JPH01320258A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To ensure superior fillability, to obtain a high density molded body and to increase the critical current density of an oxide superconductor by classifying powdery starting material for a BSCCO superconductor into three kinds of powders having different prescribed particle sizes, mixing the powders in a prescribed ratio and press-molding this mixture. CONSTITUTION:Powdery starting material for a Bi-Sr-Ca-Cu oxide (BSCCO) superconducting material is classified into first powder having 10-12mum particle size, second powder having 4-5mum particle size and third powder having <=1mum particle size. The powders are mixed in (25-30):(6-8):1 weight ratio of first powder:second powder:third powder and this mixture is press-molded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to bismuth (Bi)-strontium (Sr)-
Regarding a method for manufacturing oxide superconductors such as wires of calcium (Ca)-copper (Cu)-oxide (0) (hereinafter referred to as B5CC0) based superconducting materials, the critical current density is improved by particularly increasing the density. The present invention relates to a method for producing an oxide superconductor.

[Prior Art] In the process of processing a B5CC0-based superconducting material into a wire rod, Bi, Sr, and Ca are usually first processed.

Cu oxide or carbonate is used as a starting material, and after mixing each raw material in a predetermined amount, the mixed powder is heated at approximately 900°.
The mixture is calcined at a temperature of C to obtain a sintered body of B5CC0 powder particles. Next, this sintered body is pulverized into a powder having a predetermined particle size, and the obtained B5CC0-based powder is pressure-molded into a compact having a desired size and shape.

Thereafter, a metal pipe or the like is filled with the molded body produced in the pressure forming step, and then swaged or wire drawn together with the pipe to obtain a wire rod of a desired wire diameter.

Next, this wire is fired by heating to approximately 850 to 900'C in an oxidizing atmosphere so as to obtain desired characteristics (critical temperature Tc or critical current density Jc).

In this case, the powder to be pressure-molded conventionally has a particle size distribution as shown in FIG. FIG. 1 is a graph showing the particle size distribution of B5CC0-based oxides, with the horizontal axis representing the particle diameter and the vertical axis representing the integrated sieve depth. As is clear from FIG. 1, the raw material powder has an average particle size of 5 to 6 μm, and particles having a particle size of 25 μm or less are continuously distributed.

[Problems to be Solved by the Invention] However, a compact formed by pressure-molding a powder having such a particle size distribution does not necessarily have a high density. Furthermore, even if the pulverization method is changed to increase or decrease the average particle size in order to increase the density of the compact,
As in the case shown in FIG. 1, the situation that particles having a predetermined particle diameter or less are continuously distributed remains unchanged. Therefore, under the same pressure conditions, even if the pulverization method is changed, the density of the compact will not be significantly increased.

In this way, in the conventional manufacturing method, it is not possible to increase the density of the pressed compact, so the B5CC0-based superconductor obtained by the post-process wire drawing and sintering treatment has the drawback of low critical current density. have

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a method for producing an oxide superconductor that can sufficiently increase the density of a press-molded body, thereby significantly increasing the critical current density.

[Means for Solving the Problems] A method for producing an oxide superconductor according to the present invention includes bismuth-
Among the raw material powders for the strontium-calcium-copper-oxide superconducting material, there are a first type powder with a particle size of 10 to 12 μm, a second type powder with a particle size of 4 to 5 μm, and a second type powder with a particle size of 1 μm or less. 3rd type powder, (1st type powder): (2nd type powder)
Seed powder): (Third type powder) = (26 to 30): (6
8) to 8) are characterized in that they are mixed at a blending weight ratio of 1, and the mixed powder is press-molded.

[Function] Regarding the B5CC0-based superconducting material powder, the inventors of the present application
Powder particles of various particle sizes are collected by wind sieve classification, etc.
The raw material powder was classified into several types according to the particle size. Then, the blended weights of the powders belonging to each category were varied and mixed, and the mixed powders were molded under the same pressure conditions to determine the relationship between the particle diameter and blended weight ratio and the density of the molded body.

