CN111243818A - Superconducting joint of niobium-tin superconducting wire and niobium-titanium superconducting wire and preparation method thereof - Google Patents

Abstract

A superconducting joint of niobium-tritin superconducting wire and niobium-titanium superconducting wire and preparation method thereof, from the inside to the outside are Nb wire bundles, Nb ₃ Sn bulk distributed around the Nb wire bundles, Wood alloy and outermost layer respectively. Cu layer, and NbTi superconducting filaments are distributed in Wood's alloy. The Nb ₃ Sn bulk is obtained by sintering Nb powder, Sn powder and Cu powder. The Nb ₃ Sn/NbTi superconducting wire joint of the invention has the advantages of simple structure, low joint resistance and high structural strength.

Description

A kind of superconducting joint of niobium three tin superconducting wire and niobium titanium superconducting wire and preparation method thereof

technical field

The invention relates to a superconducting joint of Nb ₃ Sn superconducting wire and NbTi superconducting wire and a preparation method thereof.

Background technique

Since Onnis discovered superconductivity in 1911, superconducting technology has developed rapidly. Superconducting magnets are an important application part of superconducting technology. All use the strong magnetic field provided by superconducting magnets.

NbTi and Nb ₃ Sn superconductors are the most practical superconductors among low temperature superconductors. In engineering applications, the critical properties of the two superconductors, NbTi and Nb ₃ Sn superconductors, are designed to be used in combination with nested and interpolated superconducting magnets to provide The background magnetic field with a certain aperture is the most common way to use it. Among them, NbTi superconductor is a kind of superconducting alloy, which has good plasticity and can be machined. The conduction transition temperature of the NbTi superconducting wire is greater than 9K, and the upper critical magnetic field is about 11T at 4.2K. Nb ₃ Sn superconductor is an intermetallic compound, which is generally first made into a semi-finished wire, wound into a magnet, and then subjected to high temperature heat treatment to obtain the final Nb ₃ Sn superconducting phase. Nb ₃ Sn superconductor is an A15 phase structure, the superconducting transition temperature is greater than 18K, and the upper critical magnetic field can reach 25T at 4.2K.

The NbTi superconducting coil and the Nb ₃ Sn superconducting coil form an interpolated magnet, and the two coils need to be connected in series, so superconducting joints need to be made for the NbTi superconducting wire and the Nb ₃ Sn superconducting wire. The quality of the superconducting joint is very important for the overall magnet system. The existence of joint resistance will generate heat at the joint, which may cause the quench of the joint and even the quench of the overall magnet. In addition, the joint is a connection of two dissimilar materials, and the superconducting performance of the joint is difficult to achieve the performance of the original superconducting wire. Therefore, in the extreme environment where superconducting magnets operate, the joint is the weak point of the whole system, which requires key design and preparation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a superconducting joint of a niobium tritin superconducting wire and a niobium titanium superconducting wire and a preparation method thereof, so as to solve the problem that the joint resistance of the existing technology is relatively large.

The purpose of the present invention is achieved through the following technical solutions.

A superconducting joint of niobium three tin superconducting wire and niobium titanium superconducting wire, from the inside to the outside are niobium wire bundle, Nb ₃ Sn bulk distributed around the niobium wire bundle, Wood alloy and the outermost Cu layer, Wood NbTi superconducting filaments are distributed in the alloy.

The Nb ₃ Sn bulk is obtained by sintering Nb powder, Sn powder and Cu powder.

The preparation method of the niobium three tin superconducting wire and the niobium titanium superconducting wire superconducting joint of the present invention is as follows:

(1) The copper layer at the end of the Nb ₃ Sn superconducting wire and the NbTi superconducting wire is etched with nitric acid solution, the length of the corrosion section is 2cm-15cm, and the Nb multifilament, supporting core and NbTi superconducting wire end at the end of the Nb ₃ Sn superconducting wire are exposed. Part of NbTi multifilament;

(2) removing the support core at the end of the Nb ₃ Sn superconducting wire, and washing the Nb multifilament with deionized water and drying it;

(3) mix Nb powder, Sn powder and Cu powder, grind 20 minutes;

