JPH0797277A - Method for joining oxide superconductor - Google Patents

Abstract

PURPOSE:To join two highly oriented oxide superconductors without deteriorating the characteristics of the superconductive at the joined part by bringing the end surfaces of the two oxide superconductors having the same orientation directions of crystals into contact with each other, and subsequently pressing and heating the contacting superconductors under a prescribed pressure at a prescribed temperature. CONSTITUTION:Two oxide superconductors 1, 2 (e.g. Bi-Sr-Ca-Cu-O superconductor) containing at least Cu and having an orientation degree of >=2.5 in the C-axial direction are prepared. The end surfaces 3, 4 of the two oxide superconductors 1, 2 having the same crystal orientation directions are brought into contact with each other, and the contacted parts are pressed with press punches 5, 6 under a pressure of >=0.05ton/cm<2> and simultaneously heated at 500-900 deg.C to join the oxide superconductors 1, 2 to each other. Since the mutual diffusion and sintering of the end surfaces and simultaneously the orientation of the joined part due to the pressing are thereby advanced, the superconductors can be joined to each other without damaging the mutual orientation characteristics, thus the structural article having the large area and the homogeneous superconductive characteristics is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining two oxide superconductors while suppressing deterioration of characteristics.

[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 conventionally used as superconductors, and their practical application is expected. Has been done. At present, as oxide superconductors, mainly Y-Ba-Cu-O-based materials and Bi
-Sr-Ca-Cu-O system and Tl-Ba-Ca-C
The three main types are uO. 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 into practical use. On the other hand, it is desired to develop a joining technique as one method for increasing the utility value of oxide superconductors. In particular, oxide superconductors are expected to be applied to magnetic shields and the like.

Therefore, conventionally, as a method for joining oxide superconductors, a method has been proposed in which oxide superconductors are laminated and bonded together, and then heat treatment is performed.

[0004]

However, according to the conventional joining method, the superconducting property at the laminated portion is extremely deteriorated, and even if the heat treatment is performed after the laminating, the superconducting property at the end portion of the laminated portion may be deteriorated. The problem of deterioration compared to the part is unavoidable. In particular, there are problems such as a significant decrease in critical current density at the joint and a discontinuous superconducting property, and it has been very difficult to join without deterioration of the superconducting property.

Recently, it has been proposed to produce a superconducting sintered body having a high critical current density and excellent characteristics, but there is a limit to the size of the sintered body that can be produced by a general method. When manufacturing a large-sized magnetic shield body, although it is unavoidable to join individual superconductors, there is a problem that good superconducting characteristics cannot be exhibited because the characteristics deteriorate due to the joining.

[0006]

With respect to the above problems, the inventors of the present invention have repeatedly studied a method for improving superconducting characteristics particularly at the joint, and as a result, the present invention contains at least Cu and has a C-axis direction. End faces of the two oxide superconductors having the same crystal orientation direction with an orientation degree of 0.5 or more are brought into contact with each other, and a pressure of 0.05 ton / cm ² or more is applied to the contact portion. Meanwhile, the invention is characterized by heating and joining at a temperature of 500 to 900 ° C., and in another embodiment, in heating and pressurizing treatment, the corresponding contact portion is sandwiched by a ductile metal for treatment, or the end surface is treated. The two are contacted with each other through the powder of the oxide superconductor, and the two superconductors are fixed in the frame during the heat and pressure treatment.

Further, according to the present invention, the abutting portion is provided with 820-9.
It has been found that two or more sintered bodies are joined by heating to a temperature of 00 ° C. and partial melting, and a joined structure having homogeneous superconducting properties can be obtained from this.

