Letter
Electromagnetic and microwave absorbing properties of multi-walled carbon nanotubes filled with Ni nanowire

https://doi.org/10.1016/j.jallcom.2010.02.103Get rights and content

Abstract

Microwave absorption, complex permittivity and permeability of Ni nanowire filled multi-walled carbon nanotubes (MWNTs), which were synthesized by CVD of methane using Ni/Al2O3 as the catalyst, have been investigated. The real and imaginary parts of permittivity and permeability of Ni nanowire filled MWNTs composites increase with increasing Ni nanowire filled MWNTs concentration. The Ni nanowire filled MWNTs/paraffin composite achieves a reflection loss below −10 dB (90% absorption) at 6.4–11 GHz, and the minimum value is −23.1 dB at 8.0 GHz. The microwave absorption of Ni nanowire filled MWNTs/paraffin composites was attributed to both dielectric and magnetic loss. The microwave-absorbing peaks of composites containing Ni nanowire filled MWNTs shift to low frequencies with increasing concentration of Ni nanowire filled MWNTs.

Introduction

Since the discovery in 1991 [1], carbon nanotubes (CNTs) have attracted more and more attention for their unique structures, remarkable electrical and mechanical properties [2], [3]. These interesting merits of CNTs promise great potential applications in microwave absorbing materials in the near future. However, excellent microwave absorption properties cannot be obtained for unmodified CNTs because of their magnetic loss is so small [4]. To optimize the performances of CNTs as microwave absorber, it is necessary to modify CNTs by coating and filling with other nanomaterials because the coated or encapsulated second phase nanostructures on the CNTs surface or inside the cavities of CNTs may exhibit ideal electromagnetic absorption properties [5]. Several metals and rare earth oxides such as Fe [6], Co [7], [8] and Er2O3 [9] have been bound to the CNTs surface or introduced into the cavities of CNTs, and their electromagnetic and microwave absorbing properties were investigated. However, to the best of our knowledge, little has been reported about microwave absorbing performance of Ni-filled CNTs. In this paper, we investigated microwave absorption and complex permittivity and permeability of Ni nanowire filled multi-walled carbon nanotubes (MWNTs), and the possible absorbing mechanisms were discussed.

Section snippets

Experimental

MWNTs filled with Ni nanowire were synthesized in our group by CVD of methane using Ni/Al2O3 as the catalyst. Details of the catalyst and Ni nanowire filled MWNTs preparation method were described elsewhere [10]. The black product (Ni nanowire filled MWNTs, the catalyst and other forms of carbon mixture) was added in a round-bottomed flask containing distilled water and dispersed sufficiently by ultrasonication for 1 h. The solution containing the black product was centrifuged at 1000 rpm for 30 

Results and discussion

Complex permittivity and permeability represent the dielectric and dynamic magnetic properties of materials. The real parts (ɛ′ and μ′) of complex permittivity and permeability symbolize the storage and transform capability of electromagnetic energy. The imaginary parts (ɛ″ and μ″) represent the loss of electromagnetic energy. As a microwave absorber, large imaginary parts of complex permittivity and permeability are expected. Fig. 2 shows the real and imaginary parts of complex permittivity ɛr

Conclusion

In conclusion, the electromagnetic and microwave absorbing properties of Ni nanowire filled WMNTs, which were prepared by CVD of methane using Ni/Al2O3 as the catalyst, were investigated in the frequency range of 2–18 GHz. With the increase of Ni nanowire filled MWNTs concentration, the real and imaginary parts of permittivity and permeability of Ni nanowire filled MWNTs composites rise. When the concentration is 5 wt.%, the R.L. of Ni nanowire filled MWNTs/paraffin composites with thickness of 4 

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  • A review on carbon/magnetic metal composites for microwave absorption

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    At present, due to the advantages of high purity and high process controllability, CVD has been demonstrated as an effective method to produce various carbon/magnetic metal composites and has attracted increased attention in the field of microwave absorption [102–104]. For example, Zou and coworkers prepared Ni nanowire-filled MWNTs composites by CVD method using Ni/Al2O3 as the catalyst and CH4 as a carbon source [105]. The electromagnetic parameters of the composites increase with the concentration of Ni filled MWNTs.

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