Synthesis of HfB ₂ powders by reduction of HfO ₂ with BN/C in a spark plasma sintering furnace

Abstract The reduction of HfO 2 to produce HfB 2 powder currently represents the most cost-effective synthesis method. However, reduction processes employing B 2 O 3 , B 4 C or elemental B invariably involve volatile B 2 O 3 species, which damage high-temperature furnaces. This work reports an alternative approach using BN/C as reductants in a spark plasma sintering (SPS) furnace to synthesize HfB 2 . The reaction mechanism involves two sequential steps: initial reduction of HfO 2 by C to form non-stoichiometric HfC 1- x , followed by reaction between HfC 1- x and BN to yield HfB 2 . At 1,600 °C, phase-pure HfB 2 powder with ultralow oxygen content (0.47 wt.%) was obtained. The synthesized powder exhibits submicron particle size ( d 50 = 0.184 μm) and a distinctive bimodal distribution pattern.