Microwave absorption properties of SiC@SiO2@Fe3O4 hybrids in the 2–18 GHz range

To enhance the microwave absorption performance of silicon carbide nanowires（SiCNWs）, SiO_2 nanoshells with a thickness of approximately 2 nm and Fe_3O_4 nanoparticles were grown on the surface of SiCNWs to form SiC@SiO_2@Fe_3O_4 hybrids. The microwave absorption performance of the SiC@SiO_2@Fe_3O_4 hybrids with different thicknesses was investigated in the frequency range from 2 to 18 GHz using a free-space antenna-based system. The results indicate that SiC@SiO_2@Fe_3O_4 hybrids exhibit improved microwave absorption. In particular, in the case of an SiC@SiO_2 to iron（III） acetylacetonate mass ratio of 1：3, the microwave absorption with an absorber of 2-mm thickness exhibited a minimum reflection loss of-39.58 d B at 12.24 GHz. With respect to the enhanced microwave absorption mechanism, the Fe_3O_4 nanoparticles coated on SiC@SiO_2 nanowires are proposed to balance the permeability and permittivity of the materials, contributing to the microwave attenuation.

Conductance and dielectric properties of hydrogen and hydroxyl passivated SiCNWs

Based on the transport theory and the polarization relaxation model,the effects of hydrogen and hydroxyl passivation on the conductivity and dielectric properties of silicon carbide nanowires(SiCNWs)with different sizes are numerically simulated.The results show that the variation trend of conductivity and band gap of passivated SiCNWs are opposite to the scenario of the size effect of bare SiCNWs.Among the influencing factors of conductivity,the carrier concentration plays a leading role.In the dielectric properties,the bare SiCNWs have a strong dielectric response in the blue light region,while passivated SiCNWs show a more obvious dielectric response in the far ultraviolet-light region.In particular,hydroxyl passivation produces a strong dielectric relaxation in the microwave band,indicating that hydroxyl passivated SiCNWs have a wide range of applications in electromagnetic absorption and shielding.

Enhancing thermal conductivity of silicone rubber composites by insitu constructing SiC networks:A finite-element study based on first principles calculation

Polymer composites as thermal interface materials have been widely used in modern electronic equipment.In this work,we report a novel method to prepare highly through-plane thermally conductive silicone rubber(SR)composites with vertically aligned silicon carbide fibers(VA-SiCFs)entangled by SiC nanowires(SiCNWs)networks.First,a series of carbon fibers(CFs)skeletons were fabricated in sequence of coating poor thermally conductive polyacrylonitrile-based CFs with polydopamine,icetemplated assembly,and freeze-drying processes.Furthermore,VA-SiCFs networks,i.e.,long-range continuous SiCFs-SiCNWs networks,based on the prepared CFs skeletons,were in-situ obtained via template-assisted chemical vapor deposition method.The thermal conductivity enhancement mechanism of VA-SiCFs networks on its SR composites was also intensively studied by finite element simulation,based on the first principles investigation of SiC,and Foygel’s theory.The in-situ grown VA-SiCFs networks possess high intrinsic thermal conductivity without the thermal interface between fillers,acting as the high-efficiency through-plane long-range continuous thermal conduction path,in which the SiCNWs were the in-plane“thermal spreader”.The VA-SiCFs/SR composites reached a high through-plane thermal conductivity,2.13 W/(m·K),at the filler loading of 15 vol.%,which is 868.2%,and 249.2%higher than that of pure SR sample,and random-CFs@polydopamine(PDA)/SR composites at the same content,respectively.The VA-SiCFs/SR composites also exhibited good electrical insulation performance and excellent dimensional stability,which guaranteed the stable interfacial heat transfer of high-power density electronic devices.