The current study aims to investigate the effect of the type and amount of acid and base catalyst on the microstructural properties of mullite phase particles prepared by the sol-gel method (3Al2O3-2SiO2). Nona-hydrated aluminum nitrate (ANN), Tetraethyl orthosilicate (TEOS), ethanol, and water were used as starting materials. After the precise preparation method, obtained gels were dried in an inert atmosphere and heated with specific heat treatment (cycles or temperatures). DSC analysis was used to identify the proper (crystallization temperature of the particles). X-ray diffraction pattern (XRD) and scanning electron microscopy (SEM) analyses were utilized to investigate the phase crystallization and morphology of the created phases, respectively. XRD analysis showed that mullite is crystallized in all samples with acidic or basic catalyst. However, based on the results, single-phase mullite crystallized only in the presence of the optimal amount of acidic or basic catalyst. According to the SEM results, the samples synthesized at acidic pH had plate-like morphology, while basic samples had spherical morphology. Furthermore, increasing the concentrations of the catalysts did not affect the morphology of the particles. However, the type and the concentration of the catalyst had an impressive effect on the crystallization of the mullite phase.

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