Highly efficient electromagnetic wave absorbing metal-free and carbon-rich ceramics derived from hyperbranched polycarbosilazanes

The highly efficient electromagnetic (EM) wave absorbing metal-free and carbon-rich ceramics derived from hyperbranched polycarbosilazanes are presented in this contribution. The novel metal-free hyperbranched polycarbosilazanes with pendant cyano groups (hb-PCSZ-cyano) were synthesized through aminolysis reaction and subsequent Michael addition reaction, i.e., cyanoethylation reaction. As metal-free preceramic precursors, the pyrolysis of hb-PCSZ-cyano under high temperature and argon atmosphere generated carbon-rich Si-C-N multiphase ceramics. The ceramics reserve amorphous structure even at high temperature. The introduction of cyano groups in precursors leads to numerous sp₂ carbons and interface polarization in ceramics and favors the EM wave absorption performance. The minimum reflection coefficient (RC) value of Si-C-N multiphase ceramic is-59.59 dB at 12.23 GHz when the sample thickness is 2.30 mm, which means >99.99% electromagnetic waves can be absorbed. The effective absorption bandwidth (RC below-10 dB) is 4.2 GHz, covering the whole X-band (8.2-12.4 GHz). The EM wave absorption property is very excellent in comparison to current electromagnetic wave absorbing materials including transition metal-induced nanocrystals-containing ceramics. The carbon-rich Si-C-N ceramic derived from metal-free precursors provides a new strategy for highly efficient EM wave absorbing functional materials with great potential in electronic devices, antenna housings, and radomes in harsh environments.