JP5118941B2 - Manufacturing method of oxide superconducting bulk body and oxide superconducting bulk body - Google Patents

Description

    The present invention relates to a superconducting current lead, a flywheel power storage device, a superconducting magnetic levitation device, a superconducting magnetic bearing, a superconducting magnetic separation and purification device, a production method of an oxide superconducting bulk body that is being developed and applied to a linear motor, etc. The present invention relates to an oxide superconducting bulk body.

As an example of a method for producing a large oxide superconducting bulk material, a melt solidification method is known.
This melt solidification method refers to the production of an RE ₂ Ba ₁ Cu ₁ O ₅ phase or RE _{4 when} an oxide superconducting bulk body having a composition of RE ₁ Ba ₂ Cu ₃ O _7-X (RE represents a rare earth element) is produced. After heating the compact of the raw material powder to a temperature range in which the Ba ₂ Cu ₂ O ₁₀ phase and the liquid phase mainly composed of Ba—Cu—O coexist, the RE ₁ Ba ₂ Cu ₃ O _7-X phase It is a manufacturing method to obtain an oxide superconducting bulk body by cooling to the temperature just above the peritectic temperature to be generated, and gradually cooling from that temperature to grow crystals inside the precursor, and control nucleation and crystal orientation. .

In addition, a top seed melting solidification method (Top Seeding) that uses a single seed crystal and sequentially combines materials with different crystal growth start temperatures to produce an oxide superconducting bulk body by controlling the nucleation, crystal orientation, and crystal growth direction. Melt Growth) is known.
In this top seed melt solidification method, a precursor powder obtained by mixing compound powders of elements constituting an oxide superconducting bulk body is obtained and then a precursor is used to make a RE ₁ Ba ₂ Cu using this precursor. _In producing an oxide superconductor having a composition of ₃ O _7-X (RE represents a rare earth element), the RE ₂ Ba ₁ Cu ₁ O ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase, and the Ba—Cu— The precursor is heated to a temperature range in which a liquid phase containing O as a main component coexists to be in a semi-molten state, then a seed crystal is placed on the precursor in a semi-molten state, and RE ₁ Ba ₂ Cu ₃ O ₇ -Cooling to a temperature just above the peritectic temperature where the _X phase is formed, and gradually cooling from that temperature, the crystal gradually grows along the seed crystal inside the semi-molten precursor, Known as an example of a method for forming an oxide superconducting bulk material It has been.

The oxide superconducting bulk body is usually manufactured by the above-described melting method or a sintering method in which the raw material mixed powder is sintered after being compacted. In any case, the oxide superconductor is generally a kind of ceramics. Since these materials are inevitably accompanied by voids and cracks, and they tend to cause a decrease in strength, a reinforcing structure for increasing practical strength has been recognized as a problem.
From such a background, a structure in which a resin-impregnated layer is provided on the outer surface to improve the strength of the oxide superconducting bulk body is known. (See Patent Document 1) Further, in order to improve the mechanical strength of the oxide superconducting bulk body, a structure is known in which a close-contact coating layer impregnated with a resin is adhered to the outer surface of the oxide superconducting bulk body. Yes. Further, a structure in which a coating layer of a resin containing filler is provided on the outer surface in order to improve the strength of the oxide superconducting bulk body is known. (See Patent Document 3)
JP 2000-178025 A JP 2001-010879 A JP 2000-260882 A

