JPWO2005104144A1 - Manufacturing method of MgB2 superconducting wire excellent in critical current characteristics - Google Patents

Abstract

A simple and easy method for forming MgB2 having a critical temperature Tc = 39K into a wire is provided. (a) A mixed raw material of powdered Mg and B, or a mixed raw material obtained by mixing a mixed powder of Mg and B in powder form and MgB2 powder, and (b) a pellet obtained by compression molding the obtained mixed raw material And (c) the obtained pellet is enclosed in a metal tube coated with a carbon-based material, or the pellet is coated with a carbon-based material and then enclosed in a metal tube, and (d) the metal in which the pellet is enclosed The tube is drawn to obtain a wire, and (e) if necessary, the obtained wire is wound into a coil and then heat treated in an inert gas pressurized atmosphere.

Description

The present invention relates to a method for manufacturing an MgB ₂ superconducting wire, and more particularly to a manufacturing method capable of stably supplying a superconducting wire applicable to power cables, magnets, motors, generators and the like at low cost.

When a certain kind of material is cooled to a very low temperature, the electric resistance rapidly decreases and a phenomenon of completely zero is observed. This is called a superconducting phenomenon, and a material exhibiting such a phenomenon is called a superconducting material (substance). Such a superconducting material can be formed into a wire, formed into a coil shape, and a very high magnetic field can be stably generated by energizing it. Therefore, it is widely used in various devices such as medical devices that use a high magnetic field today. Currently, NbTi and Nb ₃ Sn are mainly used as superconducting materials. However, in order to obtain superconducting properties, it is necessary to cool to a very low temperature range, and expensive liquid helium (boiling point 4.2K) is required for the refrigerant. In addition, it is difficult to use a device such as a cryostat for cooling.

  As a next-generation material for superconducting substances, research on bismuth (Bi) -based and yttrium-based (Y) -based oxide high-temperature superconductors that can obtain superconducting properties at a boiling point of liquid nitrogen of 77K has been actively conducted. Problems include high material costs, complex component ratios, difficulty in mass production as wires, and high manufacturing costs.

  These oxide systems, when the temperature is raised to 77K, drastically lowers the critical current characteristics, but at temperatures around 20K, they show practical critical current characteristics, so by using a refrigerator or liquid hydrogen as a refrigerant Use at a temperature of 20K is also being considered. This is because even at a temperature of 20K, there is a significant economic effect.

Recently, as shown in Patent Document 1, an intermetallic compound superconductor MgB ₂ having a critical temperature Tc = 39K has been discovered. It can be expected to be used at a temperature of 20K, is lightweight, has abundant resources and is relatively easy to manufacture, and is actively researched and developed for practical use.
Japanese Patent Laid-Open No. 2002-219916

An object of the present invention is to develop a technique for forming MgB ₂ that exhibits such excellent characteristics into a wire.

Conventionally, various methods are known for forming a superconductor material into a wire. Among them, a powder sealed tube method (Powder-In) in which raw material powder is packed into a metal tube and wire drawing is performed. -Tube) is a relatively simple manufacturing method and is famous as a Bi-based wire manufacturing method. Since this method is also promising as a method for producing an MgB ₂ wire, it has been widely studied. And this powder sealed tube method is divided roughly into two types of methods.

(1) In-situ method This is a method in which the powder of each element constituting the superconductor is packed in a metal tube, and then the superconducting material is produced and drawn.

(2) Ex-situ method This is a method in which powder or pellets of a superconducting material are packed in a metal tube and the metal tube is drawn.

In this specification, for convenience, a metal tube filled with such powder or pellets is also referred to as a sheath tube, and the material is also referred to as a sheath material.
In the case of superconducting materials, a superconducting breakdown phenomenon (called superconducting quench) is likely to occur due to flux jump, which is a phenomenon in which magnetic flux penetrates rapidly, at a very low temperature range. The present invention will be described by taking a copper tube having a high thermal conductivity and an effect as a countermeasure against heat generation as an example of a stabilizer for the above.

The present inventors tried to wire the superconducting material MgB ₂ by an in-situ method. However, when only Mg and B are used, the critical current characteristics are insufficient, and further improvement of the characteristics is required. did.
Then, the experiment which improves a characteristic by adding 3rd elements other than Mg and B was repeated. This is because, in the study of MgB ₂ bulk, a research paper has been reported that the critical current density Jc is improved by adding Ti, SiC and diamond fine particles.

