Formation of High-Field Pinning Centers in Superconducting MgB2 Wires by Using High Hot Isostatic Pressure Process

Abstract

This paper demonstrates the effects of hot isostatic pressure (HIP) on the structure and transport critical parameters of in situ MgB 2 wires without a barrier. Our results show that only HIP and nano-boron allow the formation of more high-field pinning centers, which lead to the increase in critical current density (J c ) at high applied magnetic fields. Nano-boron and annealing at a low pressure increase the J c in the low magnetic field. This indicates that nano-particles create more high-field pinning centers. In addition, the results show that nano-boron improves the connection between the grains. Scanning electron microscope results show that HIP increases the reaction rate between Mg and B, density, and homogeneity of the MgB 2 material. Additionally, HIP allows to create a structure with small grains and voids and eliminates the significance of the number of voids. High isostatic pressure allows to obtain high J c of 10 A/mm 2 (at 4.2 K) in 10 T and increases irreversible magnetic field (B irr ) and upper critical field (B c2 Measurements show that these wires have high critical temperature of 37 K.

Analysis Method of High-Field Pinning Centers in NbTi Wires and MgB2 Wires

“…This method is used in superconducting materials with a high irreversible magnetic field. The value of B irr is dependent on high-field pinning centers [39,62,70,71]. The results in Ref.…”

“…Hot isostatic pressing (HIP) significantly increases the number of high-field pinning centers, e.g., increase in the density of dislocations, and accelerates the substitution of C for B, allowing to obtain a uniform distribution of pinning centers [27,31,35,36]. In addition, results indicate that using boron grains with nanosizes makes it possible to obtain more high-field pinning centers than usage of large particles of boron [70,71]. Studies also showed that high isostatic pressure increases the number of connections between the grains densifying material [31,36].…”

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

“…Details of the production methods are presented in [21]. All samples were heated in an argon atmosphere at temperatures ranging from 680 • C to 740 • C, and under isostatic pressures ranging from 0.1 MPa to 1.1 GPa for 40 min, as listed in Table 1 [35].…”

The Impact of High Pressure, Doping and the Size of Crystalline Boron Grains on Creation of High-Field Pinning Centers in In Situ MgB2 Wires

“…Small grains of amorphous boron increase the rate of synthesis reaction and lead to an increase in J c and B irr [21,22]. Gajda et al indicate that a high pressure of 1.1 GPa allows for a more efficient increase in the density of high-field pinning centers in in situ MgB 2 wires with nano-amorphous boron [4] than with big amorphous boron [23]. The crystalline Research (PAS) [16].…”

“…Dislocations and strains in superconducting wires can be created by cold treatment (e.g., cold isostatic pressure [2], cold drawing [3]) or hot treatment (e.g., hot isostatic pressure process which creates dislocations [4]) and also by the shrinkage of the superconducting material during the synthesis reaction [5] or substitution into crystal lattice, which creates strains in either case [6]. Dislocations created by cold treatment disappear as a result of thermal processes.…”