JP2006228665A - Oxide superconducting wire material, manufacturing method thereof, and superconducting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an oxide superconducting wire material, having high sintering density of oxide superconductor and a high critical current density, by preventing pressurizing gas from infiltrating into wire material from an end of the wire material, upon heat treatment, by sealing the end of the wire material. <P>SOLUTION: The manufacturing method of an oxide superconducting wire material comprises the steps of preparing a wire material, formed by covering the raw material powder of an oxide superconductor with a metal pipe (for example, S1 and S2); closing both ends of the wire material with a metal material (for example, S11); and heat-treating the wire material, in a pressurized atmosphere of which the ends are closed with the metal material (for example, S6). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a method for manufacturing an oxide superconducting wire, and more particularly, to a method for manufacturing an oxide superconducting wire that can increase the critical current density.

  Conventionally, as a method of manufacturing an oxide superconducting wire, after filling a metal tube with raw material powder of an oxide superconductor, a wire obtained by subjecting the metal tube to wire drawing or rolling is heat-treated to produce an oxide. A method is known in which raw material powder of a superconductor is sintered to obtain an oxide superconducting wire. However, there has been a problem that the superconducting properties of the obtained oxide superconducting wire deteriorate due to the swelling of the wire in the heat treatment step for sintering.

  Accordingly, manufacturing of an oxide superconducting wire characterized by sintering a powder of an oxide superconductor by heating a metal tube or a flat body thereof filled with the oxide superconductor powder in a pressurized atmosphere. A method has been proposed (see, for example, Patent Document 1). According to this method, it is described in Patent Document 1 that a wire having excellent superconducting properties can be obtained by pressure heat treatment.

  Specifically, a metal tube filled with oxide superconductor powder is housed in a heat-resistant and pressure-resistant sealed container, and swelling during sintering is caused by an increase in internal pressure that increases as the temperature in the sealed container increases. Attempts have been made to prevent. The internal pressure at this time can be obtained from a gas equation of state. For example, Patent Document 1 describes that an internal pressure of about 4 atm can be obtained at a heating temperature of about 900 ° C.

  However, as described above, in the method described in Patent Document 1, the internal pressure obtained with the temperature rise in the sealed container is about 4 atmospheres (0.4 MPa). As a result, there is a problem in that voids are generated between the oxide superconducting crystals during sintering, thereby reducing the critical current density.

  In addition, since the internal pressure is about 4 atmospheres (0.4 MPa), swelling of the oxide superconducting wire generated during sintering cannot be sufficiently suppressed, thereby causing a problem that the critical current density is lowered.

  On the other hand, a method for producing an oxide superconducting conductor characterized in that a metal tube filled with oxide superconducting powder or the like is maintained in a high pressure state during at least one of heat treatment and after heat treatment ( For example, see Patent Document 2). According to this method, it is described in Patent Document 2 that partial peeling at the interface between the oxide superconductor and the metal tube, which occurs during sintering, can be eliminated by placing in a high pressure state.

Specifically, by holding a metal tube filled with oxide superconducting powder in a high pressure state of 500 to 2000 kg / cm ² (about 50 to 200 MPa) at least during and after the heat treatment. A metal tube can be pressure-bonded to the sintered body side. Thereby, when a superconductor partially causes a quench phenomenon, the heat generated by the quench phenomenon can be quickly removed. In addition to this, the peeled portion becomes a stress concentration portion, and deterioration of superconducting characteristics due to distortion can be prevented.

However, in the method described in Patent Document 2 as described above, since the applied pressure is too high, 500 to 2000 kg / cm ² (about 50 to 200 MPa), it becomes difficult to control the oxygen partial pressure during the heat treatment, and the critical current density is reduced. It will decline.

  In view of this, a method for manufacturing an oxide superconducting wire has been proposed in which the total pressure applied to the wire during heat treatment is 1 MPa or more and less than 50 MPa (see, for example, Patent Document 3). According to this method, it is described in Patent Document 3 that it is possible to prevent the wire from being swollen during heat treatment. Further, in Patent Document 3, in order to prevent the wire from bulging during heat treatment, a method for preventing a pinhole from being formed in the wire during rolling of the wire, or a pinhole generated during the rolling of the wire. Describes a method of preventing pressurized gas from entering.

