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

Song, Yan, He, Lihua, Zhang, Xiaofei, Liu, Fei, Tian, Nan, Tang, Yusheng, Kong, Jie
The Journal of Physical Chemistry C 2017 v.121 no.44 pp. 24774-24785
absorption, aminolysis, argon (noble gases), ceramics, electromagnetic radiation, electronic equipment, pyrolysis, temperature
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.