Tunable electromagnetic properties and enhanced microwave absorption ability of flaky graphite/cobalt zinc ferrite composites
Graphical abstract
Introduction
Microwave absorption materials (MAMs) have received worldwide interests due to their important roles on solving electromagnetic pollution problems in human daily life [1], [2]. According to the microwave absorption mechanism, MAMs can be divided into magnetic loss type microwave absorbers and electric loss type microwave absorbers. Among these candidates, ferrites, including spinel ferrites and magnetoplumbite ferrites, are typical magnetic loss type microwave absorbers. They exhibit high complex permeability values because of their excellent nature resonance loss and magnetic hysteresis loss [3], [4], [5]. Meanwhile, carbon materials, including graphite, graphene, carbon fiber and carbon nanotube, are typical electric loss type microwave absorbers and present high complex permittivity values owing to their superior electric conductive loss and relaxation loss [6], [7], [8].
However, single microwave absorber is difficult to achieve well electromagnetic impedance matching, which needs a balance between complex permeability and complex permittivity. As a result, recent studies are focused on composite microwave absorbers, such as RGO/CoFe2O4 composites [9], Co2Z hexaferrite-BaTiO3 composites [10], SrFe12O19/α-Fe composites [11], carbon nanotube-copper phthalocyanine/magnetite [12], (Z-type barium ferrite/silica)@polypyrrole composites [13], and so on. Most of them are concerned on the preparation method and the final microwave absorption properties. To further investigate the design principle and the microwave absorption mechanisms of electric/magnetic composite microwave absorbers, the flaky graphite/cobalt zinc ferrite composites were prepared in this study. The electromagnetic properties in the frequency range of 2–18 GHz were analyzed. Furthermore, the electromagnetic impedance matching performance, the microwave attenuation ability and the electromagnetic cancellation effect were discussed.
Section snippets
Materials preparation
The flaky graphite/cobalt zinc ferrite composites were prepared by the coprecipitation method. Firstly, the necessary amount of flake-like graphite and 0.5 g sodium dodecyl benzene sulfonate were added into 200 ml deionized water. Then, the homogeneous graphite solution was obtained after ultrasonic dispersing for 1 h. Secondly, the necessary amount of Zn(NO3)2·6H2O, Co(NO3)2·6H2O and Fe(NO3)3·9H2O with the mole ratio of 1:1:4 were dissolved into the graphite solution. After magnetic stirring
Results and discussion
Fig. 1 shows the XRD patterns of as-prepared flaky graphite/cobalt zinc ferrite composites with different graphite weight ratios. It can be found that the samples showed pure cobalt zinc ferrite phase when the graphite weight ratio was less than 20 wt%. It is demonstrated that the cobalt zinc ferrite is well coated on the surface of flaky graphite because the X-ray can not transmit through the thick cobalt zinc ferrite shell-layer. However, the impurity graphitic carbon phase appeared at 33.2°
Conclusion
The flaky graphite/cobalt zinc ferrite composites were prepared by the coprecipitation method. The cobalt zinc ferrite particles assembled on the surface of flaky graphite. To obtain the pure flaky graphite/cobalt zinc ferrite composites, the graphite weight ratio should be controlled to be less than 20 wt%. The as-prepared composites showed high aspect ratio. The flake size is 5–10 μm and the thickness is about 300 nm. The flaky graphite/cobalt zinc ferrite composites with 10 wt% graphite
Acknowledgments
This work was financially supported by the Project Funded by the National Natural Science Foundation of China (51402154), Natural Science Foundation of Jiangsu Province (BK20141000) and Natural Science Foundation of Jiangsu Provincial Universities (14KJB430019).
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