CN110828059A - Hectometer-grade 37-core MgB2Magnesium diffusion preparation method of superconducting wire - Google Patents

Abstract

The invention discloses a magnesium diffusion preparation method of 100-meter-level 37-core _MgB2 superconducting wire. The method includes: first, mixing amorphous boron powder and nano-carbon powder and grinding to obtain mixed powder; second, mixing the mixed powder Filling the gap between the magnesium rod and the niobium tube to obtain the first tube-loaded composite; 3. Rotate the first tube-loaded composite to obtain a single-core wire; 4. Assemble 30 single-core wires and 7 CuNb rods to the Mongolian The second tube-loaded composite body is obtained from the Nair alloy tube; 5. The second tube-loaded composite body is swaged and drawn to obtain a 37-core wire rod; Six, 37-core MgB ₂ superconducting wire is obtained by sintering. The invention adopts the central magnesium diffusion method combined with nano carbon powder and 7-core CuNb rod to strengthen and generate dense MgB ₂ layer, which improves the critical current density of the MgB ₂ superconducting wire in the magnetic field, and improves the mechanical properties of the wire, so that the 37 The length of the core MgB ₂ superconducting wire is increased to 100 meters, which expands the use range of the MgB ₂ superconducting wire.

Description

A kind of magnesium diffusion preparation method of 100-meter-level 37-core MgB2 superconducting wire

technical field

The invention belongs to the technical field of superconducting material preparation, and in particular relates to a magnesium diffusion preparation method of a hundred-meter-level 37-core _MgB2 superconducting wire.

Background technique

Since its discovery in 2001, _{MgB 2} superconductors have attracted the attention of scientists at home and abroad because of their critical temperature of 39K, large coherence length, and no weak grain boundary connections. Magnets, low-speed and high-torque wind power motors and superconducting transmission cables are widely used.

There are a lot of holes in the MgB ₂ wire and strip prepared by the commonly used PIT (Powder In Tube) method, which reduces the effective current-carrying area of MgB ₂ , especially in the multi-core wire structure. To develop MgB ₂ superconducting wire with high critical current density, it is necessary to improve the density of superconducting core wire. In recent years, many researchers have begun to use the internal magnesium diffusion method (Internal Mg Diffusion, IMD) to produce MgB ₂ wire and strip, and the wire produced by this method is called the second-generation wire internationally. The IMD method places a magnesium rod at the center of the barrier layer and fills it with boron powder. During heat treatment, the molten magnesium rod penetrates into the boron powder to form a dense MgB layer. This method reduces the in _- situ method. A large number of holes are left after the powder reaction, and the obtained wire has an excellent critical current density.

Compared with single-core wire, multi-core wire can reduce the current loss. The central magnesium diffusion method (IMD) is very suitable for multi-core wires. Even at a temperature lower than the melting point of magnesium (650°C), magnesium can diffuse into the boron powder quickly, because the reaction between Mg and B is an exothermic reaction, which will The temperature around the magnesium core is increased, and the low-temperature heat treatment can inhibit the growth of grains, thereby improving the superconducting properties such as critical current density, and the dense MgB ₂ layer greatly improves the mechanical properties of the wire, which is more suitable for mass production.

At present, the main direction of MgB _{2 second} -generation wire preparation technology research is to obtain long-term wire processing technology and multi-core wire processing technology with practical value. In some reports on the preparation of 37-core MgB ₂ superconducting wire, the superconducting performance of the sample is very low, and only about one meter of wire can be prepared, which cannot meet the needs of the market.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a magnesium diffusion preparation method of 100-meter-level 37-core MgB ₂ superconducting wire aiming at the deficiencies of the above-mentioned prior art. The method adopts the central magnesium diffusion method combined with nano-carbon powder and 7-core CuNb rod for strengthening, and utilizes the molten magnesium rod in the heat treatment process to penetrate into the boron powder to form a dense _MgB layer, which improves the _MgB superconducting wire in the magnetic field. The critical current density in the MgB2 superconducting wire improves the mechanical properties of the wire, thereby increasing the length of the 37-core _MgB2 superconducting wire to the 100-meter level, and expanding the use range of the _MgB2 superconducting wire.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is: a magnesium diffusion preparation method of 100-meter-level 37-core MgB ₂ superconducting wire is characterized in that, the method comprises the following steps:

Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: (2-x): x, where the value of x ranges from 0.02 to 0.08;

In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, A first tube-loading composite is obtained; the diameter of the magnesium rod is 3.0mm-5.0mm;

Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 10% to 30%;

Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the single-core wire rod after drying, the CuNb rod after pickling and the Monel alloy tube are all the same;

Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain a 37-core wire; the pass processing rate of the swaging and drawing is 10% to 20%;

Step 6. After sealing both ends of the 37-core wire rod obtained in the step 5, put it into circulating argon for sintering to obtain 37-core MgB ₂ superconducting wire; the superconducting phase filling rate of the 37-core MgB ₂ superconducting wire is 8.5% or more, and the critical current density of the 37-core MgB ₂ superconducting wire at 4.2K and 4T is 5×10 ⁵ A/cm ² or more.

The invention adopts the central magnesium diffusion method to prepare 37-core _MgB2 superconducting wire rods and adopts 7-core CuNb rods to strengthen them, and utilizes the molten magnesium rods in the heat treatment process to penetrate into the boron powder to generate dense _MgB2 layers, thereby reducing the in-situ method. Magnesium powder penetrates into a large number of holes left by the boron powder reaction, which effectively improves the density of the MgB ₂ superconducting core wire, thereby increasing the critical current density of the MgB ₂ superconducting wire in the magnetic field, and the dense MgB ₂ layer bonding strengthens The strengthening effect of the rod greatly improves the mechanical properties of the wire, thereby increasing the length of the 37-core MgB ₂ superconducting wire to 100 meters, expanding the use range of the MgB ₂ wire; at the same time, the nano-carbon mixed in the boron powder The powder is doped in the MgB ₂ layer, which strengthens the connectivity of the MgB ₂ grains and effectively refines the grains. More grain boundaries formed by the grain refinement can form pinning centers, which improves the MgB ₂ superconducting wire. Critical current density in a magnetic field.

The above-mentioned magnesium diffusion preparation method of 100-meter-level 37-core _MgB2 superconducting wire is characterized in that the mass purity of the amorphous boron powder in step 1 is not less than 99%, and the particle size is 0.1 μm～10 μm; The mass purity of the nano carbon powder is not less than 99%. The quality, purity and particle size of the above-mentioned raw materials can ensure that the reaction proceeds smoothly during heat treatment.

The above-mentioned magnesium diffusion preparation method of 100-meter-level 37-core MgB ₂ superconducting wire is characterized in that the mass purity of the magnesium rod in step 2 is 99.9%-99.99%. High-quality and pure magnesium rods can ensure the formation of a thicker MgB ₂ superconducting reaction layer, which is beneficial to improve the mechanical properties of the wire.

The above-mentioned magnesium diffusion preparation method of 100-meter-level 37-core MgB ₂ superconducting wire is characterized in that the pickling of the niobium tube described in the step 2 and the pickling of the Monel alloy tube described in the step 4 are specific. The process is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydration with absolute ethanol, and drying at 50°C to 60°C; nitric acid in the mixed acid solution The mass concentration of hydrofluoric acid is 12% to 15%, and the mass concentration of hydrofluoric acid is 5% to 8%. The pickling process effectively removes oxides and impurities on the surface of the niobium tube and the Monel alloy tube, and ensures tight bonding between the core wires and the outer jacket.

