JP3285646B2 - Manufacturing method of 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 method of manufacturing a structure having an oxide superconductor, and more particularly, to a method of fabricating a structure having a high-density and highly-oriented oxide superconductor. And a manufacturing method capable of improving the

[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.

[0003] At present, oxide superconductors mainly include Y-Ba-Cu-O-based (hereinafter referred to as Y-based) and Bi-based.
Three types of -Sr-Ca-Cu-O type (hereinafter, referred to as Bi type) and Tl-Ba-Ca-Cu-O type (hereinafter, referred to as Tl type) are mainly known. For practical use, these oxide superconductors are required to have a high critical temperature and a large critical current density (current value at zero resistance). 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.

Therefore, as a method for producing an oxide superconductor having a higher density than before, a hot press method in which heating is performed while applying a high mechanical pressure has been adopted.

[0005]

However, in the hot pressing method, the critical current density of the obtained sintered body is at most 300 due to insufficient orientation of the crystal grains.
It is 0 A / cm ² or less, and has not reached a practical level at present.

Therefore, the present inventors first fired a low Tc phase calcined powder at normal pressure to generate a high Tc phase, and then performed heat treatment while applying pressure to the sintered body. It has been proposed that an oxide superconducting structure having a high orientation, a high density, and a high strength can be obtained by performing a forging treatment and performing a treatment by sandwiching the oxide ceramics.

However, according to such a method, there is a problem that the resulting structure has a non-uniform structure and the superconductivity is partially non-uniform due to pressure unevenness during pressurization.

[0008]

Means for Solving the Problems The present inventors have studied the above problems, and as a result, have further improved the previously proposed method. When laminating the oxide superconducting sintered body with oxide-based ceramic powder or relatively low-strength oxide-based ceramic sintered body and performing the treatment, the pressure is uniformly applied when the pressure is applied, and as a result, Has a homogeneous tissue as
It has been found that a structure having uniform and high superconductivity can be obtained.

That is, according to the method for producing an oxide superconducting structure of the present invention, a mixture comprising an oxide or an oxide-forming compound of an element constituting the oxide superconductor is formed or the mixture is calcined. After sintering, the formed body is once fired in an oxidizing atmosphere, and then the sintered body is passed through an oxide-based ceramic powder or an oxide-based ceramic sintered body having a flexural strength of 5 kg / mm ² or less. The pressure and heat treatment is performed under a pressure of 50 kg / cm ² or more.

Hereinafter, the present invention will be described in detail. According to the production method of the present invention, first, an oxide superconductor is formed by using an oxide powder of a metal constituting the oxide superconductor or a carbonate or nitrate powder capable of forming an oxide by firing. Weigh and mix. Specifically, when a high Tc phase is formed in the above-mentioned Bi-based oxide superconductor, Bi ₂
When Sr is set to 2 in atomic ratio using each powder of O ₃ , SrO, CaCO ₃ , and CuO, 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 production amount of the high Tc phase, PbO powder, K ₂ CO ₃ , Na ₂ CO ₃ , L
0.1 to 0.5 and Pb a i ₂ 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 700-85.
After calcination for about 1 to 20 hours in an oxidizing atmosphere at 0 ° C,
Mold.

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

Next, the compact obtained as 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 due to 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, according to the present invention, the above oxide superconducting sintered body is made of an oxide ceramic powder or an oxide ceramic sintered body having a flexural strength of 5 kg / mm ² or less, particularly 1 kg / mm ² or less. Hot forging treatment while sandwiched between the body. This processing method will be described with reference to FIG. In the figure, 1 is an oxide superconducting sintered body, 2 and 3 are press punches,
Reference numerals 4 and 5 denote oxide ceramic powders. According to the present invention, between the oxide superconductor sintered body 1 and the press punches 2 and 3, the oxide-based ceramic powders 4 and 5 are interposed, and pressure is applied in the A direction by the press punches 2 and 3. At the same time as the application, heating is performed by a suitable heating means (not shown). The pressure at this time is 50 kg / cm ² or more, and the heating temperature is 800
~ 850 ° C is suitable. By this hot forging treatment, the oxide superconducting sintered body becomes a structure having a uniform high density and a high degree of orientation.

The oxide ceramic powder used in the hot forging treatment includes Al ₂ O ₃ ,
Those made of ZrO ₂ , SiO ₂ , MgO or the like are preferable.

