Study On Electromagnetic Wave Absorption Properties Of SiCN Based Composite Ceramics

In the new era of rapid development of science and technology,wireless communication equipment is widely used in all aspects of human production and life.While making production and life comfortable and convenient,it also brings inevitable problems,such as electromagnetic wave(EMW)pollution.To address this problem,researchers all over the world have carried out extensive research on EMW absorbers to obtain excellent absorbing materials with thin thickness,light weight,low reflection loss(RL)and wide effective absorption bandwidth(EAB).The preparation of ceramics by polymer derivatization has the advantages of simple operation and environment-friendly features,because it can directly pyrolyze organic polymers to obtain ceramic materials,without going through the process of powder making,granulation,molding,etc.SiCN-based composite ceramics prepared by polymer derivatization have attracted extensive attention in the field of EMW absorbing materials due to their light weight,high temperature resistance,good thermal stability,strong oxidation resistance and excellent dielectric properties.SiCN ceramic is chosen as the ideal matrix material of EMW absorbers by researchers.However,there are still some problems in SiCN based ceramics,such as low electromagnetic wave absorptivity and narrow effective absorption bandwidth.In this paper,nano magnetic particles and conductive phase materials were introduced to improve the impedance matching and conductivity loss of materials,and a series of composites with excellent electromagnetic wave absorption properties were prepared,and their absorption mechanism was studied.In this study,the methods used in the preparation of SiCN based composite ceramics are polymer derivatization,and the specific results are as follows:(1)The polymer derived SiCN based composite ceramics containing magnetic particles were prepared by using SiCN ceramic as matrix and cobalt nanoparticles as composite magnetic phase.The effects of cobalt added amount and pyrolysis temperature on the phase composition,electromagnetic parameters and microwave absorption properties of SiCN based composite ceramics were studied.The results show that cobalt particles can react with carbon to form magnetic Co3C particles.The good dielectric property of SiCN ceramics matches the magnetic property of magnetic particles,so that the materials have excellent EMW absorption properties.When the cobalt adding amount was 2wt%and the pyrolysis temperature was 900℃,the sample had the best EMW absorption performance.At a thickness of 3 mm,the sample obtained the RLmin of-10.9 dB at 15 GHz,and the EAB(RL<-10 dB)of 3.3 GHz.At a thickness of 6 mm,the RLmin of-11.8 dB and the EAB of 4.2 GHz were obtained.(2)SiCN(CNTs)composite ceramics with excellent dielectric loss properties were prepared by dispersing carbon nanotubes(CNTs)into the SiCN ceramic matrix.The phase composition,microstructure,chemical composition,electromagnetic parameters and EMW absorption properties of SiCN(CNTs)composite ceramics at different pyrolysis temperatures were analyzed.The results show that at the pyrolysis temperature of 1100℃,the sample with a thickness of 4.4 mm had the RLmin of-38.40 dB at 18 GHz and the EAB of 1.3 GHz.The sample with a thickness of 4.7 mm had a wider EAB of 2.16 GHz.Compared with the SiCN ceramics,SiCN(CNTs)have stronger EMW absorption properties.(3)In order to tune the electromagnetic characteristics and widen the EAB of SiCN(C)ceramics,we introduced different magnetic particles(Fe,Co,Ni)into SiCN(C)ceramics,and designed magnetic particles/SiCN(CNFs)composite ceramics.The bandwidth of magnetic particles/SiCN(CNFs)composite ceramics was found to be greatly improved as compared to SiCN(C)ceramics.For example,when the thickness was 4 mm,Fe/SiCN(CNFs)had the RLmin of-15.7 dB and the EAB of 1.5 GHz,Co/SiCN(CNFs)had the RLmin of-15.6 dB and the EAB of 1.84 GHz.A thinner thickness and wider EAB were obtained in Ni/SiCN(CNFs).When the thickness was 1.4 mm,we obtained the RLmin of-13.9 dB and the EAB of 2.08 GHz for Ni/SiCN(CNFs).The analysis shows that conductive loss,interfacial polarization,dipole polarization,natural resonance and multiple reflections jointly contribute to the excellent EMW absorption properties of the composite ceramics.The SiCN(CNTs)composite ceramics and magnetic SiCN-based composite ceramics prepared in this study have the characteristics of light weight,good high temperature resistance as well as excellent EMW absorption properties.They are potential attractive materials in the field of high temperature resistant EMW absorbing materials.