Microwave-assisted synthesis of tremella-like NiCo/C composites for efficient broadband electromagnetic wave absorption at 2-40 GHz

Materials incorporating magnetic metal particles into a carbon matrix have drawn tremendous interest as electromagnetic wave (EMW) absorbers. Herein, the tremella-like assemblies of hierarchically porous nickel-cobalt/carbon (NiCo/C) were successfully prepared by a microwave-assisted method, followed by a sintering process. The sintering temperature is a vital factor for formation of carbon matrix and the metal particles. The higher temperature is helpful for the graphitization of carbon matrix and growth of NiCo alloy. The NiCo/C composite obtained at 700 degrees C displayed the best EMW absorption properties: the minimum reflection loss (RLmin) value reaches -41.6 dB at 8.4 GHz and the widest effective absorption bandwidth is up to 34.33 GHz (3.78-38.11 GHz) by adjusting the layer thickness (1.0-5.5 mm) (EAB, RL <= -10 dB). The excellent EMW absorption properties are attributed to the synergistic effect of the multiple components (magnetic NiCo and dielectric C) and hierarchically porous structure.