In any of the above-mentioned top seed melt solidification methods or the generally known sintering methods that have been developed so far, voids and cracks can cause strength reduction as long as the resulting oxide superconducting bulk material is ceramic. However, although some research and development of manufacturing processes that consciously reduce voids and cracks in the superconducting material itself can be seen in part, the technology for increasing the structural strength as an oxide superconducting bulk has been described above. A precursor provided with a resin coating layer as described in the patent literature, which has not been sufficiently developed, and in particular a precursor formed by compacting raw material powders such as a melt solidification method On the other hand, in the oxide superconducting bulk material of a type that is sensitive to crystal growth, a good reinforcing structure has not been provided.
On the other hand, it is known that this type of oxide superconducting bulk body has poor thermal conductivity, and when an oxide superconducting bulk body is supplemented with a magnetic field, there has been a problem of heat burn. In view of this point, it has been difficult to solve the problem of heat dissipation with a structure of a type in which the outer surface is coated with a resin layer.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique capable of manufacturing an oxide superconducting bulk body in which a reinforcing structure is introduced. In addition, the present invention has good crystal growth as an oxide superconductor, is excellent in superconducting properties as an oxide superconducting bulk body, and also applies a reinforcing structure to improve heat dissipation. An object of the present invention is to provide a technique for providing an oxide superconducting bulk material that can be used.

The present invention has been made in view of the above circumstances, and RE ₁ Ba ₂ Cu ₃ O _7-X (RE is Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb. In the production of an oxide superconducting bulk body having the composition of Lu), when mixing the raw material powders of the elements constituting the oxide superconducting bulk body by pressing and compacting, A precious metal reinforcement that does not melt at the heating temperature associated with the melting and solidification method is mixed in the powder and consolidated to obtain a precursor with the desired shape. It is characterized by making it.
The present invention has been made in view of the above circumstances, and is characterized in that the reinforcing body is a platinum rhodium wire.
The present invention has been made in view of the above circumstances, and the precursor is heated to be in a semi-molten state and then cooled, and the previous semi-molten state is based on the crystal structure of the seed crystal placed on the precursor. An oxide superconducting bulk body containing a reinforcing body is manufactured by a top seed melt solidification method by crystallizing a precursor to form an oxide superconducting bulk body.

The oxide superconducting bulk material of the present invention is composed of RE ₁ Ba ₂ Cu ₃ O _7-X (RE is Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. An oxide superconducting bulk body having a composition of 1) or 2), which is crystal-grown by applying a melt solidification method, and is characterized in that a noble metal reinforcement is compounded inside. And
The oxide superconducting bulk body of the present invention is characterized in that the reinforcing body is a platinum rhodium wire.
In the oxide superconducting bulk body according to the present invention, the unmelted portion of the metal material constituting the reinforcing body remains as a core portion in the reinforcing body, and the constituent material elements of the reinforcing body and the oxide superconductor are formed on the outer periphery thereof. A coating layer including a raw material element is formed, and a crystal growth region made of the raw material element of the oxide superconductor is generated on the outer side of the coating layer.

According to the production method of the present invention, it is possible to produce an oxide superconducting bulk body with improved mechanical strength by combining a reinforcing body inside. Further, since this oxide superconducting bulk body is manufactured by crystal growth by the melt solidification method, it can be an oxide superconducting bulk body having few defects and voids and good superconducting characteristics.
Furthermore, since the precious metal reinforcing body is resistant to the high heating temperature by the melt solidification method and does not dissolve, it does not hinder the crystal growth of the precursor melt while solidifying, and good crystal growth is achieved. At the same time, since the reinforcing body exists without melting even after crystal growth by the melt solidification method, the mechanical reinforcement is satisfactorily achieved and the superconducting properties are excellent, and at the same time a high-strength oxide superconducting bulk body is formed. can get.

Furthermore, since the precious metal reinforcing body has better thermal conductivity than the material constituting the oxide superconducting bulk body, the heat of the oxide superconducting bulk body can be efficiently discharged to the outside using this reinforcing body. It becomes possible to provide an oxide superconducting bulk body with good heat dissipation.
If the reinforcing body is a platinum rhodium wire in the production method of the present invention, even if the precursor is melted and solidified by the melting method, the crystal growth is not affected by the platinum rhodium wire, and a good crystal is surely made. In addition, since the reinforcing body reliably remains and reinforces without melting even in the high-temperature heating associated with the melt-solidification method, a high-strength oxide superconducting bulk body can be reliably provided.

