JP2002352648A - MgB2 superconducting wire and its manufacturing method - Google Patents

Abstract

(57) [Abstract] [Problem] Inexpensive MgB2 without using expensive Ta or Nb inner tube
A superconducting wire and a method for manufacturing the same are provided. SOLUTION: One or more MgB ₂ filaments are
A MgB ₂ superconducting wire characterized by being arranged in a matrix made of Cu or CuNi alloy, MgB ₂ powder or Mg
Prepared B ₂ green compact, packed in Cu tube or CuNi alloy tube to obtain MgB ₂ filaments performing sintering heat treatment after processing area reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an inexpensive MgB ₂ superconducting wire and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, conventional NbTi alloys and A15 type compounds have been developed.
Much higher critical temperature (about 3
New superconductor MgB with 9K)_TwoWas found. However
Et MgB _TwoIs fragile and poor in workability.
In this case, the following method is used. That is, first gold
MgB for genus_TwoPowder or MgB_TwoMaking billets by packing compacts
Then, wire it by swaging or die, or
Roll-rolled to reduce the surface area to obtain a predetermined shape. next
After heat treatment, MgB inside the wire_TwoContinuous sintering of powder
Form filament and finally obtain MgB2 superconducting wire
You.

In order to obtain a composite multifilamentary wire, the following 2
Different methods are employed. First, the first method is to fill a metal tube with MgB ₂ powder or MgB ₂ compact to prepare a composite rod with a reduced surface area, and then pack a plurality of the bars into a metal tube to prepare a composite multi-core billet. This is similarly subjected to sintering heat treatment after surface reduction. As a second method, a multi-core multi-filament billet is produced by filling a porous metal tube with MgB ₂ powder or MgB ₂ compact, and after reducing the surface area, sintering heat treatment is performed.

[0004]

In the prior art, as the metal tube, a double tube having an outer tube made of Cu or a Cu alloy disposed around the inner tube made of Ta or Nb has been used. The reason that Ta or Nb is used for the inner tube is that all of these metals have good workability and are high melting point metals,
This is because hardly react with the MgB _2. On the other hand, Cu
Cu and Cu alloys are used because they are easy to process, and parts that do not come into contact with MgB ₂ can be replaced with inexpensive materials to reduce material costs.

[0005] However, Ta and Nb used as the inner tube of the metal tube are expensive, and if the thickness of the inner tube is reduced to reduce the amount of use, on the other hand, the work of thinning is increased and the cost is increased. In other words, using an inner tube made of Ta or Nb
Which is a factor raising the manufacturing costs of the B ₂ compound superconducting wire.

The present invention has been made in view of such a situation, and has been made as a result of intensive research. It is an object of the present invention to provide an inexpensive MgB2 superconducting wire without using an expensive inner tube of Ta or Nb and a method of manufacturing the same. It is in.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, a first aspect of the present invention is a method wherein one or more MgB ₂ filaments are arranged in a matrix made of Cu or CuNi alloy. MgB ₂ superconducting wire characterized in that:

In a second embodiment of the present invention, MgB ₂ powder or MgB ₂ compact is prepared, packed in a Cu tube or CuNi alloy tube, subjected to surface reduction processing, and then subjected to a sintering heat treatment to obtain an MgB ₂ filament. A method for producing an MgB ₂ superconducting wire, characterized in that:

[0009]

Embodiments of the present invention will be described below. In the present invention, the MgB ₂ powder, or its compact, a Cu tube,
Or packed directly CuNi alloy tube, it is possible to obtain MgB ₂ filaments performing sintering heat treatment after processing area reduction.
That is, MgB _{2 in} a Cu or CuNi alloy matrix
A superconductor having a structure in which filaments are arranged can be obtained.

[0010] MgB ₂ powder green compact is prepared which were produced MgB ₂ powder to a desired size by cold isostatic working packed into a rubber container. Next, MgB ₂ powder or a compact of MgB ₂ powder is packed in a metal tube to produce a billet, which is drawn by swaging or die, or further roll-rolled to reduce the surface area, thereby obtaining a predetermined shape. I do. In order to obtain a composite multifilamentary wire, the composite rod several of working area reduction stuffed MgB ₂ powder or green compact metal tube,
Additionally, or packed in a metal tube, and or a plurality of stuffed MgB ₂ powder and a green compact a composite multi-core billet in perforated metal tube, which was reduction process similar to a predetermined shape.

Next, a sintering heat treatment is performed on the predetermined shape. The sintering heat treatment may be performed, for example, at 900 ° C. for 2 hours in an Ar gas atmosphere. Note that the heat treatment temperature is 650 ° C or higher and 1100 ° C
It is desirable that: Temperature is insufficient sintering between MgB ₂ particles low, whereas, for many the temperature is high the MgB ₂ are changes or composition MgB _4, can not be obtained a high critical current value in either case.

In the present embodiment, the metal in contact with MgB ₂ is:
It is desirable to use Cu or CuNi alloy. CuNi alloy is
The Ni content can be freely selected in consideration of the balance between the mechanical strength of the metal tube and the production cost.

