Fabrication, microstructural evolution and excellent EMW absorbing properties of SiC fibers with high iron content

Improving the electromagnetic wave (EMW) absorption performance of continuous SiC fibers is of great significance for the development of structure-function integrated composites. Doping magnetic metal elements into SiC fibers can effectively improve their dielectric/magnetic loss, which is expected to produce SiC fibers with wide frequency EMW absorption. At present, introducing metal into continuous SiC fibers generally has the disadvantages of (1) low metal content and (2) weak EMW absorption ability. In this paper, vinylferrocene (VF) with monofunctional groups was selected as the iron source to introduce Fe atoms into polycarbosilane (PCS) through chemical modification without changes in the molecular framework of PCS, which is beneficial for the melt spinning of the precursors. A series of continuous Fe-SiC fibers were prepared by polymer-derived ceramic approach, and their composition, structure and EMW properties were systematically studied. Besides SiC crystallization, the turbostratic carbon, core-shell structures of Fe5Si3@C and Fe3Si@C were identified for the continuous Fe-SiC fibers. It is worth noting that in the present work, (1) the introduction of Fe catalyzes the formation of turbostratic carbon, which can be observed at a low temperature of 900 degrees C and (2) the highest Fe content (7.70 wt%) was obtained among all the reported continuous Fe-SiC fibers. The unique microstructure of final Fe-SiC fibers demonstrated outstanding EMW absorbing performance. For the Fe-SiC-2-900 degrees C fiber, the minimum reflection loss (RLmin) reached -54.63 dB at 10.2 GHz. By adjusting the thickness, the effective absorption bandwidth of Fe-SiC-3-1200 degrees C can almost cover the X-band. The results indicate that the presented continuous Fe-SiC fibers exhibit excellent EMW absorbing performance.