JP2014026858A - Method for manufacturing tape-like re-based oxide superconducting wire material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a tape-like RE-based oxide superconducting wire material having excellent superconducting characteristics with a desired thin thickness.SOLUTION: The method for manufacturing a tape-like RE-based oxide superconducting wire material includes: a coating step of applying a superconducting raw material solution on an intermediate layer formed on a substrate; a calcination heat treatment step of calcinating the applied solution to form a calcined film; and main firing heat treatment step of laminating a calcined film by repeating the coating step and the calcination heat treatment step so as to form a superconducting layer precursor and applying a main firing heat treatment to the precursor so as to form a superconducting layer. The superconducting layer is formed of REBaCuO(RE represents at least one element selected from Y, Nd, Sm, Eu, Gd, and Ho). In the calcination heat treatment step, a batch-type electric furnace is used to make the calcined film.

Description

  The present invention relates to a method for producing a tape-shaped RE-based oxide superconducting wire, and in particular, a superconducting layer using a metal-organic deposition (MOD) method on a metal substrate on which an intermediate layer is formed. Relates to the technology of forming

Conventionally, 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. As a method for producing a tape-shaped RE-based oxide superconducting wire that is a layer of a high-temperature superconducting thin film), it is known to form a superconducting layer on a metal substrate on which an intermediate layer is formed by using the MOD method. (See Patent Document 1).

  In this MOD method, a metal organic acid salt is thermally decomposed. After a solution in which an organic compound of a metal component is uniformly dissolved is applied onto a substrate, the thin film is formed on the substrate by heating it and thermally decomposing it. It is a method of forming. Since the MOD method is a non-vacuum process, high-speed film formation is possible at low cost, and therefore has an advantage suitable for manufacturing a long tape-shaped oxide superconducting wire.

  In this MOD method, when a metal organic acid salt as a starting material is thermally decomposed, a carbonate of an alkaline earth metal (Ba or the like) is usually generated. Formation of an oxide superconductor by a solid-phase reaction via this carbonate requires high-temperature heat treatment of 800 [° C.] or higher. Furthermore, when the film thickness is increased, nucleation for crystal growth occurs from a part other than the substrate interface, so it is difficult to control the crystal growth rate. As a result, a superconducting film with excellent in-plane orientation is obtained. Difficult to get.

  As a method for producing an RE (123) superconductor by the MOD method that does not pass through carbonate, an organic acid salt containing fluorine (for example, TFA salt: trifluoroacetate) is used as a starting material, and heat treatment is performed in a steam atmosphere. There is a known method of producing via the decomposition of fluoride.

  As the MOD method using this TFA salt as a starting material, for example, methods shown in Patent Documents 2 and 3 are known. In these Patent Documents 2 and 3, a coating step of applying a superconducting raw material solution on an intermediate layer formed on a substrate and a temporary baking heat treatment step of performing a temporary baking heat treatment to produce a temporary baking film are repeatedly laminated. A pre-baked heat treatment step for producing a pre-fired film. After this laminated calcination heat treatment step, as a main calcination heat treatment, an amorphous precursor containing fluorine and water vapor are reacted to create a superconductor. Since the decomposition rate of the fluoride can be controlled by the water vapor partial pressure during the main heat treatment, the crystal growth rate of the superconductor can be controlled. As a result, a superconducting film having excellent in-plane orientation is produced.

  By the way, a tape-shaped oxide superconducting wire using a tape-shaped wire for a substrate on which a superconductor is formed is known. When this tape-shaped oxide superconducting wire is manufactured by the MOD method using the idea of Patent Documents 2 and 3, the Patent Documents 2 and 3 are substrates that can be applied by a spin coat coating method. Not intended for tape wire.

  For this reason, conventionally, when a tape-shaped oxide superconducting wire is manufactured by the MOD method, an RTR method (reel to reel) is used in the laminated calcination heat treatment.

  In the RTR method, a tape-shaped wire feeding mechanism for feeding out a tape-shaped wire rod and a winding mechanism for winding the tape-shaped wire rod are installed at both ends of the tunnel furnace in order to repeatedly perform solution coating and pre-fired film generation. In the RTR method, firing is performed by moving the tape-shaped wire rod in the tunnel furnace at a constant speed using a tape-shaped wire feed mechanism and a winding mechanism. By repeating this firing, a temporary firing heat treatment is continuously performed to produce a tape-shaped superconducting wire.

JP 2007-165153 A JP 2012-003961 A JP 2012-003962 A

  However, in the conventional MOD method, even if the RTR (reel to reel) method in which the tape-like wire is fired by moving the inside of the tunnel furnace at a constant speed is used in the laminated pre-baking heat treatment process, the desired film thickness is obtained. A superconducting layer having the desired excellent superconducting properties could not be obtained. In particular, when the film thickness of the superconducting layer was 1.5 μm or more, it was not possible to obtain superconducting characteristics having Ic of 400 A / cm or more in a self magnetic field.

  This invention is made | formed in view of this point, and it aims at providing the manufacturing method of the tape-shaped RE type oxide superconducting wire excellent in the superconducting characteristic by the desired film thickness.

