JP2019102178A - Manufacturing method of superconducting wire rod - Google Patents

Abstract

To provide a superconducting wire rod having a superconducting material having desired high critical current value even under high magnetic field environment.SOLUTION: There is provided a manufacturing method of a superconducting wire rod having an application process for applying a superconductive raw material solution onto a substrate via an intermediate layer, a calcination process for conducting a calcination treatment on the applied superconducting raw material solution to produce a calcinated film, and a main burning process for conducting a main burning treatment on a superconducting precursor produced by laminating the calcination film by repeating the application process and the calcination process to produce a superconducting layer, in which the superconducting raw material solution is manufactured by mixing a compound having 20 carbon atoms and containing Hf in an organic metal complex solution containing RE, wherein RE is at least one or more kind of element selected from a group consisting of Y, Nd, Sm, Gd, Dy, Eu, Er, Yb, Pr and Ho, Ba and Cu, and Hf is produced as a magnetic flux pinning point in the superconducting layer by the calcination treatment or the main burning treatment.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of manufacturing a superconducting wire.

The oxide superconductor has a critical temperature Tc higher than that of a metal-based superconductor such as Nb ₃ Sn or Nb ₃ Al. Therefore, oxide superconductors are used for superconducting applied devices such as superconducting magnets, superconducting power transmission cables, current limiting devices, generators, motors, transformers, etc., superconducting applied devices such as transformers, motors, etc., and these are used as liquid nitrogen temperatures. It can be operated at (77 K).

  In order to use an oxide superconductor for the above-mentioned superconducting applied equipment, it is necessary to manufacture a long wire having a high critical current density Jc and a high critical current value Ic. In order to obtain such a long wire, a structure is known in which an oxide superconductor is formed on a substrate which is a metal substrate from the viewpoint of strength and flexibility.

As an oxide superconductor, REBa ₂ Cu ₃ O _z system (here, z = 6.2 to 7 and RE is at least one selected from Y, Nd, Sm, Eu, Gd and Ho) In the following, “REBCO” (referred to simply as RE system) oxide superconductor has a critical temperature higher than the liquid nitrogen temperature (77 K). RE-based oxide superconductors have high critical current characteristics under self-magnetic field (for example, critical current value Ic 500 A / cm-width [77 K, at self-magnetic field]) when deposited to have good crystal orientation. Indicates

  The MOD method (Metal Organic Deposition Processes: metal organic acid salt deposition method) is known as a method of producing RE-based oxide superconductors. In this MOD method, a metal organic acid salt is thermally decomposed, and a solution in which an organic compound containing a metal component constituting a superconductor is uniformly dissolved is applied on a substrate and then heated to be thermally decomposed. Is a method of forming a thin film on a substrate. The MOD method is a non-vacuum process, enables high-speed film formation at low cost, and can obtain a high critical current density Jc, and thus has an advantage suitable for manufacturing a long tape-shaped oxide superconducting wire. .

  In the MOD method, when a metal organic acid salt, which is a starting material, is pyrolyzed, a carbonate of an alkaline earth metal (such as Ba) is usually formed, but an oxide superconductor by a solid phase reaction via the carbonate Requires the high temperature heat treatment of 800 ° C. or more. Furthermore, when the film is thickened, it is difficult to control the crystal growth rate because nucleation for crystal growth also occurs from a portion other than the substrate interface, and as a result, the in-plane orientation is excellent. That is, there is a problem that it is difficult to obtain a superconducting film (superconductor) having a high critical current density Jc.

  In order to solve these problems, as a method of forming an RE-based oxide superconductor without passing through a carbonate, an organic acid salt containing fluorine (eg, TFA salt: trifluoroacetate salt) is used as a starting material, There is known a TFA-MOD (Trifluoro Acetate Metal Organic Deposition) method in which a superconductor is obtained via decomposition of fluoride by performing heat treatment under control of water vapor partial pressure in the atmosphere.

  When a superconducting wire is used under an applied magnetic field environment such as a superconducting magnet, the superconducting wire has a high superconducting property (for example, a criticality of 30 A / cm-width or more under an applied magnetic field of 3 T) with respect to any magnetic field application angle. It is desirable to have a current value Ic [A / cm-width]).

  Therefore, in the TFA-MOD method, in order to prevent the movement of the quantized magnetic flux in the superconductor, the applicant of the present applicant has made it possible to use a nano-sized three-dimensional flux pinning point effective for any magnetic field direction. Has previously filed a corresponding method (see Patent Document 1).

In Patent Document 1, an organic metal salt such as Zr, which is an element that does not react with a superconductor, is added to a superconducting raw material solution used when forming a calcined film in the TFA-MOD method. Then, in the process of the reaction heat treatment in the firing step, the fine particles of BaZrO ₃ (BZO), which is a non-superconducting substance, are uniformly dispersed as magnetic flux pinning points in the superconducting thin film by reacting with Ba constituting the superconductor.

