formed by dispersing in the superconducting layer 13 as the magnetic flux pinning point 13a is BaTiO ₃ . When the additive element M is Ce, the compound formed by dispersing in the superconducting layer 13 as the magnetic flux pinning point 13a is BaCeO _{3. When} the additive element M is Sn, the superconducting layer is used as the magnetic flux pinning point 13a. The compound formed by dispersing in 13 is BaSnO ₃ . When the additive element M is Hf, the compound formed by dispersing in the superconducting layer 13 as the magnetic flux pinning point 13a is BaHfO ₃ . Each compound that becomes the magnetic flux pinning point 13 a is uniformly dispersed in the superconducting layer 13.

Further, when the additive element M is Nb, the ratio to Ba is Ba: M = 1: 0.5 to 2, and the compound formed dispersed in the superconductor as a magnetic flux pinning point is YNbBa ₂ O. ₆ , BaNb ₂ O _{6 and the} like. The compound that becomes each magnetic flux pinning point 13 a is uniformly dispersed in the superconducting layer 13.

  In the superconducting wire in which the magnetic flux pinning point 13a is formed in the superconducting layer (superconductor) 13, the molar ratio of Ba contained in the superconducting layer 13 is a ratio satisfying RE: Ba: Cu = 1: 1.5: 3. To be. Thus, by making the molar ratio of Ba smaller than the standard molar ratio (ratio satisfying RE: Ba: Cu = 1: 2: 3), the segregation of Ba is suppressed, and the Ba base at the grain boundary is suppressed. Impurity precipitation is suppressed. Superconducting layer 13 formed thereby suppresses the occurrence of cracks, improves the electrical connectivity between crystal grains, and improves Jc defined by the energization current.

In addition, when the additive element M added to the superconducting raw material solution containing TFA is Zr, a method of mixing a Zr-containing naphthenate having a high affinity with Ba into the superconducting raw material solution containing TFA is adopted. May be. As a result, while maintaining the composition of the superconducting layer 13 (RE: Ba: Cu = 1: 1.5: 3), BaZrO ₃ that forms a magnetic flux pinning point (artificial pin particle) 13a by combining with Ba is formed. The superconducting layer 13 formed in this way is dispersed in the grains forming the layer 13. The grain boundary characteristics are improved without lowering Jc due to grain boundary segregation.

Further, BaZrO ₃ formed in the superconducting layer 13 exists in nano-size and nano-interval not only in the film surface direction but also in the film thickness direction, and these effectively pin the magnetic flux, and the anisotropic of Jc with respect to the magnetic field application angle It becomes possible to remarkably improve the property. In addition, in order to control the size, density and dispersion of BaZrO ₃ , not only the amount of Zr-containing naphthenate and the like introduced, but also the oxygen partial pressure during calcination heat treatment and main calcination heat (crystallization heat) treatment, This can be achieved by controlling the water vapor partial pressure and the firing temperature. By performing these optimizations, an effective magnetic flux pinning point 13a can be introduced.

Moreover, in the oxide superconducting wire 10, the Zr-containing magnetic flux pinning points 13a can be artificially finely dispersed in the superconducting layer in the RE-based superconducting layer with a reduced Ba concentration. For this reason, the magnetic field application angle dependency (Jc _{, min} / Jc _{, max} ) of Jc is small, the magnetic field characteristic has a high Jc at a high magnetic field, and the magnetic field application angle dependency (Jc _{, min} / Jc) of Jc. _{, Max} ) can be significantly improved. Therefore, in addition to the self-magnetic field, the magnetic flux can be effectively pinned in any magnetic field application angle direction in the magnetic field, and the isotropic Jc characteristic can be obtained, resulting in high superconducting characteristics (critical current density Jc [MA / cm ² ] and critical current Ic [A / cm-width]).

<Manufacturing method of superconducting wire>
The RE-based oxide superconducting wire 10 having such a superconducting layer 13 is manufactured as shown in FIG.