  In addition, if an oxide superconducting bulk body containing a reinforcing body is manufactured by the top seed melt solidification method, an oxide superconducting bulk body having high strength and excellent superconducting characteristics with reliable crystal growth can be reliably obtained. it can.

FIG. 1 shows a disk-shaped oxide superconducting bulk precursor 1 used in the manufacturing method according to the present invention. The precursor 1 is crystal-grown by a melting method described later, and further in an oxygen atmosphere. By performing the heat treatment in FIG. 3, the disc-shaped oxide superconducting bulk body 3 shown in FIG. 3 can be obtained as the final object.
In addition, the shape of the oxide superconducting bulk body 3 and its precursor 1 is not limited to a disc shape, and can be formed into any other shape such as a rod shape or other three-dimensional shape according to the target product shape. However, in this embodiment, the disk-shaped precursor 1 is illustrated and described below.

The precursor 1 of the oxide superconducting bulk body is a consolidated body of a raw material mixture having the same composition as that of the target oxide superconducting bulk body or an approximate composition. For example, REBaCuO (RE is Y) Examples of the rare earth elements (including La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) are included. Among these, it is desirable to select an element known as a rare earth system (Nd, Sm, Gd, etc.) from the viewpoint of improving the critical current density of the oxide superconducting bulk material.
Here, for example, when the target oxide superconducting bulk has a composition of NdBa ₂ Cu ₃ O _7-X , the precursor 1 may be, for example, a powder having a composition of NdBa ₂ Cu ₃ O _7-X and Nd ₄ Ba ₂ Cu _2. When a powder having a composition of O ₁₀ is mixed and compacted and sintered in pure oxygen is a precursor, and the target oxide superconducting bulk is a composition of SmBa ₂ Cu ₃ O _7-X , the precursor for example, with _{1, SmBa 2 Cu 3 O 7} -X of the powder composition of the powder and _Sm 2 BaCuO ₅ compositions by mixing those compaction is a precursor oxide superconducting bulk body of interest GdBa ₂ Cu ₃ In the case of the composition of O _7-X , examples of the precursor 1 may include a precursor that is compacted by mixing a powder having a composition of GdBa ₂ Cu ₃ O _7-X and a powder having a composition of Gd ₂ BaCuO _5. .

Further, when the target oxide superconducting bulk body is a YBa ₂ Cu ₃ O _7-x based oxide superconducting bulk body, for example, a Y compound powder, a Ba compound powder, and a Cu compound powder are used as the precursor 1. Y: Ba: Cu = 1: 2: 3, or a precursor obtained by compacting a raw material mixed powder mixed with a composition close to that can be used. Examples of the Y compound include oxide powder, Ba carbonate powder, and Cu oxide powder. More specifically, for example, an yttrium oxide (Y ₂ O ₃ ) powder, a barium carbonate (BaCO ₃ ) powder, and a copper oxide (CuO) powder are combined with an R123 phase component (Y ₁ Ba ₂ Cu ₃ O _7-X phase component). The R211 phase component (Y ₂ Ba ₁ Cu ₁ O ₅ phase component) ratio is individually weighed and individually mixed using an agate mortar to exemplify a compacted precursor by preparing a raw material mixed powder. it can.

As the precursor 1, a raw material mixed powder having the above composition is formed into a disk shape by a pressing device or a pressing device such as a CIP device (hydrostatic pressure device). Of course, if the CIP apparatus is expensive, the manufacturing cost is lower when the precursor 1 is manufactured by the press apparatus. The size of the precursor 1 may be arbitrary, and the precursor 1 may be a size that can be manufactured by a press device or a CIP device to be used.
When the mixed powder is compacted by the above-described pressurizing apparatus, the reinforcing wire 4 is incorporated in the present invention. A linear reinforcing body 4 is inserted into the mixed powder filling.
The reinforcing body 4 used here is preferably made of a noble metal, specifically, platinum, a platinum rhodium alloy, a platinum indium alloy, a platinum palladium alloy, a platinum tungsten alloy, or the like. Although platinum (Pt) has a melting point of 1768 ° C., the melting point can be improved by adding rhodium (Rh) to platinum to form an alloy. It is more preferable to use a platinum rhodium alloy reinforcing body 4 from the viewpoint that it is difficult to dissolve. For example, since the melting point of the 87% Pt-13% Rh alloy is 1865 ° C., a platinum rhodium alloy reinforcing wire having this composition ratio can be used.

