JPH054803A - Method for manufacturing oxide superconducting structure - Google Patents

Abstract

(57) [Summary] [Structure] When manufacturing an oxide superconductor such as a Y-Ba-Cu-O system, a mixture of oxides or oxide-forming compounds of the elements constituting the oxide superconductor is formed. Alternatively, the mixture is calcined and then molded, the molded body is fired in an oxidizing atmosphere, and the sintered body 1 is further laminated with an oxide-based ceramics sintered body 4 such as Al ₂ O _3. And pressurizing with the press punches 2 and 3 and heat treatment at the same time. [Effect] The crystal grains of the oxide superconductor are highly oriented,
Moreover, high strength can be achieved as a structure having an oxide superconductor while achieving high critical temperature and high critical current density by increasing the 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 manufacturing a structure provided with an oxide superconductor, and more particularly to a structure having a highly dense and highly oriented oxide superconductor and having high strength. Manufacturing method.

[0002]

2. Description of the Related Art In recent years, oxide superconductors have been discovered as a material having a higher critical temperature Tc (temperature at which resistance becomes zero) than metal superconductors that have been conventionally used as superconductors, and their practical application is expected. Has been done.

At present, the oxide superconductors are mainly Y-Ba-Cu-O-based (hereinafter referred to as Y-based) and Bi.
Three types of -Sr-Ca-Cu-O system (hereinafter, referred to as Bi system) and Tl-Ba-Ca-Cu-O system (hereinafter, referred to as Tl system) are mainly known. These oxide superconductors are required to have a high critical temperature and a large critical current density (current value at zero resistance) when they are put to practical use. Further, it is necessary to increase the strength of the structure, but it is said that it is most important to increase the relative density and to make the structure highly dense in order to obtain such characteristics.

Therefore, as a method for producing an oxide superconductor having a higher density than in the past, a hot press method of applying heat while applying a mechanical pressure higher than in the past has been adopted.

[0005]

However, the strength of the oxide superconductor itself is low, and even if a high densification is achieved by the hot pressing method, the strength is low and it is necessary to pay attention to the handling. On the other hand, the critical current density of the obtained sintered body is 1000 A / cm ² or less at the most because the orientation of crystal grains is also insufficient, and it has not reached a practical level. Was the current situation.

Therefore, the inventors of the present invention first fire a calcined powder of a low Tc phase at atmospheric pressure to generate a sufficiently high Tc phase, and then perform heat treatment while applying pressure to the sintered body. It has been proposed that by performing so-called hot forging treatment, an excellent oxide superconductor having a high orientation and a high density and a Jc value of about 1500 to 4500 A / cm ² can be obtained, but the strength is insufficient even by such a method. Therefore, there is a problem that the handling is required with caution.

[0007]

With respect to the above problems, the inventors of the present invention have made extensive studies on a method for improving the strength, and as a result, further improved the previously proposed method, When performing hot forging treatment in the constitution, the oxide ceramics sintered body and the oxide superconductor were firmly bonded by laminating the oxide superconducting sintered body with the oxide ceramics and heat-treating it under pressure. It was found that an integrated body can be obtained, and a structure having high strength can be obtained while maintaining high superconducting properties as a structure.

That is, according to the method for producing an oxide superconducting structure of the present invention, a mixture of oxides or oxide-forming compounds of the elements constituting the oxide superconductor is molded or the mixture is calcined. After that, the molded body is once fired in an oxidizing atmosphere, and then the sintered body is laminated with an oxide ceramic and heat-treated under pressure.

The present invention will be described in detail below. According to the production method of the present invention, first, using an oxide powder of a metal forming an oxide superconductor or a carbonate or nitrate powder capable of forming an oxide by firing, a ratio capable of forming an oxide superconductor Weigh and mix. Specifically, when the high Tc phase of the Bi-based oxide superconductor described above is created, Bi ₂
When each powder of O ₃ , SrO, CaCO ₃ and CuO is used and Sr is set to 2 in atomic ratio, Bi is 1.
8-2.2, Ca 2.0-3.5, Cu 3.0-
Weigh to be in the range of 4.5. Further, PbO powder, K ₂ CO ₃ , Na ₂ CO ₃ , and L were added to the above mixture for the purpose of increasing the production amount of the high Tc phase.
i ₂ CO _{2 and the} like with Sr being 2 and Pb being 0.1 to 0.5,
K, Li and Na can be mixed in a ratio of 0.05 to 0.6. The resulting mixture is 700-85 if desired.
After calcination in an oxidizing atmosphere at 0 ° C. for about 1 to 20 hours,
Mold.

