JPH05282936A - Manufacture of oxide superconductive wire rod and tape - Google Patents

Abstract

(57) [Summary] [Objective] To provide a method for manufacturing an oxide superconducting wire and a tape capable of obtaining a high critical current density. [Structure] After filling and encapsulating oxide superconducting powder in a metal sheath material, when deforming it by a normal method such as rolling to manufacture a long tape or wire, the sheath material is pierced and filled in an intermediate step. A cutout and a small hole are formed in the powder. By providing these notches and small holes,
The air included when filling the raw material powder into the sheath is
It is removed from the sheath notch portion when the subsequent deformation processing is performed, and prevents blistering that occurs during heat treatment after processing. Furthermore, the notches and small holes serve as oxygen invasion ports necessary for heat treatment for imparting superconducting properties, so that a wire or tape having a high critical current density can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconducting tape / wire having a high critical current density. Since the oxide superconducting tape / wire has a high critical current density, it can be easily processed into a coil to generate a high magnetic field, and is mainly used as a superconducting magnet.

[0002]

2. Description of the Related Art A high critical temperature is a great advantage in superconducting applications. In particular, the discovery of Y-based, Bi-based, and Tl-based oxide superconductors that exceed the liquid nitrogen temperature reduces the cooling cost because liquid nitrogen can be used as a refrigerant, and the use of superconductivity due to the abundance of resources. It has the potential to greatly expand the field.

However, in the practical application of superconducting materials,
An important factor together with the critical temperature is the current that can flow at the operating temperature (critical current density), and in the manufacturing process, when the sheath metal is heat-treated after processing the wire rod and tape, the expansion of the gas inside the sheath causes Peeling occurs at the interface between the sheath material and the oxide superconductor inside, and at the same time the sheath material expands, causing swelling. Even after the temperature is lowered to room temperature, the expanded swelling remains in the sheath material (hereinafter referred to as swelling). The tape and wire are to maintain a uniform shape without causing this blistering. Both of these improvements are essential for practical use. The critical current density is not a characteristic peculiar to a material, but can be improved by studying a method of manufacturing the material. For example, the heat treatment is divided into two stages, crystallization of the high-temperature superconducting phase and grain boundary orientation to improve it (Japanese Journal of Applied Physics Vol.28, No.7,
1989, pp. L1204-L1206).

On the other hand, blistering has been improved by controlling the rate of temperature rise during heat treatment (44th Proceeding of Low Temperature Engineering and Superconductivity Society, P. 6). Further, it is important to control the amount of oxygen in the environment in the heat treatment for imparting superconducting properties (44th Low Temperature Engineering / Superconductivity Society Proceedings, P.6). The doctor blade method (45th, Low Temperature Engineering and Superconductivity Society Proceedings, P.229), in which one side is open to enable control of the environment, is also being considered as an effective method.

[0005]

Conventionally, since the sheath wire and tape are conventionally shielded by the sheath material, it is difficult for gas components to enter and exit the inside and outside of the sheath material. Therefore, the gas remaining in the sheath during processing of the wire is released. I can't. This is the cause of the blisters. In addition, it is difficult to adjust the oxygen content of the superconducting phase during the heat treatment for obtaining the final superconducting composition. Therefore, the invention intends to provide a method for producing an oxide superconducting wire and a tape, which simultaneously take measures against both of them.

[0006]

In order to solve the above-mentioned problems, the present invention relates to a metal sheath formed into a pipe shape by mixing powders which are raw material powders in advance and then subjecting the powders to a superconducting composition by heat treatment. Fill the material and perform processing. Manufacture of wire rods and tapes that penetrate the metal sheath material in the middle of this processing and partially cut into the oxide superconducting raw material in the sheath, and then re-process to obtain the wire diameter and tape thickness finally obtained. Is the way.

The present invention will be described in detail with reference to FIG. In the figure, as an example, the raw material is a Bi-Pb system. From weighing and kneading to heat treatment, crushing, filling,
Up to the primary processing, it is a method that has been generally used conventionally. In the case of tape production after the primary processing, the oxide superconducting material enclosed on both sides of the tape is partially cut. The processing rate of the primary processing before the cutting processing is preferably about 90% to 98%. If the processing rate is low, the oxide superconducting powder encapsulated from the processed notch will protrude outside the sheath during the next secondary processing. On the contrary, if the processing rate of the primary processing is too high, the density of the oxide superconductor inside will increase too much, and the internal air will be trapped between the powder particles, making it difficult to remove the internal air, which is one of the purposes. .. For this reason, the above-mentioned processing rate is appropriate as the processing rate until the notch is formed.

The finer the pitch of the notch, the more effective it is to remove the enclosed air. Also, in the final heat treatment for imparting superconducting properties, oxygen in the environment diffuses into the raw material through the notch and is oxidized. It has an advantage in adjusting the oxygen content of the superconductor. However, if it is too fine, the strength of the sheath material is reduced and the notch processing becomes complicated. On the contrary, if the pitch is too long, the above-mentioned effects cannot be obtained. Therefore, it is appropriate that the pitch of the notch is about 2 mm to 50 mm.

