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

Abstract

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 sp 2 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.

Enhanced electromagnetic wave absorption of Fe‐doped silicon oxycarbide nanocomposites

“…Figure summarizes the typical PDC‐based nanocomposites in terms of RL min values reported in the recent literatures . It can be seen that the PDC‐based absorbers are wildly investigated in recent years.…”

“…Figure 8 summarizes the typical PDC-based nanocomposites in terms of RL min values reported in the recent literatures. 47,[49][50][51][52][53][61][62][63][64][65][66][67][68] It can be seen that the PDC-based absorbers are wildly investigated in recent years. Both of these PDC-based absorbers have a narrow EAB.…”

“…Compared with the transition‐metal‐containing ceramics, the carbon‐rich SiBCN ceramics not only have excellent EMI absorbing properties, but also have a more stable structure at high temperature. Owing to improve the permittivity characteristic, the carbon‐rich PDC‐SiCN composite shows excellent EMI absorbing capability and the RL min reaches −59.60 dB at 12.23 GHz with the thickness of 2.30 mm . In comparison with other PDC‐based materials, SiOC ceramics not only effectively retain the tailoring structure, but also show low cost and good conductivity; thus, they have been widely used in Li ions battery, thermal protection materials, and absorbing materials .…”

“…Owing to improve the permittivity characteristic, the carbon-rich PDC-SiCN composite shows excellent EMI absorbing capability and the RL min reaches −59.60 dB at 12.23 GHz with the thickness of 2.30 mm. 47 In comparison with other PDC-based materials, SiOC ceramics not only effectively retain the tailoring structure, but also show low cost and good conductivity; thus, they have been widely used in Li ions battery, thermal protection materials, and absorbing materials. 48 Unfavorably, sole SiOC ceramics show poor EMI absorbing capability due to their low dielectric loss.…”

Microwave Absorption of Crystalline Fe/MnO@C Nanocapsules Embedded in Amorphous Carbon

“…As science and technology develop dramatically fast, electromagnetic radiation pollution has become a growing problem due to the explosive growth in the application of electronic devices, such as radar systems, local area networks, telephones, and computers. Overexposure to electromagnetic wave can not only affect the functioning of electronic equipment but also be potentially detrimental to human being and raise severe problems concerning the field of military applications [1][2][3]. Therefore, it has spurred internationally unprecedented interest in exploring microwave absorbing materials, which converts electromagnetic wave into energy in other forms [4,5].…”