The present invention will be described in detail below. According to the method for joining oxide superconductors of the present invention, first, as the oxide superconductors to be joined, two oxide superconductors containing at least Cu and having a degree of orientation in the C-axis direction of 0.5 or more. To prepare. Examples of such oxide superconductors include Bi
As the -Pb-Sr-Ca-Cu-O-based oxide superconductor, Japanese Patent Application No. 3-154530 and Japanese Patent Application No. 4-10710.
By the method described in No. 2 etc., it is possible to obtain a highly-oriented oxide superconductor having a high density and a C-axis orientation degree of 0.5 or more. As a desirable composition of the oxide superconductor, when Sr is 2 in molar ratio, Bi is 1.8 to 2.2, Ca is 2.0 to 3.5, Cu is 3.0 to 4.5, Pb is 0.1
A superconducting complex oxide containing a molar ratio of 0.5 to 0.5, and optionally K, Li and Na in an amount of 0.05 to 0.
It is contained in a ratio of 6, 0.5 or more after orientation, and a density of 5.5 g /
cm ³ or more is desirable.

Next, as shown in FIG. 1, oxide superconductors 1 and 2 having a degree of orientation in the C-axis direction of 0.5 or more are brought into contact with end surfaces 3 and 4 having the same orientation direction. , 500-90
Two or more sintered bodies can be joined by uniaxially pressing at a high temperature of 0 ° C. and a pressure of 0.05 ton / cm ² or more in a direction parallel to the contact surface, for example, with the press punches 5 and 6. Further, as a heating and pressing method, as shown in FIG. 2, a ductility of silver or the like having a thickness of 0.02 mm or more is applied between the press punch and the joint portion in the heating and pressurizing process, as shown in FIG. Pressurization and heat treatment may be performed under the above conditions through the metals 7 and 8 that are included, or as shown in FIG. 3, pressure and heat treatment may be performed by interposing oxide superconducting powder 9 between the end faces of the oxide superconductor. it can.

Further, as another aspect of the present invention, it is possible to perform the joining by heating at least the joining portion to a temperature of 820 to 900 ° C. to partially melt the joining portion. Furthermore, in such a configuration,
An oxide superconducting powder may be interposed between the end faces when the end faces are brought into contact with each other.

Further, it is preferable that the two heating and pressing processes of FIGS. 1, 2 and 3 are carried out by fixing two superconductors in the frame body 10 as shown in FIG. This is because the superconductor may be plastically deformed by the treatment and the characteristics may be deteriorated accordingly. Therefore, by fixing the superconductor in the frame and treating it as shown in FIG. 4, the superconducting characteristics in the joined body are made more uniform. be able to. The fixing in the frame can be easily performed by using a so-called hot press. Further, the end surfaces of the two superconductors that are brought into contact with each other may be inclined surfaces as shown in FIG.

In the present invention, the heating temperature is 500 to 90.
The reason for limiting the temperature to 0 ° C. is that if the temperature is lower than 500 ° C., element diffusion or sintering at the joint does not proceed, and if it exceeds 900 ° C.
This is because the oxide superconductor is decomposed and deteriorated and the superconducting characteristics are deteriorated. In the case of partial melting, the lower limit of the heating temperature depends on the material of the oxide superconductor.
It is about 0 ° C., and if it is lower than this, melting does not occur. However, when a metal such as Ag which does not react with the oxide superconductor is allowed to coexist in the joint, the melting temperature is lowered, so that it is possible to join at a temperature that does not affect the oxide superconducting properties. Become.

If partial melting is not involved, it is necessary to apply pressure, but the pressure is 0.05 ton.
If the pressure is lower than / cm ² , the reaction will not proceed at the joint and the joining will be insufficient. Therefore, the pressure will be 0.05 ton / c.
It is set to m ² or more. The upper limit of the pressure is not particularly limited, but if the pressure is too high, the apparatus for pressurizing and heating becomes large, so 10 ton / cm ² or less is appropriate.

[0014]

According to the present invention, at least Cu is contained and C
The two oxide superconductors having the same degree of orientation in the axial direction and having the same crystal orientation direction of the oxide superconductors are brought into contact with each other, and pressure heating treatment is performed under a predetermined condition. Since the sintering progresses along with the mutual diffusion and the orientation in the joint portion progresses due to the pressure at the same time, the joining can be performed without disturbing the orientation characteristics of each other and the deterioration of the superconducting characteristics at the end faces.

