Method for reducing magnetic hysteresis loss of IMD method MgB2 superconducting wire

Abstract

The invention discloses a method for reducing magnetic hysteresis loss of an IMD method MgB2 superconducting wire, which relates to the technical field of superconducting wires and comprises the following steps: inserting a first Mg rod into the center of a metal sheath; inserting a second Mg rod between the first Mg rod and the metal sheath, and filling B powder among the first Mg rod, the second Mg rod and the metal sheath to obtain a circular single-core rod; inserting the oxygen-free Cu rod and the circular single-core rod into the NCu30 pipe to obtain a multi-core composite wire; and performing heat treatment on the multi-core composite wire to obtain the MgB2 superconducting wire. The structure of the cylindrical MgB2 superconducting core wire in the IMD method wire is broken through the second Mg rod, so that the magnetic hysteresis loss of the IMD method MgB2 superconducting wire is greatly reduced on the basis of not influencing the current-carrying performance of the MgB2 superconducting layer. Mg and B are promoted to react more thoroughly, a superconducting phase is generated, and the current-carrying performance of the MgB2 superconducting layer is improved.

Description

Technical Field

[0001] This invention relates to the field of superconducting wire technology, and in particular to a method for reducing hysteresis loss in MgB2 superconducting wires produced by the IMD method. Background Technology

[0002] The applications of superconducting materials are generally divided into two categories: direct current (DC) and alternating current (AC). DC refers to a steady-state magnetic field (or generated magnetic field) that does not change over time. AC refers to an oscillating magnetic field (or generated magnetic field) that enters and exits the superconducting material at a certain frequency. This results in heat loss within the superconducting material, also known as AC loss. AC loss corresponds to heat dissipation within the superconducting material. Excessive AC loss can cause localized overheating or even eventual loss of superconductivity, increasing cooling costs and seriously threatening the stability and safety of the superconducting material.

[0003] Hysteresis loss can be calculated by measuring the hysteresis loop of a sample, generally corresponding to the area of ​​the hysteresis region within the hysteresis loop. A larger hysteresis region indicates higher hysteresis loss. According to the Bean critical state model, an important model in superconducting flux pinning, the critical current density Jc can be expressed as: ,in It is a quantity related to the sample shape and the relative position of the sample and the magnetic field. This represents the width of the hysteresis loop. The hysteresis loss Q can be expressed as: The critical current density Jc is an intrinsic property of superconducting materials. It is the magnetization intensity, therefore it can be changed To change the hysteresis loss of superconducting wires.

[0004] MgB2 superconducting wires can be classified into PIT (Particle Injection) and IMD (Integrated Molding) methods based on their fabrication processes. The PIT method involves filling a metal sheath with a mixture of magnesium and boron powders or MgB2 powder. After heat treatment, the entire core wire becomes a superconducting wire, which is cylindrical in shape. Based on the Bean critical state model, the critical current density Jc and hysteresis loop width of the cylindrical superconducting wire... The formula is: Where R is the radius of the cylindrical superconducting wire. Therefore, the hysteresis loss of the superconducting wire can only be reduced by thinning the core. However, the IMD method is different. It inserts a magnesium rod into the center of a metal sheath, and then fills the space between the magnesium rod and the metal sheath with boron powder. In the final heat treatment stage, the magnesium in the center diffuses into the surrounding boron powder to form a MgB2 superconducting layer, leaving a huge hole in the center of the core wire. The area of ​​the superconducting layer is basically equal to or even smaller than the area of ​​the hole, so the superconducting core wire is cylindrical. According to the Bean critical state model, the critical current density Jc and hysteresis loop width of the cylindrical superconducting core wire of the MgB2 superconducting wire manufactured by the IMD method are... The formula is: , where R out Let Rin be the outer radius of the cylinder, and Rin be the inner radius of the cylinder. Assuming the area of ​​the superconducting layer is equal to the area of ​​the pore, then Rin... in =0.7R out Substituting into the above formula, we can obtain That is, reducing the hysteresis loop will significantly reduce the critical current density Jc. Summary of the Invention

[0005] This invention provides a method for reducing hysteresis loss in MgB2 superconducting wires using the IMD method, thereby addressing the problem in the prior art where the IMD method significantly reduces the critical current density Jc while reducing the hysteresis loop.

