Electron microscopy observations of MgB2 wire prepared by an internal Mg diffusion method

The internal Mg diffusion (IMD) process produces a high-density MgB 2 layer with high critical current properties, which makes it an attractive and promising method for fabricating MgB 2 wires. We have obtained high critical current properties in our previous research. However, IMD-processed MgB 2 wires can have unreacted B particles remain in the reacted layer due to the long Mg diffusion distance in the B layer during heat treatment. A reduction in the amount of unreacted B particles is expected to enhance the critical current properties. In this study, we attempted to disperse Mg powder in the B layer as an additive in order to decrease the Mg diffusion distance. We found that a 6 mol% Mg powder addition to a B layer drastically decreased the amount of unreacted B particles and enhanced the critical current density to twice the value for IMD-processed MgB 2 wire with no Mg powder added. An analysis is presented that relates the microstructure to the critical current density.

Section: Resultssupporting

confidence: 93%

Enhancing the critical current properties of internal Mg diffusion-processed MgB₂wires by Mg addition

Ye¹,

Song²,

Matsumoto³

et al. 2012

“…In the larger diameter wires some of the B remains unreacted even after -10-the longest HT. The same issue has also been reported by other researchers [23]. Of course, a high J e is favored by high layer-J c combined with a fully reacted superconducting core.…”

Section: Engineering Critical Current Density J E -9-supporting

confidence: 83%

The critical current density of advanced internal-Mg-diffusion-processed MgB₂wires

Li¹,

Sumption²,

Susner³

et al. 2012

102

Recent advances in MgB 2 conductors are leading to a new level of performance.Based on the use of proper powders, proper chemistry, and an architecture which incorporates internal Mg diffusion (IMD), a dense MgB 2 structure with not only a high critical current density J c , but also a high engineering critical current density, J e , can be obtained. In this paper, a series of these advanced (or second-generation, "2G") conductors has been prepared. Scanning electron microscopy and associated energy dispersive X-ray spectroscopy were applied to characterize the microstructures and compositions of the wires, and a dense MgB 2 layer structure was observed. The best layer J c for our sample is 1.07x10 5 A/cm 2 at 10 T, 4.2 K, and our best J e is seen to be 1.67x10 4 A/cm 2 at 10 T, 4.2 K.Optimization of the transport properties of these advanced wires is discussed in terms of Bpowder choice, area fraction, and the MgB 2 layer growth mechanism. PACS: 74.70.Ad; 74.25.Sv; 74.25.Qt; 74.62.Dh Keywords: MgB 2 , layer critical current density J c , engineering critical current density J e , internal magnesium diffusion (IMD)

“…The conductor is formed by Mg from the central rod diffusing into the surrounding B precursors in certain conditions and then reacting into a MgB 2 hollow cylinder. Whereas the PIT process produces a porous MgB 2 core, the IMD process provides a dense MgB 2 layer with excellent longitudinal and transverse connectivities [14][15][16]. To calculate the critical current densities of these IMD wires, it is important to take care with the definition of the areas to which the critical current, I c , is normalized.…”

Section: Introductionmentioning

confidence: 99%

Effects of carbon concentration and filament number on advanced internal Mg infiltration-processed MgB₂strands

Sumption

Zwayer

et al. 2013

An advanced internal Mg infiltration method (AIMI) in this paper has been shown to be effective in producing superconducting wires containing dense MgB 2 layers with high critical current densities. In this study, the in-field critical current densities of a series of AIMI-fabricated MgB 2 strands were investigated in terms of C doping levels, heat treatment (HT) time and filament numbers. The highest layer J c for our monofilamentary AIMI strands is 1.5 × 10 5 A/cm 2 at 10 T, 4.2 K, when the C concentration was 3 mol% and the strand was heat-treated at 675 °C for 4 hours. Transport critical currents were also measured at 4.2 K on short samples and one-meter segments of eighteen-filament Cdoped AIMI strands. The layer J c s reached 4.3 × 10 5 A/cm 2 at 5 T and 7.1 × 10 4 A/cm 2 at 10 T, twice as high as those of the best PIT strands. The analysis of these results indicates that the AIMI strands, possessing both high layer J c s and engineering J e s after further optimization, have strong potential for commercial applications.