Solid Solution Range and Microstructures of Melt-Grown Mullite |
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| Authors: | W M KRIVEN&#; JOSEPH A PASK&#; |
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| Affiliation: | Materials and Molecular Research Division, Lawrence Berkeley Laboratory and Department of Materials Science and Mineral Engineering, University of California, Berkeley, California 94720 |
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| Abstract: | The solid solution range of melt-grown mullite was examined by crystal-chemical methods. The maximum Al2O3 content as determined by EDX was ～83.6 wt%, 75 mol%, or the nominal composition 3Al2O3.SiO2. For samples of overall composition 81 to 83 wt% Al2O3, extra lines indicating crystallographic superstructure appeared in Guinier X-ray patterns. The corresponding TEM microstructure consisted of a mullite matrix finely twinned on (001), the twins being 0.02 to 0.10 μm wide, with oriented exsolution of α-A12O3, often twinned, also being present. The analogy between mullite superstructure and that of plagioclase feldspars, as well as the relevance of these findings to the SiO2-Al2O3 metastable phase equilibria are discussed. |
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