JPH08222430A - Oxide superconducting coil, its manufacture and insulating material used for it - Google Patents

Abstract

PURPOSE: To prevent an insulating layer from reacting with superconducting wire material by using insulating paper composed of specific alumina fiber as the insulating layer. CONSTITUTION: Alumina fiber which contains 90wt.% or more Al2 O3 is put in a agitation tank provided with a high speed agitator by 70-95wt.%., and alumina fiber slurry is obtained by agitating the alumina fiber. Conifer pulp whose freeness is adjusted to 300ml or less is added to the slurry by 30-50wt.%, grain PVA of 1-10wt.% is added and the slurry is well agitated. Paper is manufactured from the paper material by using an inclined wire gauze type paper machine, and insulating paper 2 composed of continuous alumina fiber sheet is provided. The wire material 1, which is oxide superconducting wire, and the insulating paper 2 are wound together by applying tensile force to the wire material 1 and the insulating paper 2, and a single pancake coil is made. The oxide superconducting wire is coated with a metal which contains silver or gold as the major component and is permitted to have a flat circle or polygon cross-section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an oxide superconducting coil,
And an insulator for insulating between the superconducting wires of the coil.

[0002]

2. Description of the Related Art NbTi and N have been conventionally used as superconducting materials.
Metal-based superconductors such as b ₃ Sn are known. But,
These metal-based superconductors have a maximum superconducting critical temperature (Tc) of 23 K even with Nb ₃ Ge, and it was necessary to use expensive liquid helium for cooling them. However, 198
In 7 years, Tc exceeds liquid nitrogen temperature (77K) Y ₁ Ba ₂
Cu ₃ O since _X-system is _{found, Bi 2 Sr 2 Ca 1 Cu} 2 O
_X system, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _X system, and Tl ₁ Sr ₂
Ca ₁ Cu ₂ O _x system, Tl ₁ Sr ₂ Ca ₂ Cu ₃ O _x system, Tl ₂
Ba ₂ Ca ₁ Cu ₂ O _x system and Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x
A series of oxide superconducting materials were discovered one after another.

When these oxide superconducting materials can be put into practical use, inexpensive and easily available liquid nitrogen can be used, which has a great impact in the industrial field.

Further, the oxide superconductor has a Tc as described above.
In addition to the high value, it has a characteristic that the superconducting critical magnetic field is high. By utilizing this characteristic, it is possible to generate a high magnetic field of 25 Tesla (T) class, which could not be achieved by conventional metal-based superconductors. Therefore, it is particularly expected to be applied in the field of high electric power using superconducting magnets. Has been done. For use in these high-voltage fields, improvement of wire performance, homogeneity of long wire, workability and coil winding property are important.

As a method of coil winding, there is a low temperature engineering second method.
Volume 7, Issue 1. As described in 1992, pp. 70-76, the wind-and-react method of applying a predetermined heat treatment after winding to form a coil is suitable,
In that case, the selection of the insulating material used for the interlayer insulation of the coil becomes an important issue.

[0006]

The necessary characteristics of the insulating material are that it is thin enough to exhibit the performance of the coil, that it is flexible enough to be wound with the superconducting wire, and that it is wound with the superconducting wire. It is required that the insulation characteristics do not deteriorate in the heat treatment (firing) step of (1), and that it does not react with the superconductor in the firing step. In order to satisfy these requirements, it is considered that a paper-like insulator mainly composed of inorganic fibers is most desirable.

It has been proposed to use ceramic paper for the insulating layer of such an oxide superconducting coil (for example, Japanese Patent Laid-Open Nos. 4-10507 and 4-116906).

Therefore, the inventors of the present invention produced a thin sheet mainly composed of ceramic fibers (alumina silicate fiber: Al ₂ O ₃ content = about 50% by weight) and evaluated the characteristics as an insulator.

As a result, in the firing process after winding the ceramic fiber sheet together with the superconducting wire, the SiO ₂ contained in the ceramic fiber is contained in the superconducting wire through the pinholes or grain boundaries of the coating material. It has been revealed that it reacts with earth metals and deteriorates the coil performance (Tanaka et al., 51st Annual Conference of the Spring Society for Superconductivity, Low Temperature Engineering, 1994).

