Synthesis of TaB 2 powders by borothermal reduction

Borothermal reduction processes of Ta 2 O 5 with boron under vacuum were investigated. Ta 2 O 5 reacted with boron to form various borides (TaB 2 , Ta 3 B 4 , and TaB), depending on the boron/Ta 2 O 5 molar ratio and temperature. In order to prepare pure TaB 2 powders, two routes were developed. The first route was one‐step heat treatment at 1550°C. With boron/Ta 2 O 5 molar ratio of 9.0, pure TaB 2 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/Ta 2 O 5 molar ratio of 8.2, pure TaB 2 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 TaB 2 powders by the two routes suggested that byproduct boron oxides, which were previously reported as the most important factor in promoting the coarsening of ZrB 2 powders by borothermal reduction, did not lead to the significant coarsening of TaB 2 powders.