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

摘要

Highly crystalline, high-purity beta-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 Na2O, Al2O3, and Fe2O3 on the synthesis of beta-SiC whiskers, revealing that Na2O does not affect the synthesis process while Al2O3 and Fe2O3 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.