The molding can be carried out by a known molding means, for example, press molding, extrusion molding, doctor blade molding or the like.

Next, the molded body obtained as described above is fired in an oxidizing atmosphere at 840 to 855 ° C. As a result of this firing, scaly crystals of a low Tc phase are once produced, and as the firing proceeds, the low Tc phase is converted to a high Tc phase.

If this firing is carried out without applying pressure, a low-density sintered body will be formed by the growth of flaky crystals, so hot press firing may be carried out. At the end of the firing step, the scaly crystals of the sintered body are almost non-oriented.

Next, according to the present invention, hot forging treatment is carried out with the above oxide superconducting sintered body sandwiched between oxide ceramics. This processing method will be described with reference to FIG. In the figure, 1 is an oxide superconductor sintered body, 2 and 3 are press punches, and 4 and 5 are oxide type ceramics. According to the present invention, when the oxide superconductor sintered body 1 and the press punches 2 and 3 are arranged via the oxide ceramics 4 and 5, pressure is applied in the A direction by the press punches 2 and 3. At the same time, heating is performed by an appropriate heating means (not shown). At this time, a pressure of 50 kg / cm ² or more and a heating temperature of 800 to 850 ° C. are suitable.

By this hot forging treatment, the oxide superconductor sintered body and the oxide-based ceramics are bonded and integrated, and a structure containing the oxide superconductor has high strength.

The oxide ceramics used in the hot forging treatment include Al ₂ O ₃ and Z.
Those made of rO ₂ , SiO ₂ , MgO, etc. are preferable, and these oxide-based ceramics are produced by a well-known method separately from the oxide superconductor sintered body, and particularly have a theoretical density ratio of 80. % Or more of the sintered body is suitable. Further, in order to improve the strength by compounding with the oxide superconductor, the thickness of the oxide ceramics is preferably 0.05 mm or more. Further, according to this hot forging treatment, in FIG. 1, for example, Ag, Au, Cu, P is provided between the oxide superconductor 1 and the oxide ceramics 2, 3.
It is also possible to perform the treatment with a metal plate made of a ductile metal such as t having a thickness of 0.05 mm or more interposed.

[0016]

According to the constitution of the present invention, it is most important to carry out hot forging treatment in a state where the oxide superconducting sintered body obtained by firing is laminated with the oxide ceramics.

When such treatment is carried out, a part of the oxide superconductor in contact with the oxide ceramics is melted and a diffusion or glass layer is formed at the interface of the oxide ceramics. The adhesive strength between the ceramics is increased, and an integrated structure of the oxide superconductor and the oxide ceramics is produced. This dramatically improves the mechanical strength of the integrated structure.

Further, when the ductile metal is interposed, the ductile metal itself is rolled in the direction perpendicular to the A direction by the pressure from the A direction in FIG. 1, and at the same time, the sintered body 1 is also rolled in the same direction. Further, the scaly crystal particles in the sintered body are oriented and compressed and the density of the sintered body can be increased. As a result, the adhesion between the flaky crystals is dramatically improved, and the critical current density of the oxide superconductor can be further increased.

In addition to oxide-based ceramics, metallic materials, non-oxidizing ceramics such as carbides and nitrides, or oxide-based ceramics before firing are used as materials to be laminated during hot forging treatment. Although the body may be considered, noble metal materials have the problem that they are ductile, have low strength, and are expensive, and with other metals, the metal element diffuses into the oxide superconductor during processing and deteriorates superconducting properties. There is a problem. Further, the non-oxide ceramics have a problem that the oxide superconductor is exposed to a reducing atmosphere during firing and decomposes. Further, in the method of stacking oxide-based compacts and firing the oxide superconductor at the same time, it is difficult to fire the oxide superconductor at the same time because the firing temperature of the oxide superconductor itself is low.

Therefore, the material to be laminated in the present invention needs to be oxide-based already fired ceramics.

[0021]

【Example】

Example 1 Bi ₂ O ₃ , PbO, SrCO ₃ and Ca as raw material powders
The CO ₃ and CuO powders are mixed with Bi: P in a molar ratio of each metal.
b: Sr: Ca: Cu = 1.93: 0.36: 2: 3.
Weighed to 17: 4.25, then 750-810 ° C
It was calcined for 20 hours and pulverized to obtain a calcined powder containing a large amount of low Tc phase having an average particle size of 5 μm. This calcinated powder is φ12m
Molding was performed at a molding pressure of 1 ton / cm ² using a m mold to obtain a disk-shaped molded body having a thickness of about 1 mm.

