Weichao Wang,Liuying Wang,Jie Huang,Qi Gu,Yanyan Lu,Chaoqun Ge,Gu Liu
The rapid advancement of aerospace technology has subjected high-speed aircraft to increasingly severe high-temperature conditions, thereby substantially increasing the demand for high-temperature electromagnetic wave (EMW) absorbing materials. However, due to the temperature dependence of the permittivity, high-temperature EMW absorbing materials still face the challenge of maintaining consistent impedance matching performance at different temperatures. This study proposes a novel approach by in-situ constructing Si-Co alloys in amorphous SiOCN ceramics, taking advantage of the inverse temperature-dependent resistivity behavior among components to dynamically equilibrate the overall conductivity of the ceramics, thereby achieving temperature-insensitive permittivity. This strategy significantly enhances the robustness of dielectric properties against temperature fluctuations and enables effective EMW absorption within a temperature range from ambient to 800 °C at low thickness. By using the self-sacrificing template method, a porous structure was formed while ensuring the precise shaping, thereby further achieving the lightweighting of the ceramics. This lightweight dielectric ceramic with temperature-insensitive permittivity provides novel perspectives for the development of wide-temperature-range EMW absorbing materials.
In the present work, novel single-source-precursors for CNTs/Fe3Si/Fe/SiOCN ceramic nanocomposites were synthesized by the reaction of poly(methylvinyl) silazane (HTT 1800) with ferric acetylacetonate [Fe(acac)3] and carboxylic functionalized carbon nanotubes (CNTs-COOH), which were characterized by means of Fourier transform infrared spectra. The microstructure, phase evolution, electromagnetic properties and electromagnetic microwave absorbing (EMA) performance of the as-prepared ceramics were investigated in detail. The results reveal that the introduced CNTs and the in situ formed nanocrystallites, including α-Fe, Fe3Si, α-Si3N4, β-Si3N4, Si2N2O, and SiC, are dispersed in an amorphous SiOCN matrix after annealing at 900–1500 °C. The obtained ceramic powders mixed with paraffin wax possess a very low minimum reflection coefficient of −65.3 dB and a broad effective absorption bandwidth of 6 GHz (12–18 GHz) with a thickness of 1.6 mm, indicating outstanding EMA performance. This is due to (i) the increase in interfacial polarization caused by the formation of multiple hetero-interfaces and (ii) the synergistic effect of magnetic and dielectric losses. Therefore, the multicomponent CNTs/Fe3Si/Fe/SiOCN ceramic nanocomposites have promising potential for thin and high-performance EMA materials applied in a harsh environment.
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