The reason for using Cu or CuNi alloy will be described below. Since the sintering heat treatment performed after the vanishing surface processing is at a high temperature, it was conventionally thought that Cu and Ni dissolved in the MgB ₂ crystal lattice to change the lattice constant and impair the superconducting performance. However, the present inventors have found that such a solid solution phenomenon does not occur.

That is, MgB_TwoAbout Cu or CuNi
When in contact with the alloy, some Mg bonds with Cu or Ni
Mg-Cu compound or Mg-Ni compound is formed on the metal tube side
You. MgB deprived of Mg_TwoIs MgB_FourOr MgB₇Heto High B Dark
Decomposes into compounds with high B concentration
It has a high melting point and is difficult to decompose. Therefore, the inside of the metal tube
MgB loaded_TwoHigh B concentration compound at the interface between
The layer is formed thin, MgB _TwoMg diffusion from metal to metal tube is remarkable
Be inhibited.

On the other hand, since Cu and Ni hardly dissolve in B and Mg, they do not distort the MgB ₂ crystal structure. Of course,
Since part of the outer periphery of the MgB ₂ filling part (the part in contact with the metal tube) is decomposed into MgB ₄ and MgB ₇ as normal conducting substances, strictly speaking, the area of the superconducting part decreases and the critical current decreases, The degree of the decrease is only slight, and there is no practical problem.

Further, the CuNi alloy has an advantage that the workability is good within the range of the entire Ni concentration. Therefore, the Ni content of the CuNi alloy tube can be freely selected in consideration of the balance between the mechanical strength of the metal tube and Ni, which is higher than that of Cu.

In order to adjust the crystal grain size of the normal conducting matrix and to improve the mechanical strength of Cu or CuNi alloy tubes, B or Mg
Au, Ba, Be, Bi, C, Ca, Ce, Co, C with low solubility in
It is also possible to add r, Fe, Gd, Ge, Hf, La, Ta, and Ti individually or in a plural number as long as the superconductivity is not significantly impaired. Further, a method of dispersing MgO particles in Cu or CuNi alloy is also effective for improving mechanical strength. This is because MgO is hard and the bonding force between Mg and O is extremely strong, so that it is not decomposed by heat treatment during sintering and does not contaminate MgB ₂ particles.

EXAMPLES (Example 1) 99% of the MgB ₂ powder packed into a rubber container, cold isostatic processed outer diameter at a pressure of 100Mpa is to prepare a green compact of 9.8 mm. Next, compact the compact with an inner diameter of 10 mm and an outer diameter of
After putting in a 14 mm Cu tube, fit Cu lids on both ends of the tube,
The fitted portion was electron beam welded in a vacuum to produce a composite billet. Next, the billet was reduced in surface area to 1.0 mm in diameter by swaging and die drawing, and then roll-rolled to produce a tape having a thickness of 0.15 mm and a width of 3.4 mm.
Next, this tape was heat-treated at 900 ° C. for 2 hours in an Ar gas atmosphere. FIG. 1 shows a cross section of the tape after the heat treatment. Figure 1
In the figure, reference numeral 1 is a MgB2 sintered rod. Symbol 2 is a MgB4 and MgB7 producing compound. Reference numeral 3 denotes a Cu tube.

(Embodiment 2) The metal tube is made of CuNi (30wt% Ni) alloy, the other conditions are the same as in Embodiment 1, and the thickness is 0.15 m.
m, a tape having a width of 3.4 mm was produced. Next, this tape
Heat treatment was performed at 900 ° C. for 2 hours in an Ar gas atmosphere. FIG. 2 shows a cross section of the tape after the heat treatment. In FIG. 2, reference numeral 1 denotes MgB
2 is a sintered rod. Symbol 2 is a MgB4 and MgB7 producing compound. Reference numeral 5 denotes a CuNi (30 wt% Ni) tube.

(Example 3) The MgB ₂ -Cu composite round wire having a diameter of 1.0 mm before heat treatment used in Example 1 was cut into a predetermined length,
These seven pieces were again packed in a Cu tube with an inner diameter of 3.2 mm and an outer diameter of 6 mm, Cu lids were fitted at both ends, and the fitted part was electron beam welded in vacuum to produce a composite multi-core billet . Billet diameter 1.0mm by swaging and die drawing
After reducing the surface area, roll rolling was performed to produce a tape having a thickness of 0.15 mm and a width of 3.4 mm. Next, this tape was heat-treated at 900 ° C. for 2 hours in an Ar gas atmosphere. FIG. 3 shows a cross section of the tape after the heat treatment. In FIG. 3, reference numeral 1 denotes MgB2
It is a sintered rod. Symbol 2 is a MgB4 and MgB7 producing compound. Reference numeral 3 denotes a Cu tube. Reference numeral 4 denotes a Cu tube including those indicated by reference numerals 1 to 3.