However, during the heat treatment of the wire, not only the pinhole generated in the wire during rolling, but also the end of the wire becomes a portion where the superconducting filament is not covered with metal. For this reason, even if the wire is heat-treated in a pressurized atmosphere, the pressurized gas penetrates into the gap between the oxide superconducting crystals in the wire from the end of the wire, and in particular, sintering of the oxide superconductor at the end of the wire. In order to suppress the increase in density, it has been difficult to increase the critical current density.
JP-A-5-101723 Japanese Patent No. 2,592,846 International Publication No. 03/100795 Pamphlet

  By sealing the end of the wire, the present invention prevents the pressure gas from entering the wire from the end of the wire during the heat treatment, thereby enhancing the effect of pressure sintering. An object of the present invention is to provide a method for producing an oxide superconducting wire having a high sintered density and a high critical current density.

  The present invention includes a step of producing a wire having a form in which a raw material powder of an oxide superconductor is covered with a metal tube, a sealing step of sealing an end of the wire with a metal material, and sealing the end with a metal material. And a heat treatment step of heat-treating the stopped wire in a pressurized atmosphere.

  In the method for manufacturing an oxide superconducting wire according to the present invention, the sealing step includes a vacuum holding step of holding the wire in a vacuum atmosphere, and sealing an end portion of the wire held in the vacuum atmosphere with a metal material. Process. The sealing step includes a high-temperature vacuum holding step for holding the wire in a vacuum atmosphere at room temperature to 800 ° C., and an end portion of the wire held in a vacuum atmosphere at room temperature to 800 ° C. is sealed with a metal material. Stopping.

  In the method for manufacturing an oxide superconducting wire according to the present invention, a metal material having a melting point higher than the heat treatment temperature in the heat treatment step can be used as the metal material. Further, as the metal material, a coating metal material for covering the end of the wire and a sealing metal material for sealing the end of the wire and the covering metal material can be used.

  Moreover, this invention is an oxide superconducting wire manufactured by the manufacturing method of said oxide superconducting wire. Furthermore, this invention is a superconducting apparatus containing this oxide superconducting wire.

  As described above, according to the present invention, the end portion of the wire is sealed to prevent the pressurized gas from entering the wire from the end of the wire during the heat treatment, and the oxide superconductor. A method for producing an oxide superconducting wire having a high sintering density and a high critical current density can be provided.

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

In this specification, “Bi2223 phase” includes bismuth, lead, strontium, calcium, and copper, and the atomic ratio (bismuth and lead): strontium: calcium: copper is 2: 2: 2: 3. The Bi—Sr—Ca—Cu—O-based oxide superconducting phase expressed by the following equation, specifically, the (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} superconducting phase.

The “Bi2212 phase” includes bismuth, lead, strontium, calcium, and copper, and the atomic ratio (bismuth and lead): strontium: calcium: copper is approximated to 2: 2: 1: 2. is the called the BiPb-Sr-Ca-Cu- O -based oxide superconducting phase, specifically refers to _{(BiPb) 2 Sr 2 Ca 1} Cu 2 O 8 + δ superconducting phase.

  Referring to FIG. 1, an oxide superconducting wire (wire 1) having a multi-core wire structure, which is one of oxide superconducting wires according to the present invention, includes a plurality of oxide superconductor filaments 2 extending in the longitudinal direction, and And a sheath part 3 for covering. The material of each of the plurality of oxide superconductor filaments 2 is not particularly limited as long as it is an oxide exhibiting superconductivity. For example, a Bi-Pb-Sr-Ca-Cu-O-based composition is preferable. A material containing the Bi2223 phase represented by an approximate atomic ratio of bismuth and lead): strontium: calcium: copper of 2: 2: 2: 3 is optimal. The material of the sheath part 3 is not particularly limited as long as it is a highly conductive metal, but for example, silver is preferable.

  In the above description, the oxide superconducting wire having a multi-core wire structure has been described. However, an oxide superconducting wire having a single-core wire structure in which one oxide superconductor filament 2 is covered with a sheath portion 3 may be used.