  In the platinum rhodium alloy, for example, the melting point of 94% Pt-4% Rh alloy is 1835 ° C., the melting point of 90% Pt 10% Rh alloy is 1860 ° C., the melting point of 87% Pt 13% Rh alloy is 1865 ° C., 80% Pt 20 The melting point of the% Rh alloy is 1915 ° C., the melting point of the 70% Pt 30% Rh alloy is 1945 ° C., the melting point of the 60% Pt 40% Rh alloy is 1960 ° C., and the melting point of rhodium is 1960 ° C. It is preferable to use a platinum rhodium alloy having a composition ratio that can withstand the maximum heating temperature at the time of application, other noble metals, or alloys thereof. Of course, the aforementioned platinum indium alloy, platinum palladium alloy, platinum tungsten alloy, or the like may be used.

The reinforcing body 4 has a diameter of about 0.1 mm to 0.5 mm in view of the size of the oxide superconducting bulk body obtained by the melt-solidification method in the current technology having a diameter of about 10 mm to several tens of mm. It is desirable to use a plurality of, for example, about 2 to 10, for example.
The reinforcing body 4 is inserted into the mold together with the raw material mixed powder so that about four of the reinforcing bodies 4 are arranged at point-symmetrical positions surrounding the center of the precursor 1, for example, and the raw material mixed powder is consolidated by tightening the mold. Thus, a precursor 1 containing four reinforcing bodies 4 as shown in FIG. 1 is obtained. When the reinforcing body 4 is inserted into the raw material mixed powder in the molding cavity of the mold, disposing the reinforcing body 4 along the consolidation direction of the raw material mixed powder is an example of the direction in which the reinforcing body 4 is disposed. The arrangement direction of the reinforcing body 4 may be arbitrary. For example, the reinforcing body 4 may be arranged in the vertical direction, the horizontal direction, or the direction in which they are combined (oblique direction).

  Moreover, when manufacturing the precursor 1, after obtaining raw material mixed powder, the calcining grinding operation of mixing again the calcining raw material calcined at about 800 to 1000 ° C. and then pulverized by a pulverizer is performed. You may shape | mold by putting the thing with the reinforcement body 4 in the metal mold | die of a shaping | molding apparatus. Examples of the conditions for powder mixing and calcination include calcining conditions such as an agate mortar or an attritor or ball mill for about 1 hour and then calcining at about 900 ° C. for about 15 hours.

In addition, when calcining a plurality of times repeatedly for final pulverization and mixing, in order to improve the density during the subsequent heat treatment in an oxygen atmosphere, or for the purpose of preventing stress concentration in the bulk body, Ag powder or Ag _The precursor 1 is preferably prepared by mixing ₂ O powder as an additive substance into a molded body. Alternatively, it may be used a mixed powder obtained by mixing Ag powder and Ag 2 _O powder as an additive material in advance in the target composition ratio upon mixing of the raw material powder.
These additive substances may be those that improve the superconducting properties of the finally obtained oxide superconductor or that do not impair the superconducting properties. For example, if the additive substance is Ag, it can be added in a range of about 10 to 40% by mass in the state of Ag ₂ O with respect to the oxide superconductor.

