JPH05270828A - Rare earth superconductor - Google Patents

Abstract

PURPOSE:To provide a rare earth superconducting bulk body having magnetic repulsive force which can be applied for magnetic bearings. CONSTITUTION:This rare earth superconducting bulk body is a composite body consisting of RE-Ba-Cu-0 superconductor A (wherein RE is one or more elements selected from Y, Sm, Eu, Gd, Dy, Ho, Er and Yb) and silver layers B. The silver layers are arranged at certain intervals so as not to prevent the Meissner current from flowing in the bulk body induced by an external magnetic field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth-based superconductor, more specifically, RE-Ba having a strong magnetic repulsion force.
-Cu-O superconductor (however, RE is Y, Sm, Eu,
It represents one or more elements selected from the group of elements consisting of Gd, Dy, Ho, Er and Yb. The same applies hereinafter. ) And a silver layer are combined to form a bulk body structure rare earth-based superconductor.

[0002]

2. Description of the Related Art A rare earth-based superconductor formed by a so-called melting method has a strong pinning effect, and thus researches for its practical use have been actively conducted. The rare earth-based superconducting bulk body obtained by the melting method produces a magnetic repulsive force when combined with a permanent magnet, and attempts have been made to develop a magnetic bearing utilizing the magnetic repulsive force.

A typical MTG (Melt Textured) of the melting method
Growth) method, for example, in a rare-earth superconductor, is generally a superconducting phase of 123 phases (YBa ₂ Cu ₃ O _y ,
Y represents a rare earth element containing the Y element. ) Is gradually cooled from the decomposition and melting temperature of (1) to cause a peritectic reaction between the liquid phase and the 211 phase of the non-superconducting phase (Y ₂ BaCuO ₅ , where Y represents a rare earth element containing the Y element). The crystal is grown, and an unreacted 211 phase exists inside the superconducting phase crystal grown by this peritectic reaction and acts as a pinning center. Therefore, the obtained rare-earth superconductor shows high critical current density (Jc) even in the magnetic field. However, the rare earth-based superconductor obtained by the MTG method is 21
The particle size of one phase is large, its distribution is non-uniform, and
There are inconveniences such as the presence of cracks along the crystal growth direction. Therefore, the MPMG method which has improved the drawbacks of the MTG method has been proposed. In the MPMG method, it is said that the 211 phase is made finer by the melting / quenching process and the cracks are significantly reduced by adding the silver or silver oxide powder.

[0004]

An important problem in applying the rare earth-based superconductor to the above magnetic bearing is to generate a strong magnetic repulsion force. One of the factors that obstruct the magnetic repulsion is cracks present in the rare earth-based superconducting bulk body. If the rare earth-based superconducting bulk body has cracks, the superconducting current cannot flow uniformly over the entire bulk body. Therefore, the pinning force is weakened and sufficient magnetic repulsion cannot be obtained.

Even in the rare earth type superconducting bulk body formed by the MPMG method intended to improve the above MTG method and reduce cracks, the magnetic repulsive force is still insufficient. The inventors have aimed to realize a magnetic bearing by applying a rare earth-based superconductor, and in the rare earth-based superconducting bulk body obtained by a conventional melting method, suppress the development of cracks as much as possible and have excellent magnetic repulsion. The present invention has been completed as a result of earnest studies on obtaining a rare earth-based superconducting bulk material having strength.

[0006]

According to the present invention, RE-B
a-Cu-O superconductor (however, RE is Y, Sm, E
It represents one or more elements selected from the group of elements consisting of u, Gd, Dy, Ho, Er and Yb. ) And a silver layer are combined into a superconducting bulk body, wherein the silver layer is
There is provided a rare earth-based superconductor, characterized in that the bulk body is arranged at intervals so as not to impede the flow of Meissner current induced by an external magnetic field.

[0007]

The present invention is constructed as described above, and has RE-Ba-C
u-O superconductor, especially RE-B formed by melting method
The a-Cu-O-based superconducting bulk body and the silver layers are usually alternately arranged to form a composite, for example, a plurality of RE-Ba-Cu.
A structure in which an -O-based superconducting layer and a silver layer are laminated in multiple layers, and the silver layer partitions the superconductor at a predetermined interval, the internal stress is relaxed by the compounded silver layer and cracks are less likely to occur, and at the same time, cracks are generated. Even if it occurs, it is possible to prevent the generated crack from propagating in the vertical direction or the radial direction. Therefore, the cracks in the bulk body are drastically reduced, and the magnetic repulsive force due to the pinning effect is increased. Each RE-Ba-
The Cu-O-based superconducting layer has a structure in which it is separated and partitioned by a silver layer, but since the Meissner current induced in the bulk body by an external magnetic field has a multilayer structure in which it can flow without interruption in the middle, Moreover, since a through hole can be provided in the silver layer if necessary, the Meissner current is not hindered. Therefore, the RE-Ba-Cu-O-based superconducting bulk body can function as an integral superconductor.

