Synthesis of TaB2 powders by borothermal reduction

Borothermal reduction processes of Ta2O5 with boron under vacuum were investigated. Ta2O5 reacted with boron to form various borides (TaB2, Ta3B4, and TaB), depending on the boron/Ta2O5 molar ratio and temperature. In order to prepare pure TaB2 powders, two routes were developed. The first route was one‐step heat treatment at 1550°C. With boron/Ta2O5 molar ratio of 9.0, pure TaB2 powders with strong agglomeration were synthesized by the first route, and the particle size and oxygen content were 0.7 μm and 0.9 wt%, respectively. The second route consisted of two‐step heat treatment at 800°C and 1550°C plus intermediate water washing. With lower boron/Ta2O5 molar ratio of 8.2, pure TaB2 powders with less agglomeration and more uniform distribution were synthesized by the second route, and the particle size and oxygen content were 0.8 μm and 0.8 wt%, respectively. Moreover, the particle size similarity of TaB2 powders by the two routes suggested that byproduct boron oxides, which were previously reported as the most important factor in promoting the coarsening of ZrB2 powders by borothermal reduction, did not lead to the significant coarsening of TaB2 powders.