| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Nanomaterials | Wednesday Sessions |
| Session NM-WeM |
| Session: | Nano Composites |
| Presenter: | Shi G.M, Shenyang University of Technology, China |
| Correspondent: | Click to Email |
Abstract
Recently, with the rapid advancement of wireless communication, the microwave absorbing materials are becoming increasingly important for applications in some special fields such as silent rooms, radar systems and military applications. Among the candidates for EM wave absorbers, magnetic nanocapsules, i.e. magnetic nanoparticles coated with an insulator shell including graphite, oxidation etc., are now becoming a study focus of researchers. The reason is that this type of EM wave absorbers not only possess a high saturation magnetization and Snoek's limit at high frequencies, but also decrease eddy current phenomenon induced by electromagnetic wave.
The determining key factor of microwave absorption performance of the absorbents is EM impedance matching of the absorbents. Multilayer structures are a good way to increase EM impedance matching. However, the relative permittivity due to the interface polarization in the heterogeneous composites is rarely focused on. BaTiO3 with excellent dielectric/ferroelectric properties has been studied for its EM wave absorption properties, and FeNi nanoparticles with large saturation magnetization are prominent magnetic microwave absorbents. Hence, in this study, core double-shell FeNi@/BN@BaTiO3 nanocapsules were synthesized by a two-step [app:addword:synthesis] method, consisting of an arc- evaporating a FeNi-B amorphous alloy target in a mixture atmosphere of Ar and N2 and a subsequent chemical liquid deposition process . Microwave absorption properties of core double-shell FeNi@BN@BaTiO3 nanocapsules were investigated in the 1–18 GHz frequency range. High resolution transmission electron microscopy studies the core double-shell type nanocomposite with FeNi nanoparticles as the core, while BN and BaTiO3 are the inside and the outside shells, respectively. Enhanced relative permittivity made the core double-shell FeNi @BN @BaTiO3 nanocapsules with better electromagnetic impedance matching than that of a FeNi@BN and BaTiO3 mixture. Reflection loss (RL) values of FeNi@BN@BaTiO3 paraffin composite are far greater than those of the FeNi@BN –paraffin composite at the absorbent thickness from 1.1 to 6 mm . An optimal Reflection lossof -40.3 dB was reached at 10.9 GHz with 1.5 mm thickness, and the broadest absorption bandwidth of 5.9 GHz (RL<-10dB) is from 8.7 to 14.6GHz frequency range. The microwave absorptive mechanisms of BN@BaTiO3 coated FeNi nanocapsule absorbent were discussed.