[0006] On one hand, embodiments of the present invention provide a method for reducing hysteresis loss in MgB2 superconducting wires using the IMD method, comprising: The acid-washed first Mg rod is inserted into the center of the metal sheath; A second Mg rod is inserted between the first Mg rod and the metal sheath, wherein the diameter of the first Mg rod is larger than that of the second Mg rod; A single-core rod material is obtained by filling B powder between the first Mg rod, the second Mg rod and the metal sheath. The single-core rod material is rotary forged to obtain a circular single-core rod; The acid-washed oxygen-free Cu rod and the acid-washed circular single-core rod are inserted into the acid-washed NCu30 tube to obtain a multi-core composite wire blank. The multi-core composite wire blank is subjected to drawing, rotary forging and rolling processes to obtain the multi-core composite wire; The multi-core composite wire was heat-treated to obtain MgB2 superconducting wire.

[0007] In one possible implementation, the metal sheath is either a niobium tube or a composite sheath with an inner niobium tube and an outer oxygen-free Cu tube.

[0008] In one possible implementation, multiple second Mg rods are provided, with the multiple second Mg rods arranged around the first Mg rod.

[0009] In one possible implementation, filling the space between the first Mg rod, the second Mg rod, and the metal sheath to obtain the single-core rod material further includes: The B powder between the first Mg rod, the second Mg rod, and the metal sheath is oscillated using an ultrasonic transducer.

[0010] In one possible implementation, the first Mg rod is a circular wire, and the second Mg rod is one or more of a circle and a polygon.

[0011] In one possible implementation, the cross-section of the multi-core composite wire is circular.

[0012] The method for reducing hysteresis loss in MgB2 superconducting wires using the IMD method, as described in this invention, has the following advantages: (1) By breaking the cylindrical MgB2 superconducting core wire configuration in the IMD method wire by using the second Mg rod, the hysteresis loss of the IMD method MgB2 superconducting wire is greatly reduced without affecting the current carrying capacity of the MgB2 superconducting layer.

[0013] (2) By increasing the contact area between the Mg rod and the B powder through the second Mg rod, the reaction between Mg and B is more thorough and a superconducting phase is generated, which helps to improve the current carrying capacity of the MgB2 superconducting layer. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 A flowchart illustrating a method for reducing hysteresis loss in MgB2 superconducting wires using the IMD method, provided in this application embodiment; Figure 2 A schematic cross-sectional view of a MgB2 superconducting wire used in an embodiment of this application to illustrate a method for reducing hysteresis loss in MgB2 superconducting wire using the IMD method. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Figure 1 This is a flowchart illustrating a method for reducing hysteresis loss in MgB2 superconducting wires using the IMD method, provided by an embodiment of the present invention. The method includes: The acid-washed first Mg rod is inserted into the center of the metal sheath; A second Mg rod is inserted between the first Mg rod and the metal sheath, wherein the diameter of the first Mg rod is larger than that of the second Mg rod; A single-core rod material is obtained by filling B powder between the first Mg rod, the second Mg rod and the metal sheath. The single-core rod material is rotary forged to obtain a circular single-core rod; The acid-washed oxygen-free Cu rod and the acid-washed circular single-core rod are inserted into the acid-washed NCu30 tube to obtain a multi-core composite wire blank. The multi-core composite wire blank is subjected to drawing, rotary forging and rolling processes to obtain the multi-core composite wire; The multi-core composite wire was heat-treated to obtain MgB2 superconducting wire.

[0018] The metal sheath is one of a niobium tube or a composite sheath with an inner niobium tube and an outer oxygen-free Cu tube.

[0019] Multiple second Mg rods are provided, and the multiple second Mg rods are arranged around the first Mg rod.

[0020] The process of filling B powder between the first Mg rod, the second Mg rod, and the metal sheath to obtain a single-core rod material further includes: oscillating the B powder between the first Mg rod, the second Mg rod, and the metal sheath using an ultrasonic transducer.

[0021] The first Mg rod is a round wire, and the second Mg rod is one or more of round and polygonal shapes.

[0022] The cross-section of the multi-core composite wire is circular.

[0023] For example, such as Figure 1 , 2As shown, the IMD method involves inserting a magnesium rod into the center of a metal sheath, and then filling the space between the magnesium rod and the metal sheath with boron powder. During the final heat treatment stage, the magnesium in the center diffuses into the surrounding boron powder to form a MgB2 superconducting layer, leaving a large hole in the center of the core wire. The area of ​​the superconducting layer is approximately the same as or even smaller than the area of ​​the hole, thus the superconducting core wire is cylindrical. According to the Bean critical state model, the critical current density Jc and the hysteresis loop width of the cylindrical core wire are... The formula can be expressed as: , where R out R is the radius of the outer ring of the cylinder. in Let Rin be the inner radius of the cylinder. Assuming the area of ​​the superconducting layer and the area of ​​the pores are the same, then Rin = 0.7R. out Substituting into the above formula, we can obtain If a cut can be made in the cylindrical shape, the cylinder can then be unfolded into a shape with a width of approximately R. out -R in =0.3R out Its length is approximately π / 0.6R out The cuboid, at this point, according to the rectangular Bean critical state model, has ), where b is the shorter side and a is the longer side, substituting them gives us It can break the cylindrical configuration without reducing the critical current density J of the superconducting core wire. c This can significantly reduce the hysteresis loop width of superconducting wires. This reduces hysteresis loss Q.