(4) Insert the Nb multifilament into the first copper cup, and then add the mixed powder of Nb powder, Sn powder and Cu powder. Heat the Nb ₃ Sn superconducting wire together with the copper cup at the end, the heat treatment temperature is 640-660 ℃, and the holding time is 180h-220h;

(5) Take out the Nb ₃ Sn superconducting wire and the first copper cup at the end, and corrode the copper cup with nitric acid to expose the sintered block;

(6) putting the sintered block into the second copper cup, and inserting the NbTi multifilament prepared in step (1) into the second copper cup;

(7) Heating the Wood alloy, pouring it into the second copper cup after melting, pouring NbTi multifilament, and then placing it to cool down.

The molar ratio of the Nb powder, the Sn powder and the Cu powder is 3:1:5, and the particle sizes of the Nb powder, the Sn powder and the Cu powder are 5 microns to 100 microns. The heating temperature of Wood and King is 100℃-120℃.

The Nb wire at the end of the Nb ₃ Sn superconducting wire of the present invention and the mixed powder of Nb powder, Sn powder and Cu powder are sintered into a Nb ₃ Sn block through powder sintering, and the current flows from the Nb ₃ Sn superconducting wire to the Nb ₃ Sn block. Resistive or low-resistance superconducting connections. The NbTi superconducting multifilament after the corrosion of the end of the NbTi superconducting wire cannot withstand the high temperature above 600 ℃, otherwise the superconducting performance of NbTi will be seriously degraded. Therefore, only the Nb ₃ Sn superconducting wire and the first copper cup at the end are heat-treated at the same time, and then the connection between the two materials of Nb ₃ Sn and NbTi is formed by adding superconducting solder. Wood's alloy is a superconducting solder that can cast a NbTi superconducting wire with a _Nb3Sn superconducting block to form a superconducting connection.

The method of testing the joint resistance of the invention adopts a direct measurement method, and the voltage at both ends of the Nb ₃ Sn/NbTi superconducting wire joint is measured by a nanovoltmeter, and then the ratio of the voltage to the current passing through the two ends reflects the resistance of the Nb ₃ Sn/NbTi superconducting wire joint.

Description of drawings

Figure 1 is a schematic cross-sectional view of a Nb ₃ Sn superconducting wire;

Figure 2 is a schematic cross-sectional view of a NbTi superconducting wire;

Figure 3 is a schematic structural diagram of the end of the Nb ₃ Sn superconducting wire after heat treatment;

4 is a schematic structural diagram of the Nb ₃ Sn/NbTi superconducting wire joint of the present invention.

Detailed ways

The present invention is further described below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 4 , the superconducting joints of the niobium three tin superconducting wire and the niobium titanium superconducting wire of the present invention are, from the inside to the outside, the niobium wire bundle, the Nb ₃ Sn bulk distributed around the niobium wire bundle, the Wood alloy and the outermost layer, respectively. The Cu layer, with NbTi superconducting filaments distributed in Wood's alloy. The Nb ₃ Sn bulk is obtained by sintering Nb powder, Sn powder and Cu powder.

The preparation method of the superconducting joint of the niobium three tin superconducting wire and the niobium titanium superconducting wire of the present invention is as follows:

The structure of the Nb ₃ Sn superconducting wire is shown in Fig. 1, the center of the copper tube is the supporting core, and the supporting mandrel in the copper tube is the bronze matrix and the Nb multi-wire. The structure of the NbTi superconducting wire is shown in Fig. 2, respectively, and the copper tube is composed of a copper matrix and NbTi wire.

