Ultrafine ZrB2 Ceramic Powders Prepared by a Sol–Gel Method Synergized with a Carbothermic Reaction and Their Improved Sintering Performance

The sol–gel method synergized with a carbothermic reaction has been known to be one of the most promising strategies for preparing a high-quality boride and carbon-based ultrahigh-temperature ceramic, yet their growth mechanism remains underexplored. Herein, high-purity ZrB2 ceramic powders are prepared by a sol–gel method synergized with a subsequent carbothermic reaction. Specifically, sorbitol (C6H14O6) is adopted to build molecularly disperse networks of Zr–O–C–B. Structural characterizations reveal that the calcination temperature and duration have a great influence on the phase and morphological transformation of the precursor. The ZrB2 seeds start to be generated near ZrO2 particles around 1100 °C and grow from the surface to the core of ZrO2 particles with heat and mass transportation around ZrO2 driven by B2O3 at high temperature. Additionally, the ZrB2 powders could research a hardness of 22.5 GPa and a bending strength of 540 MPa after sintering, showing improved mechanical properties. This work reveals the growth mechanism of ultrafine and high-purity ZrB2 powders by a sol–gel method and a carbothermic reaction, which can be used as raw materials to obtain ZrB2 ultrahigh-temperature ceramics with improved mechanical properties.