Novel two-step process for synthesising β-SiC whiskers from coal fly ash and water glass

Abstract Highly crystalline, high-purity β-SiC whiskers were successfully synthesised from a mixed sol of coal fly ash (CFA) and water glass (a silicon resource), and activated carbon (a carbon source) in a carbothermic reduction. The efficiency of the process is over 70%. The alkali activation effects of the water glass on CFA were characterised by FTIR and MAS-NMR. In the activation reaction, silicate frameworks of water glass and CFA became connected to form a large network, producing a stable, uniform sol system. Experiments and thermodynamic analyses were used to study the effects of Na 2 O, Al 2 O 3 , and Fe 2 O 3 on the synthesis of β-SiC whiskers, revealing that Na 2 O does not affect the synthesis process while Al 2 O 3 and Fe 2 O 3 promote the elongation of the SiC whiskers. The results of this study may not only help to reduce the production cost of SiC whiskers but also allow value to be extracted from waste.