  In recent years, the required performance of the oxide superconducting wire used for a superconducting applied device is gradually increasing, and a material to be a magnetic flux pinning point is being reconsidered for further characterization in a magnetic field.

As a material to be a magnetic flux pinning point other than BZO, as shown in Patent Document 2, a superconducting wire formed using a hafnium oxide compound MHfO ₃ (wherein, M represents Ba, Sr or Ca) is known. (See Patent Document 2).

In this patent document 2, when a superconductor is formed by PLD (Pulse Laser Deposition: pulse laser deposition), a hafnium oxide compound MHfO ₃ (BHO) is mixed.

JP, 2009-164,010, A International Publication No. 2014/103995

  By the way, since the MOD method is a simple process with the PLD method and has a high manufacturing speed and can reduce cost without increasing the equipment cost when manufacturing a long oxide superconducting wire, it is possible to reduce BHO by MOD It has been studied to apply to the deposition of superconductors by

  Patent Document 2 describes that a superconducting layer in which BHO is dispersed as a magnetic flux pinning point can be formed by the MOD method.

  However, when BHO is applied in the MOD method, it is necessary to add BHO as an organic salt to the superconducting raw material solution, and unlike the PLD method, BHO is a powder to be a superconductor to be sintered as a target to be laser irradiated. Can not be mixed simply.

  The present invention has been made in view of the foregoing, and it is an object of the present invention to provide a method of manufacturing a superconducting wire including a superconducting layer having a desired high critical current value even in a high magnetic field environment.

One aspect of the method of manufacturing a superconducting wire of the present invention is
A coating step of applying a superconducting raw material solution via an intermediate layer on a substrate, a temporary baking step of forming a temporary baked film by subjecting the coated superconducting raw material solution to a temporary baking treatment, the coating step and the temporary baking A method of manufacturing a superconducting wire, comprising: performing a main baking process on a superconducting precursor generated by laminating the pre-sintered film by repeating the process and the main baking process of generating a superconducting layer;
The superconducting raw material solution contains RE (RE is at least one element selected from the group consisting of Y, Nd, Sm, Gd, Dy, Eu, Er, Yb, Pr and Ho), Ba and Cu. The organometallic complex solution is mixed with a compound having 20 or less carbon atoms containing Hf (hafnium),
The Hf is generated as a magnetic flux pinning point in the superconducting layer by the pre-baking process or the main-baking process.

  According to the present invention, it is possible to realize a superconducting wire provided with a superconducting layer having a desired high critical current value even in a high magnetic field environment.

The figure to be used for the explanation of the oxide superconducting wire of the embodiment according to the present invention The figure explaining the manufacturing method of the oxide superconducting wire of the embodiment concerning the present invention

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

Manufacturing method of the tape-shaped RE-based oxide superconducting wire according to the embodiment of the present invention, a tape-shaped REBa _y Cu ₃ O _z system (RE were selected Y, Nd, Sm, Eu, from Gd and Ho An oxide superconducting wire (herein referred to as a YBCO superconducting wire), which exhibits at least one or more elements, is manufactured.

<Oxide superconducting wire>
First, an example of the 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 the method of 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 sequentially 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 the first intermediate layer 12a, the second intermediate layer 12b, the third intermediate layer 12c, the fourth intermediate layer 12d, and the fifth intermediate layer 12e, but the number of layers constituting the intermediate layer is one. It may be composed of layers, two layers, three layers and four layers, or may be composed of six or more layers.

  The tape-shaped metal substrate 11 is, for example, nickel (Ni), a nickel alloy, stainless steel or silver (Ag). Here, the metal substrate 11 is a crystal grain non-orientation, heat resistant high strength metal substrate, and Ni-Cr (specifically, Ni-Cr-Fe-Mo-based Hastelloy (registered trademark) B, C, X) Cubic Vickers hardness (Hv) represented by materials such as W-Mo, Fe-Cr (for example, austenitic stainless steel), Fe-Ni (for example, nonmagnetic composition type), etc. ) = 150 or more nonmagnetic alloys. Here, Hastelloy (registered trademark) tape is applied as the metal substrate 11, but Inconel (registered trademark) may be used. The thickness of the metal substrate 11 is, for example, 30 to 200 μm, and preferably 100 μm or less.

  In the present embodiment, the intermediate layer 12 sequentially forms the first intermediate layer 12a, the second intermediate layer 12b, the third intermediate layer 12c, the fourth intermediate layer 12d, and the fifth intermediate layer 12e on the metal substrate 11. It is comprised by laminating | stacking.