  The manufacturing method of the oxide superconducting wire according to the present invention is a process for producing a wire having a form in which a raw material powder of an oxide superconductor is covered with a metal tube with reference to FIGS. S1 and step S2), a sealing step for sealing the end portion of the wire with a metal material (for example, step 11), and a heat treatment step for heat-treating the wire with the end portion sealed with a metal material in a pressurized atmosphere ( For example, step S6 in FIG. 2, step S4 in FIG. 3, and / or step S6) are included. By heat-treating the wire with the end sealed in a pressurized atmosphere, the pressurized gas is prevented from entering the wire from the end of the wire during this heat treatment, and the oxide superconductor is sintered. By increasing the density, an oxide superconducting wire having a high critical current density can be obtained.

  An example of the manufacturing process of the oxide superconducting wire according to the present invention will be described with reference to FIG. 2. First, the raw material powder of the oxide superconductor is filled in the metal tube (step S1). The raw material powder of the oxide superconductor is made of, for example, a material containing a Bi2223 phase, or a material containing a Bi2212 phase and / or an amorphous phase that forms a Bi2223 phase by firing.

  In addition, there is no restriction | limiting in particular as a metal pipe, However, It is preferable to use pipe | tubes, such as silver and silver alloy with high heat conductivity. Thereby, the heat generated when the superconductor partially causes a quench phenomenon can be quickly removed from the metal tube.

  Next, the metal tube filled with the raw material powder is formed into a wire having a desired diameter by wire drawing (step S2). Thereby, the wire which has the form which coat | covered the raw material powder of the oxide superconducting wire with the metal is obtained. Primary rolling is performed on this wire (step S3). After this primary rolling (step S3), the first heat treatment is performed (step S4). By these operations, an oxide superconducting phase is generated from the raw material powder.

  Next, secondary rolling is performed on the heat-treated wire (step S5). As a result, voids generated by the first heat treatment are removed. After this secondary rolling (step S5), the end of the wire is sealed (step S11). After the sealing of the wire (step S11), the second heat treatment is performed on the second-rolled wire. (Step S6). The oxide superconducting phase is sintered in the second heat treatment, and at the same time, the oxide superconducting phase is converted into a single phase.

  In the above example of the manufacturing process of the oxide superconducting wire, the case where the wire is sealed (step S11) after the second rolling (step S5) and before the second heat treatment (step S6) is described. As an example, as shown in FIG. 3, the sealing of the wire (step S11) can be performed after the first rolling (step S3) and before the first heat treatment (step S4).

  Here, from the viewpoint of reducing the gap between the oxide superconducting crystals and increasing the sintered density, as shown in FIG. 2, the end of the wire (step S11) is subjected to secondary rolling (step S5). It is preferable to carry out before the second heat treatment (step S6) later.

  The sealing step in the present embodiment preferably includes a vacuum holding step for holding the wire in a vacuum atmosphere and a step for sealing an end portion of the wire held in the vacuum atmosphere with a metal material. As shown in FIG. 4A, since the gap 2b between the oxide superconducting crystals 2a in the oxide superconductor filament 2 exists also in the rolled wire 1, the rolled wire 1 is maintained in a vacuum atmosphere. Then, after removing the gas in the gap 2b, the end portion 11 of the wire 1 from which the gas in the gap 2b has been removed is sealed with a metal material, and then heat-treated in a pressurized atmosphere, so that FIG. ), The superconductor filament 2 without voids between the oxide superconducting crystals 2a can be sintered, so that the critical current density of the superconducting wire can be increased.

  Further, the sealing step in this embodiment includes a high-temperature vacuum holding step for holding the wire in a vacuum atmosphere at room temperature to 800 ° C., and an end portion of the wire held in a vacuum atmosphere at room temperature to 800 ° C. It is more preferable to include a step of sealing with a material. Here, the room temperature refers to the temperature in a room where a person normally lives, and specifically refers to a temperature of about 10 ° C to 30 ° C.

  By holding the wire in a high-temperature vacuum atmosphere at room temperature or higher and 800 ° C. or lower, the gas in the voids between the oxide superconducting crystals can be removed more efficiently than when held in a vacuum atmosphere at room temperature. The higher the temperature in the high-temperature vacuum atmosphere, the better. However, when the temperature exceeds 780 ° C., the formed Bi2223 phase starts to melt, and when it exceeds 800 ° C., the melting of the Bi2223 phase promotes, so that the critical current value tends to decrease. . From this viewpoint, the temperature in the high-temperature vacuum atmosphere is preferably 800 ° C. or lower, and more preferably 780 ° C. or lower.