Further, according to the present invention, as shown in FIG. 2, the metal 7 and 8 are pressure-heated through a ductile metal, so that the metals 7 and 8 are pressure-heated by the ductility effect of the metal itself. At this time, the scale-like crystal particles in the oxide superconductor are oriented and compressed, and the density of the oxide superconductor can be increased. Further, since the two sintered bodies that are joined by diffusion of the ductile metal into the superconductor are locally melted to improve the diffusion rate, the joining is strengthened and the characteristics of the joined portion are further improved.

Further, the ambient temperature is the offset temperature (Tc
e) or more, a current larger than the critical current (Ic) flows, or the atmospheric magnetic field is the critical magnetic field (Hc).
When it becomes larger, the superconducting property is destroyed (quenching). However, since the oxide superconductor and the metal layer are in contact with each other, the contacting metal layer replaces this and plays a function of current propagation. The current propagation of this metal layer is inferior to that of the oxide superconductor, but this can be sufficiently compensated for during the temporary quench. Also, the ductile metal itself
Since the heat conductivity is good, the heat dissipation of the metal suppresses the heat generation of the oxide superconductor itself due to the increase of the current, thereby preventing the destruction of the superconducting characteristics.

Further, as shown in FIG. 3, when oxide superconductor powder is interposed in the joint portion, when there is a gap between the oxide superconductors 1, the powder fills this gap, so that the bonding is strengthened. The characteristics of the joint can be further improved.

Further, according to the present invention, during the heat and pressure treatment,
By fixing the two superconductors inside the frame, the superconductor is prevented from being extremely deformed, and moreover, not only in the pressing direction, but also from the periphery to the center of the pressing surface, the adhesion at the joint is further improved. Can be increased.

Further, by performing the joining while partially melting the joint, it becomes possible to improve the sinterability at the joint, and when the metal coexists during the partial melting, the melting temperature lowers. In addition, the bonding can be performed at a temperature that does not affect the superconducting property, and at the same time, the orientation at the bonded portion can be increased.

As described above, according to the structure of the present invention, since it is possible to perform the bonding without deteriorating the superconducting property, a structure having a large area and having a uniform superconducting property in the sample is obtained. As a result, it is possible to easily manufacture a large magnetic shield body or the like.

[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 each metal in a molar ratio of Bi: P.
b: Sr: Ca: Cu = 1.93: 0.36: 2: 3.
Weighed to 17: 4.25, then 750-810 ° C
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 calcination 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. When the molded body was fired in the atmosphere 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.

Next, this sintered body was pulverized to have an average particle size of 5 μm, an organic binder was added to this powder, and the mixture was mixed in toluene. Granules with a diameter of 100 μm were obtained. The granules were fed between a pair of rolls to obtain a sheet having a thickness of 400 μm.
From this sheet, a rectangular cut-out molded body having a side of 80 mm was formed.

This molded body was heated in the atmosphere at 200 to 400 ° C.
After degreasing for 10 hours, a temperature of 840 to 860 ° C 10 to 1
It was fired for 00 hours to obtain a flat superconducting sintered body having a thickness of 450 μm.

Next, five oxide superconductors are stacked, a 0.5 mm-thick plate of an alumina-based sintered body is arranged on the upper and lower surfaces of the sintered body, and 5 t are attached to the sintered body through this plate.
Hot forging treatment was performed at a pressure of on / cm ² and a temperature of 845 ° C.

Further, the sintered body obtained as described above is
Prepared, and the planes in which the orientation direction of the crystal of the end face is perpendicular to the pressing direction in the hot fusing treatment are contacted with each other.
At a pressure of 1 ton / cm ² in parallel with the contact surface at
That is, that is, joining was performed by high temperature uniaxial pressing in the same direction as the pressing direction during the hot fogging treatment.

The specific gravity of the finally obtained sintered body was examined by the Archimedes method and X-ray diffraction measurement was carried out. 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.

