Occurrence of Pseudotetragonal Mullite
- 8 March 1988
- journal article
- Published by Wiley in Journal of the American Ceramic Society
- Vol. 71 (3) , -162--164
- https://doi.org/10.1111/j.1151-2916.1988.tb05042.x
Abstract
Mullite‐type phases with about 74 wt% Al2O3 and 26 wt% SiO2 were prepared from tetraethyl orthosilicate and aluminum butylate between 950° and 1000°C. The lack of 120/210, 240/420, 041/401, and 250/520 reflection pair splitting on the X‐ray diffractograms indicates tetragonal symmetry, whereas normal mullite is orthorhombic. We believe that the tetragonal character of the phase is due to twinning and/or domain formation of orthorhombic structural units in an elementary cell scale. Therefore, the mullite‐type phase should be designated as pseudotetragonal rather than tetragonal. According to our present knowledge, pseudotetragonal mullite is formed from highly reactive metal organic compounds only. The phase is metastable and transforms gradually to orthorhombic mullite at temperatures above 1000°C.Keywords
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