Preparation And Microwave Absorbing Properties Of Metal And Metal Oxides Composites Based On Carbon Nanotubes

Nowadays,in the fields of both military and people’s livehood,better absorbing materials are badly in need.Carbon nanotubes(CNTs),because of its unique nanostructures, have a outstanding performance in the fields of electricity, mechanics and magnetism.Low density,great mechanical strength, high temperature resistance, high dielectric loss,and so on, these advanteges make CNTs an excellent absorbing material component.This paper discussed a way of oxidating multi-walled carbon nanotubes(MWNTs).And adding magnetic materials on the MWNTs to prepare composites,to change the complex permittivity and complex permeability of the carbon nanotubes,and make the composite a better microwave absorber. By changing the acid composition, respectively oxidated MWNTs,and an Ⅲ ideal way of oxidating MWNTs was found:make the volume ratio of sulfuric acid and nitric acid equal to2:1,add MWNTs into the mixed acid(1g/60mL),ultrasonic dispersing for0.5h,then heat the mixture for circumfluence under120℃for1h.By chemical nickel-plating on the surface of MWNTs,MWNTs was covered by nickel with a size of5-10nm.The permittivity of MWNTs reduced a lot,while the permeability of MWNTs didn’t change much.The Ni/MWNTs composite with a thickness of8mm exhibited a reflection loss of-9.5dB at14.5GHz. Under nitrogen, ferrocene and MWNTs were calcined at750℃, CFe15.1Fe particles with a size of about50nm were covering on the surface of MWNTs.The composite with a thickness of2mm exhibited a reflection loss of-2.5dB at6.5GHz. In the air, ferrocene and MWNTs were calcined at750℃, γ-Fe2O3particles with a size of20to50nm were covering on the surface of MWNTs.The composite with a thickness of2mm exhibited a reflection loss of-3.6dB at5GHz.BaFe12O19particles were prepared by hydrothermal method,the particles had a strong magnetic loss,and with a thickness of4mm, BaFe12O19showed a reflection loss of-20dB at9.5GHz,-22dB at14GHz and-24dB at15GHz. BaFe120,9/MWNTs composites were prepared by hydrothermal method.When the size of BaFe12O19particle was1μm, and the mass fraction of MWNTs was20%,the composite with a thickness of2mm exhibited a reflection loss of-18dB at10GHz,and the bandwidth with reflection loss below-9dB covered9-12GHz. When the size of BaFe12O19particle was among100-300nm, and the mass fraction of MWNTs was20%,the composite with a thickness of2mm exhibited a reflection loss of-25dB at16GHz,and the bandwidth corresponding to reflection loss below-10dB covered13～17.5GHz.Ni/MWNTs effectively improved the microwave absorbing properties of the carbon nanotubes in Ku band. CFe15.1-Fe/MWNTs didn’t show a good performance of microwave reflection loss. γ-Fe2O3/MWNTs decreased the reflction loss of MWNTs for1dB at5～18GHz.The composite of BaFe12O19/MWNTs showed a great performance of microwave reflection loss in X and Ku band. Among these composite materials,BaFe12O19/MWNTs composite materials had the best performance of microwave adsorption.