JPH05101724A - Manufacture of oxide superconductive wire - Google Patents

Abstract

PURPOSE:To obtain the wire rod having the excellent superconducting characteristic without sintering growth by heating a metal tube or a flat body filled with the oxide superconductor powder to generate the expansion, and thereafter, performing the flattening and the sintering. CONSTITUTION:The powder 1 of Bi group such as Bi2Sr2CaCu2Oy as oxide superconductor is filled in a tube 1 made of metal such as silver, and a processing such as rolling is performed to it through a pinch roll or the like at need to form this tube into a flat body. The temperature of this flat body is raised at about 65% of the sintering temperature or at a local melting temperature of the powder 1 or less, and is cooled to generate the expansion. Rolling and pressing is performed for flattening, and thereafter, sintering is performed at a temperature less than a melting point of the metal tube, generally, at 700-1200 deg.C to bulk the powder for integral structure. A metal coating type oxide superconducting wire having the excellent superconducting characteristic without sintering growth can be thereby obtained stably.

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 a metal-coated oxide superconducting wire which prevents sintering swelling.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a metal tube filled with oxide superconductor powder or a flat body thereof is heat-treated to sinter the oxide superconductor powder. A method for producing a superconducting wire having a metal coating layer 1 as a body 2 has been known. However, swelling during heat sintering 1
There is a problem that 1 (expanded portion) occurs. The occurrence of such swelling is particularly remarkable in the case of a tape body having a flatness of a metal tube and having a size of several tens of cm or more, which becomes a cause of deterioration of superconducting properties and an obstacle in processing into a coil or the like.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to develop a method for producing a metal-coated oxide superconducting wire which can be sintered without swelling due to heating.

[0004]

According to the present invention, a metal tube filled with oxide superconductor powder, or a flat body thereof, is heat-treated to generate swelling and then flattened to obtain a blister. The present invention provides a method for producing an oxide superconducting wire, which comprises heating the obtained flat body to sinter the oxide superconductor powder.

[0005]

[Function] By preheating the metal tube or its flat body to generate swelling in advance and flattening it and then subjecting it to sintering treatment, the reason for this is unknown, but there is no recurrence of swelling and sintering swelling. It is possible to obtain a wire rod which can prevent the occurrence of the above and have excellent superconducting properties.

[0006]

EXAMPLE FIG. 1 illustrates an oxide superconducting wire obtained by the manufacturing method of the present invention. Reference numeral 1 is a metal coating layer, and 2 is a sintered body obtained by sintering an oxide superconductor powder.

There is no particular limitation on the type of oxide superconductor used in the present invention. An example is Bi ₂ S
Bi-based oxide superconductors such as r ₂ CaCu ₂ O _y and Bi _2-x Pb _x Sr ₂ Ca ₂ Cu ₃ O _y , and Y-based oxide superconductors such as YBa ₂ Cu ₃ O _y and YBa ₂ Cu ₄ O _y. Body, Ba _- based oxide superconductors such as Ba _1-x K _x BiO ₃ , Nd _- based oxide superconductors such as Nd _2-x Ce _x CuO _y , other La-based oxide superconductors, and Tl-based oxide superconductors , Pb-based oxide superconductors and the like.

Further, the above-mentioned components such as Bi are replaced with other rare earth elements, the components such as Sr are replaced with other alkaline earth metals, and the O component is replaced with F and the like. Be done. Furthermore, the thing containing the pinning center etc. is mentioned. The pinning center-containing oxide superconductor has the advantage of exhibiting a large critical current density even under a high magnetic field due to the effect of pinning the magnetic flux by the pinning center. The oxide superconductor containing the pinning center is, for example, the MPMG method (Melt
Powdering Melt Growth) and the like.

The particle size of the oxide superconductor powder packed in the metal tube is 100 μm or less, preferably 0.1 to 10 μm. The powder can be obtained, for example, by crushing a sintered body of an oxide superconductor. As the metal tube, for example, one made of silver, gold, platinum, an alloy containing such a metal, or a high melting point alloy such as a silver-platinum alloy or a silver-palladium alloy is preferably used.