The above-mentioned magnesium diffusion preparation method of 100-meter-level 37-core MgB ₂ superconducting wire is characterized in that the outer diameter of the niobium tube described in step 2 is 10mm-12mm, and the wall thickness of the niobium tube is 1mm-2mm; step The outer diameter of the Monel alloy tube described in Section 4 is 22mm-37mm, and the wall thickness is 1.5mm-3mm. The use of the above-mentioned larger outer jacket size is beneficial to increase the length of the wire.

The above-mentioned magnesium diffusion preparation method of 100-meter-level 37-core MgB ₂ superconducting wire is characterized in that the diameter of the 37-core wire in step 5 is 0.4 mm to 1.4 mm. The above-mentioned preferred diameter is the diameter range commonly used in practical applications, which improves the practical value of the preparation method of the present invention.

The above-mentioned magnesium diffusion preparation method of 100-meter-level 37-core MgB ₂ superconducting wire is characterized in that, the sintering process described in step 6 is: heating to 600 ℃ at a rate of 10 ℃/min～20 ℃/min After ～680℃, keep warm for 1h～5h, and then cool to room temperature with the furnace. The sintering process parameters can ensure that the superconducting layer reacts completely and generates a dense _MgB2 layer.

Compared with the prior art, the present invention has the following advantages:

1. The present invention adopts the central magnesium diffusion method combined with the reinforcement of 7-core CuNb rods to prepare 37-core _MgB2 superconducting wires, and utilizes the molten magnesium rods in the heat treatment process of the preparation to penetrate into the boron powder to generate dense _MgB2 layers, reducing It can effectively improve the density of MgB ₂ superconducting core wire, and then improve the critical current density of MgB ₂ superconducting wire in the magnetic field. The dense MgB The ₂ layers improve the mechanical properties of the wire, thereby increasing the length of the 37-core MgB ₂ superconducting wire to the 100-meter level, expanding the scope of use of the MgB ₂ superconducting wire.

2. The nano-carbon powder added to the raw boron powder of the present invention is doped in the MgB ₂ layer, which strengthens the connectivity of the MgB ₂ grains, effectively refines the grains, and forms more grain boundaries due to grain refinement. The pinning center can be formed, which further improves the critical current density of the _MgB2 superconducting wire in the magnetic field, and significantly reduces the current loss in practical applications.

3. The present invention increases the length of the 37-core MgB ₂ superconducting wire to 100 meters, and obtains a long-term wire processing technology and a multi-core wire processing technology with practical value, and the obtained MgB ₂ superconducting wire is 4.2K, 4T. The critical current density can reach more than 5×10 ⁵ A/cm ² ; the superconducting core of the MgB ₂ superconducting wire prepared by the invention has high density and superconducting phase filling rate of more than 8.5%, which meets the needs of practical applications.

4. The present invention adopts the Monel alloy tube as the outer sheath material, and adopts 7-core CuNb rod to strengthen it, which reduces the cost compared with the conventional oxygen-free copper tube, and at the same time significantly improves the mechanical strength and processing of the _MgB2 superconducting wire. performance.

The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments.

Description of drawings

1 is a metallographic diagram of a 37-core wire prepared in Example 1 of the present invention.

2 is a metallographic diagram of the 37-core MgB ₂ superconducting wire prepared in Example 1 of the present invention.

FIG. 3 is the critical current density curve at 4.2K of the 37-core MgB ₂ superconducting wire prepared in Example 1 of the present invention.

