Microstructure of MgB 2 superconducting wire prepared by internal magnesium diffusion and in-situ powder-in-tube processes – Secondary phase intergrain nanolayers as an oxygen content indicator

We report an investigation of MgB 2 wires doped with BaZrO 3 nanoparticles produced by a modified internal magnesium diffusion (MIMD) process. The structure of the Nb-sheathed MgB 2 cores, transition temperature (T c ), critical current density (J c ) and pinning behaviour were studied and compared. Because the MgB 2 cores made by MIMD process are extractable, the grain connectivity and the phase composition of the cores were also analysed. The wires exhibited very good phase purity and sharp transitions with high critical temperature (close to 38 K); the best sample of the wires under study showed enhanced J c with almost 2 MA cm −2 at 4.2 K and 2 T. These results demonstrate the high quality of MgB 2 doped with BaZrO 3 nanopowder made by the MIMD method.

Section: Magnetic Characterizationsupporting

confidence: 79%

Section: Phase Composition and Microstructurecontrasting

confidence: 54%

Section: Phase Composition and Microstructurementioning

confidence: 65%

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Properties of MgB₂wires doped with BaZrO₃nanopowder made by a modified internal magnesium diffusion process

Brunner¹,

Kòváč²,

Rosová³

et al. 2017

“…It should be noted that quantitative EDS analysis is based on a presumption that the composition of the analysed volume is homogeneous [12], which is not true in this case. However, according to our previous experiences comparing the EDS result with XRD and TEM analysis [13,14] and using Casino for outgoing x-ray signals, we can conclude that well-reacted layers have a composition near to pure MgB 2 with only some B-rich grains.…”

Section: Resultsmentioning

confidence: 60%

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

Kòváč¹,

Hušek²,

Pachla³

et al. 2016

This work describes the effect of cold isostatic pressing applied to as-drawn filamentary wires in a GlidCop and/or Cu sheath made by the internal magnesium diffusion process. Critical currents of as-drawn and isostatically pressed wires at high pressures up to 2.0 GPa followed by heat treatment at 640 °C for 40 min were measured. The obtained results show an improvement in boron powder density resulting in an increase of the critical current of MgB2 layers. The engineering current density increases by 4–13 times after the high-pressure treatment, and is influenced by the density of the boron powder and by the mechanical strength of the outer sheath.

“…If the oxide impurities are nanoparticles, they may enhance the pinning centers or the irreversibility field [17,[41][42][43]. Otherwise, if the intergranular oxide impurity size is much larger than the coherence length of MgB 2 , it will decrease the effective crosssectional area of the sample, and thereby block supercurrents [44][45][46]. Heat-treatment of the PIT-processed MgB 2 samples is a conventional nucleation and growth process, which normally produces much larger grain sizes of MgO (50-200 nm) [17].…”

Section: Discussionmentioning

confidence: 99%

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

Wang

Zhang

Tang

et al. 2015

Monofilament MgB 2 /Fe wires or tapes were fabricated with two different purity crystalline boron powders, using internal magnesium diffusion (IMD) and in situ powder-in-tube (PIT) processes. To evaluate which method was more insensitive to the purity of the boron powders, a sensitivity factor was used. It was found that the IMD process was less sensitive to the purity of the boron powders, compared to the PIT method. Furthermore, J c values of the IMD-processed wires were higher than those of the PIT-processed samples. The reduced porosity and hence the increased density in the IMD-processed samples was thought to be the main reason. Although a number of B-rich particles remained in the MgB 2 region, a layer J c as high as 4.8×10 4 A cm −2 at 4.2 K and 10 T was still obtained in the IMD-processed wire, which was comparable to that of IMD-processed wires fabricated using amorphous boron powders.