JPS63285155A - Oxide type superconductive material and production thereof - Google Patents

Abstract

PURPOSE:To enable production of a superconductive material of oxide type having large critical electric current density, by connecting superconductive material particles of oxide type through an electrically conductive substance. CONSTITUTION:Superconductive material particles of oxide type are mixed with electrically conductive metal powder while stirring and the mixed powder is molded under pressure or, after the molding, may be heat-treated to give a superconductive material of oxide type. Or the mixed powder is packed into a metallic pipe and mechanically processed to reduce section area or, after the mechanical processing, may be heat-treated to produce the superconductive material of oxide type. The superconductive material of oxide type thus obtained has a sectional structure shown by the figure and superconductive material particles 1 of oxide type are mutually connected by the electrically conductive material 2. The superconductive material of oxide type having various shapes can be readily obtained by the above-mentioned production methods.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oxide-based superconducting material and a method for producing the same, and particularly relates to a material with a high critical temperature and a large critical current density used in various superconducting application devices. The present invention relates to an oxide-based superconducting material having the following properties and a method for producing the same.

[Conventional technology]

Superconducting materials have been developed in the past, for example, in Japanese Patent Application Laid-Open No. 61-2302.
Alloy-based superconducting materials disclosed in JP-A No. 09, JP-A-61-230210, etc., JP-A-61-25650
Various materials are known, such as compound-based superconducting materials disclosed in Publication No. 8 and the like. Superconducting materials are used to make electronic devices such as Josephson devices and superconducting magnets that generate strong magnetic fields. Conventional superconducting materials include Nb-Ti for alloy systems and Nb for compound systems.
3Sn has been most commonly used, but the critical temperature Tc of these materials is 9.5 for Nb-Ti and
For Sn, it is about 18, which is sufficient to maintain a superconducting state.

This required the use of expensive liquid helium as a refrigerant.

However, recently, oxide superconductors with a perovskite crystal structure and a Tc exceeding 90K have been discovered, and it has become possible to use liquid hydrogen, liquid neon, and liquid nitrogen as refrigerants.

These oxide-based superconductors have a KzNiF4 type crystal structure (L a L-XMX) 2Cu 0n-y (
Here, M has a (Ba, Sr, Ca, etc.) system and a triple layered perovskite type crystal structure (Bai-, M'
X)8Cu 5C)ry (here, M' is Y, La
Or, it can be roughly divided into lanthanide-based elements). The former has Tc around 40, and the latter has Tc around 90.

These oxide-based superconductors are produced by, for example, mixing and stirring oxide powders of each constituent element, press-molding pellets at 900°C
It is obtained by firing at 1100°C in air or oxygen atmosphere.

[Problems to be Solved by the Invention] However, for example, when using a superconducting magnet, a long wire is required for winding the coil.

Attempts are also being made to create long wires using oxide-based superconductors. One example of this method is to crush fired pellets and use the powder to make Cu, stainless steel or Cu-Ni steel.
This is a method of filling a pipe with it and reducing its cross section to create a long wire. However, a major problem with long wires made using this method is that the critical current density is almost zero, meaning that they are in a superconducting state and almost no current flows.

The present invention has been made in view of the above-mentioned points, and its purpose is to provide an oxide-based superconducting material having a large critical current density using an oxide-based superconductor having a high critical temperature, and its production. We are here to provide you with a method.

[Means for solving problems]

The oxide-based superconducting material of the present invention has a structure in which oxide-based superconductor particles are connected via a conductive substance. One of the manufacturing methods of the present invention is to mix and stir oxide-based superconductor powder and conductive metal powder, and press-mold this mixed powder, or by subsequently heat-treating the oxide-based superconductor powder and conductive metal powder. Obtain superconducting material. Furthermore, another manufacturing method of the present invention is to mix and stir oxide superconductor powder and conductive metal powder, fill a metal pipe with this mixed powder, and reduce the cross section by machining. An oxide-based superconducting material is obtained by or by subsequently performing heat treatment.

