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QUANT_HT.pdf (2.88 MB)

Quantification of High Temperature Transition Al2O3 and Their Phase Transformations

preprint
submitted on 29.06.2020 and posted on 01.07.2020 by Libor Kovarik, Mark Bowden, Amity Andersen, Nicholas R. Jaegers, Nancy Washton, János Szanyi

High temperature exposure of gamma-Al2O3 can lead to a series of polymorphic transformations, including the formation of delta-Al2O3 and theta-Al2O3. Quantification of the microstructure in the delta/theta-Al2O3 formation range represents a formidable challenge as both phases accommodate a high degree of structural disorder. In this work, we explore the use of XRD recursive stacking formalism for quantification of high temperature transition aluminas. We formulate the recursive stacking methodology for modelling of disorder in delta-Al2O3 and twinning in theta-Al2O3 and show that explicitly accounting for the disorder is necessary to reliably model the XRD patterns of high temperature transition alumina. In the second part, we use the recursive stacking approach to study phase transformation during high temperature (1050 ºC) treatment. We show that the two different intergrowth modes of delta-Al2O3 have different transformation characteristics, and that a significant portion of delta-Al2O3 is stabilized with theta-Al2O3 even after prolonged high-temperature exposures. In discussions, we outline the limitation of the current XRD approach and discuss a possible multimodal XRD and NMR approach which can improve analysis of complex transition aluminas.

Funding

This work was performed in the Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at PNNL. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

History

Email Address of Submitting Author

libor.kovarik@pnnl.gov

Institution

PNNL

Country

United States

ORCID For Submitting Author

0000-0002-2418-6925

Declaration of Conflict of Interest

no conflicts to declare

Version Notes

version 1.0

Exports