The first intermediate layer 12 a is an Al ₂ O ₃ layer formed by sputtering on the tape-shaped metal substrate 11. In the present embodiment, the first intermediate layer 12a may be a layer made of Gd ₂ Zr ₂ O ₇ (GZO), yttrium stabilized zirconia (YSZ) or the like, instead of Al ₂ O ₃ . In addition, the first intermediate layer 12a may be deposited by an RF-sputtering method, a MOD method, or the like. The first intermediate layer 12a is a bed layer, has high heat resistance, is a layer for reducing interfacial reactivity, and is used to obtain the orientation of a film disposed thereon. The thickness of the first intermediate layer 12a is about 1000 nm.

Specifically, the Al ₂ O ₃ layer as the first intermediate layer 12 a functions as a diffusion prevention layer that suppresses the diffusion of elements from the metal substrate 11. An amorphous LaMnO ₃ layer is formed as a second intermediate layer 12 b on the first intermediate layer 12 a by a sputtering method such as an RF sputtering method or an ion beam sputtering method. The film thickness of the LaMnO ₃ layer which is the second intermediate layer 12 b is, for example, 5 to 100 nm. When the film thickness of the LaMnO ₃ layer which is the second intermediate layer 12b is 5 nm or less, the continuity of the film is poor and sufficient orientation can not be obtained, and when the film thickness is 100 nm or more, the unevenness of the film surface becomes large, This is because the orientation of the MgO layer as the third intermediate layer 12c stacked in contact with the LaMnO ₃ layer which is the two intermediate layer 12b is inhibited. The LaMnO ₃ layer as the second intermediate layer 12 b is formed on the first intermediate layer 12 a within the range of more than 0 ° C. and 150 ° C. or less. This deposition temperature of LaMnO _3, when a 0.99 ° C. or less, LaMnO ₃ is a amorphous, when forming a deposition temperature of LaMnO ₃ at a temperature higher than 0.99 ° C., LaMnO ₃ is easy to crystallize It is because it inhibits the orientation of the MgO layer which is the third intermediate layer 12c in contact with the LaMnO ₃ layer.

A third intermediate layer 12c made of MgO is formed on the second intermediate layer 12b by an IBAD (Ion Beam Assisted Deposition) method. Note that in the IBAD method, while irradiating ions to the substrate to be film-formed from an oblique direction, the volume of particles generated from the target on the substrate (here, on the second intermediate layer 12c which is a LaMnO ₃ layer) (Here, the MgO layer is deposited). On the third intermediate layer 12c, a fourth intermediate layer 12d of LaMnO ₃ is formed by sputtering. In the present embodiment, the MgO layer as the third intermediate layer 12 c is configured to be sandwiched between the LaMnO ₃ layers at the top and the bottom. Furthermore, on the third intermediate layer 12c, CeO ₂ is vapor-deposited here by a sputtering method (or PLD method), and a fourth intermediate layer 12e as a cap layer of all-axis orientation is formed. A layer above the MgO layer, in the present embodiment, the fourth intermediate layer (LaMnO ₃ layer) 12 d and the fifth intermediate layer (CeO ₂ layer) 12 e prevent the reaction with the superconducting layer 13. It also works as

The CeO ₂ layer as the fifth intermediate layer 12e is known as one of the most excellent intermediate layers because it has good matching with the RE-based superconducting layer 13 and has low reactivity with the superconducting layer 13 .
The fifth intermediate layer 12e may be formed on the LaMnO ₃ layer as the fourth intermediate layer 12d by PLD (Pulsed Laser Deposition: Pulsed Laser Deposition) method instead of the sputtering method. The fifth intermediate layer 12e is, Ce-Gd-O film was added a predetermined amount of Gd in CeO _2, or a portion other metal atom or Ce-M-O systems that have been partially replaced by metal ions of Ce It may be a film made of an oxide. When Gd is added to CeO ₂ , although the generation of cracks can be suppressed, there arises a problem that the element diffusion from the metal substrate 11 can not be suppressed. However, in the present embodiment, since the Al ₂ O ₃ layer as the first intermediate layer 12 a suppresses the element diffusion from the metal substrate 11, the layer above the Al ₂ O ₃ layer as the first intermediate layer 12 a is Gd can be added to the CeO ₂ layer as a certain fifth intermediate layer 12 e. The superconducting layer 13 is formed on the fourth intermediate layer 12d by the MOD method. In addition, the intermediate layer 12 is formed on the metal substrate 11, and the object on which the superconducting layer is formed in contact with the upper surface is referred to as a substrate 15 for convenience.

  The MOD method is a method of forming a thin film, which is a superconducting layer, on the substrate 15 by heating and thermally decomposing the metal organic acid salt on the substrate 15. Specifically, in the MOD method, first, a superconducting raw material solution in which an organic compound of a metal component is uniformly dissolved is applied onto the substrate 15. Then, the substrate 15 on which the solution is applied is subjected to a temporary baking heat treatment to form an amorphous precursor, and thereafter, the crystallization heat treatment (main baking heat treatment) is applied to crystallize the precursor to obtain an oxide superconductor. Form.

