JPH05159643A - Oxide superconductive wire rod and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide the oxide superconductive wire rod, of which critical current density is improved, and the manufacture thereof. CONSTITUTION:The powder of T1 group oxide superconductive wire material is covered with the sheath material, which is essentially made of silver and palladium at 2-10weight%, and thereafter rolling and hot press and heat processing are performed to form a wire material. The oxide superconductive wire material obtained by filling the T1 group oxide superconductive material in a cover, which is essentially made of silver and palladium at 2-10weight%, can restrict the intrusion of silver into the superconductive structure to improve the critical current density.

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 Tl-based oxide superconducting wire, and more particularly to an improvement for increasing the critical current density in such a superconducting wire.

[0002]

2. Description of the Related Art In recent years, as a superconducting material exhibiting a higher critical temperature, a ceramic material, that is, an oxide superconducting material has been attracting attention. Among them, the Tl (thallium) -based superconducting material has a maximum critical temperature of about 120 K, and its practical application is expected.

The Tl-based superconducting material is Tl-Ca-Ba /
Sr-Cu-O component, or part of this component is Pb,
It is composed of a component substituted with Bi or a rare earth element, or a component in which a part of this component is substituted with Pb, Tl or a rare earth element. It is known that such superconducting materials have a plurality of superconducting phases having different crystal structures and critical temperatures. In addition, these superconducting materials are
It is also known to have large anisotropy in crystal structure and superconducting properties. That is, the crystal has a, a
Since the growth rate in the b-axis direction is high, the c-plane usually has a plate shape with a plate-like surface. Therefore, the superconducting current is
Easier to flow in the plane and higher critical current density.

Further, as one method of obtaining a long superconducting wire using such a superconducting material, the raw material powder is superconducted by coating the raw material powder on a silver metal sheath, processing it, and then subjecting it to heat treatment. A method is known in which a superconducting wire is manufactured by embodying it.

[0005]

However, the Tl oxide superconducting wire obtained by the method as described above is
There is room for further improvement in terms of critical current density. This is because in order to apply the superconducting wire to cables and magnets, it is necessary to have a high critical current density in addition to a high critical temperature.

Therefore, it is an object of the present invention to provide an oxide superconducting wire having a further improved critical current density and a method for producing the same.

[0007]

The present inventors have conducted experiments to find a method for improving the orientation of crystal grains of a superconducting phase for the purpose of improving the critical current density. In particular, using a raw material powder consisting of a desired superconducting phase, research was conducted on a processing and heat treatment method for growing superconducting phase crystal grains while orienting the crystal direction with a higher critical current density along the current direction of the wire. .. As a result, first, the superconducting phase cannot be oriented simply by heat-treating and cold-pressing the tape-shaped wire containing unheated raw material fine powder. Heat it up
That is, it was found that when hot pressing is performed to grow grains of the superconducting phase, the plate-like crystal grains of the superconducting phase are oriented parallel to the tape surface, that is, in the wire current direction.

However, when silver is used as the sheath material as in the conventional case, the silver of the sheath material is hot-pressed so that the superconducting phase crystal structure in the wire, particularly the surface layer portion 10 thereof.
It was found that it penetrates to a depth of about μm and causes deterioration of superconducting properties. Since the hot pressing is performed at around 800 ° C., silver having a melting point of about 960 ° C. was considerably softened in this step and penetrated between the grains of the superconducting material by applying a load. Of course, if the superconducting phase part is previously densified by pressing and the voids between the grains are removed, the penetration of silver can be suppressed to some extent. There was a problem that could not be obtained.

With respect to this problem, the present inventors have studied various conditions and methods, and if an alloy in which 2 to 10% by weight of palladium (Pd) is added to silver (Ag) is used as a sheath material, hot pressing is performed. In the above, it was found that the penetration of silver into the superconducting structure can be suppressed, and as a result, a wire having a high critical current density can be manufactured. The present invention has been made based on such knowledge.

That is, a method for producing an oxide superconducting wire according to the present invention is a method of forming a wire by coating a powder of a Tl-based oxide superconducting material with a sheath material, and then performing rolling, hot pressing and heat treatment. The sheath material consists essentially of silver and 2 to 10% by weight of palladium.

The oxide superconducting wire according to the present invention is
A coating portion consisting essentially of silver and 2 to 10% by weight of palladium and a Tl-based oxide superconducting material filled in the coating portion are provided.

[0012]

In the present invention, immediately after the rolling process, the fine crystal grains of the raw material are oriented in random directions with respect to each other, and voids still exist between these superconducting phase crystal grains.
Here, when the hot press treatment is performed under appropriate conditions, the superconducting phase is densified and oriented.

However, at this time, the silver softened by the hot pressing penetrates into the superconducting crystal structure, causing a decrease in the critical current density. Therefore, 2 as a sheath material
If an alloy containing 10 wt% palladium (Pd) is used, the melting point rises and the hardness also slightly increases, so that it is possible to prevent the sheath material from entering the superconducting phase portion during hot pressing. ..

