JPH06140233A - Manufacture of oxide superconducting coil - Google Patents

Abstract

PURPOSE:To improve the critical current density of an oxide superconducting coil by improving the C-axis orientation of oxide superconducting crystal in the wire material with which an oxide superconducting coil is formed. CONSTITUTION:A material, to be formed into a tape-like oxide superconducting wire material, is formed in a coil 2 by conducting heat-treatment thereon. A crystal of oxide superconducting material, having high C-axis orientational property, can be obtained by heating up the material to 830 deg.C or higher, desirably 840 deg.C or higher, in the state wherein a ceramic spring 1 is fitted to the outer or inner circumference of the coil 2, and at the same time, the load (about 10 to 20kgf/cm<2>) is applied to the coil 2 by the ceramic spring 1. As a result, the crystal of C-axis orientation can be grown easily, and the critical current density of the oxide superconducting coil can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide superconducting coil.

[0002]

2. Description of the Related Art It is known that in oxide superconductors, the higher the c-axis orientation of the crystals in the conductor, the higher the critical current density. Therefore, in order to obtain an oxide superconducting coil having a high critical current density, the conventional method has been performed as follows.
That is, the tape-shaped oxide superconducting wire is wound around the winding frame together with an insulating material, molded into a coil shape, heat-treated, and then unraveled to remove the insulating material. After that, a load is applied to the wire by straightening the wire and pressing or rolling at room temperature to improve the crystal orientation (for example, Keisuke Yamamoto et al., 1990). Autumn Low Temperature Engineering, Superconductivity Society Proceedings C2-8, etc.).

Further, recently, a ring-shaped shape memory alloy having an inner shape slightly smaller than the outer shape of a coil-shaped superconducting wire is expanded at a low temperature, fitted to the outside of the coil, and then a ring of the shape memory alloy is attached. A method of pressurizing a coil of a superconducting wire by heating it to a temperature above the martensitic transformation point has been proposed (JP-A-3-208308).

[0004]

In the conventional method, since no load is applied to the wire during the heat treatment, the oxide superconductor crystal grows in the wire in any direction. Even if this is heat-treated and then pressed or rolled to improve the crystal orientation, there is a problem that there is a limit to the improvement of orientation.

Further, in the conventional method, since a long wire formed into a coil shape is pressed or rolled, it is necessary to unravel the coil and return it to a straight line. Moreover, in order to reconstruct the intergranular bond destroyed by the press working or roll rolling, it is necessary to heat-treat the wire again.To this end, the linear wire is rewound after pressing or roll rolling. It is necessary to wind it around the insulating material together with the insulating material to form a coil shape. As a result, there is a problem that the stress applied to the wire during these steps causes fine cracks inside the wire, thereby lowering the critical current density of the wire.

Further, in the conventional method, in order to improve the orientation, it is necessary to repeat the above-mentioned series of steps 2-3 times, which causes a problem that the number of steps is significantly increased.

Further, the method using a shape memory alloy cannot be sintered at a high temperature because of problems such as change in the properties of the metal at a high temperature and weakening. JP-A-3-2083
No. 08 gazette describes that it may be sintered with the shape memory alloy ring attached, but there is no description of the sintering temperature.
At a high temperature, which is preferable for bismuth-based or thallium-based oxides, there is a problem that pressure cannot be applied because the metal becomes brittle.

[0008]

A method for manufacturing an oxide superconducting coil according to the present invention comprises a tape-shaped oxide superconducting wire wound around an winding material together with an insulating material on the outer circumference and / or the inner circumference of a coil. By applying an annular ceramic spring, a load is applied to the wire being heat-treated.

[0009]

In the method for producing an oxide superconducting wire according to the present invention, the oxide superconductor crystal grows under a load applied during the heat treatment, so that the c-axis oriented crystal growth is facilitated.

Further, in the method for producing an oxide superconducting wire according to the present invention, the oxide superconducting crystal which has already grown before the heat treatment is subjected to a load at a high temperature which is likely to be plastically changed, so that the c-axis orientation is improved. There is an action to do.

