JPS602728B2 - Method for manufacturing compound composite superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compound composite superconductor, and more particularly to a method for producing a compound composite superconductor having a low resistance matrix.

Ultra-fine compound superconductors, which are made by forming compound superconductors such as Nb3Sn and V3Ga on the surface of ultra-fine core materials, are known as stable superconducting wires with no critical current anisotropy, but they are manufactured using the selective diffusion method. As a result, the matrix after the compound is formed has a high resistance, and when the superconducting coil is quenched, it generates a large amount of heat and sometimes burns out.

In order to overcome this drawback, various wire rods have been proposed until recently. For example, as shown in Figure 1, high purity copper 2
The copper-tin alloy 1 necessary for forming the N-rich Sn layer by selective diffusion method is separated by a niobium tube 3, or the outside of the copper-tin alloy matrix 1 as shown in FIG. There is a manufacturing method that has a structure in which a diffusion barrier of tantalum or the like 4 is provided to prevent tin in the copper-tin alloy from diffusing into the copper 2 even after the NCSn layer is formed.

However, all of these refining methods have problems with plastic workability because they manufacture composites using niobium or tantalum tubes, and the manufacturing process is complicated. There are also methods such as those described above in which a part of the steel-tin alloy matrix is replaced with copper without providing a diffusion barrier to form a composite, or after manufacturing a compound composite superconductor by selective diffusion method, solid solution in the matrix is used. There is also a method of selectively extracting and removing excess tin. However, the former method is not sufficient because the tin of the copper-tin alloy diffuses into the copper during the formation process of the N-wide Sn layer, resulting in a copper-tin diluted alloy. It has disadvantages that cannot be tolerated. An object of the present invention is to eliminate the above-mentioned conventional drawbacks, to provide a method for manufacturing a compound composite superconductor having a simple manufacturing method and a low-resistance matrix.

The present invention provides a compound composite superconductor with a twisted wire structure, an oxide layer provided on the surface of the twisted wire, and one of the composites constituting the twisted wire.
A low-resistance, normal-conducting metal is placed in the gap between the twisted wires to prevent a part of the compound-forming elements from diffusing into the low-resistance, normal-conducting metal during the compound layer forming heat treatment. The present invention relates to a method for manufacturing a compound composite superconductor.

More specifically, in a method for manufacturing a compound composite superconductor in which a composite containing a compound-forming element is burnished and then heat treated to form a compound superconducting layer, the surface of the stranded wires is oxidized and the voids between the strands are filled with A method for manufacturing a compound composite superconductor characterized by depositing a molten metal of a resistive normal conductive metal.

In another manufacturing method, a compound composite superconductor is manufactured by stranding a composite containing a compound-forming element and then heat-treating it to form a compound superconductor. and at least one low-resistance normally conductive metal on which an oxide layer is formed, and
A method for manufacturing a compound composite superconductor, characterized by forming a compound superconductor layer through heat treatment. The most characteristic feature of the present invention is that an oxide layer is provided on the surface of the stranded wire or on the surface of the composite that constitutes the stranded wire, and then heat treatment is performed during the attachment of a normal conductive metal or the formation of a compound. It must not be an oxide layer that peels off or decomposes.

The most preferred method for forming an oxide layer is to immerse the material in a solution containing an oxidizing agent, such as sodium hydroxide or potassium hydroxide, and then heat it in an oxidizing or neutral atmosphere. As the low-resistance normally conductive metal to be attached to the combustion line gap, aluminum is most preferable.

To attach molten aluminum, N public Sn, V30
It is possible near or below the formation temperature of compounds such as a,
Does not adversely affect the current characteristics of the compound layer. The presence of the oxide layer is extremely important because without the oxide layer, aluminum would react with the copper-tin alloy of the stranded wire matrix, forming a brittle compound layer at the interface, or react with tin, creating a high-resistance material. . When replacing a part of the composite material constituting the stranded wire with a low-resistance normally conductive metal, copper is most preferable in terms of strength;
Also, silver may be used.

Again, the presence of the oxide layer is important because without it, tin would diffuse into the steel or silver, resulting in an alloy with relatively high resistance. Next, details of the present invention will be specifically explained.

Example 1 FIG. 3 is a schematic cross-sectional view of a twisted wire of a composite containing NCSn compound-forming elements.