As a result of repeated trials to improve critical current characteristics by adding TiH ₂ and diamond fine particles, we succeeded in increasing the critical current characteristics nearly twice by blending diamond fine particles.

However, in the case of the in-situ method, the copper tube used as the thermal stabilizer and the raw material Mg react with each other by the heat treatment, and there is a problem that MgB ₂ cannot be generated sufficiently.
Therefore, we tried wire drawing by ex-situ method using the generated MgB ₂ as raw material powder, but sufficient critical current characteristics could not be obtained unless the powder particle size was made fine, and MgB ₂ particles In order to obtain a sufficient bond between them, it is necessary to apply a considerable high pressure, and it has been difficult to achieve with a general wire drawing method.

That is, in the case of the ex-situ method, the reaction between copper and Mg can be greatly reduced compared to the in-situ method. However, in order to obtain high superconducting characteristics, the initial MgB ₂ particles are refined and the reaction is reduced. It is necessary to apply a sufficiently high pressure in order to firmly bond such fine particles. In particular, when a copper tube is used as the sheath tube, since the mechanical strength is low and the pressure is not sufficiently applied as a whole, the critical current characteristic tends to be lowered.

Therefore, we decided to investigate a method to prevent the reaction between the copper tube and Mg by an in-situ method with a proven track record of obtaining a relatively high critical current characteristic, and came up with the idea of coating a carbon-based material inside the copper tube. . In other words, since the factor that inhibits the production of MgB ₂ is the reaction between copper and Mg, by providing a carbon intermediate layer, the reaction can be prevented, and by the diffusion of carbon to some extent in MgB ₂ It was thought that the scattering between electrons increased and the upper critical magnetic field and irreversible magnetic field increased and the magnetic flux pinning effect could be expected. And when an actual experiment was conducted, it was found that there was an effect of greatly improving the critical current characteristics.

  As described above, according to the present invention, the critical current characteristics can be greatly improved by a simple method in which carbon is applied in advance to the inside of a metal tube as a sheath tube.

As another method, when the pelletized compression molded body was coated with a carbon-based material and then encapsulated in a metal tube and subjected to wire drawing, the same result as in the above case could be obtained.
Here, the present invention is as follows.
(1) In the manufacturing method of MgB ₂ wire rod
(a) Coating the carbon material on the inside of the metal tube,
(b) A mixed raw material of powdered Mg and B, or a mixed raw material obtained by mixing a mixed powder of Mg and B in powder form and MgB ₂ powder,
(c) The obtained mixed raw material is compression molded into pellets,
(d) The obtained pellets are sealed in the metal tube coated with a carbon-based material,
(e) The metal pipe enclosing the pellet is drawn to form a wire, and
(f) A method for producing an MgB ₂ wire, wherein the obtained wire is heat-treated in an inert gas atmosphere or a pressurized atmosphere.
(2) The method for producing an MgB ₂ wire according to (1) above, wherein in (f), the obtained wire is wound in a coil shape and then heat-treated in an inert gas pressurized atmosphere. .
(3) The method for producing an MgB ₂ wire according to (1), wherein the carbon-based material is a graphite-based material.
(4) The method for producing an MgB ₂ wire according to (1), wherein the wire drawing is performed in a plurality of times.
(5) The wire rod (metal body) obtained by performing the wire drawing process is further covered with another metal tube, and the wire drawing process is performed, according to any one of the above (1) to (4) The manufacturing method of MgB ₂ wire of description.
(6) A plurality of wire rods (metal bodies) obtained by the wire drawing process are covered with another metal pipe together with a metal material filling the gap, if necessary, and further wire drawing is performed. The method for producing an MgB ₂ wire according to any one of (1) to (4) above.
(7) The metal pipe for coating the carbon-based material on the inside and the other metal pipe are the same or different, and are copper, copper alloy, iron, iron alloy, carbon steel, stainless steel, nickel and nickel alloy The method for producing an MgB ₂ wire according to (5) or (6) above, which is one selected from the group consisting of:
(8) The method for producing an MgB ₂ wire according to any one of (1) to (4), wherein the heat treatment is performed at 550 to 800 ° C.
(9) In the manufacturing method of MgB ₂ wire
(a) A mixed raw material of powdered Mg and B, or a mixed raw material obtained by mixing powdered Mg and B mixed powder and MgB ₂ powder,
(b) The resulting mixed raw material is compression molded into pellets,
(c) The resulting pellet is coated with a carbon-based material,
(d) Enclose the coated pellets in a metal tube,
(e) The metal pipe enclosing the pellet is drawn to form a wire, and
(f) A method for producing an MgB ₂ wire, wherein the obtained wire is heat-treated in an inert gas atmosphere or a pressurized atmosphere.
(10) The method for producing an MgB ₂ wire according to (9) above, wherein in (f), the obtained wire is wound in a coil shape and then heat-treated in an inert gas pressurized atmosphere. .
(11) The method for producing an MgB ₂ wire according to (9), wherein the carbon-based material is a graphite-based material.
(12) The method for producing an MgB ₂ wire according to (9), wherein the wire drawing is performed in a plurality of times.
(13) The wire rod (metal body) obtained by performing the wire drawing process is further covered with another metal pipe, and the wire drawing process is performed, according to any one of the above (9) to (12) The manufacturing method of MgB ₂ wire of description.
(14) A plurality of wire rods (metal bodies) obtained by the wire drawing process are covered with another metal tube together with a metal material filling the gap, if necessary, and further wire drawing is performed. The method for producing an MgB ₂ wire according to any one of the above (9) to (12).
(15) The metal tube enclosing the pellet and the other metal tube are the same or different and are selected from the group consisting of copper, copper alloy, iron, iron alloy, carbon steel, stainless steel, nickel and nickel alloy. The method for producing an MgB ₂ wire according to the above (13) or (14), which is made of only one kind of metal.
(16) The method for producing an MgB ₂ wire according to any one of (9) to (12), wherein the heat treatment is performed at 550 to 800 ° C.