  On the superconducting layer 13 is provided a stabilization layer 14 which is a noble metal such as silver, gold, platinum or an alloy thereof and a low resistance metal. The stabilization layer 14 is formed directly on the superconducting layer 13 so that the performance deterioration caused by the reaction by the direct contact of the superconducting layer 13 with a noble metal such as gold, silver or the like or an alloy thereof is caused. To prevent. In addition to this, the stabilization layer 14 disperses the heat generated by the accident current or the alternating current to prevent the destruction and the performance deterioration due to the heat generation. The thickness of the stabilization layer 14 here is 10 to 30 μm.

The superconducting layer 13 is a 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). The layer of the high temperature superconducting thin film of The superconducting layer 13 is also referred to as an yttrium-based oxide superconductor. The superconducting layer 13 is, for example, Y of RE. Gd and the _{Y 0.77 Gd 0.23 Ba y Cu 3} O z ( hereinafter, also referred to as "YGdBCO") + and Hf pins and the superconducting layer. Here, y is 1.5 + y1, y1 is the amount of Ba that reacts with Hf, and the composition ratio of the superconducting raw material solution to be the target for forming the superconducting layer 13 (RE: Ba: Cu = 1: 1.5: 3 The Ba correction is performed by adding to the specified amount of Ba satisfying () to be smaller than 2. In the present specification, the superconducting raw material solution composition ratio (RE: Ba: Cu) refers to the atomic concentration ratio (molar ratio) of RE, Ba, and Cu. In the MOD method, the composition ratio of the formed superconducting layer can be controlled by adjusting the composition ratio of the superconducting raw material solution.

  As described above, by performing Ba correction, high concentration Zr can be added to increase the magnetic flux pinning point and improve the characteristics in the magnetic field without lowering the critical current value Ic. In this manner, for example, as a superconducting wire, it is possible to realize a composition that can anticipate Icmin = 30 A / cm-w (77 K @ 3 T) with a superconducting film thickness of 2 μm or less.

  The superconducting layer 13 is subjected to a calcination heat treatment at a temperature range of 400 to 500 [° C.] in an atmosphere with a water vapor partial pressure of 3 to 76 Torr and an oxygen partial pressure of 300 to 760 Torr on the third intermediate layer 12c. Is desirable. In addition, the superconducting layer 13 may be subjected to main heat treatment in a temperature range of 700 to 900 [° C.] in an atmosphere with a water vapor partial pressure of 30 to 600 [Torr] and an oxygen partial pressure of 0.05 to 1 [Torr]. preferable.

  Here, the superconducting layer 13 has a superconducting raw material solution composition ratio RE (Y + Gd): Ba: Cu = 1 so as to satisfy a target superconducting raw material solution composition ratio (RE: Ba: Cu = 1: 1.5: 3). : Artificial pin particles (hereinafter referred to as "magnetic flux pinning point") 13a which is an effective oxide particle formed by adding Hf as an additive element to 1.5 + y1: 3 (y1 <0.5) .

The magnetic flux pinning point (artificial pin particles) 13 a is configured with a particle size of 50 nm or less containing Hf uniformly dispersed in the superconducting layer 13. Here, the magnetic flux pinning points 13a in the superconducting layer 13 are oxide particles as control compounds such that the particle diameter of 10nm or less, in the present embodiment, a BaHfO _3. The particle diameter of the magnetic flux pinning point 13a is more effective when it is closer to the magnetic flux line size.

The number n of magnetic flux pinning points is preferably 1.0 × 10 ³ pieces ≦ n <1.0 × 10 ⁷ pieces per 1 μm ³ in the superconducting layer 13. If the number of particles is large, more magnetic flux can be pinned, which is effective. However, if the above range is exceeded, the effect of volume reduction of the superconductor becomes large, thereby inhibiting the superconducting current and eventually the superconducting characteristics Will reduce the For example, when 1.0 × 10 ⁷ or more particles are present per 1 μm ^{3, the} volume fraction will exceed 60% even if the particle diameter of the oxide particles is 5 nm, Reduce the superconducting properties.

  The amount of Hf added as an additive element needs to be 30 wt% or less, and in particular preferably 1 wt% to 10 wt% with respect to the entire superconducting layer. The reason why 1 wt% to 10 wt% is desirable is that in order to improve the characteristics in a magnetic field, it is more effective to add more additive element since more magnetic flux can be pinned. However, if the amount of Hf added is 10 wt%, that is, the volume fraction exceeds 30 vol%, the effect of decreasing the volume of the superconductor to be formed becomes large, and since the criticality that particles can exist alone is exceeded, the pinning effect It is because it causes the deterioration of the superconducting current. Furthermore, if the above range is exceeded, the precipitates are aggregated to inhibit the superconducting current. The ratio of Hf to Ba at the magnetic flux pinning point 13a is Hf: Ba = 1: 1.

