Processing of dense bulk MgB2 superconductor via pressure-assisted thermal explosion mode of SHS

Bulk MgB2 superconductor was synthesized from elemental Mg–B blends employing Reactive Forging (RF)—thermal explosion mode of Self-propagating High-temperature Synthesis (SHS)—under a moderate pressure of 200 MPa. RF of the stoichiometric Mg–2B blend conducted at 800 °C yielded near-single-phase albeit porous (92% TD) MgB2, whereas RF at 1000 °C produced a fully dense material containing significant amounts of MgO and MgB4. The addition of 20–30 wt.% Mg to the starting blend improved material's consolidation behavior at 800 °C, as well as hindered the formation of MgB4 at 1000 °C. For all the compositions and RF conditions, the combustion temperature, Tcomb of approximately 1200 °C was measured. Plastic deformation at Tcomb of the ductile MgO phase and/or residual Mg resulted in full density consolidation of the synthesized material. In all the specimens, a superconducting transition was observed at 39 K regardless of their porosity and the amount of second phases. Above 39 K, the electrical resistivity of dense MgB2 specimens with residual metallic magnesium was 30 times lower than that of the 92% dense near-single-phase MgB2.