| With the rapid development of electronic technology and communication technology in the military and civil fields,the increasing of electromagnetic interference and electromagnetic pollution problem prompted the researchers to study of electromagnetic shielding and absorbing materials.As a representative of the ceramic materials,Silicon Carbide(SiC)has a lot of excellent performances,such as wide bandgap,high thermal conductivity,high breakdown field strength,high bonding energy,high strength and hardness,high temperature and corrosion resistance,and other outstanding properties.Combine the very best of their good properties and nanostructure,SiC materials become the potential electromagnetic shielding material.Especially,SiC micro-or nanostructure materials show highly efficient microwave absorption properties due to their multi-microwave loss mechanisms.Thus far,many ways to synthesize the SiC with micro-or nanostructure have been developed,such as carbon-thermal reduction method,chemical vapor deposition(CVD),sol-gel method and so on,but these methods do not apply in fast and high efficiency synthesis.Microwave thermal treatment has the advantages of high speed,selectivity,homogeneous heating,high purity of products,easy to be industrialized,etc.It can effectively shorten the production cycle and reduce the cost.Currently,it’s getting more and more attention in materials synthesis.In this subject,microwave heating was directly applied to prepare SiC micro-or nanostructure materials.The micro-morphology,structural composition of samples were evaluated via employing a variety of analytical methods such as X-ray diffraction(XRD),Fourier transform infrared spectrometer(FT-IR),scanning electron microscope(SEM),energy dispersive spectrometer(EDS).The electromagnetic parameters of the samples in the frequency range of 8.2～12.4GHz were investigated via vector network analyzer(VNA),and the reflection loss(RL)properties were also calculated.The main research contents and results are as follows:(1)SiC micro-or nanostructure materials could be synthesized via microwave heating approach rapidly and conveniently,constituents covering silicon powders,silica dioxide powders,and artificial graphite were employed as raw materials.The microstructural analysis results indicated that,P-SiC can be synthesized directly without using any templates,substrates or catalysts.The morphology of products is nanowires,nanorods and micro-or nanograin.After the simple and controllable reaction process,the obtained products were pure,with no need to be depurated any more.The electromagnetic parameter shows,with the increase of x,the real part ε’,imaginary part ε" of complex permittivity and dielectric loss tan δE of the test samples of SiC/paraffin-x(x= 10,20,30,40,50)increased gradually,but the magnetic loss tan δM did not obviously change.The RL result shows,SiC dispersed in paraffin with different mass ratios x can directly affect the electromagnetic loss properties of the absorbing material.With the increased of SiC mass ratios,the minimum peak position of reflection loss corresponding the thickness of the material decreasd gradually.(2)By using artificial graphite powder as carbon source,silicon powder and silica powder as the silicon source,Al,Fe,Ni powder as the metal modifier,SiC micro-or nanostructure materials could be synthesized successfully via microwave heating approach.The morphology of pure-SiC is nanowires,nanorods and micro-or nanograin,Al-SiC is nanowires,nanorods and micro or nanograin also.Compared with the morphology of pure-SiC,Fe-SiC have more percentage content of nanowires.The morphology of Ni-SiC is mainly of the nanowires.The electromagnetic parameter shows,compare to the pure-SiC,Al,Fe,Ni modified SiC material,the real part ε’,imaginary part ε" of complex permittivity and dielectric loss tan δE are all increased in the frequency range of 8.2～12.4GHz,order by size Ni-SiC>Fe-SiC>Al-SiC>pure-SiC,but the magnetic loss tanδM does not obviously change.The RL result shows,the minimum peak position of reflection loss order by size Ni-SiC>Fe-SiC>Al-SiC>pure-SiC.Metal modification can improve the electromagnetic shielding performance of SiC materials.(3)SiC materials synthesized via microwave heating rapidly and conveniently using artificial graphite powder,flake graphite and graphene films as the carbon source,respectively.The SiC-FG products have the smallest density among the products which sythsis from three carbon source.The morphology of SiC-AG is composed of nanowires,nanorods and micro-or nanograin,SiC-FG is nanorod,and SiC-GN is all most nanograin.Due to the three-dimensional fleeciness structure of SiC-FG products,the average value of the real part ε’ imaginary part ε" of complex permittivity and dielectric loss tanδE is 6.407,2.004,0.313,respectively.These values are all greater than the other carbon source to synthesis of SiC/paraffin sample significantly in the frequency range of 8.2～12.4GHz,and shows the weak magnetic loss.The RL results revealed that the products using flake graphite as carbon source exhibited outstanding microwave absorption property.The minimum reflection loss can reach-18.01dB at 8.9GHz when the thickness of the match is 3.0mm.The maximum effective absorbing band can reach 3.7GHz when the thickness of the match is 2.5mm,the band of effective absorption is more than 88.5%in the frequency range of 8.2-12.4GHz. |