One aspect of the method for producing a tape-shaped RE-based oxide superconducting wire of the present invention includes a coating step of coating a superconducting raw material solution on an intermediate layer formed on a substrate, and subjecting the coated solution to a pre-baking heat treatment. The precursor of the superconducting layer is prepared by laminating the calcined film by repeating the calcining heat treatment step for producing the calcined film, the coating step and the calcining heat treatment step, and the precursor is calcined. And a main baking heat treatment step for producing a superconducting layer by performing a heat treatment, wherein the superconducting layer is REBa _y Cu ₃ O _z- based (RE is at least one selected from Y, Nd, Sm, Eu, Gd and Ho) In the method for producing a tape-shaped RE-based oxide superconducting wire, the calcining heat treatment step is performed by heat treatment in a batch type electric furnace to produce a calcined film.

  According to the present invention, a tape-shaped RE-based oxide superconducting wire having a desired film thickness and excellent superconducting characteristics can be produced.

Sectional drawing of the tape-shaped RE type oxide superconducting wire manufactured with the manufacturing method of the tape-shaped RE type oxide superconducting wire which concerns on embodiment of this invention Sectional drawing of the wire which shows the outline of the manufacturing method of the tape-shaped RE type oxide superconducting wire Schematic sectional view showing the main configuration of a heat treatment apparatus used in the method for producing the tape-shaped RE-based oxide superconducting wire Schematic showing the rotating body of the heat treatment equipment The figure which shows typically the manufacturing method of the superconducting wire by the MOD method using a heat processing apparatus. The figure which shows the temperature profile at the time of temporary baking heat processing in the heat processing equipment

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

  First, a tape-shaped RE system provided with a YBCO superconducting layer (RE-based (123) superconducting layer) manufactured using the method for manufacturing a tape-shaped RE-based oxide superconducting wire (YBCO superconducting wire) according to an embodiment of the present invention. The oxide superconducting wire will be described.

<Oxide superconducting wire>
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 (YBCO superconducting wire) 20 is in the form of a tape, on a tape-like metal substrate 21, an intermediate layer 22, a tape-like oxide superconducting layer (hereinafter referred to as “superconducting layer”) 23, stable. The layer 24 is formed by sequentially stacking layers. Here, the intermediate layer 22 includes a first intermediate layer 22a, a second intermediate layer 22b, and a third intermediate layer 22c.

  The tape-shaped metal substrate 21 is, for example, nickel (Ni), a nickel base alloy, stainless steel, or silver (Ag). Here, the metal substrate 21 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 21 is, for example, 0.1 mm or less.

The first intermediate layer 22a is a layer made of MgO formed by the IBAD method on the tape-like metal substrate 21 by the sputtering method. A second intermediate layer 22b made of LaMnO ₃ is formed on the first intermediate layer 22a by sputtering.

Furthermore, here, CeO ₂ is vapor-deposited by a sputtering method (which may be PLD) to form a third intermediate layer 22c as an omniaxially oriented cap layer. The thickness of the third intermediate layer 22c is about 1000 [nm]. When the third intermediate layer 22c is a Ce—Gd—O film in which Gd is added to a CeO ₂ film, the third intermediate layer 22c has a third intermediate layer so that the YBCO superconducting layer formed as the superconducting layer 23 has good orientation. The amount of Gd added in the film in the layer 22c is preferably 50 at% or less. A superconducting layer 23 is formed on the third intermediate layer 22c. In the superconducting wire 20, the intermediate layer 22 is formed by the first intermediate layer 22a, the second intermediate simplified layer 22b, and the third intermediate layer 22c. The metal substrate 21 and the intermediate layer 22 formed on the metal substrate 21 constitute a composite substrate 25. A superconducting layer 23 is formed on the surface of the composite substrate 25, that is, on the intermediate layer 22. The composite substrate 25 may have a biaxial orientation or may have a biaxial orientation intermediate layer 22 formed on a metal substrate 21 having no orientation. Moreover, the intermediate | middle layer 22 may be formed by 1 layer-3 layers, or 5 layers or more.

  On the superconducting layer 23, there is provided a stabilizing layer 24 which is a noble metal such as silver, gold, platinum, or an alloy thereof and is a low resistance metal. The stabilization layer 24 is formed immediately above the superconducting layer 23 to prevent performance degradation caused by the reaction of the superconducting layer 23 with a noble metal such as gold or silver or a material other than an alloy thereof. To do. In addition to this, the stabilization layer 24 disperses heat generated by an accident current or alternating current to prevent destruction and performance degradation due to heat generation. Here, the thickness of the stabilization layer 24 is 10 to 30 [μm].

The superconducting layer 23 is an all-axis oriented REBCO layer, that 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.). Here, the superconducting layer 23 is an yttrium oxide superconductor (RE123).

  Here, the superconducting layer 23 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. The artificial pin particles (magnetic flux pinning points) 23a, which are effective oxide particles, are formed. The superconducting raw material solution composition at this time is set in consideration of the composition of the artificial pin particles (in the case of Zr, Ba: Zr = 1: 1). In addition, although the superconducting layer 23 is configured to have the magnetic flux pinning point 23a, the present invention is not limited thereto, and may be a layer that does not have the magnetic flux pinning point 23a. That is, in the tape-shaped oxide superconducting wire 20, the superconducting layer 23 including the magnetic flux pinning point 23a is used. However, the present invention is not limited thereto, and at least one additional element (added metal) of Zr, Sn, Ce, Ti, Hf, and Nb is used. ) A superconducting layer not containing M may be used.

  The magnetic flux pinning point (artificial pinning point) 23a has a particle size of 50 [nm] or less including at least one additive element among Zr, Sn, Ce, Ti, Hf, and Nb, which is uniformly dispersed in the superconducting layer 23. More preferred are oxide particles as a compound having a particle size of 10 nm or less. Note that the particle size of the magnetic flux pinning point 23a is more preferably within the above-mentioned range since the effect is better when the magnetic flux line size is closer to the magnetic flux line size.