The BaHfO ₃ formed as a magnetic flux pinning point inside the superconducting layer 13 exists not only in the film surface direction but also in the film thickness direction at nanosizes and nanospaces, and these effectively pin the magnetic flux and the magnetic field The anisotropy of Jc with respect to the applied angle can be significantly improved. Also, in order to control the size, density and dispersion of BaHfO ₃ , not only the introduction amount of Hf-containing octylate etc., but also the oxygen partial pressure at the time of calcination heat treatment and main heat treatment (crystallization heat) treatment, It becomes possible by control of steam partial pressure and calcination temperature. By performing these optimizations, it becomes possible to introduce an effective flux pinning point 13a.

  The superconducting raw material solution to be the superconducting layer 13 is a mixed solution in which a metal organic acid salt containing a metal element or an organic metal compound is dissolved in an organic solvent. Examples of the organic solvent include lower alcohols such as methanol, ethanol, propanol and butanol, toluene and the like and mixed solvents thereof.

  In the present embodiment, the superconducting raw material solution contains RE (RE represents one or more elements selected from Y, Nd, Sm, Eu, Gd and Ho), an organometallic complex solution containing Ba and Cu (A mixed solution) and an Hf additive (specifically, hafnium octylate) which is a compound having 20 or less carbon atoms containing Hf having high affinity with Ba.

  Here, the mixed solution in the superconducting raw material solution is a solution in which a metal organic acid salt or an organic metal compound containing Y, Ba, and Cu in a predetermined molar ratio is dissolved in an organic solvent. When the molar number is Y: Ba: Cu = 1: y: 3, a superconducting raw material solution having a Ba molar ratio within the range of y <2 is used. In this case, in order to obtain high Jc and Ic values, the Ba molar ratio y in the superconducting raw material solution is preferably in the range of 1.0 ≦ y ≦ 1.8, more preferably Ba in the raw material solution. The molar ratio y is in the range of 1.3 ≦ y ≦ 1.7. Thereby, segregation of Ba can be suppressed, and as a result, precipitation of Ba-based impurities at grain boundaries is suppressed. Therefore, the occurrence of cracks is suppressed and the electrical connection between the crystal grains is improved, and by forming the superconducting film by the MOD method, a tape-like oxide excellent in superconducting characteristics having a high speed and uniform thick film The superconductor can be easily manufactured.

  Examples of the metal organic acid salt constituting the superconducting raw material solution include octylate of each element, naphthenate, neodecanoate, trifluoracetic acid acetate, etc., and they are uniformly dissolved in one or more organic solvents. Any material that can be applied onto the substrate 15 can be used.

  In this embodiment, the molar ratio y = 1.5 + y1 of Ba contained in the mixed solution is in the range of y <2 by using the organometallic complex solution. In addition, it can be manufactured by dispersing oxide particles (BaHf0) having a particle diameter of 50 nm or less, preferably 10 nm or less, containing Hf in the mixed solution as the magnetic flux pinning point 13a.

In addition, it is preferable to add and use the additive of (d) to the mixed solution containing the solution of following (a)-(c) as a superconducting raw material solution.
(A) RE-containing organometallic complex solution: a solution containing one or more of RE-containing propionic acid, trifluoroacetate, naphthenate, octylate, levulinate, levulinate, neodecanoate and acetate In particular, a trifluoroacetate salt solution containing RE is desirable.
(B) Organometallic complex solution containing Ba: solution of trifluoroacetate salt containing Ba (c) organometal complex solution containing Cu: naphthenic acid salt containing Cu, octylate, levulinate, neodecanoate, A solution (d) Hf additive containing any one or more of acetates; (a solution of an organometallic complex having 20 or less carbon atoms containing Hf having high affinity with Ba, more preferably 10 carbon atoms containing Hf Organic metal complex solution below

Here, in the metal complex solution containing RE of the above (a), the RE in this solution may be formed of one or more kinds of RE salts of carboxylic acids having 3 to 8 carbon atoms which do not contain a ketone group. . For example, RE in the metal complex solution of (a) may be an RE salt of propionic acid, and is preferably yttrium propionate having no fluorine atom in the yttrium salt. In addition, when the carbon atom number of the carboxylic acid which derives RE salt is smaller than 3, sufficient solubility can not be acquired and a uniform oxide superconducting thick film can not be obtained. Further, when the number of carbon atoms is more than 8, the amount of CO ₂ gas generated during the pre-baking heat treatment is increased, so that the coating film tends to scatter, making it difficult to obtain a high-quality oxide superconducting thick film. When the RE salt is Y-propionic acid containing no fluorine atom, Ba-TFA, Cu-2-ethylhexanoic acid, and components of these Y-propionic acid, Ba-TFA, Cu-2-ethylhexanoic acid It becomes a mixed solution containing the organic solvent which dissolves. At this time, the organic solvent may contain a solubilizer having an amino group that dissolves propionic acid (here, tetramethylurea). Examples of the amino group include tetramethylurea, n-octylamine, propylamine and the like. In particular, tetramethylurea is preferable because it is a high boiling point solvent.

