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TEM Characterization of Pseudotetragonal Mullite

Published online by Cambridge University Press:  02 July 2020

Bradley R. Johnson  and
Waltraud M. Kriven
Bradley R. Johnson
Affiliation:
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL , 61801, USA.
Waltraud M. Kriven
Affiliation:
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL , 61801, USA.
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Abstract

Mullite (3Al2O3•2SiO2) exists in a solid solution field (∼57-63 mol% Al2O3) as the only stable compound in the Al2O3•SiO2 phase diagram at ambient pressures. Equilibrium 3:2 mullite has an orthorhombic structure with b>a (o-mullite). However, when initially crystallized from molecularly mixed, 3:2 precursors at temperatures < 1200°C, the first phase that forms has lattice parameters with a ≈b. This structure is often termed pseudotetragonal mullite (pt-mullite), since even when the ‘a’ and ‘b’ lattice parameters are identical, they are symmetrically independent. Pseudotetragonal mullite has been shown to contain approx. 70 mol% Al2O3. with increasing time and temperature, the structure gradually assimilates the residual SiO2, and the lattice parameters change, such that by 1400°C, the material has attained its equilibrium structure and composition.

TEM was used to determine the spatial relationship between the crystalline phase and the residual, amorphous, SiO2-rich phase in pt-mullite. The starting materials were quenched, 3:2 mullite beads and fibers (made by containerless processing).

Type
Novel Microscopy Assisted Ceramic Developments in Materials Scienceand Nanotechnology (Organized by P. Gai and J. Lee)
Information
Microscopy and Microanalysis , Volume 7 , Issue S2: Proceedings: Microscopy & Microanalysis 2001, Microscopy Society of America 59th Annual Meeting, Microbeam Analysis Society 35th Annual Meeting, Long Beach, California August 5-9, 2001 , August 2001 , pp. 426 - 427
Copyright
Copyright © Microscopy Society of America 2001

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References

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