Synthesis of Magnesium Nickel Boride Aggregates via Borohydride Autogenous Pressure

We demonstrate synthesis of the ternary intermetallic MgNi(3)B(2) using autogenous pressure from the reaction of NaBH(4) with Mg and Ni metal powder. The decomposition of NaBH(4) to H(2) and B(2)H(6) commences at low temperatures in the presence of Mg and/or Ni and promotes formation of Ni-borides and MgNi(3)B(2) with the increase in temperature. MgNi(3)B(2) aggregates with Ni-boride cores are formed when the reaction temperature is >670 °C and autogenous pressure is >1.7 MPa. Morphologies and microstructures suggest that solid–gas and liquid–gas reactions are dominant mechanisms and that Ni-borides form at a lower temperature than MgNi(3)B(2). Magnetic measurements of the core-shell MgNi(3)B(2) aggregates are consistent with ferromagnetic behaviour in contrast to stoichiometric MgNi(3)B(2) which is diamagnetic at room temperature.