JPH04317415A - Production of bi-based oxide superconductor - Google Patents

Abstract

PURPOSE:To produce a Bi-based oxide superconductor free from a coarse foreign phase and excellent in superconductivity such as Jc. CONSTITUTION:The raw material A consisting essentially of the multiple oxide of Bi2Sr2Ca1Cu2Ox phase ((2212) phase) and the raw material B consisting essentially of the multiple oxide of a Bi2Sr2Cu2Oy phase are mixed so that the mixture contains 10-90wt.% of the multiple oxide of the (2212) phase. The mixture is formed into a desired shape, and the formed body is heat-treated under specified conditions. Since the multiple oxide of the (2212) phase as the reaction nucleus toward a superconductor is uniformly distributed in the mixture, the (2212) phase is converted to an oxide superconductor in a short time. As a result, the formed body is sintered at a low temp. since the multiple oxide other than the (2212) phase is contained, the foreign phase is not coarsened, and the Jc is enhanced.

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 Bi-based oxide superconductor suitable for cables, magnets, current leads, etc.

0002

[Prior Art] In recent years, Bi-Pb-Sr-Ca-Cu-
The critical temperature (T
Oxide superconductors whose temperature (c) exceeds the temperature of liquid nitrogen have been discovered, and applied research is progressing in various fields. By the way, these oxide superconductors are brittle, so in order to process them into a linear body of a predetermined shape, for example, a powdered raw material that can be made into an oxide superconductor is compacted into a predetermined shape, and then this is A method of heating and sintering to form a bulk oxide superconductor, or filling a metal pipe with the raw material to form a composite billet, and then reducing the diameter of this composite billet into a wire rod of a desired shape, It is manufactured by subjecting this wire to a predetermined heat treatment. Further, a large number of the above-mentioned oxide superconducting wires may be filled into a metal pipe to form a composite billet, or a sheet-like oxide superconductor sheathed with metal may be formed into a spiral or concentric multiplex composite. Composite billet and pear,
A method of forming a multicore oxide superconductor by subjecting these composite billets to diameter reduction processing and heat treatment is also used. Metal materials with excellent thermal and electrical conductivity such as silver, silver alloys, copper, and copper alloys are used as materials for the metal pipes or metal sheaths, but silver in particular has excellent oxygen permeability.
The obtained oxide superconductor has excellent superconducting properties and is a preferred material. Further, the metal pipe may have any shape such as round, oval, polygonal, tape, etc. Further, as a method for processing the composite billet in which the metal pipe is filled with raw materials into a desired shape, any processing method such as extrusion, drawing, swaging, rolling, etc. can be applied.

Incidentally, in recent years, oxide superconductors have been shown to have a critical current density (
It has been found that Jc) can be increased. And Bi
The system oxide superconductor includes Bi2 Sr2 CaCu2
Ox crystal phase [hereinafter abbreviated as (2212) phase. ] oxide superconductor and Bi2 Sr2 Ca2 Cu3 Ox
Crystal phase [hereinafter abbreviated as (2223) phase. ] are mainly known as oxide superconductors, but the former has better properties in liquid He than the latter;
Research on 212) phase oxide superconductors has become active. Therefore, the above-mentioned (2212) phase oxide superconductor is generally manufactured using Bi2 O3, SrCO3
, CaCO3, and CuO in predetermined amounts and mixed to form a mixed powder, which is calcined at a predetermined temperature, and then this calcined body is pulverized and mixed to form a calcined powder. The process of calcining this calcined powder again is repeated multiple times to produce a (2212) phase composite oxide, this composite oxide is molded into a desired shape, and this molded body is subjected to a predetermined heat treatment. (2212) phase oxide superconductor.

0004

[Problems to be Solved by the Invention] However, when a (2212) phase composite oxide prepared through such a process is used as a raw material, the raw material becomes difficult to sinter in the final heat treatment process. Therefore, when heated to high temperatures in an attempt to sinter, the composite oxide of the (2212) phase causes an excessive reaction and a different phase precipitates, which coarsens and deteriorates the superconducting properties of the resulting oxide superconductor. There was a problem with this.

[0005]

[Means for Solving the Problems] The present invention has been made as a result of intensive research in view of the above situation.
2) The average composition of the phase composite oxide A is the composite oxide A.
However, it was discovered that by mixing a composite oxide with a Bi2 Sr2 CuOY crystal phase and a raw material B whose main components are oxides such as CuO, this mixed raw material could be sintered at a relatively low temperature, and further research was conducted. By proceeding with this process, we have completed the present invention. That is, in the present invention, a raw material that can be made into a Bi-based oxide superconductor is molded into a desired shape, and this molded body is subjected to a predetermined heat treatment to produce a Bi-based oxide superconductor. , Bi2 Sr
2 Ca1 Cu2 Ox A raw material material (A) consisting of a composite oxide in the crystal phase has the same average composition as the A raw material material, but contains a composite oxide in the Bi2 Sr2 CuOY crystal phase and oxides such as CuO as the main components. Raw material (B)
The present invention is characterized in that a mixed raw material is used in which both are mixed so that the composite oxide of the Bi2 Sr2 CaCu2 Ox crystal phase is contained in an amount of 10 to 90% by weight.