[0027]

[Equation 1]

Further, based on the resistance method for the above-mentioned joined body, the current value when the current was gradually increased in the sample 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. At the same time, the critical temperature Tc was also measured. The critical current densities were measured in the case where the junction was not included and in the case where the electrodes were formed with the junction in-between. The results are shown in Table 1. Further, in order to measure the magnetic shield characteristics at the joint portion of the obtained sintered body, evaluation was performed by the method as shown in FIG. That is, the joint part 1
The magnetic field is applied by the magnet 14 from one surface of the bonded body 13 having 2 and the magnetic sensor 11 is arranged on the opposite side to gradually increase the applied magnetic field and increase the strength of the applied magnetic field when the magnetism is detected by the magnetic sensor 11. Was measured. The results are shown in Table 1.
It was shown to.

Example 2 The end faces of the two sintered bodies produced in Example 1 were brought into contact with each other as shown in FIG. 2, and a silver plate having a thickness of 0.1 mm was placed between the oxide superconductor and the press punch. Then, the sintered body was pressure-heated through the plate at a pressure of 1 ton / cm ² and a temperature of 845 ° C. The characteristics of the obtained structure were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 3 The superconducting calcined powder having an average particle size of 5 μm in Example 1 was interposed and abutted, and pressure heating treatment was performed at a pressure of 1 ton / cm ² and a temperature of 845 ° C. The characteristics of the obtained structure were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 4 The end faces of the two sintered bodies produced in Example 1 were brought into contact with each other so that the crystal orientation directions of the end faces were the same, and heated at 850 ° C. with a laser to bond them. At this time, it was confirmed that the joint was partially melted. The characteristics of the obtained structure were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 5 The end faces of the two sintered bodies produced in Example 1 were made so that the crystal orientation directions of the end faces were the same and the average grain size was 5
A superconducting powder having a size of μm was contacted with each other and heated to 850 ° C. with a laser for bonding. At this time, it was confirmed that the joint was partially melted. The characteristics of the obtained structure were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 6 In Example 5, when heating and joining with a laser,
A 0.1 mm Ag plate was placed at the junction of the oxide superconductor, and a laser was welded through this plate at a temperature of 845 ° C. The characteristics of the obtained structure were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 7 In Example 1, the end faces of the two sintered bodies were obliquely cut as shown in FIG. 5 and brought into contact with each other, and the pressure was set to 8 at a pressure of 1 ton / cm ^2.
Pressure heat treatment was performed at a temperature of 45 ° C. The characteristics of the obtained structure were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 8 The end faces of the two sintered bodies produced in Example 1 were brought into contact with each other so that the crystal orientation directions of the end faces were the same, and a pressure of 1 ton / cm ² was applied as shown in FIG. At a temperature of 845 ° C., a so-called hot press treatment was performed in which the sample was surrounded by a frame. The characteristics of the obtained structure were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Further, the distribution of the magnetic shielding ability was measured together with that of Example 1, and the results are shown in FIGS.

Comparative Example 1 A laminate was prepared by laminating the ends of the two sintered bodies prepared in Example 1 with an organic adhesive, and the characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 In Comparative Example 1, after lamination, heat treatment was performed in an oxidizing atmosphere at 840 ° C. to obtain a laminated body, and the characteristics of the laminated body were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 The end faces of the two sintered bodies obtained in Example 1 were brought into contact with each other at different faces in which the crystal orientation directions of the end faces were perpendicular to each other, and at 845 ° C. in the direction parallel to the end faces. 1 ton / cm
^A high temperature uniaxial pressure was applied at a pressure of ² for joining. The characteristics of the obtained structure were evaluated in the same manner as in Example 1.
The results are shown in Table 1.

Comparative Example 4 In Example 1, two sintered bodies in which scaly crystals were randomly arranged were used, and their end faces were brought into contact with each other to obtain 845.
Welded by heating with a laser at ℃. The characteristics of the obtained structure were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

The samples of Examples 1 and 8 were evaluated by the method shown in FIG. 6 in order to measure the magnetic shield distribution of the obtained sintered body. That is, a uniform magnetic field of 50 gauss was applied to the bonded body 15 by the magnet 16, the magnetic sensor 17 was moved on the surface of the bonded body, and the strength of the magnetic field at each point was measured. The results are shown in Table 1.