Next, when the molded body was fired in the air at a temperature of 840 ° C. for 150 hours, a sintered body having a specific gravity of 2.0 (based on the Archimedes method) was obtained. Further, when the structure was observed, scaly crystals of high Tc phase were randomly arranged.

On the other hand, Al ₂ O ₃ having a purity of 99% or more and a particle size of 3 μm or less selected in advance, and SiO 2, CaO, and MgO as other inclusions each have a porcelain composition ratio of 82: 12: 2: 4. It was mixed so that Vinyl acetate was added to this blended raw material, and alumina balls were used to
It was wet-milled for 6 hours. This was granulated and then molded, and the obtained molded body was held at 1450 to 1700 ° C. for 2 hours to obtain an Al ₂ O ₃ -based sintered body having a theoretical density ratio of 99%.

Next, the oxide superconductor sintered body was placed on the upper and lower surfaces of the sintered body according to FIG. 1, and a plate having a thickness of 0.5 mm made of the alumina sintered body obtained above was arranged. Through the sintered body at a pressure of 5 ton / cm ² at 845
Hot forging treatment was performed at a temperature of ° C. The sintered body thus obtained was designated as sample No. 1.

The specific gravity of the finally obtained sintered body was examined by the Archimedes method and X-ray diffraction measurement was performed. Based on the chart data of X-ray diffraction, the degree of orientation f of the (001) plane from the following equation 1 I asked.

[0026]

[Equation 1]

Further, with respect to the above-mentioned sintered body, the current value when the sample was gradually increased in liquid nitrogen and a voltage of 1 μV / cm was generated at the high voltage terminal was obtained as the critical current density Jc based on the resistance method. At the same time, the critical temperature Tc was also measured. The results are shown in Table 1.

Comparative Example 1 A sintered body (Sample No. 2) was prepared in the same manner as in Example 1 except that no oxide ceramics were used during the hot forging treatment, and the same characteristics were obtained. Was evaluated. The results are shown in Table 1.

Example 2 In Example 1, hot forging treatment was performed by placing a silver plate having a thickness of 0.1 mm between an oxide superconductor and an oxide ceramics sintered body, and baking through this plate. The tying was performed at a temperature of 820 ° C. and a pressure of 1 ton / cm ² .

With respect to the obtained sintered body (sample No, 3),
The characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0031]

[Table 1]

As is clear from Table 1, Example 1 which is a co-fired body of oxide superconductor and oxide ceramics,
Not only the strength is improved, but also the specific gravity, the degree of orientation, the Jc value, and the Tc value are excellent as compared with Comparative Example 1 including only the oxide superconductor. Furthermore, in Example 2 in which the ductile metal was interposed between the sintered body and the oxide-based ceramics during the hot forging treatment, the oxidation was superior to that of Example 1 in any of the orientation degree, the Jc value, and the Tc value. It was possible to obtain a superconductor.

In the same manner as described above, a similar test was conducted using a ZrO _{2 based} sintered body containing 3 mol% of Y ₂ O ₃ and a MgO sintered body, and the results were compared with the Al ₂ O _{3 based} sintered body. Excellent properties were obtained as well as composite.

[0034]

As described above in detail, according to the method of the present invention, oxide ceramics are laminated at the same time when hot forging a sintered body which has been densified to some extent when producing an oxide superconductor. By firing, the degree of orientation of the crystal grains of the sintered body can be increased and the density can be increased, so that an oxide superconductor having a high critical temperature and an extremely high critical current density can be stably obtained and A structure having strength can be obtained.

By thus obtaining an oxide superconductor having a high critical current density, the oxide superconductor can be further put into practical use.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a hot forging process in the method for producing an oxide superconductor according to the present invention.

[Explanation of symbols]

 1 ... Oxide superconducting sintered body 2, 3 ・ Press punch 4 ... Oxide ceramics

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication H01B 13/00 565 D 8936-5G H01L 39/24 ZAA Z 8728-4M

Claims (1)

Claim: What is claimed is: 1. Forming a mixture of oxides of oxide superconductors or compounds capable of forming oxides, or forming the mixture after calcination, and forming the mixture. 1. A method for manufacturing an oxide superconducting structure, comprising: a step of firing a molded body in an oxidizing atmosphere; and a step of laminating the sintered body with an oxide-based ceramics sintered body, pressurizing the sintered body, and simultaneously performing heat treatment.