Dielectric, Electromagnetic Interference Shielding and Absorption Properties of Si₃N₄-PyC Composite Ceramics

Pyrolytic carbon (PyC) was infiltrated into silicon nitride (Si₃N₄) ceramics by precursor infiltration and pyrolysis (PIP) of phenolic resin, and Ni nanoparticles were added into the phenolic resin to change the electric conductivity of Si₃N₄-PyC composite ceramics. Dielectric permittivity, electromagnetic interference (EMI) shielding and absorption properties of Si₃N₄-PyC composite ceramics were studied as a function of Ni content at 8.2-12.4 GHz (X-band). When Ni nanoparticles were added into phenolic resin, the electric conductivity of the prepared composite ceramics decreased with increasing Ni content, which was attributed to the decrease of graphitization degree of PyC. The decrease in electric conductivity led to the decrease in both permittivity and EMI shielding effectiveness. Since too high permittivity is harmful to the impendence match and results in the strong reflection, the electromagnetic wave absorption property of Si₃N₄-PyC composite ceramics increases with increasing Ni content. When the content of Ni nanoparticles added into phenolic resin was 2 wt%, the composite ceramics possessed the lowest electric conductivity and displayed the most excellent absorption property with a minimum reflection loss as low as -28.9 dB.