The diffusion of Fe from the shield into the in situ MgB2 material in superconducting wires

The findings of this study demonstrate that the morphology of in situ MgB2 wires examined by scanning electron microscopy (SEM) is primarily influenced by the applied polishing method, rather than by intrinsic phenomena associated with the synthesis reaction. This observation is of paramount importance for all superconducting ceramic materials. Main purpose of using fractured surfaces is to significantly better characterize of the Fe2B layer microstructure and composition. Furthermore, our paper presents the influence of the annealing temperature and initial filling densities on the diffusion of Fe from the shield into the core of the MgB2 material. Our results show that two intermetallic layers are formed during the solid-state reaction of Mg with B and long annealing time in MgB2 wires in an Fe shield. The first layer is composed of Mg and Fe, which do not form chemical bonds, and the subsequent layer consists of iron borides. To the best of the present author's knowledge, results of this kind pertaining to in situ MgB2 wires within Fe shields have not hitherto been reported. Moreover, it was demonstrated that thermal treatment in the liquid state of Mg facilitates the formation of an iron boride layer between the MgB2 core and the Fe shields. Additionally, the X-ray powder diffraction showed that the initial filling densities strongly affect the boride phases formed in Fe-shielded MgB2 wires.