An object of the present invention is to solve the above problems, and an object thereof is to provide an oxide superconducting coil having an insulating layer made of a ceramic fiber which does not react with a superconducting wire and a method for producing the same.

Another object of the present invention is to provide an insulator for an oxide superconducting coil which has a thinness and flexibility for winding with the above-mentioned layer superconducting wire and does not react with the superconducting wire in the firing process. .

[0012]

Means for Solving the Problems The gist of the present invention for solving the above problems is as follows.

[1] In an oxide superconducting coil in which an oxide superconducting wire is wound in a coil shape via an insulating layer, the insulating layer is made of alumina fiber having an Al ₂ O ₃ content of 90% by weight or more. Oxide superconducting coil that is paper.

[2] An oxide superconducting coil in which the oxide superconducting wire is covered with a metal containing silver or gold as a main component and the cross-sectional shape is flat, circular or polygonal.

[3] The oxide superconducting wire is made of Al ₂ O ₃
Oxide superconducting coil wound and insulated with an insulating paper made of alumina fiber having a content of 90% by weight or more.

[4] 70 to 95% by weight of alumina fibers having an Al ₂ O ₃ content of 90% by weight or more and a freeness of 300 m
An insulator for an oxide superconducting coil, which is composed of 30 to 5% by weight of pulp of 1 or less.

[5] The insulating paper is an oxide superconducting coil insulator containing 1 to 10% by weight of at least one kind of organic adhesive and alumina sol.

[6] An oxide superconducting wire is formed by using 70 to 95% by weight of alumina fibers having an Al ₂ O ₃ content of 90% by weight or more,
A method for producing an oxide superconducting coil, which is formed by winding an insulating paper consisting of 30 to 5% by weight of pulp having a freeness of 300 ml or less and winding it into a coil to form a single pancake coil, and then heat-treating at a predetermined temperature. .

[7] The insulating paper is a method for producing an oxide superconducting coil containing 1 to 10% by weight of at least one kind of organic adhesive and alumina sol.

By using alumina fibers having an Al ₂ O ₃ content of 90% by weight or more as the insulating material,
It was confirmed that the reaction with the alkaline earth metal in the oxide superconducting wire is less likely to occur and does not affect the characteristics of the superconducting coil.

Further, since insulating paper consisting only of alumina fibers is fragile, it is made thin (thickness: 0.
It is possible to obtain an insulating paper that is flexible and has excellent handleability.

When the superconducting coil is wound, it is necessary to wind it while applying a specific tension in order to improve the winding density. Tensile strength of such insulating paper for coils is 1K
It is desirable that it is gf / mm ² or more.

By the way, the alumina fiber is Al ₂ O ₃ --Si.
It is made into fibers by various methods using O ₂ as a starting material.
However, the alumina fiber used in the present invention is A
The content of l ₂ O ₃ is limited to 90% by weight or more. 9
If the alumina fiber content is less than 0% by weight, the reaction with the alkaline earth metal in the oxide superconducting wire is large, and the performance of the superconducting coil is significantly reduced.

In the insulating paper of the present invention, the compounding ratio of the alumina fiber and the pulp is 30 to 5% by weight of pulp with respect to the former 70 to 95% by weight. Also, the thickness of the insulating paper is 0.1m
In the case of m or less, it is desirable to mix a certain amount of organic binder in order to secure the sheet strength. Paper thickness is 0.1
If it is thicker than mm, the amount of alumina fiber may be increased, and the degree of freedom is increased accordingly, but even in that case, addition of 5% by weight of pulp is necessary.

The amount of pulp required for papermaking depends on the thickness of the insulating paper. When the paper thickness is 0.1 mm or less, the pulp content can be reduced to 20 to 30% by weight, and when the paper thickness is thicker than this, the pulp content can be reduced. However,
If the pulp content exceeds 30% by weight, the superconducting wire may be damaged due to abnormal heat generation during the preliminary firing of the superconducting wire. The pulp in the insulating paper wound around the oxide superconducting wire is completely burned and dissipated in the pre-baking stage, leaving only the alumina fiber, which functions as an insulating layer.

