两种连续SiC纤维的高温介电及吸波性能对比

采用XPS、XRD、Raman光谱等方法分析了两种典型SiC纤维的微观结构, 研究了微观结构对纤维电导性能的影响, 并揭示了其高温介电性能和吸波性能的演变规律, 对高温结构吸波复合材料的研究具有重要意义。研究表明: KD-I SiC纤维表面富碳, 而SLF SiC纤维以Si-C-O结构为主, 前者具有较高的电导率和复介电常数, 从而导致KD-I纤维与空气阻抗匹配差, 而SLF纤维的损耗较小, 因此两者在X波段的室温反射率仅为-3.2 dB和-0.3 dB。KD-I纤维的复介电常数随着温度的升高显著增大, SLF纤维的实部增幅较大而虚部略小, 两者在700℃时的复介电常数分别达到20.9-j25.0和5.0-j0.37, 高温条件下由于阻抗匹配均变差, 吸波性能无明显改善。

Comparison of High-temperature Dielectric and Microwave Absorbing Property of Two Continuous SiC Fibers

Two kinds of SiC fibers with different microstructures were analyzed by XPS, XRD and Raman spectra. The electrical conductivities of the fibers were measured, and their dielectric and microwave absorbing properties at elevated temperatures were investigated. Research results show that KD-I SiC fiber with rich carbon layers possess higher complex permittivities and electrical conductivities than do SLF SiC fiber with Si-C-O phase, resulting in poor impedance match between free space and KD-I fibers. Simultaneously, due to poor dielectric loss of SLF fiber, two fibers display inferior absorbing performance with the reflection loss values of -3.2 dB and -0.3 dB at X band, respectively. With temperatures increasing, ε° and ε? of KD-I fiber sharply increase, while the complex permittivity of SLF fiber display a small increment. Complex permittivities of two fibers are up to 20.9-j25.0 and 5.0-j0.37 at 700℃. Microwave absorbing properties of two fibers degrade at elevated temperatures, mainly ascribed to deterioration of impedance match.