Abstract
The effects of the precursor pH and composition on the synthesizing behavior, grain morphology, and grain size of mullite ceramics have been investigated using silica-rich (Al 2O 3·2SiO 2), stoichiometric (3Al 2O 3·2SiO 2), and alumina-rich (7.5Al 2O 3·2SiO 2) mullite precursor sols. Mullite precursor sol was prepared by the dissolution of aluminum nitrate enneahydrate (Al(NO 3) 3·9H 2O) into the mixture of colloidal silica sol. Precursor pH of the sols was controlled to the acidic (pH≈1.5–2) and basic (pH≈8.5–9) conditions. The synthesizing temperature of mullite phase was found to be above 1200 °C for pH≈1.5–2, and above 1300 °C for pH≈8.5–9 through X-ray diffraction (XRD) and Fourier transfer infrared spectroscopy (FT-IR) results, independent of composition. The grain size of the synthesized mullite for pH≈8.5–9 was larger than that for pH≈1.5–2 in the overall heat-treated temperature. Aspect ratio of the mullite grains was increased with an increase of the silica concentration. It was found that the grain morphology and grain size were predominantly governed by the initial composition and precursor pH, respectively.
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