  FIG. 2 is a schematic diagram for explaining a method for manufacturing the RE-based oxide superconducting wire according to the present embodiment. In FIG. 2, it demonstrates as a wire provided with a YBCO superconducting layer as RE type oxide superconducting wire.

  In the present embodiment, the oxide superconducting wire 10 which is a YBCO oxide superconducting wire is manufactured by the MOD method. In the manufacture of the oxide superconducting wire 10, after the superconducting raw material solution is applied to the substrate, a temporary baking process is performed to obtain an amorphous superconducting precursor (hereinafter referred to as “precursor”). Next, after the pre-baking process and before the main baking process for performing the crystallization heat treatment, the intermediate heat treatment is performed at a temperature lower than the main baking temperature in the main baking process and rapidly cooled to room temperature. A RE-based (YBCO) oxide superconducting wire is manufactured through subjecting the precursor subjected to the intermediate heat treatment and including the magnetic pinning in the superconducting layer to the main firing process. Details will be described below.

First, a Gd ₂ Zr ₂ O ₇ intermediate layer 12a is formed by sputtering as a template on a tape-like substrate, for example, a Ni alloy substrate (base material) 11 (see FIG. 1), and further, A second intermediate layer 12b made of MgO is formed by the IBAD method (see FIG. 1). Next, a third intermediate layer 12c made of LaMnO ₃ is formed on the second intermediate layer 12b by sputtering, and further a fourth intermediate layer 12d made of CeO ₂ is formed thereon by sputtering or PLD. The composite substrate 15 is formed by film formation (see FIG. 2).

  A superconducting raw material solution is applied on the composite substrate 15 in the coating step A to form a coating film.

  Specifically, in the coating step A of FIG. 2, a superconducting raw material solution starting from an organic acid salt containing fluorine is applied to the composite substrate 15 (intermediate layer 12 formed on the metal substrate 11) by a dip coating method. Applied.

  Here, the superconducting raw material solution is composed of Y-TFA salt (trifluoroacetate salt), Ba-TFA salt and Cu-naphthenic acid salt in an organic solvent at a ratio of Y: Ba: Cu = 1: y <2: 3. It is a dissolved mixed solution. For example, the molar ratio y of Ba contained in the superconducting raw material solution is 1.5.

  Further, in this superconducting raw material solution, an oxidation having a particle size of 50 [nm] or less, preferably 10 [nm] or less, containing Zr, Ce, Sn, Hf, Nb or Ti formed as the magnetic flux pinning point 13a. Physical particles (additive elements) are added.

In addition, it is preferable to use the following mixed solutions (a) to (d) as the superconducting raw material solution.
(A) Organometallic complex solution containing RE: a solution containing one or more of trifluoroacetate, naphthenate, octylate, levulinate, neodecanoate, and acetate containing RE, particularly RE A trifluoroacetate solution containing is desirable.
(B) Organometallic complex solution containing Ba: trifluoroacetate solution containing Ba (c) Organometallic complex solution containing Cu: Naphthenate, octylate, levulinate, neodecanoate containing Cu, A solution containing any one or more of acetates (d) An organometallic complex solution containing a metal having a high affinity with Ba: at least one metal selected from Zr, Sn, Ce, Ti, Hf, and Nb A solution containing any one or more of trifluoroacetate, naphthenate, octylate, levulinate, neodecanoate and acetate

After the superconducting raw material solution thus configured is applied to the composite substrate 15, the superconducting raw material solution applied in the temporary baking process B is temporarily fired. By the temporary baking process in the temporary baking process B, the coating film on the composite substrate 15 becomes an amorphous superconducting precursor (hereinafter referred to as “precursor”). In addition, in the coating step A, an ink jet method, a spray method, or the like can be used in addition to the dip coating method described above, but basically, any process that can continuously apply the mixed solution onto the composite substrate 15. It is not constrained by this example. The film thickness to be applied at one time is 0.01 [μm] to 2.0 [μm], preferably 0.1 [μm] to 1.0 [μm]. In the composite substrate 15, the intermediate layer formed on the base material may be formed by forming an intermediate layer made of CeO ₂ on the Gd ₂ Zr ₂ O ₇ intermediate layer.