Further, according to the method for producing an oxide superconducting wire according to the present invention, a step of unraveling the coil after the heat treatment into a linear shape, a step of re-molding the linear wire after the pressing step or the rolling step, and Since it is not necessary to perform the reheat treatment step, there is an effect that the number of steps can be reduced.

[0012]

EXAMPLE The method of the present invention is a method of forming a tape-shaped oxide superconducting wire or a material to be a tape-shaped oxide superconducting wire by heat treatment into a coil shape, and forming an annular shape on the outer circumference and / or the inner circumference of the coil. A high temperature of 830 ° C. or higher, preferably 840 ° C. or higher in a state where the ceramic spring is fitted, and a load (about 10 to 20 kgf / cm ² ) from the ceramic spring is applied to the coil at the same time, and the oxide superconductivity with high c-axis orientation is obtained. This is a method of obtaining a crystal of the material. FIG. 1 is a perspective view of the annular ceramic spring used in the method of the present invention.

The method of the present invention can be achieved only by using an annular ceramic spring. That is, in order to grow or sinter the bismuth oxide or thallium oxide superconductor, 8
A high temperature of 30 ° C. or higher is required, and there is no other material than ceramics that has strength enough to apply a load to a wire at such a high temperature.

Even if a manufacturing method similar to that of the present invention is carried out by using, for example, a metal spring or the like, the spring itself is deformed in the metal spring weakened by high temperature, so that the c-axis orientation of the superconductor is improved. Since no sufficient load is generated, the excellent effect as in the present invention cannot be obtained. Further, at a low temperature at which the metal does not become brittle, there is not much difference from the case where the pressurizing method in the conventional method is simply changed, and the excellent effect as in the present invention cannot be obtained.

The oxide superconducting wire preferably used in the method of the present invention is a bismuth oxide superconductor high temperature phase,
In addition to the low-temperature phase and thallium-based oxide superconductors, yttrium-based oxide superconductors and the like can be mentioned. Among them, a tape-shaped silver sheath wire rod using a bismuth-based oxide or thallium-based oxide superconductor is particularly preferably used.
The silver of the silver sheath has a purity of 70 to 100%.

Examples of ceramic materials preferably used in the method of the present invention include partially stabilized zirconia and silicon nitride.

The heating temperature is 830 ° C. or higher, preferably 83
The temperature is 0 to 900 ° C., and in the case of a bismuth oxide, 830 to 900 ° C. is preferable, and 845 to 855 ° C. is particularly preferable. In the case of a thallium-based oxide, it is preferably slightly higher than the above and about 890 ° C.
If the heating temperature is less than 800 ° C, it is difficult to obtain a superconducting phase.

The present invention will be described in more detail based on the following specific examples, but the present invention is not limited to these examples.

Example 1 Partially stabilized zirconia was kneaded together with polyvinyl alcohol as a binder to form a slurry, which was then formed into a sheet having a thickness of 3 mm by the doctor blade method. This was cut out into a strip shape with a width slightly wider than the wound coil width and a length corresponding to the diameter of the ring after molding. The strip is formed into a ring,
After drying and firing, an annular ceramic spring having a partial notch as shown in FIG. 1 was produced.

The reason why the spring having a notch instead of a perfect ring is to spread the annular ceramic spring and insert it into the coil. In this embodiment, the inner diameter of the annular ceramic spring is made slightly smaller than the outer diameter of the coil.

A tape-shaped oxide superconducting silver sheath wire made of a bismuth-based high-temperature phase, which is manufactured according to the conventional method, is provided around the silver reel and is made of 80% alumina and 20% silica.
Approximately 30 outside diameter by winding with a fiber tape
mm, and a height of about 40 mm was formed into a coil shape, and the annular ceramic spring was fitted on the outer circumference of the coil. FIG. 2 is a plan view showing a state in which the annular ceramic spring is fitted on the outer circumference of the coil. In the figure, 3 is a silver reel, 2 is a coil of tape-shaped oxide superconducting silver sheath wire, and 1 is an annular ceramic spring.

