Effect of carbon addition on the microstructure of Si3N4–Cfiber composites using semiconductor-waste Si sludge

Si3N4–Cfiber composites using waste-Si sludge were fabricated by hot pressing at 1850 °C for 2 h with and without the addition of carbon powder. The composites were composed of small amounts of β-Si3N4, O′SiAlON, SiC and Y2SiO5 regardless of carbon powder addition. In the composite without the addition of carbon powder, most of the carbon fibers were graphitized with fine particles. Furthermore, many cavities were observed in the interior regions of C-fibers as well as at the interfaces of Si3N4/Cfiber caused by the decomposition of them. However, in the composite with 3 wt.%C powder added, the core regions of C-fibers still existed in an amorphous. The average size of a matrix grain in the composite using 3 wt.%C powder was slightly finer than that of composite fabricated without using carbon powder, which was caused by the existence of nanometer-sized SiC particles.