The number n of oxide particles is desirably included in the superconducting layer 23 by 1.0 × 10 ³ ≦ n <1.0 × 10 ⁷ per [μm ³ ]. A large number of particles is effective because it can pin more magnetic flux, 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. The characteristics 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 superconducting raw material solution applied on the intermediate layer 22 is an organometallic complex containing RE (RE represents one or more elements selected from Y, Nd, Sm, Eu, Gd and Ho), Ba and Cu. It consists of a solution (mixed solution) and an organometallic complex solution containing at least one additional element of Zr, Sn, Ce, Ti, Hf, and Nb having a high affinity for Ba.

  That is, here, the superconducting raw material solution is a mixed 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. The number of moles is such that a raw material solution having a Ba molar ratio within the range of a <2 when Y: Ba: Cu = 1: a: 3 is used. In this case, in order to obtain high Jc and Ic values, the Ba molar ratio in the raw material solution is preferably in the range of 1.0 ≦ a ≦ 1.8, and more preferably the Ba molar ratio in the raw material solution. Is in the range of 1.3 ≦ a ≦ 1.7. Thereby, the segregation of Ba can be suppressed, and as a result, the precipitation of Ba-based impurities at the grain boundaries is suppressed. Therefore, generation of cracks is suppressed and electrical connectivity between crystal grains is improved. By forming a superconducting film by the MOD method, a tape-like oxide having a high-speed uniform thick film and excellent superconducting characteristics. Superconductors can be easily manufactured. In addition, examples of the metal organic acid salt include octyl acid salt, naphthenic acid salt, neodecanoic acid salt, and trifluoroacetic acid salt of each element. Among these, one or more of these salts are uniformly used in an organic solvent. Any material that can be dissolved and applied onto the composite substrate can be used.

  In the present embodiment, by using the organometallic complex solution, the molar ratio a of Ba contained in the superconducting raw material solution is set within the range of a <2. In addition, the mixed solution contains oxide particles having a particle size of 50 [nm] or less, preferably 10 [nm] or less, containing Zr, Ce, Sn, Hf, Nb, or Ti in the superconductor. It can manufacture by dispersing as.

In addition, it is preferable to use the following solutions (a) to (d) as the mixed solution (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

  Also, the superconducting layer 23 is calcined on the third intermediate layer 22c in an atmosphere having a water vapor partial pressure of 3 to 76 [Torr] and an oxygen partial pressure of 300 to 760 [Torr] in a temperature range of 400 to 500 [° C]. It is desirable to be heat treated. The superconducting layer 23 may be subjected to a main firing heat treatment in a temperature range of 700 to 900 [° C.] in an atmosphere having a water vapor partial pressure of 30 to 600 [Torr] and an oxygen partial pressure of 0.05 to 1 [Torr]. preferable. In the present embodiment, the superconducting layer 23 is calcined in a heat treatment apparatus 10 as a batch type electric furnace.

  The additive element (added metal) M for forming the magnetic flux pinning point 23a in the formed superconducting layer 23 is at least one of Zr, Sn, Ce, Ti, Hf, and Nb. The addition amount of the additive element M needs to be 30 wt% or less with respect to the superconductor constituent metal element, and is preferably 1 to 10 wt% with respect to the whole superconducting layer. The reason why 1 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 be pinned, so that more magnetic flux can be pinned. 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 23a is BaZrO ₃ . When the additive element M is Ti, the compound formed by dispersing in the superconducting layer 23 as the magnetic flux pinning point 23a is BaTiO ₃ . When the additive element M is Ce, the compound formed by dispersing in the superconducting layer 23 as the magnetic flux pinning point 23a is BaCeO _{3. When} the additive element M is Sn, the superconducting layer is used as the magnetic flux pinning point 23a. The compound formed by dispersing in 23 is BaSnO ₃ . When the additive element M is Hf, the compound formed by dispersing in the superconducting layer 23 as the magnetic flux pinning point 23a is BaHfO ₃ . Each compound that becomes the magnetic flux pinning point 23 a is uniformly dispersed in the superconducting layer 23.

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. In addition, the compound which becomes each magnetic flux pinning point 23 a is uniformly dispersed in the superconducting layer 23.

  In the superconducting wire in which the magnetic flux pinning points 23a are formed in the superconducting layer (superconductor) 23, the molar ratio of Ba contained in the superconducting layer 23 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. The superconducting layer 23 formed thereby suppresses the generation of cracks, improves the electrical connectivity between crystal grains, and improves Jc defined by the energization current.

  The particle size of the oxide particles containing at least one of Zr, Sn, Ce, Ti, or Hf dispersed as the magnetic flux pinning points 23a artificially introduced into the superconducting layer 23 is 50 [nm] or less. Although it is said that it is 10 [nm] or less especially.

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. Accordingly, while maintaining the composition of the superconducting layer 23 (RE: Ba: Cu = 1: 1.5: 3), BaZrO ₃ that forms a magnetic flux pinning point (artificial pin particle) 23a is formed by coupling with Ba to form a superconducting material. The superconducting layer 23 formed in this manner is dispersed in the grains forming the layer 23. The grain boundary characteristics are improved without lowering Jc due to grain boundary segregation.