(1) Etch the copper layer at the end of the Nb ₃ Sn superconducting wire and the NbTi superconducting wire with nitric acid solution, the length of the corrosion section is 2cm-15cm, and expose the Nb multifilament and supporting core at the end of the Nb ₃ Sn superconducting wire, as well as the NbTi superconducting wire NbTi polyfilaments at the ends;

(2) removing the support core at the end of the Nb ₃ Sn superconducting wire, and cleaning the Nb multifilaments with deionized water and drying them;

(3) Nb powder, Sn powder and Cu powder were mixed and ground for 20 minutes. The molar ratio of Nb powder, Sn powder and Cu powder is 3:1:5, and the particle size of Nb powder, Sn powder and Cu powder is 5 microns to 100 microns;

(4) Insert the Nb multifilament into the first copper cup 1, and then add the mixed powder of Nb powder, Sn powder and Cu powder, as shown in FIG. 3 . Heat the Nb ₃ Sn superconducting wire together with the copper cup at the end, the heat treatment temperature is 640-660 ℃, and the holding time is 180h-220h;

(5) The Nb ₃ Sn superconducting wire and the first copper cup 1 at the end were taken out, and the copper cup was etched with nitric acid to expose the sintered block. As shown in FIG. 4 , put the sintered block into the second copper cup 2, and insert the NbTi multifilament at the end of the NbTi superconducting wire into the second copper cup 2;

(6) Heating the Wood alloy at a heating temperature of 100°C-120°C, pouring it into the second copper cup 2 after melting, and pouring NbTi multifilaments. Then let it cool down.

Example 1

The copper layer at the end of Nb3Sn superconducting wire and NbTi superconducting wire was etched with nitric acid solution with a volume fraction of 40%. The length of the etching section was ₂ cm, and the Nb multifilament and supporting core at the end _of Nb3Sn superconducting wire were exposed, as well as the NbTi superconducting wire. NbTi multifilament at the end of the wire. The support core at the end of the Nb ₃ Sn superconducting wire was removed, and the Nb multifilament was washed with deionized water and then air-dried. The Nb powder, Sn powder and Cu powder were mixed and ground for 20 minutes, wherein the molar ratio of Nb powder, Sn powder and Cu powder was 3:1:5, and the particle size of Nb powder, Sn powder and Cu powder was 5 microns. Insert the Nb multifilament into the first copper cup 1, and then add the mixed powder of Nb powder, Sn powder and Cu powder. Heat the Nb ₃ Sn superconducting wire together with the copper cup at the end. The heat treatment temperature is 640°C and the holding time is 180h. The Nb ₃ Sn superconducting wire and the first copper cup 1 at the end were taken out, and the copper cup was etched with nitric acid to expose the sintered block. The sintered block is put into the second copper cup 2 , and the NbTi multifilament at the end of the NbTi superconducting wire is inserted into the second copper cup 2 . The Wood alloy is heated at a heating temperature of 100° C., poured into the second copper cup 2 after melting, and NbTi multifilament is poured. Then, it is placed to cool down, and a superconducting joint of Nb ₃ Sn and NbTi superconducting wire is obtained. After testing, the resistance of the joint is lower than the order of 1E-10.

Embodiment 2

The copper layer at the end of the Nb ₃ Sn superconducting wire and the NbTi superconducting wire was etched with a volume fraction of 50% nitric acid solution. The length of the etching section was 15 cm, and the Nb multifilament and supporting core at the end of the Nb ₃ Sn superconducting wire were exposed, as well as the NbTi superconducting wire. NbTi polyfilaments at the ends. The support core at the end of the Nb ₃ Sn superconducting wire was removed, and the Nb multifilament was washed with deionized water and then air-dried. The Nb powder, Sn powder and Cu powder were mixed and ground for 20 minutes, wherein the molar ratio of Nb powder, Sn powder and Cu powder was 3:1:5, and the particle size of Nb powder, Sn powder and Cu powder was 100 microns. Insert the Nb multifilament into the first copper cup 1, and then add the mixed powder of Nb powder, Sn powder and Cu powder. Heat the Nb ₃ Sn superconducting wire together with the copper cup at the end. The heat treatment temperature is 660°C and the holding time is 220h. The Nb ₃ Sn superconducting wire and the first copper cup 1 at the end were taken out, and the copper cup was etched with nitric acid to expose the sintered block. The sintered block is put into the second copper cup 2 , and the NbTi multifilament at the end of the NbTi superconducting wire is inserted into the second copper cup 2 . The Wood alloy is heated at a heating temperature of 120° C., poured into the second copper cup 2 after melting, and NbTi multifilament is poured. Then, it is placed to cool down, and a superconducting joint of Nb ₃ Sn and NbTi superconducting wire is obtained. After testing, the resistance of the joint is lower than the order of 1E-10.

