碳纤维增强氮化硅复合材料的制备及介电性能研究

Study on Preparation and Dielectric Properties of Carbon Fiber Reinforced Silicon Nitride Composites

为了研究以碳纤维为吸波剂的二维层状复合材料,采用热压烧结法以改性碳纤维和氮化硅为原料,在1400℃、N_(2)气氛下烧结制备了连续碳纤维增强氮化硅基复合材料。采用网络矢量分析仪测试了C_(f)/Si_(3)N_(4)复合材料在X波段的介电常数,并分析了其对电磁波的反射特性。结果表明:单层复合材料中碳纤维轴向垂直电磁波的电场方向的虚部小于平行的即损耗优于平行时的情况;双层复合材料有效地大幅降低了介电常数的实部,但仍不能达到阻抗匹配的要求,其原因一是Si没能阻止碳纤维径向的电流传导,二是相邻层碳纤维的反射电场分量合成为椭圆极化场,双层结构的各向异性不明显,反射主要取决于平行电场的分量。

In order to study two-dimensional layered composites using carbon fibers as microwave absorber,continuous carbon fibers reinforced silicon nitride composite was prepared by hot-pressing sintering method,using SiC-coated carbon fibers and silicon nitride as raw materials,and sintering at 1400℃ under N_(2) atmosphere.The complex permittivity of the C_(f)/Si_(3)N_(4) composites was measured in the X-band using a network vector analyzer,and its reflection to microwave was analyzed.The results showed that when carbon fibers are perpendicular to the electric field of microwave,the imaginary part of permittivity of the single-layer composites is smaller than the case of parallel,that is to say,the loss is better than the parallel.The double-layer composites effectively reduce the real part of permittivity compared with the single-layer composites,but they still cannot meet impedance matching.The reasons are that one is Si failed to prevent electric current conducting in the radial of the carbon fiber.Second,the reflected electric field components of the adjacent layers of carbon fibers are combined into an elliptical polarization field,and the anisotropy of the double-layer composites is not obvious,therefore the reflection of electromagnetic waves mainly depends on the components of the parallel electric field.