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8. Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

Author

Carstens, Simon, Meyer, Ralf, and Enke, Dirk

Subjects
macroporosity, lcsh:QH201-278.5, lcsh:T, calculation of specific surface areas, AAO membranes, Review, high surface area α-alumina, sol-gel, solid solutions of Mn in alumina, pore protection, lcsh:Technology, lcsh:TA1-2040, lcsh:Descriptive and experimental mechanics, lcsh:Electrical engineering. Electronics. Nuclear engineering, lcsh:Engineering (General). Civil engineering (General), lcsh:Microscopy, ddc:600, lcsh:TK1-9971, lcsh:QC120-168.85
Abstract

This article combines a systematic literature review on the fabrication of macroporous α-Al2O3 with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-Al2O3 with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-Al2O3 is given, including hydrothermal methods, pore protection approaches, dopants, anodically oxidized alumina membranes, and sol-gel syntheses. Furthermore, limitations of these routes are disclosed, as thermodynamic calculations suggest that γ-Al2O3 may be the more stable alumina modification for ABET > 175 m2/g. In fact, the highest specific surface area unobjectionably reported to date for α-Al2O3 amounts to 16–24 m2/g and was attained via a sol-gel process. In a second part, we report on some of our own results, including a novel sol-gel synthesis, designated as mutual cross-hydrolysis. Besides, the Mn-assisted α-transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of α-Al2O3 seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.

Published
2020

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