Furthermore, BaZrO ₃ formed in the superconducting layer 23 exists not only in the film surface direction but also in the film thickness direction in nano-size and nano-interval, which effectively pin the magnetic flux, and the difference in Jc with respect to the magnetic field application angle. It is possible to significantly improve the directivity. 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 heat treatment (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 23a can be introduced.

Further, in the oxide superconducting wire 20, the Zr-containing magnetic flux pinning points 23 a can be finely dispersed in the superconducting layer in the RE-based superconducting layer 23 with a reduced Ba concentration. For this reason, the magnetic field application angle dependency [Jc _{, min} / Jc _{, max} ] of Jc is small and has a magnetic field characteristic having a high Jc at a high magnetic field, and the magnetic field application angle dependency of Jc [Jc _{, min} / Jc]. _{, Max} ] can be significantly improved. Therefore, in addition to the self-magnetic field, the magnetic flux is effectively pinned in any magnetic field application angle direction in the magnetic field, and the isotropic Jc characteristic is obtained, so that the high superconducting characteristic (the critical current density Jc [Jc of Jc] / Cm ² ] and critical current Ic [A / cm]).

<Outline of production method of this tape-shaped RE oxide superconducting wire>
FIG. 2 is a cross-sectional view of the wire showing an outline of a method for manufacturing the RE-based oxide superconducting wire 20 according to the embodiment of the present invention. Here, a case where a YBCO superconducting layer is produced as a superconducting layer will be described as an example.

  First, a first intermediate layer 22a made of MgO is formed on a tape-shaped metal substrate 21, for example, a Ni alloy substrate (base material) 21 by the IBAD method (see FIG. 1).

Next, a second intermediate layer 22b made of LaMnO ₃ is formed on the first intermediate layer 22a by sputtering, and a third intermediate layer 22c made of CeO _{2 is} further formed thereon by sputtering or PLD. A composite substrate 25 is formed by film formation (see FIG. 1).

  On this composite substrate 25, a superconducting raw material solution is applied in coating step A to form a coating film. Here, the superconducting raw material solution is applied onto the composite substrate 25 by a dip coating method. As described above, this superconducting raw material solution contains Y: TFA salt (trifluoroacetate salt), Ba-TFA salt and Cu-naphthenic acid salt in an organic solvent with Y: Ba: Cu = 1: 1.5: 3. It is a mixed solution dissolved in a ratio. An additive element M such as Zr for forming a magnetic flux pinning point is added to the mixed solution. In addition, when the magnetic pinning point is not included in the superconducting layer to be produced, the additive M is not added to the mixed solution (superconducting raw material solution).

After this mixed solution (superconducting raw material solution) is applied, it is calcined in a calcining heat treatment step B. In addition, in the coating step A, it is possible to use an ink jet method, a spray method, or the like in addition to the dip coating method described above, but basically, any process that can continuously apply the mixed solution onto the composite substrate 25. It is not constrained by this example. The film thickness to be applied at one time is 0.01 to 2.0 [μm], preferably 0.1 to 1.0 [μm]. Thereby, the thickness (film thickness) of the generated superconducting layer 23 is 1.3 μm or more, for example, 1.5 μm. In the composite substrate 25, the intermediate layer formed on the base material may be formed by forming an intermediate layer made of CeO ₂ on the MgO intermediate layer.

  By repeating this coating step A and pre-baking heat treatment step B a predetermined number of times, the coating film is multi-coated on the intermediate layer of the composite substrate 25 of the tape-shaped oxide superconducting wire 20. In this way, by repeating the coating step A and the pre-baking heat treatment step B, that is, the laminated pre-baking heat treatment step, the composite substrate 25 is subjected to multi-coating, that is, pre-baking produced by coating and pre-baking. The precursor of the superconducting layer is produced by laminating the film on the composite substrate 25.

  Thereby, a film body (“precursor” shown in FIG. 2) as an amorphous superconducting precursor to be the superconducting layer 23 is formed on the intermediate layer in the composite substrate 25. After the film body containing fluorine (F) is formed on the intermediate layer in this way, in the main heat treatment step C, the crystallization heat treatment of the film body in the tape-shaped oxide superconducting wire 20 (here, the YBCO superconducting layer) Heat treatment for production) is performed in water vapor gas. As the YBCO superconducting layer 23 is generated, HF is generated. After this main baking heat treatment step C, a stabilization layer (for example, Ag stabilization layer) 24 is applied on the produced YBCO superconductor by sputtering, and post-heat treatment is performed. Thus, a superconducting wire (YBCO superconducting wire) having a YBCO layer in which magnetic flux pinning points are dispersed and magnetic field application characteristics are excellent is manufactured.

  In the method for manufacturing a tape-shaped RE-based oxide superconducting wire according to the present embodiment, the pre-baking heat treatment step B in the laminated pre-baking heat treatment step is performed using a heat treatment apparatus 10 (see FIGS. 3 and 4) shown below. . In the present embodiment, the main baking heat treatment step C is also performed using the heat treatment apparatus 10 (see FIGS. 3 and 4). Thereby, a precursor of the superconducting layer is produced. Further, the main baking heat treatment in the main baking heat treatment step C is similarly performed using the heat treatment apparatus 10. Thereby, the manufacturing method of the tape-shaped RE oxide superconducting wire according to the present embodiment produces a YBCO superconducting layer.

<Heat treatment equipment>
3 and 4 are cross-sectional views schematically showing the main configuration of the heat treatment apparatus 10 used in the pre-baking heat treatment step B (see FIG. 2). FIG. 4 shows a cylindrical rotating body 15 disposed therein.

