JPH052933A - Method for manufacturing oxide-based superconducting wire - Google Patents

Abstract

(57) [Abstract] [Purpose] To produce a silver-coated oxide superconducting wire having good J _C characteristics [Constitution] One or more electric wire materials formed by accommodating an oxide superconducting material in a silver sheath. Taking advantage of the fact that the specific gravity of silver is higher than that of oxide-based superconductor material by loading and heating in a slender heat-resistant container, sintering heat treatment is performed with the material suspended on molten silver. I do. Molten silver re-wraps the oxide-based superconducting material in the course of cooling to form a composite, so that the composite can be used as it is as a superconducting wire.

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-based superconducting wire, and more particularly to a novel method for producing a silver-coated oxide-based superconducting wire.

[0002]

2. Description of the Related Art Several methods have already been proposed as a method for converting an oxide-based superconductor into a wire rod. A typical one of them is a so-called silver-coated rolling method. This is a method of accommodating a superconducting material in a silver sheath. Since this method can use plastic working similar to that of the metal-based superconductor, it is possible to manufacture the superconducting wire relatively easily. However, the superconducting wire produced by this method has a problem in that the critical current density J _C in the magnetic field, particularly the critical current density at the liquid nitrogen temperature (77 K), is low.

On the other hand, when an oxide-based superconductor material (eg, yttrium-based oxide) is subjected to a sintering heat treatment at a high temperature, a part or all of the melted crystal structure is oriented in a preferred direction, resulting in a J _C characteristic. It is already known to improve significantly. Many methods for controlling the liquid phase state during sintering heat treatment have been studied. For example, at the International Center for Superconducting Technology Research (Superconducting Engineering Research Institute), MPM
To produce a G (M elt P owdering M elt G rowth) method coarsely crystalline bulk samples over several cm by using a, 10 ⁵ A / cm ² about the fact that a large current flows Ya in the crystal at the liquid nitrogen temperature , It has been confirmed that a good pinning effect occurs even in a high magnetic field of 1 to 5 T (Fujimoto et al. "Synthesis of YBaCuO by the melting method and the critical current characteristics", "Low Temperature Engineering", Vol. 25, No. 2, 1990). See pages 77-81).

However, it has been said that the sintering heat treatment of the oxide type superconductor material by the MPMG method or other melting method cannot be used in combination with the silver coating rolling method. The reason is that it is practically impossible to heat the silver sheath at a temperature of 1000 ° C. or higher required for the sintering heat treatment of the oxide-based superconductor because the melting point of silver is as low as 939 ° C.

[0005]

DISCLOSURE OF THE INVENTION The object of the present invention is to solve the above-mentioned problems and propose a novel method capable of subjecting a silver-coated oxide superconducting wire to a sintering heat treatment. It is to do.

[0006]

According to the method of the present invention, an oxide superconducting material is stored in a silver sheath by a silver coating rolling method, and then one or more of the electric wire materials is placed in an elongated heat-resistant container. It is characterized in that it is loaded and heated to a high temperature, and the superconducting material is subjected to a sintering heat treatment in a state of being suspended in molten silver.

Any oxide superconductor material may be used as long as its specific gravity is smaller than silver. Any known yttrium-based, bismuth-based, thallium-based, lanthanum-based oxide-based superconductor material may be arbitrarily selected. Can be used. As a result of a trial experiment conducted by the present inventors, a yttrium-based oxide superconductor material, in particular, a material formed by dispersing a (211) -phase similar oxide in (123) -phase YBaCuO having a large yttrium component It was found that it is extremely suitable for making wire rods. It is also possible to replace a part of yttrium with a lanthanoid element such as iribium, holmium, gadolinium or lanthanum.

[0008]

In general, the specific gravity of the oxide-based superconductor material is usually smaller than that of silver. Therefore, when the electric wire material containing the superconductor material in the silver sheath is loaded into a long heat-resistant container and heated, even if the silver sheath melts due to high temperature, the superconductor material floats in the molten silver. Then, the sintering heat treatment can be performed in that state. In other words, the present invention makes use of the fact that the melting point of silver is lower than that of oxide-based superconductor materials, and that the specific gravity of silver is higher than that of oxide-based superconductor materials. The material is sintered and heat treated.

