CN-122000766-A - MgB (MgB)2Preparation method of superconducting joint for multi-core wire rod

Abstract

The invention discloses a preparation method of a superconducting joint for MgB 2 multi-core wires, which comprises the steps of firstly adopting concentrated nitric acid to corrode the middle section of the MgB 2 multi-core wires to expose internal core wires, secondly immersing the core wires in molten Ti metal liquid to form a Ti protective layer, cutting the middle part of the core wires to obtain two wires to be connected, thirdly inserting Ti plating ends of the two wires to be connected into Mg/B fusion splicer through holes and compacting the Ti plating ends to form a joint structure, and fourthly performing phase-forming heat treatment. According to the invention, the Ti protective layer is introduced on the surface of the Mg/B/Nb core wire, so that the contact reaction of the metal sheath and the Mg/B fusion agent is effectively isolated, the superconducting effective area of the MgB 2 in the joint area is increased, the distortion or fracture of the Mg/B/Nb core wire is prevented, the thermal stability of the joint structure is enhanced, the electric-thermal-mechanical comprehensive stability of the superconducting joint for the MgB 2 multi-core wire is cooperatively improved, and the power-assisted MgB 2 magnet realizes continuous current operation.

Inventors

• XI DAN
• WANG YIMING
• WANG QINGYANG
• HOU HONGLI
• CHEN ZHENYU
• LIU JIXING
• YAN GUO
• LI JIANFENG
• ZHANG PINGXIANG

Assignees

• 西北有色金属研究院

Dates

Publication Date

20260508

Application Date

20260323

Claims (3)

1. 1. The preparation method of the superconducting joint for the MgB 2 multi-core wire is characterized by comprising the following steps of: Firstly, corroding the intermediate section of the MgB 2 multi-core wire by adopting concentrated nitric acid, removing an outer Monel sheath and a Cu sheath, and exposing the internal Mg/B/Nb core wires to form core wire sections to be connected; Immersing the bare core wire segment to be connected obtained in the first step into molten Ti metal liquid, removing redundant molten Ti metal liquid through a polycrystalline drawing die with the aperture matched with the diameter of the MgB 2 multi-core wire in the first step, cooling, forming an attached Ti protective layer on the surface of the bare core wire segment to be connected to obtain a MgB 2 multi-core wire with a Ti-plated layer section, and cutting from the middle part of the Ti-plated layer section to expose the Mg/B core wire inside, thereby obtaining two wires to be connected with Ti-plated ends; Filling Mg/B fusion splicer into the stainless steel cylindrical container, drilling two independent holes with the diameter equivalent to that of MgB 2 multi-core wires in the first step at the lower part of the side surface of the stainless steel cylindrical container, then respectively inserting Ti plating ends of two wires to be connected in the second step into the stainless steel cylindrical container through the two independent holes to ensure that the exposed end surfaces of the Mg/B core wires are fully contacted with the Mg/B fusion splicer, and compacting by pressing a Cu plug at the top end of the stainless steel cylindrical container to form a compact joint structure; And step four, carrying out phase-forming heat treatment on the joint structure formed in the step three and the connected MgB 2 multi-core wire rod, so as to promote the reaction of the Mg/B fusion splicer and form a connected MgB 2 superconducting phase, and obtaining the superconducting joint for the MgB 2 multi-core wire rod.
2. 2. The method for manufacturing a superconducting joint for MgB 2 multi-core wires according to claim 1, wherein in the first step, the MgB 2 multi-core wires are made of a Monel outer sheath, a Cu inner sheath, an Nb barrier layer and a black precursor including Mg and B powder, wherein the Nb barrier layer wraps the black precursor to form Mg/B/Nb core wires.
3. 3. The method for producing a superconducting joint for MgB 2 multi-core wires according to claim 1, characterized in that in the second step, the mass purity of the molten Ti metal liquid is not lower than 98%, the tensile strength of the Ti protective layer formed after cooling is not lower than 300MPa, and the thermal conductivity is not lower than 15w·k -1 ·m -1 .