[Effect]

In the oxide-based superconducting material of the present invention, the conductive material filled in the voids between the superconducting particles allows the superconducting particles to adhere well to each other, making it easier for superconducting current to flow.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The oxide superconducting material of the present invention has a cross-sectional structure shown in FIG. Oxide-based superconductor particles 1 are interconnected by conductive substance 2 .

For example, in the case of a conventional oxide superconducting material in which a metallic pipe is filled with oxide superconducting powder to reduce the cross section, adjacent oxide superconducting particles 1 are Observation using a scanning electron microscope revealed that the particles were not sufficiently closely connected, that there were voids 3 between the particles, and that the mutual connections were point-contact. In this state, individual oxide-based superconducting particles 1 have not lost their superconductivity, as shown by critical temperature measurements using the AC magnetic susceptibility method, and superconductivity is destroyed when the cross section is reduced in the metallic pipe. It has been confirmed that this is not the case. Despite this, even if an attempt is made to flow a current, a superconducting current with zero electrical resistance will not flow. This is thought to be due to insufficient mutual contact between the superconductor particles 1, and from this it was inferred that filling the voids with a conductive substance would facilitate the flow of superconducting current.

At this time, it has been well known that when superconducting particles 1 are in contact with non-superconducting conductive material 2, superconducting electrons seep out to a certain distance range. This seeping distance is called the coherent length, and in the case of oxide-based superconductors, it is about 30 or less. Therefore, it is effective to keep the mutual gap distance between the superconducting particles 1 as small as the coherent length. Conductive substance 2
If there is no superconducting current, no superconducting current can flow between the superconducting particles 1 because no superconducting electron seeping effect can be expected.

Furthermore, in the manufacturing method of the present invention, a conductive metal powder is used to form the conductive substance 2, but the conductive gold 2 powder need not be limited to a single metal and may be an alloy. However, one with good workability is desirable.

As an example, In.

Metals such as Pb, Snt Ag, Au, Cu or alloys thereof can be used.

Furthermore, in the manufacturing method of the present invention, it is possible to further improve the critical current density by performing heat treatment after machining, but at this time, the heat treatment temperature is set at a temperature that is different between the oxide-based superconductor particles and the conductive metal. A low temperature heat treatment of 700° C. or lower is desirable to avoid deterioration of superconductivity due to reaction.

The present invention will be described below with reference to specific examples.

Example 1 YzOa is a commercially available reagent as a starting material.

Using BaCO5 and CuO powder, the atomic ratio is Y:Ba:C
They were weighed so that u was 1:2:3, and mixed and stirred using a ball mill. This mixed powder was heated to 950℃ for 20 minutes.
Grilled in the air for an hour.

It was press-molded into pellets with a diameter of 30 mm and a thickness of 2 m, and was fired at a temperature of 950° C. for 15 hours in an oxygen gas stream. The cooling rate after firing was 100°C/h, and then annealing was performed in oxygen gas at a temperature of 700°C for 10 hours.

The finished pellets are cut and polished to a width of 1.
A rod-shaped sample of 5 m in diameter, 1.5 m in thickness, and 25 m in length was prepared, and the critical temperature was measured using the 4-terminal resistance method.The superconductivity onset temperature was 98, and the temperature at which it completely transitioned to superconductivity with zero electrical resistance was found to be 98. It showed 93K. In addition, when this sample was immersed in liquid nitrogen and the critical current was measured, it was 140
It was A/cd. Separately, we made a rod-shaped sample with a width of 1 m, a thickness of 1 nm, and a length of 10 m, and measured the critical temperature by applying the diamagnetic properties of superconductors using the AC magnetic susceptibility method. As a result, we found that the superconductivity onset temperature was The temperature at which it became completely superconducting was 95K and 89K.

Next, the pellets were pulverized to form tooth pads with a particle size of 50 to 100 μm. When the critical temperature of this powder was measured using the AC #F81 ratio method, it showed the same value as the rod-shaped sample, confirming that the superconductivity had not deteriorated due to pulverization.

Thereafter, four types of mixed powders were prepared by mixing and stirring 0, 1, and 5.10% by weight Sn powders (average particle size: 75 μm).

This mixed powder has an inner diameter of φ6w1. After filling a Cυ pipe with an outer diameter of 8 mm and sealing both ends, wire drawing was performed using die drawing to a diameter of 0.8+ m. The length of each completed line was approximately 10 m.

