Effect of hydrogen atmosphere on pyrolysis of cured polycarbosilane fibers

SiC-based fibers with various chemical compositions were synthesized using an irradiation-curing process. Polycarbosilane (PCS) fibers were cured by i rradiation with an electron beam in a helium atmosphere. The cured PCS fibe rs were pyrolyzed at 1300 degrees C under controlled hydrogen or argon atmo spheres, and SiC fibers with C/Si of 0.84 to 1.56 were obtained. The fibers consisted of <1.0 wt% O, <0.2 wt% N, <0.1 wt% H, with the balance being Si and C. The mechanism of pyrolytic transformation of cured PCS to SiC-based ceramics was investigated using TG/DTA analysis. Greater mass losses were observed during pyrolysis in a hydrogen atmosphere than in argon, This resu lt suggests that the hydrogen atmosphere suppresses N, evolution and helps to remove excess carbon as CB, during pyrolysis. The microstructure and mec hanical properties of the resulting SiC-based fibers were found to be very dependent on their C/Si chemical compositions.