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Si 3 N 4 ceramics modified with SiC nanofibers were prepared by gel casting aiming to enhance the dielectric and microwave absorption properties at temperatures ranging from 25 °C to 800 °C within X-band (8.2–12.4 GHz). The results indicate that the complex permittivity and dielectric loss are significantly increased with increased weight fraction of SiC nanofibers in the Si 3 N 4 ceramics. Meanwhile, both complex permittivity and dielectric loss of SiC nanofibers modified Si 3 N 4 ceramics are obviously temperature-dependent, and increase with the higher test temperatures. Increased charges mobility along conducting paths made of self-interconnected SiC nanofibers together with multi-scale net-shaped structure composed of SiC nanofibers, Si 3 N 4 grains and micro-pores are the main reason for these enhancements in dielectric properties. Moreover, the calculated microwave absorption demonstrates that much enhanced microwave attenuation abilities can be achieved in the SiC nanofibers modified Si 3 N 4 ceramics, and temperature has positive effects on the microwave absorption performance. The SiC nanofibers modified Si 3 N 4 ceramics will be promising candidates as microwave absorbing materials for high-temperature applications. [ABSTRACT FROM AUTHOR]

Home-made SiC nanofibers were introduced into Si 3 N 4 matrix for enhanced electromagnetic interference (EMI) shielding properties. The microstructural characterization revealed that SiC nanofibers modified Si 3 N 4 ceramic is composed of SiC conductive networks made of uniformly distributed SiC nanofibers, micro-pores and insulating Si 3 N 4 matrix. Moreover, EMI shielding effectiveness (SE T ) for SiC nanofibers modified Si 3 N 4 ceramic is dependent on SiC nanofibers content. When the SiC nanofibers content is increased from 0 to 8 wt%, the EMI SE T of as-prepared ceramics increased from 3.43–4.15 dB to 5.58–9.31 dB. Due to the low electrical conductivity of as-prepared ceramics, multi-reflection caused by the micro-pores and nanofibers networks is mainly responsible for the EMI shielding. The study indicates that introduction of SiC nanofibers would be a favorable solution for Si 3 N 4 based thermostructural material with an improved EMI shieding. [ABSTRACT FROM AUTHOR]

Fe/Si3N4 composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N2. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the structure of composite powders is Si3N4 coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si3N4. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si3N4. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different. [ABSTRACT FROM AUTHOR]

Silicon carbide nano-fibers (SiCNFs) were in-situ grown on the surface of carbon fibers by catalysis chemical vapor deposition (CCVD) with Ni nano-particles as catalyst at 1000 °C. The phase composition, microstructures, oxidation resistance and microwave absorption properties of the SiCNFs coated carbon fibers were investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Thermal gravity analysis (TGA) and Vector network analyzer, respectively. The results show that the as-grown nano-fibers which are mainly composed of β -SiC, present a withe-like morphology with diameter of 20–50 nm and aspect ratio of 100–150. Additionally, the TGA curves indicate that the oxidation resistance of the SiCNFs coated carbon fibers is significantly improved in comparison to the pure carbon fibers. Moreover, the investigation reveals that the microwave absorption properties of the SiCNFs coated carbon fibers are effectively enhanced. The reflectivity of the SiCNFs coated carbon fibers is less than −10 dB within the frequency ranging from 9.2 to 11.7 GHz and the lowest value of reflectivity can approach −19.9 dB when the thickness of specimen is 2 mm. While the reflection loss of the pure carbon fibers is higher than −2.1 dB within the whole band ranging from 2 and 18 GHz. The superior microwave absorbing performance of the SiCNFs coated carbon fibers is mainly attributed to the improved impedance matching as well as dissipation resulted from hopping migration. In conclusion, this study provides an effective modification approach to improve the microwave absorption properties of carbon fibers. Finally, the SiCNFs coated carbon fibers could be considered as a promising candidate in light-weight microwave absorbing materials. [ABSTRACT FROM AUTHOR]