JPH05101725A - Manufacture of oxide superconductive wire rod - Google Patents

Abstract

PURPOSE:To provide the manufacture of oxide superconductive wire rod having a high critical current density and provided with the stabilizing material on the peripheral surface thereof. CONSTITUTION:A raw wire material 1 made of the sintered body, which is composed of Bi group superconducting component, is melted locally to form a melting part 3. The melted liquid is led out from the melting part 3 through a pipe 5, and is solidified to form an oxide superconducting wire material 11 having a wire diameter of 2mm or less. Next, electroplating of Ag is applied to the peripheral surface of the oxide superconductive wire rod 11 at a current density of 0.3A/dm<2> or more.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to Bi-Sr-Ca-C.
The present invention relates to a method for producing an oxide superconducting wire starting from a sintered body having a Bi-based superconducting composition such as u-O (hereinafter referred to as BSCCO), and particularly to an oxidation method having an Ag plating layer as a stabilizing material on the peripheral surface thereof. The present invention relates to a method for manufacturing a superconducting wire.

[0002]

2. Description of the Related Art Conventionally, oxide superconducting wires have been manufactured by the following method. That is, first, an oxide powder having a superconducting composition is pressure-molded to obtain a molded body. Next, this molded body is filled and sealed in a metal pipe such as silver. Next, this metal pipe is drawn into a desired wire diameter. Then, a heat treatment is applied to sinter the powder compact of the core.

In the oxide superconducting wire thus manufactured, the oxide superconductor in the core portion is coated with a metal, and thus the metal in the coating portion acts as a stabilizer for the superconducting wire. That is, the oxide superconductor has no electric resistance in the superconducting state, but when the oxide superconductor transitions to the normal conducting state due to some disturbance factor, the electric resistance becomes significantly higher than that of a normal metal conductor. In order to prevent the high resistance state and the burnout of the wire at the time of this transition to normal conduction, a stabilizer for covering the oxide superconductor is required. Therefore, as the stabilizing material, usually Al or C, which has a low electric resistance in a low temperature range, is used.
Metals such as u and Ag are used. In addition, in the above-mentioned method for producing an oxide superconducting wire, when a silver pipe is used as the metal pipe, it is particularly called a silver sheath method.

However, the above-mentioned method for producing an oxide superconducting wire has the following drawbacks.

(1) Due to the difference in the packing density of powder compacts, the wire diameter of the core portion tends to vary.

(2) In order to measure the wire diameter of the portion (that is, the core portion) of the wire rod where the superconducting phenomenon occurs, it is necessary to remove the silver from the coating portion.

(3) Since the core made of the oxide superconductor is a sintered body, cracks are likely to occur in this portion due to slight bending stress.

(4) Since the core portion made of the oxide superconductor is a sintered body, a large number of voids are present in this portion and the crystal grains are fine, resulting in a large grain boundary area and a high critical current density. Is difficult to obtain.

Therefore, a melting method is proposed in which a wire having an oxide superconducting composition made of a sintered body is formed, and the wire is locally melted and then solidified to obtain an oxide superconducting wire having a desired wire diameter. (RSFeigelson, et.a
L., Science 240, 1642, 1988 and A, Kurosaka, et, al., A
ppl. Phys, Lett. 55 (4), I4 July, 1989 etc.). This melting method has the following advantages.

(1) Since it is possible to obtain a wire having a crystal structure in which there are few voids and the ab plane is oriented in the growing direction,
A high critical current density can be easily obtained.

(2) Since the wire rod can be formed while monitoring the wire diameter during manufacturing, it is easy to make the wire diameter uniform. In addition, the wire diameter of the manufactured wire can be measured nondestructively.

(3) Compared with a wire rod made of a sintered body,
Excellent flexibility.

[0013]

However, the above-mentioned method for producing an oxide superconducting wire by the melting method has the following problems. That is, in the oxide superconducting wire manufactured by the melting method, it is necessary to cover the peripheral surface of the oxide superconducting wire with the stabilizing material in consideration of the case of transition to the normal conducting state. Despite this necessity, at present, no technique has been established to coat the stabilizing material on the peripheral surface of the oxide superconducting wire produced by the melting method.

The present invention has been made in view of the above problems, and a core made of a wire produced by a melting and solidifying process using a sintered body of a Bi-based oxide superconducting composition as a starting material. An object of the present invention is to provide a method for producing an oxide superconducting wire, which can obtain an oxide superconducting wire in which a stabilizing material is coated on the peripheral surface of a core material with a uniform thickness and good adhesion.

