Towards Macroporous alpha-Al2O3-Routes, Possibilities and Limitations

Autor(en): Carstens, Simon
Meyer, Ralf
Enke, Dirk
Stichwörter: AAO membranes; ALPHA-ALUMINA; ANODIC POROUS ALUMINA; calculation of specific surface areas; Chemistry; Chemistry, Physical; high surface area alpha-alumina; HYDROTHERMAL SYNTHESIS; LOW-TEMPERATURE SYNTHESIS; macroporosity; Materials Science; Materials Science, Multidisciplinary; Metallurgy & Metallurgical Engineering; MOLTEN-SALT SYNTHESIS; PHASE-TRANSFORMATIONS; Physics; Physics, Applied; Physics, Condensed Matter; pore protection; sol-gel; SOL-GEL SYNTHESIS; solid solutions of Mn in alumina; STRUCTURAL TRANSFORMATIONS; SURFACE-AREA; THERMAL-STABILITY
Erscheinungsdatum: 2020
Herausgeber: MDPI
Journal: MATERIALS
Volumen: 13
Ausgabe: 7
Zusammenfassung: 
This article combines a systematic literature review on the fabrication of macroporous alpha -Al2O3 with increased specific surface area with recent results from our group. Publications claiming the fabrication of alpha -Al2O3 with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA alpha -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 gamma -Al2O3 may be the more stable alumina modification for A(BET) > 175 m(2)/g. In fact, the highest specific surface area unobjectionably reported to date for alpha -Al2O3 amounts to 16-24 m(2)/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 alpha -transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of alpha -Al2O3 seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.
DOI: 10.3390/ma13071787

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