JP3187089B2 - Oxide superconducting structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure having an oxide superconducting sintered body, and more particularly to a structure having a high-density and highly oriented oxide superconducting sintered body and having high strength. It is about.

[0002]

2. Description of the Related Art In recent years, oxide superconductors have been discovered as materials having a higher critical temperature Tc (temperature at which resistance becomes zero) than metal-based superconductors conventionally used as superconductors, and their practical use is expected. Have been. At present, as oxide superconductors, mainly Y-Ba-Cu-O-based, Bi
-Sr-Ca-Cu-O system and Tl-Ba-Ca-C
Three types of uO type are mainly known. These oxide superconductors have a high critical temperature and a critical current density (current value at zero resistance) for practical use.
Is needed to be large. In addition, 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 increase the density in order to obtain such characteristics.

[0003] Therefore, as a method for producing an oxide superconducting sintered body having a higher density than in the past, a hot press method of heating while applying a higher mechanical pressure than in the past has been adopted.

Further, as a structure using a superconductor, Ag is used.
A superconducting powder sealed in a metal pipe such as that described above has been developed as an electric wire or the like.

[0005]

However, the strength of the oxide superconducting sintered body itself is low, and even if high densification is achieved by the hot press method, the strength is low and it is necessary to pay attention to handling, and Was insufficient for In addition, the critical current density of the obtained sintered body is at most 1000 A / cm ² or less due to insufficient orientation of the crystal grains, and it has not reached a practical level at present.

Therefore, the present inventors first fired the calcined powder of the low Tc phase at normal pressure to generate a sufficiently high Tc phase, and then performed heat treatment while applying pressure to the sintered body. It has been proposed that by performing a so-called hot forging treatment, an excellent oxide superconducting sintered body having a high orientation and a high density and a Jc value of about 1500 to 4500 A / cm ² can be obtained. There was a problem that the treatment was inadequate and required careful handling.

[0007] Further, the one compounded with Ag for electric wires is useful for wire drawing, but Ag itself is expensive, and it is difficult to apply it to large structures such as magnetic shields. When the metal is used, there is a problem that some metal elements diffuse into the superconductor and deteriorate superconductivity.

[0008]

Means for Solving the Problems The inventors of the present invention have studied the above problems, especially about the structure for improving the strength, and as a result, based on the previously proposed method, have found that the oxide superconducting firing The sintered body may have a structure in which an oxide superconducting sintered body containing at least Cu as a constituent element is sandwiched by an oxide ceramic sintered body, or the oxide ceramic sintered body may be formed through a metal layer having ductility. It has been found that a rigidly joined monolith can be obtained by adopting a structure sandwiched by the binders, and a structure having high strength can be obtained while maintaining high superconducting characteristics as the structure.

Hereinafter, the structure of the present invention will be described in detail. As shown in FIG. 1, this structure is obtained by bonding an oxide superconducting sintered body 1 and oxide ceramic layers 2 and 3 on both surfaces thereof. The oxide superconducting sintered body has a three-layer structure of
The oxide ceramic sintered body has a thickness of 0.05 mm or more and a thickness of 0.05 mm or more. At the interface between the oxide superconducting sintered body 1 and the oxide ceramics 2 and 3, a part of the oxide superconducting sintered body is melted and diffused to the oxide ceramic side to have a thickness of 0.5 mm made of glass.
In the following, the presence of the intermediate diffusion layers 4 and 5 greatly improves the adhesion between the two.

As another embodiment of the present invention, as shown in FIG. 2, a ductile material having a thickness of 0.02 mm or more between the oxide superconducting sintered body 1 and the oxide ceramic sintered bodies 2 and 3 is used. Can be interposed. The metal layers 6 and 7 are oriented and compressed during the hot forging process to be described later due to the ductility effect of the metal itself, and are compressed to form the oxide superconducting sintered body. Density can be increased.

The oxide ceramic sintered body used in the present invention includes Al ₂ O ₃ , ZrO ₂ , Si
O _2, suitably made of MgO or the like, these oxide ceramic sintered body, but the oxide superconducting sintered body which is produced separately in a known manner, especially to-theoretical density ratio of 8
A sintered body of 0% or more is preferable. As the oxide superconductor, Y-Ba-Cu-O-based, Bi-Sr-Ca-
Any of Cu-based superconductors such as Cu-O-based and Tl-Ba-Ca-Cu-O-based may be used.

Next, the method of forming the above-mentioned structure will be described. First, the oxide superconductor is oxidized using a metal oxide powder or a carbonate or nitrate powder capable of forming an oxide by firing. Weigh and mix in such a ratio that a superconductor can be formed. Specifically, when a high Tc phase is formed in the above-described Bi-based oxide superconductor, Bi
_When each of the powders of ₂ O ₃ , SrO, CaCO ₃ , and CuO is used and the atomic ratio of Sr is 2, Bi is 1.
8 to 2.2, Ca is 2.0 to 3.5, Cu is 3.0 to 3.0
Weigh to 4.5 range. Further, for the purpose of increasing the generation amount of the high Tc phase, PbO powder, K ₂ CO ₃ , Na ₂ CO ₃ , Li ₂
0.1 to 0.5 and Pb of CO ₂ such as 2 Sr, K,
Li and Na can be mixed at a ratio of 0.05 to 0.6. The resulting mixture is optionally at 700-850 ° C.
After calcination for about 1 to 20 hours in an oxidizing atmosphere, molding is performed. Molding can be performed by known molding means,
For example, it is carried out by 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. By this baking, scaly crystals having a low Tc phase are once generated, and as the baking proceeds, the low Tc phase is converted into a high Tc phase.

