In-situ formation of carbon nanotubes in pyrolytic carbon-silicon nitride composite ceramics

Carbon nanotube reinforced pyrolytic carbon/silicon nitride (CNT-PyC/Si₃N₄) composite ceramics were fabricated through in-situ growth of CNTs in PyC-Si₃N₄ ceramics by precursor infiltration and pyrolysis. CNTs were in-situ formed by the addition of nano-sized Ni into phenolic resin and Si₃N₄ powder blend, and the content of CNTs increased with the increase of Ni content. Due to the formation of CNTs in the inter-particle pores of CNTs/PyC-Si₃N ₄ ceramic, the PyC wrapped Si₃N₄ particles were bridged by CNTs, which led to the increase of electrical conductivity. Different from the previously reported PyC-Si₃N₄ ceramics fabricated by chemical vapor infiltration (CVI), the PyC-Si₃N ₄ ceramics exhibited a shielding mechanism dominated by absorption. Compared to PyC-Si₃N₄ ceramics prepared with same procedure, the shielding effectiveness of CNTs-PyC/Si₃N₄ increased significantly with the formation of CNTs. With the increase of CNT content, the shielding effectiveness of CNTs/PyC-Si₃N₄ ceramics increased from 25.5 to 43.6 dB, in which the absorption shielding effectiveness increased from 15 to 30 dB over the frequency range of 8.2-12.4 GHz.