Abstract
Different reaction paths of mullite formation via sol-gel processing techniques are reviewed. These variations are due to differences in hydrolysis/gelation behaviours of the silica and alumina components used. Variations of pH during processing without altering other variables follow three different routes of mullite formation. In the highly acidic region(pH ⩽ 1), the gel does not exhibit a 980 °C exotherm but forms γ-Al2O3. Mullite forms at high temperature by diminution of α-Al2O3 and β-cristobalite, respectively. In the pH range of 3–4.5, gels exhibit a 980 °C exotherm and develop only mullite. In the highly alkaline region (pH ∼ 14), the gel produces a Si-Al spinel phase at the 980 °C exotherm and mullite formation at the ∼ 1330 °C exotherm takes place from the intermediate Si-Al spinel phase.
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Chakravorty, A.K. Effect of pH on 980 °C spinel phase-mullite formation of Al2O3-SiO2 gels. JOURNAL OF MATERIALS SCIENCE 29, 1558–1568 (1994). https://doi.org/10.1007/BF00368926
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DOI: https://doi.org/10.1007/BF00368926