Preparation of monodispersed SiO2-Al2O3 microspheres based on fly ash by thermally induced phase separation

In this study, we successfully prepared fly ash-based SiO2-Al2O3 microspheres using phase separation followed by acid leaching. Thermal analysis and X-ray diffraction were used to identify the optimal temperature range of heat treatment. The chemical composition and surface property of the microspheres were analyzed using X-ray fluorescence and contact angle measurements, and scanning electron microscopy was used to characterize the appearance of the microspheres. The results showed that the SiO2-Al2O3 microspheres were composed of 60-80 wt% SiO2 and 10-12 wt% Al2O3 with a uniform particle size, a hydrophilic surface, and high alkali resistance. Heat treatment studies revealed that the phase separation temperature should not exceed 900 degrees C to avoid crystallization. The mean particle size of the SiO2-Al2O3 microspheres decreased with an increase in the heat treatment temperature. Additionally, observing the evolution of the phase structure at 800 degrees C showed that there was fusion between the SiO2-Al2O3-enriched phases via interfacial tension in the later stage, resulting in larger spherical phase structures. Further, an increase in the Al2O3, Fe2O3, and CaO composition decreased the SiO2- Al2O3 microspheres particle size, and therefore inhibited phase separation.

Automated summary

In this study, fly ash-based SiO2-Al2O3 microspheres were successfully prepared using phase separation and acid leaching. The optimal temperature range for heat treatment was determined using thermal analysis and X-ray diffraction. X-ray fluorescence and contact angle measurements were used to analyze the chemical composition and surface properties of the microspheres, while scanning electron microscopy was used to characterize their appearance. The results showed that the SiO2-Al2O3 microspheres had a uniform particle size, hydrophilic surface, and high alkali resistance. The mean particle size decreased with an increase in the heat treatment temperature. Fusion between the SiO2-Al2O3-enriched phases via interfacial tension was observed at 800 degrees C, resulting in larger spherical phase structures. An increase in the composition of Al2O3, Fe2O3, and CaO decreased the particle size and inhibited phase separation.