Oxide ceramic matrix composites (OCMC) are extensively used as thermal structural materials due to good high-temperature resistance, mechanical properties, and oxidation resistance, but they are rarely regarded as electromagnetic wave absorbing materials due to the high resistivity of oxide ceramics/fibers. However, high-performance Al 2 O 3 fiber can be used to design and fabricate OCMC with integrated high-temperature microwave absorbing and mechanical properties by introducing dielectric material into Si-based ceramic matrix. The N610/Si 3 N 4 -SiOC composites have the prior mechanical performance because the uniformly distributed Si 3 N 4 matrix made the fiber bear effectively. After that, the Sc 2 O 3 modified SiOC matrix was filled into inter- and intra-fascicular pores forming interfacial polarization, dipole polarization, multiple reflection and scattering to attenuate the incident electromagnetic wave (EMW). The effective absorption bandwidth (EAB) and the minimum reflection coefficient (RC min ) of N610/Si 3 N 4 -SiOC(Sc) composites at the thickness of 2.75 mm reach 3.0 GHz and −42 dB in the X band, respectively. In addition, the EMW absorption performance of the composite is relatively stable with EAB max and RC min of 3.5 GHz and −41 dB in 4–18 GHz at high temperatures. This work provides a strategy for designing and fabricating OCMC with excellent mechanical properties and EMW absorption properties.
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, SiO 2 , and m -HfO 2 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, SiO 2 , m -HfO 2 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.
危险品化学品经营许可证（带存储）