Thus, according to the present invention, a metal sheath MgB ₂ wire with high critical current characteristics can be manufactured by coating the inside of a metal tube or a pellet with a carbon-based material.
More specifically, even at the preliminary experiment stage, the wire obtained by the present invention had a critical current of 419 A and a critical current density of 460 kA / cm ² in a self-magnetic field of 4.2 K in the short length.

IV curve for a short single-core MgB ₂ wire obtained by coating graphite powder on the inside of a copper tube according to Example 1 and then filling with mixed raw material, followed by heat treatment at 600 ° C. for 2 hours after wire drawing. It is. 4 is a graph comparing a short single-core MgB ₂ wire produced by changing the amount of diamond particles added to a raw material powder and an IV curve for the results of Example 1 without coating the copper tube according to Comparative Example 1. FIG. Figure 3 is a view showing the results of element mapping with EPMA of the cross section of the single core MgB ₂ wire material not coated by coating with the single core MgB ₂ wire material produced by the graphite powder. FIG. 4 is an IV curve of a short single-core MgB ₂ wire material that was prepared by coating graphite powder on the inside of a copper tube according to Example 2 and then subjected to heat treatment at a temperature of 500 to 800 ° C. for 2 hours. FIG. 4 is an IV curve of a short single-core MgB ₂ wire that was prepared by coating a graphite tube on the inside of a copper tube according to Example 3 and then heat-treated at 600 ° C. for 2 hours. IV curve for short single-core MgB ₂ / Cu wire (diameter 1.0 mm) that was prepared by coating 5-15 mol% graphite paste on the inside of a copper tube according to Example 5 and then heat-treated at 600 ° C. for 2 hours. It is. IV curve for a short single-core MgB ₂ / Cu wire (diameter 0.8 mm) that was prepared by coating 0-15 mol% graphite paste on the inside of a copper tube according to Example 5 and then heat-treated at 600 ° C. for 2 hours. It is.

Here, the basic steps of the method for producing an MgB ₂ wire according to the present invention will be described in order.
Application of carbon materials:
The coating is an important process in the present invention in that the desired critical current characteristics are obtained.

  A carbon-based material is applied to the inside of a metal tube as a base material or pellets obtained by compression molding. Carbon-based materials include metal tubes and Mg, especially when the metal tube is a copper tube, to effectively suppress the reaction between the copper tube and Mg, and to reduce the reaction products that impede critical current characteristics. It is preferable to select the material. The raw material for the carbon material is powder or paste.

  In the case of powder raw material, it is applied by dissolving in an organic solvent. After the application, it is heat-treated in an inert atmosphere and dried. The thickness after drying is not particularly limited, but may be uniform. In particular, a thickness of 10 to 100 μm is sufficient in terms of reaction suppression.

