Abstract
In order to enhance dielectric properties of polymer-derived SiC ceramics, a novel single-source-precursor was synthesized by the reaction of an allylhydrido polycarbosilane (AHPCS) and divinyl benzene (DVB) to form carbon-rich SiC. As expected, the free carbon contents of resultant SiC ceramics annealed at 1600 °C are significantly enhanced from 6.62 wt% to 44.67 wt%. After annealing at 900–1600 °C, the obtained carbon-rich SiC ceramics undergo phase separation from amorphous to crystalline feature where superfine SiC nanocrystals and turbostratic carbon networks are dispersed in an amorphous SiC(O) matrix. The dielectric properties and electromagnetic (EM) absorption performance of as-synthesized carbon-rich SiC ceramics are significantly improved by increasing the structural order and content of free carbon. For the 1600 °C ceramics mixed with paraffin wax, the minimum reflection coefficient (RCmin) reaches –56.8 dB at 15.2 GHz with the thickness of 1.51 mm and a relatively broad effective bandwidth (the bandwidth of RC values lower than –10 dB) of 4.43 GHz, indicating the excellent EM absorption performance. The carbon-rich SiC ceramics have to be considered as harsh environmental EM absorbers with excellent chemical stability, high temperature, and oxidation and corrosion resistance.
Highlights
Centimeter-wave frequency electromagnetic (EM) waves (2–18 GHz) are widely used in various environments, which require high efficient EM absorbing (EMA) materials due to the massive increasing use of high www.springer.com/journal/40145J Adv Ceram 2020, 9(5): 617–628Pristine polymer-derived ceramics (PDCs) without additional conductive fillers mostly show low dielectric loss [9,10,11,12,13,14,15,16,17]
The carbon-rich SiC ceramics were obtained by a facile PDC approach, starting from the allylhydrido polycarbosilane (AHPCS) and carbon-rich divinyl benzene (DVB)
Using Fourier transform infrared spectroscopy (FT-IR), it is confirmed that the hydrosilation between Si–H groups of AHPCS and C=C bonds of DVB occurs to form a carbon-rich single-source precursor
Summary
Centimeter-wave frequency electromagnetic (EM) waves (2–18 GHz) are widely used in various environments, which require high efficient EM absorbing (EMA) materials due to the massive increasing use of high. Compared with the incorporated carbon nanophase, the free carbon is in-situ formed and homogeneously distributed with the PDC-based ceramic matrix to avoid the agglomeration, which facilitates the resultant dielectric and EM absorbing properties. The effect of in-situ formed carbon including the concentration and/or structural evolution on the dielectric properties and EM absorbing performance of the PDCs has never been systematically discussed up to now. To keep this consideration in mind, we tried to synthesize metal-free and carbon-rich SiC with tunable free carbon contents. A relationship between the content/microstructure of in-situ formed free carbon and dielectric/EM properties of the resultant carbon-rich SiC ceramics will be acquired
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