Sintering kinetics and performance evolution of silicon-rich mullite ceramics via deformation-thermogravimetric synchronous analysis

Abstract

The solid-state reaction mechanism and sintering kinetic behavior of silicon-rich mullite ceramics still lack systematic and in-depth research. In this study, the solid-state reaction sintering process and densification behavior and mechanism of mullite were systematically examined using silicon-rich mullite precursor powder as raw material and visual high-temperature deformation-thermogravimetric comprehensive analysis technology. Results show that the sintering process of silicon-rich mullite ceramics involves multiple shrinkage stages. The mullite phase is synthesized in the range of 1300 ℃-1400 ℃, and excellent compactness can be obtained at 1550 ℃. Excess SiO₂ at high temperature forms a liquid phase, effectively promoting the formation and densification of needle-like mullite crystals. The synthesis reaction of mullite is an endothermic process, which reduces the sintering driving force. The apparent activation energy of the solid phase reaction stage is significantly increased to 1820 kJ/mol, whereas the densification stage is reduced to 550 kJ/mol. The effects of sintering temperature and heating rate on the microstructure and mechanical properties of ceramics were further studied. The findings reveal that the material obtained the best comprehensive mechanical properties when sintered to 1550 ℃ at a heating rate of 5 ℃/min. The Vickers hardness was 7.5 ± 0.29 GPa and the compressive strength was 48.2 ± 0.20 MPa. This study provides a theoretical basis and technical support for the preparation of high-performance silicon-rich mullite ceramics.