Fabrication of SiC(OAl) and SiC(Al) fibers by melt-spinning, UV curing, thermolysis and sintering of photo-sensitive polyvinylaluminocarbosilane

Abstract

SiC fiber is an important structural material in high-temperature extreme environments and nuclear energy applications. Oxidation and electron irradiation are main curing methods for the fabrication of industrial SiC fibers. In this work, a photo-sensitive polyvinylaluminocarbosilane (PVACS) is facilely prepared by blending polyaluminocarbosilane (PACS) and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (D4Vi), which can be melt spun, cured by ultraviolet irradiation at room temperature. After thermal pyrolysis and sintering, the SiC(OAl) fibers with oxygen content of 8.84 wt% and C/Si ratio of 1.34, the SiC(Al) fibers with oxygen content of 0.29 wt% and C/Si ratio of 1.03 are achieved. The cured mechanism and the structural evolution from the precursor fiber to the final ceramic fibers is investigated. The results show that homopolymerization of D4Vi is the main curing mechanism in addition to the β-addition of hydrosilylation. Different from the typical oxidative curing, the oxygen in the fibers mainly comes from D4Vi. At about 800 ℃, the SiAlxOy phase, the SiCxOy phase and free carbon are formed. At 1200 ℃, the Al-C bonds possibly in Al4C3 are formed. At around 1600 ℃, Al may exist mainly in the form of Al4O4C, and the amorphous carbon phase changes into crystalline graphitic structure. Meanwhile, a lot of mesopores and macropores in the SiC(OAl) fibers are formed due to thermal decomposition of the SiCxOy phase. However, at 1800 ℃, the SiC(Al) fibers densify again due to the formation of Al2OC and Al4SiC4 phases, which also inhibit the growth of β-SiC and favor the formation of α-SiC.