PREPARATION OF NOVEL OXIDATION RESISTANT CARBON SILICON FIBRES

A novel silicon containing carbon precursor was synthesised by reacting a petroleum pitch fraction with polydimethylsilane. The silylated pitch precursor containing about 22 wt% silicon was melt spun into fibres and then oxidatively stabilised under different conditions to render the fibres infusible. The fibres were pyrolysed and heat treated up to 1600 ℃ in inert atmosphere. The extent of stabilisation was found to be critical to development of mechanical strength of the fibres which varied with heat treatment temperature, showing a maximum at 1200 ℃ when the strength was 1.4～1.6 GPa. Modulii were low because of the lack of orientation of the carbon layer planes along the fibre axis. Optimally stabilised fibres show a drop in strength at 1300 ℃,but this stabilises at about 600 MPa over the range 1300～1600 ℃. These strengths are remarkably good considering the low modulus which is due to quite high failure strains. It was found that if during the pyrolysis process at 1200 ℃, the fibres are exposed to oxygen for a short period of time, they can form a protective silica surface layer which makes the fibres very oxidation resistant. These fibres have an average tensile strength similar to that of middle class performance carbon fibres but have the additional advantage of in situ oxidation protection at high temperatures.