Valorization of silicon cutting waste and high-alumina fly ash for sustainable synthesis of O′-sialon

Abstract

This study presents a sustainable route for preparing O′-Sialon ceramics from silicon cutting waste (SCW) and high-alumina fly ash (HAFA). SCW was used as the main reactive Si-bearing waste, whereas HAFA provided Al-containing and Si-containing mineral phases. The effects of sintering temperature (1250–1450 °C) and holding time (1–9 h) on phase evolution, microstructure, and macroscopic properties were systematically investigated. XRD results indicate that an O′-Sialon-dominant product was obtained at 1350 °C, while higher temperatures promoted the formation of β-Sialon. The sample sintered at 1350 °C for 5 h showed a bulk density of 1.95 g cm⁻³, a linear shrinkage of 11.75%, a compressive strength of 88.55 MPa, and a porosity of 30.32%. Thermodynamic analysis together with phase and microstructural characterization further suggests that Ca was mainly incorporated into Ca-containing SiAlON-related phases, whereas Fe was mainly stabilized as Fe₃Si under the present processing conditions. These results demonstrate the feasibility of up-cycling SCW and HAFA into value-added SiAlON-based ceramics, while also highlighting the need for future work on raw-material variability and scale-up.