Nano-sized amorphous/semi-crystalline boron ratio and external Mg effects on transport and structural properties in MgB2 IMD wires

In the present study, Mg diffusion process has been investigated by transport measurements and surface morphology analysis in round MgB2 wires made with internal Mg diffusion (IMD) method. These wires were produced using semi-amorphous boron, nano-sized amorphous boron or mixtures of them via cold drawing process. In addition to the conventional IMD wire production technique, a thin layer of magnesium was initially coated on the interior of the iron sheath and diffused into the boron powder during sintering. It has been found that Mg coating is effective on improving the engineering current density of IMD wires having relatively thick MgB2 cores. Surprisingly, Mg coating is also effective in non-stoichiometric hybrid IMD wires containing highly excessive amount of Mg.