3D printing “wire-on-sphere” hierarchical SiC nanowires / SiC whiskers foam for efficient high-temperature electromagnetic wave absorption

Electromagnetic wave absorption (EWA) materials for use in extreme environments are of great interest. Herein, SiC nanowires / SiC whiskers (SiC_nw/SiC_w) foam with unique “wire-on-sphere” hierarchical structure was developed for efficient high-temperature EWA. SiC_w were assembled to porous SiC_w spheres via spray drying and then SiC_w spheres were 3D printed to SiC_w foam. The catalyst-free precursor infiltration pyrolysis process was first developed to ensure that SiC_nw can intentionally grow in situ on the surface of SiC_w spheres, thereby achieving “wire-on-sphere” hierarchical structure foam. At room-temperature, the maximum electromagnetic wave effective absorption bandwidth (EAB_max) and minimum electromagnetic wave reflection coefficient (RC_min) of SiC_nw/SiC_w foam can reach 4 GHz and -57 dB, respectively. At 600 °C, the EAB_max and RC_min were 3 GHz and -15 dB, respectively. Furthermore, even oxidized at 1000–1500 °C, SiC_nw/SiC_w foam can still retain EAB_max ranging from 2.7 to 3.9 GHz and RC_min ranging from -16 dB to -64 dB, because the formation of SiO₂ layer with appropriate thickness can boost interfacial polarization and regulate impedance matching. The SiC_nw/SiC_w foam also shows the flexural strength as high as 17.05 MPa. All results demonstrate that the SiC_nw/SiC_w foam is a promising EWA material for applications of harsh environments. And the material-independent “wire-on-sphere” hierarchical structure and its novel preparation process should find the widespread use in the design and fabrication of high-efficiency EWA micro-nano materials.