SiC-coated carbon fibers for aluminum-carbon composites were synthesized with carbothermal reduction. For the SiC layer formation on the surface of carbon fiber, silica sol was coated and heat treated at a temperature of 1460 and 1500• C. SiC layer formation by carbothermal reduction complete at above 1500• C for 1 h. From TGA in atmosphere, SiC coating effectively protected against the oxidation of graphite. The thickness of the SiC coating layer ranged from 150 to 300 nm and the layer was formed homogenously along the surface of carbon fiber. As the first step of reaction for SiC formation, it is generally accepted that SiO is formed and vaporized in interface between fiber and silica. It is analogized in this work that the SiO vapor reacts directly with carbon fiber, resulting in formation of SiC phase. From the TEM results, the SiC layer was confirmed as a ZnS-type FCC structure.
aThis study aims to investigate the effects of SiC coating on the degradation of carbon short fiber in Al melt. The SiC coating on the surface of carbon short fiber is performed at 1500• C in Ar atmosphere by carbothermal reduction method after precoating with silica sol on the surface of carbon short fibers. The SiC coating layer is successfully formed with a mean thickness of 160 nm. The pure carbon short fibers without SiC coating was degraded rapidly in Al melt. After maintenance for 180 min in Al melt of 800• C, carbon fibers did not remain. On the other hand, the carbon short fibers with SiC coating layer maintained the shape of initial carbon fiber up to 180 min in Al melt. However, with increase of reaction time in Al melt, SiC coating layer gradually dissolved and after 180 min, the coating layer was not observed in some areas on the surface of fiber. Also, concentration of Al in carbon fiber increased with the maintenance time in Al melt. As a consequence, SiC coating layer can retard effectively degradation of the carbon short fibers, even though it is only a few hundred nanometers thick.
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