Construction of anti-oxidative and efficient Ni2Si/SiC/C-based microwave absorption composite by recycling coal hydrogasification residue

With the growing demand for advanced microwave absorption (MA) materials in harsh application environments, there is an urgent need to develop efficient absorbent with exceptional high-temperature oxidation resistance. Herein, we successfully fabricated novel Ni₂Si/SiC/C composites with remarkable thermal stability through a combined sol–gel embedding method and high-temperature solid-phase reaction strategy, using coal hydrogasification residue as the carbon matrix. The as-prepared Ni₂Si/SiC/C composite features a unique microstructure comprising a porous carbon skeleton decorated with SiC nanoparticles and spherical Ni₂Si coatings. By precisely tuning the stoichiometric ratios of silicon, carbon, and nickel precursors in the fabrication process, the optimized samples demonstrated outstanding MA performance at room temperature. Notably, 15Ni-SiC/C-5.0 achieved a minimum reflection loss (RL_min) of −31.18 dB with a maximum effective absorption bandwidth (EAB_max) of 4.0 GHz at a thin matching thickness of only 1.5 mm. Meanwhile, 20Ni-SiC/C-5.0 exhibited an even deeper RL_min of −37.30 dB at 5.5 mm, with an impressive broadband EAB covering 14.64 GHz across the entire tested thickness range (1.0–5.5 mm). Remarkably, after undergoing calcination at 600 °C in air for 2 h, the two samples maintained excellent MA performance, with RL_min values of −42.53 dB and −30.72 dB at 4.0 mm, respectively, demonstrating their superior high-temperature thermal stability. Further investigation revealed that the outstanding MA performance stem from an optimal combination of impedance matching, conductive loss, and polarization loss mechanisms, all of which are closely related to the composite’s microstructure. This work not only presents a high-performance, oxidation-resistant carbon-based microwave absorbent but also provides valuable insights for the future development of advanced anti-oxidative microwave absorbents.