In the method of the present invention, the reason why the ratio of the (2212) phase composite oxide to be contained in the mixed raw material is limited to 10 to 90% by weight is that if the mixed raw material is less than 10% by weight, the (2212) phase composite oxide is contained in the mixed raw material. It takes a long time for the heat treatment to react with the oxide superconductor, and during this time, precipitation and coarsening of different phases occur, and if the content exceeds 90% by weight, it becomes difficult to sinter the mixed raw material, and it becomes difficult to sinter. When the heat treatment temperature is increased (
2212) This is because the excessive reaction of the phase progresses and the different phases rapidly coarsen, resulting in a decrease in the superconducting properties of the resulting oxide superconductor. In the present invention, the method for producing the raw material A or the raw material B includes, for example, Bi2 O3, SrCO
3., CaCO3, CuO starting materials are Bi, Sr, C
Blend the elements a and Cu in an atomic ratio of 2:2:1:2, pulverize and mix to obtain a mixed powder, and heat this mixed powder at 840°C for 50 hours in the atmosphere, for example. If the pre-calcination is performed five or more times, the composite oxide becomes almost entirely of the (2212) phase. If the same mixed powder is pre-calcined once or twice at 750° C. for 50 hours, a mixture of Bi2 Sr2 CuOz phase composite oxides and oxides such as CuO can be obtained. In this way, the type of composite oxide obtained by calcining changes depending on the atmosphere, heating temperature, time, number of heating times, etc. during calcining, so please check through preliminary experiments.
It is desirable to determine the pre-firing conditions. Further, the mixed raw material is composed of raw material A whose main component is the (2212) phase and Bi2S.
Since it is produced by mixing the r2 CuOY phase composite oxide and the raw material B whose main component is an oxide such as CuO, (
2212) Phase content can be precisely adjusted. In addition, if the mixed raw material is pulverized, the (2212) phase complex oxide will not only become finer and its nucleation effect will become more pronounced, but also the foreign phases that have already become coarse during the calcination stage will become finer and harmless. In addition to this, this finely divided phase also functions to pin the magnetic flux when energized.

[0007]

[Operation] In the method of the present invention, a raw material that can be made into a Bi-based oxide superconductor is molded into a desired shape, and this molded body is subjected to a prescribed heat treatment to produce a Bi-based oxide superconductor. Raw material A, which can be made into a Bi-based oxide superconductor with a (2212) phase, has the same average composition as raw material A, but contains a composite oxide with a Bi2 Sr2 CuOY crystal phase and oxides such as CuO as the main components. Raw material B
By using a mixed raw material containing 10 to 90% by weight of composite oxide in the Bi2 Sr2 CaCu2 Ox crystal phase, sintering can be performed at a low temperature, and the nucleus of the reaction to form a superconductor. Since the composite oxide of the (2212) phase is uniformly distributed, the reaction to the (2212) phase Bi-based oxide superconductor is rapid, and therefore the (2212) phase is uniformly distributed.
12) Precipitation and coarsening of different phases due to excessive phase reaction are prevented.

[0008]

[Examples] The present invention will be explained in detail below using examples. Example 1 Bi2O3, SrCO3, CaCO3, CuO
Starting material powder such as Bi:Sr:Ca:Cu in atomic ratio is 2.
: After mixing in a ratio of 2:1:2, calcining in the atmosphere at 840°C for 20 hours, crushing this calcined body to obtain calcined powder, and calcining this calcined powder again. A process in which one cycle of calcining and pulverization of the calcined powder was repeated seven times to produce a raw material A consisting of a (2212) phase composite oxide. On the other hand, a raw material B consisting of Bi2 Sr2 Cu1 OY, CuO, etc. was prepared by repeating pre-calcination at 750° C. for 50 hours in the air twice. Next, these raw material A and raw material B are blended and mixed in various ratios such that the (2212) phase complex oxide is in the range of 10 to 90% to form a mixed raw material, and this mixed raw material is powdered. Shape 3
A rectangular rod-shaped bulk body measuring mm x 3 mm x 50 mm was prepared, and then this bulk body was heat-treated in the atmosphere at 845° C. for 50 hours to produce a (2212) phase bulk Bi-based oxide superconductor.