Usual kraft pulp can be used as the pulp. The pulp preferably has a freeness of 300 ml or less which is beaten by a usual method. The blended pulp has the properties of both the skeletal fiber and the binder fiber, but if the freeness exceeds 300 ml, the binder effect is reduced. In particular, when the paper thickness is 0.1 mm or less, the tensile strength is insufficient. Further, when the freeness is extremely low, the function of the skeletal fiber is deteriorated, the strength of the wet paper is insufficient, and the drainage property is further deteriorated to cause a problem in the papermaking process. Even if the pulp having a high freeness (350 ml or more) is mixed with the pulp having a low freeness, the freeness after the mixing is 300 ml or less (preferably 100 ml or less).
~ 300 ml) can be used.

In order to obtain the sheet strength, it is preferable to add 1 to 10% by weight of a binder which is easily scattered during the preliminary firing. For example, the sheet strength can be improved by adding fibrous or granular PVA, emulsion acrylic resin, SBR or the like to the raw material. The amount of these binder resins added is preferably 10% by weight or less in order to suppress abnormal combustion (rapid temperature rise) during pre-baking.

As another binder, a colloidal solution of alumina hydrate (alumina sol) using water as a dispersion medium may be used in combination. It is most preferable in terms of material properties if a sheet can be formed from only the alumina fiber and the alumina sol, but the alumina sol alone cannot provide the required strength in the papermaking process when the paper thickness is thin.

The insulating paper of the present invention can be produced by a conventional wet papermaking method. That is, alumina fibers are prepared in water using a disperser to a suitable fiber length to form a slurry, and pulp with the freeness adjusted in advance is added thereto,
If necessary, a suitable binder is added to prepare a papermaking raw material. Continuous papermaking is carried out using an ordinary paper machine such as a round-mesh type, a fourdrinier type, and a slanted wire-mesh type.

As the oxide superconducting material in the present invention,
For example, in the case of Y-Ba-Cu-O system, yttrium compounds, barium compounds, and copper compounds are used. In the case of Bi-Sr-Ca-Cu-O system, bismuth compound, strontium compound, calcium compound,
A copper compound is used, and if necessary, a lead compound and a barium compound are used. In the case of Tl-Sr-Ca-Cu-O system or Tl-Ba-Ca-Cu-O system, a thallium compound, a strontium compound, a barium compound, a calcium compound, a copper compound is used, and a bismuth compound, if necessary, Lead compounds are used. In addition, when using oxide superconductors such as Hg-based superconductors and Ag-based superconductors, compounds necessary for these are used. Such raw material compounds include oxides, hydroxides, carbonates, nitrates, borates, acetates and the like.

As a method for producing the oxide superconducting powder, there may be mentioned a method in which the respective compounds are crushed and mixed, and the resulting mixture is fired. In this case, all the raw material compounds may be mixed at once, or a part of the raw material compounds may be mixed in advance and then the remaining raw material compounds may be mixed. These methods can be selected depending on the superconducting material.

The processing temperature during the synthesis or intermediate firing of the oxide superconducting powder is generally 600 to 1200.
Performed at ° C. If necessary, after heating above the partial melting temperature, the non-superconducting phase is dispersed in the crystal grains of the superconducting phase in the process of cooling it to increase the pinning force.

Many methods have been proposed so far for manufacturing the oxide superconducting wire. Here, the wire drawing / rolling method will be described as an example.

After synthesizing the oxide superconductor or the precursor by the method as described above, it is crushed to have an average particle size of 1 to 5 μm and filled in a metal pipe. Next, using a draw bench, a swager, a cassette roller die, or a groove roll, wire drawing is performed at a cross-section reduction rate of 5 to 20%, and wire drawing is performed to a predetermined wire diameter. Then, if necessary, the wire rod is made to have multiple cores.

At the time of making the multi-core, a wire rod having a flat, circular or polygonal cross-section is drawn, filled into a metal pipe and stretched to a cross-section reduction rate of 5 to 20% by using the above apparatus. Line. As a result, a wire having a desired shape can be obtained, and at the same time, the density of the superconductor powder filled in the sheath can be increased.

Next, in order to further densify, the tape-shaped wire is processed by a cold or hot rolling mill, and then heat-treated in an appropriate temperature and atmosphere to obtain a wire having a high current density. To be Depending on the purpose of use, it may be used without rolling.