  The pasty raw material may be used after being dissolved in an organic solvent, or may be applied directly to the inside of the metal tube or the pellet surface. In that case, the coating thickness is preferably 10 to 100 μm. In addition, what is necessary is just to perform the application | coating operation itself of carbon-type material itself by a normal method, respectively.

Commercially available graphite paste is effective because it can be easily applied to the inside of the metal tube because the solvent has an adhesive effect.
Ingredient mix:
A mixed raw material is obtained by blending powdered Mg and B powder raw materials, or blending MgB ₂ with powdered Mg and B powder raw materials.

Compaction Molding The mixed powder prepared in this way is put into a mold as appropriate and compression molded into pellets.
The reason for making pellets is to facilitate handling and to ensure a constant raw material density over the entire length of the metal tube.

Encapsulating the pellet in the sheath tube:
The obtained pellet is sealed in a metal tube as a sheath tube. Specifically, in an inert atmosphere, a pellet is inserted from the other end into a metal tube sealed at one end, and the metal tube is sealed.

  The tube material at this time, that is, the sheath material is not particularly limited as long as sufficient workability can be secured, but usually, such as iron, iron alloy, carbon steel, stainless steel, copper, copper alloy, nickel, nickel alloy It is preferable to select from among them.

  Since superconductivity is a phenomenon that occurs in an extremely low temperature region, measures against heat for superconductors are a very important item. In the case of a superconducting wire, the sheath material plays a very important role not only as a support material but also as a thermal stabilization material in the case of superconducting quench (superconducting breakdown).

Examples of the stabilizing sheath material include copper and copper alloys as materials that have high thermal conductivity, low electrical resistivity, excellent ductility, and are easily available. However, in the case of MgB _2, it reacts when Cu and Mg of the heat treatment, it is possible to produce a compound, if it is desired to avoid the formation of compounds, stainless steel, nickel, nickel alloy, iron, iron alloy, carbon Steel or the like may be used.

  However, if a metal with poor thermal conductivity is used as a stabilizing material, the heat generated by flux jump is absorbed and the ability to be released into the refrigerant is insufficient, so a sudden disturbance of magnetic flux → a vicious cycle of heat generation causes superconductivity in an instant. Induces a quenching phenomenon that breaks the state. Since the large current flowing in the superconductor flows into the sheath material, it suddenly generates heat and the wire material burns out at once. Therefore, when it is assumed to be put into practical use, it is desirable to use a sheath material that is excellent as a stabilizing material, such as copper.

Wire drawing:
The metal tube prepared as described above and inserted with pellets is subjected to wire drawing by swaging or roller dies. The wire drawing in this case may be performed by a known method, and there is no particular limitation in the present invention.

The wire drawing may be performed in a plurality of times. The obtained wire (metal body) may be further covered with another metal tube and further drawn.
As an alternative method, a plurality of wires (metal materials) obtained by wire drawing may be coated with another metal tube together with a metal material filling the gap, if necessary, and further wire drawing may be performed. .

  In such an embodiment, when the metal tube enclosing the pellet is a copper tube, the above-mentioned another metal tube includes copper, copper alloy, nickel, nickel alloy, iron, iron alloy, stainless steel, and carbon. Any metal tube selected from steel may be used.

Heat treatment:
After finishing the wire rod (metal body) obtained by drawing to a predetermined size, and after further winding in a coil shape, in an inert atmosphere such as an Ar atmosphere, for example, at least 2 atm. In a pressurized atmosphere, heat treatment is performed by heating at a temperature of 550 to 800 ° C., preferably 550 to 750 ° C., more preferably 580 to 680 ° C. for 1 to 2 hours, and Mg and B inside the metal tube are changed to MgB ₂ Change. The reason why the pressurized atmosphere is used is to prevent generation of voids and the like. At this time, carbon coated on the inside of the metal tube diffuses and enters MgB ₂ , thereby improving the critical current characteristics. Furthermore, when the metal sheath material is a metal that reacts with a raw material such as Mg, the carbon film inside the metal tube serves as a protective layer that prevents the reaction between the metal tube and the raw material, thereby preventing the generation of impurities.

  Next, the present invention will be described more specifically with reference to examples.

