Mechanical properties and oxidation resistivity of carbon fiber/ceramic composites prepared from borosiloxane

Diphenylborosiloxane (PBS), an organometallic compound with Si–O–B bonds, was compounded with carbon fiber (CF) to form CF/ceramic composite. Three types of PBS with different molar ratios (Si/B) in the materials were used. On the PBS obtained, specific gravity, Si content, molecular weight, melting point, and infrared absorption spectrum were measured. On the basis of these results, structures of PBS were examined, which clarified that the PBS thus synthesized consisted of several components with different molecular weights. Mechanical properties and oxidation resistivity of the CF/ceramic composites obtained differed with the Si/B ratios of PBS. Mechanical strength of the CF/ceramic composites increased with increase of Si content of PBS. It was also found that, when PBS with high boron content was used, compact vitreous film consisting mainly of B₂O₃ was formed over the composite. Due to the formation of this film, oxidation resistivity of the composite was improved.