Effects of heat-treatment temperature on carbon-based composites with added illite

To investigate new applications for illite as an additive for carbon-based composites, the com- posites were prepared with and without illite at different heat-treatment temperatures. The ef- fects of the heat-treatment temperature on the chemical structure, microstructure, and thermal oxidation properties of the resulting composites were studied. As the heat-treatment tempera- ture was increased, silicon carbide SiC formation via carbothermal reduction increased until all the added illite was consumed in the case of the samples heat-treated at 2,300°C. This is attributed to the intimate contact between the SiO2 in the illite and the phenol carbon precur- sor or the carbon fibers of the preform. Among composites prepared at all temperatures, those with illite addition exhibited fewer pores, voids, and interfacial cracks, resulting in larger bulk densities and lower porosities. A delay of oxidation was not observed in the illite-containing composites prepared at 2,300°C, suggesting that the illite itself absorbed energy for exfolia- tion or other physical changes. Therefore, if the illite-containing C/C composites can reach a density generally comparable to that of other C/C composites, illite may find application as a filler for C/C composites. However, in this study, the illite-containing C/C composites exhibited low density, even when prepared at a high heat-treatment temperature of 2300°C, although the thermal oxidation of the resulting composites was improved.