[0015]

The method for producing an oxide superconducting wire according to the present invention comprises heating a raw material wire having an oxide superconducting composition to a temperature above its melting point in an oxidizing atmosphere to form a molten portion, The process of continuously drawing and solidifying the melt from this fusion zone to form a wire with a wire diameter of 2 mm or less, and the step of electroplating Ag on the peripheral surface of this wire at a current density of 0.3 A / dm ² or more. And having.

[0016]

The inventors of the present invention have found that the wire rod obtained by melting the raw material wire rod having the Bi-based oxide superconducting composition and then solidifying the wire rod is an electric conductor at room temperature, and has a denser crystal than the sintered body. Focusing on the structure, various attempts were made to coat the peripheral surface of this wire with metal by electroplating. As a result, since the Bi-based oxide superconducting wire with a wire diameter of 2 mm or less has excellent crystal orientation, the current density is set to a predetermined value or more and Ag plating is applied to the surface of the wire. It was found that the Ag plating layer can be formed with a uniform thickness and good adhesion. The present invention has been made based on such experimental results.

The reasons for limiting the wire diameter and the current density during plating will be described below.

Reason for limitation of wire diameter When an oxide superconducting wire having a wire diameter of more than 2 mm is manufactured from a raw material wire having a Bi-based oxide superconducting composition through a melting and solidifying process, the ab plane is oriented in the longitudinal direction of the wire. It is extremely difficult to obtain a wire having an oriented crystal structure, and the orientation deteriorates. Therefore, the critical current density of the superconducting wire is lowered. Further, in the Bi-based oxide superconducting wire having a wire diameter exceeding 2 mm, it is difficult to form an Ag plating layer having a uniform thickness and good adhesion in the electroplating process. Therefore, the wire diameter formed from the raw wire material through the melting and solidification process must be 2 mm or less.

Reasons for limiting the current density If the current density during electroplating is less than 0.3 A / dm ² ,
Even if the wire diameter of the wire is 2 mm or less, it is difficult to form an Ag plating layer having a uniform thickness and good adhesion. Therefore, the current density during Ag plating is 0.3 A / dm ²
It is necessary to be above.

[0020]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an apparatus for manufacturing superconducting thin wires used in an embodiment of the present invention.

A raw material wire rod 1 made of a sintered body having a superconducting composition is fixed at its upper end to a wire rod holder 6a attached to a drive shaft 8 for supplying the raw material wire rod, and is supported with its longitudinal direction being vertical. A pull-down drive shaft 7 is arranged below the supply drive shaft 8, and a pull-down guide wire 2 is fixed to a wire rod holder 6b attached to the pull-down drive shaft 7. The supply drive shaft 8 and the pull-down drive shaft 7 can be moved up and down in conjunction with each other at a predetermined relative speed by a drive device (not shown).

In the passage region of the raw material wire rod 1, a cylindrical heating furnace 9 is arranged so that its axial direction is vertical and surrounds the raw material wire rod 1. A coil-shaped heating element 10 is internally provided in the heating furnace 9. A raw material located inside the heating furnace 9 is generated by supplying electric power to the heating element 10 from an appropriate power source to generate resistance heat. The wire rod 1 and the like are heated to a predetermined temperature.

Inside the heating furnace 9, a resistance heating coil 4 for melting is arranged in the descending region of the raw material wire rod 1.
The resistance heating coil 4 has a diameter of 0.2 to 2.0 mm, for example.
The platinum wire is shaped into a coil. Further, a resistance heating wire 5b is disposed adjacently below the coil 4, and the resistance heating wire 5b also has a diameter of 0.1 to 0.5 m, for example.
It is formed by winding a platinum wire of m coaxially with the coil 4 once. The coil 4 and the heating wire 5b are adapted to be supplied with power from an appropriate power source.
By heating the coil 4 and the heating wire 5b to heat the raw material wire 1 in the portion surrounded by the coil 4 and the heating wire 5b, the raw wire material 1 can be heated to a temperature equal to or higher than its melting point and melted. The melt thus obtained is held by surface tension in the region surrounded by the coil 4 and the heating wire 5b by utilizing the wetting property of the melt, and the melted portion 3 is formed.

Further, immediately below the center of the coil 4, a pipe 5a is arranged coaxially with the coil 4, that is, with its longitudinal direction being vertical. This pipe 5a has, for example, an outer diameter
Made of platinum with a diameter of 0.1 to 2.5 mm and an inner diameter of 0.05 to 2.0 mm,
It is fixed to the resistance heating wire 5b. In addition, this pipe 5
A is also heated to a temperature equal to or higher than the melting point of the raw material wire rod 1 by resistance heating of the heating wire 5b. In this way, the pipe 5a
Is arranged in contact with the lower end of the pipe 5, the melt of the melting portion 3 penetrates to the lower end of the pipe 5a by the principle of the capillary.