If this sintering is carried out under no pressure, a sintered body having a low density is obtained by the growth of scaly crystals, so that hot press sintering may be carried out. At the end of the firing step, the scaly crystals of the sintered body are almost non-oriented.

Next, hot forging treatment is performed with the above-described oxide superconducting sintered body sandwiched between oxide-based ceramic sintered bodies. This processing method will be described with reference to FIG. In the figure, 8 is an oxide superconductive sintered body, 9 and 10 are press punches, and 11 and 12 are oxide ceramic sintered bodies.
According to the present invention, between the oxide superconducting sintered body 8 and the press punches 9, 10, the oxide-based ceramic sintered bodies 11, 1
2 and pressurizing is performed in the direction A by the press punches 9 and 10, and at the same time, heating is performed by a suitable heating means (not shown). The pressure at this time is 50 kg / c
m ² or more, and a heating temperature of 800 to 850 ° C. is appropriate.
By this hot forging treatment, the oxide superconducting sintered body 8 and the oxide ceramic sintered bodies 11 and 12 are joined and integrated, and have a high strength as a structure including the oxide superconducting sintered body. .

In the above method, as shown in FIG. 4, when the ductile metal plates 13 and 14 are interposed between the sintered oxide superconductor 8 and the sintered oxide ceramics 11 and 12, respectively. 4, the ductile metal plate itself is rolled in the direction perpendicular to the direction A by the pressure from the direction A in FIG. 4, and simultaneously, the oxide superconducting sintered body 8 is also rolled in the same direction. The flake crystal particles are oriented and compressed, and the density of the sintered body can be increased. Thereby, the critical current density of the oxide superconducting sintered body can be further increased because the adhesion between the scaly crystals is remarkably improved.

[0017]

According to the constitution of the present invention, it is most important that the oxide superconducting sintered body layer is sandwiched between the oxide ceramic sintered bodies. On the other hand, as a substance whose strength can be enhanced by complexing with an oxide superconducting sintered body, there is a problem that a noble metal material has ductility, low strength, and is expensive. There is a problem that the metal element diffuses into the oxide superconducting sintered body and deteriorates the superconducting characteristics. In addition, in non-oxide ceramic sintered bodies such as silicon nitride, silicon carbide and aluminum nitride, the firing conditions are different from those of the oxide superconducting sintered bodies, so that problems occur during firing or hot forging treatment is performed. At times, nitrogen and carbon may adversely affect the superconducting properties, and there is a problem that the bonding strength with the superconductor is low.

On the other hand, in the case of the oxide ceramic sintered body, the firing atmosphere is an oxidizing atmosphere, and there is no adverse effect due to the atmosphere during firing or heat treatment. Does not deteriorate.

According to the present invention, when a metal layer is interposed between the oxide superconducting sintered body and the oxide ceramic sintered body, the metal in the oxide superconducting sintered body is formed due to the ductility of the metal itself. The flaky crystal particles are oriented and compressed, and the density of the oxide superconducting sintered body can be increased.

As a result, the critical current density Jc of the oxide superconducting sintered body can be further increased since the adhesion between the flake crystals is remarkably improved.

In addition, since the oxide superconducting sintered body layer and the metal layer are in contact with each other, the ambient temperature becomes lower than the offset temperature (Tc
e) When the current exceeds the critical current (Ic), the superconductor layer quenches when the ambient magnetic field becomes larger than the critical magnetic field (Hc). Instead, it has the function of current propagation. The current propagation of the metal layer is inferior to that of the oxide superconducting sintered body layer, but this can be sufficiently compensated during the temporary quench. Furthermore, the heat dissipation of the metal layer suppresses the heat generation of the oxide superconducting sintered body layer itself due to an increase in current, thereby preventing the superconducting characteristics from being destroyed.

Further, in such a structure, a part of the oxide superconducting sintered body in contact with the oxide ceramic sintered body is melted to diffuse or form a glass layer at the interface of the oxide ceramic sintered body. As a result, the adhesive strength between the oxide superconducting sintered body and the oxide ceramic sintered body is increased, and an integrated structure of the oxide superconducting sintered body and the oxide ceramic sintered body is produced. Thereby, the mechanical strength of the integrated structure is dramatically improved.

Further, according to the structure of the present invention, since the oxide superconducting sintered body is not exposed to the outside air, it is possible to prevent the oxide superconducting sintered body from being decomposed and deteriorated by moisture in the air.