The oxide ceramic powder used here preferably has an average particle size of 1 mm or less.
The metal oxide powder or a powder obtained by firing the powder and pulverizing the powder to have the above-mentioned particle size may be used.

As another embodiment of the present invention, as shown in FIG. 2, instead of the oxide-based ceramic powders 4 and 5 in the example of FIG. 1, an oxide-based ceramic having a transverse rupture strength of 5 kg / mm ² or less is used. Pressurization and heat treatment is performed with the ceramic sintered bodies 6 and 7 interposed. The reason why the strength of the sintered body is limited to 5 kg / mm ² or less is that the sintered body is easily cracked and becomes particles having a particle size of 1 mm or less when a pressure of 50 kg / cm ² or more is applied.
This is because the pressure is uniformly applied. Therefore, even if the strength of the sintered body is small, if the thickness is large, it is difficult to crack finely and it may not be possible to apply a uniform pressure. Therefore, the thickness of the sintered bodies 6 and 7 should be 0.05 mm to 5 mm. Is desirable. Such an oxide-based ceramic sintered body can be obtained by molding the metal oxide powder into a predetermined shape based on a general method and firing the metal oxide powder to a relative density of 50% or more. Can be easily controlled by, for example, controlling the composition of the sintered body and the firing temperature.

According to this hot forging treatment, for example, Ag, Au, etc. are interposed between the oxide superconductor 1 and the oxide ceramic powders 4, 5 or the sintered bodies 6, 7 in FIGS. , Cu, Pt, or the like, and a metal plate having a thickness of 0.05 mm or more made of a ductile metal can be used.

[0019]

According to the constitution of the present invention, the oxide superconducting sintered body obtained by firing is laminated with an oxide ceramic powder or an oxide ceramic sintered body having a transverse rupture strength of 5 kg / mm ² or less. Hot forging is most important. When such a treatment is performed, the oxide-based ceramic powder flows at the time of pressurization, thereby eliminating pressure unevenness at the time of pressurization. The homogeneity is dramatically improved. Note that the ceramic sintered body has a similar function and effect by being finely broken when pressed. Thereby, the homogeneity of the superconducting characteristics of the integrated structure is remarkably improved.

When a ductile metal is interposed, the ductile metal itself is rolled in a direction perpendicular to the direction A by the pressure from the direction A in FIG. 1, and the sintered body 1 is also rolled in the same direction at the same time. The scaly crystal grains in the sintered body are oriented and compressed, and the density of the sintered body can be increased. Thus, the critical current density of the oxide superconductor can be further increased because the adhesion between the flake crystals is remarkably improved.

In addition, as a material to be laminated when performing the hot forging treatment, a metal material, a non-oxidizing ceramic such as a carbide or a nitride, and the like can be considered in addition to the oxide ceramic. It is difficult to take out the oxide superconductor due to close contact with the punch, and there is a problem that it is expensive. For other metals, the metal element diffuses into the oxide superconductor during processing and deteriorates the superconductivity. There is also the problem of making it work. Further, in the case of non-oxide ceramics, there is a problem that the oxide superconductor is exposed to a reducing atmosphere during firing and is decomposed.

[0022]

【Example】

Example 1 Bi ₂ O ₃ , PbO, SrCO ₃ , Ca
CO _3, molar ratio of the metal powders of CuO is Bi: P
b: Sr: Ca: Cu = 1.93: 0.36: 2: 3.
After weighing to 17: 4.25, 750-810 ° C
For 20 hours, and pulverized to obtain a calcined powder having an average particle size of 5 μm and containing a large amount of a low Tc phase. This calcined powder is φ12m
m and a molding pressure of 1 ton / cm ² to obtain a disk-shaped molded body having a thickness of about 1 mm.

Next, the above compact was fired in the atmosphere 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, a previously purified Al ₂ O ₃ having a purity of 99% or more and a particle size of 3 μm or less, and SiO ₂ , CaO and MgO with respect to Al ₂ O ₃ as other components, having a composition ratio of 82: The mixture was prepared so as to be 12: 2: 4. 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 500 to 1300 ° C. for 2 hours to obtain an Al ₂ O ₃ sintered body having a theoretical density ratio of 59%.

In addition, ZrO ₂ powder having a purity of 99% or more
After adding 3 mol% of ₂ O ₃ and molding, it was fired in an oxidizing atmosphere at 800 ° C. to obtain a sintered body having a theoretical density ratio of 55%.