As a result, it was found that the density of the molded article could be sufficiently increased by setting the particle diameter and its blending weight ratio in an appropriate relationship.

The present invention has been made based on this viewpoint, and the optimum powder blending conditions are as follows.

In other words, there are three types of raw powder: those with a particle size of 10 to 12 μm are classified as type 1 powder, those with a particle size of 4 to 5 μm as type 2 powder, and those with a particle size of 1 μm or less as type 3 powder. If the blended weight of the third type powder is 1, the powder is mixed so that the blended weight of the first type powder is 26 to 30, and the blended weight of the second type powder is 6 to 8.

A product uniformly mixed at this blending weight ratio exhibits excellent filling properties and can yield a high-density molded product. On the other hand, if the particle size falls outside this range and the blending weight ratio falls within this range, a sufficiently high density cannot be obtained. Therefore, in the present invention, a powder having a particle size range and a blending weight ratio range falling within the above-mentioned range is used for pressure molding.

When processed into a wire rod, the superconductor is usually subjected to wire processing after pressure forming and then firing treatment. Since this superconductor has a high compaction density, the obtained critical current density increases significantly.

Note that, in practice, each raw material powder has various shapes such as scaly shape, but the particle size of the powder specified in the present invention is the longest diameter of this powder particle.

[Example] Next, examples of the present invention will be specifically described.

First, B i with an average particle diameter of 6 μm as shown in FIG.
2 Sr2 Ca2 Cu30y powder was prepared.

This powder was used as a starting material powder and was classified into various particle sizes using a wind sieve. Thereafter, the powders were mixed to obtain a powder having a blending weight ratio shown in Table 1 below, and then pressure molded. In addition,
Examples 1 to 5 are within the range defined in the claims of the present application, and Comparative Examples 1 to 9 are outside this range. In addition, the conventional example was molded using the starting raw material powder itself with a continuous particle size distribution.9 The size of the pressed compact in each sample was 7 mm in diameter and 100 mm long; The pressure was 2.5 tons and molding was performed by a rubber press method. The density of this molded body can be determined by first measuring the porosity of the molded body using a mercury porosimeter.
It was calculated from this porosity. The measurement results of the apparent density of this molded body are also shown in Table 1 above.

After filling and enclosing the molded body produced by the above method into a silver pipe with a wall thickness of 1.
The wire was reduced to a diameter of n■.

Thereafter, the surface silver sheath was dissolved in methanol nitric acid, and then heat treated in an oxidizing atmosphere at 900° C. for 10 hours. The critical current density of each superconducting material produced in this way was measured in liquid nitrogen. The results are also shown in Table 1. Note that this critical current density is equal to the critical current density of the starting material powder by 1.
This is an index display when .

As is clear from Table 1, B of Examples 1 to 5
The i2 Sr2 Ca2 Cu30y superconductor shows significant improvements in both apparent density and critical current density compared to superconductors produced by the comparative method or the conventional method.

[Effects of the Invention] As explained above, according to the present invention, when press-molding the powder of B5CCO-based superconducting material, the raw material powder is molded to 10 to 12 μm (first type), based on the powder particle size. 4 to 5μ
It is classified into three types: m (2nd type) and 1 μm or less (3rd type), and the blending weight ratio is (1st type); (2nd type):
(Type 3) = (26 to 30): (6 to 8): Since the pressure molding is performed after mixing so that It can be made higher.

[Brief explanation of the drawing]

FIG. 1 is a graph showing particle size distribution.

Claims (1)

[Claims] (1) The raw material powder of bismuth-strontium-calcium-copper-oxide superconducting material has a particle size of 10 to 1
A first type powder with a particle size of 2 μm, a second type powder with a particle size of 4 to 5 μm, and a third type powder with a particle size of 1 μm or less,
Seed powder): (2nd type powder): (3rd type powder) = (26 to 30): (6 to 8): Mixed at a blending weight ratio of 1, and this mixed powder is press-molded. A method for producing an oxide superconductor.