The composite has an outer diameter of 0.25 mm and is a multi-core structure having a core material of niobium-11% zirconium alloy 6 and a matrix of copper-10% tin alloy 1.
This composite was immersed in an aqueous solution containing sodium hydroxide and then heated in the atmosphere at 500 pm to form an oxide layer 7 several micrometers thick on the outer surface of the composite. After processing 7 strands, 10 at 700qo
After heat treatment for m hours, the surface of the niobium-1% zirconium core material 6 has a thickness of about 1 micrometer of Nb3Sn.
A compound superconducting layer was produced. Thereafter, it was immersed in a molten aluminum bath to adhere aluminum 5 to the voids of the stranded wires. The electrical resistance of this composite short wire was measured by the four-probe method at varying temperatures from room temperature to 2 K.

FIG. 5 shows the results in comparison with a conventional wire. Resistance was organized as a value per unit length of wire. Compared to the resistance value of 8 for a conventional wire material that uses a copper-tin alloy as a matrix and does not have an oxide layer or aluminum attached, the resistance value of the wire material of the present invention is 10, which is reduced to about 1 of 120 at 2K. I understand. Example 2 FIG. 4 is a schematic cross-sectional view of a stranded wire of a composite containing N-rich Sn compound-forming elements.

The composite has an outer diameter of 0.25 mm and has a multicore structure with a niobium-1% zirconium alloy 6 as a core material and a copper-10% tin alloy 1 as a matrix.
This composite and a copper wire of the same size are each immersed in an aqueous solution containing sodium hydroxide, and then heated in the atmosphere at 500°C to form an oxide layer several micrometers thick on the outer surface of the composite and the outer surface of the copper wire. 7 was formed. Next, four of these composites, three copper wires 2 with an oxide layer on the surface, and a fourth
After the wires were twisted as shown in the figure, they were heat-treated at 700 oo for 10 hours to form an N-rich Sn compound superconducting layer about 1 micrometer thick on the surface of the niobium-1% zirconium core material 6. The method for measuring the electrical resistance of this composite short wire was the same as in Example 1, and the measurement results are also shown in FIG.

Compared to the resistance value 9 of the conventional wire rod, which has a composite matrix of copper and copper-tin alloy and does not have an oxide layer attached, the resistance value 11 of the wire rod of the present invention is about 1/30th at 2 PK, -Resistance value of 5 compared to 8 of conventional wire village with tin alloy matrix
It was found that the value decreased to about 1/00. Comparing the effects of Examples 1 and 2 according to the present invention, it is found that the resistance value per unit length of the wire differs depending on the cross-sectional area of the wire, the type of low-resistance normal conductive material, the cross-sectional area ratio, etc. The bran material of the present invention, which prevents diffusion into the normally conductive metal by the oxide layer, has significantly reduced resistance.

In terms of the current density of the entire wire, Example 1 is preferable, but if the number of composite wires to be twisted increases, Example 2 also provides a matrix with low resistance. In the above description, only N-rich Sn was used as the compound superconductor, but it is clear that the method of the present invention can also be applied to V30a, which can be manufactured by a similar method.

Further, by roughly combining the methods of Examples 1 and 2, a compound composite superconductor having a matrix with even lower resistance can be manufactured without reducing the current density of the entire green material of Example 2. As is clear from the above description, the method of the present invention is simpler than conventional manufacturing methods, does not impair processability, and yields a compound composite superconductor having a matrix with low resistance.

Therefore, even if a large superconducting coil is manufactured using the compound composite superconductor manufactured by the manufacturing method of the present invention, the coil will not burn out during quenching, and the amount of evaporation of liquid helium will be small, making it extremely economical. .

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views for explaining conventional examples of compound composite superconductors, and Figures 3 and 4 are cross-sectional views for explaining examples of compound composite superconductors of the present invention. , FIG. 5 is a characteristic diagram comparing the resistance values of wire rods manufactured by the present invention and the conventional manufacturing method. Explanation of the symbols: 1... Copper-tin alloy, 2... Steel, 5... Aluminum, 6... Niobium-1% zirconium alloy, 7... Oxide layer. Hair diagram Hair Z diagram Figure 3 Figure 4 Hair S diagram

Claims (1)

[Claims] 1. A method for producing a compound composite superconductor in which a composite containing a compound-forming element is stranded and then heat-treated to form a compound superconducting layer, in which the surface of the stranded wires is oxidized and the strands are bonded to each other. A method for producing a compound composite superconductor characterized by attaching a melt of a low-resistance normal-conducting metal to a void. 2. In a method for producing a compound composite superconductor in which a composite body containing a compound-forming element is twisted and then heat-treated to form a compound superconducting layer, an oxide layer is formed on the surface of a plurality of composite bodies containing a compound-forming element. A compound composite superconductor characterized in that the composite and at least one low-resistance normal conductive metal having an oxide layer formed on its surface are stranded and heat treated to form a compound superconducting layer. manufacturing method.