JPH05266726A - Oxide superconducting wire - Google Patents

Abstract

PURPOSE:To provide an oxide superconducting wire whose dependency on a magnetic field is weak with high critical current density. CONSTITUTION:Being made up of a metal tube 1 and a metal core 2 inserted therein, a cylindrical superconductive layer 3 is formed by filling a gap part K formed all along the periphery of the metal core 2 with an oxide superconducting body in such a manner that it is oriented in the radial direction like mica and is oriented in its longitudinal direction. Accordingly, a superconducting wire, which is hardly dependent on the direction of a magnetic field and is capable of providing uniform and high critical current density, can be provided. Since a superconducting wire having a round shape or a polygonal shape can also be formed, it can be wound into a coil thereby resulting in a magnet coil of high performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting wire, and more particularly to an oxide superconducting wire which is less dependent on the direction of a magnetic field and which has a uniform and high critical current density.

[0002]

BACKGROUND OF THE INVENTION Various oxide-based superconducting materials are currently known, and research is being conducted into technology for processing long materials such as wire rods and tapes for their practical use. It is being appreciated. Generally, a so-called silver sheath is used in which a silver tube is filled with an oxide-based superconducting powder and processed into a round, polygonal, or flat tape-shaped wire by processing such as wire drawing or rolling, and then heat-treated to form a superconducting wire. The law is known. Of these, an oxide superconductor whose crystal grains are flat is used to form, for example, a tape-shaped elongated body, which is subjected to processing such as pressing and heat treatment, or to a specific heat treatment, as shown in FIG. In addition, the superconducting layer 3 having a structure in which the tape-shaped silver layer 1 is oriented in a mica shape in a direction perpendicular to the plane 1a and in a longitudinal direction.
It is known that the oxide superconducting wire D is formed to obtain a high critical current density. However, in the case of a round or polygonal superconducting wire, the central part that is not in contact with the silver layer is non-oriented, and unlike the above-mentioned tape-shaped superconducting wire, a structure with a mica-like orientation cannot be formed over the entire superconducting layer, resulting in high criticality. Current density cannot be obtained.

On the other hand, it has been widely practiced to apply a superconducting wire to a magnet coil. In this case, as shown in FIG. 5, the coil 10 has a magnetic field distribution indicated by an arrow,
As a result, magnetic fields are applied to the wire wound around the coil 10 from various directions. Therefore, the performance of the magnet coil depends on the dependence of the critical current density of the superconducting wire used on the magnetic field application direction.

FIG. 6 shows a case where a magnetic field B is applied to a test piece of the above-mentioned tape-shaped superconducting wire in two directions perpendicular to the tape surface (symbols Δ, ▲) and parallel (symbols ○, ●). measuring the change in the critical current density Jc, the horizontal axis is intended magnetic field intensity, the vertical axis plotting the ratio of the critical current density Jc of each magnetic field strength with respect to the critical current density Jc ₀ o'clock applied magnetic field zero. However, the symbols Δ and ○ represent the cases where the magnetic field strength was increased, and the symbols ▲ and ● represent the cases where the magnetic field strength was demagnetized. As is clear from the figure, when the magnetic field B is applied in the direction perpendicular to the tape surface, the critical current density J increases as the magnetic field B becomes larger than when applied in parallel.
c tends to decrease, and the critical current density of the tape-shaped superconducting wire has a strong dependence on the magnetic field application direction. Therefore, even if a magnet coil is produced using the tape-shaped superconducting wire, the magnetic coil has a strong magnetic field dependency and the critical current density of the superconducting wire decreases, so that the magnet coil does not exhibit the desired performance.

An object of the present invention is to solve the above problems and to provide an oxide superconducting wire having a high critical current density, which has a weak dependence on the direction of application of a magnetic field and is useful for a magnet coil.

[0006]

As a result of various investigations, the present inventors have focused on the structure of a superconducting layer in an oxide superconducting wire and formed an oxide superconductor to form a superconducting layer having a specific structure. As a result, they have found that the above object can be achieved and completed the present invention.

That is, the oxide superconducting wire of the present invention is formed by a metal tube and a metal core inserted therein, and the void portion formed over the entire circumference of the metal core is an oxide superconductor. It is characterized in that a superconducting layer having a tubular structure filled with the oxide superconductor and oriented in the circumferential direction in the shape of mica and in the longitudinal direction is formed.

