SiCN ceramics are
one of the most important electromagnetic wave
(EMW) absorbing materials for application in harsh environments, but
research studies on optimizing phase distribution in SiCN ceramics
for excellent EMW absorbing properties are still lacking. Herein,
continuous SiCN fibers with an interfacial SiC
x
N
y
phase were prepared through
nanochannel diffusion-controlled nitridation of polycarbosilane fibers
with an NH3 gas flow. The existence of the interfacial
SiC
x
N
y
phase
distributed between the carbon-rich SiC phase and Si3N4 phase can improve the impedance matching and efficiently
promote the production of macroscopic dipole moments in the heterointerfaces
of SiC
x
N
y
–SiC
and SiC
x
N
y
–Si3N4 for an enhanced multifarious
polarization relaxation loss. The EMW absorption properties can be
further improved by optimizing the microstructure with a continuous
carbon-rich SiC phase for possessing an excellent conductive loss
by converting the EMW energy into current flow. Finally, under the
synergy of the interfacial SiC
x
N
y
phase and the continuous carbon-rich SiC phase,
SiCN fibers can present excellent EMW absorption properties with extremely
strong absorption ability (reflection loss of −63.7 dB), ultrathin
thickness (1.78 mm), and wide effective absorption bandwidth (4.20
GHz). These obtained SiCN fibers also possess excellent mechanical
properties with the tensile strength higher than 2.0 GPa and excellent
high-temperature stability up to 1500 °C. This work provides
a strategic method for optimizing the microstructure of SiCN ceramics
for admirable EMW absorption properties, and the obtained SiCN fibers
can be used as reinforcements of ceramic matrix composites for stealth
applications under harsh environments.
A novel zirconium-contained polyborosilazane (PBSZ-Zr) was synthesized by chemical modification of a liquid polyborosilazane (LPBSZ) with Cp2ZrCl2. A Si-B-C-N-Zr multinary ceramic was prepared via pyrolysis of PBSZ-Zr. The properties and the ceramization process of PBSZ-Zr, as well as the microstructural development and properties of the derived SiBCN-Zr ceramic, were well studied. The active Si-H and N-H groups in LPBSZ react with Zr-Cl in Cp2ZrCl2 to form PBSZ-Zr polymers. The Zr content of the SiBCN-Zr ceramic was 3.39 wt% when the weight ratio of Cp2ZrCl2 to LPBSZ was 20 : 100. The SiBCN-Zr ceramic remains amorphous when pyrolyzed below 1600 °C, but the crystal phases of Zr2CN, ZrC, BN, SiC, and Si3N4 were detected from a 1600 °C treated sample. Due to the low activity of free carbon at the interface of the SiBCN-Zr ceramic, the oxidation resistance of the SiBCN-Zr ceramic under air was improved compared with the SiBCN ceramic.
Polymer‐derived methods are one of the most important tools for the synthesis of ceramics with a finely dispersed microstructure. In this study, a soluble and meltable ZrC/C pre‐ceramic polymer, P‐DACZ, (which would later exhibit a high ceramic yield of 71 wt%) was synthesized via radical polymerization. By adding low molecular weight polycarbosilane in any proportion during the radical polymerization process of P‐DACZ, a soluble and meltable ZrC/SiC/C pre‐ceramic precursor, PCS‐DACZ (which would later exhibit a high ceramic yield of >80 wt%) was synthesized. After annealing at 1400 °C under an argon flow, the precursors converted into bulk ZrC/C and ZrC/SiC/C ceramic nanocomposites. The ZrC nanoparticles could resist any grain growth when heat‐treated at temperatures above 1800 °C because the C or SiC matrix prevented long‐range atomic diffusion of zirconium. Such ceramic nanocomposites would be suitable for structural and (multi)functional applications at harsh environments with high temperatures.
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