  The heat treatment apparatus 10 is a so-called batch type electric furnace. The heat treatment apparatus 10 includes a heat treatment furnace 14 including a furnace body 12 and an electric heater 13, and a cylindrical rotating body 15 disposed inside the heat treatment furnace 14 (specifically, inside the furnace body 12).

  An atmosphere gas such as oxygen gas or water vapor is introduced into the furnace body 12. The electric heater 13 is disposed outside the furnace body 12. In addition, you may use this heat processing apparatus 10 when forming an intermediate | middle layer.

  The cylindrical rotating body (cylindrical body) 15 is disposed inside the heat treatment furnace 14 so as to be rotatable with respect to the rotating shaft portion 16 in the horizontal direction. The rotator 15 is formed of a material that can withstand high temperatures and does not oxidize, such as quartz glass, ceramics, Hastelloy, or Inconel.

  A tape material 26 to be subjected to a pre-baking heat treatment is wound around the outer periphery of the rotating body 15. The tape material 26 includes a composite substrate 25 in which an intermediate layer 22 having biaxial orientation is formed on a metal substrate 21, a solution film in which a superconducting raw material solution is applied onto the composite substrate 25, or a composite substrate. 25 and a temporarily fired film as a superconducting precursor obtained by temporarily firing the mixed solution (superconducting raw material solution) applied to 25. The tape material 26 is subjected to heat treatment for generating a superconductor while being wound around the outer periphery of the rotating body 15.

  A large number of through holes 15b having a diameter equal to or less than ½ of the tape width of the tape material 26 are uniformly formed on the entire surface of the cylindrical body 15a in the cylindrical body 15a that is a cylindrical main body portion of the rotating body 15. . One end side of the cylindrical body 15a is sealed with a lid 15c. The other end side of the cylindrical body 15a is continuously connected to the inside of the lid 15d for a gas discharge pipe 17 for discharging the gas inside the cylindrical body to the outside of the heat treatment furnace 14.

  A plurality (at least four) of gas supply pipes 18 are arranged symmetrically with respect to the rotation axis of the rotating body 15 so as to be separated from the outer surface of the cylindrical body 15a. Each gas supply pipe 18 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 15a. The length of the gas supply pipe 18 is preferably longer than the height of the cylindrical body 15a. The diameter of the gas ejection holes is designed so that the gas pressure and the gas flow rate are uniform. The gas supply pipe 18 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 18 from an atmospheric gas supply device (not shown) disposed outside the heat treatment furnace 14 through a connection pipe (not shown) connected to the gas supply pipe 18.

  When the pre-baking heat treatment or the main baking heat treatment is performed by the heat treatment apparatus 10, the inside of the heat treatment furnace 14 can be maintained in a reduced pressure atmosphere. The atmosphere gas supply device is connected to a gas system that supplies an inert gas (such as argon or nitrogen), oxygen gas, and water vapor gas, and includes a mechanism that changes these atmosphere gases in accordance with a heat treatment pattern.

  The present heat treatment apparatus 10 supplies oxygen gas when the coating film or the pre-baked film is subjected to the pre-baking heat treatment at the pre-baking temperature.

  In addition, when the main heat treatment apparatus 10 performs the main heat treatment at the main calcination temperature on the superconducting precursor, water vapor gas is used as the atmosphere gas, and low oxygen atmosphere gas (inert gas and oxygen of 10,000 ppm or less) is used. Substituting with atmospheric gas).

  In addition, the heat treatment apparatus 10 includes a control unit (CPU) 19, through which temperature adjustment of the electric heater 13, control of the atmospheric gas apparatus, rotation drive control of the rotating body 15, and the like are appropriately performed. Yes. In particular, in the pre-baking heat treatment, the control unit 19 adjusts the temperature of the electric heater 13 in the pre-baking heat treatment to perform the pre-baking heat treatment on the tape material 26.

  In addition, the heat treatment apparatus 10 includes a low-oxygen atmosphere gas (inert gas and oxygen of 10,000 ppm or less) as an atmosphere gas when performing the pre-baking or the main baking heat treatment at the pre-baking temperature or the main baking temperature. Replace with atmospheric gas).

  In the heat treatment apparatus 10 configured as described above, the cylindrical rotating body 15 around which the tape material 26 is wound is rotated by a drive mechanism (not shown) at a predetermined rotation speed. At the same time, the inside of the heat treatment furnace 14 is maintained in a heated atmosphere by the electric heater 13. In addition, atmospheric gas is ejected from the numerous gas ejection holes of the gas supply pipe 18 toward the surface of the cylindrical body inside the heat treatment furnace 14 held in a heated atmosphere. The atmospheric gas is ejected from the gas ejection holes of the gas supply pipe 18 at a substantially constant flow rate. On the other hand, this atmospheric gas is sucked into the cylindrical body 15a from a large number of through holes 15b of the cylindrical body 15a, and is discharged out of the heat treatment furnace 14 via the gas discharge pipe 17 connected to the other end side of the cylindrical body 15a. Is done.

  Even in the main firing heat treatment, atmospheric gas is ejected from the numerous gas ejection holes of the gas supply pipe 18 toward the surface of the cylindrical body in the heat treatment furnace 14 held in the heating atmosphere by the electric heater 13.

  In the heat treatment apparatus 10 configured as described above, in the pre-baking heat treatment B after the superconducting raw material solution is applied (application step A in FIG. 2), the superconducting raw material solution applied on the intermediate layer is heated to temporarily A firing heat treatment step is performed.