With the above structure, a superconducting wire can be obtained which has a high critical current density equivalent to that of the tape-shaped oxide superconducting wire. Further, even when a magnetic field is applied to the superconducting wire from various directions, the magnetic field dependence is averaged and the decrease in the critical current density is alleviated.

The present invention will be described in more detail below with reference to the drawings. As shown in FIG. 1, a superconducting wire D of the present invention includes a metal tube 1 having a circular section 1 (a) or a polygonal section 1 (b),
A superconducting layer 3 having a mica-like structure is formed of an oxide superconducting material in a void portion K formed by the metal core 2 inserted therein.

In the present invention, as the metal pipe 1, a metal pipe having a silver layer formed on at least the inner peripheral surface having a polygonal shape whose cross section is circular or triangular is used. In particular,
Examples thereof include a silver tube or a multilayer metal tube made of silver, a metal layer, and a conductive metal in order from the inside. The conductive metal forming the outer peripheral surface of the multilayer metal tube is not particularly limited, copper, iron,
Examples of the material include nickel and alloys thereof, but it is preferable to use copper in terms of reactivity with an intermediate metal layer, workability, and conductivity. This conductive metal is considerably thicker than the silver on the inner peripheral surface, occupies most of the tube, and serves to stabilize the oxide superconductor.

The silver on the inner peripheral surface of the tube does not easily undergo an oxidation reaction even at high temperature when sintering an oxide superconducting material having a mica-like crystal structure, so that the atmosphere control, which is a manufacturing process of the oxide superconductor, can be controlled. to enable.

Further, between the silver on the inner peripheral surface of the tube and the conductive metal on the outer peripheral surface, a role of preventing the reaction between silver and the conductive metal at a high temperature during sintering of the oxide superconducting material is fulfilled. At the same time, the intervening metal layers do not chemically react with silver and the conductive metal, respectively. The metal layer is not specified as long as the above-mentioned action is exhibited, and tantalum, molybdenum, tungsten, rhenium, osmium, etc. are exemplified, and tantalum and molybdenum are preferable from the viewpoint of workability.

There is no particular limitation on the production of the above metal tube,
For example, it can be manufactured by swaging, electroforming, or the like. The use of this multi-layer metal tube is preferable because the amount of expensive silver used is small and the cost can be reduced.

On the other hand, as the metal core 2 to be inserted into the silver pipe or the multi-layer metal pipe, a pipe-shaped or rod-shaped metal core having a silver layer formed on at least the outer peripheral surface thereof is used. Specific examples thereof include silver pipes, silver rods, and pipes or rods of copper, iron, nickel, or alloys thereof having a silver layer formed on the outer peripheral surface thereof. Further, in the present invention, as the metal core, it is possible to use a material in which the raw material powder of the superconductor is filled inside the pipe-shaped material or a wire having the superconducting layer structure of the present invention. Further, it is also possible to use a plurality of the above-mentioned materials and store them in a metal tube and process them to obtain a superconducting wire having a multi-core structure. In the present invention, the form and material may be selected and used depending on workability, strength, cost and the like.

As the oxide superconducting material forming the superconducting layer 3 of the present invention, known oxide superconductors forming a mica-like structure such as Bi-based, Y-based, Tl-based, Pb-based, and Ba-based materials.
System, Nd system, etc. can be used, especially Bi system Bi ₂ Sr ₂ Ca ₂ Cu ₃ O
_x or Bi ₂ Sr ₂ CaCu ₂ O _y (where x is 9.80 to 1
0.25 and y are positive numbers of 8.00 to 8.35. )
The material represented by is preferably used.

It is sufficient to fill the metal tube with the above-mentioned raw material powder of the oxide superconductor to manufacture a wire rod, although it is sufficient to use a conventionally known method, but the following manufacturing processes (1) to (2) are normally performed. That is, a void is formed by a metal tube and a metal core inserted therein, the void is filled with oxide superconductor powder, and both ends of the pipe are welded and enclosed in a metal pipe. The wire base material. Next, the wire rod base material is swaged, die wire-drawn (drawing with a die) or rolled to make a thick wire a thin wire. The thin wire is sintered and oxygen-annealed (at least 800 ° C. or higher) to produce a superconducting wire. By the above method, the superconducting layer 3 having a tubular structure in which the metal tube 1 is circumferentially oriented in the shape of mica and is oriented in the longitudinal direction.
Oxide superconducting wire D in which is formed is obtained.