Needless to say, the properties required for the sheath material are that the melting point is sufficiently higher than the heat treatment temperature, that it is an electrically good conductor, that it does not react with the superconducting phase, and that it is mechanically processed. It is easy and inexpensive. An alloy obtained by adding 2 to 10% by weight of palladium (Pd) to silver sufficiently satisfies the above conditions.

If the amount of palladium added is less than 2% by weight with respect to the alloy, sufficient effects cannot be obtained in terms of raising the melting point and hardness, while if it is more than 10% by weight with respect to the alloy, the hardness is insufficient. Becomes too high, which makes machining such as rolling difficult.

Although gold or its alloy satisfies the above condition to some extent, it is inferior to the material in terms of reactivity and cost.

[0017]

As described above, according to the present invention, in a hot press for obtaining a dense and oriented superconducting phase, it is possible to prevent the problematic sheath material from entering the superconducting tissue,
An oxide superconducting wire having a high critical current density can be obtained. Therefore, the oxide superconducting wire according to the present invention has a high possibility of being put to practical use as a cable, a magnet and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following disclosure is merely a specific example of the present invention and does not limit the technical scope of the present invention.

[0019]

【Example】

Example 1 According to the method of the present invention, a Tl-based superconducting wire was manufactured as shown below.

First, each powder of Tl ₂ O ₃ , BaO ₂ , CaO, and CuO was added to Tl: Ba: Ca: Cu = 1.
After weighing, mixing and pelletizing so that the compounding ratio was 8: 2: 2: 3, the pellet was fired at 880 ° C. for 12 hours to obtain a raw material for the superconducting material. Next, this raw material was pulverized into a raw material powder, filled in a silver-10 wt% palladium alloy sheath, and then rolled into a tape shape having a thickness of 0.35 mm. Tape wire rod at 810 ℃, load 240k
After hot pressing at g, it was rolled to a thickness of 0.15 mm, and subsequently heat-treated at 780 ° C. for 12 hours.

The critical current density of the oxide superconducting wire thus obtained was 10700 A / cm ² . On the other hand, the critical current density of the wire produced by the conventional method using the silver sheath under the same conditions was 7100 A / cm ² .

Example 2 Tl ₂ O ₃ , BaCO ₃ , CaCO ₃ , and CuO powders were used as raw materials, and these were used as Tl: Ba: Ca: Cu =
After blending so as to be 1.3: 2: 3: 4, 5% by weight of PbO was further added thereto and mixed and molded. next,
The molded body was heat-treated at 875 ° C. for 16 hours to obtain a raw material for the superconducting material. This raw material was pulverized into a raw material powder, which was filled in a silver-2 wt% palladium alloy sheath and then
It was rolled into a tape having a thickness of 3 mm. The tape wire was further hot-pressed at 820 ° C. and a load of 180 kg, and then 0.
Rolled to a thickness of 12 mm, then 770 ℃, 12
A heat treatment of time was applied.

The critical current density of the oxide superconducting wire thus obtained was 12400 A / cm ² . On the other hand, the critical current density of the wire produced by the conventional method using the silver sheath under the same conditions was 8700 A / cm ² .

Example 3 Tl ₂ O ₃ , SrCO ₃ , CaCO ₃ , and CuO powders were used as raw materials, and these were used as Tl: Sr: Ca: Cu =
1.6: 1.9: 2: 3, to which 6 wt% PbO, or 6 wt% Bi ₂ O ₃ , or 3 wt% Bi ₂ O ₃ and 4 wt% After PbO was added, mixed and molded, heat treatment was carried out at 870 ° C. for 10 hours to obtain a raw material for the superconducting material. Next, this raw material was pulverized into a raw material powder, filled in a silver-5 wt% palladium alloy sheath, and then rolled into a tape shape having a thickness of 0.3 mm. The tape wire is further heated at 800 ℃, load 160
After hot pressing with kg, it was rolled to a thickness of 0.1 mm, and subsequently heat-treated at 780 ° C. for 12 hours.

The critical current density of the oxide superconducting wire thus obtained is 11900 A / c when PbO is added.
m ² , when Bi ₂ O _{3 was} added 11200 A / cm ² , B
11500 A / cm ² when i ₂ O ₃ and PbO are added
Met. On the other hand, the critical current density of the wire produced by the conventional method using the silver sheath under the same conditions is 8000 to 8200.
It was A / cm ² .

Claims (2)

[Claims] 1. A method for producing an oxide superconducting wire, comprising coating a powder of a Tl-based oxide superconducting material with a sheath material, and then performing rolling, hot pressing and heat treatment to form a wire. A method for producing an oxide superconducting wire, characterized in that the material consists essentially of silver and 2 to 10% by weight of palladium. 2. An oxide superconducting wire comprising: a coating portion consisting essentially of silver and 2 to 10% by weight of palladium; and a Tl-based oxide superconducting material filled in the coating portion.