The present invention will be described in more detail below. Starting
Ming's RE-Ba-Cu-O superconductor has RE of Y, Sm,
Element group consisting of Eu, Gd, Dy, Ho, Er and Yb
Multilayer PET containing one or more rare earth elements selected from
It is an oxide superconductor having a rovskite structure. example
For example, YBa ₂ Cu₃ O₇ -Earth oxides with different compositions
It is a superconductor. In particular, the RE-Ba-Cu-O of the present invention
System superconductors are so-called conventionally known or proposed so-called
Raw material powder is decomposed and melted by the melting method and its improved melting method.
In a series of processes such as melting, slow cooling, heat treatment, oxygen annealing
It can be obtained by processing.

As raw material powders for producing the RE-Ba-Cu-O-based superconductor in the present invention by the above-mentioned melting method or the like, RE, Ba and Cu components are RE-Ba-Cu-O-based superconductors. It is possible to use a mixed powder that is blended to form the body. For example, RE, that is, Y, Sm, Eu, G
1 selected from the group consisting of d, Dy, Ho, Er and Yb
Alternatively, a mixed powder of oxides such as an oxide of two or more elements, a carbonate or oxide of Ba, and an oxide of Cu, a calcined powder of the mixed powder of the oxide, or a frit of the mixed powder of the oxide. After firing the powder, etc., the superconducting phase REBa ₂ Cu ₃ O _y
And a non-superconducting phase RE ₂ BaCuO ₅ can be compounded and used. In addition, the above RE, Ba and C
The silver powder and / or silver oxide proposed by the MPMG method may be appropriately added to and mixed with the compounded powder of each component of u. As the raw material powder, it is usually preferable to use a powder having a particle size of 2 to 20 μm.

The silver layer of the present invention is not particularly limited, but a silver foil or a silver plate having a thickness of 100 μm to 1 mm can be preferably used. The composite of the RE-Ba-Cu-O-based superconductor and the silver layer in the present invention is a Meissner current induced by an external magnetic field when an external magnetic field is applied to the superconducting bulk body to generate a magnetic repulsive force. There is no particular limitation as long as it has an arrangement structure that does not hinder the flow of. Preferably, the superconducting layers and the silver layers are alternately arranged at a predetermined interval. For example, as shown in the explanatory view shown in FIG. 1, a multilayered laminated structure of the superconducting layer A and the silver layer B in the superconducting bulk body 1 in the axial direction, or as shown in the explanatory diagram shown in FIG. Superconducting layer A in body 1
The RE-Ba-Cu-O-based superconducting layer and the silver layer can be arranged in a concentric multiple structure of the silver layer B and the silver layer B, that is, a laminated structure in the radial direction. In this case, the distance between each RE-Ba-Cu-O-based superconducting layer and the silver layer is not particularly limited, but within a range in which a desired pinning effect is not reduced due to the development of cracks along the superconducting crystal phase. Then, the compounding method,
It is preferable that the bulk bodies are arranged at predetermined intervals that are appropriately selected according to the usage conditions of the bulk body and the presence or absence and the form of through holes described below. Usually, they are alternately arranged at intervals of about 1 to 10 mm. Further, in this case, the arrangement at substantially the same intervals, the arrangement in which the interval width is increased or decreased in a certain direction, the arrangement at completely arbitrary intervals, and the like can be selected according to the conditions as described above.

The silver layer in the present invention may be provided with through holes. When providing through holes, the size of each through hole,
The installation interval and the like can be appropriately selected depending on the compounding method, the usage conditions of the bulk body, and the like. Generally, the circular through-holes have a total area ratio of the through-holes in each silver layer of about 30.
It is preferable that the silver layer be uniformly balanced and arranged so as to be not more than%. The through-hole can be used by generally forming a hole in a silver foil or a silver plate forming a silver layer.

In the rare earth-based superconductor of the present invention, a superconductor layer formed by using the raw material mixed powder and a silver foil in which through holes are preliminarily formed are sequentially laminated or arranged and press-formed. After that, it can be manufactured as a bulk body through a series of steps such as the above-described decomposition and melting, and gradual cooling.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples. Example 1 Y ₂ O ₃ , BaCO ₃ , and CuO powder were mixed with Y, Ba and C.
It was weighed so that the atomic ratio of u was 1.8: 2.4: 3.4. Further, Ag was mixed so as to be 20% by weight by external distribution. The mixing was performed for 5 hours using a ball mill and ethanol as a solvent. The powder obtained is 950 ° C. in an oxygen stream.
After being calcined for 24 hours, the raw material mixed powder was pulverized by a dry pulverizer. 25 g of the obtained raw material mixed powder was molded into a disc shape with a pressure of 0.1 t / cm ² by a die press having a diameter of 50 mmφ. Then, a silver plate having a thickness of 300 μm and having a through hole C formed thereon in the form of the explanatory view shown in FIG.
On top of that, 20 g of the raw material mixed powder is similarly added in an amount of 0.1 t /
Press molding was performed at a pressure of cm ² . The above operation was repeated to obtain a cylindrical laminated superconducting molded body in which the Y—Ba—Cu—O based superconducting layer shown in FIG. 1 and the silver layer having the through holes were laminated.

