MgB2 Superconducting Wire Rod Production via Mechanical Milling
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Solution Overview
Problem
Existing methods for producing MgB2 superconducting wire rods, such as the Powder In Tube (PIT) method and mechanical alloying, face challenges in achieving high critical current density, particularly in round or square wires with symmetrical cross-sections, due to issues like crystallinity enhancement at high temperatures and lower packing factors, which restrict their application in homogeneous magnetic field applications like MRI.
Innovation Solution
A production method involving the mixing of magnesium and boron powders with a solid organic compound, followed by mechanical milling and heat treatment, to disperse boron particles within magnesium particles, forming a dense grain structure that enhances critical current density by reducing pore size and improving packing factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If MgB2 is synthesized at a temperature equal to or higher than 800°C, then the crystallinity is enhanced and crystal grains become larger, but the magnetic flux pinning is reduced leading to lower critical current density
Solution Approach 1:
The patent changes the synthesis temperature parameter from conventional high temperatures (≥800°C) to low temperatures (≤700°C) to achieve optimal balance between crystallinity and magnetic flux pinning. This parameter change resolves the contradiction by operating in a temperature range where both adequate crystallinity and strong pinning coexist
Solution Approach 2:
The patent applies preliminary mechanical alloying treatment before heat treatment to pre-disperse boron particles within magnesium particles. This preliminary action creates a refined microstructure that enhances pinning effectiveness at lower synthesis temperatures, resolving the contradiction between crystallinity and pinning
2Reliability
If the in situ method is used with magnesium and boron powders, then MgB2 is synthesized sufficiently with good magnetic flux pinning, but the packing factor is reduced due to volume reduction reaction and pore formation
Solution Approach 1:
The patent applies preliminary mechanical alloying to pre-mix and pre-react magnesium and boron powders, creating a more uniform distribution before the volume reduction reaction. This preliminary action minimizes pore formation during synthesis, resolving the contradiction between pinning quality and packing density
Solution Approach 2:
The patent creates a composite structure where boron particles are dispersed within magnesium particles through mechanical alloying. This composite approach optimizes both the pinning sites distribution and the overall packing factor by preventing large pore formation
3Reliability
If mechanical alloying is used to enhance reactivity of magnesium and boron powders, then higher critical current densities can be obtained, but the method is primarily effective for tapes rather than round or square wires with symmetrical cross-sections
Solution Approach 1:
The patent adapts the mechanical alloying method to work universally across different wire shapes (round, square, and tapes) by optimizing the processing parameters and die design. This makes the method versatile for various superconducting wire applications, resolving the contradiction between performance enhancement and shape adaptability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method significantly increases the critical current density of round or square wire rods with symmetrical cross-sections, enabling more efficient and homogeneous magnetic field generation, suitable for applications like MRI without the limitations of direction-dependent critical current density.
Implementation Method 1
MgB2 is synthesized by magnesium particles as a staring material, whose size is several tens of micro meters, diffusing into boron particles
Implementation Method 2
a heat treatment process of heat-treating the wire rod for synthesizing MgB2
Implementation Method 3
the magnetic flux lines receive a Lorenz force when the current is flowing
Implementation Method 4
The critical current density of the superconductor is determined by magnetic flux pinning phenomena
Data Source
AI summary
The present invention is intended to increase the critical current density of a wire rod having a shape with good symmetry such as a round wire or a square wire by making use of mechanical milling method. The production method of the present invention for the MgB2 superconducting wire rod comprises a mixing process of preparing a powder by adding a solid organic compound to a magnesium powder and a boron powder and then applying an impact to the powder to prepare a mixture of the powder in which boron particles are dispersed inside magnesium particles, a filling process of filling a metal tube with the mixture, an elongation process of elongating the metal tube filled with the mixture and a heat treatment process of heat-treating the metal tube to synthesize MgB2.