Preparation And Microwave Absorbing Performance Of Metal-doped PDCs-SiCN Ceramics

With the rapid development of modern science and technology,the research on radar and radio transmitting equipments not only promotes the progress of society and brings convenience to people's daily life,but also causes electromagnetic pollution and other problems.Therefore,electromagnetic absorbing materials have become a research hotspot in recent years.Ideal absorbing materials generally need to meet the principles of impedance matching and attenuation.In addition,novel absorbing materials also need to meet the requirements of "thin","wide","light","strong",as well as high strength,high temperature resistance,corrosion resistance and so on.The precursor conversion method can adjust the composition and structure of the resulting ceramics by designing polymer molecules and pyrolysis processes.In addition,compared to traditional sintering methods,the process requires lower temperature and more simple operation and ceramics with complex shapes can be prepared.Polymer-derived SiCN ceramics(PDCs-SiCN ceramics)have a special Si-C-N amorphous structure and contain free carbon,which has good dielectric properties.At the same time,it also has excellent oxidation resisitance,high temperature resistance,and high hardness properties,so it has been widely concerned in the field of microwave absorption field.In addition,the composite of PDCs-SiCN ceramics with magnetic materials can introduce magnetic properties,adjust electromagnetic parameters,and increase electromagnetic loss,thus improving the absorbing performance of the materials.In this study,two kinds of composite ceramic materials with magnetic materials were prepared by using precursor transformation method and using polysilazane as raw material.On the basis of the previous studies,Eu-containing PDCs-SiCN(Fe)ceramics and Ni-containing polymer-derived SiCN ceramics(PDCs-SiCN(Ni)ceramics)were prepared.The results are as follows:(1)The Eu-containing PDCs-SiCN(Fe)ceramics contain Fe and Eu elements.Eu and Fe black nearly spherical nanoparticles and distributed in the amorphous SiCN matrix.Eu-containing PDCs-SiCN(Fe)ceramics have better absorbing properties than pure PDCs-SiCN(Fe)ceramics,and they have the best absorbing performance when the addition of Eu2O3 is 25 wt%,The minimum reflection loss value is-12 dB at 16.8 GHz.(2)PDCs-SiCN(Ni)ceramics were made from Ni powder,NiO and Ni(?)complexes as different nickel sources.The PDCs-SiCN(Ni)ceramics prepared from Ni powder have the highest degree of crystallization and the highest degree of carbon crystallization.The matrix of ceramic is SiCN amorphous matrix.The PDCs-SiCN(Ni)ceramics prepared from different nickel sources have nearly spherical black Ni particles distributed in the matrix.The PDCs-SiCN(Ni)ceramics possess ferromagnetic properties and are soft magnetic materials.The ceramics prepared with Ni powder have high magnetization and coercive force.Ceramics prepared from NiO as the possess strong loss capability,while ceramics prepared from Ni powder have the best absorbing performance,and the minimum reflection loss is-40 dB at 17.1 GHz.(3)A series of PDCs-SiCN(Ni)ceramics prepared with different Ni content contain Ni element and carbon.Ni particles are distributed in amorphous SiCN matrx,and Ni particles are black and nearly spherical,with a particle size range of 20-60 nm.The higher the Ni content,the greater the magnetization of PDC-SiCN(Ni)ceramics.In PDCs-SiCN(Ni)ceramics with different Ni content,the reflection loss is minimal when the Ni content is 10 Wt%,and RL value is-40 dB at 17.2 GHz,which indicates teh optimal absorbing performance.(4)By cross-linking at different temperatures,the basic fractures of C-H bond,C=C bond,Si-H bond,and N-H bond disappear at 600 ?.The transition from organic to inorganic has been completed at a temperature of 800 ?.The cross-linking process is an endothermic process and is accompanied by two obvious mass attenuation.(5)In a series of PDCs-SiCN(Ni)ceramics successfully prepared at different pyrolysis temperatures,the main crystal phase of ceramics is Ni prepared at 900 0C and 1000 ?.and all ceramics have carbon generation.And the higher the temperature,the higher the degree of carbon crystallization.From the SEM and TEM figures,carbon is distributed in the gap of the SiCN matrix in the form of carbon nanotubes.When the pyrolysis temperature is 1200 ?,the mixmum reflection loss is-48.5 dB at 15.1 GHz,which has optimal absorbing performance.The Eu-containing PDCs-SiCN(Fe)ceramics and the PDCs-SiCN(Ni)ceramics prepared by this research have typical amorphous structure SiCN matrix,high thermal stability and strong antioxidant properties.And they also possess excellent electromagnetic absorption performance and a relatively broad application prospect.