  The coating process A and the pre-baking process B are repeated a predetermined number of times, that is, the coating film on the intermediate layer 12 of the composite substrate 15 of the tape-shaped oxide superconducting wire 10 is multi-coated. The predetermined number of times is repeated in accordance with the thickness of the coating film that becomes the superconducting layer, and the thickness of the coating film increases as the number of repetitions increases. Thus, a film body (“precursor” shown in FIG. 2) as a precursor to be a YBCO superconducting layer (hereinafter also referred to as “superconducting layer”) having a desired film thickness is formed on the intermediate layer in the composite substrate 15. To do.

  Thus, the precursor used as a superconducting layer is formed by repeating the application | coating process A and the temporary baking processing process B predetermined number of times (multi-coating).

  After the preliminary firing treatment step B for forming the precursor, the precursor is subjected to an intermediate firing treatment at a temperature lower than the main firing treatment temperature in the intermediate heat treatment step C, and then rapidly cooled to room temperature.

  The intermediate heat treatment step C includes an intermediate firing step C1 and a rapid cooling step C2. The intermediate firing step C1 is performed by subjecting the precursor after the preliminary firing to an intermediate firing treatment before the precursor reaches the crystallization temperature of YBCO in the final firing treatment, so that residual organic in the preliminary firing in the precursor is performed. The minute or surplus fluoride is discharged.

  In the rapid cooling step C2, after the intermediate firing step C1, the precursor is rapidly cooled from the temperature held in the intermediate firing process of the intermediate firing step C1 to room temperature. In the rapid cooling step C2, the precursor subjected to the intermediate baking treatment is actively cooled so as to reach the room temperature from the intermediate baking temperature in a faster time than leaving the precursor after the intermediate baking and cooling (natural cooling).

  Thereafter, in the main baking treatment step D, a crystallization heat treatment (main baking treatment) is performed on the precursor subjected to the intermediate baking treatment in the intermediate heat treatment step C. After the main firing treatment step D, a stabilization layer (for example, Ag stabilization layer) 14 (see FIG. 1) is formed on the produced YBCO superconductor by sputtering, and post-heat treatment is performed to produce a YBCO superconducting wire. Is done.

  As a result, in the firing process step D in which the firing process is performed at the crystallization temperature, a superconducting wire (YBCO superconducting wire) having a YBCO layer in which magnetic flux pinning points are uniformly dispersed and magnetic field application characteristics are excellent is manufactured. ing.

  The intermediate heat treatment step C (intermediate firing step C1, rapid cooling step C2) and the main firing treatment step D after the preliminary firing step B may be performed using, for example, a batch heat treatment apparatus 20 shown in FIGS. .

<Configuration of heat treatment equipment>
FIG. 3 is a schematic cross-sectional view showing the structure of a heat treatment apparatus in the method for producing an RE-based oxide superconducting wire according to an embodiment of the present invention, and FIG. 4 shows a cylindrical rotating body arranged inside the heat treatment apparatus. . The rotating body is formed of a material that can withstand high temperatures and does not oxidize, such as quartz glass, ceramics, Hastelloy, or Inconel.

  The heat treatment apparatus 20 is a so-called batch-type electric furnace, and includes a heat treatment furnace 24 including a furnace body 22 into which an atmospheric gas is introduced and an electric heater 23 disposed outside the furnace body 22, and a heat treatment furnace 24. And a cylindrical rotating body 25 disposed inside (in detail, inside the furnace body 22).