[0024] The first Mg rod, after being pickled, is inserted into the center of the metal sheath. A certain number of second Mg rods with smaller diameters are then inserted between the first Mg rod and the metal sheath. B powder is then filled between the second Mg rods and the metal sheath, and the rod is processed into a round single-core rod using processes such as rotary forging and rolling.

[0025] The B powder is C-coated B powder with an average particle size of 20nm~500nm and a C mass fraction of 0%~10% in the powder; the first Mg rod inserted in the center has a purity of 99.00%~99.99% and a diameter of 4.00mm~20.00mm; the second Mg rod inserted in the center has a purity of 99.00%~99.99% and a diameter of 1.00mm~5.00mm, and the number is 1~4; the metal sheath is a niobium tube, or a composite of an inner niobium tube and an outer oxygen-free Cu tube. The cladding consists of Nb tubes with a purity of 99.0%~99.9%, an outer diameter of 8.00mm~50.00mm, and a thickness of 1.00mm~10.00mm; and oxygen-free Cu tubes with a purity of 99.0%~99.9%, an outer diameter of 10.00mm~70.00mm, and a thickness of 1.00mm~10.00mm. The forging and rolling processes involve a pass-by-pass machining allowance of 5%~25%, resulting in a final circular single-core rod with a diameter of 2.00mm~10.00mm.

[0026] After being pickled, round single-core rods and oxygen-free Cu rods are inserted into pickled NCu30 tubes and processed into multi-core composite wires of specific specifications using processes such as drawing, rotary forging and rolling.

[0027] The oxygen-free Cu rod has a circular cross-section, a purity of 99.90%~99.99%, and a diameter of 2.00mm~30.00mm; the NCu30 tube has an outer diameter of 20mm~70mm, a wall thickness of 2mm~10mm, and is in the annealed state; the per-pass machining amount in the drawing, forging, and rolling processes is 5%~25%, and the final multi-core composite wire has a circular cross-section with a diameter of 0.5mm~2mm.

[0028] Finally, the multi-core composite wire is heat-treated to produce MgB2 superconducting wire.

[0029] The heat treatment temperature range is 550℃~900℃, the holding time is 0.5h~20h, and the heat treatment conditions are a vacuum or high-purity Ar gas environment, with a vacuum degree <10Pa and a high-purity Ar gas purity >90%.

[0030] In one possible embodiment, Example 1, this example includes the following steps: Step 1: Insert the first Mg rod, after pickling, into the center of the metal sheath. The Mg rod has a purity of 99.00% and a diameter of 4.00 mm. The metal sheath is an Nb / Cu composite sheath, with an inner Nb tube (99.0% purity, 8 mm outer diameter, 1 mm thickness) and an outer oxygen-free Cu tube (99.0% purity, 10 mm outer diameter, 1 mm thickness). Insert a second Mg rod between the metal sheath and the first Mg rod. The second Mg rod has a purity of 99.00% and a diameter of 1.00 mm. Fill the space between the first Mg rod, the second Mg rod, and the metal sheath with boron powder. The average particle size of the boron powder coated with carbon (C) is 20 nm, and the mass fraction of carbon in the powder is 0%. The rod is then processed into a circular single-core rod using drawing, rotary forging, and rolling, with a pass weight of 5%. The final diameter of the circular single-core rod is 2.00 mm.

[0031] Step 2: After pickling, insert 36 circular single-core rods with a diameter of 2.00 mm obtained in Step 1 and one oxygen-free Cu rod with a diameter of 2.00 mm into a pickled NCu30 tube. The NCu30 tube has an outer diameter of 20 mm and a thickness of 2 mm. Then, process it by drawing, forging, and rolling. 0.5mm circular composite line, with a processing allowance of 5% per pass.

[0032] Step 3: Obtain the results from Step 2 A 0.5mm circular composite wire, under vacuum conditions (vacuum degree <10Pa), was kept at 550℃ for 20 hours to obtain a MgB2 superconducting wire.