Comparative Example 1 A metal tube having an inner diameter of 10.0 mm and an outer diameter of
The processing conditions were the same as in Example 1, except that the inner tube was made of 10.6 mm Nb and the inner diameter was 10.8 mm, and the outer diameter was made of 14 mm Cu outer tube.
A tape having a thickness of 0.15 mm and a width of 3.4 mm was produced. next,
This tape was heat-treated at 900 ° C. for 2 hours in an Ar gas atmosphere. FIG. 4 shows a cross section of the tape after the heat treatment. In FIG. 4, reference numeral 1 denotes a MgB2 sintered rod. Reference numeral 6 denotes an Nb tube. Reference numeral 3 denotes a Cu tube. Reference numeral 3 denotes a Cu tube.

(Comparative Example 2) MgB ₂ compacts having an outer diameter of 9.8 mm were packed in a Nb tube having an inner diameter of 10 mm and an outer diameter of 10.6 mm, and then they were packed with an inner diameter of 10.8 mm and an outer diameter of 14 mm. Put in a Cu outer tube, Cu ends
A composite billet was prepared by fitting a lid made of aluminum and welding the fitted portion with an electron beam in a vacuum. After reducing the billet to a diameter of 1.0 mm by swaging and die drawing, the composite round wire was cut to a certain length, and these seven were again reduced in inner diameter.
It was packed in a 3.2 mm, 6 mm outside diameter Cu tube, fitted with Cu lids at both ends, and the fitted portion was electron beam welded in a vacuum to produce a composite multifilament billet.

After the billet is reduced to 1.0 mm in diameter by swaging and die drawing, roll rolling is performed.
A tape having a thickness of 0.15 mm and a width of 3.4 mm was produced. next,
This tape was heat-treated at 900 ° C. for 2 hours in an Ar gas atmosphere. FIG. 5 shows a cross section of the tape after the heat treatment. In FIG. 5, reference numeral 1 denotes a MgB2 sintered rod. Reference numeral 6 denotes an Nb tube. Reference numeral 3 denotes a Cu tube. Reference numeral 4 denotes a Cu tube including those indicated by reference numerals 1, 3, and 6.

With respect to the heat-treated products of Examples 1 to 3 and Comparative Examples 1 and 2, the interface between the MgB ₂ sintered filament and the metal tube was observed. In Examples 1 and 3 using a Cu tube, a heterogeneous phase having a thickness of 0.5 μm was formed at the interface, and when analyzed, it was a mixture of MgB ₄ and MgB ₇ . In Example 2 using CuNi (30 wt% Ni) alloy, a heterogeneous phase with a thickness of about 0.3 μm was generated at the interface, and when analyzed, MgB ₄ and MgB ₇ , and a trace amount of Ni were detected. . On the other hand, in the comparative example using the Nb inner tube, no heterophase was detected at the interface between the MgB ₂ and the Nb tube.

From the heat-treated products of Examples 1 to 3 and Comparative Examples 1 and 2, samples were taken from three places, and critical current measurement was performed in liquid helium by a four-terminal method. On the other hand, a cross-sectional photograph of each sample after the heat treatment was taken, and the area of the portion other than the metal tube was calculated. The obtained critical current value was divided by the area of the portion other than the metal tube to calculate a critical current density (hereinafter referred to as Jc) of the portion other than the metal tube. The results are shown in Table 1 as FIG.

As is evident from Table 1, there is almost no difference between the single-core wires Jc of Examples 1 and 2 of the present invention and Jc of Comparative Example 1.
Similarly, in comparison between multifilamentary wires, Jc of Inventive Example 3 and Jc of Comparative Example 2
There is almost no difference in Jc. Therefore, according to the present invention, it is possible to obtain equivalent superconducting characteristics without using expensive Ta tubes or Nb tubes.

[0026]

According to the manufacturing method of the MgB ₂ superconductive wire of the present invention can be produced efficiently MgB ₂ superconducting wire having excellent characteristics.
Therefore, the industrial contribution is remarkable.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a cross section of a Cu sheath single core tape (after heat treatment) of Example 1 of the present invention.

FIG. 2 is an explanatory diagram showing a cross section of a CuNi sheath single core tape (after heat treatment) of Example 2 of the present invention.

FIG. 3 is an explanatory view showing a cross section of a Cu sheath multi-core tape (after heat treatment) of Example 3 of the present invention.

FIG. 4 is an explanatory diagram showing a cross section of an Nb / Cu composite sheath single core tape (after heat treatment) of Comparative Example 1 manufactured by a conventional method.

FIG. 5 is an explanatory diagram showing a cross section of an Nb / Cu composite sheath multicore tape (after heat treatment) of Comparative Example 2 manufactured by a conventional method.

FIG. 6 shows measurement results of Examples and Comparative Examples shown in Table 1.

[Explanation of symbols]

 1 MgB2 sintered rod 2 MgB4 and MgB7 forming compound 3 Cu tube 4 Cu tube 5 CuNi (30wt% Ni) tube 6 Nb tube

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 35/58 C04B 35/58 105Y

Claims (2)

[Claims] (1) one or more MgB ₂ filaments,
An MgB ₂ superconducting wire, which is arranged in a matrix made of a Cu or CuNi alloy. 2. A prepared MgB ₂ powder or MgB ₂ powder compact, packed in Cu tube or CuNi alloy tube subjected to sintering heat treatment after machining area reduction, MgB _2, characterized in that to obtain MgB ₂ filaments Superconducting wire manufacturing method.