In-situ synthesis silicon nitride nanowires in carbon fiber felts and their effect on the mechanical properties of carbon/carbon composites

Si₃N₄ nanowires (Si₃N₄NWs) were in-situ synthesized in carbon fiber felts via catalyst-assisted pyrolysis of polyureasilazane and further to be used to reinforce carbon/carbon (C/C) composites. Effects of ferrocene-to-acetone mass ratio and synthesis temperature on the morphologies of Si₃N₄ products were investigated and their optimized values are 2:98 and 1430 °C respectively. When the ferrocene-to-acetone mass ratio is 2:98 and the temperature exceeds 1500 °C, a great number of disorganized ribbon-like products were obtained. The growth of Si₃N₄NWs or ribbons obeys a solid-liquid-gas-solid (SLGS) mechanism. Si₃N₄NWs can improve the mechanical properties of C/C composites obviously. Compared with the pure C/C specimens, the specimens doped with Si₃N₄NWs have 66.7% and 58% improvements in out-of-plane compressive and interlaminar shear strength, which can be further increased to 166.7% and 65% through coating a layer of pyrolytic carbon on carbon fibers before the immersing of PSN. These improvements are attributed to the formation of three-dimensional interlocked carbon matrix and the enhanced bonding between pyrolytic carbon plies induced by Si₃N₄NWs.