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.
Highlights
Since the first precursor ceramics using polycarbosilane were developed [1], many polymer-derived SiC-base fibers have been developed [2,3,4,5,6]
Through our research, the relationship between the strength and the residual defects contained in the fiber, which were formed during the production processes, have been clarified [12,13,14,15]
We clarified the relationship between the heat-treatment condition and the surface smoothness
Summary
Since the first precursor ceramics using polycarbosilane were developed [1], many polymer-derived SiC-base fibers have been developed [2,3,4,5,6]. Through our research, the relationship between the strength and the residual defects contained in the fiber, which were formed during the production processes, have been clarified [12,13,14,15] In these studies, we have proposed several new methods for reducing the residual defects, and demonstrated them using the conversion process, from amorphous Si-Al-C-O fiber to SiC-polycrystalline fiber (Tyranno SA). During the heat-treatment processes, a degradation of the Si-Al-C-O fiber and a subsequent sintering of the degraded fiber proceed as well, accompanied by a release of CO gas and compositional changes, to obtain the dense structure. Since these structural changes proceed in each filament, strict
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