The molded body thus obtained was placed on a dense alumina setter in an electric furnace in a nitrogen atmosphere, and after 11 hours in 6 hours.
Raise to 50 ° C., hold at that temperature for 30 minutes, then 1
The temperature is lowered to 000 ° C in 1 hour, and then 1000 ° C to 90 ° C.
The mixture was gradually cooled to 0 ° C at a cooling rate of 1 ° C / hour. After that, the atmosphere in the furnace was cooled to 450 ° C with pure oxygen, and then the temperature was changed to 450 ° C.
After heat treatment for 8 hours, it was left in a furnace to 100 ° C. or lower to obtain a cylindrical laminated sintered body in which a Y—Ba—Cu—O-based superconducting layer and a silver layer having a through hole were laminated and composited. With respect to the obtained sintered body, the magnetic repulsive force (g) with the permanent magnet was measured using the apparatus shown in FIG. In FIG. 5, the sintered body 1 was dipped in liquid nitrogen 2 in a container, and the rare earth permanent magnet 3
After attaching (surface magnetic field 4000 gauss) to the rod 4,
The magnetic repulsion force was measured when the crosshead 5 was lowered at a speed of 10 mm / min and the distance between the sintered body 1 and the rare earth permanent magnet 3 was 0.1 mm. As a result, the obtained cylindrical laminated sintered body exhibited a magnetic repulsion force of 1500 g. The cylindrical sintered body whose magnetic repulsion force was measured was vertically cut vertically so as to pass through the center of the cylindrical body. The cut surface was visually observed after polishing, and the length of a visible crack was measured. As a result, the total length of the measured cracks was 45 mm.

Comparative Example 1 85 g of the raw material mixed powder obtained in the same manner as in Example 1 was used to press-mold with a circular die press having a diameter of 30 mmφ without sandwiching a silver plate to obtain a cylindrical molded body. The obtained molded body was treated in the same manner as in Example 1 to obtain a sintered body.
With respect to the obtained sintered body, the magnetic repulsion force and the crack length on the cut surface were visually observed in the same manner as in Example 1.
As a result, the magnetic repulsion force was 600 g, and the total crack length was 160 mm.

Example 2 A raw material mixed powder was obtained in the same manner as in Example 1. On the other hand, using a silver plate having a thickness of 300 μm, the diameters of the through holes C formed in the form of the explanatory view shown in FIG. 4 are 40 mm, 30 mm, 1
5 mm cylinders were produced respectively. Inner diameter 50 mmφ,
In a rubber mold for rubber press having a height of 40 mm, the produced silver cylinders were arranged in a concentric multiple structure as shown in FIG. 2, 100 g of raw material mixed powder was filled, and a hydrostatic press was performed at 2.5 t. Then, a multi-cylinder superconducting compact was obtained. The obtained molded body was treated in the same manner as in Example 1 to obtain a multi-cylinder sintered body in which a silver cylinder having a through hole and a Y-Ba-Cu-O-based superconductor were composited. With respect to the obtained sintered body, the magnetic repulsion force and the crack length on the cut surface were visually observed in the same manner as in Example 1. As a result, the magnetic repulsive force was 1200 g, and the total crack length was 65 mm.
Met.

Comparative Example 2 A Y-Ba-Cu-O type superconducting cylinder sintered body was obtained in the same manner as in Example 2 except that the silver cylinder was not compounded. With respect to the obtained cylindrical sintered body, the magnetic repulsion force and the crack length on the cut surface were visually observed in the same manner as in Example 1. As a result, the magnetic repulsion force was 600 g, and the total crack length was 130 mm.

The Y-Ba-Cu-O-based superconductor obtained by laminating the silver plates having the through holes obtained in the above-mentioned embodiment and forming a composite has significantly more cracks than the conventional superconductor of the comparative example. It is clear that the magnetic repulsion force is reduced to more than double.

[0019]

The rare earth-based superconductor of the present invention has excellent magnetic repulsion with very few cracks, and is useful for the practical application of magnetic bearings using the superconductor.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory view showing another embodiment of the present invention.

FIG. 3 is an explanatory view showing an example of a silver layer having through holes according to the present invention.

FIG. 4 is an explanatory view showing another example of a silver layer having through holes according to the present invention.

FIG. 5 is an explanatory view of an apparatus used for measuring magnetic repulsive force used in the examples of the present invention.

[Explanation of symbols]

 A superconducting layer B silver layer C through hole 1 superconducting bulk body 2 liquid nitrogen 3 rare earth permanent magnet 4 rod 5 crosshead

Claims (3)

[Claims] 1. A RE-Ba-Cu-O-based superconductor (however,
RE is Y, Sm, Eu, Gd, Dy, Ho, Er and Y
Represents one or more elements selected from the element group consisting of b. ) And a silver layer are combined to form a superconducting bulk body, and the silver layer is arranged at intervals so as not to impede the flow of Meissner current induced by an external magnetic field in the bulk body. A rare earth-based superconductor characterized by: 2. The rare earth-based superconductor according to claim 1, wherein the silver layer has through holes. 3. The rare earth-based superconductor according to claim 1, wherein the RE-Ba-Cu-O-based superconductor is formed by a melting method.