The final heat treatment temperature of the oxide superconducting wire is 700 to 1100 ° C. In order to improve the characteristics of the superconductor in this heat treatment process, for example, Bi ₂ Sr ₂ C
For a ₁ Cu ₂ O _X superconductor, a low pressure oxygen atmosphere (e.g., 5 to 20% O ₂₎ is selected. However, Tl ₂ Ba ₂ C
In the case of an a ₂ Cu ₃ O _x superconductor, a pure oxygen atmosphere is selected because the higher the oxygen partial pressure, the better the characteristics.

It is possible to obtain the same value by using a wire rod produced by a method other than the above, for example, a thermal spraying method, a doctor blade method, a dip coating method, a screen printing method, a spray pyrolysis method or a jelly roll method. is there.

The sheath material and the substrate material of the superconducting wire are
Mainly silver, gold, palladium, platinum or silver-based alloy containing 1 to 50% by weight of gold, which does not cause corrosion during heat treatment, 1 to 50% by weight of palladium, magnesium, titanium, manganese, nickel, copper A silver-based or gold-based alloy containing is used. If necessary, the outermost layer of the superconducting wire may be reinforced with a nonmagnetic heat-resistant alloy.

The conductor thus processed into a desired structure is processed into a coil and then heat-treated by the wind-and-react method. In addition, when the deformation such as bending is small, for example, when the bending strain is 0.5% or less, the react-and-wind method of winding after heat treatment (Superconducting Communications: Volume 12, No. 3, 1993)
It may be processed by.

Due to the coil design, the insulating layer of the coil of the present invention is required to be densely wound when increasing the generated magnetic field. For that purpose, the thinner the insulating layer is, the more preferable.

After the heat treatment, it goes without saying that the superconducting property is not deteriorated, but it is important that the insulating property, the adhesion property, the strength, the heat resistance and the like are excellent.

The superconducting coil of the present invention is used for a superconducting magnet, an MRI apparatus, an NMR apparatus, a magnetic levitation train, a SOR apparatus, a SMES apparatus, a superconducting generator, a superconducting motor, a superconducting magnetic propulsion ship, a superconducting transformer and the like.

[0044]

In the present invention, by using alumina fiber having an Al ₂ O ₃ content of 90% by weight or more as the insulating paper,
Since the reaction between the alumina fiber and the alkaline earth metal in the oxide superconducting wire does not occur, deterioration of the superconducting characteristics of the coil can be suppressed.

Since a thin and flexible sheet-like insulating paper is obtained by adding a predetermined amount of pulp as a reinforcing fiber of alumina fiber and a binder, the coil can be compactly formed and occupies the entire coil. A superconducting coil having a large proportion of superconductors can be produced.

[0046]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 Al ₂ O ₃ Content 97% by Weight
Alumina fiber (B-97NL: manufactured by Denki Kagaku Kogyo) 70
kg was put into a stirring tank equipped with a high-speed stirrer and stirred for a short time to obtain an alumina fiber slurry. This slurry has a freeness of 200 ml and a solid content of 25 kg NBKP (normal softwood pulp: Neadleleaf Bleached Kraft Pu).
lp), 5 kg of granular PVA (KVG, manufactured by Denki Kagaku Kogyo Co., Ltd.) was added, and the mixture was stirred well. This papermaking raw material was made into paper by an inclined wire netting paper machine to obtain insulating paper made of continuous alumina fiber paper having a thickness of 0.1 mm.

Next, Bi ₂ O ₃ , SrO, CaO and Cu
The respective oxides of O were weighed so that the atomic molar ratios of Bi, Sr, Ca and Cu were each 2: 2: 1: 2. To this, ethanol (pure water may be used) was added, mixed with a centrifugal ball mill for 1 hour, dehydrated and dried, and then heat-treated at 820 ° C. for 10 hours in the air to obtain a Bi-2212 superconducting powder. From the results of X-ray diffraction and scanning electron microscope observation of the powder, some hetero phases of SrO and CuO were recognized.

