The critical current properties of 37-filament internal Mg diffusion-processed MgB₂wires

Abstract

Internal Mg diffusion (IMD)-processed MgB 2 wires are known to have a high-density MgB 2 core, which obviously leads to high critical current density (J c ). In this work, we first fabricated 37-filament MgB 2 wires by IMD processing, and we found that J c for SiC-added 37-filament IMD-processed MgB 2 wires achieved a value of 7.6 × 10 4 A cm −2 at 4.2 K and 10 T, which is higher than those of multi-filament wires with a smaller number of filaments (1 filament, 7 filaments) fabricated under the same conditions. We also investigated the critical current properties of both undoped and SiC-added 37-filament IMD-processed MgB 2 wires under different magnetic fields and temperatures. The undoped 37-filament IMD-processed MgB 2 wires achieved J c value of 1.6 × 10 5 A cm −2 at 20 K and 3 T. The engineering critical current density (J e ) achieved 2.8 × 10 3 A cm −2 at 20 K and 3 T. The microstructures observed by scanning electron microscopy support the view that the decrease in unreacted B particles by the short diffusion distance is mainly responsible for the high J c obtained.

Fast creation of dense MgB2phase in wires made by IMD process

“…Taking into account the values of I c maxima at 8 min and the estimated MgB 2 area, the current density, J c =9.25×10 4 −1.07×10 5 Acm −2 , was obtained at an external field of 6 T. It correlates well with the J c data of nondoped MgB 2 wires made by IMD with the same B powder [9,11]. Ye et al have presented filamentary IMD wire with non-doped and high purity B (99.99%) for which J c =10 5 Acm −2 was obtained at 6-6.5 T after HT at 640-670 °C/3-5 h [14], which are comparable to our research. Our results demonstrate that high current density MgB 2 layers can be created during very short annealing periods (8-10 min).…”

“…A much higher heating rate (50 °C min −1 ) and an apparent overshoot of established temperature (by ≈20 °C ) was applied for the present IMD wire; this has resulted in a considerably faster creation of MgB 2 phase in comparison to usual in situ processes. In our case, the time of only 8 min was sufficient for the creation of dense MgB 2 phase with thicknesses up to 90 μm at the temperature scale 650-668 °C with J c =10 5 Acm −2 at 6 T and 10 4 Acm −2 at 10 T; these parameters are nearly identical with J c values of Ye et al who presented IMD wires with high purity B (99.99%) and longer HT at 640-670 °C/3-5 h [14]. It should be noticed that the presented results are connected with the concrete form of B powder (see figure 1) and the B density layer which are affected by rolling deformation.…”

Effect of cold isostatic pressing on the transport current of filamentary MgB2wire made by the IMD process

“…J c = 10 5 A cm −2 at 6 T was measured for our previously published seven-filament IMD wire with the same boron powder and GlidCop sheath deformed by rolling [9], which correlates with the J c values of 7Gli. Ye et al have presented the properties of 37-filament IMD wire in Ta/CuNi sheath with non-doped high-purity boron (99.99%) for which J c = 10 5 A cm −2 was obtained at 6-6.5 T [15], which is comparable with J c data for the 7Gli wire. The considerably lower J c of the 6Cu wire are mainly due to the soft Cu sheath, which does not make it possible to densify the boron powder sufficiently.…”

Influence of crystalline boron powders on superconducting properties of C-doped internal Mg diffusion processed MgB2wires

“…A number of unreacted B or B-rich particles remain in the MgB 2 layer when large sized B powder is used [16,33]. Until now, these two effects mentioned above have been minimized by optimizing the wire geometry, filament number, powder choice and preparation, addition of the B layer, and heat treatment conditions, hence both high J c and J e are achieved [28,29,[34][35][36]. However, few studies have focused on the sensitivity of the IMD process to the crystallinity and purity of the boron powder.…”