In the case of a tape, the shape of the notch is not particularly limited, but after the notch is processed, further processing accompanied by plastic deformation of the sheath material is performed, so stress concentration occurs in the notch and the destruction of the tape due to this is avoided. The U notch is effective for this purpose. However, in general, the sheath material may have a slit shape using a metal having good workability such as silver or a triangular shape without any problem. The notch may be processed by cutting, or by subjecting the roll to processing and pressing or shearing the roll, as long as the desired notch is processed. If the notch width is too large, the raw material powder is pushed out of the sheath during the secondary processing. In the minimum case, it is essentially sufficient that gas molecules can pass through. Therefore, the width should be 1 mm or less. The wire is also processed with a small diameter of 1 mm or less for the same purpose as for tape.

[0010]

[Function] In forming oxide superconducting material into wire and tape,
Since the initial packing density of the raw material powder is low, air mixed during the packing remains in the metal sheath. Of these, some are removed from both ends of the sheath material during deformation processing, but cannot be completely removed. Oxygen contained in the remaining air is consumed in the superconducting phase formation reaction heat treatment, so that there is no problem, but most of the remaining air is occupied by nitrogen and remains in the metal sheath. The remaining nitrogen is the cause of blisters during reheating. The internal gas can be removed at the time of deformation processing by cutting out the sheath material and forming small holes.

Further, by providing these notches and small holes, oxygen in the environment during heat treatment for imparting superconducting characteristics penetrates into the raw material powder by diffusing through the notches without being blocked by the sheath material, and superconducting Crystallizes the phase to improve superconducting properties.

[0012]

【Example】

[Example 1] Bi ₂ O ₃ , PbO and SrCO as raw materials
_3, CaCO _3, Bi _1.8 -Pb in a molar ratio with each oxide powder CuO _0.2 -Sr _2.0 -Ca _2.0 -Cu _3.0
After that, the mixture is weighed and kneaded to obtain a superconducting phase, and heat-treated at 840 ° C. for 60 hours in an atmosphere with an oxygen partial pressure of about 50 mmHg to crystallize the superconducting phase. This was pulverized to synthesize an oxide superconducting powder.

The synthesized powder is filled in an Ag pipe having an outer diameter of 8 mmφ and an inner diameter of 5 mmφ whose one end is closed. The other end is sealed so that the filling powder does not release from the pipe during processing into wire rod / tape. At this time, if airtight, the internal air is not released during processing, so a part of the air is left open.

This pipe is processed by a swaging machine in the same way as ordinary wire processing, and the outer diameter is about 2.5 mmφ.
I chose From here, roll it into a tape with a thickness of 0.5 mm. In this state, slit-like notches having a pitch of 10 mm were formed on both sides of the tape by cutting. The appearance of the notch processing at this time is shown in FIG. After that, the tape was continuously rolled to finish the target plate thickness of 0.15 mm.

The tape finished to the target thickness is 840 ° C.2
A final heat treatment for 40 hours was performed to impart superconducting properties. At this time, no blistering occurred on the slit tape. The tape without notch processing produced under the same processing condition caused blisters during the final heat treatment, resulting in 0.15 mm
The tape of thickness swelled to a thickness of 1.3 mm.

[Example 2] Similar to the above-mentioned tape production, a wire rod having an outer diameter of 0.5 mmφ was swaged from the outer periphery toward the center, as shown in FIG. After processing a large number of small holes having a depth partially extending over the wire, wire drawing was performed to form a wire having an outer diameter of 0.2 mm. The wire rod that had been subjected to small hole processing did not cause blistering even during the final heat treatment.

[0017]

EFFECTS OF THE INVENTION According to the present invention, it is possible to prevent the oxide superconducting wire / tape from blistering during heat treatment and to increase the amount of crystallization of the oxide superconducting phase. As a result, it is possible to obtain a current that can flow through the oxide superconducting wire / tape larger than that in the conventional method.

[Brief description of drawings]

FIG. 1 is a flowchart showing steps of the present invention.

2 (a) and 2 (b) are external views of a tape and a wire rod, which are notched and have small holes.

Claims (2)

[Claims] 1. When manufacturing an oxide superconducting tape by swaging, drawing, and rolling after filling a pipe-shaped base material (sheath material), which becomes a metal base of a tape-shaped wire, with a swaging process, a drawing process, and a rolling process. It is characterized in that after the tape base material (sheath material) is pierced and a plurality of minute notches that partially cover the superconductor are formed on the longitudinal side surface of the tape in the middle of the processing step, heat treatment for imparting superconducting properties is added. Manufacturing method of oxide superconducting tape. 2. When manufacturing an oxide superconducting wire by swaging and drawing after filling a pipe-shaped substrate which becomes a linear metal substrate with an oxide superconductor,
Manufacture of oxide superconducting wire characterized by adding heat treatment for imparting superconducting properties after forming micro holes that penetrate multiple base materials and partially cover the superconductor around the wire in the middle of processing Method.