Mechanically reinforced MgB2 wires and tapes with high transport currents

Self Cite

In mono-and multifilamentary MgB 2 wires with small filament diameters a homogeneous and fine-grained MgB 2 phase is required for high transport currents and reactions with the sheath have to be avoided. Taking this into account we developed very thin steel reinforced MgB 2 wires for application as current leads in a research satellite. In situ phase formation in the wire from Mg + B powders was chosen as the most favourable method to achieve good grain connectivity and thus high transport currents. We tested the current lead wires with transport current measurements and investigated the mechanical performance with applied tensile and bending strains. With an improved processing route applying a low-temperature anneal the superconducting properties of standard undoped in situ MgB 2 wires could be further improved and critical current densities of 38 kA cm −2 at 6 T and 10 kA cm −2 at 8 T, 4.2 K could be achieved.

Section: Steel Reinforced Thin In Situ Mgb 2 Wires Transport Currentssupporting

confidence: 89%

Development and performance of thin steel reinforced MgB₂wires and low-temperaturein situprocessing for further improvements

Goldacker¹,

Schlachter²,

Obst³

et al. 2004

Self Cite

“…Sample 4 was synthesized according to the same PIT procedure as the tape analysed in the present study, except that its aspect ratio was larger (14.5). Over the measurement range (4.5 T-10 T), sample 4 showed the highest J c values and this behaviour was attributed to its larger aspect ratio [13].…”

Section: Superconducting Propertiesmentioning

confidence: 90%

“…Sample 1 was cut from one end of the tape, and sample 2 was cut from the middle of the same tape as sample 1. The original tape was prepared by a powder-in-tube process consisting of filling Fe tubes (10 mm diameter, 1.5 mm wall thickness) with commercial MgB 2 powder (Alfa Aesar) [13]. MgB 2 powders were annealed at the MgB 2 decomposition temperature (∼860 • C) to ensure an optimum densification, then the tape was annealed at 910 • C in Ar/H 2 (5%) and quenched [8].…”

Section: Sample Preparationmentioning

confidence: 99%

Superconducting properties, microstructure and chemical composition of MgB₂sheathed materials

Eyidi

Eibl

Wenzel

et al. 2003

Self Cite

The superconducting properties, the microstructure and the chemical composition of sheathed MgB 2 tapes and of one wire, all synthesized by the powder-in-tube method, were investigated. At 4.2 K critical current densities up to 10 5 A cm −2 (0 T) and 1.5 × 10 4 A cm −2 (2.5 T) were obtained by transport measurements in the wire and the tapes, respectively.In the MgB 2 matrix of all samples, oxygen was identified and mole fractions of 0-10 at% were determined by electron probe microanalysis. It was found by scanning electron microscopy that only the tapes showed boron-rich secondary phases about 10 µm in size. Comparing different tapes, the critical currents increase with the aspect ratio and decrease with the oxygen mole fraction in the MgB 2 material. In the tapes, aspect ratios were inhomogeneous and critical current densities at low fields were limited by insufficient thermal stabilization. For understanding the internal oxidation in the MgB 2 tapes, one tape was investigated by analytical transmission electron microscopy (TEM). The combination of energy-dispersive x-ray spectroscopy and electron spectroscopic imaging in the TEM yielded phase maps of this sample. It showed a heterogeneous microstructure, MgB 2 grain sizes ranged between 20 nm and 1 µm. Oxygen was primarily bound in 20 nm-1 µm MgO precipitates and secondary phases, and no boron oxides could be evidenced. Randomly distributed 50 nm-1 µm boron-rich secondary phases (MgB 4+δ , MgB 7+γ ) embedded in the MgB 2 matrix were identified. The possible reasons for the oxidation of the superconducting matrix are discussed.

“…The nature and toughness of the sheath material has a strong influence on the transport J C of MgB 2 conductors [65,97]. Cu (with a protective barrier), Fe, Ni and alloys like SS, Monel insitu wire (Fe/Cu ) [169] insitu wire (Nb/Cu/SS) [72] insitu wire (Nb/Cu/SS) [72] exsitu tape (SS) [64] exsitu wire (Fe) [170] insitu tape (Fe) [63] exsitu tape (Fe) no annealing [63] exsitu tape (Fe) annealed [63] exsitu tape (Ni) no annealing [63] exsitu tape (Ni) annealed [63] exsitu tape (Cu-Ni) [64] J C (A/cm 2 ) Field (T) are tried for long length MgB 2 conductors. The Cu sheathed conductors have high J C and good thermal stabilization for practical applications.…”

Section: Sheathsmentioning

confidence: 99%

Prospects for MgB₂superconductors for magnet application

Vinod

Kumar

Syamaprasad³

2006

219

134

Superconducting magnets have a variety of industrial, medical and research applications. This review discusses the prospects for MgB2 superconductor for practical magnet applications vis-à-vis the intermetallic low (LTS) and high temperature superconductor (HTS) cuprates. It has high TC (39 K), high JC (105–106 A cm−2 at 4.2 K and in the self-field) and HC2 (15–20 T at 4.2 K) in wire/tape geometry, with great scope for further improvement in the coming years, making it a promising candidate for practical applications. The superconducting properties of MgB2 differ from those of LTS and HTS in many ways. Besides the unusually high TC, MgB2 has a large coherence length, low anisotropy and transparent grain boundaries. The most important difference between MgB2 and other practical superconductors is that it has two superconducting gaps originating from two different bands. Tuning the scattering rates between the two bands improves the superconducting properties and the practical applicability of MgB2. The different methods of fabrication of MgB2 conductors are described and compared. Fabrication of long length MgB2 conductors is relatively easy and less expensive as compared to HTS and the method allows the use of a variety of sheath materials with suitable barriers or reinforcement. The conductors have much better mechanical properties for practical applications. The critical issues and the challenges to be addressed for realization of MgB2 superconductors as the first choice for high field magnet applications are discussed. At present MgB2 is most suited for 20–25 K operation in fields of 1–2 T.