Specifically, the Cu component contained in (c) is a copper salt of a branched saturated aliphatic carboxylic acid having 6 to 16 carbon atoms, and a copper of an alicyclic carboxylic acid having 6 to 16 carbon atoms. It consists of one or more types chosen from the group which consists of salt. The copper salt is L ² ₂ Cu · pH ₂ O (wherein L ² is a branched saturated aliphatic carboxylic acid residue having 6 to 16 carbon atoms or an alicyclic carboxylic acid residue having 6 to 16 carbon atoms , P is 0 or a possible hydration number), and is usually obtained as an anhydrous form or 1-2 hydrate. Examples of the branched saturated aliphatic carboxylic acid having 6 to 16 carbon atoms from which the copper salt is derived include 2-ethylhexanoic acid, isononanoic acid, neodecanoic acid and the like, and the copper salt includes 6 to 16 carbon atoms. Examples of derivatives of the cycloaliphatic carboxylic acid copper salt include cyclohexane carboxylic acid, methyl cyclohexane carboxylic acid, naphthenic acid and the like. Among these carboxylic acids, those derived from natural products such as naphthenic acid may contain as components the ones other than the number of carbon atoms specified in the present invention or those having no branched or alicyclic group. In the present invention, generally, commercially available products can be used as they are, regardless of the presence or absence of these components.

In the present embodiment, the superconducting layer of the oxide superconducting wire of the present embodiment is produced by the TFA-MOD method, and (d) the Hf additive needs to be added to the superconducting raw material solution to be fired. Therefore, the (d) Hf additive needs to be a compound (organic metal complex solution), and when the carbon atom is 40 or more, it is not decomposed at the time of firing and is discharged as a large number of organic residue. The discharged organic residue becomes an air gap in the superconducting layer 13 to be formed. Since no current flows in the air gap, the critical density Jc decreases. In addition, the critical current value Ic and the critical current density Jc decrease. In addition, when there is a punctuation mark, physical damage such as a crack is also likely to occur. As the Hf additive, only Hf is sufficient, and the smaller the number of carbon atoms, the smaller the amount of carbon dioxide that is decomposed and burned out as CO ₂ when the superconducting raw material solution is fired, or the decomposed and formed deposit The amount of material can be reduced.

  In the present embodiment, (d) the Hf additive is hafnium octylate, and the number of carbon atoms per one hafnium atom is eight. Also, assuming that the Cu-containing organometallic complex solution is a Cu-containing octylate salt, the Hf additive has high affinity with the Cu-containing organometallic complex solution in the mixed solution, since it is the same salt. It is easy to mix when adding the Hf additive to the mixed solution.

Further, in the oxide superconducting wire 10, in the RE-based superconducting layer in which the Ba concentration is reduced, the Hf-containing magnetic flux pinning point 13a can be finely dispersed artificially in the superconducting layer. For this reason, the magnetic field application angle dependence (Jc _{, min} / Jc _{, max} ) of Jc has a small magnetic field characteristic having a high Jc at a high magnetic field, and the magnetic field application angle dependence of Jc (Jc _{, min} / Jc) _{, Max} ) can also be significantly improved. Therefore, in addition to the self magnetic field, the magnetic flux can be effectively pinned in any magnetic field or any magnetic field application angular direction to obtain an isotropic Jc characteristic, thereby achieving high superconductivity (critical current density Jc [MA / cm ² ) and the critical current Ic [A / cm-width]) can be secured.

<Method of manufacturing superconducting wire>
An RE-based oxide superconducting wire 10 having such a superconducting layer 13 is manufactured as shown in FIG.

  FIG. 2 is a schematic view for explaining a method of manufacturing an oxide superconducting wire according to the present embodiment.

  In the present embodiment, the oxide superconducting wire 10, which is a YG dBCO oxide superconducting wire, is manufactured by the MOD method. In the production of the oxide superconducting wire 10, after a solution of a superconducting raw material is applied to a substrate, a pre-baking process is performed to form an amorphous superconducting precursor (hereinafter referred to as a "precursor"). Next, after the pre-sintering process, the precursor including the magnetic flux pinning in the superconducting layer is subjected to the main-sintering process to manufacture a RE-based (YG dBCO) oxide superconducting wire. The details will be described below.

  First, the first intermediate layer 12a, the second intermediate layer 12b, the third intermediate layer 12c, and the third intermediate layer 12c are sequentially formed on the tape-like substrate, for example, a Ni alloy substrate (base material) 11 (see FIG. 1). The fourth intermediate layer 12 d and the fifth intermediate layer 12 e are stacked and film-formed to form the substrate 15.

  The superconducting raw material solution is coated on the 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 containing an organic acid salt containing fluorine as a starting raw material is coated on the substrate 15 (the intermediate layer 12 formed on the metal substrate 11) by dip coating. Be done.

