JPH03122042A - Production of ceramic superconducting material - Google Patents

Abstract

PURPOSE:To obtain a superconducting product having high current density even in a strong magnetic field by mixing a raw material for superconducting ceramics with a substance containing noble metal element, treating the mixture in specific steps and dispersing the noble metal element in the mixture. CONSTITUTION:The objective production process in composed of (1) a step for mixing a raw material for ceramic superconducting material and a substance containing noble metal element, (2) a step to heat the mixture at the melting temperature of the raw material for the ceramic superconducting material and keep at the temperature for a prescribed period, (3) a step to cool mixture at a specific temperature to form an amorphous material, (4) a step to form the amorphous mixture in a prescribed form and (5) a step to reheat the formed article at a prescribed temperature to disperse the noble metal element in the mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a ceramic superconducting conductor that can be used for coils, cables, wiring wires, current limiters, and the like.

[Prior Art] In recent years, instead of metal superconductors which produce superconductivity at extremely low temperatures of liquid helium temperature, oxide superconductors which produce superconductivity at temperatures higher than liquid nitrogen temperature, i.e., whose critical temperature Tc is equal to liquid nitrogen tH degrees, have been developed. The above oxide superconductors are being actively developed. Among these, Y-based, Bi-based, and Tp-based oxide superconductors are attracting attention.

These ceramic superconductors exhibit excellent electrical properties at critical temperatures above the liquid nitrogen temperature, making them suitable for use as superconducting conductors in coils, cables, wiring materials, and current limiters, for example. There is.

Generally, methods for manufacturing ceramic superconducting conductors include:
A solid phase method is used. This method can be used, for example, to directly convert powdered ceramic superconductor raw materials into wires, tapes, etc.
It can be formed into a desired shape such as a ring shape or a temporary shape, or it can be composited with metal, and this metal composite can be processed into a desired shape, and then the product obtained by molding or processing can be subjected to sintering or heat treatment. It forms a ceramic superconducting conductor.

However, according to this method, the density of the ceramic superconductor after heat treatment is low, and the crystal orientation of the ceramic superconductor cannot be controlled. For this reason, high JC (7R
Current density) cannot be obtained, and large currents cannot be passed. Furthermore, the ceramic superconductor after heat treatment has many grain boundaries, and these grain boundaries become J due to the application of a magnetic field. J of ceramic superconductors to rapidly reduce (weak link). - Has an adverse effect on B characteristics.

On the other hand, in recent years, liquid phase methods have been attracting attention instead of solid phase methods. In this method, for example, a ceramic superconductor raw material is heated and melted, and then the molten raw material is rapidly cooled and formed into a tape shape, a plate shape, a wire shape, or the like. In addition, as liquid phase methods, methods such as a floating zone method and a unidirectional solidification method are used for the purpose of achieving high density and high orientation.

Ceramic superconductors obtained by these methods are J
c mosquito, OT (Tesla), 10 at liquid nitrogen temperature
The level is as high as 3 to 10'A/cd.

[Problems to be Solved by the Invention] However, the ceramic superconducting conductor obtained by the liquid phase method has a drawback that Jc decreases by one to two orders of magnitude in a high magnetic field of several T.

In reality, a ceramic superconducting conductor having a high Jc in a high magnetic field of 10 to 20 T is desired.

The present invention has been made in view of these points, and an object of the present invention is to provide a method for manufacturing a ceramic superconducting conductor that can exhibit excellent superconducting properties in a high magnetic field.

[Means for Solving the Problems] The present invention includes a step of mixing a ceramic superconductor raw material and a substance containing a noble metal element, heating the mixture to a temperature at which the ceramic superconductor raw material melts, and heating the mixture to a temperature at which the ceramic superconductor raw material melts. holding the mixture for a predetermined period of time; cooling the mixture to a predetermined temperature to make it amorphous; molding the amorphous mixture into a desired shape; A method for manufacturing a ceramic superconducting conductor, comprising a step of reheating the mixture to a temperature to disperse the noble metal element in the mixture.

Here, as the type of ceramic superconductor, YB
Y-Ba-Cu-0 series (including those in which Y is replaced with other rare earths) such as a 2 Cu 301-a, B
i2S r2CaCu20. .

B i-3r-Ca-Cu-0 system such as B j2 S r2 Ca2 Cu13 ()+o and TΩ2 B a
2 Ca Cu z O6+TΩ2 Ba2Ca2(
: u30111T(l Ba2 Ca2 Cu30g,
Examples include T, Q-Ba-Ca-Cu-0 systems (including those in which Bi and TR are partially dissolved in Pb, Sb, and In).