  In the present embodiment, the metal material used for sealing the end portion of the wire is not particularly limited, but is preferably a metal material having a melting point higher than the heat treatment temperature. By using a metal material having a melting point higher than the heat treatment temperature, it is possible to reliably prevent the pressurization gas from entering the wire from the end of the wire during the heat treatment. When forming the Bi2223 phase as a superconducting oxide, the wire may be heat-treated by raising the temperature to about 840 ° C. in an air atmosphere or to about 820 ° C. in a low oxygen atmosphere having an oxygen content of 8 mass%. Therefore, it is preferable to use a metal having a melting point higher than 840 ° C. Preferred examples of such a metal material include gold (melting point: 1063 ° C.), silver (melting point: 950 ° C. to 960 ° C.), or an alloy containing gold or silver (for example, gold wax).

  Although there is no restriction | limiting in particular in the sealing method of the wire in this embodiment, For example, as shown in FIG. 5, as an example of the sealing method of a wire, the edge part 11 of the wire 1 is used using the metal material 21 for sealing. A method of sealing (sealing method 1) is preferably used. Here, the sealing metal material 21 is not particularly limited as long as the end portion 11 of the wire 1 can be sealed. From the viewpoint of a high melting point and a high sealing effect, gold, silver, gold wax, or the like can be used. Preferably mentioned.

  Further, as the metal material, a metal material for coating for covering the end portion of the wire, and a metal material for sealing for sealing the end portion of the wire and the metal material for coating, The end can be sealed. For example, as another example of the method for sealing a wire according to the present embodiment, as shown in FIG. 6A, the end 11 of the wire 1 is covered with a covering metal material 22, and then the wire 11 shown in FIG. ), The method of sealing the end portion 11 of the wire 1 and the covering metal material 22 with the sealing metal material 21 (sealing method 2) is preferable from the viewpoint of ensuring sealing. Used. In FIG. 6A, the end of the wire is covered by bending the thin film-shaped covering metal material 22 in the order of P, Q, and R at the end 11 of the wire 1. Thus, the end of the wire can be covered. Here, the coating metal material 22 is not particularly limited as long as it can cover the end portion 11 of the wire 1, and preferably a gold thin film, a silver thin film, or the like.

  In the present embodiment, among the one or more heat treatments, heat treatment after sealing at least the ends of the wire with a metal material (second heat treatment in FIG. 2, first heat treatment in FIG. 3 (step S4) and / or Alternatively, the second heat treatment (step S6) is performed in a pressurized atmosphere. Although there is no restriction | limiting in particular in the applied pressure, It is preferable to apply the pressure of 1 Mpa or more and less than 50 Mpa as a total pressure.

  The heat treatment in the pressurized atmosphere is performed, for example, by a hot isostatic pressing method (hereinafter referred to as HIP). This HIP will be described below.

  Referring to FIG. 7, a device for performing HIP (HIP device 70) includes a pressure vessel cylinder 71, an upper lid 72 and a lower lid 73 that seal both ends of the pressure vessel cylinder 71, and pressurization in the pressure vessel cylinder 71. A pressurized gas introduction port 74 provided in the upper lid 72 for introducing gas, a heater 75 for heating the wire 1, a heat insulating layer 76, and a support 77 for supporting the wire 1 are configured.

  In the present embodiment, the wire 1 drawn and rolled after filling the raw material powder into the metal tube is supported by the support 77 in the pressure vessel cylinder 71 as a heat-treated product. In this state, a predetermined pressurized gas 68 is introduced into the pressure vessel cylinder 71 from the pressurized gas introduction port 74, whereby the pressure vessel cylinder 71 has a pressurized atmosphere of 1 MPa or more and less than 50 MPa. The wire 1 is heated to a predetermined temperature by the heater 75 in an atmosphere. This heat treatment is preferably performed in an oxygen atmosphere, and the oxygen partial pressure is preferably 0.003 MPa or more and 0.02 MPa or less. In this way, the wire 1 is heat-treated by HIP. Here, as the pressurized gas 68 introduced into the pressure vessel cylinder 71, a mixed gas of oxygen gas and inert gas is preferably used. As the inert gas, nitrogen gas, argon gas or the like is preferably used.

  The oxide superconducting wire manufactured by the manufacturing method of this embodiment has a high critical current density because the sintered density at the center and end of the wire increases to nearly 100.

