Synthesis and Electromagnetic Shielding Property of Pyrolytic Carbon‐Silicon Nitride Ceramics with Dense Silicon Nitride Coating

Pyrolytic carbon‐silicon nitride ceramics with dense silicon nitride coating ( PyC‐Si 3 N 4 /Si 3 N 4 ) were fabricated by chemical vapor infiltration of PyC into porous Si 3 N 4 ceramics combined with chemical vapor deposition of Si 3 N 4 at their surface. The electromagnetic shielding effectiveness ( SE ) of PyC‐Si 3 N 4 /Si 3 N 4 increases with the increase of PyC content and specimen thickness. When the content of PyC is 11.7 vol% and the thickness of specimen is 2.8 mm, the mean total SE of PyC‐Si 3 N 4 /Si 3 N 4 reaches 43.2 dB in the frequency range of 8.2–12.4 GHz. Due to the excellent sealing effect of dense Si 3 N 4 coating, the mean total SE of PyC‐Si 3 N 4 /Si 3 N 4 remains unchanged even after oxidation at 1100°C for 10 h in air.