Description

Preparation method of superconducting joint for MgB 2 multi-core wire Technical Field The invention belongs to the technical field of superconducting wire preparation, and particularly relates to a preparation method of a superconducting joint for MgB 2 multi-core wires. Background Nuclear Magnetic Resonance Imaging (MRI) is a core device for modern accurate medical treatment, and is important for guaranteeing health of people and improving diagnosis and treatment level. The key material for realizing the traditional MRI high field intensity magnet is a superconducting wire capable of transmitting lossless high current. The existing MRI generally selects a niobium-titanium low-temperature superconducting wire, but relies on an expensive liquid helium refrigerating system, so that the equipment acquisition cost is high, the operation and maintenance system is complex, the site requirements are severe, and the popularization and application of the MRI technology are limited. Therefore, the development of low-cost, miniaturized and light-weight MRI technology has a key meaning for promoting the popularization of the civilian of accurate medical treatment and realizing the '2035 build-up of healthy China' strategic targets. In this context, magnesium diboride (MgB 2) as a practical superconducting material provides a new path for breaking the bottleneck. The method has the core advantages that firstly MgB 2 is a practical superconducting material with the lowest theoretical density (about 2.6g/cm 3) at present, which is beneficial to developing a lighter MRI magnet, secondly, the superconducting transition temperature (T c) reaches 39K, the dependence on liquid helium can be eliminated, a cooling system is obviously simplified, the whole weight is reduced, and finally, the main raw materials magnesium (Mg) and boron (B) are rich in reserves and low in cost, and have obvious cost advantages compared with high-temperature superconducting materials such as yttrium barium copper oxide and the like. In an MRI apparatus, in order to generate a super-stable magnetic field (the magnetic field attenuation rate is required to be lower than 0.1ppm h -1), when a MgB 2 multi-core wire is adopted to wind a superconducting magnet, each magnet needs to be connected through a superconducting joint to form continuous current mode operation. Therefore, the preparation of the high-performance superconducting joint suitable for MgB 2 multi-core wires is a key link for realizing the breakthrough and application of the MRI magnet technology. At present, an MgB 2 magnet for MRI is generally prepared by adopting a winding-after-reaction process, and at the moment, the structure of an MgB 2 wire rod mainly consists of an Mg rod/powder and B powder (the powder is abbreviated as Mg/B core wire) which are coated by a metal sheath. The superconducting joint for preparing the wire is usually connected by adopting Mg powder and B powder as welding agents, and the MgB 2 superconducting joint is formed after heat treatment. However, the metal sheath (such as Monel, copper Cu) outside the wire is liable to react with the filler material, and the resultant reaction layer reduces the resultant area of the MgB 2 superconducting phase, resulting in a decrease in the current carrying performance of the joint. To circumvent this problem, the conventional method is to remove the Monel and Cu sheath by strong acid corrosion, leaving only Mg/B core wires (abbreviated as Mg/B/Nb core wires, diameter on the order of hundred microns) surrounded by niobium (Nb). However, the treatment process introduces new challenges that ① Mg/B/Nb core wires are low in strength and poor in plasticity, structural distortion and even breakage are easy to occur in the preparation process, so that the effective current carrying area of a joint is reduced, the mechanical property of the joint of the ② corroded Mg/B/Nb core wires and wires is fragile, the joint of the core wires can be broken due to tiny disturbance, and the heat conduction capacity of a joint area is reduced and the heat stability is poor after a large amount of ③ metal sheaths are removed. The problems are related to each other, so that the preparation of the high-performance MgB 2 superconducting joint is restricted, and the preparation becomes a key bottleneck for the technology to be practically applied. Disclosure of Invention The invention aims to solve the technical problem of providing a preparation method of a superconducting joint for MgB 2 multi-core wires, aiming at the defects in the prior art. According to the method, the Ti protective layer is introduced into the surface of the Mg/B/Nb core wire, so that the contact reaction of the metal sheath and the Mg/B fusion bonding agent is effectively isolated, the superconducting effective area of the joint region MgB 2 is increased, the method can also be used as a high-strength protective layer, the distortion or fracture of the Mg/B/Nb core wi