Then, using these sintered bodies, a thickness of 0.
A 5 mm plate was made. When the strength of this plate was measured three-point bending strength of the span 10 mm, Al ₂
The O ₃ -based sintered body exhibited a strength of 0.1 kg / mm ² , and the ZrO ₂ -based sintered body exhibited a strength of 0.5 kg / mm ² .

Next, according to FIG. 2, the oxide superconductor sintered body was formed on the upper and lower surfaces of the sintered body with a thickness of 0.5 mm made of the Al ₂ O ₃ -based sintered body or ZrO ₂ -based sintered body obtained above. Is placed, and 5t is applied to the sintered body through this plate.
Hot forging treatment was performed at a pressure of 845 ° C. at a pressure of on / cm ² .

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.

Further, in order to examine the homogeneity of the superconducting characteristics of the sample, a magnetic field was applied to the sample in liquid nitrogen from one surface in liquid nitrogen, and the magnetic shield characteristics on the opposite surface were measured. The results are shown in Table 1.

In another embodiment, the Al ₂ O ₃ sintered body has a strength of 1 kg / mm ² and 5 kg / mm ^2.
The above sintered bodies were prepared, and the oxide superconducting structures were prepared in combinations as shown in Table 1, and similar characteristics were evaluated.

Example 2 In Example 1, an Al ₂ O ₃ powder having a particle size of 0.1 mm and a ZrO ₂ powder having a particle size of 0.5 mm were replaced with an oxide ceramic sintered body according to FIG. The treatment was performed by interposing between a superconducting sintered body and a hot forging press punch. The properties of the obtained oxide superconducting structure were evaluated in the same manner as in Example 1. The results are shown in Tables 8 to 12.

Comparative Example In Example 1, the oxide superconductor sintered body was directly hot forged without any intervening oxide ceramic sintered body or powder (sample No. 7). 1, the transverse strength 2 during hot forging treatment
A structure was prepared in exactly the same manner as in Example 1 except that an Al ₂ O ₃ sintered body of 0 kg / mm ² was used (sample N
o.6), properties were evaluated in the same manner, and the results are shown in Table 1.

Example 3 In Example 1, the hot forging treatment was performed by further disposing a silver plate having a thickness of 0.1 mm between the oxide superconductor and the Al ₂ O ₃ sintered body. This was performed on the sintered body at a temperature of 820 ° C. at a pressure of 1 ton / cm ² .

The characteristics of the obtained structure (sample Nos. 2, 9) were evaluated in the same manner as in Example 1. Table 1 shows the results
It was shown to.

[0037]

[Table 1]

As is clear from Table 1, the samples of the present invention obtained by treating an oxide superconductor with a low-strength oxide-based ceramic sintered body or oxide ceramic powder were all used. It can be seen that a higher magnetic shield characteristic is obtained and the superconductivity is uniform in the sample as compared with Sample No. 7. Further, Ag is used for hot forging treatment.
Samples Nos. 2 and 9 in which a ductile metal was interposed between the sintered body and the oxide ceramic were more excellent in any of the degree of orientation, Jc value, and Tc value as compared with the case where no ductile metal was interposed. An oxide superconductor was obtained.

[0039]

As described in detail above, according to the method of the present invention, the oxide ceramic powder or the low-strength oxidized Pressure and heat treatment through the ceramic sintered body to increase the degree of orientation of crystal grains of the sintered body at the same time as the uniform pressure treatment and achieve high density, so that it has a high critical temperature and An oxide superconductor having an extremely high critical current density can be stably obtained, and a structure having a homogeneous structure and superconducting properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a hot forging process in one embodiment of a method for manufacturing an oxide superconducting structure according to the present invention.

FIG. 2 is a view for explaining a hot forging process in another embodiment of the method for manufacturing an oxide superconducting structure according to the present invention.

[Explanation of symbols]

 1 ... Oxide superconducting sintered body 2,3 ... Press punch 4,5 ... Oxide ceramic powder 6,7 ... Oxide ceramic sintered body

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 1/00 C04B 35/64 H01B 12/00

Claims (1)

(57) [Claims] 1. A step of molding a mixture comprising an oxide of an element constituting an oxide superconductor or a compound capable of forming an oxide, or calcining the mixture and molding the mixture, and forming the mixture in an oxidizing atmosphere. Baking in a sinter, and the sintered body is made of an oxide ceramic powder or a flexural strength of 5 kg / mm.
50 kg / via an oxide ceramic sintered body of ² or less
performing a heat treatment under a pressure of ² cm ² or more.