Selective microwave absorption of SiC–Si3N4 porous ceramics prepared by sacrificial template method

Porous SiC–Si3N4 ceramics with various pore structures were prepared by adding different amounts and sizes of pore-forming agents (Polymethyl methacrylate, PMMA). The dielectric and wave absorption properties of porous ceramics were investigated over a wide temperature and frequency range. Increasing the porosity reduced the frequency dependence of complex permittivity. When the porosity increased from 50.97% to 54.59%, the loss tangent was slightly enhanced due to pore-induced polarization. An optimal pore size range enhanced the dielectric properties, beyond which a lower loss tangent was exhibited. Increasing the porosity reduced the temperature dependence of the loss tangent, and the peak of the change rate of the loss tangent moved to a higher temperature. The minimum reflection loss at room temperature can reach - 49.61 dB at 11.91 GHz for a 1.9 mm-thick sample. The minimum reflection loss at 9.72 GHz for 25 vol% PMMA-added porous ceramic with a 2.1 mm-thick material can be as low as - 65.92 dB at 300 °C. The porosity can be changed to achieve selective electromagnetic wave absorption at different temperatures.