Effect of hold time on reaction of silicon monoxide with activated carbon fiber composites Original Research Article

Activated carbon fiber composites (ACFCs) with the specific surface area of about 1150 m2/g were reacted to produce silicon carbide fiber composites with SiO vapor generated from a mixture of Si and SiO2 at 1673 K under vacuum for various hold times ranging between 10–120 min. Chemical analysis of the converted ACFCs resulting from reaction showed that the products contained 79–90 wt.% silicon carbide, 7–13 wt.% amorphous silica and 3–8 wt.% unreacted carbon, and the composition depended on hold time. At an early stage of the SiO–C reaction during hold time, part of the excess SiO vapor generated was presumed to condense on to the converted fiber surface as amorphous silica, thereby reducing the specific surface area of the converted ACFCs. As the C–SiC conversion proceeded, the gas-phase carbon reduction of SiO2 with CO occurred and increased the specific surface area from 25 m2/g to 48 m2/g. Strength of the converted ACFCs decreased with conversion due to the increased specific surface area and crack formation in the converted carbon fiber.