The Effect and Mechanism of Iodine Curing on SiC Green Fibers Derived from Polymethylsilane (PMS) via Melt Spinning

Silicon carbide fiber (SiCf) is a promising reinforcement material due to its exceptional resistance to high temperature, oxidation, and corrosion. The chemical composition, performance, and morphology of SiCf are highly influenced by the curing process. Herein, the chemical vapor curing (CVC) method was employed to cure the green fibers derived from polymethylsilane (PMS) in iodine vapor. The unique vacant 3d subshells of PMS, in conjunction with its sigma conjugation system, enabled the coordination with iodine anions, thus promoting the cleavage of C-H, Si-H, Si-Si and Si-CH3 bonds. The conduction of dehalogenation and dehydrocyclization reactions involving alkyl iodides resulted in the generation of naphthenic and aromatic compounds. Concurrently, the structural formations of SiC4, SiSiC3, and CSiSi3 were promoted, leading to an increased ceramic yield of PMS-derived green fibers. Furthermore, an increase in iodine content correlated with rising radical concentrations when subjected to elevated iodine treatment temperatures. The delocalization of electrons, arising from the sigma conjugation system along the Si-Si skeleton, gives rise to charge transfer between PMS and iodine. As a result, the charge transfer complexes are formed, and the iodine treatment of PMS-derived green fibers proceeds through a radical reaction mechanism, distinct from that observed in the iodization processes involving polycarbosilane (PCS)-derived fibers.