  Moreover, since the superconducting device including the oxide superconducting wire manufactured by the manufacturing method of the present embodiment includes the oxide superconducting wire having a high critical current density, it has excellent superconducting characteristics. Here, the superconducting device is not particularly limited as long as it includes the oxide superconducting wire, and examples thereof include a superconducting cable, a superconducting transformer, a superconducting current limiter, and a superconducting power storage device.

(Comparative Example 1, Examples 1 to 3)
Bi ₂ O ₃ , PbO, SrCO ₃ , CaCO ₃ and CuO powders are used as raw materials for the oxide superconductor, and Bi: Pb: Sr: Ca: Cu = 1.8: 0.3: 1.9: 2.0 : The raw material powder comprised by the Bi2212 phase and the non-superconducting phase was prepared by mixing at a molar ratio of 3.0 and repeating the heat treatment and mixing. The raw material powder was filled into a 46 mm diameter silver tube and then drawn to obtain a 10 mm diameter clad wire. The 61 clad wires were bundled and inserted again into a silver tube having a diameter of 46 mm and drawn to obtain a multicore wire having a length of 2000 m in which the raw material powder was in the form of a filament.

  Next, the multifilamentary wire is subjected to primary rolling to obtain a tape-shaped silver-coated wire having a width of 4.2 mm, a thickness of 0.24 mm, and a length of 2000 m, which is composed of a 61-core filament with a silver ratio of 1.5. It was. This tape-shaped silver-coated wire was subjected to a first heat treatment in the atmosphere at 840 ° C. for 50 hours to obtain a primary wire having an oxide superconductor filament composed of a Bi2223 phase. The silver ratio means the ratio of the area of the silver (metal) part to the area of the oxide superconductor part in the cross section (width × thickness direction cross section) of the wire.

Next, the primary wire was subjected to secondary rolling at a rolling reduction of 8%. The rolling reduction is the following formula (1)
Reduction ratio (%) = {1- (Thickness of wire after rolling) / (Thickness of wire before rolling)} × 100 (1)
Is defined by

  Next, the wire rod after the secondary rolling is divided into four, one of the divided wires is left open (hereinafter, referred to as Comparative Example 1), and the other is end in an air atmosphere at 25 ° C. The other part is sealed (hereinafter referred to as Example 1), and the other is held at 780 ° C. and 10 Pa in a high-temperature vacuum atmosphere for 5 hours, and then cooled to 25 ° C. and 10 Pa in a vacuum atmosphere. Sealed (hereinafter referred to as Example 2), and the other was held in a high-temperature vacuum atmosphere at 800 ° C. and 10 Pa for 2 hours and then cooled to seal the end in a vacuum atmosphere at 25 ° C. and 10 Pa. did. Here, in Examples 1 to 3, the end of the wire is sealed in accordance with the sealing method 2 described above, after the end of the wire is covered with a silver thin film, and then the end of the wire and the silver thin film. The ends of the wire rods were sealed by applying melted gold wax (melting point: 895 ° C., composition: Au: Ag: Cu = 75.0: 12.5: 12.5 (mass%)).

  Next, a mixed gas of oxygen gas and argon gas was introduced as the pressurized gas 68 into the pressure vessel cylinder 71 of the HIP device 70 shown in FIG. The pressure vessel cylinder internal pressure (total pressure) is 28 MPa, the oxygen partial pressure is 8 kPa, and held at 820 ° C. for 50 hours, the second heat treatment is performed, and the wire rod after the secondary rolling is subjected to pressure sintering and compared. The oxide superconducting wire (secondary wire) of Example 1 and Examples 1 to 3 was obtained.

  The critical current value of the obtained oxide superconducting wire was measured in liquid nitrogen by the four probe method. Moreover, the sintered density of the oxide superconductor in the obtained oxide superconducting wire was calculated by the Archimedes method (buoyancy method) described later.

  The oxide superconducting wire of Comparative Example 1 had an average critical current value of 94A and a standard deviation of 9.4A, and a sintered density of 98% at the center and 95% at the ends. The oxide superconducting wire of Example 1 had an average critical current value of 104 A and a standard deviation of 1.2 A, and a sintered density of 99% at the center and 98% at the ends. The oxide superconducting wire of Example 2 had an average critical current value of 124 A and a standard deviation of 0.8 A, and a sintered density of 100% at the center and 100% at the end. The oxide superconducting wire of Example 3 had an average critical current value of 119 A and a standard deviation of 2.5 A, and a sintered density of 100% at the center and 100% at the ends.

