Microstructure and phase evolution of polymer-derived SiHfOC ceramic microspheres

The SiHfOC ceramic microspheres were synthesized from the polysilazane and hafnium(IV) acetylacetonate hybrid precursors through a combination of hydrothermal method and polymer-derived ceramics (PDCs) method. The SiHfOC ceramic microspheres consist of β-SiC, SiO₂, and m-HfO₂ in an amorphous SiOC matrix and are in a spherical morphology with an average size of about 2 μm. Hafnium-containing nanoparticles with ∼50-nm size are not only uniformly distributed on the surface of the ceramic microspheres but also embedded in the SiHfOC ceramic microspheres, forming a unique mosaic structure. Pyrolyzing at 1000°C offers a possibility of an in situ formation of nanocrystal nuclei in the amorphous SiOC ceramic matrix, and the subsequent annealing at 1500°C helps the small nanocrystal nuclei grow and separate the amorphous SiHfOC into a multiphase SiOC network containing β-SiC, SiO₂, m-HfO₂ nanocrystalline and free C. This research provides a methodology for preparing multicomponent ceramic microspheres that can efficiently develop high-performance PDCs modified by transition metal alkoxide.