WU Xiaohan, ZHANG Xiaoshan, ZHANG Songhe, LIU Tao, WANG Yingde

(Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, Hunan, China)

Extended Abstract:[Background and purpose] The development of new generation of aircraft has created an urgent demand for high-temperature-resistant microwave-absorbing materials. SiC fibers, which exhibit advantages, such as high-temperature resistance, oxidation resistance and electromagnetic absorption, hold promising application prospects in the field of high-temperature microwave absorption. However, the limited tunability of the inherent composition and structure of SiC fibers constrains the optimal design of their dielectric constant and microwave absorption performance. In current study, carbon nanotube (CNT) with high specific surface area and high electrical conductivity was introduced into SiC precursors through chemical grafting, resulting CNT/SiC nanofibers. This material is anticipated to exhibit favorable application prospects in the field of high-temperature microwave absorption.[Methods] SiC micro/nanofibers with various contents of carbon nanotube (CNT) were fabricated using a combination of electrospinning and precursor conversion techniques. The preparation process comprises four steps. Firstly, chemically grafted polysilicarane (PCS) precursors, which were synthesized previously by the authors, with different contents of CNT (0.05 wt.% and 0.5 wt.%), were used as raw materials and designated as x%-CNT/PCS. These precursors were mixed with xylene and N’N-dimethylformamide in a specific ratio (4:2:1) and continuously stirred for 24 h to obtain the precursor solution. Next, the precursor solution obtained in the first step was subjected to electrospinning at high-voltage electric fields ranging from 15 kV to 17 kV, with a feeding rate of 1.5 mL·h⁻¹, at ambient humidities of 25–30% RH and temperature of 32 ℃, to produce precursor fibers. Then, these precursor fibers were cured in dry air at 230 ℃ for 2 h to obtain pre-oxidized fibers. Finally, the pre-oxidized fibers were pyrolyzed at 1100 ℃ for 1 h in Ar to yield CNT/SiC micro/nanofibers.[Results] As observed from SEM images, the fibers exhibited diameters ranging from 2 μm to 6 μm, which have smooth surfaces and no apparent defects such as pores or cracks. XRD results revealed that the fibers were composed mainly of amorphous SiC_xO_y. With increasing content of CNT, the real and imaginary parts of the dielectric constant of the 0.05%-CNT/SiC composite micro/nanofibers increased to 5.27 and 1.19, respectively. When the CNT content was elevated to 0.5%, the real part of the dielectric constant further increased to approximately 5.97, while the imaginary part slightly decreased to 0.84. The incorporation of a small content of CNTs into SiC fibers significantly enhanced the microwave absorption performance. The 0.05%-CNT/SiC composite micro/nanofibers had a minimum reflection loss of −16.29 dB at 14.24 GHz, with an effective absorption bandwidth of 4.4 GHz.[Conclusions] CNT/SiC micro/nanofibers, with uniform morphology, dense structure and high aspect ratio, were fabricated using electrospinning technique combined with the precursor conversion method. CNT was introduced into polycarbosilane (PCS) through chemical bonding, enabling effective regulation of the dielectric constant of the CNT/SiC composite micro/nanofibers with a small content of CNT. When the CNT content was increased from 0 to 0.5%, the real and imaginary parts of the dielectric constant of the CNT/SiC micro/nanofibers were varied from 4.52 to 5.97 and 0.74 to 1.19, respectively. At a thickness of 2.5 mm, the CNT/SiC micro/nanofibers exhibited a minimum reflection loss of −16.29 dB at 14.24 GHz, with an effective absorption bandwidth of 4.4 GHz, demonstrating desirable microwave absorption performance.

Key words: CNT/SiC fibers; electrospinning; microwave absorption; high-temperature resistance