In the present invention, the film thickness of the cylindrical superconducting layer 3 is 10 to 150 μm, preferably 15 to 100 μm.
m, more preferably 20 to 80 μm. When the film thickness of the cylindrical superconducting layer 3 is less than 10 μm, the film thickness becomes non-uniform due to the limitation of processing accuracy, and when it exceeds 150 μm, the critical current density is lowered due to the deterioration of orientation, which is not preferable.

[0018]

According to the present invention, as shown in the partially enlarged vertical sectional view of FIG. 2, the annular superconducting layer 3 having a mica-like structure in the circumferential direction is formed in the void portion K formed by the metal tube 1 and the metal core 2. The annular superconducting layer 3 has a structure similar to that of the tape-shaped oxide superconducting wire in the small angle region (θ), and a high critical current density can be obtained. Further, as shown in a partially enlarged view of the transverse cross section of FIG. 3, since the annular superconducting layer 3 is formed in a tubular structure oriented in the longitudinal direction of the superconducting wire D, magnetic fields are applied to the superconducting wire D from various directions. Even in such a case, the dependence on the critical current density is averaged and relaxed, and a uniform critical current density can be obtained. Furthermore, since it is possible to form an oxide superconducting wire having a round or polygonal shape and a high critical current density, it is easy to wind the coil into a coil or the like.

[0019]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. Needless to say, the present invention is not limited to this embodiment. Example 1 (Production of Superconducting Wire) First, as shown in FIG.
Insert a silver rod 2 with an outer diameter of 5 mm into the center of a silver tube 1 molded to have a thickness of 0 mm, a thickness of 1.4 mm, and a length of 300 mm, and one end of the silver tube 1 has an outer diameter of 7.0 mm and a wall thickness. A silver tube 5a having a length of 0.9 mm and a length of 100 mm was inserted, the end portion was welded to fix the silver rod 2, and the one end portion was sealed. Then, in the space K formed by the silver tube 1 and the silver rod 2, the calcined Bi ₂ Sr ₂
After filling the CaCu ₂ O _y powder, a silver tube 5 b having an outer diameter of 7.0 mm, a wall thickness of 0.9 mm and a length of 100 mm is inserted into the other end of the silver tube 1 and the end is welded and sealed. A wire rod base material X was produced. This base material X was drawn until the outer diameter became 1 mm. Then, the temperature is first raised in the air at 50 ° C./hour, stopped when the temperature reaches 890 ° C., maintained in this temperature atmosphere for 10 minutes, and then lowered at 2.5 ° C./hour to 860 A Bi-type oxide superconducting wire D was produced by keeping the temperature at 40 ° C. for 40 hours, then heating by lowering the temperature at 100 ° C./hour and sintering.

(Structure of Superconducting Layer) This superconducting wire D was vertically cut and the superconducting layer 3 was observed. As shown in FIG.
As shown in, the gap K formed by the silver tube 1 and the silver rod 2 inserted into the silver tube 1 is filled with Bi ₂ Sr ₂ Ca having a film thickness of 60 μm.
A ring-shaped superconducting layer 3 filled with Cu ₂ O _y is formed, and the ring-shaped superconducting layer 3 is, as shown in a partially enlarged schematic view of FIG.
The mica-like structure was formed in the circumferential direction of the silver tube 1.
Further, when this superconducting wire D was laterally cut and the superconducting layer 3 was observed, as shown in FIG. 3, it had a cylindrical structure in which the silver rod 2 was oriented in the longitudinal direction over the entire circumference.

(Characteristics of Superconducting Wire) Further, a test piece having a length of 50 mm was sampled from the central portion of the obtained superconducting wire and the superconducting characteristics were examined. The critical temperature was 83 K and the critical current density was in liquid He. At 1.5 × 10 ⁵ A /
It was cm ² .

Comparative Example 1 Using the same Bi ₂ Sr ₂ CaCu ₂ O _y powder as in Example 1, a superconducting layer having a thickness of 60 μm was formed by a silver sheath method, and the length was 0.1 mm.
A tape-shaped superconducting wire with a width of 3.0 mm was manufactured, and a test piece with a length of 50 mm was sampled from the center of the obtained superconducting wire, and the superconducting characteristics were examined. The critical temperature was 83 K,
The critical current density is: 2.0 × 10 ⁵ A in liquid He
It was / cm ² .

