Towards Macroporous α-AlO-Routes, Possibilities and Limitations.

This article combines a systematic literature review on the fabrication of macroporous α-AlO with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-AlO with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-AlO 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-AlO may be the more stable alumina modification for > 175 m/g. In fact, the highest specific surface area unobjectionably reported to date for α-AlO amounts to 16-24 m/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 . 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-AlO seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.