The superconducting raw material solution is prepared by mixing Y-TFA salt (trifluoroacetic acid salt), Ba-TFA salt and Cu-naphthenic acid salt in an organic solvent as a mixed solution containing the above (a) to (d). It melt | dissolves in the ratio of Ba: Cu = 1: y <2: 3, and is setting it as the mixed solution which added the Hf additive. For example, the molar ratio y is 1.5 + y1 of Ba contained in the superconducting raw material solution (y1 is Ba amount to react to Hf) and, in this embodiment, since a magnetic flux pinning centers of BaHfO _3, Ba: Hf = React 1: 1. That is, in this superconducting raw material solution, the number of carbon atoms forming oxide particles (additional element) to be the magnetic flux pinning point 13a having a particle diameter of 50 nm or less, preferably 10 nm or less, containing Hf. Up to 20 compounds are added. The superconducting raw material solution contains 3 to 8 carbon atoms and is a solution containing an RE salt of carboxylic acid containing no ketone group, that is, a solution containing Y-propionic acid corresponding to the solution of (a), (b A solution containing Ba-TFA as a solution corresponding to the solution of c), a solution containing Cu-2-ethylhexanoic acid corresponding to the solution of (c), and a solution containing hafnium octylate corresponding to the solution of (d) And.

  After the superconducting raw material solution configured in this way is applied to the substrate 15, the superconducting raw material solution applied in the pre-baking process step B is pre-baked. By the pre-sintering process in the pre-sintering process step B, the coated film on the substrate 15 becomes an amorphous superconducting precursor (hereinafter, referred to as "precursor"). In the coating step A, it is possible to use an inkjet method, a spray method, etc. in addition to the above dip coating method, but basically it is a process capable of continuously applying the mixed solution on the composite substrate 15 For example, it is not restricted by this example. The film thickness applied at one time is 0.01 μm to 2.0 μm, preferably 0.1 μm to 1.0 μm.

  The coating step A and the pre-sintering step B are repeated a predetermined number of times, that is, the coated film on the intermediate layer 12 of the composite substrate 15 of the tape-shaped oxide superconducting wire 10 is multicoated. The predetermined number of times is repeated according to the thickness of the coating film to be the superconducting layer, and the thickness of the coating film becomes thicker as the number of repetitions increases. Thereby, 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 composite substrate 15. Do.

  Thus, the precursor to be the superconducting layer is formed by repeating the coating step A and the pre-baking treatment step B a predetermined number of times (multi-coating), and the subsequent main firing treatment step C includes crystallization of the precursor. Heat treatment (main firing treatment) is performed. After the main baking process C, a stabilization layer (for example, an Ag stabilization layer) 14 (see FIG. 1) is formed on the generated YG dBCO superconducting layer (superconducting layer 13) by a sputtering method, and post heat treatment is performed YG dBCO superconducting wire is manufactured.

  The pre-baking heat treatment and the main baking process are performed, for example, by passing the substrate 15 in a baking furnace (not shown) having a heater. In this case, each baking heat treatment sprays an atmosphere gas which is an oxygen gas flow containing water vapor to the substrate passing inside, while a predetermined temperature gradient (maximum reach temperature 450 ° C. in temporary baking processing, in main baking processing) It heats at 750-800 degreeC.

At this time, in particular, in the present baking treatment, the precursor is decomposed and generated, and the remaining organic component or residual fluoride in the calcination, for example, HF, CO _{2 and the} like are discharged.

  Thereby, in the main baking processing step C in which the main baking processing is performed at the crystallization temperature, the superconducting wire (YBCO superconducting wire) having the YG dBCO layer in which the magnetic flux pinning points including Hf are uniformly dispersed and which has excellent magnetic field application characteristics. Are manufactured.

  Even after the pre-baking treatment step B and before the main firing treatment step C, the precursor is subjected to a baking treatment at a temperature lower than the main firing treatment temperature and then rapidly cooled to room temperature. Good. This intermediate heat treatment is performed by subjecting the pre-baked precursor to an intermediate baking process before the precursor reaches the crystallization temperature of YG dBCO in the main baking process, to thereby obtain residual organic components in the pre-baking process. Or promote the emission of residual fluoride.

