The synthesis and microwave absorbing properties of MWCNTs and MWCNTs/ferromagnet composites

The multi-walled carbon nanotubes (MWCNTs) have been synthesized by chemical vapor deposition using camphor as carbon source and ferrocene as catalyst. The effect of different camphor/ferrocene ratio, calcination temperature and deposition substrates on the morphology and performance of the samples have been examined. The Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy confirmed the structure and growing mechanism of the MWCNTs in detail. The optimized MWCNTs have been obtained at 900 degrees C by 100:1 camphor/ferrocene ratio, whose IR extinction coefficient(alpha(e)) can reach 0.66 m(2)/g at 1400 cm(-1), with the bandwidth between 594 and 3233 cm(-1). The magnetic properties and microwave absorbing capability of Fe NPs/MWCNTs and MWCNTs/ferrite composites have been investigated by vibrating sample magnetometer and Vector network analyzer. With the addition of MWCNTs, the dielectric properties of the FeNPs/MWCNTs are enhanced in the L, S and C bands. The bandwidth (BW) below -10 dB of the 2 mm thickness ranges from 6.50 to 9.15 GHz, with the maximum RL reaching -23.78 dB at 7.8 GHz. And the peak reflection loss (RL) of the MWCNTs/ferrite can reach -18.17 dB at 3.55 GHz under 5 mm thickness, with dual-frequency absorption appearing in Ku bands at 4 and 5 mm thickness. The difference in lower frequency between the two composites suggests that MWCNTs/ferrite is expected to be an excellent tunable and broadband absorber.