Tunable electromagnetic properties and excellent thermo-stability are important criteria while choosing absorbers. Here, carbon-coated Fe3Si nanoparticles in amorphous SiCO ceramics (SiCO/C/Fe3Si) were successfully obtained via polymer-derived ceramics (PDC) from ferric acetylacetonate modified-polysilylacetylene (PSA). By adjusting the magnetic components, the structure of the absorbers could be tuned and their bandwidth varied. The absorbers with a hybrid composition (4.35 wt% Fe) possessed a minimal reflection loss (RL) of −32 dB at 9.2 GHz with a thickness of 3.5 mm and an effective bandwidth (RL < −10 dB) of about 3.6 GHz. The absorbers (12.33 wt% Fe) were enhanced and the minimal RL value was close to −41 dB at 7.9 GHz with a thickness of 3.5 mm. Simultaneously, a broad bandwidth (RL < −5 dB) appeared and covered nearly the whole S-band (2–3.95 GHz) where the RL value reached −10 dB at 2 GHz. After the second thermal treatment under 1000 °C, the minimal RL value of the absorbers (12.33 wt% Fe) remained at −33 dB at 6.6 GHz with a thickness of 4 mm, while the effective bandwidth was 3.4 GHz with a thickness of 3 mm. In addition, the formation mechanism of carbon-coated Fe3Si, which possibly resulted from the mesophase SiCFe alloy was also discussed. The as-prepared SiCO/C/Fe3Si hybrid exhibits outstanding wave absorption ability and present a huge potential for the application at high temperatures.
Due to the extremely low transmission loss, hexagonal boron nitride (h-BN) is always used as a permeable material for electromagnetic wave (EMW). However, an excellent electromagnetic absorption is achieved from two-dimensional BN based absorber just because of the polymer-derived SiCO ceramic coating on BN sheets. This novel SiCO coated BN absorber (SiCO@BN) possesses a unique core-hell structure, which acts as an electromagnetic resonant cavity for EMW absorption. The as-prepared SiCO@BN ceramics not only inherit the low density, card-structure, and good impedance matching from the BN ceramic, but also demonstrates a broad absorption because of SiCO coating layer. According to the dielectric constant, the calculated minimum reflection loss (RL min ) could reach −55.6 dB at 8.7 GHz with a thickness of 4 mm, and the broadest effective bandwidth (EBW) is nearly 6 GHz (12–17.9 GHz) at a thickness of 2.5 mm. In addition, the SiCO@BN absorbers have a good high-temperature oxidation resistance with a mass loss beneath 1.3% even after the heating process at 1000 °C in the air. The associating RL min and EBW are still −40 dB with the thickness of 4 mm and 4.8 GHz (8.9–13.7 GHz) with the thickness of 3 mm, respectively. Thence, these properties allow SiCO@BN absorber serving as a unique material under extreme environment, such as the exhaust nozzle of high speed aircraft.
Novel intermetallic compound M x Si modified SiCO ceramic microspheres (SiCOM-ms) were successfully fabricated via the ceramic precursor emulsion method. These SiCOM-ms, with grain size ranging from 3 to 8 µm, had similar “chocolate ball” shape with numerous irregular protrusion on the surface. By adjusting the magnetic components in the precursor, different intermetallic compound M x Si phases were uniformly embedded in the SiCO ceramic matrix and further effectively promoted the formation of the SiC phase and graphited carbon phase. The complex interface structure in SiCOM-ms was derived from the in-situ generated M x Si, SiC, and graphited carbon nanocrystalline , which produced an enhanced interfacial polarization for electromagnetic wave absorption. It is worth mentioning that the SiCOM microspheres exhibit excellent electromagnetic wave absorption with the minimum reflection loss (RL min ) below − 60 dB, especially in the low frequency (2–8 GHz). Moreover, the RL min of SiCOCo-ms could reach − 70.6 dB with the thickness of 4 mm, while the effective absorption bandwidth (EAB, RL<−10 dB) could reach 5.2 GHz at the thickness of 2.5 mm. As for the absorption mechanism, the impendence matching, multiple scattering, interfacial polarization and magnetic loss were all taken into consideration. This work is confident that the novel SiCOM-ms with outstanding electromagnetic performance can be considered ideal materials for electromagnetic absorbing field.
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