In the present work, novel single-source-precursors for CNTs/Fe3Si/Fe/SiOCN ceramic nanocomposites were synthesized by the reaction of poly (methylvinyl) silazane (HTT 1800) with ferric acetylacetonate [Fe(acac)3] and carboxylic functionalized carbon nanotubes...

In this work, novel carbon nanotube (CNT)/CoSi/SiOC nanocomposite ceramics with in-situ formed multi-walled CNTs and core-shell structured CoSi@C nanoparticles were successfully prepared via a single-source-precursor derived ceramic approach. Ppolymeric precursor characterization as well as phase evolution, microstructure, and electromagnetic wave (EMW) absorption properties of the ceramics were investigated in detail. The results show that the in-situ formed CNTs and magnetic CoSi@C nanoparticles provide a synergistic effect on both dielectric loss (tanδ ε ) and magnetic loss, leading to outstanding EMW absorption properties of the ceramics annealed at only 1100 ℃. (i) For the Co feeding of 6.25 wt%, the minimum reflection loss (RL min ) is −53.1 dB, and the effective absorption bandwidth (EAB) is 4.96 GHz (7.12-12.08 GHz) with a ceramic-paraffin hybrid sample thickness of 3.10 mm, achieving full X-band coverage; (ii) for the Co feeding of 9.09 wt%, the RL min value of −66.4 dB and the EAB value of 3.04 were achieved with a thickness of only 2.27 mm. Therefore, the present CNT/CoSi/SiOC nanocomposite ceramics have potential applications for thin, lightweight, and efficient EMW absorption in harsh environments.

In the present work, bulk Si3N4/HfBxN1‐x ceramic nanocomposites were successfully fabricated via a polymer‐derived ceramic approach. The chemical reaction to form the single‐source precursor was confirmed by FT‐IR and XPS, in which both Si−H and N−H groups of perhydropolysilazane react with borane dimethyl sulfide complex and tetrakis(dimethylamido) hafnium(IV). The investigation of the polymer‐to‐ceramic transformation of the synthesized precursors indicates that Hf‐ and B‐modified PHPS exhibits high ceramic yields of up to 100 wt % after pyrolysis at 1000 °C under ammonia. Moreover, XRD and TEM results show that the SiHfBN ceramics with a molar ratio of B : Hf=5 and 10 resist crystallization at temperatures up to 1500 °C and separate after annealing at 1700 °C into nanocomposites comprising of an α‐Si3N4 matrix with embedded ternary HfBxN1‐x phases, solid solutions of rock salt‐type HfN and HfB. Based on the investigation, warm‐pressing was applied to fabricate bulk SiHfBN specimens, and the oxidation behavior of samples annealed at 1700 °C was recorded at 1500 °C over a range of oxidation times between 1 and 50 h. The weight changes of Si3N4/HfBxN1‐x ceramics with B : Hf molar ratios of 2 : 1, 5 : 1 and 10 : 1 are 4.31 %, 4.37 % and 2.57 %, respectively. The formation of HfSiO4, B2O3 and SiO2 during oxidation plays a crucial role for the improvement of the oxidation resistance of the Si3N4/HfBxN1‐x ceramics.

For the first time, the present work reports the dielectric properties and electromagnetic wave (EMW) absorbing performance of polymer‐derived carbon‐rich NbC‐SiC‐C nanocomposites. In our previous work, NbC‐SiC‐C nanocomposites with the ultra‐high temperature ceramic phase NbC as the main phase were synthesized with the allylhydridopolycarbosilane (AHPCS) and niobium pentachloride (NbCl5) as starting materials. On this basis, divinyl benzene was chosen as carbon‐rich source and introduced into the AHPCS and NbCl5 to form a single‐source‐precursor. Finally, carbon‐rich NbC‐SiC‐C nanocomposites were successfully synthesized by polymer‐derived ceramic approach. Compared with ceramic samples without Nb and with lower carbon content, the carbon‐rich NbC‐SiC‐C nanocomposites show extremely enhanced EMW absorbing performance with minimum reflection coefficient of −51.1 dB at 6.88 GHz for the thickness of 2.27 mm. As a consequence, the resultant carbon‐rich NbC‐SiC‐C nanocomposite has to be considered as structure&function integrated material with excellent EMW absorption performance, which can be applied in hostile environment.