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The present work was concentrated mainly on the reaction processes of boro/carbothermal reduction (BCTR) of ZrO 2 with B 4 C and carbon in vacuum, and characterization of morphology and sinterability of the obtained ZrB 2 powder. Combining the thermodynamic calculations, X-ray diffraction results, and the trend of furnace pressure with temperature during synthesis, a detailed explanation of the reaction processes of BCTR was developed. Most of the ZrB 2 particles obtained at 16501C presented a nearly spherical morphology, whereas those synthesized at 17501C showed a nearly columnar morphology with an increased size. Compared with the powder synthesized at 17501C as well as the commercially additive-free powder used in the reported work, the ZrB 2 powder synthesized at 16501C showed a better sinterability due to its smaller particle size and lower oxygen content.

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The ZrB2 powders with submicrometric particle size and low oxygen content were synthesized by a new borothermal reduction route using ZrO2 and excess boron as raw materials. The conventional process only contained the borothermal reduction of ZrO2 with boron at 1550°C. By exploring the mechanism of ZrB2 particle coarsening during conventional process, a new borothermal reduction route was proposed. This route included the borothermal reduction of ZrO2 with boron at 1000°C, washing by hot water, and the removal of residual boron oxides at 1550°C, namely, two‐step reduction plus intermediate water‐washing (RWR). Using conventional process, the particle size and oxygen content of ZrB2 powder were about 2–3 μm and 0.68 wt%, respectively. Based on the new route, the particle size and oxygen content of ZrB2 powder were about 0.4–0.7 μm and 0.40 wt%, respectively.