Abstract: Polycarbosilane (PCS) precursor fibers were thermal oxidation treated under negative pressure.The effect of atmosphere pressure and heating temperature on weight gain, Si-H bond reaction degree, gel content, chemical structure and pyrolysis characteristics of the PCS precursor fibers were studied.The experimental results show that the weight gain, gel content, Si-H bond reaction degree and ceramic yield of the fibers are all decreased with decreasing atmosphere pressure and heating temperature.Under the atmosphere pressure of-0.02 MPa, with the temperature descended from 195 ℃ to 175 ℃, the weight gain was decreased from 9.98% to 2.80%, the Si-H bond reaction degree was decreased from 63.62% to 21.85%, the gel content was decreased from 73.53% to 1.98% and the ceramic yield was decreased from 87.81% to 81.29%.

Key words: polycarbosilane precursor fiber;negative pressure;thermal oxidation