Modification of polycarbosilane as a precursor with high ceramic yield foroxygen-free SiC fibers

Polycarbosilane (PCS) was modified by addition of 1 wt% polyborazine and su bsequent heat treatment at 70-400 degreesC. The modified PCS exhibited high ly improved ceramic yield from original 63% to 78% by heating at 70 degrees C for 10 h. The molecular weight of the PCS modified at higher temperatures markedly increased, then was rendered infusible but soluble PCS in organic solvent on heating at 300 degreesC. H-1-NMR indicated that original PCS wa s enhanced by dehydrocoupling reaction between Si-H groups. Solution of the modified PCS was hand-drawn to fibers, followed by direct pyrolysis up to 1,400 degreesC without air+curing step to convert into oxygen-free SiC fibe rs. The morphology and crystalline phase were determined by SEM and XRD ana lysis, respectively.