Preparation and properties of PAN-based carbon fiber-reinforced SiCO aerogel composites

To overcome the brittleness issue of SiCO aerogels, the polyacrylonitrile-based (PAN) carbon fiber was impregnated with SiCO sol to obtain carbon fiber-reinforced SiCO aerogel composites (C/SiCO). SiCO sol was prepared through an acid-alkaline two-step catalysis by using methyltrimethoxysilane (MTMS) and di-methyldiethoxysilane (DMDES) as precursors. C/SiCO-1, C/SiCO-2 and C/SiCO-3 were obtained after repeated impregnation of the SiCO sol and gelating, aging, supercritical drying and pyrolyzing one to three times. SEM images show that the SiCO aerogel fills the pores between the carbon fibers, and the nanoporous structure of the SiCO aerogel can effectively improve the thermal insulation of the composites. As the times of impregnation of the SiCO sol increased, the mechanical properties and oxidation resistance of C/SiCO have been improved significantly. The bending strength of C/SiCO-3 was 32.52 MPa, and the compressive strength (25%e) was 51.98 MPa. After heating at 1600 degrees C, the linear shrinkage in the thickness direction of C/SiCO-1 was 20.72%, while that of C/SiCO-3 was only 1.85%. A dense SiO2 molten oxide film formed on the surface of C/SiCO at high temperature, and its extremely low oxygen permeability effectively protected the inside of the composites.