[0033] Example 2, this example includes the following steps: Step 1: Insert the first Mg rod, after pickling, into the center of the metal sheath. The first Mg rod has a purity of 99.50% and a diameter of 10.00 mm. The metal sheath is an Nb tube with a purity of 99.5%, an outer diameter of 20 mm, and a thickness of 2 mm. Insert two second Mg rods symmetrically between the Nb tube and the central first Mg rod. The second Mg rods have a purity of 99.50% and a diameter of 3.00 mm. Fill the space between the first Mg rod, the second Mg rod, and the metal sheath with boron powder. The average particle size of the boron powder coated with carbon (C) is 100 nm, and the mass fraction of carbon in the powder is 5%. Process the material into a circular single-core rod using drawing, rotary forging, and rolling, with a pass weight of 10%. The final diameter of the circular single-core rod is 5.00 mm.

[0034] Step 2: After pickling, insert 18 circular single-core rods with a diameter of 5.00 mm obtained in Step 1 and one oxygen-free Cu rod with a diameter of 5.00 mm into a pickled NCu30 tube. The NCu30 tube has an outer diameter of 32 mm and a thickness of 3 mm. The tube is then processed by drawing, forging, and rolling. 1.0mm circular composite line, with a per-pass processing allowance of 10%.

[0035] Step 3: Obtain the results from Step 2 A 1.0 mm circular composite wire was kept at 700 ℃ for 2 h in a vacuum environment with a vacuum degree of <10 Pa to obtain a MgB2 superconducting wire.

[0036] Example 3, this example includes the following steps: Step 1: Insert the first Mg rod, after pickling, into the center of the metal sheath. The first Mg rod has a purity of 99.99% and a diameter of 20.00 mm. The metal sheath is an Nb tube with a purity of 99.9%, an outer diameter of 50 mm, and a thickness of 10 mm. Insert four second Mg rods symmetrically between the Nb tube and the central first Mg rod. These second Mg rods have a purity of 99.99% and a diameter of 5.00 mm. Fill the space between the first Mg rod, the second Mg rod, and the metal sheath with boron powder. The average particle size of the boron powder coated with carbon (C) is 500 nm, and the mass fraction of carbon in the powder is 10%. The rod is then processed into a circular single-core rod using drawing, rotary forging, and rolling processes, with a pass weight of 25%. The final diameter of the circular single-core rod is 10.00 mm.

[0037] Step 2: After pickling, insert 18 circular single-core rods with a diameter of 10.00 mm obtained in Step 1 and one oxygen-free Cu rod with a diameter of 10.00 mm into a pickled NCu30 tube. The NCu30 tube has an outer diameter of 70 mm and a thickness of 10 mm. The tube is then processed by drawing, forging, and rolling. 2.0mm circular composite line, with a per-pass processing capacity of 25%.

[0038] Step 3: Obtain the results from Step 2 A 2.0 mm circular composite wire was used to obtain a MgB2 superconducting wire with superconducting properties after being kept at 900 °C for 0.5 h in a high-purity Ar gas environment (Ar purity > 90%).

[0039] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0040] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for reducing hysteresis loss in MgB2 superconducting wires produced by the IMD method, characterized in that, include: The acid-washed first Mg rod is inserted into the center of the metal sheath; A second Mg rod is inserted between the first Mg rod and the metal sheath, wherein the diameter of the first Mg rod is larger than that of the second Mg rod; A single-core rod material is obtained by filling B powder between the first Mg rod, the second Mg rod and the metal sheath. The single-core rod material is rotary forged to obtain a circular single-core rod; The acid-washed oxygen-free Cu rod and the acid-washed circular single-core rod are inserted into the acid-washed NCu30 tube to obtain a multi-core composite wire blank. The multi-core composite wire blank is subjected to drawing, rotary forging and rolling processes to obtain the multi-core composite wire; The multi-core composite wire was heat-treated to obtain MgB2 superconducting wire.

2. The method for reducing hysteresis loss of MgB2 superconducting wire using the IMD method according to claim 1, characterized in that, The metal sheath is one of a niobium tube or a composite sheath with an inner niobium tube and an outer oxygen-free Cu tube.

3. The method for reducing hysteresis loss of MgB2 superconducting wire using the IMD method according to claim 1, characterized in that, Multiple second Mg rods are provided, and the multiple second Mg rods are arranged around the first Mg rod.

4. The method for reducing hysteresis loss of MgB2 superconducting wire using the IMD method according to claim 1, characterized in that, The process of filling B powder between the first Mg rod, the second Mg rod, and the metal sheath to obtain a single-core rod material further includes: The B powder between the first Mg rod, the second Mg rod, and the metal sheath is oscillated using an ultrasonic transducer.

5. The method for reducing hysteresis loss of MgB2 superconducting wire using the IMD method according to claim 1, characterized in that, The first Mg rod is a round wire, and the second Mg rod is one or more of round and polygonal shapes.

6. The method for reducing hysteresis loss of MgB2 superconducting wire using the IMD method according to claim 1, characterized in that, The cross-section of the multi-core composite wire is circular.

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