Synthesis of Sialon-SiC Composites from Kyanite Tailings by Carbothermal Reduction Nitridation

Abstract

Sialon-SiC composites were synthesized from kyanite tailings via the carbothermal reduction nitridation (CRN) technique. The phase composition, morphology, and microstructure of the CRN samples were investigated by x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and elected-area electron diffraction. A brief discussion on the synthesis mechanism of CRN process was investigated based on the thermodynamic analysis of the SiO2-Al2O3-C-N2 system. The results show the phase compositions depended on the synthesis temperature. With the increasing heating temperature, SiO2 was first changed into Si2N2O and then transformed into Si3Al3O3N5 through reacting with N2, Al2O3, and C. At the same time, the excess SiO2 changed into SiC by a carbothermal reduction reaction. The optimized synthesis temperature for the CRN reaction was found to be at 1550°C for 4 h. The Si3Al3O3N5 and SiC phases were proved coexisting in the same CRN particle. This transformation provided a feasible utilization route of kyanite tailings for high-temperature application.