Synthesis of niobium boride powder by solid state reaction between niobium and amorphous boron

Niobium boride powders were synthesized by solid state reaction between niobium metal powder and amorphous boron powder. The formation of niobium borides was found to be dependent on temperature. Single phases of the stable borides, NbB and NbB₂, were formed by heating mixed powders corresponding to the stoichiometric compositions at 1000 °C for 60 min. A single phase of Nb₃B₄ was obtained at a higher temperature of 1800 °C as a result of the promoted diffusion of boron atoms in niobium metal. All synthesized powders were well dispersed and had particle sizes of 5–10 μm. The sinterability of the synthesized NbB₂ powder was evaluated at high pressure (4 GPa) and temperature (1600 °C) for 15 min; a single-phase sintered compact of NbB₂ was formed with a relative density of 98% and a Vickers microhardness of 2600 kg mm⁻².