The substance containing the noble metal element may be any substance as long as it can be mixed well with the ceramic superconductor raw material. Examples of such metals include simple noble metals such as Au, Ag, and Pt, and compounds such as oxides.

Moreover, the shape of these substances may be either powder or bulk.

As the ceramic superconductor raw material, oxides, carbonates, etc. of elements constituting the ceramic superconductor, or a calcined product obtained by mixing and calcining them are used.

The temperature at which the ceramic superconductor raw material melts varies depending on the type of ceramic superconductor raw material used. For example, in a YBaCuO ceramic superconductor, 120
0 to 1400°C, and 1100 to 1300°C for BtS rcacuo-based ceramic superconductors. This is because the ceramic superconductor raw material will not be completely melted below the temperature lower limit (1200°C for Y-based systems and 1100°C for Bi-based systems), and the above-mentioned upper temperature limit (1400°C for Y-based systems) will not melt completely.
This is because if the temperature exceeds 00°C (1300°C for Bi-based), the composition of the ceramic superconductor will change.

The time period for maintaining the mixture L-v at a temperature at which the ceramic superconductor raw material melts is preferably about 1 hour.

The rate of cooling the mixture is preferably 50° C./see or higher. This is because if the cooling rate is less than 50° C./see, at least a portion of the mixture will not become amorphous. In addition, the method for cooling the mixture is as shown in FIG. 2(a), using one cooling roll 20 rotating in the direction of the arrow
A molten ceramic superconductor 22 is placed on top from a container 21.
Cooling material 23 in a laminar, linear, etc. shape is dropped.
As shown in FIG. 2(b), the molten ceramic superconductor is transferred from the container 21 to the contact area of two cooling rolls 24 and 25 that are in contact with each other and are rotating in the direction of the arrow. Examples include a twin roll method in which the coolant 26 is obtained by dropping the body 22.

Further, as a method for cooling the mixture, there is a spinning method in which a molten ceramic superconductor is spouted into a refrigerant solution placed in a container to obtain a spun coolant.

The temperature at which the amorphous mixture is reheated varies depending on the type of ceramic superconductor used, but for example,
YBaCuO system: 900-1000℃, B15rCa
For CuO type, it is 850 to 950°C. Further, the reheating time is from several hours to several tens of hours. The amorphous mixture to be reheated can be a laminar or linear mixture obtained by amorphizing the mixture using a cooling roll, or a powder by pulverizing these laminar or linear mixtures. It may be either a sheathed mill made by molding the powder into a desired shape, or a sheathed mill made by filling a metal tube with the powder after pulverization and processing the tube to reduce its surface area.

[Function] According to the method for manufacturing a ceramic superconducting conductor of the present invention,
A ceramic superconductor raw material and a substance containing a noble metal element are mixed, the mixture is melted, cooled to become amorphous, and the amorphous mixture is reheated.

By melting a ceramic superconductor mixture,
The noble metal is sufficiently dissolved in solid solution with the ceramic superconductor raw material.

By making this solid solution amorphous, the noble metal element is uniformly dispersed within the ceramic rE conductor matrix. As a result, the noble metal elements uniformly dispersed within the ceramic superconductor matrix exhibit a pin effect. Therefore, the ceramic superconductor blocks the influence of the magnetic field, making it easier for current to flow through the ceramic superconductor.

Therefore, the ceramic superconducting conductor according to the method of the present invention achieves high current density even in high magnetic fields.

[Example] Hereinafter, the present invention will be explained with reference to the drawings.

Example 1 First, powders of Bi□O,, Srco3, CaCO3, and CuO were prepared at a Bi:Sr:Ca:Cu ratio of 2:2.
:1:2.

The weighed powders were thoroughly mixed. 820 ml of mixed powder
It was calcined at °C for 20 hours. The obtained calcined product was pulverized, and 20% by weight of Ag powder was mixed with this powder. This mixed powder was heated to 1150°C and melted. Thereafter, the molten mixture was cooled by a twin roll method using an apparatus as shown in FIG. 2(b) to produce a foil-like body having a thickness of 30 to 50 μm. When this foil-like body was chemically determined by X-ray diffraction, it was found to be amorphous, and Ag was well dissolved in solid solution.

Next, this foil-like body was sufficiently crushed. The powder after pulverization was filled into an Ag vibrator having an outer diameter of 10φ and an inner diameter of 6φ. This Ag pipe was rolled to produce a tape-like body with a thickness of 0.3 mra. This tape-like body was heated to 900°C in an oxygen stream.
A ceramic superconducting conductor was produced by reheating for 1 hour.