The coil fitted with the annular ceramic spring was heat-treated in air at 850 ° C. for 100 hours, then cooled to room temperature, and the annular ceramic spring was pushed out and removed to obtain an oxide superconducting coil. By fitting the annular ceramic spring, it was possible to apply 10 kgf / cm ^{2 to the} sample at 850 ° C., which is a temperature at which the bismuth-based high temperature phase easily grows in the atmosphere.
Was being loaded. This sample was not subjected to press working or roll rolling after heat treatment and reheat treatment.

When the critical current density of the obtained oxide superconducting coil was measured at 77K and the applied magnetic field was zero Tesla 0T (hereinafter referred to as 0T), the critical current density was 7400A /
It was cm ² .

[Example 2] An annular ceramic spring was produced in the same manner as in Example 1. In this embodiment, two types of annular ceramic springs having different inner diameters were manufactured so that the inner diameter of the larger annular ceramic spring was slightly smaller than the outer diameter of the smaller annular ceramic spring.

In the same manner as in Example 1, a tape-shaped oxide superconducting silver sheath wire using a bismuth high temperature phase was formed into a coil shape. The smaller annular ceramic spring was fitted on the outer circumference of the coil, and the larger annular ceramic spring was fitted on the outer circumference thereof. Boron nitride powder was applied between the two annular ceramic springs so that the two annular ceramic springs would not sinter each other due to heat treatment. After heat-treating this in air at 850 ° C for 100 hours,
An oxide superconducting coil was manufactured in the same manner as in Example 1.
Since two annular ceramic springs are attached to the outer circumference of the coil, it is calculated that the sample is 20 k
A load of gf / cm ² was applied. This sample was not subjected to press working or roll rolling after heat treatment and reheat treatment.

When the critical current density of the obtained oxide superconducting coil was measured at 77K and 0T, the critical current density was 9
It was 800 A / cm ² .

[Example 3] An annular ceramic spring was produced in the same manner as in Example 1. In this example, two types of annular ceramic springs having different inner diameters were produced, and the inner diameter of the larger annular ceramic spring was slightly smaller than the outer diameter of the coil of the tape-shaped oxide superconducting silver sheath wire.
Further, the outer diameter of the smaller annular ceramic spring is set to be slightly larger than the inner diameter of the coil.

A tape-shaped oxide superconducting silver sheath wire made of a bismuth-based high-temperature phase, which was manufactured according to a conventional method, was manufactured by using the smaller annular ceramic spring as a winding frame.
A coil shape was formed in the same manner as in. The larger annular ceramic spring was fitted on the outer circumference of the coil. This was heat-treated in air at 850 ° C. for 100 hours, and then an oxide superconducting coil was manufactured in the same manner as in Example 1. By fitting the annular ceramic spring on the inner circumference and the outer circumference of the coil, it was calculated that 19 kgf / cm ² was applied to the sample at 850 ° C., which is a temperature at which the bismuth-based high temperature phase easily grows in the atmosphere.
Was being loaded. This sample was not subjected to press working or roll rolling after heat treatment and reheat treatment.

When the critical current density of the obtained oxide superconducting coil was measured at 77K and 0T, the critical current density was 1
It was 2100 A / cm ² .

Example 4 An annular ceramic spring having a partial cutout was prepared in the same manner as in Example 1, except that the partially stabilized zirconia in Example 1 was replaced with silicon nitride.

Heat treatment was carried out in the same manner as in Example 1 using the tape-shaped oxide superconducting silver sheath wire made of the bismuth-based high temperature phase produced according to the conventional method.

By fitting the annular ceramic spring, a load of 12 kgf / cm ² was applied to the sample at 850 ° C.

This sample was not subjected to pressing or roll rolling after heat treatment and reheat treatment.

When the critical current density of the obtained oxide superconducting coil was measured at 77K and 0T, the critical current density was 87.
It was 00 A / cm ² .

Comparative Example 1 A tape-shaped oxide superconducting silver sheath wire made of a bismuth-based high-temperature phase, which was manufactured according to a conventional method, was used as an insulating material around the silver winding frame.
It was wound together with a fiber tape of 20% silica to form a coil shape. The coil at 850 ° C in air for 2
Heat treatment was performed for 5 hours. After the coil after the heat treatment was unraveled and the wire rod was made into a linear shape, it was rolled. The wire rod after the roll rolling was wound again around the silver winding frame together with the insulating material to be formed into a coil shape, and then again heat-treated in the atmosphere at 850 ° C. for 25 hours. The above-mentioned series of steps was performed twice so that the total heat treatment time of the oxide superconducting coil was 100 hours, which was the same as in Examples 1 to 3, to manufacture an oxide superconducting coil by the conventional method.