  In this example, one end of a copper tube having a wall thickness of 2.8 mm, a diameter of 12 mm, and a total length of 200 mm is plugged, and graphite powder (99% purity, particle size of 44 μm or less) is added to the inner wall of acetone at a weight ratio of 1: 3. The solution was poured into the tube, the end on the opposite side was lightly plugged, the copper tube was leveled and slowly rotated, and the rotation continued until the acetone evaporated and the graphite adhered to the inside of the tube.

Thereafter, heat treatment was performed at 300 ° C. for 1 hour in a heat treatment furnace in an Ar atmosphere, and the copper tube was coated with graphite. Note that, when heat treatment is performed in the air, carbon constituting graphite may be diffused as CO _2, and thus heat treatment is preferably performed in an inert atmosphere.

Next, powdered Mg having a particle size of 44 μm or less and powdered amorphous B having a particle size of 1 μm or less are blended at an element ratio of 1: 2, and used as the first powder material, while MgB ₂ powder that has been reacted in advance by heat treatment is used. Separately prepared as a second powder raw material (particle size of 150 μm or less), the first and second powder raw materials were mixed at a ratio of 1: 1 to obtain a mixed raw material.

The mixed raw material thus obtained was formed into a pellet-like compression molded body having a size of 6 × 10 mm in diameter using a dedicated mold. The green density was 1.6 g / cm ² .
These pellet-like compacts, that is, pellets, were enclosed in the above-described copper tube having a thickness of 2.8 mm and a diameter of 12 mm coated with graphite.

The pellet-encapsulated copper tube thus obtained was then subjected to wire drawing, which was performed using a conventional swaging machine.
When the diameter of the copper tube became 1.0 mm by wire drawing, the copper tube was heated at 600 ° C. for 2 hours under an atmosphere of 3 atmospheres of Ar gas to cause a reaction of Mg + 2B → MgB ₂ .

The critical current characteristics of the wire thus obtained were determined by an energization method.
FIG. 1 is an IV curve obtained by measuring IV characteristics of a short sample having a length of 30 mm by a four-terminal method and evaluating a critical current based on a voltage standard of 1 μV / cm.

A critical current value exceeding 400 A was exhibited in a self-magnetic field at a temperature of 4.2 K, and the critical current density at this time reached 460 kA / cm ² . In the drawing, the cross section of the wire is shown, but the region shown in black in the center is the superconducting material, and the surroundings shown in white are copper of the sheath material.
[Comparative Example 1]
For comparison with Example 1, graphite was not applied to a copper tube having a wall thickness of 2.8 mm, a diameter of 12 mm, and a total length of 200 mm.

Next, powdered Mg having a particle size of 44 μm or less and powdered amorphous B having a particle size of 1 μm or less are blended at an element ratio of 1: 2, and used as the first powder material, while MgB ₂ powder that has been reacted in advance by heat treatment is used. Separately prepared as a second powder raw material (particle size of 150 μm or less), the first and second powder raw materials were mixed at a ratio of 1: 1 to obtain a mixed raw material.

To this mixed raw material, diamond particles having a particle size of 0.1 μm or less were added in proportions of 0%, 3%, 6%, and 10%, respectively.
The mixed raw material thus obtained was formed into a pellet-like compression molded body having a dimension of 6 × 10 mm in diameter using a dedicated mold. The green density was 1.6 g / cm ² on average.

  These pellet-shaped compression-molded bodies are encapsulated in a copper tube not coated with graphite, and a total of four wire base materials (pellet-encapsulated copper tube) with 0%, 3%, 6%, and 10% diamond particles added. Prepared.

The pellet-encapsulated copper tube thus obtained was then subjected to wire drawing, which was performed using a conventional swaging machine.
When the diameter of the copper tube became 1.0 mm by wire drawing, the copper tube was heated at 600 ° C. for 2 hours under an atmosphere of 3 atmospheres of Ar gas to cause a reaction of Mg + 2B → MgB ₂ .

The critical current characteristics of the wire thus obtained were determined by an energization method.
FIG. 2 is an IV curve obtained by measuring the IV characteristic of each short sample having a length of 30 mm by a four-terminal method in a self-magnetic field at a temperature of 4.2 K. The IV curve obtained in Example 1 is shown for comparison.

  As a result, the wire with diamond particles had the best critical current characteristics when the diamond particles were 6%, but the graphite coated with the graphite obtained in Example 1 further exceeded the critical current by about 100A. ing.