  The results are shown in Table 1 and FIG. Here, in FIG. 8, A shows the case of Comparative Example 1, B shows the case of Example 1, and C shows the case of Example 2.

  As is apparent from FIG. 8, when the end of the wire is not sealed (Comparative Example 1), the critical current of the wire decreases as it goes to the end. This is because, even in the wire after the secondary rolling, about 7% of voids exist between the oxide superconducting crystals in the oxide superconducting filament, so that the pressurized gas is at the end of the wire during the second heat treatment. This is thought to be due to the penetration of the gap into the gap.

  Here, the relationship between the temperature and the compression strength when the wire rod after secondary rolling in this example and this comparative example is compressed at a high temperature is as shown in FIG. The compressive yield strength on the vertical axis in FIG. 9 refers to a force required to change the sintered density of the oxide superconducting filament from 93% (porosity 7%) to 100% (porosity 0%). That is, it refers to the force required to further reduce the wire thickness after secondary rolling by 0.02 mm (from 0.22 mm to 0.20 m). As shown in FIG. 9, even if the pressurized gas is introduced into the pressure vessel cylinder of the HIP apparatus at 820 ° C., which is the second heat treatment temperature in this example and the comparative example, the pressure vessel cylinder internal pressure reaches 20 MPa. Will cause the pressurized gas to enter the voids of the oxide superconducting filament from the end of the wire.

  In Example 1, the sintered density of the wire becomes high at 99% at the center and 98% at the end, and in Examples 2 and 3, the sintered density of the wire is 100 at both the center and the end. On the other hand, in Comparative Example 1, the sintered density of the wire remained at 98% at the center and 95% at the end. This shows that the end of the wire is not sealed during the second heat treatment, and a high sintering density cannot be obtained if pressurized gas enters the voids of the oxide superconducting filament.

Here, the sintered density means the following formula (2)
Sintering density (%) = (ρ _f /6.45)×100 (2)
Is defined by In this formula (2), ρ _f is the measured density of the oxide superconductor filament, and 6.45 is the theoretical density of the oxide superconductor filament. The theoretical density of the oxide superconductor filament is calculated by ICP (Inductive Coupled Plasma) emission analysis and EDX (energy dispersive X-ray spectroscopy) analysis of the oxide superconducting filament in the oxide superconducting wire in this example or the comparative example. It is calculated using the atomic ratio of the Bi2223 phase in the oxide superconductor filament and the lattice constant of the Bi2223 phase (a-axis and c-axis values, etc.) calculated by the X-ray diffraction method.

On the other hand, ρ _f is calculated using the following Archimedes method. First, an oxide superconducting wire of M _t (g) is cut out. Next, the cut oxide superconducting wire is immersed in alcohol, and the mass (W (g)) of the wire in alcohol is measured, and the buoyancy acting on the oxide superconducting wire is calculated. Then, the volume (V _t (cm ³ )) of the oxide superconducting wire is calculated using a known alcohol density (ρ = 0.789 (g / cm ³ ). Specifically, the buoyancy is _expressed as F _t . Then, the following equations (3), (4)
F _t = M _t −W (3)
V _t = F _t / ρ (4)
V _t is calculated by.

Subsequently, the oxide superconducting wire is dissolved in nitric acid, and the solution is subjected to ICP emission analysis to quantify silver, and the ratio (Y) of silver in the mass of the oxide superconducting wire is calculated. Then, from the mass of the oxide superconducting wire, the mass of the filament portion of the oxide superconductor wire (M _f (g)), the mass of the sheath (M _s (g)) and has the following formula (5), (6)
M _s = M _t × Y (5)
M _f = M _t −Ms (6)
Is calculated by

Next, the volume of the sheath portion (V _s (cm ³ )) is calculated from the known silver specific gravity (10.5 (g / cm ³ )), and the volume of the oxide superconductor filament (V _f ) is calculated from the volume of the sheath portion. (Cm ³ )) is calculated. Then, the density ρ _f of the oxide superconductor filament is calculated from the volume of the oxide superconductor filament. Specifically, the following formulas (7) to (9)
V _s = M _s /10.5 (7)
V _f = V _t −V _s (8)
ρ _f = M _f / V _f (9)
To calculate ρ _f .