Embodiment 3

The copper layer at the end _of Nb3Sn superconducting wire and NbTi superconducting wire was etched with 55% nitric acid solution. The length of the etching section was 10 cm, and the Nb multifilament and supporting core at the end _of Nb3Sn superconducting wire were exposed, as well as the NbTi superconducting wire. NbTi polyfilaments at the ends. The support core at the end of the Nb ₃ Sn superconducting wire was removed, and the Nb multifilament was washed with deionized water and then air-dried. The Nb powder, Sn powder and Cu powder were mixed and ground for 20 minutes, wherein the molar ratio of Nb powder, Sn powder and Cu powder was 3:1:5, and the particle size of Nb powder, Sn powder and Cu powder was 50 microns. Insert the Nb multifilament into the first copper cup 1, and then add the mixed powder of Nb powder, Sn powder and Cu powder. The Nb ₃ Sn superconducting wire is heat treated together with the copper cup at the end, the heat treatment temperature is 650 ℃, and the holding time is 200 h. The Nb ₃ Sn superconducting wire and the first copper cup 1 at the end were taken out, and the copper cup was etched with nitric acid to expose the sintered block. The sintered block is put into the second copper cup 2 , and the NbTi multifilament at the end of the NbTi superconducting wire is inserted into the second copper cup 2 . The Wood alloy is heated at a heating temperature of 110° C., poured into the second copper cup 2 after melting, and NbTi multifilament is poured. Then, it is placed to cool down, and a superconducting joint of Nb ₃ Sn and NbTi superconducting wire is obtained. After testing, the resistance of the joint is lower than the order of 1E-9.

Claims (4)

1. a superconducting joint of niobium three tin superconducting wire and niobium titanium superconducting wire, it is characterized in that: described joint is respectively Nb tow, the Nb ₃ Sn block that is distributed around the Nb tow, Wood from inside to outside. The alloy and the outermost Cu layer; the NbTi superconducting wire distributed in Wood's alloy; the Nb ₃ Sn bulk is obtained by sintering Nb powder, Sn powder and Cu powder. 2. superconducting joint according to claim 1, is characterized in that: the superconducting joint preparation step of described niobium three tin superconducting wire and niobium titanium superconducting wire is as follows: (1) The copper layer at the end of the Nb ₃ Sn superconducting wire and the NbTi superconducting wire is etched with nitric acid solution, the length of the corrosion section is 2cm-15cm, and the Nb multifilament and supporting core at the end of the Nb ₃ Sn superconducting wire are exposed, as well as the NbTi superconducting wire NbTi polyfilaments at the ends; (2) removing the support core at the end of the Nb ₃ Sn superconducting wire, and washing the Nb multifilament with deionized water and drying it; (3) mix Nb powder, Sn powder and Cu powder, grind 20 minutes; (4) Insert the Nb multi-wire into the first copper cup (1), then add the mixed powder of Nb powder, Sn powder and Cu powder; heat the Nb ₃ Sn superconducting wire together with the copper cup (1) at the end, heat treatment The temperature is 640-660℃, and the holding time is 180h-220h; (5) take out the Nb ₃ Sn superconducting wire and the first copper cup (1) at the end, and corrode the copper cup with nitric acid to expose the sintered block; (6) putting the block sintered in step (5) into the second copper cup (2), and inserting the NbTi multifilament obtained in step (1) into the second copper cup (2); (7) Heating the Wood alloy, pouring it into the second copper cup (2) after melting, pouring NbTi multifilament, and then placing it to cool down. 3. superconducting joint according to claim 2, is characterized in that: in the mixed powder of described Nb powder, Sn powder and Cu powder, the molar ratio of Nb powder, Sn powder and Cu powder is 3:1:5 , the particle size of Nb powder, Sn powder and Cu powder is 5 microns-100 microns. 4. The superconducting joint according to claim 2, wherein the heating temperature of the Wood alloy is 100°C-120°C.

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