  FIG. 5 is a diagram schematically showing a method of manufacturing a superconducting wire by the MOD method using the heat treatment apparatus 10. 5A corresponds to the coating step A of FIG. 2, FIG. 5B corresponds to the pre-baking heat treatment step of FIG. 2B, and FIG. 5C corresponds to the main baking heat treatment step C of FIG. FIG. 5D shows a process for producing the stabilization layer 24 (see FIG. 1), and FIG. 5E shows a post-heat treatment process performed after the main firing heat treatment C (see FIGS. 5C and 2).

First, a first intermediate layer 22a by IBAD method, a second intermediate layer (LaMnO ₃ layer) 22b by sputtering method, sputtering method or PLD on Hastelloy (base material) 21 which is a tape-shaped Ni alloy substrate shown in FIG. A third intermediate layer (CeO ₂ layer) 22c is sequentially formed. Thereby, a linear composite substrate 25 is formed.

  This composite substrate 25 is immersed in a mixed solution (superconducting raw material solution) K in a coating step (corresponding to the coating step A in FIG. 2) shown in FIG. 5A. That is, the mixed solution 23 is applied to the composite substrate 2 by a dip coating method. The mixed solution (superconducting raw material solution) K is composed of Y: TFA salt (trifluoroacetate salt), Ba-TFA salt and Cu-naphthenic acid salt in an organic solvent. Y: Ba: Cu = 1: 1.5: It is a solution dissolved at a ratio of 3.

  After applying the mixed solution K to the composite substrate 25, as shown in FIG. 5B, the heat treatment apparatus 10 is used to perform temporary baking in a temporary baking step (corresponding to the temporary baking step B in FIG. 2). By repeating the coating step (see FIG. 5A) and the temporary firing step (see FIG. 5B) a predetermined number of times, a temporary fired film as a superconducting precursor is formed on the intermediate layer in the tape material 25, and the precursor-attached wire 27 is Make it.

  In the pre-baking treatment of the heat treatment apparatus 10 in this laminated pre-baking heat treatment step, the pre-baking temperature is changed stepwise to the maximum temperature of the pre-baking heat treatment (the pre-baking maximum temperature D2 shown in FIG. 6). On the other hand, temporary baking is performed. That is, in the pre-baking heat treatment step, the temperature of the pre-baking heat treatment temperature is changed to a maximum temperature D2, and the temperature increase in unit time is changed to raise the temperature step by step, thereby producing a pre-baked film. In addition, it is preferable that this maximum temperature is 300-450 [degreeC], More preferably, it is 350-400 [degreeC].

As the temperature approaches the crystallization temperature, microcrystals that become nuclei of crystallization tend to be generated in the superconducting layer. If the microcrystals are generated, there is a possibility that a portion where no epitaxial growth occurs from the Ce ₂ interface during the main firing, resulting in crystal defects. Therefore, the calcined film is made amorphous by setting the calcining temperature below the above temperature. As a result, crystal defects do not occur in the pre-baking and the superconducting characteristics of the generated superconducting layer are less likely to be deteriorated than when the pre-baking is performed above the temperature.

  In addition, since the pre-baking treatment temperature is equal to or higher than the above temperature, the volatile component such as an organic solvent does not go into the layer as compared with the case where the temperature is lower than the above temperature, and the main baking is performed while the impurities are held in the layer. Never do. Since the superconducting wire is a thin film of about 1 μm, the presence of impurities in the superconducting layer (YBCO superconducting layer) 23 significantly affects the deterioration of the superconducting characteristics. In particular, in the pre-baking treatment, it is preferable to flow oxygen into the heat treatment apparatus 10 so that organic residues such as carbon do not remain as impurities at a high temperature of 400 ° C.

  FIG. 6 is a view showing a temperature profile during the pre-baking heat treatment in the heat treatment apparatus 10.

  As shown in FIG. 6, in the pre-baking heat treatment step using the heat treatment apparatus 10, first, the tape material 26 wound around the rotating body 15 is inserted inside. Then, the rotary body 15 around which the tape material 26 is wound is heated to an initial temporary firing temperature (approximately 270 [° C.] in FIG. 6) D1 of 300 [° C.] to 450 [° C.].

  In the pre-baking heat treatment step, heating of the tape material 26 in the heat treatment path furnace 14 of the heat treatment apparatus 10 is performed so as to gradually increase from the same temperature as the room temperature to the initial pre-baking temperature D1. Thus, unlike the pre-baking heat treatment using the conventional RTR method, the tape material does not rapidly rise from the room temperature state by being rushed into the opened tunnel furnace. Therefore, bumping of the organic solvent and moisture contained in the applied mixed solution is prevented.

  Here, the initial calcination temperature is a temperature at which introduction of oxygen gas as an atmospheric gas is started inside the heat treatment furnace 14 via the gas supply pipe 18. Here, the initial calcination temperature is reached at time t1. That is, during the pre-baking heat treatment, oxygen gas is introduced into the heat treatment furnace 14 during the temperature rise at the initial pre-baking temperature.

  Next, while introducing the oxygen gas, the inside of the heat treatment furnace 14 filled with the oxygen gas is the highest temperature that is the highest temperature of the pre-baking temperature, with a gentler slope than the average of the upper temperature gradients up to the initial pre-baking temperature. Heat to the pre-baking temperature.

