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Using TEM/XRD for Classification of Transition Alumina for Astronomical Applications

Presentation #147.01 in the session Laboratory Astrophysics (LAD) Division Meeting: iPoster Session.

Published onJun 29, 2022
Using TEM/XRD for Classification of Transition Alumina for Astronomical Applications

Asymptotic Giant Branch (AGB) stars are a major contributor of dust to the Interstellar Medium (ISM). The species of dust created by AGB stars depends on their ratio of Carbon to Oxygen (C/O); for this case we are studying oxygen-rich stars where the C/O<1. The minerals we are primarily focused on in this study are aluminum oxides (aluminas). The formation of these aluminas are dependent on the temperature of the environment in which they form. The motivation for this study is to investigate a range of materials that are not naturally abundant on earth but may be important outside our solar system. The purpose of this study is twofold: (1) to determine the thermodynamic properties of the various alumina minerals; and (2) to produce infrared spectra of these aluminas for comparison with astronomically observed dust. The combination of the two datasets (thermodynamic and spectroscopic) that will be produced can then put constraints on dust formation mechanisms and test dust condensation hypotheses.

The initial set of alumina samples were obtained in two ways. First, we purchased commercial samples of aluminum hydroxide, which can be dehydroxylated to form alumina minerals. In addition, we analyzed alumina produced through smokes. In both cases, the samples were initially characterized by various microscopy techniques, including x-ray diffraction (XRD), electron diffraction, and transmission electron microscopy (TEM). All samples were then heated to (or annealed at) at least 900°C and re-characterized. The smokes had an additional heating episode, were annealed to 1500°C, and were characterized microscopically once again. These annealing episodes allowed us to observe the temperature at which the structurally-bounded water left the sample (dehydroxilation) as well as a subsequent higher temperature phase transition.

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