An average particle size of 5 μm was obtained by using a powder mill for the above powder.
It was crushed as follows and filled in an Ag pipe having an outer diameter of 6.0 mm and an inner diameter of 5.0 mm. After that, the cross-section reduction rate of 1 on the draw bench
2 to 15% of the work was applied, and the wire was drawn to an outer diameter of 1.0 mm. This is cut into 19 equal lengths, and the outer diameter is 6.0m.
m, internal diameter of 5.2 mm, after being loaded into an Ag pipe, using a draw bench and a rolling mill, the cross-sectional reduction rate of 12 to 15 in the cold.
%, Finally, Bi-2212 / 19 having a thickness of 0.1 to 0.15 mm, a width of 4 to 5 mm, and a length of 40 to 50 m.
A core tape-shaped Ag sheath wire was obtained. Annealing was performed twice at 350 ° C. for 30 minutes during the processing of the single-core and multi-core wires.

Using this wire and the alumina insulating paper having the Al ₂ O ₃ content of 97% by weight, as shown in FIG. 1, the wire 1 was applied with a tension of 10 kgf / mm ² , and the insulating paper 2 was applied with 0 tension. .
Winding was performed while applying a tension of 5 kgf / mm ² , respectively, to prepare a single pancake coil having an outer diameter of 80 mm and an inner diameter of 30 mm. The coil core 3 has an outer diameter of 30.
A mm Ag ring was used.

This was heated to 880 ° C. for 4 hours in a pure oxygen atmosphere, subjected to partial melting heat treatment at 880 ° C. for 10 minutes, then cooled to 815 ° C. at a rate of 0.25 ° C./minute, and then to room temperature. The temperature was lowered over 2 hours. Furthermore, in order to improve the superconducting property, 800 in a low pressure oxygen atmosphere (5% O ₂ ).
An annealing treatment was performed at 20 ° C. for 20 hours to obtain a Bi-2212 superconducting coil. Adhesion, strength of insulating layer after heat treatment,
A sufficiently good superconducting coil was obtained as the insulating property.

The critical current in a zero magnetic field of a short wire having a length of 50 mm which was heat treated at the same time was measured by a four-terminal resistance method, and it was 60 A at 20K and 90A at 4.2K. The criterion at this time was 1 μV / cm. Then, the critical temperature was measured and found to be 85K.

Next, the critical current of this coil was measured by the four-terminal resistance method under the condition that the external magnetic field was zero.
It was 87A at 8.5A and 4.2K. The criterion at this time was set to 10 to ¹³ Ω · m.

Next, when the wire rod was cut out from the coil and the critical temperature was measured, it was 85 K as with the short wire. Further, when the superconducting powder of this wire core was taken out and subjected to ICP analysis, it was found that Bi _1.98 Sr _2.00 Ca _0.99 Cu _2.00 O
_{It was X.}

Twelve pancake coils having the same size as the coil were laminated to prepare a 12-stage laminated coil as shown in FIG. In order to maintain the insulation of each stage of the superconducting coil 4, an Al ₂ O ₃ disc 5 having a thickness of 100 μm was inserted. The critical current of this laminated coil and the magnetic field generated at the center of the coil were measured by the four-terminal resistance method under the condition that the external magnetic field was zero. As a result, the critical current at 20K was 50 A and the generated magnetic field was 0.7.
The critical current at T and 4.2K is 85 A, and the generated magnetic field is 1.2 T.
Met.

Table 1 collectively shows the critical current values of the short wire and the single pancake coil.

[0057]

[Table 1]

Example 2 Al ₂ O ₃ content of 95% by weight
90 kg of alumina fiber (Arsen: manufactured by Denki Kagaku Kogyo)
Was charged into a stirring tank equipped with a high-speed stirrer and stirred for a short time to obtain an alumina fiber slurry. Freeness 1 for this slurry
NBKP having a solid content of 10 kg adjusted to 50 ml was added and stirred well. This papermaking raw material was made into paper by an inclined wire netting paper machine to obtain a continuous alumina insulating paper having a thickness of 0.25 mm.

Next, Bi ₂ O ₃ , PbO, SrO, CaO
And oxides of CuO, Bi, Pb, Sr, Ca, C
The atomic molar ratio of u is 1.74: 0.34: 2.0, respectively.
Weighed to be 0: 2.20: 3.00. to this,
Add ethanol (pure water is also possible) and centrifuge with a ball mill.
After mixing for an hour, dehydration and drying treatments, and then heat treatment at 790 ° C. for 10 hours were performed in the atmosphere to obtain a Bi-2223 precursor powder. From the results of X-ray diffraction and scanning electron microscope observation of the powder, the main component was the Bi-2212 phase.
In addition, Sr-Ca-Cu-O whose crystal structure cannot be identified
And substances containing SrO, CuO, etc. were included.

