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–Si3N4 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–Si3N4 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.