SiC junction enhanced carbon nanofiber aerogels with extremely high specific strength and ultra-low thermal conductivity

C/SiC aerogels with both ultra-low thermal conductivity and extremely high strength were fabricated by freeze casting. SiC junctions originated from pyrolysis of polycarbosilane (PCS) were formed between carbon nanofibers (C f ) to enhance the strength of aerogels. The effects of PCS content and total solid content on the phase composition, pore structure , thermal conductivity and compressive property were studied. The fabricated aerogels possess hierarchical pore structure. In the micro-scale, it contains circular pores with size of about 15 µm, while it is mesoporous and macroporous in the nano-scale. Both thermal conductivity and compressive strength increase with the increase in PCS content. Through tailoring PCS content and total solid content, C f /SiC aerogels with porosity of 99.5%, thermal conductivity of 33 mW·m −1 ·K −1 and compressive strength of 7.14 MPa can be obtained. The specific strength of the fabricated C f /SiC aerogels is up to 467.6 MPa/(g/cm 3 ), which is the highest value for ceramic aerogels.