When the critical current density of the oxide superconducting coil of the comparative example was measured at 77K and 0T, the critical current density was 3200A / cm ² .

From Examples 1 to 4 and Comparative Example 1, it can be seen that the critical current density of the bismuth-based oxide superconducting coil obtained by the method of the present invention is significantly higher than that obtained by the conventional method. .

Example 5 A tape-shaped thallium-based oxide superconducting silver sheath wire produced according to a conventional method was formed into a coil around the silver reel in the same manner as in Example 1. An annular ceramic spring made of partially stabilized zirconia prepared in the same manner as in Example 1 was fitted on the outer periphery of the coil, heat-treated at 890 ° C. for 100 hours in the atmosphere, cooled to room temperature, and the annular ceramic spring was removed. I got an oxide superconducting coil. By using the annular ceramic spring, a load of 10 kgf / cm ² was applied to the sample at 890 ° C.

This sample was not subjected to pressing or roll rolling after heat treatment and reheat treatment.

When the critical current density of the obtained oxide superconducting coil was measured at 77K and 0T, the critical current density was 24.
It was 00 A / cm ² .

[Comparative Example 2] A tape-shaped oxide superconducting silver sheath wire produced in the same manner as in Comparative Example 1 using a thallium-based oxide superconductor was molded into a coil shape in the same manner as in Comparative Example 1 and then compared. Heat treatment including an intermediate press was performed in the same manner as in Example 1. However, the heat treatment temperature was 890 ° C.

When the critical current density of the oxide superconducting coil of Comparative Example 2 was measured at 77K and 0T, the critical current density was 1900A / cm ² .

Although the critical current densities of the thallium-based oxide superconductors of Example 5 and Comparative Example 2 are smaller than those of the bismuth-based ones, those obtained by the method of the present invention include a roll rolling step. It can be seen that it is much larger than that obtained by the conventional method.

Scanning electron microscope observations were made on the cross sections of the silver sheath wire forming the oxide superconducting coil obtained in the above example and the silver sheath wire forming the oxide superconducting coil obtained in the comparative example. Those obtained in Examples 1 to 5 which were heat-treated using an annular ceramic spring had a clearly improved c-axis orientation as compared with those obtained in Comparative Examples 1 and 2.

[0045]

According to the method for producing an oxide superconducting wire of the present invention, the c-axis orientation of the oxide superconducting crystals in the wire forming the oxide superconducting coil is improved, so that the critical current of the oxide superconducting coil is improved. This has the effect of improving the density.

Further, according to the method for producing an oxide superconducting wire of the present invention, the step of performing heat treatment after pressing or roll rolling and then heat treatment again can be omitted, so that the number of steps can be reduced.

Further, since operations such as unraveling of the coil, press working or roll rolling, and re-shaping into a coil shape are omitted, minute cracks inside the wire caused by stress applied to the wire during these steps are generated. Is prevented, and a decrease in the critical current density of the wire is prevented.

[Brief description of drawings]

FIG. 1 is a perspective view of an annular ceramic spring of the present invention.

FIG. 2 is a plan view showing a state in which the annular ceramic spring according to the first embodiment is fitted on the outer circumference of the coil.

[Explanation of symbols]

 1 Annular ceramic spring 2 Oxide superconducting wire coil

Claims (2)

[Claims] 1. A method for producing an oxide superconducting coil, which comprises a step of winding a tape-shaped oxide superconducting wire together with an insulating material around a winding frame and forming the oxide superconducting coil into a coil shape. A method for manufacturing an oxide superconducting coil, which comprises heat-treating an annular ceramic spring fitted on the inner circumference. 2. The method for producing an oxide superconducting coil according to claim 1, wherein the material of the annular ceramic spring is silicon nitride or partially stabilized zirconia.