Iodine diffusion during iodine-vapor curing and its effects on the morphology of polycarbosilane/silicon carbide fibers

Iodine-vapor curing is used to produce continuous SiC fibers from polycarbosilane (PCS), but attempts to limit the uptake of oxygen during the curing process result in SiC fibers with different morphologies and pore types. The cause of this distinct transformation in the morphology of the fibers is determined in this study by tracing the distribution of iodine in PCS fibers cured either at a set temperature or for a given period. The results reveal that the final morphology of the fibers is dependent on the degree of iodine diffusion, or on the extent of their cross-linked area. Using this knowledge, fibers with three distinct morphologies are produced by controlling the curing conditions. Optimization of this curing process is shown to inhibit the formation of pores and retard the incorporation of oxygen, while still allowing the fibers to retain their cylindrical shape.