If the precursor 1 in the state shown in FIG. 1 is obtained, the precursor 1 is heat-treated based on the semi-melt solidification method.
Here, the semi-molten solidification method is a raw material mixed molded body obtained by mixing a plurality of compounds of each element constituting the RE-Ba-Cu-O-based oxide superconductor, that is, after obtaining the precursor 1 The precursor 1 is heated and melted at a temperature equal to or higher than the melting point to maintain the shape of the precursor 1 to be in a semi-molten state, and then a slow cooling process is performed while applying a temperature gradient, and the seed crystal is formed at the temperature immediately before crystallization. This is a method for obtaining an oxide superconducting bulk body by being placed in a part of the precursor and growing the crystal in the precursor starting from the seed crystal.
That is, the whole is heated to a temperature slightly higher than the melting point of the precursor 1 to bring the precursor 1 into a semi-molten state so that its shape does not collapse. The heating atmosphere is an oxygen atmosphere in which a small amount of oxygen is supplied in an inert gas. For example, an Ar gas atmosphere having a 1% O ₂ concentration can be selected as an example.
The heating temperature at this time is slightly different depending on the composition of the target oxide superconductor or depending on the components of the atmospheric gas in the case of heat treatment, but is generally Nd-based oxide superconductivity in a 1% O ₂ inert gas atmosphere. If it is a body, it is in the range of 1000 to 1200 ° C, and other oxide superconductors are in the range of 970 to 1200 ° C.

  If the precursor 1 is in a semi-molten state, after slightly lowering the temperature of the precursor 1, a seed crystal is placed on the upper surface at the temperature immediately before crystallization, and the temperature is gradually lowered step by step. Hold at temperature for several tens of hours and then cool in furnace. For example, after gradually cooling to a temperature several tens of degrees C lower than the temperature in the semi-molten state and installing the seed crystal 2 as shown in FIG. Then, the oxide superconductor 6 as shown in FIG. 2 can be obtained by furnace cooling. For example, when the semi-melting temperature is 1100 ° C., it is cooled to 1010 ° C., a seed crystal is placed, gradually cooled to 1000 ° C., gradually cooled to 989 ° C., then held for 60 hours, and the furnace is cooled. . Note that these cooling conditions are examples of conditions that can be applied in the present invention. As disclosed in Japanese Patent Application Laid-Open No. 2007-131510 and the like, various conditions for melt solidification are provided, and any of the conditions described in these publications may be employed. Of course, the conditions of the melt-solidification method known besides these conditions can also be applied.

Inside the precursor 1, it is decomposed into Y ₂ BaCuO ₅ (Y211 phase) and L (liquid phase) (3BaCuO ₂ + 2CuO), and the liquid phase moves downward from the Y211 phase (separate from the seed crystal). The oxide superconductor crystal having a composition ratio of YBa ₂ Cu ₃ O _7-X (Y123 phase) grew from the seed crystal while moving so as to extrude to the side). Oxide superconducting bulk body 3 having a structure shown in FIG. 3 having a composition of YBa ₂ Cu ₃ O _7-X (Y123 phase) is obtained by crystallization partially or entirely.
When the crystallization proceeds, the noble metal reinforcing body 4 having a high melting point as described above does not melt, so that the crystal growth of the oxide superconductor is not adversely affected and the target crystal growth can be performed. it can. Further, even if only a small part of the outer peripheral portion of the reinforcing body 4 is partially melted and some element diffusion is performed with the constituent elements of the surrounding raw material mixed powder, the reinforcing body 4 itself is made of a noble metal and exists in the surroundings. Since the reactivity with the oxide superconductor constituent elements is low and the influence on the crystal growth of the oxide superconductor is very small, the crystal growth by the melt solidification method is sufficiently achieved. Therefore, even if the reinforcing body 4 is provided inside, the oxide superconducting bulk body 3 which can sufficiently achieve the initial target crystal growth can be manufactured.

  In addition, in the oxide superconducting bulk body 3 of this form shown in FIG. 3, a single crystal region 5 is generated outward from the central portion where the seed crystal 2 is disposed, and a polycrystalline region 6 is generated outside thereof. The four reinforcing bodies 4 are combined in the thickness direction of the bulk body in a point-symmetric position surrounding the central portion where the seed crystal 2 is installed. The oxide superconducting bulk material 3 in this form is an example, and the single crystal region 5 may be grown in the whole region without the polycrystalline region 6 being formed. In some cases, the superconducting bulk material 3 may have a structure formed only on a part thereof. Further, the facet line indicating the section of the single crystal region may not be clearly shown as in FIG. 3, so the shape shown in FIG. 3 is shown as an example of the oxide superconducting bulk body of the present invention.

