Influence of Amorphous Boron Grain Size, High Isostatic Pressure, Annealing Temperature, and Filling Density of Unreacted Material on Structure, Critical Parameters, N-Value, and Engineering Critical Current Density in Mgb2 Wires.

Daniel Gajda,Hakan Yetiş,Andrzej J Zaleski,Małgorzata Małecka,Tomasz Czujko,Andrzej Morawski,Ibrahim Belenli,Firat Karaboğa,Doğan Avcı,Mustafa Akdoğan

doi:10.3390/ma14133600

Abstract

Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (Birr), critical temperature (Tc), upper magnetic field (Bc2), engineered critical current density (Jec), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on Birr, Tc, Bc2, Jec, and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest Birr, Tc, Bc2, Jec, and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB2.

Highlights

MgB2 wires are the most promising material for superconducting coil applications due to their inexpensive components and ability to be cooled in liquid hydrogen, or by a cryocooler
The results in Fig-in nificantly increases the n-value in MgB2 wires ure 22a and [27] suggest that MgB2 wires with large grain boron after the high isostatic pressure (HIP) process can be used to build a medium field superconducting coil, e.g., B = 5 T. These results reveal that the Mg liquid state and an isostatic pressure of 1.1 GPa significantly improve the nvalue in MgB2 wires with large boron grains
Our measurements show that samples with large boron grains and an 8% higher filling density of unreacted Mg + B material significant decrease in the irreversible magnetic field, critical temperature, upper magnetic field, engineered critical current density, and n-value, despite the high isostatic pressure treatment and the use of nanoboron in the sample

Summary

Introduction

MgB2 wires are the most promising material for superconducting coil applications due to their inexpensive components and ability to be cooled in liquid hydrogen, or by a cryocooler. The application of superconducting wires is dependent on several factors, e.g., engineering critical current density (Jec ), irreversible magnetic field (Birr ), critical temperature (Tc ), n-value (the log-log slope of the voltage vs electrical current curves during the transition of the superconducting material from a superconducting state to a normal state), and resistance in the normal state (Rn ). These parameters depend on the grain size and purity of magnesium and boron, heat treatment temperature, isostatic pressure, admixture, and wire sheath. These studies show that a greater number of structural defects in boron can accelerate the formation of the MgB2 superconducting phase

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Results

Conclusion