Influence of SiO2/Al2O3 Stoichiometry on Mullite Formation: Synthesis and Characterization via Solid State Reaction

Abstract

This study investigates the effect of varying SiO₂/Al₂O₃ weight ratios on mullite formation synthesized through a solid-state reaction route. Four samples were prepared using different alumina–silica weight ratios: S1 (2.8 g SiO₂, 7.2 g Al₂O₃), S2 (4.7 g SiO₂, 5.3 g Al₂O₃), S3 (6.4 g SiO₂, 3.6 g Al₂O₃), and S4 (3.7 g SiO₂, 6.3 g Al₂O₃), with each batch weighing 10 g. The mixed powders were calcined at 900 °C to remove moisture and impurities, followed by sintering at 1350 °C to promote mullite crystallization. X-ray diffraction confirmed the formation of the orthorhombic 3:2 mullite phase, and crystallite sizes were calculated using the Scherrer equation. SEM images showed that increasing SiO₂ content enhanced the development of elongated acicular grains due to a transient silica-rich liquid phase and increased Al–Si interdiffusion. Among the prepared compositions, S4 exhibited the highest mullite purity and most developed grain structure. This study demonstrates a simple and cost-effective approach for optimizing mullite synthesis for industrial applications.