Detailed ways

Example 1

This embodiment includes the following steps:

Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: 1.95:0.05; the mass purity of the amorphous boron powder is 99.8%, and the particle size is 0.3 μm; the mass purity of the nano carbon powder is 99.5%;

In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, The first tube-loading composite was obtained; the diameter of the magnesium rod was 4.0 mm, and the mass purity was 99.95%; the outer diameter of the niobium tube was 10 mm, and the wall thickness of the niobium tube was 1 mm; The processes are: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 55°C; the mass concentration of nitric acid in the mixed acid solution is 12%, and the mass concentration of hydrofluoric acid is 5%;

Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 15%;

Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the dried single-core wire, the pickled CuNb rod and the Monel alloy tube are all the same; the outer diameter of the Monel alloy tube is 25mm, and the wall thickness is 3mm; The specific process of pickling the Monel alloy tube is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 55°C; The mass concentration of nitric acid in the mixed acid solution is 12%, and the mass concentration of hydrofluoric acid is 5%;

Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain a 37-core wire; the pass processing rate of the swaging and drawing is 10%; the diameter of the 37-core wire is 1.4 mm;

Step 6: Seal both ends of the 37-core wire rod obtained in Step 5 and put it into a circulating argon gas for sintering to obtain a 37-core MgB ₂ superconducting wire; the sintering process is: heating at a rate of 15°C/min The temperature was kept at 650°C for 2 hours, and then cooled to room temperature with the furnace; the superconducting phase filling rate of the 37-core MgB ₂ superconducting wire was 8.5%, and the critical value of the 37-core MgB ₂ superconducting wire at 4.2K, 4T The current density J _c was 5.0×10 ⁵ A/cm ² .

The length of the 37-core MgB ₂ superconducting wire prepared in this example can reach more than 100 meters.

Fig. 1 is a metallographic diagram of the 37-core wire prepared in this embodiment. It can be seen from Fig. 1 that the core wires are evenly distributed in the 37-core wire prepared in this embodiment, and the magnesium rod is at the center of the wire.

Fig. 2 is a metallographic diagram of the 37-core MgB ₂ superconducting wire prepared in this embodiment. It can be seen from Fig. 2 that the central magnesium rod and boron powder of the 37-core MgB ₂ superconducting wire prepared in this embodiment are completely reacted, resulting in Dense MgB ₂ layers.

Fig. 3 is the critical current density curve of the 37 _- core MgB ₂ superconducting wire prepared in this example at 4.2K. It can be seen from The critical current density J _c is 5.0×10 ⁵ A/cm ² , and it has excellent superconducting properties under medium and high magnetic fields.

Example 2

This embodiment includes the following steps:

Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: 1.92:0.08; the mass purity of the amorphous boron powder is 99%, and the particle size is 0.1 μm; the mass purity of the nano carbon powder is 99%;

In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, The first tube-packed composite body is obtained; the diameter of the magnesium rod is 4.0 mm, and the mass purity is 99.99%; the outer diameter of the niobium tube is 12 mm, and the wall thickness of the niobium tube is 2 mm; The process is: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 50 ° C; the mass concentration of nitric acid in the mixed acid solution is 15%, and the mass concentration of hydrofluoric acid is 8%;

Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 20%;

Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the dried single-core wire, the pickled CuNb rod and the Monel alloy tube are all the same; the outer diameter of the Monel alloy tube is 37mm, and the wall thickness is 3mm; The specific process of pickling the Monel alloy tube is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 50 °C; The mass concentration of nitric acid in the mixed acid solution is 15%, and the mass concentration of hydrofluoric acid is 8%;

Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain a 37-core wire; the pass processing rate of the swaging and drawing is 15%; the diameter of the 37-core wire is 0.4 mm;

Step 6: Seal both ends of the 37-core wire rod obtained in Step 5 and put it into circulating argon for sintering to obtain 37-core MgB ₂ superconducting wire; the sintering process is: heating at a rate of 20°C/min The temperature was kept at 600°C for 5 hours, and then cooled to room temperature with the furnace; the filling rate of the superconducting phase of the 37-core MgB ₂ superconducting wire was 8.60%, and the critical value of the 37-core MgB ₂ superconducting wire at 4.2K, 4T The current density J _c was 5.1×10 ⁵ A/cm ² .

The length of the 37-core MgB ₂ superconducting wire prepared in this example can reach more than 100 meters.

