Preparation of zirconium diboride ultrafine hollow spheres by a combined sol–gel and boro/carbothermal reduction technique

As an important ceramic possessing many excellent properties, zirconium diboride (ZrB₂) has attracted considerable attention and found many ultra-high temperature applications. In this work, ZrB₂ ultrafine powders were successfully synthesized by a combined one-pot sol–gel and boro/carbothermal reduction method using zirconium oxychloride, boric acid and glucose as starting materials. Pure ZrB₂ was successfully synthesized at 1,500 °C for 2 h using the optimal molar ratios of n(B)/n(Zr) = 2.5 and n(C)/n(Zr) = 6.5. The as-prepared ZrB₂ powders were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive spectroscopy, selected area electron diffraction and transmission electron microscopy. The grain size and the crystalline size of the as-prepared ZrB₂ powders were found to be 1–2 μm and about 48 nm, respectively. Interestingly, some ZrB₂ ultrafine hollow spheres (UHS) with diameters from 100 to 500 nm were also in situ formed with the ZrB₂ ultrafine particles during the sol–gel and boro/carbothermal reduction process. The mechanism for the formation of these ZrB₂ UHS was also proposed based on the experimental results.