Lightweight carbonyl iron powder-based yolk-shell architectures for integrated electromagnetic wave absorption and thermal protection

The rapid development of 5G mobile communication and the increasing integration density of electronic devices pose serious challenges to electromagnetic interference control. Carbonyl iron powder (CIP), a widely used magnetic absorber, suffers from high density, limited oxidation resistance, and a narrow effective absorption bandwidth (EAB) under low filler content (60 wt%). In this work, a CIP-based yolk-shell composite structure (CIP@C@Void@ZrO₂) is designed using a sol-gel-hydrothermal-etching approach, which enables a dielectric architecture with multiple heterogeneous interfaces. The resulting material achieves a minimum reflection loss (RL_min) of −51.74 dB at a thickness of 1.8 mm, an EAB_max of 7.76 GHz (9.8–17.56 GHz) at a thickness of 2 mm, and a 41.98 % reduction in true density compared to pristine CIP. The enhanced absorption performance is attributed to multiple mechanisms, including internal cavity-induced reflection and magnetic coupling, interfacial and dipolar polarization, and Fe²⁺/Fe³⁺ hopping-enhanced conduction and polarization loss. The ceramic shell further enhances the thermal stability, increasing the oxidation resistance threshold to 325 °C and reducing the surface temperature rise by 53 % under a 217 °C heat source. This work presents a promising strategy for developing multifunctional materials combining broadband electromagnetic wave (EMW) absorption and thermal protection.