Example 3

This embodiment includes the following steps:

Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: 1.98:0.02; the mass purity of the amorphous boron powder is 99.9%, and the particle size is 10 μm; the mass purity of the nano carbon powder is 99.5%;

In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, The first tube-packed composite body is obtained; the diameter of the magnesium rod is 3.5 mm, and the mass purity is 99.9%; the outer diameter of the niobium tube is 10 mm, and the wall thickness of the niobium tube is 1.5 mm; the pickling of the niobium tube The specific processes are: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 60 ° C; the quality of nitric acid in the mixed acid solution The concentration is 13%, and the mass concentration of hydrofluoric acid is 7%;

Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 30%;

Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the dried single-core wire, the pickled CuNb rod and the Monel alloy tube are all the same; the outer diameter of the Monel alloy tube is 30mm, and the wall thickness is 2mm; The specific process of pickling the Monel alloy tube is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 60 °C; The mass concentration of nitric acid in the mixed acid solution is 13%, and the mass concentration of hydrofluoric acid is 7%;

Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain 37-core wire; the pass processing rate of the swaging and drawing is 20%; the diameter of the multi-core wire is 0.6 mm;

Step 6: Seal both ends of the 37-core wire rod obtained in Step 5 and put it into circulating argon for sintering to obtain 37-core MgB ₂ superconducting wire; the sintering process is: heating at a rate of 20°C/min The temperature was kept at 680°C for 1 h, and then cooled to room temperature with the furnace; the superconducting phase filling rate of the 37-core MgB ₂ superconducting wire was 8.58%, and the critical value of the 37-core MgB ₂ superconducting wire at 4.2K, 4T The current density J _c was 5.1×10 ⁵ A/cm ² .

The length of the 37-core MgB ₂ superconducting wire prepared in this example can reach more than 100 meters.

Example 4

This embodiment includes the following steps:

Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: 1.96:0.04; the mass purity of the amorphous boron powder is 99.9%, and the particle size is 10 μm; the mass purity of the nano carbon powder is 99.5%;

In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, The first tube-packed composite body is obtained; the diameter of the magnesium rod is 3.0 mm, and the mass purity is 99.9%; the outer diameter of the niobium tube is 11 mm, and the wall thickness of the niobium tube is 2 mm; the pickling of the niobium tube is specifically The process is: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 60 ° C; the mass concentration of nitric acid in the mixed acid solution is 13%, and the mass concentration of hydrofluoric acid is 7%;

Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 10%;

Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the single-core wire after drying, the CuNb rod after pickling and the Monel alloy tube are all the same; the outer diameter of the Monel alloy tube is 22mm, and the wall thickness is 1.5mm; The specific process of pickling the Monel alloy tube is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 60°C ; The mass concentration of nitric acid in the mixed acid solution is 13%, and the mass concentration of hydrofluoric acid is 7%;

Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain 37-core wire; the pass processing rate of the swaging and drawing is 20%; the diameter of the multi-core wire is 0.8 mm;

Step 6: Seal both ends of the 37-core wire rod obtained in Step 5 and put it into circulating argon for sintering to obtain 37-core MgB ₂ superconducting wire; the sintering process is: heating at a rate of 20°C/min The temperature was kept at 650°C for 2 hours, and then cooled to room temperature with the furnace; the superconducting phase filling rate of the 37-core MgB ₂ superconducting wire was 8.55%, and the critical value of the 37-core MgB ₂ superconducting wire at 4.2K, 4T The current density J _c was 5.2×10 ⁵ A/cm ² .

The length of the 37-core MgB ₂ superconducting wire prepared in this example can reach more than 100 meters.

