Synthesis and growth behavior of micron-sized rod-like ZrB2 powders

Using ZrOCl2·8H2O, Na2B4O7·10H2O and C12H22O11 as raw materials, micron-sized rod-like ZrB2 powders were prepared via a molten-salt-mediated carbothermal reduction from chemically homogenous precursors obtained by sol-gel method. The effects of Zr/B/C molar ratio, firing temperature, holding time and molten salt on the composition of products have been investigated, respectively. Pure micron-sized ZrB2 powders with controllable rod-like morphology were obtained at 1400 °C for 4 h holding with Zr/B/C of 1/5/5 in presence of molten salt, which has a diameter of 1-2 µm and aspect ratios of 3-10. The investigation of growth behavior showed that at the first stage, nano-size ZrB2 columns grew along the c-axis with ZrCx thin film on their top as “active-site”. Then, with consuming 'active sites', ZrB2 columns started to grow in diameter direction, and finally small columns merged into a larger rod.