Further, the arrangement position of the coil 4 and the pipe 5a and the periphery thereof are kept in an oxidizing atmosphere. For example, the entire heating furnace 9 may be in an atmosphere of oxidizing gas, or the coil 4 and the pipe 5 may be used.
It is also possible to blow an oxidizing gas around a.

The coil 4, the resistance heating wire 5b and the pipe 5a are not limited to those formed of platinum as described above, but it is necessary that they can be used in this oxidizing atmosphere.

Next, a method for manufacturing an oxide superconducting wire using the above-mentioned manufacturing apparatus will be described.

First, a BSCCO-based oxide powder compact is filled and sealed in an Ag pipe, and then the pipe is swaged to reduce its diameter to form a wire rod. After that, A on the surface
Dissolve g-sheath with nitric acid methanol.

Next, the remaining oxide wire is heat-treated in an oxidizing atmosphere at a temperature of, for example, 780 ° C. for 10 hours to obtain a raw material wire 1 made of a sintered body of BSCCO oxide.

Next, the upper end of the raw material wire 1 is fixed to the above-mentioned wire rod holder 6a, the supply drive shaft 8 is lowered, and the raw material wire 1 is arranged so that the lower end of the raw material wire 1 fits into the coil 4. To do. On the other hand, the upper end of the pulling-down guide wire 2 which is thinner than the inner diameter of the pipe 5a is inserted into the pipe 5a, and the lower end is fixed to the wire holder 6b. Then, while supplying the oxidizing gas around the coil 4 and the pipe 5a, the preheating heating element 10 is energized so that the raw wire material 1 in the heating furnace 9 is, for example,
Heat to a temperature above 700 ° C. Further, the resistance heating coil 4 for melting is energized to locally heat and melt the raw material wire rod 1. As a result, in the region surrounded by the coil 4, the fusion zone 3
Is formed. The resistance heating wire 5b for supporting the pipe is also energized to heat it to a temperature equal to or higher than the melting point of the raw material wire 1.

Next, the supply drive shaft 8 and the pull-down drive shaft 7 are moved down with a predetermined relative speed therebetween. The melt of the melting portion 3 permeates the inside of the pipe 5a and descends, goes out of the pipe from its lower end and is cooled, and solidifies into a thin wire shape to obtain the oxide superconducting wire 11. This oxide superconducting wire 1
1 is carried out downward by lowering the drive shaft 7 for pulling down. On the other hand, the raw material wire rod 1 is continuously fed into the heating furnace 9 from above by descending the feed drive shaft 8. In this way, the oxide superconducting wire 11 having a wire diameter of 2 mm or less is continuously manufactured.

Next, the oxide superconducting wire 11 thus obtained is electroplated with Ag. In this case, the current density is 0.3 A / dm ² or more. Thereby, an oxide superconducting wire having an Ag plating layer as a stabilizing material can be obtained.

In the method of this embodiment, the raw material wire rod 1 made of a sintered body is melted to form the melted portion 3, and the melt is drawn out from the melted portion 3 and solidified to obtain the oxide superconducting wire rod 11. Therefore, this superconducting wire does not have voids and has a crystal structure in which the ab plane is oriented in the longitudinal direction. Therefore, the critical current density in the superconducting state is high. In addition, the wire diameter of the superconducting wire before Ag plating should be 2
Since the thickness is less than or equal to mm and the current density during plating is set to 0.3 A / dm ² , the layer thickness of the Ag plating layer as a stabilizing material is uniform and its adhesion is good.

Next, the result of actually manufacturing the oxide superconducting wire by the method of this embodiment and examining the variation in the thickness and the adhesion of the stabilizing material will be described in comparison with the comparative example.

Example 1 A sintered rod having a Bi-based oxide superconducting composition and a wire diameter of 5 mm was used as a starting material, and the wire diameter was changed by using the above-mentioned apparatus.
A 1 mm Bi-based oxide superconducting wire was obtained. After that, in the cyan bath, the peripheral surface of the wire is energized for the time that can theoretically form a plating layer with a thickness of about 50 μm, and Ag is applied to the peripheral surface of the wire.
A plating layer was formed. The plating conditions at this time are shown in Table 1 below.
Shown in.

