Pyrolysis behaviors of iodine vapor cured fine-diameter polysilazane fibers for the preparation of SiCN ceramic fibers

Polymer-derived SiCN ceramic fibers have been developed as a new ultrahigh-temperature material that can be an alternative to the binary system of SiC and Si3N4 due to the preservation of its amorphous phase at high temperatures. In this work, a novel strategy of iodine vapor curing has been employed to cure the fine-diameter PSZ fibers. The pyrolysis behaviors of the cured PSZ fibers at various temperatures were investigated. The as-prepared fibers were characterized by TG-DSC, PY/GC/MS, FT-IR, FE-SEM, and XRD analysis. The results revealed the fine-diameter amorphous SiCN ceramic fibers have a high tensile strength of 1.08 ± 0.26 GPa after pyrolysis at various temperatures. During the process of pyrolysis, the unstable chemical bonds and active groups (i.e., N-I, Si-I, N-H, Si-H, and Si-CH3) transformed into Si3N structure with the release of iodine, CH4, NH3, cyclotrisiloxane at 300 °C. The dehydrogenation and transamination reactions occurred between the Si-H, N-H, and N-H bonds at the pyrolysis temperature of 400 °C. At the higher temperature (500─600 °C), a rearrangement reaction occurs to form some complex compounds (i.e., 3TMS and 4TMS derivative melamine and other higher molecular weight compounds) and inorganic fibers were attained at temperature ≥ 700 °C. This work revealed an important guiding significance for the pyrolysis of PSZ ceramic precursor polymer fibers.