Example 1
In Example 1, it was formed by laminating Al ₂ O ₃ , LaMnO ₃ , MgO, LaMnO ₃ , CeO ₂ in this order on Hastelloy (registered trademark) as a metal substrate and this Hastelloy (registered trademark). A substrate provided with an intermediate layer was prepared, and a superconducting wire having a REBCO superconducting layer was formed on this substrate using the superconducting raw material solution of the present embodiment according to the manufacturing method shown in FIG. 2 using the MOD method. The superconducting raw material solution used in forming this REBCO superconducting layer is TFA-Y (trifluoroacetic acid yttrium salt), TFA-Gd (trifluoroacetic acid gadolinium salt), TFA-Ba (trifluoroacetic acid barium salt), octylic acid It was set as the mixed solution which melt | dissolved Cu salt and octylic acid Hf in 1-methoxy- 2-propanol. Moreover, the metal element composition ratio in the superconducting raw material solution is as follows: Y-TFA salt 0.77: gadolinium trifluoroacetate 0.23: barium trifluoroacetate 1.60: copper octylate 3.00: hafnium octylate It is 0.10. At this time, the Hf additive to be added to the mixed solution in which the RE component, the Ba component and the Cu component are mixed in 200 mL of the superconducting raw material solution is 4.53 g of Hf, and the element C, H, O other than Hf contains 3.64 g 8 It was .17 g of additive. In Example 1, the viscosity of the superconducting raw material solution was adjusted so as to be 30 nm per layer after the main baking, and the application pre-baking was repeated 20 times. The critical current value Ic and the critical current density Jc of Example 1 were measured with respect to Example 1 manufactured using the four-terminal method conduction measurement method. In Example 1, Ic = 180 A / cm-width, Jc = 3 MA / cm ² in an environment in a 77 K self-magnetic field, and Ic = 18 A / cm-width, J c = 0 in a 77 K, 3 T magnetic environment. It was .3 MA / cm ² .

Comparative Example 1
In the preparation process of Example 1, the additive 23 containing 44 carbon atoms as the Hf additive to be added to the mixed solution in which the RE component, the Ba component and the Cu component are mixed in 200 mL of the superconducting raw material solution applied to the substrate The superconducting wire of Comparative Example 1 was manufactured as .15 g (Hf 4.53 g, element C, H, O 18.62 g other than Hf). The critical current value Ic and the critical current density Jc of Comparative Example 1 were measured with respect to Comparative Example 1 manufactured using the four-terminal method conduction measurement method. Comparative Example 1 has an Ic = 100 A / cm-width, Jc = 1.54 MA / cm ² in an environment in a 77 K self-magnetic field, and an Ic = 12 A / cm-width, Jc in a 77 K, 3 T magnetic environment. It was 0.18 MA / cm ² .

  Comparison of Example 1 with Comparative Example 1 shows that the critical current value and critical current density of Example 1 are better than Comparative Example 1 even in the self magnetic field and in the high magnetic field environment such as 3 T. The Comparing Example 1 with Comparative Example 1, the number of carbon atoms in the Hf additive is different, and here, in Comparative Example 1, a superconducting wire using Hf which is a compound having 44 carbon atoms including Hf. In Example 1, a superconducting wire is produced using an Hf additive containing 8 carbon atoms. Therefore, in the Hf additive containing Hf, when the number of carbon atoms is set to 8 rather than 40 or more, organic residue generated at the time of heat baking is reduced during superconducting film formation, and voids in the superconducting layer are smaller. It is considered to decrease.

  The method of manufacturing a superconducting wire according to the present invention has an effect of realizing a superconducting wire provided with a superconductor having a desired high critical current value even in a high magnetic field environment, and manufacture of a superconducting wire manufactured by the MOD method It is useful as a method.

DESCRIPTION OF SYMBOLS 10 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 12e 5th intermediate layer 13 superconducting layer 13a pinning point 14 Stabilization layer 15 board

Claims (4)

A coating step of applying a superconducting raw material solution via an intermediate layer on a substrate, a temporary baking step of forming a temporary baked film by subjecting the coated superconducting raw material solution to a temporary baking treatment, the coating step and the temporary baking A method of manufacturing a superconducting wire, comprising: performing a main baking process on a superconducting precursor generated by laminating the pre-sintered film by repeating the process and the main baking process of generating a superconducting layer;
The superconducting raw material solution contains RE (RE is at least one element selected from the group consisting of Y, Nd, Sm, Gd, Dy, Eu, Er, Yb, Pr and Ho), Ba and Cu. The organometallic complex solution is mixed with a compound having 20 or less carbon atoms containing Hf,
The Hf is generated as a magnetic flux pinning point in the superconducting layer by the pre-baking process or the main baking process.
A method of manufacturing a superconducting wire characterized by The compound is a compound having 10 or less carbon atoms containing Hf.
A method of manufacturing a superconducting wire according to claim 1, characterized in that. The compound is octylic acid Hf,
A method of manufacturing a superconducting wire according to claim 1, characterized in that. The organometallic complex solution is an RE salt of a carboxylic acid having 3 to 8 carbon atoms which does not contain a ketone group as an RE component, barium trifluoroacetate as a Ba component, and a branch of 6 to 16 carbon atoms as a Cu component. At least one copper salt selected from the group consisting of copper salts of saturated aliphatic carboxylic acids and copper salts of alicyclic carboxylic acids having 6 to 16 carbon atoms, and an organic solvent for dissolving these metal salt components, Contains as an essential ingredient,
The method of manufacturing a superconducting wire according to any one of claims 1 to 3, wherein

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