Urchin-like Fe3O4@C hollow spheres with core–shell structure: Controllable synthesis and microwave absorption

The steadily increasing use of microwave stealth materials in aerospace flying vehicles needs the development of lightweight absorbers with low density and high thermal stability for printing or spraying. In that regard, the structural designability of typical microwave absorbers made of Fe3O4 seems to be a significant roadmap. In this work, a hollow spherical structure with a uniform carbon shell around the urchin-like Fe3O4 core (Fe3O4@C) was produced via a two-step hydrothermal method and annealing. The Fe3O4@C absorber exhibited a strong minimum reflection loss (RLmin) of −73.5 dB at the matching thickness of 3.23 mm. The maximum effective absorption bandwidth (EABmax) was 4.78 GHz at 4.55 mm. The proposed urchin-like core–shell structure was shown to provide good impedance matching and electromagnetic loss ability due to the synergistic effect of Fe3O4 and C. In particular, the urchin-like structure increases the heterogeneous interfaces and effectively improves their polarization and relaxation. On the other hand, it reduces the density of the absorber and enhances multiple scattering attenuations of electromagnetic waves (EMWs). Therefore, the findings of the present study open up prospects for the design of high-efficiency lightweight microwave absorbers with specialized structures.