Microwave absorption performance and multiple loss mechanisms of three-dimensional porous Fe4N@Fe3O4@Fe/carbon composite

The carbon matrix composites with three-dimensional porous structure and multiple phases were prepared by heat treatment of nano-Fe and polyacrylonitrile (PAN) precursor with different content of nano-Fe. The phase and morphology changes of the samples during heat treatment were investigated, and their electromagnetic properties and microwave absorption performance were compared in the frequency range of 2–18 GHz. The Fe4N@Fe3O4@Fe/carbon composite presents a three-dimensional porous structure with an average pore size of 5 μm. Fe4N and Fe3O4 can be generated in situ by the reaction of Fe with active N and O in PAN, which is helpful to improve the dielectric and magnetic losses of the composite. PAN can be cyclized, crosslinked and pyrolyzed to form graphite carbon and amorphous carbon, and various reactions in the heat treatment process, the heterogeneous interfaces between magnetic phases and carbon matrix were formed, which can enhance the interfacial polarization relaxation. With the increase in nano-Fe content, the magnetic loss increases, and with the increase in magnetic particle content and coating thickness, the absorption peak tends to move to lower frequency. When the mass ratio of Fe/PAN in the precursor is 120%, the lowest reflection loss of the composite is − 37 dB at 13 GHz, and the effective absorption bandwidth is 3.23 GHz (11.54–14.77 GHz) with 1.5 mm thickness. When the mass ratio is 180%, the lowest reflection loss is − 33 dB at 4.7 GHz. This study not only provides a simple method to prepare porous carbon and ferromagnetic composites, but also shows that Fe4N has great potential in the application of wave absorbers.