Example 5

This embodiment includes the following steps:

Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: 1.94:0.06; the mass purity of the amorphous boron powder is 99.9%, and the particle size is 1 μm; the mass purity of the nano carbon powder is 99.9%;

In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, The first tube-packed composite body is obtained; the diameter of the magnesium rod is 3.5 mm, and the mass purity is 99.9%; the outer diameter of the niobium tube is 10 mm, and the wall thickness of the niobium tube is 1.5 mm; the pickling of the niobium tube The specific processes are: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 60 ° C; the quality of nitric acid in the mixed acid solution The concentration is 13%, and the mass concentration of hydrofluoric acid is 7%;

Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 30%;

Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the dried single-core wire, the pickled CuNb rod and the Monel alloy tube are all the same; the outer diameter of the Monel alloy tube is 30mm, and the wall thickness is 2mm; The specific process of pickling the Monel alloy tube is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 60 °C; The mass concentration of nitric acid in the mixed acid solution is 13%, and the mass concentration of hydrofluoric acid is 7%;

Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain a 37-core wire; the pass processing rate of the swaging and drawing is 20%; the diameter of the multi-core wire is 1.0 mm;

Step 6: Seal both ends of the 37-core wire rod obtained in Step 5 and put it into circulating argon for sintering to obtain 37-core MgB ₂ superconducting wire; the sintering process is: heating at a rate of 20°C/min The temperature was kept at 630°C for 3 hours, and then cooled to room temperature with the furnace; the superconducting phase filling rate of the 37-core MgB ₂ superconducting wire was 8.62%, and the critical value of the 37-core MgB ₂ superconducting wire at 4.2K, 4T The current density J _c was 5.3×10 ⁵ A/cm ² .

The length of the 37-core MgB ₂ superconducting wire prepared in this example can reach more than 100 meters.

Example 6

This embodiment includes the following steps:

Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: 1.95:0.05; the mass purity of the amorphous boron powder is 99.9%, and the particle size is 0.4 μm; the mass purity of the nano carbon powder is 99.5%;

In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, The first tube-loading composite was obtained; the diameter of the magnesium rod was 5.0 mm, and the mass purity was 99.95%; the outer diameter of the niobium tube was 11 mm, and the wall thickness of the niobium tube was 1 mm; The processes are: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 55°C; the mass concentration of nitric acid in the mixed acid solution is 14%, and the mass concentration of hydrofluoric acid is 6%;

Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 15%;

Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the dried single-core wire, the pickled CuNb rod and the Monel alloy tube are all the same; the outer diameter of the Monel alloy tube is 25mm, and the wall thickness is 3mm; The specific process of pickling the Monel alloy tube is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 55°C; The mass concentration of nitric acid in the mixed acid solution is 14%, and the mass concentration of hydrofluoric acid is 6%;

Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain a 37-core wire; the pass processing rate of the swaging and drawing is 10%; the diameter of the 37-core wire is 1.0 mm;

Step 6: Seal both ends of the 37-core wire rod obtained in Step 5 and put it into circulating argon for sintering to obtain 37-core MgB ₂ superconducting wire; the sintering process is: heating at a rate of 10°C/min The temperature was kept at 650°C for 3 hours, and then cooled to room temperature with the furnace; the filling rate of the superconducting phase of the 37-core MgB ₂ superconducting wire was 8.65%, and the critical value of the 37-core MgB ₂ superconducting wire at 4.2K, 4T The current density J _c was 5.25×10 ⁵ A/cm ² .

The length of the 37-core MgB ₂ superconducting wire prepared in this example can reach more than 100 meters.

The above descriptions are only preferred embodiments of the present invention, and do not limit the present invention in any way. Any simple modifications, changes and equivalent changes made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solutions of the present invention.