  The cylindrical rotating body 25 is disposed inside the heat treatment furnace 24 so as to be rotatable with respect to a horizontal rotation axis. A tape-shaped wire in which a precursor of a Y-based (123) superconducting layer is formed on a composite substrate 15 in which an intermediate layer having biaxial orientation is formed on a substrate that is a heat treatment object on the outer periphery of the rotating body 25. 10 (for the sake of convenience, described with the same sign as “oxide superconducting wire”) is wound and subjected to heat treatment for generating a superconductor.

  In the cylindrical body 25a of the rotating body 25, a large number of through holes 25b having a diameter equal to or less than ½ of the tape width of the tape-shaped wire 10 are uniformly formed on the entire surface of the cylindrical body 25a. One end side of the cylindrical body 25a is sealed with a lid body 25c, and the other end side is connected to a gas exhaust pipe 27 for exhausting the gas inside the cylindrical body to the outside of the heat treatment furnace 24.

  A plurality (at least four) of gas supply pipes 28 are arranged symmetrically with respect to the rotation axis of the rotating body 25 so as to be separated from the outer surface of the cylindrical body 25a. Each gas supply pipe 28 is formed with a large number of gas ejection holes (not shown) so as to eject atmospheric gas toward the surface of the cylindrical body 25a. The length of the gas supply pipe 28 is preferably longer than the height of the cylindrical body 25a. The diameter of the gas ejection hole is designed so that the gas pressure and the gas flow rate are uniform. The gas supply pipe 28 is formed of a material that can withstand high temperatures and does not oxidize, such as quartz glass, ceramics, Hastelloy, or Inconel.

  The atmospheric gas is supplied to the gas supply pipe 28 from an atmospheric gas supply device (not shown) disposed outside the heat treatment furnace 24 through a connection pipe (not shown) connected to the gas supply pipe 28.

  The heat treatment apparatus 20 is configured so that the inside of the heat treatment furnace 24 can be maintained in a reduced pressure atmosphere. The atmospheric gas supply device is connected to a gas system that supplies an inert gas, oxygen gas, dry gas, and water vapor, and includes a mechanism that changes these atmospheric gases in accordance with a heat treatment pattern. The temperature of the gas supplied from the atmospheric gas supply device may be made controllable.

  The heat treatment apparatus 20 has a quenching function by a quenching apparatus 29 that quenches the tape-shaped wire 10 in the furnace body 22 as well as a firing function including the electric heater 23. That is, the heat treatment apparatus 20 is used in the intermediate heat treatment step C, and can perform the intermediate firing step C1 of the intermediate heat treatment step C and the rapid cooling step C2. The furnace body 22 functions as a heat treatment furnace 24 together with the electric heater 23, and also functions as a cooling furnace together with the rapid cooling device 29. The rapid cooling device 29 rapidly cools the inside of the furnace body 22 as compared with natural cooling (cooling with the electric heater 23 turned off), whereby the firing temperature for the precursor of the tape-shaped wire 10 in the furnace body 22 is increased. Used in the cooling step C2 for rapidly cooling from the temperature maintained in the intermediate firing to room temperature.

  In the heat treatment apparatus 20 described above, the cylindrical rotating body 25 around which the tape-shaped wire 10 is wound is rotated by a drive mechanism (not shown) at a predetermined rotation speed. At the same time, atmospheric gas (here, water vapor gas) is ejected from the numerous gas ejection holes of the gas supply pipe 28 toward the surface of the cylindrical body inside the heat treatment furnace 24 held in a heated atmosphere by the electric heater 23. On the other hand, this atmospheric gas is sucked into the cylindrical body 25a from a large number of through holes 25b of the cylindrical body 25a, and discharged to the outside of the heat treatment furnace 24 through the gas discharge pipe 27 connected to the other end side of the cylindrical body 25a. Is done.

