Sandwich-like SiCnw/C/Si3N4 porous layered composite for full X-band electromagnetic wave absorption at elevated temperature

SiCnw/C/Si3N4 porous ceramic composites with layer-by-layer structure were successfully fabricated by freeze drying, carbonization and chemical vapor infiltration processes for excellent room and high temperature electromagnetic (EM) wave absorption properties. The sandwich-like structure within the layer and the capacitor model structure between the layers are formed inside of the composite, and these structures are beneficial to the EM wave consumption. The EM absorption properties are optimized by regulating the relative contribution of the polarization loss (primarily provide by SiCnw and defects in carbon phase) and the conductance loss (primarily offered by the conductive network formed by the carbon thin film). As an antioxidant protective layer, Si3N4 ceramic coating is prepared on the outside of the carbon film. The prepared SiCnw/C/Si3N4 porous composites show high absorption efficiency (exceed -39.7 dB), wide absorption band (cover the whole X band), small density (0.92 g/cm(3)), thin thickness (2.9 mm), and excellent high-temperature stability (stable up to 873 K). The unique structures not only facilitate EM wave absorption, but also enable the composite a compressive strength of 168 MPa.