MgB₂composite wires with Fe, Nb and Ta sheaths

Abstract

Single-core MgB2 composite wires have been made by the powder-in-tube method using commercial Mg, B and MgB2 powders (Alfa Aesar) in Fe, Nb and Ta tubes and both in situ and ex situ processes. Prepared wires were subjected to annealing at temperatures ranging from 600 °C up to 950 °C for 30 min in argon atmosphere. Resistive (R(T)) and transport current (Ic(μ0H)) measurements have shown how the sheath material that was used influences the critical temperature and critical current density. Inter-diffusion and reaction has been observed only for the iron sheath. Niobium has appeared as the best sheath material for MgB2 wires made by the in situ process but as the worst sheath material for the ex situ method. The reason is mainly due to the large transversal cracks generated in the fully Nb sheathed ex situ wires during the deformation, which are not healed by the subsequent heat treatment.

Relation between Current Transfer Length and Stability of Fe/MgB2and Fe/Nb/MgB2Conductors

“…However, in spite of the absence of chemical reaction layer between Nb and MgB 2 , the value of the surface contact resistance is about a factor 10 higher than for the S1FeIN conductor [8]. A possible explanation of this behavior might be the occurrence of the transversal cracks [7] in the MgB 2 core due to the very different thermal expansion coefficients of MgB 2 and Nb. In the case of S1FeIN conductor, apparent decay of the CTL with increasing transport current is not yet understood [8].…”

“…We analyzed two different MgB 2 conductors both prepared using in situ technique described in [6,7]. The cross-section of the first monofilament wire is square (1.1 mm × 1.1 mm), where the outer sheath is made of iron (conductor name: S1FeIN).…”

Electric Field and Energy Losses of Rounded Superconducting/Ferromagnetic Heterostructures at Self-Field Conditions

“…Therefore, as the critical current density in most of the type-II SCs is degraded by increasing the magnitude of the applied magnetic field, H a , when the SC is encompassed within or in a near proximity of a FM, the SC exhibit enlarged critical currents through wide ranges of intensities of H a . Because of this, the magnetic shielding benefits of SCFM heterostructures have been broadly reported on type-II SC cables of cylindrical cross-section composed by NbTi [12], BPSCCO [13], [14], BSCCO [15], YBCO [19], and MgB 2 [16]- [18], as well as in other SC topologies (strips and bulks) [19]- [21]. However, a crucial question here is whether the presence of a FM will affect the AC losses of the SC in conditions where only applied current is considered (self-field conditions).…”

Effect of Cu Cladding on the Mechanical Properties of Iron Sheath Material in the Drawing of Superconducting MgB2 Wires

“…Metal tubes, also called sheath metal, should be ductile and chemically compatible with MgB 2 [9]. In spite their chemical suitability as sheath materials, expensive inert materials such as niobium or tantalum are not cost-effective [10]. On the other hand, low-cost iron sheaths are found to be less reactive during the sintering process in the range of 600 to 900 • C during the formation of MgB 2 .…”