The metal tube filled with the oxide superconductor powder is tape-shaped, if necessary, by a rolling process using a pinch roll or the like, or a wire drawing process using a die or the like.
After being processed into a predetermined form such as a thin wire, it is subjected to heat treatment. This heat treatment is a pretreatment for generating blisters. At that time, a press treatment may be performed prior to the pretreatment. The pressing process is effective for stabilizing or improving the quality. The pressing process may be repeated multiple times,
In that case, a heating step is provided between the pressing process before and after. The press treatment can be performed after the pretreatment.

Since swelling due to heating usually occurs at the time of temperature rise, the heat treatment as the above-mentioned pretreatment is of a degree to which the temperature raising process of the main sintering treatment for converting the powder of the oxide superconductor into a bulk is carried out. However, it is not necessary to perform the whole process of the main sintering process. Further, unlike the case of forming an oxide superconductor containing pinning centers, it is not necessary to raise the temperature to a temperature at which the oxide superconductor partially melts. General pretreatment conditions include a temperature of about 65% of the main sintering temperature or a temperature below the partial melting temperature of the oxide superconductor,
It is a method of cooling thereafter. The heating rate is not particularly limited.

The metal tube which has been swollen by the pretreatment or the flat body thereof is flattened prior to the main sintering treatment so as to be in a swollen state. The flattening process may be performed by an appropriate method such as a rolling process using a pinch roll or the like, a pressing process using a pressing device, or the like. At that time, the thickness control of the target oxide superconductor can be performed.

The main sintering treatment is for bulking and integrating the oxide superconductor powder in the flattened flat body. In the present invention, the main sintering process may be performed on a secondary form such as a coil. The main sintering temperature is
As is conventional, it is usually performed at a temperature below the melting point of the metal tube. Generally, it is 700 to 1200 ° C.

Example 1 Particle size of Bi ₂ Sr ₂ CaCu ₂ O _y type oxide superconductor 0.1 to 1
0 μm powder is filled in a silver tube with a wall thickness of 1.0 mm and a diameter of 7.0 mm, and it is rolled with a pinch roll to have a width of 3 mm, a thickness of 0.2 mm (the thickness of the superconducting part is 100 μm), and a length of 1 m. After being processed into the tape of No. 1, it was subjected to a press treatment and a heat treatment (pretreatment). The heating conditions were such that the temperature was raised to 850 ° C. and then cooled. As a result, a large number of bulges were generated on the tape.

Next, the obtained tape was rolled through a pinch roll to be flattened, and the tape was heated at 850 to 890 ° C. for about 50 hours for main sintering to obtain an oxide superconducting wire. No swelling was observed in the obtained oxide superconducting wire. The critical temperature was 85K and the critical current density was 12000A / cm ² (63K).

On the other hand, for comparison, an oxide superconducting wire was obtained in the same manner as in Example 1 except that the formed tape was subjected to the main sintering treatment without performing the heat treatment as the pretreatment and the flattening treatment. However, sintering swelling was observed in many places in the obtained oxide superconducting wire. The critical temperature was 80K and the critical current density was 5000A / cm ² (63K).

In the above, the critical temperature is 0.1 A / c.
The temperature change of the electrical resistance was measured by the 4-terminal method while cooling with liquid nitrogen under a current density of m ² , and the generated voltage between the voltage terminals was 0.
Is the temperature at which

Further, the critical current density was cooled to 63 K while reducing the pressure in liquid nitrogen together with the power lead, the current value was gradually increased, and the change in the voltage between the voltage terminals due to the applied current was measured by the 4-terminal method. 1μv for XY recorder
It is the value obtained by dividing the current value when a voltage of / cm appears by the cross-sectional area of the superconductor.

[0019]

According to the present invention, since a method in which heat swelling is generated in advance and flattened is subjected to the main sintering treatment, a metal-covered oxide superconducting wire having no sintering swelling is obtained.
It can be stably obtained with excellent superconducting properties.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional perspective view illustrating an oxide superconducting wire according to the present invention.

FIG. 2 is a partial cross-sectional perspective view of a conventional example.

[Explanation of symbols]

 1: Metal coating layer 11: Swelling due to sintering 2: Sintered body of oxide superconductor powder

Claims (1)

[Claims] 1. A metal tube filled with oxide superconductor powder or a flat body thereof is heat-treated to generate swelling, and then flattened, and the flat body thus obtained is heat-treated. A method for manufacturing an oxide superconducting wire, comprising: sintering oxide superconductor powder.