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Mullite formation from nonstoichiometric slow hydrolyzed single phase gels

Published online by Cambridge University Press:  03 March 2011

Yong Wang
Affiliation:
Department of Chemical Engineering, Washington State University, Pullman, Washington 99164-2710
William J. Thomson
Affiliation:
Department of Chemical Engineering, Washington State University, Pullman, Washington 99164-2710
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Abstract

A comparative dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA) study was performed in the investigation of mullite and spinel formation from slowly hydrolyzed single phase gels with Al/Si ratios ranging from 1/1 to 14/1. Both metastable tetragonal mullite and spinel were observed to form at temperatures <1000 °C in the gels with Al/Si ratios <8/1 and mullite transformed to the orthorhombic structure at ∼1250 °C. However, at higher Al/Si ratios, spinel was the only crystalline phase detected at <1000 °C and orthorhombic mullite formed directly at temperatures >1250 °C. As the Al/Si ratio increases, both the tetragonal mullite and spinel formation temperatures decrease while the orthorhombic mullite formation temperature increases. Based on the Al/Si composition where the formation extents of tetragonal mullite and spinel were maximum, their compositions are estimated to be 2Al2O3 · SiO2 and 6A12O3 · SiO2, respectively.

Type
Articles
Copyright
Copyright © Materials Research Society 1995

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References

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