The Study Of M-type Barium Ferrite/Carbon Nanotubes Composite Wave-absorbing Materials

Carbon nanotubes(CNTs) which show a strong microwave absorbing capability, light weight and stability, due to their electric conductivity and the properties of surface effect, quantum size effect, volume effect and macroscopic quantum tunneling effect as nanomaterials, have been extensively studied. However, CNTs, as a typical dielectric microwave absorber, have a relatively large complex permittivity and pure CNTs has no magnetism, which cause the poor impedance match and microwave absorbing properties of CNTs in the application as microwave absorber. M-type barium ferrties are magnetic media microwave absorbers, with large uniaxial magnetic anisotropy, high magnetic loss angle tangent and good microwave absorption properties.This paper is aim to synthesize M-type barium ferrties-CNTs composites, in which M-type barium ferrties with poor electric conductivity and good magnetic properties are utilized to improve the impedance match and finally enhance the microwave absorbing capability of MWCNTs, by optimizing its magnetic property and electric conductivity.Different Cu-Ti molar ratio doped M-type barium ferrties of Ba(Cu Ti)xFe12-2xO19(x = 0, 0.5, 0.75, 1, 1.25) were prepared by sol-gel method in this paper. The characterization by XRD, XPS, ICP, SEM, VSM and vector network analysis instrument found that: the morphology was gradually becoming amorphous, and the Hc, Ms decreased, but the particle size and the microwave absorbing properties increased with Cu-Ti doping. Cu2+ reached a doping limit when x = 0.75, if the doped Cu2+ was kept in augment, some Cu-containing compounds would form and left in Ba(Cu Ti)xFe12-2xO19 powders. The minimum reflection loss value of-37 d B at 16.7 GHz was observed for the x=0.75 sample and the bandwidth(below-10 d B) reached 3 GHz.The original MWCNTs were treated with acid to improve the dispersity and the coating performance, investigating different oxidants on the modification effect. FTIR, Raman and SEM were used to characterize the morphology and surface functional groups of pure MWCNTs and treated MWCNTs. The results showed that mixed acid reflux treatment at 120 °C could effectly eliminate impurities such as amorphous carbon and metal catalysts, smoothed the surface and shortened the length of MWCNTs, carboxyl(-COOH) and hydroxyl(-OH) were successfully introduced on the surface of MWCNTs, which finally reduced the agglomeration behavior.Well modificated MWCNTs were compound with excellent magnetic properties of doped M-type barium ferrties, investigating the effect of different Cu-Ti molar ratio doped M-type barium ferrties and different MWCNTs mass fraction on the magnetic and microwave absorbing performance of M-type barium ferrties-MWCNTs composites. The results showed that the particle size and the integrality of grain reduced obviously. The imaginary parts of complex permittivity and permeability were enhanced after the MWCNTs addition which favored to the dielectric loss and magnetic loss. The reflection loss reduced fistly and then increased with the augment of MWCNTs. The minimum reflection loss value was-7 d B when mass fraction was 10 wt.%, x = 0.75, d = 0.8 mm.