Preparation of mullite monoliths with well-defined macropores and mesostructured skeletons via the sol–gel process accompanied by phase separation

Mullite monoliths with well-defined macropores and mesostructured skeletons have been prepared via the sol–gel process accompanied by phase separation in the presence of poly(ethylene oxide) (PEO). Gelation of Al2O3–SiO2 binary system with chloride salts as an additional precursor has been mediated by propylene oxide (PO) as an acid scavenger, while PEO worked as a phase-separation inducer. The dried gel and that heat-treated at 800 °C are amorphous, and γ-Al2O3 or Si–Al spinel phase nanocrystals are crystallized at 900–1000 °C. After heat-treated at and above 1100 °C for 5 h, the complete crystalline mullite is generated, and the macroporous monoliths in large dimensions of more than 15 mm × 15 mm × 10 mm are obtained. Heat-treatment at 200–1400 °C does not basically spoil the macroporous structure of monoliths, while decreases the macropore size and significantly alters the phase compositions and micro-mesoporous structure.