  In order to confirm the effect of coating to prevent the reaction between the copper tube and Mg, EPMA is applied in the direction indicated by the arrow from the top to the bottom in FIG. The copper element was used for mapping.

The result is also shown in FIG. In the figure, the left side shows no coating and the right side shows coating. The white shining area indicates the presence of copper element.
From this, it can be confirmed that the coated sample has less penetration of the copper element. From this, it is considered that the graphite coating has an effect of reducing the reaction between copper element and Mg.

  A copper tube with a wall thickness of 2.8mm, a diameter of 12mm, and a total length of 200mm is plugged on one end, and graphite powder (purity 99%, particle size 44μm or less) is dissolved in acetone at a weight ratio of 1: 3 on the inner wall. With the other end lightly plugged, the copper tube was leveled and rotated slowly until the acetone evaporated and the graphite adhered to the inside of the tube.

Thereafter, heat treatment was performed at 300 ° C. for 1 hour in a heat treatment furnace in an Ar atmosphere, and the inner surface of the copper tube was coated with graphite to obtain a base metal tube.
Next, powdered Mg having a particle size of 44 μm or less and powdered amorphous B having a particle size of 1 μm or less are blended at an element ratio of 1: 2, and used as the first powder material, while MgB ₂ powder that has been reacted in advance by heat treatment is used. Separately prepared as a second powder raw material (particle size of 150 μm or less), the first and second powder raw materials were mixed at a ratio of 1: 1 to obtain a mixed raw material.

The mixed raw material thus obtained was formed into a pellet-like compression molded body having a dimension of 6 × 10 mm in diameter using a dedicated mold. The green density was 1.6 g / cm ² .
These pellet-like compression molded bodies were sealed in a graphite tube-coated copper tube having a thickness of 2.8 mm and a diameter of 12 mm.

The pellet-encapsulated copper tube thus obtained was then subjected to wire drawing, which was performed using a conventional swaging machine.
When the diameter of the copper tube reaches 1.0mm due to wire drawing, the copper tube is heated at 500 ° C, 550 ° C, 650 ° C, 700 ° C, 750 ° C, and 800 ° C for 2 hours in an Ar gas atmosphere of 3 atm. Then, a reaction of Mg + 2B → MgB ₂ was performed.

The critical current characteristics of the wire thus obtained were determined by an energization method.
FIG. 4 is an IV curve obtained by measuring IV characteristics of a short sample having a length of 30 mm subjected to heat treatment at each temperature by a four-terminal method. In the figure, the curve at 650 ° C. almost coincides with the characteristics at 600 ° C. shown in the examples.

As can be seen, a voltage is generated in the sample heat-treated at 500 ° C. when a current is applied. This is presumably because the heat treatment temperature was too low and Mg and B in the raw material hardly changed to MgB ₂ .

In the case of heat treatment at 750 ° C. and 800 ° C., a voltage is generated even in a low current region. This is presumably because the sheath material, which is copper, and the raw material Mg easily react with each other at a high temperature, and a large amount of Mg reacts with copper, so that sufficient MgB ₂ is not generated.

In the heat treatment at 550 to 700 ° C., no voltage is generated up to a certain current value, and it is considered that MgB ₂ is sufficiently generated. Compared with the graph of Example 1, those heat-treated at 600 ° C. and 650 ° C. exceeded the critical current Ic = 400 A, and in the vicinity of this temperature range, that is, the temperature range where 580 to 680 ° C. provides the best critical current characteristics. It is judged.

  In this example, Example 1 was repeated, but a commercially available graphite paste (fast drying, for SEM, for XMA, solvent: n-butyl acetate) was directly applied to the surface of a coating material for a metal tube, which is a copper tube. . In the method of dissolving graphite in acetone shown in Example 1, the coating on the inner side of the metal tube is likely to cause uneven coating, and what is attached to the inner side of the metal tube after drying tends to peel off, whereas the graphite paste Since the solvent has the effect of an adhesive, the effect of being easily applied uniformly to the metal tube was obtained. FIG. 5 shows the results of evaluating the IV characteristics of the obtained sample.

  In this example, Example 1 was repeated, but instead of coating a copper tube with a coating material, carbon deposition was performed on a compression molded body obtained by compacting a mixed powder, that is, pellets, using a carbon deposition apparatus. As a result of evaluating the I-V characteristics of the obtained sample, the critical current exceeded 200 A and increased from the value without carbon deposition. However, the effect was smaller than when applied in the sheath tube. A further increase is expected due to improved coating conditions.