An average particle size of 5 μm was obtained by using a powder mill for the above powder.
It is crushed into the following and has an outer diameter of 6.0 mm and an inner diameter of 5.0 mm Ag /
A 10 wt% Au alloy pipe was filled. This is Example 1
The diameter is reduced in the same manner as in the above, and finally the thickness is 0.5 mm and the width is 2.6.
A Bi-2223 / 19 core tape-shaped sheath (Ag / 10% by weight Au alloy) wire having a length of mm × 30 m was obtained.

This wire was wound on a SUS drum having an outer diameter of 50 cm and heat-treated at 835 ° C. for 48 hours in the atmosphere using a large electric furnace. After heat treatment, the wire thickness is 0.3m
It was rolled to m and further heat-treated at 835 ° C. for 48 hours. Then, the wire rod is rolled to a thickness of 0.2 mm, and after the heat treatment, the wire rod has a thickness of 0.11 to 0.15 m.
rolled to m.

Using this wire and the alumina insulating paper containing 95% by weight of Al ₂ O ₃ as shown in FIG.
A tension of kgf / mm ² is applied to the insulating paper 2 and 0.6 kgf.
Winding while applying tension of 1 / mm ² respectively, outer diameter 8
A single pancake coil having a diameter of 0 mm and an inner diameter of 30 mm was produced. In addition, the winding core 3 of the coil is made of Ag having an outer diameter of 30 mm.
A ring was used.

This was placed in a 5% O ₂ atmosphere at 835 ° C. and 48
Heat treatment was performed for a period of time to obtain a Bi-2223 superconducting coil. A superconducting coil having sufficiently good adhesion, strength, and insulating properties after the heat treatment was obtained.

The critical current (four-terminal resistance method) in a zero magnetic field of a short wire with a length of 50 mm, which was heat-treated at the same time, was 5 at 77K.
A, 63K 7.5A, 20K 21A, 4.2K 3
It was 2A. The criterion ion at this time is 1 μV / c
m. After that, when the critical temperature was measured, it was 116K.
Met.

Next, the critical current (four-terminal resistance method) of this coil was measured under the condition of zero external magnetic field. It was 4.6 A at 77K, 8.5A at 63K, 20.5A at 4.2K and 4.2.
In K, it was 31A. Criterion at this time is 10
It was set to ~ ¹³ Ω · m.

Next, when the wire was cut out from the coil and the critical temperature was measured, it was 115K. Further, when the superconducting powder of this wire core was taken out and subjected to ICP analysis, it was found to be Bi _1.70 Pb _0.31 Sr _2.05 Ca _2.24 Cu _3.00 O _x .

Table 2 collectively shows the critical current values of the short wire and the single pancake coil.

[0068]

[Table 2]

Comparative Example 1 Alumina fiber containing 97% by weight of Al ₂ O ₃ (B-97NL: manufactured by Denki Kagaku Kogyo) of Example 1 was added to alumina fiber containing 80% by weight of Al ₂ O ₃ (Arsen: electrochemical). A continuous alumina insulating paper having a thickness of 0.1 mm was obtained in exactly the same manner as in Example 1 except that the continuous alumina insulating paper was used.

Next, Bi obtained in the same manner as in Example 1 was used.
-2212/19 core tape-shaped Ag sheath wire and alumina fiber paper containing 80% by weight of Al ₂ O ₃ described above were used to prepare a single pancake coil having an outer diameter of 80 mm and an inner diameter of 30 mm as shown in FIG. .

This was heat-treated in the same manner as in Example 1 in pure oxygen and low-pressure oxygen atmosphere to obtain a Bi-2212 superconducting coil. Adhesion, strength of insulating layer after heat treatment,
Although the insulation was good, the surface of the wire was discolored due to the reaction between the alumina fiber paper and the superconducting wire.

At the same time, the critical current (four-terminal resistance method) in a zero magnetic field of a short wire having a length of 50 mm which was heat treated was measured and found to be 60 A at 20K and 90A at 4.2K.
The criterion at this time was 1 μV / cm. Then, the critical temperature was measured and found to be 85K.

