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 ₃N ₄/Si ₃N ₄) were fabricated by chemical vapor infiltration of PyC into porous Si ₃N ₄ ceramics combined with chemical vapor deposition of Si ₃N ₄ at their surface. The electromagnetic shielding effectiveness (SE) of PyC-Si ₃N ₄/Si ₃N 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 ₃N ₄/Si ₃N ₄ reaches 43.2 dB in the frequency range of 8.2-12.4 GHz. Due to the excellent sealing effect of dense Si ₃N ₄ coating, the mean total SE of PyC-Si ₃N ₄/Si ₃N ₄ remains unchanged even after oxidation at 1100°C for 10 h in air.