Fabrication of SiAlCNO and SiAlC fibers from a photo-sensitive polyvinylaluminocarbosilane precursor using the ultraviolet curing method
SiC fiber is a critical structural material for high-temperature extreme environments and nuclear energy applications. Traditional methods for producing industrial SiC fibers include oxidation and electron irradiation. In this study, a photo-sensitive nitrogenous polyvinylaluminocarbosilane (PVACNS) is synthesized by uniformly blending polyaluminocarbosilane (PACS) and triallyl isocyanurate (TAIC). This precursor can be melt-spun into fibers and rapidly UV-cured at room temperature. After thermal pyrolysis at 1200°C and sintering at 1800°C of the cured fiber, amorphous SiAlCNO fibers with an oxygen content of 9.25 wt%, nitrogen content of 4.42 wt%, and a C/Si ratio of 1.60, and crystalline SiAlC fibers with an oxygen content of 0.02 wt%, nitrogen content of 0.11 wt%, and a C/Si ratio of 1.18 are obtained. The main UV curing mechanism involves homopolymerization of C = C bonds, in addition to minor hydrosilylation reaction between Si–H and C = C bonds. Between 400°C and 600°C, oxygen, nitrogen, and carbon contents decrease significantly due to the decomposition of TAIC. At 1200°C, the amorphous SiAlCNO fiber consists of amorphous SiC x O y , SiC x N y phases, and free carbon, with formation of Al–C and Al–N bonds. β-SiC begins to form at 1400°C. At higher temperatures above 1400°C, SiC x O y and SiC x N y phases decompose, leading to notable decrease in oxygen and nitrogen content at 1600°C and 1800°C. However, due to the presence of Al–C and Al–N bonds, the formation of voids and defects is inhibited and the coarsening of β-SiC is suppressed, resulting in a relatively dense structure in the SiAlC fibers at 1600°C and 1800°C.
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