Preparation and microwave absorbing properties of Fe₃O₄@C nanoparticles

Fe3O4 nanoparticles coated with amorphous carbon, namely, Fe3O4@C nanoparticles, were prepared by oxidizing nano-Fe particles, covering the surface with a layer of phenolic resin through an in situ polymerization reaction, and then carbonizing the phenolic resin to form a carbon shell layer via high-temperature calcination. The micromorphology, phase structure, electromagnetic loss characteristics and absorbing properties were studied, and the absorbing principle was analyzed. The results show that the Fe3O4@C nanoparticles have the morphology and crystal structure as Fe3O4 nanoparticles, with a diameter of approximately 200 nm and a carbon layer thickness of approximately 60 nm. In the frequency range of 2~18 GHz, the maximum reflection loss at 10.24 GHz is -11.79 dB, and the maximum effective absorption bandwidth of <-10 dB is 3.52 GHz. The improvement of the microwave absorbing properties of composites can be attributed to that the coating of carbon shell improves the complex dielectric constant and the complex permeability of the material, resulting in higher dielectric loss and magnetic loss capacity of the material.