It is demonstrated that γ-and η-aluminas (transition Al 2O3 polytypes with defect spinel structure) can effectively capture beryllium atoms. Although the bulk crystal structures of these two oxides are characterized only by slight differences in cation vacancy distributions, the interactions of Be with the two polytypes are different. For γ-Al2O3, the Be adsorption energy is high (∼5 eV per atom) and all Be atoms are captured and trapped at the surface-all attempts to move Be in the subsurface region result in its expulsion back to the surface. On the other hand, for η-alumina, Be atoms can be captured both at the surface and in octahedrally coordinated subsurface cation vacancies. This result implies that both aluminas could be successfully used for Be capture out of wastewater streams related to industrial processes of aluminum and alumina production. Also, the surface adsorption mechanism of Be at γ-Al 2O3 explains why very small additions of Be (of the order of several ppm) to Al-Mg and Al-Mg-Si casting and wrought alloys prevent run-away oxidation of these materials in the molten state, as well as ingot cracking. We also discuss possibilities to use other additives (e.g., Ca and Sr), yielding the same protective effect for aluminum alloys but which are less toxic than beryllium.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films