If the oxide superconducting bulk body 3 is provided with the reinforcing body 4 by the above steps, the oxide superconductor, which is a kind of ceramic, is reinforced with the noble metal reinforcing body 4, so that the oxidation strength is high. A superconducting bulk material 3 can be provided. In addition, since the oxide superconducting bulk body 3 can achieve good crystal growth when crystal growth is performed by a melt solidification method, the oxide superconducting bulk material 3 has a feature of excellent superconducting characteristics.
Further, when Ag is added in the range of 10 to 40% by mass in the oxide superconducting bulk body 3 according to the present invention, an appropriate amount of Ag as an additive is added to the inside of the oxide superconducting bulk body 3 to concentrate internal stress. As a result, it is possible to obtain the oxide superconducting bulk body 3 with improved strength.
Further, since the metal reinforcing body 4 is provided inside, even if it is an oxide superconducting bulk body that tends to accumulate heat, the portion 4 of the reinforcing body 4 has high thermal conductivity. It can be efficiently cooled with a refrigerant or the like, and can provide an oxide superconducting bulk body with good heat dissipation.

Next, in the oxide superconducting bulk body 3 according to the present invention, a plurality of reinforcing bodies 4 are arranged at point-symmetrical positions surrounding the center of the oxide superconducting bulk body 3, so that the oxide superconducting bulk body 3 is well balanced. Can be reinforced. The number of reinforcing bodies 4 is not particularly limited, but a range of about 2 to 10 and about 5 to 10 is desirable. By providing these number of reinforcing bodies 4, it is possible to improve heat dissipation using the reinforcing bodies 4.
For example, when the oxide superconducting bulk body 3 is used in a superconducting state after being cooled with liquid nitrogen, even if the magnetic field is moved and heat may be generated when the magnetic field is applied, the thermal conductivity Since the oxide superconducting bulk body 3 can be efficiently cooled with liquid nitrogen through the good reinforcing body 4, it is possible to suppress deterioration of superconducting properties or transition to the normal state, and a structure with good heat dissipation. Can be provided.

As starting materials, calcined powder of Dy ₁ Ba ₂ Cu ₃ O _7-X component and calcined powder of Dy ₂ Ba ₁ Cu ₁ O ₅ component were weighed so as to have a molar ratio of 1: 0.3, and organic Mixed in solvent. Further, crack prevention, the Ag 2 _O powder for purposes of melting point depression was added 20 wt%, and the raw material mixed powder.
Next, it is put into a molding cavity of a die having an inner diameter of 21 mm, and two reinforcing wires of a platinum rhodium alloy 87% Pt-13% Rh wire having a diameter of 4 mm and a length of 8 mm are almost perpendicular to the raw material mixed powder in the molding cavity. It was inserted and compacted with a pressure of 1 to 3 MPa using a uniaxial press, and formed into a disk-shaped precursor having a diameter of 21 mm and a height (thickness) of 5 mm. The position of the platinum rhodium wire was approximately 180 ° center symmetrical with respect to the center of the compact in plan view.
When the previous Ag ₂ O powder is added, precursor samples were prepared with addition amounts of 10% by mass and 30% by mass, respectively, and the results of measuring the melting point of each precursor sample in air are shown in FIG. FIG. 4 also shows the measurement results of the melting point of the precursor sample prepared without adding Ag ₂ O powder. From the results shown in FIG. 4, it is clear that the precursor sample to which the Ag ₂ O powder was added has a lower melting point.

