Thermal stability and oxidation resistance of novel carbon-silicon alloy fibres

The effect of thermal treatment on the properties and structure of carbon-s ilicon alloy fibres produced from a novel silicon-containing carbon precurs or is reported. The precursor, containing about 22 wt % Si, was melt spun i nto fibres and then oxidatively stabilized under different conditions to re nder the fibres infusible. The fibres were pyrolysed and heat treated to 16 00 degrees C in inert atmosphere. The extent of stabilization was found to be critical to the development of mechanical strength of the fibres which v aried with heat treatment temperature, showing a maximum at 1200 degrees C when the strength was 1.2-1.4 GPa. Moduli were low because of the lack of o rientation of the carbon layer planes along the fibre axis. The maximum str ength and the thermal stability at high temperatures is considerably reduce d if the fibres are excessively oxidized at the stabilization stage. Optima lly stabilized fibres show a drop in strength at 1300 degrees C but this st abilizes at about 600 MPa over the range 1300-1600 degrees C. These strengt hs are remarkably good considering the low modulus which is due to the quit e high failure strains. The fibres can show excellent resistance to oxidati on if given an initial short exposure to oxygen at high temperature. This i s considered to be due to an imperceptible layer of silica. (C) 1999 Kluwer Academic Publishers.