[0037]

[Table 1]

Example 2 A Bi-based oxide having a wire diameter of 2 mm was produced using the above-mentioned apparatus by using a sintered rod having a wire diameter of 10 mm and having the same Bi-based oxide superconducting composition as the starting material. A superconducting wire was obtained. Then, the peripheral surface of this wire was plated with Ag under the same plating conditions as in the first embodiment.

Example 3 In the same manner as in Example 1, a Bi type oxide superconducting wire having a wire diameter of 0.5 mm was obtained. Then, Ag was electroplated on the peripheral surface of this wire using a cyan bath having a bath composition shown in Table 1. However, the current density in this electroplating is 0.3 A / dm ² .

Comparative Example 1 In the same manner as in Example 2, a Bi type oxide superconducting wire having a wire diameter of 3 mm was obtained. Then, the peripheral surface of this wire was plated with Ag under the same plating conditions as in the first embodiment.

Comparative Example 2 In the same manner as in Example 1, a Bi type oxide superconducting wire having a wire diameter of 0.5 mm was obtained. Then, the peripheral surface of this wire was plated with Ag using a cyan bath having a bath composition shown in Table 1. However,
The current density in this electroplating is 0.2 A / dm ² .

Comparative Example 3 Ag was electroplated on the peripheral surface of a sintered rod having a Bi-based oxide superconducting composition and a wire diameter of 2 mm under the same plating conditions as in Example 1.

With respect to each of the wire rods of Examples and Comparative Examples thus obtained, the adhesion between the Bi-based oxide superconducting wire rod of the core material and the Ag plating layer of the covering portion and the uniformity of the thickness of the plating layer were examined. It was However, in Comparative Example 3, a phenomenon in which a part of the sintered rod was eroded by the cyan bath liquid and separated and precipitated occurred, and the presence of the portion where the Ag plating layer was formed and the portion where the Ag plating layer was not formed were remarkable. Since it was confirmed that the electroplating process occurred, the electroplating process was stopped halfway. Therefore, in Comparative Example 3, the above-mentioned adhesion and uniformity of thickness were not examined.

Regarding the adhesion, the Ag-plated wire was ultrasonically stirred in methyl alcohol for 30 minutes to obtain Ag.
It was observed whether the plating layer peeled off. Regarding the uniformity of the thickness of the plating layer, a longitudinal section observation photograph of the wire rods (50 mm in length) of Examples and Comparative Examples was taken, and the thickness of the plating layer was measured using this photograph. The results are shown in Table 2 below.

As is clear from Table 2, in Examples 1 to 3, the adhesion of the Ag plating layer as the stabilizing material is good and the thickness uniformity of the plating layer is also good. On the other hand, in Comparative Examples 1 and 2, the adhesion of the plating layer was not sufficient and the variation in the thickness of the plating layer was large. Further, in Comparative Example 3, as described above, the Ag plating layer could not be formed on the entire peripheral surface.

[0046]

[Table 2]

[0047]

As described above, according to the present invention, a raw material wire having an oxide superconducting composition is melted to form a wire having a predetermined wire diameter or less from a melt, and a predetermined current is applied to the peripheral surface of the wire. Since Ag is electroplated at a density or higher, it is possible to manufacture an oxide superconducting wire provided with a stabilizing material having a uniform thickness and good adhesion on its peripheral surface.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a superconducting thin wire manufacturing apparatus used in an embodiment of the present invention.

[Explanation of symbols]

 1; Sintered raw material wire rod 2; Pulling down guide wire rod 3; Melting part 4; Resistance heating coil 5a; Pipe 5b; Resistance heating wire 6a, 6b; Wire rod holder 7; Pulling down drive shaft 8; Raw material wire feed drive shaft 9; heating furnace 10; heating element 11; oxide superconducting wire

Front page continuation (72) Haruo Tominaga Haruo Tominaga 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Electric Line Co., Ltd. (72) Inventor Saji Akira 20 Kitakanzan, Otakamachi, Midori-ku, Aichi Prefecture 1 Chubu Electric Power Co., Inc. Power Technology Research Laboratory (72) Inventor Toshio Inoue 20 Kitakanzan, Otaka-cho, Midori-ku, Aichi Prefecture Nagoya 1 Chubu Electric Power Co., Ltd.

Claims (1)

[Claims] 1. A raw material wire having an oxide superconducting composition is heated in an oxidizing atmosphere to a temperature equal to or higher than its melting point to form a melted portion, and a melt is continuously drawn out from the melted portion to solidify the wire diameter. Of 2 mm or less, and a step of electroplating Ag on the peripheral surface of the wire with a current density of 0.3 A / dm ² or more, a method for producing an oxide superconducting wire.