Quantification of High‐Temperature Transition Al₂O₃ and Their Phase Transformations.

Kovarik, Libor; Bowden, Mark; Andersen, Amity; Jaegers, Nicholas R.; Washton, Nancy; Szanyi, János

High‐temperature treatment of γ‐Al2O3 can lead to a series of polymorphic transformations, including the formation of δ‐Al2O3 and θ‐Al2O3. Quantification of the microstructure in the range where δ‐ and θ‐Al2O3 are formed represents a formidable challenge, as both phases accommodate a high degree of structural disorder. In this work, we explore the use of an XRD recursive‐stacking formalism for the quantification of high‐temperature transition aluminas. We formulate the recursive‐stacking methodology for modelling of disorder in δ‐Al2O3 and twinning in θ‐Al2O3 and show that explicitly accounting for the disorder is necessary to reliably model the XRD patterns of high‐temperature transition alumina. We also use the recursive stacking approach to study phase transformation during high‐temperature (1050 °C) treatment. We show that the two different intergrowth modes of δ‐Al2O3 have different transformation characteristics and that a significant portion of δ‐Al2O3 is stabilized with θ‐Al2O3 even after prolonged high‐temperature exposures.

PHASE transitions; POLYMORPHIC transformations; ALUMINUM oxide

Angewandte Chemie, 2020, Vol 132, Issue 48, p21903

0044-8249

Academic Journal

10.1002/ange.202009520