Expanded graphite/cobalt ferrite/polyaniline ternary composites: Fabrication, properties, and potential applications
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Expanded graphite/cobalt ferrite/polyaniline (EG/CF/PANI) ternary composites were obtained by a two-step process. The intercalation compound, CF embedded in EG, was synthesized by a coprecipitation method. PANI could then be coated on the surface of the EG/CF microparticles by in-situ polymerization to form ternary composites of EG/CF/PANI. The results indicate that the electrical and magnetic performance of EG/CF and EG/CF/PANI composites are related to their composition. The EG/CF composite with mass ratio of 1.0 has the maximal conductivity (833.33 Scm1) among the binary composites. Saturation magnetizations (Ms) of the EG/CF composite with mEG/mCF of 0.8 is the largest among EG/CF composites, the ternary composites of EG/CF/PANI were prepared from the EG/CF composite at this mass ratio. The electromagnetic wave absorbing property of all ternary composites excelled those of EG/CF composites, and the sample with 40 wt% of PANI has the best absorption properties in the range of 8–18 GHz frequency.
I. INTRODUCTION
In recent years, the increasing need for electronic products and devices in wireless communication tools, local area networks, health care and defense sectors, and other communication equipments has led to a novel kind of pollution known as electromagnetic interference (EMI). Meanwhile, many problems have occurred along with it, for example, misoperation of precise electronic equipment and leakage of secret information occurred by the EMI, etc. Thus, EMI has become a serious problem, and much attention has been paid toward finding a suitable electromagnetic wave (EMW) absorber with wider absorbing bandwidths to solve these problems.1,2 EMW absorbers can be classified into three kinds based on their loss mechanism, namely resistor type, dielectric type, and magnetic-media type. The first type materials include graphite, conducting polymers, silicon carbide, etc. They usually have high dielectric loss factors in the highfrequency band and attenuated EMW by the electronic polarization or interfacial polarization. Dielectric materials such as barium titanate, ferroelectric ceramics, etc. belong to the second type. They have considerable absorbing bandwidth, but their applications are limited for the high intensity and cost. The third type absorbers are the magnetic-media type materials. Ferrites are relatively typical ones that have higher magnetic loss factors and attenuated EMW by the mechanism of magnetic hysteresis loss, domain-wall resonance, and natural resonance. Though they have strong absorbing capacity and broad absorbing bandwidth, their a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.317 J. Mater. Res., Vol. 26, No. 21, Nov 14, 2011
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applications are also limited due to high intensity, bad temperature stability, and poor absorbing efficiency in lower frequency range. An “ideal” EMW absorber owns such advantages as minute thickness, low density, wide bandwidth, and flexibility simultaneously. However, th
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