Wenyan Duan

Graphene-wrapped ZnO hollow spheres with enhanced electromagnetic wave absorption properties

Graphene-wrapped ZnO hollow spheres were synthesized by a two-step process, which combined a hydrothermal reaction with surface modification. The experimental results show that reduced graphene oxide sheets adhere entirely to the surface of the ZnO hollow spheres consisting of nanoparticles. The unique structure effectively decreases the density of the composite without sacrificing the contact between graphene and the nanoparticles. Different mass ratios of graphene to ZnO hollow spheres mixed in a paraffin wax matrix (50 wt%) were prepared to investigate the electromagnetic wave absorption properties in the X-band region. When the mass ratio of graphene oxide to ZnO is 12 : 88, the composite exhibits a maximum absorption of −45.05 dB at 9.7 GHz with a sample thickness of only 2.2 mm. The fundamental mechanism based on electrical conductivity and the polarization between the graphene sheets and ZnO nanoparticles is discussed. The hierarchical structure of graphene-wrapped ZnO hollow spheres exhibits a promising designable approach to lightweight electromagnetic wave absorbing materials.

Core/shell structured C/ZnO nanoparticles composites for effective electromagnetic wave absorption

Core/shell structured C/ZnO nanoparticles were synthesized by a two-step process based on hydrothermal method. The experimental results show that ZnO nanoparticles attach on the surface of carbon spheres through the surfacial functional groups. The core/shell structure enhances the electromagnetic wave attenuation capability owing to defects, multiple interfaces and optimal impedance match. Different mass percentages of C/ZnO nanoparticles were mixed in paraffin wax to investigate the electromagnetic wave absorbing and shielding performance. When the filler loading is 40 wt%, the composite shows a minimum reflection coefficient of −52 dB at 11 GHz with a sample thickness of 1.75 mm. When the mass ratio is 50 wt%, the sample has an electromagnetic shielding performance of 14.85 dB dominated by absorption. Compared with pure carbon spheres and ZnO hollow spheres, the core/shell structure of C/ZnO composites exhibits a promising route to design electromagnetic wave absorbing materials with high dielectric loss and moderate impedance match.

Synthesis and EMW absorbing properties of nano SiC modified PDC–SiOC

Nano SiC modified silicon oxycarbide (n-SiC/SiOC) ceramics were prepared through the pyrolysis of a mixture of liquid polysiloxane and n-SiC with an average grain diameter of 30 nm. After adding n-SiC, palingenetic SiC nanograins with an average grain diameter smaller than 10 nm, and nanosized free carbon were gradually separated from the amorphous SiOC phase when the annealing temperature increased from 1100 °C to 1450 °C. The various interfaces among n-SiC, in situ formed SiC nanograins, nanosized carbon and amorphous SiOC phases can obtain interfacial scattering. Eventually, the electric dipole polarization and interfacial scattering enhanced the absorption properties. The minimal reflection coefficient (RCmin) of the n-SiC/SiOC ceramics annealed at 1400 °C (n-SiC/SiOC-1400) reached −61 dB at 8.6 GHz. The widest effective absorption bandwidth (EAB) reached 3.5 GHz in the X-band, which indicates that the n-SiC/SiOC ceramics can be considered as high-performance microwave absorbing materials because of the strong absorption capability and wide absorption bandwidth.