When the cross section of the obtained ceramic superconducting conductor was observed using an EPMA (Electro Probe Micro Analyzer), it was found that Ag with an outer diameter of about 1 μm was found in the oriented ceramic superconducting crystal grains 10 rj+ as shown in Figure 1.
1 liter was dispersed.

Note that 12 in the figure is a grain boundary.

Furthermore, the JcB (current density-magnetic field) characteristics of the obtained ceramic superconducting conductor were investigated. The results are shown in characteristic curve A in FIG. Note that the Jc B characteristics were measured by a DC four-terminal method with the ceramic superconducting conductor immersed in liquid nitrogen.

Example 2 Instead of mixing Ag powder with 20 layers of ffi 96, Ag2
A ceramic superconductor was produced in the same manner as in Example 1 except that 20% by weight of O powder was mixed.

The Jc B characteristics of the obtained ceramic superconductor were investigated in the same manner as in Example 1. The results are also shown in characteristic curve B in FIG.

Example 3 Instead of mixing 20% Ag2O powder by weight, a ceramic superconducting conductor was produced using 20% Ag2O powder by weight and 1% Ag powder.

The Jc B characteristics of the obtained ceramic superconductor were investigated in the same manner as in Example 1. The results are also shown in characteristic curve C in FIG.

Example 4 Instead of mixing 20% of Ag powder, 2% of Au powder was mixed.
A ceramic superconducting conductor was produced in the same manner as in Example 1, except that the powder was mixed at zero weight and the temperature at which the mixed powder was heated was changed from 1150°C to 1200°C.

J of the obtained ceramic superconductor. -B characteristics were investigated in the same manner as in Example 1. The results are also shown along with the characteristic curve in FIG.

Comparative Example First, B 1 2 0 3 , S r CO 3 ,
C a C O 3 and CuO powder were mixed into Bi:Sr
:Ca:Cu ratio was 2:2:1:2.

The weighed powders were thoroughly mixed. 820 ml of mixed powder
It was calcined at ℃ for 20 hours. The obtained calcined product was crushed. This calcined powder was heated to 1150°C and melted. after that,
The molten mixture was cooled by a twin roll method using an apparatus as shown in FIG.
A foil-like body was prepared. When this foil-like material was measured by X-ray diffraction, it was found to be amorphous.

Next, this foil-like body was sufficiently crushed. The powder after pulverization was filled into an Ag pipe having an outer diameter of 10φ and an inner diameter of 6φ. This Ag vibrator was rolled to produce a tape-like body with a thickness of 0.3 ml. This tape-like body was heated to 900°C in an oxygen stream.
A ceramic superconducting conductor was produced by reheating for 1 hour.

When the cross section of the obtained ceramic superconductor was observed using EPMA, it was found that the ceramic superconductor crystal grains 40 were oriented as shown in FIG. In addition, 41 in the figure
is a grain boundary.

Further, the Jc B characteristics of the obtained ceramic superconducting conductor were investigated in the same manner as in Example 1. The results are shown in characteristic curve E in FIG.

As is clear from FIG. 3, the ceramic superconducting conductor obtained by the method of the present invention exhibited excellent superconducting properties even in the high magnetic field of IOT.

On the other hand, the ceramic superconducting conductor of the comparative example has L
It showed almost no superconducting properties in the high magnetic field of OT.

[Effects of the Invention] As explained above, the method for manufacturing a ceramic superconducting conductor of the present invention can produce a ceramic superconducting conductor that can exhibit excellent superconducting properties in a high magnetic field and can be applied to magnets, coils, etc. can be manufactured efficiently.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the structure of the ceramic superconducting conductor obtained by the method of the present invention, FIG.
Figure (b) is an explanatory diagram of the apparatus used in the cooling step in the method of the present invention. FIG. 3 is a graph showing the relationship between current density and magnetic field, and FIG. 4 is an explanatory diagram showing the structure of a ceramic superconductor obtained by a comparative method. 10, 40... Ceramic superconductor crystal grain, 11.
...Ag, 12.41...grain boundary, 20,24. 25... Cooling roll, 21... Container, 22... Ceramic superconductor, 23.26... Coolant.

Claims (1)

[Claims] a step of mixing a ceramic superconductor raw material and a substance containing a noble metal element; a step of heating the mixture to a temperature at which the ceramic superconductor raw material melts; and a step of holding the mixture at the temperature for a predetermined time; a step of cooling the mixture to a predetermined temperature to make it amorphous; a step of molding the amorphized mixture into a desired shape; and reheating the molded product to a predetermined temperature to add the noble metal element to the mixture. 1. A method for producing a ceramic superconducting conductor, comprising the step of dispersing the ceramic superconducting conductor.