[0042]

[Table 1]

As is clear from Table 1, in Examples 1 to 6 in which the oxide superconductor was subjected to pressure and heat treatment by bringing the end faces having the same orientation into contact with each other, the measurement was carried out at the critical current density while sandwiching the joint. However, it is understood that the deterioration from the characteristics of the oxide superconductor alone before joining and the characteristics is smaller than that of the other comparative examples. Moreover, it also showed excellent magnetic shield characteristics. Further, as is clear from the results shown in FIGS. 7 and 8, it is understood that the magnetic shield characteristics are more uniform when they are fixed in the frame and heated and pressed.

[0044]

As described above in detail, according to the present invention,
By bonding end faces having the same orientation direction to the oxide superconductor having a high C-axis orientation, it is possible to prevent the deterioration of the superconducting property at the joint portion and to provide a large area having a high critical temperature and a high critical current density. A structure having uniform superconducting properties can be obtained. As a result, it is possible to manufacture any large product such as a magnetic shield body.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining another embodiment of the present invention.

FIG. 3 is a diagram for explaining still another embodiment of the present invention.

FIG. 4 is a diagram for explaining still another embodiment of the present invention.

FIG. 5 is a diagram showing another example of abutting of the end faces in the joining method of the present invention.

FIG. 6 is a diagram for explaining a method of measuring magnetic shield characteristics.

FIG. 7 is a diagram showing a magnetic shield distribution of a bonded body obtained in an example.

8 is a diagram showing a magnetic shield distribution of the bonded body obtained in Example 1. FIG.

[Explanation of symbols]

 1, 2 Oxide superconductor 3, 4 End face 5, 6 Press punch 7, 8 Ductile metal 9 Oxide superconducting powder 10 Frame body

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C30B 29/22 501 M 8216-4G H01B 13/00 565 D 7244-5G H01L 39/24 ZAA 9276- 4M

Claims (6)

[Claims] 1. An end face having the same crystal orientation direction of two oxide superconductors containing at least Cu and having a degree of orientation in the C-axis direction of 0.5 or more is brought into contact with each other and the corresponding contact portion is contacted. While applying a pressure of 0.05 ton / cm ² or more,
A method for joining oxide superconductors, wherein the oxide superconductors are joined together by heating to a temperature of 0 to 900 ° C. 2. An end face having the same crystal orientation direction of two oxide superconductors containing at least Cu and having a degree of orientation in the C-axis direction of 0.5 or more is brought into contact with each other, and the corresponding contact portion is contacted. Oxide superconductor, wherein the sintered bodies are joined together by heating to a temperature of 500 to 900 ° C. while applying a pressure of 0.05 ton / cm ² or more through a metal having ductility. How to join. 3. Two oxide superconductors containing at least Cu and having an orientation degree in the C-axis direction of 0.5 or more and having the same crystal orientation direction are provided with an oxide superconductor powder. Abutted against each other and 0.05 ton / cm ² against the contact
A method for joining oxide superconductors, wherein the sintered bodies are joined together by heating to a temperature of 500 to 900 ° C. while applying the above pressure. 4. The method for joining oxide superconductors according to claim 1, 2, or 3, wherein the additional pressurizing treatment is performed by fixing the two oxide superconductors in a frame. 5. An end surface having the same crystal orientation direction of two oxide superconductors containing at least Cu and having a degree of orientation in the C-axis direction of 0.5 or more is brought into contact with each other, and the corresponding contact portion is provided with 820.
A method for joining oxide superconductors, characterized in that at least the abutting portion is partially melted and joined by heating to a temperature of ℃ to 900 ℃. 6. Two oxide superconductors containing at least Cu and having a degree of orientation in the C-axis direction of 0.5 or more are brought into contact with each other with their end faces having the same orientation direction of crystals, and the corresponding contact portions are made of metal. The method for joining oxide superconductors, characterized in that at least the abutting portion is partially melted and joined by heating to a temperature of 820 ° C. to 900 ° C. in the coexistence of.