  The heat treatment apparatus 20 configured in this manner is a tape-like material in which a precursor containing an additive element is formed on an intermediate layer by applying a superconducting raw material solution (application step A in FIG. 2) and pre-baking treatment B. An intermediate heat treatment step C (intermediate firing step C1 and rapid cooling step C2) and a main firing treatment step D are performed on the wire 10.

  In the heat treatment apparatus 20, as the intermediate heat treatment step C, first, as the intermediate firing step C 1, the precursor containing the additive element (for example, Zr) in the tape-shaped wire 10 is subjected to the firing treatment temperature in the firing treatment step D. Firing is performed by maintaining a low temperature for a predetermined time.

  Here, as shown in FIG. 5, the heat treatment apparatus 20 heats up to an intermediate firing temperature at a temperature lower than the main firing temperature as the intermediate firing step C1, and maintains this temperature as a constant temperature for a predetermined time. Here, the intermediate firing temperature in the intermediate firing step C1 is preferably 400 [° C.] to 700 [° C.]. Furthermore, it is preferable that the intermediate baking temperature in the intermediate baking step C1 is maintained at 2 hours or more and 5 hours or less.

If it is outside the above temperature range, unreacted compounds remain in the precursor after the intermediate firing treatment, and desired characteristics cannot be obtained. That is, if it is less than the above range, there is no effect of intermediate firing, and if it exceeds the above range, the coarsening of the magnetic flux pinning point and the coarsening and decomposition of BaF _{2 in} the precursor proceed, and unoriented REBCO crystals are likely to occur. Superconducting properties are degraded. Moreover, it is preferable that the intermediate baking temperature in the intermediate baking step C1 is higher than the temporary baking temperature in the temporary baking heat treatment step B.

  In the intermediate firing step C1, it is desirable that the predetermined time for maintaining the intermediate firing temperature is [h] in the range of film thickness [μm] × 1.0 to 10.0. If it is less than the said range, the effect of an intermediate | middle baking process does not exist and the superconducting characteristic in a magnetic field becomes low. When the above range is exceeded, the coarsening of BZO occurs, and the superconducting characteristics in the magnetic field deteriorate.

  Further, in the intermediate firing step C1, the heat treatment apparatus 20 introduces water vapor gas into the furnace body 22 from a temperature lower than the intermediate heat treatment temperature held in the intermediate firing treatment, so that the precursor of the tape-shaped wire 10 is reduced. Thus, it is preferable to perform an intermediate firing process in a steam gas atmosphere.

  In this way, by introducing the steam gas from the temperature lower than the intermediate firing temperature maintained in the intermediate firing step C1 into the furnace body 22, the intermediate firing temperature reached after the temperature rise in the furnace body 22. A sufficient amount of water vapor gas can be secured. As a result, the size of the magnetic flux pinning point in the precursor does not become coarse, becomes a size within a specific range, and can be set to a superconducting characteristic Ic50 [A / cm] or more even in an environment of 3 [T]. .

  The amorphous precursor subjected to the intermediate firing process in the intermediate firing process C1 is naturally cooled in the rapid cooling process C2 from the intermediate firing temperature held in the intermediate firing process C1 to the room temperature. Cool faster than the case.

  Here, while the inside of the furnace body 22 is made a dry gas atmosphere by the atmospheric gas supplied through the supply pipe 28, this atmosphere is supplied with cooling air into the furnace body 22 by the quenching device 29, or the furnace body. It cools rapidly by cooling 22 itself from the outside. For example, the atmospheric gas supply device supplies the dry gas into the furnace body 22 in place of the steam gas supplied during the intermediate firing after the furnace body 22 is held at the intermediate firing temperature for a predetermined time, It may be rapidly cooled to room temperature.

  The rapid cooling by the rapid cooling step C2 of the intermediate heat treatment step C is performed within 1 hour.

  In this rapid cooling step C2, the precursor is rapidly cooled at 20 [° C./minute] from the temperature maintained in the intermediate firing to the room temperature.