Next, the critical current (four-terminal resistance method) of this coil was measured under the condition of zero external magnetic field.
It was 43A at A and 4.2K. The criterion at this time was set to 10 to ¹³ Ω · m.

Next, the wire was cut out from the above coil and the critical temperature was measured and found to be 79K. Further, when the superconducting powder of this wire rod core was taken out and subjected to ICP analysis, it was found to be Bi _1.98 Sr _1.77 Ca _0.68 Cu _2.00 O _X , and the composition had a small amount of alkaline earth metal. Table 1 shows the critical current values of the short wire and the single pancake coil described above.

Comparative Example 2 Al ₂ O ₃ in Example 1
Except that the alumina fiber (B-97NL, manufactured by Denki Kagaku) containing 97% by weight was replaced with the alumina silicate fiber (SC1260D2, manufactured by Nippon Steel Chemical Co., Ltd.) containing 50% by weight Al ₂ O _{3, the same} procedure as in Example 1 was carried out. A continuous alumina silicate insulating paper having a thickness of 0.1 mm was prepared.

Next, Bi obtained in the same manner as in Example 2 was used.
-2223/19 core tape-shaped sheath (Ag-10% by weight)
A single pancake coil having an outer diameter of 80 mm and an inner diameter of 30 mm as shown in FIG. 1 was manufactured using an Au alloy) wire and the above-mentioned alumina silicate insulating paper having an Al ₂ O ₃ content of 50% by weight. This was heat treated in a 5% O ₂ atmosphere in the same manner as in Example 2 to obtain a Bi-2223 superconducting coil. Although the insulating layer after heat treatment had good adhesion, strength, and insulating properties, the alumina silicate insulating paper and the superconducting wire rod reacted, and discoloration on the wire rod surface was observed.

The critical current (four-terminal resistance method) in a zero magnetic field of a short wire with a length of 50 mm that was heat-treated simultaneously with the coil was
5A at 77K, 8.5A at 63K, 31 at 4.2K
It was A. The criterion at this time was 1 μv / cm. Then, the critical temperature was measured and found to be 116K.

Next, the critical current (four-terminal resistance method) of this coil was measured under the condition of zero external magnetic field.
A minute resistance was generated below A. Also, the critical current was 63 A at 63 K and 9 A at 4.2 K. The criterion at this time was set to 10 to ¹³ Ω · m.

Next, when the wire was cut out from the above coil and the critical temperature was measured, it was found to be 65 K, and a significant decrease in superconducting properties was observed. When the superconducting powder of this wire rod core was taken out and subjected to ICP analysis, it was found that Bi _{1 .630} Pb _{0 .40} S
_{r 1. 70 Ca 1. 67} Cu 3. a ₀₀ O _X, had become alkaline earth metal is less composition. When the composition of the insulating layer after the heat treatment is analyzed by EDX, Si contained in the aluminum silicate insulating paper in addition to Al and S which is a component in the superconducting wire.
r and Ca were detected.

Table 2 collectively shows the critical current values of the short wire and the single pancake coil.

Comparative Example 3 Al ₂ O ₃ Content 97% by Weight
Alumina fiber (B-97NL: manufactured by Denki Kagaku Kogyo) 65
kg was put into a stirring tank equipped with a high-speed stirrer and stirred for a short time to obtain an alumina fiber slurry. To this slurry, NBKP having a solid content of 35 kg adjusted to a freeness of 200 ml was added and well stirred. This papermaking raw material was made into paper by an inclined wire mesh papermaking machine to obtain a continuous aluminum insulating paper having a thickness of 0.1 mm.

When this alumina insulating paper and the Bi-2212 / 19 core tape-shaped Ag sheath wire obtained in the same manner as in Example 1 were wound in a coil shape and pre-baked, the pulp abnormally burned and the superconducting wire rod was obtained. Was damaged. Moreover, a part of the superconducting coil was short-circuited.