A sample of 201 length was cut from this wire and heat treated under various conditions.

The critical temperature and critical current density of the sample thus prepared were measured. The results are shown in the table.

In the table, the heat treatment time was 1 hour in all cases. Regarding critical temperature, see 1-1.1-2. Samples 1-3 and 2-4 could not be measured using the 4-terminal resistance method, so they were measured using the AC magnetic susceptibility method. Moreover, the critical current density is the result of measurement in liquid nitrogen.

From the above results, it is clear that in the conventional method 1-1.1-2.1-3, the critical current density was zero and no superconducting current flowed, whereas in the present invention, a superconducting current flows.

At this time, the ratio of Sn as the conductive metal powder was best around 5%, and when heat treatment was performed, the critical current density showed the maximum value at 300° C. heat treatment. If the heat treatment temperature is too high, the superconductor particles of YBa2cu5C)ry react with Sn, resulting in a decrease in the critical temperature.

In addition, the new surface of each sample shown in the table was observed under a microscope. As a result, in sample 1-1, the average particle size of superconductor particles was approximately 2
μm, and the contact was as shown in Figure 2, whereas
In -1.3-1.4-1, it was found that the superconductor particles were embedded in Sn particles that were stretched by wire drawing and were connected to each other. Furthermore, in the heat-treated samples, it was confirmed that Sn was melted so as to surround the superconductor particles.

Example 2 The 5% Sn mixed powder obtained in Example 1 was rolled to a width of 20 cm and a thickness of 0.5 wrr.

A sheet with a length of 1 m was produced.

A sample with a width of 5m+ and a length of 3am was cut out from this sheet, and the critical current density was measured in liquid nitrogen, and it was found to be 3A/
I got the CD.

In addition, in a sample in which a portion of the sheet was heat-treated at 300° C. for 1 hour, the critical current density was 130 A/aJ.

Microscope the cross section of these sheets! When observed, it was confirmed that the superconductor particles were connected to each other via Sn, as in Example 1.

Example 3 Using the 5% Sn mixed powder obtained in Example 1, a cylindrical sample with an inner diameter of 10 mm, an outer diameter of 15 mm, and a length of 30 rm was produced by press molding. This cylindrical sample was
After being heat-treated at ℃ for 1 hour, it was immersed in liquid nitrogen, a magnetic field was applied in a superconducting magnet, and the magnetic shielding effect was measured. As a result, it was found that the shielding current in the cylindrical sample was 128 A/aJ in terms of critical current density.

Example 4 Using 5% Ag powder instead of Sn, a Cu pipe was filled with the mixed powder and wire drawn in the same manner as in Example 1, and after sowing, heat treatment was performed at 300°C, 400°C, and 500°C. A sample was prepared.

The critical current density in liquid nitrogen is 53 A/aj, respectively.
174A/aJ, 238A/c+? and in this case,
The higher the heat treatment temperature, the higher the critical current density, probably due to the low reactivity with the oxide superconductor particles due to heat treatment.

〔Effect of the invention〕

As is clear from the above, according to the present invention, an oxide-based superconducting material with a high critical current density can be obtained, and the manufacturing method thereof is relatively easy, as can be seen from the above-mentioned Examples. Another advantage is that products of various shapes can be easily obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the oxide-based superconducting material of the present invention, and FIG. 2 is a cross-sectional view of a conventional oxide-based superconducting material.

Claims (1)

[Claims] 1. An oxide-based superconducting material characterized in that oxide-based superconductor particles are connected via a conductive substance. 2. An oxide material characterized in that an oxide superconducting material is obtained by mixing and stirring an oxide superconductor powder and a conductive metal powder, and press-molding the mixed powder, or by subsequently subjecting it to heat treatment. A method for manufacturing superconducting materials. 3. Oxide-based superconducting material is produced by mixing and stirring oxide-based superconducting powder and conductive metal powder, filling the mixed powder into a metallic pipe, and then reducing the cross-section, or by subsequently applying heat treatment. A method for producing an oxide-based superconducting material, characterized in that it obtains.