  Here, while introducing the oxygen gas, the heat treatment is performed for about 5 hours as the period of the wet in state from the time t1 at which the initial calcination temperature is introduced to the predetermined time t2 at which the maximum calcination temperature is reached. The calcining temperature in the furnace body 12 inside the furnace 14 is raised. In this way, a crystal heating process is performed on the coating film on the composite substrate 25 to form a temporarily fired film.

  In addition, it is desirable that the heat treatment time from the start of the pre-baking heat treatment until reaching the maximum temperature of the pre-baking treatment (preliminary baking maximum temperature) is 1 to 10 hours. More preferably, the heat treatment time from the start of the pre-baking heat treatment until reaching the pre-baking maximum temperature is preferably 2 to 7 hours before.

  As the crystallization temperature is approached, microcrystals that form crystallization nuclei are generated in the superconducting layer. Therefore, in the state of the calcined film as described above, the calcined film is preferably in an amorphous state. Therefore, the pre-baking heat treatment time is set before 10 hours when the microcrystals are generated so that the microcrystals are not generated in the film. Further, unlike the case where the calcination time is set to the above time or less than the above time, volatile components such as an organic solvent become impurities in the layer and are prevented from existing in the calcination film. Here, the inside of the heat treatment apparatus 10 is set to a maximum calcining temperature of 400 ° C. filled with oxygen so that organic residues such as carbon do not remain as impurities in the apparatus.

  After reaching the maximum temperature D2, the heat treatment apparatus 10 stops heating and stops supplying oxygen gas. That is, in the cooling period after the predetermined time D2, the supply of water vapor gas and oxygen gas is stopped.

  After performing such a pre-baking heat treatment, the mixed solution is applied again in the coating step, and then the pre-baking heat treatment is performed in the same manner as the previous pre-baking heat treatment to produce a pre-baked film. By repeating these coating steps and pre-baking heat treatment steps, multi-coating is performed to produce a precursor of the superconducting layer (YBCO superconducting layer) 23 as a thick pre-baked film.

  After the precursor of the superconducting layer (YBCO superconducting layer) 23 is produced on the intermediate layer 22 (see FIG. 1) laminated on the composite substrate 25 in the tape material 26 in this manner, the precursor-attached wire rod 27 is produced, and then FIG. The main baking step shown (corresponding to the main baking step C in FIG. 2) is performed.

  In this main firing step, the superconducting precursor film 27 is subjected to a crystallization heat treatment for the superconducting precursor film, that is, a heat treatment for generating a YBCO superconductor, to generate a superconducting layer (YBCO superconducting layer) 23.

  Next, in the stabilization layer manufacturing step shown in FIG. 5D, an Ag stabilization layer 24 as a stabilization layer is applied on the generated YBCO superconductor by sputtering, and then in the post-heat treatment step shown in FIG. To produce a YBCO superconducting wire. In the post-heat treatment step shown in FIG. 5D, heat treatment is performed using the heat treatment apparatus 10.

  5C, the heat treatment apparatus 10 uses the steam gas as the atmospheric gas in the heat treatment furnace 14 during the temperature rise, and the temperature TS [° C.] of the main firing temperature 700 to 900 [° C.]. (In this case, the main baking temperature is set to 750 [° C.]) and introduced through the gas supply pipe 18. The introduction temperature of the water vapor gas is a temperature during the temperature rise until reaching the main firing temperature (here, 750 [° C.]). The introduction start temperature of the water vapor gas is preferably a temperature from 450 [° C.] to 550 [° C.]. If the introduction temperature of the water vapor gas is a temperature from 450 [° C.] to 550 [° C.] than when the water vapor gas is introduced from around 600 [° C.] or when the water vapor gas is introduced from around 400 [° C.]. The amount of water vapor gas at the time of the main baking heat treatment temperature can be sufficiently secured.

  Next, crystallization heat treatment is performed by maintaining the temperature constant at the main firing temperature for a predetermined time while introducing water vapor gas. Here, the main calcination temperature in the furnace body 12 inside the heat treatment furnace 14 is maintained for 5 to 30 hours (more preferably 10 hours to 15 hours) as the predetermined time while introducing the steam gas. Thereby, in order to produce the YBCO superconducting layer 23, the crystal heat treatment is performed on the precursor on the composite substrate 25 constituting the oxide superconducting wire 20.

  Next, before starting the cooling of the precursor subjected to the main baking heat treatment, that is, before TF time for starting cooling in the furnace body 12 inside the heat treatment furnace 14 (here, several hours before the start of cooling, for example, 5 minutes to 2 hours before) The supply of water vapor gas is stopped. Immediately after stopping the supply of the water vapor gas, a low oxygen atmosphere gas containing an inert gas and oxygen of 10,000 ppm or less is supplied. Specifically, the inert gas is nitrogen, argon or the like, and a low oxygen atmosphere gas is supplied into the furnace body 12, and water vapor as the atmosphere gas supplied into the furnace body 12 through the gas supply pipe 18. The gas is completely replaced with a low oxygen atmosphere gas, and the removal of fluorine in the furnace body 12 is completed. In other words, in the main firing heat treatment step, the supply of water vapor gas is completely replaced by the low oxygen atmosphere gas by supplying the low oxygen atmosphere gas to the water vapor gas supplied into the heat treatment furnace (electric furnace) 14. Do before.

  In the main baking heat treatment step, the water vapor gas in the furnace body 12 can be completely replaced with the low oxygen atmosphere gas, so that the superconducting crystal is not decomposed and unreacted Ba reacts with the water vapor gas. Therefore, desired superconducting characteristics can be obtained. During this cooling, the supply of the inert gas continues.