In this example, Example 1 was repeated, but the concentration of graphite in the copper tube coating material was changed.
The amount of carbon of 5 to 15 mol% with respect to the molar ratio of MgB ₂ molecules to be baked was dissolved in acetone as a solvent, and these solutions were applied to the inside of a copper tube and dried. These prototype materials were drawn to a diameter of 1.0 mm and a diameter of 0.8 mm, respectively. The results of evaluation of IV characteristics are shown in FIGS.

  There is a tendency for the critical current to decrease as the concentration of graphite increases.

Claims (16)

In the manufacturing method of MgB ₂ wire
(a) Coating the carbon material on the inside of the metal tube,
(b) A mixed raw material of powdered Mg and B, or a mixed raw material obtained by mixing a mixed powder of Mg and B in powder form and MgB ₂ powder,
(c) The obtained mixed raw material is compression molded into pellets,
(d) The obtained pellets are sealed in the metal tube coated with a carbon-based material,
(e) The metal pipe enclosing the pellet is drawn to form a wire, and
(f) A method for producing an MgB ₂ wire, wherein the obtained wire is heat-treated in an inert gas atmosphere or a pressurized atmosphere. _{2. The} method for producing an MgB ₂ wire according to claim 1, wherein, in (f), after the obtained wire is wound in a coil shape, heat treatment is performed in an inert gas pressurized atmosphere. The method for producing an MgB ₂ wire according to claim 1, wherein the carbon-based material is a graphite-based material. The method for producing an MgB ₂ wire according to claim 1, wherein the wire drawing is performed in a plurality of times. The MgB _{2 according} to any one of claims 1 to 4, wherein the wire rod (metal body) obtained by the wire drawing process is further coated with another metal tube to perform the wire drawing process. A manufacturing method of a wire. A plurality of wire rods (metal bodies) obtained by the wire drawing process are coated with another metal pipe together with a metal material filling the gap, if necessary, and further wire drawing is performed. method of manufacturing a MgB ₂ wire material according to any one of clauses 1-4. The metal pipe for coating the carbon-based material on the inside and the other metal pipe are the same or different, and are made of copper, copper alloy, iron, iron alloy, carbon steel, stainless steel, nickel and nickel alloy The method for producing an MgB ₂ wire according to claim 5 or 6, wherein the method is one selected from the group consisting of: The method for producing an MgB ₂ wire according to any one of claims 1 to 4, wherein the heat treatment is performed at 550 to 800 ° C. In the manufacturing method of MgB ₂ wire
(a) A mixed raw material of powdered Mg and B, or a mixed raw material obtained by mixing powdered Mg and B mixed powder and MgB ₂ powder,
(b) The resulting mixed raw material is compression molded into pellets,
(c) The resulting pellet is coated with a carbon-based material,
(d) Enclose the coated pellets in a metal tube,
(e) The metal pipe enclosing the pellet is drawn to form a wire, and
(f) A method for producing an MgB ₂ wire, wherein the obtained wire is heat-treated in an inert gas atmosphere or a pressurized atmosphere. The method for producing an MgB ₂ wire according to claim 9, wherein in (f), the obtained wire is wound in a coil shape and then heat-treated in an inert gas pressurized atmosphere. The method for producing an MgB ₂ wire according to claim 9, wherein the carbon-based material is a graphite-based material. The method for producing an MgB ₂ wire according to claim 9, wherein the wire drawing is performed in a plurality of times. The MgB _{2 according} to any one of claims 9 to 12, wherein the wire rod (metal body) obtained by the wire drawing is further coated with another metal tube and wire drawing is performed. A manufacturing method of a wire. A plurality of wire rods (metal bodies) obtained by the wire drawing process are coated with another metal pipe together with a metal material filling the gap, if necessary, and further wire drawing is performed. Item 15. The method for producing an MgB ₂ wire according to any one of Items 9 to 12. The metal tube enclosing the pellet and the another metal tube are the same or different, and one type selected from the group consisting of copper, copper alloy, iron, iron alloy, carbon steel, stainless steel, nickel and nickel alloy The method for producing an MgB ₂ wire according to claim 13 or 14, wherein the MgB ₂ wire is made of a metal. The method for producing an MgB ₂ wire according to any one of claims 9 to 12, wherein the heat treatment is performed at 550 to 800 ° C.

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