Method for preparing magnesium diboride superconducting wire with graphene coated boron powder

Abstract

The invention discloses a method for preparing a magnesium diboride superconducting wire with graphene coated boron powder. The method comprises the steps of: 1, adding the spherical nano boron powder to graphene oxide solution, filtering after stirring uniformly to obtain filter residue and carrying out vacuum drying on the filter residue to obtain mixed powder; 2, carrying out heat treatment on the mixed powder to obtain the graphene coated boron powder; 3, after mixing the graphene coated boron powder with magnesium powder, grinding to obtain tubing precursor powder; 4, putting the tubing precursor powder into an Nb / Cu composite tube which is processed by acid pickling to obtain a tubing complex; 5, processing the tubing complex into a single-core wire; 6, processing into a multi-core wire by employing a bundle-drawing technology; and 7, carrying out phase-forming heat treatment, and cooling to room temperature with a furnace to obtain the magnesium diboride superconducting wire. According to the method disclosed by the invention, through adding the spherical boron powder to the graphene oxide solution, the single-layer graphene coated boron powder is realized; after the heat treatment, the graphene has no agglomeration and can be combined with the boron powder tightly and uniformly; and the phenomena of graphene contraction and nonuniformity in the traditional method are inhibited.

Description

technical field [0001] The invention belongs to the technical field of preparation of high-temperature superconducting materials, and in particular relates to a method for preparing magnesium diboride superconducting wires by coating boron powder with graphene. Background technique [0002] MgB 2 Due to its high critical temperature (Tc=39K), large coherence length, and no weak connection between grain boundaries, superconducting materials have attracted widespread attention. Since small refrigerators on the market can easily reach a low temperature of about 20K, MgB 2 Superconducting materials are considered to be expected to realize the application of 1T to 3T medical magnetic resonance imaging (MRI) magnets at 20K operating temperature. [0003] Powder in tube technology, that is, PIT (Powder In Tube) technology, due to its short process flow and easy control, is the current method for preparing MgB 2 The method commonly used for wire strips. However, how to control t...

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Problems solved by technology

However, how to control the oxidation of powder during the wire preparation process, especially the oxidation of nano-scale boron powder, has always existed. Due to its small size and relatively large area, nano-boron powder is very easy to absorb oxygen in the gas and generate oxidation on the surface of boron powder particles. Boron or boron-oxygen associations greatly reduce the reactivity of boron powder, and at the same time, the generated impurity phase reduces the performance of the final prepared wire. How to avoid oxidation of boron powder under the premise of maintaining the activity of boron powder is a multi-core wire Preparation problems to overcome

[0004] In order to increase MgB 2 The critical current density of superconducting wire strips under high magnetic field conditions must introduce effective pinning centers, and carbon is one of the most effective doping elements. Low, poor dispersion, high heat treatment temperature is required to introduce effective doping, and due to the uneven distribution of doping sources, it is easy to reunite at the grain boundary, reducing the connectivity between grains, and high temperature will lead to barrier There is an obvious diffusion reaction between layer and B

Although organic matter doping can improve the doping efficiency to a certain extent, the gas released by the decomposition of organic matter will destroy the structure of the wire and produce other by-products. Due to its limitations, it cannot be well applied to wire preparation.

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