Comparative Example 4 Al ₂ O ₃ Content 97% by Weight
Alumina fiber (B-97NL: manufactured by Denki Kagaku Kogyo) 95
kg was put into a stirring tank equipped with a high-speed stirrer and stirred for a short time to obtain an alumina fiber slurry. To this slurry, NBKP having a solid content of 3 kg adjusted to a freeness of 200 ml was added, and further 2 kg of granular PVA (KVG, manufactured by Denki Kagaku Kogyo) was added and well stirred. An attempt was made to make a continuous alumina insulating paper having a thickness of 0.1 mm from this papermaking raw material by an inclined wire netting type paper machine, but the wet paper strength was weak and continuous papermaking could not be performed because of a small amount of pulp.

[Comparative Example 5] NBKP adjusted to a freeness of 200 ml in Example 1 was adjusted to a freeness of 350 m.
A continuous alumina insulating paper sheet having a thickness of 0.1 mm was obtained in exactly the same manner as in Example 1 except that 1 g of NBKP was used.

This alumina insulating paper and a Bi-2223 / 19 core tape-shaped sheath (Ag) obtained in the same manner as in Example 2 were used.
/ 10 wt% Au alloy) wire, but the strength of the insulating paper is weak because the blended pulp has a high freeness of 350 ml, and the paper breaks frequently, and the coil cannot be produced. It was

[0086]

According to the present invention, there is no deterioration of superconducting properties due to the reaction between the superconductor and the insulating paper used for the insulating layer in the firing step, and the ratio of the superconductor to the entire coil is 20 to 20%. What was about 30 vol% is 8
It can be increased to 0 to 90 vol% and a high performance superconducting coil can be provided.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an oxide superconducting coil (single pancake coil).

FIG. 2 is a schematic cross-sectional view of an oxide superconducting laminated coil.

[Explanation of symbols]

1 ... Oxide superconducting wire, 2 ... Insulating paper, 3 ... Coil core, 4
… Oxide superconducting coil, 5… Al ₂ O ₃ disc.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiji Fukushima, 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Kazutoshi Higashiyama 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Shinichiro Takaguchi 2-3-2 Higashishinozaki, Edogawa-ku, Tokyo Honshu Paper Co., Ltd. Development Laboratory (72) Inventor Setsuo Toyoshima Edogawa-ku, Tokyo 2-3-2 Higashishinozaki Honshu Paper Co., Ltd.

Claims (7)

[Claims] 1. An oxide superconducting coil in which an oxide superconducting wire is wound in a coil shape with an insulating layer interposed therebetween, wherein the insulating layer is made of alumina fiber having an Al ₂ O ₃ content of 90% by weight or more. An oxide superconducting coil characterized by: 2. The oxide superconducting coil according to claim 1, wherein the oxide superconducting wire is covered with a metal containing silver or gold as a main component, and the cross-sectional shape thereof is flat, circular or polygonal. 3. The oxide superconducting coil according to claim 1, wherein the oxide superconducting wire is wound and insulated with an insulating paper made of alumina fiber having an Al ₂ O ₃ content of 90% by weight or more. 4. An insulator for an oxide superconducting coil, which comprises 70 to 95% by weight of alumina fibers having an Al ₂ O ₃ content of 90% by weight or more and 30 to 5% by weight of pulp having a freeness of 300 ml or less. 5. A binder 1 comprising 70 to 95% by weight of alumina fibers having an Al ₂ O ₃ content of 90% by weight or more, 30 to 5% by weight of pulp having a freeness of 300 ml or less, an organic adhesive and at least one of alumina sol. An insulating material for an oxide superconducting coil, characterized by comprising 10 to 10% by weight. 6. An oxide superconducting wire having an Al ₂ O ₃ content of 9
It is wound with an insulating paper consisting of 70 to 95% by weight of 0% by weight or more of alumina fibers and 30 to 5% by weight of pulp having a freeness of 300 ml or less, and this is wound into a coil to form a single pancake coil, and then a single pancake coil is formed. A method for manufacturing an oxide superconducting coil, characterized by performing heat treatment at a predetermined temperature. 7. An oxide superconducting wire having an Al ₂ O ₃ content of 9
70 to 95% by weight of 0% by weight or more of alumina fibers, 30 to 5% by weight of pulp having a freeness of 300 ml or less, an organic adhesive, and an insulating paper made of 1 to 10% by weight of a binder made of at least one kind of alumina sol, This is wound into a coil to form a single pancake coil,
Next, a method for producing an oxide superconducting coil, characterized by performing heat treatment at a predetermined temperature.