Highly Efficient Electromagnetic Wave Absorbing Metal-Free\nand Carbon-Rich Ceramics Derived from Hyperbranched Polycarbosilazanes

Abstract

The\nhighly efficient electromagnetic (EM) wave absorbing metal-free\nand carbon-rich ceramics derived from hyperbranched polycarbosilazanes\nare presented in this contribution. The novel metal-free hyperbranched\npolycarbosilazanes with pendant cyano groups (hb-PCSZ-cyano) were\nsynthesized through aminolysis reaction and subsequent Michael addition\nreaction, i.e., cyanoethylation reaction. As metal-free preceramic\nprecursors, the pyrolysis of hb-PCSZ-cyano under high temperature\nand argon atmosphere generated carbon-rich Si–C–N multiphase\nceramics. The ceramics reserve amorphous structure even at high temperature.\nThe introduction of cyano groups in precursors leads to numerous <i>sp</i>² carbons and interface polarization in ceramics\nand favors the EM wave absorption performance. The minimum reflection\ncoefficient (RC) value of Si–C–N multiphase ceramic\nis −59.59 dB at 12.23 GHz when the sample thickness is 2.30\nmm, which means >99.99% electromagnetic waves can be absorbed.\nThe\neffective absorption bandwidth (RC below −10 dB) is 4.2 GHz,\ncovering the whole X-band (8.2–12.4 GHz). The EM wave absorption\nproperty is very excellent in comparison to current electromagnetic\nwave absorbing materials including transition metal-induced nanocrystals-containing\nceramics. The carbon-rich Si–C–N ceramic derived from\nmetal-free precursors provides a new strategy for highly efficient\nEM wave absorbing functional materials with great potential in electronic\ndevices, antenna housings, and radomes in harsh environments.