Next, a thin film having a composition of Nd ₁ Ba ₂ Cu ₃ O _7-X is used as a seed crystal for a precursor sample to which 20% by mass of Ag ₂ O powder is added, and the following heating pattern is used in the atmosphere. Heat-treated. This thin film is obtained by forming an oxide superconducting thin film having a thickness of 10 × 10 mm ^{2 and having} a thickness of 700 nm on an MgO substrate and dividing it into a size of about 1 mm square.
In the heat treatment, the previous precursor sample was performed under the following conditions. In this heat treatment, the peak temperature is maintained at 1030 ° C. for 1 hour, and then the temperature is lowered to 975 ° C. Here, seed crystals serving as nuclei were seeded into a semi-molten bulk body, and the temperature was lowered to 930 ° C. over 100 hours so as to facilitate crystallization. Moreover, performing these heated at _1% O 2 -Ar gas atmosphere.
Thereafter, in order to eliminate oxygen deficiency due to the melt solidification method, oxygen annealing treatment was performed at 450 to 250 ° C. for 200 hours in a 100% oxygen atmosphere.

The captured magnetic field measurement results of the obtained oxide superconducting bulk material sample are shown in FIGS. The captured magnetic field characteristics were measured by cooling the sample using liquid nitrogen and setting the magnetic field applied to the sample to 1.8 T (Tesla). Further, the positions of the two platinum rhodium wires are indicated by circles in FIG.
From the results shown in FIG. 5 and FIG. 6, the sample of the present invention has a PtRh alloy reinforcing wire composited inside, but there is no particular adverse effect related to the position of the reinforcing wire in the trapping magnetic field characteristics. Even if they were combined, it seemed to be a trapped magnetic field characteristic as a result of satisfactory crystal growth around the reinforcing wire. In addition, even when looking at the chevron figure of the trapped magnetic field distribution shown in FIG. 5, there is no irregular shape or the like due to the composite of the reinforcing wires, and one peak is formed on the center side of the oxide superconducting bulk body. A suitable trapping magnetic field characteristic was obtained.
Further, the critical temperature (Tc) of the oxide superconducting bulk material sample of this example combined with the reinforcing body showed about 91 K (offset value). On the other hand, since the critical temperature (Tc) of the oxide superconducting bulk material sample not composited with the reinforcing body showed about 90 K, the oxide superconducting bulk material sample of the present invention sample is a reinforcing wire of Pt—Rh alloy. It was also found that there was almost no effect on the critical temperature due to the composite, and it was confirmed that the oxide was a good oxide superconductor.

FIG. 7 shows the reinforcing wire of the oxide superconducting bulk sample of the comparative example and the oxide superconducting bulk sample according to the present invention and the surrounding metal structure. FIG. 7 (A) is a composite of Pt reinforcing wires. Fig. 7 (B) is a diagram of the oxide superconducting bulk body reinforcing wire and surrounding metal structure, and Fig. 7 (B) shows the oxide superconducting bulk body reinforcing wire manufactured by combining Pt Rh alloy reinforcing wire and the surrounding metal. A tissue photograph is shown.
A sample to which a Pt reinforcing wire is applied melts and solidifies in the air under the above conditions, and the reinforcing wire melts. Even if a photograph is taken at a position where the reinforcing wire is combined, the presence of the reinforcing wire is confirmed. I couldn't. On the other hand, when the metal structure photograph around the reinforcing wire of the oxide superconducting bulk body in which the reinforcing wire of the Pt Rh alloy shown in FIG. 7B is combined, the existence of the reinforcing wire of the Pt Rh alloy is clearly confirmed. I was able to.
Since the composite reinforcing wire has a diameter of 400 μm (0.4 mm), from the structure photograph of FIG. 7 (B), there is a coating layer that seems to be accompanied by other elements and some diffusion in the outer peripheral portion. It seems that the entire Pt Rh alloy remained, and there was a layer due to element diffusion on the further peripheral side, but on the outer side, a region where uniform crystal growth seems to have occurred was formed. Was. On the other hand, in the structure shown in FIG. 7 (A), there was a structure in which a trace of generation of a non-uniform structure due to melting of the Pt reinforcing wire was observed.