Claims (7)

1. the magnesium diffusion preparation method of a hundred meters of grade 37 core MgB ₂ superconducting wires, is characterized in that, the method comprises the following steps: Step 1. Mix the amorphous boron powder and the nano-carbon powder evenly in an argon-protected glove box, and then put it into an agate mortar and grind to obtain a mixed powder; the molar ratio of the amorphous boron powder and the nano-carbon powder is: (2-x): x, where the value of x ranges from 0.02 to 0.08; In step 2, the magnesium rod is polished with sandpaper, scrubbed with ethanol and air-dried in turn, and then loaded into the center of the niobium tube after pickling, and then the mixed powder obtained in step 1 is filled into the gap between the magnesium rod and the niobium tube, A first tube-loading composite is obtained; the diameter of the magnesium rod is 3.0mm-5.0mm; Step 3, sealing both ends of the first tube-loading composite obtained in Step 2 and performing rotary forging to obtain a single-core wire, and then performing straightening, sizing, cutting, pickling and drying in sequence on the single-core wire; The pass processing rate of the rotary forging is 10% to 30%; Step 4: Assembling 30 single-core wires dried in step 3 and 7 pickled CuNb rods into the pickled Monel alloy tube to obtain a second tube-packed composite; In the assembly process, the 7 CuNb rods after pickling were loaded into the center of the Monel alloy tube, and the 30 single-core wires after drying were arranged in a 2-layer annular structure around the CuNb rods in the circumferential direction and loaded into the Monel alloy. In the alloy tube; the lengths of the single-core wire rod after drying, the CuNb rod after pickling and the Monel alloy tube are all the same; Step 5. Perform swaging and drawing on the second tube-loading composite obtained in step 4 to obtain a 37-core wire; the pass processing rate of the swaging and drawing is 10% to 20%; Step 6. After sealing both ends of the 37-core wire rod obtained in the step 5, put it into circulating argon for sintering to obtain 37-core MgB ₂ superconducting wire; the superconducting phase filling rate of the 37-core MgB ₂ superconducting wire is 8.5% or more, and the critical current density of the 37-core MgB ₂ superconducting wire at 4.2K and 4T is 5×10 ⁵ A/cm ² or more. 2. the magnesium diffusion preparation method of a kind of 100-meter-level 37-core MgB superconducting wire according to claim ₁ , is characterized in that, the mass purity of amorphous boron powder described in step 1 is not less than 99%, particle diameter It is 0.1 μm～10 μm; the mass purity of the nano carbon powder is not less than 99%. 3 . The method for preparing magnesium diffusion of 100-meter grade 37-core MgB ₂ superconducting wire according to claim 1 , wherein the mass purity of the magnesium rod in step 2 is 99.9% to 99.99%. 4 . 4. the magnesium diffusion preparation method of a 100-meter grade 37-core MgB ₂ superconducting wire according to claim 1, is characterized in that, the pickling of niobium tube described in step 2 and Monel described in step 4 The specific process of pickling the alloy tube is as follows: pickling with a mixed acid solution composed of nitric acid solution, hydrofluoric acid solution and water, then dehydrating with absolute ethanol, and drying at 50℃～60℃; The mass concentration of nitric acid in the mixed acid solution is 12%-15%, and the mass concentration of hydrofluoric acid is 5%-8%. 5. The magnesium diffusion preparation method of a 100-meter-level 37-core MgB ₂ superconducting wire according to claim 1, wherein the outer diameter of the niobium tube in step 2 is 10mm～12mm, and the wall of the niobium tube The thickness is 1mm-2mm; the outer diameter of the Monel alloy tube in step 4 is 22mm-37mm, and the wall thickness is 1.5mm-3mm. 6 . The method for preparing magnesium diffusion of 100-meter-level 37-core MgB ₂ superconducting wire according to claim 1 , wherein the diameter of the 37-core wire in step 5 is 0.4 mm to 1.4 mm. 7 . 7. The magnesium diffusion preparation method of a 100-meter-level 37-core MgB ₂ superconducting wire according to claim 1, wherein the sintering process described in step 6 is: 10 ℃/min～20 ℃/ The temperature was raised to 600 ℃ ~ 680 ℃ at a rate of min, and then kept for 1 h to 5 h, and then cooled to room temperature with the furnace.

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