[0024]

EXAMPLES Example 1 Bi ₂ O ₃ , PbO, SrCO ₃ , CaC
Each powder of O ₃ and CuO is mixed with a metal at a molar ratio of Bi: Pb:
Sr: Ca: Cu = 1.93: 0.36: 2: 3.1
After being weighed to 7: 4.25, it was calcined at 750 to 810 ° C for 20 hours and pulverized to obtain a calcined powder containing a large amount of a low Tc phase having an average particle size of 5 µm. This calcined powder is φ12mm
Was molded at a molding pressure of 1 ton / cm ² by using the mold described above to obtain a disk-shaped molded body having a thickness of about 1 mm.

Next, the above compact was fired in the air at a temperature of 840 ° C. for 150 hours to obtain a sintered compact having a specific gravity of 2.0 (based on the Archimedes method). When the structure was observed, scaly crystals having a 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, which has been carefully selected in advance, and SiO ₂ , CaO, and MgO as other inclusions, each having a porcelain composition ratio of 82: 12: 2: 4 It was prepared to be. Vinyl acetate was added to the prepared raw material, and wet pulverized for 16 hours using alumina balls. This was granulated and then molded, and the obtained molded body was kept at 1450 to 1700 ° C. for 2 hours to obtain an Al ₂ O ₃ sintered body having a theoretical density ratio of 99%.

Next, according to FIG.
A 0.5 mm thick plate made of the alumina sintered body obtained above was placed on the upper and lower surfaces of the sintered body, and a temperature of 845 ° C. was applied to the sintered body at a pressure of 5 ton / cm ² through the plate. Hot forging treatment.

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

[0029]

(Equation 1)

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

As a test of water resistance, the sample was immersed in water at 65 ° C. (95%).
% RH) for 1 hour, and then the critical temperature Tc (aq) was measured.

Comparative Example 1 Example 1 was repeated except that no oxide ceramic sintered body was used during the hot forging treatment.
A sintered body was prepared in exactly the same manner as described above, and the characteristics were evaluated in the same manner. The results are shown in Table 1.

Comparative Example 2 A sintered body was prepared in exactly the same manner as in Example 1 except that only one side of the oxide ceramic sintered body was used during the hot forging treatment, and the characteristics were similarly evaluated. Was done. The results are shown in Table 1.

Example 2 In Example 1, the hot forging treatment was carried out by disposing a 0.1 mm thick silver plate between the oxide superconductive sintered body and the oxide ceramic sintered body. At a pressure of 1 ton / cm ^{2 to} the sintered body through 82
Performed at a temperature of 0 ° C.

The properties of the obtained sintered body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0036]

[Table 1] As is clear from Table 1, in Example 1 in which the oxide superconducting sintered body was sandwiched by the oxide ceramic sintered bodies, Comparative Example 1 in which only the oxide superconductive sintered body was used, Compared with Comparative Example 2 having a ceramic sintered body, not only the strength is improved, but also the specific gravity, the degree of orientation, the Jc value, and the Tc value are excellent. Further, in the hot forging treatment, in which the ductile metal was interposed between the sintered body and the oxide-based ceramics sintered body in Example 2, the degree of orientation, Jc
Regardless of the value and the Tc value, an oxide superconducting sintered body that was more excellent than that of Example 1 could be obtained. In addition, it was found that all of the products of the present invention did not show any deterioration in superconductivity even in a high-humidity atmosphere, and had excellent durability.

A structure was prepared in the same manner as in Example 1 using a ZrO ₂ -based sintered body containing 3 mol% of Y ₂ O ₃ and a MgO sintered body in the same manner as described above. The same tendency as in Example 1 was observed.

[0038]

As described above, according to the present invention,
By sandwiching the oxide superconducting sintered body with the oxide ceramic sintered body, it is possible to achieve high strength as a structure without affecting the characteristics of the superconducting sintered body, In addition, a structure containing an oxide superconducting sintered body having a high critical temperature and an extremely high critical current density can be obtained because the degree of orientation of the crystal grains of the oxide superconducting sintered body can be increased and densification can be achieved. be able to. Further, since it is excellent in water resistance, it can be used in any environment and can be applied as a structure such as a magnetic shield member.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an oxide superconducting structure of the present invention.

FIG. 2 is a sectional view showing another example of the oxide superconducting structure of the present invention.

FIG. 3 is a view for explaining a method for producing the oxide superconducting structure shown in FIG. 1 of the present invention.

FIG. 4 is a view for explaining a method for producing the oxide superconducting structure shown in FIG. 2 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxide superconducting sintered compact 2, 3 Oxide ceramic sintered compact 6, 7 Metal layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 1/00 H01B 12/00-12/16 H01B 13/00 CA (STN) JICST file (JOIS)

Claims (2)

(57) [Claims] 1. An oxide superconducting structure comprising an oxide superconducting sintered body made of a composite oxide containing at least Cu and oriented in the C-axis direction, sandwiched by an oxide ceramic sintered body. body. 2. An oxide superconducting sintered body made of a composite oxide containing at least Cu and oriented in the C-axis direction is sandwiched by an oxide ceramic sintered body via a ductile metal layer. Oxide superconducting structure.