Abstract
The influence of the heating rate of the Mg + 2B mixture on the dynamics of the phase formation during the thermal explosion in the helium medium is investigated by the time-resolved X-ray diffraction method. It is shown that the MgB2 phase appears without the formation of intermediate compounds. The presence of impurity oxygen is a substantial factor affecting the formation kinetics of MgB2. The oxide film on the surface of magnesium particles has no time to form with the heating rate of the charge mixture of 150–200°C/min. A result of this circumstance is the reaction diffusion mechanism of the Mg + 2B = MgB2 reaction immediately after the melting of magnesium. Synthesis products mainly consist of MgB2 and MgO traces at a level of 5%. The thermal explosion temperature is 1100°C. A comparatively thick oxide film which retards melt spreading and shifts the onset of the formation reaction of MgB2 by 8–9 s grows on the magnesium surface at a heating rate of 30–50°C/min. Synthesis products contain MgB2 and up to 15% MgO. The thermal explosion temperature is 1020°C in this case.
Published Version
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