Since molten silver re-wraps the oxide-based superconductor to form a composite in the process of lowering the temperature, the composite can be used as it is as a superconducting wire. Although it often happens that the oxide superconductor is exposed on the surface of the silver sheath, the function as a superconducting wire is essentially unchanged. However, if an additional silver coating is applied to the exposed surface by an appropriate method, it is extremely convenient for handling the wire.

As the electric wire material before the sintering heat treatment, not only one wire but also a large number of materials of several tens to several thousands can be used. In the latter case, a superconducting wire having a multi-core structure is used. Can be configured. Moreover, it is desirable to use a powdery material prepared by a solid-phase method or a melt-quenching method as a raw material of the oxide-based superconductor housed in the silver sheath.

[0011]

EXAMPLES The production method of the present invention will be described in more detail below with reference to examples.

Example 1 First, raw materials consisting of Y ₂ O ₃ , BaCO ₃ and CuO were mixed and pre-sintered at a temperature of 900 ° C., crushed and mixed, and then pelletized. This raw material was re-sintered in an oxygen stream at a temperature of 950 ° C. and then pulverized again to obtain Y ₁ Ba ₂ Cu ₃ O _y (hereinafter referred to as “YBC
Powder) was prepared. As a result of measuring the powder raw material prepared by such a solid phase method using the magnetic susceptibility method, it was confirmed that it had a critical temperature (T _c ) of 90K. After that, by the well-known silver coating rolling method, the thickness is 0.3 m.
A tape-shaped superconducting wire material having an outer dimension of m and a width of 5 mm was prepared. The YBCU core embedded inside the material had a thickness of about 0.15 mm and a width of about 3 mm.

Next, as shown in FIG. 1 (a), the tape-shaped electric wire material 1 is placed on the bottom of a slender heat-resistant container 3 made of MgO via a silver sheet 2 having a thickness of 0.2 mm and a width of 6 mm, and its state. It was loaded into the sintering furnace at. Sintering heat treatment is 1050 in air
It was carried out by heating at a temperature of ° C for 1 hour, after which the sintering furnace was gently cooled and returned to room temperature. The wire rod after the heat treatment has a shape such that the YBCO core layer 4 exists on the silver layer 5 determined by the cross-sectional shape of the heat-resistant container 3, as shown in FIG. It was possible to understand that the YBCO core was in a floating state in the molten silver. Moreover, according to the cross-sectional microscopy result, YBCO
No evidence of mutual reaction was observed between YBC and Mg, between MgO and silver, and between YBCO and MgO.
It was confirmed that the O core layer 4 had a dense and coarse crystal structure.

The J _C value (without magnetic field) at the liquid nitrogen temperature (77 K) of the superconducting wire thus obtained was measured.
It was found that the _C value of the superconducting wire after the sintering heat treatment was 5500 A / cm ^{2 as} compared with the _C value of about 500 A / cm ² . In this embodiment, as shown in FIG. 1A, the silver sheet 2 is interposed between the electric wire material 1 and the heat resistant container 3, but the sheet is not always necessary.
This is because it is possible to melt the silver sheath itself and float the YBCO core in the wire sheath 1 alone.

In this embodiment, one silver-coated electric wire material is used, but it is possible to use a plurality of electric wire materials. In fact, as a result of subjecting the seven silver-coated electric wire raw materials formed in a fibrous shape to the same sintering heat treatment, the present inventors found that, as shown in FIG. , Although floating in molten silver, they remain in multifilament form without being integrated with each other.
It was confirmed that a wire with a multi-core structure could be manufactured. As for the J _C characteristics, it was possible to obtain the same good value as in the case of the single core wire.

