Properties of Composites of Carbon Fiber and Ceramics Prepared from Boron-rich Organometallic Compounds

Diphenylborosiloxane (PBS), a kind of organometallic compound, is synthesized from diphenylsilanediol and boric acid. PBS with high boron content was prepared by setting their mole ratio at 1: 1 (Si/B=3/3). With the PBS obtained, specific gravity, molecular weight, and infrared absorption spectrum were measured. For the ratio of Si/B=3/3, molecular weight was 453, and Si content was 7.2wt%. The infrared absorption spectrum showed a larger absorption by B-OH bond than in case of Si/B=3/1 or 3/2. Using PBS, carbon fiber (CF) and SiC powder (40wt% in acetone solution), CF/ceramics composites were prepared. Their mechanical properties, oxidation resistance, and crystal structure were investigated. Composite prepared from PBS with the ratio of Si/B=3/3, showed a bulk density of 1.32g/cm3, a bending strength of 220MPa, and Young's modulus of 30GPa. Microscopic observation by SEM recognized the formation of vitreous oxidation-resistant protective covering, which improved the oxidation resistance of composites. X-ray diffractometry gave diffraction patterns for B2O3 as well as carbon and β-SiC, and a pattern for B4C turned up by heat treatment at a high temperature of 2000°C.