Reverse advance internal magnesium diffusion process to produce dense MgB₂ bulks and high J_C wires through high pressure heat treatment

Abstract

Here we report a new versatile technique to manufacture MgB2 massive samples, called reverse advance internal magnesium diffusion (r-AIMI). The idea focuses on the goal of obtaining dense bulk or wire samples depending on synthesis conditions. In respect to the traditional AIMI procedure, in which a central Mg rod is covered with a B corona, here a Mg tube is filled with B powder and clad in a Ti external sheath, which is quite similar to the traditional (powder in tube) technique. After cold deformation, during which several intermediate low temperature heat treatments are necessary in order to relax the Ti sheath and Mg tube, samples are reacted at high temperature and ambient pressure to form a dense MgB2 core. The MgB2 phase results are totally disconnected from metallic sheath, and can be easily extracted and characterized. Critical current density measurements show values exceeding 106 A cm−2 below 1.5 T at 20 K. In the last part of the paper, we show the effect of final heat-treatment performed under high pressure to eliminate the present void and connect the external sheath to the internal MgB2 core and so permitting the electric transfer necessary for power applications of wires.

Method for the production of pure and C-doped nanoboron powders tailored for superconductive applications

“…It becomes clear that B plays an important role in enhancing the properties of MgB 2 [15,16], but for superconductive applications it represents a niche sector if compared to other applications; as a consequence of this, there are still no producers on the market offering a properly nanostructured B (i.e. containing proper pinning centres as well as B site replacement by elemental C in B grain volume), suitable for increasing the critical current density (J C ) value in high magnetic fields, which is an indispensable condition for superconducting applications [17].…”

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

“…The core uniformity is also challenging in the production of long IMD wires due to the variations in the packing density of boron powder along the IMD wire, leading to changes in the superconducting properties after heat treatment. Therefore, improving the longitudinal uniformity and J e in IMD wires is essential for large-scale applications [11,[16][17][18][19][20][21].…”