Phase and microstructural evolution in the ceramization of alumina-silica single-phase and multi-phase gels verified by molecular dynamics: Unraveling the mechanisms of gel ceramization

This study investigated the phase and microstructural evolution of Al₂O₃-SiO₂ single-phase and multi-phase gels during ceramic formation under heat treatment from 900 °C to 1400 °C. By integrating experimental characterization with molecular dynamics simulations, based on atomic-scale binding energy theory, the fundamental reasons for the observed discrepancies in experimental results were revealed. At 900 °C, crystallization of the ceramic matrix initiated, forming pores and depressions. Amorphous SiO₂ acted as a flexible interfacial barrier, reducing defect formation. Densification began by 1100 °C, followed by α-Al₂O₃ recrystallization and mullite formation at 1200 °C, accompanied by pore-grain structures. Further heating to 1300 °C and 1400 °C induced secondary recrystallization. Molecular dynamics results showed that adding amorphous SiO₂ enhanced the system's average binding energy and thermal stability. This provided atomic-level support for the experimentally observed differences in phase transformation and microstructure.