  In this way, in the intermediate heat treatment step C, by rapidly lowering the temperature from the intermediate firing temperature to room temperature within 1 hour, the particles serving as magnetic flux pinning points uniformly dispersed in the precursor are fixed finely, and the superconducting layer No coarsening occurs during firing.

  The rapid cooling process in the intermediate heat treatment step C is performed using the rapid cooling device 29, but is not limited thereto. For example, the atmospheric gas supply device may have a function as the quenching device 29. In this case, the quenching device 29 as the atmospheric gas supply device cools the dry gas itself supplied during the intermediate firing process into a cooling gas. By sending this cooling gas into the furnace body 22, the firing temperature for the precursor of the tape-shaped wire 10 in the furnace body 22 is 20 [° C.] or more per minute from the temperature maintained in the intermediate firing to the room temperature. Cooling. According to this configuration, it is not necessary to provide the quenching device 29 separately from the atmospheric gas supply device in the heat treatment device 20.

  It is preferable that the heat treatment apparatus 20 performs the main firing treatment step D continuously to the intermediate heat treatment step C (specifically, the rapid cooling step C2). That is, as shown in FIG. 5, the heat treatment apparatus 20 heats up to the main baking treatment temperature immediately after the rapid cooling from the intermediate baking treatment temperature maintained at a constant temperature to room temperature (immediately after the rapid cooling step C2) for a predetermined time. Maintain constant temperature (main baking process). For example, as the rapid cooling step C2, the precursor of the tape-shaped wire 10 is rapidly cooled from an intermediate firing temperature of 600 [° C.] to 20 [° C.] to 30 [° C.] as a room temperature, Heat to a firing temperature of 800 [° C].

  In this way, after the precursor is subjected to intermediate firing in the intermediate firing treatment and rapidly cooled, then the main firing treatment is continuously performed, and after the growth of the magnetic flux pinning point is stopped by quenching in the intermediate firing treatment. And can be crystallized.

  Further, since the intermediate heat treatment step C (intermediate firing step C1 and rapid cooling step C2) and the main firing treatment step D are performed on the precursor by the batch type heat treatment apparatus 20, it is effective in the sealed furnace body 22. Firing, rapid cooling, and firing can be performed. Thereby, an oxide superconducting wire having a superconducting layer having excellent superconducting characteristics can be stably produced. Furthermore, since the heat treatment apparatus 20 is a batch method, it can easily control the temperature and pressure as well as control the atmosphere in the furnace as compared with the case of firing by the reel-to-reel method. Become. Thereby, a stable superconducting layer can be formed, and an oxide superconducting wire can be produced in a short time.

  Further, according to the present embodiment, the manufactured RE-based oxide superconducting wire (corresponding to a tape-like wire) 10 was measured by changing the magnetic field application angle in the case of 77 [K] and 3 [T]. The ratio between the maximum value and the minimum value of the superconducting characteristic Ic value is within 1.5 times. Compared with the conventional technique, the change in the superconducting characteristic Ic due to the magnetic field application angle is small.

  As described above, according to the present embodiment, the precursor formed by temporary firing on the tape-shaped composite substrate is subjected to the intermediate firing treatment at a temperature lower than the firing temperature before the firing treatment. Compared to natural cooling, cool to room temperature. Thereby, the magnetic flux pinning points in the precursor (that is, the superconducting layer) are fixed in a dispersed state with a fine and uniform size. As a result, the magnetic flux pinning point is not coarsened, and the superconducting characteristics in the magnetic field are not significantly reduced. That is, unlike the prior art, it is possible to obtain superconducting characteristics that are less dependent on the magnetic field application angle.

