High-Performance SiC-Polycrystalline Fiber with Smooth Surface

Abstract

Polymer-derived SiC-polycrystalline fibers show excellent heat-resistance up to 2000 °C, and relatively high strength. Up to now, through our research, the relationship between the strength and residual defects of the fiber, which were formed during the production processes (degradation and sintering), has been clarified. In this paper, we addressed the relationship between the production conditions and the surface smoothness of the obtained SiC-polycrystalline fiber, using three different raw fibers (Elementary ratio: Si1Al0.01C1.5O0.4~0.5) and three different types of reactors. With increase in the oxygen content in the raw fiber, the degradation during the production process easily proceeded. In this case, the degradation reactions (SiO + 2C = SiC + CO and SiO2 + 3C = SiC + 2CO) in the inside of each filament become faster, and then the CO partial pressure on the surface of each filament was considered to be increased. As a result, according to Le Chatelier’s principle, the surface degradation reaction and grain growth of formed SiC crystals would be considered to become slower. That is to say, using the raw fiber with higher oxygen content and closed system (highest CO content in the reactor), a much smoother surface of the SiC-polycrystalline fiber could be achieved. Furthermore, the similar effect obtained by simple oxidation of the SiC-polycrystalline fiber was confirmed, and the advantageous points of the aforementioned process were also considered.

Effect of Impurities Control on the Crystallization and Densification of Polymer-Derived SiC Fibers

“…The surface of this fiber contains high oxygen and carbon contents compared to the inside. In fact, impurity gases that decompose in the vicinity of the surface can be easily released and removed during heat treatment, but the impurity gases generated in the core region diffused out to the surface, leaving large pores between the surface and the core [22,23].…”

“…PCS containing various organometallic compounds have been synthesized to fabricate polycrystalline SiC fibers by inhibiting the decomposition of oxygen impurities during the conversion from amorphous SiC to crystalline SiC [20,21]. In particular, Si-Al-C-O fibers manufactured using polyaluminocarbosilane (PACS) are representative ceramic grade fibers having a strength retention temperature of 1700 • C [21,22]. These modified PCS are usually synthesized using an autoclave or reflux system, but it is known that the blend method is good for mass production and easy application.…”