Preparation And Wave Absorbing Properties Of Silicon Carbon Nitride Ceramics

Treatment of electromagnetic radiation pollution and development of radar stealth technology makes it a hot spot that how to prepare wave absorbing materials and put them into use. Relatively high density limits the further development of traditional wave absorbing materials such as ferrite and traditional ceramics in this domain, which promotes the research in the polymer-derived ceramics like silicon carbon nitride because of their low density, excellent conductivity and good dielectric properties.Silicon carbon nitride polymer-derived ceramics has good conductivity and dielectric properties. Besides, adding metal ions like ferric ion into the materials can provide them with great magnetic performance. Therefore, silicon carbon nitride polymer-derived ceramics were prepared by pyrolysis method using polysilazane as precursor and dicumyl peroxide as cross-linking agent in this paper. The development of structures and compositions during the pyrolysis were analysed and electric properties, dielectric performance and wave absorbing ability of the materials were studied. Besides, SiCN(Fe) polymer-derived ceramics were fabricated by the same method using ferric acetylacetonate, ferrum, ferric oxide and ferroferric oxide as iron source additives. The wave absorbing properties of the materials were researched according to their electromagnetic loss.The conclusions are as follows:The cross-linking stage and pyrolysis process of polysilazane was analysed. Results from FT-IR and TG show that and polymer ceramization is accomplished at 800℃ and it reaches 75%. XPS analysis indicates that pyrolysis products are composed of complex bonds between Si, C and N and dangling bonds of C and nitrogen loss is apparent. XRD spectrum shows that SiCN polymer-derived ceramics are amorphous in structure when pyrolysed at 900℃-1350℃ while crystal structure are developed after 1400℃. As pyrolysis temperature rises between 900℃ and 1350℃, the uniformity of the materials is improved and porosity is decreased.Influences of pyrolysis temperature on the electric properties and dielectric performance were studied. Results show that at different temperatures I and V of SiCN polymer-derived ceramics are obvious linear relationship. With the increase of heat treatment temperature (1000℃-1450℃), electrical conductivities and dielectric constants of the materials increase apparently. Besides, dielectric properties are also influenced by thickness of the materials. When the thickness of it is 4mm, the material has best dielectric performance and its dielectric loss reaches 3.1 at 12.7 GHz.Influence of methacrylic acid on the microstructures, carbon content and properties such as dielectric performance and wave absorbing properties of SiCN polymer-derived ceramics are researched. When 6wt% methacrylic acid are introduced into precursors as carbon source, carbon content of the material obviously rises and then dielectric constant increases a lot. Results show that at 12.7GHz its dielectric loss is 0.75 and reflectance is-4.8dB and electromagnetic damping coefficient is 240, which indicates good wave absorbing ability.SiCN(Fe) polymer-derived ceramics were fabricated by pyro lysis using ferric acetylacetonate, ferrum, ferric oxide and ferroferric oxide as iron source additives, and microstructures, phase compositions and wave absorbing properties of the materials were studied. XRD results show two crystal phases, α-Fe and C, in the SiCN(Fe) polymer-derived ceramics. The permittivity, dielectric loss and magnetic loss all increase because of ferric phases especially when ferroferric oxide was doped. Due to electrode-mediated mechanism and polarization mechanism, resonance humps can be seen at about 10GHz in the analysis of dielectric loss and magnetic loss and dielectric loss tangent and magnetic loss tangent of the materials reaches 2.1 and 0.5, respectively. As for wave absorbing ability, reflectance and electromagnetic damping coefficient of the materials are -4.7dB and 800, respectively.Influences of adding contents of nano ferric oxide on wave absorbing performance of SiCN(Fe) polymer-derived ceramics were discussed. Results indicate that when 18 wt% nano ferric oxide is doped, dielectric loss and magnetic loss reach top. Besides, reflectance of the materials is the lowest and electromagnetic damping coefficient is the highest at 10GHz, and they are -11dB and 325, respectively, which meets the requirements of wave absorbing.In the paper, the SiCN and SiCN(Fe) polymer-derived ceramics as wave absorbing materials have a wide application prospects.