From the structural photograph shown in FIG. 7B, the oxide superconducting bulk body of this example has an unmelted portion of the metal material constituting the reinforcing body as a core portion inside the reinforcing body, and the outer peripheral portion thereof. A crystal growth region comprising a coating layer formed by partially diffusing constituent material elements of the reinforcing body and raw material elements of the oxide superconductor, and comprising the raw material elements of the oxide superconductor on the outer side of the coating layer It has been found that it has a structure formed by.
If the melting point of platinum and the heating temperature based on the melt solidification method are simply compared, it is assumed that platinum does not dissolve even at the maximum temperature based on the melt solidification method, but superconductivity at the peak temperature when the melt solidification method is performed. It can be understood that the platinum reinforcing body has melted as a result of the reaction between the compound existing in the bulk and platinum. For this reason, when using a reinforcing wire, it is desirable to use a reinforcing wire made of a metal having a high melting point as much as possible. Therefore, in this example, it was found that the reinforcing wire of PtRh alloy is more advantageous than the reinforcing wire of platinum. did.

FIG. 1 is an explanatory view showing a precursor used in carrying out the method of the present invention. FIG. 2 is a side view showing a state in which a seed crystal is installed on the precursor. FIG. 3 is a plan view showing an example of an oxide superconducting bulk body obtained according to the method of the present invention. FIG. 4 is a graph showing the relationship between the added amount of Ag ₂ O and the melting point of the precursor sample obtained in the examples. FIG. 5 is a diagram showing a trapping magnetic field characteristic of an oxide superconducting bulk material sample added with 20% by mass of Ag ₂ O obtained in Examples. FIG. 6 is a contour map of the captured magnetic field characteristics obtained in the same example. FIG. 7 shows the metal structure around the reinforcing wire of the oxide superconducting bulk sample, and FIG. 7 (A) is a photograph of the metal structure around the reinforcing wire of the oxide superconducting bulk material manufactured by combining Pt reinforcing wires. FIG. 7B is a photograph of the metal structure around the reinforcing wire of the oxide superconducting bulk material manufactured by combining the reinforcing wires of the Pt Rh alloy.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Precursor, 2 ... Seed crystal, 3 ... Oxide superconducting bulk body, 4 ... Reinforcement line, 5 ... Single-crystal region, 6 ... Polycrystalline region.

Claims (6)

RE ₁ Ba ₂ Cu ₃ O _7-X (RE represents one or more of Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.) When the oxide superconducting bulk body having the composition described above is manufactured, when the raw material powder of the elements constituting the oxide superconducting bulk body is pressed and compacted, it does not melt at the heating temperature associated with the melt solidification method in the raw material mixed powder Production of oxide superconducting bulk material characterized by inserting a precious metal reinforcement and compacting to obtain a precursor of the desired shape, and then crystal-growing this precursor by applying a melt solidification method Method.   The method for producing an oxide superconducting bulk body according to claim 1, wherein the reinforcing body is a platinum rhodium wire.   The precursor is heated to a semi-molten state and then cooled, and based on the crystal structure of the seed crystal placed on the precursor, the precursor in the semi-molten state is crystallized to form an oxide superconducting bulk body. The method for producing an oxide superconducting bulk body according to claim 1 or 2, wherein the oxide superconducting bulk body containing a reinforcing body is produced by a top seed melt solidification method. RE ₁ Ba ₂ Cu ₃ O _7-X (RE represents one or more of Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.) An oxide superconducting bulk body having a composition as described above and crystal-grown by applying a melt solidification method, wherein a reinforcing body made of noble metal is compounded inside.   The oxide superconducting bulk body according to claim 4, wherein the reinforcing body is a platinum rhodium wire.   An unmelted portion of the metal material constituting the reinforcing body remains as a core portion inside the reinforcing body, and a coating layer including the constituent material elements of the reinforcing body and the raw material elements of the oxide superconductor is formed on the outer periphery thereof. The oxide superconducting bulk body according to claim 4 or 5, wherein a crystal growth region made of a raw material element of the oxide superconductor is generated on the outer side of the coating layer.

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