<Embodiment 2> Next, an embodiment in combination with the MPMG method will be described. First, a YBCO powder that has been subjected to MPMG pre-treatment (melt quenching) is prepared. That is, as in the case of Example 1, the _y of Y _1.2 Ba ₂ Cu ₃ O _{y was determined} by the solid phase method.
A raw material pellet of YBCO having a high value of was prepared, and the pellet was housed in a platinum crucible and rapidly heated to a temperature range of 1400 ° C. to be melted, and then rapidly cooled using a copper mold at room temperature. By crushing it, MP treated YB
CO powder was obtained. This YBCO powder was incorporated into a silver sheath to prepare a silver-coated electric wire material. Thereafter, as in the case of Example 1, the YBCO core was suspended in molten silver and subjected to a sintering heat treatment to produce a desired superconducting wire.

The schedule of the heat treatment process is shown in FIG.
The dimensions of the wire material are 0.14 mm in thickness and 2.5 mm in width.
And Put the wire material in a MgO heat-resistant container and put 110
After heating to a temperature of 0 ° C. and holding for 20 minutes, it was slowly cooled to room temperature in the atmosphere. However, the cooling rate from 1000 ° C. to 950 ° C. was controlled in the range of 1 ° C./h to 20 ° C./h, and natural cooling of the sintering furnace was used at 950 ° C. or less. It was found that the YBCO core was in a partially molten state at a temperature of 1000 ° C. or higher, but was in a completely solidified state at a temperature of 950 ° C. The coated silver is in a molten state and the YBCO core is in a solidified state.
In the temperature range of 960 ° C., a sample was taken out from the heat-resistant container and the solidification of silver was controlled to prepare a superconducting wire as shown in FIG. In the figure, (a) is a wire rod in which the YBCO core layer 4 is exposed on the surface of the silver layer 5, and (b) is a YBCO core layer.
The wire rod in which the core layer 4 is left inside the silver layer 5, (c) is a wire rod having a multi-core structure using a plurality of electric wire materials.

In the YBCO core portion of the produced superconducting wire, the (211) phase is extremely finely dispersed, and the J _C
The characteristics (without magnetic field) were found to reach 10 ⁴ A / cm ² at liquid nitrogen temperature, and 7 × even in a magnetic field of 1T.
It was found to show a high value of 10 ³ A / cm ² . In addition,
It is of course possible to manufacture a wire rod having a multi-core structure also by the method of this embodiment. Also. Floating in molten silver for heat treatment prevents the generation of different phases such as BaCuO ₂ and CuO,
It was confirmed that it has the effect of stabilizing the (123) phase of the yttrium oxide.

[0019]

According to the present invention, it becomes possible to manufacture a superconducting wire having a good magnetic field characteristic even when the silver coating rolling method is used, and the _JC characteristic at a liquid nitrogen temperature is remarkably improved. I was able to improve. In addition, the manufacturing method of the present invention is extremely effective in practical use, because the length of the superconducting wire can be easily increased and a coil magnet or the like for a 77K high magnetic field can be formed.

[Brief description of drawings]

FIG. 1 is a sectional view of a heat-resistant container for explaining a first embodiment of the present invention.

FIG. 2 is a curve diagram showing a heat treatment schedule in Example 2 of the present invention.

FIG. 3 is a cross-sectional view of an oxide superconducting wire manufactured by the method of Example 2.

[Explanation of Codes] 1 ... Copper coated electric wire material 4 ... YBCO core layer 2 ... Silver sheet 5 ... Silver layer 3 ... Heat-resistant container 6 ... Multi-core YBCO core layer

Claims (3)

[Claims] 1. A molten silver containing a superconducting material prepared by loading one or a plurality of electric wire materials containing an oxide superconducting material in a silver sheath by a silver coating rolling method into a long heat-resistant container and heating. A method for producing an oxide superconducting wire, which comprises subjecting the same material to a sintering heat treatment while being suspended therein. 2. The method for producing an oxide superconducting wire according to claim 1, wherein a powdery oxide superconducting material prepared by a solid phase method is used. 3. A powdery oxide-based superconductor material prepared by a melt-quenching method is used.
The method for producing an oxide superconducting wire according to.