Preparation And Microwave Absorbing Properties Of SiC/3D Graphene Composite Powders

In recent decades,the rapid development of telecommunications,radar systems and wireless transmission has brought serious electromagnetic interference pollution to the surrounding environment.At present,the most direct and effective method to prevent electromagnetic wave interference is to use electromagnetic wave absorbing materials.Among them,silicon carbide（SIC）has good chemical resistance,excellent mechanical properties,thermal conductivity,especially in extreme conditions,which has been proved to be a promising electromagnetic absorption material.However,single silicon carbide can not meet the growing demand for high-performance microwave absorbing materials.It has become an important research direction to improve the microwave absorbing properties of silicon carbide by nano-sized and composite with other absorbing materials.Carbon based materials have the advantages of light weight,thin coverage and wide frequency band,which has been the focus of microwave absorption research.On the other hand,graphene shows great potential in microwave absorption due to its high surface area,low density,adjustable conductivity and good chemical stability,which can be used as a microwave absorbing enhancer for silicon carbide.Therefore,this paper studies the preparation and structure control of vertically oriented3D graphene（VG）based on SiC,and explores SiC/VG and SiC/C/VG composite absorbing materials with high efficiency,low cost and simple preparation process.The main experimental contents are as follows.Graphene with vertical orientation was grown on the surface of SiC nanoparticles by chemical vapor deposition（CVD）using methane as precursor and hydrogen as catalyst.The effects of methane concentration,growth temperature,reaction time and SiC carbon coating on the growth of graphene were investigated.The morphology of the composites was studied by XRD,SEM and TEM.The results show that the morphology of 3D graphene is the best when the growth temperature is 1100℃and the concentration of methane is 16.7%.The surface morphology of 3D graphene is greatly affected by time.When the time is less than 4 h,the size of graphene sheet is smaller,and when the time is longer than 6 h,flake graphite will be formed on the surface of SiC.When SiC is coated with carbon,the thickness of the carbon layer is about 10nm,and the coated carbon layer（c）has little effect on the growth of 3D graphene.SiC/C/VG-Fe₃O₄ composites with different Fe₃O₄ content were prepared by coprecipitation method with SiC/C/VG grown under optimum growth conditions.The electromagnetic absorption properties of SiC/VG,SiC/C/VG and SiC/C/VG-Fe₃O₄ were studied.The results show that the minimum reflection loss is about-14 d B at 10 GHz when the thickness of SiC/VG is 2.5 mm,and the frequency range below-10 d B is about 3.2 GHz.When the thickness of SiC/C/VG is 1.5 mm and the frequency is 3.2GHz,the maximum electromagnetic wave absorption efficiency is about-24.7 d B,and the effective absorption bandwidth is about 4.1 GHz.The SiC/C/VG-Fe₃O₄composite with 60 wt.%Fe₃O₄ has the largest reflection loss value.When the thickness of the material is 2 mm,the sample has the most absorption of electromagnetic wave near 16.3 GHz,the minimum RL value is about-45 d B,and the effective absorption bandwidth is about 3.3 GHz.