In-situ synthesis of hierarchically porous and polycrystalline carbon nanowires with excellent microwave absorption performance

To obtain a novel absorber with high absorption, small reflection and wide absorption band, carbon nanowire reinforced Si₃N₄ composite ceramics (CNW/Si₃N₄) have been prepared by catalytic chemical vapor deposition. Results show that as-received carbon nanowires (CNW) have the pitted surface and unique hierarchically (micro-, meso- and macro-) porous construction. Moreover, CNW is polycrystalline and stacked by graphene-like nanosheets with sizes of 1-2 nm. These unique structures make great contribution to the impedance match, and generate strong conductive loss and various dipoles polarization effects which greatly enhance the absorption. A minimum reflection coefficient of CNW/Si₃N₄-1.84 (1.84 wt% absorber loading) reaches -50.21 dB at 10.8 GHz and the maximum effective absorption bandwidth is 4.2 GHz covering the whole X band (8.2-12.4 GHz). It is believed that porous CNW can not only work as an excellent absorber for the attenuation of electromagnetic wave, but also show great potential to be designed as an electrode material for energy conversion and storage.