Synthesis of NbC and NbB2 by MA-SHS in air process

When the powder mixture of Nb/B/C = 2/2/1 in molar ratio was mechanically activated by grinding in a planetary ball mill and then exposed to air, it self-ignited spontaneously and the self-propagating high-temperature synthesis of NbC and NbB2 was induced. In this mechanical activation assisted self-propagating high-temperature synthesis (MA-SHS) in air, it was essential that graphite was transformed into fine, disordered carbon by mechanical activation, and intimately covered the particles of Nb metal. On the other hand, the isothermal solid-state reaction of the powder mixture of Nb/B/C = 2/2/1 in argon formed NbB2 at 1000 °C and then NbC at 1200 °C. The reaction mechanism and the morphology of the products obtained in both processes are discussed. The product with fine, homogeneous microstructure obtained in the MA-SHS in air process is expected to be a promising candidate as precursor of NbC-NbB2 composites.