Abstract
Synthesis and structural characterization of mullite phases obtained from three nominal compositions in the SiO 2Al 2O 3 system is reported and comparisons between them are established. Monosized gels with Al Si atomic ratios of 2:3, 3:1 and 9:1 were obtained and thermally treated at temperatures between 700 and 1500 °C. The thermal evolution of amorphous gels was followed by thermal analysis, X-ray diffraction and infra-red spectroscopy. The microstructural changes were studied by scanning electron microscopy and transmission electron microscopy. The formation of Al 2O 3-rich mullite started around 1000 °C for all samples and was fully developed at 1400 °C. The chemical composition of mullites changed as a function of calcining temperature. An anomalous low value of the lattice parameter a was obtained for the sample with Al Si atomic ratio of 9:1 compared with the 3:1 sample at 1400 °C, which may be due to the slow reaction rate of Al 2O 3 with SiO 2-rich glassy phase during mullite formation.
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