Phase evolution inside Fe-sheathed wires containing precursor powders consisting of a mixture of Mg and B was studied in situ by means of X-ray diffraction with hard synchrotron radiation (90keV). The Mg was found to disappear progressively during the heating stage. At 500C, the intensity of the Mg diffraction lines was reduced by about 20%. This effect was partly attributable to MgO formation. The MgB2 phase was detected from 575C. Fe2B was forming at the interface between the sheath and the ceramic core at sintering temperatures of 780 and 700C, but not at 650C. The formation rate of this phase was strongly dependent on the heat treatment temperature. Its presence could be readily detected as soon as the average interface reaction thickness exceeded 150 to 200nm.

In situ Investigations of Phase Transformations in Fe-Sheathed MgB2 Wires. J.C.Grivel, R.Pinholt, N.H.Andersen, P.Kovác, I.Husek, J.Homeyer: Superconductor Science and Technology, 2006, 19, 96-101