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 A degrees 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 mu m 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.