<Example 1>
The RE-based oxide superconducting wire shown in FIG. 1 was manufactured by the RE-based oxide superconducting wire manufacturing method of the present embodiment using the heat treatment apparatus 20. The RE-based oxide superconducting wire contains a GdZrO layer, an MgO layer, a LaMnO ₃ layer, and a CeO layer in order as an intermediate layer on the substrate, and contains 2 wt% Zr as a magnetic flux pin on the composite substrate. Y _0.77 Gd _0.23 Ba _{1.5 + z} Cu ₃ O _x Superconducting layer (superconducting layer thickness 1.5 [μm]).

  In Example 1, first, a coating process A for applying a superconducting raw material solution to a composite substrate, a temperature gradient of 2 [° C./min], a maximum heating temperature (temporary baking treatment temperature) of 400 [° C.], and a holding time of the maximum heating temperature. The precursor of the superconducting layer was formed in the pre-baking treatment step B in which the pre-baking treatment was performed under the condition of 1 [hour].

  In the intermediate firing step C1 of the intermediate heat treatment step C, the precursor is heated to a maximum heating temperature (intermediate firing temperature) of 600 [° C.] with a temperature gradient of 3 [° C./min] and held for 5 hours. Then, an intermediate baking treatment was performed. Then, in the rapid cooling step C2, the cooled dry gas is introduced into the furnace body 22 and continuously cooled for 19 minutes so as to decrease by 30 [° C./min], and the temperature of the precursor is changed from the intermediate firing temperature to room temperature. Quenched until.

  After the firing treatment and the rapid cooling treatment are performed in the intermediate heat treatment step C under such heat treatment conditions, in the main firing treatment step D, the precursor after the rapid cooling is heated from room temperature to the maximum heating temperature at a temperature gradient of 3 [° C./min]. (Main baking processing temperature) The main baking processing was performed by heating to 800 degreeC and hold | maintaining for 12 hours, and the superconducting layer was formed.

<Comparative Example 1>
In the manufacturing method of Example 1, the RE-based oxide superconducting wire was formed by performing the main baking treatment without cooling.
<Comparative example 2>
In the production method of Example 1, the RE-based oxide is obtained by leaving the precursor after the firing treatment in the intermediate heat treatment step C without performing the rapid cooling step, and performing the main firing treatment after naturally cooling to room temperature. A superconducting wire was formed.

<Reference Example 1>
In the production method of Example 1, in the rapid cooling step C1 of the intermediate heat treatment step C, cooling was performed for about 2 hours (so that the temperature decreased by 4.75 [° C./min]) from the intermediate firing temperature to room temperature.
<Reference Example 2>
In the production method of Example 1, in the rapid cooling step C1 of the intermediate heat treatment step C, the sample was rapidly cooled so as to reach room temperature in about 10 minutes from the intermediate firing temperature (4.75 [° C./minute]).

Thus, in the oxide superconducting wire obtained under these conditions, the superconducting characteristic Ic value at 77 [K], 0 [T] and the superconducting characteristic Ic value in a magnetic field environment of 77 [K], 3 [T] Table 1 shows the maximum and minimum ratio Icmax / Icmin when the application angle dependency was measured, and the maximum particle diameter of BaZrO ₃ dispersed in the superconducting layer.

  As is clear from comparison between Example 1 and Comparative Example 1 in Table 1, between the pre-baking and the main baking, the precursor that was rapidly cooled after the intermediate baking treatment was not cooled after the intermediate baking. Compared with the case where the main baking treatment is performed by raising the temperature from the intermediate baking temperature to the main baking temperature, the maximum size of the particle size of BZO can be reduced. Example 1 is compared with the oxide superconducting wire of Comparative Example 1. Thus, the superconducting characteristics under a magnetic field application environment are excellent.

In Table 1, as is clear from the comparison between Example 1 and Comparative Example 2, in the intermediate heat treatment step C, after the intermediate heat treatment, the one that is rapidly cooled has a particle size of BZO as compared with the case of natural cooling. The maximum size could be reduced, and Example 1 was superior in superconducting characteristics in a magnetic field application environment as compared with the oxide superconducting wire of Comparative Example 1.
Further, from comparison between Example 1 and Comparative Examples 1 and 2, Comparative Examples 1 and 2 both have a larger maximum particle size of BZO than Example 1, and the ratio of Icmax / Icmin is 1.5. Over. On the other hand, in Example 1, Icmax / Icmin is within 1.5.

