Study on the microwave absorbing properties of Fe nanoparticles prepared by the HEIBE method in expanded graphite matrix composites

Highlights: • On the premise of adding a small amount of magnetic iron nanoparticles to prepare an ultra-light absorbing material, the sample can obtain a good reflection loss value in the S-band. • Using urea as a nitrogen source, EG is doped to optimize its dielectric constant, and by adjusting the mass ratio of FeNPs, the absorbing performance can be effectively adjusted. • Compared with other materials of the same type, it has better matching frequency and absorbing bandwidth. • The simple material preparation process provides valuable experience for the industrial production of excellent absorbers. -- Abstract: Recent findings reveal that expanded graphite (EG) composite with metal nanoparticles has an excellent performance in the field of absorbing materials. The N-dope broken EG/FeNPs (NBEG/Fe) composites with sandwich structure and low graphitization degree were prepared through hydrothermal reaction. The doping N element further enhances the electrical conductivity of EG, the purpose is to be consistent with the high permeability of the core-shell Fe/Fe₃O₄ nanoparticles (FeNPs), which can effectively improve the matching impedance. The experimental results in the 2–18 GHz range prove that NBEG/Fe has better absorption performance than pure EG and BEG/Fe, and by changing the content of FeNPs, the purpose of effectively absorbing electromagnetic microwaves in different frequency bands can be achieved. With only 10% addition of NBEG/Fe, when the matching frequency is 15.67 and 4.51 GHz, and the matching thickness is 1.42 and 5.40 mm, the reflection loss (RL) of NBEG/Fe reaches −56.75 and −43.3 dB, the RL value of NBEG/Fe has also reached an effective absorption bandwidth of 3.92 GHz (RL ≤ 20.0 dB) in the interval 4.06–10.64 GHz. In particular, the RL value of NBEG/Fe in the S-band (at 3.74 GHz) reaches −40.3 dB at a thickness of 6.5 mm. Moreover, under the matching frequency and matching thickness good absorption performance (RL < −20.0 dB) from 2.00 GHz to 18.00 GHz is obtained.