Synthesis of submicron TiB ₂ /ZrB ₂ powders via low‐temperature carbo/borothermal reduction and calcium treatment

Abstract The traditional carbo/borothermal reduction for the preparation of TiB 2 and ZrB 2 powders struggles with impurity retention at low temperatures and abnormal grain growth (>5 µm) at high temperatures (>1600°C). In this work, the introduction of calcium treatment could effectively resolve this contradiction. Specifically, near‐complete phase transformation of raw materials into TiB 2 /ZrB 2 was achieved at lower temperatures (1400°C, 1500°C), effectively suppressing high‐temperature‐induced grain coarsening. The growth mechanisms of TiB 2 and ZrB 2 during the carbo/borothermal reduction process were dominated by the screw dislocation growth mechanism and two‐dimensional surface nucleation mechanism, respectively. Subsequent calcium treatment could eliminate residual impurities (residual carbon) and promote further reactions of residual oxides to borides. Moreover, adding excess carbon during the carbon/borothermal reduction could suppress the volatilization of B 2 O 3 , and partially replacing Ca with CaCl 2 in the calcium treatment could reduce the temperature of the following leaching step. Following these two process optimizations, single‐phase TiB 2 and ZrB 2 powders (1 µm) with low oxygen content (TiB 2 —1.11 wt.%; ZrB 2 —0.45 wt.%) and carbon content (TiB 2 —0.74 wt.%; ZrB 2 —0.68 wt.%) were obtained.