Flaky core-shell particles of iron@iron oxides for broadband microwave absorbers in S and C bands

This paper has developed a two-step process integrating mechanical milling with heat-treatment for the preparation of flaky core-shell particles of iron@iron oxides, which show large electromagnetic parameters but low dielectric loss when dispersed at a maximum filling ratio in a dielectric matrix, resulting in broad-band and strong absorption in S and C bands as a thin microwave absorbing material. In this process, prolonging the milling time increases the aspect ratio and specific surface area of the CIPs. This greatly enhances the intrinsic electromagnetic parameters but simultaneously reduces the filling capability in composites, resulting in the occurrence of the largest permeability of the composites at a moderate aspect ratio of the CIPs. The subsequent heat-treatment in air makes surface in-situ oxidation of the flaky CIPs, dramatically decreasing the dielectric loss while keeping the high permeability due to the formation of a Fe3O4 and α-FeOOH shell. Consequently, the as-designed composites with flaky CIPs may exhibit reflection loss (RL) < −6 dB in 2.5-8 GHz and a minimum RL of −11 dB at 4 GHz when the thickness is 1.2 mm. This work provides an effective and convenient route to prepare a high performance thin absorber in low frequency region.