Comparative Example 1 In Example 1, the (2212) ) phase bulk Bi-based oxide superconductor was manufactured. Comparative Example 2 The same method as Comparative Example 1 was used, except that the blending ratio of the (2212) phase composite oxide in the mixed raw material was 7%, and the heat treatment conditions in the final step were 840°C x 100 hours. A (2212) phase bulk Bi-based oxide superconductor was manufactured using the following method. Comparative Example 3 The same method as in Comparative Example 1 was used, except that the blending ratio of the (2212) phase composite oxide in the mixed raw material was 93%, and the heat treatment conditions in the final step were 880°C x 50 hours. A (2212) phase bulk Bi-based oxide superconductor was manufactured using the following method.

Example 2 The same raw material A and raw material B produced in Example 1
were mixed in various ratios to form a mixed raw material, which was filled into an Ag pipe with an outer diameter of 7 mm, an inner diameter of 4 mm, and a length of 50 mm to form a composite billet. Next, this composite billet was rolled into a wire rod with an outer diameter of 1 mmφ by groove roll rolling, and then this wire rod was flat rolled into a tape-shaped composite wire rod with a thickness of 0.2 mm. After that, this tape-shaped composite wire was heat-treated in the atmosphere at 845°C for 50 hours (22
12) A phase tape-shaped Bi-based oxide superconductor was manufactured. Comparative Example 4 In Example 2, the (2212) phase was prepared by the same method as in Example 2, except that the blending ratio of the (2212) phase composite oxide in the mixed raw material was set to less than 10% or more than 90%. A tape-shaped Bi-based oxide superconductor was manufactured.

Comparative Example 5 Comparative Example 4 was performed except that the blending ratio of the (2212) phase composite oxide in the mixed raw material was 7% and the heat treatment conditions in the final step were 840°C x 100 hours. A (2212) phase tape-shaped Bi-based oxide superconductor was manufactured by the same method as described above. Comparative Example 6 The same method as Comparative Example 4 was used, except that the blending ratio of the (2212) phase complex oxide in the mixed raw material was 93%, and the heat treatment conditions in the final step were 880°C x 50 hours. A (2212) phase tape-shaped Bi-based oxide superconductor was manufactured using the following method. The critical current density (Jc) was measured for each oxide superconductor produced in this way. Jc was measured in liquid He (4.2K) by applying a strong magnetic field of 200,000 Gauss. In addition, the formation status of different phases was investigated by microscopic observation. The results are divided into Example 1 and Comparative Examples 1 to 3, and Example 2 and Comparative Examples 4 to 6, and are shown in Tables 1 and 2, respectively.

0012

[Table 1]

[0013]

[Table 2]

[0014] As is clear from Tables 1 and 2, the products produced by the method of the present invention (Nos. 1 to 5, 11 to 15) had a Jc showed a high value. Among the products of the method of the present invention, (22
12) Those in which the blending ratio of the phase complex oxide was 20 to 40% by weight (Nos. 2, 3, 12, and 13) showed the best results. On the other hand, comparative example method products No. 6 and 16 were (22
12) Since the ratio of the composite oxide in the phase was as low as 7% by weight, there was insufficient heat treatment time for the mixed raw material to react with the (2212) phase oxide superconductor, resulting in A large amount of unreacted substances, that is, a foreign phase, remained, and the superconducting properties deteriorated. For this reason, the heat treatment time was increased for Nos. 9 and 19, but in this case, before the unreacted substances finished reacting, another heterogeneous phase precipitated and became coarse within the (2212) phase oxide superconductor. As expected, the superconducting properties were of low value. Also, No. 7, 8, 17, 18 are (221
2) There was too much composite oxide in the phase, and sintering was not performed sufficiently, resulting in the resulting oxide superconductor having a structure with many pores. For this reason, No. 10 and 2 had higher heat treatment temperatures.
0, this time an overreaction occurred and the heterophase became coarse, resulting in a low Jc value.

[0015]

[Effect] As described above, according to the method of the present invention, the foreign phase does not become coarse, so superconducting properties such as Jc are excellent (22
12) A phase Bi-based oxide superconductor can be produced, resulting in significant industrial effects.

Claims (1)

[Claims] 1. In producing a Bi-based oxide superconductor by molding a raw material that can be made into a Bi-based oxide superconductor into a desired shape and subjecting the molded body to a prescribed heat treatment,
As raw materials, Bi2 Sr2 Ca1 Cu2 O
The raw material (A) consisting of a composite oxide in x crystal phase has the same average composition as the raw material A, but Bi2 Sr2
Bi2 Sr2
A method for producing a Bi-based oxide superconductor, characterized in that a mixed raw material is used in which a complex oxide of CaCu2Ox crystal phase is mixed in an amount of 10 to 90% by weight.