Experimental Example Using the test pieces of Example 1 and Comparative Example 1 above, a magnetic field (B) was externally applied to each of them to measure the change in critical current density. In addition, in the tape-shaped superconducting wire of Comparative Example 1,
A magnetic field was applied from two directions, a vertical direction (symbol ●) and a parallel direction (symbol ○) to the tape surface. The measurement results are plotted by plotting the magnetic field strength (B) on the horizontal axis and the ratio of the critical current density (Jc) at each magnetic field strength to the critical current density (Jc ₀ ) when the applied magnetic field is 0 on the vertical axis. ,
The result is the graph shown in FIG. As is clear from this figure, the Bi-based oxide superconducting wire of Example 1 was excellent in that the dependence of the critical current density on the externally applied magnetic field direction was small.

Examples 2 to 3 and Comparative Examples 2 to 3 Bi type oxide superconducting wires were manufactured by the same method as in Example 1 except that the thickness of the superconducting layer was changed as shown in Table 1. .. The critical temperature and the critical current density of the obtained superconducting wire are as shown in Table 1.

[0025]

[Table 1]

Example 4 In Example 1, except that the silver tube 1 was replaced by a silver layer 1a on the inside, tantalum 1b on the metal layer, and a metal pipe 1 formed as copper 1c on the conductive layer metal part, all were used. By the same method, a Bi-based oxide superconducting wire D having a vertical sectional structure shown in FIG. 9 was manufactured. The critical temperature and the critical current density of the obtained superconducting wire were almost the same values as those of the superconducting wire of Example 1.

Although a round silver tube is used as the metal tube in the above embodiment, a polygonal silver tube or a multi-layer metal tube may be used to form the oxide superconducting wire. Further, although the silver rod is used as the metal core, an oxide superconducting wire can be formed by using a silver pipe or a metal rod or metal pipe having a silver layer formed on the outside. Also, as an oxide superconducting material
Although Bi ₂ Sr ₂ CaCu ₂ O _y was used, an oxide superconducting wire can be formed using Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x or another oxide superconducting material. Furthermore, although the oxide superconducting wire was sintered by a specific heat treatment, the oxide superconducting wire can be manufactured by performing a sintering by a method combining processing such as pressing and heat treatment.

[0028]

As described above, the oxide superconductor of the present invention is a superconducting wire which can obtain a uniform high critical current density that is almost independent of the magnetic field direction. Also, since it is possible to form a round or polygonal superconducting wire with high critical current density,
It is easy to wind around a coil and is useful as a magnet coil. Therefore, when the oxide superconductor of the present invention is used for a magnet coil, a high-performance magnet coil can be manufactured.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an example of an oxide superconducting wire of the present invention.

FIG. 2 is a partially enlarged schematic view of a longitudinal section showing an annular superconducting layer of an oxide superconducting wire.

FIG. 3 is a cross-sectional view showing an annular superconducting layer of an oxide superconducting wire.

FIG. 4 is a perspective view showing a superconducting layer structure of a tape-shaped oxide superconducting wire.

FIG. 5 is a graph showing that the critical current density of a tape-shaped superconducting wire when a magnetic field is applied depends on the magnetic field direction.

FIG. 6 is a cross-sectional view showing a magnetic field distribution generated in a magnet coil.

FIG. 7 is a cross-sectional view showing a production example of the oxide superconducting wire of the present invention.

FIG. 8 is a logarithmic graph showing a change in critical current density of an oxide superconducting wire when a magnetic field is applied.

FIG. 9 is a vertical sectional view showing another embodiment of the oxide superconducting wire of the present invention.

[Explanation of symbols]

 1 metal tube 2 metal core 3 superconducting layer D superconducting wire K void

Front Page Continuation (72) Inventor Junichi Kai, 8 Nishinomachi, Higashimukaijima, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Wire & Cable Co., Ltd.

Claims (5)

[Claims] 1. A void formed by a metal tube and a metal core inserted through the metal tube, the void being formed around the entire circumference of the metal core is filled with an oxide superconductor. An oxide superconducting wire characterized by forming a cylindrical superconducting layer oriented in the circumferential direction in the shape of mica and in the longitudinal direction. 2. The oxide superconducting wire according to claim 1, wherein the metal tube has a silver layer formed on at least the inner peripheral surface thereof. 3. The oxide superconducting wire according to claim 1, wherein the metal core has a pipe shape or a rod shape in which a silver layer is formed on at least the outer peripheral surface thereof. 4. The oxide superconducting wire according to claim 1, wherein the tubular superconducting layer is formed to have a thickness of 10 to 150 μm. 5. The oxide superconductor is Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _X or Bi ₂ Sr ₂ CaCu ₂ O _y (where x is 9.80 to 10.2).
5, y is a positive number from 8.00 to 8.35. ) The oxide superconducting wire according to claim 1, which is represented by