Transport and structural properties of MgB₂/Fe wires produced by redesigning internal Mg diffusion process

Abstract

We report transport, electromechanical, and structural properties of single core MgB2/Fe wire produced using a new fabrication method, called designed IMD process, which relies on the use of non-stoichiometric Mg + B pellets with excess Mg in place of a central Mg rod used in the standard internal Mg diffusion (IMD) method. Structural analysis revealed the successful formation of a porous MgB2 structure in the center and a dense circular MgB2 layer surrounding this structure in the designed-IMD wire. Fast transport I –V measurements showed that the designed IMD method increased engineering critical current density (Je) up to twice that of the IMD wires in self-field. The central porous MgB2 structure shared the applied current and indirectly behaved as an internal stabilizer against quench damage at high applied currents.

Optimized superconducting MgB2 joint made by IMD technique

“…The I c difference of 6.5% was observed between the MgB 2 wire of the joint and the joint itself. The small decrease in the I c value of the wire can be caused by heating effects occurring at high currents due to the low thermal stability of the iron sheath or/and non-uniformity in the wire core [33,34]. On the other hand, the I c of the joint wire is lower by 20% than the I c of the joint itself at 20 K under 1.5 T. Calculations also indicate that the critical current density (J c ) for undoped IMD MgB 2 wire at 20 K under 0 T is ∼623 A mm −2 in comparison to ∼87 A mm −2 under the magnetic field of 1.5 T at 20 K. This dramatic decrease in the J c is due to the lack of chemical doping for magnetic flux pinning.…”

High critical current properties of multi-filamentary MgB2 superconducting wires fabricated using an internal Mg diffusion method

“…In addition, even in single-filament IMD wires, the MgB 2 layer will suffer from poor compositional uniformity, since the Mg rod experiences severe deformation after work hardening [18,19]. To solve this, Yetis et al replaced the central Mg rod with a Mg/B cylinder formed by pressing technology and thereby increased the contact area between Mg and B [20]. The thickness of this single-filament MgB 2 layer reached 93 µm after heat treatment and therefore granted a high I c of 167 A at 33 K and self-field.…”

Mg Difüzyonu Tekniği ile Türkiye’de Saflaştırılmış Bor Kullanılarak Üretilen MgB2 için B Saflığının Süperiletkenlik Özellikleri Üzerine Etkisi

“…Ayrıca, ısıl işlem sonucunda numunede oluşan yapının gözenek yoğunluğunu azaltmak için magnezyum difüzyonu ve türevi yöntemler önerilmiş ve oldukça büyük külçe numuneler üretilmiştir [33]. Mg difüzyon yöntemi ve türevleri MgB2'nin tel formu için de popüler kullanılan bir yöntem olmuştur [34][35][36]. Hatta MgB2 tel/şerit/kabloların birbirine eklenmesi gereken ek yerlerinde, bu ekleme işlemi için de yaygın olarak kullanılan in-situ yöntem yerine Mg difüzyon yöntemi [37][38] tercih edilmeye başlanmıştır.…”