  Further, as is clear from the comparison between Example 1 and Reference Example 1 and Reference Example 2, in the intermediate heat treatment step C, the shorter the time for cooling to room temperature after the intermediate heat treatment, the larger the size of the BZO particle size. Can be made smaller.

  The method for producing an oxide superconducting wire according to the present invention has an effect of ensuring stable and high superconducting characteristics in a magnetic field application environment, and is useful as a method for producing an oxide superconducting wire disposed in a magnetic field application environment. is there.

DESCRIPTION OF SYMBOLS 10 RE type oxide superconducting wire 11 Metal substrate 12 Intermediate layer 12a 1st intermediate layer 12b 2nd intermediate layer 12c 3rd intermediate layer 12d 4th intermediate layer 13 Superconducting layer 13a Magnetic flux pinning point 14 Stabilization layer 15 Composite substrate 20 Heat processing apparatus 22 furnace body 23 electric heater 24 heat treatment furnace 25 rotating body 25a cylindrical body 25b through hole 25c lid body 27 discharge pipe 28 supply pipe 29 quenching apparatus C1 intermediate firing process C2 quenching process

Claims (7)

After applying the superconducting raw material solution on the intermediate layer formed on the substrate, a superconducting precursor is formed by subjecting it to a pre-firing treatment, and a main firing treatment is performed on the superconducting precursor, thereby providing a REBayCu3Oz system ( RE represents a tape-like RE-based oxide superconducting wire of RE, which represents at least one element selected from Y, Nd, Sm, Eu, Gd, and Ho.
The superconducting raw material solution contains RE, Ba and Cu, and Zr, Sn, Ce, Ti, Hf, Nb which forms a magnetic flux pinning point in a mixed solution in which the molar ratio of Ba is in the range of y <2. A solution containing at least one additive element,
After the temporary baking treatment and before the main baking treatment, an intermediate for baking the superconducting precursor while maintaining a temperature higher than the baking temperature in the temporary baking treatment and lower than the baking temperature in the main baking treatment. Heat treatment,
The method for producing a RE-based oxide superconducting wire characterized in that the intermediate heat treatment is performed within a period of 1 hour for rapid cooling from the firing temperature held for the superconducting precursor to room temperature. The method for producing a RE-based oxide superconducting wire according to claim 1, wherein a firing temperature of the intermediate heat treatment is 400 ° C to 700 ° C.   3. The method for producing an RE-based oxide superconducting wire according to claim 1 or 2, wherein the intermediate heat treatment is rapidly cooled from a held temperature to room temperature at 20 [deg.] C./min or more. The intermediate heat treatment is a rapid cooling from the firing temperature held to room temperature in a dry gas atmosphere not containing water vapor gas,
The main baking treatment is performed consecutively with the intermediate heat treatment, and main baking is performed on the superconducting precursor immediately after being rapidly cooled.
The method for producing an RE-based oxide superconducting wire according to any one of claims 1 to 3. By cooling the dry gas that forms the dry gas atmosphere, the dry gas is rapidly cooled from the firing temperature to room temperature,
The manufacturing method of RE type oxide superconducting wire of Claim 4. In the intermediate heat treatment, the superconducting precursor is baked in a water vapor gas atmosphere,
The method for producing a RE-based oxide superconducting wire according to any one of claims 1 to 5, wherein the water vapor gas is introduced from a temperature lower than a temperature maintained in the intermediate heat treatment.   The method for producing a RE-based oxide superconducting wire according to any one of claims 1 to 6, wherein the intermediate heat treatment and the main baking treatment are performed in a batch-type electric furnace.

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