  Thus, when manufacturing the oxide superconducting wire 20 according to the present embodiment, after applying the superconducting material solution on the metal substrate 21 via the intermediate layer 22 in the coating step A of FIG. Pre-baking heat treatment is performed in the heat treatment step B. This is repeated until a predetermined film thickness is obtained (multi-coat treatment). Next, a main firing heat treatment is performed on the tape-shaped wire 20 in the main heat treatment step C. As a result, barium fluoride can be efficiently decomposed in the main baking heat treatment, suitable crystallization is achieved with the precursor to be a superconductor, and the superconducting characteristics of the superconducting layer of the tape-shaped oxide superconducting wire to be manufactured are improved. Can do.

  According to the present embodiment, in the pre-baking treatment step shown in FIG. 5B, the pre-baked film is produced in the batch-type heat treatment apparatus 10 (see FIGS. 2 and 3 for details). That is, since the temporary baking heat treatment step is performed on the temporary baking film by the batch type heat treatment apparatus 10, the net treatment temperature is gradually increased in the sealed furnace body 12, and the baking is effectively performed. Can do. Thus, during the calcination heat treatment, unlike the conventional RTR method, the applied mixed solution (superconducting raw material solution) is not rapidly heated by rushing into a high-temperature tunnel furnace, and the mixed solution is bumped. Can be prevented. Therefore, a uniform and uniform film can be formed, and a superconducting wire excellent in superconducting characteristics can be manufactured.

  In addition, since temporary baking is performed by the batch-type heat treatment apparatus 10, the atmosphere in the furnace is not only easily controlled as compared with the case of performing the conventional reel-to-reel method, but also the temperature, pressure, etc. Easy to control. Therefore, a more stable superconducting layer (YBCO superconducting layer) 23 can be formed, and a tape-shaped RE-based oxide superconducting wire can be manufactured in a short time.

  Note that the Ni alloy substrate as the metal substrate 21 in the present embodiment may have a biaxial orientation, or may have a biaxial orientation intermediate layer formed on a metal substrate having no orientation. Further, the intermediate layer 22 is formed of one layer or a plurality of layers. In addition to the dip coating method described above, an ink jet method, a spray method, or the like can be used as a coating method in the coating step A, but basically, the mixed solution is applied onto the composite substrate 25 continuously. Any process that can do so is not limited 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.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and can be changed without departing from the gist thereof.

  The method for producing a tape-shaped RE oxide superconducting wire according to the present invention has the effect of producing a tape-shaped RE oxide superconducting wire having a desired film thickness and excellent superconducting properties, and is useful as a method for producing a superconducting wire. It is.

DESCRIPTION OF SYMBOLS 10 Heat processing apparatus 12 Furnace body 13 Electric heater 14 Heat processing furnace 15 Rotating body 15a Cylindrical body 15b Through-hole 15c, 15d Cover body 16 Rotating shaft part 17 Gas exhaust pipe 18 Gas supply pipe 20 Oxide superconducting wire 21 Metal substrate 22 Intermediate layer 23 Superconducting layer 24 Stabilizing layer 25 Composite substrate 26 Tape material 27 Wire with precursor

Claims (8)

A coating step of coating the superconducting raw material solution on the intermediate layer formed on the substrate;
A pre-baking heat treatment step of applying a pre-baking heat treatment to the applied solution to produce a pre-baking film;
A main-fired heat treatment is performed by stacking a pre-fired film by repeating the coating step and the pre-baked heat treatment step, thereby producing a superconducting layer precursor, and subjecting the precursor to a main-fired heat treatment to produce a superconducting layer. And the superconducting layer is a REBa _y Cu ₃ O _z- based (RE represents at least one element selected from Y, Nd, Sm, Eu, Gd and Ho). A method for producing a system oxide superconducting wire,
The calcining heat treatment step is a heat treatment in a batch type electric furnace to produce a calcined film.
A method for producing a tape-shaped RE-based oxide superconducting wire characterized by the above. In the pre-baking heat treatment step, in the electric furnace, the temperature is raised step by step until reaching the maximum temperature of the pre-baking heat treatment temperature, thereby producing a pre-baked film.
The method for producing a tape-shaped RE-based oxide superconducting wire according to claim 1. The maximum temperature of the pre-baking heat treatment is 300 to 450 ° C.
The method for producing a tape-shaped RE-based oxide superconducting wire according to claim 1 or 2. The maximum temperature of the pre-baking heat treatment is 350 to 400 ° C.
The method for producing a tape-shaped RE-based oxide superconducting wire according to claim 1 or 2. The heat treatment time from the start of the heat treatment to the maximum temperature in the pre-baking heat treatment is 1 to 10 hours ago.
The method for producing a tape-shaped RE-based oxide superconducting wire according to any one of claims 1 to 4. The heat treatment time from the start of the heat treatment to the maximum temperature in the pre-baking heat treatment is 2 to 7 hours ago.
The method for producing a tape-shaped RE-based oxide superconducting wire according to any one of claims 1 to 4. The batch-type electric furnace of the calcining heat treatment step is provided with a cylindrical body inside, and a calcining heat treatment is performed by winding an object to be heat-treated around the cylindrical body.
The method for producing a tape-shaped RE-based oxide superconducting wire according to any one of claims 1 to 6. The main baking heat treatment step is a step of heat treatment in a batch type electric furnace.
The method for producing a tape-shaped RE-based oxide superconducting wire according to any one of claims 1 to 7.

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