  When comparing Comparative Example 1 and Example 1, the end of the wire was sealed and heat-treated in a pressurized atmosphere, whereby the average critical current value increased from 94 A to 104 A, and the standard deviation of the critical current value It can be seen that is reduced from 9.4 A to 1.2 A. Here, since the oxide superconducting wires of Comparative Example 1 and Example 1 have the same cross-sectional area (area of the transverse section (width × thickness section)), the ends of the wires are sealed. It can be seen that an oxide superconducting wire having a large critical current density and reduced variation can be obtained by heat treatment in a pressurized atmosphere.

  Further, when Example 1 was compared with Example 2 or Example 3, the wire was placed in a vacuum atmosphere at room temperature to 800 ° C. (specifically, in the case of Example 2, at 780 ° C. and 10 Pa for 5 hours, In the case of Example 3, after holding at 800 ° C. and 10 Pa for 2 hours, the end of the wire is sealed and heat-treated in a pressurized atmosphere, compared to the case where it is not held in the vacuum atmosphere. It can be seen that the average critical current value increased from 104A to 124A or from 104A to 119A. Here, since the oxide superconducting wires of Examples 1 to 3 have the same cross-sectional area, the ends of the wires are sealed after the wires are held in a vacuum atmosphere of room temperature to 800 ° C. It can be seen that an oxide superconducting wire having a higher critical current density can be obtained by heat treatment in a pressurized atmosphere.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a partial section perspective schematic diagram showing the composition of an oxide superconducting wire notionally. It is a schematic diagram which shows an example of the manufacturing process of an oxide superconducting wire. It is a schematic diagram which shows another example of the manufacturing process of an oxide superconducting wire. It is a cross-sectional schematic diagram which shows a part of longitudinal cross-section (length x cross section of thickness direction) of an oxide superconducting wire. It is a schematic diagram which shows an example of the sealing method of the edge part of an oxide superconducting wire. It is a schematic diagram which shows another example of the sealing method of the edge part of an oxide superconducting wire. It is a cross-sectional schematic diagram of a HIP device. It is a figure which shows the relationship between the wire length of an oxide superconducting wire, and a critical current value. It is a figure which shows the relationship between the temperature in the case of compressing the wire after secondary rolling at high temperature, and compression yield strength.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Wire rod, 2 oxide superconductor filament, 2a oxide superconducting crystal, 2b space | gap, 3 sheath part, 11 edge part, 21 metal material for sealing, 22 metal material for coating | cover, 70 HIP apparatus, 71 pressure vessel cylinder, 72 Upper lid, 73 Lower lid, 74 Pressurized gas inlet, 75 heater, 76 heat insulation layer, 77 support.

Claims (7)

  A step of producing a wire having a form in which a raw material powder of an oxide superconductor is covered with a metal tube, a sealing step of sealing an end of the wire with a metal material, and sealing the end with a metal material The manufacturing method of an oxide superconducting wire including the heat treatment process which heat-processes a wire in a pressurized atmosphere.   The sealing step includes a vacuum holding step of holding the wire in a vacuum atmosphere, and a step of sealing an end portion of the wire held in the vacuum atmosphere with a metal material. The manufacturing method of the oxide superconducting wire of 1.   The sealing step includes a high-temperature vacuum holding step for holding the wire in a vacuum atmosphere at room temperature to 800 ° C., and an end portion of the wire held in the vacuum atmosphere at room temperature to 800 ° C. is sealed with a metal material. The method for producing an oxide superconducting wire according to claim 1, further comprising a step of stopping.   The method for producing an oxide superconducting wire according to any one of claims 1 to 3, wherein a metal material having a melting point higher than the heat treatment temperature is used as the metal material.   As the metal material, a metal material for covering for covering an end portion of the wire rod and a metal material for sealing for sealing the end portion of the wire rod and the metal material for covering are used. A method for producing an oxide superconducting wire according to any one of claims 1 to 4.   The oxide superconducting wire manufactured by the manufacturing method of the oxide superconducting wire in any one of Claims 1-5.   A superconducting device comprising the oxide superconducting wire according to claim 6.

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