  In the present paper we report an in-situ high-energy X-ray diffraction
analysis of MgB2 tapes during the preparation process. The experiment was
performed in a specifically designed furnace working in reducing atmosphere,
compatible with the Laue diffraction condition. The MgB2 synthesis was realized
starting from MgH2 and amorphous B in powder form as precursors, varying
reaction temperature and testing different cooling processes. We analyzed both
the MgB2 synthesis and the sintering process of tapes prepared with these
powders. Phase evolution, micro and crystallographic structure were monitored
during the different thermal treatments. Among the main results we observed the
formation of MgB2 at an extraordinary low temperature (300C), probably as a
result of a solid-state reaction between MgH2 and B. Furthermore, we studied
the dependence of the micro-structure upon the thermal treatment and its effect
on the critical current performance of the superconducting tapes.
