Carbon elimination by heat-treatment in hydrogen and its effect on thermal stability of polycarbosilane-derived silicon carbide fibers

Carbon elimination from EB-cured PCS fibers by H2-treatment and the thermal stability of resultant SiC fibers were examined through TG, chemical analysis, AES analysis, XRD analysis, resistivity measurements, SEM observation and tensile tests. The C/Si mole ratio from 1.50 to 1.05 could be achieved by H2-heat treatment at t ≧ 4 h and T = 773–1173 K. There was no difference in XRD patterns, fiber morphology and tensile strength of the fibers in the as-H2-treated state. H2-treatment at higher temperature caused the reduction in residue and the increase in resistivity of the fibers. An oxygen-rich layer was formed on the fiber surface after H2-treatment, resulting in the mass loss, the coarsening of β-SiC grains and a marked degradation of fiber strength after exposure to higher temperature. Prevention of oxygen uptake after H2-treatment is essential to improve the thermal stability of SiC fibers.