Preparation And Microwave Absorption Properties Of Hard Carbon-based Materials

Research on the wave-absorption properties of carbon(C)matrix composites has been going on for more than half a century and has achieved some practical applications.However,as an exception among Cbased materials,the microwave-absorption properties of hard carbon(HC)-based nanocomposites have been rarely studied and thus currently remain unknown.In this research work,Hard carbon@Zn O nanoparticle layers(LHC@Zn ONPs)were synthesized by pyrolysis of a mixture of Phenol formaldehyde resin and zinc oxide(Zn O)nanoparticles which is a novel HC-based composite nano-material essentially composed of Zn O nanoparticles with a diameter of approximately 25 nm and layered hard carbon(LHC)with a thickness of 100 nm.Then the nanoparticles in the synthesized LHC@Zn ONPs nano-composite were evaporated and removed by high temperature vacuum annealing method to obtain porous layered hard carbon(PLHC)materials.Finally,the morphology,elemental composition,structure and wave-absorbing properties of the synthesized nanocomposites were systematically studied and characterized by various techniques like scanning electron microscope,X-ray diffractometer,Raman spectrometer,transmission electron microscope,X-ray photoelectron spectroscopy,Fourier transform infrared spectrometer and vector network analyzer,etc.,with the aim to describe their "structureabsorbing performance" relationship.The results show that :(1)when the filling ratio of LHC@Zn ONPs to paraffin wax is 1:1.5,the best reflection loss is-38 d B at 3.3 mm absorption thickness,and the corresponding effective absorption bandwidth is 5.7 GHz.The excellent wave-absorbing properties of LHC@Zn ONPs can be attributed to the interfacial polarization at the Zn O/HC and LHC/LHC interfaces,as well as the enhanced dipole polarization caused by the defects,nanopores,and residual organic functional groups in the HC layer,etc.(2)When the filler ratio of PLHC and paraffin is 1:5,the optimal reflection loss value reaches-42 d B at the absorption thickness of 2.8 mm,and the effective absorption bandwidth reaches 6.6 GHz at the absorption thickness of 3.7 mm.The excellent absorbing performance of PLHC corresponds due to the nanoporous nature which subsequently increase the number of reflections of the incident microwaves in the sample,which enhances the chances of energy loss.At the same time,the existence of a large number of defects in the HC also increases the polarization loss of the sample.The research results described in this paper shows that HC-based nanocomposites have excellent microwave absorbing properties,which can provide new research methods for the rational design of high-performance microwave absorbing materials.